CYP11A1-derived vitamin D₃ products protect against UVB-induced inflammation and promote keratinocytes differentiation

UVB radiation mediates inflammatory responses causing skin damage and defects in epidermal differentiation. 1α,25-Dihydroxyvitamin D₃ (1,25(OH)₂D₃) interacts with the vitamin D₃ receptor (VDR) to regulate inflammatory responses. Additionally, 1,25(OH)₂D₃/VDR signaling represents a potential therapeutic target in the treatment of skin disorders associated with inflammation and poor differentiation of keratinocytes. Since the protective effect of 1,25(OH)₂D₃ against UVB-induced skin damage and inflammation is recognized, CYP11A1-derived vitamin D₃-hydroxyderivatives including 20(OH)D₃, 1,20(OH)₂D₃, 20,23(OH)₂D₃ and 1,20,23(OH)₃D₃ were tested for their anti-inflammatory and skin protection properties in UVB-irradiated human epidermal keratinocytes (HEKn). HEKn were treated with secosteroids for 24 h pre- and post-UVB (50 mJ/cm²) irradiation. Secosteroids modulated the expression of the inflammatory response genes (IL-17, NF-κB p65, and IκB-α), reducing nuclear-NF-κB-p65 activity and increasing cytosolic-IκB-α expression as well as that of pro-inflammatory mediators, IL-17, TNF-α, and IFN-γ. They stimulated the expression of involucrin (IVL) and cytokeratin 10 (CK10), the major markers of epidermal differentiation, in UVB-irradiated cells. We conclude that CYP11A1-derived hydroxyderivatives inhibit UVB-induced epidermal inflammatory responses through activation of IκB-α expression and suppression of NF-kB-p65 activity and its downstream signaling cytokines, TNF-α, and IFN-γ, as well as by inhibiting IL-17 production and activating epidermal differentiation.