MO720: Elevated Dialysate IL-6 Concentrations are Prospectively Associated with Impaired TLR-Stimulated Cytokine Release from Peritoneal Cells—a Longitudinal Cohort Study
Authors: Herzog Rebecca , Daniel-Fischer Lisa , Eibensteiner Fabian , Aufricht Christoph , Vychytil Andreas , Kratochwill Klaus 
Published: May 2022

Abstract

BACKGROUND AND AIMS
Infectious complications and peritoneal inflammation occurring in a significant proportion of PD patients lead to progressive peritoneal membrane injury and account for most peritoneal dialysis (PD) technique failures. Reduced peritoneal immune-competence, caused by the continuous exposure to PD fluids, has been described as a therapy-related pathomechanism. We therefore hypothesized a relationship between dialysate interleukin 6 (IL-6) concentrations and peritoneal host defense. We established an ex vivo stimulation assay to test host defense mechanisms in only 9 mL of PD effluent. The aim of this study was to analyse basal inflammation and immune-competence in the PD population at routine conditions to evaluate the assay as surrogate parameter of immune competence and linking it to PD vintage and clinical outcome parameters.

METHOD
We prospectively analysed 195 serial routine peritoneal equilibration tests (PETs) of 123 stable PD patients treated exclusively with low-GDP, multi-chamber PD fluids during the glucose dwells and compared the data to routine follow-up clinical data. The cohort represents 76% of all eligible PD patients treated between April 2013 and September 2020 at the local Department of Nephrology. The study was approved by the local ethics committee and was conducted in accordance with the Declaration of Helsinki. All participants underwent a standardized 4-h PET with 3.86% glucose PDF as routine follow-up to test peritoneal membrane transport function, with an additional ex vivo cell stimulation protocol. PD effluent samples were obtained at the 1- and 4-h PET timepoints and immediately processed. Effluent samples were collected directly from the drainage bags into standard 9 mL additive-free sample tubes. For ex vivo stimulation, 100 ng/mL toll-like receptor (TLR) 4 agonist LPS and TLR2 agonist Pam3Cys were added to the effluent in the 9 mL collection tubes in duplicates and incubated at 37°C for 24 h. Unstimulated samples kept in parallel were used as controls. IL-6 concentrations were measured with ELISA in the supernatants.

RESULTS
Patients were stratified into two cohorts (incident and prevalent) at 120 days of continuous PD therapy. The cohorts were statistically indistinguishable except for stratification-specific variables. During a total follow-up period of 2499 patient-months, 55 patients underwent repeated PETs. Ex vivo stimulation of peritoneal cells significantly increased the IL-6 release 20-fold compared to unstimulated controls and resulted in a dwell-time dependent increase, with a significant lower cytokine released at the 1 h PET timepoint. To assess local inflammation, IL-6 concentrations in PD effluent of the 4 h PET were analysed. PD effluent IL-6 concentrations from the entire study cohort or from incident and prevalent patient subcohorts correlated neither with patient characteristics, RRF, disease background (including prior peritonitis) nor with time on PD. Effluent IL-6 concentrations correlated significantly with markers of systemic inflammation, serum CRP and albumin, with PSTR and with peritoneal protein loss. Interestingly, effluent IL-6 concentrations also had predictive value for risk of a subsequent peritonitis episode during follow-up. Effluent IL-6 levels were, in contrast, negatively correlated with ex vivo–stimulated IL-6 release from PD effluent cells, most remarkably in PD patients with history of prior peritonitis.

CONCLUSION
This longitudinal study provides the first direct evidence in PD patients of a correlation between peritoneal inflammation and impaired peritoneal immune cell function, likely driving infectious complications. Our study results suggest a mechanistic link between peritoneal inflammation and host defense that may foster innovative therapeutic approaches to improve clinical outcomes of chronic PD.