ROLE OF THE RENIN-ANGIOTENSIN SYSTEM IN DISORDERS OF THE URINARY TRACT

Association of angiotensin-converting enzyme (ACE) gene insertion-deletion polymorphism with spondylarthropathies

Low back pain (LBP) is a common medical problem. Interaction between genetic and environmental factors predisposes individuals to LBP even at an early age. Inflammatory back pain or spondylarthropathies include ankylosing spondylitis (AS), psoriatic arthritis (PSA), reactive arthritis enteropathic and undifferentiated arthropathies. Angiotensin-converting enzyme (ACE) plays an important role in circulatory homeostasis, physiology of vasculature and inflammation. The insertion-deletion (I/D) polymorphism of the ACE gene has been shown to determine the plasma and tissue levels of ACE especially in the synovial fluid. The aim of this study was to investigate an association between ACE gene I/D polymorphism and inflammatory back pain (spondylarthropathies) secondary to ankylosing spondylitis (AS), psoriatic arthritis, inflammatory bowel disease and undifferentiated spondylarthropathies. The prevalence of ACE gene I/D polymorphism genotypes was determined in 63 patients with inflammatory back pain by polymerase chain reaction (PCR) and compared with that in 111 healthy controls. Of the 63 patients studied, 45 (71.4%) were with AS, 13 (20.6%) were with PSA, 4 (6.3%) were with reactive arthropathy and 1 (1.6%) manifested undifferentiated arthropathy. There were 43 males and 20 females. Mean age of patients was 39.0+/-11.36 years, age at onset of spondylarthropathy was 27.7+/-7.49 years and disease duration was 10.3+/-7.74 months. The controls were selected to match with the patients group in terms of gender ratio, age and ethnicity. The ACE gene polymorphism showed an overall significant difference between patients and controls (p=0.050). When the ID and II genotype frequency was combined and compared with that for DD genotype amongst patient and control groups, a considerably higher incidence was detected for ID and II genotypes than the DD genotype in spondylarthropathy patients compared to that in the controls (p=0.036). This study showed a significant association of the I-allele of ACE gene I/D polymorphism with spondylarthropathy in Kuwaiti Arabs.

Mechanisms of progression of chronic kidney disease

Chronic kidney disease (CKD) occurs in all age groups, including children. Regardless of the underlying cause, CKD is characterized by progressive scarring that ultimately affects all structures of the kidney. The relentless progression of CKD is postulated to result from a self-perpetuating vicious cycle of fibrosis activated after initial injury. We will review possible mechanisms of progressive renal damage, including systemic and glomerular hypertension, various cytokines and growth factors, with special emphasis on the renin-angiotensin-aldosterone system (RAAS), podocyte loss, dyslipidemia and proteinuria. We will also discuss possible specific mechanisms of tubulointerstitial fibrosis that are not dependent on glomerulosclerosis, and possible underlying predispositions for CKD, such as genetic factors and low nephron number.

Histopathological and ultrastructural effects of Losartan on embryonic rat kidney

The aim of our study was to investigate the histopathological, immunohistochemical and ultrastructural effects of Losartan (a selective angiotensin II type-1 receptor blocker) on renal development in rats. Twelve pregnant rats were divided into control and experimental groups. In the experimental group, Losartan (10 mg/kg/day) was given via nasogastric tube, between the sixth day of implantation and time of sacrifice on embryonic days 18 and 20. All formalin-fixed, paraffin wax-embedded renal tissue sections were stained with hematoxylin and eosin or labelled for binding of primary antibodies against transforming growth factor-beta (TGF-beta 1,-2,-3) using an avidin-biotin-peroxidase method. For electron microscopic examination, samples were fixed with glutaraldehyde and osmium tetroxide and embedded in araldite. Glomerular basement membrane (GBM) thickness was measured and compared using an unpaired t-test. Angiotensin II type-1 receptor antagonism by Losartan inhibited renal growth and delayed nephron maturation. Increased immunoreactivity of TGF-beta's was observed in developing nephron precursors and interstitial cells in the experimental group. Electron microscopical examination showed that thickening of the GBM was normal in the control group but an irregular thickening was seen in the experimental group (p < 0.001). It was also seen that epithelial cells of developing tubules underwent apoptosis in the experimental group. Thus, renal development in rats seems to depend on an intact renin-angiotensin system.

Contribution of the renin-angiotensin system to the intrarenal resistive index in chronic unilateral partial ureteral obstruction in dogs

PURPOSE

We investigated the role of the renin-angiotensin system on intrarenal hemodynamics in chronic unilateral partial ureteral obstruction (UPUO) using Doppler ultrasound (US).

METHODS

In 11 dogs with chronic UPUO, we determined the renal resistive index (RI) before and 1 h after the intravenous infusion of an angiotensin-converting enzyme (ACE) inhibitor (captopril), an angiotensin II receptor type 1 (ART1) antagonist (L-158,809), and the combination of these two drugs. Change in resistive index (ΔRI) was calculated as RI after the administration of each tested material minus baseline RI.

