Platelet-activating factor and cerebral vasospasm following subarachnoid hemorrhage

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.

Thromboelastography Parameter Predicts Outcome After Subarachnoid Hemorrhage: An Exploratory Analysis

OBJECTIVE

Hypercoagulability after subarachnoid hemorrhage (SAH) is well described and may be platelet mediated. Thromboelastography (TEG) provides a global assessment of coagulation. We sought to determine whether the maximum amplitude (MA) parameter of TEG, a measure of platelet strength and function, is associated with outcome after SAH.

METHODS

One hundred ten TEG analyses were performed for patients with moderate-to-severe SAH and compared with 6 healthy age- and sex-matched controls. TEG indices included MA, G value (G), alpha angle, and thrombus generation and were correlated to functional outcomes and laboratory tests including complete blood count, erythrocyte sedimentation rate, high sensitivity C-reactive protein, fibrinogen, and d-dimer, obtained on post-bleed days (PBDs) 1, 3, 5, 7, and 10.

RESULTS

MA was significantly elevated compared with controls on PBD 3 (70.0 mm ± 4.5 mm vs. 64.1 mm ± 6.5 mm; P = 0.02), PBD 5 (72.6 mm ± 5.3 mm vs. 64.1 mm ± 6.5 mm; P = 0.003), PBD 7 (73.0 mm ± 5.4 mm vs. 64.1 mm ± 6.5 mm; P = 0.003), and PBD 10 (73.4 mm ± 6.0 mm vs. 64.1 mm ± 6.5 mm; P = 0.005). G was significantly elevated compared with controls on PBD 3 (P = 0.03), PBD 5 (P = 0.01), PBD 7 (P = 0.01), and PBD 10 (P = 0.02). The only biomarker associated with poor outcome was CRP. Multivariate logistic regression demonstrated an association between elevated MA and outcome (odds ratio 39.1, P = 0.006) independent of CRP, age, Hunt Hess grade, and transfusion.

CONCLUSIONS

TEG indices are associated with poor outcome after SAH and may identify a platelet-mediated hypercoagulable state. The association between MA and outcome was stronger than that between traditional biomarkers and was independent of age and Hunt Hess grade.

The single and double blood injection rabbit subarachnoid hemorrhage model

Over the past 30 years, the rabbit subarachnoid hemorrhage model (SAH) has been used for investigating the post-hemorrhage pathology, especially with respect to understanding of the mechanisms of cerebral vasospasm. However, the molecular mechanisms of cerebral vasospasm remain to be elucidated. Furthermore, it is not clear whether the rabbit SAH model is suitable for the investigation of pathological conditions other than cerebral vasospasm, such as early brain injury. Therefore, the properties of the rabbit SAH model need to be validated, and the reasons for using the rabbit should be clarified. This review explores the settings and technical issues of establishing a rabbit cisterna magna single and double blood injection SAH model and discusses the characteristics and feasibilities of the models.

The effect of EGb-761 on morphologic vasospasm in canine basilar artery after subarachnoid hemorrhage

