Role of bile acid secretion in human colorectal cancer

Can a 12-gene expression signature predict the cell transforming potential of tumor promoting agents in Bhas 42 cells?

To date, long-term rodent carcinogenesis assays are the only assays recognized by regulators to assess non-genotoxic carcinogens, but their reliability has been questioned. In vitro cell transformation assays (CTAs) could represent an interesting alternative to animal models as it has the advantage of detecting both genotoxic and non-genotoxic transforming chemicals. Among them, Bhas 42 CTA uses a cell line that has been transfected with the oncogenic sequence v-Ha-ras. This sequence confers an "initiated" status to these cells and makes them particularly sensitive to non-genotoxic agents. In a previous work, transcriptomic analysis revealed that the treatment of Bhas 42 cells with transforming silica (nano)particles and 12-O-tetradecanoylphorbol-13-acetate (TPA) commonly modified the expression of 12 genes involved in cell proliferation and adhesion. In the present study, we assess whether this signature would be the same for four other soluble transforming agents, i.e. mezerein, methylarsonic acid, cholic acid and quercetin. The treatment of Bhas 42 cells for 48 h with mezerein modified the expression of the 12 genes of the signature according to the same profile as that of the TPA. However, methylarsonic acid and cholic acid gave an incomplete signature with changes in the expression of only 7 and 5 genes, respectively. Finally, quercetin treatment induced no change in the expression of all genes but exhibited higher cytotoxicty. These results suggest that among the transforming agents tested, some may share similar mechanisms of action leading to cell transformation while others may activate different additional pathways involved in such cellular process. More transforming and non-transforming agents and gene markers should be tested in order to try to identify a relevant gene signature to predict the transforming potential of non-genotoxic agents.

Vitamin D and Cancer: An Historical Overview of the Epidemiology and Mechanisms

This is a narrative review of the evidence supporting vitamin D's anticancer actions. The first section reviews the findings from ecological studies of cancer with respect to indices of solar radiation, which found a reduced risk of incidence and mortality for approximately 23 types of cancer. Meta-analyses of observational studies reported the inverse correlations of serum 25-hydroxyvitamin D [25(OH)D] with the incidence of 12 types of cancer. Case-control studies with a 25(OH)D concentration measured near the time of cancer diagnosis are stronger than nested case-control and cohort studies as long follow-up times reduce the correlations due to changes in 25(OH)D with time. There is no evidence that undiagnosed cancer reduces 25(OH)D concentrations unless the cancer is at a very advanced stage. Meta-analyses of cancer incidence with respect to dietary intake have had limited success due to the low amount of vitamin D in most diets. An analysis of 25(OH)D-cancer incidence rates suggests that achieving 80 ng/mL vs. 10 ng/mL would reduce cancer incidence rates by 70 ± 10%. Clinical trials have provided limited support for the UVB-vitamin D-cancer hypothesis due to poor design and execution. In recent decades, many experimental studies in cultured cells and animal models have described a wide range of anticancer effects of vitamin D compounds. This paper will review studies showing the inhibition of tumor cell proliferation, dedifferentiation, and invasion together with the sensitization to proapoptotic agents. Moreover, 1,25-(OH)2D3 and other vitamin D receptor agonists modulate the biology of several types of stromal cells such as fibroblasts, endothelial and immune cells in a way that interferes the apparition of metastases. In sum, the available mechanistic data support the global protective action of vitamin D against several important types of cancer.

