Hydrogen sulphide and total acid-volatile sulphide in faeces, determined with a direct spectrophotometric method

Gut microbiome carbon and sulfur metabolisms support Salmonella during pathogen infection

Salmonella enterica serovar Typhimurium is a pervasive enteric pathogen and an ongoing global threat to public health. Ecological studies in the Salmonella impacted gut remain underrepresented in the literature, discounting the microbiome mediated interactions that may inform Salmonella physiology during colonization and infection. To understand the microbial ecology of Salmonella remodeling of the gut microbiome, here we performed multi-omics approaches on fecal microbial communities from untreated and Salmonella -infected mice. Reconstructed genomes recruited metatranscriptomic and metabolomic data providing a strain-resolved view of the expressed metabolisms of the microbiome during Salmonella infection. This data informed possible Salmonella interactions with members of the gut microbiome that were previously uncharacterized. Salmonella- induced inflammation significantly reduced the diversity of transcriptionally active members in the gut microbiome, yet increased gene expression was detected for 7 members, with Luxibacter and Ligilactobacillus being the most active. Metatranscriptomic insights from Salmonella and other persistent taxa in the inflamed microbiome further expounded the necessity for oxidative tolerance mechanisms to endure the host inflammatory responses to infection. In the inflamed gut lactate was a key metabolite, with microbiota production and consumption reported amongst transcriptionally active members. We also showed that organic sulfur sources could be converted by gut microbiota to yield inorganic sulfur pools that become oxidized in the inflamed gut, resulting in thiosulfate and tetrathionate that supports Salmonella respiration. Advancement of pathobiome understanding beyond inferences from prior amplicon-based approaches can hold promise for infection mitigation, with the active community outlined here offering intriguing organismal and metabolic therapeutic targets.

Fusobacterium nucleatum and its metabolite hydrogen sulfide alter gut microbiota composition and autophagy process and promote colorectal cancer progression

IMPORTANCE

Colorectal cancer (CRC) is the second most common cancer in the world; the main treatment for CRC is immunosuppressive therapy, but this therapy is only effective for a small percentage of CRC patients, so there is an urgent need for a treatment with fewer side effects and higher efficacy. This study demonstrated that Fusobacterium nucleatum with increased abundance in CRC can regulate the autophagy process and disrupt normal intestinal microbiota by producing hydrogen sulfide, factors that may be involved in the development and progression of CRC. This study may provide a reference for future CRC treatment options that are efficient and have fewer side effects.

In vitro interactions between Blautia hydrogenotrophica, Desulfovibrio piger and Methanobrevibacter smithii under hydrogenotrophic conditions

Methanogens, reductive acetogens and sulfate-reducing bacteria play an important role in disposing of hydrogen in gut ecosystems. However, how they interact with each other remains largely unknown. This in vitro study cocultured Blautia hydrogenotrophica (reductive acetogen), Desulfovibrio piger (sulfate reducer) and Methanobrevibacter smithii (methanogen). Results revealed that these three species coexisted and did not compete for hydrogen in the early phase of incubations. Sulfate reduction was not affected by B. hydrogenotrophica and M. smithii. D. piger inhibited the growth of B. hydrogenotrophica and M. smithii after 10 h incubations, and the inhibition on M. smithii was associated with increased sulfide concentration. Remarkably, M. smithii growth lag phase was shortened by coculturing with B. hydrogenotrophica and D. piger. Formate was rapidly used by M. smithii under high acetate concentration. Overall, these findings indicated that the interactions of the hydrogenotrophic microbes are condition-dependent, suggesting their interactions may vary in gut ecosystems.

Role of Hydrogen Sulfide in Inflammatory Bowel Disease

Hydrogen sulfide (H2S), originally known as toxic gas, has now attracted attention as one of the gasotransmitters involved in many reactions in the human body. H2S has been assumed to play a role in the pathogenesis of many chronic diseases, of which the exact pathogenesis remains unknown. One of them is inflammatory bowel disease (IBD), a chronic intestinal disease subclassified as Crohn's disease (CD) and ulcerative colitis (UC). Any change in the amount of H2S seems to be linked to inflammation in this illness. These changes can be brought about by alterations in the microbiota, in the endogenous metabolism of H2S and in the diet. As both too little and too much H2S drive inflammation, a balanced level is needed for intestinal health. The aim of this review is to summarize the available literature published until June 2023 in order to provide an overview of the current knowledge of the connection between H2S and IBD.

Diversity and distribution of sulfur metabolic genes in the human gut microbiome and their association with colorectal cancer

BACKGROUND

Recent evidence implicates microbial sulfidogenesis as a potential trigger of colorectal cancer (CRC), highlighting the need for comprehensive knowledge of sulfur metabolism within the human gut. Microbial sulfidogenesis produces genotoxic hydrogen sulfide (H₂S) in the human colon using inorganic (sulfate) and organic (taurine/cysteine/methionine) substrates; however, the majority of studies have focused on sulfate reduction using dissimilatory sulfite reductases (Dsr).

RESULTS

Here, we show that genes for microbial sulfur metabolism are more abundant and diverse than previously observed and are statistically associated with CRC. Using ~ 17,000 bacterial genomes from publicly available stool metagenomes, we studied the diversity of sulfur metabolic genes in 667 participants across different health statuses: healthy, adenoma, and carcinoma. Sulfidogenic genes were harbored by 142 bacterial genera and both organic and inorganic sulfidogenic genes were associated with carcinoma. Significantly, the anaerobic sulfite reductase (asr) genes were twice as abundant as dsr, demonstrating that Asr is likely a more important contributor to sulfate reduction in the human gut than Dsr. We identified twelve potential pathways for reductive taurine metabolism and discovered novel genera harboring these pathways. Finally, the prevalence of metabolic genes for organic sulfur indicates that these understudied substrates may be the most abundant source of microbially derived H₂S.

