Production of the gaseous signal molecule hydrogen sulfide in mouse tissues

The gaseous molecule hydrogen sulfide (H(2)S) has been proposed as an endogenous signal molecule and neuromodulator in mammals. Using a newly developed method, we report here for the first time the ability of intact and living brain and colonic tissue in the mouse to generate and release H(2)S. This production occurs through the activity of two enzymes, cystathionine-gamma-lyase and cystathionine-beta-synthase. The quantitative expression of messenger RNA and protein localization for both enzymes are described in the liver, brain, and colon. Expression levels of the enzymes vary between tissues and are differentially distributed. The observation that, tissues that respond to exogenously applied H(2)S can endogenously generate the gas, strongly supports its role as an endogenous signal molecule.

Production of the gaseous signal molecule hydrogen sulfide in mouse tissues

The gaseous molecule hydrogen sulfide (H(2)S) has been proposed as an endogenous signal molecule and neuromodulator in mammals. Using a newly developed method, we report here for the first time the ability of intact and living brain and colonic tissue in the mouse to generate and release H(2)S. This production occurs through the activity of two enzymes, cystathionine-gamma-lyase and cystathionine-beta-synthase. The quantitative expression of messenger RNA and protein localization for both enzymes are described in the liver, brain, and colon. Expression levels of the enzymes vary between tissues and are differentially distributed. The observation that, tissues that respond to exogenously applied H(2)S can endogenously generate the gas, strongly supports its role as an endogenous signal molecule.

A mixture of extracts of black and green teas and mulberry leaf did not reduce weight gain in rats fed a high-fat diet

Tea extracts are used in many over-the-counter preparations claiming to promote weight loss. The rationale for this usage includes reports that green tea extract increases thermogenesis, and extracts of green and black tea and mulberry leaf inhibit the digestion/absorption of carbohydrate and fat. The investigators in this study tested the potential of increasing doses of a mixture of three extracts (50-percent black tea, 20-percent green tea, and 30-percent mulberry) to induce weight loss, steatorrhea, and blood lipid alterations in rats ingesting a high-fat diet, ad lib. The mixture was incorporated into chow in quantities of 0.5-, 3.0-, and 6.0 percent by weight; a control group received only chow. Food intake and weight were monitored daily, and quantitative fecal fat measurements were obtained weekly for four weeks. The 3.0- and 6.0-percent chows significantly increased fecal fat excretion to 15 percent of dietary fat intake (controls: 5 percent); however, no significant reduction in weight gain was observed. After four weeks of treatment, the 3.0- and 6.0-percent dosages were associated with significant reductions in serum triglycerides and increases in high-density lipoprotein (HDL) cholesterol. However, these chow concentrations were associated with significant increases in serum ALT, and the 6.0-percent chow markedly increased serum alkaline phosphatase. This study does not provide support for the utility of this combination of black tea, green tea, and mulberry extracts in weight-loss regimens and indicates that high doses of this extract combination may be hepatotoxic.

An extract of black, green, and mulberry teas causes malabsorption of carbohydrate but not of triacylglycerol in healthy volunteers

BACKGROUND

In vitro studies suggest that extracts of black, green, and mulberry teas could interfere with carbohydrate and triacylglycerol absorption via their ability to inhibit alpha-amylase, alpha-glucosidase, sodium-glucose transporters, and pancreatic lipase.

OBJECTIVE

We measured breath hydrogen and 13CO2 to investigate the ability of an extract of black, green, and mulberry tea leaves to induce malabsorption of carbohydrate and triacylglycerol in healthy volunteers.

DESIGN

In a crossover design, healthy adult volunteers randomly ingested test meals with a placebo beverage or a preparation containing an extract of black (0.1 g), green (0.1 g), and mulberry (1.0 g) teas. One test meal contained 50 g carbohydrate as white rice, 10 g butter, and 0.2 g [13C]triolein, and the beverages contained 10 g sucrose. The calorie content of the second test meal consisted entirely of lipid (30 g olive oil and 0.2 g [13C]triolein). Breath-hydrogen and 13CO2 concentrations were assessed hourly for 8 h, and symptoms were rated on a linear scale.

