Hypoperfusion of peritubular capillaries induces chronic hypoxia before progression of tubulointerstitial injury in a progressive model of rat glomerulonephritis

Chronic hypoxia likely plays a pivotal role in chronic renal disease, but the specifics of its involvement remain unclear. To elucidate how chronic hypoxia occurs and whether hypoxia participates in the progression of renal disease, the authors established an irreversible glomerulonephritis model induced by uninephrectomy and repeated anti-Thy-1 antibody injections. Glomerulosclerosis with microvascular obliteration was complete at 2 wk after antibody injection and was not restored until 11 wk. Tubulointerstitial injury was mild at 2 wk and was gradually exacerbated until 11 wk, a pattern that was in accordance with the loss of peritubular capillaries. Immunohistochemical analysis using pimonidazole revealed the augmentation of hypoxia in the cortex before the aggravation of tubulointerstitial injury and subsequent peritubular capillary loss. The preexistence of hypoxia implies that it had substantial participation in the progression of tubulointerstitial injury. To test whether blood flow was inhibited in diseased kidneys, capillaries with intact blood flow were identified by tail vein injection of biotinylated lectin specific to endothelial cells. The renal microvasculature was well recognized by lectin in the controls, whereas lectin binding to peritubular capillaries was strikingly decreased in diseased kidneys, suggesting a disturbance of blood flow. Intravital microscopy analysis confirmed that blood flow in peritubular capillaries was decreased by approximately 40% in the disease group compared with the controls. In conclusion, stagnation of blood flow in peritubular capillaries induced chronic hypoxia at an early stage in this model, which was followed by progressive tubulointerstitial injury and a loss of peritubular capillaries.     

Role of peritubular capillary loss and hypoxia in progressive tubulointerstitial fibrosis in a rat model of aristolochic acid nephropathy

BACKGROUND/AIMS: To investigate the effects of peritubular capillary (PTC) loss and hypoxia on the progression of tubulointerstitial fibrosis in a rat model of aristolochic acid nephropathy (AAN). METHODS: Female Wistar rats received Caulis aristolochiae manshuriensis (CAM) decoction by gavage for 8 weeks, and were sacrificed at 8, 12 and 16 weeks, respectively, after administration. Blood urea nitrogen (BUN), serum creatinine (Scr) and urinary protein were monitored prior to sacrifice. PTC loss and tubulointerstitial hypoxia were assessed by CD34 immunostaining and hypoxia-inducible factor-alpha subunit 1 (HIF-1alpha) expression, respectively. Myofibroblasts were assessed by alpha-smooth muscle actin (alpha-SMA) expression. The expression of angiogenic factor was assessed by vascular endothelial growth factor (VEGF). RESULTS: AAN rats differed from controls by increased BUN, Scr and 24-hour urinary protein excretion rates. There was a progressive loss of PTCs in the AAN model, which was associated with the decreased expression of VEGF. A significant increase in nuclear localization of HIF-1alpha was seen 16 weeks after treatment with CAM decoction in the context of severe tubulointerstitial damage. Multifocal tubulointerstitial fibrosis was seen in AAN rats at weeks 12 and 16, predominantly in the area of the outer stripe and outer medulla. No significant pathologic changes were found in control rats. CONCLUSION: Following the reduction of PTCs density and up-regulation of HIF-1alpha, the tubulointerstitial fibrosis area increased. Ischemia and hypoxia are the important causes of severe tubulointerstitial fibrosis in AAN rats.     

Suramin inhibits renal fibrosis in chronic kidney disease

The activation of cytokine and growth factor receptors associates with the development and progression of renal fibrosis. Suramin is a compound that inhibits the interaction of several cytokines and growth factors with their receptors, but whether suramin inhibits the progression of renal fibrosis is unknown. Here, treatment of cultured renal interstitial fibroblasts with suramin inhibited their activation induced by TGF-β1 and serum. In a mouse model of obstructive nephropathy, administration of a single dose of suramin immediately after ureteral obstruction abolished the expression of fibronectin, largely suppressed expression of α-SMA and type I collagen, and reduced the deposition of extracellular matrix proteins. Suramin also decreased the expression of multiple cytokines including TGF-β1 and reduced the interstitial infiltration of leukocytes. Moreover, suramin decreased expression of the type II TGF-β receptor, blocked phosphorylation of the EGF and PDGF receptors, and inactivated several signaling pathways associated with the progression of renal fibrosis. In a rat model of CKD, suramin abrogated proteinuria, limited the decline of renal function, and prevented glomerular and tubulointerstitial damage. Collectively, these findings indicate that suramin is a potent antifibrotic agent that may have therapeutic potential for patients with fibrotic kidney diseases.     

