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

Exploring putative enteric methanogenesis inhibitors using molecular simulations and a graph neural network

Atmospheric methane (CH4) acts as a key contributor to global warming. As CH4 is a short-lived climate forcer (12 years atmospheric lifespan), its mitigation represents the most promising means to address climate change in the short term. Enteric CH4 (the biosynthesized CH4 from the rumen of ruminants) represents 5.1% of total global greenhouse gas (GHG) emissions, 23% of emissions from agriculture, and 27.2% of global CH4 emissions. Therefore, it is imperative to investigate methanogenesis inhibitors and their underlying modes of action. We hereby elucidate the detailed biophysical and thermodynamic interplay between anti-methanogenic molecules and cofactor F430 of methyl coenzyme M reductase and interpret the stoichiometric ratios and binding affinities of sixteen inhibitor molecules. We leverage this as prior in a graph neural network to first functionally cluster these sixteen known inhibitors among ~54,000 bovine metabolites. We subsequently demonstrate a protocol to identify precursors to and putative inhibitors for methanogenesis, based on Tanimoto chemical similarity and membrane permeability predictions. This work lays the foundation for computational and de novo design of inhibitor molecules that retain/ reject one or more biochemical properties of known inhibitors discussed in this study.

Targeted isolation of Methanobrevibacter strains from fecal samples expands the cultivated human archaeome

Archaea are vital components of the human microbiome, yet their study within the gastrointestinal tract (GIT) is limited by the scarcity of cultured representatives. Our study presents a method for the targeted enrichment and isolation of methanogenic archaea from human fecal samples. The procedure combines methane breath testing, in silico metabolic modeling, media optimization, FACS, dilution series, and genomic sequencing through Nanopore technology. Additional analyzes include the co-cultured bacteriome, comparative genomics of archaeal genomes, functional comparisons, and structure-based protein function prediction of unknown differential traits. Successful establishment of stable archaeal cultures from 14 out of 16 fecal samples yielded nine previously uncultivated strains, eight of which are absent from a recent archaeome genome catalog. Comparative genomic and functional assessments of Methanobrevibacter smithii and Candidatus Methanobrevibacter intestini strains from individual donors revealed features potentially associated with gastrointestinal diseases. Our work broadens available archaeal representatives for GIT studies, and offers insights into Candidatus Methanobrevibacter intestini genomes' adaptability in critical microbiome contexts.

Update of gut gas metabolism in ulcerative colitis

INTRODUCTION

Ulcerative colitis (UC) is a chronic, nonspecific inflammatory disease of the intestine. The intestinal microbiota is essential in the occurrence and development of UC. Gut gases are produced via bacterial fermentation or chemical interactions, which can reveal altered intestinal microbiota, abnormal cellular metabolism, and inflammation responses. Recent studies have demonstrated that UC patients have an altered gut gas metabolism.

AREAS COVERED

In this review, we integrate gut gas metabolism advances in UC and discuss intestinal gases' clinical values as new biomarkers or therapeutic targets for UC, providing the foundation for further research. Literature regarding gut gas metabolism and its significance in UC from inception to October 2023 was searched on the MEDLINE database and references from relevant articles were investigated.

EXPERT OPINION

Depending on their type, concentration, and volume, gut gases can induce or alleviate clinical symptoms and regulate intestinal motility, inflammatory responses, immune function, and oxidative stress, significantly impacting UC. Gut gases may function as new biomarkers and provide potential diagnostic or therapeutic targets for UC.

Antifungal chemicals promising function in disease prevention, method of action and mechanism

The increasing use of antimicrobial drugs has been linked to the rise of drug-resistant fungus in recent years. Antimicrobial resistance is being studied from a variety of perspectives due to the important clinical implication of resistance. The processes underlying this resistance, enhanced methods for identifying resistance when it emerges, alternate treatment options for infections caused by resistant organisms, and so on are reviewed, along with strategies to prevent and regulate the formation and spread of resistance. This overview will focus on the action mechanism of antifungals and the resistance mechanisms against them. The link between antibacterial and antifungal resistance is also briefly discussed. Based on their mechanism action, antifungals are divided into three distinct categories: azoles, which target the ergosterol synthesis; 5-fluorocytosine, which targets macromolecular synthesis and polyenes, which interact physiochemically with fungal membrane sterols. Antifungal resistance can arise through a wide variety of ways. Overexpression of the target of the antifungal drug, changes to the drug target, changes to sterol biosynthesis, decreased intercellular concentration of the target enzyme, and other processes. A correlation exists between the mechanisms of resistance to antibacterial and antifungals, despite the fact that the comparison between the two is inevitably constrained by various parameters mentioned in the review. Drug extrusion via membrane pumps has been thoroughly documented in both prokaryotic and eukaryotic cells, and development of new antifungal compounds and strategies has also been well characterized.

Hydrogen Sulfide Producers Drive a Diarrhea-Like Phenotype and a Methane Producer Drives a Constipation-Like Phenotype in Animal Models

BACKGROUND

We recently demonstrated that diarrhea-predominant irritable bowel syndrome (IBS-D) subjects have higher relative abundance (RA) of hydrogen sulfide (H2S)-producing Fusobacterium and Desulfovibrio species, and constipation-predominant IBS (IBS-C) subjects have higher RA of methanogen Methanobrevibacter smithii.

AIMS

In this study, we investigate the effects of increased methanogens or H2S producers on stool phenotypes in rat models.

METHODS

Adult Sprague-Dawley rats were fed high-fat diet (HFD) for 60 days to increase M. smithii levels, then gavaged for 10 days with water (controls) or methanogenesis inhibitors. To increase H2S producers, rats were gavaged with F. varium or D. piger. Stool consistency (stool wet weight (SWW)) and gas production were measured. 16S rRNA gene sequencing was performed on stool samples.

RESULTS

In HFD diet-fed rats (N = 30), stool M. smithii levels were increased (P < 0.001) after 52 days, correlating with significantly decreased SWW (P < 0.0001) at 59 days (R = - 0.38, P = 0.037). Small bowel M. smithii levels decreased significantly in lovastatin lactone-treated rats (P < 0.0006), and SWW increased (normalized) in lovastatin hydroxyacid-treated rats (P = 0.0246), vs. controls (N = 10/group). SWW increased significantly in D. piger-gavaged rats (N = 16) on day 10 (P < 0.0001), and in F. varium-gavaged rats (N = 16) at all timepoints, vs. controls, with increased stool H2S production. 16S sequencing revealed stool microbiota alterations in rats gavaged with H2S producers, with higher relative abundance (RA) of other H2S producers, particularly Lachnospiraceae and Bilophila in F. varium-gavaged rats, and Sutterella in D. piger-gavaged rats.

CONCLUSIONS

These findings suggest that increased M. smithii levels result in a constipation-like phenotype in a rat model that is partly reversible with methanogenesis inhibitors, whereas gavage with H2S producers D. piger or F. varium results in increased colonization with other H2S producers and diarrhea-like phenotypes. This supports roles for the increased RA of methanogens and H2S producers identified in IBS-C and IBS-D subjects, respectively, in contributing to stool phenotypes.

