Genetic and clinical factors influence the baseline permeability of the peritoneal membrane

C allele in transforming growth factor-β1 rs1800471 gene polymorphisms might indicate a protective feature in encapsulating peritoneal sclerosis development

INTRODUCTION

Peritoneal fibrosis may progress in peritoneal dialysis (PD) patients to a fatal clinical condition called encapsulating peritoneal sclerosis (EPS). Transforming growth factor (TGF)-β plays a pivotal role in the pathogenesis of peritoneal fibrosis. We aimed to investigate the association among polymorphisms in the gene encoding TGF-β1, which were -509C/T (rs1800469), +869T/C (rs1982073), and +915G/C (rs1800471) in EPS patients.

METHODS

A total of 16 PD patients who were clinically and radiologically diagnosed with EPS were enrolled and 22 age- and gender-matched PD patients were selected as the non-EPS group.

RESULTS

G allele frequency at the rs1800471 gene polymorphism was significantly higher in the EPS group than non-EPS group (p = 0.005). Interestingly, the non-EPS group patients had CC or CG polymorphisms.

CONCLUSION

C allele in TGF-β1 rs1800471 gene polymorphisms might indicate a protective feature in EPS development. Knowing the presence of polymorphism may be effective in selecting renal replacement therapy in patients.

Fibrosis of Peritoneal Membrane, Molecular Indicators of Aging and Frailty Unveil Vulnerable Patients in Long-Term Peritoneal Dialysis

Peritoneal membrane status, clinical data and aging-related molecules were investigated as predictors of long-term peritoneal dialysis (PD) outcomes. A 5-year prospective study was conducted with the following endpoints: (a) PD failure and time until PD failure, (b) major cardiovascular event (MACE) and time until MACE. A total of 58 incident patients with peritoneal biopsy at study baseline were included. Peritoneal membrane histomorphology and aging-related indicators were assessed before the start of PD and investigated as predictors of study endpoints. Fibrosis of the peritoneal membrane was associated with MACE occurrence and earlier MACE, but not with the patient or membrane survival. Serum α-Klotho bellow 742 pg/mL was related to the submesothelial thickness of the peritoneal membrane. This cutoff stratified the patients according to the risk of MACE and time until MACE. Uremic levels of galectin-3 were associated with PD failure and time until PD failure. This work unveils peritoneal membrane fibrosis as a window to the vulnerability of the cardiovascular system, whose mechanisms and links to biological aging need to be better investigated. Galectin-3 and α-Klotho are putative tools to tailor patient management in this home-based renal replacement therapy.

Gene polymorphisms of VEGF and KDR are associated with initial fast peritoneal solute transfer rate in peritoneal dialysis

Background

Peritoneal dialysis (PD) is an effective and successful renal replacement therapy. The baseline peritoneal solute transfer rate (PSTR) is related to local membrane inflammation and may be partially genetically determined. Herein, we focused on vascular endothelial growth factor (VEGF) and its receptor, kinase insert domain containing receptor (KDR).

Methods

This study recruited 200 PD patients from Renji Hospital in Shanghai, China. We analysed the association between the polymorphisms of VEGF and KDR and the 4-hour dialysate-to-plasma ratio for creatinine (4 h D/P Cr), which was measured between one and three months after initiating PD.

Results

The CC genotype in VEGF rs3025039 and the AA genotype in KDR rs2071559 were both positively associated with a fast baseline PSTR (VEGF rs3025039 CC vs. TT + TC: 0.65 ± 0.12 vs. 0.61 ± 0.11; P = 0.029; KDR rs2071559 AA vs. GA + GG: 0.65 ± 0.12 vs. 0.62 ± 0.12; P = 0.039).

Conclusion

Baseline PSTR was partly determined by VEGF and KDR gene polymorphisms.

High intraperitoneal interleukin-6 levels predict ultrafiltration (UF) insufficiency in peritoneal dialysis patients: A prospective cohort study

Introduction

UF insufficiency is a major limitation in PD efficiency and sustainability. Our study object to investigate the efficacy of intraperitoneal inflammation marker, IL-6 level as a predictor of UF insufficiency in continuous ambulatory peritoneal dialysis (CAPD) patients.

Methods

Stable prevalent CAPD patients were enrolled in this prospective study. IL-6 concentration in the overnight effluent was determined and expressed as the IL-6 appearance rate (IL-6 AR). Patients were divided into two groups according to the median of IL-6 AR and prospectively followed up until death, transfer to permanent HD, recovery of renal function, kidney transplantation, transfer to other centers, lost to follow-up or to the end of study (January 31, 2021). Factors associated with UF capacity as well as dialysate IL-6 AR were assessed by multivariable linear regression. Cox proportional hazards model was used to examine the association between dialysate IL-6 AR and UF insufficiency.

Results

A total of 291 PD patients were enrolled, including 148 males (51%) with a mean age of 56.6 ± 14.1 years and a median PD duration of 33.4 (12.7–57.5) months. No correlation was found between dialysate IL-6 AR and UF capacity at baseline. PD duration was found positively correlated with baseline dialysate IL-6 AR, while 24h urine volume was negatively correlated with baseline dialysate IL-6 AR (P < 0.05). By the end of study, UF insufficiency was observed in 56 (19.2%) patients. Patients in the high IL-6 AR group showed a significantly inferior UF insufficiency-free survival when compared with their counterparts in the low IL-6 AR group (P = 0.001). In the multivariate Cox regression analysis, after adjusting for DM, previous peritonitis episode and 24h urine volume, higher baseline dialysate IL-6 AR (HR 3.639, 95% CI 1.776–7.456, P = 0.002) were associated with an increased risk of UF insufficiency. The area under the ROC curve (AUC) for baseline IL-6 AR to predict UF insufficiency was 0.663 (95% CI, 0.580–0.746; P < 0.001).

Conclusion

Our study suggested that the dialysate IL-6 AR could be a potential predictor of UF insufficiency in patients undergoing PD.

Aging of the Peritoneal Dialysis Membrane

Long-term peritoneal dialysis as currently performed, causes structural and functional alterations of the peritoneal dialysis membrane. This decay is brought about by the continuous exposure to commercially available glucose-based dialysis solutions. This review summarizes our knowledge on the peritoneum in the initial phase of PD, during the first 2 years and the alterations in function and morphology in long-term PD patients. The pseudohypoxia hypothesis is discussed and how this glucose-induced condition can be used to explain all peritoneal alterations in long-term PD patients. Special attention is paid to the upregulation of hypoxia inducing factor-1 and the subsequent stimulation of the genes coding for glucose transporter-1 (GLUT-1) and the growth factors transforming growth factor-β (TGFβ), vascular endothelial growth factor (VEGF), plasminogen growth factor activator inhibitor-1 (PAI-1) and connective tissue growth factor (CTGF). It is argued that increased pseudohypoxia-induced expression of GLUT-1 in interstitial fibroblasts is the key factor in a vicious circle that augments ultrafiltration failure. The practical use of the protein transcripts of the upregulated growth factors in peritoneal dialysis effluent is considered. The available and developing options for prevention and treatment are examined. It is concluded that low glucose degradation products/neutral pH, bicarbonate buffered solutions with a combination of various osmotic agents all in low concentration, are currently the best achievable options, while other accompanying measures like the use of RAAS inhibitors and tamoxifen may be valuable. Emerging developments include the addition of alanyl glutamine to the dialysis solution and perhaps the use of nicotinamide mononucleotide, available as nutritional supplement.

Glycoprotein 96 in Peritoneal Dialysis Effluent-Derived Extracellular Vesicles: A Tool for Evaluating Peritoneal Transport Properties and Inflammatory Status

Background

Extracellular vesicles (EVs) from peritoneal dialysis effluent (PDE), containing molecules such as proteins and microRNAs (miRNAs), may be potential biological markers to monitor peritoneal function or injury. Peritoneal inflammation is an important determinant of peritoneal solute transport rate (PSTR). Thus, the aim of this study is to determine whether the specific proteins capable of evaluating the PSTR could be found in PDE-EVs, and explore the underlying mechanism for the association between PSTR and peritoneal inflammation.

