Abstract

BACKGROUND
Skeletal muscle is the principal tissue of insulin resistance in obese non-diabetic and non-insulin dependent diabetic(NIDDM) subjects. Troglitazone(Tgz), a member of thiazolidinedione class of compounds, has been shown to improve glucose tolerance in insulin resistant state. At the celluar level, troglitazone has been shown to improve insulin action in skeletal muscle, liver and adipose tissue. However, there has been little knowledge about the mechanism of this drug in human skeletal muscle from insulin resistant subjects. METHODS: To determine the effect of troglitzone on glucose transport(GT) in skeletal muscle of obese non-diabetic and obese NIDDM patients, muscle cultures from 7 obese nondiabetic and 8 obese NlDDM subjects were grown for 4 weeks and then fused for 4 days either with or without Tgz (05ug/mL). At the end of fusion, GT activity was measured and cells were harvested for the measurement of glucose transporter protein expression. RESULTS: Tgz treatment(4 days) increased GT activity dose-dependently in skeletal muscle cell culture of both obese non-diabetic and obese NIDDM subjects. 5ug/mL troglitazone increased basal GT by 2.3 +0.3 fold in obese non-diabetic and 5.7+1.3 fold in obese NIDDM subjects (p <0.05, respectively) Absolute rate of insulin-stimulated GT was significantly increased following Tgz treatment with no enhancement of the incremental response above basal value in either group. Total memhrane GLUTl protein increased 1.7+0.3 fold(p<0.05) following troglitazone treatment(5ug/mL) in NIDDM but were unchhanged in obese non-diabetic cells. GLUT4 protein levels were not affected by Tgz treatment in either group. CONCLUSION: Troglitazone increased both basal and insulin-stimulated GT activity without enhancing the incremental insulin response above basal value in muscle cultures from insulin resistant subjects. These results indicate that troglitazone is not an insulin sensitizer in muscle cultures but acts primarily by mimicking insulin's ability to stimulate basal glucose metabolism in the insulin resistant state of obesity and NlDDM

• Keywords: Troglitazone;Glucose transport;Basal;Insulin resistance;Muscle, Skeletal;Cultured;Cells;NIDDM;Obesity