Gut Epithelial Metabolism as a Key Driver of Intestinal Dysbiosis Associated with Noncommunicable Diseases

Increased dietary protein stimulates amino acid catabolism via the gut microbiota and secondary bile acid production

Excess amino acids from a protein-rich diet are mainly catabolized in the liver. However, it is still unclear to what extent the gut microbiota may be involved in the mechanisms governing this catabolism. Therefore, the aim of this study was to investigate whether consumption of different dietary protein concentrations induces changes in the taxonomy of the gut microbiota, which may contribute to the regulation of hepatic amino acid catabolism. Consumption of a high-protein diet caused overexpression of HIF-1α in the colon and increase in mitochondrial activity, creating a more anaerobic environment that was associated with changes in the taxonomy of the gut microbiota promoting an increase in the synthesis of secondary bile acids, increased secretion of pancreatic glucagon. This effect was demonstrated in pancreatic islets, where secondary bile acids stimulated the expression of the PC2 enzyme that promotes glucagon formation. The increase in circulating glucagon was associated with an induction of the expression of hepatic amino acid-degrading enzymes, an effect attenuated by antibiotics. Thus, high protein intake in mice and humans induced the increase of different species in the gut microbiota with the capacity to produce secondary bile acids leading to an increase in secondary bile acids and glucagon levels, promoting amino acid catabolism.

Harnessing the human gut microbiota: an emerging frontier in combatting multidrug-resistant bacteria

Antimicrobial resistance (AMR) has become a major and escalating global health threat, undermining the effectiveness of current antibiotic and antimicrobial therapies. The rise of multidrug-resistant bacteria has led to increasingly difficult-to-treat infections, resulting in higher morbidity, mortality, and healthcare costs. Tackling this crisis requires the development of novel antimicrobial agents, optimization of current therapeutic strategies, and global initiatives in infection surveillance and control. Recent studies highlight the crucial role of the human gut microbiota in defending against AMR pathogens. A balanced microbiota protects the body through mechanisms such as colonization resistance, positioning it as a key ally in the fight against AMR. In contrast, gut dysbiosis disrupts this defense, thereby facilitating the persistence, colonization, and dissemination of resistant pathogens. This review will explore how gut microbiota influence drug-resistant bacterial infections, its involvement in various types of AMR-related infections, and the potential for novel microbiota-targeted therapies, such as fecal microbiota transplantation, prebiotics, probiotics, phage therapy. Elucidating the interactions between gut microbiota and AMR pathogens will provide critical insights for developing novel therapeutic strategies to prevent and treat AMR infections. While previous reviews have focused on the general impact of the microbiota on human health, this review will specifically look at the latest research on the interactions between the gut microbiota and the evolution and spread of AMR, highlighting potential therapeutic strategies.

S-ketamine alleviates morphine-induced hyperalgesia via decreasing the gut Enterobacteriaceae levels: Comparison with R-ketamine

BACKGROUND

Opioid-induced hyperalgesia (OIH) is a serious complication during the pain treatment. Ketamine has been commonly reported to treat OIH, but the mechanisms remain unclear. Gut microbiota is recently recognized as one of the important mechanisms underlying the occurrence and treatment of OIH. However, whether ketamine enantiomers could alleviate OIH through gut microbiota that still needs to be clarified.

METHODS

The OIH model was established by morphine injection for 3 consecutive days, followed by hierarchical clustering analysis of behavioral results into susceptible or resilient group. Broad-spectrum antibiotic cocktail (ABx) was used to eradicated the gut microbiota of mice. Subsequently, fecal microbiota transplantation (FMT) was performed. S- or R-ketamine was administered as pretreatment 30 min before morphine injection. Fecal samples were collected for 16S rRNA gene sequencing after completion of all behavioral tests.

RESULTS

Approximately 60% of the mice developed OIH after morphine exposure with abnormal locomotion and anxiety-like behaviors. Pseudo germ-free mice treated with ABx did not develop hyperalgesia, whereas pseudo germ-free mice that received fecal microbiota transplantation from OIH mice developed hyperalgesia. Interestingly, S-ketamine but not R-ketamine rescued mice from OIH. The principal co-ordinates analysis (PCoA) suggested that the distribution of gut microbiota differed among the groups. Importantly, levels of Enterobacteriaceae were increased in OIH susceptible group, while decreased after S-ketamine treatment.

CONCLUSION

S-ketamine but not R-ketamine was able to alleviate morphine-induced OIH, and this mechanism is probably related to decreasing the levels of gut Enterobacteriaceae.

Dietary manipulation of intestinal microbes prolongs survival in a mouse model of Hirschsprung disease

Enterocolitis is a common and potentially deadly manifestation of Hirschsprung disease (HSCR) but disease mechanisms remain poorly defined. Unexpectedly, we discovered that diet can dramatically affect the lifespan of a HSCR mouse model ( Piebald lethal , sl/sl ) where affected animals die from HAEC complications. In the sl/sl model, diet alters gut microbes and metabolites, leading to changes in colon epithelial gene expression and epithelial oxygen levels known to influence colitis severity. Our findings demonstrate unrecognized similarity between HAEC and other types of colitis and suggest dietary manipulation could be a valuable therapeutic strategy for people with HSCR.

Abstract

Hirschsprung disease (HSCR) is a birth defect where enteric nervous system (ENS) is absent from distal bowel. Bowel lacking ENS fails to relax, causing partial obstruction. Affected children often have "Hirschsprung disease associated enterocolitis" (HAEC), which predisposes to sepsis. We discovered survival of Piebald lethal ( sl/sl ) mice, a well-established HSCR model with HAEC, is markedly altered by two distinct standard chow diets. A "Protective" diet increased fecal butyrate/isobutyrate and enhanced production of gut epithelial antimicrobial peptides in proximal colon. In contrast, "Detrimental" diet-fed sl/sl had abnormal appearing distal colon epithelium mitochondria, reduced epithelial mRNA involved in oxidative phosphorylation, and elevated epithelial oxygen that fostered growth of inflammation-associated Enterobacteriaceae . Accordingly, selective depletion of Enterobacteriaceae with sodium tungstate prolonged sl/sl survival. Our results provide the first strong evidence that diet modifies survival in a HSCR mouse model, without altering length of distal colon lacking ENS.

