Involvement of poly(ADP-ribose) polymerase-1 in the progression of cell death in a model of perinatal hypoxic-ischemic brain injury

Brain damage due to perinatal hypoxia-ischemia (HI) is a cause of mortality and neurological morbidity in infants and children. In response to HI, excitotoxic levels of glutamate are released from neurons stimulating a sequence of pathophysiological events including rising intracellular calcium, mitochondrial dysfunction, production of free radicals and DNA damage. Poly(ADP-Ribose) Polymerase-1 (PARP-1) is activated in response to DNA strand breaks. In the face of massive DNA damage, PARP-1 is over-activated and depletes cellular energy. Although DNA damage is well documented after perinatal HI, the involvement of PARP-1 in the progression of injury has not been examined. We tested the hypothesis that PARP-1 mediates cell death following HI in the immature brain by participating in apoptotic and necrotic cell death. HI was induced in 7-day-old rat brains by ligation of a single carotid artery followed by systemic exposure to hypoxia (7.6--7.8% oxygen). Cell death, PARP-1 and apoptosis were evaluated at multiple time points between 0.5 and 48 hours post-injury. We observed biphasic changes in the level of PARP-1 in the ipsilateral cortex that correlated with biphasic changes in cell death and apoptosis. In contrast to many studies, we also reported induction of apoptosis in the contraiateral cortex. This transient peak in apoptosis was associated with elevated levels of PARP-1. Inhibition of PARP-1 activity with 3-aminobenzimide (3-AB) delayed the onset of cell death for at least 24 hours post-injury. Inhibition of cell death was associated with a trend toward decreased inflammatory cytokine expression in the ipsilateral cortex. These studies established precedence to continue studies of PARP-1 in the immature brain and to further examine the effects of PARP-1 inhibition on the manifold functions of PARP-1. These studies also reveal that a single dose of 3-AB is not an effective treatment for permanently preventing cell death but suggests multiple doses with 3-AB may be effective. In conclusion, the results discussed in this dissertation suggest PARP-1 is a mediator of cell death after HI in the immature brain and that inhibiting PARP-1 activity after HII may be an effective strategy for attenuating the associated neurologic sequelae.