2008 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.
To define the biochemical, molecular and pathophysiologic processes that underlie the apparent effects of vitamin D and calcium in the modulation of cancer development, and to examine how genetic background and environmental factors further impact these effects.
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.
All of our work in the past year has focused on how availability of 1-carbon nutrients, in conjunction with select genetic and environmental factors, modulate the risk of common cancers. This is directly relevant to NP 107 Action Plan, Component 6, Prevention of Obesity and Disease: Relationship between diet, genetics and lifestyle, as well as Component 7, Health promoting properties of plant and animal foods.
We completed a study which demonstrates that a combined mild deficiency state of vitamins B2, B6, B12 and folate amplifies multiple components of the Wnt-signaling pathway in the colon in a manner that is conducive to carcinogenesis, and that the effects are greatly magnified compared to those effects observed with single deficiency states. A second original research publication similarly demonstrated a synergistic effect of the multiple deficiency state on the p53 cell-signaling pathway. We have successfully begun breeding colony mice that are genetically-engineered to enable us to examine more detailed aspects of the enhancement of Wnt signaling.
We completed a pilot study demonstrating that select polymorphisms in uracil-processing enzymes are associated with a substantial increase in the amount of uracil that is incorporated into the DNA of human subjects. We completed another epidemiologic study demonstrating that several newly identified polymorphisms in a variety of folate-dependent enzymes are associated with significant differences in plasma folate and homocysteine levels.
We have completed the creation of a novel mouse strain that has a critical folate-dependent enzyme, MTHFR, ‘knocked-out’ of its genome. This will enable us to define the cellular mechanisms that explain how common variants in this enzyme in the human population greatly modify the risk of colorectal cancer.
We completed a study which demonstrates that higher levels of genomic DNA methylation in human blood DNA predict a decreased risk of colorectal adenomas. Moreover, high levels of folate intake did not further increase the level of DNA methylation.
We successfully created a genetic construct that we plan to use in the conduct of mechanistic studies that are designed to examine the dietary determinants of cellular transformation in a nude mouse model. The construct, when inserted into mouse colonocytes, will enable them to become an immortalized cell line and one whose clones will fluoresce, enabling their detection in vivo.
We have completed a rodent study that is designed to examine how excessive alcohol consumption interacts with dietary folate inadequacy to enhance colorectal carcinogenesis and we are presently analyzing the results of the study.
Role of Genomic methylation of leukocyte DNA in relation to colorectal adenoma among asymptomatic women.
There is very little understanding about systemic defects in DNA which predispose people to the development of pre-cancerous polyps in the colon. We completed a study which demonstrates that higher levels of “DNA methylation” in human blood (an intrinsic feature of DNA which varies in amount between individuals) predict a decreased risk of pre-cancerous polyps of the colon in women. Moreover, high levels of folate intake did not further increase the level of DNA methylation. By identifying features of blood DNA that predict the risk of polyp development, future investigations might exploit this as a screening tool for cancer. Further, this study begins to define those dietary factors that might modify the risk of developing cancer and might impact on the utility of this potential screening tool. NP107, Component 6, Prevention of Obesity and Disease: Relationship between Diet, Genetics, and Lifestyle.
Development of a novel mouse strain that lacks a critical folate dependent enzyme, methylenetetrahydrofolate reductase (MTHFR).
A common variant of the MTHFR enzyme in humans markedly reduces the likelihood of developing colon cancer; an understanding of how this effect is mediated would enhance our ability to exploit folate as a cancer chemopreventive agent. We completed the creation of a novel mouse strain in which the MTHFR gene has been eliminated. Development of this mouse provides us with an animal model that will enable us to unravel the means by which this enzyme variant protects against cancer, and thereby will contribute to the future use of folate as a cancer chemopreventive agent.
NP107, Component 6, Prevention of Obesity and Disease: Relationship between Diet, Genetics, and Lifestyle.
A diet with mild inadequacies of multiple B-vitamins enhances cellular pathways leading to cancer in the colon.
It is not yet known what cell signaling pathway mediates the effects of 1-carbon nutrients, such as B vitamins, on cancer risk. We completed a study which demonstrates that a combined mild deficiency state of vitamins B2, B6, B12 and folate amplifies multiple components of a biochemical pathway in the cells that line the colon in a manner that promotes carcinogenesis, and that the effects are greatly magnified compared to those effects observed with single deficiency states. We also similarly demonstrated a synergistic effect of the multiple deficiency state on an alternative biochemical pathway, which is consistent with the above since the two pathways possess intersect in several ways. These studies advance our understanding of the mechanisms by which B vitamins modulate cancer risk, a critical foundation upon which public health measures can feasibly be created to help prevent common cancers. NP107, Component 6, Prevention of Obesity and Disease: Relationship between Diet, Genetics, and Lifestyle.
5.Significant Activities that Support Special Target Populations
|Number of Non-Peer Reviewed Presentations and Proceedings||2|
|Number of Newspaper Articles and Other Presentations for Non-Science Audiences||1|
Liu, Z., Choi, S., Crott, J.W., Keyes, M.K., Jang, H., Smith, D., Kim, M., Laird, P.W., Bronson, R., Mason, J.B. 2007. Mild depletion of dietary folate combined with other B-vitamins alters multiple components of the Wnt pathway in the mouse colon. Journal of Nutrition. 137(12):2701-08.
Crott, J.W., Liu, Z., Keyes, M.K., Choi, S., Jang, H., Moyer, M., Mason, J.B. 2008. Moderate folate depletion modulates the expression of selected genes involved in cell cycle, intracellular signaling, and folate uptake in human colonic epithelial cell lines. Journal of Nutritional Biochemistry. 19(5):328-335.
Keyes, M.K., Jang, H., Mason, J.B., Liu, Z., Crott, J., Smith, D., Friso, S., Choi, S. 2007. Older age and dietary folate are determinants of genomic and p16-specific DNA methylation in mouse colon. Journal of Nutrition. 131(7):1713-1717.
Keyes, M.K., Jang, H., Mason, J.B., Liu, Z., Crott, J.W., Smith, D., Friso, S., Choi, S. 2007. Genomic and p16-specific DNA methylation of the mouse colon: elder age and dietary folate as interactive determinants. Journal of Nutrition. 137(7):1713-1717.
Mason, J.B. 2007. Gastrointestinal Cancer: Nutritional Support. In: Kelsen, D.P., Editor. Principles and Practice ofo Gastrointestinal Oncology. 2nd Edition. Lippincott Williams & Wilikins. p. 87-101.
Liu, Z., Choi, S., Crott, J.W., Smith, D., Mason, J.B. 2008. Multiple B-vitamin inadequacy amplifies alterations induced by folate depletion in p53 expression and its downstream effector MDM2. International Journal of Cancer. 123(3):519-525.
Mason, J.B. 2007. Vitamins, Trace Minerals, and Other Micronutrients. In: Goldman, L., Ausiello, D. Cecil Medicine 23rd Edition. Philadelphia, PA: Saunders Elsevier. p.1626-1639.