Experimental tinea unguium model to assess topical antifungal agents using the infected human nail with dermatophyte in vitro

Therapy for onychomycosis is difficult because a complete cure requires long-term treatment. Although strong systemic antifungal drugs are potent enough to achieve a cure, they often have side effects. Therefore, one approach is to develop a new topical antifungal drug to act directly on the nail tissue. In this study, we developed a new in vitro model for assessing antifungal activity using the human nail. An O-ring was fixed with silicon bond to the dorsal surface of the nail. An antifungal agent applied to the surface will penetrate the nail tissue. The ventral side of the nail was placed on an agar plate inoculated with conidia of Trichophyton mentagrophytes. Nail specimens were infected with the fungi from the agar, and a clear fungal colony formed on the agar surrounding the nail on the fifth day of cultivation. After 14 days, the fungal colony in the control groups was shown to be expanding over the entire nail. The fungal colony in the group treated with sodium pyrithione had disappeared. Although the in vitro antifungal activity of sodium pyrithione has poor potency among the agents used, it showed remarkable antifungal activity, as assessed by image analysis. This model enables one to evaluate the activity of a topical antifungal agent that has penetrated human nail tissue, and it may facilitate research on a topical agent for onychomycosis.