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Mar. Drugs 2020, 18, 217 6 of 11 The results presented in Figure 3 indicate that growth-inhibition increased for all types of lecithin coated with chitosan. These data indicate the increased sensitivity of MCF-7 cells toward curcumin-loaded chitosan-coated liposomes. Rapeseed and soya liposomes induced the proliferation of MCF7 cells at low concentrations, but they increased the growth-inhibition at higher concentrations. Salmon liposomes were toxic to MCF-7 cells at different concentrations. Moreover, the coating of liposomes with chitosan led to the growth of MCF7 cells at low concentrations, whereas it significantly increased growth-inhibition at higher concentrations. 3. Materials and Methods Salmon lecithin, from Salmo salar, was obtained by enzymatic hydrolysis. The lipids were extracted by the use of an enzymatic process without any organic solvent, as described previously [53], whilst rapeseed and soya lecithins were commercial lecithins from the Solae Europe SA society. Chitosan (deacetylation degree up to 75%), curcumin, boron trifluoride (14% in methanol), acetonitrile (≥99.9%), chloroform (≥99.9%), methanol (≥99.9%) and hexane (≥99.9%) were all purchased from Sigma-Aldrich (Saint-Quentin-Fallavier, France) and Fisher Scientific (Illkirch, France). Acetic acid (≥99.8%) was supplied by Prolabo-VWR. All the organic solvents were analytical grade reagents. 3.1. Preparation of Chitosan-coated Liposomes To prepare the liposome solution, 1.5 g of lecithin and 10 mg curcumin were dissolved in ethanol, then a thin lipid film was formed on the wall of the flask using a Rotavapor by completely evaporating the ethanol under vacuum, then the lipid film was hydrated with 47.5 mL of distilled water and the suspension was agitated using a magnetic stirrer for 4 h in an inert nitrogen atmosphere. In total, 0.5 g of chitosan and 0.5 mL of acetic acid were then added to the solution. The suspension was mixed again for 4 h under the same conditions. After that, the solution was first sonicated at 40 kHz for 5 min (1s on, 1s stop) in an ice bath and then homogenized using a high-pressure homogenizer (EmulsiFlex-C3, Sodexim SA, Muizon, France) in aliquots of 50 mL under a pressure of 1500 bar for 7–8 cycles. 3.2. Physicochemical Characterization and Stability Analysis The mean diameter, particle size distribution and ζ-potential of vesicles were determined upon the dilution of the samples (1:200) using the DLS technique, by employing a Zetasizer Nano ZS (Malvern Instruments Ltd., Worcestershire, UK). Empty and curcumin-loaded chitosan-coated liposomes were stored in a drying room at 4 ◦C and 37 ◦C for five weeks. The mean particle size, PDI and ζ-potential of all formulations were analyzed every 3 days. 3.3. Encapsulation Efficiency of Curcumin The curcumin’s concentration was determined via reverse-phase HPLC (Shimadzu, Kyoto, Japan), using a Zorbex SB-C18 column (5μm, 4.6mm×250mm). The mobile phase consisted of 2% acetic acid, methanol and acetonitrile, at a ratio of 30:5:65. The elution was carried out with a flow rate of 0.5 mL/min. A twenty microliter aliquot of the solution was injected into the HPLC at ambient temperature and a wavelength of 425 nm was used for detection. The retention time for curcumin was about 8.49 min and its linearity was obtained in the range of 2 to 20 μg/mL. The total drug content of the suspensions was determined by dissolving chitosan-coated liposomes in methanol and measuring the drug content with HPLC. First, the entrapment efficiencies of the curcumin were determined by the centrifugation of the nanoliposome at 1000 g for 10 min, to separate the free curcumin, and then the supernatant was re-centrifuged at 200,000 g for 4 h to separate the unloaded curcumin. The free drug in the supernatant was detected by HPLC. The total drug content of the suspensions was also determined using a similar procedure. The encapsulation efficiency was calculated as: EE % = ((total drug - free drug)/total drug) × 100PDF Image | Growth-Inhibitory Effect of Chitosan-Coated Liposomes Encapsulating Curcumin
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