[Liposomes--a new slow-release dosage form. I. Phospholipids; production and characterization of liposomes]

Physicochemical characterisation of liposomes with encapsulated local anaesthetics

Local anaesthetics may be added to intravenous o/w emulsions of propofol to reduce the initial pain of injection. Due to incompatibility problems of the emulsion on the addition of a local anaesthetic solution, prior encapsulation of the drug within liposomes is suggested. The liposomes were prepared with the sonication method and loaded with either lidocaine hydrochloride (LiHCl) or prilocaine hydrochloride (PrHCl). The liposomal systems were characterised with photon correlation spectroscopy (PCS) in terms of mean particle size and polydispersity. Lamellarity and lamellar thickness were determined by small angle X-ray scattering (SAXS). Visualisation of drug-loaded liposomes was performed with transmission electron microscopy (TEM) after freeze fracture replication of the samples. Depending on the manufacturing procedure mean particle sizes of the drug-free liposomes varied from 150 +/- 9 nm to 102 +/- 2 nm. Drug-loaded liposomes manufactured the same way showed reduced particle sizes of 125 +/- 1 nm and 85 +/- 7 nm, respectively. Determination of bilayer thickness by SAXS yielded 6.2 +/- 0.2 nm in the case of full hydration whereas the bilayer thickness without the hydration shell was just 4.4 +/- 0.2 nm. The small particle sizes achieved are appropriate for intravenous administration.

Transformation of a liposomal dispersion containing ibuprofen lysinate and phospholipids into mixed micelles - physico-chemical characterization and influence on drug permeation through excised human stratum corneum

Our study is meant as a contribution to the investigation of molecular association of phospholipids and amphiphilic substances like, e.g. non-steroidal anti-inflammatory drugs. Our research focused on physico-chemical characterization of ternary systems containing ibuprofen lysinate, lecithin and water. The influence of the resulting microstructures on drug release and permeation through excised human stratum corneum was also investigated. Depending on the mixing ratio different physical states (lamellar and hexagonal liquid crystals, micellar solutions, liposomal dispersions and biphasic systems) were determined by gross, polarizing microscopic and small angle-X-ray analysis. A special emphasis was laid upon the storage-induced transformation of liposomal dispersions into mixed micellar solutions and its influence on drug release and permeation. A model for the transformation process is presented. Drug release of the liposomal dispersion (Da=1.1x10-5 cm2/s) and of the identically composed mixed micellar solution (Da=2.9x10-5 cm2/s) was delayed compared with the data of the aqueous drug solution (Da=4.7x10-5 cm2/s). Because of the association of ibuprofen lysinate molecules with phospholipid molecules within the liposomal and the mixed micellar system the share of free ibuprofen lysinate monomers, which can pass through the dialysis membrane in the release experiment, is markedly reduced. The results of permeation experiments of these systems, however, did not correspond to the release data. The permeability of the mixed micellar solution rose after 6 weeks of storage (P=4.2x10-8 cm/s), and almost reached the permeation of the aqueous solution (P=3.9x10-8 cm/s), whereas the permeation of the liposomal dispersion was very slow (P=1.5x10-8 cm/s). The different colloidal microstructures of the formulations obviously resulted in divergent interactions with the permeation barrier - the stratum corneum - and subsequently in different permeation behavior.

Electrically induced fusion of different human cell types

The fusion of human cells of the cerebrospinal fluid and of the peripheral blood is reported, as well as the fusion of these cells with tomato protoplasts. The cells were fused by applying short-time electric pulses after dielectrophoretic collection. The importance of this method for diagnosis and therapy is discussed and possible applications are mentioned.

Antineoplastic activity and toxicity of some alkylating cytostatics (cyclophosphamide, CCNU, cytostasan) encapsulated in liposomes in different murine tumour models

The encapsulation of Cyclophosphamide in MLV (PC:CH 1:1) revealed a total loss of antineoplastic activity in the P 388 tumour model compared to an equal dose of the free drug, though a moderate toxicity, registered as decrease of leukocyte and platelet counts, was still present. CCNU in liposomes of different size and composition showed in lower doses a diminished therapeutic effectiveness in the P388 or L 1210 leukaemia and the B 16 melanoma, while in higher doses toxic deaths occurring with the free drug could be prevented totally by using liposomes. Liposomal encapsulation also influenced body weight change and leukocyte counts, causing them to be less drastically reduced than with use of the free drug. The entrapment of Cytostasan, an N-lost derivative, had the same effect on the increase of lifespan of tumour-bearing animals (mammary carcinoma 1142 A) as equal doses of the free drug and caused only a slight improvement of toxicity. In general, liposomal encapsulation of alkylating cytostatics seems advantageous only for certain lipophilic drugs.

Immunoglobulins as targeting agents for liposome encapsulated drugs

Recent literature dealing with the immunoglobulin-liposome combination as a tool for drug targeting is reviewed. Mechanisms for binding of immunoglobulins to liposomes are discussed. Results obtained so far by using this concept both to induce specific liposome-cell interactions in in vitro cell cultures and to target drug containing liposomes to selected tissues in animal studies are evaluated.