Distal Gastrectomy with Billroth II Reconstruction is Associated with Oralization of Gut Microbiome and Intestinal Inflammation: A Proof-of-Concept Study

Gut Microbiome Changes After Neoadjuvant Chemotherapy and Surgery in Patients with Gastric Cancer

BACKGROUND/OBJECTIVES

Neoadjuvant chemotherapy (NAC) followed by radical gastrectomy is the current standard approach for locally advanced gastric cancer (GC) in the West. Both NAC and gastrectomy can significantly influence the gut microbiome, potentially leading to clinically significant changes. However, no longitudinal studies to date support this hypothesis. This study investigates gut microbiome changes throughout GC treatment, including NAC and gastrectomy.

METHODS

This longitudinal observational study included GC patients undergoing NAC followed by gastrectomy. Fecal microbiome composition, intestinal inflammation (fecal calprotectin), and gut permeability (LBP, sCD14) markers were investigated at baseline, after NAC, and after gastrectomy.

RESULTS

A total of 38 patients were included in the study. The results showed that NAC did not affect the gut microbiome composition at the phylum level. In contrast, radical gastrectomy led to an increased abundance of Bacteroidetes and Proteobacteria and a decreased abundance of Firmicutes and Actinobacteria. Furthermore, NAC alone did not impact alpha or beta diversity, while a combination of NAC and gastrectomy significantly influenced both. After gastrectomy, the gut microbiome composition analysis also revealed enrichment of oralization-associated bacterial species such as Escherichia-Shigella, Streptococcus equinus, uncultured Streptococcus species, and species from the Enterobacteriaceae family. Intestinal inflammation and gut permeability markers did not significantly change throughout the treatment.

CONCLUSIONS

The radical treatment of advanced GC with NAC and radical surgery has long-term effects on the gut microbiome, characterized by gut microbiome oralization. These sustained alterations primarily stem from the radical gastrectomy rather than the NAC. Since previous studies have linked oralization-associated dysbiosis to various gastrointestinal symptoms, this study highlights the gut microbiome as a potential therapeutic target to enhance the quality of life in long-term survivors following gastrectomy.

Effects of intratumoral microbiota on tumorigenesis, anti-tumor immunity, and microbe-based cancer therapy

Intratumoral microbiota (IM) has emerged as a significant component of the previously thought sterile tumor microenvironment (TME), exerting diverse functions in tumorigenesis and immune modulation. This review outlines the historical background, classification, and diversity of IM, elucidating its pivotal roles in oncogenicity, cancer development, and progression, alongside its influence on anti-tumor immunity. The signaling pathways through which IM impacts tumorigenesis and immunity, including reactive oxygen species (ROS), β-catenin, stimulator of interferon genes (STING), and other pathways [NF-κB, Toll-like receptor (TLR), complement, RhoA/ROCK, PKR-like ER kinase (PERK)], are discussed comprehensively. Furthermore, we briefly introduce the clinical implications of IM, emphasizing its potential as a target for novel cancer therapies, diagnostic biomarkers, and prognostic indicators. Notably, microbe-based therapeutic strategies such as fecal microbiome transplantation (FMT), probiotics regulation, bacteriotherapy, bacteriophage therapy, and oncolytic virotherapy are highlighted. These strategies hold promise for enhancing the efficacy of current cancer treatments and warrant further exploration in clinical settings.

The Impact of Gastrectomy on Inflammatory Bowel Disease Risk in Gastric Cancer Patients: A Critical Analysis

Gastrectomy, a prevalent surgical procedure for gastric cancer, results in substantial alterations to the gastrointestinal tract, including reduced gastric acid production and significant modifications to the gut microbiota. These changes can impair postoperative recovery, influence metabolic functions, and predispose patients to inflammatory bowel disease (IBD). Studies have shown an increased risk of IBD, particularly Crohn's disease (CD) and ulcerative colitis (UC), in patients following gastrectomy and bariatric surgeries such as Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG). For instance, patients undergoing RYGB have a higher hazard ratio for developing CD, while SG patients show an increased risk for UC. The surgical alteration of the gastrointestinal tract promotes dysbiosis, with a significant increase in pathogenic bacteria and a decrease in beneficial microbial populations. This dysbiosis can impair the intestinal mucosal barrier and promote systemic inflammation. Understanding the mechanisms behind these changes and their clinical implications is essential for developing effective postoperative management strategies. Probiotics and enhanced recovery after surgery (ERAS) protocols have shown promise in mitigating these adverse effects, improving gut microbiota balance, and enhancing patient outcomes. Further research is necessary to fully elucidate the long-term impacts of gastrectomy on gastrointestinal health and to refine therapeutic approaches for postoperative care.