CONCLUSIONS

Our findings significantly expand knowledge of microbial sulfur metabolism in the human gut. We show that genes for microbial sulfur metabolism in the human gut are more prevalent than previously known, irrespective of health status (i.e., in both healthy and diseased states). Our results significantly increase the diversity of pathways and bacteria that are associated with microbial sulfur metabolism in the human gut. Overall, our results have implications for understanding the role of the human gut microbiome and its potential contributions to the pathogenesis of CRC. Video abstract.

Metabolic Influences of Gut Microbiota Dysbiosis on Inflammatory Bowel Disease

Inflammatory bowel diseases (IBD) are chronic medical disorders characterized by recurrent gastrointestinal inflammation. While the etiology of IBD is still unknown, the pathogenesis of the disease results from perturbations in both gut microbiota and the host immune system. Gut microbiota dysbiosis in IBD is characterized by depleted diversity, reduced abundance of short chain fatty acids (SCFAs) producers and enriched proinflammatory microbes such as adherent/invasive E. coli and H₂S producers. This dysbiosis may contribute to the inflammation through affecting either the immune system or a metabolic pathway. The immune responses to gut microbiota in IBD are extensively discussed. In this review, we highlight the main metabolic pathways that regulate the host-microbiota interaction. We also discuss the reported findings indicating that the microbial dysbiosis during IBD has a potential metabolic impact on colonocytes and this may underlie the disease progression. Moreover, we present the host metabolic defectiveness that adds to the impact of symbiont dysbiosis on the disease progression. This will raise the possibility that gut microbiota dysbiosis associated with IBD results in functional perturbations of host-microbiota interactions, and consequently modulates the disease development. Finally, we shed light on the possible therapeutic approaches of IBD through targeting gut microbiome.

Diet posttranslationally modifies the mouse gut microbial proteome to modulate renal function

Associations between chronic kidney disease (CKD) and the gut microbiota have been postulated, yet questions remain about the underlying mechanisms. In humans, dietary protein increases gut bacterial production of hydrogen sulfide (H2S), indole, and indoxyl sulfate. The latter are uremic toxins, and H2S has diverse physiological functions, some of which are mediated by posttranslational modification. In a mouse model of CKD, we found that a high sulfur amino acid-containing diet resulted in posttranslationally modified microbial tryptophanase activity. This reduced uremic toxin-producing activity and ameliorated progression to CKD in the mice. Thus, diet can tune microbiota function to support healthy host physiology through posttranslational modification without altering microbial community composition.

Gut microbiota and neuroinflammation in pathogenesis of hypertension: A potential role for hydrogen sulfide

Inflammation and gut dysbiosis are hallmarks of hypertension (HTN). Hydrogen sulfide (H2S) is an important freely diffusing molecule that modulates the function of neural, cardiovascular and immune systems, and circulating levels of H2S are reduced in animals and humans with HTN. While most research to date has focused on H₂S produced endogenously by the host, H2S is also produced by the gut bacteria and may affect the host homeostasis. Here, we review an association between neuroinflammation and gut dysbiosis in HTN, with special emphasis on a potential role of H2S in this interplay.

TLR2 and TLR4 interact with sulfide system in the modulation of mouse colonic motility

BACKGROUND

H₂ S is a neuromodulator that may inhibit intestinal motility. H₂ S production in colon is yielded by cystathionine β-synthase (CBS) and cystathionine γ-lyase (CSE) enzymes and sulfate-reducing bacteria (SRB). Toll-like receptors (TLRs) recognize intestinal microbiota. The aim of this work was to evaluate the influence of TLR2 and TLR4 on the endogenous and SRB-mediated synthesis of H₂ S and its consequences on the colonic motility of mouse.

METHODS

Muscle contractility studies were performed in colon from WT, Tlr2^-/- , and Tlr4^-/- mice. The mRNA levels of TLR2, TLR4, CBS, CSE, and SRB were measured by real-time PCR. Free sulfide levels in colon and feces were determined by colorimetric assays.

RESULTS

NaHS and GYY4137, donors of H₂ S, reduced the contractility of colon. Aminooxyacetic acid (AOAA), inhibitor of CBS, and D-L propargylglycine (PAG), inhibitor of CSE, increased the contractility of colon. In vivo treatment with NaHS or GYY4137 inhibited the spontaneous contractions and upregulated TLR2 expression. The in vivo activation of TLR4 with lipopolysaccharide increased the contractile response to PAG, mRNA levels of CSE, and the free sulfide levels of H₂ S in colon. In Tlr2^-/- and Tlr4^-/-  mice, the contractions induced by AOAA and PAG and mRNA levels of CBS and CSE were lower with respect to WT mice. Deficiency of TLR2 or TLR4 provokes alterations in free sulfide levels and SRB of colon.

CONCLUSIONS AND INFERENCES

Our study demonstrates interaction between TLR2 and TLR4 and the sulfide system in the regulation of colonic motility and contributes to the pathophysiology knowledge of intestinal motility disorders.

