17Beta-estradiol activates adenosine A(2a) receptor after subarachnoid hemorrhage

The role of Tenascin C in intracerebral hemorrhage-induced secondary brain injury in rats via induction of neuronal cell death and neuroinflammation

BACKGROUND

Spontaneous intracerebral hemorrhage (ICH) is a major cause of stroke that causes high rates of disability and mortality in adults. Tenascin C (TNC) protein, one of the matricellular proteins associated with platelet-derived growth factor receptor (PDGFR) activation, has been reported to induce neuronal apoptosis. However, the role and underlying mechanisms of TNC in ICH-induced secondary brain injury (SBI) have not yet been fully explained. The main purpose of this study was to explore the role of TNC and its potential mechanisms in ICH.

METHODS

An ICH model was established by injecting autologous blood into the right basal ganglia in male Sprague Dawley (SD) rats, and imatinib, an inhibitor of PDGFR, was used to inhibit the release of TNC.

RESULTS

We found that TNC protein was significantly increased in the brain tissues after ICH and expressed in both neurons and microglia. We also found that the TNC level was elevated in the cerebrospinal fluid (CSF) after ICH. Additionally, we observed that the infiltration of activated microglia and the release of TNFα and IL-1β induced by ICH were decreased after inhibition of the protein levels of TNC and cleaved-TNC by a chemical inhibitor (imatinib). Furthermore, imatinib improved neuronal cell death and neurobehavioral abnormalities induced by ICH.

CONCLUSION

In summary, our study revealed that TNC protein plays an important role in ICH-induced SBI, and inhibition of TNC could alleviate ICH-induced neuroinflammation, neuronal cell death, and neurobehaviour. Therefore, TNC may be a potential therapeutic target for ICH-induced SBI.

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.

Concentrations of estradiol, progesterone and testosterone in sefrum and cerebrospinal fluid of patients with aneurysmal subarachnoid hemorrhage correlate weakly with transcranial Doppler flow velocities

Background

The implication of the steroids estradiol, progesterone and testosterone in cerebral vasospasm after aneurysmal subarachnoid hemorrhage (aSAH) has not been comprehensively assessed. In rodents, studies suggested beneficial effects of steroids on cerebral vasospasm after experimental SAH. Studies in humans are warranted, however, a general dilemma of human studies on neuroactive substances is that the brain is not directly accessible and that concentrations in the periphery may not adequately parallel concentrations in the central compartments. In the present study, concentrations of estradiol, progesterone and testosterone in serum and cerebrospinal fluid (CSF) of patients with aSAH were determined. Blood flow velocities in cerebral arteries were measured by transcranial Doppler sonography (TCD). The aim of this study was to evaluate the correlations between the cerebral blood flow velocities and levels of estradiol, progesterone and testosterone in CSF and serum.

Results

Samples of serum and CSF of 42 patients with aSAH were collected concomitantly daily or every other day via the arterial line and the external ventricular drainage for two weeks after the hemorrhage. Blood flow velocities in the cerebral arteries were determined by TCD. Total estradiol, progesterone and testosterone concentrations were measured by electro-chemiluminescence immunoassay. The strength of correlation was assessed by Spearman’s rank correlation coefficient. The correlation analysis revealed very weak correlations between cerebral blood flow velocities and concentrations of estradiol, progesterone and testosterone levels in both compartments with correlation coefficients below 0.2.

Conclusions

In humans with aSAH, merely very weak correlations between flow velocities in cerebral arteries and concentrations of estradiol, progesterone and testosterone in serum and CSF were demonstrated. These results suggest a limited influence of the respective steroids on cerebral vascular tone although vasodilatory effects were described in rodent studies. Thus, the implication of steroids in processes of neurological deterioration warrants further clarification.

