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A healthy glow from within

Researchers are developing products that would darken the skin while protecting it from solar radiation.

June 06, 2005|Michael Stroh | Baltimore Sun

With summer approaching, millions are rushing to tanning salons to get their bronze on. Others are turning to a growing arsenal of creams and sprays that tint the skin's surface.

However, some of these concoctions result in a faux glow, and most offer little protection from the sun's potentially deadly rays.

But recent discoveries about the skin's response to solar radiation offer hope that it may soon be possible to trick the body's tanning machinery so a drug can be developed that offers even the pastiest of the population a protective chestnut glow.

A few academic and commercial labs around the world are reporting some preliminary success.

"Our understanding of the biology of pigmentation has really come far in the past 10 years," says biologist Hee-Young Park of Boston University, where researchers are working on a DNA-based tanning lotion.

The push toward sunless tans is less about cosmetics than about preventing cancer, researchers say.

The incidence of melanoma, the deadliest skin cancer, more than tripled among Caucasians from 1980 to 2003.

This year the disease is expected to kill 10,500 people in the United States; about 20% of Americans will develop some form of skin malignancy during their lifetimes.

Researchers have known for years that blacks and others with naturally dark skin are less susceptible to cancer than paler Caucasians. A tan, in other words, seems to serve as nature's sunscreen.

But producing sun-kissed skin in the lab is a challenge that dates back more than half a century.

In "Black Like Me," a 1959 expose of racism in America, white journalist John Howard Griffin darkened his skin by ingesting psoralens, a class of chemicals that make the skin more sensitive to the sun.

Today doctors know that the drugs can suppress the immune system, so their use is restricted to treating serious skin conditions such as psoriasis.

Sunless tanners have their own drawbacks. Early formulations relied on carotenoids, naturally occurring pigments that help make flamingos pink and carrots orange. Most people who used them turned a similar hue.

They can also pose health risks. Canthaxanthin, a common carotenoid found in some sunless tanning pills sold overseas, is banned by the Food and Drug Administration because it can cause retinal deposits.

The only FDA-approved pigment for sunless tanners is a chemical called dihydroxyacetone, which works by staining the skin. Although it provides a better bronze, it doesn't provide protection from the sun's harmful rays.

Because any exposure to ultraviolet radiation can injure DNA and potentially trigger cancerous growths, researchers want to find a way to generate a genuine tan with little or no sunlight.

"It's been slow, unfortunately," says dermatologist Barbara Gilchrest at Boston University. One reason, she says, is that the scientific story of the savage tan turns out to be more complicated than expected.

When ultraviolet radiation strikes the skin's outermost layer -- the epidermis -- it awakens squid-like cells called melanocytes. These cells start cranking out melanin, a dark brown pigment that gradually gets soaked up by the vast sea of surrounding skin cells.

Melanin does more than make the skin look tan -- it also helps deflect incoming radiation from sensitive DNA. Although some melanin particles scatter throughout the skin cells, others settle over the cells' DNA-containing nuclei.

"It looks like a hat," says biologist Daniel B. Yarosh, president of AGI Dermatics in Freeport, N.Y., a company developing therapies to repair DNA damage caused by sun exposure.

Recent discoveries about what happens when this protective mechanism fails are now providing strategies to designers of sunless tanning drugs.

When ultraviolet radiation damages skin cell DNA, the body responds by dispatching repair enzymes to prune snippets of corrupt genetic code.

Gilchrest and her team at Boston University have discovered that this response also serves as a key signal to melanocytes to start producing protective pigment.

In a series of animal experiments during the last decade, scientists have even shown that introducing damaged DNA fragments into skin cells can fool them into thinking they're under assault from ultraviolet radiation. The result: darkening skin.

Now Gilchrest and her team are trying to develop a lotion that could work on people. "The idea would be something you could get in a tube or a bottle and put it on and get a tan," she says.

An approach based on DNA fragments would have advantages over a bronzer or a sunscreen -- it could heal DNA damage even as it makes skin darker. In a 2004 study, the Boston University team found that smearing DNA fragments on the backs of hairless mice reduced their chances of developing skin cancer after ultraviolet exposure.

Scientists in Australia, meanwhile, are taking a different tack.

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