Level of selenium-containing proteins in the body instrumental in preventing cancer

Selenium, an essential dietary mineral that can act as an antioxidant when incorporated into proteins, has been shown in many studies to reduce the incidence of cancers -- notably lung, colorectal and prostate.

"The problem is, nobody seems to know how the mechanism works, and that's not trivial," said Alan Diamond, professor of human nutrition at the University of Illinois at Chicago and principal investigator in an ongoing multidisciplinary study set up at UIC to help answer that question.

"Knowing how it works allows you to maximize-out its benefits," he said.

Diamond and his colleagues report in the May 23 issue of the Proceedings of the National Academy of Sciences on research findings using specially bred transgenic mice that suggest it is the level of selenium-containing proteins in the body that is instrumental in preventing cancer, and that dietary selenium plays a role in stimulating the body's level of these selenoproteins.

Two genetically manipulated mice were mated. One was prone to developing prostate cancer. The other had lower levels of selenoproteins. Approximately 50 offspring that carried both traits were studied to see if the reduced levels of selenoproteins accelerated cancer development. As the researchers suspected, it did.

"It's a hardcore link in an animal model system of selenium-containing proteins to prostate cancer and, by extrapolation, the mechanism by which selenium prevents cancer," said Diamond.

Further research is underway to corroborate the stimulating effect of dietary selenium in enhancing levels of protective selenoproteins. Diamond added that much work remains to be done to discover exactly how selenoproteins play their protective role, and in whom.

At least 25 different selenoproteins have been found in the human body. But what role each plays is not known, nor is it known if certain persons are genetically more -- or less -- receptive to the benefits of these proteins, or to a selenium supplement, Diamond said.

The effectiveness of selenium may be due to its effects on a single selenoprotein, or combinations of several members of this class. One selenoprotein in particular, glutathione peroxidase, is of special interest to Diamond and his associates. They plan to run new tests using new mice genetically modified to reduce levels of just this one selenoprotein.

"If reductions result in accelerated prostate cancer, then we have our player," he said.

Other UIC faculty participating in the study include Veda Diwadkar-Navsariwala, post-doctoral researcher in human nutrition; Gain Prins, professor of urology; Steven Swanson, associate professor of medicinal chemistry and pharmacognosy; Lynn Birch, research specialist in urology; Vera Ray, clinical assistant professor of pathology; Sadam Hedayat, distinguished professor of statistics; and Daniel Lantvit, research specialist in pharmaceutical sciences.