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J Bolard

Publications and source records attributed to J Bolard.

At least 73 records · Page 4Linked to original sources
PubMed1986

Structural features determining the haemolytic activity of vacidin A derivatives.

The haemolytic activity of aromatic heptaene antifungal antibiotics (vacidin A and its analogues) can be decreased by chemical modification. It has been shown that the ionic state of the polar head of the antibiotic molecule is essential for this activity. The effect of the net charge of the antibiotic molecule on association constant, K, between polyene and membrane-located cholesterol; and the number, n, of antibiotic molecules per one erythrocyte critical for lysis induction was investigated. In addition, changes in the structure of the polyene-cholesterol complex were monitored by circular dichroism spectroscopy. Zwitterionic native antibiotics (vacidin A and gedamycin), the negatively charged N'-acetyl derivatives and the positively charged methyl esters were used in these studies. The results presented indicate that two different phenomena are responsible for the decrease in the haemolytic activity of the compounds studied: for N'-acetyl derivatives the decrease of activity is mainly a result of lower affinity of negatively charged molecules to the membranes; for methyl esters the drastic decrease of activity is mainly a result of the different structure of the antibiotic-cholesterol complex. The permeabilizing species formed from these complexes are characterized by very low efficiency of ion permeation.

Antifungal Agents↗
PubMed1985

Interaction of adriamycin with negatively charged model membranes: evidence of two types of binding sites.

The interaction of the antitumor compound adriamycin with negatively charged unilamellar phospholipid vesicles was studied. The negative charges were provided by cardiolipin or phosphatidic acid. By analyzing the changes in the circular dichroism spectrum of adriamycin, we demonstrated the presence of two different spectral patterns corresponding to two different binding sites (I and II) on the vesicles. In site I, the amino sugar of adriamycin is bound to the ionized phosphate of either cardiolipin or phosphatidic acid, and the dihydroxyanthraquinone lies outside the bilayer. In site II, the amino sugar is still bound to the phosphate, but the dihydroxyanthraquinone moiety is embedded in the bilayer. This has been shown by measuring spectroscopically the binding of the aglycon part to an external probe and by measuring the susceptibility of bound adriamycin to reduction by NADH dehydrogenase.

Cardiolipins↗
PubMed1985

Interaction of the polyene antibiotic etruscomycin with large unilamellar lipid vesicles: binding and proton permeability inducement.

The effect of the polyene antibiotic etruscomycin on the permeability of large unilamellar lipid vesicles was investigated. Proton leakage was induced in egg-yolk phosphatidylcholine (EPC) vesicles only when sterol was present in the membrane; the extent of leakage was limited. High etruscomycin/lipid ratios (R) were necessary (R greater than 0.1). Higher percentages of sterol increased the permeability, slightly more strongly for ergosterol than for cholesterol. Dipalmitoylphosphatidylcholine (DPPC) vesicles were more sensitive to permeability inducement, even in the absence of sterol in the bilayer (inducement for R greater than 0.06). The interactions of etruscomycin with the vesicles were examined by circular dichroism, fluorescence and 31P-NMR. In the range of antibiotic concentration where permeability was induced, R greater than 0.1 for EPC vesicles, R greater than 0.06 for DPPC vesicles, etruscomycin exhibited characteristic circular dichroism spectra independent of the presence of sterol. Under the same conditions, 31P-NMR and fluorescence studies indicated a destruction or a fusion of the vesicle bilayer. At lower etruscomycin concentrations (R less than 0.03), the etruscomycin circular dichroism spectra were different, indicating that the interaction with membranes containing ergosterol differed from that with membranes containing cholesterol. From correlating the increase in fluorescence intensity with this interaction, as well as from exchange experiments, it was inferred that etruscomycin at a low antibiotic/lipid ratio is more strongly bound to ergosterol-containing vesicles than to cholesterol-containing vesicles. These results and their comparison with the results obtained with other polyene antibiotics indicate that at low R etruscomycin resembles amphotericin rather than filipin in its preferential binding to ergosterol-containing vesicles. At higher R, that is in conditions where permeability is induced, the selectivity is different. The corresponding mechanism seems not to involve the formation of an etruscomycin-sterol channel, since the hydrophobic chain of the complex would be too short to form a channel.

Antifungal Agents↗
PubMed1985

Transfer of amphotericin B from gel state vesicles to mycoplasma cells: biphasic action on potassium transport and permeability.

The action of amphotericin B on the K+ permeability of Mycoplasma mycoides var. capri cells, containing either cholesterol or ergosterol in their membranes, was studied. When the drug, solubilized in dimethyl sulfoxide, was added directly to the cell suspension, a slightly greater sensitivity to permeabilization was observed for ergosterol-containing cells, confirming the data reported in the literature. When amphotericin B bound to gel state phospholipid vesicles was added to the cell suspension, two effects on cholesterol-containing cells were observed. First, the K+ active transport rates increased; membrane permeabilization and K+ leakage were subsequently detected. For ergosterol-containing cells these sequential events were observed only at amphotericin B concentrations below 10(-6) M. At higher concentrations only K+ leakage was observed. The second permeabilization effect varied with the amphotericin B concentration in different ways in the two types of cells. The permeabilization of ergosterol-containing membranes depended on the amphotericin B/phospholipid molar ratio, whereas the permeabilization of cholesterol-containing membranes did not. In general, the latter remained fairly constant when the total amphotericin B concentration in the medium varied.

