Colon cancer checks in when bile acids check out: the bile acid-nuclear receptor axis in colon cancer

Bile's Hidden Weapon: Modulating the Microbiome and Tumor Microenvironment

The human gut microbiome is a dynamic and intricate ecosystem, composed of trillions of microorganisms that play a pivotal role in maintaining overall health and well-being. However, the gut microbiome is constantly exposed to various environmental factors, including the bile produced by the liver, which can significantly impact its composition and function. Bile acids, secreted by the liver and stored in the gallbladder, modulate the gut microbiome, influencing its composition and function. This altered microbiome profile can, in turn, impact the tumor microenvironment (TME), promoting an immunosuppressive environment that favors tumor growth and metastasis. Furthermore, changes in the gut microbiome can also influence the production of bile acids and other metabolites that directly affect cancer cells and their behavior. Moreover, bile acids have been shown to shape the microbiome and increase antibiotic resistance, underscoring the need for targeted interventions. This review provides a comprehensive overview of the intricate relationships between bile, the gut microbiome, and the TME, highlighting the mechanisms by which this interplay drives cancer progression and resistance to therapy. Understanding these complex interactions is crucial for developing novel therapeutic strategies that target the gut-bile-TME axis and improve patient outcomes.

Bariatric Surgery Is Associated with Lower Concentrations of Fecal Secondary Bile Acids and Their Metabolizing Microbial Enzymes: A Pilot Study

INTRODUCTION

Excess body fat elevates colorectal cancer risk. While bariatric surgery (BRS) induces significant weight loss, its effects on the fecal stream and colon biology are poorly understood. Specifically, limited data exist on the impact of bariatric surgery (BRS) on fecal secondary bile acids (BA), including lithocholic acid (LCA), a putative promotor of colorectal carcinogenesis.

METHODS

This cross-sectional case-control study included 44 patients with obesity; 15 pre-BRS (controls) vs. 29 at a median of 24.1 months post-BRS. We examined the fecal concentrations of 11 BA by liquid chromatography and gene abundance of BA-metabolizing bacterial enzymes through fecal metagenomic sequencing. Differences were quantified using non-parametric tests for BA levels and linear discriminant analysis (LDA) effect size (LEfSe) for genes encoding BA-metabolizing enzymes.

RESULTS

Total fecal secondary BA concentrations trended towards lower levels post- vs. pre-BRS controls (p = 0.07). Individually, fecal LCA concentrations were significantly lower post- vs. pre-BRS (8477.0 vs. 11,914.0 uM/mg, p < 0.008). Consistent with this finding, fecal bacterial genes encoding BA-metabolizing enzymes, specifically 3-betahydroxycholanate-3-dehydrogenase (EC 1.1.1.391) and 3-alpha-hydroxycholanate dehydrogenase (EC 1.1.1.52), were also lower post- vs. pre-BRS controls (LDA of - 3.32 and - 2.64, respectively, adjusted p < 0.0001). Post-BRS fecal BA concentrations showed significant inverse correlations with weight loss, a healthy diet quality, and increased physical activity.

CONCLUSIONS

Concentrations of LCA, a secondary BA, and bacterial genes needed for BA metabolism are lower post-BRS. These changes can impact health and modulate the colorectal cancer cascade. Further research is warranted to examine how surgical alterations and the associated dietary changes impact bile acid metabolism.

From Crypts to Cancer: A Holistic Perspective on Colorectal Carcinogenesis and Therapeutic Strategies

Colorectal cancer (CRC) represents a significant global health burden, with high incidence and mortality rates worldwide. Recent progress in research highlights the distinct clinical and molecular characteristics of colon versus rectal cancers, underscoring tumor location's importance in treatment approaches. This article provides a comprehensive review of our current understanding of CRC epidemiology, risk factors, molecular pathogenesis, and management strategies. We also present the intricate cellular architecture of colonic crypts and their roles in intestinal homeostasis. Colorectal carcinogenesis multistep processes are also described, covering the conventional adenoma-carcinoma sequence, alternative serrated pathways, and the influential Vogelstein model, which proposes sequential APC, KRAS, and TP53 alterations as drivers. The consensus molecular CRC subtypes (CMS1-CMS4) are examined, shedding light on disease heterogeneity and personalized therapy implications.

Sulfation of chondroitin and bile acids converges to antagonize Wnt/β-catenin signaling and inhibit APC deficiency-induced gut tumorigenesis

