Gut microbiota-motility interregulation: insights from in vivo, ex vivo and in silico studies

Development and Application of a Selective Analytical Method for Indole Metabolites in Urine: Dietary Exposure Biomarkers for Broccoli Consumption

The identification of dietary exposure biomarkers is crucial for advancing our understanding of the health benefits of specific foods. Broccoli, a vegetable with well-known anticancer properties, contains active ingredients, such as isothiocyanates with indole side chains. Hence, indole metabolites related to broccoli consumption have the potential to serve as biomarkers of dietary exposure. In this work, we developed a new analytical method for indole metabolites in urine using a poly(deep eutectic solvents)-molecularly imprinted polymer/vinyl-functionalized graphene oxide (PDESs-MIP/VGO) in miniaturized centrifugal pipet-tip solid-phase extraction (CPT-SPE) coupled with liquid chromatography. This method integrates the strengths of PDESs-MIP/VGO, including rich adsorption interactions, high adsorption capacity, and excellent selectivity, with the simplicity and cost-effectiveness of CPT-SPE. The proposed method demonstrated low limits of quantification (1.2-2.5 ng mL-1), high accuracy (91.7-104.8%), and good precision (relative standard deviation ≤4.4%). By applying this method to analyze indole metabolites in urine, our results suggested that indole-3-carbinol and indole-3-acetonitrile have the potential to emerge as reliable dietary exposure biomarkers for broccoli intake. Furthermore, highly selective analytical methods based on molecular imprinting technology are advantageous for precise screening and analysis of dietary exposure biomarkers associated with food consumption.

CFP/Yit: An Inbred Mouse Strain with Slow Gastrointestinal Transit

BACKGROUND

Gastrointestinal transit (GIT) is influenced by factors including diet, medications, genetics, and gut microbiota, with slow GIT potentially indicating a functional disorder linked to conditions, such as constipation. Although GIT studies have utilized various animal models, few effectively model spontaneous slow GIT.

AIMS

We aimed to characterize the GIT phenotype of CFP/Yit (CFP), an inbred mouse strain with suggested slow GIT.

METHODS

Female and male CFP mice were compared to Crl:CD1 (ICR) mice in GIT and assessed based on oral gavage of fluorescent-labeled 70-kDa dextran, feed intake, fecal amount, and fecal water content. Histopathological analysis of the colon and analysis of gut microbiota were conducted.

RESULTS

CFP mice exhibited a shorter small intestine and a 1.4-fold longer colon compared to ICR mice. The median whole-GIT time was 6.0-fold longer in CFP mice than in ICR mice. CFP mice demonstrated slower gastric and cecal transits than ICR mice, with a median colonic transit time of 4.1 h (2.9-fold longer). CFP mice exhibited lower daily feed intakes and fecal amounts. Fecal water content was lower in CFP mice, apparently attributed to the longer colon. Histopathological analysis showed no changes in CFP mice, including tumors or inflammation. Moreover, CFP mice had a higher Firmicutes/Bacteroidota ratio and a relative abundance of Erysipelotrichaceae in cecal and fecal contents.

CONCLUSIONS

This study indicates that CFP mice exhibit slow transit in the stomach, cecum, and colon. As a novel mouse model, CFP mice can contribute to the study of gastrointestinal physiology and disease.

Microbiota-derived acetylcholine can promote gut motility in Drosophila melanogaster

The gut microbiota is crucial for intestinal health, including gastrointestinal (GI) motility. How commensal bacterial species influence GI motility has not been fully elucidated. A major factor of GI motility is the gut contraction promoting the propulsive movement of orally ingested materials. Here, we developed a method to monitor and quantify gut contractions in living Drosophila melanogaster larvae. We found that the culture medium of an isolated strain Lactiplantibacillus plantarum Lsi promoted gut contraction in vivo, which was not observed in Leuconostoc sp. Leui nor Acetobacter persici Ai culture medium. To identify bacteria-derived metabolites, we performed metabolome analysis of the culture media by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Of the 66 metabolites detected, we found that some metabolites changed in a species-specific manner. Among them, acetylcholine was specifically produced by L. plantarum. Feeding exogenous acetylcholine increased the frequency of gut contractions, which was blocked by D-tubocurarine, an inhibitor of nicotinic acetylcholine receptors. In this study, we propose a mechanism by which the gut microbiota influences Drosophila gut motility. This article is part of the theme issue 'Sculpting the microbiome: how host factors determine and respond to microbial colonization'.

