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Barley β -glucan reduces blood cholesterol levels via interrupting bile acid metabolism

2017; Cambridge University Press; Volume: 118; Issue: 10 Linguagem: Inglês

10.1017/s0007114517002835

1475-2662

Yanan Wang, Scott Harding, Sijo Joseph Thandapilly, Susan M. Tosh, Peter J.H. Jones, Nancy Ames,

Natural Antidiabetic Agents Studies

Abstract Underlying mechanisms responsible for the cholesterol-lowering effect of β -glucan have been proposed, yet have not been fully demonstrated. The primary aim of this study was to determine whether the consumption of barley β -glucan lowers cholesterol by affecting the cholesterol absorption, cholesterol synthesis or bile acid synthesis. In addition, this study was aimed to assess whether the underlying mechanisms are related to cholesterol 7 α hydroxylase ( CYP7A1 ) SNP rs3808607 as proposed by us earlier. In a controlled, randomised, cross-over study, participants with mild hypercholesterolaemia ( n 30) were randomly assigned to receive breakfast containing 3 g high-molecular weight (HMW), 5 g low-molecular weight (LMW), 3 g LMW barley β -glucan or a control diet, each for 5 weeks. Cholesterol absorption was determined by assessing the enrichment of circulating 13 C-cholesterol over 96 h following oral administration; fractional rate of synthesis for cholesterol was assessed by measuring the incorporation rate of 2 H derived from deuterium oxide within the body water pool into the erythrocyte cholesterol pool over 24 h; bile acid synthesis was determined by measuring serum 7 α -hydroxy-4-cholesten-3-one concentrations. Consumption of 3 g HMW β -glucan decreased total cholesterol (TC) levels ( P =0·029), but did not affect cholesterol absorption ( P =0·25) or cholesterol synthesis ( P =0·14). Increased bile acid synthesis after consumption of 3 g HMW β -glucan was observed in all participants ( P =0·049), and more pronounced in individuals carrying homozygous G of rs3808607 ( P =0·033). In addition, a linear relationship between log (viscosity) of β -glucan and serum 7 α- HC concentration was observed in homozygous G allele carriers. Results indicate that increased bile acid synthesis rather than inhibition of cholesterol absorption or synthesis may be responsible for the cholesterol-lowering effect of barley β -glucan. The pronounced TC reduction in G allele carriers of rs3808607 observed in the previous study may be due to enhanced bile acid synthesis in response to high-viscosity β -glucan consumption in those individuals.