Pruritus In Mice Research Articles

ATF4 inhibits TRPV4 function and controls itch perception in rodents and nonhuman primates.

Acute and chronic itch are prevalent and incapacitating, yet the neural mechanisms underlying both acute and chronic itch are just starting to be unraveled. Activated transcription factor 4 (ATF4) belongs to the ATF/CREB transcription factor family and primarily participates in the regulation of gene transcription. Our previous study has demonstrated that ATF4 is expressed in sensory neurons. Nevertheless, the role of ATF4 in itch sensation remains poorly understood. Here, we demonstrate that ATF4 plays a significant role in regulating itch sensation. The absence of ATF4 in dorsal root ganglion (DRG) neurons enhances the itch sensitivity of mice. Overexpression of ATF4 in sensory neurons significantly alleviates the acute and chronic pruritus in mice. Furthermore, ATF4 interacts with the transient receptor potential cation channel subfamily V member 4 (TRPV4) and inhibits its function without altering the expression or membrane trafficking of TRPV4 in sensory neurons. In addition, interference with ATF4 increases the itch sensitivity in nonhuman primates and enhances TRPV4 currents in nonhuman primates DRG neurons; ATF4 and TRPV4 also co-expresses in human sensory neurons. Our data demonstrate that ATF4 controls pruritus by regulating TRPV4 signaling through a nontranscriptional mechanism and identifies a potential new strategy for the treatment of pathological pruritus.

Spinal Caspase-6 Contributes to Intrathecal Morphine-induced Acute Itch and Contact Dermatitis-induced Chronic Itch Through Regulating the Phosphorylation of Protein Kinase Mζ in Mice

Patients receiving neuraxial treatment with morphine for pain relief often experience a distressing pruritus. Neuroinflammation-mediated plasticity of sensory synapses in the spinal cord is critical for the development of pain and itch. Caspase-6, as an intracellular cysteine protease, is capable of inducing central nociceptive sensitization through regulating synaptic transmission and plasticity. Given the tight interaction between protein kinase Mζ (PKMζ) and excitatory synaptic plasticity, this pre-clinical study investigates whether caspase-6 contributes to morphine-induced itch and chronic itch via PKMζ. Intrathecal morphine and contact dermatitis were used to cause pruritus in mice. Morphine antinociception, itch-induced scratching behaviors, spinal activity of caspase-6, and phosphorylation of PKMζ and ERK were examined. Caspase-6 inhibitor Z-VEID-FMK, exogenous caspase-6 and PKMζ inhibitor ZIP were utilized to reveal the mechanisms and prevention of itch. Herein, we report that morphine induces significant scratching behaviors, which is accompanied by an increase in spinal caspase-6 cleavage and PKMζ phosphorylation (but not expression). Intrathecal injection of Z-VEID-FMK drastically reduces morphine-induced scratch bouts and spinal phosphorylation of PKMζ, without abolishing morphine analgesia. Moreover, intrathecal strategies of ZIP dose-dependently reduce morphine-induced itch-like behaviors. Spinal phosphorylation of ERK following neuraxial morphine is down-regulated by ZIP therapy. Recombinant caspase-6 directly exhibits scratching behaviors and spinal phosphorylation of ERK, which is compensated by PKMζ inhibition. Also, spinal inhibition of caspase-6 and PKMζ reduces the generation and maintenance of dermatitis-induced chronic itch. Together, these findings demonstrate that spinal caspase-6 modulation of PKMζ phosphorylation is important in the development of morphine-induced itch and dermatitis-induced itch in mice.

Vascular Endothelial Growth Factor a Promotes Chronic Itch via VEGFA-VEGFR2-PI3K-TRPV1 Axis in Allergic Contact Dermatitis.

