Trimethylamine N-oxide, a gut microbiota-dependent metabolite of choline, is positively associated with the risk of primary liver cancer: a case-control study

Circulating Gut Microbe-Derived Metabolites Are Associated with Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is the third leading cause of cancer death worldwide. The gut microbiome has been implicated in outcomes for HCC, and gut microbe-derived products may serve as potential non-invasive indices for early HCC detection. This study evaluated differences in plasma concentrations of gut microbiota-derived metabolites.

METHODS

Forty-one patients with HCC and 96 healthy controls were enrolled from surgical clinics at the Cleveland Clinic from 2016 to 2020. Gut microbiota-derived circulating metabolites detectable in plasma were compared between patients with HCC and healthy controls. Hierarchical clustering was performed for generating heatmaps based on circulating metabolite concentrations using ClustVis, with Euclidean and Ward settings and significant differences between metabolite concentrations were tested using a binary logistic regression model.

RESULTS

In patients with HCC, 25 (61%) had histologically confirmed cirrhosis. Trimethylamine (TMA)-related metabolites were found at higher concentrations in those with HCC, including choline (p < 0.001), betaine (p < 0.001), carnitine (p = 0.007), TMA (p < 0.001) and trimethylamine N-oxide (TMAO, p < 0.001). Notably, concentrations of P-cresol glucuronide (p < 0.001), indole-lactic acid (p = 0.038), 5-hydroxyindoleacetic acid (p < 0.0001) and 4-hydroxyphenyllactic acid (p < 0.001) were also increased in those with HCC compared to healthy controls. Hierarchical clustering of the metabolite panel separated patients based on the presence of HCC (p < 0.001), but was not able to distinguish between patients with HCC based on the presence of cirrhosis (p = 0.42).

CONCLUSIONS

Gut microbiota-derived metabolites were differentially abundant in patients with HCC versus healthy controls. The observed perturbations of the TMAO pathway in HCC seem particularly promising as a target of future research and may have both diagnostic and therapeutic implications.

Trimethylamine N-oxide: a meta-organismal axis linking the gut and fibrosis

BACKGROUND

Tissue fibrosis is a common pathway to failure in many organ systems and is the cellular and molecular driver of myriad chronic diseases that are incompletely understood and lack effective treatment. Recent studies suggest that gut microbe-dependent metabolites might be involved in the initiation and progression of fibrosis in multiple organ systems.

MAIN BODY OF THE MANUSCRIPT

In a meta-organismal pathway that begins in the gut, gut microbiota convert dietary precursors such as choline, phosphatidylcholine, and L-carnitine into trimethylamine (TMA), which is absorbed and subsequently converted to trimethylamine N-oxide (TMAO) via the host enzyme flavin-containing monooxygenase 3 (FMO3) in the liver. Chronic exposure to elevated TMAO appears to be associated with vascular injury and enhanced fibrosis propensity in diverse conditions, including chronic kidney disease, heart failure, metabolic dysfunction-associated steatotic liver disease, and systemic sclerosis.

CONCLUSION

Despite the high prevalence of fibrosis, little is known to date about the role of gut dysbiosis and of microbe-dependent metabolites in its pathogenesis. This review summarizes recent important advances in the understanding of the complex metabolism and functional role of TMAO in pathologic fibrosis and highlights unanswered questions.

Trimethylamine N-oxide promotes the proliferation and migration of hepatocellular carcinoma cell through the MAPK pathway

Trimethylamine-n-oxide (TMAO) is a metabolite of intestinal flora following the consumption of phosphatidylcholine-rich foods. Clinical cohort studies have shown that plasma TMAO may be a risk factor for cancer development, including hepatocellular carcinoma (HCC), but fundamental research data supporting this hypothesis are lacking. In this study, HCC cells were treated with TMAO in vivo and in vitro to evaluate the effect on some indicators related to the malignancy degree of HCC, and the relevant molecular mechanisms were explored. In vitro, TMAO promoted the proliferation and migration of HCC cells and significantly upregulated the expression of proteins related to epithelial-mesenchymal transformation (EMT). In vivo, after HCC cells were inoculated subcutaneously in nude mice given water containing TMAO, the tumors grew faster and larger than those in the mice given ordinary water. The immunohistochemistry analysis showed that proliferation, migration and EMT-related proteins in the tumor tissues were significantly upregulated by TMAO. Furthermore, TMAO obviously enhanced the phosphorylation of MAPK signaling molecules in vivo and in vitro. In conclusion, TMAO promotes the proliferation, migration and EMT of HCC cells by activating the MAPK pathway.

The gut microbiota derived metabolite trimethylamine N-oxide: Its important role in cancer and other diseases

An expanding body of research indicates a correlation between the gut microbiota and various diseases. Metabolites produced by the gut microbiota act as mediators between the gut microbiota and the host, interacting with multiple systems in the human body to regulate physiological or pathological functions. However, further investigation is still required to elucidate the underlying mechanisms. One such metabolite involved in choline metabolism by gut microbes is trimethylamine (TMA), which can traverse the intestinal epithelial barrier and enter the bloodstream, ultimately reaching the liver where it undergoes oxidation catalyzed by flavin-containing monooxygenase 3 (FMO3) to form trimethylamine N-oxide (TMAO). While some TMAO is eliminated through renal excretion, remaining amounts circulate in the bloodstream, leading to systemic inflammation, endoplasmic reticulum (ER) stress, mitochondrial stress, and disruption of normal physiological functions in humans. As a representative microbial metabolite originating from the gut, TMAO has significant potential both as a biomarker for monitoring disease occurrence and progression and for tailoring personalized treatment strategies for patients. This review provides an extensive overview of TMAO sources and its metabolism in human blood, as well as its impact on several major human diseases. Additionally, we explore the latest research areas related to TMAO along with future directions.

