A new test to predict reversibility of hydronephrotic atrophy after stable partial unilateral ureteral obstruction

Evaluation of Renal Histopathological Changes, as a Predictor of Recoverability of Renal Function Following Pyeloplasty for Ureteropelvic Junction Obstruction

Background:

Pyeloplasty is a widely accepted treatment for ureteropelvic junction obstruction (UPJO). However, the renal function recoverability after pyeloplasty is still a matter of debate. Different parameters have been used to predict renal functional recoverability after corrective surgery, with conflicting results.

Objectives:

In this study, renal biopsy was carried on a series of cases of UPJO, during pyeloplasty, to study the extent of histological alterations in renal parenchyma, as a result of obstruction, and its predictive value in renal function recoverability after pyeloplasty.

Patients and Methods:

We retrospectively analyzed the renal biopsy obtained during pyeloplasty in 53 adult patients. Histopathological changes were graded on a scale of 1 to 3, according to their severity, and compared with the differential renal function (DRF) revealed on the preoperative and postoperative follow up diethylene triamine pentaacetic acid (DTPA) renal scan. A Fischer’s t test was used to evaluate statistical differences between values.

Results:

This study showed a linear relationship between the severity of histological changes and renal function recovery, after pyeloplasty. Out of 24 obstructed renal units (ORU), with minimal histopathological changes (grade I), 21 ORU (87.5%), with > 35% DRF preoperatively, showed significant improvement in renal function after 12 months of pyeloplasty (P < 0.05). On the other hand, all kidneys (n = 29) with moderate to severe obstructive changes (grade II and III) had minimal improvement in DRF, after pyeloplasty, which was clinically insignificant (P > 0.05). Renal function deterioration after pyeloplasty was not observed in any of the cases.

Conclusions:

The severity of pathological changes in renal parenchyma, due to UPJO, is a good predictor of renal function recoverability, after pyeloplasty. The ORUs, with DRF > 35%, usually have normal (grade I) renal biopsy and might be expected to present better functional recoverability after pyeloplasty.

(99m) T c-DTPA Study to Validate an Experimental Model of Ureteral Obstruction in Rabbits: Preliminary Results

Objective. To create a ureteral obstruction experimental model that can be proved through (99m)Tc-DTPA renal scintigraphy and histopathological studies, without causing total renal function loss. Materials and Methods. Ten New Zealand white rabbits were submitted to a surgical experiment to create a model of unilateral obstruction to urinary flow. Surgery procedure provided unilateral ureteral obstruction (left kidney) to urinary flow and posteriorly was evaluated by (99m)Tc-DTPA renal scintigraphy and histopathological study. (99m)Tc-DTPA renal study was performed to detect and quantify signs of obstruction and to evaluate renal function. Statistical analysis was performed through the Student t-test with a significance level of P<0.05. Results. Nine of the ten rabbits presented left renal unit obstruction and one nonobstructive on the (99m)Tc-DTPA and histopathological studies. All the right renal units, which were not submitted to surgical procedure, were nonobstructed by the studies. There was a general agreement between scintigraphy and histopathological results in both groups. Conclusion. The experimental model promoted the creation of ureteral obstruction in rabbits, confirmed by nuclear medicine scintigraphy and histopathology, and could be used in further studies to better understand urinary obstruction.

Role of urinary biomarkers in the diagnosis of congenital upper urinary tract obstruction

Background:

Congenital obstructive uropathy constitutes a significant cause of morbidity in children. Currently, there is no reference standard for the diagnosis of renal obstruction in children. The noninvasive measurement of biomarkers in voided urine has considerable appeal as a potential application in children with congenital obstructive nephropathy. The aim of the present review is to explore the current role of biomarkers in the diagnosis and follow-up of obstructive uropathy in children.

Materials and Methods:

The literature database (PubMed) was searched from inception to May 2007 regarding the role of urinary biomarkers in the diagnosis and follow-up of children with congenital obstructive uropathy.

Results:

The review included 23 experimental and 33 prospective controlled clinical studies. Several cytokines, peptides, enzymes and microproteins were identified as major contributors to or ensuing from obstruction-induced renal fibrosis and apoptosis. The most important biomarkers were transforming growth factor-β₁ (TGFβ₁), epidermal growth factor (EGF), endothelin-1 (ET-1), urinary tubular enzymes [N-acetyl-β-D-glucosaminidase (NAG), γ-glutamyl transferase (GGT) and alkaline phosphatase (ALP)], and microproteins [β₂-microglobulin (β₂M), microalbumin (M. Alb) and micrototal protein (M.TP)]. All biomarkers showed different degrees of success but the most promising markers were TGFβ₁, ET-1 and a panel of tubular enzymes. These biomarkers showed sensitivity of 74.3% to 100%, specificity of 80% to 90% and overall accuracy of 81.5% to 94% in the diagnosis of congenital obstructive uropathy in children. Moreover, some of the markers were valuable in differentiation between dilated non-obstructed kidneys in need of conservative management and obstructed kidneys in need of surgical correction. Some studies demonstrated that urinary biomarkers are helpful in the evaluation of success of treatment of children with congenital renal obstruction. Some limitations of the previous studies include lack of different types of controls and small sample size. Larger studies with variable controls are invited to confirm the clinical usefulness of biomarkers in the diagnosis and follow-up of children with congenital obstructive uropathy.

