High levels of palmitic acid lead to insulin resistance due to changes in the level of phosphorylation of the insulin receptor and insulin receptor substrate-1

Abstract

Insulin resistance is defined as the decrease in the glucose disposal in response to insulin by the target tissues. High concentrations of nonesterified fatty acids (NEFA) in plasma have been implicated with many insulin resistance states. We evaluated several aspects of the insulin resistance induced by palmitic acid in rats and found that after treatment with 0.09 g/kg of palmitic acid there is a delay in the curve of tolerance to glucose. We measured the changes in protein phosphorylation in samples from abdominus rectus muscle and there was a decrease of 64 and 75% in the levels of phosphorylation in tyrosine of the insulin receptor and insulin receptor substrate-1, respectively. This diminution in the tyrosine phosphorylation is consistent with a decrease in the main pathway known to be activated after insulin treatment, the mitogen activated protein kinases (MAPKs). If the animals were treated with inhibitors of PKC, like sphingosine, there was a prevention of the effect of palmitic acid determined at the level of tyrosine phosphorylation. According with this result, we found an increase in the phosphorylations in serine of the insulin receptor after the treatment with palmitate. These results suggest that PKC has a role as negative regulator (by phosphorylation in serine) of the insulin receptors activation in the insulin resistance induced by palmitic acid.