Abstract

Persistent itch often accompanies allergic contact dermatitis (ACD), but the underlying mechanisms remain largely unexplored. We previously demonstrated that CXCL10/ CXCR3 signaling activated a subpopulation of cutaneous primary sensory neurons and mediated itch response after contact hypersensitivity (CHS), a murine model of ACD, induced by squaric acid dibutylester. The purpose of this study was to determine the ionic mechanisms underlying CXCL10-induced neuronal activation and allergic itch. In whole-cell recordings, CXCL10 triggered a current in dorsal root ganglion (DRG) neurons innervating the area of CHS. This current was modulated by intracellular Cl- and blocked by the general Cl- channel inhibitors. Moreover, increasing Ca2+ buffering capacity reduced this current. In addition, blockade of Cl- channels significantly suppressed CXCL10-induced Ca2+ response. In behavioral tests, injection of CXCL10 into CHS site exacerbated itch-related scratching behaviors. Moreover, the potentiating behavioral effects of CXCL10 were attenuated by either of two Cl- channel blockers. Thus, we suggest that the Cl- channel acts as a downstream target mediating the excitatory and pruritic behavioral effects of CXCL10. Cl- channels may provide a promising therapeutic target for the treatment of allergic itch in which CXCL10/CXCR3 signaling may participate.
jn.00187.2017.fulljn.00187.2017.full

TNF-a/TNFR1 Signaling is Required for the Full Expression of Acute and Chronic Itch in Mice via Peripheral and Central Mechanisms

art10.1007s12264-017-0124-3

Xiuhua Miao1 • Ya Huang2 • Teng-Teng Liu2 • Ran Guo2 • Bing Wang2 • Xue-Long Wang3 • Li-Hua Chen4 • Yan Zhou2 • Ru-Rong Ji5,6 • Tong Liu1,2
Received: 11 November 2016 / Accepted: 9 February 2017
Ó Shanghai Institutes for Biological Sciences, CAS and Springer Science+Business Media Singapore 2017

Abstract Increasing evidence suggests that cytokines and chemokines play crucial roles in chronic itch. In the present study, we evaluated the roles of tumor necrosis factor-alpha (TNF-a) and its receptors TNF receptor subtype-1 (TNFR1) and TNFR2 in acute and chronic itch in mice. Compared to wild-type (WT) mice, TNFR1-knockout (TNFR1-KO) and TNFR1/R2 double-KO (DKO), but not TNFR2-KO mice, exhibited reduced acute itch induced by compound 48/80 and chloroquine (CQ). Application of the TNF-synthesis inhibitor thalidomide and the TNF-a antagonist etanercept dose-dependently suppressed acute itch. Intradermal injection of TNF-a was not sufficient to evoke scratching, but potentiated itch induced by com- pound 48/80, but not CQ. In addition, compound 48/80 induced TNF-a mRNA expression in the skin, while CQ induced its expression in the dorsal root ganglia (DRG) and spinal cord. Furthermore, chronic itch induced by dry skin was reduced by administration of thalidomide and etaner- cept and in TNFR1/R2 DKO mice. Dry skin induced TNF- a expression in the skin, DRG, and spinal cord and TNFR1 expression only in the spinal cord. Thus, our findings suggest that TNF-a/TNFR1 signaling is required for the full expression of acute and chronic itch via peripheral and central mechanisms, and targeting TNFR1 may be benefi- cial for chronic itch treatment.
Keywords Itch Tumor necrosis factor Tumor necrosis factor receptor Spinal cord Central sensitization

Mechanisms of Pruritogen-Induced Activation of Itch Nerves in Isolated Mouse Skin

Ru, F1., Sun, H1., Jurcakova, D.1,3, Herbstsomer, R.A1., Meixong, J2., Dong, X2, Undem, B.J. 1
Departments of Medicine1 and Neuroscience2, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA, 3Department of Pathophysiology, Biomedical Center Martin, Jessenius Medical School, Comenius University, Martin, Slovakia

