Genetically Predicted Causal Effects of Gut Microbiota and Gut Metabolites on Digestive Tract Cancer: A Two-Sample Mendelian Randomization Analysis

Background

Evidence from numerous observational studies and clinical trials has linked gut microbiota and metabolites to digestive tract cancer. However, the causal effect between these factors remains uncertain.

Methods

Data for this study were obtained from the MiBioGen, TwinsUK Registry, and FinnGen (version R8). Two-sample Mendelian randomization analysis with inverse variance weighting method was primarily used, and the results were validated by heterogeneity analysis, pleiotropy test, and sensitivity analysis.

Results

At P < 5 × 10-8, our analysis identified four gut microbiotas as risk factors for digestive tract cancer and six as risk factors for colorectal cancer. Conversely, one gut microbiota exhibited protection against bile duct cancer, and two showed protective effects against stomach cancer. At P < 1 × 10-5, our investigation revealed five, six, three, eight, eight, and eight gut microbiotas as risk factors for esophageal, stomach, bile duct, liver, pancreatic, and colorectal cancers, respectively. In contrast, four, two, eight, two, two, and five gut microbiotas exhibited protective effects against these cancers. Additionally, GABA, a metabolite of gut microbiota, displayed a significant protective effect against colorectal cancer.

Conclusion

In conclusion, specific gut microbiota and metabolites play roles as risk factors or protective factors for digestive tract cancer, and a causal relationship between them has been established, offering novel insights into gut microbiota-mediated cancer development.

Gut microbiota in alcohol-related liver disease: pathophysiology and gut-brain cross talk

Alcohol-related liver disease (ALD) from excessive alcohol intake has a unique gut microbiota profile. The disease progression-free survival in ALD patients has been associated with the degree of gut dysbiosis. The vicious cycles between gut dysbiosis and the disease progression in ALD including: an increase of acetaldehyde production and bile acid secretion, impaired gut barrier, enrichment of circulating microbiota, toxicities of microbiota metabolites, a cascade of pro-inflammatory chemokines or cytokines, and augmentation in the generation of reactive oxygen species. The aforementioned pathophysiology process plays an important role in different disease stages with a spectrum of alcohol hepatitis, ALD cirrhosis, neurological dysfunction, and hepatocellular carcinoma. This review aims to illustrate the pathophysiology of gut microbiota and clarify the gut-brain crosstalk in ALD, which may provide the opportunity of identifying target points for future therapeutic intervention in ALD.

Recent Advances in the Polish Research on Polysaccharide-Based Nanoparticles in the Context of Various Administration Routes

Polysaccharides are the most abundant polymers in nature. They exhibit robust biocompatibility, reliable non-toxicity, and biodegradable character; thus, they are employed in multiple biomedical applications. The presence of chemically accessible functional groups on the backbone of biopolymers (amine, carboxyl, hydroxyl, etc.) makes them suitable materials for chemical modification or drug immobilisation. Among different drug delivery systems (DDSs), nanoparticles have been of great interest in scientific research in the last decades. In the following review, we want to address the issue of rational design of nanoparticle (NP)-based drug delivery systems in reference to the specificity of the medication administration route and resulting requirements. In the following sections, readers can find a comprehensive analysis of the articles published by authors with Polish affiliations in the last few years (2016-2023). The article emphasises NP administration routes and synthetic approaches, followed by in vitro and in vivo attempts toward pharmacokinetic (PK) studies. The 'Future Prospects' section was constructed to address the critical observations and gaps found in the screened studies, as well as to indicate good practices for polysaccharide-based nanoparticle preclinical evaluation.

Enterocloster alcoholdehydrogenati sp. nov., a Novel Bacterial Species Isolated from the Feces of a Patient with Alcoholism

Strain C5-48T, an anaerobic intestinal bacterium that potentially accumulates acetaldehyde at levels exceeding its minimum mutagenic concentration (50 µM) in the colon and rectum, was isolated from the feces of a patient with alcoholism. The 16S rRNA gene sequence of strain C5-48T showed high similarity to the corresponding sequences of Lachnoclostridium edouardi Marseille-P3397T (95.7%) and Clostridium fessum SNUG30386T (94.7%). However, phylogenetic analysis using the sequences of the 16S rRNA, rpoB, and hsp60 genes and whole-genome analysis strongly suggested that C5-48T should be included in the genus Enterocloster. The novelty of strain C5-48T was further confirmed by comprehensive average nucleotide identity (ANI) calculations based on its whole-genome sequence, which showed appreciable ANI values with known Enterocloster species (e.g., 74.3% and 73.4% with Enterocloster bolteae WAL 16351T and Enterocloster clostridioformis ATCC 25537T, respectively). The temperature range for growth of strain C5-48T was 15-37 °C with an optimum of 37 °C. The pH range for growth was 5.5-10.5 with an optimum of 7.5. The major constituents of the cell membrane lipids of strain C5-48T were 16:0, 14:0, and 18:1 ω7c dimethyl acetal fatty acids. On the basis of the genotypic and phenotypic properties, Enterocloster alcoholdehydrogenati sp. nov. is proposed, with the type strain C5-48T (= JCM 33305T = DSM 109474T).

Volatile Markers for Cancer in Exhaled Breath-Could They Be the Signature of the Gut Microbiota?

It has been shown that the gut microbiota plays a central role in human health and disease. A wide range of volatile metabolites present in exhaled breath have been linked with gut microbiota and proposed as a non-invasive marker for monitoring pathological conditions. The aim of this study was to examine the possible correlation between volatile organic compounds (VOCs) in exhaled breath and the fecal microbiome by multivariate statistical analysis in gastric cancer patients (n = 16) and healthy controls (n = 33). Shotgun metagenomic sequencing was used to characterize the fecal microbiota. Breath-VOC profiles in the same participants were identified by an untargeted gas chromatography-mass spectrometry (GC-MS) technique. A multivariate statistical approach involving a canonical correlation analysis (CCA) and sparse principal component analysis identified the significant relationship between the breath VOCs and fecal microbiota. This relation was found to differ between gastric cancer patients and healthy controls. In 16 cancer cases, 14 distinct metabolites identified from the breath belonging to hydrocarbons, alcohols, aromatics, ketones, ethers, and organosulfur compounds were highly correlated with 33 fecal bacterial taxa (correlation of 0.891, p-value 0.045), whereas in 33 healthy controls, 7 volatile metabolites belonging to alcohols, aldehydes, esters, phenols, and benzamide derivatives correlated with 17 bacterial taxa (correlation of 0.871, p-value 0.0007). This study suggested that the correlation between fecal microbiota and breath VOCs was effective in identifying exhaled volatile metabolites and the functional effects of microbiome, thus helping to understand cancer-related changes and improving the survival and life expectancy in gastric cancer patients.

