Historical manuscript. The original scientific context and references are preserved.
Lisha Zhao
Keywords: Liposome, Encapsulation, Drug delivery, Novel strategy
Recently, the development of novel encapsulation systems to deliver drugs and nutraceuticals for enhanced stability and bioavailabitlity has drawn growing attention [1]. Liposome is one of promising encapsulation systems to deliver a number of drugs, bioactives and nutracueticals. Liposomes are versatile colloidal nanovesicles composed of one (or more) bilayer of phospholipids surrounding an aqueous core. Hydrophobic, hydrophilic and/or amphiphilic compounds can be encapsulated into liposomes for various applications. Due to the similarity to natural cell membranes, liposomes show great biocompatibility and biodegradability for delivery purposes. Liposomes have played significant roles in diagnosis and treatment of a variety of diseases as one of most powerful delivery systems, and quire recently, have also drawn increasing attention in nutraceutical, food and cosmetic industry [2-3].
Encapsulation of drugs or bioactives into liposomes can bring about following advantages: (1) protects the encapsulated agents against unfavorable external conditions, such as light, heat, specific enzymatic degradation; (2) reduces the potential side effects and targets delivery to specific organs (2) improves the cellular uptake for enhanced efficacy and bioavailability; (3) controlled release and modulated circulation of drugs and bioactives by regulation of particle properties. At present, tradition lab-scale preparation methods to produce liposomes include thin film hydration, ethanol injection, reverse phase evaporation and detergent depletion methods. Since the traditional methods usually result in low reproducibility and heterogeneity in particle size distribution, several innovative preparations such as dual asymmetric centrifugation, cross-flow filtration detergent depletion, microfluidic hydrodynamic focusing and supercritical fluid preparation have been developed to overcome the drawbacks in traditional preparation and gained considerable success [4].
Although with a number of merits, liposomes still have a few challenges in their formulations. The low encapsulation efficiency for hydrophilic compounds, instability of phospholipid membrane and drug leakage as well as hydrolysis of ester bonds during long term storage still need to be resolved using novel strategies. Active or remote loading using adjusted pH or ionic gradients have been developed to significantly increase the encapsulation efficiency and even retention rate to achieve enhance efficacy of hydrophilic drugs. Incorporation of cholesterol or phytosterols into the bilayers works to modulate the membrane permeability and reduce the leakage of encapsulated agents. The application of synthetic phospholipids with functional groups or polymer combinations facilitate the stimuli-responsive properties in vesicles [5] and allow modulation of release properties. In addition, addition of synthetic inorganic or polymer nanoparticles to stabilize liposomes has emerged as a promising strategy to create hybrid vesicular systems [6]. With increasing innovative strategies, liposomes show great premise in biomedical and nutraceutical applications and have a bright future with many novel possibilities as a powerful delivery system.
References
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