Cellular and Microbial In Vitro Modelling of Gastrointestinal Cancer

Human diseases are multifaceted, starting with alterations at the cellular level, damaging organs and their functions, and disturbing interactions and immune responses. In vitro systems offer clarity and standardisation, which are crucial for effectively modelling disease. These models aim not to replicate every disease aspect but to dissect specific ones with precision. Controlled environments allow researchers to isolate key variables, eliminate confounding factors and elucidate disease mechanisms more clearly. Technological progress has rapidly advanced model systems. Initially, 2D cell culture models explored fundamental cell interactions. The transition to 3D cell cultures and organoids enabled more life-like tissue architecture and enhanced intercellular interactions. Advanced bioreactor-based devices now recreate the physicochemical environments of specific organs, simulating features like perfusion and the gastrointestinal tract's mucus layer, enhancing physiological relevance. These systems have been simplified and adapted for high-throughput research, marking significant progress. This review focuses on in vitro systems for modelling gastrointestinal tract cancer and the side effects of cancer treatment. While cell cultures and in vivo models are invaluable, our main emphasis is on bioreactor-based in vitro modelling systems that include the gut microbiome.

Disease- and stage-specific alterations of the oral and fecal microbiota in Alzheimer's disease

Microbial communities in the intestinal tract are suggested to impact the ethiopathogenesis of Alzheimer's disease (AD). The human microbiome might modulate neuroinflammatory processes and contribute to neurodegeneration in AD. However, the microbial compositions in patients with AD at different stages of the disease are still not fully characterized. We used 16S rRNA analyses to investigate the oral and fecal microbiota in patients with AD and mild cognitive impairment (MCI; n = 84), at-risk individuals (APOE4 carriers; n = 17), and healthy controls (n = 50) and investigated the relationship of microbial communities and disease-specific markers via multivariate- and network-based approaches. We found a slightly decreased diversity in the fecal microbiota of patients with AD (average Chao1 diversity for AD = 212 [SD = 66]; for controls = 215 [SD = 55]) and identified differences in bacterial abundances including Bacteroidetes, Ruminococcus, Sutterella, and Porphyromonadaceae. The diversity in the oral microbiota was increased in patients with AD and at-risk individuals (average Chao1 diversity for AD = 174 [SD = 60], for at-risk group = 195 [SD = 49]). Gram-negative proinflammatory bacteria including Haemophilus, Neisseria, Actinobacillus, and Porphyromonas were dominant oral bacteria in patients with AD and MCI and the abundance correlated with the cerebrospinal fluid biomarker. Taken together, we observed a strong shift in the fecal and the oral communities of patients with AD already prominent in prodromal and, in case of the oral microbiota, in at-risk stages. This indicates stage-dependent alterations in oral and fecal microbiota in AD which may contribute to the pathogenesis via a facilitated intestinal and systemic inflammation leading to neuroinflammation and neurodegeneration.

Unveiling the Gastrointestinal Microbiome Symphony: Insights Into Post-Gastric Cancer Treatment Microbial Patterns and Potential Therapeutic Avenues

