Breath Methane Excretion Is not An Accurate Marker of Colonic Methane Production in Irritable Bowel Syndrome

Chronic constipation and gut microbiota: current research insights and therapeutic implications

Chronic constipation is a prevalent clinical condition. Its etiology and pathogenesis have not yet been fully understood. In recent years, mounting evidence suggests a close association between chronic constipation and intestinal dysbiosis, including alterations in the colony structure and metabolites, as well as the modulation of bowel movements via the brain-gut-microbiota axis. With the deepening of related research, probiotic-related therapies are expected to become a potential first-line treatment for chronic constipation in the future. In this review, we summarize the current research insights into the intricate relationships between chronic constipation and the gut microbiota and briefly discuss several different approaches for treating chronic constipation. The findings from this review may advance our understanding of the pathological mechanisms underlying chronic constipation and, ultimately, translate them into improvements in patient care.

Prevalence of methanogens and associated factors in patients with irritable bowel syndrome and healthy controls in a Southeastern Mexican population

INTRODUCTION

Methane (CH₄) is an inert gas produced by colonic anaerobes and has been associated with different intestinal diseases, including irritable bowel syndrome (IBS). According to geographic region, the prevalence of methanogens varies, being higher in Africa (80%) and lower in the United States (35-40%). In Mexico, the prevalence of methanogens is unknown.

AIM

To evaluate the prevalence of CH₄ producers and associated factors in a group of patients with IBS and controls in a Mexican population.

MATERIALS AND METHODS

A baseline fasting measurement of alveolar H₂ and CH₄ gas was carried out, by gas chromatography (stationary phase), in consecutive patients diagnosed with IBS and a control group. Subjects with baseline levels of H₂ of 0 ppm and CH₄ ≥ 5 ppm were classified as methanogenic.

RESULTS

A total of 132 controls (53.8% women) and 67 patients with IBS (76% women) were included. The overall prevalence (n = 199) of methanogenic subjects was 38% (n = 76) (95% CI: 0.31-0.45) and they had a greater prevalence of overweight/obesity (56.5 vs 39.8%, P = .028). The prevalence of methanogens in the healthy controls was 41.6% (95% CI: 0.33-0.49), whereas, in the patients with IBS, it was 31.4% (n = 21, 71% IBS-C and 29% IBS-M).

CONCLUSIONS

The prevalence of methanogens in our study on a Mexican population was comparable to that reported in other populations and was associated with overweight/obesity. One-third of the patients with IBS presented with methanogens. Said microorganisms were particularlyassociated with the constipation-predominant IBS subtype.

Menstrual Cycle Variation in MRI-Based Quantification of Intraluminal Gas in Women With and Without Dysmenorrhea

Women frequently report increased bloating, flatulence, and pain during the perimenstrual period. However, it is unknown whether women have more intraluminal gas during menses. To evaluate whether pain-free women or women with dysmenorrhea have different amounts of intraluminal bowel gas during the menses, we utilized magnetic resonance imaging (MRI) to determine colonic gas volumes throughout the menstrual cycle. To avoid dietary influence, the participants were instructed to avoid gas-producing foods before their scheduled MRI. We verified the measurement repeatability across the reviewers and obtained an intraclass correlation coefficient of 0.92. There were no significant differences in intraluminal gas volume between menses and non-menses scans (p = 0.679). Even among the women with dysmenorrhea, there was no significant difference in the intraluminal gas volume between menses and non-menses (p = 0.753). During menstruation, the participants with dysmenorrhea had less intraluminal gas than participants without dysmenorrhea (p = 0.044). However, the correlation between the bowel gas volume and the pain symptoms were not significant (p > 0.05). Although increased bowel symptoms and bloating are reported in the women with dysmenorrhea during menses, our results do not support the hypothesis that increased intraluminal gas is a contributing factor. Although dietary treatment has been shown in other studies to improve menstrual pain, the mechanism responsible for abdominal symptoms requires further investigation. Our findings demonstrate that the intraluminal bowel gas volume measurements are feasible and are unaffected by menses under a controlled diet. The method described might prove helpful in future mechanistic studies in clarifying the role of intraluminal bowel gas in other conditions.

Methanogen Abundance Thresholds Capable of Differentiating In Vitro Methane Production in Human Stool Samples

BACKGROUND

Intestinal methane (CH₄) gas production has been associated with a number of clinical conditions and may have important metabolic and physiological effects.