Neuroprotective Effects of a Smoothened Receptor Agonist against Early Brain Injury after Experimental Subarachnoid Hemorrhage in Rats

The sonic hedgehog (Shh) signaling pathway plays a fundamental role in the central nervous system (CNS) development, but its effects on neural cell survival and brain repair after subarachnoid hemorrhage (SAH) has not been well-investigated. The present study was undertaken to evaluate the influence of an agonist of the Shh co-receptor Smoothened (Smo), purmorphamine (PUR), on early brain injury (EBI) as well as the underlying mechanisms after SAH. PUR was administered via an intraperitoneal injection with a dose of 0.5, 1, and 5 mg/kg at 2, 6, 24, and 46 h after SAH in rat model. The results showed that PUR treatment significantly ameliorated brain edema, improved neurobehavioral function, and attenuated neuronal cell death in the prefrontal cortex (PFC), associated with a decrease in Bax/Bcl-2 ratio and suppression of caspase-3 activation at 48 h after SAH. PUR also promoted phospho-ERK levels. Additionally, PUR treatment markedly decreased MDA concentration accompanied with the elevation in the expression of nuclear factor erythroid 2-related factor 2 and heme oxygenase-1 in PFC. Notably, PUR treatment significantly reversed the changes of Shh pathway mediators containing Patched, Gli1, and Shh by SAH insult, and the neuroprotection of PUR on SAH was blocked by Smo antagonist cyclopamine. These results indicated that PUR exerts neuroprotection against SAH-evoked injury in rats, mediated in part by anti-apoptotic and anti-oxidant mechanism, up-regulating phospho-ERK levels, mediating Shh signaling molecules in the PFC.

A1 adenosine receptor attenuates intracerebral hemorrhage-induced secondary brain injury in rats by activating the P38-MAPKAP2-Hsp27 pathway

Background

This study was designed to determine the role of the A1 adenosine receptors in intracerebral hemorrhage (ICH)-induced secondary brain injury and the underlying mechanisms.

Methods

A collagenase-induced ICH model was established in Sprague–Dawley rats, and cultured primary rat cortical neurons were exposed to oxyhemoglobin at a concentration of 10 μM to mimic ICH in vitro. The A1 adenosine receptor agonist N(6)-cyclohexyladenosine and antagonist 8-phenyl-1,3-dipropylxanthine were used to study the role of A1 adenosine receptor in ICH-induced secondary brain injury, and antagonists of P38 and Hsp27 were used to study the underlying mechanisms of A1 adenosine receptor actions.

Results

The protein level of A1 adenosine receptor was significantly increased by ICH, while there was no significant change in protein levels of the other 3 adenosine receptors. In addition, the A1 adenosine receptor expression could be increased by N(6)-cyclohexyladenosine and decreased by 8-phenyl-1,3-dipropylxanthine under ICH conditions. Activation of the A1 adenosine receptor attenuated neuronal apoptosis in the subcortex, which was associated with increased phosphorylation of P38, MAPK, MAPKAP2, and Hsp27. Inhibition of the A1 adenosine receptor resulted in opposite effects. Finally, the neuroprotective effect of the A1 adenosine receptor agonist N(6)-cyclohexyladenosine was inhibited by antagonists of P38 and Hsp27.

Conclusions

This study demonstrates that activation of the A1 adenosine receptor by N(6)-cyclohexyladenosine could prevent ICH-induced secondary brain injury via the P38-MAPKAP2-Hsp27 pathway.

Neuroprotective Effects of Hydrogen Sulfide Against Early Brain Injury and Secondary Cognitive Deficits Following Subarachnoid Hemorrhage

