[A study of microproteinuria in patients with diabetes mellitus]

In order to investigate the early renal damage in diabetes mellitus, 89 diabetics without proteinuria by dipsticks and 67 normal control subjects were examined by means of SDS-PAGE. The relationships between electrophoretic patterns of urinary protein and duration of diabetes, age of patients, metabolic controls and stages of retinopathy were examined. 1) The percentage of higher molecular weight (MW) proteins (67,000 less than or equal to MW) was larger in diabetics than that in controls. Especially the percentage of proteins with MW between 67,000 and 94,000, which include transferrin was 13.9 +/- 6.9% in diabetics, significantly higher than that in controls (10.3 +/- 5.1%) (P less than 0.01). On the contrary, the percentage of low MW proteins (MW less than 67,000) was relatively small in diabetics. 2) The excretion of higher MW proteins increased until 16 years of diabetic duration, however that decreased after 16 years. Especially in the group with duration longer than 20 years, excretion of low MW proteins increased. 3) Electrophoretic patterns of urinary proteins in patients with good metabolic control were similar to those in normal controls. 4) Excretion of higher MW proteins increased in patients with retinopathic complication suggesting the progression to microangiopathy. From the above results, we concluded that increased excretion of higher MW proteins in diabetics may be the results of GBM damages in protein selectivity. In patients with longer history of diabetes, predominant excretion of urinary low MW proteins may be the result of tubular dysfunction due to macroangiopathy.