Biomedical subjects

Shalaby W Shalaby

Publications and source records attributed to Shalaby W Shalaby.

4 recordsLinked to original sources

PubMed2005

Direct correlation between adsorption-induced changes in protein structure and platelet adhesion.

It is widely recognized that adsorbed proteins on biomaterial surfaces tend to initiate thrombus formation, although the specific mechanisms involved are still not well understood. In attempts to decrease the conformational change of adsorbed proteins, surface treatments that reduce surface hydrophobicity have been considered, such as the sulfonation of low-density polyethylene and isotactic polypropylene. The objectives of this present research were to study how changes in surface chemistry influence the degree of conformational change of adsorbing proteins and to investigate the correlation between the change in adsorbed protein structure and platelet response. Adsorbed porcine serum albumin and porcine fibrinogen were used as the model proteins for determining the effects of sulfonation on protein conformational change. Circular dichroism spectroscopy studies showed that the proteins were less altered structurally on the sulfonated surfaces. Platelet adhesion studies were used to correlate the number of adhered platelets with the amount of conformational change in adsorbed proteins on the polymer surface. The results of these studies show a linear correlation between platelet adhesion and the degree of adsorption-induced protein conformational change. These findings suggest that the degree of protein conformational change after adsorption is a dominant mechanism governing platelet interactions with biomaterial surfaces.

Adsorption↗

PubMed2004

Absorbable microparticulate cation exchanger for immunotherapeutic delivery.

An absorbable microparticulate cation exchanger was synthesized as a versatile carrier for biologically active proteins. In this work, acid-terminated polyglycolide (or polyglycolic acid) microparticulates (PG-MP) were surface modified for either sustained release of cytokines or as a platform for immunomodulation. The intended goal was to achieve in situ recruitment/maturation of dendritic cells and activation of T cells for tumor immunotherapy. PG-MP were prepared with a volume weighted mean diameter of 7.02 micro (range: 2.09-14.58 micro). Accessible carboxylic acid groups were determined to be 0.3 mmol/g with a corresponding zeta potential of -21.87 mV in phosphate-buffered saline. Under low magnification, scanning electron microscopy (SEM) revealed a highly textured surface due to processing from repetitive jet milling. However, a moderately porous architecture was noted at higher magnification. Electron spectroscopy for chemical analysis was used to characterize the PG-MP surface before and after adsorption of human granulocyte-macrophage colony stimulating factor (GM-CSF). Adsorption of GM-CSF on PG-MP (PG-GMCSF) resulted in a modest increase in the surface atomic concentration of nitrogen (0.97%). Pretreating the surface with poly-L-lysine (PG/Lys-GMCSF) prior to adding GM-CSF produced a nearly threefold increase in the surface nitrogen concentration (4.20% compared to 1.47%). This manipulation not only increased loading content, but also prolonged the release of GM-CSF released from 6 days to 26 days. ESCA on the post-release PG-MP samples (PG-GMCSF and PG/Lys-GMCSF) revealed a similar residual surface nitrogen concentration (2.26% vs. 2.35%). The observation was consistent with irreversibly adsorbed GM-CSF. It is postulated that irreversibly bound GM-CSF is released over time as a function of microparticulate degradation. Biological activity of released GM-CSF was confirmed by the proliferation of a GM-CSF-dependent cell line (TF-1) in the presence of microparticulates. PG-MP mediated activation of T cells was achieved through irreversible adsorption of either antimouse cd3 plus antimouse cd28 monoclonal antibodies (alpha-cd3/cd28-MP) or antihuman CD3 plus antihuman CD28 monoclonal antibodies (alpha-CD3/CD28-MP) on PG-MP. Irreversibly adsorbed antibodies were capable of activating both resting mouse and human T cells. Intracellular flow cytometry on mouse T cells revealed that nearly 50% of the activated cells produced interferon-gamma (IFN-gamma). This was consistent with a TH-1 or cell-mediated response. In vivo efficacy was evaluated in a mouse flank tumor model showing a significant antitumor effect both alone and in combination. Combination therapy was most effective at preventing tumor implantation (8/8 mice) and was able induce tumor regression (4/7 mice) and/or stable disease (3/7 mice) in a regression model. In these studies, immunohistochemistry was used to confirm local recruitment of dendritic cells. In conclusion, the PG-MP represents a novel absorbable cation exchanger that can be readily manipulated to deliver biologically active proteins for immunotherapy.

Absorption↗

PubMed2003

Development of novel substrates for tumor immunotherapy.

Acid-terminated polyglycolide microparticles (PG-MP) were prepared as a versatile substrate that could be surface-modified for either immobilization of anti-cd3 and anti-cd28 mAb to activate T cells or sustained release of granulocyte-macrophage colony stimulating factor (GM-CSF) for dendritic cell (DC) recruitment and maturation. PG-MP were prepared with a volume-weighted mean diameter of 56 or 57 microm. Accessible carboxylic acid group concentration was determined by potentiometric titration to be 0.3 mmole/g and corresponded to a zeta potential of -21.87 mV. PG-MP immobilized with either anti-human CD3/CD28 or anti-mouse cd3/cd28 induced significant proliferation of T cells. Intracellular flow cytometry in activated mouse T cells was significant for IFN-gamma, but not IL-4. Microparticles surface-modified for GM-CSF release were prepared from either PG-MP or PG pre-treated with poly-L-lysine (PG-Lys) to manipulate surface charge. GM-CSF released from PG-Lys-MP was observed for up to 26 days. The biologic activity of released GM-CSF was confirmed by using a h-GM-CSF-dependent cell line. The efficacy of the alpha-cd3/cd28-MP and GMCSF-MP was studied in a syngeneic mouse tumor prevention and regression model. Co-injection of Meth A fibrosarcoma cells with alpha-cd3/cd28-MP and GMCSF-MP completely prevented tumor implantation (0/24). The regression model showed complete tumor regression in four of seven animals and stable disease in three of seven. In the latter study, a dramatic level of DC infiltration was observed compared to controls.

Animals↗

PubMed2002

In vitro evaluation of phosphonylated low-density polyethylene for vascular applications.

The use of catheters for vascular applications is often complicated by the development of friction between the catheter material and the vessel wall, which leads to endothelial cell removal and intimal lesions. Phosphonylation, a chemical surface treatment, has been proposed as a means of increasing the hydrophilicity of low-density polyethylene (LDPE), a commonly used catheter material, in efforts to impart lubricity to the material and reduce vascular tissue damage. In an in vitro tribological study, phosphonylated LDPE produced a lower coefficient of friction and allowed greater retention of endothelial cells on vessels as compared to untreated LDPE when the materials were reciprocated against normal porcine aorta. Chemical characterizations of the LDPE before and after friction testing involving Fourier transform infrared and energy-dispersive X-ray (EDX) confirmed the phosphorus content on phosphonylated LDPE. Election spectroscopy for chemical analysis (ESCA) and atomic force micrscope (AFM) analyses verified that proteins initially adsorb to both the phosphonylated and untreated LDPE surfaces and that the proteins interfere with water to lubricate the surfaces. However, with repeated friction, proteins are removed from the surface and hydrophilicity, as imparted by phosphonylation, becomes a principal factor in the lubrication process.

Animals↗