腹膜透析对人腹膜形态结构的影响

目的 探讨腹膜透析（腹透）对人腹膜，重点在间皮层形态结构的影响及其意义。方法 采用光镜，扫描电镜和透射电镜对10例正常对照者，12例尿毒症非透析患者以及10例腹透患者的腹膜活检标本进行形态学观察。结果 尿毒症非透析患者腹膜的结构与正常对照者相似，而腹透患者的腹膜形态结构随着透析时间而呈进行性改变。主要表现为间质细胞表面微绒毛减少，消失，间皮细胞从基底膜脱落直至完全消失，最后只剩下裸露的纤维结缔组织。结论 腹膜透析可引起腹膜的形态学明显改变，这可能是长期腹膜透析引起腹膜衰竭的原因之一。进一步深入研究腹膜结构与功能间关系能为人们了解长期腹透对腹膜影响的病理生理机制并进而寻找保护腹膜的手段提供理论依据。     

Toward better dialysis compatibility: advances in the biochemistry and pathophysiology of the peritoneal membranes

Peritoneal dialysis (PD) has modified our concept of the peritoneal membrane, which is now a topic of active research. Peritoneal solute transport progressively increases with time on PD, enhances the dissipation of the osmotic gradient and, eventually, reduces ultrafiltration capacity. The causes of peritoneal membrane failure remain elusive. Recurrent episodes of peritonitis are not a prerequisite for the development of ultrafiltration failure. Functionally, the changes of the failing peritoneal membrane are best described as an increased functional area of exchange for small solutes between blood and dialysate. Histologically, these events are associated with vascular proliferation and structural changes of pre-existing vessels. Gathered evidence, including information on the composition of peritoneal cavity fluids and its dependence on the uremic environment, have cast a new light on the molecular mechanisms of decline in peritoneal membrane function. Chronic uremia per se modifies the peritoneal membrane and increases the functional area of exchange for small solutes. Biochemical alterations in the peritoneum inherent to uremia might be, at least in part, accounted for by severe reactive carbonyl compounds overload originating both from uremic circulation and PD fluid ("peritoneal carbonyl stress"). The molecular events associated with long-term PD are similar but more severe than those present in chronic uremia without PD, including modifications of nitric oxide synthase (NOS) and angiogenic growth factors expression, and advanced glycation and lipoxidation of the peritoneal proteins. This review focuses on reactive carbonyls and their association with a number of molecular changes observed in peritoneal tissues. This hypothetical approach will require further testing. Nevertheless, the insights gained on the peritoneal membrane offer a new paradigm to assess the effect of uremic toxins on serosal membranes. Furthermore, the progresses made in the dissection of the molecular events leading to peritoneal membrane failure open new avenues to develop safe, more biocompatible peritoneal dialysis technologies.     

Peritoneal dialysis fluid-induced changes of the peritoneal membrane are reversible after peritoneal rest in rats.

BACKGROUND: Peritoneal dialysis (PD) is associated with functional and structural alterations of the peritoneal membrane. However, the (ir)reversibility of these pathological changes of the peritoneum is not understood fully. METHODS: In an experimental PD model, rats (n = 15) received daily 10 ml conventional glucose containing PD fluid, via peritoneal catheters connected to implanted subcutaneous mini vascular access ports. After 5 weeks of treatment, the first group of animals (PDF; n = 10) was sacrificed, while peritoneal catheters of the remaining group of rats (PD-rest; n = 5) were removed 1 week later. The latter group (PD-rest) was sacrificed 12 weeks after removing catheters. At both time points, untreated rats were included as controls. Cellular and morphological parameters were analysed by light and electron microscopy. RESULTS: Rats exposed to PD fluid for 5 weeks showed a severe angiogenesis in various peritoneal tissues. Peritoneal rest resulted in a significant reduction in blood vessel density in visceral (mesentery, P<0.05), but not in parietal peritoneum. Five weeks' exposure to PD fluid resulted in a profound fibrosis in the parietal peritoneum, whereas the degree of fibrosis was significantly reduced in the PD-rest group (P<0.02). Daily exposure to PD fluid induced a higher number of mast cells in the omentum compared with untreated rats, whereas peritoneal rest normalized the increased mast cell density completely (P<0.03). Likewise, continued PD fluid instillation evoked a strong omental milky spot response, which was returned to the control level after peritoneal rest (P<0.009). Furthermore, the number of mesothelial cells on the liver was significantly increased in rats treated with PD fluid, whereas animals from the PD-rest group had a lower number of mesothelial cells, although this was not statistically significant (P = 0.08). Finally, as evidenced by electron microscopy, daily exposure to PD fluid resulted in severe damage to the mesothelial cell layer covering the peritoneum, whereas this cell layer was completely recovered after peritoneal rest. CONCLUSIONS: We show that PD fluid-induced cellular and morphological alterations of the peritoneal membrane are generally reversible.     

