Background—F₂ isoprostanes are stable, free radical–catalyzed products of arachidonic acid that reflect lipid peroxidation in vivo.

Methods and Results—Specific assays were developed by use of mass spectrometry for the F₂ isoprostanes iPF_2α-III and iPF_2α-VI and arachidonic acid (AA). Urinary excretion of the 2 F₂ isoprostanes was significantly increased in hypercholesterolemic patients, whereas substrate AA in urine did not differ between the groups. iPF_2α-III (pmol/mmol creatinine) was elevated (P<0.0005) in homozygous familial hypercholesterolemic (HFH) patients (85±5.5; n=38) compared with age- and sex-matched normocholesterolemic control subjects (58±4.2; n=38), as were levels of iPF_2α-VI (281±22 versus 175±13; P<0.0005). Serum cholesterol correlated with urinary iPF_2α-III (r=0.41; P<0.02) and iPF_2α-VI (r=0.39; P<0.03) in HFH patients. Urinary excretion of iPF_2α-III (81±10 versus 59±4; P<0.05) and iPF_2α-VI (195±18 versus 149±20; P<0.05) was also increased in moderately hypercholesterolemic subjects (n=24) compared with their controls. Urinary excretion of iPF_2α-III and iPF_2α-VI was correlated (r=0.57; P<0.0001; n=106). LDL iPF_2α-III levels (ng/mg arachidonate) were elevated (P<0.01) in HFH patients (0.32±0.08) compared with controls (0.09±0.02). The concentrations of iPF₂-III in LDL and urine were significantly correlated (r=0.42; P<0.05) in HFH patients.

Conclusions—Asymptomatic patients with moderate and severe hypercholesterolemia have evidence of oxidant stress in vivo.