A Villin-Driven Fxr Transgene Modulates Enterohepatic Bile Acid Homeostasis and Response to an n-6-Enriched High-Fat Diet.

A diet high in n-6 polyunsaturated fatty acids (PUFAs) may contribute to inflammation and tissue damage associated with obesity and pathologies of the colon and liver. One contributing factor may be dysregulation by n-6 fatty acids of enterohepatic bile acid (BA) metabolism. The farnesoid X receptor (FXR) is a nuclear receptor that regulates BA homeostasis in the liver and intestine. This study aims to compare the effects on FXR regulation and BA metabolism of a palm oil-based diet providing 28% energy (28%E) from fat and low n-6 linoleic acid (LA, 2.5%E) (CNTL) with those of a soybean oil-based diet providing 50%E from fat and high (28%E) in LA (n-6HFD). Wild-type (WT) littermates and a transgenic mouse line overexpressing the Fxrα1 isoform under the control of the intestine-specific Villin promoter (Fxrα1TG) were fed the CNTL or n-6HFD starting at weaning through 16 weeks of age. Compared to the CNTL diet, the n-6HFD supports higher weight gain in both WT and FxrαTG littermates; increases the expression of Fxrα1/2, and peroxisome proliferator-activated receptor-γ1 (Pparγ1) in the small intestine, Fxrα1/2 in the colon, and cytochrome P4507A1 (Cyp7a1) and small heterodimer protein (Shp) in the liver; and augments the levels of total BA in the liver, and primary chenodeoxycholic (CDCA), cholic (CA), and ß-muricholic (ßMCA) acid in the cecum. Intestinal overexpression of the Fxra1TG augments expression of Shp and ileal bile acid-binding protein (Ibabp) in the small intestine and Ibabp in the proximal colon. Conversely, it antagonizes n-6HFD-dependent accumulation of intestinal and hepatic CDCA and CA; hepatic levels of Cyp7a1; and expression of Pparγ in the small intestine. We conclude that intestinal Fxrα1 overexpression represses hepatic de novo BA synthesis and protects against n-6HFD-induced accumulation of human-specific primary bile acids in the cecum.

n-6 Linoleic Acid Induces Epigenetics Alterations Associated with Colonic Inflammation and Cancer.

The farnesoid-X-receptor (FXR) protects against inflammation and cancer of the colon through maintenance of intestinal bile acid (BA) homeostasis. Conversely, higher levels of BA and cyclooxygenase-2 (COX-2) are risk factors for inflammation and cancer of the colon. In the United States, n-6 linoleic acid (LA) is the most commonly used dietary vegetable fat. Metabolism of n-6 fatty acids has been linked to a higher risk of intestinal cancer. The objectives of this study were to investigate in colonic mucosa the effects of a high-fat diet rich in LA (n-6HFD) on CpG methylation of Fxr and prostaglandin-endoperoxide synthase-2 (Ptsg-2) genes, and the impact on the expression of tumor suppressor adenomatous polyposis Coli (Apc) and proliferative cyclin D1 (Ccnd1) genes. Weaned C57BL/6J male mice were fed for 6 weeks either an n-6HFD containing 44% energy (44%E) from 22% safflower oil (SO, 76% LA by weight) or a 13% energy (13%E) control diet (Control) from SO (5% by weight). Mice fed the n-6HFD had reduced (60%) Fxr promoter CpG methylation and increased (~50%) Fxr mRNA. The expression of FXR-target ileal bile acid-binding protein (Ibabp), small heterodimer protein (Shp), and anti-inflammatory peroxisome proliferator-activated-γ1 genes was increased. The n-6HFD reduced Ptgs-2 CpG methylation, increased the expression of Cox-2, and increased Apc CpG methylation in colonic mucosa. Accordingly, reduced expression of Apc was coupled to accumulation of c-JUN and Ccnd1, respectively cofactor and gene targets for the ß-catenin/Wnt signaling pathway. Finally, the n-6HFD reduced the expression of histone deacetylase-1 while favoring the accumulation of acetylated histone 3. We conclude that an n-6HFD epigenetically modifies Fxr, leading to the activation of downstream factors that participate in BA homeostasis. However, epigenetic activation of Ptsg-2 coupled with silencing of Apc and accumulation of C-JUN and Ccnd1 may increase the risk of inflammation and cancer of the colon.

Mediterranean Diet: Prevention of Colorectal Cancer.

Colorectal cancer (CRC) is the third most common cancer diagnosis and the second and third leading cause of cancer mortality in men and women, respectively. However, the majority of CRC cases are the result of sporadic tumorigenesis via the adenoma-carcinoma sequence. This process can take up to 20 years, suggesting an important window of opportunity exists for prevention such as switching toward healthier dietary patterns. The Mediterranean diet (MD) is a dietary pattern associated with various health benefits including protection against cardiovascular disease, diabetes, obesity, and various cancers. In this article, we review publications available in the PubMed database within the last 10 years that report on the impact of a MD eating pattern on prevention of CRC. To assist the reader with interpretation of the results and discussion, we first introduce indexes and scoring systems commonly used to experimentally determine adherence to a MD, followed by a brief introduction of the influence of the MD pattern on inflammatory bowel disease, which predisposes to CRC. Finally, we discuss key biological mechanisms through which specific bioactive food components commonly present in the MD are proposed to prevent or delay the development of CRC. We close with a discussion of future research frontiers in CRC prevention with particular reference to the role of epigenetic mechanisms and microbiome related to the MD eating pattern.

