Comparison of the interaction of the anti-viral chemotherapeutic agents amantadine and tromantadine with model phospholipid membranes

Partitioning and localization of spin-labeled amantadine in lipid bilayers: an EPR study

EPR was used to study the distribution of the spin-labeled amantadine (AA-SL) between the bulk hydrophobic-hydrocarbon solvent, light paraffin oil, and water and between hydrophobic-hydrocarbon chain region of lipid membranes and water. The AA-SL molecules were soluble in both hydrophobic and polar regions of investigated systems. It was shown that the partition coefficient of AA-SL between the hydrocarbon region of the L-alpha-dimyristoylphosphatidylcholine fluid-phase membrane and water is much higher than between bulk hydrocarbon solvent and water. Furthermore, the partitioning of AA-SL into membranes of multilamellar liposomes made of L-alpha-dimyristoylphosphatidylcholine, L-alpha-dipalmitoylphosphatidylcholine, and L-alpha-distearoylphosphatidylcholine was studied as a function of temperature, indicating no abrupt change at the main phase transition of these membranes. It is also clear from our data that AA-SL can penetrate into the gel-phase membrane practically with the same partitioning as into the fluid-phase membrane. Furthermore, it was shown that at least part of the AA-SL molecule is deeply buried in the hydrocarbon chain region of the membrane.

Lysophosphatidylcholine mediates the mode of insertion of the NH2-terminal SIV fusion peptide into the lipid bilayer

We report here on the interaction of a synthetic 12 residue peptide corresponding to the N-terminal sequence of gp32 from SIV with phospholipid bilayers. This peptide has been shown to induce lipid mixing of PC/PE/SM/Chol LUV (large unilamellar vesicles) at pH 7.4 and 37 degrees C [(1992) in: Advances in Membrane Fluidity, vol. 6, pp. 365-376, Wiley-Liss]. In the present study, this fusion process was inhibited by the addition of lysophosphatidylcholine (lysoPC) to the lipid bilayer of PC/PE/SM/Chol LUV. Fourier transform infrared spectroscopy (FTIR) reveals that the orientation of the SIV fusion peptide with respect to the lipid acyl chains depends on the presence of lysoPC in the lipid bilayer but that the peptide secondary structure and the amount of lipid-associated peptides do not depend on the lipid composition. The peptide is obliquely inserted into the lipid bilayer of vesicles without lysoPC, whereas it is oriented parallel to the lipid-water interface in the vesicles containing lysoPC. The data provide evidence that the orientation of the SIV fusion peptide depends on the lipid composition, and that this mediates its fusogenic activity.

Orientation and structure of the NH2-terminal HIV-1 gp41 peptide in fused and aggregated liposomes

For several retroviruses, the N-terminal hydrophobic sequence of the viral envelope glycoprotein has been shown to play a crucial role in the interaction between the virus and the host cell membrane. We report here on the interaction of a synthetic 16 residues peptide corresponding to the gp41 NH2-terminal sequence of Human Immunodeficiency Virus with the phospholipid bilayer. Fluorescence energy transfer measurements show that this peptide can induce lipid mixing of large unilamellar vesicles (LUV) of various compositions at pH 7.4 and 37 degrees C. LUV undergo fusion, provided they contained phosphatidylethanolamine (PE) in their lipid composition. To provide insight into the mechanism of the fusion event, the peptide secondary structure and orientation in the lipid bilayer were determined using Fourier Transform Infrared Spectroscopy (FTIR). The peptide adopts mainly a beta-sheet conformation in the absence of lipids. After interaction with LUV the beta-sheet is partly converted into alpha-helix. The orientation of the peptide with respect to the lipid acyl chains depends on the presence of PE in the lipid bilayer. The peptide is inserted into the lipid bilayer with the helix axis oriented parallel to the lipid acyl chains in the fused vesicles, whereas it is adsorbed parallel to the lipid/water interface in the aggregated vesicles. The role of the two kinds of orientation during the fusion event is discussed.

The location of amantadine hydrochloride and free base within phospholipid multilayers: a neutron and X-ray diffraction study

Concomitant neutron and X-ray studies were undertaken in order to locate accurately the anti-influenza and Parkinson's disease drug amantadine in multilayers of 1,2-dioleoyl-sn-glycero-3-phosphocholine. The X-ray data were phased using the swelling series method and the neutron data were phased using D2O/H2O exchange and a variation of the isomorphous replacement technique. The sets of data complement each other and reveal two populations of amantadine within the bilayer. One site is close to the bilayer surface, the other is much deeper. The majority of the amantadine occupies the surface site. The relative occupancy, but not the position, of the two locations appears to be dependent upon the initial protonation state of the drug. No evidence of bilayer perturbation was observed with either the protonated or the deprotonated forms of amantadine.

