Mariam Elorza - Academia.edu (original) (raw)
Papers by Mariam Elorza
MGG Molecular & General Genetics, 1971
... Nature (Lond.) 184, 170-171 (1959). Svoboda, A., Farka§, V., Bauer, S. : Response of yeast pr... more ... Nature (Lond.) 184, 170-171 (1959). Svoboda, A., Farka§, V., Bauer, S. : Response of yeast protoplasts to 2-deoxyglucose. Antonie v. Leeuwenhoek 35, B ll-B 12 (1969). ... Chem. 31, 1199-1201 (1959). Communicated by W. Gajewski Dr. M. Victoria Elorza Dr. Herbert N. Arst, Jr. ...
Journal of General Microbiology, 1975
Sdcchdromyces cereviside was treated with a mixture of toluene and ethanol to make it permeable t... more Sdcchdromyces cereviside was treated with a mixture of toluene and ethanol to make it permeable to small molecules. This treatment unmasked a glucan synthetase activity which was assayed with UDP-[U-14C]gl~~~se. About 60 % of the polymer formed was p-( I -q)glucan. No labelled lipids were detected.
Protoplasts 1983, 1983
Accumulation of chitin and glucan on S. cerevisiae and C. albicans protoplasts begins shortly aft... more Accumulation of chitin and glucan on S. cerevisiae and C. albicans protoplasts begins shortly after resuspension in the regeneration medium, and mannoprotein molecules also appear retained by the regenerating wall after 30-60 minutes in S. cerevisiae or after a longer lag period in C. albicans. Nevertheless, a considerable fraction of the synthesized mannoproteins, which in SDS-acrylamide gels exhibit a different pattern from that of wall manno-proteins of cells, are still released to the growth medium during at least eight hours. De novo synthesis of chitin synthase, but not of glucan synthase, is observed in S. cerevisiae from about 30 minutes after initiation of the regeneration process. The interaction between microfibrils of nascent chitin formed by C. albicans protoplasts is altered by strains as Calcofluor White or Congo Red. In the presence of the former one, no microcrystalline lattice of the polymer is formed and protoplasts do not regenerate correctly.
Plant Carbohydrates II, 1981
Yeast, 1997
We have isolated a 4.0-kb fragment from a genomic library of Candida albicans which contained two... more We have isolated a 4.0-kb fragment from a genomic library of Candida albicans which contained two open reading frames (ORFs). One of them is homologous to a prolyl-tRNA synthetase that catalyses the charging of a specific tRNA by proline (CaPRS). A deduced sequence of 575 amino acids representing a polypeptide of 66.2 kDa was determined. A FASTA search indicated that the CaPRSp had an overall similarity of 54.4% with the product of a Saccharomyces cerevisiae ORF (YER087) and 43.8% with the prolyl-tRNA synthetase of Escherichia coli (COLIPRO). Consensus Class II aminoacyl-tRNA synthetase sequences were identified by the PROSITE program. CaPRS was localized to chromosome R of the C. albicans genome and CaPRS DNA hybridized to a major RNA transcript of 1.7 kb under all conditions tested.
Yeast, 1997
We have isolated a 4.0-kb fragment from a genomic library of Candida albicans which contained two... more We have isolated a 4.0-kb fragment from a genomic library of Candida albicans which contained two open reading frames (ORFs). One of them is homologous to a prolyl-tRNA synthetase that catalyses the charging of a specific tRNA by proline (CaPRS). A deduced sequence of 575 amino acids representing a polypeptide of 66.2 kDa was determined. A FASTA search indicated that the CaPRSp had an overall similarity of 54.4% with the product of a Saccharomyces cerevisiae ORF (YER087) and 43.8% with the prolyl-tRNA synthetase of Escherichia coli (COLIPRO). Consensus Class II aminoacyl-tRNA synthetase sequences were identified by the PROSITE program. CaPRS was localized to chromosome R of the C. albicans genome and CaPRS DNA hybridized to a major RNA transcript of 1.7 kb under all conditions tested.
Biochemical and Biophysical Research Communications, 1969
Journal of Molecular Liquids, 2014
ABSTRACT This work focuses on the effect of 2,2,2-trifluoroethanol (TFE) on certain micellar prop... more ABSTRACT This work focuses on the effect of 2,2,2-trifluoroethanol (TFE) on certain micellar properties of Triton X-165 (TX-165) in aqueous solutions. The results obtained from various experimental techniques are used to interpret the interactions in the systems studied. The added TFE has strong effect on lowering the cloud point (CP) in the solutions of TX-165. This effect is consistent with partial dehydration of the oxyethylene groups in the micelle. The decrease of both the critical micelle concentration (CMC) and the CP with the increase of TFE concentration is justified by the interaction between TFE molecule and the oxyethylene group of TX-165, by the low hydrogen bond ability of the hydroxyl oxygen atom of TFE and by the water structure maker effect of TFE. The micelle aggregation number determined by fluorescence decreases initially with the increase of TFE concentration and then increases for the highest TFE concentrations. Fluorescence quenching data indicate that about 45% of pyrene probe is accessible to the quencher (TFE). The results of viscosity are consistent with ellipsoidal shape of TX-165 micelles. The changes in the intrinsic viscosity with increasing TFE concentration may reflect changes in the solvation of micelles and conformational changes in the polar head groups in the micelle. These factors affect the packing of the monomers and the micelle aggregation number. The TFE cosolvent confers hydrophobicity to the micelles of TX-165.
