Stability of human methanogenic flora over 35 years and a review of insights obtained from breath methane measurements

Selection of a cut-off for high- and low-methane producers using a spot-methane breath test: results from a large north American dataset of hydrogen, methane and carbon dioxide measurements in breath

BACKGROUND

Levels of breath methane, together with breath hydrogen, are determined by means of repeated collections of both, following ingestion of a carbohydrate substrate, at 15-20 minutes intervals, until 10 samples have been obtained. The frequent sampling is required to capture a rise of hydrogen emissions, which typically occur later in the test: in contrast, methane levels are typically elevated at baseline. If methane emissions represent the principal objective of the test, a spot methane test (i.e. a single-time-point sample taken after an overnight fast without administration of substrate) may be sufficient.

METHODS

We analysed 10-sample lactulose breath test data from 11 674 consecutive unique subjects who submitted samples to Commonwealth Laboratories (Salem, MA, USA) from sites in all of the states of the USA over a one-year period. The North American Consensus (NAC) guidelines criteria for breath testing served as a reference standard.

RESULTS

The overall prevalence of methane-positive subjects (by NAC criteria) was 20.4%, based on corrected methane results, and 18.9% based on raw data. In our USA dataset, the optimal cut-off level to maximize sensitivity and specificity was ≥4 ppm CH4, 94.5% [confidential interval (CI): 93.5-95.4%] and 95.0% (CI: 94.6-95.5%), respectively. The use of a correction factor (CF) (5% CO2 as numerator) led to reclassifications CH4-high to CH4-low in 0.7 % and CH4-low to CH4-high in 2.1%.

CONCLUSIONS

A cut-off value for methane at baseline of either ≥4 ppm, as in our USA dataset, or ≥ 5 ppm, as described in a single institution study, are both highly accurate in identifying subjects at baseline that would be diagnosed as 'methane-positive' in a 10-sample lactulose breath test for small intestinal bacterial overgrowth.

Abundance and Diversity of Hydrogenotrophic Microorganisms in the Infant Gut before the Weaning Period Assessed by Denaturing Gradient Gel Electrophoresis and Quantitative PCR

Delivery mode (natural vs. cesarean) and feeding type (breast vs. formula feeding) are relevant factors for neonatal gut colonization. Biomolecular methods have shown that the ecological structure of infant microbiota is more complex than previously proposed, suggesting a relevant presence of unculturable bacteria. It has also been postulated that among unculturable bacteria, hydrogenotrophic populations might play a key role in infant health. Sulfate-reducing bacteria (SRB), acetogens, and methanogenic archaea use hydrogenotrophic pathways within the human colon. However, to date, few studies have reported detection of hydrogenotrophic microorganisms in newborns, possibly because of limitations on available group-specific, culture-independent quantification procedures. In the present work, we analyzed 16 fecal samples of healthy babies aged 1-6 months by means of quantitative PCR (qPCR) targeting the 16S rRNA or metabolic functional genes and by denaturing gradient gel electrophoresis (DGGE). qPCR data showed quantifiable levels of methanogens, SRB, and acetogens in all samples, indicating that the relative abundances of these microbial groups were not affected by delivery mode (natural vs. caesarian). DGGE revealed a high prevalence of the Blautia genus within the acetogenic bacteria despite strong interindividual variability. Our preliminary results suggest that hydrogenotrophic microorganisms, which have been a neglected group to date, should be included in future ecological and metabolic studies evaluating the infant intestinal microbiota.

Short article: Risk of small intestinal bacterial overgrowth with chronic use of proton pump inhibitors in children

BACKGROUND

Some theorize that prolonged use of proton pump inhibitors (PPIs) may increase the risk of small intestinal bacterial overgrowth (SIBO). Chronic acid suppression and resultant hypochlorhydria may lead to an altered intraluminal environment, which, in turn, may promote the growth of bacteria in the small intestine. A handful of studies measured the risk of SIBO in adults taking PPIs and obtained mixed results; however, this risk has not been exclusively measured in children.

AIM

This study aimed to measure the risk of SIBO in children taking PPI versus those not taking PPI.

PATIENTS AND METHODS

This was a prospective cohort study. Evaluation of SIBO was performed using the glucose hydrogen breath test. Patients younger than 18 years of age taking a PPI longer than 6 months were compared with healthy control participants. After ingestion of glucose substrate, breath samples were obtained every 15 min for 2 h. An increase in breath hydrogen or methane above 12 ppm was considered diagnostic of SIBO.

RESULTS

Overall, 83 participants were tested, of whom 56 were taking PPIs. SIBO was detected in five (8.9%) of the 56 participants taking PPI versus one (3.7%) of the 27 participants in the control group (P=0.359), with a relative risk of 2.4 (95% confidence interval: 0.29-19.6).

CONCLUSION

To our knowledge, this is the first study in the English literature measuring the risk of SIBO in children taking PPIs. Our results indicate a potential risk of SIBO in chronic PPI users; however, this is not statistically significant. This is an important finding as PPIs are readily prescribed for children and are often taken longer than 6 months' duration.

Lactulose Breath Test Gas Production in Childhood IBS Is Associated With Intestinal Transit and Bowel Movement Frequency

OBJECTIVES

In adults with irritable bowel syndrome (IBS), bacterial gas production (colonic fermentation) is related to both symptom generation and intestinal transit. Whether gas production affects symptom generation, psychosocial distress, or intestinal transit in childhood IBS is unknown.

METHODS

Children (ages 7-17 years) with pediatric Rome III IBS completed validated psychosocial questionnaires and a 2-week daily diary capturing pain and stooling characteristics. Stool form determined IBS subtype. Subjects then completed a 3-hour lactulose breath test for measurement of total breath hydrogen and methane production. Carmine red was used to determine whole intestinal transit time.

RESULTS

A total of 87 children (mean age 13 ± 2.6 [standard deviation] years) were enrolled, of whom 50 (57.5%) were girls. All children produced hydrogen and 51 (58.6%) produced methane. Hydrogen and methane production did not correlate with either abdominal pain frequency/severity or psychosocial distress. Hydrogen and methane production did not differ significantly by IBS subtype. Methane production correlated positively with whole intestinal transit time (r = 0.31, P < 0.005) and inversely with bowel movement frequency (r = -0.245, P < 0.05). Methane production (threshold 3 ppm) as a marker for identifying IBS-C had a sensitivity of 60% and specificity of 42.9%.

