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Biomedical subjects

G Siebert

Publications and source records attributed to G Siebert.

At least 37 records · Page 2Linked to original sources
PubMed1987

In vitro assessment of nystose as a sugar substitute.

Nystose represents a fructooligosaccharide with two fructose molecules linked via beta(1----2) bonds to the fructosyl moiety of sucrose. This tetrasaccharide was subjected to an array of in vitro tests designed for the assessment of potential sugar substitutes before animal or human studies. beta-Fructosidase from yeast cleaved nystose at about 5% of the initial rate observed with sucrose. The terminal fructose was released first. Glycosyltransferase from Streptococcus mutans #620 did not utilize nystose for the formation of a glucan-type polysaccharide. Anaerobic fermentation of nystose by a suspension of mixed dental plaque microorganisms and by S. mutans NCTC 10449 was about half as fast as with sucrose. Thin-layer chromatography at various reaction times with S. mutans NCTC 10449 indicated the terminal fructose as the site of first attack. Analyses for free monosaccharides confirmed these data because free fructose exceeded free glucose at early reaction times far more than would follow from the 3:1 ratio of fructose to glucose in the nystose molecule. High pressure liquid chromatography assays demonstrated lactic and acetic acids as the main fermentation products. Carbohydrases from human jejunal mucosa did not attack nystose. However, cecal anaerobic microorganisms of the rat fermented nystose rapidly into acids.

Animals↗
PubMed1987

Mitochondrial malic enzyme in human leukocytes.

Leukocyte samples from 316 unrelated blood donors were screened for malic enzyme (MEM). The frequency of the common allele in this investigation was MEM1 = 0.63. There is evidence for the existence of a rare fourth allele MEM4.

Humans↗
PubMed1986

[A stepwise method of evaluating sugar substitutes--a preliminary study using enzymes. 1. Alpha-glucosidase from yeast].

alpha-Glucosidase from yeast was checked for its catalytic potency under a variety of experimental conditions. Michaelis constants and maximal velocities are reported for 7 disaccharides of the glucosyl-fructosyl or glucosyl-glucosyl type, 4 disaccharide alcohols, and 2 mixtures of each 2 disaccharide alcohols. Reduction of a carbonyl group is of less importance for the substrate properties than the type of the glycoside bond; consequences for the suitability of potential sugar substitutes are derived.

Disaccharides↗
PubMed1986

Prefeeding-dependent anaerobic metabolization of xenobiotics by intestinal bacteria--methods for acarbose metabolites in an artificial colon.

The biotransformation of Acarbose (Bay g 5421) by an artificial in vitro system with viable intestinal microorganisms was investigated. The bacteria were obtained from the colon of man or from the caecum and colon of rats and were incubated anaerobically with 14C-Acarbose in a nutrient solution. The metabolites were separated and purified by chromatographic methods and identified by nuclear magnetic resonance (1H; 13C) spectrometry and by mass spectrometry. Metabolites in man and rat are component 2 (minus the terminal glucose of Acarbose), a basic disaccharide consisting of rings B and C, and component 1. This latter substance is formed, after hydrolytic cleavage of the internal glucose of Acarbose, by spontaneous rearrangement of rings A and B (Acarviosine) into a tricyclic oxazolidine. The metabolite pattern of Acarbose is changed profoundly after several weeks of pretreatment of man or rat with this compound. The microflora adapted in such a manner yields in addition methylated, hexosylated, and n-butyroylated derivatives of Acarbose and/or component 2.

Acarbose↗
PubMed1986

An experimental study of bio-availability of fluoride from dietary sources in man.

After single, oral doses, 8 h profiles of fluoride (F) concentrations in plasma and saliva, and 24 h urinary excretions were determined in healthy adult volunteers. Bio-availability of F from dietary sources was evaluated in relation to that of NaF. Between 2 and 10 mg of F administered all 3 variables were dose-dependent. However, digestion, the chemical state of F, and interaction with accompanying foods may modify the kinetics of F passage through the human body. Low bio-availabilities were observed for most solid foods such as fish and algal flour and for mammalian and fish bones, when used as typical components of fluoride-rich foods such as meat- and fish-products. This data is important in the determination of optimum levels of F supplementation in human nutrition for caries-prevention programmes.

