Peritoneal Dialysis Effluent Research Articles

Proteomic analysis in peritoneal dialysis patients with different peritoneal transport characteristics

Peritoneal membranes can be categorized as high, high average, low average, and low transporters, based on the removal or transport rate of solutes. In this study, we used proteomic analysis to determine the differences in proteins removed by different types of peritoneal membranes. Peritoneal transport characteristics in patients who received peritoneal dialysis therapy were assessed by a peritoneal equilibration test. Two-dimensional differential gel electrophoresis technology followed by quantitative analysis was performed to study the variation in protein expression from peritoneal dialysis effluents (PDE) among different groups. Proteins were identified by MALDI-TOF-MS/MS analyses. Further validation in PDE or serum was performed utilizing ELISA analysis. Proteomics analysis revealed ten protein spots with significant differences in intensity levels among different groups, including vitamin D-binding protein, complement C3, apolipoprotein-A1, complement factor C4A, haptoglobin, alpha-1 antitrypsin, immunoglobulin kappa light chain, alpha-2-microglobulin, retinol-binding protein 4 and transthyretin. The levels of vitamin D-binding protein, complement C3, and apolipoprotein-A1 in PDE derived from different groups were greatly varied (P<0.05). However, no significant difference was found in the serum levels of these proteins among different groups (P>0.05 for all groups). This study provides a novel overview of the differences in PDE proteomes of four types of peritoneal membranes. Vitamin D-binding protein, complement C3, and apolipoprotein-A1 showed enhanced expression in PDE of patients with high transporter.

Cancer Antigen 125 as a Biomarker in Peritoneal Dialysis: Mesothelial Cell Health or Death?

The concentration or appearance rate of cancer antigen 125 (CA125) in peritoneal dialysis (PD) effluent has been used for many years as a biomarker for mesothelial cell mass in patients on PD. However, this marker has limitations, and emerging evidence has raised doubts as to its significance. This review explores our current understanding of CA125, its prominent role in studies of "biocompatible" PD solutions, and the ongoing uncertainty concerning its interpretation as a measure of mesothelial cell health.

Dialysate cancer antigen 125 in long-term peritoneal dialysis patients

Structural and functional peritoneal membrane changes are associated with long-term peritoneal dialysis. These changes can lead to ultrafiltration failure and peritoneal fibrosis, reducing the efficacy of the peritoneal membrane to remove waste and balance fluid and electrolytes. The loss of mesothelial cells from the basement membrane is one of the major characteristics in peritoneal membrane structural change. Thus, if the reduction of peritoneal mesothelial cell mass in peritoneal dialysis patients is monitored, signs of ultrafiltration failure and peritoneal fibrosis can be detected early. One of biomarkers that can be used to indicate the change in peritoneal mesothelial cell mass is CA125, which is produced by mesothelial cells. In this article, we review the measurement and clinical use of CA125 in peritoneal dialysate effluent. Additionally, we address the data and studies on the association between dialysate CA125 levels and factors related to ultrafiltration failure and peritoneal fibrosis, including the parameters used to monitor the functional status of the peritoneal membrane. Our review shows that dialysate CA125 can be used to evaluate the peritoneal membrane in noninfected patients to predict peritoneal fibrosis, and it can also be used as a biomarker of biocompatible dialysis solutions.

Developing a reproducible method for the high-resolution separation of peritoneal dialysate proteins on 2-D gels

PurposeDespite recent progress in the proteomic analysis of peritoneal dialysate effluent (PDE), there remains unresolved problems in the development of an optimal sample preparation method. Experimental designWe examined five protocols for concentrating PDE proteins and the effects of immobilized pH gradient (IPG) strips with different pH ranges and sample loading techniques. In addition, we examined three kits for depleting high abundance proteins by SDS–PAGE and two-dimensional gel electrophoresis (2-DE). ResultsPDE proteins precipitated with 75% acetonitrile (ACN) showed the greatest number of protein spots by 2-DE, with over 800 distinct spots. Higher-resolution images were obtained using IPG strips with a pH range of 4–7. The ProteoPrep immunoaffinity albumin and IgG depletion kit removed high abundance proteins with higher efficiency and more compatibility with isoelectric focusing (IEF). Removing high abundance proteins also increased the resolution and improved the intensity of low abundance proteins. Conclusion and clinical relevanceHigh-resolution 2-DE images of PDE proteins were obtained by concentrating samples with 75% ACN, using pH 4–7 IPG strips, and depleting high abundance proteins. This optimized method will enable future studies to discover predictive biomarkers of disease in patients on dialysis.

