WASHINGTON Cheap Torey Krug Jersey , Feb. 19 (Xinhua) -- Much of the damage that ultraviolet radiation (UV) does to skin occurs hours after sun exposure, and this delayed reaction appears to be due to the skin pigment melanin, a U.S. study said Thursday.
Melanin, which gives skin its color, is usually thought of as a protective pigment, blocking the UV radiation that damages DNA and contributes to skin cancer.
But there was also evidence from studies suggesting that melanin was associated with skin cell damage.
In the new study, Douglas Brash Cheap David Krejci Jersey , professor of the Yale University, and his colleagues first exposed mouse and human melanocytes, the cells that make the melanin, to radiation from a UV lamp.
The radiation caused a type of DNA damage known as a cyclobutane dimer (CPD), in which two DNA "letters" attach and bend the DNA, preventing the information it contains from being read correctly.
The researchers were surprised to find that the melanocytes not only generated CPDs immediately but continued to do so more than three hours after UV exposure ended. Cells without melanin generated CPDs only during the UV exposure.
The results, published in the U.S. journal Science Cheap Danton Heinen Jersey , showed that melanin had both carcinogenic and protective effects.
"If you look inside adult skin, melanin does protect against CPDs. It does act as a shield," said Brash. "But it is doing both good and bad things."
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.
Further research showed that the UV light activated two enzymes that combined to "excite" an electron in melanin, and that the energy generated from this process, known as chemiexcitation, in turn, causes the same DNA damage that sunlight caused in daytime.
Chemiexcitation has previously been seen only in lower plants and animals.
While noting that news of the carcinogenic effect of melanin is disconcerting Cheap Zdeno Chara Jersey , the researchers also said that the slowness of chemiexcitation may allow time for new preventive tools, such as an "evening-after" sunscreen designed to block the energy transfer.
Chinese President Xi Jinping (L) holds a welcome ceremony for Brunei's Sultan Haji Hassanal Bolkiah before their talks in Beijing, capital of China, Sept. 13, 2017. (XinhuaXie Huanchi)
BEIJING, Sept. 13 (Xinhua) -- Chinese President Xi Jinping held talks with Brunei's Sultan Haji Hassanal Bolkiah here on Wednesday, with the two agreeing to promote cooperation within the Belt and Road Initiative Cheap Brandon Carlo Jersey , and work for stronger bilateral ties.
"China appreciates Brunei's efforts in strengthening China-ASEAN relations, and hopes to align the Belt and Road Initiative with ASEAN's development plan," Xi said.
Calling the two countries close neighbors across the sea, mutually reliable friends and partners, Xi said the two countries have established strategic cooperative ties, cemented political mutual trust, and achieved fruitful cooperation over the years.
This year marks the start of the second 25 years of China-Brunei diplomatic relations. China-Brunei ties are at a key stage of development Cheap Riley Nash Jersey , Xi said, adding China is ready to share governance experience with Brunei, synergize their development strategies, and promote closer cooperation in various areas.
He called on both sides to maintain high-level exchanges, deepen political mutual trust and support each other on issues concerning respective core interests and major concerns.
Xi appreciated Brunei's support for the Belt and Road Initiative. The two leaders agreed to boost closer cooperation in such areas as infrastructure, energy, halal food Cheap Anders Bjork Jersey , agriculture, fishery, and the digital economy.
He asked the two countries to cement defense and law-enforcement cooperation, as well as exchanges in education, sports, public health, tourism Cheap Bobby Orr Jersey , media and other areas.
The two countries should enhance cooperation in regional and international affairs, and coordination in frameworks such as the United Nations and the Asia-Pacific Economic Cooperation (APEC), Xi said.
Regarding the situation in the South China Sea, Xi said it has stabilized and showed positive momentum. "China hopes to work with Brunei and parties concerned to make the South China Sea the sea of peace, friendship and cooperation."
The Sultan congratulated on China's achievements, and expressed support for the Belt and Road Initiative.
He hailed the progress of China-Brunei ties since the forging of diplomatic relations, inviting more Chinese enterprises to invest in his country.
Brunei is ready to maintain high-level exchanges with China Jake DeBrusk Jersey , expand cultural exchanges, jointly safeguard peace and stability of the South China Sea, and boost stronger ASEAN-China relations, the Sultan said.
The two heads of state witnessed the signing of several cooperation documents regarding the Belt and Road Initiative, infrastructure and health.
Chinese Premier Li Keqiang and top legislator Zhang Dejiang also met with the Sultan earlier on Wednesday.
Li said China regards ASEAN as a diplomatic priority and will continue to support the ASEAN Community building and its centrality in regional cooperation.
China will work with Brunei to promote the East Asian Leaders' meetings on cooperation later this year to produce more outcomes that contribute to regional stability, cooperation and prosperity, he said.
Zhang said the National People's Congress of China eyes stronger exchanges and cooperation with Brunei's State Legislative Council Charlie McAvoy Jersey , to implement the consensus reached by the two heads of state, and contribute to stronger bilateral strategic cooperative ties.
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