The PDE-thiolome as an indicator of Peritoneal Membrane vulnerability

Abstract

Background and Aims: Peritoneal membrane health is crucial for peritoneal dialysis effectiveness [1]. Strategies to overcome peritoneal membrane (PM) injury and fibrosis remain an unmet need in PD, due to many factors [2]. Among these is the lack of early indicators to identify patients at higher risk before structural damage becomes irreversible. While oxidative stress is recognized as an early trigger in fibrotic processes [3], most studies have focused on oxygen radical species. Here, we hypothesize that non-radical pro-oxidants, namely oxidized thiols, e.g. cysteine, might promote PM fibrosis. Therefore, this study aims to assess the endogenous thiol-profile, which we define as the "thiolome" [4], in peritoneal dialysis effluent (PDE) that associates with PM fibrosis. PDE was used as a proxy of the membrane´s microenvironment.

Methods: We conducted a cross-sectional study in incident PD patients at ULSLO (Ethics: NMS 50/2019; ULSLO 2024-63). PM biopsies were obtained during catheter insertion, and sub-mesothelial thickness (STM) was measured. Serum α-Klotho was quantified using ELISA, with levels below 742 pg/mL used as a proxy for fibrosis risk [1]. Cysteine (Cys), glutathione (GSH), and cysteinylglycine (CysGly) were measured in PDE via high-performance liquid chromatography with fluorescence detection [4]. Each thiol was assessed in three forms, reduced, free oxidized, and protein-bound, with total and free total levels calculated. Univariate analyses were performed, and principal component analysis (PCA) was applied to evaluate overall thiol profile patterns.

Results: A total of 41 patients were included (mean age 55 ± 2 years; 30% female), with 16 (39%) presenting histological signs of fibrosis. The most variable thiol fractions (>50%) included total GSH, GSSX, and protein-bound forms of Cys, GSH, and CysGly. PCA did not distinguish fibrotic from non-fibrotic profiles and showed no clear association with STM. However, univariate analysis revealed a positive correlation between total Cys and STM (r = 0.33, p < 0.05). Additionally, patients with serum α-Klotho <742 pg/mL had significantly higher levels of total and oxidized Cys (p = 0.03 and 0.02) and CysGly (p = 0.03 and 0.01).

Conclusion: Our data suggests a link between lower α-Klotho levels, disrupted thiol metabolism, and PM fibrosis. These findings support the potential of Cys and CysGly as putative early markers for identifying patients at risk of membrane injury.