The dissimilar interactions of the calcium antagonist flunarizine with different phospholipid classes and molecular species: a differential scanning calorimetry study

Mitolysosome exocytosis, a mitophagy-independent mitochondrial quality control in flunarizine-induced parkinsonism-like symptoms

Mitochondrial quality control plays an important role in maintaining mitochondrial homeostasis and function. Disruption of mitochondrial quality control degrades brain function. We found that flunarizine (FNZ), a drug whose chronic use causes parkinsonism, led to a parkinsonism-like motor dysfunction in mice. FNZ induced mitochondrial dysfunction and decreased mitochondrial mass specifically in the brain. FNZ decreased mitochondrial content in both neurons and astrocytes, without affecting the number of nigral dopaminergic neurons. In human neural progenitor cells, FNZ also induced mitochondrial depletion. Mechanistically, independent of ATG5- or RAB9-mediated mitophagy, mitochondria were engulfed by lysosomes, followed by a vesicle-associated membrane protein 2- and syntaxin-4-dependent extracellular secretion. A genome-wide CRISPR knockout screen identified genes required for FNZ-induced mitochondrial elimination. These results reveal not only a previously unidentified lysosome-associated exocytosis process of mitochondrial quality control that may participate in the FNZ-induced parkinsonism but also a drug-based method for generating mitochondria-depleted mammal cells.

Clinically Approved Ion Channel Inhibitors Close Gates for Hepatitis C Virus and Open Doors for Drug Repurposing in Infectious Viral Diseases

Chronic hepatitis C virus (HCV) infection causes severe liver disease and affects ca. 146 million individuals. Novel directly acting antivirals targeting HCV have revolutionized treatment. However, high costs limit access to therapy. Recently, several related drugs used in humans to treat allergies or as neuroleptics emerged as potent HCV cell entry inhibitors. Insights into their antiviral modes of action may increase opportunities for drug repurposing in hepatitis C and possibly other important human viral infections.

Flunarizine prevents hepatitis C virus membrane fusion in a genotype-dependent manner by targeting the potential fusion peptide within E1

To explore mechanisms of hepatitis C viral (HCV) replication we screened a compound library including licensed drugs. Flunarizine, a diphenylmethylpiperazine used to treat migraine, inhibited HCV cell entry in vitro and in vivo in a genotype-dependent fashion. Analysis of mosaic viruses between susceptible and resistant strains revealed that E1 and E2 glycoproteins confer susceptibility to flunarizine. Time of addition experiments and single particle tracking of HCV demonstrated that flunarizine specifically prevents membrane fusion. Related phenothiazines and pimozide also inhibited HCV infection and preferentially targeted HCV genotype 2 viruses. However, phenothiazines and pimozide exhibited improved genotype coverage including the difficult to treat genotype 3. Flunarizine-resistant HCV carried mutations within the alleged fusion peptide and displayed cross-resistance to these compounds, indicating that these drugs have a common mode of action.

CONCLUSION

These observations reveal novel details about HCV membrane fusion; moreover, flunarizine and related compounds represent first-in-class HCV fusion inhibitors that merit consideration for repurposing as a cost-effective component of HCV combination therapies.

Protective effect of T-type calcium channel blocker flunarizine on cisplatin-induced death of auditory cells

Changes in intracellular Ca2+ level are involved in a number of intracellular events, including triggering of apoptosis. The role of intracellular calcium mobilization in cisplatin-induced hair cell death, however, is still unknown. In this study, the effect of calcium channel blocker flunarizine (Sibelium), which is used to prescribe for vertigo and tinnitus, on cisplatin-induced hair cell death was investigated in a cochlear organ of Corti-derived cell line, HEI-OC1, and the neonatal (P2) rat organ of Corti explant. Cisplatin induced apoptotic cell death showing nuclear fragmentation, DNA ladder, and TUNEL positive in both HEI-OC1 and primary organ of Corti explant. Flunarizine significantly inhibited the cisplatin-induced apoptosis. Unexpectedly, flunarizine increased the intracellular calcium ([Ca2+]i) levels of HEI-OC1. However, the protective effect of flunarizine against cisplatin was not mediated by modulation of intracellular calcium level. Treatment of cisplatin resulted in ROS generation and lipid peroxidation in HEI-OC1. Flunarizine did not attenuate ROS production but inhibited lipid peroxidation and mitochondrial permeability transition in cisplatin-treated cells. This result suggests that the protective mechanism of flunarizine on cisplatin-induced cytotoxicity is associated with direct inhibition of lipid peroxidation and mitochondrial permeability transition.

