Biocompatible Solutions and Long-Term Changes in Peritoneal Solute Transport

Glucose-induced pseudohypoxia and advanced glycosylation end products explain peritoneal damage in long-term peritoneal dialysis

Long-term peritoneal dialysis is associated with the development of peritoneal membrane alterations, both in morphology and function. Impaired ultrafiltration (UF) is the most important functional change, and peritoneal fibrosis is the major morphological alteration. Both are caused by the continuous exposure to dialysis solutions that are different from plasma water with regard to the buffer substance and the extremely high-glucose concentrations. Glucose has been incriminated as the major cause of long-term peritoneal membrane changes, but the precise mechanism has not been identified. We argue that glucose causes the membrane alterations by peritoneal pseudohypoxia and by the formation of advanced glycosylation end products (AGEs). After a summary of UF kinetics including the role of glucose transporters (GLUT), and a discussion on morphologic alterations, relationships between function and morphology and a survey of the pathogenesis of UF failure (UFF), it will be argued that impaired UF is partly caused by a reduction in small pore fluid transport as a consequence of AGE-related vasculopathy and - more importantly - in diminished free water transport due to pseudohypoxia, caused by increased peritoneal cellular expression of GLUT-1. The metabolism of intracellular glucose will be reviewed. This occurs in the glycolysis and in the polyol/sorbitol pathway, the latter is activated in case of a large supply. In both pathways the ratio between the reduced and oxidised form of nicotinamide dinucleotide (NADH/NAD+ ratio) will increase, especially because normal compensatory mechanisms may be impaired, and activate expression of hypoxia-inducible factor-1 (HIF-1). The latter gene activates various profibrotic factors and GLUT-1. Besides replacement of glucose as an osmotic agent, medical treatment/prevention is currently limited to tamoxifen and possibly Renin/angiotensis/aldosteron (RAA) inhibitors.

The Peritoneal Membrane and its Role in Peritoneal Dialysis

A healthy and functional peritoneal membrane is key to achieve sufficient ultrafiltration and to restore fluid balance, a major component of high-quality prescription in patients treated with peritoneal dialysis (PD). Variability in membrane function at the start of PD or changes over time on treatment influence dialysis prescription and outcomes, and dysfunction of the peritoneal membrane contributes to fluid overload and associated complications. In this review, we summarize the current knowledge about the structure, function and pathophysiology of the peritoneal membrane with a focus on clinical implications for patient-centered care. We also discuss the molecular and genetic mechanisms of solute and water transport across the peritoneal membrane, including the role of aquaporin water channels in crystalloid vs. colloid osmosis; why and how to assess membrane function using peritoneal equilibration tests; the etiologies of membrane dysfunction and their specific management; and the impact of genetic variation on membrane function and outcomes in patients treated with PD. This review also identifies the gaps in current knowledge and perspectives for future research to improve our understanding of the peritoneal membrane and, ultimately, to improve the care of patients treated with PD.

How peritoneal dialysis transforms the peritoneum and vasculature in children with chronic kidney disease-what can we learn for future treatment?

Children with chronic kidney disease (CKD) suffer from inflammation and reactive metabolite-induced stress, which massively accelerates tissue and vascular aging. Peritoneal dialysis (PD) is the preferred dialysis mode in children, but currently used PD fluids contain far supraphysiological glucose concentrations for fluid and toxin removal and glucose degradation products (GDP). While the peritoneal membrane of children with CKD G5 exhibits only minor alterations, PD fluids trigger numerous molecular cascades resulting in major peritoneal membrane inflammation, hypervascularization, and fibrosis, with distinct molecular and morphological patterns depending on the GDP content of the PD fluid used. PD further aggravates systemic vascular disease. The systemic vascular aging process is particularly pronounced when PD fluids with high GDP concentrations are used. GDP induce endothelial junction disintegration, apoptosis, fibrosis, and intima thickening. This review gives an overview on the molecular mechanisms of peritoneal and vascular transformation and strategies to improve peritoneal and vascular health in patients on PD.

