Short chain fatty acids and methylamines produced by gut microbiota as mediators and markers in the circulatory system

Bringing gut microbiota into the spotlight of clinical research and medical practice

Despite the increasing scientific interest and expanding role of gut microbiota (GM) in human health, it is rarely reported in case reports and deployed in clinical practice. Proteins and metabolites produced by microbiota contribute to immune system development, energy homeostasis and digestion. Exo- and endogenous factors can alter its composition. Disturbance of microbiota, also known as dysbiosis, is associated with various pathological conditions. Specific bacterial taxa and related metabolites are involved in disease pathogenesis and therefore can serve as a diagnostic tool. GM could also be a useful prognostic factor by predicting future disease onset and preventing hospital-associated infections. Additionally, it can influence response to treatments, including those for cancers, by altering drug bioavailability. A thorough understanding of its function has permitted significant development in therapeutics, such as probiotics and fecal transplantation. Hence, GM should be considered as a ground-breaking biological parameter, and it is advisable to be investigated and reported in literature in a more consistent and systematic way.

Gut microbiota dependant trimethylamine N-oxide and hypertension

The human gut microbiota environment is constantly changing and some specific changes influence the host's metabolic, immune, and neuroendocrine functions. Emerging evidence of the gut microbiota's role in the development of cardiovascular disease (CVD) including hypertension is remarkable. There is evidence showing that alterations in the gut microbiota and especially the gut-dependant metabolite trimethylamine N-oxide is associated with hypertension. However, there is a scarcity of literature addressing the role of trimethylamine N-oxide in hypertension pathogenesis. In this review, we discuss the impact of the gut microbiota and gut microbiota dependant trimethylamine N-oxide in the pathogenesis of hypertension. We present evidence from both human and animal studies and further discuss new insights relating to potential therapies for managing hypertension by altering the gut microbiota.

Metabolite interactions between host and microbiota during health and disease: Which feeds the other?

Metabolites produced by the host and microbiota play a crucial role in how human bodies develop and remain healthy. Most of these metabolites are produced by microbiota and hosts in the digestive tract. Metabolites in the gut have important roles in energy metabolism, cellular communication, and host immunity, among other physiological activities. Although numerous host metabolites, such as free fatty acids, amino acids, and vitamins, are found in the intestine, metabolites generated by gut microbiota are equally vital for intestinal homeostasis. Furthermore, microbiota in the gut is the sole source of some metabolites, including short-chain fatty acids (SCFAs). Metabolites produced by microbiota, such as neurotransmitters and hormones, may modulate and significantly affect host metabolism. The gut microbiota is becoming recognized as a second endocrine system. A variety of chronic inflammatory disorders have been linked to aberrant host-microbiota interplays, but the precise mechanisms underpinning these disturbances and how they might lead to diseases remain to be fully elucidated. Microbiome-modulated metabolites are promising targets for new drug discovery due to their endocrine function in various complex disorders. In humans, metabolotherapy for the prevention or treatment of various disorders will be possible if we better understand the metabolic preferences of bacteria and the host in specific tissues and organs. Better disease treatments may be possible with the help of novel complementary therapies that target host or bacterial metabolism. The metabolites, their physiological consequences, and functional mechanisms of the host-microbiota interplays will be highlighted, summarized, and discussed in this overview.

Methyl-Based Methanogenesis: an Ecological and Genomic Review

Methyl-based methanogenesis is one of three broad categories of archaeal anaerobic methanogenesis, including both the methyl dismutation (methylotrophic) pathway and the methyl-reducing (also known as hydrogen-dependent methylotrophic) pathway. Methyl-based methanogenesis is increasingly recognized as an important source of methane in a variety of environments. Here, we provide an overview of methyl-based methanogenesis research, including the conditions under which methyl-based methanogenesis can be a dominant source of methane emissions, experimental methods for distinguishing different pathways of methane production, molecular details of the biochemical pathways involved, and the genes and organisms involved in these processes. We also identify the current gaps in knowledge and present a genomic and metagenomic survey of methyl-based methanogenesis genes, highlighting the diversity of methyl-based methanogens at multiple taxonomic levels and the widespread distribution of known methyl-based methanogenesis genes and families across different environments.

