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Murota H, Katayama I. Evolving understanding on the aetiology of thermally provoked itch. Eur J Pain 2015; 20:47-50. [PMID: 26415614 PMCID: PMC5055078 DOI: 10.1002/ejp.777] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/08/2015] [Indexed: 11/17/2022]
Abstract
Background and objectives Itch is one of the major symptoms in dermatology clinics, and severely impairs the quality of life. Itch is frequently produced by environmental stimuli, especially heat or warmth. Changes of temperature on the skin surface and noxious heat stimuli augment and develop itch, respectively. Thermally provoked itch is sometimes intractable with existing treatments. Data bases and data treatment Recent researches, linking heat sensation and itch, were searched in MEDLINE literature database through PubMed. Results Recent studies of the transient receptor potential cation channel subfamily vanilloid type 1 (TRPV1), the calcitonin gene‐related peptide (CGRP) and the vesicular glutamate transporter 2 (VGLUT2), which link noxious heat and itch, contribute to a much better understanding of the thermally evoked itch process. From a clinical perspective, a warm sensation is a major provocative factor for subjects with atopic dermatitis. The accumulation of artemin (also known as enovin or neublastin) in the dermis of lesional skin can possibly provide a pathological mechanism for warmth‐provoked itch. Conclusions This mini‐review describes recent results of both basic and clinical research related to thermally provoked itch.
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Affiliation(s)
- H Murota
- Department of Dermatology, Course of Integrated Medicine, Graduate School of Medicine, Osaka University, Suita, Japan
| | - I Katayama
- Department of Dermatology, Course of Integrated Medicine, Graduate School of Medicine, Osaka University, Suita, Japan
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202
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Luo J, Feng J, Liu S, Walters ET, Hu H. Molecular and cellular mechanisms that initiate pain and itch. Cell Mol Life Sci 2015; 72:3201-23. [PMID: 25894692 PMCID: PMC4534341 DOI: 10.1007/s00018-015-1904-4] [Citation(s) in RCA: 66] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2014] [Revised: 03/20/2015] [Accepted: 04/07/2015] [Indexed: 12/17/2022]
Abstract
Somatosensory neurons mediate our sense of touch. They are critically involved in transducing pain and itch sensations under physiological and pathological conditions, along with other skin-resident cells. Tissue damage and inflammation can produce a localized or systemic sensitization of our senses of pain and itch, which can facilitate our detection of threats in the environment. Although acute pain and itch protect us from further damage, persistent pain and itch are debilitating. Recent exciting discoveries have significantly advanced our knowledge of the roles of membrane-bound G protein-coupled receptors and ion channels in the encoding of information leading to pain and itch sensations. This review focuses on molecular and cellular events that are important in early stages of the biological processing that culminates in our senses of pain and itch.
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Affiliation(s)
- Jialie Luo
- Department of Anesthesiology, The Center for the Study of Itch, Washington University School of Medicine, 660 S. Euclid Ave., St. Louis, MO, 63110, USA
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203
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Kim YS, Kim YB, Kim WB, Yoon BE, Shen FY, Lee SW, Soong TW, Han HC, Colwell CS, Lee CJ, Kim YI. Histamine resets the circadian clock in the suprachiasmatic nucleus through the H1R-CaV1.3-RyR pathway in the mouse. Eur J Neurosci 2015. [DOI: 10.1111/ejn.13030] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Yoon Sik Kim
- Department of Physiology and Neuroscience Research Institute; Korea University College of Medicine; Seoul 136-705 Korea
| | - Young-Beom Kim
- Department of Physiology and Neuroscience Research Institute; Korea University College of Medicine; Seoul 136-705 Korea
| | - Woong Bin Kim
- Department of Physiology and Neuroscience Research Institute; Korea University College of Medicine; Seoul 136-705 Korea
| | - Bo-Eun Yoon
- Center for Neural Science and Center for Functional Connectomics; Korea Institute of Science and Technology; Seoul 136-791 Korea
- Department of Nanobiomedical Science; Dankook University; Chungnam Korea
| | - Feng-Yan Shen
- Department of Physiology and Neuroscience Research Institute; Korea University College of Medicine; Seoul 136-705 Korea
| | - Seung Won Lee
- Department of Physiology and Neuroscience Research Institute; Korea University College of Medicine; Seoul 136-705 Korea
| | - Tuck-Wah Soong
- Department of Physiology; Yong Loo Lin School of Medicine; National University of Singapore Bik MD9; Singapore Singapore
| | - Hee-Chul Han
- Department of Physiology and Neuroscience Research Institute; Korea University College of Medicine; Seoul 136-705 Korea
| | - Christopher S. Colwell
- Department of Psychiatry & Biobehavioral Sciences; University of California-Los Angeles; Los Angeles CA USA
| | - C. Justin Lee
- Center for Neural Science and Center for Functional Connectomics; Korea Institute of Science and Technology; Seoul 136-791 Korea
| | - Yang In Kim
- Department of Physiology and Neuroscience Research Institute; Korea University College of Medicine; Seoul 136-705 Korea
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Yang D, Hong JH. Dexmedetomidine Modulates Histamine-induced Ca(2+) Signaling and Pro-inflammatory Cytokine Expression. THE KOREAN JOURNAL OF PHYSIOLOGY & PHARMACOLOGY : OFFICIAL JOURNAL OF THE KOREAN PHYSIOLOGICAL SOCIETY AND THE KOREAN SOCIETY OF PHARMACOLOGY 2015; 19:413-20. [PMID: 26330753 PMCID: PMC4553400 DOI: 10.4196/kjpp.2015.19.5.413] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/06/2015] [Revised: 05/06/2015] [Accepted: 05/10/2015] [Indexed: 01/22/2023]
Abstract
Dexmedetomidine is a sedative and analgesic agent that exerts its effects by selectively agonizing α2 adrenoceptor. Histamine is a pathophysiological amine that activates G protein-coupled receptors, to induce Ca(2+) release and subsequent mediate or progress inflammation. Dexmedetomidine has been reported to exert inhibitory effect on inflammation both in vitro and in vivo studies. However, it is unclear that dexmedetomidine modulates histamine-induced signaling and pro-inflammatory cytokine expression. This study was carried out to assess how dexmedetomidine modulates histamine-induced Ca(2+) signaling and regulates the expression of pro-inflammatory cytokine genes encoding interleukin (IL)-6 and -8. To elucidate the regulatory role of dexmedetomidine on histamine signaling, HeLa cells and human salivary gland cells which are endogenously expressed histamine 1 receptor were used. Dexmedetomidine itself did not trigger Ca(2+) peak or increase in the presence or absence of external Ca(2+). When cells were stimulated with histamine after pretreatment with various concentrations of dexmedetomidine, we observed inhibited histamine-induced [Ca(2+)]i signal in both cell types. Histamine stimulated IL-6 mRNA expression not IL-8 mRNA within 2 hrs, however this effect was attenuated by dexmedetomidine. Collectively, these findings suggest that dexmedetomidine modulates histamine-induced Ca(2+) signaling and IL-6 expression and will be useful for understanding the antagonistic properties of dexmedetomidine on histamine-induced signaling beyond its sedative effect.
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Affiliation(s)
- Dongki Yang
- Department of Physiology, College of Medicine, Gachon University, Incheon 406-799, Korea
| | - Jeong Hee Hong
- Department of Physiology, College of Medicine, Gachon University, Incheon 406-799, Korea
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205
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Mediators, Receptors, and Signalling Pathways in the Anti-Inflammatory and Antihyperalgesic Effects of Acupuncture. EVIDENCE-BASED COMPLEMENTARY AND ALTERNATIVE MEDICINE 2015; 2015:975632. [PMID: 26339274 PMCID: PMC4539069 DOI: 10.1155/2015/975632] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/11/2014] [Accepted: 03/30/2015] [Indexed: 12/21/2022]
Abstract
Acupuncture has been used for millennia to treat allergic diseases including both intermittent rhinitis and persistent rhinitis. Besides the research on the efficacy and safety of acupuncture treatment for allergic rhinitis, research has also investigated how acupuncture might modulate immune function to exert anti-inflammatory effects. A proposed model has previously hypothesized that acupuncture might downregulate proinflammatory neuropeptides, proinflammatory cytokines, and neurotrophins, modulating transient receptor potential vallinoid (TRPV1), a G-protein coupled receptor which plays a central role in allergic rhinitis. Recent research has been largely supportive of this model. New advances in research include the discovery of a novel cholinergic anti-inflammatory pathway activated by acupuncture. A chemokine-mediated proliferation of opioid-containing macrophages in inflamed tissues, in response to acupuncture, has also been demonstrated for the first time. Further research on the complex cross talk between receptors during inflammation is also helping to elucidate the mediators and signalling pathways activated by acupuncture.