Estimated glomerular filtration rate -a more stable indicator than creatinine clearance in peritoneal dialysis practice.

Objective: The usefulness of estimated glomerular filtration rate may not be restricted to pre-dialysis patients, since we reported that estimated glomerular filtration rate was well correlated with measured total creatinine clearance in peritoneal dialysis patients. To clarify the clinical usefulness of estimated glomerular filtration rate as a parameter for peritoneal dialysis adequacy, we retrospectively surveyed estimated glomerular filtration rate and total creatinine clearance in peritoneal dialysis patients treated at JA Toride Medical Center.Patients and Methods: A total of 114 data sets of estimated glomerular filtration rate and total creatinine clearance from 21 PD patients treated at JA Toride Medical Center were collected from November 2010 to October 2011. The patients consisted of 15 men and six women with an average age of 66.6 ± 12.6 years (46–95 years old). The average number of samples was 5.4 ± 1.5 (2 to 7) per patient.Results: The collected data showed less correlation of estimated glomerular filtration rate and total creatinine clearance (r. = 0.435) than that of a previous cross-sectional study (r. = 0.836). As reported in pre-dialysis patients, the differences between estimated glomerular filtration rate and total creatinine clearance were correlated with total creatinine excretion in urine and PD effluent (r. = 0.821). The differences were also correlated with normalized protein catabolic rate, which was one of the main determinant factors for total creatinine excretion (r. = 0.636). A similar tendency was apparently observed in one patient with poor compliance to diet therapy and fluctuating dietary intake. From the analysis of these data, serum creatinine seemed to fluctuate less possibly due to compensatory capacity of the residual renal function in small solute clearance.Conclusions: Consequently, estimated glomerular filtration rate was turned out to be a more stable parameter than total creatinine clearance, which might be a desirable feature in long-term follow-up of peritoneal dialysis patients.

Are the Mesothelial-to-Mesenchymal Transition, Sclerotic Peritonitis Syndromes, and Encapsulating Peritoneal Sclerosis Part of the Same Process?

Mesothelial-to-mesenchymal transition (MMT) is an autoregulated physiological process of tissue repair that in uncontrolled conditions, such as peritoneal dialysis (PD), can lead to peritoneal fibrosis. The maximum expression of sclerotic peritoneal syndromes (SPS) is the encapsulating peritoneal sclerosis (EPS) for which no specific treatment exists. The SPS includes a wide range of peritoneal fibrosis that appears progressively and is considered as a reversible process, while EPS does not. EPS is a serious complication of PD characterized by a progressive intra-abdominal inflammatory process that results in bridles and severe fibrous tissue formation which cover and constrict the viscera. Recent studies show that transdifferentiated mesothelial cells isolated from the PD effluent correlate very well with the clinical events such as the number of hemoperitoneum and peritonitis, as well as with PD function (lower ultrafiltration and high Cr-MTC). In addition, in peritoneal biopsies from PD patients, the MMT correlates very well with anatomical changes (fibrosis and angiogenesis). However, the pathway to reach EPS from SPS has not been fully and completely established. Herein, we present important evidence pointing to the MMT that is present in the initial peritoneal fibrosis stages and it is perpetual over time, with at least theoretical possibility that MMT initiated the fibrosing process to reach EPS.

Characterization of peritoneal dialysis effluent-derived cells: diagnosis of peritoneal integrity

To assess the integrity of the peritoneal membrane, we characterized the functionality of the cellular components derived from peritoneal dialysis effluent (PDE). About 3 % of all cells collected from the PDE attached to the plastic dish, and 97.1 ± 3.1 % of the adherent cells expressed CK-18 (PDE-HPMC). A typical cobble-stone-like morphology under neutralized PD solution was obtained over 65 out of 74 primary cultures (88 %) while only 53 % under acidic PD solution in a previous report by Yanez-Mo et al. However, 26.6 ± 10.3 % of PDE-HPMC expressed the EMT marker α-SMA. Transepithelial resistance (TER) as a marker of cell polarity was 34 % lower than that of omentum-derived(OM)-HPMC. We found a significant decrease in the rate of PDE-HPMC proliferation compared to OM-HPMC, accompanied by a significant increase of cell area within the tertiary passage. Comparison of TER, α-SMA and SA-β-Gal between CAPD durations suggests that cell polarity weakens with increased duration of CAPD, reflecting the occurrence of EMT and cell senescence. We conclude that functional characterization of cellular components in PDE reflects how well the peritoneum is preserved.

