Longitudinal relationship between solute transport and ultrafiltration capacity in peritoneal dialysis patients

The relationship between changes in peritoneal permeability with CA-125 and HIF-1α

BACKGROUND

Peritoneal fibrosis (PF) is a major, persistent complication of prolonged peritoneal dialysis that eventually leads to peritoneal ultrafiltration failure and termination of peritoneal dialysis. Prolonged exposure to high glucose concentrations, degradation products, uremic toxins, and episodes of peritonitis can cause some changes in the peritoneal membrane, resulting in intraperitoneal inflammation and PF, leading to failure of ultrafiltration and dialysis. CA-125 can be used as a biomarker of peritoneal mesothelial cell count in the peritoneal dialysate and for monitoring cell count in PD patients. Hypoxia-inducible factor 1-alpha (HIF-1α) has been reported to cause PF, but has not been reported to be associated with changes in peritoneal structure. We hypothesized that peritoneal adequacy can be followed using HIF-1α and CA-125 values. In the present study, therefore, we investigated the relationship between HIF-1α and CA-125 levels and parietal membrane permeability changes in PD patients.

METHODS

Forty-five patients were included in the study. Peritoneal permeability was constant in 20 of these, while peritoneal permeability increased in 11 and decreased in 14. The HIF-1α value from the blood samples of the patients and the CA-125 measurement from the peritoneal fluids were measured. The relationship between peritoneal variability and CA-125 and HIF levels after follow-up was investigated.

RESULTS

We compared serum HIF-1α and peritoneal fluid CA-125 levels in the three groups receiving peritoneal dialysis treatment. HIF-1α levels increased with peritoneal permeability changes, while CA-125 levels decreased. In patients with high to low permeability changes, HIF-1α levels were higher compared to those with stable or low to high changes, which was statistically significant. Conversely, CA-125 levels significantly decreased in patients whose peritoneal permeability changed from high to low, compared to the other two groups.

CONCLUSION

Changes in peritoneal structure can be followed with biomarkers. It has been shown that CA-125 and HIF-1α levels can guide the changes in the peritoneal membrane. This can be useful in the monitoring of peritoneal dialysis.

Physiology of peritoneal dialysis; pathophysiology in long-term patients

The microvascular wall of peritoneal tissues is the main barrier in solute and water transport in the initial phase of peritoneal dialysis (PD). Small solute transport is mainly by diffusion through inter-endothelial pores, as is hydrostatic fluid transport with dissolved solutes. Water is also transported through the intra-endothelial water channel aquaporin-1(AQP-1) by a glucose-induced crystalloid osmotic gradient (free water transport). In the current review the physiology of peritoneal transport will be discussed both during the first years of PD and after long-term treatment with emphasis on the peritoneal interstitial tissue and its role in free water transport. Attention will be paid to the role of glucose-induced pseudohypoxia causing both increased expression of fibrogenetic factors and of the glucose transporter GLUT-1. The former leads to peritoneal fibrosis, the latter to a reduced crystalloid osmotic gradient, explaining the decrease in free water transport as a cause of ultrafiltration failure. These phenomena strongly suggest that the extremely high dialysate glucose concentrations are the driving force of both morphologic and functional peritoneal alterations that may develop during long-term PD.

Predicting solute transfer rate in patients initiating peritoneal dialysis

BACKGROUND

While assessment of membrane characteristics is fundamental to peritoneal dialysis (PD) prescription in patients initiating therapy, peritoneal equilibration test has theoretical and practical drawbacks. We wished to determine whether an equation using simple clinical variables could predict fast (above population mean) peritoneal solute transfer rate without dialysate sampling.

METHODS

We measured peritoneal solute transfer rate, as determined by peritoneal equilibration test using the 4-h dialysate to plasma creatinine ratio, in consecutive PD outpatients attending a single tertiary hospital for their first clinical follow-up within 3 months of dialysis initiation. An equation estimating peritoneal solute transfer rate based on readily available clinical variables was generated in a randomly selected modeling group and tested in a distinct validation group.

RESULTS

We included 712 patients, with 562 in the modeling group and 150 in the validation group. Mean age was 58.4 ± 15.9 with 431 (60.5%) men. Mean peritoneal solute transfer rate value was 0.73 ± 0.13. An equation based on gender, race, serum sodium and albumin yielded a receiving operator characteristics (ROC) area under the curve (AUC) to detect fast peritoneal solute transfer rate (> 0.73) of 0.74 (0.67-0.82). Estimated peritoneal solute transfer rate values based on percentiles 15th (> 0.66), 20th (> 0.68), 25th (> 0.69) and 30th (> 0.70) could rule out fast peritoneal solute transfer rate with negative predictive values of 100%, 93.5%, 84.2% and 80.0%, respectively.

CONCLUSIONS

An equation based on simple clinical variables allows ruling out fast transport in a significant proportion of patients initiating PD with a high degree of confidence without requiring dialysate sampling. This could prove useful in guiding dialysis prescription of PD patients in daily clinical practice, particularly in low-resource settings.

The Peritoneal Membrane and Its Role in Peritoneal Dialysis

A healthy and functional peritoneal membrane is key to achieving sufficient ultrafiltration and restoring 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 versus colloid osmosis; why and how to assess membrane function using peritoneal equilibration tests; the etiologies of membrane dysfunction and their specific management; and the effect 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, the care of patients treated with PD.

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 centre-calculated cutoff value is better for identifying fast peritoneal solute transfer of patients on peritoneal dialysis than the traditional value: a retrospective cohort study

Background

The mean 4-h dialysate to plasma ratio of creatinine (4-h D/Pcr) is a vital cutoff value for recognizing the fast peritoneal solute transfer rate (PSTR) in patients on peritoneal dialysis (PD); however, it shows a noticeable centre effect. We aimed to investigate our centre-calculated cutoff value (CCV) of 4-h D/Pcr and compare it with the traditional cutoff value (TCV) (0.65).

Methods

In this study, we enrolled incident PD patients at our centre from 2008 to 2019, and divided them into fast or non-fast PSTR groups according to baseline 4-h D/Pcr-based CCV or TCV. We compared the efficiency of the fast PSTR recognized by two cutoff values in predicting mortality, ultrafiltration (UF) insufficiency and technical survival.

Results

In total, 1905 patients were enrolled, with a mean 4-h D/Pcr of 0.71 ± 0.11. Compared with TCV (0.65), CCV (0.71) showed superiority in predicting mortality of PD patients [hazard ratio (HR) 1.27, 95% confidence interval (CI) 1.02-1.59 vs HR 1.24, 95% CI 0.97-1.59]. The odds ratio (OR) of the fast PSTR in centre classification was slightly higher than traditional classification in predicting UF insufficiency (OR 1.67, 95% CI 1.25-2.24 vs OR 1.60, 95% CI 1.15-2.22). Additionally, the restricted cubic splines 4-h D/Pcr has an S-shaped association with mortality and UF insufficiency, and the inflection points of 4-h D/Pcr were 0.71 (equal to CCV).

