Development and optimization of baicalin-loaded solid lipid nanoparticles prepared by coacervation method using central composite design

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Abstract

The objective of this study was to design and optimize a novel baicalin-loaded solid lipid nanoparticles (SLNs) carrier system composed of a stearic acid alkaline salt as lipid matrix and prepared as per the coacervation method in which fatty acids precipitated from their sodium salt micelles in the presence of polymeric nonionic surfactants. A two-factor five-level central composite design (CCD) was introduced to perform the experiments. A quadratic polynomial model was generated to predict and evaluate the independent variables with respect to the dependent variables. The composition of optimal formulation was determined as 0.69% (w/v) lipid and 26.64% (w/w) drug/lipid ratio. The results showed that the optimal formulation of baicalin-loaded SLN had entrapment efficiency (EE) of 88.29%, particle size of 347.3 nm and polydispersity index (PDI) of 0.169. The morphology of nanoparticles was found to be nearly spherical in shape by scanning electron microscopy (SEM) observation. The differential scanning calorimetry (DSC) analysis indicated that the drug incorporated into SLN was not in an amorphous form but in a crystalline state. The Cmax, MRT, AUMC0→∞ and AUC0→∞ values of SLN were approximately 1.6-fold, 1.9-fold, 5.0-fold and 2.6-fold greater than that of reference preparation, respectively.

Introduction

Solid lipid nanoparticles (SLNs) are particles with a mean diameter between 50 and 1000 nm, which were developed at the beginning of the 1990s as a drug delivery system in order to overcome the drawbacks associated with the traditional colloidal dispersions (Muller et al., 2000). The development of SLN has attracted an increasing attention in pharmaceutical fields during recent years owing to the excellent tolerability and advantages compared to liposomes or other polymeric nanoparticles (Attama, 2011). Currently SLN has been considered as one of the most promising drug carriers and administrated in many routes for dermal, peroral, parenteral, ocular, pulmonary applications. Several techniques for SLN fabrication have been developed in the last decade, including high-pressure homogenization, microemulsion techniques, and solvent emulsification evaporation methods (Zhang et al., 2009). Each of the mentioned techniques has its own disadvantage, such as the need for technically sophisticated equipment, the high operative temperature, or the use of toxic organic solvent (Corrias and Lai, 2011). The coacervation method is another novel, solvent-free technique that has been reported recently in the literature for the preparation of SLN (Battaglia et al., 2010). This method depends on slowly neutralization of fatty acids alkaline salts with an acidic solution (coacervating solution) in the presence of different stabilizing agents. When the pH of the micellular solution of fatty acid salts is lowered, precipitation of solid lipid micelles consisting of fatty acids occurs due to proton exchange between the acid solution and the soap (Bianco et al., 2010). By offering a feasible and accessible method, at present this technique has opened a promising approach to circumvent the forementioned shortcomings in SLN preparation process.

A coherent strategy for successful evaluation and optimization of the formulation parameters in an efficient approach is necessary. It is generally accepted that the property of SLN is under the influence of the relative amount of lipid and ratio of solid lipid to drugs in the formulation. However, a systematic investigation of the simultaneous influence of multiple formulation variables on the SLN prepared by means of coacervation method has not yet been undertaken. Therefore the objective of the present study was to probe the different variables affecting the physicochemical characterizations of SLN in order to obtain the maximum entrapment efficiency (EE) and the smallest particle size as possible.

Response surface methodology (RSM), supported by statistical software, is a well-established approach for pharmaceutical formulation development and optimization allowing extraction of maximal information out of few well-designed experiments. Central composite factor design (CCD), one of the techniques in RSM, is suitable for pharmaceutical blending problems allowing investigation with the least number of experiments and selection of the optimal composition for achieving the presetting target (El-Malah et al., 2006). CCD has been extensively adopted to optimize the nanoparticulate formulations (Gonzalez-Mira et al., 2011, Jin et al., 2008). Those studies demonstrated the apparent advantage of CCD utilization in the formula optimization process for drug delivery system design.

Baicalin (7-D-glucuronic acid, 5,6-dihydroxy flavone) (Fig. 1), one of the major bioactive flavone glucuronides present in the radix of Scutellaria baicalensis, is generally used in traditional Chinese medicine as a remedy for the treatment of inflammation, fever and allergic diseases (Xing et al., 2005). Due to the glycosyl group on the ring, baicalin is low hydrophilic and poorly absorbed after oral administration, which causes low bioavailability and limits its therapeutic efficacy and clinical application (Shen et al., 2003, Tsai and Tsai, 2004).

It is generally accepted that SLN has been proposed as a significant drug carrier system, thus incorporation of baicalin into SLN carrier may be regarded as a potential approach for oral administration in order to improve the bioavailability. Attempts of enhancement in ocular bioavailability of baicalin using nanoparticulate drug delivery system has been reported in literature (Liu et al., 2010b).

The aim of this study was to design and optimize a novel baicalin-loaded SLN carrier system composed of a stearic acid alkaline salt as lipid matrix and prepared according to the coacervation method in which fatty acids precipitated from their sodium salt micelles in the presence of polymeric nonionic surfactants. After evaluating the main and interaction variables which affect EE, particle size and polydispersity index (PDI), such as the amount of lipid and the drug/lipid ratio, a two-factor five-level central composite design was employed to schedule and perform the experiments. In this study, stearate sodium was selected as a lipid matrix. Optimized SLN formulation was prepared on the basis of the predicted optimum levels of the independent variables of the factorial design. Morphological examination and differential scanning calorimetry (DSC) were also performed to characterize the properties of SLN. Furthermore the pharmacokinetics of free and nanoparticle encapsulated baicalin were also evaluated after oral administration to Wistar rats.

Section snippets

Materials

Baicalin was purchased from Zhucheng Haotian Pharmaceutical Co. Ltd., (>98%, Shandong, China). Baicalin standard was provided by the National Institute for the Control of Pharmaceutical and Biological Products (Beijing, China). Hydroxypropylmethyl cellulose (HPMC, 60RT4000) was supplied by Shandong Ruitai Chemical Co. Ltd. Stearate sodium was purchased from Kemiou Chemical Agent Company (Tianjin, China). Other chemicals and reagents used were chromatographic or analytical grade.

Preparation of SLN

Baicalin-loaded

Mechanism of coacervation method to produce SLN

The production of SLN intended for oral administration of baicalin was tailored as per the coacervation separation technique described in the previously published literature (Battaglia et al., 2010, Battaglia et al., 2011, Gallarate et al., 2010). The study deals with the mechanism of SLN formation by coacervation and the principle behind incorporation of baicalin into these nanoparticulate systems. In this process, stearate sodium, an anionic surfactant selected as the lipid matrix in the

Conclusion

The present work provides an illustration for further understanding of the applicability of coacervation technique as a feasible approach for delivery insoluble drugs and active ingredients into lipid nanoparticles and highlights its advantages for preparation SLN carrier system. Optimization of an SLN formulation is a complex process, which requires to consider a large number of variables and their interactions with each other. This study conclusively demonstrates that the optimal formulations

Acknowledgments

This work was supported by grants from National Nature Science Foundation of China (No. 81102820) and Program from the National Basic Research of China (No. 2009CB930300).

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