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      Taurolidine and congeners activate hTRPA1 but not hTRPV1 channels and stimulate CGRP release from mouse tracheal sensory nerves

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          Abstract

          Taurolidine has long been in clinical use as an antimicrobial irrigation that does not impede wound healing. It can even be administered intravenously (30 g/day) to treat sepsis or to exert newly recognized antineoplastic actions. Only one irritant effect is reported, that is, to temporarily induce burning pain of unknown origin when applied to body cavities or peripheral veins. The structure of the molecule suggested the chemoreceptor channel TRPA1 as a potential target, which was verified measuring stimulated CGRP release from sensory nerves of the isolated mouse trachea and calcium influx in hTRPA1‐transfected HEK293 cells. With both methods, the concentration–response relationship of taurolidine exceeded the threshold value below 500  μmol/L and 100  μmol/L, respectively, and reached saturation at 1 mmol/L. The clinical 2% taurolidine solution did not evoke greater or longer lasting responses. The reversible tracheal response was abolished in TRPA1 −/− but retained in TRPV1 −/− mice. Consistently, hTRPV1‐ HEK showed no calcium influx as a response, likewise native HEK293 cells and hTRPA1‐ HEK deprived of extracellular calcium did not respond to taurolidine 1 mmol/L. The metabolite taurultam and its oxathiazine derivative, expected to cause less burning pain, showed weak tracheal irritancy only at 10 mmol/L, acting also through hTRPA1 but not hTRPV1. In conclusion, taurolidine, its metabolite, and a novel derivative showed no unspecific cellular effects but selectively, concentration‐dependently and reversibly activated the irritant receptor TRPA1 in CGRP‐expressing, thus nociceptive, neurons. The clinical solution of 2% taurolidine (~70 mmol/L) can, thus, rightly be expected to cause transient burning pain and neurogenic inflammation.

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          Ethical guidelines for investigations of experimental pain in conscious animals.

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            TRPA1 channels mediate acute neurogenic inflammation and pain produced by bacterial endotoxins

            Gram-negative bacteria are a major class of human pathogens comprising many different virulent species1. Infections by these bacteria cause diseases that represent serious global health problems such as pneumonia, meningitis, gastroenteritis and gonorrhoea. The mammalian innate immune system uses a limited set of pattern-recognition receptors to trigger defence mechanisms against microbial infections2 3. The most potent immunostimulatory cue produced by Gram-negative bacteria is lipopolysaccharide (LPS), an abundant outer wall glycolipid that is released locally and into the circulation on bacterial lysis. In vertebrates, the lipid portion of LPS, termed lipid A, binds to the protein complex formed by MD-2 and Toll-like receptor 4 (TLR4) in immune cells. This triggers the synthesis of proinflammatory cytokines (tumour necrosis factor (TNF)-α, interleukin (IL)-1, IL-6) that, through the recruitment of macrophages and eosinophils, induce inflammation and pain, followed by eventual bacterial lysis and clearance4 5. However, the response of the immune system is relatively slow and cannot account for some of the immediate effects of LPS. For instance, tail-flick hyperalgesia starts a few minutes after intraperitoneal (i.p.) LPS injection6. Also, LPS produces a strong fall in blood pressure within minutes of injection, long before TNF-α is detectable in the circulation7. Interestingly, nociceptive and vascular responses to injected LPS are abrogated by section of visceral sensory afferents6 8 9 implying a neural component that would act as a fast pathway in the LPS signalling mechanism. LPS can activate sensory neurons in culture10 11. Moreover, the recent identification of TLR4 in sensory neurons suggested that some of the rapid LPS effects could be mediated by direct stimulation of sensory afferents10 11 12. Nonetheless, no molecular mechanism has yet been put forward to relate TLR4 stimulation to the fast activation of sensory neurons. Here we use a combination of techniques, including electrical recordings of primary sensory neurons, the application of blockers of TLR4 signalling and behavioural testing in different transgenic mice, and obtained conclusive evidence that TRPA1-expressing peripheral sensory afferents are directly activated by LPS in a TLR4-independent manner. We also dissect out the molecular mechanisms linking LPS exposure to the activation of peptidergic sensory terminals and the development of acute neurogenic inflammation and pain. Collectively, these findings could lead to new strategies for the treatment of pain, inflammation and vascular shock during bacterial infections. Results LPS activates TRPA1-expressing nociceptors Using intracellular calcium imaging, we found that LPS extracted from Escherichia coli (10 μg ml−1) stimulated 17.8% (32/180) of wild-type (WT) mouse nodose (that is, vagal) sensory neurons innervating the viscera (Fig. 1a,d). Notably, nodose neurons isolated from Tlr4 knockout (KO) mice responded to LPS with similar incidence (32/136, P=0.26, Fisher’s exact test; Fig. 1b,d) and amplitude (P=0.6, unpaired