Emerging role of intestinal microbiota and microbial metabolites in metabolic control

Kinetics of imidazole propionate from orally delivered histidine in mice and humans

Imidazole Propionate (ImP), a gut-derived metabolite from histidine, affects insulin signaling in mice and is elevated in type 2 diabetes (T2D). However, the source of histidine and the role of the gut microbiota remain unclear. We conducted an intervention study in mice and humans, comparing ImP kinetics in mice on a high-fat diet with varying histidine levels and antibiotics, and assessed ImP levels in healthy and T2D subjects with histidine supplementation. Results show that dietary histidine is metabolized to ImP, with antibiotic-induced gut microbiota suppression reducing ImP levels in mice. In contrast, oral histidine supplementation resulted in increases in circulating ImP levels in humans, whereas antibiotic treatment increased ImP levels, which was associated with a bloom of several bacterial genera that have been associated with ImP production, such as Lactobacilli. Our findings highlight the gut microbiota's crucial role in regulating ImP and the complexity of translating mouse models to humans.

Celiac Disease and Gut Microbiota: Herbal Treatment and Gluten-Free Diet

Celiac disease (CD) manifests as a targeted autoimmune response that adversely affects the small intestine, primarily affecting individuals with a particular genetic predisposition. Diagnosis centers on identifying this gluten-sensitive enteropathy, which can be ameliorated through the implementation of a gluten-free diet (GFD), correlating with mucosal healing and symptom alleviation. The human microbiota, a vast symbiotic community within the gastrointestinal tract, profoundly impacts human health. Advances in genome sequencing have elucidated the intricate relationship between gut microbiota and autoimmune diseases, including CD, emphasizing the significant role of dietary patterns in shaping the gut microbiota. The influence of GFD on microbiota composition, the only clinically validated treatment for CD, leads to a nutritional shift and potential macronutrient imbalance. Emerging research also highlights the therapeutic potential of various herbs with antioxidant, anti-inflammatory, antimicrobial, gastroprotective, and immunomodulatory properties as complementary approaches to manage CD. This chapter synthesizes the complex interactions between genetics, diet, gut microbiota, and potential herbal interventions in CD, paving the way for more comprehensive understanding and management strategies.

Regulating role of Pleurotus ostreatus insoluble dietary fiber in high fat diet induced obesity in rats based on proteomics and metabolomics analyses

This study aims to reveal the effects of Pleurotus ostreatus insoluble dietary fiber (POIDF) on liver protein and cecal metabolites in obese rats and its potential mechanism by intestinal microbes. It was found that POIDF contained the structural characteristics of cellulose and hemicellulose, as well as amorphous diffraction peaks. POIDF could reduce the body weight and organ index of obese rats, regulate dyslipidemia, and improve the pathological changes of liver and epididymis fat. Further experimental results showed that POIDF could regulate the abundance of bacteria related to lipid metabolism, and maintain intestinal homeostasis. The metabolomics results showed that the fatty acyls pathway in the cecum contents was the pathway with the highest concentration of small molecule metabolites. POIDF supplementation regulated the expression of liver key proteins, as well as biosynthesis of amino acids, steroid biosynthesis, arachidonic acid metabolism and PPAR signaling pathway. Omics association analysis found that POIDF could further regulate liver proteins and their signaling pathways, regulate the levels of fatty acyls and amino acid metabolites in the gut and the enrichment of related pathways, and play a therapeutic or preventive role in obesity after degradation by intestinal microbiota.

Role of the Intestine and Its Gut Microbiota in Metabolic Syndrome and Obesity

The metabolic syndrome (MetSyn) is currently one of the biggest global health challenges because of its impact on public health. MetSyn includes the cluster of metabolic disorders including obesity, high blood pressure, hyperglycemia, high triglyceride levels, and hepatic steatosis. Together, these abnormalities increase the cardiovascular risk of individuals and pose a threat to healthcare systems worldwide. To better understand and address this complex issue, recent research has been increasingly focusing on unraveling the delicate interplay between metabolic disorders and the intestines and more specifically our gut microbiome. The gut microbiome entails all microorganisms inhabiting the gastrointestinal tract and plays a pivotal role in metabolic processes and overall health of its host. Emerging evidence proves an association between the gut microbiome composition and aspects of MetSyn, such as obesity. Understanding these relationships is crucial because they offer valuable insights into the mechanisms underlying development and progression of metabolic disorders and possible treatment options. Yet, how should we interpret this relationship? This review focuses on the interplay between the gut and MetSyn. In addition, we have reviewed the existing evidence of the gut microbiome and its association with and impact on metabolic disorders, in an attempt to understand the complex interactions and nature of this association. We also explored potential therapeutic options targeting the gut to modify metabolic disorders and obesity.