Access to New Cytotoxic Triterpene and Steroidal Acid-TEMPO Conjugates by Ugi Multicomponent-Reactions

Multicomponent reactions, especially the Ugi-four component reaction (U-4CR), provide powerful protocols to efficiently access compounds having potent biological and pharmacological effects. Thus, a diverse library of betulinic acid (BA), fusidic acid (FA), cholic acid (CA) conjugates with TEMPO (nitroxide) have been prepared using this approach, which also makes them applicable in electron paramagnetic resonance (EPR) spectroscopy. Moreover, convertible amide modified spin-labelled fusidic acid derivatives were selected for post-Ugi modification utilizing a wide range of reaction conditions which kept the paramagnetic center intact. The nitroxide labelled betulinic acid analogue 6 possesses cytotoxic effects towards two investigated cell lines: prostate cancer PC3 (IC₅₀ 7.4 ± 0.7 μM) and colon cancer HT29 (IC₅₀ 9.0 ± 0.4 μM). Notably, spin-labelled fusidic acid derivative 8 acts strongly against these two cancer cell lines (PC3: IC₅₀ 6.0 ± 1.1 μM; HT29: IC₅₀ 7.4 ± 0.6 μM). Additionally, another fusidic acid analogue 9 was also found to be active towards HT29 with IC₅₀ 7.0 ± 0.3 μM (CV). Studies on the mode of action revealed that compound 8 increased the level of caspase-3 significantly which clearly indicates induction of apoptosis by activation of the caspase pathway. Furthermore, the exclusive mitochondria targeting of compound 18 was successfully achieved, since mitochondria are the major source of ROS generation.

Effects and mechanism of the bile acid (farnesoid X) receptor on the Wnt/β-catenin signaling pathway in colon cancer

The downregulation of farnesoid X receptor (FXR; gene name, nuclear receptor subfamily 1 group h member 4), an enteric nuclear bile acid receptor, has been reported in colorectal carcinoma (CRC), and FXR expression has been inversely correlated with CRC stage and clinical outcome. FXR knockdown in chronic colitis mouse models of intestinal tumorigenesis results in early mortality and increased tumor progression via promoting Wnt signaling. The aim of the present study was to explore the effects and mechanism of FXR on the Wnt/β-catenin signal pathway in CRC. FXR and β-catenin protein expression levels were detected in an ulcerative colitis mouse model and human colon cancer cell lines (HT-29, Caco-2 and HCT-116). Gain- and loss-of-function studies were conducted by transfecting colon cancer cells with FXR siRNA and treating them with the FXR agonist GW4064. Subsequently, β-catenin transcriptional activity was measured using the dual-luciferase assay, and β-catenin/TCF4 complex levels and β-catenin protein and mRNA expression levels were determined. FXR and β-catenin expression levels were inversely associated in both the animal model and colon cancer cells. The Wnt signaling pathway was activated by increased β-catenin/TCF4 complex levels upon FXR silencing; however, mRNA and protein levels of β-catenin were not significantly affected. The FXR agonist GW4064 significantly inhibited the proliferation of cells but promoted the transcriptional activity of β-catenin. Thus, the present study demonstrated that FXR influences the Wnt/β-catenin signaling pathway. Furthermore, loss of FXR expression promotes the transcriptional activity of β-catenin, whereas FXR activation results in the opposite effect.

Identification of perturbed signaling pathways from gene expression data using information divergence

Abnormal regulation of signaling pathways is the key causative factor in several diseases. Although many methods have been proposed to identify significantly differential pathways between two conditions via microarray gene expression datasets, most of them concentrate on differences in the pathway components-either the differential expression or the correlation of genes in a given pathway. However, as biological functional units, signaling pathways may have diverse activity patterns across different biological contexts. In order to detect overall changes in pathways, we propose an analysis model called SPAID (Signaling Pathway Analysis based on Information Divergence). SPAID is based on the concept of information divergence, which can be used to compare two conditions by computing the differential probability distribution of the regulation capacity. We compared SPAID with several classical algorithms using different datasets, and the results indicate that SPAID produces higher repeatability, has better performance and universality, and extracts more comprehensive information regarding the underlying biological processes. In conclusion, by introducing the idea of information divergence, our study measures differences in pathways from an overall perspective and will provide a complementary analysis framework for pathway analysis.

