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

Symptom Profile of Patients With Intestinal Methanogen Overgrowth: A Systematic Review and Meta-analysis

BACKGROUND & AIMS

Archaea constitute one of the main 3 domains of the tree of life, distinct from eukaryotes and bacteria. Excessive luminal loads of methanogenic archaea (intestinal methanogen overgrowth [IMO]) have been implicated in the pathophysiology of various diseases, including constipation. To elucidate the phenotypical presentation of IMO, we performed a systematic review and meta-analysis of the prevalence and severity of gastrointestinal symptoms in subjects with IMO as compared with subjects without IMO.

METHODS

Electronic databases, including OVID MEDLINE and Cochrane Database from inception until September 2023, were systematically searched. Prevalence rates, odds ratios (ORs), standardized mean difference (SMD), and 95% confidence intervals (CIs) of symptoms were calculated.

RESULTS

Nineteen studies were included (1293 patients with IMO and 3208 controls). Patients with IMO exhibited various gastrointestinal symptoms, including bloating (78%), constipation (51%), diarrhea (33%), abdominal pain (65%), nausea (30%), and flatulence (56%). Patients with IMO had a significantly higher prevalence of constipation as compared with controls (47% vs 38%; OR, 2.04; 95% CI, 1.48-2.83; P < .0001) along with lower prevalence of diarrhea (37% vs 52%; OR, 0.58; 95% CI, 0.37-0.90; P = .01) and nausea (32% vs 45%; OR, 0.75; 95% CI, 0.60-0.94; P = .01). Patients with IMO had higher severity of constipation (SMD, 0.77; 95% CI, 0.11-1.43; P = .02) and lower severity of diarrhea (SMD, -0.71; 95% CI, -1.39 to -0.03; P = .04). Significant heterogeneity was detected.

CONCLUSION

Patients with IMO exhibit a higher rate and severity of constipation along with lower rate and severity of diarrhea. The distinct phenotype of patients with IMO should be incorporated in patient-reported outcome measures and further correlated with mechanistic microbiome studies.

Prevalence of small intestinal bacterial overgrowth in irritable bowel syndrome (IBS): Correlating H 2 or CH 4 production with severity of IBS

Background and Aim

The prevalence and the role of small intestinal bacterial overgrowth (SIBO) in irritable bowel syndrome (IBS) remain unclear, as the literature provides heterogeneous information on the subject. The aim of this study was to determine the prevalence of SIBO in IBS and to assess the correlation between methane and hydrogen levels measured during breath tests and the severity of IBS.

Method

Two-hundred and forty-seven patients with IBS were prospectively included. A glucose breath test (GBT) measured H₂ and CH₄ production to diagnose SIBO. A test was positive when H₂ values exceeded 12 ppm in the first 90 min and/or when a CH₄ value exceeded 10 ppm at any time. IBS severity (IBS-SSS), quality of life (GIQLI), and anxiety and depression (HAD) were assessed to investigate the correlation with H₂ and CH₄ production.

Results

The prevalence of SIBO in IBS was 36.4% (9.7% with H₂, 26.7% with CH₄). CH₄ levels were significantly higher in the predominantly constipated patients (P = 0.00), while H₂ levels were significantly higher within the diarrheal phenotype (P = 0.01). IBS severity was not correlated with either H₂ levels (r = 0.02; P = 0.84) or CH₄ levels (r = 0.05; P = 0.64). H₂ production was inversely correlated with the quality of life (r = -0.24; P = 0.03) and significantly correlated with the HAD scale (r = 0.22; P = 0.03). The pain and discomfort experienced during GBT was not correlated with methane levels (r = -0.09, P = 0.40), hydrogen levels (r = -0.01, P = 0.93), or sum of both (r = 0.06, P = 0.58), but significantly associated with IBS severity (r = 0.50, P <0.00).

Conclusion

SIBO has a high prevalence in IBS but does not increase its severity. Individual susceptibility to pain may have a greater influence on the severity of IBS.

