Peritoneal Solute Transport and Inflammation

The Versatility of Biological Field-Effect Transistor-Based Biosensors (BioFETs) in Point-of-Care Diagnostics: Applications and Future Directions for Peritoneal Dialysis Monitoring

Peritoneal dialysis (PD) is a vital treatment for end-stage renal disease patients, but its efficacy is often compromised by complications such as infections and peritoneal fibrosis. Biological field-effect transistors (BioFETs) present a promising solution for rapid, sensitive, and non-invasive detection of indicators and biomarkers associated with these complications, potentially enabling early intervention. However, BioFETs are yet to be adopted for PD monitoring. This review presents a forward-looking analysis of the capacity and potential integration of BioFETs into PD management systems, highlighting their capacity to monitor both routine indicators of dialysis efficiency and metabolic status, as well as specific biomarkers for complications such as inflammation and fibrosis. We examine the challenges in adapting BioFETs for PD applications, focusing on key areas for improvement, including sensitivity, specificity, stability, reusability, and clinical integration. Furthermore, we discuss various approaches to address these challenges, which are crucial for developing point-of-care (PoC) and multiplexed wearable devices. These advancements could facilitate continuous, precise, and user-friendly monitoring, potentially revolutionizing PD complication management and enhancing patient care.

Profiling cytokines in peritoneal effluent through a targeted multiplex cytokine panel provides novel insight into the localized proinflammatory processes in patients undergoing peritoneal dialysis

Objectives

The number of relevant markers indicating local intraperitoneal inflammation in patients undergoing peritoneal dialysis (PD) is limited. Therefore, this study aimed to evaluate the compatibility of peritoneal effluent (PE) for proteomic analysis and assess its potential utility in immunoprofiling studies.

Methods

This pilot study included six PD patients from the Peritoneal Dialysis Center, Department of Nephrology, Transplantology, and Internal Medicine in Szczecin, Poland. All patients were clinically stable, with no signs of infections or malignancy at the time of study. PE samples were collected during routine surveillance visits at the Peritoneal Dialysis Center. Proteomic analysis of the samples was conducted using the Olink® (Olink Proteomics AB, Uppsala, Sweden) Target 48 Cytokine panel.

Results

PE samples were successfully analyzed, with 28 out of 45 proteins found within the limit of quantitation (LOQ) and 32 out of 45 proteins detected above the limit of detection (LOD). No significant interference from the matrix was observed in the assay. Biomarkers associated with low-grade inflammation showed varied levels, and the observed patterns were comparable across all patients.

Conclusion

This study suggests that utilizing a cytokine panel with relative quantification is a promising method for PE immunoprofiling.

Exploring the Role of Cell-Free Nucleic Acids and Peritoneal Dialysis: A Narrative Review

INTRODUCTION

Cell-free nucleic acids (cf-NAs) represent a promising biomarker of various pathological and physiological conditions. Since its discovery in 1948, cf-NAs gained prognostic value in oncology, immunology, and other relevant fields. In peritoneal dialysis (PD), blood purification is performed by exposing the peritoneal membrane. Relevant sections: Complications of PD such as acute peritonitis and peritoneal membrane aging are often critical in PD patient management. In this review, we focused on bacterial DNA, cell-free DNA, mitochondrial DNA (mtDNA), microRNA (miRNA), and their potential uses as biomarkers for monitoring PD and its complications. For instance, the isolation of bacterial DNA in early acute peritonitis allows bacterial identification and subsequent therapy implementation. Cell-free DNA in peritoneal dialysis effluent (PDE) represents a marker of stress of the peritoneal membrane in both acute and chronic PD complications. Moreover, miRNA are promising hallmarks of peritoneal membrane remodeling and aging, even before its manifestation. In this scenario, with multiple cytokines involved, mtDNA could be considered equally meaningful to determine tissue inflammation.

CONCLUSIONS

This review explores the relevance of cf-NAs in PD, demonstrating its promising role for both diagnosis and treatment. Further studies are necessary to implement the use of cf-NAs in PD clinical practice.

Systemic and local complement activation in peritoneal dialysis patients via conceivably distinct pathways

BACKGROUND

Despite several advantages compared to haemodialysis (HD), peritoneal dialysis (PD) remains an underused dialysis technique due to its high technique failure rate related to membrane fibrosis and peritonitis events. Previous work has suggested a harmful role for the complement system in these processes, highlighting the need for a more comprehensive examination in PD.