Amphotericin B↗
PubMed1985

Raman spectra of nystatin. Influence of impurities.

The Raman spectra of the polyene antibiotic nystatin have been investigated between 1500 and 1650 cm-1. Only one band is observed in the resonance Raman spectra obtained with a 3045 A excitation radiation. Two major bands are observed in the preresonance spectra of pure nystatin obtained with a 4545 A excitation. A supplementary band at 1557 cm-1 observed in the preresonance spectra of samples of commercial origin is ascribed to the presence of heptaene impurities, the Raman spectra of which are preferentially enhanced by resonance, owing to the closer proximity of their absorption to the excitation radiation.

Chemical Phenomena↗
PubMed1984

Inhibition by Cu2+ of amphotericin B induced lysis of erythrocytes.

Amphotericin B-induced lysis of erythrocytes is diminished in the presence of Cu2+, but the prelytic amphotericin B-induced K+ leakage is unaffected. These results and the weak binding of Cu2+ to amphotericin B, demonstrated by circular dichroism and EPR studies, are consistent with the view that Cu2+ protects erythrocytes by increasing their resistance to lysis.

Amphotericin B↗
PubMed1984

Enhancement of amphotericin B selectivity by antibiotic incorporation into gel state vesicles. A circular dichroism and permeability study.

The permeability induced in cholesterol-or ergosterol-containing phospholipid vesicles by Amphotericin B incorporated into Dipalmitoyl Phosphatidylcholine vesicles has been studied in parallel with Circular Dichroism spectroscopy measurements. In our conditions, Amphotericin B is 5 to 10 times more selective to ergosterol- than to cholesterol-containing vesicles. Such a large difference is not observed when Amphotericin B is directly added to the vesicles suspension as its solution in organic solvent.

Amphotericin B↗
PubMed1984

Effect of surface curvature on the interaction of single lamellar phospholipid vesicles with aromatic and nonaromatic heptaene antibiotics (vacidin A and amphotericin B).

The interactions of unilamellar lipid vesicles with vacidin A, an aromatic heptaene antibiotic, and with amphotericin B, a nonaromatic heptaene antibiotic were compared. Uptake of both antibiotics, monitored by circular dichroism, was found to be faster with small vesicles than with large ones. By combining permeability measurements (Gary-Bobo and Cybulska, J. Antibiotics 35, 1068 (1982)) and circular dichroism spectra, we found that for vacidin A, the same permeability inducing species is formed regardless of vesicles size. However, at a given concentration of antibiotic, less of the permeability inducing species is formed in the presence of small vesicles than in the presence of large vesicles. This may account for the differences between small and large vesicles in antibiotics-induced permeability. For amphotericin B, the permeability inducing species formed in the presence of small vesicles differs from that formed in the presence of large vesicles.

Amphotericin B↗
PubMed1984

UV-induced small structural changes in the T7 bacteriophage studied by melting methods.

UV optical absorption and circular dichroism (CD) properties (spectra and melting curves) of T7 bacteriophage were investigated to detect "in situ" structural damages which can be related to the biological inactivation due to UV irradiation. UV doses (0.2-1.2 kJ/m2 at 254 nm) near to the biologically effective minimal dose were applied where the initial genetic damage (approximately 10 events/phage) was observed. The decrease of the melting temperature of the helix-coil transition and the broadening of the transition range indicate the destabilization of the intraphage structure due to the presence of about 0.1-0.6% damaged base concentration.

Circular Dichroism↗
PubMed1984

Interaction of plasma proteins and lipoproteins with amphotericin B.

Amphotericin B (AmB) binds to the cholesterol in lipoproteins, as determined by comigration in density gradient ultracentrifugation and changes in the circular dichroic spectrum. The saturation curve and Scatchard plots obtained with circular dichroism suggest that four to 10 cholesterol molecules in low-density lipoproteins bind to one molecule of AmB. AmB interacts more rapidly with low- and very-low-density lipoproteins than with high-density lipoproteins, but the circular dichroic spectrum of the complexed species is the same in all three cases. AmB also binds to other proteins in blood, but much higher concentrations of these proteins than of lipoproteins are needed for comparable binding. Interaction with lipoproteins stabilizes the antifungal activity of AmB. Interaction with lipoproteins and with much higher concentrations of other proteins in blood can also inhibit the effects of AmB on red blood cells, which contain cholesterol in their plasma membranes, but not the effects on Candida albicans, whose membranes contain ergosterol. An appropriate inference is that, when used clinically, AmB circulates in blood bound to lipoproteins and other proteins. The toxic and therapeutic effects of AmB in clinical situations are thus contingent on competitive interactions between sterol-containing cellular membranes of the host and the parasite and components of blood, such as lipoproteins and proteins.

