Gastric Cancer: The Microbiome Beyond Helicobacter pylori

Impacts of Helicobacter pylori infection and eradication on gastrointestinal microbiota: An up-to-date critical review and future perspectives

ABSTRACT

Helicobacter pylori ( H. pylori ) infects approximately half of the population worldwide and causes chronic gastritis, peptic ulcers, and gastric cancer. Test-and-treat strategies have been recommended for the prevention of H. pylori -associated diseases. Advancements in high-throughput sequencing technologies have broadened our understanding of the complex gastrointestinal (GI) microbiota and its role in maintaining host homeostasis. Recently, an increasing number of studies have indicated that the colonization of H. pylori induces dramatic alterations in the gastric microbiota, with a predominance of H. pylori and a reduction in microbial diversity. Dysbiosis of the gut microbiome has also been observed after H. pylori infection, which may play a role in the development of colorectal cancer. However, there is concern regarding the impact of antibiotics on the gut microbiota during H. pylori eradication. In this review, we summarize the current literature concerning how H. pylori infection reshapes the GI microbiota and the underlying mechanisms, including changes in the gastric environment, immune responses, and persistent inflammation. Additionally, the impacts of H. pylori eradication on GI microbial homeostasis and the use of probiotics as adjuvant therapy are also discussed. The shifts in the GI microbiota and their crosstalk with H. pylori  may provide potential targets for H. pylori -related gastric diseases and extragastric manifestations.

Association between gut microbiota and gastric cancers: a two-sample Mendelian randomization study

Background

Gastric cancer (GC) is the fifth most commonly diagnosed cancer worldwide, with its etiology attributed to a complex interplay of genetic, dietary, environmental factors, and infections such as Helicobacter pylori. Despite the known risk factors, the role of gut microbiota in the development of gastric cancer remains insufficiently explored. This study aims to elucidate the causal relationship between gut microbiota and gastric cancer using a two-sample Mendelian Randomization (MR) approach.

Methods

Utilizing genome-wide association study (GWAS) summary data from the MiBioGen consortium and gastric cancer datasets, we selected instrumental variables for MR analysis based on their association with specific microbiota. We employed several MR methods, including inverse variance weighted (IVW), MR-Egger, weighted median, and others, to estimate the causal effects of gut microbiota diversity on the risk of developing gastric cancer.

Results

Our analysis identified significant associations between certain gut microbiota and gastric cancer risk. Specifically, taxa such as Clostridium sensustricto1 (OR = 0.540, 95%CI: 0.354-0.823, p = 0.004), Actinomycetales (OR = 0.756, 95%CI: 0.613-0.932, p = 0.009), Selenomonadales (OR = 0.816, 95%CI: 0.666-1.000, p < 0.05), Negativicutes (OR = 0.816, 95%CI: 0.666-1.000, p < 0.05), Rikenellaceae (OR = 0.863, 95%CI: 0.746-0.999, p = 0.048) were found to have a protective effect against gastric cancer. Conversely, an increased risk of gastric cancer was associated with the abundance of Roseburia (OR = 1.342, 95%CI: 1.071-1.681, p = 0.011), Family XI (OR = 1.132, 95%CI: 1.012-1.267, p = 0.030), and Eubacterium brachy group (OR = 1.207, 95%CI: 1.074-1.355, p = 0.002). The findings were robust across various MR methods and were not driven by any single SNP, indicating a genuine causal relationship.

Conclusion

Our studies have shown that there is a causal relationship between intestinal flora and gastric cancer at the genetic level. Clostridium sensustricto1, Actinomycetales, Rikenellaceae, Selenomonadales, Negativicutes, and Actinomycetaceae as having a protective role against GC, while Roseburia, Family XI, and Eubacterium brachy group were associated with an increased risk.