Changes of the Gastric Mucosal Microbiome Associated With Histological Stages of Gastric Carcinogenesis

Combined DNA Methylation and Gastric Microbiome Marker Predicts Helicobacter pylori-Negative Gastric Cancer

Background/Aims

While DNA methylation and gastric microbiome are each associated with gastric cancer (GC), their combined role in predicting GC remains unclear. This study investigated the potential of a combined DNA methylation and gastric microbiome signature to predict Helicobacter pylori-negative GC.

Methods

In this case-control study, we conducted quantitative methylation-specific polymerase chain reaction to measure the methylation levels of DKK3, SFRP1, EMX1, NKX6-1, MIR124-3, and TWIST1 in the gastric mucosa from 75 H. pylori-negative patients, including chronic gastritis (CG), intestinal metaplasia (IM), and GC. A combined analysis of DNA methylation and gastric microbiome, using 16S rRNA gene sequencing, was performed in 30 of 75 patients.

Results

The methylation levels of DKK3, SFRP1, EMX1, MIR124-3, and TWIST1 were significantly higher in patients with GC than in controls (all q<0.05). MIR124-3 and TWIST1 methylation levels were higher in patients with IM than those with CG and also in those with GC than in those with IM (all q<0.05). A higher methylation level of TWIST1 was an independent predictor for H. pylori-negative GC after adjusting for age, sex, and atrophy (odds ratio [OR], 15.15; 95% confidence interval [CI], 1.58 to 145.46; p=0.018). The combination of TWIST1 methylation and GC microbiome index (a microbiome marker) was significantly associated with H. pylori-negative GC after adjusting for age, sex, and atrophy (OR, 50.00; 95% CI, 1.69 to 1,476; p=0.024).

Conclusions

The combination of TWIST1 methylation and GC microbiome index may offer potential as a biomarker for predicting H. pylori-negative GC.

Gastric microbiome signature for predicting metachronous recurrence after endoscopic resection of gastric neoplasm

BACKGROUND

Changes in gastric microbiome are associated with gastric carcinogenesis. Studies on the association between gastric mucosa-associated gastric microbiome (MAM) and metachronous gastric cancer are limited. This study aimed to identify gastric MAM as a predictive factor for metachronous recurrence following endoscopic resection of gastric neoplasms.

METHOD

Microbiome analyses were conducted for 81 patients in a prospective cohort to investigate surrogate markers to predict metachronous recurrence. Gastric MAM in non-cancerous corporal biopsy specimens was evaluated using Illumina MiSeq platform targeting 16S ribosomal DNA.

RESULTS

Over a median follow-up duration of 53.8 months, 16 metachronous gastric neoplasms developed. Baseline gastric MAM varied with Helicobacter pylori infection status, but was unaffected by initial pathologic diagnosis, presence of atrophic gastritis, intestinal metaplasia, or synchronous lesions. The group with metachronous recurrence did not exhibit distinct phylogenetic diversity compared with the group devoid of recurrence but showed significant difference in β-diversity. The study population could be classified into two distinct gastrotypes based on baseline gastric MAM: gastrotype 1, Helicobacter-abundant; gastrotype 2: Akkermansia-abundant. Patients in gastrotype 2 showed higher risk of metachronous recurrence than gastrotype (Cox proportional hazard analysis, adjusted hazard ratio [95% confidence interval]: 5.10 [1.09-23.79]).

CONCLUSIONS

Gastric cancer patients can be classified into two distinct gastrotype groups by their MAM profiles, which were associated with different risk of metachronous recurrence.

Indications of Helicobacter pylori Eradication Treatment and Its Influence on Prescriptions and Effectiveness (Hp-EuReg)

BACKGROUND

The influence of indications for Helicobacter pylori investigation on prescriptions and effectiveness is unknown. The aim of the study was to assess the impact of indications for H. pylori investigation on prescriptions, effectiveness, compliance, and tolerance.

METHODS

International, prospective, non-interventional registry of the management of H. pylori infection by European gastroenterologists (Hp-EuReg). Treatment-näive patients registered from 2013 to 2023 at e-CRF AEG-REDCap were analyzed. The effectiveness was assessed by modified intention-to-treat analysis.

RESULTS

Overall, 53,636 treatment-naïve cases from 34 countries were included. Most frequent indications were: dyspepsia with normal endoscopy (49%), non-investigated dyspepsia (20%), duodenal ulcer (11%), gastric ulcer (7.7%), and gastroesophageal reflux disease (GERD) (2.6%). Therapy effectiveness varied by indication: duodenal ulcer (91%), gastric ulcer (90%), preneoplastic lesions (90%), dyspepsia with normal endoscopy (89%), GERD (88%), and non-investigated dyspepsia (87%). Bismuth-metronidazole-tetracycline and clarithromycin-amoxicillin-bismuth quadruple therapies achieved 90% effectiveness in all indications except GERD. Concomitant clarithromycin-amoxicillin-tinidazole/metronidazole reached 90% cure rates except in patients with non-investigated dyspepsia; whereas sequential clarithromycin-amoxicillin-tinidazole/metronidazole proved optimal (≥90%) in patients with gastric ulcer only. Adverse events were higher in patients treated for dyspepsia with normal endoscopy and duodenal ulcer compared with the remaining indications (23% and 28%, p < 0.001). Therapeutic compliance was higher in patients with duodenal ulcer and preneoplastic lesions (98% and 99%, p < 0.001).

CONCLUSION

In Europe, patients with gastric or duodenal ulcers and preneoplastic lesions showed higher H. pylori treatment effectiveness. Bismuth and non-bismuth quadruple therapies achieved optimal results in almost all indications.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT02328131.

Gut microbiome alterations during gastric cancer: evidence assessment of case-control studies

Objectives

The study aims to systematically identify the alterations in gut microbiota that observed in gastric cancer through comprehensive assessment of case-control studies.

Methods

The systematic literature search of PubMed, Embase, Cochrane Library, and Web of Science was conducted to identify case-control studies that compared the microbiomes of individuals with and without gastric cancer. Quality of included studies was evaluated with the Newcastle-Ottawa Quality Assessment Scale (NOS). Meta-analyses utilized a random-effects model, and subgroup and sensitivity analyses were performed to assess study heterogeneity. All data analyses were performed using the "metan" package in Stata 17.0, and the results were described using log odds ratios (log ORs) with 95% confidence intervals (CIs).

Results

A total of 33 studies involving 4,829 participants were eligible for analysis with 29 studies provided changes in α diversity and 18 studies reported β diversity. Meta-analysis showed that only the Shannon index demonstrated statistical significance for α-diversity [-5.078 (-9.470, -0.686)]. No significant differences were observed at the phylum level, while 11 bacteria at genus-level were identified significant changed, e.g., increasing in Lactobacillus [5.474, (0.949, 9.999)] and Streptococcus [5.095, (0.293, 9.897)] and decreasing in Porphyromonas and Rothia with the same [-8.602, (-11.396, -5.808)]. Sensitivity analysis indicated that the changes of 9 bacterial genus were robust. Subgroup analyses on countries revealed an increasing abundance of Helicobacter and Streptococcus in Koreans with gastric cancer, whereas those with gastric cancer from Portugal had a reduced Neisseria. Regarding the sample sources, the study observed an increase in Lactobacillus and Bacteroides in the gastric mucosa of people with gastric cancer, alongside Helicobacter and Streptococcus. However, the relative abundance of Bacteroides decreased compared to the non-gastric cancer group, which was indicated in fecal samples.

Conclusion

This study identified robust changes of 9 bacterial genus in people with gastric cancer, which were country-/sample source-specific. Large-scale studies are needed to explore the mechanisms underlying these changes.

Systematic Review

Unique Identifier: CRD42023437426 https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42023437426.

