Abstract 5256: Identification of a Novel Epoxyeicosatrienoic Acid (EET) Receptor: EETs Function as Selective, Endogenous Thromboxane Receptor Antagonists
Introduction: Epoxyeicosatrienoic acids (EETs) are cytochrome P450 metabolites of arachidonic acid which elicit vasodilatory, anti-inflammatory and anti-thrombotic effects. Interestingly, however, the mechanism by which EETs function remains unclear and was therefore investigated in the present study. Since previous reports suggest EET mediated vasodilation is dependent on large-conductance Ca2+-activated K+ (BKCa) and vanilloid transient receptor potential (TRPV4) channels, the ability of 14,15 EET to induce vasodilation was investigated in BKCa and TRPV4 homozygous knockout mouse isolated aorta.
Results: Contrasting previous reports, neither BKCa nor TRPV4 gene deletion significantly altered the potency of 14,15 EET-induced reversal of tone established with the thromboxane receptor [TP] agonist U46619. Surprisingly, whereas 14,15 EET reversed U46619-contractile tone of rat isolated aorta (IC50 1.2μM), the eicosanoid had no effect on either phenylephrine- or endothelin-1-contractile tone. The remaining three EET regioisomers (5,6 EET, 8,9 EET, 11,12 EET) acted similarly, suggesting EETs might function as TP antagonists. Consistent with competitive TP antagonism, 14,15 EET pretreatment (1–10μM) inhibited U46619-induced vasoconstriction in a concentration-dependent manner (pA2 5.9). TP antagonism was observed in mouse and dog isolated arteries and rat tertiary bronchi, indicating that the effects are not specific to one species or tissue. Accordant with the functional potency at TP, 14,15 EET bound to recombinant human TP with a Ki of 3.2μM. In contrast, 14,15 EET showed weaker affinities for other prostanoid receptors including DP, FP, EP1–4 and IP (Kis 6.1, 5.3, 42.6, 19.7, 13.2, 20.2 and >25μM, respectively) and no appreciable affinity (Kis >10μM) for 51 “non-prostanoid” receptors/ion channels. Consistent with these data, 14,15 EET failed to inhibit (Kb>10μM) “non-TP” prostanoid receptor mediated function in multiple cell/tissue-based assays.
Conclusions: EETs function as novel “endogenous” G-protein-coupled receptor competitive antagonists, inducing vasodilation via direct TP inhibition. Such observations might help develop novel strategies targeting the EET pathway for treatment of cardiovascular disease.