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.

Inhibition of STAT3 by S3I-201 suppress peritoneal fibroblast phenotype conversion and alleviate peritoneal fibrosis.

Peritoneal fibrosis is a common pathological response to long-term peritoneal dialysis (PD) and a major cause for PD discontinuation. Understanding the cellular and molecular mechanisms underlying the induction and progression of peritoneal fibrosis is of great interest. In our study, in vitro study revealed that signal transducer and activator of transcription 3 (STAT3) is a key factor in fibroblast activation and extracellular matrix (ECM) synthesis. Furthermore, STAT3 induced by IL-6 trans-signalling pathway mediate the fibroblasts of the peritoneal stroma contributed to peritoneal fibrosis. Inhibition of STAT3 exerts an antifibrotic effect by attenuating fibroblast activation and ECM production with an in vitro co-culture model. Moreover, STAT3 plays an important role in the peritoneal fibrosis in an animal model of peritoneal fibrosis developed in mice. Blocking STAT3 can reduce the peritoneal morphological changes induced by chlorhexidine gluconate. In conclusion, our findings suggested STAT3 signalling played an important role in peritoneal fibrosis. Therefore, blocking STAT3 might become a potential treatment strategy in peritoneal fibrosis.

Targeting carcinoma-associated mesothelial cells with antibody-drug conjugates in ovarian carcinomatosis.

Ovarian carcinomatosis is characterized by the accumulation of carcinoma-associated mesothelial cells (CAMs) in the peritoneal stroma and mainly originates through a mesothelial-to-mesenchymal transition (MMT) process. MMT has been proposed as a therapeutic target for peritoneal metastasis. Most ovarian cancer (OC) patients present at diagnosis with peritoneal seeding, which makes tumor progression control difficult by MMT modulation. An alternative approach is to use antibody-drug conjugates (ADCs) targeted directly to attack CAMs. This strategy could represent the cornerstone of precision-based medicine for peritoneal carcinomatosis. Here, we performed complete transcriptome analyses of ascitic fluid-isolated CAMs in advanced OC patients with primary-, high-, and low-grade, serous subtypes and following neoadjuvant chemotherapy. Our findings suggest that both cancer biological aggressiveness and chemotherapy-induced tumor mass reduction reflect the MMT-associated changes that take place in the tumor surrounding microenvironment. Accordingly, MMT-related genes, including fibroblast activation protein (FAP), mannose receptor C type 2 (MRC2), interleukin-11 receptor alpha (IL11RA), myristoylated alanine-rich C-kinase substrate (MARCKS), and sulfatase-1 (SULF1), were identified as specific actionable targets in CAMs of OC patients, which is a crucial step in the de novo design of ADCs. These cell surface target receptors were also validated in peritoneal CAMs of colorectal cancer peritoneal implants, indicating that ADC-based treatment could extend to other abdominal tumors that show peritoneal colonization. As proof of concept, a FAP-targeted ADC reduced tumor growth in an OC xenograft mouse model with peritoneal metastasis-associated fibroblasts. In summary, we propose MMT as a potential source of ADC-based therapeutic targets for peritoneal carcinomatosis. © 2023 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Peritoneal Protein Loss With Time in Peritoneal Dialysis.

Longitudinal evolution of peritoneal protein loss (PPL), a reflection of hydrostatic pressure-driven leak of plasma proteins through the large-pore pathway, is not clear. Time on PD causes loss of mesothelial cells, vasculopathy, and increased thickness of the submesothelial fibrous layer. Are these structural changes associated with progressive increase of PPL, in a parallel with the rise in the D/P creatinine? The aim of the present study was to identify longitudinal changes of PPL over time. This single-center, longitudinal study included 52 peritoneal dialysis (PD) patients with a median follow-up of 26.5 months, evaluated at two different time points with a minimum interval of 6 months. Repeated measures analysis was performed using paired sample t-test or the nonparametric Wilcoxon signed-rank test, depending on the distribution. After a median interval of 15.5 months, lower levels of residual renal function and urine volume, lower Kt/V, and creatinine clearance were found. D/P creatinine and PPL were stable, but a decrease in ultrafiltration was present. Systemic inflammation, nutrition, and volume overload showed no significant change with time on PD. Analysis of a subpopulation with over 48 months between initial and subsequential assessment (n = 11) showed again no difference in inflammation, nutritional and hydration parameters from baseline, but importantly PPL decreased after more than 4 years on PD (mean difference 1.2 g/24, p = 0.033). D/P creatinine and dip of sodium remained unchanged. The absence of deleterious effects of time on PD is reassuring, pointing to the benefit of updated PD prescription, including the standard use of more biocompatible solutions towards membrane preservation and adjusted prescription avoiding overhydration and inflammation while maintaining nutritional status. After controlling for confounders, PPL may act as a biomarker of acquired venous vasculopathy, even if small pore fluid transport rates and free water transport are preserved.