This review delved into the intricate relationship between the gastrointestinal microbiome and gastric cancer, particularly focusing on post-treatment alterations, notably following gastrectomy, and the effects of anticancer therapies. Following gastrectomy, analysis of fecal samples revealed an increased presence of oral cavity aerotolerant and bile acid-transforming bacteria in the intestine. Similar changes were observed in the gastric microbiome, highlighting significant alterations in taxon abundance and emphasizing the reciprocal interaction between the oral and gastric microbiomes. In contrast, the impact of chemotherapy and immunotherapy on the gut microbiome was subtle, although discernible differences were noted between treatment responders and non-responders. Certain bacterial taxa showed promise as potential prognostic markers. Notably, probiotics emerged as a promising approach for postgastrectomy recovery, displaying the capacity to alleviate inflammation, bolster immune responses, and maintain a healthy gut microbiome. Several strains, including Bifidobacterium, Lactobacillus, and Clostridium butyricum, exhibited favorable outcomes in postoperative patients, suggesting their potential roles in comprehensive patient care. In conclusion, understanding the intricate interplay between the gastrointestinal microbiome and gastric cancer treatment offers prospects for predicting responses and enhancing postoperative recovery. Probiotics, with their positive impact on inflammation and immunity, have emerged as potential adjuncts in patient care. Continued research is imperative to fully harness the potential of microbiome-based interventions in the management of gastric cancer.

Incidence and clinical relevance of postoperative diarrhea after minimally invasive gastrectomy for gastric cancer: a single institution retrospective study of 1476 patients

PURPOSE

Postoperative diarrhea (PD) remains one of the significant complications. Only a few studies focused on PD after minimally invasive surgery. We aimed to investigate PD after minimally invasive gastrectomy for gastric cancer.

METHODS

A total of 1476 consecutive patients with gastric cancer undergoing laparoscopic or robotic gastrectomy between 2009 and 2019 at our institution were retrospectively reviewed. PD was defined as continuous diarrhea for ≥ 2 days, positive stool culture, or positive clostridial antigen test. The incidence, causes, and related clinical factors were analyzed.

RESULTS

Of the 1476 patients, the median age was 69 years. Laparoscopic and robotic approaches were performed in 1072 (72.6%) and 404 (27.4%), respectively. Postoperative complications with Clavien-Dindo classification grade of ≥ IIIa occurred in 108 (7.4%) patients. PD occurred in 89 (6.0%) patients. Of the 89 patients with PD, Clostridium difficile, enteropathogenic Escherichia coli, and methicillin-resistant Staphylococcus aureus were detected in 24 (27.0%), 16 (33.3%), and 7 (14.6%) patients, respectively. Multivariate analysis revealed that age ≥ 75 years (OR 1.62, 95% CI [1.02-2.60], p = 0.042) and postoperative complications (OR 6.04, 95% CI [3.54-10.32], p < 0.001) were independent risk factors for PD. In patients without complications, TG (OR 1.88) and age of ≥ 75 years(OR 1.71) were determined as independent risk factors.

CONCLUSION

The incidence of PD following minimally invasive gastrectomy for gastric cancer was 6.0%. Older age and TG were obvious risk factors in such a surgery, with the latter being a significant risk even in the absence of complications.

RGI-Type Pectic Polysaccharides Modulate Gut Microbiota in a Molecular Weight-Dependent Manner In Vitro

In this study, the fermentation characteristics of high rhamnogalacturonan I pectic polysaccharides (RGI) and free-radical degraded RGI (DRGI) were evaluated by a human fecal batch-fermentation model, and their structural properties were also investigated. As a result, the M_w of RGI decreased from 246.8 to 11.6 kDa, and the branches were broken dramatically. Fermentation showed that RGI degraded faster and produced more acetate and propionate than DRGI. Both of them reduced the Firmicutes/Bacteroidetes ratio and promoted the development of Bacteroides, Bifidobacterium, and Lactobacillus, bringing benefits to the gut ecosystem. However, the composition and metabolic pathways of the microbiota in RGI and DRGI were different. Most of the dominant bacteria of RGI (such as [Eubacterium]_eligens_group) participated in carbohydrate utilization, leading to better performance in glucolipid metabolism and energy metabolism. This work elucidated that large molecular weight matters in the gut microbiota modulatory effect of RGI-type pectic polysaccharides in vitro.

Tributyrin and anise mixture supplementation improves growth performance, nutrient digestibility, jejunal villus height, and fecal microbiota in weaned pigs

Introduction

The objective of this study was to investigate the effects of dietary supplementation of tributyrin and anise mixture (TA) on growth performance, apparent nutrient digestibility, fecal noxious gas emission, fecal score, jejunal villus height, hematology parameters, and fecal microbiota of weaned pigs.

