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.     

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.     

Clinical outcomes and peritoneal histology in patients starting peritoneal dialysis are related to diabetic status and serum albumin levels

Peritoneal morphological changes seem to be related to dialysis solutions bioincompatibility and to infections, but the uremic milieu per se may also contribute to peritoneal changes. The influence of diabetes and diabetes-associated comorbidities on peritoneal histological changes in the pre-dialysis stage have been insufficiently studied. The aim of this study is to analyze the effect of diabetes and serum albumin levels on peritoneal histology and certain clinical variables such as peritoneal permeability, technique failure, and general mortality in patients starting peritoneal dialysis (PD) treatment. Eighteen PD patients without diabetes (uremic non-diabetic group, U-ND) and 65 with diabetes (uremic diabetic group, U-D) were studied prospectively. Clinical and biochemical variables were registered, and a parietal peritoneum biopsy was obtained at the time of the peritoneal catheter placement. Peritoneal histology was evaluated by light microscopy and immunohistochemistry. A control group of 15 non-uremic, non-diabetic (NU-ND) patients who underwent non-complicated elective abdominal surgery was also studied and used as control. The proportion of patients with peritoneal morphological changes as evaluated by light microscopy was higher in the two groups of uremic patients than in the control. The U-D group had higher mesothelial loss (40.9 vs 29.4%), higher mesothelial basement membrane thickening (45.5 vs 23.5%), higher proportion of vascular wall thickening/sclerosis (39.7 vs 11.1%), and higher proportion of inflammatory infiltrate (45.4 vs 23.6%) than the U-ND group. Uremic patients had lower density of mesothelial cells and higher density of inflammatory cells than the control, as evaluated by immunohistochemistry. These changes were even more striking in the U-D group than in the U-ND group. On the other hand, inflammatory infiltration to the peritoneum, mesothelial cell loss, and mesothelial basement membrane thickening were associated with higher technique failure and mortality. However, when the serum albumin level was introduced into the model, the aforementioned associations became nonsignificant. In conclusion, uremia and diabetes were associated with important peritoneal histological changes before starting PD treatment. Diabetes associated with uremia was more strongly related to the peritoneal changes than uremia per se. Hypoalbuminemia and peritoneal inflammatory infiltrate were markedly associated with technique failure and mortality in patients starting PD treatment.     

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.     

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.     

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。     

Does uremia cause vascular dysfunction?

Vascular dysfunction induced by uremia has 4 main aspects. (1) Atherosclerosis is increased. Intima-media thickness is increased, and animal studies have established that uremia accelerates atherosclerosis. Uremic toxins are involved in several steps of atherosclerosis. Leukocyte activation is stimulated by guanidines, advanced glycation end products (AGE), p-cresyl sulfate, platelet diadenosine polyphosphates, and indoxyl sulfate. Endothelial adhesion molecules are stimulated by indoxyl sulfate. Migration and proliferation of vascular smooth muscle cells (VSMC) are stimulated by local inflammation which could be triggered by indoxyl sulfate and AGE. Uremia is associated with an increase in von Willebrand factor, thrombomodulin, plasminogen activator inhibitor 1, and matrix metalloproteinases. These factors contribute to thrombosis and plaque destabilization. There is also a decrease in nitric oxide (NO) availability, due to asymmetric dimethylarginine (ADMA), AGE, and oxidative stress. Moreover, circulating endothelial microparticles (EMP) are increased in uremia, and inhibit the NO pathway. EMP are induced in vitro by indoxyl sulfate and p-cresyl sulfate. (2) Arterial stiffness occurs due to the loss of compliance of the vascular wall which induces an increase in pulse pressure leading to left ventricular hypertrophy and a decrease in coronary perfusion. Implicated uremic toxins are ADMA, AGE, and oxidative stress. (3) Vascular calcifications are increased in uremia. Their formation involves a transdifferentiation process of VSMC into osteoblast-like cells. Implicated uremic toxins are mainly inorganic phosphate, as well as reactive oxygen species, tumor necrosis factor and leptin. (4) Abnormalities of vascular repair and neointimal hyperplasia are due to VSMC proliferation and lead to severe reduction of vascular lumen. Restenosis after coronary angioplasty is higher in dialysis than in nondialysis patients. Arteriovenous fistula stenosis is the most common cause of thrombosis. Uremic toxins such as indoxyl sulfate and some guanidine compounds inhibit endothelial proliferation and wound repair. Endothelial progenitor cells which contribute to vessel repair are decreased and impaired in uremia, related to high serum levels of β(2)-microglobulin and indole-3 acetic acid. Overall, there is a link between kidney function and cardiovascular risk, as emphasized by recent meta-analyses. Moreover, an association has been reported between cardiovascular mortality and uremic toxins such as indoxyl sulfate, p-cresol and p-cresyl sulfate.     