Role of Gut Microbial Metabolites in the Pathogenesis of Primary Liver Cancers

Hepatobiliary malignancies, which include hepatocellular carcinoma (HCC) and cholangiocarcinoma (CCA), are the sixth most common cancers and the third leading cause of cancer-related death worldwide. Hepatic carcinogenesis is highly stimulated by chronic inflammation, defined as fibrosis deposition, and an aberrant imbalance between liver necrosis and nodular regeneration. In this context, the gut-liver axis and gut microbiota have demonstrated a critical role in the pathogenesis of HCC, as dysbiosis and altered intestinal permeability promote bacterial translocation, leading to chronic liver inflammation and tumorigenesis through several pathways. A few data exist on the role of the gut microbiota or bacteria resident in the biliary tract in the pathogenesis of CCA, and some microbial metabolites, such as choline and bile acids, seem to show an association. In this review, we analyze the impact of the gut microbiota and its metabolites on HCC and CCA development and the role of gut dysbiosis as a biomarker of hepatobiliary cancer risk and of response during anti-tumor therapy. We also discuss the future application of gut microbiota in hepatobiliary cancer management.

The Interplay Between Dietary Choline and Cardiometabolic Disorders: A Review of Current Evidence

PURPOSE OF REVIEW

Choline is an essential nutrient for human health and cellular homeostasis as it is necessary for the synthesis of lipid cell membranes, lipoproteins, and the synthesis of the neurotransmitter acetylcholine. The aim of this review is to analyze the beneficial effects of choline and its significance in cellular metabolism and various inflammatory pathways, such as the inflammasome. We will discuss the significance of dietary choline in cardiometabolic disorders, such as non-alcoholic fatty liver disease (NAFLD), cardiovascular disease (CVD), and chronic kidney disease (CKD) as well as in cognitive function and associated neuropsychiatric disorders.

RECENT FINDINGS

Choline deficiency has been related to the development of NAFLD and cognitive disability in the offspring as well as in adulthood. In sharp contrast, excess dietary intake of choline mediated via the increased production of trimethylamine by the gut microbiota and increased trimethylamine-N-oxide (TMAO) levels has been related to atherosclerosis in most studies. In this context, CVD and CKD through the accumulation of TMAO, p-Cresyl-sulfate (pCS), and indoxyl-sulfate (IS) in serum may be the result of the interplay between excess dietary choline, the increased production of TMAO by the gut microbiota, and the resulting activation of inflammatory responses and fibrosis. A balanced diet, with no excess nor any deficiency in dietary choline, is of outmost importance regarding the prevention of cardiometabolic disorders as well as cognitive function. Large-scale studies with the use of next-generation probiotics, especially Akkermansia muciniphila and Faecalibacterium prausnitzii, should further examine their therapeutic potential in this context.

Blood-Based Multiomics-Guided Detection of a Precancerous Pancreatic Tumor

Over a decade ago, longitudinal multiomics analysis was pioneered for early disease detection and individually tailored precision health interventions. However, high sample processing costs, expansive multiomics measurements along with complex data analysis have made this approach to precision/personalized medicine impractical. Here we describe in a case report, a more practical approach that uses fewer measurements, annual sampling, and faster decision making. We also show how this approach offers promise to detect an exceedingly rare and potentially fatal condition before it fully manifests. Specifically, we describe in the present case report how longitudinal multiomics monitoring (LMOM) helped detect a precancerous pancreatic tumor and led to a successful surgical intervention. The patient, enrolled in an annual blood-based LMOM since 2018, had dramatic changes in the June 2021 and 2022 annual metabolomics and proteomics results that prompted further clinical diagnostic testing for pancreatic cancer. Using abdominal magnetic resonance imaging, a 2.6 cm lesion in the tail of the patient's pancreas was detected. The tumor fluid from an aspiration biopsy had 10,000 times that of normal carcinoembryonic antigen levels. After the tumor was surgically resected, histopathological findings confirmed it was a precancerous pancreatic tumor. Postoperative omics testing indicated that most metabolite and protein levels returned to patient's 2018 levels. This case report illustrates the potentials of blood LMOM for precision/personalized medicine, and new ways of thinking medical innovation for a potentially life-saving early diagnosis of pancreatic cancer. Blood LMOM warrants future programmatic translational research with the goals of precision medicine, and individually tailored cancer diagnoses and treatments.

The impact of chronic Trimethylamine N-oxide administration on liver oxidative stress, inflammation, and fibrosis

TMAO, a gut microbiota derived byproduct, has been associated with various cardiometabolic diseases by promoting oxidative stress and inflammation. The liver is the main organ for TMAO production and chronic exposure to high doses of TMAO could alter its function. In this study, we evaluated the effect of chronic exposure of high TMAO doses on liver oxidative stress, inflammation, and fibrosis. TMAO was administered daily via gastric gavage to laboratory rats for 3 months. Blood was drawn for the quantification of TMAO, and liver tissues were harvested for the assessment of oxidative stress (MDA, GSH, GSSG, GPx, CAT, and 8-oxo-dG) and inflammation by quantification of IL-1α, TNF-α, IL-10, TGF-β, NOS and COX-2 expression. The evaluation of fibrosis was made by Western blot analysis of α-SMA and Collagen-3 protein expression. Histological investigation and immunohistochemical staining of iNOS were performed in order to assess the liver damage. After 3 months of TMAO exposure, TMAO serum levels enhanced in parallel with increases in MDA and GSSG levels in liver tissue and lower values of GSH and GSH/GSSG ratio as well as a decrease in GPx and CAT activities. Inflammation was also highlighted, with enhanced iNOS, COX-2, and IL-10 expression, without structural changes and without induction of liver fibrosis.

Contributions of the Microbiome-Derived Metabolome for Risk Assessment and Prognostication of Pancreatic Cancer

BACKGROUND

Increasing evidence implicates microbiome involvement in the development and progression of pancreatic ductal adenocarcinoma (PDAC). Studies suggest that reflux of gut or oral microbiota can lead to colonization in the pancreas, resulting in dysbiosis that culminates in release of microbial toxins and metabolites that potentiate an inflammatory response and increase susceptibility to PDAC. Moreover, microbe-derived metabolites can exert direct effector functions on precursors and cancer cells, as well as other cell types, to either promote or attenuate tumor development and modulate treatment response.

