Effect of troglitazone on the desaturases in a rat model of insulin-resistance induced by a sucrose-rich diet

A sucrose-rich diet generates time-dependent metabolic disorders similar to those found in diabetes type 2. After 8 month (mo) this diet evoked in the rat an increase of blood glucose, free fatty acids (FFA) and triacylycerides (TG) without insulin modification, an interruption of liver stearoyl-CoA desaturase-1 (SCD-1) mRNA and activity increase found at 6 mo, and an enhacement of Δ6 and Δ5 desaturase mRNA and Δ6 activity. We found that the administration of troglitazone (TRO), a peroxisome-proliferator-activated receptors γ (PPAR-γ) agonist, for 2 mo normalized plasma FFA, TG, and glucose without altering the insulinemia. It depressed liver SCD-1 mRNA in both control and sucrose-fed rats, decreasing the 18:1n-9/18:0 ratio in serum and liver lipids, and eliminated the increasing effect on mRNA and activity of Δ6 and Δ5 desaturases. These findings evidence again that desaturases are not affected through an insulin resistant effect evoked by the sucrose-rich diet and TRO recovers the altered metabolic plasma parameters as it corresponds to a PPAR-γ agonist, but its effect on hepatic desaturases can not be attributed to a direct action on liver by PPAR-γ, insulin, and even by an insulin sensitizing mechanism, suggesting it would be evoked indirectly through hepatic PPAR-α deactivation induced by the FFA decrease.