Oxidative stress and Ca++ toxicity are mechanisms of hypoxic-ischemic (HI) brain injury. This work investigates if partial inhibition of mitochondrial respiratory chain protects HI-brain by limiting generation of oxidative radicals during reperfusion. HI-insult was produced in p10 mice treated with complex-I (C-I) inhibitor, pyridaben (P), or vehicle. Administration of P significantly decreased extent of HI injury. Mitochondria isolated from the ischemic hemisphere in P-treated animals showed reduced H2O2 emission, less oxidative damage to the mitochondrial matrix, and increased tolerance to Ca++ triggered opening of permeability transition pore. Protective effect of P administration was also observed when the reperfusion-driven oxidative stress was augmented by the exposure to 100% O2 which exacerbated brain injury only in V-treated mice. In vitro, intact brain mitochondria dramatically increased H2O2 emission in response to hyperoxia, resulting in substantial loss of Ca++ buffering capacity. However, in the presence of C-I inhibitor, rotenone, or antioxidant, catalase, these effects of hyperoxia were abolished. Our data suggest that the reperfusion-driven recovery of C-I dependent mitochondrial respiration contributes not only to the cellular survival, but also causes an oxidative damage to the mitochondria, potentiating a loss of Ca++ buffering capacity. This highlights a novel neuroprotective strategy against HI-brain injury where the major therapeutic principle is a pharmacological attenuation, rather than an enhancement of mitochondrial oxidative metabolism during early reperfusion.

This study investigated whether mitochondrial dysfunction contributes to alveolar developmental arrest in a mouse model of bronchopulmonary dysplasia (BPD). To induce BPD, 3-day-old mice were exposed to 75% O 2 . Mice were studied at two time points of hyperoxia (72 h or 2 wk) and after 3 weeks of recovery in room air (RA). A separate cohort of mice was exposed to pyridaben, a complex-I (C-I) inhibitor, for 72 hours or 2 weeks. Alveolarization was quantified by radial alveolar count and mean linear intercept methods. Pulmonary mitochondrial function was defined by respiration rates, ATP-production rate, and C-I activity. At 72 hours, hyperoxic mice demonstrated significant inhibition of C-I activity, reduced respiration and ATP production rates, and significantly decreased radial alveolar count compared with controls. Exposure to pyridaben for 72 hours, as expected, caused significant inhibition of C-I and ADP-phosphorylating respiration. Similar to hyperoxic littermates, these pyridaben-exposed mice exhibited significantly delayed alveolarization compared with controls. At 2 weeks of exposure to hyperoxia or pyridaben, mitochondrial respiration was inhibited and associated with alveolar developmental arrest. However, after 3 weeks of recovery from hyperoxia or 2 weeks after 72 hours of exposure to pyridaben alveolarization significantly improved. In addition, there was marked normalization of C-I and mitochondrial respiration. The degree of hyperoxia-induced pulmonary simplification and recovery strongly (r 2 5 0.76) correlated with C-I activity in lung mitochondria. Thus, the arrest of alveolar development induced by either hyperoxia or direct inhibition of mitochondrial oxidative phosphorylation indicates that bioenergetic failure to maintain normal alveolar development is one of the fundamental mechanisms responsible for BPD.

Hypoxic-ischemic (HI) brain injury in infants is a leading cause of lifelong disability. We report a novel pathway mediating oxidative brain injury after hypoxia-ischemia in which C1q plays a central role. Neonatal mice incapable of classical or terminal complement activation because of C1q or C6 deficiency or pharmacologically inhibited assembly of membrane attack complex were subjected to hypoxia-ischemia. Only C1q Ϫ/Ϫ mice exhibited neuroprotection coupled with attenuated oxidative brain injury. This was associated with reduced production of reactive oxygen species (ROS) in C1q Ϫ/Ϫ brain mitochondria and preserved activity of the respiratory chain. Compared with C1qϩ/ϩ neurons, cortical C1q Ϫ/Ϫ neurons exhibited resistance to oxygen-glucose deprivation. However, postischemic exposure to exogenous C1q increased both mitochondrial ROS production and mortality of C1q Ϫ/Ϫ neurons. This C1q toxicity was abolished by coexposure to antioxidant Trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid). Thus, the C1q component of complement, accelerating mitochondrial ROS emission, exacerbates oxidative injury in the developing HI brain. The terminal complement complex is activated in the HI neonatal brain but appeared to be nonpathogenic. These findings have important implications for design of the proper therapeutic interventions against HI neonatal brain injury by highlighting a pathogenic priority of C1q-mediated mitochondrial oxidative stress over the C1q deposition-triggered terminal complement activation.

Background and Purpose-This work was undertaken to determine to what degree long-term neurofunctional outcome of neonatal hypoxic-ischemic (HI) brain injury in mice correlates with anatomical extent of cerebral damage assessed by magnetic resonance imaging (MRI) and histopathology. Methods-On postnatal day 7, mice were subjected to HI. At 7 to 9 weeks after HI neurofunctional outcome was assessed by water-maze, rota-rod, and open-field test performance, followed by cerebral MRI and histopathology evaluation.