Formation of all- trans-retinoic acid and 13- cis-retinoic acid from all- trans-retinyl palmitate in humans

Abstract

Increments of levels of both 13- cis- and all- trans-retinoic acid in human plasma were observed after either a physiologic or a pharmacologic oral dose of all- trans-retinyl palmitate. Subjects receiving a physiologic dose showed mean ± SEM plasma rises over baseline as follows: all- trans-retinoic acid = 1.1 ± 0.3 nmol/L and 13- cis-retinoic acid = 4.7 ± 1.1 nmol/L, which represented increases in 1.3 fold and 1.9 fold over fasting plasma levels. Those receiving a pharmacologic dose showed mean ± SEM plasma rises over baseline as follows: all- trans -retinoic acid = 11.5 ± 2.6 nmol/L and 13-cis -retinoic acid = 37.5 ± 6.1 nmol/L, which represented increases of 3.9-fold and 8.4-fold over fasting plasma levels. Moreover, areas under the curve of the means of all- trans- and 13- cis-retinoic acid over 24 hours showed that larger amounts of 13- cis-retinoic acid appear in the circulation than all- trans-retinoic acid after feeding all- trans-retinyl palmitate. The increase in retinoic acid in the circulation may be an important source of retinoic acid for some organs.