Curcumin-loaded solid lipid particles by PGSS technology
Graphical abstract
Introduction
In the last decades, pharmaceutical research has devoted many efforts in order to generate new, more potent and highly selective drugs. However, many newly designed molecules failed to access the market due to low clinical acceptability, namely poor biopharmaceutical properties and pharmacokinetic profile. Molecules of natural origin have raised the pharmaceutical industry interest since they are regarded as valuable alternatives to new chemical entities for their intrinsic molecular selectivity toward biological targets and limited toxicity. Accordingly, over the years, traditional medicine has inspired the research of innovative therapeutic options.
Curcuma longa, a herbaceous perennial plant from Zingiberaceae family, commonly cited as “turmeric”, has been used for over 4000 years by Asian medicine for treating gastrointestinal irritation, liver disorders, microbial infections, skin wounds, arthritic pain, stress, and mood disorders [1]. The therapeutic activity of turmeric is ascribed to curcumin, the main biologically active molecule so far isolated from turmeric root. Curcumin, which has been proved to possess potent anti-inflammatory activity, interferes with a variety of pathways regulating the inflammation process by a multi-target mechanism that results in many biological activities, including antioxidant, anticancer, analgesic and gastro-protective activity.
The curcumin molecule contains phenol moieties connected by an unsaturated bond, which confers low polarity, poor solubility in water and high sensitivity to photo and thermal degradation [2], [3]. These features greatly limit the development of suitable formulations. The low chemical stability of curcumin, which is responsible of the short shelf life of curcumin-based products, and the poor water solubility dramatically affects the absorption and bioavailability of this active molecule with consequent unsatisfactory pharmacokinetic profile and reduced efficacy [4], [5], [6].
Encapsulation techniques have been largely studied in order to overcome the poor biopharmaceutical features of many compounds with high pharmacological activity. Micro- and nano-encapsulation can provide a useful mean to enhance the physico-chemical stability of bioactive molecules while improving the drug absorption through physiological barriers [7], [8]. Several papers report the investigation of solid lipid nanoparticles (SLN) as carriers of choice for curcumin [9], [10]. SLN are composed of solid lipids, usually “Generally Recognized as Safe” (GRAS) status conferred by the FDA [11], that endow these vehicles with relatively higher physical stability than that of other lipid-based particulate systems, namely liposomes.
Particle size and composition are the key factors dictating the oral absorption of particulate systems. It is a consensus that particles smaller than 100 nm can be absorbed after oral administration through the intestinal endothelium, which leads to enhanced drug bioavailability [7], [12]. Lipid particles of micrometric scale were also found to enhance the absorption of molecules across the intestinal endothelium as a result of the lipid component effect on drug dissolution and mucosae permeability alteration [12], [13]. Thus, solid lipid particles (SLP) with a broad size range have been studied for pharmaceutical applications.
SLP have been prepared using a variety of excipients including glycerides, waxes and fatty acids. However, one of the main issues associated to the use of these materials is the loss of the encapsulated active molecules from SLP due to crystallization of the lipid matrix through their shelf life [14], [15]. Once the lipid components self-organize in a crystal lattice, the bioactive molecule is forced to phase-separate from the matrix. To delay the crystallization of the lipid matrix and promote the homogeneous dispersion of the active molecules within the matrix, amorphous lipid molecules, such as natural phosphatidylcholines, have been included in the lipid mixtures [16], [17]. Accordingly, 1,2-dilinoleoyl-sn-glycero-3-phosphocholine, the main component of Epikuron200®, was widely used for this purpose. The unsaturation on the two linoleoyl moieties reduces the crystallization of this soybean derived lecithin.
The traditional methods for SLP production present significant drawbacks, such as the use of relevant volumes of organic solvents, residual solvent contamination in the final product, harsh conditions, namely high temperatures. Furthermore, these methods include a number of time consuming steps, which further complicate the SLP preparation [11]. Supercritical fluid (SCF) technology has emerged as an interesting alternative for the production of particulate formulations for a wide range of applications. Carbon dioxide (CO2) is a non-toxic and non-inflammable fluid and possesses a relatively low critical temperature and pressure. CO2 is the gas of choice for supercritical processes, including chromatographic methods for enantioselective separation [18], [19], chemical extraction from natural sources [20], pharmaceutical and cosmetic tailoring [21], food processing [22], as well as for processing of pharmaceuticals that can be degraded under harsh conditions. Furthermore, depending on the nature of the biologically active compound, supercritical CO2 can be used as solvent, anti-solvent or solute [23], [24].
