Seeds and Prostate Cancer

[Guest guest]

Online paper in Proceedings of the National Academy of Sciences:

http://www.pnas.org/papbyrecent.shtml

December 14, 2004

Purdue University

The form of vitamin E found in many plant seeds - but not in most

manufactured nutritional supplements - might halt the growth of

prostate and lung cancer cells, according to a Purdue University

study.

A team led by Qing Jiang (pronounced " ching zhang " ) has found that

gamma-tocopherol, which occurs naturally in walnuts, pecans, sesame

seeds, and in corn and sesame oils, inhibits the proliferation of

lab-cultured human prostate and lung cancer cells. The vitamin's

presence interrupts the synthesis of certain fatty molecules called

sphingolipids, important components of cell membranes. However, the

gamma-tocopherol leaves healthy human prostate cells unaffected,

which could give it value as an anticancer agent.

" This is the first time gamma-tocopherol has been shown to induce

death in lab-grown human cancer cells while leaving healthy cells

alone, " said Jiang, who is an assistant professor of foods and

nutrition in the College of Consumer and Family Sciences. " This

could be wonderful news for cancer patients if the effect can be

reproduced in animal models. But because most nutritional

supplements contain only alpha-tocopherol, a different form of

vitamin E that alone does not have these anticancer properties, it

may be better to supplement the diet with mixed forms of vitamin E.

The study shows that the anticancer effect is enhanced when mixed

forms are used. "

Jiang's research appears in the current (week of Dec. 13) online

edition of the scientific journal Proceedings of the National

Academy of Sciences. She co-authored the paper with Wong,

Henrik Fyrst, D. Saba and Bruce N. Ames of the Children's

Hospital Oakland Research Institute in Oakland, Calif.

Scientists have been studying vitamin E for more than three-quarters

of a century, but most efforts have focused largely on alpha-

tocopherol, one of eight known forms in the vitamin's family. Alpha-

tocopherol was found early on to have the most beneficial effects on

laboratory animals fed diets deficient in vitamin E, and also is the

major form found in body tissues. For these reasons, it has been

nearly the only form of the vitamin to be included in most

manufactured nutritional supplements.

" Since then, alpha-tocopherol has justifiably earned a good

reputation as an antioxidant, which helps to fight against damage

caused by unwanted free radicals, " Jiang said. " But its familiarity

has perhaps attracted research away from the other seven forms of

vitamin E, and since gamma-tocopherol is the vitamin's most commonly

occurring natural form in the American diet, I grew interested in it

a few years ago. "

In 2000 another study by Jiang and colleagues found that gamma-

tocopherol inhibits inflammation, which had already been implicated

in cancer development. They theorized that it might retard the

progress of cancer and cardiovascular disease, and to test their

hypothesis they exposed cultures of cancerous prostate and lung

cells to the vitamin. Normal prostate epithelial cells were used as

a control group.

" We discovered that as we increased the quantity of gamma-

tocopherol, the cancer cells grew more slowly, " Jiang said. " But the

normal prostate cells were not affected and grew normally. This

could indicate that the vitamin could be used to target lung and

prostate cancer cells without the damaging side effects of

chemotherapy. "

The study also revealed that gamma-tocopherol caused cell death by

interrupting sphingolipid synthesis.

" This is also a novel discovery, " Jiang said. " Although there have

been prior indications that some form of vitamin E may cause cell

death in some mouse cell lines, we are the first to provide a

mechanism for such an effect. "

Gamma-tocopherol, though rarely available in vitamin pills, is

nevertheless found in abundance in the typical American diet. Many

nuts are rich in it, including walnuts and pecans, as are cooking

oils such as corn and sesame oil.

Though Jiang said she would be cautious about using food sources to

slow prostate or lung cancer's progress in humans, she said that

high-risk groups such as older men could benefit from

supplementation - if carried out with prudence.

" Foods rich in gamma-tocopherol are also rich in fats, and some

products bring other hazards as well, " she said. " Corn oil, for

example, is rich in linolic acid, which has been shown to promote

certain types of cancer in some studies. But sesame seeds and pecans

seem to be good all-around choices. "

Jiang said the next step for her research team would be testing the

effect of gamma-tocopherol and mixed forms of vitamin E on animal

cancers.

" Although this discovery is promising, we do not yet know whether

gamma-tocopherol has any effect on cancer in living creatures, " she

said. " We hope that future research not only will clarify whether

gamma-tocopherol could have applications in human cancer treatment,

but also will show how we might supplement the body with the vitamin

to prevent cancer from developing in the first place. These

questions will continue to direct our work. "

This research was funded in part by the National Institutes of

Health.