RESULTS

With the carbohydrate-containing meal, the tea extract resulted in a highly significant increase in breath-hydrogen concentrations, which indicated appreciable carbohydrate malabsorption. A comparison of hydrogen excretion after the carbohydrate-containing meal with that after the nonabsorbable disaccharide lactulose suggested that the tea extract induced malabsorption of 25% of the carbohydrate. The tea extract did not cause triacylglycerol malabsorption or any significant increase in symptoms.

CONCLUSION

This study provides the basis for additional experiments to determine whether the tea extract has clinical utility for the treatment of obesity or diabetes.

Use of breath carbon monoxide measurements to assess erythrocyte survival in subjects with chronic diseases

Anemia is very common in patients with chronic diseases. To determine the role of increased red blood cell (RBC) turnover in such subjects, we estimated RBC survival in three groups of chronically ill patients using a simple technique in which RBC life span is estimated via measurements of breath carbon monoxide concentration. The study groups consisted of subjects with: (1) osteoarthritis, (2) rheumatoid arthritis, and (3) anemia who were hospitalized for treatment of a variety of chronic illnesses. None of the anemic subjects had evidence of hemorrhage, a deficiency state, or a marrow abnormality to account for their reduced hemoglobin concentration. Subjects with osteoarthritis had a mean RBC life span (127 +/- 25 days) that did not differ significantly from normal (122 +/- 23 days). In contrast, RBC life span was significantly reduced (P < 0.001) in both the rheumatoid arthritis subjects (90 +/- 15 days) and the anemic, hospitalized patients (87 +/- 33 days). The hemoglobin concentration of the rheumatoid patients was near normal (13.5 +/- 1.5 g/dl), indicating that the marrow was compensating for the reduced RBC life span, whereas no such compensation was apparent in the anemic, chronically ill subjects. We conclude that a modest (approximately 25%) reduction in RBC life span commonly occurs in patients with chronic disease, and this reduction becomes clinically relevant in subjects whose marrow cannot respond with increased RBC output.

Use of breath carbon monoxide to measure the influence of prosthetic heart valves on erythrocyte survival

First-generation prosthetic heart valves commonly caused sufficient red blood cell (RBC) injury to induce hemolytic anemia. Although multiple studies have shown that new-generation valves are not associated with anemia, the extent to which these valves are injurious to RBCs is not known, because RBC survival not has not been measured in these subjects. Using a technique that uses breath carbon monoxide (CO) to quantify RBC turnover, this study measured RBC life span in 38 subjects with normally functioning, new-generation valves. Erythrocyte survival averaged 98.8 +/- 23 and 103 +/- 15 days, respectively, in 20 subjects with mechanical valves and 18 subjects with bioprosthetic valves (p >0.05). However, these life spans were significantly (p <0.01) less than those of healthy subjects (122 +/- 23 days) and a group of elderly subjects with osteoarthritis (128 +/- 26 days). The mean hemoglobin concentrations of the 2 groups of valve patients were within normal limits. In conclusion, new-generation heart valves commonly are associated with a small degree of hemolysis that is compensated for by increased RBC production.

Stability of human methanogenic flora over 35 years and a review of insights obtained from breath methane measurements

BACKGROUND & AIMS

Breath methane measurements reflect the in situ activity of the methanogenic colonic flora. Thirty-five years ago we found that 34% of healthy adult subjects were methane producers (breath methane level >1 ppm above atmospheric methane levels). The current study presents a new survey of breath methane levels designed to determine if the activity of the methanogenic flora has changed over the past 35 years. In addition, we review insights into the methanogenic flora that have resulted from breath methane measurements.

METHODS

The end-alveolar breath methane concentrations of 212 healthy adults living in the Minneapolis area were determined via gas chromatography. The influence of sex, age, and bowel movement frequency on methane production was assessed.

RESULTS

The findings that 36.4% of participants were methane producers, with a mean methane concentration in these producers of 16.6 ppm, are strikingly similar to the values of 33.6% and 15.2 ppm observed 35 years ago. Neither sex nor age showed a statistically significant relationship to methane production. There was a negative correlation between frequency of bowel movements and breath methane concentration in methane producers.

