Modification of endothelial nitric oxide synthase through AMPK after experimental subarachnoid hemorrhage

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.

Role of endothelial nitric oxide synthase for early brain injury after subarachnoid hemorrhage in mice

The first few hours and days after subarachnoid hemorrhage (SAH) are characterized by cerebral ischemia, spasms of pial arterioles, and a significant reduction of cerebral microperfusion, however, the mechanisms of this early microcirculatory dysfunction are still unknown. Endothelial nitric oxide production is reduced after SAH and exogenous application of NO reduces post-hemorrhagic microvasospasm. Therefore, we hypothesize that the endothelial NO-synthase (eNOS) may be involved in the formation of microvasospasms, microcirculatory dysfunction, and unfavorable outcome after SAH. SAH was induced in male eNOS deficient (eNOS^-/-) mice by endovascular MCA perforation. Three hours later, the cerebral microcirculation was visualized using in vivo 2-photon-microscopy. eNOS^-/- mice had more severe SAHs, more severe ischemia, three time more rebleedings, and a massively increased mortality (50 vs. 0%) as compared to wild type (WT) littermate controls. Three hours after SAH eNOS^-/- mice had fewer perfused microvessels and 40% more microvasospasms than WT mice. The current study indicates that a proper function of eNOS plays a key role for a favorable outcome after SAH and helps to explain why patients suffering from hypertension or other conditions associated with impaired eNOS function, have a higher risk of unfavorable outcome after SAH.

Therapeutic effect of and mechanisms underlying the effect of miR-195-5p on subarachnoid hemorrhage-induced vasospasm and brain injury in rats

Objectives

There is much evidence suggesting that inflammation contributes majorly to subarachnoid hemorrhage (SAH)-induced cerebral vasospasm and brain injury. miRNAs have been found to modulate inflammation in several neurological disorders. This study investigated the effect of miR-195-5p on SAH-induced vasospasm and early brain injury in experimental rats.

Methods

Ninety-six Sprague-Dawley male rats were randomly and evenly divided into a control group (no SAH, sham surgery), a SAH only group, a SAH + NC-mimic group, and a SAH + miR-195-5p group. SAH was induced using a single injection of blood into the cisterna magna. Suspensions containing NC-mimic and miR-195-5p were intravenously injected into rat tail 30 mins after SAH was induced. We determined degree of vasospasm by averaging areas of cross-sections the basilar artery 24h after SAH. We measured basilar artery endothelial nitric oxide synthase (eNOS), inducible nitric oxide synthase (iNOS), nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κ B), phosphorylated NF-κ B (p-NF-κ B), inhibitor of NF-κ B (Iκ Bα) and phosphorylated-Iκ Bα (p-Iκ Bα). Cell death assay was used to quantify the DNA fragmentation, an indicator of apoptotic cell death, in the cortex, hippocampus, and dentate gyrus. Tumor necrosis factor alpha (TNF-α) levels were measured using sample protein obtained from the cerebral cortex, hippocampus and dentate gyrus.

Results

Prior to fixation by perfusion, there were no significant physiological differences among the control and treatment groups. SAH successfully induced vasospasm and early brain injury. MiR-195-5p attenuated vasospasam-induced changes in morphology, reversed SAH-induced elevation of iNOS, p-NF-κ B, NF-κ B, and p-Iκ Bα and reversed SAH-induced suppression of eNOS in the basilar artery. Cell death assay revealed that MiR-195-5p significantly decreased SAH-induced DNA fragmentation (apoptosis) and restored TNF-α level in the dentate gyrus.

Conclusion

In conclusion, MiRNA-195-5p attenuated SAH-induced vasospasm by up-regulating eNOS, down-regulating iNOS and inhibiting the NF-κ B signaling pathway. It also protected neurons by decreasing SAH-induced apoptosis-related cytokine TNF-α expression in the dentate gyrus. Further study is needed to elucidate the detail mechanism underlying miR-195-5p effect on SAH-induced vasospasm and cerebral injury. We believe that MiR-195-5p can potentially be used to manage SAH-induced cerebral vasospasm and brain injury.

Bakuchiol Attenuates Oxidative Stress and Neuron Damage by Regulating Trx1/TXNIP and the Phosphorylation of AMPK After Subarachnoid Hemorrhage in Mice

Subarachnoid hemorrhage (SAH) is a fatal cerebrovascular condition with complex pathophysiology that reduces brain perfusion and causes cerebral functional impairments. An increasing number of studies indicate that early brain injury (EBI), which occurs within the first 72 h of SAH, plays a crucial role in the poor prognosis of SAH. Bakuchiol (Bak) has been demonstrated to have multiorgan protective effects owing to its antioxidative and anti-inflammatory properties. The present study was designed to investigate the effects of Bak on EBI after SAH and its underlying mechanisms. In this study, 428 adult male C57BL/6J mice weighing 20 to 25 g were observed to investigate the effects of Bak administration in an SAH animal model. The neurological function and brain edema were assessed. Content of MDA/3-NT/8-OHdG/superoxide anion and the activity of SOD and GSH-Px were tested. The function of the blood-brain barrier (BBB) and the protein levels of claudin-5, occludin, zonula occludens-1, and matrix metalloproteinase-9 were observed. TUNEL staining and Fluoro-Jade C staining were conducted to evaluate the death of neurons. Ultrastructural changes of the neurons were observed under the transmission electron microscope. Finally, the roles of Trx, TXNIP, and AMPK in the protective effect of Bak were investigated. The data showed that Bak administration 1) increased the survival rate and alleviated neurological functional deficits; 2) alleviated BBB disruption and brain edema; 3) attenuated oxidative stress by reducing reactive oxygen species, MDA, 3-NT, 8-OHdG, gp91^phox, and 4-HNE; increased the activities of SOD and GSH-Px; and alleviated the damage to the ultrastructure of mitochondria; 4) inhibited cellular apoptosis by regulating the protein levels of Bcl-2, Bax, and cleaved caspase-3; and 5) upregulated the protein levels of Trx1 as well as the phosphorylation of AMPK and downregulated the protein levels of TXNIP. Moreover, the protective effects of Bak were partially reversed by PX-12 and compound C. To summarize, Bak attenuates EBI after SAH by alleviating BBB disruption, oxidative stress, and apoptosis via regulating Trx1/TXNIP expression and the phosphorylation of AMPK. Its powerful protective effects might make Bak a promising novel drug for the treatment of EBI after SAH.

