Tissue factor is associated with the nonbacterial thrombotic endocarditis induced by a hypobaric hypoxic environment in rats

Abstract

 High-altitude hypoxia causes a hypercoagulable state. In our previous study on the blood coagulation system in rats, nonbacterial thrombotic endocarditis (NBTE) developed after 4–12 weeks’ exposure to the equivalent of 5500 m in altitude. We hypothesized that TF (tissue factor)-producing cells in the cardiac valves might be induced by the hypobaric hypoxic environment (HHE) and then trigger NBTE. A total of 170 male Wistar rats were housed in a chamber at the equivalent of 5500 m altitude for 1–12 weeks. We measured TF activity in the plasma and studied morphological changes in the mitral valves using immunohistochemical and immunoelectrical methods for TF protein and in situ hybridization for TF mRNA. After 4 weeks or more of exposure to HHE, 28 of the 56 surviving rats had developed NBTE. After 4–8 weeks’ exposure to HHE, the plasma TF activity level was significantly higher than in control rats. There was a significant correlation between plasma TF activity and the incidence of NBTE. After 1 weeks’ exposure to HHE, immunoreactivity for TF protein was detected in foamy macrophages and stromal cells in the cardiac valves. In rats with NBTE, TF protein was present in foamy macrophages and spindle stromal cells and focally present in the extracellular matrix. TF mRNA was detected in some foamy macrophages within the thrombus, TF protein was localized to the rough endoplasmic reticulum and plasma membrane of many macrophages, some fibroblasts, and a few endocardial cells. TF is associated with the pathogenesis of the NBTE induced by exposure to HHE. The accumulation of TF-producing macrophages during exposure to HHE may be responsible for initiating thrombus formation.