Methods

A total of 150 21-day-old crossbred weaned pigs [(Landrace × Yorkshire) × Duroc] were used in a randomized complete block design experiment. All pigs were randomly assigned to 3 groups based on the initial body weight (6.19 ± 0.29 kg). Each group had 10 replicate pens with 5 pigs (three barrows and two gilts) per pen. The experimental period was 42 days and consisted of 3 phases (phase 1, days 1-7; phase 2, days 8-21; phase 3, days 22-42). Dietary treatments were based on a corn-soybean meal-basal diet and supplemented with 0.000, 0.075, or 0.150% TA.

Results and discussion

We found that dietary supplementation of graded levels of TA linearly improved body weight, body weight gain, average daily feed intake, and feed efficiency (P < 0.05). TA supplementation also had positive effects on apparent dry matter, crude protein, and energy digestibility (P < 0.05) and jejunal villus height (P < 0.05). The emission of ammonia from feces decreased linearly with the dose of TA increased (P < 0.05). Moreover, TA supplementation was capable to regulate the fecal microbiota diversity, manifesting in a linearly increased Chao1 index and observed species and a linearly decreased Pielou's index (P < 0.05). The abundance of Lactobacillus reuteri, Lactobacillus amylovorus, Clostridium butyricum were increased, while the abundance of Prevotella copri was decreased, by treatment (P < 0.05). Therefore, we speculated that TA supplementation would improve growth performance and reduce fecal ammonia emission through improving nutrient digestibility, which was attributed to the increase of jejunal villus height and the regulation of fecal microbiota.

Ultra-early weaning alters growth performance, hematology parameters, and fecal microbiota in piglets with same genetic background

Piglets with the same genetic background were used to investigate the effects of different lengths of suckling period on growth performance, hematology parameters, and fecal microbiota. All piglets were born by a sow (Landrace×Yorkshire). On day 14 postpartum, a total of 16 piglets [Duroc×(Landrace×Yorkshire)] with a similar initial body weight (2.48 ± 0.25 kg) were randomly assigned into two groups with four replicates per group, two pigs per replicate pen (one barrow and one gilt). On day 14 of age, experiment started, piglets from the first group were weaned (14W), whereas the others continued to receive milk until day 28 of age (28W). The experiment completed on day 70 of age, last 56 days. Growth performance parameters including body weight, average daily gain, feed intake, feed efficiency, and growth rate and hematology parameters including immunoglobulin A (IgA), immunoglobulin G (IgG), immunoglobulin M (IgM), albumin, globulin, and total protein were measured in this study. Additionally, a technique of 16S rRNA gene sequencing was used to analyze fecal microbiota for revealing how the changes in the lengths of suckling period on intestinal microbiota. We found that ultra-early weaning impaired growth performance of piglets, whose worse body weight, average daily gain, feed intake, feed efficiency, and growth rate were observed in 14W group at all measured timepoints in comparison with those in 28W group (P < 0.05). Moreover, higher contents of serum IgA (P = 0.028), IgG (P = 0.041), and IgM (P = 0.047), as well as lower contents of serum albumin (P = 0.002), albumin-to-globulin ratio (P = 0.003), and total protein (P = 0.004), were observed in 14W group in comparison with those in 28W group on day 28 of age, but not on day 70 of age. High-throughput pyrosequencing of 16S rRNA indicated that the intestinal microbiota richness in 14W group was lower than that in 28W group (P < 0.05); moreover, in comparison with 28W group at all sampling timepoints, fecal microbiota in 14W group showed more beneficial bacteria and fewer pathogenic bacteria (P < 0.05). Therefore, we considered that ultra-early weaning had positive effects on immune status and fecal microbiota composition in piglets, but negative effects on growth performance and fecal microbiota abundance.

What are the late effects of older gastric cancer survivors?: A scoping review

Objective

Methods

Results

Conclusions

Clinical Efficacy of Laparoscopic Billroth II Subtotal Gastrectomy Plus Lienal Polypeptide Injection for Gastric Cancer

Objective

To evaluate the clinical efficacy of laparoscopic Billroth II subtotal gastrectomy plus lienal polypeptide injection for gastric cancer.