Although the neuroprotective effects of hydrogen sulfide (H₂ S) have been demonstrated in several studies, whether H₂ S protects against early brain injury (EBI) and secondary cognitive dysfunction in subarachnoid hemorrhage (SAH) model remains unknown. This study was undertaken to evaluate the influence of H₂ S on both acute brain injury and neurobehavioral changes as well as the underlying mechanisms after SAH. The H₂ S donor, NaHS, was administered via an intraperitoneal injection at a dose of 5.6 mg/kg at 2 h, 6 h, 24 h, and 46 h after SAH in rat model. The results showed that NaHS treatment significantly improved brain edema and neurobehavioral function, and attenuated neuronal cell death in the prefrontal cortex, associated with a decrease in Bax/Bcl-2 ratio and suppression of caspase-3 activation at 48 h after SAH. NaHS also promoted phospho-Akt and phospho-ERK levels. Furthermore, NaHS treatment significantly enhanced the levels of brain-derived neurotrophic factor (BDNF) and phospho-CREB. Importantly, NaHS administration improved learning and memory performance in the Morris water maze test at 7 days post-SAH in rats. These results demonstrated that NaHS, as an exogenous H₂ S donor, could significantly alleviate the development of EBI and cognitive dysfunction induced by SAH via Akt/ERK-related antiapoptosis pathway, and upregulating BDNF-CREB expression.

Human tissue kallikrein ameliorates cerebral vasospasm in a rabbit model of subarachnoid hemorrhage

OBJECTIVES

Cerebral vasospasm (CVS) and early brain injury are major causes of morbidity and mortality following subarachnoid hemorrhage (SAH). We investigated the efficiency of human tissue kallikrein (HTK) to prevent CVS in a rabbit model of SAH.

METHODS

Forty-eight Japanese white rabbits were randomly divided into four groups (n = 12 each): control (sham-operated), SAH, SAH + phosphate-buffered saline (PBS, vehicle), and SAH + HTK. Basilar artery (BA) diameters were measured by three-dimensional computed tomography angiography at three time points. Endothelin-1 (ET-1) and nitric oxide (NO) levels in the cerebrospinal fluid (CSF) were assayed 24 h before and 5 and 7 days after SAH. After the last measurement, the animals were killed, and endothelial cell apoptosis was assessed. Bax and Bcl-2 levels in the BA were measured by western blotting.

RESULTS

HTK was found to significantly reduce CVS following SAH in rabbits. Inverse changes were observed in ET-1 and NO levels in the CSF collected from the SAH group. HTK increased levels of NO, which has a vasodilatory effect, but did not affect levels of ET-1, which has a vasoconstrictive effect. CTA revealed that HTK treatment significantly increased BA diameter. Moreover, HTK treatment reduced the number of apoptotic cells following SAH, presumably by increasing and decreasing Bcl-2 and Bax expression, respectively.

CONCLUSION

HTK ameliorated CVS and inhibited apoptosis in the BA in a rabbit model of SAH.

Neuroprotective role of an N-acetyl serotonin derivative via activation of tropomyosin-related kinase receptor B after subarachnoid hemorrhage in a rat model

N-[2-(5-hydroxy-1H-indol-3-yl) ethyl]-2-oxopiperidine-3-carboxamide (HIOC), an N-acetyl serotonin derivative, selectively activates tropomyosin-related kinase receptor B (TrkB). This study is to investigate a potential role of HIOC on ameliorating early brain injury after experimental subarachnoid hemorrhage (SAH). One hundred and fifty-six adult male Sprague-Dawley rats were used. SAH model was induced by endovascular perforation. TrkB small interfering RNA (siRNA) or scramble siRNA was injected intracerebroventricularly 24h before SAH. HIOC was administrated intracerebroventricularly 3h after SAH and compared with brain-derived neurotrophic factor (BDNF). SAH grade and neurologic scores were evaluated for the outcome study. For the mechanism study, the expression of TrkB, phosphorylated TrkB (p-TrkB), phosphorylated extracellular signal regulated kinase (p-ERK), B-cell lymphoma 2 (Bcl-2) and cleaved caspase 3 (CC3) was detected by Western blots, and neuronal injury was determined by double immunofluorescence staining of neuronal nuclei and terminal deoxynucleotidyl transferase-mediated uridine 5'-triphosphate-biotin nick end-labeling. Knocking down of TrkB decreased the expression of Bcl-2 and aggravated neurologic deficits 24h after SAH. HIOC activated TrkB/ERK pathway, decreased neuronal cell death, and improved neurobehavioral outcome, and these effects were abolished by TrkB siRNA. HIOC was more potent than BDNF in reduction of apoptosis 24h post-SAH. Thus, we conclude that administration of HIOC activated TrkB/ERK signaling cascade and attenuated early brain injury after SAH. HIOC may be a promising agent for further treatment for SAH and other stroke events.

