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

Friend or foe? The role of SIRT6 on macrophage polarized to M2 subtype in acute kidney injury to chronic kidney disease

Acute kidney injury (AKI) substantially increases the risk of developing and worsening chronic kidney disease (CKD). The shift from AKI to CKD is a complex process that involves various cell types, with macrophages playing a key role in responding to renal injury. M1 and M2 macrophages-the two main types of macrophages-have distinct functions at various stages. M1 macrophages induce kidney damage by secreting pro-inflammatory cytokines immediately after injury, whereas M2 macrophages subsequently facilitate kidney tissue repair. The conversion of macrophages from the M1 to M2 subtype is vital for effective repair after renal injury. However, when M2 macrophages infiltrate persistently, they can paradoxically cause fibrosis, thereby complicating recovery. As a key epigenetic regulatory factor, the deacetylase SIRT6 exerts various biological effects through its enzymatic reactions, including the regulation of cellular metabolism, antioxidant stress response, and inhibition of fibrosis. SIRT6 is expressed in all major types of renal resident cells and is demonstrated to protect the kidneys. SIRT6 promotes the transition from the M1 to M2 subtype; nevertheless, this process poses the risk of fibrosis if macrophages remain in the M2 subtype because of the influence of SIRT6. This review aimed (i) to delve into the intricate role of SIRT6 in macrophage polarization toward the M2 subtype in the context of the progression from AKI to CKD and (ii) to explore potential strategies that may effectively target and mitigate the progression from AKI to CKD.

Relationship between glucose to lymphocyte ratio and the first peritonitis episode in patients treated with peritoneal dialysis

This study aimed to investigate the potential relationship between baseline glucose to lymphocyte ratio (GLR) levels and the first episode of peritonitis in patients treated with peritoneal dialysis (PD). A total of 314 patients treated with PD were included and divided into three groups based on GLR tertiles: tertile 1 (GLR ≤ 4.23); tertile 2 (4.23 < GLR ≤ 5.96), and tertile 3 (GLR > 5.96). The relationships between GLR and the first peritonitis episode were analyzed using Kaplan-Meier curves and multivariable Cox regression models. Competitive risk analysis, subgroup and sensitivity analyses were performed to validate the robustness of the findings. During a median follow-up of 27 months, 123 (39.17%) patients developed the first episode of peritonitis. The incidence of the first peritonitis episode increased with the higher GLR tertiles (tertile 1: 32.08%, tertile 2: 37.50%, tertile 3: 48.08%). Kaplan-Meier curves revealed significant differences in the cumulative incidence of the first peritonitis episode among the GLR tertiles (Log-Rank test, P = 0.018). After full adjustment for confounding factors, patients in tertile 3 remained at significantly higher risk for the first episode of peritonitis compared to those in tertile 1 (HR 2.633, 95% CI 1.223-5.668, P = 0.013). Competitive risk models and sensitivity analysis further confirmed this association. Our study suggests that elevated GLR is associated with an increased risk of the first peritonitis episode in patients with PD.

Development and validation of a nomogram for predicting refractory peritoneal dialysis related peritonitis

OBJECTIVE

To identify the risk factors of refractory peritoneal dialysis related peritonitis (PDRP) and construct a nomogram to predict the occurrence of refractory PDRP.

METHODS

Refractory peritonitis was defined as the peritonitis episode with persistently cloudy bags or persistent dialysis effluent leukocyte count >100 × 109/L after 5 days of appropriate antibiotic therapy. The study dataset was randomly divided into a 70% training set and a 30% validation set. Univariate logistic analysis, LASSO regression analysis, and random forest algorithms were utilized to identify the potential risk factors for refractory peritonitis. Independent risk factors identified using multivariate logistic analysis were used to construct a nomogram. The discriminative ability, calibrating ability, and clinical practicality of the nomogram were evaluated using the receiver operating characteristic curve, Hosmer-Lemeshow test, calibration curve, and decision curve analysis.

RESULTS

A total of 294 peritonitis episodes in 178 patients treated with peritoneal dialysis (PD) were enrolled, of which 93 were refractory peritonitis. C-reactive protein, serum albumin, diabetes mellitus, PD duration, and type of causative organisms were independent risk factors for refractory peritonitis. The nomogram model exhibited excellent discrimination with an area under the curve (AUC) of 0.781 (95% CI: 0.716-0.847) in the training set and 0.741 (95% CI: 0.627-0.855) in the validation set. The Hosmer-Lemeshow test and calibration curve indicated satisfactory calibration ability of the predictive model. Decision curve analysis revealed that the nomogram model had good clinical utility in predicting refractory peritonitis.