METHODS

Plasma levels of C1q, mannose-binding lectin (MBL), Properdin, Factor D, C3d/C3-ratio and soluble membrane attack complex (sC5b-9) were determined in PD patients (n = 55), HD patients (n = 41), non-dialysis chronic kidney disease (CKD) patients (n = 15) and healthy controls (n = 14). Additionally, C1q, MBL, Properdin, Factor D and sC5b-9 levels were assessed in the peritoneal dialysis fluid (PDF). In a subgroup, interleukin-6, matrix metalloproteinase-2 (MMP-2), myeloperoxidase (MPO) and elastase were measured in the PDF.

RESULTS

PD patients had significantly higher systemic levels of sC5b-9 compared to healthy controls, CKD and HD patients (p < 0.001). Plasma levels of C1q and C3d/C3-ratios were significantly associated with systemic sC5b-9 levels (p < 0.001). Locally, sC5b-9 was detected in the PDF of all PD patients, and levels were approximately 33% of those in matched plasma, but they did not correlate. In the PDF, only Properdin levels remained significantly associated with PDF sC5b-9 levels in multivariate analysis (p < 0.001). Additionally, PDF levels of sC5b-9 positively correlated with elastase, MPO and MMP-2 levels in the PDF (p < 0.01).

CONCLUSIONS

Our data reveal both systemic and local complement activation in PD patients. Furthermore, these two processes seem independent considering the involvement of different pathways and the lack of correlation.

Association of serum thymosin β4 with malnutrition-inflammation-atherosclerosis syndrome in peritoneal dialysis patients: a cross-sectional study

BACKGROUND

Malnutrition-inflammation-atherosclerosis (MIA) syndrome may worsen the prognosis of peritoneal dialysis (PD) patients. Serum thymosin β4 (sTβ4) protects against inflammation, fibrosis and cardiac dysfunction.

OBJECTIVES

The present study aimed to characterize the association between sTβ4 and MIA syndrome as well as to investigate the potential of regulating sTβ4 to improve the prognosis of PD patients.

METHODS

We performed a cross-sectional, single-center pilot study involving 76 PD patients. Demographic characteristics, clinical characteristics, nutritional profiles, inflammatory mediators, atherosclerosis-related factors and sTβ4 levels were collected and subjected to association analysis for sTβ4 and MIA syndrome.

RESULTS

sTβ4 levels did not significantly vary with sex or primary disease in PD patients. Ages and PD features did not vary between patients with different levels of sTβ4. PD patients with higher levels of sTβ4 had significantly higher levels of nutritional indicators, including subjective global nutritional assessment (SGA) (p < 0.001) and serum albumin (ALB) (p < 0.001) but lower levels of inflammatory and atherosclerotic indicators, including serum C reaction protein (CRP) (p = 0.009), the right common carotid artery (RCCA) intimal thickness (p < 0.001) and the left common carotid artery (LCCA) intimal thickness (p = 0.02). Correlation analysis showed that sTβ4 was positively associated with SGA (p < 0.001) and serum ALB (p < 0.001) but negatively associated with CRP (p = 0.020), RCCA intimal thickness (p < 0.001) and LCCA intimal thickness (p = 0.033). In multiple adjusted models, the prevalence of MIA syndrome was significantly decreased in PD patients with increased levels of sTβ4 when patients without MIA syndrome were compared to those with all indicators of MIA syndrome (OR = 0.996, 95% CI 0.993-0.999, p = 0.003) or those with at least one indicator of MIA syndrome (OR = 0.997, 95% CI 0.995-0.998, p < 0.001).

CONCLUSIONS

The sTβ4 level decreases in PD patients with MIA syndrome. The prevalence of MIA syndrome decreases significantly as the level of sTβ4 increases in PD patients.

Encapsulating Peritoneal Sclerosis in a Patient Receiving Peritoneal Dialysis and Glucocorticoid Therapy

Encapsulating peritoneal sclerosis (EPS) is a fatal complication of peritoneal dialysis. A 68-year-old man undergoing peritoneal dialysis for 10 years started receiving daily 50 mg of glucocorticoids for idiopathic pulmonary sclerosis. At the transition to hemodialysis, a peritoneal biopsy was performed, which demonstrated mild histological changes, including no fibrin formation and mild T lymphocyte infiltration at the time of 6.5 mg glucocorticoids. However, five months later, he developed EPS when receiving 2.5 mg glucocorticoids. Afterward, over 5 mg daily glucocorticoids were required to avoid the recurrence of EPS. These findings suggest that glucocorticoids may conceal peritoneal inflammation, a main contributor to EPS.

Iron status and anemia control are related to peritoneal membrane properties in peritoneally dialyzed patients

Background

Characteristics of peritoneal membrane is unique and individually different in peritoneal dialysis patients. Relationship between specific nature of peritoneal transport, anemia and inflammation has not yet been extensively studied. We attempted to outline the complex interplay of several biomarkers of iron status and their association with peritoneal transport, degree of inflammation and residual renal function.

