Safety evaluation of 2-aza-8-oxohypoxanthine based on in vitro and human patch tests

2-Azahypoxanthine (AHX) and imidazole-4-carboxamide (ICA) are fairy-ring causing compounds from a mushroom-forming fungus, Lepista sordida, and 2-aza-8-oxohypoxanthine (AOH) is a metabolite of AHX in plants. However, the safety of AOH had not yet been elucidated. In this study, we focused on AOH and performed safety evaluations of the compound using in vitro and human patch tests for cosmetic applications. In the Ames test, AOH was not mutagenic to any of the test bacterial strains (> 5000 μg/plate). In vitro skin irritation and skin sensitization studies using reconstructed human epidermis and peptides that contained lysine and cysteine showed that AOH was not a skin irritant (cell viability > 50%) and did not exhibit skin sensitization. This compound also did not exhibit cytotoxicity under ultraviolet- or sham-irradiation in the alternative phototoxicity test using BALB/c 3T3 cells (mean photo effect < 0.1) and no skin reaction was observed in the patch test on human skin. Thus, we concluded that AOH is safe as a cosmetic ingredient. This is the first study in which safety evaluation tests were performed on AOH.