The action of polyene antibiotics on lipid bilayer membranes in the presence of several cations and anions

ATP-dependent Ca uptake into plant membrane vesicles

Membrane vesicles were extracted from etiolated and light-grown plants, a plant cell suspension culture, and an alga. Upon addition of ATP and Mg(2+), active Ca(2+) uptake into the vesicles against a concentration gradient was shown. The dependence of this uptake on ATP and Mg(2+) concentrations, pH, and temperature is described. In the absence of oxalate, equilibrium between Ca(2+) uptake and efflux was reached after about 30 min. In the presence of oxalate, Ca(2+) accumulation continued for at least 120 min. Ca(2+) efflux from preloaded vesicles did not depend on ATP. Addition of the ionophores A23187 and Ro 20-0006/006 caused an immediate release of accumulated free Ca(2+). ATP-dependent Ca(2+) uptake was not inhibited by 10 muM oligomycin.

Alamethicin as a permeabilizing agent for measurements of Ca(2+)-dependent ATPase activity in proteoliposomes, sealed membrane vesicles, and whole cells

The channel-forming antibiotic peptide alamethicin was used in measurements of Ca-ATPase activity in sarcoplasmic reticulum (SR) vesicles, proteoliposomes containing Ca(2+)-ATPase from SR, and native human platelets. Alamethicin was used as a permeabilizing agent providing for a free access of the whole cells or sealed vesicles interiors for ions, ATP, and other reactants. The experiments were carried out with the use of alamethicin preparations obtained in our laboratory and that purchased from the Upjohn Company (antibiotic U-22,324). A comparative study of the effects of Ca(2+)-ionophore A23187 and alamethicin was performed on native SR vesicles containing Ca(2+)-ATPase molecules with right orientation and SR vesicles treated with cholate in order to randomize Ca(2+)-ATPase molecules orientation in the membrane. It was found out that alamethicin, like A-23187, prevents the ATP-dependent Ca2+ accumulation by the vesicles and therefore activates the Ca(2+)-ATPase. Maximal specific activities of the Ca(2+)-ATPase in native SR vesicles in the presence of either alamethicin, or A23187, or both of them, are equal in all cases to 20 activity units (mumol Pi per min per mg protein). The operative range of alamethicin concentrations is 5-25 micrograms/ml and is a little wider than that for A23187. The ATPase activity of the SR vesicles treated with cholate reached 20 units in the presence of alamethicin while in the presence of A23187 it was only 10 units. These data suggest that alamethicin unlike A23187 allows ATP to reach the ATPase's active centers from the inside of the SR vesicles with 'randomized' membranes, the ATP transport through the membrane not being the rate-limiting stage of ATP hydrolysis. It was shown that diffusion flux of ATP through a BLM in the presence of alamethicin may reach 10% of the flux through the hole without the BLM. With the use of alamethicin it was found out that the quality of randomization of the ATPase molecules orientation in the membrane depends on the proteoliposome preparation technique. The ATP transport through the alamethicin pores makes possible the use of alamethicin in accurate measurements of Ca(2+)-ATPase activity in whole cells. A method was developed for determination of the activity of human platelets was found to be 90-100 nmol Pi per min per mg protein.

Corneal epithelial permeability of dry eyes before and after treatment with artificial tears

PURPOSE

The question of whether artificial tears can lead to objective improvement of ocular surface disease in dry eyes is still unanswered. The aim of the current study is to assess the influence of artificial tears on corneal epithelial permeability of dry eyes. Furthermore, the effect of benzalkonium chloride, used as a preservative of artificial tears, on corneal epithelial permeability is investigated.

METHODS

The corneal epithelial permeability of 40 dry eye patients (80 eyes) was measured by computerized objective fluorophotometry before and 6 weeks after treatment with artificial tears containing either polyvinyl pyrrolidone 2% without preservative (20 patients) or polyvinyl pyrrolidone 2% preserved with benzalkonium chloride 0.005% (20 patients).

