O/W-Emulsion as Formed by Cholesterol-Bearing Pullulan

Colloidal stability formed from trioctanoylglyceride(TriC₈) and cholesterol-bearing pullulans (CHP) has been investigated. Pullulans (M_w. 30000, 50000, and 137000) were substituted in part by cholesteryl groups, and the substitution degree of the cholesterol moieties was 2-6 per hundred glucose units. When TriC₈ was emulsified with a given amount of CHP under sonication, a very stable O/W-emulsion was obtained. The hydrodynamic diameter determined by DLS was approximately 100-200 nm. The particle size of oil droplets was due to the temperature, the duration, and the power of sonication. The higher the substitution degree of cholesterol of CHP employed was, the more stable the emulsion obtained was, and the less the amount of CHP required was to obtain relatively stable emulsion. Similarly, the larger the molecular weight of CHP was, the smaller the particle size was. The O/W-emulsion so obtained was stable enough even in the presence of the Ca²⁺ ion of physiological concentration. Using this technique, a lipophilic antitumor drug, α-linolenic acid (ALA), also was able to be well emulsified by mixing with a suitable amount of TriC₈ in the presence of CHP. These newly developed O/W-emulsion stabilized by cholesterol-bearing pullulan derivative was promising in making a potent carrier of lipophilic drugs.