Dialysate cyclophilin A as a predictive marker for historical peritonitis in patients undergoing peritoneal dialysis

Introduction

No markers have been used to diagnose historical peritoneal dialysis (PD)-related peritonitis. Cyclophilin A (CypA) is associated with glucose toxicity and inflammation. We hypothesize that dialysate CypA can be a marker for historical peritonitis (at least 3 months free from peritonitis).

Method

An enzyme-linked immunosorbent assay kit was used to measure the concentration of dialysate CypA. Clinical and laboratory data were collected to correlate with historical peritonitis. Mann-Whitney U test and Chi-square test were used for analysis. Receiver operating characteristic (ROC) analysis was used to evaluate predictive power.

Results

Out of a total of 31 patients who had undergone PD for at least 2 years, 18 had no history of PD-related peritonitis, while 13 had experienced PD-related peritonitis at least once. Overall, the patients in this population were in good health (normal white blood cell count, no anemia, normal electrolyte and serum albumin levels). There were no significant differences between patients with and without a history of peritonitis, except for blood white blood cell count (5650.6 ± 1848.4 vs. 7154.6 ± 2056.8, p = 0.032) and dialysate CypA value (24.27 ± 22.715 vs. 54.41 ± 45.63, p = 0.020). In the univariate analysis, only the dialysate CypA level showed a statistically significant association with historical peritonitis (HR = 1.030, 95 % CI = 1.010-1.062, p = 0.046). The AUC for dialysate CypA (>34.83 ng/mL) was 0.748, with a sensitivity of 0.615 and specificity of 0.833.

Conclusion

PD peritonitis poses a significant threat to the long-term use of peritoneal dialysis. Based on our study, even in the absence of concurrent infection, dialysate CypA can serve as a predictive marker for historical peritonitis, demonstrating high predictive power along with fair sensitivity and good specificity.

SARS-CoV-2 impact on ACE2 expression in NSCLC: mRNA and protein insights COVID-19 associated (ACE2) expression in non-small cell lung cancer (NSCLC)

Non-small cell lung cancer (NSCLC) is a pervasive and challenging global health concern. This research delves into the intricate relationship between NSCLC and ACE2 expression, exploring the potential impact of COVID-19 history on this interaction. Tissue samples were meticulously gathered from a cohort of 32 NSCLC patients, 18 of whom had a documented history of COVID-19 infection. The methodology included extensive investigations, such as cell dissociation, histopathological analysis, immunohistochemistry, cell culture, adhesion assays, immunocytochemistry, RNA isolation, and RT-PCR analysis. The results of this comprehensive study unearthed intriguing findings regarding ACE2 expression patterns within NSCLC tissues. Notably, variations were observed in ACE2 profiles between individuals with and without a prior record of COVID-19 infection, hinting at a dynamic interplay. These discoveries carry profound implications for both the understanding of NSCLC progression and the response to COVID-19 in patients with pre-existing NSCLC. The interrelationship between ACE2 expression, NSCLC, and COVID-19, as revealed in this study, may significantly influence patient outcomes and, potentially, therapeutic strategies. In summary, this research serves as an essential contribution to the growing body of knowledge on NSCLC, offering unique insights into the intricate connections between ACE2, COVID-19, and NSCLC. This information may open new avenues for tailored treatment approaches and clinical management strategies, ultimately benefiting patients grappling with NSCLC in the background of the current COVID-19 pandemic.

SARS-CoV-2 virus associated angiotensin converting enzyme 2 expression modulation in colorectal cancer: Insights from mRNA and protein analysis COVID-19 associated (ACE2) expression in colorectal cancer

The SARS-CoV-2 virus gains entry into human cells by exploiting the angiotensin-converting enzyme 2 (ACE2), a key component known as the spike protein (S), as a point of entry. Initially, SARS-CoV-2 suppresses the natural function of ACE2, leading to a gradual decline in cell health. Additionally, individuals with cancer are considered more susceptible to COVID-19. This study investigates the expression patterns of ACE2 in colorectal cancer (CRC) patients with and without a history of COVID-19 infection. RT-PCR was used to analyze samples from both cancerous and adjacent non-affected colorectal tissues of 47 CRC patients, comprising two groups: 24 CRC patients with no history of COVID-19 and 23 CRC patients with a recent history of COVID-19 infection. Epithelial CR cells were isolated from both types of tissues and cultured to evaluate cell adhesion. Immunohistochemistry analyses were conducted to examine ACE2 protein expression using various ACE2 antibodies for both cell types. The study revealed ACE2 mRNA expression in all CRC tissues of patients with and without a history of COVID-19. ACE2 expression was significantly higher in CRC patients without a history of COVID-19. Notably, the non-affected colorectal cancer (NACRC) tissues of patients without a history of COVID-19 also showed ACE2 expression, whereas no ACE2 expression was detected in the biopsies of CRC patients with a positive COVID-19 history. ACE2 antibodies were employed to validate ACE2 protein expression at the mRNA level. COVID-19 appears to downregulate ACE2 expression in both CRC and NACRC tissues of CRC patients with a positive history of COVID-19 infection.

Polycaprolactone/Chitosan Composite Nanofiber Membrane as a Preferred Scaffold for the Culture of Mesothelial Cells and the Repair of Damaged Mesothelium

Mesothelial cells are specific epithelial cells lining the serosal cavity and internal organs. Nonetheless, few studies have explored the possibility to culture mesothelial cells in a nanostructure scaffold for tissue engineering applications. Therefore, this study aims to fabricate nanofibers from a polycaprolactone (PCL) and PCL/chitosan (CS) blend by electrospinning, and to elucidate the effect of CS on the cellular response of mesothelial cells. The results demonstrate that a PCL and PCL/CS nanofiber membrane scaffold could be prepared with a comparable fiber diameter (~300 nm) and porosity for cell culture. Blending CS with PCL influenced the mechanical properties of the scaffold due to interference of PCL crystallinity in the nanofibers. However, CS substantially improves scaffold hydrophilicity and results in a ~6-times-higher cell attachment rate in PCL/CS. The mesothelial cells maintain high viability in both nanofiber membranes, but PCL/CS provides better maintenance of cobblestone-like mesothelial morphology. From gene expression analysis and immunofluorescence staining, the incorporation of CS also results in the upregulated expression of mesothelial marker genes and the enhanced production of key mesothelial maker proteins, endorsing PCL/CS to better maintain the mesothelial phenotype. The PCL/CS scaffold was therefore chosen for the in vivo studies, which involved transplanting a cell/scaffold construct containing allograft mesothelial cells for mesothelium reconstruction in rats. In the absence of mesothelial cells, the mesothelium wound covered with PCL/CS showed an inflammatory response. In contrast, a mesothelium layer similar to native mesothelium tissue could be obtained by implanting the cell/scaffold construct, based on hematoxylin and eosin (H&E) and immunohistochemical staining.