Excess fluid distribution affects tacrolimus absorption in peritoneal dialysis patients

Excess fluid distribution is a common disorder in peritoneal dialysis (PD) patients. Tacrolimus malabsorption may also occur in PD patients, and may lead to acute allograft rejection after transplantation. The purpose of this study was to evaluate the relationship between tacrolimus pharmacokinetics and excess fluid distribution according to pre-transplant dialysis modality. We retrospectively analyzed 41 adult living-donor kidney transplantations, including nine PD patients and 32 hemodialysis (HD) patients. We examined tacrolimus pharmacokinetics in the peri-operative period and determined the association between the tacrolimus absorption rate and body weight reduction. The absorption efficacy of tacrolimus was evaluated as the dose-normalized tacrolimus absorption rate. Tacrolimus concentrations in PD effluent were measured by high-performance liquid chromatography. The tacrolimus absorption rate on the day before kidney transplantation tended to be lower in PD patients than in HD patients; however, the rate improved after kidney transplantation and was similar in both groups of patients. The peak tacrolimus concentration time was later in PD patients than in HD patients. The body weight reduction after kidney transplantation was greater in PD patients than in HD patients, and was significantly associated with the change in tacrolimus absorption rate (p=0.04, r=0.32). Only 0.002% of the oral tacrolimus dose was removed by PD itself. Excess fluid distribution in PD patients appears to contribute to tacrolimus malabsorption rather than PD itself. We should consider the risk of tacrolimus malabsorption in patients with possible excess fluid distribution, particularly in PD patients.

An unusual cause of non-infectious peritonitis in a peritoneal dialysis patient

We report a 48-year-old woman with end-stage renal disease receiving continuous ambulatory peritoneal dialysis who presented with polyarthritis. Painless cloudy peritoneal dialysis effluent was also noted incidentally. Analyses of the effluent dialysate showed increased leukocyte count with a predominance of lymphocytes. Empirical intraperitoneal cefazolin was given initially. Routine cultures of effluent dialysate were negative for bacteria, fungi, and mycobacteria. Cytology revealed no malignant cells. However, the turbidity of effluent dialysate was still increased after 1 week of antibiotic treatment. In the meantime, laboratory tests showed significant antinuclear antibody positivity. Additional serology testing found positive antihistone antibody. On reviewing the patient's current medications, we found that she had been taking hydralazine for the past 3 months. Because drug-induced lupus was suspected, hydralazine was discontinued and low-dose steroids were initiated. Clinical symptoms and cloudy dialysate rapidly abated afterwards. There was no relapse of arthralgia during the next 1-year period of follow-up.

Coxsackievirus B1 peritonitis in a patient treated with continuous ambulatory peritoneal dialysis: a case report and brief review of the literature

We report a case of viral peritonitis caused by coxsackievirus B1 in a 79-year-old male undergoing continuous ambulatory peritoneal dialysis (CAPD), and review the English language literature. Clinicians should be aware of viral peritonitis in patients on CAPD presenting with a viral syndrome and mononuclear peritoneal dialysis effluent. Currently, viral diagnostic tests are available to confirm the diagnosis and avoid unnecessary treatment with antibiotics.

Intraperitoneal Vancomycin Concentrations during Peritoneal Dialysis–Associated Peritonitis: Correlation with Serum Levels

For the treatment of peritoneal dialysis-associated peritonitis (PDP), it has been suggested that serum concentrations of vancomycin be kept above 12 mg/L-15 mg/L. However, studies correlating vancomycin concentrations in serum and peritoneal dialysate effluent (PDE) during active infection are sparse. We undertook the present study to investigate this issue and to determine whether achieving the recommended serum level of vancomycin results in therapeutic levels intraperitoneally. We studied patients treated with intraperitoneal (i.p.) vancomycin for non-gram-negative PDP. We gave a single dose (approximately 30 mg/kg) at presentation, and we subsequently measured vancomycin levels in PDE on day 5; we wanted to determine if efflux of vancomycin from serum to PDE during a 4-hour dwell was consistent and resulted in therapeutic levels. Of the 48 episodes of PDP studied, serum vancomycin concentrations exceeding 12 mg/L were achieved in 98% of patients, but in 11 patients (23%), a PDE vancomycin level below 4 mg/L--the minimal inhibitory concentration (MIC) of many gram-positive organisms--was observed at the end of a 4-hour dwell on day 5. The correlation between the concentrations of vancomycin in serum and PDE (from efflux of antibiotic over 4 hours) was statistically significant, but poor (R(2) = 0.18). Our data support the International Society for Peritoneal Dialysis statement that adequate serum vancomycin concentrations can be achieved with intermittent dosing (single dose every 5 days), but cannot guarantee therapeutic PDE levels in the treatment of PDP. Intermittent dosing of vancomycin may not consistently result in PDE concentrations markedly greater than MIC of many important pathogens. Although the clinical significance of this finding remains to be determined, it may be preferable to give smaller but more frequent doses of PDE vancomycin (continuous dosing) for adults with PDP (as is currently recommended for children).