Association of Differential Metabolites With Small Intestinal Microflora and Maternal Outcomes in Subclinical Hypothyroidism During Pregnancy

Objective

To investigate the association of differential metabolites with small intestinal microflora and maternal outcomes in subclinical hypothyroidism (SCH) during pregnancy.

Methods

The plasma of pregnant women in the SCH group and control group was analyzed by liquid chromatography-mass spectrometry (LC-MS), obtaining differential metabolites. Then, methane and hydrogen breath tests were performed in both groups, and basic clinical data and maternal outcome information were collected. Finally, differential metabolites were analyzed for small intestinal bacterial overgrowth (SIBO) and pregnancy outcomes using Spearman correlation analysis.

Results

(1) Multivariate statistics: There were 564 different metabolites in positive ion mode and 226 different metabolites in negative ion mode. (2) The positive rate of the methane hydrogen breath test in the SCH group was higher than that in the control group (p<0.05). (3) KEGG pathway analysis revealed that differential metabolites were mainly involved in bile secretion, cholesterol metabolism, and other pathways. (4) Serum cholesterol (TC) and triglyceride (TG) levels and hypertensive disorder complicating pregnancy (HDCP) were higher in the SCH group (p<0.05), and newborn birth weight (BW) was lower than that in the control group (p<0.05). (5) SIBO was negatively correlated with glycocholic acid and BW, and positively correlated with TC. Glycocholic acid was negatively correlated with TG but positively correlated with BW. TG was positively correlated with HDCP.

Conclusion

Differential metabolites in the SCH group during pregnancy were disordered with small intestinal bacteria, which may affect pregnancy outcomes, and bile acids and cholesterol may be potential biomarkers for studying their mechanism of action.

Methane positive small intestinal bacterial overgrowth in inflammatory bowel disease and irritable bowel syndrome: A systematic review and meta-analysis

Several studies reported a potential role of methane producing archaea in the pathophysiology of irritable bowel syndrome (IBS) and inflammatory bowel disease (IBD). We conducted a systematic review and meta-analysis to assess the prevalence of methane positive small intestinal bacterial overgrowth (SIBO) in IBS and IBD compared with controls. MEDLINE (PubMed) and Embase electronic databases were searched from inception until March 2021 for case-control and prevalence studies reporting SIBO in IBS and IBD. We extracted data from published studies and calculated pooled prevalence of SIBO in IBS or IBD, odds ratios (OR), and 95% CIs, utilizing a random effects model. The final dataset included 17 independent studies assessing the prevalence of methane positive SIBO in 1,653 IBS-patients and 713 controls, and 7 studies assessing the prevalence of methane positive SIBO in 626 IBD-patients and 497 controls, all utilizing breath test for SIBO diagnosis. Prevalence of methane positive SIBO in IBS and IBD was 25.0% (95% CI 18.8-32.4) and 5.6% (95% CI 2.6-11.8), respectively. Methane positive SIBO in IBS was not increased compared to controls (OR = 1.2, 95% CI 0.8-1.7, P = .37) but was significantly more prevalent in IBS-C as compared to IBS-D (OR = 3.1, 95% CI 1.7-5.6, P = .0001). The prevalence of methane-positive SIBO in patients with IBD was 3-fold lower at 7.4% (95% CI 5.4-9.8) compared to 23.5% (95% CI 19.8-27.5) in controls. The prevalence of methane positive SIBO was significantly lower in Crohn's disease as compared to ulcerative colitis, (5.3%, 95% CI 3.0-8.5 vs. 20.2%, 95% CI 12.8-29.4). This systematic review and meta-analysis suggests methane positivity on breath testing is positively associated with IBS-C and inversely with IBD. However, the quality of evidence is low largely due to clinical heterogeneity of the studies. Thus, causality is uncertain and further studies are required.

Reference values for intake of six types of soluble and insoluble fibre in healthy UK inhabitants based on the UK Biobank data

OBJECTIVE

To obtain a set of reference values for the intake of different types of dietary fibre in a healthy UK population.

DESIGN

This descriptive cross-sectional study used the UK Biobank data to estimate the dietary patterns of healthy individuals. Data on fibre content in different foods were used to calculate the reference values which were then calibrated using real-world data on total fibre intake.

