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

Acute Haemostatic Depletion and Failure in Patients with Traumatic Brain Injury (TBI): Pathophysiological and Clinical Considerations

BACKGROUND

Because of the aging population, the number of low falls in elderly people with pre-existing anticoagulation is rising, often leading to traumatic brain injury (TBI) with a social and economic burden. Hemostatic disorders and disbalances seem to play a pivotal role in bleeding progression. Interrelationships between anticoagulatoric medication, coagulopathy, and bleeding progression seem to be a promising aim of therapy.

METHODS

We conducted a selective search of the literature in databases like Medline (Pubmed), Cochrane Library and current European treatment recommendations using relevant terms or their combination.

RESULTS

Patients with isolated TBI are at risk for developing coagulopathy in the clinical course. Pre-injury intake of anticoagulants is leading to a significant increase in coagulopathy, so every third patient with TBI in this population suffers from coagulopathy, leading to hemorrhagic progression and delayed traumatic intracranial hemorrhage. In an assessment of coagulopathy, viscoelastic tests such as TEG or ROTEM seem to be more beneficial than conventional coagulation assays alone, especially because of their timely and more specific gain of information about coagulopathy. Furthermore, results of point-of-care diagnostic make rapid "goal-directed therapy" possible with promising results in subgroups of patients with TBI.

CONCLUSIONS

The use of innovative technologies such as viscoelastic tests in the assessment of hemostatic disorders and implementation of treatment algorithms seem to be beneficial in patients with TBI, but further studies are needed to evaluate their impact on secondary brain injury and mortality.

Coagulopathy and Progression of Intracranial Hemorrhage in Traumatic Brain Injury: Mechanisms, Impact, and Therapeutic Considerations

BACKGROUND

Traumatic brain injury (TBI) remains one of the most challenging health and socioeconomic problems of our times. Clinical courses may be complicated by hemostatic abnormalities either pre-existing or developing with TBI.

OBJECTIVE

To review frequencies, patterns, mechanisms, novel approaches to diagnostics, treatment, and outcomes of hemorrhagic progression and coagulopathy after TBI.

METHODS

Selective review of the literature in the databases Medline (PubMed) and Cochrane Reviews using different combinations of the relevant search terms was conducted.

RESULTS

Of the patients, 20% with isolated TBI display laboratory coagulopathy upon hospital admission with profound effect on morbidity and mortality. Preinjury use of antithrombotic agents may be associated with higher rates of hemorrhagic progression and delayed traumatic intracranial hemorrhage. Further testing may display various changes affecting platelet function/numbers, pro- and/or anticoagulant factors, and fibrinolysis as well as interactions between brain tissues, vascular endothelium, mechanisms of inflammation, and blood flow dynamics. The nature of hemostatic disruptions after TBI remains elusive but current evidence suggests the presence of both a hyper- and hypocoagulable state with possible overlap and lack of distinction between phases and states. More "global" hemostatic assays, eg, viscoelastic and thrombin generation tests, may provide more detailed and timely information on the overall hemostatic potential thereby allowing early "goal-directed" therapies.

CONCLUSION

Whether timely and targeted management of hemostatic abnormalities after TBI can protect against secondary brain injury and thereby improve outcomes remains elusive. Innovative technologies for diagnostics and monitoring offer windows of opportunities for precision medicine approaches to managing TBI.

Effect of thrombin injection on cerebral vascular in rats with subarachnoid hemorrhage

Objective

To evaluate the effect of thrombin (TM) injection via the cerebellomedullary cistern on cerebral vessels in rats with subarachnoid hemorrhage (SAH).

Methods

Eighteen rats were randomly divided into three groups. In the A1 group, physiological saline was injected via the cerebellomedullary cistern; in the A2 group, 3 U of TM was injected into the subarachnoid space; and in the A3 group, SAH models were established and 3 U of TM was injected with the first injection of whole blood. Three days later, basilar artery specimens were collected for pathological examination.

Results

The basilar arterial lumen cross-sectional area was significantly smaller in the A2 versus the A1 group, and proteinase-activated receptor (PAR)-1 and tumor necrosis factor (TNF)-α average optical densities were significantly higher (all P < 0.05). Basilar arterial lumen cross-sectional areas were significantly smaller in the A3 than the A2 group and average TNF-α optical densities were significantly lower (both P < 0.05), while those of PAR-1 did not differ significantly.

Conclusions

There was no significant difference in the extent of cerebral vasospasm between SAH and non-SAH model groups following TM injection into the subarachnoid space, so TM was considered to be an independent factor affecting cerebral vasospasm.