Running Title: Characterization of itch causing nerves

Mechanisms of Pruritogen-Induced Activation of Itch Nerves in Isolated Mouse Skin

Key Points Summary
Chloroquine (CQ) stimulates itch nerves and causes intense scratching in mice by activating the G- Protein Coupled Receptor (GPCR) MrgprA3. It is not known how stimulation of MrgprA3 (or other GPCRs) leads to activation of the itch nerve terminals in the skin, but previous studies have found that TRPA1 gene deletion blocks CQ-induced scratching.
In the present study we used a novel dorsal skin-nerve preparation to evaluate mechanisms underlying CQ- and histamine-induced action potential discharge in itch nerve terminals.
We found that CQ activation of the nerves requires the beta3 isoform of phospholipase C, however, TRPA1 or other TRP channel are not required. Evidence is provided for a role for calcium-activated chloride channels such as TMEM16a in GPCR-activation of itch nerve terminals.
The mechanism by which TRP channels participate in pruritogen-induced scratching may involve sites of action other than the primary afferent terminals.

Tmem100 Is a Regulator of TRPA1-TRPV1 Complex and Contributes to Persistent Pain

mmc2
Hao-Jui Weng,1,2 Kush N. Patel,1 Nathaniel A. Jeske,3 Sonya M. Bierbower,3 Wangyuan Zou,4 Vinod Tiwari,5 Qin Zheng,1 Zongxiang Tang,6 Gary C.H. Mo,7 Yan Wang,1,8 Yixun Geng,1 Jin Zhang,1,7 Yun Guan,5 Armen N. Akopian,9,*
and Xinzhong Dong1,10,*
1Departments of Neuroscience and Neurosurgery, School of Medicine, Johns Hopkins University, Baltimore, MD 21205, USA 2Department of Dermatology, National Taiwan University Hospital, Taipei City 100, Taiwan
3Department of Physiology, University of Texas Health Science Center, San Antonio, TX 78229, USA
4Department of Anesthesiology, Xiangya Hospital, Central South University, Changsha, Hunan 410008, China
5Department of Anesthesiology and Critical Care, School of Medicine, Johns Hopkins University, Baltimore, MD 21205, USA 6Nanjing University of Chinese Medicine, Nanjing 210046, China
7Department of Pharmacology and Molecular Sciences, School of Medicine, Johns Hopkins University, Baltimore, MD 21205, USA 8West China School of Stomatology, Sichuan University, Chengdu, Sichuan 610041, China
9Department of Endodontics, University of Texas Health Science Center, San Antonio, TX 78229, USA
10Howard Hughes Medical Institute, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
*Correspondence: akopian@uthscsa.edu (A.N.A.), xdong2@jhmi.edu (X.D.)
http://dx.doi.org/10.1016/j.neuron.2014.12.065

TRPA1 and TRPV1 are crucial pain mediators, but how their interaction contributes to persistent pain is unknown. Here, we identify Tmem100 as a potenti- ating modulator of TRPA1-V1 complexes. Tmem100 is coexpressed and forms a complex with TRPA1 and TRPV1 in DRG neurons. Tmem100-deficient mice show a reduction in inflammatory mechanical hyperalgesia and TRPA1- but not TRPV1-mediated pain. Single-channel recording in a heterologous system reveals that Tmem100 selectively potenti- ates TRPA1 activity in a TRPV1-dependent manner. Mechanistically, Tmem100 weakens the association of TRPA1 and TRPV1, thereby releasing the inhibi- tion of TRPA1 by TRPV1. A Tmem100 mutant, Tmem100-3Q, exerts the opposite effect; i.e., it en- hances the association of TRPA1 and TRPV1 and strongly inhibits TRPA1. Strikingly, a cell-permeable peptide (CPP) containing the C-terminal sequence of Tmem100-3Q mimics its effect and inhibits persistent pain. Our study unveils a context-depen- dent modulation of the TRPA1-V1 complex, and Tmem100-3Q CPP is a promising pain therapy.

