Encapsulation of Curcumin-Loaded Liposomes for Colonic Drug Delivery in a pH-Responsive Polymer Cluster Using a pH-Driven and Organic Solvent-Free Process
The present study aimed to develop and optimize liposome formulation for the colonic delivery of biologically active compounds. A strategy to facilitate such targeting is to formulate liposomes with a polymer coating sensitive to the pH shifts in the gastrointestinal tract. To this end, liposomes encapsulating curcumin-chosen as the biologically active compound model-and coated with the pH-responsive polymer Eudragit S100 were prepared and characterized. Curcumin was encapsulated into small
... ated into small unilamellar vesicles (SUVs) by the micelle-to-vesicle transition method (MVT) in a simple and organic solvent-free way. Curcumin-loaded liposomes were coated with Eudragit S100 by a fast and easily scalable pH-driven method. The prepared liposomes were evaluated for size, surface morphology, entrapment efficiency, stability, in vitro drug release, and curcumin antioxidant activity. In particular, curcumin-loaded liposomes displayed size lower than 100 nm, encapsulation efficiency of 98%, high stability at both 4 • C and 25 • C, high in vitro antioxidant activity, and a cumulative release that was completed within 200 min. A good Eudragit S100 coating which did not alter the properties of the curcumin-loaded liposomes was obtained. The present work therefore provides a fast and solvent-free method to prepare pH-responsive polymer-coated liposomes for the colonic delivery of biologically active compounds. Molecules 2018, 23, 739 2 of 15 its antioxidant, anti-inflammatory, antiamyloid, antidiabetic, anti-cystic fibrosis, and antimicrobial properties [1, 2] . The interest in this molecule has undergone a tremendous increase since its anticarcinogenic activity also emerged, demonstrating its effectiveness through multiple mechanisms of action at various stages of the disease development [3, 4] . However, curcumin shows a very poor bioavailability in vivo, due to its low aqueous solubility and instability, rapid metabolism, and clearance, that definitely limits its use both as a nutraceutical and as a drug  . Therefore, various strategies devoted to overcoming this limitation have been developed over the years, from the inclusion in suitable (nano)carriers to chemical modification and cocrystal synthesis [2,       . A very popular and promising approach exploits the loading of curcumin into phospholipid-based liposomes. Liposomes are small vesicles arising from the spontaneous self-assembling of phospholipids dispersed in an aqueous medium. Lipid molecules organize themselves to form a double-layer structure very close to the natural cell membranes, enclosing an internal aqueous core. Liposomes are therefore biocompatible and biodegradable, and are widely used as delivery systems for stabilizing both hydrophilic and hydrophobic drugs and overcoming cellular and tissue barriers. Several drug-loaded liposomes are currently in clinical use  . Curcumin can be incorporated into liposomes with good yields and in a stable manner, with sustained release properties. Furthermore, compared with free curcumin, curcumin-loaded liposomes exhibited good stability against neutral and alkaline pH levels  that are found at the absorption site in the colonic region. Colon-targeted drug delivery proves to be a profitable strategy for the treatment of both local and systemic diseases. Indeed, this region of the digestive system is characterized by near-neutral pH conditions, low enzymatic activity, low bile salt concentrations, and long residence time  . However, liposomes are not naturally suited to oral drug delivery due to their susceptibility to digestion  . Coupling the advantages of colonic and liposome drug delivery is a goal that can be achieved by coating vesicles with a suitable polymer layer, such as chitosan derivatives [6, 13] or methacrylic acid copolymers [11, 12, 14] . In particular, Eudragit S100 is a polymer made of methacrylic acid and methacrylic acid methyl ester, with pH-dependent solubility and suitability for colonic drug delivery. Indeed, it allows the release of a cargo in the region of the gastrointestinal tract of pH > 7, that is, the large intestine or colon, where proteolytic enzymes and bile salt are low in concentration  . Previous works have shown the coverage of liposomes with Eudragit S100, exploiting the electrostatic interaction between the anionic polymer and cationic liposomes or using a double emulsion-solvent evaporation technique [11, 12] . In this work, we encapsulated curcumin into small unilamellar vesicles (SUVs) or nanoliposomes by the micelle-to-vesicle transition (MVT) method in a simple, easy, effective, and organic solvent-free way  ; and without introducing cationic components into the bilayer which may lead to toxic effects both in vitro and in vivo  . Afterwards, these curcumin-loaded liposomes were embedded into pH-responsive Eudragit S100 clusters. Differently from what has been proposed previously , we have achieved this encapsulation without the use of problematic organic solvents (dichloromethane, propanol, etc.) by a fast, simple, and easily scalable pH-driven method.