Methods

A total of 58 patients treated with peritoneal dialysis either CAPD or APD for at least 3 months were enrolled in this study. Full blood count, traditional markers of iron status (transferrin saturation-TSAT and ferritin), serum erythroferrone-ERFE, soluble transferrin receptor (sTfR), hepcidin, zonulin, growth differentiation factor -15 (GDF15), IL-16, hsCRP and hypoxia-inducible factor-α (HIF-1-α; in serum and dialysate) were measured using commercially available tests. We also performed Peritoneal Equilibrium Test and assessed GFR level.

Results

Hb levels above 10 g/dL was found in 74% of patients. Hb levels positively correlated with residual renal function and nutritional status. Adequate iron status was diagnosed in 69% of subjects, only in 9% of patients, criteria for absolute iron deficiency were met. Serum ERFE correlated inversely with hepcidin levels but was not associated with erythropoietin stimulating agent dose. Peritoneal transport had strong correlation with dialysate sTfR (p < 0.05), dialysate hepcidin (p < 0.05), dialysate GDF15 (p < 0.01) and dialysate zonulin (p < 0.001) levels, as well as serum IL6 (p = 0.03), serum hs-CRP (p = 0.04) and dialysate hs-CRP (p = 0.04).

Conclusion

Residual kidney function contributes considerably to better control of anemia. Various degree of inflammation is inherent to PD patients. Additionally, fast-average peritoneal transport is associated with greater degree of inflammation and higher concentration of markers of iron status, GDF15 and zonulin in dialysate. This finding may indicate more effective clearance of higher-range middle molecules in fast-average transporters. The role of ERFE as a marker of erythropoiesis in PD patients requires further investigation.

Relationship between peritoneal solute transport and dialysate inflammatory markers in peritoneal dialysis patients: A cross-sectional study

BACKGROUND

The associated factors of peritoneal small solute transport was not fully understood. This research aimed to investigate the connection between dialysate inflammatory markers (e.g. macrophage migration inhibitory factor, MIF) in peritoneal dialysis (PD) effluent and peritoneal solute transport rate (PSTR) properties.

SUBJECTS AND DESIGN

A total of 80 stable PD patients in the First ShaoYang Hospital were enrolled in present study. Overnight PD effluent and serum inflammatory markers including MIF, MCP-1, VEGF, IL-6, TNFα and TGFβ were detected. Pearson correlation analysis and Logistic regression was performed to determine the risk factors for the increased PSTR.

RESULTS

A trend toward increased values of MIF, MCP-1 and IL-6 in PD effluent was observed in subjects with high PSTR when compared with those with low PSTR. The Pearson correlation test showed that D/P Cr exhibited positive correlations with dialysis effluent MIF (r=0.32, p=0.01), MCP-1 (r=0.47, p=0.01), IL-6 (r=0.48, p=0.01). Conversely, no significant correlation was found between D/P Cr and TGF-β (r=0.04, p=0.70), TNF-ɑ (r=0.22, p=0.05), VEGF (r=0.02, p=0.86) and serum inflammatory markers. In the unadjusted regression analysis, dialysis effluent MIF (OR 2.41), MCP-1 (OR 1.72), IL-6 (OR 1.55) were associated with high PSTR condition. Multivariate logistic regression analysis showed that the adjusted odds ratios (OR) of dialysis effluent MIF for high PSTR were 2.47 in all subjects (p=0.03).

CONCLUSION

Elevated MIF, MCP-1 and IL-6 levels in PD effluent were associated with increased PSTR. Elevated dialysis effluent MIF levels was an independent risk factor for high PSTR in subjects with PD treatment.

Changes in erythropoiesis-stimulating agent responsiveness after transfer to combined therapy with peritoneal dialysis and hemodialysis for patients on peritoneal dialysis: A prospective multicenter study in Japan

INTRODUCTION

Inadequate dialysis and fluid overload are corrected after starting combined therapy with peritoneal dialysis (PD) and hemodialysis (HD). However, the effects on anemia management has not been elucidated.

METHODS

We conducted a prospective, multicenter, observational cohort study of 40 PD patients (age, 60 ± 10 years; male, 88%; median PD duration, 28 months) starting combined therapy and investigated changes in several clinical parameters, including erythropoiesis-stimulating agent (ESA) resistance index (ERI).

RESULTS

ERI decreased significantly during 6 months after switching to combined therapy (from 11.8 [IQR 8.0-20.4] units/week/kg/(g/dL) to 7.8 [IQR 3.9-18.6] units/week/kg/(g/dL), p = 0.047). Body weight, urinary volume, serum creatinine and the dialysate-to-plasma creatinine ratio (D/P Cr) decreased, whereas hemoglobin and serum albumin increased. In subgroup analysis, the changes in ERI were not affected by cause for starting combined therapy, PD holiday and D/P Cr.