t-test; Supplementary Fig. 1b), thus excluding mediation of this effect by TLR4. Interestingly, the vast majority of WT and Tlr4 KO neurons that responded to LPS also responded to 100 μM cinnamaldehyde (CA) and 100 nM capsaicin (Fig. 1a,b,e), indicating that they are polymodal nociceptor neurons13 14, and raising the possibility that the neuronal response to LPS was mediated by the wide-spectrum chemo-nociceptor channel TRPA1 (refs 13, 15, 16). Indeed, we found that nodose neurons from Trpa1 KO mice responded to LPS with significantly lower incidence (6.6%, 14/212, P S. marcescens>S. minnesota) and the great majority of LPS responders had a nociceptive phenotype (Fig. 5e,f). These results strongly suggest that the capacity of a given LPS to activate TRPA1 correlates with its ability to induce mechanical alterations in the plasma membrane. We also found that trinitrophenol (TNP), a negatively charged amphiphatic compound inducing mechanical tension of the lipid membrane, and known to modulate the gating of mechanosensitive channels29, including TRPA1 (ref. 30) also potentiated LPS activity. Pretreatment with TNP strongly potentiated [Ca2+] i responses to low concentrations of LPS in mTRPA1 cells (Supplementary Fig. 8a–d). LPS effects on TRPA1 are TLR4 independent Generally, LPS effects on neurons have been linked to activation of the TLR4 signalling pathway10. However, as shown earlier, we found that the excitatory effects of LPS were still observed on sensory neurons isolated from Tlr4 KO mice. We also tested CLI-095, a novel specific inhibitor of TLR4 signalling31. As shown in Fig. 6a–c, pretreatment for 10 min with 1 μM CLI-095 did not affect the subsequent response to LPS in nodose neurons; neither the percentage of responding neurons nor the amplitude of the response was significantly affected. Similar results were obtained in TRPA1-expressing CHO cells (Supplementary Fig. 9). In addition, CHO cells transfected with human TLR4 did not show a TRPA1-like current when acutely exposed to LPS (Supplementary Fig. 10). Altogether, these results strongly support a TLR4-independent mechanism of action of LPS on TRPA1 channels. We took additional steps to verify that activation of TRPA1 was truly mediated by LPS. To minimize the possible role of a contaminant, we tested ultrapure forms of LPS (see Methods). As shown in Supplementary Fig. 11, ultrapure LPS from E. coli (2 μg ml−1) also activated TRPA1-expressing cells. Moreover, the ultrapure form of S. minnesota R595, at a 10 times higher concentration, showed almost no response, similar to the results obtained from a different source (see Fig. 5c,d). Strikingly, an ultrapure LPS from Rhodobacter sphaeroides, which acts as a competitive antagonist of TLR4 (ref. 32), also activated TRPA1-expressing cells (Supplementary Fig. 11), strongly suggesting a TLR4-independent mechanisms of action. In contrast, the same preparations of LPS had the expected effects on human TLR4 signalling (Supplementary Fig. 11d). Polymyxin B is a cationic cyclic polypeptide antibiotic that is widely used to neutralize the effects of endotoxin contamination in biological samples33. The action of polymyxin B is based on its binding, by electrostatic interaction, to the anionic lipid A. Incubation of LPS with polymyxin B completely eliminated the activation of TRPA1 by LPS (Fig. 6d,e). In contrast, activation of TRPA1 by AITC was minimally reduced (Fig. 6f). This result suggests that the inhibitory action of polymyxin B is not directly on the channel (for example, pore block) and further implicates lipid A in the effects observed. Acute neuropeptide release by LPS depends on TRPA1 activity TRPA1 participates in neurogenic inflammation and vasodilation34 35 36. To test whether activation of peptidergic sensory terminals by LPS leads to neuropeptide release and neurogenic inflammation14 37, we used an isolated mouse trachea preparation. The trachea is densely innervated with peptidergic vagal fibres that release calcitonin gene-related peptide (CGRP) in response to capsaicin38 39. Brief incubation of tracheal halves with acrolein, an electrophilic TRPA1 activator and product of oxidative stress, also present in fumes and as a toxic metabolite of chemotherapy agents15, produced a dose-dependent release of CGRP (Supplementary Fig. 12). Application of LPS (30–100 μg ml−1) to tracheal halves induced a modest but significant CGRP release (Fig. 7a). In addition, a brief pretreatment of the trachea with the membrane crenator TNP produced a massive potentiation of the CGRP release evoked by LPS (P<10−4) and by acrolein (P<0.01; Fig. 7a). Notably, responses to individual agonists, or potentiated response to LPS in the presence of TNP were fully abrogated in Trpa1 KO mouse tracheas (Fig. 7a), indicating that they depend strictly on activation of TRPA1 channels. We also observed a fourfold potentiation of CGRP release from the trachea by LPS in the presence of the endogenous TRPA1 agonist HNE (Fig. 7b), fully consistent with the synergistic action of both agonists on TRPA1 whole-cell currents as we have shown (Supplementary Fig. 6). Collectively, these results indicate that LPS, both alone and in combination with other endogenous inflammatory mediators, can activate TRPA1 in sensory nerve terminals leading to acute neurogenic inflammation. Neurovascular responses to LPS involve activation of TRPA1 Systemic bacterial invasion can cause massive peripheral