Progesterone attenuates experimental subarachnoid hemorrhage-induced vasospasm by upregulation of endothelial nitric oxide synthase via Akt signaling pathway

Cerebral vasospasm is the leading cause of mortality and morbidity in patients after aneurysmal subarachnoid hemorrhage (SAH). However, the mechanism and adequate treatment of vasospasm are still elusive. In the present study, we evaluate the effect and possible mechanism of progesterone on SAH-induced vasospasm in a two-hemorrhage rodent model of SAH. Progesterone (8 mg/kg) was subcutaneously injected in ovariectomized female Sprague-Dawley rats one hour after SAH induction. The degree of vasospasm was determined by averaging the cross-sectional areas of basilar artery 7 days after first SAH. Expressions of endothelial nitric oxide synthase (eNOS) and phosphorylated Akt (phospho-Akt) in basilar arteries were evaluated. Prior to perfusion fixation, there were no significant differences among the control and treated groups in physiological parameters recorded. Progesterone treatment significantly (P < 0.01) attenuated SAH-induced vasospasm. The SAH-induced suppression of eNOS protein and phospho-Akt were relieved by progesterone treatment. This result further confirmed that progesterone is effective in preventing SAH-induced vasospasm. The beneficial effect of progesterone might be in part related to upregulation of expression of eNOS via Akt signaling pathway after SAH. Progesterone holds therapeutic promise in the treatment of cerebral vasospasm following SAH.

Controversies and evolving new mechanisms in subarachnoid hemorrhage

Despite decades of study, subarachnoid hemorrhage (SAH) continues to be a serious and significant health problem in the United States and worldwide. The mechanisms contributing to brain injury after SAH remain unclear. Traditionally, most in vivo research has heavily emphasized the basic mechanisms of SAH over the pathophysiological or morphological changes of delayed cerebral vasospasm after SAH. Unfortunately, the results of clinical trials based on this premise have mostly been disappointing, implicating some other pathophysiological factors, independent of vasospasm, as contributors to poor clinical outcomes. Delayed cerebral vasospasm is no longer the only culprit. In this review, we summarize recent data from both experimental and clinical studies of SAH and discuss the vast array of physiological dysfunctions following SAH that ultimately lead to cell death. Based on the progress in neurobiological understanding of SAH, the terms "early brain injury" and "delayed brain injury" are used according to the temporal progression of SAH-induced brain injury. Additionally, a new concept of the vasculo-neuronal-glia triad model for SAH study is highlighted and presents the challenges and opportunities of this model for future SAH applications.

Therapeutic implications of estrogen for cerebral vasospasm and delayed cerebral ischemia induced by aneurysmal subarachnoid hemorrhage

Cerebral vasospasm (CV) remains the leading cause of delayed morbidity and mortality following aneurysmal subarachnoid hemorrhage (SAH). However, increasing evidence supports etiologies of delayed cerebral ischemia (DCI) other than CV. Estrogen, specifically 17 β -estradiol (E2), has potential therapeutic implications for ameliorating the delayed neurological deterioration which follows aneurysmal SAH. We review the causes of CV and DCI and examine the evidence for E2-mediated vasodilation and neuroprotection. E2 potentiates vasodilation by activating endothelial nitric oxide synthase (eNOS), preventing increased inducible NOS (iNOS) activity caused by SAH, and decreasing endothelin-1 production. E2 provides neuroprotection by increasing thioredoxin expression, decreasing c-Jun N-terminal kinase activity, increasing neuroglobin levels, preventing SAH-induced suppression of the Akt signaling pathway, and upregulating the expression of adenosine A2a receptor. The net effect of E2 modulation of these various effectors is the promotion of neuronal survival, inhibition of apoptosis, and decreased oxidative damage and inflammation. E2 is a potentially potent therapeutic tool for improving outcomes related to post-SAH CV and DCI. However, clinical evidence supporting its benefits remains lacking. Given the promising preclinical data available, further studies utilizing E2 for the treatment of patients with ruptured intracranial aneurysms appear warranted.

