Urinary enzymes as biomarkers of renal injury in experimental nephrotoxicity of immunosuppressive drugs

A forward to optimization of antivenom therapy: An in vivo study upon the effectiveness of the antivenom against early and delayed nephrotoxicity induced by the venom of the Iranian scorpion Hemiscorpius lepturus in rat

The aim of the present in vivo study was to identify the optimal effective dose, the most favorable time and the route of administration of the available polyvalent scorpion antivenom against the toxic effects induced by Hemiscorpius lepturus (H. lepturus) venom in rat. The end point for assessment included measurement of alanin-amino-peptidase (AAP) and N-acetyl-b-d-glucosaminidase (NAG), biochemical urine analysis and histopathological assessment. The results showed that a single subcutaneous 50 μg of the venom produced significant increase in the AAP and NAG enzyme activity, urinary biochemical parameters and induced histopathological structural abnormalities in the renal system. The optimal effective co-administered dose of the antivenom was 0.5 ml, which when administered 1 and 2 h of envenomation by intravenous (IV) and subcutaneous (SC) routes respectively produced significant protection against these toxic effects. Prudently, the significance of these findings need to be assessed in further clinical studies.

Emergence of biomarkers in nephropharmacology

Blood-urea nitrogen, serum creatinine and urine output have long been used as markers of kidney function despite their known limitations. In the past few years, a number of novel biomarkers have been identified in the urine and blood that can detect kidney injury early. Although, to date, none of these biomarkers are in clinical use, many have been validated as reliable and sensitive, allowing detection of kidney injury before serum creatinine levels rise and urine output drops. These markers have been evaluated in great detail in animal models and to a lesser extent in humans in postcardiopulmonary bypass and sepsis. There is relatively scarse data on the use of these biomarkers in the detection of kidney injury associated with the use of pharmacologic agents. The purpose of this article is to summarize these data and highlight the potential utility of these biomarkers in nephropharmacology.

Effects of sirolimus alone or in combination with cyclosporine A on renal ischemia/reperfusion injury

Calcineurin inhibitors exacerbate ischemic injury in transplanted kidneys, but it is not known if sirolimus protects or exacerbates the transplanted kidney from ischemic injury. We determined the effects of sirolimus alone or in combination with cyclosporin A (CsA) on oxygenated and hypoxic/reoxygenated rat proximal tubules in the following in vitro groups containing 6-9 rats per group: sirolimus (10, 50, 100, 250, 500, and 1000 nanog/mL); CsA (100 microg/mL); sirolimus (50 and 250 nanog/mL) + CsA (100 microg/mL); control; vehicle (20% ethanol). For in vivo studies, 3-week-old Wistar rats (150-250 g) were submitted to left nephrectomy and 30-min renal artery clamping. Renal function and histological evaluation were performed 24 h and 7 days after ischemia (I) in five groups: sham, I, I + SRL (3 mg x kg(-1) x day(-1), po), I + CsA (3 mg x kg(-1) x day(-1), sc), I + SRL + CsA. Sirolimus did not injure oxygenated or hypoxic/reoxygenated proximal tubules and did not potentiate the tubular toxic effects of CsA. Neither drug affected the glomerular filtration rate (GFR) at 24 h. GFR was reduced in CsA-treated rats on day 7 (0.5 +/- 0.1 mL/min) but not in rats receiving sirolimus + CsA (0.8 +/- 0.1 mL/min) despite the reduction in renal blood flow (3.9 +/- 0.5 mL/min). Acute tubular necrosis regeneration was similar for all groups. Sirolimus alone was not toxic and did not enhance hypoxia/reoxygenation injury or CsA toxicity to proximal tubules. Despite its hemodynamic effects, sirolimus protected post-ischemic kidneys against CsA toxicity.

Neutrophil gelatinase-associated lipocalin (NGAL): a new marker of cyclosporine nephrotoxicity?

