Abstract 191: Immobilized ApoA-I and High Density Lipoproteins are Anti-thrombotic and Inhibit Smooth Muscle Cell Attachment and Proliferation

Abstract

Aim: The clinical efficacy of current endovascular stents is limited by thrombosis and restenosis. Plasma activated coated stainless steel (PAC) is able to covalently bind proteins to stainless steel (SS) surfaces in their bioactive state. High density lipoproteins (HDL) and its main apolipoprotein constituent apoA-I regulate key biological processes involved in restenosis and thrombosis, highlighting their potential for immobilization on PAC stent surfaces. We hypothesized that covalently bound apoA-I or reconstituted HDL (rHDL) to PAC will retain its biological properties and improve stent patency. Methods and Results: Covalent binding of 125I labelled apoA-I and rHDL was increased on PAC compared to SS (p<0.001). Thrombosis formation under static conditions was assessed by scanning electron microscopy. Thrombi were strikingly reduced on PAC and completely absent on PAC+apoA-I and PAC+rHDL, while extensive thrombi formed on all SS samples at all time points. Thrombus formation under flow conditions using a Chandler Loop (0.5U/ml heparin) showed PAC, PAC+apoA-I and PAC+rHDL had 98%, 97% and 94% lower thrombus weights, compared to SS samples, respectively (p<0.05). Lower heparin concentrations (0.3U/ml) revealed that PAC+apoA-I and PAC+rHDL were superior to PAC alone in reducing thrombus weights (98% and 95%, respectively, p<0.01). P-selectin protein expression was measured by ELISA in the plasma from the Chandler loop assay (0.3U/ml heparin). Plasma exposed to PAC+apoA-I had reduced p-selectin levels (32%) compared to the PAC control (p<0.05). Immobilized apoA-I and rHDL on PAC reduced smooth muscle cell (SMC) attachment by 70% and 80%, respectively, p<0.05. Conversely, endothelial cell (EC) attachment was increased by 36% on PAC+apoA-I (p<0.05). Immobilized PAC+apoA-I and PAC+rHDL also reduced TNF-α-induced SMC proliferation (26% and 20% respectively), compared to the PAC control (p<0.05). Conclusion: ApoA-I and rHDL covalently bind to PAC surfaces. Immobilized apoA-I and rHDL retain their anti-thrombotic properties, inhibit SMC attachment and proliferation, and increase EC attachment. This may represent a novel site-directed approach to increase stent patency.