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Biomedical subjects

N D Weiner

Publications and source records attributed to N D Weiner.

At least 37 records · Page 2Linked to original sources
PubMed1988

Topical ciclosporin for psoriasis: in vitro skin penetration and clinical study.

In contrast to oral administration, topical ciclosporin is not effective in the treatment of psoriasis. This may be due to the drug's inability to penetrate the stratum corneum or to a need for systemic metabolism of ciclosporin to active metabolites. We conducted a preliminary evaluation of the ability of ciclosporin, in a variety of vehicles, to penetrate excised human skin in a two-compartment diffusion cell, a standard in vitro technique for evaluating percutaneous drug delivery. A high-pressure liquid chromatography assay for ciclosporin did not detect the passage of ciclosporin through skin. This finding was consistent through multiple trials, some of which evaluated Azone or liposomal formulations, which are reported to enhance the penetrability of certain compounds. These results indicate that ciclosporin is unable to penetrate human skin in the vehicles tested. This may explain the lack of clinical efficacy we demonstrated in 5 patients with psoriasis treated with topical ciclosporin for 14-16 days.

Administration, Topical↗
PubMed1987

Aminoglycoside antibiotics preferentially increase permeability in phosphoinositide-containing membranes: a study with carboxyfluorescein in liposomes.

The rate of release from multilamellar liposomes of the fluorescent probe carboxyfluorescein was determined as a measure of membrane permeability. Liposomes of phosphatidylcholine and different anionic phospholipids were incubated with low (1 microM) and high (3 mM) concentrations of calcium in the absence or presence of aminoglycoside antibiotics. The leakage of carboxyfluorescein into the medium was not caused by liposomal fusion as no vesicle fusion was observed in experiments with terbium and dipicolinic acid-loaded liposomes. The basal rate of carboxyfluorescein release (in the absence or presence of 1 microM calcium) from all types of liposomes ranged from 0.1 to 0.3% of trapped carboxyfluorescein per hour. The presence of 3 mM calcium caused the greatest increase in the rate of carboxyfluorescein release (about 9-fold) in liposomes containing phosphatidylinositol 4,5-bisphosphate (PIP2) whereas liposomes containing the other anionic phospholipids (phosphatidylserine, phosphatidylinositol and phosphatidylinositol 4-phosphate) showed an approximate 5-fold increase. In the presence of 1 microM calcium, the aminoglycosides neomycin and gentamicin also increased the rate of carboxyfluorescein release, with PIP2-containing liposomes showing a 3-5-times greater response than the other liposomes, releasing up to 4.6% of trapped carboxyfluorescein per hour. This drug-induced release was dose-dependent and antagonized by calcium. In the presence of 3 mM calcium, 0.1 mM gentamicin or neomycin were ineffective while the drug at 1 mM affected carboxyfluorescein release from PIP2-liposomes only. The aminoglycoside antibiotics, neomycin, gentamicin, tobramycin, kanamycin, amikacin, netilmicin, as well as neamine and spectinomycin (all at 0.1 mM) showed a graded effect on the rate of carboxyfluorescein release from PIP2-containing vesicles in the presence of 0.1 mM calcium. The magnitude of the effect correlated well with the ototoxicity of the drugs previously determined directly in cochlear perfusions in the guinea pig. The study demonstrates that aminoglycoside antibiotics are capable of altering membrane permeabilities and that this effect is most pronounced if PIP2 is present in the bilayers. The excellent correlation between this membrane action and the in-situ toxicity of the drugs further establishes the specific role of PIP2 in the molecular mechanism of aminoglycoside-induced hearing loss. Moreover, it confirms the usefulness of such physicochemical models for the screening and prediction of aminoglycoside toxicity.

Aminoglycosides↗
PubMed1984

Interaction of calcium and neomycin with anionic phospholipid-lecithin liposomes. A differential scanning calorimetry study.

