Alessandra Strocchi

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 12 g 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 12 g of lactulose increased their breath H2 levels over 20 ppm when tested with 20 g. 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.

Fasting breath hydrogen in celiac disease

We studied the possible clinical significance of high basal levels of H2 by analyzing the breath excreted by the following fasting subjects: 50 healthy volunteers, 149 subjects with functional bowel disorders, 16 patients with small bowel bacterial overgrowth proven by bacteriology, 34 patients with untreated celiac disease, 40 patients with celiac disease on a gluten-free diet, and 40 patients with disorders of the small intestine other than celiac disease (disease controls). The fasting levels of H2 in untreated celiac patients (mean 22.5 +/- 19.3 ppm) were significantly higher than those in healthy volunteers (5.8 +/- 3.1 ppm), patients with functional bowel disorders (6.6 +/- 4.4 ppm), treated celiac patients (9.9 +/- 8.1 ppm), and disease controls (7.0 +/- 6.7 ppm). No significant difference was found between patients with untreated celiac disease and bacterial overgrowth (mean 14.7 +/- 14.0 ppm). The percentage of patients with elevated H2 fasting levels in untreated celiac disease (58.8%) was significantly higher than that in the other groups, except for the patients with bacterial overgrowth (43.7%). In 14 celiac patients, studied before and after a gluten-free diet, fasting H2 levels decreased from 26.6 +/- 18 to 11.6 +/- 10 ppm, becoming normal only in those patients with healing of intestinal lesions. Our results show that high fasting H2 levels are a frequent feature of untreated celiac disease and that the return to normal of these levels is predictive of villous regrowth.

Factors affecting hydrogen production and consumption by human fecal flora. The critical roles of hydrogen tension and methanogenesis.

We studied the influence of hydrogen tension (PH2) and methanogenesis on H2 production and consumption by human fecal bacteria. Hydrogen consumption varied directly with PH2, and methanogenic feces consumed H2 far more rapidly than did nonmethanogenic feces. At low PH2, H2 production greatly exceeded consumption and there was negligible accumulation of the products of H2 catabolism, methane and sulfide. Thus, incubation at low PH2 allowed the first reported measurements of absolute as opposed to net H2 production. Feces incubated at high and intermediate PH2 had a net H2 production of only 1/900 and 1/64 of absolute production. Glucose fermentation by fecal bacteria yielded an absolute H2 production of 80 ml/g, a value far in excess of that excreted by volunteers ingesting lactulose. We conclude that most H2 produced by colonic bacteria is consumed and methanogenesis and fecal stirring (via its influence on fecal PH2) are critical determinants of H2 consumption and, hence, net H2 production. Study of fecal samples from four subjects with low breath H2 excretion after lactulose showed that absolute H2 production was normal, and the low H2 excretion apparently reflected increased consumption due to rapid methanogenesis (two subjects) and decreased luminal stirring (two subjects).

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.

Treatment of small intestine bacterial overgrowth with rifaximin, a non-absorbable rifamycin

In twelve patients affected by small bowel bacterial overgrowth, diagnosed by means of the lactulose hydrogen breath test, the therapeutic efficacy of a non-absorbable derivative of rifamycin, rifaximin, was evaluated. This study showed that this drug has a satisfactory therapeutic efficacy in contaminated small bowel syndrome and, at the doses tested, is free of side-effects.

Lactose intolerance and bone mass in postmenopausal Italian women

Previous studies on the role of lactose malabsorption in the pathogenesis of postmenopausal osteoporosis have yielded conflicting results and further information is needed. To date, all studies have been carried out on populations with a low prevalence of lactose malabsorption and the lactose intestinal absorptive capacity was tested using a non-physiological dose of lactose. In fifty-eight Italian postmenopausal women (mean age 57 (SD 7) years), bone mineral density (BMD) at lumbar spine, H2 breath response after ingestion of 20 g lactose, intensity of symptoms of intolerance after a lactose load and daily Ca intake were evaluated. No differences were found between women with or without a positive H2 breath test with regard to BMD (-1.2 (SD 0.9) v. -0.9 (SD 0.8)) and Ca intake (509 (SD 266) v. 511 (SD 313) mg/d). On the contrary, both BMD and Ca intake were significantly lower in women with lactose malabsorption and symptoms of intolerance (-1.5 (SD 0.7) and 378 (SD 220) mg/d) than in those with malabsorption without symptoms (-0.9 (SD 0.9) and 624 (SD 254) mg/d). Moreover, in lactose malabsorbers Ca intake was correlated inversely with symptom score (rs -0.31, P < 0.05) and positively with BMD (rs 0.42, P < 0.005). Our results show that in Italian postmenopausal women Ca intake and BMD are not influenced directly by lactose malabsorption; the appearance of symptoms of intolerance seems to influence BMD unfavourably through a reduced Ca intake.

