17,18-Epoxyeicosatetraenoic Acid Targets PPARγ and p38 Mitogen-Activated Protein Kinase to Mediate Its Anti-inflammatory Effects in the Lung

This study sought to assess putative pathways involved in the anti-inflammatory effects of 17,18-epoxyeicosatetraenoic acid (17,18-EpETE), as measured by a decrease in the contractile reactivity and Ca2+ sensitivity of TNF-alpha-pretreated human bronchi. Tension measurements performed in the presence of 12-(3-adamantan-1-yl-ureido)-dodecanoic acid (AUDA), a soluble epoxide hydrolase (sEH)-specific inhibitor, demonstrated that 17,18-EpETE reduced the reactivity of TNF-alpha-pretreated tissues. The overexpression of sEH detected in patients with asthma and TNF-alpha-treated bronchi contributed to the maintenance of hyperresponsiveness in our models, which involved intracellular proinflammatory cascades. The inhibition of peroxisome proliferator-activated receptor (PPAR)gamma by GW9662 abolished 17,18-EpETE + AUDA-mediated anti-inflammatory effects by inducing I kappa B alpha degradation and cytokine synthesis, indicating that PPAR gamma is a molecular target of epoxy-eicosanoids. Western blot analysis revealed that 17,18-EpETE pretreatment reversed the phosphorylation of p38 mitogen-activated protein kinase (p38-MAPK) induced by TNF-alpha in human bronchi. The Ca2+ sensitivity of human bronchial explants was also quantified on beta-escin permeabilized preparations. The presence of SB203580, a p38-MAPK inhibitor, reversed the effect induced by epoxy-eicosanoid in the presence of AUDA on TNF-alpha-triggered Ca2+ hypersensitivity by increasing the phosphorylation level of PKC Potentiated Inhibitor Protein-17 (CPI-17) regulatory protein. Moreover, PPAR gamma ligands, such as rosiglitazone and 17,18-EpETE, decreased the expression of CPI-17, both at the mRNA and protein levels, whereas this effect was countered by GW9662 treatment in TNF-alpha-treated bronchi. These results demonstrate that 17,18-EpETE is a potent regulator of human lung inflammation and concomitant hyperresponsiveness, and may represent a valuable asset against critical inflammatory bronchial disorder.