Allergic contact dermatitis (ACD), a prevalent skin disorder affecting up to 20% of the population, triggers significant discomfort and health implications. Our research investigates the pivotal role of Vascular Endothelial Growth Factor A (VEGFA) in chronic itching associated with ACD. Bioinformatics methods were utilized to identify differentially expressed genes (DEGs) between ACD models and patients. In vivo models of chronic pruritus in mice induced by 2,4-dinitrofluorobenzene (DNFB) were employed. Mice were administered subcutaneously with a VEGFA inhibitor, sFlt1, and compared to a control group. Real-time RT-PCR, Western blot, and immunohistochemical staining were performed to evaluate VEGFA expression and the impact of sFlt1 on itching behavior. The analysis revealed that VEGFA is significantly upregulated in ACD skin, primarily expressed by keratinocytes. Administration of the VEGFA inhibitor sFlt1 in the ACD mouse model led to a substantial reduction in scratching behavior, indicating that VEGFA may mediate pruritus through the VEGFA-VEGFR2-PI3K-TRPV1 signaling pathway. These findings suggest that VEGFA plays a crucial role in ACD-associated pruritus and may serve as a potential therapeutic target. However, further research is required to validate these findings and to explore additional molecular pathways involved in the pruritic response in ACD.

Curcumin inhibits the pruritus in mice through mast cell MrgprB2 receptor.

Curcumin is a diketone compound extracted from the rhizomes of some plants in the Zingiberaceae and Araceae family. It possesses a variety of biological activities, including antioxidant, anti-inflammatory and anti-cancer properties. However, the cellular and molecular antipruritic mechanisms of curcumin remain to be explored. Our objective was to study the role of curcumin in pruritus and determine whether its antipruritic effect is related to MrgprB2 receptor. The effect of curcumin on pruritus in mice was examined by scratching behavior test. The antipruritic mechanism of curcumin was explored by using transgenic mice (MrgprB2-/- mice, MrgprB2CreTd/tomato mice), histological analysis, western blot and immunofluorescence. In addition, the relationship between curcumin and MrgprB2/X2 receptor was studied in vitro by using calcium imaging, plasmid transfection and molecular docking RESULTS: In the current study, we found that curcumin had obvious antipruritic effect. Its antipruritic effect was related to the regulation of MrgprB2 receptor activation and mast cells tryptase release. In vitro, mouse peritoneal mast cells activated by compound 48/80 could be inhibited by curcumin. In addition, curcumin was also found to suppress the calcium flux in MrgprX2 or MrgprB2-overexpression HEK cells induced by compound 48/80, substance P, and PAMP 9-20, displaying the specific relation with the MrgprB2/X2 receptor. Moreover, molecular docking results showed that curcumin had affinity to MrgprX2 protein. Overall, these results indicated that curcumin has the potential to treat pruritus induced by mast cell MrgprB2 receptor.

Jingfang Granules improve glucose metabolism disturbance and inflammation in mice with urticaria by up-regulating LKB1/AMPK/SIRT1 axis

Ethnopharmacological relevanceJingfang Granule (JFG) is a Traditional Chinese Medicine prescription to empirically treat skin disease such as urticaria in clinical practice. However, the potential mechanisms of JFG on urticaria are not fully defined. Aim of studyThe aim of this study is to investigate the mechanisms of JFG in treating urticaria through an OVA/aluminum hydroxide induced urticaria mice model. Materials and methodsKM mice were injected intraperitoneally (i.p.) with OVA/aluminium hydroxide to establish the model with urticaria. After the mice were administered JFG, itching degree and hematoxylin and eosin (H&E) staining were used to assess the protective effect of JFG on mice with urticaria. The regulatory networks were investigated by proteomics and central carbon metabolomics. Spleen T lymphocyte subsets were detected by flow cytometry. Peripheral blood cytokines were detected using ELISA kits or Cytometric Bead Array (CBA) kits. The protein expression of skin tissue was detected by western blot or immunohistochemical staining. ResultsJFG significantly relived skin tissue lesions and skin pruritus in mice with urticaria. Meanwhile, JFG significantly decreased IgE, IL-1β, IL-6, IL-4, TNF-α and IL-17A levels and increased IFN-γ levels in the serum of urticaria mice by inhibiting the expression of inflammation associated proteins including TLR4 and p-NF-κB p65, p-ERK1/2, p-JNK and p-p38, NLRP3, ASC and cleaved caspase-1. The results of proteomics, central carbon metabolomics, western blot and immunohistochemical staining confirmed that JFG inhibited Glycolysis/Gluconeogenesis and Pentose phosphate pathway in the skin tissue of urticaria mice by activating the LKB1/AMPK/SIRT1 axis and then downregulating the protein expressions of Glut1, TORC2, p-CREB, PEPCK, HNF4α and G6Pase. ConclusionThe current study demonstrates that JFG is effective in treating OVA/aluminum hydroxide-induced skin lesions and inflammation in mice, and JFG exhibits the clinical benefits via modulating LKB1/AMPK/SIRT1 axis, which in turn inhibits Glycolysis/Gluconeogenesis and Pentose phosphate pathway.

