Prevention of the Hypercontractile Response to Thrombin by Proteinase-Activated Receptor-1 Antagonist in Subarachnoid Hemorrhage

Abstract

Background and Purpose-Cerebral vasospasm is one of the major complications of subarachnoid hemorrhage (SAH). Its pathogenesis still remains elusive, and effective therapeutic strategies are yet to be established. We investigated the role of proteinase-activated receptor-1 (PAR1) in the hypercontractile state in SAH. Methods-Rabbit double hemorrhage model was used as a model of SAH. The contractile response to thrombin and the PAR1 expression were evaluated in the isolated rings of basilar artery. Results-Thrombin exhibited only a minor contractile effect in the control, whereas it induced augmented contractions in SAH. The expression of PAR1 was upregulated in SAH. Intracisternal injection of PAR1 antagonist E5555 prevented the enhancement of the contractile responses to thrombin in SAH. The maximal prevention was obtained with 2 g/kg weight/injection. The contractile responses to K ϩ depolarization or endothelin-1 remained unaffected. The upregulation of PAR1 was also prevented by E5555 (2 g/kg weight/injection) to a level similar to that seen in the control. Ex vivo treatment with E5555 (1 mol/L) inhibited the contraction induced by thrombin, whereas it had little effect on the contraction induced by K ϩ depolarization or endothelin-1, in the basilar artery of SAH. E5555 also inhibited the [Ca 2ϩ ] i elevation induced by thrombin, but not trypsin, in cultured smooth muscle cells. Conclusions-PAR1 plays a critical role in upregulating PAR1 itself, thereby enhancing the contractile response to thrombin in SAH. PAR1 could thus be a therapeutic target. However, the usefulness of PAR1 antagonist remains to be investigated in vivo. (Stroke. 2007;38:3259-3265.)

Current Perspective on the Role of the Thrombin Receptor in Cerebral Vasospasm After Subarachnoid Hemorrhage

“…In contrast, in the basilar artery isolated from the SAH model animals, thrombin induced a significantly enhanced contraction at lower concentrations (22 -24). The enhanced reactivity was also observed with a agonist peptide for proteinase-activated receptor (PAR) 1 (PAR 1 -AP), but not for PAR 4 (PAR 4 -AP), thus suggesting that PAR 1 is a major receptor mediating the contractile effect of thrombin after SAH (22,23). Similar enhancement of the reactivity was also observed with platelet-derived growth factor, an α-adrenoceptor agonist, and endothelin-1, but not for high K + -depolarization or phorbol ester (24,25).…”

“…Use of a PAR 1 antagonist not only inhibits the contractile effect of thrombin, but also prevents the upregulation of PAR 1 and the resultant increased reactivity to thrombin (Fig. 3) (23). Targeting PAR 1 can therefore potentially provide an effective therapeutic strategy for both preventing cerebral vasospasm and alleviating the contraction of the spastic artery.…”

Basic and Translational Research on Proteinase-Activated Receptors: The Role of Thrombin Receptor in Cerebral Vasospasm in Subarachnoid Hemorrhage

“…Clot removal, by either surgery (13) or intrathecal application of fibrinolytic agents such as urokinase or tissue plasminogen activator (16 -18), has (10,12,35), plasmin (36), fibrin degradation products (55,56) Platelet-derived substances: serotonin (57,58), thromboxane A2 (25, 59), platelet-derived growth factor (60) Prostaglandins: PGF2α (61, 62), PGE2 (63) Reactive oxygen species and related materials: lipid hydroperoxide (6) Lipid mediators: sphingosine 1-phosphate (64), arachidonic acid (65) Vasoactive substances: endothelin-1 (66,67), angiotensin II (57,58) Increased vascular responsiveness Endothelial damage and dysfunction (3) Increased contractile responsiveness of smooth muscle Increased receptor function: PAR1 (42,43), PDGFR (68) Alteration of signaling proteins: increased activity of Rho kinase (7, 8) Table 2. Current therapeutic strategies for the treatment of cerebral vasospasm…”

“…However, it still remains to be investigated. Therefore, the role of thrombin and PAR 1 in cerebral vasospasm was investigated using a rabbit double hemorrhage model of SAH (42,43).…”

“…The rabbit SAH model was prepared by injecting autologous blood into the cisterna magna on day 0 and day 2 (42,43). The control rabbits received injections of physiological saline solution in place of autologous blood, while intact rabbits received no intervention.…”