Analysis of urinary protein in diabetics; its clinical implications as a predictor of nephropathy

We analyzed the components of urinary proteins in 58 diabetic patients with either short duration or long-standing disease using sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis (SDS-PAGE), in comparison with 21 healthy volunteers. It was found that the percentage of protein with a molecular weight (Mr) of 140 kDa was greater in diabetics with normal renal function and negative clinical proteinuria (less than 100 mg/24 h) than in normals. In patients with clinical proteinuria (greater than 100 mg/24 h), the percentage of protein with an Mr of 67 kDa (presumably albumin) was predominantly increased, while the percentage of lower Mr proteins was considerably decreased. A positive correlation existed between the total urinary protein excretion and the percentage of 67 kDa protein in diabetics without clinical proteinuria (r = 0.487, p less than 0.01), but not in normal subjects. Recovery of glycemic control led to a decrease of urine proteins with an Mr lower than 67 kDa, while deterioration of the control resulted in an increase in these proteins. The present data confirm the idea that analysis of the components of urine proteins by SDS-PAGE represents a useful approach to understanding the glomerular and tubular functions in diabetic patients. Additionally, this investigation appears to provide biochemical evidence that dysfunction of the glomerular permselectivity to plasma proteins might already have occurred in diabetic patients without clinical evidence of diabetic nephropathy.