Lipoxin A₄ and Aspirin-Triggered 15-Epi-Lipoxin A₄ Antagonize TNF-α-Stimulated Neutrophil-Enterocyte Interactions In Vitro and Attenuate TNF-α-Induced Chemokine Release and Colonocyte Apoptosis in Human Intestinal Mucosa Ex Vivo

Abstract

Lipoxins (LXs) are lipoxygenase-derived eicosanoids and putative endogenous braking signals for inflammation in the gastrointestinal tract and other organs. Aspirin triggers the production of 15-epimers during cell-cell interaction in a cytokine-primed milieu, and aspirin-triggered 15-epi-5(S),6(R),15(S)-trihydroxy-7,9,13-trans-11-cis-eicosatetraenoic acid (15-epi-LXA₄) may contribute to the bioactivity profile of this prototype nonsteroidal anti-inflammatory drug in vivo. We determined the effect of LXA₄, 15-(R/S)-methyl-11,12-dehydro-LXA₄ methyl ester (15-(R/S)-methyl-LXA₄), and stable analogs of LXA₄ on TNF-α-stimulated neutrophil-enterocyte interaction in vitro and TNF-α-stimulated chemokine release, changes in mucosal architecture, and enterocyte apoptosis in cytokine-activated intact human colonic mucosa ex vivo. LXA₄, 15-(R/S)-epi-LXA₄, and 16-phenoxy-11,12-dehydro-17,18,19,20-tetranor-LXA₄ methyl ester (16-phenoxy-LXA₄) inhibited TNF-α-stimulated neutrophil adherence to epithelial monolayers at nanomolar concentrations. In parallel experiments involving human colonic mucosa ex vivo, LXA₄potently attenuated TNF-α-stimulated release of the C-X-C chemokine IL-8, and the C-C chemokines monocyte-chemoattractant protein-1 (MCP-1) and RANTES. Exposure of strips of normal human colonic mucosa to TNF-α induced disruption of mucosa architecture and enhanced colonocyte apoptosis via a caspase-3-independent mechanism. Prior exposure of the mucosa strips to 15-(R/S)-methyl-LXA₄ attenuated TNF-α-stimulated colonocyte apoptosis and protected the mucosa against TNF-α-induced mucosal damage. In aggregate, our data demonstrate that lipoxins and aspirin-triggered 15-epi-LXA₄ are potent antagonists of TNF-α-mediated neutrophil-enterocyte interactions in vitro, attenuate TNF-α-triggered chemokine release and colonocyte apoptosis, and are protective against TNF-α-induced morphological disruption in human colonic strips ex vivo. Our observations further expand the anti-inflammatory profile of these lipoxygenase-derived eicosanoids and suggest new therapeutic approaches for the treatment of inflammatory bowel disease.