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206
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Chigbu DI, Coyne AM. Update and clinical utility of alcaftadine ophthalmic solution 0.25% in the treatment of allergic conjunctivitis. Clin Ophthalmol 2015; 9:1215-25. [PMID: 26185412 PMCID: PMC4501164 DOI: 10.2147/opth.s63790] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
Allergic disorders of the ocular surface are primarily characterized as IgE- and/or T-lymphocyte-mediated disorders that affect the cornea, conjunctiva, and eyelid. Approximately 40% of individuals in the developed countries have allergic conjunctivitis, and as such, it is the most common form of ocular allergy. Seasonal allergic conjunctivitis is the most prevalent type of allergic conjunctivitis that impacts the quality of life of patients. This article reviews the pharmacology, pharmacodynamics, pharmacokinetics, clinical trials, clinical efficacy, and safety of alcaftadine. Histamine and the pathological mechanism of ocular allergy will be briefly reviewed with the intent of providing a background for the detailed discussion on the clinical utility of alcaftadine in allergic conjunctivitis. The Medline PubMed, Elsevier Science Direct, and Google Scholar databases were used to search for evidence-based literature on histamine and immunopathological mechanism of allergic conjunctivitis, as well as on pharmacology, pharmacodynamics, pharmacokinetics, clinical trials, and clinical efficacy of alcaftadine. The treatment and management goals of allergic conjunctivitis are to prevent or minimize the inflammatory cascade associated with allergic response in the early stages of the pathological mechanism. It is of note that activation of histamine receptors on immune and nonimmune cells are associated with allergen-induced inflammation of the conjunctiva and its associated ocular allergic manifestations, including itching, edema, hyperemia, and tearing. Alcaftadine is an efficacious multiple action antiallergic therapeutic agent with inverse agonist activity on H1, H2, and H4 receptors, as well as anti-inflammatory and mast cell stabilizing effects that could provide therapeutic benefits to patients with allergic conjunctivitis.
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Affiliation(s)
- DeGaulle I Chigbu
- Pennsylvania College of Optometry Salus University, Elkins Park, PA, USA
| | - Alissa M Coyne
- Pennsylvania College of Optometry Salus University, Elkins Park, PA, USA
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207
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Pradhananga S, Shim WS. Caffeic acid exhibits anti-pruritic effects by inhibition of multiple itch transmission pathways in mice. Eur J Pharmacol 2015; 762:313-21. [PMID: 26057691 DOI: 10.1016/j.ejphar.2015.06.006] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2015] [Revised: 06/01/2015] [Accepted: 06/02/2015] [Indexed: 01/09/2023]
Abstract
Itch is an unpleasant sensation that evokes a desire to scratch. Although often regarded as a trivial 'alarming' sensation, itch may be debilitating and exhausting, leading to reduction in quality of life. In the current study, the question of whether caffeic acid can be used to alleviate itch sensation induced by various pruritic agents, including histamine, chloroquine, SLIGRL-NH2, and β-alanine was investigated. It turned out that histamine-induced intracellular calcium increase was significantly blocked by caffeic acid in HEK293T cells that express H1R and TRPV1, molecules required for transmission of histamine-induced itch in sensory neurons. In addition, inhibition of histamine-induced intracellular calcium increase by caffeic acid was demonstrated in primary cultures of mouse dorsal root ganglion (DRG). When chloroquine, an anti-malaria agent known to induce histamine-independent itch - was used, it was also found that caffeic acid inhibits the induced response in both DRG and HEK293T cells that express MRGPRA3 and TRPA1, underlying molecular entities responsible for chloroquine-mediated itch. Likewise, intracellular calcium changes by SLIGRL-NH2 - an itch-inducing agent via PAR2 and MRGPRC11 - were decreased by caffeic acid as well. However, it was found that caffeic acid is not capable of inhibiting β-alanine-induced responses via its specific receptor MRGPRD. Finally, in vivo scratching behavior tests showed that caffeic acid indeed has anti-scratching effects against histamine, chloroquine, and SLIGRL-NH2 administration but not by β-alanine. Overall, the current study demonstrated that caffeic acid has anti-itch effects by inhibition of multiple itch mechanisms induced by histamine, chloroquine and SLIGRL-NH2.
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Affiliation(s)
- Sabindra Pradhananga
- College of Pharmacy, Gachon University, Hambakmoeiro 191, Yeonsu-gu, Incheon 406-799, Republic of Korea
| | - Won-Sik Shim
- College of Pharmacy, Gachon University, Hambakmoeiro 191, Yeonsu-gu, Incheon 406-799, Republic of Korea.
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208
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Mediators of Chronic Pruritus in Atopic Dermatitis: Getting the Itch Out? Clin Rev Allergy Immunol 2015; 51:263-292. [DOI: 10.1007/s12016-015-8488-5] [Citation(s) in RCA: 200] [Impact Index Per Article: 22.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
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209
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Ho JC, Lee CH. TRP channels in skin: from physiological implications to clinical significances. Biophysics (Nagoya-shi) 2015; 11:17-24. [PMID: 27493510 PMCID: PMC4736792 DOI: 10.2142/biophysics.11.17] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2014] [Accepted: 12/08/2014] [Indexed: 01/29/2023] Open
Abstract
TRP channels are expressed in various cells in skin. As an organ system to border the host and environment, many nonneuronal cells, including epidermal keratinocytes and melanocytes, express several TRP channels functionally distinct from sensory processing. TRPV1 and TRPV3 in keratinocytes of the epidermis and hair apparatus inhibit proliferation, induce terminal differentiation, induce apoptosis, and promote inflammation. Activation of TRPV4, 6, and TRPA1 promotes regeneration of the severed skin barriers. TRPA1 also enhances responses in contact hypersensitivity. TRPCs in keratinocytes regulate epidermal differentiation. In human diseases with pertubered epidermal differentiation, the expression of TRPCs are altered. TRPMs, which contribute to melanin production in melanocytes, serve as significant prognosis markers in patients with metastatic melanoma. In summary, not only act in sensory processing, TRP channels also contribute to epidermal differentiation, proliferation, barrier integration, skin regeneration, and immune responses. In diseases with aberrant TRP channels, TRP channels might be good therapeutic targets.
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Affiliation(s)
- Ji-Chen Ho
- Department of Dermatology, Kaohsiung Chang Gung Memorial Hospital and Chang Gung University College of Medicine, Kaohsiung, Taiwan
| | - Chih-Hung Lee
- Department of Dermatology, Kaohsiung Chang Gung Memorial Hospital and Chang Gung University College of Medicine, Kaohsiung, Taiwan
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210
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Jang Y, Lee WJ, Hong GS, Shim WS. Red ginseng extract blocks histamine-dependent itch by inhibition of H1R/TRPV1 pathway in sensory neurons. J Ginseng Res 2015. [PMID: 26199558 PMCID: PMC4506365 DOI: 10.1016/j.jgr.2015.01.004] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Background Korean Red Ginseng—a steamed root of Panax ginseng Meyer—has long been used as a traditional medicine in Asian countries. Its antipruritic effect was recently found, but no molecular mechanisms were revealed. Thus, the current study focused on determining the underlying molecular mechanism of Korean Red Ginseng extract (RGE) against histamine-induced itch at the peripheral sensory neuronal level. Methods To examine the antipruritic effect of RGE, we performed in vivo scratching behavior test in mice, as well as in vitro calcium imaging and whole-cell patch clamp experiments to elucidate underlying molecular mechanisms. Results The results of our in vivo study confirmed that RGE indeed has an antipruritic effect on histamine-induced scratching in mice. In addition, RGE showed a significant inhibitory effect on histamine-induced responses in primary cultures of mouse dorsal root ganglia, suggesting that RGE has a direct inhibitory effect on sensory neuronal level. Results of further experiments showed that RGE inhibits histamine-induced responses on cells expressing both histamine receptor subtype 1 and TRPV1 ion channel, indicating that RGE blocks the histamine receptor type 1/TRPV1 pathway in sensory neurons, which is responsible for histamine-dependent itch sensation. Conclusion The current study found for the first time that RGE effectively blocks histamine-induced itch in peripheral sensory neurons. We believe that the current results will provide an insight on itch transmission and will be helpful in understanding how RGE exerts its antipruritic effects.
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Affiliation(s)
- Yongwoo Jang
- Sensory Research Center, Creative Research Initiatives, College of Pharmacy, Seoul National University, Seoul, Korea ; Department of Psychiatry and Program in Neuroscience, McLean Hospital, Harvard Medical School, Belmont, MA, USA
| | - Wook-Joo Lee
- College of Pharmacy, Gachon University, Incheon, Korea
| | - Gyu-Sang Hong
- Sensory Research Center, Creative Research Initiatives, College of Pharmacy, Seoul National University, Seoul, Korea
| | - Won-Sik Shim
- College of Pharmacy, Gachon University, Incheon, Korea
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211
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Valtcheva MV, Davidson S, Zhao C, Leitges M, Gereau RW. Protein kinase Cδ mediates histamine-evoked itch and responses in pruriceptors. Mol Pain 2015; 11:1. [PMID: 25558916 PMCID: PMC4298070 DOI: 10.1186/1744-8069-11-1] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2014] [Accepted: 12/23/2014] [Indexed: 01/28/2023] Open
Abstract
Background Itch-producing compounds stimulate receptors expressed on small diameter fibers that innervate the skin. Many of the currently known pruritogen receptors are Gq Protein-Coupled Receptors (GqPCR), which activate Protein Kinase C (PKC). Specific isoforms of PKC have been previously shown to perform selective functions; however, the roles of PKC isoforms in regulating itch remain unclear. In this study, we investigated the novel PKC isoform PKCδ as an intracellular modulator of itch signaling in response to histamine and the non-histaminergic pruritogens chloroquine and β-alanine. Results Behavioral experiments indicate that PKCδ knock-out (KO) mice have a 40% reduction in histamine-induced scratching when compared to their wild type littermates. On the other hand, there were no differences between the two groups in scratching induced by the MRGPR agonists chloroquine or β-alanine. PKCδ was present in small diameter dorsal root ganglion (DRG) neurons. Of PKCδ-expressing neurons, 55% also stained for the non-peptidergic marker IB4, while a smaller percentage (15%) expressed the peptidergic marker CGRP. Twenty-nine percent of PKCδ-expressing neurons also expressed TRPV1. Calcium imaging studies of acutely dissociated DRG neurons from PKCδ-KO mice show a 40% reduction in the total number of neurons responsive to histamine. In contrast, there was no difference in the number of capsaicin-responsive neurons between KO and WT animals. Acute pharmacological inhibition of PKCδ with an isoform-specific peptide inhibitor (δV1-1) also significantly reduced the number of histamine-responsive sensory neurons. Conclusions Our findings indicate that PKCδ plays a role in mediating histamine-induced itch, but may be dispensable for chloroquine- and β-alanine-induced itch.