vasodilation, leading to a severe drop in blood pressure, a life-threatening condition known as septic shock40. Considering that chemical stimulation of TRPA1 in sensory fibres innervating resistance arteries induces potent vasodilation24 34 35 36, we tested whether this channel was involved in the vascular response to LPS. Using pressure myography ex vivo, we found that LPS (100 μg ml−1) induced a strong dilation in WT mouse mesenteric arteries precontracted with the alpha1 adrenergic agonist phenylephrine (2 μM; Fig. 7c and Supplementary Fig. 13a). Notably, this effect was significantly reduced by the specific TRPA1 inhibitor HC-030031 (10 μM) and by genetic ablation of TRPA1 (Fig. 7c and Supplementary Fig. 13b). Moreover, in Trpa1 KO animals, the residual LPS-induced dilation was completely insensitive to HC-030031 (Fig. 7c and Supplementary Fig. 13b). Thus, TRPA1 appears to participate in the vasodilation response to LPS, although other yet unidentified targets also appear to contribute to the arterial vasomotor responses. Acute LPS-induced hypersensitivity engages TRPA1 but not TLR4 The typical symptoms of local Gram-negative bacterial infections include inflammation, pain and mechanical hypersensitivity41 42. They were readily reproduced experimentally with intraplantar injections of purified E. coli LPS in WT mice (Fig. 7d,e). Consistent with a major role of TRPA1 as a LPS effector, we found that such responses were severely attenuated in Trpa1 KO mice (Fig. 7d,e). A similar attenuation of mechanical hyperalgesia to LPS injection in Trpa1 KO mice was reported recently43. Moreover, the local inflammation caused by LPS molecules with different lipid A shape was strongly correlated with their ability to stimulate mTRPA1 in vitro (r=0.91, P<0.01; Fig. 7f) linear correlation coefficient (n=7). In contrast, acute pain responses, local tissue swelling and mechanical hyperalgesia developed normally in Tlr4 KO mice following LPS injection (Supplementary Fig. 14). Notably, mechanical hyperalgesia resolved more rapidly in Tlr4 KO mice compared with wild type, suggesting that immune response pathways are engaged by LPS in a slower timescale compared with TRPA1 activation. TRPA1 is not critical for LPS systemic inflammatory response As deletion of TRPA1 produces such prominent effects on nociceptive and neurovascular response to LPS, we wondered whether other, well-established, systemic responses to LPS were affected as well. In mice, i.p. application of high doses of LPS produces a profound and long-lasting hypothermia44. As previously described, the injection of 3 mg kg−1 E. coli LPS produced a marked hypothermia in WT mice (Supplementary Fig. 15). The severity and time course of this hypothermic response was nearly identical in Trpa1 KO littermates. Activation of TLR4 by LPS is known to potently activate immune cells (for example, hepatic macrophages) to produce and release proinflammatory cytokines such as TNF-α and IL-6 (refs 4, 45). Indeed, i.p. LPS treatment (0.75 and 1 mg kg−1 for 1 h) increased dose dependently circulating serum IL-6 levels from an undetectable baseline after saline injection (Supplementary Fig. 16a). As was the case for thermoregulatory responses, we did not find differences in the levels of IL-6 between both genotypes of mice. Moreover, LPS treatment (1 mg kg−1 for 1 h) also increased IL-6 messenger RNA levels in the liver in both types of mice similarly (Supplementary Fig. 16b). Discussion Here we demonstrate that TRPA1 channels are key participants in the biological response to LPS, a microbial signature molecule, translating the presence of elevated LPS into a rapid nociceptor response and neurogenic inflammation. Therefore, LPS appears as a totally novel class of biological toxin among the large number of natural compounds that are detected by TRPA1 channels (reviewed by Nilius et al.16). The ancient nature of LPS and the fact that the role of TRPA1 in chemical avoidance is conserved from flies to mammals underscores the evolutionary significance of this alert mechanism in animals14 46 47 48. It is noteworthy that bacterial sepsis is accompanied by severe redox imbalance, favouring the oxidant state49, a condition that also leads to robust TRPA1 channel activation24 50. Our findings also raise the question of how this channel can function as such an extremely broadly tuned chemo-nocisensor. In the light of previous studies and of the present results, it seems clear that rather than using specific molecular determinants (that is, the key and lock concept), TRPA1 activation relies on the general physico-chemical properties of the agonist. Whereas highly reactive electrophilic irritants are detected by their capacity to modify covalently key amino-acid residues in the amino terminus of the TRPA1 channel47 51, our results suggest that LPS modulates TRPA1 activity by inducing mechanical perturbations in the plasma membrane. This result is in line with the known mechanosensing function of TRPA1 in visceral52 and somatic53 54 neurons. The activation of TRPA1 by LPS in cell-free membrane patches indicates that the mechanism underlying this effect does not require other intermediate molecules, but additional experiments, including the characterization of LPS action after incorporation of TRPA1 into artificial lipid bilayers of defined composition, are needed to substantiate this point. Nevertheless, it is noteworthy that different forms of LPS activated