Liposomes types

FIGURE 8 Antitumor activity of free DXR and DXR entrapped in different liposome types in solid IgM immunocytoraa-bearing Lou/M Wsl rats. 2 mg DXR/kg body weight was injected i.v. daily for 5 days (0-4) followed by one additional injection at day 11 after start of therapy. Results obtained during the first 21 days after start of treatment are shown. Treatment groups consisted of 10 animals. 

Figure 1.1. Schematic representation of four major liposome types. Conventional liposomes are either neutral or negatively charged. Stealth liposomes are sterically stabilized and carry a polymer coating to obtain a prolonged circulation time in the body. Immunoliposomes are antibody targeted liposomes and can consist of either conventional or sterically stabilized liposomes. Positive charge on cationic liposomes can be created in various ways. Reproduced from reference [112] with permission.

X-Y Liu, Q Yang, N Kamo, J Miyake. Effect of liposome type and membrane fluidity on drug-membrane partitioning analyzed by immobilized liposome chromatography. J Chromatogr A 913 123-131, 2001. 

Alveolar accumulation of carriers is an important toxicological consideration, although for liposomes, type-II cells will utilize administered phospholipids in the production of lung surfactant. 

Ma, L., Ramachandran, C., and Weiner, N. D. (1991), Partitioning of a homologous series of alkyl p-amino benzoates in dipalmitoyl phosphatidyl choline liposomes Effect of liposomes type, Int. J. Pharm., 70, 209-218. 

Solvent system Particle size Liposomes (type, charge)... 

Chemical composition Conventional liposomes (CL), pH sensitive liposomes, cationic liposomes, immunoliposomes and long circulating liposomes. The chemical composition of each liposome type gives particular characteristics to the final liposomal formulation that tnay be ideal for its systematic administration. 

The relative efficaqr of entrapment of contrast materials into different liposomes as well as advantages and disadvantages of various liposome types were analyzed by Tilcock (157). Liposomal contrast agents have been used for experimental diagnostic imaging of liver, spleen, brain, cardio-vascular system, tumors, inflammations and infections (156, 158). 

Dried reconstituted vesicles (DRV) are liposomes that are formulated under mild conditions and have the capability to entrap substantially high amounts of hydrophilic solutes (compared with other types of liposomes). These characteristics make this liposome type ideal for entrapment of labile substances, as peptide, protein or DNA vaccines and sensitive drugs. In this chapter, we initially introduce all possible types of DRV liposomes (in respect to the encapsulated molecule characteristics and/or their applications in therapeutics) and discuss in detail the preparation methodologies for each type. 

The permeability of polymersome membranes for a given solute has been reported to be at least 10 times smaller compared to common phosphohpid membranes (8). Retention of encapsulants (eg dextrans, sucrose, physiological saline) over periods of months has been observed for small 100 nm polymersomes prepared by liposome-type extrusion techniques (49) as well as with 10 p.m giant vesicles. Permeability and membrane hydration have been shown to be inversely related to the bending modulus (165). It is suggested that membrane permeability and membrane hydration are related to the ability of the membrane to locally bend so as to create holes for solute permeation. 

Irrespective of the actual mechanism behind the reduction of cholesterol absorption by plant sterols, solubilization in the emulsified fat phase of the food digest is a prerequisite for plant sterols to be incorporated into the micelles. Plant sterols need to be incorporated into mixed micelles or other liposome-type entities with micellar-type structure before they can enter into the enterocytes or their cell walls. Esterified sterols and stanols are fat-soluble and can directly enter and mix homogeneously into the fat phase of a food digest. On the other hand, the ability of free sterols and stanols to reduce cholesterol absorption is highly dependent on the extent to which they are first solubilized... 

The functions of liposomes, such as interaction, incorporation, recognition, and stabilization, are attributed to the microfluidity of a membrane and its ttansitional state [2], Lipids dispersed in water can form a variety of structures, for example, the liposome-type structure at low lipid/water ratios. As temperature increases, the lipid phase shifts from a crystalline to a condensed gel-like state and then to a fluidic, expanded state, and such a transition state at the corresponding temperature can be determined by various methods [2,16]. 

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