Dietary Factors in Sulfur Metabolism and Pathogenesis of Ulcerative Colitis

The biogeography of inflammation in ulcerative colitis (UC) suggests a proximal to distal concentration gradient of a toxin. Hydrogen sulfide (H₂S) has long been considered one such toxin candidate, and dietary sulfur along with the abundance of sulfate reducing bacteria (SRB) were considered the primary determinants of H₂S production and clinical course of UC. The metabolic milieu in the lumen of the colon, however, is the result of a multitude of factors beyond dietary sulfur intake and SRB abundance. Here we present an updated formulation of the H₂S toxin hypothesis for UC pathogenesis, which strives to incorporate the interdependency of diet composition and the metabolic activity of the entire colon microbial community. Specifically, we suggest that the increasing severity of inflammation along the proximal-to-distal axis in UC is due to the dilution of beneficial factors, concentration of toxic factors, and changing detoxification capacity of the host, all of which are intimately linked to the nutrient flow from the diet.

Modulation of colonic hydrogen sulfide production by diet and mesalazine utilizing a novel gas-profiling technology

Excessive hydrogen sulfide (H₂S) production from gut microbial metabolism may have clinically important relevance in the pathogenesis of gut disorders, including ulcerative colitis. However, little is known regarding factors that alter its production. Using a newly-designed in vitro gas-profiling technology, the study aimed to verify real-time H₂S measurement reproducibility and thereafter, assess its production following exposure to dietary factors and 5-aminosalicylate acid (5-ASA). Measurements of H₂S, carbon dioxide, hydrogen and methane measurements were compared between gas-profiling systems. Homogenized slurries were prepared from freshly-passed healthy human feces. Fifty ml slurries were aliquoted into separate fermentation chambers and substrates added including 1 g highly fermentable fructo-oligosaccharides (FOS) or resistant starch Hi-Maize (RS), or minimally fermentable psyllium or sterculia, 1 g cysteine, 0.9 g sodium sulfate or 1.2 mL of 1 M 5-ASA alone or in combinations. H₂S release was sampled every 5 mins over 4-h and expressed relative to unspiked controls. RS suppressed H₂S production by a mean 89.0 (SEM 4.8)% and FOS by 82.2 (6.2)% compared to <35 (17)% by psyllium and sterculia (p<0.001, two-way ANOVA). Cysteine stimulated H₂S production by 1557 (532)%. The addition of FOS to slurries containing cysteine significantly suppressed H₂S by 90 (2)% over the addition of 5-ASA (0.3 (2)%, p<0.001). Sulfate and 5-ASA had minimal overall effects. In conclusion, the H₂S-profiling technology is a reproducible tool. Production of H₂S is greatly enhanced by sulfur-amino acids but not inorganic sulfate, and is effectively suppressed by readily fermentable fibers. These findings inform potential designs of dietary therapies to reduce H₂S production in vivo.

Hydrogen Sulfide and Sulfate Prebiotic Stimulates the Secretion of GLP-1 and Improves Glycemia in Male Mice

Recently, the gastrointestinal microbiome, and its metabolites, has emerged as a potential regulator of host metabolism. However, to date little is known on the precise mechanisms of how this regulation occurs. Hydrogen sulfide (H2S) is abundantly produced in the colon by sulfate-reducing bacteria (SRB). H2S is a bioactive gas that plays regulatory roles in many systems, including metabolic hormone regulation. This gas metabolite is produced in close proximity to the glucagonlike peptide-1 (GLP-1)-secreting cells in the gut epithelium. GLP-1 is a peptide hormone that plays pivotal roles in both glucose homeostasis and appetite regulation. We hypothesized that H2S can directly regulate GLP-1 secretion. We demonstrated that H2S donors (NaHS and GYY4137) directly stimulate GLP-1 secretion in murine L-cells (GLUTag) and that this occurs through p38 mitogen-activated protein kinase without affecting cell viability. We then increased SRB in mice by supplementing the diet with a prebiotic chondroitin sulfate for 4 weeks. Mice treated with chondroitin sulfate had elevated Desulfovibrio piger levels in the feces and increased colonic and fecal H2S concentration. These animals also had enhanced GLP-1 and insulin secretion, improved oral glucose tolerance, and reduced food consumption. These results indicate that H2S plays a stimulatory role in GLP-1 secretion and that sulfate prebiotics can enhance GLP-1 release and its downstream metabolic actions.

Decreased mucosal sulfide detoxification is related to an impaired butyrate oxidation in ulcerative colitis

BACKGROUND

Defective detoxification of sulfides leads to damage to the mucosa and may play a role in the etiology of ulcerative colitis (UC). The colonic mucosal thiosulfate sulfurtransferase (TST) enzyme removes H(2) S by conversion to the less toxic thiocyanate. In this study we measured colonic mucosal TST enzyme activity and gene expression in UC and controls. In addition, the influence of sulfides on butyrate oxidation was evaluated.

METHODS

Colonic mucosal biopsies were collected from 92 UC patients and 24 controls. TST activity was measured spectrophotometrically. To assess gene expression, total RNA from biopsies was used for quantitative reverse-transcription polymerase chain reaction (RT-PCR). In 20 UC patients, gene expression was reassessed after their first treatment with infliximab. To evaluate the effect of sulfides on butyrate oxidation, biopsies were incubated with 1.5 mM NaHS.

