RESUMEN
The transient receptor potential ankyrin 1 (TRPA1) ion channel on peripheral terminals of nociceptive primary afferent nerve fibres contributes to the transduction of noxious stimuli to electrical signals, while on central endings in the spinal dorsal horn, it amplifies transmission to spinal interneurons and projection neurons. The centrally propagating nociceptive signal that is induced and amplified by TRPA1 not only elicits pain sensation but also contributes to peripheral neurogenic inflammation through a peripheral axon reflex or a centrally mediated back propagating dorsal root reflex that releases vasoactive agents from sensory neurons in the periphery. Endogenous TRPA1 agonists that are generated under various pathophysiological conditions both in the periphery and in the spinal cord have TRPA1-mediated pro-nociceptive and pro-inflammatory effects. Among endogenous TRPA1 agonists that have been shown to play a role in the pathogenesis of pain and inflammatory conditions are, for example, methylglyoxal, 4-hydroxynonenal, 12-lipoxygenase-derived hepoxilin A3, 5,6-epoxyeicosatrienoic acid and reactive oxygen species, while mustard oil and cinnamaldehyde are most commonly used exogenous TRPA1 agonists in experimental studies. Among selective TRPA1 antagonists are HC-030031, A-967079, AP-14 and Chembridge-5861528. Recent evidence indicates that TRPA1 plays a role also in transition of acute to chronic pain. Due to its location on a subpopulation of pain-mediating primary afferent nerve fibres, blocking the TRPA1 channel is expected to have antinociceptive, antiallodynic and anti-inflammatory effects.
Asunto(s)
Ancirinas/metabolismo , Inflamación/metabolismo , Dolor/metabolismo , Canales de Potencial de Receptor Transitorio/metabolismo , Acetanilidas/farmacología , Acroleína/análogos & derivados , Acroleína/farmacología , Aldehídos/farmacología , Animales , Ancirinas/antagonistas & inhibidores , Humanos , Inflamación/patología , Planta de la Mostaza , Oximas/farmacología , Dolor/patología , Aceites de Plantas/farmacología , Purinas/farmacología , Médula Espinal/efectos de los fármacos , Médula Espinal/metabolismo , Médula Espinal/fisiopatología , Canales de Potencial de Receptor Transitorio/antagonistas & inhibidoresRESUMEN
Peripheral diabetic neuropathy (PDN) is a devastating complication of diabetes mellitus (DM). Here we test the hypothesis that the transient receptor potential ankyrin 1 (TRPA1) ion channel on primary afferent nerve fibers is involved in the pathogenesis of PDN, due to sustained activation by reactive compounds generated in DM. DM was induced by streptozotocin in rats that were treated daily for 28 days with a TRPA1 channel antagonist (Chembridge-5861528) or vehicle. Laser Doppler flow method was used for assessing axon reflex induced by intraplantar injection of a TRPA1 channel agonist (cinnamaldehyde) and immunohistochemistry to assess substance P-like innervation of the skin. In vitro calcium imaging and patch clamp were used to assess whether endogenous TRPA1 agonists (4-hydroxynonenal and methylglyoxal) generated in DM induce sustained activation of the TRPA1 channel. Axon reflex induced by a TRPA1 channel agonist in the plantar skin was suppressed and the number of substance P-like immunoreactive nerve fibers was decreased 4 weeks after induction of DM. Prolonged treatment with Chembridge-5861528 reduced the DM-induced attenuation of the cutaneous axon reflex and loss of substance P-like immunoreactive nerve fibers. Moreover, in vitro calcium imaging and patch clamp results indicated that reactive compounds generated in DM (4-hydroxynonenal and methylglyoxal) produced sustained activations of the TRPA1 channel, a prerequisite for adverse long-term effects. The results indicate that the TRPA1 channel exerts an important role in the pathogenesis of PDN. Blocking the TRPA1 channel provides a selective disease-modifying treatment of PDN.