Vascular endothelial growth factor-mediated peritoneal neoangiogenesis in peritoneal dialysis

Peritoneal dialysis (PD) is an important renal replacement therapy for patients with end-stage renal diseases, which is limited by peritoneal neoangiogenesis leading to ultrafiltration failure (UFF). Vascular endothelial growth factor (VEGF) and its receptors are key angiogenic factors involved in almost every step of peritoneal neoangiogenesis. Impaired mesothelial cells are the major sources of VEGF in the peritoneum. The expression of VEGF will be up-regulated in specific pathological conditions in PD patients, such as with non-biocompatible peritoneal dialysate, uremia and inflammation, and so on. Other working cells (i.e. vascular endothelial cells, macrophages and adipocytes) can also stimulate the secretion of VEGF. Meanwhile, hypoxia and activation of complement system further aggravate peritoneal injury and contribute to neoangiogenesis. There are several signalling pathways participating in VEGF-mediated peritoneal neoangiogenesis including tumour growth factor-β, Wnt/β-catenin, Notch and interleukin-6/signal transducer and activator of transcription 3. Moreover, VEGF is highly expressed in dialysate effluent of long-term PD patients and is associated with peritoneal transport function, which supports its role in the alteration of peritoneal structure and function. In this review, we systematically summarize the angiogenic effect of VEGF and evaluate it as a potential target for the prevention of peritoneal neoangiogenesis and UFF. Preservation of the peritoneal membrane using targeted therapy of VEGF-mediated peritoneal neoangiogenesis may increase the longevity of the PD modality for those who require life-long dialysis.

The Effect of Advanced Glycation End-Products and Aminoguanidine on Tnfα Production by Rat Peritoneal Macrophages

Objective

To evaluate the effect of advanced glycation end-products (AGEs) and the inhibitor of their formation, aminoguanidine, on tumor necrosis factor-α (TNFα) production (as a functional marker) by rat peritoneal macrophages (PMΦ).

Design

Charles River rats underwent a daily intraperitoneal injection of peritoneal dialysis solution [(PDS), 4.25 g/dL dextrose; Dialine, Travenol, Ashdod, Israel] for a 2-month period (group E). Another group of rats was subjected to the same protocol with the addition of 25 mg/kg aminoguanidine (group A). Three control groups were utilized: ( 1 ) rats that were injected daily with aminoguanidine only (group AO), ( 2 ) rats that were injected with Dulbecco's phosphate-buffered saline (group D), and ( 3 ) rats in which no intervention was carried out (group C). After 2 months, PMΦ were isolated from rat peritoneal effluent and their TNFα production measured by ELISA in cell-free culture supernatants, in both the basal state and after 24-hour stimulation with lipopolysaccharide (LPS). The concentrations of AGEs in peritoneal effluent were assayed and correlated to TNFα levels. PMΦ obtained from normal rats were then incubated for 24 hours with ( 1 ) the peritoneal effluent of each of the above respective groups, with or without LPS; ( 2 ) increasing concentrations of AGEs (0 - 250 μg/mL); and ( 3 ) increasing concentrations of aminoguanidine (0 - 7.5 mg/mL), and TNFα secretion again determined.

Results

After 2 months of daily intraperitoneal injection of PDS, in the basal state, TNFα production was significantly higher in PMΦ isolated from the peritoneal effluent groups (groups E, A, and AO) compared to controls (group C). Following LPS stimulation, a further increase in TNFα secretion was seen, with a significantly greater response in group AO versus groups E, A, and D. Effluent AGEs were markedly elevated only in group E. No correlation was found between TNFα secretion by these PMΦ and the concentration of AGEs. On incubation with the respective peritoneal effluents (groups E, A, and AO), in both the basal and stimulated state, TNFα production by PMΦ from normal rats was significantly enhanced compared to group C. Incubation with increasing concentrations of AGEs or aminoguanidine resulted in an increase of TNFα secretion by these PMΦ.

Conclusions

Following intermittent intraperitoneal administration of glucose-based PDS, rat PMΦ are chronically activated, as evidenced by increased basal TNFα secretion. The peritoneal effluent of such treated animals is capable of stimulating TNFα production by normal rat PMΦ. These data suggest that glucose-based PDS acts as a primer of PMΦ, which retain their ability to further stimulation by LPS. Although, in vitro, AGEs promote TNFα secretion by normal rat PMΦ, in vivo, their influence is probably modulated by other factors. Aminoguanidine has a specific inducing effect on rat PMΦ, independent of glucose-based PDS.

Bicarbonate/Lactate Dialysis Solution ImprovesIn VivoFunction of Peritoneal Host Defense in Rats

Objective

To assess the in vivo peritoneal inflammatory reaction in rats dialyzed with neutral, bicarbonatelactate-buffered dialysis fluid.

Methods

Chronic peritoneal dialysis was performed for 4 weeks in Wistar rats with two solutions: (1) 40 mmol/l lactate-buffered fluid, pH 5.2, with a glucose concentration of 2.27 gldl (lac); and, (2) 15 mmolll lactate and 25 mmolll bicarbonate-buffered fluid, pH 7.0 -7.5, with a glucose concentration of 2.27gldl (Bic-lac). After 4 weeks, two peritoneal equilibration tests (PET 1 and PET 2) were performed in all animals with each respective solution. PET 1 was done with test solutions alone, whereas, on a subsequent day, PET 2 was performed with test solutions supplemented with endotoxin [lipopolysaccharide (IPS)] to induce peritonitis.

