Methylglyoxal Impairs the Insulin Signaling Pathways Independently of the Formation of Intracellular Reactive Oxygen Species

Abstract

Nonenzymatic glycation is increased in diabetes and leads to elevated levels of advanced glycation end products (AGEs), which link hyperglycemia to the induction of insulin resistance. In hyperglycemic conditions, intracellularly formed ␣-ketoaldehydes, such as methylglyoxal, are an essential source of intracellular AGEs, and the abnormal accumulation of methylglyoxal is related to the development of diabetes complications in various tissues and organs. We have previously shown in skeletal muscle that AGEs induce insulin resistance at the level of metabolic responses. Therefore, it was important to extend our work to intermediates of the biosynthetic pathway leading to AGEs. Hence, we asked the question whether the reactive ␣-ketoaldehyde methylglyoxal has deleterious effects on insulin action similar to AGEs. We analyzed the impact of methylglyoxal on insulin-induced signaling in L6 muscle cells. We demonstrate that a short exposure to methylglyoxal induces an inhibition of insulin-stimulated phosphorylation of protein kinase B and extracellular-regulated kinase 1/2, without affecting insulin receptor tyrosine phosphorylation. Importantly, these deleterious effects of methylglyoxal are independent of reactive oxygen species produced by methylglyoxal but appear to be the direct consequence of an impairment of insulin-induced insulin receptor substrate-1 tyrosine phosphorylation subsequent to the binding of methylglyoxal to these proteins. Our data suggest that an increase in intracellular methylglyoxal content hampers a key molecule, thereby leading to inhibition of insulin-induced signaling. By such a mechanism, methylglyoxal may not only induce the debilitating complications of diabetes but may also contribute to the pathophysiology of diabetes in general.

Methylglyoxal impairs insulin signalling and insulin action on glucose-induced insulin secretion in the pancreatic beta cell line INS-1E

“…Assuming that the cell-associated MGO is indeed intracellular, this would mean that at a concentration of 0.5 mmol/l, approximately 60 μmmol/l of this α-ketoaldehyde is within the cells. Similar observations have been reported concerning the incorporation of MGO into rat L6 skeletal muscle cells [15], and into rat aortic smooth muscle cells [26].…”

“…14 C]MGO The incorporation of [2-14 C] MGO into INS-1E cells was determined as previously described [15]. Details are provided in the ESM.…”

“…Measurement of production of ROS The intracellular reactive oxygen species (ROS) were measured by CM-DCF fluorescence as previously described [15]. Details are provided in the ESM.…”

“…We previously reported that human glycated albumin treatment of cells and dietary AGEs given to mice induce insulin resistance in vitro [13] and in vivo [14], respectively, via a selective protein kinase C alpha activation. We have also shown that MGO induces insulin resistance in skeletal muscle cells through direct chemical modification of IRS proteins [15]. Finally, MGO is thought to exert deleterious effects on insulin secretion [16][17][18][19][20][21].…”

Evidence Against a Role for the Parkinsonism-associated Protein DJ-1 in Methylglyoxal Detoxification

“…Methylglyoxal reacts with cysteine, lysine and arginine residues on proteins to form advanced glycation end-products (AGEs) that affect protein function (5,6). Administration of MG to mice, rats, or cells in culture, results in physiological changes observed in diabetic patients such as collagen accumulation in kidneys, hypercholesterolemia, microvasculature degeneration, and insulin resistance (7)(8)(9).…”