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NGF Sensitizes Nociceptors for Cowhage- but Not Histamine-Induced Itch in Human Skin

2012; Elsevier BV; Volume: 133; Issue: 1 Linguagem: Inglês

10.1038/jid.2012.242

1523-1747

Roman Rukwied, Maurice Main, Benjamin Weinkauf, Martin Schmelz,

Circadian rhythm and melatonin

atopic dermatitis area under the curve nerve growth factor transient receptor potential visual analog scale TO THE EDITOR Chronic itch has been associated with increased levels of epidermal nerve growth factor (NGF) and enhanced neuronal signaling, for instance in atopic dermatitis (AD) patients (Tominaga et al., 2009Tominaga M. Tengara S. Kamo A. et al.Psoralen-ultraviolet A therapy alters epidermal Sema3A and NGF levels and modulates epidermal innervation in atopic dermatitis.J Dermatol Sci. 2009; 55: 40-46Abstract Full Text Full Text PDF PubMed Scopus (99) Google Scholar; Yamaguchi et al., 2009Yamaguchi J. Aihara M. Kobayashi Y. et al.Quantitative analysis of nerve growth factor (NGF) in the atopic dermatitis and psoriasis horny layer and effect of treatment on NGF in atopic dermatitis.J Dermatol Sci. 2009; 53: 48-54Abstract Full Text Full Text PDF PubMed Scopus (102) Google Scholar. Experimentally, pruritus can be elicited in AD independent of histamine (Ikoma et al., 2004Ikoma A. Fartasch M. Heyer G. et al.Painful stimuli evoke itch in patients with chronic pruritus: Central sensitization for itch.Neurology. 2004; 62: 212-217Crossref PubMed Scopus (182) Google Scholar. Spicules from Mucuna pruriens (cowhage) also produce sensations of itch when inserted into the epidermis of humans (Namer et al., 2008Namer B. Carr R. Johanek L.M. et al.Separate peripheral pathways for pruritus in man.J Neurophysiol. 2008; 100: 2062-2069Crossref PubMed Scopus (207) Google Scholar; Sikand et al., 2009Sikand P. Shimada S.G. Green B.G. et al.Similar itch and nociceptive sensations evoked by punctate cutaneous application of capsaicin, histamine and cowhage.Pain. 2009; 144: 66-75Abstract Full Text Full Text PDF PubMed Scopus (132) Google Scholar. Cowhage activates mechanoresponsive "polymodal" C-nociceptors in humans and also Aδ fibers in monkey (Ringkamp et al., 2011Ringkamp M. Schepers R.J. Shimada S.G. et al.A role for nociceptive, myelinated nerve fibers in itch sensation.J Neurosci. 2011; 31: 14841-14849Crossref PubMed Scopus (115) Google Scholar and evokes itch sensations at an intensity comparable to histamine but without an accompanying axon reflex flare reaction. Our understanding of nonhistaminergic itch has increased tremendously during the past decade. Increased levels of NGF mRNA and elevated keratinocyte and serum NGF content have both been linked to itch in animal models (Takano et al., 2005Takano N. Sakurai T. Kurachi M. Effects of anti-nerve growth factor antibody on symptoms in the NC/Nga mouse, an atopic dermatitis model.J Pharmacol Sci. 2005; 99: 277-286Crossref PubMed Scopus (85) Google Scholar; Yamaura et al., 2011Yamaura K. Doi R. Suwa E. et al.A novel animal model of pruritus induced by successive application of glucocorticoid to mouse skin.J Toxicol Sci. 2011; 36: 395-401Crossref PubMed Scopus (12) Google Scholar. Anti-NGF treatment in these animals significantly reduced dermatitis scores, the number of epidermal nerve fibers, and scratching behavior (Takano et al., 2005Takano N. Sakurai T. Kurachi M. Effects of anti-nerve growth factor antibody on symptoms in the NC/Nga mouse, an atopic dermatitis model.J Pharmacol Sci. 2005; 99: 277-286Crossref PubMed Scopus (85) Google Scholar. In AD patients, enhanced levels of NGF in epidermal and horny layers correlated with the severity of itching (Tominaga et al., 2009Tominaga M. Tengara S. Kamo A. et al.Psoralen-ultraviolet A therapy alters epidermal Sema3A and NGF levels and modulates epidermal innervation in atopic dermatitis.J Dermatol Sci. 2009; 55: 40-46Abstract Full Text Full Text PDF PubMed Scopus (99) Google Scholar; Yamaguchi et al., 2009Yamaguchi J. Aihara M. Kobayashi Y. et al.Quantitative analysis of nerve growth factor (NGF) in the atopic dermatitis and psoriasis horny layer and effect of treatment on NGF in atopic dermatitis.J Dermatol Sci. 2009; 53: 48-54Abstract Full Text Full Text PDF PubMed Scopus (102) Google Scholar. We therefore hypothesized that NGF sensitizes