Arachidonic acid metabolites induce TRPV1‐mediated inflammation

Abstract

IntroductionTransient receptor potential cation channel subfamily V member 1 (TRPV1) is a non‐specific cation channel localised to sensory C‐fibres. Opening of the TRPV1 channel leads to cell membrane depolarization, resulting in the release of neuropeptides including calcitonin gene‐related peptide and substance P (SP). These neuropeptides play an important role in vasodilatation, vascular leakage and cell migration during acute inflammatory responses [1, 2]. Endogenous activators of TRPV1 are thought to include the arachidonic acid (AA) metabolites 12‐hydroperoxyeicosatetraenoyl acid (12‐HpETE) and 20‐hydroxyeicosatetraenoic acid (20‐HETE) [3]. However, whether these lipids underlie TRPV1 activation in inflammatory responses is unknown.AimTo investigate the role of TRPV1 in the acute inflammatory response and to determine whether arachidonic acid metabolites might play a role in its endogenous activation.MethodsLipopolysaccharide (LPS, 100 μg Ecoli 055:B5), zymosan activated serum (ZAS) (50%), SP (1 nmol) or AA (30, 100 and 300 nmol)‐induced skin oedema formation were determined in TRPV1 knockout (KO) and wild type (WT) littermate mice using a modified Miles assay method. The roles of 12‐HpETE and 20‐HETE were investigated by treating animals with the 12‐HpETE synthesis inhibitor cinnamyl‐3, 4‐dihydroxy‐a‐cyanocinnamate (CDC) (8 mg/kg, i.p.) or the 20‐HETE synthesis inhibitor 17‐octadecynoic acid (17‐ODYA, 35 mg/kg,i.p.). The effects of pharmacological blockade of TRPV1 and the SP receptor neurokinin 1 (NK1) were tested using AMG‐9810 (30 mg/kg, i.p.) and SR‐140333 (0.1 μmol/kg i.v) respectively.ResultsThe oedema response to LPS (P<0.01) and ZAS (P<0.05) were reduced by ~ 53 and 43% respectively in TRPV1 KO animals compared to WT mice (LPS: 24.6 ± 3.8 μl, ZAS: 48.4 ± 9.0 μl n=13). In WT mice treatment with AMG‐9810 (n=13) reduced the LPS (P<0.01), ZAS (P<0.01) and AA (P<0.001) response, by ~ 43, 22 and 36% respectively compared with vehicle treated mice (LPS: 19.4 ± 2.2, ZAS: 42.2 ± 3.2, AA: 47.6 ± 5.9 μl n=13). 17‐ODYA (n=15) significantly reduced LPS (P<0.05), ZAS (P<0.01) and AA (P<0.05,) induced oedema by ~ 47, 24 and 29% compared to vehicle treated mice (LPS: 19.6 ± 2.7, ZAS: 48.1 ± 4.7, arachidonic acid: 47.0 ± 6.6 μl n=13). NK1 receptor blockade reduced AA‐induced (300 nmol) oedema from 43.4 ± 3.9 μl to 29.0 ± 1.8 μl (n=13, p<0.001).ConclusionOur findings suggest that TRPV1 plays an important role in vascular permeability during an acute inflammatory response induced by diverse stimuli. In addition our findings suggest that the endogenous activator of TRPV1 in these scenarios is 20‐HETE. Furthermore, the NK1 receptor plays a key role in mediating the AA oedema response induced by endogenous TRPV1 activation, indicating that 20‐HETE is the endogenous activator and SP is the downstream mediator of TRPV1.Support or Funding InformationA.H. is supported by The Trustees of the Professor Derek Willoughby PhD Fund for Inflammatory Research.