RESUMO
Hyperalgesic priming is a preclinical model of the transition from acute to chronic pain characterized by a leftward shift in the dose-response curve for and marked prolongation of prostaglandin E2 (PGE2)-induced mechanical hyperalgesia, in vivo. In vitro, priming in nociceptors is characterized by a leftward shift in the concentration dependence for PGE2-induced nociceptor sensitization. In the present in vitro study we tested the hypothesis that a mu-opioid receptor (MOR) agonist opioid analgesic, morphine, can produce priming by its direct action on nociceptors. We report that treatment of nociceptors with morphine, in vitro, produces a leftward shift in the concentration dependence for PGE2-induced nociceptor sensitization. Our findings support the suggestion that opioids act directly on nociceptors to induce priming.
Assuntos
Dinoprostona , Morfina , Nociceptores , Morfina/farmacologia , Animais , Nociceptores/efeitos dos fármacos , Nociceptores/metabolismo , Dinoprostona/metabolismo , Dinoprostona/farmacologia , Receptores Opioides mu/metabolismo , Analgésicos Opioides/farmacologia , Masculino , Ratos , Gânglios Espinais/efeitos dos fármacos , Gânglios Espinais/metabolismo , Hiperalgesia/induzido quimicamente , Hiperalgesia/tratamento farmacológico , Ratos Sprague-Dawley , Relação Dose-Resposta a DrogaRESUMO
Reactive sulfur species including sulfides, polysulfides and cysteine hydropersulfide play extensive roles in health and disease, which involve modification of protein functions through the interaction with metals bound to the proteins, cleavage of cysteine disulfide (S-S) bonds and S-persulfidation of cysteine residues. Sulfides over a wide micromolar concentration range enhance the activity of Cav3.2 T-type Ca2+ channels by eliminating Zn2+ bound to the channels, thereby promoting somatic and visceral pain. Cav3.2 is under inhibition by Zn2+ in physiological conditions, so that sulfides function to reboot Cav3.2 from Zn2+ inhibition and increase the excitability of nociceptors. On the other hand, polysulfides generated from sulfides activate TRPA1 channels via cysteine S-persulfidation, thereby facilitating somatic, but not visceral, pain. Thus, Cav3.2 function enhancement by sulfides and TRPA1 activation by polysulfides, synergistically accelerate somatic pain signals. The increased activity of the sulfide/Cav3.2 system, in particular, appears to have a great impact on pathological pain, and may thus serve as a therapeutic target for treatment of neuropathic and inflammatory pain including visceral pain.
Assuntos
Canais de Cálcio Tipo T , Sulfetos , Canal de Cátion TRPA1 , Sulfetos/farmacologia , Canal de Cátion TRPA1/metabolismo , Humanos , Canais de Cálcio Tipo T/metabolismo , Canais de Cálcio Tipo T/fisiologia , Animais , Zinco/metabolismo , Dor/metabolismo , Dor/tratamento farmacológico , Nociceptores/metabolismo , Nociceptores/efeitos dos fármacosRESUMO
Nociceptive sensory neurons convey pain-related signals to the CNS using action potentials. Loss-of-function mutations in the voltage-gated sodium channel NaV1.7 cause insensitivity to pain (presumably by reducing nociceptor excitability) but clinical trials seeking to treat pain by inhibiting NaV1.7 pharmacologically have struggled. This may reflect the variable contribution of NaV1.7 to nociceptor excitability. Contrary to claims that NaV1.7 is necessary for nociceptors to initiate action potentials, we show that nociceptors can achieve similar excitability using different combinations of NaV1.3, NaV1.7, and NaV1.8. Selectively blocking one of those NaV subtypes reduces nociceptor excitability only if the other subtypes are weakly expressed. For example, excitability relies on NaV1.8 in acutely dissociated nociceptors but responsibility shifts to NaV1.7 and NaV1.3 by the fourth day in culture. A similar shift in NaV dependence occurs in vivo after inflammation, impacting ability of the NaV1.7-selective inhibitor PF-05089771 to reduce pain in behavioral tests. Flexible use of different NaV subtypes exemplifies degeneracy - achieving similar function using different components - and compromises reliable modulation of nociceptor excitability by subtype-selective inhibitors. Identifying the dominant NaV subtype to predict drug efficacy is not trivial. Degeneracy at the cellular level must be considered when choosing drug targets at the molecular level.