Methods

Sixty patients undergoing peritoneal dialysis (PD) were divided into two groups: high/high average transport (H/A) group (PET >0.65) and low/low average transport (L/A) group (PET <0.65). EVs derived from PDE (PDE-EVs) were isolated by ultracentrifugation. Proteomic analysis was performed to explore the differentially expressed proteins and identify the potential biomarkers in PDE-EVs from the two groups, and we focused on glycoprotein 96 (GP96) as it could be involved in the inflammatory process. The expression of GP96 in PDE-EVs and inflammatory cytokines was quantified by real-time PCR and enzyme-linked immunosorbent assay. The infiltration of macrophages and neutrophils into the peritoneum was detected using immunohistochemistry in a PD rat model.

Results

The expression of PDE-EVs-GP96 was significantly higher in the H/A group, and was positively correlated with the PSTR and the level of the inflammatory factor interleukin (IL)-6. GP96-enriched EVs enhanced the secretion of proinflammatory cytokines IL-1β, IL-6, tumor necrosis factor (TNF)-α, and IL-8 in macrophages, which was reversed by a pharmacological GP96-specific inhibitor (PU-WS13). The GP96 inhibitor also reduced local peritoneal inflammation by decreasing the infiltration of inflammatory cells and levels of proinflammatory cytokines (IL-6 and TNF-α) and chemokines (CCL2, CXCL1, and CXCL2) in a PD rat model.

Conclusions

PDE-EVs-GP96 is a new promising tool to evaluate the status of peritoneal inflammation and PSTR, and the mechanism may be related to affecting the inflammatory properties of macrophages.

The Peritoneal Membrane—A Potential Mediator of Fibrosis and Inflammation among Heart Failure Patients on Peritoneal Dialysis

Peritoneal dialysis is a feasible, cost-effective, home-based treatment of renal replacement therapy, based on the dialytic properties of the peritoneal membrane. As compared with hemodialysis, peritoneal dialysis is cheaper, survival rate is similar, residual kidney function is better preserved, fluid and solutes are removed more gradually and continuously leading to minimal impact on hemodynamics, and risks related to a vascular access are avoided. Those features of peritoneal dialysis are useful to treat refractory congestive heart failure patients with fluid overload. It was shown that in such patients, peritoneal dialysis improves functional status and quality of life, reduces hospitalization rate, and may decrease mortality rate. High levels of serum proinflammatory cytokines and fibrosis markers, among other factors, play an important part in congestive heart failure pathogenesis and progression. We demonstrated that those levels decreased following peritoneal dialysis treatment in refractory congestive heart failure patients. The exact mechanism of beneficial effect of peritoneal dialysis in refractory congestive heart failure is currently unknown. Maintenance of fluid balance, leading to resetting of neurohumoral activation towards a more physiological condition, reduced remodeling due to the decrease in mechanical pressure on the heart, decreased inflammatory cytokine levels and oxidative stress, and a potential impact on uremic toxins could play a role in this regard. In this paper, we describe the unique characteristics of the peritoneal membrane, principals of peritoneal dialysis and its role in heart failure patients.

A genome-wide association study suggests correlations of common genetic variants with peritoneal solute transfer rates in patients with kidney failure receiving peritoneal dialysis

Movement of solutes across the peritoneum allows for the use of peritoneal dialysis to treat kidney failure. However, there is a large inter-individual variability in the peritoneal solute transfer rate (PSTR). Here, we tested the hypothesis that common genetic variants are associated with variability in PSTR. Of the 3561 participants from 69 centers in six countries, 2850 with complete data were included in a genome-wide association study. PSTR was defined as the four-hour dialysate/plasma creatinine ratio from the first peritoneal equilibration test after starting PD. Heritability of PSTR was estimated using genomic-restricted maximum-likelihood analysis, and the association of PSTR with a genome-wide polygenic risk score was also tested. The mean four-hour dialysate/plasma creatinine ratio in participants was 0.70. In 2212 participants of European ancestry, no signal reached genome-wide significance but 23 single nucleotide variants at four loci demonstrated suggestive associations with PSTR. Meta-analysis of ancestry-stratified regressions in 2850 participants revealed five single-nucleotide variants at four loci with suggestive correlations with PSTR. Association across ancestry strata was consistent for rs28644184 at the KDM2B locus. The estimated heritability of PSTR was 19%, and a permuted model polygenic risk score was significantly associated with PSTR. Thus, this genome-wide association study of patients receiving peritoneal dialysis bolsters evidence for a genetic contribution to inter-individual variability in PSTR.

AQP1 Promoter Variant, Water Transport, and Outcomes in Peritoneal Dialysis

BACKGROUND

Variability in ultrafiltration influences prescriptions and outcomes in patients with kidney failure who are treated with peritoneal dialysis. Variants in AQP1, the gene that encodes the archetypal water channel aquaporin-1, may contribute to that variability.

METHODS

We gathered clinical and genetic data from 1851 patients treated with peritoneal dialysis in seven cohorts to determine whether AQP1 variants were associated with peritoneal ultrafiltration and with a risk of the composite of death or technique failure (i.e., transfer to hemodialysis). We performed studies in cells, mouse models, and samples obtained from humans to characterize an AQP1 variant and investigate mitigation strategies.

RESULTS

The common AQP1 promoter variant rs2075574 was associated with peritoneal ultrafiltration. Carriers of the TT genotype at rs2075574 (10 to 16% of patients) had a lower mean (±SD) net ultrafiltration level than carriers of the CC genotype (35 to 47% of patients), both in the discovery phase (506±237 ml vs. 626±283 ml, P = 0.007) and in the validation phase (368±603 ml vs. 563±641 ml, P = 0.003). After a mean follow-up of 944 days, 139 of 898 patients (15%) had died and 280 (31%) had been transferred to hemodialysis. TT carriers had a higher risk of the composite of death or technique failure than CC carriers (adjusted hazard ratio, 1.70; 95% confidence interval [CI], 1.24 to 2.33; P = 0.001), as well as a higher risk of death from any cause (24% vs. 15%, P = 0.03). In mechanistic studies, the rs2075574 risk variant was associated with decreases in AQP1 promoter activity, aquaporin-1 expression, and glucose-driven osmotic water transport. The use of a colloid osmotic agent mitigated the effects of the risk variant.

CONCLUSIONS

A common variant in AQP1 was associated with decreased ultrafiltration and an increased risk of death or technique failure among patients treated with peritoneal dialysis. (Funded by the Swiss National Science Foundation and others.).

