Jacques Caspers

Evidence of a specific complex between adriamycin and negatively-charged phospholipids

Membrane-model systems (monolayers, small unilamellar vesicles) were used to study the interaction between adriamycin (ADM) and phospholipids. Adsorption of 3H-labeled adriamycin on different phospholipid monolayers demonstrated the specificity of adriamycin for negatively-charged phospholipids (cardiolipin, phosphatidylserine, phosphatidic acid). The stoichiometry has been found to be approx. 2 mol (1.8) adriamycin per mol cardiolipin and approx. 1 mol (0.75) adriamycin per mol phosphatidylserine and phosphatidic acid. No adsorption was detected with neutral lipids. Surface-potential measurements confirm the formation of a complex stabilized by electrostatic interactions without penetration of the drug into the lipid lipophilic phase. Some adriamycin derivatives were used to discriminate between the ionized hydrophilic and hydrophobic contributions in the complex formation. The absorption spectrum of adriamycin in the presence of cardiolipin resembles the behavior of the ADM-DNA complex. Moreover, the association constants of the two complexes are very similar (cardiolipin-ADM, 1.6 . 10(6) . M-1; ADM-DNA, 2.4 . 10(6) . M-1). To explain the high affinity of cardiolipin for adriamycin, we proposed that two essential interactions are responsible for the complex stabilization: an electrostatic interaction between the protonated amino groups of the sugar residues and the ionized phosphate residues, and an interaction between adjacent anthraquinone chromophores. These data strongly suggest competitive behavior between a membrane site and the target. Consequently, it must be assumed that the lipidic components of the cell membrane structure may be an important determinant in the behavior of adriamycin. This observation should be kept in mind in the building of new derivatives.

Evidence of a complex between adriamycin derivatives and cardiolipin: Possible role in cardiotoxicity

Most of the mitochondrial damage induced by antimitotic drugs of the adriamycin family could be due to the high affinity of these drugs for the membrane. The prime interaction between the anthracycline drug and this membrane would explain specific alterations observed on mitochondria. Cardiolipin has been proposed as a privileged target. We have tested this hypothesis here. Model membranes (lipid monolayers, liposomes) were used to demonstrate the interaction between these anthracycline drugs and different phospholipids. A new surface potential technique showed the specificity of adriamycin derivatives for cardiolipin whereas no complexation was observed with neutral phospholipids (dipalmitoyl lecithin and egg lecithin). Association constants were evaluated and a good correlation was obtained between the mitochondrial toxicity of each drug and its affinity for cardiolipin. Fluorescence measurements were carried out in order to locate precisely the position of the drug in the lipid bilayer. Perturbations of the lipid organization after complex formation were analysed using phospholipase A2 as an enzymic probe.

Acido-basic properties of lipophilic substances: A surface potential approach

Abstract A general procedure allowing the acido-basic properties of lipophilic compounds to be defined is described. Drugs are spread at the air-water interface and the surface potential is recorded at different pH values of the aqueous subphase. Comparison of this experimental parameter and the Gouy-Chapman theory prediction allows the calculation of the acid (or basic) dissociation constants and the surface charge density.

Conformation of a copolypeptide at the air—water interface

Abstract A change of conformation of macromolecules has been investigated at the air-water interface. The model chosen is a copolypeptide of glutamic acid and methyl glutamate. The modification of the conformation of the copolypeptide is induced by changing the pH of the support. The presence of electrostatic charges on the spread macromolecules has as consequence an abrupt change of the surface properties. Measurements of surface potential and surface viscoelasticity demonstrate a discontinuity in the surface behavior for a pH of the subphase of about 7.5 units. This result is interpreted as a transition from the helical conformation to the coiled conformation at the air-water interface.