Unveiling the gastric microbiota: implications for gastric carcinogenesis, immune responses, and clinical prospects

High-throughput sequencing has ushered in a paradigm shift in gastric microbiota, breaking the stereotype that the stomach is hostile to microorganisms beyond H. pylori. Recent attention directed toward the composition and functionality of this 'community' has shed light on its potential relevance in cancer. The microbial composition in the stomach of health displays host specificity which changes throughout a person's lifespan and is subject to both external and internal factors. Distinctive alterations in gastric microbiome signature are discernible at different stages of gastric precancerous lesions and malignancy. The robust microbes that dominate in gastric malignant tissue are intricately implicated in gastric cancer susceptibility, carcinogenesis, and the modulation of immunosurveillance and immune escape. These revelations offer fresh avenues for utilizing gastric microbiota as predictive biomarkers in clinical settings. Furthermore, inter-individual microbiota variations partially account for differential responses to cancer immunotherapy. In this review, we summarize current literature on the influence of the gastric microbiota on gastric carcinogenesis, anti-tumor immunity and immunotherapy, providing insights into potential clinical applications.

The relationship between gastric microbiome features and responses to neoadjuvant chemotherapy in gastric cancer

Background

Emerging evidence demonstrates that the gastrointestinal microbiome has the potential to be a biomarker in neoadjuvant chemoradiotherapy for colorectal cancer (CRC). Yet studies on the impact of the gastric microbiome (GM) on the response to neoadjuvant chemotherapy (NACT) are still scarce.

Methods

Forty-eight patients with gastric cancer participated in this retrospective study, and 16S rRNA sequencing was performed to evaluate formalin-fixed and paraffin-embedded (FFPE) tissue biospecimens and fresh-frozen tissues.

Results

In this study, 16 bacterial taxa at different levels, including Bacillus, Anaerococcus, and Chloroflexi, were identified to be enriched before NACT in response (R) patients in group FFPE. In contrast, 6 bacterial taxa, such as Haemophilus, Veillonellaceae (Veillonella), etc. were enriched after NACT, in which we reported for the first time that the phylum Chloroflexi was enriched before NACT in R patients. Thirty-one bacterial taxa of Coriobacteriaceae, Ruminococcaceae, Veillonellaceae, and Lachnospiraceae were identified in group mucosa as being enriched in R patients. In comparison, 4 bacterial taxa dominated by the phylum Proteobacteria were enriched in NR patients. Notably, the family Veillonellaceae was found in both tissue samples, and the metabolic pathways, including the citrate cycle (TCA cycle) and various amino acids, including alanine, were found to be potentially predictive in both sample species.

Conclusion

There are differences in the features of the GM for different NACT response results. The causal relationship deserves to be confirmed by further investigations.

The role of microbiota in gastric cancer: A comprehensive review

BACKGROUND

Gastric cancer (GC) continues to pose a significant global threat in terms of cancer-related fatalities. Despite notable advancements in medical research and therapies, further investigation is warranted to elucidate its underlying etiology and risk factors. Recent times have witnessed an escalated emphasis on comprehending the role of the microbiota in cancer development.

METHODS

This review briefly delves into recent developments in microbiome-related research pertaining to gastric cancer.

RESULTS

According to studies, the microbiota can influence GC growth by inciting inflammation, disrupting immunological processes, and generating harmful microbial metabolites. Furthermore, there is ongoing research into how the microbiome can impact a patient's response to chemotherapy and immunotherapy.

CONCLUSION

The utilization of the microbiome for detecting, preventing, and managing stomach cancer remains an active area of exploration.

LncRNA LINC01278 Regulates the Prognosis and Related Mechanisms of Gastric Cancer by Targeting miR-129-5p

Gastric cancer, a prevalent malady within the digestive tract, has a complex pathological mechanism and numerous patients. The regulation of gastric cancer process by long non-coding RNA (lncRNA) presented new prospects for the study of its molecular mechanism and the treatment of patients. The abnormal expressed genes in gastric cancer were screened by GSE193109 dataset. The correlation between LINC01278 and the likelihood of survival in patients suffering from gastric cancer was investigated by Kaplan-Meier survival curve and multivariate Cox analysis. LINC01278 in gastric cancer tissue samples and cells was verified via RT-qPCR. The cell counting kit-8 (CCK-8) and transwell assay were selected to detect the growth activity of gastric cancer cells. The association between LINC01278 and miR-129-5p was validated through luciferase reporter assay and RNA-binding protein immunoprecipitation (RIP) assay. Correlation analysis of clinical features revealed an association between LINC01278 and the prognosis in gastric cancer patients. LINC01278 was actively expressed in gastric cancer, which exerts a tumor-promoting effect. Silencing LINC01278 suppressed the biological function of tumor cells through spongiform miR-129-5p. LINC01278 has the potential to serve as a novel biomarker, offering new avenues of research for the prognosis and treatment of gastric cancer.

Exploration of gastric carcinogenesis from the relationship between bile acids and intestinal metaplasia and intragastric microorganisms (H. pylori and non-H. pylori)

Gastric cancer (GC) is a prevalent form of cancer, with Helicobacter pylori (H. pylori) infection being the most common risk factor. Recent studies have highlighted the role of long-term irritation of the gastric mucosa caused by bile reflux in the development of cancer. Bile acids (BAs), which are a significant component in bile reflux, have the potential to promote gastric carcinogenesis through various mechanisms. These mechanisms include the induction of intestinal metaplasia (IM), inhibition of H. pylori activity, modification of H. pylori colonization, and alteration of the abundance and composition of microorganisms in the stomach. Defining the mechanism of bile acid-induced gastric carcinogenesis could potentially be an effective approach to prevent GC. Hence, this paper aims to review the mechanism of bile acid-induced IM, the association between BAs and H. pylori infection as well as microorganisms in the stomach, and the correlation between BAs and gastric carcinogenesis. The ultimate goal is to elucidate the role of BAs in the development of GC.

Predicting Personalized Diets Based on Microbial Characteristics between Patients with Superficial Gastritis and Atrophic Gastritis

BACKGROUND

gastritis is a common stomach disease with a high global incidence and can potentially develop into gastric cancer. The treatment of gastritis focuses on medication or diets based on national guidelines. However, the specific diet that can alleviate gastritis remains largely unknown.

METHODS

we propose a microbiota-directed dietary strategy that investigates potential food factors using microbial exogenous metabolites. Given the current lack of understanding of the repeatable characteristics of gastric microbiota, we conducted a meta-analysis to identify the features of gastric bacteria. Local samples were collected as validation cohorts. Furthermore, RevEcoR was employed to identify bacteria's exogenous metabolites, and FooDB was used to retrieve foods that can target specific bacteria.

RESULTS

Bacteroides, Weissella, Actinomyces, Atopobium, Oribacterium, Peptostreptococcus, and Rothia were biomarkers between superficial gastritis (SG) and atrophic gastritis (AG) (AG_N) without H. pylori infection, whereas Bacillus, Actinomyces, Cutibacterium, Helicobacter, Novosphingobium, Pseudomonas, and Streptococcus were signatures between SG and AG (AG_P) with H. pylori infection. According to the exogenous metabolites, adenosyloobalamin, soybean, common wheat, dates, and barley were regarded as potential candidates for AG_N treatment, while gallate was regarded as a candidate for AG_P treatment.

CONCLUSIONS

this study firstly profiled the gastric microbiota of AG and SG with or without H. pylori and provided a recommended diet for global AG according to exogenous metabolites.

Diabetes Mellitus and Gastric Cancer: Correlation and Potential Mechanisms

This review summarizes the correlation between diabetes mellitus (DM) and gastric cancer (GC) from the perspectives of epidemiology, drug use, and potential mechanisms. The association between DM and GC is inconclusive, and the positive direction of the association reported in most published meta-analyses suggests that DM may be an independent risk factor for GC. Many clinical investigations have shown that people with DM and GC who undergo gastrectomy may have better glycemic control. The potential link between DM and GC may involve the interaction of multiple common risk factors, such as obesity, hyperglycemia and hyperinsulinemia, H. pylori infection, and the use of metformin. Although in vitro and in vivo data support that H. pylori infection status and metformin can influence GC risk in DM patients, there are conflicting results. Patient survival outcomes are influenced by multiple factors, so further research is needed to identify the patients who may benefit.

