Methanolic extract of Momordica cymbalaria enhances glucose uptake in L6 myotubes in vitro by up-regulating PPAR-γ and GLUT-4 / 中国天然药物

The present study was undertaken to evaluate the influence of the methanolic fruit extract of Momordica cymbalaria (MFMC) on PPARγ (Peroxisome Proliferator Activated Receptor gamma) and GLUT-4 (Glucose transporter-4) with respect to glucose transport. Various concentrations of MFMC ranging from 62.5 to 500 μg·mL(-1) were evaluated for glucose uptake activity in vitro using L6 myotubes, rosiglitazone was used as a reference standard. The MFMC showed significant and dose-dependent increase in glucose uptake at the tested concentrations, further, the glucose uptake activity of MFMC (500 μg·mL(-1)) was comparable with rosigilitazone. Furthermore, MFMC has shown up-regulation of GLUT-4 and PPARγ gene expressions in L6 myotubes. In addition, the MFMC when incubated along with cycloheximide (CHX), which is a protein synthesis inhibitor, has shown complete blockade of glucose uptake. This indicates that new protein synthesis is required for increased GLUT-4 translocation. In conclusion, these findings suggest that MFMC is enhancing the glucose uptake significantly and dose dependently through the enhanced expression of PPARγ and GLUT-4 in vitro.

In vitro glucose uptake activity of Tinospora crispa in skeletal muscle cells

Background: In South Asian countries, stems of the plant, Tinnospora crispa, Linn (TC) are often used as a folk medicine in the treatment of type 2 diabetes mellitus. Though TC’s antiglycemic activity has been demonstrated in diabetic rats, the mechanism for its action has not yet been elucidated. Objective: To investigate the effect of TC’s aqueous extract (TCA) on glucose transport activity in skeletal muscle cell line. Materials and methods: A skeletal muscle cell line, L6 myoblasts, was used for this study. The myoblasts grown to the stage of fused myotubes were pre-incubated with and without TCA for 24 hours. Then, a 2-[³H]-deoxy-D-glucose (2-DG) uptake test was made in a 24-well plate for 10 minutes. In the downstream transport regulation studies, the TCA pre-incubated cells was either treated or untreated with specific inhibitors of the PI3-Kinase (wortmannin) and p38 MAP-Kinase (SB203580) pathways prior to the uptake test. All studies were carried out in triplicate with a minimum of three independent experiments. Results were expressed as mean±SE and compared with student’s t test for a level of significance at p \< 0.05. Results: TCA at 4 mg/mL significantly enhances glucose uptake of L6 myotubes in dose and time dependent manner with the half maximum effects at 24 hours (196.60±11.09%, p \< 0.05). The effect was completely abolished by a cytoskeletal blockade (10 μM of cytochalasin B), supportive of active glucose transport activity. Both wortmannin and SB203580 have no effect on the TCA-stimulated glucose uptake. Conclusion: Tinospora crispa enhances glucose transport of L6 myotubes in an insulin-independent pathway in a time- and dose-dependent manner.