Sorting out cancer IQs in browned meat.

The same chemical reaction that imparts a desirable flavor to browned meats also produces a host of powerful mutagens know as heterocyclic amines (HCAs). In animals, researchers have linked these food-borne mutagens -- especially one known as IQ -- to an increased risk of cancers in the colon and other organs. However, a central question remained: How does IQ foster such cancers, since no HCA is carcinogenic without first being metabolized, or transformed -- either by intestinal bacteria or mammalian cells.

A new study now all but exonerates what for some six years had been the leading suspect behind cooked meat's colon-cancer risk: 7-OHIQ -- a bacterially derived metabolite of IQ.

Commonly found in feces, 7-OHIQ was identified during the 1980s as a direct-acting mutagen in the Ames test, a bacterial assay used to screen for potential carciongens. However, bacteria lack some DNA-repair mechanisms that mammals possess to detoxify certain mutagens, explains John H. Weisburger of the American Health Foundation (AHF) in Valhalla, N.Y. So his new studies investigated 7-OHIQ not only in an assay using rat-liver cells, but also in chronic feeding tests with rats and mice.

In the Jan. 5 JOURNAL OF THE NATIONAL CANCER INSTITUTE (JNCI), Weisburger's team reports that the additional tests demonstrate beyond a reasonable doubt that 7-OHIQ "is not carcinogenic, in marked contrast to IQ."

The new studies suggest gut bacteria pay little if any important role in the carcinogenic transformation of IQ or related HCA's, according to an accompanying editorial in JNCI by Fred F. Kadlubar of the National Center for Toxicological Research in Jefferson, Ark.

In a second JNCI editorial, a trio of researchers at Japan's National Cancer Center in Tokyo argue that "it is time to shift to a strategy of cancer prevention and accept that human carcinogenesis is largely due to an accumulation of many kinds of carcinogenic factors, each of which in itself may have little impact." Toward that end, these scientists recommend that people avoid over-cooking meat and fish and that they remove any HCA-rich char that forms during cooking.

However, aficionados of char-broiled meats may one day be able to dine on such fare with relative impunity. Weisburger has identified a combination of amino acids that, when spread on meat prior to cooking, prevents the formation of HCAs (SN:2/15/92, p.104). Though he holds a patent for this, Weisburger says, "I've been too involved in other work yet to [commercialize] the patent."

In the Sept. 1, 1993 CANCER RESEARCH, AHF researchers reported another tack in fighting HCAs. Their preliminary data show that in male rats fed low doses of IQ for four years, supplementing the diet with a bacterium prevented colon cancer in all animals, inhibited small-intestine tumors in 80 percent, and suppressed liver tumors in almost 40 percent. Data from female rats suggest the bacterial supplement also may cut the incidence of IQ-related breast cancers.

Bandaru S. Reddy of AHF says European and Japanses manufacturers already add this bacterium, Bifidobacteium longum, to yogurt and some soft drinks. He suspects B. longum's IQ-shielding effects may trace to its ability to suppress certain other bacteria -- such as E. coli -- from transforming bile acids (which the body uses to absorb fats) into "secondary" acids. "Secondary bile acids are strong promoters of colon tumors," Reddy notes.

Finally, Weisburger says preliminary data from his lab indicate that tea or extracts from it may reduce the mutagenicity of IQ.