Adult↗
PubMed1985

Acesulfame K, cyclamate and saccharin inhibit the anaerobic fermentation of glucose by intestinal bacteria.

The caecal microflora of Cara rats was incubated in the pH stat with glucose under anaerobic conditions, and the acid production was measured. In the presence of the sweeteners Acesulfame K, Cyclamate and Saccharin, inhibition of the fermentation of glucose was observed with ED50 values of 260, 251, and 140 mM, respectively. The nutritional relevance of these observations is probably slight; an interpretation in terms of bacterial physiology leads to the proposal that the sweeteners may act on glucose transport systems at the bacterial cytomembrane.

Anaerobiosis↗
PubMed1985

Effect of Acarbose on the production of hydrogen and methane and on hormonal parameters in young adults under standardized low-fibre mixed diets.

Short and middle term effects of Acarbose were studied in volunteers on a standardized, low-fibre, mixed diet for the development of tolerance phenomena with gas exhalations and some peptide hormone levels as main parameters. Both hydrogen and methane were measured quantitatively as diurnal profiles. Acarbose caused an about 20-fold increase of H2 exhalation and had only moderate effects on methane production, indicating the presence of fermentable carbohydrates in the large bowel. Methanogenic individuals exhaled significantly less H2 than did non-methanogenic subjects. Changes in blood glucose, serum insulin, GIP, gastrin, and plasma glucagon, caused by Acarbose, reflected delayed glucose absorption and were plausible within the regulatory framework of carbohydrate assimilation. When the Acarbose regime was maintained for 5 weeks on a controlled diet, abdominal sensations like e.g. meteorism declined remarkably while carbohydrate fermentation remained high and lowered GIP was sustained. Thus functional responses of the gastro-intestinal tract to altered carbohydrate supplies, elicited by Acarbose, were found by 3 independent parameters: anaerobic gas production, peptide hormone levels, and subjective abdominal sensations. The objective parameters seem to remain constant in the longer run, while subjective parameters show long-term adaptation.

Acarbose↗
PubMed1985

Fluoride content of selected human food, pet food and related materials.

A survey was made of the fluoride content of selected human foods, some animal feeds, and related materials, with the purpose of a better characterization of products whose fluoride may contribute to the intake of fluoride by man as well as by some kinds of animals. Uptake of fluoride, especially from food with or without a foregoing food chain, was found to be more widely spread than has been documented previously. The major source of fluoride is represented by marine organisms, regardless of the ways by which man or animals are exposed to fluoride. As a consequence of the detailed analytical data given, recommendations would extend towards i) a more wide-spread analytical control of foods and feeds for fluoride, ii) an intensified assessment of fluoride bioavailabilities from foods and feeds, and iii) the consideration of such data in the evaluation of fluoride supplementations for optimized intakes, as recommended.

Animal Feed↗
PubMed1985

Dose dependence of breath hydrogen and methane in healthy volunteers after ingestion of a commercial disaccharide mixture, Palatinit.

Breath hydrogen and methane were determined by gas chromatography in eleven normal individuals given a low-fibre, mixed diet (control) and after ingestion of 20-50 g Palatinit/d, an equimolar mixture of D-glucosyl-alpha(1----1)-D-mannitol and D-glucosyl-alpha(1----6)-D-glucitol (Isomalt). A linear relation was found (r 0.85; P less than 0.001) between the amount of Palatinit ingested and breath H2 per 10 h in subjects who did not exhale methane. If methane was formed in addition to H2, the sum of both gases followed a linear dose-effect relation. The mouth-to-caecum time, indicated by the first increase in breath H2 after ingestion, was shortened by about half, yet no sign of diarrhoea was observed. Stool weight and stool frequency did not change significantly. The linear relation between a dose of 20-50 g Palatinit and exhalation of H2 (eventually plus methane) indicated that a relatively constant fraction of the dose given underwent cleavage and absorption in the small intestine, the remainder being transported into the large bowel. Microbial gas formation in the colon as well as the fractional transfer of these gases into the expiratory air occurred at fixed proportions, thus allowing an insight into colonic microbial contributions to carbohydrate utilization in the human large bowel.

Adult↗