Raspberry pomace alters cecal microbial activity and reduces secondary bile acids in rats fed a high-fat diet

The profile of bile acids (BA) largely depends on the enzymatic activity of the microbiota, but this can be modulated by the dietary addition of biologically active compounds, e.g., polyphenols and polyunsaturated fatty acids. The aim of this study was to examine the effect of dietary raspberry pomace as a rich source of biologically active compounds on microbial activity and the BA profile in the caecum of rats fed a high-fat diet. Wistar rats were fed the standard diet AIN-93, a high-fat diet or a modified high-fat diet enriched with 7% different types of processed raspberry pomaces produced by standard grinding and fine grinding, with or without seeds. Rats fed the high-fat diet for 8 weeks showed some disorders in liver function and cecal BA, as manifested by an increased concentration of cholesterol, total BA in the liver and cholic, deoxycholic, and β-muricholic acids in the cecal digesta. In general, irrespective of the type of raspberry pomace, these dietary preparations decreased liver cholesterol, hepatic fibroblast growth factor receptor 4, peroxisome proliferator-activated receptor alpha, cecal ammonia and favorable changed BA profile in the cecum. However, among all dietary pomaces, the finely ground preparation containing seeds had the greatest beneficial effect on the caecum by modulating bacterial activity and reducing the levels of secondary BA.

Deoxycholic acid transformations catalyzed by selected filamentous fungi

More than 100 filamentous fungi strains, mostly ascomycetes and zygomycetes from different phyla, were screened for the ability to convert deoxycholic acid (DCA) to valuable bile acid derivatives. Along with 11 molds which fully degraded DCA, several strains were revealed capable of producing cholic acid, ursocholic acid, 12-keto-lithocholic acid (12-keto-LCA), 3-keto-DCA, 15β-hydroxy-DCA and 15β-hydroxy-12-oxo-LCA as major products from DCA. The last metabolite was found to be a new compound. The ability to catalyze the introduction of a hydroxyl group at the 7(α/β)-positions of the DCA molecule was shown for 32 strains with the highest 7β-hydroxylase activity level for Fusarium merismoides VKM F-2310. Curvularia lunata VKM F-644 exhibited 12α-hydroxysteroid dehydrogenase activity and formed 12-keto-LCA from DCA. Acremonium rutilum VKM F-2853 and Neurospora crassa VKM F-875 produced 15β-hydroxy-DCA and 15β-hydroxy-12-oxo-LCA, respectively, as major products from DCA, as confirmed by MS and NMR analyses. For most of the positive strains, the described DCA-transforming activity was unreported to date. The presented results expand the knowledge on bile acid metabolism by filamentous fungi, and might be suitable for preparative-scale exploitation aimed at the production of marketed bile acids.

Colorectal cancer drug target prediction using ontology-based inference and network analysis

Identification of novel drug targets is a critical step in drug development. Many recent studies have produced multiple types of data, which provides an opportunity to mine the relationships among them to predict drug targets. In this study, we present a novel integrative approach that combines ontology reasoning with network-assisted gene ranking to predict new drug targets. We utilized colorectal cancer (CRC) as a proof-of-concept use case to illustrate the approach. Starting from FDA-approved CRC drugs and the relationships among disease, drug, gene, pathway, and SNP in an ontology representing PharmGKB data, we inferred 113 potential CRC drug targets. We further prioritized these genes based on their relationships with CRC disease genes in the context of human protein-protein interaction networks. Thus, among the 113 potential drug targets, 15 were selected as the promising drug targets, including some genes that are supported by previous studies. Among them, EGFR, TOP1 and VEGFA are known targets of FDA-approved drugs. Additionally, CCND1 (cyclin D1), and PTGS2 (prostaglandin-endoperoxide synthase 2) have reported to be relevant to CRC or as potential drug targets based on the literature search. These results indicate that our approach is promising for drug target prediction for CRC treatment, which might be useful for other cancer therapeutics.