Injury and progressive loss of peritubular capillaries in the development of chronic allograft nephropathy

BACKGROUND: Chronic allograft nephropathy (CAN) remains the most important cause of late renal graft loss. However, the mechanism for graft dysfunction and the process of the development of CAN are not well understood. This study examined the role of microvascular injury in the development of CAN. METHODS: We studied renal biopsies obtained from grafts with CAN (N= 79) and pretransplant control kidneys (N= 20). Microvascular injury was examined morphologically, and was correlated with interstitial fibrosis, glomerular sclerosis, graft function, and the severity of CAN. The humoral and cellular immunity involved in CAN were examined by C4d, CD3, and TIA-1 staining. RESULTS: In all the cases of CAN, microvascular injury was evident with or without CD3-positive T cells, TIA-1-positive cytotoxic cells, and/or C4d+ complement deposition. Irrespective of chronic rejection (N= 14), C4d+ chronic humoral rejection (N= 6), or other CAN, the development process of CAN was characterized by injury and progressive loss of identifiable peritubular capillaries (PTCs) accompanied with the development of interstitial fibrosis. Injured PTCs were characterized morphologically by the process of angioregression with the presence of apoptotic cells, lamination of the basement membrane, and loss of PTCs. The low number of PTCs correlated significantly with the severity of CAN (r=-0.74, P < 0.001), the development of interstitial fibrosis (r=-0.75, P < 0.001), graft dysfunction (r=-0.69, P < 0.001), and also correlated weakly with proteinuria (r=-0.45, P < 0.05). In the glomeruli, capillary loss significantly correlated with the degree of glomerular sclerosis (r=-0.66, P < 0.001) and proteinuria (r=-0.65, P < 0.001), but did not correlate with the severity of CAN (r=-0.24, P > 0.05) or graft dysfunction (r=-0.32, P > 0.05). CONCLUSION: CAN was characterized by progressive injury to the renal microvasculature and the development of renal scarring. In particular, injury, angioregression and progressive loss of the PTC network strongly contributed to the development of interstitial fibrosis and graft dysfunction in CAN, and might play a crucial role in the development of CAN.     

Rejection of peritubular capillaries in renal allo- and xeno-graft

The microvasculature plays an important role in the pathogenesis of humoral- and cell-mediated renal allo- and xeno-graft rejection. Peritubular capillary (PTC) endothelium expresses the major histocompatibility complex (MHC) class I and II antigens in the resting phase, as does the glomerular capillary endothelium, suggesting that these cells may be major immune targets. However, the role of PTCs in renal allo- and xeno-graft rejection is unclear. In this review, we discuss injury and subsequent remodeling of PTCs in both humoral- and cell-mediated rejection in allo- and xeno-grafts. Recent evidence suggests that PTC injury and endothelial cell death occur during both cell- and humoral-mediated rejection. Severe PTC rejection contributes to deterioration of graft function and acute graft loss. The mild but recurrent form of PTC rejection is associated with progressive interstitial fibrosis and chronic rejection. Following endothelial injury, the remaining PTC endothelium activates with up-regulation of allo-antigens and adhesion molecules, and down-regulation of anti-coagulant proteins. Subsequent to this, more severe rejection and graft dysfunction occur. Therefore, a careful analysis of cellular- and antibody-mediated rejection in PTCs is important in the diagnosis of rejection, prediction of graft prognosis, and in further development of new anti-rejection therapies.     

Rejection of peritubular capillaries in renal allo- and xeno-grafts

The microvasculature plays an important role in the pathogenesis of humoral- and cell-mediated renal allo- and xeno-graft rejection. Peritubular capillary (PTC) endothelium expresses the major histocompatibility complex (MHC) class I and II antigens in the resting phase, as does the glomerular capillary endothelium, suggesting that these cells may be major immune targets. However, the role of PTCs in renal allo- and xeno-graft rejection is unclear. In this review, we discuss injury and subsequent remodeling of PTCs in both humoral- and cell-mediated rejection in allo- and xeno-grafts. Recent evidence suggests that PTC injury and endothelial cell death occur during both cell- and humoral-mediated rejection. Severe PTC rejection contributes to deterioration of graft function and acute graft loss. The mild but recurrent form of PTC rejection is associated with progressive interstitial fibrosis and chronic rejection. Following endothelial injury, the remaining PTC endothelium activates with up-regulation of allo-antigens and adhesion molecules, and down-regulation of anti-coagulant proteins. Subsequent to this, more severe rejection and graft dysfunction occur. Therefore, a careful analysis of cellular- and antibody-mediated rejection in PTCs is important in the diagnosis of rejection, prediction of graft prognosis, and in further development of new anti-rejection therapies.     