RESULTS

Before treatment, the epithelial permeability of the dry eye patients was found to be 2.7 times that of a control group. After treatment, the epithelial permeability of patients treated with unpreserved polyvinyl pyrrolidone 2% had decreased significantly (-37%; P less than 0.001), whereas patients who had been treated with polyvinyl pyrrolidone 2% preserved with benzalkonium chloride 0.005% showed an increase in epithelial permeability (+21%; P = 0.05%).

CONCLUSION

These data suggest that, in dry eyes, treatment with unpreserved artificial tears may lead to an objective improvement in corneal surface disease. However, this effect may be counteracted by preservation of tear substitutes with benzalkonium chloride.

The nature of the conductance increase induced by filipin in cholesterol-containing planar lipid bilayers

The effects of the polyene antibiotic filipin on the conductance and permeability of planar lipid bilayers were investigated under voltage-clamp conditions. The membrane conductance of lipid bilayers containing no cholesterol was not affected by filipin. In the presence of cholesterol containing lipid bilayers, filipin induced a 10(4)-10(5)-fold increase in transmembrane conductance. This conductance increase was dependent on the ionic species present in solution, decreasing in the following order: GCsCl greater than GNaAc greater than GKCl greater than GNaCl greater than CaCl2 greater than GNa2SO4 greater than GBaCl2 greater than GMgCl2. Reversal potential measurements in simple biionic conditions revealed the following relative permeability sequence: PK greater than PCl greater than PNa approximately Pac approximately PBa greater than PCs greater than PMg approximately PCa greater than Psulphate. The filipin-sterol mediated increase in membrane conductance was independent of the membrane potential. The increase in membrane current following a step alteration in membrane potential occurred instantaneously and had no dependence on the previous value of the holding membrane potential. We propose that the filipin-sterol complex forms ion channels in lipid membranes. These channels are found in a single configuration (open state) and select preferentially monovalent cations or anions over divalent ions. Our experimental results are discussed in relation to the effects of other polyene antibiotics on the membrane permeability, and also in relation to experimental problems previously reported with the use of filipin in planar lipid bilayers.

Effect of nystatin, amphotericin B and amphotericin B methyl ester on Saccharomyces cerevisiae with different lipid composition

Saccharomyces cerevisiae was cultured under anaerobiosis in semi-complete medium to which either palmitoleic or oleic acid was added. Cells were grown at 20 degrees C or 30 degrees C. The levels of total lipids, total sterols, and phospholipids were higher in cells grown at 20 degrees C than at 30 degrees C. The effects of nystatin (NYS), amphotericin B (AMB), and amphotericin B methyl ester (AME) were evaluated by determining cell viability and liberation of intracellular compounds. The loss of cell viability is higher in the first 30 minutes of incubation with the drugs and is the same regardless of the type of cells obtained. Low molecular weight compounds and ions such as K+ are liberated a few minutes after incubation with the drugs whereas proteins and substances absorbing at 260 nm are liberated later. Phosphate liberation comes after K+ and before compounds of higher molecular weights.

Diffusion of Mn2+ ions into liposomes mediated by phosphatidate and monitored by the activation of an encapsulated enzymatic system

Transbilayer diffusion of Mn2+ ions occurred in liposomes formed from dipalmitoyl-phosphatidylcholine or egg-yolk phosphatidylcholine and egg-yolk phosphatidate (molar ratio 2:1) containing DNA and DNase I within their aqueous compartments. Cation diffusion was demonstrated by the hydrolytic activity of DNase I, activated by the Mn2+ ions that diffused into the vesicles, and this was confirmed by light scattering. Phosphatidate, a cone-shaped lipid which has been synthesized under simulated prebiotic conditions, was necessary for cation diffusion across the liposome membranes. Such liposomes represent a simple precellular system that interchanges cations with the surroundings and provides a microenvironment for enzymatic reactions, as evidenced by the hydrolysis of DNA by DNase I inside these closed lipid compartments.