Microbial-Related Metabolites May Be Involved in Eight Major Biological Processes and Represent Potential Diagnostic Markers in Gastric Cancer

Metabolites associated with microbes regulate human immunity, inhibit bacterial colonization, and promote pathogenicity. Integrating microbe and metabolome research in GC provides a direction for understanding the microbe-associated pathophysiological process of metabolic changes and disease occurrence. The present study included 30 GC patients with 30 cancerous tissues and paired non-cancerous tissues (NCs) as controls. LC-MS/MS metabolomics and 16S rRNA sequencing were performed to obtain the metabolic and microbial characteristics. Integrated analysis of the microbes and metabolomes was conducted to explore the coexistence relationship between the microbial and metabolic characteristics of GC and to identify microbial-related metabolite diagnostic markers. The metabolic analysis showed that the overall metabolite distribution differed between the GC tissues and the NC tissues: 25 metabolites were enriched in the NC tissues and 42 metabolites were enriched in the GC tissues. The α and β microbial diversities were higher in the GC tissues than in the NC tissues, with 11 differential phyla and 52 differential genera. In the correlation and coexistence integrated analysis, 66 differential metabolites were correlated and coexisted, with specific differential microbes. The microbes in the GC tissue likely regulated eight metabolic pathways. In the efficacy evaluation of the microbial-related differential metabolites in the diagnosis of GC, 12 differential metabolites (area under the curve [AUC] >0.9) exerted relatively high diagnostic efficiency, and the combined diagnostic efficacy of 5 to 6 microbial-related differential metabolites was higher than the diagnostic efficacy of a single feature. Therefore, microbial diversity and metabolite distribution differed between the GC tissues and the NC tissues. Microbial-related metabolites may be involved in eight major metabolism-based biological processes in GC and represent potential diagnostic markers.

Diversification and deleterious role of microbiome in gastric cancer

Gut microbiota dictates the fate of several diseases, including cancer. Most gastric cancers (GC) belong to gastric adenocarcinomas (GAC). Helicobacter pylori colonizes the gastric epithelium and is the causative agent of 75% of all stomach malignancies globally. This bacterium has several virulence factors, including cytotoxin-associated gene A (CagA), vacuolating cytotoxin (VacA), and outer membrane proteins (OMPs), all of which have been linked to the development of gastric cancer. In addition, bacteria such as Escherichia coli, Streptococcus, Clostridium, Haemophilus, Veillonella, Staphylococcus, and Lactobacillus play an important role in the development of gastric cancer. Besides, lactic acid bacteria (LAB) such as Bifidobacterium, Lactobacillus, Lactococcus, and Streptococcus were found in greater abundance in GAC patients. To identify potential diagnostic and therapeutic interventions for GC, it is essential to understand the mechanistic role of H. pylori and other bacteria that contribute to gastric carcinogenesis. Furthermore, understanding bacteria-host interactions and bacteria-induced inflammatory pathways in the host is critical for developing treatment targets for gastric cancer.

Leveraging existing 16S rRNA microbial data to identify diagnostic biomarker in Chinese patients with gastric cancer: a systematic meta-analysis

IMPORTANCE

Gastric cancer is a significant and growing health problem in China. Studies have revealed significant differences in gastric microbiota between patients with gastric cancer and non-cancerous patients, suggesting that microbiota may play a role in tumorigenesis. In this meta-analysis, existing 16S rRNA microbial data were analyzed to find combinations consisting of five genera, which had good efficacy in distinguishing gastric cancer from non-cancerous patients in multiple types of samples. These results lend support to the use of microbial markers in detecting gastric cancer. Moreover, these biomarkers are plausible candidates for further mechanistic research into the role of the microbiota in tumorigenesis.

The role of microbiota in the development and treatment of gastric cancer

The stomach was once considered a sterile organ until the discovery of Helicobacter pylori (HP). With the application of high-throughput sequencing technology and macrogenomics, researchers have identified fungi and fivemajor bacterial phyla within the stomachs of healthy individuals. These microbial communities exert regulatory influence over various physiological functions, including energy metabolism and immune responses. HP is a well-recognized risk factor for gastric cancer, significantly altering the stomach's native microecology. Currently, numerous studies are centered on the mechanisms by which HP contributes to gastric cancer development, primarily involving the CagA oncoprotein. However, aside from exogenous infections such as HP and EBV, certain endogenous dysbiosis can also lead to gastric cancer through multiple mechanisms. Additionally, gut microbiota and its metabolites significantly impact the development of gastric cancer. The role of microbial therapies, including diet, phages, probiotics and fecal microbiota transplantation, in treating gastric cancer should not be underestimated. This review aims to study the mechanisms involved in the roles of exogenous pathogen infection and endogenous microbiota dysbiosis in the development of gastric cancer. Also, we describe the application of microbiota therapy in the treatment and prognosis of gastric cancer.

Changes in salivary microbiota due to gastric cancer resection and its relation to gastric fluid microbiota

Gastric cancer is one of the leading causes of death worldwide, and resections are performed to cure the disease. We have previously reported the changes in the gastric microbiota after gastric cancer resection, which may be associated with the oral microbiota; however, the changes in the oral microbiota remain uncharacterized. This study aimed to characterize the changes in the salivary microbiota caused by gastric cancer resection and to evaluate their association with the gastric fluid microbiota. Saliva and gastric fluid samples were collected from 63 patients who underwent gastrectomy before and after surgery, and a 16S rRNA metagenomic analysis was performed to compare the microbiota composition. The number of bacterial species in the salivary microbiota decreased, and the bacterial composition changed after the resection of gastric cancer. In addition, we identified several bacterial genera that varied significantly in the salivary microbiota, some of which also showed similar changes in the gastric fluid microbiota. These findings indicate that changes in the gastric environment affect the oral microbiota, emphasizing the close association between the oral and gastric fluid microbiota. Our study signifies the importance of focusing on the oral microbiota in the perioperative period of gastrectomy in patients with gastric cancer.

Reactive Oxygen Species and H. pylori Infection: A Comprehensive Review of Their Roles in Gastric Cancer Development

Gastric cancer (GC) is the fifth most common cancer worldwide and makes up a significant component of the global cancer burden. Helicobacter pylori (H. pylori) is the most influential risk factor for GC, with the International Agency for Research on Cancer classifying it as a Class I carcinogen for GC. H. pylori has been shown to persist in stomach acid for decades, causing damage to the stomach's mucosal lining, altering gastric hormone release patterns, and potentially altering gastric function. Epidemiological studies have shown that eliminating H. pylori reduces metachronous cancer. Evidence shows that various molecular alterations are present in gastric cancer and precancerous lesions associated with an H. pylori infection. However, although H. pylori can cause oxidative stress-induced gastric cancer, with antioxidants potentially being a treatment for GC, the exact mechanism underlying GC etiology is not fully understood. This review provides an overview of recent research exploring the pathophysiology of H. pylori-induced oxidative stress that can cause cancer and the antioxidant supplements that can reduce or even eliminate GC occurrence.

The role of gastric microecological dysbiosis in gastric carcinogenesis

Gastric cancer (GC) is the leading cause of cancer-related death worldwide, and reducing its mortality has become an urgent public health issue. Gastric microecological dysbiosis (including bacteria, fungi, viruses, acid suppressants, antibiotics, and surgery) can lead to gastric immune dysfunction or result in a decrease in dominant bacteria and an increase in the number and virulence of pathogenic microorganisms, which in turn promotes development of GC. This review analyzes the relationship between gastric microecological dysbiosis and GC, elucidates dynamic alterations of the microbiota in Correa's cascade, and identifies certain specific microorganisms as potential biomarkers of GC to aid in early screening and diagnosis. In addition, this paper presents the potential of gastric microbiota transplantation as a therapeutic target for gastric cancer, providing a new direction for future research in this field.

The Local Microbiome in Esophageal Cancer and Treatment Response: A Review of Emerging Data and Future Directions

The incidence of esophageal cancer is increasing worldwide, with established risk factors explaining only a small fraction of cases. Currently, there are no established screening protocols in most countries, and treatment options are limited. The human microbiome has been implicated in carcinogenesis and the cancer treatment response. The advent of nucleic acid sequencing technologies has enabled more comprehensive, culture-independent bacterial identification. Across several tumor types, studies of tissue-specific microbiomes have shown associations between the overall microbiome composition, the relative abundance of specific bacteria, and tumorigenesis. Furthermore, in the era of cancer immunotherapy, several studies have demonstrated that the microbiome and specific bacteria may modify treatment responses and the risk of immune-related adverse events.

