Methylglyoxal (MG) is a reactive alpha-dicarbonyl that is thought to contribute to diabetic complications either as a direct toxin or as a precursor for advanced glycation end products. It is produced primarily from triose phosphates and is detoxified to D-lactate (DL) by the glyoxalase pathway. Because guanidino compounds can block dicarbonyl groups, we have investigated the effects of the diamino biguanide compound metformin and of hyperglycemia on MG and its detoxification products in type 2 diabetes. MG and DL were measured by high-performance liquid chromatography in plasma from 57 subjects with type 2 diabetes. Of these subjects, 27 were treated with diet, sulfonylureas, or insulin (nonmetformin), and 30 were treated with metformin; 28 normal control subjects were also studied. Glycemic control was determined by HbA1c. MG was significantly elevated in diabetic subjects versus the normal control subjects (189.3 +/- 38.7 vs. 123.0 +/- 37 nmol/l, P = 0.0001). MG levels were significantly reduced by high-dosage (1,500-2,500 mg/day) metformin (158.4 +/- 44.2 nmol/l) compared with nonmetformin (189.3 +/- 38.7 nmol/l, P = 0.03) or low-dosage (< or = 1,000 mg/day) metformin (210.98 +/- 51.0 nmol/l, P = 0.001), even though the groups had similar glycemic control. Conversely, DL levels were significantly elevated in both the low- and high-dosage metformin groups relative to the nonmetformin group (13.8 +/- 7.7 and 13.4 +/- 4.6 vs. 10.4 +/- 3.9 micromol/l, P = 0.03 and 0.06, respectively). MG correlated with rising HbA1c levels (R = 0.4, P = 0.03, slope = 13.2) in the nonmetformin subjects but showed no increase with worsening glycemic control in the high-dosage metformin group (R = 0.0004, P = 0.99, slope = 0.02). In conclusion, MG is elevated in diabetes and relates to glycemic control. Metformin reduces MG in a dose-dependent fashion and minimizes the effect of worsening glycemic control on MG levels. To the extent that elevated MG levels lead to their development, metformin treatment may protect against diabetic complications by mechanisms independent of its antihyperglycemic effect.

OBJECTIVE -Chronic hyperglycemia is known to increase tissue glycation and diabetic complications, but controversy exists regarding the independent role of increased postprandial glucose excursions. To address this question, we have studied the effect of postprandial glycemic excursions (PPGEs) on levels of methylglyoxal (MG) and 3-deoxyglucosone (3-DG), two highly reactive precursors of advanced glycation end products (AGEs).RESEARCH DESIGN AND METHODS -We performed 4-month crossover studies on 21 subjects with type 1 diabetes and compared the effect of premeal insulin lispro or regular insulin on PPGEs and MG/3-DG excursions. PPGE was determined after standard test meal (STMs) and by frequent postprandial glucose monitoring. HbA 1c and postprandial MG and D-lactate were measured by HPLC, whereas 3-DG was determined by gas chromatography/mass spectroscopy.RESULTS -Treatment with insulin lispro resulted in a highly significant reduction in PPGEs relative to the regular insulin-treated group (P ϭ 0.0005). However, HbA 1c levels were similar in the two groups, and no relationship was observed between HbA 1c and PPGE (P ϭ 0.93). Significant postprandial increases in MG, 3-DG, and D-lactate occurred after the STM. Excursions of MG and 3-DG were highly correlated with levels of PPGE (R ϭ 0.55, P ϭ 0.0002 and R ϭ 0.61, P ϭ 0.0004; respectively), whereas a significant inverse relationship was seen between PPGE and D-lactate excursions (R ϭ 0.40, P ϭ 0.01). Conversely, no correlation was observed between HbA1c and postprandial MG, 3-DG, or D-lactate levels.CONCLUSIONS -Increased production of MG and 3-DG occur with greater PPGE, whereas HbA1c does not reflect these differences. Reduced PPGE also leads to increased production of D-lactate, indicating a role for increased detoxification in reducing MG levels. The higher postprandial levels of MG and 3-DG observed with greater PPGE may provide a partial explanation for the adverse effects of glycemic lability and support the value of agents that reduce glucose excursions. Diabetes Care 24:726 -732, 2001