Evaluation of the anesthetic-lipid association constant: A monolayer approach

A new approach is presented which allows to describe the binding of different local anesthetics to lipids. Lipids (DL- alpha-dipalmitoylphosphatidylcholine, phosphatidylserine, cardiolipin) are spread at the air-water interface and the anesthetic (procaine, butacaine, tetracaine) injected into the aqueous subphase. The equilibrium constants associated to the interfacial reaction: D+ (subphase) +L- (monolayer) in equilibrium DL (monolayer) (where D+ denotes the anesthetics, L- the lipid anionic site and DL the complex) are calculated from an experimental evaluation of the surface potential of the lipid monolayer. This mode of determination is based essentially on the good correlation between the experimental values of the surface potential and the theoretical predictions from the Gouy-Chapman theory. Fluorescence measurements on liposomes are carried out in order to locate the position of the drug in the lipid layer. This method can be extended to any positively charged drug-anionic lipid interaction.

Lipid—drug electrostatic interactions in model membranes

Abstract Model membranes have been used to describe the interaction between charged drugs (acridine orange, ethidium bromide) and lipids. A new method of evaluation of the surface charge density is described. It allows, from surface potential measurements, the evaluation of the drug-lipid association constant. The low perturbation of the monolayer dipole orientation after complexation is correlated to the low penetration of the drug into the lipid bilayer of liposomes as shown by a fluorescence titration technique.

Ionization state of amiodarone mediates its mode of interaction with lipid bilayers

Amiodarone is a potent antianginal and antiarrhythmic drug which affects the lipid dynamics. The influence of amiodarone ionization on the lipid transition temperature and enthalpy associated to the liquid crystalline to gel state transition was studied in multilamellar vesicles (MLV) of dipalmitoylphosphatidylcholine (DPPC) by differential scanning measurements (DSC) at different pH. These data were correlated with the calculated number of charged amiodarone molecules inserted into the lipid vesicles. The procedure of calculation requires the knowledge of the intrinsic ionization constant of amiodarone and the area occupied per amiodarone molecule in the close packed state; it can be applied successfully to water insoluble amphiphilic molecules. Only the ionized form of amiodarone molecule destabilizes the lipid matrix organisation whereas no effect was observed with the uncharged form. This destabilizing effect could be explained in terms of a modification of the drug structure induced by its ionization state or in terms of its distribution in the lipid matrix, as an isolated molecule or assembled in clusters depending on its ionization state.

A23187 Ionophore—ca2+ interfacial complex: a monolayer approach

This paper presents a new approach to study A23187 ionophore in an aqueous environment. The ionophore was spread at the air—water interface. Surface pressure and tritium—hydrogen surface exchange measurements demonstrated the conformational stability of A23187 in the free and complexed forms at the interface. Exchange measurements suggested that the A23187 ionophore adopts an interfacial conformation in which hydrogen bonds are not accessible to the aqueous solvent. Surface potential measurements allowed the calculation of the intrinsic dissociation constant of the ionophore carboxylic group in an aqueous environment (pKi = 5). The ionophore activity sequence for bivalent ions was Ca2+>Mg2+⇓Ba2+ . This sequence is comparable to those obtained by other authors inorganic solution. Surface radioactivity measurements performed with 45Ca2+ in the subphase demonstrated the formation of a neutral complex between two negatively charged ionophore molecules and one Ca2+ ion. This reaction was only observed at pH higher than 5. The association constant of the interfacial ionophore-Ca2+ complex was calculated.

Interfacial valinomycin-K+ and antamanide-Na+ complex: Role of the surface charge density

Abstract In order to determine the role of the membrane charge density on the ionophore-ion (valinomycin-K+, antamanide-Na+) complexation process at the lipid-water interface, antibiotic-palmitic acid mixed monolayers are spread at the air-water interface. By changing the composition of the subphase (pH, nature of the cation) and of the mixed film, it is possible to modify the surface charge density and the cationic environment of the spread ionophore. Surface potential measurements are interpreted in terms of the Gouy-Chapman theory and demonstrate that the surface charge density determines the ionophore binding capacity.

Interfacial properties of an (Na++K+)-activated adenosine triphosphatase: A monolayer approach

The monolayer approach has been used to study an (Na + +K + )-activated ATPase, free and in its lipidic environment. Surface pressure, surface tritium-hydrogen exchange, and surface viscosity measurements of ATPase-lipid films suggest the following: A lipid-ATPase interaction depends on the nature of the lipid; the globular ATPase molecule induces complete fluidity of the lipid layer; the ATPase orientation in the mixed films depends on the lipid fluidity.