Pharmacological Characterization of a Novel Mouse Model of Cholestatic Pruritus.

Patients with cholestatic liver diseases, such as primary biliary cirrhosis, usually suffer from pruritus. However, the pathogenesis of cholestatic pruritus is unclear, and there is no current effective treatment for it. In order to find a treatment for the condition, an appropriate mouse model should be developed. Therefore, here, we established a surgically-induced mouse model of cholestatic pruritus. The bile duct was ligated in order to block bile secretion from the anterior, right, and left lobes, with the exception of the caudate lobe. Serum levels of total bile acid increased after bile duct ligation (BDL). The spontaneous hind paw scratching was also increased in BDL mice. Spontaneous scratching was reduced in BDL mice by naloxone (µ-opioid receptor antagonist), U-50,488H (κ-opioid receptor agonist), and clonidine (α2-adrenoceptor agonist). Azelastine (H1 receptor antagonist with membrane-stabilizing activity) slightly reduced scratching. However, terfenadine (H1 receptor antagonist), methysergide (serotonin (5-HT)2 receptor antagonist), ondansetron (5-HT3 receptor antagonist), proteinase-activated receptor 2-neutralizing antibody, fluvoxamine (selective serotonin reuptake inhibitor), milnacipran (serotonin-noradrenalin reuptake inhibitor), and cyproheptadine (H1 and 5-HT2 receptor antagonist) did not affect scratching. These results suggested that partial obstruction of bile secretion in mice induced anti-histamine-resistant itching and that central opioid system is involved in cholestatic itching.

Involvement of Leukotriene B4 Released from Keratinocytes in Itch-associated Response to Intradermal Interleukin-31 in Mice.

A recent study suggests that interleukin-31 (IL-31) exerts its effect via indirect mechanisms rather than through direct stimulation of cutaneous nerves. However, the underlying peripheral mechanisms of IL-31-induced itch in the skin remain unclear. Therefore, the present study investigated the peripheral mechanisms underlying IL-31-induced itch in mice. IL-31-induced itch-related response was inhibited by anti-allergic drugs (tranilast and azelastine), but not by an H1 histamine receptor antagonist (terfenadine). Furthermore, a 5-lipoxygenase inhibitor (zileuton), but not a cyclooxygenase inhibitor (indomethacin), and a leuko-triene B4 (LTB4) receptor antagonist (CMHVA) attenuated the action of IL-31. IL-31 receptor-immunoreactivity was observed in the epidermis and primary sensory neurones. IL-31 receptor mRNA was expressed in mouse keratinocytes and dorsal root ganglia neurones. IL-31 increased the production of LTB4 in mouse keratinocytes. These results suggest that IL-31 elicits itch not only through direct action on primary sensory neurones, but also by inducing LTB4 production in keratinocytes.

Prophylactic Administration of Aucubin Inhibits Paclitaxel-Induced Mechanical Allodynia via the Inhibition of Endoplasmic Reticulum Stress in Peripheral Schwann Cells.

Paclitaxel is a chemotherapeutic agent that causes peripheral neuropathy as its major dose-limiting side effect. However, the peripheral neuropathy is difficult to manage. A study we recently conducted showed that repetitive administration of aucubin as a prophylactic inhibits paclitaxel-induced mechanical allodynia. However, the mechanisms underlying the anti-allodynic activity of aucubin, which is a major component of Plantaginis Semen, was unclear. In addition to mechanical allodynia, aucubin inhibited spontaneous and mechanical stimuli-induced firing in spinal dorsal horn neurons; however, catalpol, a metabolite of aucubin, did not show these effects. Furthermore, paclitaxel induced the expression of CCAAT/enhancer-binding protein homologous protein, a marker of endoplasmic reticulum (ER) stress, in the sciatic nerve and a Schwann cell line (LY-PPB6 cells); however, this effect was inhibited by aucubin. These results suggest that aucubin inhibits paclitaxel-induced mechanical allodynia through the inhibition of ER stress in peripheral Schwann cells.

Involvement of mast cells and proteinase-activated receptor 2 in oxaliplatin-induced mechanical allodynia in mice.

