Treatment of diabetic rats with insulin or a synthetic insulin receptor agonist peptide leads to divergent metabolic responses

In addition to lowering of blood glucose, treatment with insulin also induces lipid synthesis and storage. Patients with type 2 diabetes often suffer from lipid-related comorbidities including dyslipidemia, obesity, and fatty liver disease. We examined here in two separate studies changes in lipid dynamics in Zucker diabetic fatty (ZDF) rats, in response to 7 days of treatment with either insulin or the insulin receptor agonist peptide S597. In concert with blood glucose normalization, the treated rats displayed large increases in hepatic de novo lipid synthesis and deposition of newly synthesized lipids in adipose tissue depots, accompanied by weight gain and expansion of adipose depots. In both treatment groups, heavy water labeling revealed that after 2 h (study A), de novo lipogenesis was responsible for 80% of newly stored hepatic triglyceride (TG)-palmitate, and after 5 days (study B), ∼60% of newly deposited TG-palmitate in adipose tissues originated from this pathway. Interestingly, in both studies, treatment with the insulin mimetic peptide resulted in significantly lower blood TG levels, plasma TG production rates, and hepatic de novo synthesized fatty acid in plasma TG compared with insulin. There were no differences in plasma TG turnover (clearance rate) in response to either treatment, consistent with differential actions on the liver. These results show that in ZDF rats, treatment with a synthetic insulin-receptor-activating peptide or with insulin to lower blood glucose is accompanied by different effects on hepatic lipid anabolism and blood TG profiles.