Intra-articular MIA is associated with referred mechanical hypersensitivity and increased release of CGRP from primary afferent fibres in the dorsal horn where second-order neuron activation is associated with a microglial response. Antagonism of CGRP receptor activation provides a therapeutic avenue for the treatment of pain in OA.

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 2ϩ -activated K ϩ (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␣,9␣-(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 Ͼ 10 M). 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 M, 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 Ͼ25 M, respectively) and no appreciable affinity (K i values Ͼ10 M) 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 proteincoupled 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.Upon release from cell membranes, arachidonic acid can be converted to a range of eicosanoids by three principal classes of enzymes: cyclooxygenases (COX), lipoxygenases, and cytochrome P450 monooxygenases. The P450 epoxygenases can introduce an epoxide to any of the four double bonds (5,6, 8,9, 11,12, and 14,15) of arachidonic acid, resulting in the generation of four distinct EET regioisomers (Capdevila et al., 1990). Each EET can be further metabolized to dihydroxyeicosatrienoic acids (DHETs) by soluble epoxide hydrolase (sEH), resulting in the generation of four corresponding DHET regioisomers.Since their discovery more than 25 years ago (Capdevila et Article, publication date, and citation information can be found at

Most conditions associated with ageing result from an age-related loss in the function of cells and tissues that maintain body homeostasis. In osteoarthritis (OA) patients, an inadequate response to stress or joint injury can lead to tissue destruction which can result in chronic pain. Here, we evaluated the development of monoiodoacetate (MIA)-induced OA in 3-, 15- and 22-month-old mice and assessed the pain-like behaviours and the spinal microglial changes associated with MIA administration. We observed that in aged mice, nocifensive behaviour was significantly attenuated in comparison to young adults despite similar knee joint pathology. Specifically referred mechanical allodynia associated with the MIA initial inflammatory phase (0–10 days) was significantly attenuated in 22-month-old mice. In contrast, the late phase of MIA-induced mechanical allodynia was comparable between age groups. Significant increase of microglia cell numbers was detected in 3, but not 15- and 22-month-old spinal cords. Furthermore, in the zymosan model of acute inflammation, mechanical allodynia was attenuated, and microglial response was less robust in 22 compared to 3-month-old mice. This study suggests that nocifensive responses to damaging stimuli are altered with advancing age and microglial response to peripheral damage is less robust.

No abstract

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 Ca 2+ -activated K + (BK Ca ) and vanilloid transient receptor potential (TRPV4) channels, the ability of 14,15 EET to induce vasodilation was investigated in BK Ca and TRPV4 homozygous knockout mouse isolated aorta. Results: Contrasting previous reports, neither BK Ca 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 (IC 50 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 (pA 2 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 K i of 3.2μM. In contrast, 14,15 EET showed weaker affinities for other prostanoid receptors including DP, FP, EP 1–4 and IP (K i s 6.1, 5.3, 42.6, 19.7, 13.2, 20.2 and >25μM, respectively) and no appreciable affinity (K i s >10μM) for 51 “non-prostanoid” receptors/ion channels. Consistent with these data, 14,15 EET failed to inhibit (K b >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.