Smad3 deficiency attenuates renal fibrosis, inflammation,and apoptosis after unilateral ureteral obstruction

BACKGROUND: Transforming growth factor-beta (TGF-beta) has been implicated in the development of renal fibrosis induced by unilateral ureteral obstruction (UUO). However, there is little information on signaling pathways mediating TGF-beta activity involved in molecular and cellular events leading to renal fibrosis induced by UUO. In this study, we sought to determine whether Smad3, a major signaling component of TGF-beta, mediated renal fibrosis induced by UUO. METHODS: Renal fibrosis, inflammation, and apoptosis induced by UUO were macroscopically and histologically compared between wild-type mice and Smad3 null mice. RESULTS: Gross appearance of the kidney after UUO showed relatively intact kidney in Smad3 null mice [Smad3(-/-) mice] when compared with that of wild-type mice [Smad3(+/+) mice]. Renal interstitial fibrosis based on the interstitial area stained with Aniline-blue or Sirius red solution was significantly attenuated in the obstructed kidney of Smad3(-/-) mice when compared with that of Smad3(+/+) mice. Deposition of type I and type III collagens were also significantly reduced in the obstructed kidney of Smad3(-/-) mice. In addition, the numbers of myofibroblasts, macrophages, and CD4/CD8 T cells infiltrated into the kidney after UUO were significantly attenuated in the obstructed kidney of Smad3(-/-) mice when compared with that of Smad3(+/+) mice. Furthermore, terminal deoxynucleotidyltransferase-mediated deoxyuridine triphosphate (dUTP) nick-end labeling (TUNEL) staining after UUO showed significantly reduced number of tubular apoptotic cells in the obstructed kidney of Smad3(-/-) mice when compared with that of Smad3(+/+) mice. Endogenous Smad pathway was activated in the obstructed kidney after UUO in wild-type mice as judged by the increase of phosphorylated Smad2 or phosphorylated Smad2/3-positive cells in renal interstitial area. CONCLUSION: Smad3 deficiency attenuated renal fibrosis, inflammation, and apoptosis after UUO, suggesting that Smad3 was a key molecule mediating TGF-beta activity leading to real fibrosis after UUO.     

Glomerular filtration response to acute ureteral obstruction in the dog

In order to assess the glomerular filtration responses to acute ureteral obstruction in the dog we employed an established method that does not require timed urine collections. Our results show a 57 per cent increase in renal blood flow (baseline: 203.8 +/- 50.9 vs. 319 +/- 69.4 ml./min. at 105 minutes; no. = 7) that was associated with a monophasic decrease in filtration fraction to -70 per cent at 120 minutes (0.26 +/- 0.025 vs. 0.08 +/- 0.007) and an increase in ureteral pressure to 63.1 +/- 6.1 mm. Hg at 120 minutes. A biphasic GFR response was noted with an initial small increase (baseline: 32.5 +/- 7.5 vs. 36.3 +/- 11.0 ml./min. at 2 minutes) followed by a continual decline to -55 per cent at 120 minutes (to 14.5 +/- 2.6 ml./min.). This investigation has confirmed the results of micropuncture studies showing maintenance of GFR early after complete ureteral ligation.     

Gene expression in response to acute unilateral ureteral obstruction

Acute unilateral ureteral obstruction results in differential growth characteristics of both the ipsilateral and contralateral kidney. The obstructed kidney undergoes cellular atrophy following an initial phase of interstitial proliferation while the contralateral kidney hypertrophies. To evaluate the molecular events occurring in both kidneys after obstruction, we examined the expression of growth related (c-fos, c-myc, cH-ras, HSP 70), cell maintenance (beta-actin), and cellular damage (TRPM-2) genes at the mRNA level. In the contralateral kidney an early and transitory induction of c-fos and c-myc expression occurred while a bimodal induction was noted in the obstructed kidney. The patterns of cH-ras, HSP 70 and actin expression also differed in both kidneys. Induction of TRPM-2 was noted only in the obstructed kidney. Rapid gene activation is evident in both the contralateral and obstructed kidney following unilateral ureteral obstruction. The patterns of expression are distinct and may reflect the cellular response to stress (cell death and stromal proliferation) in the obstructed kidney versus a response to a systemic stimulus resulting in cellular hypertrophy in the contralateral kidney.     