Methane mitigation in ruminants with structural analogues and other chemical compounds targeting archaeal methanogenesis pathways

Ruminants are responsible for enteric methane production contributing significantly to the anthropogenic greenhouse gases in the atmosphere. Moreover, dietary energy is lost as methane gas without being available for animal use. Therefore, many mitigation strategies aiming at interventions at animals, diet, and microbiota have been explored by researchers. Specific chemical analogues targeting the enzymes of the methanogenic pathway appear to be more effective in specifically inhibiting the growth of methane-producing archaea without hampering another microbiome, particularly, cellulolytic microbiota. The targets of methanogenesis reactions that have been mainly investigated in ruminal fluid include methyl coenzyme M reductase (halogenated sulfonate and nitrooxy compounds), corrinoid enzymes (halogenated aliphatic compounds), formate dehydrogenase (nitro compounds, e.g., nitroethane and 2-nitroethanol), and deazaflavin (F420) (pterin and statin compounds). Many other potential metabolic reaction targets in methanogenic archaea have not been evaluated properly. The analogues are specifically effective inhibitors of methanogens, but their efficacy to lower methanogenesis over time reduces due to the metabolism of the compounds by other microbiota or the development of resistance mechanisms by methanogens. In this short review, methanogen populations inhabited in the rumen, methanogenesis pathways and methane analogues, and other chemical compounds specifically targeting the metabolic reactions in the pathways and methane production in ruminants have been discussed. Although many methane inhibitors have been evaluated in lowering methane emission in ruminants, advancement in unravelling the molecular mechanisms of specific methane inhibitors targeting the metabolic pathways in methanogens is very limited.

Inclusion of the fungus Pleurotus florida in the diet affects performance and feed efficiency traits in calves: a case study on Ravi buffalo

The objective of the study was to investigate the effects of inclusion of Pleurotus florida treated wheat straw in the total mixed rations (TMRs) on feed intake, growth performance, nutrient digestibility, and nitrogen retention in male buffalo calves. As a pilot study, four TMRs, i.e., TMR1 having 0% P. florida treated wheat straw (FTWS), TMR2 (20% FTWS), TMR3 (40% FTWS), and TMR4 (60% FTWS) with berseem hay as basal diet, were formulated. Sixteen Nili-Ravi male buffalo calves (aged 10-12 months, weighing 73 ± 2.50 kg) were divided into four equal groups and randomly assigned one of four TMRs. A significant increase (P < 0.05) was observed in all nutrients intake, their digestibility, weight gain, and nitrogen retention with TMRs incorporated with FTWS. Highest feed conversion ratio (FCR) of 2.63 was noted with TMR1-0% and the lowest FCR (1.80) with TMR4-60%, on the other hand. In conclusion, the TMR4 (60% FTWS) has the potential to increase the weight gain, nutrient digestibility, nitrogen retention, and feed efficiency in buffalo calves. Therefore, inclusion of 60% Pleurotus florida treated wheat straw is recommended as TMRs with berseem hay based basal diet for feeding buffaloes calves.

Methanogenic archaea in the human gastrointestinal tract

The human microbiome is strongly interwoven with human health and disease. Besides bacteria, viruses and eukaryotes, numerous archaea are located in the human gastrointestinal tract and are responsible for methane production, which can be measured in clinical methane breath analyses. Methane is an important readout for various diseases, including intestinal methanogen overgrowth. Notably, the archaea responsible for methane production are largely overlooked in human microbiome studies due to their non-bacterial biology and resulting detection issues. As such, their importance for health and disease remains largely unclear to date, in particular as not a single archaeal representative has been deemed to be pathogenic. In this Perspective, we discuss the current knowledge on the clinical relevance of methanogenic archaea. We explain the archaeal unique response to antibiotics and their negative and positive effects on human physiology, and present the current understanding of the use of methane as a diagnostic marker.

Gut Non-Bacterial Microbiota: Emerging Link to Irritable Bowel Syndrome

As a common functional gastrointestinal disorder, irritable bowel syndrome (IBS) significantly affects personal health and imposes a substantial economic burden on society, but the current understanding of its occurrence and treatment is still inadequate. Emerging evidence suggests that IBS is associated with gut microbial dysbiosis, but most studies focus on the bacteria and neglect other communities of the microbiota, including fungi, viruses, archaea, and other parasitic microorganisms. This review summarizes the latest findings that link the nonbacterial microbiota with IBS. IBS patients show less fungal and viral diversity but some alterations in mycobiome, virome, and archaeome, such as an increased abundance of Candida albicans. Moreover, fungi and methanogens can aid in diagnosis. Fungi are related to distinct IBS symptoms and induce immune responses, intestinal barrier disruption, and visceral hypersensitivity via specific receptors, cells, and metabolites. Novel therapeutic methods for IBS include fungicides, inhibitors targeting fungal pathogenic pathways, probiotic fungi, prebiotics, and fecal microbiota transplantation. Additionally, viruses, methanogens, and parasitic microorganisms are also involved in the pathophysiology and treatment. Therefore, the gut nonbacterial microbiota is involved in the pathogenesis of IBS, which provides a novel perspective on the noninvasive diagnosis and precise treatment of this disease.

Distinctive Clinical Correlates of Small Intestinal Bacterial Overgrowth with Methanogens

BACKGROUND AND AIMS

Most patients with small intestinal bacterial overgrowth (SIBO) produce hydrogen by fermentation of dietary carbohydrates; however, ∼30% of patients with SIBO are colonized with Archaea, anaerobic organisms that produce methane. SIBO is associated with a plethora of symptoms and conditions, but their diagnostic significance is unclear. We aimed to determine if specific symptoms and conditions are associated with methanogenic SIBO.

METHODS

This study received institutional review board approval (IRB00059873). In this retrospective cross-sectional study, we queried a database of glucose breath tests conducted for suspected SIBO at our tertiary care medical center, which included data on the presence or absence of gastrointestinal symptoms and conditions often associated with SIBO. All patients had undergone a standardized breath testing protocol.

RESULTS

In a cohort of 1461 patients, 33.1% were SIBO positive; of these, 49.8% produced only hydrogen, 38.8% produced only methane, and 11.4% produced both gases. The following factors distinguished patients with hydrogen-producing SIBO, but not methanogenic SIBO, from SIBO-negative patients: vitamin B₁₂ deficiency (odds ratio, 1.44; confidence interval [CI], 1.01-2.06; P = .046), Roux-en-Y gastric bypass (odds ratio, 2.14; CI, 1.09-4.18; P = .027), cholecystectomy (odds ratio, 1.42; CI, 1.06-1.91; P = .020), and diabetes (odds ratio, 1.59; CI, 1.13-2.24; P = .008). The absence of vitamin B₁₂ deficiency was the sole discriminating factor between methanogenic and hydrogenic SIBO (odds ratio, 0.57; CI, 0.34-0.97; P = .038).

CONCLUSIONS

Patients with SIBO caused by methane-producing Archaea display a different spectrum of associated symptoms and clinical conditions compared with patients with SIBO caused by hydrogen-producing bacteria, particularly a lower incidence of vitamin B₁₂ deficiency.

