Epoxyeicosatrienoic acids function as selective, endogenous antagonists of native thromboxane receptors: identification of a novel mechanism of vasodilation.
Epoxy- and dihydroxy-eicosatrienoic acids (EETs and DHETs) are vasoactive cytochrome P450 metabolites of arachidonic acid. Interestingly, however, the mechanism(s) by which EETs/DHETs mediate smooth muscle relaxation remains unclear. In contrast to previous reports, where dilation was purportedly large-conductance Ca(2+)-activated K(+) (BK(Ca)) and/or transient receptor potential cation channel, subfamily V, member 4 (TRPV4) channel-mediated, 14,15-EET-induced vasodilation [reversal of contractile tone established with the thromboxane receptor (TP) agonist 15-hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic acid (U-46619)] was unaltered in BK(Ca) and TRPV4 knockout mouse isolated aortae compared with wild-type controls, indicating a significant BK(Ca)/TRPV4-resistant mechanism. Whereas all EET and DHET regioisomers reversed U-46619 contraction in rat aortae and mouse mesenteric resistance arteries, these eicosanoids failed to alter phenylephrine-induced contraction, suggesting that they mediated dilation via a "TP-selective" mechanism. Competitive TP antagonism was also observed in nonvascular tissue, including rat fundus and tertiary bronchus, indicating that the effect is not specific to blood vessels. Such effects were TP-selective because 14,15-EET failed to inhibit "non-TP" prostanoid receptor-mediated function in multiple cell/tissue-based assays (K(b) > 10 microM). In accordance, 14,15-EET inhibited specific [(3)H]7-(3-((2-((phenylamino)carbonyl)hydrazino)-methyl)-7-oxabicyclo(2.2.1)hept-2-yl)-5-heptenoic acid (SQ-29548) binding to human recombinant TP receptor, with a K(i) value of 3.2 microM, and it showed weaker affinity for non-TP prostanoid receptors, including DP, FP, EP(1-4), and IP receptors (K(i) values of 6.1, 5.3, 42.6, 19.7, 13.2, 20.2, and >25 microM, respectively) and no appreciable affinity (K(i) values >10 microM) for a diverse array of pharmacologically distinct receptors, including the leukotriene receptors Cys-LT(1/2) and BLT(1). As such, EETs/DHETs represent a unique class of "endogenous" G protein-coupled receptor competitive antagonists, inducing vasodilation via direct TP inhibition. Thus, EETs/DHETs represent novel autoregulatory agents, directly modulating the actions of cyclooxygenase-derived eicosanoids following arachidonic acid mobilization.
Behm
David J
DJ
Metabolic Pathways Center of Excellence for Drug Discovery, GlaxoSmithKline, King of Prussia, Pennsylvania 19406-0939, USA. david.j.behm@gsk.com
Ogbonna
Andrea
A
Wu
Charlene
C
Burns-Kurtis
Cynthia L
CL
Douglas
Stephen A
SA
D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid / Q000494:pharmacology; D015126:8,11,14-Eicosatrienoic Acid / Q000031:analogs & derivatives / Q000494:pharmacology*; D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects / Q000502:physiology*; D001095:Arachidonic Acids / Q000494:pharmacology; D006168:Guinea Pigs; D006893:Hydroxyeicosatetraenoic Acids / Q000494:pharmacology; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D051381:Rats; D017207:Rats, Sprague-Dawley; D017482:Receptors, Thromboxane / Q000819:agonists / Q000187:drug effects / Q000502:physiology; D013152:Splanchnic Circulation / Q000187:drug effects / Q000502:physiology; D050916:TRPV Cation Channels / Q000172:deficiency / Q000235:genetics / Q000502:physiology; D014132:Trachea / Q000187:drug effects / Q000502:physiology; D014655:Vascular Resistance / Q000187:drug effects; D014661:Vasoconstriction / Q000187:drug effects / Q000502:physiology; D014664:Vasodilation / Q000187:drug effects / Q000502:physiology*
D001095:Arachidonic Acids; D006893:Hydroxyeicosatetraenoic Acids; D017482:Receptors, Thromboxane; D050916:TRPV Cation Channels; C486576:Trpv4 protein, mouse; D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; C046782:14,15-epoxy-5,8,11-eicosatrienoic acid; D015126:8,11,14-Eicosatrienoic Acid