CXCL14 downregulation in human keratinocytes is a potential biomarker for a novel in vitro skin sensitization test.

To elucidate the roles of epidermal keratinocytes in the toxicological outcomes of chemically induced contact dermatitis, genome-scale transcriptional analyses were performed using normal human keratinocytes (NHKCs) treated with 10 µM sodium lauryl sulfate (SLS) or 5 µM urushiol. In Gene Ontology (GO) enrichment analyses, SLS- and urushiol-induced upregulated DEGs are commonly associated with the regulation of pro-inflammatory responses and epidermal differentiation processes in NHKCs whereas cellular protein metabolic process was also identified as a commonly downregulated DEG signature. Among the downregulated DEGs, CXCL14 was investigated as a potential biomarker for a new in vitro skin sensitization test using OECD TG429 reference chemicals. CXCL14 was significantly downregulated in NHKCs in response to 62.5% of the OECD TG429 sensitizers in a concentration-dependent manner. When the sensitizer-induced upregulation of chemokine CXCL8 was included in the analysis, 87.5% of the OECD TG429 reference sensitizing chemicals significantly induced either CXCL8 upregulation or CXCL14 downregulation in NHKCs. Only one OECD TG429 reference non-sensitizer changed the constitutive CXCL14 expression in NHKCs whereas five out of six non-sensitizers altered CXCL8 production. The reference irritating non-sensitizer SLS caused a false-positive outcome. The downregulation of constitutively expressed CXCL14 was regulated by both the MAPK/ERK and JAK3/STAT6 pathways in NHKCs. CXCL14 can be used as a mechanism-based biomarker in the development of in vitro skin sensitization tests and may help improve the distinction between allergenic sensitizers and non-sensitizers.

Selenium bioisosteric replacement of adenosine derivatives promoting adiponectin secretion increases the binding affinity to peroxisome proliferator-activated receptor δ.

N6-(3-Iodobenzyl)adenosine-5'-N-methyluronamide (1a, IB-MECA) exhibited polypharmacological characteristics targeting A3 adenosine receptor (AR), peroxisome proliferator-activated receptor (PPAR) γ, and PPARδ, simultaneously. The bioisosteric replacement of oxygen in 4'-oxoadenosines with selenium significantly increased the PPARδ-binding activity. 2-Chloro-N6-(3-iodobenzyl)-4'-selenoadenosine-5'-N-methyluronamide (3e) and related 4'-selenoadenosine derivatives significantly enhanced adiponectin biosynthesis during adipogenesis in human bone marrow mesenchymal stem cells (hBM-MSCs). The PPARδ-binding affinity, but not the A3 AR binding affinity, of 4'-selenoadenosine derivatives correlated with their adiponectin secretion stimulation. Compared with the sugar ring of 4'-oxoadenosine, that of 4'-selenoadenosine was more favorable in forming the South sugar conformation. In the molecular docking simulation, the South sugar conformation of compound 3e formed additional hydrogen bonds inside the PPARδ ligand-binding pocket compared with the North conformation. Therefore, the sugar conformation of 4'-selenoadenosine PPAR modulators affects the ligand binding affinity against PPARδ.

Keratinocyte-derived IL-36γ plays a role in hydroquinone-induced chemical leukoderma through inhibition of melanogenesis in human epidermal melanocytes.

Chemical leukoderma is an acquired type of vitiligo that can be initiated by various exogenous chemicals such as hydroquinone (HQ), rhododendrol (RD), or 4-tertiary butyl phenol (4-TBP). Despite the importance of epidermal keratinocytes in diverse dermatological conditions, their toxicological role in chemical leukoderma is poorly understood. To elucidate their role in the pathogenesis of chemical leukoderma, genome-scale transcriptional analysis was performed in human epidermal keratinocytes (HEKs) treated with a sub-cytotoxic HQ concentration (10 µM). The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway-based functional enrichment analysis of HQ-induced differentially expressed genes (DEGs) revealed that HQ significantly upregulated DEGs related to the IL-17 signaling pathway and significantly downregulated DEGs associated with melanogenesis in HEKs. The meta-analysis between the HQ-induced and cytokine-induced transcriptional data (GSE53751) showed that 58 DEGs were commonly upregulated between HQ- and IL-17A-treated HEKs. Notably, the expression of IL36G was significantly increased in HEKs in response to both HQ and IL-17A. IL-36γ (2 µg/ml) directly inhibits melanin biosynthesis in cultured human epidermal melanocytes (HEMs) and downregulates the gene transcription of key enzymes in the melanogenesis pathway including TYR, DCT, and TYRP1. Moreover, IL-36γ autocrinally regulated keratinocyte function to produce the proinflammatory cytokines IL-36γ, IL-6, and CXCL8/IL-8 in a concentration-dependent manner, suggesting that IL-36γ may stimulate the amplification cycle of cutaneous inflammation. In this regard, hydroquinone-induced IL-36γ from human keratinocytes plays a pivotal role in the development of chemical leukoderma by autocrinally or paracrinally modulating the crosstalk between keratinocytes and melanocytes.

