Recanalization of arterial thrombus, and inhibition with beta-radiation in a new murine carotid occlusion model: MRNA expression of angiopoietins, metalloproteinases, and their inhibitors.

Background: Recanalization is an important physiologic phenomenon because it can efficiently reestablish circulation after thrombosis. We attempted to characterize molecular events related to recanalization or organization of arterial thrombus in a new murine model by studying genes reported to be involved in angiogenesis or neointima formation.

Methods: Platinum coils, radioactive phosphorus 32 coils or not, were implanted in the carotid artery in mice to cause thrombotic occlusion. The outcome of the occlusion was followed up with transmyocardial angiography and pathologic analysis at 2, 6, or 15 days. Angiographic results were compared with the Pearson chi2 test. Messenger RNA expression of von Willebrand factor (vWF); smooth muscle alpha-actin (SMA+); platelet endothelial cell adhesion molecule-1 (PECAM-1); vascular endothelium cadherin (VE-Cad); endothelial nitric oxide synthase (eNOS); vascular cell adhesion molecule-1 (VCAM-1); tumor necrosis factor alpha (TNF-alpha); matrix metalloproteinase (MMP-9, MMP-12, and MMP-14), and tissue inhibitors of MMPs (TIMPs: TIMP-1, TIMP-2, TIMP-3, TIMP-4); angiopoietins (Ang-1, Ang-2); and receptors Tie-1 and Tie-2, were analyzed with reverse transcriptase polymerase chain reaction 2, 6, and 15 days after surgery. Levels of mRNA expression were compared with analysis of variance and the Student t test.

Results: Carotid arteries implanted with nonradioactive 0.015-caliber coils were occluded in 84% of arteries on day 2, but in only 57% of arteries on day 15, which confirms that recanalization occurred in this model. Arteries implanted with 0.015-caliber 32P coils did not become recanalized, and 100% were occluded on day 15 (n = 13; P = .006). Recanalization was associated with endothelial-like cell-lined channels, whereas persistent occlusion was caused by complete filling of the lumen with conjunctive tissue. Coil occlusion, with or without recanalization, was followed by decreased expression of vWf, VE-Cad, eNOS, VCAM-1, MMP-2, TIMP-1, and TIMP-2; stable expression of PECAM-1, SMA+, and TIMP-3; and overexpression of Ang-1 and Ang-2, MMP-9, MMP-14, and TIMP-4. Statistically significant differences when arteries were implanted with 32P coils included decreased expression of TIMP-4 (P = .011) and increased expression of MMP-9 (P = .02).

Conclusion: Recanalization and organization of arterial thrombus is associated with expression of genes involved in angiogenesis and neointima formation. Recanalization can be prevented with beta-radiation, but molecular mechanisms remain to be refined.

Clinical Relevance: A better understanding of molecular mechanisms involved in angiogenesis has permitted its regulation as a new option in treatment of various diseases. Inhibition of angiogenesis may help control diseases such as cancer, arthritis, or diabetes retinopathy. On the other hand, stimulation of angiogenesis may palliate conditions associated with insufficient blood supply, such as ischemic heart disease or critical limb ischemia. Yet little is known regarding recanalization (to be differentiated from thrombolysis), a cellular process that occurs concurrently with thrombus "organization." Recanalization is an important physiologic phenomenon because it can efficiently reestablish antegrade circulation after thrombosis both in veins and in arteries, and could be modulated for therapeutic purposes. Thus our efforts at better understanding of mechanisms involved in recanalization could be used, in addition to its promotion to recover flow after thrombotic occlusions, to prevent its occurrence after endovascular interventions designed to permanently occlude aneurysms.