Effect of dietary histidine content on the change in content of skin urocanic acid isomers in hairless mice irradiated with ultraviolet B

Hairless mice were fed with a 10% amino acid mixture diet (control diet, 0.42% histidine content), the control diet without histidine (histidine-free diet), or the control diet rich in histidine (histidine-rich diet; histidine content, 4.2%) for 32 days. They were irradiated with UV light of 312 nm for 30 min, and skin samples were periodically taken for measuring the urocanic acid isomers. Total urocanic acid isomers were decreased by UV irradiation in all the three groups, the recovery being the fastest in the histidine-rich group. The percentage increase in cis-urocanic acid/total urocanic acid was quickly increased by UVB irradiation. The recovery of the ratio was slightly higher in the histidine-rich group, although the total urocanic acid level was higher in the histidine-rich group than in the others. Therefore, the absolute cis-urocanic acid content in the skin was almost the same among the three groups. These results indicate that the increased histidine intake strengthened UVB protection without any decrease in immune suppression.