Prevalence and progression of chronic kidney disease after renal transplantation

Background

We studied the prevalence of chronic kidney disease (CKD) and its progression after kidney transplantation.

Methods

We retrospectively analyzed the evolution of renal graft function, as estimated by the Cockcroft-Gault equation in 567 patients. CKD was classified in accordance with the National Kidney Foundation/Kidney Disease Outcome Quality Initiative with progression estimated by calculating the slope over time.

Results

Creatinine clearance (CrCL) at 1 year after transplantation was 57.8 ± 15.5 mL/min with 61.9% patients presenting de novo chronic renal failure. The 1-year-CrCl provided the best correlation with the 3-year CrCl (R² = 0.58; P < .001). Medians of slope (MS) among all patients was −2.38 ± 5.7 mL/min/y (−11.9 mL/min over 5 years). Patients who reached a CrCl < 60 at 1 year after transplantation showed a MS of −3.92 ± 6.5, while the others, −2.03 ± 5.2 mL/min/y (P = .046). Similarly, patients who reached a CrCL < 60 at 3 years after transplantation displayed a MS of −1.49 ± 3.5 mL/min/y, while the others, 0.62 ± 3.0 mL/min/y (P < .001).

Conclusions

The majority of renal transplant patients present de novo chronic renal failure already at 1 year posttransplantation. The rate of graft functional deterioration was 2.38 mL/min/y. It was worse among patients who displayed a CrCL less than 60 mL/min both at 1 and at 3 years. One-year CrCL was a good marker for 3-year CrCL.     

Disease progression and outcomes in chronic kidney disease and renal transplantation

BACKGROUND: It is unknown whether renal transplant recipients (RTR) have better outcomes and disease progression rates compared to patients with chronic kidney disease (CKD) when matched for the level of kidney function. METHODS: We analyzed data on 1762 patients with CKD (N = 872) and RTR (N = 890) over 16 years, applying the new Kidney/Disease Outcomes Quality Initiative (K/DOQI) staging system for CKD in a single center retrospective study. Patients were further divided based their native kidney disease. We determined disease progression by the slope of creatinine clearance decline and patient and kidney survival rates adjusted for age, gender and stage of kidney function, using Cox proportional hazards models. RESULTS: The overall rate of creatinine clearance decline in patients with CKD was -6.6 +/- 8.7 mL/min/year compared to -1.9 +/- 4.7 mL/min/year in RTR (P < 0.0001). The rate of decline per stage of CKD was also significantly lower in RTR. Whereas overall kidney survival was higher in RTR compared to patients with CKD (49.6% vs. 17.2%, respectively, P < 0.001), patient survival was not statistically different between the two groups (74.7% vs. 80.3%, respectively, P = 0.25). CONCLUSION: RTR had similar mortality rates compared to patients with CKD despite enjoying slower rates of disease progression and better kidney survival rates. These data suggest that RTR are a unique subset of patients with CKD whose comorbid conditions likely offset the potential benefits of slower rates of progression.     

Rapamycin markedly slows disease progression in a rat model of polycystic kidney disease

