ABSTRACT
Probing drug/lipid interactions at the molecular level represents an important challenge in pharmaceutical research and membrane biophysics. Previous studies showed differences in accumulation and intracellular activity between two fluoroquinolones, ciprofloxacin and moxifloxacin, that may actually result from their differential susceptibility to efflux by the ciprofloxacin transporter. In view of the critical role of lipids for the drug cellular uptake and differences observed for the two closely related fluoroquinolones, we investigated the interactions of these two antibiotics with lipids, using an array of complementary techniques. Moxifloxacin induced, to a greater extent than ciprofloxacin, an erosion of the DPPC domains in the DOPC fluid phase (atomic force microscopy) and a shift of the surface pressure-area isotherms of DOPC/DPPC/fluoroquinolone monolayer toward lower area per molecule (Langmuir studies). These effects are related to a lower propensity of moxifloxacin to be released from lipid to aqueous phase (determined by phase transfer studies and conformational analysis) and a marked decrease of all-trans conformation of acyl-lipid chains of DPPC (determined by ATR-FTIR) without increase of lipid disorder and change in the tilt between the normal and the germanium surface (also determined by ATR-FTIR). All together, differences of ciprofloxacin as compared to moxifloxacin in their interactions with lipids could explain differences in their cellular accumulation and susceptibility to efflux transporters.
Subject(s)
Anti-Bacterial Agents/chemistry , Aza Compounds/chemistry , Ciprofloxacin/chemistry , Membrane Lipids/chemistry , Membrane Microdomains/chemistry , Phospholipids/chemistry , Quinolines/chemistry , Complex Mixtures/chemistry , Fluoroquinolones/chemistry , Microscopy, Atomic Force/methods , Molecular Conformation , Moxifloxacin , Phase Transition , Spectroscopy, Fourier Transform Infrared/methods , Surface PropertiesABSTRACT
Gliadin is a fraction of wheat gluten, a protein supramolecular complex known for its remarkable and biotechnologically relevant viscoelastic properties. Very high molecular mass characterise these systems, thus hindering high-resolution structural investigations. It is known, however, that these proteins comprise rather extended, extensively interassociated structures, which respond for their peculiar mechanical behaviour. Besides these properties, some of gluten's fractions, such as gliadin, are also known to be involved in a nutritionally relevant pathology of auto-immune character, the celiac disease, supposedly related to some unusual structural features of the protein. Despite its medical relevance, however, the role played by gliadin in the etiology of the celiac disease is not sufficiently understood to date. In this work, we investigated the role of gliadin on mechanical properties of a membrane model of dioleoylphosphatidylcholine (DOPC) giant unilamellar vesicles. The technique of micropipette aspiration, coupled to videomicroscopy, was applied. The microvesicles, produced by electric field pulsing over metal-covered plates, were suctioned into the micropipettes under varying applied pressures. A significant increase in the values of the bilayer curvature constant, k(c), was observed, with a saturation effect being verified at around 0.02-0.03 gliadin/DOPC mass ratio, indicating that the membrane becomes less elastic in the presence of the protein. Possible correlations between the observed membrane fluctuation properties and the celiac disease etiology are suggested and discussed.