Susceptibility to Colorectal Cancer Based on HSD17B4 rs721673 and rs721675 Polymorphisms and Alcohol Intake among Taiwan Biobank Participants: A Retrospective Case Control Study Using the Nationwide Claims Data

Colorectal cancer (CRC) is a major public health issue, and there are limited studies on the association between 17β-hydroxysteroid dehydrogenase type 4 (HSD17B4) polymorphism and CRC. We used two national databases from Taiwan to examine whether HSD17B4 rs721673, rs721675, and alcohol intake were independently and interactively correlated with CRC development. We linked the Taiwan Biobank (TWB) participants’ health and lifestyle information and genotypic data from 2012 to 2018 to the National Health Insurance Database (NHIRD) to confirm their medical records. We performed a genome-wide association study (GWAS) using data from 145 new incident CRC cases and matched 1316 healthy, non-CRC individuals. We calculated the odds ratios (OR) and 95% confidence intervals (CI) for CRC based on multiple logistic regression analyses. HSD17B4 rs721673 and rs721675 on chromosome 5 were significantly and positively correlated with CRC (rs721673 A > G, aOR = 2.62, p = 2.90 × 10−8; rs721675 A > T, aOR = 2.61, p = 1.01 × 10−6). Within the high-risk genotypes, significantly higher ORs were observed among the alcohol intake group. Our results demonstrated that the rs721673 and rs721675 risk genotypes of HSD17B4 might increase the risk of CRC development in Taiwanese adults, especially those with alcohol consumption habits.

Systematic Review: Contribution of the Gut Microbiome to the Volatile Metabolic Fingerprint of Colorectal Neoplasia

Colorectal cancer (CRC) has been associated with changes in volatile metabolic profiles in several human biological matrices. This enables its non-invasive detection, but the origin of these volatile organic compounds (VOCs) and their relation to the gut microbiome are not yet fully understood. This systematic review provides an overview of the current understanding of this topic. A systematic search using PubMed, Embase, Medline, Cochrane Library, and the Web of Science according to PRISMA guidelines resulted in seventy-one included studies. In addition, a systematic search was conducted that identified five systematic reviews from which CRC-associated gut microbiota data were extracted. The included studies analyzed VOCs in feces, urine, breath, blood, tissue, and saliva. Eight studies performed microbiota analysis in addition to VOC analysis. The most frequently reported dysregulations over all matrices included short-chain fatty acids, amino acids, proteolytic fermentation products, and products related to the tricarboxylic acid cycle and Warburg metabolism. Many of these dysregulations could be related to the shifts in CRC-associated microbiota, and thus the gut microbiota presumably contributes to the metabolic fingerprint of VOC in CRC. Future research involving VOCs analysis should include simultaneous gut microbiota analysis.

Colon microbiota modulation by dairy-derived diet: new strategy for prevention and treatment of colorectal cancer

An unbalanced diet is one of the well-known risk factors for the development of colorectal cancer (CRC). This type of cancer is currently the main cause of cancer-related deaths worldwide, urging the need for new and more effective preventive and therapeutic approaches. It is already known that CRC patients have alterations in the microbial community and metabolism. In this regard, a concept that has been recently attracting the attention of the scientific community is the development of functional food or nutraceuticals, as a new and more effective strategy to overcome CRC patient-associated dysbiosis. Particularly, dairy product enriched diets are the major dairy source of dietary calcium, vitamin D and folate intake, which are well-known to have a protective effect against CRC development. In addition, these products are rich in both pre- and probiotics, constituting a double strategy to modulate both the intestinal microbiota composition and the production of microbial metabolites. Short-chain fatty acids (SCFA), namely, acetate, butyrate, and propionate, are major contributors to colonic homeostasis since they regulate several biological and metabolic processes. In this review, we performed a state of art study concerning the use of dietary patterns, specifically the dairy-derived diet, in the modulation of the human microbiota and their potential use as pre-, pro- or synbiotics for the development of new preventive and therapeutic strategies for CRC.

Interaction between microbiota and immunity and its implication in colorectal cancer

Colorectal cancer (CRC) is one of the leading causes of cancer-related death in the world. Besides genetic causes, colonic inflammation is one of the major risk factors for CRC development, which is synergistically regulated by multiple components, including innate and adaptive immune cells, cytokine signaling, and microbiota. The complex interaction between CRC and the gut microbiome has emerged as an important area of current CRC research. Metagenomic profiling has identified a number of prominent CRC-associated bacteria that are enriched in CRC patients, linking the microbiota composition to colitis and cancer development. Some microbiota species have been reported to promote colitis and CRC development in preclinical models, while a few others are identified as immune modulators to induce potent protective immunity against colitis and CRC. Mechanistically, microbiota regulates the activation of different immune cell populations, inflammation, and CRC via crosstalk between innate and adaptive immune signaling pathways, including nuclear factor kappa B (NF-κB), type I interferon, and inflammasome. In this review, we provide an overview of the potential interactions between gut microbiota and host immunity and how their crosstalk could synergistically regulate inflammation and CRC, thus highlighting the potential roles and mechanisms of gut microbiota in the development of microbiota-based therapies to prevent or alleviate colitis and CRC.

Gut microbiome features associated with liver fibrosis in Hispanics, a population at high risk for fatty liver disease

BACKGROUND AND AIMS

Hispanics are disproportionately affected by NAFLD, liver fibrosis, cirrhosis, and HCC. Preventive strategies and noninvasive means to identify those in this population at high risk for liver fibrosis, are urgently needed. We aimed to characterize the gut microbiome signatures and related biological functions associated with liver fibrosis in Hispanics and identify environmental and genetic factors affecting them.