Effects of cyclooxygenase - 2 inhibitor on peritoneal function and angiogenesis in uremic peritoneal dialysis rats

Objective To investigate the effects of the cyclooxygenase-2 (COX-2) inhibitor (celecoxib) on angiogenesis and peritoneal function of uremic peritoneal dialysis rats. Methods Forty - eight male SD rats were selected, and they were randomly divided into five groups: normal control group(n=8), sham operation group(n=8), uremia group(5/6 nephrectomy, n=8), PD group [4.25% PD solution, 2 weeks PD model(n=8) and 4 weeks PD model(n=8)], PD + celecoxib intervention group[treated by celecoxib(20 mg/kg) via oral gavage, n=8].The peritoneum of uremic peritoneal dialysis rats was observed in different dialysis time from peritoneal structures, functions, peritoneal tissue capillary density (microvessel density, MVD) and COX-2, vascular endothelial growth factor (VEGF) expression level, and the impacts of celecoxib on uremic peritoneal dialysis rats peritoneal angiogenesis and peritoneal function were study. Results With the conduct of the peritoneal dialysis, peritoneal thickness increased, the inflammatory cells infiltrated, peritoneal equilibration test (PET) showed that ultrafiltration volume decreased significantly (P＜0.05), the amount of glucose transport rate rised significantly (P＜0.05), but the celecoxib could improve net ultrafiltration volume (P＜0.05), and reduce the glucose transport rate (P＜0.05). The peritoneal tissue MVD and COX - 2, VEGF expression were significantly increased in uremia group and PD group compared with that in the normal control group (all P＜0.05), were significantly lower in PD + Celecoxib intervention group than that in uremia group (P＜0.05). The correlation analysis showed that the level of COX-2 protein expression with MVD, VEGF protein expression was positively correlated (both P＜0.05), the level of VEGF protein expression and MVD was positively correlated (P＜0.05). Conclusions In vivo high glucose dialysate and uremia environmental can stimulate the COX-2 and VEGF expression raised, and the capillaries production increased in peritoneal tissue. Celecoxib can alleviate the change of peritoneal tissue morphology and function in long-term peritoneal dialysis rats. Celecoxib inhibits the peritoneal neovascularization of uremic peritoneal dialysis rats, possibly through inhibition of COX-2 expression to reduce the production of VEGF.     

血管内皮生长因子和内皮抑素在人腹膜组织的表达及其与腹膜毛细血管新生的关系

目的 检测血管内皮生长因子（VEGF）和血管内皮抑素（ES）在人腹膜组织表达,探讨两者与腹膜血管新生之间的关系。 方法 取健康对照者、尿毒症非透析患者以及腹透患者的腹膜标本,用反转录聚合酶链反应（RT-PCR）检测VEGF和ES mRNA的表达;组织免疫组化染色检测VEGF和ES蛋白质水平的表达;CD34染色计数腹膜组织毛细血管密度（MVD）。 结果 各组腹膜均有VEGF及ES表达;健康对照组、尿毒症非透析组、腹透组VEGF mRNA的相对表达量依次为0.47±0.01、0.62±0.02、0.74±0.02。VEGF免疫组化染色阳性区平均灰度值依次为95.673±2.01、117.126±2.07、140.184±2.25。ES免疫组化染色阳性区平均灰度值依次为94.902±2.38、113.380±2.33、145.489±3.05。尿毒症非透析组、腹透组VEGF mRNA和蛋白表达水平及ES蛋白表达水平表达均高于健康对照组,且腹透组升高更为明显,差异均具有统计学意义（均P < 0.05）。3组ES在mRNA水平表达量依次为0.42±0.02、0.43±0.03、0.43±0.02,各组表达差异无统计学意义（P > 0.05）。3组腹膜MVD依次为3.05±0.45、5.98±0.47、9.62±0.49,尿毒症非透析组、腹透组均高于健康对照组,且腹透组增高更为明显,差异均具有统计学意义（均P < 0.05）。 结论 腹膜透析患者腹膜组织VEGF mRNA和蛋白表达水平升高,ES蛋白表达水平也升高,这可能在长期透析所致腹膜组织新生毛细血管形成过程中发挥一定作用。     

Peritoneal morphologic changes in a peritoneal dialysis rat model correlate with angiopoietin/Tie-2