CONCLUSIONS

The activity of the methanogenic flora of healthy adults remained remarkably stable over the past 35 years despite widespread antibiotic use and dietary changes. A literature review revealed that many associations have been shown between methane production and clinical states, but it remains to be determined if methanogens actively influence human physiology or are simply a marker of colonic function.

Association between fecal hydrogen sulfide production and pouchitis

PURPOSE

The beneficial effect of antibiotics in pouchitis suggests that an unidentified fecal bacterial product causes this condition. A candidate compound is hydrogen sulfide, a highly toxic gas produced by certain fecal bacteria, which causes tissue injury in experimental models. We investigated hydrogen sulfide release and sulfate-reducing bacterial counts in pouch contents to determine whether hydrogen sulfide production correlates with pouchitis.

METHODS

During incubation at 37 degrees C, the production of hydrogen sulfide, methylmercaptan, carbon dioxide, and hydrogen were studied using fresh fecal specimens obtained from 50 patients with ileoanal pouches constructed after total proctocolectomy for ulcerative colitis (n = 45) or for familial adenomatous polyposis (n = 5). Patients with ulcerative colitis were divided into five groups: a) no history of pouchitis (pouch for at least 2 years; n = 8); b) past episode(s) of pouchitis but no active disease for the previous year (n = 9); c) pouchitis in the past year but presently inactive (n = 9); d) ongoing antibiotic treatment (metronidazole or ciprofloxacin) for pouchitis (n = 11); e) currently suffering from pouchitis (n = 8).

RESULTS

Release of hydrogen sulfide when pouchitis was active (6.06 +/- 1.03 micromol g(-1) 4 h(-1)) or had occurred in the past year (4.71 +/- 0.41 pmol g(-1) 4 h(-1)) was significantly higher (P < 0.05) than when pouchitis had never occurred (1.71 +/- 0.43 micromol g(-1) 4 h(-1)) or had been inactive in the past year (2.62 +/- 0.49 micromol g(-1) 4 h(-1)). Antibiotic therapy was associated with very low hydrogen sulfide release (0.68 +/- 0.29 micromol g(-1) 4 h(-1)). Pouch contents from familial adenomatous polyposis patients produced significantly less hydrogen sulfide (0.75 +/- 0.09 micromol g(-1) 4 h(-1)) than did any group of nonantibiotic-treated ulcerative colitis patients. Sulfate-reducing bacterial counts in active pouchitis (9.5 +/- 0.5 log10/g) were significantly higher than in those who never experienced pouchitis (7.38 +/- 0.32 log10/g), and these counts fell dramatically with antibiotic treatment. No statistically significant differences in carbon dioxide and hydrogen were observed among the groups not receiving antibiotics.

CONCLUSIONS

Pouch contents of patients with ongoing pouchitis or an episode within the previous year released significantly more hydrogen sulfide than did the contents of patients who never had an attack of pouchitis and those with longstanding inactive disease. The response to therapy with metronidazole or ciprofloxacin was associated with marked reductions in hydrogen sulfide release and sulfate-reducing bacteria. These results provide a rationale for additional studies to determine whether the high sulfide production is a cause or effect of pouchitis. The lower hydrogen sulfide production by pouch contents of familial adenomatous polyposis vs. patients with ulcerative colitis suggests a fundamental difference in gut sulfide metabolism that could have implications for the etiology of ulcerative colitis as well as the pouchitis of patients with ulcerative colitis.

Effectiveness of devices purported to reduce flatus odor

OBJECTIVE

A variety of charcoal-containing devices are purported to minimize problems with odoriferous rectal gas; however, the evidence supporting the efficacy of these products is virtually all anecdotal. We objectively evaluated the ability of these devices to adsorb two malodorous, sulfide gases (hydrogen sulfide and methylmercaptan) instilled at the anus.

METHODS

Via a tube, 100 ml of nitrogen containing 40 ppm of sulfide gases and 0.5% H(2) was instilled at the anus of six healthy volunteers who wore gas impermeable Mylar pantaloons over their garments. Since H(2) is not adsorbed by charcoal, the fraction of the sulfide gases removed could be determined from the concentration ratio of sulfide gas: H(2) in the pantaloon space relative to the ratio in instilled gas.