CONCLUSION

Although detailed mechanism was unclear, ESA responsiveness improved after switching from PD alone to combined therapy.

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

Background

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

Methods

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

Results

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

Conclusions

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

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.

Cefazolin Plus Ceftazidime versus Cefazolin Monotherapy in the Treatment of Culture-Negative Peritonitis: A Retrospective Cohort Study

Background

Based on current ISPD guidelines, it is unclear as to whether ceftazidime should be discontinued in subsequent management of culture-negative peritonitis if it is used as empirical gram-negative coverage. Herein, we aim to compare the clinical outcomes of cefazolin plus ceftazidime versus cefazolin alone.

Methods

This was a retrospective cohort study. Adult peritoneal dialysis (PD) patients who were diagnosed with culture-negative peritonitis between 2014 and 2020 were included. Patients were categorized into two groups according to treatment regimen. Primary response rate, peritonitis relapse rate, and time to primary response were compared. Factors that predicted primary response were determined using Cox regression analysis.

Results

A total of 58 patients were included in the study. Of these, 42 received cefazolin plus ceftazidime and 16 received cefazolin monotherapy. Overall, the mean age was 65.7±10.4 years. Most of the patients (81.3%) were prescribed continuous ambulatory peritoneal dialysis. Initial effluent WBC was 4211±10357 in the combination group and 3833±6931 cell/mm³ in the monotherapy group (p=0.89). There was no significant difference in primary response at day 5 between the two groups (95.2% in the combination group vs93.7% in the monotherapy group, p=0.82). However, cumulative probability of primary response by the Kaplan–Meier analysis in the combination group was higher than in the monotherapy group (p=0.02). Adjusted HR of serum potassium level to predict a primary response was 1.83 according to multivariate analysis (p=0.03). There was no difference between the two groups in terms of peritonitis relapse or catheter removal.

Conclusion

This is the first study to compare clinical outcomes between cefazolin plus ceftazidime versus cefazolin monotherapy in culture-negative peritonitis. Our results suggest that if peritonitis is resolving at day 3, discontinuation of ceftazidime could yield favorable treatment outcomes and might be appropriate for subsequent management. However, the risk of not having gram-negative coverage should be considered.

Peritoneal transport status and first episode of peritonitis: a large cohort study

BACKGROUND

Peritonitis is one of the most serious complications of peritoneal dialysis (PD). This study aimed to explore the relationship between peritoneal transport status and the first episode of peritonitis, as well as the prognosis of patients undergoing continuous ambulatory peritoneal dialysis (CAPD).

METHOD

A retrospective cohort study was conducted, analyzing data of CAPD patients from 1st January 2009, to 31st December 2017. Baseline data within 3 months after PD catheter placement was recorded. Cox multivariate regression analysis was performed to determine the risk factors for the first episode of peritonitis, technique failure and overall mortality.

RESULTS

A total of 591 patients were included in our analysis, with a mean follow-up visit of 49 months (range: 27-75months). There were 174 (29.4%) patients who had experienced at least one episode of peritonitis. Multivariate Cox regression analysis revealed that a higher peritoneal transport status (high and high-average) (HR 1.872, 95%CI 1.349-2.599, p = 0.006) and hypoalbuminemia (HR 0.932,95% CI 0.896, 0.969, p = 0.004) were independent risk factors for the occurrence of the first episode of peritonitis. In addition, factors including gender (male) (HR 1.409, 95%CI 1.103, 1.800, p = 0.010), low serum albumin (HR 0.965, 95%CI 0.938, 0.993, p = 0.015) and the place of residence (rural) (HR 1.324, 95%CI 1.037, 1.691, p = 0.024) were independent predictors of technique failure. Furthermore, low serum albumin levels (HR 0.938, 95%CI 0.895, 0.984, p = 0.008) and age (>65years) (HR 1.059, 95%CI 1.042, 1.076, p < 0.001) were significantly associated with the risk of overall mortality of PD patients.

CONCLUSIONS

Baseline hypoalbuminemia and a higher peritoneal transport status are risk factors for the first episode of peritonitis. Factors including male gender, hypoalbuminemia, and residing in rural areas are associated with technique failure, while hypoalbuminemia and age (>65years) are predictors of the overall mortality in PD patients. Nevertheless, the peritoneal transport status does not predict technique failure or overall mortality of PD patients.

