RETINOIC ACID METABOLISM IN CULTURED RETINAL-PIGMENT EPITHELIAL-CELLS

Purpose. To examine the stability of retinoic acid administered to cul tured bovine retinal pigment epithelial (RPE) cells and to determine i f RPE cells metabolize retinoic acid by a cytochrome P-450 mechanism. Methods. Retinoic acid metabolism was examined in cultured RPE cells a nd subcellular fractions quantitatively by a thin-layer chromatography procedure and qualitatively by normal and reverse phase high-performa nce liquid chromatography. Results. Cultured bovine RPE cells were fou nd to have an activity that converts retinoic acid into more polar met abolites rapidly released from the cell. The highest specific activity for this process is found in the post-mitochondrial pellet (100,000g) , is induced by retinoic acid, and is inhibited by ketoconazole. The m ajor product of the RPE cell-mediated metabolism of retinoic acid is 4 -oxo-retinoic acid, a known P-450 monooxygenase product of retinoic ac id. The retinoic acid metabolizing activity is greatest in primary RPE cultures and decreases with aging in culture. Conclusions. These data suggest that a cytochrome P-450 monooxygenase is involved in the meta bolism of retinoic acid in RPE cells, and this is similar to the findi ngs of other investigators using other cells and tissues. The authors' findings suggest that the RPE may be important in the deactivation of this biologically potent retinoid in the retina.