Effluent decoy receptor 2 as a novel biomarker of peritoneal fibrosis in peritoneal dialysis patients

BACKGROUND

Peritoneal fibrosis (PF) is a common complication of peritoneal dialysis (PD), but a specific and sensitive biomarker for PF is lacking. The present study aimed to determine the use of effluent decoy receptor 2 (eDcR2) as a biomarker for PF in PD patients.

METHODS

PD patients (n = 248) were recruited, and peritoneal specimens were collected at PD initiation (n = 30) and cessation (n = 33). Enzyme-linked immunoassay was used to measure eDcR2 and the eDcR2 appearance rate (eDcR2-AR) was calculated. The levels of DcR2 mRNA and protein were determined. The correlation of eDcR2 level with peritoneal function, histological parameters and DcR2 expression were analysed. Receiver operating characteristic (ROC) analysis was used to assess the diagnostic performance of eDcR2 for PF, which was defined as a submesothelial thickness 150 µm or more. Co-localisation of DcR2 with a mesothelial marker, fibroblast markers and fibrotic markers were determined.

RESULTS

The eDcR2-AR level correlated with PD duration, D/P Cr values, peritoneal Kt/V and peritoneal injury scores, especially submesothelial thickness (r = 0.638, p < 0.001). DcR2 was primarily expressed in peritoneal fibroblasts, and co-localised with α-SMA, vimentin, collagen I and fibronectin, but not with E-cadherin. Peritoneal DcR2 expression had a positive correlation with eDcR2-AR. ROC analysis indicated eDcR2 had an area under the curve of 0.907 for detection of PF (sensitivity: 78.6%, specificity: 100%) and the best cut-off value was 392.5 pg/min.

CONCLUSION

The eDcR2-AR level is a potential biomarker for assessing PF in PD patients. Effluent DcR2 was mainly derived from peritoneal fibroblasts and DcR2-positive cells may accelerate PF, suggesting that it may be a potential therapeutic target.

Insulin resistance in cardiovascular disease, uremia, and peritoneal dialysis

Diabetic nephropathy is highly correlated with the occurrence of other complications of type 1 diabetes (T1D) and type 2 diabetes (T2D) mellitus; for example, hypertension with cardiovascular disease (CVD) being the most frequent cause of death in patients with end-stage renal disease and undergoing renal dialysis. Hyperglycemia and insulin resistance (IR) are responsible for the micro- and macrovascular complications of diabetes through different mechanisms. In particular, IR plays a key role in the etiology of atherosclerosis in both diabetic and non-diabetic patients. IR - exacerbated by organ-level selectivity - is more important than glycemic control per se in determining cardiovascular outcomes. This may be exacerbated by the fact that IR is organ and pathway specific due to the only selective loss of sensitivity to insulin action of specific pathways/processes. Therefore, it is counterintuitive that the use of peritoneal dialysis (PD) in (frequently) diabetic renal disease patients should involve their exposure to high daily doses of glucose peritoneally. In view of the controversy about the causal association between glucose load and CVD in PD patients, we discuss the role that selective IR may play in the progression of CVD in diabetic renal end-stage patients. In discussing these associations, we propose that reducing glucose exposure in PD solutions may be beneficial especially if coupled with strategies that address IR directly, and the avoidance of excessive use of insulin treatment in T2D.

Sulodexide Prevents Peritoneal Fibrosis by Downregulating the Expression of TGF-β1 and Its Signaling Pathway Molecules