The Association of Circulating CD14++CD16+ Monocytes, Natural Killer Cells and Regulatory T Cells Subpopulations With Phenotypes of Cardiovascular Disease in a Cohort of Peritoneal Dialysis Patients

The altered expression of immune cells including monocyte subsets, natural killer (NK) cells and CD4+CD25+ regulatory T cells (Tregs) in end-stage kidney disease, affect the modulation of inflammation and immunity with significant clinical implications. The aim of this study was to investigate the profile of specific immune cells subpopulations and their correlations with phenotypes of established cardiovascular disease (CVD), including coronary artery disease (CAD) and heart failure (HF) in peritoneal dialysis (PD) patients.

Materials and Methods: 29 stable PD patients and 13 healthy volunteers were enrolled. Demographic, laboratory, bioimpedance measurements, lung ultrasound and echocardiography data were collected. The peripheral blood immune cell subsets analysis was performed using flow cytometry.

Results: PD patients compared to normal controls had lower total lymphocytes (22.3 ± 6.28 vs. 31.3 ± 5.54%, p = <0.001) and B-lymphocytes (6.39 ± 3.75 vs. 9.72 ± 3.63%, p = 0.01) as well as higher CD14++CD16+ monocytes numbers (9.28 ± 6.36 vs. 4.75 ± 2.75%, p = 0.0002). PD patients with prevalent CAD had NK cells levels elevated above median values (85.7 vs. 40.9%, p = 0.04) and lower B cells counts (3.85 ± 2.46 vs. 7.2 ± 3.77%, p = 0.03). Patients with increased NK cells (>15.4%) had 3.8 times higher risk of CAD comparing with patients with lower NK cell levels (95% CI, 1.86 – 77.87; p = 0.034). B cells were inversely associated with the presence of CAD (increase of B-lymphocyte by 1% was associated with 30% less risk for presence of CAD (95% CI, −0.71 – 0.01; p = 0.05). Overhydrated patients had lower lymphocytes counts (18.3 ± 4.29% vs. 24.7 ± 6.18%, p = 0.006) and increased NK cells [20.5% (14.3, 23.6) vs. 13.21% (6.23, 19.2), p = 0.04)]. In multiple logistic regression analysis the CRP (OR 1.43; 95% CI, 1.00 – 2.05; p = 0.04)] and lymphocytes counts (OR 0.79; 95% CI, 0.63–0.99; p = 0.04)] were associated with the presence of lung comets. Patients with higher NK cells (>15.4%, n = 15) were more likely to be rapid transporters (D/P creatinine 0.76 ± 0.1 vs. 0.69 ± 0.08, p = 0.04). Patients displaying higher Tregs (>1.79%) were older (70.8 ± 10.7 years vs. 57.7 ± 14.7years, p = 0.011) and had higher nPCR (0.83 ± 0.14 vs. 0.91 ± 0.17, p = 0.09).

Conclusion: Future research is required to evaluate the role of immune cells subsets as potential tools to identify patients at the highest risk for complications and guide interventions.

Presence of galectin-3 in peritoneal dialysate. Does it have a role in the peritoneal membrane inflammatory process?

Peritoneal dialysis (PD) causes structural and functional changes in the peritoneal membrane, which are attributed to local inflammatory process. This study assessed the presence of galectin-3 (Gal-3), a known inflammatory modulator, in dialysate effluent and correlated its levels with markers of inflammatory process. Gal-3 levels in serum and dialysate effluent were measured in prevalent PD patients on morning visits (n = 27) or during peritoneal equilibration tests (PET, n = 16), it association with clinical and laboratory parameters, including dialysate/plasma creatinine (D/P creatinine) and interleukin-6 (IL-6) levels was analysed. Gal-3 levels in dialysate effluent correlated with D/P creatinine (0.663, p = 0.005) and dialysate effluent IL-6 levels (0.674, p = 0.002), but not with serum Gal-3 levels or dialysis vintage. Patients who were high transporters had higher Gal-3 levels in dialysate effluent, as compared to lower transporters. In multivariate regression analysis, dialysate IL-6 level was the strongest predictor of dialysate Gal-3 levels. This study found Gal-3 in dialysate effluent correlated with D/P creatinine and dialysate IL-6 levels. These findings may imply that Gal-3 has a role in the intraperitoneal inflammatory process. However, this needs to be investigated further.

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

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

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.

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.

Prognostic significance of peritoneal dialysis effluent mitochondrial DNA level

BACKGROUND

Mitochondrial DNA (mtDNA) resembles bacterial DNA and potentially triggers local and systemic inflammation. We evaluate the prognostic implications of PD effluent mtDNA level in peritoneal dialysis (PD) patients.

METHODS

We measured mtDNA in the PD effluent (PDE) sediment and supernatant of 168 incident PD patients. All patients were followed for hospitalization, technique and overall survival.