Traduction des Recommandations de l'ISPD pour l'évaluation du dysfonctionnement de la membrane péritonéale chez l'adulte

Informations concernant cette traductionDans le cadre d’un accord de partenariat entre l’ISPD et le RDPLF, le RDPLF est le traducteur français officiel des recommandations de l’ISPD. La traduction ne donne lieu à aucune compensation financière de la part de chaque société et le RDPLF s’est engagé à traduire fidèlement le texte original sous la responsabilité de deux néphrologues connus pour leur expertise dans le domaine. Avant publication le texte a été soumis à l’accord de l’ISPD. La traduction est disponible sur le site de l’ISPD et dans le Bulletin de la Dialyse à Domicile.Le texte est, comme l’original, libremement téléchargeable sous licence copyright CC By 4.0https://creativecommons.org/licenses/by/4.0/Cette traduction est destinée à aider les professionnels de la communauté francophone à prendre connaissance des recommandations de l’ISPD dans leur langue maternelle. Toute référence dans un article doit se faire au texte original en accès libre :Peritoneal Dialysis International https://doi.org/10.1177/0896860820982218 Dans les articles rédigés pour des revues françaises, conserver la référence à la version originale anglaise ci dessus, mais ajouter «version française  https://doi.org/10.25796/bdd.v4i3.62673"»TraducteursDr Christian Verger, néphrologue, président du RDPLFRDPLF, 30 rue Sere Depoin, 95300 Pontoise – FranceProfesseur Max Dratwa, néphrologueHôpital Universitaire Brugmann – Bruxelles – Belgique

The prognosis and risk factors of baseline high peritoneal transporters on patients with peritoneal dialysis

The relationship between baseline high peritoneal solute transport rate (PSTR) and the prognosis of peritoneal dialysis (PD) patients remains unclear. The present study combined clinical data and basic experiments to investigate the impact of baseline PSTR and the underlying molecular mechanisms. A total of 204 incident CAPD patients from four PD centres in Shanghai between 1 January 2014 and 30 September 2020 were grouped based on a peritoneal equilibration test after the first month of dialysis. Analysed with multivariate Cox and logistic regression models, baseline high PSTR was a significant risk factor for technique failure (AHR 5.70; 95% CI 1.581 to 20.548 p = 0.008). Baseline hyperuricemia was an independent predictor of mortality (AHR 1.006 95%CI 1.003 to 1.008, p < 0.001) and baseline high PSTR (AOR 1.007; 95%CI 1.003 to 1.012; p = 0.020). Since uric acid was closely related to high PSTR and adverse prognosis, the in vitro experiments were performed to explore the underlying mechanisms of which uric acid affected peritoneum. We found hyperuricemia induced epithelial‐to‐mesenchymal transition (EMT) of cultured human peritoneal mesothelial cells by activating TGF‐β1/Smad3 signalling pathway and nuclear transcription factors. Conclusively, high baseline PSTR induced by hyperuricaemia through EMT was an important reason of poor outcomes in CAPD patients.

Orosomucoid can predict baseline peritoneal transport characteristics in peritoneal dialysis patients and reduce peritoneal proteins loss

Peritoneal dialysis (PD) is a replacement therapy for end-stage renal disease patients. In the first 4-8 weeks of PD, the patients were given an empirical dialysis prescription due to unknown peritoneal transport characteristics. Proteomic analysis could be used to identify serum biomarkers. In a discovery set, patients were divided into three groups according to the peritoneal equilibration test (PET) results: high (H), high average (HA), low average and low (LA&L) groups. A total of 1051 identified proteins were screened by Nano HPLC-MS/MS. The top two proteins among different peritoneal transport characteristics were Orosomucoid 2 (ORM2) and C-reactive protein (CRP). In a validation set, CRP was significantly elevated in H group than LA&L group, consistent with proteomic analysis. Serum ORM2 was enhanced in LA&L group compared with H and HA group. The expression of ORM2 in peritoneum was also enriched in LA&L group. At last, supplying exogenous ORM could reduce peritoneal proteins loss, without causing a pro-inflammatory response in mice. ORM2 and CRP could be used as biomarkers to predict the baseline peritoneal transport characteristics, and guide the early PD treatment. ORM may serve as a novel therapeutic target for decreasing peritoneal proteins loss in PD patients. SIGNIFICANCE: Peritoneal dialysis (PD) is associated with the functional alterations of the peritoneum. PD patients were often given an empirical dialysis prescription due to the unknown peritoneal transport characteristics in the first 4-8 weeks since PD started. Therefore, it is urgently needed to find biomarkers to predict the baseline peritoneal transport characteristics. In this study, we employed a proteomic analysis to identify serum biomarkers in a training set and verified the screened biomarkers in a validation set. We also found that Orosomucoid (ORM) has the potential to decrease peritoneal proteins loss in PD therapy.

ISPD recommendations for the evaluation of peritoneal membrane dysfunction in adults: Classification, measurement, interpretation and rationale for intervention

Lay summary

Peritoneal dialysis (PD) uses the peritoneal membrane for dialysis. The peritoneal membrane is a thin layer of tissue that lines the abdomen. The lining is used as a filter to help remove extra fluid and poisonous waste from the blood. Everybody is unique. What is normal for one person’s membrane may be very different from another person’s. The kidney care team wants to provide each person with the best dialysis prescription for them and to do this they must evaluate the person’s peritoneal lining. Sometimes dialysis treatment itself can cause the membrane to change after some years. This means more assessments (evaluations) will be needed to determine whether the person’s peritoneal membrane has changed. Changes in the membrane may require changes to the dialysis prescription. This is needed to achieve the best dialysis outcomes. A key tool for these assessments is the peritoneal equilibration test (PET). It is a simple, standardized and reproducible tool. This tool is used to measure the peritoneal function soon after the start of dialysis. The goal is to understand how well the peritoneal membrane works at the start of dialysis. Later on in treatment, the PET helps to monitor changes in peritoneal function. If there are changes between assessments causing problems, the PET data may explain the cause of the dysfunction. This may be used to change the dialysis prescription to achieve the best outcomes. The most common problem with the peritoneal membrane occurs when fluid is not removed as well as it should be. This happens when toxins (poisons) in the blood cross the membrane more quickly than they should. This is referred to as a fast peritoneal solute transfer rate (PSTR). Since more efficient fluid removal is associated with better outcomes, developing a personal PD prescription based on the person’s PSTR is critically important. A less common problem happens when the membrane fails to work properly (also called membrane dysfunction) because the peritoneal membrane is less efficient, either at the start of treatment or developing after some years. If membrane dysfunction gets worse over time, then this is associated with progressive damage, scarring and thickening of the membrane. This problem can be identified through another change of the PET. It is called reduced ‘sodium dip’. Membrane dysfunction of this type is more difficult to treat and has many implications for the individual. If the damage is major, the person may need to stop PD. They would need to begin haemodialysis treatment (also spelled hemodialysis). This is a very important and emotional decision for individuals with kidney failure. Any decision that involves stopping PD therapy or transitioning to haemodialysis therapy should be made jointly between the clinical team, the person on dialysis and a caregiver, if requested. Although evidence is lacking about how often tests should be performed to determine peritoneal function, it seems reasonable to repeat them whenever there is difficulty in removing the amount of fluid necessary for maintaining the health and well-being of the individual. Whether routine evaluation of membrane function is associated with better outcomes has not been studied. Further research is needed to answer this important question as national policies in many parts of the world and the COVID-19 has placed a greater emphasis and new incentives encouraging the greater adoption of home dialysis therapies, especially PD. For Chinese and Spanish Translation of the Lay Summary, see Online Supplement Appendix 1.

Key recommendations

Guideline 1:

A pathophysiological taxonomy: A pathophysiological classification of membrane dysfunction, which provides mechanistic links to functional characteristics, should be used when prescribing individualized dialysis or when planning modality transfer (e.g. to automated peritoneal dialysis (PD) or haemodialysis) in the context of shared and informed decision-making with the person on PD, taking individual circumstances and treatment goals into account. (practice point)

Guideline 2a:

Identification of fast peritoneal solute transfer rate (PSTR): It is recommended that the PSTR is determined from a 4-h peritoneal equilibration test (PET), using either 2.5%/2.27% or 4.25%/3.86% dextrose/glucose concentration and creatinine as the index solute. (practice point) This should be done early in the course dialysis treatment (between 6 weeks and 12 weeks) (GRADE 1A) and subsequently when clinically indicated. (practice point)

Guideline 2b:

Clinical implications and mitigation of fast solute transfer: A faster PSTR is associated with lower survival on PD. (GRADE 1A) This risk is in part due to the lower ultrafiltration (UF) and increased net fluid reabsorption that occurs when the PSTR is above the average value. The resulting lower net UF can be avoided by shortening glucose-based exchanges, using a polyglucose solution (icodextrin), and/or prescribing higher glucose concentrations. (GRADE 1A) Compared to glucose, use of icodextrin can translate into improved fluid status and fewer episodes of fluid overload. (GRADE 1A) Use of automated PD and icodextrin may mitigate the mortality risk associated with fast PSTR. (practice point)

Guideline 3:

Recognizing low UF capacity: This is easy to measure and a valuable screening test. Insufficient UF should be suspected when either (a) the net UF from a 4-h PET is <400 ml (3.86% glucose/4.25% dextrose) or <100 ml (2.27% glucose /2.5% dextrose), (GRADE 1B) and/or (b) the daily UF is insufficient to maintain adequate fluid status. (practice point) Besides membrane dysfunction, low UF capacity can also result from mechanical problems, leaks or increased fluid absorption across the peritoneal membrane not explained by fast PSTR.