Proof-of-principle study to detect metabolic changes in peritoneal dialysis effluent in patients who develop encapsulating peritoneal sclerosis

Prolonged peritoneal dialysis (PD) therapy can result in the development of encapsulating peritoneal sclerosis (EPS), characterized by extensive sclerosis of the peritoneum with bowel adhesions often causing obstruction. As a proof-of-principle study, holistic profiling of endogenous metabolites has been applied in a prospective collection of PD effluent collected in multiple UK renal centres over 6 years in order to investigate metabolic differences in PD effluent between PD therapy patients who later developed clinically defined EPS (n = 11) and controls, who were matched for PD vintage, age and gender (n = 11). 'Fit-for-purpose' analytical methods employing gas chromatography-mass spectrometry (MS), direct injection MS and quality control samples were developed and validated. These methods were applied in a proof-of-principle study to define metabolic differences in PD effluent related to subsequent development of EPS. Changes in amino acids, amines and derivatives, short-chain fatty acids and derivatives and sugars were observed prior to EPS developing, and changes in the metabolomic profiles could be detected. There is potential for applying metabolic profiles to identify patients at risk of developing EPS although long-term prospective studies with larger patient cohorts are required.

Experience in Primary Culture of Human Peritoneal Mesothelial Cell

To compare the growth condition between different sources and different culture environments, mesothelial cells were isolated from omentum and peritoneal dialysate effluent (PDE), seeded at different densities (5 × 10⁵, 1 × 10⁵, 5 × 10⁴, 1 × 10⁴, 5 × 10³, 1 × 10³ and 5 × 10² cells/cm², respectively), supported with different fetal calf serum (FCS) concentrations (3%, 6%, 10% and 15%) and grown in dishes with and without gelatin pre-coating. Growth condition was evaluated by simple morphological observation. Cells phenotype was examined by immunofluorescent staining. The results showed that omentum-derived mesothelial cells generally showed a uniform growth pattern with good quality. Alternatively, there was a wide patient-to-patient variation in PDE-derived culture. Heterogeneous colonies composed of a mixture of large, small or abortive mesothelial colonies as well as fibroblastoid colonies were frequently observed. A minimum seeding density of 5 × 10³ cells/cm² is required for the omentum-derived mesothelial cells to grow to confluent monolayer (1-5 × 10⁴ cells/cm² for initial culture from fresh PDE). Appropriate seeding density is always associated with successful culture in omentumbased culture, but not in PDE-based culture. Mesothelial cells could grow to confluency regardless of FCS concentration and gelatin pre-coating. However, growth rate was slower in lower FCS concentrations and on dishes without gelatin coating. Most cells in culture expressed cytokeratin and vimentin, but not VWF. Alpha-smooth muscle actin frequently appeared in cytokeratin+ mesothelial cells, especially in higher FCS concentrations and in PDE-derived culture. Our data demonstrate that PDE, in contrast to omentum, provides a source of mesothelial cells with poor and unstable quality for primary culture. Healthy cell quality and sufficient seeding density seem to be the most important factors for successful culture of mesothelial cells. The frequent occurrence of epithelial-to-mesenchymal transition in cultured mesothelial cells indicates the feasibility of mesothelial cells to undergo phenotype change upon environment changes, especially following chronic exposure to uremic environment and dialysate in peritoneal dialysis patients.

