Revisiting the goldilocks phenomenon: folate and colorectal cancer risk

Folic acid: friend or foe in cancer therapy

Folic acid plays a crucial role in diverse biological processes, notably cell maturation and proliferation. Here, we performed a literature review using articles listed in electronic databases, such as PubMed, Scopus, MEDLINE, and Google Scholar. In this review article, we describe contradictory data regarding the role of folic acid in cancer development and progression. While some studies have confirmed its beneficial effects in diminishing the risk of various cancers, others have reported a potential carcinogenic effect. The current narrative review elucidates these conflicting data by highlighting the possible molecular mechanisms explaining each point of view. Further multicenter molecular and genetic studies, in addition to human randomized clinical trials, are necessary to provide a more comprehensive understanding of the relationship between folic acid and cancer.

Dietary Uridine Decreases Tumorigenesis in the ApcMin/+ Model of Intestinal Cancer

BACKGROUND

Dietary deoxyuridine and uridine have been shown to have opposing effects on neural tube defect (NTD) incidence in the serine hydroxymethyltransferase 1 (Shmt1+/- ) mouse model of folate-responsive NTDs, which are mediated by changes in de novo thymidylate biosynthesis. Alterations in folate-mediated one-carbon metabolism that protect against NTDs increased cancer risk in some studies.

OBJECTIVE

This study examined the effects of the dietary pyrimidine nucleosides uridine, thymidine, or deoxyuridine on intestinal tumorigenesis in the ApcMin/+ mouse model [a mouse model lacking one copy of the adenomatosis polypsis coli (APC) gene] of spontaneous intestinal tumor formation. This study also evaluated the effects of uridine and deoxyuridine in culture medium on antifolate efficacy in Caco-2 and HeLa cell lines.

METHODS

ApcMin/+ male mice (n = 10-14/group) were fed folate-deficient diets containing uridine, thymidine, or deoxyuridine from weaning until 17 wk of age. Total intestinal tumors were analyzed and biomarkers of folate status and metabolism were measured, including plasma folate concentrations, colon uracil content, and SHMT1 concentrations.

RESULTS

ApcMin/+ mice fed dietary uridine showed a 50% reduction in total intestinal tumors, but neither dietary deoxyuridine nor thymidine affected tumorigenesis. Dietary nucleoside supplementation also increased plasma folate concentrations in ApcMin/+ mice, as has been observed in the Shmt1+/- mouse model. Neither uridine nor deoxyuridine in culture media affected antifolate efficacy in either HeLa or Caco-2 cell lines.

CONCLUSIONS

Dietary uridine, which is teratogenic in mice, decreases intestinal tumor formation in the ApcMin/+ mouse model. Dietary uridine mimics the effect of the common methylene tetrahydrofolate reductase (MTHFR) C677T variant in protecting against colorectal cancer, while contributing to the risk of NTDs.

Lifestyle Modifications and Colorectal Cancer

Many studies suggest that Western lifestyle and dietary factors may be responsible for the high incidence of colorectal cancer in industrialized countries. Consumption of high amounts of red and processed meat and low intake of fiber and multiple protective phytochemicals found in fruits, vegetables, and whole grains might be responsible for the high incidence of this neoplasm in the Western world. Additionally, obesity, lack of physical activity, tobacco and alcohol use, sleep deprivation, and other factors have been proven to further increase the risk of colorectal cancer. Identifying and understanding the mechanisms through which they impact colon carcinogenesis is needed for the introduction of protective lifestyle recommendations.

Opposing roles of folate in prostate cancer

The US diet has been fortified with folic acid to prevent neural tube defects since 1998. The Physician Data Queries from the National Cancer Institute describe folate as protective against prostate cancer, whereas its synthetic analog, folic acid, is considered to increase prostate cancer risk when taken at levels easily achievable by eating fortified food or taking over-the-counter supplements. We review the present literature to examine the effects of folate and folic acid on prostate cancer, help interpret previous epidemiologic data, and provide clarification regarding the apparently opposing roles of folate for patients with prostate cancer. A literature search was conducted in Medline to identify studies investigating the effect of nutrition and specifically folate and folic acid on prostate carcinogenesis and progression. In addition, the National Health and Nutrition Examination Survey database was analyzed for trends in serum folate levels before and after mandatory fortification. Folate likely plays a dual role in prostate carcinogenesis. There remains conflicting epidemiologic evidence regarding folate and prostate cancer risk; however, there is growing experimental evidence that higher circulating folate levels can contribute to prostate cancer progression. Further research is needed to clarify these complex relationships.