RESULTS

Measurements with no device in place showed that subjects' garments removed 22.0 +/- 5.3% of the sulfide gases, and results obtained with each device were corrected for this removal. The only product that adsorbed virtually all of the sulfide gases was briefs constructed from an activated carbon fiber fabric. Pads worn inside the underwear removed 55-77% of the sulfide gases. Most cushions were relatively ineffective, adsorbing about 20% of the gases.

CONCLUSIONS

The ability of charcoal-containing devices to adsorb odoriferous rectal gases is limited by incomplete exposure of the activated carbon to the gases. Briefs made from carbon fiber are highly effective; pads are less effective, removing 55-77% of the odor; cushions are relatively ineffective.

Use of alveolar carbon monoxide to measure the effect of ribavirin on red blood cell survival

A major side effect of ribavirin (RBV) treatment is anemia. While this anemia is thought to result from increased RBC turnover, RBC survival has not been determined in subjects receiving RBV due to the complexity of the techniques commonly used to quantitate RBC life span. We recently described a simple, rapid, non-invasive technique that utilizes measurements of alveolar carbon monoxide (CO) concentration to determine RBC survival. In the present report, this method was employed to assess RBC survival in patients receiving RBV for hepatitis C. Each of the 31 measurements of RBC survival in 12 subjects with RBV-associated anemia was below the lower limit of normal (77 days), and the average survival (46 +/- 14 days) in these subjects was only about 38% of that of healthy controls (122 +/- 23 days). Five hepatitis C patients not undergoing RBV treatment had normal RBC survivals (112 +/- 17 days). While the mean reticulocyte percentage was significantly elevated in subjects treated with RBV, 59% of these measurements fell within the limits of normal. We conclude that RBV-associated anemia consistently is associated with reduced RBC survival as determined from breath CO measurements and that this reduced survival frequently is not associated with an elevated reticulocyte count.

Relationship between GHb concentration and erythrocyte survival determined from breath carbon monoxide concentration

OBJECTIVE

Subjects with decreased erythrocyte survival have an unusually low GHb percentage. The goal of this study was to determine whether hyperglycemia, as reflected by GHb percentage, is associated with decreased erythrocyte survival.

RESEARCH DESIGN AND METHODS

Erythrocyte survival was quantitated in 23 subjects with type 2 diabetes, and these values were correlated with the subjects' GHb percentage. Erythrocyte survival was determined from the difference between the subjects' alveolar carbon monoxide (CO) concentration and atmospheric CO concentration. Reticulocyte counts were obtained in 16 subjects.

RESULTS

Although the vast majority of the subjects had erythrocyte life spans that fell within the normal range (123 +/- 23 days), there was a highly significant inverse correlation (r = -0.66, P < 0.01) between life span and GHb percentage, with an average decline in life span of 6.9 days for each 1% rise in GHb. The reticulocyte count inversely correlated with erythrocyte life span (r = -0.77, P < 0.01).

CONCLUSIONS

Hyperglycemia, as evidenced by high GHb percentage, is associated with an appreciable decrease in erythrocyte life span. Because GHb appears to be formed over the lifetime of the erythrocyte, this decreased erythrocyte survival suggests that high GHb percentages may systematically underestimate the true degree of hyperglycemia.

The effect of antibiotics and bismuth on fecal hydrogen sulfide and sulfate-reducing bacteria in the rat

Colonic bacteria produce the highly toxic thiol, hydrogen sulfide. Despite speculation that this compound induces colonic mucosal injury, there is little information concerning manipulations that might reduce its production. We studied the effect of antibiotics and bismuth on the production of hydrogen sulfide in rats. Baseline fecal samples were analyzed for hydrogen sulfide concentration and release rate during incubation and numbers of sulfate-reducing bacteria. Groups of six rats received daily doses of ciprofloxacin, metronidazole, or sulfasalazine for one week, and feces were reanalyzed. Bismuth subnitrate was then added to the antibiotic regimens. While sulfide production and sulfate-reducing bacteria were resistant to treatment with ciprofloxacin or metronidazole, bismuth acted synergistically with ciprofloxacin to inhibit sulfate-reducing bacteria growth and to reduce sulfide production. Combination antibiotic-bismuth therapy could provide insights into the importance of sulfide and sulfate-reducing bacteria in both human and animal models of colitis and have clinical utility in the treatment of antibiotic-resistant enteric pathogens.

