Inhibition of methanogenesis by human bile

Liraglutide targets the gut microbiota and the intestinal immune system to regulate insulin secretion

AIMS

Liraglutide controls type 2 diabetes (T2D) and inflammation. Gut microbiota regulates the immune system and causes at least in part type 2 diabetes. We here evaluated whether liraglutide regulates T2D through both gut microbiota and immunity in dysmetabolic mice.

METHODS

Diet-induced dysmetabolic mice were treated for 14 days with intraperitoneal injection of liraglutide (100 µg/kg) or with vehicle or Exendin 4 (10 µg/kg) as controls. Various metabolic parameters, the intestinal immune cells were characterized and the 16SrDNA gene sequenced from the gut. The causal role of gut microbiota was shown using large spectrum antibiotics and by colonization of germ-free mice with the gut microbiota from treated mice.

RESULTS

Besides, the expected metabolic impacts liraglutide treatment induced a specific gut microbiota specific signature when compared to vehicle or Ex4-treated mice. However, liraglutide only increased glucose-induced insulin secretion, reduced the frequency of Th1 lymphocytes, and increased that of TReg in the intestine. These effects were abolished by a concomitant antibiotic treatment. Colonization of germ-free mice with gut microbiota from liraglutide-treated diabetic mice improved glucose-induced insulin secretion and regulated the intestinal immune system differently from what observed in germ-free mice colonized with microbiota from non-treated diabetic mice.

CONCLUSIONS

Altogether, our result demonstrated first the influence of liraglutide on gut microbiota and the intestinal immune system which could at least in part control glucose-induced insulin secretion.

Small Intestinal Bacterial Overgrowth and Irritable Bowel Syndrome - An Update

Small intestinal bacterial overgrowth (SIBO) is one manifestation of gut microbiome dysbiosis and is highly prevalent in IBS (Irritable Bowel Syndrome). SIBO can be diagnosed either by a small bowel aspirate culture showing ≥10³ colony-forming units (CFU) per mL of aspirate, or a positive hydrogen lactulose or glucose breath test. Numerous pathogenic organisms have been shown to be increased in subjects with SIBO and IBS, including but not limited to Enterococcus, Escherichia coli, and Klebsiella. In addition, Methanobrevibacter smithii, the causal organism in a positive methane breath test, has been linked to constipation predominant irritable bowel syndrome (IBS-C). As M. smithii is an archaeon and can overgrow in areas outside of the small intestine, it was recently proposed that the term intestinal methanogen overgrowth (IMO) is more appropriate for the overgrowth of these organisms. Due to gut microbiome dysbiosis, patients with IBS may have increased intestinal permeability, dysmotility, chronic inflammation, autoimmunity, decreased absorption of bile salts, and even altered enteral and central neuronal activity. As a consequence, SIBO and IBS share a myriad of symptoms including abdominal pain, distention, diarrhea, and bloating. Furthermore, gut microbiome dysbiosis may be associated with select neuropsychological symptoms, although more research is needed to confirm this connection. This review will focus on the role of the gut microbiome and SIBO in IBS, as well as novel innovations that may help better characterize intestinal overgrowth and microbial dysbiosis.

Long-term monitoring of breath methane

In recent years, methane as a component of exhaled human breath has been considered as a potential bioindicator providing information on microbial activity in the intestinal tract. Several studies indicated a relationship between breath methane status and specific gastrointestinal disease. So far, almost no attention has been given to the temporal variability of breath methane production by individual persons. Thus here, for the first time, long-term monitoring was carried out measuring breath methane of three volunteers over periods between 196 and 1002days. Results were evaluated taking into consideration the health status and specific medical intervention events for each individual during the monitoring period, and included a gastroscopy procedure, a vaccination, a dietary change, and chelate therapy. As a major outcome, breath methane mixing ratios show considerable variability within a person-specific range of values. Interestingly, decreased breath methane production often coincided with gastrointestinal complaints whereas influenza infections were mostly accompanied by increased breath methane production. A gastroscopic examination as well as a change to a low-fructose diet led to a dramatic shift of methane mixing ratios from high to low methane production. In contrast, a typhus vaccination as well as single chelate injections resulted in significant short-term methane peaks. Thus, this study clearly shows that humans can change from high to low methane emitters and vice versa within relatively short time periods. In the case of low to medium methane emitters the increase observed in methane mixing ratios, likely resulting from immune reactions and inflammatory processes, might indicate non-microbial methane formation under aerobic conditions. Although detailed reaction pathways are not yet known, aerobic methane formation might be related to cellular oxidative-reductive stress reactions. However, a detailed understanding of the pathways involved in human methane formation is necessary to enable comprehensive interpretation of methane breath levels.