Cellular, circuit and transcriptional framework for modulation of itch in the central amygdala.

Itch is an unpleasant sensation that elicits robust scratching and aversive experience. However, the identity of the cells and neural circuits that organize this information remains elusive. Here, we show the necessity and sufficiency of chloroquine-activated neurons in the central amygdala (CeA) for both itch sensation and associated aversion. Further, we show that chloroquine-activated CeA neurons play important roles in itch-related comorbidities, including anxiety-like behaviors, but not in some aversive and appetitive behaviors previously ascribed to CeA neurons. RNA-sequencing of chloroquine-activated CeA neurons identified several differentially expressed genes as well as potential key signaling pathways in regulating pruritis. Finally, viral tracing experiments demonstrate that these neurons send projections to the ventral periaqueductal gray that are critical in modulation of itch. These findings reveal a cellular and circuit signature of CeA neurons orchestrating behavioral and affective responses to pruritus in mice.

Reduced spontaneous itch in mouse models of cholestasis

Pruritus is one of the most distressing symptoms in cholestatic patients. Plasma autotaxin (ATX) activity correlates with the severity of pruritus in cholestatic patients, but the pathophysiology is unclear. To study pruritus in mice, we measured scratch activity in cholestatic Atp8b1 mutant mice, a model for Progressive Familial Intrahepatic Cholestasis type 1, and wild type mice (WT) with alpha-naphthylisothiocyanate (ANIT)-induced cholestasis. To induce cholestasis, Atp8b1 mutant mice received a diet containing 0.1% cholic acid (CA) and WT mice were treated with ANIT. In these mice ATX was also overexpressed by transduction with AAV-ATX. Scratch activity was measured using an unbiased, electronic assay. Marked cholestasis was accomplished in both Atp8b1 mutant mice on a CA-supplemented diet and in ANIT-treatment in WT mice, but scratch activity was decreased rather than increased while plasma ATX activity was increased. Plasma ATX activity was further increased up to fivefold with AAV-ATX, but this did not induce scratch activity. In contrast to several reports two cholestatic mouse models did not display increased scratch activity as a measure of itch perception. Increasing plasma ATX activity by overexpression also did not lead to increased scratch activity in mice. This questions whether mice are suitable to study cholestatic itch.

Activation of Transient Receptor Potential Vanilloid-3 Channels in Keratinocytes Induces Pruritus in Humans.

Carvacrol, a natural transient receptor potential vanilloid-3 activator, has been reported to cause pruritus in mice. This study aimed to evaluate the effects of carvacrol and various antipruritic agents in humans. A stimulation test with carvacrol, β-alanine, and histamine was performed. After application of the pruritic solutions, the skin was stimulated with pinpricks. In inhibition test A, Forsythia suspensa extract, containing forsythoside B (a transient receptor potential vanilloid-3 inhibitor), was applied by pricking prior to stimulation with pruritogens. In inhibition test B, olopatadine solution, tacrolimus ointment, and Scutellaria baicalensis root extract were applied, and carvacrol was applied to the same region. Carvacrol induces moderate pruritus in humans. The pruritus was relieved by Forsythia suspensa extract and olopatadine solution after 20 min of application and by tacrolimus ointment and Scutellaria baicalenis extract after 24 h of application. These results suggest that carvacrol is a pruritogen in humans, and that carvacrol-induced pruritus is inhibited by various antipruritic agents.

