Fake tanner wards off skin cancer
Plant extract triggers pigmentation to protect fair skin.
There is hope for fair-skinned people who long for a tan. Researchers have found a chemical from a tropical mint plant that works both as a sunless tanner and as a solar shield in fair-skinned mice.
If the compound works for people too, it could prove a boon for the cosmetics industry and a life-saver for people with a rare genetic disorder that keeps them indoors. Unlike other sunless tanners on the market that simply dye the skin, forskolin prompts the body to produce a real tan, protecting against ultraviolet radiation.
Most people with fair skin burn instead of tanning because they have a disfunctional skin protein called the melanocortin-1 receptor (Mc1r), which normally produces an ultraviolet-protecting pigment called melanin.
Researchers have speculated that there may be other ways to get the body to produce protective melanin. David Fisher, from the Dana-Farber Cancer Institute in Boston, Massachusetts, and his colleagues wondered whether activating an enzyme called adenylate cyclase, which can help to trigger production of dark pigments, would allow tanning even if a person had no functioning Mc1r. Forskolin extract from the Coleus plant, they found, activates this enzyme.
The team took a number of mice genetically engineered to have a rare disorder called xeroderma pigmentosum, in which cells are unable to repair DNA damage done by radiation. They shaved them, and exposed them to ultraviolet blasts (equivalent to a few hours on a Florida beach in July) once a day for 20 weeks.
Fair-skinned mice with the disorder, with non-functioning Mc1r, were burned by the rays and developed skin inflammation and scarring. After about 5 weeks, half the mice showed signs of skin cancer; after 30 weeks they were all dead.
But similar mice lathered with forskolin lotion for a month before the treatment, and again before each ultraviolet exposure, fared much better. In a few weeks their skin was nearly black, and they were as protected from sunburn as mice with natural tans (but without the tough, leathery look of natural tanning). It took about 50 weeks for half of them to show tumours, the team reports in Nature1.
Showing that tanning can happen without functioning Mc1r is a breakthrough, says Marie-Dominique Galibert of the CNRS in Rennes, France. But she cautions that no one yet knows how this "powerful new pathway" works on a molecular level.
The researchers say forskolin should be an effective shield against both ultraviolet-A and ultraviolet-B for both fair-skinned and dark-skinned animals. Albinos would not be good candidates as they lack the ability to create any melanin at all.
The work could also help people with xeroderma pigmentosum, who are about 2,000 times more prone to getting skin cancer than the average fair-skinned person. People with this rare condition cannot go outside without getting extremely burnt; affected children can get cancer at a very young age.
But forskolin isn't ready for human use just yet. The team needs to look in detail at what it does to the skin, and to ensure it is safe.
Coleus itself has been around a long time (it has been traditionally used as a spice, or medicinally for heart troubles or stomach cramps). But applying extracts to the skin is a new idea that needs testing.
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- D'Orazio J. A., et al. Nature, 443. 340 - 344 (2006).
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