a-967079 and Disease-Models--Animal

Methylglyoxal (MGO) is a reactive glycolytic metabolite associated with painful diabetic neuropathy at plasma concentrations between 500 nM and 5 μM. The mechanisms through which MGO causes neuropathic pain at these pathological concentrations are not known. Because MGO has been linked to diabetic neuropathic pain, which is prevalent and poorly treated, insight into this unsolved biomedical problem could lead to much needed therapeutics. Our experiments provide compelling evidence that ∼1-μM concentrations of MGO activate the integrated stress response (ISR) in IB4-positive nociceptors in the dorsal root ganglion (DRG) of mice in vivo and in vitro. Blocking the integrated stress response with a specific inhibitor (ISRIB) strongly attenuates and reverses MGO-evoked pain. Moreover, ISRIB reduces neuropathic pain induced by diabetes in both mice and rats. Our work elucidates the mechanism of action of MGO in the production of pain at pathophysiologically relevant concentrations and suggests a new pharmacological avenue for the treatment of diabetic and other types of MGO-driven neuropathic pain.

Topics: Analgesics, Non-Narcotic; Animals; Diabetes Mellitus, Experimental; Disease Models, Animal; DNA-Binding Proteins; Ganglia, Spinal; Heat-Shock Proteins; Lectins; Male; Mice; Mice, Inbred C57BL; Mice, Inbred ICR; Mice, Transgenic; Nociceptors; Oximes; Pain; Pain Threshold; Phosphorylation; Pyruvaldehyde; Signal Transduction; Stress, Physiological; Transcription Factors

Topics: Administration, Cutaneous; Animals; Aprepitant; Behavior, Animal; Calcineurin Inhibitors; Dermatitis, Contact; Disease Models, Animal; Filaggrin Proteins; Ganglia, Spinal; Humans; Intermediate Filament Proteins; Male; Mice; Mice, Inbred BALB C; Mice, Transgenic; Ointments; Oxazolone; Oximes; Pruritus; Skin; Substance P; Tacrolimus; TRPA1 Cation Channel

Topics: Animals; CD4-Positive T-Lymphocytes; Cell Line; Disease Models, Animal; Female; Humans; Imiquimod; Male; Mice; Mice, Knockout; Neurons; Oximes; Psoriasis; Skin; TRPA1 Cation Channel; TRPV Cation Channels

The aim of this research was to assess the antinociceptive activity of the transient receptor potential (TRP) channel TRPV1, TRPM8, and TRPA1 antagonists in neurogenic, tonic, and neuropathic pain models in mice. For this purpose, TRP channel antagonists were administered into the dorsal surface of a hind paw 15 min before capsaicin, allyl isothiocyanate (AITC), or formalin. Their antiallodynic and antihyperalgesic efficacies after intraperitoneal administration were also assessed in a paclitaxel-induced neuropathic pain model. Motor coordination of paclitaxel-treated mice that received these TRP channel antagonists was investigated using the rotarod test. TRPV1 antagonists, capsazepine and SB-366791, attenuated capsaicin-induced nociceptive reaction in a concentration-dependent manner. At 8 µg/20 µl, this effect was 51% (P<0.001) for capsazepine and 37% (P<0.05) for SB-366791. A TRPA1 antagonist, A-967079, reduced pain reaction by 48% (P<0.05) in the AITC test and by 54% (P<0.001) in the early phase of the formalin test. The test compounds had no influence on the late phase of the formalin test. In paclitaxel-treated mice, they did not attenuate heat hyperalgesia but N-(3-aminopropyl)-2-{[(3-methylphenyl)methyl]oxy}-N-(2-thienylmethyl) benzamide hydrochloride salt (AMTB), a TRPM8 antagonist, reduced cold hyperalgesia and tactile allodynia by 31% (P<0.05) and 51% (P<0.01), respectively. HC-030031, a TRPA1 channel antagonist, attenuated tactile allodynia in the von Frey test (62%; P<0.001). In conclusion, distinct members of TRP channel family are involved in different pain models in mice. Antagonists of TRP channels attenuate nocifensive responses of neurogenic, tonic, and neuropathic pain, but their efficacies strongly depend on the pain model used.

