Proteomic profile of mesothelial exosomes isolated from peritoneal dialysis effluent of children with focal segmental glomerulosclerosis

Peritoneal dialysis (PD) is the worldwide recognized preferred dialysis treatment for children affected by end-stage kidney disease (ESKD). However, due to the unphysiological composition of PD fluids, the peritoneal membrane (PM) of these patients may undergo structural and functional alterations, which may cause fibrosis. Several factors may accelerate this process and primary kidney disease may have a causative role. In particular, patients affected by steroid resistant primary focal segmental glomerulosclerosis, a rare glomerular disease leading to nephrotic syndrome and ESKD, seem more prone to develop peritoneal fibrosis. The mechanism causing this predisposition is still unrecognized. To better define this condition, we carried out, for the first time, a new comprehensive comparative proteomic mass spectrometry analysis of mesothelial exosomes from peritoneal dialysis effluent (PDE) of 6 pediatric patients with focal segmental glomerular sclerosis (FSGS) versus 6 patients affected by other primary renal diseases (No FSGS). Our omic study demonstrated that, despite the high overlap in the protein milieu between the two study groups, machine learning allowed to identify a core list of 40 proteins, with ANXA13 as most promising potential biomarker, to distinguish, in our patient population, peritoneal dialysis effluent exosomes of FSGS from No FSGS patients (with 100% accuracy). Additionally, the Weight Gene Co-expression Network Analysis algorithm identified 17 proteins, with PTP4A1 as the most statistically significant biomarker associated to PD vintage and decreased PM function. Altogether, our data suggest that mesothelial cells of FSGS patients are more prone to activate a pro-fibrotic machinery. The role of the proposed biomarkers in the PM pathology deserves further investigation. Our results need further investigations in a larger population to corroborate these findings and investigate a possible increased risk of PM loss of function or development of encapsulating peritoneal sclerosis in FSGS patients, thus to eventually carry out changes in PD treatment and management or implement new solutions.

Cefoperazone and sulbactam-related eosinophilic peritonitis: a case report and literature review

Eosinophilic peritonitis (EP) is a well-described complication of peritoneal dialysis that occurs because of an overreaction to constituents that are related to the catheter or tubing, peritoneal dialysate, pathogenic infection, or intraperitoneal drug use. EP caused by antibiotic use is rare. We present the case of a patient with cefoperazone and sulbactam-related EP. A 59-year-old woman who was undergoing peritoneal dialysis presented with peritonitis with abdominal pain and turbid peritoneal dialysis. Empiric intraperitoneal cefazolin in combination with cefoperazone and sulbactam was started after peritoneal dialysis effluent cultures were performed. Her peritonitis achieved remission in 2 days with the help of cephalosporin, but she developed EP 1 week later, when her dialysate eosinophil count peaked at 49% of the total dialysate white blood cells (absolute count, 110/mm3). We excluded other possible causes and speculated that cefoperazone and sulbactam was the probable cause of EP. The patient continued treatment with cefoperazone and sulbactam for 14 days. EP resolved within 48 hours after stopping cefoperazone and sulbactam. Thus, EP can be caused by cefoperazone and sulbactam use. Physicians should be able to distinguish antibiotic-related EP from refractory peritonitis to avoid technique failure.

FC 101PROTEOMIC PROFILE OF MESOTHELIAL EXOSOMES ISOLATED FROM PERITONEAL DIALYSIS EFFLUENT OF CHILDREN WITH FOCAL SEGMENTAL GLOMERULOSCLEROSIS