CONTENT

The occurrence of microbial metabolites in biofluids thereby enables risk assessment and prognostication of PDAC, as well as having potential for design of interception strategies. In this review, we first highlight the relevance of the microbiome for progression of precancerous lesions in the pancreas and, using liquid chromatography-mass spectrometry, provide supporting evidence that microbe-derived metabolites manifest in pancreatic cystic fluid and are associated with malignant progression of intraductal papillary mucinous neoplasm(s). We secondly summarize the biomarker potential of microbe-derived metabolite signatures for (a) identifying individuals at high risk of developing or harboring PDAC and (b) predicting response to treatment and disease outcomes.

SUMMARY

The microbiome-derived metabolome holds considerable promise for risk assessment and prognostication of PDAC.

Investigating the Influence of Gut Microbiota-related Metabolites in Gastrointestinal Cancer

Gastrointestinal (GI) cancer is a major health concern due to its prevalence, impact on well-being, high mortality rate, economic burden, and potential for prevention and early detection. GI cancer research has made remarkable strides in understanding biology, risk factors, and treatment options. An emerging area of research is the gut microbiome's role in GI cancer development and treatment response. The gut microbiome, vital for digestion, metabolism, and immune function, is increasingly linked to GI cancers. Dysbiosis and alterations in gut microbe composition may contribute to cancer development. Scientists study how specific bacteria or microbial metabolites influence cancer progression and treatment response. Modulating the gut microbiota shows promise in enhancing treatment efficacy and preventing GI cancers. Gut microbiota dysbiosis can impact GI cancer through inflammation, metabolite production, genotoxicity, and immune modulation. Microbes produce metabolites like short-chain fatty acids, bile acids, and secondary metabolites. These affect host cells, influencing processes like cell proliferation, apoptosis, DNA damage, and immune regulation, all implicated in cancer development. This review explores the latest research on gut microbiota metabolites and their molecular mechanisms in GI cancers. The hope is that this attempt will help in conducting other relevant research to unravel the precise mechanism involved, identify microbial signatures associated with GI cancer, and develop targets.

Intestinal microbiota: A bridge between intermittent fasting and tumors

Intestinal microbiota and their metabolites are essential for maintaining intestinal health, regulating inflammatory responses, and enhancing the body's immune function. An increasing number of studies have shown that the intestinal microbiota is tightly tied to tumorigenesis and intervention effects. Intermittent fasting (IF) is a method of cyclic dietary restriction that can improve energy metabolism, prolong lifespan, and reduce the progression of various diseases, including tumors. IF can affect the energy metabolism of tumor cells, inhibit tumor cell growth, improve the function of immune cells, and promote an anti-tumor immune response. Interestingly, recent research has further revealed that the intestinal microbiota can be impacted by IF, in particular by changes in microbial composition and metabolism. These findings suggest the complexity of the IF as a promising tumor intervention strategy, which merits further study to better understand and encourage the development of clinical tumor intervention strategies. In this review, we aimed to outline the characteristics of the intestinal microbiota and its mechanisms in different tumors. Of note, we summarized the impact of IF on intestinal microbiota and discussed its potential association with tumor suppressive effects. Finally, we proposed some key scientific issues that need to be addressed and envision relevant research prospects, which might provide a theoretical basis and be helpful for the application of IF and intestinal microbiota as new strategies for clinical interventions in the future.

The Association of Circulating L-Carnitine, γ-Butyrobetaine and Trimethylamine N-Oxide Levels with Gastric Cancer

Our study aimed to evaluate the association between gastric cancer (GC) and higher concentrations of the metabolites L-carnitine, γ-butyrobetaine (GBB) and gut microbiota-mediated trimethylamine N-oxide (TMAO) in the circulation. There is evidence suggesting that higher levels of TMAO and its precursors in blood can be indicative of either a higher risk of malignancy or indeed its presence; however, GC has not been studied in this regard until now. Our study included 83 controls without high-risk stomach lesions and 105 GC cases. Blood serum L-carnitine, GBB and TMAO levels were measured by ultra-high-performance liquid chromatography–mass spectrometry (UPLC/MS/MS). Although there were no significant differences between female control and GC groups, we found a significant difference in circulating levels of metabolites between the male control group and the male GC group, with median levels of L-carnitine reaching 30.22 (25.78–37.57) nmol/mL vs. 37.38 (32.73–42.61) nmol/mL (p < 0.001), GBB–0.79 (0.73–0.97) nmol/mL vs. 0.97 (0.78–1.16) nmol/mL (p < 0.05) and TMAO–2.49 (2.00–2.97) nmol/mL vs. 3.12 (2.08–5.83) nmol/mL (p < 0.05). Thus, our study demonstrated the association between higher blood levels of L-carnitine, GBB, TMAO and GC in males, but not in females. Furthermore, correlations of any two investigated metabolites were stronger in the GC groups of both genders in comparison to the control groups. Our findings reveal the potential role of L-carnitine, GBB and TMAO in GC and suggest metabolic differences between genders. In addition, the logistic regression analysis revealed that the only significant factor in terms of predicting whether the patient belonged to the control or to the GC group was the blood level of L-carnitine in males only. Hence, carnitine might be important as a biomarker or a risk factor for GC, especially in males.

Association between Levels of Trimethylamine N-Oxide and Cancer: A Systematic Review and Meta-Analysis

Cancer is the second leading cause of death in the world. Reports on the effect of Trimethylamine-N-oxide (TAMO), a small amine oxide generated by gut microbial metabolism of choline, betaine, and carnitine, on cancer are inconsistent. Therefore, this systematic review and meta-analysis summarize the effect of TAMO on cancer incidence. A systematic search was conducted in PubMed, Scopus, Web of Science, and Embase. Data were pooled using the random-effects method and were expressed as weighted mean difference (WMD) and 95% confidence intervals (CI). The pooled results of 16 studies, including 5930 participants, showed that the association between TMAO levels and cancer incidence is insignificant (Odds Ratio: 0.97, 95% CI: (0.64, 1.46), P-value = 0.871). Subgroup analysis showed that urinary TMAO levels were negatively associated with cancer incidence; in contrast, a direct and positive association was observed between serum TMAO levels and cancer incidence. However, "gender" and the "TMAO measuring method" were the potential sources of discrepancies. Meta-regression analysis did not reveal any significant association between duration of studies, age, female ratio, subjects-control, and subjects-case. The present study demonstrates that serum TAMO levels were insignificantly associated with cancer incidence.