Amphotericin B↗
PubMed1983

Circular dichroism study of the interaction between aromatic heptaene antibiotics and small unilamellar vesicles.

Unlike the non-aromatic heptaene amphotericin B, only two types of complex are revealed by circular dichroism when the aromatic heptaenes interact with lipid vesicles. The first is formed when no permeability is observed. The second one is correlated with the appearance of permeability. The cholesterol concentration and the physical state of the membrane have influence only on the amount of the permeabilizing species. These results indicate important differences in the membrane properties of aromatic and non-aromatic heptaenes.

Anti-Bacterial Agents↗
PubMed1983

Differences in the interaction of the polyene antibiotic amphotericin B with cholesterol- or ergosterol-containing phospholipid vesicles. A circular dichroism and permeability study.

The selective toxicity of the polyene antibiotic amphotericin B between pathogenic eukaryotic organisms and animal cells has often been said to originate in the presence of ergosterol in fungal membranes instead of cholesterol, found in membranes of animal cells. We have tested this hypothesis by measuring the proton efflux induced by amphotericin B in egg yolk phosphatidylcholine small unilamellar vesicles. By measuring circular dichroism under the same conditions, we monitored the interaction of the antibiotic and its conformational changes. Sterol-free vesicles are sensitive to amphotericin B, but the sensitivity of sterol-containing vesicles is always greater and increasingly so with increasing sterol concentration. Ergosterol-containing vesicles are more sensitive than cholesterol-containing vesicles. On the other hand, numerous amphotericin B conformers can be detected in sterol-containing vesicles, depending upon both the concentration of sterol and the amphotericin B sterol ratio. It appears that one conformer, or maybe two at high amphotericin B concentration, is responsible for the induced permeability. From their circular dichroism spectra, these two conformers are the same in the presence of ergosterol or cholesterol. The concentration of amphotericin B necessary to obtain the two conformers is higher with cholesterol than with ergosterol, which agrees with the permeability results.

Amphotericin B↗
PubMed1983

Circular dichroism studies in the near UV of ligand binding to chicken liver dihydrofolate reductase.

Circular dichroism spectra in the near UV (250-400 nm) were recorded for chicken liver dihydrofolate reductase and its complexes with substrates, inhibitor methotrexate, and cofactor NADPH. The spectra obtained with methotrexate are very like those published for bacterial dihydrofolate reductases. Thus we suggest that the conformations of methotrexate at the active site of the chicken liver enzyme and that of the enzyme from Lactobacillus casei which has been described extensively in X-ray studies show a great similarity. The same similarity does not hold in the case of the substrate dihydrofolate where the C.D. spectra of binary complexes obtained with enzymes from different sources are different.

Animals↗
PubMed1982

Association of the polyene antibiotic amphotericin B with phospholipid vesicles: perturbation by temperature changes.

Conformational changes of amphotericin B in the presence of cholesterol as well as in the presence of bilayer vesicles of phosphatidylcholine with saturated fatty acid chains of various lengths (14 less than n less than 22) have been monitored by circular dichroism (CD). It has been shown that the observed species are not only dependent on such parameters as the cholesterol content of the vesicles, the vesicles' physical state, and the number of amphotericin B molecules per vesicle, but also on the time elapsed after mixing and the thermal treatment of the system, which may create irreversible changes. In particular, heating through the transition temperature (Tc) vesicles containing cholesterol and loaded with amphotericin below Tc leads to the expulsion into the aqueous medium of a cholesterol-amphotericin complex, a phenomenon which affords an explanation for some of the electron paramagnetic resonance and resonance Raman results. It has also been shown by gel filtration, ultracentrifugation, and Tc determination that interaction of amphotericin B with vesicles in the gel state induces fusion or aggregation of the vesicles, which is not the case (or at least weakly) when the vesicles are in the liquid crystalline state. This aggregation is the more rapid the nearer the temperature of the reaction is to Tc. This study confirms the great complexity of events which may occur during interaction of amphotericin B with model membranes and presents some results which complement those of studies performed with other spectroscopic methods.

Amphotericin B↗
PubMed1981

[Incorporation of (3R,3'R)zeaxanthin in vesicles of dipalmitoyl phosphatidylcholine. Circular dichroism analysis].

The organization of carotenoids in biological membranes has been investigated by monitoring by circular dichroism the incorporation of (3R, 3'R) zeaxanthin in small unilamellar vesicles of dipalmitoyl phosphatidylcholine (DPPC). For ratios zeaxanthin/phospholipid greater than 1/30, a drastic circular dichroism increase indicates the existence of a new type of interaction between zeaxanthin and DPPC.

Biophysical Phenomena↗
PubMed1980

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.

Amphotericin B↗