Guideline 4a:

Diagnosing intrinsic membrane dysfunction (manifesting as low osmotic conductance to glucose) as a cause of UF insufficiency: When insufficient UF is suspected, the 4-h PET should be supplemented by measurement of the sodium dip at 1 h using a 3.86% glucose/4.25% dextrose exchange for diagnostic purposes. A sodium dip ≤5 mmol/L and/or a sodium sieving ratio ≤0.03 at 1 h indicates UF insufficiency. (GRADE 2B)

Guideline 4b:

Clinical implications of intrinsic membrane dysfunction (de novo or acquired): in the absence of residual kidney function, this is likely to necessitate the use of hypertonic glucose exchanges and possible transfer to haemodialysis. Acquired membrane injury, especially in the context of prolonged time on treatment, should prompt discussions about the risk of encapsulating peritoneal sclerosis. (practice point)

Guideline 5:

Additional membrane function tests: measures of peritoneal protein loss, intraperitoneal pressure and more complex tests that estimate osmotic conductance and ‘lymphatic’ reabsorption are not recommended for routine clinical practice but remain valuable research methods. (practice point)

Guideline 6:

Socioeconomic considerations: When resource constraints prevent the use of routine tests, consideration of membrane function should still be part of the clinical management and may be inferred from the daily UF in response to the prescription. (practice point)

Risk Factors for Cardiovascular Disease in Patients Undergoing Peritoneal Dialysis

Patients on peritoneal dialysis (PD) are at high cardiovascular risk. Although some risk factors are unmodifiable (for example, age, sex, genetics), others are exacerbated in the unfriendly uremic milieu (inflammation, oxidative stress, mineral disturbances) or contribute per se to kidney disease and cardiovascular progression (diabetes mellitus, hypertension). Moreover, several factors associated with PD therapy may both increase (by altered lipid profile, hyperinsulinemia, and formation of advanced glycation end-products) and decrease (by better blood pressure control and anemia management) cardiovascular risk. The present review discusses recent findings and therapy trends in cardiovascular research on the PD population, with emphasis on the roles of inflammation, insulin resistance, homocysteinemia, dyslipidemia, vascular calcification, and genetics/epigenetics.

Non-invasive assessment of peritoneal membrane alterations

The peritoneal dialysis membrane is subject to remodelling in the course of peritoneal dialysis. In the absence of longitudinal morphological studies, this process is mainly studied indirectly by the investigation of changes in peritoneal transport. Non-invasive assessment of the peritoneum is also possible by assessment of substances that originate from peritoneal tissues and can be determined either as their gene expression in peritoneal effluent cells and/or as proteins in peritoneal effluent. Three of these biomarkers will be discussed, because longitudinal data are available. Cancer antigen 125 (CA 125) is present on the mesothelium,while its gene (MUC 16) is expressed in peritoneal effluent cells and is related to dialysate CA 125 protein. The constitutive production and the small intra-individual variability of 15% indicate its usefulness as a follow-up marker of mesothelial cell mass. Dialysate appearance rate is higher on biocompatible than on conventional solutions, but both decrease during long-term follow-up. Interleukin-6 (Il-6) is present in peritoneal effluent due to both transport from the circulation and local intraperitoneal production. Its appearance rate is unrelated to its gene expression in peritoneal cells. The intra-individual variation of effluent Il-6 averages 28%, hampering the interpretation of cross-sectional values. The relationships between effluent Il-6 and peritoneal transport have been interpreted as microinflammation, but are difficult to interprete due to mathematical coupling. Plasminogen activator inhibitor-1 (PAI-1) is encoded by the SERPINE 1 gene. A relationship is present between effluent concentration and gene expression. PAI-1 production is stimulated by glucose. PAI-1 appearance rate increases with PD duration. The sensitivity of effluent PAI-1 for the diagnosis of encapsulating peritoneal sclerosis was 100% one year prior to the diagnosis and the specificity 56%. It can be concluded that the discussed biomarkers are useful extensions to transport in assessment of the peritoneum during dialysis.  

The Fate of Older Diabetic Patients on Peritoneal Dialysis: Myths and Mysteries and Suggestions for Further Research

The outcome of older and especially of female diabetic patients appears to be worse on peritoneal dialysis (PD) than on hemodialysis (HD). This opinion is based mostly on data coming from the USA, whereas data from other regions seem to give a more balanced picture. The questions arise whether indeed outcome is worse in this patient group, and what might be the underlying reasons for this; further research to unravel this phenomenon is warranted. This review proposes several suggestions for further exploration. The observed differences in outcome might be attributable to differences in treatment practices and experience with PD versus HD. As cardiovascular mortality is a major killer in end-stage renal disease patients, differences in fluid homeostasis and how it is achieved are potential explanations. Fluid balance is potentially more difficult to obtain in PD patients, especially as in the past it was spuriously suggested that fluid restriction was less important in PD patients. PD and HD might also have different impacts on factors related to inflammation, insulin resistance, and hormone balance. The adipocytokine network is of special interest in this respect. It is also possible that bias introduced by the way we measure body composition might have a more negative impact on PD than on HD patients. Finally, it still is not fully established that if diabetic patients are treated appropriately, their outcome on PD is worse than that on HD; further observational trials in this respect are needed. All these topics require further clarification and investigation.

Encapsulating Peritoneal Sclerosis: Pathophysiology and Current Treatment Options

Encapsulating peritoneal sclerosis (EPS) is a life-threatening complication of long-term peritoneal dialysis (PD), which may even occur after patients have switched to hemodialysis (HD) or undergone kidney transplantation. The incidence of EPS varies across the globe and increases with PD vintage. Causative factors are the chronic exposure to bioincompatible PD solutions, which cause long-term modifications of the peritoneum, a high peritoneal transporter status involving high glucose concentrations, peritonitis episodes, and smoldering peritoneal inflammation. Additional potential causes are predisposing genetic factors and some medications. Clinical symptoms comprise signs of intestinal obstruction and a high peritoneal transporter status with incipient ultrafiltration failure. In radiological, macro-, and microscopic studies, a massively fibrotic and calcified peritoneum enclosed the intestine and parietal wall in such cases. Empirical treatments commonly used are corticosteroids and tamoxifen, which has fibrinolytic properties. Immunosuppressants like azathioprine, mycophenolate mofetil, or mTOR inhibitors may also help with reducing inflammation, fibrin deposition, and collagen synthesis and maturation. In animal studies, N-acetylcysteine, colchicine, rosiglitazone, thalidomide, and renin-angiotensin system (RAS) inhibitors yielded promising results. Surgical treatment has mainly been performed in severe cases of intestinal obstruction, with varying results. Mortality rates are still 25–55% in adults and about 14% in children. To reduce the incidence of EPS and improve the outcome of this devastating complication of chronic PD, vigorous consideration of the risk factors, early diagnosis, and timely discontinuation of PD and therapeutic interventions are mandatory, even though these are merely based on empirical evidence.

Opportunities and Challenges for Genetic Studies of End-Stage Renal Disease in Canada

Purpose of review:

Genetic testing can improve diagnostic precision in some patients with end-stage renal disease (ESRD) providing the potential for targeted therapy and improved patient outcomes. We sought to describe the genetic architecture of ESRD and Canadian data sources available for further genetic investigation into ESRD.

