Sulphide quinone reductase contributes to hydrogen sulphide metabolism in murine peripheral tissues but not in the CNS.

BACKGROUND AND PURPOSE: Hydrogen sulphide (H(2) S) is gaining acceptance as a gaseous signal molecule. However, mechanisms regarding signal termination are not understood. We used stigmatellin and antimycin A, inhibitors of sulphide quinone reductase (SQR), to test the hypothesis that the catabolism of H(2) S involves SQR. EXPERIMENTAL APPROACH: H(2) S production and consumption were determined in living and intact mouse brain, liver and colonic muscularis externa using gas chromatography and HPLC. Expressions of SQR, ethylmalonic encephalopathy 1 (Ethe1) and thiosulphate transferase (TST; rhodanese) were determined by RT-PCR and immunohistochemistry. KEY RESULTS: In the colonic muscularis externa, H(2) (35) S was catabolized to [(35) S]-thiosulphate and [(35) S]-sulphate, and stigmatellin reduced both the consumption of H(2) (35) S and formation of [(35) S]-thiosulphate. Stigmatellin also enhanced H(2) S release by the colonic muscularis externa. In the brain, catabolism of H(2) (35) S to [(35) S]-thiosulphate and [(35) S]-sulphate, which was stigmatellin-insensitive, partially accounted for H(2) (35) S consumption, while the remainder was captured as unidentified (35) S that was probably bound to proteins. Levels of mRNA encoding SQR were higher in the colonic muscularis externa and the liver than in the brain. CONCLUSIONS AND IMPLICATIONS: These data support the concept that termination of endogenous H(2) S signalling in the colonic muscularis externa occurs via catabolism to thiosulphate and sulphate partially via a mechanism involving SQR. In the brain, it appears that H(2) S signal termination occurs partially through protein sequestration and partially through catabolism not involving SQR. As H(2) S has beneficial effects in animal models of human disease, we suggest that selective inhibition of SQR is an attractive target for pharmaceutical development.

Comparison of volatile sulfur compound concentrations measured with a sulfide detector vs. gas chromatography.

The accuracy of the Halimeter, an inexpensive, simple instrument that measures total breath volatile sulfur compounds (VSCs), has not been adequately tested. We compared Halimeter measurements with those obtained with a specific and sensitive gas chromatographic (GC) technique. The Halimeter gave different, biexponential responses to a constant concentration of different VSCs: The relative response rate and sensitivity were hydrogen sulfide > methyl mercaptan > dimethylsulfide. The transient peak VSC concentration of oral samples was reached long before the sulfide detector fully responded. The GC measurement of initial total VSCs in breath samples was 2.7+/-0.48 times greater than the peak concentration of the Halimeter. However, the plateau phase measurement of the Halimeter was 25% greater than that of GC. While GC and Halimeter measurements positively correlated, appreciable differences were observed. In studies where relatively precise VSC measurements are required, GC is the preferable technique.

Laparoscopic-assisted resection of colorectal malignancies: a systematic review.

OBJECTIVE: To compare the safety and efficacy of laparoscopic-assisted resection of colorectal malignancies with open colectomy. METHODS: Two search strategies were devised to retrieve literature from the Medline, Current Contents, Embase, and Cochrane Library databases until July 1999. Inclusion of papers was determined using a predetermined protocol, independent assessments by two reviewers, and a final consensus decision. English language papers were selected. Acceptable study designs included randomized controlled trials, controlled clinical trials, case series, or case reports. Fifty-two papers met the inclusion criteria. They were tabulated and critically appraised in terms of methodology and design, outcomes, and the possible influence of bias, confounding, and chance. RESULTS: Little high-level evidence was available. Laparoscopic resection of colorectal malignancy was more expensive and time-consuming, but little evidence suggests high rates of port site recurrence. The new procedure's advantages revolve around early recovery from surgery and reduced pain. CONCLUSIONS: The evidence base for laparoscopic-assisted resection of colorectal malignancies is inadequate to determine the procedure's safety and efficacy. Because of inadequate evidence detailing circumferential marginal clearance of tumors and the necessity of determining a precise incidence of cardiac and other major complications, along with wound and port site recurrence, it is recommended that a controlled clinical trial, ideally with random allocation to an intervention and control group, be conducted. Long-term survival rates need to be a primary aim of such a trial.

Spontaneous fluctuations in the concentrations of oral sulfur-containing gases.

