Preparation , Analysis and Cholesterol Lowering Effect of a Novel Microcrystalline β - sitosterol Suspension in Oil

Christiansen, L.I, 2002. Preparation, analysis and cholesterol lowering effect of a novel microcrystalline β-sitosterol suspension in oil and phase behaviour of β-sitosterol with cholesterol. Dissertationes Biocentri Viikki Universitatis Helsingiensis 11/2002, pp. 54 ISBN 952-10-0508-4 (print) ISBN 952-10-0509-2 (pdf) ISSN 1239-9469 Few efforts have been made to formulate preparations suitable for oral administration of free plant sterols. Technological problems are associated with free crystalline plant sterols due to their poor solubility in oil and insolubility in water and relatively large daily doses. Crystallisation of anhydrous and hydrated cholesterol crystals in several environments, including physiological conditions, has been widely studied. On the contrary, few structural studies concerning free crystalline β-sitosterol or other plant sterols have been published. In the present study, preparation and analyses of a novel microcrystalline β-sitosterol suspension in oil and its cholesterol lowering effect is described. In addition, different pseudopolymorphic forms of β-sitosterol are characterised and phase behaviour of a βsitosterol-cholesterol binary system in aqueous as well as in non-aqueous environments is studied. β-sitosterol was observed to exist in three different pseudopolymorphic forms with different water contents: anhydrated, hemihydrated and monohydrated crystals. β-sitosterol suspensions in oil were prepared by adding water to supersaturated sterol in oil solutions. Addition of water to the composition resulted in a decrease in sterol solubility in oil and in the formation of monohydrated needle-shaped crystals instead of plate-like anhydrous crystals. Needle-shaped particles formed structured suspensions with shear thinning behaviour. A high sterol concentration resulted in high supersaturation and thus in formation of microcrystalline (crystal length ≈ 10 μm) crystals. Microcrystalline β-sitosterol suspension in oil lowered effectively serum cholesterol levels in hypercholesterolemic subjects and the effect was comparable to earlier results with fat-soluble esterified plant sterols and stanols. A daily dose of 1.5 g plant sterol in microcrystalline form was enough to reach the significant cholesterol lowering effect. β-sitosterol and cholesterol exhibited solid solubility over a wide range of different proportions. The crystal structure, thermal behaviour and habit of the mixed crystals varied with composition. Cholesterol, β-sitosterol, and the mixed crystals formed anhydrous crystals in the absence of water and monohydrated crystals in the presence of water. The presence of β-sitosterol decreased the total sterol solubility in the aqueous system. Thus, the presence of plant sterols may facilitate the crystallisation of cholesterol in physiological environments. On the basis of the present study, it is quite evident that crystallisation of sterols in the lumen of intestine may lead to restricted absorption of cholesterol and thus cause a decrease in serum cholesterol levels.