Topics: Acetanilides; Analgesics; Animals; Benzamides; Capsaicin; Cold Temperature; Disease Models, Animal; Formaldehyde; Hyperalgesia; Isothiocyanates; Male; Mice; Neuralgia; Oximes; Paclitaxel; Pain Measurement; Purines; Thiophenes; Touch; Transient Receptor Potential Channels; TRPA1 Cation Channel; TRPM Cation Channels; TRPV Cation Channels

Cold hypersensitivity is evident in a range of neuropathies and can evoke sensations of paradoxical burning cold pain. Ciguatoxin poisoning is known to induce a pain syndrome caused by consumption of contaminated tropical fish that can persist for months and include pruritus and cold allodynia; at present no suitable treatment is available. This study examined, for the first time, the neural substrates and molecular components of Pacific ciguatoxin-2-induced cold hypersensitivity. Electrophysiological recordings of dorsal horn lamina V/VI wide dynamic range neurones were made in non-sentient rats. Subcutaneous injection of 10 nm ciguatoxin-2 into the receptive field increased neuronal responses to innocuous and noxious cooling. In addition, neuronal responses to low-threshold but not noxious punctate mechanical stimuli were also elevated. The resultant cold hypersensitivity was not reversed by 6-({2-[2-fluoro-6-(trifluoromethyl)phenoxy]-2-methylpropyl}carbamoyl)pyridine-3-carboxylic acid, an antagonist of transient receptor potential melastatin 8 (TRPM8). Both mechanical and cold hypersensitivity were completely prevented by co-injection with the Nav 1.8 antagonist A803467, whereas the transient receptor potential ankyrin 1 (TRPA1) antagonist A967079 only prevented hypersensitivity to innocuous cooling and partially prevented hypersensitivity to noxious cooling. In naive rats, neither innocuous nor noxious cold-evoked neuronal responses were inhibited by antagonists of Nav 1.8, TRPA1 or TRPM8 alone. Ciguatoxins may confer cold sensitivity to a subpopulation of cold-insensitive Nav 1.8/TRPA1-positive primary afferents, which could underlie the cold allodynia reported in ciguatera. These data expand the understanding of central spinal cold sensitivity under normal conditions and the role of these ion channels in this translational rat model of ciguatoxin-induced hypersensitivity.

Topics: Aniline Compounds; Animals; Ciguatoxins; Cold Temperature; Cryopyrin-Associated Periodic Syndromes; Disease Models, Animal; Furans; Male; Microelectrodes; NAV1.8 Voltage-Gated Sodium Channel; Neurons; Neurotransmitter Agents; Nicotinic Acids; Oximes; Rats, Sprague-Dawley; Spinal Cord; Touch; TRPA1 Cation Channel; TRPC Cation Channels; TRPM Cation Channels; Voltage-Gated Sodium Channel Blockers

