Neovascularization during venous thrombosis organization: A preliminary study

Purpose: Thrombus organization after venous thromboembolism leading to reca nalization occurs at a variable rate. The angiogenic chemokine interleukin- 8 (IL-8) has been found in thrombus months after thrombus initiation. We hy pothesize that thrombus organization involves neovascularization and leukoc yte influx and that IL-8 administered at thrombus induction will promote th rombus organization. Methods: A group of rats underwent inferior vena caval occlusive thrombosis . At thrombus induction and every 24 hours, the rats were administered IL-8 (1 mu g) or serum albumin. The rats were killed at either day 4, day 8, or day 12, and, at death, colloidal carbon was perfused via the heart. The in ferior vena cava was isolated, measured, weighed, and formalin fixed. The s ections were stained with anti-polymorphonuclear leukocyte antibody, the en dothelial marker factor VIII-related antigen, and with hematoxylin and eosi n. Thrombus neovascularization (colloidal carbon) with morphometric analysi s was normalized to the total thrombus area. In addition, the rats underwen t perfusion with fluorescein isothiocyanate dextran (molecular weight, 150, 000) at death to correlate with colloidal carbon perfusion, and thrombus fl uorescence was determined. Results: Thrombus cellularity initially involved neutrophils, followed by m onocytes. Significantly more neutrophils, monocytes, and cells that were de fined as spindle shaped (fibroblasts and endothelial cells) were noted in t he animals treated with IL-8. Neovascularization was significantly increase d at day 4 in the animals treated with IL-8 versus the animals treated with Serum albumin and was corroborated with a significant increase in thrombus fluorescein isothiocyanate dextran fluorescence at day 4 in the rats treat ed with IL-8. Colloidal carbon perfusion was noted within vascular channels without extravasation and colocalized with factor VIII-related antigen. Conclusion: This study shows that thrombus organization involves neovascula rization and that IL-8 augments thrombus organization.