Methods

Between May 2018 and January 2021, 110 patients with gastric cancer treated in Jingzhou First People's Hospital were recruited and assigned via the random number table method to either an observation group or a control group, with 55 patients in each group. All patients received laparoscopic Billroth II subtotal gastrectomy, and the observation group additionally received lienal polypeptide injection. Outcome measures include surgical indexes, clinical efficacy, and adverse events.

Results

The patients in the observation group had significantly less intraoperative hemorrhage volume, smaller surgical wounds, shorter time lapse before passing gas and hospital stay, and longer operation time than those in the control group (P < 0.001). The observation group showed significantly higher efficacy than the control group (P=0.001). The observation group had a significantly lower incidence of toxic side effects and adverse events than the control group (P < 0.05). After treatment, the CD3+ and CD4+ levels were significantly elevated and the CD8+ level was decreased, with higher CD3+ and CD4+ levels and lower CD8+ levels in the observation group than in the control group (P < 0.05).

Conclusion

In the treatment of patients with gastric cancer, laparoscopic Billroth II subtotal gastrectomy plus lienal polypeptide injection features promising efficacy, improves the immune function of patients, effectively reduces the occurrence of toxic side effects and adverse reactions, with less trauma and rapid recovery, which shows good potential for use in clinical application.

The Implication of Gastric Microbiome in the Treatment of Gastric Cancer

Simple Summary

Gastric cancer (GC) represents the fifth most common cancer worldwide. Recent developments in PCR and metagenomics clarify that the stomach contains a powerful microbiota. Conventional treatments for GC that include surgery, chemotherapy, and radiotherapy are not very effective. That’s why new therapeutic strategies are needed. The intestinal microbiota is involved in oncogenesis and cancer prevention, and the effectiveness of chemotherapy. Recent studies have shown that certain bacteria may enhance the effect of some traditional antineoplastic drugs and immunotherapies.

Abstract

Gastric cancer (GC) is one of the most common and deadly malignancies worldwide. Helicobacter pylori have been documented as a risk factor for GC. The development of sequencing technology has broadened the knowledge of the gastric microbiome, which is essential in maintaining homeostasis. Recent studies have demonstrated the involvement of the gastric microbiome in the development of GC. Therefore, the elucidation of the mechanism by which the gastric microbiome contributes to the development and progression of GC may improve GC’s prevention, diagnosis, and treatment. In this review, we discuss the current knowledge about changes in gastric microbial composition in GC patients, their role in carcinogenesis, the possible therapeutic role of the gastric microbiome, and its implications for current GC therapy.

Oral and Stool Microbiome Coalescence and Its Association With Antibiotic Exposure in Acute Leukemia Patients

Failure to maintain segregation of oral and gut microbial communities has been linked to several diseases. We sought to characterize oral-fecal microbiome community coalescence, ectopic extension of oral bacteria, clinical variables contributing to this phenomenon, and associated infectious consequences by analyzing the 16S rRNA V4 sequences of longitudinal fecal (n=551) and oral (n=737) samples from 97 patients with acute myeloid leukemia (AML) receiving induction chemotherapy (IC). Clustering observed in permutation based multivariate analysis of variance (PERMANOVA) of Bray-Curtis dissimilarity and PCoA plot of UniFrac distances between intra-patient longitudinal oral-stool sample pairs suggested potential oral-stool microbial community coalescence. Bray-Curtis dissimilarities and UniFrac distances were used to create an objective definition of microbial community coalescence. We determined that only 23 of the 92 patients exhibited oral-stool community coalescence. This was validated through a linear mixed model which determined that patients who experienced coalescence had an increased proportion of shared to unique OTUs between their oral-stool sample pairs over time compared to non-coalesced patients. Evaluation of longitudinal microbial characteristics revealed that patients who experienced coalescence had increased stool abundance of Streptococcus and Stenotrophomonas compared to non-coalesced patients. When treated as a time-varying covariate, each additional day of linezolid (HR 1.15, 95% CI 1.06 – 1.24, P <0.001), meropenem (HR 1.13, 95% CI 1.05 – 1.21, P = 0.001), metronidazole (HR 1.13, 95% CI 1.05 – 1.21, P = 0.001), and cefepime (HR 1.10, 95% CI 1.01 – 1.18, P = 0.021) increased the hazard of oral-stool microbial community coalescence. Levofloxacin receipt was associated with a lower risk of microbiome community coalescence (HR 0.75, 95% CI 0.61 – 0.93, P = 0.009). By the time of neutrophil recovery, the relative abundance of Bacteroidia (P<0.001), Fusobacteria (P=0.012), and Clostridia (P=0.013) in the stool were significantly lower in patients with oral-gut community coalescence. Exhibiting oral-stool community coalescence was associated with the occurrence of infections prior to neutrophil recovery (P=0.002), as well as infections during the 90 days post neutrophil recovery (P=0.027). This work elucidates specific antimicrobial effects on microbial ecology and furthers the understanding of oral/intestinal microbial biogeography and its implications for adverse clinical outcomes.