APPROACH AND RESULTS

Subjects of the population-based Cameron County Hispanic Cohort (CCHC; n = 217) were screened by vibration-controlled transient elastography (FibroScan). Among them, 144 (66.7%) had steatosis and 28 (13.0%) had liver fibrosis. The gut microbiome of subjects with liver fibrosis was enriched with immunogenic commensals (e.g., Prevotella copri, Holdemanella, Clostridiaceae 1) and depleted of Bacteroides caccae, Parabacteroides distasonis, Enterobacter, and Marinifilaceae. The liver fibrosis-associated metagenome was characterized by changes in the urea cycle, L-citrulline biosynthesis and creatinine degradation pathways, and altered synthesis of B vitamins and lipoic acid. These metagenomic changes strongly correlated with the depletion of Parabacteroides distasonis and enrichment of Prevotella and Holdemanella. Liver fibrosis was also associated with depletion of bacterial pathways related to L-fucose biosynthesis. Alcohol consumption, even moderate, was associated with high Prevotella abundance. The single-nucleotide polymorphisms rs3769502 and rs7573751 in the NCK adaptor protein 2 (NCK2) gene positively associated with high Prevotella abundance.

CONCLUSION

Hispanics with liver fibrosis display microbiome profiles and associated functional changes that may promote oxidative stress and a proinflammatory environment. These microbiome signatures, together with NCK2 polymorphisms, may have utility in risk modeling and disease prevention in this high-risk population.

The Mucosally-Adherent Rectal Microbiota Contains Features Unique to Alcohol-Related Cirrhosis

Most studies examining correlations between the gut microbiota and disease states focus on fecal samples due to ease of collection, yet there are distinct differences when compared to samples collected from the colonic mucosa. Although fecal microbiota has been reported to be altered in cirrhosis, correlation with mucosal microbiota characterized via rectal swab has not been previously described in this patient population. We conducted a cross-sectional analysis using 39 stool and 39 rectal swabs from adult patients with cirrhosis of different etiologies and performed shotgun metagenomic sequencing. Bacterial growth studies were performed with Escherichia coli. Two asaccharolytic bacterial taxa, Finegoldia magna and Porphyromonas asaccharolytica, were increased in rectal swabs relative to stool (FDR < 0.01). Genomic analysis of the microbiome revealed 58 genes and 16 pathways that differed between stool and rectal swabs (FDR < 0.05), where rectal swabs were enriched for pathways associated with protein synthesis and cellular proliferation but decreased in carbohydrate metabolism. Although no features in the fecal microbiome differentiated cirrhosis etiologies, the mucosal microbiome revealed decreased abundances of E. coli and Enterobacteriaceae in alcohol-related cirrhosis relative to non-alcohol related cirrhosis (FDR < 0.05). In vitro bacterial culture studies showed that physiological concentrations of ethanol and its oxidative metabolites inhibited E. coli growth in a pH- and concentration-dependent manner. Characterization of the mucosally associated gut microbiome via rectal swab revealed findings consistent with amino acid/nitrogen abundance versus carbohydrate limitation in the mucosal microenvironment as well as unique features of alcohol-related cirrhosis possibly consistent with the influence of host-derived metabolites on the composition of mucosally adherent microbiota.

Crosstalk between gut microbiota and host lipid metabolism in a mouse model of alcoholic liver injury by chronic baijiu or ethanol feeding

A growing body of evidence highlights the important role of gut microbiota and host metabolism, particularly for lipid metabolism, in the development and progression of alcoholic liver disease (ALD). However, the effects of fermented alcoholic beverages on gut microbiota and host lipid metabolism remain under-investigated. Moreover, the crosstalk between gut microbiota and host lipid metabolism is still unclear in experimental ALD. Baijiu is a traditional Chinese alcoholic beverage. It contains large amounts of small molecule bioactive compounds in addition to a significant amount of ethanol (EtOH). In this study, we showed that baijiu caused lower degrees of liver injury than pure EtOH as revealed by phenotypic, biochemical and histologic analyses. Furthermore, baijiu and EtOH gavage resulted in different gut microbiota structures. Specifically, the baijiu group had a significantly higher abundance of Ruminococcus, Oscillospira, Mucispirillum, Bilophila, Parabacteroides and Odoribacter and a lower abundance of Helicobacter and Prevotella than that of the EtOH group. Using a targeted metabolomics approach, we also observed a greater than 19% increase of total hepatic free fatty acids (FFAs) after baijiu feeding and a 33% increase of hepatic FFAs after EtOH feeding. Baijiu feeding significantly increased total hepatic mono-unsaturated FAs (MUFAs). In contrast, polyunsaturated fatty acids (PUFAs), MUFAs and saturated FAs were significantly increased by EtOH feeding. Finally, Spearman's rank correlation showed that the increased levels of FFAs (mainly C20 and C22 unsaturated FAs) significantly correlated with key different gut microbiota, including a positive correlation with Desulfovibrio, Maihella, Helicobacter, Acholeplasma, Parasutterella, Prevotella, AF12 and Alistipes, and a negative correlation with Dorea, Olsenella, Adlercreutzia and Akkermansia. Our results suggest that compounds in baijiu attenuated the development of ALD and thus provided supporting evidence that the host-gut microbiota metabolic interactions play an important role in the development of ALD.

The Role of Diet and Lifestyle in Early-Onset Colorectal Cancer: A Systematic Review

Simple Summary

This systematic review sifted through the exogenous dietary and lifestyle risk factors associated with early-onset colorectal cancer, going through the putative involvement of these exogenous risk factors in epigenetic and microbiota modifications. Given the burden of early-onset colorectal cancer and its globally increasing trend with scant literature on its pathogenesis, we believe it would be of benefit to highlight the importance of further systematic and large studies. Indeed, dietary and lifestyle modification could complement colorectal screening for early-onset colorectal cancer prevention.

Abstract

The incidence of early-onset colorectal cancer, defined as colorectal cancer occurring in young adults under the age of 50, is increasing globally. Knowledge of the etiological factors in young adults is far from complete. Questionable eoCRCs’ exogenous factors are represented by processed meat, sugary drinks, alcohol, Western dietary pattern, overweight and obesity, physical inactivity, and smoking, though with heterogeneous results. Therefore, we performed a systematic review to summarize the current evidence on the role of diet and lifestyle as eoCRC risk factors. We systematically searched PubMed, Scopus, and EMBASE up to July 2021, for original studies evaluating diet, alcohol, physical activity, BMI, and smoking in eoCRC and included twenty-six studies. Indeed, the exogenous factors could represent modifiable key factors, whose recognition could establish areas of future interventions through public health strategies for eoCRC primary prevention. Additionally, we discussed the role of additional non-modifiable risk factors, and of epigenetic regulation and microbiota as mediators of the eoCRC triggered by diet and lifestyle.

