Phospholipids occurring in cell membranes and lipoproteins are converted into oxidized phospholipids (OxPL) by oxidative stress promoting atherosclerotic plaque formation. Here, OxPL were characterized as novel targets in acute and chronic inflammatory pain. Oxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine (OxPAPC) and its derivatives were identified in inflamed tissue by mass spectrometry and binding assays. They elicited calcium influx, hyperalgesia and induced pro-nociceptive peptide release. Genetic, pharmacological and mass spectrometric evidence in vivo as well as in vitro confirmed the role of transient receptor potential channels (TRPA1 and TRPV1) as OxPAPC targets. Treatment with the monoclonal antibody E06 or with apolipoprotein A-I mimetic peptide D-4F, capturing OxPAPC in atherosclerosis, prevented inflammatory hyperalgesia, and in vitro TRPA1 activation. Administration of D-4F or E06 to rats profoundly ameliorated mechanical hyperalgesia and inflammation in collagen-induced arthritis. These data reveal a clinically relevant role for OxPAPC in inflammation offering therapy for acute and chronic inflammatory pain treatment by scavenging OxPAPC.

Antinociceptive pathways are activated in the periphery in inflammatory pain, for instance resolvins and opioid peptides. Resolvins are biosynthesized from omega-3 polyunsaturated fatty acids such as eicosapentaenoic acid and docosahexaenoic acid. Resolvin D1 (RvD1) and resolvin E1 (RvE1) initiate the resolution of inflammation and control of hypersensitivity via induction of anti-inflammatory signaling cascades. RvD1 binds to lipoxin A4/annexin-A1 receptor/formyl-peptide receptor 2 (ALX/FPR2), RvE1 to chemerin receptor 23 (ChemR23). Antinociception of RvD1 is mediated by interaction with transient receptor potential channels ankyrin 1 (TRPA1). Endogenous opioid peptides are synthesized and released from leukocytes in the tissue and bind to opioid receptors on nociceptor terminals. Here, we further explored peripheral mechanisms of RvD1 and chemerin (Chem), the ligand of ChemR23, in complete Freund’s adjuvant (CFA)-induced hindpaw inflammation in male Wistar rats. RvD1 and Chem ameliorated CFA-induced hypersensitivity in early and late inflammatory phases. This was prevented by peripheral blockade of the μ-opioid peptide receptor (MOR) using low dose local naloxone or by local injection of anti-β-endorphin and anti-met-enkephalin (anti-ENK) antibodies. Naloxone also hindered antinociception by the TRPA1 inhibitor HC-030031. RvD1 did not stimulate the release of β-endorphin from macrophages and neutrophils, nor did RvD1 itself activate G-proteins coupled MOR or initiate β-arrestin recruitment to the membrane. TRPA1 blockade by HC-030031 in inflammation in vivo as well as inhibition of the TRPA1-mediated calcium influx in dorsal root ganglia neurons in vitro was hampered by naloxone. Peripheral application of naloxone alone in vivo already lowered mechanical nociceptive thresholds. Therefore, either a perturbation of the balance of endogenous pro- and antinociceptive mechanisms in early and late inflammation, or an interaction of TRPA1 and opioid receptors weaken the antinociceptive potency of RvD1 and TRPA1 blockers.

Melanoma is the most dangerous form of skin cancer occurring in Caucasians with rising incidence. They are remarkably resistant to conventional anti-tumour therapies like chemotherapy and radiotherapy. Therefore, new treatment strategies are urgently needed. Anti-tumour effects of phytochemicals such as allyl isothiocyanate or cinnamaldehyde have been demonstrated in various melanoma models in vitro and in vivo. Considering their high potency as transient receptor potential A1 (TRPA1)-activating compounds, we examined the functional expression of TRPA1 channels in different melanoma cell lines as well as in non-malignantly transformed primary melanocytes. The presence of TRPA1 transcripts could be detected in most of the melanoma cell lines. Furthermore, single-cell calcium imaging and patch clamp electrophysiology confirmed the presence of functional TRPA1 channels in those cell lines. Proliferation assays revealed that allyl isothiocyanate and cinnamaldehyde clearly reduce the proliferation of melanoma cells, but this effect is independent of an activation of TRPA1 channels, making it unlikely that ionic currents through TRPA1 are responsible for the anti-tumour effects of mustard oil and cinnamaldehyde.

These authors contributed equally. BACKGROUND AND PURPOSEROS and their downstream molecules such as oxidized phospholipids (OxPL) and 4-hydroxynonenal activate TRPA1 and TRPV1 (vanilloid 1) cation channels in vivo and in vitro shaping thermal and mechanical hypersensitivity in inflammatory pain. E06/T15 is a monoclonal autoantibody against oxidized phosphatidylcholine (OxPC) used in diagnostics in arteriosclerosis. Recently, we provided evidence that E06 also ameliorates inflammatory pain. Here, we studied E06 for local treatment against hypersensitivity evoked by endogenous and exogenous agonists of TRPA1 or TRPV1 channels. EXPERIMENTAL APPROACHWe utilized a combination of reflexive and complex behavioural pain measurements, live-cell calcium imaging and OxPC-binding assays. The lipid peroxidation metabolite 4-hydroxynonenal, hydrogen peroxide as a source of ROS, allyl isothiocyanate and capsaicin were used to activate their respective receptors. KEY RESULTSAll irritants induced thermal and mechanical hypersensitivity, spontaneous nocifensive and affective-motivational behaviour, as well as calcium influx in HEK TRPA1 -or HEK TRPV1 -cells and dorsal root ganglion neurons. E06 prevented prolonged mechanical hypersensitivity induced by all irritants except for H 2 O 2 . E06 did not alter immediate irritant-induced nocifensive or affective motivational behaviour. In vitro, E06 blocked only 4-hydroxynonenal-induced calcium influx although this compound did not bind to E06. After 1-3 h, all tested irritants elicited formation of OxPC in paw tissue. CONCLUSIONS AND IMPLICATIONSE06 ameliorates not only inflammatory pain but also prolonged hypersensitivity due to formation of OxPC. This supports the view that neutralizing certain OxPL as endogenous activators of TRPA1 or TRPV1 channels may be valuable for pain therapy. Abbreviations

Apomorphine is a non-narcotic derivative of morphine, which acts as a dopamine agonist and is clinically used to treat "offstates" in patients suffering from Parkinson's disease. Adverse effects of apomorphine treatment include severe emesis and nausea, and ulceration and pain at the injection site. We wanted to test whether sensory transient receptor potential (TRP) channels are a molecular target for apomorphine. Here, we show that rTRPV1, rTRPV2, rTRPV3, and mTRPV4, as well as hTRPM8, and rTRPM3, which are expressed in dorsal root ganglion neurons, are insensitive toward apomorphine treatment. This also applied to the cellular redox sensor hTRPM2. On the contrary, human TRPA1 could be concentrationdependently modulated by apomorphine. Whereas the addition of apomorphine in the low micromolar range produced an irreversible activation of the channel, application of higher concentrations caused a reversible voltage-dependent inhibition of heterologously expressed TRPA1 channels, resulting from a reduction of single-channel open times. In addition, we provide evidence that apomorphine also acts on endogenous TRPA1 in cultured dorsal root ganglion neurons from rats and in the enterochromaffin model cell line QGP-1, from which serotonin is released upon activation of TRPA1. Our study shows that human TRPA1 is a target for apomorphine, suggesting that an activation of TRPA1 might contribute to adverse side effects such as nausea and painful injections, which can occur during treatment with apomorphine.