Caffeic acid phenethyl ester restores mitochondrial homeostasis against peritoneal fibrosis induced by peritoneal dialysis through the AMPK/SIRT1 pathway

Increasing evidence suggests that peritoneal fibrosis induced by peritoneal dialysis (PD) is linked to oxidative stress. However, there are currently no effective interventions for peritoneal fibrosis. In the present study, we explored whether adding caffeic acid phenethyl ester (CAPE) to peritoneal dialysis fluid (PDF) improved peritoneal fibrosis caused by PD and explored the molecular mechanism. We established a peritoneal fibrosis model in Sprague-Dawley rats through intraperitoneal injection of PDF and lipopolysaccharide (LPS). Rats in the PD group showed increased peritoneal thickness, submesothelial collagen deposition, and the expression of TGFβ1 and α-SMA. Adding CAPE to PDF significantly inhibited PD-induced submesothelial thickening, reduced TGFβ1 and α-SMA expression, alleviated peritoneal fibrosis, and improved the peritoneal ultrafiltration function. In vitro, peritoneal mesothelial cells (PMCs) treated with PDF showed inhibition of the AMPK/SIRT1 pathway, mitochondrial membrane potential depolarization, overproduction of mitochondrial reactive oxygen species (ROS), decreased ATP synthesis, and induction of mesothelial-mesenchymal transition (MMT). CAPE activated the AMPK/SIRT1 pathway, thereby inhibiting mitochondrial membrane potential depolarization, reducing mitochondrial ROS generation, and maintaining ATP synthesis. However, the beneficial effects of CAPE were counteracted by an AMPK inhibitor and siSIRT1. Our results suggest that CAPE maintains mitochondrial homeostasis by upregulating the AMPK/SIRT1 pathway, which alleviates oxidative stress and MMT, thereby mitigating the damage to the peritoneal structure and function caused by PD. These findings suggest that adding CAPE to PDF may prevent and treat peritoneal fibrosis.

MiR-454-3p regulates high glucose-induced mesothelial-mesenchymal transition and glycolysis in peritoneal mesothelial cells by targeting STAT3

BACKGROUND

The quality of life of patients receiving long-term peritoneal dialysis (PD) is significantly impacted by the onset of peritoneal fibrosis (PF), and one of the pathological changes is mesothelial-mesenchymal transition (MMT). In this study, we investigated the potential roles of miR-454-3p and signal transducer and activator of transcription 3 (STAT3) in the progression of peritoneal MMT and the underlying mechanisms.

METHODS

Peritoneums were collected to detect morphology via hematoxylin-eosin staining and differentially expressed miRNAs were detected via RT-qPCR. PD effluent-derived cell populations in the peritoneal cavity were isolated from the effluents of 20 PD patients to determine miR-454-3p, STAT3, and MMT markers via Western blotting and RT-qPCR. The relationship between miR-454-3p and STAT3 was examined via a dual-luciferase reporter assay. Western blotting and RT-qPCR were utilized to evaluate the expression of STAT3, MMT markers, and glycolytic enzymes. Immunofluorescence staining revealed the localization and expression of MMT markers and STAT3.

RESULTS

MiR-454-3p was downregulated in the peritoneums and PD effluent-derived cell populations of long-term PD patients. High glucose (HG) treatment promoted HMrSV5 cell MMT and glycolysis. MiR-454-3p overexpression alleviated HG-induced MMT and suppressed the expression of STAT3 and glycolytic enzymes. In contrast, the miR-454-3p inhibitor exacerbated HG-induced MMT and promoted the expression of glycolytic enzymes and STAT3. Moreover, STAT3 was the target of miR-454-3p.

CONCLUSIONS

This study demonstrated the protective role of miR-454-3p in HG-induced MMT and glycolysis in HMrSv5 cells, suggesting that miR-454-3p may prevent MMT by suppressing glycolytic enzymes via the STAT3/PFKFB3 pathway in the HG environment.

Risk factors and outcomes in patients who switched from peritoneal dialysis to physician-oriented or patient-oriented kidney replacement therapy

BACKGROUND

We aimed to compare the cardiovascular events and mortality in patients who underwent either physician-oriented or patient-oriented kidney replacement therapy (KRT) conversion due to discontinuation of peritoneal dialysis (PD).

METHODS

Patients with end-stage kidney disease who were receiving PD and required a switch to an alternative KRT were included. They were divided into physician-oriented group or patient-oriented group based on the decision-making process. Logistic regression analysis was used to explore the influencing factors related to KRT conversion in PD patients. The association of physician-oriented or patient-oriented KRT conversion with outcomes after the conversion was assessed by using Cox proportional hazards models.

RESULTS

A total of 257 PD patients were included in the study. The median age at catheterization was 35 years. 69.6% of the participants were male. The median duration of PD was 20 months. 162 participants had patient-oriented KRT conversion, while 95 had physician-oriented KRT conversion. Younger patients, those with higher education levels, higher income, and no diabetes were more likely to have patient-oriented KRT conversion. Over a median follow-up of 39 months, 40 patients experienced cardiovascular events and 16 patients died. Physician-oriented KRT conversion increased nearly 3.8-fold and 4.0-fold risk of cardiovascular events and death, respectively. After adjusting for confounders, physician-oriented KRT conversion remained about a 3-fold risk of cardiovascular events.

CONCLUSION

Compared to patient-oriented KRT conversion, PD patients who underwent physician-oriented conversion had higher risks of cardiovascular events and all-cause mortality. Factors included age at catheterization, education level, annual household income, and history of diabetes mellitus.

Pressure induces peritoneal fibrosis and inflammation through CD44 signaling

Peritoneal dialysis (PD) is a widely used sustainable kidney replacement therapy. Prolonged use of PD fluids is associated with mesothelial-mesenchymal transition, peritoneal fibrosis, and eventual ultrafiltration (UF) failure. However, the impact of pressure on the peritoneum remains unclear. In the present study, we hypothesized increased pressure is a potential contributing factor to peritoneal fibrosis and investigated the possible mechanisms. In vitro experiments found that pressurization led to a mesenchymal phenotype, the expression of fibrotic markers and inflammatory factors in human mesothelial MeT-5A cells. Pressure also increased cell proliferation and augmented cell migration potential in MeT-5A cells. The mouse PD model and human peritoneum equilibrium test (PET) data both showed a positive association between higher pressure and increased small solute transport, along with decreased net UF. Mechanistically, we found that significant upregulation of CD44 in mesothelial cells upon pressurization. Notably, the treatment of CD44 neutralizing antibodies prevented pressure-induced phenotypic changes in mesothelial cells, while a CD44 inhibitor oligo-fucoidan ameliorated pressure-induced peritoneal thickening, fibrosis, and inflammation in PD mice. To conclude, intraperitoneal pressure results in peritoneal fibrosis in PD via CD44-mediated mesothelial changes and inflammation. CD44 blockage can be utilized as a novel preventive approach for PD-related peritoneal fibrosis and UF failure.

JPH203 alleviates peritoneal fibrosis via inhibition of amino acid-mediated mTORC1 signaling

BACKGROUND AND AIMS

The mesothelial-mesenchymal transition (MMT) of mesothelial cells has been recognized as a critical process during progression of peritoneal fibrosis (PF). Despite its crucial role in amino acid transport and metabolism, the involvement of L-type amino acid transporter 1 (LAT1) and the potential therapeutic role of its inhibitor, JPH203, in fibrotic diseases remain unexplored. Considering the paucity of research on amino acid-mediated mTORC1 activation in PF, our study endeavors to elucidate the protective effects of JPH203 against PF and explore the involvement of amino acid-mediated mTORC1 signaling in this context.