Differential effects of biocompatible peritoneal dialysis fluids on human mesothelial and endothelial cells in 2D and 3D phenotypes.

INTRODUCTION: Peritoneal dialysis (PD) is a life maintaining treatment in patients with end-stage renal disease. Its chronic application leads to peritoneal mesothelial layer denudation and fibrotic transformation along with vascular activation of inflammatory pathways. The impact of different PD fluids (PDF) on mesothelial and endothelial cell function and repair mechanisms are not comprehensively described. MATERIALS AND METHODS: Mesothelial (MeT-5A) and endothelial cells (EA.hy926) were cultured in 1:1 ratio with cell medium and different PDF (icodextrin-based, amino acid-based, and glucose-based). Cell adhesion, cell migration, and cell proliferation in 2D and spheroid formation and collagen gel contraction assays in 3D cell cultures were performed. RESULTS: Cell proliferation and cell-mediated gel contraction were both significantly decreased in all conditions. 3D spheroid formation was significantly reduced with icodextrin and amino acid PDF, but unchanged with glucose PDF. Adhesion was significantly increased by amino acid PDF in mesothelial cells and decreased by icodextrin and amino acid PDF in endothelial cells. Migration capacity was significantly decreased in mesothelial cells by all three PDF, while endothelial cells remained unaffected. CONCLUSIONS: In 3D phenotypes the effects of PDF are more uniform in both mesothelial and endothelial cells, mitigating spheroid formation and gel contraction. On the contrary, effects on 2D phenotypes are more uniform in the icodextrin and amino acid PDF as opposed to glucose ones and affect mesothelial cells more variably. 2D and 3D comparative assessments of PDF effects on the main peritoneal membrane cell barriers, the mesothelial and endothelial, could provide useful translational information for PD studies.

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 TGFß1 and α-SMA. Adding CAPE to PDF significantly inhibited PD-induced submesothelial thickening, reduced TGFß1 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.

Proteomic Characterization of Peritoneal Extracellular Vesicles in a Mouse Model of Peritoneal Fibrosis.

Peritoneal fibrosis progression is regarded as a significant cause of the loss of peritoneal function, markedly limiting the application of peritoneal dialysis (PD). However, the pathogenesis of peritoneal fibrosis remains to be elucidated. Tissue-derived extracellular vesicles (EVs) change their molecular cargos to adapt the environment alteration, mediating intercellular communications and play a significant role in organ fibrosis. Hence, we performed, for the first time, four-dimensional label-free quantitative liquid chromatography-tandem mass spectrometry proteomic analyses on EVs from normal peritoneal tissues and PD-induced fibrotic peritoneum in mice. We demonstrated the alterations of EV concentration and protein composition between normal control and PD groups. A total of 2339 proteins containing 967 differentially expressed proteins were identified. Notably, upregulated proteins in PD EVs were enriched in processes including response to wounding and leukocyte migration, which participated in the development of fibrosis. In addition, EV proteins of the PD group exhibited unique metabolic signature compared with those of the control group. The glycolysis-related proteins increased in PD EVs, while oxidative phosphorylation and fatty acid metabolism-related proteins decreased. We also evaluated the effect of cell-type specificity on EV proteins, suggesting that mesothelial cells mainly cause the alterations in the molecular composition of EVs. Our study provided a useful resource for further validation of the key regulator or therapeutic target of peritoneal fibrosis.

Complement terminal pathway inhibition reduces peritoneal injuries in a rat peritonitis model.