Results

During PET 1 no consistent differences were detected in peritoneal permeability between the lac and Bic-lac groups. Total dialysate cell count in the Bic-lac animals was lower than in rats treated with lac fluid: that is, at 8 hours, the respective counts were 1858 ± 524 cellslμl versus 2785 ± 1162 cellslμl (p < 0.01). Dialysate from animals dialyzed with Bic-lac contained more macrophages (at 4 hours: 53.6% ± 35.8% versus 35.8% ± 8.8%, p < 0.001) and fewer neutrophils (at 4 hours: 3.6% ± 1.8% versus 15.4%± 6.1%, p < 0.001) as compared to those dialyzed with the lac solution. Concentration of nitrites in 8-hour dwell dialysate samples from Bic-lac rats was lower than that in the lac group (0.98 ± 0.28 μmollml versus 2.32 ± 0.87 μmollml, p < 0.002), but cytokine levels in the dialysates were comparable. During PET 2, the in -crease in peritoneal permeability resulting from the lPS induced inflammatory response was similar for both test solutions. Dialysate cell count was higher in the lac group versus the Bic-lac group (at 8 hours: 8789 ± 4862 cellslμl versus 3961 ± 581 cellslμl, p < 0.001), contained more neutrophils (at 8 hours: 80.0% ± 11.3% versus 54.8% ± 4.4%, p < 0.001) and fewer macrophages (at 8 hours: 6.8% ± 5.6% versus 21.2% ± 3.3%, p < 0.05). During peritonitis, we found a higher overall dialysate concentration of both tumor necrosis factor (TNFα: +53%, p < 0.05) and of interferon gamma (lFN-y: +303%, p < 0.02), in the Bic-lac group than in the lac group.

Conclusions

A lower dialysate cell count, higher percentage of macrophages, and lower percentage of neutrophils in dialysate suggest that Bic-lac fluid induces a diminished nonspecific inflammatory response of the peritoneal cavity during dialysis. However, after in vivo stimulation, peritoneal cells from animals dialyzed with Bic-lac solution possess an augmented ability to produce inflammatory cytokines.

Peritoneal Defense Using Icodextrin Or Glucose for Daytime Dwell in Ccpd Patients

Objective

To investigate peritoneal defense during icodextrin use in continuous cyclic peritoneal dialysis (CCPD).

Design

In an open, prospective, 2-year follow-up study, CCPD patients were randomized to either glucose (Glu) or icodextrin (Ico) for their long daytime dwell.

Setting

University hospital and teaching hospital.

Patients

Both established and patients new to CCPD were included. A life expectancy of more than 2 years, a stable clinical condition, and written informed consent were necessary before entry. Patients aged under 18 years, those who had peritonitis in the previous month, and women of childbearing potential, unless taking adequate contraceptive precautions, were excluded. Thirty-eight patients (19 Glu, 19 Ico) started the study. The median follow-up was 16 and 17 months for Glu and Ico respectively (range 0.5 – 25 months and 5 – 25 months, respectively).

Outcome Measures

Peritoneal defense characteristics and peritoneal dialysis-related infections were recorded every 3 months.

Results

Total peritoneal white cell count tended to decrease over time in both groups. After 1 year, absolute numbers and percentages of effluent peritoneal macrophages (PMΦs) were significantly higher in Ico than in Glu patients; this difference in the percentage persisted after 2 years. Percentage of mesothelial cells increased over time in Ico patients. The phagocytic capacity of PMΦs decreased over time, resulting in a borderline significant difference for coagulase-negative staphylococci ( p = 0.05) and a significant difference for Escherichia coli ( p < 0.05) phagocytosis in favor of Ico patients. PMΦ oxidative metabolism remained stable over time without a difference between the groups. PMΦ cytokine production and effluent opsonic capacity also remained stable over time. Finally, 16 peritonitis episodes in Glu and 14 in Ico patients occurred. Glucose patients had 37 and Ico patients 32 exit-site infections during the study.

Conclusion

CCPD patients using Ico did equally as well as Glu-treated patients with respect to clinical infections and most peritoneal defense characteristics. However, in a few peritoneal defense tests, Ico-treated patients did better.

The Effects of Peritoneal Dialysis Solutions on Peritoneal Host Defense

Conventional peritoneal dialysis fluid (PDF) is a bioincompatible solution owing to the acidic pH, the high glucose concentrations and the associated hyperosmolarity, the high lactate concentrations, and the presence of glucose degradation products (GDPs). This unphysiologic composition adversely affects peritoneal host defense and may thus contribute to the development of PD-related peritonitis. The viability of polymorphonuclear leukocytes, monocytes, peritoneal macrophages, and mesothelial cells is severely depressed in the presence of conventional PDF. In addition, the production of inflammatory cytokines and chemoattractants by these cells is markedly affected by conventional PDF. Further, conventional PDF hampers the recruitment of circulating leukocytes in response to an infectious stimulus. Finally, phagocytosis, respiratory burst, and bacterial killing are markedly lower when polymorphonuclear leukocytes, monocytes, and peritoneal macrophages are exposed to conventional PDF. Although there are a few discrepant results, all major PDF components have been implicated as causative factors. Generally, novel PDF with alternative osmotic agents or with alternative buffers, neutral pH, and low GDP content have much milder inhibitory effects on peritoneal host defense. Clinical studies, however, still need to demonstrate their superiority with respect to the incidence of PD-related peritonitis.

Changes in the Peritoneal Interstitium and Their Effect on Peritoneal Transport

Transperitoneal transport is a complicated process that includes diffusion and convection across the walls of blood microvessels into tissue interstitium, transport through the interstitium, and final passage across the peritoneum to the dialysis solution in the cavity. The purpose of this paper is to briefly review the normal physiology of this process and then to summarize the events that occur in response to inflammation within the cavity. These events begin with stimulation of macrophages, which in turn secrete cytokines. The cytokines stimulate mesothelial cells and fibroblasts in the tissue to synthesize and secrete other mediators. Those mediators initiate the complex events through which leukocytes migrate from blood vessel lumens through the interstitium and into the cavity. Much of the available data is from model in vitro systems, and therefore in vivo events must be deduced or hypothesized.

High Glucose Solution and Spent Dialysate Stimulate the Synthesis of Transforming Growth Factor-β1of Human Peritoneal Mesothelial Cells: Effect of Cytokine Costimulation

Objective

To investigate the effect of high glucose and spent peritoneal dialysate on the transforming growth factor-β1(TGFβ1) synthesis of cultured human peritoneal mesothelial cells (HPMCs) and to examine the effect of costimulation with high glucose or spent dialysate, and cytokines, interleukin-1β (IL-1β), and tumor necrosis factor-α (TNFα) on TGFβ1synthesis of HPMCs.