Assuntos
Analgésicos , Benzenossulfonamidas , Nociceptores , Éteres Fenílicos , Animais , Analgésicos/farmacologia , Nociceptores/metabolismo , Nociceptores/efeitos dos fármacos , Canal de Sódio Disparado por Voltagem NAV1.7/metabolismo , Canal de Sódio Disparado por Voltagem NAV1.7/genética , Camundongos , Potenciais de Ação/efeitos dos fármacos , Dor/tratamento farmacológico , Humanos , Canais de Sódio/metabolismo , Canais de Sódio/genética , Canal de Sódio Disparado por Voltagem NAV1.8/metabolismo , Canal de Sódio Disparado por Voltagem NAV1.8/genéticaRESUMO
Recently, we showed that while atogepant-a small-molecule calcitonin gene-related peptide (CGRP) receptor antagonist-does not fully prevent activation of meningeal nociceptors, it significantly reduces a cortical spreading depression (CSD)-induced early response probability in C fibres and late response probability in Aδ fibres. The current study investigates atogepant effect on CSD-induced activation and sensitization of high threshold (HT) and wide dynamic range (WDR) central dura-sensitive trigeminovascular neurons. In anaesthetized male rats, single-unit recordings were used to assess effects of atogepant (5 mg/kg) versus vehicle on CSD-induced activation and sensitization of HT and WDR trigeminovascular neurons. Single cell analysis of atogepant pretreatment effects on CSD-induced activation and sensitization of central trigeminovascular neurons in the spinal trigeminal nucleus revealed the ability of this small molecule CGRP receptor antagonist to prevent activation and sensitization of nearly all HT neurons (8/10 versus 1/10 activated neurons in the control versus treated groups, P = 0.005). In contrast, atogepant pretreatment effects on CSD-induced activation and sensitization of WDR neurons revealed an overall inability to prevent their activation (7/10 versus 5/10 activated neurons in the control versus treated groups, P = 0.64). Unexpectedly however, in spite of atogepant's inability to prevent activation of WDR neurons, it prevented their sensitization (as reflected their responses to mechanical stimulation of the facial receptive field before and after the CSD). Atogepant' ability to prevent activation and sensitization of HT neurons is attributed to its preferential inhibitory effects on thinly myelinated Aδ fibres. Atogepant's inability to prevent activation of WDR neurons is attributed to its lesser inhibitory effects on the unmyelinated C fibres. Molecular and physiological processes that govern neuronal activation versus sensitization can explain how reduction in CGRP-mediated slow but not glutamate-mediated fast synaptic transmission between central branches of meningeal nociceptors and nociceptive neurons in the spinal trigeminal nucleus can prevent their sensitization but not activation.
Assuntos
Antagonistas do Receptor do Peptídeo Relacionado ao Gene de Calcitonina , Depressão Alastrante da Atividade Elétrica Cortical , Transtornos de Enxaqueca , Ratos Sprague-Dawley , Animais , Masculino , Transtornos de Enxaqueca/prevenção & controle , Transtornos de Enxaqueca/tratamento farmacológico , Ratos , Antagonistas do Receptor do Peptídeo Relacionado ao Gene de Calcitonina/farmacologia , Antagonistas do Receptor do Peptídeo Relacionado ao Gene de Calcitonina/uso terapêutico , Depressão Alastrante da Atividade Elétrica Cortical/efeitos dos fármacos , Depressão Alastrante da Atividade Elétrica Cortical/fisiologia , Núcleo Espinal do Trigêmeo/efeitos dos fármacos , Receptores de Peptídeo Relacionado com o Gene de Calcitonina/metabolismo , Nociceptores/efeitos dos fármacos , Nociceptores/fisiologia , Neurônios/efeitos dos fármacos , Neurônios/fisiologiaRESUMO
Unmyelinated tactile (C-tactile or CT) afferents are abundant in arm hairy skin and have been suggested to signal features of social affective touch. Here, we recorded from unmyelinated low-threshold mechanosensitive afferents in the peroneal and radial nerves. The most distal receptive fields were located on the proximal phalanx of the third finger for the superficial branch of the radial nerve and near the lateral malleolus for the peroneal nerve. We found that the physiological properties with regard to conduction velocity and mechanical threshold, as well as their tuning to brush velocity, were similar in CT units across the antebrachial (n = 27), radial (n = 8), and peroneal (n = 4) nerves. Moreover, we found that although CT afferents are readily found during microneurography of the arm nerves, they appear to be much more sparse in the lower leg compared with C-nociceptors. We continued to explore CT afferents with regard to their chemical sensitivity and found that they could not be activated by topical application to their receptive field of either the cooling agent menthol or the pruritogen histamine. In light of previous studies showing the combined effects that temperature and mechanical stimuli have on these neurons, these findings add to the growing body of research suggesting that CT afferents constitute a unique class of sensory afferents with highly specialized mechanisms for transducing gentle touch.NEW & NOTEWORHY Unmyelinated tactile (CT) afferents are abundant in arm hairy skin and are thought to signal features of social affective touch. We show that CTs are also present but are relatively sparse in the lower leg compared with C-nociceptors. CTs display similar physiological properties across the arm and leg nerves. Furthermore, CT afferents do not respond to the cooling agent menthol or the pruritogen histamine, and their mechanical response properties are not altered by these chemicals.
