Comments for:

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Factor XII: Inflammation versus coagulation

Submitter: Allen P. Kaplan | kaplana@musc.edu

Department of Medicine, Medical University of South Carolina, Charleston, South Carolina, USA.

Published November 25, 2008

Maas et. al. have demonstrated that misfolded protein aggregates formed by denaturation or by surface adsorption can activate Factor XII (FXII), leading to kallikrein generation (and presumably, bradykinin formation) without initiating blood coagulation (1). The phenomenon is demonstrable with many structurally unrelated substances if an amorphous aggregate is produced for testing. Since FXIIa clearly converts FXI to FXIa (2), the absence of coagulation is unanticipated and is discussed by Dr. Schmaier in his accompanying Commentary (3). I am writing to call attention to four areas I would like to discuss in greater detail.

First, Aβ protein (in the form of Aβ 1–38, Aβ 1–40, or Aβ 1–42) has been shown not only to activate Factor XII, but also to convert prekallikrein to kallikrein, cleave high–molecular weight kininogen, and produce bradykinin when Aβ aggregates were incubated with a mixture of these proteins (4). The relative rate of aggregation and contact activation paralleled the known neurotoxicity (5) of these peptides (Aβ 1–42 > Aβ 1–40 > Aβ 1–38). The monomeric form of Aβ was inactive, and in their study Maas et. al. demonstrated that amyloid fibrils of Aβ did not stimulate FXII-dependent kallikrein generation (1). Thus the intermediate protein aggregates are responsible for the biologic activity being measured and such aggregates may be responsible for neuronal toxicity (6).

Second, Dr. Schmaier points out that prekallikrein activation might be favored over FXI activation because of the higher concentration of plasma prekallikrein and he questions the sensitivity of the FXIa–C1 inhibitor assay as a measure of FXI activation (3). However α1-antitrypsin contributes significantly to FXI activation (7) and measurement of one enzyme-inhibitor complex may be insufficient if activation is subtle. Another possibility is conversion of FXIIa to FXIIf, a 30 kDa fragment that activates prekallikrein but which retains only 2–4% of the coagulant activity of FXIIa (8). Use of the α-FXIIa and β-FXIIa designation (9) in which α-FXIIa is synonymous with FXIIf, assumed activation of FXII to either form of FXIIa by cleavages (9) either within a disulfide bridge or external to it, that were not sequential. But the original thesis that FXII is activated to form FXIIa, which is next activated to form FXIIf (10), proved to be correct (11, 12) and should be standard nomenclature.

Third, the absence of bleeding in patients deficient in FXII, prekallikrein, or high–molecular weight kininogen has been a dilemma since these proteins were discovered, and FXI activation by thrombin (13) may not explain it (14, 15). Dr. Schmaier points out (3) recent evidence of a role for FXII in pathologic thrombosis but not in normal hemostasis. However, the assumption that absence of clotting in vitro has to imply bleeding as a consequence may be erroneous. Platelets may supply trophic factors (16) for endothelial cells but why should endothelial cell integrity be lost if the capacity to clot via blood proteins is compromised? Bleeding might not stop well once it starts (poor fibrin clot) but why should it start spontaneously (e.g. hemarthrosis in FVIII deficiency)? Thus I do not think “bleeding” is really understood and I offer the idea that bradykinin stimulation of endothelial cells has a role and that the only plasma deficiencies in which stimulated bradykinin formation is absent (deficiencies of FXII, prekallikrein, and high–molecular weight kininogen) result in protection from bleeding. Presence or absence of bleeding in a combined FXII and FVIII deficiency might answer the question.

Finally, Dr. Schmaier notes (3) the possible FXII bypass in which endothelial cell–derived prolylcarboxypeptidase (17) can lead to prekallikrein activation and bradykinin formation when incubated with a prekallikrein and high–molecular weight kininogen mixture. He fails to mention that HSP90 purified from endothelial cells does the same thing (18). Neither HSP90 nor prolylcarboxypeptidase is a prekallikrein activator like FXIIa or FXIIf (although the title of Reference 17 suggests that it does); they only interact with the prekallikrein- high–molecular weight kininogen complex and do so stoichiometrically to activate prekallikrein. Both are inhibited by corn trypsin inhibitor. However HSP90 is not known to have proteolytic activity and prolylcarboxypeptidase might not be functioning as an endopeptidase, as originally proposed (17).