RESULTS

TST enzyme activity and gene expression were significantly decreased in UC patients vs. controls (P < 0.001). UC patients, classified into disease activity subgroups, showed a significantly decreased TST activity and gene expression in the subgroups as compared to healthy subjects (P < 0.05 for all). In 20 patients, gene expression was reassessed after their first infliximab therapy. In responders to infliximab, a significant increase in TST gene expression was observed. However, TST mRNA levels did not return to control values after therapy in the responders. In controls, but not in UC, sulfide significantly decreased butyrate oxidation.

CONCLUSIONS

We found an impaired detoxification mechanism of sulfide at TST protein and RNA level in UC. Inflammation was clearly associated with the observed TST deficiency.

Microbial pathways in colonic sulfur metabolism and links with health and disease

Sulfur is both crucial to life and a potential threat to health. While colonic sulfur metabolism mediated by eukaryotic cells is relatively well studied, much less is known about sulfur metabolism within gastrointestinal microbes. Sulfated compounds in the colon are either of inorganic (e.g., sulfates, sulfites) or organic (e.g., dietary amino acids and host mucins) origin. The most extensively studied of the microbes involved in colonic sulfur metabolism are the sulfate-reducing bacteria (SRB), which are common colonic inhabitants. Many other microbial pathways are likely to shape colonic sulfur metabolism as well as the composition and availability of sulfated compounds, and these interactions need to be examined in more detail. Hydrogen sulfide is the sulfur derivative that has attracted the most attention in the context of colonic health, and the extent to which it is detrimental or beneficial remains in debate. Several lines of evidence point to SRB or exogenous hydrogen sulfide as potential players in the etiology of intestinal disorders, inflammatory bowel diseases (IBDs) and colorectal cancer in particular. Generation of hydrogen sulfide via pathways other than dissimilatory sulfate reduction may be as, or more, important than those involving the SRB. We suggest here that a novel axis of research is to assess the effects of hydrogen sulfide in shaping colonic microbiome structure. Clearly, in-depth characterization of the microbial pathways involved in colonic sulfur metabolism is necessary for a better understanding of its contribution to colonic disorders and development of therapeutic strategies.

Mechanisms of microbial hydrogen disposal in the human colon and implications for health and disease

In the human gastrointestinal tract, dietary components, including fiber, that reach the colon are fermented principally to short-chain fatty acids, hydrogen, and carbon dioxide. Microbial disposal of the hydrogen generated during anaerobic fermentation in the human colon is critical to optimal functioning of this ecosystem. However, our understanding of microbial hydrogenotrophy is fragmented and, at least as it occurs in the colon, is mostly theoretical in nature. Thorough investigation and integration of knowledge on the diversity of hydrogenotrophic microbes, their metabolic variation and activities as a functional group, as well as the nature of their interactions with fermentative bacteria, are necessary to understand hydrogen metabolism in the human colon. Here, we review the limited data available on the three major groups of H(2)-consuming microorganisms found in the human colon [methanogens, sulfate-reducing bacteria (SRB), and acetogens] as well as evidence that end products of their metabolism have an important impact on colonic health.

Emerging role of hydrogen sulfide in colonic physiology and pathophysiology

Hydrogen sulfide (H₂S) is a toxic gas that is now recognized as an important mediator of many physiological processes. In the colon, H₂S is produced both endogenously and by naturally occurring sulfate-reducing bacteria (SRB). The full arrays of its effects in the gastrointestinal tract are still being elucidated, but they range from motility to carcinogenesis. We examined the evidence relating to H₂S as a modulator of colonic function and disease. H₂S is implicated in modulation of colonic compliance through its action on smooth muscle. There is also evidence linking H₂S to colonic nociception, inflammatory bowel disease (IBD), and colorectal cancer. The exact mechanisms and pathways by which H₂S exerts its multitude of effects are not yet fully understood, but its involvement in physiological and pathophysiological conditions of the colon is becoming evident. Elucidating the intricate effects of H₂S in the colon and understanding the exact nature of its interactions with the colon makes pharmacological modulation of H₂S production and metabolism potential targets for treatment of a multitude of colonic conditions in the future.

Luminal sulfide and large intestine mucosa: friend or foe?

Hydrogen sulfide (H(2)S) is present in the lumen of the human large intestine at millimolar concentrations. However, the concentration of free (unbound) sulfide is in the micromolar range due to a large capacity of fecal components to bind the sulfide. H(2)S can be produced by the intestinal microbiota from alimentary and endogenous sulfur-containing compounds including amino acids. At excessive concentration, H(2)S is known to severely inhibit cytochrome c oxidase, the terminal oxidase of the mitochondrial electron transport chain, and thus mitochondrial oxygen (O(2)) consumption. However, the concept that sulfide is simply a metabolic troublemaker toward colonic epithelial cells has been challenged by the discovery that micromolar concentration of H(2)S is able to increase the cell respiration and to energize mitochondria allowing these cells to detoxify and to recover energy from luminal sulfide. The main product of H(2)S metabolism by the colonic mucosa is thiosulfate. The enzymatic activities involved in sulfide oxidation by the colonic epithelial cells appear to be sulfide quinone oxidoreductase considered as the first and rate-limiting step followed presumably by the action of sulfur dioxygenase and rhodanese. From clinical studies with human volunteers and experimental works with rodents, it appears that H(2)S can exert mostly pro- but also anti-inflammatory effects on the colonic mucosa. From the available data, it is tempting to propose that imbalance between the luminal concentration of free sulfide and the capacity of colonic epithelial cells to metabolize this compound will result in an impairment of the colonic epithelial cell O(2) consumption with consequences on the process of mucosal inflammation. In addition, endogenously produced sulfide is emerging as a prosecretory neuromodulator and as a relaxant agent toward the intestinal contractibility. Lastly, sulfide has been recently described as an agent involved in nociception in the large intestine although, depending on the experimental design, both pro- and anti-nociceptive effects have been reported.