Renal hemodynamic response to ureteral obstruction during converting enzyme inhibition

Acute unilateral obstruction (UUO) of the pig kidney is associated with an increased secretion of intrarenally generated angiotensin II (ANG II). In order to clarify the importance of this intrarenal ANG II generation during acute UUO, ipsilateral and contralateral renal blood flow and renal secretion rate of ANG II were determined in pigs during continuous infusion of an angiotensin I converting enzyme (ACE) inhibitor. Pigs were operatively equipped with electromagnetic flow probes and catheters in the renal veins and aorta. Intravenous administration of the ACE inhibitor SQ 14 225 (captopril), 1 mg/kg per hour, resulted in a significant increase in renal blood flow in the contralateral kidney from 340±28 ml/min to 435±36 ml/min (P<0.01), whereas renal blood flow in the ipsilateral kidney was significantly reduced from 388±23 ml/min to 248±24 ml/min, similar to the reduction in controls. Captopril reduced mean aortic blood pressure, renal vascular resistance consistently on both sides, and plasma concentrations of ANG II and aldosterone from all sample sites. Renal secretion rate of ANG II showed a clear tendency to be reduced from the ipsilateral kidney. The results suggest that in UUO a compensatory increase in renal blood flow may be inhibited in part due to an enhanced secretion of ANG II in the ipsilateral kidney. However, a captopril-mediated inhibition of bradykinin breadown may also explain some of the observed changes.     

Triptolide attenuates renal interstitial fibrosis in rats with unilateral ureteral obstruction

Aim: Extracts of Tripterygium wilfordii Hook F. have been used to treat glomerulonephritis for more than 30 years in China. Most of the anti‐inflammatory and immunosuppressive activities of these extracts can be attributed to triptolide (Trip). The present study was to investigate the effect of Trip on renal interstitial fibrosis in a model of unilateral ureteral obstruction (UUO). Methods: UUO or sham‐operated rats were randomly assigned to receive mycophenolate mofetil (MMF), Trip or vehicle and were killed on days 7 and 14 after UUO or sham operation. Kidney specimens were fixed for immunohistochemistry for myofibroblasts (α‐smooth muscle actin, α‐SMA), macrophages (ED‐1), monocyte chemoattractant protein‐1 (MCP‐1) and osteopontin. Interstitial collagen deposition and amounts of transforming growth factor‐β1 (TGF‐β1) were determined by Sirius red staining and enzyme‐linked immunosorbent assay, respectively. The mRNA expression of TGF‐β1, connective tissue growth factor (CTGF), MCP‐1 and osteopontin were measured by real‐time polymerase chain reaction analysis. Results: The scores for the density of α‐SMA‐ and ED‐1‐positive cells, the staining of MCP‐1 and osteopontin, interstitial collagen deposition and amounts of TGF‐β1 were significantly reduced by MMF or Trip. MMF or Trip significantly reduced the mRNA expression of TGF‐β1, CTGF, MCP‐1 and osteopontin. Conclusion: Trip significantly attenuated tubulointerstitial fibrosis in a rat UUO model and the effect of Trip on renal fibrosis was similar to that of MMF. Trip may be useful as a potential candidate in the treatment of renal fibrosis.     

Renal hemodynamic and ureteral pressure changes in response to ureteral obstruction: the role of nitric oxide

PURPOSE: Triphasic changes in renal blood flow and ureteral pressure after unilateral ureteral obstruction have long been known. The contribution of nitric oxide to the decline in renal blood flow and ureteral pressure in unilateral ureteral obstruction was studied in this model using arginine infusion and by studying the effect of 2 inhibitors of nitric oxide synthase (NOS). MATERIALS AND METHODS: Left ureteral obstruction was created in dogs. Renal blood flow and ureteral pressure were monitored. Groups 1 to 4 underwent unilateral ureteral obstruction and group 5 dogs underwent sham operation. Groups 2 to 5 received an infusion of arginine at hour 18 of obstruction that was sustained for 1 hour. In addition, NOS inhibitors were administered to dogs in groups 3 (N-monomethyl-L-arginine) and 4 (triamcinolone diacetate). RESULTS: Arginine administration at 18 hours of obstruction caused a significant increase in renal blood flow and ureteral pressure compared to sham operated animals. Triamcinolone diacetate eliminated the increase in renal blood flow and ureteral pressure, whereas N-monomethyl-L-arginine did not, reflecting the competitive nature of its inhibition of NOS. CONCLUSIONS: Arginine infusion 18 hours after unilateral ureteral obstruction led to increases in renal blood flow and ureteral pressure that were not seen in control animals. These results suggest that the nitric oxide system of the kidney is activated in unilateral ureteral obstruction. Since the addition of arginine is accompanied by an increase in renal blood flow and ureteral pressure, it further suggests that a lack of availability of substrate for NOS may explain the decrease in renal blood flow and ureteral pressure in obstruction. Providing substrate may be a way of maintaining renal blood flow in unilateral ureteral obstruction.     

