| "Safe" Tan Triggered by Plant Extract, Study Says |
|
20 September 2006, for National Geographic News The elusive goal of gaining a natural tan without braving the sun or the tanning booth may be within reach. A new study suggests that many fair-skinned people retain the ability to safely produce large amounts of melanin, the pigment that colors people's skin. Exposure to the sun's ultraviolet (UV) radiation triggers melanin production in humans, creating tanned skin. But too much UV light can also cause skin cancer and other ailments (related news: "Tanning 'Buzz' Could Lead to Addiction" [August 2005]). David Fisher, a medical doctor and cancer researcher at the Dana-Farber Cancer Institute in Boston, Massachusetts, led a team that applied a plant extract called forskolin to mice's skin. Mice that were normally fair-skinned became deeply tanned after a few weeks of daily forskolin application. "I was blown away," Fisher said. The tanning also protected the mice from UV radiation, and the level of protection made the tanned mice "indistinguishable from genetically black-skinned mice," Fisher said. He and colleagues report their findings in today's issue of the journal Nature. But, Fisher says, the team needs to do more studies to see if the extract is safe for people. "This is experimental," Fisher said. "This is not something people should be putting on their skin." Tanned Mice People have evolved to produce different amounts of skin pigment depending on where their ancestors lived, apparently as a trade-off between the benefits and harms of sunlight. (Related photos: "Unmasking Skin" in National Geographic magazine.) UV light from the sun helps the human body create vitamin D, which is essential for strong bones. But the rays also damage DNA, which can lead to cancer and can break down another important vitamin in the body known as folate. Today fair-skinned people often get too much sun and face high levels of skin cancer. "It is largely the result of human populations with very fair skin moving around the world from locations where there was very limited sun exposure into areas like Florida or Arizona or Australia." So far methods for artificial tanning have faced big obstacles. The tans may look fake or create serious side effects, and the color change may not actually protect against UV rays. Researchers have therefore been searching for ways to activate the body's own machinery for producing pigment. But finding an animal in which to study this process had been a problem. Most furry mammals carry their pigment-producing cells in the hair follicles, where they put pigment into fur rather than skin. So Fisher and colleagues used a strain of mice that was genetically engineered so their skin mimicked that of humans, with pigment cells distributed throughout the skin. The mice also carried a mutation similar to that of many Europeans so that they were born fair-skinned. The researchers found that when treated with the plant extract forskolin, the engineered mice tanned deeply, producing much more of the pigment melanin. Also, the cells placed the pigment above the nuclei, where human cells place melanin to protect the nuclei and DNA inside them from UV rays. The tanning took a few weeks to kick in and faded after a few weeks. It did not seem to have any side effects after a year of use, Fisher says. See the Light The study proves that a compound can activate cells that normally don't produce much pigment, says molecular geneticist Rick Sturm of the University of Queensland in Brisbane, Australia. "It's a nice proof of something that we've suspected for a long time, but no one has been able to show in an animal," Sturm said. But Sturm is concerned that stimulating pigment-producing cells could still create melanoma—cancer of the pigment cells themselves. Zalfa Abdel-Malek, at the University of Cincinnati Medical Center in Ohio, argues that forskolin is not a good candidate for a tanning drug for people. Forskolin works by boosting levels of a chemical called cyclic AMP, which many types of cells use for signaling each other. This raises the specter of general side effects throughout the body, Abdel-Malek says. "This is never going to see the light, as far as I can tell," she said. Instead she and her colleagues are testing proteins that target just the pigment-producing cells, which she thinks could be a more promising approach. Fisher, the study co-author, is also cautious about the drug's potential use in people. "We don't assume that this drug, forskolin, is going to be the one to work in humans," he said. "This was just the first one that we tested." © National Geographic Society, all rights reserved
|