Cytotoxic role of methylglyoxal in rat retinal pericytes: Involvement of a nuclear factor-kappaB and inducible nitric oxide synthase pathway

Methylglyoxal (MGO), a cytotoxic metabolite, is produced from glycolysis. Elevated levels of MGO are observed in a number of diabetic complications, including retinopathy, nephropathy and cardiomyopathy. Loss of retinal pericyte, a hallmark of early diabetic retinal changes, leads to the development of formation of microaneurysms, retinal hemorrhages and neovasculization. Herein, we evaluated the cytotoxic role of MGO in retinal pericytes and further investigated the signaling pathway leading to cell death. Rat primary retinal pericytes were exposed to 400 μM MGO for 6 h. Retinal vessels were prepared from intravitreally MGO-injected rat eyes. We demonstrated apoptosis, nuclear factor-kappaB (NF-κB) activation and inducible nitric oxide synthase (iNOS) induction in cultured pericytes treated with MGO and MGO-injected retinal vessels. In MGO-treated pericytes, TUNEL-positive nuclei were markedly increased, and NF-κB was translocalized into the nuclei of pericytes, which paralleled the expression of iNOS. The treatment of pyrrolidine dithiocarbamate (an NF-κB inhibitor) or l-N6-(1-iminoethyl)-lysine (an iNOS inhibitor) prevented apoptosis of MGO-treated pericytes. In addition, in intravitreally MGO-injected rat eyes, TUNEL and caspase-3-positive pericytes were significantly increased, and activated NF-κB and iNOS were highly expressed. These results suggest that the increased expression of NF-κB and iNOS caused by MGO is involved in rat retinal pericyte apoptosis.