Enzymuria as a marker of renal injury and disease: studies of N-acetyl-beta-glucosaminidase, alanine aminopeptidase and lysozyme in patients with renal disease

Biomarkers of immunosuppressant organ toxicity after transplantation: status, concepts and misconceptions

INTRODUCTION

A major challenge in transplantation is improving long-term organ transplant and patient survival. Immunosuppressants protect the transplant organ from alloimmune reactions, but sometimes also exhibit limiting side effects. The key to improving long-term outcome following transplantation is the selection of the correct immunosuppressive regimen for an individual patient for minimizing toxicity while maintaining immunosuppressive efficacy.

AREAS COVERED

Proteomics and metabolomics have the potential to develop sensitive and specific diagnostic tools for monitoring early changes in cell signal transduction, regulation and biochemical pathways. Here, we review the steps required for the development of molecular markers from discovery, mechanistic and clinical qualification to regulatory approval, and present a critical discussion of the current status of molecular marker development as relevant for the management and individualization of immunosuppressive drug regimens.

EXPERT OPINION

Although metabolomics and proteomics-based studies have yielded several candidate molecular markers, most published studies are poorly designed, statistically underpowered and/or often have not gone beyond the discovery stage. Most molecular marker candidates are still at an early stage. Due to the high complexity of and the resources required for diagnostic marker development, initiatives and consortia organized and supported by funding agencies and regulatory agencies will be critical.

Does the antiviral therapy of patients with chronic hepatitis exert nephrotoxic effects?

INTRODUCTION

HBV and HCV chronic hepatitis can be accompanied by secondary renal disease. In addition, these patients receive antiviral drugs with potential nephrotoxicity. It is known that interferon (IFN) therapy in HCV-infected kidney transplant recipients is followed by rejection of the transplant in 50% of the cases. Ribavirin is contraindicated in hemodialyzed patients and in patients with a GFR <50 ml/min/1.73 m(2). IFN therapy requires dosage reduction and close monitoring in patients with a GFR <50 ml/min/1.73 m(2) and in patients with end stage renal disease. The aim of our study was to assess the nephrotoxicity of antiviral drugs in patients with chronic hepatitis by measuring three renal biomarkers: urinary albumin, N-acetyl-β-D-glucosaminidase (NAG) and α 1-microglobulin, as well as glomerular filtration rate (GFR-MDRD4) before and at 6 months of therapy.

METHODS

Fifty-five patients (28 male and 27 female, with a mean age of 47.85 ± 12.03 years) with chronic hepatitis (40 patients with HCV, 13 patients with HBV, 1 patient with HBV+HCV, and 1 patient with HBV+HDV) were enrolled into the study. Different antiviral drug associations were used on a case-by-case basis. The 40 patients with HCV chronic hepatitis received either Peg-IFN-α 2a+Ribavirin (37 patients) or Peg-IFN-α 2b+Ribavirin (3 patients). The 13 patients with HBV chronic hepatitis received Peg-IFN-α 2a (9 patients), Lamivudine (2 patients), Entecavir (1 patient), or Adefovir (1 patient). The patient with HBV+HCV chronic hepatitis received Peg-IFN-α 2a+Ribavirin. The patient with HBV+HDV chronic hepatitis received IFN-α 2a. Urinary albumin (ELISA), NAG (colorimetrical method), α 1-microglobulin (ELISA), and serum creatinine were measured before and at 6 months of antiviral therapy. Urinary markers were expressed as either mg/gCr (for albumin and α 1-microglobulin) or U/gCr (for NAG). Statistical analysis (Pearson's correlation coefficient, paired t-test and χ(2)-test) was performed.

RESULTS

At 6 months of therapy urinary albumin/gCr did not increase significantly: 16.58 ± 23.39 vs. 15.85 ± 24.96 mg/gCr before therapy, p = 0.87. Urinary NAG/gCr did not increase significantly: 4.21 ± 3.37 vs. 3.83 ± 3.2 U/gCr before therapy, p = 0.53. Urinary α 1-microglobulin/gCr was almost unchanged: 4.38 ± 4.47 vs. 4.38 ± 3.57 mg/gCr before therapy, p = 0.99. The GFR did not decline significantly: 92.41 ± 22.21 vs. 94.59 ± 36.1 ml/min/1.73 m(2) before therapy, p = 0.7. Ten patients (18.18%) were albuminuric before therapy, and 14 patients (25.45%) were albuminuric at 6 months of therapy, a non-significant increase (p = 0.35). We found a correlation between urinary albumin/gCr and NAG/gCr and between urinary albumin/gCr and α 1-microglobulin/gCr both at baseline and at 6 months of therapy: r = 0.54, p = 0.0005; r = 0.29, p = 0.03; r = 0.51, p = 0.0005; and r = 0.4, p = 0.002, respectively. In the patient receiving Adefovir, a known nephrotoxic drug, two of the three biomarkers (urinary albumin/gCr and NAG/gCr) increased, most notably NAG/gCr. Both HCV and HBV chronic hepatitis therapy were associated with non-significant changes in renal biomarker excretion and GFR.

CONCLUSIONS

With the exception of Adefovir, all of the drug associations used in this study were safe.

