Growth factors and the regulation of bone remodeling.

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Abstract

Authors

E Canalis, T McCarthy, M Centrella

Biosynthesis of somatostatin in canine fundic D cells.

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The observation that virtually all of the somatostatin-like immunoreactivity in the stomach consists of somatostatin-14 (S14), to the exclusion of somatostatin-28 (S28), suggests a unique pattern of prosomatostatin posttranslational processing. In order to examine the mechanisms by which S14 is produced from its precursor in the stomach, we investigated the biosynthesis of somatostatin in isolated canine fundic D cells. D cells pulse-labeled with [35S]cysteine revealed a cycloheximide inhibitable time-dependent incorporation of radioactivity into S14. A small fraction of radioactivity was incorporated into S28 but not into larger precursors. However, when the cells were incubated with monensin (1 microM), incorporation of radioactivity into a presumed somatostatin precursor was noted. Upon transfer of [35S]cysteine prelabeled cells to radioactivity-free medium, no conversion of S28 to S14 could be detected and the decrease of labeled S14 in cells correlated with a complimentary increase in the culture medium. Exogenous somatostatin inhibited somatostatin biosynthesis in a fashion that could be blocked by pertussis toxin pretreatment. Stimulation of prelabeled D cells with tetradecanoyl phorbol 13-acetate (10(-7) M) or forskolin (10(-4) M) for 2 h resulted in release of 41 and 33% of the newly synthesized radioactive S14, respectively, while only 9 and 6% of the total cell content of radioimmunoassayable somatostatin was secreted. These data suggest that: (a) somatostatin is synthesized in fundic D cells primarily as S14, (b) S14 is produced by rapid processing of a larger precursor but there is little, if any, conversion of S28 to S14, (c) somatostatin biosynthesis is autoregulated, and (d) newly synthesized S14 is preferentially released from D cells in response to stimulation.

Authors

T Chiba, J Park, T Yamada

Aggregation-related association of lipid with the cytoskeleton of rabbit and human platelets prelabeled with [3H]palmitic acid. Similar effects of adenosine diphosphate- and thrombin-induced aggregation.

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Abstract

To investigate the association of lipid with the cytoskeleton of platelets during aggregation, rabbit and human platelets were isolated and labeled with [3H]palmitic acid; lipid extraction showed approximately 80% in phospholipid. Limited aggregation was induced with ADP or thrombin, and the cytoskeleton was isolated after lysis with 1% Triton X-100, 5 mM EGTA. Cytoskeleton from unactivated platelets had approximately 0.03% of the total label in the platelets, but after aggregation with ADP (2 microM) or thrombin (0.1 U/ml) for 20-30 s, 1.5-8% of the label was with the cytoskeleton. Fibrinogen enhanced aggregation and the association of label with the cytoskeleton; incorporation of label increased exponentially as aggregation proceeded, decreased exponentially during deaggregation, and appeared to be related to the number of sites of contact. Inhibitors that increase cyclic AMP inhibited aggregation and cytoskeletal labeling, but aspirin had no effect. Some experiments were done with DNase I and Ca2+ in the Triton X-100 lysis medium to cause actin depolymerization, under conditions in which the Ca2+-dependent protease activity was inhibited. This greatly reduced the association of label with the cytoskeleton at early time points, but when aggregation had proceeded further, a large proportion of the label was not dissociated by this treatment. These findings, electron microscopy, and the enrichment of the cytoskeleton of aggregated platelets with only some of the membrane proteins that were labeled by the 125I-lactoperoxidase method, indicated that with limited aggregation, the 3H-labeled lipid was mainly associated with the cytoskeleton and not with trapped membrane fragments resulting from incomplete lysis. Since the pattern of cytoskeleton labeling ([3H]palmitate) and the selective association of some membrane proteins with the cytoskeleton/lipid complex was the same with ADP and thrombin, the reactions must be dependent on aggregation and not on events associated with the release of granule contents.

Authors

A Livne, M A Packham, M A Guccione, J F Mustard

Interaction of dietary cholesterol and triglycerides in the regulation of hepatic low density lipoprotein transport in the hamster.

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Abstract

These studies report the effects of dietary cholesterol and triglyceride on rates of receptor-dependent and receptor-independent LDL transport in the liver of the hamster. In animals fed diets enriched with 0.1, 0.25, or 1% cholesterol for 1 mo, receptor-dependent LDL transport in the liver was suppressed by 43, 63, and 77%, respectively, and there were reciprocal changes in plasma LDL-cholesterol concentrations. In addition, dietary triglycerides modified the effect of dietary cholesterol on hepatic LDL transport and plasma LDL concentrations so that at each level of cholesterol intake, polyunsaturated triglycerides diminished and saturated triglycerides accentuated the effect of dietary cholesterol. When animals were raised from weaning on diets containing small amounts of cholesterol, the decline in receptor-dependent LDL transport was nearly abolished by the addition of polyunsaturated or monounsaturated triglycerides, but was markedly augmented by the addition of saturated lipids. When animals raised on diets containing cholesterol and saturated triglycerides were returned to the low cholesterol, low triglyceride control diet, hepatic receptor-dependent LDL transport and plasma LDL-cholesterol concentrations returned essentially to normal within 2 wk. Neither receptor-independent LDL transport nor the receptor-dependent uptake of asialofetuin was significantly altered by dietary cholesterol or triglyceride suggesting that the effect of these lipids on hepatic LDL receptor activity was specific and not due to a generalized alteration in the physiochemical properties of hepatic membranes. These studies demonstrate the important role of saturated triglycerides in augmenting the effect of cholesterol in suppressing hepatic LDL receptor activity and elevating LDL-cholesterol levels.

Authors

D K Spady, J M Dietschy

Metabolism of cerebroside sulfate and subcellular distribution of its metabolites in cultured skin fibroblasts from controls, metachromatic leukodystrophy, and globoid cell leukodystrophy.

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With pulse-chase study of 1-[14C]stearic acid-labeled cerebroside sulfate (14C-CS) and subsequent subcellular fractionation by Percoll gradient, the metabolism of CS and translocation of its metabolites in human skin fibroblasts from controls, metachromatic leukodystrophy (MLD), and globoid cell leukodystrophy (GLD) were studied. In control skin fibroblasts, CS was transported to lysosome and metabolized there to galactosylceramide (GalCer) and ceramide (Cer) within 1 h. During the chase period, radioactivity was increased at plasma membrane plus Golgi as phospholipids and no accumulation of GalCer or Cer was found in lysosome. In MLD fibroblasts, 95% of 14C-CS taken up was unhydrolyzed at 24 h-chase and accumulated at not only lysosome but also plasma membrane. In GLD fibroblasts, GalCer was accumulated throughout the subcellular fractions and more accumulated mainly at plasma membrane plus Golgi with longer pulse. This translocation of lipid from lysosome seems to have considerable function, even in lipidosis, which may result in an imbalance of the sphingolipid pattern on the cell surface and these changes might be one of causes of neuronal dysfunction in sphingolipidosis.

Authors

K Inui, M Furukawa, S Okada, H Yabuuchi

Phagocyte-derived lactate stimulates oxygen consumption by Neisseria gonorrhoeae. An unrecognized aspect of the oxygen metabolism of phagocytosis.

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Abstract

O2 consumption resulting from interaction of Neisseria gonorrhoeae and human neutrophils represents a composite of O2 consumed by the two cell systems. Experiments studying the relative contribution of each system suggested the possibility that gonococci increased their metabolic activity in response to interaction with neutrophils. This hypothesis was confirmed by demonstrating that undifferentiated HL-60 cells, which are unable to undergo a respiratory burst, induce a two- to three-fold increase in gonococcal O2 consumption. Gonococcal capacity to adhere to HL-60 cells did not correlate with extent of metabolic stimulation. Stimulatory activity was demonstrable in cell-free supernatant from neutrophils or HL-60 cells, and increased with duration of incubation. Supernatant applied to a G-15 Sephadex column yielded fractions that stimulated gonococcal O2 consumption. Elution profiles were similar for HL-60 cells, neutrophils, and a stimulatory factor previously isolated from pooled human serum. This stimulatory factor(s) failed to adhere to DEAE or C-18 HPLC columns. Stimulatory activity release from myeloid cells was inhibited by incubation at 4 degrees C or in the presence of NaF, indicating a critical role for glucose metabolism. Lactate, the principal product of resting neutrophil glucose catabolism, was demonstrable in cell-free supernatants after incubation at 37 degrees C. Lactate accumulation was inhibited by NaF and decreased temperature of incubation. Lactate at levels present in cell-free supernatant increased gonococcal O2 consumption twofold and restored stimulatory activity to dialyzed serum. Live, but not heat-killed gonococci eliminated lactate released from neutrophils during phagocytosis. Gonococci are able to utilize host-derived lactate to enhance their rate of O2 metabolism.

Authors

B E Britigan, D Klapper, T Svendsen, M S Cohen

Regulation of human lung fibroblast glycosaminoglycan production by recombinant interferons, tumor necrosis factor, and lymphotoxin.

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Abstract

Mononuclear cells may be important regulators of fibroblast glycosaminoglycan (GAG) biosynthesis. However, the soluble factors mediating these effects, the importance of intercytokine interactions in this regulation and the mechanisms of these alterations remain poorly understood. We analyzed the effect of recombinant (r) tumor necrosis factor (TNF), lymphotoxin (LT), and gamma, alpha, and beta 1 interferons (INF-gamma, -alpha and -beta 1), alone and in combination, on GAG production by normal human lung fibroblasts. rTNF, rLT, and rINF-gamma each stimulated fibroblast GAG production. In addition, rIFN-gamma synergized with rTNF and rLT to further augment GAG biosynthesis. In contrast, IFN-alpha A, -alpha D, and -beta 1 neither stimulated fibroblast GAG production nor interacted with rTNF or rLT to regulate GAG biosynthesis. The effects of the stimulatory cytokines and cytokine combinations were dose dependent and were abrogated by the respective monoclonal antibodies. In addition, these cytokines did not cause an alteration in the distribution of GAG between the fibroblast cell layer and supernatant. However, the stimulation was at least partially specific for particular GAG moieties with hyaluronic acid biosynthesis being markedly augmented without a comparable increase in the production of sulfated GAGs. Fibroblast prostaglandin production did not mediate these alterations since indomethacin did not decrease the stimulatory effects of the cytokines. In contrast, protein and mRNA synthesis appeared to play a role since the stimulatory effects of the cytokines were abrogated by cyclohexamide and actinomycin D, respectively. In addition, the cytokines and cytokine combinations increased cellular hyaluronate synthetase activity in proportion to their effects on hyaluronic acid suggesting that induction of this enzyme(s) is important in this stimulatory process. These studies demonstrate that IFN-gamma, TNF, and LT are important stimulators of fibroblast GAG biosynthesis, that interactions between these cytokines may be important in this regulatory process, that these cytokines predominantly stimulate hyaluronic acid production and that this effect may be mediated by stimulation of fibroblast hyaluronate synthetase activity.