Kojyl cinnamate esters are peroxisome proliferator-activated receptor α/γ dual agonists.

Adiponectin is an adipocytokine with insulin-sensitizing, anti-inflammatory, anti-atherosclerotic, and anti-aging properties. Compounds with the ability to promote adiponectin secretion are of interest for the development of anti-aging drugs to improve skin-aging phenotypes. In the phenotypic assay to measure adiponectin secretion during adipogenesis in human adipose tissue-derived mesenchymal stem cells (hAT-MSCs), kojyl cinnamate ester derivatives increased adiponectin secretion. A target identification study showed that the kojyl cinnamate ester derivatives competitively bound to peroxisome proliferator-activated receptor α/γ (PPARα/γ). The upregulation of adiponectin production induced by kojyl cinnamate ester derivatives was significantly correlated with PPARα and PPARγ binding activities. Kojyl cinnamate ester derivatives significantly increased the transcription of genes encoding cholesterol and fatty acid synthesizing enzymes in hAT-MSCs. Notably, the kojyl cinnamate esters upregulated the gene transcription of lipid metabolic enzymes in human epidermal keratinocytes, which are important in the integrity of skin permeability barrier. In addition, the kojyl cinnamate esters that function as PPARα/γ dual modulators inhibited ultraviolet B irradiation-induced inflammation in human epidermal keratinocytes. Therefore, kojyl cinnamate ester derivatives are a novel class of PPARα/γ dual agonists with the potential to improve skin-aging phenotypes.

Benzophenone-3 and benzophenone-8 exhibit obesogenic activity via peroxisome proliferator-activated receptor γ pathway.

Benzophenone-3 (BP-3) and benzopenone-8 (BP-8) are commonly used ultraviolet (UV) filter ingredients in diverse sunscreen products. Recently, the obesogenic activity of avobenzone, a long wave UV A filter, was elucidated in the adipogenesis model of human bone marrow mesenchymal stem cells (hBM-MSCs). In this study, the obesogenic potentials of BP-3 and BP-8 were investigated because of their chemical similarity to avobenzone. During the adipogenesis in hBM-MSCs, BP-3 and BP-8 (EC50, 25.05 and 43.20 µM, respectively) potently promoted adiponectin secretion than avobenzone (EC50, 72.69 µM). In target identification, both BP-3 and BP-8 directly bound to peroxisome proliferator-activated receptor γ (PPARγ), which was associated with the recruitment of steroid receptor coactivator-2 (SRC-2). BP-3 functioned as a PPARγ full agonist whereas BP-8 was a PPARγ partial agonist. In addition, BP-3 and BP-8 significantly increased the gene transcription of PPARα, PPARγ, and major lipid metabolism-associated enzymes in human epidermal keratinocytes, a major target site of UV filters in human skin. This study suggests that BP-3 and BP-8 are obesogenic environmental chemicals similar to phthalates, bisphenols, and organotins.

Diallyl Biphenyl-Type Neolignans Have a Pharmacophore of PPARα/γ Dual Modulators.

Adiponectin secretion-promoting compounds have therapeutic potentials in human metabolic diseases. Diallyl biphenyl-type neolignan compounds, magnolol, honokiol, and 4-O-methylhonokiol, from a Magnolia officinalis extract were screened as adiponectin- secretion promoting compounds in the adipogenic differentiation model of human bone marrow mesenchymal stem cells (hBM-MSCs). In a target identification study, magnolol, honokiol, and 4-O-methylhonokiol were elucidated as PPARα and PPARγ dual modulators. Diallyl biphenyl-type neolignans affected the transcription of lipid metabolism-associated genes in a different way compared to those of specific PPAR ligands. The diallyl biphenyl-type neolignan structure provides a novel pharmacophore of PPARα/γ dual modulators, which may have unique therapeutic potentials in diverse metabolic diseases.