Effect of fibrin-fibrinogen degradation products on human basilar artery preparations

Inflammatory Pathways Following Subarachnoid Hemorrhage

Aneurysmal subarachnoid hemorrhage (SAH) is an acute cerebrovascular emergency resulting from the rupture of a brain aneurysm. Despite only accounting for 5% of all strokes, SAH imposes a significant health burden on society due to its relatively young age at onset. Those who survive the initial bleed are often afflicted with severe disabilities thought to result from delayed cerebral ischemia (DCI). Consequently, elucidating the underlying mechanistic pathways implicated in DCI development following SAH remains a priority. Neuroinflammation has recently been implicated as a promising new theory for the development of SAH complications. However, despite this interest, clinical trials have failed to provide consistent evidence for the use of anti-inflammatory agents in SAH patients. This may be explained by the complexity of SAH as a plethora of inflammatory pathways have been shown to be activated in the disease. By determining how these pathways may overlap and interact, we hope to better understand the developmental processes of SAH complications and how to prevent them. The goal of this review is to provide insight into the available evidence regarding the molecular pathways involved in the development of inflammation following SAH and how SAH complications may arise as a result of these inflammatory pathways.

Late cerebral ischaemia after subarachnoid haemorrhage: is cerebrovascular receptor upregulation the mechanism behind?

Late cerebral ischaemia after subarachnoid haemorrhage (SAH) carries high morbidity and mortality because of reduced cerebral blood flow (CBF) and subsequent cerebral ischaemia. This is associated with upregulation of contractile receptors in cerebral artery smooth muscles via the activation of intracellular signalling. In addition, delayed cerebral ischaemia after SAH is associated with inflammation and disruption of the blood-brain barrier (BBB). This article reviews recent evidence concerning the roles of vasoconstrictor receptor upregulation, inflammation and BBB breakdown in delayed cerebral ischaemia after SAH. In addition, recent studies investigating the role of various intracellular signalling pathways in these processes and the possibilities of targeting signalling components in SAH treatment are discussed. Studies using a rat SAH model have demonstrated that cerebral arteries increase their sensitivity to endogenous agonists such as ET-1 and 5-HT by increasing their smooth muscle expression of receptors for these after SAH. This is associated with reduced CBF and neurological deficits. A number of signal transduction components mediating this receptor upregulation have been identified, including the MEK-ERK1/2 pathway. Inhibition of MEK-ERK1/2 signalling has been shown to prevent cerebrovascular receptor upregulation and normalize CBF and neurological function after SAH in rats. At the same time, in rat SAH, certain cytokines and BBB-regulating proteins are upregulated in cerebral artery smooth muscles and treatment with MEK-ERK1/2 inhibitors prevents the induction of these proteins. Thus, inhibitors of MEK-ERK1/2 signalling exert multimodal beneficial effects in SAH.

Mechanisms of cerebral vasospasm in subarachnoid haemorrhage

Cerebrovascular spasm is a slowly developing constriction of the cerebral arteries, which frequently follows subarachnoid haemorrhage and is associated with considerable morbidity and mortality. The condition has been studied by use of models of subarachnoid haemorrhage in the whole animal and examination of isolated blood vessels or vascular smooth muscle cells in culture. The condition probably arises from the action of haemoglobin released from erythrocytes trapped in the subarachnoid clots, although the mechanism of action of haemoglobin remains uncertain. Systemic pharmacotherapy to avert or reverse vasospasm is still experimental.

Effect of GSH on cerebral vasospasm in dogs

Reduced glutathinone (tau-glutamylcysteinglycine, GSH) is a scavenger for oxygen radicals and plays in important role in protection of cells from ischemia and from the harmful effects of free oxygen radicals. Free oxygen radicals due to cerebral vasospasm increase in both vasospasm and proliferative vasculopathy. This experiment was performed to determine whether GSH plays a role in cerebral vasospasm after subarachnoid hemorrhage by preventing the harmful effects of free oxygen radicals. In this study, GSH was administered intraarterially and intracisternally following vasospasm of the canine basilar artery. Less vasospasm was observed in the group treated with GSH intraarterially following subarachnoid hemorrhage than in the one treated with GSH intracisternally and in the control group. The arterial wall was investigated ultrastructurally. We evaluated the effect of the anti-oxidating substance through the activity of superoxide dismutase in the arterial wall. We compared the effect of glutathione reductase in the two groups treated with GSH intraarterially and intracisternally. Arterial degeneration was more prominent in the group in which GSH was used intracisternally, while the superoxide dismutase levels were low. In contrast, arterial degeneration was less in the other group in which GSH was used intraarterially, while the superoxide dismutase levels were high.

Endothelial injury following experimental subarachnoid hemorrhage in rats: effects on brain blood flow

BACKGROUND

The leading cause of death and disability in patients suffering from aneurysmal subarachnoid hemorrhage (SAH) is cerebral vasospasm, a persistent, progressive, and often irreversible constriction of cerebral arteries. A wide array of pathological changes occur in cerebral arteries following SAH, with endothelial injury being the earliest and most consistent one. Since intact endothelium modulates many reflexes that influence vascular tone, damage to them may represent a significant contributor to cerebral vasospasm.

