Chronic exposure to ketone bodies impairs glucose uptake in adult cardiomyocytes in response to insulin but not vanadate: the role of PI3-K.

There is a strong positive correlation between insulin resistance and cardiac diseases. We have already shown that chronic exposure to the ketone body beta-hydroxybutyrate (OHB) decreases insulin-mediated activation of protein kinase B (PKB) and glucose uptake in cardiomyocytes. To gain further insights into the mechanism underlying ketone body-induced insulin resistance, we examined whether OHB alters activation of the insulin-signaling cascade and whether the insulinomimetic agent vanadate could bypass insulin resistance and stimulate glucose uptake in these cells. Cardiomyocytes were incubated with 5 mM OHB, 50 microM vanadate or both for 16 h before the measurement of glucose uptake or the activation of insulin-signaling molecules. While chronic exposure to OHB did not alter insulin- or vanadate-mediated activation of the insulin receptor, it suppressed insulin receptor substrate-1 (IRS-1) tyrosine phosphorylation in response to both agonists. Furthermore, this treatment decreased by 54 and 36% the phosphorylation of the p85 regulatory subunit of phosphatidylinositol 3-kinase (PI3-K) and PKB in response to insulin, whereas it did not alter vanadate-mediated activation of these enzymes. Although insulin did not significantly stimulate p38MAPK phosphorylation, vanadate increased it by 3.8-fold. Furthermore, chronic exposure to OHB potentiated vanadate's action, resulting in a 250% increase in enzyme activation compared to control cells. Though OHB induced a 2.1-fold increase of basal ERK1/2 phosphorylation, inhibition of this enzyme with the MEK inhibitor PD98059 demonstrated that ERK1/2 did not participate in OHB-induced insulin resistance. In conclusion, ketone bodies promote insulin resistance probably through decreased activation of the PI3-K/PKB signaling cascade. Furthermore, vanadate can bypass insulin resistance and stimulate glucose uptake in OHB-treated cardiomyocytes.