Higher Prevalence of Bacteroides fragilis in Crohn's Disease Exacerbations and Strain-Dependent Increase of Epithelial Resistance

Gut bacterial quorum sensing molecules and their association with inflammatory bowel disease: Advances and future perspectives

Inflammatory Bowel Disease (IBD) is an enduring inflammatory disease of the gastrointestinal tract (GIT). The complexity of IBD, its profound impact on patient's quality of life, and its burden on healthcare systems necessitate continuing studies to elucidate its etiology, refine care strategies, improve treatment outcomes, and identify potential targets for novel therapeutic interventions. The discovery of a connection between IBD and gut bacterial quorum sensing (QS) molecules has opened exciting opportunities for research into IBD pathophysiology. QS molecules are small chemical messengers synthesized and released by bacteria based on population density. These chemicals are sensed not only by the microbial species but also by host cells and are essential in gut homeostasis. QS molecules are now known to interact with inflammatory pathways, therefore rendering them potential therapeutic targets for IBD management. Given these intriguing developments, the most recent research findings in this area are herein reviewed. First, the global burden of IBD and the disruptions of the gut microbiota and intestinal barrier associated with the disease are assessed. Next, the general QS mechanism and signaling molecules in the gut are discussed. Then, the roles of QS molecules and their connection with IBD are elucidated. Lastly, the review proposes potential QS-based therapeutic targets for IBD, offering insights into the future research trajectory in this field.

Nontoxigenic Bacteroides fragilis: A double-edged sword

The contribution of commensal microbes to human health and disease is unknown. Bacteroides fragilis (B. fragilis) is an opportunistic pathogen and a common colonizer of the human gut. Nontoxigenic B. fragilis (NTBF) and enterotoxigenic B. fragilis (ETBF) are two kinds of B. fragilis. NTBF has been shown to affect the host immune system and interact with gut microbes and pathogenic microbes. Previous studies indicated that certain strains of B. fragilis have the potential to serve as probiotics, based on their observed relationship with the immune system. However, several recent studies have shown detrimental effects on the host when beneficial gut bacteria are found in the digestive system or elsewhere. In some pathological conditions, NTBF may have adverse reactions. This paper presents a comprehensive analysis of NTBF ecology from the host-microbe perspective, encompassing molecular disease mechanisms analysis, bacteria-bacteria interaction, bacteria-host interaction, and the intricate ecological context of the gut. Our review provides much-needed insights into the precise application of NTBF.

Colorectal Disease and the Gut Microbiome: What a Surgeon Needs to Know

The gut microbiome is defined as the microorganisms that reside within the gastrointestinal tract and produce a variety of metabolites that impact human health. These microbes play an intricate role in human health, and an imbalance in the gut microbiome, termed gut dysbiosis, has been implicated in the development of varying diseases. The purpose of this review is to highlight what is known about the microbiome and its impact on colorectal cancer, inflammatory bowel disease, constipation, Clostridioides difficile infection, the impact of bowel prep, and anastomotic leaks.

Deciphering Microbial Shifts in the Gut and Lung Microbiomes of COVID-19 Patients

COVID-19, caused by SARS-CoV-2, results in respiratory and cardiopulmonary infections. There is an urgent need to understand not just the pathogenic mechanisms of this disease but also its impact on the physiology of different organs and microbiomes. Multiple studies have reported the effects of COVID-19 on the gastrointestinal microbiota, such as promoting dysbiosis (imbalances in the microbiome) following the disease's progression. Deconstructing the dynamic changes in microbiome composition that are specifically correlated with COVID-19 patients remains a challenge. Motivated by this problem, we implemented a biomarker discovery pipeline to identify candidate microbes specific to COVID-19. This involved a meta-analysis of large-scale COVID-19 metagenomic data to decipher the impact of COVID-19 on the human gut and respiratory microbiomes. Metagenomic studies of the gut and respiratory microbiomes of COVID-19 patients and of microbiomes from other respiratory diseases with symptoms similar to or overlapping with COVID-19 revealed 1169 and 131 differentially abundant microbes in the human gut and respiratory microbiomes, respectively, that uniquely associate with COVID-19. Furthermore, by utilizing machine learning models (LASSO and XGBoost), we demonstrated the power of microbial features in separating COVID-19 samples from metagenomic samples representing other respiratory diseases and controls (healthy individuals), achieving an overall accuracy of over 80%. Overall, our study provides insights into the microbiome shifts occurring in COVID-19 patients, shining a new light on the compositional changes.

