Gastric microbiome profile throughout gastric carcinogenesis: beyond helicobacter

Gastrointestinal Microbiota in Gastric Cancer: Potential Mechanisms and Clinical Applications-A Literature Review

Emerging evidence highlights the crucial role of gastrointestinal microbiota in the pathogenesis of gastric cancer. Helicobacter pylori (H. pylori) infection stands out as a primary pathogenic factor. However, interventions such as anti-H. pylori therapy, gastric surgeries, immunotherapy, and chronic inflammation significantly remodel the gastric microbiome, implicating a broader spectrum of microorganisms in cancer development. These microbial populations can modulate gastric carcinogenesis through various mechanisms, including sustained chronic inflammation, bacterial genotoxins, alterations in short-chain fatty acids, elevated gastrointestinal bile acids, impaired mucus barrier function, and increased concentrations of N-nitrosamines and lactic acid. The dynamic changes in gut microbiota also critically influence the outcomes of anti-cancer therapies by modifying drug bioavailability and metabolism, thus affecting therapeutic efficacy and side effect profiles. Additionally, the effectiveness of radiotherapy can be significantly impacted by gut microbiota alterations. Novel therapeutic strategies targeting the microbiome, such as dietary interventions, probiotic and synbiotic supplementation, and fecal microbiota transplantation, are showing promise in cancer treatment. Understanding the intricate relationship between the gut microbiota and gastric cancer is essential for developing new, evidence-based approaches to the prevention and treatment of this malignancy.

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.

Do atrophic gastritis and intestinal metaplasia reverse after Helicobacter pylori eradication?

BACKGROUND

It's still controversial whether Helicobacter pylori (H. pylori) eradication can reverse atrophic gastritis (AG) and intestinal metaplasia (IM). Therefore, we performed a meta-analysis to estimate the effect of H. pylori eradication on AG and IM.

METHODS

We searched the PubMed, Web of Science and EMBASE datasets through April 2023 for epidemiological studies, which provided mean glandular atrophy (GA) or IM score before and after H. pylori eradication, or provided ORs, RRs or HRs and 95% CIs for the association of AG or IM with H. pylori eradication. Weighted mean difference (WMD) and pooled ORs and 95%CIs were used to estimate the effect of H. pylori eradication on AG and IM.

RESULTS

Twenty articles with a total of 5242 participants were included in this meta-analysis. H. pylori eradication significantly decreased GA score in the antrum (WMD -0.36; 95% CI: -0.52, -0.19, p < 0.01), GA score in the corpus (WMD -0.35; 95% CI: -0.52, -0.19, p < 0.01), IM score in the antrum (WMD -0.16; 95% CI: -0.26, -0.07, p < 0.01) and IM score in the corpus (WMD -0.20; 95% CI: -0.37, -0.04, p = 0.01). H. pylori eradication significantly improved AG (pooled OR 2.96; 95% CI: 1.70, 5.14, p < 0.01) and IM (pooled OR 2.41; 95% CI: 1.24, 4.70, p < 0.01). The association remained significant in the subgroup analyses by study design, sites of lesions, regions and follow-up time. Although Publication bias was observed for AG, the association remained significant after trim-and-fill adjustment.

CONCLUSIONS

H. pylori eradication could significantly improve AG and IM at early stage.

[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.

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.

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.

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.

New Insights into the Relationship between Gut Microbiota and Radiotherapy for Cancer

Cancer is the second most common cause of death among humans in the world, and the threat that it presents to human health is becoming more and more serious. The mechanisms of cancer development have not yet been fully elucidated, and new therapies are changing with each passing day. Evidence from the literature has validated the finding that the composition and modification of gut microbiota play an important role in the development of many different types of cancer. The results also demonstrate that there is a bidirectional interaction between the gut microbiota and radiotherapy treatments for cancer. In a nutshell, the modifications of the gut microbiota caused by radiotherapy have an effect on tumor radiosensitivity and, as a result, affect the efficacy of radiotherapy and show a certain radiation toxicity, which leads to numerous side effects. What is of new research significance is that the "gut-organ axis" formed by the gut microbiota may be one of the most interesting potential mechanisms, although the relevant research is still very limited. In this review, we combine new insights into the relationship between the gut microbiota, cancer, and radiotherapy. Based on our current comprehensive understanding of this relationship, we give an overview of the new cancer treatments based on the gut microbiota.

A literature review on the potential clinical implications of streptococci in gastric cancer

Streptococcus is widely found in nature and the human body, and most species are not pathogenic. In recent years, studies have found that Streptococcus is associated with gastric cancer. Streptococcus was found to be enriched in the oral cavity, stomach and intestine of gastric cancer patients and found to be increased in gastric cancer tissues, suggesting that Streptococcus may be the pathogenic bacteria underlying gastric cancer. This review discusses the discovery of Streptococcus, the relationship between Streptococcus and gastric cancer, and the possible carcinogenic mechanism of Streptococcus and summarizes the progress of the research on the role of Streptococcus in gastric cancer to provide new ideas for the early detection, diagnosis and treatment of gastric cancer.

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.

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.