Nutritional Interventions to Reduce Methane Emissions in Ruminants

Methane is the single largest source of anthropogenic greenhouse gases produced in ruminants. As global warming is a main concern, the interest in mitigation strategies for ruminant derived methane has strongly increased over the last years. Methane is a natural by-product of anaerobic microbial (bacteria, archaea, protozoa, and fungi) fermentation of carbohydrates and, to a lesser extent, amino acids in the rumen. This gaseous compound is the most prominent hydrogen sink product synthesized in the rumen. It is formed by the archaea, the so-called methanogens, which utilize excessive ruminal hydrogen. Different nutritional strategies to reduce methane production in ruminants have been investigated such as dietary manipulations, plant extracts, lipids and lipid by-products, plant secondary metabolites, flavonoids, phenolic acid, statins, prebiotics, probiotics, etc. With the range of technical options suggested above, it is possible to develop best nutritional strategies to reduce the ill effects of livestock on global warming. These nutritional strategies seem to be the most developed means in mitigating methane from enteric fermentation in ruminants and some are ready to be applied in the field at the moment.

Dietary Plant Polyphenols as the Potential Drugs in Neurodegenerative Diseases: Current Evidence, Advances, and Opportunities

Neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD), and Huntington's disease (HD), are characterized by the progressive degeneration of neurons. Although the etiology and pathogenesis of neurodegenerative diseases have been studied intensively, the mechanism is still in its infancy. In general, most neurodegenerative diseases share common molecular mechanisms, and multiple risks interact and promote the pathologic process of neurogenerative diseases. At present, most of the approved drugs only alleviate the clinical symptoms but fail to cure neurodegenerative diseases. Numerous studies indicate that dietary plant polyphenols are safe and exhibit potent neuroprotective effects in various neurodegenerative diseases. However, low bioavailability is the biggest obstacle for polyphenol that largely limits its adoption from evidence into clinical practice. In this review, we summarized the widely recognized mechanisms associated with neurodegenerative diseases, such as misfolded proteins, mitochondrial dysfunction, oxidative damage, and neuroinflammatory responses. In addition, we summarized the research advances about the neuroprotective effect of the most widely reported dietary plant polyphenols. Moreover, we discussed the current clinical study and application of polyphenols and the factors that result in low bioavailability, such as poor stability and low permeability across the blood-brain barrier (BBB). In the future, the improvement of absorption and stability, modification of structure and formulation, and the combination therapy will provide more opportunities from the laboratory into the clinic for polyphenols. Lastly, we hope that the present review will encourage further researches on natural dietary polyphenols in the treatment of neurodegenerative diseases.

Inhibition of in Vitro Rumen Methane Production by Three Statins

The aim of this study was to evaluate the effects of increasing concentrations of three pure statins on in vitro methane production and rumen fermentation. The effects of atorvastatin, rosuvastatin and simvastatin at three concentrations (1, 10, and 100 mg/L of culture fluid) were evaluated using in vitro 24 h batch incubation of buffered rumen fluid with a 70:30 forage:concentrate substrate. All statins tested demonstrated the ability to reduce methanogenesis. Methane inhibition potential was decreasing in the following order: simvastatin>atorvastatin>rosuvastatin. Methane production was reduced (P<0.05) by simvastatin at 10 mg/L (by 9.3%) and by atorvastatin at 100 mg/L (by 13.2%) without compromising fermentation and feed digestibility. Simvastatin at 100 mg/L decreased methane production by 26.2%, however, net production of volatile fatty acids (nVFA) was also reduced (P<0.05). The only effect of rosuvastatin was a slight reduction (P<0.05) of methane proportion at 10 and 100 mg/L. Simvastatin and atorvastatin at 100 mg/L increased (P<0.05) relative proportion of propionate at the expense of acetate and butyrate. Ammonia-N concentrations were not affected (P>0.05) by statins. The current study demonstrated that selected statins could selectively decrease methane production. The effects of statins on methanogenesis and overall rumen fermentation vary depending on statin type and concentration. Hydrophobic statins, such as simvastatin and atorvastatin, seem to be more effective compared to the hydrophilic statins, such as rosuvastatin.

Lovastatin as a supplement to mitigate rumen methanogenesis: an overview

Methane from enteric fermentation is the gas with the greatest environmental impact emitted by ruminants. Lovastatin (Lv) addition to feedstocks could be a strategy to mitigate rumen methane emissions via decreasing the population of methanogenic archaea (MA). Thus, this paper provides the first overview of the effects of Lv supplementation, focusing on the inhibition of methane production, rumen microbiota, and ruminal fermentation. Results indicated that Lv treatment had a strong anti-methanogenic effect on pure strains of MA. However, there are uncertainties from in vitro rumen fermentation trials with complex substrates and rumen inoculum.

Solid-state fermentation (SSF) has emerged as a cost-effective option to produce Lv. In this way, SSF of agricultural residues as an Lv-carrier supplement in sheep and goats demonstrated a consistent decrease in ruminal methane emissions. The experimental evidence for in vitro conditions showed that Lv did not affect the volatile fatty acids (VFA). However, in vivo experiments demonstrated that the production of VFA was decreased. Lv did not negatively affect the digestibility of dry matter during in vitro and in vivo methods, and there is even evidence that it can induce an increase in digestibility. Regarding the rumen microbiota, populations of MA were reduced, and no differences were detected in alpha and beta diversity associated with Lv treatment. However, some changes in the relative abundance of the microbiota were induced. Further studies are recommended on: (i) Lv biodegradation products and stability, as well as its adsorption onto the solid matter in the rumen, to gain more insight on the “available” or effective Lv concentration; and (ii) to determine whether the effect of Lv on ruminal fermentation also depends on the feed composition and different ruminants.

Going Beyond Bacteria: Uncovering the Role of Archaeome and Mycobiome in Inflammatory Bowel Disease

Inflammatory Bowel Disease (IBD) is a multifaceted class of relapsing-remitting chronic inflammatory conditions where microbiota dysbiosis plays a key role during its onset and progression. The human microbiota is a rich community of bacteria, viruses, fungi, protists, and archaea, and is an integral part of the body influencing its overall homeostasis. Emerging evidence highlights dysbiosis of the archaeome and mycobiome to influence the overall intestinal microbiota composition in health and disease, including IBD, although they remain some of the least understood components of the gut microbiota. Nonetheless, their ability to directly impact the other commensals, or the host, reasonably makes them important contributors to either the maintenance of the mucosal tissue physiology or to chronic intestinal inflammation development. Therefore, the full understanding of the archaeome and mycobiome dysbiosis during IBD pathogenesis may pave the way to the discovery of novel mechanisms, finally providing innovative therapeutic targets that can soon implement the currently available treatments for IBD patients.

The host-associated archaeome

Host-associated microbial communities have an important role in shaping the health and fitness of plants and animals. Most studies have focused on the bacterial, fungal or viral communities, but often the archaeal component has been neglected. The archaeal community, the so-called archaeome, is now increasingly recognized as an important component of host-associated microbiomes. It is composed of various lineages, including mainly Methanobacteriales and Methanomassiliicoccales (Euryarchaeota), as well as representatives of the Thaumarchaeota. Host-archaeome interactions have mostly been delineated from methanogenic archaea in the gastrointestinal tract, where they contribute to substantial methane production and are potentially also involved in disease-relevant processes. In this Review, we discuss the diversity and potential roles of the archaea associated with protists, plants and animals. We also present the current understanding of the archaeome in humans, the specific adaptations involved in interaction with the resident microbial community as well as with the host, and the roles of the archaeome in both health and disease.