Simplification of the end-alveolar carbon monoxide technique to assess erythrocyte survival

We have described a simple, rapid method for determining red blood cell (RBC) life span based on measurement of alveolar carbon monoxide (CO) concentration corrected for atmospheric CO as determined with a device that simulates the body's equilibration with CO. This study was designed to determine whether direct measurements of ambient CO can be substituted for sampling with the equilibrator device. Atmospheric samplings obtained in our medical center over a period of weeks indicated that CO concentration was sufficiently constant that a single ambient CO measurement at the time of breath collection adequately corrected for atmospheric CO. Additional studies with volunteers showed that overnight CO concentrations in the subjects' home environments also remained relatively constant, suggesting that accurate assessment of RBC life span can be obtained from alveolar CO concentrations and home atmospheric samples collected on a subject's arising in the morning. Using this technique, we found that the RBC life span of 40 healthy volunteers averaged 122 +/- 23 days, a value comparable to that obtained with complex cohort labeling methods. No significant correlation was observed between RBC life span and reticulocyte count in these individuals. The ability of this simple technique to detect increased RBC turnover was demonstrated in 4 subjects being treated with ribavirin and interferon for hepatitis C, a treatment reported to shorten RBC life span. Measurement of CO in samples collected by these four subjects in their home environments indicated that each had a shortened RBC life span (range 30-69 days).

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.

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.

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.

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.

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.

Lactose maldigestion is not an impediment to the intake of 1500 mg calcium daily as dairy products

BACKGROUND

A National Institutes of Health consensus conference concluded that a daily calcium intake of 1500 mg reduces the severity of osteoporosis. Because dairy products are the main natural source of dietary calcium, a diet providing 1500 mg Ca must contain large quantities of dairy products. However, it is widely believed that the lactose content of these products will not be tolerated by persons with lactose maldigestion (approximately 30% of the adult US population).

OBJECTIVE

We evaluated the symptoms of lactose maldigestion and digestion when the diet was supplemented with dairy products providing 1300 mg Ca/d.

DESIGN

Sixty-two women (31 with lactose maldigestion and 31 without) were studied in a double-blind, randomized protocol. Symptoms were compared during 1-wk periods when the diet was supplemented with 480 mL (2 cups) milk, 56 g cheese, and 240 mL yogurt provided as conventional products (34 g lactose/d) or as lactose-hydrolyzed products (2 g lactose/d).

RESULTS

Women who digested lactose reported no significant difference in symptoms between the 2 treatment periods. Women with lactose maldigestion reported significantly increased flatus frequency and subjective impression of rectal gas during the period of high lactose intake; however, bloating, abdominal pain, diarrhea, and the global perception of overall symptom severity were not significantly different between the 2 treatment periods.

CONCLUSION

The symptoms resulting from lactose maldigestion are not a major impediment to the ingestion of a dairy-rich diet supplying approximately 1500 mg Ca/d.

Bismuth subsalicylate markedly decreases hydrogen sulfide release in the human colon

BACKGROUND & AIMS

Hydrogen sulfide is one of the main malodorous compounds in human flatus. This toxic gas also has been implicated in the pathogenesis of ulcerative colitis. Therefore, a treatment that reduces colonic H2S levels could be clinically useful in the treatment of flatus odor and of ulcerative colitis. In this study the ability of bismuth subsalicylate, a compound that binds H2S, to reduce H2S release in the colon, was tested.

METHODS

Homogenates made from human and rat feces were incubated with and without bismuth subsalicylate, and gas production was measured. Fecal samples from 10 healthy subjects were analyzed before and after ingestion of bismuth subsalicylate (524 mg four times a day) for 3-7 days.

RESULTS

Fecal homogenates showed a dose-dependent relationship between the concentration of bismuth subsalicylate and H2S release. Treatment of subjects with bismuth subsalicylate produced a >95% reduction in fecal H2S release.