Breath hydrogen sulfide (H2S) and methyl-mercaptan (CH3SH) concentrations are used as quantitative indicators of halitosis. However, measurements of these gases in duplicate oral samplings often show poor reproducibility. To determine if this poor reproducibility is an artifact of the collection/analytical procedure or a true biological phenomenon, we used a standardized technique to collect from 20 to 30 oral gas samples at two-minute intervals from 11 healthy subjects. The samples were analyzed for sulfur gases and CO2. Sizable variations in H2S and CH3SH concentrations were not associated with alterations in CO2, indicating that the variations did not reflect variable contamination with atmospheric or pulmonary gas. In addition, fluctuations in H2S and CH3SH were not identical and often were not random. We conclude that minute-to-minute variability in oral sulfur gas concentrations is a true biological phenomenon. This fluctuation complicates experimental studies designed to show that interventions alter halitosis.

Gas production by feces of infants.

BACKGROUND: Intestinal gas is thought to be the cause abdominal discomfort in infants. Little is known about the type and amount of gas produced by the infant's colonic microflora and whether diet influences gas formation. METHODS: Fresh stool specimens were collected from 10 breast-fed infants, 5 infants fed a soy-based formula, and 3 infants fed a milk-based formula at approximately 1, 2, and 3 months of age. Feces were incubated anaerobically for 4 hours at 37 degrees C followed by quantitation of hydrogen (H2), methane (CH4), carbon dioxide (CO2), hydrogen sulfide (H2S), methanethiol (CH3SH), and dimethyl sulfide (CH3SCH3) in the head-space. RESULTS: H2 was produced in greater amounts by breast-fed infants than by infants in either formula group, presumably the consequence of incomplete absorption of breast milk oligosaccharides. CH4 was produced in greater amounts by infants fed soy formula than by infants on other diets. CO2 was produced in similar amounts by infants in all feeding groups. Production of CH3SH was conspicuously low by feces of breast-fed infants and production of H2S was high by soy-formula-fed infants. CH3SCH3 was not detected. Only modest changes with age were observed and there was no relation between gas production and stool consistency, although stools were more likely to be malodorous when concentrations of H2S and/or CH3SH were high. CONCLUSIONS: Gas release by infant feces is strongly influenced by an infant's diet. Of particular interest are differences in production of the highly toxic sulfur gases, H2S and CH3SH, because of the role that these gases may play in certain intestinal disorders of infants.

Oxidation of hydrogen sulfide and methanethiol to thiosulfate by rat tissues: a specialized function of the colonic mucosa.

Colonic bacteria release large quantities of the highly toxic thiols hydrogen sulfide (H(2)S) and methanethiol (CH(3)SH). These gases rapidly permeate the colonic mucosa, and tissue damage would be expected if the mucosa could not detoxify these compounds rapidly. We previously showed that rat cecal mucosa metabolizes these thiols via conversion to thiosulfate. The purpose of the present study in rats was to determine if this conversion of thiols to thiosulfate is (a) a generalized function of many tissues, or (b) a specialized function of the colonic mucosa. The tissues studied were mucosa from the cecum, right colon, mid-colon, ileum, and stomach; liver; muscle; erythrocytes; and plasma. The metabolic rate was determined by incubating homogenates of the various tissues with H(2)(35)S and CH(3)(35)SH and measuring the rate of incorporation of (35)S into thiosulfate and sulfate. The detoxification activity of H(2)S (expressed as nmol/mg per min) that resulted in thiosulfate production was at least eight times greater for cecal and right colonic mucosa than for the non-colonic tissues. Thiosulfate production from CH(3)SH was at least five times more rapid for cecal and right colonic mucosa than for the non-colonic tissues. We conclude that colonic mucosa possesses a specialized detoxification system that allows this tissue to rapidly metabolize H(2)S and CH(3)SH to thiosulfate. Presumably, this highly developed system protects the colon from what otherwise might be injurious concentrations of H(2)S and CH(3)SH. Defects in this detoxification pathway possibly could play a role in the pathogenesis of various forms of colitis.

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.

A comparison of the effect of loperamide in oral or suppository form vs placebo in patients with ileo-anal pouches.

