A time course of NADPH-oxidase up-regulation and endothelial nitric oxide synthase activation in the hippocampus following neurotrauma

Abstract

Nicotinamide adenine dinucleotide phosphate oxidase (NADPH-oxidase; NOX) is a complex enzyme responsible for increased levels of reactive oxygen species (ROS), superoxide (O2•−). NOX-derived O2•− is a key player in oxidative stress and inflammation-mediated multiple secondary injury cascades (SIC) following traumatic brain injury (TBI). The O2•− reacts with nitric oxide (NO), produces various reactive nitrogen species (RNS), and contributes to apoptotic cell death. Following a unilateral cortical contusion, young adult rats were killed at various times postinjury (1, 3, 6, 12, 24, 48, 72, and 96h). Fresh tissue from the hippocampus was analyzed for NOX activity, and level of O2•−. In addition we evaluated the translocation of cytosolic NOX proteins (p67Phox, p47Phox, and p40Phox) to the membrane, along with total NO and the activation (phosphorylation) of endothelial nitric oxide synthase (p-eNOS). Results show that both enzymes and levels of O2•− and NO have time-dependent injury effects in the hippocampus. Translocation of cytosolic NOX proteins into membrane, NOX activity, and O2•− were also increased in a time-dependent fashion. Both NOX activity and O2•− were increased at 6h. Levels of p-eNOS increased within 1h, with significant elevation of NO at 12h post-TBI. Levels of NO failed to show a significant association with p-eNOS, but did associate with O2•−. NOX up-regulation strongly associated with both the levels of O2•− and the total NO. The initial 12h post-TBI are very important as a possible window of opportunity to interrupt SIC. It may be important to selectively target the translocation of cytosolic subunits for the modulation of NOX function.