It has been hypothesized that glucose-induced insulin resistance is mediated by accumulation of UDP- N-acetylhexosamines (UDP-HexNAcs). In a previous study on rat epitrochlearis muscles incubated with high concentrations of glucose and insulin (Kawanaka K, D-H Han, J Gao, LA Nolte, and JO Holloszy. J Biol Chem 276: 20101–20107, 2001), we found that insulin resistance developed even when the increase in UDP-Hex-NAcs was prevented. Furthermore, actinomycin D completely prevented glucose-induced insulin resistance despite a greater accumulation of UDP-HexNAcs. In the present study, we used the same epitrochlearis muscle preparation, as well as the rat hemidiaphragm, to determine whether, like glucose, glucosamine causes insulin resistance by an actinomycin D-inhibitable process. Incubation of diaphragm muscles with 10 mM glucosamine for 3 h resulted in an approximately fivefold increase in UDP-HexNAcs, an ∼50% reduction in insulin responsiveness of glucose transport, and a 58% reduction in ATP concentration. These effects of glucosamine were not prevented by actinomycin D. Incubation of epitrochlearis muscles with 20 mM glucosamine for 3 h or with 10 mM glucosamine for 5 h also caused large decreases in insulin responsiveness of glucose transport but with no reduction in ATP concentration. Actinomycin D did not prevent the glucosamine-induced insulin resistance. The insulin-induced increases in tyrosine phosphorylation of insulin receptor substrate (IRS)-1 and the binding of PI 3-kinase to IRS-1 were decreased ∼60% in epitrochlearis muscles exposed to glucosamine. This is in contrast to glucose-induced insulin resistance, which was not associated with impaired insulin signaling. These results provide evidence that glucosamine and glucose induce insulin resistance by different mechanisms.
Effects of cellular ATP depletion on glucose transport and insulin signaling in 3T3-L1 adipocytes
