Relationship between the structure of compounds and the effect of Pluronic L61 on their permeation through lipid membranes

Abstract

In view of the earlier observation that the incorporation of Pluronics in lipid membranes enhances their permeability to various drugs, the relationship between the structure of a permeant and the Pluronic-induced acceleration of its membrane transport was studied. The extent of acceleration defined as the ratio of the apparent permeation rate constants in the presence and in the absence of Pluronic, k/k 0, was determined for 21 weak acids and bases. Multiparameter correlations of the obtained data with various structural characteristics of the solutes transferable were constructed. Twelve structural parameters of the permeants were examined. The best correlation was achieved with a linear combination of the three parameters: the McGowan volume V of a compound, its proton-donating ability A, and the projection of the dipole moment of the molecule onto the normal to the membrane surface μZ, ln(k/k 0) = −0.87-0.44μZ + 0.31 V + 0.28A, R = 0.90. This means that Pluronic preferably accelerates the permeation of large molecules containing proton-donating groups and molecules incorporated in the lipid bilayer in such a manner that the vector of their dipole moment is aligned with the dipole potential of the membrane.