W. G. Brydon

Serum 7α-hydroxy-4-cholesten-3-one and selenohomocholyltaurine (sehcat) whole body retention in the assessment of bile acid induced diarrhoea

Objective: To assess the reliability of serum 7α-hydroxy-4-cholesten-3-one (7α-3ox-C) in the differential diagnosis of bile acid induced diarrhoea by comparison with 75selenohomocholyltaurine whole body retention (SeHCAT WBR). Design: One hundred and sixty-four patients with chronic diarrhoea were investigated prospectively in two centres (Edinburgh and Sweden) by two different tests which measure bile acid loss or synthesis: the SeHCAT test which measures the 7-day SeHCAT WBR and serum 7α-3ox-C which reflects the rate of bile acid synthesis. Results: Forty-six patients had SeHCAT WBR of less than 10% (19 with ileal disease or resection, nine with idiopathic bile acid induced diarrhoea and 18 with miscellaneous causes for bile acid induced diarrhoea). All patients with ileal or idiopathic disease showed a favourable response to treatment as did 13 of the miscellaneous group. Serum 7α-3ox-C was raised in all subjects with ileal disease/resection, seven patients with idiopathic disease and all subjects in the miscellaneous group who responded to treatment. Sixteen out of 118 patients with SeHCAT WBR greater than or equal to 10% had raised serum 7α-3ox-C. Conclusion: The positive predictive value of serum 7a-3ox-C was 74%. The high negative predictive value (98%) of serum 7α-3ox-C indicates the possible use of this test for excluding bile acid malabsorption in this population. All but two subjects who responded to treatment had raised serum 7a-3ox-C concentrations. The possibility that the sensitivity of the test can be improved by repeat testing needs to be further investigated. There was a significant correlation between fractional catabolic rate (FCR) SeHCAT and serum 7α-3ox-C (r = 0.63, P< 0.0001). Further data are required to validate the reference range in women over 70 years of age.

Measurement of water-holding properties of fibre and their faecal bulking ability in man.

Experiments to measure the effect of a fibre source in the diet on stool bulk are difficult and lack precision. In vitro methods which would identify fibre sources that are effective for clinical and epidemiologic use would be valuable. One important property of fibre which influences the ability of fibre to increase stool weight is its water-holding capacity (WHC). WHC was measured using centrifugation, filtration, suction pressure and water flow-rate techniques using fibre concentrates of potato, cereal bran and gum arabic. Dietary supplementation of three preparations of potato fibre (20 g/d) had no significant effect on stool weight but 16 g bran/d increased stool weight from 107 (SE 44) g/d to 174 (SE 51) g/d. The effects of these fibres on stool weight can be related to the nature of the water-holding properties of fibre rather than absolute WHC.

A study of the effects of dietary gum arabic in the rat

Gum arabic (GA) is a water-soluble polysaccharide (molecular weight approximately 850 000) containing rhamnose, arabinose, glucuronic acid and galactose. The metabolism of GA has been studied in the rat. Adult male Wistar rats were given GA incorporated into either an Oxoid breeders (OB) diet or an elemental (Elem) diet. Intestinal contents were examined for precipitable GA using acidified ethanol. GA was found from stomach to small intestine but not in the caecum, colon or rectum. Caecal excision and restoration of intestinal continuity resulted in GA recovery from stomach to rectum. Excreted methane, hydrogen and volatile fatty acids (VFA) were measured as indicators of bacterial activity in the caecum and colon. Methane excretion increased on the OB + GA diet and H2 concentrations remained unaltered. The Elem diet abolished gas production. When the animals were given the Elem + GA diet, H2 and methane were only produced after 28 d. Faecal VFA increased with increasing GA intake, acetate concentration increased and butyrate concentration decreased with increasing GA dosage. Significant decreases in concentrations of VFA were found from caecum to left colon and from left colon to faeces. It can be concluded that GA degradation occurs in the caecum and is associated with increased methane excretion, increased VFA concentrations and changes in the proportions of various VFA in the faeces.

An experimental design to study colonic fibre fermentation in the rat: the duration of feeding

1. The time-course of metabolic adaptation by rats to diets containing either wheat bran or gum arabic was studied during a 12-week period. 2. Stool weight was increased with wheat bran but not with gum arabic, and had stabilized after 4 weeks. 3. Bacterial mass as measured by diaminopimelic acid content had stabilized by week 4. Bacterial mass increased on feeding gum arabic but was unchanged with wheat bran. 4. There was increased caecal short-chain fatty acid, hydrogen and methane production with gum arabic but not with wheat bran. The change in caecal metabolic activity was slow to stabilize (8-12 weeks at least). 5. The faecal excretion of bile acids increased twofold with the wheat-bran-supplemented diet compared with the gum-arabic-supplemented and unsupplemented diets. Relatively greater amounts of muricholic acids were present in the caeca and faeces of gum-arabic-fed rats compared with the other groups.

Dietary effects of sodium alginate in humans.

Following a 7-day control period, five male volunteers consumed a weight of sodium alginate corresponding to 175 mg/kg body weight for 7 days, followed by 200 mg sodium alginate per kg body weight for a further 16 days. Measurements before and at the end of the 23-day period of dietary supplementation showed that sodium alginate acted as a faecal bulking agent for all volunteers, giving a significant (p less than 0.01) increase in daily wet weight, and also increases in the water content and daily dry weight, but no change in faecal pH. Although the dietary transit time remained constant for two volunteers, it decreased for two, and increased slightly for one, with little resulting change in the overall mean value. The ingestion of sodium alginate had no significant effect on (a) haematological indices, (b) plasma biochemistry parameters, (c) urinalysis parameters, (d) blood glucose and plasma insulin concentrations, (e) breath hydrogen concentrations. No allergic responses were reported by, nor observed in, any of the volunteers. The study therefore indicates that the ingestion of sodium alginate at a high level for 23 days caused no effects other than those normally associated with a polysaccharide bulking agent; in particular, the enzymatic and other sensitive indicators of adverse toxicological effects remained unchanged.

