Activation of pro-apoptotic cascade by dopamine in renal epithelial cells is fully dependent on hydrogen peroxide generation by monoamine oxidases

Dopamine plays a critical role in regulation of different renal functions, including glomerular filtration, renin secretion, and sodium excretion. Recent studies have shown that some of the dopamine effects in the proximal tubule may involve hydrogen peroxide (H2O2) generation by the catecholamine-degrading enzyme monoamine oxidases (MAO). The present study is an investigation of the potential role of H2O2 generated by MAO during dopamine degradation in apoptosis of proximal tubule cells. Dopamine concentrations between 50 and 200 muM induced apoptosis of rat proximal tubule and monoamine oxidase B-transfected HEK 293 cells (+73% compared with untreated cells) but not in wild-type HEK 293 cell lacking monoamine oxidases. Apoptosis of proximal tubule cells was preceded by an increase in the ratio of Bax/Bcl2 proteins, the release of mitochondrial cytochrome c, caspase-3 activation, and DNA fragmentation. All these events required dopamine internalization into the cells, its metabolism by MAO, and H2O2 production, as they were prevented by the dopamine uptake inhibitor GBR-12909, the irreversible MAO inhibitor pargyline, or the antioxidant N-acetylcysteine. These results show that, in renal proximal tubule cells, dopamine induces oxidative stress, activation of proapoptotic cascade, and cell apoptosis exclusively by mechanisms involving H2O2 production by monoamine oxidases.