Inhibition Efficiency of Cholesterol Monohydrate Crystallization by Linoleic Acid and Ethyl Linoleate

Abstract

Inhibiting the crystallization of cholesterol monohydrate (ChM) crystals is crucial for preventing the progression of high cholesterol symptoms into gallstones and atherosclerosis. In recent years, cholesterol-lowering functional substances containing linoleic acid (LA) or its analogue ethyl linoleate (EL) have emerged as promising alternatives to pharmaceuticals, offering similar functions without the associated side effects. In this study, the impact of LA or EL on the crystallization of ChM crystals was investigated. The results demonstrated that both additives effectively prolonged the nucleation induction time of ChM crystals and therefore inhibited the nucleation of ChM crystals. However, the nucleation inhibition efficiency of LA on ChM nucleation was higher than that of EL. This difference is due to the stronger interaction of LA containing carboxyl groups with the cholesterol molecules in the solution than that of EL containing ester groups. Furthermore, the growth kinetics of ChM crystals were revealed by an in situ optical microscope. The results illustrated that the growth rate of ChM crystals along [010] and [100] directions decreased in the presence of LA or EL. Along the [010] direction, the growth inhibition efficiency of LA was always higher than that of EL. This is because the binding between LA with carboxyl groups and the hydroxyl groups exposed on the (010) face of the ChM crystals was stronger than those of ester groups in EL. Meanwhile, along the [100] direction, the growth inhibition efficiency of EL is always higher than that of LA. This is because EL binds to the exposed methyl groups on the (100) face of the ChM crystals primarily through van der Waals forces and other noncovalent interactions, enhancing the growth inhibition efficiency on the (100) face of ChM crystals. These binding modes have been confirmed by molecular simulation. This study not only demonstrated the importance of the molecular structure of additives in modulating ChM crystallization behavior but also provided insights that develop novel therapeutic strategies for preventing atherosclerosis, cardiovascular diseases, and cholesterol gallstone formation.