Small molecule metabolites: discovery of biomarkers and therapeutic targets

Metabolic abnormalities lead to the dysfunction of metabolic pathways and metabolite accumulation or deficiency which is well-recognized hallmarks of diseases. Metabolite signatures that have close proximity to subject's phenotypic informative dimension, are useful for predicting diagnosis and prognosis of diseases as well as monitoring treatments. The lack of early biomarkers could lead to poor diagnosis and serious outcomes. Therefore, noninvasive diagnosis and monitoring methods with high specificity and selectivity are desperately needed. Small molecule metabolites-based metabolomics has become a specialized tool for metabolic biomarker and pathway analysis, for revealing possible mechanisms of human various diseases and deciphering therapeutic potentials. It could help identify functional biomarkers related to phenotypic variation and delineate biochemical pathways changes as early indicators of pathological dysfunction and damage prior to disease development. Recently, scientists have established a large number of metabolic profiles to reveal the underlying mechanisms and metabolic networks for therapeutic target exploration in biomedicine. This review summarized the metabolic analysis on the potential value of small-molecule candidate metabolites as biomarkers with clinical events, which may lead to better diagnosis, prognosis, drug screening and treatment. We also discuss challenges that need to be addressed to fuel the next wave of breakthroughs.

Nutritional implications in the mechanistic link between the intestinal microbiome, renin-angiotensin system, and the development of obesity and metabolic syndrome

Obesity and metabolic disorders represent a significant global health problem and the gut microbiota plays an important role in modulating systemic homeostasis. Recent evidence shows that microbiota and its signaling pathways may affect the whole metabolism and the Renin-Angiotensin System (RAS), which in turn seems to modify microbiota. The present review aimed to investigate nutritional implications in the mechanistic link between the intestinal microbiome, renin-angiotensin system, and the development of obesity and metabolic syndrome components. A description of metabolic changes was obtained based on relevant scientific literature. The molecular and physiological mechanisms that impact the human microbiome were addressed, including the gut microbiota associated with obesity, diabetes, and hepatic steatosis. The RAS interaction signaling and modulation were analyzed. Strategies including the use of prebiotics, symbiotics, probiotics, and biotechnology may affect the gut microbiota and its impact on human health.

Disruption of the lung-gut-brain axis is responsible for cortex damage induced by pulmonary exposure to zinc oxide nanoparticles

Increasing evidence shows that gut microbiota is important for host health in response to metal nanomaterials exposure. However, the effect of gut microbiota on the cortex damage caused by pulmonary exposure to zinc oxide nanoparticles (ZnONPs) remains mainly unknown. In this study, a total of 48 adult C57BL/6J mice were intratracheally instilled with 0.6 mg/kg ZnONPs in the presence or absence of antibiotics (ABX) treatment. Besides, 24 mice were treated with or without fecal microbiota transplantation (FMT) after the intraperitoneal administration of ABX. Our results demonstrated for the first time that dysbiosis induced by ABX treatment significantly aggravated cortex damage induced by pulmonary exposure to ZnONPs. Such damage might highly occur through the induction of oxidative stress, manifested by the enhancement of antioxidative enzymes and products of lipid peroxidation. However, ferroptosis was not involved in this process. Interestingly, our data revealed that ABX treatment exacerbated the alterations of gut-brain peptides (including Sst, Sstr2, and Htr4) induced by ZnONPs in both gut and cortex tissues. Moreover, fecal microbiota transplantation (FMT) was able to alleviate cerebral cortex damage, oxidative stress, and alterations of gut-brain peptides induced by pulmonary exposure to ZnONPs. The results together indicate that pulmonary exposure to ZnONPs causes cerebral cortex damage possibly via the disruption of the lung-gut-brain axis. These findings not only propose valuable insights into the mechanism of ZnONPs neurotoxicity but also provide a potential therapeutic method against brain disorders induced by pulmonary exposure to ZnONPs. AVAILABILITY OF DATA AND MATERIALS: The datasets used and/or analyzed during the current study are available from the The corresponding author on reasonable request.

The lipid-lowering effects of fenugreek gum, hawthorn pectin, and burdock inulin

Objective

The present study aimed to investigate the lipid-lowering effects and mechanisms of fenugreek gum (FG), hawthorn pectin (HP), and burdock inulin (BI) on high-fat diet (HFD)-induced hyperlipidemic rats.

