Effect of glucolipotoxicity and rosiglitazone upon insulin secretion

Type 2 diabetes is characterised by elevated blood glucose and fatty acid concentrations, and aberrant expression of exocytotic soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins. Restoration of normoglycaemia is often accomplished through use of the thiazolidinedione drug rosiglitazone (RSG), although little is known of its actions on the pancreas. Here we report that high glucose resulted in 96.6+/-0.2% inhibition of secretagogue-stimulated insulin secretion and 44.9+/-6.2% reduction in beta-cell insulin content. High glucose and lipid resulted in altered target-SNARE expression, syntaxin 1 becoming barely detectable whilst SNAP-25 was greatly up-regulated. RSG intervention further increased the expression of SNAP-25, but did not up-regulate syntaxin 1 expression. In summary, high glucose results in almost total attenuation of stimulated insulin secretion, partial depletion of beta-cell insulin stores and dysregulation of SNARE protein expression. RSG up-regulates SNAP-25 expression, but crucially not syntaxin 1 and hence fails to enhance insulin secretion.