Long-term use of etomidate disrupts the intestinal homeostasis and nervous system in mice

Etomidate (ETO) is used as an anesthetic in surgery, but it is being abused in some populations. The damage caused by long-term intake of ETO to intestinal and brain functions is not yet clear, and it remains to be determined whether the drug affects the central nervous system through the gut-brain axis. This study aimed to investigate the neurotoxic and gastrointestinal effects of ETO at doses of 1 mg/kg and 3 mg/kg in mice over 14 consecutive days. The results showed that long-term injection of ETO led to drug resistance in mice, affecting their innate preference for darkness and possibly inducing dependence on ETO. The levels of 5-hydroxytryptamine in the brain, serum, and colon decreased by 37%, 51%, and 42% respectively, while the levels of γ-aminobutyric acid reduced by 38%, 52%, and 41% respectively. H&E staining revealed that ETO reduced goblet cells in the colon and damaged the intestinal barrier. The expression of tight junction-related genes Claudin4 and ZO-1 was downregulated. The intestinal flora changed, the abundance of Akkermansia and Lactobacillus decreased by 33% and 14%, respectively, while Klebsiella increased by 18%. TUNEL results showed that high-dose ETO increased apoptotic cells in the brain. The expression of Claudin1 in the brain was downregulated. Untargeted metabolomics analysis of the colon and brain indicated that ETO caused abnormalities in glycerophospholipid metabolism. Abnormal lipid metabolism might lead to the production or accumulation of lipotoxic metabolites, causing central nervous system diseases. ETO induced changes in the intestinal flora and metabolism, further affecting the central nervous system through the gut-brain axis. The study unveiled the detrimental effects on the brain and gastrointestinal system resulting from long-term intake of ETO, which holds significant implications for comprehending the adverse impact of ETO abuse on human health.

In Vitro Human Gastrointestinal Tract Simulation Systems: A Panoramic Review

Simulated human gastrointestinal (GI) tract systems are important for their applications in the fields of probiotics, nutrition and health. To date, various in vitro gut systems have been available to study GI tract dynamics and its association with health. In contrast to in vivo investigations, which are constrained by ethical considerations, in vitro models have several benefits despite the challenges involved in mimicking the GI environment. These in vitro models can be used for a range of research, from simple to dynamic, with one compartment to several compartments. In this review, we present a panoramic development of in vitro GI models for the first time through an evolutionary timeline. We tried to provide insight on designing an in vitro gut model, especially for novices. Latest developments and scope for improvement based on the limitations of the existing models were highlighted. In conclusion, designing an in vitro GI model suitable for a particular application is a multifaceted task. The bio-mimicking of the GI tract specific to geometrical, anatomical and mechanical features remains a challenge for the development of effective in vitro GI models. Advances in computer technology, artificial intelligence and nanotechnology are going to be revolutionary for further development. Besides this, in silico high-throughput technologies and miniaturisation are key players in the success of making in vitro modelling cost-effective and reducing the burden of in vivo studies.

Lab-on-chip technologies for exploring the gut-immune axis in metabolic disease

The continued rise in metabolic diseases such as obesity and type 2 diabetes mellitus poses a global health burden, necessitating further research into factors implicated in the onset and progression of these diseases. Recently, the gut-immune axis, with diet as a main regulator, has been identified as a possible role player in their development. Translation of conventional 2D in vitro and animal models is however limited, while human studies are expensive and preclude individual mechanisms from being investigated. Lab-on-chip technology therefore offers an attractive new avenue to study gut-immune interactions. This review provides an overview of the influence of diet on gut-immune interactions in metabolic diseases and a critical analysis of the current state of lab-on-chip technology to study this axis. While there has been progress in the development of "immuno-competent" intestinal lab-on-chip models, with studies showing the ability of the technology to provide mechanical cues, support longer-term co-culture of microbiota and maintain in vivo-like oxygen gradients, platforms which combine all three and include intestinal and immune cells are still lacking. Further, immune cell types and inclusion of microenvironment conditions which enable in vivo-like immune cell dynamics as well as host-microbiome interactions are limited. Future model development should focus on combining these conditions to create an environment capable of hosting more complex microbiota and immune cells to allow further study into the effects of diet and related metabolites on the gut-immune ecosystem and their role in the prevention and development of metabolic diseases in humans.

The Landscape of Gut Microbiota and Its Metabolites: A Key to Understanding the Pathophysiology of Pattern in Chinese Medicine

Liver Stagnation and Spleen Deficiency (LSSD) is a Chinese Medicine (CM) pattern commonly observed in gastrointestinal (GI) diseases, yet its biological nature remains unknown. This limits the global use of CM medications for treating GI diseases. Recent studies emphasize the role of gut microbiota and their metabolites in the pathogenesis and treatment of LSSD-associated GI diseases. There is increasing evidence supporting that an altered gut microbiome in LSSD patients or animals contributes to GI and extra-intestinal symptoms and affects the effectiveness of CM therapies. The gut microbiota is considered to be an essential component of the biological basis of LSSD. This study aims to provide an overview of existing research findings and gaps for the pathophysiological study of LSSD from the gut microbiota perspective in order to understand the relationship between the CM pattern and disease progression and to optimize CM-based diagnosis, prevention, and therapy.