Short-Chain Fatty Acid (SCFA) as a Connecting Link between Microbiota and Gut-Lung Axis-A Potential Therapeutic Intervention to Improve Lung Health

The microbiome is an integral part of the human gut, and it plays a crucial role in the development of the immune system and homeostasis. Apart from the gut microbiome, the airway microbial community also forms a distinct and crucial part of the human microbiota. Furthermore, several studies indicate the existence of communication between the gut microbiome and their metabolites with the lung airways, called "gut-lung axis". Perturbations in gut microbiota composition, termed dysbiosis, can have acute and chronic effects on the pathophysiology of lung diseases. Microbes and their metabolites in lung stimulate various innate immune pathways, which modulate the expression of the inflammatory genes in pulmonary leukocytes. For instance, gut microbiota-derived metabolites such as short-chain fatty acids can suppress lung inflammation through the activation of G protein-coupled receptors (free fatty acid receptors) and can also inhibit histone deacetylase, which in turn influences the severity of acute and chronic respiratory diseases. Thus, modulation of the gut microbiome composition through probiotic/prebiotic usage and fecal microbiota transplantation can lead to alterations in lung homeostasis and immunity. The resulting manipulation of immune cells function through microbiota and their key metabolites paves the way for the development of novel therapeutic strategies in improving the lung health of individuals affected with various lung diseases including SARS-CoV-2. This review will shed light upon the mechanistic aspect of immune system programming through gut and lung microbiota and exploration of the relationship between gut-lung microbiome and also highlight the therapeutic potential of gut microbiota-derived metabolites in the management of respiratory diseases.

Host-gut microbiota interactions during pregnancy

Mammalian pregnancy is characterized by a well-known suite of physiological changes that support fetal growth and development, thereby positively affecting both maternal and offspring fitness. However, mothers also experience trade-offs between current and future maternal reproductive success, and maternal responses to these trade-offs can result in mother-offspring fitness conflicts. Knowledge of the mechanisms through which these trade-offs operate, as well as the contexts in which they operate, is critical for understanding the evolution of reproduction. Historically, hormonal changes during pregnancy have been thought to play a pivotal role in these conflicts since they directly and indirectly influence maternal metabolism, immunity, fetal growth and other aspects of offspring development. However, recent research suggests that gut microbiota may also play an important role. Here, we create a foundation for exploring this role by constructing a mechanistic model linking changes in maternal hormones, immunity and metabolism during pregnancy to changes in the gut microbiota. We posit that marked changes in hormones alter maternal gut microbiome composition and function both directly and indirectly via impacts on the immune system. The gut microbiota then feeds back to influence maternal immunity and metabolism. We posit that these dynamics are likely to be involved in mediating maternal and offspring fitness as well as trade-offs in different aspects of maternal and offspring health and fitness during pregnancy. We also predict that the interactions we describe are likely to vary across populations in response to maternal environments. Moving forward, empirical studies that combine microbial functional data and maternal physiological data with health and fitness outcomes for both mothers and infants will allow us to test the evolutionary and fitness implications of the gestational microbiota, enriching our understanding of the ecology and evolution of reproductive physiology.

Protein supplementation changes gut microbial diversity and derived metabolites in subjects with type 2 diabetes

High-protein diets are promoted for individuals with type 2 diabetes (T2D). However, effects of dietary protein interventions on (gut-derived) metabolites in T2D remains understudied. We therefore performed a multi-center, randomized-controlled, isocaloric protein intervention with 151 participants following either 12-week high-protein (HP; 30Energy %, N = 78) vs. low-protein (LP; 10 Energy%, N = 73) diet. Primary objectives were dietary effects on glycemic control which were determined via glycemic excursions, continuous glucose monitors and HbA1c. Secondary objectives were impact of diet on gut microbiota composition and -derived metabolites which were determined by shotgun-metagenomics and mass spectrometry. Analyses were performed using delta changes adjusting for center, baseline, and kidney function when appropriate. This study found that a short-term 12-week isocaloric protein modulation does not affect glycemic parameters or weight in metformin-treated T2D. However, the HP diet slightly worsened kidney function, increased alpha-diversity, and production of potentially harmful microbiota-dependent metabolites, which may affect host metabolism upon prolonged exposure.

Signalling cognition: the gut microbiota and hypothalamic-pituitary-adrenal axis

Cognitive function in humans depends on the complex and interplay between multiple body systems, including the hypothalamic-pituitary-adrenal (HPA) axis. The gut microbiota, which vastly outnumbers human cells and has a genetic potential that exceeds that of the human genome, plays a crucial role in this interplay. The microbiota-gut-brain (MGB) axis is a bidirectional signalling pathway that operates through neural, endocrine, immune, and metabolic pathways. One of the major neuroendocrine systems responding to stress is the HPA axis which produces glucocorticoids such as cortisol in humans and corticosterone in rodents. Appropriate concentrations of cortisol are essential for normal neurodevelopment and function, as well as cognitive processes such as learning and memory, and studies have shown that microbes modulate the HPA axis throughout life. Stress can significantly impact the MGB axis via the HPA axis and other pathways. Animal research has advanced our understanding of these mechanisms and pathways, leading to a paradigm shift in conceptual thinking about the influence of the microbiota on human health and disease. Preclinical and human trials are currently underway to determine how these animal models translate to humans. In this review article, we summarize the current knowledge of the relationship between the gut microbiota, HPA axis, and cognition, and provide an overview of the main findings and conclusions in this broad field.

