Abstract 2001 Neuroprotective Strategies for Hypoxic-Ischemic Encephalopathy Platform, Sunday, 5/2

A growing body of epidemiologic and experimental evidence implicates inflammatory cells and mediators in the pathogenesis of perinatal brain injury. Platelet-activating factor (PAF) is a lipid inflammatory mediator implicated in the pathogenesis of ischemia-reperfusion injury of various organs, including the CNS. Treatment with the PAF receptor antagonist BN 52021 attenuates cerebral hypoxic-ischemic (HI) damage in neonatal rats (Pediatr, Res. 40:797). The mechanism and locus of action by which PAF induces injury in HI immature CNS tissue are unknown. To determine whether PAF mediates cerebral HI damage at a vascular vs. parenchymal level, we used the PAF-degrading enzyme recombinant plasma PAF-acetylhydrolase (rPAF-AH; gift of ICOS Corp., Bothell WA), comparing its neuroprotective efficacy by systemic (i.p.) vs. direct intracerebroventricular (i.c.v.) injection. rPAF-AH is a large (45 kDa) protein which is unlikely to cross the intact blood-brain barrier. We used a postnatal day 7 rat model of unilateral carotid ligation followed by timed hypoxia (8% O2) exposure, which produces unilateral cortical, striatal and hippocampal infarction, that evolves to unilateral regional atrophy. We injected rPAF-AH either i.p. (10 mg/kg, n=7; or 30 mg/kg, n=6; or vehicle, n=10) or i.c.v. (7 µg/1 µl, n=11; or vehicle, n=12) 1 h prior to hypoxia exposure (2 h, 8% O2). Bilateral cortical, striatal and hippocampal volumes were calculated from regional area measurements obtained 5 days post-lesioning, by image analysis of regularly spaced coronal sections, using NIH Image. Percent ipsilateral cerebral hemisphere swelling 4 days after lesioning was calculated using wet/dry hemisphere weights. In controls, moderately severe ipsilateral cortical, striatal and hippocampal infarction and atrophy evolved, 5 days after lesioning. Systemic injection of rPAF-AH had no effect on either the mean severity of ipsilateral tissue loss or the mean percentage of ipsilateral brain swelling. In contrast, direct i.c.v. injection of rPAF-AH resulted in attenuation of hypoxic-ischemic cortical and striatal damage, 5 days after HI lesioning. In rPAF-AH treated animals, the mean percentage right sided tissue loss, compared to the intact left side, calculated using the formula 100*(L-R)/L, was reduced in both regions [mean ± SD, control vs. rPAF-AH: cortex 44 ± 32 vs. 19 ± 26, p<0.02, Mann-Whitney; striatum 27 ± 11 vs. 11 ± 13, p<0.02, Mann-Whitney; hippocampus 39 ± 27 vs. 18 ± 22, p=0.08, Mann-Whitney]. Pre-HI treatment with rPAF-AH by the i.c.v. route resulted in approximately 60% reduction of the severity of cortical and striatal damage. Thus rPAF-AH treatment attenuated neonatal cerebral hypoxic-ischemic damage only when the blood-brain barrier was bypassed. These results support the hypothesis that PAF is a pathophysiologic mediator of neonatal cerebral hypoxic-ischemic injury. Furthermore, these results suggest that PAF exerts its deleterious effects in neonatal cerebral HI mainly in brain parenchyma, rather than at the vascular/endothelial level.

(Supported by UCP Grant R-608-97, AHA-MI Grant 08GS9789 and NIH Grant NS37036)