The aim of work was to investigate whether serum and urinary neutrophil gelatinase-associated lipocalin(sNGAL and uNGAL, respectively) are potential biomarkers of early cyclosporine A (CsA) nephrotoxicity in steroid-dependent nephrotic children (SDNS). The study group (I) consisted of 19 children with SDNS aged 9.46+/-5.52 years treated with CsA. The children were examined four times: at proteinuria relapse, prior to CsA treatment,then after 3, 6, and 12 months of CsA treatment. The control group (II) consisted of 18 healthy children aged 3-15 years. A commercial enzyme-linked immunosorbent assay method was used to measure NGAL concentration.The sNGAL level in SDNS children prior to the administration of CsA was similar to that in the healthy controls (p>0.05), but it increased significantly during the course of treatment (p<0.01). The uNGAL/creatinine (cr) ratio in SDNS patients was higher before the withdrawal of CsA therapy (p<0.05), and was also increased at the consecutive examinations (p<0.01). There was a positive correlation between both sNGAL and uNGAL levels and CsA serum level. However, based on the serum and urinary NGAL/cr receiver operating characteristic curve and area under the curve (AUC) analysis, it remains uncertain whether uNGAL is a good predictor of cyclosporine nephropathy. Both sNGAL and uNGAL concentrations increased during the course of CsA treatment. Further studies in larger groups of patients are therefore necessary to confirm our experimental data that increased NGAL levels may be a non-invasive marker for the early detection of tubulointerstitial damage in CsA nephrotoxicity.

Determination of urinary enzymes as a marker of early renal damage in diabetic patients

Diagnosis of diabetic nephropathy in the early stages is very important since there are no clinical signs or symptoms. Urinary N-acetyl-beta-D-glucosaminidase (NAG) excretion has been recommended as a tubular dysfunction marker that elevates before other markers, such as microalbuminuria and a decrease in creatinine clearance. In this study, we compared excretion of urinary enzymes with other markers that are used routinely in diabetic nephropathy assessment. Urinary NAG, lactate dehydrogenase (LDH), alkaline phosphatase (AP) activities, urea, creatinine, and albumin, with levels of serum glucose and creatinine and whole blood glycosylated hemoglobin (HbA1c) were measured in 32 diabetes mellitus patients and 25 healthy subjects (controls). Notably, urinary NAG, AP, LDH excretion, and microalbuminuria in the diabetic patients group were significantly increased compared to those in the control groups (P<0.001, P<0.05, P<0.01, and P<0.01, respectively). Meanwhile, our results showed that the urinary NAG excretion had the highest sensitivity and specificity (100% and 87.5%, respectively) compared to other markers. We showed that measuring urinary NAG excretion could be useful for the assessment of renal failure in diabetes mellitus patients and confirmed the use of NAG as a routine screening test.

Mechanistic biomarkers for cytotoxic acute kidney injury

Acute kidney injury is a common condition and is associated with a high mortality rate. It has been recognised that routinely used measures of renal function, such as levels of blood urea nitrogen and serum creatinine, increase significantly only after substantial kidney injury occurs and then with a time delay. Insensitivity of such tests delays the diagnosis in humans, making it particularly challenging to administer putative therapeutic agents in a timely fashion. Furthermore, this insensitivity affects the evaluation of toxicity in preclinical studies by allowing drug candidates, which have low, but nevertheless important, nephrotoxic side effects in animals, to pass the preclinical safety criteria only to be found to be clinically nephrotoxic with great human costs. This review presents the current status of sensitive and specific biomarkers to detect preclinical and clinical renal injury and summarises the techniques used to quantitate these biomarkers in biological fluids.

FK506 nephrotoxicity

Tacolimus (FK506) is a potent immunosuppressive agent with significant nephrotoxic properties. FK506 is complexed with an intracellular binding protein FKBP-12. Both the immunosuppressive and nephrotoxic effects may be linked to the inhibitory effect of this complex on calcineurin. The initial phase of FK506 nephrotoxicity is associated with a reduction in renal blood flow and glomerular filtration rate. More significant microvascular injury may follow with endothelial damage. Tubular epithelial cell vacuolation, atrophy and micocalcification may be associated with the development of irreversible interstitial fibrosis. At times, mesangial cell proliferation adds to the glomerular abnormalities. These effects may be mediated by the inhibitory effect on calcineurin and its role in regulating cellular calcium channels. FK506 stimulates several inflammatory cytokines, such as transforming growth factor-beta, with potential deleterious effects. Also abnormalities in the reninangiotensin system, endothelin, renal prostaglandins, adrenergic receptors may all play a role in the nephrotoxic effects.