The rodent transient receptor potential ankyrin-1 (TRPA1) channel has been hypothesized to serve as a temperature sensor for thermoregulation in the cold. We tested this hypothesis by using deletion of the Trpa1 gene in mice and pharmacological blockade of the TRPA1 channel in rats. In both Trpa1(-/-) and Trpa1(+/+) mice, severe cold exposure (8°C) resulted in decreases of skin and deep body temperatures to ∼8°C and 13°C, respectively, both temperatures being below the reported 17°C threshold temperature for TRPA1 activation. Under these conditions, Trpa1(-/-) mice had the same dynamics of body temperature as Trpa1(+/+) mice and showed no weakness in the tail skin vasoconstriction response or thermogenic response to cold. In rats, the effects of pharmacological blockade were studied by using two chemically unrelated TRPA1 antagonists: the highly potent and selective compound A967079, which had been characterized earlier, and the relatively new compound 43 ((4R)-1,2,3,4-tetrahydro-4-[3-(3-methoxypropoxy)phenyl]-2-thioxo-5H-indeno[1,2-d]pyrimidin-5-one), which we further characterized in the present study and found to be highly potent (IC50 against cold of ∼8 nm) and selective. Intragastric administration of either antagonist at 30 mg/kg before severe (3°C) cold exposure did not affect the thermoregulatory responses (deep body and tail skin temperatures) of rats, even though plasma concentrations of both antagonists well exceeded their IC50 value at the end of the experiment. In the same experimental setup, blocking the melastatin-8 (TRPM8) channel with AMG2850 (30 mg/kg) attenuated cold-defense mechanisms and led to hypothermia. We conclude that TRPA1 channels do not drive autonomic thermoregulatory responses to cold in rodents.

Topics: Animals; Autonomic Nervous System; Body Temperature Regulation; CHO Cells; Cold Temperature; Cricetulus; Disease Models, Animal; Dose-Response Relationship, Drug; Female; Gene Expression Regulation; HSP90 Heat-Shock Proteins; Intracellular Signaling Peptides and Proteins; Male; Mice; Mice, Transgenic; Oximes; Pain; Rats; Rats, Sprague-Dawley; Rats, Wistar; Skin Temperature; Thermosensing; TRPM Cation Channels

Visceral afferents expressing transient receptor potential (TRP) channels TRPV1 and TRPA1 are thought to be required for neurogenic inflammation and development of inflammatory hyperalgesia. Using a mouse model of chronic pancreatitis (CP) produced by repeated episodes (twice weekly) of caerulein-induced AP (AP), we studied the involvement of these TRP channels in pancreatic inflammation and pain-related behaviors. Antagonists of the two TRP channels were administered at different times to block the neurogenic component of AP. Six bouts of AP (over 3 wks) increased pancreatic inflammation and pain-related behaviors, produced fibrosis and sprouting of pancreatic nerve fibers, and increased TRPV1 and TRPA1 gene transcripts and a nociceptive marker, pERK, in pancreas afferent somata. Treatment with TRP antagonists, when initiated before week 3, decreased pancreatic inflammation and pain-related behaviors and also blocked the development of histopathological changes in the pancreas and upregulation of TRPV1, TRPA1, and pERK in pancreatic afferents. Continued treatment with TRP antagonists blocked the development of CP and pain behaviors even when mice were challenged with seven more weeks of twice weekly caerulein. When started after week 3, however, treatment with TRP antagonists was ineffective in blocking the transition from AP to CP and the emergence of pain behaviors. These results suggest: (1) an important role for neurogenic inflammation in pancreatitis and pain-related behaviors, (2) that there is a transition from AP to CP, after which TRP channel antagonism is ineffective, and thus (3) that early intervention with TRP channel antagonists may attenuate the transition to and development of CP effectively.

Topics: Amidines; Analgesics, Opioid; Analysis of Variance; Animals; Antigens, Differentiation; Calcitonin Gene-Related Peptide; Calcium; Ceruletide; Disease Models, Animal; Disease Progression; Exploratory Behavior; Extracellular Signal-Regulated MAP Kinases; Ganglia, Spinal; Gene Expression Regulation; Injections, Intraperitoneal; Male; Mice; Mice, Inbred C57BL; Monocytes; Morphine; Neutrophil Infiltration; Nodose Ganglion; Oximes; Pain; Pain Measurement; Pancreas; Pancreatitis, Chronic; Peroxidase; Pyridines; RNA, Messenger; Sensory Receptor Cells; Time Factors; Transient Receptor Potential Channels; TRPA1 Cation Channel; TRPV Cation Channels