Progress in Colloid & Polymer Science, 1996
ABSTRACT The destabilization of phosphatidylcholine bilayer membranes by the bile salt sodium deo... more ABSTRACT The destabilization of phosphatidylcholine bilayer membranes by the bile salt sodium deoxycholate was studied from steady-state fluorescence anisotropy measurements. FATVET liposomes of DPPC composition were prepared by sequential extrusion through polycarbonate membranes and characterized for their overall inner volume, average size and size distribution, and lamellarity. Interactions between acyl chains in the lipid matrix, which reflect in rotational diffusion motion in the DPH molecules, are perturbed by the presence of the bile salt in the medium (even at low concentrations) below and above the main transition phase temperature of pure DPPC bilayers. Its effects on the the lipid matrix are clearly reflected in the DPH steady state fluorescence anisotropy (r s) measurements. The resolution of r s into its static (r ∞) and dynamic component (r d) shows that DOC affects both the amplitude and the velocity of DPH movements. However, at temperatures below the gel ↔ liquid crystal phase transition point, the static component (that reflects chain order) is more markedly affected than is the dynamic component (which reflects bilayer fluidity). Thus, at 31°C, angle ϑ, a measure of the amplitude of DPH oscillations, rises from 23° to 52° over the DOC concentration range from zero to 2.0 mM (equivalent to a effective molar ratio in bilayer of R 3 25° = 0.12); at 45°C, however, it varies from 62° to 77°. These changes in the bilayer packing status my be responsible for the alteration in the retention ability of liposomal formulations of the cytostatic agent 5-fluorouracil at sub-solubilizing concentrations of deoxycholate [Elorza et al., J. Pharm. Sci. (submitted)]
International Journal of Pharmaceutics, 1993
ABSTRACT Phenylbutazone (PhB) is a powerful anti-inflammatory drug that is very sparingly soluble... more ABSTRACT Phenylbutazone (PhB) is a powerful anti-inflammatory drug that is very sparingly soluble in water (solubility ⋍ 1 × 10−3M). This drug is capable of altering the phase transition temperature of phospholipid bilayers consisting of pure dimyristoyl- or dipalmitoylphosphatidylcholine without changing their calorimetric enthalpy (ΔHcal), but decreasing their cooperativity unit size, as shown by differential scanning calorimetric (DSC) measurements. On interaction with PhB, multilamellar liposomes (MLV) of dimyristoylphosphatidylcholine (DMPC) undergo lateral phase separation owing to the immiscibility in the bilayer plane. In the authors' view, phenylbutazone lies preferentially in the polar region of the bilayer. In this way, the intercalated drug molecules can disrupt hydrogen bonds spanning between adjacent head-groups, thereby destroying the specific structural arrangement of a specific polar head-group region. The pH of the medium is the determining factor — through the degree of ionization of the drug and the interface — on which qualitative and quantitative changes in the main thermotropic transition of phospholipids induced by PhB depend.
International Journal of Pharmaceutics, 1993
ABSTRACT Phenylbutazone (PhB) is a powerful anti-inflammatory drug that is very sparsely soluble ... more ABSTRACT Phenylbutazone (PhB) is a powerful anti-inflammatory drug that is very sparsely soluble in water (). This drug is capable of altering the phase transition temperature of phospholipid bilayers consisting of pure dimyristoyl- or dipamitoyl phosphatidylcholine without changing their calorimetric enthalpy (ΔHcal), but decreasing their cooperativity unit size, as shown by differential scanning calorimetric (DSC) measurements. On interaction with PhB, multilamellar liposomes (MLV) of dimyristoylphosphatidylcholine (DMPC) undergo lateral phase separation owing to the immiscibility in the bilayer plane. In the authors' opinion, phenylbutazone lies preferentially in the polar region of the bilayer. In this way, the intercalated drug molecules can disrupt hydrogen bonds spanning between adjacent head-groups, thereby destroying the specific structural arrangement of a specific polar head-group region. The pH of the medium is the determining factor — through the degree of ionization of the drug and the interface - on which qualitative and quantitative changes in the main thermotropic transition of phospholipids induced by PhB depend.
