Increased carnitine palmitoyl transferase 1 expression and decreased sterol regulatory element-binding protein 1c expression are associated with reduced intramuscular triglyceride accumulation after insulin therapy in high-fat-diet and streptozotocin-induced diabetic rats.

We previously reported that early insulin treatment reduced intramuscular triglyceride content in type 2 diabetes mellitus Sprague-Dawley rats; the underlying mechanisms are, however, not completely understood. Here we investigated the regulation of insulin on molecular expressions involved in lipid metabolism pathways in skeletal muscle of high-fat-diet and streptozotocin-induced diabetic Sprague-Dawley rats. Neutral protamine Hagedorn insulin and gliclazide were initiated at the third day after streptozotocin injection and lasted for 3 weeks. Compared with normal rats, untreated diabetic rats had a 30% and 61% increase in lipoprotein lipase protein expression and activity, which were decreased by insulin and gliclazide (P < .05). Fatty acid translocase protein was down-regulated by 45% in untreated diabetic rats, which was up-regulated by 31% and 26% with insulin and gliclazide, respectively (P < .05). Insulin failed to affect fatty acid transport protein 1 and fatty acid binding protein expressions. Carnitine palmitoyl transferase 1 had a 47% decrease in untreated diabetic rats, which was normalized by insulin (P < .05). Moreover, compared with normal rats, untreated diabetic rats had higher expressions of sterol regulatory element-binding protein 1c, tumor necrosis factor alpha, and Tyr(705) phosphorylation of signal transducer and activator of transcription 3 levels, which all were down-regulated after insulin treatment. These results suggested that early insulin reduced intramuscular triglyceride levels in diabetic rats potentially through amelioration of lipid dysfunction and inhibition of lipid synthesis.