There is a significant body of epidemiological evidence linking intake of certain vegetables with decreased risk of several cancers (1, 2). Garlic (Allium sativum L.) is a vegetable for which consumption has been associated with prevention of breast, colorectal, lung, liver, and stomach cancers (3, 4). The anticarcinogenic potential of garlic is most likely derived from organosulfur compounds, and is further influenced by oligosaccharides, flavonoids, arginine, and selenium (4). The major organosulfur compounds in undisturbed garlic bulbs are γ-glutamyl-S-alk(en)yl-L-cysteines and S-alk(en)yl-L-cysteine sulfoxides (predominantly alliin (S-allylcysteine sulfoxide)). When garlic tissue is crushed, the endogenous enzyme alliinase catalyzes the degradation of alliin to alkyl alkane-thiosulfinates, including allicin, which provide garlic with its distinctive odor. Allicin is unstable, and decomposes to sulfides, ajoene, and dithiins. E-Ajoene, Z-ajoene, allicin, allixin, allyl mercaptan, allyl methyl sulfide, diallyl disulfide, diallyl sulfide, diallyl trisulfide, S-allyl cysteine, and S-allylmercaptocysteine are among the sulfur compounds in garlic that have been reported to have anticarcinogenic and/or antitumorigenic properties (5). Investigations using chemically induced carcinogen models indicate that water- and lipid-soluble allyl sulfur compounds are similarly suppressive, but that tumor proliferation/apoptosis depends on the allyl sulfur species provided. Preclinical studies have identified several mechanisms by which intake of garlic and its bioactive compounds are anticarcinogenic. These include altering the biotransformation of procarcinogens by influencing phase I and II enzymes, inhibition of nitrosamine formation, stimulation of free radical scavenging, and inhibition of DNA adduct formation (6). In addition, antitumorigenic activity of garlic may result from immune system potentiation (7). Although preclinical studies provide compelling evidence for garlic's role in cancer prevention, controlled clinical trials are lacking. The importance of genetic variability in determining response to dietary treatments is becoming increasingly recognized. For example, a single nucleotide polymorphism in the gene that encodes for superoxide dismutase influences the ability of diet to reduce breast cancer risk. Genetic variations in the genes that encode for glutathione S-transferase enzymes influence the potential protective effects of Brassica vegetables on cancer risk. Thus, genotyping of clinical study volunteers strengthens study design and the ability to draw conclusions from study results. The purpose of this agreement is to characterize the biological response to dietary exposure to the naturally occurring organosulfur compounds in garlic. Specifically, the proposed studies will compare the availability and metabolism of organosulfur compounds from different garlic preparations, and contrast the responses to these sources in terms of ability to reduce DNA damage and to monitor genetic and proteomic expression changes resulting from chronic and acute exposures. IV. Statement of Work To conduct a series of phase I studies involving double-blind intervention with naturally occurring constituents of garlic. Briefly the protocol will involve the following components: Subject Recruitment: Healthy men and women will be recruited by the Beltsville Human Nutrition Research Center from individuals residing in the surrounding community. Each prospective volunteer will sign an informed consent and be evaluated for eligibility on the basis of a physical examination, standard clinical chemistries, and health and diet histories. Treatment: Subjects will be assigned randomly to treatments consisting of varying amounts of garlic selected for homogeneity of organosulfur compound concentration. The exposure range will be limited to intakes that are within typical dietary exposures worldwide. All preparations will be administered daily as foods, either as the intact food item or an extract incorporated into a food matrix. Subjects will receive that assigned dietary regiment for up to 60 days. Endpoints: Blood and urine samples will be collected from subjects before and after each dietary intervention. These samples will be analyzed for biomarkers of cancer risk, such as factors reflecting DNA damage, markers of inflammation, and activity of drug metabolizing enzymes. Measurements may include (but will not be limited to) 8-OH-deoxyguanosine, lymphocyte DNA damage (COMET), F2-isoprostanes, interleukin 6, C-reactive protein, and other markers of cancer risk. Publication of Results: The results will be published in the open, peer-reviewed scientific literature. Authorship will be consistent with the policies of both agencies;it is anticipated that authorship will reflect the contributions of Drs. Clevidence and Milner as well as their collaborating colleagues involved with these undertakings.