In vitro mucin degradation and paracellular permeability by fecal water from Crohn's disease patients

Aim: This study aimed to examine the impact of fecal water (FW) of active and remissive Crohn's disease (CD) patients on mucin degradation and epithelial barrier function. Methods: FW and bacterial membrane vesicles (MVs) were isolated from fresh fecal samples of six healthy controls (HCs) and 12 CD patients. Bacterial composition was determined by 16S rRNA gene amplicon sequencing. Results: In vitro FW-induced mucin degradation was higher in CD samples versus HC (p < 0.01), but not associated with specific bacterial genera. FW of three remissive samples decreased transepithelial electrical resistance in Caco-2 cells by 78-87% (p < 0.001). MVs did not induce barrier alterations. Conclusion: The higher mucin-degradation capacity of CD-derived FW might suggest contributions of microbial products to CD pathophysiology.

The gut ileal mucosal virome is disturbed in patients with Crohn's disease and exacerbates intestinal inflammation in mice

Gut bacteriome dysbiosis is known to be implicated in the pathogenesis of inflammatory bowel disease (IBD). Crohn's disease (CD) is an IBD subtype with extensive mucosal inflammation, yet the mucosal virome, an empirical modulator of the bacteriome and mucosal immunity, remains largely unclear regarding its composition and role. Here, we exploited trans-cohort CD patients and healthy individuals to compositionally and functionally investigate the small bowel (terminal ileum) virome and bacteriome. The CD ileal virome was characterised by an under-representation of both lytic and temperate bacteriophages (especially those targeting bacterial pathogens), particularly in patients with flare-up. Meanwhile, the virome-bacteriome ecology in CD ileal mucosa was featured by a lack of Bifidobacterium- and Lachnospiraceae-led mutualistic interactions between bacteria and bacteriophages; surprisingly it was more pronounced in CD remission than flare-up, underlining the refractory and recurrent nature of mucosal inflammation in CD. Lastly, we substantiated that ileal virions from CD patients causally exacerbated intestinal inflammation in IBD mouse models, by reshaping a gut virome-bacteriome ecology preceding intestinal inflammation (microbial trigger) and augmenting microbial sensing/defence pathways in the intestine cells (host response). Altogether, our results highlight the significance of mucosal virome in CD pathogenesis and importance of mucosal virome restoration in CD therapeutics.

Candida spp. in Human Intestinal Health and Disease: More than a Gut Feeling

Fungi are an essential part of the normal collection of intestinal microorganisms, even though their collective abundance comprises only 0.1-1% of all fecal microbes. The composition and role of the fungal population is often studied in relation to early-life microbial colonization and development of the (mucosal) immune system. The genus Candida is frequently described as one of the most abundant genera, and altered fungal compositions (including elevated abundance of Candida spp.) have been linked with intestinal diseases such as inflammatory bowel disease and irritable bowel syndrome. These studies are performed using both culture-dependent and genomic (metabarcoding) techniques. In this review, we aimed to summarize existing data on intestinal Candida spp. colonization in relation to intestinal disease and provide a brief overview of the biological and technical challenges in this field, including the recently described role of sub-species strain variation of intestinal Candida albicans. Together, the evidence for a contributing role of Candida spp. in pediatric and adult intestinal disease is quickly expanding, even though technical and biological challenges may limit full understanding of host-microbe interactions.

Gut microbiome, metabolome, host immunity associated with inflammatory bowel disease and intervention of fecal microbiota transplantation

Gut dysbiosis has been associated with inflammatory bowel disease (IBD), one of the most common gastrointestinal diseases. The microbial communities play essential roles in host physiology, with profound effects on immune homeostasis, directly or via their metabolites and/or components. There are increasing clinical trials applying fecal microbiota transplantation (FMT) with Crohn's disease (CD) and ulcerative colitis (UC). The restoration of dysbiotic gut microbiome is considered as one of the mechanisms of FMT therapy. In this work, latest advances in the alterations in gut microbiome and metabolome features in IBD patients and experimental mechanistic understanding on their contribution to the immune dysfunction were reviewed. Then, the therapeutic outcomes of FMT on IBD were summarized based on clinical remission, endoscopic remission and histological remission of 27 clinical trials retrieved from PubMed which have been registered on ClinicalTrials.gov with the results been published in the past 10 years. Although FMT is established as an effective therapy for both subtypes of IBD, the promising outcomes are not always achieved. Among the 27 studies, only 11 studies performed gut microbiome profiling, 5 reported immune response alterations and 3 carried out metabolome analysis. Generally, FMT partially restored typical changes in IBD, resulted in increased α-diversity and species richness in responders and similar but less pronounced shifts of patient microbial and metabolomics profiles toward donor profiles. Measurements of immune responses to FMT mainly focused on T cells and revealed divergent effects on pro-/anti-inflammatory functions. The very limited information and the extremely confounding factors in the designs of the FMT trials significantly hindered a reasonable conclusion on the mechanistic involvement of gut microbiota and metabolites in clinical outcomes and an analysis of the inconsistencies.