METHODS

We established the transforming growth factor beta 1 (TGF-β1) induced MMT model in primary human mesothelial cells and the peritoneal dialysis fluid (PDF) induced PF model in mice. The therapeutic effects of JPH203 on PF were then examined on these two models by real-time quantitative polymerase chain reaction, western blotting, immunofluorescence staining, Masson's trichrome staining, H&E staining, picro-sirius red staining, and immunohistochemistry. The involvement of amino acid-mediated mTORC1 signaling was screened by RNA sequencing and further verified by western blotting in vitro.

RESULTS

LAT1 was significantly upregulated and JPH203 markedly attenuated fibrotic phenotype both in vitro and in vivo. RNA-seq unveiled a significant enrichment of mTOR signaling pathway in response to JPH203 treatment. Western blotting results indicated that JPH203 alleviates PF by inhibiting amino acid-mediated mTORC1 signaling, which differs from the direct inhibition observed with rapamycin.

CONCLUSION

JPH203 alleviates PF by inhibiting amino acid-mediated mTORC1 signaling.

Aquaporin-1 and Osmosis: From Physiology to Precision in Peritoneal Dialysis

The discovery of the aquaporin family of water channels has provided a molecular counterpart to the movement of water across biological membranes. The distribution of aquaporins in specific cell types, their selectivity and very high capacity for water permeation, and the control of their expression and/or trafficking are key to sustain osmosis in multiple tissues. Here, we review the convergent evidence demonstrating that aquaporin-1 (AQP1) facilitates water transport across endothelial cells in the peritoneal membrane, a key process for peritoneal dialysis-the leading modality of home-based dialysis therapy for patients with kidney failure. Genetic and pharmacologic studies in mouse and cell models indicated that AQP1 plays a critical role in crystalloid osmosis, with clinically relevant effects on water transport and risk of death and technique failure for patients on dialysis. By contrast, AQP1 plays no role in colloid osmosis. These studies substantiate potential strategies to improve free water transport and ultrafiltration in patients treated by peritoneal dialysis.

Genistein inhibits HIF-1α and attenuates high glucose-induced peritoneal mesothelial-mesenchymal transition and fibrosis via the mTOR/OGT pathway

Peritoneal fibrosis has been linked to hypoxia-inducible factor 1-alpha (HIF-1α) as well as O-linked-N-acetylglucosaminylation (O-GlcNAcylation) in peritoneal dialysis (PD). Genistein, recognized for its HIF-1α inhibitory and antifibrotic effects, presents a potential intervention against peritoneal mesothelial-mesenchymal transition (MMT) as well as fibrosis in PD. This study employed human peritoneal mesothelial cells (HPMCs) together with adenine-induced chronic kidney disease (CKD) rats undergoing peritoneal dialysis to explore Genistein's role in high glucose-induced peritoneal MMT and fibrosis. Our findings reveal that Genistein exerts anti-MMT and anti-fibrotic effects by inhibiting HIF-1α in HPMCs under high glucose conditions. Genistein inhibited O-GlcNAcylation status of HIF-1α through the mTOR/O-GlcNAc transferase (OGT) pathway, promoting its ubiquitination as well as the subsequent proteasomal degradation. In adenine-induced CKD rats undergoing peritoneal dialysis, Genistein suppressed the mTOR/OGT expression and reduced the abundance of O-GlcNAcylation along with HIF-1α in the peritoneum. Additionally, Genistein protected against increased peritoneal thickness, fibrosis, and angiogenesis, while improving peritoneal function. Based on our results, it could be inferred that Genistein might inhibit the abundance of HIF-1α via the mTOR/OGT pathway, thereby ameliorating MMT as well as fibrosis in PD.

Selective activation of PPARα by pemafibrate mitigates peritoneal inflammation and fibrosis through suppression of NLRP3 inflammasome and modulation of inflammation

Peritoneal inflammation and fibrosis remain major challenges to the long-term maintenance of peritoneal dialysis. Pemafibrate, a selective peroxisome proliferator-activated receptor α (PPARα) modulator, has been implicated in the management of fibrosis-related disorders. We investigated whether pemafibrate ameliorates peritoneal inflammation and fibrosis and explored the underlying mechanisms in mice with methylglyoxal (MGO)-induced peritoneal fibrosis (MGO mice). MGO mice exhibited peritoneal fibrosis with increased expression of mesenchymal markers, transforming growth factor-β1 (TGF-β1), and substantial deposition of extracellular matrix (ECM) proteins. Additionally, MGO mice exhibited peritoneal inflammation as indicated by elevated tumor necrosis factor-α expression and macrophage infiltration in peritoneal tissue. These effects were mitigated by pemafibrate treatment, which also restored peritoneal membrane function. Furthermore, pemafibrate promoted anti-inflammatory macrophage polarization in both mice and THP-1 cells. In human peritoneal mesothelial cells (HPMCs), pemafibrate effectively inhibited interferon-γ-induced production of TGF-β1 and ECM while suppressing the proinflammatory cytokines nuclear factor-κB (NF-κB) and activator protein 1. The NF-κB inhibitory effect of pemafibrate involved stabilization of the NF-κB inhibitory protein IkBα. Notably, pemafibrate hindered activation of the NLR family pyrin domain containing 3/caspase-1 axis in interferon-γ-stimulated THP-1 cells. These findings suggest that pemafibrate ameliorates peritoneal inflammation and fibrosis, making it a promising candidate for peritoneal fibrosis therapy.

Zinc: a potential star for regulating peritoneal fibrosis

Peritoneal dialysis (PD) is a commonly used renal replacement therapy for patients with end-stage renal disease (ESRD). During PD, the peritoneum (PM), a semi-permeable membrane, is exposed to nonbiocompatible PD solutions. Peritonitis can occur, leading to structural and functional PM disorders, resulting in peritoneal fibrosis and ultrafiltration failure, which are important reasons for patients with ESRD to discontinue PD. Increasing evidence suggests that oxidative stress (OS) plays a key role in the pathogenesis of peritoneal fibrosis. Furthermore, zinc deficiency is often present to a certain extent in patients undergoing PD. As an essential trace element, zinc is also an antioxidant, potentially playing an anti-OS role and slowing down peritoneal fibrosis progression. This study summarises and analyses recent research conducted by domestic and foreign scholars on the possible mechanisms through which zinc prevents peritoneal fibrosis.

Pathophysiological Mechanisms of Peritoneal Fibrosis and Peritoneal Membrane Dysfunction in Peritoneal Dialysis

The characteristic feature of chronic peritoneal damage in peritoneal dialysis (PD) is a decline in ultrafiltration capacity associated with pathological fibrosis and angiogenesis. The pathogenesis of peritoneal fibrosis is attributed to bioincompatible factors of PD fluid and peritonitis. Uremia is associated with peritoneal membrane inflammation that affects fibrosis, neoangiogenesis, and baseline peritoneal membrane function. Net ultrafiltration volume is affected by capillary surface area, vasculopathy, peritoneal fibrosis, and lymphangiogenesis. Many inflammatory cytokines induce fibrogenic growth factors, with crosstalk between macrophages and fibroblasts. Transforming growth factor (TGF)-β and vascular endothelial growth factor (VEGF)-A are the key mediators of fibrosis and angiogenesis, respectively. Bioincompatible factors of PD fluid upregulate TGF-β expression by mesothelial cells that contributes to the development of fibrosis. Angiogenesis and lymphangiogenesis can progress during fibrosis via TGF-β-VEGF-A/C pathways. Complement activation occurs in fungal peritonitis and progresses insidiously during PD. Analyses of the human peritoneal membrane have clarified the mechanisms by which encapsulating peritoneal sclerosis develops. Different effects of dialysates on the peritoneal membrane were also recognized, particularly in terms of vascular damage. Understanding the pathophysiologies of the peritoneal membrane will lead to preservation of peritoneal membrane function and improvements in technical survival, mortality, and quality of life for PD patients.

