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Alpha, beta‐Amyrin Ameliorates Glucose Uptake in Palmitate‐induced Insulin Resistance in C2C12 Cell

Insulin resistance is closely related to the metabolic syndrome that is characterized by a set of diseases that include obesity, dyslipidemia and diabetes mellitus. Due to a considerable increase of these diseases in the last decades, several studies are being carried out worldwide aiming to find solutions to prevent and to treat insulin resistance. Therefore, we decided to investigate the effects of the mixture of triterpenes alpha, beta‐Amyrin (AMI) on insulin resistance (IR) induced by sodium palmitate in skeletal muscle cells (C2C12), since previous studies regarding AMI conducted by our laboratory showed that AMI is able to improve insulin resistance in a hypercaloric diet obesity model. For this purpose, undifferentiated C2C12 cells (myoblasts) were maintained in horse serum (2%) for 6–10 days to induce differentiation to myotubes. The cytotoxic effect of AMI (3.12–400 μg/ml) on myoblasts and myotubes cells was assessed by the 3‐(4,5‐Dimethylthiazol‐2‐yl)‐2,5‐Diphenyltetrazolium Bromide (MTT) assay. The effect of AMI (12.5, 25 and 50 μg/ml) was also evaluated in a glucose uptake model with 2‐[N‐(7‐Nitrobenz‐2‐oxa‐1,3‐diazol‐4‐yl) Amino]‐2‐Deoxy‐D‐glucose (2‐NBDG) in non‐resistant myotubes as well as in a model of insulin resistance induced by sodium palmitate (500 μM) complexed to 2% BSA for 24 h. After incubation, free 2‐NBDG was washed and fluorescence densities in cell monolayers were measured with a fluorescence microplate reader (Biotek Instruments, USA) set at an excitation wavelength of 485 nm and an emission wavelength of 535 nm. The protein (PT) concentration of each sample was determined by the Lowry method. Results were expressed as mean ± SEM of three independent experiments, each in triplicate. For multiple comparison of parametric data, One‐way ANOVA was used, followed by Tukey's post test. Values of p <0.05 were considered statistically significant. AMI (3.12–400 μg/mL) did not promote reduction of cell viability when compared to the control group, both in myoblasts and myotubes. In myotubes, AMI (25 ug/mL) increased glucose uptake (2.40 ± 0.60 2‐NBGD/PT) when compared to the control group (0.98 ± 0.06 2‐NBGD/PT). In the IR model, AMI (25 and 50μg/mL) also increased glucose uptake (1.3 ± 0.0 and 1.9 ± 0.1 2‐NBDG/PT) in myotubes, as well as rosiglitazone 20 μM (1.4 ± 0.0 2‐NBDG/PT) when compared to the IR control group (0.8 ± 0.1 2‐NBGD/PT). These preliminary results suggest that AMI improves glucose uptake in physiological and insulin resistance models in myotubes. These data corroborate with in vivo findings where AMI is able to improve insulin resistance in a hypercaloric diet obesity model. Studies are being conducted to elucidate the molecular mechanisms involved in these effects.