A new paramagnetic analogue of cholesterol as a tool for studying molecular interactions of genuine cholesterol

The synthesis of a new paramagnetic (nitroxide) analogue of cholesterol is described. This compound (called CNO) contains a doxyl group in the lateral chain at position 25. Our results show that CNO retains three molecular interactions which characterize authentic cholesterol: It assumes an orientation perpendicular to the phospholipid bilayer with the doxyl group buried in the membrane core, as seen by ESR spectroscopy. It widens the transition temperature of dimyristoylphosphatidylcholine, to the same extent as cholesterol, as measured by Raman and ESR spectroscopies. It interacts with polyene antibiotics, such as amphotericin B and filipin, in the same manner as its model. This was proved on the one hand by the change in fluorescence of self quenched vesicle-entrapped calcein, after dilution in the external medium, provoked by filipin, and on the other hand by fluorescence quenching provoked by cobalt ions entering the vesicles under the influence of amphotericin B. We concluded that CNO, although it has a side chain different from genuine cholesterol, can help to solve many physiologically meaningful questions related to the distribution and movement rate of cholesterol itself.

Latrotoxin-induced fusion of liposomes with bilayer phospholipid membranes

Liposomes containing amphotericin B as ionophoric marker were used to investigate the fusion of bilayer phospholipid membranes with liposomes. It was found that latrotoxin isolated from black widow spider venom induced the fusion of liposomes with planar bilayer when liposomes and latrotoxin were administered at opposite sides of the membrane.

How do the polyene macrolide antibiotics affect the cellular membrane properties?

In the 1970's great strides were made in understanding the mechanism of action of amphotericin B and nystatin: the formation of transmembrane pores was clearly demonstrated in planar lipid monolayers, in multilamellar phospholipid vesicles and in Acholeplasma laidlawii cells and the importance of the presence and of the nature of the membrane sterol was analyzed. For polyene antibiotics with shorter chains, a mechanism of membrane disruption was proposed. However, recently obtained data on unilamellar vesicles have complicated the situation. It has been shown that: membranes in the gel state (which is not common in cells), even if they do not contain sterols may be made permeable by polyene antibiotics, several mechanisms may operate, simultaneously or sequentially, depending on the antibiotic/lipid ratio, the time elapsed after mixing and the mode of addition of the antibiotic, there is a rapid exchange of the antibiotic molecules between the vesicles. Although pore formation is apparently involved in the toxicity of amphotericin B and nystatin, it is not the sole factor which contributes to cell death, since K+ leakage induced by these antibiotics is separate from their lethal action. The peroxidation of membrane lipids, which has been demonstrated for erythrocytes and Candida albicans cells in the presence of amphotericin B, may play a determining role in toxicity concurrently with colloid osmotic effect. On the other hand, it has been shown that the action of polyene antibiotics on cells is not always detrimental: at sub-lethal concentrations these drugs stimulate either the activity of some membrane enzymes or cellular metabolism. In particular, some cells of the immune system are stimulated. Furthermore, polyene antibiotics may act synergistically with other drugs, such as antitumor or antifungal compounds. This may occur either by an increased incorporation of the drug, under the influence of a polyene antibiotic-induced change of membrane potential, for example, or by a direct interaction of both drugs. That fungal membranes contain ergosterol while mammalian cell membranes contain cholesterol, has generally been considered the basis for the selective toxicity of amphotericin B and nystatin for fungi. Actually, in vitro studies have not always borne out this assumption, thereby casting doubt on the use of polyene antibiotics as antifungal agents in mammalian cell culture media.(ABSTRACT TRUNCATED AT 400 WORDS)

Interaction of nystatin with nystatin-resistant Candida tropicalis

Nystatin-resistant yeast Candida tropicalis was obtained after UV illumination and plating on nystatin-containing media. The mutant contained no ergosterol in the plasma membrane but bound nystatin to a degree similar to that of the wild strain (1.2 vs. 1.5 nmol per mg dry solid). Respiration of the mutant on glucose was reduced by 36% in the presence of 25 microM nystatin. This corresponded to a 25-43% decrease of the uptake of monosaccharides. Transport of amino acids was reduced by nystatin in the mutant by 44-86%, as compared with a 84-95% reduction in the wild strain. The intracellular ATP content was reduced by nystatin equally in the wild strain and in the mutant (by 43 and 47%). Nystatin appears to affect specifically membrane transport processes of nonelectrolytes while both the H+-extruding ATPase and the membrane potential are unaffected.

