Role of endothelial nitric oxide synthetase in arteriogenesis after stroke in mice

The Unexpected Role of the Endothelial Nitric Oxide Synthase at the Neurovascular Unit: Beyond the Regulation of Cerebral Blood Flow

Nitric oxide (NO) is a highly versatile gasotransmitter that has first been shown to regulate cardiovascular function and then to exert tight control over a much broader range of processes, including neurotransmitter release, neuronal excitability, and synaptic plasticity. Endothelial NO synthase (eNOS) is usually far from the mind of synaptic neurophysiologists, who have focused most of their attention on neuronal NO synthase (nNOS) as the primary source of NO at the neurovascular unit (NVU). Nevertheless, the available evidence suggests that eNOS could also contribute to generating the burst of NO that, serving as volume intercellular messenger, is produced in response to neuronal activity in the brain parenchyma. Herein, we review the role of eNOS in both the regulation of cerebral blood flow and of synaptic plasticity and discuss the mechanisms by which cerebrovascular endothelial cells may transduce synaptic inputs into a NO signal. We further suggest that eNOS could play a critical role in vascular-to-neuronal communication by integrating signals converging onto cerebrovascular endothelial cells from both the streaming blood and active neurons.

Traditional uses, chemical compounds, pharmacological activities and clinical studies on the traditional Chinese prescription Yi-Gan San

ETHNOPHARMACOLOGICAL RELEVANCE

A widely used traditional prescription, Yi-Gan San (YGS) is a remedy for neurodegenerative disorders. The formulation consists of seven Chinese medicinal materials in specific proportions, namely Uncariae Ramulus cum Uncis (Uncaria rhynchophylla (Miq.) Miq. ex Havil.), Bupleuri Radix (Bupleurum chinense DC.), Angelicae Sinensis Radix (Angelica sinensis (Oliv.) Diels), Chuanxiong Rhizoma (Ligusticum wallichii Franch.), Poria (Poria cocos (Schw.) Wolf), Atractylodis Macrocephalae Rhizoma (Atractylodes macrocephala Koidz.) and Glycyrrhizae Radix et Rhizoma (Glycyrrhiza uralensis Fisch.). Using YGS has been shown to alleviate various behavioural and psychological symptoms of dementia (BPSD).

AIM OF THIS REVIEW

The goal of this review is to give up-to-date information about the traditional uses, chemistry, pharmacology and clinical efficacy of YGS based on the scientific literature and to learn the current focus and provide references in the next step.

MATERIALS AND METHODS

The database search room was accessed using the search terms "Yi-Gan San" and "Yokukansan" to obtain results from resources such as Web of Science, PubMed, Google Scholar and Sci Finder Scholar. We not only consulted the literature of fellow authors for this review but also explored classical medical books.

RESULTS

YGS has been used to cure neurosis, sleeplessness, night weeping and restlessness in infants. Its chemical components primarily consist of triterpenes, flavonoids, phenolics, lactones, alkaloids and other types of compounds. These active ingredients displayed diverse pharmacological activities to ameliorate BPSD by regulating serotonergic, glutamatergic, cholinergic, dopaminergic, adrenergic, and GABAergic neurotransmission. In addition, YGS showed neuroprotective, antistress, and anti-inflammatory effects. The majority of cases of neurodegenerative disorders are treated with YGS, including Alzheimer's disease and dementia with Lewy bodies.

CONCLUSIONS

Based on previous studies, YGS has been used as a traditional prescription in East Asia, such as Japan, Korea and China, and it has diverse chemical compounds and multiple pharmacological activities. Nevertheless, few experimental studies have focused on chemical and quantitative YGS studies, suggesting that further comprehensive research on its chemicals and quality assessments is critical for future evaluations of drug efficacy.

Structural brain abnormalities in endothelial nitric oxide synthase-deficient mice revealed by high-resolution magnetic resonance imaging

INTRODUCTION

Endothelial nitric oxide synthase (eNOS) produces nitric oxide, which is essential for a variety of physiological functions in the brain. Previous work has demonstrated the detrimental effects of eNOS deficiency on brain function in male eNOS knockout (eNOS KO) mice. However, the effect of eNOS deficiency on brain structure and any association between these effects and sex is unknown.

METHODS

This study used three-dimensional high-resolution ex vivo magnetic resonance imaging and behavioral tests of anxiety and cognitive performance to investigate structure-function relationships in the brain of female and male eNOS KO mice in young adulthood.

RESULTS

While there were no differences in anxiety-like behavior or locomotion, there was a sex-specific deficit in contextual fear memory retention in male, but not in female, eNOS mice compared to wild-type controls. Moreover, we found that eNOS deficiency induced changes in multiple brain regions that are involved in learning and fear memory including the hippocampus, amygdala, hypothalamus, and areas of the cortex. Several of these MRI-detectable neuroanatomical changes were dependent on sex.