AIMS

In this study, taxonomic and functional gene analyses and in vitro CH₄ gas measurements were used to determine if molecular markers can potentially serve as clinical tests for colonic CH₄ production.

METHODS

We performed a cross-sectional study involving full stool samples collected from 33 healthy individuals. In vitro CH₄ gas measurements were obtained after 2-h incubation of stool samples and used to characterize samples as CH₄ positive (CH₄+) and CH₄ negative (CH₄-; n = 10 and 23, respectively). Next, we characterized the fecal microbiota through high-throughput DNA sequencing with a particular emphasis on archaeal phylum Euryarchaeota. Finally, qPCR analyses, targeting the mcrA gene, were done to determine the ability to differentiate CH₄+ versus CH₄- samples and to delineate major methanogen species associated with CH₄ production.

RESULTS

Methanobrevibacter was found to be the most abundant methane producer and its relative abundance provides a clear distinction between CH₄+ versus CH₄- samples. Its sequencing-based relative abundance detection threshold for CH₄ production was calculated to be 0.097%. The qPCR-based detection threshold separating CH₄+ versus CH₄- samples, based on mcrA gene copies, was 5.2 × 10⁵ copies/g.

CONCLUSION

Given the decreased time-burden placed on patients, a qPCR-based test on a fecal sample can become a valuable tool in clinical assessment of CH₄ producing status.

Bacterial metabolites trimethylamine N-oxide and butyrate as surrogates of small intestinal bacterial overgrowth in patients with a recent decompensated heart failure

In patients with heart failure (HF), the exhaled concentrations of hydrogen after a breath test-a non-invasive assessment of small intestinal overgrowth- has been related to HF severity and higher risk of adverse outcomes. Indeed, two intestinal bacterial metabolites-blood Trimethylamine N-Oxide (TMAO) and butyrate-have been related to a worse prognosis in HF. However, the relationship between the exhaled concentrations of hydrogen after a breath test and these two metabolites remains unknown. Thus, in this post-hoc analysis, we sought to evaluate whether these two metabolites are associated with the exhaled concentrations of hydrogen after a breath test in patients with a recent admission for HF. We included 60 patients with a recent hospitalization for HF. Cumulative hydrogen over time was integrated into a single measurement by the area under the concentration curve (AUC-H2). A linear regression multivariable analysis was used to evaluate the associations. A 2-sided p-value < 0.05 was considered to be statistically significant. The median (p25-p75) amino-terminal pro-brain natriuretic peptide, AUC-H2, TMAO, and Butyrate were 4789 pg/ml (1956-11149), 1615 (700-2585), 0.68 (0.42-1.12), and 0.22 ± 13, respectively. After multivariate adjustment, TMAO and butyrate were significantly associated with AUC-H2 (p = 0.027 and p = 0.009, respectively). For TMAO, this association was positive and for butyrate, negative. Bacterial-origin metabolites TMAO and Butyrate were independently related to AUC-H2 in patients with a recent hospitalization for acute HF.

Breath Methane Does Not Correlate With Constipation Severity or Bloating in Patients With Constipation

GOALS

We aimed to study (1) if the breath methane level on glucose breath testing (GBT) was associated with constipation severity and (2) compare methane levels between patients with constipation and diarrhea.

BACKGROUND

The breath methane level has been associated with constipation and its severity. However, a few recent studies have questioned these associations.

STUDY

Patients presenting consecutively to a tertiary care gastroenterology motility laboratory for GBT were included. GBT was performed using 75-g glucose load following a standard, institutional protocol. Constipation and irritable bowel syndrome (IBS) severity was measured using Patient Assessment of Constipation Symptoms (PAC-SYM) and IBS-symptom severity scale (IBS-SSS).

RESULTS

In the cohort of 79 constipated patients, there was no significant correlation between baseline or maximum methane levels with total PAC-SYM score. IBS-SSS or bloating severity also did not correlate with baseline or maximum methane levels. The baseline or maximum methane levels of ≥3 and 5 ppm were equally distributed among those with constipation (n=79) and diarrhea (n=122). Only baseline methane levels of ≥10 and ≥20 ppm significantly correlated with constipation (P<0.001 for both).

