The Anticancer Effect of Selenium-enriched Ramps
In an earlier newsletter article, I reported on the emergence of selenium as a potent anticancer agent ("Selenium and Cancer: New Views", LPI Newsletter Fall/Winter 1997). Three human studies conducted in China and in the United States have shown that Thanks to a pilot project award from LPI, my colleagues and I have been able to complete an animal study to evaluate the anticancer activity of selenium-enriched ramps (Allium tricoccum), also known as wild leeks. Wild ramps are found in the Appalachian Mountains from northern Georgia to Quebec, Canada, and have a much stronger sulfurous odor than garlic. Since selenium-enriched garlic was shown by other investigators to markedly reduce chemically induced tumors in rats, we wanted to determine if selenium-enriched ramps would have similar effects. Plants that have a high sulfur content incorporate more selenium than other plants, and ramps contain possibly more sulfur than garlic.
In collaboration with Dr. Carl Polan, a colleague at Virginia Polytechnic Institute and State University (Virginia Tech), ramps were transplanted from the wild just as they were coming through the ground and grown in a bed of peat moss and vermiculite containing selenium in the form of selenate, an inorganic selenium salt. The highest amount of selenium (300 milligrams/kilogram) in this growth mixture resulted in ramps with as much as 700 mg of selenium per kg. A level of about 600 mg of selenium per kg was achieved in ramps grown hydroponically with 120 mg of selenium per liter of solution. To get these high levels of selenium in ramps, very high levels had to be used in the growth medium, probably because of the relatively short growing period of these plants. They start to come up around the first of April and are dead by the first of June, whereas garlic, for example, can be grown in selenium-enriched beds for as long as nine months. Ramps are usually harvested near the end of April. For our experiments, young ramps were transplanted to a large bed of the peat moss-vermiculite mixture with selenium. After the plants died at the end of May, the bulbs were harvested. They were then dried, ground, and sent to Dr. Clement Ip at Rowell Park Cancer Center, Buffalo, New York, for the cancer experiment. Rats were given a carcinogen, N-methyl-N-nitrosourea, that produces mammary tumors and fed diets containing ground ramp bulbs or ground ramp bulbs enriched with selenium. While the regular ramp bulb diet had very little effect on tumor incidence, tumor incidence was reduced by 43% in the rats that consumed the selenium-enriched ramps (see figure below). An analysis of rat tissues revealed that selenium did not accumulate as it does when supplemented as selenomethionine (a selenium analog of methionine, an essential sulfur-containing amino acid). This is desirable because it lessens the chance of selenium toxicity.
With the assistance of Dr. Peter Uden at the University of Massachusetts, the ramps were analyzed to determine which selenium compounds were present. Selenate and several organic selenium compoundsSe-DL-cystathionine, Se-methyl-DL-selenocysteine, and glutamyl-Se-methyl-L-selenocysteinewere detected, with Se-methyl-DL-selenocysteine the most abundant. Interestingly, this compound has been shown to be the most effective selenium compound against tumorigenesis in animals. Ramps may produce this compound as a self-defense against the toxicity of selenium. We also showed that the selenium incorporated into ramps was about 15% more bioavailable in rats than inorganic selenium; i.e. it was taken up better from the diet by tissues. Therefore, the strategy of incorporating selenium into vegetables is sound and effective.
Recent results indicate that the leaves of enriched ramps contain about three times as much selenium as the bulbs. Other than selenomethionine, the selenium compounds in the leaves could not be identified, which means that the leaves appear to contain a completely different group of selenium compounds than the bulbs. Our furture work will focus on the identification of these selenium compounds in enriched ramp leaves and on the anticancer effect of the whole plant rather than just the bulbs. This animal experiment confirms the anticancer effect of selenium observed in other studies and provides new information on the types of selenium incorporated into food.
Last updated November, 1999
Honoring a Scientific Giant with Nutritional Research Toward Longer, Better Lives
|Please send any comments, suggestions, or questions about The Linus Pauling Institute to firstname.lastname@example.org|