Mechanisms of NLRP3 inflammasome activation and its role in NSAID-induced enteropathy

Nonsteroidal anti-inflammatory drugs (NSAIDs) induce cytokines, including tumor necrosis factor-α and interleukins (ILs), in the small intestine via a Toll-like receptor 4 (TLR4)-dependent pathway, leading to intestinal ulceration. Activation of the inflammasome promotes pro-caspase-1 cleavage, leading to pro-IL-1β maturation. We examined the role of NLRP3 inflammasome in NSAID-induced enteropathy. Small intestinal damage developed 3 h after indomethacin administration, accompanied by increases in IL-1β and NLRP3 mRNA expression and mature caspase-1 and IL-1β levels. In vivo blocking of IL-1β using neutralizing antibodies attenuated indomethacin-induced damage, whereas exogenous IL-1β aggravated it. NLRP3(-/-) and caspase-1(-/-) mice exhibited resistance to the damage with reduction of mature IL-1β production. This resistance was abolished by exogenous IL-1β. TLR4 deficiency prevented intestinal damage and inhibited upregulation of NLRP3 and IL-1β mRNAs and maturation of pro-caspase-1 and pro-IL-1β, whereas TLR4 activation by its agonists exerted opposite effects. Apyrase, an adenosine triphosphate (ATP) scavenger, or Brilliant Blue G, a purinergic P2X7 receptor antagonist, inhibited the damage as well as caspase-1 activation and IL-1β processing, despite there being sufficient amounts of pro-IL-1β and NLRP3. These results suggest that NLRP3 inflammasome-derived IL-1β plays a crucial role in NSAID-induced enteropathy and that both TLR4- and P2X7-dependent pathways are required for NLRP3 inflammasome activation.