Peritonitis and the resulting peritoneal injuries are common problems that prevent long-term peritoneal dialysis (PD) therapy in patients with end-stage kidney diseases. Previously, we have analyzed the relationship between the complement system and progression of peritoneal injuries associated with PD, particularly focusing on the early activation pathways and effects of the anaphylatoxins. We here utilized a novel mAb 2H2 that blocks assembly of the membrane attack complex (MAC) to investigate roles of the complement terminal pathway in PD-associated peritoneal injury. We intraperitoneally injected mAb 2H2 anti-C5b-7 (2.5 or 5 mg/rat) once or twice over the five-day course of the experiment to investigate the effects of inhibiting formation of MAC in a fungal rat peritonitis model caused by repeated intraperitoneal administration of zymosan after methylglyoxal pretreatment (Zy/MGO model). Rats were sacrificed on day 5 and macroscopic changes in both parietal and visceral peritoneum evaluated. Peritoneal thickness, the abundance of fibrinogen and complement C3 and MAC deposition in tissue and accumulation of inflammatory cells were pathologically assessed. The results showed that mAb 2H2, but not isotype control mAb, reduced peritoneal thickness and accumulation of inflammatory cells in a dose and frequency-dependent manner in the Zy/MGO model. These effects were accompanied by decreased C3, MAC, and fibrinogen deposition in peritoneum. In conclusion, in the rat Zy/MGO model, complement terminal pathway activation and MAC formation substantially contributed to development of peritoneal injuries, suggesting that MAC-targeted therapies might be effective in preventing development of peritoneal injuries in humans.

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.

Peritoneal transformation shortly after kidney transplantation in pediatric patients with preceding chronic peritoneal dialysis.

BACKGROUND: The unphysiological composition of peritoneal dialysis (PD) fluids induces progressive peritoneal fibrosis, hypervascularization and vasculopathy. Information on these alterations after kidney transplantation (KTx) is scant. METHODS: Parietal peritoneal tissues were obtained from 81 pediatric patients with chronic kidney disease stage 5 (CKD5), 72 children on PD with low glucose degradation product (GDP) PD fluids, and from 20 children 4-8 weeks after KTx and preceding low-GDP PD. Tissues were analyzed by digital histomorphometry and quantitative immunohistochemistry. RESULTS: While chronic PD was associated with peritoneal hypervascularization, after KTx vascularization was comparable to CKD5 level. Submesothelial CD45 counts were 40% lower compared with PD, and in multivariable analyses independently associated with microvessel density. In contrast, peritoneal mesothelial denudation, submesothelial thickness and fibrin abundance, number of activated, submesothelial fibroblasts and of mesothelial-mesenchymal transitioned cells were similar after KTx. Diffuse peritoneal podoplanin positivity was present in 40% of the transplanted patients. In subgroups matched for age, PD vintage, dialytic glucose exposure and peritonitis incidence, submesothelial hypoxia-inducible factor 1-alpha abundance and angiopoietin 1/2 ratio were lower after KTx, reflecting vessel maturation, while arteriolar and microvessel p16 and cleaved Casp3 were higher. Submesothelial mast cell count and interleukin-6 were lower, whereas transforming growth factor-beta induced pSMAD2/3 was similar as compared with children on PD. CONCLUSIONS: Peritoneal membrane damage induced with chronic administration of low-GDP PD fluids was less severe after KTx. While peritoneal microvessel density, primarily defining PD transport and ultrafiltration capacity, was normal after KTx and peritoneal inflammation less pronounced, diffuse podoplanin positivity and profibrotic activity were prevalent.

Fasting influences aquaporin expression, water transport and adipocyte metabolism in the peritoneal membrane.

BACKGROUND: The water channels aquaporin-1 (AQP1) and AQP7 are abundantly expressed in the peritoneal membrane. While AQP1 facilitates water transport during peritoneal dialysis (PD), the role of AQP7, which mediates glycerol transport during fasting, remains unknown. METHODS: We investigated the distribution of AQP7 and AQP1 and used a mouse model of PD to investigate the role of AQP7 in the peritoneal membrane at baseline and after fasting. RESULTS: Single nucleus RNA-sequencing revealed that AQP7 was mostly detected in mature adipocytes, whereas AQP1 was essentially expressed in endothelial cells. Fasting induced significant decreases in whole body fat, plasma glucose, insulin and triglycerides, as well as higher plasma glycerol and corticosterone levels in mice, paralleled by major decreases in adipocyte size and levels of fatty acid synthase and leptin, and increased levels of hormone-sensitive lipase mRNAs in the peritoneum. Mechanistically, fasting upregulated the expression of AQP1 and AQP7 in the peritoneum, with increased ultrafiltration but no change in small solute transport. Studies based on Aqp1 and Aqp7 knockout mice and RU-486 inhibition demonstrated that the glucocorticoid induction of AQP1 mediates the increase in ultrafiltration whereas AQP7 regulates the size of adipocytes in the peritoneum. CONCLUSIONS: Fasting induces a coordinated regulation of lipolytic and lipogenic factors and aqua(glycero)porins in the peritoneum, driving structural and functional changes. These data yield novel information on the specific roles of aquaporins in the peritoneal membrane and indicate that fasting improves fluid removal in a mouse model of PD.