Choline supplementation regulates gut microbiome diversity, gut epithelial activity, and the cytokine gene expression in gilts

Choline is an essential nutrient that is necessary for both fetal development and maintenance of neural function, while its effect on female ovarian development is largely unexplored. Our previous study demonstrated that choline supplementation promotes ovarian follicular development and ovulation, although its underlying mechanism was unclear. To uncover the potential regulation pathway, eighteen female Yorkshire × Landrace gilts were fed with either standard commercial diet (Control group, n = 9) or choline supplemented diet (Choline group, additional 500 mg/kg of control diet, n = 9) from day 90 of age to day 186. At day 186, feces samples were analyzed for effects on the gut microbiome using 16S ribosomal RNA gene V3-V4 region sequencing with Illumina MiSeq, serum samples were analyzed for trimethylamine (TMA) and trimethylamine-N-oxide (TMAO) using HILIC method, and jejunum tissues were analyzed for immune related gene expression using qRT-PCR. Our results show that choline supplementation did not alter the circulating level of TMA and TMAO (P > 0.05), but rather increased gut microbiome alpha diversity (P < 0.05). Beta diversity analysis results showed that the choline diet mainly increased the abundance of Firmicutes, Proteobacteria, and Actinobacteria, but decreased the abundance of Bacteroidetes, Spirochaetes, and Euryarchaeota at the phyla level. Meta-genomic analysis revealed that choline supplementation activated pathways in the gut microbiota associated with steroid hormone biosynthesis and degradation of infertility-causing environmental pollutants (bisphenol, xylene, and dioxins). To further verify the effect of choline on intestinal activity, a porcine intestine cell line (IPEC-J2) was treated with serial concentrations of choline chloride in vitro. Our data demonstrated that choline promoted the proliferation of IPEC-J2 while inhibiting the apoptotic activity. qRT-PCR results showed that choline significantly increased the expression level of Bcl2 in both IPEC-J2 cells and jejunum tissues. The expression of IL-22, a cytokine that has been shown to impact ovarian function, was increased by choline treatment in vitro. Our findings reveal the beneficial effect of choline supplementation on enhancing the gut microbiome composition and intestinal epithelial activity, and offer insights into how these changes may have contributed to the ovarian development-promoting effect we reported in our previous study.

Multi-Omics Analyses Identify Signatures in Patients with Liver Cirrhosis and Hepatocellular Carcinoma

Gut bacterial/viral dysbiosis, changes in circulating metabolites, and plasma cytokines/chemokines have been previously associated with various liver diseases. Here, we analyzed the associations between fecal microbial composition, circulating metabolites, and plasma cytokines/chemokines in patients with liver cirrhosis (LC) and hepatocellular carcinoma (HCC). We recruited 10 HCC patients, 18 LC patients, and 17 healthy individuals. Their stool samples were used for gene sequencing of bacterial 16S rRNA and viral genomes, while plasma samples were utilized for the determination of endotoxin, zonulin, metabolite, and cytokine/chemokine levels. Dysbiosis was observed among gut bacteria and viruses, with significant changes in abundance at the genus and species levels, respectively. However, no differences were found between cohorts in the alpha and beta diversity. Plasma lipopolysaccharides and zonulin, but not trimethylamine N-oxide, were progressively increased in LC and HCC subjects. Profiling plasma metabolites and selected cytokines/chemokines revealed differential changes in the LC and HCC cohorts. Following joint correlation and correlation network analyses, regardless of etiology, common network signatures shared by LC and HCC patients were characterized by the gut virus Stenotrophomonas virus DLP5 and the uncultured Caudovirales phage, plasma metabolites pyruvic acid and acetic acid, and plasma cytokines/chemokines eotaxin and PDGF-AB/BB, respectively. Additionally, LC- and HCC-specific correlation networks were also identified. This study provides novel insights into altered gut microbial/viral composition that may contribute to pre-HCC disorders, metabolic reprogramming, or inflammatory microenvironments for hepatocarcinogenesis.

Utilizing Gut Microbiota to Improve Hepatobiliary Tumor Treatments: Recent Advances

Hepatobiliary tumors, which include cholangiocarcinoma, hepatocellular carcinoma (HCC), and gallbladder cancer, are common cancers that have high morbidity and mortality rates and poor survival outcomes. In humans, the microbiota is comprised of symbiotic microbial cells (10-100 trillion) that belong to the bacterial ecosystem mainly residing in the gut. The gut microbiota is a complicated group that can largely be found in the intestine and has a dual role in cancer occurrence and progression. Previous research has focused on the crucial functions of the intestinal microflora as the main pathophysiological mechanism in HCC development. Intestinal bacteria produce a broad range of metabolites that exhibit a variety of pro- and anticarcinogenic effects on HCC. Therefore, probiotic alteration of the gut microflora could promote gut flora balance and help prevent the occurrence of HCC. Recent evidence from clinical and translational studies suggests that fecal microbiota transplant is one of the most successful therapies to correct intestinal bacterial imbalance. We review the literature describing the effects and mechanisms of the microbiome in the gut in the context of HCC, including gut bacterial metabolites, probiotics, antibiotics, and the transplantation of fecal microbiota, and discuss the potential influence of the microbiome environment on cholangiocarcinoma and gallbladder cancer. Our findings are expected to reveal therapeutic targets for the prevention of hepatobiliary tumors, and the development of clinical treatment strategies, by emphasizing the function of the gut microbiota.

