Non-Thermal Effects of Near-Infrared Irradiation on Melanoma

Malignant melanoma is considered to be the most aggressive form of skin neoplasms. Over the past few decades, the incidence rate of melanoma has steadily risen throughout the world. The risks of developing melanoma consist of intrinsic and environmental factors. Intrinsic factors generally include a family history and an inherited genotype, while the most relevant environmental factor is sun exposure. Exposure to ultraviolet (UV) radiation is the most important environmental carcinogen (Travers et al., 2008) and plays a significant role in the development of melanoma (Wolf et al., 1994). Sunscreens reduce the effects of UV radiation on human skin (Ananthaswamy et al., 1997). Nevertheless, sunscreens have failed to protect against an increase in UV radiation-induced melanomas (Wolf et al., 1994). Various kinds of UV blocking materials, such as sunblocks, films, paints, and fibers are often used to prevent skin damage from UV exposure. Although individuals all over the world use various kinds of sunscreens, unwanted biological influences such as rosasea, erythema ab igne, long-term vasodilation, muscle thinning, and sagging still occur (Tanaka et al., 2010c). Most sunscreens can only block UV and not visible light or near-infrared (NIR) radiation. Sunlight that reaches the human skin contains solar energy composed of 6.8% UV light, 38.9% visible light, and 54.3% infrared (IR) radiation (Kochevar et al., 1999). In addition to natural NIR, human skin is increasingly exposed to artificial NIR from medical devices and from electrical appliances (Schieke et al., 2003; Schroeder et al., 2008). Thus, we are exposed to tremendous amounts of NIR. Both UV and visible light radiation are attenuated by melanin (Anderson & Parrish, 1981), whereas NIR can penetrate deep into human tissue where it can cause photochemical changes (Karu, 1999). We previously reported that NIR penetrates the skin and is absorbed by sweat on the skin surface, water in the dermis (Tanaka et al. 2009a, 2009b), hemoglobin in dilated vessels (Tanaka et al., 2009b, 2011c), myoglobin in the superficial muscle (Tanaka et al., 2010c), bone cortical mass, and is scattered by adipose cells (Tanaka et al., 2011b). NIR irradiation induces strand breaks and cell death by apoptosis (Tirlapur & König, 2001) as well as the cell death of cancer cells and bone marrow cells (Tanaka et al., 2010b, 2011b). In addition, NIR irradiation is used as a therapeutic option for the treatment of wound healing