The leaky gut and the gut microbiome in sepsis - targets in research and treatment

Both a leaky gut (a barrier defect of the intestinal surface) and gut dysbiosis (a change in the intestinal microbial population) are intrinsic to sepsis. While sepsis itself can cause dysbiosis, dysbiosis can worsen sepsis. The leaky gut syndrome refers to a status with which there is an increased intestinal permeability allowing the translocation of microbial molecules from the gut into the blood circulation. It is not just a symptom of gastrointestinal involvement, but also an underlying cause that develops independently, and its presence could be recognized by the detection, in blood, of lipopolysaccharides and (1→3)-β-D-glucan (major components of gut microbiota). Gut-dysbiosis is the consequence of a reduction in some bacterial species in the gut microbiome, as a consequence of intestinal mucosal immunity defect, caused by intestinal hypoperfusion, immune cell apoptosis, and a variety of enteric neuro-humoral-immunity responses. A reduction in bacteria that produce short-chain fatty acids could change the intestinal barriers, leading to the translocation of pathogen molecules, into the circulation where it causes systemic inflammation. Even gut fungi might be increased in human patients with sepsis, even though this has not been consistently observed in murine models of sepsis, probably because of the longer duration of sepsis and also antibiotic use in patients. The gut virobiome that partly consists of bacteriophages is also detectable in gut contents that might be different between sepsis and normal hosts. These alterations of gut dysbiosis altogether could be an interesting target for sepsis adjuvant therapies, e.g., by faecal transplantation or probiotic therapy. Here, current information on leaky gut and gut dysbiosis along with the potential biomarkers, new treatment strategies, and future research topics are mentioned.

Wholegrain fermentation affects gut microbiota composition, phenolic acid metabolism and pancreatic beta cell function in a rodent model of type 2 diabetes

The intestinal microbiota plays an important role in host metabolism via production of dietary metabolites. Microbiota imbalances are linked to type 2 diabetes (T2D), but dietary modification of the microbiota may promote glycemic control. Using a rodent model of T2D and an in vitro gut model system, this study investigated whether differences in gut microbiota between control mice and mice fed a high-fat, high-fructose (HFHFr) diet influenced the production of phenolic acid metabolites following fermentation of wholegrain (WW) and control wheat (CW). In addition, the study assessed whether changes in metabolite profiles affected pancreatic beta cell function. Fecal samples from control or HFHFr-fed mice were fermented in vitro with 0.1% (w/v) WW or CW for 0, 6, and 24 h. Microbiota composition was determined by bacterial 16S rRNA sequencing and phenolic acid (PA) profiles by UPLC-MS/MS. Cell viability, apoptosis and insulin release from pancreatic MIN6 beta cells and primary mouse islets were assessed in response to fermentation supernatants and selected PAs. HFHFr mice exhibited an overall dysbiotic microbiota with an increase in abundance of proteobacterial taxa (particularly Oxalobacteraceae) and Lachnospiraceae, and a decrease in Lactobacillus. A trend toward restoration of diversity and compositional reorganization was observed following WW fermentation at 6 h, although after 24 h, the HFHFr microbiota was monodominated by Cupriavidus. In parallel, the PA profile was significantly altered in the HFHFr group compared to controls with decreased levels of 3-OH-benzoic acid, 4-OH-benzoic acid, isoferulic acid and ferulic acid at 6 h of WW fermentation. In pancreatic beta cells, exposure to pre-fermentation supernatants led to inhibition of insulin release, which was reversed over fermentation time. We conclude that HFHFr mice as a model of T2D are characterized by a dysbiotic microbiota, which is modulated by the in vitro fermentation of WW. The differences in microbiota composition have implications for PA profile dynamics and for the secretory capacity of pancreatic beta cells.

Monitoring of inflammation using novel biosensor mouse model reveals tissue- and sex-specific responses to Western diet

Obesity is an epidemic, and it is characterized by a state of low-grade systemic inflammation. A key component of inflammation is the activation of inflammasomes, multiprotein complexes that form in response to danger signals and that lead to activation of caspase-1. Previous studies have found that a Westernized diet induces activation of inflammasomes and production of inflammatory cytokines. Gut microbiota metabolites, including the short-chain fatty acid butyrate, have received increased attention as underlying some obesogenic features, but the mechanisms of action by which butyrate influences inflammation in obesity remain unclear. We engineered a caspase-1 reporter mouse model to measure spatiotemporal dynamics of inflammation in obese mice. Concurrent with increased capsase-1 activation in vivo, we detected stronger biosensor signal in white adipose and heart tissues of obese mice ex vivo and observed that a short-term butyrate treatment affected some, but not all, of the inflammatory responses induced by Western diet. Through characterization of inflammatory responses and computational analyses, we identified tissue- and sex-specific caspase-1 activation patterns and inflammatory phenotypes in obese mice, offering new mechanistic insights underlying the dynamics of inflammation.