CONCLUSIONS

We found that constipation and bloating severity did not correlate with methane levels on GBT. In addition, only higher baseline methane levels (≥10 and ≥20 ppm) significantly correlated with constipation as baseline methane levels up to 5 ppm were equally common in patients with diarrhea and constipation. Baseline methane levels had better correlation with constipation compared with maximum levels of methane achieved.

Relationships of Microbiome Markers With Extraintestinal, Psychological Distress and Gastrointestinal Symptoms, and Quality of Life in Women With Irritable Bowel Syndrome

INTRODUCTION

Altered microbial diversity has been associated with gastrointestinal (GI) symptoms in persons with irritable bowel syndrome (IBS). Less is known about the relationship of microbiome with extraintestinal pain and psychological distress symptoms and quality of life (QOL) in persons with IBS. We aimed to evaluate the relationship of fecal microbiota to GI symptoms, stool consistency, psychological distress, extraintestinal pain, and QOL in participants meeting Rome III criteria for IBS.

METHODS

Seventy-six women completed a 28-day diary that included GI, stool consistency, psychological distress, and extraintestinal pain ratings. Participants completed the IBS-Specific Quality of Life questionnaire. Stool samples were collected and analyzed by 16S rRNA gene sequencing. Principal component analysis was performed and the first 2 components (PC1, PC2) were used to test relationships among bacterial families and clinical measures.

RESULTS

Participants were categorized as IBS constipation (n=22), IBS diarrhea (n=39), IBS mixed (n=13), and IBS unsubtyped (n=2). There was a significant group effect for the Firmicutes to Bacteroidetes ratio and PC1. Lower microbial diversity and richness were associated with increased urgency and extraintestinal pain, worse QOL, and looser stools. Lower extraintestinal pain was associated with increased Rikenellaceae, Christensenellaceae, Dehalobabacteriaceae, Oscillospiraceae, Mogibacteriaceae, Ruminococcaceae, Sutterellaceae, Desulfovibrionaceae, and Erysipelotrichaceae abundances. QOL was positively associated with many of these same bacterial families. Higher Firmicutes to Bacteroidetes ratio was positively associated with loose stools. There were no statistically significant relationships between daily psychological distress or abdominal pain and bacterial families.

CONCLUSIONS

Stool microbial diversity and composition are linked to daily extraintestinal symptoms, stool consistency, and QOL in women with IBS.

Clinical Management of the Microbiome in Irritable Bowel Syndrome

Background

A growing body of evidence suggests that dysbiosis contributes to the onset and symptomatology of irritable bowel syndrome (IBS) and other functional bowel disorders. Changes to the gastrointestinal microbiome may contribute to the underlying pathophysiology of IBS.

Methods

The present review summarizes the potential effects of microbiome changes on GI transit, intestinal barrier function, immune dysregulation and inflammation, gut–brain interactions and neuropsychiatric function.

Results

A multimodal approach to IBS management is recommended in accordance with current Canadian guidelines. Pharmacologic treatments are advised to target the presumed underlying pathophysiological mechanism, such as dysregulation of GI transit, peristalsis, intestinal barrier function and pain signalling. The management plan for IBS may also include treatments directed at dysbiosis, including dietary modification and use of probiotics, which may promote the growth of beneficial bacteria, affect intestinal gas production and modulate the immune response; and the administration of periodic short courses of a nonsystemic antibiotic such as rifaximin, which may re-establish microbiota diversity and improve IBS symptoms.

Conclusion

Dysregulated host–microbiome interactions are complex and the use of microbiome-directed therapies will necessarily be empiric in individual patients. A management algorithm comprising microbiome- and nonmicrobiome-directed therapies is proposed.

Evaluation of lactulose, lactose, and fructose breath testing in clinical practice: A focus on methane

Background and Aim

Breath testing (BT) is used to identify carbohydrate malabsorption and small intestine bacterial overgrowth. Measuring methane alongside hydrogen is advocated to reduce false-negative studies, but the variability of methane production is unknown. The aim of this study is to examine the effect of high methane production on hydrogen excretion after ingesting lactulose, fructose, or lactose.