Sources of information:

We performed PubMed searches of English, peer-reviewed articles using keywords “chronic kidney disease,” “ESRD,” “genetics,” “sequencing,” and “administrative databases,” and searched for nephrology-related Mendelian diseases on the Online Mendelian Inheritance in Man database.

Methods:

In this narrative review, we discuss our evolving understanding of the genetic architecture of kidney disease and ESRD, the risks and benefits of using genetic data to help diagnose and manage patients with ESRD, existing public Canadian biobanks and databases, and a vision for future genetic studies of ESRD in Canada.

Key findings:

ESRD has a polygenic architecture including rare Mendelian mutations and common small effect genetic polymorphism contributors. Genetic testing will improve diagnostic accuracy and contribute to a precision medicine approach in nephrology. However, the risk and benefits of genetic testing needs to be considered from an individual and societal perspective, and further research is required. Merging existing health data, linking biobanks and administrative databases, and forming Canadian collaborations hold great potential for genetic research into ESRD. Large sample sizes are necessary to perform the suitably powered investigations required to bring this vision to reality.

Limitations:

This is a narrative review of the literature discussing future directions and opportunities. It reflects the views and academic biases of the authors.

Implications:

National collaborations will be required to obtain sample sizes required for impactful, robust research. Merging established datasets may be one approach to obtain adequate samples. Patient education and engagement will improve the value of knowledge gained.

Peritoneal Membrane Preservation

Peritoneal dialysis (PD) is a successfully used method for renal replacement therapy. However, long-term PD may be associated with peritoneal fibrosis and ultrafiltration failure. The key factors linked to their appearance are repeated episodes of inflammation associated with peritonitis and long-term exposure to bioincompatible PD fluids. Different strategies have been proposed to preserve the peritoneal membrane. This article reviews the functional and structural alterations related to PD and strategies whereby we may prevent them to preserve the peritoneal membrane. The use of new, more biocompatible, PD solutions is promising, although further morphologic studies in patients using these solutions are needed. Blockade of the renin-angiotensin-aldosterone system appears to be efficacious and strongly should be considered. Other agents have been proven in experimental studies, but most of them have not yet been tested appropriately in human beings.

Peritoneal Water Transport Characteristics of Diabetic Patients Undergoing Peritoneal Dialysis: A Longitudinal Study

BACKGROUND

Volume overload is frequent in diabetics undergoing peritoneal dialysis (PD), and may play a significant role in the excess mortality observed in these patients. The characteristics of peritoneal water transport in this population have not been studied sufficiently.

METHOD

Following a prospective, single-center design we made cross-sectional and longitudinal comparisons of peritoneal water transport in 2 relatively large samples of diabetic and nondiabetic PD patients. We used 3.86/4.25% glucose-based peritoneal equilibration tests (PET) with complete drainage at 60 min, for these purposes.

MAIN RESULTS

We scrutinized 59 diabetic and 120 nondiabetic PD patients. Both samples showed relatively similar characteristics, although diabetics were significantly more overhydrated than nondiabetics. The baseline PET disclosed lower ultrafiltration (mean 439 mL diabetics vs. 532 mL nondiabetics, p = 0.033) and sodium removal (41 vs. 53 mM, p = 0.014) rates in diabetics. One hundred and nine patients (36 diabetics) underwent a second PET after 12 months, and 45 (14 diabetics) underwent a third one after 24 months. Longitudinal analyses disclosed an essential stability of water transport in both groups, although nondiabetic patients showed a trend where an increase in free water transport (p = 0.033) was observed, which was not the case in diabetics.

CONCLUSIONS

Diabetic patients undergoing PD present lower capacities of ultrafiltration and sodium removal than their nondiabetic counterparts. Longitudinal analyses disclose an essential stability of water transport capacities, both in diabetics and nondiabetics. The clinical significance of these differences deserves further analysis.

Does Peritoneal Protein Transport Increase with Peritoneal Dialysis Therapy Duration and Lead to Extracellular Water Overload in Peritoneal Dialysis Patients?

Faster peritoneal transport status has been associated with adverse outcomes for peritoneal dialysis (PD) patients. Peritoneal protein clearance, through large pores, may be a surrogate marker of local inflammation. We wished to determine whether peritoneal protein transport increased with PD duration or was associated with extracellular water (ECW) expansion. We studied the relationships between 4 h Dialysate (D)/Serum (S) protein and ECW excess, using multifrequency bioelectrical impedance assessments, in 103 PD patients with up to 4 years of prospectively collected peritoneal equilibrium test (PET) results. 4 h PET D/S total protein and creatinine ratios were stable over time (K-W test, P = 0.063 and P = 0.3357, respectively). The initial PET 4 h D/S creatinine and D/S total protein correlated with ECW excess (r = 0.33, P = 0.003, and r = 0.27, P = 0.019, respectively), but thereafter there was no association. CRP and albumin did not correlate with 4 h D/S creatinine or total protein. Serial 4 h D/S total protein and 4 h D/S creatinine correlated all time points (P < 0.001). At the start of PD therapy, over-hydration (ECW excess) was observed with higher 4 h D/S creatinine and 4 h D/S total protein ratios, suggesting initial exposure to PD fluids causes faster transport. Thereafter changes in peritoneal creatinine and total protein transport mirrored each other suggesting that similar factors lead to changes in both small and large pore transport, and there was no sustained increase in larger pore transport with therapy time.

The Current State of Peritoneal Dialysis

Technical innovations in peritoneal dialysis (PD), now used widely for the long-term treatment of ESRD, have significantly reduced therapy-related complications, allowing patients to be maintained on PD for longer periods. Indeed, the survival rate for patients treated with PD is now equivalent to that with in-center hemodialysis. In parallel, changes in public policy have spurred an unprecedented expansion in the use of PD in many parts of the world. Meanwhile, our improved understanding of the molecular mechanisms involved in solute and water transport across the peritoneum and of the pathobiology of structural and functional changes in the peritoneum with long-term PD has provided new targets for improving efficiency and for intervention. As with hemodialysis, almost half of all deaths on PD occur because of cardiovascular events, and there is great interest in identifying modality-specific factors contributing to these events. Notably, tremendous progress has been made in developing interventions that substantially reduce the risk of PD-related peritonitis. Yet the gains have been unequal among individual centers, primarily because of unequal clinical application of knowledge gained from research. The work to date has further highlighted the areas in need of innovation as we continue to strive to improve the health and outcomes of patients treated with PD.

Possible role of IL-6 and TIE2 gene polymorphisms in predicting the initial high transport status in patients with peritoneal dialysis: an observational study

OBJECTIVES

The aim of this study was to investigate the effect of interleukin (IL)-6 and TIE2 gene polymorphisms on baseline peritoneal transport property.

DESIGN

An observational study.

SETTING

Renji Hospital in Shanghai, China.

PARTICIPANTS

This study included 220 patients with continuous ambulatory peritoneal dialysis (PD).

OUTCOME MEASURES

Patients were divided into 2 groups based on the results of an initial peritoneal equilibration test performed within 3 months of starting PD therapy: group 1 consisted of low/low average transporters (n=123), and group 2 consisted of high/high average transporters (n=97). We genotyped TIE2 and IL-6 polymorphisms and analysed their effects on baseline transport status.

RESULTS

The genotype AT in IL-6 Rs13306435 and the genotype CC in TIE2 Rs639225 were both negatively associated with a higher initial peritoneal transport status (IL-6 Rs13306435: OR=0.408, 95% CI 0.227 to 0.736; TIE2 Rs639225: OR=0.188, 95% CI 0.044 to 0.806).

CONCLUSIONS

IL-6 and TIE2 polymorphisms are associated with baseline peritoneal transport property.