DESIGN

peer-reviewed, published studies describing the role of local, gastrointestinal-specific microbiota or the role of the gut microbiome in treatment responses were reviewed. PubMed was searched from 1 September 2022 to 1 November 2022, using the following terms in combination: "microbiome", "tumor microbiome", "esophageal cancer", "cancer", "cancer treatment", and "immunotherapy". Original research articles were considered, and other reviews or editorials were discarded. In total, approximately 250 articles were considered.

RESULTS

over 70 studies describing microbiome research in either gastrointestinal carcinogenesis or the systemic treatment response were identified and reviewed.

CONCLUSIONS

a growing body of evidence supports the role of the esophageal microbiome in both esophageal tumorigenesis and the immune checkpoint inhibitor response. More well-designed, comprehensive studies are required to collect the appropriate clinical, microbial, and immunophenotype data that are needed to clarify the precise role of the microbiome in esophageal carcinogenesis and treatment.

The role of the gut microbiota in gastric cancer: the immunoregulation and immunotherapy

Gastric cancer (GC) is one of the most common cancers, leading to the deaths of millions of people worldwide. Therefore, early detection and effective therapeutic strategies are of great value for decreasing the occurrence of advanced GC. The human microbiota is involved not only in the maintenance of physiological conditions, but also in human diseases such as obesity, diabetes, allergic and atopic diseases, and cancer. Currently, the composition of the bacteria in the host, their functions, and their influence on disease progression and treatment are being discussed. Previous studies on the gut microbiome have mostly focused on Helicobacter pylori (Hp) owing to its significant role in the development of GC. Nevertheless, the enrichment and diversity of other bacteria that can modulate the tumor microenvironment are involved in the progression of GC and the efficacy of immunotherapy. This review provides systematic insight into the components of the gut microbiota and their application in GC, including the specific bacteria of GC, their immunoregulatory effect, and their diagnostic value. Furthermore, we discuss the relationship between the metabolism of microbes and their potential applications, which may serve as a new approach for the diagnosis and treatment of GC.

[Gastric Cancer and Gastric Microbiome]

Gastric cancer remains a significant disease burden in Korea, with Helicobacter pylori infections being the most crucial risk factor. With the advent of next-generation sequencing, the role of gastric microbiota in gastric cancer has attracted increasing attention. Studies have shown that the gastric microbiota of patients with gastric cancer differs in composition from that of the controls, with reduced microbial diversity. Lactic acid bacteria and oral microflora are often enriched in gastric cancer and are believed to induce chronic inflammation or promote the production of nitroso compounds. This review focuses on recent studies comparing the gastric microbiome in gastric cancer patients and controls.

Relative and Quantitative Characterization of the Bovine Bacterial Ocular Surface Microbiome in the Context of Suspected Ocular Squamous Cell Carcinoma

The ocular surface microbiome is altered in certain disease states. The aim of this study was to characterize the bovine bacterial ocular surface microbiome (BBOSM) in the context of ocular squamous cell carcinoma (OSCC). The conjunctiva of normal (n = 28) and OSCC (n = 10) eyes of cows aged 2 to 13 years from two farms in Louisiana and Wyoming were sampled using individual sterile swabs. DNA extraction followed by 16S ribosomal ribonucleic acid (rRNA) gene sequencing and real-time polymerase chain reaction (RT-PCR) were performed to, respectively, assess the relative and absolute BBOSM. Discriminant analysis (DA) was performed using RT-PCR data, and relative abundance analysis was performed using 16S rRNA gene sequencing data. The 11 most abundant phyla in both normal and OSCC-affected cows were identified using 16S rRNA gene sequencing analysis. The relative abundance of Euryarchaeota was found to be significantly lower (p = 0.0372) in OSCC eyes compared to normal eyes. Relative abundance differences within and between geographic locations were also identified. Quadratic DA categorized samples as OSCC or normal with 100% sensitivity and 83.3-100% specificity. Relative abundance analysis identified relative BBOSM phylum alterations in OSCC. Quadratic DA can be used to accurately categorize BBOSM from normal and OSCC ocular surface samples.

Evaluation of the Oesophagogastric Cancer-Associated Microbiome: A Systematic Review and Quality Assessment

OBJECTIVE

Oesophagogastric cancer is the fifth most common cancer worldwide, with poor survival outcomes. The role of bacteria in the pathogenesis of oesophagogastric cancer remains poorly understood.

DESIGN

A systematic search identified studies assessing the oesophagogastric cancer microbiome. The primary outcome was to identify bacterial enrichment specific to oesophagogastric cancer. Secondary outcomes included appraisal of the methodology, diagnostic performance of cancer bacteria and the relationship between oral and tissue microbiome.

RESULTS

A total of 9295 articles were identified, and 87 studies were selected for analysis. Five genera were enriched in gastric cancer: Lactobacillus, Streptococcus, Prevotella, Fusobacterium and Veillonella. No clear trends were observed in oesophageal adenocarcinoma. Streptococcus, Prevotella and Fusobacterium were abundant in oesophageal squamous cell carcinoma. Functional analysis supports the role of immune cells, localised inflammation and cancer-specific pathways mediating carcinogenesis. STORMS reporting assessment identified experimental deficiencies, considering batch effects and sources of contamination prevalent in low-biomass samples.

CONCLUSIONS

Functional analysis of cancer pathways can infer tumorigenesis within the cancer-microbe-immune axis. There is evidence that study design, experimental protocols and analytical techniques could be improved to achieve more accurate and representative results. Whole-genome sequencing is recommended to identify key metabolic and functional capabilities of candidate bacteria biomarkers.

Gastric microbiota: an emerging player in gastric cancer

Gastric cancer (GC) is a common cancer worldwide with a high mortality rate. Many microbial factors influence GC, of which the most widely accepted one is Helicobacter pylori (H. pylori) infection. H. pylori causes inflammation, immune reactions and activation of multiple signaling pathways, leading to acid deficiency, epithelial atrophy, dysplasia and ultimately GC. It has been proved that complex microbial populations exist in the human stomach. H. pylori can affect the abundance and diversity of other bacteria. The interactions among gastric microbiota are collectively implicated in the onset of GC. Certain intervention strategies may regulate gastric homeostasis and mitigate gastric disorders. Probiotics, dietary fiber, and microbiota transplantation can potentially restore healthy microbiota. In this review, we elucidate the specific role of the gastric microbiota in GC and hope these data can facilitate the development of effective prevention and therapeutic approaches for GC.

Helicobacter pylori infection

Helicobacter pylori infection causes chronic gastritis, which can progress to severe gastroduodenal pathologies, including peptic ulcer, gastric cancer and gastric mucosa-associated lymphoid tissue lymphoma. H. pylori is usually transmitted in childhood and persists for life if untreated. The infection affects around half of the population in the world but prevalence varies according to location and sanitation standards. H. pylori has unique properties to colonize gastric epithelium in an acidic environment. The pathophysiology of H. pylori infection is dependent on complex bacterial virulence mechanisms and their interaction with the host immune system and environmental factors, resulting in distinct gastritis phenotypes that determine possible progression to different gastroduodenal pathologies. The causative role of H. pylori infection in gastric cancer development presents the opportunity for preventive screen-and-treat strategies. Invasive, endoscopy-based and non-invasive methods, including breath, stool and serological tests, are used in the diagnosis of H. pylori infection. Their use depends on the specific individual patient history and local availability. H. pylori treatment consists of a strong acid suppressant in various combinations with antibiotics and/or bismuth. The dramatic increase in resistance to key antibiotics used in H. pylori eradication demands antibiotic susceptibility testing, surveillance of resistance and antibiotic stewardship.

