Understanding the switch from pain-to-itch in dermatitis

Novel C15 Triene Triazole, D-A Derivatives Anti-HepG2, and as HDAC2 Inhibitors: A Synergy Study

A series of novel C15 urushiol derivatives were designed by introducing a pechmann structure and F-, Cl-, and Br-nitro substituents with different electronic properties into its alkyl side chain, as well as a triazolyl functional group in its aromatic oxide. Their chemical structures were determined based on the analysis of the NMR (nuclear magnetic resonance) spectroscopic and mass spectrometric data. The results showed that compound 4 exhibited a strong inhibition of the HepG2 cell proliferation (half maximal inhibitory concentration (IC50): 2.833 μM to human hepatocellular carcinoma (HepG2), and 80.905 μM to human normal hepatocytes (LO2)). Furthermore, it had an excellent synergistic effect with levopimaric acid. The nitrogen atom of the triazole ring formed a hydrogen-bonding interaction with Gly103, Gly154, and Tyr308, which made compound 4 bind to histone deacetylase (HDAC)2 more tightly. One triazole ring and His33 formed a π–π stacking effect; the other, whose branches were deep into the pocket, further enhanced the interaction with HDAC2. Meanwhile, compound 4 involved a hydrophobic interaction with the residues Phe210 and Leu276. The hydrophobic interaction and π–π stacking provided powerful van der Waals forces for the compounds.

Identification of an epidermal keratinocyte AMPA glutamate receptor involved in dermatopathies associated with sensory abnormalities

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This study presents the discovery of AMPA glutamate receptors in mouse and human epidermal keratinocytes and their potential role in the physiopathology of itch or pain.

Introduction: Epidermal keratinocytes are increasingly recognized as active participants in the sensory transduction of itch and pain, processes known to involve primary afferent glutamatergic neurons. However, the role of keratinocyte glutamate signaling in sensory functioning is not fully understood. Here, we present the observation of α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid–type glutamate receptors (AMPARs) in epidermal keratinocytes.

Methods: Immunohistochemical and in situ hybridization analyses were conducted to assess the expression of AMPAR subunits in epidermal keratinocytes in mouse and human skin samples, and in organotypic cultures of human keratinocytes. In addition, reverse transcription PCR further confirmed the expression of GluA4-containing AMPAR in epidermal keratinocytes.

Results: We found prominent immunolabeling for the GluA4 subunit of AMPAR in keratinocytes of glabrous and hairy skin of mouse epidermis, as well as in human epidermal keratinocytes. Reverse transcription PCR confirmed Gria4 transcript expression in epidermal mouse keratinocytes. In addition, expression of GRIA4 mRNA was confirmed in epidermal human keratinocytes by in situ hybridization. Immunohistochemical studies conducted in human skin biopsies from patients with atopic dermatitis and postherpetic neuralgia demonstrate that keratinocyte expression of GluA4 can be altered under pathological conditions. Moreover, a decrease of GluA4 expression was observed in organotypic cultures of human keratinocytes after direct application of algogenic agents.

Conclusion: We provide evidence that GluA4-containing AMPARs are expressed in epidermal keratinocytes, that human pruritic and painful dermatopathologies have alterations in the keratinocyte expression levels of GluA4-containing AMPAR, and that itch- and pain-producing substances can directly regulate their production in keratinocytes.