Sulfation is a crucial and prevalent conjugation reaction involved in cellular processes and mammalian physiology. 3'-Phosphoadenosine 5'-phosphosulfate (PAPS) synthase 2 (PAPSS2) is the primary enzyme to generate the universal sulfonate donor PAPS. The involvement of PAPSS2-mediated sulfation in adenomatous polyposis coli (APC) mutation-promoted colonic carcinogenesis has not been reported. Here, we showed that the expression of PAPSS2 was decreased in human colon tumors along with cancer stages, and the lower expression of PAPSS2 was correlated with poor prognosis in advanced colon cancer. Gut epithelial-specific heterozygous Apc deficient and Papss2-knockout (ApcΔgut-HetPapss2Δgut) mice were created, and the phenotypes were compared to the spontaneous intestinal tumorigenesis of ApcΔgut-Het mice. ApcΔgut-HetPapss2Δgut mice were more sensitive to gut tumorigenesis, which was mechanistically accounted for by the activation of Wnt/β-catenin signaling pathway due to the suppression of chondroitin sulfation and inhibition of the farnesoid X receptor (FXR)-transducin-like enhancer of split 3 (TLE3) gene regulatory axis. Chondroitin sulfate supplementation in ApcΔgut-HetPapss2Δgut mice alleviated intestinal tumorigenesis. In summary, we have uncovered the protective role of PAPSS2-mediated chondroitin sulfation and bile acids-FXR-TLE3 activation in the prevention of gut carcinogenesis via the antagonization of Wnt/β-catenin signaling. Chondroitin sulfate may be explored as a therapeutic agent for Papss2 deficiency-associated colonic carcinogenesis.

Epigenetic disruption of the RARγ complex impairs its function to bookmark AR enhancer interactions required for enzalutamide sensitivity in prostate cancer

The current study in prostate cancer (PCa) focused on the genomic mechanisms at the cross-roads of pro-differentiation signals and the emergence of lineage plasticity. We explored an understudied cistromic mechanism involving RARγ's ability to govern AR cistrome-transcriptome relationships, including those associated with more aggressive PCa features. The RARγ complex in PCa cell models was enriched for canonical cofactors, as well as proteins involved in RNA processing and bookmarking. Identifying the repertoire of miR-96 bound and regulated gene targets, including those recognition elements marked by m6A, revealed their significant enrichment in the RARγ complex. RARγ significantly enhanced the AR cistrome, particularly in active enhancers and super-enhancers, and overlapped with the binding of bookmarking factors. Furthermore, RARγ expression led to nucleosome-free chromatin enriched with H3K27ac, and significantly enhanced the AR cistrome in G2/M cells. RARγ functions also antagonized the transcriptional actions of the lineage master regulator ONECUT2. Similarly, gene programs regulated by either miR-96 or antagonized by RARγ were enriched in alternative lineages and more aggressive PCa phenotypes. Together these findings reveal an under-investigated role for RARγ, modulated by miR-96, to bookmark enhancer sites during mitosis. These sites are required by the AR to promote transcriptional competence, and emphasize luminal differentiation, while antagonizing ONECUT2.

Genomically anchored vitamin D receptor mediates an abundance of bioprotective actions elicited by its 1,25-dihydroxyvitamin D hormonal ligand

The nuclear vitamin D receptor (VDR) mediates the actions of its physiologic 1,25-dihydroxyvitamin D3 (1,25D) ligand produced in kidney and at extrarenal sites during times of physiologic and cellular stress. The ligand-receptor complex transcriptionally controls genes encoding factors that regulate calcium and phosphate sensing/transport, bone remodeling, immune function, and nervous system maintenance. With the aid of parathyroid hormone (PTH) and fibroblast growth factor 23 (FGF23), 1,25D/VDR primarily participates in an intricate network of feedback controls that govern extracellular calcium and phosphate concentrations, mainly influencing bone formation and mineralization, ectopic calcification, and indirectly supporting many fundamental roles of calcium. Beyond endocrine and intracrine effects, 1,25D/VDR signaling impacts multiple biochemical phenomena that potentially affect human health and disease, including autophagy, carcinogenesis, cell growth/differentiation, detoxification, metabolic homeostasis, and oxidative stress mitigation. Several health advantages conferred by 1,25D/VDR appear to be promulgated by induction of klotho, an anti-aging renal peptide hormone which functions as a co-receptor for FGF23 and, like 1,25D, regulates nrf2, foxo, mTOR and other cellular protective pathways. Among hundreds of genes for which expression is modulated by 1,25D/VDR either primarily or secondarily in a cell-specific manner, the resulting gene products (in addition to those expressed in the classic skeletal mineral regulatory tissues kidney, intestine, and bone), fall into multiple biochemical categories including apoptosis, cholesterol homeostasis, glycolysis, hypoxia, inflammation, p53 signaling, unfolded protein response and xenobiotic metabolism. Thus, 1,25D/VDR is a bone mineral control instrument that also signals the maintenance of multiple cellular processes in the face of environmental and genetic challenges.

Nutrition and Microbiome Interactions in Human Cancer

Individual physiologic responses to changes in dietary patterns can vary widely to affect cancer risk, which is driven by multiple host-specific factors (eg, genetics, epigenetics, inflammatory and metabolic states, and the colonizing microbiome). Emerging evidence indicates that diet-induced microbiota alterations are key modulators of several host functions important to tumor etiology, progression, and response to cancer therapy. Thus, diet may potentially be used to target alterations of the microbiota as an effective means to improve outcomes across the cancer continuum (from cancer prevention to tumor development and progression, to effects on treatment and survivorship). This review will focus on recent examples of functional interactions between dietary components (nutrients and non-nutrients) and the gastrointestinal microbiome, which are 2 critical and malleable environmental variables in cancer risk that affect host immune, metabolic, and cell signaling functions and may provide insights for novel cancer therapeutic and preventive strategies.