Methods

A retrospective audit was performed of patients with gastrointestinal symptoms who underwent BT. Following a low fermentable carbohydrate diet for 24-h, a fasting BT before consuming 35 ml lactulose, 35 g fructose, or lactose in 200 ml water, followed by BT every 10-15 min for up to 3-h, was performed. A positive test was defined as a ≥20 ppm rise of hydrogen or methane from baseline. A high methane producer had an initial reading of ≥5 ppm. Breath hydrogen and methane production were measured as area under the curve. Chi-squared tests were used to compare proportions of those meeting the cut-off criteria.

Results

Of patients, 26% (28/106) were high methane producers at their initial lactulose test. The test-retest repeatability of methane production was high, with the same methane production status before ingesting lactose in all (70/70) and before ingesting fructose in most (71/73). Methane production was highly variable during testing, with 38% (10/26) having ≥1 reading lower than baseline. Hydrogen produced by high or low methane producers did not differ (1528 [960-3645] ppm min vs 2375 [1810-3195] ppm min [P = 0.11]). Symptoms and breath test results were not positively related.

Conclusion

The validity of including an increase of ≥20 ppm methane to identify carbohydrate malabsorption or small intestine bacterial overgrowth should be questioned due to the variability of readings during testing.

Detection of Intestinal Tissue Perfusion by Real-Time Breath Methane Analysis in Rat and Pig Models of Mesenteric Circulatory Distress

OBJECTIVES

Methane (CH4) breath test is an established diagnostic method for gastrointestinal functional disorders. Our aim was to explore the possible link between splanchnic circulatory changes and exhaled CH4 in an attempt to recognize intestinal perfusion failure.

DESIGN

Randomized, controlled in vivo animal study.

SETTING

University research laboratory.

SUBJECTS

Anesthetized, ventilated Sprague-Dawley rats (280 ± 30 g) and Vietnamese minipigs (31 ± 7 kg).

INTERVENTIONS

In the first series, CH4 was administered intraluminally into the ileum before 45 minutes mesenteric ischemia or before reperfusion in non-CH4 producer rats to test the appearance of the gas in the exhaled air. In the porcine experiments, the superior mesenteric artery was gradually obstructed during consecutive, 30-minute flow reductions and 30-minute reperfusions achieving complete occlusion after four cycles (n = 6), or nonocclusive mesenteric ischemia was induced by pericardial tamponade (n = 12), which decreased superior mesenteric artery flow from 351 ± 55 to 182 ± 67 mL/min and mean arterial pressure from 96.7 ± 18.2 to 41.5 ± 4.6 mm Hg for 60 minutes.

MEASUREMENTS AND MAIN RESULTS

Macrohemodynamics were monitored continuously; RBC velocity of the ileal serosa or mucosa was recorded by intravital videomicroscopy. The concentration of exhaled CH4 was measured online simultaneously with high-sensitivity photoacoustic spectroscopy. The intestinal flow changes during the occlusion-reperfusion phases were accompanied by parallel changes in breath CH4 output. Also in cardiac tamponade-induced nonocclusive intestinal ischemia, the superior mesenteric artery flow and RBC velocity correlated significantly with parallel changes in CH4 concentration in the exhaled air (Pearson's r = 0.669 or r = 0.632, respectively).

CONCLUSIONS

we report a combination of in vivo experimental data on a close association of an exhaled endogenous gas with acute mesenteric macro- and microvascular flow changes. Breath CH4 analysis may offer a noninvasive approach to follow the status of the splanchnic circulation.

Reevaluating our understanding of lactulose breath tests by incorporating hydrogen sulfide measurements

Background and Aim

Breath testing has become a commonly used tool in gastroenterology to evaluate changes in the fermentation pattern of the gut microbiome. Currently, hydrogen and methane gas concentrations are measured in breath testing and evaluated against specific cut‐off values for interpretation as normal or abnormal. However, microbial gas kinetics is a complex process that is not currently fully considered when interpreting breath gas results. Gas exchange between hydrogen producers and hydrogen consumers (methanogens and sulfate‐reducing bacteria) is a process whereby hydrogen availability is determined by both its production and removal. Hydrogen sulfide is a crucial gas involved in this process as it is a major hydrogen‐consumptive pathway involved in energy exchange.

Methods

This is a cross‐sectional study evaluating lactulose breath testing with the inclusion of hydrogen sulfide measurements in patients referred for breath testing for gastrointestinal symptoms of bloating, excessive gas, and/or abdominal pain.