The interactions of calcium and neomycin with liposomes of various anionic phospholipids plus lecithin were studied by differential scanning calorimetry. Phosphatidylinositol bisphosphate differed from other acidic phospholipids in its interactions with both calcium and neomycin. Calcium, at concentrations as low as 1 mM, induced the appearance of a second transition peak in phosphatidylinositol bisphosphate-enriched liposomes only. Neomycin acted antagonistically and precluded this phase separation. In addition, neomycin lowered the phase transition temperature of phosphatidylinositol bisphosphate-lecithin liposomes while it raised the transition temperature of all other anionic phospholipid-lecithin liposomes tested. This fluidizing effect of neomycin and the antagonism to calcium may induce critical alterations of properties of biological membranes. The study supports and extends our previous findings and conclusions that phosphatidylinositol bisphosphate may play a crucial role in the expression of aminoglycoside toxicity.

Calcium↗
PubMed1984

Characterization of aminoglycoside-lipid interactions and development of a refined model for ototoxicity testing.

Aminoglycoside interactions with various phospholipids were measured in three model systems and compared with the ototoxicities of the drugs: (a) competition for [14C]neomycin binding; (b) competition for 45Ca2+ binding; and (c) effect on surface pressure of monomolecular lipid films. The efficacies of the antibiotics in displacing neomycin from phosphatidylserine, phosphatidylinositol or phosphatidylinositol bisphosphate were netilmicin greater than neomycin greater than or equal to gentamicin; the efficacies in displacing calcium from phosphatidylinositol, phosphatidylinositol phosphate or phosphatidylinositol bisphosphate were netilmicin greater than gentamicin greater than neomycin much greater than kanamycin greater than spectinomycin. Neither measure correlated well with the ototoxicities of the drugs which were quantitated at equimolar drug concentrations in cochlear perfusions: neomycin greater than gentamicin greater than or equal to tobramycin greater than netilmicin greater than or equal to amikacin. When monomolecular films of phosphatidylcholine with phosphatidylserine, cardiolipin, phosphatidylinositol, or phosphatidylinositol phosphate or bisphosphate were challenged with neomycin, the phosphatidylinositol bisphosphate film showed a unique dose-dependent increase in surface pressure while the others showed a decrease or no significant effect. The abilities of aminoglycosides to increase the surface pressure of a film of phosphatidylcholine:phosphatidylinositol bisphosphate (1:1 molar ratio) in the presence of 3 mM CaCl2 correlated well with their toxicities. Non-ototoxic cations increased the film pressure or left it unaffected. The results confirm the unique interactions between aminoglycosides and phosphatidylinositol bisphosphate as a possible basis of a mechanism of toxicity and development of a drug-screening system.

Aminoglycosides↗
PubMed1983

Monolayer studies of insulin-lipid interactions.

The interactions between insulin and various lipids were studied by monolayer penetration experiments at constant surface area. The increase in surface pressure, delta II, of a lipid film depended upon the particular lipid used and the concentration of insulin in the subphase. For all lipids studied, delta II was dependent on the initial surface pressure of the lipid film. Evidence of the interaction between insulin and the lipids was found in the ability of insulin to penetrate lipid films with initial pressures greater than 16 dynes/cm, the maximum surface pressure obtained by insulin alone. For phospholipids, both the nonpolar and polar regions influenced the degree of interaction with insulin. Saturated chain lecithins exhibited less penetration than phospholipids with unsaturated hydrocarbon chains. The net charge of the lipid was not found to be an important determinant of penetration; however, the structure of the polar group can have a dramatic effect. Insulin penetration of mixed lipid films cannot be predicted by the penetration characteristics of the pure components. The possible role of these interactions in determining the geography of the insulin molecule within the liposome and its resultant effects on the stability is discussed.

Animals↗
PubMed1983

Effects of calcium and neomycin on phase behavior of phospholipid bilayers.