Linking dysbiosis to precancerous stomach through inflammation: Deeper than and beyond imaging

Upper gastrointestinal endoscopy is considered the gold standard for gastric lesions detection and surveillance, but it is still associated with a non-negligible rate of missing conditions. In the Era of Personalized Medicine, biomarkers could be the key to overcome missed lesions or to better predict recurrence, pushing the frontier of endoscopy to functional endoscopy. In the last decade, microbiota in gastric cancer has been extensively explored, with gastric carcinogenesis being associated with progressive dysbiosis. Helicobacter pylori infection has been considered the main causative agent of gastritis due to its interference in disrupting the acidic environment of the stomach through inflammatory mediators. Thus, does inflammation bridge the gap between gastric dysbiosis and the gastric carcinogenesis cascade and could the microbiota-inflammation axis-derived biomarkers be the answer to the unmet challenge of functional upper endoscopy? To address this question, in this review, the available evidence on the role of gastric dysbiosis and chronic inflammation in precancerous conditions of the stomach is summarized, particularly targeting the nuclear factor-κB (NF-κB), toll-like receptors (TLRs) and cyclooxygenase-2 (COX-2) pathways. Additionally, the potential of liquid biopsies as a non-invasive source and the clinical utility of studied biomarkers is also explored. Overall, and although most studies offer a mechanistic perspective linking a strong proinflammatory Th1 cell response associated with, but not limited to, chronic infection with Helicobacter pylori, promising data recently published highlights not only the diagnostic value of microbial biomarkers but also the potential of gastric juice as a liquid biopsy pushing forward the concept of functional endoscopy and personalized care in gastric cancer early diagnosis and surveillance.

Dynamic variations of the gastric microbiota: Key therapeutic points in the reversal of Correa's cascade

Correa's cascade is a dynamic process in the development of intestinal-type gastric cancer (GC), and its pathological features, gastric microbiota and interactions between microorganisms and their hosts vary at different developmental stages. The characteristics of cells, tissues and gastric microbiota before or after key therapeutic points are critical for monitoring malignant transformation and early tumour reversal. This review summarises the pathological features of gastric mucosa, characteristics of gastric microbiota, specific microbial markers, microbe-microbe interactions and microbe-host interactions at different stages in Correa's cascade. The markers related to each Correa's cascade point were analysed in detail. We attempted to identify key therapeutic points for early cancer reversal and provide a novel approach to reduce the incidence of GC and improve precise treatment.

Helicobacter pylori and gastric microbiota homeostasis: progress and prospects

Helicobacter pylori, a Gram-negative microaerobic bacteria belonging to the phylum Proteobacteria, can colonize in the stomach and duodenum, and cause a series of gastrointestinal diseases such as gastritis, gastric ulcer and even gastric cancer. At present, the high diversity of the microorganisms in the stomach has been confirmed with culture-independent methods; some researchers have also studied the stomach microbiota composition at different stages of H. pylori carcinogenesis. Here, we mainly review the possible role of H. pylori-mediated microbiota changes in the occurrence and development of gastric cancer to provide new ideas for preventing H. pylori infection and regulating microecological imbalance.

Alteration of gastric microbiota and transcriptome in a rat with gastric intestinal metaplasia induced by deoxycholic acid

Objective

Bile reflux plays a key role in the development of gastric intestinal metaplasia (GIM), an independent risk factor of gastric cancer. Here, we aimed to explore the biological mechanism of GIM induced by bile reflux in a rat model.

Methods

Rats were treated with 2% sodium salicylate and allowed to freely drink 20 mmol/L sodium deoxycholate for 12 weeks, and GIM was confirmed by histopathological analysis. Gastric microbiota was profiled according to the 16S rDNA V3-V4 region, gastric transcriptome was sequenced, and serum bile acids (BAs) were analyzed by targeted metabolomics. Spearman's correlation analysis was used in constructing the network among gastric microbiota, serum BAs, and gene profiles. Real-time polymerase chain reaction (RT-PCR) measured the expression levels of nine genes in the gastric transcriptome.

Results

In the stomach, deoxycholic acid (DCA) decreased the microbial diversity but promoted the abundances of several bacterial genera, such as Limosilactobacillus, Burkholderia-Caballeronia-Paraburkholderia, and Rikenellaceae RC9 gut group. Gastric transcriptome showed that the genes enriched in gastric acid secretion were significantly downregulated, whereas the genes enriched in fat digestion and absorption were obviously upregulated in GIM rats. The GIM rats had four promoted serum BAs, namely cholic acid (CA), DCA, taurocholic acid, and taurodeoxycholic acid. Further correlation analysis showed that the Rikenellaceae RC9 gut group was significantly positively correlated with DCA and RGD1311575 (capping protein-inhibiting regulator of actin dynamics), and RGD1311575 was positively correlated with Fabp1 (fatty acid-binding protein, liver), a key gene involved in fat digestion and absorption. Finally, the upregulated expression of Dgat1 (diacylglycerol acyltransferase 1) and Fabp1 related to fat digestion and absorption was identified by RT-PCR and IHC.

Conclusion

DCA-induced GIM enhanced gastric fat digestion and absorption function and impaired gastric acid secretion function. The DCA-Rikenellaceae RC9 gut group-RGD1311575/Fabp1 axis might play a key role in the mechanism of bile reflux-related GIM.

Gastric Cancer: The Microbiome Beyond Helicobacter pylori

Gastric cancer remains an important global health burden. Helicobacter pylori is the major etiological factor in gastric cancer, infecting the stomach of almost half of the population worldwide. Recent progress in microbiome research offered a new perspective on the complexity of the microbial communities of the stomach. Still, the role of the microbiome of the stomach beyond H. pylori in gastric carcinogenesis is not well understood and requires deeper investigation. The gastric bacterial communities of gastric cancer patients are distinct from those of patients without cancer, but the microbial alterations that occur along the process of gastric carcinogenesis, and the mechanisms through which microorganisms influence cancer progression still need to be clarified. Except for Epstein-Barr virus, the potential significance of the virome and of the mycobiome in gastric cancer have received less attention. This chapter updates the current knowledge regarding the gastric microbiome, including bacteria, viruses, and fungi, within the context of H. pylori-mediated carcinogenesis. It also reviews the possible roles of the local gastric microbiota, as well as the microbial communities of the oral and gut ecosystems, as biomarkers for gastric cancer detection. Finally, it discusses future perspectives and acknowledges limitations in the area of microbiome research in the gastric cancer setting, to which further research efforts should be directed. These will be fundamental not only to increase our current understanding of host-microbial interactions but also to facilitate translation of the findings into innovative preventive, diagnostic, and therapeutic strategies to decrease the global burden of gastric cancer.

Analysis of gastric microbiome reveals three distinctive microbial communities associated with the occurrence of gastric cancer

Background

Gastric microbial dysbiosis were reported to be associated with gastric cancer (GC). This study aimed to explore the variation, diversity, and composition patterns of gastric bacteria in stages of gastric carcinogenesis based on the published datasets.

Methods

We conducted a gastric microbial analysis using 10 public datasets based on 16S rRNA sequencing, including 1270 gastric biopsies of 109 health control, 183 superficial gastritis (SG), 135 atrophic gastritis (AG), 124 intestinal metaplasia (IM), 94 intraepithelial neoplasia (IN), 344 GC, and 281 adjacent normal tissues. And QIIME2-pipeline, DESeq2, NetMoss2, vegan, igraph, and RandomForest were used for the data processing and analysis.

Results

We identified three gastric microbial communities among all the gastric tissues. The first community (designate as GT-H) was featured by the high abundance of Helicobacter. The other two microbial communities, namely GT-F, and GT-P, were featured by the enrichment of phylum Firmicutes and Proteobacteria, respectively. The distribution of GC-associated bacteria, such as Fusobacterium, Peptostreptococcus, Streptococcus, and Veillonella were enriched in tumor tissues, and mainly distributed in GT-F type microbial communities. Compared with SG, AG, and IM, the bacterial diversity in GC was significantly reduced. And the strength of microbial interaction networks was initially increased in IM but gradually decreased from IN to GC. In addition, Randomforest models constructed in in GT-H and GT-F microbial communities showed excellent performance in distinguishing GC from SG and precancerous stages, with varied donated bacteria.