Small Intestinal Bacterial Overgrowth: How to Diagnose and Treat (and Then Treat Again)

Small intestinal bacterial overgrowth (SIBO) is a condition with presentation that can vary from asymptomatic to steatorrhea and malnutrition. Small bowel aspiration and culture is the current gold standard of diagnosis; however, this is invasive and is not without risk to the patient. Breath testing is a noninvasive and less expensive alternative method; however, it lacks diagnostic sensitivity and specificity. Novel diagnostic methods being studied include gas-sensing capsules. The mainstay of treatment is antibiotics; alternative therapies include herbal medications, dietary modifications, and prokinetic agents. Further investigation into less invasive and less harmful diagnostic methods and treatment options is warranted.

Improving Nutritive Value of Purple Field Corn Residue and Rice Straw by Culturing with White-Rot Fungi

It was hypothesized that white-rot fungus fermented with rice straw and purple field corn improves nutrient utilization via enhanced digestibility and lowers methane (CH₄) production due to the effects of the lovastatin compound. The aim of the current experiment was to investigate the effect of inoculation of two fungi belonging to white-rot fungus type on feed value and ruminal fermentation characteristic. The experiment was carried out according to a completely randomized 3 × 3 factorial design: three roughage sources (rice straw, purple corn stover, and purple corn field cob) for three inoculation methods (untreated, P. ostreatus treated, and V. volvacea treated). The two fungi increased concentration of lovastatin when compared to the untreated, and P. ostreatus had higher lovastatin production potential than V. volvacea (p < 0.05). The yield of lovastatin was obtained from rice straw fermentation with P. ostreatus. The monomeric anthocyanin content (MAC) in untreated purple field corn cobs was higher than in the fermentation groups. Ruminal fermentation gas production from soluble fractions ranged from −2.47 to 1.14 and differed among the treatments (p < 0.01). In comparison to all treatments, the gas production rate for the insoluble fraction was significantly highest (p < 0.01) in treatment alone, in which purple field corn stover was fermented with P. ostreatus and V. volvacea. There was significant interaction in in vitro dry matter digestibility at 12 h of incubation. Purple field corn cob had a higher significant effect on in vitro DM digestibility at 12 and 24 h after incubation when compared to that of other groups. Moreover, current research has found that roughage fermented with P. ostreatus and V. volvacea increased in vitro DM digestibility at 24 h after incubation. Fermenting roughage with fungi did not affect rumen pH, which ranged from 6.60 to 6.91 (p > 0.05), while P. ostreatus resulted in increased levels of ruminal ammonia-nitrogen concentrations. Propionic acid increased in all roughages fermented with P. ostreatus or V. volvacea after 8 h of ruminal fermentation testing. The two fungi fermented as substrate treatments had significantly lower (p < 0.05) CH₄ production. Based on the improved rumen DM digestibility and reduced CH₄ production, P. ostreatus and V. volvacea could be utilized for enhancing feeding efficiency of roughage.

Eating Disorders and Gastrointestinal Diseases

Eating disorders (ED) are frequently associated with a wide range of psychiatric or somatic comorbidities. The most relevant ED are anorexia nervosa (AN), bulimia nervosa (BN), and binge eating disorders (BED). Patients with ED exhibit both upper and lower gastrointestinal (GI) symptoms. Evidence of alterations throughout the GI tract in ED will be analyzed given the role of the GI tract in food intake and its regulation. It remains a matter of debate whether GI disorders are inherent manifestations of ED or the results of malnutrition occurring from ED. Moreover, recent clinical studies have highlighted the growing role of intestinal microbiota in the pathogenesis of ED, making it possible to hypothesize a modulation of intestinal microbiota as a co-adjuvant to standard therapy. The aim of this review is to analyze the link between ED and GI diseases and to present, where known, the potential key factors underlying these conditions. Conclusions: The presence of GI disorders should be investigated in patients with ED. Screening for ED should also be encouraged in individuals seeking treatment for unexplained GI complaints to better address therapeutic issues that surround these difficult medical conditions.

Eating Disorders and Gastrointestinal Diseases

Eating disorders (ED) are frequently associated with a wide range of psychiatric or somatic comorbidities. The most relevant ED are anorexia nervosa (AN), bulimia nervosa (BN), and binge eating disorders (BED). Patients with ED exhibit both upper and lower gastrointestinal (GI) symptoms. Evidence of alterations throughout the GI tract in ED will be analyzed given the role of the GI tract in food intake and its regulation. It remains a matter of debate whether GI disorders are inherent manifestations of ED or the results of malnutrition occurring from ED. Moreover, recent clinical studies have highlighted the growing role of intestinal microbiota in the pathogenesis of ED, making it possible to hypothesize a modulation of intestinal microbiota as a co-adjuvant to standard therapy. The aim of this review is to analyze the link between ED and GI diseases and to present, where known, the potential key factors underlying these conditions. Conclusions: The presence of GI disorders should be investigated in patients with ED. Screening for ED should also be encouraged in individuals seeking treatment for unexplained GI complaints to better address therapeutic issues that surround these difficult medical conditions.

Pleurotus Ostreatus and Volvariella Volvacea Can Enhance the Quality of Purple Field Corn Stover and Modulate Ruminal Fermentation and Feed Utilization in Tropical Beef Cattle

This objective is to elucidate the effect of purple field corn stover treated with Pleurotus ostreatus and Volvarialla volvacea on feed utilization, ruminal ecology, and CH4 synthesis in tropical beef cattle. Four male Thai native beef cattle (100 ± 30 kg of body weight (BW) were assigned randomly as a 2 × 2 factorial arrangement in a 4 × 4 Latin square design. Factor A (roughage sources) was rice straw and purple field corn stover and factor B was species of white-rot fungi (P. ostreatus and V. volvacea). After fermentation, crude protein (CP) was increased in rice straw and purple field corn stover fermented with P. ostreatus and V. volvacea. The unfermented purple field corn stover contained 11.8% dry matter (DM) of monomeric anthocyanin (MAC), whereas the MAC concentration decreased when purple field corn stover was fermented with white rot fungi. There were no changes (p > 0.05) in DM intake of body weight (BW) kg/d and g/kg BW0.75 among the four treatments. The organic matter (OM), CP, and acid detergent fiber (ADF) intake were different between rice straw and purple field corn stover and were the greatest in the purple field corn stover group. Moreover, the current study showed that neutral detergent fiber (NDF) and ADF digestion was higher in purple field corn stover than in rice straw, but there were no significant differences between P. ostreatus and V. volvacea. There were significant effects of roughage sources on ammonia nitrogen (NH3-N) at 4 h after feeding. Bacterial population was changed by feeding with purple field corn stover fermented with P. ostreatus and V. volvacea. On the other hand, the number of protozoa was reduced by approximately 33% at 4 h after feeding with purple field corn stover (p < 0.01). Propionic acid concentration was different between roughage sources (p < 0.01) enhanced with purple field corn stover fermented with P. ostreatus and V. volvacea. In addition, methane production decreased by 15% with purple field corn stover fermented with P. ostreatus and V. volvacea compared to rice straw. There were significant differences on all nitrogen balances parameters (p < 0.05), except the fecal N excretion (p > 0.05) were not changed. Furthermore, microbial crude protein and efficiency of microbial N synthesis were enhanced when purple field corn stover fermented with P. ostreatus and V. volvacea was fed compared to rice straw group. Base on this study, it could be summarized that P. ostreatus or V. volvacea can enhance the quality of purple field corn stover and modulate rumen fermentation and feed digestion in Thai native beef cattle.