Enriched and Decreased Intestinal Microbes in Active VKH Patients

Purpose

To determine the possible microbiome related to Vogt–Koyanagi–Harada (VKH) disease in comparison to patients with noninfectious anterior scleritis and healthy people.

Methods

Fecal samples were extracted from 42 individuals, including 11 patients with active VKH, 11 healthy people, and 20 patients with noninfectious anterior scleritis. We amplified the V3 to V4 16S ribosomal DNA (rDNA) region to obtain the target sequence. Then, the target sequence was amplified by polymerase chain reaction. The obtained target sequences were sequenced by high-throughput 16S rDNA analysis.

Results

At the genus level, there were three enriched (Stomatobaculum, Pseudomonas, Lachnoanaerobaculum) and two depleted (Gordonibacter, Slackia) microbes that were detected only in patients with VKH. There were 10 enriched and 12 depleted microbes that were observed in both patients with VKH disease and noninfectious anterior scleritis (P < 0.05). The interactions of these microbes were graphed. Tyzzerella and Eggerthella were the nodes of interaction between these microorganisms, which were regulated by both positive and negative aspects, but the expression level in patients with active VKH was upregulated.

Conclusions

Special or nonspecial enrichment and decreased intestinal microbes were observed in patients with active VKH. The action mechanism of these microbes needs further study.

Time-course alterations of gut microbiota and short-chain fatty acids after short-term lincomycin exposure in young swine

Increasing evidence suggests that antibiotic administration causes gut injury, negatively affecting nutrient digestion, immune regulation, and colonization resistance against pathogens due to the disruption of gut microbiota. However, the time-course effects of therapeutic antibiotics on alterations of gut microbes and short-chain fatty acids (SCFAs) in young swine are still unknown. In this study, twenty piglets were assigned into two groups and fed commercial diets with or without lincomycin in the first week for a 28-day trial period. Results showed that 1-week lincomycin exposure (LE) did reduce the body weight on day 14 (p = 0.0450) and 28 (p = 0.0362). The alpha-diversity notably reduced after 1-week LE, and then gradually raised and reached the control group level in the second week on cessation of LE, indicated by the variation of Sobs, Chao, Shannon, and ACE index (p < 0.05). Beta-diversity analysis revealed that the distinct microbial cluster existed persistently for the whole trial period between two groups (p < 0.001). The relative abundance of most microbes including fiber-degrading (e.g., Agathobacter and Coprococcus), beneficial (e.g., Lactobacillus and Mitsuokella), or pathogenic bacteria (e.g., Terrisporobacter and Lachnoclostridium) decreased (LDA score > 3), and the concentration of SCFAs also diminished in the feces of 1-week lincomycin-administrated young swine, indicating that therapeutic LE killed most bacteria and reduced SCFA production with gut dysbiosis occurring. After the LE stopped, the state of gut dysbiosis gradually attenuated and formed new gut-microbe homeostasis distinct from microbial homeostasis of young pigs unexposed to lincomycin. The increased presence of potential pathogens, such as Terrisporobacter, Negativibacillus, and Escherichia-Shigella, and decreased beneficial bacteria, such as Lactobacillus and Agathobacter, were observed in new homeostasis reshaped by short-lincomycin administration (LDA score > 3 or p < 0.05), adversely affecting gut development and health of young pigs. Collectively, these results suggested that severe disruption of the commensal microbiota occurred after short-term LE or termination of LE in young swine. KEY POINTS: • Therapeutic lincomycin exposure induced gut dysbiosis, killing most bacteria and reducing short-chain fatty acid production. • Gut dysbiosis gradually attenuated and formed new homeostasis after lincomycin exposure stopped. • The new homeostasis, increased Escherichia-Shigella etc. and decreased Lactobacillus etc., was potentially harmful to gut health.