International Journal of Pharmaceutics, 1997
ABSTRACT The destabilization of vesicles obtained by cyclic freezing-thawing and extrusion (FATVE... more ABSTRACT The destabilization of vesicles obtained by cyclic freezing-thawing and extrusion (FATVET) bilayer membranes consisting of L-α-dipalmitoyl phosphatidylcholine (DPPC) by the bile salt sodium deoxycholate (DOC) was studied from turbidimetric, entrapped solute release and steady-state fluorescence anisotropy measurements. Based on turbidity measurements, bilayer membranes in a rigid gel state are more resistant to lysis by deoxycholate than are bilayers in a fluid liquid-crystal state. Thus, the [detergent]total/[phospholipid] mole ratio, Rtsat, needed to saturate the bilayers at 25°C (T<Tm) is three times greater than that at 50°C (T>Tm) also, Rtsol, which corresponds to complete solubilization of the bilayers, is twice higher at 25°C than it is at 50°C. However, this does not mean that bilayer saturation or complete solubilization calls for increased DOC concentrations, as shown by the fact that the effective mole ratios for both events, Resat and Resol, are identical at 25°C and 50°C. The ability of DOC molecules to intercalate themselves between DPPC molecules therefore appears to be decreased by tightly packed phospholipid molecules. Thus, the partition coefficient for the sub-solubilization range, Re, is almost 3 times lower at 25°C than it is at 50°C. On the other hand, the Resat, Resol and K values for FATVETs{egg yolk lecithin (EYL)} at 25°C are virtually identical with those for FATVETs{DPPC} at 50°C. Hence, for a series of phospholipid analogues, the partition coefficient K for a surfactant/liposome system is bound to depend primarily on the physical state of the bilayer. The retention properties of FATVETs{DPPC} are impaired at sub-lytic DOC levels thus, 5-fluorouracil (5-FU) leakage under these conditions amounts to Re50%=0.09, which is somewhat smaller than Resat (1.2–1.4). This may be the result of the packing and structural changes undergone by lamellae prior to solubilization of the bilayers. The 1,6-diphenyl-1,3,5-hexatriene (DPH) steady-state fluorescence anisotropy results also suggest that DOC alters acyl chain packing, diminishes transition cooperativeness and decreases the orderliness of acyl chains.
Journal of Pharmaceutical Sciences, 1993
0 In this work we studied the particle size distribution of three liposomal preparations by quasi... more 0 In this work we studied the particle size distribution of three liposomal preparations by quasi-elastic light scattering spectroscopy. Sized unilamellar vesicles of small diameter (s-SUV) were prepared by ultrasonication and subsequent centfigation followed by extrusion through polycarbonate membranes of 0.5-pm pore size. Large unilamellar vesicles were obtained by reversed-phase evaporation (REV) and extrusion through polycarbonate filters with or without preliminary freezing-thawing cycles (VET, and VET,,, respectively). After preparation, REV were sized to small diameter REV (s-REV) by extrusion through 0.4-and 0.2-pm polycarbonate membranes. According to the results, the s-SUV preparations were made up of two subpopulations, the major of which consisted of vesicles that were 26 nm in mean diameter and accounted for 95% of the overall s-SUV population. The s-REV dispersions always resolved into two populations centered at 120 and 380 nm, the relative proportions of which depended on the pore size of the filters used. VET structures were composed of a single population of vesicles that were -100 nm in mean diameter. Cholesterol inclusion into the bilayer composition extended the distribution without altering its mean value. On the other hand, the internal volumes calculated from mean diameters or assuming a Gaussian distribution were inconsistent with experimental data obtained by usual techniques.
Journal of Microencapsulation, 1993
Liposomes can be produced by using various techniques such as mechanical agitation, ultrasonicati... more Liposomes can be produced by using various techniques such as mechanical agitation, ultrasonication, ether injection, detergent dialysis, reversed-phase evaporation, extrusion through polycarbonate filters of appropriate pore size, etc. Each procedure provides liposomes with their own perculiar features so the choice of a given one to obtain suitable vesicles for use as drug delivery systems should be based on careful experimentation. In this work we tested three liposome preparation methods that provide unilamellar structures with high yields. In fact, unilamellar vesicles of small diameters (SUV) were prepared by ultrasonication and large unilamellar vesicles (LUV) were obtained by (a) reversed-phase evaporation (REV) and (b) extrusion through polycarbonate filters--with or without preliminary freezing-thawing (VETI and VETII, respectively). According to the results obtained, subsequent filtration of the SUV and REV liposomal preparations results in dramatically decreased average diameters and polydispersity indices, as well as in marked changes in their encapsulation parameters and in lipid losses. Among extruded liposomes, those obtained with preliminary freezing-thawing (VETII) resulted in a higher lipid recovery, even though their average hydrodynamic diameter and polydispersity index as measured by quasi-elastic light-scattering spectroscopy (QELSS) were quite similar to those of the VETI counterparts.
