Eicosanoids produced from the conversion of arachidonic acid at the cell membrane have been shown to participate in host defense in the gastrointestinal system
[26]. While the role of prostaglandins has been extensively studied in the pathogenesis of inflammatory bowel disease (IBD ), recent work has demonstrated that lipoxygenase products might play a role in autoimmune-related gut inflammation
[26][27].
Alox15 and its encoded 12-LOX is expressed in the intestinal epithelium
[28]. Indeed, high levels of 12-HETE have been found in colonic mucosal tissue from patients with inflammatory bowel disease by thin-layer chromatography and high-performance liquid chromatography
[27][29]. The neutrophil chemoattractant hepoxilin A3 (HXA
3) is a downstream metabolite of 12-HPETE, and HXA
3 functions in polymorphonuclear leukocyte (PMN) recruitment to sites of mucosal inflammation. Using a model that has been described to study basolateral to apical PMN transepithelial migration
[30], it has been demonstrated that HXA
3 promotes the final step of PMN recruitment to sites of inflammation by establishing a gradient across the epithelial tight junction. Inhibition of 12-LOXs by treatment with the small molecule inhibitor baicalein lead to blockage of HXA
3 generation and inhibition of PMN transmigration stimulated by
Salmonella typhimurium infection
[31]. Furthermore, 12-LOXs have been shown to play a pathophysiological role in an animal model of IBD. In a dextran sodium sulfate (DSS) induced colitis model that was restricted to female mice,
Alox15−/− mice were robustly protected from colitis and weight loss by a mechanism involving sustained epithelial tight junction protein expression
[32]. Interestingly, expression of
Alox15 was not seen in healthy mouse colon but was significantly upregulated in the inflamed colon after 8 days of DSS induced colitis. Expression was restricted to the stromal cells, which represent invading leukocytes. Inflammatory marker analysis revealed that
Alox15 deficient mice exhibited less colonic macrophage infiltration assessed by F4/80 staining and mRNA analysis of distal colon revealed increased iNOS and TNF-α expression. Colon permeability studies revealed that
Alox15 deficient mice had significantly reduced permeability and higher functional ZO-1 expression compared to the DSS-treated control mice.
Thus, products of 12-LOXs appear to play a dual role in gut inflammatory disease by affecting gut epithelial cell integrity and by promoting polymorphonuclear leukocyte migration.