Conclusions

The CCV of 4-h D/Pcr for identifying fast PSTR was 0.71. It was superior to TCV in predicting mortality and UF insufficiency.

Peritoneal equilibration testing: Your questions answered

The peritoneal equilibration test (PET), first described in 1987, is a semiquantitative assessment of peritoneal transfer characteristics in patients undergoing peritoneal dialysis. It is typically performed as a 4-h exchange using 2.27/2.5% dextrose dialysate with serial measurements of blood and dialysate creatinine, urea, and glucose concentrations. The percentage absorption of glucose and D/P creatinine ratio are used to determine peritoneal solute transfer rates. It is used to both help guide peritoneal dialysis prescriptions and to prognosticate. There are several derivative tests which have been described in the literature. In this review, we describe the original PET, the various iterations of the PET, the information gleaned, and the use in the setting of poor solute clearance and in the diagnosis of membrane dysfunction, and limitations of the PET.

Increased Peritoneal Protein Loss and Diabetes: Is There a Link?

Increased peritoneal protein loss has been associated with the fast transport of small molecules, diabetes mellitus (DM), and a reduced survival in patients on peritoneal dialysis (PD), although some studies did not confirm the association with survival. In this single-center retrospective study, we investigated the relationship of baseline peritoneal albumin and protein loss with transport status, comorbidities including DM, and survival in 106 incident PD patients during the period of July 2005–June 2014. Five-year survival rate was determined using Cox-regression analysis. There were not significant differences in D/Pcr or peritoneal protein and albumin loss between diabetics and non-diabetics. In the group of 66 non-diabetics, high and high-average transporters for creatinine had higher values for both peritoneal protein (11.85 ± 6.77 vs. 7.85 ± 4.36 g/day; p = 0.002) and albumin (5.03 ± 2.32 vs. 3.72 ± 1.54 g/day; p = 0.016) loss as compared to slow transporters. However, in the group of 40 diabetics, this association was not observed. Upon multivariable regression analysis, the independent association of D/PCr with peritoneal albumin (β = 0.313; p = 0.008) and protein (β = 0.441; p = 0.001) loss was found only in non-diabetics in whom ultrafiltration also appeared as a significant predictor of peritoneal protein loss (β = 0.330; p = 0.000). A high comorbidity grade, older age, and low serum albumin were associated with mortality, but both peritoneal protein and albumin loss as well as D/Pcr were not determinants of survival. Baseline peritoneal protein and albumin loss was not associated with DM and did not predict survival. The clinical significance of the absence of association between fast peritoneal transport status and peritoneal protein flux in diabetics should be evaluated in a prospective study comprising a greater number of diabetics with evaluation of overhydration as a main inducing variable of protein leak.

From MIA to FIFA: The vicious matrix of frailty, inflammation, fluid overload and atherosclerosis in peritoneal dialysis

Cardiovascular disease (CVD) is a major cause of mortality and morbidity in peritoneal dialysis (PD) patients. Two decades ago, the common co-existence of malnutrition and systemic inflammation PD patients with atherosclerosis and CVD led to the proposed terminology of 'malnutrition-inflammation-atherosclerosis (MIA) syndrome'. Although the importance of malnutrition is well accepted, frailty represents a more comprehensive assessment of the physical and functional capability of the patient and encompasses the contributions of sarcopenia (a key component of malnutrition), obesity, cardiopulmonary as well as neuropsychiatric impairment. In recent years, it is also increasingly recognized that fluid overload is not only the consequence but also play an important role in the pathogenesis of CVD. Moreover, fluid overload is closely linked with the systemic inflammatory status, presumably by gut oedema, gastrointestinal epithelial barrier dysfunction and leakage of bacterial fragments to the systemic circulation. There are now a wealth of published evidence to show intricate relations between frailty, inflammation, fluid overload and atherosclerotic disease in patients with chronic kidney disease (CKD) and those on PD, a phenomenon that we propose the term 'FIFA complex'. In this system, frailty and atherosclerotic disease may be regarded as two patient-oriented outcomes, while inflammation and fluid overload are two inter-connected pathogenic processes. However, there remain limited data on how the treatment of one component affect the others. It is also important to define how treatment of fluid overload affect the systemic inflammatory status and to develop effective anti-inflammatory strategies that could alleviate atherosclerotic disease and frailty.

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.

Oxidative Stress-Induced Alterations of Cellular Localization and Expression of Aquaporin 1 Lead to Defected Water Transport upon Peritoneal Fibrosis

Being one of the renal replacement therapies, peritoneal dialysis (PD) maintains around 15% of end-stage kidney disease patients’ lives; however, complications such as peritoneal fibrosis and ultrafiltration failure during long-term PD compromise its application. Previously, we established a sodium hypochlorite (NaClO)-induced peritoneal fibrosis porcine model, which helped to bridge the rodent model toward pre-clinical human peritoneal fibrosis research. In this study, the peritoneal equilibration test (PET) was established to evaluate instant functional changes in the peritoneum in the pig model. Similar to observations from long-term PD patients, increasing small solutes transport and loss of sodium sieving were observed. Mechanistic investigation from both in vivo and in vitro data suggested that disruption of cytoskeleton induced by excessive reactive oxygen species defected intracellular transport of aquaporin 1, this likely resulted in the disappearance of sodium sieving upon PET. Functional interference of aquaporin 1 on free water transport would result in PD failure in patients.

Incremental Versus Standard (Full-Dose) Peritoneal Dialysis

Incremental peritoneal dialysis (PD), defined as less than “standard dose” PD prescription, has a number of possible benefits, including better preservation of residual kidney function (RKF), reduced risk of peritonitis, lower peritoneal glucose exposure, lesser environmental impact, and reduced costs. Patients commencing PD are often new to kidney replacement therapy and possess substantial RKF, which may allow safe delivery of an incremental prescription, often in the form of lower frequency or duration of PD. This has the potential to help improve quality of life (QOL) and life participation through reducing time requirements and burden of treatment. Alternatively, incremental PD could potentially contribute to reduced small solute clearance, fluid overload, or patient reluctance to increase dialysis prescription when later needed. This review discusses the definition, rationale, uptake, potential advantages and disadvantages, and clinical trial evidence pertaining to the use of incremental PD.