Comparative pharmacokinetics and renal effects of cyclosporin A and cyclosporin G in renal allograft recipients

Cyclosporin G (CSG) has produced less nephrotoxicity than cyclosporin A (CSA) at equivalent doses in animal models. Conflicting results have been reported concerning differences in the pharmacokinetics of CSA and CSG in preclinical studies, and no data exist regarding the effect of steady-state oral administration of CSG on renal function in transplant patients or CSG-induced release of endothelin and nitric oxide (NO) in vivo. The objective of the study was to examine steady-state pharmacokinetic profiles of adult renal allograft recipients receiving CSA and CSG in relation to concentrations of endothelin-1 and NO2/NO3 in urine and plasma, creatinine clearance (Clcr), and urinary excretion of N-acetyl-beta-D-glucosaminidase (NAG) 9 months after transplantation. Concentrations of CSA and CSG were measured in whole blood over a 12-hour dose interval by both a monoclonal and polyclonal fluorescence polarization radioimmunoassay for CSA. A metabolite fraction was defined as the numerical difference between the levels obtained at each time point by both assays. Patient groups were defined as follows: group 1: initial CSA (n = 6); group 2: initial CSG (n = 7); group 3: five of the seven patients in group 2 taking CSG subsequently undergoing conversion to CSA; group 4: the same five patients in group 3 restudied 1 month after 1:1 dosage conversion to CSA; and group 5: CSA groups 1 and 4 combined (n = 11). In group 1, the metabolite fraction accounted for 32% to 54% of the total measurable drug concentration at each time point, whereas in group 2, the metabolite fraction accounted for at most 10% to 15% of the total drug levels measurable by polyclonal fluorescence polarization radioimmunoassay. Although there were no significant differences in any of the mean pharmacokinetic parameters between groups using monoclonal fluorescence polarization radioimmunoassay, the normalized area under the concentration-time curve (NAUC) value was less in four of five patients after conversion from CSG to CSA, with a more variable and delayed time to reach peak concentration (tmax) but equivalent apparent oral clearance (Clpa) values. Clcr was found to change significantly with time in groups 1 and 5 but not in group 2, with CSA producing a more profound and sustained decrease than CSG. Endothelin-1 and NO2/NO3 levels in plasma and urine remained relatively constant after administration of both CSA and CSG, and there were no significant differences between groups 3 and 4 regarding mean endothelin-1 and NO2/NO3 concentrations in plasma, urinary release of endothelin-1 and NO2/NO3, and mean AUC of endothelin-1 and AUC of NO2/NO3. However, monoclonal NAUC correlated significantly with total urinary endothelin-1 within CSA groups 1 and 5 but not within CSG group 2. Metabolite NAUC correlated significantly with total urinary NAG within CSA group 1. Although limited by the small number of patients, this study suggests that 1) CSG may produce less of a reduction in Clcr over time after oral administration at steady state than does CSA, and 2) this beneficial effect of CSG may be in part due to decreased intrarenal release of endothelin-1, as urinary excretion of endothelin-1 seemed to correlate better with CSA than with CSG exposure.

Angiotensin I converting enzyme activity in uranyl nitrate induced acute renal failure in rats

Angiotensin I converting enzyme (ACE) was measured in urine, serum, and tissues from rats with acute renal failure (ARF) induced by a single subcutaneous injection (15 mg/kg BW) of uranyl nitrate (UN). Urine was collected daily until day 5, when rats were sacrificed by decapitation for the obtention of blood serum and tissues. Other groups of rats were sacrificed on days 1 and 2. These rats showed proteinuria and polyuria. The damage to the kidney proximal tubule was shown by (a) histological analysis at light and electron microscopy levels on days 1, 2, and 5, (b) the increase in urinary excretion of dipeptidyl aminopeptidase IV and N-acetyl-beta-D-glucosaminidase on days 1-5, and (c) the low molecular weight proteinuria pattern on day 1. In addition, the histological analysis at the ultrastructural level showed normal glomeruli appearance on days 1 and 2, but structural alterations on day 5. These data suggest that the increased urinary excretion of enzymes and proteins is a consequence of the tubular injury on days 1 and 2, and of tubular and glomerular injury on day 5. ACE activity increased in urine on days 1-5 and in serum on day 5. Tissue ACE activity increased in lung, small intestine, and adrenal glands; and remained unchanged in testis, aorta, brain, kidney, heart, and liver. Our data suggest that: (a) the increase in serum ACE may be secondary to the changes in tissue ACE activity, and (b) the urine ACE increase may be due to the kidney proximal tubule damage. This work supports the contention that an increase in urine ACE may be an indicator of injury to the proximal tubule.