Antioxidants Attenuate Acute and Chronic Itch: Peripheral and Central Mechanisms of Oxidative Stress in Pruritus

Feng-Ming Zhou1,3 • Ruo-Xiao Cheng1,3 • Shuai Wang1,2 • Ya Huang3 • Yong-Jing Gao4 • Yan Zhou3 • Teng-Teng Liu3 • Xue-Long Wang5 • Li-Hua Chen2 • Tong Liu1,3

Antioxidants Attenuate Acute and Chronic Itch Peripheral and Central Mechanisms of Oxidative Stress in Pruritus

Received: 1 July 2016 / Accepted: 27 August 2016
ⓒ Shanghai Institutes for Biological Sciences, CAS and Springer Science+Business Media Singapore 2016

Abstract
Itch (pruritus) is one of the most disabling syndromes in patients suffering from skin, liver, or kidney diseases. Our previous study highlighted a key role of oxidative stress in acute itch. Here, we evaluated the effects of antioxidants in mouse models of acute and chronic itch and explored the potential mechanisms. The effects of systemic administration of the antioxidants N-acetyl-L-cysteine (NAC) and N-tert-butyl-α-phenylnitrone (PBN) were determined by behavioral tests in mouse models of acute itch induced by compound 48/80 or chloroquine, and chronic itch by treatment with a mixture of acetone-diethyl-ether-water. We found that systemic administration of NAC or PBN significantly alleviated compound 48/80- and chloroquine-induced acute itch in a dose-dependent manner, attenuated dry skin-induced chronic itch, and suppressed oxidative stress in the affected skin. Antioxidants significantly decreased the accumulation of intracellular reactive oxygen species directly induced by compound 48/80 and chloroquine in the cultured dorsal root ganglia-derived cell line ND7-23. Finally, the antioxidants remarkably inhibited the compound 48/80-induced phosphorylation of extracellular signal-regulated kinase in the spinal cord. These results indicated that oxidative stress plays a critical role in acute and chronic itch in the periphery and spinal cord and antioxidant treatment may be a promising strategy for anti-itch therapy.

Keywords

Oxidative stressAntioxidantsItchTRPA1Extracellular signal-regulated kinase
Feng-Ming Zhou and Ruo-Xiao Cheng have contributed equally to this work.

Li-Hua Chen chenlihua@suda.edu.cn
Tong Liu liutong80@suda.edu.cn
1 Department of Neurology, The Second Affiliated Hospital of Soochow University, Suzhou 215004, China
2 Jiangsu Key Laboratory of Preventive and Translational Medicine for Geriatric Diseases, Department of Nutrition and Food Hygiene, School of Public Health, Soochow University, Suzhou 215123, China
3 Institute of Neuroscience, Soochow University, Suzhou 215123, China
4 Institute of Nautical Medicine, Nantong University,Nantong 226001, China
5 Beijing Electric Power Hospital, Beijing 100073, China

Inhibition of TRPV1 channels by a naturally occurring omega-9 fatty acid reduces pain and itch

Inhibition of TRPV1 channels by a naturally occurring omega-9 fatty acid reduces pain and itch

Sara L. Morales-La ́zaro1, Itzel Llorente1, Fe ́lix Sierra-Ram ́ırez1, Ana E. Lo ́pez-Romero1, Miguel Ort ́ız-Renter ́ıa1, Barbara Serrano-Flores1, Sidney A. Simon2, Leo ́n D. Islas3 & Tamara Rosenbaum1

The transient receptor potential vanilloid 1 (TRPV1) ion channel is mainly found in primary nociceptive afferents whose activity has been linked to pathophysiological conditions including pain, itch and inflammation. Consequently, it is important to identify naturally occurring antagonists of this channel. Here we show that a naturally occurring mono- unsaturated fatty acid, oleic acid, inhibits TRPV1 activity, and also pain and itch responses in mice by interacting with the vanilloid (capsaicin)-binding pocket and promoting the stabilization of a closed state conformation. Moreover, we report an itch-inducing molecule, cyclic phosphatidic acid, that activates TRPV1 and whose pruritic activity, as well as that of histamine, occurs through the activation of this ion channel. These findings provide insights into the molecular basis of oleic acid inhibition of TRPV1 and also into a way of reducing the pathophysiological effects resulting from its activation.

