PLASMA LDL AND HDL SUBSPECIES ARE HETEROGENOUS IN PARTICLE CONTENT OFTOCOPHEROLS OXYGENATED AND HYDROCARBON CAROTENOIDS - RELEVANCE TO OXIDATIVE RESISTANCE AND ATHEROGENESIS

Epidemiological data indicate that dietary tocopherols and carotenoids can exert cardioprotective effects, which may be mediated by their an tioxidant actions. The oxidative modification of LDL underlies the ath erogenicity of these cholesterol-rich particles. The resistance of LDL to oxidation is influenced by several endogenous factors, among which the content of tocopherols and carotenoids is prominent. Of the exoge nous factors, HDL inhibits oxidation of LDL via several mechanisms. In view of the paucity of data on the distribution of diverse tocopherol and carotenoid components among the apoB- and apoA-I-containing lipop roteins of human plasma, we evaluated the quantitative and qualitative features of the LDL and HDL particle subspecies in normolipidemic sub jects. The bulk of tocopherols and hydrocarbon carotenoids (lycopene, alpha- and beta-carotene) was transported in LDL (45% and 76%, respect ively), in contrast to the oxygenated carotenoids (lutein/zeaxanthin, canthaxanthin, and beta-cryptoxanthin), which were equally distributed between LDL and HDL. alpha-Tocopherol content was independently assoc iated with lipid core size (cholesteryl eater and triglyceride) in VLD L, LDL, and HDL (P<.005); by contrast, the particle content of the oxy genated carotenoids lutein/zeaxanthin and canthaxanthin was strongly r elated to that of phospholipids. A significant and progressive decreas e in the molar content of alpha- and gamma-tocopherols was found with increase in density from light to dense LDL subspecies (LDL1 to LDL5); a similar trend was observed in HDL subspecies. Furthermore, particle contents of lutein/zeaxanthin, beta-cryptoxanthin. beta-carotene, and lycopene were markedly reduced in small, dense LDL (LDL5, d=1.050 to 1.065 g/mL). We conclude that diminished contents in such carotenoids as well as in tocopherols could underlie not only the diminished oxida tive resistance of small, dense LDL but also reduced tissue targeting of antioxidants in subjects with a dense LDL phenotype.