References

1. Maas, C., et. al. 2008. Misfolded proteins activate Factor XII in humans, leading to kallikrein formation without initiating coagulation. J. Clin. Invest. 118:3208–3218.
2. Kurachi, K., and Davie, E. 1977. Activation of human factor XI (plasma thromboplastin antecedent) by factor XIIa (activated Hageman factor). Biochem. 16:5831–5839.
3. Schmaier, A. 2008. The elusive physiologic role of Factor XII. J. Clin. Invest. 118:3006–3009.
4. Shibayama, Y., et al. 1999. Zinc-dependent activation of the plasma kinin-forming cascade by aggregated beta amyloid protein. Clin. Immunol. 90:89–99.
5. Barelli, H., et al. 1997. Characterization of new polyclonal antibodies specific for 40 and 42 amino acid-long amyloid beta peptides: their use to examine the cell biology of presenilins and the immunohistochemistry of sporadic Alzheimer's disease and cerebral amyloid angiopathy cases. Mol. Med. 3:695–707.
6. Lesne, S., et al. 2006. A specific amyloid-beta protein assembly in the brain impairs memory. Nature. 440:352–357.
7. Heck, L.W., and Kaplan, A.P. 1974. Substrates of Hageman factor. I. Isolation and characterization of human factor XI (PTA) and inhibition of the activated enzyme by alpha 1-antitrypsin. J. Exp. Med. 140:1615–1630.
8. Kaplan, A.P., and Austen, K.F. 1970. A pre-albumin activator of prekallikrein. J. Immunol. 105:802–811.
9. Revak, S., et al. 1978. Surface and fluid phase activities of two forms of activated Hageman factor produced during contact activation of plasma. J. Exp. Med. 147:719–729.
10. Kaplan, A.P., and Austen, K.F. 1971. A prealbumin activator of prekallikrein. II. Derivation of activators of prekallikrein from active Hageman factor by digestion with plasmin. J. Exp. Med. 133:696–712.
11. Dunn, J.T., Silverberg, M., and Kaplan, A.P. 1982. The cleavage and formation of activated human Hageman factor by autodigestion and by kallikrein. J. Biol. Chem. 257:1779–1784.
12. Dunn, J.T., and Kaplan, A.P. 1982. Formation and structure of human Hageman factor fragments. J. Clin. Invest. 70:627–631.
13. Gailani, D., and Broze, G.J., Jr. 1991. Factor XI activation in a revised model of blood coagulation. Science. 253:909–912.
14. Brunnee, T., et al. 1993. Activation of factor XI in plasma is dependent on factor XII. Blood. 81:580–586.
15. Pedicord, D., Seiffert, D., and Blat, Y. 2007. Feedback activation of factor XI by thrombin does not occur in plasma. Proc. Natl. Acad. Sci. 104:12855–12860.
16. Nachman, R., and Rafii, S. 2008. Platelets, petechiae, and preservation of the vascular wall. New Engl. J. Med. 359:1261–1270.
17. Shariat-Madar, Z., Mahdi, F., and Schmaier, A. 2004. Recombinant prolylcarboxypeptidase activates plasma prekallikrein. Blood. 103:4554–4561.
18. Joseph, K., Tholanikunnel, B., and Kaplan, A. 2002. Heat shock protein 90 catalyzes activation of the prekallikrein-kininogen complex in the absence of factor XII. Proc. Natl. Acad. Sci. 99:896–900.

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Response to Kaplan

Submitter: Alvin H. Schmaier | Schmaier@case.edu

Division of Hematology and Oncology, Case Western Reserve University and University Hospitals Case Medical Center, Cleveland, Ohio, USA.