Preliminary observations on the association between serum IL-6 and hydration status and cardiovascular risk in patients treated with peritoneal dialysis

INTRODUCTION

Systemic inflammation, as defined by elevated blood IL-6, is a strong independent predictor of peritoneal dialysis (PD) patient survival. The present study has aimed to determine whether there exists a particular "phenotype" associated with high systemic IL-6 that characterizes PD patients in terms of their fluid status and cardiac parameters.

METHODS

Fifty-seven prevalent PD patients were classified according to serum concentrations of IL-6. The degree of overhydration was assessed by bioimpedance analysis (BIA). Echocardiography and serum concentrations of NT-proBNP and troponin T were used to assess cardiovascular risk.

RESULTS

Patients with high serum IL-6 were older, more often diabetic, treated with PD for longer, and significantly more overhydrated. There was a significant correlation between serum IL-6, hydration status (r=0.38; p=0.002) and serum albumin (r=-0.35; p=0.009). Multivariate regression analysis confirmed a strong association of overhydration, hypoalbuminemia, and systemic IL-6 concentration. Patients with high IL-6 had significantly increased levels of both NT-proBNP (r=0.36; p=0.006) and TnT (r=0.50; p<0.001) in the absence of abnormalities in echocardiography.

CONCLUSIONS

High systemic IL-6 identifies PD patients with increased cardiovascular risk that is significantly related to overhydration. Thus, the measurement of serum IL-6 may contribute to the more accurate assessment of cardiovascular status in patients undergoing PD.

The Mutual Relationship Between Peritonitis and Peritoneal Transport

♦

BACKGROUND

Preservation of the peritoneum is required for long-term peritoneal dialysis (PD). We investigated the effect of multiple peritonitis episodes on peritoneal transport. ♦

METHODS

Prospectively collected data from 479 incident PD patients treated between 1990 and 2010 were analyzed, using strict inclusion criteria: follow-up of at least 3 years with the availability of a Standard Peritoneal Permeability Analysis (SPA) in the first year after start of PD and within the third year of PD, without peritonitis preceding the first SPA. For the purpose of the study, we only included patients who remained peritonitis-free (n = 28) or who experienced 3 or more peritonitis episodes (n = 16). ♦

RESULTS

At baseline the groups were similar with regard to small solute and fluid transport. However, the frequent peritonitis group had lower peritoneal protein clearances compared to the no peritonitis group, resulting in lower dialysate concentrations of proteins: albumin 196.5 mg/L vs 372.5 mg/L, IgG 36.4 mg/L vs 65.0 mg/L, and α-2-macroglobulin (A2M) 1.9 mg/L vs 3.6 mg/L, p <0.01. No differences in serum concentrations were present. A comparison between the transport slopes over time in both groups showed a positive time trend of mass transfer area coefficient (MTAC) creatinine (p = 0.03) and glucose absorption (p = 0.09) and a negative trend of transcapillary ultrafiltration (p = 0.06), when compared to the no peritonitis group. Frequent peritonitis did not affect free water transport. ♦

CONCLUSIONS

Slow initial peritoneal transport rates of serum proteins result in lower dialysate concentrations, and likely a lower opsonic activity, which is a risk factor for peritonitis. Patients with frequent peritonitis show an increase in small solute transport and a concomitant decrease of ultrafiltration. In long-term peritonitis-free PD patients, small solute transport decreased, while ultrafiltration increased. This suggests that frequent peritonitis leads to an increase of the vascular peritoneal surface area without all the structural membrane alterations that may develop after long-term PD.

Genetic strain differences in the development of peritoneal fibroproliferative processes in mice

Fibroproliferative processes are regulated by a wide variety of tissue components and genetic factors. However, whether there are genetic differences in peritoneal fibroproliferative tissue formation, with consequent differences in response to drug treatment, is unclear. We characterize the influence of the genetic background on peritoneal fibroproliferative tissue induced by sponge implants in DBA/1, Swiss, C57BL/6, and BALB/c mouse strains. In addition, responses to dipyridamole in the implants were evaluated. Angiogenesis, assessed by intra-implant hemoglobin content, was highest in Swiss mice, whereas levels of vascular endothelial growth factor were highest in C57BL/6 mice. The levels of pro-inflammatory cytokines and of inflammatory enzymes (myeloperoxidase- and N-acetyl-β-D-glucosaminidase) were also strain-related. The pro-fibrogenic markers transforming growth factor beta-1 and collagen were lowest in implants placed in DBA/1 mice, whereas those in C57BL/6 mice had the highest levels. Differential sensitivity to dipyridamole was also observed, with this compound being pro-angiogenic in implants placed in DBA/1 mice but antiangiogenic in implants placed in Swiss. An overall anti-inflammatory response was observed in the inbred strains. Antifibrogenic effects were observed only in implants placed in C57BL/6 mice. These important strain-related differences in the development of peritoneal fibrosis and in response to dipyridamole must be considered in the design and analysis of studies on fibrogenesis in mice.

Association of IL-6 and a functional polymorphism in the IL-6 gene with cardiovascular events in patients with CKD

BACKGROUND AND OBJECTIVES

High serum IL-6 is a major risk factor for cardiovascular disease (CVD) in the general population. This cytokine is substantially increased in patients with CKD, but it is still unknown whether the link between IL-6 and CVD in CKD is causal in nature.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

In a cohort of 755 patients with stages 2-5 CKD, consecutively recruited from 22 nephrology units in southern Italy, this study assessed the relationship of serum IL-6 with history of CVD, as well as with incident cardiovascular (CV) events (mean follow up±SD, 31±10 months) and used the functional polymorphism (-174 G/C) in the promoter of the IL-6 gene to investigate whether the link between IL-6 and CV events is causal.

RESULTS

In adjusted analyses, serum IL-6 above the median value was associated with history of CVD (P<0.001) and predicted the incidence rate of CV events (hazard ratio, 1.66; 95% confidence interval [95% CI], 1.11 to 2.49; P=0.01). Patients homozygous for the risk allele (C) of the -174 G/C polymorphism had higher levels of IL-6 than did those with other genotypes (P=0.04). Homozygous CC patients more frequently had a history of CVD (odds ratio, 2.15; 95% CI, 1.15 to 4.00; P=0.02) as well as a 87% higher rate of incident CV events (hazard ratio, 1.87; 95% CI, 1.02 to 3.44; P=0.04) compared with other genotypes.

CONCLUSIONS

In patients with stages 2-5 CKD, high serum IL-6 is associated with history of CVD and predicts incident CV events. The parallel relationship with history of CVD and incident CV events of the -174 G/C polymorphism in the IL-6 gene suggests that IL-6 may be causally involved in the high CV risk in this population.

Genetic Polymorphisms and Peritoneal Membrane Function

BACKGROUND

Outcomes for peritoneal dialysis (PD) patients are affected by the characteristics of the peritoneal membrane, which may be determined by genetic variants. We carried out a systematic review of the literature to identify studies which assessed the association between genetic polymorphisms, peritoneal membrane solute transport, and clinical outcomes for PD patients.

METHODS

The National Library of Medicine was searched using a variety of strategies. Studies which met our inclusion criteria were reviewed and data abstracted. Our outcomes of interest included: high transport status peritoneal membrane, risk for peritonitis, encapsulating peritoneal sclerosis (EPS), patient and technique survival. We combined data from studies which evaluated the same genetic polymorphism and the same outcome.

RESULTS

We evaluated 18 relevant studies. All studies used a candidate gene approach. Gene polymorphisms in the interleukin (IL)-6 gene were associated with peritoneal membrane solute transport in several studies in different ethnic populations. Associations with solute transport and polymorphisms in endothelial nitric oxide synthase and receptor for advanced glycation end product genes were also identified. There was evidence of a genetic predisposition for peritonitis found in 2 studies, and for EPS in 1 study. Survival was found to be associated with a polymorphism in vascular endothelial growth factor and technique failure was associated with a polymorphism in the IL-1 receptor antagonist.