Breath Methane Levels Are Increased Among Patients with Diverticulosis

BACKGROUND

Diverticulosis and its complications are important healthcare problems in the USA and throughout the Western world. While mechanisms as to how diverticulosis occurs have partially been explored, few studies examined the relationship between colonic gases such as methane and diverticulosis in humans.

AIM

This study aimed to demonstrate a significant relationship between methanogenic Archaea and development of diverticulosis.

METHODS

Subjects who consecutively underwent hydrogen breath test at Rush University Medical Center between 2003 and 2010 were identified retrospectively through a database. Medical records were reviewed for presence of a colonoscopy report. Two hundred and sixty-four subjects were identified who had both a breath methane level measurement and a colonoscopy result. Additional demographic and clinical data were obtained with chart review.

RESULTS

Mean breath methane levels were higher in subjects with diverticulosis compared to those without diverticulosis (7.89 vs. 4.94 ppm, p = 0.04). Methane producers (defined as those with baseline fasting breath methane level >5 ppm) were more frequent among subjects with diverticulosis compared to those without diverticulosis (50.9 vs. 34 %, p = 0.0025). When adjusted for confounders, breath methane levels and age were the two independent predictors of diverticulosis on colonoscopy with logistic regression modeling.

CONCLUSIONS

Methanogenesis is associated with the presence of diverticulosis. Further studies are needed to confirm our findings and prospectively evaluate a possible etiological role of methanogenesis and methanogenic archaea in diverticulosis.

Age dependent breath methane in the German population

Methane which can sometimes be found in exhaled breath of humans is known to reflect in situ intestinal methanogenic activity. In recent years, several factors have been studied in order to understand their relevance to methane production in the intestinal tract. However, the relationship between age and methane producing status has hitherto not been sufficiently investigated. In the present study we evaluated the relationship between age and percentage of breath methane producers in the German population in 428 subjects with ages ranging from 4 to 95 years. When subjects were divided into age groups of 15 years, an increase in the percentage of breath methane producers with age was observed. The near linear increase (R(2)=0.977) from 5% for children (1-15 years) to 57% for the elderly (>75 years) may indicate a continuous development in the human gut methanogenic flora throughout lifetime. However, when subjects were compared on 5 year age intervals, an interruption in the percentage of methane producers in the sixth and seventh decade was noted. We further revealed an age dependence on the ratio of female to male producers. This is shown by a dominance in female breath methane producers during the first half of life which afterwards is replaced by a dominance in male breath methane producers with an approximately linear decrease in the ratio between 20 and 65 years (R(2)=0.926). These observations might suggest a relationship between methanogenic activity and hormonal factors. Using our data, we predict that the percentage of breath CH4 producers within the German population will increase from its current value of 30% (2013) to 35% by 2050.

Emerging aspects of food and nutrition on gut microbiota

The human gastrointestinal tract contains a highly complex ecosystem that harbors various microorganisms, which together create a unique environment within each individual. There is growing awareness that dietary habits are one of the essential factors contributing to the microbial diversity and community configuration that ultimately affects human health. From an evolutionary perspective, human dietary history can be viewed as a central factor in the selection of the gut microbial community and stabilization of the mutualistic host-microbial interaction, that together drive host phenotype. Herein, current knowledge concerning the influence of major dietary macrostructure and individual food ingredients is presented. This knowledge will provide perspectives for personalized gut microbiota management and, ultimately, movement toward an era of personalized nutrition and medicine.

Ecology and characteristics of methanogenic archaea in animals and humans

In this review, the molecular techniques used in animal-based-methanogen studies will be discussed along with how methanogens interact not only with other microorganisms but with their animal hosts as well. These methods not only indicate the diversity and levels of methanogens, but also provide insight on their ecological functions. Most molecular techniques have been based on either 16S rRNA genes or methyl-coenzyme M reductase, a ubiquitous enzyme in methanogens. The most predominant methanogens in animals belong to the genus Methanobrevibacter. Besides methanogens contributing to overall H2 balance, methanogens also have mutual interactions with other bacteria. In addition to shared metabolic synergism, the host animal retrieves additional energy from the diet when methanogens are co-colonized with other normal flora. By comparing genes in methanogens with other bacteria, possible gene transfer between methanogens and other bacteria in the same environments appears to occur. Finally, diets in conjunction with the genetics of methanogens and hosts may represent the biological framework that dictate the extent of methanogen prevalence in these ecosystems. In addition, host evolution including the immune system could serve as an additional selective pressure for methanogen colonization.