Verapamil prevents the apoptotic and hemodynamic changes in response to unilateral ureteral obstruction

Introduction: Obstruction of the urinary tract has marked effects on renal blood flow, glomerular filtration rate (GFR), and tubular function. Moreover, ureteral obstruction results in an injury response that can progress to irreversible renal fibrosis and tubular atrophy by apoptosis. Methods: We examined the effect of a calcium channel blocker (verapamil) on renal functions and the abundance of apoptotic (p53, Fas, proliferating cell nuclear antigen [PCNA]) markers 1 week after Unilateral Ureteral Obstruction (UUO). Results: Immunohistochemistry studies revealed that UUO was markedly associated with up-regulation in the expression of p53 (1550 ± 82 vs 100 ± 23%), Fas (657 ± 48 vs 100 ± 31%), and proliferating cell nuclear antigen (945 ± 70 vs 100 ± 17% of sham levels). Administration of verapamil normalized the up-regulation of apoptotic markers p53 (724 ± 116 vs 1550 ± 82%); Fas (162 ± 38 vs 657 ± 48%) and PCNA (353 ± 54 vs 945 ± 70%). Furthermore, tubular diameter, as an important marker for detecting tubular atrophy was significantly decreased compared to those in UUO rabbits. The percent area of interstitial fibrosis in UUO kidneys was significantly greater than that in Verapamil-treated kidneys. Importantly, Verapamil reduced the development of interstitial fibrosis in UUO rabbits. We measured the GFR and renal blood flow in UUO. Short-term Verapamil challenge partially prevented the decrease in GFR (non-treated UUO: 62 ± 14; Verapamil + UUO: 119 ± 7; Sham: 127 ± 23 μL·min⁻¹·kg body wt⁻¹, P < 0.05) and renal blood flow (non-treated UUO: 1.1 ± 0.4; Verapamil + UUO: 5.0 ± 0.2; sham: 6.3 ± 0.2 mL·min⁻¹·kg body wt⁻¹, P < 0.05). Conclusion: Verapamil significantly prevents impairment in renal function and also prevents the up-regulation of p53, Fas, and PCNA during UUO, demonstrating a marked renoprotective effect of Verapamil treatment in conditions with urinary tract obstruction.     

Losartan attenuates renal vasoconstriction in response to acute unilateral ureteral occlusion in pigs

Unilateral ureteral obstruction in pigs is associated with an enhanced, de novo generation of angiotensin II from the ipsilateral kidney. In order to further investigate the role of this system during unilateral ureter obstruction, the renal hemodynamic response to the non-peptide angiotensin II antagonist losartan was investigated. Danish land race pigs were operated on under general anesthesia. Catheters were placed in both renal veins by x-ray and ultrasonic flow probes were mounted on the renal arteries. Losartan (2 mg/kg/h) was administered intravenously to an experimental group ( n=9) continuously over 8 h of unilateral ureteral occlusion. This group was then compared to a matched control group which received only saline ( n=6). Ipsilateral pelvic pressure, renal blood flow using ultrasound transit time, glomerular filtration rate, mean arterial pressure and heart rate were measured. Renal handling of angiotensin II was examined by determining the renal extraction and secretion rates of immunoreactive angiotensin II. The anticipated reduction in ipsilateral renal blood flow after the onset of obstruction was attenuated in the losartan treated pigs, but the ipsilateral glomerular filtration rate was unaffected as compared with the controls. In the losartan group, the increase in renal vascular resistance was significantly reduced compared with un-treated controls (141+/-25% vs 217+/-24%, P<0.05). Plasma immunoreactive angiotensin II increased significantly from all three sample locations in both groups after the onset of obstruction, being more pronounced in the losartan treated group in which immunoreactive angiotensin II from the ipsilateral renal vein increased from 5.1+/-0.5 pmol/l to 41.6+/-19.6 pmol/l, P=0.027. In the controls immunoreactive angiotensin II increased from 2.7+/-0.3 pmol/l to 24.8+/-10.2 pmol/l. Furthermore, plasma aldosterone was significantly reduced after losartan administration (from 80.4 pmol/l to 36.0 pmol/l, P=0.005), indicating effective blockade of the angiotensin II type-1 receptor. The results from the present study suggest that continuous intravenous administration of losartan blocks the angiotensin II receptor mediated effects in the pig. Losartan is able to reduce ipsilateral vasoconstriction in the obstructed kidney during unilateral ureter obstruction supporting the view that angiotensin II is an important mediator of vasoconstriction during unilateral ureter obstruction in the pig model with acute unilateral occlusion of the ureter.     

