Kidney transplantation is the most efficient and economically sound treatment mode for patients with chronic renal insufficiency, restoring organism homeostasis and quality of life. Even with modern highly efficient immunosuppressive therapy pathological processes are developed in transplant with time, leading to its dysfunction. Functional and structural changes in the kidney occur before increase in serum creatinine or proteinuria, which makes early diagnosis of kidney allograft (KAG) dysfunction difficult, and calls for the search of new, more sensitive and specific markers. Moreover, in cases of KAG dysfunction it is important to determine whether damage is ongoing or we deal with an irreversible sclerosis and atrophy in the allograft.
The aim of the study was to investigate the diagnostic value of the en-zymemia and enzymuria as markers of chronic KAG dysfunction evaluating in the serum and urine enzymes of brush border– -glutamiltransferase (-GGT, EC 18.104.22.168) and alkaline phosphatase (AP, EC 22.214.171.124), cytosol – alanine aminotransferase (ALT, EC 126.96.36.199), lysosomes – N-acetyl--D-hexosaminidase (NAG, EC 188.8.131.52) and mitochondria – aspartateaminotransferase (AST, EC 184.108.40.206).
AP, -GGT, ALT, AST were measured by standard laboratory methods using the spectrophotometer «ÀÐÅL» (Japon). NAG activity was measured in the urine by a colorimetric assay. In brief, this method uses the substrate 4-nitrophenyl-N-acetyl--D-glucosaminide, which is hydrolyzed by NAG when present in the urinary sample. This reaction releases p-Nitrophenol, which is measured by spectrophotometry.
Analysis of the results showed no significant differences in the activity of the enzymes in the blood, that demonstrates the inutility of enzymes studies in the serum in the monitoring of patients with chronic KAG dysfunction. Significant increase in the urinary excretion of -GGT, AP, NAG and AST in patients with chronic KAG dysfunction indicates the continuing damage of the epithelium of the proximal tubules and requires therapeutic interventions.
In the study of relations between the activity of the studied enzymes in urine we showed the moderate degree of correlation between the activity of AP and -GGT in urine (R=0,60) may be due to colocalization of these enzymes in the brush border. The moderate correlation of the full range of the studied enzymes in urine with NAG activity (R=0,47–0,67) may be indicative of a deeper damage of renal proximal tubules epithelial cells up to cytolysis.
Application of univariant logistic regression revealed that only the activity of AP (OR=1,13, P=0,04) and NAG (OR=1,26, P=0,01) were significantly associated with the risk of KAG dysfunction. Multivariate analysis showed that only the activity of NAG in urine had an independent predictive value (OR=1,38, P=0,01). Among the studied enzymes only active lysosomal enzyme NAG in urine shows a deep irreversible damage to proximal tubular epithelium of the kidney and is an independent predictor of KAG chronic dysfunction.
Our findings suggest the diagnostics value of urinary enzymes, first of all, NAG, that indicates the active damage of the epithelium of the proximal tubules and requires prescribing of pathogenetically relevant therapy.
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