Protective mechanism of Taxifolin for chlorpyrifos neurotoxicity in BV2 cells

Chlorpyrifos (CPF) is an organophosphorus pesticide that can damage the central nervous system in children upon exposure. Taxifolin (Tax) exerts protective effects against neurotoxins; however, the mechanism has not yet been illustrated. The current study used BV2 cells to investigate the protective mechanism underlying the organophosphorus pesticide taxifolin on CPF-induced neurotoxicity, which might present a therapeutic potential for the prevention and treatment of the nervous system diseases in children. BV2 cells were randomly divided into 4 groups: DMSO, CPF, Tax, and Tax + CPF. The viability, morphocytology, oxidative stress, inflammatory reaction, and autophagocytosis have been studied in the cells using Western blot analysis, CCK-8 assay, enzyme-linked immunosorbent assay, and immunofluorescence to estimate the level of LC3 II. As a result, CPF was found to exert a significant toxic effect on BV2 cells that was characterized by rounded cell body, atrophic synapse, poor adhesion, cell aggregation, inflammation, oxidative reaction, and autophagy. Tax treatment has a protective effect on CPF-induced neurotoxicity via downregulation of ROS, TNF-α, IFN-γ, and p62 levels and increased LC3 II level, which in turn, improved the viability and activity of BV2 cells. This phenomenon suggested that Tax can reduce the inflammation and oxidative stress and promote autophagy. Furthermore, the current study suggested that the protective mechanism of Tax on CPF-induced BV2 cell toxicity was via up-regulation of pAMPK level and activation of Nrf2/HO-1 signaling pathway.

Vitamin D attenuates cerebral artery remodeling through VDR/AMPK/eNOS dimer phosphorylation pathway after subarachnoid hemorrhage in rats

The role of vitamin D3 (VitD3) in the upregulation of osteopontin (OPN) and eNOS in the endothelium of cerebral arteries after subarachnoid hemorrhage (SAH) is investigated. The endovascular perforation SAH model in Sprague-Dawley rats ( n = 103) was used. The VitD3 pretreatment (30 ng/kg) increased endogenous OPN and eNOS expression in cerebral arteries compared with naïve rats ( n = 5 per group). Neurobehavioral scores were significantly improved in Pre-SAH+VitD3 group compared with the SAH group. The effects of VitD3 were attenuated by intracerebroventricular (i.c.v) injections of siRNA for the vitamin D receptor (VDR) and OPN in Pre-SAH+VitD3+VDR siRNA and Pre-SAH+VitD3+OPN siRNA rats, respectively ( n = 5 per group). The significant increase of VDR, OPN and decrease of C44 splicing in the cerebral arteries of Pre-SAH+VitD3 rats lead to an increase in basilar artery lumen. The increase in VDR expression led to an upregulation and phosphorylation of AMPK and eNOS, especially dimer form, in endothelium of cerebral artery. The results provide that VitD3 pretreatment attenuates cerebral artery remodeling and vasospasm through the upregulation of OPN and phosphorylation of AMPK (p-AMPK) and eNOS (p-eNOS) at Ser1177-Dimer in the cerebral arteries. Vitamin D may be a useful new preventive and therapeutic strategy against cerebral artery remodeling in stroke patients.

Scutellarin attenuates vasospasm through the Erk5-KLF2-eNOS pathway after subarachnoid hemorrhage in rats

Angiographic vasospasm, especially in the early phases (<72h) of subarachnoid hemorrhage (SAH), is one of the major complications after an aneurysm rupture and is often the cause of delayed neurological deterioration. Scutellarin (SCU), a flavonoid extracted from the traditional Chinese herb Erigeron breviscapus, has been widely accepted as an antioxidant, but the effect of SCU on vasospasm after SAH remains elusive. Endovascular perforation was conducted to induce SAH in Sprague-Dawley rats. Then, the underlying mechanism of the anti-vasospasm effect of SCU was investigated using a modified Garcia scale, India ink angiography, cross-sectional area analysis, immunohistochemistry staining and western blot. SCU (50μM, 100mg/kg) alleviated angiographic vasospasm and improved neurological function 48h after SAH and enhanced the expression of endothelial nitric oxide synthase (eNOS) at the intima of cerebral arteries. In addition, SCU upregulated the expression of phosphorylated extracellular-regulated kinase 5 (p-Erk5) and Kruppel-like factor 2 (KLF2) at 48h after SAH. However, the effects of SCU were reversed by the Erk5 inhibitor XMD8-92. Our results indicate that SCU could attenuate vasospasm and neurological deficits via modulating the Erk5-KLF2-eNOS pathway after SAH, which may provide an experimental basis for the clinical use of SCU treatment in SAH patients.

