Abstract

Background: The proximal kidney tubule contains a large number of lysosomesinvolved in the breakdown of intracellular as well as reabsorbed proteins. When tubular protein reabsorptionis overburdened or when there is tubular cell damage, higher urinary excretion of lysosomal enzymes,e.g. cathepsins and N-acetyl-beta-D-glucosaminidase (NAG), can be found. We compared urinary cathepsinB (CB) activity with NAG in diabetic patients. Material/Methods: Using fluorogenic substrates, urinaryand plasma CB and NAG activities in 130 type 2 diabetic patients with varying stages of albuminuria and42 control subjects were determined. Early morning urine samples were used. Results: In the patients,only higher values of plasma NAG were found. In urine, CB and NAG activities increased progressivelyfrom normoalbuminuria, through microalbuminuria to macroalbuminuria group. The normoalbuminuria grouphad both enzyme activities higher than healthy controls. Urine CB activity in the patients also increasedgradually to tertiles of urinary NAG. Only urinary CB activity was significantly associated with glycemicstate. The correlation was stronger in the patients with poor glycemic control. The plasma/urine ratiosfor both CB and NAG decreased in the patients compared with controls. Conclusions: Determination of urinaryCB activity might be useful as a non-invasive surrogate marker of incipient nephropathy.

Keywords: Acetylglucosaminidase - urine, Aged, 80 and over, Albuminuria - urine, Biological Markers - urine, Case-Control Studies, Cathepsin B - urine, Diabetes Mellitus, Type 2 - urine, Diabetic Nephropathies - urine