The angiopoietin/Tie-2 system plays an important role in the initiation of angiogenesis. However, the role of angiopoietin/Tie-2 in peritoneal angiogenesis and fibrosis is unclear. In our study we investigated the peritoneal morphologic changes in a uremic peritoneal dialysis (PD) rat model, focusing on the relationship between angiopoietin/Tie-2 and peritoneal angiogenesis. We subjected uremic (subtotal nephrectomy) rats to dialysis, using a standard PD solution, for 10 days, 28 days, or 56 days, and compared them with uremic rats that had not undergone dialysis and control rats. Functional [dialysate-to-plasma (D/P) creatinine; ultrafiltration (UF)] and structural (vessel density and thickness of the submesothelial extracellular matrix) changes of the peritoneum were quantified. Levels of angiopoietin (Ang)-1, Ang-2, Tie-2 and vascular endothelial growth factor (VEGF) were examined in the peritoneum by real-time quantitative polymerase chain reaction (PCR) and related to angiogenesis. The uremic group that had not undergone dialysis was characterized by increased vessel density in the peritoneum compared with that of the control, which correlated with decreased UF and increased D/P creatinine. Progressive angiogenesis and fibrosis were found in the PD groups when compared with the uremic non-dialyzed or control group, accompanied by an increased D/P creatinine that occurred in the PD group after 56 days, while UF decreased. Furthermore, Ang-2 and VEGF levels increased, while Tie-2 level decreased significantly in the uremic non-dialyzed group compare with the control. This tendency was more obvious in the PD groups than in the uremic non-dialyzed or control group, but no difference was found among the PD groups. Both VEGF and Ang-2 correlated positively with vessel density, while Tie-2 correlated negatively. We confirmed angiogenesis and fibrosis changes of the peritoneum as a result of uremic status and PD therapy in the uremic PD rat model. An increased level of Ang-2 and a reduced level of Tie-2 in conditions of uremia and PD therapy correlated with peritoneal angiogenesis and functional deterioration.     

Chronic uremia induces permeability changes, increased nitric oxide synthase expression, and structural modifications in the peritoneum

Advanced glycation end products (AGE), growth factors, and nitric oxide contribute to alterations of the peritoneum during peritoneal dialysis (PD). These mediators are also involved in chronic uremia, a condition associated with increased permeability of serosal membranes. It is unknown whether chronic uremia per se modifies the peritoneum before PD initiation. A rat model of subtotal nephrectomy was used to measure peritoneal permeability after 3, 6, and 9 wk, in parallel with peritoneal nitric oxide synthase (NOS) isoform expression and activity and structural changes. Uremic rats were characterized by a higher peritoneal permeability for small solutes and an increased NOS activity due to the up-regulation of endothelial and neuronal NOS. The permeability changes and increased NOS activities correlated with the degree of renal failure. Focal areas of vascular proliferation and fibrosis were detected in uremic rats, in relation with a transient up-regulation of vascular endothelial growth factor and basic fibroblast growth factor, as well as vascular deposits of the AGE carboxymethyllysine and pentosidine. Correction of anemia with erythropoietin did not prevent the permeability or structural changes in uremic rats. Thus, in this rat model, uremia induces permeability and structural changes in the peritoneum, in parallel with AGE deposits and up-regulation of specific NOS isoforms and growth factors. These data suggest an independent contribution of uremia in the peritoneal changes during PD and offer a paradigm to better understand the modifications of serosal membranes in uremia.     

Advanced glycation and lipidoxidation of the peritoneal membrane: respective roles of serum and peritoneal fluid reactive carbonyl compounds

BACKGROUND: Advanced glycation of proteins has been incriminated in the progressive alteration of the peritoneal membrane during chronic peritoneal dialysis (PD). Advanced glycation end products (AGEs) result from a modification of proteins by reactive carbonyl compounds (RCOs). RCOs resulting from glucose breakdown are present in commercial PD fluid. They also accumulate in uremic plasma. The present study was undertaken to evaluate the respective contribution of these two sources of RCOs in the genesis of peritoneal AGEs. METHODS: Three major RCOs formed during heat sterilization of PD fluid, that is, glyoxal, methylglyoxal, and 3-deoxyglucosone, and total RCOs were measured in commercial PD fluid and in PD effluent. The generation of pentosidine, used as a surrogate marker for AGEs, during one-week incubations of PD fluid and effluent samples fortified with bovine serum albumin (BSA) was measured by high-performance liquid chromatography. Peritoneal samples were stained with antibodies specific for two AGEs derived from carbohydrate-dependent RCOs, Nepsilon-(carboxymethyl)lysine (CML) and pentosidine, or for two advanced lipoxidation end products (ALEs) derived from lipid-dependent RCOs, malondialdehyde (MDA)-lysine and 4-hydroxynonenal (HNE)-protein adduct. RESULTS: Glyoxal, methylglyoxal, and 3-deoxyglucosone were identified in commercial PD fluid. Their levels in PD effluents decreased with dwell time probably by diffusion into blood circulation. In contrast, the levels of total RCOs were initially low in commercial PD fluid, increased in PD effluent with dwell time probably by diffusion from circulation into the peritoneal cavity, and after 12 hours, reached values observed in uremic serum. The relevance of the rise in total RCOs for AGE formation is demonstrated by a parallel increase in the generation of pentosidine during incubations of PD effluents. In contrast with RCOs present in glucose-rich PD fluid, RCOs diffusing from uremic circulation originate from both carbohydrates and lipids. Their role in the modification of peritoneal proteins is demonstrated by the immunohistochemical study of peritoneal tissue. Two AGEs and two ALEs increase in parallel in the mesothelial layers and in vascular wall of small arteries in the peritoneum. CONCLUSIONS: Protein modification of the peritoneum is determined not only by RCOs originating in PD fluid, but also by RCOs originating from the uremic circulation. The present data might be relevant to current attempts to improve PD fluid toxicity by lowering its glucose content.     