Design

HPMCs were exposed to different concentrations of glucose (30, 60, and 90 mmol/L) or spent peritoneal dialysate for 48 hours in the absence or presence of IL-1β (1 ng/mL) and TNFα (1 ng/mL). TGFβ1mRNA expression was assessed by Northern blot analysis and TGFβ1protein release by Western blot analysis and enzymelinked immunosorbent assay (ELISA).

Results

Exposure of HPMCs to high glucose conditions (30, 60, and 90 mmol/L of D-glucose) induced 2.3-, 3.6-, and 4.0-fold increases in TGFβ1mRNA expression of HPMC with enhanced TGFβ1protein synthesis and secretion into the media, whereas there were no significant changes in TGFβ1synthesis with equimolar concentrations of D-mannitol. Incubation with spent dialysate also significantly increased TGFβ1mRNA expression and protein secretion compared to control media ( p < 0.05). Stimulation with IL-1β (1 ng/mL) or TNFα (1 ng/mL) resulted in a significant increase in TGFβ1mRNA expression after 48 hours: 2.7 and 2.1 times the control level, respectively. However, TNFα-induced increase in TGFβ1mRNA expression was not translated into TGFβ1protein secretion, while IL-1β stimulation induced a significant increase in TGFβ1protein secretion as well as TGFβ1mRNA expression. Combined stimulation by high glucose or spent dialysate, together with IL-1β or TNFα, showed a greater increase in TGFβ1mRNA expression and protein secretion compared to stimulation by high glucose or spent dialysate alone.

Conclusion

Our results clearly show that high glucose solution and spent dialysate themselves might be sufficient to stimulate the production of TGFβ1by peritoneal mesothelial cells. In peritoneal dialysis patients, this state of chronic induction of TGFβ1is further exacerbated in the presence of peritonitis because of the stimulatory effect of proinflammatory cytokines, resulting in augmented TGFβ1synthesis, thus promoting peritoneal fibrosis.

Ex Vivo Analysis of Dialysis Effluent-Derived Mesothelial Cells as an Approach to Unveiling the Mechanism of Peritoneal Membrane Failure

During peritoneal dialysis (PD), the peritoneum is exposed to bioincompatible dialysis fluids, which causes progressive fibrosis and angiogenesis and, ultimately, ultrafiltration failure. In addition, repeated episodes of peritonitis or hemoperitoneum may accelerate all these processes. Fibrosis has been classically considered the main cause of peritoneal membrane functional decline. However, in parallel with fibrosis, the peritoneum also displays increases in capillary number (angiogenesis) and vasculopathy in response to PD. Nowadays, there is emerging evidence pointing to peritoneal microvasculature as the main factor responsible for increased solute transport and ultrafiltration failure. However, the pathophysiologic mechanism(s) involved in starting and maintaining peritoneal fibrosis and angiogenesis remain(s) elusive. Peritoneal stromal fibroblasts have been considered (for many years) the cell type mainly involved in structural and functional alterations of the peritoneum; whereas mesothelial cells have been considered mere victims of peritoneal injury caused by PD. Recently, ex vivo cultures of effluent-derived mesothelial cells, in conjunction with immunohistochemical analysis of peritoneal biopsies from PD patients, have identified mesothelial cells as culprits, at least in part, in peritoneal membrane deterioration. This review discusses recent findings that suggest new peritoneal myofibroblastic cells may arise from local conversion of mesothelial cells by epithelial-to-mesenchymal transition during the repair responses that take place in PD. The transdifferentiated mesothelial cells may retain a permanent mesenchymal state, as long as initiating stimuli persist, and contribute to PD-induced fibrosis and angiogenesis, and hence to membrane failure. Future therapeutic interventions could be designated in order to prevent or reverse epithelial-to-mesenchymal transition of mesothelial cells, or its pernicious effects.

Preparation of Gelatin and Gelatin/Hyaluronic Acid Cryogel Scaffolds for the 3D Culture of Mesothelial Cells and Mesothelium Tissue Regeneration

Mesothelial cells are specific epithelial cells that are lined in the serosal cavity and internal organs. Nonetheless, few studies have explored the possibility to culture mesothelial cells in a three-dimensional (3D) scaffold for tissue engineering applications. Towards this end, we fabricated macroporous scaffolds from gelatin and gelatin/hyaluronic acid (HA) by cryogelation, and elucidated the influence of HA on cryogel properties and the cellular phenotype of mesothelial cells cultured within the 3D scaffolds. The incorporation of HA was found not to significantly change the pore size, porosity, water uptake kinetics, and swelling ratios of the cryogel scaffolds, but led to a faster scaffold degradation in the collagenase solution. Adding 5% HA in the composite cryogels also decreased the ultimate compressive stress (strain) and toughness of the scaffold, but enhanced the elastic modulus. From the in vitro cell culture, rat mesothelial cells showed quantitative cell viability in gelatin (G) and gelatin/HA (GH) cryogels. Nonetheless, mesothelial cells cultured in GH cryogels showed a change in the cell morphology and cytoskeleton arrangement, reduced cell proliferation rate, and downregulation of the mesothelium specific maker gene expression. The production of key mesothelium proteins E-cadherin and calretinin were also reduced in the GH cryogels. Choosing the best G cryogels for in vivo studies, the cell/cryogel construct was used for the transplantation of allograft mesothelial cells for mesothelium reconstruction in rats. A mesothelium layer similar to the native mesothelium tissue could be obtained 21 days post-implantation, based on hematoxylin and eosin (H&E) and immunohistochemical staining.

Effects of Rapamycin on the Epithelial-to-mesenchymal Transition of Human Peritoneal Mesothelial Cells

The preservation of the peritoneal membrane is crucial for long-term survival in peritoneal dialysis. Epithelial-to-mesenchymal transition (EMT) is a process demonstrated in mesothelial cells (MC), responsible for negative peritoneal changes and directly related to PD. EMT enables neovascularization and fibrogenic capabilities in MC. Vascular endothelial growth factor (VEGF) is the mediator for neo-vascularization. Rapamycin is a potent immunosuppressor with antifibrotic action in renal allografts and has a demonstrated anti-VEGF effect. We performed this study with the hypothesis that rapamycin may regulate the EMT of MC.