Tenascin-C causes neuronal apoptosis after subarachnoid hemorrhage in rats

The role of tenascin-C (TNC), a matricellular protein, in brain injury is unknown. The aim of this study was to examine if TNC causes neuronal apoptosis after subarachnoid hemorrhage (SAH), a deadly cerebrovascular disorder, using imatinib mesylate (a selective inhibitor of platelet-derived growth factor receptor [PDGFR] that is reported to suppress TNC induction) and recombinant TNC. SAH by endovascular perforation caused caspase-dependent neuronal apoptosis in the cerebral cortex irrespective of cerebral vasospasm development at 24 and 72 h post-SAH, associated with PDGFR activation, mitogen-activated protein kinases (MAPKs) activation, and TNC induction in rats. PDGFR inactivation by an intraperitoneal injection of imatinib mesylate prevented neuronal apoptosis, as well as MAPKs activation and TNC induction in the cerebral cortex at 24 h. A cisternal injection of recombinant TNC reactivated MAPKs and abolished anti-apoptotic effects of imatinib mesylate. The TNC injection also induced TNC itself in SAH brain, which may internally augment neuronal apoptosis after SAH. These findings suggest that TNC upregulation by PDGFR activation causes neuronal apoptosis via MAPK activation, and that the positive feedback mechanisms may exist to augment neuronal apoptosis after SAH. TNC-induced neuronal apoptosis would be a new target to improve outcome after SAH.

Interference of apoptosis in the pathophysiology of subarachnoid hemorrhage

Programmed cell death is crucial for the correct development of the organism and the clearance of harmful cells like tumor cells or autoreactive immune cells. Apoptosis is initiated by the activation of cell death receptors and in most cases it is associated with the activation of the cysteine proteases, which lead to apoptotic cell death. Cells shrink, chromatin clumps and forms a large, sharply demarcated, crescent-shaped or round mass; the nucleus condenses, apoptotic bodies are formed and eventually dead cells are engulfed by a neighboring cell or cleared by phagocytosis. The authors have summarized the most important data concerning apoptosis in subarachnoid hemorrhage that have been issued in the medical literature in the last 20 years.

17β-Estradiol attenuates secondary injury through activation of Akt signaling via estrogen receptor alpha in rat brain following subarachnoid hemorrhage

BACKGROUND

Apoptosis is implicated in vasospasm and the long-term sequelae of subarachnoid hemorrhage (SAH). This study tested the hypothesis that attenuation of SAH-induced apoptosis after 17β-estradiol (E2) treatment is associated with an increase in phosphorylation of Akt via estrogen receptor-α (ER-α) in rats.

MATERIALS AND METHODS

We examined the expression of phospho-Akt, ERα and ERβ, and apoptosis in cerebral cortex, hippocampus, and dentate gyrus in a two-hemorrhage SAH model in rats. We subcutaneously implanted other rats with a silicone rubber tube containing E2; they received daily injections of nonselective estrogen receptor antagonist (ICI 182,780), selective ERα-selective antagonist (methyl-piperidino-pyrazole), or ERβ-selective antagonist (R,R-tetrahydrochrysene) after the first hemorrhage.

RESULTS

At 7 d after the first SAH, protein levels of phospho-Akt and ERα were significantly decreased and caspase-3 was significantly increased in the dentate gyrus. The cell death assay revealed that DNA fragmentation was significantly increased in the dentate gyrus. Those actions were reversed by E2 and blocked by ICI 182,780 and methyl-piperidino-pyrazole, but not R,R-tetrahydrochrysene. However, there were no significant changes in the expression of the protein levels of phospho-Akt, ERα, ERβ, and caspase-3, and DNA fragmentation after SAH.