Protective effect of Cyclo(His-Pro) on peritoneal fibrosis through regulation of HDAC3 expression

Peritoneal dialysis is a common treatment for end-stage renal disease, but complications often force its discontinuation. Preventive treatments for peritoneal inflammation and fibrosis are currently lacking. Cyclo(His-Pro) (CHP), a naturally occurring cyclic dipeptide, has demonstrated protective effects in various fibrotic diseases, yet its potential role in peritoneal fibrosis (PF) remains uncertain. In a mouse model of induced PF, CHP was administered, and quantitative proteomic analysis using liquid chromatography-tandem mass spectrometry was employed to identify PF-related protein signaling pathways. The results were further validated using human primary cultured mesothelial cells. This analysis revealed the involvement of histone deacetylase 3 (HDAC3) in the PF signaling pathway. CHP administration effectively mitigated PF in both peritoneal tissue and human primary cultured mesothelial cells, concurrently regulating fibrosis-related markers and HDAC3 expression. Moreover, CHP enhanced the expression of nuclear factor erythroid 2-related factor 2 (Nrf2) while suppressing forkhead box protein M1 (FOXM1), known to inhibit Nrf2 transcription through its interaction with HDAC3. CHP also displayed an impact on spleen myeloid-derived suppressor cells, suggesting an immunomodulatory effect. Notably, CHP improved mitochondrial function in peritoneal tissue, resulting in increased mitochondrial membrane potential and adenosine triphosphate production. This study suggests that CHP can significantly prevent PF in peritoneal dialysis patients by modulating HDAC3 expression and associated signaling pathways, reducing fibrosis and inflammation markers, and improving mitochondrial function.

Role of endothelial hyaluronan in peritoneal membrane transport and disease conditions during peritoneal dialysis

Peritoneal membrane dysfunction in peritoneal dialysis (PD) is primarily attributed to angiogenesis; however, the integrity of vascular endothelial cells can affect peritoneal permeability. Hyaluronan, a component of the endothelial glycocalyx, is reportedly involved in preventing proteinuria in the normal glomerulus. One hypothesis suggests that development of encapsulating peritoneal sclerosis (EPS) is triggered by protein leakage due to vascular endothelial injury. We therefore investigated the effect of hyaluronan in the glycocalyx on peritoneal permeability and disease conditions. After hyaluronidase-mediated degradation of hyaluronan on the endothelial cells of mice, macromolecules, including albumin and β2 microglobulin, leaked into the dialysate. However, peritoneal transport of small solute molecules was not affected. Pathologically, hyaluronan expression was diminished; however, expression of vascular endothelial cadherin and heparan sulfate, a core protein of the glycocalyx, was preserved. Hyaluronan expression on endothelial cells was studied using 254 human peritoneal membrane samples. Hyaluronan expression decreased in patients undergoing long-term PD treatment and EPS patients treated with conventional solutions. Furthermore, the extent of hyaluronan loss correlated with the severity of vasculopathy. Hyaluronan on endothelial cells is involved in the peritoneal transport of macromolecules. Treatment strategies that preserve hyaluronan in the glycocalyx could prevent the leakage of macromolecules and subsequent related complications.

Omega-3 polyunsaturated fatty acids protect peritoneal mesothelial cells from hyperglycolysis and mesothelial-mesenchymal transition through the FFAR4/CaMKKβ/AMPK/mTOR signaling pathway

Peritoneal fibrosis is a severe clinical complication associated with peritoneal dialysis (PD) and impacts its efficacy and patient outcomes. The process of mesothelial-mesenchymal transition (MMT) in peritoneal mesothelial cells plays a pivotal role in fibrogenesis, whereas metabolic reprogramming, characterized by excessive glycolysis, is essential in MMT development. No reliable therapies are available despite substantial progress made in understanding the mechanisms underlying peritoneal fibrosis. Protective effect of omega-3 polyunsaturated fatty acids (ω3 PUFAs) has been described in PD-induced peritoneal fibrosis, although the detailed mechanisms remain unknown. It is known that ω3 PUFAs bind to and activate the free fatty acid receptor 4 (FFAR4). However, the expression and role of FFAR4 in the peritoneum have not been investigated. Thus, we hypothesized that ω3 PUFAs would alleviate peritoneal fibrosis by inhibiting hyperglycolysis and MMT through FFAR4 activation. First, we determined FFAR4 expression in peritoneal mesothelium in humans and mice. FFAR4 expression was abnormally decreased in patients on PD and mice and HMrSV5 mesothelial cells exposed to PD fluid (PDF); this change was restored by the ω3 PUFAs (EPA and DHA). ω3 PUFAs significantly inhibited peritoneal hyperglycolysis, MMT, and fibrosis in PDF-treated mice and HMrSV5 mesothelial cells; these changes induced by ω3 PUFAs were blunted by treatment with the FFAR4 antagonist AH7614 and FFAR4 siRNA. Additionally, ω3 PUFAs induced FFAR4, Ca2+/calmodulin-dependent protein kinase kinase β (CaMKKβ), and AMPK and suppressed mTOR, leading to the inhibition of hyperglycolysis, demonstrating that the ω3 PUFAs-mediated FFAR4 activation ameliorated peritoneal fibrosis by inhibiting hyperglycolysis and MMT via CaMKKβ/AMPK/mTOR signaling. As natural FFAR4 agonists, ω3 PUFAs may be considered for the treatment of PD-associated peritoneal fibrosis.

Unravelling the role of Sildenafil and SB204741 in suppressing fibrotic potential of peritoneal fibroblasts obtained from PD patients

Introduction: Peritoneal fibrosis (PF) results in technique failure in peritoneal dialysis (PD) patients. Peritoneal fibroblasts are characterized by increase in the ACTA2 gene, responsible for alpha smooth muscle actin (α-SΜΑ), extracellular matrix (ECM) production, and inflammatory cytokines production, which are the are key mediators in the pathogenesis of PF. 5-hydroxytryptamine (5-HT; serotonin) induces ECM synthesis in fibroblasts in a transforming growth factor-beta 1 (TGF-β1) dependent manner. The purpose of our study was to identify the potential mechanism and role of sildenafil and 5HT2B receptor inhibitor (SB204741) combination in attenuating PD-associated peritoneal fibrosis. Methods: Studies were performed to determine the effect of TGF-β1, sildenafil, and SB204741 on human peritoneal fibroblasts (HPFBs) isolated from the parietal peritoneum of patients in long-term PD patients (n = 6) and controls (n = 6). HPFBs were incubated with TGF-β1 (10 ng/mL) for 1 h and later with TGF-β1 (10 ng/mL)/[sildenafil (10 µM) or SB204741 (1 µM)] and their combination for 24 h (post-treatment strategy). In the pre-treatment strategy, HPFBs were pre-treated with sildenafil (10 µM) or SB204741 (1 µM) and a combination of the two for 1 h and later with only TGF-β1 (10 ng/mL) for 24 h. Results: The anti-fibrotic effects of the combination of sildenafil and SB204741 were greater than that of each drug alone. In TGF-β1-stimulated HPFBs, pro-fibrotic genes (COL1A1, COL1A2, ACTA2, CTGF, FN1, and TGFB1) exhibited higher expression than in controls, which are crucial targets of sildenafil and SB204741 against peritoneal fibrosis. The synergistic approach played an anti-fibrotic role by regulating the pro- and anti-fibrotic gene responses as well as inflammatory cytokine responses. The combination treatment significantly attenuated peritoneal fibrosis, as evident by the almost complete amelioration of ACTA2 expression, restoration of anti-fibrotic genes (MMP2/TIMP1), and, at least, by reducing the expression of pro-inflammatory cytokines (IFN-γ, IL-4, IL-17, IL-1β, IL-6, TNF-α, and TGF-β1) along with an increase in IL-10 levels. Discussion: Taken together, the above research evidences that the combination of sildenafil and SB204741 may have therapeutic potential in suppressing peritoneal fibrosis due to peritoneal dialysis.