Inhibition of EZH2 suppresses peritoneal angiogenesis by targeting a VEGFR2/ERK1/2/HIF-1α-dependent signaling pathway.

The catalytic subunit of polycomb repressive complex 2 (PRC2), enhancer of zeste homolog 2 (EZH2), has been reported to be involved in angiogenesis in some tumors and autoimmune diseases. However, the mechanisms by which EZH2 regulates peritoneal angiogenesis remain unclear. We detected the expression of EZH2 in clinical samples and the peritoneal tissue of a mouse peritoneal fibrosis model induced by chlorhexidine gluconate (CG). In addition, we further investigated the mechanisms by which inhibition of EZH2 by 3-deazaneplanocin A (3-DZNeP) alleviated the CG-induced peritoneal fibrosis mouse model in vivo and 3-DZNeP or EZH2 siRNA treatment in cultured human peritoneal mesothelial cells (HPMCs) and human umbilical vein endothelial cells (HUVECs). The expression of EZH2 in the peritoneum of long-term peritoneal dialysis (PD) patients and the CG-induced peritoneal fibrosis mouse model was remarkably increased and this was positively associated with higher expression of vascular markers (CD31, CD34, VEGF, p-VEGFR2). Peritoneal injection of 3-DZNeP attenuated angiogenesis in the peritoneum of CG-injured mice; improved peritoneal membrane function; and decreased phosphorylation of STAT3, ERK1/2, and activation of Wnt1/ß-catenin. In in vitro experiments, we demonstrated that inhibition of EZH2 by 3-DZNeP or EZH2 siRNA decreased tube formation and the migratory ability of HUVECs via two pathways: the Wnt1/ß-catenin pathway and the IL-6/STAT3 pathway. Suppression of the Wnt1/ß-catenin pathway and the IL-6/STAT3 pathway subsequently reduced VEGF production in HPMCs. Using specific inhibitors of VEGFR2, ERK1/2, and HIF-1α, we found that a VEGFR2/ERK1/2/HIF-1α axis existed and contributed to angiogenesis in vitro. Moreover, phosphorylation of VEGFR2 and activation of the ERK1/2 pathway and HIF-1α in HUVECs could be suppressed by inhibition of EZH2. Taken together, the results of this study suggest that EZH2 may be a novel target for preventing peritoneal angiogenesis in PD patients. © 2022 The Pathological Society of Great Britain and Ireland.

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.

Association of longitudinal high-sensitive C-reactive protein levels with changing membrane characteristics in peritoneal dialysis.

BACKGROUND: Increasing peritoneal permeability with ultrafiltration and solute removal inadequacy is a challenging issue in peritoneal dialysis (PD). Decreasing permeability is less frequent but also results in diminished solute clearance. We evaluated the association between longitudinal high-sensitive C-reactive protein (hs-CRP) values and the change in transport characteristics of the peritoneal membrane in PD patients. METHODS: This is a retrospective, single-center study of incident PD patients. An increase or decrease in peritoneal transport status is defined as two or more categories of a rise or decline in the peritoneal equilibration test (PET) from their baseline during follow-up. The 4-h dialysate/plasma creatinine ratio was used to classify transport characteristics. Hs-CRP values were obtained from the routine annual examinations of the patients. RESULTS: Baseline demographics, residual kidney function, frequency of high glucose-containing dialysate, and icodextrin use were similar between the groups. Total episodes of peritonitis within the first 5 years of follow-up were higher in stable transporters than in increased and decreased transporters (p = 0.009). Stable transporters' mean hs-CRP values did not change within 5 years (Wilks' λ = 0.873, F (2.317, 180.740) = 2.210, p = 0.10). Increased and decreased transporters' hs-CRP values significantly raised over the years (Wilks' λ = 0.422, F (1.979, 77.163) = 3.405, p = 0.04 and Wilks' λ = 0.558, F (3.673, 66.107) = 4.396, p = 0.001, respectively). CONCLUSIONS: Our study shows that the peritoneal membrane may change into different characteristics in many patients over time, despite very low peritonitis frequencies and similar baseline characteristics that may be significantly affected by systemic inflammation.

Protein Loss in Peritoneal Effluent: Different Meaning for 24-h versus PET Samples.

