Modifications of cellular lipids induce insulin resistance in cultured hepatoma cells.

We altered the cellular lipid composition of an insulin sensitive rat hepatoma cell line through supplementation of the culture medium with linoleic acid (18:2) or 25-hydroxycholesterol, and we studied the effects on insulin stimulation of aminoacid transport system A and glycogen synthesis. The basal rate of sodium-dependent aminoisobutyric acid uptake was slightly reduced in hydroxysterol-treated cells and increased in 18:2-enriched cells. Maximal insulin stimulation of transport was decreased by about 40% in both 18:2 and 25-hydroxycholesterol modified cells, as compared to control cells. In addition to reduced responsiveness, the hydroxysterol-treated cells also showed a diminished sensitivity to insulin, as revealed by a right-shift of the dose-response curve leading to a ED50 of 1.2 X 10(-8) M (P less than 0.02), as compared to 2.45 X 10(-9) M in control cells and 2.13 X 10(-9) M in 18:2 enriched cells. Concerning glycogen synthesis, the basal rate was unaffected by 25-hydroxycholesterol supplementation and slightly reduced in cells enriched in 18:2. Maximal insulin stimulation of glycogen synthesis was reduced by about 40% in both types of lipid modified cells. 25-Hydroxycholesterol again provoked a decrease in sensitivity to insulin: the ED50 was enhanced to 4.9 X 10(-9) M (P less than 0.05), as compared to 1.25 X 10(-9) M in control cells and 1.57 X 10(-9) M in 18:2-supplemented cells. Taken together with the previously reported changes of insulin binding to lipid modified hepatoma cells (Bruneau et al. (1987) Biochim. Biophys. Acta 928, 287-296) our results demonstrate an influence of alterations of the cellular lipid composition on both binding and biological actions of insulin, leading to an insulin-resistant state. Divergences between insulin binding and action were obtained and it was suggested that post-binding events may be responsible for the observed changes. Our findings may be relevant to experimental and clinical states of insulin resistance.