The inflammasome as future therapeutic target: Development of inflammasome challenge tests

I are multiprotein complexes inducing pro-inflammatory cytokine production in response to infection and tissue injury. The end product of inflammasome activity is caspase-1-induced release of effector molecules such as IL-1 β and IL-18 from immune cells. Despite the common outcome, the variety of triggers that initiate inflammasome activity is large, and moreover eight different inflammasome subclasses have been described. The inflammasome is a potential therapeutic target for chronic inflammatory diseases such as chronic kidney disease and atherosclerosis. To test the effects of future inflammasometargeted therapies, an ‘inflammasome bioassay’ is highly warranted. The inflammasome’s capacity to sense widely divergent ligands, and the diversity in inflammasome subclasses, indicates that a single bioassay may not be sufficient to assess potential inflammasome-modulating effects of new compounds. Therefore, we developed a set of bioassays inducing inflammasome activity, so-called ‘inflammasome challenges’. Variables that were explored included matrix/cells (whole blood, PBMCs, THP1), triggers, incubation time (3-24 hours), dose-response relationship, single trigger versus immune cell priming followed by a second trigger, and inflammasome end products (IL-1β, IL-18). We successfully developed a set of inflammasome challenges, comprising inflammasome activation by LPS alone and by different triggers after LPS priming (extracellular ATP, aluminium hydroxide, cholesterol crystals, oligomeric β-amyloid). The short-term LPS inflammasome challenge was demonstrated to be sensitive to modulation of inflammasome activity, as assessed with a direct caspase-1 inhibitor. These inflammasome challenges can be applied in translational drug development as readout measures for inflammasome inhibition, and moreover will provide mechanistic insight in regulation of inflammasome activity.