Towards use of MRI-guided ultrasound for treating cerebral vasospasm

Cerebral vasospasm is a major cause of morbidity and mortality in patients with subarachnoid hemorrhage (SAH), causing delayed neurological deficits in as many as one third of cases. Existing therapy targets induction of cerebral vasodilation through use of various drugs and mechanical means, with a range of observed efficacy. Here, we perform a literature review supporting our hypothesis that transcranially delivered ultrasound may have the ability to induce therapeutic cerebral vasodilation and, thus, may one day be used therapeutically in the context of SAH. Prior studies demonstrate that ultrasound can induce vasodilation in both normal and vasoconstricted blood vessels in peripheral tissues, leading to reduced ischemia and cell damage. Among the proposed mechanisms is alteration of several nitric oxide (NO) pathways, where NO is a known vasodilator. While in vivo studies do not point to a specific physical mechanism, results of in vitro studies favor cavitation induction by ultrasound, where the associated shear stresses likely induce NO production. Two papers discussed the effects of ultrasound on the cerebral vasculature. One study applied clinical transcranial Doppler ultrasound to a rodent complete middle cerebral artery occlusion model and found reduced infarct size. A second involved the application of pulsed ultrasound in vitro to murine brain endothelial cells and showed production of a variety of vasodilatory chemicals, including by-products of arachidonic acid metabolism. In sum, nine reviewed studies demonstrated evidence of either cerebrovascular dilation or elaboration of vasodilatory compounds. Of particular interest, all of the reviewed studies used ultrasound capable of transcranial application: pulsed ultrasound, with carrier frequencies ranging between 0.5 and 2.0 MHz, and intensities not substantially above FDA-approved intensity values. We close by discussing potential specific treatment paradigms of SAH and other cerebral ischemic disorders based on MRI-guided transcranial ultrasound.

N-cadherin coordinates AMP kinase-mediated lung vascular repair

Injury to the pulmonary circulation compromises endothelial barrier function and increases lung edema. Resolution of lung damage involves restoring barrier integrity, a process requiring reestablishment of endothelial cell-cell adhesions. However, mechanisms underlying repair in lung endothelium are poorly understood. In pulmonary microvascular endothelium, AMP kinase α1 (AMPKα1) stimulation enhances recovery of the endothelial barrier after LPS-induced vascular damage. AMPKα1 colocalizes to a discrete membrane compartment with the adhesion protein neuronal cadherin (N-cadherin). This study sought to determine N-cadherin's role in the repair process. Short-hairpin RNA against full-length N-cadherin or a C-terminally truncated N-cadherin, designed to disrupt the cadherin's interactions with intracellular proteins, were expressed in lung endothelium. Disruption of N-cadherin's intracellular domain caused translocation of AMPK away from the membrane and attenuated AMPK-mediated restoration of barrier function in LPS-treated endothelium. AMPK activity measurements indicated that lower basal AMPK activity in cells expressing the truncated N-cadherin compared with controls. Moreover, the AMPK stimulator 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) failed to increase AMPK activity in cells expressing the modified N-cadherin, indicating uncoupling of a functional association between AMPK and the cadherin. Isolated lung studies confirmed a physiologic role for this pathway in vivo. AMPK activation reversed LPS-induced increase in permeability, whereas N-cadherin inhibition hindered AMPK-mediated repair. Thus N-cadherin coordinates the vascular protective actions of AMPK through a functional link with the kinase. This study provides insight into intrinsic repair mechanisms in the lung and supports AMPK stimulation as a modality for treating vascular disease.

Chemerin plays a protective role by regulating human umbilical vein endothelial cell-induced nitric oxide signaling in preeclampsia

The aim of this study was to determine chemerin levels in preeclampsia and to assess the effects of this anti-inflammatory factor on endothelial nitric oxide synthase (eNOS), nuclear factor (NF)-κB, and vascular cell adhesion molecule (VCAM) expression in human umbilical vein endothelial cells (HUVECs). Serum chemerin and eNOS levels were measured by enzyme-linked immunosorbent assays, while chemerin mRNA and protein levels were measured by fluorescent quantitative polymerase chain reaction and Western blotting, respectively. Nitric oxide (NO) concentrations were determined with a colorimetric method. Akt and eNOS phosphorylation were assessed by Western blotting. We also tested the effects of the phosphoinositide 3-kinase inhibitor LY294002 and the eNOS inhibitor L-NAME. NF-κB p65 and VCAM-1 phosphorylation were assessed by Western blotting to investigate the role of chemerin in tumor necrosis factor (TNF)-α-induced HUVEC injury. Serum chemerin levels were increased in preeclampsia, while eNOS was decreased. Chemerin mRNA and protein were both increased in placentae from patients with preeclampsia. Furthermore, chemerin serum level positively correlated with blood pressure, body mass index, and serum insulin and was negatively correlated with serum eNOS. Chemerin dose-dependently increased NO concentrations in supernatants. Chemerin can increase eNOS and Akt levels in HUVECs, and these results could be partly blocked by LY294002 and L-NAME. Chemerin significantly decreased TNF-α-induced NF-κB and VCAM-1 in HUVECs, and these changes were partly inhibited by LY294002 and L-NAME. Chemerin may play a protective role by regulating NO signaling. Future studies should assess the role of chemerin in preeclampsia and other vascular diseases.