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Affiliation(s)
| | | | | | | | - Robert W Gereau
- Washington University Pain Center and Department of Anesthesiology, Washington University in St, Louis, 660 S, Euclid Ave, Box 8054, 63110 St, Louis, MO, USA.
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212
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Abstract
Histamine is one of the best-characterized pruritogens in humans. It is known to play a role in pruritus associated with urticaria as well as ocular and nasal allergic reactions. Histamine mediates its effect via four receptors. Antihistamines that block the activation of the histamine H₁receptor, H₁R, have been shown to be effective therapeutics for the treatment of pruritus associated with urticaria, allergic rhinitis, and allergic conjunctivitis. However, their efficacy in other pruritic diseases such as atopic dermatitis and psoriasis is limited. The other histamine receptors may also play a role in pruritus, with the exception of the histamine H₂receptor, H₂R. Preclinical evidence indicates that local antagonism of the histamine H₃receptor, H₃R, can induce scratching perhaps via blocking inhibitory neuronal signals. The histamine H₄receptor, H₄R, has received a significant amount of attention as to its role in mediating pruritic signals. Indeed, it has now been shown that a selective H₄R antagonist can inhibit histamine-induced itch in humans. This clinical result, in conjunction with efficacy in various preclinical pruritus models, points to the therapeutic potential of H₄R antagonists for the treatment of pruritus not controlled by antihistamines that target the H₁R.
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Affiliation(s)
- Robin L Thurmond
- Janssen Research and Development, L.L.C., San Diego, CA, 92121, USA,
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213
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Tóth BI, Szallasi A, Bíró T. Transient receptor potential channels and itch: how deep should we scratch? Handb Exp Pharmacol 2015; 226:89-133. [PMID: 25861776 DOI: 10.1007/978-3-662-44605-8_6] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Over the past 30 years, transient receptor potential (TRP) channels have evolved from a somewhat obscure observation on how fruit flies detect light to become the center of drug discovery efforts, triggering a heated debate about their potential as targets for therapeutic applications in humans. In this review, we describe our current understanding of the diverse mechanism of action of TRP channels in the itch pathway from the skin to the brain with focus on the peripheral detection of stimuli that elicit the desire to scratch and spinal itch processing and sensitization. We predict that the compelling basic research findings on TRP channels and pruritus will be translated into the development of novel, clinically useful itch medications.
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Affiliation(s)
- Balázs I Tóth
- DE-MTA "Lendület" Cellular Physiology Research Group, Department of Physiology, University of Debrecen, Debrecen, 4032, Hungary
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214
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Abstract
Protease-activated receptors (PARs) have been implicated in a variety of physiological functions, as well as somatosensation and particularly itch and pain. Considerable attention has focused on PARs following the finding they are upregulated in the skin of atopic dermatitis patients. The present review focuses on recent studies showing that PARs are critically involved in itch and sensitization of itch. PARs are expressed by diverse cell types including primary sensory neurons, keratinocytes, and immune cells and are activated by proteases that expose a tethered ligand. Endogenous proteases are also released from diverse cell types including keratinocytes and immune cells. Exogenous proteases released from certain plants and insects contacting the skin can also induce itch. Increased levels of proteases in the skin contribute to inflammation that is often accompanied by chronic itch which is not predominantly mediated by histamine. The neural pathway signaling itch induced by activation of PARs is distinct from that mediating histamine-induced itch. In addition, there is evidence that PARs play an important role in sensitization of itch signaling under conditions of chronic itch. These recent findings suggest that PARs and other molecules involved in the itch-signaling pathway are good targets to develop novel treatments for most types of chronic itch that are poorly treated with antihistamines.
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Affiliation(s)
- Tasuku Akiyama
- Department of Dermatology, Anatomy and Cell Biology/Temple Itch Center, Temple University School of Medicine, Philadelphia, PA, 19140, USA
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215
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Takanami K, Sakamoto H, Matsuda KI, Satoh K, Tanida T, Yamada S, Inoue K, Oti T, Sakamoto T, Kawata M. Distribution of gastrin-releasing peptide in the rat trigeminal and spinal somatosensory systems. J Comp Neurol 2014; 522:1858-73. [PMID: 24254931 DOI: 10.1002/cne.23506] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2013] [Revised: 08/30/2013] [Accepted: 11/15/2013] [Indexed: 12/12/2022]
Abstract
Gastrin-releasing peptide (GRP) has recently been identified as an itch-specific neuropeptide in the spinal sensory system in mice, but there are no reports of the expression and distribution of GRP in the trigeminal sensory system in mammals. We characterized and compared GRP-immunoreactive (ir) neurons in the trigeminal ganglion (TG) with those in the rat spinal dorsal root ganglion (DRG). GRP immunoreactivity was expressed in 12% of TG and 6% of DRG neurons and was restricted to the small- and medium-sized type cells. In both the TG and DRG, many GRP-ir neurons also expressed substance P and calcitonin gene-related peptide, but not isolectin B4 . The different proportions of GRP and transient receptor potential vanilloid 1 double-positive neurons in the TG and DRG imply that itch sensations via the TG and DRG pathways are transmitted through distinct mechanisms. The distribution of the axon terminals of GRP-ir primary afferents and their synaptic connectivity with the rat trigeminal sensory nuclei and spinal dorsal horn were investigated by using light and electron microscopic histochemistry. Although GRP-ir fibers were rarely observed in the trigeminal sensory nucleus principalis, oralis, and interpolaris, they were predominant in the superficial layers of the trigeminal sensory nucleus caudalis (Vc), similar to the spinal dorsal horn. Ultrastructural analysis revealed that GRP-ir terminals contained clear microvesicles and large dense-cored vesicles, and formed asymmetric synaptic contacts with a few dendrites in the Vc and spinal dorsal horn. These results suggest that GRP-dependent orofacial and spinal pruriceptive inputs are processed mainly in the superficial laminae of the Vc and spinal dorsal horn.
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Affiliation(s)
- Keiko Takanami
- Department of Anatomy and Neurobiology, Kyoto Prefectural University of Medicine, Kawaramachi-Hirokoji, Kamigyo-ku, Kyoto, 602-8566, Japan
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216
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Takanami K, Sakamoto H. The Gastrin-Releasing Peptide Receptor (GRPR) in the Spinal Cord as a Novel Pharmacological Target. Curr Neuropharmacol 2014; 12:434-43. [PMID: 25426011 PMCID: PMC4243033 DOI: 10.2174/1570159x12666140923201432] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2014] [Revised: 07/28/2014] [Accepted: 09/10/2014] [Indexed: 12/02/2022] Open
Abstract
Gastrin-releasing peptide (GRP) is a mammalian neuropeptide that acts through the G protein-coupled receptor, GRP receptor (GRPR). Increasing evidence indicates that GRPR-mediated signaling in the central nervous system plays an important role in many physiological processes in mammals. Additionally, we have recently reported that the GRP system within the lumbosacral spinal cord not only controls erection but also triggers ejaculation in male rats. This system of GRP neurons is sexually dimorphic, being prominent in male rats but vestigial or absent in females. It is suggested that the sexually dimorphic GRP/GRPR system in the lumbosacral spinal cord plays a critical role in the regulation of male sexual function. In parallel, it has been reported that the somatosensory GRP/GRPR system in the spinal cord contributes to the regulation of itch specific transmission independently of the pain transmission. Interestingly, these two distinct functions in the same spinal region are both regulated by the neuropeptide, GRP. In this report, we review findings on recently identified GRP/GRPR systems in the spinal cord. These GRP/GRPR systems in the spinal cord provide new insights into pharmacological treatments for psychogenic erectile dysfunction as well as for chronic pruritus.
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Affiliation(s)
- Keiko Takanami
- Department of Anatomy and Neurobiology, Kyoto Prefectural University of Medicine, Kawaramachi-Hirokoji, Kamigyo-ku, Kyoto 602-8566, Japan
| | - Hirotaka Sakamoto
- Ushimado Marine Institute (UMI), Graduate School of Natural Science and Technology, Okayama University, Ushimado, Setouchi, Okayama 701-4303, Japan
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217
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Zhang X. Targeting TRP ion channels for itch relief. Naunyn Schmiedebergs Arch Pharmacol 2014; 388:389-99. [PMID: 25418889 DOI: 10.1007/s00210-014-1068-z] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2014] [Accepted: 11/11/2014] [Indexed: 12/13/2022]
Abstract
Acute itch (pruritus) is unpleasant and acts as an alerting mechanism for removing irritants. However, severe chronic itch is debilitating and impairs the quality of life. Rapid progress has been made in recent years in our understanding of the fundamental neurobiology of itch. Notably, several temperature-sensitive transient receptor potential (thermo-TRP) ion channels have emerged as critical players in many types of itch, in addition to pain. They serve as markers that define the itch neural pathway. Thermo-TRP ion channels are thus becoming attractive targets for developing effective anti-pruritic therapies.