Conclusion:

Urinary biomarkers are a promising tool that could be used as a noninvasive assessment of congenital renal obstruction in children.

Renal tubular dysfunction measured by N-acetyl-beta glucosaminidase/Creatinine activity index in children receiving antiepileptic drugs: a randomized controlled trial

To evaluate renal side-effects of anti-epileptic medication by valproate (VPA) and carbamazepine (CBZ), we performed a prospective study to assess renal tubular function by measuring N-acetyl-β glucosaminidase (NAG)/Cr activity index in epileptic children. The study was conducted on 112 children who were diagnosed with epilepsy (28 patients were observed before treatment with anti-epileptics, 28 children were administered VPA, 28 children were treated with CBZ, and 28 healthy children were selected age &sex matched for). An especial NAG assay kit was used for quantitative measuring of NAG in patient urine samples. The patients receiving VPA exhibited higher rate of NAG activity compared with the two groups which not receiving anti-epileptic drugs. Measurement of urinary NAG/Cr index in the children who received CBZ also, was significantly higher than those who were not administered anti-epileptic drugs. The measurement of NAG/Cr index in the VPA group was significantly higher than that in the CBZ group (NAG index: 2.75 versus 1.71). Children on anti-epileptic treatment with VPA or CBZ might demonstrate signs of renal tubular dysfunction, reflected by NAG/Cr activity index. This side effect can be potentially more occurred following VPA administration.

Relation between radionuclide imaging and pathologic findings of ureteropelvic junction obstruction in neonatal hydronephrosis

OBJECTIVE

An excessive amount of collagen fibers around the muscle cells in the ureteropelvic junction could be responsible for obstruction in patients with hydronephrosis. We aimed to elucidate the ultrastructure of the ureters and correlate this finding with the prognostic outcome and to correlate the histopathological findings with diuretic radionuclide renography findings.

MATERIAL AND METHODS

Biopsy specimens of 20 children who underwent dismembered pyeloplasty for ureteropelvic junction obstruction were analyzed. The patients were grouped according to their age: infants (<12 months) and others (>12 months). Diuretic radionuclide imaging was performed using (99m)Tc mercaptylacetyltriglycine in the pre- and postoperative periods. Changes in differential renal function and excretion patterns on diuretic renography were evaluated in relation to the findings noted on histopathological examination of the biopsy specimens. Excretion patterns were classified as follows: A, normal; B, responsive to diuretic; C, minimal response to diuretic with some excretion after postural change; and D, very poor/no drainage despite diuretics. Biopsy materials were analyzed for the presence and extent of inflammation, fibrosis and changes in the smooth muscle layer using Masson's trichrome stain and immunohistochemical staining. Histopathological findings were graded from zero to three, depending on severity.

RESULTS

In patients aged <12 months, preoperative differential renal function (DRF) was associated with fibrosis (F) and smooth muscle hypertrophy (SMH) [mean (SD) DRF for both F and SMH were Grade 0-1, 47.8% (6.4%); Grade 2-3, 36.2% (11.3%); p<0.05]; and change in DRF was associated with inflammation [Grade 0-1, -0.1% (4.0%); Grade 2-3, 5.8% (3.0%); p<0.05]. Excretion patterns or improvement in excretion were not associated with any of the histopathological features. Change in DRF was significantly associated with inflammation Grade 2-3 (beta coefficient, 5.8; 95% CI 1.4-10.3).

CONCLUSIONS

Histopathological evaluation of renal parenchymal biopsy specimens obtained during pyeloplasty may be useful to provide an objective method for predicting the recovery of renal function. In addition, this will allow comparison of the types of histopathological alterations with the changes in differential renal function in order to predict the potential final improvement.

Increased urinary N-acetyl-beta-D-glucosaminidase activity in children with hydronephrosis

OBJECTIVE

Hydronephrosis leads to deterioration of renal function. As urinary N-acetyl-beta-D-glucosaminidase (U-NAG) activity is considered a sensitive marker of renal tubular impairment, our aim was to measure U-NAG in children with hydronephrosis and to look for a relationship among selected clinical parameters.

MATERIALS AND METHODS

We studied 31 children (22 boys and 9 girls, mean age 2.3 +/- 2.5 years) with hydronephrosis grade 1-4 that had U-NAG/creatinine ratio (U-NAG/Cr) measured.

RESULTS

The U-NAG/Cr was significantly higher in patients with hydronephrosis compared to reference data (p = 0.002). There was no difference in U-NAG/Cr between children with unilateral and bilateral hydronephrosis (p = 0.51). There was no significant difference in U-NAG/Cr between children with grades 1-3 (pooled data) and grade 4, respectively (p = 0.89). There was no correlation between U-NAG/Cr and the grade of hydronephrosis (r = 0.01).

CONCLUSIONS

U-NAG/Cr is increased in children with hydronephrosis grade 1-4, and there is no relationship with the grade of hydronephrosis. U-NAG is a useful marker of renal tubular dysfunction, however its relationship with the degree of kidney damage in patients with hydronephrosis should be considered as doubtful.