Intestinal gases: influence on gut disorders and the role of dietary manipulations

The inner workings of the intestines, in which the body and microbiome intersect to influence gut function and systemic health, remain elusive. Carbon dioxide, hydrogen, methane and hydrogen sulfide, as well as a variety of trace gases, are generated by the chemical interactions and microbiota within the gut. Profiling of these intestinal gases and their responses to dietary changes can reveal the products and functions of the gut microbiota and their influence on human health. Indeed, different tools for measuring these intestinal gases have been developed, including newly developed gas-sensing capsule technology. Gases can, according to their type, concentration and volume, induce or relieve abdominal symptoms, and might also have physiological, pathogenic and therapeutic effects. Thus, profiling and modulating intestinal gases could be powerful tools for disease prevention and/or therapy. As the interactions between the microbiota, chemical constituents and fermentative substrates of the gut are principally influenced by dietary intake, altering the diet, which, in turn, changes gas profiles, is the main therapeutic approach for gastrointestinal disorders. An improved understanding of the complex interactions within the intestines that generate gases will enhance our ability to prevent, diagnose, treat and monitor many gastrointestinal disorders.

Targeting the gut microbiota for the treatment of irritable bowel syndrome

Irritable bowel syndrome (IBS) is a chronic gastrointestinal disorder that affects an estimated 11% of people across the world. IBS patients are one of the largest subgroups seen in gastroenterology clinics, exhibit a lesser quality of life, and take greater use of the healthcare system. The exact etiology of IBS remains uncertain. Alterations in the gut microbiome may characterize apotential mechanism in the pathogenesis of IBS. This hypothesis is paralleled by rodent models in which manipulation of the gut microbiota leads to disturbed physiological functions along the brain-gut axis. Recent research in IBS treatments has redirected its focus towards gu microbiome based therapeutics. In this review, we discuss potential roles of enteric bacteria in the pathogenesis of IBS and its comorbidities. We then explore the manipulation of the enteric microbiota by prebiotics, probiotics, antibiotics, dietary changes, and fecal microbiota transfer. We also discuss the positive and negative effects of these therapeutics on IBS symptoms.

Recent advances in the pharmacological management of constipation predominant irritable bowel syndrome

Introduction: Irritable bowel syndrome (IBS) is a complex functional gut disorder that typically manifests in early adult years. More than a third of IBS patients are diagnosed with predominant constipation subtype (IBS-C). This syndrome has a distressing impact on the quality of life and is challenging both for patients and physicians.Areas covered: This review focuses on the pathophysiology of constipation in IBS and presents current management options. It also covers the latest findings that may lead to novel pharmacological options in IBS-C management. The authors intend to highlight the results of published research including abstracts, records from the clinicaltrials.gov database (second and third phases of the study) and information from original FDA documents.Expert opinion: Current therapeutic options for IBS-C treatment are based on linaclotide, lubiprostone, plecanatide, and the reintroduced tegaserod. Drugs present on the market as well as those in pre-clinical development should increase the lower esophageal sphincter pressure, promote gastric motility, accelerate gastric emptying and improve gastro-duodenal coordination. Most significantly, they shall not induce severe side effects.

Methane Production and Bioactivity-A Link to Oxido-Reductive Stress

Biological methane formation is associated with anoxic environments and the activity of anaerobic prokaryotes (Archaea). However, recent studies have confirmed methane release from eukaryotes, including plants, fungi, and animals, even in the absence of microbes and in the presence of oxygen. Furthermore, it was found that aerobic methane emission in plants is stimulated by a variety of environmental stress factors, leading to reactive oxygen species (ROS) generation. Further research presented evidence that molecules with sulfur and nitrogen bonded methyl groups such as methionine or choline are carbon precursors of aerobic methane formation. Once generated, methane is widely considered to be physiologically inert in eukaryotes, but several studies have found association between mammalian methanogenesis and gastrointestinal (GI) motility changes. In addition, a number of recent reports demonstrated anti-inflammatory potential for exogenous methane-based approaches in model anoxia-reoxygenation experiments. It has also been convincingly demonstrated that methane can influence the downstream effectors of transiently increased ROS levels, including mitochondria-related pro-apoptotic pathways during ischemia-reperfusion (IR) conditions. Besides, exogenous methane can modify the outcome of gasotransmitter-mediated events in plants, and it appears that similar mechanism might be active in mammals as well. This review summarizes the relevant literature on methane-producing processes in eukaryotes, and the available results that underscore its bioactivity. The current evidences suggest that methane liberation and biological effectiveness are both linked to cellular redox regulation. The data collectively imply that exogenous methane influences the regulatory mechanisms and signaling pathways involved in oxidative and nitrosative stress responses, which suggests a modulator role for methane in hypoxia-linked pathologies.

Small Intestinal Bacterial Overgrowth in Children: A State-Of-The-Art Review

Small intestinal bacterial overgrowth (SIBO) is a heterogenous and poorly understood entity characterised by an excessive growth of select microorganisms within the small intestine. This excessive bacterial biomass, in turn, disrupts host physiology in a myriad of ways, leading to gastrointestinal and non-gastrointestinal symptoms and complications. SIBO is a common cause of non-specific gastrointestinal symptoms in children, such as chronic abdominal pain, abdominal distention, diarrhoea, and flatulence, amongst others. In addition, it has recently been implicated in the pathophysiology of stunting, a disease that affects millions of children worldwide. Risk factors such as acid-suppressive therapies, alterations in gastrointestinal motility and anatomy, as well as impoverished conditions, have been shown to predispose children to SIBO. SIBO can be diagnosed via culture-dependant or culture-independent approaches. SIBO's epidemiology is limited due to the lack of uniformity and consensus of its diagnostic criteria, as well as the paucity of literature available. Antibiotics remain the first-line treatment option for SIBO, although emerging modalities such as probiotics and diet manipulation could also have a role. Herein, we present a state-of-the-art-review which aims to comprehensively outline the most current information on SIBO in children, with particular emphasis on the gut microbiota.

[Methanobrevibacter smithii in irritable bowel syndrome: a clinical and molecular study]

AIM

To assess the role of Methanobrevibacter smithii in patients with irritable bowel syndrome associated with small intestinal bowel overgrowth.

MATERIALS AND METHODS

Sixty - seven patients with IBS according to Rome IV were enrolled into the study in whom hydrogen breath test was performed. Thirty - two healthy subjects with negative breath test was used as a control. All IBS symptoms assessed daily with 5 grade Lykert scale for 7 days, stool was assessed by Brystol stool scale. M. smithii was confirmed in stool samples by PCR.

RESULTS AND DISCUSSION

In 67 IBS patients CH4 overproduction was found in 32 (47.7%), H2 overproduction in 31 (46.2%) and normal values in 4 (5.9%) by hydrogen breath test. M. smithii was confirmed by stool PCR in all patients with CH4 overproduction. Severity and prevalence of main clinical features of IBS were similar in both SIBO groups but were significantly higher than in control (p.

