Lipophilic antioxidants in blood plasma as markers of atherosclerosis: therole of alpha-carotene and gamma-tocopherol

Oxidative theory of atherosclerosis implies that plasma levels of lipophili c antioxidants might serve as indicators of lipoprotein oxidation in the ar terial wall and as markers of the development of atherosclerosis. However, it is unknown whether the measurement of plasma antioxidants is able to ref lect atherogenesis or its risk. In order to assess whether the levels of li pophilic antioxidants in human plasma can discriminate between subjects wit h and without atherosclerosis, we measured the lipophilic antioxidants alph a-tocopherol, gamma-tocopherol, alpha-carotene, beta-carotene and ubiquinol -10 in plasma of 34 patients with coronary heart disease (CHD) and in 40 co ntrol subjects. We found that alpha-carotene and gamma-tocopherol were sign ificantly lower in plasma of CHD patients compared to controls. This decrea se was significantly independent of whether the antioxidants were expressed as its absolute amounts in plasma (P < 0.001 for alpha-carotene, and P = 0 .001 for gamma-tocopherol) or normalized to plasma lipids (P < 0.001 for bo th). In contrast, beta-carotene was only lower in plasma of CHD patients in comparison to controls, when normalized to the lipids (P = 0.02). Independ ent contributions of different parameters to the variation in these plasma antioxidants were estimated using multiple regression approach. The analysi s showed that both the decrease in alpha-carotene and the decrease in gamma -tocopherol were significantly associated only with the presence of CHD (P < 0.001 for each regression), while the decrease in beta-carotene was signi ficantly related to the presence of hyperlipidaemia (P < 0.001). In strikin g contrast, no decrease in plasma alpha-tocopherol and ubiquinol-10 was det ected in the patient group independently of how these antioxidants were exp ressed. These data suggest that plasma levels of alpha-carotene and gamma-t ocopherol may represent markers of atherosclerosis in humans. Measuring the se antioxidants may be of clinical importance as a practical approach to as sess atherogenesis and/or its risk. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.