Obstructed Versus Dilated Nonobstructed Kidneys in Children With Congenital Ureteropelvic Junction Narrowing: Role of Urinary Tubular Enzymes

PURPOSE

We evaluated the role of voided urine lysosomal enzyme N-acetyl-beta-D-glucosaminidase and brush border enzymes alkaline phosphatase and gamma-glutamyl transferase in differentiating between children with ureteropelvic junction obstruction in need of pyeloplasty and those with dilated nonobstructed kidneys suitable for conservative treatment.

MATERIALS AND METHODS

The study included 35 children with unilateral ureteropelvic junction obstruction treated with pyeloplasty (study group) and 15 children with dilated nonobstructed kidneys who were treated conservatively and followed for 15 months (control group). Voided urine samples were obtained before treatment from both groups, and from the study group at 1, 2, 3, 6, 9 and 12 months postoperatively and the control group at 3, 9 and 15 months of followup. N-acetyl-beta-D-glucosaminidase, alkaline phosphatase and gamma-glutamyl transferase were measured in urine samples collected from both groups.

RESULTS

In the study group the activities of preoperative urinary N-acetyl-beta-D-glucosaminidase, alkaline phosphatase and gamma-glutamyl transferase were significantly higher than in the control group. A cutoff value of 7.8 mU/mg creatinine N-acetyl-beta-D-glucosaminidase yielded a sensitivity of 97.1%, a specificity of 80% and an overall accuracy of 92%. A cutoff value of 34.5 IU/gm creatinine alkaline phosphatase resulted in a sensitivity of 91.4%, a specificity of 100% and an overall accuracy of 94%. A cutoff value of 54 IU/gm creatinine gamma-glutamyl transferase yielded a sensitivity of 62.9%, a specificity of 100% and an overall accuracy of 74%. The combination of urinary N-acetyl-beta-D-glucosaminidase and alkaline phosphatase resulted in a sensitivity of 100%, a specificity of 80% and an overall accuracy of 94%. Compared to preoperative activities, N-acetyl-beta-D-glucosaminidase, alkaline phosphatase and gamma-glutamyl transferase decreased significantly at 12 months after pyeloplasty in the study group.

CONCLUSIONS

Voided urinary N-acetyl-beta-D-glucosaminidase, alkaline phosphatase and gamma-glutamyl transferase are accurate markers for differentiating between children with ureteropelvic junction obstruction requiring pyeloplasty and those with dilated nonobstructed kidneys suitable for conservative treatment. Measurement of these enzymes in voided urine could be used as a noninvasive tool for long-term followup of children with ureteropelvic junction obstruction after pyeloplasty and those receiving conservative treatment.

[Prognostic markers for congenital hydronephroses]

Watchful waiting has become the standard therapy in most cases of asymptomatic unilateral congenital hydronephroses with normal renal function. Simple, reliable, and noninvasive prognostic parameters that predict an increased risk of functional deterioration either at the initial evaluation or during follow-up would be most useful. At the moment the diameter of the renal pelvis and especially its increase is the most useful prognostic parameter, while an "obstructed" washout at furosemide isotope renography is of limited prognostic value. Preclinical and preliminary clinical studies indicate that the measurement of molecules in the urine of affected children such as TGF-31 and MCP-1 that are involved in the signal transduction during hydronephrotic atrophy might become well accepted as useful prognostic parameters in the near future.

Elevated plasma concentrations of transforming growth factor-beta 1 in patients with unilateral ureteral obstruction

We measured plasma concentrations of TGF-beta 1 in patients with obstructive ureteral calculi and compared them with the plasma concentrations of healthy volunteers. The present study was a prospective study containing a homogenous group of patients with unilateral ureteral obstruction (UUO). The study consisted of patients with ureteral stones less than 7 mm in diameter that caused mild to moderate obstruction. All patients were referred by the emergency department of our hospital and examined between April 2003 and April 2004. The presence and characteristics of both stone and obstruction were determined by plain abdominal x-ray and gray-scale ultrasonography (US). Blood samples were collected from both patients and control individuals on admission and 1 week after conservative follow-up. The plasma TGF-beta 1 concentration was determined using a quantitative sandwich enzyme immunoassay specific for TGF-beta 1. There were 35 patients with 20 women and 15 men (average age 26.8+/-5.9 years), and 15 volunteers in the control group, with nine women and six men (average age 24.2+/-4.5 years). Average stone size was 5.6 mm+/-1.2 mm (range 3.5-7) for the patient group. US showed the presence of mild hydronephrosis in 24 and moderate hydronephrosis in 11 patients. Plasma concentrations of TGF-beta 1 in patients with ureteral obstruction (1,117+/-5.8 ng/ml, range 36-2,442 ng/ml) were significantly higher than those in the healthy control group (32+/-4 ng/ml) on admission (P<0.001). There was a significant increase in TGF-beta 1 plasma concentrations in the patient group (33,525+/-6.8 ng/ml, range 1,107-73,288 ng/ml) after 1 week follow-up (P<0.001). Ureteral obstruction increases plasma TGF-beta 1 concentrations in patients with ureteral stones as in UUO models in animal studies. A concomitant treatment with an anti-fibrotic agent may reduce the incidence of renal injury during obstruction.

Recoverability of renal function after treatment of adult patients with unilateral obstructive uropathy and normal contralateral kidney: A prospective study

OBJECTIVES

To study the methods of prediction of recoverability of renal function after the treatment of adult patients with unilateral obstructive uropathy and a normal contralateral kidney.