The Microbiome-Gut-Brain Axis, a Potential Therapeutic Target for Substance-Related Disorders

Substance addiction is a complex worldwide public health problem. It endangers both personal life and social stability, causing great loss on economy. Substance-related disorder is considered to be a complicated chronic brain disorder. It resulted from interactions among pharmacological properties of addictive substances, individual susceptibility, and social–environmental factors. Unfortunately, there is still no ideal treatment for this disorder. Recent lines of evidence suggest that gut microbiome may play an important role in the pathogenesis of neuropsychiatric disorders, including substance-related disorders. This review summarizes the research on the relationship between gut microbiome and substance-related disorders, including different types of substance, different individual susceptibility, and the occurrence and development of substance-induced mental disorders. We also discuss the potentiation of gut microbiome in the treatment of substance-related disorders, especially in the treatment of substance-induced mental disorders and manipulation on individuals’ responsiveness to addictive substances.

Gut microbiome and resistome changes during the first wave of the COVID-19 pandemic in comparison with pre-pandemic travel-related changes

COVID-19-associated measures had a greater impact on gut microbiota, ARGs, and BRGs than did pre-pandemic international travel. During the COVID-19 pandemic, Actinobacteria richness decreased while genes conferring resistance to beta-lactam, polystyrene and phthalate increased. Such alterations may affect both colonisation resistance and acquisition and spread of antimicrobial resistance in future travels.

Molecular Mechanisms of Alcohol-Induced Colorectal Carcinogenesis

The etiology of colorectal cancer (CRC) is complex. Approximately, 10% of individuals with CRC have predisposing germline mutations that lead to familial cancer syndromes, whereas most CRC patients have sporadic cancer resulting from a combination of environmental and genetic risk factors. It has become increasingly clear that chronic alcohol consumption is associated with the development of sporadic CRC; however, the exact mechanisms by which alcohol contributes to colorectal carcinogenesis are largely unknown. Several proposed mechanisms from studies in CRC models suggest that alcohol metabolites and/or enzymes associated with alcohol metabolism alter cellular redox balance, cause DNA damage, and epigenetic dysregulation. In addition, alcohol metabolites can cause a dysbiotic colorectal microbiome and intestinal permeability, resulting in bacterial translocation, inflammation, and immunosuppression. All of these effects can increase the risk of developing CRC. This review aims to outline some of the most significant and recent findings on the mechanisms of alcohol in colorectal carcinogenesis. We examine the effect of alcohol on the generation of reactive oxygen species, the development of genotoxic stress, modulation of one-carbon metabolism, disruption of the microbiome, and immunosuppression.

Free radical-mediated acetaldehyde formation by model reactions of dietary components: effects of meat, wine, cooking oil and coffee

Background

Alcohol consumption and the ingestion of red meat and oxidized cooking oil are risk factors of gastric and colorectal cancers. We reported that acetaldehyde (AcAld) is generated from Heme/Mb/Meat-Linoleate-EtOH model reaction mixtures, and thus could be a new plausible mechanism for the carcinogenesis (Kasai and Kawai, ACS Omega, 2021).

Results

In this study, we investigated the effects of wine and coffee, in addition to meat components, on this reaction. Depending on the conditions, such as pH, reaction time and choice of free hemin, myoglobin (Mb), as well as meat extracts (raw meat, baked meat, salami), wine and coffee enhanced AcAld formation. Polyphenols in red wine and coffee may stimulate AcAld formation by acting as pro-oxidants in the presence of Heme/Mb/Meat. In a model reaction of Mb + EtOH + H₂O₂, we observed time-dependent AcAld formation. In support of these in vitro data, after the consumption of a red meat-rich diet with red wine, the fecal AcAld level significantly increased as compared to the levels associated with a diet of fish + wine, or red meat without alcohol.

Conclusions

These results suggested that AcAld generation from dietary components may be an important mechanism of gastrointestinal tract carcinogenesis.

Characterization of the gut-liver-muscle axis in cirrhotic patients with sarcopenia

BACKGROUND & AIM

Sarcopenia is frequent in cirrhosis and is associated with unfavourable outcomes. The role of the gut-liver-muscle axis in this setting has been poorly investigated. The aim of this study was to identify gut microbiota, metabolic and inflammatory signatures associated with sarcopenia in cirrhotic patients.

METHODS

Fifty cirrhotic patients assessed for the presence of sarcopenia by the quantification of muscle mass and strength were compared with age- and sex-matched controls. A multiomic analysis, including gut microbiota composition and metabolomics, serum myokines and systemic and intestinal inflammatory mediators, was performed.

RESULTS

The gut microbiota of sarcopenic cirrhotic patients was poor in bacteria associated with physical function (Methanobrevibacter, Prevotella and Akkermansia), and was enriched in Eggerthella, a gut microbial marker of frailty. The abundance of potentially pathogenic bacteria, such as Klebsiella, was also increased, to the detriment of autochthonous ones. Sarcopenia was associated with elevated serum levels of pro-inflammatory mediators and of fibroblast growth factor 21 (FGF21) in cirrhotic patients. Gut microbiota metabolic pathways involved in amino acid, protein and branched-chain amino acid metabolism were up-regulated, in addition to ethanol, trimethylamine and dimethylamine production. Correlation networks and clusters of variables associated with sarcopenia were identified, including one centred on Klebsiella/ethanol/FGF21/Eggerthella/Prevotella.

CONCLUSIONS

Alterations in the gut-liver-muscle axis are associated with sarcopenia in patients with cirrhosis. Detrimental but also compensatory functions are involved in this complex network.

Effects of multi-species probiotic supplementation on alcohol metabolism in rats

Probiotics are known to protect against liver damage induced by the alcohol and acetaldehyde accumulation associated with alcohol intake. However, there have been few studies of the direct effect of probiotics on alcohol metabolism, and the types of probiotics that were previously analyzed were few in number. Here, we investigated the effects of 19 probiotic species on alcohol and acetaldehyde metabolism. Four probiotic species that had a relatively high tolerance to alcohol and metabolized alcohol and acetaldehyde effectively were identified: Lactobacillus gasseri CBT LGA1, Lactobacillus casei CBT LC5, Bifidobacterium lactis CBT BL3, and Bifidobacterium breve CBT BR3. These species also demonstrated high mRNA expression of alcohol and acetaldehyde dehydrogenases. ProAP4, a mixture of these four probiotics species and excipient, was then administered to rats for 2 weeks in advance of acute alcohol administration. The serum alcohol and acetaldehyde concentrations were significantly lower in the ProAP4-administered group than in the control and excipient groups. Thus, the administration of ProAP4, containing four probiotic species, quickly lowers blood alcohol and acetaldehyde concentrations in an alcohol and acetaldehyde dehydrogenasedependent manner. Furthermore, the serum alanine aminotransferase activity, which is indicative of liver damage, was significantly lower in the ProAP4 group than in the control group. The present findings suggest that ProAP4 may be an effective means of limiting alcohol-induced liver damage.