Authors

J A Elias, R C Krol, B Freundlich, P M Sampson

Evidence suggesting a role for hydroxyl radical in gentamicin-induced acute renal failure in rats.

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Abstract

The protective effect of hydroxyl radical scavengers and iron chelators has strongly implicated the hydroxyl radical in several models of tissue injury. Based on in vitro studies showing gentamicin-enhanced generation of reactive oxygen metabolites in renal cortical mitochondria, we examined the effect of hydroxyl radical scavengers and iron chelators in gentamicin-induced acute renal failure. Rats treated with gentamicin (G) alone (100 mg/kg, s.c. x 8 d) developed advanced renal failure (BUN 215 +/- 30 mg/dl) compared to saline-treated controls (BUN 16 +/- 1 mg/dl, P less than 0.001). In contrast, rats treated with gentamicin and either dimethylthiourea (DMTU, an hydroxyl radical scavenger, 125 mg/kg, i.p. twice a day) or deferoxamine (DFO, an iron chelator, 20 mg/day by osmotic pump) had significantly lower BUN (G + DMTU 48.8 +/- 8 mg/dl, P less than 0.001, n = 8; G + DFO 30 +/- 7 mg/dl, P less than 0.001, n = 8). In separate experiments, treatment with two other hydroxyl radical scavengers (dimethyl sulfoxide or sodium benzoate) and a second iron chelator (2,3,dihydroxybenzoic acid) had a similar protective effect on renal function (as measured by both BUN and creatinine). In addition, histological evidence of damage was markedly reduced by the interventional agents. Finally, concurrent treatment with DMTU prevented the gentamicin induced increase in renal cortical malondialdehyde content (G: 4.4 +/- 0.2 nmol/mg; G + DMTU: 3.1 +/- 0.2 nmol/mg, P less than 0.0001, n = 8) suggesting that the protective effect of DMTU was related to free radical mechanisms rather than to some other effect. Taken together, these data strongly support a role for hydroxyl radical or a similar oxidant in gentamicin-induced acute renal failure.

Authors

P D Walker, S V Shah

High efficiency covalent radiolabeling of the human androgen receptor. Studies in cultured fibroblasts using dihydrotestosterone 17 beta-bromoacetate.

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Abstract

Analysis of mutations affecting the androgen receptor protein in human cells has been limited because of the low abundance and lability of these proteins in target tissues. All methods used to date have been based on the noncovalent interaction of radiolabeled androgens with the receptor's ligand binding site. We report here synthesis and use of the electrophilic affinity label dihydrotestosterone 17 beta-bromoacetate. This ligand, prepared as a radioactive compound of high specific activity, rapidly and covalently binds to a protein of 58,000 daltons in cytosol from normal genital skin fibroblasts. This protein is a high affinity, saturable specific binding site for the ligand and was not detectable in cultured cells from a subject with androgen resistance or in receptor-negative nongenital fibroblasts. The efficiency of incorporation of the covalent radiolabel into the 58-kD protein is greater than 80% based on estimates of receptor content using noncovalent ligands in intact cell assays. These studies demonstrate that dihydrotestosterone 17 beta-bromoacetate is useful for high efficiency covalent labeling of the human androgen receptor in crude cytosolic extracts from cultured cells.

Authors

W J Kovacs, M K Turney

Histopathological heterogeneity of neuropathy in insulin-dependent and non-insulin-dependent diabetes, and demonstration of axo-glial dysjunction in human diabetic neuropathy.

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Abstract

Altered sorbitol and myo-inositol metabolism, (Na,K)-ATPase function, electrochemical sodium gradients, axonal swelling, and distortion and disruption of the node of Ranvier ("axo-glial dysjunction") directly implicate hyperglycemia in the pathogenesis of neuropathy in diabetic rats, but the relevance of this sequence to clinical neuropathy in heterogeneous groups of diabetic patients remains to be established. Fascicular sural nerve morphometry in 11 patients with neuropathy complicating insulin-dependent diabetes revealed a pattern of interrelated structural changes strikingly similar to that of the diabetic rat when compared to age-matched controls. 17 older non-insulin-dependent diabetic patients with comparable duration and severity of hyperglycemia and severity of neuropathy, displayed similar nerve fiber loss, paranodal demyelination, paranodal remyelination and segmental demyelination compared to age-matched controls, but axo-glial dysjunction was replaced by Wallerian degeneration as the primary manifestation of fiber damage, and fiber loss occurred in a spatial pattern consistent with an ischemic component. The mechanistic model developed from the diabetic rat does indeed appear to apply to human diabetic neuropathy, but superimposed hormonal, metabolic, vascular, and/or age-related effects alter the morphologic expression of the neuropathy in non-insulin dependent diabetes.

Authors

A A Sima, V Nathaniel, V Bril, T A McEwen, D A Greene

Mechanism of inhibition of immunoglobulin G-mediated phagocytosis by monoclonal antibodies that recognize the Mac-1 antigen.

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Abstract

We have investigated the effects of the monoclonal antibodies against the cell surface molecule Mac-1 on C3bi-mediated rosetting and IgG-mediated rosetting and phagocytosis by human peripheral blood monocytes. Highly purified M1/70 F(ab')2, used in the fluid phase, inhibited both monocyte functions. Half-maximal C3bi rosette inhibition occurred at a concentration of 2 nM F(ab')2 M1/70. An equivalent decrease in IgG-mediated rosetting required 10 nM M1/70 F(ab')2, and 50% inhibition of IgG-mediated phagocytosis required 7 nM antibody. Mo-1 F(ab')2 inhibited EC3bi binding with an ID50 of 0.3 nM, whereas 50% decrease in IgG-mediated rosetting required 70 nM of this antibody. OKM1 did not inhibit rosettes of sheep erythrocytes opsonized with IgG antibody (EA) at all. F(ab')2 M1/70 did not affect the binding of monomeric human IgG to monocytes, but did substantially decrease the binding of IgG aggregates. Half-maximal inhibition of aggregated IgG binding at 0 degrees C occurred at 8 nM F(ab')2 M1/70, very close to the concentration that caused equivalent inhibition of IgG-mediated phagocytosis. Aggregated IgG inhibited the binding of radiolabeled M1/70 to monocytes by approximately 40%, suggesting that some, but not all Mac-1 molecules were associated with IgG receptors under these conditions. When cells were allowed to adhere to surfaces coated with M1/70 or Mo-1 F(ab')2, C3bi-mediated rosetting was inhibited, but IgG mediated-phagocytosis was unaffected. Moreover, the dose response of inhibition of phagocytosis by fluid-phase F(ab')2, of anti-Mac-1 monoclonals was similar on monocytes adherent to albumin-coated and antibody-coated surfaces. Kinetic experiments showed that even prolonged incubation of monocytes on M1/70 coated surfaces did not lead to inhibition of EA binding nor did these incubations alter the dose response for inhibition of EA binding by fluid-phase M1/70 F(ab')2. This suggested that not all molecules recognized by M1/70 are freely mobile in the plasma membrane. Indeed, only approximately 60% of 125I-M1/70-biding sites were lost even after 4 h when monocytes were adherent to M1/70-coated surfaces. We conclude that some anti-Mac-1 antibodies can inhibit EA binding because of their epitope specificity, independent of any direct interaction with monocyte Fc receptors. This interference with IgG-Fc receptor-mediated binding and ingestion apparently occurs because of antibody binding to a subpopulation of Mac-1 molecules which are associated with IgG Fc receptors and remain on the apical membrane of monocytes adherent to anti-Mac-1-coated surfaces. We suggest that there may be two functionally distinct molecules on human monocytes recognized by M1/70 and Mo-1 that can be distinguished by their mobility in the plane of the monocyte membrane. The more mobile form of Mac-1 is involved in C3bi rosettes, and does not affect IgG-mediated phagocytosis. The other antigen recognized by M1/70 does not diffuse within the plane of the membrane; ligation of the latter molecule by antibody is associated with inhibition of IgG-mediated phagocytosis.

Authors

E J Brown, J F Bohnsack, H D Gresham

Effects of a high potassium diet on electrical properties of cortical collecting ducts from adrenalectomized rabbits.

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Abstract

The cortical collecting tubule is one of the main nephron sites where mineralocorticoids and a high potassium diet modulate sodium (Na) and potassium (K) transport. In this study we explored the steroid-independent effects of a high K diet on the electrical transport properties of the isolated rabbit cortical collecting tubule principal cells. The electrophysiological analysis included transepithelial and single-cell potential measurements and equivalent circuit analysis. Rabbits were adrenalectomized (ADX) and received either a control diet (300 meq K/kg diet) or a high K diet (600 meq/kg diet) for 10 d before the experiment. The mean plasma K of ADX control animals was 6.9 mM, that of ADX animals on the high K diet 8.3 mM. The transepithelial potential difference was significantly elevated in the high K group (-3.5 mV, lumen negative), compared with ADX controls (-1.4 mV). The basolateral membrane potential in high K animals was also significantly elevated (-73 mV, cell negative, compared with -63 mV in controls). Estimates of the apical membrane partial Na and K conductances (GaNa and GaK) and of ion currents (IaNa and IaK) also demonstrated stimulation by the high K diet. In the high K group, both GaNa and GaK (0.56 and 2.67 mS.cm-2) were higher than control values (0.27 and 1.17 mS.cm-2). IaNa and IaK were also higher in high K animals (47.8 and -26.2 microA.cm-2) compared with control animals (22.4 and -11.6 microA.cm-2). Thus, a high K intake per se can induce electrophysiological changes consistent with stimulation of Na reabsorption and K secretion.

