Mitigation of Hypoxic‐Ischemic Damage in Newborn Rats by Misoprostol, a Prostaglandin E2 Receptor Agonist

Abstract

Hypoxic‐Ischemic (HI) episodes occur in approximately 50% of preterm infants and result in significant morbidity and mortality. HI activates the nuclear transcription factor HIF1α, which in turn up‐regulates a variety of antioxidant response element‐driven genes including Bnip3, whose protein product has a pivotal role in hypoxia‐induced apoptosis and/or necrosis. Increased Bnip3 expression has been implicated in necrotizing enterocolistis (NEC), an inflammatory bowel disease of premature infants. Previously our laboratory has shown that Misoprostol, a prostaglandin E2 receptor agonist, mitigates the effects of Bnip3 in an enterocyte cell model. We hypothesized that misoprostol regulates intestinal Bnip3 activity in a rat model of HI. Dams and their pups were exposed to environmental hypoxia (10% O2) or normoxia (21% O2) from post‐natal days (PND) 3–10. Experimental animals were injected subcutaneously with 0.1mg/kg Misoprostol each day between PND 3–10, while control animals received saline injections over the same period. PND10 pups were sacrificed, and transverse colon regions were isolated and analyzed for Bnip3 protein expression via western blotting. HI induced a 17‐fold increase in Bnip3 protein expression (p<0.001); in contrast, Misoprostol induced a 72% decrease in protein expression (p<0.05) in hypoxic rats. To explore this effect mechanistically, we examined mitochondrial permeability transition pore (mPTP) opening in HEK293 cells. As expected, Bnip3 transfection increased mPTP opening, whereas Misoprostol inhibited mPTP opening in cells transfected with Bnip3. Furthermore, cotransfection with both Bnip3 and protein kinase A (PKA) mitigated Bnip3‐induced cell death in 3T3 fibroblasts. Finally, we present data showing that PKA phosphorylates Bnip3 protein. We suggest that misoprostol may attenuate hypoxia‐induced cell death via cAMP/PKA signaling pathways.Support or Funding InformationAthabasca UniversityNatural Sciences and Engineering Research Council of CanadaChildren's Hospital Research Institute of Manitoba