Highlights

Two different standard mouse diets alter survival in the Piebald lethal ( sl/sl ) mouse model of Hirschsprung disease, without impacting extent of distal colon aganglionosis (the region lacking ENS). Piebald lethal mice fed the "Detrimental" diet had many changes in colon epithelial transcriptome including decreased mRNA for antimicrobial peptides and genes involved in oxidative phosphorylation. Detrimental diet fed sl/sl also had aberrant-appearing mitochondria in distal colon epithelium, with elevated epithelial oxygen that drives lethal Enterobacteriaceae overgrowth via aerobic respiration. Elimination of Enterobacteriaceae with antibiotics or sodium tungstate improves survival of Piebald lethal fed the "Detrimental diet".

Graphical abstract

Molecular Mechanisms of Skatole-Induced Inflammatory Responses in Intestinal Epithelial Caco-2 Cells: Implications for Colorectal Cancer and Inflammatory Bowel Disease

Inflammatory cytokines, such as tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6), in intestinal epithelial cells significantly contribute to inflammatory bowel disease (IBD) and colorectal cancer (CRC). Given our previous findings that TNF-α is upregulated in intestinal epithelial Caco-2 cells induced by skatole, a tryptophan-derived gut microbiota metabolite, the present study aimed to explore the relationship between skatole and IL-6, alongside TNF-α. Skatole elevated the promoter activity of IL-6 as well as TNF-α, and increased IL-6 mRNA expression and protein secretion. In addition to activating NF-κB, the NF-κB inhibitor BAY 11-7082 reduced skatole-induced cell survival and the mRNA expression of IL-6 and TNF-α. NF-κB activation was attenuated by the extracellular signal-regulated kinase (ERK) pathway inhibitor U0126 and the p38 inhibitor SB203580, but not by the c-Jun N-terminal kinase (JNK) inhibitor SP600125. U126 and SB203580 also decreased the skatole-induced increase in IL-6 expression. When skatole-induced AhR activation was inhibited by CH223191, in addition to promoting NF-κB activation, IL-6 expression was enhanced in a manner similar to that previously reported for TNF-α. Taken together, these results suggest that skatole-elicited NF-κB activation induces IL-6 and TNF-α expression, although AhR activation partially suppresses this process. The ability of skatole to increase the expression of IL-6 and TNF-α may significantly affect the development and progression of these diseases. Moreover, the balance between NF-κB and AhR activation appears to govern the skatole-induced increases in IL-6 and TNF-α expression. Therefore, the present findings provide new insights into the mechanisms linking tryptophan-derived gut microbiota metabolites with colorectal disease.

Reconstituting gut microbiota-colonocyte interactions reverses diet-induced cognitive deficits: The beneficial of eucommiae cortex polysaccharides

Rationale: Consumption of a high-fat diet (HFD) has been implicated in cognitive deficits and gastrointestinal dysfunction in humans, with the gut microbiota emerging as a pivotal mediator of these diet-associated pathologies. The introduction of plant-based polysaccharides into the diet as a therapeutic strategy to alleviate such conditions is gaining attention. Nevertheless, the mechanistic paradigm by which polysaccharides modulate the gut microbiota remains largely undefined. This study investigated the mechanisms of action of Eucommiae cortex polysaccharides (EPs) in mitigating gut dysbiosis and examined their contribution to rectifying diet-related cognitive decline. Methods: Initially, we employed fecal microbiota transplantation (FMT) and gut microbiota depletion to verify the causative role of changes in the gut microbiota induced by HFD in synapse engulfment-dependent cognitive impairments. Subsequently, colonization of the gut of chow-fed mice with Escherichia coli (E. coli) from HFD mice confirmed that inhibition of Proteobacteria by EPs was a necessary prerequisite for alleviating HFD-induced cognitive impairments. Finally, supplementation of HFD mice with butyrate and treatment of EPs mice with GW9662 demonstrated that EPs inhibited the expansion of Proteobacteria in the colon of HFD mice by reshaping the interactions between the gut microbiota and colonocytes. Results: Findings from FMT and antibiotic treatments demonstrated that HFD-induced cognitive impairments pertaining to neuronal spine loss were contingent on gut microbial composition. Association analysis revealed strong associations between bacterial taxa belonging to the phylum Proteobacteria and cognitive performance in mice. Further, introducing E. coli from HFD-fed mice into standard diet-fed mice underscored the integral role of Proteobacteria proliferation in triggering excessive synaptic engulfment-related cognitive deficits in HFD mice. Crucially, EPs effectively counteracted the bloom of Proteobacteria and subsequent neuroinflammatory responses mediated by microglia, essential for cognitive improvement in HFD-fed mice. Mechanistic insights revealed that EPs promoted the production of bacteria-derived butyrate, thereby ameliorating HFD-induced colonic mitochondrial dysfunction and reshaping colonocyte metabolism. This adjustment curtailed the availability of growth substrates for facultative anaerobes, which in turn limited the uncontrolled expansion of Proteobacteria. Conclusions: Our study elucidates that colonocyte metabolic disturbances, which promote Proteobacteria overgrowth, are a likely cause of HFD-induced cognitive deficits. Furthermore, dietary supplementation with EPs can rectify behavioral dysfunctions associated with HFD by modifying gut microbiota-colonocyte interactions. These insights contribute to the broader understanding of the modulatory effects of plant prebiotics on the microbiota-gut-brain axis and suggest a potential therapeutic avenue for diet-associated cognitive dysfunction.

[Research progress on the relationship between anemia and neonatal necrotizing enterocolitis]

Neonatal necrotizing enterocolitis (NEC) is the most common inflammatory intestinal disease in preterm infants, with a high incidence and mortality rate. The etiology and mechanisms of NEC are not yet fully understood, and multiple factors contribute to its occurrence and development. Recent studies have found that anemia is a risk factor for NEC in neonates, but the specific pathogenic mechanism remains unclear. This article reviews recent research on the relationship between anemia and NEC, providing a reference for further understanding the impact of anemia on intestinal injury and its association with NEC.

Nurturing gut health: role of m6A RNA methylation in upholding the intestinal barrier

The intestinal lumen acts as a critical interface connecting the external environment with the body's internal state. It's essential to prevent the passage of harmful antigens and bacteria while facilitating nutrient and water absorption. The intestinal barriers encompass microbial, mechanical, immunological, and chemical elements, working together to maintain intestinal balance. Numerous studies have associated m6A modification with intestinal homeostasis. This review comprehensively outlines potential mechanisms through which m6A modification could initiate, exacerbate, or sustain barrier damage from an intestinal perspective. The pivotal role of m6A modification in preserving intestinal equilibrium provides new insights, guiding the exploration of m6A modification as a target for optimizing preventive and therapeutic strategies for intestinal homeostasis.