CONCLUSIONS

Lactulose breath test total methane production may serve as a biomarker of whole intestinal transit time and bowel movement frequency in children with IBS. In children with IBS, lactulose breath test hydrogen and methane production did not, however, correlate with abdominal pain, IBS subtype, or psychosocial distress.

The clinical value of breath hydrogen testing

Breath hydrogen testing for assessing the presence of carbohydrate malabsorption is frequently applied to refine dietary restrictions on a low fermentable carbohydrate (FODMAP) diet. Its application has also been extended for the detection of small intestinal bacterial overgrowth. Recently, several caveats of its methodology and interpretation have emerged. A review of the evidence surrounding its application in the management of patients with a functional bowel disorder was performed. Studies were examined to assess limitations of testing methodology, interpretation of results, reproducibility, and how this relates to clinical symptoms. A wide heterogeneity in testing parameters, definition of positive/negative response, and the use of clinically irrelevant doses of test carbohydrate were common methodological limitations. These factors can subsequently impact the sensitivity, specificity, and false positive or negative detection rates. Evidence is also increasing on the poor intra-individual reproducibility in breath responses with repeated testing for fructose and lactulose. On the basis of these limitations, it is not surprising that the diagnosis of small intestinal bacterial overgrowth based on a lactulose breath test yields a wide prevalence rate and is unreliable. Finally, symptom induction during a breath test has been found to correlate poorly with the presence of carbohydrate malabsorption. The evidence suggests that breath hydrogen tests have limited clinical value in guiding clinical decision for the patient with a functional bowel disorder.

Constipation: Pathophysiology and Current Therapeutic Approaches

Chronic constipation is a common, persistent condition affecting many patients worldwide, presenting significant economic burden and resulting in substantial healthcare utilization. In addition to infrequent bowel movements, the definition of constipation includes excessive straining, a sense of incomplete evacuation, failed or lengthy attempts to defecate, use of digital manoeuvres for evacuation of stool, abdominal bloating, and hard consistency of stools. After excluding secondary causes of constipation, chronic idiopathic or primary constipation can be classified as functional defecation disorder, slow-transit constipation (STC), and constipation-predominant irritable bowel syndrome (IBS-C). These classifications are not mutually exclusive and significant overlap exists. Initial therapeutic approach to primary constipation, regardless of aetiology, consists of diet and lifestyle changes such as encouraging adequate fluid and fibre intake, regular exercise, and dietary modification. Laxatives are the mainstay of pharmacologic treatment for potential long-term therapy in patients who do not respond to lifestyle or dietary modification. After a failed empiric trial of laxatives, diagnostic testing is necessary to understand underlying anorectal and/or colonic pathophysiology. No single test provides a comprehensive assessment for primary constipation; therefore, multiple tests are used to provide complementary information to one another. Dyssynergic defecation, a functional defecation disorder, is an acquired behavioural disorder of defecation present in two-thirds of adult patients, where an inability to coordinate the abdominal, recto-anal, and pelvic floor muscles during attempted defecation exists. Biofeedback therapy is the mainstay treatment for dyssynergic defecation aimed at improving coordination of abdominal and anorectal muscles. A large percentage of patients with dyssynergic defecation also exhibit rectal hyposensitivity and may benefit from the addition of sensory retraining. Our understanding of the pathophysiology of STC is evolving. The advent of high-resolution colonic manometry allows for the improved identification of colonic motor patterns and may provide further insight into pathophysiological mechanisms. In a minority of cases of STC, identification of colonic neuropathy suggests a medically refractory condition, warranting consideration of colectomy. The pathophysiology of IBS-C is poorly understood with multiple etiological factors implicated. Pharmacological advances in the treatment of primary constipation have added therapeutic options to the armamentarium of this disorder. Drug development in the secretagogue, serotonergic prokinetic, and ileal bile acid transporter inhibition pathways has yielded current and future medical treatment options for primary chronic constipation.

Gut Bacteria and Hydrogen Sulfide: The New Old Players in Circulatory System Homeostasis

Accumulating evidence suggests that gut bacteria play a role in homeostasis of the circulatory system in mammals. First, gut bacteria may affect the nervous control of the circulatory system via the sensory fibres of the enteric nervous system. Second, gut bacteria-derived metabolites may cross the gut-blood barrier and target blood vessels, the heart and other organs involved in the regulation of the circulatory system. A number of studies have shown that hydrogen sulfide (H₂S) is an important biological mediator in the circulatory system. Thus far, research has focused on the effects of H₂S enzymatically produced by cardiovascular tissues. However, some recent evidence indicates that H₂S released in the colon may also contribute to the control of arterial blood pressure. Incidentally, sulfate-reducing bacteria are ubiquitous in mammalian colon, and H₂S is just one among a number of molecules produced by the gut flora. Other gut bacteria-derived compounds that may affect the circulatory system include methane, nitric oxide, carbon monoxide, trimethylamine or indole. In this paper, we review studies that imply a role of gut microbiota and their metabolites, such as H₂S, in circulatory system homeostasis.

Diagnosis and treatment of small intestinal bacterial overgrowth

A huge number of bacteria are hosted in the gastrointestinal tract, following a gradient increasing towards the colon. Gastric acid secretion and intestinal clearance provide the qualitative and quantitative partitioning of intestinal bacteria; small intestinal bacteria overgrowth (SIBO) occurs when these barrier mechanisms fail. Diagnosis of SIBO is challenging due to the low specificity of symptoms, the frequent association with other diseases of the gastrointestinal tract and the absence of optimal objective diagnostic tests. The therapeutic approach to SIBO is oriented towards resolving predisposing conditions, and is supported by antibiotic treatment to restore the normal small intestinal microflora and by modifications of dietary habits for symptomatic relief. In the near future, metagenomics and metabolomics will help to overcome the uncertainties of SIBO diagnosis and the pitfalls of therapeutic management, allowing the design of a personalized strategy based on the direct insight into the small intestinal microbial community.

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.

Update on diagnostic value of breath test in gastrointestinal and liver diseases

In the field of gastroenterology, breath tests (BTs) are used intermittently as diagnostic tools that allow indirect, non-invasive and relatively less cumbersome evaluation of several disorders by simply quantifying the appearance in exhaled breath of a metabolite of a specific substrate administered. The aim of this review is to have an insight into the principles, methods of analysis and performance parameters of various hydrogen, methane and carbon BTs which are available for diagnosing gastrointestinal disorders such as Helicobacter pylori infection, small intestinal bacterial overgrowth, and carbohydrate malabsorption. Evaluation of gastric emptying is routinely performed by scintigraphy which is however, difficult to perform and not suitable for children and pregnant women, this review has abridged the 13C-octanoic acid test in comparison to scintigraphy and has emphasized on its working protocol and challenges. A new development such as electronic nose test is also highlighted. Moreover we have also explored the limitations and constraints restraining the wide use of these BT. We conclude that breath testing has an enormous potential to be used as a diagnostic modality. In addition it offers distinct advantages over the traditional invasive methods commonly employed.