Piezo channels in the intestinal tract

The intestine is the largest mechanosensitive organ in the human body whose epithelial cells, smooth muscle cells, neurons and enteroendocrine cells must sense and respond to various mechanical stimuli such as motility, distension, stretch and shear to regulate physiological processes including digestion, absorption, secretion, motility and immunity. Piezo channels are a newly discovered class of mechanosensitive ion channels consisting of two subtypes, Piezo1 and Piezo2. Piezo channels are widely expressed in the intestine and are involved in physiological and pathological processes. The present review summarizes the current research progress on the expression, function and regulation of Piezo channels in the intestine, with the aim of providing a reference for the future development of therapeutic strategies targeting Piezo channels.

Extent of Abdominal Aortic Calcification Is Associated With Incident Rapid Weight Loss Over 5 Years: The Perth Longitudinal Study of Ageing Women

BACKGROUND

Abdominal aortic calcification (AAC), a marker of vascular disease, is associated with disease in other vascular beds including gastrointestinal arteries. We investigated whether AAC is related to rapid weight loss over 5 years and whether rapid weight loss is associated with 9.5-year all-cause mortality in community-dwelling older women.

METHODS

Lateral spine images from dual-energy x-ray absorptiometry (1998/1999) were used to assess AAC (24-point AAC scoring method) in 929 older women. Over 5 years, body weight was assessed at 12-month intervals. Rapid weight loss was defined as >5% decrease in body weight within any 12-month interval. Multivariable-adjusted logistic regression was used to assess AAC and rapid weight loss and Cox regression to assess the relationship between rapid weight loss and 9.5-year all-cause mortality.

RESULTS

Mean±SD age of women was 75.0±2.6 years. During the initial 5 years, 366 (39%) women presented with rapid weight loss. Compared with women with low AAC (24-point AAC score 0-1), those with moderate (24-point AAC score 2-5: odds ratio, 1.36 [95% CI, 1.00-1.85]) and extensive (24-point AAC score 6+: odds ratio, 1.59 [95% CI, 1.10-2.31]) AAC had higher odds for presenting with rapid weight loss. Results remained similar after further adjustment for dietary factors (alcohol, protein, fat, and carbohydrates), diet quality, blood pressure, and cholesterol measures. The estimates were similar in subgroups of women who met protein intake (n=599) and physical activity (n=735) recommendations (extensive AAC: odds ratios, 1.81 [95% CI, 1.12-2.92] and 1.58 [95% CI, 1.02-2.44], respectively). Rapid weight loss was associated with all-cause mortality over the next 9.5 years (hazard ratio, 1.49 [95% CI, 1.17-1.89]; P=0.001).

CONCLUSIONS

AAC extent was associated with greater risk for rapid weight loss over 5 years in older women, a risk for all-cause mortality. Since the association was unchanged after taking nutritional intakes into account, these data support the possibility that vascular disease may play a role in the maintenance of body weight.

Behavior, intestinal health, and growth of small sea cucumbers Apostichopus japonicus in different color morphs

Selecting high-quality seeds with long-term advantages in behavior, intestinal health, and growth are the key to improve production efficiency of sea cucumber aquaculture. It is proposed to distinguish the seed quality of sea cucumbers by color morphs. In the present study, we carried out a 6-week experiment to investigate behavior, intestinal health, and growth of small sea cucumbers Apostichopus japonicus in different color morphs. We found that dark-colored seeds of sea cucumber were significantly more adhesive than those with light-colored seeds. This indicates that the dark-colored seeds of A. japonicus are more adaptive in complex environments in stock enhancement. Food consumption and defecation outputs of dark-colored seeds were significantly higher than those of light-colored seeds. In addition, the feces of dark-colored seeds of sea cucumber had significantly lower crude protein content and better intestinal morphology, but there was no advantage in digestive enzyme activities. This suggests that there are potential digestive benefits in dark-colored seeds. Further, dark-colored seeds of A. japonicus showed significantly better intestinal microbiota composition and faster growth rate than that of light-colored seeds. In conclusion, the present results prove that dark-colored seeds of sea cucumber have long-term advantages in behavior, intestinal health and growth. Overall, this study provides important information for the early selection of seeds and the consequent production efficiency in sea cucumber aquaculture.

Pharmacomicrobiomics of cell-cycle specific anti-cancer drugs - is it a new perspective for personalized treatment of cancer patients?

