Magnetic stents retain nanoparticle-bound antirestenotic drugs transported by lipid microbubbles.

PURPOSE: Coating coronary stents with antirestenotic drugs revolutionized interventional cardiology. We developed a system for post-hoc drug delivery to uncoated stents. METHODS: We coupled rapamycin or a chemically similar fluorescent dye to superparamagnetic nanoparticles. The antiproliferative activity of rapamycin coupled to nanoparticles was confirmed in vitro in primary porcine vascular cells. The particles were then incorporated into lipid based microbubbles. Commercially available stents were made magnetizable by nickel plating and used to induce strong field gradients in order to capture magnetic microbubbles from flowing liquids when placed in an external magnetic field. RESULTS: Nanoparticle bound Rapamycin dose dependently inhibited cell proliferation in vitro. Magnetic microcbubbles carrying coated nanoparticles were caught by magnets placed external to a flow-through tube. Plating commercial stents with nickel resulted in increased deposition at stent struts and allowed for widely increased distance of external magnets. Deposition depended on circulation time and velocity and distance of magnets. Deposited microbubbles were destroyed by ultrasound and delivered their cargo to targeted sites. CONCLUSIONS: Drugs can be incorporated into nanoparticle loaded microbubbles and thus be delivered to magnetizable stents from circulating fluids by applying external magnetic fields. This technology could allow for post-hoc drug coating of already implanted vascular stents.

Prothrombotic effects of diclofenac on arteriolar platelet activation and thrombosis in vivo.

BACKGROUND: Diclofenac, like selective cyclooxygenase-2 inhibitors, which alter vascular levels of platelet active prostaglandins, has been reported to increase rates of acute myocardial infarction. OBJECTIVE: The study was performed to investigate, in an animal model of arterial thrombosis in vivo, whether diclofenac differentially influences platelet activation and thrombosis in vessels under non-stimulated conditions or during acute systemic inflammation, such as induced by tumor necrosis factor-alpha (TNF-alpha). METHODS: Platelet-vessel wall interaction (PVWI), firm platelet adhesion and arterial thrombosis following vessel injury were analyzed by intravital microscopy in arterioles of hamsters in the dorsal skinfold chamber model. Prostacyclin [prostaglandin I(2) (PGI(2))] and thromboxane A(2) (TxA(2)) metabolites were measured. In vitro, endothelial adhesion molecule expression in cultured human microvascular endothelial cells was analyzed. RESULTS: Under non-stimulated conditions, diclofenac (1 mg kg(-1)) enhanced PVWI, which was not mediated by increased adhesion molecule expression, but by decreased systemic PGI(2) levels. Following ferric chloride-induced endothelial injury, diclofenac accelerated thrombotic vessel occlusion time, an effect that was reversed by the stable PGI(2) analog iloprost. TNF-alpha, through induction of endothelial adhesion molecule expression, also enhanced PVWI, firm adhesion, and arterial thrombosis, but simultaneous treatment with TNF-alpha and diclofenac did not have an additive effect. CONCLUSIONS: By decreasing levels of PGI(2) without, at the same time, altering prothrombotic TxA(2) levels, diclofenac can exert prothrombotic effects. However, this is not the case when an inflammatory situation is created by TNF-alpha treatment. These data may explain the enhanced risk of acute myocardial infarction observed in patients taking diclofenac.