Translational Approaches with Antioxidant Phytochemicals against Alcohol-Mediated Oxidative Stress, Gut Dysbiosis, Intestinal Barrier Dysfunction, and Fatty Liver Disease

Emerging data demonstrate the important roles of altered gut microbiomes (dysbiosis) in many disease states in the peripheral tissues and the central nervous system. Gut dysbiosis with decreased ratios of Bacteroidetes/Firmicutes and other changes are reported to be caused by many disease states and various environmental factors, such as ethanol (e.g., alcohol drinking), Western-style high-fat diets, high fructose, etc. It is also caused by genetic factors, including genetic polymorphisms and epigenetic changes in different individuals. Gut dysbiosis, impaired intestinal barrier function, and elevated serum endotoxin levels can be observed in human patients and/or experimental rodent models exposed to these factors or with certain disease states. However, gut dysbiosis and leaky gut can be normalized through lifestyle alterations such as increased consumption of healthy diets with various fruits and vegetables containing many different kinds of antioxidant phytochemicals. In this review, we describe the mechanisms of gut dysbiosis, leaky gut, endotoxemia, and fatty liver disease with a specific focus on the alcohol-associated pathways. We also mention translational approaches by discussing the benefits of many antioxidant phytochemicals and/or their metabolites against alcohol-mediated oxidative stress, gut dysbiosis, intestinal barrier dysfunction, and fatty liver disease.

Sex- and age-related trajectories of the adult human gut microbiota shared across populations of different ethnicities

Lifelong sex- and age-related trajectories of the human gut microbiota remain largely unexplored. Using metagenomics, we derived the gut microbial composition of 2,338 adults (26-76 years) from a Han Chinese population-based cohort where metabolic health, hormone levels and aspects of their lifestyles were also recorded. In this cohort, and in three independent cohorts distributed across China, Israel and the Netherlands, we observed sex differences in the gut microbial composition and a shared age-related decrease in sex-dependent differences in gut microbiota. Compared to men, the gut microbiota of premenopausal women exhibited higher microbial diversity and higher abundances of multiple species known to have beneficial effects on host metabolism. We also found consistent sex-independent, age-related gut microbial characteristics across all populations, with the presence of members of the oral microbiota being the strongest indicator of older chronological age. Our findings highlight the existence of sex- and age-related trajectories in the human gut microbiota that are shared between populations of different ethnicities and emphasize the pivotal links between sex hormones, gut microbiota and host metabolism.

Fusobacterium nucleatum in biopsied tissues from colorectal cancer patients and alcohol consumption in Korea

The roles of individual bacteria and their relationship in the development of colorectal cancer (CRC) remain unclear. We aimed to determine the prevalence of CRC-associated bacteria using quantitative real-time PCR (qPCR) or 16S rRNA analysis and the statistical correlations of patient demographics and clinical characteristics comprising alcohol consumption with CRC-associated bacteria. We determined the prevalence of five CRC-associated bacterial species in 38 CRC patients (39 samples) and 21 normal individuals using qPCR, and the relative abundance of bacterial taxa in the gut microbiome was assessed using 16S rRNA analysis. Fusobacterium nucleatum was the only bacterium that was significantly (P < 0.0001) more prevalent in the cancer tissue (82.1%) than in the normal tissue (0%) by qPCR. 16S rRNA analysis showed a significant correlation between six operational taxonomic units (OTUs), namely, the genera Fusobacterium, Peptostreptococcus, Collinsella, Prevotella, Parvimonas, and Gemella, in patients with CRC. An integrated analysis using 16S rRNA data and epidemiological characteristics showed that alcohol consumption was significantly correlated with the abundance of Fusobacterium OTUs. The correlation of alcohol consumption with the abundance of Fusobacterium OTUs in cancer tissue discovered using 16S rRNA analysis suggests a possible link between alcohol metabolism and subsequent tumorigenesis caused by F. nucleatum.

The gut microbiome and potential implications for early-onset colorectal cancer

Recently, there has been an unexpected trend toward increased incidence of colorectal cancer in younger individuals, particularly distal colon and rectal cancer in those under age 50. There is evidence to suggest that the human gut microbiome may play a role in carcinogenesis. The microbiome is dynamic and varies with age, geography, ethnicity and diet. Certain bacteria such as Fusobacterium nucleatum have been implicated in the development of colorectal and other gastrointestinal cancers. Recent data suggest that bacteria can alter the inflammatory and immune environment, influencing carcinogenesis, lack of treatment response and prognosis. Studies to date focus on older patients. Because the microbiome varies with age, it could be a potential explanation for the rise in early-onset colorectal cancer.

Gut microbiota compositional and functional fingerprint in patients with alcohol use disorder and alcohol-associated liver disease

BACKGROUND & AIMS

Alcohol use disorder (AUD) represents the most common cause of liver disease. The gut microbiota plays a critical role in the progression of alcohol-related liver damage. Aim of this study was to characterize the gut microbial composition and function in AUD patients with alcohol-associated liver disease (AALD).

METHODS

This study included 36 AUD patients (14 with cirrhosis) who were active drinkers and an equal number of matched controls. Stool microbial composition, serum levels of lipopolysaccharide, cytokines/chemokines and gut microbiota functional profile were assessed.

RESULTS

AUD patients had a decreased microbial alpha diversity as compared to controls (0.092 vs 0.130, P = .047) and a specific gut microbial signature. The reduction of Akkermansia and the increase in Bacteroides were able to identify AUD patients with an accuracy of 93.4%. Serum levels of lipopolysaccharide (4.91 vs 2.43, P = .009) and pro-inflammatory mediators (tumour necrosis factor alpha 60.85 vs 15.08, P = .001; interleukin [IL] 1beta 4.43 vs 1.72, P = .0001; monocyte chemoattractant protein 1 225.22 vs 16.43, P = .006; IL6 1.87 vs 1.23, P = .008) were significantly increased in AUD patients compared to controls and in cirrhotic patients compared to non-cirrhotic ones (IL6 3.74 vs 1.39, P = .019; IL8 57.60 vs 6.53, P = .004). The AUD-associated gut microbiota showed an increased expression of gamma-aminobutyric acid (GABA) metabolic pathways and energy metabolism.