Tissue-specific actions of FXR in metabolism and cancer

The nuclear Farnesoid X Receptor (FXR) is a transcription factor critically involved in metabolic homeostasis in the gut-liver axis. FXR activity is mediated by hormonal and dietary signals and driven by bile acids (BAs), which are the natural FXR ligands. Given the great physiological importance in BA homeostasis, as well as in the regulation of glucose and lipid metabolism, FXR plays a pivotal role in the pathogenesis of a wide range of disease of the liver, biliary tract and intestine, including hepatic and colorectal cancer. In the last years several studies have shown the relative FXR tissue-specific importance, highlighting synergism and additive effects in the liver and intestine. Gain- and loss-of-FXR-function mouse models have been generated in order to identify the biological processes and the molecular FXR targets. Taking advantage of the knowledge on the structure-activity relationship of BAs for FXR, semi-synthetic and synthetic molecules have been generated to obtain more selective and powerful FXR activators than BAs. This article is part of a Special Issue entitled: Linking transcription to physiology in lipodomics.

Lack of human tissue-specific correlations for rodent pancreatic and colorectal carcinogens

To better understand the relationships between chemical exposures and human cancer causation, incidence data for human cancer types were identified and pancreatic and colorectal cancers were studied in-depth to assess whether data supporting the causation of pancreatic or colorectal tumors by chemicals in rodents is predictive of causation by the same chemicals of the same tumors in humans. A search of the Carcinogenic Potency Database, the National Toxicology Program (NTP) technical report database, and the published literature identified 38 and 39 chemicals reported to cause pancreatic and colorectal tumors, respectively, in mice or rats. For each of these chemicals, searches were conducted of the International Agency for Research on Cancer monographs, the NTP Report on Carcinogens, and the published literature for evidence of induction of the same tumors in humans. Based on this evaluation, no conclusive evidence was identified to suggest that chemicals reported to cause pancreatic or colorectal tumors in rodents also cause these tumors in humans. These findings suggest that pancreatic tumor data from mouse and rat bioassays are of limited utility with regard to predicting similar tumor induction in humans. For colorectal cancer, a lack of correlation was noted for the vast majority of chemicals.

Relative Expression of Vitamin D Hydroxylases, CYP27B1 and CYP24A1, and of Cyclooxygenase-2 and Heterogeneity of Human Colorectal Cancer in Relation to Age, Gender, Tumor Location, and Malignancy: Results from Factor and Cluster Analysis

Previous studies on the significance of vitamin D insufficiency and chronic inflammation in colorectal cancer development clearly indicated that maintenance of cellular homeostasis in the large intestinal epithelium requires balanced interaction of 1,25-(OH)₂D₃ and prostaglandin cellular signaling networks. The present study addresses the question how colorectal cancer pathogenesis depends on alterations of activities of vitamin D hydroxylases, i.e., CYP27B1-encoded 25-hydroxyvitamin D-1α-hydroxylase and CYP24A1-encoded 25-hydroxyvitamin D-24-hydroxylase, and inflammation-induced cyclooxygenase-2 (COX-2). Data from 105 cancer patients on CYP27B1, VDR, CYP24A1, and COX-2 mRNA expression in relation to tumor grade, anatomical location, gender and age were fit into a multivariate model of exploratory factor analysis. Nearly identical results were obtained by the principal factor and the maximum likelihood method, and these were confirmed by hierarchical cluster analysis: Within the eight mutually dependent variables studied four independent constellations were found that identify different features of colorectal cancer pathogenesis: (i) Escape of COX-2 activity from restraints by the CYP27B1/VDR system can initiate cancer growth anywhere in the colorectum regardless of age and gender; (ii) variations in COX-2 expression are mainly responsible for differences in cancer incidence in relation to tumor location; (iii) advancing age has a strong gender-specific influence on cancer incidence; (iv) progression from well differentiated to undifferentiated cancer is solely associated with a rise in CYP24A1 expression.

Bile salts predict liver regeneration in rabbit model of portal vein embolization

BACKGROUND

Portal vein embolization (PVE) is employed to increase future remnant liver (FRL) volume through induction of hepatocellular regeneration in the nonembolized liver lobe. The regenerative response is commonly determined by CT volumetry after PVE. The aim of the study was to examine plasma bile salts and triglycerides in the prediction of the regenerative response following PVE.