Effect of hydrogen sulfide on cyclic AMP production in isolated bovine and porcine neural retinae

Hydrogen sulfide (H(2)S) has been reported to exert pharmacological effects on neural and non-neural tissues from several mammalian species. In the present study, we examined the role of the intracellular messenger, cyclic AMP in retinal response to H(2)S donors, sodium hydrosulfide (NaHS) and sodium sulfide (Na(2)S) in cows and pigs. Isolated bovine and porcine neural retinae were incubated in oxygenated Krebs buffer solution prior to exposure to varying concentrations of NaHS, Na(2)S or the diterpene activator of adenylate cyclase, forskolin. After incubation at different time intervals, tissue homogenates were prepared for cyclic AMP assay using a well established methodology. In isolated bovine and porcine retinae, the combination of both phosphodiesterase inhibitor, IBMX (2 mM) and forskolin (10 microM) produced a synergistic increase (P < 0.001) in cyclic AMP concentrations over basal levels. NaHS (10 nM-100 microM) produced a time-dependent increase in cyclic AMP concentrations over basal levels which reached a maximum at 20 min in both bovine and porcine retinae. At this time point, both NaHS and Na(2)S (10 nM-100 microM) caused a significant (P < 0.05) dose-dependent increase in cyclic AMP levels in bovine and porcine retinae. For instance, NaHS (100 nM) elicited a four-fold and three-fold increase in cyclic AMP concentrations in bovine and porcine retinae respectively whilst higher concentrations of Na(2)S (100 microM) produced a much lesser effect in both species. In bovine and porcine retinae, the effects caused by forskolin (10 microM) on cyclic AMP production were not potentiated by addition of low or high concentrations of both NaHS and Na(2)S. We conclude that H(2)S donors can increase cyclic AMP production in isolated neural retinae from cows and pigs. Bovine retina appears to be more sensitive to the stimulatory effect of H(2)S donors on cyclic nucleotide production than its porcine counterpart indicating that species differences exist in the magnitude of this response. Furthermore, effects produced by forskolin on cyclic AMP formation were not additive with those elicited by H(2)S donors suggesting that these agents may share a common mechanism in their action on the adenylyl cyclase pathway.

Development of a screening method to determine the pattern of fermentation metabolites in faecal samples using on-line purge-and-trap gas chromatographic-mass spectrometric analysis. J Chromatogr A. 2009;1216:1476-1483. [PMID: 19167006 DOI: 10.1016/j.chroma.2008.12.095]

An on-line screening method to analyse volatile organic compounds (VOCs) in faecal samples was developed. VOCs were isolated from a standard solution or faecal samples using a purge-and-trap system and identified and quantified by GC-MS. The experimental conditions were optimised and the performance of the system was evaluated. Linear calibration curves were obtained with correlation coefficients of at least 0.992. RSDs within and between days were less than 10%. The method was successfully applied to the analysis of faecal samples, yielding 135 different volatile organic compounds identified in 11 faecal samples. Of those, 22 VOCs were found in all volunteers, whereas 34 VOCs were person-specific.

The effects of bismuth, iron, zinc and nitrate on free sulfide in batch cultures seeded with fecal flora

BACKGROUND

Hydrogen sulfide (H2S) and methanthiol (CH3SH) have been implicated as bacterially derived toxins which may be damaging to the gut mucosa. The addition of nitrate and metals that bind sulfide could potentially reduce the concentrations of these toxic gases. In this study, the effects of iron, zinc, bismuth and nitrate on free H2S concentrations in fecal batch cultures were investigated.

METHODS

Stool samples were collected from six healthy subjects. Ten percent fecal slurries was made up with phosphate buffer. One milliliter of fecal slurry and 1 ml of metal solution were added to 28 ml anaerobic broth in a 30-ml vial giving final metal concentrations of 0.1, 0.5 and 1.0 mmol/l. For a control, the metal iron solution was replaced by 1 ml of water. After 24 h of incubation at 37 degrees C, 1 ml of the supernatant from the broth was distilled by microdistillation and sulfide determined by HPLC using amperometric detection.

RESULTS

A significant reduction in H2S (P<0.05) of 57% was seen with 1.0 mmol/l zinc, but not with 0 and 0.5 mmol/l zinc treatments. Iron at 0.1, 0.5 and 1.0 mmol/l significantly reduced H2S concentrations (P<0.05) by 36%, 44% and 58%, respectively. Bismuth, the most effective metal, reduced H2S concentrations by more than 90% for all treatments. Both magnesium citrate and magnesium acetate did not affect sulfide concentrations, while 41% and 68% reductions were seen from the addition of 0.5 and 1.0 mmol/l magnesium nitrate, respectively (P<0.05).

CONCLUSIONS

Bismuth, iron, zinc and nitrate are effective at reducing free H2S concentrations in batch cultures. Side effects of these metals may limit their use in vivo. Nitrate is considered toxic because of its contribution to the formation of the carcinogenic nitrite and nitrosamine, though results presented here may indicate a beneficial effect in the large intestine.