RESULTS

At the baseline measurement, significant differences in RI were seen between obstructed and nonobstructed kidneys. ACE inhibitor, ART1 antagonist, or the combination of these drugs did not result in any significant changes in RI in either obstructed or nonobstructed kidneys. However, in obstructed kidneys, ΔRI in the combination of ACE inhibitor and ART1 antagonist were significantly greater than those in ACE inhibitor or ART1 antagonist alone, whereas there were no significant differences in those values in nonobstructed kidneys.

CONCLUSION

These observations suggest that the renin-angiotensin system in dogs with chronic UPUO may not contribute significantly to the differences in intrarenal RI between obstructed and nonobstructed kidneys. However, the angiotensin-producing pathways and angiotensin II receptor subtypes other than ACE and ART1 may have some different effects between obstructed and nonobstructed kidneys.

Downregulation of the expression of bone morphogenetic protein 7 in experimental pyelonephritis

Bone morphogenetic protein 7 (BMP 7) is a member of the transforming growth factor (TGF) beta superfamily and is involved in regeneration, repair, and development of specific tissues, for example kidney, gut, lens, and skeleton. BMP 7 has emerged as a renotrophic factor and experimental studies have shown its protective role against fibrotic processes. Tubulointerstitial changes are present in the pyelonephritic kidney which progresses to fibrosis. Renal fibrosis may lead to significant morbidity in the form of hypertension, proteinuria, and loss of renal function. The objective of this study was to investigate BMP 7 expression in experimental acute and chronic pyelonephritis models. Eighteen Wistar rats were injected with 0.1 mL solution containing E. coli ATCC 25922 10(10) cfu mL(-1) into left renal medullae. Six rats were used as a sham group and were given 0.1 mL 0.9% NaCl. Pyelonephritic rats were sacrificed 24 h (group I, n=6), 1 week (group II, n=6), and 6 weeks (group III, n=6) after E. coli injection. Serum creatinine levels were analyzed. Renal tissues were studied histopathologically by use of hematoxylin and eosin and scored for diagnosis of pyelonephritis. BMP 7 expression was studied semiquantitatively by immunohistochemical staining. Acute (group I) and chronic (group II and group III) pyelonephritic histopathological changes were observed in experimental pyelonephritic groups. A gradual decrease in BMP 7 expression was observed in the tubulointerstitial and tubular area of the pyelonephritic kidneys, mildest in the acute pyelonephritic group and most severe in the chronic pyelonephritic 6th week group. A statistically significant difference was observed between tubulointerstitial BMP 7 expression by groups I and III (P=0.017) and by groups III and IV (P=0.000). Tubular BMP 7 expression was statistically significantly different between groups II and IV (P=0.009) and between groups III and IV (P=0.002). The data imply that BMP 7 has a major role in chronic pyelonephritis. Tubulointerstitial and tubular BMP 7 expression also had a significant negative correlation with fibrosis, tubular, atrophy, and vascular changes. Serum creatinine levels of the study group were all normal. We conclude that the decrease in renal BMP 7 expression in experimental chronic pyelonephritis is one of the factors responsible for fibrotic changes in persistent renal damage.

Voie excrétrice supérieure : physiologie, physiopathologie des obstructions et explorations fonctionnelles

The urine is transported from the renal papilla to the bladder through the upper urinary tract which allows this transport to be safe and comfortable, i.e., without any risk or pain for the kidney. This active transport depends on the smooth muscle contractile properties. The upper urinary tract is totally autonomous; this feature allows the preservation of its function after renal transplantation. However, despite its accessory role, the autonomous nervous system can modulate its activity. Upper urinary tract obstruction involves adaptative mechanisms which are different depending on the type (acute, chronic, acquired or congenital) of obstruction. Functional evaluations of the upper urinary tract are aimed at identify the urine transport conditions and the relationship between obstruction and clinical conditions such as hydronephrosis, pain or impaired renal function.

Molecular genetics of renal development

The understanding of the complex branching morphogenesis of the early kidney is at an early stage; however, a framework is emerging that suggests numerous active genes sequentially switching on and reciprocally influencing each other. Much of our understanding of this process comes from studies of rodents specifically engineered to lack a particular gene responsible for an inductive agent or receptor. This review attempts to place newly discovered genetic programs within an organized framework of sequential renal development.