Asunto(s)
Diabetes Mellitus Experimental/tratamiento farmacológico , Nefropatías Diabéticas/prevención & control , Fibras Nerviosas/efectos de los fármacos , Neuronas Aferentes/efectos de los fármacos , Fármacos del Sistema Sensorial/farmacología , Piel/inervación , Canales Catiónicos TRPC/antagonistas & inhibidores , Animales , Canales de Calcio/genética , Canales de Calcio/metabolismo , Señalización del Calcio/efectos de los fármacos , Diabetes Mellitus Experimental/complicaciones , Diabetes Mellitus Experimental/metabolismo , Diabetes Mellitus Experimental/fisiopatología , Nefropatías Diabéticas/etiología , Nefropatías Diabéticas/metabolismo , Nefropatías Diabéticas/fisiopatología , Células HEK293 , Humanos , Masculino , Potenciales de la Membrana , Fibras Nerviosas/metabolismo , Proteínas del Tejido Nervioso/antagonistas & inhibidores , Proteínas del Tejido Nervioso/genética , Proteínas del Tejido Nervioso/metabolismo , Conducción Nerviosa/efectos de los fármacos , Neuronas Aferentes/metabolismo , Umbral del Dolor/efectos de los fármacos , Ratas , Reflejo/efectos de los fármacos , Sustancia P/metabolismo , Canal Catiónico TRPA1 , Canales Catiónicos TRPC/agonistas , Canales Catiónicos TRPC/genética , Canales Catiónicos TRPC/metabolismo , Factores de Tiempo , Transfección , Canales de Potencial de Receptor Transitorio/antagonistas & inhibidores , Canales de Potencial de Receptor Transitorio/genética , Canales de Potencial de Receptor Transitorio/metabolismoRESUMEN
The transient receptor potential ankyrin 1 (TRPA1) ion channel is expressed on nociceptive primary afferent neurons. On the proximal nerve ending within the spinal dorsal horn, TRPA1 regulates transmission to spinal interneurons, and thereby pain hypersensitivity. Here we assessed whether the contribution of the spinal TRPA1 channel to pain hypersensitivity varies with the experimental pain model, properties of test stimulation or the behavioral pain response. The antihypersensitivity effect of intrathecally (i.t.) administered Chembridge-5861528 (CHEM; a selective TRPA1 channel antagonist; 5-10µg) was determined in various experimental models of pain hypersensitivity in the rat. In spinal nerve ligation and rapid eye movement (REM) sleep deprivation models, i.t. CHEM attenuated mechanical hypersensitivity. Capsaicin-induced secondary (central) but not primary (peripheral) mechanical hypersensitivity was also reduced by i.t. administration of CHEM or A-967079, another TRPA1 channel antagonist. Formalin-induced secondary mechanical hypersensitivity, but not spontaneous pain, was suppressed by i.t. CHEM. Moreover, mechanical hypersensitivity induced by cholekystokinin in the rostroventromedial medulla was attenuated by i.t. pretreatment with CHEM. Independent of the model, the antihypersensitivity effect induced by i.t. CHEM was predominant on responses evoked by low-intensity stimuli (⩽6g). CHEM (10µg i.t.) failed to attenuate pain behavior in healthy controls or mechanical hypersensitivities induced by i.t. administrations of a GABA(A) receptor antagonist, or NMDA or 5-HT(3) receptor agonists. Conversely, i.t. administration of a TRPA1 channel agonist, cinnamon aldehyde, induced mechanical hypersensitivity. The results indicate that the spinal TRPA1 channel exerts an important role in secondary (central) pain hypersensitivity to low-intensity mechanical stimulation in various pain hypersensitivity conditions. The spinal TRPA1 channel provides a promising target for the selective attenuation of a central mechanism contributing to pathophysiological pain.
