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

Vasospasm following aneurysmal subarachnoid hemorrhage: Thrombocytopenia a marker

Background:

Symptomatic vasospasm (SV) is often seen after aneurysmal subarachnoid hemorrhage (aSAH). The pathophysiology suggests that platelets initiate the process and are consumed. This is likely to result in thrombocytopenia. The objective of this study was to find out if thrombocytopenia preceded or followed SV and to analyze the relationship between the two.

Materials and Methods:

The platelet counts of 74 patients were studied on day 1, 3, 5, 7, 9, 11, and 14 following aSAH. Clinical symptoms and raised velocities on transcranial Doppler were studied on the same days to determine SV. The relationship of platelet counts and SV were analyzed.

Results:

Thirty-nine (52.7%) patients developed SV. Platelet counts dropped on postictal day (PID) 3-7 and SV was commonly seen on PID 5-9. The median platelet counts were significantly lower in patients with SV when compared to those without SV. Platelet count <150,000/mm³ on PID 1 and 7 had statistically significant association (P < 0.001) with SV. The odds ratio was 5.1, 6.9, and 5.1 on PID 5, 7, and 9, respectively, for patients with relative thrombocytopenia (P < 0.001).

Conclusions:

There is a strong correlation between thrombocytopenia and SV. A platelet count < 150,000/mm³ on PID 1 and 7 predicts presence of SV. The relative risk of developing SV is >5 times for a patient with relative thrombocytopenia especially on PID 5-9. Additionally, it appears that thrombocytopenia precedes vasospasm and may be an independent predictor. However, this requires further studies for validation.

The role of magnesium in the management of cerebral vasospasm

Subarachnoid hemorrhage (SAH) is characterized by bleeding into the subarachnoid space, often caused by ruptured aneurysm. Aneurysmal rupture occurs in 700,000 individuals per year worldwide, with 40,000 cases taking place in the United States. Beyond the high mortality associated with SAH alone, morbidity and mortality are further increased with the occurrence of cerebral vasospasm, a pathologic constriction of blood vessels that can lead to delayed ischemic neurologic deficits (DIND). Treatment of cerebral vasospasm is a source of contention. One extensively studied therapy is Magnesium (Mg) as both a competitive antagonist of calcium at the N-methyl D-aspartate (NMDA) receptor, and a noncompetitive antagonist of both IP3 and voltage-gated calcium channels, leading to smooth muscle relaxation. In our literature review, several animal and human studies are summarized in addition to two Phase III trials assessing the use of intravenous Mg in the treatment of SAH (IMASH and MASH-2). Though many studies have shown promise for the use of Mg in SAH, there has been inconsistency in study design and outcomes. Furthermore, the results of the recently completed clinical trials have shown no significant benefit from using intravenous Mg as adjuvant therapy in the treatment of cerebral vasospasm.

Role of bilirubin oxidation products in the pathophysiology of DIND following SAH

Despite intensive research efforts, by our own team and many others, the molecules responsible for acute neurological damage following subarachnoid hemorrhage (SAH) and contributing to delayed ischemic neurological deficit (DIND) have not yet been elucidated. While there are a number of candidate mechanisms, including nitric oxide (NO) scavenging, endothelin-1, protein kinase C (PKC) activation, and rho kinase activation, to name but a few, that have been investigated using animal models and human trials, we are, it seems, no closer to discovering the true nature of this complex and enigmatic pathology. Efforts in our laboratory have focused on the chemical milieu present in hemorrhagic cerebrospinal fluid (CSF) following SAH and the interaction of the environment with the molecules generated by SAH and subsequent events, including NO scavenging, immune response, and clot breakdown. We have identified and characterized a group of molecules formed by the oxidative degradation of bilirubin (a clot breakdown product) and known as BOXes (bilirubin oxidation products). We present a synopsis of the characterization of BOXes as found in human SAH patients' CSF and the multiple signaling pathways by which BOXes act. In summary, BOXes are likely to play an essential role in the etiology of acute brain injury following SAH, as well as DIND.

PKC and Rho in vascular smooth muscle: activation by BOXes and SAH CSF

Cerebral vasospasm (CV) remains a significant cause of delayed neurological deficit and ischemic damage after subarachnoid hemorrhage (SAH), despite intensive research effort. The current lack of an effective therapeutic approach is somewhat due to our lack of understanding regarding the mechanism by which this pathological constriction develops. Recent evidence implicates bilirubin oxidation products (BOXes) in the etiology of CV after SAH: BOXes are found in cerebrospinal fluid from SAH patients with symptomatic or angiographically visible vasospasm (CSFV) but not in CSF from SAH patients with no vasospasm (CSFC). We have previously published research suggesting that the etiology of CV comprises two components: a physiological stimulation to constrict and a pathological failure to relax. Both these components are elicited by CSFV, but not CSFC, and BOXes synthesized in the laboratory potentiate physiological constriction in arterial smooth muscle in vitro, and elicit contraction in pial arteries in vivo. In this paper, we will present our results concerning the action of BOXes on arterial smooth muscle constriction, compared with CSFV. We will also present evidence implicating temporal changes in PKC isoforms and Rho expression in both BOXes- and CSFV-elicited smooth muscle responses.