The Ocean's Pharmacy: Health Discoveries in Marine Algae

Non-communicable diseases (NCDs) represent a global health challenge, constituting a major cause of mortality and disease burden in the 21st century. Addressing the prevention and management of NCDs is crucial for improving global public health, emphasizing the need for comprehensive strategies, early interventions, and innovative therapeutic approaches to mitigate their far-reaching consequences. Marine organisms, mainly algae, produce diverse marine natural products with significant therapeutic potential. Harnessing the largely untapped potential of algae could revolutionize drug development and contribute to combating NCDs, marking a crucial step toward natural and targeted therapeutic approaches. This review examines bioactive extracts, compounds, and commercial products derived from macro- and microalgae, exploring their protective properties against oxidative stress, inflammation, cardiovascular, gastrointestinal, metabolic diseases, and cancer across in vitro, cell-based, in vivo, and clinical studies. Most research focuses on macroalgae, demonstrating antioxidant, anti-inflammatory, cardioprotective, gut health modulation, metabolic health promotion, and anti-cancer effects. Microalgae products also exhibit anti-inflammatory, cardioprotective, and anti-cancer properties. Although studies mainly investigated extracts and fractions, isolated compounds from algae have also been explored. Notably, polysaccharides, phlorotannins, carotenoids, and terpenes emerge as prominent compounds, collectively representing 42.4% of the investigated compounds.

NAD metabolic therapy in metabolic dysfunction-associated steatotic liver disease: Possible roles of gut microbiota

Metabolic dysfunction-associated steatotic liver disease (MASLD), formerly named non-alcoholic fatty liver disease (NAFLD), is induced by alterations of hepatic metabolism. As a critical metabolites function regulator, nicotinamide adenine dinucleotide (NAD) nowadays has been validated to be effective in the treatment of diet-induced murine model of MASLD. Additionally, gut microbiota has been reported to have the potential to prevent MASLD by dietary NAD precursors metabolizing together with mammals. However, the underlying mechanism remains unclear. In this review, we hypothesized that NAD enhancing mitochondrial activity might reshape a specific microbiota signature, and improve MASLD progression demonstrated by fecal microbiota transplantation. Here, this review especially focused on the mechanism of Microbiota-Gut-Liver Axis together with NAD metabolism for the MASLD progress. Notably, we found significant changes in Prevotella associated with NAD in a gut microbiome signature of certain MASLD patients. With the recent researches, we also inferred that Prevotella can not only regulate the level of NAD pool by boosting the carbon metabolism, but also play a vital part in regulating the branched-chain amino acid (BCAA)-related fatty acid metabolism pathway. Altogether, our results support the notion that the gut microbiota contribute to the dietary NAD precursors metabolism in MASLD development and the dietary NAD precursors together with certain gut microbiota may be a preventive or therapeutic strategy in MASLD management.

Metabolic Interaction Between Host and the Gut Microbiota During High-Fat Diet-Induced Colorectal Cancer

Colorectal cancer (CRC) is the second-highest cause of cancer-associated mortality among both men and women worldwide. One of the risk factors for CRC is obesity, which is correlated with a high-fat diet prevalent in Western dietary habits. The association between an obesogenic high-fat diet and CRC has been established for several decades; however, the mechanisms by which a high-fat diet increases the risk of CRC remain unclear. Recent studies indicate that gut microbiota strongly influence the pathogenesis of both high-fat diet-induced obesity and CRC. The gut microbiota is composed of hundreds of bacterial species, some of which are implicated in CRC. In particular, the expansion of facultative anaerobic Enterobacteriaceae, which is considered a microbial signature of intestinal microbiota functional imbalance (dysbiosis), is associated with both high-fat diet-induced obesity and CRC. Here, we review the interaction between the gut microbiome and its metabolic byproducts in the context of colorectal cancer (CRC) during high-fat diet-induced obesity. In addition, we will cover how a high-fat diet can drive the expansion of genotoxin-producing Escherichia coli by altering intestinal epithelial cell metabolism during gut inflammation conditions.

Traditional Chinese Medicine formula Dai-Zong-Fang alleviating hepatic steatosis in db/db mice via gut microbiota modulation

Introduction: Hepatic steatosis is a hepatic pathological change closely associated with metabolic disorders, commonly observed in various metabolic diseases such as metabolic syndrome (MetS), with a high global prevalence. Dai-Zong-Fang (DZF), a traditional Chinese herbal formula, is widely used in clinical treatment for MetS, exhibiting multifaceted effects in reducing obesity and regulating blood glucose and lipids. This study aims to explore the mechanism by which DZF modulates the gut microbiota and reduces hepatic steatosis based on the gut-liver axis. Methods: This study utilized db/db mice as a disease model for drug intervention. Body weight and fasting blood glucose were monitored. Serum lipid and transaminase levels were measured. Insulin tolerance test was conducted to assess insulin sensitivity. Hematoxylin and eosin (HE) staining was employed to observe morphological changes in the liver and intestine. The degree of hepatic steatosis was evaluated through Oil Red O staining and hepatic lipid determination. Changes in gut microbiota were assessed using 16S rRNA gene sequencing. Serum lipopolysaccharide (LPS) levels were measured by ELISA. The expression levels of intestinal tight junction proteins, intestinal lipid absorption-related proteins, and key proteins in hepatic lipid metabolism were examined through Western blot and RT-qPCR. Results: After DZF intervention, there was a decrease in body weight, alleviation of glucose and lipid metabolism disorders, reduction in serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels, and mitigation of insulin resistance in mice. DZF significantly modulated the diversity of the gut microbiota, with a notable increase in the abundance of the Bacteroidetes phylum. PICRUSt indicated that DZF influenced various functions in gut microbiota, including carbohydrate and amino acid metabolism. Following DZF intervention, serum LPS levels decreased, intestinal pathological damage was reduced, and the expression of intestinal tight junction protein occludin was increased, while the expression of intestinal lipid absorption-related proteins cluster of differentiation 36 (CD36) and apolipoprotein B48 (ApoB48) were decreased. In the liver, DZF intervention resulted in a reduction in hepatic steatosis and lipid droplets, accompanied by a decrease fatty acid synthase (FASN) and stearoyl-CoA desaturase 1 (SCD1) and fatty acid transport protein 2 (FATP2). Conversely, there was an increase in the expression of the fatty acid oxidation-related enzyme carnitine palmitoyltransferase-1𝛂 (CPT-1𝛂). Conclusion: DZF can regulate the structure and function of the intestinal microbiota in db/db mice. This ameliorates intestinal barrier damage and the detrimental effects of endotoxemia on hepatic metabolism. DZF not only inhibits intestinal lipid absorption but also improves hepatic lipid metabolism from various aspects, including de novo lipogenesis, fatty acid uptake, and fatty acid oxidation. This suggests that DZF may act on the liver and intestine as target organs, exerting its effects by improving the intestinal microbiota and related barrier and lipid absorption functions, ultimately ameliorating hepatic steatosis and enhancing overall glucose and lipid metabolism.