Inhibitory Effects and Potential Mechanism of Yokukansankachimpihange on SDS-induced Itch-associated Responses in Mice

Yokukansankachimpihange (YKSCH) is a Chinese formula proven in Japan to be an effective treatment for pruritus in patients with atopic dermatitis or chronic urticaria and dry eczema with psychoneurotic symptoms, such as insomnia. Sodium dodecyl sulfate (SDS) may cause skin irritation in both humans and animals. Adverse effects, such as skin dryness, barrier destruction, dermatitis, and pruritus, developed following the repeated application of 10% SDS to a local site. Therefore, the present study investigated the antipruritic effects of YKSCH on skin irritation induced by a repeated SDS stimulation in mice and attempted to elucidate the underlying mechanism of action. ICR mice were stimulated with 10% SDS and co-treated with oral YKSCH extract for four days. Only oral YKSCH extract was administered on the fifth day. Scratching behavior was observed 24 h after the last application of SDS. Intraepidermal nerve growth was investigated by an immunofluorescence analysis. NGF concentrations in the epidermis were measured using an enzyme-linked immunosorbent assay. The expression of amphiregulin (Areg) and semaphorin 3A (Sema3A) was assessed by quantitative real-time PCR. The oral administration of YKSCH (200-400 mg/kg) dose-dependently suppressed pruritus, significantly reduced intraepidermal nerve growth, and down-regulated epidermal Areg mRNA expression in SDS-treated mice. These results suggest that YKSCH exerts antipruritic effects against SDS-induced pruritus in mice. The mechanism of action of YKSCH may involve reductions in intraepidermal nerve density due to the down-regulated expression of Areg.

Perampanel attenuates scratching behavior induced by acute or chronic pruritus in mice

An itch is defined as an unpleasant sensation that evokes a desire to scratch. Glutamate is a major excitatory neurotransmitter in the mammalian central nervous system and has a crucial role in pruriceptive processing in the spinal dorsal horn. It is well known that glutamate exerts its effects by binding to various glutamate receptors including α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors, and that AMPA/kainate receptors play a crucial role in pruriceptive processing; however, the precise role of AMPA receptors remains uncertain. Perampanel, an antiepileptic drug, is an antagonist of AMPA receptors. Pretreatment with perampanel dose-dependently attenuated the induction of scratching, a behavior typically associated with pruritus, by intradermal administration of the pruritogen chloroquine. In addition, the induction of scratching in mice painted with diphenylcyclopropenone and NC/Nga mice treated with Biostir AD, animal models of contact dermatitis and atopic dermatitis, respectively, was dose-dependently alleviated by administration of perampanel. These findings indicate that AMPA receptors play a crucial role in pruriceptive processing in mice with acute or chronic pruritus.

Topical Treatment of Pruritic Skin Disease and the Role of Community Pharmacists

Itching, or pruritus, can be defined as an unpleasant sensation that evokes the desire to scratch. Pruritus is most commonly associated with a primary skin disorder such as atopic dermatitis (AD), psoriasis, etc., and can have a major impact on the quality of life of those patients. Itch-induced scratching can further damage the skin barrier, leading to a worsening of symptoms. For that reason, it is important to manage pruritus. Topical glucocorticoids are commonly the first-line therapy in the management of AD and psoriasis patients. We found that topical glucocorticoids induce pruritus in mice under certain conditions. Topical glucocorticoids may induce pruritus in a mouse model of allergic contact dermatitis via inhibition of prostaglandin (PG)D2 production in antigen-mediated activated mast cells in the skin. Additionally, topical glucocorticoids do not induce pruritus in healthy skin. These results indicate the importance of controlling skin inflammation to a healthy level by applying sufficient quantities of glucocorticoids to avoid glucocorticoid-induced pruritus. However, topical "steroid phobia" is common in Japan, and most patients apply inadequate amounts of topical glucocorticoids for this reason. This may cause glucocorticoid-induced pruritus in patients by prolonging the skin inflammation. We conducted a survey regarding community pharmacists' instructions on the application quantity of topical glucocorticoids and found that most community pharmacists have experienced inappropriate instructions concerning this point.

