Zeaxanthin Inhibits Hypoxia-Induced VEGF Secretion by RPE Cells through Decreased Protein Levels of Hypoxia-Inducible Factors-1α

Hypoxia is the most important stimulus leading to upregulation of VEGF in the retina and this is caused by accumulation of hypoxia-inducible factors-1 alpha (HIF-1 alpha) protein. The effects of zeaxanthin, a natural phytochemical, on the VEGF and HIF-1 alpha expression in the primary culture of human retinal pigment epithelial (RPE) cells were studied. An in vitro RPE cell hypoxia model was established by placing cells under 1% oxygen pressure or by adding cobalt chloride (CoCl2) to the culture medium. RPE cells and conditioned media were collected from cultures treated with and without zeaxanthin under normoxic and hypoxic conditions. VEGF and HIF-1 alpha protein and RNA levels were measured by ELISA kits and RT-PCR, respectively. Hypoxia caused a significant increase of VEGF expression and accumulation of HIF-1 alpha in RPE cells. Zeaxanthin at 50-150 mu M significantly inhibited the expression of VEGF and accumulation of HIF-1 alpha protein caused by hypoxia but did not affect expression of VEGF and HIF-1 alpha under normoxic conditions. This is the first report on the effect of zeaxanthin on VEGF and HIF-1 alpha levels in cultured RPE cells and suggests that zeaxanthin may have potential value in the prevention and treatment of various retinal diseases associated with vascular leakage and neovascularization.