Authors

S Muto, S Sansom, G Giebisch

Regulation of cell pH by ambient bicarbonate, carbon dioxide tension, and pH in the rabbit proximal convoluted tubule.

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Abstract

To study the regulation of cell pH by ambient pH, carbon dioxide tension (PCO2), and bicarbonate (HCO3), cell pH was measured in the isolated, in vitro microperfused rabbit proximal convoluted tubule using the fluorescent dye (2',7')-bis-(carboxyethyl)-(5,6)-carboxyfluorescein. For the same changes in external pH, changes in [HCO3] and PCO2 affected cell pH similarly ([HCO3]: pHi/pHe = 0.67, PCO2: pHi/pHe = 0.64, NS). Isohydric changes in extracellular [HCO3] and PCO2 did not change cell pH significantly. Changes in peritubular [HCO3] elicited larger changes in cell pH than changes in luminal [HCO3], which were enhanced by peritubular 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonate (SITS). The cell pH defense against acute increases and decreases in PCO2 was inhibited by sodium, but not by chloride removal. Peritubular SITS inhibited the cell pH defense against increases and decreases of PCO2, whereas luminal amiloride inhibited cell pH defense against increases in PCO2. Conclusions: (a) Steady-state cell pH changes in response to changes in extracellular [HCO3] and PCO2 are quantitatively similar for a given change in extracellular pH; (b) the rate of the basolateral Na/(HCO3)3 cotransporter is a more important determinant of cell pH than the rate of the apical membrane mechanism(s); (c) cell pH defense against acute changes in PCO2 depends on the basolateral Na/(HCO3)3 cotransporter (acid and alkaline loads) and the luminal Na/H antiporter (acid loads).

Authors

R Krapf, C A Berry, R J Alpern, F C Rector Jr

Transsulfuration in an adult with hepatic methionine adenosyltransferase deficiency.

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We investigated sulfur and methyl group metabolism in a 31-yr-old man with partial hepatic methionine adenosyltransferase (MAT) deficiency. The patient's cultured fibroblasts and erythrocytes had normal MAT activity. Hepatic S-adenosylmethionine (SAM) was slightly decreased. This clinically normal individual lives with a 20-30-fold elevation of plasma methionine (0.72 mM). He excretes in his urine methionine and L-methionine-d-sulfoxide (2.7 mmol/d), a mixed disulfide of methanethiol and a thiol bound to an unidentified group X, which we abbreviate CH3S-SX (2.1 mmol/d), and smaller quantities of 4-methylthio-2-oxobutyrate and 3-methylthiopropionate. His breath contains 17-fold normal concentrations of dimethylsulfide. He converts only 6-7 mmol/d of methionine sulfur to inorganic sulfate. This abnormally low rate is due not to a decreased flux through the primarily defective enzyme, MAT, since SAM is produced at an essentially normal rate of 18 mmol/d, but rather to a rate of homocysteine methylation which is abnormally high in the face of the very elevated methionine concentrations demonstrated in this patient. These findings support the view that SAM (which is marginally low in this patient) is an important regulator that helps to determine the partitioning of homocysteine between degradation via cystathionine and conservation by reformation of methionine. In addition, these studies demonstrate that the methionine transamination pathway operates in the presence of an elevated body load of that amino acid in human beings, but is not sufficient to maintain methionine levels in a normal range.

Authors

W A Gahl, I Bernardini, J D Finkelstein, A Tangerman, J J Martin, H J Blom, K D Mullen, S H Mudd

Regulation of lipoprotein lipase immunoreactive mass in isolated human adipocytes.

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Previous studies of human adipose tissue lipoprotein lipase (LPL) have focused on enzyme catalytic activity, and have not measured the LPL protein directly. To study the regulation of the LPL protein, an antibody against purified bovine LPL was used. To demonstrate the specificity of the antiserum, adipose homogenates were Western blotted, and adipocytes were radiolabeled and the cell homogenates immunoprecipitated, yielding a single specific band at 53 kD. Breakdown products of LPL were demonstrated at 35 and 20 kD by Western blotting. An ELISA for human adipose LPL was established, in which LPL was sandwiched between affinity-purified antibody and biotinylated affinity-purified antibody. The standard curves for bovine LPL and human adipose LPL were parallel, and LPL activity correlated strongly with LPL immunoreactive mass. Thus, the bovine LPL standard curve was used to estimate LPL immunoreactive mass from human adipose tissue. The regulation of LPL activity and immunoreactive mass were compared in cultured adipocytes in the presence an absence of insulinlike growth factor-I/somatomedin C (IGF-I), insulin, and fetal bovine serum. IGF-I and a high insulin concentration (70 nM) stimulated only the heparin-releasable (HR) component of LPL activity and immunoreactive mass, and neither IGF-I nor insulin affected LPL specific activity. In contrast, 10% fetal bovine serum stimulated HR activity, HR mass, and cellular extractable (EXT) immunoreactive mass, with no effect on EXT activity. This resulted in a decrease in EXT specific activity in response to serum. The effects of the locally produced nucleosides adenosine and inosine were studied in a similar manner. As with serum, adenosine stimulated HR activity, HR mass, and EXT immunoreactive mass, resulting in a decrease in EXT specific activity. Inosine stimulated an increase in HR activity and HR mass, but had no effect on EXT, and thus did not change LPL specific activity. Thus, a sensitive ELISA for adipose tissue LPL has been developed using a specific, well-characterized antibody. Regulation of human LPL immunoreactive mass was demonstrated in vitro by IGF-I, serum, high concentrations of insulin, adenosine, and inosine. This method will permit further investigations into the regulation of the LPL protein.

Authors

P A Kern, J M Ong, J W Goers, M E Pedersen

Seasonal modulation of the circadian time structure of circulating T and natural killer lymphocyte subsets from healthy subjects.

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A seasonal modulation of the circadian time structure of circulating T and natural killer (NK) lymphocyte subtypes was documented in five healthy men aged 24-36 yr. Venous blood was obtained every 4 h for 24 h from each subject in January, March, June, August, and November 1984. Three subjects were also studied in April and/or August and/or November 1983 for the T subsets only. Mononuclear cells were isolated on Ficoll-Paque gradient and aliquots were incubated with OKT3, OKT4, OKT8, or HNK-1 monoclonal antibodies for characterizing all, T, T helper, T suppressor-cytotoxic, and NK lymphocytes, respectively, under an epifluorescence microscope. An effect of both sampling time and study month was statistically validated (P less than 0.01) with both two-way analysis of variance and cosinor for the peripheral counts in total, pan-T, T helper, and NK lymphocytes (cells per cubic millimeter). Seasonal changes affected both the circadian patterns and the 24-h mean values. Thus the double amplitude (total extent of variation) of the circadian rhythm in circulating total, T and T helper lymphocytes varied between 0 in March (P greater than 0.30; no rhythm) and up to 46-68% of the 24-h-mean (M) in November, with acrophases (times of maximum, 0) localized in the first half of the night (P less than 0.001). Maximal values were found at 8:30 h for both T suppressor-cytotoxic and NK lymphocytes; a smaller second peak was also found at 20:30 h, and a 12-h rhythm was validated by cosinor (P less than 0.0001), with no patient change in waveform along the year scale. A circannual rhythm was statistically validated by cosinor for total (0 in November), pan-T (0 in March), T suppressor-cytotoxic (0 in December), and NK lymphocytes (0 in October). A rhythm with a period equal to 6 mo was found for circulating T helper cells with 0 occurring both in April and October. Seasonal variations in the incidence of several immunologically related diseases may correspond to an endogenous circannual time structure.

Authors

F A Lévi, C Canon, Y Touitou, A Reinberg, G Mathé

Purification and partial characterization of hepatocyte growth factor from plasma of a patient with fulminant hepatic failure.

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Abstract

Human hepatocyte growth factor (hHGF) has been purified approximately 209,000-fold with 18% yield from plasma of a patient with fulminant hepatic failure. The purification involves heat treatment of plasma, ammonium sulfate precipitation, and chromatography on Affi-Gel Blue, heparin-Sepharose, and hydroxylapatite. Purified hHGF shows several bands with molecular weights between 76,000 and 92,000. Each band shows growth-stimulating activity on cultured hepatocytes which is proportional to the intensity of the band. After reduction of the sample with 2-mercaptoethanol, SDS-PAGE yields two chains with molecular weights of 31,500-34,500 and 54,000-65,000. The effect of hHGF on DNA synthesis by hepatocytes is half-maximal at 3.5 ng/ml. hHGF stimulates proliferation of cultured hepatocytes more effectively than human epidermal growth factor (hEGF) or insulin, and the effect of hHGF is additive or synergistic with the maximal effects of hEGF and insulin. These results suggest that hHGF is a new growth factor which is different from hEGF.

Authors

E Gohda, H Tsubouchi, H Nakayama, S Hirono, O Sakiyama, K Takahashi, H Miyazaki, S Hashimoto, Y Daikuhara

Decreased stimulatory guanosine triphosphate binding protein in dogs with pressure-overload left ventricular failure.

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Abstract

Alterations in the level and function of the stimulatory guanyl nucleotide binding protein (Gs) from the cardiac sarcolemma were examined in a canine model of heart failure. The present study is based on our previous investigations that demonstrated both a loss of beta-adrenergic agonist high-affinity binding sites and a decreased adenylate cyclase activity in sarcolemma from failing hearts. Using cholera toxin and [32P]NAD, we labeled the alpha subunit of Gs (Gs alpha) and found a 59% reduction in the level of this protein. Further, a 50% reduction in Gs activity was noted in a reconstitution assay utilizing membranes from the mouse S49 lymphoma cell line cyc-, which is deficient in Gs. These data suggest that, in this model of pressure-overload left ventricular failure, the acquired defect in the beta-adrenergic receptor/adenylate cyclase system involves a deficiency in the coupling protein Gs. Such an abnormality may explain the decreased adrenergic responsiveness of the failing left ventricle.