CONCLUSIONS

There is evidence that characteristics of the peritoneal membrane and clinical outcomes for PD patients have genetic determinants. The most consistent association was between IL-6 gene polymorphisms and peritoneal membrane solute transport.

Gremlin promotes peritoneal membrane injury in an experimental mouse model and is associated with increased solute transport in peritoneal dialysis patients

The peritoneal membrane becomes damaged in patients on peritoneal dialysis (PD). Gremlin 1 (GREM1) inhibits bone morphogenic proteins (BMPs) and plays a role in kidney development and fibrosis. We evaluated the role of gremlin in peritoneal fibrosis and angiogenesis. In a cohort of 32 stable PD patients, GREM1 concentration in the peritoneal effluent correlated with measures of peritoneal membrane damage. AdGrem1, an adenovirus to overexpress gremlin in the mouse peritoneum, induced submesothelial thickening, fibrosis, and angiogenesis in C57BL/6 mice, which was associated with decreased expression of BMP4 and BMP7. There was evidence of mesothelial cell transition to a mesenchymal phenotype with increased α smooth muscle actin expression and suppression of E-cadherin. Some of the GREM1 effects may be reversed with recombinant BMP7 or a pan-specific transforming growth factor β (TGF-β) antibody. Neovascularization was not inhibited with a TGF-β antibody, suggesting a TGF-β-independent angiogenic mechanism. Swiss/Jackson Laboratory (SJL) mice, which are resistant to TGF-β-induced peritoneal fibrosis, responded in a similar fashion to AdGrem1 as did C57BL/6 mice with fibrosis, angiogenesis, and mesothelial-to-mesenchymal transition. GREM1 was associated with up-regulated TGF-β expression in both SJL and C57BL/6 mice, but SJL mice demonstrated a defective TGF-β-induced GREM1 expression. In summary, GREM1 induces fibrosis and angiogenesis in mouse peritoneum and is associated with increased solute transport in these PD patients.

Optimizing peritoneal dialysis prescription for volume control: the importance of varying dwell time and dwell volume

Not only adequate uremic toxin removal but also volume control is essential in peritoneal dialysis (PD) to improve patient outcome. Modification of dwell time impacts on both ultrafiltration (UF) and purification. A short dwell favors UF but preferentially removes small solutes such as urea. A long dwell favors uremic toxin removal but also peritoneal fluid reabsorption due to the time-dependent loss of the crystalloid osmotic gradient. In particular, the long daytime dwell in automated PD may result in significant water and sodium reabsorption, and in such cases icodextrin should be considered. Increasing dwell volume favors the removal of solutes such as sodium due to the increased volume of diffusion and the recruitment of peritoneal surface area. A very large fill volume with too high an intraperitoneal pressure (IPP) may, however, result in back-filtration and thus reduced UF and sodium clearance. Based on these principles and the individual transport and pressure kinetics obtained from peritoneal equilibration tests and IPP measurements, we suggest combining short dwells with a low fill volume to favor UF with long dwells and a large fill volume to favor solute removal. Results from a recent randomized cross-over trial and earlier observational data in children support this concept: the absolute UF and UF relative to the administered glucose increased and solute removal and blood pressure improved.

Intraperitoneal interleukin-6 levels predict peritoneal solute transport rate: a prospective cohort study

BACKGROUND

To evaluate the association of dialysate interleukin-6 (IL-6), a marker of ongoing peritoneal inflammation, with the alteration of peritoneal solute transport rate (PSTR) in continuous ambulatory peritoneal dialysis (CAPD) patients.

METHODS

Stable CAPD patients were enrolled in the present study. A total of 128 patients were analyzed in this prospective study. IL-6 concentration in the overnight effluent was determined and expressed as the IL-6 appearance rate (IL-6AR). Mass transfer area coefficients of creatinine (MTACcr) were measured at enrollment and 12 months later. Logistic regression was used to examine the association between IL-6AR and change in MTACcr.

RESULTS

Multivariable linear regression showed that historical glucose exposure was significantly associated with dialysate IL-6AR level [β = 0.008 (0.001-0.015), p = 0.021]. After 12 months, MTACcr was significantly increased [6.40 (4.70-8.75) vs. 7.14 (5.69-8.73) ml/min, p = 0.004], while ultrafiltration capacity decreased [4 h UF 340 (220-400) vs. 280 (180-380) ml, p = 0.006]. Compared to the patients with stable PSTR, the dialysate IL-6AR in patients with increasing PSTR was significantly higher [277.08 (247.45-349.53) vs. 263.18 (69.94-286.72) pg/min, p = 0.015]. Patients with increasing PSTR had lower residual renal function [0.79 (0-2.12) vs. 1.70 (0.39-3.38) ml/min, p = 0.006] and less urine output [225 (0-600) vs. 500 (125-900) ml/24 h, p = 0.014]. Logistic analysis showed that both high dialysate IL-6AR [OR 1.333 and 95% CI (1.024-1.735), p = 0.033] and low RRF [OR 0.831 and 95% CI (0.699-0.988), p = 0.036] were independent risk factors for increasing PSTR.

CONCLUSIONS

This prospective study suggests that intraperitoneal IL-6 is a predictor of increasing PSTR in peritoneal dialysis patients.

Inflammatory factors for hypoalbuminemia in Japanese peritoneal dialysis patients

AIM

Hypoalbuminaemia is a common complication of peritoneal dialysis (PD), and the leakage of albumin through peritoneal membrane may be a principal reason for hypoalbuminaemia. However, the relationship between peritoneal inflammation, peritoneal transport properties and hypoalbuminaemia has not been fully elucidated.

METHODS

A cross-sectional study was performed on 76 Japanese PD patients who had been using a low-glucose PD solution and icodextrin. Systemic inflammatory markers of C-reactive protein (CRP) and serum interleukin-6 (IL-6), peritoneal effluent markers of dialysate IL-6 and CA125, the dialysate-to-plasma ratio of creatinine (D/Pcr) and the dialysate protein concentration were measured and examined for their relationship with hypoalbuminaemia.

RESULTS

There was a significant positive correlation between serum IL-6 and dialysate IL-6, mean dialysate IL-6 being significantly higher than mean serum IL-6, suggesting that intraperitoneal inflammation was a principal origin of systemic inflammation. Both serum and dialysate IL-6 were significantly correlated with serum albumin (r= -0.25, P<0.05 and r=-0.32, P<0.01, respectively). Dialysate IL-6 was significantly correlated with D/Pcr and the dialysate protein concentration, and there was a significantly positive association between D/Pcr and the dialysate protein concentration. Dialysate CA125, which is argued to be a marker of mesothelial cell mass in this study, was positively correlated with D/Pcr and the dialysate protein concentration. The dialysate protein, dialysate IL-6 and dialysate CA125 all increased according to the peritoneal transport rate defined by D/Pcr. A multiple-regression analysis showed that serum albumin was independently associated with the age, D/Pcr and serum IL-6.

CONCLUSION

Hypoalbuminaemia was attributable to both the increased peritoneal permeability and systemic inflammation, and intraperitoneal inflammation might contribute to developing these complications.

Peritoneal equilibration test in costa rica: discrepancies from other populations

Objective. Continuous Ambulatory Peritoneal Dialysis (CAPD) is a kidney replacement therapy that has been recently incorporated in developing countries. We aim to establish our reference values, to compare them with the original and the Mexican population, and to associate some variables with the type of peritoneal transport. Methods. Thirty peritoneal equilibration tests (PET) were performed. The ratio for D/P creatinine and the D/D0 ratio for glucose were calculated and compared to reference values. We conducted a retrospective analysis to correlate peritoneal transporters with some predictive variables. Results. D/P creatinine ratio at 2 hours, D/D0 glucose ratio at 4 hours, and net ultrafiltrate volume (nUFV) were significantly different from those reported by Twardowski et al. The results documented in the Mexican population only coincide with our results for the D/P creatinine ratio at 4 hours. Any of the studied variables were associated with a specific type of peritoneal transport. Conclusions. Peritoneal permeability among Costa Rican CAPD patients is different from the original population described by Twardowski et al. and from other Latin-American population. This supports the theory that ethnical differences could be responsible for such variations and they validate our statement that each region should possess value references of their own.

