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Effects of troglitazone and vanadate on insulin resistance induced by oleic acid in cultured rat hepatocytes

Free fatty acids reduce insulin binding and degradation and are capable of exerting post-binding perturbations of insulin action in isolated rat hepatocytes. The aim of this study was to elucidate mechanism of post-binding perturbations and effects of troglitazone and vanadate on insulin resistance induced by oleic acid in cultured rat hepatocytes. Materials and Hepatocytes were pre-incubated in M199 serum-free medium in the absence and presence of 0, 4 mmol/l oleic acid, with or without 0.08 mmol/l insulin or 2 mg/l troglitazone or 1 mmol/l vanadate or 0, 1 mmol/l phorbol 12- myristate 13-acetate, or 20 mmol/l polymyxin B, or 1 mmol/l wortmannin. After 4 h hepatocytes were incubated in Hanks-Hepes medium containing 2 g/l albumin and a-amino 14C-isobutyric acid (14C-AIB) to the final concentration of 1 mmol/l. One hour later, hepatocytes were quickly frozen in liquid nitrogen. The cells were digested in 0.2 N NaOH and an aliquot were taken for determination of protein and radioactivity. Insulin significantly (86%) increased AIB transport. Oleic acid strongly reduced insulin effect (more than 50%). Troglitazone normalised insulin effect. Vanadate mimic normal insulin effect and oleic acid do not reduced this effect (60% increased). TPA, polymyxin B, or wortmannin did not have any significant influence on insulin resistance. These results indicate that troglitazone is able to prevent and reverse insulin resistance induced by oleic acid. This insulin resistance was probably results of changes in receptors or early post-binding perturbations without involving of protein kinase C or IP3-kinase.

amino acid transport; cultured hepatocytes; insulin; insulin resistance; oleic acid; troglitazone; vanadate

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