A consortia of clinical E. coli strains with distinct in vitro adherent/invasive properties establish their own co-colonization niche and shape the intestinal microbiota in inflammation-susceptible mice

BACKGROUND

Inflammatory bowel disease (IBD) patients experience recurrent episodes of intestinal inflammation and often follow an unpredictable disease course. Mucosal colonization with adherent-invasive Escherichia coli (AIEC) are believed to perpetuate intestinal inflammation. However, it remains unclear if the 24-year-old AIEC in vitro definition fully predicts mucosal colonization in vivo. To fill this gap, we have developed a novel molecular barcoding approach to distinguish strain variants in the gut and have integrated this approach to explore mucosal colonization of distinct patient-derived E. coli isolates in gnotobiotic mouse models of colitis.

RESULTS

Germ-free inflammation-susceptible interleukin-10-deficient (Il10-/-) and inflammation-resistant WT mice were colonized with a consortium of AIEC and non-AIEC strains, then given a murine fecal transplant to provide niche competition. E. coli strains isolated from human intestinal tissue were each marked with a unique molecular barcode that permits identification and quantification by barcode-targeted sequencing. 16S rRNA sequencing was used to evaluate the microbiome response to E. coli colonization. Our data reveal that specific AIEC and non-AIEC strains reproducibly colonize the intestinal mucosa of WT and Il10-/- mice. These E. coli expand in Il10-/- mice during inflammation and induce compositional dysbiosis to the microbiome in an inflammation-dependent manner. In turn, specific microbes co-evolve in inflamed mice, potentially diversifying E. coli colonization patterns. We observed no selectivity in E. coli colonization patterns in the fecal contents, indicating minimal selective pressure in this niche from host-microbe and interbacterial interactions. Because select AIEC and non-AIEC strains colonize the mucosa, this suggests the in vitro AIEC definition may not fully predict in vivo colonization potential. Further comparison of seven E. coli genomes pinpointed unique genomic features contained only in highly colonizing strains (two AIEC and two non-AIEC). Those colonization-associated features may convey metabolic advantages (e.g., iron acquisition and carbohydrate consumption) to promote efficient mucosal colonization.

CONCLUSIONS

Our findings establish the in vivo mucosal colonizer, not necessarily AIEC, as a principal dysbiosis driver through crosstalk with host and associated microbes. Furthermore, we highlight the utility of high-throughput screens to decode the in vivo colonization dynamics of patient-derived bacteria in murine models. Video Abstract.

TCM syndrome differentiation in colorectal cancer patients assisted by differences in gut microbiota: An exploratory study

Objective

To explore the difference in gut microbiota between different traditional Chinese Medicine (TCM) syndromes in patients with colorectal cancer (CRC) and its internal relationship.

Methods

From June 2020 to August 2021, 109 colorectal cancer patients with a clear pathological diagnosis who had not yet undergone surgery or chemotherapy were classified according to the TCM syndrome classification, and the feces samples of 109 patients with preoperative colorectal cancer were collected. 16s rRNA gene sequencing was used to determine gut microbiota diversity and abundance in CRC patients with different TCM syndrome, and LEfSe analysis was made to screen different TCM syndrome for differential representative microbiota.

Results

109 patients were divided into 5 syndromes by TCM syndrome classification, which were Liver and Kidney Yin Deficiency Syndrome (LKYDS, n = 19), Spleen Deficient Qi Stagnation Syndrome (SDQSS, n = 30), Stasis and Poison Obstruction Syndrome (SPOS, n = 17), Damp-Heat Syndrome (DHS, n = 30), Qi and Blood Deficiency Syndrome (QBDS, n = 13). Alpha diversity index showed significant differences among the five groups of TCM syndromes, with Shannon index being highest in the SDQSS group and lowest in the LKYDS (p = 0.003). ACE index being highest in the SDQSS group and lowest in the SPOS (p = 0.010). PD whole tree index being highest in the SDQSS group and lowest in the SPOS (p = 0.017). Similarly, beta diversity showed significant differences among the five groups of TCM syndromes, with principal coordinate analysis (PCo1 = 31.86 %, PCo2 = 5.62 %) showing separation and coincidence between the groups, and Adonis group differences showing coincidence between the QBDS-LKYDS (p = 0.702), QBDS-DHS (p = 0.133), and SDQSS-DHS (p = 0.260) groups. LEfSe analysis revealed that the representative microbiota of DHS patients was Dialister sp Marseille P5638 (LDA = 3.05, p＜0.001), the representative microbiota of SPOS patients was Oscillospirales (LDA = 4.78, p = 0.029), the representative microbiota of SDQSS patients was Selenomonadaceae (LDA = 3.94, p = 0.003), the representative microbiota of LKYDS patients was Dialister (LDA = 4.19, p = 0.001), and the representative microbiota of QBDS patients was Akkermansia muciniphila (LDA = 4.23, p = 0.006).

Conclusions

There are significant differences in gut microbiota between different TCM syndromes in CRC patients. The five microbiota, Dialister sp Marseille P5638, Oscillospirales, Selenomonadaceae, Dialister, and Akkermansia muciniphila, may be differential markers of TCM syndrome in CRC and are expected to be one of the bases for accurate TCM syndrome differentiation of CRC.

Longitudinal effects of oral administration of antimicrobial drugs on fecal microbiota of horses

BACKGROUND

Antimicrobial drug-associated diarrhea (AAD) is the most common adverse effect in horses receiving antimicrobials. Little information on how oral administration of antimicrobials alters intestinal microbiota in horses is available.

OBJECTIVE

Investigate changes of the fecal microbiota in response to oral administration of antimicrobials.

ANIMALS

Twenty healthy horses.

METHODS

Prospective, longitudinal study. Horses were randomly assigned to 4 groups comprising 4 horses each: group 1 (metronidazole); group 2 (erythromycin); group 3 (doxycycline); group 4 (sulfadiazine/trimethoprim, SMZ-TMP); and group 5 (control). Antimicrobials were administered for 5 days. Fecal samples were obtained before (day 0) and at 1, 2, 3, 4, 5, 6, and 30 days of the study period. Fecal microbiota was characterized by high throughput sequencing of the V4 region of the 16S rRNA.