Advances in stem cell therapy for peritoneal fibrosis: from mechanisms to therapeutics

Peritoneal fibrosis (PF) is a pathophysiological condition caused by a variety of pathogenic factors. The most important features of PF are mesothelial-mesenchymal transition and accumulation of activated (myo-)fibroblasts, which hinder effective treatment; thus, it is critical to identify other practical approaches. Recently, stem cell (SC) therapy has been indicated to be a potential strategy for this disease. Increasing evidence suggests that many kinds of SCs alleviate PF mainly by differentiating into mesothelial cells; secreting cytokines and extracellular vesicles; or modulating immune cells, particularly macrophages. However, there are relatively few articles summarizing research in this direction. In this review, we summarize the risk factors for PF and discuss the therapeutic roles of SCs from different sources. In addition, we outline effective approaches and potential mechanisms of SC therapy for PF. We hope that our review of articles in this area will provide further inspiration for research on the use of SCs in PF treatment.

Brahma-related gene 1 acts as a profibrotic mediator and targeting it by micheliolide ameliorates peritoneal fibrosis

BACKGROUND

Progressive peritoneal fibrosis is a worldwide public health concern impacting patients undergoing peritoneal dialysis (PD), yet there is no effective treatment. Our previous study revealed that a novel compound, micheliolide (MCL) inhibited peritoneal fibrosis in mice. However, its mechanism remains unclear. Brahma-related gene 1 (BRG1) is a key contributor to organ fibrosis, but its potential function in PD-related peritoneal fibrosis and the relationship between MCL and BRG1 remain unknown.

METHODS

The effects of MCL on BRG1-induced fibrotic responses and TGF-β1-Smads pathway were examined in a mouse PD model and in vitro peritoneal mesothelial cells. To investigate the targeting mechanism of MCL on BRG1, coimmunoprecipitation, MCL-biotin pulldown, molecular docking and cellular thermal shift assay were performed.

RESULTS

BRG1 was markedly elevated in a mouse PD model and in peritoneal mesothelial cells cultured in TGF-β1 or PD fluid condition. BRG1 overexpression in vitro augmented fibrotic responses and promoted TGF-β1-increased-phosphorylation of Smad2 and Smad3. Meanwhile, knockdown of BRG1 diminished TGF-β1-induced fibrotic responses and blocked TGF-β1-Smad2/3 pathway. MCL ameliorated BRG1 overexpression-induced peritoneal fibrosis and impeded TGF-β1-Smad2/3 signaling pathway both in a mouse PD model and in vitro. Mechanically, MCL impeded BRG1 from recognizing and attaching to histone H3 lysine 14 acetylation by binding to the asparagine (N1540) of BRG1, in thus restraining fibrotic responses and TGF-β1-Smad2/3 signaling pathway. After the mutation of N1540 to alanine (N1540A), MCL was unable to bind to BRG1 and thus, unsuccessful in suppressing BRG1-induced fibrotic responses and TGF-β1-Smad2/3 signaling pathway.

CONCLUSION

Our research indicates that BRG1 may be a crucial mediator in peritoneal fibrosis and MCL targeting N1540 residue of BRG1 may be a novel therapeutic strategy to combat PD-related peritoneal fibrosis.

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.

Peritoneal Expression of Membrane Complement Regulators Is Decreased in Peritoneal Dialysis Patients with Infected Peritonitis

In peritoneal dialysis (PD) patients, fungi and Pseudomonas aeruginosa are considered important causative microorganisms for peritonitis with poor prognosis. Our objective was to explore expressions of membrane complement (C) regulators (CRegs) and tissue injuries in the peritoneum of patients with PD-related peritonitis, including fungal and Pseudomonas aeruginosa peritonitis. In peritoneal biopsy tissues obtained at PD catheter removal, we investigated the severity of peritonitis-associated peritoneal injuries and the expression of CRegs, CD46, CD55, and CD59 against peritoneal tissues without any episode of peritonitis. In addition, we evaluated peritoneal injuries among fungal and Pseudomonas aeruginosa-peritonitis (P1) and Gram-positive bacterial peritonitis (P2). We also observed deposition of C activation products such as activated C and C5b-9 and measured sC5b-9 in the PD fluid of patients. As a result, the severity of peritoneal injuries correlated inversely with the expression of peritoneal CRegs. Peritoneal CReg expression in peritonitis was significantly reduced compared to no peritonitis. Peritoneal injuries were more severe in P1 than in P2. CReg expression was further decreased and C5b-9 further increased in P1 than in P2. In conclusion, severe peritoneal injuries due to fungal and Pseudomonas aeruginosa-peritonitis decreased CReg expression and increased deposition of activated C3 and C5b-9 in the peritoneum, suggesting that peritonitis, particularly fungal and Pseudomonas aeruginosa-peritonitis, might induce susceptibility to further peritoneal injuries due to excessive C activation.

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.

Novel Aspects of the Immune Response Involved in the Peritoneal Damage in Chronic Kidney Disease Patients under Dialysis

Chronic kidney disease (CKD) incidence is growing worldwide, with a significant percentage of CKD patients reaching end-stage renal disease (ESRD) and requiring kidney replacement therapies (KRT). Peritoneal dialysis (PD) is a convenient KRT presenting benefices as home therapy. In PD patients, the peritoneum is chronically exposed to PD fluids containing supraphysiologic concentrations of glucose or other osmotic agents, leading to the activation of cellular and molecular processes of damage, including inflammation and fibrosis. Importantly, peritonitis episodes enhance peritoneum inflammation status and accelerate peritoneal injury. Here, we review the role of immune cells in the damage of the peritoneal membrane (PM) by repeated exposure to PD fluids during KRT as well as by bacterial or viral infections. We also discuss the anti-inflammatory properties of current clinical treatments of CKD patients in KRT and their potential effect on preserving PM integrity. Finally, given the current importance of coronavirus disease 2019 (COVID-19) disease, we also analyze here the implications of this disease in CKD and KRT.

The expression of matrix metalloproteinase-12 in the peritoneum of rats with continuous peritoneal dialysis

BACKGROUND

Peritoneal dialysis (PD) is an important alternative treatment for end-stage renal disease. Continuous exposure to non-physiological fluids during PD is associated with pathological responses, such as sustained microinflammation, leading to tissue fibrosis and angiogenesis. However, the effect of PD fluid on submesothelial cells has not yet been investigated in detail.

METHODS

We investigated the association between macrophages and the expression of matrix metalloproteinase-12 (MMP-12), an elastin proteinase secreted by macrophages, in the peritoneal tissue of rats undergoing continuous PD.

RESULTS

Morphological data revealed that the submesothelial layer of the peritoneum in PD model rats was markedly thickened, with fibrosis and angiogenesis. In the fibrillization area, elastin was disorganized and fragmented, and macrophages accumulated, which tended to have M2 characteristics. The expression of MMP-12 was enhanced by continuous exposure to PD fluid, suggesting that MMP-12 expression may be involved in PD fluid-induced peritoneal damage.

CONCLUSIONS

The results of this study may lead to a better understanding of the mechanisms underlying fibrosis in PD.