Authors

J P Longabaugh, D E Vatner, S F Vatner, C J Homcy

Pyrimidine base degradation in cultured murine C-1300 neuroblastoma cells and in situ tumors.

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Dihydropyrimidine dehydrogenase (DPD), the initial, rate-limiting step in pyrimidine degradation, was studied in two cell lines of murine neuroblastoma (MNB-T1 and MNB-T2) that were derived from C-1300 MNB tumor carried in A/J mice. The MNB-T2 (low malignancy) cell line was originally derived from the in situ tumor and carried in tissue culture for more than 100 passages; the MNB-T1 (high malignancy) line consisted of a new sub-culture that was also established from the in situ MNB tumor. DPD activity was determined in cytosolic preparations of MNB utilizing high performance liquid chromatography to separate the radiolabeled substrate ([2-14C]thymine) from [2-14C]dihydrothymine. The apparent affinity of DPD for NADPH in MNB cells (Km approximately 0.08 mM) was identical to that of A/J mouse brain and liver. The DPD activity of the high malignancy (MNB-T1) cell line was 14.3% of that observed in the low malignancy (MNB-T2) line. In situ tumors formed after implantation of high malignancy (MNB-T1) cells into A/J mice had only 25.2% of the DPD activity observed in tumors derived from low malignancy (MNB-T2) cells. When MNB-T2 cells were injected into naive A/J mice, tumors developed in only 68% of animals, the tumor growth rate was slow and a mortality of 20% was observed. In contrast, tumors derived from injected MNB-T1 cells showed a faster growth rate and 100% mortality. Most MNB-T2 derived tumors were not lethal and ultimately resolved while the MNB-T1 derived tumors were invariably lethal. These studies support the concept that the levels of DPD activity in neoplastic cells are inversely related to their malignant expression and also provide a model to study differences between neuroblastoma cell lines derived from the same in situ tumor but which manifest different neoplastic behavior.

Authors

M Tuchman, R F O'Dea, M L Ramnaraine, B L Mirkin

Atrial natriuretic factor gene expression in ventricles of rats with spontaneous biventricular hypertrophy.

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Abstract

A subset of Wistar-Kyoto (WKY) rats that spontaneously develops biventricular hypertrophy (BVH) in response to increased cardiac output was evaluated for ventricular expression of the atrial natriuretic factor (ANF) gene. Normal WKY rats had low levels of left ventricular ANF mRNA and minimally detectable ANF transcripts in the right ventricle. In contrast, BVH rats showed a sixfold greater ANF mRNA concentration in the left ventricle than age-matched WKY controls. BVH right ventricular ANF mRNA levels equaled those found in BVH left ventricles and were dramatically greater than WKY right ventricular controls. Unlike experimental models of hypertrophy, both left and right ventricles significantly increase ANF gene transcripts in the natural development of BVH. The left and right ventricles can concordantly respond to hypertrophy and increase ANF gene transcription.

Authors

R T Lee, K D Bloch, J M Pfeffer, M A Pfeffer, E J Neer, C E Seidman

Quantitative study of insulin secretion and clearance in normal and obese subjects.

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Abstract

The secretion and hepatic extraction of insulin were compared in 14 normal volunteers and 15 obese subjects using a previously validated mathematical model of insulin secretion and rate constants for C-peptide derived from analysis of individual decay curves after intravenous bolus injections of biosynthetic human C-peptide. Insulin secretion rates were substantially higher than normal in the obese subjects after an overnight fast (86.7 +/- 7.1 vs. 50.9 +/- 4.8 pmol/m2 per min, P less than 0.001, mean +/- SEM), over a 24-h period on a mixed diet (279.6 +/- 24.2 vs. 145.8 +/- 8.8 nmol/m2 per 24 h, P less than 0.001), and during a hyperglycemic intravenous glucose infusion (102.2 +/- 10.8 vs. 57.2 +/- 2.8 nmol/m2 per 180 min, P less than 0.001). Linear regression analysis revealed a highly significant relationship between insulin secretion and body mass index. Basal hepatic insulin extraction was not significantly different in the normal and obese subjects (53.1 +/- 3.8 vs. 51.6 +/- 4.0%). In the normal subjects, fasting insulin did not correlate with basal hepatic insulin extraction, but a significant negative correlation between fasting insulin and hepatic insulin extraction was seen in obesity (r = -0.63, P less than 0.02). This finding reflected a higher extraction in the six obese subjects with fasting insulin levels within the range of the normal subjects than in the nine subjects with elevated fasting insulin concentrations (61 +/- 3 vs. 45 +/- 6%, P less than 0.05). During the hyperglycemic clamp, the insulin secretion rate increased to an average maximum of 6.2-fold over baseline in the normal subjects and 5.8-fold in the obese subjects. Over the same time, the peripheral insulin concentration increased 14.1-fold over baseline in the normals and 16.6-fold over baseline in the obese, indicating a reduction in the clearance of endogenously secreted insulin. Although the fall in insulin clearance tended to be greater in the obese subjects, the differences between the two groups were not statistically significant. Thus, under basal, fasting conditions and during ingestion of a mixed diet, the hyperinsulinemia of obesity results predominantly from increased insulin secretion. In patients with more marked basal hyperinsulinemia and during intense stimulation of insulin secretion, a reduction in insulin clearance may contribute to the greater increase in peripheral insulin concentrations that are characteristic of the obese state.+

Authors

K S Polonsky, B D Given, L Hirsch, E T Shapiro, H Tillil, C Beebe, J A Galloway, B H Frank, T Karrison, E Van Cauter

Twenty-four-hour profiles and pulsatile patterns of insulin secretion in normal and obese subjects.

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Abstract

The pattern of endogenous insulin secretion over a 24-h period, which included three mixed meals, was evaluated in 14 normal volunteers and 15 obese subjects. Insulin secretory rates were calculated from plasma C-peptide levels using individually derived C-peptide kinetic parameters and a validated open two-compartment model of peripheral C-peptide kinetics. Insulin secretion rates were consistently elevated in the obese subjects under basal conditions (11.6 +/- 1.2 vs. 5.4 +/- 0.5 nmol/h) and in the 4 h after breakfast (139 +/- 15 vs. 63 +/- 5 nmol/4 h, P less than 0.001), lunch (152 +/- 16 vs. 67 +/- 5 nmol/4 h, P less than 0.001), and dinner (145 +/- 18 vs. 65 +/- 6 nmol/4 h, P less than 0.001). In the normal subjects, basal insulin secretion represented 50 +/- 2.1% of total 24-h insulin production, insulin secretion returned to baseline between meals, and equal quantities of insulin were secreted in the 4 h after breakfast, lunch, and dinner, despite the fact that subjects consumed half the number of calories at breakfast compared to lunch and dinner. Overall glucose responses were also similar after the three meals. In contrast, the pattern of insulin secretion in obese subjects was largely normal, albeit set at a higher level. However, the insulin secretion rate after meals did not return to baseline, and the secretion rate immediately before lunch (350.5 +/- 81.9 pmol/min) and dinner (373.6 +/- 64.8 pmol/min) was considerably higher than the secretion rate immediately before breakfast (175.5 +/- 18.5 pmol/min). In these overweight subjects, the glucose response after lunch was lower than after dinner. Analysis of individual 24-h insulin secretory profiles in the normal subjects revealed that insulin secretion was pulsatile. On average 11.1 +/- 0.5 pulses were produced in each 24-h period. The most prevalent temporal distribution of postmeal secretory pulses was two pulses after breakfast and three pulses after both lunch and dinner. Insulin secretion was also pulsatile during the period without meal stimuli: 3.9 +/- 0.3 pulses occurred during the period of overnight sampling and in the 3-h period before ingestion of the breakfast meal. In the obese subjects, the number and timing of secretory pulses was similar to those of normal volunteers, although the amplitude of the pulses was significantly greater. In both groups of subjects, greater than 80% of insulin pulses were concomitant with a pulse in glucose concentration in the postmeal period. The concomitancy rate was significantly lower in the interval without the meal stimuli, averaging 47% in both groups. Thus in obesity, although hypersecretion of insulin can be documented, the temporal pattern of secretion i s largely unaltered, which suggests that the functioning beta cell mass is enhance, but normal regulatory mechanisms influencing secretion are still operative.

Authors

K S Polonsky, B D Given, E Van Cauter

Activation of Ca2+-dependent K+ channels in human B lymphocytes by anti-immunoglobulin.

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Abstract

Many mammalian cell types exhibit Ca2+-dependent K+ channels, and activation of these channels by increasing intracellular calcium generally leads to a hyperpolarization of the plasma membrane. Their presence in B lymphocytes is as yet uncertain. Crosslinking Ig on the surface of B lymphocytes is known to increase the level of free cytoplasmic calcium ([Ca2+]i). However, rather than hyperpolarization, a depolarization has been reported to occur after treatment of B lymphocytes with anti-Ig. To determine if Ca2+-dependent K+ channels are present in B lymphocytes, and to examine the relationship between intracellular free calcium and membrane potential, we monitored [Ca2+]i by means of indo-1 and transmembrane potential using bis(1,3-diethylthiobarbituric)trimethine oxonol in human tonsillar B cells activated by anti-IgM. Treatment with anti-IgM induced a biphasic increase in [Ca2+]i and a simultaneous hyperpolarization. A similar hyperpolarization was induced by ionomycin, a Ca2+ ionophore. Delaying the development of the [Ca2+]i response by increasing the cytoplasmic Ca2+-buffering power delayed the hyperpolarization. Conversely, eliminating the sustained phase of the [Ca2+]i response by omission of external Ca2+ abolished the prolonged hyperpolarization. In fact, a sizable Na+-dependent depolarization was unmasked. This study demonstrates that in human B lymphocytes, Ca2+-dependent K+ channels can be activated by crosslinking of surface IgM. Moreover, it is likely that, by analogy with voltage-sensitive Ca2+ channels, Na+ can permeate through these ligand-gated Ca2+ "channels" in the absence of extracellular Ca2+.

