Relationship of the Esophageal Microbiome and Tissue Gene Expression and Links to the Oral Microbiome: A Randomized Clinical Trial

Etiologic factors for Barrett's esophagus: toward countermeasures in Asia

INTRODUCTION

Over the past several decades, Europe and the United States have experienced a rapid increase in esophageal adenocarcinoma. Research and countermeasures against Barrett's esophagus, its precancerous lesion, are progressing. Because esophageal adenocarcinoma has an extremely poor prognosis when diagnosed in an advanced stage, recommendations for early cancer detection have been made based on the various proven etiological factors of Barrett's esophagus and the actual cancer risk of Barrett's esophagus. In recent years, there have been indications of an increase in esophageal adenocarcinoma in Japan, and a similar trend of cancer will occur shortly in other Asian countries. Consequently, Asian countries must implement similar countermeasures against Barrett's esophagus and esophageal adenocarcinoma, referencing the knowledge gained thus far in Europe and the United States.

AREAS COVERED

This review summarizes the latest findings on the etiologic factors of Barrett's esophagus and discusses the differences between Westerners and Asians. The current status of Barrett's esophagus in Japan and other Asian countries is also summarized.

EXPERT OPINION

The etiological factors and cancer incidence of Barrett's esophagus in Asia diverge somewhat from those observed in Europe and America. Therefore, it is imperative to implement measures that are tailored to the actual circumstances of Asian people.

Chlorhexidine digluconate mouthwash alters the oral microbial composition and affects the prevalence of antimicrobial resistance genes

Introduction

Chlorhexidine (CHX) is a commonly used antiseptic in situations of limited oral hygiene ability such as after periodontal surgery. However, CHX is also considered as a possible factor in the emergence of cross-resistance to antibiotics. The aim of this study was to analyze the changes in the oral microbiota and the prevalence of antimicrobial resistance genes (ARGs) due to CHX treatment.

Materials and methods

We analyzed the oral metagenome of 20 patients who applied a 0.2% CHX mouthwash twice daily for 4 weeks following periodontal surgical procedures. Saliva and supragingival plaque samples were examined before, directly after 4 weeks, and another 4 weeks after discontinuing the CHX treatment.

Results

Alpha-diversity decreased significantly with CHX use. The Bray-Curtis dissimilarity increased in both sample sites and mainly streptococci showed a higher relative abundance after CHX treatment. Although no significant changes of ARGs could be detected, an increase in prevalence was found for genes that encode for tetracycline efflux pumps.

Conclusion

CHX treatment appears to promote a caries-associated bacterial community and the emergence of tetracycline resistance genes. Future research should focus on CHX-related changes in the microbial community and whether the discovered tetracycline resistance genes promote resistance to CHX.

Saliva assay: a call for methodological standardization

The oral cavity provides an ideal environment for microorganisms, including bacteria, viruses, and fungi, to flourish. Increasing attention has been focused on the connection between the oral microbiome and both oral and systemic diseases, spurring active research into the collection and analysis of specimens for healthcare purposes. Among the various methods for analyzing the oral microbiome, saliva analysis is especially prominent. Saliva samples, which can be collected non-invasively, provide information on the systemic health and oral microbiome composition of an individual. This review was performed to evaluate the current state of the relevant research through an examination of the literature and to suggest an appropriate assay method for investigating the oral microbiome. We analyzed articles published in English in SCI(E) journals after January 1, 2000, ultimately selecting 53 articles for review. Articles were identified through keyword searches in the PubMed, Embase, Cochrane, Web of Science, and CINAHL databases. Three experienced researchers conducted full-text assessments following title and abstract screening to select appropriate papers. Subsequently, they organized and analyzed the desired data. Our review revealed that most studies utilized unstimulated saliva samples for oral microbiome analysis. Of the 53 studies examined, 29 identified relationships between the oral microbiome and various diseases, such as oral disease, Behçet disease, cancer, and oral lichen planus. However, the studies employed diverse methods of collection and analysis, which compromised the reliability and accuracy of the findings. To address the limitations caused by methodological inconsistencies, a standardized saliva assay should be established.

