Effect of Tinospora crispa on glucose uptake in skeletal muscle: role of glucose transporter 1 expression and extracellular signal-regulated kinase1/2 activation

Abstract

Background: Tinospora crispa (TC) has been used for years as diabetic remedy in Thai-traditional medicine. It has recently been reported that the aqueous extract from TC’s dried stem enhances glucose transport of L6 myotubes. Objective: Investigate the effects of the water-ethanol extract of T. crispa (WETC) on glucose transport in a rat muscle cell-line L6 myotubes, and explore the mechanism of action of T. crispa in muscle cells. Materials and methods: Glucose uptake rate was determined with the [3H] 2-deoxyglucose uptake method and the cell viability was assessed by sulforhodamine B (SRB) assay. Expressions of glucose transporter 1 (GLUT1), GLUT4, extracellular signal regulated kinase 1/2 (ERK1/2), and AMP-activated protein kinase (AMPK) were measured by quantitative Reverse transcriptase-polymerase chain reaction (RT-PCR) and Western blot analysis. Results: At 400 μg/mL, WETC significantly stimulated glucose uptake into L6 myotubes after 24 hours incubation (246.10.1% above basal; p <0.05). The enhancement of glucose transport by WETC was blocked by cycloheximide, a protein synthesis inhibitor. The up-regulation of GLUT1 protein was accompanied by a significant increased in GLUT1 mRNA expression. ERK1/2 was significantly activated in WETC-treated L6 myotubes. In addition, WETC treatment increased AMPK activity in L6 myotubes. Conclusion: T. crispa increased glucose transport activity of L6 myotubes by enhancing GLUT1 expression, a result of AMPK stimulation. Keywords: AMPK, ERK1/2, Glucose uptake, GLUT1, GLUT4, Tinospora crispa