skin nociceptors in AD patients and thereby increases pruritus. In healthy volunteers, intradermally administered NGF chronically sensitizes nociceptors, resulting in a localized hyperalgesia to heat and a prolonged mechanical hyperalgesia (Rukwied et al., 2010Rukwied R. Mayer A. Kluschina O. et al.NGF induces non-inflammatory localized and lasting mechanical and thermal hypersensitivity in human skin.Pain. 2010; 148: 407-413Abstract Full Text Full Text PDF PubMed Scopus (136) Google Scholar; Obreja et al., 2011Obreja O. Kluschina O. Mayer A. et al.NGF enhances electrically induced pain, but not axon reflex sweating.Pain. 2011; 152: 1856-1863Abstract Full Text Full Text PDF PubMed Scopus (26) Google Scholar. It is unclear whether such NGF-mediated nociceptor sensitization also modulates the sensitivity to various pruritic stimuli. We therefore injected 1μg NGF intradermally in healthy male volunteers (n=13, age 36±11) and investigated their itch response to histamine iontophoresis (15mC) and cowhage spicule insertion (15–20 spicules). Stimuli were applied at a time point coinciding with the development of maximum heat (day 7) and maximum mechanical hyperalgesia (day 21) determined in a previous human trial (Rukwied et al., 2010Rukwied R. Mayer A. Kluschina O. et al.NGF induces non-inflammatory localized and lasting mechanical and thermal hypersensitivity in human skin.Pain. 2010; 148: 407-413Abstract Full Text Full Text PDF PubMed Scopus (136) Google Scholar. Assuming that histamine- and cowhage-induced itch are mediated by separate classes of primary afferent neurons (Johanek et al., 2007Johanek L.M. Meyer R.A. Hartke T. et al.Psychophysical and physiological evidence for parallel afferent pathways mediating the sensation of itch.J Neurosci. 2007; 27: 7490-7497Crossref PubMed Scopus (158) Google Scholar; Namer et al., 2008Namer B. Carr R. Johanek L.M. et al.Separate peripheral pathways for pruritus in man.J Neurophysiol. 2008; 100: 2062-2069Crossref PubMed Scopus (207) Google Scholar, our expectation was that the time course of heat hyperalgesia would parallel that of increased histamine sensitivity (mediated by mechano-insensitive "silent" nociceptors) following NGF and similarly that the time courses of mechanical hyperalgesia and cowhage-induced itch (mediated by "polymodal" nociceptors) would be comparable (Namer et al., 2008Namer B. Carr R. Johanek L.M. et al.Separate peripheral pathways for pruritus in man.J Neurophysiol. 2008; 100: 2062-2069Crossref PubMed Scopus (207) Google Scholar. Maximum histamine-induced itch within the NGF-treated site did not differ between day 7 (28±5, visual analog scale (VAS)) and day 21 (VAS 27±7). VAS area under the curve (AUC) values calculated during the 10-min recording period were also similar at days 7 (492±122) and 21 (489±112). There were no significant differences between histamine-induced itch responses recorded from treated and untreated skin (P<0.6, Wilcoxon test, Figure 1a). Epidermal application of cowhage spicules at the NGF-treated site on day 7 evoked a peak itch sensation of VAS 25±5 and an AUC of 359±69, both of which were not significantly different from values obtained from control skin (VAS 23±6, AUC 349±73). In contrast, 21 days after NGF treatment, cowhage-induced itch was significantly enhanced compared with the control sites, with a maximum itch of VAS 35±7 (P<0.05, Wilcoxon test) at day 21 and a corresponding AUC of 522±98 (P<0.02, Wilcoxon test, Figure 1b). To differentially quantify "silent" nociceptor sensitization, we also analyzed the axon reflex flare using laser Doppler imaging. In comparison with control skin, NGF did not augment histamine-induced flare responses at either day 7 (16±1 vs. 18±2cm2) or day 21 (15±2 vs. 16±1cm2). As in humans (Johanek et al., 2007Johanek L.M. Meyer R.A. Hartke T. et al.Psychophysical and physiological evidence for parallel afferent pathways mediating the sensation of itch.J Neurosci. 