Peritoneal dialysis is one of the main renal replacement treatments. However, long-term peritoneal dialysis keeps the peritoneum in contact with the sugar-containing nonphysiological peritoneal fluid, which leads to recurrent peritonitis, peritoneal fibrosis, and failure of ultrafiltration. Transforming growth factor-β1 (TGF-β1), related cytokines, and inflammatory factors are closely related to peritoneal fibrosis. Sulodexide (SLX) is a new type of glycosaminoglycan preparation, which is involved in the formation of an anionic charge barrier and can maintain the selective permeability of vascular endothelial cells. In this study, the innovative analysis of SLX specifically prevents the process of peritoneal dialysis peritoneal fibrosis by downregulating the expression of TGF-β1 and its signaling pathway molecules. We randomly divided 30 rats into three groups. The blank control group received no treatment. The peritoneal dialysis model group was injected with 4.25% peritoneal dialysate (PDF) 20 ml daily, and the SLX group was injected with 4.25% PDF 20 ml + sulodexide (SLX) 20 mg/kg daily. After 8 weeks of dialysis, the rats were sacrificed, and the peritoneal function test was performed to determine the amount of glucose transport and ultrafiltration. The thickness of peritoneal per unit area was observed under high magnification. The level of inflammation in peritoneal tissue and the expression of TGF-β1/Smad were detected. The results showed that SLX can significantly improve peritoneal tissue thickening and inflammation, can downregulate the expression of TGF-β1, Smad2, Smad3, and Smad7 in peritoneal tissue, and improve the progression of peritoneal fibrosis.

Survival of Peritoneal Membrane Function on Biocompatible Dialysis Solutions in a Peritoneal Dialysis Cohort Assessed by a Novel Test

Background: Longitudinal surveillance of peritoneal membrane function is crucial in defining patients with a risk of ultrafiltration failure. Long PD is associated with increased low molecular weight solute transport and decreased ultrafiltration and free water transport. Classic PET test only provides information about low molecular solute transport, and the vast majority of longitudinal studies are based on this test and include patients using conventional dialysates. Our aim was to prospectively analyze longitudinal data on peritoneal function in patients on biocompatible solutions using a novel test. Methods: Membrane function data were collected based on uni-PET (a combination of modified and mini PET). A total of 85 patients (age 61.1 ± 15.1 years) with at least one test/year were included. Results: The median follow up was 36 months (21.3, 67.2). A total of 219 PETs were performed. One-way repeated measures ANOVA showed that there were no statistically significant differences over time in ultrafiltration, free water transport, ultrafiltration through small pores, sodium removal, D/D0 and D/PCre in repeated PET-tests. Twenty-three tests revealed ultrafiltration failure in 16 (18.8%) patients. Those patients were longer on PD, had higher D/P creatinine ratios, lower ultrafiltration at one hour with lower free water transport and higher urine volume at baseline. Multivariate analysis revealed that the variation of ultrafiltration over repeated PET-tests independently correlated only with D/Pcreatinine, free water transport and ultrafiltration through small pores. Conclusions. Uni-PET is a combination of two tests that provides more information on the function of the membrane compared with PET. Our study on a PD cohort using only biocompatible solutions revealed that function membrane parameters remained stable over a long time. Ultrafiltration failure was correlated with increased D/P creatinine and decreased free water transport and ultrafiltration through small pores.

Do low GDP neutral pH solutions prevent or retard peritoneal membrane alterations in long-term peritoneal dialysis?

Several studies have been published in the last decade on the effects of low glucose degradation product (GDP) neutral pH (L-GDP/N-pH) dialysis solutions on peritoneal morphology and function during the long-term PD treatment. Compared to conventional solutions, the impact of these solutions on the morphological and functional alterations of the peritoneal membrane is discussed, including those of effluent proteins that reflect the status of peritoneal tissues. Long-term PD with conventional solutions is associated with the loss of mesothelium, submesothelial and interstitial fibrosis, vasculopathy, and deposition of advanced glycosylation end products (AGEs). L-GDP/N-pH solutions mitigate these alterations, although vasculopathy and AGE deposition are still present. Increased vascular density was found in some studies. Small solute transport increases with PD duration on conventional solutions. Initially, higher values are present on L-GDP/N-pH treatment, but these may be reversible and remain stable with PD duration. Consequently, ultrafiltration (UF) is lower initially but remains stable thereafter. At 5 years, UF and small pore fluid transport are higher, while free water transport decreased only slightly during follow-up. Cancer antigen 125 was initially higher on L-GDP/N-pH solutions, suggesting better mesothelial preservation but decreased during follow-up. Therefore, L-GDP/N-pH solutions may not prevent but reduce and retard the peritoneal alterations induced by continuous exposure to glucose-based dialysis fluids.