Authors

S L MacDougall, S Grinstein, E W Gelfand

Tumor necrosis factor expression in human epithelial tumor cell lines.

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Abstract

Tumor necrosis factor (TNF) is a monokine with in vitro cytotoxicity for some but not all tumor cells. The basis for sensitivity and resistance to the antitumor effects of this agent remains unclear. The present studies have monitored the effects of TNF on 14 epithelial tumor cell lines. Eleven of these cell lines were resistant to the growth inhibitory effects of TNF (50% inhibitory concentration greater than 1,000 U/ml). 12 of the 14 tumor cell lines has detectable levels of high affinity cell surface TNF binding sites, thus suggesting that resistance was not often due to the absence of cell surface TNF receptors. Northern blot analysis demonstrated that three of the eleven resistant cell lines expressed detectable levels of TNF mRNA. Furthermore, both sensitive and resistant epithelial tumor cells had the capacity to express TNF transcripts in the presence of the protein synthesis inhibitor, cycloheximide. Finally, the presence of TNF expression at the RNA level is shown to be associated with the production of a TNF-like protein in the resistant Ov-D ovarian carcinoma cells. These findings suggest that certain human epithelial tumor cell lines inherently resistant to TNF also express this cytokine.

Authors

D R Spriggs, K Imamura, C Rodriguez, E Sariban, D W Kufe

Increased renal catabolism of 1,25-dihydroxyvitamin D3 in murine X-linked hypophosphatemic rickets.

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Abstract

The hypophosphatemic (Hyp) mouse, a murine homologue of human X-linked hypophosphatemic rickets, is characterized by renal defects in brush border membrane phosphate transport and vitamin D3 metabolism. The present study was undertaken to examine whether elevated renal 25-hydroxyvitamin D3-24-hydroxylase activity in Hyp mice is associated with increased degradation of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] by side chain oxidation. Metabolites of 1,25(OH)2D3 were separated by HPLC on Zorbax SIL and identified by comparison with standards authenticated by mass spectrometry. Production of 1,24,25-trihydroxyvitamin D3, 24-oxo-1,25-dihydroxyvitamin D3, and 24-oxo-1,23,25-trihydroxyvitamin D3 was twofold greater in mitochondria from mutant Hyp/Y mice than from normal +/Y littermates. Enzyme activities, estimated by the sum of the three products synthesized per milligram mitochondrial protein under initial rate conditions, were used to estimate kinetic parameters. The apparent Vmax was significantly greater for mitochondria from Hyp/Y mice than from +/Y mice (0.607 +/- 0.064 vs. 0.290 +/- 0.011 pmol/mg per protein per min, mean +/- SEM, P less than 0.001), whereas the apparent Michaelis-Menten constant (Km) was similar in both genotypes (23 +/- 2 vs. 17 +/- 5 nM). The Km for 1,25(OH)2D3 was approximately 10-fold lower than that for 25-hydroxyvitamin D3 [25(OH)D3], indicating that 1,25(OH)2D3 is perhaps the preferred substrate under physiological conditions. In both genotypes, apparent Vmax for 25(OH)D3 was fourfold greater than that for 1,25(OH)2D3, suggesting that side chain oxidation of 25(OH)D3 may operate at pharmacological concentrations of substrate. The present results demonstrate that Hyp mice exhibit increased renal catabolism of 1,25(OH)2D3 and suggest that elevated degradation of vitamin D3 hormone may contribute significantly to the clinical phenotype in this disorder.

Authors

H S Tenenhouse, A Yip, G Jones

Elevation of total homocysteine in the serum of patients with cobalamin or folate deficiency detected by capillary gas chromatography-mass spectrometry.

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Abstract

To determine if levels of serum total homocysteine are elevated in patients with either cobalamin or folate deficiency, we utilized a new capillary gas chromatographic-mass spectrometric technique to measure total homocysteine in the serum of 78 patients with clinically confirmed cobalamin deficiency and 19 patients with clinically confirmed folate deficiency. Values ranged from 11 to 476 mumol/liter in the cobalamin-deficient patients and 77 of the 78 patients had values above the normal range of 7-22 mumol/liter as determined for 50 normal blood donors. In the cobalamin-deficient patients, serum total homocysteine was positively correlated with serum folate, mean corpuscular volume, serum lactate dehydrogenase, serum methylmalonic acid, and the degree of neurologic involvement, and inversely correlated with platelets and hematocrit. In the folate-deficient patients, values for serum total homocysteine ranged from 17 to 185 mumol/liter and 18 of the 19 patients had values above the normal range. Some patients with pernicious anemia who were intermittently treated with cyanocobalamin were found to have elevated serum levels of total homocysteine while they were free of hematologic and neurologic abnormalities. The measurement of serum total homocysteine will help define the incidence of cobalamin deficiency and folate deficiency in various patient populations.

Authors

S P Stabler, P D Marcell, E R Podell, R H Allen, D G Savage, J Lindenbaum

Major parietal cell antigen in autoimmune gastritis with pernicious anemia is the acid-producing H+,K+-adenosine triphosphatase of the stomach.

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Abstract

In autoimmune gastritis antibodies against a membrane-bound parietal cell antigen of previously unknown function are present in the sera of patients. In this study, a vesicular membrane preparation of porcine gastric mucosa cells was found to be a potent antigenic source. This preparation blocked greater than 90% of antibody binding to a lysate of gastric mucosa cells. The membrane fraction contained H+,K+-ATPase (EC 3.6.1.36) as the major protein, which in sodium dodecyl sulfate-polyacrylamide gel electrophoresis migrated with a weight of 92 kD. After reduction and alkylation, this component was resolved into two bands of similar staining intensity (92 and 88 kD). Immunoblotting analysis showed that sera of patients recognized antigen with pattern identical to the major protein of the vesicular membranes. Protein A-Sepharose beads preincubated with immunoglobulins of five individual patient (but not control) sera were all found to reduce both the H+,K+-ATPase activity and the amount of parietal cell antigen of a preparation of vesicular membranes solubilized in n-octylglucoside. Taken together, the results of this study indicate that the major parietal cell antigen is identical to the acid-producing enzyme, H+,K+-ATPase, of the parietal cell.

Authors

F A Karlsson, P Burman, L Lööf, S Mårdh

Expression of crossreactive idiotypes by human antibodies specific for the capsular polysaccharide of Hemophilus influenzae B.

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Abstract

Human antibodies specific, for polyribosyl-ribitol-phosphate (PRP), the capsular polysaccharide of Hemophilus influenzae b, were studied using idiotypic analysis. Antisera were prepared against purified F(ab')2 anti-PRP from two unrelated adults, H.H. and P.T. After repeated absorption with IgG myeloma proteins and with PRP-absorbed normal human Ig and donor Ig, anti-idiotypic (anti-Id) sera were obtained that specifically reacted with anti-PRP antibodies. Anti-IdHH and anti-IdPT reciprocally crossreacted with H.H. and P.T. anti-PRP antibodies and F(ab')2 fragments, and also reacted with the serum anti-PRP antibodies from three additional adults unrelated to P.T. and H.H. Both anti-Id sera partially inhibited anti-PRP paratopes but not anti-tetanus toxoid paratopes. PRP did not inhibit anti-Id recognition of shared or crossreactive idiotypic (CRI) determinants. Naturally occurring and PRP immunization-induced anti-PRP antibodies expressed CRI. While CRI titer increased after immunization, the increase was usually less than the rise in total anti-PRP antibody. Quantitative differences in CRI expression were also apparent between natural and immunization-induced H.H. and P.T. anti-PRP antibodies as shown by their differential inhibitability by anti-Id. Our data demonstrate that anti-PRP antibodies from five unrelated adults express CRI determinants that are probably distant from the PRP combining site. Naturally occurring and immunization-induced anti-PRP antibodies share CRI and therefore appear to be clonally related, although immunization apparently induces the expression CRI-negative antibodies as well. These results, taken with previous studies showing restricted and identical anti-PRP isoelectric focusing spectrotypes in unrelated adults, suggest that some PRP-specific V domains are structurally conserved and probably germ-line encoded.

Authors

A H Lucas

Interleukin 1: a mitogen for human vascular smooth muscle cells that induces the release of growth-inhibitory prostanoids.

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Abstract

There is much interest in defining the signals that initiate abnormal proliferation of cells in a variety of states characterized by the presence of mononuclear phagocytes. Since IL-1 is a major secretory product of activated human monocytes we examined whether this cytokine can stimulate the growth of human vascular smooth muscle cells (SMC). Neither recombinant IL-1 (rIL-1) alpha (less than or equal to 5.0 ng/ml) nor beta (less than or equal to 100 ng/ml) stimulated SMC growth during 2-d incubations under usual conditions. IL-1 did stimulate SMC to produce prostanoids such as PGE1 or PGE2 that can inhibit SMC proliferation. When prostaglandin synthesis was inhibited by indomethacin or aspirin both rIL-1 alpha and beta (greater than or equal to 1 ng/ml) markedly increased SMC growth. In longer-term experiments (7-28 d) rIL-1 stimulated the growth of SMC even in the absence of cyclooxygenase inhibitors. The addition of exogenous PGE1 or PGE2 (but not PGF1 alpha, PGF2 alpha, PGI2) to indomethacin-treated SMC blocked their mitogenic response to rIL-1. Antibody to IL-1 (but not to platelet-derived growth factor [PDGF]) abolished the mitogenic response of SMC to rIL-1. Exposure of SMC to rIL-1 or PDGF caused rapid (maximal at 1 h) and transient (baseline by 3 h) expression of the c-fos proto-oncogene, determined by Northern analysis. We conclude that IL-1 is a potent mitogen for human SMC. Endogenous prostanoid production simultaneously induced by IL-1 appears to antagonize this growth-promoting effect in the short term (2 d) but not during more prolonged exposures. IL-1 produced by activated monocytes at sites of tissue inflammation or injury may thus mediate both positive and negative effects on SMC proliferation that are temporally distinct.