CONCLUSION

This nomogram can accurately predict refractory peritonitis in patients treated with PD.

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.

Impact of Peritoneal Neutrophil Extracellular Traps on Peritoneal Characteristics and Technical Failure in Patients Undergoing Peritoneal Dialysis

INTRODUCTION

Peritoneal dialysis (PD) is an effective home therapy for end-stage kidney disease. However, continuous exposure to PD fluids with high glucose concentration and recurrent peritonitis may lead to the activation of cellular and molecular processes of peritoneal damage, including inflammation and fibrosis. In particular, recent studies have highlighted the role of neutrophils in chronic inflammation. This study explores how neutrophil extracellular traps (NETs) affect peritoneal membrane function and contribute to technical failures in PD patients.

METHODS

We conducted a prospective observational study involving 250 noninfectious and 30 acute peritonitis patients. NETs were measured using nucleosome and myeloperoxidase DNA levels in PD fluids. Monocyte chemoattractant protein-1 (MCP-1) and matrix metalloproteinase-8 (MMP-8) were also measured to assess peritoneal inflammation and damage.

RESULTS

A significant increase in peritoneal NETs, as determined by nucleosome and myeloperoxidase DNA levels, was observed in patients with acute peritonitis compared to patients without peritonitis. Even in noninfectious samples, NET levels were widely distributed and closely correlated with levels of MCP-1 and MMP-8. Higher levels of peritoneal NETs were closely associated with increased 4-h dialyzate/peritoneal (D/P) creatinine ratio and 1-h D/P sodium levels, indicating a higher prevalence of fast transport and limited free water transport. These factors were associated with a higher risk of technical failure. During a mean follow-up of 34 months, 39.2% (98 patients) switched from PD to hemodialysis, with higher NET levels significantly increasing the risk by 1.9 times (95% confidence interval: 1.27-2.83, p = 0.020).

CONCLUSION

This study suggests the importance of peritoneal NETs not only as markers of acute inflammation but also as significant immunological predictors of chronic peritoneal membrane inflammation and dysfunction and as potential risk factors for technical failure.

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.

The role of macrophage-derived Exosomes in reversing peritoneal fibrosis: Insights from Astragaloside IV

BACKGROUND

Peritoneal dialysis (PD) is a successful renal replacement therapy for end-stage renal disease. Long-term PD causes mesothelial-mesenchymal transition (MMT) of peritoneal mesothelial cells (PMCs), leading to peritoneal fibrosis (PF), which reduces the efficiency of PD. Macrophages are thought to play a role in the onset and perpetuation of peritoneal injury. However, the mechanisms by which macrophages-PMCs communication regulates peritoneal fibrosis are not fully understood resulting in a lack of disease-modifying drugs. Astragaloside IV (AS-IV) possessed anti-fibrotic effect towards PF in PD whereas the mechanistic effect of AS-IV in PD is unknown.

METHODS

The primary macrophages were extracted and treated with LPS or AS-IV, then co-cultured with primary PMCs in transwell plates. The macrophage-derived exosomes were extracted and purified by differential centrifugation, then co-cultured with primary PMCs. Small RNA-seq was used to detect differential miRNAs in exosomes, and then KEGG analysis and q-PCR were performed for validation. In vivo PD rat models were established by inducing with high-glucose peritoneal dialysis fluid and different concentrations of AS-IV and exosomes were intraperitoneal injection. Through qRT-PCR, western blotting, and luciferase reporting, candidate proteins and pathways were validated in vivo and in vitro. The functions of the validated pathways were further investigated using the mimic or inhibition strategy. PF and inflammatory situations were assessed.

RESULTS

We found AS-IV reversed the MMT of PMCs caused by LPS-stimulated macrophages and the improving effect was mediated by macrophage-derived exosomes in vitro. We also demonstrated that AS-IV significantly reduced the MMT of PMCs in vitro or PF in a rat PD model via regulating exosome-contained miR-204-5p which targets Foxc1/β-catenin signaling pathway.

CONCLUSION

AS-IV attenuates macrophage-derived exosomes induced fibrosis in PD through the miR-204-5p/Foxc1 pathway.