Integrated Analysis Reveals the Gut Microbial Metabolite TMAO Promotes Inflammatory Hepatocellular Carcinoma by Upregulating POSTN

Liver cancer has a high mortality rate. Chronic inflammation is one of the leading causes of hepatocellular carcinoma. Recent studies suggested high levels of trimethylamine N-oxide (TMAO) may correlate with increased risk of inflammatory-induced liver cancer. However, the mechanisms by which TMAO promotes liver cancer remain elusive. Here, we established a model of inflammatory-induced liver cancer by treating Hepa1-6 cells and Huh7 cells with TNF-α. TMAO synergistically increased the proliferation, migration and invasion of Hepa1-6 cells and Huh7 cells in the presence of TNF-α. We conducted bulk RNA-Seq of the TMAO-treated cell model of inflammatory Hepatocellular carcinoma (HCC) and evaluated the influence of the differentially expressed genes (DEGs) on clinical prognosis using Kaplan-Meier Plotter Database and Gene Expression Profiling Interactive Analysis (GEPIA) database. Univariate and multivariate Cox regression analyses of tumor microenvironment and DEGs were performed using Timer2.0. Upregulation of POSTN, LAYN and HTRA3 and downregulation of AANAT and AFM were positively related to poorer overall survival in human liver cancer. Moreover, higher expression of POSTN and HTRA3 positively correlated with infiltration of neutrophils, which can promote tumor progression. In vitro experiments showed TMAO activates ILK/AKT/mTOR signaling via POSTN, and knocking down POSTN significantly reduced ILK/AKT/mTOR signaling and the tumorigenicity of Hepa1-6 cells and Huh7 cells. Collectively, our results suggest the gut microbial metabolite TMAO and POSTN may represent potential therapeutic targets for liver cancer.

Gut microbiota-derived metabolite trimethylamine-N-oxide and multiple health outcomes: an umbrella review and updated meta-analysis

BACKGROUND

Trimethylamine-N-oxide (TMAO) is a gut microbiota-derived metabolite produced from dietary nutrients. Many studies have discovered that circulating TMAO concentrations are linked to a wide range of health outcomes.

OBJECTIVES

This study aimed to summarize health outcomes related to circulating TMAO concentrations.

METHODS

We searched the Embase, Medline, Web of Science, and Scopus databases from inception to 15 February, 2022 to identify and update meta-analyses examining the associations between TMAO and multiple health outcomes. For each health outcome, we estimated the summary effect size, 95% prediction CI, between-study heterogeneity, evidence of small-study effects, and evidence of excess-significance bias. These metrics were used to evaluate the evidence credibility of the identified associations.

RESULTS

This umbrella review identified 24 meta-analyses that investigated the association between circulating TMAO concentrations and health outcomes including all-cause mortality, cardiovascular diseases (CVDs), diabetes mellitus (DM), cancer, and renal function. We updated these meta-analyses by including a total of 82 individual studies on 18 unique health outcomes. Among them, 14 associations were nominally significant. After evidence credibility assessment, we found 6 (33%) associations (i.e., all-cause mortality, CVD mortality, major adverse cardiovascular events, hypertension, DM, and glomerular filtration rate) to present highly suggestive evidence.

CONCLUSIONS

TMAO might be a novel biomarker related to human health conditions including all-cause mortality, hypertension, CVD, DM, cancer, and kidney function. Further studies are needed to investigate whether circulating TMAO concentrations could be an intervention target for chronic disease.This review was registered at www.crd.york.ac.uk/prospero/ as CRD42021284730.

Balancing the Equation: A Natural History of Trimethylamine and Trimethylamine-N-oxide

Trimethylamine (TMA) and its N-oxide (TMAO) are ubiquitous in prokaryote and eukaryote organisms as well as in the environment, reflecting their fundamental importance in evolutionary biology, and their diverse biochemical functions. Both metabolites have multiple biological roles including cell-signaling. Much attention has focused on the significance of serum and urinary TMAO in cardiovascular disease risk, yet this is only one of the many facets of a deeper TMA-TMAO partnership that reflects the significance of these metabolites in multiple biological processes spanning animals, plants, bacteria, and fungi. We report on analytical methods for measuring TMA and TMAO and attempt to critically synthesize and map the global functions of TMA and TMAO in a systems biology framework.

Dietary Patterns and Associated Microbiome Changes that Promote Oncogenesis

The recent increases in cancer incidences have been linked to lifestyle changes that result in obesity and metabolic syndrome. It is now evident that these trends are associated with the profound changes that occur in the intestinal microbiome, producing altered microbial population signatures that interact, directly or indirectly, with potentially pro-carcinogenic molecular pathways of transcription, proliferation, and inflammation. The effects of the entire gut microbial population on overall health are complex, but individual bacteria are known to play important and definable roles. Recent detailed examinations of a large number of subjects show a tight correlation between habitual diets, fecal microbiome signatures, and markers of metabolic health. Diets that score higher in healthfulness or diversity such as plant-based diets, have altered ratios of specific bacteria, including an increase in short-chain fatty acid producers, which in turn have been linked to improved metabolic markers and lowered cancer risk. Contrarily, numerous studies have implicated less healthy, lower-scoring diets such as the Western diet with reduced intestinal epithelial defenses and promotion of specific bacteria that affect carcinogenic pathways. In this review, we will describe how different dietary patterns affect microbial populations in the gut and illustrate the subsequent impact of bacterial products and metabolites on molecular pathways of cancer development, both locally in the gut and systemically in distant organs.

Gut Microbiome-Dependent Metabolic Pathways and Risk of Lethal Prostate Cancer: Prospective Analysis of a PLCO Cancer Screening Trial Cohort

BACKGROUND

Diet and the gut microbiome have a complex interaction that generates metabolites with an unclear effect on lethal prostate cancer risk. Identification of modifiable risk factors for lethal prostate cancer is challenging given the long natural history of this disease and difficulty of prospectively identifying lethal cancers.

METHODS

Mass spectrometry was performed on baseline serum samples collected from 173 lethal prostate cancer cases and 519 controls enrolled in the Prostate, Lung, Colorectal, and Ovarian Cancer Screening trial. Baseline serum levels of choline, carnitine, betaine, γ-butyrobetaine, crotonobetaine, phenylacetylglutamine, hippuric acid, and p-cresol sulfate were quantified and analyzed by quartile. Conditional multivariable logistic regression analysis associated analyte levels with lethal prostate cancer incidence after adjusting for body mass index and PSA. The Cochran-Armitage test evaluated analyte level trends across quartiles.