The dietary effects of xanthan gum in man

Following a 7-day control period, 5 male volunteers consumed, on each of 23 consecutive days, a weight of xanthan gum equal to 15 times the current acceptable daily intake (10 mg/kg b.w.) approved by the EEC and by the Joint FAO/WHO Expert Committee on Food Additives; thus, the lightest and heaviest of the volunteers consumed 10.4 g and 12.9 g respectively of xanthan daily. Measurements before and at the end of the test period showed that the ingestion of xanthan, as a pre-hydrated gel, acted as a bulking agent in terms of its effects on faecal wet and dry weight and intestinal transit time but had no significant effect on plasma biochemistry, haematological indices, urinalysis parameters, glucose tolerance and insulin tests, serum immunoglobulins, triglycerides, phospholipids and HDL cholesterol, breath hydrogen and breath methane concentrations. There was a moderate (10%) reduction in serum cholesterol and a significant increase in faecal bile acid concentrations. The data indicate that the ingestion of xanthan caused no adverse dietary nor physiological effects in any of the subjects. In particular, all of the enzymatic and other parameters that act as sensitive indicators of adverse toxicological effects remained unchanged.

The dietary effects of gellan gum in humans

Following a 7-day control period, five female and five male volunteers consumed a weight of gellan gum corresponding to 175 mg/kg body weight for 7 days, followed by 200 mg gellan gum per kg body weight for a further 16 days. Measurements before and at the end of the 23-day test period showed that the gellan gum acted as a faecal bulking agent for the male volunteers and for four of the females. Dietary transit time increased for 2 females and 2 males, and decreased for 3 females and 3 males. Faecal bile acid concentrations increased for 4 females and for 4 males; the average increases were from 0.69 to 0.83 mmol/24 h (females) and from 1.22 to 1.44 mmol/24 h (males). Gellan gum ingestion had no significant effect on (a) plasma biochemistry parameters; (b) haematological indices; (c) urinalysis parameters; (d) blood glucose and plasma insulin concentrations; (e) breath hydrogen concentrations. There were no significant changes in HDL cholesterol, triglyceride or phospholipid concentrations. Serum cholesterol concentrations decreased significantly (P less than 0.1) by 13% on average for females, and by 12%, on average, for males. The data indicate that the ingestion of gellan gum at a high level for 23 days caused no adverse dietary or physiological effects in any of the volunteers. In particular, the enzymatic and other indicators of adverse toxicological effects remained unchanged.

Fermentation of wheat bran and gum arabic in rats fed on an elemental diet

1. Gum arabic and wheat bran were added to an elemental diet (100 g/kg) in order to study their metabolism in the caeca of adult male albino Wistar rats. 2. Dry stool weight (g/d) over 12 weeks was 0.70 (SE 0.05) on the elemental control diet. Wheat bran increased mean dry stool weight to 1.09 (SE 0.08), an increase of 56%. There was no significant difference between faecal weights (0.65 (SE 0.08)) of the gum-arabic-supplemented group and the unsupplemented group. 3. Wet caecal-sac weight, dry caecal-contents weight, and faecal and caecal bacterial mass (measured by 2,6-diaminopimelic acid) all increased significantly with the gum-arabic-supplemented diet but not with the wheat-bran-supplemented diet. 4. Total short-chain fatty acids (mostly acetate) increased in the caecum and faeces with the gum-arabic-supplemented diet but not with the wheat-bran-supplemented diet. 5. Breath hydrogen and methane production decreased to negligible amounts over the 12 weeks of the experiment.

Fermentation and subsequent disposition of 14C-labelled plant cell wall material in the rat

A 14C-labelled plant cell wall preparation (14C-PCW) produced from spinach (Spinacia oleracea L.) cell culture exhibits uniform labelling of the major polysaccharide groups (%): pectins 53, hemicellulose 13, cellulose 21, starch 3. This 14C-PCW preparation has been used in rat studies as a marker for plant cell wall metabolism. Metabolism of the 14C-PCW occurred largely over the first 24 h. This was due to fermentation in the caecum. The pectic fraction of the plant cell walls was degraded completely in the rat gastrointestinal tract, but some [14C]cellulose was still detected after 24 h in the colon. Of the 14C, 22% was recovered in the host liver, adipose tissue and skin, 26% excreted as 14CO2 and up to 18% was excreted in the faeces. There was no urinary excretion of 14C. In vitro fermentation using a caecal inoculum showed reduced 14CO2 production, 12% compared with 26% in the intact rat. 14C-PCW is a useful marker to investigate the fate of plant cell wall materials in the gastrointestinal tract. These studies show both bacterial fermentation of the 14C-PCW and host metabolism of the 14C-labelled fermentation products.

The influence of peripheral vascular disease on methanogenesis in man

Methane is produced by anaerobic bacterial metabolism in the colon and is excreted in the breath of only a proportion of healthy adults. Factors influencing methane excretion have still to be elucidated. The colonic vascular circulation may influence the intestinal environment facilitating growth of methanogens. The incidence of breath methane excretion has been investigated in patients with peripheral vascular disease and a control patient group. The proportions of subjects excreting methane in the control hospital group (43%) and in patients with predominantly femoro-popliteal disease (30%) were significantly less than in patients with predominantly aorto-iliac disease (83%) (P less than 0.005 and P less than 0.001, respectively). The presence of abdominal aortic arterial disease appears to be associated with a high incidence of methane excretion.