In the “Particles Generated from Gas Saturated Solutions” (PGSS) process, CO2 is employed as a solute. A molten mixture composed of the lipid matrix forming materials and the bioactive molecule is saturated by CO2 at supercritical conditions. This remarkably reduces the viscosity of the molten mass allowing for its outflow to the expansion chamber through a micrometric nozzle. Curcumin loaded SLP have been mainly prepared by hot homogenization [10], [25], [26] and microemulsion [27], [28] techniques. According to the preparation conditions, namely materials and process parameters, these techniques have been found to produce either nanoparticles with size below 100 nm or microparticles with size of a few hundred μm, while the curcumin loading was usually below 5%, w/w [10], [29]. With respect to these methods, SCF-based technologies can operate under mild conditions as it may avoid high temperatures and the use of organic solvents or co-excipients, namely emulsifiers. Furthermore the SCF processes result in straightforward powder production, which limits the number of the overall steps for particle preparation, namely solvent elimination and particle recovery. Therefore, the use of SCF technology can yield beneficial outcomes for the formulation of SLP. For example, curcumin loaded nanoparticles with size below 100 nm and 38%, w/w, drug loading were obtained by anti-solvent supercritical methods [30]. Precipitation by PGSS technique has been found to be an interesting approach for the encapsulation of fragile drugs in SLP [31], [32], [33]. Recent interesting studies showed that PGSS can be successfully used to prepare curcumin/PEG fine powders without drug degradation [34].
In order to exploit the advantages of PGSS in the production of SLP, we investigated for the first time the exploitation of this process for preparation of curcumin loaded SLP for pharmaceutical applications. This work was aimed at investigating the process feasibility and at providing a first preliminary assessment of the effect of the operative conditions, namely DMSO feed and the use of helium in the lipid mixture preparation on the particulate product features by the physical characterization of the particles. At our best knowledge, no study has been reported so far in the available literature describing curcumin loaded lipid particles using PGSS.
Section snippets
Materials
Tristearin (≥99%), dimethysulfoxide (DMSO, 99%), dichloromethane (DCM, ≥99.5%) and citric acid (99%) were purchased from Sigma-Aldrich (St. Louis, MO, USA). Epikuron 200 (soy phosphatidylcoline PC) was a kind gift from Cargill Inc. (Krefeld, Germany). The 98% pure curcumin, HPLC grade methanol, ethanol and acetonitrile were obtained from Merck (Darmstadt, Germany). The CO2 (99.99%), synthetic air (99.99%) and N2 (99.99%) were purchased from Rivoira (Padova, Italy). All chemicals were used as
PGSS bench-scale unit
The preparation of SLP microparticles was carried out using the system shown in Fig. 1 according to a batch process. Liquid CO2 stored in a main reservoir kept at 5 °C by a chiller (Lauda, Würzburg, Germany) was pumped by a piston pump (DOXE Office Meccaniche Gallaratesi, Milan, Italy) to feed the mix chamber and a secondary reservoir. The secondary reservoir worked as a back-pressure chamber to keep the pressure constant inside the mix chamber during the expansion step. The bottom of the mix
Results
The pharmaceutical ingredients used for the SLP preparation, namely lipids and phospholipids, were selected on the basis of their regulatory status and physicochemical properties. All materials are in fact approved by the main regulatory agencies (FDA and EMA) for oral formulations. Furthermore, these materials possess proper fluidity in a large range of combinations suitable for processing the matrixes under supercritical or near-critical conditions.
DMSO was added to the mixture to
Conclusions
The results reported in the present study show that a few main critical operative conditions dictate the PGSS process for the production of curcumin loaded Solid lipid Particles (SLP). The feed ratio of DMSO used for the preparation of the lipid mass as well as the use of helium were found to be relevant to prepare SLP with suitable biopharmaceutical properties. By using small feed ratios of DMSO and helium during the curcumin/lipid mixture preparation it was possible to obtain dimensionally
Acknowledgements
We would like to thank the FIOCRUZ—Unit CPqGM staff for helping with morphological analysis.
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2021, Advanced Powder TechnologyCitation Excerpt :Miglyol 812 is an attractive medium-chain triglyceride oil, with a structure similar to the one of some solid lipids, facilitating their combination [14], and improving the solubility of the encapsulated active compounds [15] into the system. Solid microparticles can be employed in several applications, with relevance for the encapsulation of sensitive compounds providing stabilisation and protection for uses, e.g., in the food industry [16]. Curcumin consists in a natural hydrophobic phenolic compound typically used as a natural food colourant [17], presenting other features including antimicrobial [18–22], anti-inflammatory [23,24] and anticancer properties [25].