Congenital unilateral ureteropelvic junction obstruction of the rat: a useful animal model for human ureteropelvic junction obstruction?

Current perspectives on congenital obstructive nephropathy

Congenital obstructive nephropathy is the leading cause of chronic renal disease in children. As a result, it represents a tremendous societal burden in terms of morbidity and mortality, as well as in health care expenses of caring for children with chronic kidney disease and end-stage renal disease. The various diagnostic, prognostic, and therapeutic challenges associated with congenital obstructive nephropathy highlight the importance of developing effective experimental models for studying this disease process. In this review, we define the clinical entity that is congenital obstructive nephropathy, outline the current standards of diagnosis and care, and discuss the utilization of current experimental models designed to help clarify some of the clinical conundrums associated with this important disease.

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.

Pathogenesis of renal injury in the megabladder mouse: a genetic model of congenital obstructive nephropathy

Congenital obstructive nephropathy (CON) is the most common cause of chronic renal failure in children often leading to end-stage renal disease. The megabladder (mgb) mouse exhibits signs of urinary tract obstruction in utero resulting in the development of hydroureteronephrosis and progressive renal failure after birth. This study examined the development of progressive renal injury in homozygous mgb mice (mgb-/-). Renal ultrasound was used to stratify the disease state of mgb-/- mice, whereas surgical rescue was performed using vesicostomy. The progression of renal injury was characterized using a series of pathogenic markers including alpha smooth muscle isoactin (α-SMA), TGF-β1, connective tissue growth factor (CTGF), E-cadherin, F4/80, Wilm's tumor (WT)-1, and paired box gene (Pax) 2. This analysis indicated that mgb-/- mice are born with pathologic changes in kidney development that progressively worsen in direct correlation with the severity of hydronephrosis. The initiation and pattern of fibrotic development observed in mgb-/- kidneys appeared distinctive from previous animal models of obstruction. These observations suggest that the mgb mouse represents a unique small animal model for the study of CON.

Endothelin-1-induced activation of rat renal pelvic contractions depends on cyclooxygenase-1 and Rho kinase

Upper urinary tract peristalsis is generated in the proximal renal pelvis that connects to the renal parenchyma at the pelvis-kidney junction. It may be exposed to the high renal endothelin-1 (ET-1) concentrations. Dietary NaCl restriction increases renal pelvic ET(A) receptor expression. We investigated the contribution of ET(A) and ET(B) receptors to ET-1-stimulated rat renal pelvic contractions and whether the sensitivity of renal pelvic contractile activity to ET-1 stimulation increases with dietary NaCl restriction. We tested whether ET-1-induced contractile activity depends on cyclooxygenase (COX)-1 or -2 and to what extent spontaneous as well as agonist-induced peristalsis depends on Rho kinases (ROCK). Contractions of isolated renal pelvises were investigated by myography. ET-1 concentration-dependently increased pelvic contractile activity up to 400% of basal activity. ET(A) but not ET(B) receptor blockade inhibited ET-1-induced pelvic contractions. Basal and ET-1-stimulated contractions were similar in renal pelvises from rats on a high-NaCl diet or on a NaCl-deficient diet. COX-1 inhibition reduced spontaneous and almost completely blocked the ET-1-induced pelvic contractions. ROCK inhibition reduced spontaneous and ET-1 stimulated pelvic contractile activity by 90%. RT-PCR revealed that both ROCK isoenzymes are present in the renal pelvic wall. Western blot analyses did not show increased phosphorylation of ROCK substrates myosin phosphatase target subunit 1, ezrin, radixin, and moesin in ET-1-treated isolated renal pelvises. ET-1 is a powerful ET(A) receptor-dependent activator of renal pelvic contractions. COX-1 and ROCK activity are required for the ET-1 effects on pelvic contractions, which are not significantly affected by dietary NaCl intake.

Localization of genetic loci controlling hydronephrosis in the Brown Norway rat and its association with hematuria

The aim of this study was to investigate the genetic basis of congenital hydronephrosis (HN), a poorly defined pathological entity, with a rat model. The Brown Norway (BN) strain spontaneously presents a high incidence of apparently asymptomatic HN, whereas the LOU strain does not. A backcross was established between these two strains [BN x (BN x LOU)] and a genomewide scan was performed with 193 microsatellite markers on 121 males and 118 females of this population, which had been phenotyped and scored for HN severity (defined as degree of renal pelvic dilation), followed by linkage analysis with Mapmaker/QTL software. Bilateral HN score was significantly linked to a locus on chromosome 6 (Z scores 4.4 and 4.8 for all rats and for females, respectively). Suggestive loci were identified on chromosomes 2 (for only right-sided HN) and 4. This is the first study in rats to identify genetic loci for HN. Three candidate genes present in these loci were sequenced and insertions detected in Id2 and Agtr1b genes in BN, which did not, however, lead to modified expression as measured by quantitative PCR. Production of a congenic line for part of the chromosome 6 locus confirmed its involvement in HN, but the phenotype was mild. Evidence of hematuria was observed in 9.6% of the backcross rats, mostly males and only in kidneys with HN, but not necessarily in the most severely affected. Hematuria also occurs in the BN colony used here, where it is due to papilloma-like lesions involving pelvic epithelial proliferation, but not in the LOU rat.

Diagnosis of Ureteropelvic Junction Obstruction in Children: Role of Endothelin-1 in Voided Urine

OBJECTIVES

To examine the role of voided urine endothelin-1 (ET-1) in the diagnosis and follow-up of children with ureteropelvic junction obstruction.

METHODS

The study included 35 children with unilateral ureteropelvic junction obstruction who underwent pyeloplasty and 30 control children, including 10 healthy children, 10 with vesicoureteral reflux, and 10 with renal stones. Voided urine samples were obtained from the children in the study group before surgery and from the renal pelvis by needle aspiration during pyeloplasty. Bladder urine samples were also collected from the study group 1, 2, 3, 6, 9, and 12 months postoperatively. Bladder urine samples were also collected from all 30 control children. ET-1 was measured in the urine samples collected from the study and control groups.

RESULTS

The preoperative ET-1 level in the voided urine of the study group was significantly greater than its level in each of the three control groups. For the whole study group, a cutoff value of 3 fmol/mg creatinine gave a sensitivity of 74.3%, a specificity of 90%, and an overall accuracy of 81.5%. In 8 children (1 year old or younger), a cutoff value of 4 fmol/mg creatinine gave a sensitivity and specificity of 100%. Compared with the preoperative value, ET-1 had decreased significantly at 12 months after pyeloplasty.

CONCLUSIONS

The ET-1 level in voided urine is a useful marker that could be used as a noninvasive tool for the diagnosis and long-term follow-up of children with ureteropelvic junction obstruction.