Authors

P Libby, S J Warner, G B Friedman

Glucocorticoid regulation of insulin receptor gene transcription in IM-9 cultured lymphocytes.

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Abstract

We have reported that glucocorticoids increase steady state insulin receptor mRNA levels in target cells. In the present study using IM-9 cultured human lymphocytes, we investigated the mechanism responsible for this glucocorticoid mediated increase in insulin receptor mRNA levels. Incubation of IM-9 cells with 100 nM dexamethasone for 4 h stimulated a parallel increase in both polysomal and nuclear insulin receptor RNAs indicating that glucocorticoids did not alter the nuclear transport of insulin receptor RNA. Dexamethasone did not alter insulin receptor mRNA half life (t 1/2 = 140 +/- 20 min), indicating that glucocorticoids did not influence mRNA stability. Furthermore, the dexamethasone-induced increase in insulin receptor mRNA levels was not blocked by pretreatment of cells with cycloheximide indicating that the glucocorticoid effect was independent of new protein synthesis. When the labeled transcripts from nuclear run-off incubations were then hybridized to immobilize human insulin receptor cDNA, a three- to fourfold increase in transcriptional activity was observed. This transcriptional effect occurred before the increase in steady state insulin receptor mRNA levels and over the same range of dexamethasone concentrations. These studies indicate therefore a direct effect of glucocorticoids on insulin receptor gene transcription, and demonstrate that the insulin receptor gene is under hormonal control.

Authors

A R McDonald, I D Goldfine

Platelet glycoproteins Ia, Ic, and IIa are physicochemically indistinguishable from the very late activation antigens adhesion-related proteins of lymphocytes and other cell types.

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Abstract

The very late activation antigens (VLA) are a subset of the superfamily of cell surface glycoproteins that serve as receptors from extracellular matrix proteins. One or more of the VLA heterodimers are present on T lymphocytes and most other cell types, including platelets. We have used VLA-specific monoclonal antibodies to isolate the reactive platelet membrane molecules. We have identified them as previously characterized platelet surface glycoproteins and have compared them with VLA molecules isolated from lymphocytes and other cells. Utilizing one-dimensional SDS-PAGE, two-dimensional O'Farrell gel electrophoresis, and nonreduced-reduced two-dimensional gel electrophoresis, we show that reduced VLA molecules of platelets are composed of three chains of molecular weights 165,000, 145,000, and 140,000 that possess the physicochemical properties of platelet glycoproteins GPIa, GPIc alpha, and GPIIa. GPIa corresponds to the VLA 165,000 alpha 2-chain, GPIIa corresponds to a 145,000 Mr VLA beta-chain, and GPIc alpha corresponds to a 140,000 Mr VLA alpha-chain. The polypeptide structure of VLA molecules on platelets and lymphocytes are very similar or identical. Platelet proteins GPIa and GPIIa exist as a mixed heterodimer in detergent lysates and correspond with the VLA-2 heterodimer found on activated T lymphocytes and other cell types. The platelet glycoproteins GPIIa and GPIc form a second mixed heterodimer. The mAb A-1A5, which binds to the VLA beta chain, binds to platelet GPIIa and precipitates both the GPIIa-GPIa and GPIIa-GPIc heterodimers, and binds to 4,926 +/- 740 sites per platelet. A VLA-2-specific mAb, 12F1, which binds to the VLA alpha 2-chain reacts with GPIa and immunoprecipitates only the GPIIa-GPIa heterodimer, and binds to 1,842 +/- 449 sites per platelet. The similarity of VLA chains and platelet GPIIa, GPIa, and GPIc molecules suggests that these molecules may have similar functions on various cell types.

Authors

K D Pischel, H G Bluestein, V L Woods Jr

B lymphocytes from X-linked agammaglobulinemia. Delayed expression of light chain and demonstration of Lyonization in carriers.

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Abstract

We report an unusual phenotype of B cells in a patient with X-linked agammaglobulinemia (XLA), and cellular evidence for Lyonization of B cells from his mother and sister. The patient has a failure of B cell maturation at the stage of early B lymphocytes, associated with production of D(mu delta) H chain. The phenotype of his B cells includes: (a) limitation to expression of the mu and delta H chain isotypes, (b) production of mu and delta H chains of reduced size and (c) delayed expression of L chain. Peripheral blood and B cell lines from the patient's mother and sister include 50% cells that express H chain without L chain. B cell lines from the mother and sister produce full-length mu and gamma H chains and truncated mu and delta chains corresponding to the H chains produced by the patient's B cells. Clones with normal and XLA phenotype have been isolated from B cell lines derived from the patient's mother. We conclude that the dimorphism of mother's and sister's B cells results from Lyonization, implying that the gene defect in XLA is intrinsic to B lymphocytes.

Authors

J Schwaber, J Payne, R Chen

Interactions of spectrin in hereditary elliptocytes containing truncated spectrin beta-chains.

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Abstract

An abnormal spectrin, in which one subunit is truncated, has been detected in a large German family. The inheritance is autosomal dominant. The affected members of the family suffer in widely varying degree from a microcytic hemolytic anemia. The red cell morphology varies correspondingly from smooth elliptocytes to predominantly poikilocytes. The abnormal spectrin makes up approximately 30% of the total and is almost entirely present as the dimer. The truncated chain is not phosphorylated by the endogenous cAMP-independent kinase, and it has been identified as a chain of beta-type, using monoclonal antibodies. Because a univalent terminal spectrin alpha-chain fragment will bind to normal dimers with an association constant lower by only a factor of two than that for the self-association of the dimers, it would be expected that the mutant dimers (alpha beta') would readily enter into an association with normal (alpha beta) dimers to give alpha 2 beta beta' tetramers (though not with each other). In dilute solution this is indeed observed, and the diminution in tetramer concentration when 30% of normal spectrin is replaced by alpha beta' dimers, amounts to only a small proportion. Moreover, in the membrane skeleton, if there is pairwise apposition of dimer units, only 9% of pairings will be between units that cannot associate. We have shown that the failure of alpha beta' dimers to enter into heterologous associations in situ is not due to the elimination of the ankyrin binding site near the truncated end of the beta-chain: this site is fully functional, as judged by rebinding to spectrin-depleted vesicles. When the spectrin is extracted from the membrane in the cold, the material released initially consists almost entirely of alpha beta' dimers; when the spectrin of normal membranes is partly dissociated to dimers in situ by warming at low ionic strength, extraction in the cold then leads similarly to much more rapid release of the dimer than of the tetramer. The similar rates of liberation of normal and abnormal dimer make it unlikely that the interaction of the latter with the membrane is in any way defective. When mixtures of alpha beta and alpha beta' dimers are bound to spectrin-depleted inside-out membrane vesicles from normal cells and tetramers are allowed to form by equilibration at 30 degrees C, the proportion of the abnormal species appearing in the tetramer is much lower than would be expected on a statistical basis. The relation of the self-association equilibrium on the membrane to that of spectrin in dilute solution is analyzed.

Authors

S W Eber, S A Morris, W Schröter, W B Gratzer

Neutrophil adherence to human endothelium in vitro occurs by CDw18 (Mo1, MAC-1/LFA-1/GP 150,95) glycoprotein-dependent and -independent mechanisms.

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Abstract

Components of the CDw18 leukocyte surface glycoprotein complex (Mo1/LFA-1/GP 150,95 or MAC-1, LFA-1 family) are required for some adhesion-related functions of human neutrophils (PMNs). We evaluated the ability of monoclonal antibodies (MoAb) directed against specific determinants on the CDw18 glycoproteins to inhibit neutrophil adherence to cultured human endothelial cells (EC) stimulated by a variety of agonists, including thrombin and leukotriene C4, which induce the EC-dependent adhesion of PMNs. MoAb 60.3, an antibody that binds to an epitope common to the 3 heterodimer subunits of the neutrophil CDw18 complex, potently inhibited (90-100%) the rapid (5-30 minute) adherence response stimulated by N-formyl-methyionyl-leucyl-phenylalanine, leukotriene B4, platelet-activating factor, phorbol myristate acetate, Ionophore A23187, and tumor necrosis factor. MoAbs directed against epitopes on the alpha polypeptide of the CD11b (Mol, MAC-1) heterodimer also inhibited PMN adherence to EC and to cell-free surfaces induced by these agonists. In contrast, the anti-CDw18 MoAbs had a trivial effect on maximal EC-dependent neutrophil adherence stimulated by thrombin and leukotriene C4, and incompletely inhibited PMN adherence induced by these agonists under submaximal conditions. These findings indicate that there is an alternative mechanism for neutrophil adherence, presumably resulting from molecular alterations of the EC surface, that does not require the PMN CDw18 glycoproteins. They also suggest that the inability to adhere to endothelium may not completely account for the defect in chemotaxis that is observed in vivo in neutrophils that are deficient in the CDw18 complex.

Authors

G A Zimmerman, T M McIntyre

Human T cell leukemia virus-I-associated T-suppressor cell inhibition of erythropoiesis in a patient with pure red cell aplasia and chronic T gamma-lymphoproliferative disease.