Results

A total of 159 patients were analyzed between October 2016 and June 2017. Mean hydrogen concentrations with a positive trend through a 3‐h period (R² = 0.97), mean methane concentrations with a positive trend (R² = 0.69), and mean hydrogen sulfide concentrations with a negative trend (R² = −0.71) were observed.

Conclusion

By incorporating energy exchange in the interpretation of the lactulose breath test, we reevaluated specific breath gas profiles, including those commonly described as “hydrogen nonproducers” and the “double‐peak” phenomenon.

The diagnosis of small intestinal bacterial overgrowth: Two steps forward, one step backwards?

Small intestinal bacterial overgrowth (SIBO) was originally described decades ago as a cause of malabsorption among individuals with abnormal intestinal anatomy and/or impaired gastric acid secretion and intestinal motor functions. More recently, the concept of SIBO has been expanded to explain symptoms among a much broader patient population-a move that brings the definition of SIBO into much sharper focus. For largely logistical reasons, breath tests and, especially, those based on the excretion of hydrogen consequent on the fermentation of unabsorbed carbohydrate substrates, have almost entirely replaced jejunal aspirates in the diagnosis of SIBO. Ever bedeviled by concerns regarding their reliability, hydrogen breath tests have now come under even more critical scrutiny with the study from Sundin and colleagues in this issue suggesting that their sole function is to detect carbohydrate malabsorption and that they are incapable of defining SIBO.

Hydrogen- and Methane-Based Breath Testing and Outcomes in Patients With Heart Failure

BACKGROUND

Recent evidence endorses gut microbiota dysregulation in the pathophysiology of heart failure (HF). Small intestinal bacterial overgrowth (SIBO) might be present in HF and associated with poor clinical outcomes. Lactulose breath testing is a simple noninvasive test that has been advocated as a reliable indicator of SIBO. In patients with HF, we aimed to evaluate the association with clinical outcomes of the exhaled hydrogen (H₂) and methane (CH₄) concentrations through the lactulose breath test.

METHODS AND RESULTS

We included 102 patients with HF in which lactulose SIBO breath tests were assessed. Cumulative gas was quantified by the area under the receiver operating characteristic curve of CH₄ (AUC-CH₄) and H₂ (AUC-H₂). Clinical end points included the composite of all-cause death with either all-cause or HF hospitalizations, recurrent all-cause hospitalizations, and recurrent HF hospitalizations. Medians (interquartile ranges) of AUC-H₂ and AUC-CH₄ were 1290 U (520-2430) and 985 U (450-2120), respectively. In multivariable analysis, AUC-H₂ (per 1000 U) was associated with all-cause death/all-cause hospitalization (hazard ratio [HR] 1.21, 95% CI 1.04-1.40; P = .012), all-cause death/HF hospitalization (HR 1.20, 95% CI 1.03-1.40; P = .021), and an increase in the rate of recurrent all-cause (incidence rate ratio [IRR] 1.31, 95% CI 1.14-1.51; P < .001) and HF (IRR 1.41, 95% CI 1.15-1.72; P = .001) hospitalizations. AUC-CH₄ was not associated with any of these end points.

CONCLUSIONS

AUC-H₂, a safe and noninvasive method for SIBO estimation, is associated with higher risk of long-term adverse clinical events in patients with HF. In contrast, AUC-CH₄ did not show any prognostic value.

A low FODMAP diet is associated with changes in the microbiota and reduction in breath hydrogen but not colonic volume in healthy subjects

Background & aims

Ingestion of poorly digested, fermentable carbohydrates (fermentable oligo-, di-, mono-saccharides and polyols; FODMAPs) have been implicated in exacerbating intestinal symptoms and the reduction of intake with symptom alleviation. Restricting FODMAP intake is believed to relieve colonic distension by reducing colonic fermentation but this has not been previously directly assessed. We performed a randomised controlled trial comparing the effect of a low FODMAP diet combined with either maltodextrin or oligofructose on colonic contents, metabolites and microbiota.

Methods

A parallel randomised controlled trial in healthy adults (n = 37). All subjects followed a low FODMAP diet for a week and supplemented their diet with either maltodextrin (MD) or oligofructose (OF) 7g twice daily. Fasted assessments performed pre- and post-diet included MRI to assess colonic volume, breath testing for hydrogen and methane, and stool collection for microbiota analysis.

