Evaluation of the Effect of Retroviral Gene Transduction on Vascular Endothelial Cell Adhesion

Optimizing fluorescent labeling of endothelial cells for tracking during long-term studies of autologous transplantation

BACKGROUND

The fluorescent marker PKH26 has been demonstrated to be useful for the tracking of endothelial cells in short-term studies; however, the optimal labeling conditions for long-term implants have not been determined. This study was designed to evaluate the effects of PKH26 on endothelial cell proliferation and to identify labeling conditions that would yield the greatest fluorescence over time without adversely affecting cell viability.

MATERIALS AND METHODS

Canine jugular vein endothelial cells (CJVECs) were labeled with 0. 04 microM PKH26. Proliferation of labeled and control cells was assessed for 8 consecutive days by [(3)H]thymidine uptake. In a second experiment, CJVECs were labeled at concentrations of 0, 5, 8, 10, and 20 micromol/L. Cells were maintained in culture for 60 days. The fluorescence intensity of each cell population was measured using two techniques. At baseline and at 60 days, fluorescence was measured using a fluorescence-activated cell sorter. On days 14, 28, 45, and 60 fluorescence was measured by constructing gray-scale histograms from photomicrographs taken of each flask under rhodamine illumination. Mean viable cell number for each concentration was determined after 60 days.

RESULTS

In the first experiment, PKH26-labeled and unlabeled CJVECs demonstrated nearly identical growth curves, suggesting that PKH26 had no adverse effect on proliferation. In the second experiment, after 60 days, the 10 and 20 microM groups displayed greater fluorescence by histogram than the 0, 5, or 8 microM groups; however, they were not significantly different from each other (mean intensity 8.2 vs 9.1, P > 0.05, Student-Newman-Keuls test for multiple comparisons). Over 60 days, the cells labeled with 20 microM PKH26 experienced the only significant decrease in viable cells compared to the unlabeled group (5.5 x 10(5) vs 9.6 x 10(5) cells/flask, P < 0.05). Importantly, we observed no significant differences in cell number between the 10 microM group and the lower concentrations compared to the unlabeled cells (P > 0.05).

CONCLUSIONS

We conclude that a concentration of 10 microM PKH26 provides the optimal labeling condition for endothelial cells when long-term tracking is desired.

Biomaterials and cardiovascular devices

In the field of cardiovascular surgery there is presently a lack of biomaterials possessing essential characteristics of the native tissue or organ which is to be replaced. This paper describes various biomaterials that have been introduced into the circulatory system and the complex reactions that subsequently occur. The risk of infection is also discussed as well as prevention and treatment regimes that can be used. Examples of future biomaterial development are outlined in an attempt to achieve biocompatibility.

Effect of retroviral transduction on human endothelial cell phenotype and adhesion to Dacron vascular grafts

PURPOSE

Retroviral transduction for genetic enhancement of endothelial cell (EC) anti-thrombotic phenotype offers potential for improving the clinical success of vascular graft seeding; however, application of this technique may bring concomitant alteration in cell functionality.

METHODS

Human microvascular ECs were transduced with a retroviral vector encoding for the marker gene beta-galactosidase. Transduced endothelial cells (rtECs) and nontransduced endothelial cells (ntECs) were evaluated by flow cytometry for expression of intercellular adhesion molecule (ICAM)-1 and tissue factor (TF) on both smooth (coverslips) and graft (Dacron, 6 mm inside diameter) surfaces under static and shear exposed conditions. Graft EC retention was measured after 6-hour pulsatile perfusions. Platelet and neutrophil adherence was measured on perfused coverslips.

RESULTS

Lower levels of ICAM-1 were expressed by rtECs on coverslips under both static (p < 0.01 vs static ntECs) and shear exposed conditions (p < 0.01 vs static and shear ntECs). Accordingly, fewer polymorphonuclear leukocytes adhered to rtEC monolayers (p < 0.01 vs ntECs). No difference in ICAM-1 and TF expression by static graft seeded rtECs and ntECs was observed. However, graft-seeded rtECs that were exposed to wall shear stress displayed less TF than sheared ntECs (p < 0.05). Transduction did not affect EC retention to the sheared graft surface.

CONCLUSIONS

These data suggest that retroviral transduction does not elicit a prothrombotic/proinflammatory phenotype, rather indices of these states appear in some conditions to be reduced. Further, transduction does not adversely affect EC adherence to Dacron graft surfaces under arterial hemodynamics.

Retroviral mediated gene transduction alters integrin expression on vascular endothelial cells

Genetically recombinant endothelial cells (rEC) may improve the patency of small diameter vascular grafts by preventing thrombosis or limiting neointimal hyperplasia. Previous work has shown that rEC have reduced adhesion to vascular bypass grafts in vivo. Poor adhesion may be due to altered adhesion (integrin) receptors. This study evaluated the expression of the alpha 5 beta 1 (fibronectin), alpha 2 beta 1 (collagen IV), and alpha v beta 3 (vitronectin) integrin subunits on rEC. Human umbilical vein EC or canine jugular vein EC were transduced with neoR, neoR and human tPA or hygromycin resistance genes using retroviral vectors. Naive EC and EC exposed to empty viral particles (mEC) were controls. Naive EC, mEC, and all rEC's were evaluated for alpha and beta subunits for each integrin receptor studied using immunoblotting. Blotting for alpha 2, alpha 5, and alpha v exhibited expression of the alpha integrin subunits in all cells. The beta 1 and beta 3 subunits were present in mEC and nEC but were absent or truncated in all rEC. The decreased adhesion of rEC's to synthetic vascular grafts may be accounted for by their altered beta 1 and beta 3 integrin subunit expression. The beta subunit is critical for organization of the cytoskeleton and cellular signal transduction. Diminished beta subunit expression in rEC is neither vector specific nor related to retroviral exposure alone. Alteration of beta integrin expression may be to associated with the over-expression of phosphotransferase genes such as neoR or hygromycin B used as selectable markers in gene transfer protocols.