Role of cyclic AMP sensor Epac1 in masseter muscle hypertrophy and myosin heavy chain transition induced by β2-adrenoceptor stimulation

The predominant isoform of β-adrenoceptor (β-AR) in skeletal muscle is β2-AR and that in the cardiac muscle is β1-AR. We have reported that Epac1 (exchange protein directly activated by cAMP 1), a new protein kinase A-independent cAMP sensor, does not affect cardiac hypertrophy in response to pressure overload or chronic isoproterenol (isoprenaline) infusion. However, the role of Epac1 in skeletal muscle hypertrophy remains poorly understood. We thus examined the effect of disruption of Epac1, the major Epac isoform in skeletal muscle, on masseter muscle hypertrophy induced by chronic β2-AR stimulation with clenbuterol (CB) in Epac1-null mice (Epac1KO). The masseter muscle weight/tibial length ratio was similar in wild-type (WT) and Epac1KO at baseline and was significantly increased in WT after CB infusion, but this increase was suppressed in Epac1KO. CB treatment significantly increased the proportion of myosin heavy chain (MHC) IIb at the expense of that of MHC IId/x in both WT and Epac1KO, indicating that Epac1 did not mediate the CB-induced MHC isoform transition towards the faster isoform. The mechanism of suppression of CB-mediated hypertrophy in Epac1KO is considered to involve decreased activation of Akt signalling. In addition, CB-induced histone deacetylase 4 (HDAC4) phosphorylation on serine 246 mediated by calmodulin kinase II (CaMKII), which plays a role in skeletal muscle hypertrophy, was suppressed in Epac1KO. Our findings suggest that Epac1 plays a role in β2-AR-mediated masseter muscle hypertrophy, probably through activation of both Akt signalling and CaMKII/HDAC4 signalling.

Estradiol reduces ferrous citrate complex-induced NOS2 up-regulation in cerebral endothelial cells by interfering the nuclear factor kappa B transactivation through an estrogen receptor β-mediated pathway

Hemorrhagic stroke caused leakage of red blood cells which converts to hemoglobin, heme, and iron accumulated at the lesions. High concentration of ferrous iron from subarachnoid hemorrhage (SAH) induced cerebral vasospasm. Using the two-hemorrhage SAH model in rats, we previously demonstrated that estradiol (E2) significantly attenuated the SAH-induced vasospasm by inhibiting the NOS2 expression. Adding ferrous citrate (FC) complexes to the primary cultured mouse cerebral endothelial cells (CEC) to mimic the SAH conditions, we also showed that FC up-regulates NOS2 through nuclear translocation of NFκB induced by free radicals generation. Here, we further studied the molecular mechanism underlying E2-mediated reduction of the FC-induced up-regulation of NOS2. Treatment with E2 (100 nM) reduced the FC (100 µM)-induced increases of free radical generation and the levels of NOS2 mRNA and protein in the CEC. Moreover, E2 also prevented the FC-induced increases of IκBα phosphorylation, NFκB nuclear translocation, NFκB binding onto the NOS2 promoter, and the NOS2 promoter luciferase activity. However, knock-down the estrogen receptor β (ERβ), but not ERα, abolished the E2-mediated prevention on the FC-induced increases of NOS2 mRNA and protein. The data from the present study suggest that E2 inhibited NOS2 gene expression by interfering with NFκB nuclear translocation and NFκB binding onto the NOS2 through an ERβ-mediated pathway. Our results provide the molecular basis for designing the applicable therapeutic or preventive strategies in the treatment SAH patients.

Dissociation of hyperglycemia from altered vascular contraction and relaxation mechanisms in caveolin-1 null mice

Hyperglycemia and endothelial dysfunction are associated with hypertension, but the specific causality and genetic underpinning are unclear. Caveolin-1 (cav-1) is a plasmalemmal anchoring protein and modulator of vascular function and glucose homeostasis. Cav-1 gene variants are associated with reduced insulin sensitivity in hypertensive individuals, and cav-1(-/-) mice show endothelial dysfunction, hyperglycemia, and increased blood pressure (BP). On the other hand, insulin-sensitizing therapy with metformin may inadequately control hyperglycemia while affecting the vascular outcome in certain patients with diabetes. To test whether the pressor and vascular changes in cav-1 deficiency states are related to hyperglycemia and to assess the vascular mechanisms of metformin under these conditions, wild-type (WT) and cav-1(-/-) mice were treated with either placebo or metformin (400 mg/kg daily for 21 days). BP and fasting blood glucose were in cav-1(-/-) > WT and did not change with metformin. Phenylephrine (Phe)- and KCl-induced aortic contraction was in cav-1(-/-) < WT; endothelium removal, the nitric-oxide synthase (NOS) blocker L-NAME (N(ω)-nitro-L-arginine methyl ester), or soluble guanylate cyclase (sGC) inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) enhanced Phe contraction, and metformin blunted this effect. Acetylcholine-induced relaxation was in cav-1(-/-) > WT, abolished by endothelium removal, L-NAME or ODQ, and reduced with metformin. Nitric oxide donor sodium nitroprusside was more potent in inducing relaxation in cav-1(-/-) than in WT, and metformin reversed this effect. Aortic eNOS, AMPK, and sGC were in cav-1(-/-) > WT, and metformin decreased total and phosphorylated eNOS and AMPK in cav-1(-/-). Thus, metformin inhibits both vascular contraction and NO-cGMP-dependent relaxation but does not affect BP or blood glucose in cav-1(-/-) mice, suggesting dissociation of hyperglycemia from altered vascular function in cav-1-deficiency states.