Assuntos
Afeto , Antipruriginosos/farmacologia , Agonistas dos Receptores Histamínicos/farmacologia , Mecanorreceptores/fisiologia , Mentol/farmacologia , Fibras Nervosas Amielínicas/fisiologia , Nervo Fibular/fisiologia , Percepção do Tato/fisiologia , Adulto , Vias Aferentes/efeitos dos fármacos , Vias Aferentes/fisiologia , Antipruriginosos/administração & dosagem , Feminino , Histamina/farmacologia , Agonistas dos Receptores Histamínicos/administração & dosagem , Humanos , Perna (Membro)/inervação , Masculino , Mecanorreceptores/efeitos dos fármacos , Mentol/administração & dosagem , Fibras Nervosas Amielínicas/efeitos dos fármacos , Nociceptores/efeitos dos fármacos , Nociceptores/fisiologia , Nervo Fibular/efeitos dos fármacos , Nervo Radial/efeitos dos fármacos , Nervo Radial/fisiologia , Percepção do Tato/efeitos dos fármacos , Adulto JovemRESUMO
The King Baboon spider, Pelinobius muticus, is a burrowing African tarantula. Its impressive size and appealing coloration are tempered by reports describing severe localized pain, swelling, itchiness, and muscle cramping after accidental envenomation. Hyperalgesia is the most prominent symptom after bites from P. muticus, but the molecular basis by which the venom induces pain is unknown. Proteotranscriptomic analysis of P. muticus venom uncovered a cysteine-rich peptide, δ/κ-theraphotoxin-Pm1a (δ/κ-TRTX-Pm1a), that elicited nocifensive behavior when injected into mice. In small dorsal root ganglion neurons, synthetic δ/κ-TRTX-Pm1a (sPm1a) induced hyperexcitability by enhancing tetrodotoxin-resistant sodium currents, impairing repolarization and lowering the threshold of action potential firing, consistent with the severe pain associated with envenomation. The molecular mechanism of nociceptor sensitization by sPm1a involves multimodal actions over several ion channel targets, including NaV1.8, KV2.1, and tetrodotoxin-sensitive NaV channels. The promiscuous targeting of peptides like δ/κ-TRTX-Pm1a may be an evolutionary adaptation in pain-inducing defensive venoms.
Assuntos
Nociceptores/efeitos dos fármacos , Papio/metabolismo , Peptídeos/farmacologia , Venenos de Aranha/farmacologia , Aranhas/metabolismo , Potenciais de Ação/efeitos dos fármacos , Animais , Gânglios Espinais/efeitos dos fármacos , Hiperalgesia/tratamento farmacológico , Canais Iônicos/metabolismo , Camundongos , Dor/tratamento farmacológico , Tetrodotoxina/farmacologiaRESUMO
Peripheral A1 adenosine receptor signaling has been shown to have analgesic effects in a variety of pain conditions. However, it is not yet fully elucidated for the precise molecular mechanisms. Acid sensing ion channels (ASICs) are expressed predominantly in nociceptive sensory neurons responding to protons. Given that both A1 adenosine receptors and ASICs are present in dorsal root ganglia (DRG) neurons, we therefore investigated whether there was a cross-talk between the two types of receptors. Herein, electrophysiological recordings showed that the A1 adenosine receptor agonist N6-cyclopentyladenosine (CPA) suppressed acid-induced currents and action potentials, which were mediated by ASICs, in rat DRG neurons. CPA inhibited the maximum response to protons, as shown a downward shift of concentration-response curve for protons. The CPA-induced suppression of ASIC currents was blocked by the A1 adenosine receptor antagonist KW-3902 and also prevented by intracellular application of the Gi/o-protein inhibitor pertussis toxin, the adenylate cyclase activator forskolin, and the cAMP analog 8-Br-cAMP. Finally, intraplantar pretreatment of CPA dose-dependently relieved acid-induced nociceptive responses in rats through peripheral A1 adenosine receptors. These results suggested that CPA suppressed ASICs via A1 adenosine receptors and intracellular Gi/o-proteins and cAMP signaling cascades in rat DRG neurons, which was a novel potential mechanism underlying analgesia of peripheral A1 adenosine receptors.
Assuntos
Canais Iônicos Sensíveis a Ácido/efeitos dos fármacos , Agonistas do Receptor A1 de Adenosina/farmacologia , Antagonistas do Receptor A1 de Adenosina/farmacologia , Analgesia , Fenômenos Eletrofisiológicos/efeitos dos fármacos , Gânglios Espinais/efeitos dos fármacos , Nociceptividade/efeitos dos fármacos , Nociceptores/efeitos dos fármacos , Receptor A1 de Adenosina/efeitos dos fármacos , Animais , Comportamento Animal/efeitos dos fármacos , RatosRESUMO
The incidence of chronic pain is especially high in women, but the underlying mechanisms remain poorly understood. Interleukin-23 (IL-23) is a pro-inflammatory cytokine and contributes to inflammatory diseases (e.g., arthritis and psoriasis) through dendritic/T cell signaling. Here we examined the IL-23 involvement in sexual dimorphism of pain, using an optogenetic approach in transgenic mice expressing channelrhodopsin-2 (ChR2) in TRPV1-positive nociceptive neurons. In situ hybridization revealed that compared to males, females had a significantly larger portion of small-sized (100-200 µm2) Trpv1+ neurons in dorsal root ganglion (DRG). Blue light stimulation of a hindpaw of transgenic mice induced intensity-dependent spontaneous pain. At the highest intensity, females showed more intense spontaneous pain than males. Intraplantar injection of IL-23 (100 ng) induced mechanical allodynia in females only but had no effects on paw edema. Furthermore, intraplantar IL-23 only potentiated blue light-induced pain in females, and intrathecal injection of IL-23 also potentiated low-dose capsaicin (500 ng) induced spontaneous pain in females but not males. IL-23 expresses in DRG macrophages of both sexes. Intrathecal injection of IL-23 induced significantly greater p38 phosphorylation (p-p38), a marker of nociceptor activation, in DRGs of female mice than male mice. In THP-1 human macrophages estrogen and chemotherapy co-application increased IL-23 secretion, and furthermore, estrogen and IL-23 co-application, but not estrogen and IL-23 alone, significantly increased IL-17A release. These findings suggest a novel role of IL-23 in macrophage signaling and female-dominant pain, including C-fiber-mediated spontaneous pain. Our study has also provided new insight into cytokine-mediated macrophage-nociceptor interactions, in a sex-dependent manner.
