Effect of Troglitazone on Glycogen synthase Activity in Human skeletal Muscle Culture from Obese Non-Diabetic and Obese Non-insulin Dependent Diabetes Mellitus

Carter, Leslie Abrams; Ciaraldi, Theodore; Henry, Robert R; Park, Kyong Soo; Lee, Hong Kyu

Abstract

BACKGROUND: Skeletal muscle is the principal tissue of insulin resistance in obese and non-insulin dependent diabetic(NIDDM) subjects. Troglitazone, a member of thiazolidinedione class of compounds, has been shown to improve glucose tolerance in insulin resistant state. At the cellular level, troglitazone has been shown to improve insulin action in skeletal muscle, liver and adipose tissue. However, there has been no direct assessment of mechanism of this drug in insulin resistant human skeletal muscle from obese and obese NIDDM subjects.
METHODS
To determine the effect of troglitzone on skeletal muscle glycogen synthase(GS) activity in insulin resistant human skeletal muscle, muscle cultures from 7 obese non-diabetic and 8 obese NIDDM subjects were grown for 4 weeks and then fused for 4 days either with or without troglitzone(0~5ug/mL) and harvested for GS activity and protein measurement. GS activity was measured by enzymatic method and protein expression was measured by Western blot using polyclonal antibody specific for C-terminal end of GS protein,
RESULTS
Troglitzone increased GS activity(GS activity at 0.1 mM G6P and fractional velocity) dose-dependently in both obese non-diabetic and type II diabetes and the increased GS activity by troglitzone was mostly basal rather than insulin-stimulated. Basal fractional velocity of GS increased 2.8+/-0.7 and 3.7 +/-1.2 fold in obese non-diabetic and type II diabetes respectively. There was no changes in GS total activity and GS protein expression in either group with troglitzone treatment..
CONCLUSION
Troglitazone has effects to improve glycogen synthase activity in skeletal tnuscle of obese and obese NIDDM subjects.