761 The impact of 308-nm excimer laser on human keratinocytes of organ cultured human skin

Abstract

The 308-nm excimer laser (EL) is a new ultraviolet B phototherapy instrument for various types of skin diseases including psoriasis, atopic dermatitis and vitiligo. Although the action of EL on these diseases is considered to be due to its anti-inflammatory properties at least by increasing the levels of regulatory T cells, the effects on keratinocytes have not been fully understood. Here, we investigated the effect of 308-nm EL on human keratinocytes by using human skin organ culture system. We irradiated human skin specimens by an EL device (Thera Beam UV308; USHIO, Tokyo, Japan) at various doses, including 300, 400 and 600 mJ/cm2 at day 0 and then organ cultured for 7 days. The effects of EL on the epidermis of organ cultured human skin were evaluated by HE histochemistry, Ki-67, TUNEL, β1 integrin, CK10, Involucrin and CK16 immunohistochemistry. As a result, organ cultured human skin irradiated at 600 mJ/cm2 at day 2 showed obvious damage of the epidermis. This was correlated to the significantly increased number of apoptotic cells detected by TUNEL immunofluorescence. However, obvious newly formed keratinized layer of epidermis was observed at 600 mJ/cm2 at day 5. Interestingly, the number of Ki-67 positive proliferating cells within the epidermis was significantly increased at 300, 400 and 600 mJ/cm2 after day 5. The expression of b1 integrin, which is one of epidermal stem cells (SC)s markers was significantly increased at 300 and 600 mJ/cm2 at day 5. In addition, the expression of differentiation-related molecules including CK10, CK16 and Involucrin was increased by EL at day 5. Here, we showed (1) EL irradiation not only induced apoptosis of epidermal keratinocytes but also stimulated their proliferation and differentiation, (2) EL also stimulated epidermal SCs. These results indicate that in addition to its well-known anti-inflammatory properties, EL may play a role as a stimulator for epidermal keratinocytes proliferation as well as SCs activity. This might be utilized for a novel treatment for wound healing.