INTRODUCTION: Quantification of peritoneal protein loss (PPL) may be expressed according to a timely collection (24-h measurement or 4-h PET assessment) and as a concentration. The aim of this study was to compare the quantification methods of 24-h and 4-h collections. METHODS: This study included 81 prevalent peritoneal dialysis patients. Demographics and clinical and bioelectrical impedance features were registered. PPL was measured (4-h PET and 24-h results) and peritoneal protein clearance was calculated. A linear regression model was performed. RESULTS: Age and continuous ambulatory peritoneal dialysis (compared to cycler) were positively associated with greater PPL on 24-h collections. Neither cardiovascular disease, hypertension, diabetes nor the comorbidity Charlson Index was significantly associated with PPL. There was a consistent univariable relationship with D/P creatinine, whichever sampling method was used. Only 24-h measurements of PPL correlated with body composition variables. In multiple linear regression analysis, D/P creatinine association with PPL stands out. On the other hand, 24-h determinations (in grams or clearance) were associated with overhydration. PET protein quantification was associated with peritoneal creatinine clearance. DISCUSSION/CONCLUSION: Different methods sign different pathophysiological pathways. PET protein loss quantification should be regarded as a marker of peritoneal membrane intrinsic permeability. Measurements of a 24-h sample might be closer to patients' clinical status and prognosis, signalizing opportunities for therapy intervention.

The Association between Serum Chemerin and Peritoneal Membrane Transport Function in Patients Undergoing Incident Peritoneal Dialysis: A Prospective Cohort Study.

INTRODUCTION: Some biomarkers in drained dialyzate or peritoneal membrane have been found related to the dialyzate/plasma ratio of creatinine at 4 h (D/P Cr) in patients undergoing peritoneal dialysis (PD). But so far, there is no report on serum markers. Some biomarkers are associated with cardiovascular diseases (CVDs). Chemerin is a multifunctional chemoattractant adipokine which plays important roles in inflammation, adipogenesis, and metabolism. We intended to investigate the role of chemerin in the peritoneal membrane transport function and CVDs in incident PD patients. METHODS: This prospective cohort study was conducted in our PD center. The patients underwent initial standardized peritoneal equilibration test after PD for 4-6 weeks. Level of serum chemerin was determined via enzyme-linked immunosorbent assay. The patients' CVDs were recorded during the follow-up period. RESULTS: 151 eligible patients with a mean age of 46.59 ± 13.52 years were enrolled, and the median duration of PD was 25.0 months. The median concentration of serum chemerin was 29.09 ng/mL. Baseline D/P Cr was positively correlated with serum chemerin (r = 0.244, p = 0.003). The multivariate analyses revealed that serum chemerin (p = 0.002), age (p = 0.041), albumin (p = 0.000), and high-density lipoprotein (p = 0.022) were independent factors of D/P Cr. The serum chemerin level was significantly higher in diabetes mellitus (DM) patients than that of patients without DM (36.45 ng/mL vs. 27.37 ng/mL, p = 0.000), and there was a significant statistical difference in CVDs between the high chemerin group (≥29.09 ng/mL) and low chemerin group (<29.09 ng/mL) (42 vs. 21%, p = 0.009). CONCLUSIONS: Serum chemerin has a positive correlation with baseline D/P Cr in incident PD patients. It may be a biomarker that can predict the baseline transport function of the peritoneal membrane, and serum chemerin may be a risk factor of CVDs for incident PD patients. Multicenter studies with a larger sample size are warranted in the future.

Phloretin Improves Ultrafiltration and Reduces Glucose Absorption during Peritoneal Dialysis in Rats.

BACKGROUND: Harmful glucose exposure and absorption remain major limitations of peritoneal dialysis (PD). We previously showed that inhibition of sodium glucose cotransporter 2 did not affect glucose transport during PD in rats. However, more recently, we found that phlorizin, a dual blocker of sodium glucose cotransporters 1 and 2, reduces glucose diffusion in PD. Therefore, either inhibiting sodium glucose cotransporter 1 or blocking facilitative glucose channels by phlorizin metabolite phloretin would reduce glucose transport in PD. METHODS: We tested a selective blocker of sodium glucose cotransporter 1, mizagliflozin, as well as phloretin, a nonselective blocker of facilitative glucose channels, in an anesthetized Sprague-Dawley rat model of PD. RESULTS: Intraperitoneal phloretin treatment reduced glucose absorption by >30% and resulted in a >50% higher ultrafiltration rate compared with control animals. Sodium removal and sodium clearances were similarly improved, whereas the amount of ultrafiltration per millimole of sodium removed did not differ. Mizagliflozin did not influence glucose transport or osmotic water transport. CONCLUSIONS: Taken together, our results and previous results indicate that blockers of facilitative glucose channels may be a promising target for reducing glucose absorption and improving ultrafiltration efficiency in PD.

