2017.06.29

Asthma-like airway inflammation and responses in a rat model of atopic dermatitis induced by neonatal capsaicin treatment.

Han RT1,2, Kim S3, Choi K1,2, Jwa H1,2, Lee J1,2, Kim HY1,2, Kim HJ4, Kim HR5, Back SK6, Na HS1,2.

Abstract

Recent studies have shown that approximately 70% of patients with severe atopic dermatitis (AD) develop asthma. Development of AD in infancy and subsequent other atopic diseases such as asthma in childhood is referred to as atopic march. However, a causal link between the diseases of atopic march has remained largely unaddressed, possibly due to lack of a proper animal model. Recently, we developed an AD rat model showing chronically relapsing dermatitis and scratching behaviors induced by neonatal capsaicin treatment. Here, we investigated whether our model also showed asthmatic changes, with the aim of expanding our AD model into an atopic march model. First, we confirmed that capsaicin treatment (50 mg/kg within 24 h after birth) induced dermatitis and scratching behaviors until 6 weeks of age. After that, the mRNA expression of Th1 and Th2 cytokines, such as IFN-γ and TNF-α, and IL-4, IL-5, and IL-13, respectively, was quantified with quantitative real-time polymerase chain reaction in the skin and the lungs. The number of total cells and eosinophils was counted in bronchoalveolar lavage (BAL) fluid. The levels of IgE in the serum and BAL fluid were determined with enzyme-linked immunosorbent assay. Paraffin-embedded sections (4 μm) were stained with hematoxylin/eosin to analyze the morphology of the lung and the airway. Airway responsiveness was measured in terms of airway resistance and compliance using the flexiVent system. In the capsaicin-treated rats, persistent dermatitis developed, and scratching behaviors increased over several weeks. The levels of IgE in the serum and BAL fluid as well as the mRNA expression of Th2 cytokines, including IL-4, IL-5, and IL-13, in both the skin and the lungs were elevated, and the number of eosinophils in the BAL fluid was also increased in the capsaicin-treated rats compared to control rats. Morphological analysis of the airway revealed smooth muscle hypertrophy and extensive mucus plug in the capsaicin-treated rats. Functional studies demonstrated an increment of the airway resistance and a decrement of lung compliance in the capsaicin-treated rats compared to control rats. Taken together, our findings suggested that neonatal capsaicin treatment induced asthma-like airway inflammation and responses in juvenile rats.

17.06.30

Journal Club 2017. 06. 23.

Involvement of TRPV1 and TDAG8 in Pruriception Associated with Noxious Acidosis

Shing-Hong Lin1, Martin Steinhoff2,3,4, Akihiko Ikoma4, Yen-Ching Chang5, Yuan-Ren Cheng1,6, Ravi Chandra Kopparaju1,7, Satoshi Ishii8, Wei-Hsin Sun5 and Chih-Cheng Chen1,6,7,9

Acid-Sensing Ion Channel and Pruritus

Itch and pain are closely related but are distinct sensations. Intradermal injection of acid generates pain in both rodents and humans; however, few studies have addressed the intriguing question of whether acid (protons) can evoke itch like other algogens by spatial contrast activation of single nociceptors. Here, we report that (i) citric acid (0.2 mol/L) pH-dependently induced a scratching response in mice when applied intradermally to nape or cheek skin, (ii) acidified buffer elevated intracellular calcium levels in dorsal root ganglion pruri- ceptors, and (iii) injection of intradermal citric acid (pH 3.0) into the nape induced a pruritogen-like but not algogen-like c-Fos immunoreactivity pattern in the cervical spinal cord. Using pharmacological and genetic approaches, we identified potential acid-sensing channels/receptors involved in acidic citrate-evoked itch. Results indicate that TRPV1, but neither ASIC3 nor TRPA1, is involved in the acidic citrate-induced scratching response. Furthermore, one of the proton-sensing G-proteinecoupled receptors, TDAG8, was highly (w71%) expressed in Nppbþ dorsal root ganglion pruriceptors. Itch induced by acidic citrate, but not a-methyl-5- hydroxytryptamine, chloroquine, compound 48/80, or bile acid, was markedly decreased in TDAG8e/e mice. In a heterologous expression system, TDAG8 potentiated the acid-induced calcium response by regulating TRPV1. Thus, protons could evoke pruriception by acting on TDAG8 to regulate TRPV1 activation with its mechanism of future therapeutic relevance.

Journal of Investigative Dermatology (2017) 137, 170e178; doi:10.1016/j.jid.2016.07.037

2017.06.09

Methylglyoxal evokes pain by stimulating TRPA1.

Abstract

Diabetic neuropathy is a severe complication of long-standing diabetes and one of the major etiologies of neuropathic pain. Diabetes is associated with an increased formation of reactive oxygen species and the electrophilic dicarbonyl compound methylglyoxal (MG). Here we show that MG stimulates heterologously expressed TRPA1 in CHO cells and natively expressed TRPA1 in MDCK cells and DRG neurons. MG evokes [Ca(2+)]i-responses in TRPA1 expressing DRG neurons but is without effect in neurons cultured from Trpa1(-/-) mice. Consistent with a direct, intracellular action, we show that methylglyoxal is significantly more potent as a TRPA1 agonist when applied to the intracellular face of excised membrane patches than to intact cells. Local intraplantar administration of MG evokes a pain response in Trpa1(+/+) but not in Trpa1(-/-) mice. Furthermore, persistently increased MG levels achieved by two weeks pharmacological inhibition of glyoxalase-1 (GLO-1), the rate-limiting enzyme responsible for detoxification of MG, evokes a progressive and marked thermal (cold and heat) and mechanical hypersensitivity in wildtype but not in Trpa1(-/-) mice. Our results thus demonstrate that TRPA1 is required both for the acute pain response evoked by topical MG and for the long-lasting pronociceptive effects associated with elevated MG in vivo. In contrast to our observations in DRG neurons, MG evokes indistinguishable [Ca(2+)]i-responses in pancreatic β-cells cultured from Trpa1(+/+) and Trpa1(-/-) mice. In vivo, the TRPA1 antagonist HC030031 impairs glucose clearance in the glucose tolerance test both in Trpa1(+/+) and Trpa1(-/-) mice, indicating a non-TRPA1 mediated effect and suggesting that results obtained with this compound should be interpreted with caution. Our results show that TRPA1 is the principal target for MG in sensory neurons but not in pancreatic β-cells and that activation of TRPA1 by MG produces a painful neuropathy with the behavioral hallmarks of diabetic neuropathy.

journal.pone.0077986

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