Methane and the gastrointestinal tract

INTRODUCTION

Several gases are produced through enteric fermentation in the intestinal tract. Carbon dioxide, hydrogen, hydrogen sulfide, and methane are thought to be the most common of these. Recent evidence suggests that methane may not be inert. In this review article, we summarize the findings with methane.

METHODS

This is a review article discussing the various component gases in the gastrointestinal tract and their relevance to health and disease. Specific attention was paid to understanding methane.

RESULTS

The majority of these gases are eliminated via flatus or absorbed into systemic circulation and expelled from the lungs. Excessive gas evacuation or retention causes gastrointestinal functional symptoms such as belching, flatulence, bloating, and pain. Between 30 and 62% of healthy subjects produce methane. Methane is produced exclusively through anaerobic fermentation of both endogenous and exogenous carbohydrates by enteric microflora in humans. Methane is not utilized by humans, and analysis of respiratory methane can serve as an indirect measure of methane production. Recent literature suggests that gases such as hydrogen sulfide and methane may have active effects on gut function. In the case of hydrogen sulfide, evidence demonstrates that this gaseous product may be produced by human eukaryotic cells. However, in the case of methane, there is increasing evidence that this gas has both physical and biological effects on gut function. It is now often associated with functional constipation and may have an active role here.

CONCLUSION

This review of the literature discusses the significance of enteric flora, the biogenesis of methane, and its clinical associations. Furthermore, we examine the evidence for an active role of methane in gastrointestinal motility and the potential applications to future therapeutics.

Small intestinal bacterial overgrowth syndrome

Human intestinal microbiota create a complex polymicrobial ecology. This is characterised by its high population density, wide diversity and complexity of interaction. Any dysbalance of this complex intestinal microbiome, both qualitative and quantitative, might have serious health consequence for a macro-organism, including small intestinal bacterial overgrowth syndrome (SIBO). SIBO is defined as an increase in the number and/or alteration in the type of bacteria in the upper gastrointestinal tract. There are several endogenous defence mechanisms for preventing bacterial overgrowth: gastric acid secretion, intestinal motility, intact ileo-caecal valve, immunoglobulins within intestinal secretion and bacteriostatic properties of pancreatic and biliary secretion. Aetiology of SIBO is usually complex, associated with disorders of protective antibacterial mechanisms (e.g. achlorhydria, pancreatic exocrine insufficiency, immunodeficiency syndromes), anatomical abnormalities (e.g. small intestinal obstruction, diverticula, fistulae, surgical blind loop, previous ileo-caecal resections) and/or motility disorders (e.g. scleroderma, autonomic neuropathy in diabetes mellitus, post-radiation enteropathy, small intestinal pseudo-obstruction). In some patients more than one factor may be involved. Symptoms related to SIBO are bloating, diarrhoea, malabsorption, weight loss and malnutrition. The gold standard for diagnosing SIBO is still microbial investigation of jejunal aspirates. Non-invasive hydrogen and methane breath tests are most commonly used for the diagnosis of SIBO using glucose or lactulose. Therapy for SIBO must be complex, addressing all causes, symptoms and complications, and fully individualised. It should include treatment of the underlying disease, nutritional support and cyclical gastro-intestinal selective antibiotics. Prognosis is usually serious, determined mostly by the underlying disease that led to SIBO.

Alteration of sulfate and hydrogen metabolism in the human colon by changing intestinal transit rate

OBJECTIVES

Changes in intestinal transit rate are also implicated in the etiology of many colonic diseases and strongly influence many metabolic processes in the colon. We set out to investigate whether intestinal transit time could influence the activity of the hydrogen-consuming bacterial flora and sulfate metabolism.

METHODS

Normal volunteers underwent four interventions while taking a low-sulfate diet: placebo, sulfate supplements, or sulfate supplements with either senna or loperamide. Stools were cultured and analyzed for sulfate, sulfide, methionine, sulfate reduction rates, methionine reduction rates, acetic acid production rates, methane production rates, short-chain fatty acids, and bile acids. Urine was analyzed for sulfate.

