Biomedical subjects

R Olmo

Publications and source records attributed to R Olmo.

10 recordsLinked to original sources

PubMed2005

Structural and functional implications of the hexokinase-nickel interaction.

The interaction between nickel and yeast hexokinase was studied. The binding of nickel showed a positive cooperativity, and saturation was not reached. The nickel binding induced modifications in the secondary structure of the protein; thus, a lost of alpha helix and beta turns, as well as an increase of the random structure and beta sheet was observed. The monomer/dimmer equilibrium of the protein was modified in the presence of nickel, and the monomer state was mainly obtained at the highest nickel concentrations studied. These changes on the protein structure caused a decrease in the enzyme activity. According to kinetic studies, nickel caused a non-competitive inhibition when glucose was the variable substrate and a linear competitive inhibition when ATP was the variable substrate.

Adenosine Triphosphate↗

PubMed2005

5-Fluorouracil-loaded microspheres prepared by spray-drying poly(D,L-lactide) and poly(lactide-co-glycolide) polymers: characterization and drug release.

5-Fluorouracil (5-FU), a hydrosoluble anti-neoplastic drug, was encapsulated in microspheres of poly(D,L-lactide) (PLA) and poly(lactide-co-glycolide) (PLGA) polymers using the spray-drying technique, in order to obtain small size microspheres with a significant drug entrapment efficiency. Drug-loaded microspheres included between 47 +/- 11 and 67 +/- 12 microg 5-FU mg(-1) microspheres and the percentage of entrapment efficiency was between 52 +/- 12 and 74 +/- 13. Microspheres were of small size (average diameter: 0.9 +/- 0.4-1.4 +/- 0.8 microm microspheres without drug; 1.1 +/- 0.5-1.7 +/- 0.9 microm 5-FU-loaded microspheres) and their surface was smooth and slightly porous, some hollows or deformations were observed in microspheres prepared from polymers with larger Tg. A fractionation process of the raw polymer during the formation of microspheres was observed as an increase of the average molecular weight and also of Tg of the polymer of the microspheres. The presence of 5-FU did not modify the Tg values of the microspheres. Significant interactions between the drug and each one of the polymers did not take place and total release of the included drug was observed in all cases. The time needed for the total drug release (28-129 h) was in the order PLA > PLGA 75/25 > PLGA 50/50. A burst effect (17-20%) was observed during the first hour and then a period of constant release rate (3.52 +/- 0.82-1.46 +/- 0.26 microg 5-FU h(-1) per milligram of microspheres) up to 8 or 13 h, depending on the polymer, was obtained.

Antimetabolites, Antineoplastic↗

PubMed2004

Cytarabine release from comatrices of albumin microspheres in a poly(lactide-co-glycolide) film: in vitro and in vivo studies.

Cytarabine (ara-C) was included in albumin microspheres and these microspheres were immersed in a poly(lactide-co-glycolide) (PLGA) film to constitute a comatrix system to develop a prolonged form of release. Cytarabine-loaded albumin microspheres were synthesized by emulsion, and 25 or 50 mg of drug were included in the disperse phase. Thus, microspheres with 46+/-4 microg drug/mg microspheres and 50+/-5 microg drug/mg microspheres were obtained, which means a percentage of incorporation efficiency of 42+/-4% and 25+/-2%, respectively. These cytarabine-loaded microspheres were used to prepare PLGA-comatrices. Kinetic release studies indicated that total cytarabine release only takes place in the presence of protease, probably due to the fact that glutaraldehyde establishes covalent links with the amine side group of the drug and cross-links it with the protein matrix. A slower kinetic release of the drug was obtained from PLGA-comatrices, although only 80% of the included cytarabine was released on day 7. The comatrices were subcutaneously implanted in the back of rats and in both cases the ara-C administered dose was 36 mg of ara-C per kg of body weight. The drug was detected in plasma 10 days. The mean residence time (MRT) of the drug administered by these comatrices was 87-91 times larger when compared to the value obtained when the drug was administered in solution by intraperitoneal injection. The histological studies show that a degradative process of the comatrices takes place. The comatrices do not damage surrounding tissue; a normal regeneration of the implanted zone was observed.

Animals↗

PubMed2003

Preparation of bupivacaine-loaded poly(epsilon-caprolactone) microspheres by spray drying: drug release studies and biocompatibility.

Poly(epsilon-caprolactone) microspheres containing bupivacaine were prepared by the spray-drying process. The average size of drug loaded microspheres was less than 3 microm in diameter, and the percentage of entrapment efficiency was 91 +/- 3%. In vitro drug release kinetic in phosphate buffer at 37 degrees C showed a hyperbolic profile, with a burst-effect during the first hour. Subcutaneous injection of bupivacaine-loaded microspheres in the back of rats caused an increase in drug concentration in plasma. Maximum bupivacaine concentration in plasma was 237 +/- 58 ng/ml at 105 h, and drug was detected in plasma for 16 days. The half-life time of the drug was increased by more than 125 times with regard to that of the drug administered in a solution by intraperitoneal injection. After 30 days of injection, a mass formed by microspheres surrounded by a thin fibrous capsule was observed. Small blood vessels and multinucleate foreign body giant cells with macrophagic function around microspheres were detected. After 60 days of injection a subcutaneous mass was also observed, which was formed of more degraded dispersed microspheres in conjunctive tissue, which had a normal structure. Thus, bupivacaine-loaded poly(epsilon-caprolactone) microspheres could be considered as a device to be used in the treatment of severe pain that is not responsive to opioids for example in cancer-related syndromes or in intractable herpetic neuralgia.

Anesthetics, Local↗

PubMed2001

Effect of cadmium acetate on the conformation of lysozyme: functional implications.