Biochemical markers of renal disease in primary Sjögren's syndrome

Primary Sjögren's syndrome (SS) is characterized by an inflammatory process in the salivary and lacrimal glands, but the kidneys may also be involved. Renal tubular functions were studied in 27 patients with SS, all females, age 37-78. Both SS-patients with and without known distal renal tubular acidosis (dRTA) were included, dRTA was found in 18/27 (67%), impaired urine concentrating ability in 13/27 (48%). Hypocitraturia was identified in 20/27 (74%) and reduced tubular reabsorption of phosphate (TRP%) in 18/27 (67%). Tubular proteinuria (alpha 1-mikroglobulin) was present in 11/24 (46%), and tubular enzymuria (NAG) in 7/24 (29%). Hypocitraturia and/or dRTA were found in all patients with any kind of abnormal renal tubular function test. All except one of the patients with dRTA not treated with sodium bicarbonate had hypocitraturia. We conclude that distal tubular dysfunction was common in our SS-patients, but a concommitant proximal dysfunction was also seen. Determination of urinary citrate represents a valuable test for detection of renal disease in SS.

Changes in urinary enzyme levels following the use of antihypertensive agents in patients with essential hypertension

When choosing antihypertensive agents for the treatment of hypertension, it is necessary to consider the predisposition of individuals to renal damage, which may be associated with the long-term effect of such agents. In this respect, this study examined the effect of two commonly used antihypertensive drugs (Brinerdin and Minizide) on renal function over 24 months in patients diagnosed as having essential hypertension. We utilized urinary enzyme studies, which are indicators of subtle renal dysfunction. Other parameters of glomerular and tubular function were also determined in the pretreatment period, as well as during and at the end of treatment of 28 patients (16 males and 12 females) with therapeutic doses of Brinerdin and 22 patients (12 males and 10 females) with conventional doses of Minizide. During the follow-up period, blood pressure (BP) fell from a mean of 160/108 +/- 9/4 (SD) mmHg to 130/90 +/- 7/4 on Brinerdin and from a mean of 160/106 +/- 5/2 (SD) mmHg to 130/90 +/- 8/5 on Minizide. There was no significant difference in the levels of BP between the patients taking Minizide and those taking Brinerdin before, during, and at the end of treatment. Significant elevation (p < 0.05) of the levels of urinary protein, lactate dehydrogenase (LDH), and N-acetyl-B-D-glycosaminidase (NAG) was observed in patients on Minizide during treatment, and these levels remained elevated during the latter part of the study. Normotensive, untreated, age- and sex-matched control subjects showed no such urinary parameter changes.(ABSTRACT TRUNCATED AT 250 WORDS)

Urinary N-acetyl-beta-D-glucosaminidase as a marker of renal injury in adjuvant arthritis

In the present study we have determined if renal damage occurs with adjuvant arthritis (AA). As a sensitive indicator of renal injury in tubular cells, urinary N-acetyl-beta-D-glucosaminidase (NAG) was measured at predetermined times after arthritis induction. Urinary protein, sodium and potassium excretion were also evaluated. NAG levels in arthritic animals were higher than those in healthy ones from day 12 after induction and the levels remained high during the study period. A significant positive correlation was noted between urinary NAG excretion and disease severity reflected by hind paw edema. Protein excretion also increased in arthritic animals but there was no correlation between urinary protein, NAG levels, and degree of inflammation. Changes in urine sodium and potassium levels did not reach statistical significance. Thus, we can conclude that some renal damage occurred in this experimental model of chronic inflammation.

Evaluation of the renal tubulo-toxic effect of gossypol by urinary protein analysis with SDS-polyacrylamide gel electrophoresis

The present study assessed the urinary protein with SDS-PAGE technique and by using gentamicin as a positive control for a comparative study to evaluate the renal toxic effect of gossypol. Results indicated that gentamicin could induce proteinuria by alteration of glomerular permeability to cause over-filtration of high molecular weight proteins, damage the brush border (BB) membrane of proximal renal tubules and impair tubular reabsorption function. Gossypol could also induce proteinuria in certain cases of guinea pigs but not at all in gossypol-treated rats. However, an increase in low molecular weight protein bands (M.W. range 20-30 kd) in urinary electrophoregram of gossypol-treated rats were detectable.

Diagnostic significance of different urinary enzymes in patients suffering from chronic renal diseases

The urinary enzymes alanine aminopeptidase (EC 3.4.11.2), alkaline phosphatase (EC 3.1.3.1), gamma-glutamyltransferase (EC 2.3.2.2), N-acetyl-beta-D-glucosaminidase (EC 3.2.1.30), and ribonuclease (EC 3.1.4.22) were measured in 66 healthy persons and 52 patients suffering from chronic renal diseases (pyelonephritis, glomerulonephritis). The residual renal function of patients characterized by 99mTc-diethylenetriaminopentaacetate isotope clearance was only moderately reduced. Except for gamma-glutamyltransferase, patients generally showed increased urinary enzyme excretions. N-Acetyl-beta-D-glucosaminidase was more sensitive to detect renal dysfunction than the other enzymes and the conventional parameters serum creatinine, total protein excretion, and the measurement of glomerular filtration rate. The determination of this enzyme can be recommended as a suitable diagnostic parameter in nephrology.