Assessment of the size selectivity of peritoneal permeability by the restriction coefficient to protein transport

Transport of serum proteins from the circulation to peritoneal dialysate in peritoneal dialysis patients mainly focused on total protein. Individual proteins have hardly been studied. We determined serum and effluent concentrations of four individual proteins with a wide molecular weight range routinely in the standardised peritoneal permeability analysis performed yearly in all participating patients. These include β2-microglobulin, albumin, immunoglobulin G and α2-macroglobulin. The dependency of transport of these proteins on their molecular weight and diffusion coefficient led to the development of the peritoneal protein restriction coefficient (PPRC), which is the slope of the relation between the peritoneal clearances of these proteins and their free diffusion coefficients in water, when plotted on a double logarithmic scale. The higher the PPRC, the more size restriction to transport. In this review, we discuss the results obtained on the PPRC under various conditions, such as effects of various osmotic agents, vasoactive drugs, peritonitis and the hydrostatic pressure gradient. Long-term follow-up of patients shows an increase of the PPRC, the possible causes of which are discussed. Venous vasculopathy of the peritoneal microcirculation is the most likely explanation.

Optimised versus standard automated peritoneal dialysis regimens pilot study (OptiStAR): A randomised controlled crossover trial

BACKGROUND

The continuous global rise of end-stage kidney disease creates a growing demand of economically beneficial home-based kidney replacement therapies such as peritoneal dialysis (PD). However, undesirable absorption and exposure of peritoneal tissues to glucose remain major limitations of PD.

METHODS

We compared a reference (standard) automated PD regimen 6 × 2 L 1.36% glucose (76 mmol/L) over 9 h with a novel, theoretically glucose sparing (optimised) prescription consisting of 'ultrafiltration cycles' with high glucose strength (126 mmol/L) and 'clearance cycles' with ultra-low, physiological glucose (5 mmol/L) for approximately 40% of the treatment time. Twenty-one prevalent PD patients underwent the optimised regimen (7 × 2 L 2.27% glucose + 5 × 2 L 0.1% glucose over 8 h) and the standard regimen in a crossover fashion. Six patients were excluded from data analysis.

RESULTS

Median glucose absorption was 43 g (IQR 41-54) and 44 g (40-55) for the standard and optimised intervention, respectively (p = 1). Ultrafiltration volume, weekly Kt/V creatinine and urea were significantly improved during optimised interventions, while no difference in sodium removal was detected. Post hoc analysis showed significantly improved ultrafiltration efficiency (ml ultrafiltration per gram absorbed glucose) during optimised regimens. No adverse events were observed except one incidence of drain pain.

CONCLUSION

Optimised treatments were feasible and well tolerated in this small pilot study. Despite no difference in absorbed glucose, results indicate possible improvements of ultrafiltration efficiency and small solute clearances by optimised regimens. Use of optimised prescriptions as glucose sparing strategy should be evaluated in larger study populations.

Acquired Decline in Ultrafiltration in Peritoneal Dialysis: The Role of Glucose

Ultrafiltration is essential in peritoneal dialysis (PD) for maintenance of euvolemia, making ultrafiltration insufficiency-preferably called ultrafiltration failure-an important complication. The mechanisms of ultrafiltration and ultrafiltration failure are more complex than generally assumed, especially after long-term treatment. Initially, ultrafiltration failure is mainly explained by a large number of perfused peritoneal microvessels, leading to a rapid decline of the crystalloid osmotic gradient, thereby decreasing aquaporin-mediated free water transport. The contribution of peritoneal interstitial tissue to ultrafiltration failure is limited during the first few years of PD, but becomes more important in long-term PD due to the development of interstitial fibrosis, which mainly consists of myofibroblasts. A dual hypothesis has been developed to explain why the continuous exposure of peritoneal tissues to the extremely high dialysate glucose concentrations causes progressive ultrafiltration decline. First, glucose absorption causes an increase of the intracellular NADH/NAD⁺ ratio, also called pseudohypoxia. Intracellular hypoxia stimulates myofibroblasts to produce profibrotic and angiogenetic factors, and the glucose transporter GLUT-1. Second, the increased GLUT-1 expression by myofibroblasts increases glucose uptake in these cells, leading to a reduction of the osmotic gradient for ultrafiltration. Reduction of peritoneal glucose exposure to prevent this vicious circle is essential for high-quality, long-term PD.

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

Blockade of Autophagy Prevents the Development and Progression of Peritoneal Fibrosis

Peritoneal fibrosis (PF) is a major cause of ultrafiltration failure in long-term peritoneal dialysis (PD) patients. Nevertheless, limited measures have been shown to be effective for the prevention and treatment of PF. Some views reveal that activation of autophagy ameliorates PF but others demonstrate that autophagy promotes PF. It is obvious that the role of autophagy in PF is controversial and further studies are needed. Here, we investigated the role of autophagy in rat models of PF and damaged cultured human peritoneal mesothelial cells (HPMCs). Autophagy was highly activated in fibrotic peritoneum from two PF rat models induced by 4.25% peritoneal dialysate fluid (PDF) and 0.1% chlorhexidine gluconate (CG). Blockade of autophagy with 3-MA effectively prevented PF in both models and reversed epithelial to mesenchymal transition (EMT) by down-regulating TGF-β/Smad3 signaling pathway and downstream nuclear transcription factors Slug and Snail. Treatment with 3-MA also inhibited activation of EGFR/ERK1/2 signaling pathway during PF. Moreover, 3-MA prominently decreased STAT3/NF-κB-mediated inflammatory response and macrophage infiltration, and prevented peritoneal angiogenesis through downregulation of β-catenin signal. In addition, TGF-β1 stimulation up-regulated autophagic activity as evidenced by the increased autophagosome in vitro. Exposure of HPMCs to TGF-β1 resulted in the induction of EMT and activation of TGF-β/Smad3, EGFR/ERK1/2 signaling pathways. Treatment with 3-MA blocked all these responses. In addition, delayed administration of 3-MA was effective in reducing EMT induced by TGF-β1. Taken together, our study indicated that autophagy might promote PF and 3-MA had anti-fibrosis effect in vivo and in vitro. These results suggest that autophagy could be a potential target on PF therapy for clinical patients with long-term PD.

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.

Peritoneal Dialysis Guidelines 2019 Part 1 (Position paper of the Japanese Society for Dialysis Therapy)

Approximately 10 years have passed since the Peritoneal Dialysis Guidelines were formulated in 2009. Much evidence has been reported during the succeeding years, which were not taken into consideration in the previous guidelines, e.g., the next peritoneal dialysis PD trial of encapsulating peritoneal sclerosis (EPS) in Japan, the significance of angiotensin-converting enzyme inhibitors (ACEIs) and angiotensin receptor blockers (ARBs), the effects of icodextrin solution, new developments in peritoneal pathology, and a new international recommendation on a proposal for exit-site management. It is essential to incorporate these new developments into the new clinical practice guidelines. Meanwhile, the process of creating such guidelines has changed dramatically worldwide and differs from the process of creating what were “clinical practice guides.” For this revision, we not only conducted systematic reviews using global standard methods but also decided to adopt a two-part structure to create a reference tool, which could be used widely by the society’s members attending a variety of patients. Through a working group consensus, it was decided that Part 1 would present conventional descriptions and Part 2 would pose clinical questions (CQs) in a systematic review format. Thus, Part 1 vastly covers PD that would satisfy the requirements of the members of the Japanese Society for Dialysis Therapy (JSDT). This article is the duplicated publication from the Japanese version of the guidelines and has been reproduced with permission from the JSDT.