Journal of Colloid and Interface Science, 2009
The effect of 2,2,2-trifluoroethanol (TFE) on micellar properties of Triton X-100 (TX-100) in aqu... more The effect of 2,2,2-trifluoroethanol (TFE) on micellar properties of Triton X-100 (TX-100) in aqueous solutions was investigated by cloud point (CP), viscosity, surface tension, and fluorescence techniques. The critical micelle concentration (CMC) values of the corresponding mixtures were obtained by the pyrene 1:3 ratio method and by surface tension data using the pendant drop technique. All the techniques provided about the same values for the CMC. Up to 0.83 M TFE increased the CMC by 30%. The small increase in the CMC is consistent with a slight increase in the solubility of the TX-100. Fluorescence measurements indicate that the TFE decreased the aggregation number by about 30%. The CP decrease and the intrinsic viscosity increase with TFE concentration are consistent with a preferential interaction of TFE with TX-100 micelles. TFE molecules form hydrophobic domains in the micellar layer palisade because they hydrogen bond with the oxyethylene group in TX-100. The intrinsic viscosity data are consistent with an increase in micelle hydrodynamic radius owing to the presence of TFE.
European Journal of Pharmaceutical Sciences, 2013
Acyclovir (ACV) is one of the drugs of choice for the treatment of epidermal, ocular or systemic ... more Acyclovir (ACV) is one of the drugs of choice for the treatment of epidermal, ocular or systemic herpetic infections. Nevertheless, its trans-mucosal limited absorption and the scarce contact time of the formulation with the mucosal surface - especially in the ocular mucosa - constitute a big limitation of the antiviral efficiency. The most effective way to solve these problems is to increase the quantity and the residence time of the drug over the ocular surface. In order to cope with all these requirements, micro-particles (MPs) and nano-particles (NPs) containing ACV have been developed using cross-linked chitosan with tripolyphosphate (TPP) due to the biocompatibility, bio-adhesion ability and the potential power as penetration enhancer of this polymer. Particles were characterized by Fourier-transformed infrared (FTIR) spectroscopy, X-ray diffraction, SEM, Zeta potential and particle size. Encapsulation efficiency and release profiles in flow through diffusion cells were also determined. Besides the Slug Mucosal Irritation (SMI) assay has been applied as an alternative to the Draize test to predict the mucosal irritation of the selected formulation. FTIR and X-ray results suggested an electrostatic interaction ACV-Chitosan that made ACV be molecularly dispersed within the polymer matrix. Encapsulation efficiency was 75% for MP and 16% for NP. Release profiles in flow through diffusion cells were also determined. From the diffusion profiles, it was found that the amounts of ACV effectively diffused in 24h were 30, 430 and 80 μg for the ACV solution, MP and NP respectively. SMI results showed that chitosan-based particles induced moderate irritation and mild tissue damage, what supposes that ACV-MP constitute a promising alternative for further development of an antiviral formulation.
Biomaterials, 2007
Poly(D,L-lactide-co-glycolide) (PLGA) biodegradable microspheres with gentamicin for local treatm... more Poly(D,L-lactide-co-glycolide) (PLGA) biodegradable microspheres with gentamicin for local treatment of microbial bone infection were prepared and characterized. Gentamicin was assayed spectrophotometrically at 332 nm after derivation with the o-phthalaldehyde; biodegradable polymers studied did not interfere with this method of gentamicin analysis. PLGA microspheres were made by the double emulsion solvent evaporation method with modifications. The first W(1)/O emulsion was obtained by ultrasonication or high-speed homogenization, and a large aqueous phase W(2) (200 ml) was used. The ultrasonication method increases the microsphere percentage observed in the 20-40 microm size range and, in all cases SEM-microphotographs revealed homogeneous and spherically shaped particles with smooth surfaces. The method including ultrasonication proposed in the present work improved the encapsulation efficiency of gentamicin by nearly 100% (97.94%). Several mathematical models based on heterogeneous hydrolytic degradation were applied to evaluate their suitability in describing gentamicin released from PLGA microspheres. Two models, one of them including an autocatalytic process, were finally proposed to contribute to understand the mass transport mechanism involved in drug release from these microspheres.
Biochimica et Biophysica Acta (BBA) - Biomembranes, 1993
Entrapment of the anti-tumoral drug 5-fluorouracil (5-FU) in unilamellar liposomes prepared by fr... more Entrapment of the anti-tumoral drug 5-fluorouracil (5-FU) in unilamellar liposomes prepared by freeze-thawing extrusion technique (FATVET) and the reverse-phase evaporation method (REV) from natural (bovine brain) sphingomyelin (SM) and synthetic distearoylphosphatidylcholine (DSPC) phospholipids was studied. Reverse-phase evaporation vesicles obtained from DSPC sized through polycarbonate membranes of 0.2/zm pore size were found to entrap roughly double amounts of drug than did extruded liposomes (0.1 /zm pore size); however, s-REV in these preparations were more heterogenous in vesicle size than FATVET. The rate of in vitro drug release from the liposomes was found to be dependent of the bilayer composition and the method used to prepare the vesicles. The permeability coefficient P obtained was approx. 10-11 m/s. The results suggest that 5-FU release is kinetically controlled by an interfacial process seemingly dependent on the surface activity of the drug. Also, the physical state of the bilayer determines the retention capacity of the vesicles. Thus, liposomes consisting of distearoylphosphatidylcholine whose acyl chains were in a gel state at the working temperature (37°C) retained 70% of encapsulated 5-FU after 1 h, whereas liposomes composed of natural bovine brain sphingomyelin retained only 15% over the same period.