可溶性酪氨酸激酶2融合蛋白对尿毒症腹膜透析大鼠腹膜形态和功能的影响

目的 研究可溶性酪氨酸激酶2融合蛋白（sTie-2-Fc）对尿毒症腹膜透析大鼠腹膜血管新生、溶质转运和超滤功能的影响。 方法 32只雄性Wistar大鼠按数字随机法分为假手术组、尿毒症组、尿毒症腹透组和sTie-2-Fc干预组（均n=8）。尿毒症腹透组和sTie-2-Fc干预组大鼠经腹透管每天2次腹腔灌注4.25%葡萄糖透析液（3 ml/100 g体质量）共4周,sTie-2-Fc干预组大鼠每次灌注时在透析液中加入1 μg sTie-2-Fc。各组大鼠处死前行腹膜平衡试验,检测腹膜转运和超滤功能,取大网膜标本行抗CD31免疫组化染色并计血管数。 结果 与假手术组大鼠相比,尿毒症组大鼠的2 h腹透液和血肌酐比值（D/Pcr）增高（0.78±0.05比0.70±0.09,P = 0.028）,腹透液2 h与0 h葡萄糖比值（D/D0）降低（0.69±0.05比0.76±0.07,P = 0.033）,腹膜超滤量（UF,ml）减少（2.29±0.50比4.58±1.64,P = 0.005）,腹膜血管数量增加[（5.8±3.0）/HP比（1.6±0.5）/HP,P < 0.01]。尿毒症腹透组大鼠的溶质转运较尿毒症组大鼠进一步增高（D/Pcr: 0.89±0.05比0.78±0.05,P < 0.01;D/D0:0.47±0.09 比0.69±0.05, P < 0.01）,UF（ml）减少（0.40±0.59比2.29±0.50,P = 0.005）,腹膜血管数量增多[（16.7±1.2）/HP比（5.8±3.0）/HP,P < 0.01]。干预组大鼠使用sTie-2-Fc后,UF（ml）较尿毒症腹透组大鼠显著增加（1.56±0.48比0.40±0.59,P = 0.014）,腹膜血管数量显著减少[（9.2±1.2）/HP比（16.7±1.2）/HP,P ＜ 0.01],但两组大鼠的D/Pcr和D/D0差异均无统计学意义。 结论 sTie-2-Fc使尿毒症腹透大鼠腹膜血管新生减少,超滤增加,有利于保护腹膜结构和功能,可能是防治腹透后腹膜结构和功能改变的另一靶点。     

Epithelial to mesenchymal transition and peritoneal membrane failure in peritoneal dialysis patients: pathologic significance and potential therapeutic interventions

Peritoneal dialysis (PD) is a form of renal replacement and is based on the use of the peritoneum as a semipermeable membrane across which ultrafiltration and diffusion take place. Nevertheless, continuous exposure to bioincompatible PD solutions and episodes of peritonitis or hemoperitoneum cause acute and chronic inflammation and injury to the peritoneal membrane, which progressively undergoes fibrosis and angiogenesis and, ultimately, ultrafiltration failure. The pathophysiologic mechanisms that are involved in peritoneal functional impairment have remained elusive. Resident fibroblasts and infiltrating inflammatory cells have been considered the main entities that are responsible for structural and functional alterations of the peritoneum. Recent findings, however, demonstrated that new fibroblastic cells may arise from local conversion of mesothelial cells (MC) by epithelial-to-mesenchymal transition (EMT) during the inflammatory and repair responses that are induced by PD and pointed to MC as protagonists of peritoneal membrane deterioration. Submesothelial myofibroblasts, which participate in inflammatory responses, extracellular matrix accumulation, and angiogenesis, can originate from activated resident fibroblasts and from MC through EMT. This heterogeneous origin of myofibroblasts reveals new pathogenic mechanisms and offers novel therapeutic possibilities. This article provides a comprehensive review of recent advances on understanding the mechanisms that are implicated in peritoneal structural alterations, which have allowed the identification of the EMT of MC as a potential therapeutic target of membrane failure.     