Trans fatty acid derived phospholipids show increased membrane cholesterol and reduced receptor activation as compared to their cis analogs

The consumption of trans fatty acid (TFA) is linked to the elevation of LDL cholesterol and is considered to be a major health risk factor for coronary heart disease. Despite several decades of extensive research on this subject, the underlying mechanism of how TFA modulates serum cholesterol levels remains elusive. In this study, we examined the molecular interaction of TFA-derived phospholipid with cholesterol and the membrane receptor rhodopsin in model membranes. Rhodopsin is a prototypical member of the G-protein coupled receptor family. It has a well-characterized structure and function and serves as a model membrane receptor in this study. Phospholipid-cholesterol affinity was quantified by measuring cholesterol partition coefficients. Phospholipid-receptor interactions were probed by measuring the level of rhodopsin activation. Our study shows that phospholipid derived from TFA had a higher membrane cholesterol affinity than their cis analogues. TFA phospholipid membranes also exhibited a higher acyl chain packing order, which was indicated by the lower acyl chain packing free volume as determined by DPH fluorescence and the higher transition temperature for rhodopsin thermal denaturation. The level of rhodopsin activation was diminished in TFA phospholipids. Since membrane cholesterol level and membrane receptors are involved in the regulation of cholesterol homeostasis, the combination of higher cholesterol content and reduced receptor activation associated with the presence of TFA-phospholipid could be factors contributing to the elevation of LDL cholesterol.

Trans fatty acid derived phospholipids show increased membrane cholesterol and reduced receptor activation as compared to their cis analogs

The consumption of trans fatty acid (TFA) is linked to the elevation of LDL cholesterol and is considered to be a major health risk factor for coronary heart disease. Despite several decades of extensive research on this subject, the underlying mechanism of how TFA modulates serum cholesterol levels remains elusive. In this study, we examined the molecular interaction of TFA-derived phospholipid with cholesterol and the membrane receptor rhodopsin in model membranes. Rhodopsin is a prototypical member of the G-protein coupled receptor family. It has a well-characterized structure and function and serves as a model membrane receptor in this study. Phospholipid-cholesterol affinity was quantified by measuring cholesterol partition coefficients. Phospholipid-receptor interactions were probed by measuring the level of rhodopsin activation. Our study shows that phospholipid derived from TFA had a higher membrane cholesterol affinity than their cis analogues. TFA phospholipid membranes also exhibited a higher acyl chain packing order, which was indicated by the lower acyl chain packing free volume as determined by DPH fluorescence and the higher transition temperature for rhodopsin thermal denaturation. The level of rhodopsin activation was diminished in TFA phospholipids. Since membrane cholesterol level and membrane receptors are involved in the regulation of cholesterol homeostasis, the combination of higher cholesterol content and reduced receptor activation associated with the presence of TFA-phospholipid could be factors contributing to the elevation of LDL cholesterol.

An index of lipid phase diagrams

There is a growing awareness of the utility of lipid phase behavior data in studies of membrane-related phenomena. Such miscibility information is commonly reported in the form of temperature-composition (T-C) phase diagrams. The current index is a conduit to the relevant literature. It lists lipid phase diagrams, their components and conditions of measurement, and complete bibliographic information. The main focus of the index is on lipids of membrane origin where water is the dispersing medium. However, it also includes records on acylglycerols, fatty acids, cationic lipids, and detergent-containing systems. The miscibility of synthetic and natural lipids with other lipids, with water, and with biomolecules (proteins, nucleic acids, carbohydrates, etc.) and non-biological materials (drugs, anesthetics, organic solvents, etc.) is within the purview of the index. There are 2188 phase diagram records in the index, the bulk (81%) of which refers to binary (two-component) T-C phase diagrams. The remainder is made up of more complex (ternary, quaternary) systems, pressure-T phase diagrams, and other more exotic miscibility studies. The index covers the period from 1965 through to July, 2001.