Intestinal bacteria are equipped with an enzyme apparatus that is involved in the active biotransformation of xenobiotics, including drugs. Pharmacomicrobiomics, a new area of pharmacology, analyses interactions between bacteria and xenobiotics. However, there is another side to the coin. Pharmacotherapeutic agents can significantly modify the microbiota, which consequently affects their efficacy. In this review, we comprehensively gathered scientific evidence on the interplay between anticancer therapies and gut microbes. We also underlined how such interactions might impact the host response to a given therapy. We discuss the possibility of modulating the gut microbiota to increase the effectiveness/decrease the incidence of adverse events during tumor therapy. The anticipation of the future brings new evidence that gut microbiota is a target of interest to increase the efficacy of therapy.

50-year history and perspective on biomechanics of swimming microorganisms: Part II. Collective behaviours

The paired review papers in Parts I and II describe the 50-year history of research on the biomechanics of swimming microorganisms and its prospects in the next 50 years. Parts I and II are divided not by the period covered, but by the content of the research: Part I explains the behaviours of individual microorganisms, and Part II explains collective behaviour. In the 1990s, the description of microbial suspensions as a continuum progressed, and macroscopic flow structures such as bioconvection were analysed. The continuum model was later extended to analyse various phenomena such as flow induced trapping of microorganisms and accumulation of cells at interfaces. In the 2000s, the collective behaviour of swimming microorganisms came into the limelight, and physicists as well as biomechanics researchers carried out many studies probing microorganism collectivity. In particular, research on the turbulence-like flow structure of dense bacterial suspensions has led to dramatic developments in the field of microbial biomechanics. Efforts to bridge the cellular scale to the macroscopic scale by extracting macroscopic physical quantities from the microstructure of cell suspensions are also underway. This Part II reviews these collective behaviours of swimming microorganisms and discusses future prospects of the field.

Colon-Targeted Delivery of Indole Acetic Acid Helps Regulate Gut Motility by Activating the AHR Signaling Pathway

Intestinal peristalsis is vital for gastrointestinal physiology and host homeostasis and is frequently dysregulated in intestinal disorders. Gut microbiota can regulate gut motility, especially through the tryptophan metabolism pathway. However, the role of indoles as microbial tryptophan metabolites in colonic function requires further exploration. Here, we show that the delivery of indole acetic acid (IAA) targeting the colon can improve gut motility by activating the aryl hydrocarbon receptor (AHR). To achieve colon-targeted delivery, Eudragit S-100 (ES) and chitosan (CS) were used as drug carriers. After optimisation, IAA-loaded ES-coated CS nanoparticles exhibited an encapsulation efficiency of 83% and a drug-loading capacity of 16%. These nanoparticles exhibited pH-dependent characteristics and remained stable in acidic conditions and the upper intestine. In simulated intestinal fluid (pH 7.4) and colonic lumen, considerable amounts of IAA were released after approximately 4 h. Compared with free IAA, the nanoparticles exerted enhanced therapeutic effects on gut movement disorders induced by loperamide. The efficacy of IAA treatment was attributable to the activation of the AHR signalling pathway and increased levels of AHR agonists. Furthermore, the oral administration of IAA-loaded nanoparticles promoted serotonin secretion and maintained the intestinal barrier function. The experimental outcomes demonstrate the efficiency of the proposed colon-specific delivery system and highlight the role of IAA, produced by gut microbiota metabolism, in regulating gut peristalsis through AHR activation.

The voltage-gated sodium channel, para, limits Anopheles coluzzii vector competence in a microbiota dependent manner

The voltage-gated sodium channel, para, is a target of DDT and pyrethroid class insecticides. Single nucleotide mutations in para, called knockdown resistant or kdr, which contribute to resistance against DDT and pyrethroid insecticides, have been correlated with increased susceptibility of Anopheles to the human malaria parasite Plasmodium falciparum. However, a direct role of para activity on Plasmodium infection has not yet been established. Here, using RNA-mediated silencing, we provide in vivo direct evidence for the requirement of wild-type (wt) para function for insecticide activity of deltamethrin. Depletion of wt para, which is susceptible to insecticide, causes deltamethrin tolerance, indicating that insecticide-resistant kdr alleles are likely phenocopies of loss of para function. We then show that normal para activity in An. coluzzii limits Plasmodium infection prevalence for both P. falciparum and P. berghei. A transcriptomic analysis revealed that para activity does not modulate the expression of immune genes. However, loss of para function led to enteric dysbiosis with a significant increase in the total bacterial abundance, and we show that para function limiting Plasmodium infection is microbiota dependent. In the context of the bidirectional "enteric microbiota-brain" axis studied in mammals, these results pave the way for studying whether the activity of the nervous system could control Anopheles vector competence.