Methane and Constipation-predominant Irritable Bowel Syndrome: Entwining Pillars of Emerging Neurogastroenterology

Functional gut disorders have long known to cause depravity in quality of life. Among the group of these heterogeneous disorders, irritable bowel syndrome (IBS) has been known to affect a large chunk of our population. IBS is not as simple as it sounds. Caused by a multitude of factors, the heterogeneity of this disorder has laid the foundation for research and the new principles of neurogastroenterology. Dysbiosis and methane production are one of the forthcoming factors that are currently under investigation. Down the road of exclusive enteric anaerobic fermentation of polysaccharides, methane is produced. It was considered to be an inert gas in the past, with little to no role in gut activity but now it is established that it has an impressive role in the etiology of constipation-predominant IBS (C-IBS). Acting as a neurotransmitter, it is known to affect ileal and colonic transit time, which has currently been shown in animal studies. Many laxatives, ionophore antibiotics, drugs like rifamixin and neomycin have been targeted against this very principle. Lately, lovastatin has emerged as a potential pharmacologic therapy to devoid the gut of methane without disrupting the gut niche in itself and has shown promise in relieving the symptoms of C-IBS. The goal of this article is to compile and assemble the literature available on IBS and the neuromodulation of methane to teach physicians and research scientists about the current age of gastroenterology and the growing need to emphasize the role of methane in the symptomatology of functional gut disorders like C-IBS.

[Modern conception of the pathogenesis of neurodegenerative diseases and therapeutic strategy]

Here we discuss the pathogenesis of the inflammatory and degenerative nervous system disorders on the example of Parkinson's disease, Alzheimer's disease, multiple sclerosis. Common mechanisms of neurodegeneration in these diseases are reviewed. The role of neurodegeneration as the main process leading to the resistant disability of patients with multiple sclerosis is discussed. The authors consider a contribution of inflammatory process and chronic infection to the manifestation and progressing of a neurodegenerative disease and discuss the use of treatment not usually indicated including interferon, anti-inflammatory drugs, statin, vitamin D, monoclonal antibodies, correction of the intestinal microbiota in Parkinson's disease and Alzheimer's disease.

Crystal structure of archaeal HMG-CoA reductase: insights into structural changes of the C-terminal helix of the class-I enzyme

3-hydroxy-3-methylglutaryl-CoA reductase (HMGR) catalyses the last step in mevalonate biosynthesis. HMGR is the target of statin inhibitors that regulate cholesterol concentration in human blood. Here, we report the properties and structures of HMGR from an archaeon Methanothermococcus thermolithotrophicus (mHMGR). The structures of the apoenzyme and the NADPH complex are highly similar to those of human HMGR. A notable exception is C-terminal helix (Lα10-11) that is straight in both mHMGR structures. This helix is kinked and closes the active site in the human enzyme ternary complex, pointing to a substrate-induced structural rearrangement of C-terminal in class-I HMGRs during the catalytic cycle.

Individual variations in cardiovascular-disease-related protein levels are driven by genetics and gut microbiome

Despite a growing body of evidence, the role of the gut microbiome in cardiovascular diseases (CVDs) is still unclear. Here we present a systems-genome-wide and metagenome-wide association study on plasma concentrations of 92 CVD-related proteins in the population cohort Lifelines-DEEP. We identified genetic components for 73 proteins and microbial associations for 41 proteins, of which 31 were associated to both. The genetic and microbial factors identified mostly exert additive effects and collectively explain up to 76.6% of inter-individual variation (17.5% on average). Genetics contributes most to concentrations of immune-related proteins, while the gut microbiome contributes most to proteins involved in metabolism and intestinal health. We found several host-microbe interactions that impact proteins involved in epithelial function, lipid metabolism and central nervous system function. This study reveals important evidence for a joint genetic and microbial effect in cardiovascular disease and provides directions for future applications in personalized medicine.

Methanobacterium formicicum as a target rumen methanogen for the development of new methane mitigation interventions: A review

Methanobacterium formicicum (Methanobacteriaceae family) is an endosymbiotic methanogenic Archaean found in the digestive tracts of ruminants and elsewhere. It has been significantly implicated in global CH₄ emission during enteric fermentation processes. In this review, we discuss current genomic and metabolic aspects of this microorganism for the purpose of the discovery of novel veterinary therapeutics. This microorganism encompasses a typical H₂ scavenging system, which facilitates a metabolic symbiosis across the H₂ producing cellulolytic bacteria and fumarate reducing bacteria. To date, five genome-scale metabolic models (iAF692, iMG746, iMB745, iVS941 and iMM518) have been developed. These metabolic reconstructions revealed the cellular and metabolic behaviors of methanogenic archaea. The characteristics of its symbiotic behavior and metabolic crosstalk with competitive rumen anaerobes support understanding of the physiological function and metabolic fate of shared metabolites in the rumen ecosystem. Thus, systems biological characterization of this microorganism may provide a new insight to realize its metabolic significance for the development of a healthy microbiota in ruminants. An in-depth knowledge of this microorganism may allow us to ensure a long term sustainability of ruminant-based agriculture.

Changes in microbiota composition, bile and fatty acid metabolism, in successful faecal microbiota transplantation for Clostridioides difficile infection

Background

Alteration of the gut microbiota by repeated antibiotic treatment increases susceptibility to Clostridioides difficile infection. Faecal microbiota transplantation from donors with a normal microbiota effectively treats C. difficile infection.

Methods

The study involved 10 patients with recurrent C. difficile infection, nine of whom received transplants from individual donors and one who received a donor unit from a stool bank (OpenBiome).

Results

All individuals demonstrated enduring post-transplant resolution of C. difficile- associated diarrhoea. Faecal microbiota diversity of recipients significantly increased, and the composition of the microbiota resembled that of the donor. Patients with C. difficile infection exhibited significantly lower faecal levels of secondary/ bile acids and higher levels of primary bile acids. Levels of secondary bile acids were restored in all transplant recipients, but to a lower degree with the OpenBiome transplant. The abundance increased of bacterial genera known from previous studies to confer resistance to growth and germination of C. difficile. These were significantly negatively associated with primary bile acid levels and positively related with secondary bile acid levels. Although reduced levels of the short chain fatty acids, butyrate, propionate and acetate, have been previously reported, here we report elevations in SCFA, pyruvic and lactic fatty acids, saturated, ω-6, monounsaturated, ω-3 and ω-6 polyunsaturated fatty acids (PUFA) in C. difficile infection. This potentially indicates one or a combination of increased dietary FA intake, microbial modification of FAs or epithelial cell damage and inflammatory cell recruitment. No reversion to donor FA profile occurred post-FMT but ω-3 to ω-6 PUFA ratios were altered in the direction of the donor. Archaeal metabolism genes were found in some samples post FMT.

Conclusion

A consistent metabolic signature was identified in the post-transplant microbiota, with reduced primary bile acids and substantial restoration of secondary bile acid production capacity. Total FA levels were unchanged but the ratio of inflammatory to non-inflammatory FAs decreased.

Electronic supplementary material

The online version of this article (10.1186/s12876-018-0860-5) contains supplementary material, which is available to authorized users.