Trifluoperazine induces domain formation in zwitterionic phosphatidylcholine but not in charged phosphatidylglycerol bilayers

The interaction of trifluoperazine with the zwitterionic lipids dipalmitoylphosphatidylcholine and dimyristoylphosphatidylcholine and with anionic dimyristoylphosphatidylglycerol was studied by means of microcalorimetry and fluorescence spectroscopy. Intercalation of drug molecules into the lipid bilayers was confirmed by the observed differential scanning calorimetry peak broadening and the decrease in chain-melting temperatures. For trifluoperazine:lipid mole ratios higher than 0.4 and 0.6 (for dipalmitoylphosphatidylcholine and dimyristoylphosphatidylcholine, respectively) the deconvolution of transition profiles into two Gaussian components was possible, which suggests phase separation in the studied mixtures. Deconvolution of the thermograms was not possible for any of the drug:dimyristoylphosphatidylglycerol mole ratios studied. To confirm the existence of phase separation in trifluoperazine-phosphatidylcholine mixtures fluorescence spectroscopy experiments were performed using Laurdan as a probe. From the generalised polarisation versus excitation wavelength dependences, recorded at different temperatures, we conclude that a phase separation occurs in the gel state of the studied trifluoperazine-phosphatidylcholine mixtures. We attribute the existence of domains in the bilayer to the dissimilar interactions of two protonation forms of trifluoperazine with phosphatidylcholine molecules. Structural defects present at domain boundaries could be related to the trifluoperazine induced increase of membrane permeability and fluidity. This may partially explain the mechanism of multidrug resistance modulation by trifluoperazine.

Are lipid phase transitions responsible for chilling damage in human platelets?

In previous studies we have proposed that the well-known chilling-induced activation of human blood platelets can be ascribed at least in part to a thermotropic phase transition in membrane lipids. The evidence that this is the case is reviewed and amplified in this review, followed by an examination of the available physical data concerning phase transitions in lipid mixtures that mimic the mixture found in platelet membranes. Assuming complete mixing at all temperatures and equal contributions of the members of the mixture to the phase transition, the lipid mixture found in platelets should give values for Tm ranging from about 1 degrees C to about 16 degrees C, depending on the isomers present in the mixture. (The former value is not in agreement with the observed Tm, but the latter is in excellent agreement.) However, examination of the phase diagram for a binary pair of lipids found in platelet membranes shows that ideal mixing almost certainly does not occur; instead of a linear phase diagram, a convex one was obtained. This shape for the phase diagram, which would displace Tm to an unexpectedly elevated temperature, is in agreement with previously published phase diagrams for mixtures of this type. The prediction, based on thermodynamic properties of lipids found in the platelets, is that Tm will be displaced upward in more complex mixtures of the composition found in platelets, a prediction that requires experimental testing.

Nisin promotes the formation of non-lamellar inverted phases in unsaturated phosphatidylethanolamines

Nisin, a peptide used as a food preservative, is shown, by 31P-nuclear magnetic resonance and infrared spectroscopy, to perturb the structure of membranes formed of unsaturated phosphatidylethanolamine (PE) and to induce the formation of inverted non-lamellar phases. In the case of dioleoyl-sn-glycero-3-phosphatidylethanolamine (DOPE), nisin promotes the formation of inverted hexagonal phase. Similarly, the peptide induces the formation of an isotropic phase, most likely a cubic phase, with 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphatidylethanolamine (POPE). It is proposed that the insertion of the peptide in the bilayer shifts the amphiphilic balance by increasing the hydrophobic contribution and is at the origin of the changes in the polymorphic propensities of PE. This is supported by the fact that the presence of cholesterol in the PE bilayer inhibits the power of nisin to perturb the membrane structure, most likely because the peptide insertion is difficult in the fluid ordered phase. This finding provides insight into possible antibacterial mechanisms of nisin.

Influence of the antiallergic drug oxatomide and derivatives on membrane structures: relation with inhibition of calcium influx in rat basophilic leukemia cells

Oxatomide is an H1 antihistaminic drug that also inhibits mediator release from mast cells. From previous studies, it appeared that inhibition of the influx of extracellular calcium is the major cause of this inhibition of exocytosis. Here, we explored the role of drug-membrane interactions in the inhibition of mediator release. We investigated the effects on phase transition and fluidity of artificial membranes. All compounds studied distorted the phase transition in L-alpha-dipalmitoylphosphatidylcholine liposomes, which correlated with the drug-induced increase in membrane fluidity measured by fluorescence anisotropy of the bilayer interacting probe 1-[4-(trimethylamino)-phenyl]-6-phenylhexa-1,3,5-triene. Erythrocytes were used to study membrane effects on a cellular level. The hypotonic-induced haemolysis of erythrocytes was inhibited by the drugs. Compounds which increased membrane fluidity of liposomes to a greater extent were also more active in decreasing haemolysis. Drug-induced disturbance of the membranes is related to their effect on the activity of store-operated Ca2+ channels. The activity of these channels in rat basophilic leukemia cells, assayed as 45Ca2+ influx, was most effectively inhibited by oxatomide derivatives, thereby inducing a more rigid membrane structure. Small changes in molecular structure affect the activity of the drugs and these structure-activity relations are discussed.