Function of the master energy regulator adenosine monophosphate-activated protein kinase in stroke

Adenosine monophosphate-activated protein kinase (AMPK) is an evolutionarily conserved signaling molecule that is emerging as one of the most important energy sensors in the body. AMPK monitors cellular energy status and is activated via phosphorylation when energy stores are low. This allows for maintenance of energy homeostasis by promoting catabolic pathways for ATP production and limiting processes that consume ATP. Growing number of stimuli have been shown to activate AMPK, and AMPK has been implicated in many diverse biological processes, including cell polarity, autophagy, and senescence. The effect of AMPK activation and its biological functions are extremely diverse and depend on both the overall energy "milieu" and the location and duration of activation. AMPK has tissue- and isoform-specific functions in the brain vs. periphery. These functions and the pathways activated also appear to differ by cell location (hypothalamus vs. cortex), cell type (astrocyte vs. neuron), and duration of exposure. Short bursts of AMPK activation have been found to be involved in ischemic preconditioning and neuronal survival; however, prolonged AMPK activity during ischemia leads to neuronal cell death. AMPK may also underlie some of the beneficial effects of hypothermia, a potential therapy for ischemic brain injury. This review discusses the role of AMPK in ischemic stroke, a condition of severe energy depletion.

Genetics of cerebral vasospasm

Cerebral vasospasm (CV) is a major source of morbidity and mortality in aneurysmal subarachnoid hemorrhage (aSAH). It is thought that an inflammatory cascade initiated by extravasated blood products precipitates CV, disrupting vascular smooth muscle cell function of major cerebral arteries, leading to vasoconstriction. Mechanisms of CV and modes of therapy are an active area of research. Understanding the genetic basis of CV holds promise for the recognition and treatment for this devastating neurovascular event. In our review, we summarize the most recent research involving key areas within the genetics and vasospasm discussion: (1) Prognostic role of genetics—risk stratification based on gene sequencing, biomarkers, and polymorphisms; (2) Signaling pathways—pinpointing key inflammatory molecules responsible for downstream cellular signaling and altering these mediators to provide therapeutic benefit; and (3) Gene therapy and gene delivery—using viral vectors or novel protein delivery methods to overexpress protective genes in the vasospasm cascade.

Suppression of the Rho/Rho-kinase pathway and prevention of cerebral vasospasm by combination treatment with statin and fasudil after subarachnoid hemorrhage in rabbit

The Rho/Rho-kinase pathway is considered important in the pathogenesis of sustained smooth muscle cell contraction during cerebral vasospasm after aneurysmal subarachnoid hemorrhage (SAH). The aims of this study were to investigate whether combination treatment, with pitavastatin as an inhibitor of RhoA and fasudil as an inhibitor of Rho-kinase, prevents the cerebral vasospasm. SAH was simulated using the double-hemorrhage rabbit model, and pitavastatin, or fasudil, or both (combination treatment) were administrated. The basilar artery (BA) cross-sectional area only in the combination treatment group was statistically larger than in the SAH group (p < 0.05). BA Rho-kinase, as measured by ELISA, was statistically reduced only in the combination treatment group compared with the SAH group (p < 0.05). In the other two treatment groups, pitavastatin or fasudil treatment group showed larger BA cross-sectional areas and lower value for BA Rho-kinase, but there were no statistically significant differences compared with the SAH group. The expression of endothelial nitric oxide synthase (eNOS), evaluated by immunohistochemistry in the pitavastatin group and the combination group, was higher than in the SAH group. Results indicate that combination treatment could extensively prevent cerebral vasospasm due to the synergic effect of combining pitavastatin and fasudil on the Rho/Rho-kinase pathway and on eNOS.

Liraglutide, a long-acting GLP-1 mimetic, and its metabolite attenuate inflammation after intracerebral hemorrhage

The inflammatory response plays a pivotal role in propagating injury of intracerebral hemorrhage (ICH). Glucagon-like-peptide-1 (GLP-1) is a hormone with antidiabetic effect and may also have antiinflammatory properties. Despite consensus that the glucoregulatory action is mediated by the GLP-1 receptor (GLP-1R), mechanisms in the brain remain unclear. We investigated the effect of a long-acting GLP-1 analog, liraglutide, and its truncated metabolite, GLP-1(9-36)a from dipeptidyl peptidase-4 (DPP-4) cleavage in ICH-induced brain injury. Primary outcomes were cerebral edema formation, neurobehavior, and inflammatory parameters. GLP-1(9-36)a, GLP-1R inhibitor, adenosine monophosphate-activated protein kinase (AMPK) phosphorylation inhibitor and DPP-4 inhibitor were administered to examine the mechanisms of action. Liraglutide suppressed neuroinflammation, prevented brain edema and neurologic deficit following ICH, which were partially reversed by GLP-1R inhibitor and AMPK phosphorylation inhibitor. Liraglutide-mediated AMPK phosphorylation was unaffected by GLP-1R inhibitor, and was found to be induced by GLP-1(9-36)a. GLP-1(9-36)a showed salutary effects on primary outcomes that were reversed by AMPK phosphorylation inhibitor but not by GLP-1R inhibitor. Liraglutide and DPP-4 inhibitor co-administration reversed liraglutide-mediated AMPK phosphorylation and antiinflammatory effects. Liraglutide exerted duals actions and the antiinflammatory effects are partially mediated by its metabolite in a phosphorylated AMPK-dependent manner. Therapies that inhibit GLP-1 degradation may weaken the metabolite-mediated effects.