Effects of Silk Fibroin Moisturizing Cream on Acetone/Ether-Induced Dry Skin Pruritus in Mice

Objectives: The morbidity of dry and itchy skin was high during a person’s lifetime and it had a significant negative impact. This study aimed to investigate the positive effect of silk fibroin moisturizing cream on dry skin pruritus induced by acetone/ether-water (AEW) method in mice. Method: We established a dry skin model in mice with AEW treatment, and the control group was treated with ultrapure water. The mice in AEW model group were locally administrated with silk fibroin moisturizing cream (SilkArmor)®. The transepidermal water loss (TEWL), scratching behavior, condition of skin erythema, skin histology (by hematoxylin-eosin staining) and the results of electron microscopy were measured to evaluate the positive effect of SilkArmor on dry and itchy skin in mice. Results: The TEWL value, spontaneous scratching behavior and erythema score were significantly increased after AEW modeling compared with the control group. There was no significant difference in the TEWL value, scratching behavior and erythema score between the SilkArmor group and the control group (P > 0.05). Compared with the AEW group, the value of TEWL, scratching behavior and the erythema score of mice in the AEW + SilkArmor group were improved, with statistically significant differences (P < 0.05). Skin histopathology and electron microscopy also showed that SilkArmor had certain improvement and repairment on AEW-induced skin pathological changes. Conclusions: A dry skin model was successfully established in this experiment, showing that SilkArmor brought an obvious alleviation to AEW-induced dry and itchy skin in mice.

Differential effects of functionally different histamine H4 receptor ligands on acute irritant dermatitis in mice.

The anti-inflammatory effects of histamine H4 receptor (H4R) antagonists opened new therapeutic options for the treatment of inflammatory/allergic diseases, but the role of H4R in inflammation is far from being solved. Aim of the present study was to investigate the role of structurally related H4R ligands of the aminopyrimidine class with different efficacies and functionalities (neutral antagonist ST-994, partial agonist ST-1006, inverse agonist ST-1012, and partial inverse agonist ST-1124) on croton oil-induced ear edema and pruritus in mice. The H4R ligands were administered subcutaneously before topical application of croton oil. While ST-1006 and ST-1124 were ineffective at any dose tested (10-100 mg/kg), both ST-994 and ST-1012 (30 and 100 mg/kg) significantly reduced croton oil-induced ear edema. Moreover, ST-994, ST-1006, and ST-1124, but not ST-1012, significantly inhibited croton oil-induced ear pruritus at 30 mg/kg. In accordance with results obtained with the reference H4R antagonist JNJ7777120 (100 mg/kg), histological examination of inflamed ear tissue indicated that treatment with ST-994 (30 mg/kg) led to a significant reduction in the inflammatory severity score and in the number of eosinophils infiltrating the tissue, while the number of degranulated mast cells in inflamed tissues was increased in comparison with the number of intact mast cells. These data indicate that croton oil-induced ear inflammation and pruritus seem to be clearly, but variably, affected by the H4R ligands tested. The potential advantage of dual effect of the H4R neutral antagonist ST-994 has to be carefully considered as a new therapeutic approach to the treatment of inflammatory diseases.

Peripheral serotonin receptor 2B and transient receptor potential channel 4 mediate pruritus to serotonergic antidepressants in mice

Peripheral serotonin receptor 2B and transient receptor potential channel 4 mediate pruritus to serotonergic antidepressants in mice

The discovery of benzoxazine sulfonamide inhibitors of NaV1.7: Tools that bridge efficacy and target engagement

The voltage-gated sodium channel NaV1.7 has received much attention from the scientific community due to compelling human genetic data linking gain- and loss-of-function mutations to pain phenotypes. Despite this genetic validation of NaV1.7 as a target for pain, high quality pharmacological tools facilitate further understanding of target biology, establishment of target coverage requirements and subsequent progression into the clinic. Within the sulfonamide class of inhibitors, reduced potency on rat NaV1.7 versus human NaV1.7 was observed, rendering in vivo rat pharmacology studies challenging. Herein, we report the discovery and optimization of novel benzoxazine sulfonamide inhibitors of human, rat and mouse NaV1.7 which enabled pharmacological assessment in traditional behavioral rodent models of pain and in turn, established a connection between formalin-induced pain and histamine-induced pruritus in mice. The latter represents a simple and efficient means of measuring target engagement.