The chemotherapeutic agent oxaliplatin induces neuropathic pain, a dose-limiting side effect, but the underlying mechanisms are not fully understood. Here, we show the potential involvement of cutaneous mast cells in oxaliplatin-induced mechanical allodynia in mice. A single intraperitoneal injection of oxaliplatin induced mechanical allodynia, which peaked on day 10 after injection. Oxaliplatin-induced mechanical allodynia was almost completely prevented by congenital mast cell deficiency. The numbers of total and degranulated mast cells was significantly increased in the skin after oxaliplatin administration. Repetitive topical application of the mast cell stabilizer azelastine hydrochloride inhibited mechanical allodynia and the degranulation of mast cells without affecting the number of mast cells in oxaliplatin-treated mice. The serine protease inhibitor camostat mesilate and the proteinase-activated receptor 2 (PAR2) antagonist FSLLRY-NH2 significantly inhibited oxaliplatin-induced mechanical allodynia. However, it was not inhibited by the H1 histamine receptor antagonist terfenadine. Single oxaliplatin administration increased the activity of cutaneous serine proteases, which was attenuated by camostat and mast cell deficiency. Depletion of the capsaicin-sensitive primary afferents by neonatal capsaicin treatment almost completely prevented oxaliplatin-induced mechanical allodynia, the increase in the number of mast cells, and the activity of cutaneous serine proteases. These results suggest that serine protease(s) released from mast cells and PAR2 are involved in oxaliplatin-induced mechanical allodynia. Therefore, oxaliplatin may indirectly affect the functions of mast cells through its action on capsaicin-sensitive primary afferents.

5-HT1A receptor agonists, xaliproden and tandospirone, inhibit the increase in the number of cutaneous mast cells involved in the exacerbation of mechanical allodynia in oxaliplatin-treated mice.

Oxaliplatin causes peripheral neuropathy as a major dose-limiting side effect, and the control of this neuropathy is difficult. This study was designed to investigate whether prophylactic repetitive administration of 5-HT1A receptor agonists inhibits oxaliplatin-induced mechanical allodynia in mice. Repetitive administration of 5-HT1A receptor agonists (xaliproden and tandospirone) inhibited mechanical allodynia induced by a single intraperitoneal injection of oxaliplatin. These agonists also inhibited oxaliplatin-induced mast cell migration, which is involved in the induction of mechanical allodynia. These results suggest that the prophylactic repetitive administration of 5-HT1A receptor agonists attenuates oxaliplatin-induced mechanical allodynia by inhibiting the cutaneous mast cell migration.

Thromboxane A2 is Involved in Itch-associated Responses in Mice with Atopic Dermatitis-like Skin Lesions.

To investigate the mechanisms underlying itching in atopic dermatitis, we examined whether thromboxane (TX) A2, an arachidonic acid metabolite, is involved in spontaneous scratching, an itch-related response, in NC mice with atopic dermatitis-like skin lesions. The TXA2 receptor (TP) antagonist ONO-3708 inhibited the spontaneous scratching. The mRNA expression of TX synthase (TXSyn) distributed mainly in epidermis and the concentration of TXB2, a metabolite of TXA2, were increased in lesional skin. Scratching caused by the PAR2 agonist SLIGRL-NH2 was suppressed by ONO-3708. SLIGRL-NH2-induced scratching decreased approximately 75% in TP-deficient mice, compared to wild-type mice. In primary cultures of mouse keratinocytes, SLIGRL-NH2 induced the production of TXA2, as evidenced by the increased TXB2, which was inhibited by the TXSyn inhibitor sodium ozagrel and a PAR2-neutralizing antibody. Taken together, these results suggest that epidermal TXA2, which may be produced via PAR2 activation, is involved in itching in atopic dermatitis.

Methods for preclinical assessment of antipruritic agents and itch mechanisms independent of mast-cell histamine.

