A new enzyme-linked immunosorbent assay for urine and serum concentrations of the carboxyterminal domain (NCI) of collagen IV. Application in type I (insulin-dependent) diabetes

Abstract

The major collagenous component of glomerular basement membrane (GBM) is collagen IV. Serum concentrations of the carboxyterminal end (NCI) of collagen IV have been proposed to be related to GBM turnover, which has been suspected to increase in diabetes mellitus. For the quantification of serum and urinary concentrations of NCI, a specific, sensitive enzyme-linked immunosorbent assay (ELISA) with monoclonal antibodies was developed. The detection limit of the assay was 30 ug/1 at the 50% intercept of the standard curve. The intra- and interassay coefficients of variation were 6.2% and 13.9% for serum, respectively, and 11.9% and 39.7% for urine, respectively. The levels of NCI in serum and urine in 67 insulin-dependent diabetics and in 90 sex- and age-matched controls were compared. There were no differences in the serum concentrations of NCI between the diabetics and healthy controls. As a group, the diabetics had a higher urinary excretion of NCI than the controls (20.1 vs 12.5 ng/min, 2p<0.05). Furthermore, the results showed that the excretion of NCI in the urine was normal when the urinary albumin excretion rate (AER) was normal (<6.5 μg/min). The excretion was increased during the early stage of incipient diabetic nephropathy (AER 6.5-30 μg/min) and decreased to normal values with progression to clinical diabetic nephropathy (AER above 500 μg/min). Thus, it is suggested that an increased urinary excretion of NCI may be an early marker for incipient diabetic nephropathy.

Key Words:

• basement membrane
• collagen IV
• diabetes mellitus
• diabetic nephropathy
• ELISA
• NCI
• urinary albumin