RESULTS

Horses remained healthy throughout the study. Richness and diversity in doxycycline, erythromycin, and metronidazole, but not SMZ-TMP groups, was significantly lower (P < .05) at multiple time points after administration of antimicrobials compared with samples from day 0. Main changes in the microbiota were observed during the time of antimicrobial administration (day 2-5; weighted and unweighted UniFrac PERMANOVA P < .05). Administration of erythromycin, doxycycline and, to a lesser extent, metronidazole produced a pronounced alteration in the microbiota compared with day 0 samples by decreasing the abundance of Treponema, Fibrobacter, and Lachnospiraceae and increasing Fusobacterium and Escherichia-Shigella.

CONCLUSIONS AND CLINICAL IMPORTANCE

Oral administration of antimicrobials alters the intestinal microbiota of healthy horses resembling horses with dysbiosis, potentially resulting in intestinal inflammation and predisposition to diarrhea.

Short-chain fatty acids in cancer pathogenesis

Cancer is a multi-step process that can be viewed as a cellular and immunological shift away from homeostasis in response to selected infectious agents, mutations, diet, and environmental carcinogens. Homeostasis, which contributes importantly to the definition of "health," is maintained, in part by the production of short-chain fatty acids (SCFAs), which are metabolites of specific gut bacteria. Alteration in the composition of gut bacteria, or dysbiosis, is often a major risk factor for some two dozen tumor types. Dysbiosis is often characterized by diminished levels of SCFAs in the stool, and the presence of a "leaky gut," permitting the penetration of microbes and microbial derived molecules (e.g., lipopolysaccharides) through the gut wall, thereby triggering chronic inflammation. SCFAs attenuate inflammation by inhibiting the activation of nuclear factor kappa B, by decreasing the expression of pro-inflammatory cytokines such as tumor necrosis factor alpha, by stimulating the expression of anti-inflammatory cytokines such as interleukin-10 and transforming growth factor beta, and by promoting the differentiation of naïve T cells into T regulatory cells, which down-regulate immune responses by immunomodulation. SCFA function epigenetically by inhibiting selected histone acetyltransferases that alter the expression of multiple genes and the activity of many signaling pathways (e.g., Wnt, Hedgehog, Hippo, and Notch) that contribute to the pathogenesis of cancer. SCFAs block cancer stem cell proliferation, thereby potentially delaying or inhibiting cancer development or relapse by targeting genes and pathways that are mutated in tumors (e.g., epidermal growth factor receptor, hepatocyte growth factor, and MET) and by promoting the expression of tumor suppressors (e.g., by up-regulating PTEN and p53). When administered properly, SCFAs have many advantages compared to probiotic bacteria and fecal transplants. In carcinogenesis, SCFAs are toxic against tumor cells but not to surrounding tissue due to differences in their metabolic fate. Multiple hallmarks of cancer are also targets of SCFAs. These data suggest that SCFAs may re-establish homeostasis without overt toxicity and either delay or prevent the development of various tumor types.

Effect of time of sample collection after onset of diarrhea on fecal microbiota composition of calves

BACKGROUND

The effect of time of sample collection after onset of diarrhea on the fecal microbiota composition of calves is unknown.

OBJECTIVE

Compare the fecal microbiota of calves with diarrhea onset on the day of sampling (D <24h), and calves having had diarrhea for >24 to 48 hours (D 24-48h).

ANIMALS

Thirty-one diarrheic calves (20 D <24h and 11 D 24-48h), 3 to 7 days of age.

METHODS

Cross-sectional study. Diarrhea was defined as a calf with loose feces or watery feces. Assessment of the fecal microbiota was performed by sequencing of 16S ribosomal RNA gene amplicons.

RESULTS

Richness and diversity were not statistically different between D <24h and D 24-48h (P > .05), but bacterial membership and structure differed significantly (AMOVA, P < .001 for both comparisons). Linear discriminant analysis effect size (LefSe) showed an enrichment of Faecalibacterium, Phocaeicola, Lachnospiracea, and Lactobacillus in the feces of D <24h calves, whereas Escherichia/Shigella, Ligilactobacillus, Clostridium_Sensu_Stricto, Clostridium_Incerta_Sedis, and Enterococcus were enriched in the D 24-48h calves.

CONCLUSION AND CLINICAL IMPORTANCE

Rapid changes in fecal microbiota occur during the first 48 hours of diarrhea with an enrichment of lactic acid-producing bacteria in D <24h followed by an enrichment in Escherichia/Shigella and Clostridium spp. in D 24-48h. The time from diarrhea onset to sampling appears to affect the bacterial composition. Researchers should standardize times for fecal collection based on the time of diarrhea.

Targeting PPARs for therapy of atherosclerosis: A review

Atherosclerosis, a chief pathogenic factor of cardiovascular disease, is associated with many factors including inflammation, dyslipidemia, and oxidative stress. Peroxisome proliferator-activated receptors (PPARs) are nuclear receptors and are widely expressed with tissue- and cell-specificity. They control multiple genes that are involved in lipid metabolism, inflammatory response, and redox homeostasis. Given the diverse biological functions of PPARs, they have been extensively studied since their discovery in 1990s. Although controversies exist, accumulating evidence have demonstrated that PPAR activation attenuates atherosclerosis. Recent advances are valuable for understanding the mechanisms of action of PPAR activation. This article reviews the recent findings, mainly from the year of 2018 to present, including endogenous molecules in regulation of PPARs, roles of PPARs in atherosclerosis by focusing on lipid metabolism, inflammation, and oxidative stress, and synthesized PPAR modulators. This article provides information valuable for researchers in the field of basic cardiovascular research, for pharmacologists that are interested in developing novel PPAR agonists and antagonists with lower side effects as well as for clinicians.

A consortia of clinical E. coli strains with distinct in-vitro adherent/invasive properties establish their own co-colonization niche and shape the intestinal microbiota in inflammation-susceptible mice

Background

Inflammatory bowel disease (IBD) patients experience recurrent episodes of intestinal inflammation and often follow an unpredictable disease course. Mucosal colonization with adherent-invasive Escherichia coli (AIEC) are believed to perpetuate intestinal inflammation. However, it remains unclear if the 24-year-old AIEC in-vitro definition fully predicts mucosal colonization in-vivo. To fill this gap, we have developed a novel molecular barcoding approach to distinguish strain variants in the gut and have integrated this approach to explore mucosal colonization of distinct patient-derived E. coli isolates in gnotobiotic mouse models of colitis.