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Affiliation(s)
- Xuming Zhang
- Rowett Institute of Nutrition and Health & Institute of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen, AB25 2ZD, UK,
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218
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Caterina MJ. TRP channel cannabinoid receptors in skin sensation, homeostasis, and inflammation. ACS Chem Neurosci 2014; 5:1107-16. [PMID: 24915599 PMCID: PMC4240254 DOI: 10.1021/cn5000919] [Citation(s) in RCA: 79] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
![]()
In
the skin, cannabinoid lipids, whether of endogenous or exogenous
origin, are capable of regulating numerous sensory, homeostatic, and
inflammatory events. Although many of these effects are mediated by
metabotropic cannabinoid receptors, a growing body of evidence has
revealed that multiple members of the transient receptor potential
(TRP) ion channel family can act as “ionotropic cannabinoid
receptors”. Furthermore, many of these same TRP channels are
intimately involved in cutaneous processes that include the initiation
of pain, temperature, and itch perception, the maintenance of epidermal
homeostasis, the regulation of hair follicles and sebaceous glands,
and the modulation of dermatitis. Ionotropic cannabinoid receptors
therefore represent potentially attractive targets for the therapeutic
use of cannabinoids to treat sensory and dermatological diseases.
Furthermore, the interactions between neurons and other cell types
that are mediated by cutaneous ionotropic cannabinoid receptors are
likely to be recapitulated during physiological and pathophysiological
processes in the central nervous system and elsewhere, making the
skin an ideal setting in which to dissect general complexities of
cannabinoid signaling.
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Affiliation(s)
- Michael J. Caterina
- Departments of Neurosurgery,
Biological Chemistry, and Neuroscience, Neurosurgery Pain Research
Institute, Center for Sensory Biology, Johns Hopkins School of Medicine, 725 N. Wolfe St., Baltimore, Maryland 21205, United States
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219
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Veldhuis NA, Poole DP, Grace M, McIntyre P, Bunnett NW. The G Protein–Coupled Receptor–Transient Receptor Potential Channel Axis: Molecular Insights for Targeting Disorders of Sensation and Inflammation. Pharmacol Rev 2014; 67:36-73. [DOI: 10.1124/pr.114.009555] [Citation(s) in RCA: 114] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
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220
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Rosa AC, Fantozzi R. The role of histamine in neurogenic inflammation. Br J Pharmacol 2014; 170:38-45. [PMID: 23734637 DOI: 10.1111/bph.12266] [Citation(s) in RCA: 117] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2012] [Revised: 02/13/2013] [Accepted: 03/28/2013] [Indexed: 12/21/2022] Open
Abstract
The term 'neurogenic inflammation' has been adopted to describe the local release of inflammatory mediators, such as substance P and calcitonin gene-related peptide, from neurons. Once released, these neuropeptides induce the release of histamine from adjacent mast cells. In turn, histamine evokes the release of substance P and calcitonin gene-related peptide; thus, a bidirectional link between histamine and neuropeptides in neurogenic inflammation is established. The aim of this review is to summarize the most recent findings on the role of histamine in neurogenic inflammation, with particular regard to nociceptive pain, as well as neurogenic inflammation in the skin, airways and bladder.
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Affiliation(s)
- A C Rosa
- Dipartimento di Scienza e Tecnologia del Farmaco, University of Turin, Italy.
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221
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Min H, Lee H, Lim H, Jang YH, Chung SJ, Lee CJ, Lee SJ. TLR4 enhances histamine-mediated pruritus by potentiating TRPV1 activity. Mol Brain 2014; 7:59. [PMID: 25139109 PMCID: PMC4237911 DOI: 10.1186/s13041-014-0059-9] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2014] [Accepted: 08/07/2014] [Indexed: 01/12/2023] Open
Abstract
Background Recent studies have indicated that Toll-like receptor 4 (TLR4), a pathogen-recognition receptor that triggers inflammatory signals in innate immune cells, is also expressed on sensory neurons, implicating its putative role in sensory signal transmission. However, the possible function of sensory neuron TLR4 has not yet been formally addressed. In this regard, we investigated the role of TLR4 in itch signal transmission. Results TLR4 was expressed on a subpopulation of dorsal root ganglia (DRG) sensory neurons that express TRPV1. In TLR4-knockout mice, histamine-induced itch responses were compromised while TLR4 activation by LPS did not directly elicit an itch response. Histamine-induced intracellular calcium signals and inward currents were comparably reduced in TLR4-deficient sensory neurons. Reduced histamine sensitivity in the TLR4-deficient neurons was accompanied by a decrease in TRPV1 activity. Heterologous expression experiments in HEK293T cells indicated that TLR4 expression enhanced capsaicin-induced intracellular calcium signals and inward currents. Conclusions Our data show that TLR4 on sensory neurons enhances histamine-induced itch signal transduction by potentiating TRPV1 activity. The results suggest that TLR4 could be a novel target for the treatment of enhanced itch sensation.
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Affiliation(s)
| | | | | | | | | | | | - Sung Joong Lee
- Department of Neuroscience and Physiology, Dental Research Institute, School of Dentistry, Seoul National University, Seoul 110-749, Korea.
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Abstract
Peripheral nociceptors are excited by the activation of membrane receptors and ion channels. The heat-sensitive TRPV1 ion channel responds to various noxious chemical and thermal stimuli, causing pain and itch. Here, we show that TRPV1 is coexpressed with PKCβII in a subset of mouse sensory neurons and that, in these neurons, TRPV1 binds directly to PKCβII, leading to the activation and translocation of PKCβII. Activated PKCβII, in turn, significantly increases the responsiveness of TRPV1 by phosphorylating Thr705. The heat sensitivity of TRPV1 is almost eliminated by either knocking down PKCβII or mutating Thr705; however, neither of these manipulations affects the potentiation of TRPV1 caused by the activation of PKCε. PKCβII thus acts as an auxiliary subunit of TRPV1 by forming a population-dependent TRPV1 ion channel complex controlling the sensitivity of TRPV1 and setting the threshold for pain and itch.
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223
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A randomised trial evaluating the effects of the TRPV1 antagonist SB705498 on pruritus induced by histamine, and cowhage challenge in healthy volunteers. PLoS One 2014; 9:e100610. [PMID: 25047038 PMCID: PMC4105653 DOI: 10.1371/journal.pone.0100610] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2013] [Accepted: 05/22/2014] [Indexed: 12/26/2022] Open
Abstract
BACKGROUND Transient receptor potential vanilloid type 1 (TRPV1) is a non-selective cation channel widely expressed in skin tissues, and peripheral sensory nerve fibres. Activation of TRPV1 releases neuropeptides; the resulting neurogenic inflammation is believed to contribute to the development of pruritus. A TRPV1 antagonist has the potential to perform as an anti-pruritic agent. SB705498 is a TRPV1 antagonist that has demonstrated in vitro activity against cloned TRPV1 human receptors and when orally administered has demonstrated pharmacodynamic activity in animal models and clinical studies. OBJECTIVES To select a topical dose of SB705498 using the TRPV1 agonist capsaicin; to confirm engagement of the TRPV1 antagonistic action of SB705498 and assess whether the dose selected has an effect on itch induced by two challenge agents. METHODS A clinical study was conducted in 16 healthy volunteers to assess the effects of 3 doses of SB705498 on skin flare induced by capsaicin. Subjects with a robust capsaicin response were chosen to determine if the selected topical formulation of SB705498 had an effect on challenge agent induced itch. RESULTS Following capsaicin challenge the greatest average reduction in area of flare was seen for the 3% formulation. This dose was selected for further investigation. Itch intensity induced by two challenge agents (cowhage and histamine) was assessed on the Computerised Visual Analogue Scale. The difference in average itch intensity (Weighted Mean Over 15 Mins) between the 3% dose of SB705498 and placebo for the cowhage challenge was -0.64, whilst the histamine challenge showed on average a -4.65 point change. CONCLUSIONS The 3% topical formulation of SB705498 cream was clinically well tolerated and had target specific pharmacodynamic activity. However there were no clinically significant differences on pruritus induced by either challenge agent in comparison to placebo. SB705498 is unlikely to be of symptomatic benefit for histaminergic or non-histaminergic induced itch. TRIAL REGISTRATION ClinicalTrials.gov NCT01673529.
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224
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Receptors, cells and circuits involved in pruritus of systemic disorders. Biochim Biophys Acta Mol Basis Dis 2014; 1842:869-92. [DOI: 10.1016/j.bbadis.2014.02.007] [Citation(s) in RCA: 68] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2013] [Revised: 02/16/2014] [Accepted: 02/18/2014] [Indexed: 12/12/2022]
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225
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Three functionally distinct classes of C-fibre nociceptors in primates. Nat Commun 2014; 5:4122. [PMID: 24947823 PMCID: PMC4072246 DOI: 10.1038/ncomms5122] [Citation(s) in RCA: 66] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2014] [Accepted: 05/14/2014] [Indexed: 01/01/2023] Open
Abstract
In primates, C-fibre polymodal nociceptors are broadly classified into two groups based on mechanosensitivity. Here we demonstrate that mechanically sensitive polymodal nociceptors that respond either quickly (QC) or slowly (SC) to a heat stimulus differ in responses to a mild burn, heat sensitization, conductive properties and chemosensitivity. Superficially applied capsaicin and intradermal injection of β-alanine, an MrgprD agonist, excite vigorously all QCs. Only 40% of SCs respond to β-alanine, and their response is only half that of QCs. Mechanically insensitive C-fibres (C-MIAs) are β-alanine insensitive but vigorously respond to capsaicin and histamine with distinct discharge patterns. Calcium imaging reveals that β-alanine and histamine activate distinct populations of capsaicin-responsive neurons in primate dorsal root ganglion. We suggest that histamine itch and capsaicin pain are peripherally encoded in C-MIAs, and that primate polymodal nociceptive afferents form three functionally distinct subpopulations with β-alanine responsive QC fibres likely corresponding to murine MrgprD-expressing, non-peptidergic nociceptive afferents.
