M. Auxiliadora Bajo

Epithelial to Mesenchymal Transition and Peritoneal Membrane Failure in Peritoneal Dialysis Patients: Pathologic Significance and Potential Therapeutic Interventions

Peritoneal dialysis (PD) is a form of renal replacement and is based on the use of the peritoneum as a semipermeable membrane across which ultrafiltration and diffusion take place. Nevertheless, continuous exposure to bioincompatible PD solutions and episodes of peritonitis or hemoperitoneum cause acute and chronic inflammation and injury to the peritoneal membrane, which progressively undergoes fibrosis and angiogenesis and, ultimately, ultrafiltration failure. The pathophysiologic mechanisms that are involved in peritoneal functional impairment have remained elusive. Resident fibroblasts and infiltrating inflammatory cells have been considered the main entities that are responsible for structural and functional alterations of the peritoneum. Recent findings, however, demonstrated that new fibroblastic cells may arise from local conversion of mesothelial cells (MC) by epithelial-to-mesenchymal transition (EMT) during the inflammatory and repair responses that are induced by PD and pointed to MC as protagonists of peritoneal membrane deterioration. Submesothelial myofibroblasts, which participate in inflammatory responses, extracellular matrix accumulation, and angiogenesis, can originate from activated resident fibroblasts and from MC through EMT. This heterogeneous origin of myofibroblasts reveals new pathogenic mechanisms and offers novel therapeutic possibilities. This article provides a comprehensive review of recent advances on understanding the mechanisms that are implicated in peritoneal structural alterations, which have allowed the identification of the EMT of MC as a potential therapeutic target of membrane failure.

Immunohistochemical characterization of fibroblast subpopulations in normal peritoneal tissue and in peritoneal dialysis-induced fibrosis

Peritoneal fibrosis is one of the most common morphological changes observed in continuous ambulatory peritoneal dialysis (CAPD) patients. Both resident fibroblasts and new fibroblast-like cells derived from the mesothelium by epithelial-to-mesenchymal transition are the main cells involved fibrogenesis. In order to establish markers of peritoneal impairment and pathogenic clues to explain the fibrogenic process, we conducted an immunohistochemical study focused on peritoneal fibroblasts. Parietal peritoneal biopsies were collected from four patient groups: normal controls (n=15), non-CAPD uremic patients (n=17), uremic patients on CAPD (n=27) and non-renal patients with inguinal hernia (n=12). To study myofibroblastic conversion of mesothelial cells, α-smooth muscle actin (SMA), desmin, cytokeratins and E-cadherin were analyzed. The expression of CD34 by fibroblasts was also analyzed. Fibroblasts from controls and non-CAPD uremic patients showed expression of CD34, but no myofibroblastic or mesothelial markers. The opposite pattern was present during CAPD-related fibrosis. Expression of cytokeratins and E-cadherin by fibroblast-like cells and α-SMA by mesothelial and stromal cells supports that mesothelial-to-myofibroblast transition occurs during CAPD. Loss of CD34 expression correlated with the degree of peritoneal fibrosis. The immunophenotype of fibroblasts varies during the progression of fibrosis. Myofibroblasts seem to derive from both activation of resident fibroblasts and local conversion of mesothelial cells.

Gastrointestinal and pancreatic function in peritoneal dialysis patients: their relationship with malnutrition and peritoneal membrane abnormalities

BACKGROUND Malnutrition is frequent in peritoneal dialysis (PD) patients, but the contribution of gastrointestinal (GI) dysfunction has not been well established. METHODS We studied GI function in 49 stable PD patients to ascertain its relationship with malnutrition. After an overload fat diet, fecal fat, sugar, starch and nitrogen, intestinal protein permeability (alpha(1)-antitrypsin fecal clearance [C-alpha(1)-AT]), fecal chymotrypsin (CT), GI hormones and gastrin, pepsinogen I and II, cholecystokinin (CCK), gastrin releasing peptide (GRP), and neuropeptide Y (NPY) were measured. Vasoactive intestinal polypeptide (VIP), substance P (SP), and tumor necrosis factor (TNF-alpha) and biochemical nutritional markers were evaluated. RESULTS All patients showed high fecal sugar. Elevated fecal nitrogen was found in 21 patients, 6 with high C-alpha(1)-AT. High fecal starch levels appeared in 21, fat in 20, and low fecal CT in 39 patients. These determinations showed inverse relation with nutritional markers. Increased fecal C-alpha(1)-AT values were associated with lower serum albumin. Fecal CT values showed a negative linear correlation with serum albumin and were inversely associated with retinol-binding protein, normalized protein nitrogen appearance, and serum iron. High plasma levels of pancreatic stimulating hormones were found: gastrin, CCK, and VIP. These levels were higher in patients with a worse pancreatic exocrine function. Higher values of other GI hormones, gastrin, pepsinogen I and II, CCK, GRP, and TNF-alpha. Normal concentrations of NPY, VIP, and PS were observed. CONCLUSION GI abnormalities (malabsorption, maldigestion, pancreatic dysfunction, and protein losing enteropathy) are present in an important number of PD patients. These features are negatively associated to nutrition.

