Lipid-Based Delivery Systems: Liposomes and Lipid-Core Micelles—Properties and Applications
INTRODUCTION There are three main reasons behind using various drug delivery systems (DDS): to protect a drug against the inactivating action of the biological surrounding, to protect normal nonpathological tissues against nonspecific toxic action of a drug, and to favorably change and control drug pharmacokinetics. The clinical utility of most conventional therapies is limited either by the inability to deliver therapeutic drug concentrations to the target tissues or by severe and harmful toxic effects on normal organs and tissues. Different approaches have been suggested to overcome these problems by providing “selective” delivery to the required area (organs, tissues, or cells affected by the disease), which is usually achieved via the use of selected DDS, such as molecular conjugates and colloidal particulates, suitable for this purpose. Among different types of particulate carriers, liposomes and polymeric micelles, including lipid-core micelles, are the most advanced and well investigated. They are aimed to significantly modify and improve biological properties of the carrier-loaded drugs and enhance their therapeutic activity. Microreservoir-type systems such as liposomes (mainly for water-soluble drugs) and micelles (mainly for water-insoluble drugs) have certain advantages over other DDS, such as possibility to easily control composition, size, and in vivo stability; relatively easy way of their preparation and scaling up; good drug loading; and ability to be made specifically targeted using just a small quantity of a targeting component, since just a few targeting moieties attached to their surface can carry multiple drug moieties loaded into the reservoir. In addition, liposomes and micelles when stay long enough in the blood are capable of “passive” targeting into pathological site via the so-called enhanced permeability and retention (EPR) effect, that is, penetration into the tissue through the compromised (leaky) vasculature characteristic for various pathological states, such as tumors, infarcts, and inflammations (1,2). Here, we will briefly discuss the properties and application of these lipid-based DDS. Some other lipid-based nanocarriers, such as solid lipid nanoparticles, will be left outside of our scope.