Benfotiamine protects against peritoneal and kidney damage in peritoneal dialysis

Residual renal function and the integrity of the peritoneal membrane contribute to morbidity and mortality among patients treated with peritoneal dialysis. Glucose and its degradation products likely contribute to the deterioration of the remnant kidney and damage to the peritoneum. Benfotiamine decreases glucose-induced tissue damage, suggesting the potential for benefit in peritoneal dialysis. Here, in a model of peritoneal dialysis in uremic rats, treatment with benfotiamine decreased peritoneal fibrosis, markers of inflammation, and neovascularization, resulting in improved characteristics of peritoneal transport. Furthermore, rats treated with benfotiamine exhibited lower expression of advanced glycation endproducts and their receptor in the peritoneum and the kidney, reduced glomerular and tubulointerstitial damage, and less albuminuria. Increased activity of transketolase in tissue and blood contributed to the protective effects of benfotiamine. In primary human peritoneal mesothelial cells, the addition of benfotiamine led to enhanced transketolase activity and decreased expression of advanced glycation endproducts and their receptor. Taken together, these data suggest that benfotiamine protects the peritoneal membrane and remnant kidney in a rat model of peritoneal dialysis and uremia.     

Peritoneal dialysis: changes to the structure of the peritoneal membrane and potential for biocompatible solutions

BACKGROUND: Peritoneal dialysis (PD) is now established as a viable and successful alternative to hemodialysis (HD) for patients starting on renal replacement therapy. A number of studies have confirmed that equivalent adequacy and fluid balance are provided at least for the first four to five years of renal replacement therapy (RRT). Loss of peritoneal membrane function remains a major factor leading to treatment failure in a significant number of patients on PD. Numerous studies have suggested a relationship between these changes in function and structural changes in the membrane. A careful analysis of peritoneal biopsies from PD patients would allow the clear identification of those changes unique to PD, in addition to indicating possible correlations with glucose exposure as well as other functional parameters. METHODS: We systematically examined peritoneal biopsies from 13 normal individuals, 29 uremic predialysis patients, 55 HD patients, and 157 patients on long-term PD. Well-oriented specimens were stained with toluidine blue and examined by a blinded pathologist. Limited clinical data has allowed a preliminary analysis of structure-function relationships. RESULTS: The median thickness of the submesothelial compact collagenous zone was 40 microm in normal individuals, 150 microm in uremic patients, 150 microm in patients on HD, and 2550 microm in patients on PD (P < 0.001 for all vs. normal individuals). Compact zone thickness increased significantly with duration of PD therapy (0 to 24 months, 180 microm;>97 months, 600 microm). Vascular changes comprised progressive subendothelial hyalinization of postcapillary venules, with luminal narrowing or obliteration. These changes were present in uremic patients and increased significantly with PD duration (P = 0.0001). CONCLUSIONS: These data indicate that morphologic changes in the postcapillary venules and the submesothelial compact zone of PD patients begin during the uremic phase of their illness. This is then worsened by time spent on PD. The relationships with glucose exposure or glucose degradation products have yet to be established.     

血管生成素2与腹膜透析时腹膜血管新生的关系

目的 观察血管生成素2（Angpt-2）和腹膜透析（腹透）时腹膜血管新生的关系。 方法 5/6肾切除制作尿毒症大鼠模型,成模后在腹腔内植入腹透管,根据大鼠体质量每天经腹透管注入定量腹透液（4.25%,Dineal）。按腹透时间分为未腹透组、腹透10 d组、28 d组及56 d组。假手术非尿毒症非透析大鼠为对照组。大网膜抗CD31免疫组化染色后作血管计数,观察腹膜血管新生。用实时定量PCR和Western 印迹分别检测腹膜Angpt-2和血管内皮生长因子（VEGF）表达量变化,同时检测腹膜血管数和Angpt-2、VEGF表达量的关系。 结果 未腹透组、腹透10 d、28 d及56 d组腹膜血管数显著高于对照组[（5±3）、（10±5）、（17±5）及（19±4）比（1±1） 个/HP,均P < 0.05]。腹透28 d组腹膜血管数显著高于腹透10 d组（P < 0.05）,但与56 d组差异无统计学意义。未腹透组或腹透各组腹膜Angpt-2和VEGF表达显著高于对照组（均P < 0.01）,而Angpt-2和VEGF表达量并未随透析时间延长而增加。Angpt-2和VEGF表达量和腹膜血管数呈正相关（r = 0.7756,P < 0.01;r = 0.5223,P < 0.05）。 结论 尿毒症状态和腹透促进腹膜血管新生。腹膜Angpt-2表达增加和腹膜血管新生呈正相关。Angpt-2将可能成为治疗腹膜血管新生的另一靶点     