Inhibition of EZH2 mitigates peritoneal fibrosis and lipid precipitation in peritoneal mesothelial cells mediated by klotho.

BACKGROUND: Peritoneal fibrosis caused by long-term peritoneal dialysis (PD) is the main reason why patients withdraw from PD treatment. Lipid accumulation in the peritoneum was shown to participate in fibrosis, and klotho is a molecule involved in lipid metabolism. GSK343 (enhancer of zeste 2 polycomb repressive complex 2 subunit (EZH2) inhibitor) has been verified to inhibit epithelial mesenchymal transdifferentiation (EMT) and peritoneal fibrosis, but its related mechanism remains unclear. This study aimed to investigate whether lipid accumulation was involved in the effect of GSK343 and its related mechanism. MATERIALS AND METHODS: First, the expression of EZH2, klotho and EMT indices in human peritoneal mesothelial cells (HMrSV5) incubated with high glucose (HG) levels was detected. After EZH2 was inhibited by GSK343, Western blot (WB), wound healing and Transwell assays were used to explore the effect of GSK343. EZH2 and klotho expression was also detected. Oil red O and Nile red staining and triglyceride (TG) detection kits were used to detect lipid accumulation. A rescue experiment with small interfering RNA specific for klotho (si-klotho) on the basis of GSK343 was also conducted to verify that GSK343 exerted its effect via klotho. In in vivo experiments, rats were administered GSK343, and the related index was assessed. RESULTS: In our study, we revealed that the expression of EZH2 was significantly upregulated and klotho was significantly downregulated in HMrSV5 cells induced by high glucose. With the aid of GSK343, we found that lipid deposition caused by HG was significantly decreased. In addition, EMT and fibrosis were also significantly alleviated. Moreover, GSK343 could also restore the downregulation of klotho. To further verify whether klotho mediated the effect of EZH2, a rescue experiment with si-klotho was also conducted. The results showed that si-klotho could counteract the protective effect of GSK343 on high glucose-induced lipid accumulation and fibrosis. In vivo experiments also revealed that GSK343 could relieve peritoneal fibrosis, lipid deposition and EMT by mitigating EZH2 and restoring klotho expression. CONCLUSIONS: Combining these findings, we found that EZH2 regulated lipid deposition, peritoneal fibrosis, and EMT mediated by klotho. To our knowledge, this is the first study to demonstrate the effect of the EZH2-klotho interaction on peritoneal fibrosis. Hence, EZH2 and klotho could act as potential targets for the treatment of peritoneal fibrosis.

Parthenolide alleviates peritoneal fibrosis by inhibiting inflammation via the NF-κB/ TGF-ß/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-ß1 (TGF-ß1), 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-ß/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-ß1 expression and the phosphorylation of IκBα and NF-κBp65. The changes in the levels of TGF-ß1 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-ß1 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-ß/Smad signaling axis.

Development of a refined ex vivo model of peritoneal adhesion formation, and a role for connexin 43 in their development.

Despite many advances across the surgical sciences, post-surgical peritoneal adhesions still pose a considerable risk in modern-day procedures and are highly undesirable. We have developed a novel mouse peritoneal strip ex vivo adhesion model which may serve to bridge the gap between single cell culture systems and in vivo animal drug testing for the assessment of potential anti-adhesion agents, and study of causality of the process. We investigated the optimal conditions for adhesion formation with mouse peritoneal tissue strips by modifying an existing ex vivo rat model of peritoneal adhesions. We assessed the impact of the following conditions on the formation of adhesions: contact pressure, abrasions, and the presence of clotted blood. Macroscopic adhesions were detected in all mouse peritoneal strips exposed to specific conditions, namely abrasions and clotted blood, where peritoneal surfaces were kept in contact with pressure using cotton gauze in a tissue cassette. Adhesions were confirmed microscopically. Interestingly, connexin 43, a gap junction protein, was found to be upregulated at sites of adhesions. Key features of this model were the use of padding the abraded tissue with gauze and the use of a standardised volume of clotted blood. Using this model, peritoneal strips cultured with clotted blood between abraded surfaces were found to reproducibly develop adhesion bands at 72 h. Our goal is to develop a model that can be used in genetically modified mice in order to dissect out the role of particular genes in adhesion formation and to test drugs to prevent adhesion formation.