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

Abstract

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.

Isoliquiritigenin Ameliorates Indomethacin-Induced Small Intestinal Damage by Inhibiting NOD-Like Receptor Family, Pyrin Domain-Containing 3 Inflammasome Activation

“…Our previous study revealed inflammasome activation in inflammatory cells, including macrophages, during the development of NSAID-induced small intestinal damage [7]. In addition, it has been reported that isoliquiritigenin is rapidly metabolized and only a small amount is retained in the small intestine [17].…”

“…This signal promotes inflammasome assembly, leading to pro-caspase-1 and pro-IL-1β maturation [14]. We previously demonstrated that the lipopolysaccharide/TLR-4 axis mediated the first signal and the ATP/P2X 7 receptor axis mediated the second signal in NSAID-induced enteropathy [7]. Previous in vitro studies have demonstrated that isoliquiritigenin prevents TLR-4-mediated nuclear factor-κB activation by inhibiting homodimerization of TLR-4 [15], in addition to attenuating ASC oligomerization [10].…”

“…Isoliquiritigenin prevented pro-caspase-1 and pro-IL-1β maturation, and protection against indomethacin-induced small intestinal damage was completely abolished by the administration of exogenous IL-1β. We previously reported that the NLRP3 inflammasome was activated during the development of NSAID-induced enteropathy, and that NLRP3 inflammasome-derived IL-1β played a crucial role in inducing intestinal damage [7]. Together with the findings that caspase-1 –/– and NLRP3 –/– mice exhibited less severe damage compared with wild-type mice and isoliquiritigenin did not further inhibit small intestinal damage in these deficient mice, these data strongly suggest that isoliquiritigenin mediates protection against indomethacin-induced small intestinal damage by inhibiting NLRP3 inflammasome activation (Fig.…”

“…IL-1β is a major proinflammatory cytokine that possesses similar biological activity to TNF-α. Because NLRP3 inflammasome-derived IL-1β plays a key role in the pathogenesis of NSAID-induced small intestinal damage in mice [7], drugs inhibiting NLRP3 inflammasome activation could be potential therapeutic candidates for treatment of severe enteropathy. We focused on a flavonoid derived from the roots of Glycyrrhiza species, isoliquiritigenin, which is relatively inexpensive and safe.…”

“…The inflammasome is composed of 3 proteins: pattern recognition receptors such as NOD-like receptor (NLR) family proteins and pyrin and HIN domain – containing protein family proteins; an adaptor protein, apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC); and pro-caspase-1. Recently, we demonstrated that the NLR family, pyrin domain-containing 3 (NLRP3) inflammasome was specifically activated in mice with NSAID-induced damage to the small intestine, and damage was mediated by IL-1β derived from the NLRP3 inflammasome [7]. These data suggest that drug candidates targeting NLRP3 inflammasome activation could potentially be used to treat NSAID-induced enteropathy.…”