METHODS

Changes in local cerebellar blood flow (LCBF) and pathological alterations in major cerebral arteries were studied and compared in rats at various time intervals following SAH. SAH induced by the subarachnoid injection of 0.3 ml of whole blood. Sham rats received a subarachnoid injection of 0.3 ml of isotonic saline.

RESULTS

Except for an immediate but transient decrease, LCBF remained unchanged over a 3 day period following saline injection. Likewise, there were no pathological alterations in cerebral arteries of saline-injected rats. In contrast, the subarachnoid injection of whole blood produced significant changes in both LCBF and cerebral arteries. Within 30 minutes post-blood injection, LCBF became significantly decreased and remained so for 4 hours. However, within 24 hours, LCBF had returned to control levels where it remained for 3 days. Endothelial injury was observed in the basilar and middle cerebral arteries from 30 minutes through 4 hours, the same periods in which LCBF was significantly reduced. Within 24 hours, the time period in which LCBF had rebounded to control ranges, cerebral arteries showed no evidence of endothelial damage and resembled control cells.

CONCLUSION

The results indicate a direct correlation between changes in LCBF and the structural integrity of endothelial cells in the early stages following SAH. The lack of chronically depressed LCBF (after 1 day) may be related to the quick structural repair of endothelium.

Impairment of endothelium-dependent relaxation in human basilar artery after subarachnoid hemorrhage

BACKGROUND AND PURPOSE

The goal of this study was to determine the alterations in vascular reactivity of human basilar artery after subarachnoid hemorrhage.

METHODS

Human basilar arteries were obtained from subjects who died within 1 day after subarachnoid hemorrhage and control subjects who died from causes other than brain involvement. Basilar artery strips were suspended for isometric tension recording in Krebs-Ringer solution. Morphometric study was also carried out on paraffin-embedded sections stained with van Gieson's elastica stain of preselected sites from the basilar arteries. The intimal and medial area and the intimal index ([intimal area/area circumscribed by internal elastic lamina] x 100) were evaluated.

RESULTS

Contractile responses to KCl, norepinephrine, and 5-hydroxytryptamine did not differ between subarachnoid hemorrhage and control groups. The endothelium-dependent relaxation responses to thrombin, bradykinin, and calcium ionophore A23187 were less for the subarachnoid hemorrhage group than for the control group. However, the endothelium-independent response to sodium nitroprusside of the subarachnoid hemorrhage group did not differ from that of the control group. Morphometric measurements were comparable between the two groups.

CONCLUSIONS

These results suggest that the decreased relaxation responses to thrombin and bradykinin occur at the level of endothelial cells and not smooth muscle cells and that decreased relaxation may be involved in delayed vasospasm after subarachnoid hemorrhage. Although the decreased relaxation was observed within 1 day after subarachnoid hemorrhage, a period in which delayed spasm does not occur, this time difference may be dependent on the severity of bleeding after rupture of an aneurysm.

Erythrocytes are essential for development of cerebral vasculopathy resulting from subarachnoid hemorrhage in cats

In an effort to determine which blood elements play a critical role in the development of cerebral vasospasm, adult cats were subjected to prepontine injection of either autogenous whole blood or erythrocyte-free blood containing latex beads as a substitute morphologic marker. Seven or 10 days later the cats were anesthetized and perfused with fixative, and the basilar arteries were prepared for light and electron microscopy. Successful clot deposition was confirmed by the presence of numerous erythrocytes or latex beads within the adventitia of vessels. In agreement with previous studies, instillation of whole blood produced luminal narrowing associated with profound ultrastructural changes in all layers of the vascular wall. No significant alterations, however, occurred in arteries bathed in erythrocyte-free blood. These findings suggest first, that erythrocytes are essential for the development of the vasculopathy associated with chronic cerebral vasospasm, and second, that the role, if any, of other blood elements is not autonomous.

Vasodilator proteins: role in delayed cerebral vasospasm

Blood proteins could play a critical role in the pathogenesis of cerebral vasospasm in subarachnoid hemorrhage (SAH) as agonists and as antagonists of vasoconstriction. The present study was designed primarily to quantify the inhibition produced by antithrombin III of the phasic responses elicited by cumulative doses of KCl, serotonin (5-HT), uridine triphosphate (UTP), and thrombin in isolated canine basilar arteries, and to ascertain whether other proteins might act similarly. Antithrombin III (1 unit/ml and 3 units/ml) given 2 min beforehand inhibited all agonists. The inhibition was not dependent on a functional endothelium nor due to stimulation of the electrogenic sodium pump. Alpha2-macroglobulin (0.1 mg/ml and 0.4 mg/ml) inhibited the contractile responses to high K+, 5-HT and thrombin. Kallikrein (1 and 4 units/ml) did not inhibit UTP but inhibited high K+ and 5-HT through an effect on the endothelium. Kallikrein (1 unit/ml) irreversibly blocked the responses to thrombin. Globulins (3 mg/ml) and fibrinogen (0.3 mg/ml) were not inhibitory. The results demonstrate that anticoagulant proteins are very effective nonspecific inhibitors of the vasoconstriction, whereas the serine protease kallikrein selectively blocks thrombin. The remarkable potency of antithrombin III suggests that it may protect cerebral arteries from exhibiting vasospasm in SAH.