A systematic review of studies on the faecal microbiota in anorexia nervosa: future research may need to include microbiota from the small intestine

PURPOSE

Anorexia nervosa (AN) is a poorly understood and often chronic condition. Deviations in the gut microbiota have been reported to influence the gut-brain axis in other disorders. Therefore, if present in AN, it may impact on symptoms and illness progression. A review of the gut microbiota studies in AN is presented.

METHOD

A literature search on PubMed yielded 27 articles; 14 were selected and based on relevance, 9 articles were included. The findings were interpreted in the larger context of preclinical research and clinical observations.

RESULTS

8 out of 9 included studies analysed microbiota from faeces samples, while the last analysed a protein in plasma produced by the gut. Two studies were longitudinal and included an intervention (i.e., weight restoration), five were cross-sectional, one was a case report, and the last was a case series consisting of three cases. Deviations in abundance, diversity, and microbial composition of the faecal microbiota in AN were found.

CONCLUSION

There are currently only a few studies on the gut microbiota in AN, all done on faeces samples, and not all describe the microbiota at the species level extensively. The Archaeon Methanobrevibacter smithii was increased in participants with a BMI < 25 in one study and specifically in AN patients in three studies. Methanobrevibacter smithii may, if detected, be a benchmark biomarker for future studies. We propose that microbiota samples could also be collected from the small intestine, where a major exchange of nutrients takes place and where the microbiota may have a biological impact on AN.

Elevated methane levels in small intestinal bacterial overgrowth suggests delayed small bowel and colonic transit

Limited research exists regarding the relationship between small intestinal bacterial overgrowth (SIBO), small bowel transit (SBT), and colonic transit (CT). Furthermore, symptom analysis is limited between the subtypes of SIBO: hydrogen producing (H-SIBO) and methane producing (M-SIBO). The primary aims of this study are to: compare the SBT and CT in patients with a positive lactulose breath test (LBT) to those with a normal study; compare the SBT and CT among patients with H-SIBO or M-SIBO; compare the severity of symptoms in patients with a positive LBT to those with a normal study; compare the severity of symptoms among patients with H-SIBO or M-SIBO.A retrospective review was performed for 89 patients who underwent a LBT and whole gut transit scintigraphy (WGTS) between 2014 and 2016. Seventy-eight patients were included. WGTS evaluated gastric emptying, SBT (normal ≥40% radiotracer bolus accumulated at the ileocecal valve at 6 hours), and CT (normal geometric center of colonic activity = 1.6-7.0 at 24 hours, 4.0-7.0 at 48 hours, 6.2-7.0 at 72 hours; elevated geometric center indicates increased transit). We also had patients complete a pretest symptom survey to evaluate nausea, bloating, constipation, diarrhea, belching, and flatulence.A total of 78 patients (69 females, 9 males, mean age of 48 years, mean BMI of 25.9) were evaluated. Forty-seven patients had a positive LBT (H-SIBO 66%, M-SIBO 34%). Comparison of SBT among patients with a positive LBT to normal LBT revealed no significant difference (62.1% vs 58.6%, P = .63). The mean accumulated radiotracer was higher for H-SIBO compared to M-SIBO (71.5% vs 44.1%; P < .05). For CT, all SIBO patients had no significant difference in geometric centers of colonic activity at 24, 48, and 72 hours when compared to the normal group. When subtyping, H-SIBO had significantly higher geometric centers compared to the M-SIBO group at 24 hours (4.4 vs 3.1, P < .001), 48 hours (5.2 vs 3.8, P = .002), and at 72 hours (5.6 vs 4.3, P = .006). The symptom severity scores did not differ between the positive and normal LBT groups. A higher level of nausea was present in the H-SIBO group when compared to the M-SIBO group.Overall, the presence of SIBO does not affect SBT or CT at 24, 48, and 72 hours. However, when analyzing the subtypes, M-SIBO has significantly more delayed SBT and CT when compared to H-SIBO. These results suggest the presence of delayed motility in patients with high methane levels on LBT.

Small Intestinal Bacterial Overgrowth: Nutritional Implications, Diagnosis, and Management

Small intestinal bacterial overgrowth (SIBO), characterized by the presence of excessive bacteria in the small intestine, is typically described as a malabsorptive syndrome occurring in the context of gut stasis syndromes. SIBO is now considered to be a disorder associated with diverse clinical conditions without classic risk factors for SIBO and a cause of several nonspecific gastrointestinal and nongastrointestinal symptoms. Because there is currently no gold standard for diagnosing SIBO, its prevalence and role in the pathogenesis of other diseases remain uncertain; as does optimal treatment of patients with relapsing symptoms.

A Review of Microbiota and Irritable Bowel Syndrome: Future in Therapies

Irritable bowel syndrome (IBS), one of the most frequent digestive disorders, is characterized by chronic and recurrent abdominal pain and altered bowel habit. The origin seems to be multifactorial and is still not well defined for the different subtypes. Genetic, epigenetic and sex-related modifications of the functioning of the nervous and immune-endocrine supersystems and regulation of brain-gut physiology and bile acid production and absorption are certainly involved. Acquired predisposition may act in conjunction with infectious, toxic, dietary and life event-related factors to enhance epithelial permeability and elicit mucosal microinflammation, immune activation and dysbiosis. Notably, strong evidence supports the role of bacterial, viral and parasitic infections in triggering IBS, and targeting microbiota seems promising in view of the positive response to microbiota-related therapies in some patients. However, the lack of highly predictive diagnostic biomarkers and the complexity and heterogeneity of IBS patients make management difficult and unsatisfactory in many cases, reducing patient health-related quality of life and increasing the sanitary burden. This article reviews specific alterations and interventions targeting the gut microbiota in IBS, including prebiotics, probiotics, synbiotics, non-absorbable antibiotics, diets, fecal transplantation and other potential future approaches useful for the diagnosis, prevention and treatment of IBS.

Gut Microbiota-Based Therapies for Irritable Bowel Syndrome

Irritable bowel syndrome (IBS) is a common, heterogeneous disorder characterized by abdominal pain associated with changes in bowel habits. The pathogenesis of IBS is multifactorial and may relate to alterations in the gut microbiota, changes in visceral sensation and motility, and genetic and environmental factors. Administration of systemic antibiotics may increase the risk of IBS by altering gastrointestinal homeostasis. Therapeutic interventions for IBS with diarrhea that are thought to target alterations in the gut microbiota include the nonsystemic antibiotic rifaximin, the medical food serum-derived bovine immunoglobulin, prebiotics, probiotics, and dietary modification. SYN-010 is a modified-release statin formulation that reduces methane production by Methanobrevibacter smithii and is currently in development for the treatment of patients with constipation-predominant IBS. Use of these interventions in the management of patients with IBS may function to restore a healthy gut microbiota and ameliorate symptoms of IBS.