Methods

In this study, high-fat diet (HFD) together with fat emulsion administration were used to establish hyperlipidemia model. The biochemical indices were assayed after administration of FG, HP, and BI. Their effects were evaluated by factor analysis. Alterations of gut microbiota and short chain fatty acids (SCFAs) in the cecal were assessed to illustrate the mechanism of lipid lowering.

Results

The supplementation of FG, HP, and BI on HFD-fed rats decreased the levels of serum lipid and reduced the HFD-related liver and testicle damage. In the scatter plot of factor analysis, HP and BI were closer to normal fat diet (NFD) group in restoring the severity of hyperlipidemia, while FG and HP enhanced the excretion of cholesterol and bile acids (BAs). The levels of total SCFAs, especially butyric acid reduced by HFD were increased by HP. The ratio of Firmicutes to Bacteroidetes increased by HFD was reduced by HP and BI. FG, HP, and BI enriched intestinal probiotics, which were related to bile acid excretion or lipid-lowering.

Conclusions

FG inhibited the absorption of cholesterol and enhanced the excretion of it, as well as increased the abundance of beneficial bacteria. While BI restored the imbalance of intestinal microbiota. HP enhanced the excretion of cholesterol and BAs, and restored the imbalance of intestinal microbiota. It was also utilized by intestinal microorganisms to yield SCFAs. This study suggested that FG, HP, and BI possessed the potential to be utilized as dietary supplements for obesity management.

Targeting the gut to prevent and counteract metabolic disorders and pathologies during aging

Impairment of gut function is one of the explanatory mechanisms of health status decline in elderly population. These impairments involve a decline in gut digestive physiology, metabolism and immune status, and associated to that, changes in composition and function of the microbiota it harbors. Continuous deteriorations are generally associated with the development of systemic dysregulations and ultimately pathologies that can worsen the initial health status of individuals. All these alterations observed at the gut level can then constitute a wide range of potential targets for development of nutritional strategies that can impact gut tissue or associated microbiota pattern. This can be key, in a preventive manner, to limit gut functionality decline, or in a curative way to help maintaining optimum nutrients bioavailability in a context on increased requirements, as frequently observed in pathological situations. The aim of this review is to give an overview on the alterations that can occur in the gut during aging and lead to the development of altered function in other tissues and organs, ultimately leading to the development of pathologies. Subsequently is discussed how nutritional strategies that target gut tissue and gut microbiota can help to avoid or delay the occurrence of aging-related pathologies.

Urinary and faecal metabolic characteristics in APP/PS1 transgenic mouse model of Alzheimer's disease with and without cognitive decline

Alzheimer's disease (AD) has been considered to be a systematic metabolic disorder, but little information is available about metabolic changes in the urine and feces. In this study, we investigated urinary and faecal metabolic profiles in amyloid precursor protein/presenilin 1 (APP/PS1) mice at 3 and 9 months of age (3 M and 9 M) and age-matched wild-type (WT) mice by using ¹H NMR-based metabolomics, and aimed to explore changes in metabolic pathways during amyloid pathology progression and identify potential metabolite biomarkers at earlier stage of AD. The results show that learning and memory abilities were impaired in APP/PS1 mice relative to WT mice at 9 M, but not at 3 M. However, metabolomics analysis demonstrates that AD disrupted metabolic phenotypes in the urine and feces of APP/PS1 mice at both 3 M and 9 M, including amino acid metabolism, microbial metabolism and energy metabolism. In addition, several potential metabolite biomarkers were identified for discriminating AD and WT mice prior to cognitive decline with the AUC values from 0.755 to 0.971, such as taurine, hippurate, urea and methylamine in the urine as well as alanine, leucine and valine in the feces. Therefore, our results not only confirmed AD as a metabolic disorder, but also contributed to the identification of potential biomarkers at earlier stage of AD.

Gut microbiota and renin-angiotensin system: a complex interplay at local and systemic levels

Gut microbiota is a potent biological modulator of many physiological and pathological states. The renin-angiotensin system (RAS), including the local gastrointestinal RAS (GI RAS), emerges as a potential mediator of microbiota-related effects. The RAS is involved in cardiovascular system homeostasis, water-electrolyte balance, intestinal absorption, glycemic control, inflammation, carcinogenesis, and aging-related processes. Ample evidence suggests a bidirectional interaction between the microbiome and RAS. On the one hand, gut bacteria and their metabolites may modulate GI and systemic RAS. On the other hand, changes in the intestinal habitat caused by alterations in RAS may shape microbiota metabolic activity and composition. Notably, the pharmacodynamic effects of the RAS-targeted therapies may be in part mediated by the intestinal RAS and changes in the microbiome. This review summarizes studies on gut microbiota and RAS physiology. Expanding the research on this topic may lay the foundation for new therapeutic paradigms in gastrointestinal diseases and multiple systemic disorders.