Effect of prostacyclin and adenosine triphosphate on vasospasm of canine basilar artery

Cerebral vasospasm is one of the most important factors influencing morbidity and mortality of intracranial operations or diseases. Platelet aggregation and adhesion is increased in spastic vessels. Degradation of platelets liberates mediators, which in turn increase vasospasm, thus creating a vicious cycle. Healthy vessels cope with this by increasing the synthesis of prostacyclin. The purpose of this study was to increase experimentally the levels of arterial prostacyclin and adenosine triphosphate (ATP) in animals through intraarterial injection of these substances because they are lower in spastic vessels. Prostacyclin promotes antiaggregation and dilatation, increases blood flow, inhibits thromboxane A2, and prevents synthesis of angiotensin II. Most of these effects were done by increasing cyclic adenosine monophosphate (cAMP). After injecting autogenous blood into the cisterna magna of male dogs, both the acute and chronic phases of vasospasm and the degenerative changes in the arterial wall were observed. Injecting ATP increased the severity of vasospasm. During vasospasm it was found that when prostacyclin is used intraarterially, vasodilatation began, but degeneration of the arterial wall could not be prevented. In the group of animals in which both ATP and prostacyclin were used, there was no degeneration of the arterial wall and the basilar artery was seen to be normal when viewed under the electron microscope.

The role of the prostacyclin-thromboxane system in cerebral vasospasm following induced subarachnoid hemorrhage in the rabbit

Subarachnoid hemorrhage (SAH) was induced in 50 rabbits by injecting 1.25 cc/kg of autologous, well heparinized, fresh arterial blood into the cisterna magna, followed by suspending the animals in a head-down position at 30 degrees for 15 minutes. The animals were evenly divided into five groups: a control group, or groups receiving post-SAH prostacyclin (PGI2), carbacyclin, thromboxane A2 (TXA2) synthetase inhibitor (OKY-1581), or nutralipid. Radiographic vertebrobasilar arterial spasm was demonstrated on the 3rd day post-SAH in the control animals. This was decreased in the prostacyclin and the carbacyclin groups and was absent in the OKY-1581 and the nutralipid groups. Cerebral blood flow (CBF) measurements on the 4th day post-SAH using the xenon-133 technique failed to reveal any significant difference between the prostacyclin, the carbacyclin, and the control groups, but flows in the nutralipid and the OKY-1581 groups were significantly higher. There was a good correlation between the clinical status and the CBF. Intracytoplasmic vacuolation and detachment of the vascular endothelium, seen ultrastructurally, may account for the impaired synthesis of prostacyclin. Exogenous prostacyclin and carbacyclin decreased vasospasm but failed to improve cerebral perfusion. OKY-1581 blocked the synthesis of the potent vasoconstrictor, TXA2, which is not only formed during platelet aggregation but also induces platelet aggregation. Nutralipid contains linolenic acid, a precursor of eicosapentaenoic acid (EPA), which is more potent in inhibiting platelet aggregation and in blocking TXA2 production. The various fatty acid constituents of nutralipid bind to albumin and thereby shorten the half-life of TXA2.

Prediction of cerebral vasospasm value of fibrinogen degradation products (FDP) in the cerebro-spinal fluid (CSF) for prediction of vasospasm following subarachnoid haemorrhage due to a ruptured aneurysm

In a new treatment regimen with antifibrinolytic drugs in patients with aneurysmal subarachnoid haemorrhages, we have systematically controlled the level of fibrinogen degradation products (FDP) in the cerebrospinal fluid (CSF). The frequency of severe vasospasm with clinical ischaemia has been compared with the patient's initial level of FDP. Fifty patients have been included in this study. (All in Hunt and Hess's grades I or II on their arrival.) Patients with a secondary deterioration unrelated to vasospasm were excluded. The FDP levels were measured in the first three days following the bleeding and we were informed of them at the end of the study. The diagnosis of severe vasospasm was confirmed by arteriography and computed tomography (CT) and it was named "severe" when accompanied with signs of clinical ischaemia. Twenty patients developed a severe vasospasm with clinical ischaemia. In these patients, the mean value of the initial FDP level was between 80 and 320 mcg/ml compared with 20 to 80 mcg/ml for those who had not developed clinical ischaemia (p = 0.0009). Furthermore, two different groups may be discriminated by their initial FDP level: FDP greater than 80 mcg/ml; n = 23, 65% severe vasospasm; FDP less than 80 mcg/ml; n = 27.8% no severe vasospasm (p less than 0.001). These results do not imply a direct role of FDP in pathophysiological mechanisms of vasospasm, but they suggest a relationship between the clot lysis and the appearance of vasospasm with clinical ischaemia. To our knowledge this is the first time that such a predictive role can be attributed to the initial FDP level in the prognosis of vasospasm.