Response of chronic renal failure mice to peritoneal Staphylococcus epidermidis challenge: impact of repeated peritoneal instillation of dialysis solution

The effect of repeated instillation of peritoneal dialysis (PD) solution on the peritoneal clearance of a Staphylococcus epidermidis challenge was investigated in a mouse model of surgically induced chronic renal failure. For periods of up to 2 weeks, mice bearing peritoneal catheter implants underwent daily (3 mL) or twice daily (1.5 mL) peritoneal instillation of PD solution (4.25% dextrose) by transcutaneous injection into the catheter lumen. Peritoneal instillation of PD solution did not have a significant influence on the microbiological status of peritoneal structures of renal failure or sham-operated mice following experimental intracatheter S epidermidis inoculation with 10(6) colony-forming units (CFU) (assessment 48 hours after inoculation) or 10(8) CFU (assessment 1 week after inoculation). Microbiological and scanning electron microscopy (SEM) assessments of recovered peritoneal catheters demonstrated that S epidermidis remained associated with the catheter site after other peritoneal structures had become culture negative. SEM of the parietal peritoneum revealed striking morphologic alterations of the mesothelial surface as a consequence of daily PD solution infusion. In the absence of S epidermidis inoculation, repeated instillation of PD solution caused a marked acute peritoneal inflammation without evidence of a concomitant systemic inflammatory response. Furthermore, peritoneal inflammatory response to S epidermidis challenge was augmented by the infusion procedure. Concurrent assessments of inflammatory response and microbiological status revealed that, in spite of heightened peritoneal inflammatory response with peritoneal infusion, bacterial clearance from the catheter site was not improved. Although the animal preparation was limited to peritoneal infusion without drainage, the influence of repeated peritoneal instillation of hyperosmolar, acidic PD solution on the response of mice to S epidermidis challenge was successfully addressed.     

Vascular proliferation and enhanced expression of endothelial nitric oxide synthase in human peritoneum exposed to long-term peritoneal dialysis

Long-term peritoneal dialysis (PD) is associated with alterations in peritoneal permeability and loss of ultrafiltration. These changes originate from increased peritoneal surface area, but the morphologic and molecular mechanisms involved remain unknown. The hypothesis that modifications of activity and/or expression of nitric oxide synthase (NOS) isozymes might play a role in these modifications, via enhanced local production of nitric oxide, was tested in this study. NOS activities were measured by the L-citrulline assay in peritoneal biopsies from seven control subjects, eight uremic patients immediately before the onset of PD, and 13 uremic patients on short-term (<18 mo, n = 6) or long-term(>18 mo, n = 7) PD. Peritoneal NOS activity is increased fivefold in long-term PD patients compared with control subjects. In uremic patients, NOS activity is positively correlated with the duration of PD. Increased NOS activity is mediated solely by Ca(2+)-dependent NOS and, as shown by immunoblotting, an upregulation of endothelial NOS. The biologic relevance of increased NOS in long-term PD was demonstrated by enhanced nitrotyrosine immunoreactivity and a significant increase in vascular density and endothelial area in the peritoneum. Immunoblotting and immunostaining studies demonstrated an upregulation of vascular endothelial growth factor (VEGF) mostly along the endothelium lining peritoneal blood vessels in long-term PD patients. In the latter, VEGF colocalized with the advanced glycation end product pentosidine deposits. These data provide a morphologic (angiogenesis and increased endothelial area) and molecular (enhanced NOS activity and endothelial NOS upregulation) basis for explaining the permeability changes observed in long-term PD. They also support the implication of local advanced glycation end product deposits and liberation of VEGF in that process.     