Stabilization of clathrin coated vesicles by amantadine, tromantadine and other hydrophobic amines

Amantadine and related compounds stabilized the structure of purified pig brain clathrin coated vesicles (CCV) at biologically relevant concentrations. Incubation of purified CCV for 30 min at 25 degrees C or 37 degrees C caused the release of clathrin, as determined by a centrifugation assay, and a reduction in the number of coated vesicles, by electron microscopy. Amantadine (10 mM), tromantadine (1 mM), amidine D295 (cyclohexylcarboximidamide-(N-benzyl)hydrochloride (10 mM), chloroquine (0.1 mM) and monodansylcadaverine (10 mM) significantly reduced the extent of dissociation.

Inhibition of virus-induced cell fusion by apolipoprotein A-I and its amphipathic peptide analogs

Apolipoprotein A-I (apoA-I), the major protein component of serum high-density lipoproteins (HDL), was found to inhibit herpes simplex virus (HSV)-induced cell fusion at physiological (approximately 1 microM) concentrations, whereas HDL did not exert any inhibitory effect. Lipid-associating, synthetic amphipathic peptides corresponding to residues 1-33 (apoA-I[1-33]) or residues 66-120 (apoA-I[66-120]) of apoA-I, also inhibited HSV-induced cell fusion, whereas a peptide corresponding to residues 8-33 of apoA-I (apoA-I[8-33]), which fails to associate with lipids, did not exert any inhibitory effect. These results suggest that lipid binding may be a prerequisite for peptide-mediated fusion inhibition. Consistent with this idea, a series of lipid-binding 22-amino-acid-residue-long synthetic amphipathic peptides that correspond to the amphipathic helical domains of apoA-I (A-I consensus series), or 18-residue-long model amphipathic peptides (18A series), were found to exert variable levels of fusion-inhibitory activity. The extent of fusion-inhibitory activity did not correlate with hydrophobic moment, hydrophobicity of the nonpolar face, helix-forming ability, or lipid affinity of the different peptides. Peptides in which the nonpolar face was not interrupted by a charged residue displayed greater fusion-inhibitory activity. Also, the presence of positively charged residues at the polar-nonpolar interface was found to correlate with higher fusion-inhibitory activity.

Tromantadine inhibits a late step in herpes simplex virus type 1 replication and syncytium formation

Addition of tromantadine after virus penetration inhibited HSV-1 induced syncytium formation and virus production in HEp-2 and VERO cells and acted additively with neutralizing antibody in blocking virus spread and cytopathology. Inhibition of syncytium formation in VERO cells infected with 0.01 pfu/cell of HSV-1 GC+ was observed at a concentration greater than 25 micrograms/ml. The extent of inhibition was dependent upon the multiplicity of infection and cell type. Tromantadine inhibited a late event in HSV-1 replication which appeared to be sensitive to cycloheximide. Reversal of the inhibitory effect of tromantadine on syncytium formation required new protein synthesis. HSV-1 gB, gC, and gD were synthesized in the presence of tromantadine and could be detected on the cell surface by immunofluorescence. Tromantadine most likely inhibits a cellular process that is required for syncytium formation, such as glycoprotein processing, which occurs after the synthesis of the fusion protein but before its expression on the cell surface.

Liposomes of enviroxime and phosphatidylcholine: definition of the drug-phospholipid interactions

Interaction of the antiviral compound, enviroxime (E), with natural and synthetic phosphatidylcholines in organic and aqueous media was studied. Although insoluble in chloroform, E dissolved in chloroform solutions containing phosphatidylcholines. Solvation was directly related to the length of the fatty acid chains of the phospholipid. Proton spin resonance studies suggested an interaction of the fatty acid chains with the aromatic rings of E. Suspension of E-phosphatidylcholine mixtures of molar ratios up to 0.7:1.0 in aqueous media resulted in the formation of multilamellar liposomes. Liposomes containing E were more stable permeability barriers than those prepared with phospholipid alone, a property previously observed with cholesterol. Competition experiments suggested that E bound to the same sites in lipid bilayers as does cholesterol. These data indicate that E is incorporated into lipid bilayers of liposomes and that it alters the physical properties of the liposomes in a manner similar to that of cholesterol.

Modulation of the bilayer to hexagonal phase transition of phosphatidylethanolamines by acylglycerols

The effect of mono-, di- and triacylglycerols on the bilayer to hexagonal phase (HII) transition was studied by differential scanning calorimetry and 31P-NMR spectroscopy. The acylglycerols were mixed with either dielaidoylphosphatidylethanoline or with 1-palmitoyl-2-oleoylphosphatidylethanolamine. Acylglycerols of lauric, oleic and stearic acids were utilized. All of the acylglycerols lowered the bilayer to HII phase transition temperature. Diacylglycerols were much better HII phase promoters than monoacylglycerols while triacylglycerols were the most potent bilayer phase destabilizers. Fatty acid composition generally had less of an effect except for the monoacylglycerols where bilayer destabilization increased from monolaurin to monostearin to monoolein. The most marked difference in behaviour resulting from changes in the fatty acid composition of the acylglycerol occurred with tristearin. This was the only acylglycerol which decreased the bilayer to HII phase transition temperature only below a mol fraction of 0.005. Above this mol fraction, further addition of tristearin had no effect on the bilayer to HII phase transition. These results suggest that the tristearin has limited solubility in phosphatidylethanolamine.