Phases and phase transitions of the phosphatidylcholines

LIPIDAT (http://www.lipidat.chemistry.ohio-state.edu) is an Internet accessible, computerized relational database providing access to the wealth of information scattered throughout the literature concerning synthetic and biologically derived polar lipid polymorphic and mesomorphic phase behavior and molecular structures. Here, a review of the data subset referring to phosphatidylcholines is presented together with an analysis of these data. This subset represents ca. 60% of all LIPIDAT records. It includes data collected over a 43-year period and consists of 12,208 records obtained from 1573 articles in 106 different journals. An analysis of the data in the subset identifies trends in phosphatidylcholine phase behavior reflecting changes in lipid chain length, unsaturation (number, isomeric type and position of double bonds), asymmetry and branching, type of chain-glycerol linkage (ester, ether, amide), position of chain attachment to the glycerol backbone (1,2- vs. 1,3-) and head group modification. Also included is a summary of the data concerning the effect of pressure, pH, stereochemical purity, and different additives such as salts, saccharides, amino acids and alcohols, on phosphatidylcholine phase behavior. Information on the phase behavior of biologically derived phosphatidylcholines is also presented. This review includes 651 references.

Enhancement of acetylcholine release by homoanatoxin-a from Oscillatoria formosa

The strain NIVA-CYA 92 of Oscillatoria formosa Bory ex Gormont produces phycotoxins with neurotoxic properties. Chemical analysis by gas chromatography/mass spectrometry of a water extract of lyophilized material of the organism showed the presence of only homoanatoxin-a. The mechanism of action of homoanatoxin-a on peripheral cholinergic nerves is so far not known. The neurotoxicity of O. formosa containing homoanatoxin-a was investigated in rat bronchi, rat brain synaptosomes and in GH(4)C(1) cells. The water extract of lyophilized material of the organism produced a concentration-dependent reversible increase in the release of [(3)H]acetylcholine from both K(+) (51 mM) depolarised and non-depolarised cholinergic nerves of the rat bronchial smooth muscle. The K(+)-evoked release of [(3)H]acetylcholine was enhanced by about 75% by a water extract from 15-20 mg/ml of lyophilized algal material. The enhanced release of [(3)H]acetylcholine was substantially reduced by the L-type Ca(2+)-channel blocker verapamil (100 μM) and not by the N-type Ca(2+)-channel blocker ω-conotoxin GVIA (1.0 μM) or the P-type Ca(2+)-channel blocker ω-agatoxin IV-A (0.2 μM). Chelation of intra-cellular Ca(2+) by 1,2-bis-(aminofenoxi)etan-N,N,N',N'-tetraacidic acid/acetoxymethyl (BAPTA/AM) (30 μM) had no effect on the phycotoxin-induced release of [(3)H]acetylcholine, indicating that an extracellular pool of Ca(2+) was important for the action of the phycotoxin on the release of [(3)H]acetylcholine from peripheral cholinergic nerves. In rat brain synaptosomes the algal extract enhanced the influx of (45)Ca(2+) in a tetrodotoxin (1.0 μM) and ω-conotoxin MVIIC (blocker of N-, P- and Q-type Ca(2+) channels) (1.0 μM) insensitive manner. Patch-clamp studies showed that the phycotoxin opened endogenous voltage dependent L-type Ca(2+) channels in neuronal GH(4)C(1) cells. These Ca(2+) channels and the effect of the toxin on the channels were blocked by the L-type Ca(2+)-channel antagonist gallopamil (200 μM). The present results suggest, therefore, that the investigated strain of O. formosa contains homoanatoxin-a, which enhances the release of acetylcholine from peripheral cholinergic nerves through opening of endogenous voltage dependent neuronal L-type Ca(2-) channels.

