Enhanced susceptibility to oxidation and diminished vitamin E content of LDL from patients with stable coronary artery disease.

BACKGROUND Convincing evidence points to oxidative modification of LDL as an important trigger in a complex chain of events leading to atherosclerosis. We investigated the occurrence of enhanced susceptibility of LDL to oxidation and decreased vitamin E concentration in LDL as additional risk factors promoting atherosclerosis among patients with established coronary artery disease (CAD). METHODS We examined 132 patients with angiographically confirmed CAD and compared them with 111 healthy control individuals. We measured conjugated diene production to assess susceptibility of LDL to copper-mediated oxidation. Vitamin E content of LDL was measured by HPLC. RESULTS The mean lag time of LDL oxidation and LDL alpha-tocopherol/LDL-cholesterol ratio were lower in the patients with CAD (55 +/- 14 min and 2.4 +/- 1.0 mmol/mmol) than in the controls (63 +/- 13 min and 2.9 +/- 1.1 mmol/mmol; P <0.0001 and <0.001, respectively). Multiple stepwise regression analysis demonstrated the lag time (odds ratio, 1.96; 95% confidence interval, 1.34-2.87; P <0.0001) and concentration of vitamin E in LDL (odds ratio, 1.65; 95% confidence interval, 1.16-2.33; P <0.005) as independent determinants of CAD. Significant inverse Spearman rank correlations were found between lag time (r = -0.285; P <0.001) or concentration of vitamin E in LDL (r = -0.197; P <0.002) and severity of CAD. Lag times were not significantly correlated with serum C-reactive protein or ferritin. CONCLUSIONS Our data suggest that a short LDL oxidation lag time and a low concentration of vitamin E in LDL might be independent coronary risk factors for stable CAD in Iranian people.