The transient receptor potential ankyrin 1 (TRPA1) ion channel is expressed on nociceptive primary afferent nerve fibers. On the distal ending, it is involved in transduction of noxious stimuli, and on the proximal ending (within the spinal dorsal horn), it regulates transmission of nociceptive signals. Here we studied whether the cutaneous or spinal TRPA1 ion channel contributes to mechanical hypersensitivity or guarding, an index of spontaneous pain, in an experimental model of postoperative pain in the rat.. A skin plus deep-tissue incision was performed under general anesthesia in the plantar skin of one hind paw, after which the incised skin was closed with sutures. Postoperative pain and hypersensitivity were assessed 24-48 h after the operation. Guarding pain was assessed by scoring the hind-paw position. Mechanical hypersensitivity was assessed with a calibrated series of monofilaments applied to the wound area in the operated paw or the contralateral control paw. Chembridge-5861528, a TRPA1 channel antagonist, was administered intaperitoneally (10-30 mg/kg), intraplantarly (10-30 μg), or intrathecally (10 μg) in attempts to suppress guarding and hypersensitivity.. Intraperitoneal or ipsi- but not contralateral intraplantar treatment with Chembridge-5861528 reduced mechanical hypersensitivity and guarding in the operated limb. Intrathecal treatment attenuated hypersensitivity but not guarding. Intraplantar Chembridge-5861528 suppressed preferentially mechanical hyperalgesia and intrathecal Chembridge-5861528 tactile allodynia.. The TRPA1 channel in the skin contributes to sustained as well noxious mechanical stimulus-evoked postoperative pain, whereas the spinal TRPA1 channel contributes predominantly to innocuous mechanical stimulus-evoked postoperative pain.

Topics: Animals; Disease Models, Animal; Hyperalgesia; Hypnotics and Sedatives; Male; Motor Activity; Oximes; Pain, Postoperative; Rats; Rats, Wistar; TRPA1 Cation Channel; TRPC Cation Channels; TRPV Cation Channels

Despite the increasing interest in TRPA1 channel as a pain target, its role in cold sensation and body temperature regulation is not clear; the efficacy and particularly side effects resulting from channel blockade remain poorly understood. Here we use a potent, selective, and bioavailable antagonist to address these issues. A-967079 potently blocks human (IC(50): 51 nmol/L, electrophysiology, 67 nmol/L, Ca(2+) assay) and rat TRPA1 (IC(50): 101 nmol/L, electrophysiology, 289 nmol/L, Ca(2+) assay). It is >1000-fold selective over other TRP channels, and is >150-fold selective over 75 other ion channels, enzymes, and G-protein-coupled receptors. Oral dosing of A-967079 produces robust drug exposure in rodents, and exhibits analgesic efficacy in allyl isothiocyanate-induced nocifensive response and osteoarthritic pain in rats (ED(50): 23.2 mg/kg, p.o.). A-967079 attenuates cold allodynia produced by nerve injury but does not alter noxious cold sensation in naive animals, suggesting distinct roles of TRPA1 in physiological and pathological states. Unlike TRPV1 antagonists, A-967079 does not alter body temperature. It also does not produce locomotor or cardiovascular side effects. Collectively, these data provide novel insights into TRPA1 function and suggest that the selective TRPA1 blockade may present a viable strategy for alleviating pain without untoward side effects.

Topics: Animals; Blood Pressure; Body Temperature; Body Temperature Regulation; Calcitonin Gene-Related Peptide; Calcium; Calcium Channels; Cells, Cultured; Cold Temperature; Disease Models, Animal; Drug Interactions; Ganglia, Spinal; Heart Rate; Humans; Hyperalgesia; Inhibitory Concentration 50; Isothiocyanates; Magnetic Resonance Imaging; Male; Mice; Nerve Tissue Proteins; Neurons; Oximes; Pain; Pain Measurement; Rats; Rats, Sprague-Dawley; Reaction Time; Sensation; Sensory Thresholds; Transient Receptor Potential Channels; Tritium; TRPA1 Cation Channel; TRPV Cation Channels