MGG Molecular & General Genetics, 1971
... Nature (Lond.) 184, 170-171 (1959). Svoboda, A., Farka§, V., Bauer, S. : Response of yeast pr... more ... Nature (Lond.) 184, 170-171 (1959). Svoboda, A., Farka§, V., Bauer, S. : Response of yeast protoplasts to 2-deoxyglucose. Antonie v. Leeuwenhoek 35, B ll-B 12 (1969). ... Chem. 31, 1199-1201 (1959). Communicated by W. Gajewski Dr. M. Victoria Elorza Dr. Herbert N. Arst, Jr. ...
Journal of General Microbiology, 1975
Sdcchdromyces cereviside was treated with a mixture of toluene and ethanol to make it permeable t... more Sdcchdromyces cereviside was treated with a mixture of toluene and ethanol to make it permeable to small molecules. This treatment unmasked a glucan synthetase activity which was assayed with UDP-[U-14C]gl~~~se. About 60 % of the polymer formed was p-( I -q)glucan. No labelled lipids were detected.
Protoplasts 1983, 1983
Accumulation of chitin and glucan on S. cerevisiae and C. albicans protoplasts begins shortly aft... more Accumulation of chitin and glucan on S. cerevisiae and C. albicans protoplasts begins shortly after resuspension in the regeneration medium, and mannoprotein molecules also appear retained by the regenerating wall after 30-60 minutes in S. cerevisiae or after a longer lag period in C. albicans. Nevertheless, a considerable fraction of the synthesized mannoproteins, which in SDS-acrylamide gels exhibit a different pattern from that of wall manno-proteins of cells, are still released to the growth medium during at least eight hours. De novo synthesis of chitin synthase, but not of glucan synthase, is observed in S. cerevisiae from about 30 minutes after initiation of the regeneration process. The interaction between microfibrils of nascent chitin formed by C. albicans protoplasts is altered by strains as Calcofluor White or Congo Red. In the presence of the former one, no microcrystalline lattice of the polymer is formed and protoplasts do not regenerate correctly.
Plant Carbohydrates II, 1981
Yeast, 1997
We have isolated a 4.0-kb fragment from a genomic library of Candida albicans which contained two... more We have isolated a 4.0-kb fragment from a genomic library of Candida albicans which contained two open reading frames (ORFs). One of them is homologous to a prolyl-tRNA synthetase that catalyses the charging of a specific tRNA by proline (CaPRS). A deduced sequence of 575 amino acids representing a polypeptide of 66.2 kDa was determined. A FASTA search indicated that the CaPRSp had an overall similarity of 54.4% with the product of a Saccharomyces cerevisiae ORF (YER087) and 43.8% with the prolyl-tRNA synthetase of Escherichia coli (COLIPRO). Consensus Class II aminoacyl-tRNA synthetase sequences were identified by the PROSITE program. CaPRS was localized to chromosome R of the C. albicans genome and CaPRS DNA hybridized to a major RNA transcript of 1.7 kb under all conditions tested.
Yeast, 1997
We have isolated a 4.0-kb fragment from a genomic library of Candida albicans which contained two... more We have isolated a 4.0-kb fragment from a genomic library of Candida albicans which contained two open reading frames (ORFs). One of them is homologous to a prolyl-tRNA synthetase that catalyses the charging of a specific tRNA by proline (CaPRS). A deduced sequence of 575 amino acids representing a polypeptide of 66.2 kDa was determined. A FASTA search indicated that the CaPRSp had an overall similarity of 54.4% with the product of a Saccharomyces cerevisiae ORF (YER087) and 43.8% with the prolyl-tRNA synthetase of Escherichia coli (COLIPRO). Consensus Class II aminoacyl-tRNA synthetase sequences were identified by the PROSITE program. CaPRS was localized to chromosome R of the C. albicans genome and CaPRS DNA hybridized to a major RNA transcript of 1.7 kb under all conditions tested.
Biochemical and Biophysical Research Communications, 1969
Journal of Molecular Liquids, 2014
ABSTRACT This work focuses on the effect of 2,2,2-trifluoroethanol (TFE) on certain micellar prop... more ABSTRACT This work focuses on the effect of 2,2,2-trifluoroethanol (TFE) on certain micellar properties of Triton X-165 (TX-165) in aqueous solutions. The results obtained from various experimental techniques are used to interpret the interactions in the systems studied. The added TFE has strong effect on lowering the cloud point (CP) in the solutions of TX-165. This effect is consistent with partial dehydration of the oxyethylene groups in the micelle. The decrease of both the critical micelle concentration (CMC) and the CP with the increase of TFE concentration is justified by the interaction between TFE molecule and the oxyethylene group of TX-165, by the low hydrogen bond ability of the hydroxyl oxygen atom of TFE and by the water structure maker effect of TFE. The micelle aggregation number determined by fluorescence decreases initially with the increase of TFE concentration and then increases for the highest TFE concentrations. Fluorescence quenching data indicate that about 45% of pyrene probe is accessible to the quencher (TFE). The results of viscosity are consistent with ellipsoidal shape of TX-165 micelles. The changes in the intrinsic viscosity with increasing TFE concentration may reflect changes in the solvation of micelles and conformational changes in the polar head groups in the micelle. These factors affect the packing of the monomers and the micelle aggregation number. The TFE cosolvent confers hydrophobicity to the micelles of TX-165.