Alpha-klotho and peritoneal membrane status: A hypothesis generating study

BACKGROUND

Long-term success of peritoneal dialysis relies on the integrity of the peritoneal membrane. This proof-of-concept study addressed the hypothesis that fibrosis is already present in the membrane at pre-dialysis and that the membrane status is related to the individual's uraemic fingerprint.

METHODS

A clinical-mechanistic, transversal, single-centre study was conducted. Pre-dialysis peritoneal biopsies were scored considering the submesothelial compact zone thickness (STM), vasculopathy and inflammation. We investigated if the membrane status could be inferred from a panel of proteins (α-Klotho, Galectin-3, FGF21, FGF23, Tweak, TNFα and hsPCR) in blood.

RESULTS

A total 58 incident patients aged 56 ± 15 years old were included, 31% female, 55% hypertension, 29% diabetic and 24% obese. Person-to-person STM was found to be highly variable and 38% of patients were fibrosis positive. Both α-Klotho (Spearman r = -.7491, p < 0.001) and FGF21 (Spearman r = -.5102, p < 0.001) were negatively associated with STM. α-Klotho, but not FGF21, was able to discriminate fibrosis from nonfibrosis with/without inflammation and vasculopathy. PLS models identified α-Klotho as the protein most relevant for fibrosis. α-Klotho was independently associated with fibrosis of the peritoneal membrane (OR = .991 (.896-.997), p = 0.002).

CONCLUSION

Before the start of dialysis in incident patients, some patients already present fibrosis of the peritoneal membrane and other patients do not. Our findings suggest that α-Klotho may be implicated in fibrosis of the peritoneal membrane.

Inhibition of Transglutaminase 2 Reduces Peritoneal Injury in a Chlorhexidine-Induced Peritoneal Fibrosis Model

Long-term peritoneal dialysis (PD) is often associated with peritoneal dysfunction leading to withdrawal from PD. The characteristic pathologic features of peritoneal dysfunction are widely attributed to peritoneal fibrosis and angiogenesis. The detailed mechanisms remain unclear, and treatment targets in clinical settings have yet to be identified. We investigated transglutaminase 2 (TG2) as a possible novel therapeutic target for peritoneal injury. TG2 and fibrosis, inflammation, and angiogenesis were investigated in a chlorhexidine gluconate (CG)-induced model of peritoneal inflammation and fibrosis, representing a noninfectious model of PD-related peritonitis. Transforming growth factor (TGF)-β type I receptor (TGFβR-I) inhibitor and TG2-knockout mice were used for TGF-β and TG2 inhibition studies, respectively. Double immunostaining was performed to identify cells expressing TG2 and endothelial-mesenchymal transition (EndMT). In the rat CG model of peritoneal fibrosis, in situ TG2 activity and protein expression increased during the development of peritoneal fibrosis, as well as increases in peritoneal thickness and numbers of blood vessels and macrophages. TGFβR-I inhibitor suppressed TG2 activity and protein expression, as well as peritoneal fibrosis and angiogenesis. TGF-β1 expression, peritoneal fibrosis, and angiogenesis were suppressed in TG2-knockout mice. TG2 activity was detected by α-smooth muscle actin-positive myofibroblasts, CD31-positive endothelial cells, and ED-1-positive macrophages. CD31-positive endothelial cells in the CG model were α-smooth muscle actin-positive, vimentin-positive, and vascular endothelial-cadherin-negative, suggesting EndMT. In the CG model, EndMT was suppressed in TG2-knockout mice. TG2 was involved in the interactive regulation of TGF-β. As inhibition of TG2 reduced peritoneal fibrosis, angiogenesis, and inflammation associated with TGF-β and vascular endothelial growth factor-A suppression, TG2 may provide a new therapeutic target for ameliorating peritoneal injuries in PD.

Inflammatory chemokine (C-C motif) ligand 8 inhibition ameliorates peritoneal fibrosis

Peritoneal fibrosis (PF) is an irreversible complication of peritoneal dialysis (PD) that leads to loss of peritoneal membrane function. We investigated PD effluent and serum levels and the tissue expression of chemokine (C-C motif) ligand 8 (CCL8) in patients with PD. Additionally, we investigated their association with PF in a mouse model. Eighty-two end-stage renal disease (ESRD) patients with PD were examined. CCL8 levels were measured via enzyme-linked immunosorbent assays in PD effluents and serum and analyzed with peritoneal transport parameters. Human peritoneal mesothelial cells (hPMCs) were obtained from the PD effluents of 20 patients. Primary cultured hPMCs were treated with recombinant (r) transforming growth factor (TGF)-β, and CCL8 expression was assessed via western blotting. As the duration of PD increased, the concentration of CCL8 in PD effluents significantly increased. Correlations between peritoneal transport parameters and dialysate CCL8 levels were observed. Western blotting analysis showed that CCL8 was upregulated via rTGF-β treatment, accompanied by increases in markers of inflammation, fibrosis, senescence, and apoptosis in hPMCs after induction of fibrosis with rTGF-β. Anti-CCL8 monoclonal antibody (mAb) treatment suppressed the rTGF-β-induced increase in all analyzed markers. Immunohistochemical analysis revealed that CCL8 along with fibrosis- and inflammation-related markers were significantly increased in the PF mouse model. Functional blockade of CCL8 using a CCR8 inhibitor (R243) abrogated peritoneal inflammation and fibrosis in vivo. In conclusion, high CCL8 levels in PD effluents may be associated with an increased risk of PD failure, and the CCL8 pathway is associated with PF. CCL8 blockade can ameliorate peritoneal inflammation and fibrosis.

Activation of AMPK-PGC-1α pathway ameliorates peritoneal dialysis related peritoneal fibrosis in mice by enhancing mitochondrial biogenesis

BACKGROUND

The pathogenesis of peritoneal dialysis (PD)-related peritoneal fibrosis (PF) is not clearly understood, and current treatment options are limited.

METHODS

In this study, the effect of PD-related PF on mitochondrial biogenesis was investigated, and the effect of activation of the adenosine monophosphate-activated protein kinase (AMPK)-PGC-1α (peroxisome proliferator-activated receptor γ coactivator-1α) pathway on PF was evaluated in mice.

RESULTS

In a mouse model of PD-related PF, AMPK-PGC-1α signaling (phospho-AMPK, PGC-1α, NRF-1, NRF-2 and TFAM expression) was downregulated, mitochondrial DNA (mtDNA) levels were reduced, and mitochondrial structure was damaged in the peritoneum. In addition, TdT-mediated dUTP nick-end labeling (TUNEL) staining showed typical apoptosis characteristics in peritoneal mesothelial cells (PMCs). Activation of the AMPK-PGC-1α pathway (PGC-1α overexpression or metformin, which is an agonist of AMPK) upregulated phospho-AMPK, PGC-1α, nuclear respiratory factors 1 (NRF-1) and 2 (NRF-2), and mitochondrial transcription factor A (TFAM) expression and mtDNA content, improved mitochondrial morphological manifestations, inhibited apoptosis of PMCs and alleviated PF.

CONCLUSION

Our study may suggest that activation of the AMPK-PGC-1α pathway ameliorates PD-related PF by enhancing mitochondrial biogenesis.