Mucosal Interactions between Genetics, Diet, and Microbiome in Inflammatory Bowel Disease

Numerous reviews have discussed gut microbiota composition changes during inflammatory bowel diseases (IBD), particularly Crohn’s disease (CD). However, most studies address the observed effects by focusing on studying the univariate connection between disease and dietary-induced alterations to gut microbiota composition. The possibility that these effects may reflect a number of other interconnected (i.e., pantropic) mechanisms, activated in parallel, particularly concerning various bacterial metabolites, is in the process of being elucidated. Progress seems, however, hampered by various difficult-to-study factors interacting at the mucosal level. Here, we highlight some of such factors that merit consideration, namely: (1) the contribution of host genetics and diet in altering gut microbiome, and in turn, the crosstalk among secondary metabolic pathways; (2) the interdependence between the amount of dietary fat, the fatty acid composition, the effects of timing and route of administration on gut microbiota community, and the impact of microbiota-derived fatty acids; (3) the effect of diet on bile acid composition, and the modulator role of bile acids on the gut microbiota; (4) the impact of endogenous and exogenous intestinal micronutrients and metabolites; and (5) the need to consider food associated toxins and chemicals, which can introduce confounding immune modulating elements (e.g., antioxidant and phytochemicals in oils and proteins). These concepts, which are not mutually exclusive, are herein illustrated paying special emphasis on physiologically inter-related processes.

Electronic Noses for Well-Being: Breath Analysis and Energy Expenditure

The wealth of information concealed in a single human breath has been of interest for many years, promising not only disease detection, but also the monitoring of our general well-being. Recent developments in the fields of nano-sensor arrays and MEMS have enabled once bulky artificial olfactory sensor systems, or so-called "electronic noses", to become smaller, lower power and portable devices. At the same time, wearable health monitoring devices are now available, although reliable breath sensing equipment is somewhat missing from the market of physical, rather than chemical sensor gadgets. In this article, we report on the unprecedented rise in healthcare problems caused by an increasingly overweight population. We first review recently-developed electronic noses for the detection of diseases by the analysis of basic volatile organic compounds (VOCs). Then, we discuss the primary cause of obesity from over eating and the high calorific content of food. We present the need to measure our individual energy expenditure from our exhaled breath. Finally, we consider the future for handheld or wearable devices to measure energy expenditure; and the potential of these devices to revolutionize healthcare, both at home and in hospitals.

Obesity and the microbiome

Obesity constitutes a significant and rapidly increasing public health challenge and is associated with significant co-morbidities and healthcare costs. Although undoubtedly multifactorial, research over the last decade has demonstrated that the microbes that colonize the human gut may contribute to the development of obesity through roles in polysaccharide breakdown, nutrient absorption, inflammatory responses and gut permeability. Studies have consistently shown that the Firmicutes to Bacteroidetes ratio, in particular, is increased in obesity and reduces with weight loss. In addition, we and others have shown that the methanogenic Archaea may also contribute to altered metabolism and weight gain in the host. However, much remains to be learned about the roles of different gut microbial populations in weight gain and obesity and the underlying mechanisms before we can begin to approach targeted treatments.

The gut microbiome of healthy Japanese and its microbial and functional uniqueness

The human gut microbiome has profound influences on the host's health largely through its interference with various intestinal functions. As recent studies have suggested diversity in the human gut microbiome among human populations, it will be interesting to analyse how gut microbiome is correlated with geographical, cultural, and traditional differences. The Japanese people are known to have several characteristic features such as eating a variety of traditional foods and exhibiting a low BMI and long life span. In this study, we analysed gut microbiomes of the Japanese by comparing the metagenomic data obtained from 106 Japanese individuals with those from 11 other nations. We found that the composition of the Japanese gut microbiome showed more abundant in the phylum Actinobacteria, in particular in the genus Bifidobacterium, than other nations. Regarding the microbial functions, those of carbohydrate metabolism were overrepresented with a concurrent decrease in those for replication and repair, and cell motility. The remarkable low prevalence of genes for methanogenesis with a significant depletion of the archaeon Methanobrevibacter smithii and enrichment of acetogenesis genes in the Japanese gut microbiome compared with others suggested a difference in the hydrogen metabolism pathway in the gut between them. It thus seems that the gut microbiome of the Japanese is considerably different from those of other populations, which cannot be simply explained by diet alone. We postulate possible existence of hitherto unknown factors contributing to the population-level diversity in human gut microbiomes.

Diagnosing lactose malabsorption in children: difficulties in interpreting hydrogen breath test results

Lactose malabsorption (LM) is caused by insufficient enzymatic degradation of the disaccharide by intestinal lactase. Although hydrogen (H2) breath tests (HBTs) are routinely applied to diagnose LM, false-negative results are not uncommon. Thirty-two pediatric patients (19 females, 13 males) were included in this prospective study. After oral lactose administration (1 g kg(-1) bodyweight to a maximum of 25 g), breath H2 was measured by electrochemical detection. HBT was considered positive if H2 concentration exceeded an increase of  ⩾20 ppm from baseline. In addition to H2, exhaled methane (CH4), blood glucose concentrations and clinical symptoms (flatulence, abdominal pain, diarrhea) were monitored. A positive HBT indicating LM was found in 12/32 (37.5%) patients. Only five (41.7%, 5/12) of these had clinical symptoms during HBT indicating lactose intolerance (LI). Decreased blood glucose concentration increments (⩽20 mg dL(-1) (⩽1.1 mmol L(-1))) were found in 3/5 of these patients. CH4 concentrations  ⩾10 ppm at any time during the test were observed in 5/32 (15.6%) patients and in 9/32 (28.1%) between 1 ppm and 9 ppm above baseline after lactose ingestion. In patients with positive HBT 10/12 (83.3%) showed elevated CH4 (>1 ppm) above baseline in breath gas, whereas in patients with negative HBT this figure was only 4/17 (23.5%). In addition to determining H2 in exhaled air, documentation of clinical symptoms, measurement of blood glucose and breath CH4 concentrations may be helpful in deciding whether in a given case an HBT correctly identifies patients with clinically relevant LM.