Longitudinal study of small solute transport and peritoneal protein clearance in peritoneal dialysis patients

BACKGROUND AND OBJECTIVES

Peritoneal protein clearance (Pcl) is determined by both effective (small pores) membrane area and relative capillary leakiness (large pores). It is not known how these two components change with duration of peritoneal dialysis (PD) in the context of progressive membrane injury and differential attrition of patients with higher Pcl, which has been associated with increased mortality risk in several studies.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Patients treated continuously from 2000 to 2011 for a minimum of 4 years were selected from the longitudinal prospective Stoke PD Study. Pcl, membrane area (peritoneal solute transport rate [PSTR]), dialysis prescription, and residual renal function were measured every 6 months, along with comorbidity and peritonitis events. Multilevel multivariate analysis was used to determine associations with Pcl over time, taking into account within-subject correlations.

RESULTS

From 280 incident patients, 335 datasets were analyzed from 49 patients receiving treatment for 4 years. Pcl correlated with PSTR at baseline (R=0.61; P<0.01), but over time there was progressive uncoupling of this relationship (year 4, R=0.28; P=0.05) with increasing PSTR (0.66-0.74; P<0.01) and stable Pcl (78.4-81.9 ml/d; P=0.7). Multivariate analysis found that age, PSTR, daily ultrafiltration, and sodium removal were significant predictors of Pcl when adjusted for sex, comorbidity, glucose exposure, and residual renal function. Peritonitis was associated with increased PSTR but a similar pattern of uncoupling.

CONCLUSION

There is a progressive dissociation of the small- and large-pore pathways with time on PD, which would be in keeping with a switch from local inflammation early on to progressive fibrosis, combined with increased vascular surface area. Measuring longitudinal changes in Pcl may complement membrane function tests used to monitor progressive injury.

Independent effects of systemic and peritoneal inflammation on peritoneal dialysis survival

Systemic inflammation, as evidenced by elevated inflammatory cytokines, is a feature of advanced renal failure and predicts worse survival. Dialysate IL-6 concentrations associate with variability in peritoneal small solute transport rate (PSTR), which has also been linked to patient survival. Here, we determined the link between systemic and intraperitoneal inflammation with regards to peritoneal membrane function and patient survival as part of the Global Fluid Study, a multinational, multicenter, prospective, combined incident and prevalent cohort study (n=959 patients) with up to 8 years of follow-up. Data collected included patient demographic characteristics, comorbidity, modality, dialysis prescription, and peritoneal membrane function. Dialysate and plasma cytokines were measured by electrochemiluminescence. A total of 426 survival endpoints occurred in 559 incident and 358 prevalent patients from 10 centers in Korea, Canada, and the United Kingdom. On patient entry to the study, systemic and intraperitoneal cytokine networks were dissociated, with evidence of local cytokine production within the peritoneum. After adjustment for multiple covariates, systemic inflammation was associated with age and comorbidity and independently predicted patient survival in both incident and prevalent cohorts. In contrast, intraperitoneal inflammation was the most important determinant of PSTR but did not affect survival. In prevalent patients, the relationship between local inflammation and membrane function persisted but did not account for an increased mortality associated with faster PSTR. These data suggest that systemic and local intraperitoneal inflammation reflect distinct processes and consequences in patients treated with peritoneal dialysis, so their prevention may require different therapeutic approaches; the significance of intraperitoneal inflammation requires further elucidation.

Are the Mesothelial-to-Mesenchymal Transition, Sclerotic Peritonitis Syndromes, and Encapsulating Peritoneal Sclerosis Part of the Same Process?

Mesothelial-to-mesenchymal transition (MMT) is an autoregulated physiological process of tissue repair that in uncontrolled conditions, such as peritoneal dialysis (PD), can lead to peritoneal fibrosis. The maximum expression of sclerotic peritoneal syndromes (SPS) is the encapsulating peritoneal sclerosis (EPS) for which no specific treatment exists. The SPS includes a wide range of peritoneal fibrosis that appears progressively and is considered as a reversible process, while EPS does not. EPS is a serious complication of PD characterized by a progressive intra-abdominal inflammatory process that results in bridles and severe fibrous tissue formation which cover and constrict the viscera. Recent studies show that transdifferentiated mesothelial cells isolated from the PD effluent correlate very well with the clinical events such as the number of hemoperitoneum and peritonitis, as well as with PD function (lower ultrafiltration and high Cr-MTC). In addition, in peritoneal biopsies from PD patients, the MMT correlates very well with anatomical changes (fibrosis and angiogenesis). However, the pathway to reach EPS from SPS has not been fully and completely established. Herein, we present important evidence pointing to the MMT that is present in the initial peritoneal fibrosis stages and it is perpetual over time, with at least theoretical possibility that MMT initiated the fibrosing process to reach EPS.

Protecting the peritoneal membrane: factors beyond peritoneal dialysis solutions

Functional deterioration of the peritoneal membrane in patients on peritoneal dialysis has been described as being the result of a combination of neoangiogenesis and fibrosis. Glucose, glucose degradation products, and the unphysiological pH of the dialysate solution contribute to these changes. Although newer solutions clearly perform better in terms of their biocompatibility in an in vitro setting and in animal models, the benefit of such solutions over older solutions in the clinical setting is so far unproven. The difficulties in showing a benefit of the newer, more biocompatible solutions in the clinical setting can be explained by the fact that other factors also affect the properties of the peritoneal membrane. These factors are often neglected in clinical studies, which results in unnoticed differences in case-mix and blurs the potential impact of the novel solutions. However, many of these factors are modifiable, and attention should be paid to them in clinical practice to maintain the integrity of the peritoneal membrane. This Review focuses on factors that potentially influence the integrity of the peritoneal membrane, other than those associated with the peritoneal dialysis fluid itself.

Transforming growth factor β-induced peritoneal fibrosis is mouse strain dependent

BACKGROUND

Encapsulating peritoneal sclerosis (EPS) is a rare but devastating complication of peritoneal dialysis. The etiology is unclear, but genetic predisposition may be a contributing factor. We used adenovirus-mediated gene transfer of transforming growth factor (TGF) β1 to the peritoneum in four genetically distinct laboratory mouse strains to assess differences in fibrogenic response.

METHODS

Mice from four genetic backgrounds (C57BL/6J, DBA/2J, C3H/HeJ and SJL/J) received an intraperitoneal injection of an adenovirus expressing TGFβ1 (AdTGFβ1) or control adenovirus (AdDL) and were assessed 4 and 10 days after infection. Submesothelial thickening, angiogenesis and gene expression were quantified from peritoneal tissue. Protein was extracted from omental tissue and assessed for collagen, E-cadherin and TGFβ signaling pathway proteins.

RESULTS

There was a graded response among the mouse strains to the peritoneal overexpression of TGFβ1. TGFβ1 induced a significant fibrogenic response in the C57BL/6J mice, whereas the SJL/J mice were resistant. The DBA/2J and the C3H/HeJ mice had intermediate responses. A similar graded response was seen in collagen protein levels in the omental tissue and in fibrosis-associated gene expression. TGFβ type 1 receptor and SMAD signaling pathways appeared to be intact in all the mouse strains.

CONCLUSIONS

There were significant differences in mouse strain susceptibility to peritoneal fibrosis, suggesting that genetic factors may play a role in the development of peritoneal fibrosis and possibly EPS. As early TGFβ1 signaling mechanisms appear to be intact, we hypothesize that fibrosis resistance in the SJL/J mice lies further down the wound-healing cascade or in an alternate, non-SMAD pathway.