Cholesterol Reduces Partitioning of Antifungal Drug Itraconazole into Lipid Bilayers

Abstract

Cholesterol plays a crucial role in modulating the physicochemical properties of biomembranes, both increasing mechanical strength and decreasing permeability. Cholesterol is also a common component of vesicle-based delivery systems, including liposome-based drug delivery systems (LDSs). However, its effect on the partitioning of drug molecules to lipid membranes is very poorly recognized. Herein, we performed a combined experimental/computational study of the potential for the use of the LDS formulation for the delivery of the antifungal drug itraconazole (ITZ). We consider the addition of cholesterol to the lipid membrane. Since ITZ is only weakly soluble in water, its bioavailability is limited. Use of an LDS has thus been proposed. We studied lipid membranes composed of cholesterol, 1-palmitoyl-2-oleoyl- sn -glycerol-3-phosphocholine (POPC), and ITZ using a combination of computational molecular dynamics (MD) simulations of lipid bilayers and Brewster angle microscopy (BAM) experiments of monolayers. Both experimental and computational results show separation of cholesterol and ITZ. Cholesterol has a strong preference to orient parallel to the bilayer normal. However, ITZ, a long and relatively rigid molecule with weakly hydrophilic groups along the backbone, predominantly locates below the interface between the hydrocarbon chain region and the polar region of the membrane, with its backbone oriented parallel to the membrane surface; the orthogonal orientation in the membrane could be the cause of the observed separation. In addition, fluorescence measurements demonstrated that the affinity of ITZ for the lipid membrane is decreased by the presence of cholesterol, which is thus probably not a suitable formulation component of an LDS designed for ITZ delivery.

Mechanistic Understanding From Molecular Dynamics Simulation in Pharmaceutical Research 1: Drug Delivery

“…MD simulations showed that this is not the right choice because cholesterol and itraconazole do not mix well and separate into small domains (Poojari et al, 2020). This observation was next validated in experimental studies, which showed decreased affinity of itraconazole toward liposomes containing cholesterol (Poojari et al, 2020). The observed behavior of the itraconazole may be explained by its structure: it is a long rigid molecule with a few weakly polar groups distributed along the molecule backbone.…”

“…Thus, the incorporation of cholesterol into the liposome-itraconazole formulation was the next step. MD simulations showed that this is not the right choice because cholesterol and itraconazole do not mix well and separate into small domains (Poojari et al, 2020). This observation was next validated in experimental studies, which showed decreased affinity of itraconazole toward liposomes containing cholesterol (Poojari et al, 2020).…”

Revealing the structure deformation in multi-component lipids by dynamic speckle pattern analysis

“…Multilayer lipid membranes are essential to life, perform many essential functions in biology, and regulate many cellular processes 1 . Multilayered lipid membranes have a variety of functional advantages over single-lipid membranes, such as to organize processes spatially, significantly increase membrane protein concentration because of an increase in surface area, and compartmentalize molecules 2 .…”

“…Chol also can play the same position in vesicle-based delivery systems, including liposome-based drug delivery systems. However, its position in the partitioning of drug molecules to lipid membranes is poorly identified 1 . In general, Chol can modify the physical properties of a lipid membrane.…”

Computational and Experimental Advances in Biomembranes: Resolving Their Complexity

“…Understanding the mechanism of translocation and binding of a variety of drugs, transfection reagents, and antifungal/ antimicrobial compounds also remains a hot topic, 17,18 with additional complexity arising from the presence of certain lipids, 19 synergetic effects, 20 and modulation of pH. 21,22 Apart from these more applied studies, this Virtual Special Issue includes exciting contributions aimed at increasing our understanding of fundamental physical mechanisms that govern membrane behavior.…”