This study investigated the effects of Ginkgo biloba extract (EGb-76l), an anti-oxidant and platelet-activating factor antagonist, on basilar artery vasospasm in an experimental canine subarachnoid hemorrhage model. Morphometric analyses were performed, and serum and cerebrospinal fluid endothelin-l levels were measured by radioimmunoassay. Comparisons were made between treated and untreated groups. Twenty-four mongrel dogs were randomly assigned to three groups. The animals in group 1 (n = 8) were not subjected to subarachnoid hemorrhage and received no treatment. In this group, serum and cerebrospinal fluid endothelin-l levels were measured daily for 8 days. On day 9, the animals were killed and their basilar arteries were excised for histopathological examination. In group 2 (n = 8), subarachnoid hemorrhage was produced using autologous arterial blood, and daily intravenous boluses of saline were administered for the next 8 days. Assessments of endothelin-l levels and the basilar arteries were performed as described for group 1. In group 3 (n = 8), subarachnoid hemorrhage was produced using autologous arterial blood, and daily intravenous boluses of EGb-761 were administered for 8 days. Endothelin-1 levels and the basilar arteries were assessed as described above. The groups' serum endothelin-1, cerebrospinal fluid endothelin-1, and histopathological findings were compared. In group 1, the serum and cerebrospinal fluid endothelin-1 levels did not change significantly over the 8 days, and histopathological examination of the basilar arteries revealed no abnormalities. In group 2, the serum and cerebrospinal fluid endothelin-1 levels increased abruptly and significantly on day 2, and remained high to the end of the study period (day 8). Histopathological examination revealed marked vasospasm. In group 3, the serum and cerebrospinal fluid endothelin-1 levels followed the same pattern observed in group 2; however, the arteries showed significantly less vasospasm than that observed in group 2. The study findings did not provide information about the mechanism of action of the platelet-activating factor-antagonist EGb-761, but they clearly show that this agent decreases morphologic vasospasm in the dog basilar artery.

Cerebral vasospasm after subarachnoid hemorrhage: putative role of inflammation

Cerebral vasospasm is a common, formidable, and potentially devastating complication in patients who have sustained subarachnoid hemorrhage (SAH). Despite intensive research efforts, cerebral vasospasm remains incompletely understood from both the pathogenic and therapeutic perspectives. At present, no consistently efficacious and ubiquitously applied preventive and therapeutic measures are available in clinical practice. Recently, convincing data have implicated a role of inflammation in the development and maintenance of cerebral vasospasm. A burgeoning (although incomplete) body of evidence suggests that various constituents of the inflammatory response, including adhesion molecules, cytokines, leukocytes, immunoglobulins, and complement, may be critical in the pathogenesis of cerebral vasospasm. Recent studies attempting to dissect the cellular and molecular basis of the inflammatory response accompanying SAH and cerebral vasospasm have provided a promising groundwork for future studies. It is plausible that the inflammatory response may indeed represent a critical common pathway in the pathogenesis of cerebral vasospasm pursuant to SAH. Investigations into the nature of the inflammatory response accompanying SAH are needed to elucidate the precise role(s) of inflammatory events in SAH-induced pathologies.

Platelets play an essential role in the aetiology of cerebral vasospasm after subarachnoid haemorrhage

Platelets have long been implicated in the aetiology of cerebral vasospasm (CV) after subarachnoid haemorrhage (SAH). It was noticed that vasospastic CSF (CSF(V)) could be formed in vitro by the mixing of control blood (with platelets) and non-SAH CSF. We also propose a hypothesis for the aetiology of CV after SAH based on this and previous research. This study also aims to determine which blood fraction is responsible for the stimulation of O(2) consumption and vasospasm of blood vessels. Control blood was separated into various fractions and mixed with non-SAH CSF. The activity of the resulting mixture and the blood fraction alone were assessed. Only the fractions containing platelets mixed with CSF showed vasoactivity. These data suggest that platelets plus some component in the CSF produce vasoactive factors with actions similar to CSF(V). This study may help to elucidate the aetiology of CV after SAH.

Effect of a platelet-activating factor antagonist, E5880, on cerebrovasospasm following subarachnoid hemorrhage in a canine double-hemorrhage model

We investigated the effects of a platelet-activating factor (PAF) antagonist, E5880 (1-ethyl-2-[N-(2-methoxy)benzoyl-N-[(2)-2-methoxy-3-(4-octadecycarbamoylox)piperidinocarbonyloxy-propyloxy]carbonyl]aminomethyl-pyridiniumchloride), on subarachnoid hemorrhage-induced prolongation of cerebral circulation time and decrease in the basilar artery diameter in a canine double-hemorrhage model. Animals were assigned to three groups, control (saline), E5880 1.2 mg/kg and E5880 2.4 mg/kg. For measurement of cerebral circulation time, regions of interest were chosen at the basilar artery and the straight sinus in order to obtain time-density curves. Cerebral circulation time was defined as the difference between the arterial and venous peaks. Cerebral circulation time and basilar artery diameter were assessed by intra-arterial digital subtraction angiography (IA-DSA) on Days 0, 2 and 7. The prolongation of cerebral circulation time following subarachnoid hemorrhage was significantly inhibited by intravenous administration of 2.4 mg/kg of E5880. Basilar artery constriction was also reduced by E5880. Thus, E5880 had preventive effects on the prolongation of cerebral circulation time and the vasoconstriction of basilar artery in this model. These results suggest that E5880 may have a preventive effect on neurological symptoms aggravated by cerebrovascular lesions following subarachnoid hemorrhage.