Calcium ion (Ca2+, 5 mM) caused a large upward shift in the transition temperature (Tc) of dipalmitoyl phosphatidylglycerol liposomes, apparently interacting with external and internal lipid in the bilayer. Neomycin (1 mM) caused only a small shift, apparently not penetrating the internal lipid domains. When liposomes were first incubated with Ca2+ followed by neomycin, the shift in Tc indicated displacement of Ca2+ by the drug. Liposomes of dipalmitoyl phosphatidylcholine or distearoyl phosphatidylcholine did not interact significantly with either cation. In mixed dipalmitoyl phosphatidylcholine-dipalmitoyl phosphatidylglycerol and distearoyl phosphatidylcholine-dipalmitoyl phosphatidylglycerol liposomes, addition of Ca2+ or neomycin resulted in phase separation.

Calcium↗
PubMed1982

Lysine and polylysine: correlation of their effects on polyphosphoinositides in vitro with ototoxic action in vivo.

Low concentrations of poly-L-lysine, a polycationic hydrophilic molecule, caused a large expansion of polyphosphoinositide monolayers and produced a significant loss of cochlear microphonic potentials in perilymphatic perfusions in the guinea pig. In contrast, the monomeric L-lysine had only slight effects on polyphosphoinositide monolayers and did not affect cochlear microphonic potentials even at concentrations as high as 10 mM. These data substantiate the hypothesis that the expansion of polyphosphoinositide monolayers by a drug is an indicator of its ototoxicity.

Animals↗
PubMed1981

Delivery of liposome membrane-associated sterols through silastic membranes.

The transport of sterols incorporated into the lecithin bilayer of small unilamellar liposomes through a model membrane was studied. A two-chamber diffusion cell containing liposomes with incorporated [4-14C)cholesterol or beta-[4-14C]sitosterol in the donor chamber and liposomes with unlabeled cholesterol in the receiver chamber was used. The permeability coefficients of the sterols through silastic rubber membranes which served as a model membrane were measured. The permeability for cholesterol incorporated into liposomes in a phosphatidyl choline/cholesterol molar ratio of 1 : 1, produced by sonication for 1 h, and subsequent centrifugation at 100 000 X g for 1 h, was 1.6 . 10(-8) cm sec-1. Dilution of the liposome suspension did not change the permeability coefficient significantly. The permeability coefficient of sitosterol incorporated into liposomes was about 4-times smaller than that of cholesterol. These results suggest that the sterols were delivered to the silastic membrane by the intact liposomes and that free solute was not involved in the transport to the membrane to a significant degree. The large differences in the permeability coefficients between cholesterol and sitosterol indicate that an aqueous interfacial barrier was crossed by the sterol during the delivery to the membrane.

Cholesterol↗
PubMed1979

Interactions of neomycin with monomolecular films of polyphosphoinositides and other lipids.

The interactions of calcium and the aminoglycosidic antibiotic, neomycin, with various lipids were investigated in monomolecular films. Lipids were spread over a subphase of 0.05 M N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid, pH 7.0, and NaCl to give an ionic strength of 0.2. Measurements of surface pressure (pi) were taken with a Wilhelmy balance. In the absence of Ca2+, 1 muM--1 mM neomycin in the subphase decreased pi (i.e. condensed films) of all acidic lipids tested. In the presence of 1 mM Ca2+, neomycin did not change pi of films of phosphatidylserine, phosphatidylinositol and phosphatidic acid while it lowered pi of cardiolipin and cerebroside sulfate films. A unique pattern of interaction was observed with polyphosphoinositide monolayers. In the absence of Ca2+, 1 muM neomycin decreased pi followed by an increase of pi at higher neomycin concentrations. Ca2+ (1 mM) condensed the film significantly more than did neomycin. However, as little as 1 muM neomycin induced expansion of the calcium/lipid film which at 1 mM neomycin reached the same pi as in the absence of Ca2+. Such expansion was observed at all pressures of the film including the collapse pressure indicating a strong 'complex' between the drug and polyphosphoinositide not antagonized by Ca2+. In the absence of possible hydrophobic interactions, both the condensation and the expansion of the film should be mediated by ionic forces. Combined in vivo and in vitro evidence is discussed to suggest the polyphosphoinositides as the physiological receptors for aminoglycosides in the mammalian cell membrane.