Modeling of breath methane concentration profiles during exercise on an ergometer

We develop a simple three compartment model based on mass balance equations which quantitatively describes the dynamics of breath methane concentration profiles during exercise on an ergometer. With the help of this model it is possible to estimate the endogenous production rate of methane in the large intestine by measuring breath gas concentrations of methane.

Small Bowel Bacterial Overgrowth in Children

OBJECTIVES

The aim of study was to perform a comprehensive review of the pathogenesis, available diagnostic procedures, prevalence, clinical manifestations, and consequences of small bowel bacterial overgrowth (SBBO) as well as treatment options in the pediatric population.

METHODS

A literature search including MEDLINE, PubMed, and Web of Science databases was performed.

RESULTS

SBBO is found in a variety of childhood conditions in which the normal homeostatic mechanisms restricting bacterial colonization in the small bowel are disturbed by congenital or acquired anatomical abnormalities, diminished gastric acid secretion, congenital alteration of intestinal motility or acquired small bowel diseases, or other chronic disorders including primary or acquired immunodeficiency. Data show that SBBO may be an underrecognized cause of pediatric morbidity. Although several diagnostic tests for SBBO determination are available, each has its drawbacks and limitations. Indeed, there is still no "criterion standard" for SBBO diagnosis in the pediatric population. Owing to lack of established guidelines and few published interventional studies that assess the effectiveness of SBBO therapy, treatment of children with SBBO remains empiric and comprises antibiotic or probiotic therapy.

CONCLUSIONS

Further research is needed to determine the clinical impact of SBBO and to establish diagnostic and therapeutic guidelines applicable to children.

Stable isotope and high precision concentration measurements confirm that all humans produce and exhale methane

Mammalian formation of methane (methanogenesis) is widely considered to occur exclusively by anaerobic microbial activity in the gastrointestinal tract. Approximately one third of humans, depending on colonization of the gut by methanogenic archaea, are considered methane producers based on the classification terminology of high and low emitters. In this study laser absorption spectroscopy was used to precisely measure concentrations and stable carbon isotope signatures of exhaled methane in breath samples from 112 volunteers with an age range from 1 to 80 years. Here we provide analytical evidence that volunteers exhaled methane levels were significantly above background (inhaled) air. Furthermore, stable carbon isotope values of the exhaled methane unambiguously confirmed that this gas was produced by all of the human subjects studied. Based on the emission and stable carbon isotope patterns of various age groups we hypothesize that next to microbial sources in the gastrointestinal tracts there might be other, as yet unidentified, processes involved in methane formation supporting the idea that humans might also produce methane endogenously in cells. Finally we suggest that stable isotope measurements of volatile organic compounds such as methane might become a useful tool in future medical research diagnostic programs.

Inhaled Methane Limits the Mitochondrial Electron Transport Chain Dysfunction during Experimental Liver Ischemia-Reperfusion Injury

BACKGROUND

Methanogenesis can indicate the fermentation activity of the gastrointestinal anaerobic flora. Methane also has a demonstrated anti-inflammatory potential. We hypothesized that enriched methane inhalation can influence the respiratory activity of the liver mitochondria after an ischemia-reperfusion (IR) challenge.

METHODS

The activity of oxidative phosphorylation system complexes was determined after in vitro methane treatment of intact liver mitochondria. Anesthetized Sprague-Dawley rats subjected to standardized 60-min warm hepatic ischemia inhaled normoxic air (n = 6) or normoxic air containing 2.2% methane, from 50 min of ischemia and throughout the 60-min reperfusion period (n = 6). Measurement data were compared with those on sham-operated animals (n = 6 each). Liver biopsy samples were subjected to high-resolution respirometry; whole-blood superoxide and hydrogen peroxide production was measured; hepatocyte apoptosis was detected with TUNEL staining and in vivo fluorescence laser scanning microscopy.

RESULTS

Significantly decreased complex II-linked basal respiration was found in the normoxic IR group at 55 min of ischemia and a lower respiratory capacity (~60%) and after 5 min of reperfusion. Methane inhalation preserved the maximal respiratory capacity at 55 min of ischemia and significantly improved the basal respiration during the first 30 min of reperfusion. The IR-induced cytochrome c activity, reactive oxygen species (ROS) production and hepatocyte apoptosis were also significantly reduced.

CONCLUSIONS

The normoxic IR injury was accompanied by significant functional damage of the inner mitochondrial membrane, increased cytochrome c activity, enhanced ROS production and apoptosis. An elevated methane intake confers significant protection against mitochondrial dysfunction and reduces the oxidative damage of the hepatocytes.

Comparative metabolomics in vegans and omnivores reveal constraints on diet-dependent gut microbiota metabolite production

OBJECTIVE

The consumption of an agrarian diet is associated with a reduced risk for many diseases associated with a 'Westernised' lifestyle. Studies suggest that diet affects the gut microbiota, which subsequently influences the metabolome, thereby connecting diet, microbiota and health. However, the degree to which diet influences the composition of the gut microbiota is controversial. Murine models and studies comparing the gut microbiota in humans residing in agrarian versus Western societies suggest that the influence is large. To separate global environmental influences from dietary influences, we characterised the gut microbiota and the host metabolome of individuals consuming an agrarian diet in Western society.

DESIGN AND RESULTS

Using 16S rRNA-tagged sequencing as well as plasma and urinary metabolomic platforms, we compared measures of dietary intake, gut microbiota composition and the plasma metabolome between healthy human vegans and omnivores, sampled in an urban USA environment. Plasma metabolome of vegans differed markedly from omnivores but the gut microbiota was surprisingly similar. Unlike prior studies of individuals living in agrarian societies, higher consumption of fermentable substrate in vegans was not associated with higher levels of faecal short chain fatty acids, a finding confirmed in a 10-day controlled feeding experiment. Similarly, the proportion of vegans capable of producing equol, a soy-based gut microbiota metabolite, was less than that was reported in Asian societies despite the high consumption of soy-based products.

CONCLUSIONS

Evidently, residence in globally distinct societies helps determine the composition of the gut microbiota that, in turn, influences the production of diet-dependent gut microbial metabolites.