Progress in Colloid & Polymer Science, 1996
ABSTRACT The destabilization of phosphatidylcholine bilayer membranes by the bile salt sodium deo... more ABSTRACT The destabilization of phosphatidylcholine bilayer membranes by the bile salt sodium deoxycholate was studied from steady-state fluorescence anisotropy measurements. FATVET liposomes of DPPC composition were prepared by sequential extrusion through polycarbonate membranes and characterized for their overall inner volume, average size and size distribution, and lamellarity. Interactions between acyl chains in the lipid matrix, which reflect in rotational diffusion motion in the DPH molecules, are perturbed by the presence of the bile salt in the medium (even at low concentrations) below and above the main transition phase temperature of pure DPPC bilayers. Its effects on the the lipid matrix are clearly reflected in the DPH steady state fluorescence anisotropy (r s) measurements. The resolution of r s into its static (r ∞) and dynamic component (r d) shows that DOC affects both the amplitude and the velocity of DPH movements. However, at temperatures below the gel ↔ liquid crystal phase transition point, the static component (that reflects chain order) is more markedly affected than is the dynamic component (which reflects bilayer fluidity). Thus, at 31°C, angle ϑ, a measure of the amplitude of DPH oscillations, rises from 23° to 52° over the DOC concentration range from zero to 2.0 mM (equivalent to a effective molar ratio in bilayer of R 3 25° = 0.12); at 45°C, however, it varies from 62° to 77°. These changes in the bilayer packing status my be responsible for the alteration in the retention ability of liposomal formulations of the cytostatic agent 5-fluorouracil at sub-solubilizing concentrations of deoxycholate [Elorza et al., J. Pharm. Sci. (submitted)]
International Journal of Pharmaceutics, 1993
ABSTRACT Phenylbutazone (PhB) is a powerful anti-inflammatory drug that is very sparingly soluble... more ABSTRACT Phenylbutazone (PhB) is a powerful anti-inflammatory drug that is very sparingly soluble in water (solubility ⋍ 1 × 10−3M). This drug is capable of altering the phase transition temperature of phospholipid bilayers consisting of pure dimyristoyl- or dipalmitoylphosphatidylcholine without changing their calorimetric enthalpy (ΔHcal), but decreasing their cooperativity unit size, as shown by differential scanning calorimetric (DSC) measurements. On interaction with PhB, multilamellar liposomes (MLV) of dimyristoylphosphatidylcholine (DMPC) undergo lateral phase separation owing to the immiscibility in the bilayer plane. In the authors' view, phenylbutazone lies preferentially in the polar region of the bilayer. In this way, the intercalated drug molecules can disrupt hydrogen bonds spanning between adjacent head-groups, thereby destroying the specific structural arrangement of a specific polar head-group region. The pH of the medium is the determining factor — through the degree of ionization of the drug and the interface — on which qualitative and quantitative changes in the main thermotropic transition of phospholipids induced by PhB depend.
International Journal of Pharmaceutics, 1993
ABSTRACT Phenylbutazone (PhB) is a powerful anti-inflammatory drug that is very sparsely soluble ... more ABSTRACT Phenylbutazone (PhB) is a powerful anti-inflammatory drug that is very sparsely soluble in water (). This drug is capable of altering the phase transition temperature of phospholipid bilayers consisting of pure dimyristoyl- or dipamitoyl phosphatidylcholine without changing their calorimetric enthalpy (ΔHcal), but decreasing their cooperativity unit size, as shown by differential scanning calorimetric (DSC) measurements. On interaction with PhB, multilamellar liposomes (MLV) of dimyristoylphosphatidylcholine (DMPC) undergo lateral phase separation owing to the immiscibility in the bilayer plane. In the authors' opinion, phenylbutazone lies preferentially in the polar region of the bilayer. In this way, the intercalated drug molecules can disrupt hydrogen bonds spanning between adjacent head-groups, thereby destroying the specific structural arrangement of a specific polar head-group region. The pH of the medium is the determining factor — through the degree of ionization of the drug and the interface - on which qualitative and quantitative changes in the main thermotropic transition of phospholipids induced by PhB depend.
