Intramitochondrial pyruvate attenuates hydrogen peroxide-induced apoptosis in bovine pulmonary artery endothelium

In the hydrogen peroxide (H₂O₂) apoptosis model of the murine thymocyte, redox reactant and antioxidant pyruvate prevents programmed cell death. We tested the hypothesis that such protection was mediated, at least in part, via pyruvate handling by mitochondrial metabolism. Cultured bovine pulmonary artery endothelial cells were incubated for 30 min with 0.5 mM H₂O₂ in the absence and presence of 0.5 mM -cyano-3-hydroxycinnamate, as a selective inhibitor of the mitochondrial pyruvate transporter. In controls H₂O₂ decreased cell viability by 30% within 24 h; this was associated with apoptosis-like bodies, nuclear condensation, and biochemical DNA damage consistent with programmed cell death. Pyruvate (0.1–20 mM) enhanced cell viability in a dose-dependent manner, with 85% viable cells at 3 mM and no DNA laddering, no positive nick-end labeling (TUNEL), and no detectable Annexin V or propidium iodide staining. In contrast, using 5 mM L-lactate as a cytosolic reductant or acetate as a redox-neutral substrate, cell death increased to 40%, which was associated with intense DNA laddering, positive TUNEL and Hoechst 33258 assays. -Cyano-3-hydroxycinnamate alone did not significantly decrease endothelial viability but reduced viability from 85 ± 3 to 71 ± 4% (p = 0.023) in presence of 3 mM pyruvate plus H₂O₂; pathological cell morphology and DNA laddering under the same conditions suggested loss of pyruvate protection against apoptosis. Since -cyano-3-hydroxycinnamate re-distributed medium pyruvate and L-lactate consistent with selective blockade of pyruvate uptake into the mitochondria, the findings support the hypothesis that pyruvate protection against H₂O₂ apoptosis is mediated in part via the mitochondrial matrix compartment. Possible mediators include anti-apoptotic bcl-2 and/or products of mitochondrial pyruvate metabolism such as citrate that affect metabolic regulation and anti-oxidant status in the cytoplasm.