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United States Department of Agriculture

Agricultural Research Service

2007 Annual Report

1a.Objectives (from AD-416)
LAB:Vitamins and Carcinogenesis To determine the complex roles the 'one-carbon nutrients', (methionine, choline and the B-vitamins, folate, B12, B6, and B2), as well as components of the diet that are one-carbon antagonists (such as alcohol) play in modifying metabolic and genetic pathways that lead to human cancer.

To define how the mechanistic knowledge acquired through objective #1 should be used to modify dietary habits, nutritional supplementation, and other nutritional interventions in order to prevent cancer. New advances made by this laboratory can thus be translated into public health initiatives that effectively reduce the burden of cancer in our society.

1b.Approach (from AD-416)
LAB:Vitamins and Carcinogenesis Mechanistic questions will largely be examined in studies utilizing cell cultures and animal models. We have several cell lines derived from normal human colonic epithelial cells. The availability of one-carbon nutrients for these cells can easily be manipulated to examine the consequences of limited, or supplemental levels of nutrient availability. A variety of mouse models will also be used to examine the consequences of limited nutrient availability, including genetically engineered animals who either have a predisposition towards colon cancer or a polymorphism in a folate-dependent enzyme. Studies conducted in human volunteers, in which they undergo folate depletion for several weeks, will also be used to examine mechanistic questions, whereas intervention trials, where people at enhanced risk of colon cancer are randomly chosen to receive folate or placebo, will be used to translate this mechanistic work into answers regarding the possible utility of folate in the prevention of cancer.

1) Folic Acid Fortification and National Rates of Colorectal Cancer (CRC). We examined the national cancer databases for the U.S. and Canada and observed a temporal association between a rise in CRC rates and the institution of folic acid fortification. Fortification of enriched uncooked cereal grains with folic acid began in the United States and Canada in 1996 and 1997, respectively, and became mandatory in 1998. Concurrently, the United States and Canada experienced abrupt reversals of the downward trend in colorectal cancer (CRC) incidence that the two countries had enjoyed in the preceding decade: absolute rates of CRC began to increase in 1996 (United States) and 1998 (Canada), peaked in 1998 (United States) and 2000 (Canada), and have continued to exceed the pre-1996/1997 trends by 4 to 6 additional cases per 100,000 individuals. The statistically significant increase in rates is also evident when the data for each country are analyzed separately for men and women. Changes in the rate of colorectal endoscopic procedures do not seem to account for this increase in CRC incidence. Our observations alone do not prove causality but are consistent with the known effects of folate on existing neoplasms, as shown in both preclinical and clinical studies. We therefore hypothesize that the institution of folic acid fortification may have been wholly or partly responsible for the observed increase in CRC rates in the mid-1990s. Using nationally-representative data, this study raises a genuine concern about the safety of nationwide folic acid fortification. Our observations should be taken into account in future deliberations by countries that are considering the institution or enhancement of national folic acid fortification programs. This work is aligned with National Program 107 Human Nutrition Component 4 Nutrient Requirements.

2) Age and folate status as co-determinants of p16 expression in the mouse colon. The mechanisms by which elder age and inadequate dietary folate enhance the risk of colorectal cancer (CRC) are unknown. This study was designed to determine the effects of aging and dietary folate on select features of DNA methylation in the colon that are relevant to carcinogenesis. Old and young male mice were randomly divided into 3 groups and fed diets containing 0, 4.5, or 18 micromoles folate/kg (deplete, replete, and supplemented groups, respectively) for 20 wk. Old mice had significantly lower genomic DNA methylation compared with young mice at each level of dietary folate and markedly higher p16 promoter methylation. In old mice, genomic and p16 promoter DNA methylation each increased in a manner that was directly related to dietary folate. Age-related enhancement of p16 expression occurred in folate-replete and folate-supplemented groups, but not in the folate-deplete group. In conclusion, aging decreases genomic DNA methylation and increases promoter methylation and expression of p16 in mouse colons. This effect is dependent on the level of dietary folate. Our observations are important since they provide insight into how the interactions between elder age and folate status determine the risk of developing colon cancer: such a mechanistic understanding is important if we are to intelligently design public health measures that effectively and safely use nutrients such as folate in the prevention of cancer. This work is aligned with National Program 107 Human Nutrition Component 6-Prevention of Obesity and Disease: Relationship between Diet, Genetics, and Lifestyle.

5.Significant Activities that Support Special Target Populations

6.Technology Transfer

Number of non-peer reviewed presentations and proceedings8
Number of newspaper articles and other presentations for non-science audiences6

Last Modified: 7/27/2016
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