Gastrectomy impact on the gut microbiome in patients with gastric cancer: A comprehensive review

Gastric cancer is one of the most common malignancies worldwide and gastrectomy remains the only potentially curative treatment option for this disease. However, the surgery leads to significant physiological and anatomical changes in the gastrointestinal (GI) tract including loss of the gastric barrier, an increase in oxygenation levels in the distal gut, and biliary diversion after gastrectomy. These changes in the GI tract influence the composition of the gut microbiome and thus, host health. Gastrectomy-induced dysbiosis is characterized by increased abundance of typical oral cavity bacteria, an increase in aero-tolerant bacteria (aerobes/facultative anaerobes), and increased abundance of bile acid-transforming bacteria. Furthermore, this dysbiosis is linked to intestinal inflammation, small intestinal bacterial overgrowth, various GI symptoms, and an increased risk of colorectal cancer.

Gastric Cancer Microbiome

Identifying a microbiome pattern in gastric cancer (GC) is hugely debatable due to the variation resulting from the diversity of the studied populations, clinical scenarios, and metagenomic approach. H. pylori remains the main microorganism impacting gastric carcinogenesis and seems necessary for the initial steps of the process. Nevertheless, an additional non-H. pylori microbiome pattern is also described, mainly at the final steps of the carcinogenesis. Unfortunately, most of the presented results are not reproducible, and there are no consensual candidates to share the H. pylori protagonists. Limitations to reach a consistent interpretation of metagenomic data include contamination along every step of the process, which might cause relevant misinterpretations. In addition, the functional consequences of an altered microbiome might be addressed. Aiming to minimize methodological bias and limitations due to small sample size and the lack of standardization of bioinformatics assessment and interpretation, we carried out a comprehensive analysis of the publicly available metagenomic data from various conditions relevant to gastric carcinogenesis. Mainly, instead of just analyzing the results of each available publication, a new approach was launched, allowing the comprehensive analysis of the total sample amount, aiming to produce a reliable interpretation due to using a significant number of samples, from different origins, in a standard protocol. Among the main results, Helicobacter and Prevotella figured in the "top 6" genera of every group. Helicobacter was the first one in chronic gastritis (CG), gastric cancer (GC), and adjacent (ADJ) groups, while Prevotella was the leader among healthy control (HC) samples. Groups of bacteria are differently abundant in each clinical situation, and bacterial metabolic pathways also diverge along the carcinogenesis cascade. This information may support future microbiome interventions aiming to face the carcinogenesis process and/or reduce GC risk.

[Proton Pump Inhibitors and their Microbiome-Mediated Side Effects]

Proton pump inhibitors are valuable treatment options for gastric acid associated diseases, such as peptic ulcer disease or reflux diseases. Due to their irreversible inhibition of the proton pumps in the parietal cells of the stomach, gastric acid secretion can be effectively reduced. With the reduction in gastric acid, however, proton pump inhibitors also block a highly conserved, crucial part of the unspecific immune system. The gastric barrier protects the body - and here mainly the intestinal microbiome - from food-borne pathogens and oral bacteria that can reach more distal parts of the gastrointestinal tract during proton pump inhibitor therapy. Resulting changes in the intestinal microbiome, such as the reduction in microbial diversity or small intestinal bacterial overgrowth, can be linked to side effects of (long-term) proton pump inhibitor therapy, such as the increased risk of Clostridium difficile infections or gastrointestinal discomfort. In liver cirrhosis patients, the increase in oral bacteria in the intestine is associated with intestinal inflammation and permeability, and can even be used as a biomarker for 3-year liver related mortality. Therefore, microbiome-mediated side effects should be included in the risk assessment of proton pump inhibitor therapy and the evaluation of potential alternatives.