Pleiotrophin triggers inflammation and increased peritoneal permeability leading to peritoneal fibrosis

Long-term peritoneal dialysis induces peritoneal fibrosis with submesothelial fibrotic tissue. Although angiogenesis and inflammatory mediators are involved in peritoneal fibrosis, precise molecular mechanisms are undefined. To study this, we used microarray analysis and compared gene expression profiles of the peritoneum in control and chlorhexidine gluconate (CG)-induced peritoneal fibrosis mice. One of the 43 highly upregulated genes was pleiotrophin, a midkine family member, the expression of which was also upregulated by the solution used to treat mice by peritoneal dialysis. This growth factor was found in fibroblasts and mesothelial cells within the underlying submesothelial compact zones of mice, and in human peritoneal biopsy samples and peritoneal dialysate effluent. Recombinant pleiotrophin stimulated mitogenesis and migration of mouse mesothelial cells in culture. We found that in wild-type mice, CG treatment increased peritoneal permeability (measured by equilibration), increased mRNA expression of TGF-β1, connective tissue growth factor and fibronectin, TNF-α and IL-1β expression, and resulted in infiltration of CD3-positive T cells, and caused a high number of Ki-67-positive proliferating cells. All of these parameters were decreased in peritoneal tissues of CG-treated pleiotrophin-knockout mice. Thus, an upregulation of pleiotrophin appears to play a role in fibrosis and inflammation during peritoneal injury.

Relation between microRNA expression in peritoneal dialysis effluent and peritoneal transport characteristics.

Background: The role of microRNAs (miRNAs) in peritoneal transport is uncertain. Methods: We studied 82 new peritoneal dialysis (PD) patients, 22 prevalent patients without ultrafiltration problem, and 6 patients with documented ultrafiltration problem. Peritoneal transport was determined by standard peritoneal equilibration test (PET). RNA was extracted from the PD effluent after PET, and intra-peritoneal expression of miRNA targets were quantified. Results: There were significant difference in the PDE expressions of miR-15a and miR-21. There were modest inverse correlations between ultrafiltration volume and PDE expression of miR-17 (r = −0.198, p = 0.041) and miR-377 (r = −0.201, p = 0.041). There was an inverse correlations between dialysate-to-plasma creatinine concentration at 4 hours and PDE expression of miR-192 (r = −0.199, p = 0.040); while mass transfer area coefficient of creatinine correlated with PDE expression of miR-192 (r = −0.191, p = 0.049) and miR-377 (r = 0.201, p = 0.041). Amongst 7 randomly selected patients who had repeat PET after one year, there was a significant correlation between baseline PDE expression of miR-377 and change in ultrafiltration volume (r = −0.852, p = 0.015). Conclusion: The miRNA expression in PDE, including miR-15a, miR-17, miR-21, miR-30, miR-192, and miR-377, correlated with peritoneal transport characteristics. Our result suggests that miRNA may play a role in the regulation of peritoneal membrane function.

Relation between MicroRNA Expression in Peritoneal Dialysis Effluent and Peritoneal Transport Characteristics

Background:The role of microRNAs (miRNAs) in peritoneal transport is uncertain.Methods:We studied 82 new peritoneal dialysis (PD) patients, 22 prevalent patients without ultrafiltration problem, and 6 patients with documented ultrafiltration problem. Peritoneal transport was determined by standard peritoneal equilibration test (PET). RNA was extracted from the PD effluent after PET, and intra-peritoneal expression of miRNA targets were quantified.Results:There were significant difference in the PDE expressions of miR-15a and miR-21. There were modest inverse correlations between ultrafiltration volume and PDE expression of miR-17 (r= −0.198,p= 0.041) and miR-377 (r= −0.201,p= 0.041). There was an inverse correlations between dialysate-to-plasma creatinine concentration at 4 hours and PDE expression of miR-192 (r= −0.199,p= 0.040); while mass transfer area coefficient of creatinine correlated with PDE expression of miR-192 (r= −0.191,p= 0.049) and miR-377 (r= 0.201,p= 0.041). Amongst 7 randomly selected patients who had repeat PET after one year, there was a significant correlation between baseline PDE expression of miR-377 and change in ultrafiltration volume (r= −0.852,p= 0.015).Conclusion:The miRNA expression in PDE, including miR-15a, miR-17, miR-21, miR-30, miR-192, and miR-377, correlated with peritoneal transport characteristics. Our result suggests that miRNA may play a role in the regulation of peritoneal membrane function.