The smooth muscle relaxant effect of hydrogen sulphide in vitro: evidence for a physiological role to control intestinal contractility

1. Sodium hydrogen sulphide (NaHS), a donor of hydrogen sulphide (H(2)S), produced dose-related relaxation of the rabbit isolated ileum (EC(50), 76.4+/-7.9 microM) and rat vas deferens (EC(50), 64.8+/-5.4 microM) and reduced ACh-mediated contraction of the guinea-pig isolated ileum. 2. NaHS also reduced the response of the guinea-pig (EC(50), 80.0+/-5.7 microM) and rat (EC(50), 108.2+/-11.2 microM) ileum preparations to electrical stimulation of the intramural nerves. In guinea-pig ileum this effect was spontaneously reversible and mimicked by sodium nitroprusside (SNP, EC(50), 2.1 microM). Combination of NaHS (20 microM) with SNP (0.5 microM) produced a greater than additive inhibition of the twitch response of the ileum to electrical stimulation. 3. The inhibitory effect of NaHS on the field-stimulated guinea-pig ileum was unaffected by pretreatment with L-NAME (100 microM), indomethacin (10 microM), naloxone (1 microM) or glibenclamide (100 microM). Furthermore, NaHS (200 microM) did not affect the contractile response of the ileum to KCl (10 to 60 mM). 4. Propargylglycine (PAG, 1 mM) and beta-cyanoalanine (BCA, 1 mM) (inhibitors of cystathionine-gamma-lyase) but not aminooxyacetic acid (AOAA, 1 mM) (inhibitor of cystathionine-beta-synthetase) caused a slowly developing increase in the contraction of the guinea-pig ileum to field stimulation. This effect was reversed by cysteine (1 mM). 5. These results show that NaHS relaxes gastrointestinal and urogenital smooth muscle and suggest that H(2)S is responsible for these effects. The possibility that endogenous H(2)S, formed as a consequence of activation of intramural nerves, plays a part in controlling the contractility of the guinea-pig ileum is discussed.

Assay methods and biological roles of labile sulfur in animal tissues

Sulfur is a chemically and biologically active element. Sulfur compounds in animal tissues can be present in two forms, namely stable and labile forms. Compounds such as methionine, cysteine, taurine and sulfuric acid are stable sulfur compounds. On the other hand, acid-labile sulfur and sulfane sulfur compounds are labile sulfur compounds. The sulfur atoms of labile sulfur compounds are liberated as inorganic sulfide by acid treatment or reduction. Therefore, the determination of sulfide is the basis for the determination of labile sulfur. Determination of sulfide has been performed by various methods, including spectrophotometry after derivatization, ion chromatography, high-performance liquid chromatography after derivatization, gas chromatography, and potentiometry with a sulfide ion-specific electrode. These methods were originally developed for the determination of sulfide in air and water samples and were then applied to biological samples. The metabolic origin of labile sulfur in animal tissues is cysteine. The pathways of cysteine metabolism leading to the formation of sulfane sulfur are discussed. Finally, reports on the physiological roles and pathological considerations of labile sulfur are reviewed.

The smooth muscle relaxant effect of hydrogen sulphide in vitro: evidence for a physiological role to control intestinal contractility

1. Sodium hydrogen sulphide (NaHS), a donor of hydrogen sulphide (H(2)S), produced dose-related relaxation of the rabbit isolated ileum (EC(50), 76.4+/-7.9 microM) and rat vas deferens (EC(50), 64.8+/-5.4 microM) and reduced ACh-mediated contraction of the guinea-pig isolated ileum. 2. NaHS also reduced the response of the guinea-pig (EC(50), 80.0+/-5.7 microM) and rat (EC(50), 108.2+/-11.2 microM) ileum preparations to electrical stimulation of the intramural nerves. In guinea-pig ileum this effect was spontaneously reversible and mimicked by sodium nitroprusside (SNP, EC(50), 2.1 microM). Combination of NaHS (20 microM) with SNP (0.5 microM) produced a greater than additive inhibition of the twitch response of the ileum to electrical stimulation. 3. The inhibitory effect of NaHS on the field-stimulated guinea-pig ileum was unaffected by pretreatment with L-NAME (100 microM), indomethacin (10 microM), naloxone (1 microM) or glibenclamide (100 microM). Furthermore, NaHS (200 microM) did not affect the contractile response of the ileum to KCl (10 to 60 mM). 4. Propargylglycine (PAG, 1 mM) and beta-cyanoalanine (BCA, 1 mM) (inhibitors of cystathionine-gamma-lyase) but not aminooxyacetic acid (AOAA, 1 mM) (inhibitor of cystathionine-beta-synthetase) caused a slowly developing increase in the contraction of the guinea-pig ileum to field stimulation. This effect was reversed by cysteine (1 mM). 5. These results show that NaHS relaxes gastrointestinal and urogenital smooth muscle and suggest that H(2)S is responsible for these effects. The possibility that endogenous H(2)S, formed as a consequence of activation of intramural nerves, plays a part in controlling the contractility of the guinea-pig ileum is discussed.