Alterations in intestinal Archaea composition in pediatric patients with Crohn's disease based on next-generation sequencing - a pilot study

Intestinal dysbiosis can lead to the induction of systemic immune-mediated inflammatory diseases, such as Crohn's disease Although archaea are part of the commensal microbiota, they are still one of the least studied microorganisms. The aim of our study was the standardization of the optimal conditions and primers for sequencing of the gut archaeome using Next Generation Sequencing, and evaluation of the differences between the composition of archaea in patients and healthy volunteers, as well as analysis of the changes that occur in the archaeome of patients depending on disease activity. Newly diagnosed patients were characterized by similar archeal profiles at every taxonomic level as in healthy individuals (the dominance of Methanobacteria at the class level, and Methanobrevibacter at the genus level). In turn, in patients previously diagnosed with Crohn's disease (both in active and remission phase), an increased prevalence of Thermoplasmata, Thermoprotei, Halobacteria (at the class level), and Halococcus, Methanospaera or Picrophilus (at the genus level) were observed. Furthermore, we have found a significant correlation between the patient's parameters and the individual class or species of Archaea. Our study confirms changes in archaeal composition in pediatric patients with Crohn's disease, however, only in long-standing disease. At the beginning of the disease, the archeal profile is similar to that of healthy people. However, in the chronic form of the disease, significant differences in the composition of archaeome begin to appear. It seems that some archaea may be a good indicator of the chronicity and activity of Crohn's disease.

Intestinal organoids: A thriving and powerful tool for investigating dietary nutrients-intestinal homeostasis axis

Dietary nutrients regulate intestinal homeostasis through a variety of complex mechanisms, to affect the host health. Nowadays, various models have been used to investigate the dietary nutrients-intestinal homeostasis axis. Different from the limited flux in animal experiments, limited intestinal cell types and distorted simulation of intestinal environment of 2D cells, intestinal organoid (IO) is a 3D culture system of mini-gut with various intestinal epithelial cells (IECs) and producibility of intestinal biology. Therefore, IOs is a powerful tool to evaluate dietary nutrients-intestinal homeostasis interaction. This review summarized the application of IOs in the investigation of mechanisms for macronutrients (carbohydrates, proteins and fats) and micronutrients (vitamins and minerals) affecting intestinal homeostasis directly or indirectly (polysaccharides-intestinal bacteria, proteins-amino acids). In addition, new perspectives of IOs in combination with advanced biological techniques and their applications in precise nutrition were proposed.

Multi-omics analysis reveals the interaction of gut microbiome and host microRNAs in ulcerative colitis

BACKGROUND

Inflammatory bowel disease (IBD) is a chronic inflammation of the gastrointestinal tract that co-occurs with gut microbiota dysbiosis; however, its etiology remains unclear. MicroRNA (miRNA)-microbiome interactions play an essential role in host health and disease.

METHODS

To investigate the gut microbiome and host miRNA profiles in colitis, we used a Dextran Sulfate Sodium (DSS)-induced ulcerative colitis (UC) model. Metagenomic sequencing and metabolome profiling were performed to explore typical microbiota and metabolite signatures in colitis, whereas mRNA and miRNA sequencing were used to determine differentially expressed miRNAs and their target genes in the inflamed colon.

RESULTS

A total of 986 miRNAs were identified between the two groups, with 41 upregulated and 21 downregulated miRNAs in colitis mice compared to the control group. Notably, the target genes of these significantly altered miRNAs were primarily enriched in the immune and inflammation-related pathways. Second, LEfSe analysis revealed bacterial biomarkers distinguishing the two groups, with significantly higher levels of commonly encountered pathogens such as Escherichia coli and Shigella flexneri in the UC group, whereas beneficial species such as Bifidobacterium pseudolongum were more abundant in the control group. Microbiota metabolites histamine, N-acetylhistamine, and glycocholic acid were found to be downregulated in colitis mice. Spearman correlation further revealed the potential crosstalk between the microbiota profile and colonic miRNA, revealing the possibility of microbiome-miRNA interactions involved in IBD development.