Parthenolide alleviates peritoneal fibrosis by inhibiting inflammation via the NF-κB/ TGF-β/Smad signaling axis

Peritoneal fibrosis is a common complication of peritoneal dialysis (PD) with a complicated pathogenesis and limited treatments. Parthenolide (PTL), a recognized nuclear factor-κB (NF-κB) inhibitor extracted from Tanacetum balsamita, has been widely used to treat various inflammatory diseases and has been proven to improve peritoneal fibrosis in PD mice by selectively inhibiting the phosphorylation of Smad2/3. Transforming growth factor-β1 (TGF-β1), via Smad-dependent signaling, has a pivotal role in promoting pathogenic of fibrosis. To investigate whether PTL can inhibit peritoneal fibrosis, we affected the interaction between NF-κB and the TGF-β/Smad2/3 pathway. Long dwell peritoneal dialysis fluid (PDF) and peritoneum tissues were collected from continuous ambulatory peritoneal dialysis (CAPD) patients. PTL was administered intragastrically into a PD mouse model by daily infusion of 4.25% dextrose-containing PDF. Treated HMrSV5 cells or rat peritoneal mesothelial cells (RPMCs) were treated with high glucose(138 mM) at the same concentration as 2.5% dextrose-containing PDF and PTL. PD-related peritoneal fibrosis samples indicated an increase in inflammation, and PTL decreased the levels of inflammatory cytokines (L-6, TNF-α, and MCP-1). PTL inhibited high glucose-induced mesothelial-to-mesenchymal transition (MMT), as indicated by a reduced expression of fibrosis markers (fibronectin, collagen I, and α-SMA) and increased expression of the epithelial marker E-cadherin. PTL also significantly decreased TGF-β1 expression and the phosphorylation of IκBα and NF-κBp65. The changes in the levels of TGF-β1 expression and p-p65 or p65 showed similar trends according to western blot, immunohistochemistry, and immunofluorescence assays in vitro and in vivo. Chromatin immunoprecipitation (ChIP) and luciferase reporter assays were used to confirm that PTL regulates the transcription of TGF-β1 induced by high glucose through NF-κBp65. In summary, PTL induces a therapeutic effect in peritoneal fibrosis by inhibiting inflammation via the NF-κB/ TGF-β/Smad signaling axis.

Involvement of Mitochondrial Dysfunction in the Inflammatory Response in Human Mesothelial Cells from Peritoneal Dialysis Effluent

Recent studies have related mitochondrial impairment with peritoneal membrane damage during peritoneal dialysis (PD) therapy. Here, we assessed the involvement of mitochondrial dysfunction in the inflammatory response in human mesothelial cells, a hallmark in the pathogenesis of PD-related peritoneal membrane damage. Our ex vivo studies showed that IL-1β causes a drop in the mitochondrial membrane potential in cells from peritoneal effluent. Moreover, when mitochondrial damage was induced by inhibitors of mitochondrial function, a low-grade inflammatory response was generated. Interestingly, mitochondrial damage sensitized mesothelial cells, causing a significant increase in the inflammatory response induced by cytokines, in which ROS generation and NF-κB activation appear to be involved, since inflammation was counteracted by both mitoTEMPO (mitochondrial ROS scavenger) and BAY-117085 (NF-κB inhibitor). Furthermore, the natural anti-inflammatory antioxidant resveratrol significantly attenuated the inflammatory response, by reversing the decline in mitochondrial membrane potential and decreasing the expression of IL-8, COX-2 and PGE2 caused by IL-1β. These findings suggest that IL-1β regulates mitochondrial function in mesothelial cells and that mitochondrial dysfunction could induce an inflammatory scenario that sensitizes these cells, causing significant amplification of the inflammatory response induced by cytokines. Resveratrol may represent a promising strategy in controlling the mesothelial inflammatory response to PD.

Dual therapy with an angiotensin receptor blocker and a JAK1/2 inhibitor attenuates dialysate-induced angiogenesis and preserves peritoneal membrane structure and function in an experimental CKD rat model

BACKGROUND

Peritoneal dialysis (PD) is limited by reduced efficacy over time. We previously showed that a Janus kinase 1/2 inhibitor (JAK1/2i) reduced inflammation, hypervascularity and fibrosis induced by 4.25% dextrose dialysate (4.25%D) intraperitoneally (IP) infused for 10 days in rats with normal kidney function. JAK/STAT signalling mediates inflammatory pathways, including angiotensin signalling. We now tested the effect of long-term JAK1/2i and/or an angiotensin receptor blocker (ARB) on peritoneal membrane (PM) in polycystic kidneys (PCK) rats infused with 4.25%D.

METHODS

Except for controls, all PCK rats had a tunnelled PD catheter: (1) no infusions; (2) 4.25%D; (3) 4.25%D + JAK1/2i (5 mg/kg); (4) 4.25%D +losartan (5 mg/kg); and (5) 4.25%D + losartan +JAK1/2i (5 mg/kg each) IP BID × 16 weeks (N = 5/group). PM VEGFR2 staining areas and submesothelial compact zone (SMCZ) width were morphometrically measured. Peritoneal equilibration testing measured peritoneal ultrafiltration (UF) by calculating dialysate glucose at time 0 and 90 min (D/D₀ glucose).

RESULTS

4.25%D caused hypervascularity, SMCZ widening, fibrosis and UF functional decline in PCK rats. Angiogenesis was significantly attenuated by JAK1/2i ± ARB but not by ARB monotherapy. Both treatments reduced SMCZ area. UF was preserved consistently by dual therapy (p < 0.05) but with inconsistent responses by monotherapies.

CONCLUSION

Long-term JAK1/2i ± ARB reduced angiogenesis and fibrosis, and the combination consistently maintained UF. In clinical practice, angiotensin inhibition has been advocated to maintain residual kidney function. Our study suggests that adding JAK1/2i to angiotensin inhibition may preserve PM structure and UF.

Fibrosis of Peritoneal Membrane as Target of New Therapies in Peritoneal Dialysis

Peritoneal dialysis (PD) is an efficient renal replacement therapy for patients with end-stage renal disease. Even if it ensures an outcome equivalent to hemodialysis and a better quality of life, in the long-term, PD is associated with the development of peritoneal fibrosis and the consequents patient morbidity and PD technique failure. This unfavorable effect is mostly due to the bio-incompatibility of PD solution (mainly based on high glucose concentration). In the present review, we described the mechanisms and the signaling pathway that governs peritoneal fibrosis, epithelial to mesenchymal transition of mesothelial cells, and angiogenesis. Lastly, we summarize the present and future strategies for developing more biocompatible PD solutions.

Peritoneal calprotectin level in peritoneal dialysis patients

BACKGROUND

Calprotectin is an important molecule in the initiation and progression of the inflammatory process. Systemic and local intraperitoneal inflammation are distinct processes and consequences in peritoneal dialysis (PD). We aimed to evaluate dialysate calprotectin levels and its associations with peritonitis and dialysis adequacy in PD patients.

METHODS

Forty-four PD patients were included in this prospective study. Calprotectin concentration was evaluated in 24-h peritoneal drainage fluid. Patients were followed-up for 1 year, and peritonitis episodes were recorded. Dialysate calprotectin levels were compared to dialysis adequacy parameters and peritonitis frequency.

RESULTS

The mean age of patients was 54.9±12.7 years. Median PD duration was 54 (23-76) months. Seventeen patients (38.6%) had previous peritonitis episodes. During follow-up, 15 of 44 patients (34.1%) had peritonitis. The median calprotectin concentration was 79.5 (75.2-86.3) ng/ml. The patients were divided into low and high calprotectin groups according to median value. In the high calprotectin group, BMI was found higher (p = 0.04). There was no significant relationship between calprotectin concentration and peritonitis during follow-up (p = 0.29). However, the patients that have had previous peritonitis had higher calprotectin concentrations (p = 0.02). The patients who had higher erythrocyte sedimentation rate (ESR) levels also had higher calprotectin concentrations (p = 0.01).

