Technetium 99m–Labeled Annexin V Scintigraphy of Platelet Activation in Vegetations of Experimental Endocarditis

Abstract

Background-The pathophysiology of infective endocarditis involves a pathogen/host tissue interaction, leading to formation of infected thrombotic vegetations. Annexin V is a ligand of phosphatidylserines exposed by activated platelets and apoptotic cells. Because vegetations are platelet-fibrin clots in which platelet proaggregant activity is enhanced by bacterial colonization, we investigated the ability of annexin V labeled with technetium Tc 99m ( 99m Tc-ANX) to provide functional imaging of these vegetations in experimental models of infective endocarditis. This ability was assessed in rabbits and rats because of the different interest of these 2 species in preclinical analysis. Methods and Results-Nonbacterial thrombotic endocarditis was induced with the use of a catheter left indwelling through the aortic or tricuspid valve, and animals were injected with either a bacterial inoculum or saline. Scintigraphic investigations were performed 5 days later and showed a higher 99m Tc-ANX uptake by vegetations in infected versus noninfected animals (ratio, 1.3 for in vivo acquisitions and 2 for autoradiography; PϽ0.0001 for all), whereas no significant uptake was present in controls. Right-sided endocarditis was associated with pulmonary uptake foci corresponding to emboli. Histological analysis of vegetations showed a specific uptake of 99m Tc-ANX at the interface between circulating blood and vegetation. In parallel, underlying myocardial tissue showed myocyte apoptosis and mucoid degeneration, without extracellular matrix degradation at this stage. Conclusions-99m Tc-ANX is suitable for functional imaging of platelet-fibrin vegetations in endocarditis, as well as embolic events.99m Tc-ANX uptake reflects mainly platelet activation in the luminal layer of vegetations. This uptake is enhanced by bacterial colonization. (Circulation. 2008;117:781-789.) Key Words: endocarditis Ⅲ imaging Ⅲ nuclear medicine Ⅲ thrombus Ⅲ valves I nfective endocarditis remains a diagnostic and therapeutic challenge, as evidenced by the stability of its incidence over time and its morbidity and mortality rates. 1,2 In addition to the direct valvular damage due to endocardial vegetations, embolic events are frequent and life-threatening complications of infective endocarditis. 3 In this context, morphological imaging such as echocardiography is useful for the diagnosis and may have a prognostic value in predicting embolic events. 4 Clinical Perspective p 789The endocardial thrombotic vegetation represents a specific model of pathogen/host tissue interaction, involving the formation of a septic thrombus leading to injury of both underlying valvular and cardiac tissue and to possible peripheral septic dissemination. 5 Pathogen-platelet molecular interactions are probably one of the main determinants of vegetation formation 6 and growth that are linked to septic thrombus formation, including platelet activation and aggregation 7 and fibrin-fibronectin deposition. 8,9 The pathological consequences of vegetation formation, including degradatio...

Predominant Role of Host Proteases in Myocardial Damage Associated with Infectious Endocarditis Induced by Enterococcus faecalis in a Rat Model

“…Aortic valve endocarditis was induced in 16 male Wistar rats as described by Durack et al in rabbits (15), following a protocol adapted to rats by our group (13). The study was designed with 80% power to detect a relative 50% difference in vegetation area between groups.…”

“…In brief, a polyethylene catheter (PE 10; Clay Adams) was connected to an invasive blood pressure monitor and inserted into the left ventricle via the right carotid artery under ketamine-xylazine anesthesia. The left-ventricular location of the catheter was checked on the pressure curve as previously described (13). The catheter remained indwelling throughout the experiment in order to induce mechanical injury that would lead to the formation of a nonbacterial endocardial thrombus (vegetation).…”

“…The main objectives of the present study were to assess host proteolytic activities (gelatinases, elastase, and plasmin) contained in the vegetation and their cytotoxic potential in a rat model of experimental infective endocarditis (13,14). In particular, we aimed at separating the respective involvement of the bacterial and nonbacterial biological components of the infective endocarditis thrombus in myocardial/valvular tissue degradation and fibrinolytic activity and thereby providing evidence of a pivotal role of host proteases.…”

Radiolabeled Fucoidan as a P-Selectin Targeting Agent for In Vivo Imaging of Platelet-Rich Thrombus and Endothelial Activation

“…Six male Wistar rats (Janvier) were used in the study. The procedure was derived from the classic model, as described previously (23). In brief, a polyethylene catheter (PE10; Clay Adams) was inserted into the left ventricle under pressure monitoring through the right carotid artery in anesthetized rats (ketamine-xylazine).…”

“…Twenty-four hours after catheterization, rats underwent bacterial inoculation (10 8 colony-forming units of Enterococcus faecalis JH2-2) by the left jugular vein under halothane anesthesia. Vegetations of infective endocarditis are platelet-rich thrombi, in which biologic activity is enhanced by bacterial colonization (23). Imaging was performed 4 d later.…”