CONCLUSIONS

The present study shows that a beneficial effect of E2 in attenuating SAH-induced apoptosis is associated with activation of the expression of phospho-Akt and ERα, and alteration in caspase-3 protein expression via an ERα-dependent mechanism in the dentate gyrus. These data support further the investigation of E2 in the treatment of SAH in humans.

Serum biomarkers of spontaneous intracerebral hemorrhage induced secondary brain injury

Intracerebral hemorrhage (ICH) is a devastating form of stroke associated with a high rate of morbidity and mortality. It is now believed that much of this damage occurs in the subacute period following the initial insult via a cascade of complex pathophysiologic pathways that continues to be investigated. Increased levels of certain serum proteins have been identified as biomarkers that may reflect or directly participate in the inflammation, blood brain barrier disruption, endothelial dysfunction, and neuronal and glial toxicity that occur during this secondary period of cerebral injury. Some of these biomarkers have the potential to serve as therapeutic targets or surrogate endpoints for future research or clinical trials. Others may someday augment current clinical techniques in diagnosis, risk-stratification, prognostication, treatment decision and measurement of therapeutic efficacy. While much work remains to be done, biomarkers show significant potential to expand clinical options and improve clinical management, thereby reducing mortality and improving functional outcomes in ICH patients.

Advances in neuroprotective strategies: potential therapies for intracerebral hemorrhage

Intracerebral hemorrhage (ICH) is associated with higher mortality and morbidity than any other form of stroke. However, there currently are no treatments proven to improve outcomes after ICH, and therefore, new effective therapies are urgently needed. Growing insight into ICH pathophysiology has led to the development of neuroprotective strategies that aim to improve the outcome through reduction of secondary pathologic processes. Many neuroprotectants target molecules or pathways involved in hematoma degradation, inflammation or apoptosis, and have demonstrated potential clinical benefits in experimental settings. We extensively reviewed the current understanding of ICH pathophysiology as well as promising experimental neuroprotective agents with particular focus on their mechanisms of action. Continued advances in ICH knowledge, increased understanding of neuroprotective mechanisms, and improvement in the ability to modulate molecular and pathologic events with multitargeting agents will lead to successful clinical trials and bench-to-bedside translation of neuroprotective strategies.

Maturation and the role of PKC-mediated contractility in ovine cerebral arteries

Ca2+-independent pathways such as protein kinase C (PKC), extracellular-regulated kinases 1 and 2 (ERK1/2), and Rho kinase 1 and 2 (ROCK1/2) play important roles in modulating cerebral vascular tone. Because the roles of these kinases vary with maturational age, we tested the hypothesis that PKC differentially regulates the Ca2+-independent pathways and their effects on cerebral arterial contractility with development. We simultaneously examined the responses of arterial tension and intracellular Ca2+ concentration and used Western immunoblot analysis to measure ERK1/2, RhoA, 20 kDa regulatory myosin light chain (MLC20), PKC-potentiated inhibitory protein of 17 kDa (CPI-17), and caldesmon. Phorbol 12,13-dibutyrate (PDBu)-mediated PKC activation produced a robust contractile response, which was increased a further 20 to 30% by U-0126 (MEK inhibitor) in cerebral arteries of both age groups. Of interest, in the fetal cerebral arteries, PDBu leads to an increased phosphorylation of ERK2 compared with ERK1, whereas in adult arteries, we observed an increased phosphorylation of ERK1 compared with ERK2. Also, in the present study, RhoA/ROCK played a significant role in the PDBu-mediated contractility of fetal cerebral arteries, whereas in adult cerebral arteries, CPI-17 and caldesmon had a significantly greater role compared with the fetus. PDBu also led to an increased MLC20 phosphorylation, a response blunted by the inhibition of myosin light chain kinase only in the fetus. Overall, the present study demonstrates an important maturational shift from RhoA/ROCK-mediated to CPI-17/caldesmon-mediated PKC-induced contractile response in ovine cerebral arteries.