Assuntos
Gânglios Espinais/efeitos dos fármacos , Interleucina-23/toxicidade , Fibras Nervosas Amielínicas/efeitos dos fármacos , Nociceptores/efeitos dos fármacos , Limiar da Dor/efeitos dos fármacos , Dor/induzido quimicamente , Canais de Cátion TRPV/metabolismo , Animais , Capsaicina , Channelrhodopsins/genética , Channelrhodopsins/metabolismo , Modelos Animais de Doenças , Feminino , Gânglios Espinais/metabolismo , Gânglios Espinais/fisiopatologia , Humanos , Interleucina-17/metabolismo , Luz , Macrófagos/efeitos dos fármacos , Macrófagos/metabolismo , Masculino , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Fibras Nervosas Amielínicas/metabolismo , Nociceptores/metabolismo , Optogenética , Dor/genética , Dor/metabolismo , Dor/fisiopatologia , Caracteres Sexuais , Células THP-1 , Canais de Cátion TRPV/genética , Proteínas Quinases p38 Ativadas por Mitógeno/metabolismoRESUMO
Mepyramine, a first-generation antihistamine targeting the histamine H(1) receptor, was extensively prescribed to patients suffering from allergic reactions and urticaria. Serious adverse effects, especially in case of overdose, were frequently reported, including drowsiness, impaired thinking, convulsion, and coma. Many of these side effects were associated with the blockade of histaminergic or cholinergic receptors. Here we show that mepyramine directly inhibits a variety of voltage-gated sodium channels, including the Tetrodotoxin-sensitive isoforms and the main isoforms (Nav1.7, Nav1.8, and Nav1.9) of nociceptors. Estimated IC50 were within the range of drug concentrations detected in poisoned patients. Mepyramine inhibited sodium channels through fast- or slow-inactivated state preference depending on the isoform. Moreover, mepyramine inhibited the firing responses of C- and Aß-type nerve fibers in ex vivo skin-nerve preparations. Locally applied mepyramine had analgesic effects on the scorpion toxin-induced excruciating pain and produced pain relief in acute, inflammatory, and chronic pain models. Collectively, these data provide evidence that mepyramine has the potential to be developed as a topical analgesic agent.
Assuntos
Artrite Experimental/complicações , Gânglios Espinais/efeitos dos fármacos , Canal de Sódio Disparado por Voltagem NAV1.8/fisiologia , Nociceptores/efeitos dos fármacos , Dor/tratamento farmacológico , Pirilamina/farmacologia , Bloqueadores dos Canais de Sódio/farmacologia , Potenciais de Ação , Animais , Gânglios Espinais/metabolismo , Gânglios Espinais/patologia , Antagonistas dos Receptores Histamínicos H1/farmacologia , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Canal de Sódio Disparado por Voltagem NAV1.8/química , Nociceptores/metabolismo , Nociceptores/patologia , Dor/etiologia , Dor/metabolismo , Dor/patologiaRESUMO
The advantage of locally applied anesthetics is that they are not associated with the many adverse effects, including addiction liability, of systemically administered analgesics. This therapeutic approach has two inherent pitfalls: specificity and a short duration of action. Here, we identified nociceptor endocytosis as a promising target for local, specific, and long-lasting treatment of inflammatory pain. We observed preferential expression of AP2α2, an α-subunit isoform of the AP2 complex, within CGRP+/IB4- nociceptors in rodents and in CGRP+ dorsal root ganglion neurons from a human donor. We utilized genetic and pharmacological approaches to inhibit nociceptor endocytosis demonstrating its role in the development and maintenance of acute and chronic inflammatory pain. One-time injection of an AP2 inhibitor peptide significantly reduced acute and chronic pain-like behaviors and provided prolonged analgesia. We evidenced sexually dimorphic recovery responses to this pharmacological approach highlighting the importance of sex differences in pain development and response to analgesics.