CONCLUSIONS

Our data reveal the relationships between multi-omic features during UC and suggest that targeting specific miRNAs may provide new avenues for the development of effective miRNA-based therapeutics.

Current evidence and clinical relevance of drug-microbiota interactions in inflammatory bowel disease

Background

Inflammatory bowel disease (IBD) is a chronic relapsing-remitting disease. An adverse immune reaction toward the intestinal microbiota is involved in the pathophysiology and microbial perturbations are associated with IBD in general and with flares specifically. Although medical drugs are the cornerstone of current treatment, responses vary widely between patients and drugs. The intestinal microbiota can metabolize medical drugs, which may influence IBD drug (non-)response and side effects. Conversely, several drugs can impact the intestinal microbiota and thereby host effects. This review provides a comprehensive overview of current evidence on bidirectional interactions between the microbiota and relevant IBD drugs (pharmacomicrobiomics).

Methods

Electronic literature searches were conducted in PubMed, Web of Science and Cochrane databases to identify relevant publications. Studies reporting on microbiota composition and/or drug metabolism were included.

Results

The intestinal microbiota can both enzymatically activate IBD pro-drugs (e.g., in case of thiopurines), but also inactivate certain drugs (e.g., mesalazine by acetylation via N-acetyltransferase 1 and infliximab via IgG-degrading enzymes). Aminosalicylates, corticosteroids, thiopurines, calcineurin inhibitors, anti-tumor necrosis factor biologicals and tofacitinib were all reported to alter the intestinal microbiota composition, including changes in microbial diversity and/or relative abundances of various microbial taxa.

Conclusion

Various lines of evidence have shown the ability of the intestinal microbiota to interfere with IBD drugs and vice versa. These interactions can influence treatment response, but well-designed clinical studies and combined in vivo and ex vivo models are needed to achieve consistent findings and evaluate clinical relevance.

Association between ustekinumab therapy and changes in specific anti-microbial response, serum biomarkers, and microbiota composition in patients with IBD: A pilot study

BACKGROUND

Ustekinumab, is a new therapy for patients with IBD, especially for patients suffering from Crohn's disease (CD) who did not respond to anti-TNF treatment. To shed light on the longitudinal effect of ustekinumab on the immune system, we investigated the effect on skin and gut microbiota composition, specific immune response to commensals, and various serum biomarkers.

METHODOLOGY/PRINCIPAL FINDINGS

We recruited 11 patients with IBD who were monitored over 40 weeks of ustekinumab therapy and 39 healthy controls (HC). We found differences in the concentrations of serum levels of osteoprotegerin, TGF-β1, IL-33, and serum IgM antibodies against Lactobacillus plantarum between patients with IBD and HC. The levels of these biomarkers did not change in response to ustekinumab treatment or with disease improvement during the 40 weeks of observation. Additionally, we identified differences in stool abundance of uncultured Subdoligranulum, Faecalibacterium, and Bacteroides between patients with IBD and HC.

CONCLUSION/SIGNIFICANCE

In this preliminary study, we provide a unique overview of the longitudinal monitoring of fecal and skin microbial profiles as well as various serum biomarkers and humoral and cellular response to gut commensals in a small cohort of patients with IBD on ustekinumab therapy.

The Therapeutic Role of Short-Chain Fatty Acids Mediated Very Low-Calorie Ketogenic Diet-Gut Microbiota Relationships in Paediatric Inflammatory Bowel Diseases

The very low-calorie ketogenic diet (VLCKD) has been recognized as a promising dietary regimen for the treatment of several diseases. Short-chain fatty acids (SCFAs) produced by anaerobic bacterial fermentation of indigestible dietary fibre in the gut have potential value for their underlying epigenetic role in the treatment of obesity and asthma-related inflammation through mediating the relationships between VLCKD and the infant gut microbiota. However, it is still unclear how VLCKD might influence gut microbiota composition in children, and how SCFAs could play a role in the treatment of inflammatory bowel disease (IBD). To overcome this knowledge gap, this review aims to investigate the role of SCFAs as key epigenetic metabolites that mediate VLCKD-gut microbiota relationships in children, and their therapeutic potential in IBD.