Synthesis and biological evaluation of novel orally available 1-phenyl-6-aminouracils containing dimethyldihydrobenzofuranol structure for the treatment of allergic skin diseases.

We have designed and efficiently synthesized novel 1-phenyl-6-aminouracils by replacing the chroman moiety in CX-659S, a nonsteroidal dermatologic candidate, with dimethyldihydrobenzofuranol to cancel CX-659S asymmetric center. Medicinal chemistry effort culminated in the discovery of 13d bearing a 3-methyl group at the 1-phenyl group as a promising compound. Compound 13d, having good in vitro ADME profile and moderate oral bioavailability in mice, showed potent anti-inflammatory activity against hapten-induced contact hypersensitivity reaction in mice following topical and oral administration. The effects of 13d were equipotent to that of tacrolimus or prednisolone. In addition, compound 13d, having potent hydroxyl radical-scavenging activity, showed more potent suppressive effect on substance P-induced pruritus in mice than oxatomide.

Microglia are Involved in Pruritus Induced by DNFB via the CX3CR1/p38 MAPK Pathway

Background/Aims: Pruritus, also known as itch, is a common, unpleasant sensation that can be difficult to treat. Frequently, chronic itch is associated with the development of neuropathic pain resulting from nerve injury or insult. Previous studies have shown the involvement of spinal microglia in the development of neuropathic pain, but their role in chronic pruritus is unclear. Methods: For this study, we constructed a model of chronic pruritus in mice using repeated applications of 2, 4-dinitrofluorobenzene (DNFB) and showed prolonged scratching behavior in treated mice that continued for at least 7 d after the final DNFB treatment. Results: Scratching was accompanied by activation of spinal microglia and both were reduced by an inhibitor of microglial activity. We also showed that microglial activation entailed increased signaling in the p38 MAPK pathway, and treatment with a p38 inhibitor reduced scratching in DNFB-treated mice. We also examined the role of fractalkine/CX3CR1 signaling in the development of DNFB-induced pruritus and showed that intrathecal administration of antiserum against either CX3CR1or FKN inhibited p38 activity and decreased scratching. Conclusion: Our results suggest that microglia are involved in pruritus induced by DNFB via FKN/CX3CR1/p38MAPK pathways similar to those participating in the development of neuropathic pain.

Ribes fasciculatum var. chinense Attenuated Allergic Inflammation In Vivo and In Vitro.

Ribes fasciculatum var. chinense MAX. (R. fasciculatum) has traditionally been used in Korea to treat inflammatory diseases. However, the exact mechanism that accounts for the anti-inflammatory effect of R. fasciculatum is not completely understood. We aimed to ascertain the pharmacological effects of R. fasciculatum on both compound 48/80- or histamine-induced scratching behaviors and 2, 4-dinitrochlorobenzene (DNCB)-induced atopic dermatitis (AD) in mice. Additionally, to find a possible explanation for the anti-inflammatory effects of R. fasciculatum, we evaluated the effects of R. fasciculatum on the production of inflammatory mediators in LPS-stimulated macrophage cells. Treatment of R. fasciculatum significantly reduced compound 48/80- or histamine-induced the pruritus in mice. R. fasciculatum attenuated the AD symptoms such as eczematous, erythema and dryness and serum IgE levels in AD model. Additionally, R. fasciculatum inhibited the production of tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6). The maximal rates of TNF-α and IL-6 inhibition by R. fasciculatum (1 mg/ml) were approximately 32.12% and 46.24%, respectively. We also showed that R. fasciculatum inhibited the activation of nuclear factor-kappa B in LPS-stimulated macrophages. Collectively, the findings of this study provide us with novel insights into the pharmacological actions of R. fasciculatum as a potential molecule for use in the treatment of allergic inflammatory diseases.

