Ascorbic acid-dependent cytoprotection of ovarian cells by leukocyte and nonleukocyte peroxidases

Luteal cells contain high levels of ascorbic acid that is secreted by stimulation with agents like luteinizing hormone (LH) and prostaglandin F2 alpha (PGF2 alpha). One role for interstitial ascorbic acid, we propose, may be the detoxification of H2O2 by regeneration of catalytically active peroxidase. By serving as a preferred secondary substrate, ascorbic acid regenerates the catalytically active peroxidase that is inhibited irreversibly by H2O2 alone. To test this hypothesis, luteal cells were incubated in the absence and presence of peroxidases and H2O2, and the maximal cyclic AMP and steroidogenic response to LH was examined. In luteal cells, H2O2 is known to severely inhibit LH-sensitive cyclic AMP accumulation and steroidogenesis, and the addition of lactoperoxidase, myeloperoxidase, eosinophil peroxidase, or ascorbic acid (1 mM) alone had no effect on these responses to H2O2. However, co-incubation of ascorbic acid and the peroxidases completely reversed the inhibition of cyclic AMP accumulation and steroidogenesis produced by H2O2. These findings and the results that show direct oxidation of ascorbic acid in the presence of peroxidase and H2O2, but not with H2O2 alone, support the conclusion that ascorbic acid released from cells may detoxify H2O2 by regenerating the catalytically active state of peroxidases.