Glyoxalase System in Clinical Diabetes Mellitus and Correlation with Diabetic Complications

1. The metabolism of methylglyoxal by the glyoxalase system may be linked to the development of diabetic complications. The glyoxalase system was characterized in blood samples from patients with insulin-dependent diabetes mellitus (n = 43), patients with non-insulin-dependent diabetes mellitus (n = 107) and 21 normal healthy control subjects.

2. The concentrations of glyoxalase metabolites, methylglyoxal, S-D-lactoylglutathione and D-lactate, were increased in diabetic patients, relative to normal control subjects: methylglyoxal [median, range (n) pmol/g], insulin-dependent patients, 470.7, 85.6-1044.3 (42), P < 0.001, non-insulin-dependent patients, 286.8, 54.7-2370 (105), P < 0.001, control subjects, 79.8, 25.3-892.9 (21); S-D-lactoylglutathione [mean ± SD (n) pmol/10⁶ erythrocytes], combined diabetic patients, 3.37 ± 0.85 (24), control subjects 4.76 ± 1.95 (8) P < 0.05; D-lactate [mean ± SD or median, range (n) nmol/g], insulin dependent patients, median 18.3, 5.7-57.4 (42), P < 0.001, non-insulin-dependent patients, 20.0 ± 8.9, 2.6-48.4 (105), P < 0.001, control subjects 9.7 ± 4.3, 1.8-19.7 (21). The reduced glutathione concentrations in blood samples from the insulin-dependent and non-insulin-dependent diabetic patient groups were not different from the control group values (P>0.05).

3. The activities of glyoxalase enzymes in erythrocytes were increased: glyoxalase I activity [mean ± SD (n) m-units/10⁶ erythrocytes] was increased in diabetic patients, relative to normal control subjects: insulin-dependent patients, 4.35 ± 1.54 (41), P < 0.001; non-insulin-dependent patients, 4.61 ± 1.79 (101), P < 0.001; control subjects, 3.21 ± 1.81 (21); glyoxalase II activity [mean ± SD (n) m-units/10⁶ erythrocytes] was increased in the non-insulin-dependent diabetic patient group, relative to normal control subjects [non-insulin-dependent diabetic patients, 2.10 ± 0.46 (102); subject controls, 1.83 ± 0.27 (21); P < 0.05].

4. In insulin-dependent diabetic patients, the concentration of methylglyoxal correlated positively with the duration of diabetes, and the concentration of D-lactate correlated positively with haemoglobin A_1c and negatively with the reduced glutathione concentration. D-Lactate concentration correlated positively with blood glucose concentration in patients with non-insulin-dependent diabetes mellitus.

5. There was a positive logistic correlation of duration of disease with retinopathy, nephropathy, neuropathy, or any combination thereof. Retinopathy also gave a positive logistic correlation with haemoglobin A_1c concentrations and a negative logistic correlation with D-lactate concentration.

6. When paired for duration of diabetes, patients with retinopathy, neuropathy or nephropathy, or any combination thereof, had significantly higher age, level of haemoglobin A_1c and glyoxalase I activity than patients with uncomplicated diabetes (P < 0.05).

7. We conclude that the glyoxalase system is modified in erythrocytes in both insulin-dependent and non-insulin-dependent diabetic patients and that this modification is related to the development of diabetic complications.