Oatmeal porridge: impact on microflora-associated characteristics in healthy subjects

Oatmeal porridge has been consumed for centuries and has several health benefits. We aimed to investigate the effect of oatmeal porridge on gut microflora functions. A total of ten healthy subjects ingested 60 g oatmeal porridge daily for 1 week. The following microflora-associated characteristics were assessed before and after the intervention: intestinal gas production following lactulose ingestion, faecal excretion of SCFA and faecal levels of urease and β-galactosidase. In addition, rectal levels of PGE2 were measured. Microbial fermentation as evaluated by intestinal gas production and excretion of SCFA did not change significantly following the dietary intervention. However, faecal levels of β-galactosidase and urease decreased after eating oatmeal porridge (P=0·049 and 0·031, respectively). Host inflammatory state, as measured by rectal levels of PGE2, also decreased, but the change was not significant (P=0·168). The results suggest that oatmeal porridge has an effect on gut microbial functions and may possess potential prebiotic properties that deserve to be investigated further.

Role of the Gut Microbiome in Obesity and Diabetes Mellitus

Type 2 diabetes mellitus (T2DM) and obesity represent two of the biggest global health challenges of this century and are associated with significant comorbidities and healthcare costs. Although multiple factors undoubtedly contribute to the development and progression of DM and obesity, research over the last decade has demonstrated that the microbes that colonize the human gut may play key contributory roles. Gut microbes are now known to codevelop with the human host and are strongly influenced by mode of birth and early diet and nutrition, as well as environmental and other factors including antibiotic exposure. Gut microbes contribute to human health through roles in polysaccharide breakdown, nutrient absorption, inflammatory responses, gut permeability, and bile acid modification. Numerous studies have suggested that disruptions in the relative proportions of gut microbial populations may contribute to weight gain and insulin resistance, including alterations in Gammaproteobacteria and Verrucomicrobia and the ratios of Firmicutes to Bacteroidetes in weight gain and possible alterations in butyrate-producing bacteria such as Faecalibacterium prausnitzii in DM. In addition, it has been shown that the methanogenic Archaea may contribute to altered metabolism and weight gain in the host. However, the majority of studies are performed with stool or colonic samples and may not be representative of the metabolically active small intestine. Studies predominantly in rodent models are beginning to elucidate the mechanisms by which gut microbes contribute to DM and obesity, but much remains to be learned before we can begin to approach targeted treatments.

Breath methane in functional constipation: response to treatment with Ispaghula husk

BACKGROUND

Colonic fermentation produces hydrogen (H2 ), and also produces methane (CH4 ) in subjects with methanogenic flora (M+). Methane production has been associated with chronic constipation (CC) and with changes in gut motility. To determine CH4 production in CC compared to controls, and to assess whether the therapeutic response to Ispaghula husk in CC differs between CH4 -producers and non-producers.

METHODS

Forty-eight patients with functional constipation or irritable bowel syndrome-constipation and 19 healthy age-and-sex-matched volunteers (HV) filled in a 1-week symptom diary and a dietary questionnaire. They then underwent a lactulose breath test (LBT) to measure H2 and CH4 production (peak and area under the time-concentration curve, AUC-) and a colonic transit time (CTT) assessment. In patients, measurements were repeated after a 4-week treatment with Ispaghula husk.

KEY RESULTS

Prevalence of M+ in patients was 60.5% vs 52.6% in HV (p = 0.37). Patients had significantly longer CTT and greater production of both H2 and CH4 during LBT. There was a significant correlation between CH4 production and CTT (r = 0.51; p = 0.07). Treatment response rate was similar for M+ and M- patients (58.3% vs 52.9%; p = 0.76) as were the increases in bowel movements and Bristol score, changes in abdominal discomfort and bloating. In M+, treatment reduced CTT (-10 ± 35 h; p = 0.029 vs baseline) and CH4 levels: peak CH4 (-13 ± 24 ppm; p = 0.014) and CH4 -AUC (-817 ± 3100 ppm/min; p = 0.04).

CONCLUSIONS & INFERENCES

Although CH4 production has been associated with CC pathophysiology, we found that CH4 status did not negatively affect the response to Ispaghula husk treatment. The measurement of CH4 levels as a biomarker tool for CC requires further appraisal.

Methanogen communities in stools of humans of different age and health status and co-occurrence with bacteria

Hydrogenotrophic methanogens live in a synthrophic relationship with the human gut microbiota as the terminal part of the anaerobic food chain. Methanobrevibacter smithii of the Methanobacteriales is the prevailing archaeal species. Recently, methylotrophic archaea of the novel order Methanomassiliicoccales were isolated from human stools. Few data exist on the prevalence, abundance, persistence and ecology of these methanogens in humans. This study investigated methanogen communities in 26 healthy and obese children (8-14 years) and 18 adults (28-78 years) using quantitative PCR. Samples were obtained from nine females before and after giving birth. Bacterial groups linked to the abundance of methanogens in adult females were identified using a 16S rRNA gene amplicon data set. A total of 89% and 65% of adults and children, respectively, carried Methanobacteriales. Methanomassiliicoccales were recovered from 50% of the adults and one child. Mean relative abundance of Methanomassiliicoccales in adults was lower than that of Methanobacteriales (0.10% versus 0.52%). Both Methanobacteriales and Methanomassiliicoccales formed stable communities in females before and after giving birth. Methanobacteriales co-occurred with bacterial taxonomic groups associated with the trophic chain from carbohydrate degradation to hydrogen and formate formation. Relative abundance was inversely correlated to Blautia. Negative correlation with little characterized groups within the Clostridiales indicated possible interactions of Methanomassiliicoccales with the bacterial community.

Exhaled methane concentration profiles during exercise on an ergometer

Exhaled methane concentration measurements are extensively used in medical investigation of certain gastrointestinal conditions. However, the dynamics of endogenous methane release is largely unknown. Breath methane profiles during ergometer tests were measured by means of a photoacoustic spectroscopy based sensor. Five methane-producing volunteers (with exhaled methane level being at least 1 ppm higher than room air) were measured. The experimental protocol consisted of 5 min rest--15 min pedalling (at a workload of 75 W)--5 min rest. In addition, hemodynamic and respiratory parameters were determined and compared to the estimated alveolar methane concentration. The alveolar breath methane level decreased considerably, by a factor of 3-4 within 1.5 min, while the estimated ventilation-perfusion ratio increased by a factor of 2-3. Mean pre-exercise and exercise methane concentrations were 11.4 ppm (SD:7.3) and 2.8 ppm (SD:1.9), respectively. The changes can be described by the high sensitivity of exhaled methane to ventilation-perfusion ratio and are in line with the Farhi equation.