METHODS

PVE of the cranial liver lobe was performed in 15 rabbits, divided into three groups: NaCl (control), gelatin sponge (short-term occlusion), and polyvinyl alcohol particles with coils (PVAc, long-term occlusion). In all rabbits CT volumetry and blood sampling were performed prior to PVE and on days 3 and 7. Plasma bile salts and triglycerides were correlated with volume increase of the nonembolized liver lobe.

RESULTS

After 3 and 7 d, respectively, FRL volume was increased in both embolized groups, with the largest hypertrophy response observed in the PVAc group. Plasma bile salt levels were increased after PVE, especially in the PVAc group at day 3 (P < 0.01 compared to gelatin sponge). Plasma bile salts at day 3 predicted FRL volume increase at day 7 showing a positive correlation of 0.811 (P < 0.001). Levels of triglycerides were not significantly altered in either of the PVE procedures.

CONCLUSIONS

Plasma bile salt levels early after PVE strongly correlated with the regenerative response in a rabbit model of PVE, showing more pronounced elevation with larger volume increase of the nonembolized lobe. Therefore, plasma bile salts, but not triglycerides, can be used in the prediction of the regenerative response after PVE.

Expression of the nuclear bile acid receptor/farnesoid X receptor is reduced in human colon carcinoma compared to nonneoplastic mucosa independent from site and may be associated with adverse prognosis

The nuclear bile acid receptor/farnesoid X receptor (FXR; NR1H4) is involved in bile acid homeostasis, cell proliferation and apoptosis and has been linked to intestinal carcinogenesis in mice. Aim of this study was to analyze FXR expression in human normal intestinal mucosa and colon carcinoma. We achieved systematic mapping of FXR expression of human intestinal mucosa and analysis of 75 human colon carcinomas using FXR immunohistochemistry on formalin-fixed, paraffin-embedded tissue. FXR expression gradually decreased from terminal ileum to the sigmoid colon with strongest expression in the terminal ileum (p < 0.001). FXR expression in carcinomas was reduced compared to peritumoral nonneoplastic mucosa (p < 0.000). Loss of FXR expression was significantly correlated with grading in tumors of the right colon (p = 0.008). FXR expression in tumor and normal tissue showed an inverse correlation with stage. FXR expression in tumor was inversely correlated with clinical outcome. No association was found with patients' age and sex. In nonneoplastic mucosa FXR expression concurred with low expression of Ki-67. In carcinomas, no association was found between FXR expression and Ki-67 and cyclin D1, respectively. Development of colon carcinoma in humans is associated with reduced FXR expression independent of site and may reflect an impaired defense against potentially carcinogenic bile acids along their intestinal gradient. In contrast to normal colon mucosa, FXR expression in carcinomas is not associated with low proliferation. Colon carcinomas with FXR expression seem to be associated with lower stage and a more favourable outcome compared to FXR negative carcinomas.

Cholesterol-lowering activity of the major polyphenols in grape seed

The major polyphenols in grape seed have been shown to have beneficial health effects in the prevention of dyslipidemia and cardiovascular diseases. In this present study, we investigated the cholesterol-lowering activity of three major polyphenolic compounds found in grape seed. The results showed that gallic acid, catechin, and epicatechin significantly inhibited pancreatic cholesterol esterase in a concentration-dependent manner. Moreover, they bound to taurocholic acid, taurodeoxycholic acid, and glycodeoxycholic acid at levels ranging from 38.6% to 28.2%. At the concentration of 0.2 mg/mL, gallic acid, catechin, and epicatechin reduced the formation of cholesterol micelles 27.26 ± 2.17%, 11.88 ± 0.75%, and 19.49 ± 3.71%, respectively. These findings clearly demonstrate that three major polyphenolic compounds present in a particular grape seed have cholesterol-lowering activity by inhibiting pancreatic cholesterol esterase, binding of bile acids, and reducing solubility of cholesterol in micelles which may result in delayed cholesterol absorption.