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Abstract

Human retroviruses have recently been linked with T cell lymphoproliferative disorders and with the acquired immune deficiency syndrome. We investigated the mechanisms for acquired pure red cell aplasia and cutaneous anergy in a patient with the chronic T gamma-lymphoproliferative disease (T gamma-LPD) syndrome. Patient marrow erythroid progenitors (BFU-E) were 17 +/- 9% of control and were selectively increased to 88-102% of control after marrow T cell depletion. Patient Leu 2+ suppressor T cells spontaneously produced high titers of human gamma-interferon and resulted in a concentration-dependent selective inhibition (74-91%) of BFU-E when co-cultured with autologous or allogeneic marrow. Conditioned media (CM) derived from patient Leu 2+ T cells similarly inhibited growth of autologous or allogeneic marrow BFU-E. The inhibitory factor derived from patient CM was acid-labile (pH 2) and sensitive to trypsin; prior treatment of patient T cells with anti-HLA-DR monoclonal antibody plus complement abrogated the suppressive effect of T cell-derived CM. Patient peripheral blood mononuclear cells (PBMC) were unable to support growth of cultured interleukin 2 (IL 2)-dependent T cells, but responded to exogenous IL 2 in vitro with a 16-21-fold augmentation, relative to control, in mitogen-induced proliferation. Antibodies to HTLV-I core proteins p19 and p24 but not to HTLV-III proteins were detected in patient serum by Western blotting; patient cultured PBMC stained (7-11%) with antibodies to p19 and p24. Patient cultured PBMC demonstrated integrated HTLV-I genomic sequences by the Southern technique and expressed both specific HTLV-I genomic sequences by RNA dot blot plus reverse transcriptase activity. Utilizing a cloned DNA probe for the beta chain of the T cell receptor gene, patient PMBC demonstrated gene rearrangements providing presumptive evidence for clonality. The presence in serum of HTLV-I p19 and p24 antibodies, the expression of p19 and p24 core antigens on patient mononuclear cells, the evidence of HTLV-I proviral integration sequences and the expression of HTLV-I genomic sequences in patient cells, indicates infection with HTLV-I and raises the possibility of an etiologic link between human retrovirus infection and some instances of large granular lymphocytic leukemia (T gamma-LPD).

Authors

L J Levitt, G R Reyes, D K Moonka, K Bensch, R A Miller, E G Engleman

Oral carnitine therapy in children with cystinosis and renal Fanconi syndrome.

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Abstract

11 children with either cystinosis or Lowe's syndrome had a reduced content of plasma and muscle carnitine due to renal Fanconi syndrome. After treatment with oral L-carnitine, 100 mg/kg per d divided every 6 h, plasma carnitine concentrations became normal in all subjects within 2 d. Initial plasma free fatty acid concentrations, inversely related to free carnitine concentrations, were reduced after 7-20 mo of carnitine therapy. Muscle lipid accumulation, which varied directly with duration of carnitine deficiency (r = 0.73), improved significantly in three of seven rebiopsied patients after carnitine therapy. One Lowe's syndrome patient achieved a normal muscle carnitine level after therapy. Muscle carnitine levels remained low in all cystinosis patients, even though cystinotic muscle cells in culture took up L-[3H]carnitine normally. The half-life of plasma carnitine for cystinotic children given a single oral dose approximated 6.3 h; 14% of ingested L-carnitine was excreted within 24 h. Studies in a uremic patient with cystinosis showed that her plasma carnitine was in equilibrium with some larger compartment and may have been maintained by release of carnitine from the muscle during dialysis. Because oral L-carnitine corrects plasma carnitine deficiency, lowers plasma free fatty acid concentrations, and reverses muscle lipid accumulation in some patients, its use as therapy in renal Fanconi syndrome should be considered. However, its efficacy in restoring muscle carnitine to normal, and the optimal dosage regimen, have yet to be determined.

Authors

W A Gahl, I Bernardini, M Dalakas, W B Rizzo, G S Harper, J M Hoeg, O Hurko, J Bernar

Lipoprotein metabolism during acute inhibition of lipoprotein lipase in the cynomolgus monkey.

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Abstract

To clarify the role of lipoprotein lipase (LPL) in the catabolism of nascent and circulating very low density lipoproteins (VLDL) and in the conversion of VLDL to low density lipoproteins (LDL), studies were performed in which LPL activity was inhibited in the cynomolgus monkey by intravenous infusion of inhibitory polyclonal or monoclonal antibodies. Inhibition of LPL activity resulted in a three- to fivefold increase in plasma triglyceride levels within 3 h. Analytical ultracentrifugation and gradient gel electrophoresis demonstrated an increase predominantly in more buoyant, larger VLDL (Sf 400-60). LDL and high density lipoprotein (HDL) cholesterol levels fell during this same time period, whereas triglyceride in LDL and HDL increased. Kinetic studies, utilizing radiolabeled human VLDL, demonstrated that LPL inhibition resulted in a marked decrease in the catabolism of large (Sf 400-100) VLDL apolipoprotein B (apoB). The catabolism of more dense VLDL (Sf 60-20) was also inhibited, although to a lesser extent. However, there was a complete block in the conversion of tracer in both Sf 400-100 and 60-20 VLDL apoB into LDL during LPL inhibition. Similarly, endogenous labeling of VLDL using [3H]leucine demonstrated that in the absence of LPL, no radiolabeled apoB appeared in LDL. We conclude that although catabolism of dense VLDL continues in the absence of LPL, this enzyme is required for the generation of LDL.

Authors

I J Goldberg, N A Le, H N Ginsberg, R M Krauss, F T Lindgren

Biliary physiology in rats with bile ductular cell hyperplasia. Evidence for a secretory function of proliferated bile ductules.

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Abstract

To establish the role of the biliary epithelium in bile formation, we studied several aspects of biliary physiology in control rats and in rats with ductular cell hyperplasia induced by a 14-d extrahepatic biliary obstruction. Under steady-state conditions, spontaneous bile flow was far greater in obstructed rats (266.6 +/- 51.9 microliters/min per kg) than in controls (85.6 +/- 10.6 microliters/min per kg), while excretion of 3-hydroxy bile acids was the same in the two groups. Infusion of 10 clinical units (CU)/kg per h secretin produced a minimal choleretic effect in controls (+3.8 +/- 1.9 microliters/min per kg) but a massive increase in bile flow in the obstructed animals (+127.8 +/- 34.9 microliters/min per kg). Secretin choleresis was associated with an increase in bicarbonate biliary concentration and with a decline in [14C]mannitol bile-to-plasma ratio, although solute biliary clearance significantly increased. Conversely, administration of taurocholate (5 mumol/min per kg) produced the same biliary effects in control rats and in rats with proliferated biliary ductules. In the obstructed animals, the biliary tree volume measured during taurocholate choleresis (67.4 +/- 15.8 microliters/g liver) was significantly greater than that determined during the increase in bile flow induced by secretin (39.5 +/- 10.4 microliters/g liver). These studies indicate that, in the rat, the proliferated bile ductules/ducts spontaneously secrete bile and are the site of secretin choleresis. Furthermore, because the proliferated cells expressed phenotypic traits of bile ductular cells, our results suggest that whereas under normal conditions the biliary ductules/ducts in the rat seem to contribute little to bile formation, secretion of water and electrolytes is a property of biliary epithelial cells.

Authors

G Alpini, R Lenzi, L Sarkozi, N Tavoloni

Kniest dysplasia is characterized by an apparent abnormal processing of the C-propeptide of type II cartilage collagen resulting in imperfect fibril assembly.

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Abstract

Epiphyseal and growth plate cartilages from four cases of Kniest dysplasia have been studied. In each case collagen fibril organization appeared abnormal by electron microscopy compared with age-matched normal cartilages: fibrils were much thinner, of irregular shape and did not exhibit the characteristic banding pattern. This was associated with the absence (compared with normal cartilage) of the C-propeptide of type II collagen (chondrocalcin) from the extracellular matrix of epiphyseal cartilages, although it was detected (as in normal cartilages) in the lower hypertrophic zone of the growth plate in association with calcifying cartilage. The C-propeptide was abnormally concentrated in intracellular vacuolar sites in Kniest cartilages and its total content was reduced in all cases but not in all cartilages. Moreover, it was not a part of the procollagen molecule. In contrast, type II collagen alpha-chain size was normal, indicating the formation of a triple helix. Also type II collagen content was normal and it was present in extracellular sites and only occasionally detected intracellularly. These observations suggest that the defect in Kniest dysplasia may result from the secretion of type II procollagen lacking the C-propeptide and abnormal fibril formation, and that the C-propeptide is normally required for fibril formation.

Authors

A R Poole, I Pidoux, A Reiner, L Rosenberg, D Hollister, L Murray, D Rimoin

Homozygous hypobetalipoproteinemia: a disease distinct from abetalipoproproteinemia at the molecular level.

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Abstract

apoB DNA, RNA, and protein from two patients with homozygous hypobetalipoproteinemia (HBL) were evaluated and compared with normal individuals. Southern blot analysis with 10 different cDNA probes revealed a normal gene without major insertions, deletions, or rearrangements. Northern and slot blot analyses of total liver mRNA from HBL patients documented a normal size apoB mRNA that was present in greatly reduced quantities. ApoB protein was detected within HBL hepatocytes utilizing immunohistochemical techniques; however, it was markedly reduced in quantity when compared with control samples. No apoB was detectable in the plasma of HBL individuals with an ELISA assay. These data are most consistent with a mutation in the coding portion of the apoB gene in HBL patients, leading to an abnormal apoB protein and apoB mRNA instability. These results are distinct from those previously noted in abetalipoproteinemia, which was characterized by an elevated level of hepatic apoB mRNA and accumulation of intracellular hepatic apoB protein.

Authors

R S Ross, R E Gregg, S W Law, J C Monge, S M Grant, K Higuchi, T J Triche, J Jefferson, H B Brewer Jr

Synthetic human parathyroid hormone-like protein stimulates bone resorption and causes hypercalcemia in rats.

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Abstract

Parathyroid hormone-like adenylate cyclase-stimulating proteins (hACSPs) have been implicated as one of the calcemic, bone-resorbing agents in patients with humoral hypercalcemia of malignancy. We report the synthesis of an amino-terminal hACSP fragment, Tyr36 hACSP (1-36) amide. The synthetic hACSP is a potent agonist of renal membrane adenylate cyclase (Km, 1.7 X 10(-10)) and of bone cell adenylate cyclase (Km 1 X 10(-9)M). It is a potent bone-resorbing agent in vitro, stimulating 45Ca release from fetal rat long bones at a concentration of 10(-9) M. When infused via osmotic minipumps into rats, it is also a potent calcemic factor in vivo, inducing a rise in serum calcium from (mean +/- SD) 10.6 +/- 0.6 to 19.7 +/- 3.2 mg/dl when infused at 1.4 micrograms/h and from 9.9 +/- 0.7 to 11.4 +/- 1.2 mg/dl when infused at 0.14 micrograms/h. These findings indicate that biologically active hACSP fragments can be synthesized. One such synthetic peptide possesses the in vitro and in vivo bioactivities demonstrated in native, tumor-derived hACSPs. It is also a potent calcemic, bone-resorbing agent.