Published November 25, 2008

Dear Editors, I appreciate the comments of Dr. Kaplan, whose letter embellishes several aspects related to Factor XII (FXII) contact activation on amyloid, which due to space limitations I was unable to present in my original Commentary (1). Alpha-1–antitrypsin by virtue of its plasma concentration also is a major inhibitor of FXIa but its 2^nd order rate constant of inhibition (4.1 x 10³ M^-1min^-1) is less than that of C1 inhibitor (14.6 x 10³ M^-1min^-1) (2). When FXIa is added to plasma, 47% of FXIa complexes with C1 inhibitor and 24% complexes with α1-antitrypsin (3). I agree with Dr. Kaplan that there has never been clarity in the field on the nomenclature used to describe activated forms of FXII. I also agree with Dr. Kaplan that the absence of clotting does not imply bleeding since deficiencies of FXII, prekallikrein, high-molecular-weight kininogen, dysfibrinogenemias of the bβ chain, and lupus anticoagulants have reduced in vitro clotting without bleeding. In further agreement with Dr. Kaplan, the fact that mice deficient in FXII, kininogen, and bradykinin B2 receptor are protected against thrombosis suggests that in vivo bradykinin release may contribute to shortening of arterial thrombosis times (4–6). However, in vitro, bradykinin stimulates NO formation, tissue plasminogen activator release, and prostacyclin formation from cultured cells, events that protect against thrombosis (7–9). Alternatively, reduction of prolylcarboxypeptidase (PRCP) and pharmacologic inhibition of prekallikrein (PK) and PRCP in mice are associated with shortened arterial thrombosis times (10). Lastly, the mechanism by which PRCP activates PK is unknown. Recent studies suggest that the C-terminal Pro-Val bond of prekallikrein could be a substrate of PRCP resulting in PK activation (11). At present, there is no experimental evidence to support that hypothesis.

References

1. Schmaier, A. 2008. The elusive physiologic role of Factor XII. J. Clin. Invest. 118:3006–3009.
2. Scott, C.F., Schapria, M., James, H.L., Cohen, A.B., and Colman, R.W.1982. Inactivation of factor XIa by plasma protease inhibitors: predominate role of alpha 1-protease inhibitor and protective effect of high molecular weight kininogen. J. Clin. Invest. 69:844–852.
3. Wuillemin, W.A., et al. 1995. Inactivation of factor XIa in human plasma assesses by measuring factor Xia-protease inhibitor comlexes: major role for C1 inhibitor. Blood. 85:1517–1526.
4. Renne, T., et al. 2005. Defective thrombus formation in mice lacking coagulation factor XII. J. Exp. Med. 202:271–281.
5. Merkoulov, S., et al. 2008. Deletion of murine kininogen gene 1 (mKng1) causes loss of plasma kininogen and delays thrombosis. Blood. 111:1272–1281.
6. Shariat-Madar, Z., et al. 2006. Bradykinin B2 receptor knockout mice are protected from thrombosis by increased nitric oxide and prostacyclin. Blood. 108:192–199.
7. Palmer, R.M.J., Ferrige, A.G., and Moncada, S. 1987. Nitric oxide release accounts for the biologic activity of endothelium-derived relaxing factor. Nature. 327:524–526.
8. Hong, S.L. 1980. Effect of bradykinin and thrombin on prostatcylin synthesis in endothelial cells from calf and pig aorta and human umbilical cord vein. Thromb. Res. 18:787–796.
9. Smith, D., Gilbert, M., and Owen, W.G. 1983. Tissue plasminogen activator release in vivo in response to vasoactive agents. Blood. 66:835–839.
10. Adams, G.N., et al. 2008. Prolylcarboxypeptidase Murine Hypomorphs are Arterially Hypertensive and Prothrombotic. Abstract, American Society of Hematology Meeting, December, 2008.
11. Hooley, E., McEwan, P.A., and Emsley, J. 2007. Molecular modelling of the prekallikrein structure provide insights into HK binding and zymogen activation. 2007. J Thromb Haemost. 5:2461–2466.