Fructose-induced peroxynitrite production is mediated by methylglyoxal in vascular smooth muscle cells

Methylglyoxal (MG), a highly reactive molecule, has been implicated in the development of insulin resistance. We investigated whether fructose, a precursor of MG, induced ONOO^- generation and whether this process was mediated via endogenously increased MG formation. Fructose significantly increased MG generation in vascular smooth muscle cells (VSMCs) in a concentration and time dependent manner. The intracellular production of MG was increased by 153 ± 23% or 259 ± 28% after cells were treated 6 h with fructose (15 mM or 30 mM), compared with production from untreated cells (p < 0.01, n = 4 for each group). A significant increase in the production of ONOO^-, NO, and O₂^.-, was found in the cells treated with fructose (15 mM) or MG (10 μM). Fructose- or MG-induced ONOO^- generation was significantly inhibited by MG scavengers, including reduced glutathione or N-acetyl-l-cysteine, and by O₂^.- or NO inhibitors, such as diphenylene iodonium, superoxide dismutase or N-nitro-l-arginine methyl ester. Moreover, an enhanced iNOS expression was also observed in the cells treated directly with MG which was significantly inhibited when co-application with N-acetyl-l-cysteine. Our results demonstrated that fructose is capable of inducing a significant increase in ONOO^- production, which is mediated by an enhanced formation of endogenous MG in VSMCs.