Authors

A F Stewart, M Mangin, T Wu, D Goumas, K L Insogna, W J Burtis, A E Broadus

Low density lipoproteins transfer bacterial lipopolysaccharides across endothelial monolayers in a biologically active form.

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Abstract

Rabbit aortic endothelial cells (RAECs) were grown on micropore filters in a device that allowed in situ determination of transendothelial electrical resistance (TEER). Incubation of confluent RAEC monolayers with 2 ng.ml-1 of bacterial LPS for 3 h did not change the protein content or the number of cells on the filters, but resulted in a marked decline in TEER (from 14.1 +/- 0.9 to 5.1 +/- 0.6 omega.cm2) and a significant increase in LDL transport across the monolayers (from 154 +/- 13 to 456 +/- 41 ng. h-1 per cm2). In contrast, exposure of RAEC monolayers for 3 d to as much as 5 micrograms.ml-1 of LPS complexed to LDL (LPS-LDL) did not alter the TEER or LDL transport. LPS-LDL was transported across the monolayers at the same rate as LDL. While microgram quantities of LPS complexed to LDL did not disrupt the integrity of the endothelial monolayer, incubation of RAECs with transported LPS-LDL at concentrations of 25-100 ng LPS.ml-1 resulted in a two- to ninefold increase in the secretion of monocyte chemotactic activity by these cells. Incubation of rabbit aortic smooth muscle cells with transported LPS-LDL at concentrations of 25-100 ng LPS.ml-1 resulted in a two- to threefold increase in the secretion of monocyte chemotactic activity. We propose that LDL protects endothelial cells from the acute toxicity of LPS but the resulting complexes are transported across the endothelium in a biologically active form that can initiate an inflammatory response.

Authors

M Navab, G P Hough, B J Van Lenten, J A Berliner, A M Fogelman

Chronic granulomatous disease due to a defect in the cytosolic factor required for nicotinamide adenine dinucleotide phosphate oxidase activation.

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Abstract

The superoxide-generating enzyme of human neutrophils, NADPH oxidase, is present in a dormant state in unstimulated neutrophils. It can be converted to an active form in a cell-free system if both the plasma membrane and cytosol fractions are incubated together in the presence of arachidonic acid. This system was used to determine the nature of the biochemical defect in seven patients with the autosomal recessive, cytochrome b-positive form of chronic granulomatous disease (CGD). A severe deficiency in the cytosol factor was identified in each patient. The defective activity was not caused by the presence of an inhibitor, nor could it be restored to normal by combining cytosol fractions from different patients. In contrast, the membrane fractions from all seven patients contained normal levels of NADPH oxidase when activated in the presence of control cytosol. Of family members tested (obligate heterozygotes for this disorder), seven of eight had intermediate levels of cytosol factor activity. The respiratory burst defect in this form of CGD is caused by an abnormality in the cytosolic factor required for NADPH oxidase activation.

Authors

J T Curnutte, R L Berkow, R L Roberts, S B Shurin, P J Scott

Relation of mesangial IgA glomerulonephritis to polymorphism of immunoglobulin heavy chain switch region.

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Abstract

We have investigated the switch regions of Ig heavy chain genes of patients with IgA glomerulonephritis (IgA-GN) using restriction fragment length polymorphism (RFLP) analysis. Genomic DNA from patients and controls was digested with the restriction endonuclease Sst I and transferred to nylon membranes using the Southern blot procedure and hybridized with a probe homologous to the switch region of the Ig C mu gene (S mu) which detects RFLPs in both S mu and the switch region of the Ig C alpha 1 gene (S alpha 1). A significant decrease in the frequency of the 2.6;2.1 kb heterozygous S mu phenotype was found in patients with IgA-GN (P = 0.003). With respect to the S alpha 1 region, there was a significant increase in the frequency of the 7.4 kb S alpha 1 phenotype (P = 0.002). In addition, a significant increase in the frequency of the 7.4 kb S alpha 1 allele was found (P = 0.0002). These results suggest that gene(s) within the Ig heavy chain loci may be important in the pathogenesis of IgA-GN.

Authors

A G Demaine, M Rambausek, J F Knight, D G Williams, K I Welsh, E Ritz

Detection of a protein-acetaldehyde adduct in the liver of rats fed alcohol chronically.

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Abstract

We report here the formation in vivo of a protein-acetaldehyde adduct (protein-AA) in liver when rats were fed alcohol chronically. This chemically modified protein was demonstrated by electroimmunotransblot technique and with rabbit polyclonal antibodies that recognize acetaldehyde adduct as an epitope (i.e., both anti-hemocyanin-AA IgG and anti-myoglobin-AA IgG). It has a molecular weight of 37,000. It can be detected in the liver of rats fed the alcohol-containing American Institute of Nutrition 1976 liquid diet for only 1 wk. Since the protein profiles of soluble hepatic proteins from alcohol-fed and control rats were identical on SDS-PAGE, the peroxidase-positive band demonstrated by electroimmunotransblot was most likely not a new protein synthesized de novo. Borohydride reduction was not necessary to stabilize this protein-AA. Intraperitoneal injections of ethanol (2 g/kg body wt) at 8-h intervals to rats over a 24-h period did not produce any detectable protein-AA in the liver. Incubation of the liver homogenate from a control liver with acetaldehyde without sodium cyanoborohydride for 4 h also failed to generate any protein-AA. Therefore, the formation of the 37-kD protein-AA in vivo reported here is dependent on chronic alcohol consumption.

Authors

R C Lin, R S Smith, L Lumeng

Peritubular cells are the site of erythropoietin synthesis in the murine hypoxic kidney.

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Abstract

Erythropoietin (Epo)-producing cells were identified in the murine hypoxic kidney by in situ hybridization. Profound anemia was induced in order to greatly increase Epo production. This resulted in high levels of Epo mRNA in the kidney. 35S-labeled DNA fragments of the murine Epo gene were used as probes for in situ hybridization. Control experiments conducted in parallel included kidneys of nonanemic mice, RNase-treated hypoxic kidney sections, and 35S-labeled non-Epo-related DNA. The Epo probe gave a specific hybridization signal in the hypoxic kidney in the cortex and to a lesser extent in the outer medulla. Glomerular and tubular cells were not labeled. All positive cells were identified as peritubular cells. Using immunofluorescence, we showed that cells with the same topography contained Factor VIII-related antigen. These data demonstrated that peritubular cells, most likely endothelial cells, constitute the major site of Epo production in the murine hypoxic kidney.

Authors

C Lacombe, J L Da Silva, P Bruneval, J G Fournier, F Wendling, N Casadevall, J P Camilleri, J Bariety, B Varet, P Tambourin

Reduction of experimental canine myocardial reperfusion injury by a monoclonal antibody (anti-Mo1, anti-CD11b) that inhibits leukocyte adhesion.

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Abstract

A monoclonal antibody (904) that binds to a leukocyte cell adhesion-promoting glycoprotein, (Mo1; CD11b/CD18) was administered (1 mg/kg, iv.) to open chest anesthetized dogs 45 min after the induction of regional myocardial ischemia. Ischemia was produced by occluding the left circumflex coronary artery (LCX) for 90 min and then reperfusing for 6 h. There was no difference between control and antibody treated groups with respect to arterial blood pressure, heart rate, or LCX blood flow. Administration of antibody produced no observable effect on circulating neutrophil counts, suggesting that antibody-bound neutrophils were not cleared from the circulation. The mean size of myocardial infarct expressed as percentage of the area at risk of infarction that resulted was reduced by 46% with anti-Mo1 treatment (25.8 +/- 4.7%, n = 8) compared to control (47.6 +/- 5.7%, n = 8; P less than 0.01). The area at risk of infarction was similar between groups. Circulating (serum) antibody excess was confirmed in all 8 anti-Mo1 treated dogs by immunofluorescence analysis. Analysis of ST segment elevation on the electrocardiogram as an indicator of the severity of ischemia suggests that the anti-Mo1 reduces infarct size independent of the severity of ischemia. An additional group of dogs (n = 5) was tested with a control monoclonal antibody of the same subtype (murine IgG1) and was found to produce no significant reduction in myocardial infarct size. Accumulation of neutrophils within the myocardium was significantly attenuated with 904 treatment when analyzed by histological methods. These data demonstrate that administration of anti-Mo1 monoclonal antibody after the induction of regional myocardial ischemia results in reduced myocardial reperfusion injury as measured by ultimate infarct size.

Authors

P J Simpson, R F Todd 3rd, J C Fantone, J K Mickelson, J D Griffin, B R Lucchesi

An initiator codon mutation in ornithine-delta-aminotransferase causing gyrate atrophy of the choroid and retina.

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Abstract

Gyrate atrophy of the choroid and retina (GA) is an autosomal recessive chorioretinal degeneration caused by deficiency of the mitochondrial matrix enzyme, ornithine-delta-aminotransferase (OAT). To study the molecular basis of the mutations causing GA, we cloned and sequenced the human OAT cDNA and determined the intron-exon arrangement of the structural gene. Using the cDNA template, we synthesized antisense RNA probes and performed RNase A protection experiments with RNA from four Lebanese GA patients. We found a probe-target mismatch at the 5' end of the first coding exon and amplified this region of the patients' genomic DNA using the polymerase chain reaction. Sequence analysis showed a G----A transition, changing the initiator ATG (methionine) codon to ATA. This mutation segregates with the GA allele in both pedigrees. Initiation of translation at the closest in-frame methionine codon would truncate OAT by 138 amino acids, eliminating the entire mitochondrial leader sequence and 113 amino acids of the mature peptide.

Authors

G A Mitchell, L C Brody, J Looney, G Steel, M Suchanek, C Dowling, V Der Kaloustian, M Kaiser-Kupfer, D Valle