STAT3/HIF-1α signaling activation mediates peritoneal fibrosis induced by high glucose

BACKGROUND

Epithelial-mesenchymal transition (EMT) of mesothelial cells is a key step in the peritoneal fibrosis (PF). Recent evidence indicates that signal transducer and activator of transcription 3 (STAT3) might mediate the process of renal fibrosis, which could induce the expression of hypoxia-inducible factor-1α (HIF-1α). Here, we investigated the effect of STAT3 activation on HIF-1α expression and the EMT of mesothelial cells, furthermore the role of pharmacological blockade of STAT3 in the process of PF during peritoneal dialysis (PD) treatment.

METHODS

Firstly, we investigated the STAT3 signaling in human peritoneal mesothelial cells (HPMCs) from drained PD effluent. Secondly, we explored the effect of STAT3 signaling activation on the EMT and the expression of HIF-1α in human mesothelial cells (Met-5A) induced by high glucose. Finally, peritoneal fibrosis was induced by daily intraperitoneal injection with peritoneal dialysis fluid (PDF) so as to explore the role of pharmacological blockade of STAT3 in this process.

RESULTS

Compared with the new PD patient, the level of phosphorylated STAT3 was up-regulated in peritoneal mesothelial cells from long-term PD patients. High glucose (60 mmol/L) induced over-expression of Collagen I, Fibronectin, α-SMA and reduced the expression of E-cadherin in Met-5A cells, which could be abrogated by STAT3 inhibitor S3I-201 pretreatment as well as by siRNA for STAT3. Furthermore, high glucose-mediated STAT3 activation in mesothelial cells induced the expression of HIF-1α and the profibrotic effect of STAT3 signaling was alleviated by siRNA for HIF-1α. Daily intraperitoneal injection of high-glucose based dialysis fluid (HG-PDF) induced peritoneal fibrosis in the mice, accompanied by the phosphorylation of STAT3. Immunostaining showed that phosphorylated STAT3 was expressed mostly in α-SMA positive cells in the peritoneal membrane induced by HG-PDF. Administration of S3I-201 prevented the progression of peritoneal fibrosis, angiogenesis, macrophage infiltration as well as the expression of HIF-1α in the peritoneal membrane induced by high glucose.

CONCLUSIONS

Taken together, these findings identified a novel mechanism linking STAT3/HIF-1α signaling to peritoneal fibrosis during long-term PD treatment. It provided the first evidence that pharmacological inhibition of STAT3 signaling attenuated high glucose-mediated mesothelial cells EMT as well as peritoneal fibrosis.

Effects of bicarbonate/lactate-buffered neutral peritoneal dialysis fluids on angiogenesis-related proteins in patients undergoing peritoneal dialysis

Background

In order to facilitate the safe and long-term delivery of peritoneal dialysis (PD), it is necessary to improve the biocompatibility of peritoneal dialysis fluids (PDFs). The novel bicarbonate/lactate-buffered neutral PDFs (B/L-PDFs) are expected to be improved biocompatible. This study evaluated the biocompatibility of B/L-PDFs by analysis on the profile of angiogenesis-related proteins in drained dialysate of patients undergoing PD.

Methods

Concentrations of 20 angiogenesis-related proteins in the dialysate were semi-quantitatively determined using a RayBio® Human Angiogenesis Antibody Array and were compared between B/L-PDFs and conventional lactate-buffered neutral PDFs (L-PDFs).

Results

The expression of growth-related oncogene (GRO α/β/γ), which belongs to the CXC chemokine family, decreased significantly after use of the B/L-PDFs compared to the L-PDFs (P = 0.03). The number of the proteins with lower level in the B/L-PDFs compared with L-PDFs was significantly negatively correlated with the PD duration (Spearman ρ = − 0.81, P = 0.004).

Conclusion

This study suggested that B/L-PDFs are more biocompatible than conventional PDFs.

Clinical factors affecting cerebral oxygenation in patients undergoing peritoneal dialysis

BACKGROUND

Although cerebral regional oxygen saturation (rSO₂) is significantly lower in hemodialysis (HD) patients than that in healthy controls, investigations on cerebral oxygenation in peritoneal dialysis (PD) patients are limited. We aimed to confirm the cerebral oxygenation status and identify the factors affecting cerebral rSO₂ in PD patients.

METHODS

Thirty-six PD patients (21 men and 15 women; mean age, 62.8 ± 12.7 years) were recruited. In addition, 27 healthy volunteers (17 men and 10 women; mean age, 43.5 ± 18.8 years) were recruited as a control group. Cerebral rSO₂ was monitored at the forehead using an INVOS 5100c oxygen saturation monitor.

RESULTS

Cerebral rSO₂ was significantly lower in PD patients than that in healthy controls (57.0 ± 7.3% vs 68.9 ± 8.6%, p < 0.001); moreover, cerebral rSO₂ was significantly correlated with natural logarithm (Ln)-PD duration (r = -0.389, p = 0.019) and serum albumin concentration (r = 0.370, p = 0.026) in a simple linear regression analysis. Multivariable linear regression analysis was performed using variables that showed a significant correlation and p < 0.20 (serum creatinine, serum sodium, Ln-C-reactive protein, and dosage of erythropoiesis-stimulating agent) with the cerebral rSO₂. Cerebral rSO₂ was independently associated with Ln-PD duration (standardized coefficient: -0.339) and serum albumin concentration (standardized coefficient: 0.316).

CONCLUSIONS

Cerebral rSO₂ was significantly affected by the PD duration and serum albumin concentration. Further prospective studies are needed to clarify whether preventing a decrease in serum albumin concentration leads to the maintenance of cerebral oxygenation in patients undergoing PD.

Low-GDP, pH-neutral solutions preserve peritoneal endothelial glycocalyx during long-term peritoneal dialysis

BACKGROUND

During peritoneal dialysis (PD), solute transport and ultrafiltration are mainly achieved by the peritoneal blood vasculature. Glycocalyx lies on the surface of endothelial cells and plays a role in vascular permeability. Low-glucose degradation product (GDP), pH-neutral PD solutions reportedly offer higher biocompatibility and lead to less peritoneal injury. However, the effects on the vasculature have not been clarified.