The Impact of Long-Term Macrolide Exposure on the Gut Microbiome and Its Implications for Metabolic Control

Long-term low-dose macrolide therapy is now widely used in the treatment of chronic respiratory diseases for its immune-modulating effects, although the antimicrobial properties of macrolides can also have collateral impacts on the gut microbiome. We investigated whether such treatment altered intestinal commensal microbiology and whether any such changes affected systemic immune and metabolic regulation. In healthy adults exposed to 4 weeks of low-dose erythromycin or azithromycin, as used clinically, we observed consistent shifts in gut microbiome composition, with a reduction in microbial capacity related to carbohydrate metabolism and short-chain fatty acid biosynthesis. These changes were accompanied by alterations in systemic biomarkers relating to immune (interleukin 5 [IL-5], IL-10, monocyte chemoattractant protein 1 [MCP-1]) and metabolic (serotonin [5-HT], C-peptide) homeostasis. Transplantation of erythromycin-exposed murine microbiota into germ-free mice demonstrated that changes in metabolic homeostasis and gastrointestinal motility, but not systemic immune regulation, resulted from changes in intestinal microbiology caused by macrolide treatment. Our findings highlight the potential for long-term low-dose macrolide therapy to influence host physiology via alteration of the gut microbiome. IMPORTANCE Long-term macrolide therapy is widely used in chronic respiratory diseases although its antibacterial activity can also affect the gut microbiota, a key regulator of host physiology. Macrolide-associated studies on the gut microbiota have been limited to short antibiotic courses and have not examined its consequences for host immune and metabolic regulation. This study revealed that long-term macrolides depleted keystone bacteria and impacted host regulation, mediated directly by macrolide activity or indirectly by alterations to the gut microbiota. Understanding these macrolide-associated mechanisms will contribute to identifying the risk of long-term exposure and highlights the importance of targeted therapy for maintenance of the gut microbiota.

Impaired colonic motility in high-glycemic diet-induced diabetic mice is associated with disrupted gut microbiota and neuromuscular function

Background

Similar to the high-fat diet (HFD), the high-glycemic diet (HGD) contributes to the development and progression of type 2 diabetes mellitus (T2DM). However, the effect of HGD on gastrointestinal motility in T2DM and its underlying mechanisms remain unclear.

Methods

Thirty C57BL/6J mice were randomly designated into the normal-feeding diet (NFD) group, HFD group, and HGD group. The plasma glucose, plasma insulin, and gastrointestinal motility were examined. Meanwhile, the tension of isolated colonic smooth muscle rings was calculated, and the gut microbiota was analyzed by 16s rDNA high-throughput sequencing.

Result

After 16 weeks of HGD feeding, obesity, hyperglycemia, insulin resistance, and constipation were observed in HGD mice. Autonomic contraction frequency of the colonic neuromuscular system and electrical field stimulation-induced contractions were reduced in HGD mice. On the contrary, neuronal nitric oxide synthase activity and neuromuscular relaxation were found to be enhanced. Finally, gut microbiota analysis revealed that Rhodospirillaceae abundance significantly increased at the family level in HGD mice. At the genus level, the abundance of Insolitispirillum increased remarkably, whereas Turicibacter abundance decreased significantly in HGD mice.

Conclusion

HGD induced constipation in obese diabetic mice, which we speculated that it may be related to neuromuscular dysmotility and intestinal microbiota dysbiosis.

Antispasmodic Effect of Valeriana pilosa Root Essential Oil and Potential Mechanisms of Action: Ex Vivo and In Silico Studies

Infusions of Valeriana pilosa are commonly used in Peruvian folk medicine for treating gastrointestinal disorders. This study aimed to investigate the spasmolytic and antispasmodic effects of Valeriana pilosa essential oil (VPEO) on rat ileum. The basal tone of ileal sections decreased in response to accumulative concentrations of VPEO. Moreover, ileal sections precontracted with acetylcholine (ACh), potassium chloride (KCl), or barium chloride (BaCl2) were relaxed in response to VPEO by a mechanism that depended on atropine, hyoscine butylbromide, solifenacin, and verapamil, but not glibenclamide. The results showed that VPEO produced a relaxant effect by inhibiting muscarinic receptors and blocking calcium channels, with no apparent effect on the opening of potassium channels. In addition, molecular docking was employed to evaluate VPEO constituents that could inhibit intestinal contractile activity. The study showed that α-cubebene, β-patchoulene, β-bourbonene, β-caryophyllene, α-guaiene, γ-muurolene, valencene, eremophyllene, and δ-cadinene displayed the highest docking scores on muscarinic acetylcholine receptors and voltage-gated calcium channels, which may antagonize M2 and/or M3 muscarinic acetylcholine receptors and block voltage-gated calcium channels. In summary, VPEO has both spasmolytic and antispasmodic effects. It may block muscarinic receptors and calcium channels, thus providing a scientific basis for its traditional use for gastrointestinal disorders.