RESULTS

The median PD effluent supernatant and sediment mtDNA levels were 255.4 unit (interquartile range [IQR] 157.5-451.3) and 201.6 unit (IQR 147.8-267.3), respectively. Serum C-reactive protein level closely with PDE sediment mtDNA level (r = 0.471, p < 0.001) and less with supernatant mtDNA level (r = 0.156, p = 0.044). PDE supernatant mtDNA level correlates with dialysate-to-plasma creatinine ratio at 4 h (D/P4) (r = 0.361, p < 0.001) but not with any clinical outcome. PDE sediment mtDNA was an independent predictor of technique survival (p = 0.011) and the duration of hospitalization (p = 0.044) after adjusting for clinical confounding factors.

CONCLUSIONS

PDE sediment mtDNA level significantly correlated with systemic inflammation, while PDE supernatant mtDNA level correlated with peritoneal transport. PDE sediment mtDNA level also independently predicted technique survival and duration of hospitalization. The mechanism of the different implications between PDE sediment and supernatant mtDNA levels deserves further investigations.

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.

Higher Eosinophils Predict Death-Censored Technique Failure in Peritoneal Dialysis Patients

INTRODUCTION

Eosinophilia (eosinophil fraction of leukocytes >5%), an indicative parameter for bioincompatibility in various circumstances, is well established in hemodialysis. However, change in eosinophil count (EOC) and its association with death-censored technique failure among peritoneal dialysis (PD) patients remain unclear.

METHODS

We compared eosinophils before and after PD initiation among 1,432 eligible continuous ambulatory PD patients regularly followed up in our PD center during 2007-2018. Risk factors of early-stage eosinophilia were examined by the logistic regression test. The relationship of early-stage eosinophilia and EOC with death-censored technique failure was examined using the Cox proportional hazards model for overall patients and for men and women separately.

RESULTS

After PD initiation, the EOC and percentage of patients with eosinophilia were significantly increased compared with baseline. Being male (odds ratio [OR]: 2.26; 95% confidence interval [CI]: 1.55-3.31; p < 0.001) and higher EOC at baseline (100 cells/μL increase, OR: 1.62; 95% CI: 1.45-1.82; p < 0.001) were risk factors of early-stage eosinophilia after PD initiation. During follow-up, 204 death-censored technique failures were recorded. In fully adjusted models, each with 100 cells/μL increase in EOC, the adjusted hazard ratios (HRs) of technique failure were 1.11 (95% CI: 1.03-1.20; p = 0.009) in the whole cohort, 1.29 (95% CI: 1.10-1.51; p = 0.002) in women, and 1.07 (95% CI: 0.97-1.17; p = 0.196) in men. Eosinophilia was significantly associated with the risk of technique failure for women (HR: 2.24; 95% CI: 1.07-4.70; p = 0.033), which was especially significant for women aged <55 years (HR: 7.61; 95% CI: 1.88-30.90; p = 0.005).

CONCLUSION

EOC was increased significantly after PD initiation, and increased numbers of eosinophils were associated with higher death-censored technique failure in PD patients, especially women.

Excessive salt intake increases peritoneal solute transport rate via local tonicity-responsive enhancer binding protein in subtotal nephrectomized mice

BACKGROUND

High peritoneal transport is associated with high mortality and technical failure in peritoneal dialysis (PD). Baseline peritoneal solute transport rate (PSTR) as measured by the peritoneal equilibration test (PET) within 6 months after PD initiation varies between patients. Sodium is reported to be stored in the skin or muscle of dialysis patients. This study investigated whether excessive salt intake in uremic mice caused peritoneal alterations without exposure to PD fluid.

METHODS

Sham-operated (Sham) and subtotal nephrectomized (Nx) mice were randomly given tap water or 1% sodium chloride (NaCl)-containing water for 8 weeks. PET was then performed to evaluate peritoneal function. Human mesothelial cell line Met-5A was used for in vitro studies.

RESULTS

We observed higher PSTR in Nx mice with 1% NaCl-containing drinking water (Nx + salt) compared with those with tap water (Nx + water), along with enhanced angiogenesis and inflammation in the peritoneum. Blockade of interleukin (IL)-6 signaling rescued peritoneal transport function in Nx + salt mice. In cultured Met-5A, additional NaCl in the medium upregulated IL-6 as well as vascular endothelial growth factor-A, associated with increased expression and nuclear translocation of tonicity-responsive enhancer binding protein (TonEBP). Knockdown of TonEBP lowered the induction caused by high tonicity. Peritoneal TonEBP expression was higher in Nx + salt mice, while removal of high-salt diet lowered TonEBP level and improved peritoneal transport function.

CONCLUSIONS

Excessive dietary salt intake caused peritoneal membrane functional and structural changes under uremic status. TonEBP regulated hypertonicity-related inflammatory changes and might play a crucial role in high baseline peritoneal transport.