SETTING

UK Biobank is a prospective cohort study of over 500 000 individuals from across the United Kingdom with the participants aged between 40 and 69 years.

PARTICIPANTS

UK Biobank contains information on over 500 000 participants. This study was performed using the data on 19 990 individuals (6941 men, 13 049 women) who passed stringent quality control and filtering procedures and had reported above-zero intake of the analysed foods.

RESULTS

A set of reference values for the intake of six different types of soluble and insoluble fibres (cellulose, hemicelluloses, pectin and lignin), including the corresponding totals, was developed and calibrated using real-world data.

CONCLUSIONS

To our knowledge, this is the first study to establish specific reference values for the intake of different types of dietary fibre. It is well known that effects exerted by different types of fibre both directly and through modulation of microbiota are numerous. Conceivably, a deficit or excess intake of specific types of dietary fibre may detrimentally affect human health. Filling this knowledge gap opens new avenues for research in discussion in studies of nutrition and microbiota and offers valuable tools for practitioners worldwide.

Application of methane and hydrogen-based breath test in the study of gestational diabetes mellitus and intestinal microbes

OBJECTIVE

Gestational diabetes mellitus (GDM) is a common complication of pregnancy. The purpose of this study was to compare the incidence of small intestinal bacterial overgrowth (SIBO) in patients with GDM and the control group by methane and hydrogen lactulose breath test (LBT), and to explore its relationship with inflammation, vitamins, and the outcomes of maternal and child.

METHODS

LBT was detected in 220 GDM patients, 160 pregnancy control patients and 160 pre-pregnancy control patients. The fasting blood glucose, white blood cells, vitamin A, D, E, neonatal weight, neonatal blood glucose and so on were compared and analyzed.

RESULTS

There was no statistical significance in the general data of the three groups. The proportion of abdominal distension in the GDM group was higher than that in the other two groups (P < 0.001). The positive rates of SIBO + in GDM group, gestational control group and pre-pregnancy control group were 54.55%, 27.50% and 14.38%, respectively. The average abundance of hydrogen and methane in GDM group was significantly higher than that in control group at each time point. In the GDM group, SIBO + subjects had higher levels of fasting blood glucose, glycoglycated hemoglobin, C-reactive protein, neonatal weight, and lower levels of vitamin D and neonatal blood glucose (P < 0.001).

CONCLUSION

Patients with GDM have a high incidence of SIBO, and SIBO may further increase their blood glucose by affecting inflammatory response and vitamin level, and even affect the outcome of mother and child.

Changes in oral flora of patients with functional dyspepsia

To explore the changes in oral flora in people with functional dyspepsia (FD). Unstimulated saliva was collected from 21 FD patients diagnosed according to the Rome IV criteria and from 12 healthy controls (HCs) for 16SrRNA sequencing. The pH of saliva samples and community periodontal index (CPI) were tested. The prevalence of small intestinal bacterial overgrowth (SIBO) was obtained by the methane-and hydrogen-based breath test. At the phylum level, FD patients had a higher relative abundance of Spirochaetes and a lower relative abundance of Fusobacteria, TM7 and Proteobacteria than HCs (p < 0.01). In the saliva, Kingella and Abiotrophia genus levels showed significant changes between the FD and HC groups (p < 0.01). Salivary species level marker Intermedia was significantly different between FD and HC groups (p < 0.01). The oral pH of FD patients was higher than that of HCs (p < 0.01). The mean CPI of the FD group was 1.52 and that of the HC group was 0.17 (p < 0.01). Moreover, 71.4% of the FD group was positive for SIBO. The oral flora of FD patients was different from that of HCs. Spirochaetes, Kingella, Abiotrophia, and Intermedia may be diagnostic indicators of FD.

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.

[Influencing Factors on Lactulose Breath Test Results]

BACKGROUND/AIMS

This study aimed to identify the demographic and clinical factors associated with positive breath-test results and to assess the relationship between hydrogen and methane production in patients with suspected irritable bowel syndrome (IBS).