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226
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Understanding the switch from pain-to-itch in dermatitis. Neurosci Lett 2014; 579:188-9. [PMID: 24905172 DOI: 10.1016/j.neulet.2014.05.018] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2014] [Accepted: 05/07/2014] [Indexed: 11/22/2022]
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227
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Kido-Nakahara M, Buddenkotte J, Kempkes C, Ikoma A, Cevikbas F, Akiyama T, Nunes F, Seeliger S, Hasdemir B, Mess C, Buhl T, Sulk M, Müller FU, Metze D, Bunnett NW, Bhargava A, Carstens E, Furue M, Steinhoff M. Neural peptidase endothelin-converting enzyme 1 regulates endothelin 1-induced pruritus. J Clin Invest 2014; 124:2683-95. [PMID: 24812665 DOI: 10.1172/jci67323] [Citation(s) in RCA: 67] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
In humans, pruritus (itch) is a common but poorly understood symptom in numerous skin and systemic diseases. Endothelin 1 (ET-1) evokes histamine-independent pruritus in mammals through activation of its cognate G protein-coupled receptor endothelin A receptor (ETAR). Here, we have identified neural endothelin-converting enzyme 1 (ECE-1) as a key regulator of ET-1-induced pruritus and neural signaling of itch. We show here that ETAR, ET-1, and ECE-1 are expressed and colocalize in murine dorsal root ganglia (DRG) neurons and human skin nerves. In murine DRG neurons, ET-1 induced internalization of ETAR within ECE-1-containing endosomes. ECE-1 inhibition slowed ETAR recycling yet prolonged ET-1-induced activation of ERK1/2, but not p38. In a murine itch model, ET-1-induced scratching behavior was substantially augmented by pharmacological ECE-1 inhibition and abrogated by treatment with an ERK1/2 inhibitor. Using iontophoresis, we demonstrated that ET-1 is a potent, partially histamine-independent pruritogen in humans. Immunohistochemical evaluation of skin from prurigo nodularis patients confirmed an upregulation of the ET-1/ETAR/ECE-1/ERK1/2 axis in patients with chronic itch. Together, our data identify the neural peptidase ECE-1 as a negative regulator of itch on sensory nerves by directly regulating ET-1-induced pruritus in humans and mice. Furthermore, these results implicate the ET-1/ECE-1/ERK1/2 pathway as a therapeutic target to treat pruritus in humans.
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228
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Kaneko Y, Szallasi A. Transient receptor potential (TRP) channels: a clinical perspective. Br J Pharmacol 2014; 171:2474-507. [PMID: 24102319 PMCID: PMC4008995 DOI: 10.1111/bph.12414] [Citation(s) in RCA: 283] [Impact Index Per Article: 28.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2013] [Revised: 08/28/2013] [Accepted: 08/31/2013] [Indexed: 12/14/2022] Open
Abstract
Transient receptor potential (TRP) channels are important mediators of sensory signals with marked effects on cellular functions and signalling pathways. Indeed, mutations in genes encoding TRP channels are the cause of several inherited diseases in humans (the so-called 'TRP channelopathies') that affect the cardiovascular, renal, skeletal and nervous systems. TRP channels are also promising targets for drug discovery. The initial focus of research was on TRP channels that are expressed on nociceptive neurons. Indeed, a number of potent, small-molecule TRPV1, TRPV3 and TRPA1 antagonists have already entered clinical trials as novel analgesic agents. There has been a recent upsurge in the amount of work that expands TRP channel drug discovery efforts into new disease areas such as asthma, cancer, anxiety, cardiac hypertrophy, as well as obesity and metabolic disorders. A better understanding of TRP channel functions in health and disease should lead to the discovery of first-in-class drugs for these intractable diseases. With this review, we hope to capture the current state of this rapidly expanding and changing field.
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Affiliation(s)
- Yosuke Kaneko
- Discovery Research Alliance, Ono Pharmaceutical Co. LtdOsaka, Japan
| | - Arpad Szallasi
- Department of Pathology and Laboratory Medicine, Monmouth Medical CenterLong Branch, NJ, USA
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229
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Le Pichon CE, Chesler AT. The functional and anatomical dissection of somatosensory subpopulations using mouse genetics. Front Neuroanat 2014; 8:21. [PMID: 24795573 PMCID: PMC4001001 DOI: 10.3389/fnana.2014.00021] [Citation(s) in RCA: 167] [Impact Index Per Article: 16.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2014] [Accepted: 03/24/2014] [Indexed: 11/13/2022] Open
Abstract
The word somatosensation comes from joining the Greek word for body (soma) with a word for perception (sensation). Somatosensory neurons comprise the largest sensory system in mammals and have nerve endings coursing throughout the skin, viscera, muscle, and bone. Their cell bodies reside in a chain of ganglia adjacent to the dorsal spinal cord (the dorsal root ganglia) and at the base of the skull (the trigeminal ganglia). While the neuronal cell bodies are intermingled within the ganglia, the somatosensory system is in reality composed of numerous sub-systems, each specialized to detect distinct stimuli, such as temperature and touch. Historically, somatosensory neurons have been classified using a diverse host of anatomical and physiological parameters, such as the size of the cell body, degree of myelination, histological labeling with markers, specialization of the nerve endings, projection patterns in the spinal cord and brainstem, receptive tuning, and conduction velocity of their action potentials. While useful, the picture that emerged was one of heterogeneity, with many markers at least partially overlapping. More recently, by capitalizing on advances in molecular techniques, researchers have identified specific ion channels and sensory receptors expressed in subsets of sensory neurons. These studies have proved invaluable as they allow genetic access to small subsets of neurons for further molecular dissection. Data being generated from transgenic mice favor a model whereby an array of dedicated neurons is responsible for selectively encoding different modalities. Here we review the current knowledge of the different sensory neuron subtypes in the mouse, the markers used to study them, and the neurogenetic strategies used to define their anatomical projections and functional roles.
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Affiliation(s)
- Claire E. Le Pichon
- National Institute of Neurological Disorders and Stroke, National Institutes of HealthBethesda, MD, USA
| | - Alexander T. Chesler
- Intramural Pain Program, Section on Sensory Cells and Circuits, National Center for Complementary and Alternative Medicine, National Institutes of HealthBethesda, MD, USA
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230
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Fu K, Qu L, Shimada SG, Nie H, LaMotte RH. Enhanced scratching elicited by a pruritogen and an algogen in a mouse model of contact hypersensitivity. Neurosci Lett 2014; 579:190-4. [PMID: 24704378 DOI: 10.1016/j.neulet.2014.03.062] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2014] [Revised: 03/24/2014] [Accepted: 03/26/2014] [Indexed: 02/08/2023]
Abstract
Chemical pruritogens and algogens evoke primarily itch and pain, respectively, when administered to the skin of healthy human subjects. However, the dominant sensory quality elicited by an algesic chemical stimulus may change in patients with chronic itch where bradykinin, elicits itch in addition to pain. Here we tested whether normally pruritic and algesic chemicals evoked abnormal itch- or pain-like behaviors in the mouse after the development of contact hypersensitivity (CHS), an animal model of allergic contact dermatitis. Mice previously sensitized to a hapten (squaric acid dibutylester) applied to the abdomen, exhibited spontaneous itch-like scratching and pain-like wiping directed to the site on the cheek of the CHS elicited by a subsequent challenge with the same hapten. In comparison with responses of control mice, CHS mice exhibited a significant increase in the scratching evoked by bovine adrenal medulla 8-22, a peptide that elicits a histamine-independent itch, but did not alter the scratching to histamine. Bradykinin, an algogen that elicited only wiping in control mice, additionally evoked significant scratching in CHS mice. Thus, within an area of CHS, histamine-independent itch is enhanced and chemically evoked pain is accompanied by itch.
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Affiliation(s)
- Kai Fu
- Department of Anesthesiology, Yale University School of Medicine, New Haven, CT 06520, USA; Guangdong Province Key Laboratory of Pharmacodynamic Constituents of TCM and New Drugs Research, College of Pharmacy, Jinan University, Guangzhou 510632, Guangdong, China
| | - Lintao Qu
- Department of Anesthesiology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Steven G Shimada
- Department of Anesthesiology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Hong Nie
- Guangdong Province Key Laboratory of Pharmacodynamic Constituents of TCM and New Drugs Research, College of Pharmacy, Jinan University, Guangzhou 510632, Guangdong, China.
| | - Robert H LaMotte
- Department of Anesthesiology, Yale University School of Medicine, New Haven, CT 06520, USA.
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231
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Lucaciu OC, Connell GP. Itch sensation through transient receptor potential channels: a systematic review and relevance to manual therapy. J Manipulative Physiol Ther 2014; 36:385-93. [PMID: 23896168 DOI: 10.1016/j.jmpt.2013.05.018] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2012] [Revised: 12/14/2012] [Accepted: 12/27/2012] [Indexed: 10/26/2022]
Abstract
OBJECTIVE Patients may present with a complaint of "itchiness" or an "odd sensation" that can be relieved by manual therapy treatment options, which demonstrates the relevance of transient receptor potential (TRP) channels. There are studies that identify the role of various TRP channels as modulators of the itch sensation; however, discrepancies in the literature exist with respect to the overall neural pathway of the itch sensation, musculoskeletal implications, and decisive therapeutic implications. The purpose of this study was to review the literature and rate the quality of published articles regarding the role of TRP channels in the itch sensation. METHODS A systematic search of relevant literature that was published in English by a peer-reviewed journal between January 2000 and June 2012 was performed in PubMed. Studies that met the predetermined inclusion criteria regarding the relationship between TRP channels and itch were identified and then evaluated for methodological quality by the Downs and Black Quality Index score system and were summarized. RESULTS Nine studies were identified that met the inclusion criteria, all of which had fair methodological quality from the perspective of the modified Downs and Black Quality Index. TRPA1, TRPM8, and TRPV1-4 were indicated as key channels responsible for the transmission of the itch sensation. TRPV1 channels convey histamine-dependent itch, and TRPA1 channels convey histamine-independent itch. Temperature, nerve growth factor, and substance-P were also described as important itch modulators. There are similarities between the neural pathways responsible for itch, pain, and temperature, which explain the ability of noxious temperature to suppress the desire to scratch. Although transcutaneous electrical nerve stimulation, innocuous vibration, and cutaneous field stimulation have demonstrated relatively weak attenuation of itch, the use of topical capsaicin, noxious heat, and noxious cold have been demonstrated as effective therapies. CONCLUSIONS The findings of this review show that studies have assessed the function of TRP channels and itch, rather than identifying the relationship between itch and effective noninvasive treatment options. Therefore, TRP channels could serve as important, complex clinical targets for manual therapists.