CONCLUSIONS

The ability of bismuth subsalicylate to dramatically reduce H2S could provide a clinically useful means of controlling fecal and/or flatus odor and of decreasing the putative injurious effects of H2S on the colonic mucosa.

Fecal hydrogen sulfide production in ulcerative colitis

OBJECTIVE

Sulfide, a product of sulfate-reducing bacteria, has been proposed to play an etiologic role in ulcerative colitis. Ulcerative colitis feces have increased numbers and activity of sulfate-reducing bacteria, but only modestly increased sulfide. However, fecal sulfide exists largely in the volatile, highly toxic H2S form that moves rapidly from feces to surrounding gas. Our aim was to quantify the fecal release of H2S and other volatiles (CO2, H2, CH4, methanethiol, and dimethylsulfide).

METHODS

Fecal samples from 25 subjects with ulcerative colitis and 17 controls were incubated in 4-L containers, and gas release was assessed at intervals over 24 h.

RESULTS

H2S release by ulcerative colitis feces was elevated 3-4-fold at every measurement point compared with normal feces (p < 0.003 at 24 h). The only other significant difference was increased CO2 release by ulcerative colitis feces at 1 h. Supplementation of fecal homogenates with sulfur-containing substrates showed that organic compounds (mucin, cysteine, taurocholate) provided more readily utilizable substrate for H2S production than did sulfate.

CONCLUSIONS

Increased H2S release is a relatively localized metabolic aberration of ulcerative colitis feces. This increased H2S may reflect abnormalities of the fecal bacteria and/or substrate availability.

Factors influencing frequency of flatus emission by healthy subjects

The purpose of the present study was to measure the frequency of flatus emission by 25 healthy subjects and to determine if factors commonly thought to influence flatulence actually correlate with the frequency of gas passage. Over a one-week period on their usual diet, subjects passed gas 10 +/- 1 times/day [upper limit of normal (mean + 2 SD): 20 times/day]. The addition of the nonabsorbable disaccharide lactulose (10 g/day) to the diet significantly (P < 0.01) increased flatus frequency to 19 +/- 2.4 times per day. Gender, age, and the ability of an individual's colonic flora to produce methane had no significant influence on flatus frequency either on the basal or lactulose-supplemented diets. Some subjects consistently passed gas more often than did others. These individual differences appeared to result, in part, from differences in the ability of the flora to produce gas from a given quantity of fermentable material.

Ashkenazi Jews, sulfur gases, and ulcerative colitis

Fecal pathogens have been suspected to cause ulcerative colitis, yet none have been identified. Meanwhile, the 400 species comprising normal colonic flora have received little attention as potential pathogens. Sulfate-reducing bacteria (SRB), a frequent colonic commensal, have been identified in greater numbers in people with ulcerative colitis. The bacteria produce hydrogen sulfide, a toxic compound with the potential to cause colonic injury and possibly ulcerative colitis. If these bacteria are pathogenic, high-risk populations may harbor greater numbers of these organisms in their colons. We compared a group with a high incidence of ulcerative colitis, Ashkenazi Jews, to a control population to assess carriage rates for SRB. Breath samples were collected to indirectly determine colonic conditions. No difference was found between the two groups studied.

Use of maltose hydrolysis measurements to characterize the interaction between the aqueous diffusion barrier and the epithelium in the rat jejunum

Rates of intestinal absorption and surface hydrolysis are determined by the interaction of two barriers: poorly stirred fluid adjacent to the mucosa, and the epithelial cell. These two barriers commonly are modeled as a fixed, flat layer of epithelium covered by a fixed thickness of unstirred fluid. To more accurately simulate these barriers in a villous mucosa, maltase activity (measured in vitro) was distributed over an anatomically correct model of rat jejunal villi. We then determined what interaction of the aqueous and epithelial barriers best predicted in vivo maltose hydrolysis rates measured over a broad range of infusate concentrations. Hydrolysis was accurately predicted by a model in which unstirred fluid extended from 20 microm over the villous tips throughout the intervillous space. In this model, the depth of diffusion into the intervillous space is inversely proportional to the efficiency of epithelial handling of the solute. As a result, both the aqueous barrier and the functional surface area are variables rather than constants. Some implications of our findings (relative to the conventional model) include: higher predicted Vmax, efficient handling of low concentrations of a solute at the villous tips while high concentrations must penetrate thick aqueous barriers, and sensitive regulation of transport rates via ease of access to the intervillous space.