Calcium↗
PubMed1977

Enzymatic activity of pig heart mitochondrial malate dehydrogenase monomolecular films by surface exchange technique.

A technique for studying the catalytic activity of enzymes spread as a film at an air-water interface, by exchanging the subphase under the film to remove unspread enzyme molecules, was developed, and its effectiveness was studied using surface-spread mitochondrial malate dehydrogenase. Mitochondrial malate dehydrogenase formed stable films which gave reproducible pi-A curves. The enzyme activity was measured by the oxidation rate of reduced nicotinamide adenine dinucleotide (NADH) in the presence of the substrate oxalacetic acid. Oxalacetic acid and NADH were injected into the subphase. The catalytic activity of the enzyme was dependent on the surface pressure of the film. The maximum catalytic activity was observed at a surface pressure of 4.4 dynes/cm. The activity was higher at intermediate surface pressures than at very low or very high surface pressures. A high bulk catalytic activity was observed in the unstable region, i.e., at a high degree of compression, of the film. The catalytic activity of the surface-spread enzyme was only a fraction of an equivalent amount of enzyme in solution.

Animals↗
PubMed1977

Effect of lipids on enzymatic activity of pig heart mitochondrial malate dehydrogenase monomolecular films.

The effect of various lipids on the enzymatic activity of pig heart mitochondrial malate dehydrogenase monomolecular films was studied using the subphase exchange technique described previously. Surface pressure-surface area (pi-A) curves of mixed films of enzyme with dipalmitoyllecithin, egg lecithin, cholesterol, and phospholipids extracted from pig hearts showed that the enzyme interacted with all of the lipids and that the enzyme remained in the film at pressures well above the collapse pressure of malate dehydrogenase in the absence of lipid. The surface enzyme activity was dependent on surface pressure for each lipid; in all cases, the lipids greatly broadened the range of surface pressures where surface enzyme activity was observed. The pi-A and enzyme activity data showed good correlation. Although the simple model system employed does not simulate the complexity of the biological membrane, it gives some evidence for the role of lipids in the stability of membrane-bound enzymes.

Animals↗
PubMed1977

Effects of neomycin on polyphosphoinositides in inner ear tissues and monomolecular films.

The effect of neomycin on polyphosphoinositides was studied in vivo and in vitro. In vivo, the incorporation of 32Pi into phosphatidylinositol phosphate and phosphatidylinositol diphosphate was measured in inner ear tissues. Concentrations of neomycin which decreased the electrophysiological response of the chochlea to sound stimulation also decreased labeling of phosphatidylinositol diphosphate. In vitro experiments with brain tissues and polyphosphoinositide extracts indicated a direct interaction between the lipids and neomycin. Neomycin interacts strongly with monomolecular films of polyphosphoinositides. The interaction appears to be complex and is a function of neomycin concentration in the subphase and surface pressure of the film. Condensation of the polyphosphoinositide film is favored at low neomycin concentrations and low film pressures while expansion of the film is favored at high neomycin concentrations and high film pressures. The interactions of neomycin with other negatively charged films (phosphatidyl inositol and phosphatidyl serine) are much weaker, particularly at low neomycin concentrations. The metabolic and physiological consequences of the neomycin/polyphosphoinositide interaction are discussed in regard to the ototoxicity of the drug.

Animals↗
PubMed1976

Interactions of neomycin and calcium in synaptosomal membranes and polyphosphoinostide monolayers.

Neomycin and related aminoglycosidic antibiotics displace calcium from synaptosomes of guinea pig cerebral cortex and from preparations of phosphatidylinositol diphosphate. At low drug concentrations, inhibition of synaptosomal calcium binding is competitive (Ki = 3-10(-5) M), at high concentrations it is non-competitive (Ki = 4-10(-4) M). Monomolecular films of phosphatidylinositol diphosphate are contracted by low concentrations of neomycin in the subphase, and are expanded at high concentrations. This expansion perists even at the collapse pressure indicating a strong interaction between the drug and the lipid.

Animals↗