MC from human omentum were cultured. When mesothelial cells reached confluence, some of them were stimulated with r-TGF-ß (1 ng/mL) to induce EMT, co-administered with rapamycin (0.2, 2, 4, 20 and 40 nM). Other groups of cells received similar doses of rapamycin or r-TGF-ß, separately. Cells were analyzed at 6, 24, 48 hours and 7 days. As markers of EMT we included α-SMA, E-cadherin and snail nuclear factor by quantitative RT-PCR.

EMT markers and regulators demonstrated the following changes with rapamycin: E-cadherin (a protective gene for EMT) increased 2.5-fold relative to controls under 40 nM, at 24h. Importantly, rapamycin inhibited snail expression induced by TGF-ß at 6h, whereas TGF-ß increased snail 10fold. At day 7, rapamycin showed no anti-EMT properties. An important decrease in α-SMA expression by MC after rapamycin addition was observed.

In conclusion, rapamycin shows a mild protective effect on EMT, as it increases E-cadherin and decreases α-SMA expression. Consequently, rapamycin might partially regulate the epithelial-to-mesenchymal transition of mesothelial cells.

Periostin-Binding DNA Aptamer Treatment Ameliorates Peritoneal Dialysis-Induced Peritoneal Fibrosis

Peritoneal fibrosis is a major complication in peritoneal dialysis (PD) patients, which leads to dialysis discontinuation. Periostin, increased by transforming growth factor β1 (TGF-β1) stimulation, induces the expression of extracellular matrix (ECM) genes. Aberrant periostin expression has been demonstrated to be associated with PD-related peritoneal fibrosis. Therefore, the effect of periostin inhibition by an aptamer-based inhibitor on peritoneal fibrosis was evaluated. In vitro, TGF-β1 treatment upregulated periostin, fibronectin, α-smooth muscle actin (α-SMA), and Snail expression and reduced E-cadherin expression in human peritoneal mesothelial cells (HPMCs). Periostin small interfering RNA (siRNA) treatment ameliorated the TGF-β1-induced periostin, fibronectin, α-SMA, and Snail expression and restored E-cadherin expression in HPMCs. Similarly, the periostin-binding DNA aptamer (PA) also attenuated fibronectin, α-SMA, and Snail upregulation and E-cadherin downregulation in TGF-β1-stimulated HPMCs. In mice treated with PD solution for 4 weeks, the expression of periostin, fibronectin, α-SMA, and Snail was significantly increased in the peritoneum, whereas E-cadherin expression was significantly decreased. The thickness of the submesothelial layer and the intensity of Masson's trichrome staining in the PD group were significantly increased compared to the untreated group. These changes were significantly abrogated by the intraperitoneal administration of PA. These findings suggest that PA can be a potential therapeutic strategy for peritoneal fibrosis in PD patients.

A pathogenetic role for endothelin-1 in peritoneal dialysis-associated fibrosis

In patients undergoing peritoneal dialysis (PD), chronic exposure to nonphysiologic PD fluids elicits low-grade peritoneal inflammation, leading to fibrosis and angiogenesis. Phenotype conversion of mesothelial cells into myofibroblasts, the so-called mesothelial-to-mesenchymal transition (MMT), significantly contributes to the peritoneal dysfunction related to PD. A number of factors have been described to induce MMT in vitro and in vivo, of which TGF-β1 is probably the most important. The vasoconstrictor peptide endothelin-1 (ET-1) is a transcriptional target of TGF-β1 and mediates excessive scarring and fibrosis in several tissues. This work studied the contribution of ET-1 to the development of peritoneal damage and failure in a mouse model of PD. ET-1 and its receptors were expressed in the peritoneal membrane and upregulated on PD fluid exposure. Administration of an ET receptor antagonist, either bosentan or macitentan, markedly attenuated PD-induced MMT, fibrosis, angiogenesis, and peritoneal functional decline. Adenovirus-mediated overexpression of ET-1 induced MMT in human mesothelial cells in vitro and promoted the early cellular events associated with peritoneal dysfunction in vivo. Notably, TGF-β1-blocking peptides prevented these actions of ET-1. Furthermore, a positive reciprocal relationship was observed between ET-1 expression and TGF-β1 expression in human mesothelial cells. These results strongly support a role for an ET-1/TGF-β1 axis as an inducer of MMT and subsequent peritoneal damage and fibrosis, and they highlight ET-1 as a potential therapeutic target in the treatment of PD-associated dysfunction.

Polymicrobial peritonitis following colonoscopic polypectomy in a peritoneal dialysis patient

Patients undergoing continuous ambulatory peritoneal dialysis (CAPD) are at an increased risk of peritonitis following colonoscopy with or without polypectomy. Guidelines for peritoneal dialysis patients recommend administration of prophylactic antibiotics and drainage of the abdomen before colonoscopy. In this report, we describe a 53-year-old woman on CAPD who underwent colonoscopy with polypectomy and developed peritonitis within 24 hours. She presented with severe abdominal pain, typical rebounding tenderness, and turbid dialysate containing increased white blood cells with a predominance of neutrophils. A culture of the patient's peritoneal fluid grew polymicrobial species including Escherichia coli, Klebsiella pneumoniae, and Enterococcus faecalis. She was treated with intraperitoneal and intravenous administration of combination antibiotics, and she fully recovered within 3 weeks. We suggest that nephrologists and endoscopists should be familiar with the risks and follow the guidelines to prevent such complications in CAPD patients. If peritonitis occurs, medical therapy with antibiotics should be considered before surgical intervention for catheter salvage.

Are ex vivo mesothelial cells representative of the in vivo transition from epithelial-to-mesenchymal cells in peritoneal membrane?

BACKGROUND

We investigated whether ex vivo mesothelial cells found in peritoneal dialysis (PD) effluents were representative of the in vivo epithelial-to-mesenchymal transition (EMT) in peritoneal membrane.

METHODS

Thirty-six male Sprague-Dawley rats were equally divided into three groups: Group C (control), no PD; Group D, infused with 4.25% Dianeal and Group P, infused with 4.25% Physioneal. PD infusions (25 mL) were given twice daily for 8 weeks. The in vivo study included morphometric analyses performed on the peritoneal membranes of tissue specimens obtained at the end of the study. The ex vivo study included peritoneal mesothelial cells collected from PD effluent and cultured to confluence. Cells were scored with light microscopy.