CONCLUSIONS

AUD patients present a specific gut microbial fingerprint, associated with increased endotoxaemia, systemic inflammatory status and functional alterations that may be involved in the progression of the AALD and in the pathogenesis of AUD.

Alcohol consumption increases susceptibility to pneumococcal pneumonia in a humanized murine HIV model mediated by intestinal dysbiosis

Alcohol use in persons living with HIV (PLWH) worsens the severity of bacterial pneumonia. However, the exact mechanism(s) by which this occurs remain ill-defined. We hypothesized that alcohol in the setting of HIV infection decreases Streptococcus pneumoniae clearance from the lung through mechanisms mediated by the gut microbiota. Humanized BLT (bone marrow, liver, thymus) mice were infected with 1 × 104 TCID50 of HIV (BAL and JRCSF strains) via intraperitoneal (i.p.) injection. One week post-HIV infection, animals were switched to a Lieber-DeCarli 5% ethanol diet or an isocaloric control diet for 10 days. Alcohol-fed animals were also given two binges of 2 g/kg ethanol on days 5 and 10. Feces were also collected, banked, and the community structures were analyzed. Mice were then infected with 1 × 105 CFU (colony-forming units) of S. pneumoniae and were sacrificed 48 h later. HIV-infected mice had viral loads of ∼2 × 104 copies/mL of blood 1 week post-infection, and exhibited an ∼57% decrease in the number of circulating CD4+ T cells at the time of sacrifice. Fecal microbial community structure was significantly different in each of the feeding groups, as well as with HIV infection. Alcohol-fed mice had a significantly higher burden of S. pneumoniae 48 h post-infection, regardless of HIV status. In follow-up experiments, female C57BL/6 mice were treated with a cocktail of antibiotics daily for 2 weeks and recolonized by gavage with intestinal microbiota from HIV+ ethanol-fed, HIV+ pair-fed, HIV- ethanol-fed, or HIV- pair-fed mice. Recolonized mice were then infected with S. pneumoniae and were sacrificed 48 h later. The intestinal microbiota from alcohol-fed mice (regardless of HIV status) significantly impaired clearance of S. pneumoniae. Collectively, these data indicate that alcohol feeding, as well as alcohol-associated intestinal dysbiosis, compromise pulmonary host defenses against pneumococcal pneumonia. Determining whether HIV infection acts synergistically with alcohol use in impairing pulmonary host defenses will require additional study.

Contributing Roles of CYP2E1 and Other Cytochrome P450 Isoforms in Alcohol-Related Tissue Injury and Carcinogenesis

The purpose of this review is to briefly summarize the roles of alcohol (ethanol) and related compounds in promoting cancer and inflammatory injury in many tissues. Long-term chronic heavy alcohol exposure is known to increase the chances of inflammation, oxidative DNA damage, and cancer development in many organs. The rates of alcohol-mediated organ damage and cancer risks are significantly elevated in the presence of co-morbidity factors such as poor nutrition, unhealthy diets, smoking, infection with bacteria or viruses, and exposure to pro-carcinogens. Chronic ingestion of alcohol and its metabolite acetaldehyde may initiate and/or promote the development of cancer in the liver, oral cavity, esophagus, stomach, gastrointestinal tract, pancreas, prostate, and female breast. In this chapter, we summarize the important roles of ethanol/acetaldehyde in promoting inflammatory injury and carcinogenesis in several tissues. We also review the updated roles of the ethanol-inducible cytochrome P450-2E1 (CYP2E1) and other cytochrome P450 isozymes in the metabolism of various potentially toxic substrates, and consequent toxicities, including carcinogenesis in different tissues. We also briefly describe the potential implications of endogenous ethanol produced by gut bacteria, as frequently observed in the experimental models and patients of nonalcoholic fatty liver disease, in promoting DNA mutation and cancer development in the liver and other tissues, including the gastrointestinal tract.

Ethanol-Mediated Stress Promotes Autophagic Survival and Aggressiveness of Colon Cancer Cells via Activation of Nrf2/HO-1 Pathway

Epidemiological studies suggest that chronic alcohol consumption is a lifestyle risk factor strongly associated with colorectal cancer development and progression. The aim of the present study was to examine the effect of ethanol (EtOH) on survival and progression of three different colon cancer cell lines (HCT116, HT29, and Caco-2). Our data showed that EtOH induces oxidative and endoplasmic reticulum (ER) stress, as demonstrated by reactive oxygen species (ROS) and ER stress markers Grp78, ATF6, PERK and, CHOP increase. Moreover, EtOH triggers an autophagic response which is accompanied by the upregulation of beclin, LC3-II, ATG7, and p62 proteins. The addition of the antioxidant N-acetylcysteine significantly prevents autophagy, suggesting that autophagy is triggered by oxidative stress as a prosurvival response. EtOH treatment also upregulates the antioxidant enzymes SOD, catalase, and heme oxygenase (HO-1) and promotes the nuclear translocation of both Nrf2 and HO-1. Interestingly, EtOH also upregulates the levels of matrix metalloproteases (MMP2 and MMP9) and VEGF. Nrf2 silencing or preventing HO-1 nuclear translocation by the protease inhibitor E64d abrogates the EtOH-induced increase in the antioxidant enzyme levels as well as the migration markers. Taken together, our results suggest that EtOH mediates both the activation of Nrf2 and HO-1 to sustain colon cancer cell survival, thus leading to the acquisition of a more aggressive phenotype.