Comparison of Longitudinal Membrane Function in Peritoneal Dialysis Patients According to Dialysis Fluid Biocompatibility

Introduction

Preservation of peritoneal function is essential in long-term peritoneal dialysis. Biocompatible dialysis solutions might prevent or postpone the membrane alteration resulting in ultrafiltration failure and consecutive morbidity and mortality.

Methods

We conducted an observational cohort study in which we made a longitudinal comparison between the course of peritoneal solute and fluid transport during treatment with conventional and biocompatible solutions. Therefore, prospectively collected peritoneal transport data from the yearly standard peritoneal permeability analysis were analyzed in 251 incident patients treated between 1994 and censoring in 2016. Fluid transport included small pore and free water transport. Solute transport was assessed by creatinine mass transfer area coefficient and glucose absorption. Linear mixed models including change point analyses were performed. Interaction with peritonitis was examined.

Results

One hundred thirty-five patients received conventional and 116 biocompatible solutions. Sixty-seven percent (conventional) and 64% (biocompatible) of these underwent minimally three transport measurements. Initially, biocompatible fluids showed higher small solute transport and lower ultrafiltration than conventional fluids up to 3 years. Thereafter, conventional fluids showed an increase in small solute transport (+2.7 ml/min per year; 95% confidence interval [CI]: 0.9 to 4.5) and a decrease of free water transport (−28.0 ml/min per year; 95% CI: −60.4 to 4.4). These were minor or absent in biocompatible treatment. Peritonitis induced a decrease of transcapillary ultrafiltration after 2 years on dialysis with conventional solutions (−291 ml/min per year; 95% CI: −550 to −32) while this was absent in biocompatible treatment.

Conclusion

Despite a higher initial solute transport with biocompatible solutions, these have less influence on functional long-term peritoneal alterations than conventional solutions.

The osmo-metabolic approach: a novel and tantalizing glucose-sparing strategy in peritoneal dialysis

Peritoneal dialysis (PD) is a viable but under-prescribed treatment for uremic patients. Concerns about its use include the bio-incompatibility of PD fluids, due to their potential for altering the functional and anatomical integrity of the peritoneal membrane. Many of these effects are thought to be due to the high glucose content of these solutions, with attendant issues of products generated during heat treatment of glucose-containing solutions. Moreover, excessive intraperitoneal absorption of glucose from the dialysate has many potential systemic metabolic effects. This article reviews the efforts to develop alternative PD solutions that obviate some of these side effects, through the replacement of part of their glucose content with other osmolytes which are at least as efficient in removing fluids as glucose, but less impactful on patient metabolism. In particular, we will summarize clinical studies on the use of alternative osmotic ingredients that are commercially available (icodextrin and amino acids) and preclinical studies on alternative solutions under development (taurine, polyglycerol, carnitine and xylitol). In addition to the expected benefit of a glucose-sparing approach, we describe an ‘osmo-metabolic’ approach in formulating novel PD solutions, in which there is the possibility of exploiting the pharmaco-metabolic properties of some of the osmolytes to attenuate the systemic side effects due to glucose. This approach has the potential to ameliorate pre-existing co-morbidities, including insulin resistance and type-2 diabetes, which have a high prevalence in the dialysis population, including in PD patients.

