Isoelectric focusing of urinary transferrin for detection of early stages of diabetic nephropathy

Urinary albumin (ALB) and transferrin (TF) are useful markers for impaired renal function. Compared to ALB, TF is more readily excreted into urine from an early stage of renal failure because of its smaller number of negative charges. However, few evidence of a change in isoelectric point (pI) value of urinary TF in nephropathy patients has been reported. We analyzed pI values of urinary TF by an isoelectric focusing, and compared the results in normal subjects with those in diabetic patients at various stages of nephropathy. Urine samples of diabetics were randomly collected from 24 patients and 7 healthy volunteers. An apotransferrin with a high pI value was detected in samples of healthy subjects. However, the pI value of TF bands derived from diabetic patients shifted to the lower side, and the more nephropathy stages progressed, greater change of pI value was detected. In addition, TF with low iron-binding capacity was detected in some samples from diabetics. These results suggest that determination of the pI value of urinary TF in diabetic patients may be useful diagnostic markers for an early detection of diabetic nephropathy.