The Bile Acid Receptor TGR5 Activates the TRPA1 Channel to Induce Itch in Mice

Patients with cholestatic disease have increased systemic concentrations of bile acids (BAs) and profound pruritus. The G-protein-coupled BA receptor 1 TGR5 (encoded by GPBAR1) is expressed by primary sensory neurons; its activation induces neuronal hyperexcitability and scratching by unknown mechanisms. We investigated whether the transient receptor potential ankyrin 1 (TRPA1) is involved in BA-evoked, TGR5-dependent pruritus in mice. Co-expression of TGR5 and TRPA1 in cutaneous afferent neurons isolated from mice was analyzed by immunofluorescence, in situ hybridization, and single-cell polymerase chain reaction. TGR5-induced activation of TRPA1 was studied in in HEK293 cells, Xenopus laevis oocytes, and primary sensory neurons by measuring Ca(2+) signals. The contribution of TRPA1 to TGR5-induced release of pruritogenic neuropeptides, activation of spinal neurons, and scratching behavior were studied using TRPA1 antagonists or Trpa1(-/-) mice. TGR5 and TRPA1 protein and messenger RNA were expressed by cutaneous afferent neurons. In HEK cells, oocytes, and neurons co-expressing TGR5 and TRPA1, BAs caused TGR5-dependent activation and sensitization of TRPA1 by mechanisms that required Gβγ, protein kinase C, and Ca(2+). Antagonists or deletion of TRPA1 prevented BA-stimulated release of the pruritogenic neuropeptides gastrin-releasing peptide and atrial natriuretic peptide B in the spinal cord. Disruption of Trpa1 in mice blocked BA-induced expression of Fos in spinal neurons and prevented BA-stimulated scratching. Spontaneous scratching was exacerbated in transgenic mice that overexpressed TRG5. Administration of a TRPA1 antagonist or the BA sequestrant colestipol, which lowered circulating levels of BAs, prevented exacerbated spontaneous scratching in TGR5 overexpressing mice. BAs induce pruritus in mice by co-activation of TGR5 and TRPA1. Antagonists of TGR5 and TRPA1, or inhibitors of the signaling mechanism by which TGR5 activates TRPA1, might be developed for treatment of cholestatic pruritus.

Effect of conjugated linoleic acid on compound 48/80-induced pruritus in mice

Pruritus is one of the most important symptoms of allergic inflammatory skin disease. Conjugated linoleic acid (CLA) has been reported to have preventive effects against allergic inflammation. The objective of this study was to determine whether or not oral administration of CLA suppresses pruritus induced by compound 48/80 (composed of N-methyl-p-methoxy phenethylamine with formaldehyde) in mice, and if so, whether or not this effect is associated with serum histamine and prostaglandin (PG) E2 levels. Liquid CLA mixture (36.25% 9c-11t CLA, 36.95% 10t-12c CLA, 1.12% 9c-11c, and 1.94% t9-t11 CLA) was emulsified in 0.5% carboxymethyl cellulose (CMC) sodium salt and orally administered to mice at doses of 200 mg/kg once per day for 3 days. Similarly, disodium chromoglycate (DSCG), an antipruritic substance, was administered orally at the same concentrations as the negative control. Compound 48/80, a pruritus-inducing reagent, was subcutaneously injected 30 minutes after final administration of CLA. Scratching behavior of mice was counted just after compound 48/80 injection. Serum histamine and PGE2 concentrations were evaluated individually. Mice administered with CLA showed reduced frequency of scratching behavior compared to those without CLA. Antipruritic activities in CLA-treated and DSCG-treated groups were 48.5% and 26.8%, respectively. CLA and DSCG also diminished serum concentrations of histamine and PGE2 compared to compound 48/80 alone, respectively. This result suggests that dietary CLA has an antipruritic effect by down-regulating serum histamine and PGE2 levels for relief of compound 48/80-induced scratching behavior in mice, which will be useful in allergic pruritus as a preventive medicine.