Alterations in the expression of protease-activated receptor 1 and tumor necrosis factor-α in the basilar artery of rats following a subarachnoid hemorrhage

The present study aimed to investigate the expression of protease-activated receptor 1 (PAR1) and tumor necrosis factor (TNF)-α in a rat model of subarachnoid hemorrhage (SAH)-induced cerebral vasospasm (CVS). The rat models were established by twice injecting blood into the cisterna magna, after which the following experimental groups were established: The normal group, the SAH3d group, the SAH5d group and the SAH7d group. The rats were perfused and the basilar artery was removed for histological examination. The cross-sectional area of the basilar artery lumen was measured using computer software; and the protein expression of PAR1 and TNF-α was detected by immunohistochemistry. The cross-sectional area of the basilar artery of the rats in the SAH model groups was significantly decreased in a time-dependent manner, as compared with the normal group. The protein expression of PAR1 and TNF-α in the SAH3d, SAH5d and SAH7d groups was significantly increased over time (P<0.05), as compared with the normal group. CVS was detected in the basilar artery, and was associated with wall thickening and significant narrowing of the lumen, thus suggesting that the present model may be used for investigating cerebrovascular disease following SAH. The immunohistochemical analyses demonstrated that the protein expression of PAR1 and TNF-α was significantly increased in the basilar artery of the SAH model rats, and were positively correlated with the degree of CVS.

Quantitative analysis of hemorrhage clearance and delayed cerebral ischemia after subarachnoid hemorrhage

OBJECTIVE

Initial hemorrhage burden is an independent predictor for delayed cerebral ischemia (DCI) in patients with aneurysmal subarachnoid hemorrhage (aSAH). However, the association between clot clearance and DCI still remains to be elucidated.

METHODS

Quantitative analysis of hemorrhage volume and clot clearance was made in 116 consecutive patients who were scanned within 24 h from onset. Cisternal plus intraventricular hemorrhage volume (CIHV) was calculated as clot volume from the initial scans and scans performed up to 7 days after onset. Clot clearance was calculated as a percentage of residual clot volume compared with the clot volume on the initial scan. Initial clot volume and clot clearance were dichotomized to evaluate the association with DCI.

RESULTS

Included patients were aged 55.5±15.2 years with a female preponderance (65.5%, (76/116)). The group with higher initial clot volume (≥17.2 mL) had higher odds for DCI (OR 4.3, 95% CI 1.3 to 14.0, p=0.015). However, the rate of DCI was not different between high and low clot clearance groups (26.7% vs 31.0%, p=0.66). Clot clearance rate was similar in patients with and without DCI up to day 7 after onset.

CONCLUSIONS

The quantitative clot clearance rate is not an independent predictor for DCI.

Mechanisms underlying increased vascular smooth muscle contractility in the rabbit basilar artery following subarachnoid hemorrhage

Increased vascular contractility plays an important role in the development of cerebral vasospasm following subarachnoid hemorrhage (SAH). Here, we summarize our current knowledge regarding molecular mechanisms that contribute to increased smooth muscle contractility of rabbit basilar artery following SAH. Our studies demonstrated that upregulation of receptor expression, impairment of feedback regulation of receptor activity, and enhancement of myofilament Ca²⁺ sensitization might lead to increased smooth muscle contractility following SAH.

Suppression of the Rho/Rho-kinase pathway and prevention of cerebral vasospasm by combination treatment with statin and fasudil after subarachnoid hemorrhage in rabbit

The Rho/Rho-kinase pathway is considered important in the pathogenesis of sustained smooth muscle cell contraction during cerebral vasospasm after aneurysmal subarachnoid hemorrhage (SAH). The aims of this study were to investigate whether combination treatment, with pitavastatin as an inhibitor of RhoA and fasudil as an inhibitor of Rho-kinase, prevents the cerebral vasospasm. SAH was simulated using the double-hemorrhage rabbit model, and pitavastatin, or fasudil, or both (combination treatment) were administrated. The basilar artery (BA) cross-sectional area only in the combination treatment group was statistically larger than in the SAH group (p < 0.05). BA Rho-kinase, as measured by ELISA, was statistically reduced only in the combination treatment group compared with the SAH group (p < 0.05). In the other two treatment groups, pitavastatin or fasudil treatment group showed larger BA cross-sectional areas and lower value for BA Rho-kinase, but there were no statistically significant differences compared with the SAH group. The expression of endothelial nitric oxide synthase (eNOS), evaluated by immunohistochemistry in the pitavastatin group and the combination group, was higher than in the SAH group. Results indicate that combination treatment could extensively prevent cerebral vasospasm due to the synergic effect of combining pitavastatin and fasudil on the Rho/Rho-kinase pathway and on eNOS.