Results

The low FODMAP diet was associated with a reduction in Bifidobacterium and breath hydrogen, which was reversed by oligofructose supplementation. The difference in breath hydrogen between groups post-intervention was 27ppm (95% CI 7 to 50, P<0.01). Colonic volume increased significantly from baseline in both groups (OF increased 110ml (19.6%), 95% CI 30ml to 190ml, P = 0.01; MD increased 90ml (15.5%), 95% CI 6ml to 175ml, P = 0.04) with no significant difference between them. Colonic volumes correlated with total breath hydrogen + methane. A divergence in Clostridiales abundance was observed with increased abundance of Ruminococcaceae in the maltodextrin group, while in the oligofructose group, Lachnospiraceae decreased. Subjects in either group with high methane production also tended to have high microbial diversity, high colonic volume and greater abundance of methanogens.

Conclusion

A low FODMAP diet reduces total bacterial count and gas production with little effect on colonic volume.

Breath methane concentrations and markers of obesity in patients with functional gastrointestinal disorders

Background

Obesity is associated with changes in the intestinal microbiome and methane-producing archaea may be involved in energy homeostasis.

Objective

The objective of this article is to investigate the associations between intestinal methane production, waist circumference and body mass index (BMI) as biomarkers for obesity.

Methods

Breath methane and hydrogen concentrations were measured over five hours following fructose or lactose ingestion in 1647 patients with functional gastrointestinal disorders. The relationships between gas concentrations and measures of obesity were investigated by stratifying gas concentration-time profiles by BMI and waist circumference, and, conversely, BMI and waist circumference by peak breath hydrogen and methane concentrations.

Results

Following fructose ingestion, patients with lower BMI and lesser waist circumference had greater breath methane concentrations (all p < 0.003). Conversely, patients with increased methane concentrations had lower BMI (p < 0.001) and waist circumference (p = 0.02). After lactose ingestion, BMI and waist circumference were not associated with significant differences in methane. However, greater methane concentrations were associated with a lower BMI (p < 0.002), but not with waist circumference.

Conclusion

In this large group of patients mainly negative associations between breath methane concentrations and anthropometric biomarkers of obesity were evident. Studies investigating microbial methane production and energy homoeostasis in different populations are of substantial interest to distinguish epiphenomena from true causality.A follow-up study was registered at Clinical trials.gov NCT02085889.

Assessing the colonic microbiome, hydrogenogenic and hydrogenotrophic genes, transit and breath methane in constipation

BACKGROUND

Differences in the gut microbiota and breath methane production have been observed in chronic constipation, but the relationship between colonic microbiota, transit, and breath tests remains unclear.

METHODS

In 25 healthy and 25 constipated females we evaluated the sigmoid colonic mucosal and fecal microbiota using 16S rRNA gene sequencing, abundance of hydrogenogenic FeFe (FeFe-hydA) and hydrogenotrophic (methyl coenzyme M reductase A [mrcA] and dissimilatory sulfite reductase A [dsrA]) genes with real-time qPCR assays, breath hydrogen and methane levels after oral lactulose, and colonic transit with scintigraphy.

KEY RESULTS

Breath hydrogen and methane were not correlated with constipation, slow colon transit, or with abundance of corresponding genes. After adjusting for colonic transit, the abundance of FeFehydA, dsrA, and mcrA were greater (P<.005) in colonic mucosa, but not stool, of constipated patients. The abundance of the selected functional gene targets also correlated with that of selected taxa. The colonic mucosal abundance of FeFe-hydA, but not mcrA, correlated positively (P<.05) with breath methane production, slow colonic transit, and overall microbiome composition. In the colonic mucosa and feces, the abundance of hydrogenogenic and hydrogenotrophic genes were positively correlated (P<.05). Breath methane production was not associated with constipation or colonic transit.

CONCLUSIONS & INFERENCES

Corroborating our earlier findings with 16S rRNA genes, colonic mucosal but not fecal hydrogenogenic and hydrogenotrophic genes were more abundant in constipated vs. healthy subjects independent of colonic transit. Breath gases do not directly reflect the abundance of target genes contributing to their production.

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.