Renal response during acute unilateral ureteral obstruction in rats

The early renal response to unilateral ureteral occlusion (UUO) and its mechanism have been extensively studied in dogs but seldom discussed in the most frequently used laboratory animals, rats. The acute phase of the renal response to UUO was studied in female rats weighing 190-236 g. We recorded the ureteral pressure and changes in renal parameters throughout 120 minutes of UUO in control (US, UUO + saline, n = 10), L-arginine-treated (UA, n = 10), and right-nephrectomized rats (UO, UUO in one kidney, n = 9). Ureteral pressure increased in all three groups of rats after complete ureteral obstruction. The extent of the increase was not significantly different between US and UA rats but was significantly higher in the UO rats. In US rats, the cortical microvascular blood flow (CMVBF), measured by a laser Doppler flowmeter, declined significantly, from 321 +/- 10 perfusion units (PU) to 260 +/- 11 PU. The percentage of drop in CMVBF at 120 minutes of UUO was significantly greater in UO (25.7 +/- 3.8 %) than in US (19 +/- 2.1%) and in UA (14 +/- 2%) rats. Acute UUO reduced the glomerular filtration rate (GFR) in US and UO rats, whereas L-arginine attenuated this decrease. The excretion of nitrate/nitrite was increased after UUO. Giving N(G)-nitro-L-arginine methyl ester hydrochloride (L-NAME, 12 mg/kg/h) during UUO did not reduce CMVBF more severely. Western blot analysis of endothelial nitric oxide synthase expression in the renal cortex and medulla protein extracts revealed no differences between US and sham-operated rats. Acute UUO did not lead to renal hyperemia in rats. Reduction of nitric oxide during UUO might contribute to the decrease of renal circulation during UUO.     

Post-rejection ureteral obstruction owing to ureteral adherence to graft inferior pole

We describe 2 renal transplant patients with increasing plasma creatinine levels after resolution of acute rejection episodes. Antegrade pyelography demonstrated adherence of the ureter to the inferior pole of the kidney with partial obstruction in both cases, which was confirmed at operation.     

Unilateral ureteral obstruction secondary to sarcoidosis

An episode of unilateral ureteral obstruction secondary to sarcoidosis is described. Corticosteroid treatment resulted in prompt and complete resolution of the obstruction and associated lymphadenopathy. We believe this represents the first reported case of ureteral obstruction secondary to sarcoidosis.     

Bilateral ureteral obstruction secondary to endometriosis

Endometriotic ureteral obstruction is an uncommon but serious event often unrecognized until hydronephrotic renal atrophy has occurred. A case of bilateral endometriotic ureteral obstruction treated with danazol (Danocrine) is reported, and the literature is reviewed.     

Dietary arginine supplementation attenuates renal damage after relief of unilateral ureteral obstruction in rats

BACKGROUND: Progression of renal injury after relief of unilateral ureteral obstruction (UUO) has been demonstrated. Nitric oxide (NO) may be an effective intervention due to its vasodilatory, antifibrotic, and anti-apoptotic effects. Herein, we used dietary L-arginine (ARG) supplementation in a UUO relief model. METHODS: This study comprised group 1, control (no treatment). All other rats were subject to 3-day UUO, which was then relieved, and the rats maintained for 7 additional days. Group 2, no additional treatment; group 3, L-ARG; group 4, L-NAME, NO synthase inhibitor; group 5, ARG and L-NAME. Urinary NO(2/3) was quantified. GFR and ERPF were measured at day 10. Interstitial fibrosis and fibroblast expression, macrophage infiltration, tubular apoptosis, and proliferation, NOS expression, and the levels of tissue TGF-beta were evaluated. RESULTS: Urinary NO(2/3) was significantly increased by ARG treatment and decreased by L-NAME. GFR and ERPF measured 7 days following relief were not significantly different in the previously obstructed kidneys (POK) of groups 2 and 3. L-NAME significantly reduced GFR and ERPF in the POK. ARG significantly reduced apoptosis, macrophage infiltration, and fibroblast expression in the POK. L-NAME exacerbated the effects on apoptosis and fibroblasts. Fibrosis was minimal in groups 1 through 3, but was significantly increased by L-NAME. ARG did not affect renal NOS expression and tissue TGF-beta1 levels. CONCLUSION: Dietary ARG supplementation during UUO relief did not improve ERPF or GFR. However, renal damage, including fibrosis, apoptosis, and macrophage infiltration was significantly improved by ARG treatment. This suggests that increasing NO availability could be beneficial in the setting of UUO relief.