| Summary: | 碩士 === 高雄醫學大學 === 醫學檢驗生物技術學系碩士班 === 105 === In sunlight, ultraviolet A (UVA) and ultraviolet B (UVB) are the main external factors that cause skin damage. Sun-protection clothes and sunscreens were introduced to protect the skin from UV irradiation induced damages. Our previous study indicated that the equivalent UVB surface exposure delivered at different irradiance has different impacts on cell differentiation as well as UVB-induced photocarcinogenic potential. A thoroughly review of the literature indicated that although sunscreen use has significantly increased, the incidences of sunburn and skin cancer have not been reduced. In the present study, we investigated the effects of UVA irradiation on skin photoaging using equivalent UVA fluence but different UVA irradiance, and also the possible molecular mechanisms involved. Cultured human dermal fibroblasts (HDFs) and hairless mice (SKH-1) were used as in vitro and in vivo experiments, respectively. Both the cultured HDFs and SKH-1 mice were irradiated with high-irradiance UVA (HIUVA) and low-irradiance UVA (LIUVA; 50 % irradiance of HIUVA). The results demonstrated that LIUVA treated HDFs showed significantly lower type I collagen and higher matrix metalloproteinase-1 (MMP-1) expressions as compared to their HIUVA treated counterparts. In addition, LIUVA radiation induced higher reactive oxygen species (ROS) production, p38 MAPK and c-Jun N-terminal kinases (JNK) phosphorylation as compared to their HIUVA treated counterparts. However, pretreated with N-acetylcysteine (NAC) markedly decreased intracellular formation of ROS increased by LIUVA irradiation, decreased p38 MAPK and JNK phosphorylation by LIUVA irradiation, enhanced type I collagen synthesis suppressed by LIUVA irradiation, and reduced MMP-1 expression stimulated by LIUVA irradiation. Our findings suggested that at equivalent fluence, UVA radiation at LI has higher photoaging potential as compared to its HI counterpart.
In vivo, the results demonstrated that LIUVA treated SKH-1 showed significantly lower type I collagen, higher MMP-1 and lower catalase expressions as compared to their HIUVA treated counterparts. In addition, a more significant decrease the elasticity of the skin and wrinkle formation in the dorsal skin caused by LIUVA was observed.
Application of sunscreens on the skin is the most common way for the public to protect against skin damage (such as photocarcinogenesis and photoaging) after sun exposure. Sunscreen can be used to prolonged the time to develop UVA-induced erythema response (sunburn) by reducing the irradiance (photon density) of UVA radiation. Therefore, it was likely that with sunscreen use, it is likely for an individual to prolong duration spend under the sun, either intentionally or unintentionally. According to our present results, reduction of UVA irradiance by a physical filter (a scenario similar to sunscreen use) may produce higher photoaging potential. Therefore, the way of using sunscreen (putting on enough or reapplying after a period of time, or avoid prolonging sun exposure time) are proposed to contribute to effectiveness of sunscreen use.
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