The presence of an extractable substance in the CSF of humans with cerebral vasospasm after subarachnoid haemorrhage that correlates with phosphatase inhibition

The blood-brain barrier and the neurovascular unit in subarachnoid hemorrhage: molecular events and potential treatments

The response of the blood-brain barrier (BBB) following a stroke, including subarachnoid hemorrhage (SAH), has been studied extensively. The main components of this reaction are endothelial cells, pericytes, and astrocytes that affect microglia, neurons, and vascular smooth muscle cells. SAH induces alterations in individual BBB cells, leading to brain homeostasis disruption. Recent experiments have uncovered many pathophysiological cascades affecting the BBB following SAH. Targeting some of these pathways is important for restoring brain function following SAH. BBB injury occurs immediately after SAH and has long-lasting consequences, but most changes in the pathophysiological cascades occur in the first few days following SAH. These changes determine the development of early brain injury as well as delayed cerebral ischemia. SAH-induced neuroprotection also plays an important role and weakens the negative impact of SAH. Supporting some of these beneficial cascades while attenuating the major pathophysiological pathways might be decisive in inhibiting the negative impact of bleeding in the subarachnoid space. In this review, we attempt a comprehensive overview of the current knowledge on the molecular and cellular changes in the BBB following SAH and their possible modulation by various drugs and substances.

Bilirubin Oxidation Products and Cerebral Vasoconstriction

Key evidence in support of the hypothesis that bilirubin oxidation products (BOXes) contribute to the vasoconstriction associated with subarachnoid hemorrhage (SAH) are the (1) presence of BOXes in cerebral spinal fluid from SAH patients and (2) ability of one or more BOXes to elicit vasoconstriction. We critically evaluate this key evidence, detail where gaps remain, and describe recent approaches that will address these gaps.

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.

Dopamine D2-receptor-mediated increase in vascular and endothelial NOS activity ameliorates cerebral vasospasm after subarachnoid hemorrhage in vitro

INTRODUCTION

Cerebral vasospasm after subarachnoid hemorrhage (SAH) is a serious complication resulting in delayed neurological deficit, increased morbidity, mortality, longer hospital stays, and rehabilitation time. It afflicts approximately 35 per 100,000 Americans per year, and there is currently no effective therapy. We present in vitro data suggesting that increasing intrinsic nitric oxide relaxation pathways in vascular smooth muscle via dopaminergic agonism ameliorates cerebral vasospasm after SAH.

METHODS

Cerebrospinal fluid (CSF) from patients with cerebral vasospasm after SAH (CSF(V)) was used to induce vasospasm in porcine carotid artery in vitro. Dopamine was added to test its ability to reverse spasm, and specific dopamine receptor antagonists were used to determine which receptor mediated the protection. Immunohistochemical techniques confirmed the presence of dopamine receptor subtypes and the involvement of NOS in the mechanism of dopamine protection.

RESULTS

Dopamine receptor 1, 2, and 3 subtypes are all present in porcine carotid artery. Dopamine significantly reversed spasm in vitro (67% relaxation), and this relaxation was prevented by Haloperidol, a D(2)R antagonist (10% relaxation, P < 0.05), but not by D(1) or D(3)-receptor antagonism. Both eNOS and iNOS expression were increased significantly in response to CSF(V) alone, and this was significantly enhanced by addition of dopamine, and blocked by Haloperidol.

CONCLUSION

Cerebral vasospasm is significantly reversed in a functional measure of vasospasm in vitro by dopamine, via a D(2)R-mediated pathway. The increase in NOS protein seen in both the endothelium and vascular smooth muscle in response to CSF(V) is enhanced by dopamine, also in a D(2)R-dependent mechanism.

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.

Vascular dysfunction in human and rat cirrhosis: role of receptor-desensitizing and calcium-sensitizing proteins