Stimulation of human and canine neutrophil metabolism by amphotericin B

The effect of an antifungal agent, amphotericin B, on human and canine neutrophil metabolism was studied. Commercial preparations of amphotericin B in concentrations ranging from 5 to 100 micrograms/ml stimulated neutrophil chemiluminescence in the presence of 10(-8) M luminol. This response was blocked by 2-deoxyglucose, a metabolic inhibitor, and by the absence of extracellular calcium ions. Neither pure amphotericin B nor the solubilizing agent present in the commercial preparation, alone or in combination, stimulated neutrophil chemiluminescence. Commercial amphotericin B caused an increase in oxygen uptake by neutrophils but no detectable superoxide anion production. Neutrophils were injured by commercial amphotericin B, as shown by an increase in trypan blue dye uptake but not cell lysis. Binding of amphotericin B to neutrophil membrane sterol with a subsequent alteration in membrane configuration is the most likely cause of metabolic stimulation.

Corneal cytotoxicity of topically applied drugs, vehicles and preservatives

The toxicity and side effects of drugs and their adjuncts are reviewed according to effect on corneal epithelium, stroma, and endothelium, when topically applied to healthy or wounded surfaces, or introduced into the anterior chamber of the eye. Corneal research techniques are reviewed, including scanning and transmission electron microscopy, electrophysiological techniques, and specular microscope observation. Clinical interpretation of these results is discussed. Reviews of specific toxicologic techniques and of medications are cited. Present research makes it increasingly apparent that not only medications but also their preservatives cannot be considered innocuous. Preservatives may be effective yet less damaging to the ocular integument when used at lower concentrations than those presently available commercially. Complete avoidance of preservatives by the use of special dispensing systems is found increasingly desirable.

Interaction between phospholipid bilayer membranes and the polyene antibiotic amphotericin B: lipid state and cholesterol content dependence

The interaction between amphotericin B and egg yolk phosphatidylcholine, dimyristoyl (DMPC) and dipalmitoyl phosphatidylcholine (DPPC) phospholipid bilayer vesicles has been monitored by the circular dichroism (CD) spectra of amphotericin B at a 1 . 10(-5) M concentration. This method has revealed that amphotericin B may be present in a number of different forms depending on the time elapsed after the mixing, the cholesterol content of the vesicles and the vesicles' physical state. Some striking features of these CD detected species are the following: with egg yolk phosphatidylcholine and a molar cholesterol percentage lower than 25, at 25 degrees C several forms are coexistent, their amount is time-dependent; with dipalmitoyl or dimyristoyl phosphatidylcholines without cholesterol or with a cholesterol molar percentage lower than 25, in the gel state, a form different from the former appears very rapidly; with egg yolk phosphatidylcholine, DMPC and DPPC at a molar cholesterol percentage between 25 and 50 a new form is monitored, identical in the three cases and observed in the liquid crystalline state as well as in the gel state. In the case of the three phospholipids without cholesterol a definite interaction with the antibiotic is observed but with different characteristics according to the nature of lipid. With amphotericin B 'Fungizone' the same species are monitored but their appearance is much slower. Two explanations are proposed for the origin of the discrepancies between CD and electronic absorption.

Effect of potential cytostatic and immune modulating chemicals on the plasma membrane of red blood cells (RBC) as revealed by osmotic hemolysis, cell electrophoresis and scanning electron microscopy (SEM)

The influence on red blood cells (RBC) of two cancerostatic-(ZIMET 3106 and ZIMET 3393) and two immunomodulating agents (ZIMET 3164 and ZIMET 86/76) administered subcutaneously, or intraperitoneally in case of the radiolabelled N-mustard compounds, to mice, was studied by means of measurements of the radiolabelled compounds in blood, by cell electrophoresis, filipin-induced hemolysis of pretreated RBC and by scanning electronmicroscopy. The portion of doses applied which binds to RBC-surface decreases in the sequence of ZIMET 3106, ZIMET 3164, ZIMET 3393 and ZIMET 86/76. However, the highest reduction of the electrophoretic mobility and protection from filipin-induced hemolysis of pretreated RBC was found with ZIMET 3164. In both tests ZIMET 86/76 proved to be ineffective. These findings are in good agreement with the modifications demonstrated in pretreated RBC after filipin-induced hemolysis by means of SEM. The results presented point to a N-mustard specific interaction between the cholesterol of the membrane and/or other membrane constituents. However, these fundamental differences found in binding affinity, surface-charges and membrane interactions caused by the chemically similar compounds cannot be attributed merely to the N-mustard group.