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.     

Peritoneal mesothelial cell biology in peritoneal dialysis

SUMMARY: Progressive peritoneal membrane hyperpermeability, ultrafiltration failure, and peritoneal fibrosis have been observed in long-term peritoneal dialysis (PD) patients, and these alterations in peritoneal structure and function may be responsible for the poor technique survival in PD. While frequent and/or severe peritonitis can result in alterations of the peritoneum, continuous exposure of the peritoneum to PD solutions may also adversely affect peritoneal structure and function. Peritoneal mesothelial cells (PMC) are directly and continuously exposed to unphysiological components of PD solution. Low pH, lactate, hyperosmolality, and glucose degradation products (GDP) reduce PMC viability and proliferation. High glucose, GDP, and advanced glycation end products (AGE) upregulate vascular endothelial growth factor (VEGF), monocyte chemoattractant protein (MCP)-1, transforming growth factor (TGF)-β1, plasminogen activator inhibitor (PAI)-1, and extracellular matrix protein expression by PMC, and may thus lead to peritoneal hyperpermeability, ultrafiltration failure, and peritoneal fibrosis, as observed in long-term PD. Activation of diacylglycerol (DAG)-protein kinase C (PKC) and generation of reactive oxygen species (ROS) are important upstream signalling events in high glucose-induced PMC activation. Thus, strategies to inhibit high glucose-induced PKC activation and ROS generation and the use of new PD solutions with non-glucose osmotic agents, pH neutral solutions, or solutions containing low GDP may allow better preservation of the structural and functional integrity of the peritoneal membrane during long-term PD.     

Advanced glycation end products in clinical nephrology

As a result of oxidative and carbonyl stress, advanced glycation end products (AGEs) are involved in the pathogenesis of severe and frequent diseases and their fatal vascular/cardiovascular complications, i.e. diabetes mellitus and its complications (nephropathy, angiopathy, neuropathy and retinopathy, renal failure and uremic and dialysis-associated complications), atherosclerosis and dialysis-related amyloidosis, neurodegenerative diseases, and rheumatoid arthritis. They are formed via non-enzymatic glycation which is specifically enhanced through the presence of oxidative and carbonyl stress, and their ability to form glycoxidation products in peptide and protein structures finally modulating or inducing biological reactivity. Food can be another source of AGEs; however, high serum AGEs in hemodialysis patients might reflect nutritional status better. Several methods of renal replacement therapy have been studied in connection with the AGE removal, but unfortunately the possibilities are still unsatisfactory even if high flux dialysis, hemofiltration, or hemodiafiltration give better results than conventional low flux dialysis. AGEs are currently being studied in the patients on peritoneal dialysis as their precursors can be formed in the dialysis fluid. AGEs can cause damage to the peritoneum and so a loss of ultrafiltration capacity. Many compounds give promising results in AGE inhibition (inhibition of formation of AGEs, inhibition of their action or degradation of AGEs), are tested for these properties, and eventually undergo clinical studies (e.g. aminoguanidine, OPB-9195, pyridoxamine, antioxidants, N-phenacylthiazolium bromide, antihypertensive drugs, angiotensin-converting enzyme inhibitors and angiotensin II receptor-1 antagonists).     