Environmental Factors, Gut Microbiota, and Colorectal Cancer Prevention

The substantial burden of colorectal cancer and increasing trend in young adults highlight the importance of lifestyle modification as a complement to screening for colorectal cancer prevention. Several dietary and lifestyle factors have been implicated in the development of colorectal cancer, possibly through the intricate metabolic and inflammatory mechanisms. Likewise, as a key metabolic and immune regulator, the gut microbiota has been recognized to play an important role in colorectal tumorigenesis. Increasing data support that environmental factors are crucial determinants for the gut microbial composition and function, whose alterations induce changes in the host gene expression, metabolic regulation, and local and systemic immune response, thereby influencing cancer development. Here, we review the epidemiologic and mechanistic evidence regarding the links between diet and lifestyle and the gut microbiota in the development of colorectal cancer. We focus on factors for which substantial data support their importance for colorectal cancer and their potential role in the gut microbiota, including overweight and obesity, physical activity, dietary patterns, fiber, red and processed meat, marine omega-3 fatty acid, alcohol, and smoking. We also briefly describe other colorectal cancer-preventive factors for which the links with the gut microbiota have been suggested but remain to be mechanistically characterized, including vitamin D status, dairy consumption, and metformin use. Given limitations in available evidence, we highlight the need for further investigations in the relationship between environmental factors, gut microbiota, and colorectal cancer, which may lead to development and clinical translation of potential microbiota-based strategies for cancer prevention.

Colorectal cancer mutational profiles correlate with defined microbial communities in the tumor microenvironment

Variation in the gut microbiome has been linked to colorectal cancer (CRC), as well as to host genetic variation. However, we do not know whether, in addition to baseline host genetics, somatic mutational profiles in CRC tumors interact with the surrounding tumor microbiome, and if so, whether these changes can be used to understand microbe-host interactions with potential functional biological relevance. Here, we characterized the association between CRC microbial communities and tumor mutations using microbiome profiling and whole-exome sequencing in 44 pairs of tumors and matched normal tissues. We found statistically significant associations between loss-of-function mutations in tumor genes and shifts in the abundances of specific sets of bacterial taxa, suggestive of potential functional interaction. This correlation allows us to statistically predict interactions between loss-of-function tumor mutations in cancer-related genes and pathways, including MAPK and Wnt signaling, solely based on the composition of the microbiome. In conclusion, our study shows that CRC microbiomes are correlated with tumor mutational profiles, pointing towards possible mechanisms of molecular interaction.

Role of intestinal flora in colorectal cancer from the metabolite perspective: a systematic review

Colorectal cancer is one of the most common human malignant tumors. Recent research has shown that colorectal cancer is a dysbacteriosis-induced disease; however, the role of intestinal bacteria in colorectal cancer is unclear. This review explores the role of intestinal flora in colorectal cancer. In total, 57 articles were included after identification and screening. The pertinent literature on floral metabolites in colorectal cancer from three metabolic perspectives - including carbohydrate, lipid, and amino acid metabolism - was analyzed. An association network regarding the role of intestinal flora from a metabolic perspective was constructed by analyzing the previous literature to provide direction and insight for further research on intestinal flora in colorectal cancer.

Colorectal Cancer and Alcohol Consumption-Populations to Molecules

Colorectal cancer (CRC) is a major cause of morbidity and mortality, being the third most common cancer diagnosed in both men and women in the world. Several environmental and habitual factors have been associated with the CRC risk. Alcohol intake, a common and rising habit of modern society, is one of the major risk factors for development of CRC. Here, we will summarize the evidence linking alcohol with colon carcinogenesis and possible underlying mechanisms. Some epidemiologic studies suggest that even moderate drinking increases the CRC risk. Metabolism of alcohol involves ethanol conversion to its metabolites that could exert carcinogenic effects in the colon. Production of ethanol metabolites can be affected by the colon microbiota, another recently recognized mediating factor to colon carcinogenesis. The generation of acetaldehyde and alcohol's other metabolites leads to activation of cancer promoting cascades, such as DNA-adduct formation, oxidative stress and lipid peroxidation, epigenetic alterations, epithelial barrier dysfunction, and immune modulatory effects. Not only does alcohol induce its toxic effect through carcinogenic metabolites, but alcoholics themselves are predisposed to a poor diet, low in folate and fiber, and circadian disruption, which could further augment alcohol-induced colon carcinogenesis.

Links of gut microbiota composition with alcohol dependence syndrome and alcoholic liver disease

BACKGROUND

Alcohol abuse has deleterious effects on human health by disrupting the functions of many organs and systems. Gut microbiota has been implicated in the pathogenesis of alcohol-related liver diseases, with its composition manifesting expressed dysbiosis in patients suffering from alcoholic dependence. Due to its inherent plasticity, gut microbiota is an important target for prevention and treatment of these diseases. Identification of the impact of alcohol abuse with associated psychiatric symptoms on the gut community structure is confounded by the liver dysfunction. In order to differentiate the effects of these two factors, we conducted a comparative "shotgun" metagenomic survey of 99 patients with the alcohol dependence syndrome represented by two cohorts-with and without liver cirrhosis. The taxonomic and functional composition of the gut microbiota was subjected to a multifactor analysis including comparison with the external control group.

RESULTS

Alcoholic dependence and liver cirrhosis were associated with profound shifts in gut community structures and metabolic potential across the patients. The specific effects on species-level community composition were remarkably different between cohorts with and without liver cirrhosis. In both cases, the commensal microbiota was found to be depleted. Alcoholic dependence was inversely associated with the levels of butyrate-producing species from the Clostridiales order, while the cirrhosis-with multiple members of the Bacteroidales order. The opportunist pathogens linked to alcoholic dependence included pro-inflammatory Enterobacteriaceae, while the hallmarks of cirrhosis included an increase of oral microbes in the gut and more frequent occurrence of abnormal community structures. Interestingly, each of the two factors was associated with the expressed enrichment in many Bifidobacterium and Lactobacillus-but the exact set of the species was different between alcoholic dependence and liver cirrhosis. At the level of functional potential, the patients showed different patterns of increase in functions related to alcohol metabolism and virulence factors, as well as pathways related to inflammation.

CONCLUSIONS

Multiple shifts in the community structure and metabolic potential suggest strong negative influence of alcohol dependence and associated liver dysfunction on gut microbiota. The identified differences in patterns of impact between these two factors are important for planning of personalized treatment and prevention of these pathologies via microbiota modulation. Particularly, the expansion of Bifidobacterium and Lactobacillus suggests that probiotic interventions for patients with alcohol-related disorders using representatives of the same taxa should be considered with caution. Taxonomic and functional analysis shows an increased propensity of the gut microbiota to synthesis of the toxic acetaldehyde, suggesting higher risk of colorectal cancer and other pathologies in alcoholics.

