P2.G129: Sex-specific effects of complement modulation in a rat model of neonatal hypoxic-ischemic encephalopathy

Background: There is an urgent need to gain new insights into the mechanisms of brain injury in neonatal hypoxic-ischemic encephalopathy (HIE), in order to develop new therapies. The complement system plays critical homeostatic roles in the developing brain. However, a dysregulated complement response in ischemic-reperfusion injuries such as HIE can propagate neuroinflammation, leading to worse outcomes. C5a is a powerful anaphylatoxin central to all the complement pathways, and exerts its effects by engagement with the receptor C5aR1. HIE increases systemic C5a levels and expression of C5aR1 in the brain, and inhibition of C5a-C5aR1 signaling with PMX205 is neuroprotective in a rat model of neonatal HIE. (Fig.1) There are notable sex differences in neonates with HIE, with females likely to have better outcomes. The goal of this study was to measure sex specific differences in treatment response in neonatal rats treated with low, medium, and high doses of PMX205, a potent inhibitor of the C5a-C5aR1 interaction.

Methods: Term equivalent rat pups were subjected to the Vannucci model of neonatal HIE – (unilateral carotid ligation + 8% hypoxia for 1h). They were subsequently treated with 0.3 mg/kg, 1 mg/kg, or 3 mg/kg of PMX205. Control groups included NT (untreated HIE) and Sham rats. Rats were harvested 72h after injury. Hemispheric loss was measured and stratified by sex between the 3 different groups via whole brain images and coronal slices. H&E staining was performed on paraffin embedded brain sections to compare structural differences between the groups.

Results: Female rats with HIE showed a decrease in cortical loss when treated with PMX205 at 0.3 mg/kg and 1 mg/kg (P < 0.05) with no benefit at the higher dose (3 mg/kg) when compared to NT rats. Male rats with HIE showed less benefit from treatment with PMX205 at any dose (n=8 rats per group). (Fig.2).

Conclusion: These results demonstrate that complement modulation with PMX205 may be a viable therapeutic in neonatal HIE, but results are sexually dimorphic. This underscores the need to stratify results by sex in preclinical and clinical trials, enabling the development of much needed custom therapeutics for neonatal HIE. Future studies include long-term neurobehavioral assays to test if anatomical neuroprotection translates to long-term functional improvement.