1 Instituto de Fisiolog ́ıa Celular, Universidad Nacional Auto ́noma de Me ́xico, Circuito exterior s/n, Coyoacan 04510, Mexico. 2 Department of Neurobiology, Duke University, 327C Bryan Research Building, Durham, North Carolina 27710, USA. 3 Departamento de Fisiolog ́ıa, Facultad de Medicina, Universidad Nacional Auto ́noma de Me ́xico, Circuito escolar s/n, Coyoacan 04510, Mexico. Correspondence and requests for materials should be addressed to T.R. (email: trosenba@ifc.unam.mx).

A histamine-independent itch path- way is required for allergic ocular itch

A histamine-independent itch pathway is required for allergic ocular itch

Cheng-Chiu Huang, PhDa, Yu Shin Kim, PhDb, William P. Olson, BSc, Fengxian Li, MDa, d, Changxiong Guo, BAa, Wenqin Luo, MD, PhDc, Andrew J.W. Huang, MD, MPHe, Qin Liu, PhDa, e,

From athe Department of Anesthesiology and the Center for the Study of Itch, Washing- ton University School of Medicine, St Louis, Mo; bthe Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, Md; cthe Department of Neuroscience, University of Pennsylvania School of Medicine, Philadelphia, Pa; dthe Department of Anesthesiology, Zhujiang Hospital, Southern Medical University, Guangzhou, China; and ethe Department of Ophthalmology and Visual Sciences, Washington University School of Medicine, St Louis, Mo.

Itch is the cardinal symptom of allergic conjunctivitis and afflicts 15% to 20% of the population worldwide. Histamine produced by conjunctival mast cells has been implicated as the principal itch mediator that activates histamine receptors on primary sensory fibers to induce allergic ocular itch.1 However, antihistamines cannot completely relieve ocular itch in many cases, suggesting the involvement of a histamine-independent itch pathway. Herein, we sought to identify the histamine- independent neural pathway involved in allergic conjunctivitis and to develop new therapeutic strategies for allergic ocular itch.

Enhanced itch elicited by capsaicin in a chronic itch model

Enhanced itch elicited by capsaicin in a chronic itch model

Guang Yu, PhD1,2, Niuniu Yang, MD1, Fengxian Li, MD2,3, Meijuan Chen, PhD1, Changxiong J Guo, BS2, Changming Wang, PhD1, Danyou Hu, BS1, Yan Yang, BS1, Chan Zhu, BS1,
Zhongli Wang, PhD1, Hao Shi, MD1, Tana Gegen, MD1, Ming Tang, MS1, Qian He, MS1, Qin Liu, PhD2 and Zongxiang Tang, PhD1

Abstract
Chronic itch (pruritus) is an important clinical problem. However, the underlying molecular basis has yet to be understood. The Transient Receptor Potential Vanilloid 1 channel is a heat-sensitive cation channel expressed in primary sensory neurons and involved in both thermosensation and pain, but its role in chronic itch remains elusive. Here, we for the first time revealed an increased innervation density of Transient Receptor Potential Vanilloid 1-expressing sensory fibers in the skin afflicted with chronic itch. Further analysis indicated that this phenomenon is due to an expansion of Transient Receptor Potential Vanilloid 1-expressing sensory neurons under chronic itch conditions. As a functional correlates of this neuronal expansion, we observed an enhanced neuronal responsiveness to capsaicin under the dry skin conditions. Importantly, the neuronal hypersensitivity to capsaicin results in itch, rather than pain sensation, suggesting that the up-regulated Transient Receptor Potential Vanilloid 1 underlies the pain-to-itch switch under chronic itchy conditions. The study shows that there are different mechanisms of chronic pain and itching, and Transient Receptor Potential Vanilloid 1 plays an important role in chronic itch.