METHODS

Peritoneal tissues from 11 patients treated with conventional acidic solutions (acidic group) and 11 patients treated with low-GDP, pH-neutral solutions (neutral group) were examined. Control tissues were acquired from 5 healthy donors of kidney transplants (control group). CD31 and ratio of luminal diameter to vessel diameter (L/V ratio) were evaluated to identify endothelial cells and vasculopathy, respectively. Immunostaining for heparan sulfate (HS) domains and Ulex europaeus agglutinin-1 (UEA-1) binding was performed to assess sulfated glycosaminoglycans and the fucose-containing sugar chain of glycocalyx.

RESULTS

Compared with the acidic group, the neutral group showed higher CD31 positivity. L/V ratio was significantly higher in the neutral group, suggesting less progression of vasculopathy. Both HS expression and UEA-1 binding were higher in the neutral group, whereas HS expression was markedly more preserved than UEA-1 binding in the acidic group. In vessels with low L/V ratio, which were found only in the acidic group, HS expression and UEA-1 binding were diminished, suggesting a loss of glycocalyx.

CONCLUSION

Peritoneal endothelial glycocalyx was more preserved in patients treated with low-GDP, pH-neutral solution. The use of low-GDP, pH-neutral solutions could help to protect peritoneal vascular structures and functions.

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.

Associations between dialysate interleukin-6 and Tie-2 and peritoneal solute transport rate and outcomes for patients undergoing peritoneal dialysis: A prospective cohort study

Objectives

We designed this prospective observational study to clarify the associations between dialysate IL-6, a marker of ongoing peritoneal inflammation, Tie2, an important factor in angiogenesis in the peritoneum, and a high peritoneal solute transport rate (PSTR) in patients undergoing peritoneal dialysis (PD) and to investigate their outcome predictive roles.

Methods

A total of 60 stable continuous ambulatory peritoneal dialysis (CAPD) patients from a single center in China were analyzed in this prospective study. We measured dialysate levels of IL-6 and Tie-2 using ELISAs. Our primary study endpoint was all-cause mortality with 10 years' follow-up.

Results

For the evaluation of PSTR, we used the Dialysis/Plasma creatinine (D/Pcr) ratio. We subdivided the patients into two groups for statistical evaluation: low and low average D/Pcr (<0.64; L/A), and high and high average D/Pcr (≥0.65; H/A) transporters. The mean levels of dialysates IL-6 (21.71 ± 8.88 pg/mL) and Tie-2 (1.23 ± 0.43 ng/mL) were significantly higher in the H/A (high and high average, group than those in the L/A group (13.94 ± 5.43 pg/mL, p<0.001 and 0.95 ± 0.43 ng/mL, p=0.019; respectively). Moreover, IL-6 and Tie-2 were positively correlated with D/Pcr (r=0.366, p=0.004 and r=0.402, p=0.001; respectively). Both dialysates IL-6 and Tie-2 were independent determinants of a high peritoneal solute transport rate. After follow-up for 42.65±18.08 months, 30 patients (50.0%) had died. An increased D/Pcr increased the risk of all-cause mortality in patients with CAPD (p=0.018), but the dialysates IL-6 and Tie2 were not independent predictors of all-cause mortality (p>0.05).

Conclusion

Our results suggest that patients undergoing CAPD have a high peritoneal solute transport status with local peritoneal inflammation and angiogenesis. Increased D/Pcr is a relative risk factor for mortality and technique failure in patients undergoing CAPD.

Mechanisms of Peritoneal Fibrosis: Focus on Immune Cells-Peritoneal Stroma Interactions

Peritoneal fibrosis is characterized by abnormal production of extracellular matrix proteins leading to progressive thickening of the submesothelial compact zone of the peritoneal membrane. This process may be caused by a number of insults including pathological conditions linked to clinical practice, such as peritoneal dialysis, abdominal surgery, hemoperitoneum, and infectious peritonitis. All these events may cause acute/chronic inflammation and injury to the peritoneal membrane, which undergoes progressive fibrosis, angiogenesis, and vasculopathy. Among the cellular processes implicated in these peritoneal alterations is the generation of myofibroblasts from mesothelial cells and other cellular sources that are central in the induction of fibrosis and in the subsequent functional deterioration of the peritoneal membrane. Myofibroblast generation and activity is actually integrated in a complex network of extracellular signals generated by the various cellular types, including leukocytes, stably residing or recirculating along the peritoneal membrane. Here, the main extracellular factors and the cellular players are described with emphasis on the cross-talk between immune system and cells of the peritoneal stroma. The understanding of cellular and molecular mechanisms underlying fibrosis of the peritoneal membrane has both a basic and a translational relevance, since it may be useful for setup of therapies aimed at counteracting the deterioration as well as restoring the homeostasis of the peritoneal membrane.

Lipid microsphere-coated PGE1 improves peritoneal transport and reduces inflammation in peritoneal dialysis: A randomized clinical pilot trial

OBJECTIVE

To evaluate the effects of lipid microspheres coated with prostaglandin E1 (lipo-PGE1) on peritoneal transport function and inflammation in patients with end-stage renal disease undergoing continuous ambulatory peritoneal dialysis (CAPD).

METHODS

In total, 89 patients were randomly allocated to the lipo-PGE1 and control groups. All the patients received conventional treatment, and those in the lipo-PGE1 group received lipo-PGE1 intravenously for 2 weeks. The levels of β2-microglobulin (β2-MG), cystatin C, albumin, urea, creatinine, interleukin-6 (IL-6), matrix metalloproteinase-2 (MMP-2), and high-sensitivity C-reactive protein (hs-CRP) were measured before and at 1 and 2 weeks after treatment.

RESULTS

In the lipo-PGE1 group, the peritoneal clearance rates of β2-MG, cystatin C, and albumin were significantly increased comparing with pre-treatment values, and the IL-6 appearance rate (AR) in the peritoneal dialysate and the serum levels of IL-6 and hs-CRP were markedly decreased (p < 0.05). The lipo-PGE1 group had significantly higher peritoneal clearance rates of β2-MG and cystatin C and lower IL-6 AR in the peritoneal dialysate than the control group (p < 0.05).

CONCLUSIONS

Lipid microspheres coated with prostaglandin E1 may increase the peritoneal clearance of moderately sized molecules and macromolecules with insignificant effect on the clearance of small molecules. The reduction in IL-6 level following treatment with lipo-PGE1 may alleviate inflammation.

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)

Maximizing the Success of Peritoneal Dialysis in High Transporters

This article reviews the current understanding of high transport status in the peritoneal dialysis population and emphasizes survival can be improved for high transporters. To address the current state of knowledge on high peritoneal membrane transport, the negative impact of an increased peritoneal solute transport rate is first discussed. The potential downside of high transport status, notably on survival outcomes (as supported by registry data and meta-analysis), is highlighted. Based on recent advances and clinical studies, ways of maximizing the success of peritoneal dialysis treatment in high transporters are discussed, and management strategies are proposed.