Physiology of sulfide in the rat colon: use of bismuth to assess colonic sulfide production

Colonic bacteria produce hydrogen sulfide, a toxic compound postulated to play a pathogenetic role in ulcerative colitis. Colonic sulfide exposure has previously been assessed via measurements of fecal sulfide concentration. However, we found that <1% of fecal sulfide of rats was free, the remainder being bound in soluble and insoluble complexes. Thus fecal sulfide concentrations may reflect sulfide binding capacity rather than the toxic potential of feces. We utilized bismuth subnitrate to quantitate intracolonic sulfide release based on observations that bismuth 1) avidly binds sulfide; 2) quantitatively releases bound sulfide when acidified; and 3) does not influence fecal sulfide production by fecal homogenates. Rats ingesting bismuth subnitrate excreted 350 +/- 18 micromol/day of fecal sulfide compared with 9 +/- 1 micromol/day in control rats. Thus the colon normally absorbs approximately 340 micromol of sulfide daily, a quantity that would produce local and systemic injury if not efficiently detoxified by the colonic mucosa. Studies utilizing bismuth should help to clarify the factors influencing sulfide production in the human colon.

Copper-induced inhibition of growth of Desulfovibrio desulfuricans G20: assessment of its toxicity and correlation with those of zinc and lead

The toxicity of copper [Cu(II)] to sulfate-reducing bacteria (SRB) was studied by using Desulfovibrio desulfuricans G20 in a medium (MTM) developed specifically to test metal toxicity to SRB (R. K. Sani, G. Geesey, and B. M. Peyton, Adv. Environ. Res. 5:269-276, 2001). The effects of Cu(II) toxicity were observed in terms of inhibition in total cell protein, longer lag times, lower specific growth rates, and in some cases no measurable growth. At only 6 microM, Cu(II) reduced the maximum specific growth rate by 25% and the final cell protein concentration by 18% compared to the copper-free control. Inhibition by Cu(II) of cell yield and maximum specific growth rate increased with increasing concentrations. The Cu(II) concentration causing 50% inhibition in final cell protein was evaluated to be 16 microM. A Cu(II) concentration of 13.3 microM showed 50% inhibition in maximum specific growth rate. These results clearly show significant Cu(II) toxicity to SRB at concentrations that are 100 times lower than previously reported. No measurable growth was observed at 30 microM Cu(II) even after a prolonged incubation of 384 h. In contrast, Zn(II) and Pb(II), at 16 and 5 microM, increased lag times by 48 and 72 h, respectively, but yielded final cell protein concentrations equivalent to those of the zinc- and lead-free controls. Live/dead staining, based on membrane integrity, indicated that while Cu(II), Zn(II), and Pb(II) inhibited growth, these metals did not cause a loss of D. desulfuricans membrane integrity. The results show that D. desulfuricans in the presence of Cu(II) follows a growth pattern clearly different from the pattern followed in the presence of Zn(II) or Pb(II). It is therefore likely that Cu(II) toxicity proceeds by a mechanism different from that of Zn(II) or Pb(II) toxicity.

Measurement of fecal sulfide using gas chromatography and a sulfur chemiluminescence detector

We describe a simple technique to measure sulfide in fecal homogenates (or any other liquid milieu), which involves acidification followed by the G.C. measurement of H2S in a gas space equilibrated with a small quantity of homogenate. An internal standard of Zn35S added to the homogenate permits correction for incomplete recovery of H2S in the gas space. The use of a sulfur chemiluminescence detector, which specifically and sensitively responds to sulfur-containing compounds, greatly facilitates this measurement.

Contribution of dietary protein to sulfide production in the large intestine: an in vitro and a controlled feeding study in humans

BACKGROUND

Hydrogen sulfide is a luminally acting, bacterially derived cell poison that has been implicated in ulcerative colitis. Sulfide generation in the colon is probably driven by dietary components such as sulfur-containing amino acids (SAAs) and inorganic sulfur (eg, sulfite).

OBJECTIVE

We assessed the contribution of SAAs from meat to sulfide production by intestinal bacteria with use of both a model culture system in vitro and an in vivo human feeding study.

DESIGN

Five healthy men were housed in a metabolic suite and fed a sequence of 5 diets for 10 d each. Meat intake ranged from 0 g/d with a vegetarian diet to 600 g/d with a high-meat diet. Fecal sulfide and urinary sulfate were measured in samples collected on days 9 and 10 of each diet period. Additionally, 5 or 10 g bovine serum albumin or casein/L was added to batch cultures inoculated with feces from 4 healthy volunteers. Concentrations of sulfide, ammonia, and Lowry-reactive substances were measured over 48 h.

RESULTS

Mean (+/-SEM) fecal sulfide concentrations ranged from 0.22 +/- 0.02 mmol/kg with the 0-g/d diet to 3.38 +/- 0.31 mmol/kg with the 600-g/d diet and were significantly related to meat intake (P: < 0.001). Sulfide formation in fecal batch cultures supplemented with both bovine serum albumin and casein correlated with protein digestion, as measured by the disappearance of Lowry-reactive substances and the appearance of ammonia.

CONCLUSION

Dietary protein from meat is an important substrate for sulfide generation by bacteria in the human large intestine.

