Each sample was repeated three times using 105 cells per test.
The cells treated with PBS were set as the control. Results and discussion Preparation and characterization of BLPs Formulation variables selleck screening library influence the physicochemical properties of insulin-loaded liposomes such as entrapment efficiency and particle size [32, 33]. It is of high importance to effectively entrap insulin into liposomes so as to reduce the bulk dosage and avoid waste of drug. The main variables including lipid/cholesterol ratio, drug/lipid ratio, the buffer pH upon hydration, and phase ratio in preparing W/O emulsion were optimized to obtain liposomes with high insulin entrapment efficiency and suitable particle size. Figure 1 shows the effects of preparative variables on the entrapment efficiency and particle size. The presence of cholesterol exerts significant influence on the properties of the lipid bilayers of the liposomes. It is known that the addition of cholesterol to lipid bilayers decreases its permeability to water [34]. Suitable lipid/cholesterol ratio will accommodate more insulin molecules and generate liposomes with desirable membrane fluidity, which are helpful to prevent the leakage of insulin from the internal aqueous compartments. The liposomes with a lipid/cholesterol ratio of
3/1 or 4/1 produced higher insulin entrapment (Figure 1A). Considering the factors that influenced drug BVD-523 supplier entrapment and 3-deazaneplanocin A resistant permeability to water, a lipid/cholesterol ratio of 3/1 seemed to be more promising. The effect of drug/lipid ratio on the entrapment efficiency Ponatinib molecular weight is shown in Figure 1B, from which we could see that the entrapment efficiency increased as the lipid content increased. Generally,
high proportion of lipid in liposomes can generate more space to host more insulin molecules. Figure 1C showed that the buffer solution of pH 3.8 used for hydration was most suitable to prepare liposomes. Lower entrapment efficiencies were obtained around the isoelectric point of insulin (pH 5.3 to 5.4), which may be attributed to the loss of insulin because of reduced solubility. The particle size of liposomes increased as the pH increased owing to the change of surface charge. In general, natural phospholipids such as soybean or egg lecithins are negatively charged. When pH goes up, the charge density of phospholipids will raise correspondingly, which results in more electrostatic repulsion that is unfavorable to form small liposomes. Higher organic-aqueous phase ratio resulted in higher entrapment efficiency as observed from Figure 1D because increasing the organic phase was beneficial to the formation of fine emulsions, which would lead to fine insulin dispersion in the mixed lipids. Figure 1 The effects of formulation variables on entrapment efficiency and particle size. (A) Ratios of lipid/cholesterol and (B) drug/lipid, (C) pH upon hydration, and (D) organic/aqueous ratio of phase.