Transmembrane electron transfer in diabetic nephropathy

OBJECTIVE - Erythrocytes (red blood cells [RBCs]) reduce extracellular ferr icyanide by transmembrane transfer of reducing equivalents involving ascorb ate recycling. RESEARCH DESIGN AND METHODS - Because ascorbate regeneration is glutathione (GSH) dependent and cells may be depleted of GSH in diabetes, we measured RBC GSH, plasma sulfhydryl (SH) groups, and RBC-mediated ferricyanide reduc tion in 30 type 1 diabetic patients (age 34 +/- 10 years, disease duration 20 +/- 8 years; no complications, n = 10; retinopathy, n = 10; nephropathy, n = 10), their 36 siblings (age 39 +/- 13 years), and matched healthy volu nteers. RESULTS - Fasting plasma glucose was 15 +/- 7 mmol/l (vs. 5 +/- 1 in contro l subjects, P < 0.001), HbA(1c) 8.4 +/- 1.5% (vs. 5.4 +/- 0.3, P < 0.001), GSH 0.76 +/- 0.12 mg/ml packed RBCs (vs. 0.88 +/- 0.18, P < 0.01), SH group s 401 +/- 72 mu mol/l (vs. 444 +/- 56, P < 0.05), and ferrocyanide generati on 15 +/- 5 mu mol/ml RBC per h (vs. 13 +/- 5, NS). In comparison with 10 n ormoalbuminuric diabetic subjects with retinopathy, 10 patients with diabet ic nephropathy had similar fasting plasma glucose, HbA(1c), and SH groups; lower RBC GSH (0.73 +/- 0.08 vs. 0.85 +/- 0.11, P < 0.05); and higher ferro cyanide generation (18 +/- 4 vs. 14 +/- 5, P < 0.05). The 10 patients witho ut complications differed from the 10 healthy volunteers in glycemic contro l and RBC GSH. RBC electron transfer correlated with plasma lactate (r = 0. 8, P = 0.01) only in the uncomplicated group. No difference was detected be tween siblings and healthy control subjects or between siblings of subjects in the nephropathy and retinopathy groups. Among diabetic patients, the ra te of ferrocyanide generation was associated with urinary albumin excretion , plasma creatinine, and SH groups (multiple r = 0.6, P < 0.01). CONCLUSIONS - Transmembrane electron transfer is selectively increased in d iabetic nephropathy, where RBC GSH is also depleted. The abnormality is pec uliar to the nephropathy group and not contributed by familial or hereditar y components because the electron flow was normal in siblings. The close re lationship between cytosolic NADH and RBC electron transfer observed in dia betic patients without complications seems to be lost in the microangiopath ic patients. Whereas patients with retinopathy alone still had normal activ ity of the RBC-reducing system, patients with nephropathy showed significan tly increased activity, unrelated to metabolic parameters or plasma lactate concentration and correlated with renal function parameters and plasma thi ols.