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Affiliation(s)
- Octavian C Lucaciu
- Department of Anatomy, Canadian Memorial Chiropractic College, Toronto, Ontario, Canada
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232
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Abstract
Chemicals that are used experimentally to evoke itch elicit activity in diverse subpopulations of cutaneous pruriceptive neurons, all of which also respond to painful stimuli. However, itch is distinct from pain: it evokes different behaviours, such as scratching, and originates from the skin or certain mucosae but not from muscle, joints or viscera. New insights regarding the neurons that mediate the sensation of itch have been gained from experiments in which gene expression has been manipulated in different types of pruriceptive neurons as well as from comparisons between psychophysical measurements of itch and the neuronal discharges and other properties of peripheral and central pruriceptive neurons.
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233
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Zhao ZQ, Huo FQ, Jeffry J, Hampton L, Demehri S, Kim S, Liu XY, Barry DM, Wan L, Liu ZC, Li H, Turkoz A, Ma K, Cornelius LA, Kopan R, Battey JF, Zhong J, Chen ZF. Chronic itch development in sensory neurons requires BRAF signaling pathways. J Clin Invest 2014; 123:4769-80. [PMID: 24216512 DOI: 10.1172/jci70528] [Citation(s) in RCA: 86] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2013] [Accepted: 08/12/2013] [Indexed: 12/17/2022] Open
Abstract
Chronic itch, or pruritus, is associated with a wide range of skin abnormalities. The mechanisms responsible for chronic itch induction and persistence remain unclear. We developed a mouse model in which a constitutively active form of the serine/threonine kinase BRAF was expressed in neurons gated by the sodium channel Nav1.8 (BRAF(Nav1.8) mice). We found that constitutive BRAF pathway activation in BRAF(Nav1.8) mice results in ectopic and enhanced expression of a cohort of itch-sensing genes, including gastrin-releasing peptide (GRP) and MAS-related GPCR member A3 (MRGPRA3), in nociceptors expressing transient receptor potential vanilloid 1 (TRPV1). BRAF(Nav1.8) mice showed de novo neuronal responsiveness to pruritogens, enhanced pruriceptor excitability, and heightened evoked and spontaneous scratching behavior. GRP receptor expression was increased in the spinal cord, indicating augmented coding capacity for itch subsequent to amplified pruriceptive inputs. Enhanced GRP expression and sustained ERK phosphorylation were observed in sensory neurons of mice with allergic contact dermatitis– or dry skin–elicited itch; however, spinal ERK activation was not required for maintaining central sensitization of itch. Inhibition of either BRAF or GRP signaling attenuated itch sensation in chronic itch mouse models. These data uncover RAF/MEK/ERK signaling as a key regulator that confers a subset of nociceptors with pruriceptive properties to initiate and maintain long-lasting itch sensation.
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234
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Bautista DM, Wilson SR, Hoon MA. Why we scratch an itch: the molecules, cells and circuits of itch. Nat Neurosci 2014; 17:175-82. [PMID: 24473265 PMCID: PMC4364402 DOI: 10.1038/nn.3619] [Citation(s) in RCA: 235] [Impact Index Per Article: 23.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2013] [Accepted: 12/03/2013] [Indexed: 12/17/2022]
Abstract
Itch is described as an irritating sensation that triggers a desire to scratch. However, this definition hardly seems fitting for the millions of people who suffer from intractable itch. Indeed, the Buddhist philosopher Nāgārjuna more aptly stated, "There is pleasure when an itch is scratched. But to be without an itch is more pleasurable still." Chronic itch is widespread and very difficult to treat. In this review we focus on the molecules, cells and circuits in the peripheral and central nervous systems that drive acute and chronic itch transmission. Understanding the itch circuitry is critical to developing new therapies for this intractable disease.
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Affiliation(s)
- Diana M Bautista
- 1] Department of Molecular and Cell Biology, University of California Berkeley, Berkeley, California, USA. [2] Helen Wills Neuroscience Institute, University of California, Berkeley, Berkeley, California, USA
| | - Sarah R Wilson
- 1] Department of Molecular and Cell Biology, University of California Berkeley, Berkeley, California, USA. [2] Helen Wills Neuroscience Institute, University of California, Berkeley, Berkeley, California, USA
| | - Mark A Hoon
- Molecular Genetics Unit, Laboratory of Sensory Biology, National Institute of Dental and Craniofacial Research/NIH, Bethesda, Maryland, USA
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235
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Undem BJ, Taylor-Clark T. Mechanisms underlying the neuronal-based symptoms of allergy. J Allergy Clin Immunol 2014; 133:1521-34. [PMID: 24433703 DOI: 10.1016/j.jaci.2013.11.027] [Citation(s) in RCA: 123] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2013] [Revised: 11/05/2013] [Accepted: 11/13/2013] [Indexed: 12/13/2022]
Abstract
Persons with allergies present with symptoms that often are the result of alterations in the nervous system. Neuronally based symptoms depend on the organ in which the allergic reaction occurs but can include red itchy eyes, sneezing, nasal congestion, rhinorrhea, coughing, bronchoconstriction, airway mucus secretion, dysphagia, altered gastrointestinal motility, and itchy swollen skin. These symptoms occur because mediators released during an allergic reaction can interact with sensory nerves, change processing in the central nervous system, and alter transmission in sympathetic, parasympathetic, and enteric autonomic nerves. In addition, evidence supports the idea that in some subjects this neuromodulation is, for reasons poorly understood, upregulated such that the same degree of nerve stimulus causes a larger effect than seen in healthy subjects. There are distinctions in the mechanisms and nerve types involved in allergen-induced neuromodulation among different organ systems, but general principles have emerged. The products of activated mast cells, other inflammatory cells, and resident cells can overtly stimulate nerve endings, cause long-lasting changes in neuronal excitability, increase synaptic efficacy, and also change gene expression in nerves, resulting in phenotypically altered neurons. A better understanding of these processes might lead to novel therapeutic strategies aimed at limiting the suffering of those with allergies.
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Affiliation(s)
- Bradley J Undem
- Division of Allergy & Clinical Immunology, Johns Hopkins School of Medicine, Baltimore, Md.
| | - Thomas Taylor-Clark
- Department of Molecular Pharmacology & Physiology, Morsani College of Medicine, University of South Florida, Tampa, Fla
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Abstract
The itch-scratch reflex serves as a protective mechanism in everyday life. However, chronic persistent itching can be devastating. Despite the clinical importance of the itch sensation, its mechanism remains elusive. In the past decade, substantial progress has been made to uncover the mystery of itching. Here, we review the molecules, cells, and circuits known to mediate the itch sensation, which, coupled with advances in understanding the pathophysiology of chronic itching conditions, will hopefully contribute to the development of new anti-itch therapies.
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Affiliation(s)
- Liang Han
- The Solomon H. Snyder Department of Neuroscience, Center for Sensory Biology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205;
| | - Xinzhong Dong
- The Solomon H. Snyder Department of Neuroscience, Center for Sensory Biology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205;
- Howard Hughes Medical Institute, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205;
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237
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Rossbach K, Bäumer W. PCR detects bands consistent with the expression of receptors associated with pruritus in canine dorsal root ganglia. Vet Dermatol 2013; 25:9-e4. [PMID: 24289149 DOI: 10.1111/vde.12093] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/12/2013] [Indexed: 01/17/2023]
Abstract
BACKGROUND Various mediators are involved in the induction of itch, i.e. pruritus; however, the in vivo pharmacology of pruritus seems to be different in distinct species, and little is known about receptors that are involved in the induction of itch in dogs. The species differences in the mediation of pruritus might be explained by species differences in receptor expression in the sensory nerves, including the dorsal root ganglia (DRG). HYPOTHESIS/OBJECTIVES The aim of the study was to analyse the expression of receptors for various mediators of pruritus in canine DRG. METHODS Dorsal root ganglia of 14 dogs, which were euthanized for reasons not related to this study, were analysed. Multiple DRG per dog were dissected and, after homogenization of the DRG tissues, total RNA was isolated, reverse transcribed to complementary DNA and amplified with custom-synthesized primers. RESULTS The following receptors were found in canine DRG: transient receptor potential cation channel subfamily V member 1, tachykinin receptor 1, Toll-like receptor 7, endothelin receptor type A, opioid receptors μ1 and κ1, histamine H1 -H4 receptors and the interleukin-31 receptor complex. CONCLUSIONS AND CLINICAL IMPORTANCE PCR analysis detected bands consistent with the expression of receptors associated with pruritus in canine DRG.
