Genetically engineered smooth muscle cells as linings to improve the biocompatibility of cardiovascular prostheses

The seeding of the blood-contacting surfaces of cardiovascular prostheses with autologous endothelial cells to improve their biocompatibility has had little success. In most instances, cells have sloughed off under flow conditions. The performance of left ventricular assist devices (LVADs) designed to stabilize patients awaiting donor hearts for transplantation has been remarkably good. After prolonged implantation, pump surfaces become covered with a pannus of smooth muscle-like cells (myofibroblasts). Occasional islands of endothelial cells have been identified on top of such cell layers. Therefore, in an attempt to accelerate the beneficial conditioning and improve biomaterial-blood compatibility of LVAD internal surfaces, their seeding with autologous, genetically engineered smooth muscle cells (SMCs) was investigated.

Since routine testing of the Thermocardiosystems HeartMate LVAD is carried out in calves, SMCs were isolated from calves, propagated in culture, and transduced with NO synthase genes to yield stable production of NO. Previous studies had demonstrated that SMCs attached strongly to the biomaterials that compose the internal surfaces of LVADs. Transduction of NO synthase gene expression in the SMCs was achieved by electroporation and antibiotic (G418) selection. Inhibition of smooth muscle cell proliferation by NO has been documented, and the same molecule has been shown to inhibit platelet adhesion to cell surfaces. Cells transduced with NO synthase expressed enzyme protein at consistently high levels for several passages in culture; however, NO production was dependent on the supplementation of culture medium with a source of tetrahydrobiopterin (sepiapterin). Under such conditions, transduced cells were growth-inhibited compared with mock-transfected controls. Induction of GTP cyclohydrolase (the rate-limiting enzyme for the production of tetrahydrobiopterin) expression also resulted in NO production by NO synthase-transduced cells.

Preliminary studies have shown that SMCs form strong attachments to the surface materials of LVADs and that their proliferation rates could be controlled after transformation with NO synthase under conditions that support production of NO. Therefore, genetically engineered SMCs may provide an improved blood biomaterial interface for cardiovascular prostheses.