Protective effects of a cyclic nitrone antioxidant in animal models of endotoxic shock and chronic bacteremia

Evidence of a role for oxygen-derived free radicals in the pathophysiology of endotoxic shock has been found in animal models. However, the importance of free radicals in chronic models of bacterial infection has not been examined. In this study a novel nitrone radical spin trap is described and its activity in animal models of endotoxic shock and chronic bacteremia were explored. MDL 101,002 is a cyclized variant of alpha-phenyl N-tert-butyl nitrone (PBN), an established spin trap. MDL 101,002 can react with free radicals to form persistent adducts as demonstrated by electron paramagnetic resonance (EPR) spectroscopy. This agent is about 10 times more potent than PBN as an in vitro antioxidant and scavenger of hydroxyl radicals. In a rat endotoxic shock model MDL 101,002 (3-30 mg/kg, i.p.) administered 30 min prior to endotoxin (30 mg/kg, i.p.) treatment reduced mortality in a dose-dependent manner. Peroxide-enhanced chemiluminescence in hepatic homogenates from endotoxin treated rats was elevated indicating that oxidative stress and antioxidant depletion was increased. Importantly, treatment with MDL 101,002 (30 mg/kg, i.p.) 30 min prior to, and 120 min following endotoxin, minimized the increase in chemiluminescence. MDL 101,002 also reduced mortality in a model of chronic bacteremia employing implantation of infected fibrin clots into the peritoneal cavity of gentamicin-treated leukopenic rats. MDL 101,002 (2.5 mg/kg/hr) increased survival from 24% to 52% in these rats. These data are consistent with a role for free radicals in the pathophysiology of endotoxic shock and suggest free radicals are also important mediators in chronic models of sepsis.