Increased tubular epithelial cell proliferation is a prerequisite for cyst formation and expansion in polycystic kidney disease (PKD). Rapamycin is a potent antiproliferative agent. The aim of the present study was to determine the effect of rapamycin on tubular cell proliferation, cyst formation, and renal failure in the Han:SPRD rat model of PKD. Heterozygous (Cy/+) and littermate control (+/+) male rats were weaned at 3 wk of age and then treated with rapamycin 0.2 mg/kg per d intraperitoneally or vehicle (ethanol) for 5 wk. Vehicle-treated Cy/+ rats had a more than doubling of kidney size compared with +/+ rats. Rapamycin reduced the kidney enlargement by 65%. Rapamycin significantly reduced the cyst volume density in Cy/+ rats by >40%. Blood urea nitrogen was 59% increased in vehicle-treated Cy/+ rats compared with +/+ rats. Rapamycin reduced the blood urea nitrogen to normal in Cy/+ rats. The number of proliferating cell nuclear antigen (PCNA)-positive cells per noncystic tubule was eightfold increased in vehicle-treated Cy/+ compared with +/+ rats. Rapamycin significantly reduced the number of PCNA-positive cells in noncystic tubules of Cy/+ rats. In addition, the number of PCNA-positive cells per cyst in Cy/+ rats was significantly reduced by rapamycin. In summary, in a rat model of PKD, rapamycin treatment (1) decreases proliferation in cystic and noncystic tubules, (2) markedly inhibits renal enlargement and cystogenesis, and (3) prevents the loss of kidney function.     

Thromboxane synthesis inhibition increases renal prostacyclin and prevents renal disease progression in rats with remnant kidney

Previous studies have demonstrated that inhibition of thromboxane A2-dependent platelet aggregation by the thromboxane A2 synthase inhibitor, OKY 1581, ameliorated the progressive kidney disease of rats with subtotal renal ablation. OKY 1581 also decreased the excessive renal thromboxane A2 synthesis and lowered systemic blood pressure. In the same model, a low dose aspirin and a specific thromboxane A2 receptor antagonist failed to influence proteinuria, glomerulosclerosis, and hypertension, thus excluding a role for either platelet or renal thromboxane A2 in renal disease progression. The aims of this study were to establish (1) whether a thromboxane A2 synthase inhibitor different from OKY 1581 could retard the progression of glomerular disease in rats with remnant kidney and (2) whether this effect was associated with an increase in renal synthesis of the vasodilatory prostacyclin. Treatment of rats with renal mass ablation with FCE 22178 (100 mg/kg by gavage and 200 mg/kg in the drinking water) for 35 days starting 10 days after surgical ablation was associated with an improvement in renal function in comparison with rats receiving the vehicle alone. Proteinuria was significantly lower, and rats were partially protected from the development of glomerulosclerosis. Systolic blood pressure was significantly lower than in animals given the vehicle. Urinary thromboxane B2 excretion was significantly decreased, and urinary 6-keto-prostaglandin F1 alpha increased in respect to vehicle-treated rats. We conclude that FCE 22178 limits glomerular injury in rats with remnant kidney.     

慢性马兜铃酸肾病血小板反应因子1高表达与肾间质纤维化及微血管丢失的关系

目的 探讨血小板反应因子1（TSP-1）与慢性马兜铃酸肾病（CAAN）肾间质纤维化及肾小管周围毛细血管（PTC）丢失的关系。方法 36只SD大鼠被随机分为CAAN模型组（用关木通浸膏水溶液间断灌胃）及对照组（仅自来水灌胃），每组18只。分别于第4、8和12周处死6只大鼠，用肾组织切片做免疫组化染色。对TSP-1、转化生长因子-β1（TGF-β1）、氨基肽酶P（APP）、血管内皮生长因子（VEGF）及Ⅰ型胶原（ColⅠ）的表达进行半定量分析。结果 与对照组比较，模型组大鼠肾间质TSP-1、肾小管TGF-β1及肾间质Col Ⅰ表达均显著上调（P均〈0．01）。3者间表达量呈显著正相关（r=0．925、0．910、0．857，P均〈0．01）。模型组大鼠肾间质APP表达明显下调（P〈0．01），与TSP-1、Col Ⅰ表达量呈显著负相关（r=-0．945、-0．883，P均〈0．01）。模型组肾小管VEGF表达上调（P〈0．01），其表达量与APP呈显著负相关（r=-0．607，P〈0．01），而与TGF-β1星显著正相关（r=0．625，P〈0．01）。结论 TSP-1-TGF-β轴表达增强及与TSP-1相关的PTC丢失均可能参与CAAN肾间质纤维化，而VEGF表达上调为代偿表现。     

螺内酯对肾间质纤维化中细胞增殖凋亡失衡的影响

螺内酯是醛固酮受体拮抗剂，传统认为是弱效利尿剂，新近发现它能改善单侧输尿管梗阻（UUO）大鼠肾间质纤维化病变程度，但作用机制尚不清楚。本研究从细胞增殖凋亡失衡角度来探讨醛固酮受体拮抗剂对UUO大鼠肾间质纤维化的作用。