Assuntos
Peptídeo Relacionado com Gene de Calcitonina/metabolismo , Dor Crônica/tratamento farmacológico , Endocitose/efeitos dos fármacos , Nociceptores/efeitos dos fármacos , Complexo 2 de Proteínas Adaptadoras/antagonistas & inibidores , Complexo 2 de Proteínas Adaptadoras/genética , Complexo 2 de Proteínas Adaptadoras/metabolismo , Subunidades alfa do Complexo de Proteínas Adaptadoras/antagonistas & inibidores , Subunidades alfa do Complexo de Proteínas Adaptadoras/genética , Subunidades alfa do Complexo de Proteínas Adaptadoras/metabolismo , Animais , Dor Crônica/metabolismo , Dor Crônica/fisiopatologia , Epiderme/inervação , Feminino , Gânglios Espinais/metabolismo , Humanos , Inflamação , Masculino , Camundongos , Neurônios Aferentes/efeitos dos fármacos , Neurônios Aferentes/metabolismo , Nociceptores/metabolismo , Nociceptores/fisiologia , Peptídeos/administração & dosagem , Peptídeos/metabolismo , Peptídeos/farmacologia , RNA Interferente Pequeno/administração & dosagem , RNA Interferente Pequeno/genética , RNA Interferente Pequeno/farmacologiaRESUMO
OBJECTIVE: Volatile anesthetics are widely used for general anesthesia during surgical operations. Voltage-gated Na+ channels expressed in central neurons are major targets for volatile anesthetics; but it is unclear whether these drugs modulate native tetrodotoxin-resistant (TTX-R) Na+ channels, which are involved in the development and maintenance of inflammatory pain. METHODS: In this study, we examined the effects of sevoflurane on TTX-R Na+ currents (INa) in acutely isolated rat dorsal root ganglion neurons, using a whole-cell patch-clamp technique. RESULTS: Sevoflurane slightly potentiated the peak amplitude of transient TTX-R INa but more potently inhibited slow voltage-ramp-induced persistent INa in a concentration-dependent manner. Sevoflurane (0.86 ± 0.02 mM) (1) slightly shifted the steady-state fast inactivation relationship to hyperpolarizing ranges without affecting the voltage-activation relationship, (2) reduced the extent of use-dependent inhibition of Na+ channels, (3) accelerated the onset of inactivation and (4) delayed the recovery from inactivation of TTX-R Na+ channels. Thus, sevoflurane has diverse effects on TTX-R Na+ channels expressed in nociceptive neurons. CONCLUSIONS: The present results suggest that the inhibition of persistent INa and the modulation of the voltage dependence and inactivation might be, at least in part, responsible for the analgesic effects elicited by sevoflurane.
Assuntos
Anestésicos Inalatórios/farmacologia , Gânglios Espinais/citologia , Nociceptores/efeitos dos fármacos , Sevoflurano/farmacologia , Canais de Sódio/efeitos dos fármacos , Animais , Potenciais da Membrana , Neurônios/efeitos dos fármacos , Neurônios/metabolismo , Nociceptores/metabolismo , Técnicas de Patch-Clamp , Ratos , Canais de Sódio/metabolismo , Tetrodotoxina , Canais de Sódio Disparados por Voltagem/efeitos dos fármacos , Canais de Sódio Disparados por Voltagem/metabolismoRESUMO
Although sex dimorphism is increasingly recognized as an important factor in pain, female-specific pain signaling is not well studied. Here we report that administration of IL-23 produces mechanical pain (mechanical allodynia) in female but not male mice, and chemotherapy-induced mechanical pain is selectively impaired in female mice lacking Il23 or Il23r. IL-23-induced pain is promoted by estrogen but suppressed by androgen, suggesting an involvement of sex hormones. IL-23 requires C-fiber nociceptors and TRPV1 to produce pain but does not directly activate nociceptor neurons. Notably, IL-23 requires IL-17A release from macrophages to evoke mechanical pain in females. Low-dose IL-17A directly activates nociceptors and induces mechanical pain only in females. Finally, deletion of estrogen receptor subunit α (ERα) in TRPV1+ nociceptors abolishes IL-23- and IL-17-induced pain in females. These findings demonstrate that the IL-23/IL-17A/TRPV1 axis regulates female-specific mechanical pain via neuro-immune interactions. Our study also reveals sex dimorphism at both immune and neuronal levels.
Assuntos
Receptor alfa de Estrogênio/metabolismo , Interleucina-17/metabolismo , Interleucina-23/metabolismo , Macrófagos/metabolismo , Dor Nociceptiva/metabolismo , Nociceptores/metabolismo , Canais de Cátion TRPV/metabolismo , Animais , Células Cultivadas , Feminino , Humanos , Interleucina-17/farmacologia , Interleucina-23/farmacologia , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Fibras Nervosas Amielínicas/metabolismo , Fibras Nervosas Amielínicas/fisiologia , Dor Nociceptiva/fisiopatologia , Nociceptores/efeitos dos fármacos , Nociceptores/fisiologia , Fatores Sexuais , Transdução de SinaisRESUMO
Contemporary approaches to human health risk assessment for respiratory tract irritants are variable and controversial. This manuscript provides an in-depth analysis and assessment of the applicability of the classical respiratory depression 50 % (RD50) assay with focus on the Log-linear extrapolation of the non-sensory irritant threshold (RD0 or RD10) relative to the contemporary Point of Departure (POD) U.S.-EPA benchmark approach. Three prototypic volatile chemically reactive irritants are used to exemplify the pros and cons of this alternative approach. These irritants differ in physicochemical properties affecting water-solubility and lipophilicity. Depending on these variables, a vapor may preferentially be retained in the extrathoracic region (ET), the tracheobronchial region (TB), and the pulmonary region (PU); although a smooth transition between these regions occurs at increasingly high concentrations. Each region has its specific nociceptors sensing irritants and regional-specific response to injury. The alternative approach using rats identified the chemical-specific critical region of respiratory tract injury. Statistically derived PODs on ET-TB related sensory irritation provide important information for ET-TB irritants but not for PU irritants. The POD of ET-TB irritants from acute and repeated studies decreased substantially. In summary, statistically derived PODs improve the risk assessment of respiratory tract irritants; however, those from repeated exposures should be given preference to those from acute exposures.