The impact of gut microbiota metabolites on cellular bioenergetics and cardiometabolic health

Recent research demonstrates a reciprocal relationship between gut microbiota-derived metabolites and the host in controlling the energy homeostasis in mammals. On the one hand, to thrive, gut bacteria exploit nutrients digested by the host. On the other hand, the host utilizes numerous products of gut bacteria metabolism as a substrate for ATP production in the colon. Finally, bacterial metabolites seep from the gut into the bloodstream and interfere with the host’s cellular bioenergetics machinery. Notably, there is an association between alterations in microbiota composition and the development of metabolic diseases and their cardiovascular complications. Some metabolites, like short-chain fatty acids and trimethylamine, are considered markers of cardiometabolic health. Others, like hydrogen sulfide and nitrite, demonstrate antihypertensive properties. Scientific databases were searched for pre-clinical and clinical studies to summarize current knowledge on the role of gut microbiota metabolites in the regulation of mammalian bioenergetics and discuss their potential involvement in the development of cardiometabolic disorders. Overall, the available data demonstrates that gut bacteria products affect physiological and pathological processes controlling energy and vascular homeostasis. Thus, the modulation of microbiota-derived metabolites may represent a new approach for treating obesity, hypertension and type 2 diabetes.

The immunoenhancement effects of sea buckthorn pulp oil in cyclophosphamide-induced immunosuppressed mice

In this study, the immunomodulatory effect of sea buckthorn (SBT) pulp oil was elucidated in immunosuppressed Balb/c mice induced by cyclophosphamide (CTX). The results showed that SBT pulp oil could reverse the decreasing trend of body weight, thymus/spleen index and hematological parameters induced by CTX. Compared with immunosuppressive mice induced by CTX, SBT pulp oil could enhance NK cytotoxicity, macrophage phagocytosis, and T lymphocyte proliferation, and regulate the proportion of T cell subsets in mesenteric lymph nodes (MLN), and promote the production of secretory immunoglobulin A (sIgA), IFN-γ, IL-2, IL-4, IL-12 and TNF-α in the intestines. In addition, SBT pulp oil can promote the production of short fatty acids (SCFAs), increase the diversity of gut microbiota, improve the composition of intestinal flora, increase the abundance of Alistipes, Bacteroides, Anaerotruncus, Lactobacillus, ASF356, and Roseburia, while decreasing the abundance of Mucispirillum, Anaeroplasma, Pelagibacterium, Brevundimonas, Ochrobactrum, Acinetobacter, Ruminiclostridium, Blautia, Ruminiclostridium, Oscillibacter, and Faecalibaculum. This study shows that SBT pulp oil can regulate the diversity and composition of intestinal microflora in CTX-induced immunosuppressive Balb/c mice, thus enhancing the intestinal mucosa and systemic immune response. The results can provide a basis for understanding the function of SBT pulp oil and its application as a new probiotic and immunomodulator.

EfgA is a conserved formaldehyde sensor that leads to bacterial growth arrest in response to elevated formaldehyde

Normal cellular processes give rise to toxic metabolites that cells must mitigate. Formaldehyde is a universal stressor and potent metabolic toxin that is generated in organisms from bacteria to humans. Methylotrophic bacteria such as Methylorubrum extorquens face an acute challenge due to their production of formaldehyde as an obligate central intermediate of single-carbon metabolism. Mechanisms to sense and respond to formaldehyde were speculated to exist in methylotrophs for decades but had never been discovered. Here, we identify a member of the DUF336 domain family, named efgA for enhanced formaldehyde growth, that plays an important role in endogenous formaldehyde stress response in M. extorquens PA1 and is found almost exclusively in methylotrophic taxa. Our experimental analyses reveal that EfgA is a formaldehyde sensor that rapidly arrests growth in response to elevated levels of formaldehyde. Heterologous expression of EfgA in Escherichia coli increases formaldehyde resistance, indicating that its interaction partners are widespread and conserved. EfgA represents the first example of a formaldehyde stress response system that does not involve enzymatic detoxification. Thus, EfgA comprises a unique stress response mechanism in bacteria, whereby a single protein directly senses elevated levels of a toxic intracellular metabolite and safeguards cells from potential damage.