Keywords
Chronic itch, pain, Transient Receptor Potential Vanilloid 1, calcium imaging Date received: 5 January 2016; revised: 20 March 2016; accepted: 20 March 2016

Anti-pruritic effect of baicalin and its metabolites, baicalein and oroxylin A, in mice

Anti-pruritic effect of baicalin and its metabolites, baicalein and oroxylin A, in mice

Hien-trung TRINH1, Eun-ha JOH1, Ho-young KWAK2, Nam-in BAEK2, Dong-hyun KIM1, *
1Department of Pharmaceutical Science and Department of Life and Pharmaceutical Sciences, Kyung Hee University, 1, Hoegi, Dongdaemun-ku, Seoul 130–701, Korea; 2Graduate School of Biotechnology and PMRC, Kyung Hee University, 1, Seochunri, Suwon, Kyunggi-Do 449–701, Korea
Aim: To explore whether intestinal micro ora plays a role in anti-pruritic activity of baicalin, a main constituent of the rhizome of Scutellaria baicalensis (SB).
Methods: Baicalin was anaerobically incubated with human fecal micro ora, and its metabolites, baicalein and oroxylin A, were isolated. The inhibitory effect of baicalin and its metabolites was accessed in histamine- or compound 48/80-induced scratching behavior in mice.
Results: Baicalin was metabolized to baicalein and oroxylin A, with metabolic activities of 40.2±26.2 and 1.2±1.1 nmol·h-1·mg-1 wet weight of human fecal micro ora, respectively. Baicalin (20, 50 mg/kg) showed more potent inhibitory effect on histamine-induced scratching behavior when orally administered than intraperitoneally. In contrast, baicalein and oroxylin A had more potent inhibitory effect when the intraperitoneally administered. The anti-scratching behavior activity of oral baicalin and its metabolites was in proportion to their inhibition on histamine-induced increase of vascular permeability with oroxylin A more potent than baicalein and baicalin. In Magnus test using guinea pig ileum, oroxylin A is more potent than baicalein and baicalin in inhibition of histamine-induced contraction. The anti-scratching behavioral effect of oral baicalin was signi cantly reduced when oral antibiotics were simultaneously administered, whereas the effect of baicalein and oroxylin A were not affected.
Conclusion: Oral baicalin may be metabolized by intestinal micro ora into baicalein and oroxylin A, which ameliorate pruritic reactions through anti-histamine action.
Keywords: Scutellaria baicalensis; baicalin; baicalein; oroxylin A; scratching behavior; metabolism; histamine Acta Pharmacologica Sinica (2010) 31: 718–724; doi: 10.1038/aps.2010.42; published online 10 May 2010

Osthole inhibits histamine-dependent itch via modulating TRPV1 activity

srep25657

Osthole, an active coumarin isolated from Cnidium monnieri (L.) Cusson, has long been used in China as an antipruritic herbal medicine; however, the antipruitic mechanism of osthole is unknown. We studied the molecular mechanism of osthole in histamine-dependent itch by behavioral test, Ca2+ imaging,
and electrophysiological experiments. First, osthole clearly remitted the scratching behaviors of mice induced with histamine, HTMT, and VUF8430. Second, in cultured dorsal root ganglion (DRG) neurons, osthole showed a dose-dependent inhibitory e ect to histamine. On the same neurons, osthole also decreased the response to capsaicin and histamine. In further tests, the capsaicin-induced inward currents were inhibited by osthole. These results revealed that osthole inhibited histamine-dependent itch by modulating TRPV1 activity. This study will be helpful in understanding how osthole exerts anti- pruritus e ects and suggests that osthole may be a useful treatment medicine for histamine-dependent itch.