METHODS

The demographic and clinical factors of 268 patients with suspected IBS, who had undergone a lactulose breath test, were analyzed.

RESULTS

Of 268 patients included in this study, 143 (53.4%) were females. The median age and BMI of the patients was 58.0 years (range, 18.0-80.0 years) and 22.5 kg/m2 (range, 14.4-34.3 kg/m2), respectively. A weak positive correlation was observed between the BMI and baseline hydrogen level (rho=0.134, p=0.031). Women were significantly more likely to show a ≥20 ppm increase in hydrogen within 90 min (early hydrogen increase, p=0.049), a ≥10 ppm increase in methane within 90 min (early methane increase, p=0.001), and a ≥10 ppm increase in methane between 90 min and 180 min (late methane increase, p=0.002) compared to men. The baseline hydrogen level was related to the baseline methane level (rho=0.592, p<0.001) and the maximal hydrogen level within 90 min was related to maximal methane level within 90 min (rho=0.721, p<0.001). Patients with an early hydrogen increase (43.8%) were more likely to show a positive result for an early methane increase compared to patients without an early increase in hydrogen (0%, p<0.001).

CONCLUSIONS

Women were associated with high rates of positive lactulose breath-test results. In addition, methane production was correlated with hydrogen production.

Microbiota stability in healthy individuals after single-dose lactulose challenge-A randomized controlled study

BACKGROUND AND AIMS

Lactulose is a common food ingredient and widely used as a treatment for constipation or hepatic encephalopathy and a substrate for hydrogen breath tests. Lactulose is fermented by the colon microbiota resulting in the production of hydrogen (H2). H2 is a substrate for enteropathogens including Salmonella Typhimurium (S. Typhimurium) and increased H2 production upon lactulose ingestion might favor the growth of H2-consuming enteropathogens. We aimed to analyze effects of single-dose lactulose ingestion on the growth of intrinsic Escherichia coli (E. coli), which can be efficiently quantified by plating and which share most metabolic requirements with S. Typhimurium.

METHODS

32 healthy volunteers (18 females, 14 males) were recruited. Participants were randomized for single-dose ingestion of 50 g lactulose or 50 g sucrose (controls). After ingestion, H2 in expiratory air and symptoms were recorded. Stool samples were acquired at days -1, 1 and 14. We analyzed 16S microbiota composition and abundance and characteristics of E. coli isolates.

RESULTS

Lactulose ingestion resulted in diarrhea in 14/17 individuals. In 14/17 individuals, H2-levels in expiratory air increased by ≥20 ppm within 3 hours after lactulose challenge. H2-levels correlated with the number of defecations within 6 hours. E. coli was detectable in feces of all subjects (2 x 10(2)-10(9) CFU/g). However, the number of E. coli colony forming units (CFU) on selective media did not differ between any time point before or after challenge with sucrose or lactulose. The microbiota composition also remained stable upon lactulose exposure.

CONCLUSION

Ingestion of a single dose of 50 g lactulose does not significantly alter E. coli density in stool samples of healthy volunteers. 50 g lactulose therefore seems unlikely to sufficiently alter growth conditions in the intestine for a significant predisposition to infection with H2-consuming enteropathogens such as S. Typhimurium (www.clinicaltrials.gov NCT02397512).

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.

Breath Hydrogen Testing in East and Southeast Asia

Breath hydrogen tests are popular, noninvasive tests for the assessment of carbohydrate fermentation in patients with irritable bowel syndrome (IBS) and functional dyspepsia (FD). There is limited information regarding the utility of breath hydrogen and methane tests in IBS and FD patients in East and Southeast Asia. This review aims to summarize current literature about common indications of breath testing in this region, the genesis of functional gastrointestinal symptoms by provocative breath testing and provide suggestions for correct use. The most common testing indication is the assessment of lactose intolerance, followed by small intestinal bacterial overgrowth (SIBO) and differentiation of intestinal gas profiles in research setting. Studies in this region not only documented a high prevalence of lactose malabsorption but a population, both healthy and IBS, that is highly symptomatic to typical lactose intakes. Breath hydrogen assessment of other fermentable carbohydrates (FODMAPs) are fairly uncommon, whereas methane breath testing is almost nonexistent. Cumulative hydrogen production following lactulose was also not excessive in IBS patients compared with controls. The evidence however, for the detection of SIBO suggests limited reliability in the use of lactulose or glucose breath testing alone and inconclusive data on its correlation with symptoms. Conversely, little has been carried out in FD. In conclusion, breath testing should be limited in the predicting patients with SIBO for directing clinical management but can be considered in the objective assessment of lactose malabsorption within a low FODMAP diet. Recommendations to improve the interpretation of breath testing in research were also provided.