Role of the Gut Microbiota and Its Metabolites in Tumorigenesis or Development of Colorectal Cancer

Colorectal cancer (CRC) is the most common cancer of the digestive system with high mortality and morbidity rates. Gut microbiota is found in the intestines, especially the colorectum, and has structured crosstalk interactions with the host that affect several physiological processes. The gut microbiota include CRC-promoting bacterial species, such as Fusobacterium nucleatum, Escherichia coli, and Bacteroides fragilis, and CRC-protecting bacterial species, such as Clostridium butyricum, Streptococcus thermophilus, and Lacticaseibacillus paracasei, which along with other microorganisms, such as viruses and fungi, play critical roles in the development of CRC. Different bacterial features are identified in patients with early-onset CRC, combined with different patterns between fecal and intratumoral microbiota. The gut microbiota may be beneficial in the diagnosis and treatment of CRC; some bacteria may serve as biomarkers while others as regulators of chemotherapy and immunotherapy. Furthermore, metabolites produced by the gut microbiota play essential roles in the crosstalk with CRC cells. Harmful metabolites include some primary bile acids and short-chain fatty acids, whereas others, including ursodeoxycholic acid and butyrate, are beneficial and impede tumor development and progression. This review focuses on the gut microbiota and its metabolites, and their potential roles in the development, diagnosis, and treatment of CRC.

d-Serine agonism of GluN1-GluN3 NMDA receptors regulates the activity of enteric neurons and coordinates gut motility

The enteric nervous system (ENS) is a complex network of diverse molecularly defined classes of neurons embedded in the gastrointestinal wall and responsible for controlling the major functions of the gut. As in the central nervous system, the vast array of ENS neurons is interconnected by chemical synapses. Despite several studies reporting the expression of ionotropic glutamate receptors in the ENS, their roles in the gut remain elusive. Here, by using an array of immunohistochemistry, molecular profiling and functional assays, we uncover a new role for d-serine (d-Ser) and non-conventional GluN1-GluN3 N-methyl d-aspartate receptors (NMDARs) in regulating ENS functions. We demonstrate that d-Ser is produced by serine racemase (SR) expressed in enteric neurons. By using both in situ patch clamp recording and calcium imaging, we show that d-Ser alone acts as an excitatory neurotransmitter in the ENS independently of the conventional GluN1-GluN2 NMDARs. Instead, d-Ser directly gates the non-conventional GluN1-GluN3 NMDARs in enteric neurons from both mouse and guinea-pig. Pharmacological inhibition or potentiation of GluN1-GluN3 NMDARs had opposite effects on mouse colonic motor activities, while genetically driven loss of SR impairs gut transit and fluid content of pellet output. Our results demonstrate the existence of native GluN1-GluN3 NMDARs in enteric neurons and open new perspectives on the exploration of excitatory d-Ser receptors in gut function and diseases.

Cinnamic acid regulates the intestinal microbiome and short-chain fatty acids to treat slow transit constipation

BACKGROUND

Slow transit constipation (STC) is a disorder with delayed colonic transit. Cinnamic acid (CA) is an organic acid in natural plants, such as Radix Scrophulariae (Xuan Shen), with low toxicity and biological activities to modulate the intestinal microbiome.

AIM

To explore the potential effects of CA on the intestinal microbiome and the primary endogenous metabolites-short-chain fatty acids (SCFAs) and evaluate the therapeutic effects of CA in STC.

METHODS

Loperamide was applied to induce STC in mice. The treatment effects of CA on STC mice were assessed from the 24 h defecations, fecal moisture and intestinal transit rate. The enteric neurotransmitters: 5-hydroxytryptamine (5-HT) and vasoactive intestinal peptide (VIP) were determined by the enzyme-linked immunosorbent assay. Hematoxylin-eosin and Alcian blue and Periodic acid Schiff staining were used to evaluate intestinal mucosa's histopathological performance and secretory function. 16S rDNA was employed to analyze the composition and abundance of the intestinal microbiome. The SCFAs in stool samples were quantitatively detected by gas chromatography-mass spectrometry.

RESULTS

CA ameliorated the symptoms of STC and treated STC effectively. CA ameliorated the infiltration of neutrophils and lymphocytes, increased the number of goblet cells and acidic mucus secretion of the mucosa. In addition, CA significantly increased the concentration of 5-HT and reduced VIP. CA significantly improved the diversity and abundance of the beneficial microbiome. Furthermore, the production of SCFAs [including acetic acid (AA), butyric acid (BA), propionic acid (PA) and valeric acid (VA)] was significantly promoted by CA. The changed abundance of Firmicutes, Akkermansia, Lachnoclostridium, Monoglobus, UCG.005, Paenalcaligenes, Psychrobacter and Acinetobacter were involved in the production of AA, BA, PA and VA.