OBJECTIVE: The effect of the anti-diarrhoeal drug, loperamide hydrochloride, on bowel function in patients with an ileo-anal pouch was studied by means of a blinded, three-tailed, case-controlled and randomized crossover trial, using a daily dose of 12 mg in either oral (4 mg t.d.s.) or suppository (6 mg b.d.) form. PATIENTS AND METHODS: Daily stool frequency was recorded in a diary and an objective measure of pouch motor function was obtained at the end of each treatment phase. Ten subjects (seven males, three females) aged 23-50 years (median 38 years) were studied 9-48 months (median 27 months) after ileostomy closure. Eight pouches had been constructed for ulcerative colitis and two for familial adenomatous polyposis (9J, 1W). RESULTS: Mean daily stool frequency during the oral loperamide phase was lower than during both the placebo (P=0.05) and suppository (P < 0.02) phases. Stool frequency did not differ significantly between placebo and suppository phases. There was a strong inverse correlation between mean daily stool frequency and pouch capacity (r=-0.82 after both oral and suppository phases). Large isolated pouch contractions were evident in five of eight subjects studied; suppression was observed in two of the five after oral loperamide and in three of the five after loperamide suppositories. Rhythmic pouch contractions were seen in four subjects and suppression was evident after loperamide suppositories (but not after oral loperamide) in three. A daily oral dose of 12 mg loperamide significantly lowered stool frequency in pouch patients and modified some aspects of pouch contraction. Loperamide suppositories produced more prominent suppression of pouch contractions but did not lower stool frequency. CONCLUSION: This suggests that the beneficial effect of oral loperamide is primarily due to its action on intestine proximal to the pouch itself.

Nutritional supplements used in weight-reduction programs increase intestinal gas in persons who malabsorb lactose.

OBJECTIVE: To determine if ingestion of 2 doses of milk-based dietary supplements produce gaseous symptoms in subjects who malabsorb lactose. DESIGN: Randomized, controlled, crossover trial. SUBJECTS/SETTING: Ten community-based subjects who malabsorb lactose. INTERVENTION: Ingestion of 2 standard servings of milk-based supplements (a powder reconstituted in fat-free milk or a ready-to-drink preparation) or low-lactose control preparations. MAIN OUTCOME MEASURES: Frequency of flatus passage and subjective impression of bloating, flatulence, and abdominal discomfort. STATISTICAL ANALYSIS: Wilcoxon signed-rank test. RESULTS: The high lactose content (27 g) of 2 servings of the powder-based supplement ingested without other food resulted in a marked increase in daily flatus passages from the basal level of 9.7+/-8.2 to 30+/-14 (mean+/-SD), and a significant increase in the subjects' perception of gas. In contrast, the lower lactose content (18.4 g) of 2 servings of a ready-to-drink supplement resulted in a flatus frequency of 17+/-10 (P=.14 vs baseline) and no significant increase in the perception of increased gas. Neither supplement resulted in a significant increase in bloating, abdominal pain, or diarrhea. The lactose content of the liquid supplement was reduced by 80% following overnight incubation with an over-the-counter lactase preparation. APPLICATIONS/CONCLUSIONS: Persons who malabsorb lactose should be aware that sizable increases in rectal gas commonly occur when milk-based powders reconstituted in milk are used as meal replacements. In contrast, gas problems probably will be minor following ingestion of 2 doses of a ready-to-drink, milk-based supplement. The lactose content of these supplements can be markedly reduced by overnight incubation with over-the-counter lactase preparations, and this manipulation should be beneficial for subjects troubled by the increased gas caused by the consumption of lactose-containing supplements.

Morning breath odor: influence of treatments on sulfur gases.

We assessed the effects of several treatments on the concentrations of oral sulfur-containing gases, compounds thought to be responsible for morning breath. Upon awakening in the morning, healthy volunteers collected oral gas samples before and for eight hours after the following treatments: no treatment, brushing the teeth with toothpaste, brushing the tongue, rinsing with 5 mL of 3% hydrogen peroxide, breakfast ingestion, or swallowing two BreathAsure capsules. The gas samples were analyzed for sulfur-containing volatiles via gas chromatography. Baseline collections usually contained three sulfur gases: hydrogen sulfide, methanethiol, and dimethylsulfide. The effectiveness of a treatment was determined via comparison of the areas under gas concentrations-time curves with and without treatment. Brushing the teeth or ingestion of BreathAsure had no apparent influence on the sulfur gases. Ingestion of breakfast and tongue brushing resulted in strong trends toward decreased sulfur gases. Hydrogen peroxide significantly reduced the sulfur gas concentrations for eight hours.