RESULTS

Relative to those in the first quartile, cases with the highest baseline levels of choline (Q4 OR: 2.19; 95% CI, 1.23-3.90; P-trend: 0.005) and betaine (Q4 OR: 1.86; 95% CI, 1.05-3.30; P-trend: 0.11) exhibited increased odds of developing lethal prostate cancer. Higher baseline serum levels of phenylacetylglutamine (Q4 OR: 2.55; 95% CI, 1.40-4.64; P-trend: 0.003), a gut microbiome metabolite of phenylalanine with adrenergic activity, were also associated with lethal prostate cancer.

CONCLUSIONS

Baseline serum levels of one-carbon methyl donors and adrenergic compounds resulting from human and gut microbiota-mediated metabolism are associated with increased lethal prostate cancer risk.

IMPACT

Dietary composition, circulating metabolite levels, and downstream signaling pathways may represent modifiable risk factors associated with incident lethal prostate cancer. Beta-adrenergic blockade represents an additional target for oncologic risk reduction.

The MttB superfamily member MtyB from the human gut symbiont Eubacterium limosum is a cobalamin-dependent γ-butyrobetaine methyltransferase

The production of trimethylamine (TMA) from quaternary amines such as l-carnitine or γ-butyrobetaine (4-(trimethylammonio)butanoate) by gut microbial enzymes has been linked to heart disease. This has led to interest in enzymes of the gut microbiome that might ameliorate net TMA production, such as members of the MttB superfamily of proteins, which can demethylate TMA (e.g., MttB) or l-carnitine (e.g., MtcB). Here, we show that the human gut acetogen Eubacterium limosum demethylates γ-butyrobetaine and produces MtyB, a previously uncharacterized MttB superfamily member catalyzing the demethylation of γ-butyrobetaine. Proteomic analyses of E. limosum grown on either γ-butyrobetaine or dl-lactate were employed to identify candidate proteins underlying catabolic demethylation of the growth substrate. Three proteins were significantly elevated in abundance in γ-butyrobetaine-grown cells: MtyB, MtqC (a corrinoid-binding protein), and MtqA (a corrinoid:tetrahydrofolate methyltransferase). Together, these proteins act as a γ-butyrobetaine:tetrahydrofolate methyltransferase system, forming a key intermediate of acetogenesis. Recombinant MtyB acts as a γ-butyrobetaine:MtqC methyltransferase but cannot methylate free cobalamin cofactor. MtyB is very similar to MtcB, the carnitine methyltransferase, but neither was detectable in cells grown on carnitine nor was detectable in cells grown with γ-butyrobetaine. Both quaternary amines are substrates for either enzyme, but kinetic analysis revealed that, in comparison to MtcB, MtyB has a lower apparent K_m for γ-butyrobetaine and higher apparent V_max, providing a rationale for MtyB abundance in γ-butyrobetaine-grown cells. As TMA is readily produced from γ-butyrobetaine, organisms with MtyB-like proteins may provide a means to lower levels of TMA and proatherogenic TMA-N-oxide via precursor competition.

Impact of Plant-Based Meat Alternatives on the Gut Microbiota of Consumers: A Real-World Study

Eating less meat is increasingly seen as a healthier, more ethical option. This is leading to growing numbers of flexitarian consumers looking for plant-based meat alternatives (PBMAs) to replace at least some of the animal meat they consume. Popular PBMA products amongst flexitarians, including plant-based mince, burgers, sausages and meatballs, are often perceived as low-quality, ultra-processed foods. However, we argue that the mere industrial processing of ingredients of plant origin does not make a PBMA product ultra-processed by default. To test our hypothesis, we conducted a randomised controlled trial to assess the changes to the gut microbiota of a group of 20 participants who replaced several meat-containing meals per week with meals cooked with PBMA products and compared these changes to those experienced by a size-matched control. Stool samples were subjected to 16S rRNA sequencing. The resulting raw data was analysed in a compositionality-aware manner, using a range of innovative bioinformatic methods. Noteworthy changes included an increase in butyrate metabolising potential-chiefly in the 4-aminobutyrate/succinate and glutarate pathways-and in the joint abundance of butyrate-producing taxa in the intervention group compared to control. We also observed a decrease in the Tenericutes phylum in the intervention group and an increase in the control group. Based on our findings, we concluded that the occasional replacement of animal meat with PBMA products seen in flexitarian dietary patterns can promote positive changes in the gut microbiome of consumers.

Total volatile basic nitrogen and trimethylamine in muscle foods: Potential formation pathways and effects on human health

The use of total volatile basic nitrogen (TVB-N) as a quality parameter for fish is rapidly growing to include other types of meat. Investigations of meat quality have recently focused on TVB-N as an index of freshness, but little is known on the biochemical pathways involved in its generation. Furthermore, TVB-N and methylated amines have been reported to exert deterimental health effects, but the relationship between these compounds and human health has not been critically reviewed. Here, literature on the formative pathways of TVB-N has been reviewed in depth. The association of methylated amines and human health has been critically evaluated. Interventions to mitigate the effects of TVB-N on human health are discussed. TVB-N levels in meat can be influenced by the diet of an animal, which calls for careful consideration when using TVB-N thresholds for regulatory purposes. Bacterial contamination and temperature abuse contribute to significant levels of post-mortem TVB-N increases. Therefore, controlling spoilage factors through a good level of hygiene during processing and preservation techniques may contribute to a substantial reduction of TVB-N. Trimethylamine (TMA) constitutes a significant part of TVB-N. TMA and trimethylamine oxide (TMA-N-O) have been related to the pathogenesis of noncommunicable diseases, including atherosclerosis, cancers, and diabetes. Proposed methods for mitigation of TMA and TMA-N-O accumulation are discussed, which include a reduction in their daily dietary intake, control of internal production pathways by targeting gut microbiota, and inhibition of flavin monooxygenase 3 enzymes. The levels of TMA and TMA-N-O have significant health effects, and this should, therefore, be considered when evaluating meat quality and acceptability. Agreed international values for TVB-N and TMA in meat products are required. The role of feed, gut microbiota, and translocation of methylated amines to muscles in farmed animals requires further investigation.