Comparison of the gut microbiome composition among individuals with acute or long-standing spinal cord injury vs. able-bodied controls

Objective: Compare the gut microbiome composition among individuals with acute spinal cord injury (A-SCI), long-standing SCI (L-SCI), vs. able-bodied (AB) controls.Design: Cross-sectional study.Setting: The University of Alabama at Birmingham.Participants: Seven adults with A-SCI (36 ± 12 years, 2F/5M, C4-T10, and American Spinal Injury Association Impairment Scale [AIS] A-D), 25 with L-SCI (46 ± 13 years, 6F/19M, C4-L1, and AIS A-D), and 25 AB controls (42 ± 13 years, 9F/16M).Methods: Stool samples were collected after a median of 7 days and 18 years after injury in the A-SCI and L-SCI groups, respectively. Gut microbiome composition was analyzed using the 16S rRNA sequencing technique and QIIME software. The abundances of bacteria communities among groups were compared using the Kruskal-Wallis test adjusted for age.Results: Several alpha diversity indices were different among groups (Chao1, Observed species, and Phylogenetic Diversity), but not others (Shannon and Simpson). Beta diversity differed among each pair of groups (P < 0.05). A number of microbial communities were differentially abundant among the groups (P < 0.05).Conclusion: Our results revealed differences in the gut microbiome composition among groups. Compared to the AB controls, the SCI groups demonstrated microbiome profiles that shared features linked to metabolic syndrome, inflammation-related bowel disorders, depressive disorders, or antibiotics use, whereas the L-SCI group's microbiome included features linked to reduced physical activity compared to the A-SCI and AB controls. Our results provided preliminary data and a scientific foundation for future studies investigating the impact of the gut microbiome composition on long-term health in individuals with SCI.

Extracellular vesicles and pasteurized cells derived from Akkermansia muciniphila protect against high-fat induced obesity in mice

Background

Several studies have shown that probiotics have beneficial effects on weight control and metabolic health. In addition to probiotics, recent studies have investigated the effects of paraprobiotics and postbiotics. Therefore, we evaluated the preventive effects of live and pasteurized Akkermansia muciniphila MucT (A. muciniphila) and its extracellular vesicles (EVs) on HFD-induced obesity.

Results

The results showed that body weight, metabolic tissues weight, food consumption, and plasma metabolic parameters were increased in the HFD group, whereas A. muciniphila preventive treatments inhibited these HFD. The effects of pasteurized A. muciniphila and its extracellular vesicles were more noticeable than its active form. The HFD led to an increase in the colonic, adipose tissue, and liver inflammations and increased the expression of genes involved in lipid metabolism and homeostasis. Nevertheless, these effects were inhibited in mice that were administered A. muciniphila and its EVs. The assessment of the gut microbiota revealed significant differences in the microbiota composition after feeding with HFD. However, all treatments restored the alterations in some bacterial genera and closely resemble the control group. Also, the correlation analysis indicated that some gut microbiota might be associated with obesity-related indices.

Conclusions

Pasteurized A. muciniphila and its EVs, as paraprobiotic and postbiotic agents, were found to play a key role in the regulation of metabolic functions to prevent obesity, probably by affecting the gut-adipose-liver axis.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-021-01709-w.

Involvement of Probiotics and Postbiotics in the Immune System Modulation

Intestinal microbiota interacts with other systems, especially the immune system, which is responsible for protecting the body by recognizing “stranger” (pathogen associated molecular patterns-PAMPs) and “danger” (damage-associated molecular patterns-DAMPs) molecular motifs. In this manner, it plays an important role in the pathogenesis of various diseases and health. Despite the use of probiotics that modulate the intestinal microbiota in providing health benefits and in the treatment of diseases, there are some possible concerns about the possibility of developing adverse effects, especially in people with suppressed immune systems. Since probiotics provide health benefits with bioactive compounds, studies are carried out on the use of products containing non-living probiotic microorganisms (paraprobiotics) and/or their metabolites (postbiotics) instead of probiotic products. It is even reported that these microbial compounds have more immunomodulatory activities than living microorganisms via some possible mechanism and eliminates some disadvantages of probiotics. Considering the increasing use of functional foods in health and disease, further studies are needed with respect to the benefits and advantages of parabiotic and/or postbiotic use in the food and pharmaceutical industry as well as immune system modulation. Although probiotics have been extensive studied for a long time, it seems that postbiotics are promising tools for future research and applications according to the recent literature. This review aimed to evaluate the interaction of probiotics and postbiotics with the immune systems and also their advantages and disadvantages in the area of food-pharmaceutical industry and immune system modulation.

Gut microbiome composition and serum metabolome profile among individuals with spinal cord injury and normal glucose tolerance or prediabetes/type 2 diabetes

OBJECTIVE

To compare the gut microbiome composition and serum metabolome profile among individuals with spinal cord injury (SCI) and normal glucose tolerance (NGT) or prediabetes/type 2 diabetes (P/DM).

DESIGN

Cross-sectional design.

SETTING

Research university.

PARTICIPANTS

A total of 25 adults with SCI were included in the analysis and categorized as NGT (n=16) or P/DM (n=9) based on their glucose concentration at minute 120 during a 75-g oral glucose tolerance test. The American Diabetes Association diagnosis guideline was used for grouping participants.