Itch is a sensation that provokes a desire to scratch. Mast-cell histamine was thought to be a key itch mediator. However, histamine and mast-cell degranulation were reported not to elicit scratching in animals. It was difficult to investigate the pathophysiology of itching and to evaluate the antipruritic efficacy of chemical agents in the early 1990 s. We showed that hind-paw scratching and biting were elicited by stimulation with pruritogenic agents in mice. Those results demonstrated for the first time that cutaneous itching could be evaluated behaviorally in animals. We established various animal models of pathological itch of the skin (dry skin, mosquito allergy, surfactant-induced pruritus, and herpes zoster) and mucus membranes (pollen allergy). Mast-cell histamine did not play a key role in itching in any animal model examined except for the pollen allergy model. Histamine is not an exclusive itch mediator of mast cells; tryptase and leukotriene B4 released from mast cells also act as itch mediators. Epidermal keratinocytes release several itch mediators, such as leukotriene B4, sphingosylphosphorylcholine, thromboxane A2, nociceptin, nitric oxide, and histamine, which may play important roles in pathological itching. Appropriate animal models of pathological itching are needed for pharmacological evaluation of the antipruritic efficacy of chemical agents.

Milnacipran inhibits oxaliplatin-induced mechanical allodynia through spinal action in mice.

We investigated whether milnacipran, a serotonin-noradrenaline reuptake inhibitor, would have therapeutic effect on oxaliplatin-induced mechanical allodynia in mice. A single intraperitoneal injection of oxaliplatin (3 mg/kg) induced mechanical allodynia, which peaked on day 10 after injection and almost completely subsided by day 20. Ten days post-oxaliplatin injection, the intraperitoneal administration of milnacipran (3-30 mg/kg) significantly and dose-dependently inhibited the established mechanical allodynia. Intrathecal injections of milnacipran (2.1-21 µg/site) also significantly and dose-dependently inhibited mechanical allodynia, but intracisternal and intracereboventricular injections at the same doses did not. The present results suggest that milnacipran is effective against oxaliplatin-induced mechanical allodynia and that the antiallodynic effect is mainly mediated by actions on the spinal cord.

Noradrenergic modulation of itch transmission in the spinal cord.

Inhibition of both itching and scratching is important in the treatment of chronic pruritic diseases, because itching has a negative impact on quality of life and vigorous scratching worsens skin conditions. Pharmacological modulation of itch transmission in the dorsal horn is an effective way to inhibit both itching and scratching in pruritic diseases. Pruriceptive transmission in the spinal dorsal horn undergoes inhibitory modulation by the descending noradrenergic system. The noradrenergic inhibition is mediated by excitatory α1-adrenoceptors located on inhibitory interneurons and inhibitory α2-adrenoceptors located on central terminals of primary sensory neurons. The descending noradrenergic system and α-adrenoceptors in the dorsal horn are potential targets for antipruritic drugs.

A mouse model of peripheral postischemic dysesthesia: involvement of reperfusion-induced oxidative stress and TRPA1 channel.

Peripheral postischemic dysesthesia was examined behaviorally in mice and we investigated the underlying molecular mechanism with a focus on oxidative stress. Hind-paw ischemia was induced by tight compression of the ankle with a rubber band, and reperfusion was achieved by cutting the rubber tourniquet. We found that reperfusion after ischemia markedly provoked licking of the reperfused hind paw, which was significantly inhibited by systemic administration of the antioxidant N-acetyl-l-cysteine and the transient receptor potential (TRP) A1 channel blocker HC-030031 [2-(1,3-dimethyl-2,6-dioxo-1,2,3,6-tetrahydro-7H-purin-7-yl)-N-(4-isopropylphenyl)acetamide]. Postischemic licking was also significantly inhibited by an intraplantar injection of another antioxidant, phenyl-N-tert-butylnitrone. The TRPV1 channel blocker BCTC [N-(4-tert-butylphenyl)-4-(3-chloropyridin-2-yl)tetrahydropyrazine-1(2H)-carboxamide] did not inhibit postischemic licking. An intraplantar injection of hydrogen peroxide elicited hind-paw licking, which was inhibited by N-acetyl-l-cysteine, phenyl-N-tert-butylnitrone, and HC-030031. Postischemic licking was not affected by chemical depletion of sensory C-fibers, but it was inhibited by morphine, which has been shown to inhibit the C- and Aδ-fiber-evoked responses of dorsal horn neurons. Interestingly, postischemic licking was not inhibited by gabapentin and pregabalin, which have been shown to inhibit the C-fiber- but not Aδ-fiber-evoked response. The present results suggest that ischemia-reperfusion induces oxidative stress, which activates TRPA1 channels to provoke postischemic licking. It has been suggested that this behavior is mediated by myelinated (probably Aδ-type) afferent fibers. Oxidative stress and TRPA1 channels may be potential targets to treat peripheral ischemia-associated dysesthesia.

