Release of proteins via ion exchange from albumin-heparin microspheres

Albumin-heparin and albumin microspheres were prepared as ion exchange gels for the controlled release of positively charged polypeptides and proteins. The adsorption isotherms of chicken egg and human lysozyme, as model proteins, on microspheres were obtained. An adsorption isotherm of chicken egg lysozyme on albumin-heparin microspheres was linear until saturation was abruptly reached,\ud \ud The adsorption isotherms of human lysozyme at low and high ionic strength were typical of adsorption isotherms of proteins on ion exchange gels. The adsorption of human lysozyme on albumin-heparin and albumin microspheres fit the Freundlich equation suggesting heterogeneous binding sites. This was consistent with the proposed multivalent, electrostatic interactions between human lysozyme and negatively charged microspheres. Scatchard plots of the adsorption processes of human lysozyme on albumin-heparin and albumin microspheres suggested negative cooperativity, while positive cooperativity was observed for chicken egg lysozyme adsorption on albumin-heparin microspheres.\ud \ud Human lysozyme loading of albumin-heparin microspheres was 3 times higher than with albumin microspheres, with long term release occurring via an ion exchange mechanism. Apparent diffusion coefficients of 2.1 × 10-1 and 3.9 × 10-11cm2/sec were obtained for the release of human lysozyme from albumin-heparin and albumin microspheres, respectively. The release was found to be independent of diffusion, since the rate determining step was likely an adsorption/desorption processes. An apparent diffusion coefficient of 4.1 × 10-12 cm2/sec was determined for the release of chicken egg lysozyme from albumin-heparin microspheres.\ud \ud Low release of the lysozymes from albumin-heparin microspheres was observed in deionized water, consistent with the proposed ion exchange release mechanism. Overall, albumin-heparin microspheres demonstrated enhanced ion exchange characteristics over albumin microspheres

Release of macromolecules from albumin-heparin microspheres

Hydrophilic microspheres based on albumin-heparin conjugates have been prepared as a macromolecular delivery system. The soluble albumin-heparin conjugate was synthesized and crosslinked in a water-in-oil emulsion with glutaraldehyde to form microspheres in the same manner as for albumin microsphere preparation. The microspheres were characterized in terms of their size and swelling properties. The loading of macromolecules into albumin-heparin microspheres was carried out concurrently and after microsphere preparation. FITC-dextran was applied as a model macromolecule. A higher loading content was achieved when loading was carried out concurrently with microsphere preparation than when loaded subsequently. Prolonged release of FITC-dextran from albumin-heparin microspheres was achieved and attributed to the high molecular weight of the macromolecule. The release of FITC-dextran was modulated by crosslinking density, loading content and the method of drug incorporation. Apparently, the mechanism of FITC-dextran release from albumin-heparin microspheres was dependent on the method of drug incorporation. For release of FITC-dextran from the microspheres, assuming negligible interactions, a diffusion coefficient of 1.7 × 10¿9 cm2/s was determined

Iterative graph cuts for image segmentation with a nonlinear statistical shape prior

Shape-based regularization has proven to be a useful method for delineating objects within noisy images where one has prior knowledge of the shape of the targeted object. When a collection of possible shapes is available, the specification of a shape prior using kernel density estimation is a natural technique. Unfortunately, energy functionals arising from kernel density estimation are of a form that makes them impossible to directly minimize using efficient optimization algorithms such as graph cuts. Our main contribution is to show how one may recast the energy functional into a form that is minimizable iteratively and efficiently using graph cuts.Comment: Revision submitted to JMIV (02/24/13

Preparation and characterization of microspheres of albumin-heparin conjugates

Albumin-heparin microspheres have been prepared as a new drug carrier. A soluble albumin-heparin conjugate was synthesized by forming amide bonds between human serum albumin and heparin. After purification the albumin-heparin conjugate was crosslinked in a water-in-oil emulsion to form albumin-heparin microspheres. The composition of the conjugate was determined by amino acid analysis. The swelling properties of albumin-heparin microspheres were investigated as a function of pH and ionic strength and compared with albumin microspheres. Albumin-heparin and albumin microspheres exhibited stimuli-sensitive swelling. Both microsphere systems exhibited low swelling at low pH and high swelling at higher pH caused by ionization of amino acids of serum albumin. The swelling of albumin-heparin microspheres was more sensitive toward ionic strength than that of albumin microspheres. This was due to the greater negative charge of the albumin-heparin microspheres. Surfaces of albumin-heparin and albumin microspheres were characterized by ESCA, contact angle measurements, electrophoresis, and scanning electron microscopy. Surface analysis indicated the presence of heparin at the albumin-heparin microsphere/water interface

The development of an fMRI protocol to investigate vmPFC network topology underlying the generalization of behavioral control

Description: Experiencing behavioral control over stress can have long lasting and generalizing effects. The controllability of a physical threat, for example, affects the processing of subsequent social stress. Animal research has shown that the vmPFC plays a critical role in behavioral control and orchestrating subcortical responses. However, translational research on these neural systems in humans is sparse and we therefore aimed to develop a paradigm to test the generalization effect of behavioral control on vmPFC functioning. A pilot study was performed in which subjects (n=18) were first randomly assigned to one of two versions of a signal detection task, where feedback was either paired with a controllable or an uncontrollable mild shock. Subsequently, subjects underwent a social evaluative threat fMRI paradigm to measure their response to the anticipation of speaking in public. The analyses tested whether the controllability manipulation influenced behavioral and physiological responses and vmPFC network topology. Results showed that overall subjects were faster to respond to potential shock trials in the signal detection task, and there was a trend significant difference between the controllable or uncontrollable group. No significant differences between the two groups were observed on other behavioral or physiological responses. fMRI results showed higher vmPFC efficiency in the controllable threat group at baseline and recovery but similar to the uncontrollable group during speech anticipation. The current report establishes the feasibility of the protocol and adequately-powered follow-up research is needed to further evaluate the generalization effect on the behavioral, physiological and neural level