Long-term peritoneal dialysis treatment provokes activation of genes related to adaptive immunity

Permanent irritation of the peritoneum during peritoneal dialysis (PD) treatment leads to local chronic inflammation and subsequently activation of processes driving fibrogenesis in the long-term. The aim of the study was to compare the peritoneal effluent transcriptome of 20 patients treated less and 13 patients treated more than 2 years using microarray analysis. An increased expression of genes associated with an immune response was observed in long-term treated patients with well preserved peritoneal function, when compared to patients treated less than 2 years. From 100 genes highly expressed in long-term patients, a significant up-regulation of six was found by RT-qPCR: LY9 (lymphocyte antigen 9), TNSFR4 (tumor necrosis factor receptor superfamily, member 4), CD 79A (CD79a molecule), CCR7 (chemokine C-C receptor 7), CEACAM1 (carcinoembryonic antigen-related cell adhesion molecule 1) and IL2RA (interleukin 2 receptor alpha chain). Furthermore, the effluent cell population was analysed. A positive relationship between the number of granulocytes and NK cells on one hand, and duration of PD treatment on the other, was shown. We conclude, that the mechanisms of adaptive immunity promoting T helper 2 cells response are activated in the long-term before functional alterations develop. It consequently might trigger the fibrosis promoting processes.

Dialysate cell-free mitochondrial DNA fragments as a marker of intraperitoneal inflammation and peritoneal solute transport rate in peritoneal dialysis

BACKGROUND

Mitochondrial DNA (mtDNA) released into extracellular subsequent to cell injury and death can promote inflammation in patients and animal models. However, the effects of peritoneal dialysate cell-free mtDNA on intraperitoneal inflammation and peritoneal solute transport rate (PSTR) in peritoneal dialysis (PD) patients remain unclear.

METHODS

We select the incident patients who began PD therapy between January 1, 2009, and December 30, 2010. Peritoneal dialysate was collected at the time of peritoneal equilibration test. The cell-free mtDNA, IL-6, IL-17A, TNF-α and IFN-γ were measured. All patients were followed till December 2017. The results were compared with PSTR and patient survival.

RESULTS

One hundred and eighty-nine patients were included in the study. The average age was 47.1 ± 13.5 years, 55.6% of the patients were males. The average PSTR was 0.66 ± 0.12, the median dialysate mtDNA levels were 4325 copies/ul. The median concentrations of IL-6, IL-17A, TNF-α and IFN-γ were 25.9, 10.8, 25.8 and 17.9 pg/ml, respectively. We found that dialysate mtDNA was significantly correlated with PSTR (r = 0.461, P < 0.001), IL-6 (r = 0.568, P < 0.001), TNF-α (r = 0.454, P < 0.001) and IFN-γ (r = 0.203, P = 0.005). After adjustment for multiple covariates, dialysate mtDNA levels were independently correlated with IL-6 and PSTR. Dialysate mtDNA levels were not associated with patient survival.

CONCLUSIONS

We found that dialysate mtDNA levels correlated with the degree of intraperitoneal inflammatory status in PD patients. Peritoneal effluent mtDNA was an independent determinant of PSTR but did not affect patient survival.

Acidic organelles mediate TGF-β1-induced cellular fibrosis via (pro)renin receptor and vacuolar ATPase trafficking in human peritoneal mesothelial cells

TGF-β1, which can cause renal tubular injury through a vacuolar-type H⁺-ATPase (V-ATPase)-mediated pathway, is induced by the glucose degradation product methylglyoxal to yield peritoneal injury and fibrosis. The present study investigated the roles of V-ATPase and its accessory protein, the (pro)renin receptor, in peritoneal fibrosis during peritoneal dialysis. Rats daily administered 20 mM methylglyoxal intraperitoneally developed significant peritoneal fibrosis after 7 days with increased expression of TGF-β and V-ATPase, which was reduced by the inhibition of V-ATPase with co-administration of 100 mM bafilomycin A1. The (pro)renin receptor and V-ATPase were expressed in acidic organelles and cell membranes of human peritoneal mesothelial cells. TGF-β1 upregulated the expression of collagens, α-SMA, and EDA-fibronectin, together with ERK1/2 phosphorylation, which was reduced by inhibition of V-ATPase, (pro)renin receptor, or the MAPK pathway. Fibronectin and the soluble (pro)renin receptor were excreted from cells by acidic organelle trafficking in response to TGF-β1; this excretion was also suppressed by inhibition of V-ATPase. Soluble (pro)renin receptor concentrations in effluents of patients undergoing peritoneal dialysis were associated with the dialysate-to-plasma ratio of creatinine. Together, these results demonstrate a novel fibrosis mechanism through the (pro)renin receptor and V-ATPase in the acidic organelles of peritoneal mesothelial cells.

