Evaluation of Diabetic Albuminuria by Assaying the Negative Charge of Urinary Albumin

Abstract

To evaluate themechanism of diabetic albuminuria (DA), an assay method for the negative charge (NC) of albumin (ALB) with variable degrees of glycation based on alcian blue (AB) binding was developed. In the in vitro study, AB billding capacity (ABBC), defined as the decrease in absorbance at 650 nm of the AB solution supernatant, increased linearly with an increasing amount of serum and urinary protein, or purified ALB, but no ABBC was detected with purified γ-globulin. ALB was shown to be a major binding component not only by celluloseacetate electrophoresis of serum and urine sample safter incubation with AB, but by the reciproncal relationliship between ABBC and free ALB concentrations in AB solution supernatants in vitro.ABBC was positively correlated with serum glycated ALB (S-GA) concentration and increased pH, and was negatively correlated with NaCl concentration.In the in vivo study in subjects with micro albuminuria, a reciprocal relationship was found between SGA and urinary glycated ALB (UGA). and between S-GA and urinary ABBC in non diabetic conitrol subjects, but this changed to a positive correlation in patients with diabetes when SGA exceeded 17.6%. In sublects with macro-albuminuria, U-ABBC was low and no correlation between S GA was observed in eiher control subjects or patients with diabetes.
It is concluded that the NC assay based on ionic ABBC is useful as an index of ALB g1ycatlon, and that the mechanism of urinary ALB excretion in the patients with DA, but not in the control subjects with non-diabetic albuminuria, was CB damage.