照射強度對於紫外線A所誘導之皮膚老化的影響

Effects of irradiance on UVA-induced skin aging

洪于婷(Yu-Ting Hung)

指導教授 ： 吳慶軒

高雄醫學大學/健康科學院/醫學檢驗生物技術學系碩士班/碩士(2017年)

摘要

在陽光照射中，紫外線A (ultraviolet A; UVA) 與紫外線B (ultraviolet B; UVB) 是造成皮膚損傷的主要外在因素。日常生活中人們常以防曬衣或防曬乳作為阻擋 UV 之防護，避免因 UV 照射所造成之皮膚傷害。我們過去的研究發現，相同 UVB 的照射劑量 (fluence) 但不同的照射強度 (irradiance) 對於細胞之分化與 UVB 引發之皮膚癌有明顯不同的影響。許多過去的研究報告指出，雖然防曬乳使用越來越頻繁，但是曬傷與皮膚癌的發生率卻沒有因此降低。因此在本研究中，我們嘗試使用相同之 UVA 照射劑量但不同的 UVA 照射強度探討其對於皮膚光老化之影響及其中可能的影響分子機制。我們使用人類真皮纖維母細胞 (HDFs) 與無毛鼠 (hairless mice; SKH-1) 進行實驗。UVA (CL-1000L; 5 J/cm2) 之照射分成兩組: (1) 高照射強度UVA (high irradiance UVA; HIUVA) 及 (2) 低照射強度UVA (low-irradiance UVA; LIUVA; 照射強度為 HI 的 50%)。研究結果發現 LIUVA 比 HIUVA 造成更多的 type I collagen 減少與 matrix metalloproteinase-1 (MMP-1) 增加，並誘導 HDFs 產生更多 reactive oxygen species (ROS) 及更顯著的 p38 MAPK 及 c-Jun-N-terminal kinase (JNK) 磷酸化表現。然而，若先以 N-acetylcysteine (NAC) 前處理 HDFs 後再照射 UVA ，則能夠明顯降低細胞照射 LIUVA 後之 ROS 表現、p38 MAPK 和 JNK 磷酸化的增加，並提升因為 LIUVA 照射後的 type I collagen 表現之減少及降低因為 LIUVA 照射後 MMP-1 之表現增加。 根據這些研究結果顯示 LIUVA 誘導的這些效應皆為透過 ROS 之產生而造成顯著的皮膚老化之現象。在動物模式中，LIUVA 照射相較於 HIUVA 造成更明顯的 SKH-1 真皮層之 type I collagen 減少、MMP-1增加、catalase減少、背部皮膚彈性下降和背部皮膚皺紋形成。表示經由 In vivo 和 In vitro 之研究皆發現 LIUVA 相較於 HIUVA 照射會造成較明顯的光老化現象。
使用防曬乳是一般民眾最常用於保護陽光照射後對於皮膚傷害 (如光致癌與光老化) 之方法。皮膚塗抹防曬乳可藉由降低 UVA 之照射強度而延長 UVA 造成皮膚曬傷之時間。因此，人們可能因為塗抹了防曬乳而不小心或刻意延長在陽光下曝曬之時間。然而根據我們的研究結果顯示，利用降低照射強度的物理性濾片 (physical filter) 降低 UVA 照射強度 (即模擬防曬乳塗抹) 後可能具有更高之皮膚老化的潛在風險。因此，防曬乳的使用方式與觀念 (如塗抹量充足與否或塗抹一段時間後須追加塗抹或避免延長陽光曝曬時間等) 正確與否常常是決定防曬乳有效與否之重要因素。

關鍵字

紫外線A ； 照射強度 ； 光老化

並列摘要

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.

並列關鍵字

UVA ； irradiance ； photoaging

參考文獻

Antell, D. E. and E. M. Taczanowski. (1999). How environment and lifestyle choices influence the aging process. Ann Plast Surg, 43(6), 585-588.

Arpino, V., M. Brock and S. E. Gill. (2015). The role of TIMPs in regulation of extracellular matrix proteolysis. Matrix Biol, 44-46, 247-254.

Ballard, J. W. O. and M. D. Dean. (2001). The mitochondrial genome: mutation, selection and recombination. Current opinion in genetics & development, 11(6), 667-672.

Battie, C., S. Jitsukawa, F. Bernerd, S. Del Bino, C. Marionnet and M. Verschoore. (2014). New insights in photoaging, UVA induced damage and skin types. Exp Dermatol, 23 Suppl 1, 7-12.

Berneburg, M., N. Gattermann, H. Stege, M. Grewe, K. Vogelsang, T. Ruzicka and J. Krutmann. (1997). Chronically Ultraviolet‐exposed Human Skin Shows a Higher Mutation Frequency of Mitochondrial DNA as Compared to Unexposed Skin and the Hematopoietic System. Photochemistry and photobiology, 66(2), 271-275.