A systemic review of the role of enterotoxic Bacteroides fragilis in colorectal cancer

Enterotoxigenic Bacteroides fragilis (ETBF) has received significant attention for a possible association with, or causal role in, colorectal cancer (CRC). The goal of this review was to assess the status of the published evidence supporting (i) the association between ETBF and CRC and (ii) the causal role of ETBF in CRC. PubMed and Scopus searches were performed in August 2021 to identify human, animal, and cell studies pertaining to the role of ETBF in CRC. Inclusion criteria included the use of cell lines, mice, exposure to BFT or ETBF, and detection of bft. Review studies were excluded, and studies were limited to the English language. Quality of study design and risk of bias analysis was performed on the cell, animal, and human studies using ToxRTools, SYRCLE, and NOS, respectively. Ninety-five eligible studies were identified, this included 22 human studies, 24 animal studies, 43 cell studies, and 6 studies that included both cells and mice studies. We found that a large majority of studies supported an association or causal role of ETBF in CRC, as well as high levels of study bias was detected in the in vitro and in vivo studies. The high-level heterogeneity in study design and reporting made it difficult to synthesize these findings into a unified conclusion, suggesting that the need for future studies that include improved mechanistic models, longitudinal in vitro and in vivo evidence, and appropriate control of confounding factors will be required to confirm whether ETBF has a direct role in CRC etiopathogenesis.

Intestinal strictures in Crohn's disease: a 2021 update

Intestinal strictures remain one of the most intractable and common complications of Crohn's disease (CD). Approximately 70% of CD patients will develop fibrotic strictures after 10 years of CD diagnosis. Since specific antifibrotic therapies are unavailable, endoscopic balloon dilation and surgery remain the mainstay treatments despite a high recurrence rate. Besides, there are no reliable methods for accurately evaluating intestinal fibrosis. This is largely due to the fact that the mechanisms of initiation and propagation of intestinal fibrosis are poorly understood. There is growing evidence implying that the pathogenesis of stricturing CD involves the intricate interplay of factors including aberrant immune and nonimmune responses, host-microbiome dysbiosis, and genetic susceptibility. Currently, the progress on intestinal strictures has been fueled by the advent of novel techniques, such as single-cell sequencing, multi-omics, and artificial intelligence. Here, we perform a timely and comprehensive review of the substantial advances in intestinal strictures in 2021, aiming to provide prompt information regarding fibrosis and set the stage for the improvement of diagnosis, treatment, and prognosis of intestinal strictures.

Neurophysiological Effects of the Anterior Cingulate Cortex on the Exacerbation of Crohn’s Disease: A Combined fMRI-MRS Study

Background

Crohn’s disease (CD) is characterized by repetitive phases of remission and exacerbation, the quality of life of patients with CD is strongly influenced by disease activity, as patients in the active phase experience significantly worse symptoms. To investigate the underlying mechanism of how the course of CD is exacerbated based on the bi-directionality of the brain-gut axis (BGA), we conducted a multi-modality neuroimaging study that combined resting-state functional magnetic resonance imaging (rs-fMRI) with proton magnetic resonance spectroscopy (MRS) to detect abnormalities in the anterior cingulate cortex (ACC).

Materials and Methods

Clinical scales including Visual Analog Scale (VAS) and Hospital Anxiety and Depression Scale (HADS) were used to evaluate the degree of abdominal pain and mood state of participants. We made a comparison between CD patients in the active phase, the remission phase and healthy controls (HCs), not only employed the innovative wavelet-transform to analyze the amplitude of low frequency fluctuation (ALFF) but also compared the sensitivity of wavelet-transform and the traditional fast Fourier transform (FFT). Brain metabolites such as glutamate (Glu), myo-inositol (mIns) and gamma-aminobutyric acid (GABA) were also detected. Then correlation analysis was made to see whether changes in the ACC correlated with CD’s clinical symptoms.

Results

CD patients in the active phase showed higher VAS scores (p = 0.025), the scores of anxiety and depression were also higher (all p < 0.05). Wavelet-transform is slightly more sensitive in the current research. Patients in the active phase exhibited higher ALFF in the left ACC and the left superior frontal gyrus, medial (SFGmed). Patients in the active phase showed increased Glu levels in the ACC than patients in the remission phase or HCs (p = 0.039 and 0.034 respectively) and lower levels of mIns than HCs (p = 0.036). There was a positive correlation between mWavelet-ALFF values of the ACC and HADS-depression scores in CD patients (r = 0.462, p = 0.006). Besides, concentrations of Glu positively correlated with mWavelet-ALFF in the ACC in all participants (r = 0.367, p = 0.006).