Results

Germ-free inflammation-susceptible interleukin-10-deficient (Il10-/-) and inflammation-resistant WT mice were colonized with a consortia of AIEC and non-AIEC strains, then given a murine fecal transplant to provide niche competition. E. coli strains isolated from human intestinal tissue were each marked with a unique molecular barcode that permits identification and quantification by barcode-targeted sequencing. 16S rRNA sequencing was used to evaluate the microbiome response to E. coli colonization. Our data reveal that specific AIEC and non-AIEC strains reproducibly colonize the intestinal mucosa of WT and Il10-/- mice. These E. coli expand in Il10-/- mice during inflammation and induce compositional dysbiosis to the microbiome in an inflammation-dependent manner. In turn, specific microbes co-evolve in inflamed mice, potentially diversifying E. coli colonization patterns. We observed no selectivity in E. coli colonization patterns in the fecal contents, indicating minimal selective pressure in this niche from host-microbe and interbacterial interactions. Because select AIEC and non-AIEC strains colonize the mucosa, this suggests the in vitro AIEC definition may not fully predict in vivo colonization potential. Further comparison of seven E. coli genomes pinpointed unique genomic features contained only in highly colonizing strains (two AIEC and two non-AIEC). Those colonization-associated features may convey metabolic advantages (e.g., iron acquisition and carbohydrate consumption) to promote efficient mucosal colonization.

Conclusions

Our findings establish the in-vivo mucosal colonizer, not necessarily AIEC, as a principal dysbiosis driver through crosstalk with host and associated microbes. Furthermore, we highlight the utility of high-throughput screens to decode the in-vivo colonization dynamics of patient-derived bacteria in murine models.

Lactobacillus paracasei L9 ameliorated obesity-associated metabolic parameters and relevant gut microbiota in mice fed a high-fat diet

The purpose of the present study was to determine whether Lactobacillus paracasei L9 (L9) supplementation prevents diet-induced obesity in C57BL/6J mice. Four-week-old mice were fed a high-fat diet (HFD) for 12 weeks and then supplemented with or without L9 for another 12 weeks. Weight gain, white adipose tissue weight, plasma lipid levels of total cholesterol, triglyceride, and low-density lipoprotein-cholesterol were significantly increased in the HFD group compared with those in the control group and were decreased by L9 treatment. The fat deposits in the liver and epididymal adipose tissue were increased in the HFD group compared with the normal chow diet group and decreased by L9 treatment. Reverse transcriptase-polymerase chain reaction analyses revealed that L9 suppressed pro-inflammatory cytokine and lipid synthesis-related genes in epididymal adipose tissue. This study used Illumina Miseq sequencing to explore alterations of the gut microbiome. L9 ameliorated HFD-induced structural dysbiosis and gut bacteria that were positively related with obesity phenotypes were obviously decreased. Altogether, the findings indicate that administration of L9 ameliorates HFD-induced hyperlipidemia and lipid accumulation in liver and inflammation associated with intestinal dysbiosis in obese mice. These findings suggest that L9 supplementation may provide a natural alternative to attenuate obesity.

Toxic effects of glyphosate on histopathology and intestinal microflora of juvenile Litopenaeus vannamei

Glyphosate is a widely used broad-spectrum herbicide, its pollution to the surrounding conditions can't be ignored. It has been reported that glyphosate has poisonous impacts on aquatic animals. In this study, juvenile Litopenaeus vannamei (L. vannamei) was exposed to glyphosate, and the lethal concentration 50 (LC₅₀) of glyphosate to juvenile L. vannamei for 48 h was 47.6 mg/L. The histological analysis for intestine and hepatopancreas and the intestinal microorganisms of L. vannamei were evaluated after 48 h of exposure to glyphosate with LC₅₀. The histological analysis results showed that the lumen of hepatic tubules was diffused and deformed, the hepatic tubules were ruptured and intestinal villi were fallen off seriously after exposure to glyphosate for 48 h Moreover, the intestinal microbial composition and structure of L. vannamei were changed, with the abundance of Alphaproteobacteria increased significantly. The abundance of Rhodobacteraceae, Vibrio and Legionella increased, but there was no significant difference. The abundance of Bacillus, Paraburkholderia, Enhydrobacter, Comamonas and Alkanindiges decreased significantly. However, the homeostasis of intestinal microorganisms was destroyed. Phenotypic prediction of the two groups of microorganisms revealed a significant increase in the abundance of Facultatively Anaerobic in the glyphosate challenged group. This study suggested that hepatopancreas and intestinal tissue of L. vannamei were seriously damaged after 48 h of exposure to glyphosate with LC₅₀, and intestinal microbial homeostasis was disrupted.

A Novel Strategy for Alzheimer's Disease Based on the Regulatory Effect of Amyloid-β on Gut Flora

Alzheimer's disease (AD) is one of the most common neurodegenerative diseases worldwide. The accumulation of amyloid-β (Aβ) protein and plaque formation in the brain are two major causes of AD. Interestingly, growing evidence demonstrates that the gut flora can alleviate AD by affecting amyloid production and metabolism. However, the underlying mechanism remains largely unknown. This review will discuss the possible association between the gut flora and Aβ in an attempt to provide novel therapeutic directions for AD treatment based on the regulatory effect of Aβ on the gut flora.

Bioactive compounds modulating Toll-like 4 receptor (TLR4)-mediated inflammation: pathways involved and future perspectives

Chronic inflammation is associated with the development and progression of several noncommunicable diseases, such as diabetes, cardiovascular disease, chronic kidney disease, cancer, and nonalcoholic fatty liver disease. Evidence suggests that pattern recognition receptors that identify pathogen-associated molecular patterns and danger-associated molecular patterns are crucial in chronic inflammation. Among the pattern recognition receptors, Toll-like receptor 4 (TLR4) stimulates several inflammatory pathway agonists, such as nuclear factor-κB, interferon regulator factor 3, and nod-like receptor pyrin domain containing 3 pathways, which consequently trigger the expression of pro-inflammatory biomarkers, increasing the risk of noncommunicable disease development and progression. Studies have focused on the antagonistic potential of bioactive compounds, following the concept of food as a medicine, in which nutritional strategies may mitigate inflammation via TLR4 modulation. Thus, this review discusses preclinical evidence concerning bioactive compounds from fruit, vegetable, spice, and herb extracts (curcumin, resveratrol, catechin, cinnamaldehyde, emodin, ginsenosides, quercetin, allicin, and caffeine) that may regulate the TLR4 pathway and reduce the inflammatory response. Bioactive compounds can inhibit TLR4-mediated inflammation through gut microbiota modulation, improvement of intestinal permeability, inhibition of lipopolysaccharide-TLR4 binding, and decreasing TLR4 expression by modulation of microRNAs and antioxidant pathways. The responses directly mitigated inflammation, especially nuclear factor-κB activation and inflammatory cytokines release. These findings should be considered for further clinical studies on inflammation-mediated diseases.