In vitro study and comparison of caecal methanogenesis and fermentation pattern in the brown hare (Lepus europaeus) and domestic rabbit (Oryctolagus cuniculus)

The brown hare and the domestic rabbit are mid-sized herbivorous mammals and hindgut fermenters, though their digestive physiologies differ in some traits. The objective of this study was to estimate and compare the caecal microbial activity in hares and rabbits via an analysis of the following end-products of in vitro caecal fermentation: methane, total gas production, short chain fatty acids and ammonia concentration. Hare caecal methanogenesis occurred at a much lower level (0.25 mmol/kg for samples incubated without substrate and 0.22 mmol/kg for samples incubated with substrate) than that of the rabbit (15.49 and 11.73 mmol/kg, respectively) (P<0.001). The impact of the substrate’s presence on caecal methanogenesis was not significant, though its presence increased the total gas production during fermentation (P<0.001). Hare caecal microflora produced a lower short chain fatty acids concentration than did rabbit microorganisms (P<0.05). In unincubated hare samples, the short chain fatty acids concentration was 28.4 mmol/kg, whereas in unincubated rabbit samples, the short chain fatty acids concentration was 51.8 mmol/kg. The caecal fermentation pattern of the hare was characterised by higher propionate and isobutyrate molar proportions compared with those observed in rabbit caecum (P<0.01). No significant changes in the ammonia concentration in either rabbit or hare caecum were found. The results obtained indicate some differences in the activity of the microbial populations colonising the hare and rabbit caecum, particularly in regards to methanogenic Archaea.

The role of methane in mammalian physiology-is it a gasotransmitter?

Mammalian methanogenesis is widely considered to be an exclusive sign of anaerobic microbial activity in the gastrointestinal tract. This commonly held view was challenged, however, when in vitro and in vivo investigations demonstrated the possibility of nonmicrobial methane formation in aerobic organisms, in plants and animals. The aim of this review is to discuss the available literature data on the biological role of methane. When we evaluate the significance of methane generation in the mammalian physiology, the question may be examined: is it a gas mediator? Overall the data do not fully support the gasotransmitter concept, but they do support the notion that methane liberation may be linked to redox regulation and may be connected with hypoxic events leading to, or associated with a mitochondrial dysfunction. In this respect, the available information suggests that hypoxia-induced methane generation may be a necessary phenomenon of aerobic life, and perhaps a surviving evolutionary trait in the eukaryote cell.

Gut microbial and short-chain fatty acid profiles in adults with chronic constipation before and after treatment with lubiprostone

Identifying specific gut microorganisms associated with chronic constipation may be useful for diagnostic and therapeutic purposes. The objective of this study was to evaluate whether or not the gut microbial community of constipated subjects had specific microbial signatures and to assess the effects of lubiprostone treatment on the gut microbial community. Stool diaries, breath H2 and CH4 levels, and stool samples were collected from ten healthy subjects and nine patients meeting the Rome III criteria for chronic functional constipation. Constipated subjects received lubiprostone for four weeks, during which stool diaries were maintained. Stool samples were evaluated for gut microbial communities using pyrosequencing and quantitative real-time PCR (qPCR) targeting 16S-rRNA gene, along with concentrations of short-chain fatty acids (SCFAs) using high-performance liquid chromatography. Prior to treatment, gut microbial profiles were similar between constipated subjects and healthy subjects, while iso-butyrate levels were significantly higher in constipated subjects compared with healthy subjects. Despite increases in stool frequency and improvements in consistency after lubiprostone treatment, gut microbial profiles and community diversity after treatment showed no significant change compared to before treatment. While we did not observe a significant difference in either breath methane or archaeal abundance between the stool samples of healthy and constipated subjects, we confirmed a strong correlation between archaeal abundance measured by qPCR and the amount of methane gas exhaled in the fasting breath. Butyrate levels, however, were significantly higher in the stool samples of constipated subjects after lubiprostone treatment, suggesting that lubiprostone treatment had an effect on the net accumulation of SCFAs in the gut. In conclusion, lubiprostone treatment improved constipation symptoms and increased levels of butyrate without substantial modification of the gut microbial structure.

Breath testing for small intestinal bacterial overgrowth: maximizing test accuracy

The diagnosis of small intestinal bacterial overgrowth (SIBO) has increased considerably owing to a growing recognition of its association with common bowel symptoms including chronic diarrhea, bloating, abdominal distention, and the irritable bowel syndrome. Ideally, an accurate and objective diagnosis of SIBO should be established before initiating antibiotic treatment. Unfortunately, no perfect test exists for the diagnosis of SIBO. The current gold standard, small-bowel aspiration and quantitative culture, is limited by its high cost, invasive nature, lack of standardization, sampling error, and need for dedicated infrastructure. Although not without shortcomings, hydrogen breath testing provides the simplest noninvasive and widely available diagnostic modality for suspected SIBO. Carbohydrates such as lactulose and glucose are the most widely used substrates in hydrogen breath testing, with glucose arguably providing greater testing accuracy. Lactose, fructose, and sorbitol should not be used as substrates in the assessment of suspected SIBO. The measurement of methane in addition to hydrogen can increase the sensitivity of breath testing for SIBO. Diagnostic accuracy of hydrogen breath testing in SIBO can be maximized by careful patient selection for testing, proper test preparation, and standardization of test performance as well as test interpretation.

Archaea and the human gut: New beginning of an old story

Methanogenic archaea are known as human gut inhabitants since more than 30 years ago through the detection of methane in the breath and isolation of two methanogenic species belonging to the order Methanobacteriales, Methanobrevibacter smithii and Methanosphaera stadtmanae. During the last decade, diversity of archaea encountered in the human gastrointestinal tract (GIT) has been extended by sequence identification and culturing of new strains. Here we provide an updated census of the archaeal diversity associated with the human GIT and their possible role in the gut physiology and health. We particularly focus on the still poorly characterized 7^th order of methanogens, the Methanomassiliicoccales, associated to aged population. While also largely distributed in non-GIT environments, our actual knowledge on this novel order of methanogens has been mainly revealed through GIT inhabitants. They enlarge the number of final electron acceptors of the gut metabolites to mono- di- and trimethylamine. Trimethylamine is exclusively a microbiota-derived product of nutrients (lecithin, choline, TMAO, L-carnitine) from normal diet, from which seems originate two diseases, trimethylaminuria (or Fish-Odor Syndrome) and cardiovascular disease through the proatherogenic property of its oxidized liver-derived form. This therefore supports interest on these methanogenic species and its use as archaebiotics, a term coined from the notion of archaea-derived probiotics.