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Affiliation(s)
- Kristine Rossbach
- Institute of Pharmacology, Toxicology and Pharmacy, University of Veterinary Medicine Hannover, Bünteweg 17, 30559, Hannover, Germany
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238
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Bielory L, Duttachoudhury S, McMunn A. Bepotastine besilate for the treatment of pruritus. Expert Opin Pharmacother 2013; 14:2553-69. [PMID: 24191914 DOI: 10.1517/14656566.2013.849242] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
INTRODUCTION Bepotastine besilate 1.5% is a newly approved second-generation topical antihistamine indicated for the pruritus associated with allergic conjunctivitis. In Japan, the oral formulation is approved to manage pruritus associated with allergic rhinitis and urticaria. AREAS COVERED Bepotastine is a piperidine derivative that antagonizes H1 receptors with high selectivity. It has been labeled a dual-acting or multiple-acting antiallergic medication, because it inhibits histamine at H1 receptors and stabilizes mast cells to prevent histamine release. Bepotastine may also have other immunoactive properties, such as inhibition of eosinophil migration, interleukin-5 (IL-5), leukotrienes (e.g., LTB4) and platelet-activating factor (PAF). Human clinical trials demonstrate the efficacy and safety of systemic and ophthalmic bepotastine for pruritus relief, limited penetration across the blood-brain-barrier and kinetics suitable for twice-daily administration. EXPERT OPINION Bepotastine besilate 1.5% ophthalmic solution is a safe and effective treatment option for allergic conjunctivitis associated pruritus. Side-effect profile is similar to other ocular antihistamine agents. Additional comparative-effectiveness studies would further advance its clinical use. Oral bepotastine is a safe and effective treatment option approved in Japan for allergic rhinitis, urticaria and pruritus associated with skin diseases.
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Affiliation(s)
- Leonard Bielory
- Rutgers University/Robert Wood Johnson University Hospital , New Brunswick, NJ 07081 , USA +1 973 912 9817 ; +1 206 333 1884 ;
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239
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Abstract
Itch is the most common symptom described by our patients. Treating this symptom can be challenging. A revolution is ongoing in understanding the pathophysiology of itch and will allow this challenge to be met. The present authors review and update the current understanding of the pathophysiology of itch.
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Affiliation(s)
- Lilit Garibyan
- Department of Dermatology, Massachusetts General Hospital, Boston, Massachusetts 02129, USA
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240
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Abstract
While considerable effort has been made to investigate the neural mechanisms of pain, much less effort has been devoted to itch, at least until recently. However, itch is now gaining increasing recognition as a widespread and costly medical and socioeconomic issue. This is accompanied by increasing interest in the underlying neural mechanisms of itch, which has become a vibrant and rapidly-advancing field of research. The goal of the present forefront review is to describe the recent progress that has been made in our understanding of itch mechanisms.
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Affiliation(s)
- Tasuku Akiyama
- University of California, Davis, Department of Neurobiology, Physiology & Behavior, 1 Shields Avenue, Davis, CA 95616, United States
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241
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Abstract
INTRODUCTION Chronic pruritus (CP), defined as itch lasting for > 6 weeks, is a burdensome symptom of several different diseases, dermatological and systemic, with a high negative impact on the quality of life of patients. Given the manifold aetiologies of CP, therapy is often difficult. In recent years, however, novel substances have been developed for treatment of certain CP entities and identified targets. AREAS COVERED In this review, the authors present a survey of targets currently believed to be promising (H4R, IL-31, MOR, KOR, GRPR, NGF, NK-1R, TRP channels) and related investigational drugs that are in the preclinical or clinical stage of development. Some substances have already undergone clinical testing, but only one of them (nalfurafine) has been licensed so far. Many of them are most likely to exert their effects on the skin and interfere there with the cutaneous neurobiology of CP. EXPERT OPINION Currently, the most promising candidates for new therapeutic agents in CP are neurokinin-1 receptor antagonists and substances targeting the kappa- or mu-opioid receptor, or both. They have the potential to target the neuronal pathway of CP and are thus of interest for several CP entities. The goal for the coming years is to validate these concepts and move forward in developing new drugs for the therapy of CP.
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Affiliation(s)
- Heike Benecke
- University Medicine Göttingen, Center Nanoscale Microscopy and Molecular Physiology of the Brain, Humboldtallee 23, 37073 Göttingen, Germany
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242
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NAKAGAWA H, HIURA A. Four Possible Itching Pathways Related to the TRPV1 Channel, Histamine, PAR-2 and Serotonin. Malays J Med Sci 2013; 20:5-12. [PMID: 24043991 PMCID: PMC3773347] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2013] [Accepted: 05/06/2013] [Indexed: 06/02/2023] Open
Abstract
The following four possible pathways for itching sensation have been suggested by recent reports. 1) Histaminergic TRPV1-positive pathway: Although histamine-positive nerve fibers cannot strictly be classified as "itch specific" due to their excitation also by pure algogens (making them itch-selective), the existence of a subpopulation of nociceptors responsible for itching is strongly suggested. Moreover, the TRPV1-expressing neurons have been suggested to be the main sensors and mediators of itching. 2) Histaminergic TRPV1-negative pathway: The scratching behavior caused by itching was not different between capsaicin-pre-treated and vehicle-treated (control) mast cell-rich NC mice. This result suggests the existence of a capsaicin-insensitive (TRPV1-negative) histaminergic pathway. 3) Non-histaminergic PAR-2 pathway: Protease-activated receptor 2 (PAR-2) has been shown to play a role in the itching of atopic dermatitis (AD). The itch evoked by cowhage (a non-histaminergic pruritogen that activates PAR-2) is very similar in characteristics to the itch evoked by conditions such as AD. 4) Non-histaminergic serotonin (5-HT) pathway: 5-HT alone applied to the human skin evokes an itching sensation and has been suggested to be involved in the itching associated with pruritic diseases, such as polycythemia vera and cholestasis.
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Affiliation(s)
- Hiroshi NAKAGAWA
- Dentistry for Persons with Disability, Tokushima University Hospital, 3-18-15 Kuramoto cho, Tokushima 770, Japan
| | - Akio HIURA
- Dentistry for Persons with Disability, Tokushima University Hospital, 3-18-15 Kuramoto cho, Tokushima 770, Japan
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243
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Liu B, Escalera J, Balakrishna S, Fan L, Caceres AI, Robinson E, Sui A, McKay MC, McAlexander MA, Herrick CA, Jordt SE. TRPA1 controls inflammation and pruritogen responses in allergic contact dermatitis. FASEB J 2013; 27:3549-63. [PMID: 23722916 DOI: 10.1096/fj.13-229948] [Citation(s) in RCA: 167] [Impact Index Per Article: 15.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Allergic contact dermatitis is a common skin disease associated with inflammation and persistent pruritus. Transient receptor potential (TRP) ion channels in skin-innervating sensory neurons mediate acute inflammatory and pruritic responses following exogenous stimulation and may contribute to allergic responses. Genetic ablation or pharmacological inhibition of TRPA1, but not TRPV1, inhibited skin edema, keratinocyte hyperplasia, nerve growth, leukocyte infiltration, and antihistamine-resistant scratching behavior in mice exposed to the haptens, oxazolone and urushiol, the contact allergen of poison ivy. Hapten-challenged skin of TRPA1-deficient mice contained diminished levels of inflammatory cytokines, nerve growth factor, and endogenous pruritogens, such as substance P (SP) and serotonin. TRPA1-deficient sensory neurons were defective in SP signaling, and SP-induced scratching behavior was abolished in Trpa1(-/-) mice. SP receptor antagonists, such as aprepitant inhibited both hapten-induced cutaneous inflammation and scratching behavior. These findings support a central role for TRPA1 and SP in the integration of immune and neuronal mechanisms leading to chronic inflammatory responses and pruritus associated with contact dermatitis.
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Affiliation(s)
- Boyi Liu
- Department of Pharmacology, Yale School of Medicine, 333 Cedar St., New Haven, CT 06510, USA
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244
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Abstract
Itch is triggered by somatosensory neurons expressing the ion channel TRPV1 (transient receptor potential cation channel subfamily V member 1), but the mechanisms underlying this nociceptive response remain poorly understood. Here, we show that the neuropeptide natriuretic polypeptide b (Nppb) is expressed in a subset of TRPV1 neurons and found that Nppb(-/-) mice selectively lose almost all behavioral responses to itch-inducing agents. Nppb triggered potent scratching when injected intrathecally in wild-type and Nppb(-/-) mice, showing that this neuropeptide evokes itch when released from somatosensory neurons. Itch responses were blocked by toxin-mediated ablation of Nppb-receptor-expressing cells, but a second neuropeptide, gastrin-releasing peptide, still induced strong responses in the toxin-treated animals. Thus, our results define the primary pruriceptive neurons, characterize Nppb as an itch-selective neuropeptide, and reveal the next two stages of this dedicated neuronal pathway.
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Affiliation(s)
- Santosh K. Mishra
- Molecular Genetics Unit, Laboratory of Sensory Biology, NIDCR, NIH, Building 49, Room 1A16, 49 Convent Drive, Bethesda MD20892
| | - Mark A. Hoon
- Molecular Genetics Unit, Laboratory of Sensory Biology, NIDCR, NIH, Building 49, Room 1A16, 49 Convent Drive, Bethesda MD20892
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245
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Activity-dependent silencing reveals functionally distinct itch-generating sensory neurons. Nat Neurosci 2013; 16:910-8. [PMID: 23685721 PMCID: PMC3695070 DOI: 10.1038/nn.3404] [Citation(s) in RCA: 108] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2013] [Accepted: 04/18/2013] [Indexed: 02/06/2023]
Abstract
The peripheral terminals of primary sensory neurons detect histamine and non-histamine itch-provoking ligands through molecularly distinct transduction mechanisms. It remains unclear, however, whether these distinct pruritogens activate the same or different afferent fibers. We utilized a strategy of reversibly silencing specific subsets of murine pruritogen-sensitive sensory axons by targeted delivery of a charged sodium-channel blocker and found that functional blockade of histamine itch did not affect the itch evoked by chloroquine or SLIGRL-NH2, and vice versa. Notably, blocking itch-generating fibers did not reduce pain-associated behavior. However, silencing TRPV1+ or TRPA1+ neurons allowed AITC or capsaicin respectively to evoke itch, implying that certain peripheral afferents may normally indirectly inhibit algogens from eliciting itch. These findings support the presence of functionally distinct sets of itch-generating neurons and suggest that targeted silencing of activated sensory fibers may represent a clinically useful anti-pruritic therapeutic approach for histaminergic and non-histaminergic pruritus.