Effect of the polyene antibiotic filipin and the calcium ionophore A23187 on sodium transport in isolated frog skin (Rana temporaria)

Addition of filipin (50 micrometer) to the inside bathing solution of the frog skin resulted in a transient increase in the active sodium transport [measured as short-circuit current (SCC)]. The filipin-induced increase in the SCC required the presence of calcium. The calcium ionophore A23187 (4 micrometer) also induced a transient increase in the SCC. After the activation of the SCC by A23187, the SCC could not be activated by filipin. This indicates that the polyene antibiotic filipin acts as a calcium ionophore. Higher concentrations (40 micrometer) of A23187 resulted in a shrinking of the cells in the transporting cell layer. A23187 also increased the potassium-42 exchange in the isolated epithelium. It is suggested that calcium ionophores enhanced the intracellular calcium concentration; this increase in the calcium concentration resulted in an increase in the potassium permeability of the inward-facing membrane. The increase in the potassium permeability might explain the observed increase in the SCC.

Effect of the polyene antibiotic filipin on the permeability of the inward- and the outward-facing membranes of the isolated from skin (Rana temporaria)

The effect of the polyene antibiotic filipin on the electrical properties and the passive permeability of the cell membranes was investigated. The addition of filipin to the outside bathing solution has the following effects: 1. it results in a drastic reduction in the transepithelial resistance and potential, 2. it causes a 10-20 times increase in the passive transepithelial chloride, sodium and sucrose flux, 3. it results in the formation of an amiloride insensitive sodium pathway in the outward facing membrane, 4. it results in an active outward transport of potassium, 5. it results in a highly significant swelling of all the cells in the epithelium. The addition of filipin to the inside bathing solution has the following effects 1. it results in an activation of the active sodium transport, 2. it causes a slight increase in the passive transepithelial chloride and sodium permeabilities but has no effect on the sucrose permeability, 3. it has no effect on the amiloride inhibition of the short-circuit current, 4. it has no effect on the volume of the cells in the epithelium. It is suggested that the addition of filipin to the outside bathing solution increases the direct sodium flow from cell to cell in neighbour layers. Furthermore these experiments indicate that the outward facing membrane of the isolated frog skin has a high cholesterol content as compared with the cholesterol content of the inward facing membrane.

Freeze-fracture ultrastructural alterations induced by filipin, pimaricin, nystatin and amphotericin B in the plasmia membranes of Epidermophyton, Saccharomyces and red complex-induced membrane lesions

The effects of chemically different polyenes on fungal membranes (Epidermaphyton floccosum, a human pathogenic fungus, and Saccharomyces cerevisiae) and human red blood cell membranes were studied by freeze-fracture electron microscopy in order to elucidate the interaction of these antibiotics with ergosterol. Each type of neutral, small amphoteric and large amphoteric polyenes produces a distinct morphoneutral, small amphoteric and large amphoteric polyenes produces a distinct morphological effect on the fungal membranes: (1) Pit formation type. Filipin, a neutral polyene, produces 250-300 A diameter "pits" or "invagination" both in ergosterol-containing fungal plasma membranes and cholesterol-containing red blood cell ghost membranes. (2) Network particle aggregation type. The small amphoteric polyene, pimaricin, produces a network of membrane particle aggregation which encloses 1000 A diameter particle-free areas in fungal membranes. These areas are slightly elevated toward the outside of the cell. (3) Random particle aggregation type. The large amphoteric polyenes, amphotericin B and nystatin, cause a random segregation of the fungal plasma membrane and the red blood cell ghost membranes into particle-free and aggregated areas. It is concluded that these morphological differences are due to different mechanisms of polyene-sterol interactions in which the different size of the mocrolide ring in the antibiotic structure may be involved. Since all of these antibiotics, except filipin, cause no alterations on whole red blood cells detectable by negative staining and freeze-fracture electron microscopy, it is possible that they have a higher affinity to ergosterol than cholesterol in membranes.

