Fruits, veggies used in sunblock tests
Thanks to the efforts of UA researchers, sunblock labels could soon list the contents of your refrigerator's crisper and vegetable bin.
Drs. Marianne Powell, Dave Alberts and Dan Liebler at the University of Arizona Cancer Research Center are testing lemon peels, green tea, garlic and other natural extracts to help prevent and slow the development of melanoma, the most serious form of skin cancer.
The UA lab is one of few that has successfully developed pre-clinical models demonstrating the ability of natural extracts to block the growth of pre-malignant lesions.
Sunblocks currently on the market work by reflecting or absorbing ultra-violet radiation. The products Powell and her colleagues are testing interfere with internal skin-cell processes that are aggravated by exposure to UV radiation.
"When you go out in the sun and get that nice warm feeling, that's UV light getting into skin cells ... which can create permanent structure damage in DNA which can lead to cancer," Liebler said.
The UA's research "is important because we will determine exactly how they (the natural products) work on a cellular level," Powell said. The products block pathways in cells that lead to cancerous growth or DNA damage.
Cancer Center researchers have had the most success with citrus fruit peels and green tea extracts and Vitamin E. Those products block skin-cell processes that could lead to tumor development. Green tea extract and Vitamin E also stop cells from creating chemicals that can damage DNA and suppress the immune system.
Researchers will test those products within the next year. If the tests are successful, the products could land in sunblock bottles by the year 2000.
"While sunscreen absorbs UV more strongly, Vitamin E was more effective at preventing sun damage," Liebler said. "Incorporating (the natural substances) into sunscreens may lead to a better product."
If citrus peel and other extracts are proven to prevent melanoma, they will be the first chemicals found to do so. Although evidence suggests that sunblock prevents melanoma, it has not been proven.
But don't automatically toss the sunscreen.
Dr. Tim Bowden and others at the UA Cancer Center have found that sunblocks do prevent carcinomas - the most common type of skin cancer.
Until a few years ago, researchers thought that only one type of ultra-violet radiation, UVB, was harmful.
Recent research by Drs. John Simon and Kerry Hanson at the University of California at San Diego demonstrated that skin damage may be caused by a wide range of UV radiation, including ultraviolet A rays. Until such research was done, sunscreens just protected against UVB radiation.
"It is important that their (Simon and Hanson's) research made headlines," Powell said. "People need to be conscious that it's not a good idea to slather up with baby oil and go lie by the pool."
Simon and Hanson's research focused on a light-sensitive molecule in skin cells that absorbs UVB radiation. Such absorption can bring about sunburn, cancer and immune system suppression. Hanson said researchers aren't certain how UVB radiation causes damage, but they think it interferes with the body's ability to fight harmful substances called antigens.
"If you're exposed to an antigen, your body can't fight it - in turn, you develop a tumor," Hanson said. "There is a lot of photobiology going on right now to study exactly how that (immune system suppression) happens."
UVA is absorbed by the same skin molecules as UVB radiation, but absorption of UVA isn't nearly as strong. It takes 1,000 times longer to get a sunburn from UVA light, Hanson said.
But "you don't have to have a sunburn to have a suppressed immune system," Hanson said. Simon and Hanson found UVA to be harmful, even though "the effects of UVB are much more dramatic."
The absorption of UVA radiation causes the production of a reactive oxygen species, a molecule that leads to the destruction of cell membranes and lipids that make up the skin.
"We think of photo-aging as cosmetic - just getting deep wrinkles," Hanson said. "It damages the structural integrity of skin, which in turn could lead to a suppressed immune system. We should be concerned on a cellular level."
Sunblock manufacturers have responded to the need for protection from UVA radiation. SPF numbers, however, only reflect a product's screening ability for UVB rays, according to the Arizona Cancer Center.
When shopping for a sunscreen that will protect against UVA radiation, look for oxybenzone, sulisobenzone, zinc oxide, titanium dioxide and Parsol 1789.
Sarah Spivack can be reached via e-mail at Sarah.Spivack@wildcat.arizona.edu.