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The aim of this study was to investigate the effect of Taaptimjann wax apple [Syzygium samarangense (Blume) Merrill. & L.M. Perry var. Samarangense] on hepatic insulin signaling in the liver of male diabetic rats. Diabetic rats were induced in Sprague-Dawley rats using a single intraperitoneal (i.p.) injection of streptozotocin [STZ; 65 mg/kg body weight (b.w.)]. Then, wax apple at dose of 100 mg/kg b.w./day was orally administered to diabetic rats for a period of 4 weeks. At the end of experiment, blood glucose level, and lipid peroxidation were evaluated. Hepatic expression levels of insulin signaling proteins were also measured using Western blot analysis. The results clearly showed STZ induction provided an increase in blood glucose level and maintained hyperglycemia throughout this experiment. Also, the expression levels of insulin signaling-related proteins; insulin receptor-β (InR-β), phospho-insulin receptor substrate 1 [p-IRS1 (Ser307)], and phospho-JNK [p-JNK (Thr183/Tyr185)] were upregulated. Malondialdehyde (MDA) level was also noted in liver of STZ-induced diabetic rats. However, treatment with wax apple at a dose of 100 mg/kg b.w. to STZ-induced diabetic rats produced a significant decrease in blood glucose level, which correlated with downregulation of InR-β, p-IRS1 (Ser307), and p-JNK (Thr183/Tyr185) proteins in the liver. Wax apple also diminished the level of MDA in liver of diabetic rats. These findings therefore suggest that wax apple could improve hepatic insulin signaling pathway in STZ-induced diabetic rats, which is associated with decreased oxidative stress.
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