Diagnostic Accuracy of MMP-8 and IL-6-Based Point-of-Care Testing to Detect Peritoneal Dialysis-Related Peritonitis: A Single-Center Experience

BACKGROUND

Peritoneal dialysis-related peritonitis (PDRP) is the most common complication of peritoneal dialysis (PD), which can lead to poor outcomes if not diagnosed and treated early. We aimed to investigate the diagnostic accuracy of MMP-8 and IL-6-based point-of-care tests (POCTs) in diagnosing PDRP in PD patients.

METHODS

This retrospective chart review study was conducted at a comprehensive kidney center in Qatar. It involved all adult PD patients who underwent PDRP from July 2018 to October 2019 and for whom MMP-8 and IL-6-based POCTs were used to diagnose presumptive peritonitis. Measures of diagnostic accuracy were computed. Peritoneal fluid effluent analysis was the reference standard.

RESULTS

We included 120 patients (68 [56.7%] females, ages 55.6 ± 15.6 years, treatment duration 39.5 ± 30.4 months [range: 5-142 months]). In this population, MMP-8 and IL-6-based POCTs yielded 100% in all dimensions of diagnostic accuracy (sensitivity, specificity, positive and negative predictive values).

CONCLUSIONS

MMP-8 and IL-6-based POCTs might be helpful in the early detection of PDRP. This monocentric observation requires further confirmation in a prospective multicentric setting.

Postoperative Outcomes After Gastrointestinal Surgery in Patients Receiving Chronic Kidney Replacement Therapy: A Population-based Cohort Study

OBJECTIVE

This study evaluated the postoperative mortality and morbidity outcomes following the different subtypes of gastrointestinal (GI) surgery over a 15-year period.

BACKGROUND

Patients receiving chronic kidney replacement therapy (KRT) experience higher rates of general surgery compared with other surgery types. Contemporary data on the types of surgeries and their outcomes are lacking. KRT was defined as patients requiring chronic dialysis (hemodialysis or peritoneal dilaysis) or having a functioning kidney transplant long-term.

METHODS

All incident and prevalent patients aged greater than 18 years identified in the Australia and New Zealand Dialysis and Transplant (ANZDATA) Registry as receiving chronic KRT were linked with jurisdictional hospital admission datasets between January 1, 2000 until December 31, 2015. Patients were categorized by their KRT modality [hemodialysis (HD), peritoneal dialysis (PD), home hemodialysis (HHD), and kidney transplant (KT)]. GI surgeries were categorized as upper gastrointestinal (UGI), bowel (small and large bowel), anorectal, hernia surgery, cholecystectomy, and appendicectomy. The primary outcome was the rates of the different surgeries, estimated using Poisson models. Secondary outcomes were risks of 30-day/in-hospital postoperative mortality risk and nonfatal outcomes and were estimated using logistic regression. Independent predictors of 30-day mortality were examined using comorbidity-adjusted Cox models.

RESULTS

Overall, 46,779 patients on chronic KRT were linked to jurisdictional hospital datasets, and 9,116 patients were identified as having undergone 14,540 GI surgeries with a combined follow-up of 76,593 years. Patients on PD had the highest rates of GI surgery (8 per 100 patient years), with hernia surgery being the most frequent. Patients on PD also had the highest risk of 30-day postoperative mortality following the different types of GI surgery, with the risk being more than 2-fold higher after emergency surgery compared with elective procedures. Infective postoperative complications were more common than cardiac complications. This study also observed a U-shaped association between body mass index (BMI) and mortality, with a nadir in the 30 to 35 kg/m 2 group.

CONCLUSIONS

Patients on chronic KRT have high rates of GI surgery and morbidity, particularly in those who receive PD, are older, or are either underweight or moderately obese.

Mechanisms of mesothelial cell response to viral infections: HDAC1-3 inhibition blocks poly(I:C)-induced type I interferon response and modulates the mesenchymal/inflammatory phenotype