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246
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Than JYXL, Li L, Hasan R, Zhang X. Excitation and modulation of TRPA1, TRPV1, and TRPM8 channel-expressing sensory neurons by the pruritogen chloroquine. J Biol Chem 2013; 288:12818-27. [PMID: 23508958 PMCID: PMC3642326 DOI: 10.1074/jbc.m113.450072] [Citation(s) in RCA: 69] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2013] [Revised: 03/17/2013] [Indexed: 01/12/2023] Open
Abstract
The sensations of pain, itch, and cold often interact with each other. Pain inhibits itch, whereas cold inhibits both pain and itch. TRPV1 and TRPA1 channels transduce pain and itch, whereas TRPM8 transduces cold. The pruritogen chloroquine (CQ) was reported to excite TRPA1, leading to the sensation of itch. It is unclear how CQ excites and modulates TRPA1(+), TRPV1(+), and TRPM8(+) neurons and thus affects the sensations of pain, itch, and cold. Here, we show that only 43% of CQ-excited dorsal root ganglion neurons expressed TRPA1; as expected, the responses of these neurons were completely prevented by the TRPA1 antagonist HC-030031. The remaining 57% of CQ-excited neurons did not express TRPA1, and excitation was not prevented by either a TRPA1 or TRPV1 antagonist but was prevented by the general transient receptor potential canonical (TRPC) channel blocker BTP2 and the selective TRPC3 inhibitor Pyr3. Furthermore, CQ caused potent sensitization of TRPV1 in 51.9% of TRPV1(+) neurons and concomitant inhibition of TRPM8 in 48.8% of TRPM8(+) dorsal root ganglion neurons. Sensitization of TRPV1 is caused mainly by activation of the phospholipase C-PKC pathway following activation of the CQ receptor MrgprA3. By contrast, inhibition of TRPM8 is caused by a direct action of activated Gαq independent of the phospholipase C pathway. Our data suggest the involvement of the TRPC3 channel acting together with TRPA1 to mediate CQ-induced itch. CQ not only elicits itch by directly exciting itch-encoding neurons but also exerts previously unappreciated widespread actions on pain-, itch-, and cold-sensing neurons, leading to enhanced pain and itch.
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Affiliation(s)
- Jonathan Y.-X. L. Than
- From the Department of Pharmacology, University of Cambridge, Cambridge CB2 1PD, United Kingdom
| | - Lin Li
- From the Department of Pharmacology, University of Cambridge, Cambridge CB2 1PD, United Kingdom
| | - Raquibul Hasan
- From the Department of Pharmacology, University of Cambridge, Cambridge CB2 1PD, United Kingdom
| | - Xuming Zhang
- From the Department of Pharmacology, University of Cambridge, Cambridge CB2 1PD, United Kingdom
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247
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Liu T, Ji RR. New insights into the mechanisms of itch: are pain and itch controlled by distinct mechanisms? Pflugers Arch 2013; 465:1671-85. [PMID: 23636773 DOI: 10.1007/s00424-013-1284-2] [Citation(s) in RCA: 134] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2012] [Revised: 04/13/2013] [Accepted: 04/14/2013] [Indexed: 12/30/2022]
Abstract
Itch and pain are closely related but distinct sensations. They share largely overlapping mediators and receptors, and itch-responding neurons are also sensitive to pain stimuli. Itch-mediating primary sensory neurons are equipped with distinct receptors and ion channels for itch transduction, including Mas-related G protein-coupled receptors (Mrgprs), protease-activated receptors, histamine receptors, bile acid receptor, toll-like receptors, and transient receptor potential subfamily V1/A1 (TRPV1/A1). Recent progress has indicated the existence of an itch-specific neuronal circuitry. The MrgprA3-expressing primary sensory neurons exclusively innervate the epidermis of skin, and their central axons connect with gastrin-releasing peptide receptor (GRPR)-expressing neurons in the superficial spinal cord. Notably, ablation of MrgprA3-expressing primary sensory neurons or GRPR-expressing spinal cord neurons results in selective reduction in itch but not pain. Chronic itch results from dysfunction of the immune and nervous system and can manifest as neural plasticity despite the fact that chronic itch is often treated by dermatologists. While differences between acute pain and acute itch are striking, chronic itch and chronic pain share many similar mechanisms, including peripheral sensitization (increased responses of primary sensory neurons to itch and pain mediators), central sensitization (hyperactivity of spinal projection neurons and excitatory interneurons), loss of inhibitory control in the spinal cord, and neuro-immune and neuro-glial interactions. Notably, painful stimuli can elicit itch in some chronic conditions (e.g., atopic dermatitis), and some drugs for treating chronic pain are also effective in chronic itch. Thus, itch and pain have more similarities in pathological and chronic conditions.
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Affiliation(s)
- Tong Liu
- Pain Signaling and Plasticity Laboratory, Department of Anesthesiology and Neurobiology, Duke University Medical Center, 595 LaSalle Street, GSRB-I, Room 1027A, DUMC 3094, Durham, NC, 27710, USA,
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248
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Abstract
The transient receptor potential (TRP) superfamily consists of 28 members in mammals (27 in human) that act as polymodal sensors and ion channels. They regulate cellular calcium influx, generate depolarization thereby triggering voltage dependent cellular processes, and in turn they are critical in inducing the metabolic activities of cells. It is increasingly apparent that many of the inflammatory mediators released in allergic reactions involve at least two of these ion channels, the 'Vanilloid' TRPV1 and the 'Ankyrin" TRPA1. This review mainly focuses on TRPV1 and TRPA1 and the role they have in the allergic response and how these receptors may be influenced in exercise-induced anaphylaxis. The threshold to react to an allergen for mast cells and lymphocytes can be reduced by activating the melastatin channel TRPM4. This channel is briefly discussed in the context of allergy.
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249
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Alemi F, Kwon E, Poole DP, Lieu T, Lyo V, Cattaruzza F, Cevikbas F, Steinhoff M, Nassini R, Materazzi S, Guerrero-Alba R, Valdez-Morales E, Cottrell GS, Schoonjans K, Geppetti P, Vanner SJ, Bunnett NW, Corvera CU. The TGR5 receptor mediates bile acid-induced itch and analgesia. J Clin Invest 2013; 123:1513-30. [PMID: 23524965 DOI: 10.1172/jci64551] [Citation(s) in RCA: 266] [Impact Index Per Article: 24.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2012] [Accepted: 01/17/2013] [Indexed: 12/23/2022] Open
Abstract
Patients with cholestatic disease exhibit pruritus and analgesia, but the mechanisms underlying these symptoms are unknown. We report that bile acids, which are elevated in the circulation and tissues during cholestasis, cause itch and analgesia by activating the GPCR TGR5. TGR5 was detected in peptidergic neurons of mouse dorsal root ganglia and spinal cord that transmit itch and pain, and in dermal macrophages that contain opioids. Bile acids and a TGR5-selective agonist induced hyperexcitability of dorsal root ganglia neurons and stimulated the release of the itch and analgesia transmitters gastrin-releasing peptide and leucine-enkephalin. Intradermal injection of bile acids and a TGR5-selective agonist stimulated scratching behavior by gastrin-releasing peptide- and opioid-dependent mechanisms in mice. Scratching was attenuated in Tgr5-KO mice but exacerbated in Tgr5-Tg mice (overexpressing mouse TGR5), which exhibited spontaneous pruritus. Intraplantar and intrathecal injection of bile acids caused analgesia to mechanical stimulation of the paw by an opioid-dependent mechanism. Both peripheral and central mechanisms of analgesia were absent from Tgr5-KO mice. Thus, bile acids activate TGR5 on sensory nerves, stimulating the release of neuropeptides in the spinal cord that transmit itch and analgesia. These mechanisms could contribute to pruritus and painless jaundice that occur during cholestatic liver diseases.
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Affiliation(s)
- Farzad Alemi
- Department of Surgery, UCSF, San Francisco, California 94121, USA
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250
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Lavinka PC, Dong X. Molecular signaling and targets from itch: lessons for cough. COUGH 2013; 9:8. [PMID: 23497684 PMCID: PMC3630061 DOI: 10.1186/1745-9974-9-8] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/16/2012] [Accepted: 02/08/2013] [Indexed: 01/05/2023]
Abstract
Itch is described as an unpleasant sensation that elicits the desire to scratch, which results in the removal of the irritant from the skin. The cough reflex also results from irritation, with the purpose of removing said irritant from the airway. Could cough then be similar to itch? Anatomically, both pathways are mediated by small-diameter sensory fibers. These cough and itch sensory fibers release neuropeptides upon activation, which leads to inflammation of the nerves. Both cough and itch also involve mast cells and their mediators, which are released upon degranulation. This common inflammation and interaction with mast cells are involved in the development of chronic conditions of itch and cough. In this review, we examine the anatomy and molecular mechanisms of itch and compare them to known mechanisms for cough. Highlighting the common aspects of itch and cough could lead to new thoughts and perspectives in both fields.
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Affiliation(s)
- Pamela Colleen Lavinka
- The Solomon H, Snyder Department of Neuroscience, Center for Sensory Biology, Johns Hopkins University School of Medicine, 725 N Wolfe Street, Baltimore, MD, 21205, USA.
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