Phytosterol Ester Constituents Affect Micellar Cholesterol Solubility in Model Bile |
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Authors: | Andrew W Brown Jiliang Hang Patrick H Dussault Timothy P Carr |
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Affiliation: | (1) Department of Nutrition and Health Sciences, University of Nebraska-Lincoln, 316 Leverton Hall, Lincoln, NE 68583-0806, USA;(2) Department of Chemistry, University of Nebraska-Lincoln, Lincoln, NE, USA; |
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Abstract: | Plant sterols and stanols (phytosterols) and their esters are nutraceuticals that lower LDL cholesterol, but the mechanisms
of action are not fully understood. We hypothesized that intact esters and simulated hydrolysis products of esters (phytosterols
and fatty acids in equal ratios) would differentially affect the solubility of cholesterol in model bile mixed micelles in
vitro. Sodium salts of glycine- and taurine-conjugated bile acids were sonicated with phosphatidylcholine and either sterol
esters or combinations of sterols and fatty acids to determine the amount of cholesterol solubilized into micelles. Intact
sterol esters did not solubilize into micelles, nor did they alter cholesterol solubility. However, free sterols and fatty
acids altered cholesterol solubility independently (no interaction effect). Equal contents of cholesterol and either campesterol,
stigmasterol, sitosterol, or stigmastanol (sitostanol) decreased cholesterol solubility in micelles by approximately 50% compared
to no phytosterol present, with stigmasterol performing slightly better than sitosterol. Phytosterols competed with cholesterol
in a dose-dependent manner, demonstrating a 1:1 M substitution of phytosterol for cholesterol in micelle preparations. Unsaturated
fatty acids increased the micelle solubility of sterols as compared with saturated or no fatty acids. No differences were
detected in the size of the model micelles. Together, these data indicate that stigmasterol combined with saturated fatty
acids may be more effective at lowering cholesterol micelle solubility in vivo. |
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