RESULTS

PD for 8 weeks induced significant EMT. The in vivo expression of EMT markers (α-smooth muscle actin:E-cadherin ratio, matrix metalloproteinase-2 and Snail) was higher in Group D than in Group P. However, ex vivo EMT marker expression was similar in cells derived from Groups D and P. A significant correlation was observed among in vivo EMT markers. Moreover, the ex vivo cell score increased with time on PD. However, changes in the ex vivo cell score did not correlated with changes in the in vivo EMT marker expression. Furthermore, we found no correlation between ex vivo and in vivo cells in the expression of EMT markers.

CONCLUSIONS

In this animal study, ex vivo findings did not reflect the in vivo EMT changes in the peritoneum. It may be necessary to improve the current methodology for ex vivo studies.

An integrin-activating peptide, PHSRN, ameliorates inhibitory effects of conventional peritoneal dialysis fluids on peritoneal wound healing

BACKGROUND

Bioincompatible peritoneal dialysis fluids (PDFs) cause pathological changes in the peritoneal membrane, related to membrane dysfunction and progressive peritoneal fibrosis. We investigated the effects of Pro-His-Ser-Arg-Asn (PHSRN) peptide, one of the fibronectin cell-binding domains that activates integrins and reinforces wound healing, on peritoneal remodelling in a rat peritoneal injury model undergoing peritoneal dialysis.

METHODS

The peritoneal mesothelial monolayer was removed by a stripping procedure in rats receiving conventional high glucose-containing PDF supplemented with or without PHSRN or control His-Ser-Pro-Asn-Hrg (HSPNR) peptides. Effects of PHSRN on cell motility and signalling molecules were examined in cultured rat peritoneal mesothelial cells (RPMCs) and normal rat kidney fibroblasts (NRKs).

RESULTS

The cytokeratin- and HBME-1-positive mesothelial cell monolayer was selectively removed by the procedure. By day 6, HBME-1-positive cells had regenerated to 53.3 +/- 6.5% of the peritoneal surface in the control group. Regeneration of the mesothelial layer was delayed in the PDF group (35.2 +/- 10.2%, P < 0.05), but PHSRN reversed the effects of PDF (51.7 +/- 9.6%, P < 0.05). PDF treatment increased thickening of granulomatous submesothelial tissue and numbers of ED1-, CD31- and alpha-smooth muscle actin-positive cells, but PHSRN ameliorated these effects. HSPNR had no effects on mesothelial regeneration or peritoneal wound healing. PHSRN, but not HSPNR, recovered glucose-induced inhibition of cell motility and phosphorylation of focal adhesion kinase and its downstream p130(Cas) in RPMCs and NRKs.

CONCLUSIONS

These results suggest that PHSRN has beneficial effects on peritoneal regeneration by reducing the inhibitory effects of conventional PDF on integrin-mediated wound healing.

Peritoneal Defense Mechanisms—the Effects of New Peritoneal Dialysis Solutions

It remains to be determined whether the peritoneal dialysis procedure induces abnormalities in the normal host defenses of the abdominal cavity and whether these perturbations are important in the pathogenesis of peritonitis. The peritoneum is a smooth membrane that lines the abdominal cavity and participates in the diffusion of water and solutes during peritoneal dialysis. The diaphragmatic lymphatic uptake and the opsonization of micro-organisms, with phagocytosis and killing by peritoneal macrophages, mesothelial cells, lymphocytes, polymorphonuclear leukocytes, and newly defined proteins such as defensins, play a combined role in the peritoneal host defense. Because the composition of earlier peritoneal dialysis fluids is clearly non-physiologic, continuous exposure of peritoneal cells to these solutions may result in an impairment of the local peritoneal host defense mechanisms. However, with the newer solutions, it has been shown that peritoneal defense mechanisms may improve.

Inflammatory cytokines stimulate the adhesion of colon carcinoma cells to mesothelial monolayers

Surgical handling of the peritoneum causes an inflammatory reaction, during which a potentially lethal cocktail of active mediators is produced, including cytokines and growth factors. The aim of this study was to investigate the effects of inflammatory cytokines on the interaction between tumor and mesothelial cells. Tumor cell adhesion to a mesothelial monolayer was assessed after preincubation of the mesothelium with interleukin (IL)-1beta, IL-6, and tumor necrosis factor (TNF)-alpha. Preincubation of the mesothelial monolayer with IL-1beta or TNF-alpha resulted in enhanced tumor cell adhesion of Caco2 and HT29 colon carcinoma cells. The amount of stimulation for the Caco2 cells was between 20% and 40% and for HT29 cells between 30% and 70%. Blocking experiments with anti-IL-1beta and anti-TNF-alpha resulted in significant inhibition of the cytokine-stimulated tumor cell adhesion. The presented results prove that IL-1beta and TNF-alpha are significant stimulating factors in tumor cell adhesion in vitro and may therefore account for tumor recurrence to the peritoneum in vivo.

Peroxisome proliferator-activated receptor-gamma is expressed by rat peritoneal mesothelial cells: its potential role in peritoneal cavity local defense

BACKGROUND/AIMS

Peritoneal mesothelial cells (PMCs) play an important role in peritoneal inflammatory and immune response. It was reported that the peroxisomal proliferator-activated receptor-gamma (PPARgamma) ligand could effectively reduce inflammatory processes. However, the expression and function of PPARgamma in PMCs has not been reported. This study was to investigate the expression of PPARgamma in rat PMCs and the effect of PPARgamma activation on the production of CD40 and ICAM-1 induced by lipopolysaccharide (LPS).

METHODS

Rat PMCs (RPMCs) were harvested from the peritoneal cavity of Sprague-Dawley rats and maintained under defined in vitro conditions. The cells were treated separately with LPS, 15d-PGJ(2), and ciglitazone at different time points. The mRNA and protein expression of PPARgamma, CD40 and ICAM-1 were detected by RT-PCR and Western blot, respectively. The intracellular distribution of PPARgamma was detected by immunocytochemistry.

RESULTS

RPMCs expressed PPARgamma both at the mRNA and protein level. The specific signals for PPARgamma were mainly localized in the nucleus with weak staining in the cytoplasm. Stimulation of RPMCs with LPS resulted in a time-dependent increase in the expression of PPARgamma with the peak of mRNA at 3 h and protein at 12 h. Thereafter the expression of PPARgamma gradually attenuated. The mRNA expressions for CD40, ICAM-1 and protein expression of ICAM-1 were significantly upregulated following stimulation with LPS. Both 15d-PGJ(2) and ciglitazone decreased the expression of CD40 mRNA and ICAM-1 protein. However, ciglitazone was less effective than 15d-PGJ(2).