INTERVENTIONS

Not applicable.

MAIN OUTCOME MEASURE(S)

A stool sample was collected and used to assess the gut microbiome composition (alpha and beta diversity, microbial abundance) via the 16s rRNA sequencing technique. A fasting serum sample was used for liquid chromatography-mass spectrometry-based untargeted metabolomics analysis, the results from which reflect the relative quantity of metabolites detected and identified. Gut microbiome and metabolomics data were analyzed by the Quantitative Insights into Microbial Ecology 2 and Metaboanalyst platforms, respectively.

RESULTS

Gut microbiome alpha diversity (Pielou's evenness index, Shannon's index) and beta diversity (weighted UniFrac distances) differed between groups. Compared with participants with NGT, participants with P/DM had less evenness in microbial communities. In particular, those with P/DM had a lower abundance of the Clostridiales order and higher abundance of the Akkermansia genus, as well as higher serum levels of gut-derived metabolites, including indoxyl sulfate and phenylacetylglutamine (P < 0.05 for all).

CONCLUSION(S)

Our results provide evidence for altered gut microbiome composition and dysregulation of gut-derived metabolites in participants with SCI and P/DM. Both indoxyl sulfate and phenylacetylglutamine have been implicated in the development of cardiovascular diseases in the able-bodied population. These findings may inform future investigations in the field of SCI and cardio-metabolic health.

Unravelling the potential of gut microbiota in sustaining brain health and their current prospective towards development of neurotherapeutics

Increasing incidences of neurological disorders, such as Parkinson's disease (PD), multiple sclerosis (MS), Alzheimer's disease (AD) and amyotrophic lateral sclerosis (ALS) are being reported, but an insight into their pathology remains elusive. Findings have suggested that gut microbiota play a major role in regulating brain functions through the gut-brain axis. A unique bidirectional communication between gut microbiota and maintenance of brain health could play a pivotal role in regulating incidences of neurodegenerative diseases. Contrarily, the present life style with changing food habits and disturbed circadian rhythm may contribute to gut homeostatic imbalance and dysbiosis leading to progression of several neurological disorders. Therefore, dysbiosis, as a primary factor behind intestinal disorders, may also augment inflammation, intestinal and blood-brain barrier permeability through microbiota-gut-brain axis. This review primarily focuses on the gut-brain axis functions, specific gut microbial population, metabolites produced by gut microbiota, their role in regulating various metabolic processes and role of gut microbiota towards development of neurodegenerative diseases. However, several studies have reported a decrease in abundance of a specific gut microbial population and a corresponding increase in other microbial family, with few findings revealing some contradictions. Reports also showed that colonization of gut microbiota isolated from patients suffering from neurodegenerative disease leads to the development of enhance pathological outcomes in animal models. Hence, a systematic understanding of the dominant role of specific gut microbiome towards development of different neurodegenerative diseases could possibly provide novel insight into the use of probiotics and microbial transplantation as a substitute approach for treating/preventing such health maladies.

Fecal transplantation and butyrate improve neuropathic pain, modify immune cell profile, and gene expression in the PNS of obese mice

Obesity affects over 2 billion people worldwide and is accompanied by peripheral neuropathy (PN) and an associated poorer quality of life. Despite high prevalence, the molecular mechanisms underlying the painful manifestations of PN are poorly understood, and therapies are restricted to use of painkillers or other drugs that do not address the underlying disease. Studies have demonstrated that the gut microbiome is linked to metabolic health and its alteration is associated with many diseases, including obesity. Pathologic changes to the gut microbiome have recently been linked to somatosensory pain, but any relationships between gut microbiome and PN in obesity have yet to be explored. Our data show that mice fed a Western diet developed indices of PN that were attenuated by concurrent fecal microbiome transplantation (FMT). In addition, we observed changes in expression of genes involved in lipid metabolism and calcium handling in cells of the peripheral nerve system (PNS). FMT also induced changes in the immune cell populations of the PNS. There was a correlation between an increase in the circulating short-chain fatty acid butyrate and pain improvement following FMT. Additionally, butyrate modulated gene expression and immune cells in the PNS. Circulating butyrate was also negatively correlated with distal pain in 29 participants with varied body mass index. Our data suggest that the metabolite butyrate, secreted by the gut microbiome, underlies some of the effects of FMT. Targeting the gut microbiome, butyrate, and its consequences may represent novel viable approaches to prevent or relieve obesity-associated neuropathies.