The Salivary Microbiome and Predicted Metabolite Production Are Associated with Barrett's Esophagus and High-Grade Dysplasia or Adenocarcinoma

BACKGROUND

Esophageal adenocarcinoma (EAC) is rising in incidence, and established risk factors do not explain this trend. Esophageal microbiome alterations have been associated with Barrett's esophagus (BE) and dysplasia and EAC. The oral microbiome is tightly linked to the esophageal microbiome; this study aimed to identify salivary microbiome-related factors associated with BE, dysplasia, and EAC.

METHODS

Clinical data and oral health history were collected from patients with and without BE. The salivary microbiome was characterized, assessing differential relative abundance of taxa by 16S rRNA gene sequencing and associations between microbiome composition and clinical features. Microbiome metabolic modeling was used to predict metabolite production.

RESULTS

A total of 244 patients (125 non-BE and 119 BE) were analyzed. Patients with high-grade dysplasia (HGD)/EAC had a significantly higher prevalence of tooth loss (P = 0.001). There were significant shifts with increased dysbiosis associated with HGD/EAC, independent of tooth loss, with the largest shifts within the genus Streptococcus. Modeling predicted significant shifts in the microbiome metabolic capacities, including increases in L-lactic acid and decreases in butyric acid and L-tryptophan production in HGD/EAC.

CONCLUSIONS

Marked dysbiosis in the salivary microbiome is associated with HGD and EAC, with notable increases within the genus Streptococcus and accompanying changes in predicted metabolite production. Further work is warranted to identify the biological significance of these alterations and to validate metabolic shifts.

IMPACT

There is an association between oral dysbiosis and HGD/EAC. Further work is needed to establish the diagnostic, predictive, and causal potential of this relationship.

Experimental Modeling of Host-Bacterial Interactions in Head and Neck Squamous Cell Carcinoma

The microscopic species colonizing the human body, collectively referred to as the microbiome, play a crucial role in the maintenance of tissue homeostasis, immunity, and the development of disease. There is evidence to suggest associations between alterations in the microbiome and the development of head and neck squamous cell carcinomas (HNSCC). The use of two-dimensional (2D) modeling systems has made significant strides in uncovering the role of microbes in carcinogenesis; however, direct mechanistic links remain in their infancy. Patient-derived three-dimensional (3D) HNSCC organoid and organotypic models have recently been described. Compared to 2D models, 3D organoid culture systems effectively capture the genetic and epigenetic features of parent tissue in a patient-specific manner and may offer a more nuanced understanding of the role of host-microbe responses in carcinogenesis. This review provides a topical literature review assessing the current state of the field investigating the role of the microbiome in HNSCC; including in vivo and in vitro modeling methods that may be used to characterize microbiome-epithelial interactions.

The Salivary Microbiome and Predicted Metabolite Production are Associated with Progression from Barrett's Esophagus to Esophageal Adenocarcinoma

Esophageal adenocarcinoma (EAC) is rising in incidence and associated with poor survival, and established risk factors do not explain this trend. Microbiome alterations have been associated with progression from the precursor Barrett's esophagus (BE) to EAC, yet the oral microbiome, tightly linked to the esophageal microbiome and easier to sample, has not been extensively studied in this context. We aimed to assess the relationship between the salivary microbiome and neoplastic progression in BE to identify microbiome-related factors that may drive EAC development. We collected clinical data and oral health and hygiene history and characterized the salivary microbiome from 250 patients with and without BE, including 78 with advanced neoplasia (high grade dysplasia or early adenocarcinoma). We assessed differential relative abundance of taxa by 16S rRNA gene sequencing and associations between microbiome composition and clinical features and used microbiome metabolic modeling to predict metabolite production. We found significant shifts and increased dysbiosis associated with progression to advanced neoplasia, with these associations occurring independent of tooth loss, and the largest shifts were with the genus Streptococcus. Microbiome metabolic models predicted significant shifts in the metabolic capacities of the salivary microbiome in patients with advanced neoplasia, including increases in L-lactic acid and decreases in butyric acid and L-tryptophan production. Our results suggest both a mechanistic and predictive role for the oral microbiome in esophageal adenocarcinoma. Further work is warranted to identify the biological significance of these alterations, to validate metabolic shifts, and to determine whether they represent viable therapeutic targets for prevention of progression in BE.

Effects of antimicrobial mouthwashes on the human oral microbiome: Systematic review of controlled clinical trials

OBJECTIVES

This review aimed to assess the impact of mouthwashes on the composition of the human oral microbiome.