Combined argatroban and anti-oxidative agents prevents increased vascular contractility to thrombin and other ligands after subarachnoid haemorrhage

BACKGROUND AND PURPOSE

Increased vascular contractility plays a fundamental role in cerebral vasospasm in subarachnoid haemorrhage (SAH). We investigated the role of thrombin and its receptor, proteinase-activated receptor 1 (PAR1), and other G protein-coupled receptors in the increased contractility, and examined the preventive effects of the thrombin inhibitor, argatroban, and anti-oxidative agents, vitamin C and tempol.

EXPERIMENTAL APPROACH

A rabbit model of SAH was utilized. Contractile responses of the isolated basilar artery and the level of oxidative stress of brain tissues were evaluated.

KEY RESULTS

Contractile responses to thrombin and PAR1-activating peptide (PAR1-AP) were enhanced and prolonged after SAH. The thrombin-induced contraction persisted even after terminating thrombin stimulation. When sequentially stimulated with PAR1-AP, the second response was maintained in SAH, while it was substantially attenuated in the control. Only a combination of argatroban with vitamin C or tempol prevented both the enhancement and prolongation of the contractile response to PAR1-AP and restored the reversibility of the thrombin-induced contraction. The responses to angiotensin II, vasopressin and PGF(2α) were enhanced and prolonged after SAH to varying degrees, and responded differently to the treatment. The response to vasopressin exhibited a similar phenomenon to that seen with PAR1-AP. Oxidative stress was increased in SAH, and normalized by the treatment with argatroban, vitamin C or their combination.

CONCLUSIONS AND IMPLICATIONS

Increased vascular reactivity to agonists in SAH was attributable to the enhancement and prolongation of the contractile response. A combination of argatroban and anti-oxidative agents was required to prevent both the enhancement and prolongation of the contractile response.

Mechanisms underlying potentiation of endothelin-1-induced myofilament Ca(2+) sensitization after subarachnoid hemorrhage

Increased vascular smooth muscle contractility has an important role in the development of cerebral vasospasm after subarachnoid hemorrhage (SAH). Myofilament Ca(2+) sensitivity is a major determinant of smooth muscle contractility. We investigated changes in the Ca(2+)-sensitizing effect of endothelin-1 (ET-1) and the mechanisms underlying ET-1-induced Ca(2+) sensitization after SAH using a rabbit SAH model. After SAH, the contractile response to ET-1 was enhanced, and the ET(A) receptor expression was upregulated in the basilar artery. In α-toxin-permeabilized preparations, ET-1 induced enhanced and prolonged contraction after SAH, suggesting that ET-1-induced Ca(2+) sensitization is potentiated after SAH. Endothelin-1-induced Ca(2+) sensitization became less sensitive to inhibitors of Rho-associated coiled-coil protein kinase (ROCK) and protein kinase C (PKC) after SAH. The expression of PKCα, ROCK2, PKC-potentiated phosphatase inhibitor of 17 kDa (CPI-17) and myosin phosphatase target subunit 1 (MYPT1) was upregulated, and the level of phosphorylation of CPI-17 and MYPT1 was elevated after SAH. This study demonstrated for the first time that the Ca(2+)-sensitizing effect of ET-1 on myofilaments is potentiated after SAH. The increased expression and activity of PKCα, ROCK2, CPI-17, and MYPT1, as well as the upregulation of ET(A) receptor expression are suggested to underlie the enhanced and prolonged Ca(2+) sensitization induced by ET-1.

Reversible protease-activated receptor 1 downregulation mediated by Ankaferd blood stopper inducible with lipopolysaccharides inside the human umbilical vein endothelial cells

Ankaferd Blood Stopper (ABS) is a novel topical hemostatic agent with pleiotropic actions indicated in clinical hemorrhages. Protease-activated receptor 1 (PAR-1) is located in the crossroads of hemostasis, inflammation, infection, apoptosis and tumorigenesis. ABS-induced formation of the protein network with vital erythroid aggregation covers the entire physiological hemostatic process. The aim of this study is to assess the effects of ABS on PAR-1 in the Human Umbilical Vein Endothelial Cells (HUVEC) model, in relation to the "ipopolysaccharides (LPS)-challenge" to endothelium. For this purpose, ABS 10 μL and 100 μL, had been applied to HUVEC within the time periods of 5 minutes (min), 25 min, 50 min, 6 hours (h) and 24 h. The cells have lifted from the plastic surface and adhered to each other during theABSapplication to the HUVECs. After 24 hours the cells returned to normal baseline level. We observed dose-dependent reversible PAR-1 down-regulation mediated by ABS inside the human umbilical vein endothelial cells. ABS-induced sustained PAR-1 down-regulation in the presence of LPS. Those findings indicated that ABS hemostatic agent may act as a topical biological response modifier by acting on PAR-1 at the vascular endothelial and cellular level.