Fecal microbiota transplantation alters the susceptibility of obese rats to type 2 diabetes mellitus

Obesity is one of the susceptibility factors for type 2 diabetes (T2DM), both of which could accelerate the aging of the body and bring many hazards. A causal relationship is present between intestinal microbiota and body metabolism, but how the microbiota play a role in the progression of obesity to T2DM has not been elucidated. In this study, we transplanted healthy or obese-T2DM intestinal microbiota to ZDF and LZ rats, and used 16S rRNA and targeted metabonomics to evaluate the directional effect of the microbiota on the susceptibility of obese rats to T2DM. The glycolipid metabolism phenotype could be changed bidirectionally in obese rats instead of in lean ones. One possible mechanism is that the microbiota and metabolites alter the structure of the intestinal tract, and improve insulin and leptin resistance through JAK2 / IRS / Akt pathway. It is worth noting that 7 genera, such as Lactobacillus, Clostridium and Roche, can regulate 15 metabolites, such as 3-indolpropionic acid, acetic acid and docosahexaenoic acid, and have a significant improvement on glycolipid metabolism phenotype. Attention to intestinal homeostasis may be the key to controlling obesity and preventing T2DM.

Revealing links between gut microbiome and its fungal community in Type 2 Diabetes Mellitus among Emirati subjects: A pilot study

Type 2 diabetes mellitus (T2DM) drastically affects the population of Middle East countries with an ever-increasing number of overweight and obese individuals. The precise links between T2DM and gut microbiome composition remain elusive in these populations. Here, we performed 16 S rRNA and ITS2- gene based microbial profiling of 50 stool samples from Emirati adults with or without T2DM. The four major enterotypes initially described in westernized cohorts were retrieved in this Emirati population. T2DM and non-T2DM healthy controls had different microbiome compositions, with an enrichment in Prevotella enterotype in non-T2DM controls whereas T2DM individuals had a higher proportion of the dysbiotic Bacteroides 2 enterotype. No significant differences in microbial diversity were observed in T2DM individuals after controlling for cofounding factors, contrasting with reports from westernized cohorts. Interestingly, fungal diversity was significantly decreased in Bacteroides 2 enterotype. Functional profiling from 16 S rRNA gene data showed marked differences between T2DM and non-T2DM controls, with an enrichment in amino acid degradation and LPS-related modules in T2DM individuals, whereas non-T2DM controls had increased abundance of carbohydrate degradation modules in concordance with enterotype composition. These differences provide an insight into gut microbiome composition in Emirati population and its potential role in the development of diabetes mellitus.

A Uniquely Altered Oral Microbiome Composition Was Observed in Pregnant Rats With Porphyromonas gingivalis Induced Periodontal Disease

Porphyromonas gingivalis is an anaerobic bacterium commonly found in the oral cavity and associated with the development of periodontal disease. P. gingivalis has also been linked to several systemic vascular and inflammatory diseases including poor pregnancy outcomes. Little is known about the changes in the oral flora during pregnancy in connection to P. gingivalis infection. This pilot study aims to explore changes in the oral microbiome due to P. gingivalis inoculation and pregnancy in an in vivo rat model of periodontal disease. A metagenomic sequencing analysis targeting seven of the 16S rRNA gene variable regions was performed for oral samples collected at the following time points: baseline control (week 0), P. gingivalis inoculated (week 11), P. gingivalis inoculated and pregnant rat at necropsy (week 16). A second set of animals were also sampled to generate a sham-inoculated (week 11) control group. We found that the rat oral microbiome profiles were more similar to that of the human oral cavity compared to previous reports targeting one or two 16S variable regions. Overall, there appears to be a relatively stable core microbiome in the oral cavity. As expected, P. gingivalis induced periodontal disease resulted in oral microbiome dysbiosis. During pregnancy, some aspects of the oral microbiome shifted toward a more baseline-like profile. However, population analyses in terms of dissimilarity measures and especially metagenomic based predictions of select characteristics such as cell morphology, oxygen requirement, and major metabolite synthesis showed that pregnancy did not restore the composition of the oral microbiome. Rather, a uniquely altered oral microbiome composition was observed in pregnant rats with pre-established periodontal disease.

Response of gut microbiota in type 2 diabetes to hypoglycemic agents

PURPOSE

Accumulated evidence has indicated that the gut microbiome affected the pharmacology of anti-diabetic agents, and their metabolic products induced by the agents transformed the structure of gastrointestinal microbiota in return. However, the studies around heredity, ethnicity, or living condition, referring to human microbiome were mostly represented by an occidental pattern partial and rare studies that focused on the effect of several first-line hypoglycemic agents on the gut flora in a single medical center. Therefore, we aimed to explore the interaction between gut microbiome and type 2 diabetes (T2D) or hypoglycemics in Chinese population.

METHODS

A total of 130 T2D patients with a specific hypoglycemic treatment and 50 healthy volunteers were enrolled in this study. Gut microbiome compositons were analyzed by 16S ribosomal RNA gene-based sequencing protocol.

RESULTS

Hypoglycemic agents contributed to the alteration of specific species in gut bacteria rather than its total diversity. Metformin increased the abundance of Spirochaete, Turicibacter, and Fusobacterium. Insulin also increased Fusobacterium, and α-glucosidase inhibitors (α-GIs) contributed to the plentitude of Bifidobacterium and Lactobacillus. Both metformin and insulin improved taurine and hypotaurine metabolism, and α-GI promoted several amino acid pathways. Although the community of gut microbiota with metformin and insulin showed similarity, significant differences were available in each diabetic group with hypoglycemia.