METHOD

An electronic search algorithm was adapted to MEDLINE-PubMed, Scopus, Embase and ISI Web of Science, and reference lists of relevant sources were manually searched. Inclusion criteria were controlled clinical trials published in English whose population were adult individuals who rinse with antimicrobial mouthwashes and that analysed changes in the oral microbiome by metataxonomy, metagenomics or phylogenetic microarray. Identified studies were screened and assessed following the PRISMA guidelines, and results were compiled into qualitative synthesis of the evidence.

RESULTS

Five controlled clinical studies were included. These studies found associations between the daily use of mouthwashes and changes in the oral microbiome, but the nature of the effect varied according to the mouthwash. Chlorhexidine (CHX) rinses lowered microbial diversity. While 7-day use of CHX led to increases in the abundance of Neisseria, Streptococcus and Granulicatella and a decrease in the abundance of Actinomyces, its prolonged use led to widespread reductions in several genera and species. Cetylpyridinium chloride-containing mouthwashes specifically lowered the abundance of gingivitis-associated genera. In contrast, N-acetyl cysteine-based mouthwashes did not promote changes in the oral microbiome.

CONCLUSIONS

Despite substantial heterogeneity, we found evidence to support the hypothesis that CHX and CPC mouthwashes promote changes in oral microbial structure and/or reductions in community diversity that favour the resolution of dysbiosis. However, future large population-based studies of adequate duration are needed to fully understand the extent to which antimicrobial mouthwashes modulate the microbiome.

Oral microbiota in oropharyngeal cancers: Friend or foe?

Oral microbiome is a complex population of micro-organisms, which by cross-talking with the local immune system, plays a major role in the immune homeostasis of the oral cavity, further contributing in the physiology of the gastro-intestinal microbiota. Understanding their involvement in the onset and pathogenesis of oropharyngeal cancers is paramount, despite very few reports deal with the fundamental role exerted by oral microbiota disorders, such as dysbiosis and impairment in the oral microbiome composition as causative factors in the development of oropharyngeal tumors. Current research, via metabolomic or meta-transcriptomic analyses, is wondering how this complex microbial population regulates the immune homeostasis in oral and pharyngeal mucosa and whether changes in bacterial composition may give insights on the role of oral microbiome in the development of oropharyngeal tumors, so to prevent their occurrence.

Varied Composition and Underlying Mechanisms of Gut Microbiome in Neuroinflammation

The human gut microbiome has been implicated in a host of bodily functions and their regulation, including brain development and cognition. Neuroinflammation is a relatively newer piece of the puzzle and is implicated in the pathogenesis of many neurological disorders. The microbiome of the gut may alter the inflammatory signaling inside the brain through the secretion of short-chain fatty acids, controlling the availability of amino acid tryptophan and altering vagal activation. Studies in Korea and elsewhere highlight a strong link between microbiome dynamics and neurocognitive states, including personality. For these reasons, re-establishing microbial flora of the gut looks critical for keeping neuroinflammation from putting the whole system aflame through probiotics and allotransplantation of the fecal microbiome. However, the numerosity of the microbiome remains a challenge. For this purpose, it is suggested that wherever possible, a fecal microbial auto-transplant may prove more effective. This review summarizes the current knowledge about the role of the microbiome in neuroinflammation and the various mechanism involved in this process. As an example, we have also discussed the autism spectrum disorder and the implication of neuroinflammation and microbiome in its pathogenesis.

Human Microbiota in Esophageal Adenocarcinoma: Pathogenesis, Diagnosis, Prognosis and Therapeutic Implications

Esophageal adenocarcinoma (EAC) is one of the main subtypes of esophageal cancer. The incidence rate of EAC increased progressively while the 5-year relative survival rates were poor in the past two decades. The mechanism of EAC has been studied extensively in relation to genetic factors, but less so with respect to human microbiota. Currently, researches about the relationship between EAC and the human microbiota is a newly emerging field of study. Herein, we present the current state of knowledge linking human microbiota to esophageal adenocarcinoma and its precursor lesion—gastroesophageal reflux disease and Barrett’s esophagus. There are specific human bacterial alternations in the process of esophageal carcinogenesis. And bacterial dysbiosis plays an important role in the process of esophageal carcinogenesis via inflammation, microbial metabolism and genotoxicity. Based on the human microbiota alternation in the EAC cascade, it provides potential microbiome-based clinical application. This review is focused on novel targets in prevention, diagnosis, prognosis, and therapy for esophageal adenocarcinoma.