Conclusions

This study identified three types of gastric microbiome with different patterns of composition which helps to clarify the potential key bacteria in the development of gastric carcinogenesis.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-022-02594-y.

Tumor microbiome - an integral part of the tumor microenvironment

The tumor microenvironment (TME) plays a significant role in tumor progression and cancer cell survival. Besides malignant cells and non-malignant components, including immune cells, elements of the extracellular matrix, stromal cells, and endothelial cells, the tumor microbiome is considered to be an integral part of the TME. Mounting evidence from preclinical and clinical studies evaluated the presence of tumor type-specific intratumoral bacteria. Differences in microbiome composition between cancerous tissues and benign controls suggest the importance of the microbiome-based approach. Complex host-microbiota crosstalk within the TME affects tumor cell biology via the regulation of oncogenic pathways, immune response modulation, and interaction with microbiota-derived metabolites. Significantly, the involvement of tumor-associated microbiota in cancer drug metabolism highlights the therapeutic implications. This review aims to summarize current knowledge about the emerging role of tumor microbiome in various types of solid malignancies. The clinical utility of tumor microbiome in cancer progression and treatment is also discussed. Moreover, we provide an overview of clinical trials evaluating the role of tumor microbiome in cancer patients. The research focusing on the communication between the gut and tumor microbiomes may bring new opportunities for targeting the microbiome to increase the efficacy of cancer treatment and improve patient outcomes.

Altered Gastric Microbiota and Inflammatory Cytokine Responses in Patients with Helicobacter pylori-Negative Gastric Cancer

The role of the gastric mucosal microbiome in Helicobacter pylori-negative gastric cancer (GC) remains unclear. Therefore, we aimed to characterize the microbial alterations and host inflammatory cytokine responses in H. pylori-negative GC. Gastric mucosal samples were obtained from 137 H. pylori-negative patients with GC (n = 45) and controls (chronic gastritis or intestinal metaplasia, n = 92). We performed 16S rRNA gene sequencing (n = 67), a quantitative reverse transcription-polymerase chain reaction to determine the relative mRNA expression levels of TNF (tumor necrosis factor), IL1B (interleukin 1 beta), IL6 (interleukin 6), CXCL8 (C-X-C motif chemokine ligand 8), IL10 (interleukin 10), IL17A (interleukin 17A), TGFB1 (transforming growth factor beta 1) (n = 113), and the correlation analysis between sequencing and expression data (n = 47). Gastric mucosal microbiota in patients with GC showed reduced diversity and a significantly different composition compared to that of the controls. Lacticaseibacillus was significantly enriched, while Haemophilus and Campylobacter were depleted in the cancer group compared to the control group. These taxa could distinguish the two groups in a random forest algorithm. Moreover, the combined relative abundance of these taxa, a GC microbiome index, significantly correlated with gastric mucosal IL1B expression, which was elevated in the cancer group. Overall, altered gastric mucosal microbiota was found to be associated with increased mucosal IL1B expression in H. pylori-negative GC.

Oral Microbiota and Tumor-A New Perspective of Tumor Pathogenesis

Microorganisms have long been known to play key roles in the initiation and development of tumors. The oral microbiota and tumorigenesis have been linked in epidemiological research relating to molecular pathology. Notably, some bacteria can impact distal tumors by their gastrointestinal or blood-borne transmission under pathological circumstances. Certain bacteria drive tumorigenesis and progression through direct or indirect immune system actions. This review systemically discusses the recent advances in the field of oral microecology and tumor, including the oncogenic role of oral microbial abnormalities and various potential carcinogenesis mechanisms (excessive inflammatory response, host immunosuppression, anti-apoptotic activity, and carcinogen secretion) to introduce future directions for effective tumor prevention.

Characteristics of gut microbiota in patients with gastric cancer by surgery, chemotherapy and lymph node metastasis

BACKGROUND

Gastric cancer (GC) is a malignant gastrointestinal tumor that can result in high mortality. Surgery and chemotherapy are often used for the effective treatment of GC. In addition, lymph node metastasis is a significant factor affecting the therapy of GC. Current researches have revealed that gut microbiota has the potential as biomarkers to distinguish healthy people and GC patients. However, the relationship between surgery, chemotherapy, and lymph node metastasis is still unclear.

METHODS

In this study, 16S rRNA sequencing was used to investigate 157 GC fecal samples to identify the role of surgery, chemotherapy, and lymph node metastasis. Immunohistochemical analysis was used to value the expression of Ki67, HER2 in GC patient tissues.

RESULTS

There exist some gut microbiotas which can distinguish surgery from non-surgery GC patients, including Enterococcus, Megasphaera, Corynebacterium, Roseburia, and Lachnospira. Differences between lymph node metastasis and chemotherapy in GC patients are not significant. Moreover, we found the abundance of Blautia, Ruminococcus, Oscillospira were related to the expression of Ki67 and the abundance of Prevotella, Lachnospira, Eubacterium, Desulfovibiro were correlated with the expression of HER2.

CONCLUSIONS

The choice of treatment has a certain impact on the intestinal flora of patients with gastric cancer. Our research shows that surgery has a great effect on the intestinal flora of patients with gastric cancer. However, there were no significant differences in the characteristics of intestinal flora in patients with gastric cancer whether they received chemotherapy or whether they had lymph node metastasis. In addition, the association of gut microbiota with Ki67 and HER2 indicators is expected to provide the possibility of gut microbiota as a tumor prognostic marker.

Relationships among microbiota, gastric cancer, and immunotherapy

Currently, conventional neoadjuvant therapy or postoperative adjuvant therapy, such as chemotherapy and radiation therapy, can only bring limited survival benefits to gastric cancer (GC). Median survival after palliative chemotherapy is also low, at about 8–10 months. Immunotargeting is a new option for the treatment of GC, but has not been widely replicated. The highly immunosuppressed tumor microenvironment (TME) discounts the efficacy of immunotherapy for GC. Therefore, new strategies are needed to enhance the immune response of the TME. This paper reviewed the relationship between microorganisms and GC, potential links between microorganisms and immunotherapy and research of microorganisms combined immunotherapy.

Alterations in the gastric microbiota and metabolites in gastric cancer: An update review

Gastric cancer (GC) is one of the leading causes of cancer mortality worldwide. Numerous studies have shown that the gastric microbiota can contribute to the occurrence and development of GC by generating harmful microbial metabolites, suggesting the possibility of discovering biomarkers. Metabolomics has emerged as an advanced promising analytical method for the analysis of microbiota-derived metabolites, which have greatly accelerated our understanding of host-microbiota metabolic interactions in GC. In this review, we briefly compiled recent research progress on the changes of gastric microbiota and its metabolites associated with GC. And we further explored the application of metabolomics and gastric microbiome association analysis in the diagnosis, prevention and treatment of GC.

Influences of Helicobacter pylori infection on diversity, heterogeneity, and composition of human gastric microbiomes across stages of gastric cancer development

BACKGROUND

About a half of the world's population is infected with Helicobacter pylori (H. pylori), but only 1%-3% of them develop gastric cancer. As a primary risk factor for gastric cancer, the relationship between H. pylori infection and gastric microbiome has been a focus in recent years.

MATERIALS AND METHODS

We reanalyze 11 human gastric microbiome datasets with or without H. pylori, covering the healthy control (HC) and four disease stages (chronic gastritis (CG), atrophic gastritis (AG), intestinal metaplasia (IM), and gastric cancer (GC)) of gastric cancer development to quantitatively compare the influences of the H. pylori infection and disease stages on the diversity, heterogeneity, and composition of gastric microbiome. Four medical ecology approaches including (i) diversity analysis with Hill numbers, (ii) heterogeneity analysis with Taylor's power law extensions (TPLE), (iii) diversity scaling analysis with diversity-area relationship (DAR) model, and (iv) shared species analysis were applied to fulfill the data reanalysis.

RESULTS

(i) The influences of H. pylori infection on the species diversity, spatial heterogeneity, and potential diversity of gastric microbiome seem to be more prevalent than the influences of disease stages during gastric cancer development. (ii) The influences of H. pyloriinfection on diversity, heterogeneity, and composition of gastric microbiomes in HC, CG, IM, and GC stages appear more prevalent than those in AG stage.