CONCLUSIONS

Gut microbiota is significantly associated with anti-diabetic agents. The gut microbiome and metabolism have shown respective characteristics in different T2D groups, which were also significantly different from the healthy group. This study provides some new insights for identification and exploration of the pathogenesis of T2D.

Structured exercise alters the gut microbiota in humans with overweight and obesity-A randomized controlled trial

OBJECTIVES

Studies suggest that exercise affects the composition and function of the human gut microbiota, yet this has not been investigated in a randomized controlled trial. The primary aim of this study was to assess if exercise alters the diversity, composition and functional potential of the gut microbiota in free-living humans. A secondary aim was to test whether alpha diversity was associated with phenotypical outcomes.

METHODS

Eighty eight participants with overweight or obesity completed a 6-month randomized controlled trial with 4 arms; habitual living (CON), active commuting by bike (BIKE) and leisure-time exercise of moderate (MOD) or vigorous intensity (VIG). Faecal samples for 16 s rRNA gene amplicon sequencing were collected prior to randomization and again after 3 and 6 months, with simultaneous registration of phenotypical outcomes and diet.

RESULTS

Shannon's diversity index increased by 5% in VIG (CI95 1-9%, P = 0.012) at 3 months compared with CON. No associations were observed between alpha diversity and phenotypical outcomes. Beta diversity changed in all exercise groups compared with CON, particularly the participants in VIG showed decreased heterogeneity. No genera changed significantly. The inferred functional potential of the microbiota in the exercise groups was increased, primarily at 3 months and in MOD.

CONCLUSION

Structured exercise induced subtle changes to the human gut microbiota. Cardiorespiratory fitness and fat mass were not associated with alpha diversity.

Genetic determinants of gut microbiota composition and bile acid profiles in mice

The microbial communities that inhabit the distal gut of humans and other mammals exhibit large inter-individual variation. While host genetics is a known factor that influences gut microbiota composition, the mechanisms underlying this variation remain largely unknown. Bile acids (BAs) are hormones that are produced by the host and chemically modified by gut bacteria. BAs serve as environmental cues and nutrients to microbes, but they can also have antibacterial effects. We hypothesized that host genetic variation in BA metabolism and homeostasis influence gut microbiota composition. To address this, we used the Diversity Outbred (DO) stock, a population of genetically distinct mice derived from eight founder strains. We characterized the fecal microbiota composition and plasma and cecal BA profiles from 400 DO mice maintained on a high-fat high-sucrose diet for ~22 weeks. Using quantitative trait locus (QTL) analysis, we identified several genomic regions associated with variations in both bacterial and BA profiles. Notably, we found overlapping QTL for Turicibacter sp. and plasma cholic acid, which mapped to a locus containing the gene for the ileal bile acid transporter, Slc10a2. Mediation analysis and subsequent follow-up validation experiments suggest that differences in Slc10a2 gene expression associated with the different strains influences levels of both traits and revealed novel interactions between Turicibacter and BAs. This work illustrates how systems genetics can be utilized to generate testable hypotheses and provide insight into host-microbe interactions.

Non-targeted metabolomic biomarkers and metabotypes of type 2 diabetes: A cross-sectional study of PREDIMED trial participants

AIM

To characterize the urinary metabolomic fingerprint and multi-metabolite signature associated with type 2 diabetes (T2D), and to classify the population into metabotypes related to T2D.

METHODS

A metabolomics analysis using the 1H-NMR-based, non-targeted metabolomic approach was conducted to determine the urinary metabolomic fingerprint of T2D compared with non-T2D participants in the PREDIMED trial. The discriminant metabolite fingerprint was subjected to logistic regression analysis and ROC analyses to establish and to assess the multi-metabolite signature of T2D prevalence, respectively. Metabotypes associated with T2D were identified using the k-means algorithm.

RESULTS

A total of 33 metabolites were significantly different (P<0.05) between T2D and non-T2D participants. The multi-metabolite signature of T2D comprised high levels of methylsuccinate, alanine, dimethylglycine and guanidoacetate, and reduced levels of glutamine, methylguanidine, 3-hydroxymandelate and hippurate, and had a 96.4% AUC, which was higher than the metabolites on their own and glucose. Amino-acid and carbohydrate metabolism were the main metabolic alterations in T2D, and various metabotypes were identified in the studied population. Among T2D participants, those with a metabotype of higher levels of phenylalanine, phenylacetylglutamine, p-cresol and acetoacetate had significantly higher levels of plasma glucose.

CONCLUSION

The multi-metabolite signature of T2D highlights the altered metabolic fingerprint associated mainly with amino-acid, carbohydrate and microbiota metabolism. Metabotypes identified in this patient population could be related to higher risk of long-term cardiovascular events and therefore require further studies. Metabolomics is a useful tool for elucidating the metabolic complexity and interindividual variation in T2D towards the development of stratified precision nutrition and medicine. Trial registration at www.controlled-trials.com: ISRCTN35739639.

