By Sean Henahan, Access Excellence

ATLANTA - A compound isolated from garlic has shown potent anti-tumor effects in preliminary studies, reported researchers at Experimental Biology '95, a meeting of 18 scientific societies.

The compound, known as diallyl disulfide (DADS), caused tumors of human colon cancer cells transplanted into mice to shrink and die, reported Sujatha Sundaram, a researcher at Penn State University.

In the study, mice with transplanted tumor cells from human colon cancer were treated with 1 milligram of DADS dissolved in corn oil three times a week for three weeks. The treatment shrunk tumors started by the cells by 60 percent. In contrast, similar tumors grew steadily in mice treated with just corn oil.

The researchers attribute the anti-tumor effect of DADS to its ability to alter cancer-cell sulfur compounds linked to cell division. This change in mineral balance likely contributes to a shutdown of cell growth, notes Dr. John Milner, head of the department of nutrition at Penn State University.

The current findings follow previous in vitro research by Sundaram and Milner indicating that DADS killed tumor cells of human colon, lung and skin cancers. The finding adds to a growing body of evidence that garlic can suppress human cancer cells in lab cultures and in test animals.

"Our latest study confirms these earlier observations about DADS and related, oil-soluble compounds in garlic. We extended use of DADS from lab cultures to animals and it still suppressed tumors. There is epidemiological evidence that links garlic consumption with a lower risk of colon cancer," he said. "Our latest studies support these findings," said Milner.

In another presentation at the conference, Milner and colleagues described how a water-soluble substance in processed garlic, S-allylcysteine (SAC), inhibited both a carcinogen's binding to rat breast cells and the incidence of breast tumors in rats. This is the second carcinogen that Milner has shown is inhibited from binding to rat breast cells by SAC.

"Our body of research indicates that more than one mechanism exists by which garlic compounds can inhibit either carcinogen-induced tumors or cancer cell growth," Milner said.

Garlic, a mainstay of folk medicine, is gaining increasing respect from the medical research community. A series of recent studies in human volunteers showed that other compounds extracted from garlic had significant effects on both elevated cholesterol levels and high blood pressure.

Current research suggests that these cardiovascular effects are primarily associated with a component of garlic called alliin, and its by products. Several studies have shown that garlic inhibits HMG-CoA reductase, an enzyme associated with cholesterol production in the liver. In this way garlic resembles the "statin" anti-cholesterol drugs such as lovastatin, which also inhibit HMG-CoA reductase.

Researchers hypothesize that the blood pressure lowering effects of garlic have to do with its effects within the circulatory system. Preliminary research indicates that compounds in garlic influence calcium dependent processes, such as platelet aggregation, lysosomal enzyme release and maintenance of vascular muscle tone.

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