Intracranial hemorrhage: mechanisms of secondary brain injury

ICH is a disease with high rates of mortality and morbidity, with a substantial public health impact. Spontaneous ICH (sICH) has been extensively studied, and a large body of data has been accumulated on its pathophysiology. However, the literature on traumatic ICH (tICH) is limited, and further investigations of this important topic are needed. This review will highlight some of the cellular pathways in ICH with an emphasis on the mechanisms of secondary injury due to heme toxicity and to events in the coagulation process that are common to both sICH and tICH.

Exploring neuroprotective drug therapies for intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is a devastating neurological disorder with high mortality and poor prognosis, for which virtually no effective drug therapies are available at present. Experimental animal models, based on intrastriatal injection of collagenase or autologous blood, have enabled great advances in elucidation of cellular/molecular events contributing to brain pathogenesis associated with ICH. Many lines of evidence indicate that blood constituents, including hemoglobin-derived products as well as proteases such as thrombin, play important roles in the pathogenic events. Inflammatory reactions involving neutrophils, activated microglia, and production of proinflammatory cytokines also constitute a critical aspect of pathology leading to neurodegeneration and tissue damage. Efforts are continuing to find drugs that potentially alleviate pathological and neurological outcomes of ICH. Various drugs that possess antioxidative, anti-inflammatory or neurotrophic/neuroprotective properties have been demonstrated to produce therapeutic effects on ICH animal models. Drugs already in clinical use such as minocycline, statins, and several nuclear receptor ligands are among the list of effective drugs, but whether they also show therapeutic efficacy in human ICH patients remains unproven. Here, current knowledge of ICH pathogenesis and problems arising with respect to exploration of new drug candidates are discussed.

Current perspective on the role of the thrombin receptor in cerebral vasospasm after subarachnoid hemorrhage

Cerebral vasospasm is a persistent arterial narrowing typically observed during the 3 - 14 days after subarachnoid hemorrhage (SAH). Vasospasm is frequently associated with ischemic neurological deficits or even death, resulting in a poor prognosis for patients with SAH. However, the mechanism underlying cerebral vasospasm remains elusive, and no effective therapeutic strategies have been established. A large amount of thrombin is produced during SAH. Recent investigations have uncovered a key role of the thrombin receptor in the pathogenesis of cerebral vasospasm. Thrombin has little contractile effect in the normal cerebral artery, but it induces an enhanced and prolonged contraction after SAH, owing to the up-regulation of thrombin receptor PAR(1) (proteinase-activated receptor 1) and the impairment of receptor desensitization in arterial smooth muscle. Thrombin-mediated activation of PAR(1) is an irreversible process, as it is initiated by the proteolytic removal of the N-terminal region. Since the mechanism of receptor desensitization is impaired after SAH, the thrombin-induced contraction irreversibly persists even after terminating thrombin stimulation. Intrathecal administration of a PAR(1) antagonist prevents the PAR(1) up-regulation and the increased reactivity to thrombin. PAR(1) is suggested to play a key role in cerebral vasospasm and may be useful as a therapeutic target for prevention and treatment of cerebral vasospasm.

Impaired feedback regulation of the receptor activity and the myofilament Ca2+ sensitivity contributes to increased vascular reactiveness after subarachnoid hemorrhage

Cerebral vasospasm determines the prognosis of subarachnoid hemorrhage (SAH). The increased vascular reactiveness has an important role in the development of cerebral vasospasm. This study analyzed the roles of the receptor-mediated signaling and the myofilament Ca(2+) sensitivity in the increased vascular reactiveness in SAH, using the basilar artery of a rabbit SAH model. Endothelin-1, thrombin, and phenylephrine induced transient increases in [Ca(2+)](i), myosin light chain phosphorylation, and contraction in the controls. All these responses were not only enhanced but also became sustained in SAH. In the sequential stimulation of thrombin receptor or alpha(1)-adrenoceptor, the second response was substantially attenuated in the controls, whereas it was maintained in SAH. The thrombin-induced contraction in SAH irreversibly persisted even after terminating the thrombin stimulation. This contraction was completely reversed by trypsin and a Galpha(q) inhibitor YM254890, thus suggesting the sustained receptor activity during the sustained contraction. YM254890 also inhibited the endothelin-1- and phenylephrine-induced sustained contraction. Furthermore, the GTPgammaS-induced transient contraction in the control alpha-toxin-permeabilized strips was converted to a sustained contraction in SAH. The results provide the first evidence that the feedback inactivation of the receptor activity and the myofilament Ca(2+) sensitivity was impaired in SAH, thus contributing to the increased vascular reactiveness.