Harnessing conserved signaling and metabolic pathways to enhance the maturation of functional engineered tissues

The development of induced-pluripotent stem cell (iPSC)-derived cell types offers promise for basic science, drug testing, disease modeling, personalized medicine, and translatable cell therapies across many tissue types. However, in practice many iPSC-derived cells have presented as immature in physiological function, and despite efforts to recapitulate adult maturity, most have yet to meet the necessary benchmarks for the intended tissues. Here, we summarize the available state of knowledge surrounding the physiological mechanisms underlying cell maturation in several key tissues. Common signaling consolidators, as well as potential synergies between critical signaling pathways are explored. Finally, current practices in physiologically relevant tissue engineering and experimental design are critically examined, with the goal of integrating greater decision paradigms and frameworks towards achieving efficient maturation strategies, which in turn may produce higher-valued iPSC-derived tissues.

Reactive Oxygen Species/Reactive Nitrogen Species as Messengers in the Gut: Impact on Physiology and Metabolic Disorders

Significance: The role of reactive oxygen/nitrogen species as "friend" or "foe" messengers in the whole body is well characterized. Depending on the concentration in the tissue considered, these molecular actors exert beneficial or deleterious impacts leading to a pathological state, as observed in metabolic disorders such as type 2 diabetes and obesity. Recent Advances: Among the tissues impacted by oxidation and inflammation in this pathological state, the intestine is a site of dysfunction that can establish diabetic symptoms, such as alterations in the intestinal barrier, gut motility, microbiota composition, and gut/brain axis communication. In the intestine, reactive oxygen/nitrogen species (from the host and/or microbiota) are key factors that modulate the transition from physiological to pathological signaling. Critical Issues: Controlling the levels of intestinal reactive oxygen/nitrogen species is a complicated balance between positive and negative impacts that is in constant equilibrium. Here, we describe the synthesis and degradation of intestinal reactive oxygen/nitrogen species and their interactions with the host. The development of novel redox-based therapeutics that alter these processes could restore intestinal health in patients with metabolic disorders. Future Directions: Deciphering the mode of action of reactive oxygen/nitrogen species in the gut of obese/diabetic patients could result in a future therapeutic strategy that combines nutritional and pharmacological approaches. Consequently, preventive and curative treatments must take into account one of the first sites of oxidative and inflammatory dysfunctions in the body, that is, the intestine. Antioxid. Redox Signal. 37, 394-415.

Microenvironmental Factors that Shape Bacterial Metabolites in Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) is a significant global health problem that involves chronic intestinal inflammation and can involve severe comorbidities, including intestinal fibrosis and inflammation-associated colorectal cancer (CRC). Disease-associated alterations to the intestinal microbiota often include fecal enrichment of Enterobacteriaceae, which are strongly implicated in IBD development. This dysbiosis of intestinal flora accompanies changes in microbial metabolites, shaping host:microbe interactions and disease risk. While there have been numerous studies linking specific bacterial taxa with IBD development, our understanding of microbial function in the context of IBD is limited. Several classes of microbial metabolites have been directly implicated in IBD disease progression, including bacterial siderophores and genotoxins. Yet, our microbiota still harbors thousands of uncharacterized microbial products. In-depth discovery and characterization of disease-associated microbial metabolites is necessary to target these products in IBD treatment strategies. Towards improving our understanding of microbiota metabolites in IBD, it is important to recognize how host relevant factors influence microbiota function. For example, changes in host inflammation status, metal availability, interbacterial community structure, and xenobiotics all play an important role in shaping gut microbial ecology. In this minireview, we outline how each of these factors influences gut microbial function, with a specific focus on IBD-associated Enterobacteriaceae metabolites. Importantly, we discuss how altering the intestinal microenvironment could improve the treatment of intestinal inflammation and associated disorders, like intestinal fibrosis and CRC.

Escherichia/Shigella, SCFAs, and Metabolic Pathways-The Triad That Orchestrates Intestinal Dysbiosis in Patients with Decompensated Alcoholic Cirrhosis from Western Mexico

Gut microbiota undergoes profound alterations in alcohol cirrhosis. Microbiota-derived products, e.g., short chain fatty acids (SCFA), regulate the homeostasis of the gut-liver axis. The objective was to evaluate the composition and functions of the intestinal microbiota in patients with alcohol-decompensated cirrhosis. Fecal samples of 18 patients and 18 healthy controls (HC) were obtained. Microbial composition was characterized by 16S rRNA amplicon sequencing, SCFA quantification was performed by gas chromatography (GC), and metagenomic predictive profiles were analyzed by PICRUSt2. Gut microbiota in the cirrhosis group revealed a significant increase in the pathogenic/pathobionts genera Escherichia/Shigella and Prevotella, a decrease in beneficial bacteria, such as Blautia, Faecalibacterium, and a decreased α-diversity (p < 0.001) compared to HC. Fecal SCFA concentrations were significantly reduced in the cirrhosis group (p < 0.001). PICRUSt2 analysis indicated a decrease in acetyl-CoA fermentation to butyrate, as well as an increase in pathways related to antibiotics resistance, and aromatic amino acid biosynthesis. These metabolic pathways have been poorly described in the progression of alcohol-related decompensated cirrhosis. The gut microbiota of these patients possesses a pathogenic/inflammatory environment; therefore, future strategies to balance intestinal dysbiosis should be implemented. These findings are described for the first time in the population of western Mexico.

The Impact of Air Pollution on Gut Microbiota and Children’s Health: An Expert Consensus

Air pollution is an unseen threat to children’s health because it may increase the risk of respiratory infection, atopy, and asthma, and also alter gut microbiota compositions. The impact of air pollution on children’s health has not been firmly established. A literature review followed by a series of discussions among experts were performed to develop a theoretical framework on how air pollution could affect various bodily organs and functions in children. We invited experts from different backgrounds, such as paediatricians, nutritionists, environmental health experts, and occupational health experts, to provide their views on this matter. This report summarizes the discussion of multidisciplinary experts on the impact of air pollution on children’s health. The report begins with a review of air pollution’s impact on allergy and immunology, neurodevelopment, and cardiometabolic risks, and ends with the conceptualization of a theoretical framework. While the allergic and immunological pathway is one of the most significant pathways for air pollution affecting children’s health in which microbiotas also play a role, several pathways have been proposed regarding the ability to affect neurodevelopment and cardiometabolic risk. Further research is required to confirm the link between air pollution and the gut microbiota pathway.