CONCLUSIONS

There is constitutive expression of PPARgamma in cultured RPMCs and PPARgamma ligands which strongly inhibit LPS-induced CD40 and ICAM-1 production in RPMCs. It suggested that PPARgamma might play a part in the local defense of the peritoneal cavity by downregulating inflammatory mediators, which may play a potential role in preventing peritoneal fibrosis induced by peritonitis. Further in vivo study is needed to demonstrate the long-term effects.

Mesenchymal conversion of mesothelial cells as a mechanism responsible for high solute transport rate in peritoneal dialysis: role of vascular endothelial growth factor

BACKGROUND

During peritoneal dialysis (PD), the peritoneum is exposed to bioincompatible dialysis fluids that cause epithelial-to-mesenchymal transition of mesothelial cells, fibrosis, and angiogenesis. Ultrafiltration failure is associated with high transport rates and increased vascular surface, indicating the implication of vascular endothelial growth factor (VEGF). Sources of VEGF in vivo in PD patients remain unclear. We analyzed the correlation between epithelial-to-mesenchymal transition of mesothelial cells and both VEGF level and peritoneal functional decline.

METHODS

Effluent mesothelial cells were isolated from 37 PD patients and analyzed for mesenchymal conversion. Mass transfer coefficient for creatinine (Cr-MTC) was used to evaluate peritoneal function. VEGF concentration was measured by using standard procedures. Peritoneal biopsy specimens from 12 PD patients and 6 controls were analyzed immunohistochemically for VEGF and cytokeratin expression.

RESULTS

Nonepithelioid mesothelial cells from effluent produced a greater amount of VEGF ex vivo than epithelial-like mesothelial cells (P < 0.001). Patients whose drainage contained nonepithelioid mesothelial cells had greater serum VEGF levels than those with epithelial-like mesothelial cells in their effluent (P < 0.01). VEGF production ex vivo by effluent mesothelial cells correlated with serum VEGF level (r = 0.6; P < 0.01). In addition, Cr-MTC correlated with VEGF levels in culture (r = 0.8; P < 0.001) and serum (r = 0.35; P < 0.05). Cr-MTC also was associated with mesothelial cell phenotype. VEGF expression in stromal cells, retaining mesothelial markers, was observed in peritoneal biopsy specimens from high-transporter patients.

CONCLUSION

These results suggest that mesothelial cells that have undergone epithelial-to-mesenchymal transition are the main source of VEGF in PD patients and therefore may be responsible for a high peritoneal transport rate.

Peritoneal dialysis and epithelial-to-mesenchymal transition of mesothelial cells

BACKGROUND

During continuous ambulatory peritoneal dialysis, the peritoneum is exposed to bioincompatible dialysis fluids that cause denudation of mesothelial cells and, ultimately, tissue fibrosis and failure of ultrafiltration. However, the mechanism of this process has yet to be elucidated.

METHODS

Mesothelial cells isolated from effluents in dialysis fluid from patients undergoing continuous ambulatory peritoneal dialysis were phenotypically characterized by flow cytometry, confocal immunofluorescence, Western blotting, and reverse-transcriptase polymerase chain reaction. These cells were compared with mesothelial cells from omentum and treated with various stimuli in vitro to mimic the transdifferentiation observed during continuous ambulatory peritoneal dialysis. Results were confirmed in vivo by immunohistochemical analysis performed on peritoneal-biopsy specimens.

RESULTS

Soon after dialysis is initiated, peritoneal mesothelial cells undergo a transition from an epithelial phenotype to a mesenchymal phenotype with a progressive loss of epithelial morphology and a decrease in the expression of cytokeratins and E-cadherin through an induction of the transcriptional repressor snail. Mesothelial cells also acquire a migratory phenotype with the up-regulation of expression of alpha2 integrin. In vitro analyses point to wound repair and profibrotic and inflammatory cytokines as factors that initiate mesothelial transdifferentiation. Immunohistochemical studies of peritoneal-biopsy specimens from patients undergoing continuous ambulatory peritoneal dialysis demonstrate the expression of the mesothelial markers intercellular adhesion molecule 1 and cytokeratins in fibroblast-like cells entrapped in the stroma, suggesting that these cells stemmed from local conversion of mesothelial cells.

CONCLUSIONS

Our results suggest that mesothelial cells have an active role in the structural and functional alteration of the peritoneum during peritoneal dialysis. The findings suggest potential targets for the design of new dialysis solutions and markers for the monitoring of patients.

Immunology of the peritoneal cavity: relevance for host-tumor relation

The peritoneal membrane, formed by a single layer of mesothelial cells, lines the largest cavity of the human body. Anatomic structures of the peritoneal cavity, along with resident leukocyte populations, play an important role in the defense against microorganisms invading by breaching the gut integrity or ascending through the female genital tract. Local immune mechanisms in the peritoneal cavity are also important in patients undergoing peritoneal dialysis and in women with endometriosis. There is now extensive evidence demonstrating the significance of peritoneal immune mechanisms in the control of metastatic spread. Leukocytes belonging to both the innate and adaptive immune systems are present in the peritoneal cavity of normal subjects as well as in patients with intra-abdominal cancer. There is now increased understanding of the mechanisms that not only allow the tumor cells to escape the detection and destruction by the host immune system, but also to use the inflammatory mechanisms to promote tumor growth and spread inside the peritoneal cavity. Malignant ascites represents a model for the study of the interaction between tumor cells and the host immune system as well for the analysis of the tumor microenviroment. The peritoneal immune system may be stimulated by intraperitoneal administration of biologic agents. This peritoneal immunotherapy may be used for palliation of malignant ascites, or as a consolidation strategy in patients with minimal residual disease.