CONCLUSION

Our study confirmed the impact of H. pylori infection on human gastric microbiomes: The influences of H. pylori infection on the diversity, heterogeneity, and composition of gastric microbiomes appear to be disease-stage dependent.

Effects of probiotics on gastric microbiota and its precombination with quadruple regimen for Helicobacter pylori eradication

OBJECTIVES

This study aimed to assess the efficacy and safety of probiotics for Helicobacter pylori (H. pylori) eradication therapy as well as their effects on gastric microbiota.

METHODS

Patients who had failed H. pylori eradication therapy for at least twice were prospectively enrolled during March 2019 and March 2021. A 2-week administration of compound Lactobacillus acidophilus probiotic (1 g thrice daily) followed by a 10-day quadruple bismuth-containing H. pylori eradication therapy was administrated. Endoscopy was performed, and gastric biopsy samples were obtained for drug sensitivity testing and 16S rRNA gene sequencing before and after probiotic treatment. Eradication was evaluated by the ¹³ C-urea breath test at least 4 weeks after treatment completion. Adverse events (AEs) were recorded.

RESULTS

Thirty-seven patients were included. Probiotic supplementation had no effects on the diversity, community structure, and composition of gastric microbiota and no inhibition on H. pylori activity. However, it increased some of the beneficial bacteria such as Blautia, Dorea, and Roseburia (P < 0.05). The overall eradication rate was 97.3% (95% confidence interval [CI] 91.8%-100%). AEs, mainly dizziness, nausea, diarrhea, and chest distress, were detected in six individuals, all of which were resolved upon cessation of antibiotic administration. Dyspeptic symptoms were improved after probiotic supplementation and at treatment completion (both P < 0.001).

CONCLUSIONS

H. pylori-infected individuals might benefit from probiotics followed by a quadruple bismuth-containing eradication therapy. Further studies with large sample sizes are warranted.

The Emerging Roles of Human Gut Microbiota in Gastrointestinal Cancer

The gut microbiota is composed of a large number of microorganisms with a complex structure. It participates in the decomposition, digestion, and absorption of nutrients; promotes the development of the immune system; inhibits the colonization of pathogens; and thus modulates human health. In particular, the relationship between gut microbiota and gastrointestinal tumor progression has attracted widespread concern. It was found that the gut microbiota can influence gastrointestinal tumor progression in independent ways. Here, we focused on the distribution of gut microbiota in gastrointestinal tumors and further elaborated on the impact of gut microbiota metabolites, especially short-chain fatty acids, on colorectal cancer progression. Additionally, the effects of gut microbiota on gastrointestinal tumor therapy are outlined. Finally, we put forward the possible problems in gut microbiota and the gastrointestinal oncology field and the efforts we need to make.

Bile Acid-Microbiome Interaction Promotes Gastric Carcinogenesis

Bile reflux gastritis (BRG) is associated with the development of gastric cancer (GC), but the specific mechanism remains elusive. Here, a comprehensive study is conducted to explore the roles of refluxed bile acids (BAs) and microbiome in gastric carcinogenesis. The results show that conjugated BAs, interleukin 6 (IL-6), lipopolysaccharide (LPS), and the relative abundance of LPS-producing bacteria are increased significantly in the gastric juice of both BRG and GC patients. A secondary BA, taurodeoxycholic acid (TDCA), is significantly and positively correlated with the LPS-producing bacteria in the gastric juice of these patients. TDCA promotes the proliferation of normal gastric epithelial cells (GES-1) through activation of the IL-6/JAK1/STAT3 pathway. These results are further verified in two mouse models, one by gavage of TDCA, LPS, and LPS-producing bacteria (Prevotella melaninogenica), respectively, and the other by bile reflux (BR) surgery, mimicking clinical bile refluxing. Moreover, the bile reflux induced gastric precancerous lesions observed in the post BR surgery mice can be prevented by treatment with cryptotanshinone, a plant-derived STAT3 inhibitor. These results reveal an important underlying mechanism by which bile reflux promotes gastric carcinogenesis and provide an alternative strategy for the prevention of GC associated with BRG.

16S rRNA sequencing-based evaluation of the protective effects of Hua-Zhuo-Jie-Du on rats with chronic atrophic gastritis

Background

Disturbance of the intestinal flora is a pathogenic factor for chronic atrophic gastritis (CAG). Hua-Zhuo-Jie-Du (HZJD) has been shown to be an effective Chinese herbal preparation for treating CAG. However, the effects of HZJD on the intestinal flora of CAG is unclear. In this study, we probed the regulating effects of HZJD on intestinal microbes in CAG rats using 16S rRNA gene sequencing.

Methods

High-performance liquid chromatography (HPLC) analysis was used to perform quality control of HZJD preparations. We then administered 1-methyl-3-nitro-1-nitrosoguanidine (200 μg/ml) to Sprague–Dawley rats to establish a CAG model. HZJD and vitacoenzyme were administered orally to these rats over a 10 week period. Hematoxylin and eosin (H&E) staining was performed to observe the histopathology of CAG rats. A rarefaction curve, species accumulation curve, Chao1 index, and ACE index were calculated to assess the alpha diversity. Principal component analysis (PCA), non-metric multi-dimensional scaling (NMDS), and unweighted pair group method with arithmetic mean (UPGMA) were conducted to examine the beta diversity. The LEfSe method was used to identify differential bacteria. Differential function analysis used PCA based on KEGG function prediction.

Results

HPLC showed that our HZJD preparation method was feasible. H&E staining showed that HZJD significantly improved the pathological state of the gastric mucosa in CAG rats. The rarefaction curve and species accumulation curve showed that the sequencing data were reasonable. The Chao1 and ACE indices were significantly increased in CAG rats compared to the N group. Following HZJD and vitacoenzyme treatment, the Chao1 and ACE indices were decreased. PCA, NMDS, and UPGMA results showed that the M group was separated from the N, HZJD, and V groups, and LEfSe results showed that the relative abundance of Akkermansia, Oscillospira, Prevotella, and CF231 were significantly higher in the N group. Proteobacteria and Escherichia were significantly enriched in the M group, Allobaculum, Bacteroides, Jeotgalicoccus, Corynebacterium, and Sporosarcina were significantly enriched in the V group, and Firmicutes, Lactobacillus, and Turicibacter were significantly enriched in the HZJD group.

Conclusion

HZJD exhibited a therapeutic effect on the intestinal flora of CAG rats.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12906-022-03542-z.

Multi-omics reveals microbiome, host gene expression, and immune landscape in gastric carcinogenesis

To date, there has been no multi-omic analysis characterizing the intricate relationships between the intragastric microbiome and gastric mucosal gene expression in gastric carcinogenesis. Using multi-omic approaches, we provide a comprehensive view of the connections between the microbiome and host gene expression in distinct stages of gastric carcinogenesis (i.e., healthy, gastritis, cancer). Our integrative analysis uncovers various associations specific to disease states. For example, uniquely in gastritis, Helicobacteraceae is highly correlated with the expression of FAM3D, which has been previously implicated in gastrointestinal inflammation. In addition, in gastric cancer but not in adjacent gastritis, Lachnospiraceae is highly correlated with the expression of UBD, which regulates mitosis and cell cycle time. Furthermore, lower abundances of B cell signatures in gastric cancer compared to gastritis may suggest a previously unidentified immune evasion process in gastric carcinogenesis. Our study provides the most comprehensive description of microbial, host transcriptomic, and immune cell factors of the gastric carcinogenesis pathway.

•

Multi-omics finds genetic, microbial, and immunological links in gastric cancer

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Helicobacteraceae was highly associated with the expression of inflammation genes

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Pasteurellaceae and Lachnospiraceae were associated with cancer-related genes

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B cell infiltration was prominent in gastritis tissues but not in gastric cancer

Microbiome changes in the gastric mucosa and gastric juice in different histological stages of Helicobacter pylori-negative gastric cancers

BACKGROUND

The gastric microbiota in patients with gastric cancer (GC) has received increasing attention, but the profiling of the gastric microbiome through the histological stages of gastric tumorigenesis remains poorly understood, especially for patients with Helicobacter pylori-negative GC (HPNGC).