In cirrhosis, vascular hypocontractility leads to vasodilation and contributes to portal hypertension. Impaired activation of contractile pathways contributes to vascular hypocontractility. Angiotensin II type 1 receptors (AT1-Rs) are coupled to the contraction-mediating RhoA/Rho-kinase pathway and may be desensitized by phosphorylation through G-protein-coupled receptor kinases (GRKs) and binding of beta-arrestin-2. In the present study, we analyzed vascular hypocontractility to angiotensin II in cirrhosis. Human hepatic arteries were obtained during liver transplantation. In rats, cirrhosis was induced by bile duct ligation (BDL). Contractility of rat aortic rings was measured myographically. Protein expression and phosphorylation were analyzed by Western blot analysis. Immunoprecipitation was performed with protein A-coupled Sepharose beads. Myosin light chain (MLC) phosphatase activity was assessed as dephosphorylation of MLCs. Aortas from BDL rats were hyporeactive to angiotensin II and extracellular Ca2+. Expression of AT1-R and Galphaq/11,12,13 remained unchanged in hypocontractile rat and human vessels, whereas GRK-2 and beta-arrestin-2 were up-regulated. The binding of beta-arrestin-2 to the AT1-R was increased in hypocontractile rat and human vessels. Inhibition of angiotensin II-induced aortic contraction by the Rho-kinase inhibitor Y-27632 was pronounced in BDL rats. Basal phosphorylation of the ROK-2 substrate moesin was reduced in vessels from rats and patients with cirrhosis. Analysis of the expression and phosphorylation of Ca(2+)-sensitizing proteins (MYPT1 and CPI-17) in vessels from rats and patients with cirrhosis suggested decreased Ca2+ sensitivity. Angiotensin II-stimulated moesin phosphorylation was decreased in aortas from BDL rats. MLC phosphatase activity was elevated in aortas from BDL rats.

CONCLUSION

Vascular hypocontractility to angiotensin II in cirrhosis does not result from changes in expression of AT1-Rs or G-proteins. Our data suggest that in cirrhosis-induced vasodilation, the AT1-R is desensitized by GRK-2 and beta-arrestin-2 and that changed patterns of phosphorylated Ca(2+) sensitizing proteins decrease Ca(2+) sensitivity.

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.

Signaling mechanisms in cerebral vasospasm

The elusive nature of events that sustain cerebral vasospasm after subarachnoid hemorrhage resulting from a ruptured aneurysm presents major challenges in designing effective therapies for this frequently devastating condition. Protracted cerebral artery constriction entails several dynamic components in intracellular signaling events initiated by endothelial factors, products of hemolysate, and numerous kinases, as well as increased intracellular Ca(2+). The rationale for potential treatment modalities and their efficacy are discussed in this brief review.

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.

Vascular smooth muscle function: The physiology and pathology of vasoconstriction

Vascular smooth muscle is the contractile component of arteries and veins. The control of contraction and relaxation is dependent upon intracellular and extracellular signals. Abnormal contractions can cause and or contribute to pathology such as hypertension, ischemia and infarction. In this review, we address the vascular pathogenesis associated with hypertension and subarachnoid hemorrhage induced cerebral vasospasm. Hypertension is a multifactorial disease with many causes and a profound impact on the cardiovascular system, whereas subarachnoid hemorrhage induced cerebral vasospasm is a pathological vasoconstriction often causing infarction that is thought to be 'caused' by a factor or factors in the CSF following the hemorrhage. However, the mechanism by which the vessels are constricted is unknown. Although the causes for these two pathological vasoconstrictions remain to be determined, we conclude that the common denominator is that these contractile changes result in pathology with devastating consequences to human health.

Increase of metabolic activity and disruption of normal contractile protein distribution by bilirubin oxidation products in vascular smooth-muscle cells

OBJECT

Cerebral vasospasm is a common cause of morbidity and death following aneurysmal subarachnoid hemorrhage (SAH). Previous research has shown that bilirubin oxidation products (BOXes) are present in the cerebral spinal fluid in patients with SAH-induced cerebral vasospasm and can contribute to vasoconstriction and vasospasm in vitro and in vivo. The events leading to cerebral vasospasm are not understood; however, one component of the occlusion may be due to vascular remodeling. In this study the authors have investigated the actions of BOXes, okadaic acid ([OA], a phosphatase inhibitor), and phorbol-12 myristate-13 acetate ([PMA], a protein kinase activator) on vascular smooth-muscle cell (VSMC) morphology and metabolism.

METHODS

Immunohistochemical analysis was performed to assess VSMC morphology and alpha-smooth-muscle actin (alphaSMA) distribution following the application of BOXes, OA, or PMA. Changes in the level of lactate dehydrogenase (LDH) release and oxidative metabolism were also measured. The BOXes, OA, or PMA caused VSMCs to change their shape and exhibit altered alphaSMA distribution. These treatments increased LDH release (p < 0.05), which is an index of increased cell stress. Oxidative metabolism significantly increased at low and high doses of BOXes, that is, 143 +/- 8.5% and 180 +/- 11.8%, respectively (p < 0.0001). Both PMA and OA also caused a significant increase in metabolism.

CONCLUSIONS

The authors concluded that BOXes, OA, and PMA alter VSMC morphology and metabolic activity, events that have been observed during vascular remodeling. Although the mechanism remains unclear, the results indicate that BOXes may play a role in the vascular remodeling that occurs following aneurysmal SAH.