Peritoneal dialysis fluids with a physiologic pH based on either lactate or bicarbonate buffer-effects on human mesothelial cells

Conventional lactate (Lac)-buffered peritoneal dialysis (PD) solutions have turned out to be detrimental to human peritoneal cells, especially because of a low pH. In the present study, we focus on potential differences between Lac and bicarbonate (Bic) as a buffer when adjusted to a physiological pH. All test fluids were buffered with either 40 mmol/L of Lac or 34 mmol/L of Bic, sterile filtered, and adjusted to a pH of 7.4. Osmotic agents used were 1.36% glucose (Glu), 3.86% Glu, 1% amino acids (AA), and 7.5% Glu polymer (Glupoly). Human peritoneal mesothelial cells (HPMCs) were isolated from the omentum majus, grown to confluence, and incubated after the second passage for 15 minutes (37 degrees C and 5% carbon dioxide) with the test fluids. Cytotoxicity was controlled by measuring apoptotic and necrotic cells with cytofluorometry. Aerobic cell metabolism (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide [MTT] assay) and intracellular adenosine triphosphate (ATP) concentrations were measured to assess cell viability. Release of interleukin-6 (IL-6) from HPMCs was determined as a parameter of cellular host defense. No significant difference in apoptosis or necrosis rates was found between the solutions adjusted to normal pH. However, in the MTT assay, Bic solutions were superior to corresponding Lac pendants at an identical pH of 7.4 (P < 0.01). Intracellular ATP concentrations reflected a very similar pattern (P < 0.05). Glupoly in combination with Lac showed an impaired pattern with both the MTT and ATP assays. Regarding IL-1beta-stimulated IL-6 release, there was a small, but not significantly better, response for Bic. Differences in manifest cell cytotoxicity reflected by apoptosis and necrosis rates could not be detected comparing PD solutions buffered with Lac or Bic at a physiological pH. However, distinct parameters of cell metabolism were superior with Bic compared with Lac. Especially Glupoly was inferior in combination with Lac as a buffer.

Synthesis of C-X-C and C-C chemokines by human peritoneal fibroblasts: induction by macrophage-derived cytokines

Leukocyte accumulation during peritonitis is believed to be controlled by chemotactic factors released by resident peritoneal macrophages or mesothelial cells. Recent data indicate, however, that in many tissues fibroblasts play a key role in mediating leukocyte recruitment. We have therefore examined human peritoneal fibroblasts (HPFBs) for the expression and regulation of C-X-C and C-C chemokines. Quiescent HPFBs secreted monocyte chemoattractant protein (MCP)-1 and interleukin (IL)-8 constitutively. This release could be dose-dependently augmented with the pro-inflammatory cytokines IL-1beta and tumor necrosis factor-alpha. Stimulated IL-8 production reached a plateau within 48 hours while MCP-1 continued to accumulate throughout 96 hours. Induction of IL-8 and MCP-1 synthesis by HPFBs was also triggered by peritoneal macrophage-conditioned medium. This effect was partly related to the presence of IL-1beta as demonstrated by IL-1 receptor antagonist inhibition. Pretreatment of HPFBs with actinomycin D or puromycin dose-dependently reduced cytokine-stimulated IL-8 and MCP-1 secretion, which suggested de novo chemokine synthesis. Indeed, exposure of HPFBs to IL-1beta and tumor necrosis factor-alpha produced a significant up-regulation of IL-8 and MCP-1 mRNA. This effect was associated with the rapid induction of nuclear factor-kappaB binding activity mediated through p65 and p50 subunits, and with a transient increase in the mRNA expression for RelB and inhibitory protein kappaB-alpha proteins. These data indicate that peritoneal fibroblasts are capable of generating large quantities of chemokines under a tight control of nuclear factor-kappaB/Rel transcription factors. Thus, peritoneal fibroblast-derived chemokines may contribute to the intraperitoneal recruitment of leukocytes during peritonitis.

IL-17 stimulates intraperitoneal neutrophil infiltration through the release of GRO alpha chemokine from mesothelial cells

IL-17 is a newly discovered cytokine implicated in the regulation of hemopoiesis and inflammation. Because IL-17 production is restricted to activated T lymphocytes, the effects exerted by IL-17 may help one to understand the contribution of T cells to the inflammatory response. We investigated the role of IL-17 in leukocyte recruitment into the peritoneal cavity. Leukocyte infiltration in vivo was assessed in BALB/Cj mice. Effects of IL-17 on chemokine generation in vitro were examined in human peritoneal mesothelial cells (HPMC). Administration of IL-17 i.p. resulted in a selective recruitment of neutrophils into the peritoneum and increased levels of KC chemokine (murine homologue of human growth-related oncogene alpha (GROalpha). Pretreatment with anti-KC Ab significantly reduced the IL-17-driven neutrophil accumulation. Primary cultures of HPMC expressed IL-17 receptor mRNA. Exposure of HPMC to IL-17 led to a dose- and time-dependent induction of GROalpha mRNA and protein. Combination of IL-17 together with TNF-alpha resulted in an increased stability of GROalpha mRNA and synergistic release of GROalpha protein. Anti-IL-17 Ab blocked the effects of IL-17 in vitro and in vivo. IL-17 is capable of selectively recruiting neutrophils into the peritoneal cavity via the release of neutrophil-specific chemokines from the peritoneal mesothelium.

l-2-oxothiazolidine-4-carboxylic acid modulates function of peritoneal mesothelial cells in vitro

The influence of the glutathione precursor, l-2-oxothiazolidine-4-carboxylic acid (OTZ), on the function of human peritoneal mesothelial cells in vitro, in conditions that mimic the in vivo effect of peritoneal dialysis solutions on mesothelium, was studied. Mesothelial monolayers were exposed to dialysis fluids (Dianeal 1.36 or Dianeal 3.86; Baxter Healthcare Corp, Round Lake, IL) that were diluted gradually with pooled-effluent dialysate obtained from patients undergoing continuous ambulatory peritoneal dialysis. In vitro exposure of mesothelium to standard dialysis fluid enhances their susceptibility to injury by hydrogen peroxide. OTZ added to dialysis solution in concentrations of 1 mmol/L prevented the toxic effect of hydrogen peroxide, probably by increasing intracellular glutathione. Mesothelial cells exposed to dialysis fluid become activated, evidenced by increased release of interleukin-6 and hyaluronan. OTZ used in concentrations of 1 mmol/L reduced that effect. Furthermore, the addition of glucose to the culture medium in a concentration of 45 mmol/L inhibits the proliferation of mesothelial cells; the presence of OTZ, 1 mmol/L, partially prevents the inhibitory effect of glucose. The results presented in this report show that by augmenting the intracellular concentration of glutathione in mesothelial cells by the addition of OTZ to the dialysis fluid, we can increase their resistance to the acute toxicity of free radicals and long-term toxicity of glucose. In addition, mesothelial cells with an increased glutathione level are less activated after their exposure to dialysis fluid.