Appropriate use and misuse of blood concentration measurements to quantitate first-pass metabolism.

First-pass metabolism commonly is determined from the difference in the area under the blood concentration time curve (AUC) that is observed with oral versus intravenous administration of a compound. It is not fully appreciated that this technique serves as an accurate indicator of first-pass metabolism only when the clearance of the compound under consideration is first order (unsaturated) throughout the range of blood concentrations observed in the study. For example, multiple publications continue to mistakenly use AUC measurements to assess the first-pass metabolism of ethanol, a compound cleared primarily via zero-order kinetics. This report briefly reviews the physiologic basis of measurements of first-pass metabolism, demonstrates the errors that result from application of this technique when clearance is not first order, and, using ethanol as an example, describes a technique that can be used to measure first-pass metabolism when clearance deviates from first order.

An understanding of excessive intestinal gas.

Complaints of "excessive gas" from patients are very common but are difficult, if not impossible, for the physician to document. This review addresses the pathophysiology and management of such complaints, looking at the sources and routes of elimination, excessive eructation, bloating, and distention. In addition, common flatulence problems are summarized, including excessive flatus volume and noxious flatus.

Binding of hydrogen sulfide by bismuth does not prevent dextran sulfate-induced colitis in rats.

Several lines of evidence suggest that ulcerative colitis could be caused by excessive bacterial production of H2S in the colon. A rodent model of colitis involves the feeding of nonabsorbable, carbohydrate-bound sulfate in the form of dextran sulfate or carrageenan. The observation that metronidazole blocks the development of this colitis suggested that the injurious agent could be a sulfur-containing compound (such as H2S) that is released during the bacterial metabolism of the nonabsorbed sulfate. We tested this possibility by feeding rats dextran sulfate, with or without bismuth subsalicylate, a compound that avidly binds H2S. Bismuth subsalicylate reduced the fecal release of H2S in dextran sulfate-treated rats to values well below that of controls. Nevertheless, all the animals developed colitis. We conclude that excessive H2S production does not play a role in the dextran sulfate model of colitis.

Site of bismuth absorption from bismuth subsalicylate: implications for treatment of colonic conditions.

Poorly absorbed bismuth preparations may benefit a variety of chronic colonic conditions including ulcerative colitis. Bismuth-induced neurotoxicity is a potential complication of the chronic use of these preparations, and a less-absorbable form of bismuth is needed. If bismuth absorption occurs primarily in the upper gut, a delayed-release bismuth preparation could reduce absorption. We studied the site of bismuth absorption from bismuth subsalicylate (BSS) in rats. For 15 days, BSS (50 mg/day) was ingested or infused directly into the cecum via a chronically implanted cannula. Oral BSS resulted in serum and urine bismuth levels many times higher (3.5 +/- 0.3 microg/liter and 1,570 +/- 286 microg/g creatinine, respectively) than with cecal administration (undetectable (<1.5 microg/liter) and 75 +/- 25 microg/g creatinine). Thus, bismuth absorption from BSS occurred almost entirely in the upper gut. These findings provide a rationale for a similar study of delayed-release bismuth preparations in humans.

Detoxification of hydrogen sulfide and methanethiol in the cecal mucosa.

Colonic bacteria liberate large quantities of the highly toxic gases hydrogen sulfide (H(2)S) and methanethiol (CH(3)SH). The colonic mucosa presumably has an efficient means of detoxifying these compounds, which is thought to occur through methylation of H(2)S to CH(3)SH and CH(3)SH to dimethylsulfide (CH(3)SCH(3)). We investigated this detoxification pathway by incubating rat cecal mucosal homogenates with gas containing H(2)S, CH(3)SH, or CH(3)SCH(3). Neither CH(3)SH nor CH(3)SCH(3) was produced during H(2)S catabolism, whereas catabolism of CH(3)SH liberated H(2)S but not CH(3)SCH(3). Thus, H(2)S and CH(3)SH are not detoxified by methylation to CH(3)SCH(3). Rather, CH(3)SH is demethylated to H(2)S, and H(2)S is converted to nonvolatile metabolites. HPLC analysis of the homogenate showed the metabolite to be primarily thiosulfate. Analysis of cecal venous blood obtained after intracecal instillation of H(2)(35)S revealed that virtually all absorbed H(2)S had been oxidized to thiosulfate. The oxidation rate of H(2)S by colonic mucosa was 10,000 times greater than the reported methylation rate. Conversion to thiosulfate appears to be the mechanism whereby the cecal mucosa protects itself from the injurious effects of H(2)S and CH(3)SH, and defects in this detoxification possibly could play a role in colonic diseases such as ulcerative colitis.