CONCLUSION

CA could treat STC effectively by ameliorating the composition and abundance of the intestinal microbiome to regulate the production of SCFAs.

Gut-on-a-Chip Models: Current and Future Perspectives for Host-Microbial Interactions Research

The intestine contains the largest microbial community in the human body, the gut microbiome. Increasing evidence suggests that it plays a crucial role in maintaining overall health. However, while many studies have found a correlation between certain diseases and changes in the microbiome, the impact of different microbial compositions on the gut and the mechanisms by which they contribute to disease are not well understood. Traditional pre-clinical models, such as cell culture or animal models, are limited in their ability to mimic the complexity of human physiology. New mechanistic models, such as organ-on-a-chip, are being developed to address this issue. These models provide a more accurate representation of human physiology and could help bridge the gap between clinical and pre-clinical studies. Gut-on-chip models allow researchers to better understand the underlying mechanisms of disease and the effect of different microbial compositions on the gut. They can help to move the field from correlation to causation and accelerate the development of new treatments for diseases associated with changes in the gut microbiome. This review will discuss current and future perspectives of gut-on-chip models to study host-microbial interactions.

Cystic Fibrosis-Related Gut Dysbiosis: A Systematic Review

BACKGROUND AND AIMS

Cystic Fibrosis (CF) is associated with gut dysbiosis, local and systemic inflammation, and impaired immune function. Gut microbiota dysbiosis results from changes in the complex gut milieu in response to CF transmembrane conductance regulator (CFTR) dysfunction, pancreatic malabsorption, diet, medications, and environmental influences. In several diseases, alteration of the gut microbiota influences local and systemic inflammation and disease outcomes. We conducted a systematic review of the gut microbiota in CF and explored factors influencing dysbiosis.

METHODS

An electronic search of three databases was conducted in January 2019, and re-run in June 2021. Human, animal, and in vitro studies were included. The primary outcome was differences in the gut microbiota between people with CF (pwCF) and healthy controls. Secondary outcomes included the relationship between the gut microbiota and other factors, including diet, medication, inflammation, and pulmonary function in pwCF.

RESULTS

Thirty-eight studies were identified. The literature confirmed the presence of CF-related gut dysbiosis, characterized by reduced diversity and several taxonomic changes. There was a relative increase of bacteria associated with a pro-inflammatory response coupled with a reduction of those considered anti-inflammatory. However, studies linking gut dysbiosis to systemic and lung inflammation were limited. Causes of gut dysbiosis were multifactorial, and findings were variable. Data on the impact of CFTR modulators on the gut microbiota were limited.

CONCLUSIONS

CF-related gut dysbiosis is evident in pwCF. Whether this influences local and systemic disease and is amenable to interventions with diet and drugs, such as CFTR modulators, requires further investigation.

Stimulatory Effect of Lactobacillus Metabolites on Colonic Contractions in Newborn Rats

Microbiota are known to play an important role in gastrointestinal physiology and pathophysiology. Microbiota and their metabolites can affect gut motility, neural regulation and the enteric endocrine systems and immune systems of the gut. The use of fermented/hydrolyzed products may be a promising new avenue for stimulating gastrointestinal motility. The purpose of this study was to investigate the effect of lactobacillus metabolites (PP), produced using a U.S.-patented fermentation method, on rat colon motility in vitro. The distal colon was incised from newborn male Wistar rats. A sensitive tensometric method for the study of colon contractions was used. The [Ca2+]i in colon tissue was registered using a computerized ratiometric system for an intracellular ion content assay (Intracellular Imaging and Photometry System, Intracellular imaging, Inc. Cincinnati, OH, USA). The cumulative addition of PP induced contraction with sigmoid dose responses with ED50 = 0.13 ± 0.02% (n = 4), where 10% PP was accepted as a maximal dose. This contraction was accompanied by an increase in the concentration of [Ca2+]i. It was shown that introducing Lactobacillus metabolites produced using a U.S.-patented fermentation method quickly stimulates dose-dependent colon contractions and an increase in intracellular calcium. The direct application of PP via enema to the colon could stimulate colon motility and suppress pathogenic microbiota, owing to the antagonistic property of PP on pathogens.

