Differential Role of Components of the Fibrinolytic System in the Formation and Removal of Thrombus Induced by Endothelial Injury

Abstract

SummaryThe role of fibrinolytic system components in thrombus formation and removal in vivo was investigated in groups of six mice deficient in urokinase-type plasminogen activator (u-PA), tissue-type plasminogen activator (t-PA), or plasminogen activator inhibitor-1 (PAI-1) (u-PA-/-, t-PA-/- or PAI-1-/-, respectively) or of their wild type controls (u-PA+/+, t-PA+/+ or PAI-1+/+). Thrombus was induced in the murine carotid artery by endothelial injury using the photochemical reaction between rose bengal and green light (540 nm). Blood flow was continuously monitored for 90 min on day 0 and for 20 min on days 1, 2 and 3. The times to occlusion after the initiation of endothelial injury in u-PA+/+, t-PA+/+ or PAI-1+/+ mice were 9.4 ± 1.3, 9.8 ± 1.1 or 9.7 ± 1.6 min, respectively. u-PA-/- and t-PA-/- mice were indistinguishable from controls, whereas that of PAI-1-/- mice were significantly prolonged (18.4 ± 3.7 min). Occlusion persisted for the initial 90 min observation period in 10 of 18 wild type mice and was followed by cyclic reflow and reocclusion in the remaining 8 mice. At day 1, persistent occlusion was observed in 1 wild type mouse, 8 mice had cyclic reflow and reocclusion and 9 mice had persistent reflow. At day 2, all injured arteries had persistent reflow. Persistent occlusion for 90 min on day 0 was observed in 3 u-PA-/-, in all t-PA-/- mice at day 1 and in 2 of the t-PA-/-mice at day 2 (p <0.01 versus wild type mice). Persistent patency was observed in all PAI-1-/- mice at day 1 and in 5 of the 6 u-PA-/- mice at day 2 (both p <0.05 versus wild type mice). In conclusion, t-PA increases the rate of clot lysis after endothelial injury, PAI-1 reduces the time to occlusion and delays clot lysis, whereas u-PA has little effect on thrombus formation and spontaneous lysis.

Profibrinolytic, Antithrombotic, and Antiinflammatory Effects of an Insulin-Sensitizing Strategy in Patients in the Bypass Angioplasty Revascularization Investigation 2 Diabetes (BARI 2D) Trial

“…It shifts the balance between thrombosis and fibrinolysis, favoring thrombosis. 12,13 It portends an increased risk of MI. 14 Insulin increases synthesis and concentrations of PAI-1 in blood, 15–20 as do mediators of inflammation.…”

Role of 2-Antiplasmin in Cardiovascular System

“…Clot lysis experiments confirmed that the endogenous thrombolysis potential is significantly enhanced in α2-AP -/-mice, indicating a physiological role of α2-AP in fibrin surveillance [38]. We have previously reported that tPA increases the rate of clot lysis after endothelial injury [34] and other study showed the functional significance of α2-AP as a direct inhibitor of tPA, which explains the basis of the accepted role of α2-AP as a regulator of fibrin persistence and thrombus resistance to lysis [39].…”

“…We found that deficiency in α2-AP led to different result in formation and removal of arterial and venous thrombus in mice [30,31]. Indeed, we applied an experimental procedure to induce endothelial injury both in the murine carotid artery and jugular vein [32][33][34]. The time to occlusion by the development of thrombus in the carotid artery was slightly prolonged in α2-AP -/-mice, whereas it was markedly prolonged in jugular vein, compared with wild type mice [30].…”

“…Two VEGF tyrosinekinase receptors, VEGFR-1 (Flt-1) and VEGFR-2 (Flk-1), have been shown to bind VEGF with high affinity [58]. We previously reported that endothelial injury using a photosensitive dye compound develops reproducible thrombus formation in the murine carotid artery [34,59]. Recently we found a novel aspect between α2-AP -/-and α2-AP +/+ mice on endothelial injury [60].…”

Does plasmin have anticoagulant activity?

“…However, several studies have alluded to this possibility. Matsuno et al39 found that Plg-deficient mice had shorter arterial occlusion times after photochemical carotid injury (Table 1) whereas a deficiency of α 2 -AP, PAI-1, or vitronectin deficiency resulted in delayed occlusion times 39–42. Patency of the injured carotids was more rapid in the PAI-1 and AP-deficient mice than wild-type (WT) mice (Table 1).…”