Mechanism of action of the epileptogenic drug pentylenetetrazol on a cloned neuronal potassium channel

The action of the epileptogenic agent pentylenetetrazol (PTZ) on a cloned potassium channel of the rat brain was studied. The Kv1.1 channel was expressed in oocytes of Xenopus laevis and potassium currents were investigated in outside-out and inside-out membrane patches. The results show that PTZ increased the multi-channel potassium currents at strongly negative potentials and decreased them at potentials positive to -35 mV both in outside-out and inside-out membrane patches. The extent and manner of PTZ action, the concentration dependence as well as the onset and time course of the PTZ effect were the same both in outside-out and inside-out membrane patches. The single-channel potassium currents showed an increase in open probability and frequency of opening and a decrease in close time at -50 mV and vice versa at 0 mV with application of PTZ. The amplitude of single-channel current, the open time and the latency to the first channel opening remained almost unchanged under PTZ. The results indicate that PTZ acts via the cell membrane and influences the membrane-associated part of the potassium channel. Thereby, PTZ accelerates the transition from the inactivated to the open state of the channel at strongly negative potentials and reduces it at slightly negative and positive potentials. This mechanism may be the basis for a gate function which is in favour of the development of epileptic discharges.

Molecular parameters involved in aminoglycoside nephrotoxicity

Aminoglycoside antibiotics are hydrophilic molecules consisting of an animated cyclitol associated with amino sugar. They bind in vivo as well as in vitro to negatively charged membranes. Their use as chemotherapeutic agents is unfortunately accompanied by oto- and nephrotoxic reactions, and the purpose of this review is to examine the role of the molecular interactions between aminoglycosides and membranes in the development of nephrotoxicity. 31P Nuclear magnetic resonance (NMR) and fluorescence depolarization have been used to characterize the effect of aminoglycosides on phosphate heads and fatty acyl chains of phospholipids. 15N NMR has been used to obtain interesting information on regioselective interactions of amino groups of antibiotics with phospholipids. The binding of aminoglycosides with negatively charged membranes is associated with impairment of phospholipid catabolism, change in membrane permeability, and membrane aggregation. Biochemical analysis and 1H NMR spectroscopy have brought information on the molecular mechanism involved in the impairment of phospholipid catabolism. Nephrotoxic aminoglycosides could induce sequestration of phosphatidylinositol and therefore reduce the amount of negative charge available for optimal lysosomal phospholipase activity toward phosphatidylcholine included in liposomes that also contain cholesterol and sphingomyelin. Conformational analysis shows that aminoglycosides, which have a high potency to inhibit lysosomal phospholipase activity, adopt an orientation parallel to the lipid/water interface. This orientation of the aminoglycoside molecule at the interface is also critical to explain the marked increase of membrane permeability induced by less nephrotoxic aminoglycosides such as isepamicin and amikacin. This effect is indeed only observed with aminoglycosides oriented perpendicular to this interface, probably related to the creation of a local condition of disorder. The impairment of phospholipid catabolism, which is considered to be an early and significant step in the development of aminoglycoside toxicity, is therefore not related to the change in membrane permeability. However, the role of this latter phenomenon and of membrane aggregation for aminoglycoside nephrotoxicity could be further investigated.

Inhibition of mediator release in RBL-2H3 cells by some H1-antagonist derived anti-allergic drugs: relation to lipophilicity and membrane effects

In a model for mucosal mast cells (RBL-2H3 cells) a set H1-antagonist derived anti-allergic drugs containing a diphenylmethyl piperazinyl moiety was examined for their ability to inhibit release of the mediator beta-hexosaminidase. Cells were activated with antigen or the calcium ionophore A23187, whether or not in combination with the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA). Oxatomide, hydroxyzine and cetirizine inhibit the antigen induced beta-hexosaminidase release. The release triggered by A23187, whether or not in combination with TPA is hardly influenced by the compounds. A biphasic dependence of the inhibition of exocytosis in RBL cells on lipophilicity is observed with the optimum at log P is 5-6. The extremely lipophilic compounds meclozine and buclizine are not active in this model. pH dependence of the effect of the drugs shows that especially the uncharged species are active in inhibiting exocytosis. The investigated compounds show an effect on phase transitions in L-alpha-phosphatidylcholine dipalmitoyl liposomes as assayed with differential scanning calorimetry (DSC). For the less extremely lipophilic compounds the induced changes in the phospholipid membranes increased with lipophilicity. The relation between structural features of the drug and the interaction with phospholipids is discussed in view of the DSC results. We conclude that location of the active drugs at the membrane or the membrane/protein interface is important for the inhibiting activity on exocytosis. This could affect several membrane related processes, which are abundant in the early phases of the IgE-mediated signal transduction process.