Assuntos
Irritantes/toxicidade , Nociceptores/efeitos dos fármacos , Sistema Respiratório/efeitos dos fármacos , Animais , Humanos , Exposição por Inalação , Irritantes/administração & dosagem , Irritantes/química , Masculino , Ratos , Ratos Endogâmicos BN , Ratos Wistar , Sistema Respiratório/patologia , Medição de Risco/métodos , Especificidade da EspécieRESUMO
High molecular weight hyaluronan (HMWH), a well-established treatment for osteoarthritis pain, is anti-hyperalgesic in preclinical models of inflammatory and neuropathic pain. HMWH-induced anti-hyperalgesia is mediated by its action at cluster of differentiation 44 (CD44), the cognate hyaluronan receptor, which can signal via phosphoinositide 3-kinase (PI3K), a large family of kinases involved in diverse cell functions. We demonstrate that intrathecal administration of an oligodeoxynucleotide (ODN) antisense to mRNA for PI3Kγ (a Class I PI3K isoform) expressed in dorsal root ganglia (DRGs), and intradermal administration of a PI3Kγ-selective inhibitor (AS605240), markedly attenuates HMWH-induced anti-prostaglandin E2 (PGE2) hyperalgesia, in male and female rats. Intradermal administration of inhibitors of mammalian target of rapamycin (mTOR; rapamycin) and protein kinase B (AKT; AKT Inhibitor IV), signaling molecules downstream of PI3Kγ, also attenuates HMWH-induced anti-hyperalgesia. In vitro patch-clamp electrophysiology experiments on cultured nociceptors from male rats demonstrate that some HMWH-induced changes in generation of action potentials (APs) in nociceptors sensitized by PGE2 are PI3Kγ dependent (reduction in AP firing rate, increase in latency to first AP and increase in slope of current ramp required to induce AP) and some are PI3Kγ independent [reduction in recovery rate of AP afterhyperpolarization (AHP)]. Our demonstration of a role of PI3Kγ in HMWH-induced anti-hyperalgesia and reversal of nociceptor sensitization opens a novel line of research into molecular targets for the treatment of diverse pain syndromes.SIGNIFICANCE STATEMENT We have previously demonstrated that high molecular weight hyaluronan (HMWH) attenuates inflammatory hyperalgesia, an effect mediated by its action at cluster of differentiation 44 (CD44), the cognate hyaluronan receptor, and activation of its downstream signaling pathway, in nociceptors. In the present study, we demonstrate that phosphoinositide 3-kinase (PI3K)γ and downstream signaling pathway, protein kinase B (AKT) and mammalian target of rapamycin (mTOR), are crucial for HMWH to induce anti-hyperalgesia.
Assuntos
Classe Ib de Fosfatidilinositol 3-Quinase/metabolismo , Ácido Hialurônico/uso terapêutico , Hiperalgesia/tratamento farmacológico , Hiperalgesia/metabolismo , Nociceptores/metabolismo , Proteínas Proto-Oncogênicas c-akt/metabolismo , Animais , Feminino , Ácido Hialurônico/farmacologia , Masculino , Nociceptores/efeitos dos fármacos , Medição da Dor/efeitos dos fármacos , Medição da Dor/métodos , Ratos , Ratos Sprague-Dawley , Transdução de Sinais/efeitos dos fármacos , Transdução de Sinais/fisiologiaRESUMO
Chronic pain is a leading health and socioeconomic problem and an unmet need exists for long-lasting analgesics. SNAREs (soluble N-ethylmaleimide-sensitive factor attachment protein receptors) are required for neuropeptide release and noxious signal transducer surface trafficking, thus, selective expression of the SNARE-cleaving light-chain protease of botulinum neurotoxin A (LCA) in peripheral sensory neurons could alleviate chronic pain. However, a safety concern to this approach is the lack of a sensory neuronal promoter to prevent the expression of LCA in the central nervous system. Towards this, we exploit the unique characteristics of Pirt (phosphoinositide-interacting regulator of TRP), which is expressed in peripheral nociceptive neurons. For the first time, we identified a Pirt promoter element and cloned it into a lentiviral vector driving transgene expression selectively in peripheral sensory neurons. Pirt promoter driven-LCA expression yielded rapid and concentration-dependent cleavage of SNAP-25 in cultured sensory neurons. Moreover, the transcripts of pain-related genes (TAC1, tachykinin precursor 1; CALCB, calcitonin gene-related peptide 2; HTR3A, 5-hydroxytryptamine receptor 3A; NPY2R, neuropeptide Y receptor Y2; GPR52, G protein-coupled receptor 52; SCN9A, sodium voltage-gated channel alpha subunit 9; TRPV1 and TRPA1, transient receptor potential cation channel subfamily V member 1 and subfamily A member 1) in pro-inflammatory cytokines stimulated sensory neurons were downregulated by viral mediated expression of LCA. Furthermore, viral expression of LCA yielded long-lasting inhibition of pain mediator release. Thus, we show that the engineered Pirt-LCA virus may provide a novel means for long lasting pain relief.
