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-1ß 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-1ß and NLRP3 mRNA expression and mature caspase-1 and IL-1ß levels. In vivo blocking of IL-1ß using neutralizing antibodies attenuated indomethacin-induced damage, whereas exogenous IL-1ß aggravated it. NLRP3(-/-) and caspase-1(-/-) mice exhibited resistance to the damage with reduction of mature IL-1ß production. This resistance was abolished by exogenous IL-1ß. TLR4 deficiency prevented intestinal damage and inhibited upregulation of NLRP3 and IL-1ß mRNAs and maturation of pro-caspase-1 and pro-IL-1ß, 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-1ß processing, despite there being sufficient amounts of pro-IL-1ß and NLRP3. These results suggest that NLRP3 inflammasome-derived IL-1ß plays a crucial role in NSAID-induced enteropathy and that both TLR4- and P2X7-dependent pathways are required for NLRP3 inflammasome activation.
Subject(s)
Caspase 1/metabolism , Inflammasomes/metabolism , Interleukin-1beta/metabolism , Intestine, Small/immunology , NLR Family, Pyrin Domain-Containing 3 Protein/metabolism , Toll-Like Receptor 4/metabolism , Ulcer/immunology , Animals , Anti-Inflammatory Agents, Non-Steroidal , Caspase 1/genetics , Cells, Cultured , Disease Models, Animal , Humans , Indomethacin , Interleukin-1beta/genetics , Mice , Mice, Inbred C57BL , Mice, Knockout , NLR Family, Pyrin Domain-Containing 3 Protein/genetics , Receptors, Purinergic P2X7/metabolism , Signal Transduction , Toll-Like Receptor 4/genetics , Ulcer/chemically inducedABSTRACT
Small intestinal injury caused by non-steroidal anti-inflammatory drugs (NSAIDs) or aspirin is an epoch making topic in clinical field with the aid of new devices, capsule endoscopy and double balloon enteroscopy to look at small intestine directly. However, the injury has been reported in animals since more than 40 years ago. Proposed mechanisms are impairment of mucosal defense through inhibition of cyclooxygenase (COX) resulting in deficiency of prostaglandins, and mitochondrial disorder. Possible aggressive factors are NSAIDs/aspirin themselves, bile, and enterobacteria. Translocation of enterobacteria through the mucosa impaired integrity may be the first step of the injury. Bacterial lipopolysaccharides stimulate toll-like receptor-4 in macrophages, which increases proinflammatory cytokines through MyD88 signaling pathway. Finally neutrophils are activated and the small intestinal mucosa is injured with the attacks of NSAIDs/aspirin themselves, bile, and proteolytic enzymes and active oxygen species released by neutrophils. Candidates of treatment tools are prostaglandin derivatives, mucoprotective drugs, probiotics, and mitochondrial protective drugs such as metronidazole and cyclosporin A. Further clinical studies are needed to elucidate the effect in humans.