Effects of low concentrations of cis- and trans-urocanic acid on cytokine elaboration by keratinocytes

The urocanic acid cis isomer (cis-UCA) is a possible cutaneous photoreceptor for the immunomodulatory phenomena that follow ultraviolet B irradiation. Several experiments in animals show an inhibitory action of cis-UCA on cellular immunity. However, the action of cis-UCA on the synthesis of cytokines in keratinocytes remains unknown. Long-term cultures of normal human keratinocytes were prepared in a serum-free medium, and stimulated with 1 μg/ml of phorbol 12-myristate 13-acetate (TPA) and UCA or UVB-UCA (10–100 μg/ml). Synthesis of the following cytokines was measured using ELISA and Northern blot techniques: TNF-α, IL-1α, IL-1β, IL-6, IL-8 and TGF-β1. TPA increased TNF-α protein levels in culture supernatants. No changes in IL-1α and IL-1β protein levels were detected in basal culture supernatant after TPA stimulus. TPA augmented RNA expression for TNF-α, IL-1α, IL-1β and TGF-β1. UCA isomers did not induce cytokine changes in protein synthesis. Expression of IL-1α and IL-1β genes was increased after exposure to 100 μg/ml UVB-UCA (70 μg/ml cis-UCA). A slight increase in TNF-α RNA expression was detected when the dose of UVB-UCA reached 100 μg/ml. No effects on cytokine synthesis were found after UCA stimulus. These results suggest that low doses of cis-UCA do not effect cytokine synthesis by keratinocytes.