A reappraisal of the magnitude and implications of the intestinal unstirred layer

Until recently, a variety of studies had suggested that luminal stirring in the jejunum is relatively poor, with unstirred layers of about 600 microns reported for humans and 300-900 microns for animals. Unstirred layers of this magnitude would markedly retard the absorption of all solutes, and diffusion through this layer would be the rate-limiting step in the uptake of all rapidly absorbed compounds. As a result, luminal stirring, rather than epithelial transport, would be the major variable influencing absorption rate. However, recent studies in dogs and humans have shown that the unstirred layer has a maximal apparent thickness of only about 40 microns. This layer is far thinner than what can be achieved in vitro with vigorous stirring with a magnetic bar, suggesting that some unique stirring mechanism, perhaps villous contractions, is responsible for this extraordinarily efficient mixing. A 40-microns unstirred layer would produce only about 1/15 the resistance of the previously reported 600 microns value; with this thinner layer, alterations in either luminal stirring or epithelial function could readily influence the absorption rate of rapidly transported compounds.

β-Galactosidase from Aspergillus niger in adult lactose malabsorption: a double-blind crossover study

An assessment was made of the efficacy of a β‐galactosidase, obtained from Aspergillus niger and added to intact milk, in decreasing lactose malabsorption and intolerance. Sixteen adult patients with malabsorption and intolerance to this sugar were studied in a double‐blind crossover study vs. placebo. A 5‐hour hydrogen breath test was used to assess malabsorption of lactose contained in 400 ml milk. When compared with placebo, the addition of exogenous lactase to intact milk caused a statistically significant reduction in the maximum breath H2 concentration (P < 0.01) and in the cumulative H2 excretion (P < 0.005). In the same way, the cumulative index for gastrointestinal intolerance was significantly lower (P < 0.005) after the ingestion of lactase‐added milk. This study demonstrates that enzyme replacement therapy, with β‐galactosidases obtained from Aspergillus niger, is effective in decreasing lactose malabsorption and its consequent intolerance in adult subjects with lactase deficiency.

Decreased plasma postheparin diamine oxidase levels in celiac disease

The highest diamine oxidase activity is contained in small-bowel mucosa and, after heparin administration, the enzyme is released by the intestine into the plasma. Previous experimental studies showed that measurement of plasma postheparin diamine oxidase activity is a sensitive test for quantitating the length and severity of small-bowel mucosal injury. On this basis, we measured plasma diamine oxidase activity in celiac disease, a condition characterized by a loss of mature enterocyte mass. Twenty-five untreated celiac patients, 21 celiac patients on a gluten-free diet, 16 patients with small-bowel diseases other than celiac disease (abnormal controls), and 18 healthy controls were studied. Diamine oxidase activity was measured using [14C]putrescine as substrate and expressed as units per milliliter of plasma. Basal diamine oxidase levels in controls and patients were too low for significant differences between the groups to be detected. After preliminary experiments in which, on separate occasions, heparin was intravenously administered at doses of 75 and 150 units/kg and in which the second blood sample was taken 10 and 30 min after heparin injection, it was decided to use the 150 unit/kg dose and to measure plasma diamine oxidase activity in the blood sample taken 10 min after heparin stimulation in all the remaining subjects taking part in the study. Postheparin diamine oxidase levels were significantly lower in untreated celiac patients (mean 1.53 units/ml) than in healthy controls (mean 5.85), treated celiac patients (mean 4.82), and abnormal controls (mean 2.62). Except in three patients, no overlap between healthy controls and untreated celiac patients was observed. No significant difference was detected between healthy controls and treated celiac patients. Our results show that plasma postheparin diamine oxidase activity mirrors not only mucosal damage but also mucosal recovery of the small bowel, thus providing a new circulating marker for the status of the human intestinal mucosa. Measurement of plasma diamine oxidase may represent a useful test to screen patients for intestinal biopsy and to follow up the response to gluten-free diet.

Original contributionMixing of the intestinal content and variations of fermentation capacity do not affect the results of hydrogen breath test

Abstract Objectives Although the hydrogen (H2) breath test has been in use for many years for diagnosis of sugar malabsorption, research is still underway to improve its diagnostic accuracy. In this study, we investigated whether possible confusing factors caused by the ingestion of the test solution itself (such as the delivery to the colon of other fermentable substrates pre-existing in the small bowel lumen, the release of preformed H2 trapped in the feces, or differences in the fermenting capacity of the colonic bacteria) may interfere with the increase of breath H2 concentration, an expression of malabsorption of the test substrate. Methods In 25 patients with untreated celiac disease and 23 sex- and age-matched healthy volunteers, breath H2 excretion was measured after ingestion of a 250-ml solution containing sorbitol, a poorly absorbed alcohol sugar. On 2 other separate days, 12 randomly selected subjects in each group underwent breath H2 excretion measurement after ingestion of 250 ml of a sugar free, nonabsorbable electrolyte solution and 250 ml of a solution containing lactulose, a nonabsorbable disaccharide. Results After sorbitol ingestion, celiac disease patients showed a significantly higher breath H2 excretion than did healthy volunteers. Otherwise, breath H2 responses to electrolyte solution and lactulose showed no difference between the two groups of subjects. Conclusions In a group of patients with sugar malabsorption, increased breath H2 excretion does reflect malabsorption. The washout or the mixing of the intestinal content or intergroup difference of fermenting activity of the colonic bacteria do not represent interfering factors and do not modify the accuracy of the H2 breath test in day-to-day clinical practice.