Shimizu T, Koizumi H, Nishino H, Abe R, Ohkawara A
Department of Dermatology, Hokkaido University School of Medicine, Sapporo, Japan.
Acta Derm Venereol. 1998 Sep;78(5):348-50. doi: 10.1080/000155598443024.
Urocanic acid (UCA), one of the skin's major components for absorbing UV radiation, is present naturally in the stratum corneum as a trans-isomer. On absorption of UVB radiation either in vitro or in the skin, UCA undergoes trans- to cis-isomerization in a dose-dependent manner. Although the mechanism by which cis-UCA suppresses immunity remains unelucidated, recent studies have indicated that cis-UCA appears to inhibit the induction of cyclic AMP in fibroblasts, which suggests that this molecule plays an active role in modifications to the skin. Here, we report that although neither trans-UCA nor cis-UCA increases cyclic AMP in the pig epidermis, cis-UCA actively down-regulates the increase of cyclic AMP induced by histamine. The effects of cis-UCA on the pig epidermis are revealed through the modulation of the effects caused by histamine. These findings suggest that in the pig epidermis, the initial biochemical and cellular event for UVB-induced immune suppression--that is, the step immediately following the isomerization of trans-UCA to cis-UCA--is down-regulation of cyclic AMP brought about by the activity of cis-UCA.
尿刊酸（UCA）是皮肤吸收紫外线辐射的主要成分之一，它以反式异构体的形式天然存在于角质层中。在体外或皮肤中吸收中波紫外线（UVB）辐射后，UCA会以剂量依赖的方式发生反式到顺式的异构化。尽管顺式UCA抑制免疫的机制尚不清楚，但最近的研究表明，顺式UCA似乎会抑制成纤维细胞中环磷酸腺苷（cAMP）的诱导，这表明该分子在皮肤的修饰中起积极作用。在此，我们报告，虽然反式UCA和顺式UCA都不会增加猪表皮中的cAMP，但顺式UCA会积极下调组胺诱导的cAMP增加。顺式UCA对猪表皮的影响是通过调节组胺引起的效应来揭示的。这些发现表明，在猪表皮中，UVB诱导免疫抑制的初始生化和细胞事件——即反式UCA异构化为顺式UCA之后紧接着的步骤——是由顺式UCA的活性导致的cAMP下调。