Methanosphaera stadtmanae induces a type IV hypersensitivity response in a mouse model of airway inflammation

Despite improved awareness of work‐related diseases and preventive measures, many workers are still at high risk of developing occupational hypersensitivity airway diseases. This stems from a lack of knowledge of bioaerosol composition and their potential effects on human health. Recently, archaea species were identified in bioaerosols, raising the possibility that they play a major role in exposure‐related pathology. Specifically, Methanosphaera stadtmanae (MSS) and Methanobrevibacter smithii (MBS) are found in high concentrations in agricultural environments and respiratory exposure to crude extract demonstrates immunomodulatory activity in mice. Nevertheless, our knowledge of the specific impact of methanogens exposure on airway immunity and their potential to induce airway hypersensitivity responses in workers remains scant. Analysis of the lung mucosal response to methanogen crude extracts in mice demonstrated that MSS and MBS predominantly induced T_H17 airway inflammation, typical of a type IV hypersensitivity response. Furthermore, the response to MSS was associated with antigen‐specific IgG₁ and IgG_2a production. However, despite the presence of eosinophils after MSS exposure, only a weak T_H2 response and no airway hyperresponsiveness were observed. Finally, using eosinophil and mast cell‐deficient mice, we confirmed that these cells are dispensable for the T_H17 response to MSS, although eosinophils likely contribute to the exacerbation of inflammatory processes induced by MSS crude extract exposure. We conclude that, as MSS induces a clear type IV hypersensitivity lung response, it has the potential to be harmful to workers frequently exposed to this methanogen, and that preventive measures should be taken to avoid chronic hypersensitivity disease development in workers.

Excessive alcohol consumption induces methane production in humans and rats

Various studies have established the possibility of non-bacterial methane (CH₄) generation in oxido-reductive stress conditions in plants and animals. Increased ethanol input is leading to oxido-reductive imbalance in eukaryotes, thus our aim was to provide evidence for the possibility of ethanol-induced methanogenesis in non-CH₄ producer humans, and to corroborate the in vivo relevance of this pathway in rodents. Healthy volunteers consumed 1.15 g/kg/day alcohol for 4 days and the amount of exhaled CH₄ was recorded by high sensitivity photoacoustic spectroscopy. Additionally, Sprague-Dawley rats were allocated into control, 1.15 g/kg/day and 2.7 g/kg/day ethanol-consuming groups to detect the whole-body CH₄ emissions and mitochondrial functions in liver and hippocampus samples with high-resolution respirometry. Mitochondria-targeted L-alpha-glycerylphosphorylcholine (GPC) can increase tolerance to liver injury, thus the effects of GPC supplementations were tested in further ethanol-fed groups. Alcohol consumption was accompanied by significant CH₄ emissions in both human and rat series of experiments. 2.7 g/kg/day ethanol feeding reduced the oxidative phosphorylation capacity of rat liver mitochondria, while GPC significantly decreased the alcohol-induced CH₄ formation and hepatic mitochondrial dysfunction as well. These data demonstrate a potential for ethanol to influence human methanogenesis, and suggest a biomarker role for exhaled CH₄ in association with mitochondrial dysfunction.

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.