Biofilm formation of mucosa-associated methanoarchaeal strains

Although in nature most microorganisms are known to occur predominantly in consortia or biofilms, data on archaeal biofilm formation are in general scarce. Here, the ability of three methanoarchaeal strains, Methanobrevibacter smithii and Methanosphaera stadtmanae, which form part of the human gut microbiota, and the Methanosarcina mazei strain Gö1 to grow on different surfaces and form biofilms was investigated. All three strains adhered to the substrate mica and grew predominantly as bilayers on its surface as demonstrated by confocal laser scanning microscopy analyses, though the formation of multi-layered biofilms of Methanosphaera stadtmanae and Methanobrevibacter smithii was observed as well. Stable biofilm formation was further confirmed by scanning electron microscopy analysis. Methanosarcina mazei and Methanobrevibacter smithii also formed multi-layered biofilms in uncoated plastic μ-dishes^TM, which were very similar in morphology and reached a height of up to 40 μm. In contrast, biofilms formed by Methanosphaera stadtmanae reached only a height of 2 μm. Staining with the two lectins ConA and IB4 indicated that all three strains produced relatively low amounts of extracellular polysaccharides most likely containing glucose, mannose, and galactose. Taken together, this study provides the first evidence that methanoarchaea can develop and form biofilms on different substrates and thus, will contribute to our knowledge on the appearance and physiological role of Methanobrevibacter smithii and Methanosphaera stadtmanae in the human intestine.

The intestinal archaea Methanosphaera stadtmanae and Methanobrevibacter smithii activate human dendritic cells

The methanoarchaea Methanosphaera stadtmanae and Methanobrevibacter smithii are known to be part of the indigenous human gut microbiota. Although the immunomodulatory effects of bacterial gut commensals have been studied extensively in the last decade, the impact of methanoarchaea in human's health and disease was rarely examined. Consequently, we studied and report here on the effects of M. stadtmanae and M. smithii on human immune cells. Whereas exposure to M. stadtmanae leads to substantial release of proinflammatory cytokines in monocyte-derived dendritic cells (moDCs), only weak activation was detected after incubation with M. smithii. Phagocytosis of M. stadtmanae by moDCs was demonstrated by confocal microscopy as well as transmission electronic microscopy (TEM) and shown to be crucial for cellular activation by using specific inhibitors. Both strains, albeit to different extents, initiate a maturation program in moDCs as revealed by up-regulation of the cell-surface receptors CD86 and CD197 suggesting additional activation of adaptive immune responses. Furthermore, M. stadtmanae and M. smithii were capable to alter the gene expression of antimicrobial peptides in moDCs to different extents.

Taken together, our findings strongly argue that the archaeal gut inhabitants M. stadtmanae and M. smithii are specifically recognized by the human innate immune system. Moreover, both strains are capable of inducing an inflammatory cytokine response to different extents arguing that they might have diverse immunomodulatory functions. In conclusion, we propose that the impact of intestinal methanoarchaea on pathological conditions involving the gut microbiota has been underestimated until now.

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.

Methanogens, methane and gastrointestinal motility

Anaerobic fermentation of the undigested polysaccharide fraction of carbohydrates produces hydrogen in the intestine which is the substrate for methane production by intestinal methanogens. Hydrogen and methane are excreted in the flatus and in breath giving the opportunity to indirectly measure their production using breath testing. Although methane is detected in 30%-50% of the healthy adult population worldwide, its production has been epidemiologically and clinically associated with constipation related diseases, like constipation predominant irritable bowel syndrome and chronic constipation. While a causative relation is not proven yet, there is strong evidence from animal studies that methane delays intestinal transit, possibly acting as a neuromuscular transmitter. This evidence is further supported by the universal finding that methane production (measured by breath test) is associated with delayed transit time in clinical studies. There is also preliminary evidence that antibiotic reduction of methanogens (as evidenced by reduced methane production) predicts the clinical response in terms of symptomatic improvement in patients with constipation predominant irritable bowel syndrome. However, we have not identified yet the mechanism of action of methane on intestinal motility, and since methane production does not account for all constipation associated cases, there is need for high quality clinical trials to examine methane as a biomarker for the diagnosis or as a biomarker that predicts antibiotic treatment response in patients with constipation related disorders.

A double-blind placebo-controlled randomized trial on probiotics in small bowel bacterial overgrowth in children treated with omeprazole

OBJECTIVE

To evaluate the incidence of small bowel bacterial overgrowth (SBBO) in children treated with omeprazole, and to test whether probiotics influence the incidence.

METHODS

A double-blinded, placebo-controlled trial was performed in 70 children treated orally during four weeks with 20mg omeprazole per day. Lactobacillus rhamnosus R0011 (1.9×10(9) cfu) and Lactobacillus acidophilus R0052 (0.1×10(9) cfu) were simultaneously given daily to 36 subjects (probiotic group), while 34 subjects received placebo (placebo group). The diagnosis of SBBO was based on the development of suggestive symptoms, in combination with a positive glucose breath test.

RESULTS

After one month of proton pump inhibitor (PPI) treatment, 30% (21/70) had a positive breath test suggesting SBBO; of these 62% were symptomatic. Five children developed SBBO-like symptoms, but had a negative breath test; and 44 (63%) were symptom free and had a negative breath test. There was no difference in the incidence of positive breath tests in the probiotic versus the placebo group (33% vs 26.5%; p=0.13).

CONCLUSIONS

Since symptoms suggesting SBBO developed in 26% of PPI-treated children, and since the glucose breath test was abnormal in 72% of these, this side-effect should be more frequently considered. The probiotic tested did not decrease the risk to develop SBBO.

Association between symptoms of irritable bowel syndrome and methane and hydrogen on lactulose breath test

Whether hydrogen and methane gas produced during lactulose breath test (LBT) are associated with symptoms of irritable bowel syndrome (IBS) is not determined. We aimed to investigate whether hydrogen and methane on LBT are associated with IBS symptoms. Sixty-eight IBS patients meeting the Rome III criteria for IBS, and 55 healthy controls, underwent LBT. The IBS subjects recorded their customary gastrointestinal symptoms on a questionnaire using visual analogue scales. LBT positivity was defined to be above 20 ppm rise of hydrogen or 10 ppm rise of methane within 90 min. Gas amounts produced during LBT were determined by calculating area under the curve of hydrogen and methane excretion. Symptom severity scores were not different between the LBT (+) IBS and LBT (-) IBS subjects and also between methane producers and non-methane producers. Gas amounts produced during LBT were not associated with IBS symptoms, except a weak correlation between total gas amounts and a few IBS symptoms such as bloating (r = 0.324, P = 0.039), flatulence (r = 0.314, P = 0.046) and abdominal pain (r = 0.364, P = 0.018) only in LBT (+) IBS. In conclusion, hydrogen and methane gas on LBT are not useful for predicting the customary symptoms and subtypes of IBS.