Asunto(s)
Ancirinas/metabolismo , Canales de Calcio/metabolismo , Hiperalgesia/metabolismo , Hiperalgesia/patología , Médula Espinal/metabolismo , Acetanilidas/uso terapéutico , Análisis de Varianza , Animales , Ancirinas/agonistas , Ancirinas/antagonistas & inhibidores , Capsaicina/efectos adversos , Colecistoquinina/efectos adversos , Cinnamomum zeylanicum/efectos adversos , Modelos Animales de Enfermedad , Relación Dosis-Respuesta a Droga , Formaldehído/efectos adversos , Hiperalgesia/tratamiento farmacológico , Hiperalgesia/etiología , Masculino , N-Metilaspartato/efectos adversos , Dimensión del Dolor/métodos , Enfermedades del Sistema Nervioso Periférico/complicaciones , Purinas/uso terapéutico , Ratas , Ratas Wistar , Privación de Sueño/complicaciones , Médula Espinal/efectos de los fármacos , Canal Catiónico TRPA1 , Canales Catiónicos TRPCRESUMEN
Previous results indicate that intaperitoneal administration of a TRPA1 channel antagonist attenuates diabetic hypersensitivity. We studied whether the antihypersensitivity effect induced by a TRPA1 channel antagonist in diabetic animals is explained by action on the TRPA1 channel in the skin, the spinal cord, or both. For comparison, we determined the contribution of cutaneous and spinal TRPA1 channels to development of hypersensitivity induced by topical administration of mustard oil in healthy controls. Diabetes mellitus was induced by streptozotocin in the rat. Hypersensitivity was assessed by the monofilament- and paw pressure-induced limb withdrawal response. Intrathecal (i.t.) administration of Chembridge-5861528 (CHEM, a TRPA1 channel antagonist) at doses 2.5-5.0 microg/rat markedly attenuated diabetic hypersensitivity, whereas 20 microg of CHEM was needed to produce a weak attenuation of diabetic hypersensitivity with intraplantar (i.pl.) administrations. In controls, i.pl. administration of CHEM (20 microg) produced a weak antihypersensitivity effect at the mustard oil-treated site. I.t. administration of CHEM (10 microg) in controls produced a strong antihypersensitivity effect adjacent to the mustard oil-treated area (site of secondary hyperalgesia), while it failed to influence hypersensitivity at the mustard oil-treated area (site of primary hyperalgesia). A reversible antagonism of the rat TRPA1 channel by CHEM was verified using in vitro patch clamp recordings. The results suggest that while cutaneous TRPA1 channels contribute to mechanical hypersensitivity induced by diabetes or topical mustard oil, spinal TRPA1 channels, probably on central terminals of primary afferent nerve fibers, play an important role in maintenance of mechanical hypersensitivity in these conditions.
Asunto(s)
Canales de Calcio/metabolismo , Neuropatías Diabéticas , Hiperalgesia/metabolismo , Umbral del Dolor/fisiología , Piel/metabolismo , Médula Espinal/metabolismo , Aldehídos/farmacología , Análisis de Varianza , Animales , Ancirinas , Antihipertensivos/farmacología , Línea Celular Transformada , Inhibidores de Cisteína Proteinasa/farmacología , Neuropatías Diabéticas/inducido químicamente , Neuropatías Diabéticas/metabolismo , Neuropatías Diabéticas/patología , Modelos Animales de Enfermedad , Relación Dosis-Respuesta a Droga , Vías de Administración de Medicamentos , Humanos , Hiperalgesia/inducido químicamente , Masculino , Potenciales de la Membrana/efectos de los fármacos , Potenciales de la Membrana/genética , Planta de la Mostaza/efectos adversos , Dimensión del Dolor , Umbral del Dolor/efectos de los fármacos , Técnicas de Placa-Clamp , Aceites de Plantas/efectos adversos , Ratas , Ratas Wistar , Piel/inervación , Médula Espinal/efectos de los fármacos , Canal Catiónico TRPA1 , Canales Catiónicos TRPC , Factores de Tiempo , TransfecciónRESUMEN
BACKGROUND: The TRPA1 ion channel modulates excitability of nociceptors, and it may be activated by compounds resulting from oxidative insults. Diabetes mellitus produces oxidative stress and sensory neuropathy. The authors tested the hypothesis that diabetes-induced endogenous compounds acting on the TRPA1 ion channel contribute to development and maintenance of mechanical hypersensitivity. METHODS: Diabetes mellitus was induced by streptozotocin. Mechanical hypersensitivity was assessed by the monofilament and paw pressure tests. Chembridge-5861528 (CHEM; a TRPA1 channel antagonist, a derivative of HC-030031) or vehicle was administered acutely or twice daily for 10 days in diabetic animals. For comparison, effects of CHEM were assessed in a group of healthy control animals. RESULTS: Acute administration of CHEM attenuated mechanically induced withdrawal responses in diabetic and control groups. The maximal effect (over 50% elevation of the paw pressure threshold) by acute administration of CHEM was obtained in 30 min. The lowest dose producing a significant attenuation was 10 mg/kg in the diabetic group and 30 mg/kg in the healthy controls. Chronic administration of CHEM (30 mg/kg twice daily) for a week in the diabetic group attenuated development of mechanical hypersensitivity. CONCLUSIONS: Reduction of pain-related behavior by a lower dose of the TRPA1 channel antagonist in the diabetic than in the control group suggests that endogenous compounds resulting from diabetes mellitus and acting on the TRPA1 channel contribute to diabetic hypersensitivity. Prolonged antihypersensitivity effect after chronic treatment suggests that daily administration of a TRPA1 channel antagonist may prevent development of diabetic hypersensitivity.