Infectious peritonitis is a leading cause of peritoneal functional impairment and a primary factor for therapy discontinuation in peritoneal dialysis (PD) patients. Although bacterial infections are a common cause of peritonitis episodes, emerging evidence suggests a role for viral pathogens. Toll-like receptors (TLRs) specifically recognize conserved pathogen-associated molecular patterns (PAMPs) from bacteria, viruses, and fungi, thereby orchestrating the ensuing inflammatory/immune responses. Among TLRs, TLR3 recognizes viral dsRNA and triggers antiviral response cascades upon activation. Epigenetic regulation, mediated by histone deacetylase (HDAC), has been demonstrated to control several cellular functions in response to various extracellular stimuli. Employing epigenetic target modulators, such as epidrugs, is a current therapeutic option in several cancers and holds promise in treating viral diseases. This study aims to elucidate the impact of TLR3 stimulation on the plasticity of human mesothelial cells (MCs) in PD patients and to investigate the effects of HDAC1-3 inhibition. Treatment of MCs from PD patients with the TLR3 agonist polyinosinic:polycytidylic acid (Poly(I:C)), led to the acquisition of a bona fide mesothelial-to-mesenchymal transition (MMT) characterized by the upregulation of mesenchymal genes and loss of epithelial-like features. Moreover, Poly(I:C) modulated the expression of several inflammatory cytokines and chemokines. A quantitative proteomic analysis of MCs treated with MS-275, an HDAC1-3 inhibitor, unveiled altered expression of several proteins, including inflammatory cytokines/chemokines and interferon-stimulated genes (ISGs). Treatment with MS-275 facilitated MMT reversal and inhibited the interferon signature, which was associated with reduced STAT1 phosphorylation. However, the modulation of inflammatory cytokine/chemokine production was not univocal, as IL-6 and CXCL8 were augmented while TNF-α and CXCL10 were decreased. Collectively, our findings underline the significance of viral infections in acquiring a mesenchymal-like phenotype by MCs and the potential consequences of virus-associated peritonitis episodes for PD patients. The observed promotion of MMT reversal and interferon response inhibition by an HDAC1-3 inhibitor, albeit without a general impact on inflammatory cytokine production, has translational implications deserving further analysis.

Intercellular communication in peritoneal dialysis

Long-term peritoneal dialysis (PD) causes structural and functional alterations of the peritoneal membrane. Peritoneal deterioration and fibrosis are multicellular and multimolecular processes. Under stimulation by deleterious factors such as non-biocompatibility of PD solution, various cells in the abdominal cavity show differing characteristics, such as the secretion of different cytokines, varying protein expression levels, and transdifferentiation into other cells. In this review, we discuss the role of various cells in the abdominal cavity and their interactions in the pathogenesis of PD. An in-depth understanding of intercellular communication and inter-organ communication in PD will lead to a better understanding of the pathogenesis of this disease, enabling the development of novel therapeutic targets.

HDAC1-3 inhibition increases SARS-CoV-2 replication and productive infection in lung mesothelial and epithelial cells

Background

Despite the significant progress achieved in understanding the pathology and clinical management of SARS-CoV-2 infection, still pathogenic and clinical issues need to be clarified. Treatment with modulators of epigenetic targets, i.e., epidrugs, is a current therapeutic option in several cancers and could represent an approach in the therapy of viral diseases.

Results

Aim of this study was the analysis of the role of histone deacetylase (HDAC) inhibition in the modulation of SARS-CoV-2 infection of mesothelial cells (MCs).MeT5A cells, a pleura MC line, were pre-treated with different specific class I and IIb HDAC inhibitors. Unexpectedly, treatment with HDAC1-3 inhibitors significantly increased ACE2/TMPRSS2 expression, suggesting a role in favoring SARS-CoV-2 infection. We focused our analysis on the most potent ACE2/TMPRSS2 inducer among the inhibitors analysed, MS-275, a HDAC1-3 inhibitor. ACE2/TMPRSS2 expression was validated by Western Blot (WB) and immunofluorescence. The involvement of HDAC inhibition in receptor induction was confirmed by HDAC1/HDAC2 silencing. In accordance to the ACE2/TMPRSS2 expression data, MS-275 increased SARS-CoV-2 replication and virus propagation in Vero E6 cells.Notably, MS-275 was able to increase ACE2/TMPRSS2 expression and SARS-CoV-2 production, although to a lesser extent, also in the lung adenocarcinoma cell line Calu-3 cells.Mechanistically, treatment with MS-275 increased H3 and H4 histone acetylation at ACE2/TMPRSS2 promoters, increasing their transcription.

Conclusion

This study highlights a previously unrecognized effect of HDAC1-3 inhibition in increasing SARS-CoV-2 cell entry, replication and productive infection correlating with increased expression of ACE2 and TMPRSS2. These data, while adding basic insight into COVID-19 pathogenesis, warn for the use of HDAC inhibitors in SARS-CoV-2 patients.