AIM

To characterize microbial profiles of gastric mucosa and juice for HPNGC carcinogenesis and identify distinct taxa in precancerous lesions.

METHODS

The 16S rRNA gene analysis was performed on gastric mucosa from 134 Helicobacter pylori-negative cases, including 56 superficial gastritis (SG), 9 atrophic gastritis (AG), 27 intestinal metaplasia (IM), 29 dysplasia (Dys), and 13 GC cases, to investigate differences in gastric microbial diversity and composition across the disease stages. In addition, paired gastric mucosa and juice samples from 18 SG, 18 IM, and 18 Dys samples were analyzed. α-Diversity was measured by Shannon and Chao1 indexes, and β-diversity was calculated using partial least squares discrimination analysis (PLS-DA). Differences in the microbial composition across disease stages in different sample types were assessed using the linear discriminant analysis effect size.

RESULTS

The diversity and composition of the bacterial microbiota in the gastric mucosa changed progressively across stages of gastric carcinogenesis. The diversity of the gastric mucosa microbiota was found to be significantly lower in the IM and Dys groups than in the SG group, and the patients with GC had the lowest bacterial community richness (P < 0.05). Patients with IM and those with Dys had similar gastric mucosa microbiota profiles with Ralstonia and Rhodococcus as the predominant genera. Microbial network analysis showed that there was increasing correlation strength between IM and Dys (|correlation threshold|≥ 0.5, P < 0.05). GC and its precancerous lesions have distinguishable bacterial taxa; our results identified HPNGC-associated bacteria Streptococcaceae and Lactobacillaceae (P < 0.05). Additionally, across precancerous lesion stages from AG to Dys in Helicobacter pylori-negative patients, Burkholderiaceae abundance continuously increased, while Streptococcaceae and Prevotellaceae abundance presented a continuous downward trend. Furthermore, the microbial diversity was higher in gastric juice (P < 0.001) than in the mucosa, while PLS-DA revealed a statistically significant difference between the two groups (ANOSIM, P = 0.001). A significant difference in the microbial structure was identified, with Proteobacteria being more prevalent in the gastric mucosa and Firmicutes being more abundant in gastric juice.

CONCLUSION

Our results provide insights into potential taxonomic biomarkers for HPNGC and its precancerous stages and assist in predicting the prognosis of IM and Dys based on the mucosal microbiota profile.

Gastrointestinal Microbiota Changes in Patients With Gastric Precancerous Lesions

Background

Gastric microbiota may be involved in gastric cancer. The relationship between gastrointestinal microbes and the risk of gastric cancer is unclear. This study aimed to explore the gastric and intestinal bacteria associated with gastritis and gastric precancerous lesions. We conducted a case-control study by performing 16S rRNA gene analysis of gastric biopsies, juices, and stool samples from 148 cases with gastritis or gastric precancerous lesions from Anhui and neighboring provinces, China. And we validated our findings in public datasets.

Results

Analysis of microbial sequences revealed decreased bacterial alpha diversity in gastric bacteria during the progression of gastritis. Helicobacter pylori was the main contributor to the decreased microbial composition and diversity in the gastric mucosa and had little influence on the microbiota of gastric juice and feces. The gastric mucosal genera Gemella, Veillonella, Streptococcus, Actinobacillus, and Hemophilus had the higher degree of centrality across the progression of gastric precancerous lesions. And Acinetobacter may contribute to the occurrence of intraepithelial neoplasia. In addition, the microbial model of H. pylori-positive gastric biopsies and feces showed value in the prediction of gastric precancerous lesions.

Conclusions

This study identified associations between gastric precancerous lesions and gastric microbiota, as well as the changes in intestinal microbiota, and explored their values in the prediction of gastric precancerous lesions.

Alterations in Gastric Mucosal Microbiota in Gastric Carcinogenesis: A Systematic Review and Meta-Analysis

Background: The gastric microbiota profile alters during gastric carcinogenesis. We aimed to identify the alterations in the alpha diversity and relative abundance of bacterial phyla and genera of gastric microbiota in the development of gastric cancer (GC). Methods: The systematic review was performed based on a published protocol with the registration number CRD42020206973. We searched through PubMed, EMBASE and Cochrane databases, as well as conference proceedings and references of review articles (May 2021) for observational studies reporting either the relative abundance of bacterial phyla or genera, or alpha diversity indexes in both GC and non-cancer groups. Selection of studies and data extraction were performed independently by two researchers, with disagreements resolved through discussion. Risk of bias was assessed using the self-modified Newcastle-Ottawa Scale. Results of random-effects meta-analyses were presented as mean differences (MD). Results: Our systematic review included 751 GC patients and 792 non-cancer patients from 14 case-control studies. Gastric cancer group had fewer operational taxonomic units (OTUs) (MD = -68.52, 95%CI: -126.65 to -10.39) and a lower Simpson index (MD = -0.13, 95%CI: -0.20 to -0.07) compared with non-cancer group. At the phylum level, gastric cancer group had a higher abundance of Firmicutes (MD = 7.11, 95%CI: 1.76 to 12.46). At the genus level, Streptococcus (MD = 3.03, 95%CI: 0.07 to 6.00) and Lactobacillus (MD = 5.15, 95%CI: 1.27 to 9.04) were found to be enriched in GCgroup. The relative abundance of the rest bacterial phyla or genera analyzed in our study did not significantly differ between two groups. Subgroup analyses indicated that the source of samples was the major source of interstudy heterogeneity. Conclusion: This systematic review suggested that gastric microbiota dysbiosis occurred in gastric carcinogenesis, with alpha diversity declined and microbiota composition altered.

Gastric Microbiota beyond H. pylori: An Emerging Critical Character in Gastric Carcinogenesis

Gastric cancer (GC) is one of the global leading causes of cancer death. The association between Helicobacter pylori, which is a predominant risk factor for GC, with GC development has been well-studied. Recently, accumulating evidence has demonstrated the presence of a large population of microorganisms other than H. pylori in the human stomach. Existing sequencing studies have revealed microbial compositional and functional alterations in patients with GC and highlighted a progressive shift in the gastric microbiota in gastric carcinogenesis with marked enrichments of oral or intestinal commensals. Moreover, using a combination of gastric bacterial signatures, GC patients could be significantly distinguished from patients with gastritis. These findings, therefore, emphasize the importance of a collective microbial community in gastric carcinogenesis. Here, we provide an overview of non-H. pylori gastric microbes in gastric carcinogenesis. The molecular mechanisms of gastric microbes-related carcinogenesis and potential clinical applications of gastric microbiota as biomarkers of GC are also explored.

Mucosal microbial microenvironment in early gastric neoplasia and non-neoplastic gastric disease

BACKGROUND AND AIM

The biological characterization of microbial environment in early gastric cancer (EGC), other than Helicobacter pylori, is limited. This study aimed to explore the microbial microenvironment in chronic gastritis (CG), fundic gland polyps (FGPs), low-grade intraepithelial neoplasia (LGIN), and EGC.

METHODS

16S-rRNA gene sequencing and bioinformatic analysis were performed on 63 individuals with 252 mucosal biopsies or endoscopic submucosal dissection margin samples from endoscopy.

RESULTS

The microbiota in gastric LGIN functions analogously to EGC in terms of functional prediction. Neoplastic lesions showed a significant difference to CG or FGPs in beta diversity of the microbiota. Bacteria genera including Paracoccus, Blautia, Barnesiella, Lactobacillus, Thauera, Collinsella were significantly enriched in gastric neoplastic mucosa (LGIN and EGC) compared with non-neoplastic tissues (CG and FGPs). While Pseudomonas and Kingella were depleted in neoplastic tissues. FGPs showed a distinctive microbial network system that negatively interacted with Helicobacter.

CONCLUSIONS

In terms of the mucosal microbial microenvironment, gastric LGIN and EGC showed no significant difference as early neoplastic lesions. We observed a coordinated microbial microenvironment that correlated negatively with Helicobacter.