CONCLUSION

Peritoneal calprotectin concentrations were correlated with higher BMI and ESR, and it was higher in patients with previous peritonitis episodes. To our knowledge, this is the first study to examine the peritoneal calprotectin levels in PD patients. Further studies are needed to determine the use of peritoneal calprotectin as an inflammatory marker in PD.

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.

Gut microbial metabolite TMAO increases peritoneal inflammation and peritonitis risk in peritoneal dialysis patients

Trimethylamine-N-oxide (TMAO), a gut microbiota-produced metabolite, is accumulated in chronic kidney disease (CKD) patients. It is well known to contribute to CKD-related cardiovascular complications. However, the effect of TMAO on peritoneal dialysis (PD)-related peritonitis remains largely unknown. Here, we demonstrate that serum concentrations of TMAO were positively correlated with C-reactive protein levels, and the appearance rate of dialysate IL-6 and PAI-1, in PD patients. During the follow-up period of 28.3 ± 8.0 months, patients with higher TMAO levels (≥50 μM) had a higher risk of new-onset peritonitis (HR, 3.60; 95%CI, 1.18-10.99; P=0.025) after adjusting for sex, age, diabetes, PD duration, BUN, rGFR, C-reactive protein, BMI and β2-M. In CKD rat models, TMAO significantly promoted peritoneal dialysate-induced inflammatory cell infiltration, inflammatory cytokines production in the peritoneum. In vitro study revealed that TMAO directly induced primary peritoneal mesothelial cell necrosis, together with increased production of pro-inflammatory cytokines including CCL2, TNF-α, IL-6, and IL-1β. In addition, TMAO significantly increased TNF-α-induced P-selectin production in mesothelial cells, as well as high glucose-induced TNF-α and CCL2 expression in endothelial cells. In conclusion, our data demonstrate that higher levels of TMAO exacerbate peritoneal inflammation and might be a risk factor of incidence of peritonitis in PD patients.

Intraperitoneal microbial contamination drives post-surgical peritoneal adhesions by mesothelial EGFR-signaling

Abdominal surgeries are lifesaving procedures but can be complicated by the formation of peritoneal adhesions, intra-abdominal scars that cause intestinal obstruction, pain, infertility, and significant health costs. Despite this burden, the mechanisms underlying adhesion formation remain unclear and no cure exists. Here, we show that contamination of gut microbes increases post-surgical adhesion formation. Using genetic lineage tracing we show that adhesion myofibroblasts arise from the mesothelium. This transformation is driven by epidermal growth factor receptor (EGFR) signaling. The EGFR ligands amphiregulin and heparin-binding epidermal growth factor, are sufficient to induce these changes. Correspondingly, EGFR inhibition leads to a significant reduction of adhesion formation in mice. Adhesions isolated from human patients are enriched in EGFR positive cells of mesothelial origin and human mesothelium shows an increase of mesothelial EGFR expression during bacterial peritonitis. In conclusion, bacterial contamination drives adhesion formation through mesothelial EGFR signaling. This mechanism may represent a therapeutic target for the prevention of adhesions after intra-abdominal surgery.

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

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

Transfer factor treatment in management of peritonitis condition: An experimental study in rat

Background

There is a role for the immune system in improving the outcome of peritonitis cases in children. Transfer factors are one immunomodulatory treatment that can increase the activity of natural killer (NK) cells to produce interferon-gamma (IFN-γ), which is thought to increase the phagocytic activity of macrophages. This study analyzed the effects of transfer factors on the phagocytic activity of macrophages in the intraperitoneal fluid of a Wistar rat model of peritonitis.

Methods

This experimental study had a post-test-only control group design and was carried out at the Laboratory of Pharmacology and Microbiology of Padjadjaran University, Bandung, Indonesia. It analyzed the effect of transfer factors on the phagocytic activity of macrophages in the intraperitoneal fluid of Wistar rats experiencing peritonitis after being injected with Escherichia coli. An unpaired comparative t-test was performed using the SPSS program to analyze the difference between transfer factor administration and macrophage phagocytic activity levels.

Results

There was a statistically significant difference between the phagocytosis index values of macrophages in samples treated with transfer factors and those that were untreated (p = 0.005).

Conclusions

Transfer factors increased the phagocytic activity of macrophages in a Wistar rat model of peritonitis. This suggests that transfer factors could have a role as an immunomodulatory treatment for peritonitis.

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

Incremental peritoneal dialysis is a safe and feasible prescription in incident patients with preserved residual kidney function

BACKGROUND

Incremental peritoneal dialysis (PD) is recommended as a component of high-quality care by the international society for PD; however, its feasibility and clinical outcomes have not been widely reported. The aim of this study is to describe our experience with incremental PD.

METHODS

This was a retrospective cohort study of incident PD patients at Eastern Health between 2015 and 2019. Patients who stopped PD within 30 days were excluded. Incremental PD was defined in CAPD as using <8 L/day of exchange volume and in automated PD as dialysing without a last fill. Dialysis modality accorded with patient and physician preferences.

RESULTS

The 96 patients were included in this study; 54 with incremental PD. Compared to full-dose PD, incremental PD patients were more likely to be female, had less comorbid diabetes (28% vs. 52%) and higher residual kidney function (RKF) (Kt/V 2.0 ± 0.7 vs. 1.4 ± 0.7). Age, BMI and starting eGFR did not differ between groups. Incremental PD exposed patients to lower exchange volumes (4.4 ± 2.1 vs. 8.5 ± 1.1 L/day), glucose load (46 ± 41 g/day vs. 119 ± 46) and was associated with a longer peritonitis-free survival. PD technique survival, rates of peritonitis or hospitalization were comparable between groups. Predictors for longer incremental PD use included older age and higher starting eGFR.

CONCLUSIONS

Incremental PD is a feasible, goal-directed initial prescription in patients with RKF with comparable peritonitis rates and technique survival. Validation of this prescription in prospective studies is warranted.

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.

Risk factors and clinical outcomes of encapsulating peritoneal sclerosis: A case-control study from China

BACKGROUND

Encapsulating peritoneal sclerosis (EPS) is an uncommon, but serious complication in patients with continuous ambulatory peritoneal dialysis (PD) who have a considerable mortality rate. This study aimed to identify risk factors and outcomes of EPS in Chinese patients on PD.

METHODS

Sixteen patients on PD who met the International Society for Peritoneal Dialysis criteria for diagnosis of EPS in the First Affiliated Hospital of Sun Yat-Sen University from 1997 to 2018 were included. Patients without EPS were matched for age, sex and the duration of PD and selected at a 1:3 ratio for the controls. A case-control study was conducted to analyse the clinical profile and risk factors associated with EPS in patients.

RESULTS

The prevalence of EPS in patients on PD in our centre was 0.55%. The percentage of EPS significantly increased with the duration of PD. In univariate regression analysis, a history of peritonitis (odds ratios (OR): 2.83; 95% confidence interval (CI): 0.82-9.68; p = 0.08), peritoneal glucose exposure (OR: 1.12; 95% CI: 1.03-1.22; p < 0.01) and a high peritoneal transport status (OR: 14.70; 95% CI: 1.85-117.02; p < 0.01) were associated with EPS in patients on PD. However in the multivariate model, only a high peritoneal transport status (adjusted odds ratios (aOR): 13.65; 95% CI: 1.69-109.96; p = 0.01) was independently associated with EPS.

CONCLUSION

The rate of EPS significantly increases with the duration of PD. Progressive peritoneal dysfunction, especially a high peritoneal transport status, is associated with a higher risk of EPS in this population.

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.