Influence of ruminal methane on digesta retention and digestive physiology in non-lactating dairy cattle

Enteric methane (CH4) production is a side-effect of herbivore digestion, but it is unknown whether CH4 itself influences digestive physiology. We investigated the effect of adding CH4 to, or reducing it in, the reticulorumen (RR) in a 4×4 Latin square experiment with rumen-fistulated, non-lactating cows, with four treatments: (i) control, (ii) insufflation of CH4 (iCH4), (iii) N via rumen fistula, (iv) reduction of CH4 via administration of bromochloromethane (BCM). DM intake (DMI), apparent total tract digestibility, digesta mean retention times (MRT), rumen motility and chewing activity, spot breath CH4 emission (CH4exhal, litre/kg DMI) as well as CH4 dissolved in rumen fluid (CH4RRf, µg/ml) were measured. Data were analysed using mixed models, including treatment (or, alternatively, CH4exhal or CH4RRf) and DMI relative to body mass0·85 (rDMI) as covariates. rDMI was the lowest on the BCM treatment. CH4exhal was highest for iCH4 and lowest for BCM treatments, whereas only BCM affected (reduced) CH4RRf. After adjusting for rDMI, CH4RRf had a negative association with MRT in the gastrointestinal tract but not in the RR, and negative associations with fibre digestibility and measures of rumination activity. Adjusting for rDMI, CH4exhal had additionally a negative association with particle MRT in the RR and a positive association with rumen motility. Thus, higher rumen levels of CH4 (CH4exhal or CH4RRf) were associated with shorter MRT and increased motility. These findings are tentatively interpreted as a feedback mechanism in the ruminant digestive tract that aims at mitigating CH4 losses by shortening MRT at higher CH4.

Assessment of intestinal malabsorption

Significant efforts have been made in the last decade to either standardize the available tests for intestinal malabsorption or to develop new, more simple and reliable techniques. The quest is still on and, unfortunately, clinical practice has not dramatically changed. The investigation of intestinal malabsorption is directed by the patient's history and baseline tests. Endoscopy and small bowel biopsies play a major role although non-invasive tests are favored and often performed early on the diagnostic algorithm, especially in paediatric and fragile elderly patients. The current clinically available methods and research tools are summarized in this review article.

Metabolic effects of eradicating breath methane using antibiotics in prediabetic subjects with obesity

OBJECTIVE

Methanogens colonizing the human gut produce methane and influence host metabolism. This study examined metabolic parameters in methane-producing subjects before and after antibiotic treatment.

METHODS

Eleven prediabetic methane-positive subjects (9F, 2M) with obesity (BMI 35.17 ± 7.71 kg/m(2) ) aged 47 ± 9 years were recruited. Subjects underwent breath testing, symptom questionnaire, oral glucose tolerance test (OGTT), lipid profile, and stool Methanobrevibacter smithii levels, gastric transit, and energy utilization analyses. After a 10-day antibiotic therapy (neomycin 500 mg bid/rifaximin 550 mg tid), all testing was repeated.

RESULTS

Baseline stool M. smithii levels correlated with breath methane (R = 0.7, P = 0.05). Eight subjects (73%) eradicated breath methane and showed reduced stool M. smithii (P = 0.16). After therapy, methane-eradicated subjects showed significant improvements in low-density lipoprotein (LDL) (P = 0.028), total cholesterol (P = 0.01), and insulin levels on OGTT (P = 0.05 at 120 minutes), lower blood glucose levels on OGTT (P = 0.054 at 90 minutes), significant reductions in bloating (P = 0.018) and straining (P = 0.059), and a trend toward lower stool dry weight. No changes were detected in gastric emptying time or energy harvest.

CONCLUSIONS

Breath methane eradication and M. smithii reduction are associated with significant improvements in total cholesterol, LDL, and insulin levels and with lower glucose levels in prediabetic subjects with obesity. The underlying mechanisms require further elucidation.

Relationship Between Microbiota of the Colonic Mucosa vs Feces and Symptoms, Colonic Transit, and Methane Production in Female Patients With Chronic Constipation

BACKGROUND & AIMS

In fecal samples from patients with chronic constipation, the microbiota differs from that of healthy subjects. However, the profiles of fecal microbiota only partially replicate those of the mucosal microbiota. It is not clear whether these differences are caused by variations in diet or colonic transit, or are associated with methane production (measured by breath tests). We compared the colonic mucosal and fecal microbiota in patients with chronic constipation and in healthy subjects to investigate the relationships between microbiota and other parameters.