Gut microbiome responses in the metabolism of human dietary components: Implications in health and homeostasis

The gut microbiome and its link with human health and disease have gained a lot of attention recently. The microbiome executes its functions in the host by carrying out the transformation of dietary components and/or de novo synthesis of various essential nutrients. The presence of complex microbial communities makes it difficult to understand the host-microbiome interplay in the metabolism of dietary components. This review attempts to uncover the incredible role of the gut microbiome in the metabolism of dietary components, diet-microbiome interplay, and restoration of the microbiome. The in silico analysis performed in this study elucidates the functional description of essential/hub genes involved in the amino acid degradation pathway, which are mutually present in the host and its gut microbiome. Hence, the computational model helps comprehend the inter-and intracellular molecular networks between humans and their microbial partners.

Nutrition-Based Management of Inflammaging in CKD and Renal Replacement Therapies

Access to renal transplantation guarantees a substantial improvement in the clinical condition and quality of life (QoL) for end-stage renal disease (ESRD) patients. In recent years, a greater number of older patients starting renal replacement therapies (RRT) have shown the long-term impact of conservative therapies for advanced CKD and the consequences of the uremic milieu, with a frail clinical condition that impacts not only their survival but also limits their access to transplantation. This process, referred to as “inflammaging,” might be reversible with a tailored approach, such as RRT accompanied by specific nutritional support. In this review, we summarize the evidence demonstrating the presence of several proinflammatory substances in the Western diet (WD) and the positive effect of unprocessed food consumption and increased fruit and vegetable intake, suggesting a new approach to reduce inflammaging with the improvement of ESRD clinical status. We conclude that the Mediterranean diet (MD), because of its modulative effects on microbiota and its anti-inflammaging properties, may be a cornerstone in a more precise nutritional support for patients on the waiting list for kidney transplantation.

Targeting the Gut Microbiota in Chagas Disease: What Do We Know so Far?

Chagas disease (CD) is a tropical and still neglected disease caused by Trypanosoma cruzi that affects >8 million of people worldwide. Although limited, emerging data suggest that gut microbiota dysfunction may be a new mechanism underlying CD pathogenesis. T. cruzi infection leads to changes in the gut microbiota composition of vector insects, mice, and humans. Alterations in insect and mice microbiota due to T. cruzi have been associated with a decreased immune response against the parasite, influencing the establishment and progression of infection. Further, changes in the gut microbiota are linked with inflammatory and neuropsychiatric disorders, comorbid conditions in CD. Therefore, this review article critically analyses the current data on CD and the gut microbiota of insects, mice, and humans and discusses its importance for CD pathogenesis. An enhanced understanding of host microbiota will be critical for the development of alternative therapeutic approaches to target CD, such as gut microbiota-directed interventions.

Longitudinal profiling of the gut microbiome in patients with psoriatic arthritis and ankylosing spondylitis: a multicentre, prospective, observational study

BACKGROUND

Psoriasis is a chronic inflammatory disease of the skin affecting 2-3% of UK population. 30% of people affected by psoriasis will develop a distinct form of arthritis within 10 years of the skin condition onset. Although the pathogenesis of psoriatic arthritis is still unknown, there is a genetic predisposition triggered by environmental factors. Limited but convincing evidence link the gut microbiome to psoriatic arthritis. The Microbiome in Psoriatic ARThritis (Mi-PART) study propose is to characterise the microbiome-metabolic interface in patients affected by psoriatic arthritis to deepen our understanding of the pathogenesis of the disease.

METHODS

This is a multicentre, prospective, observational study. Psoriatic arthritis (n = 65) and ankylosing spondylitis (n = 30) patients will be recruited in addition to a control group of healthy volunteers (n = 30). Patients eligibility will be evaluated against the Criteria for Psoriatic Arthritis (CASPAR), the Bath Ankylosing Spondylitis Activity Index (BASDAI) and the healthy volunteers who fulfil study inclusion and exclusion criteria. Information regarding their medical and medication history, demographics, diet and lifestyle will be collected. All the participants in the study will be asked to complete a 7-day food diary, to provide stool samples and to complete quality of life questionnaires. Routine clinical laboratory tests will be performed on blood and urine samples. Patients and healthy volunteers with gastrointestinal symptoms, previous history of cancer, gastrointestinal surgery in the previous 6 months or alcohol abuse will be excluded from the study.