Biomarkers of Irritable Bowel Syndrome

Traditionally, irritable bowel syndrome (IBS) has not been regarded as an organic disease, and the pathophysiology of IBS is heterogeneous. Currently, the diagnosis of IBS is based upon the Rome diagnostic criteria. The performance of these criteria is only modest in predicting IBS, and moreover their validation is lacking. Additionally, as functional symptoms are common in the general population, healthy controls or volunteers are difficult to define and there is currently no definition of “normal” in the Rome criteria. Due to the weaknesses of the current diagnostic criteria, patients and doctors expect new gold standard diagnostic tools. Various etiologic mechanisms result in potential biomarkers. The focus of this research has been to find non-invasive biomarkers from serum, breath gas, and fecal materials. Though biomarkers should be based on biological and pathogenic processes, most biomarkers for IBS have been developed to identify organic diseases and therefore eliminate IBS. To date, these types of biomarkers for IBS have been disappointing. The purposes of developing biomarkers include improvement of diagnosis, differentiation from other organic diseases, and discrimination of IBS subtypes. A true mechanistic biomarker would make it possible to rule in IBS, rather than to rule out other organic diseases. New serologic biomarkers for diarrhea-predominant IBS have been introduced based on the pathophysiologic findings from a rat model and validation in a large-scale clinical trial. Further investigations of abnormal organic findings from each subtype of IBS would enable the development of new, simple subtype-specific biomarkers.

Archaea prevalence in inflamed pulp tissues

Archaea have been detected in several ecological niches of the human body such as the large intestine, skin, vagina as well as the oral cavity. At present, archaea are recognized as nonpathogenic microorganisms. However, some data indicate that they may be involved in the etiopathogenesis of several diseases, including intestinal diseases as well as oral diseases: periodontitis, peri-implantitis and endodontitis. In this study, on the basis of 16S rRNA gene sequence analysis, we examined whether archaea might be present in inflamed pulp tissues and contribute to the development of endodontic infection. In comparison, we also determined selected bacterial species associated with endodontitis. We detected archaea in 85% of infected endodontic samples. In addition, Prevotella intermedia, Porphyromonas gingivalis, Tannerella forsythia and Treponema denticola were present in inflamed pulp tissue samples and Treponema denticola occurred with the highest frequency (70%). Further analysis revealed the presence of methanogenic archaea in analyzed samples. Direct sequencing of archaeal 16S rRNA gene PCR products indicated the occurrence of methanogenic archaea in inflamed pulp tissues; phylogenetically most similar were Methanobrevibacter oralis and Methanobrevibacter smithii. Therefore, our results show that methanogenic archaea are present in inflamed pulp tissues and may participate in the development of endodontic infection.

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.

Breath tests and irritable bowel syndrome

Breath tests are non-invasive tests and can detect H₂ and CH₄ gases which are produced by bacterial fermentation of unabsorbed intestinal carbohydrate and are excreted in the breath. These tests are used in the diagnosis of carbohydrate malabsorption, small intestinal bacterial overgrowth, and for measuring the orocecal transit time. Malabsorption of carbohydrates is a key trigger of irritable bowel syndrome (IBS)-type symptoms such as diarrhea and/or constipation, bloating, excess flatulence, headaches and lack of energy. Abdominal bloating is a common nonspecific symptom which can negatively impact quality of life. It may reflect dietary imbalance, such as excess fiber intake, or may be a manifestation of IBS. However, bloating may also represent small intestinal bacterial overgrowth. Patients with persistent symptoms of abdominal bloating and distension despite dietary interventions should be referred for H₂ breath testing to determine the presence or absence of bacterial overgrowth. If bacterial overgrowth is identified, patients are typically treated with antibiotics. Evaluation of IBS generally includes testing of other disorders that cause similar symptoms. Carbohydrate malabsorption (lactose, fructose, sorbitol) can cause abdominal fullness, bloating, nausea, abdominal pain, flatulence, and diarrhea, which are similar to the symptoms of IBS. However, it is unclear if these digestive disorders contribute to or cause the symptoms of IBS. Research studies show that a proper diagnosis and effective dietary intervention significantly reduces the severity and frequency of gastrointestinal symptoms in IBS. Thus, diagnosis of malabsorption of these carbohydrates in IBS using a breath test is very important to guide the clinician in the proper treatment of IBS patients.

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.