Mechanisms of pyruvate inhibition of oxidant-induced apoptosis in human endothelial cells

Abstract

We have recently demonstrated that the redox reactant pyruvate prevents hydrogen peroxide (H 2O 2)-induced endothelial apoptosis and that its anti-apoptotic feature is mediated partially through the mitochondrial compartment. However, little is known about molecular signal pathways that mediate the anti-apoptotic feature of pyruvate. A biochemical approach to elucidate such signal pathways was attempted in human umbilical vein endothelial cells (HUVECs). Effects of antioxidant pyruvate were compared with those of cytosolic reductant l-lactate, redox-neutral acetate, and malate-aspartate shuttle blocker aminooxyacetate. Various indices of endothelial apoptosis were correlated with cell viability. Submillimolar H 2O 2 caused >50% cell killing, as manifested by its oxidant insult. The massive cell death induced by H 2O 2 was inhibited by pyruvate but not by l-lactate or aminooxyacetate, suggesting a role of cytosolic NADH reducing equivalents, possibly via stimulated oxidant generation. The induction and nuclear translocation of p53 by H 2O 2 was blocked by pyruvate and appeared to be somewhat enhanced by l-lactate or aminooxyacetate in association with oxidant generation. Nuclear translocation of p53 accompanied the transactivation of bax and downregulation of bcl-2. The pyruvate-related redox manipulation inhibited the H 2O 2-induced p53 activation, restored the downregulated bcl-2 and the upregulated bax, and hence enhanced the bcl-2/bax expression ratio. In contrast, l-lactate, acetate, or aminooxyacetate had no such effect. These results indicate that pyruvate could modulate key regulatory signal pathways in cytosol and mitochondrial matrix, thereby inactivating endothelial death pathways. Furthermore, it is suggested that stabilizing the expression of bcl-2 and bax genes by metabolic antioxidants may be an effective strategy for endothelial protection against oxidative stress.