Dialysate cancer antigen 125 in long-term peritoneal dialysis patients

Structural and functional peritoneal membrane changes are associated with long-term peritoneal dialysis. These changes can lead to ultrafiltration failure and peritoneal fibrosis, reducing the efficacy of the peritoneal membrane to remove waste and balance fluid and electrolytes. The loss of mesothelial cells from the basement membrane is one of the major characteristics in peritoneal membrane structural change. Thus, if the reduction of peritoneal mesothelial cell mass in peritoneal dialysis patients is monitored, signs of ultrafiltration failure and peritoneal fibrosis can be detected early. One of biomarkers that can be used to indicate the change in peritoneal mesothelial cell mass is CA125, which is produced by mesothelial cells. In this article, we review the measurement and clinical use of CA125 in peritoneal dialysate effluent. Additionally, we address the data and studies on the association between dialysate CA125 levels and factors related to ultrafiltration failure and peritoneal fibrosis, including the parameters used to monitor the functional status of the peritoneal membrane. Our review shows that dialysate CA125 can be used to evaluate the peritoneal membrane in noninfected patients to predict peritoneal fibrosis, and it can also be used as a biomarker of biocompatible dialysis solutions.     

Incomplete activation of intraperitoneal clindamycin phosphate during peritoneal dialysis

Clindamycin phosphate (C-PO4) must be hydrolyzed to the active antibiotic, but whether this occurs within the peritoneal cavity during peritoneal dialysis is unknown. Therapeutic peritoneal levels are difficult to achieve after intravenous administration, so direct intraperitoneal instillation is preferred in treating dialysis-associated peritonitis. Therefore, the activation of C-PO4 in peritoneal dialysate was investigated. Fresh and 'uremic' peritoneal dialysates of 1.5 and 4.25% dextrose concentrations at pHs of 5.1 and 7.4 did not activate C-PO4. Clindamycin hydrochloride in this same fluid was active, ruling out uremic deactivators. A patient with peritonitis was treated with intraperitoneal C-PO4, and therapeutic (greater than 5 micrograms/ml) serum and peritoneal levels were achieved. Infected (exudative) peritoneal dialysate drained from another patient with peritonitis activated C-PO4 in vitro. Commercial alkaline phosphatase added to uremic dialysate also activated C-PO4 in vitro. C-PO4 was instilled into the peritoneal cavities of 10 noninfected patients. Exposure to the peritoneal membrane at two concentrations resulted in a 3% activation of C-PO4. From these observations it is clear that C-PO4 is only partially activated intraperitoneally. Uremia or uremic products in the dialysate do not deactivate the antibiotic. Exudative material (bacteria, white blood cells and proteins) in infected dialysate contribute to activation of C-PO4. The peritoneal membrane further assists in activation. We recommend that C-PO4 be administered at a concentration of 167 mg/l of dialysate to ensure therapeutic peritoneal levels of the active antibiotic, especially after the exudative phase clears.     

Long-term peritoneal membrane changes

There is increasing evidence that long-term peritoneal dialysis (PD) is associated with structural changes in the peritoneal membrane. These consist of thickening of the sub-mesothelial space owing to collagen deposition and alterations in small blood vessel morphology. These alterations become more pronounced with duration of PD therapy. These changes are associated with a tendency to increasing small solute transport rate with reduced ultrafiltration. The relationship between these structural and functional changes remains unknown, but the evidence suggests that both peritonitis and exposure to dialysate contribute. The most likely components of the fluid responsible for this effect are glucose and/or its degradation products generated during heat sterilisation. Serial monitoring of peritoneal function is well established, but repeat biopsies are not practical. Effluent markers are not yet of proven value but do alter in response to a change in dialysate composition. Hopefully, a combination of reduced inflammation and more biocompatible fluids will reduce long-term changes in peritoneal membrane structure and function with a consequent improvement in patient and technique survival.     

