The effect of epidermal levels of urocanic acid on 25-hydroxyvitamin D synthesis and inflammatory mediators upon narrowband UVB irradiation

摘要

Background/Purpose Urocanic acid (UCA) absorbs ultraviolet (UV)B radiation in the epidermis which may interfere with phototherapy. Therefore, the influence of individual levels of UCA on immune reactivity and vitamin D synthesis induced by narrowband UVB radiation was assessed. Methods Twenty-eight subjects with irritant contact dermatitis of the hands were irradiated with suberythemal doses of narrowband UVB radiation on their unaffected lower forearms on three consecutive days. Stratum corneum tape strips and epidermal interstitial fluid (ISF) as well as blood samples were analyzed. Results Narrowband UVB irradiation led to the conversion of trans-UCA into its ds-isomer in the epidermis. The observed increase in 25-hydroxyvitamin D serum concentrations was inversely correlated with the baseline levels of trans-UCA. Furthermore, UVB irradiation induced significant changes in the levels of CXCL10/IP-10, CCL2/MCP-1, CCL4/MIP-10, and the IL-IRA/ IL-loc ratio. The levels of IL-loc and CXCL9/MIG showed a trend toward increase. The changes in the levels of inflammatory and immunomodula-tory mediators did not depend on baseline levels of trans-UCA. Conclusion The results suggest that epidermal levels of trans-UCA affect vitamin D synthesis, but not cutaneous immune reactivity upon repeated exposure to suberythemal doses of narrowband UVB radiation. However, this requires further exploration.