Editing of a Specific Strain of Escherichia coli in the Mouse Gut Using Native Phages

There is a lack of methodological investigation of the in situ functions of bacterial species in microecosystems. Here, we used native phages as a microbial editing tool for eliminating Escherichia coli strain MG1655 labeled with green fluorescent protein (GFP) in the mouse gut. The virulent phages (W1 and W3) possessed host specificity at both the genus and species levels, resulting in an 8.8-log10 difference in the titer of viable bacteria after 12 h of phage treatment compared with that in the phage-free control in an in vitro test. In vivo, they reduced strain MG1655 colonizing the mouse gut at concentrations of 106 to 108 CFU g-1 to a 102 CFU g-1 level, which is almost undetectable by the plate colony-counting method. Moreover, the impact of phage treatment on the microbial community structure of the mouse gut was not significant (P > 0.05), indicating that native phages can effectively edit a target bacterium, with limited perturbation of microbial diversity and relative abundance. Therefore, we developed an engineering technique for investigation of the functions of a specific bacterium by depleting its abundance in microecosystems. IMPORTANCE This report describes a gut engineering technique for investigation of the functions of a specific bacterium. Native phages with host specificity can knock down the corresponding E. coli strain in the mouse gut with limited perturbation of microbial diversity and relative abundance, indicating that they, as a microbial editing tool, can effectively edit the abundance of a target bacterium. Such an approach is undoubtedly of interest in the context of lack of knowledge of how to methodologically study the in situ function of a specific species in a complex microecosystem.

The Gut Microbiome and Its Implication in the Mucosal Digestive Disorders

The gastrointestinal (GI) tract is one of the most studied compartments of the human body as it hosts the largest microbial community including trillions of germs. The relationship between the human and its associated flora is complex, as the microbiome plays an important role in nutrition, metabolism and immune function. With a dynamic composition, influenced by many intrinsic and extrinsic factors, there is an equilibrium maintained in the composition of GI microbiota, translated as "eubiosis". Any disruption of the microbiota leads to the development of different local and systemic diseases. This article reviews the human GI microbiome's composition and function in healthy individuals as well as its involvement in the pathogenesis of different digestive disorders. It also highlights the possibility to consider flora manipulation a therapeutic option when treating GI diseases.

Changing Flows Balance Nutrient Absorption and Bacterial Growth along the Gut

Small intestine motility and its ensuing flow of luminal content impact both nutrient absorption and bacterial growth. To explore this interdependence we introduce a biophysical description of intestinal flow and absorption. Rooted in observations of mice we identify the average flow velocity as the key control of absorption efficiency and bacterial growth, independent of the exact contraction pattern. We uncover self-regulation of contraction and flow in response to nutrients and bacterial levels to promote efficient absorption while restraining detrimental bacterial overgrowth.

Crosstalk between the Gut Microbiome and Colonic Motility in Chronic Constipation: Potential Mechanisms and Microbiota Modulation

Chronic constipation (CC) is a highly prevalent and burdensome gastrointestinal disorder. Accumulating evidence highlights the link between imbalances in the gut microbiome and constipation. However, the mechanisms by which the microbiome and microbial metabolites affect gut movement remain poorly understood. In this review, we discuss recent studies on the alteration in the gut microbiota in patients with CC and the effectiveness of probiotics in treating gut motility disorder. We highlight the mechanisms that explain how the gut microbiome and its metabolism are linked to gut movement and how intestinal microecological interventions may counteract these changes based on the enteric nervous system, the central nervous system, the immune function, and the ability to modify intestinal secretion and the hormonal milieu. In particular, microbiota-based approaches that modulate the levels of short-chain fatty acids and tryptophan catabolites or that target the 5-hydroxytryptamine and Toll-like receptor pathways may hold therapeutic promise. Finally, we discuss the existing limitations of microecological management in treating constipation and suggest feasible directions for future research.

Role of gut microbiota-derived signals in the regulation of gastrointestinal motility

The gastrointestinal (GI) tract harbors trillions of commensal microbes, called the gut microbiota, which plays a significant role in the regulation of GI physiology, particularly GI motility. The GI tract expresses an array of receptors, such as toll-like receptors (TLRs), G-protein coupled receptors, aryl hydrocarbon receptor (AhR), and ligand-gated ion channels, that sense different gut microbiota-derived bioactive substances. Specifically, microbial cell wall components and metabolites, including lipopeptides, peptidoglycan, lipopolysaccharides (LPS), bile acids (BAs), short-chain fatty acids (SCFAs), and tryptophan metabolites, mediate the effect of gut microbiota on GI motility through their close interactions with the enteroendocrine system, enteric nervous system, intestinal smooth muscle, and immune system. In turn, GI motility affects the colonization within the gut microbiota. However, the mechanisms by which gut microbiota interacts with GI motility remain to be elucidated. Deciphering the underlying mechanisms is greatly important for the prevention or treatment of GI dysmotility, which is a complication associated with many GI diseases, such as irritable bowel syndrome (IBS) and constipation. In this perspective, we overview the current knowledge on the role of gut microbiota and its metabolites in the regulation of GI motility, highlighting the potential mechanisms, in an attempt to provide valuable clues for the development of gut microbiota-dependent therapy to improve GI motility.