Effects of fenofibrate and insulin on the biosynthesis of unsaturated fatty acids in streptozotocin diabetic rats

Both insulin and PPAR-α up-modulate hepatic Δ9, Δ6 and Δ5 desaturating enzymes involved in the biosynthesis of mono- and polyunsaturated fatty acids. Currently, we have examined for 9 days the independent and simultaneous effects of daily glargine insulin and fenofibrate administration on the insulinemia, glycemia, hepatic acyl-CoA oxidase activity and mRNAs and enzymatic activities of stearoyl-CoA desaturase-1 (SCD-1) and Δ5 desaturase in streptozotocin diabetic rats. Glargine insulin depressed the hyperglycemia of diabetic rats at 4 h, but not after 24 h of injection. Fenofibrate increased the radioimmunoreactive insulinemia in non-diabetic rats without changing the glycemia. Insulin increased the mRNAs and activities of SCD-1 and Δ5 desaturase depressed in diabetic rats. Fenofibrate increased acyl-CoA oxidase activity, and the mRNAs and activities of both desaturating enzymes in non-diabetic, diabetic and insulin-treated diabetic rats, but was less effective in the mRNAs modification of diabetic animals. Therefore, insulin, and fenofibrate through PPAR-α activation, enhance liver mRNAs and activities of SCD-1 and Δ5 desaturases independently and synergistically through different mechanisms. Insulin and fenofibrate independently increased the 18:1/18:0 ratio in liver lipids, increasing the fluidity of the membranes. The 20:4/18:2 ratio was maintained. Fenofibrate increased palmitic acid, but decreased stearic acid percentage in liver lipids.