Advanced glycation end-products and peritoneal sclerosis

Long-term continuous ambulatory peritoneal dialysis (CAPD) often causes peritoneal fibrosis and sclerosis with a loss of function, and some CAPD patients develop sclerosing encapsulating peritonitis. Glucose-based peritoneal dialysis fluids readily produce glucose degradation products by heat sterilization, and glucose degradation products accelerate the formation of advanced glycation end-products (AGE) in the peritoneal cavity. The accumulation of AGE is observed in peritoneal mesothelial and submesothelial layers in CAPD patients, accompanied by enhanced expression of various growth factors and peritoneal thickening. The expression of transforming growth factor-beta1 (TGF-beta1), macrophage-colony stimulating factor, and vascular endothelial growth factor (VEGF) is distributed in the peritoneum similarly to that of AGE. In CAPD patients with low ultrafiltration (UF) capacity, peritoneal membrane is thickened owing to an increase in the number of cells such as fibroblasts and macrophages and collagen in the submesothelial layer. AGE is detected in the fibroblasts and macrophages as well as degenerated collagen. These cells in the submucosal layer are almost positive for the receptor for AGE (RAGE) and uptake AGE. The intensity of AGE accumulation and the expression of growth factors are associated with the severity of UF impairment. In fact, the accumulation of AGE and the expression of growth factors are recognized most markedly in the peritoneum of CAPD patients with low UF and sclerosing encapsulating peritonitis. In conclusion, long-time CAPD with heat-sterilized peritoneal dialysis fluid promotes AGE accumulation in the peritoneal membrane and alteration in peritoneal cell function and dialysis quality, followed by peritoneal sclerosis, and, finally, sclerosing encapsulating peritonitis.     

Gentamicin removal during intermittent peritoneal dialysis

Gentamicin removal during intermittent peritoneal dialysis was studied in 13 uremic patients. The peak serum level after 80 mg of gentamicin intravenous drip was 6.00 +/- 1.3 micrograms/ml with a serum half-life of 13.6 +/- 4.07 h. The gentamicin dialysate level did not correlate with the corresponding serum concentration. The peritoneal gentamicin clearance (10.0 +/- 3.65 ml/min) correlated with the rate of protein loss, but not with the peritoneal clearances of urea and creatinine. When 4% glucose dialysate was used, the clearance of the drug increased considerably along with the ultrafiltration rate. Adding gentamicin (5 micrograms/ml) to the dialysate resulted in a sustained serum drug level. The mechanism of gentamicin transport through the peritoneal membrane is discussed. The study demonstrated significant removal of gentamicin during intermittent peritoneal dialysis.     

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.     

Peritoneal transport of vancomycin during peritoneal dialysis

The peritoneal transport of vancomycin during peritoneal dialysis was studied in 11 uremic patients following intravenous and intraperitoneal administration of vancomycin. The half-life of vancomycin was about 18 h and the clearance of vancomycin 6.1 ml/min (range 4.2--9.8) during the period of dialysis. Following intraperitoneal administration of vancomycin 50 micrograms/ml of dialysate, serum concentrations from 5.1 to 21.5 micrograms/ml were obtained and 35% of the instilled amount of vancomycin was absorbed during 15 h of dialysis. The peritoneal transport of vancomycin indicates that the dosage should be increased during peritoneal dialysis. Peritonitis caused by Staphylococcus aureus may be treated by peritoneal dialysis with vancomycin added to the dialysate.     

Vascular endothelial growth factor is essential for hyperglycemia-induced structural and functional alterations of the peritoneal membrane.