Topical E6005, a novel phosphodiesterase 4 inhibitor, attenuates spontaneous itch-related responses in mice with chronic atopy-like dermatitis.

Atopic dermatitis is a chronic inflammatory cutaneous disease with difficult-to-treat pruritus. Although phosphodiesterase (PDE) 4 inhibitors have an anti-inflammatory effect on inflammatory skin diseases, such as atopic dermatitis, their acute antipruritic activities remain unclear. Therefore, in this study, we examined whether E6005, a novel PDE4 inhibitor, has antipruritic activity in dermatitis, using a mouse model of atopic dermatitis (NC/Nga mice). A single topical application of E6005 inhibited spontaneous hind-paw scratching, an itch-associated response and spontaneous activity of the cutaneous nerve in mice with chronic dermatitis. The cutaneous concentration of cAMP was significantly decreased in mice with chronic dermatitis, and this decrease was reversed by topical E6005 application. These results suggest that E6005 increases the cutaneous concentration of cAMP to relieve dermatitis-associated itching. Thus, E6005 may be a useful therapy for pruritic dermatitis such as atopic dermatitis.

Gabapentin inhibits bortezomib-induced mechanical allodynia through supraspinal action in mice.

Bortezomib, an inhibitor of proteasome holoenzyme, is used to treat relapsed and refractory multiple myeloma. Peripheral neuropathy is a treatment-limiting adverse effect of bortezomib and is very difficult to control. In this study, we examined the efficacy of gabapentin in inhibiting bortezomib-induced peripheral neuropathy. Single intravenous injections of bortezomib (0.03 - 0.3 mg/kg) dose-dependently induced mechanical allodynia with a peak effect 12 days after injection. Bortezomib (0.3 mg/kg) also caused mechanical hyperalgesia, but neither affected thermal nociception nor induced cold allodynia. Bortezomib increased the response of the saphenous nerve to weak punctate stimulation but not response to cool stimulation of the skin. When administered 12 days after bortezomib injection, oral and intracisternal gabapentin markedly inhibited mechanical allodynia. Intrathecal, but not intraplantar, gabapentin had a tendency to reduce mechanical allodynia. The antiallodynic activity of orally administered gabapentin was suppressed by noradrenaline, but not serotonin, depletion in the spinal cord. Bortezomib did not affect the expression levels of the calcium channel α2δ-1 subunit, a high-affinity binding site of gabapentin, in the plantar skin, spinal cord, medulla oblongata, and pons. These results suggest that gabapentin inhibits bortezomib-induced mechanical allodynia, most likely through the activation of the descending noradrenergic system.

Surfactant-induced chronic pruritus: Role of L-histidine decarboxylase expression and histamine production in epidermis.

Shampoo and cleansers containing anionic surfactants including sodium dodecyl sulphate (SDS) often cause pruritus in humans. Daily application of 1-10% SDS for 4 days induced hind-paw scratching (an itch-related behaviour) in a concentration-dependent manner, and 10% SDS also caused dermatitis, skin dryness, barrier disruption, and an increase in skin surface pH in mice. SDS-induced scratching was inhibited by the opioid receptor antagonist naloxone and the H histamine receptor antagonist terfenadine. Mast-cell deficiency did not inhibit SDS-induced scratching, although it almost completely depleted histamine in the dermis. Treatment with SDS increased the histamine content of the epidermis, but not that of the dermis. SDS treatment increased the gene expression and post-translation processing of L-histidine decarboxylase in the epidermis. The present results suggest that repeated application of SDS induces itch through increased production of epidermal histamine, which results from an increase in the gene expression and post-translation processing of L-histidine decarboxylase.