Intraperitoneal IL-6 Signaling in Incident Patients Treated with Icodextrin and Glucose Bicarbonate/Lactate–Based Peritoneal Dialysis Solutions

In this study, we compared the activity of interleukin-6 (IL-6), a marker of ongoing peritoneal inflammation and biocompatibility, and its other signaling components, the soluble IL-6 receptor (sIL-6R) and soluble Gp130 (sGp130), in peritoneal effluent from patients treated with icodextrin-based (E) peritoneal dialysis (PD) solution and glucose-based bicarbonate/lactate-buffered (P) solution. Using baseline peritoneal ultrafiltration capacity, 33 stable incident PD patients were allocated either to P only (n = 20) or to P plus E for the overnight dwell (n = 13). We used ELISA to determine IL-6, sIL-6R, and sGp130 in timed overnight effluent at 1, 6, and 12 months after PD initiation. Flow cytometry was used to measure expression of IL-6R and Gp130 on isolated peritoneal leukocytes at the same time points. Peritonitis was an exclusion criterion. At all time points, levels of IL-6 and sIL-6R, and the appearance rates of IL-6 (90.5 pg/min vs. 481.1 pg/min, p < 0.001; 138.6 pg/min vs. 1187.5 pg/min, p < 0.001; and 56.1 pg/min vs. 1386.0 pg/min, p < 0.001), sIL-6R (2035.3 pg/min vs. 4907.0 pg/min, p < 0.01; 1375.0 pg/min vs. 6348.4 pg/min, p < 0.01; and 1881.3 pg/min vs. 5437.8 pg/min, p < 0.01), and sGp130 (37.6 ng/min vs. 65.4 ng/min, p < 0.01; 39.2 ng/min vs. 80.6 ng/min, p < 0.01; 27.8 ng/min vs. 71.0 ng/min, p < 0.01) were significantly higher in peritoneal effluent from E-treated patients than from P-treated patients. Expression of IL6-R and Gp130 on individual leukocyte types isolated from PD effluent did not differ between E- and P-treated patients. The numbers of white blood cells present in effluent were higher in E-treated than in P-treated patients at all time points, but no significant differences were seen in the differential counts or in the number of exfoliated mesothelial cells. The IL-6 parameters in effluent from E-treated patients correlated with their plasma C-reactive protein. Despite the increased activation of the IL-6 system, no increase in peritoneal permeability as assessed by the dialysate-to-plasma ratio of creatinine in E effluent or by systemic inflammation was observed throughout the study. Higher levels of IL-6, its soluble receptors, and leukocyte expression were observed in E-treated than in P-treated patients, but this difference was not associated with alterations in peritoneal permeability or systemic inflammation during 1 year of follow-up. Leukocyte counts in effluent from E-treated patients were within the normal range previously reported for glucose solutions. This lack of clinical consequences may be a result of a parallel rise in sIL-6R and sGp130, which are known to control the biologic activity of IL-6. The utility of IL-6 level determinations, in isolation, for assessing the biocompatibility of PD solutions is questionable.

Bacterial Peritonitis due to Duodenal Perforation by a Fish Bone in an Elderly Peritoneal Dialysis Patient

The patient, a 77-year-old-man, began peritoneal dialysis (PD) in August 2005. In January 2009, he developed lower abdominal pain and cloudy PD effluent. A diagnosis of peritonitis was made and Escherichia coli was detected in cultures of the PD effluent. An abdominal computed tomography scan showed a fish bone in the duodenal wall. An upper gastrointestinal endoscopy was performed, and a 3-cm fish bone was removed. We thus recommend careful investigation with the possibility of enteric peritonitis from the intestinal tract when E. coli is detected in effluent cultures during PD.

MicroRNAs in peritoneal dialysis effluent are promising biomarkers for peritoneal fibrosis in peritoneal dialysis patients

Peritoneal fibrosis is a common complication of long-term peritoneal dialysis, and contributes to encapsulating peritoneal sclerosis and eventually peritoneal ultrafiltration failure, which restricts the wide application of peritoneal dialysis. Therefore, the prevention and treatment of peritoneal fibrosis is important to maintain peritoneal membrane integrity and prolong peritoneal dialysis treatment. Unfortunately, neither specific biomarkers nor effective therapies are available for peritoneal fibrosis in the clinic up to now. Emerging evidence suggests that extracellular microRNAs in body fluids are promising biomarkers for the diagnosis of diseases. microRNAs were reported to be involved in multiple fibrotic diseases and the serum levels of specific microRNAs were correlated with the degree of fibrosis. Moreover, extracellular microRNAs were found in peritoneal fluids and ascites. Based on these findings, here we present our hypothesis that extracellular microRNAs associated with peritoneal epithelial-to-mesenchymal transition and fibrosis could potentially be detected in peritoneal dialysis effluent, and serve as novel biomarkers for early assessment and diagnosis of peritoneal fibrosis.

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

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. 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. 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. 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.