Comparing the lipid membrane affinity and permeation of drug-like acids: the intriguing effects of cholesterol and charged lipids.
OBJECTIVE
Lipid bilayers regulate the passage of solutes into and between cellular compartments. A general prerequisite for this passage is the partitioning of the solute into the bilayer. We investigated the relationship between bilayer partitioning and permeation of three drug-like acids in liposomal systems consisting of phosphatidylcholine alone or mixed with cholesterol or charged lipids.


METHODS
Bilayer partitioning was determined by equilibrium dialysis. Bilayer permeation was studied with a luminescence assay which is based on the energy transfer of the permeant to intraliposomal terbium(III).


RESULTS
The influence of the lipid composition on the pH-dependent membrane affinity was in accordance with the membrane rigidity and possible electrostatic interactions between the acids and the lipids. However, there was no direct relationship between membrane affinity and permeation. This seeming discrepancy was closer analyzed with numerical simulations of the permeation process based on the single rate constants for partitioning and translocation. The simulations were in line with our experimental findings.


CONCLUSIONS
Depending on the single rate constants and on the geometry of the system, lipid bilayer permeation may positively, negatively or not correlate with the bilayer affinity of the permeant.
Thomae
Anita V
AV
Institute of Pharmaceutical Sciences, Department of Chemistry and Applied Biosciences, ETH Zurich, Wolfgang-Pauli-Strasse 10, CH-8093 Zurich, Switzerland.
Koch
Tamara
T
Panse
Christian
C
Wunderli-Allenspach
Heidi
H
Krämer
Stefanie D
SD
D000147:Acids, Heterocyclic / Q000737:chemistry*; D000465:Algorithms; D000588:Amines / Q000737:chemistry; D001565:Benzoates / Q000737:chemistry*; D002723:Chlorobenzoates / Q000737:chemistry; D002784:Cholesterol / Q000737:chemistry*; D003198:Computer Simulation; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D008051:Lipid Bilayers / Q000737:chemistry*; D008055:Lipids / Q000737:chemistry*; D008081:Liposomes / Q000737:chemistry*; D009539:Nicotinic Acids / Q000737:chemistry; D010539:Permeability; D010713:Phosphatidylcholines / Q000737:chemistry; D010716:Phosphatidylinositols / Q000737:chemistry; D020156:Salicylic Acid / Q000737:chemistry; D062367:ortho-Aminobenzoates / Q000737:chemistry
D000147:Acids, Heterocyclic; D000588:Amines; D001565:Benzoates; D002723:Chlorobenzoates; D008051:Lipid Bilayers; D008055:Lipids; D008081:Liposomes; D009539:Nicotinic Acids; D010713:Phosphatidylcholines; D010716:Phosphatidylinositols; D062367:ortho-Aminobenzoates; C031385:anthranilic acid; D002784:Cholesterol; C009317:stearylamine; D020156:Salicylic Acid; C011866:2-hydroxynicotinic acid