Effect of Different Dialysis Modalities on Microinflammatory Status and Endothelial Damage

BACKGROUND AND OBJECTIVES We studied the relationship between microinflammation and endothelial damage in chronic kidney disease (CKD) patients on different dialysis modalities. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS Four groups of CKD stage 5 patients were studied: 1) 14 nondialysis CKD patients (CKD-NonD); 2) 15 hemodialysis patients (HD); 3) 12 peritoneal dialysis patients with residual renal function >1 ml/min (PD-RRF >1); and 4) 13 peritoneal dialysis patients with residual renal function <or=1 ml/min (PD-RRF <or=1). Ten healthy subjects served as controls. CD14(+)CD16(+) cells and apoptotic endothelial microparticles (EMPs) were measured by flow cytometry. Serum vascular endothelial growth factor (VEGF) was measured by ELISA. RESULTS CKD-NonD and HD patients had a higher percentage of CD14(+)CD16(+) monocytes than PD groups and controls. CD14(+)CD16(+) was similar in the PD groups, regardless of their RRF, and controls. The four uremic groups displayed a marked increase in apoptotic EMPs and VEGF compared with controls. Apoptotic EMPs and VEGF were significantly higher in HD patients than in CKD-NonD and both PD groups. However, there were no significant differences between CKD-NonD and the two PD groups. There was a correlation between CD14(+)CD16(+) and endothelial damage in CKD-NonD and HD patients, but not in PD and controls. CONCLUSIONS There was an increase in CD14(+)CD16(+) only in CKD-NonD and HD patients. In these patients, there was a relationship between increased CD14(+)CD16(+) and endothelial damage. These results strongly suggest that other factors unrelated to the microinflammatory status mediated by CD14(+)CD16(+) are promoting the endothelial damage in PD, regardless of their RRF.

Reacciones de hipersensibilidad a membranas sintéticas de hemodiálisis

Undergoing a haemodialysis (HD) session poses a certain risk of hypersensitivity adverse reactions as large quantities of blood are in contact with various synthetic materials. Hypersensitivity reactions to ethylene oxide and non-biocompatible membranes, such as cuprophane, have been described in HD. Cases of hypersensitivity with biocompatible membranes, such as polysulfone, and even polysulfone-polyvinylpyrrolidone, have also been reported. In this article we describe six cases of mostly early-stage hypersensitivity reactions to HD occurring in our department, characterised by malaise, desaturation, bronchospasm and arterial hypotension, with good response to the session’s temporary suspension and with reappearance in subsequent sessions that used a synthetic dialyser. No hypersensitivity reactions reappeared in successive observations when the sessions were carried out using a cellulose membrane.

Two-in-One Protocol: Simultaneous Small-Pore and Ultrasmall-Pore Peritoneal Transport Quantification

