Shlomo Margel

Dispersion polymerization of styrene in polar solvents: Effect of reaction parameters on microsphere surface composition and surface properties, size and size distribution, and molecular weight

Polystyrene microspheres were prepared by dispersion polymerization of styrene in a mixture of ethanol and 2-methoxy ethanol. Surface characterization of the formed particles was performed by x-ray photoelectron spectroscopy and critical surface tension measurements. The influence of different reaction parameters, i.e., monomer concentration, stabilizer type (polyvinylpyrrolidone, copolymers of vinylpyrrolidone and vinylacetate and polyvinylace tate), stabilizer concentration and molecular weight, and initiator type and concentration, on the molecular weight and on the size and size distribution of the formed polystyrene microspheres was investigated. The correlation between the surface composition and wett ability properties of the particles surface and their size and size distribution was also demonstrated.

Radiopaque iodinated polymeric nanoparticles for X-ray imaging applications

Recently we described iodinated homopolymeric radiopaque nanoparticles of 28.9+/-6.3 nm dry diameter synthesized by emulsion polymerization of 2-methacryloyloxyethyl(2,3,5-triiodobenzoate) (MAOETIB). The nanoparticle aqueous dispersion, however, was not stable and tended to agglomerate, particularly at weight concentration of dispersed nanoparticles above approximately 0.3%. The agglomeration rate increases as the concentration of nanoparticles in aqueous phase rises and prevents the potential in vivo use as contrast agent for medical X-ray imaging. Here we describe efforts to overcome this limitation by synthesis of iodinated copolymeric nanoparticles of 25.5+/-4.2 nm dry diameter, by emulsion copolymerization of the monomer, MAOETIB, with a low concentration of glycidyl methacrylate (GMA). The surface of resulting copolymeric nanoparticles is far more hydrophilic than that of polyMAOETIB (PMAOETIB) nanoparticles. Therefore, P(MAOETIB-GMA) nanoparticles are significantly more stable against agglomeration in aqueous continuous phase. After intravenous injection of P(MAOETIB-GMA) nanoparticles in rats and mice (including those with a liver cancer model) CT-imaging revealed a significant enhanced visibility of the blood pool for 30 min after injection. Later, lymph nodes, liver and spleen strongly enhanced due to nanoparticle uptake by the reticuloendothelial system. This favorably enabled the differentiation of cancerous from healthy liver tissue and suggests our particles for tumor imaging in liver and lymph nodes.

Natural antibodies and their significance in active immunization and protection against a defined pathogen in fish

Natural antibody activity against Aeromonas salmonicida extracellular A-layer protein (A-protein) showed large individual variations in a farmed group of 101 goldfish (Carassius auratus L.). Statistical analyses of these variations led us to divide this group into homogeneous high and low naturally active (HNA and LNA) subgroups. The HNA fish were largely protected against experimental infection with a virulent atypical A. salmonicida strain, while 100% morbidity was recorded in the LNA group. In the course of active immunization with a particulate form of A-protein, a significant antibody response was exhibited by the LNA group only. Significance and implication of these results in vaccination practice are discussed.

Convection-enhanced delivery of maghemite nanoparticles: Increased efficacy and MRI monitoring

Convection-enhanced drug delivery (CED) is a novel approach to delivering drugs into brain tissue. Drugs are delivered continuously via a catheter, enabling large volume distributions of high drug concentrations with minimum systemic toxicity. Previously we demonstrated that CED formation/extent of small molecules may be significantly improved by increasing infusate viscosities. In this study we show that the same methodology can be applied to monodispersed maghemite nanoparticles (MNPs). For this purpose we used a normal rat brain model and performed CED of MNPs over short infusion times. By adding 3% sucrose or 3%-6% polyethylene glycol (PEG; molecular weight 400) to saline containing pristine MNPs, we increased infusate viscosity and obtained increased CED efficacy. Further, we show that CED of dextran-coated MNPs (dextran-MNPs) resulted in increased efficacy over pristine MNPs (p < 0.007). To establish the use of MRI for reliable depiction of MNP distribution, CED of fluorescent dextran-MNPs was performed, demonstrating a significant correlation between the distributions as depicted by MRI and spectroscopic images (r(2) = 0.74, p < 0.0002). MRI follow-up showed that approximately 80%-90% of the dextran-MNPs were cleared from the rat brain within 40 days of CED; the rest remained in the brain for more than 4 months. MNPs have been tested for applications such as targeted drug delivery and controlled drug release and are clinically used as a contrast agent for MRI. Thus, combining the CED method with the advantages of MNPs may provide a powerful tool to treat and monitor brain tumors.

Polyglutaraldehyde: A new reagent for coupling proteins to microspheres and for labeling cell-surface receptors. II. simplified labeling method by means of non-magnetic and magnetic polyglutaraldehyde microspheres

Procedures were developed for the synthesis of a new immunoreagent in form of polyglutaraldehyde (PGL) microspheres in sizes ranging from about 50 nm to 1.5 micron. Addition of fluorochromes during synthesis yielded microspheres of high fluorescence intensity. By carrying out the polymerization of glutaraldehyde in presence of iron oxide, magnetic PGL microspheres were produced. Antibody conjugates obtained by interaction of PGL microspheres with immunoglobulins were used to label human red blood cells (RBC) and lymphocytes. A simple method for the separation of magnetically labeled human RBC from unlabeled cells was demonstrated.