METHODS

This prospective study included 91 consecutive adult patients with the diagnosis of unilateral obstructive uropathy and a normal contralateral kidney. All patients had a nonequivocal cause of obstruction that was successfully relieved after treatment. All patients underwent plain abdominal x-ray, gray-scale ultrasonography, Doppler ultrasonography, excretory urography, and technetium-99m-diethylenetriamine pentaacetic acid radioisotope renography before and after treatment. Patients were seen regularly at 3, 6, and 12 months for a mean duration of 13 +/- 6 months (range 6 to 36). At each visit, ultrasonography and renography were performed, and excretory urography was performed at least once during follow-up. Several renographic and ultrasound parameters were studied before and after treatment to evaluate their value in predicting the recoverability of renal function. The difference between the selective renographic glomerular filtration rate (GFR) of the ipsilateral kidney before treatment and its mean value after treatment was considered as the reference variable to which all other variables were compared. All prognostic parameters were evaluated by both univariate and multivariate analyses.

RESULTS

On univariate analysis, the factors that significantly affected the recoverability of renal function after the relief of obstruction included preoperative renographic GFR, renal perfusion, parenchymal thickness, parenchymal echogenicity, corticomedullary differentiation, reduction of the renal resistive index of the corresponding kidney, and compensatory hypertrophy of the contralateral normal kidney. However, using multivariate analysis, only the preoperative selective renographic GFR and renal perfusion of the corresponding kidney sustained their statistical significance as independent factors affecting renal functional recovery. A preoperative GFR value of 10 mL/min/1.73 m2 was estimated as the cutoff point that can determine the best prediction of stabilization or improvement of renal function after the relief of obstruction.

CONCLUSIONS

Preoperative renographic clearance and perfusion of the corresponding kidney were the only predictors of recoverability of unilateral renal obstruction. Kidneys with a renographic GFR of less than 10 mL/min/1.73 m2 were irreversibly damaged. Improvement or stabilization of function can be expected after relief of obstruction of kidneys with a renographic GFR of 10 mL/min/1.73 m2 or greater.

Antenatally detected, unilateral dilatation of the renal pelvis: a critical review. 2. postnatal non-operative treatment--long-term hazards, urgent research

BACKGROUND

Even after two decades, there is still much discussion about the postnatal treatment of antenatally detected, isolated pelvic dilatation (consistent with pyelo-ureteral junction obstruction). A recent review concluded that non-operative expectancy seemed safe - even after 17 years in certain cases. However, the final outcome, i.e. when these children have reached old age, is remote.

OBJECTIVE

This review takes stock of conceivable long-term hazards and evaluates prognosticating tools, and offers a basis for protocols for future randomized controlled trials. Long-term hazards: Symptoms in this context are generally considered ominous. In the antenatally detected cases, i.e. primarily asymptomatic, symptoms have been reported but they were not necessarily combined with renal damage. Hydronephroses, so mild, that they are written off, may deteriorate later on (indeed insidiously), although probably seldom. Urgent research: A predictor of outcome is eagerly pursued but hard to obtain, due to the difficulty in defining true obstruction in compliant systems such as the urinary one. Ordinary diagnostics offer no help, but there are promising innovations: constant pressure/flow assessment (flow necessary to keep a preset intrapelvic pressure), NAG/creatinine in pelvic urine, and TGFbeta-1 in voided urine. Renal microstructure, sometimes severely damaged early (which disagrees with the good results with expectancies) could possibly herald future deterioration.

CONCLUSION

Adverse developments should be meticulously documented and published swiftly, so policy can be changed if necessary, before it is too late. Cognizance of their existence, not necessarily frequency and statistics, is then first order. Efforts to design prognosticating tools has also high priority.

Partial unilateral ureteral obstruction in rats

This review comprises an overview of the current knowledge on experimental partial unilateral ureteral obstruction (PUUO) and a summary of our latest original experimental PUUO studies in rats. Neonatal PUUO is the type of obstruction that is most often encountered in pediatric clinical practice. However, the pathogenesis of PUUO is still incompletely understood. Most of our knowledge on PUUO has been derived from experimental studies in a variety of animal models. Although progress has been made, the natural history of congenital hydronephrosis is still incompletely described. The effects on kidney functions of long-term urinary tract obstruction, especially PUUO, have been less intensively studied. Recently, we created models with mild and severe PUUO in young rats by embedding the upper one fourth or the upper two thirds of the left ureter into the psoas muscle, respectively. Thereafter, the technique was used to create mild and severe PUUO in newborn rats and magnetic resonance imaging studies showed that both mild and severe obstruction caused a time-dependent decrease in renal blood flow. Compensatory increase in total kidney volume and renal vein blood flow in contralateral non-obstructed kidneys was not detectable when functional deterioration in the partially obstructed kidneys was present. Finally, we investigated the dynamic changes in renal relative signal intensity (RSI) of gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA) using magnetic resonance imaging in rats with partial, complete unilateral ureteral obstruction and sham-operated controls. The results showed that changes in Gd-DTPA RSI are compatible with the known physiological and anatomical changes in kidneys in response to ureteral obstruction and useful for distinguishing an obstructed from a non-obstructed collecting system and also for differentiating a partially obstructed from a completely obstructed collecting system.

