Inhibitory effect of cholesterol on interaction between cytoplasmic actin and liposomes, and restorative effect of high osmotic pressure

Unravelling the in vivo dynamics of liposomes: Insights into biodistribution and cellular membrane interactions

Liposomes, as a colloidal drug delivery system dating back to the 1960s, remain a focal point of extensive research and stand as a highly efficient drug delivery method. The amalgamation of technological and biological advancements has propelled their evolution, elevating them to their current status. The key attributes of biodegradability and biocompatibility have been instrumental in driving substantial progress in liposome development. Demonstrating a remarkable ability to surmount barriers in drug absorption, enhance stability, and achieve targeted distribution within the body, liposomes have become pivotal in pharmaceutical research. In this comprehensive review, we delve into the intricate details of liposomal drug delivery systems, focusing specifically on their pharmacokinetics and cell membrane interactions via fusion, lipid exchange, endocytosis etc. Emphasizing the nuanced impact of various liposomal characteristics, we explore factors such as lipid composition, particle size, surface modifications, charge, dosage, and administration routes. By dissecting the multifaceted interactions between liposomes and biological barriers, including the reticuloendothelial system (RES), opsonization, enhanced permeability and retention (EPR) effect, ATP-binding cassette (ABC) phenomenon, and Complement Activation-Related Pseudoallergy (CARPA) effect, we provide a deeper understanding of liposomal behaviour in vivo. Furthermore, this review addresses the intricate challenges associated with translating liposomal technology into practical applications, offering insights into overcoming these hurdles. Additionally, we provide a comprehensive analysis of the clinical adoption and patent landscape of liposomes across diverse biomedical domains, shedding light on their potential implications for future research and therapeutic developments.

Interaction of cytoskeletal proteins with membrane lipids

Rapid and significant progress has been made in understanding lipid/protein interactions involving cytoskeletal components and the plasma membrane. Covalent and noncovalent lipid modifications of cytoskeletal proteins mediate their interaction with lipid bilayers. The application of biophysical techniques such as differential scanning colorimetry, neutron reflection, electron spin resonance, CD spectroscopy, nuclear magnetic resonance, and hydrophobic photolabeling, allow various folding stages of proteins during electrostatic adsorption and hydrophobic insertion into lipid bilayers to be analyzed. Reconstitution of proteins into planar lipid films and liposomes help to understand the architecture of biological interfaces. During signaling events at plasma membrane interfaces, lipids are important for the regulation of catalytic protein functions. Protein/lipid interactions occur selectively and with a high degree of specificity and thus have to be considered as physiologically relevant processes with gaining impact on cell functions.

Effect of membrane cholesterol on calcium phosphate formation in aqueous suspensions of anionic liposomes

The present study examined the effect of membrane cholesterol on liposome-mediated calcium phosphate precipitation in metastable aqueous solutions (2.25 mM Ca2+ and 1.5 mM inorganic phosphate) at 22 degrees C, pH 7.4 and 240 mOsm. The liposomes were prepared from 7:2:X molar mixtures of phosphatidylcholine, dicetylphosphate, and cholesterol (x = 0, 1, 5, or 9) and contained either 0 or 50 mM encapsulated phosphate. The membranes were made permeable to Ca2+ by addition of the cationophore, X-537A. Changes in external Ca2+ concentration were used as the principal monitor of the course of precipitation. Without encapsulated phosphate, 7:2:X liposomes (with or without ionophore) induced no precipitation. With 50 mM encapsulated phosphate and in the presence of ionophore, precipitation significantly depended on the cholesterol level in the membrane. At 0 and 10 mole% cholesterol, precipitate developed rapidly both within and outside the liposomes. At 35 and 50 mole% cholesterol, no observable intraliposomal precipitation occurred, and extraliposomal precipitation started only after an induction period of 24 hours. Delayed extraliposomal precipitation also took place in PO4-containing liposomes without added ionophore. In this latter case, however, cholesterol was essential for this precipitation to occur with the optimum level being around 10 mole%. Suppression of ionophore-mediated intraliposomal precipitation at higher cholesterol levels could be related to the inflexible cholesterol molecules making the membrane more rigid, thereby restricting Ca-ionophore transport. This restriction could be reversed with ethanol. Delayed extraliposomal precipitation in the absence of added ionophore (or at higher cholesterol levels in its presence) could be explained by seeding from low, unobserved levels of intraliposomal precipitate formed during slow, unfacilitated Ca2+ leakage into the liposomal interior.

Research on the mechanism of interaction between actin and membrane lipids

Using an in vitro system involving pure actin and liposomes, we have established that actin may interact with membrane lipids without any intermediate proteins, and that the mechanism of interaction depends upon the concentration of divalent cation. In the absence of divalent cation, actin increases membrane permeability. Low concentrations (1 mM) of divalent cation potentialize this interaction. In the presence of high divalent cation concentration, actin deposits on the surface of liposomes in a crystalline organization and reduces the membrane microviscosity as shown by the polarization of fluorescence of the DPH probe. We propose that actin interacts with lipids by hydrophobic association which is facilitated by initial electrostatic binding.