TRPA1 in proportion to their ability to produce inflammation in vivo, which suggests a close relation between both processes. Recently, Hardie and Franze55 showed, in a very elegant way, that activation of light-sensitive TRP and TRPL channels in Drosophila photoreceptors is mediated by rapid mechanical perturbation of the plasma membrane caused by phosphatidylinositol 4,5-bisphosphate (PIP2) depletion downstream of PLC activation by light. This study is very relevant to the hypothetical activation of TRPA1 under pathophysiological conditions because TRPA1 is also activated by G-protein-coupled receptors that activate PLC and deplete PIP2 (refs 15, 23). In the context of infection, the production of some inflammatory mediators (for example, bradykinin and trypsin) that couple to Gq/11 will also lead to PIP2 depletion. Thus, the mechanical perturbations produced by LPS hypothesized in our study could act synergistically with those produced by changes in PIP2 levels, leading to TRPA1 gating. Sensory neurons express a number of TLR4 signalling elements, including TLR4, making it plausible that TLR4 signalling participates in sensory responses to LPS11. Indeed, several recent studies have implicated TLR4 in rapid responses to LPS in sensory neurons, including the sensitization of TRPV1 channels10. However, a number of results clearly indicate that TLR4 is dispensable for the excitatory actions of LPS on TRPA1. First and foremost, responses in sensory neurons from Tlr4 KO mice were indistinguishable from those observed in WT animals. Second, incubation with a specific inhibitor of TLR4 signalling did not affect responses to LPS in TRPA1-expressing neurons or recombinant TRPA1 channels. Moreover, acute pain and tissue swelling peaked normally in Tlr4 KO mice in vivo. Obviously, under in vivo conditions, circulating LPS will engage the available TLR4 machinery, including the production of proinflammatory cytokines, which could participate in the slow sensitization of nociceptors. Consistent with this view, we observed a faster resolution of the mechanical hypersensitivity, following local LPS injection, in Tlr4 KO mice. In vivo, we envision both effector pathways of LPS acting synergistically on somatic and visceral neurons. Our observation that LPS excites somatic and visceral nociceptor neurons via a mechanism dependent on TRPA1 activation and independent of TLR4 can readily explain acute pain and neurogenic inflammation induced by LPS. Similar concentrations of LPS have been used to evoke pain behaviour in experimental animals42. The activation of TLR4 occurs at lower LPS levels than those required to activate TRPA1 channels. However, severe endotoxemia can bring plasma LPS levels into the micromolar range56, levels also encountered in urine and locally inflamed tissues57. Moreover, we found strong (that is, 10-fold) potentiation of LPS-induced activation of TRPA1 by other TRPA1 agonists, including endogenous modulators (for example, HNE), suggesting that in the context of a bacterial infection in vivo, the levels of LPS required to activate TRPA1 may be lower than what we found experimentally. It should be noted that the ex vivo preparations we used (that is, the superfused trachea and the isolated tongue), in contrast to the skin in vivo, cannot reflect secondary inflammatory reactions, like plasma extravasation, accumulation of inflammatory mediators (for example, bradykinin, thrombocytes and immune cells), which, together, may complement or amplify, like we found with HNE or acrolein, the excitatory effects of LPS on TRPA1 to activate nociceptors58. The modest but significant effect of LPS alone on tracheal CGRP release is not surprising, because even prostaglandin E2, the most widely acknowledged nociceptor sensitizer, shows no effect of its own on nociceptor discharge and CGRP release but ‘only’ facilitates heat and chemical responses59. Finally, these avascular ex vivo preparations cannot be compared directly with dissociated sensory neurons in culture with respect to chemosensitivity, because the nerve endings do not reach the very surface of the mucosa, formed by epithelial cells and their tight junctions. TRPA1-mediated calcium influx in sensory terminals leads to release of neuropeptides13 24, thereby triggering rapid TRPA1-dependent vasodilation, local inflammation and sustained mechanical hyperalgesia. Recently, it was established that TRPA1-mediated substance P release in the colon plays a necessary role in experimental colitis60, providing further support for a causal link between TRPA1 channels and neuroimmune processes. Other studies have indicated the essential role of TRPA1 in the pathophysiology of asthma37, a disease with a significant immunological component. We found that in the absence of TRPA1 the proinflammatory and pro-algesic actions of LPS are severely curtailed. Interaction of LPS with the MD-2–TLR4 complex leading to activation of the transcription factor nuclear factor-kappaB (NF-κB) and cytokine production is the canonical pathway of LPS signalling2. The identification of TRPA1 as a functional target for LPS may represent an important missing link between the stimulation of afferent sensory fibres and the immune responses during a bacterial challenge. We tentatively conclude that TRPA1 channels and pattern receptors like TLR4 act as synergic sensory mechanisms, alerting the host about the presence of pathogens, allergens and