♦ Background: Reduced free water transport (FWT) through ultrasmall pores contributes to net ultrafiltration failure (UFF) and should be seen as a sign of more severe functional deterioration of the peritoneal membrane. The modified peritoneal equilibration test (PET), measuring the dip in dialysate Na concentration, estimates only FWT. Our aim was to simultaneously quantify small-solute transport, FWT, and small-pore ultrafiltration (SPUF) during a single PET procedure. ♦ Methods: We performed a 4-hour, 3.86% glucose PET, with additional measurement of ultrafiltration (UF) at 60 minutes, in 70 peritoneal dialysis patients (mean age: 50 ± 16 years; 61% women; PD vintage: 26 ± 23 months). We calculated the dialysate-to-plasma ratios (D/P) of creatinine and Na at 0 and 60 minutes, and the Na dip (DipD/PNa60′), the delta dialysate Na 0-60 (ΔDNa0-60), FWT, and SPUF. ♦ Results: Sodium sieving (as measured by ΔDNa0-60) correlated strongly with the corrected DipD/PNa60′ (r = 0.85, p < 0.0001) and the corrected FWT (r = 0.41, p = 0.005). Total UF showed better correlation with FWT than with indirect measurements of Na sieving (r = 0.46, p < 0.0001 for FWT; r = 0.360, p < 0.0001 for DipD/PNa60′). Corrected FWT fraction was 0.45 ± 0.16. A negative correlation was found between time on PD and both total UF and FWT (r = -0.253, p = 0.035 and r = -0.272, p = 0.023 respectively). The 11 patients (15.7%) diagnosed with UFF had lower FWT (89 mL vs 164 mL, p < 0.05) and higher D/P creatinine (0.75 vs 0.70, p < 0.05) than did the group with normal UF. The SPUF correlated positively with FWT in the normal UF group, but negatively in UFF patients (r = -0.709, p = 0.015). Among UFF patients on PD for a longer period, 44.4% had a FWT percentage below 45%. ♦ Conclusions: Measurement of FWT and SPUF is feasible by simultaneous quantification during a modified 3.86% glucose PET, and FWT is a decisive parameter for detecting causes of UFF in addition to increased effective capillary surface.

Mast Cell Quantification in Normal Peritoneum and During Peritoneal Dialysis Treatment

CONTEXT Mast cells (MCs) have been implicated in fibrogenesis, angiogenesis, and immunity against bacteria. These 3 mechanisms participate in the peritoneal pathology secondary to peritoneal dialysis (PD) treatment. Despite their potential relevance to PD-related pathology, few studies have focused on MCs. OBJECTIVE To evaluate possible variations in the number of MCs during PD treatment. DESIGN A quantitative study of tissue MCs in normal and pathologic peritoneum. Parietal peritoneal biopsies were collected from 4 groups: (1) normal controls (n = 9), (2) uremic non-PD patients (n = 16), (3) uremic patients on PD (n = 26), and (4) non-renal patients with inguinal hernia (n = 20). MCs were evaluated using immunohistochemistry for the detection of tryptase. The total number of cross sections of vessels per peritoneal field was examined in 22 of the 26 peritoneal biopsies of PD patients. RESULTS PD tissue samples showed fibrosis, mesothelial cell loss, and variable hyalinizing vasculopathy. The number of MCs was similar in normal controls and non-PD uremic patients (mean +/- SE: 7.13 +/- 0.67 and 7.74 +/- 0.74 MCs/mm2, respectively). Peritoneal dialysis patients showed a reduction (4 +/- 0.38 MCs/mm2, P < .001), whereas hernia sac samples showed an increase (10.59 +/- 3.48 MCs/mm2). MC reduction showed no correlation with time on dialysis, fibrosis, number of vessels, or previous episodes of peritonitis. CONCLUSIONS The peritoneum of patients receiving PD treatment shows a reduction of MCs. Despite such a reduction, fibrosis takes place, suggesting that MCs do not play a critical role in fibrosis genesis. Mast cell loss may be a contributory factor to peritonitis episodes in PD patients.