Prevalence of lactose malabsorption in Mexican children: importance of measuring methane in expired air

BACKGROUND AND AIMS

To compare the prevalence of lactose malabsorption (LM) in children by analyzing hydrogen content in expired air vs. the inclusion of methane excretion.

METHODS

A total of 138 children (4-17 years old) attending different boarding schools in Mexico were included in this study. To measure H₂ and CH₄ in expired air, breath samples were collected before administering whole milk (240 mL for 4- to 6-year-old children and 360 mL for 7- to 17-year-old children) and at 60, 120, 180, and 240 min afterward. A coprological examination was also carried out.

RESULTS

Methane production prevalence was 47.8% (29.7% of the children produced methane and hydrogen, whereas 18.1% produced methane only). When measuring only exhaled hydrogen in expired air (H₂ ≥20 ppm), prevalence of LM was 31%; however, when methane concentration was considered (H₂ + (CH₄ x 2)) ≥18 ppm, prevalence increased significantly to 44%. Among children with LM, 51.6% presented intestinal parasites.

CONCLUSIONS

Methane should be measured in exhaled air to improve diagnosis of LM in populations with a high prevalence of methane production.

Colonic methane production modifies gastrointestinal toxicity associated with adjuvant 5-fluorouracil chemotherapy for colorectal cancer

GOALS

To investigate the association of colonic methane, formed by methanogenic achaea, and pH with gastrointestinal symptoms during colorectal cancer chemotherapy.

BACKGROUND

Adjuvant 5-fluorouracil chemotherapy reduces recurrences in colorectal cancer, but causes severe gastrointestinal toxicity, partly related to disturbed intestinal microbiota.

STUDY

Resected colorectal cancer patients (n=143) were analyzed for colonic methanogenesis and pH before and during the 24 weeks of 5-fluorouracil chemotherapy and for gastrointestinal symptoms during chemotherapy. This study was performed within the setting of an intervention study on the effects of Lactobacillus on chemotherapy-related gastrointestinal toxicity. The site of resected cancer, resection type, stoma, chemotherapy regimen, hypolactasia, and Lactobacillus intervention were considered as possible confounding factors, and multivariate models were constructed.

RESULTS

Baseline methane producers had less frequent diarrhea (more than or equal to moderate) during chemotherapy than nonproducers [odds ratio (OR), 0.42; 95% confidence interval (CI), 0.20 to 0.88; P=0.022] and more frequent constipation (OR, 4.56; 95% CI, 2.01 to 10.32; P<0.001). Baseline fecal pH was also associated with symptoms during chemotherapy; higher the pH, the lower the risk of diarrhea (OR, 0.56; 95% CI, 0.31 to 1.02; P=0.058) and higher the risk of constipation (OR, 2.23; 95% CI, 1.35 to 3.68; P=0.002). In multivariate stepwise models, methanogenesis was a significant explaining factor with inverse association with diarrhea and positive association with constipation. Fecal pH, which was significantly associated with methane production, was no longer a significant explaining factor when methanogensis was included in the model.

CONCLUSIONS

Methane producer status has a role in determining whether patient experiences diarrhea or constipation during 5-fluorouracil therapy. This underscores the importance of intestinal microbiota in the development of intestinal toxicity during 5-fluorouracil therapy.

Contributions of the microbial hydrogen economy to colonic homeostasis

Colonic gases are among the most tangible features of digestion, yet physicians are typically unable to offer long-term relief from clinical complaints of excessive gas. Studies characterizing colonic gases have linked changes in volume or composition with bowel disorders and shown hydrogen gas (H(2)), methane, hydrogen sulphide, and carbon dioxide to be by-products of the interplay between H(2)-producing fermentative bacteria and H(2) consumers (reductive acetogens, methanogenic archaea and sulphate-reducing bacteria [SRB]). Clinically, H(2) and methane measured in breath can indicate lactose and glucose intolerance, small intestinal bacterial overgrowth and IBS. Methane levels are increased in patients with constipation or IBS. Hydrogen sulphide is a by-product of H(2) metabolism by SRB, which are ubiquitous in the colonic mucosa. Although higher hydrogen sulphide and SRB levels have been detected in patients with IBD, and to a lesser extent in colorectal cancer, this colonic gas might have beneficial effects. Moreover, H(2) has been shown to have antioxidant properties and, in the healthy colon, physiological H(2) concentrations might protect the mucosa from oxidative insults, whereas an impaired H(2) economy might facilitate inflammation or carcinogenesis. Therefore, standardized breath gas measurements combined with ever-improving molecular methodologies could provide novel strategies to prevent, diagnose or manage numerous colonic disorders.

The effects of methane and hydrogen gases produced by enteric bacteria on ileal motility and colonic transit time

BACKGROUND

Gases produced by intestinal flora may modulate intestinal motor function in healthy individuals as well as those with functional bowel disease. Methane, produced by enteric bacteria in the human gut, is associated with slowed intestinal transit and constipation. The effects of hydrogen, another main gas produced by bacterial fermentation in the gut, on small bowel and colonic motor function remains unrecognized. Therefore, we set out to investigate whether intestinal gases including methane and hydrogen could influence the small bowel motility and colonic transit.

METHODS

Guinea pig ileum was placed in the peristaltic bath with tension transducers attached to measure velocity and amplitude of peristaltic contraction before and after the infusion of control, hydrogen, and methane gases. Also, changes in the intraluminal pressures were monitored before and after the gas infusions.

KEY RESULTS

Methane decreased peristaltic velocity and increased contraction amplitude significantly of guinea pig ileum (P < 0.05). The AUC of intraluminal pressure was significantly increased with methane in guinea pig ileum (P < 0.05). In a second experiment, guinea pig colon was placed in the peristaltic bath to measure transit time before and after control, hydrogen, methane, and methane-hydrogen mixture gas infusions. Hydrogen shortened colonic transit time by 47% in the proximal colon, and by 10% in the distal colon, when compared with baselines (P < 0.05).

CONCLUSIONS & INFERENCES

Methane delayed ileal peristaltic conduction velocity by augmenting contractility. Hydrogen shortened colonic transit, and that effect was more prominent in the proximal colon than distal colon.