RESULTS

The addition of sulfate alone increased fecal and urinary excretion of sulfate, fecal sulfide, sulfate reduction rates, and acetic acid production rates; it reduced fecal methanogenic bacterial concentrations. Faster intestinal transit increased fecal sulfate, sulfide, bile acids, the reduction rates of sulfate, and methionine and the production rates of acetic acid. Reduction in fecal methanogens and methane production was seen. The reverse effects were seen with loperamide.

CONCLUSIONS

Both sulfate supplements and changes in intestinal transit rate markedly alter the activity of the colonic bacterial flora with respect to sulfate metabolism and hydrogen disposal. Dietary influences on intestinal transit and sulfate consumption may influence disease processes. While a variety of processes govern sulfate metabolism and hydrogen disposal, our knowledge is far from complete. How far the observed changes in sulfate metabolism seen in certain diseases are relevant to the pathogenesis of the disease or secondary to the disease itself is unclear.

Molecular characterization of the microbial species that colonize human ileal and colonic mucosa by using 16S rDNA sequence analysis

AIM

The aim of this study was to characterize the bacterial community adhering to the mucosa of the terminal ileum, and proximal and distal colon of the human digestive tract.

METHODS AND RESULTS

Pinch samples of the terminal ileum, proximal and distal colon were taken from a healthy 35-year-old, and a 68-year-old subject with mild diverticulosis. The 16S rDNA genes were amplified using a low number of PCR cycles, cloned, and sequenced. In total, 361 sequences were obtained comprising 70 operational taxonomic units (OTU), with a calculated coverage of 82.6%. Twenty-three per cent of OTU were common to the terminal ileum, proximal colon and distal colon, but 14% OTU were only found in the terminal ileum, and 43% were only associated with the proximal or distal colon. The most frequently represented clones were from the Clostridium group XIVa (24.7%), and the Bacteroidetes (Cytophaga-Flavobacteria-Bacteroides) cluster (27.7%).

CONCLUSION

Comparison of 16S rDNA clone libraries of the hindgut across mammalian species confirms that the distribution of phylogenetic groups is similar irrespective of the host species. Lesser site-related differences within groups or clusters of organisms, are probable.

SIGNIFICANCE AND IMPACT

This study provides further evidence of the distribution of the bacteria on the mucosal surfaces of the human hindgut. Data contribute to the benchmarking of the microbial composition of the human digestive tract.

Shared and unique environmental factors determine the ecology of methanogens in humans and rats

OBJECTIVE

This study ascertains the relative contributions of genetics and environment in determining methane emission in humans and rats. There is considerable interest in the factors determining the microbial species that inhabit the colon. Methanogens. which are archaebacteria, are an easily detected colonic luminal bacteria because they respire methane. They are present in some but not all human colons and lower animal hindguts. Opinion varies on the nature of the factors influencing this ecology with some studies proposing the existence of host genetic influences.

METHODS

Methane emission was measured in human twin pairs by gas chromatography, and structural equation modeling was used to determine the proportion of genetic and environmental determinants. The importance of the timing of environmental effects and rat strain on the trait of methane emission were ascertained by experiments with cohabiting methanogenic and nonmethanogenic rats.

RESULTS

Analysis of breath samples from 274 adolescent twin pairs and their families indicated that the major influences on the trait of methane emission are the result of shared (53%, 95% confidence interval 39-61) and unique environmental (47%, 95% confidence interval 38-56) effects. No significant autosomal genetic effects were detected, but as observed in other studies, men (37%) were less likely to excrete methane in their breath than women (63%). Investigation of methane emission in rats indicated that environmental effects in this animal are most potent during the weaning period, with stable gut microbial ecology thereafter for some but not all rat strains.

CONCLUSIONS

These results are consistent with shared and unique environmental factors being the main determinants of the ecology of this colonic microbe.