TRPA1 Mechanoreceptors Mediate the IL-6 Response to a Single PD Dwell in the Rat

BACKGROUND

The development of modern, biocompatible peritoneal dialysis (PD) fluids has not entirely eliminated the local pro-inflammatory effects of PD fluid administration. The present study was performed in order to establish the importance of known signaling pathways connected to mechano-, osmo- and chemo-sensors of the transient receptor potential (TRP) family for the acute inflammatory response to PD.

METHODS

Rats were exposed to a single 4-hour dwell of lactate-buffered, 2.5% glucose, filter-sterilized PD fluid through an implanted PD catheter. In some groups, the PD dwell was preceded by intravenous administration of blockers of TRPV1 (BCTC), TRPA1 (HC030031), or neurokinin 1 (NK1) (Spantide II) receptors. Cytokine messenger ribonucleic acid (mRNA) expressions were quantified in tissue biopsies (real-time polymerase chain reaction [qPCR]), and cytokine concentrations were quantified in dialysate samples by enzyme-linked immunosorbent assay (ELISA). Tissue expressions of TRPV1, TRPA1, and NK1 were evaluated immuno-histochemically.

RESULTS

The PD dwell induced peritoneal synthesis of Il1b, Tnf, and Il6 and a secretion of interleukin-6 (IL-6) into the dialysate. The catheter implantation already induced the transcription of Il1b and Tnf but did not significantly affect Il6 transcription. The Il6 response to the PD dwell could be virtually eliminated by blocking TRPA1 but was not affected by TRPV1 blockade. Blocking the substance P receptor, NK1, produced an insignificant trend towards Il6 inhibition. TRPA1 and NK1 showed a stronger immuno-reactivity than TRPV1 on cells of the peritoneal tissue.

CONCLUSION

The results show that IL-6 synthesis and secretion were connected to acute PD fluid exposure, and this response was triggered by TRPA1 receptors, possibly located to non-neuronal cells.

Recommendations for pathological diagnosis on biopsy samples from peritoneal dialysis patients

Peritoneal dialysis (PD) has been established as an essential renal replacement therapy for patients with end stage renal disease during the past half century. Histological evaluation of the peritoneal membrane has contributed to the pathophysiological understanding of PD-related peritoneal injury such as peritonitis, fibrosis, and encapsulating peritoneal sclerosis (EPS). Hyalinizing peritoneal sclerosis (HPS), also known as simple sclerosis, is observed in almost all of PD patients. HPS is morphologically characterized by fibrosis of the submesothelial interstitium and hyalinizing vascular wall, particularly of the post-capillary venule (PCV). Two histological factors, the thickness of submesothelial compact zone (SMC) and the lumen/vessel ratio (L/V) at the PCV, have been used for the quantitative evaluation of HPS. The measuring system on SMC thickness and L/V ratio is easy and useful for evaluating the severity of HPS. On the other hand, EPS is characterized by unique encapsulation of the intestines by an "encapsulating membrane". This newly formed membranous structure covers the visceral peritoneum of the intestines, which contains fibrin deposition, angiogenesis, and proliferation of fibroblast-like cells and other inflammatory cells. This review will cover the common understandings of PD-related peritoneal alterations and provide a basic platform for clinical applications and future studies in this field.

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

INTRODUCTION

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Preventing peritoneal membrane fibrosis in peritoneal dialysis patients

Long-term peritoneal dialysis causes morphologic and functional changes in the peritoneal membrane. Although mesothelial-mesenchymal transition of peritoneal mesothelial cells is a key process leading to peritoneal fibrosis, and bioincompatible peritoneal dialysis solutions (glucose, glucose degradation products, and advanced glycation end products or a combination) are responsible for altering mesothelial cell function and proliferation, mechanisms underlying these processes remain largely unclear. Peritoneal fibrosis has 2 cooperative parts, the fibrosis process itself and the inflammation. The link between these 2 processes is frequently bidirectional, with each one inducing the other. This review outlines our current understanding about the definition and pathophysiology of peritoneal fibrosis, recent studies on key fibrogenic molecular machinery in peritoneal fibrosis, such as the role of transforming growth factor-β/Smads, transforming growth factor-β β/Smad independent pathways, and noncoding RNAs. The diagnosis of peritoneal fibrosis, including effluent biomarkers and the histopathology of a peritoneal biopsy, which is the gold standard for demonstrating peritoneal fibrosis, is introduced in detail. Several interventions for peritoneal fibrosis based on biomarkers, cytology, histology, functional studies, and antagonists are presented in this review. Recent experimental trials in animal models, including pharmacology and gene therapy, which could offer novel insights into the treatment of peritoneal fibrosis in the near future, are also discussed in depth.