Influencia de la fermentación colónica en los esteroles de la dieta

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Publication date
2018
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14/12/2018
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Abstract
The addition of plant sterols (PS) to several foods is added due to its hypocholesterolemic effect, in order to “maintain normal blood cholesterol levels” and “prevention of cardiovascular diseases”. PS present low absorption (2-3%), while the absorption of cholesterol range between 30 and 60%. Unabsorbed sterols reach the colon and are transformed by the microbiota. The microbial biotransformation pathway of cholesterol to coprostanol, coprostanone and cholestanol is widely known. PS are also metabolized by the microbiota to phytostanones, phytostenones and phytostanols. The objective of the present doctoral thesis is to evaluate the influence of colonic fermentation on dietary sterols and the impact of these on the intestinal microbiota through in vivo and/or in vitro studies. A method to determination of sterols and its metabolites in feces by gas chromatography with mass spectrometry is developed and validated. In vitro colonic fermentation assays are performed using high concentrations of PS in static and dynamic models (TIM-2). The impact of gut microbiota on sterol after the intake a PS-enriched milk based fruit beverage (2g/day) is studied through a randomized, double-blind crossover trial involving 40 postmenopausal women with moderate hypercholesterolemia, who ingest the beverage daily for 6 weeks. The validated method shows good linearity (r >0.96), high sensitivity (LOD: 0.10-3.88 μg/g freeze-dry feces and LOQ: 0.34-12.94 μg/g), precision (intra and inter-day (RSD%) 0.9-9.2 and 2.1-11.3, respectively) and accuracy (80-119%). In vivo and in vitro studies show that high concentrations of PS modify the biotransformation of sterols, since a reduction in the metabolism of animal sterols has been observed, mainly in the concentration of coprostanol. In addition, an increase in the microbial metabolism of PS, with an increase in colonic concentrations of ethylcoprostanol and ethylcoprostanone has been found. In the presence of high concentrations of PS, the production of short chain fatty acids is similar or in some cases greater than control, therefore the microbial metabolic activity of carbohydrates is not modified. The high concentrations of PS are correlated with a decrease in the proportion of species of Erysipelotrichaceae family and with an increase of Eubacterium hallii and species of the genus Catenibactrerium, Coprococcus and Clostridium. In addition, the production of methylcoprostanone are negatively correlated with the Clostridiales order, with the genera Peptostreptococcus and Methanobrevibacter, and positively with Bacteroides.
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