Gut microbiome and health: mechanistic insights

The gut microbiota is now considered as one of the key elements contributing to the regulation of host health. Virtually all our body sites are colonised by microbes suggesting different types of crosstalk with our organs. Because of the development of molecular tools and techniques (ie, metagenomic, metabolomic, lipidomic, metatranscriptomic), the complex interactions occurring between the host and the different microorganisms are progressively being deciphered. Nowadays, gut microbiota deviations are linked with many diseases including obesity, type 2 diabetes, hepatic steatosis, intestinal bowel diseases (IBDs) and several types of cancer. Thus, suggesting that various pathways involved in immunity, energy, lipid and glucose metabolism are affected.In this review, specific attention is given to provide a critical evaluation of the current understanding in this field. Numerous molecular mechanisms explaining how gut bacteria might be causally linked with the protection or the onset of diseases are discussed. We examine well-established metabolites (ie, short-chain fatty acids, bile acids, trimethylamine N-oxide) and extend this to more recently identified molecular actors (ie, endocannabinoids, bioactive lipids, phenolic-derived compounds, advanced glycation end products and enterosynes) and their specific receptors such as peroxisome proliferator-activated receptor alpha (PPARα) and gamma (PPARγ), aryl hydrocarbon receptor (AhR), and G protein-coupled receptors (ie, GPR41, GPR43, GPR119, Takeda G protein-coupled receptor 5).Altogether, understanding the complexity and the molecular aspects linking gut microbes to health will help to set the basis for novel therapies that are already being developed.

Gut microbiome and health: mechanistic insights

The gut microbiota is now considered as one of the key elements contributing to the regulation of host health. Virtually all our body sites are colonised by microbes suggesting different types of crosstalk with our organs. Because of the development of molecular tools and techniques (ie, metagenomic, metabolomic, lipidomic, metatranscriptomic), the complex interactions occurring between the host and the different microorganisms are progressively being deciphered. Nowadays, gut microbiota deviations are linked with many diseases including obesity, type 2 diabetes, hepatic steatosis, intestinal bowel diseases (IBDs) and several types of cancer. Thus, suggesting that various pathways involved in immunity, energy, lipid and glucose metabolism are affected.In this review, specific attention is given to provide a critical evaluation of the current understanding in this field. Numerous molecular mechanisms explaining how gut bacteria might be causally linked with the protection or the onset of diseases are discussed. We examine well-established metabolites (ie, short-chain fatty acids, bile acids, trimethylamine N-oxide) and extend this to more recently identified molecular actors (ie, endocannabinoids, bioactive lipids, phenolic-derived compounds, advanced glycation end products and enterosynes) and their specific receptors such as peroxisome proliferator-activated receptor alpha (PPARα) and gamma (PPARγ), aryl hydrocarbon receptor (AhR), and G protein-coupled receptors (ie, GPR41, GPR43, GPR119, Takeda G protein-coupled receptor 5).Altogether, understanding the complexity and the molecular aspects linking gut microbes to health will help to set the basis for novel therapies that are already being developed.

Mitochondria-Microbiota Interaction in Neurodegeneration

Alzheimer’s and Parkinson’s are the two best-known neurodegenerative diseases. Each is associated with the excessive aggregation in the brain and elsewhere of its own characteristic amyloid proteins. Yet the two afflictions have much in common and often the same amyloids play a role in both. These amyloids need not be toxic and can help regulate bile secretion, synaptic plasticity, and immune defense. Moreover, when they do form toxic aggregates, amyloids typically harm not just patients but their pathogens too. A major port of entry for pathogens is the gut. Keeping the gut’s microbe community (microbiota) healthy and under control requires that our cells’ main energy producers (mitochondria) support the gut-blood barrier and immune system. As we age, these mitochondria eventually succumb to the corrosive byproducts they themselves release, our defenses break down, pathogens or their toxins break through, and the side effects of inflammation and amyloid aggregation become problematic. Although it gets most of the attention, local amyloid aggregation in the brain merely points to a bigger problem: the systemic breakdown of the entire human superorganism, exemplified by an interaction turning bad between mitochondria and microbiota.

A Modern-World View of Host-Microbiota-Pathogen Interactions

The microbiota-the diverse set of commensal microbes that normally colonize humans-represents the first line of defense against infectious diseases. In this review, we summarize the direct and indirect mechanisms by which the microbiota modulates susceptibility to, and severity of, infections, with a focus on immunological mechanisms. Moreover, we highlight some of the ways that modern-world lifestyles have influenced the structure-function relationship between the microbiota and infectious diseases. Ultimately, understanding how the microbiota influences infectious risks will facilitate development of microbiota-derived therapeutics that bolster host defenses.

The lung-gut axis during viral respiratory infections: the impact of gut dysbiosis on secondary disease outcomes

Bacteria that colonize the human gastrointestinal tract are essential for good health. The gut microbiota has a critical role in pulmonary immunity and host's defense against viral respiratory infections. The gut microbiota's composition and function can be profoundly affected in many disease settings, including acute infections, and these changes can aggravate the severity of the disease. Here, we discuss mechanisms by which the gut microbiota arms the lung to control viral respiratory infections. We summarize the impact of viral respiratory infections on the gut microbiota and discuss the potential mechanisms leading to alterations of gut microbiota's composition and functions. We also discuss the effects of gut microbial imbalance on disease outcomes, including gastrointestinal disorders and secondary bacterial infections. Lastly, we discuss the potential role of the lung-gut axis in coronavirus disease 2019.

Microbe-Driven Genotoxicity in Gastrointestinal Carcinogenesis

The intestinal epithelium serves as a barrier to discriminate the outside from the inside and is in constant exchange with the luminal contents, including nutrients and the microbiota. Pathogens have evolved mechanisms to overcome the multiple ways of defense in the mucosa, while several members of the microbiota can exhibit pathogenic features once the healthy barrier integrity of the epithelium is disrupted. This not only leads to symptoms accompanying the acute infection but may also contribute to long-term injuries such as genomic instability, which is linked to mutations and cancer. While for Helicobacter pylori a link between infection and cancer is well established, many other bacteria and their virulence factors have only recently been linked to gastrointestinal malignancies through epidemiological as well as mechanistic studies. This review will focus on those pathogens and members of the microbiota that have been linked to genotoxicity in the context of gastric or colorectal cancer. We will address the mechanisms by which such bacteria establish contact with the gastrointestinal epithelium-either via an existing breach in the barrier or via their own virulence factors as well as the mechanisms by which they interfere with host genomic integrity.