The use of magnetite-doped polymeric microspheres in calibrating cell tracking velocimetry

Continuous magnetic separation, in which there is no accumulation of mass in the system, is an inherently dynamic process, requiring advanced knowledge of the separable species for optimal instrument operation. By determining cell magnetization in a well-defined field, we may predict the cell trajectory behavior in the well-characterized field environments of our continuous separators. Magnetization is determined by tracking the migration of particles with a technique known as cell tracking velocimetry (CTV). The validation of CTV requires calibration against an external standard. Furthermore, such a standard, devoid of the variations and instabilities of biological systems, is needed to reference the method against day-to-day shifts or trends. To this end, a method of synthesizing monodisperse, magnetite-doped polymeric microspheres has been developed. Five sets of microspheres differing in their content of magnetite, and each of approximately 2.7 microm diameter, are investigated. An average gradient of 0.18 T/mm induces magnetic microsphere velocities ranging from 0.45 to 420 microns/s in the CTV device. The velocities enable calculation of the microsphere magnetization. Magnetometer measurements permit the determination of magnetization at a flux density comparable to that of the CTV magnets analysis region, 1.57 T. A comparison of the results of the CTV and magnetometer measurements shows good agreement.

Glial cell line-derived neurotrophic factor-conjugated nanoparticles suppress acquisition of cocaine self-administration in rats

The neurotrophic factor glial cell line-derived neurotrophic factor (GDNF) may have therapeutic potential for preventing and treating cocaine addiction. Previously, we found that transplantation of a GDNF-expressing astrocyte cell line into the striatum and nucleus accumbens attenuates cocaine-seeking behavior in Sprague-Dawley rats. However, as a potential treatment for humans, cell transplantation presents several technical and ethical complications. Nanoparticulate systems are a safe and effective method for introducing exogenous compounds into the brain. Therefore, we examined the effect of GDNF-conjugated nanoparticles microinjected into the striatum and nucleus accumbens on cocaine self-administration in rats. GDNF-conjugated nanoparticles blocked the acquisition of cocaine self-administration compared to control treatments. Furthermore, a cocaine dose response demonstrated that decreased lever response in rats that received GDNF-conjugated nanoparticles persisted after substitution with different cocaine doses. This effect is not due to a non-specific disruption of locomotor or operant behavior, as seen following a water operant task. The current study is one of the first demonstrations that drug-conjugated nanoparticles may be effective in treating brain disorders. These findings suggest that GDNF-conjugated nanoparticles may serve as a novel potential treatment for drug addiction.

Novel effective immunoadsorbents based on agarose-polyaldehyde microsphere beads: synthesis and affinity chromatography.

Agarose-polyaldehyde microsphere beads were produced by encapsulating polyacrolein microspheres or polyglutaraldehyde microspheres with agarose. Magnetic beads were formed by carrying out the encapsulation procedure in the presence of ferrofluidic particles. Proteins were bound covalently, at physiological pH, to the beads through their aldehyde groups to produce the Schiff base products. The conjugates, beads-proteins, were used successfully in affinity chromatography for specific purification of antibodies. Leaching of the proteins bound to the beads under physiological conditions and eluting conditions was not detected. The agarose-polyaldehyde microsphere beads are suggested as alternatives to the supports currently used in affinity chromatography.

Synthesis of fluorescent-maghemite nanoparticles as multimodal imaging agents for amyloid-β fibrils detection and removal by a magnetic field

Early diagnosis in Alzheimers disease (AD), before the onset of marked clinical symptoms, is critical in preventing the irreversible neuronal damage that eventually leads to dementia and ultimately death. Therefore, there is an urgent need for in vivo imaging agents, which are valuable as specific biomarkers to demonstrate the location and density of amyloid plaques in the living human brain. The present manuscript describes a novel method for selective marking of Abeta(40) fibrils by non-fluorescent gamma-Fe(2)O(3) and fluorescent-magnetic gamma-Fe(2)O(3)-rhodamine or gamma-Fe(2)O(3)-Congo red nanoparticles, and the complete removal of the magnetized fibrils from the aqueous continuous phase by a magnetic field. These fluorescent-maghemite nanoparticles as multimodal imaging agents have a great advantage due to the combination of the magnetic and fluorescence imaging into one nanostructured system. This hybrid system, which selectively marks Abeta(40) fibrils, might enable the early detection of plaques using both MRI and fluorescence microscopy, and therefore may be applied in in vivo AD diagnosis studies. These fluorescent-magnetic nanoparticles may also be useful as selective biomarkers to detect the location and the removal of other amyloid plaques derived from different amyloidogenic proteins that lead to neurodegenerative diseases, e.g., Parkinsons, Huntingtons, mad cow, and prion diseases.

Polyglutaraldehyde: a new reagent for coupling proteins to microspheres and for labeling cell-surface receptors.

Glutaraldehyde polymerized in basic aqueous solutions was found to react with low molecular weight amines, immunoglobulins and hemoglobin. The polyglutaraldehyde was covalently bound to hypdrophilic microspheres. The rate of addition of proteins to the polyglutaraldehyde-derivatized microspheres was investigated spectrophotometrically as a function of pH and temperature. The reaction of polyglutaraldehyde was found to be faster than that of the monomer. The findings led to successful labeling of human lymphocyte subpopulations.