Metabolism of carotenoid analogs in humans.

Single oral doses (100 mumol) in peanut oil of 4,4'-dimethoxy-beta-carotene, ethyl beta-apo-8'-carotenoate, and beta-apo-8'-carotenal were administered to healthy adult male subjects (n = 4-6). Blood samples were taken frequently thereafter, and serum carotenoids and retinoids were analyzed by HPLC. The metabolism of the three analogs was very different; 4,4'-dimethoxy-beta-carotene was oxidized at the 4 and 4' positions but apparently not cleaved, whereas ethyl beta-apo-8'-carotenoate was not detectably metabolized, and beta-apo-8'-carotenal was extensively converted to its corresponding acid, alcohol, and fatty acyl ester and detectably converted to retinyl ester and possibly to two shorter beta-apocarotenals. Serum concentrations of endogenous retinoids and carotenoids, except as noted above, were not affected in any case. Kinetically, the maximum serum concentrations, areas under the curve, and mean sojourn times for the three analogs differed by 50-, 270-, and 5-fold, respectively. For any given analog, however, the fractional standard deviations for these parameters were only 0.2-0.5.