The effects of carnosine pretreatment on the inflammatory response and the PI3K/Akt signaling pathway following hypoxia-ischemia in neonatal rats

An increasing number of studies have demonstrated that carnosine plays a neuroprotective role in many types of brain injury. We have previously shown that carnosine has both short-term and long-lasting neuroprotective effects in a hypoxia-ischemia(HI) rat model. In the mature brain, post-ischemia neuronal survival involves in activation of the phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway, whether the activation of PI3K/Akt pathway also plays an important role in the immature brain still remain unclear.The goal of this study is to detect the effection of carnosine on inflammation response following HI, further evidencing neuroprotection of carnosine. We measured total Akt, phospho-Akt (p-AKT) and tumor necrosis factor receptor 1 (TNFR1) protein levels by western blot assay and tumor necrosis factor- (TNF-) and TNFR1 mRNA expression using real-time RT-PCR. We found the carnosine-pretreated group had statistically significant downregulation of TNF- mRNA levels 24 h after HI (P < 0.05). Similar results were observed when we measured TNFR1 mRNA levels both 24h and 72h after HI (P < 0.05). And the TNFR1 protein expression after HI was markedly decreased at 24 and 72 h post-HI in the carnosine-pretreated rats(P < 0.05). Nevertheless, the rats pretreated with carnosine showed a marked increase in p-Akt levels (P< 0.05). And the pro-apoptotic protein Bad was also examined using immunohistochemistry after 24 and 72 h of all groups. We found significantly fewer Bad-positive cells in the carnosine-pretreated group at each time point after HI (P < 0.05). These findings suggest that carnosine pretreatment inhibits the HI-induced inflammatory response, and neuroprotection mechanism of carnosine involved in activation of the PI3K/Akt signaling pathway.