DISCUSSION

The aim of this trial is to characterise the microbiome of psoriatic arthritis patients and to compare it with microbiome of healthy volunteers and of patient with ankylosing spondylitis in order to define if different rheumatologic conditions are associated with characteristic microbiome profiles. Investigating the role of the microbiome in the development of psoriatic arthritis could deepen our understanding of the pathogenesis of the disease and potentially open the way to new therapies.

How strong is the evidence that gut microbiota composition can be influenced by lifestyle interventions in a cardio-protective way?

Alterations in composition and function of the gut microbiota have been demonstrated in diseases involving the cardiovascular system, particularly coronary heart disease and atherosclerosis. The data are still limited but the typical altered genera include Roseburia and Faecalibacterium. Plausible mechanisms by which microbiota may mediate cardio-protective effects have been postulated, including the production of metabolites like trimethylamine (TMA), as well as immunomodulatory functions. This raises the question of whether it is possible to modify the gut microbiota by lifestyle interventions and thereby improve cardiovascular health. Nevertheless, lifestyle intervention studies that have involved modifications of dietary intake and/or physical activity, as well as investigating changes in the gut microbiota and subsequent modifications of the cardioprotective markers, are still scarce, and the results have been inconclusive. Current evidence points to benefits of consuming high-fibre foods, nuts and an overall healthy dietary pattern to achieve beneficial effects on both gut microbiota and serum cardiovascular markers, primarily lipids. The relationship between physical exercise and gut microbiota is probably complex and may be dependent on the intensity of exercise. In this article, we review the available evidence on lifestyle, specifically diet, physical activity and smoking as modifiers of the gut microbiota, and subsequently as modifiers of serum cardiovascular health markers. We have attempted to elucidate the plausible mechanisms and further critically appraise the caveats and gaps in the research.

Dietary bioactive ingredients to modulate the gut microbiota-derived metabolite TMAO. New opportunities for functional food development

There is a growing body of clinical evidence that supports a strong association between elevated circulating trimethylamine N-oxide (TMAO) levels with increased risk of developing adverse cardiovascular outcomes such as atherosclerosis and thrombosis. TMAO is synthesized through a meta-organismal stepwise process that involves (i) the microbial production of TMA in the gut from dietary precursors and (ii) its subsequent oxidation to TMAO by flavin-containing monooxygenases in the liver. Choline, l-carnitine, betaine, and other TMA-containing compounds are the major dietary precursors of TMA. TMAO can also be absorbed directly from the gastrointestinal tract after the intake of TMAO-rich foods such as fish and shellfish. Thus, diet is an important factor as it provides the nutritional precursors to eventually produce TMAO. A number of studies have attempted to associate circulating TMAO levels with the consumption of diets rich in these foods. On the other hand, there is growing interest for the development of novel food ingredients that reduce either the TMAO-induced damage or the endogenous TMAO levels through the interference with microbiota and host metabolic processes involved in TMAO pathway. Such novel functional food ingredients would offer great opportunities to control circulating TMAO levels or its effects, and potentially contribute to decrease cardiovascular risk. In this review we summarize and discuss current data regarding the effects of TMA precursors-enriched foods or diets on circulating TMAO levels, and recent findings regarding the circulating TMAO-lowering effects of specific foods, food constituents and phytochemicals found in herbs, individually or in extracts, and their potential beneficial effect for cardiovascular health.

Short-term high-intensity interval training exercise does not affect gut bacterial community diversity or composition of lean and overweight men

NEW FINDINGS

What is the central question of this study? Does short-term high-intensity interval training alter the composition of the microbiome and is this associated with exercise-induced improvements in cardiorespiratory fitness and insulin sensitivity? What is the main finding and its importance? Although high-intensity interval training increased insulin sensitivity and cardiovascular fitness, it did not alter the composition of the microbiome. This suggests that changes in the composition of the microbiome that occur with prolonged exercise training might be in response to changes in metabolic health rather than driving exercise training-induced adaptations.