Ferrous citrate up-regulates the NOS2 through nuclear translocation of NFκB induced by free radicals generation in mouse cerebral endothelial cells

Previous studies indicate that the inducible nitric oxide synthase 2 (NOS2) of the brain vascular tissue in experimental subarachnoid hemorrhage (SAH) rats is a critical factor for inducing cerebral vasospasm. However, the underlying molecular mechanisms remain to be elucidated. Here, we applied ferrous citrate (FC) complexes to the primary cultured mouse cerebral endothelial cell (CEC) to mimic the SAH conditions and to address the issue how SAH-induced NOS2 up-regulation. Using immunocytochemical staining technique, we demonstrated that NOS2 was expressed in the cultured CEC. Treatment of the CEC with FC induced increases of the intracellular level of ROS, nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB) nuclear translocation as well as NFκB binding onto the NOS promoter, and the levels of NOS2 mRNA and protein. These effects were abolished by pre-treatment of the cell with N-Acetyl-Cysteine (NAC), a reactive oxygen species (ROS) scavenger. In the present study, two previously predicted NFκB binding sites were confirmed in the NOS2 promoter within the range of −1529 bp to −1516 bp and −1224 bp to −1210 bp. Interestingly, both NFκB binding sites are involved in the FC-activated NOS2 transcriptional activity; the binding site located at −1529 bp to −1516 bp played a greater role than the other binding site located at −1224 bp to −1210 bp in the mouse CEC. These findings highlight the molecular mechanism underlying FC-induced up-regulation of NOS2 in the mouse CEC.

Ginsenoside Rb1 reverses H2O2-induced senescence in human umbilical endothelial cells: involvement of eNOS pathway

OBJECTIVE

Senescence of endothelial cells has been implicated in endothelial dysfunction and atherogenesis. This study investigated the effects of Rb1, a major ginsenoside in ginseng, on H2O2-induced senescence in primary human umbilical vein endothelial cells (HUVECs).

METHODS AND RESULTS

Real-time PCR and Western blot were used to detect the mRNA and protein expression, respectively. H2O2 (40∼100 μmol/L) effectively increased SA-β-gal activity and PAI-1 mRNA levels, two important senescence related biomarkers, in HUVECs, which were dramatically inhibited by Rb1 pre-incubation. Furthermore, Rb1 administration reversed the H2O2-decreased protein and mRNA levels of eNOS and its phosphorylation at Ser-1177, and the increased eNOS phosphorylation at Thr-495. As a result, Rb1 pretreatment restored the NO generation, as assayed by nitrate reductase method. However, pretreatment with L-NAME, a NOS inhibitor, abolished all the inhibitory effects of Rb1 on senescence. Importantly, Rb1 modulated the H2O2-altered caveolin-1 and pAkt, two most important regulators of eNOS expression and activity, in HUVECs.

CONCLUSIONS

We showed that Rb1 effectively protects HUVECs from senescence through eNOS modulation.

Acute therapeutic use of 5-aminoimidazole-4-carboxamide ribonucleoside extends survival interval in response to severe hemorrhagic shock

This study tests the hypothesis that pretreatment and/or posttreatment with 5-aminoimidazole-4-carboxamide ribonucleoside (AICAR), an inducer of adenosine monophosphate-activated protein, will extend the golden hour of survival time in rats subjected to severe hemorrhagic shock in the absence of available fluid resuscitation. Three days before hemorrhage, at 24-h intervals, animals were given three i.p. injections of AICAR (pretreatment) or saline (control/posttreatment). At the end of hemorrhage, animals (control/pretreatment) received a single i.v. injection of saline, whereas the posttreatment group received a single i.v. injection of AICAR (posttreatment). All treatment groups received the same total volume of fluid both before and immediately after hemorrhage. Both AICAR treatment groups had significantly(P < 0.01) extended survival time during the decompensatory phase of shock when compared with saline control group, pretreatment: 324 ± 21 min; posttreatment: 187 ± 16 min; and saline: 55 ± 10 min. Heart rate was significantly (P < 0.01) decreased following hemorrhage for pretreatment animals versus saline controls, 237 ± 16 vs. 312 ± 33 beats/min, respectively. Heart rate for both the pretreatment and posttreatment animals was also significantly (P < 0.01) lower after 30 min versus saline control group, pretreatment: 247 ± 13 beats/min; posttreatment: 240 ± 20 beats/min; saline: 415 ± 18 beats/min. Lactate levels were also significantly reduced 6.3 ± 0.71 mmol/L (pretreatment), 7.1 ± 0.47 mmol/L (posttreatment), 8.9 ± 0.21 mmol/L (saline). The improvement in hemodynamic stability is reflected in the significant increase in the golden-hour survival time in animals subjected to severe hemorrhagic shock.