Predictive value of renal histological changes for postoperative renal function improvement in children with congenital ureteropelvic junction stenosis

BACKGROUND

The aim of this study was to evaluate the relationship between renal function, as measured by diuretic radionuclide renography, and the outcome of pyeloplasty. A study was designed to evaluate renal parenchymal biopsy specimens derived from children undergoing corrective surgery for ureteropelvic junction (UPJ) stenosis, and compare these to preoperative and postoperative renal function status.

METHODS

Thirty-five children with congenital unilateral UPJ stenosis were evaluated. In addition to all conventional diagnostic procedures for UPJ stenosis, differential renal functional (DRF) activity was assessed in each of these children by obtaining 99mTc diethylenetriaminepentaacetic acid renogram curves. All children underwent dismembered pyeloplasty, and follow-up renogram evaluation was conducted 6 and 12 months after surgical repair. Biopsy specimens from renal cortical regions obtained during the surgical correction of UPJ stenosis were evaluated, and changes in renal histology were graded from I to V according to their severity. Spearman's correlation test was used to compare the histological evaluation results and the basal, 6- and 12-month follow-up DRF findings. A Wilcoxon paired test was used to evaluate statistical differences between values.

RESULTS

The findings showed a positive correlation between the severity of histological changes and DRF activity. All kidneys (22) with a DRF activity value of < 40% preoperatively demonstrated at least grade III changes when biopsy specimens were examined. Of children with a DRF activity value > 40% (13), only three showed severe histological changes. Histological grades were correlated between basal (r = -0.4; P = 0.019), 6-month (r = 0.54; P = 0.002) and 12-month (r = 0.54; P = 0.02) findings. In the Wilcoxon paired test, there was a statistically significant difference between basal and 6-month values (P < 0.05), and also between basal and 12-month values (P < 0.01). There was no statistically significant difference between 6- and 12-month values (P > 0.20).

CONCLUSION

Comparative evaluation of postoperative renal function with DRF activity and renal parenchymal histological alterations revealed a close correlation in terms of renal function improvement potential following reconstructive surgery in children with UPJ stenosis.

Recoverability of renal function after relief of acute complete ureteral obstruction: clinical prospective study of the role of renal resistive index

OBJECTIVES

To study the values of the renal resistive index (RI) before and at different points after relief of obstructive anuria and to correlate these values with the corresponding values of serum creatinine and with the recovery of renal function after release of obstruction.

METHODS

A total of 32 consecutive patients with obstructive anuria were prospectively evaluated by measurement of RI before drainage and at 3 days, 1 week, 2 weeks, and 4 weeks after drainage. Serum creatinine was measured at all points of the RI examination. Moreover, RI was measured in an age and sex-matched control group of 24 consecutive healthy donors and volunteers.

RESULTS

The study included 40 obstructed and 48 normal kidneys. In the obstructed kidneys, the mean RI values decreased significantly from 0.78 +/- 0.05 before drainage to 0.70 +/- 0.09 at 3 days after drainage (P <0.001) with an additional significant reduction to 0.68 +/- 0.08 at 7 days after drainage (P <0.01) and stabilized thereafter. Serum creatinine decreased significantly from 8.4 +/- 4.4 mg/dL before drainage to 4.7 +/- 3.8 mg/dL 3 days after drainage (P <0.001) and then to 3.6 +/- 3.7 mg/dL 7 days after drainage (P <0.001) and stabilized thereafter. The correlation between the RI and serum creatinine at the overall points of measurement was good. Obstructed kidneys were classified into two groups according to the recovery of renal function after obstruction relief: those that showed significant improvement of serum creatinine (24 kidneys, group 1) and those with no significant improvement of serum creatinine (16 kidneys, group 2). In group 1, the difference between the mean RI values before and after drainage was statistically significant (0.78 +/- 0.05 versus 0.64 +/- 0.06, P <0.001); in group 2, the difference between the before and after drainage RI values was not significant (0.781 +/- 0.040 versus 0.779 +/- 0.039). The mean RI of the normal kidneys was 0.66 +/- 0.04. A comparison between the mean RI values of the control group and the mean RI values of the obstructed patients after drainage showed no significant difference in group 1; markedly higher values were noted in group 2 at all points after drainage.

CONCLUSIONS

In the setting of acute complete renal obstruction, the RI has a good positive correlation with serum creatinine. Recovery of renal function could not be predicted from the changes in RI before obstruction release. However, a reversal of a previously elevated RI could be used as an early indicator that renal function recovery is likely.

N-acetyl-glucosaminidase (NAG) excretion in partially obstructed weanling rats

The understanding of pathophysiology of obstructed uropathy has been facilitated by animal models with partial ureteric obstruction. Some studies on partially obstructed adult rats have drawn attention to a biphasic pattern of obstructive uropathy: an initial 'destructive' phase and a 'steady' phase in which renal deterioration no longer occurs and in which relief of obstruction would be of no advantage. We aimed to verify if this pattern applies also to younger (weanling) rats with more immature kidneys, resembling those of the human fetus. We measured the NAG-values in the urine samples of partially obstructed animals at different intervals of obstruction and in those of controls. The biphasic pattern proved to be the same as in adult rats as was previously documented, but the turning point occurred earlier (between 10 and 15 days of obstruction). Furthermore, there is evidence of low level values of N-Acetyl-Glucosaminidase (NAG) in the early phase of obstruction (5 days), demonstrating that the increase of tubular enzyme is not due to the operation itself. There is evidence that, if the 'destructive' phase can be precisely identified by biochemical studies, this could help identifying those subjects who could benefit from relief of obstruction.