3D Organoids: An Untapped Platform for Studying Host-Microbiome Interactions in Esophageal Cancers

The microbiome is an emerging key co-factor in the development of esophageal cancer, the sixth leading cause of cancer death worldwide. However, there is a paucity of data delineating how the microbiome contributes to the pathobiology of the two histological subtypes of esophageal cancer: esophageal squamous cell carcinoma and esophageal adenocarcinoma. This critical knowledge gap is partially due to inadequate modeling of host-microbiome interactions in the etiology of esophageal cancers. Recent advances have enabled progress in this field. Three dimensional (3D) organoids faithfully recapitulate the structure and function of the normal, preneoplastic, and neoplastic epithelia of the esophagus ex vivo and serve as a platform translatable for applications in precision medicine. Elsewhere in the gastrointestinal (GI) tract, the co-culture of 3D organoids with the bacterial microbiome has fostered insight into the pathogenic role of the microbiome in other GI cancers. Herein, we will summarize our current understanding of the relationship between the microbiome and esophageal cancer, discuss 3D organoid models of esophageal homeostasis, review analogous models of host-microbiome interactions in other GI cancers, and advocate for the application of these models to esophageal cancers. Together, we present a promising, novel approach with the potential to ameliorate the burden of esophageal cancer-related morbidity and mortality via improved prevention and therapeutic interventions.

Challenges in Determining the Role of Microbiome Evolution in Barrett's Esophagus and Progression to Esophageal Adenocarcinoma

Esophageal adenocarcinoma (EAC) claims the lives of half of patients within the first year of diagnosis, and its incidence has rapidly increased since the 1970s despite extensive research into etiological factors. The changes in the microbiome within the distal esophagus in modern populations may help explain the growth in cases that other common EAC risk factors together cannot fully explain. The precursor to EAC is Barrett's esophagus (BE), a metaplasia adapted to a reflux-mediated microenvironment that can be challenging to diagnose in patients who do not undergo endoscopic screening. Non-invasive procedures to detect microbial communities in saliva, oral swabs and brushings from the distal esophagus allow us to characterize taxonomic differences in bacterial population abundances within patients with BE versus controls, and may provide an alternative means of BE detection. Unique microbial communities have been identified across healthy esophagus, BE, and various stages of progression to EAC, but studies determining dynamic changes in these communities, including migration from proximal stomach and oral cavity niches, and their potential causal role in cancer formation are lacking. Helicobacter pylori is negatively associated with EAC, and the absence of this species has been implicated in the evolution of chromosomal instability, a main driver of EAC, but joint analyses of microbiome and host genomes are needed. Acknowledging technical challenges, future studies on the prediction of microbial dynamics and evolution within BE and the progression to EAC will require larger esophageal microbiome datasets, improved bioinformatics pipelines, and specialized mathematical models for analysis.

Minimal Associations between Short-Term Dietary Intake and Salivary Microbiome Composition

Background: Increasing evidence points to the esophageal microbiome as an important co-factor in esophageal neoplasia. Esophageal microbiome composition is strongly influenced by the oral microbiome. Salivary microbiome assessment has emerged as a potential non-invasive tool to identify patients at risk for esophageal cancer, but key host and environmental factors that may affect the salivary microbiome have not been well-defined. This study aimed to evaluate the impact of short-term dietary intake on salivary microbiome composition. Methods: Saliva samples were collected from 69 subjects prior to upper endoscopy who completed the Automated Self-Administered 24-Hour (ASA24) Dietary Assessment. Salivary microbiome composition was determined using 16S rRNA amplicon sequencing. Results: There was no significant correlation between alpha diversity and primary measures of short-term dietary intake (total daily calories, fat, fiber, fruit/vegetables, red meat intake, and fasting time). There was no evidence of clustering on beta diversity analyses. Very few taxonomic alterations were found for short-term dietary intake; an increased relative abundance of Neisseria oralis and Lautropia sp. was associated with high fruit and vegetable intake, and an increased relative abundance of a taxon in the family Gemellaceae was associated with increased red meat intake. Conclusions: Short-term dietary intake was associated with only minimal salivary microbiome alterations and does not appear to have a major impact on the potential use of the salivary microbiome as a biomarker for esophageal neoplasia.