Nitric oxide related pathophysiological changes following subarachnoid haemorrhage

Subarachnoid hemorrhage (SAH) comprises only about 7% of all strokes worldwide but is associated with severe mortality and morbidity. SAH is associated with a number of secondary pathologies, such as: transient cerebral vasospasm, delayed ischemic neuronal deficit (DIND), cortical spreading depression, microcirculatory modifications, microthrombosis and ischemic complications. Available data demonstrate that there are complex interactions among these secondary complications, and NO plays an important role among the interactions. NO has been implicated to be a crucial molecule in eliminating vasospasm, facilitating neuroprotection, anti-microthrombosis, cerebral ischemic tolerance and promoting endothelial cell function. Therefore, therapeutic agent targeting a key component in the pathopyhysiology of SAH such as NO and its related enzymes would be favorable for future development of SAH drugs. Alternatively, because of the complex nature of the secondary complications after SAH, agents with multiple efficacies on these complications, or the combination of several agents such as NO donors, oxide radical scavengers and neuroprotectants might be more desirable.

Simvastatin re-couples dysfunctional endothelial nitric oxide synthase in experimental subarachnoid hemorrhage

Reduced endothelial nitric oxide synthase (eNOS) function has been linked to secondary complications of subarachnoid hemorrhage (SAH). We previously found that there is increased eNOS function after SAH but that it is uncoupled, leading to secondary complications such as vasospasm, microthromboembolism and neuronal apoptosis. Here we test the hypothesis that recoupling eNOS with simvastatin can prevent these complications. SAH was created in mice that were treated with vehicle or simvastatin starting 2 weeks before or 30 minutes after SAH. SAH increased phosphorylated eNOS which was prevented by pre- or post-treatment with simvastatin. Simvastatin pre-treatment also prevented the increase in eNOS monomer formation that was associated with SAH, decreased superoxide anion radical production and increased NO. These changes were associated with decreased vasospasm, microthromboemboli and neuronal injury. The data suggest that simvastatin re-couples eNOS after SAH, leading to decreased secondary complications such as vasospasm, microthromboemboli and neuronal injury.

Endothelial nitric oxide synthase mediates endogenous protection against subarachnoid hemorrhage-induced cerebral vasospasm

BACKGROUND AND PURPOSE

Vasospasm-induced delayed cerebral ischemia remains a major source of morbidity in patients with aneurysmal subarachnoid hemorrhage (SAH). We hypothesized that activating innate neurovascular protective mechanisms by preconditioning (PC) may represent a novel therapeutic approach against SAH-induced vasospasm and neurological deficits and, secondarily, that the neurovascular protection it provides is mediated by endothelial nitric oxide synthase (eNOS).

METHODS

Wild-type mice were subjected to hypoxic PC or normoxia followed 24 hours later by SAH. Neurological function was analyzed daily; vasospasm was assessed on post-surgery Day 2. Nitric oxide availability, eNOS expression, and eNOS activity were also assessed. In a separate experiment, wild-type and eNOS-null mice were subjected to hypoxic PC or normoxia followed by SAH and assessed for vasospasm and neurological deficits.

RESULTS

PC nearly completely prevented SAH-induced vasospasm and neurological deficits. It also prevented SAH-induced reduction in nitric oxide availability and increased eNOS activity in mice with and without SAH. PC-induced protection against vasospasm and neurological deficits was lost in wild-type mice treated with the nitric oxide synthase inhibitor N(G)-nitro-l-arginine methyl ester and in eNOS-null mice.

CONCLUSIONS

Endogenous protective mechanisms against vasospasm exist, are powerful, and can be induced by PC. eNOS-derived nitric oxide is a critical mediator of PC-induced neurovascular protection. These data provide strong "proof-of-principle" evidence that PC represents a promising new strategy to reduce vasospasm and delayed cerebral ischemia after SAH.

Advances in experimental subarachnoid hemorrhage

Subarachnoid hemorrhage (SAH) remains to be a devastating disease with high mortality and morbidity. Two major areas are becoming the focus of the research interest of SAH: these are cerebral vasospasm (CVS) and early brain injury (EBI). This mini review will provide a broad summary of the major advances in experimental SAH during the last 3 years. Treatments interfering with nitric oxide (NO)- or endothelin-pathways continue to show antispasmotic effects in experimental SAH. HIF 1 may play both a detrimental and beneficial role in the setting of SAH, depending on its activation stage. Inflammation and oxidative stress contribute to the pathophysiology of both CVS and EBI. Apoptosis, a major component of EBI after SAH, also underlie the etiology of CVS. Since we recognize now that CVS and EBI are the two major contributors to the significant mortality and morbidity associated with SAH, ongoing research will continue to elucidate the underlying pathophysiological pathways and treatment strategies targeting both CVS and EBI may be more successful and improve outcome of patients with SAH.

Uncoupling of endothelial nitric oxide synthase after experimental subarachnoid hemorrhage

We studied whether endothelial nitric oxide synthase (eNOS) is upregulated and uncoupled in large cerebral arteries after subarachnoid hemorrhage (SAH) and also whether this causes cerebral vasospasm in a mouse model of anterior circulation SAH. Control animals underwent injection of saline instead of blood (n=16 SAH and n=16 controls). There was significant vasospasm of the middle cerebral artery 2 days after SAH (lumen radius/wall thickness ratio 4.3 ± 1.3 for SAH, 23.2 ± 2.1 for saline, P<0.001). Subarachnoid hemorrhage was associated with terminal deoxynucleotidyl transferase dUTP nick-end labeling, cleaved caspase-3, and Fluoro-Jade-positive neurons in the cortex and with CA1 and dentate regions in the hippocampus. There were multiple fibrinogen-positive microthromboemboli in the cortex and hippocampus after SAH. Transgenic mice expressing lacZ under control of the eNOS promoter had increased X-gal staining in large arteries after SAH, and this was confirmed by the increased eNOS protein on western blotting. Evidence that eNOS was uncoupled was found in that nitric oxide availability was decreased, and superoxide and peroxynitrite concentrations were increased in the brains of mice with SAH. This study suggests that artery constriction by SAH upregulates eNOS but that it is uncoupled and produces peroxynitrite that may generate microemboli that travel distally and contribute to brain injury.