International Journal of Pharmaceutics, 1997
ABSTRACT The destabilization of vesicles obtained by cyclic freezing-thawing and extrusion (FATVE... more ABSTRACT The destabilization of vesicles obtained by cyclic freezing-thawing and extrusion (FATVET) bilayer membranes consisting of L-α-dipalmitoyl phosphatidylcholine (DPPC) by the bile salt sodium deoxycholate (DOC) was studied from turbidimetric, entrapped solute release and steady-state fluorescence anisotropy measurements. Based on turbidity measurements, bilayer membranes in a rigid gel state are more resistant to lysis by deoxycholate than are bilayers in a fluid liquid-crystal state. Thus, the [detergent]total/[phospholipid] mole ratio, Rtsat, needed to saturate the bilayers at 25°C (T<Tm) is three times greater than that at 50°C (T>Tm) also, Rtsol, which corresponds to complete solubilization of the bilayers, is twice higher at 25°C than it is at 50°C. However, this does not mean that bilayer saturation or complete solubilization calls for increased DOC concentrations, as shown by the fact that the effective mole ratios for both events, Resat and Resol, are identical at 25°C and 50°C. The ability of DOC molecules to intercalate themselves between DPPC molecules therefore appears to be decreased by tightly packed phospholipid molecules. Thus, the partition coefficient for the sub-solubilization range, Re, is almost 3 times lower at 25°C than it is at 50°C. On the other hand, the Resat, Resol and K values for FATVETs{egg yolk lecithin (EYL)} at 25°C are virtually identical with those for FATVETs{DPPC} at 50°C. Hence, for a series of phospholipid analogues, the partition coefficient K for a surfactant/liposome system is bound to depend primarily on the physical state of the bilayer. The retention properties of FATVETs{DPPC} are impaired at sub-lytic DOC levels thus, 5-fluorouracil (5-FU) leakage under these conditions amounts to Re50%=0.09, which is somewhat smaller than Resat (1.2–1.4). This may be the result of the packing and structural changes undergone by lamellae prior to solubilization of the bilayers. The 1,6-diphenyl-1,3,5-hexatriene (DPH) steady-state fluorescence anisotropy results also suggest that DOC alters acyl chain packing, diminishes transition cooperativeness and decreases the orderliness of acyl chains.
Journal of Pharmaceutical Sciences, 1993
0 In this work we studied the particle size distribution of three liposomal preparations by quasi... more 0 In this work we studied the particle size distribution of three liposomal preparations by quasi-elastic light scattering spectroscopy. Sized unilamellar vesicles of small diameter (s-SUV) were prepared by ultrasonication and subsequent centfigation followed by extrusion through polycarbonate membranes of 0.5-pm pore size. Large unilamellar vesicles were obtained by reversed-phase evaporation (REV) and extrusion through polycarbonate filters with or without preliminary freezing-thawing cycles (VET, and VET,,, respectively). After preparation, REV were sized to small diameter REV (s-REV) by extrusion through 0.4-and 0.2-pm polycarbonate membranes. According to the results, the s-SUV preparations were made up of two subpopulations, the major of which consisted of vesicles that were 26 nm in mean diameter and accounted for 95% of the overall s-SUV population. The s-REV dispersions always resolved into two populations centered at 120 and 380 nm, the relative proportions of which depended on the pore size of the filters used. VET structures were composed of a single population of vesicles that were -100 nm in mean diameter. Cholesterol inclusion into the bilayer composition extended the distribution without altering its mean value. On the other hand, the internal volumes calculated from mean diameters or assuming a Gaussian distribution were inconsistent with experimental data obtained by usual techniques.
Journal of Microencapsulation, 1993
Liposomes can be produced by using various techniques such as mechanical agitation, ultrasonicati... more Liposomes can be produced by using various techniques such as mechanical agitation, ultrasonication, ether injection, detergent dialysis, reversed-phase evaporation, extrusion through polycarbonate filters of appropriate pore size, etc. Each procedure provides liposomes with their own perculiar features so the choice of a given one to obtain suitable vesicles for use as drug delivery systems should be based on careful experimentation. In this work we tested three liposome preparation methods that provide unilamellar structures with high yields. In fact, unilamellar vesicles of small diameters (SUV) were prepared by ultrasonication and large unilamellar vesicles (LUV) were obtained by (a) reversed-phase evaporation (REV) and (b) extrusion through polycarbonate filters--with or without preliminary freezing-thawing (VETI and VETII, respectively). According to the results obtained, subsequent filtration of the SUV and REV liposomal preparations results in dramatically decreased average diameters and polydispersity indices, as well as in marked changes in their encapsulation parameters and in lipid losses. Among extruded liposomes, those obtained with preliminary freezing-thawing (VETII) resulted in a higher lipid recovery, even though their average hydrodynamic diameter and polydispersity index as measured by quasi-elastic light-scattering spectroscopy (QELSS) were quite similar to those of the VETI counterparts.
Journal of Colloid and Interface Science, 2009
The effect of 2,2,2-trifluoroethanol (TFE) on micellar properties of Triton X-100 (TX-100) in aqu... more The effect of 2,2,2-trifluoroethanol (TFE) on micellar properties of Triton X-100 (TX-100) in aqueous solutions was investigated by cloud point (CP), viscosity, surface tension, and fluorescence techniques. The critical micelle concentration (CMC) values of the corresponding mixtures were obtained by the pyrene 1:3 ratio method and by surface tension data using the pendant drop technique. All the techniques provided about the same values for the CMC. Up to 0.83 M TFE increased the CMC by 30%. The small increase in the CMC is consistent with a slight increase in the solubility of the TX-100. Fluorescence measurements indicate that the TFE decreased the aggregation number by about 30%. The CP decrease and the intrinsic viscosity increase with TFE concentration are consistent with a preferential interaction of TFE with TX-100 micelles. TFE molecules form hydrophobic domains in the micellar layer palisade because they hydrogen bond with the oxyethylene group in TX-100. The intrinsic viscosity data are consistent with an increase in micelle hydrodynamic radius owing to the presence of TFE.