Effect of the JAK2/STAT3 signaling pathway on epithelial mesenchymal transition of the peritoneum in uremic peritoneal dialysis rats

Objective To investigate whether the JAK2/STAT3 signaling pathway is involved in the epithelial-mesenchymal transition (EMT) of peritoneal mesothelial cells in uremic peritoneal dialysis (PD) rats. Methods A total of 48 male Sprague-Dawley (SD) rats were randomly separated into six groups: normal control group (NC group, n=8), sham group (n=8), uremic group (n=8), PD group (n=8), S3I-201 control group (n=8) and S3I-201 group (n=8). Uremic model generated by 5/6 nephrectomy surgery in rats was established. The rats of PD group, S3I-201 control group and S3I-201 group received daily infusion of 4.25% glucose-based peritoneal dialysate fluid (3 ml/100 g) from PD catheters for 28 days. Rats of S3I-201 group were injected with STAT3 inhibitor S3I-201 (2.5 mg/kg) solution from the catheters every other day; the same dose of the solvent of S3I-201 was simultaneously given to S3I-201 control group rats. After PD for 28 days, peritoneal function, pathologic changes, and microvessel density (MVD) were evaluated. Creatinine, urea nitrogen and interleukin-6 (IL-6) concentration in blood and dialysate, and protein and mRNA levels of phospho-JAK2 (p-JAK2), phospho-STAT3 (p-STAT3), E-cadherin, alpha-smooth muscle actin (α-SMA) and vascular endothelial growth factor (VEGF) in peritoneum were determined. Results Uremia and peritoneal dialysate could aggravate the peritoneal function and elevate peritoneal thickness and MVD. They could also increased the concentration of IL-6 in blood and dialysate and the expression levels of α-SMA, VEGF, p-JAK2 and p-STAT3 in peritoneum, while lowering E-cadherin expression in peritoneum. These manifestations were even more remarkable in PD group compared to those in uremic group. There was no statistical difference between the S3I-201 control group and the PD group as regards all the index (all P＞0.05). Compared with the S3I-201 control group, the rats treated with S3I-201 showed better peritoneal function. S3I-201 could reduce peritoneal thickness (P＜0.05), MVD (P＜0.05), the concentration of IL-6 in blood and dialysate, the mRNA and protein expression of α-SMA, VEGF, p-JAK2 and p-STAT3 (all P＜0.05), while enhance the mRNA and protein expression of E-cadherin (all P＜0.05). Conclusions After STAT3 is inhibited, the peritoneal thickness, MVD and IL-6 concentration in PD rats are decreased, and EMT is also inhibited, while peritoneal function is improved. The JAK2/STAT3 signaling pathway may thus be involved in the process of EMT of peritoneum in uremic peritoneal dialysis rats by regulating the expression of IL-6.     

Effects of atorvastatin on development of peritoneal fibrosis in rats on peritoneal dialysis

Rational: Peritoneal sclerosis is one of the important complications of long-term peritoneal dialysis (PD). In this study, efficacy of atorvastatin on peritoneal histology and functions in non-uremic rats on PD was tested. Objectives: Twenty-two non-uremic Wistar albino rats were randomized into three groups: Sham (intraperitoneal saline), peritoneal dialysis (PD, intraperitoneal 3.86% dextrose containing PD solution), and treatment (TX, intraperitoneal 3.86% dextrose containing PD solution plus atorvastatin added into drinking water). At the end of a 4-week period, 1 h peritoneal equilibration test was performed. Serum lipids and certain cytokines, mediators, markers, and antioxidant enzyme activities in serum and dialysate were studied. Peritoneal thickness was measured and peritoneal inflammation, fibrosis, and vascular proliferation were scored in histological sections. Main findings: In histological examinations, inflammation, fibrosis, and vascular proliferation were significantly more frequent in PD group than Sham group and it seemed to decrease significantly when atorvastatin was used in conjunction with PD. Additionally, peritoneum was significantly thicker in PD group when compared to that of Sham and TX groups. Serum parameters did not significantly differ between groups. On the other hand, dialysate glutathione reductase (GR) activity and TGF-β were significantly lower in TX group than that of the PD group, whereas dialysate IL-6 level was higher in TX group. Principal conclusions: In our study, atorvastatin use appeared to diminish structural changes in peritoneum. Decreased expression of TGF-β in dialysate may be one of the possible underlying mechanisms.     

Molecular mechanisms modifying the peritoneal membrane exposed to peritoneal dialysis

Over time, a significant proportion of patients an peritoneal dialysis (PD) develop an increased permeability for small solutes, which induces a faster absorption of glucose, and ultrafiltration failure by early dissipation of the osmotic gradient. Vascular proliferation and vasodilatation of preexisting vessels might represent the structural basis for increased effective peritoneal surface area encountered in these PD patients. Animal models have shown that local release of growth factors and nitric oxide in the peritoneal membrane (PM) may lead to the development of areas of neovascularization and/or submesothelial fibrosis. Long-term exposure to conventional, glucose-based dialysis fluids plays a central role in the pathogenesis of these structural modifications. Glucose degradation products and reactive carbonyl species, which are present both in glucose-based dialysates and uremic plasma, accelerate the formation of the advanced glycation end products in the PM, which may in turn initiate a range of cellular responses including stimulation of monocytes, secretion of inflammatory cytokines, proliferation of vascular smooth muscle cells, stimulation of growth factors, and secretion of matrix proteins. The changes in the PM may also be potentiated by uremia and hyperglycemia per se. These new insights into the molecular mechanisms operating in the PM have provided rationale for novel therapeutic strategies including the development of glucose-free PD solutions and two-chamber bags.     