Biological Effects of XyloCore, a Glucose Sparing PD Solution, on Mesothelial Cells: Focus on Mesothelial-Mesenchymal Transition, Inflammation and Angiogenesis

Glucose-based solutions remain the most used osmotic agents in peritoneal dialysis (PD), but unavoidably they contribute to the loss of peritoneal filtration capacity. Here, we evaluated at a molecular level the effects of XyloCore, a new PD solution with a low glucose content, in mesothelial and endothelial cells. Cell viability, integrity of mesothelial and endothelial cell membrane, activation of mesothelial and endothelial to mesenchymal transition programs, inflammation, and angiogenesis were evaluated by several techniques. Results showed that XyloCore preserves mesothelial and endothelial cell viability and membrane integrity. Moreover XyloCore, unlike glucose-based solutions, does not exert pro-fibrotic, -inflammatory, and -angiogenic effects. Overall, the in vitro evidence suggests that XyloCore could represent a potential biocompatible solution promising better outcomes in clinical practice.

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.

Thymol alleviates AGEs-induced podocyte injury by a pleiotropic effect via NF-κB-mediated by RhoA/ROCK signalling pathway

Advanced glycation end products (AGE) are those of the most powerful pathogenic factors that related to diabetic complications. In our study, we investigated the beneficial effects of thymol on AGE induced cell injury and apoptosis in human podocytes (HPCs) and attempted to clarify its mechanisms. Our results revealed that stimulation with AGE could significantly activate RhoA/NF-κB pathway. Results showed thymol could markedly suppress inflammatory responses, cell apoptosis and disordered cytoskeleton. Also thymol restored the expression of podocin, restrained migration capacity. Western blot analysis indicated that it could restore the expression of RhoA, ROCK and vimentin, nephrin, podocin and p65 and IκBα phosphorylation. Moreover, si-RhoA also suppressed the expression of pro-inflammatory cytokines, ROCK, and vimentin and the phosphorylation of p65 and IκBα. In conclusion, thymol inhibits AGE-induced cell injury in HPCs by suppressing the RhoA-NF-κB pathway and may be apromising therapeutic agent.

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.

Ameliorative role of SIRT1 in peritoneal fibrosis: an in vivo and in vitro study

Background

Peritoneal fibrosis is one of the major complications induced by peritoneal dialysis (PD). Damaged integrity and function of peritoneum caused by peritoneal fibrosis not only limits the curative efficacy of PD and but affects the prognosis of patients. However, the detailed mechanisms underlying the process remain unclear and therapeutic strategy targeting TGF‐β is deficient. Transforming growth factor‐β (TGF‐β) signaling participates in the progression of peritoneal fibrosis through enhancing mesothelial-mesenchymal transition of mesothelial cells.

Methods

The study aims to demonstrate the regulatory role of Sirtuin1 (SIRT1) to the TGF‐β signaling mediated peritoneal fibrosis. SIRT1^−/− mice were used to establish animal model. Masson’s staining and peritoneal equilibration assay were performed to evaluate the degree of peritoneal fibrosis. QRT-PCR assays were used to estimate the RNA levels of Sirt1 and matrix genes related to peritoneal fibrosis, and their protein levels were examined by Western blot assays.

Results

SIRT1 significantly decreased in vivo post PD treatment. SIRT1 knockout exacerbated peritoneal fibrosis both in vivo and vitro. Overexpression of SIRT1 efficiently inhibited peritoneal fibrosis by inhibiting the peritoneal inflammation and the activation of TGF‐β signaling.

Conclusion

SIRT1 ameliorated peritoneal fibrosis both in vivo and in vitro through inhibiting the expression of protein matrix induced by TGF‐β signaling.

Mesenchymal stem cells cultured in serum-free medium ameliorate experimental peritoneal fibrosis

BACKGROUND

Mesenchymal stem cells (MSCs) provide potential treatments for peritoneal fibrosis. However, MSCs cultured in media containing serum bring risks of infection and other problems. In this study, we compared the effect of human MSCs in serum-free medium (SF-MSCs) on peritoneal fibrosis with that of MSCs cultured in medium containing 10% fetal bovine serum (10%MSCs).

METHODS

Peritoneal fibrosis was induced by intraperitoneally injecting 0.1% chlorhexidine gluconate (CG). SF-MSCs or 10%MSCs were intraperitoneally administered 30 min after the CG injection. Ten days after the CG and MSC injections, we performed histological analyses and peritoneal equilibrium testing. In the in vitro experiments, we used transforming growth factor (TGF)-β1-stimulated human peritoneal mesothelial cells incubated in conditioned medium from MSCs to examine whether the SF-MSCs showed enhanced ability to produce antifibrotic humoral factors.

RESULTS

Histological staining showed that the SF-MSCs significantly suppressed CG-induced cell accumulation and thickening compared with that of the 10%MSCs. Additionally, the SF-MSCs significantly inhibited mesenchymal cell expression, extracellular matrix protein deposition and inflammatory cell infiltration. Peritoneal equilibration testing showed that compared with administering 10%MSCs, administering SF-MSCs significantly reduced the functional impairments of the peritoneal membrane. The in vitro experiments showed that although the conditioned medium from MSCs suppressed TGF-β1 signaling, the suppression did not significantly differ between the SF-MSCs and 10%MSCs.

CONCLUSIONS

Serum-free culture conditions can enhance the antifibrotic abilities of MSCs by suppressing inflammation. Administering ex vivo expanded SF-MSCs may be a potential therapy for preventing peritoneal fibrotic progression.

Adipose-derived mesenchymal stem cells attenuate dialysis-induced peritoneal fibrosis by modulating macrophage polarization via interleukin-6

Background

Life-long peritoneal dialysis (PD) as a renal replacement therapy is limited by peritoneal fibrosis. Previous studies showed immunomodulatory and antifibrotic effects of adipose-derived mesenchymal stem cells (ADSCs) on peritoneal fibrosis. However, the role of the peritoneal macrophage in this process remains uninvestigated.

Methods

We examined the therapeutic effects of ADSC and bone marrow-derived mesenchymal stem cells (BM-MSC) in the rat model of dialysis-induced peritoneal fibrosis using methylglyoxal. In addition, treatment of macrophages with the conditioned medium of ADSC and BM-MSC was performed individually to identify the beneficial component of the stem cell secretome.

Results

In the in vivo experiments, we found dialysis-induced rat peritoneal fibrosis was attenuated by both ADSC and BM-MSC. Interestingly, ADSC possessed a more prominent therapeutic effect than BM-MSC in ameliorating peritoneal membrane thickening while also upregulating epithelial cell markers in rat peritoneal tissues. The therapeutic effects of ADSC were positively associated with M2 macrophage polarization. In the in vitro experiments, we confirmed that interleukin-6 (IL-6) secreted by MSCs upon transforming growth factor-β1 stimulation promotes M2 macrophage polarization.

Conclusions

In dialysis-induced peritoneal fibrosis, MSCs are situated in an inflammatory environment of TGF-β1 and secrete IL-6 to polarize macrophages into the M2 phenotype. Our findings reveal a previously unidentified role of tissue macrophage in this antifibrotic process. ADSC has the advantage of abundance and accessibility, making the application values extremely promising.

Graphical abstract

In dialysis-induced peritoneal fibrosis, peritoneal mesothelial cells secrete transforming growth factor-β1 (TGF-β1) when exposed to methylglyoxal (MGO)-containing peritoneal dialysate. When situated in TGF-β1, the inflammatory environment induces mesenchymal stem cells to secrete interleukin-6 (IL-6), IL-6 polarizes macrophages into the M2 phenotype. The dominant peritoneal tissue M2 macrophages, marked by upregulated Arg-1 expression, account for the attenuation of MGO-induced dedifferentiation of peritoneal mesothelial cells to maintain epithelial integrity.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02270-4.