title: An action spectrum for the production of cis-urocanic acid in human skin in vivo.
abstract: Urocanic acid (UCA) is present at millimolar concentrations in mammalian epidermis and undergoes photoisomerization from the naturally occurring trans-isomer to the cis-isomer on exposure to ultraviolet radiation (UVR). Cis-UCA causes downregulation of various immune responses in mouse and human experimental models and has been proposed as both a chromophore and a mediator of UV-induced immune suppression. In this study, the wavelength dependence from 260-340 nm for trans to cis-UCA photoisomerization in human skin was analyzed in five healthy volunteers. The resulting action spectrum demonstrated maximal cis-UCA production in the UVB spectral region of 280-310 nm. This spectral peak is red-shifted to longer wavelengths compared with the erythemal action spectrum. The cis-UCA action spectrum can be used to predict the ability of sunscreens to protect against UVR-induced cis-UCA formation and may assist in explaining discrepancies between sunscreens' abilities to protect against erythema and photoimmunosuppression.
authors.affiliation: Medical Microbiology, University of Edinburgh, Edinburgh, UK.
authors.forename: Pauline
authors.initials: P
authors.lastname: McLoone
authors.forename: Eniko
authors.initials: E
authors.lastname: Simics
authors.forename: Alan
authors.initials: A
authors.lastname: Barton
authors.forename: Mary
authors.initials: M
authors.lastname: Norval
authors.forename: Neil K
authors.initials: NK
authors.lastname: Gibbs
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D008297:Male; D012867:Skin / Q000378:metabolism* / Q000528:radiation effects*; D013473:Sunscreening Agents / Q000494:pharmacology; D014466:Ultraviolet Rays; D014560:Urocanic Acid / Q000378:metabolism*
chemical_list: D013473:Sunscreening Agents; D014560:Urocanic Acid