Plant sterol/stanol can decrease blood cholesterol level by inhibiting cholesterol absorption in the intestine. One of the mechanisms for the cholesterol-lowering effect has been reported that the competitive solubilization between cholesterol and sterol/stanol in bile salt micelles is essential cause. I have performed competitive solubilization experiments in simplified system (bile salt-cholesterol-competitive compound) to clarify the cholesterol-lowering effect by changing the molecular shape of compounds including polycyclic aromatic compounds, long-chain alkylbenzenes, and sterol/stanol species. The results of competitive solubilization revealed that cholestanol has the largest cholesterol-lowering effect. In contrast, brassicasterol and stigmasterol have little ability to decrease cholesterol solubility in a mixed binary system. By applying thermodynamic analyses to these results, the Gibbs energy changes (ΔG°) of solubilization for sterol/stanol species with cholesterol-lowering effects show larger negative values than that for cholesterol. Their molecular dynamics and solubilization sites were measured by the ¹H-NMR method. These results indicated that the aromatics were solubilized in micellar palisade layer interacting with 19-methyl protons, whereas, the sterols were solubilized to match the micellar structure via the steroids interaction.

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