Long-term peritoneal dialysis is associated with the development of functional and structural alterations of the peritoneal membrane. Long-term exposure to the high glucose concentrations in conventional peritoneal dialysate has been implicated in the pathogenesis of peritoneal hyperpermeability and neoangiogenesis. Vascular endothelial growth factor (VEGF) is an endothelial-specific growth factor that potently stimulates microvascular permeability and proliferation. High glucose exposure upregulates VEGF expression in various cell types and tissues. This study investigated whether VEGF plays a pathogenetic role in hyperglycemia-induced microvascular dysfunction in the peritoneal membrane. The peritoneal microcirculation of streptozotocin-induced diabetic rats and age-matched controls was studied in vivo with a combination of functional and morphologic techniques. The diabetic microcirculation was characterized by an elevated transport of small solutes, indicating the presence of an increased effective vascular surface area. The leakage of FITC-albumin was more rapid in diabetic vessels, suggesting hyperpermeability for macromolecules. Structurally, an increased vascular density with focal areas of irregular capillary budding was found in the diabetic peritoneum. The hyperglycemia-induced structural and functional microvascular alterations were prevented by long-term treatment with neutralizing anti-VEGF monoclonal antibodies, whereas treatment with isotype-matched control antibodies had no effect. VEGF blockade did not influence microvascular density or macromolecular leakage in control rats, demonstrating specificity for the hyperglycemia-induced alterations. The present results thus support an causative link among high glucose exposure, upregulation of VEGF, and peritoneal microvascular dysfunction.     

Optimal use of peritoneal dialysis fluids in type 2 diabetes mellitus patients

The glucose side-effects, the main osmotic agent in conventional peritoneal dialysis (PD) solutions, are structural and functional changes of the peritoneal membrane, especially diabetic alterations in the microvasculature. Therefore, hyperpermeability with high small solutes transport and less ultrafiltration necessitates more and more high glucose concentration solutions. Glucose degradation products (PDF) and advanced glycation end-products (AGE) are formed and may induce peritoneal membrane alterations. More biocompatible solutions have to be used with less PDF and physiological pH. Icodextrin containing PD solutions have beneficial effect on sustained ultrafiltration for long dwells in PD, limitating fluid overload common in PD patients above all during peritonitis episodes. Amino acid-based PD solutions contribute to the prevention of malnutrition often observed in the diabetic PD population.     

Oxidative stress during peritoneal dialysis: implications in functional and structural changes in the membrane

Progressive peritoneal fibrosis, membrane hyperpermeability, and ultrafiltration failure have been observed in patients on long-term peritoneal dialysis (PD). The present study tested the hypothesis that reactive oxygen species (ROS) generated by conventional PD solution (PDS) mediate functional and structural alterations of peritoneal membrane in vivo. Sprague-Dawley rats were randomized to control, PDS, PDS with an antioxidant, and PDS with an angiotensin II (Ang II) receptor blocker. Commercial PDS containing 3.86% glucose (20-30 ml) with or without N-acetylcystein (NAC) 10 mM or losartan 5 mg/kg was administered intraperitoneally twice a day for 12 weeks. Control rats received sham injection. Rats treated with PDS had significantly lower drain volume and D(4)/D(0) glucose, but higher D(4)/P(4) creatinine and increased membrane thickness and endothelial NOS (eNOS) expression compared to control rats. Omental transforming growth factor (TGF)-beta1, vascular endothelial growth factor (VEGF), collagen I, and heat-shock protein (hsp) 47 expression and lipid peroxide levels and dialysate VEGF and Ang II concentrations were significantly increased in rats treated with PDS compared to control. All of these changes were prevented by both NAC and losartan. In conclusion, the present study demonstrates that ROS generated by conventional PDS are, in large part, responsible for peritoneal fibrosis and membrane hyperpermeability. We suggest that antioxidants or Ang II receptor blockers may allow better preservation of the structural and functional integrity of the peritoneal membrane during long-term PD.