The effects of sucrose and arsenic on muscular insulin signaling pathways differ between the gastrocnemius and quadriceps muscles

Abstract

IntroductionInsulin resistance in muscle can originate from a sedentary lifestyle, hypercaloric diets, or exposure to endocrine-disrupting pollutants such as arsenic. In skeletal muscle, insulin stimulates glucose uptake by translocating GLUT4 to the sarcolemma. This study aimed to evaluate the alterations induced by sucrose and arsenic exposure in vivo on the pathways involved in insulinstimulated GLUT4 translocation in the quadriceps and gastrocnemius muscles.MethodsMale Wistar rats were treated with 20% sucrose (S), 50 ppm sodium arsenite (A), or both (A+S) in drinking water for 8 weeks. We conducted an intraperitoneal insulin tolerance (ITT) test on the seventh week of treatment. The quadriceps and gastrocnemius muscles were obtained after overnight fasting or 30 min after intraperitoneal insulin injection. We assessed changes in GLUT4 translocation to the sarcolemma by cell fractionation and abundance of the proteins involved in GLUT4 translocation by Western blot.ResultsMale rats consuming S and A+S gained more weight than control and Atreated animals. Rats consuming S, A, and A+S developed insulin resistance assessed through ITT. Neither treatments nor insulin stimulation in the quadriceps produced changes in GLUT4 levels in the sarcolemma and Akt phosphorylation. Conversely, A and A+S decreased protein expression of Tether containing UBX domain for GLUT4 (TUG), and A alone increased calpain-10 expression. All treatments reduced this muscle’s protein levels of VAMP2. Conversely, S and A treatment increased basal GLUT4 levels in the sarcolemma of the gastrocnemius, while all treatments inhibited insulin-induced GLUT4 translocation. These effects correlated with lower basal levels of TUG and impaired insulin-stimulated TUG proteolysis. Moreover, animals treated with S had reduced calpain-10 protein levels in this muscle, while A and A+S inhibited insulin-induced Akt phosphorylation.ConclusionArsenic and sucrose induce systemic insulin resistance due to defects in GLUT4 translocation induced by insulin. These defects depend on which muscle is being analyzed, in the quadriceps there were defects in GLUT4 retention and docking while in the gastrocnemius the Akt pathway was impacted by arsenic and the proteolytic pathway was impaired by arsenic and sucrose.

Mediating Role of Liver Dysfunction in the Association between Arsenic Exposure and Diabetes in Chinese Adults: A Nationwide Cross-Sectional Study of China National Human Biomonitoring (CNHBM) 2017–2018

“…As-induced liver injury or dysfunction can impact these processes, leading to imbalances in glucose levels. 22,23 Besides, liver dysfunction caused by As exposure may exacerbate hepatic IR, leading to poor management of blood glucose levels 62,63 Serum ALT levels are commonly associated with liver fat, 64 and they may reflect an indirect marker of hepatic IR because an excess of fat accumulation in the liver induces liver IR. 65 This study demonstrated a greater portion of the mediating effect in nondrinkers than in the overall population.…”

“…It helps in the processes of gluconeogenesis and glycogenolysis, and it stores excess glucose as glycogen. As-induced liver injury or dysfunction can impact these processes, leading to imbalances in glucose levels. , Besides, liver dysfunction caused by As exposure may exacerbate hepatic IR, leading to poor management of blood glucose levels , Furthermore, the efficiency of As metabolism and detoxification may further decline because of the impaired liver tissue caused by chronic low As exposure. Serum ALT levels are commonly associated with liver fat, and they may reflect an indirect marker of hepatic IR because an excess of fat accumulation in the liver induces liver IR .…”