Magnetic Resonance Imaging Contrast Agent Targeted Toward Activated Platelets Allows In Vivo Detection of Thrombosis and Monitoring of Thrombolysis

Background— Platelets are the key to thrombus formation and play a role in the development of atherosclerosis. Noninvasive imaging of activated platelets would be of great clinical interest. Here, we evaluate the ability of a magnetic resonance imaging (MRI) contrast agent consisting of microparticles of iron oxide (MPIOs) and a single-chain antibody targeting ligand-induced binding sites (LIBS) on activated glycoprotein IIb/IIIa to image carotid artery thrombi and atherosclerotic plaques.

Methods and Results— Anti-LIBS antibody or control antibody was conjugated to 1-μm MPIOs (LIBS MPIO/control MPIO). Nonocclusive mural thrombi were induced in mice with 6% ferric chloride. MRI (at 9.4 T) was performed once before and repeatedly in 12-minute-long sequences after LIBS MPIO/control MPIO injection. After 36 minutes, a significant signal void, corresponding to MPIO accumulation, was observed with LIBS MPIOs but not control MPIOs ( P <0.05). After thrombolysis, in LIBS MPIO-injected mice, the signal void subsided, indicating successful thrombolysis. On histology, the MPIO content of the thrombus, as well as thrombus size, correlated significantly with LIBS MPIO-induced signal void (both P <0.01). After ex vivo incubation of symptomatic human carotid plaques, MRI and histology confirmed binding to areas of platelet adhesion/aggregation for LIBS MPIOs but not for control MPIOs.

Conclusions— LIBS MPIOs allow in vivo MRI of activated platelets with excellent contrast properties and monitoring of thrombolytic therapy. Furthermore, activated platelets were detected on the surface of symptomatic human carotid plaques by ex vivo MRI. This approach represents a novel noninvasive technique allowing the detection and quantification of platelet-containing thrombi.

[Helping antibodies. Targeted antithrombotic and fibrinolytic therapy]

The development of monoclonal antibodies facilitated an enormous progress in modern medicine in the last years. The targeted inhibition of defined molecular structures allows therapeutic concepts, which before were inconceivable. There are numerous antibodies in clinical use within the area of tumour therapy, chronically inflammatory diseases, transplantation, infections and also in cardiovascular medicine. Different antibody formats are used such as IgG molecules, Fab fragments and single chain antibodies. Single chain antibodies represent the smallest functional form of the antibody and are used preferentially as recombinant antibodies. The therapeutic possibilities of antibody technology are extended by fusion to radioactive or therapeutically active substances. This review focuses on the application of antibodies and fusion proteins as antithrombotic and fibrinolytic drugs. The use of antibodies allows the development of inhibitory agents with clearly defined functional properties, as for example for activation-specific GPIIb/IIIa-blockade. In addition antibodies can be used for targeting antithrombotic and fibrinolytic agents to the thrombus, allowing an effective local action with less bleeding complications.

[Factor Xa-inhibition in interventional cardiology]

The recently established correlation between bleeding events and clinical outcomes in patients with coronary artery disease undergoing either non-invasive or invasive treatment for acute coronary syndromes (ACS) highlights the unmet need for safer anticoagulants that can be used in conjunction with dual or triple antiplatelet therapy. The central position of the coagulation factors IIa and Xa within the coagulation system account for their prominent role as targets for anticoagulants. Unfractionated heparin (UFH) achieves a variable indirect inhibition of both factors. The low molecular weight heparins (LMWH) show favourable pharmacokinetics over UFH and have a more pronounced activity against factor Xa as opposed to thrombin which may partially account for the benefits observed with LMWH in clinical trials. New agents that have been developed allow for a selective inhibition of factor Xa. Recently, exciting results have been reported with an indirect selective inhibitor of factor Xa in patients with ST-elevation myocardial infarction (STEMI) -acute coronary syndromes (ACS) and non-STEMI-ACS. In this article the pharmacology of the indirect selective factor Xa inhibitors Fondaparinux and Idraparinux will be discussed along with the direct selective factor Xa inhibitors DX-9065a and Otamixaban in the setting of interventional cardiology.

Determinanten des insensiblen Flüssigkeitsverlustes

Accurate perioperative fluid balance is the basis of a targeted infusion regimen. However, neither the initial status nor perioperative changes of the fluid compartments can be reliably measured in daily routine. In particular, insensible losses are not consistently assessed, so that substitution therapy is generally empirical. The object of this paper is to communicate the scientific data on this topic. Preoperative fasting (10 h) does not per se cause intravascular hypovolemia. In adults, total basal evaporation by way of the skin and airways and of any wounds during major abdominal interventions is usually less than 1 ml/kg/h. An inconstant fluid and protein shift towards the interstitial space perioperatively seems to be associated with hypervolemia, which suggests it should be preventable. The decisive factor in this context seems to be deterioration of the endothelial glycocalyx, whose further patho-physiological impact is currently only partially known. Clinical studies have revealed a link between fluid restriction and improved outcome after major abdominal surgery.