Gut Microbiota: Influence on Carcinogenesis and Modulation Strategies by Drug Delivery Systems to Improve Cancer Therapy

Gut microbiota have close interactions with the host. It can affect cancer progression and the outcomes of cancer therapy, including chemotherapy, immunotherapy, and radiotherapy. Therefore, approaches toward the modulation of gut microbiota will enhance cancer prevention and treatment. Modern drug delivery systems (DDS) are emerging as rational and promising tools for microbiota intervention. These delivery systems have compensated for the obstacles associated with traditional treatments. In this review, the essential roles of gut microbiota in carcinogenesis, cancer progression, and various cancer therapies are first introduced. Next, advances in DDS that are aimed at enhancing the efficacy of cancer therapy by modulating or engineering gut microbiota are highlighted. Finally, the challenges and opportunities associated with the application of DDS targeting gut microbiota for cancer prevention and treatment are briefly discussed.

Intestinal Microbiota and Liver Diseases: Insights into Therapeutic Use of Traditional Chinese Medicine

Liver disease is a leading cause of global morbidity and mortality, for which inflammation, alcohol use, lipid metabolic disorders, disturbance to bile acid metabolism, and endotoxins are common risk factors. Traditional Chinese Medicine (TCM) with its "holistic approach" is widely used throughout the world as a complementary, alternative therapy, due to its clinical efficacy and reduced side effects compared with conventional medicines. However, due to a lack of reliable scientific evidence, the role of TCM in the prevention and treatment of liver disease remains unclear. Over recent years, with the rapid development of high-throughput sequencing, 16S rRNA detection, and bioinformatics methodology, it has been gradually recognized that the regulation of intestinal microbiota by TCM can play a substantial role in the treatment of liver disease. To better understand how TCM regulates the intestinal microbiota and suppresses liver disease, we have reviewed and analyzed the results of existing studies and summarized the relationship and risk factors between intestinal microbiota and liver disease. The present review summarizes the related mechanisms by which TCM affects the composition and metabolites of the intestinal microbiome.

Hepatocellular Carcinoma and Obesity, Type 2 Diabetes Mellitus, Cardiovascular Disease: Causing Factors, Molecular Links, and Treatment Options

Hepatocellular carcinoma (HCC) is the most common type of primary liver cancer, which will affect more than a million people by the year 2025. However, current treatment options have limited benefits. Nonalcoholic fatty liver disease (NAFLD) is the fastest growing factor that causes HCC in western countries, including the United States. In addition, NAFLD co-morbidities including obesity, type 2 diabetes mellitus (T2DM), and cardiovascular diseases (CVDs) promote HCC development. Alteration of metabolites and inflammation in the tumor microenvironment plays a pivotal role in HCC progression. However, the underlying molecular mechanisms are still not totally clear. Herein, in this review, we explored the latest molecules that are involved in obesity, T2DM, and CVDs-mediated progression of HCC, as they share some common pathologic features. Meanwhile, several therapeutic options by targeting these key factors and molecules were discussed for HCC treatment. Overall, obesity, T2DM, and CVDs as chronic metabolic disease factors are tightly implicated in the development of HCC and its progression. Molecules and factors involved in these NAFLD comorbidities are potential therapeutic targets for HCC treatment.

Colon Carcinogenesis: The Interplay Between Diet and Gut Microbiota

Colorectal cancer (CRC) incidence increases yearly, and is three to four times higher in developed countries compared to developing countries. The well-known risk factors have been attributed to low physical activity, overweight, obesity, dietary consumption including excessive consumption of red processed meats, alcohol, and low dietary fiber content. There is growing evidence of the interplay between diet and gut microbiota in CRC carcinogenesis. Although there appears to be a direct causal role for gut microbes in the development of CRC in some animal models, the link between diet, gut microbes, and colonic carcinogenesis has been established largely as an association rather than as a cause-and-effect relationship. This is especially true for human studies. As essential dietary factors influence CRC risk, the role of proteins, carbohydrates, fat, and their end products are considered as part of the interplay between diet and gut microbiota. The underlying molecular mechanisms of colon carcinogenesis mediated by gut microbiota are also discussed. Human biological responses such as inflammation, oxidative stress, deoxyribonucleic acid (DNA) damage can all influence dysbiosis and consequently CRC carcinogenesis. Dysbiosis could add to CRC risk by shifting the effect of dietary components toward promoting a colonic neoplasm together with interacting with gut microbiota. It follows that dietary intervention and gut microbiota modulation may play a vital role in reducing CRC risk.

The gut microbiome-bile acid axis in hepatocarcinogenesis

Hepatocellular carcinoma (HCC) is the most common primary liver malignancy and is a leading cause of cancer-related deaths globally, with few effective therapeutic options. Bile acids (BAs) are synthesized from cholesterol in the liver and can be modulated by farnesoid X receptor (FXR) and G-protein coupled BA receptor 1 (GPBAR1/TGR5). Alterations in BAs can affect hepatic metabolic homeostasis and contribute to the pathogenesis of liver cancer. Increasing evidence points to the key role of bacterial microbiota in the promotion and development of liver cancer. They are also involved in the regulation of BA synthesis and metabolism. The purpose of this review is to integrate related articles involving gut microbiota, BAs and HCC, and review how the gut microbiota-BA signaling axis can possibly influence the development of HCC.