30 Years of Peritoneal Dialysis Development: The past and the Future

A review is given of 30 years of development in peritoneal dialysis (PD). After a short description of the first 20 years, the main emphasis is put on the last 10 years. Subjects discussed are the increasing use of PD in high-risk populations, peritonitis and other catheter-related problems, adequacy of dialysis and nutrition, patient outcomes in comparison with hemodialysis, and peritoneal membrane changes with time on PD. Topics that have emerged during the last decade and the challenges for the next decennium are discussed. The great importance of quality assurance in fast-growing PD populations and of prevention of long-term membrane alterations are emphasized.

A Pyruvate-Buffered Dialysis Fluid Induces Less Peritoneal Angiogenesis and Fibrosis than a Conventional Solution

Background

Conventional lactate-buffered peritoneal dialysis (PD) fluids containing glucose and glucose degradation products are believed to contribute to the development of fibrosis and angiogenesis in the dialyzed peritoneum. To reduce potential negative effects of lactate, pyruvate was substituted as a buffer and its effects on peritoneal pathological alterations were studied in a chronic peritoneal exposure model in the rat.

Methods

20 Wistar rats were infused intraperitoneally with pyruvate-buffered ( n = 9) or lactate-buffered PD fluid. After 20 weeks of daily infusion, peritoneal function was assessed. In omental peritoneal tissue, the number of blood vessels was analyzed following alpha-smooth muscle actin staining. The degree of fibrosis was quantitated in Picro Sirius Red-stained sections and by assessment of the hydroxyproline content. Plasma lactate/pyruvate and beta-hydroxybutyrate/acetoacetate (BBA/AA) ratios were determined. Plasma and dialysate vascular endothelial growth factor (VEGF) levels were quantitated by ELISA.

Results

The mass transfer area coefficient of creatinine was higher and the dialysate-to-plasma ratio of sodium was lower in pyruvate-treated animals compared to the lactatetreated group (0.11 vs 0.05 mL/min, p < 0.05, and 78% vs 89%, p < 0.05). The BBA/AA ratio tended to be lower in the pyruvate animals ( p = 0.07). The number of blood vessels was lower in pyruvate-treated animals (16 vs 37 per field, p < 0.001). Total surface area, luminal area, and wall/total area of the vessels were larger in the pyruvate group. The degree of fibrosis was lower in intersegmental and perivascular areas of pyruvate-exposed animals. Effluent VEGF was higher in the pyruvate group.

Conclusions

Replacement of lactate by pyruvate resulted in changes in peritoneal solute transport, accompanied by a reduction in both peritoneal membrane angiogenesis and fibrosis, suggesting potentially novel mechanisms to reduce glucose-driven alterations to the peritoneal membrane in PD patients.

Physiological Properties of the Peritoneum in an Adult Peritoneal Dialysis Population over a Three-Year Period

Objectives

To describe the physiological properties of the peritoneal membrane in adult patients treated with peritoneal dialysis (PD) and to analyze the effects of patient characteristics and time.

Design

Observational study.

Setting

Department of Nephrology at the Sahlgrenska University Hospital.

Method

Peritoneal function was analyzed by the Personal Dialysis Capacity (PDC) test, based on the three-pore theory of capillary transport. The functional PDC variables are absorption, large-pore flow, and the area parameter (A0/Δx), which determines the diffusion of small solutes. The ultra-filtration (UF) coefficient is determined mainly by A0/Δx.

Patients

All patients ( n = 280) who had at least one PDC test done between September 1990 and August 1999.

Results

In 249 patients examined soon after start of PD, area was 19000 (SD 7100) cm2/cm/1.73 m2, large-pore flow 0.112 (SD 0.052) mL/min/1.73 m2, and the UF coefficient 0.071 (SD 0.032) mL/minute/mmHg/1.73 m2. Absorption was 1.54 (SD +2.64, –0.97) mL/min/1.73 m2. Large-pore flow was greater in patients with severe comorbidity than in patients with fewer comorbid conditions. Elderly patients had a lower UF coefficient than did younger patients ( p < 0.05). Repeated PDC tests were performed in 208 patients during a mean observation time of 18.4 months. There was a slight increase in the slope of the area-versus-time curve of 54 cm2/cm/1.73 m2 per month (approximately 10% after 3 years, p < 0.01); all other parameters remained constant.

Conclusion

Patient characteristics have an impact on peritoneal performance already at the start of dialysis. Peritoneal function can remain essentially stable during medium long-term PD.

Association of adipocytokines with peritoneal function

BACKGROUND

Preservation of peritoneal function is crucial for the continuation of peritoneal dialysis (PD). A previous study suggested that blood cholesterol is involved in the preservation of peritoneal function; therefore, we determined whether adipocytokines can predict peritoneal function preservation.

METHODS

Eighty patients were enrolled. Serum adiponectin, leptin, apelin, various blood components, and estimated glomerular filtration rate (eGFR) (mL/min/m²) were measured. In addition, the duration of PD, presence or absence of peritonitis and diabetes mellitus, body mass index, urine output, peritoneal K_t/V, renal K_t/V, weekly K_t/V, peritoneal creatinine clearance rate (CCr), renal CCr, weekly CCr, use or nonuse of statin products, dialysate volume, glucose exposure, and use or nonuse of icodextrin dialysate were assessed. Peritoneal equilibration tests were performed at 6-month intervals, and dialysate-to-plasma [D/P] ratio and glucose uptake ratio [D/D₀] were measured. Associations of the baseline values and their percent changes with various adipocytokines and test items were evaluated.

RESULTS

Multiple regression analyses identified adiponectin (p = 0.0392, p = 0.0348) as a significant predictive factor of D/P and D/D₀ ratios. eGFR was identified as a significant predictive factor (p = 0.015) of percent change in the D/P ratio. Apelin (p = 0.0484), high-density lipoprotein cholesterol (p = 0.0066), dialysate volume (p = 0.0223), and urine output (p = 0.0020) were identified as factors affecting the duration of PD.

CONCLUSIONS

Adipocytokines are a predictive factor of peritoneal function and the duration of PD in patients undergoing PD.