Paracellular intestinal transport of six-carbon sugars is negligible in the rat

BACKGROUND & AIMS

Active D-glucose absorption has been theorized to increase convective flow and enhance tight junction permeability such that paracellular transport becomes the major mechanism of D-glucose absorption. This concept was tested in rats by measuring the absorption of four gavaged, nonmetabolizable six-carbon sugars (L-glucose, L-galactose, L-mannose, and D-mannitol) thought to be absorbed solely by the paracellular route.

METHODS

Uptake of gavaged probes was measured by recovery in 24-hour urine specimen collections.

RESULTS

L-glucose (71.2% +/- 2.4%) absorption exceeded that of the other probes (1.4%-9%). Coadministration of 3.0 mol/L D-glucose, 0.22 mol/L D-glucose, or chow significantly reduced the absorption of L-glucose to 38.1% +/- 7.2%, 61% +/- 3.3%, and 53.6% +/- 3.5%, respectively, but did not influence the absorption of the other six-carbon probes.

CONCLUSIONS

(1) L-glucose seems to have a weak affinity for a D-glucose carrier and is not a marker of paracellular transport, and (2) paracellular transport accounts for a minimal fraction of D-glucose uptake; this fraction is not enhanced by ingestion of D-glucose or chow.

Factors affecting the ability of a high beta-galactosidase yogurt to enhance lactose absorption

Lactose in yogurt is better absorbed by lactase-deficient subjects than is an equivalent quantity of lactose in milk, presumably because of the microbial activity of the beta-galactosidase present in yogurt. In this study, we describe a process that increases the beta-galactosidase of yogurt 5- to 6-fold and the ability of this high lactase yogurt to enhance lactose absorption in lactase-deficient subjects. These subjects ingested the yogurt meals after a 12-h fast, and lactose malabsorption was determined by measuring breath hydrogen. Breath hydrogen was reduced 39% following ingestion of high lactase yogurt from that after consumption of conventional yogurt, indicating that the high lactase yogurt enhanced lactose absorption. However, the reduction after high lactase yogurt was less than expected, given the 5- to 6-fold increment in beta-galactosidase measured in vitro. In vivo activity of beta-galactosidase requires that the enzyme resist acid denaturation in the stomach. The beta-galactosidase in high lactase yogurt was much less acid resistant than was the beta-galactosidase in conventional yogurt, and the relative inability of high lactase yogurt to enhance lactose absorption was likely due to the destruction of the beta-galactosidase in the stomach.

Study of constancy of hydrogen-consuming flora of human colon

The constancy of the hydrogen consuming flora of the human colon was studied in 15 healthy subjects via two measurements obtained 18 to 36 months apart. Hydrogen disappearance rate and the major products of H2-consuming bacteria, methane and sulfide, were measured during incubation of fecal homogenates with excess hydrogen and sulfate. In 11/15, the hydrogen consumption rate and the predominant hydrogen-consuming pathway (methanogenesis, sulfate reduction, or neither) remained constant. However, major shifts in these pathways were observed in four subjects, with two losing and two gaining the ability to produce methane. Methanogenesis was associated with the highest hydrogen consumption rate. This study demonstrates that clinically unrecognizable, major alterations of the colonic flora occur in healthy subjects. Understanding of the factors responsible for these alterations might allow for therapeutic manipulation of the colonic flora.

Shaking of the intact rat and intestinal angulation diminish the jejunal unstirred layer

A sizeable pre-epithelial diffusion barrier (unstirred layer) is present during perfusion of the rat jejunum. In the present study, three rapidly transported compounds, CO, [14C]warfarin, and glucose (5.5 mmol/L), were used as probes to assess the ability of manipulations to reduce the unstirred layer. This layer was 700-800 microns thick in a 30-cm jejunal segment perfused in conventional fashion on the abdominal wall. Placement of four sharp angulations in the segment or replacement in the abdominal cavity reduced the maximal unstirred layer to 200-400 microns. Increasingly rapid shaking of the anesthetized, intact rat on a platform shaker produced progressively thinner unstirred layers. At 250 revolutions per minute, the maximal layer ranged from 32 to 68 microns for the three probes and may have been appreciably less if the epithelium offered appreciable resistance. Shaking yields a > 15-fold reduction in unstirred layer resistance and provides a means for measuring this resistance and for obtaining more accurate assessment of the true in vivo transport Michaelis constant (Km) of any compound.