Fermentation by gut microbiota cultured in a simulator of the human intestinal microbial ecosystem is improved by supplementing a soygerm powder

An in vitro model, designated the Simulator of the Human Intestinal Microbial Ecosystem (SHIME), was used to study the effect of a soygerm powder rich in beta-glycosidic phytoestrogenic isoflavones on the fermentation pattern of the colon microbiota and to determine to what extent the latter metabolize the conjugated phytoestrogens. Initially, an inoculum prepared from human feces was introduced into the reactor vessels and stabilized over 3 wk using a culture medium. This stabilization period was followed by a 2-wk control period during which the microbiota were monitored. The microbiota were then subjected to a 2-wk treatment period by adding 2.5 g/d soygerm powder to the culture medium. The addition resulted into an overall increase of bacterial marker populations (Enterobacteriaceae:, coliforms, Lactobacillus: sp., Staphylococcus: sp. and Clostridium: sp.), with a significant increase of the Lactobacillus: sp. population. The short-chain fatty acid (SCFA) concentration increased approximately 30% during the supplementation period; this was due mainly to a significant increase of acetic and propionic acids. Gas analysis revealed that the methane concentration increased significantly. Ammonium and sulfide concentrations were not influenced by soygerm supplementation. Use of an electronic nose apparatus indicated that odor concentrations decreased significantly during the treatment period. The beta-glycosidic bonds of the phytoestrogenic isoflavones were cleaved under the conditions prevailing in the large intestine. The increased bacterial fermentation after addition of the soygerm powder was paralleled by substantial metabolism of the free isoflavones (genistein, daidzein and glycitein), resulting in recovery of only 12-17% of the supplemented isoflavones.

The effect of porcine bile acids on methane production by rumen contents in vitro

Hindgut fermentation differs from rumen fermentation by a lower methane production and the presence of reductive acetogenesis. Bile acids which are lost into the lower digestive tract may have a promoting effect on reductive acetogenesis in the hindgut. In this experiment it was investigated if bile acids induce reductive acetogenesis in rumen fermentation in vitro. Rumen contents from a fistulated cow were incubated in vitro with ground hay and increasing amounts of porcine bile acids or bile acid salts. Bile acids inhibited methane production up to 70% of the control incubation. The concomitant increase in propionate production compensated for the lower methane production so that the 2H-recoveries were in a normal range between 79-92%. Therefore the occurrence of reductive acetogenesis could be excluded. It is concluded, that bile acids are a controlling factor in caecal methanogenesis.

Alkyl halides, super hydrogen production and the pathogenesis of pneumatosis cystoides coli

BACKGROUND AND AIMS

The colons of patients with pneumatosis cystoides coli produce excessive H2. Exposure to alkyl halides could explain this. Six consecutive patients who had pneumatosis cystoides coli while taking chloral hydrate (1-5+ g/day) are reported. Patients 2 and 3 were investigated after they had ceased chloral hydrate treatment. One produced methane, the other did not. (Pneumatosis cystoides coli patients are non-methanogenic according to the literature.) Both had overnight fasting breath H2 of less than 10 ppm. A literature review disclosed just one patient who was using chloral at the time of diagnosed pneumatosis cystoides coli, but an epidemic of the disease in workers exposed to trichloroethylene.

METHODS

(i) In vitro experiments with human faeces: chloral or closely related alkyl halides were added to anaerobic faecal cultures derived from four methane-producing and three non-methanogenic human subjects. H2 and CH4 gases were measured. (ii) In vivo animal experiment: chloral hydrate was added to drinking water of four Wistar rats, and faecal H2 compared with control rats.

RESULTS

Alkyl halides increased H2 up to 900 times in methanogenic and 10 times in non-methanogenic faecal cultures. The Ki of chloral was 0.2 mM. Methanogenesis was inhibited in concert with the increase in net H2. In the rat experiment, chloral hydrate increased H2 10 times, but did not cause pneumatosis.

CONCLUSIONS

Chloral and trichloroethylene are alkyl halides chemically similar to chloroform, a potent inhibitor of H2 consumption by methanogens and acetogens. These bacteria are the most important H2-consuming species in the colon. It is postulated that exposure to these alkyl halides increases net H2 production, which sets the scene for "counterperfusion supersaturation" and the formation of gas cysts. In recent times, very low prescribing rates for chloral have caused primary pneumatosis cystoides to become extremely rare. As with primary pneumatosis, secondary pneumatosis cystoides, which occurs if there is small bowel bacterial overgrowth distal to a proximally located gut obstruction, is predicted by counterperfusion supersaturation. "Inherent unsaturation" due to metabolism of O2 is a safety factor, which could explain why gas bubbles do not form more often in tissue with high H2 tension.