METHODS

Sigmoid colonic mucosal and fecal microbiota samples were collected from 25 healthy women (controls) and 25 women with chronic constipation and evaluated by 16S ribosomal RNA gene sequencing (average, 49,186 reads/sample). We assessed associations between microbiota (overall composition and operational taxonomic units) and demographic variables, diet, constipation status, colonic transit, and methane production (measured in breath samples after oral lactulose intake).

RESULTS

Fourteen patients with chronic constipation had slow colonic transit. The profile of the colonic mucosal microbiota differed between constipated patients and controls (P < .05). The overall composition of the colonic mucosal microbiota was associated with constipation, independent of colonic transit (P < .05), and discriminated between patients with constipation and controls with 94% accuracy. Genera from Bacteroidetes were more abundant in the colonic mucosal microbiota of patients with constipation. The profile of the fecal microbiota was associated with colonic transit before adjusting for constipation, age, body mass index, and diet; genera from Firmicutes (Faecalibacterium, Lactococcus, and Roseburia) correlated with faster colonic transit. Methane production was associated with the composition of the fecal microbiota, but not with constipation or colonic transit.

CONCLUSIONS

After adjusting for diet and colonic transit, the profile of the microbiota in the colonic mucosa could discriminate patients with constipation from healthy individuals. The profile of the fecal microbiota was associated with colonic transit and methane production (measured in breath), but not constipation.

Review article: inhibition of methanogenic archaea by statins as a targeted management strategy for constipation and related disorders

BACKGROUND

Observational studies show a strong association between delayed intestinal transit and the production of methane. Experimental data suggest a direct inhibitory activity of methane on the colonic and ileal smooth muscle and a possible role for methane as a gasotransmitter. Archaea are the only confirmed biological sources of methane in nature and Methanobrevibacter smithii is the predominant methanogen in the human intestine.

AIM

To review the biosynthesis and composition of archaeal cell membranes, archaeal methanogenesis and the mechanism of action of statins in this context.

METHODS

Narrative review of the literature.

RESULTS

Statins can inhibit archaeal cell membrane biosynthesis without affecting bacterial numbers as demonstrated in livestock and humans. This opens the possibility of a therapeutic intervention that targets a specific aetiological factor of constipation while protecting the intestinal microbiome. While it is generally believed that statins inhibit methane production via their effect on cell membrane biosynthesis, mediated by inhibition of the HMG-CoA reductase, there is accumulating evidence for an alternative or additional mechanism of action where statins inhibit methanogenesis directly. It appears that this other mechanism may predominate when the lactone form of statins, particularly lovastatin lactone, is administered.

CONCLUSIONS

Clinical development appears promising. A phase 2 clinical trial is currently in progress that evaluates the effect of lovastatin lactone on methanogenesis and symptoms in patients with irritable bowel syndrome with constipation. The review concludes with an outlook for the future and subsequent work that needs to be done.

Additional Value of CH₄ Measurement in a Combined (13)C/H₂ Lactose Malabsorption Breath Test: A Retrospective Analysis

The lactose hydrogen breath test is a commonly used, non-invasive method for the detection of lactose malabsorption and is based on an abnormal increase in breath hydrogen (H₂) excretion after an oral dose of lactose. We use a combined ¹³C/H₂ lactose breath test that measures breath ¹³CO₂ as a measure of lactose digestion in addition to H₂ and that has a better sensitivity and specificity than the standard test. The present retrospective study evaluated the results of 1051 ¹³C/H₂ lactose breath tests to assess the impact on the diagnostic accuracy of measuring breath CH₄ in addition to H₂ and ¹³CO₂. Based on the ¹³C/H₂ breath test, 314 patients were diagnosed with lactase deficiency, 138 with lactose malabsorption or small bowel bacterial overgrowth (SIBO), and 599 with normal lactose digestion. Additional measurement of CH₄ further improved the accuracy of the test as 16% subjects with normal lactose digestion and no H₂-excretion were found to excrete CH₄. These subjects should have been classified as subjects with lactose malabsorption or SIBO. In conclusion, measuring CH₄-concentrations has an added value to the ¹³C/H₂ breath test to identify methanogenic subjects with lactose malabsorption or SIBO.