European Journal of Pharmaceutical Sciences, 2013
Acyclovir (ACV) is one of the drugs of choice for the treatment of epidermal, ocular or systemic ... more Acyclovir (ACV) is one of the drugs of choice for the treatment of epidermal, ocular or systemic herpetic infections. Nevertheless, its trans-mucosal limited absorption and the scarce contact time of the formulation with the mucosal surface - especially in the ocular mucosa - constitute a big limitation of the antiviral efficiency. The most effective way to solve these problems is to increase the quantity and the residence time of the drug over the ocular surface. In order to cope with all these requirements, micro-particles (MPs) and nano-particles (NPs) containing ACV have been developed using cross-linked chitosan with tripolyphosphate (TPP) due to the biocompatibility, bio-adhesion ability and the potential power as penetration enhancer of this polymer. Particles were characterized by Fourier-transformed infrared (FTIR) spectroscopy, X-ray diffraction, SEM, Zeta potential and particle size. Encapsulation efficiency and release profiles in flow through diffusion cells were also determined. Besides the Slug Mucosal Irritation (SMI) assay has been applied as an alternative to the Draize test to predict the mucosal irritation of the selected formulation. FTIR and X-ray results suggested an electrostatic interaction ACV-Chitosan that made ACV be molecularly dispersed within the polymer matrix. Encapsulation efficiency was 75% for MP and 16% for NP. Release profiles in flow through diffusion cells were also determined. From the diffusion profiles, it was found that the amounts of ACV effectively diffused in 24h were 30, 430 and 80 μg for the ACV solution, MP and NP respectively. SMI results showed that chitosan-based particles induced moderate irritation and mild tissue damage, what supposes that ACV-MP constitute a promising alternative for further development of an antiviral formulation.
Biomaterials, 2007
Poly(D,L-lactide-co-glycolide) (PLGA) biodegradable microspheres with gentamicin for local treatm... more Poly(D,L-lactide-co-glycolide) (PLGA) biodegradable microspheres with gentamicin for local treatment of microbial bone infection were prepared and characterized. Gentamicin was assayed spectrophotometrically at 332 nm after derivation with the o-phthalaldehyde; biodegradable polymers studied did not interfere with this method of gentamicin analysis. PLGA microspheres were made by the double emulsion solvent evaporation method with modifications. The first W(1)/O emulsion was obtained by ultrasonication or high-speed homogenization, and a large aqueous phase W(2) (200 ml) was used. The ultrasonication method increases the microsphere percentage observed in the 20-40 microm size range and, in all cases SEM-microphotographs revealed homogeneous and spherically shaped particles with smooth surfaces. The method including ultrasonication proposed in the present work improved the encapsulation efficiency of gentamicin by nearly 100% (97.94%). Several mathematical models based on heterogeneous hydrolytic degradation were applied to evaluate their suitability in describing gentamicin released from PLGA microspheres. Two models, one of them including an autocatalytic process, were finally proposed to contribute to understand the mass transport mechanism involved in drug release from these microspheres.
Biochimica et Biophysica Acta (BBA) - Biomembranes, 1993
Entrapment of the anti-tumoral drug 5-fluorouracil (5-FU) in unilamellar liposomes prepared by fr... more Entrapment of the anti-tumoral drug 5-fluorouracil (5-FU) in unilamellar liposomes prepared by freeze-thawing extrusion technique (FATVET) and the reverse-phase evaporation method (REV) from natural (bovine brain) sphingomyelin (SM) and synthetic distearoylphosphatidylcholine (DSPC) phospholipids was studied. Reverse-phase evaporation vesicles obtained from DSPC sized through polycarbonate membranes of 0.2/zm pore size were found to entrap roughly double amounts of drug than did extruded liposomes (0.1 /zm pore size); however, s-REV in these preparations were more heterogenous in vesicle size than FATVET. The rate of in vitro drug release from the liposomes was found to be dependent of the bilayer composition and the method used to prepare the vesicles. The permeability coefficient P obtained was approx. 10-11 m/s. The results suggest that 5-FU release is kinetically controlled by an interfacial process seemingly dependent on the surface activity of the drug. Also, the physical state of the bilayer determines the retention capacity of the vesicles. Thus, liposomes consisting of distearoylphosphatidylcholine whose acyl chains were in a gel state at the working temperature (37°C) retained 70% of encapsulated 5-FU after 1 h, whereas liposomes composed of natural bovine brain sphingomyelin retained only 15% over the same period.