Oligonol promotes glucose uptake by modulating the insulin signaling pathway in insulin-resistant HepG2 cells via inhibiting protein tyrosine phosphatase 1B
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Insulin resistance and protein tyrosine phosphatase 1B (PTP1B) overexpression are strongly associated with type 2 diabetes mellitus (T2DM), which is characterized by defects in insulin signaling and glucose intolerance. In a previous study, we demonstrated oligonol inhibits PTP1B and α-glucosidase related to T2DM. In this study, we examined the molecular mechanisms underlying the anti-diabetic effects of oligonol in insulin-resistant HepG2 cells. Glucose uptake was assessed using a fluorescent glucose tracer, 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxyglucose, and the signaling pathway was investigated by western blotting. Oligonol significantly increased insulin-provoked glucose uptake and decreased PTP1B expression, followed by modulation of ERK phosphorylation. In addition, oligonol activated insulin receptor substrate 1 by reducing phosphorylation at serine 307 and increasing that at tyrosine 895, and enhanced the phosphorylations of Akt and phosphatidylinositol 3-kinase. Interestingly, it also reduced the expression of two key enzymes of gluconeogenesis (glucose 6-phosphatase and phosphoenolpyruvate carboxykinase), attenuated oxidative stress by scavenging/inhibiting peroxynitrite, and reactive oxygen species (ROS) generation, and augmented the expression of nuclear factor kappa B. These findings suggest oligonol improved the insulin sensitivity of insulin-resistant HepG2 cells by attenuating the insulin signaling blockade and modulating glucose uptake and production. Furthermore, oligonol attenuated ROS-related inflammation and prevented oxidative damage in our in vitro model of type 2 diabetes. These result indicate oligonol has promising potential as a treatment for T2DM.
KeywordsProtein tyrosine phosphatase 1B Diabetes mellitus Insulin-resistant HepG2 cells Oligonol Glucose uptake Insulin signaling
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Conflict of interest
J. S. Choi is a Consultant for Amino Up Chemical Co. Ltd., which partly funded this research, and provided the test material, Oligonol. H. Fujii and A. Sato are in an employment relationship with the Amino Up Chemical Co. Ltd. H. A. Jung, T. Yokozawa, C. H. Park, H. K. Bhakta and P. Paudel state that there are no conflicts of interest.
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