Protective effect of hochuekkito,a Kampo prescription,against ultraviolet B irradiation‐induced skin damage in hairless mice

A Kampo prescriptions, hochuekkito (HET) has been utilized for treating functional conditions such as general fatigue, compromised state and gastrointestinal motility disorder. Recently, HET has attracted the attention of dermatologists because of its clinically positive effects in atopic dermatitis (AD) treatment. To explain this positive effect of HET, we examined its protective ability against oxidative skin stress using a murine model. The dorsal region of 8‐week‐old male HR‐1 hairless mice, which were raised on a HET (0%, 2% and 10%) mixed diet, was irradiated once with 70 mJ/cm² of ultraviolet (UV)‐B light. After 4 days, transepidermal water loss (TEWL) and stratum corneum water content (SCWC), were determined as a measure of degree of skin dysfunction. To estimate the amount of active oxygen generated, the stratum corneum catalase activity (SCCA) and stratum corneum carbonylated protein (SCCP) content in the tape‐stripped stratum corneum samples were measured. We also measured the H₂O₂ scavenging ability of HET, and analyzed the changes in the expression levels of several inflammation and oxidative stress‐related genes in the skin of HET‐fed mice. In control mice, exposure to UV‐B led to significant increases in TEWL and SCCP and significant decreases in SCWC and SCCA. These UV‐B‐induced changes were reduced in mice administrated HET, and the reduction was HET dose‐dependent. Our results suggested that HET offered a protective effect against UV‐B‐induced skin damage. We also found that HET had relatively low ability to scavenge H₂O₂, and expression level of cyclooxygenase‐2 mRNA decreased in HET‐fed mouse.