Characteristics of protein excretion in patients with acute urinary retention

OBJECTIVE

To evaluate changes in protein leakage in the glomerular filtration barrier, and in the ability of the tubule to reabsorb proteins during and after acute urinary retention (AUR).

PATIENTS AND METHODS

Glomerular and tubular function was investigated in 24 men during AUR (mean age 68 years, mean retention time 31 h and mean retention volume 1140 mL) who were then followed for 6 months by measuring the urinary excretion of glomerular and tubular proteins, and the glomerular filtration rate (GFR). Retention was relieved by inserting a suprapubic catheter and the cause of retention treated one month later. No patient had a previous renal disease or diabetes.

RESULTS

During AUR, and after 1 and 6 months, albuminuria was detected in 100%, 92% and 54% of patients, and increased excretion of alpha1-microglobulin in 52%, 36% and 58%, of IgG in 79%, 58% and 40%, and of IgG4 in 67%, 42% and 20%, respectively. The mean GFR was normal during retention and during the follow-up.

CONCLUSION

AUR causes disturbances in both the glomerular filtration and tubular reabsorption of proteins. Albuminuria and increased excretion of IgG, IgG4 and alpha1-microglobulin occurred in most patients during AUR. After relieving retention, the albuminuria and elevated alpha1-microglobulin excretion persisted, indicating slight glomerular dysfunction and a permanent defect in the proximal tubule to reabsorb proteins. This could be caused partly by previous chronic obstruction. AUR should be relieved immediately and the basic cause treated effectively to prevent further deterioration of renal function.

A review on urinary proteins in outflow disease of the upper urinary tract

INTRODUCTION

[corrected] No review articles on outflow disease of the upper urinary tract discuss urinary protein excretion.

DISCUSSION

Following acute partial and/or complete ureteral obstruction (UO) or chronic partial UO, alpha-1-microglobulin excretion is significantly higher than in the reference population or patients with proven renal dilatation without obstruction, but is not found to be diagnostic for these conditions as such. Chronic partial UO is followed first by a destructive and then by a steady-state phase in renal damage. The observed increase in tubular proteinuria during the destructive phase correlates with the decrease in absolute dimercaptosuccinic acid (DMSA) uptake. If the destructive phase is not followed by a stable phase, a mixed tubular and glomerular proteinuria is seen. Urinary alpha-1-microglobulin excretion is found to be diagnostically useful in vesico-ureteral reflux (VUR) patients, increases with higher intravesical-intrapyelic pressure, correlates with the decrease in absolute DMSA uptake or with urinary epidermal growth factor excretion (both markers of the number of functioning nephrons) and predicts the outcome after treatment.

CONCLUSION

alpha-1-Microglobulin is useful in the detection of renal tubular damage in patients with outflow disease of the upper tract, is diagnostic for VUR but is not so for ureteral obstruction.

Fetal partial urethral obstruction causes renal fibrosis and is associated with proteolytic imbalance

PURPOSE

We determine whether fetal bladder outlet obstruction induces renal fibrosis, and is associated with an alteration in the regulation of connective tissue degradation and the presence of fibrogenic interstitial cells.

MATERIALS AND METHODS

Partial bladder outlet obstruction was surgically induced in 33 fetal sheep at 95 days of gestation. These animals and 24 normal age matched controls were sacrificed at 109, 116 and 135 (term) days of gestation, and the kidneys were rapidly retrieved, drained and weighed. Representative whole kidney samples were snap frozen for assessment of deoxyribonucleic acid, protein and collagen content. Morphometric analysis and alpha-smooth muscle actin immunohistochemistry were performed on histological specimens from formalin fixed kidneys. Tissue extract from fresh kidney specimens were analyzed for metalloproteinase and tissue inhibitor of metalloproteinase activity. Urine samples obtained at the time of sacrifice were analyzed for electrolyte, creatinine and N-acetyl glucosaminidase excretion.

RESULTS

All obstructed kidneys were hydronephrotic and larger than age matched controls. Obstructed kidneys at term showed interstitial fibrosis, as measured by increased extracellular matrix volume fraction (45% in male obstructed kidneys versus 2.5% in normal male kidneys, p = 0.0004), increased total collagen content (120 mg./kidney in male obstructed versus 20 mg. in normal male animals, p = 0.016) and collagen/deoxyribonucleic acid content per kidney (2.78 versus 0.53 mg./mg., p = 0.016). Metalloproteinase-1 activity was significantly lower in obstructed kidneys (210 versus 380 U./mg. protein in normal kidneys). Tissue inhibitor of metalloproteinase activity was undetectable in both groups. The presence of an increased population of myofibroblasts often associated with fibrotic processes was seen by alpha-smooth muscle actin staining which was localized to interstitial cells throughout the cortex in obstructed kidneys.

CONCLUSIONS

Fetal partial bladder outlet obstruction induces renal interstitial fibrosis as early as 2 weeks after obstruction. A possible mechanism for this process is a shift in proteolytic activity to reduce matrix degradation in obstructed kidneys. These changes might be mediated by the increased number of fibrogenic interstitial cells. The observations suggest several potential approaches to developing an understanding of congenital obstructive uropathy.