Development of a Modified-Release Formulation of Lovastatin Targeted to Intestinal Methanogens Implicated in Irritable Bowel Syndrome With Constipation

There is growing evidence that methane production, predominantly by Methanobrevibacter smithii, in the intestines is a cause of constipation, pain, and bloating in irritable bowel syndrome with constipation (IBS-C). M smithii resides primarily in the large intestine but can also colonize the small intestine. In vitro studies found that the prodrug lactone form of lovastatin, found in cholesterol-lowering drugs, inhibited methane production in stool samples from patients with IBS-C. However, the cholesterol-lowering lovastatin β-hydroxyacid was ineffective at inhibiting methane production in this system. A considerable amount of lovastatin is converted to hydroxyacid in the stomach and is absorbed. It was hypothesized that galenic innovations could protect lovastatin from the stomach and allow release in 2 strategic locations, the duodenum and the ileocecal region, to reach M smithii. The desired release profile was achieved by developing an oral dosage form containing lovastatin and coated with 2 different enteric polymers that enabled a pH-dependent "dual pulse" drug release. Combinations of the 2 coated tablets were encapsulated together to deliver the desired amount of lovastatin to the targeted intestinal locations. The capsules have been tested in vitro and in vivo and show promise in treating IBS-C.

A review on comparative mechanistic studies of antimicrobial peptides against archaea

Archaea was until recently considered as a third domain of life in addition to bacteria and eukarya but recent studies support the existence of only two superphyla (bacteria and archaea). The fundamental differences between archaeal, bacterial, and eukaryal cells are probably the main reasons for the comparatively lower susceptibility of archaeal strains to current antimicrobial agents. The possible emerging pathogenicity of archaea and the role of archaeal methanogens in methane emissions, a potent greenhouse gas, has led many researchers to examine the sensitivity patterns of archaea and make attempts to find agents that have significant anti-archaeal activity. Even though antimicrobial peptides (AMPs) are well known with several published reviews concerning their mode of action against bacteria and eukarya, to our knowledge, to date no reviews are available that focus on the action of these peptides against archaea. Herein, we present a review on all the peptides that have been tested against archaea. In addition, in an attempt to shed more light on possible future work that needs to be performed we have included a brief overview of the chemical characteristics, spectrum of activity, and the known mechanism of action of each of these peptides against bacteria and/or fungi. We also discuss the nature of and key physiological differences between Archaea, Bacteria, and Eukarya that are relevant to the development of anti-archaeal peptides. Despite our relatively limited knowledge about archaea, available data suggest that AMPs have an even broader spectrum of activity than currently recognized.

Lovastatin lactone may improve irritable bowel syndrome with constipation (IBS-C) by inhibiting enzymes in the archaeal methanogenesis pathway

Methane produced by the methanoarchaeon Methanobrevibacter smithii ( M. smithii) has been linked to constipation, irritable bowel syndrome with constipation (IBS-C), and obesity. Lovastatin, which demonstrates a cholesterol-lowering effect by the inhibition of HMG-CoA reductase, may also have an anti-methanogenesis effect through direct inhibition of enzymes in the archaeal methanogenesis pathway. We conducted protein-ligand docking experiments to evaluate this possibility. Results are consistent with recent clinical findings.

METHODS

F420-dependent methylenetetrahydromethanopterin dehydrogenase ( mtd), a key methanogenesis enzyme was modeled for two different methanogenic archaea: M. smithii and Methanopyrus kandleri. Once protein models were developed, ligand-binding sites were identified. Multiple ligands and their respective protonation, isomeric and tautomeric representations were docked into each site, including F420-coenzyme (natural ligand), lactone and β-hydroxyacid forms of lovastatin and simvastatin, and other co-complexed ligands found in related crystal structures.

RESULTS

1) Generally, for each modeled site the lactone form of the statins had more favorable site interactions compared to F420; 2) The statin lactone forms generally had the most favorable docking scores, even relative to the native template PDB ligands; and 3) The statin β-hydroxyacid forms had less favorable docking scores, typically scoring in the middle with some of the F420 tautomeric forms. Consistent with these computational results were those from a recent phase II clinical trial ( NCT02495623) with a proprietary, modified-release lovastatin-lactone (SYN-010) in patients with IBS-C, which showed a reduction in symptoms and breath methane levels, compared to placebo.

CONCLUSION

The lactone form of lovastatin exhibits preferential binding over the native-F420 coenzyme ligand in silico and thus could inhibit the activity of the key M. smithii methanogenesis enzyme mtd in vivo. Statin lactones may thus exert a methane-reducing effect that is distinct from cholesterol lowering activity, which requires HMGR inhibition by statin β-hydroxyacid forms.

Lovastatin lactone may improve irritable bowel syndrome with constipation (IBS-C) by inhibiting enzymes in the archaeal methanogenesis pathway

Methane produced by the methanoarchaeon Methanobrevibacter smithii ( M. smithii) has been linked to constipation, irritable bowel syndrome with constipation (IBS-C), and obesity. Lovastatin, which demonstrates a cholesterol-lowering effect by the inhibition of HMG-CoA reductase, may also have an anti-methanogenesis effect through direct inhibition of enzymes in the archaeal methanogenesis pathway. We conducted protein-ligand docking experiments to evaluate this possibility. Results are consistent with recent clinical findings.

METHODS

F420-dependent methylenetetrahydromethanopterin dehydrogenase ( mtd), a key methanogenesis enzyme was modeled for two different methanogenic archaea: M. smithii and Methanopyrus kandleri. Once protein models were developed, ligand-binding sites were identified. Multiple ligands and their respective protonation, isomeric and tautomeric representations were docked into each site, including F420-coenzyme (natural ligand), lactone and β-hydroxyacid forms of lovastatin and simvastatin, and other co-complexed ligands found in related crystal structures.

RESULTS

1) Generally, for each modeled site the lactone form of the statins had more favorable site interactions compared to F420; 2) The statin lactone forms generally had the most favorable docking scores, even relative to the native template PDB ligands; and 3) The statin β-hydroxyacid forms had less favorable docking scores, typically scoring in the middle with some of the F420 tautomeric forms. Consistent with these computational results were those from a recent phase II clinical trial ( NCT02495623) with a proprietary, modified-release lovastatin-lactone (SYN-010) in patients with IBS-C, which showed a reduction in symptoms and breath methane levels, compared to placebo.

CONCLUSION

The lactone form of lovastatin exhibits preferential binding over the native-F420 coenzyme ligand in silico and thus could inhibit the activity of the key M. smithii methanogenesis enzyme mtd in vivo. Statin lactones may thus exert a methane-reducing effect that is distinct from cholesterol lowering activity, which requires HMGR inhibition by statin β-hydroxyacid forms.

How to Test and Treat Small Intestinal Bacterial Overgrowth: an Evidence-Based Approach

Small intestinal bacterial overgrowth (SIBO) is characterized by an excessive amount of bacteria in the small intestine and a constellation of symptoms that include bloating, pain, gas, and diarrhea. Although known for many decades, there is a lack of consensus and clarity regarding the natural history and methods for its diagnosis. Several tests have been proposed, including the glucose breath test, lactulose breath test, small intestinal aspiration and culture, and others. However, there is a lack of standardization of these tests and their interpretation. Treatment of SIBO remains empirical; generally, broad spectrum antibiotics are recommended for 2 weeks (amoxicillin, rifaximin, ciprofloxacin, etc.) but evidence for their use is fair. Clearly, there is a strong need to develop a systematic approach for the management of SIBO and to perform multicenter clinical trials for the treatment of SIBO. In this review, we will discuss the current evidence for the diagnosis and treatment of SIBO, which includes (1) elimination/modification of the underlying causes, (2) induction of remission (antibiotics and elemental diet), and (3) maintenance of remission (promotility drugs, dietary modifications, repeat or cyclical antibiotics).