environmental irritants3. TRPA1 would be involved in the early steps of the response cascade, sensing potentially damaging compounds, in parallel with the well-established production of proinflammatory cytokines. The recent discovery of activation of the NF-κB signalling pathway following TRPA1 activation provides independent support to our view61. Thus, identification of TRPA1 as a new target for LPS opens novel avenues for the treatment of adverse biological responses of Gram-negative bacterial infections. Finally, the recent report describing the activation of nociceptors by N-formylated peptides and the pore-forming toxin α−haemolysin isolated from bacteria, by mechanisms independent of immune pathways62, suggests that direct activation of nociceptors by bacterial products may be a more general signalling mechanism than previously recognized. Methods Animals Experiments were performed in accordance with the guidelines established by the European Communities Council Directive (86/609/ECC), by Spanish Royal Decree 1201/2005 and the Ethics Committee of the Catholic University, Leuven.: Tlr4 KO mice on a C57BL/6 background, originally generated by Hoshino et al.63 were kindly provided by C Guerri Centro de Investigación Príncipe Felipe (CIPF) and by H Hammad and B Lambrecht (VIB, Ghent, Belgium). Trpa1 KO mice were provided by D Corey64. Trpv1 KO mice, originally generated in D Julius laboratory18, were obtained from Jackson. Neuronal culture Neuronal culturing methods were similar to those used previously65 66. TG and nodose ganglia were isolated from young adult male mice (postnatal months 1–3), WT and Trpa1 KO siblings64, Tlr4 KO (ref. 63) and Trpv1 KO (ref. 18), and incubated for 1 h with 0.07% collagenase XI+0.3% Dispase at 37 °C. Thereafter, ganglia were mechanically dissociated and cultured in minimal essential medium with Earle’s balanced salt solution and L-Glutamine (Invitrogen) supplemented with 10% fetal bovine serum (Invitrogen), 1% minimal essential medium vitamin solution (Invitrogen), 100 μg ml−1 penicillin/streptomycin and 100 ng ml−1 nerve growth factor (NGF). Cells were plated on poly-L-lysine-coated glass coverslips and used after 1 day in culture. Cell culture CHO-K1 cells, from the American Type Culture Collection, were cultured in DMEM containing 10% of fetal bovine serum, 2% glutamax (Invitrogen), 1% non-essential amino acids (Invitrogen) and 200 μg ml−1 penicillin/streptomycin. An inducible CHO-K1 cell line stably expressing mouse TRPA1 channels was kindly provided by Ardem Patapoutian (The Scripps Research Institute, USA)13 and cultured as detailed for the parental cell line. Expression of TRPA1 was induced by application of 0.25–0.5 μg ml−1 tetracycline 4–18 h before recording. HEK-293 cells, from the European Collection of Cell Cultures (Salisbury, UK), were seeded in 18 mm glass coverslips coated with poly-L-lysine (0.1 mg ml−1) and grown in DMEM containing 10% (v/v) human serum, 2 mM L-glutamine, 2 U ml−1 penicillin and 2 mg ml−1 streptomycin at 37 °C in a humidity-controlled incubator with 10% CO2. Human TRPA1, TRPV1, TRPM8 and TRPV2 were cloned in the pAGGS-IRES-GFP vector and transiently transfected in HEK-293 cells using Trans-IT-293 reagents (Mirus, Madison, MI, USA). Transfected cells were identified by the expression of GFP (green fluorescent protein). Calcium imaging Calcium-imaging experiments were conducted with the fluorescent indicator Fura-2. Cells were incubated with 5 μM Fura-2-acetoxymethylester (Invitrogen) for 60 min at 37 °C. Fluorescence measurements were made with a Zeiss Axioskop FS (Germany) upright microscope fitted with an ORCA ER charge-coupled device camera (Hamamatsu, Japan). Fura-2 was excited at 340 and 380 nm with a rapid switching monochromator (TILL Photonics, Germany). Mean fluorescence intensity ratios (F340/F380) were displayed online with Metafluor software (Molecular Devices, Sunnyvale, USA). The control bath solution contained (in mM) 140 NaCl, 3 KCl, 2.4 CaCl2, 1.3 MgCl2, 10 HEPES and 10 glucose, and was adjusted to a pH of 7.4 with NaOH. Bath temperature was maintained at 34–36 °C by a custom-built Peltier device. Patch-clamp electrophysiology Whole-cell voltage-clamp recordings were performed with standard patch pipettes (3–6 MΩ resistance) made of borosilicate glass capillaries (Harvard Apparatus Ltd, UK) and contained (in mM) 140 NaCl, 5 CsCl, 10 EGTA, 10 HEPES, (305 mOsm kg−1; pH 7.4, adjusted with NaOH). The control bath solution was kept at room temperature except for HC-030031 experiments (32±1 °C). During calcium-free experiments, the bath solution was as follows (in mM): 140 NaCl, 3 KCl, 1.3 MgCl2, 10 HEPES, 1 EGTA, 10 glucose. Current signals were recorded with an Axopatch 200B patch-clamp amplifier (Molecular Devices). Stimulus delivery and data acquisition were performed using pClamp 9 software (Molecular Devices). Current development was monitored with repetitive (0.5 Hz) injections of 500 ms duration voltage ramps from −100 to +100 mV, and the voltage steps consisted in a series of 400 ms duration steps ranging from −150 to +175 mV followed by an invariant pulse to −75 mV (400 ms). The holding potential was set to 0 mV. Outside-out patch recordings on mTRPA1 cells were performed in the absence of intracellular and extracellular Ca2+. Patch pipettes (3–6 MΩ resistance) contained the standard internal solution (see above) and the calcium-free bath solution (see above). Currents were