Melatonin attenuates brain edema via the PI3K/Akt/Nrf2 pathway in rats with cerebral ischemia-reperfusion injury

This study aimed to explore the neuroprotective effects of Melatonin (Mel) administration on cerebral ischemia-reperfusion injury (CIRI) and elucidate its underlying mechanism in vivo to provide a theoretical foundation for the clinical application of Mel. CIRI models were established in male adult Sprague Dawley rats by middle cerebral artery occlusion (MCAO) for 2 hours in male adult Sprague Dawley rats. Water content of brain tissue was assessed using both dry/wet weight method and T2-weighted Imaging (T2WI). The infarct volume of the brain was measured by 2,3,5-triphenyltetrazolium chloride (TTC) staining. Cell morphology changes and brain damage were detected through hematoxylin & eosin (H&E) staining and NeuN immunofluorescence staining. The integrity of blood-brain barrier (BBB) was examined using transmission electron microscopy (TEM). The expression of aquaporin 4 (AQP4) protein was quantified through western blots analysis and immunofluorescence staining. The expression of p-PI3K, p-AKT and Nrf2 were detected by immunohistochemistry staining and western blots analysis. Compared with the CIRI group, Mel administration significantly reduced the infarct volume and ameliorated the morphology alterations, accompanied by an increase in the number of neurons. The water content of brain tissue decreased significantly, and the value of relative average diffusion coefficient (rADC) of injured brain increased in the CIRI + Mel group as compared with the CIRI group. Compared with the CIRI group, Mel administration improved the damage to the tight junctions of endothelial cells in the cerebral cortex. The expression of AQP4 protein decreased, and that of p-PI3K, p-AKT and Nrf2 proteins increased in the CIRI + Mel group compared with the CIRI group. After administration of p-PI3K inhibitor LY294002, the expression of AQP4 was upregulated, and that of the p-PI3K, p-AKT and Nrf2 protein decreased compared with the CIRI + Mel group. Mel administration exerts neuroprotective effects against CIRI by mitigating brain edema through upregulating the PI3K/AKT/Nrf2 signaling pathway, and then attenuating brain damage in CIRI rats.