The epidermal environment’s influence on the dermal environment in response to external stress

Introduction: The outermost layer of the skin, the epidermis, is directly exposed to external stress (e.g., irradiation, allergens and chemicals). Changes in epidermal conditions/environment in response to this stress could also influence conditions of the dermis, located directly beneath the epidermis. Yet, whether/how any epidermal environment changes in response to external stress affect dermal functions has not been completely clarified. Methods: We employed ultraviolet irradiation B (UVB) (which does not reach the dermis) as a model of external stress. Human keratinocytes and human dermal fibroblasts were treated with UVB and conditioned medium of keratinocytes exposed to UVB (UVB-keratinocyte-M), respectively. We assessed 1) inflammatory markers in keratinocytes; 2) matrix metalloproteases (MMP) levels and collagen degradation in fibroblasts; 3) Ex vivo organ-cultured human skin were treated with UVB. MMP levels and collagen degradation were examined; 4) Test whether the mixture of agent (agent cocktail) consists of dihydroceramide, niacin amide, resveratrol, glucosyl hesperidin and phytosterol ester that has been shown to improve skin barrier integrity can mitigate influence of UVB is skin; and 5) a pilot one-arm human clinical test to assess efficacy of formulation containing agent cocktail on skin function. Results: Inflammatory-cytokine and -lipid mediator production were increased in cultured keratinocytes treated with UVB, while matrix MMP-1, -3 and -9 production was increased in fibroblasts incubated with UVB-keratinocyte-M. mRNA expression of COL1A1 (that codes Type 1 collagen) levels was decreased in fibroblasts incubated with UVB-keratinocyte-M. The study using ex vivo organ-cultured human skin showed both MMP-1 and MMP-9 expression were increased in both epidermis and dermis, and increased dermal collagen degradation following UVB irradiation. Increased MMP production and collagen degradation were attenuated by application of an agent cocktail. Finally, a pilot clinical study demonstrated that the formulation containing our agent cocktail likely has the ability to improve skin hydration, increase skin elasticity and reduce the appearance of wrinkles. Conclusion: Epidermal Changes in epidermal environment and conditions in response to external stress, affect dermal conditions, and these negative effects of external stress on various skin layers can be pharmacologically mitigated.