Interactions of ibuprofen with Langmuir monolayers of membrane lipids

Abstract

DPPC (1,2-dipalmitoyl- sn-glycero-3-phosphocholine) Langmuir monolayers were employed as model membranes for the studies of interactions with an amphiphilic drug — ibuprofen. The mode of interactions was found to be ibuprofen concentration dependent. The maximal value of compressibility constant, 270 mN/m is obtained for ibuprofen 10 − 5 –10 − 6 M solutions indicating that already in contact with such diluted drug solutions, the DPPC monolayer becomes more solid than in contact with pure water or saliva solutions, thus the organization of molecules is more compact or condensed. In contrary, the effect of concentrated ibuprofen solutions is opposite. Moreover, in the “diluted ibuprofen range” the molecules do not partition into the lipid layer since the limiting area for the lipid did not increase but in contrary was found to decrease upon contact with such solutions, and a disappearance of phase transition was observed. Contact with diluted solution of ibuprofen does not influence collapse pressure while making the condensed monolayer more solid. In diluted solutions of S-ibuprofen (10 − 6 –10 − 5 M) the value of dipole moment is larger than for pure water or saliva subphases reflecting the organizing effect of ibuprofen. In concentrated ibuprofen solutions the dipole moment decreases which indicates partial compensation of charges upon incorporation of ibuprofen into the hydrophobic region of the lipid layer. Under these conditions, ibuprofen interferes with the cooperative interactions of the DPPC molecules in the layer and perturbs the structure of the monolayer.