The ability of diphenylpiperazines to prevent neuronal death in dorsal root ganglion neurons in vitro after nerve growth factor deprivation and in vivo after axotomy

The mechanism of neuroprotection by the calcium channel antagonist flunarizine against neuronal death is unknown. We investigated the ability of other calcium channel antagonists (cinnarizine, nimodipine, nicardipine, diltiazem, and verapamil), calmodulin antagonists, and calpain inhibitors to prevent neuronal death in rat dorsal root ganglion neurons in vitro after nerve growth factor (NGF) deprivation and the ability of cinnarizine and diltiazem to protect in vivo after axotomy. In vitro, only neurons treated with cinnarizine or flunarizine were protected from death after withdrawal. In vivo, cinnarizine, but not diltiazem, protected dorsal root ganglion neurons in rats after unilateral sciatic nerve crush. Intracellular calcium concentration ([Ca2+]i) was evaluated with fura 2 after NGF deprivation in vitro. Neurons "committed to die" 24 h after NGF deprivation displayed a decline in [Ca2+]i before visible morphological deterioration consistent with cell death. The influx of extracellular calcium was not necessary to produce neuronal death. Neurons deprived of NGF gradually lost the ability to respond to elevated external potassium with an increase in [Ca2+]i during the first 24 h after trophic factor deprivation. After 24 h, neurons deprived of NGF could not be rescued by readministration of NGF. Neurons protected from cell death with diphenylpiperazines maintained their response to high external potassium, suggesting continued membrane integrity. We speculate that diphenylpiperazines may protect sensory neurons via an unknown mechanism that stabilizes cell membranes.

Binding of the calcium antagonist flunarizine to phosphatidylcholine bilayers: charge effects and thermodynamics

We have examined the partitioning/transfer of the Ca2+ antagonist flunarizine from the aqueous phase into phospholipid bilayers. We show that the binding of the cationic amphiphilic drug flunarizine to phospholipid bilayers displays traditional linear concentration-dependent characteristics once unmasked of electrostatic effects. The coefficient for the binding/partitioning of flunarizine to phosphatidylcholine was found to be 28700 M-1, supporting the notion that this drug may be particularly membrane-active. The thermodynamics of the partitioning/transfer process have also been studied using high-sensitivity titration calorimetry. Binding was found to be predominantly enthalpy-driven with only a small entropic contribution; delta H = -22.1 kJ.mol-1 (-5.3 kcal.mol-1) at 27 degrees C. This is in conflict with established ideas of entropy-driven partitioning of drugs into phospholipid membranes as a result of the 'hydrophobic effect'. The strong enthalpic nature of binding is interpreted as being indicative of strong lipophilic interactions between the drug and the phospholipid phase.

Effect of intra-erythrocytic magnesium ions on invasion by Plasmodium falciparum

Exclusion of magnesium ions from resealed ghosts or their extraction from intact human red cells by means of an ionophore results in a reversible drop in susceptibility to invasion by Plasmodium falciparum merozoites in vitro. Resealed ghosts, containing magnesium-ATP and diluted cytosol, are invaded with high efficiency only when the original hypotonic lysis is carried out in the presence of magnesium ions. This effect is not related to the loss of membrane-associated constituents when magnesium ions are absent. Ghosts containing calcium ions, together with the protective agent, flunarizine, were essentially resistant to invasion; this effect is again at least partially reversible. A possible explanation of these phenomena is that entry of the merozoite may be inhibited by breakdown of the host cell phospholipid asymmetry, with the appearance of aminophospholipids at the outer cell surface.

The ability of cationic amphiphilic compounds to depress the transition temperature of dipalmitoylphosphatidic acid liposomes depends on the spatial arrangement of the lipophilic moiety

The hypothesis was tested with the help of model compounds that the ability of cationic amphiphilic drugs to depress the phase-transition temperature Tt of dipalmitoylphosphatidic acid (DPPA) liposomes depends on the spatial arrangement of the lipophilic moiety. The main structure of the compounds with identical cationic side chain was 1-dimethylamino-3-phenylpropane (compound I). A further phenyl ring was introduced either at C3 of the propane chain (compound II) to broaden the lipophilic moiety, or in para-position of the phenyl ring (compound III) to elongate it. As shown by differential scanning calorimetry, the reduction of Tt (control 64 degrees) amounted for compound I to 29 degrees, for compound II to 28 degrees and for compound III to 53 degrees. In order to assess the binding affinity of the compounds to DPPA, their inhibitory effect on 45Ca(2+)-binding to DPPA films was measured. The IC50 values were 2100 microM for compound I, 40 microM for compound II, and 9 microM for compound III. Thus, binding affinity corresponded with the hydrophobicity of the compounds. In contrast, the depressing effect on the transition temperature was only augmented by the additional phenyl ring when substituted in the elongating position.