The role of WNT5A and Ror2 in peritoneal membrane injury

Patients on peritoneal dialysis are at risk of developing peritoneal fibrosis and angiogenesis, which can lead to dysfunction of the peritoneal membrane. Recent evidence has identified cross‐talk between transforming growth factor beta (TGFB) and the WNT/β‐catenin pathway to induce fibrosis and angiogenesis. Limited evidence exists describing the role of non‐canonical WNT signalling in peritoneal membrane injury. Non‐canonical WNT5A is suggested to have different effects depending on the receptor environment. WNT5A has been implicated in antagonizing canonical WNT/β‐catenin signalling in the presence of receptor tyrosine kinase‐like orphan receptor (Ror2). We co‐expressed TGFB and WNT5A using adenovirus and examined its role in the development of peritoneal fibrosis and angiogenesis. Treatment of mouse peritoneum with AdWNT5A decreased the submesothelial thickening and angiogenesis induced by AdTGFB. WNT5A appeared to block WNT/β‐catenin signalling by inhibiting phosphorylation of glycogen synthase kinase 3 beta (GSK3B) and reducing levels of total β‐catenin and target proteins. To examine the function of Ror2, we silenced Ror2 in a human mesothelial cell line. We treated cells with AdWNT5A and observed a significant increase in fibronectin compared with AdWNT5A alone. We also analysed fibronectin and vascular endothelial growth factor (VEGF) in a TGFB model of mesothelial cell injury. Both fibronectin and VEGF were significantly increased in response to Ror2 silencing when cells were exposed to TGFB. Our results suggest that WNT5A inhibits peritoneal injury and this is associated with a decrease in WNT/β‐catenin signalling. In human mesothelial cells, Ror2 is involved in regulating levels of fibronectin and VEGF.

IL-6 trans-signaling drives a STAT3-dependent pathway that leads to structural alterations of the peritoneal membrane

IL-6 is a vital inflammatory factor in the peritoneal cavity of patients undergoing peritoneal dialysis (PD). The present study examined the effect of IL-6 trans-signaling on structural alterations of the peritoneal membrane. We investigated whether the epithelial-to-mesenchymal transition (EMT) process of human peritoneal mesothelial cells (HPMCs) and the production of proangiogenic factors were controlled by IL-6 trans-signaling. Its role in the peritoneal alterations was detected in a mouse model. The morphology of HPMCs and levels of cytokines in PD effluent were also explored. Stimulation of HPMCs with the IL-6 and soluble IL-6 receptor complex (IL-6/S) promoted the EMT process of HPMCs depending on the STAT3 pathway. In a coculture system of HPMCs and human umbilical vein endothelial cells, IL-6/S mediated the production of VEGF and angiopoietins so as to downregulate the expression of endothelial junction molecules and finally affect vascular permeability. Daily intraperitoneal injection of high glucose-based dialysis fluid induced peritoneal fibrosis, angiogenesis, and macrophage infiltration in a mouse model, accompanied by phosphorylation of STAT3. Blockade of IL-6 trans-signaling prevented these peritoneum alterations. The fibroblast-like appearance of HPMCs ex vivo was upregulated in patients undergoing prevalent PD accompanied by increasing levels of IL-6, VEGF, and angiopoietin-2 in the PD effluent. Taken together, these findings identified a critical link between IL-6 trans-signaling and structural alterations of the peritoneal membrane, and it might be a potential target for the treatment of patients undergoing PD who have developed peritoneal alterations.

Sodium toxicity in peritoneal dialysis: mechanisms and "solutions"

The major trials in peritoneal dialysis (PD) have demonstrated that increasing peritoneal clearance of small solutes is not associated with any advantage on survival, whereas sodium and fluid overload heralds higher risk of death and technique failure. On the other hand, higher sodium and fluid overload due to loss of residual kidney function (RKF) and higher transport membrane is associated with poor patient and technique survival. Recent experimental studies also show that, independently from fluid overload, sodium accumulation in the peritoneal interstitium exerts direct inflammatory and angiogenetic stimuli, with consequent structural and functional changes of peritoneum, while in patients with Chronic Kidney Disease sodium stored in interstitial skin acts as independent determinant of left ventricular hypertrophy. Noteworthy, this tissue pool of sodium is modifiable being removed by dialysis. Therefore, novel PD strategies to optimize sodium removal, including the use of bimodal and/or low-sodium solutions, are actively tested. Nonetheless, a holistic approach aimed at preserving peritoneal function and the kidney may represent the key of therapy success in the hard task of preserving adequate sodium balance in PD patients. In this review, we describe the available evidence on sodium toxicity in PD, either related or unrelated to fluid overload, and we also discuss about possible "solutions" to preserve or restore sodium balance in PD patients.

Free Water Transport and Its Association with Cardiovascular Status in Children on Peritoneal Dialysis

Background:Volume overload is one of the most important factors associated with left ventricular hypertrophy (LVH) and cardiovascular disease in chronic peritoneal dialysis (PD) patients. MiniPET is a reliable tool to evaluate free water transport (FWT). In a clinical setting, the significance of FWT has not been evaluated in terms of outcome in children on PD. The objective was to define a FWT value of clinical significance in children on PD, fixing its relationship to left ventricular mass index (LVMI) as a well-known outcome parameter.Methods:MiniPET was performed with 3.86% glucose, 1-h long, to measure FWT in PD patients > 6 years old. An echocardiogram (ECG) was performed within 2 months of the MiniPET. Left ventricular hypertrophy was defined as LVMI ≥ 38.6 g/height^2.7 (95th percentile). Receiver operating characteristic curve (ROC) analysis was used to determine the cut-off value of FWT searching the highest sensitivity and specificity to differentiate patients with normal/abnormal LVMI. A p < 0.05 was considered significant.Results:Forty-six studies were performed on 32 patients, 16 males; mean age 11.59 ± 3.07 years. Mean normalized FWT (nFWT) was 144.4 ± 84.8 mL/m², corresponding to 46.7% of total ultrafiltration. Mean LVMI was 42 ± 11.3 g/m^2.7 with a negative correlation to nFWT (p < 0.01). Eighteen out of 32 patients had LVH. The ROC analysis (nFWT vs LVMI) showed an area under the curve of 0.71 (95% confidence interval [CI], 0.53 - 0.89; p = 0.04), allowing a cut-off nFWT value of 110 mL/m² to be defined, dividing the population into 2 groups of patients according to the LVMI cut-off value of 38,6 g/m^2.7.Conclusions:The nFWT showed an inverse correlation to LVMI. A nFWT value < 110 mL/m² was significantly associated with LVH. The negative relationship observed between nFWT and LVMI, and the cut-off level for nFWT according to the 95th percentile of LVMI, suggest that the regular evaluation of nFWT could become a useful tool in assessing the capacity of PD treatment to keep patients' volume status under control, avoiding cardiovascular impairment.