First-pass gastric mucosal metabolism of ethanol is negligible in the rat

Ethanol metabolism by gastric alcohol dehydrogenase (ADH) is thought to be an important determinant of peripheral ethanol time-concentration curves (AUCs) in rats and humans. We quantitated this metabolism in rats by measuring the gastric absorption of oral ethanol (0.25 g/kg) and the gastric venous-arterial (V-A) difference of ethanol versus ethanol metabolites (acetate, acetaldehyde, and bicarbonate). Over 1 h, approximately 20% of the ethanol was absorbed from the stomach and 70% was emptied into the duodenum. The gastric V-A difference of ethanol metabolites was less than 4% of that of ethanol. Thus, gastric metabolism accounted for less than 1% (less than 4% of 20% absorbed) of the dose. This negligible metabolism was predictable from the low affinity of gastric ADH for ethanol. In contrast, gastric ADH has a high affinity for octanol, and 66% of this compound was metabolized during gastric absorption. Evidence supporting gastric metabolism of ethanol largely derives from the lower AUCs observed after oral than after intravenous administration; however, we observed increasingly higher AUCs with increasingly rapid portal vein infusions of identical ethanol doses. We conclude that gastric metabolism of ethanol is negligible in the rat, and differences in AUCs ascribed to gastric metabolism may reflect differences in ethanol absorption.

Competition for hydrogen by human faecal bacteria: evidence for the predominance of methane producing bacteria

Studies of sludge have shown that some species of sulphate reducing bacteria outcompete methane producing bacteria for the common substrate H2. A similar competition may exist in human faeces where the methane (CH4) producing status of an individual depends on the faecal concentration of sulphate reducing bacteria. To determine if non-methanogenic faeces outcompete CH4 producing faeces for H2, aliquots of each type of faeces were incubated alone or mixed together, with or without addition of 10% H2 and/or 20 mmol/l sulphate. Methane producing faeces consumed H2 significantly more rapidly and reduced faecal H2 tension to a lower value compared with non-methanogenic faeces. The mixture of the two types of faeces yielded significantly more CH4 than CH4 producing faeces alone (mean (SD) 8.5 (1.3) v 2.9 (0.45) mmol/l of homogenate per 24 hours, p less than 0.01). Faecal sulphide concentrations were similar in CH4 producing and non-producing homogenates both before and after 24 hours of incubation. The addition of sulphate to the homogenates did not significantly influence CH4 production or sulphide formation. Our results suggest that in human faeces methane producing bacteria outcompete other H2 consuming bacteria for H2.

Physiological measurements of luminal stirring in the dog and human small bowel

The resistance to absorption resulting from poor stirring of luminal contents (RLum) is considered to be equivalent to an unstirred layer of greater than 600 microns in the human small intestine. We measured RLum in the jejunum of conscious dogs by assessing the absorption rate of two rapidly absorbed probes, glucose, and [14C]warfarin. When RLum was expressed as an unstirred layer, the maximal thickness of the unstirred layer (assuming negligible epithelial cell resistance) was only approximately 35 and 50 microns for perfusion rates of 26 and 5 ml/min, respectively. Maximal unstirred layer thickness for the human jejunum, calculated from previous studies of glucose absorption, yielded a mean value of only 40 microns (range: 23 to 65 microns). Since epithelial resistance appears to be negligible during absorption of low concentrations of glucose, the maximal unstirred layer of 40 microns should be close to the true value for glucose in the human small intestine. We conclude that the unstirred layer for rapidly absorbed compounds in dogs and man are less than one-tenth of previously reported values, but this layer still may remain the rate limiting step in absorption of rapidly transported compounds.