Dysregulated fluid homeostasis is frequent in haemodialysis (HD) patients and is linked to inflammation which may be elicited by endotoxemia. The impact of hypervolemia on immune cells has not been studied in detail. Therefore, we analysed the hypervolemic activation of peripheral blood mononuclear cells (PBMCs) in HD with special focus on the NLRP3 inflammasome response. First, 45 HD were included in the observational study. Immune parameters including cell counts, caspase-1, oxidative stress, cytokine gene expression and serum analysis (IL-1ß, IL-6, IL-10) were all measured at two time points. Fluid status was evaluated by electrical bioimpedance vector analysis, defining hypervolemia (H) as >75 vector percentile. Then, 17 patients were classified as hypervolemic (H-HD), 19 as normovolemic (N-HD) and 9 failed to meet the inclusion criteria. Monocytes were elevated and lymphocytes were decreased by hypervolemia. NLRP3 inflammasome components, caspase-1 and IL-1ß expression were not statistically different between the two groups. Serum IL-6 levels were significantly elevated in H-HD. IL-10 mRNA transcripts were elevated by 2-fold in H-HD but were not efficiently translated. We conclude that the NLRP3 inflammasome is not activated by hypervolemia thus refuting the thesis that endotoxemia may be a main driver for inflammation in H-HD. Nevertheless, inflammation is generally higher in H-HD compared to N-HD patients and is not sufficiently balanced by anti-inflammatory mechanisms.

Background and Aims Hypervolemia is frequent in haemodialysis (HD) patients and is linked to inflammation, which may be further enhanced by endotoxemia. The impact of hypervolemia on immune cells i.e. a main monocytic defence mechanism - the NLRP3 inflammasome, has not been studied in detail. Therefore, we hypothesized that endotoxinemia putatively present in hyper- but normovolemic patients can trigger the activation of caspase-1 and thus increasing IL-1ß secretion. Method 45 HD patients were included in the observational study, measuring immune parameters (cell counts, caspase-1, oxidative stress, cytokine gene expression and serum analysis (IL-1ß) at two time points (directly after dialysis BS1) and three days later after the long dialysis free interval (BS2). Fluid status was evaluated by electrical bioimpedance vector analysis, defining hypervolemia (H) as >75 vector percentile. Data collected after the long dialysis interval is presented in this paper. Results Seventeen patients were classified as hyper-(H-HD), 19 as normovolemic (N-HD), 9 failed to meet the inclusion criteria. Monocytes were elevated and lymphocytes decreased by hypervolemia. Oxidative stress was slightly elevated in H-HD. However, neither caspase-1 frequency (H: 77.9±4.2% vs. 79.2±6.9%, p=0.916) nor caspase-1 expression (MFI, H: 42.8±13.3 vs. 43.6±17.1, p=0.880) were different. In vitro stimulation of PBMC’s by specific NLRP3 inflammasome stimulation significantly increased caspase activity in both cohorts to the same extent (89.9±22.6 vs. 88.0±23.3, p=0.900). As a result of it both IL-1ß mRNA expression (1.7±1.9 vs N: 1.1±0.8, 0.306) and serum IL-1ß (pg/ml) did not differ between the groups (H: 1.99±0.2 vs. N: 1.98±0.6, p<0.135). Conclusion The NLRP3 inflammasome is not activated thus refuting the hypothesis that endotoxemia is a main driver for inflammation in H-HD.