Topical surfactant-induced pruritus: involvement of histamine released from epidermal keratinocytes.

Surfactants, an important component of cleansers, often cause itch in humans. Topical application of sodium laurate and N-lauroylsarcosine sodium salt to the skin of mice immediately (for 1-1.5 hours) increased scratching, and the former increased scratching again between 2 and 3 hours after application. Thus, we examined the mechanisms of sodium laurate-induced delayed scratching. Sodium laurate (0.1%-10%) increased delayed scratching and skin surface pH in a concentration-dependent manner. N-lauroylsarcosine sodium salt had no effect on these parameters, and sodium hydroxide solution did not increase delayed scratching. Sodium laurate-induced delayed scratching was markedly inhibited by the H(1) histamine receptor antagonist terfenadine, but it was not affected by mast cell deficiency. Sodium laurate application had no effect on the number of total and degranulated mast cells, and did not induce plasma extravasation or the infiltration of inflammatory cells in the skin. Sodium laurate application increased the histamine content of the epidermis, but not that of the dermis, in normal and mast cell-deficient mice. Sodium laurate application increased the ratio of 53-kDa l-histidine decarboxylase (HDC, a key enzyme for histamine production) to 74-kDa HDC in the mouse epidermis and in a human keratinocyte culture. Sodium laurate increased histamine in the human keratinocyte culture, without affecting cell viability. The present results suggest that sodium laurate induced delayed scratching at an alkaline pH through the increased production of histamine in keratinocytes, which may be due to enhanced processing of 74-kDa to 53-kDa HDC.

Milnacipran inhibits itch-related responses in mice through the enhancement of noradrenergic transmission in the spinal cord.

We investigated whether milnacipran, a serotonin-noradrenaline reuptake inhibitor, exhibits an antipruritic effect through the spinal action in mice. Intrathecal injections of milnacipran (0.1 - 10 µg/site) significantly suppressed serotonin-induced biting, which is an itch-related response. However, such an effect was not observed with fluvoxamine (10 µg/site), which is a selective serotonin reuptake inhibitor. Furthermore, an intraperitoneal injection of milnacipran (10 mg/kg) inhibited serotonin-induced biting. When phentolamine (1.0 µg/site), a non-selective α-adrenoceptor antagonist, was intrathecally injected, it inhibited the above response of milnacipran. These results suggest that milnacipran suppresses itching through the inhibition of noradrenaline reuptake in the spinal cord.

Prevention of topical surfactant-induced itch-related responses by chlorogenic acid through the inhibition of increased histamine production in the epidermis.

Effects of chlorogenic acid on surfactant-induced itching were studied in mice. Topical application of sodium laurate increased hind-paw scratching, an itch-related response, 2 h after application, which was inhibited by topical post-treatment with chlorogenic acid. Sodium laurate increased the histamine content and 53-kDa L-histidine decarboxylase in the epidermis, which were also inhibited by post-treatment with chlorogenic acid. These results suggest that topical chlorogenic acid is effective in the prevention of itching induced by anionic surfactants. The inhibitory activity of chlorogenic acid may be due to the inhibition of an increase in histamine in the epidermis.

Association of denervation severity in the dermis with the development of mechanical allodynia and hyperalgesia in a murine model of postherpetic neuralgia.

