Nanostructured lipid carriers containing Amphotericin B: Development, in vitro release assay, and storage stability

Abstract

Nanostructured-lipid-carriers (NLC) can improve the encapsulation rate and the stability of drugs. The aim of this study was to develop an amphotericin B (AmB)-containing-NLC (AmB-NLC). An experimental design was applied in order to determine the component concentration within the final formulation. The prepared NLC had their stability assessed on the basis of particle size, polydispersity index (PDI), zeta potential, and AmB recovery rate. NLC were also lyophilized (LYO) and optimized in order to improve their shelf-life. The experimental design presented the optimal component concentration as 7:3 (w/w) solid:liquid lipid ratio and 3% of surfactants. The produced NLC were white translucent, becoming yellow translucent when AmB was incorporated. For lyophilization, maltose was the best cryoprotectant using a 48 h freeze-drying cycle. Both the LYO-AmB-NLC and LYO-NLC were readily dispersible in water. The dried systems had slightly different physicochemical properties; however, they maintained their high encapsulation efficiency of above 90%. Additionally, thermal studies confirmed the entrapment of the AmB into the systems. The in vitro release profile, assessed 24 h after particle preparation, fitted the Baker-Lonsdale model. In conclusion, all the results together revealed that the developed NLC can be an available alternative as a drug delivery system for AmB.

Introduction

Recognized as the gold standard drug for treating systemic fungal infections [1,2] and leishmaniasis [[3], [4], [5]], amphotericin B (AmB) is a classic example of a molecule whose physicochemical properties lead to difficulties in its formulation and therapeutic use [6,7]. Despite its clinical importance, the major drawback to developing new AmB formulations is related to the AmB's limited aqueous solubility profile [[8], [9], [10], [11]]. As a consequence, AmB presents low bioavailability for oral administration and, therefore, its use is restricted to intravenous infusion and local application [12,13].

Nowadays, several commercially available lipid-based products containing AmB, whose production is based on nanotechnological approaches, have been developed in order to improve the AmB therapeutic index by reducing its toxicity [7,14,15]. In addition, the ability of AmB to form complexes with lipid molecules came up as a possible strategy to stabilize this drug in a self-associated state, preventing its interaction with cholesterol in human cell membranes. Based on this approach, lipid complexes such as Abelcet^®, Amphocil^®, and Amphotec^® were developed [[16], [17], [18]].

Also, the development of liposomes loaded with AmB brought to the market the product AmBisome [14,19]. However, toxic events are still reported during the administration of all these new formulations, especially nephrotoxicity [[20], [21], [22]]. In this regard, several approaches such as microemulsions, liquid crystals, lipid nanospheres and nanosomal formulations have been considered to reduce the AmB toxicity by means of new formulations. Currently, the maintenance of the AmB therapeutic effect and the reduction of nephrotoxicity are the most important goals of AmB lipidic formulations [11,[23], [24], [25], [26], [27], [28], [29], [30]].

The advantages of lipid formulations as drug delivery systems have been scientifically recognized for several decades. In addition, among the available pharmaceutical excipients, lipids are the most versatile ones because they can provide a wide range of formulations with the potential to increase the bioavailability, the therapeutic index, and the biocompatibility of poorly soluble drugs [[31], [32], [33]]. Emulsions, microemulsions, liposomes, lipid complexes, and nanoemulsions [[34], [35], [36]] are good examples of lipid formulations.

Furthermore, as an alternative for the traditional lipid systems, solid lipid nanoparticles consist of a matrix constituted by one or more solid lipids [37,38] These systems were described for the delivery of both insoluble [39] and water-soluble molecules [40]. In particular, a new generation of this kind of system, namely nanostructured lipid carriers (NLC), has been studied in the recent years. NLC consist of a matrix composed of a mixture of solid and liquid lipids [[41], [42], [43], [44]]. Importantly, NLC show the potential to enhance the drug encapsulation rate and the storage stability [45]. Therefore, the aim of this study was to develop an NLC containing AmB and to evaluate the physicochemical and pharmaceutical properties of this formulation.