LOW-DENSITY-LIPOPROTEIN COMPOSITION AND OXIDIZABILITY IN CORONARY-DISEASE - APPARENT FAVORABLE EFFECT OF BETA-BLOCKERS

The oxidative modification of LDL in vivo may have an important role in atherogenesis. To determine whether LDL fatty acid, anti-oxidant composition and sensitivity to oxidation in vitro is different in subjects with established atherosclerosis we compared 20 men with angiogram proven coronary disease with 25 controls without clinical evidence of arterial disease. LDL-cholesterol, total triglycerides and LDL fatty acid composition did not differ significantly between the groups, LDL oxidation lag time and oxidation rate in coronary patients (132 min, 0.02 absorbance units/min) and controls (140, 0.017) were not significantly different. However coronary disease subjects taking beta-blockers had evidence for reduced LDL oxidizability (lag time 148 +/- 7 min; oxidation rate 0.017 +/- 0.002 abs units/min) compared with those not on beta-blockers (lag time 114 +/- 7 min, rate 0.025 +/- 0.003, P < 0.005). LDL beta-carotene was significantly lower in coronary patients (0.92 mumol/mmol LDL cholesterol; controls 1.58; P = 0.001). LDL alpha-tocopherol appeared lower in coronary patients (2.8 mumol/mmol LDL cholesterol; controls 3.3; P = 0.056) and was significantly lower in smokers (2.56; non-smokers 3.24; P = 0.04). LDL oxidation rate was negatively correlated with LDL alpha-tocopherol (r = -0.51, P = 0.005). In multiple regression analysis of LDL composition, LDL alpha-tocopherol was correlated as the dependent variable with LDL beta-carotene (r = 0.52, P = 0.005) and stearic acid (r = -0.43, P = 0.02), whilst LDL beta-carotene as the dependent variable was correlated with LDL alpha-tocopherol (r = 0.56, P = 0.003), linoleic acid (r = -0.60, P = 0.001) and docosahexaenoic acid (r = -0.47, P = 0.02). This study has shown depressed LDL antioxidant vitamin levels in coronary disease subjects compared with controls; however, comparison of LDL oxidizability between the two groups may have been confounded by the favourable influence of beta-blockers and reduction in smoking in the coronary group. The apparent effect of beta-blockers in reducing LDL susceptibility to oxidation may be an important mechanism by which these drugs improve outcome in patients after myocardial infarction.