Background and Aims Peritoneal dialysis (PD) is the worldwide preferred dialysis treatment for children affected by end stage kidney disease. However, due to the unphysiological composition of PD fluids, the peritoneal mesothelium of these patients may undergo structural and functional alterations, which may cause fibrosis. Several factors may accelerate this process and primary kidney disease may have a causative role. In particular, patients affected by corticosteroid resistant focal segmental glomerulosclerosis (FSGS), a rare glomerular disease leading to nephrotic syndrome, seems more prone to develop peritoneal fibrosis. The mechanism causing this predisposition is still unrecognized. To better define this condition, we carried out, for the first time, a new comprehensive comparative proteomic mass spectrometry analysis of mesothelial exosomes from peritoneal dialysis effluent (PDE). Method We enrolled 12 paediatric patients on PD. Half of them affected by FSGS and the others affected by other disorders (NO FSGS). Exosomes from mesothelial peritoneal cells were isolated by centrifugation and, using a biotinylated antibody and streptavidin magnetic beads. Exosome size was determined by dynamic light scattering, and antigen profile of exosomes was assayed by western blot. Mass spectrometry data were analyzed by unsupervised hierarchical clustering using multidimensional scaling, in order to identify outliers and dissimilarity between samples. The normalized data were used to construct a co-expression network using the weighted gene co-expression network analysis (WGCNA). A weighted adjacency matrix was constructed, and transformed into a topological overlap matrix, which measures the network connectivity of all proteins. To identify the relationship between each module and each clinical trait, we used module eigengenes (MEs) and calculated the correlation between MEs and the clinical traits. To identify the hub proteins of modules that maximize the discrimination between FSGS and NO FSGS samples, we applied T-test, and non-linear support vector machine (SVM) learning. Finally, gene set enrichment analysis was done to build a functional proteins network based on their Gene Ontology (GO) annotations extracted from the Gene Ontology Consortium. Results Our omic study demonstrated that SVM allowed a complete distinction of the whole proteomic exosome mesothelial content of FSGS versus NO FSGS (100% accuracy). Out of the 2490 identified proteins, 40% (995) were involved in endothelial to mesenchymal transition /fibrosis and in the TGF-B pathway. The WGCNA analysis highlighted a total of 40 proteins were that maximize the discrimination between FSGS and NO FSGS patients (Figure 1A). Their expression profile is reported in a heatmap diagram (Figure 1B). Additionally, we performed GO enrichment analysis (Figure 2) and the algorithm identified that some of the discriminative proteins (TIMP1, CTHRC1, SPARC, CHMP4B, COL5A2, ANXA13, FNC2 and CENP-E) were also highly correlated to the peritoneal dialysis vintage, fibrosis, EMT and PM disease. Conclusion Our data demonstrated, for the first time, that mesothelial cells of FSGS are more prone to activate a pro-fibrotic machinery with exosomes having a primary role in this process. Moreover, they indicated that identified FSGS-associated element in mesothelial exosome protein could be employed as potential new biomarkers of mesothelial integrity. Finally, results highlighted that FSGS should be treated with more biocompatible dialysis solution, reduce the length of time on PD and personalize type and regimens of PD to minimize the risk of rapid loss of peritoneal membrane.

Variability in Culture-Negative Peritonitis Rates in Pediatric Peritoneal Dialysis Programs in the United States

Background and objectivesInternational guidelines suggest a target culture-negative peritonitis rate of <15% among patients receiving long-term peritoneal dialysis. Through a pediatric multicenter dialysis collaborative, we identified variable rates of culture-negative peritonitis among participating centers. We sought to evaluate whether specific practices are associated with the variability in culture-negative rates between low– and high–culture-negative rate centers.Design, setting, participants, & measurementsThirty-two pediatric dialysis centers within the Standardizing Care to Improve Outcomes in Pediatric End Stage Renal Disease (SCOPE) collaborative contributed prospective peritonitis data between October 1, 2011 and March 30, 2017. Clinical practice and patient characteristics were compared between centers with a ≤20% rate of culture-negative peritonitis (low-rate centers) and centers with a rate >20% (high-rate centers). In addition, centers completed a survey focused on center-specific peritoneal dialysis effluent culture techniques.ResultsDuring the 5.5 years of observation, 1113 patients had 1301 catheters placed, totaling 19,025 patient months. There were 620 episodes of peritonitis in 378 patients with 411 catheters; cultures were negative in 165 (27%) peritonitis episodes from 125 (33%) patients and 128 (31%) catheters. Low-rate centers more frequently placed catheters with a downward-facing exit site and two cuffs (P<0.001), whereas high-rate centers had more patients perform dialysis themselves without the assistance of an adult care provider (P<0.001). The survey demonstrated that peritoneal dialysis effluent culture techniques were highly variable across centers. No consistent practice or technique helped to differentiate low- and high-rate centers.ConclusionsCulture-negative peritonitis is a frequent complication of maintenance peritoneal dialysis in children. Despite published recommendations for dialysis effluent collection and culture methods, great variability in culture techniques and procedures exists among individual dialysis programs and respective laboratory processes.

Rare cause of Peritoneal Dialysis–Related Peritonitis in a child: Abiotrophi defectiva

Background: Abiotrophia defective is a frequently reported clinical infection; however, it is rarely implicated in peritoneal dialysis–related infections in peritonitis patients. Case presentation: We report a rare case of peritoneal dialysis–related peritonitis caused by Abiotrophia defective in a child. A 12-year-old Chinese child with a history of chronic kidney disease stage 5 presented with abdominal pain and vomiting. She had a cell count of 567.10 × 106/L cells, of which 84% were polymorphonuclear. Peritoneal dialysis effluent was cultured using standard protocols, and the organism was identified as Abiotrophia defective by matrix-assisted laser desorption ionization-time of flight mass spectrometry. The patient responded well to ceftazidime and vancomycin, and ten days later, peritoneal dialysis effluent culture and white cell counts were negative. Conclusion: This is the first case of Abiotrophia defective peritoneal dialysis-Peritonitis in a chronic kidney disease stage 5 child reported in Asia. This infection may be more prevalent, but has been overlooked until the recent introduction of techniques such as matrix-assisted laser desorption ionization-time of flight mass spectrometry and 16S RNA sequencing. Clinicians and microbiologists should pay greater attention to this organism in patients with peritoneal dialysis -Peritonitis, as its pathogenicity is often underestimated.