Conclusion

Abnormal spontaneous activity and metabolic levels in the ACC were detected in CD patients in the active phase along with severer abdominal pain and worse mood state, these may contribute to the exacerbation of CD. Therefore, the ACC might be a potential neural alternative for managing the exacerbation of CD.

Gut Microbial Antigenic Mimicry in Autoimmunity

The gut microbiota plays a major role in the developmental biology and homeostasis of cells belonging to the adaptive and innate arms of the immune system. Alterations in its composition, which are known to be regulated by both genetic and environmental factors, can either promote or suppress the pathogenic processes underlying the development of various autoimmune diseases, including inflammatory bowel disease, multiple sclerosis, systemic lupus erythematosus, type 1 diabetes and rheumatoid arthritis, to just name a few. Cross-recognition of gut microbial antigens by autoreactive T cells as well as gut microbe-driven alterations in the activation and homeostasis of effector and regulatory T cells have been implicated in this process. Here, we summarize our current understanding of the positive and negative associations between alterations in the composition of the gut microbiota and the development of various autoimmune disorders, with a special emphasis on antigenic mimicry.

Human Norovirus Induces Aquaporin 1 Production by Activating NF-κB Signaling Pathway

Human norovirus (HuNoV) is one of the major pathogens of acute nonbacterial gastroenteritis. Due to the lack of a robust and reproducible in vitro culture system and an appropriate animal model, the mechanism underlying HuNoV-caused diarrhea remains unknown. In the current study, we found that HuNoV transfection induced the expression of aquaporin 1 (AQP1), which was further confirmed in the context of virus infection, whereas the enterovirus EV71 (enterovirus 71) did not have such an effect. We further revealed that VP1, the major capsid protein of HuNoV, was crucial in promoting AQP1 expression. Mechanistically, HuNoV induces AQP1 production through the NF-κB signaling pathway via inducing the expression, phosphorylation and nuclear translocation of p65. By using a model of human intestinal epithelial barrier (IEB), we demonstrated that HuNoV and VP1-mediated enhancement of small molecule permeability is associated with the AQP1 channel. Collectively, we revealed that HuNoV induced the production of AQP1 by activating the NF-κB signaling pathway. The findings in this study provide a basis for further understanding the significance of HuNoV-induced AQP1 expression and the potential mechanism underlying HuNoV-caused diarrhea.

Bacterial Species Associated With Human Inflammatory Bowel Disease and Their Pathogenic Mechanisms

Inflammatory bowel disease (IBD) is a chronic inflammatory condition of the gastrointestinal tract with unknown etiology. The pathogenesis of IBD results from immune responses to microbes in the gastrointestinal tract. Various bacterial species that are associated with human IBD have been identified. However, the microbes that trigger the development of human IBD are still not clear. Here we review bacterial species that are associated with human IBD and their pathogenic mechanisms to provide an updated broad understanding of this research field. IBD is an inflammatory syndrome rather than a single disease. We propose a three-stage pathogenesis model to illustrate the roles of different IBD-associated bacterial species and gut commensal bacteria in the development of human IBD. Finally, we recommend microbe-targeted therapeutic strategies based on the three-stage pathogenesis model.

The Link between Gut Dysbiosis Caused by a High-Fat Diet and Hearing Loss

This review aims to provide a conceptual and theoretical overview of the association between gut dysbiosis and hearing loss. Hearing loss is a global health issue; the World Health Organisation (WHO) estimates that 2.5 billion people will be living with some degree of hearing loss by 2050. The aetiology of sensorineural hearing loss (SNHL) is complex and multifactorial, arising from congenital and acquired causes. Recent evidence suggests that impaired gut health may also be a risk factor for SNHL. Inflammatory bowel disease (IBD), type 2 diabetes, diet-induced obesity (DIO), and high-fat diet (HFD) all show links to hearing loss. Previous studies have shown that a HFD can result in microangiopathy, impaired insulin signalling, and oxidative stress in the inner ear. A HFD can also induce pathological shifts in gut microbiota and affect intestinal barrier (IB) integrity, leading to a leaky gut. A leaky gut can result in chronic systemic inflammation, which may affect extraintestinal organs. Here, we postulate that changes in gut microbiota resulting from a chronic HFD and DIO may cause a systemic inflammatory response that can compromise the permeability of the blood-labyrinth barrier (BLB) in the inner ear, thus inducing cochlear inflammation and hearing deficits.