CHAPEL HILL - Vitamins A and E, which normally boost human health in numerous ways, also appear to keep cancer cells from dying through the natural protective process scientists call apoptosis, new University of North Carolina at Chapel Hill research shows.
As a result, giving patients those vitamins may prevent cancer cells from self-destructing and work against cancer therapy, scientists say.
Researchers at UNC-CH's schools of public health and medicine presented their findings Monday (12/13) during a news conference at the American Society for Cell Biology's annual meeting in Washington, D.C. Drs. Rudolph Salganik, research professor of nutrition, and Terry Van Dyke, professor of biochemistry and biophysics, directed the studies.
"We believe this work is important because it may make cancer treatments more effective," Salganik said. "It suggests that cancer patients, especially those undergoing chemotherapy or radiation therapy, may do better on an antioxidant-depleted diet."
The scientist and his colleagues study reactive oxygen species (ROS), which play a central role in the series of signals that allow cells to kill bacteria and viruses, destroy toxins and trigger the apototic "suicide" of defective cells such as cancer, he said. Antioxidants, such as vitamins A and E, protect normal cells from the damaging effects of ROS but apparently also can prevent the targeted apoptotic death of cancer cells that threaten humans and other mammals, the new work suggests.
Other researchers involved were Drs. Craig D. Albright, research assistant professor of nutrition; and Steven H. Zeisel, professor of nutrition and pediatrics and chair of nutrition.
The UNC-CH experiments involved putting mice that were predisposed to developing brain tumors on specially modified diets that were either supplemented with standard amounts of antioxidants or were antioxidant deficient for four months. Researchers then carefully monitored the rodents' health and their brain tumors, if any, to see how the animals fared on the different diets.
Mice receiving extra vitamins A and E showed no benefit in either the size or incidence of brain tumors, Salganik said. They also had relatively short lives.
"Interestingly and more importantly, in animals that received antioxidant-depleted diets, brain tumors were significantly reduced in size because of induction of oxidant stress due to what are commonly called free radicals in the brain tumors," Albright said. "Higher levels of cell death was restricted only to the brain tumors, while normal tissues were not affected by depletion of antioxidants in the mouse diets."
In mice getting low levels of vitamins A and E, no negative effects were seen in normal cells, but about 19 percent of tumor cells showed evidence of apoptosis. In those ingesting normal quantities of antioxidant vitamins, only about 3 percent of tumor cells were apototic.
The group's findings may explain two previous clinical studies showing that heavy smokers who ate a diet high in beta-carotene antioxidants had significantly higher rates of lung cancer, Salganik said.
"These new studies raise important issues regarding the advisability of ingesting high levels of antioxidants as a potential anti-cancer benefit," Albright said. "Clearly, more studies are needed at the clinical level in human populations to address the real value of antioxidant supplements or antioxidant depletion in people at risk of developing cancer."
Salganik said he hoped clinical studies would begin within a year or two. Van Dyke is a member of the UNC Lineberger Comprehensive Cancer Center.
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