Recent studies on the delivery of hydrophilic drugs in nanoparticulate systems

Abstract

This review discusses some approaches developed by the Turin University Pharmaceutical Technology group to enhance the entrapment efficiency of mainly hydrophilic molecules within nanoparticulate systems, and to optimize their delivery. Many attempts have been made to increase, either passively or actively, the delivery of hydrophilic drugs. One approach consists of their association to liposomes, in some cases by developing lipophilic prodrugs of anticancer hydrophilic molecules, and encapsulating them in liposomes; in some cases these are then further conjugated with suitable vectors, to increase targeting efficiency. The transformation of hydrophilic drugs into lipophilic prodrugs can also overcome problems of poor entrapment efficiency, and the frequentlyobserved rapid release from polymer nanocarriers, for example nanospheres or nanocapsules obtained from various PEGylated poly(alkylcyanoacrylate) copolymers. Strategies have also been developed to enhance hydrophilic drug entrapment in solid lipid nanoparticles (SLN). Of these, hydrophobic ion pairing (HIP) was designed to enable various antitumor drugs to be entrapped in SLN produced by the coacervation method. The w/o/w emulsion solvent dilution technique may also be employed to entrap peptide drugs, such as insulin, directly in the inner aqueous phase. Another strategy entails covalent linkage of antitumoral and antiviral drugs to a squalenoyl-derived chain; this produces bioconjugates that spontaneously self-assemble in an aqueous medium as stable nanoparticles. Another development comprises mesoporous silica nanoparticles with immobilized hydrophilic antioxidants, for topical applications. Ordered mesoporous silica (MCM-41) nanoparticles were complexed with hydrophilic antioxidants (Trolox ® or rutin) employing different inclusion procedures, varying solvent and pretreatment of the silica matrix; on exposure to UV illumination, mesoporous silica significantly improved stability over time. Finally, polymer-shelled and perfluoropentane-cored nanobubbles have been designed as versatile multifunctional carriers for the delivery of gases, drugs and genes; the size range is below 500 nm, with shell thickness in the 30-50 nm range.(lectins), or macromolecular conjugates to tumor tissues. Further, collaboration with several European research groups lead to the development of particulate delivery systems (liposomes, polymer nanoparticles) and, more recently, to the squalenoylation platform. Colloidal systems, such as liposomes, nanoparticles, and microemulsions, have mainly been reported in the literature for use as carriers of hydrophobic drugs. Delivery of hydrophilic molecules is a challenging goal, which requires multidisciplinary approaches. This review essentially focused on the various strategies that may be employed to deliver hydrophilic active substances. Many drugs are hydrophilic, and many of these are low-molecular weight molecules (less than 500 Da). According to the United States Pharmacopeia (USP), hydrophilic drugs are classified in the range ve...

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