Effects of tetramethylpyrazine on nitric oxide/cGMP signaling after cerebral vasospasm in rabbits

Tetramethylpyrazine (TMP), an ingredient of Chinese herbal Szechwan lovage rhizome, shows vasorelaxant effect. Cerebral vasospasm (CVS) after subarachnoid hemorrhage (SAH) is associated with high mortality and morbidity. Here, we evaluated the effect of TMP in a model of CVS and sought to identify the underlying mechanisms of action. A rabbit SAH model was established by injection of the autoblood via cisterna magna. Cerebral blood flow and arterial diameter were measured by Transcranial Doppler (TCD) and Computed Tomography Angiography (CTA). Expression of eNOS and PDE-V in basilar artery (BA) was assessed by western blots. Levels of nitric oxide (NO) in plasma and cerebral spinal fluid, and of intra-endothelium Ca(2+) were measured. Significantly reduced diameter and accelerated blood flow velocity were detected in BAs of SAH animals (P<0.05 vs. sham group). Expression of eNOS and NO was increased, and PDE-V expression was reduced by TMP.TMP ameliorated cerebral vasospasm (P<0.05 vs. SAH group), and L-NAME (a NOS inhibitor) partly abrogated the effects of TMP. TMP induced a dose-dependent increase of intra-endothelium Ca(2+). The current results demonstrated that the vasorelaxant effect of TMP was at least in part via regulation of NO/cGMP signaling.

Effects of metformin in experimental stroke

BACKGROUND AND PURPOSE

Adenosine 5'-monophosphate-activated protein kinase (AMPK) is an important sensor of energy balance. Stroke-induced AMPK activation is deleterious because both pharmacological inhibition and genetic deletion of AMPK are neuroprotective. Metformin is a known AMPK activator but reduces stroke incidence in clinical populations. We investigated the effect of acute and chronic metformin treatment on infarct volume and AMPK activation in experimental stroke.

METHODS

Male mice were subjected to middle cerebral artery occlusion after acute (3 days) or chronic (3 weeks) administration of metformin. Infarct volumes, AMPK activation, lactate accumulation, and behavioral outcomes were assessed. The roles of neuronal nitric oxide synthase and AMPK were examined using mice with targeted deletion of AMPK or neuronal nitric oxide synthase.

RESULTS

Acute metformin exacerbated stroke damage, enhanced AMPK activation, and led to metabolic dysfunction. This effect was lost in AMPK and neuronal nitric oxide synthase knockout mice. In contrast, chronic metformin given prestroke was neuroprotective, improved stroke-induced lactate generation, and ameliorated stroke-induced activation of AMPK. Similarly, the neuroprotective effect of chronic prestroke metformin was lost in neuronal nitric oxide synthase knockout mice.

CONCLUSIONS

AMPK is an important potential target for stroke treatment and prevention. These studies show that the timing, duration, and amount of AMPK activation are key factors in determining the ultimate downstream effects of AMPK on the ischemic brain.

AMPK inhibition in health and disease

All living organisms depend on dynamic mechanisms that repeatedly reassess the status of amassed energy, in order to adapt energy supply to demand. The AMP-activated protein kinase (AMPK) alphabetagamma heterotrimer has emerged as an important integrator of signals managing energy balance. Control of AMPK activity involves allosteric AMP and ATP regulation, auto-inhibitory features and phosphorylation of its catalytic (alpha) and regulatory (beta and gamma) subunits. AMPK has a prominent role not only as a peripheral sensor but also in the central nervous system as a multifunctional metabolic regulator. AMPK represents an ideal second messenger for reporting cellular energy state. For this reason, activated AMPK acts as a protective response to energy stress in numerous systems. However, AMPK inhibition also actively participates in the control of whole body energy homeostasis. In this review, we discuss recent findings that support the role and function of AMPK inhibition under physiological and pathological states.

Effects of AMP-activated protein kinase in cerebral ischemia

AMP-activated protein kinase (AMPK) is a serine threonine kinase that is highly conserved through evolution. AMPK is found in most mammalian tissues including the brain. As a key metabolic and stress sensor/effector, AMPK is activated under conditions of nutrient deprivation, vigorous exercise, or heat shock. However, it is becoming increasingly recognized that changes in AMPK activation not only signal unmet metabolic needs, but also are involved in sensing and responding to 'cell stress', including ischemia. The downstream effect of AMPK activation is dependent on many factors, including the severity of the stressor as well as the tissue examined. This review discusses recent in vitro and in vivo studies performed in the brain/neuronal cells and vasculature that have contributed to our understanding of AMPK in stroke. Recent data on the potential role of AMPK in angiogenesis and neurogenesis and the interaction of AMPK with 3-hydroxy-3-methy-glutaryl-CoA reductase inhibitors (statins) agents are highlighted. The interaction between AMPK and nitric oxide signaling is also discussed.