CAN EPS DEVELOPMENT BE AVOIDED WITH EARLY INTERVENTIONS? THE POTENTIAL ROLE OF TAMOXIFEN—A SINGLE-CENTER STUDY

♦ Background: Encapsulating peritoneal sclerosis (EPS) is a severe complication of peritoneal dialysis (PD). Identification of patients at high risk for EPS (“EPS-prone”) and delivery of appropriate interventions might prevent its development. Our aim was to evaluate the clinical characteristics and outcomes of all EPS and EPS-prone patients diagnosed at our PD unit. ♦ Methods: For a 30-year period representing our entire PD experience, we retrospectively identified all patients with EPS (diagnosed according to International Society for Peritoneal Dialysis criteria) and all patients defined as EPS-prone because they met at least 2 established criteria (severe peritonitis, PD vintage greater than 3 years, severe hemoperitoneum, overexposure to glucose, and acquired ultrafiltration failure). ♦ Results: Of 679 PD patients, we identified 20 with EPS, for an overall prevalence of 2.9%. Mean age at diagnosis was 50.2 ± 16.4 years, with a median PD time of 77.96 months (range: 44.36 - 102.7 months) and a median follow-up of 30.91 months (range: 4.6 - 68.75 months). Of patients with EPS, 10 (50%) received tamoxifen, 10 (50%) received parenteral nutrition, and 2 (10%) underwent adhesiolysis, with 25% mortality related to EPS. Another 14 patients were identified as EPS-prone. Median follow-up was 54.05 months (range: 11.9 - 87.04 months). All received tamoxifen, and 5 (36%) received corticosteroids; none progressed to full EPS. We observed no differences in baseline data between the groups, but the group with EPS had been on PD longer (84 ± 53 months vs 39 ± 20 months, p = 0.002) and had a higher cumulative number of days of peritoneal inflammation from peritonitis (17.2 ± 11.1 days vs 9.8 ± 7.9 days, p = 0.015). Overall mortality was similar in the groups. The incidence of EPS declined during our three decades of experience (5.6%, 3.9%, and 0.3%). ♦ Conclusions: Being a serious, life-threatening complication of PD, EPS requires high suspicion to allow for prompt diagnosis and treatment. Early detection of EPS-prone states and delivery of appropriate intervention might prevent EPS development. Tamoxifen seems to be a key strategy in prevention, but caution should be used in interpreting our results. Additional randomized controlled studies are needed.

THE INFLUENCE OF INITIAL PERITONEAL TRANSPORT CHARACTERISTICS, INFLAMMATION, AND HIGH GLUCOSE EXPOSURE ON PROGNOSIS FOR PERITONEAL MEMBRANE FUNCTION

♦ Background: Fast transport status, acquired with time on peritoneal dialysis (PD), is a pathology induced by peritoneal exposure to bioincompatible solutions. Fast transport has important clinical consequences and should be prevented. ♦ Objective: We analyzed the repercussions of initial peritoneal transport characteristics on the prognosis for peritoneal membrane function, and also whether the influence of peritonitis and high exposure to glucose are different according to the initial peritoneal transport characteristics or the moment when such events occur. ♦ Methods: The study included 275 peritoneal dialysis patients with at least 2 peritoneal function studies (at baseline and 1 year). Peritoneal kinetic studies were performed at baseline and annually. Those studies consist of a 4-hour dwell with glucose (1.5% during 1981 - 1990, and 2.27% during 1991 - 2002) to calculate the peritoneal mass transfer coefficients of urea and creatinine (milliliters per minute) using a previously described mathematical model. ♦ Results: Membrane prognosis and technique survival were independent of baseline transport characteristics. Fast transport and ultrafiltration (UF) failure are reversible conditions, provided that peritonitis and high glucose exposure are avoided during the early dialysis period. The first year on PD is a main determining factor for the membrane’s future, and the mass transfer coefficient of creatinine at year 1 is the best functional predictor of future PD history. After 5 years on dialysis, permeability frequently increases, and UF decreases. Icodextrin is associated with peritoneal protection. ♦ Conclusions: Peritoneal membrane prognosis is independent of baseline transport characteristics. Intrinsic fast transport and low UF are reversible conditions when peritonitis and high glucose exposure are avoided during the early dialysis period. Icodextrin helps in glucose avoidance and is associated with peritoneal protection.

Tissue distribution of hyalinazing vasculopathy lesions in peritoneal dialysis patients ☆: An autopsy study

Uremia is considered capable of inducing structural anomalies of the peritoneum, including hyalinizing vasculopathy (HV). To further elucidate the contribution of uremia to the severity of HV, we performed an autopsy study of peritoneal dialysis (PD) patients with severe peritoneal HV lesions. Uremia is a systemic condition and, if capable of inducing HV, it will be expected to be detected outside the peritoneum. Seven autopsy cases of PD patients showing prominent peritoneal HV lesions were selected. Histological slides from the peritoneum, abdominal organs, heart and pericardium, lungs, visceral pleura, and central nervous system were reviewed. Peritoneal lesions were intense in all patients with prominent HV, fibrosis, and a variable presence of inflammation, fibrin, and calcification. Except for focal HV lesions in the intestinal submucosa of one diabetic patient, HV lesions were limited to the peritoneal membrane. None of the other extraperitoneal tissues showed such lesions. In conclusion, extraperitoneal vessels of PD patients show no relevant HV lesions when compared to peritoneal ones. This observation suggests that PD-related factors are the main contributors to the severity of vasculopathy. Uremia may participate in the development of the lesion but it does not seem to be responsible for its severity.