Urinary alpha 1-microglobulin detects uropathy. A prospective study in 483 urological patients

PURPOSE

The aim of the study was to evaluate prospectively urinary alpha 1-microglobulin as a marker of proximal tubular damage following acute pyelonephritis and outflow disease of the upper urinary tract in a urological population with minimal exclusion criteria. We also measured the urinary gamma-glutamyltransferase activity, urinary albumin, urinary and serum creatinine, serum IgA and serum alpha 1-microglobulin.

PATIENTS AND METHODS

We studied 483 urological patients (age: 1 to 92 years, 297 men, 186 women) excluding patients receiving nephrotoxic drugs, or suffering from type 1 diabetes or renal diseases. There were 141 patients with urinary tract infection but no fever, 36 patients with high fever of non-renal origin, 51 patients with acute pyelonephritis and 156 patients with outflow disease of the upper tract, and 99 patients were included in the reference population.

RESULTS

For acute pyelonephritis, vesico-ureteral reflux, and ureteral obstruction, urinary alpha 1-microglobulin had a sensitivity of 94%, 90% and 63% respectively and a specificity of 67%, 77% and 76%. The area under the curve of the receiver operator characteristic curve was significantly (p < 0.001) higher for urinary alpha 1-microglobulin than for albumin or gamma-glutamyltransferase activity. Unexpected positive results were found in acute prostatitis. The urinary alpha 1-microglobulin was the only parameter which differentiated between acute prostatitis and pyelonephritis (p < 0.001). Creatinine clearance or age had little and gender had no influence on the urinary excretion of alpha 1-microglobulin. Urine production rate significantly increases the urinary alpha 1-microglobulin/creatinine ratio.

CONCLUSION

Our results suggest that the urinary alpha 1-microglobulin/creatinine ratio is a diagnostically useful marker of tubular damage in acute pyelonephritis and vesico-ureteral reflux in the urological population. Following renal colic and chronic ureteral obstruction, a significant increase in urinary alpha 1-microglobulin excretion was observed.

Constant elevation in renal pelvic pressure induces an increase in urinary N-acetyl-beta-D-glucosaminidase in a nonobstructive porcine model

PURPOSE

To clarify the physiological significance of renal pelvic pressure elevations encountered in the evaluation of hydronephrotic kidney we examined the effects of different levels of renal pelvic pressure on the induction of renal injury.

MATERIALS AND METHODS

A nonobstructive porcine model was created in which the urine drained against a constant predetermined pressure gradient. Renal pelvic pressure of 10, 20 and 40 cm. was created in 2, 2 and 4 animals, respectively. During 18 to 23 hours serial urinary N-acetyl-beta-D-glucosaminidase levels were determined as an indicator of renal tubular injury. Tissue specimens were examined histologically and renal arterial blood flow was monitored.

RESULTS

Urinary N-acetyl-beta-D-glucosaminidase levels in the kidneys subjected to 10 cm. water remained essentially unchanged. However, at 20 and 40 cm. water statistically significant increases were observed. Similarly, renal arterial blood flow was unchanged at 10 cm. water but it became significantly lower than in controls at 20 and 40 cm. water. Histological evaluation revealed mild to moderate tubular dilatation in the kidneys subjected to 20 and 40 cm. water.

CONCLUSIONS

Excessively high collecting system pressure induced renal cellular injury, as reflected by an increase in urinary N-acetyl-beta-D-glucosaminidase levels. While renal pelvic pressure up to 10 cm. water appeared to be innocuous, renal cellular injury was evident within as little as 1 hour at renal pelvic pressures 20 cm. water or greater. The degree of N-acetyl-beta-D-glucosaminidase in the urine also correlated with a decrease in renal arterial blood flow.

Urinary levels of the renal tubular enzyme N-acetyl-beta-D-glucosaminidase in unilateral obstructive uropathy

Elevated urinary levels of the renal tubular enzyme, N-acetyl-beta-D-glucosaminidase (NAG), have been shown to be associated with reversible tubular damage and, therefore, may serve as an indicator of tubular damage in the setting of presumed obstruction uropathy. This study compares urinary NAG levels in children with apparent upper tract obstruction with normal children to assess the sensitivity of this assay for the detection of possible renal tubular damage. The study included 40 children 3 weeks to 16 years old with unilateral ureteropelvic junction obstruction (30) or primary obstructive megaureter (10). Urine was obtained from the bladder in all children and from the renal pelvis or ureter in 30 patients at surgery. Pelvic and ureteral urinary NAG levels were consistently higher than bladder levels. In patients with ureteropelvic junction obstruction NAG levels were 7 times higher than normal (76 units per mg., p < 0.0001) and 3 times higher than normal in patients with obstructive megaureter (29 units per mg., p < 0.001). The mean bladder urinary NAG levels in patients with ureteropelvic junction obstruction (17.6 units per mg. creatinine, standard error of mean 2.01, p < 0.001) and megaureters (19.2 units per mg. creatinine, standard error of mean 3.6, p < 0.049) were elevated above control patients (10.6 units per mg. creatinine, standard error of mean 1.02). Elevated urinary NAG levels in the renal pelvis, ureter and bladder may be helpful in identifying upper tract obstruction, which if left untreated, might cause progressive renal deterioration.