Blood pressure and volume management in dialysis: conclusions from a Kidney Disease: Improving Global Outcomes (KDIGO) Controversies Conference

Blood pressure (BP) and volume control are critical components of dialysis care and have substantial impacts on patient symptoms, quality of life, and cardiovascular complications. Yet, developing consensus best practices for BP and volume control have been challenging, given the absence of objective measures of extracellular volume status and the lack of high-quality evidence for many therapeutic interventions. In February of 2019, Kidney Disease: Improving Global Outcomes (KDIGO) held a Controversies Conference titled Blood Pressure and Volume Management in Dialysis to assess the current state of knowledge related to BP and volume management and identify opportunities to improve clinical and patient-reported outcomes among individuals receiving maintenance dialysis. Four major topics were addressed: BP measurement, BP targets, and pharmacologic management of suboptimal BP; dialysis prescriptions as they relate to BP and volume; extracellular volume assessment and management with a focus on technology-based solutions; and volume-related patient symptoms and experiences. The overarching theme resulting from presentations and discussions was that managing BP and volume in dialysis involves weighing multiple clinical factors and risk considerations as well as patient lifestyle and preferences, all within a narrow therapeutic window for avoiding acute or chronic volume-related complications. Striking this challenging balance requires individualizing the dialysis prescription by incorporating comorbid health conditions, treatment hemodynamic patterns, clinical judgment, and patient preferences into decision-making, all within local resource constraints.

Icodextrin Versus Glucose Solutions for the Once-Daily Long Dwell in Peritoneal Dialysis: An Enriched Systematic Review and Meta-analysis of Randomized Controlled Trials

RATIONALE & OBJECTIVE

The efficacy and safety of icodextrin versus glucose-only peritoneal dialysis (PD) regimens is unclear. The aim of this study was to compare once-daily long-dwell icodextrin versus glucose among patients with kidney failure undergoing PD.

STUDY DESIGN

Systematic review of randomized controlled trials (RCTs), enriched with unpublished data from investigator-initiated and industry-sponsored studies.

SETTING & STUDY POPULATIONS

Individuals with kidney failure receiving regular PD treatment enrolled in clinical trials of dialysate composition.

SELECTION CRITERIA FOR STUDIES

Medline, Embase, CENTRAL, Ichushi Web, 10 Chinese databases, clinical trials registries, conference proceedings, and citation lists from inception to November 2018. Further data were obtained from principal investigators and industry clinical study reports.

DATA EXTRACTION

2 independent reviewers selected studies and extracted data using a prespecified extraction instrument.

ANALYTIC APPROACH

Qualitative synthesis of demographics, measurement scales, and outcomes. Quantitative synthesis with Mantel-Haenszel risk ratios (RRs), Peto odds ratios (ORs), or (standardized) mean differences (MDs). Risk of bias of included studies at the outcome level was assessed using the Cochrane risk-of-bias tool for RCTs.

RESULTS

19 RCTs that enrolled 1,693 participants were meta-analyzed. Ultrafiltration was improved with icodextrin (medium-term MD, 208.92 [95% CI, 99.69-318.14] mL/24h; high certainty of evidence), reflected also by fewer episodes of fluid overload (RR, 0.43 [95% CI, 0.24-0.78]; high certainty). Icodextrin-containing PD probably decreased mortality risk compared to glucose-only PD (Peto OR, 0.49 [95% CI, 0.24-1.00]; moderate certainty). Despite evidence of lower peritoneal glucose absorption with icodextrin-containing PD (medium-term MD, -40.84 [95% CI, -48.09 to-33.59] g/long dwell; high certainty), this did not directly translate to changes in fasting plasma glucose (-0.50 [95% CI, -1.19 to 0.18] mmol/L; low certainty) and hemoglobin A_1c levels (-0.14% [95% CI, -0.34% to 0.05%]; high certainty). Safety outcomes and residual kidney function were similar in both groups; health-related quality-of-life and pain scores were inconclusive.

LIMITATIONS

Trial quality was variable. The follow-up period was heterogeneous, with a paucity of assessments over the long term. Mortality results are based on just 32 events and were not corroborated using time-to-event analysis of individual patient data.

CONCLUSIONS

Icodextrin for once-daily long-dwell PD has clinical benefit for some patients, including those not meeting ultrafiltration targets and at risk for fluid overload. Future research into patient-centered outcomes and cost-effectiveness associated with icodextrin is needed.