Mechanism of vitamin E inhibition of cyclooxygenase activity in macrophages from old mice: role of peroxynitrite

Vitamin E inhibits cyclooxygenase activity in macrophages from old mice by reducing peroxynitrite production. PGE2 is a proinflammatory mediator that has been linked to a variety of age-associated diseases such as cancer, arthritis, and cardiovascular disease. Furthermore in the aged, increased cyclooxygenase (COX)-2-mediated PGE2 production contributes to decline in T-cell-mediated function. Previously we reported that increased macrophage PGE2 production in the aged is due to higher COX-2 activity and that supplementation with vitamin E significantly reduced the age-associated increase in macrophage PGE2 production posttranslationally without changing COX-2 expression. Peroxynitrite, a product of nitric oxide (NO) and superoxide (O2−), increases the activity of COX without affecting its expression. Thus, we investigated if vitamin E inhibits COX activity through decreasing peroxynitrite formation. Macrophages from old mice had higher PGE2 levels, COX activity, and NO levels than those from young mice, all of which were significantly reduced by vitamin E. When added individually, inhibitors of NO and O2− did not significantly reduce COX activity; however, when the inhibitors were combined, COX activity was significantly reduced in macrophages from old mice fed 30 ppm vitamin E. Increasing NO levels alone using SNAP or O2− levels, using X/XO, had no effect; however, increasing peroxynitrite levels using Sin-1 or X/XO + SNAP significantly increased COX activity in macrophages from old mice fed 500, but not those fed 30 ppm vitamin E. These data strongly suggest that peroxynitrite plays an important role in the vitamin E-induced inhibition of COX activity. These findings have important implications for designing interventions to reverse and/or delay age-associated dysregulation of immune and inflammatory responses and diseases associated with them.