BACKGROUND: Postherpetic neuralgia (PHN) is a common complication of herpes zoster and remains a challenging condition of neuropathic pain. Allodynia, a prominent feature of PHN, extends beyond the margins of the initial rash area. In the present study, we investigated the association between cutaneous denervation and the development of postherpetic allodynia and hyperalgesia by using a murine model of PHN. METHODS: Female C57BL/6j mice were used. Herpes simplex virus type-1 (HSV1) was inoculated on the unilateral shin, a region that is predominantly innervated by L3 dorsal root ganglion (DRG) neurons. After the zoster-like skin lesions healed, mice were classified by the presence of mechanical allodynia and hyperalgesia in the plantar aspect of the ipsilateral hindpaw. Scarred lumbar (innervated by L2-4 DRG neurons) and the ipsilateral plantar (innervated by L3-5 DRG neurons) skin sections were immunostained with an antibody against protein gene product (PGP)9.5. The number of PGP9.5-immunoreactive (IR) profiles in the epidermis and dermis were analyzed for quantification of cutaneous innervation. RESULTS: In the epidermis of the scarred lumbar skin, the intraindividual mean number of PGP9.5-IR profiles was significantly decreased in mice inoculated with HSV1. The intraindividual maximum and mean numbers of PGP9.5-IR profiles in the epidermis of the scarred skin were not significantly different between mice with and without postherpetic allodynia and hyperalgesia. In the dermis of the scarred lumbar skin, the intraindividual maximum and mean numbers of PGP9.5-IR profiles were significantly decreased in mice with postherpetic allodynia and hyperalgesia, but not in mice without these symptoms. The intraindividual minimum number of PGP9.5-IR profiles in the dermis and epidermis was significantly decreased by HSV1 inoculation. HSV1 inoculation significantly decreased the intraindividual mean number of PGP9.5-IR profiles in the epidermis, but not dermis, of the plantar skin on the inoculated side. CONCLUSIONS: The present results suggest that the severity of dermal denervation in the scarred skin is associated with the development of postherpetic allodynia and hyperalgesia that extend beyond the margins of the initial rash area. The decrease of epidermal nerve density in the scarred and stimulation skins may not be associated with postherpetic allodynia and hyperalgesia.

Potential new therapeutic targets for pathological pruritus.

Very few approved medications are indicated for the treatment of pruritus, and drug development for pruritic diseases is awaited. During the past two decades, progress has been made in understanding the molecular basis of the physiology and pathophysiology of pruritus. Newly identified potential targets for pathological pruritus include receptors (histamine H4 receptor, leukotriene B4 receptors, interleukin-31 receptor A, bombesin BB2 receptor, toll-like receptor 3, α-adrenoceptor, and opioid µ- and κ-receptors), channels (transient receptor potential (TRP) V3 and TRPA1 channels), and enzymes (histidine decarboxylase, sphingomyelin glucosylceramide deacylase, 5-lipoxygenase, leukotriene A4 hydrolase, and autotaxin). The development of specific, effective blockers and agonists/antagonists of these targets is awaited.

Saliva contact during infancy and allergy development in school-age children.

Background: Parent-child saliva contact during infancy might stimulate the child's immune system for effective allergy prevention. However, few studies have investigated its relation to allergy development in school-age children. Objective: We sought to investigate the relationship between parent-child saliva contact during infancy and allergy development at school age. Methods: We performed a large multicenter cross-sectional study involving Japanese school children and their parents. The self-administered questionnaires including questions from the International Study of Asthma and Allergies in Childhood were distributed to 3570 elementary and junior high school children in 2 local cities. Data were analyzed for the relationship between saliva contact during infancy (age <12 months) and the risk of allergy development, specifically eczema, allergic rhinitis, and asthma. For detailed Methods, please see the Methods section in this article's Online Repository at www.jacionline.org. Results: The valid response rate was 94.7%. The mean and median age of children was 10.8 ± 2.7 and 11 (interquartile range, 9-13) years, respectively. Saliva contact via sharing eating utensils during infancy was significantly associated with a lower risk of eczema (odds ratio, 0.53; 95% CI, 0.34-0.83) at school age. Saliva contact via parental sucking of pacifiers was significantly associated with a lower risk of eczema (odds ratio, 0.24; 95% CI, 0.10-0.60) and allergic rhinitis (odds ratio, 0.33; 95% CI, 0.15-0.73), and had a borderline association with the risk of asthma in school-age children. Conclusions: Saliva contact during infancy may reduce the risk of developing eczema and allergic rhinitis in school-age children.