BET Protein Inhibitor JQ1 Ameliorates Experimental Peritoneal Damage by Inhibition of Inflammation and Oxidative Stress

Peritoneal dialysis (PD) is a current replacement therapy for end-stage kidney diseases (ESKDs). However, long-term exposure to PD fluids may lead to damage of the peritoneal membrane (PM) through mechanisms involving the activation of the inflammatory response and mesothelial-to-mesenchymal transition (MMT), leading to filtration failure. Peritoneal damage depends on a complex interaction among external stimuli, intrinsic properties of the PM, and subsequent activities of the local innate-adaptive immune system. Epigenetic drugs targeting bromodomain and extra-terminal domain (BET) proteins have shown beneficial effects on different experimental preclinical diseases, mainly by inhibiting proliferative and inflammatory responses. However the effect of BET inhibition on peritoneal damage has not been studied. To this aim, we have evaluated the effects of treatment with the BET inhibitor JQ1 in a mouse model of peritoneal damage induced by chlorhexidine gluconate (CHX). We found that JQ1 ameliorated the CHX-induced PM thickness and inflammatory cell infiltration. Moreover, JQ1 decreased gene overexpression of proinflammatory and profibrotic markers, together with an inhibition of the nuclear factor-κB (NF-κB) pathway. Additionally, JQ1 blocked the activation of nuclear factor erythroid 2-related factor 2 (NRF2) and restored changes in the mRNA expression levels of NADPH oxidases (NOX1 and NOX4) and NRF2/target antioxidant response genes. To corroborate the in vivo findings, we evaluated the effects of the BET inhibitor JQ1 on PD patients' effluent-derived primary mesothelial cells and on the MeT-5A cell line. JQ1 inhibited tumor necrosis factor-α (TNF-α)-induced proinflammatory gene upregulation and restored MMT phenotype changes, together with the downmodulation of oxidative stress. Taken together, these results suggest that BET inhibitors may be a potential therapeutic option to ameliorate peritoneal damage.

Tamoxifen exerts anti-peritoneal fibrosis effects by inhibiting H19-activated VEGFA transcription

BACKGROUND

Peritoneal dialysis (PD) remains limited due to dialysis failure caused by peritoneal fibrosis. Tamoxifen (TAM), an inhibitor of estrogen receptor 1 (ESR1), has been reported to treat fibrosis, but the underlying mechanism remains unknown. In this study, we sought to explore whether tamoxifen played an anti-fibrotic role by affecting transcription factor ESR1.

METHODS

ESR1 expression was detected in the human peritoneum. Mice were daily intraperitoneally injected with 4.25% glucose PD dialysate containing 40 mM methylglyoxal for 2 weeks to establish PD-induced peritoneal fibrosis. Tamoxifen was administrated by daily gavage, at the dose of 10 mg/kg. Chromatin immunoprecipitation (ChIP) and dual-luciferase reporter assay were performed to validate ESR1 bound H19 promoter. Gain-of-function and loss-of-function experiments were performed to investigate the biological roles of H19 on the mesothelial-mesenchymal transition (MMT) of human peritoneal mesothelial cells (HPMCs). Intraperitoneal injection of nanomaterial-wrapped 2'-O-Me-modified small interfering RNA was applied to suppress H19 in the mouse peritoneum. RNA immunoprecipitation and RNA pull-down assays demonstrated binding between H19 and p300. Exfoliated peritoneal cells were obtained from peritoneal dialysis effluent to analyze the correlations between ESR1 (or H19) and peritoneal solute transfer rate (PSTR).

RESULTS

ESR1 was increased significantly in the peritoneum after long-term exposure to PD dialysate. Tamoxifen treatment ameliorated high glucose-induced MMT of HPMCs, improved ultrafiltration rate, and decreased PSTR of mouse peritoneum. Tamoxifen reduced the H19 level by decreasing the ESR1 transcription of H19. Depletion of H19 reversed the pro-fibrotic effect of high glucose while ectopic expression of H19 exacerbated fibrotic pathological changes. Intraperitoneal injection of nanomaterial-wrapped 2'-O-Me-modified siRNAs targeting H19 mitigated PD-related fibrosis in mice. RNA immunoprecipitation (RIP) and RNA pull-down results delineated that H19 activated VEGFA expression by binding p300 to the VEGFA promoter and inducing histone acetylation of the VEGFA promoter. ESR1 and H19 were promising targets to predict peritoneal function.

CONCLUSIONS

High glucose-induced MMT of peritoneal mesothelial cells in peritoneal dialysis via activating ESR1. In peritoneal mesothelial cells, ESR1 transcribed the H19 and H19 binds to transcription cofactor p300 to activate the VEGFA. Targeting ESR1/H19/VEGFA pathway provided new hope for patients undergoing peritoneal dialysis.