Assuntos
Toxinas Botulínicas Tipo A/farmacologia , Neuropeptídeos/metabolismo , Dor/prevenção & controle , Sistema Nervoso Periférico/metabolismo , Células Receptoras Sensoriais/metabolismo , Proteína 25 Associada a Sinaptossoma/metabolismo , Animais , Animais Recém-Nascidos , Feminino , Humanos , Masculino , Fusão de Membrana , Proteínas de Membrana/genética , Proteínas de Membrana/metabolismo , Camundongos , Camundongos Endogâmicos C57BL , Nociceptores/efeitos dos fármacos , Nociceptores/metabolismo , Dor/genética , Dor/metabolismo , Dor/patologia , Sistema Nervoso Periférico/efeitos dos fármacos , Ratos , Ratos Sprague-Dawley , Células Receptoras Sensoriais/efeitos dos fármacos , Proteína 25 Associada a Sinaptossoma/genéticaRESUMO
Bacterial products are able to act on nociceptive neurons during pathogenic infection. Neurogenic inflammation is an active part of pain signaling and has recently been shown to impact host-pathogen defense. Bacillus anthracis Edema Toxin (ET) produces striking edema in peripheral tissues, but the cellular mechanisms involved in tissue swelling are not completely understood. Here, we find that nociceptive neurons play a role in ET-induced edema and inflammation in mice. Subcutaneous footpad infection of B. anthracis Sterne caused ET-dependent local mechanical allodynia, paw swelling and body weight gain. Subcutaneous administration of ET induced paw swelling and vascular leakage, the early phases of which were attenuated in the absence of Trpv1+ or Nav1.8+ nociceptive neurons. Nociceptive neurons express the anthrax toxin receptor ANTXR2, but this did not mediate ET-induced edema. ET induced local cytokine expression and neutrophil recruitment, which were dependent in part on Trpv1+ nociceptive neurons. Ablation of Trpv1+ or Nav1.8+ nociceptive neurons also attenuated early increases in paw swelling and body weight gain during live B. anthracis infection. Our findings indicate that nociceptive neurons play an active role in inflammation caused by B. anthracis and Edema Toxin to potentially influence bacterial pathogenesis.
Assuntos
Antraz/complicações , Antígenos de Bactérias/toxicidade , Toxinas Bacterianas/toxicidade , Inflamação/etiologia , Nociceptores/metabolismo , Animais , Antraz/fisiopatologia , Bacillus anthracis , Camundongos , Camundongos Endogâmicos C57BL , Nociceptores/efeitos dos fármacosRESUMO
Vincristine (VCR) is a widely used chemotherapy drug that induced peripheral painful neuropathy. Yet, it still lacks an ideal therapeutic strategy. The transient receptor potential (TRP) channels, purinergic receptor (P2Y), and mitogen-activated protein kinase (MAPK) signaling play a crucial role in the pathogenesis of neuropathic pain. Withametelin (WMT), a potential Phytosteroid isolated from datura innoxa, exhibits remarkable neuroprotective properties. The present investigation was designed to explore the effect of withametelin on VCR-induced neuropathic pain and its underlying molecular mechanism. Initially, the neuroprotective potential of WMT was confirmed against hydrogen peroxide (H2O2)-induced PC12 cells. To develop potential candidates for neuropathic pain treatment, a VCR-induced neuropathic pain model was established. Vincristine (75 µg/kg) was administered intraperitoneally (i.p.) for 10 consecutive days (day 1-10) for the induction of neuropathic pain. Gabapentin (GBP) (60 mg/kg, i.p.) and withametelin (0.1 and 1 mg/kg i.p.) treatments were given after the completion of VCR injection on the 11th day up to 21 days. The results revealed that WMT significantly reduced VCR-induced pain hypersensitivity, including mechanical allodynia, cold allodynia, and thermal hyperalgesia. It reversed the VCR-induced histopathological changes in the brain, spinal cord, and sciatic nerve. It inhibited VCR-induced changes in the biochemical composition of the myelin sheath of the sciatic nerve. It markedly downregulated the expression levels of TRPV1 (transient receptor potential vanilloid 1); TRPM8 (Transient receptor potential melastatin 8); and P2Y nociceptors and MAPKs signaling, including ERK (Extracellular Signal-Regulated Kinase), JNK (c-Jun N-terminal kinase), and p-38 in the spinal cord. It suppressed apoptosis by regulating Bax (Bcl2-associated X-protein), Bcl-2 (B-cell-lymphoma-2), and Caspase-3 expression. It considerably attenuated inflammatory cytokines, oxidative stress, and genotoxicity. This study suggests that WMT treatment suppressed vincristine-induced neuropathic pain by targeting the TRPV1/TRPM8/P2Y nociceptors and MAPK signaling.