sampled at 20 kHz and low-pass filtered at 2 kHz. Current development was continuously monitored with repetitive (0.5 Hz) injections of 500 ms duration voltage ramps from −100 to +100 mV from a holding potential of 0 mV. Patch-clamp data were analysed with WinASCD software written by Dr Guy Droogmans (ftp://ftp.cc.kuleuven.ac.be/pub/droogmans/winascd.zip) and Origin 7.0 (OriginLab Corporation). Current-clamp recordings of cultured nodose neurons Perforated-patch current-clamp recordings were performed on cultured nodose neurons from adult mice. Standard patch pipettes (2–5 MΩ) were made of borosilicate glass capillaries (Harvard Apparatus Ltd) and contained (in mM) 105 K gluconate, 35 KCl, 10 NaCl, 10 HEPES, 0.1 EGTA and 1 mg ml−1 amphotericin B, pH 7.4. The external solution was identical to the one used in voltage-clamp recordings. Before electrical recordings, neurons expressing TRPA1 were identified with Ca2+ microfluorimetry (see above) by their response to 10 μM nifedipine, a potent, reversible and non-electrophilic activator of TRPA1 channels22. Recordings of lingual nerve afferents The animals were killed by exposure to CO2 and quickly decapitated. The tongue was carefully dissected, split at the midline and placed in a recording chamber and continuously perfused (3 ml min−1) with physiological saline (in mM): NaCl 128, KCl 5, NaH2PO4 1, NaHCO3 26, CaCl2 2.4, MgCl2 1.3 and glucose 10. This solution was gassed with carbogen to pH 7.4. Temperature of the solution was kept around 34 °C and could be modified with a water-cooled, home-designed, Peltier device. Fine filaments of the lingual nerve were split with fine forceps and placed on a platinum electrode for extracellular recording. Electrical signals were alternating current-amplified and high pass filtered. Data were captured and analysed using a CED 1401 interface and Spike 2 software (Cambridge Electronic Design, Cambridge, UK). Single units were detected online using a threshold-based criterion and sorted manually afterwards to remove artefacts. Arterial pressure myography Mice were killed by CO2 inhalation and decapitation. The mesenteric bed was removed and transferred to ice-cold solution (in mM): NaCl 124, NaHCO3 25, KCl 5.5, KH2PO4 1.2, MgSO4 1.2, glucose 5.5, CaCl2 2.5 (pH 7.4 when aerated with 95% O2–5% CO2). Second- and third-branch arteries were removed, dissected free of the adherent fat, cannulated and mounted in a pressure myograph (Danish Myotechnology, Aarhus, Denmark) for measurement of diameter. Before testing the effect of LPS or HC-030031 on arterial tone, arteries were allowed to equilibrate at 70 mm Hg and 37 °C, and after 60 min were precontracted with phenylephrine 2 μM. Assay of TLR4 activity Activation of TLR4 by different forms of ultrapure LPS was tested in HEK-Blue-hTLR4 cells (InvivoGen, San Diego, USA). These HEK-293 cells stably express human TLR4, MD-2, CD14 and an NF-κB-inducible alkaline phosphatase reporter gene system. Expression of secreted alkaline phosphatase was detected with Quanti-Blue (InvivoGen) and quantified by reading the absorbance with a spectrophotometer at 620–655 nm. Cells were maintained in complete DMEM with selective antibiotics, as described by the manufacturer’s instructions (InvivoGen). For testing, cells were plated on 96-well plates at 25,000 cells per well, and were incubated with different concentrations of LPS for 16 h. Analysis of IL-6 levels WT and TRPA1 KO mice were injected i.p. with 0.75 or 1 mg kg−1 E. coli LPS 055:B5 (Sigma-Aldrich) or saline and killed by decapitation 1 h later. Serum and liver were quickly collected and immediately frozen and stored at −80 °C. IL-6 serum levels were determined by enzyme-linked immunosorbent assay (R&D Systems, Minneapolis, USA). Liver analysis of IL-6 messenger RNA levels was performed by reverse transcriptase PCR. Total RNA was extracted using Trizol Reagent (Invitrogen). Reverse transcriptase PCR was performed with a specific set of primers: forward: 5′-GCCACTCCTTCTGTGACTCCAGCT-3′. Reverse: 5′-ACCACTTCACAAGTCGGAGGCTT-3′. Hypoxanthine guanine phosphoribosyl-transferase was used as a housekeeping gene. The amplified products were resolved in a 2% agarose gel and quantified by densitometry using a digital imaging system (Molecular Analyst, Bio-Rad). The PCR products were digested with specific restriction enzymes to determine their specificity. CGRP enzyme immunoassay and analysis The CGRP content of the incubation fluid was measured using a commercial enzyme immunoassay kits with a detection threshold of 2 pg ml−1 (Bertin Pharma, Montigny-le-Bretonneux, France). For this purpose, 100 μl fluid samples were stored on ice and mixed, immediately following the trachea incubation period, with 25 μl of fivefold concentrated commercial CGRP enzyme immunoassay buffer that contained a cocktail of peptidase inhibitors. The CGRP contents were determined after the end of the experiment; the antibody reactions took place overnight. Enzyme immunoassay plates were scored photometrically using a microplate reader (Dynatech, UK). All results are presented as measured by the enzyme immunoassay in pg CGRP per ml incubation fluid. To reduce interindividual and day-to-day baseline variability, the data were normalized to the second baseline value (before any stimulation). This value was subtracted from all data points so that only the absolute change in CGRP release (Δ pg ml−1) is displayed in the figures. Statistical