Methylglyoxal induces prostaglandin E2 production in rat mesangial cells.

The formation of methylglyoxal (MG), a reactive dicarbonyl compound, is accelerated under hyperglycemia, presumably contributing to tissue injury in diabetes. On the other hand, prostaglandin E2 (PGE2) has been implicated in glomerular hyperfiltration, a characteristic change in the early stage of diabetic nephropathy. We therefore examined whether MG was capable of inducing PGE2 production in rat mesangial cells (RMC) to address a possible mechanism by which hyperglycemia-derived dicarbonyls accelerated the development of diabetic nephropathy. RMC were incubated with 0 - 200 microM of MG, followed by determination of secreted PGE2 by enzyme immunoassay (EIA). We further investigated the intracellular mechanisms mediating the MG-induced PGE2 synthesis, focusing particularly on cyclooxygenase-2 (COX-2) and the MAPK superfamily. Our results indicated that MG induced PGE2 production in a dose-dependent manner, accompanied by augmentation of COX-2 mRNA expression. This MG-induced PGE2 production was significantly suppressed by inhibiting either ERK1/2 or p38 MAPK, implicating involvement of the MAPK superfamily. Our results suggest a potential role of MG in the development of diabetic nephropathy through PGE2 production, and may serve as a novel insight into the therapeutic strategies for diabetic nephropathy.

Relation between serum 3-deoxyglucosone and development of diabetic microangiopathy.

OBJECTIVE: 3-Deoxyglucosone (3-DG), a highly reactive intermediate of the glycation reaction, has been suggested to contribute to the development of diabetes complications. To verify this hypothesis, we assessed the relation between serum 3-DG concentrations and the severity of diabetic microangiopathy in diabetic patients. RESEARCH DESIGN AND METHODS: We conducted a high-performance liquid chromatography assay to determine the serum 3-DG concentrations of 110 diabetic patients with different degrees of severity of diabetic microangiopathy and 57 age-matched control subjects. RESULTS: The fasting serum 3-DG level in diabetic patients was significantly (P < 0.001) higher than that in control subjects (353 +/- 110 vs. 199 +/- 53 nmol/l). The 3-DG levels were significantly (P < 0.001) elevated even in the diabetic patients showing normoalbuminuria (n = 62, 322 +/- 79 nmol/l) compared with control subjects. The 3-DG levels were further elevated in the patients with microalbuminuria (n = 30, 383 +/- 146 nmol/l) and overt proteinuria (n = 18, 410 +/- 100 nmol/l) (P = 0.027 and P < 0.001 vs. normoalbuminuria group, respectively). This phenomenon was basically reproduced in a category of retinopathy. Furthermore, the diabetic patients with low nerve conduction velocity showed a tendency to display higher 3-DG levels. CONCLUSIONS: The present results show that the fasting serum 3-DG level is elevated in diabetic patients and that the patients with relatively higher 3-DG levels were prone to suffer from more severe complications, indicating a possible association of 3-DG with diabetic microangiopathy.

Methylglyoxal induces apoptosis through activation of p38 mitogen-activated protein kinase in rat mesangial cells.

BACKGROUND: The formation of methylglyoxal (MG), a highly reactive dicarbonyl compound, is accelerated through several pathways, including the glycation reaction under diabetic conditions, presumably contributing to tissue injury in diabetes. On the other hand, apoptotic cell death of glomerular cells has been suggested to play a role in the development of glomerulosclerosis in various types of glomerular injuries. We therefore examined whether MG was capable of inducing apoptosis in rat mesangial cells to address the possible mechanism by which hyperglycemia-related products accelerated pathologic changes in diabetic glomerulosclerosis. METHODS: Rat mesangial cells were incubated with 0 to 400 micromol/L MG, followed by the detection of apoptosis by both TUNEL method and electrophoretic analysis for DNA fragmentation. In addition, we investigated intracellular mechanisms mediating MG-induced apoptosis, focusing especially on the p38 mitogen-activated protein kinase (MAPK) pathway. RESULTS: MG induced apoptosis in rat mesangial cells in a dose-dependent manner and was accompanied by the activation of p38alpha isoform. Aminoguanidine and N-acetyl-l-cysteine inhibited the MG-induced p38 MAPK activation, as well as apoptosis in rat mesangial cells, suggesting the involvement of oxidative stress in these phenomena. SB203580, a specific inhibitor of p38 MAPK also suppressed the MG-induced apoptosis in rat mesangial cells. CONCLUSIONS: These results suggest a potential role for MG in glomerular injury through p38 MAPK activation under diabetic conditions and may serve as a novel insight into the therapeutic strategies for diabetic nephropathy.