Diabesity and mood disorders: Multiple links through the microbiota-gut-brain axis

The global prevalence of diabesity is on the rise, and the clinical, social and economic health burden arising from this epidemic is aggravated by a significant co-morbidity of diabesity with neuropsychiatric disease, particularly depression. Importantly, not only is the prevalence of mood disorders elevated in patients with type 2 diabetes, depressed patients are also more prone to develop diabetes. This reciprocal relationship calls for a molecular and systemic analysis of diabesity-brain interactions to guide preventive and therapeutic strategies. The analysis we are presenting in this review is modelled on the microbiota-gut-brain axis, which provides the brain with information from the gut not only via the nervous system, but also via a continuous stream of microbial, endocrine, metabolic and immune messages. This communication network offers important clues as to how obesity and diabetes could target the brain to provoke neuropsychiatric disease. There is emerging evidence that the gut microbiota is orchestrating a multiplicity of bodily functions that are intimately related to the immune, metabolic and nervous systems and that gut dysbiosis spoils the homeostasis between these systems. In our article we highlight two groups of molecular links that seem to have a significant bearing on the impact of diabesity on the brain. On the one hand, we focus on microbiota-related metabolites such as short-chain fatty acids, tryptophan metabolites, immune stimulants and endocannabinoids that are likely to play a mediator role. On the other hand, we discuss signalling molecules that operate primarily in the brain, specifically neuropeptide Y, brain-derived neurotrophic factor and γ-amino butyric acid, that are disturbed by microbial factors, obesity and diabetes and are relevant to mental illness. Finally, we address the usefulness of diet-related interventions to suspend the deleterious relationship between diabesity and mood disorders.

Gut metabolome meets microbiome: A methodological perspective to understand the relationship between host and microbe

It is well established that gut microbes and their metabolic products regulate host metabolism. The interactions between the host and its gut microbiota are highly dynamic and complex. In this review we present and discuss the metabolomic strategies to study the gut microbial ecosystem. We highlight the metabolic profiling approaches to study faecal samples aimed at deciphering the metabolic product derived from gut microbiota. We also discuss how metabolomics data can be integrated with metagenomics data derived from gut microbiota and how such approaches may lead to better understanding of the microbial functions. Finally, the emerging approaches of genome-scale metabolic modelling to study microbial co-metabolism and host-microbe interactions are highlighted.

Evaluating Causality of Gut Microbiota in Obesity and Diabetes in Humans

The pathophysiology of obesity and obesity-related diseases such as type 2 diabetes mellitus (T2DM) is complex and driven by many factors. One of the most recently identified factors in development of these metabolic pathologies is the gut microbiota. The introduction of affordable, high-throughput sequencing technologies has substantially expanded our understanding of the role of the gut microbiome in modulation of host metabolism and (cardio)metabolic disease development. Nevertheless, evidence for a role of the gut microbiome as a causal, driving factor in disease development mainly originates from studies in mouse models: data showing causality in humans are scarce. In this review, we will discuss the quality of evidence supporting a causal role for the gut microbiome in the development of obesity and diabetes, in particular T2DM, in humans. Considering overlap in potential mechanisms, the role of the gut microbiome in type 1 diabetes mellitus will also be addressed. We will elaborate on factors that drive microbiome composition in humans and discuss how alterations in microbial composition or microbial metabolite production contribute to disease development. Challenging aspects in determining causality in humans will be postulated together with strategies that might hold potential to overcome these challenges. Furthermore, we will discuss means to modify gut microbiome composition in humans to help establish causality and discuss systems biology approaches that might hold the key to unravelling the role of the gut microbiome in obesity and T2DM.

Extracellular Vesicles in Metabolic Syndrome

Metabolic syndrome defines a cluster of interrelated risk factors for cardiovascular disease and diabetes mellitus. These factors include metabolic abnormalities, such as hyperglycemia, elevated triglyceride levels, low high-density lipoprotein cholesterol levels, high blood pressure, and obesity, mainly central adiposity. In this context, extracellular vesicles (EVs) may represent novel effectors that might help to elucidate disease-specific pathways in metabolic disease. Indeed, EVs (a terminology that encompasses microparticles, exosomes, and apoptotic bodies) are emerging as a novel mean of cell-to-cell communication in physiology and pathology because they represent a new way to convey fundamental information between cells. These microstructures contain proteins, lipids, and genetic information able to modify the phenotype and function of the target cells. EVs carry specific markers of the cell of origin that make possible monitoring their fluctuations in the circulation as potential biomarkers inasmuch their circulating levels are increased in metabolic syndrome patients. Because of the mixed components of EVs, the content or the number of EVs derived from distinct cells of origin, the mode of cell stimulation, and the ensuing mechanisms for their production, it is difficult to attribute specific functions as drivers or biomarkers of diseases. This review reports recent data of EVs from different origins, including endothelial, smooth muscle cells, macrophages, hepatocytes, adipocytes, skeletal muscle, and finally, those from microbiota as bioeffectors of message, leading to metabolic syndrome. Depicting the complexity of the mechanisms involved in their functions reinforce the hypothesis that EVs are valid biomarkers, and they represent targets that can be harnessed for innovative therapeutic approaches.