Thiolmethyltransferase activity in the human colonic mucosa: implications for ulcerative colitis

Ulcerative colitis is associated with a selective reduction of n-butyrate oxidation by the colonic epithelial cells although the reason for this has been unclear. Colonic epithelial cell n-butyrate oxidation can be inhibited in vitro by incubation with sulphide but the role of mucosal detoxification of sulphide in the metabolic welfare of the colonic mucosa has not been examined. This study aimed to assess the role mucosal detoxification of sulphide by thiolmethyltransferase (TMT)-mediated methylation may play in protecting the healthy colonic mucosa from the adverse effects of luminal sulphide. Colonic epithelial cell suspensions from healthy human proximal (n = 9) and distal colon (n = 10) were incubated in the presence of 14C-labelled n-butyrate (5 mmol/L) alone, butyrate plus sodium hydrogen sulphide (NaHS) (1.5 mmol/L), or butyrate plus NaHS plus S-adenosyl-methionine 1,4 butane disulphonate (SAMe) (5 mmol/L). Study end points were metabolic performance (14CO2 production) and mucosal TMT activity. Incubation with NaHS induced a significant inhibition of 14CO2 production compared with control incubations (P < 0.001) which was similar for proximal and distal colonic cell suspensions. S-adenosyl-methionine 1,4 butane disulphonate reversed this effect completely in proximal but not in distal cell incubations, suggesting a greater susceptibility of the distal colon to the sulphide effect. Although median whole mucosal TMT values did not differ between proximal and distal colonic mucosa, a non-normal distribution of distal TMT values was observed. However, neither the degree of sulphide inhibition of control 14CO2 production nor the degree to which SAMe reversed this inhibition correlated with whole mucosal TMT activity. The study concluded that regional variation exists in TMT activity in the human colon but whilst methylation appears to protect colonic epithelial cells against sulphide-induced inhibition of n-butyrate oxidation, this cannot be directly correlated with mucosal TMT activity.

Hydrogen sulphide produces diminished fatty acid oxidation in the rat colon in vivo: implications for ulcerative colitis

BACKGROUND

Several lines of evidence suggest a possible role for reduced forms of sulphur (including sulphide) in ulcerative colitis. The aims of this study were to assess the metabolic profile of colonic epithelial cells after treatment in vivo with hydrogen sulphide and correlate this with mucosal histological appearances.

METHODS

Adult Sprague-Dawley rats had antegrade Roux-en-Y colostomies fashioned to allow access to the 'in-flow' bowel. Animals were treated with 2 mL sodium hydrosulphide (10, 20, 30 mmol/L) or saline control twice daily via the stoma for four (acute experiments) and 90 (chronic experiments) days. Isolated colonic epithelial cell suspensions prepared from such animals were incubated in the presence of [1-14C]-labelled n-butyrate (5 mmol/L) or [6-14C]glucose (5 mmol/L). Metabolic performance was measured radiometrically (14CO2 production) and enzymatically (ketone body production and lactogenesis). The histological appearances of treated mucosa were scored for acute inflammatory changes.

RESULTS

There was a highly significant reduction in 14CO2 production from both n-butyrate and glucose in all groups compared to the control in both acute and chronic experiments. There was no difference between groups with respect to histological appearance and no evidence of acute inflammation in any specimen.

CONCLUSIONS

Sodium hydrosulphide impairs rat colonic epithelial metabolic performance in vivo, but does not produce mucosal inflammation.

A possible role for bile acid in the control of methanogenesis and the accumulation of hydrogen gas in the human colon

This study investigated a possible role for primary bile acid in the control of methanogenesis in the human colon. Production of hydrogen and methane was measured in anaerobic faecal cultures derived from faeces of six 'non-methanogenic' and three methanogenic healthy humans. Using a sensitive technique for gas measurement, methane was detected in all faecal cultures, including those from 'non-methanogenic' humans. Bile acid inhibited methanogenesis in a dose-response fashion in the in vitro 'non-methanogenic' and methanogenic faecal cultures. Inhibition was significant at bile acid concentrations > 0.05%. Methanogenesis correlated with methanogen (methanogenic bacteria) numbers. If this inhibition occurs in vivo, then it would explain much of the epidemiology of non-methanogenesis in humans. From an analysis of net hydrogen production by the faecal cultures, it is inferred that bile acid inhibits other hydrogen-consuming bacteria in addition to methanogens. These in vitro data suggest a major role for bile acid in the accumulation of hydrogen gas in the colon. Possible links between bile acid induced accumulation of gas and irritable bowel syndrome are discussed.

Prevalence and consistency of low breath H2 excretion following lactulose ingestion. Possible implications for the clinical use of the H2 breath test

The clinical use of the H2 breath test is limited by the finding that a variable fraction of the population fails to excrete appreciable H2 during colonic carbohydrate fermentation. Therefore, we assessed the ability to increase breath H2 excretion in 371 patients (224 female, 147 male) by administering the nonabsorbable sugar lactulose. Following 12g of lactulose, 27% of 94 patients did not increase their breath H2 concentration over 20 ppm and were considered low H2 excretors. Ingestion of 20 g of lactulose in 277 patients yielded a frequency of low H2 excretors of 14%. Six of 10 patients that were low H2 excretors after 12g of lactulose increased their breath H2 levels over 20 ppm when tested with 20g. In 35 patients tested with the same amount of lactulose on two separate occasions, the subject frequently altered his or her H2 producing status over a period of a few weeks. Low H2 excretors had a significantly higher breath CH4 concentration, both fasting (22 +/- 34 ppm) and after lactulose (51 +/- 58 ppm) compared to the remaining patients (5 +/- 13 ppm and 16 +/- 40 ppm, respectively). While the mean age of low excretors (54 +/- 17 years) was significantly higher than the others (44 +/- 17 years), no difference was found for sex prevalence and stool pH. This study demonstrates that respiratory H2 excretion following lactulose ingestion is not consistent and suggests that the application of too restrictive criteria could lead to improper interpretation of the H2 breath test.