The pathophysiology of ureteral obstruction

Ureteral obstruction can have a variety of causes intrinsic or extrinsic to the kidney. The effects of obstruction are examined from the perspectives of duration, severity, totality, and the presence of complicating factors. There is a difference in the postobstructive pathophysiology depending on whether one or both ureters were obstructed. Atrial natriuretic peptide may be important in postobstructive diuresis, and preliminary evidence suggests a role for it as protection against nephron ischemia in acute obstruction. The potential for recovery of renal function after relief of obstruction depends on the duration and degree of obstruction, the condition of the contralateral kidney, and the presence or absence of infection. Ability to acidify the urine to pH < 6.0 preoperatively may be a good predictor of the recovery potential of an obstructed kidney. Urine concentrations of lysosomal enzymes such as N-acetylglucosaminidase also may be useful for this purpose, as may measurement of creatinine clearance in urine obtained from a nephrostomy tube.

The response of the fetal kidney to obstruction

In a fetal ovine model the renal effects of different anatomic levels of fetal urinary obstruction were studied. Parameters of prenatal renal growth and differentiation were characterized and correlated with the patterns of renal response to in utero obstruction. Complete ureteral or urethral obstruction was produced in the sheep fetus at 55 to 60 days of gestation. Animals were delivered and sacrificed at near term (140 days), and the kidneys were removed and prepared for analysis. Parameters examined included weight, histology, glomerular number and total surface area, as well as urinary sodium, creatinine, osmolarity and N-acetyl glucosaminidase. Three patterns of response were identified, producing hydronephrotic, cystic or dysgenetic kidneys. Hydronephrotic kidneys were usually the result of bladder outlet obstruction or ureteral obstruction with spontaneous urinary decompression. These kidneys were large (20.7 gm. versus normal 10.8 gm., p less than 0.0001), with thinning of cortical parenchyma that was structurally intact. Glomerular number and surface area were normal. Cystic kidneys were large (14.2 gm., p less than 0.05) with grossly visible cysts and an effaced medulla. Cortical structure was distorted by cysts but basic elements were intact. Glomerular number and surface area were not reduced. Dysgenetic kidneys were small (3.9 gm., p less than 0.0001) with markedly abnormal cortical structure and little recognizable medulla. Histological elements similar to fetal structures were present, including cuboidal/columnar tubular epithelium and peritubular mesenchymal collars. Glomerular number and surface area were significantly less than normal (p less than 0.001). The kidneys contralateral to unilaterally obstructed kidneys were significantly larger than normal (16.2 gm., p less than 0.0001), with normal histology, glomerular number and surface area, indicating in utero contralateral renal hypertrophy. Urinary sodium was variably affected in the hydronephrotic kidneys and was identical to plasma in the dysgenetic kidneys. These results indicate the technical feasibility of in utero models of urinary obstruction. Renal growth and patterns of differentiation were markedly affected by in utero obstruction. They should be a major focus in the investigation of congenital obstructive uropathy, since normal processes of renal growth and differentiation form the basis for postnatal function.

Urinary levels of renal tubular enzyme N-acetyl-beta-D-glucosaminidase in relation to grade of vesicoureteral reflux

Elevated urinary levels of the renal tubular enzyme N-acetyl-beta-D-glucosaminidase (NAG) have been shown to be associated with tubular damage. To determine whether urinary levels of NAG would be abnormal and/or vary with the severity of vesicoureteral reflux, bladder urine was obtained from 31 children without reflux and 32 children with various grades of reflux. Nonrefluxing controls were obtained from children undergoing evaluation for a history of infection, hematuria or voiding abnormality. Patients with evidence of obstruction, neuropathic bladder dysfunction, urinary tract infection or renal failure were excluded. Bladder (32 cases) and ureteral (5 cases) urine from children with reflux was obtained at cystography or at antireflux surgery. Control and reflux patients were not significantly different with regard to sex or age. The mean urinary NAG level in nonrefluxing control patients was 10.63 IU/mg. (range 0.94 to 26.61, standard error of mean 0.43). Mean urinary NAG for all patients with reflux was 16.47 IU/mg. (range 2.85 to 52.02, standard error of mean 0.9). Two children with intrarenal reflux had urinary NAG levels of 52 and 48 IU/mg. Urinary NAG levels are elevated with higher grades of reflux and this relatively simple assay may have clinical usefulness in the assessment of tubular dysfunction associated with reflux.

Hydronephrotic atrophy after stable mild or severe partial ureteral obstruction: natural history and recovery after relief of obstruction

After stable mild or severe partial unilateral ureteral obstruction in rats, the ratio of renal dry weight to whole body weight changes in two phases. In a "destructive phase" of two to six weeks, slight weight reduction occurs in the kidneys with mild obstruction and pronounced weight reduction occurs in those with severe obstruction. Then, in a "steady-state phase", there is no further weight reduction in kidneys with either mild or severe obstruction. Relief of ureteral obstruction during the steady-state phase does not result in an increase in renal dry weight. We conclude that the development of hydronephrotic atrophy after stable mild or severe partial unilateral ureteral obstruction can not be influenced by relief of obstruction in the steady-state phase.