Feasibility of producing pectin-coated gastroresistant liposomes

Polymer-coated liposomes are extensively studied for the administration of bioactives, as they have the ability to improve physical stability, control release and protect the encapsulated active during digestion (increasing its gastro-resistance), since liposomes have low resistance to gastric pH, salts bile and enzymes. Pectin is a polysaccharide already known by the food industry as a gelling, thickening and stabilizing agent, with the advantage of being non-toxic and having a low production cost. In addition, pectin is also resistant to low pH conditions and to digestion by proteases and amylases present in the stomach, characteristics that make pectin a promising polymer for coating liposomes and making it gastro-resistant. In this study, Lipoid S45 phospholipid (PS45, non-hydrogenated phospholipid, composed of at least 45% phosphatidylcholine and 10-18% phosphatidylethanolamine) was used to produce liposome by the ultrasonic method (tip homogenizer). Then, a dispersion of pectin (polysaccharide mixed in 5 mM phosphate buffer and pH 7.0) was added to the liposomes under continuous magnetic stirring. Pectin was used at concentrations of 250, 500 and 750 mg/100 mL, named as R1, R2 and R3 respectively. The addition of pectin to the liposomes was standardized and performed by dripping with the aid of a peristaltic pump. Liposomes were characterized for hydrodynamic diameter, size distribution, polydispersity, zeta potential and accelerated stability (LumiSizer). The liposomes presented mean hydrodynamic diameters of 132 ± 8.4 nm (without coating), 130 ± 1.2 nm (R1), 146 ± 1.5 nm (R2) and 177 ± 2.1 nm (R3) remaining stable for 21 days of refrigerated storage, and vesicle size distributions were multimodal. The polydispersity values showed values of 0.23 ± 0.02, 0.34 ± 0.03, 0.39 ± 0.01, 0.44 ± 0.03 for the dispersions produced with no coatings and with coatings R1, R2 and R3 respectively. This increase in the hydrodynamic diameter of the coated liposomes is a result of the polymeric coating. The zeta potential values obtained were -63.11 ± 7.11 mV (without covering), -24.67 ± 2.32 mV, -25.68 ± 1.44 mV and - 35.13 ± 2.75 mV for R1, R2 and R3 respectively. These pectin-coated liposome zeta potential values were affected by the interaction of pectin surface charge with liposome charge. The instability index for the uncoated liposome was 0.044 ± 0.006 and for the coated ones it was 0.159 ± 0.007 (R1), 0.166 ± 0.002 (R2) and 0.655 ± 0.007, indicating that the coating with a greater amount of pectin led to a increased system instability.
Therefore, the data obtained indicated that the production of pectin-coated liposomes is feasible, and they remained stable for 21 days, but that there are limitations to the amount of polysaccharide that can be added to them so that the coating is effective and the presence of excess pectin does not destabilize the system.