Inhibition of 5-Lipoxygenase-Derived Leukotrienes and Hemiketals as a Novel Anti-Inflammatory Mechanism of Urolithins.

Abstract

Urolithins (Uro), gut microbial metabolites derived from ellagic acid (EA), reach significant concentrations in the human colon. Uro-A exerts anti-inflammatory activity in animal models of inflammatory bowel diseases (IBDs). It is hypothesized that Uro can modulate the biosynthesis of leukocyte-derived inflammatory eicosanoids from the 5-lipoxygenase (5-LOX), cyclooxygenase-2 (COX-2), and 5-LOX/COX-2 pathways, relevant in the onset and progression of IBDs, including 5-hydroxyeicosatetraenoic acids (5-HETEs), leukotriene-B4 (LTB4 ), prostaglandin E2 (PGE2 ), and hemiketals (HKE2 and HKD2 ). Leukocytes, obtained from six healthy donors, are stimulated with lipopolysaccharide and calcium ionophore A23187. Uro, at concentrations found in the human colon (1-15µm), decrease eicosanoid biosynthesis and COX-2 levels in the activated leukocytes. In contrast, EA and conjugated Uro (glucuronides and sulfates) are inactive. Uro-A and isourolithin-A reduce the formation of the 5-LOX/COX-2 products HKE2 and HKD2 through the COX-2 pathway (down-regulation of COX-2 and PGE2), whereas Uro-C reduces 5-HETE and LTB4 via inhibition of 5-LOX. The results show that physiologically relevant colonic Uro target eicosanoid biosynthetic pathways. The effect on HKs and LTB4 formation is unprecedented and expands the knowledge on anti-inflammatory mechanisms of Uro against IBDs.