ABSTRACT

Regular exercise reduces the risk of metabolic diseases, and the composition of the gut microbiome has been associated with metabolic function. We investigated whether short-term high-intensity interval training (HIIT) altered the diversity and composition of the bacterial community and whether there were associations with markers of insulin sensitivity or aerobic fitness. Cardiorespiratory fitness ( V ̇ O 2 peak ) and body composition (dual energy X-ray absorptiometry scan) were assessed and faecal and fasted blood samples collected from 14 lean (fat mass 21 ± 2%, aged 29 ± 2 years) and 15 overweight (fat mass 33 ± 2%, aged 31 ± 2 years) men before and after 3 weeks of HIIT training (8-12 × 60 s cycle ergometer bouts at V ̇ O 2 peak power output interspersed by 75 s rest, three times per week). Gut microbiome composition was analysed by 16S rRNA gene amplicon sequencing. The HIIT significantly increased the aerobic fitness of both groups (P < 0.001) and improved markers of insulin sensitivity (lowered fasted insulin and HOMA-IR; P < 0.001) in the overweight group. Despite differences in the abundance of several bacterial taxa being evident between the lean and overweight group, HIIT did not affect the overall bacterial diversity or community structure (α-diversity or β-diversity). No associations were found between the top 50 most abundant bacterial genera and cardiorespiratory fitness markers; however, significant associations (P < 0.05) were observed between the abundance of the bacterial species Coprococcus_3, Blautia, Lachnospiraceae_ge and Dorea and insulin sensitivity markers in the overweight group. Our results suggest that short-term HIIT does not greatly impact the overall composition of the gut microbiome, but that certain microbiome genera are associated with insulin sensitivity markers that were improved by HIIT in overweight participants.

TMAO, a seafood-derived molecule, produces diuresis and reduces mortality in heart failure rats

Trimethylamine-oxide (TMAO) is present in seafood which is considered to be beneficial for health. Deep-water animals accumulate TMAO to protect proteins, such as lactate dehydrogenase (LDH), against hydrostatic pressure stress (HPS). We hypothesized that TMAO exerts beneficial effects on the circulatory system and protects cardiac LDH exposed to HPS produced by the contracting heart. Male, Sprague-Dawley and Spontaneously-Hypertensive-Heart-Failure (SHHF) rats were treated orally with either water (control) or TMAO. In vitro, LDH with or without TMAO was exposed to HPS and was evaluated using fluorescence correlation spectroscopy. TMAO-treated rats showed higher diuresis and natriuresis, lower arterial pressure and plasma NT-proBNP. Survival in SHHF-control was 66% vs 100% in SHHF-TMAO. In vitro, exposure of LDH to HPS with or without TMAO did not affect protein structure. In conclusion, TMAO reduced mortality in SHHF, which was associated with diuretic, natriuretic and hypotensive effects. HPS and TMAO did not affect LDH protein structure.

Heart failure is a common cause of death in industrialized countries with aging populations. Japan, however, has lower rates of heart failure and fewer deaths linked to this disease than the United States or Europe, despite having the highest proportion of elderly people in the world. Dietary differences between these regions may explain the lower rate of heart failure in Japan. The Japanese diet is rich in seafood, which contains nutrients that promote heart health, such as omega-3 fatty acids.

Seafood also contains other compounds, including trimethylamine oxide (TMAO). Fish that live in deep waters undergo high pressures, which can damage their proteins, but TMAO seems to protect the proteins from harm. In humans, eating seafood increases TMAO levels in the blood and urine, but it is unclear what effects this has on heart health. Increased levels of TMAO in the blood are associated with cardiovascular diseases, but scientists are not sure whether TMAO itself harms the heart. A toxic byproduct of gut bacteria called TMA is converted in TMAO in the body, so it is possible that TMA rather than TMAO is to blame.

To assess the effects of dietary TMAO on heart failure, Gawrys-Kopczynska et al. fed the compound to healthy rats and rats with heart failure for one year. TMAO had no effects on the healthy rats. Of the rats with heart failure that were fed TMAO, all of them survived the year, while one third of rats with heart failure that were not fed TMAO died. TMAO-treated rats with heart failure had lower blood pressure and urinated more than untreated rats with the condition.

The experiments suggest that dietary TMAO may mimic the effects of heart failure treatments, which remove excess water and salt and lower pressure on the heart. More studies are needed to confirm whether TMAO has this same effect on humans.