Retinoic acid transport to lens epithelium in human aqueous humor

Retinoids, in particular retinoic acid, are required for the normal growth and maintenance of many types of cells, including epithelial cells. The metabolism of lens epithelial cells, which are exposed to aqueous humor in the anterior chamber, is thought to be dependent upon aqueous humor dynamics. In human eyes undergoing cataract surgery, we measured retinoic acid levels using reverse-phase high performance liquid chromatography to investigate the possible role of aqueous humor in the transport of retinoic acid to lens epithelial cells. The retinoic acid level in the aqueous humor and the lens epithelial cells was 23.3 +/- 2.3 pmol/ml and 1.8 +/- 0.8 pmol/micrograms protein, respectively. Fluorescence spectra study suggested the presence of endogenous retinoid-protein complexes in the aqueous humor. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that the major protein in aqueous humor was albumin, a natural carrier protein of retinoic acid in the blood. From these results, we conclude that the aqueous humor may supply retinoic acid to the lens epithelial cells in human eyes.