Structural variations of lysozyme as a consequence of its interaction with CdAc2, as well as the implications on the protein functionality have been studied. Variations in the conformation of the macromolecule are seen, however these changes are not reflected on the secondary structure. The interaction of the salt with the polypeptide chain is weak and thermodynamically unfavourable. Molecular aggregates (dimer forms) are observed at the highest salt concentrations. This interaction causes an inhibitory effect on lysozyme, the activity loss being 50% at the highest salt concentration studied. The inhibition is of mixed type with an uncompetitive component. Thus cadmium does not bind to the active site of the enzyme which is in accordance with the not very large activity loss observed. The substrate inhibition of lysozyme is favoured in the presence of the salt, so interaction with the macromolecule is at low affinity sites.

Acetates↗

PubMed2000

Chitosan microspheres in PLG films as devices for cytarabine release.

Cytarabine was included in chitosan microspheres and several of these microspheres were embedded in a poly(lactide-co-glycolide) (PLG) film to constitute a comatrix system, to develop a prolonged release form. Chitosan microspheres, in the range of 92+/-65 microm, having good spherical geometry and a smooth surface incorporating cytarabine, were prepared. The cytarabine amount included in chitosan microspheres was 43.7 microg of ara-C per milligram microsphere. The incorporation efficiency of the cytarabine in microspheres was 70.6%. Total cytarabine release from microspheres in vitro was detected at 48 h. Inclusion of cytarabine-loaded microspheres in poly(lactide-co-glycolide) film initiated a slower release of the drug and, in this way, the maximum of cytarabine released (80%) took place in vitro at 94.5 h. Comatrices, with 8.7 mg of cytarabine, signifying a dose of 34.5 microg/kg, were subcutaneously implanted in the back of rats. Maximum plasma cytarabine concentration was 18.5+/-1.5 microg/ml, 48 h after the device implantation and the drug was detected in plasma for 13 days. The histological studies show a slow degradative process. After 6 months of implantation, most of the microspheres of the matrix seemed to be intact, the comatrix appeared surrounded by conjunctive tissue and small blood vessels and nerve packets were detected in the periphery of the implant.

Animals↗

PubMed2000

Analysis of aluminum-yeast hexokinase interaction: modifications on protein structure and functionality.

The aluminum and yeast hexokinase interaction was studied. Structural changes were correlated with variations in protein functionality. Results show two different behaviors: At low metal concentrations preferential adsorption of metal (and water exclusion) induces aggregate formation. No significant changes in the protein structure occur, but there is a continuous loss of activity (from the first concentration). At large salt concentrations a monomerization process and a conformational change in the secondary structure as well as in the three-dimensional structure take place. This change reduces the percentage of alpha-helix conformation, gives thermal stability to the protein, and allows the exposure of some tryptophan residue and hydrophobic regions. The protein inhibition increases. Conformational change and monomerization may allow access of the metal to the substrate site, mainly the ATP site. The inhibition in any case is of mixed type with a competitive component.

Adenosine Triphosphate↗

PubMed1996

Release of 5-fluorouracil from poly(acrylamide-co-monopropyl itaconate) hydrogels.

The aim of this work was to test the application of copolymeric poly(acrylamide-co-monopropyl itaconate) (A-MPI) hydrogels on the release of 5-fluorouracil (5-FU). The equilibrium degree of swelling in saline solution was 83 +/- 2%. 5-FU, as the sodium salt, was trapped in gels by placing it in the polymerization feed mixture. The diffusion coefficients for both swelling of the gels and the release of 5-FU were determined, in addition to the activation energies for both processes. To determine the applicability of these copolymers, A-MPI (75:25) gel was subcutaneously implanted in rats and the drug plasma concentration was determined by HPLC.

Acrylamide↗

PubMed1995

Preferential interactions in the H2O/lysozyme/AlCl3 system.

The preferential interactions of lysozyme with solvent components is studied in aqueous solutions of AlCl3. The interaction parameter is negative at large salt concentrations, indicating that the interaction process of both salt and protein is thermodynamically favorable. The transfer free-energy parameter and the solubility data show that aluminum chloride is a salting-in agent for lysozyme. Moreover, these preferential interactions also are correlated with both protein solubility in the solvent medium and the influence of salt on the lysozyme structure. Viscometric and refractometric studies show that lysozyme can undergo a conformational change at 1 mM of salt, and spectrophotometric studies indicate a protein activity of approximately 75% at 10 mM of salt. Therefore, neither the interaction of AlCl3 with the lysozyme nor the conformational change undergone directly affect the catalytic amino acid residues of the active site.

Adsorption↗

PubMedDate not supplied

In vitro controlled release of bupivacaine from albumin microspheres and a co-matrix formed by microspheres in a poly(lactide-co-glycolide) film.

Albumin microspheres cross-linked with glutaraldehyde and loaded with bupivacaine, a local anaesthetic, were synthesized (138 +/- 59 microm diameter). A matrix formed by bupivacaine-loaded microspheres in a poly(lactide-co-glycolide) film was prepared in order to improve the controlled release of the drug. In vitro release of the drug was determined in phosphate buffer at 37 degrees C in the absence and in the presence of protease type VIII to mimic a biological system. The effect of temperature and protease on bupivacaine as a function of time was examined; both of them cause a degradative effect on the drug. A rapid release (60 +/- 8% of the drug) takes place at 1 h, and maximum release is found at 50 +/- 6 h from microspheres with swelling. In the presence of protease, maximum release of bupivacaine from microspheres is found at 28 +/- 2 h; the microspheres disappear at 8 days. Inclusion of bupivacaine-loaded microspheres in a poly(lactide-co-glycolide) film causes a slower release of the drug, up to 18 days, with swelling. In the presence of protease, the polymer protects bupivacaine-loaded microspheres from degradation, which takes place at 20 days.

Animals↗