SUN­LIGHT CON­TIN­UES TO DAM­AGE SKIN IN THE DARK

Beauty Cosmedica Singapore - - Beauty Flash -

Much of the dam­age that ul­tra­vi­o­let ra­di­a­tion (UV) does to skin oc­curs hours af­ter sun ex­po­sure, a team of Yale-led re­searchers con­cluded in a study.

Ex­po­sure to UV light from the sun or from tan­ning beds can dam­age the DNA in melanocytes, the cells that make the melanin that gives skin its color. This dam­age is a ma­jor cause of skin can­cer, the most com­mon form of can­cer in the United States. In the past, ex­perts be­lieved that melanin pro­tected the skin by block­ing harm­ful UV light. But there was also ev­i­dence from stud­ies sug­gest­ing that melanin was as­so­ci­ated with skin cell dam­age.

In the cur­rent study, Dou­glas E. Brash, clin­i­cal pro­fes­sor at the Yale School of Med­i­cal, and his co-au­thors first ex­posed mouse and hu­man melanocyte cells to ra­di­a­tion from a UV lamp. The ra­di­a­tion caused a type of DNA dam­age known as a cy­clobu­tane dimer (CPD). To the re­searchers' sur­prise, the melanocytes not only gen­er­ated CPDs im­me­di­ately, but also con­tin­ued to do so hours af­ter UV ex­po­sure ended.

The re­searchers next tested the ex­tent of dam­age that oc­curred af­ter sun ex­po­sure by pre­vent­ing nor­mal DNA re­pair in mouse sam­ples. They found that half of the CPDs in melanocytes were "dark CPDs" -- CPDs cre­ated in the dark. In search­ing for an ex­pla­na­tion of these re­sults, San­jay Premi, as­so­ciate re­search sci­en­tist in the Brash lab­o­ra­tory, dis­cov­ered that the UV light ac­ti­vated two en­zymes that com­bined to "ex­cite" an elec­tron in melanin.

The energy gen­er­ated from this process -known as chemiex­ci­ta­tion -- was trans­ferred to DNA in the dark, cre­at­ing the same DNA dam­age that sun­light caused in day­time. How­ever, the slow­ness of chemiex­ci­ta­tion may al­low time for new pre­ven­tive tools, such as an "evening-af­ter" sun­screen de­signed to block the energy trans­fer.

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