Lysolipid containing liposomes for transendothelial drug delivery

Abstract

BackgroundDesigning efficient 'vectors', to deliver therapeutics across endothelial barriers, in a controlled manner, remains one of the key goals of drug development. Recently, transcytosis of liposome encapsulated fluorescence marker calcein across a tight cell barrier was studied. The most efficient liposomes were found to be liposomes containing sufficient amount of alkyl phospholipid (APL) perifosine. APLs have similar structure as lysophosphatidyl choline (LPC), since APLs were synthesized as metabolically stable analogues of LPC, which increases endothelial permeability directly by inducing endothelial cell contraction, resulting in formation of gaps between endothelial cells. Since one of the unique properties of lysolipid, containing liposomal formulations is dynamic equilibrium of lysolipids, which are distributed among liposomes, micelles, and free form, such liposomes represent a reservoir of free lysolipids. On the other hand lysolipid containing liposomes also represent a reservoir of an encapsulated hydrophilic drug.Presentation of the hypothesisWe hypothesize that free lysolipids, with highest concentration in vicinity of drug carrying liposomes, compromise endothelial integrity, primarily where concentrations of liposomes is the highest, in a similar manner as LPC, by formation of gaps between endothelial cells. Liposome encapsulated drug, which leaks from liposomes, due to liposome destabilization, caused by lysolipid depletion, can therefore be efficiently transported across the locally compromised endothelial barrier.Testing the hypothesisThis hypothesis could be verified: by measuring binding of perifosine and other lysolipids to albumin and to lysophospholipid receptor (LPL-R) group; formation of stress fibers and subsequent cell contraction; activation of RhoA, and endothelial barrier dysfunction; by a synthesis of other LPC analogues with high critical micellar concentration and measuring their effect on transendothelial permeability in presence and absence of albumin.Implications of the hypothesisWe propose that lysolipid containing liposomal formulations might be used as nonspecific transendothelial transport vector, since leakage of liposome encapsulated active drug occurs simultaneously with the release of the lysolipids. The concentration of the active drug is therefore expected to be the highest at the site of compromised endothelial barrier. By appropriate choice of the lysolipids an endothelial barrier would stay open only for a short time. Use of such liposomes would potentially maximize the delivery of the drug while limiting the passage of toxic substances and pathogens across the endothelial barrier. Combining lysolipid containing liposomes with superparamagnetic iron oxide nanoparticles or a targeting ligand might be required to efficiently localize drug delivery to a disease affected tissue and to avoid endothelial disruption over the entire body.

Lipase-catalyzed production of lysophospholipids

“…LPLs have also industrial and pharmaceutical uses such as emulsifiers and wetting agents for the food-processing (Kasinos et al, 2014) and cosmetic industries (Yahagi et al, 2011), components of liposomes for use in drug delivery (Koklic and Trancar, 2012) and adjuvant in vaccines (Cmielewski et al, 2010).…”

How Perifosine Affects Liposome-Encapsulated Drug Delivery Across a Cell Barrier

“…This is generally known as the condensing effect of CH toward phospholipids [48,49]. We have previously hypothesized that perifosine might interact with barrier-forming cells if the liposome membrane contains more perifosine than CH [26]. In the present work, we demonstrated that this is not the case.…”

“…In the recent investigations of larger series of liposomes with different amount of perifosine it was shown that perifosine increases membrane fluidity of liposomes as well as the release of liposome encapsulated content [25]. On the basis of these results, we proposed a hypothesis explaining a probable transport mechanism of liposome-encapsulated molecules across cell barriers [26]. The hypothesis is based on the published results, which show that perifosine as well as other synthetic analogs of LPC reversibly open epithelial tight junctions, probably through their incorporation into the cell membrane lipid bilayer [21].…”

“…We assumed that perifosine-containing liposomal formulations represent a source of perifosine, which might be transported into barrier-forming endo-or epithelial cells and induce changes in their cell shape. As a result, gaps are formed between cells which enable the passage of liposomes through the barrier [26].…”

“…However, calcein transported across the MDCK cell barrier was found to be released from liposomes [8], indicating that whole, intact liposomes, cannot be transported across the cell barrier. Therefore, we proposed a hypothesis that leakage of liposome-encapsulated content is as important as the amount of perifosine in the liposomal formulation [26]. To test this hypothesis, we formulated different liposomal formulations with different lipid compositions, as presented in Table 1, and measured transepithelial transport of liposome-encapsulated calcein.…”