Effect of a platelet-activating factor receptor antagonist, E5880, on cerebral vasospasm after aneurysmal subarachnoid hemorrhage--open clinical trial to investigate efficacy and safety

The efficacy and safety of a new platelet-activating factor receptor antagonist, E5880, were investigated for preventing cerebral vasospasm after subarachnoid hemorrhage (SAH) in 71 patients with SAH who underwent surgery for ruptured aneurysms within 3 days. Intravenous E5880 administration (300 micrograms or 1200 micrograms twice daily) was begun within 4 days and continued for 14 days. The incidence of symptomatic vasospasm, low-density area on computed tomography, and angiographic vasospasm was lower than in placebo groups in previous studies. Clinical outcome was favorable compared with previous studies. No clinically important adverse events were observed. These results suggest that E5880 is safe and effective in the treatment of patients with cerebral vasospasm due to SAH.

U74389G prevents vasospasm after subarachnoid hemorrhage in dogs

OBJECTIVE

Oxygen-derived free radicals may contribute to vasospasm after the rupture of an intracranial aneurysm through direct vasoconstricting effects occurring within the arterial wall or, secondarily, by causing lipid peroxidation in the subarachnoid erythrocytes with secondary induction of vasoconstriction. U74389G is a potent inhibitor of lipid peroxidation and a scavenger of oxygen-derived free radicals. This study determined the relative contributions of oxygen-derived free radicals and lipid peroxidation to vasospasm in the double-hemorrhage dog model.

METHODS

Sixteen dogs underwent baseline (Day 0) cerebral angiography and induction of subarachnoid hemorrhage by two injections of blood into the cisterna magna 2 days apart. They were randomized to receive drug vehicle (n=8) or U74389G (n=8, 3 mg/kg of body weight/d) intravenously. Drug administration and end point analysis were blinded. The end points were angiographic vasospasm, as assessed by comparison of angiograms obtained before and 7 days after subarachnoid hemorrhage, and the levels of malondialdehyde and salicylate hydroxylation products (dihydroxybenzoic acids) in cerebrospinal fluid and of malondialdehyde in subarachnoid blood clots and basilar arteries 7 days after hemorrhage.

RESULTS

Comparisons within groups of Day 0 and Day 7 angiograms and between groups of angiograms obtained at Day 7, showed significant vasospasm in animals in the vehicle group (mean+/-standard error, 51%+/-4) but not in the U74389G group (25%+/-11, P < 0.05, unpaired t test). High-pressure liquid chromatographic assays of malondialdehyde and dihydroxybenzoic acids in cerebrospinal fluid, subarachnoid blood clots, and basilar arteries showed no significant differences between groups.

CONCLUSION

The significant prevention of vasospasm by U74389G without change in levels of indicators of free radical reactions suggests that the effect of the drug is related to other processes occurring in the arterial wall and that cerebrospinal fluid levels of oxygen radicals and lipid peroxides are not useful markers of vasospasm.

A platelet activating factor antagonist attenuates the effects of testicular ischemia

PURPOSE

Platelet activating factor, a biochemical marker and lipid mediator of ischemic injury, has been demonstrated in several organ systems. The objective of this study was to investigate the possible role of platelet activating factor in testicular ischemic injury.

