Graft protection in bypass surgery: siRNA-mediated silencing of adhesion molecules.

The outcome of patients after coronary bypass grafting is greatly influenced by the type of graft material employed, especially regarding the rate of graft restenosis. Besides direct thrombotic events, the leukocyte-endothelial interaction modulated by adhesion molecules is identified to be the central cause leading to graft alterations. This study deals with a new therapeutic concept in order to achieve superior protection of a new bypass graft by blocking the adhesion molecule expression pathway with RNA interference to inhibit the initial leukocyte adhesion and transmigration. Leukocyte binding to adhesion molecules on activated human venous endothelial cells (HVECs) was determined by video-assisted microscopy in a flow chamber mimicking physiological conditions. The cells under study were sequentially transfected in a nonviral manner with specific short interfering RNA-sequences (siRNA) targeting E-selectin, intercellular adhesion molecule, and vascular adhesion molecule. After stimulation of adhesion molecule expression by tumor necrosis factor, a leukocyte-rich suspension was run through the chamber and the attaching leukocytes were counted. Transfection with specific siRNA targeting three different adhesion molecules resulted in a highly significant reduction of leukocyte attachment to activated HVECs in each case compared to the controls (p < 0.05). Transfection with a mixture out of all three siRNA-sequences showed the lowest leukocyte adhesion (p < 0.05) compared to the controls. siRNA-sequences inhibit the adhesion molecule expression on HVECs in an extremely effective way; not only in a single transfection of specific molecules but also in a parallel transfection of multiple sequences in one transfection. Accordingly, siRNA treatment significantly reduced adhesion of leukocyte cells to HVECs compared to controls. This study showed for the first time an effective knockdown of the leukocyte-endothelium interactions by transfection of HVECs with a cocktail consisting of three highly specific siRNAs against three different endothelial adhesion molecules.