Assuntos
Sistema de Sinalização das MAP Quinases/efeitos dos fármacos , Neuralgia/tratamento farmacológico , Nociceptores/efeitos dos fármacos , Fitosteróis/farmacologia , Receptores Purinérgicos P2Y/química , Canais de Cátion TRPM/antagonistas & inibidores , Canais de Cátion TRPV/antagonistas & inibidores , Vincristina/toxicidade , Animais , Antineoplásicos Fitogênicos/toxicidade , Masculino , Camundongos , Camundongos Endogâmicos BALB C , Neuralgia/induzido quimicamente , Neuralgia/metabolismo , RatosRESUMO
Transient receptor potential vanilloid 1 (TRPV1) ion channel is a nociceptor critically involved in pain sensation. Direct blockade of TRPV1 exhibits significant analgesic effects but also incurs severe side effects such as hyperthermia, causing failures of TRPV1 inhibitors in clinical trials. In order to selectively target TRPV1 channels that are actively involved in pain-sensing, peptidic positive allosteric modulators (PAMs) based on the high-resolution structure of the TRPV1 intracellular ankyrin-repeat like domain are de novo designed. The hotspot centric approach is optimized for protein design; its usage in Rosetta increases the success rate in protein binder design. It is demonstrated experimentally, with a combination of fluorescence resonance energy transfer (FRET) imaging, surface plasmon resonance, and patch-clamp recording, that the designed PAMs bind to TRPV1 with nanomolar affinity and allosterically enhance its response to ligand activation as it is designed. It is further demonstrated that the designed PAM exhibits long-lasting in vivo analgesic effects in rats without changing their body temperature, suggesting that they have potentials for developing into novel analgesics.
Assuntos
Analgésicos/farmacologia , Nociceptores/efeitos dos fármacos , Dor/tratamento farmacológico , Canais de Cátion TRPV/efeitos dos fármacos , Regulação Alostérica/efeitos dos fármacos , Animais , Modelos Animais de Doenças , Masculino , Peptídeos , RatosRESUMO
Bile acid reflux in the esophagus plays a role in the pathogenesis of certain esophageal disorders, where it can induce esophageal pain and heartburn. The present study aimed to determine whether bile acid, deoxycholic acid (DCA), directly activates and sensitizes esophageal vagal nociceptive afferent C-fiber subtypes. DCA-elicited effects on vagal nodose and jugular neurons were studied by calcium imaging. Its effects on esophageal-labeled nodose and jugular neurons were then determined by patch-clamp recording. At nodose and jugular C-fiber nerve endings in the esophagus, DCA-evoked action potentials (APs) were compared by extracellular single-unit recordings in ex vivo esophageal-vagal preparations. DCA application induced calcium influxes in nodose and jugular neurons and elicited inward currents in esophageal-labeled nodose and jugular neurons. In the presence of DCA, the current densities elicited by capsaicin were enhanced in those labeled neurons. Consistently, DCA perfusion at nerve terminals in the esophagus evoked APs in about 50% of esophageal nodose and jugular C-fibers. In DCA-sensitive C-fibers, DCA perfusion also sensitized the fibers such that the subsequent response to capsaicin was amplified. Collectively, these results provide new evidence that DCA directly activates and sensitizes nociceptive nodose and jugular C-fibers in the esophagus. Such activation and sensitization effects may contribute to bile acid-induced esophageal nociceptive symptoms that are refractory to proton-pump inhibitor therapy.NEW & NOTEWORTHY Bile acid reflux in the esophagus can induce pain and heartburn in certain esophageal disorders, but the underlying neuronal mechanism is still unclear. The present study demonstrated that bile acid, deoxycholic acid (DCA), directly activates esophageal vagal afferent nodose and jugular nociceptive C-fibers and sensitizes their response to capsaicin. Such effects may contribute to bile acid-induced esophageal nociceptive symptoms that refractory to proton-pump inhibitors (PPIs) therapy.
Assuntos
Potenciais de Ação , Colagogos e Coleréticos/farmacologia , Ácido Desoxicólico/farmacologia , Esôfago/fisiologia , Nociceptores/fisiologia , Animais , Sinalização do Cálcio , Células Cultivadas , Esôfago/inervação , Cobaias , Fibras Nervosas Amielínicas/efeitos dos fármacos , Fibras Nervosas Amielínicas/fisiologia , Nociceptores/efeitos dos fármacos , Nociceptores/metabolismo , Nervo Vago/efeitos dos fármacos , Nervo Vago/fisiologiaRESUMO
Family with sequence similarity 19 (chemokine (C-C motif)-like) member A5 (FAM19A5) is a chemokine-like secretory protein recently identified as involved in the regulation of osteoclast formation, post-injury neointima formation, and depression. Although roles for FAM19A5 have been described in nervous system development and psychiatric disorders, its role in the nervous system remains poorly understood. Here, we analyzed the evolutionary history of FAM19A genes in vertebrates and identified FAM19A5l, a paralogous zebrafish gene originating from a common ancestral FAM19A5 gene. Further, zebrafish FAM19A5l is expressed in trigeminal and dorsal root ganglion neurons as well as distinct neuronal subsets of the central nervous system. Interestingly, FAM19A5l+ trigeminal neurons are nociceptive neurons that localized with TRPA1b and TRPV1 and respond to mustard oil treatment. Behavioral analysis further revealed that the nociceptive response to mustard oil decreases in FAM19A5l-knockout zebrafish larvae. In addition, TRPA1b and NGFa mRNA levels are down- and upregulated in FAM19A5l-knockout and -overexpressing transgenic zebrafish, respectively. Together, our data suggest that FAM19A5l plays a role in nociceptive responses to mustard oil by regulating TRPA1b and NGFa expression in zebrafish.