comparisons were performed using the Statistica 7 software (Statsoft, Tulsa, USA). The baseline-normalized ΔCGRP values were entered into a one-way analysis of variance followed by Fisher’s least significant difference test, focusing on the peak values of stimulated CGRP release; *P<0.05 was considered significant. Data points represent means±s.e.m. of the given number (n) of experiments. Behavioural testing Behavioural studies were performed on littermates that were wild type or homozygous null at the Trpa1 or Tlr4 allele. All experiments were scored by a tester blind to genotype and to drugs injected. A total of 51 wild type, 25 Trpa1 KO and 6 Tlr4 KO male mice (2–3 months old) were used. To measure acute nocifensive responses, mice were placed within transparent plastic cylinders and allowed to accommodate for 2 h. LPS (5 μg μl−1) was prepared in PBS and delivered via intraplantar injection in a volume of 10 μl using a 30 G needle coupled to a Hamilton syringe. Immediately after injection, nocifensive time was scored as the total time spent licking, lifting, guarding, shaking or biting of the injected hind paw over a period of 10 min. A separate group of animals received injection of vehicle alone. Mechanical thresholds were determined with Von Frey hairs using a modified version of Dixon’s up-down method67. Procedures and intraplantar dosis of LPS were identical to those used for nocifensive responses. Mice were placed in transparent plastic cylinders (13 cm diameter × 8 cm height) on a metal mesh platform and calibrated von Frey filaments were applied to the plantar surface of the hind paw for up to 2 s with sufficient force to cause the filament to bow. Brisk withdrawal of the hind paw during or immediately after application was considered a positive response. The threshold force required to elicit withdrawal of the paw (50% hind paw withdrawal) was determined from two separate trials. Data presented are from both left and right hind paws averaged together, as there were no laterality effects. To examine the effects of LPS on body temperature (Tb), animals (adult male mice) were adapted to a Plexiglass chamber (15 × 15 × 30 cm3) in a room at 23±1 °C. Baseline rectal temperature was recorded with a thermoprobe connected to a digital thermometer (Lendhermack, model IM902C). At time zero (10:00 day time), immediately after a second measure of Tb, vehicle (PBS) or 3 mg kg−1 of E. coli LPS were injected i.p. Thereafter, Tb was monitored at 1 h interval for 7 h, and the following morning. Chemical reagents LPS from E. coli, S. typhimurium, S. minnesota and P. aeruginosa (purified by gel-filtration chromatography), and K. pneumoniae, S. marcescens (purified by phenol extraction) were purchased from Sigma-Aldrich. N. meningitidis LPS was purified by phenol extraction at the Center for Vaccines Research and Production (Finlay Institute, Havana, Cuba). The quality of this LPS (40.5 × 106 EU ml−1) was determined with a Kinetic-QCL Limulus amebocyte lysate, using the programme Wiea QCL and a Lonza kit. LPSs were dissolved as a stock solution in endotoxin-free distilled water, or PBS for behavioural experiments, at a concentration of 5 mg ml−1. Other ultrapure forms of LPS were purchased from InvivoGen (San Diego, USA), obtained by repeated phenol extractions and prepared as sterile stock solutions with sterile water and diluted right before use. These included LPS from E. coli strain 0111:B4, S. minnesota and R. sphaeroides. Table 1 summarizes the source and characteristics of the different LPS used. Diphosphoryl lipid A (from E. coli F583 Rd mutant, Sigma) was dissolved in a glass tube at a concentration of 1 mg ml−1 in chloroform/methanol (3:1 v/v). The suspension was heated up to 40 °C and solvent was dried by rotary evaporation under a stream of N2. The glass tubes were supplemented with extracellular solution and subjected to sonication for 40 min. Synthetic monophosphoryl lipid A (InvivoGen) was prepared as a 1-mg ml−1 solution in dimethyl sulphoxide (DMSO). Control experiments contained the same concentration of vehicle. CLI-095 (InvivoGen), also known as TAK-242, was prepared as a 3-mM stock solution in DMSO. Polymyxin B (InvivoGen) was prepared as a 50-mg ml−1 stock in distilled water. AITC, CA, TNP and HNE were stored as stock solutions and diluted immediately before the experiments. HC-030031 was purchased from Tocris and stored in a DMSO solution at 100 mM. Data analysis Data are reported as mean±s.e.m. Dose–response data were normalized to the maximum response of the drug in each case and then were fitted with the Hill equation using the Levenberg–Marquardt method implemented in Origin 7.0 software. The s.e.m. were used as weights in fitting where applicable. When comparing two means, statistical significance (P<0.05) was assessed by Student’s two-tailed t-test. When comparing proportions between two experimental groups (for example, percentage of responding neurons), we used Fisher’s exact test. Author contributions V.M. initiated and coordinated the project, performed most patch-clamp experiments, calcium-imaging experiments in TG neurons and contributed to the final version of the manuscript; Y.A.A. characterized the responses to different forms of LPS, effects of LPS on human TRPs, the effect of polymixin B and performed behavioural experiments; E.L. performed current-clamp and calcium-imaging experiments in nodose neurons, S.T. performed measurements