Carotenoids, mostly the xanthophylls, exchange between plasma lipoproteins

Carotenoids are exclusively transported by lipoproteins; in vitro studies suggest that they might protect these particles against oxidation. Little is known about the factors that govern the distribution of these micronutrients among lipoproteins. The objective of this study was to assess whether carotenoids are exchanged between lipoproteins and what factors, if any, were involved. In the first experiment, different groups of trout were fed for five days with either a carotenoid-free diet or with diets containing 80 mg pure carotenoid per kilogram of feed. Lipoproteins were separated by ultracentrifugation and carotenoid-rich, high-density lipoproteins (HDL) were incubated for two hours at 37 degrees C with carotenoid-free, very low-density lipoproteins (VLDL), and vice versa. After incubation, lipoproteins were re-separated and carotenoids were quantified to measure the transfer. The same experiments were done in the presence of cholesteryl ester transfer protein (CETP) and lecithin cholesterol acyltransferase (LCAT) inhibitors. In a second experiment, the exchange was measured between human VLDL and HDL. In trout, incubation of carotenoid-rich HDL with carotenoid-free VLDL resulted in the appearance of carotenoids in VLDL, and inversely. The higher the hydrophobicity of a carotenoid, the lower its proportion in HDL after incubation. CETP and LCAT inhibitors significantly increased the proportion of carotenoids in HDL after incubation. Results obtained with human lipoproteins showed that the xanthophyll lutein transferred between lipoproteins, but could not show any carotenes (alpha-carotene, beta-carotene, and lycopene) transfer. We conclude that carotenoids, chiefly the xanthophylls, exchange between lipoproteins. The transfer depends on plasma factor(s) sensitive to CETP and/or LCAT inhibitors.