Effect of melatonin on cellular energy depletion mediated by peroxynitrite and poly (ADP-ribose) synthetase activation in an acute model of inflammation

DNA single-strand breakage and activation of the nuclear enzyme poly (ADP-ribose) synthetase (PARS) triggers an energy-consuming, inefficient repair cycle, which contributes to peroxynitrite-induced cellular injury. Recently, we proposed that during an acute model (pleurisy), cellular injury is mediated by peroxynitrite formation and consequent PARS activation. Here, we investigated whether in vivo melatonin treatment inhibits cellular injury induced by peroxynitrite production and PARS activation in macrophages collected from rats subjected to carrageenan-induced pleurisy. Macrophages harvested from the pleural cavity exhibited a significant production of peroxynitrite, as measured by the oxidation of the fluorescent dye dihydrorhodamine 123. Furthermore, carrageenan-induced pleurisy caused a suppression of macrophage mitochondrial respiration, DNA strand breakage, activation of PARS, and reduction of cellular levels of NAD+. In vivo treatment with melatonin [12.5 or 25 or 50 mg/kg, intraperitoneally (i.p.), 30 min before carrageenan] significantly reduced peroxynitrite formation in a dose-dependent manner and prevented the appearance of DNA damage, decrease in mitochondrial respiration, loss of cellular levels of NAD+, and PARS activation. Our study supports the view that the antioxidant and anti-inflammatory effect of melatonin is also correlated with the inhibition of peroxynitrite production and PARS activation. In conclusion, melatonin may be a novel pharmacological approach to prevent cell injury in acute inflammation.