Glutamine protects myocardial ischemia-reperfusion injury in rats through the PI3K/Akt signaling pathway

OBJECTIVE To study the protective mechanism of glutamine (Gln) on myocardial ischemia-reperfusion (IR) injury in rats through the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) signaling pathway. MATERIALS AND METHODS A total of 30 healthy SD rats weighing 200-300 g were used in this experiment. They were randomly divided into 3 groups: sham group (n=10), myocardial IR injury group (IR group, n=10), IR+Gln group (n=10). The protein expression levels of phosphorylated Akt (p-Akt), total Akt (t-Akt), phosphorylated mammalian target of rapamycin (p-mTOR), mTOR, proliferating cell nuclear antigen (PCNA), P21, and Tubulin were determined by Western blotting (WB). Quantitative Polymerase Chain Reaction (qPCR) was applied to detect the messenger ribonucleic acid (mRNA) levels of Akt and mTOR. 3-(4,5)-dimethylthiazol(-z-y1)-3,5-diphenyl tetrazolium bromide (MTT) test was utilized to examine the proliferation ability of cardiomyocytes in vitro. Besides, the contents of the inflammatory cytokines, tumor necrosis factor-alpha (TNF-α), and interleukin-6 (IL-6) were measured via enzyme-linked immunosorbent assay (ELISA). Cell apoptosis in each group was examined through Hoechst staining. RESULTS Compared with those in the sham group, ratios of p-AKT/AKT, p-mTOR/mTOR, and the level of PCNA extremely significantly decreased, but the level of P21 notably increased in IR group (p<0.01). In comparison with those in the IR group, ratios of p-AKT/AKT, p-mTOR/mTOR, and the level of PCNA were remarkably raised, while the level of P21 was remarkably reduced in IR+Gln group (p<0.05). QRT-PCR results manifested that there were no significant differences in the mRNA levels of Akt and mTOR among the three groups [no significant difference (NS)]. Moreover, the cell proliferation ability in IR group was remarkably lower than that in the sham group (p<0.01), while it was enhanced in the IR+Gln group compared with that in the IR group (p<0.05). Additionally, IR group had significantly elevated expression levels of TNF-α and IL-6 compared with the sham group (p<0.01), whereas the IR+Gln group had notably decreased expression levels of TNF-α and IL-6 compared with IR group (p<0.05). In comparison with that in the sham group, the apoptosis in IR group was significantly raised (p<0.01), and compared with that in the IR group, the apoptosis in the IR+Gln group prominently decreased (p<0.05). The contents of the inflammatory cytokines, TNF-α, and IL-6 presented the same trends among the three groups. CONCLUSIONS Gln activates the PI3K/Akt signaling pathway by increasing the levels of p-AKT and p-mTOR. Gln can increase the PCNA level and reduce the P21 level, so as to enhance the proliferation ability of cardiomyocytes. Besides, Gln reduces the levels of inflammatory cytokines, TNF-α, and IL-6, and inhibits cell apoptosis. Finally, Gln can protect cells from myocardial IR injury by activating the PI3K/Akt signaling pathway.