Pancreatic supplements reduce symptomatic response of healthy subjects to a high fat meal.

In a double-blind, crossover study, we determined whether microencapusulated pancreatic enzymes reduce postprandial symptoms experienced by healthy volunteers after ingestion of a high calorie, high fat meal. At 7 AM, 18 subjects ingested 185 g of cookies (1196 calories and 72 g of fat) with three pancrelipase capsules or a placebo. The severity of gastrointestinal symptoms and flatus passages were recorded for 15-17 hr, and end-alveolar samples were obtained hourly for 10 hr. Ingestion of pancreatic supplements was associated with a significant (P = 0.049) reduction in bloating over the entire recording period, and with significant reductions in bloating, gas, and fullness during the dinner to bedtime period. Pancreatic supplements had no significant effect on breath H2 or CH4 concentration. The finding that pancreatic supplements reduce postprandial symptoms in healthy subjects suggests that these supplements also might be beneficial in irritable bowel syndrome.

Failure of activated charcoal to reduce the release of gases produced by the colonic flora.

OBJECTIVE: Activated charcoal is used to treat excessive volume or malodor of intestinal gas. Our previous studies demonstrated that activated charcoal failed to bind appreciable quantities of the volumetrically important gut gases. However, the odor of feces and flatus derives primarily from trace quantities of sulfur-containing gases, primarily H2S and methanethiol, which should avidly bind to activated charcoal. The goal of this study was to determine if ingestion of activated charcoal reduces the fecal release of sulfur gases. METHODS: Five healthy human volunteers ingested 0.52 g of activated charcoal four times daily for 1 wk and the fecal liberation of intestinal gases was measured before and after the activated charcoal treatment. In an effort to explain the in vivo results, additional in vitro studies were performed to compare the binding capacity of charcoal to the sulfur gas released by feces. RESULTS: Ingestion of activated charcoal produced no significant reduction in the fecal release of any of the sulfur-containing gases, nor was total fecal gas release or abdominal symptoms significantly influenced. In vitro studies suggested that the failure of ingested charcoal to reduce liberation of sulfur gases probably is explained by the saturation of charcoal binding sites during passage through the gut. CONCLUSION: Commonly employed doses of activated charcoal do not appreciably influence the liberation of fecal gases.

Gas production in human ingesting a soybean flour derived from beans naturally low in oligosaccharides.

BACKGROUND: Ingestion of soy products may cause excessive intestinal gas. This gas results from colonic bacterial fermentation of the indigestible oligosaccharides raffinose and stachyose, which are present in high concentrations in legumes. OBJECTIVE: The objective of the study was to compare gas production and gaseous symptoms in healthy volunteers after ingestion of 34 and 80 g soy flour made from either conventional soybeans or soybeans naturally low in indigestible oligosaccharides. DESIGN: In a double-blind, randomized, crossover protocol, breath hydrogen (an indicator of carbohydrate malabsorption), flatus frequency, and abdominal symptoms were assessed after subjects ingested the soy products and after 2 control meals (rice or lactose-hydrolyzed milk). RESULTS: The sum of breath-hydrogen concentrations for 8 h was significantly greater (P < 0.005) after 34 g conventional soy (60.4+/-9.4 ppm) than after low-oligosaccharide soy (34.3+/-8.1 ppm). Greater differences were observed with 80-g doses: 157.9+/-19.4 ppm after conventional soy and 50.8+/-6.8 ppm after low-oligosaccharide soy (P < 0.001). Flatus frequency (7.5+/-1.9 times/12 h) was significantly greater (P = 0.039) after ingestion of 80 g conventional soy than after the control, rice meal (3.2+/-0.8 times/12 h), whereas flatus frequency after the low-oligosaccharide soy meal (3.9+/-0.7 times/12 h) was comparable with that after the rice meal. There were no significant differences in the severity of other abdominal symptoms. CONCLUSION: Soy flour derived from low-oligosaccharide soybeans resulted in less gas production than that derived from conventional soybeans.