Prevalence and influencing factors of peritoneal calcification in patients with long peritoneal dialysis duration

Objective To investigate the prevalence and related factors of peritoneal calcification in peritoneal dialysis (PD) patients with long dialysis duration, and to explore the relationship between peritoneal calcification and vascular calcification. Methods This cross-section study enrolled PD patients who had received PD for more than 4 years in Peking University People's Hospital. Peritoneal calcification and abdominal aortic calcification were reviewed by CT scan. Demographic data, clinical characteristics, laboratory data including calcium phosphorus metabolism indexes (Ca, P, ALP and iPTH) and PD adequacy were collected. The influencing factors of peritoneal calcification were analyzed by Logistic regression analysis. The correlation between peritoneal calcification and abdominal aortic calcification were tested by Spearman correlation analysis. SPSS 19.0 was used for statistical analysis. Results (1) Seventy-nine PD patients were enrolled: 32 males (40.5%); mean age was (58.7±13.1) years and average PD duration was 77.25(58.00, 88.00) months. The major primary diseases were glomerulonephritis (46.8%) and diabetic nephropathy (30.4%). (2) 6 patients (7.6%) had CT-detectable peritoneal calcification. 77(97.5%) patients were found with various degrees of peritoneal thickening. The prevalence of peritoneal calcification was 7.6% in patients with PD duration more than 4 years, 10.3% in patients with PD duration more than 6 years, 18.8% in patients with PD duration more than 8 years and 40.0% in patients with PD duration more than 10 years, showing an increasing trend. Compared with non-peritoneal calcification group, the patients in peritoneal calcification group received higher doses of Vitamin D (P＜0.001) and lower triglyceride levels (P=0.041). The patients were divided into two groups according to whether dialysis duration was longer than 9 years, and the proportion of patients with long PD duration in peritoneal calcification group was higher (P=0.013). Logistic regression analysis showed that PD duration, calcium and phosphorus metabolism indexes were not independent risk factors of peritoneal calcification. High vitamin D dose was an independent risk factor for peritoneal calcification (B=2.667, OR=14.394, 95%CI 1.655 - 125.165, P=0.016). (3) 74 patients were found with abdominal aortic calcification in different degrees, and the prevalence rate of abdominal aortic calcification was 93.7%. Spearman correlation analysis showed that there was no correlation between peritoneal calcification and vascular calcification (r=0.70, P=0.542). Conclusions The prevalence of peritoneal calcification in long PD duration patients is low. Peritoneal calcification may be associated with high Vitamin D dose and long PD duration.     

Pathogenesis and treatment of peritoneal membrane failure

Peritoneal dialysis (PD) is a viable treatment option for end stage renal disease (ESRD) patients worldwide. PD may provide a survival advantages over hemodialysis (HD) in the early years of treatment. However, the benefits of PD are short-lived, as peritoneal membrane failure ensues in many patients, owing mainly to structural and functional changes in the peritoneal membrane from the use of conventional bio-incompatible PD solutions, which are hyperosmolar, acidic, have lactate buffer and contain high concentrations of glucose and glucose degradation products (GDPs). Current data suggest that chronic exposure of the peritoneum to contemporary PD fluids provokes activation of various inflammatory, fibrogenic and angiogenic cytokines, interplay of which leads to progressive peritoneal fibrosis, vasculopathy and neoangiogenesis. There is emerging evidence that peritoneal vascular changes are mainly responsible for increased solute transport and ultrafiltration failure in long-term PD. However, the precise pathophysiologic mechanisms initiating and propagating peritoneal fibrosis and angiogenesis remain elusive. The protection of the peritoneal membrane from long-term toxic and metabolic effects of high GDP-containing, conventional, glucose-based solutions is a prime objective to improve PD outcome. Recent development of new, more biocompatible, PD solutions should help to preserve peritoneal membrane function, promote ultrafiltration, improve nutritional status and, hopefully, preserve peritoneal membrane and improve overall PD outcomes. Elucidation of molecular mechanisms involved in the cellular responses leading to peritoneal fibrosis and angiogenesis spurs new therapeutic strategies that might protect the peritoneal membrane against the consequences of longstanding PD.