of LPS effects on mesenteric arteries, B.D. performed experiments on lingual nerve fibres; O.F. measured LPS effects on transfected cells, J.M. tested the interaction between LPS and TNP and helped in behavioural experiments; C.F. performed most behavioural experiments; A.T. provided reagents; T.K. measured GCRP release from tracheal sensory terminals; B.N. measured thermoregulatory responses and IL-6 release; A.S. characterized the responses to different forms of LPS in sensory neurons; R.S., P.R., M.T.P., J.R.L., T.V. and C.B. supervised experiments in their laboratories and contributed to the final version of the manuscript. K.T. analysed single-channel data, performed behavioural experiments, coordinated the project and drafted the article and F.V. coordinated the project, analysed data and drafted the article. Additional information How to cite this article: Meseguer, V. et al. TRPA1 channels mediate acute neurogenic inflammation and pain produced by bacterial endotoxins. Nat. Commun. 5:3125 doi: 10.1038/ncomms4125 (2014). Supplementary Material Supplementary Information Supplementary Figures 1-16
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              Identification of transmembrane domain 5 as a critical molecular determinant of menthol sensitivity in mammalian TRPA1 channels.

              TRPA1 is a member of the transient receptor potential (TRP) family of ion channels and is expressed in a subset of nociceptive neurons. An increasing body of evidence suggests that TRPA1 functions as a chemical nocisensor for a variety of reactive chemicals, such as pungent natural compounds and environmental irritants. Activation of TRPA1 by reactive compounds has been demonstrated to be mediated through covalent modification of cytoplasmic cysteines located in the N terminus of the channel, rather than classical lock-and-key binding. TRPA1 activity is also modulated by numerous nonreactive chemicals, but the underlying mechanism is unknown. Menthol, a natural nonreactive cooling compound, is best known as an activator of TRPM8, a related TRP ion channel required for cool thermosensation in vivo. More recently, menthol has been shown to be an activator of mouse TRPA1 at low concentrations, and a blocker, at high concentrations. Here, we show that human TRPA1 is only activated by menthol, whereas TRPA1 from nonmammalian species are insensitive to menthol. Mouse-human TRPA1 chimeras reveal the pore region [including transmembrane domain 5 (TM5) and TM6] as the critical domain determining whether menthol can act as an inhibitor. Furthermore, chimeras between Drosophila melanogaster and mammalian TRPA1 highlight specific residues within TM5 critical for menthol responsiveness. Interestingly, this TM5 region also determines the sensitivity of TRPA1 to other chemical modulators. These data suggest separable structural requirements for modulation of TRPA1 by covalent and nonreactive molecules. Whether this region is involved in binding or gating of TRPA1 channels is discussed.
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                Author and article information

                Journal
                Pharmacol Res Perspect
                Pharmacol Res Perspect
                10.1002/(ISSN)2052-1707
                PRP2
                Pharmacology Research & Perspectives
                John Wiley and Sons Inc. (Hoboken )
                2052-1707
                01 February 2016
                February 2016
                : 4
                : 1 ( doiID: 10.1111/prp2.2016.4.issue-1 )
                : e00204
                Affiliations
                [ 1 ] Institute of Physiology and PathophysiologyFriedrich‐Alexander‐University of Erlangen‐Nürnberg ErlangenGermany
                [ 2 ]Geistlich Pharma AG WolhusenSwitzerland
                Author notes
                [*] [* ] Correspondence

                Peter W. Reeh, Department of Physiology and Pathophysiology, Friedrich‐Alexander‐University of Erlangen‐Nürnberg, Universitaetsstrasse 17, D‐91054 Erlangen, Germany. Tel: +49 91318522228; Fax: +49 91318522497; E‐mail: peter.reeh@ 123456fau.de

                Article
                PRP2204
                10.1002/prp2.204
                4777271
                26977296
                1eee452d-0940-4e77-8562-0c6e382d7e5a
                © 2016 The Authors. Pharmacology Research & Perspectives published by John Wiley & Sons Ltd, British Pharmacological Society and American Society for Pharmacology and Experimental Therapeutics.

                This is an open access article under the terms of the Creative Commons Attribution‐NonCommercial‐NoDerivs License, which permits use and distribution in any medium, provided the original work is properly cited, the use is non‐commercial and no modifications or adaptations are made.

                History
                : 10 November 2015
                : 17 November 2015
                : 19 November 2015
                Page count
                Pages: 8
                Categories
                Original Article
                Original Articles
                Custom metadata
                2.0
                prp2204
                February 2016
                Converter:WILEY_ML3GV2_TO_NLMPMC version:4.9.1 mode:remove_FC converted:10.07.2016

                anticancer agents,bacterial infections,ca‐imaging,pain,transgenic mice

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