Composite Outcome Improves Feasibility of Clinical Trials in Peritoneal Dialysis

Background:Peritoneal dialysis (PD) is complicated by a high rate of adverse events that might be attributed to cytotoxicity of currently used PD fluids. However, clinical development of novel PD fluids is virtually non-existent, in part due to difficulties in recruiting sufficiently large populations for adequately powered trials. The aim of this study is to understand the potential impact of introducing composite outcomes on clinical trial feasibility in PD.Methods:A composite outcome "major adverse peritoneal events (MAPE)" was designed to combine clinically relevant complications of PD, such as (1) technical failure (cause-specific for peritonitis and/or insufficient dialysis), (2) peritonitis, and (3) peritoneal membrane deterioration. Incidence rates of individual endpoints were obtained from the literature and expert panel estimations, and population sizes were computed based on Chi-square test for adequately powered confirmatory randomized controlled clinical trials with 2 parallel arms.Results:Incidence rates for technical failure, peritonitis, and peritoneal membrane deterioration were estimated at 15%, 50%, and 23%, respectively, at 2 years follow-up, with adequate agreement between the literature and expert opinion. Assuming that a given intervention reduces adverse outcomes by 30%, an adequately powered clinical trial needs to recruit up to 1,720 patients when studying individual outcomes. Combining endpoints increases power in simulated trials despite considerable overlap, and the composite outcome MAPE reduces the required population to 202 patients aiming for 80% power.Conclusion:Introduction of the composite outcome MAPE, covering relevant major adverse peritoneal events, may improve the feasibility of clinical trials to adequately test novel PD fluids.

Biocompatible Solutions and Long-Term Changes in Peritoneal Solute Transport

BACKGROUND AND OBJECTIVES

The inflammation-driven increase in peritoneal solute transport rate that occurs during long-term peritoneal dialysis is associated with higher mortality, hospitalization, and encapsulating peritoneal sclerosis. Because biocompatible solutions were developed to mitigate these effects, we examined the association with their use and longitudinal peritoneal solute transport rate.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We analyzed subjects from the multinational prospective Global Fluid Study with three or more peritoneal solute transport rate measurements >2 months from the start of peritoneal dialysis. Follow-up was for 7.5 years (median, 2.3 years; interquartile range, 1.8-3.6) in biocompatible solutions and 12.8 years (median, 3.2 years; interquartile range, 1.9-4.3) for standard solutions. Using a random intercept/slopes multilevel model, we examined the association of patients using biocompatible solutions and peritoneal solute transport rate over time, adjusting for center effects, dialysate dextrose concentration, baseline dialysate IL-6 concentration, icodextrin use, residual kidney function, and peritonitis.

RESULTS

Of 366 patients, the 71 receiving biocompatible solutions throughout their time on peritoneal dialysis had a mean adjusted dialysate-to-plasma creatinine ratio of 0.67 compared with 0.72 for standard solutions (P=0.02). With duration of treatment, there was a continuous increase in peritoneal solute transport rate in patients using standard solutions (range, 2 months to 4 years). In contrast, patients using biocompatible solutions had peritoneal solute transport rates that plateaued after 2 years of therapy. These changes in peritoneal solute transport rate were independent of baseline inflammation and time-varying predictors of faster peritoneal solute transport rate. In patients suffering episodes of peritonitis while using standard solutions, there was an associated increase in peritoneal solute transport rate of 0.020 (95% confidence interval, 0.01 to 0.03) per episode, whereas in patients using biocompatible solutions, there was no change in this parameter (-0.014; 95% confidence interval, -0.03 to <0.01).

CONCLUSIONS

These data suggest that a different temporal pattern in changes in peritoneal solute transport rate occurs during the course of peritoneal dialysis according to solution type and that patients using biocompatible solutions may avoid the increase in solute transport associated with peritonitis.

Associations Between Peritoneal Glucose Exposure, Glucose Degradation Product Exposure, and Peritoneal Membrane Transport Characteristics in Peritoneal Dialysis Patients: Secondary Analysis of the balANZ Trial

BACKGROUND

Glucose is the most commonly used osmotic medium in peritoneal dialysis (PD) solutions, and its use has been associated with both local and systemic adverse effects. Previous, single-center, observational cohort studies have reported conflicting findings regarding whether a relationship exists between peritoneal glucose exposure and peritoneal small solute transport rate.

METHODS

In this secondary analysis of the balANZ multicenter, multinational, randomized controlled trial of a neutral pH, ultra-low glucose degradation product (biocompatible) versus conventional PD solutions over a 2-year period, the relationship between time varying peritoneal glucose exposure and change in peritoneal solute transport rate, (measured as dialysate to plasma creatinine ratio at 4 hours [D:PCr_4h]), was evaluated using multivariable, multilevel linear regression. Baseline peritoneal glucose exposure was also assessed as either a continuous or categorical variable.

RESULTS

The study included 165 patients (age 58.1 ± 14.2 years, 55% male, 33% diabetic). Peritoneal glucose exposure increased over time (coefficient 1.49, 95% confidence interval [CI] 1.07 - 1.92 and was not significantly associated with change in D:PCr_4h (coefficient 0.00004, 95% CI -0.0001 - 0.0002, p = 0.68). Similar results were found when peritoneal glucose exposure was examined as a baseline continuous or categorical variable. A significant 2-way interaction was observed with PD solution type, whereby a progressive increase in D:PCr_4h was seen in the patients receiving conventional PD solution, but not in those receiving biocompatible solution.

CONCLUSIONS

Increases in peritoneal solute transport rate in PD patients over time were not associated with peritoneal glucose exposure, although a strong and positive association with PD solution glucose degradation product content was identified. Peritoneal glucose exposure may be a less important consideration than peritoneal glucose degradation product exposure with respect to peritoneal membrane function over time.

Mechanisms of Crystalloid versus Colloid Osmosis across the Peritoneal Membrane

Background Osmosis drives transcapillary ultrafiltration and water removal in patients treated with peritoneal dialysis. Crystalloid osmosis, typically induced by glucose, relies on dialysate tonicity and occurs through endothelial aquaporin-1 water channels and interendothelial clefts. In contrast, the mechanisms mediating water flow driven by colloidal agents, such as icodextrin, and combinations of osmotic agents have not been evaluated.Methods We used experimental models of peritoneal dialysis in mouse and biophysical studies combined with mathematical modeling to evaluate the mechanisms of colloid versus crystalloid osmosis across the peritoneal membrane and to investigate the pathways mediating water flow generated by the glucose polymer icodextrin.ResultsIn silico modeling and in vivo studies showed that deletion of aquaporin-1 did not influence osmotic water transport induced by icodextrin but did affect that induced by crystalloid agents. Water flow induced by icodextrin was dependent upon the presence of large, colloidal fractions, with a reflection coefficient close to unity, a low diffusion capacity, and a minimal effect on dialysate osmolality. Combining crystalloid and colloid osmotic agents in the same dialysis solution strikingly enhanced water and sodium transport across the peritoneal membrane, improving ultrafiltration efficiency over that obtained with either type of agent alone.Conclusions These data cast light on the molecular mechanisms involved in colloid versus crystalloid osmosis and characterize novel osmotic agents. Dialysis solutions combining crystalloid and colloid particles may help restore fluid balance in patients treated with peritoneal dialysis.