Magnesium infusion for vasospasm prophylaxis after subarachnoid hemorrhage

Object

Despite the application of current standard therapies, vasospasm continues to result in death or major disability in patients treated for ruptured aneurysms. The authors investigated the effectiveness of continous MgSO4 infusion for vasospasm prophylaxis.

Methods

Seventy-six adults (mean age 54.6 years; 71% women; 92% Caucasian) were included in this comparative matched-cohort study of patients with aneurysmal subarachnoid hemorrhage on the basis of computed tomography (CT) findings. Thirty-eight patients who received continuous MgSO4 infusion were matched for age, race, sex, treatment option, Fisher grade, and Hunt and Hess grade to 38 historical control individuals who did not receive MgSO4 infusion. Twelve grams of MgSO4 in 500 ml normal saline was given intravenously daily for 12 days if the patient presented within 48 hours of aneurysm rupture. Vasospasm was diagnosed on the basis of digital substraction angiography, CT angiography, and transcranial Doppler ultrasonography, and evidence of neurological deterioration.

Symptomatic vasospasm was present at a significantly lower frequency in patients who received MgSO4 infusion (18%) compared with patients who did not receive MgSO4 (42%) (p = 0.025). There was no significant difference in mortality rate at discharge (p = 0.328). A trend toward improved outcome as measured by the modifed Rankin Scale (p = 0.084), but not the Glasgow Outcome Scale (p = 1.0), was seen in the MgSO4-treated group.

Conclusions

Analysis of the results suggests that MgSO4 infusion may have a role in cerebral vasospasm prophylaxis if therapy is initiated within 48 hours of aneurysm rupture.

Bilirubin oxidation products (BOXes) and their role in cerebral vasospasm after subarachnoid hemorrhage

Many factors have been postulated to cause delayed subarachnoid hemorrhage (SAH)-induced vasospasm, including hemoglobin, nitric oxide, endothelin, and free radicals. We propose that free radicals (because of the high levels that are produced in the blood clots surrounding blood vessels after SAH) act on bilirubin, biliverdin, and possibly heme to produce BOXes (Bilirubin OXidized Products). Bilirubin oxidation products act on vascular smooth muscle cells to produce chronic vasoconstriction and vasospasm combined with a vasculopathy because of smooth muscle cell injury. This review summarizes recent evidence that BOXes play a role in SAH-induced vasospasm. The data supporting a role for BOXes includes (1) identification of molecules in cerebrospinal fluid (CSF) of patients with vasospasm after SAH that have structures consistent with BOXes; (2) BOXes are vasoactive in vitro and mimic the biochemical actions of CSF of patients with vasospasm; (3) BOXes are vasoactive in vivo, constricting rat cerebral vessels; and (4) there is a correlation between clinical occurrence of vasospasm and BOXes concentration in our preliminary study of patients with SAH. Since oxidation of bilirubin, biliverdin, and perhaps heme is proposed to produce BOXes that contribute to vasospasm, either blocking bilirubin formation, inactivating bilirubin or BOXes, or removing all of the blood clot before vasospasm are potential treatment targets.

Effects of common medications on cerebral vasospasm after subarachnoid haemorrhage

Cerebral vasospasm is a common and serious complication of aneurysmal subarachnoid haemorrhage (SAH). At present, no consistently effective preventative and therapeutic measures are available, perhaps because of incomplete understanding of the pathogenesis of vasospasm. Experimental studies provide evidence that the incidence and severity of vasospasm after SAH can be modulated by drugs that affect neurotransmitter levels, intracellular signalling mechanisms, vascular smooth muscle function, inflammation and cellular proliferation, and the concentration of 'spasmogenic' factors. Preliminary clinical studies indicate that some illicit drugs and common prescription medications can have similar effects in humans. Recognition of these pharmacological effects is important because medications that can worsen or alleviate vasospasm are frequently administered to SAH patients to treat coincident medical problems.

Bilirubin production and oxidation in CSF of patients with cerebral vasospasm after subarachnoid hemorrhage

Delayed cerebral vasospasm after subarachnoid hemorrhage (SAH) remains a significant cause of mortality and morbidity; however, the etiology is, as yet, unknown, despite intensive research efforts. Research in this laboratory indicates that bilirubin and oxidative stress may be responsible by leading to formation of bilirubin oxidation products (BOXes), so we investigated changes in bilirubin concentration and oxidative stress in vitro, and in cerebral spinal fluid (CSF) from SAH patients. Non-SAH CSF, a source of heme oxygenase I (HO-1), and blood were incubated, and in vitro bilirubin production measured. Cerebrospinal fluid from SAH patients was collected, categorized using stimulation of vascular smooth muscle metabolism in vitro, and information obtained regarding occurrence of vasospasm in the patients. Cerebral spinal fluid was analyzed for hemoglobin, total protein and bilirubin, BOXes, malonyldialdehyde and peroxidized lipids (indicators of an oxidizing environment), and HO-1 concentration. The formation of bilirubin in vitro requires that CSF is present, as well as whole, non-anti-coagulated blood. Bilirubin, BOXes, HO-1, and peroxidized lipid content were significantly higher in CSF from SAH patients with vasospasm, compared with nonvasospasm SAH CSF, and correlated with occurrence of vasospasm. We conclude that vasospasm may be more likely in patients with elevated BOXes. The conditions necessary for the formation of BOXes are indeed present in CSF from SAH patients with vasospasm, but not CSF from SAH patients without vasospasm.