Acid-sensing ion channel 3 is required for agmatine-induced histamine-independent itch in mice.

Introduction: Itch is a common symptom of many skin and systemic diseases. Identifying novel endogenous itch mediators and the downstream signaling pathways involved will contribute to the development of new strategies for the treatment of chronic itch. In the present study, we adopted behavioral testing, patch clamp recording and metabonomics analysis to investigate the role of agmatine in itch and the underlying mechanism. Methods: Behavioral analysis was used to evaluate the establishing of acute and chronic itch mice model, and to test the effects of different drugs or agents on mice itch behavior. Western blotting analysis was used to test the effect of agmatine on phosphorylation of ERK (p-ERK) expression in the spinal cord. Patch clamp recording was used to determine the effect agmatine on the excitability of DRG neurons and the role of ASIC3. Finally, the metabonomics analysis was performed to detect the concentration of agmatine in the affected skin under atopic dermatitis or psoriasis conditions. Results: We fused a mouse model and found that an intradermal injection of agmatine (an endogenous polyamine) into the nape of the neck or cheek induced histamine-independent scratching behavior in a dose-dependent manner. In addition, the ablation of nociceptive C-fibers by resiniferatoxin (RTX) abolished agmatine-induced scratching behavior. However, agmatine-induced itch was not affected by the pharmacological inhibition of either transient receptor potential vanilloid 1 (TRPV1) or transient receptor potential ankyrin 1 (TRPA1); similar results were obtained from TRPV1-/- or TRPA1-/- mice. Furthermore, agmatine-induced itch was significantly suppressed by the administration of acid-sensing ion channel 3 (ASIC3) inhibitors, APETx2 or amiloride. Agmatine also induced the upregulation of p-ERK in the spinal cord; this effect was inhibited by amiloride. Current clamp recording showed that the acute perfusion of agmatine reduced the rheobase and increased the number of evoked action potentials in acute dissociated dorsal root ganglion (DRG) neurons while amiloride reversed agmatine-induced neuronal hyperexcitability. Finally, we identified significantly higher levels of agmatine in the affected skin of a mouse model of atopic dermatitis (AD) when compared to controls, and the scratching behavior of AD mice was significantly attenuated by blocking ASIC3. Discussion: Collectively, these results provide evidence that agmatine is a novel mediator of itch and induces itch via the activation of ASIC3. Targeting neuronal ASIC3 signaling may represent a novel strategy for the treatment of itch.

Melatonin attenuates acute and chronic itch in mice: the antioxidant and anti-inflammatory effects of melatonin receptors.

Background: Itch is a common symptom of skin diseases and significantly reduces patients' quality of life. Melatonin has anti-inflammatory and antioxidant effects. Our study examined the potential anti-itch effects of melatonin (N-acetyl-5-methoxytryptamine) in mice. Methods: We detected the effects of melatonin and its receptors on acute and chronic itch by conducting itching behavioral experiments in male C57 mice. Reactive oxygen species (ROS) levels and calcium ion (Ca2+) mobilization during acute itching production were explored using flow cytometry and calcium imaging techniques. Melatonin expression in the serum of the chronic itch model mice was determined by enzyme-linked immunoassays. Hematoxylin and eosin staining show the effects of melatonin on skin thickness in a chronic itch model. Cytokine and chemokine levels were determined by quantitative polymerase chain reaction. Results: We discovered that compound 48/80 (C48/80)- and chloroquine (CQ)-induced scratching were significantly decreased by intraperitoneal (i.p), intradermal, and intrathecal administration of melatonin in a dose-dependent manner in mice, and the co-administration of melatonin receptor antagonists abolished the anti-itch effects of i.d melatonin. The incubation of melatonin significantly decreased the intracellular ROS levels induced by C48/80 and CQ in cultured ND7/23 cells from a mouse x rat hybridoma nerve as neuron. Melatonin inhibited intracellular Ca2+ increases induced by CQ (but not C48/80) in cultured dorsal root ganglia (DRG) neurons. Melatonin (50 mg/kg i.p) attenuated imiquimod (IMQ)- or acetone and diethyl ether followed by acetone-ether-water (AEW)-induced chronic itch and epidermal hyperplasia in mice. Finally, melatonin treatment reduced the IMQ-induced expression of ST2 and interleukin-33 (IL-33) or the AEW-induced expression of interleukin 31 (IL-31) and interleukin 31 receptor A (IL-31 RA) in the mice. Conclusions: Collectively, our results indicate that melatonin attenuates acute and chronic itch, possibly via melatonin receptors, and its antioxidant, and anti-inflammatory effects in mice.

The Role of Transient Receptor Potential A1 and G Protein-Coupled Receptor 39 in Zinc-Mediated Acute and Chronic Itch in Mice.

Itching is a common symptom of many skin or systemic diseases and has a negative impact on the quality of life. Zinc, one of the most important trace elements in an organism, plays an important role in the regulation of pain. Whether and how zinc regulates itching is largely unclear. Herein, we explored the role of Zn2+ in the regulation of acute and chronic itch in mice. It is found that intradermal injection (i.d.) of Zn2+ dose-dependently induced acute itch and transient receptor potential A1 (TRPA1) participated in Zn2+-induced acute itch in mice. Moreover, the pharmacological analysis showed the involvement of histamine, mast cells, opioid receptors, and capsaicin-sensitive C-fibers in Zn2+-induced acute itch in mice. Systemic administration of Zn2+ chelators, such as N,N,N',N'-Tetrakis(2-pyridylmethyl)ethylenediamine (TPEN), pyrithione, and clioquinol were able to attenuate both acute itch and dry skin-induced chronic itch in mice. Quantitative polymerase chain reaction (Q-PCR) analysis showed that the messenger RNA (mRNA) expression levels of zinc transporters (ZIPs and ZnTs) significantly changed in the dorsal root ganglia (DRG) under dry skin-induced chronic itch condition in mice. Activation of extracellular signal-regulated kinase (ERK) pathway was induced in the DRG and skin by the administration of zinc or under dry skin condition, which was inhibited by systemic administration of Zn2+ chelators. Finally, we found that the expression of GPR39 (a zinc-sensing GPCR) was significantly upregulated in the dry skin mice model and involved in the pathogenesis of chronic itch. Together, these results indicated that the TRPA1/GPR39/ERK axis mediated the zinc-induced itch and, thus, targeting zinc signaling may be a promising strategy for anti-itch therapy.