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.

Oxidation of bilirubin produces compounds that cause prolonged vasospasm of rat cerebral vessels: a contributor to subarachnoid hemorrhage-induced vasospasm

The authors have previously shown that bilirubin-oxidation products (BOXes) are present in CSF of subarachnoid hemorrhage patients with vasospasm, and that BOXes cause vasoconstriction in vitro. This study determined whether BOXes cause vasospasm in vivo. Identical volumes of either lysed blood or standardized amounts of BOXes were injected into the cisterna magna of adult rats. BOX injections caused 6 of 10 rats to die within 10 minutes, whereas 12 of 12 rats survived for 24 hours after blood injections. The mechanism for this significant (P < or = 0.01) increase in mortality was unclear. To directly test whether BOXes produced vasospasm, a cranial window technique was used. Application of 20 microL of 10-micromol/L bilirubin had little effect on the vessels. However, application of BOXes produced marked, dose-dependent small artery and arteriole vasospasm that approached a 90% decrease in diameter by 40 minutes after application in some vessels, and persisted for at least 24 hours. To determine if BOX-mediated vasospasm led to cortical injury, histology and immunocytochemistry were performed on animals that survived for 24 hours. There was a BOX-related stress protein response for HSP25 and HSP32 (HO-1) without evidence of infarction. The finding that the BOXes produce vasospasm of cerebral vessels in vivo, in conjunction with BOXes being found in CSF of vasospasm patients, supports our hypothesis that BOXes contribute to or cause cerebral vasospasm after subarachnoid hemorrhage.

Protein kinase C and cerebral vasospasm

Twenty-five years after the discovery of protein kinase C (PKC), the physiologic function of PKC, and especially its role in pathologic conditions, remains a subject of great interest with 30,000 studies published on these aspects. In the cerebral circulation, PKC plays a role in the regulation of myogenic tone by sensitization of myofilaments to calcium. Protein kinase C phosphorylates various ion channels including augmenting voltage-dependent Ca2+ channels and inhibiting K+ channels, which both lead to vessel contraction. These actions of PKC amplify vascular reactivity to different agonists and may be critical in the regulation of cerebral artery tone during vasospasm. Evidence accumulated during at least the last decade suggest that activation of PKC in cerebral vasospasm results in a delayed but prolonged contraction of major arteries after subarachnoid hemorrhage. Most of the experimental results in vitro or in animal models support the view that PKC is involved in cerebral vasospasm. Implication of PKC in cerebral vasospasm helps explain increased arterial narrowing at the signal transduction level and alters current perceptions that the pathophysiology is caused by a combination of multiple receptor activation, hemoglobin toxicity, and damaged neurogenic control. Activation of protein kinase C also interacts with other signaling pathways such as myosin light chain kinase, nitric oxide, intracellular Ca2+, protein tyrosine kinase, and its substrates such as mitogen-activated protein kinase. Even though identifying PKC revolutionized the understanding of cerebral vasospasm, clinical advances are hampered by the lack of clinical trials using selective PKC inhibitors.

Oxidative degradation of bilirubin produces vasoactive compounds

Subarachnoid haemorrhage is often followed by haemolysis and concomitant oxidative stress, and is frequently complicated by pathological vasoconstriction or cerebral vasospasm. It is known that upregulation of haem oxygenase (HO-1) is induced by oxidative stress and results in release of biliverdin and bilirubin (BR), which are scavengers of reactive oxygen species (ROS). Here we report biomimetic studies aimed at modelling pathological conditions leading to oxidative degradation of BR. Oxidative degradation products of BR, formed by reaction with hydrogen peroxide (an ROS model system), demonstrated biological activity by stimulating oxygen consumption and force development in vascular smooth muscle from porcine carotid artery. Analogous biological activity was observed with vasoactive cerebrospinal fluid from subarachnoid haemorrhage patients. Three degradation products of BR were isolated: two were assigned as isomeric monopyrrole (C9H11N2O2) derivatives, 4-methyl-5-oxo-3-vinyl-(1, 5-dihydropyrrol-2-ylidene)acetamide and 3-methyl-5-oxo-4-vinyl-(1, 5-dihydropyrrol-2-ylidene)acetamide and the third was 4-methyl-3-vinylmaleimide (MVM), a previously isolated photodegradation product of biliverdin. Possible mechanisms of oxidative degradation of BR are discussed. Tentative assignment of these structures in the cerebrospinal fluid (CSF) of cerebral vasospasm patients has been made. It is proposed that one or more of the degradation products of biliverdin or bilirubin are involved in complications such as vasospasm and or pathological vasoconstriction associated with haemorrhage.