2007; 27: 7490-7497Crossref PubMed Scopus (158) Google Scholar, no axon reflex flare was apparent after application of cowhage, neither at the control nor at the NGF site (flare area <0.8±0.2cm2, data not shown). We further assessed heat pain thresholds and mechanical pain for pressure (100kPa), pinprick (150mN), and impact stimuli (8ms−1) (Rukwied et al., 2010Rukwied R. Mayer A. Kluschina O. et al.NGF induces non-inflammatory localized and lasting mechanical and thermal hypersensitivity in human skin.Pain. 2010; 148: 407-413Abstract Full Text Full Text PDF PubMed Scopus (136) Google Scholar. Heat pain thresholds after NGF were reduced by 5±0.4°C at day 7 and 21, but this reduction did not correlate with the histamine- or enhanced cowhage-induced itch (Spearman's r=0.059, P=0.77 (histamine) and r=0.023, P=0.91 (cowhage), Figure 2a). In contrast, pain upon mechanical stimulation increased after NGF (VAS from 3±0.8 to 19±4 (pressure), VAS from 3±1 to 9±3 (pinprick), and VAS from 5±2 to 21±3 (impact)) and each of these increases correlated with cowhage-induced itch sensations (Spearman's r=0.67, P<0.0002 (pressure), r=0.7, P<0.00001 (pinprick), r=0.55, P<0.003 (impact pain, Figure 2b)). Our data demonstrate that NGF sensitizes cowhage- but not histamine-induced itch. The absence of sensitization to histamine at a time point showing the maximum increase in heat sensitivity is surprising. Apparently, sensitization of transient receptor potential (TRPV1) does not necessarily lead to increased histamine responses, even though histamine-induced itch is elevated inside the eczema of AD (Hosogi et al., 2006Hosogi M. Schmelz M. Miyachi Y. et al.Bradykinin is a potent pruritogen in atopic dermatitis: a switch from pain to itch.Pain. 2006; 126: 16-23Abstract Full Text Full Text PDF PubMed Scopus (154) Google Scholar and TRPV1 knockout mice showed reduced behavioral itch responses to histamine (Imamachi et al., 2009Imamachi N. Park G.H. Lee H. et al.TRPV1-expressing primary afferents generate behavioral responses to pruritogens via multiple mechanisms.Proc Natl Acad Sci USA. 2009; 106: 11330-11335Crossref PubMed Scopus (338) Google Scholar. Thus, central mechanisms may be of greater importance for histamine-induced itch. The involvement of central components was demonstrated recently with the injection of substance P into the dorsal horn of naked mole rats, leading to altered nociceptor connectivity in the spinal cord, thereby determining the presence or absence of itch behaviour (Smith et al., 2010Smith E.S. Blass G.R. Lewin G.R. et al.Absence of histamine-induced itch in the African naked mole-rat and "rescue" by Substance P.Mol Pain. 2010; 6: 29Crossref PubMed Scopus (33) Google Scholar. We found a remarkable sensitization to cowhage itch at the NGF-treated site, and the intensity of cowhage-evoked itch correlated with the level of mechanical hyperalgesia. In humans, cowhage activates virtually all mechanosensitive "polymodal" units (Namer et al., 2008Namer B. Carr R. Johanek L.M. et al.Separate peripheral pathways for pruritus in man.J Neurophysiol. 2008; 100: 2062-2069Crossref PubMed Scopus (207) Google Scholar and also some mechanosensitive Aδ fibers in the monkey (Ringkamp et al., 2011Ringkamp M. Schepers R.J. Shimada S.G. et al.A role for nociceptive, myelinated nerve fibers in itch sensation.J Neurosci. 2011; 31: 14841-14849Crossref PubMed Scopus (115) Google Scholar. Intradermally administered NGF induces a prominent sensitization of nociceptors, (Rukwied et al., 2010Rukwied R. Mayer A. Kluschina O. et al.NGF induces non-inflammatory localized and lasting mechanical and thermal hypersensitivity in human skin.Pain. 2010; 148: 407-413Abstract Full Text Full Text PDF PubMed Scopus (136) Google Scholar and thus elevated NGF levels in AD skin (Tominaga et al., 2009Tominaga M. Tengara S. Kamo A. et al.Psoralen-ultraviolet A therapy alters epidermal Sema3A and NGF levels and modulates epidermal innervation in atopic dermatitis.J Dermatol Sci. 2009; 55: 40-46Abstract Full Text Full Text PDF PubMed Scopus (99) Google Scholar; Yamaguchi et al., 2009Yamaguchi J. Aihara M. Kobayashi Y. et al.Quantitative analysis of nerve growth factor (NGF) in the atopic dermatitis and psoriasis horny layer and effect of treatment on NGF in atopic dermatitis.J Dermatol Sci. 2009; 53: 48-54Abstract Full Text Full Text PDF PubMed Scopus (102) Google Scholar also may sensitize primary afferents thereby contributing to chronic pruritus. Tests of cowhage sensitivity and potential antipruritic effects of anti-NGF strategies in AD patients are crucially required to assess the clinical relevance of neuronal sensitization by NGF for their spontaneous and evoked itch.