MATERIALS AND METHODS

Five groups of 6 male Sprague-Dawley rats were studied, including group 1-nonoperated controls, group 2-sham operated controls, group 3-those that underwent administration of 10 micrograms./kg. exogenous platelet activating factor into the left testicular artery, group 4-those that underwent 4 hours of testicular ischemia and group 5-those that received pretreatment with 0.4 mg./kg. of the platelet activating factor antagonist CV-6209 intravenously before 4 hours of testicular ischemia. Ipsilateral and contralateral testes were examined histologically and seminiferous tubular diameters were measured.

RESULTS

Exogenous platelet activating factor administration in group 3 and 4 hours of ischemia in group 4 resulted in a similar extent of histological degeneration of the experimental testicle. Pretreatment with CV-6209 in group 5 resulted in a marked decrease in hemorrhagic discoloration, vascular congestion and histological changes noted with ischemia in group 4.

CONCLUSIONS

The results of this study suggest that platelet activating factor has a biochemical role in tissue injury associated with testicular ischemia. Also, administration of a platelet activating factor antagonist before the ischemic event decreases seminiferous tubule degeneration.

Involvement of platelet-activating factor (PAF) in glutamate neurotoxicity in rat neuronal cultures

To clarify the role of platelet-activating factor (PAF) in glutamate neurotoxicity, in vitro experiments using primary neuronal cultures were performed. The anti-PAF immunoglobulin-G (aPAF-IgG) and the three PAF receptor antagonists (BN52021, CV6209, and E5880) were tested for their neuroprotective activity in primary neuronal cultures isolated from embryonic rat cerebral cortex. The cultured neurons were exposed to glutamate (1 mM) for 60 min. Twenty-four hours after this exposure, aPAF-IgG demonstrated evidence of protective effects against neuronal damage in a dose-dependent manner. Protective effects also were observed in cultures treated with the three PAF antagonists (P < 0.05 at 1 microg/ml aPAF-IgG, P < 0.01 at 100 microM BN52021, P < 0.05 at 10 nM CV6209 and P < 0.01 at 10 nM E5880). The Fura-2 assay was used to estimate whether low dosages of exogenous PAF affect cultured neurons. The cultured neurons were loaded with Fura-2/AM. After preincubation for 120 min, the Fura-2-loaded neurons were exposed to various concentrations of PAF for 60 min. By measuring the fluorescent intensity of the medium as representing the amount of Fura-2 released from damaged neurons, we detected an increased release of Fura-2, even at low doses of PAF (P < 0.01 at 10 nM PAF). We further studied PAF production by neurons in response to glutamate. The level of PAF measured in the medium exposed to glutamate was significantly higher than the level in the medium unexposed to glutamate (P < 0.05). Our results suggest an important role of PAF in glutamate neurotoxicity.

Platelet-activating factor in the CNS

Platelet-activating factor (PAF) is a phospholipid synthesized in a variety of cells throughout the body. Platelet-activating factor has been identified in the CNS and has a number of diverse physiological and pathological functions. It has been shown to be a modulator of many CNS processes, ranging from long-term potentiation (LTP) to neuronal differentiation. Excessive levels of PAF appear to play an important role in neuronal cell injury, such as that resulting from ischaemia, inflammation, human immunodeficiency syndrome (HIV) and meningitis. The beneficial effects of PAF receptor antagonists are many and give rise to possible therapeutic strategies for neurotrauma.

Prevention of cerebrovasospasm following subarachnoid hemorrhage in rabbits by the platelet-activating factor antagonist, E5880

