Biomedical subjects

Maria Helena Andrade Santana

Publications and source records attributed to Maria Helena Andrade Santana.

4 recordsLinked to original sources

PubMed2006

Poly-lactide-co-glycolide microparticle sizes: a rational factorial design and surface response analysis.

Microsphere size is a primary determinant of solute release velocity. We present here a rational way for producing PLGA microspheres with different and controlled sizes. The following process variables were studied: Stirring velocity during the second emulsion step, dispersed and continuous phases volume ratio, and poly(vinyl alcohol) concentration in the continuous phase. A full factorial experimental design 2(3) with triplicate at the central point was used to determine the influence of variables on PLGA microsphere mean size. The stirring velocity and poly(vinyl alcohol) concentration were the main variables at 0.95 significance level. An influence of PVA and stirring velocity on microspheres size is observed, there is no correlation for DP/CP volume ratio on size of microspheres. By combining the two variables--the stirring velocity and poly(vinyl alcohol) concentration, the surface response was analyzed. The increase of poly(vinyl alcohol) concentration with concomitant increase on stirring velocity produced microspheres with the lower sized. In contrast the lower poly(vinyl alcohol) concentration and the lower stirring velocity used produced the higher microspheres sized. Uniformly spherical and smooth microspheres (4-15 microm of diameter) were obtained. No significant difference was observed on Ponca S loading within the experimental region. Our results open the possibility of formulating PLGA microspheres with custom sizes performing a minimum of experiments as required for specific applications.

Antigens↗

PubMed2004

Receptor-mediated biological responses are prolonged using hydrophobized ligands.

Hormone-receptor interactions occur following three-dimensional diffusion of the ligand to the membrane-embedded receptor. However, prior hydrophobization of the ligand might restrict its movement to two dimensions along the membrane surface, and the biological response might therefore be modulated. This idea was tested using the C-terminal nonapeptide, CCK9, of the satiating hormone, cholecystokinin (CCK). The hormone was lipidated by linking it covalently to distearoylphosphatidylethanolamine via a poly(ethylene glycol) (PEG) spacer. The desired conjugate was isolated by thin-layer chromatography and incorporated into preformed small unilamellar dimyristoylphosphatidylcholine (DMPC) vesicles. The hormone-bearing vesicles were injected intraperitoneally into Wistar rats and food intake monitored. Compared to the biological effect elicited by the same amount of soluble non-derivatized CCK9, food intake reduction showed a delayed onset, but lasted for a significantly longer time. We believe this prolonged effect was due to the transfer of the derivatized CCK9 from the vesicles to the natural membrane containing the hormone receptor. Ultimately, this event may result in sustained receptor occupation and, thus, food intake reduction. The underlying mechanism for the physiological effects observed may be of relevance in interpreting results obtained using artificial measuring devices; for example, the signal produced by biosensors may be drastically affected by the hydrophobicity of the ligand.

Animals↗

PubMed2003

Lipid membrane with low proton permeability.

This work reports the production of a liposomal formulation, having a lipidic membrane with known chemical composition and a low proton permeability, as confirmed by physicochemical characterization of the maintenance of a transmembranic pH gradient. These liposomes consist of DSPC, DSPE-PEG, DSPG and cholesterol, with low internal pH. To verify the low proton permeability of these liposomal bilayers, a study of proton migration according to the fluorescence quenching of 9-aminoacridine (9AA), as well as CPT-11 encapsulation, were used to monitor the acidification of the intravesicular space. Both experiments showed that this liposomal formulation is able to maintain a transmembranic proton gradient.

Aminacrine↗

PubMed2002

Attachment of water-soluble proteins to the surface of (magnetizable) phospholipid colloids via NeutrAvidin-derivatized phospholipids.

The present work describes the incorporation of a functionalized phospholipid derivative into the phospholipid bilayer of both classical small unilamellar vesicles and recently developed magnetoliposomes, resulting in unique biocolloid structures onto which peripheral water-soluble enzymes can be immobilized on the surfaces. In the first part of this work, a synthesis protocol is outlined for a universal membrane anchor for water-soluble proteins. Dioleoylphosphatidylethanolamine-N-dodecanyl was used as the starting lipid molecule. After activation of the terminal -COOH group, alpha,omega-diamino-poly(ethylene glycol), used as a hydrophilic, flexible spacer arm, was coupled covalently. Subsequently, NeutrAvidin was bound, after blocking the free -NH(2) groups with citraconic anhydride. In the second part, the resulting lipid-NeutrAvidin derivative was incorporated into small unilamellar vesicles comprised of dimyristoylphosphatidylglycerol. FPLC with Superdex 200 as the column matrix clearly showed that biotinylated alkaline phosphatase, which served as a representative model of water-soluble proteins, was attached to the vesicles. Furthermore, magnetoliposomes, constructed of the same type of phospholipid molecules, were presented as interesting colloids to assess the degree of enzyme immobilization in a rapid and elegant manner. Potential applications that can emerge from this study are briefly discussed.

Avidin↗