EFFECTS OF ANTIOXIDANT VITAMINS ON RENAL AND HEPATIC ERYTHROPOIETIN PRODUCTION

Effects of antioxidant vitamins on hypoxia-induced erythropoietin prod uction. An important role in O-2 sensing has been assigned to microsom al and membrane-bound b-type cytochromes which generate regulatory rea ctive O-2 species (ROS). Recently, ROS have been shown to suppress the in vitro synthesis of erythropoietin (Epo). We investigated the poten tial of the antioxidant vitamins A, E and C to enhance renal and hepat ic Epo production. Renal effects were studied in isolated serum-free p erfused rat kidneys. In control experiments without antioxidant vitami ns, Epo secretion amounted to 441 +/- 23 mU/g kidney (mean +/- SEM, N = 5) during the three hour period of hypoxic perfusion (arterial pO(2) 35 mm Hg). Epo secretion significantly increased to 674 +/- 92 mU/g k idney (N = 7) when vitamins A (0.5 mu g/ml), E (0.5 mu g/ml) and C (10 mu g/ml) in combination were added to the perfusion medium. The effec ts of the single vitamins were studied in Epo-producing hepatoma cell cultures (lines HepG2 and Hep3B). Vitamin A induced a dose-dependent i ncrease (half-maximal stimulation at 0.2 mu g/ml) in the production of immunoreactive Epo during 24 hours of incubation (such as 680 +/- 51 U Epo/g cell protein in HepG2 cultures with 3 mu g/ml retinol acetate compared to 261 +/- 15 U/g in untreated controls; N = 4). In contrast, vitamin E (tested from 0.05 to 500 mu g/ml) and vitamin C (tested fro m 2 to 200 mu g/ml) did not increase Epo production in hepatoma cell c ultures. Thus, while vitamins E and C may have the potential to protec t cells from oxidative damage, vitamin A exerts a specific stimulation of Epo production. Preliminary evidence suggests that this effect of vitamin A involves increased mRNA levels of hypoxia-inducible factor 1 alpha (HIF-1 alpha).