Renin-angiotensin system polymorphisms and renal scarring

The purpose of the study was to determine whether DNA polymorphisms at the renin-angiotensin-aldosterone (RAS) genes were associated with evolution to renal scar formation and, consequently, with reflux nephropathy (RN) in patients with vesicoureteral reflux (VUR). Some authors have suggested that the DD genotype of the angiotensin-converting enzyme (ACE) gene would be an adverse renal prognosis factor. We recruited 246 patients (aged 3 months to 22 years) from four Spanish hospitals. These included 69 patients with VUR, 110 with RN (determined by absence/presence of renal scarring on dimercaptosuccinc acid scan), 27 with chronic renal failure due to RN, and 40 patients (control group) with urinary tract infection and normal findings on renal ultrasonography and voiding cystoureterogram. The ACE I/D, angiotensin II type 1 receptor AT1 A1166C, angiotensin II type 2 receptor A3123C AT2, and angiotensinogen AGT M235T polymorphisms were determined on the basis of polymerase chain reaction amplification. ACE serum levels were determined by spectrophotometric methods. We found no statistical differences in the distribution of RAS polymorphisms between the different groups. The ACE D allele was linked to higher ACE serum levels. We found no association between ACE I/D polymorphism and presence of hypertension, proteinuria, grade of VUR, or unilateral/bilateral VUR. Patients with the DD genotype had a lower incidence of febrile urinary tract infection as a first symptom of VUR/RN (P<0.05). We conclude that genetic polymorphisms of RAS components are not independent prognostic indicators of renal scarring in patients with VUR.

Angiotensin converting enzyme gene insertion/deletion polymorphism in idiopathic nephrotic syndrome in Kuwaiti Arab children

OBJECTIVE

Angiotensin converting enzyme (ACE) gene insertion/deletion (I/D) polymorphism influence the circulating and cellular levels of ACE and has been shown to be a risk factor in a number of diseases including IgA nephropathy. We have investigated the association of ACE gene I/D polymorphism with the clinical presentation of idiopathic nephrotic syndrome (INS) in Kuwaiti children.

MATERIALS AND METHODS

The genotypes for ACE gene I/D polymorphism were determined in 102 subjects (54 INS cases and 48 healthy controls) using a PCR method.

RESULTS

The distribution of DD, ID and II genotypes was 70%, 20% and 10% in INS cases compared with 52%, 46% and 2% in the controls. The mean age of onset of the disease was significantly lower in the INS cases with DD genotype (37 months) compared with cases with II genotype (65 months, p < 0.05). The clinical manifestation of the disease was considerably severe in cases with DD genotypes compared with cases having ID and II genotypes. The INS cases with DD genotype also showed a significantly higher incidence of steroid sensitivity and steroid dependence. Seventy-three per cent of the INS cases with minimal change lesion had a DD genotype. Also 70% of the cases which needed cytotoxic drugs had DD genotype.

CONCLUSION

Our data suggest an association of the D-allele of the ACE gene I/D polymorphism with the clinical manifestation of INS in Kuwaiti Arab children.

Kidney development: regulatory molecules crucial to both mice and men

Although the study of embryonic kidney development began in the 1950s, three decades passed until scientists began identifying the molecular controls of renal organogenesis. Most of these advances have come from mouse gene targeting and rodent kidney explant manipulation. Translation of the rodent data to human congenital kidney disease has only just begun. The activities of those regulatory molecules proven to be used in common appear remarkably similar in mouse and human renal development. Examples of these genes include glial cell line-derived neurotrophic factor (GDNF), RET, PAX2, Wilms tumor suppressor (WT1), and components in the renin-angiotensin pathway. Other factors that participate in mouse renal organogenesis, such as N-Myc, may later be proven important in human kidney development.

Angiotensin-converting enzyme gene insertion/deletion polymorphism and renal damage in childhood uropathies

BACKGROUND

The activation of the renin-angiotensin system in various renal disorders is well established. Congenital urological abnormalities, such as obstruction and reflux, are common causes of renal failure in children contributing to approximately 25% of chronic renal failure in this age group. While the outlook relates to the severity of initial renal damage, there is considerable heterogeneity in renal parenchymal destruction among individuals and the reasons for this heterogeneity are not fully understood. A polymorphism within intron 16 of the angiostensin-converting enzyme (ACE) gene has been shown to influence the activity of the renin-angiotensin system, thus, it may also have an impact on the expression of renal disorders. We have determined the incidence of this ID polymorphism of the ACE gene in 47 Kuwaiti children with different urological abnormalities leading to variable degrees of renal impairment and in 48 healthy control subjects with a similar ethnic background.

METHODS

Blood samples were collected from the patients (n = 47) and controls (n = 48), total genomic DNA extracted and the ACE genotypes were determined using a polymerase chain reaction-based method.

RESULTS

The DD genotype was detected in 27/47 (57%) cases compared with 25/48 (52%) controls (P = 0.439). The heterozygous genotype ID was found in 14/47 (29%) cases compared with 22/48 (46%) controls (P = 0.0138). The homozygous II genotype was detected in 6/47 (13%) cases compared with 1/48 (2%) controls (P = 0.0247). The D allele of ACE gene was detected in 41/47 (87%) uropathy cases when individuals with homozygous DD and heterozygous ID genotypes were considered collectively. The incidence of parenchymal damage was considerably higher in uropathy cases with DD genotype (62%) compared with those having ID (26%) and II (12%) genotypes.

CONCLUSIONS

Our data suggest an association of D allele of the ACE gene insertion/deletion polymorphism and congenital urological abnormalities, which result in parenchymal damage in Kuwaiti Arab children.