Abstract 530: Bacterial Infection is a Mechanism Underlying a Failure of Thrombus Resolution in Chronic Thromboembolic Pulmonary Hypertension
Background: Chronic thromboembolic pulmonary hypertension (CTEPH) results from single or recurrent pulmonary thromboemboli arising from sites of venous thrombosis. In patients with CTEPH, thromboemboli do not resolve, but form endothelialized, fibrotic obstructions of the pulmonary vascular bed. Mechanisms underlying thrombus organisation are poorly understood. Because of the observation that infected intravenous leads enhance the likelihood of CTEPH, we tested the hypothesis that bacterial infection causes a failure of thrombus resolution.
Methods: Human thromboendarterectomy specimens were sterilly collected during surgery and analyzed with a bacterial 16S ribosomal DNA screening protocol. In a next step, a mouse model of venous thrombus formation was employed to investigate thrombus resolution in the absence and presence of low doses of staphylococcus aureus (0,15ml of 105 /ml injected as a single bolus into the tail vein). On days 1, 3, 7, 14 and 28 after thrombus induction, animals were sacrificed, thrombi were harvested, fixed and embedded in paraffin.
Results: 520bp PCR products were obtained in 16 of 25 CTEPH thrombi, but in only 4 thrombi derived from patients with acute pulmonary embolism. Cross-sectional area analysis demonstrated that thrombi from infected animals were larger than control thrombi (day 7: median cross-sectional area (CSA) 0,431 versus 0,279mm2; day 28: median CSA 0,128 versus 0,018mm2, n=8, p<0,05). Volumetry confirmed significantly larger thrombus volumes on days 3 and 28 (day 3: median thrombus volume 1,798 versus 1,441mm3; day 28 median thrombus volume 0,427 versus 0,056mm3, n=8, p<0,05). Real-time PCR demonstrated increasing expression of connective tissue growth factor (CTGF) in thrombi over the observation period, contrasting a decline of CTGF expression in controls.
Discussion: The data demonstrate that infection with staphylococcus aureus enhances thrombus formation and persistence. CTGF expression analysis suggests that abnormal thrombus organization occurs after bacterial infection.