NLRP-3 inflammasome activation can result in interleukin-1β (IL-1β) release and inflammatory cell death (pyroptosis). Caspase-1 is able to trigger both processes. However, other caspases, caspase-4, -5 and -8, are believed to initiate pyroptosis without affecting IL-1 secretion. In this study, we evaluated two cardiovascular risk groups, haemodialysis patients (HD) and patients with intact kidney function but high blood pressure (BP), to analyse the mechanisms driving pyroptosis. Twenty HD were age-, gender- and diabetes-matched to BP. We found a common pyroptotic pattern in both patient groups, at which pyroptosis rates but not IL-1 β levels were significantly higher in monocytes (HD vs. BP: p < 0.05), granulocytes (p < 0.01) and lymphocytes (p < 0.01) of HD patients. As uremic toxins are drivers of inflammation and regulated cell death, we applied a monocyte- and macrophage-like THP-1 model system to demonstrate that the protein-bound uremic toxin indoxyl sulfate (IS) is an inducer of pyroptotic cell death, particularly engaging caspase-4/caspase-5 and to a lesser extent caspase-8 and caspase-1. These data suggest that the uremic toxin IS can mediate pyroptosis in HD patients and the inflammatory caspase-4 and/or caspase-5 contribute to pyroptosis rates to a higher extent in comparison to caspase-1.
Keywords: caspase-1; caspase-4; haemodialysis; hypertension; immune cells; indoxyl sulfate; pyroptosis.