Dietary choline, rather than betaine intake, is associated with hepatocellular carcinoma mortality

The dietary intakes of choline and betaine have been related to the mortality of some neoplasms, but their effects on hepatocellular carcinoma (HCC) mortality are still unknown. We examined the associations between dietary choline, five choline-containing compounds, different choline forms, betaine intake and HCC mortality. In total, 905 newly diagnosed HCC patients were enrolled in the Guangdong Liver Cancer Cohort study. Dietary intake was assessed by a valid food frequency questionnaire. Liver cancer-specific mortality (LCSM) and all-cause mortality (ACM) were calculated. Hazard ratios (HRs) and 95% confidence intervals (CIs) were computed by Cox proportional hazards models. It was found that a higher total choline intake was associated with lower ACM, Q4 vs. Q1: HR = 0.72, 95% CI: 0.53-0.97, Ptrend = 0.012 in the fully adjusted model. The associations between total choline intake and LCSM were not significant. Similar associations were found between water-soluble choline intake and HCC mortality, where the fully adjusted HR for ACM was 0.72, 95% CI: 0.53-0.98, Ptrend = 0.017. However, null associations were found between neither phosphatidylcholine (the most abundant lipid-soluble choline) nor total lipid-soluble choline intake and HCC mortality. These results implied that the favorable associations between the total choline intake and ACM were more attributed to water-soluble choline. Furthermore, no significant associations were observed between betaine intake and HCC mortality. Future human intervention trials regarding choline supplementation and liver disease recovery should take the forms into consideration rather than just the total amount alone.

Serum choline is associated with hepatocellular carcinoma survival: a prospective cohort study

BACKGROUND

Higher choline and betaine levels have been linked to lower risk of liver cancer, whereas existing data in relation to hepatocellular carcinoma (HCC) prognosis are scarce. Our objective was to examine the associations of the serum choline and betaine with HCC survival.

METHODS

866 newly diagnosed HCC patients were enrolled in the Guangdong Liver Cancer Cohort. Serum choline and betaine were assessed using high-performance liquid chromatography with online electro-spray ionization tandem mass spectrometry. Liver cancer-specific survival (LCSS) and overall survival (OS) were calculated. Cox proportional hazards models were used to estimate the hazard ratios (HRs) and 95% confidence intervals (CIs).

RESULTS

Serum choline levels were associated with better LCSS (T3 vs. T1: HR = 0.69, 95% CI: 0.51-0.94; P -trend < 0.05) and OS (T3 vs. T1: HR = 0.73, 95% CI: 0.54-0.99; P -trend < 0.05). The associations were significantly modified by C-reactive protein (CRP) levels but not by other selected prognostic factors including sex, age, etc. The favorable associations between serum choline and LCSS and OS were only existed among patients with CRP ≥3.0 mg/L. No significant associations were found between serum betaine levels and either LCSS or OS.

CONCLUSIONS

This study revealed that higher serum choline levels were associated with better HCC survival, especially in HCC patients with systemic inflammation status. No significant associations were found between serum betaine and HCC survival. Our findings suggest the benefits of choline on HCC survival.

TRIAL REGISTRATION

The Guangdong Liver Cancer Cohort was registered at clinicaltrials.gov as NCT03297255.

Colorectal cancer: The epigenetic role of microbiome

Colorectal cancer (CRC) is the third most common cancer in men (746000 cases per year) and the second most common cancer in women globally (614000 cases per year). The incidence rate of CRC in developed countries (737000 cases per year) is higher than that in less developed countries (624000 cases per year). CRC can arise from genetic causes such as chromosomal instability and microsatellite instability. Several etiologic factors underlie CRC including age, diet, and lifestyle. Gut microbiota represent a proven cause of the disease, where they play pivotal roles in modulating and reshaping the host epigenome. Several active microbial metabolites have been found to drive carcinogenesis, invasion, and metastasis via modifying both the methylation landscape along with histone structure in intestinal cells. Gut microbiota, in response to diet, can exert both beneficial and harmful functions in humans, according to the intestinal balance of number and types of these bacteria. Although the intestinal microbial community is diverse among individuals, these microbes cumulatively produce 100-fold more proteins than the human genome itself, which calls for further studies to elaborate on the complicated interaction between these microorganisms and intestinal cells. Therefore, understanding the exact role that gut microbiota play in inducing CRC will help attain reliable strategies to precisely diagnose and treat this fatal disease.

The Microbial Metabolite Trimethylamine N-Oxide Links Vascular Dysfunctions and the Autoimmune Disease Rheumatoid Arthritis

Diet and microbiota each have a direct impact on many chronic, inflammatory, and metabolic diseases. As the field develops, a new perspective is emerging. The effects of diet may depend on the microbiota composition of the intestine. A diet that is rich in choline, red meat, dairy, or egg may promote the growth, or change the composition, of microbial species. The microbiota, in turn, may produce metabolites that increase the risk of cardiovascular disease. This article reviews our current understanding of the effects of the molecule trimethylamine-N-oxide (TMAO) obtained from food or produced by the microbiota. We review the mechanisms of actions of TMAO, and studies that associate it with cardiovascular and chronic kidney diseases. We introduce a novel concept: TMAO is one among a group of selective uremic toxins that may rise to high levels in the circulation or accumulate in various organs. Based on this information, we evaluate how TMAO may harm, by exacerbating inflammation, or may protect, by attenuating amyloid formation, in autoimmune diseases such as rheumatoid arthritis.

Dietary Additives and Supplements Revisited: The Fewer, the Safer for Liver and Gut Health

Purpose of Review

The supplementation of dietary additives into processed foods has exponentially increased in the past few decades. Similarly, the incidence rates of various diseases, including metabolic syndrome, gut dysbiosis and hepatocarcinogenesis, have been elevating. Current research reveals that there is a positive association between food additives and these pathophysiological diseases. This review highlights the research published within the past 5 years that elucidate and update the effects of dietary supplements on liver and intestinal health.

Recent Findings

Some of the key findings include: enterocyte dysfunction of fructose clearance causes non-alcoholic fatty liver disease (NAFLD); non-caloric sweeteners are hepatotoxic; dietary emulsifiers instigate gut dysbiosis and hepatocarcinogenesis; and certain prebiotics can induce cholestatic hepatocellular carcinoma (HCC) in gut dysbiotic mice. Overall, multiple reports suggest that the administration of purified, dietary supplements could cause functional damage to both the liver and gut.

Summary

The extraction of bioactive components from natural resources was considered a brilliant method to modulate human health. However, current research highlights that such purified components may negatively affect individuals with microbiotal dysbiosis, resulting in a deeper break of the symbiotic relationship between the host and gut microbiota, which can lead to repercussions on gut and liver health. Therefore, ingestion of these dietary additives should not go without some caution!