Genistein Prevents BRCA1 CpG Methylation and Proliferation in Human Breast Cancer Cells with Activated Aromatic Hydrocarbon Receptor.

Background: Previous studies have suggested a causative role for agonists of the aromatic hydrocarbon receptor (AhR) in the etiology of breast cancer 1, early-onset (BRCA-1)-silenced breast tumors, for which prospects for treatment remain poor. Objectives: We investigated the regulation of BRCA1 by the soy isoflavone genistein (GEN) in human estrogen receptor α (ERα)-positive Michigan Cancer Foundation-7 (MCF-7) and ERα-negative sporadic University of Arizona Cell Culture-3199 (UACC-3199) breast cancer cells, respectively, with inducible and constitutively active AhR. Methods: In MCF-7 cells, we analyzed the dose- and time-dependent effects of GEN and (-)-epigallocatechin-3-gallate (EGCG) control, selected as prototype dietary DNA methyltransferase (DNMT) inhibitors, on BRCA-1 expression after AhR activation with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and in TCDD-washout experiments. We compared the effects of GEN and EGCG on BRCA1 cytosine-phosphate-guanine (CpG) methylation and cell proliferation. Controls for DNA methylation and proliferation were changes in expression of DNMT-1, cyclin D1, and p53, respectively. In UACC-3199 cells, we compared the effects of GEN and α-naphthoflavone (αNF; 7,8-benzoflavone), a synthetic flavone and AhR antagonist, on BRCA1 expression and CpG methylation, cyclin D1, and cell growth. Finally, we examined the effects of GEN and αNF on BRCA1, AhR-inducible cytochrome P450 (CYP)-1A1 (CYP1A1) and CYP1B1, and AhR mRNA expression. Results: In MCF-7 cells, GEN exerted dose- and time-dependent preventative effects against TCDD-dependent downregulation of BRCA-1. After TCDD washout, GEN rescued BRCA-1 protein expression while reducing DNMT-1 and cyclin D1. GEN and EGCG reduced BRCA1 CpG methylation and cell proliferation associated with increased p53. In UACC-3199 cells, GEN reduced BRCA1 and estrogen receptor-1 (ESR1) CpG methylation, cyclin D1, and cell growth while inducing BRCA-1 and CYP1A1. Conclusions: Results suggest preventative effects for GEN and EGCG against BRCA1 CpG methylation and downregulation in ERα-positive breast cancer cells with activated AhR. GEN and flavone antagonists of AhR may be useful for reactivation of BRCA1 and ERα via CpG demethylation in ERα-negative breast cancer cells harboring constitutively active AhR.

Inactivation of Adenomatous Polyposis Coli Reduces Bile Acid/Farnesoid X Receptor Expression through Fxr gene CpG Methylation in Mouse Colon Tumors and Human Colon Cancer Cells.

BACKGROUND: The farnesoid X receptor (FXR) regulates bile acid (BA) metabolism and possesses tumor suppressor functions. FXR expression is reduced in colorectal tumors of subjects carrying inactivated adenomatous polyposis coli (APC). Identifying the mechanisms responsible for this reduction may offer new molecular targets for colon cancer prevention. OBJECTIVE: We investigated how APC inactivation influences the regulation of FXR expression in colonic mucosal cells. We hypothesized that APC inactivation would epigenetically repress nuclear receptor subfamily 1, group H, member 4 (FXR gene name) expression through increased CpG methylation. METHODS: Normal proximal colonic mucosa and normal-appearing adjacent colonic mucosa and colon tumors were collected from wild-type C57BL/6J and Apc-deficient (Apc(Min) (/+)) male mice, respectively. The expression of Fxr, ileal bile acid-binding protein (Ibabp), small heterodimer partner (Shp), and cyclooxygenase-2 (Cox-2) were determined by real-time polymerase chain reaction. In both normal and adjacent colonic mucosa and colon tumors, we measured CpG methylation of Fxr in bisulfonated genomic DNA. In vitro, we measured the impact of APC inactivation and deoxycholic acid (DCA) treatment on FXR expression in human colon cancer HCT-116 cells transfected with silencing RNA for APC and HT-29 cells carrying inactivated APC. RESULTS: In Apc(Min) (/+) mice, constitutive CpG methylation of the Fxrα3/4 promoter was linked to reduced (60-90%) baseline Fxr, Ibabp, and Shp and increased Cox-2 expression in apparently normal adjacent mucosa and colon tumors. Apc knockdown in HCT-116 cells increased cellular myelocytomatosis (c-MYC) and lowered (∼50%) FXR expression, which was further reduced (∼80%) by DCA. In human HCT-116 but not HT-29 colon cancer cells, DCA induced FXR expression and lowered CpG methylation of FXR. CONCLUSIONS: We conclude that the loss of APC function favors the silencing of FXR expression through CpG hypermethylation in mouse colonic mucosa and human colon cells, leading to reduced expression of downstream targets (SHP, IBABP) involved in BA homeostasis while increasing the expression of factors (COX-2, c-MYC) that contribute to inflammation and colon cancer.