Interaction of the polyene antibiotics with lipid bilayer vesicles containing cholesterol

The interaction of the polyene antibiotics, amphotericin B, nystatin and filipin with cholesterol-containing single bilayer lipid vesicles has been characterized using gel permeation chromatography and proton magnetic resonance. All three antibiotics bind to vesicles at low concentrations without causing a large amount of vesicle destruction. The strength of binding as determined by gel permeation studies is greater for filipin and amphotericin than for nystatin. Nystatin and amphotericin B at these low concentrations induce a rapid loss of internal vesicle contents consistents consistent with pore formation. Filipin induces no leakage beyond that expected from partial vesicle destruction or general detergent action. At antibiotic levels above 1:1 antibiotic: cholesterol ratios the NMR results show all three antibiotics to cause extensive vesicle destruction. The onset of this behavior, which appears to be independent of the total antibiotic concentraion, indicates a well defined antibiotic : cholesterol interaction stoichiometry. Despite the fact that cholesterol is required for antibiotic activity, the NMR spectra prior to vesicle destruction show no changes indicative of an antibiotic-induced reversal of cholesterol restriction of phosphatidylcholine mobility. The contrast with polyene antibiotic behavior in more extended bilayers is discussed.

Transport of acyclic polyols in Saccharomyces cerevisiae

Acyclic polyols (erythritol, xylitol, ribitol, D-arabinitol, mannitol, sorbitol and galactitol) are not metabolized by Saccharomyces cerevisiae. They are taken up by a fast non-active process, reaching 40-70% distribution referred to total cell water. The uptake is insensitive to temperature, pH (between 4 and 8), 2,4-dinitrophenol and uranyl ions. Its initial rate rises linearly with concentration from 10(-5)M to 1M. The process resembles simple diffusion through large pores or the trapping of the whole solution on the surface. Protoplasts behave like whole cells in this respect. Only erythritol shows a second type of uptake which is inhibitor-insensitive but temperature-dependent.

Sequence of biosynthesis of the components of the polyene macrolides candidin and candihexin: macrolide aglycones as intracellular components

A sequential formation of the single components of the polyene macrolide candidin complex (heptaene) has been found. In addition to the three components occurring in the candidin complex at the end of the fermentation, two other "early" all-trans heptaene components have been characterized. They exist only during the phase of active biosynthesis of candidin. Two of the components of the polyene macrolide candihexin complex (hexaene) that have been described as lacking amino sugar were the only intracellular (mycelium-associated) components observed under conditions in which no extracellular polyene remained attached to the producing cell. The results indicate that glycosylation of the macrolide ring takes place during the secretion process.

Fluorescence studies of the binding of the polyene antibiotics filipin 3, amphotericin B, nystatin, and lagosin to cholesterol

The interactions of filipin III, amphotericin B, nystatin, and lagosin with sterols in aqueous suspension and in vesicles were followed by fluorescence excitation spectra and by measurement of polarized fluorescence intensities. The equilibrium constants for association of the polyene antibiotics with aqueous suspensions of cholesterol follow the order filipin III > amphotericin B > nystatin > lagosin, in agreement with the order reported for the extent of damage these antibiotics cause in natural and model membranes. Fluorescence polarization measurements show that hydrophobic forces are primarily responsible for the formation of the complexes. Filipin III undergoes a large enhancement in fluorescence polarization on binding to aqueous suspensions of cholesterol and epi-cholesterol, and to vesicles of lecithin-cholesterol, lecithin-beta-cholestanol, and lecithinergosterol. Small increases in polarization occur on interaction of filipin III with vesicles derived from lecithin and epi-cholesterol, thiocholesterol, and androstan-3beta-ol. Amphotericin B undergoes a relatively constant enhancement in fluorescence polarization on interaction with the various lecithin-sterol vesicles used and does not display the selectivity exhibited by filipin III. It is suggested that filipin III serves as a probe of lecithin-sterol interaction.