Effect of Lactobacillus fermentum ZS40 on the NF-κB signaling pathway in an azomethane-dextran sulfate sodium-induced colon cancer mouse model

The occurrence of intestinal diseases such as colon cancer is closely related to the intestinal flora. Lactobacillus fermentum is a gut probiotic that plays an important role in chronic intestinal inflammation and colon cancer. In the current study, we investigated the effect of Lactobacillus fermentum ZS40 on NF-κB signaling pathway of azomethane-dextran sulfate sodium (AOM-DSS) -induced colon cancer in mice. Animals were divided into control group (NC), AOM-DSS-induced model group (CRC), AOM-DSS plus high-dose Lactobacillus fermentum ZS40 (ZS40-H), AOM-DSS plus low-dose Lactobacillus fermentum ZS40 (ZS40-L), AOM-DSS plus Lactobacillus bulgaricus (BLA), and AOM-DSS plus sulfasalazine (SD)-treated group. Observation of animal physiological activity (body weight and defecation), biochemical measurements, histopathological examination of colon tissue, qPCR to evaluate the expression of inflammation-related genes, immunohistochemical analysis of CD34 and CD117, and Western blot analysis of NF-κB signaling pathway were performed. Compared with the CRC group, the ZS40-H, ZS40-L, BLA, and SD groups had decreased levels of colon cancer marker proteins CD34 and CD117, and the number of abnormal colonic lesions observed by colon histology decreased, while the ZS40-H group showed excellent results. In addition, all probiotic interventions showed weight loss effects. The expression of inflammatory stimulators TNF-α and IL-1β in the probiotic treatment group decreased; the expression of key proteins IκBα and p65 in the NF-κB signaling pathway also decreased, resulting in a decrease in the expression of the target protein Cox-2. Therefore, administration of Lactobacillus fermentum ZS40 as a probiotic can alleviate intestinal inflammation and prevent colon cancer in mice.

New Insights into Bile Acids Related Signaling Pathways in the Onset of Colorectal Cancer

Colorectal cancer (CRC) ranks as the second among the causes of tumor death worldwide, with an estimation of 1.9 million new cases in 2020 and more than 900,000 deaths. This rate might increase by 60% over the next 10 years. These data are unacceptable considering that CRC could be successfully treated if diagnosed in the early stages. A high-fat diet promotes the hepatic synthesis of bile acids (BAs) increasing their delivery to the colonic lumen and numerous scientific reports correlate BAs, especially secondary BAs, with CRC incidence. We reviewed the physicochemical and biological characteristics of BAs, focusing on the major pathways involved in CRC risk and progression. We specifically pointed out the role of BAs as signaling molecules and the tangled relationships among their nuclear and membrane receptors with the big bang of molecular and cellular events that trigger CRC occurrence.

Bile acids, bile pigments and colorectal cancer risk

PURPOSE OF REVIEW

The gut microbial co-metabolism of bile-derived compounds (e.g. bile acids and bile pigments) affects colorectal cancer (CRC) risk. Here, we review recent findings with focus on selected novel aspects of bile-associated effects with interesting but unclear implications on CRC risk.

RECENT FINDINGS

Numerous studies demonstrated novel biotransformation of bile acids by gut bacteria (e.g. microbial conjugation of bile acids), resulting in diverse bile acid compounds that show complex interactions with host receptors (e.g. FXR, TGR5). In addition, YAP-associated signalling in intestinal epithelial cells is modulated via bile acid receptor TGR5 and contributes to colonic tumorigenesis. Finally, studies indicate that serum levels of the bile pigment bilirubin are inversely associated with CRC risk or intestinal inflammation and that bilirubin affects gut microbiota composition.

SUMMARY

Bile acids and bile pigments have multiple effects on intestinal microbe-host interactions, which may collectively modulate long-term CRC risk of the host.

Nuclear receptors: from molecular mechanisms to therapeutics

Nuclear receptors are classically defined as ligand-activated transcription factors that regulate key functions in reproduction, development, and physiology. Humans have 48 nuclear receptors, which when dysregulated are often linked to diseases. Because most nuclear receptors can be selectively activated or inactivated by small molecules, they are prominent therapeutic targets. The basic understanding of this family of transcription factors was accelerated in the 1980s upon the cloning of the first hormone receptors. During the next 20 years, a deep understanding of hormone signaling was achieved that has translated to numerous clinical applications, such as the development of standard-of-care endocrine therapies for hormonally driven breast and prostate cancers. A 2004 issue of this journal reviewed progress on elucidating the structures of nuclear receptors and their mechanisms of action. In the current issue, we focus on the broad application of new knowledge in this field for therapy across diverse disease states including cancer, cardiovascular disease, various inflammatory diseases, the aging brain, and COVID-19.