Effects of antioxidant vitamins on renal and hepatic erythropoietin production

An important role in O₂ sensing has been assigned to microsomal and membrane-bound b-type cytochromes which generate regulatory reactive O₂ species (ROS). Recently, ROS have been shown to suppress the in vitro synthesis of erythropoietin (Epo). We investigated the potential of the antioxidant vitamins A, E and C to enhance renal and hepatic Epo production. Renal effects were studied in isolated serum-free perfused rat kidneys. In control experiments without antioxidant vitamins, Epo secretion amounted to 441 ± 23 mU/g kidney (mean ± SEM, N = 5) during the three hour period of hypoxic perfusion (arterial pO₂ 35 mm Hg). Epo secretion significantly increased to 674 ± 92 mU/g kidney (N = 7) when vitamins A (0.5 μg/ml), E (0.5 μg/ml) and C (10 μg/ml) in combination were added to the perfusion medium. The effects of the single vitamins were studied in Epo-producing hepatoma cell cultures (lines HepG2 and Hep3B). Vitamin A induced a dose-dependent increase (half-maximal stimulation at 0.2 μg/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 μg/ml retinol acetate compared to 261 ± 15 U/g in untreated controls; N = 4). In contrast, vitamin E (tested from 0.05 to 500 μg/ml) and vitamin C (tested from 2 to 200 μg/ml) did not increase Epo production in hepatoma cell cultures. Thus, while vitamins E and C may have the potential to protect 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 1α (HIF-1α).