Environmental influences in the etiology of colorectal cancer: the premise of metabolomics

PURPOSE OF REVIEW

In this review we discuss how environmental exposures predominate the etiology of colorectal cancer (CRC). With CRC being a personalized disease influenced by genes and environment, our goal was to explore the role metabolomics can play in identifying exposures, assessing the interplay between co-exposures, and the development of personalized therapeutic interventions.

RECENT FINDINGS

Approximately 10 % of CRC cases can be explained by germ-line mutations, whereas the prevailing majority are caused by an initiating exposure event occurring decades prior to diagnosis. Recent research has shown that dietary metabolites are linked to a procarcinogenic or protective environment in the colon which is modulated by the microbiome. In addition, excessive alcohol has been shown to increase the risk of CRC and is dependent on diet (folate), the response of microbiome, and genetic polymorphisms within the folate and alcohol metabolic pathways. Metabolomics can not only be used to identify this modulation of host metabolism, which could affect the progression of the tumors but also response to targeted therapeutics.

SUMMARY

This review highlights the current understanding of the multifaceted etiology and mechanisms of CRC development but also highlights where the field of metabolomics can contribute to a greater understanding of environmental exposure in CRC.

Molecular Basis of Alcohol-Related Gastric and Colon Cancer

Many meta-analysis, large cohort studies, and experimental studies suggest that chronic alcohol consumption increases the risk of gastric and colon cancer. Ethanol is metabolized by alcohol dehydrogenases (ADH), catalase or cytochrome P450 2E1 (CYP2E1) to acetaldehyde, which is then further oxidized to acetate by aldehyde dehydrogenase (ALDH). Acetaldehyde has been classified by the International Agency for Research on Cancer (IARC) as a Group 1 carcinogen to humans. The acetaldehyde level in the stomach and colon is locally influenced by gastric colonization by Helicobacter pylori or colonic microbes, as well as polymorphisms in the genes encoding tissue alcohol metabolizing enzymes, especially ALDH2. Alcohol stimulates the uptake of carcinogens and their metabolism and also changes the composition of enteric microbes in a way to enhance the aldehyde level. Alcohol also undergoes chemical coupling to membrane phospholipids and disrupts organization of tight junctions, leading to nuclear translocation of β-catenin and ZONAB, which may contributes to regulation of genes involved in proliferation, invasion and metastasis. Alcohol also generates reactive oxygen species (ROS) by suppressing the expression of antioxidant and cytoprotective enzymes and inducing expression of CYP2E1 which contribute to the metabolic activation of chemical carcinogens. Besides exerting genotoxic effects by directly damaging DNA, ROS can activates signaling molecules involved in inflammation, metastasis and angiogenesis. In addition, alcohol consumption induces folate deficiency, which may result in aberrant DNA methylation profiles, thereby influencing cancer-related gene expression.

Screening by Total Colonoscopy Following Fecal Immunochemical Tests and Determinants of Colorectal Neoplasia in Japanese Men With Alcohol Dependence

Aims

Alcohol consumption increases the risk of colorectal adenoma and cancer. The fecal immunochemical test (FIT) is a widely used screening method for detecting colorectal neoplasia. We evaluated the results of screening and risk factors for colorectal neoplasia in individuals with alcohol dependence.

Methods

Total colonoscopic screening was performed for 1006 Japanese men with alcohol dependence (462 FIT-positive and 544 FIT-negative). Advanced neoplasia was defined as neoplasia ≥10 mm, villous or tubulovillous adenoma, high-grade adenoma, or carcinoma.

Results

The detection rates for non-advanced adenoma, advanced neoplasia and intramucosal or invasive carcinoma were 38.7%, 39.4% and 9.7% for the FIT-positive group, and 33.3%, 10.8% and 2.2% for the FIT-negative group, respectively. Advanced neoplasia, especially carcinoma, was detected more frequently in the distal colon than in the proximal colon in the FIT-positive group. The respective multivariate odds ratios (ORs; 95% confidence interval) for non-advanced adenoma and advanced neoplasia were 2.83 (2.06–3.88) and 9.13 (6.19–13.5) for a positive FIT (vs. negative), 1.68 (1.39–2.02) and 1.83 (1.45–2.30) for age (per +10 years), 1.54 (1.06–2.23) and 1.88 (1.17–3.03) for current smoking (vs. non-smokers), and 1.35 (0.96–1.92) and 1.59 (1.02–2.48) for the presence of marked macrocytosis (mean corpuscular volume ≥106 fl vs. <106 fl). Genetic polymorphisms of alcohol dehydrogenase-1B and aldehyde dehydrogenase-2 did not affect the risk of colorectal neoplasia.

Conclusion

The detection rate for advanced colorectal neoplasia was extremely high in the FIT-positive group but remained high even in the FIT-negative group. An older age, smoking and macrocytosis were predictors of advanced colorectal neoplasia.

Short summary

Total colonoscopic screening was performed for 1006 Japanese alcoholic men (462 fecal immunochemical test [FIT]-positive and 544 FIT-negative). The detection rate for advanced colorectal neoplasia was extremely high in the FIT-positive group (39.4%) and high in the FIT-negative group (10.8%). Ageing, smoking and macrocytosis were predictors of advanced colorectal neoplasia.

Ecophysiological consequences of alcoholism on human gut microbiota: implications for ethanol-related pathogenesis of colon cancer

Chronic consumption of excess ethanol increases the risk of colorectal cancer. The pathogenesis of ethanol-related colorectal cancer (ER-CRC) is thought to be partly mediated by gut microbes. Specifically, bacteria in the colon and rectum convert ethanol to acetaldehyde (AcH), which is carcinogenic. However, the effects of chronic ethanol consumption on the human gut microbiome are poorly understood, and the role of gut microbes in the proposed AcH-mediated pathogenesis of ER-CRC remains to be elaborated. Here we analyse and compare the gut microbiota structures of non-alcoholics and alcoholics. The gut microbiotas of alcoholics were diminished in dominant obligate anaerobes (e.g., Bacteroides and Ruminococcus) and enriched in Streptococcus and other minor species. This alteration might be exacerbated by habitual smoking. These observations could at least partly be explained by the susceptibility of obligate anaerobes to reactive oxygen species, which are increased by chronic exposure of the gut mucosa to ethanol. The AcH productivity from ethanol was much lower in the faeces of alcoholic patients than in faeces of non-alcoholic subjects. The faecal phenotype of the alcoholics could be rationalised based on their gut microbiota structures and the ability of gut bacteria to accumulate AcH from ethanol.