Recently, an important role of platelet-activating factor (PAF), an inflammation mediator, has been demonstrated in the genesis of cerebral vasospasm following subarachnoid hemorrhage (SAH). In the current study, the authors examined whether intravenous administration of the novel PAF antagonist, E5880, can prevent vasospasm following SAH in rabbits. A vasospasm model was produced in three groups of rabbits using two subarachnoid injections of autologous arterial blood, followed by intravenous administration of distilled water (control), a low dose of E5880 (0.1 mg/kg in distilled water), or a high dose of E5880 (0.5 mg/kg in distilled water). Neurological deterioration was largely prevented in the rabbits that received E5880. Basilar artery constriction was also reduced by both doses of E5880. Histological examination at autopsy predominantly showed ischemic changes in the brain. Animals in each E5880-treated group exhibited ischemic changes less frequently than those in the control group. Plasma thromboxane B2 concentrations were reduced in rabbits treated with E5880. Platelet-activating factor was immunolocalized in the intima and media of the basilar artery in the control group. The PAF immunoreactivity demonstrated in the basilar artery was decreased in the E5880 groups in a dose-dependent manner. Thus, this study provides evidence that PAF may play a role in the pathogenesis of vasospasm after SAH and that intravenous administration of E5880 is a promising approach in preventing vasospasm.

Platelet-activating factor and antiphospholipid antibodies in subarachnoid haemorrhage

The purpose of this study was to measure plasma platelet-activating factor (PAF) concentration, PAF-acetylhydrolase activities, anti-phospholipid antibody (aPLs) titers, and platelet function in patients with subarachnoid haemorrhage (SAH) and to assess the association of these variables with the development of cerebral vasospasm. Thirty-two patients with SAH due to ruptured cerebral aneurysm were studied. Plasma PAF concentration, PAF-acetylhydrolase activity, platelet count and aggregability, and plasma factor 4 (PF4) concentrations were measured regularly until approximately 2 weeks after SAH. aPLs, including lupus anticoagulant and anti-cardiolipin IgG and IgM were measured within 3 days after SAH. Plasma PAF concentration in patients with SAH showed the highest value on the occasion during 5 to 9 days after SAH. The concentrations were higher in patients with infarction due to vasospasm than in patients without cerebral infarction on any occasions after SAH. Plasma PAF-acetylhydrolase activities did not change in patients, regardless of the presence of cerebral infarction after SAH. Increased platelet consumption and aggregability and higher concentrations of PF 4 were detected in patients with cerebral infarction and not in patients without cerebral infarction. The patients with cerebral infarction due to cerebral vasospasm had aPLs more frequently than the control volunteers. Our findings indicate that increased plasma PAF and aPLs may contribute to the pathogenesis of cerebral vasospasm after SAH.

Platelet-activating factor (PAF) concentration and PAF acetylhydrolase activity in cerebrospinal fluid of patients with subarachnoid hemorrhage

The authors studied the sequential changes in platelet-activating factor (PAF) and PAF acetylhydrolase in the cerebrospinal fluid (CSF) of patients with subarachnoid hemorrhage (SAH). Levels of PAF in CSF showed a gradual increase after the onset of SAH, with a subsequent decrease. The PAF concentration between 5 and 9 days after SAH was greater in patients with cerebral infarction due to vasospasm than in patients without infarction. Conversely, PAF acetylhydrolase activity decreased gradually after SAH, then increased. The enzyme activity for the same period was smaller in patients with cerebral infarction than in patients without infarction. The distribution of the days of maximum PAF concentration and minimum PAF acetylhydrolase activity did not differ significantly between the two groups. The CSF as a source of PAF acetylhydrolase activity gave an apparent Michaelis constant value of 90.8 microM and a maximum velocity of 0.2 nmol/min/mg. The optimum pH level for the PAF acetylhydrolase activity obtained from CSF was 6.5. The enzyme activity of CSF increased, depending on the incubation temperature, ranging from 25 degrees to 45 degrees C. Ethylene-glycol tetra-acetic acid (1 mM) was found to inhibit PAF acetylhydrolase activity in CSF obtained from patients with SAH. Unaltered PAF acetylhydrolase activity was inhibited by adding an aliquot of CSF and minimum PAF acetylhydrolase activity decreased following SAH. Two peaks of inhibitory activity were detected on Sephacryl S-200 HR gel filtration: one was eluted in void volume and the other with an apparent molecular mass of 13 kD. The inhibitory activity was very labile and was lost completely within 3 days of incubation at 4 degrees C. The regulation of the PAF concentration in the CSF of SAH patients is discussed.