CONCLUSION

The observation that eNOS deficiency impacts brain structure at an early age demonstrates the importance of eNOS for healthy brain development.

Endothelial Cells and the Cerebral Circulation

Endothelial cells form the innermost layer of all blood vessels and are the only vascular component that remains throughout all vascular segments. The cerebral vasculature has several unique properties not found in the peripheral circulation; this requires that the cerebral endothelium be considered as a unique entity. Cerebral endothelial cells perform several functions vital for brain health. The cerebral vasculature is responsible for protecting the brain from external threats carried in the blood. The endothelial cells are central to this requirement as they form the basis of the blood-brain barrier. The endothelium also regulates fibrinolysis, thrombosis, platelet activation, vascular permeability, metabolism, catabolism, inflammation, and white cell trafficking. Endothelial cells regulate the changes in vascular structure caused by angiogenesis and artery remodeling. Further, the endothelium contributes to vascular tone, allowing proper perfusion of the brain which has high energy demands and no energy stores. In this article, we discuss the basic anatomy and physiology of the cerebral endothelium. Where appropriate, we discuss the detrimental effects of high blood pressure on the cerebral endothelium and the contribution of cerebrovascular disease endothelial dysfunction and dementia. © 2022 American Physiological Society. Compr Physiol 12:3449-3508, 2022.

Changes in the Plasma and Platelet Nitric Oxide Biotransformation Metabolites during Ischemic Stroke-A Dynamic Human LC/MS Metabolomic Study

Despite improvement in the management of modifiable cardiovascular risk factors, ischemic stroke remains the leading cause of morbidity and mortality in the adult population. The aim of this study was to analyze the time-dependent dynamic differences in expression of the nitric oxide (NO) metabolic pathway in the platelet and plasma compartment between subjects with and without ischemic stroke. Additionally, the interplay between these parameters and platelet aggregation was investigated. A total of 418 patients in acute phase of non-cardioembolic stroke were investigated. Following the inclusion and exclusion criteria, finally 40 subjects with stroke and 39 demographically matched healthy participants were enrolled. Neurological physical examination, followed by assessment of the platelet and plasma levels of the nitric oxide synthase (NOS) inhibitors, including asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA), as well as NOS substrate-L-Arginine were performed dynamically three times within the first 24-h, then on the 3rd and 7th day after the stroke onset, which was compared with the healthy control. The platelet L-Arginine concentration was significantly higher on the 1st and 3rd day of stroke, while the plasma levels were significantly lower on exact days in comparison to the control. The competitive NOS-inhibitors in platelets were stably elevated in stroke subjects, whereas no significant differences in plasma compartment were noted. The arachidonic-acid-induced platelet aggregation was negatively associated with the platelet NOS substrate bioavailability, as assessed by the L−Arginine ADMA-ratio on the 3rd and 7th day. Subjects with non-cardioembolic ischemic stroke are characterized by elevated platelet levels of NOS inhibitors. Management of stroke results in increasing the platelet L-Arginine concentration and subsequent NO bioavailability in the platelet compartment.

Downregulation of the endothelial histone demethylase JMJD3 is associated with neointimal hyperplasia of arteriovenous fistulas in kidney failure

Jumonji domain-containing protein-3 (JMJD3), a histone H3 lysine 27 (H3K27) demethylase, promotes endothelial regeneration, but its function in neointimal hyperplasia (NIH) of arteriovenous fistulas (AVFs) has not been explored. In this study, we examined the contribution of endothelial JMJD3 to NIH of AVFs and the mechanisms underlying JMJD3 expression during kidney failure. We found that endothelial JMJD3 expression was negatively associated with NIH of AVFs in patients with kidney failure. JMJD3 expression in endothelial cells (ECs) was also downregulated in the vasculature of chronic kidney disease (CKD) mice. In addition, specific knockout of endothelial JMJD3 delayed EC regeneration, enhanced endothelial mesenchymal transition, impaired endothelial barrier function as determined by increased Evans blue staining and inflammatory cell infiltration, and accelerated neointima formation in AVFs created by venous end to arterial side anastomosis in CKD mice. Mechanistically, JMJD3 expression was downregulated via binding of transforming growth factor beta 1-mediated Hes family transcription factor Hes1 to its gene promoter. Knockdown of JMJD3 enhanced H3K27 methylation, thereby inhibiting transcriptional activity at promoters of EC markers and reducing migration and proliferation of ECs. Furthermore, knockdown of endothelial JMJD3 decreased endothelial nitric oxide synthase expression and nitric oxide production, leading to the proliferation of vascular smooth muscle cells. In conclusion, we demonstrate that decreased expression of endothelial JMJD3 impairs EC regeneration and function and accelerates neointima formation in AVFs. We propose increasing the expression of endothelial JMJD3 could represent a new strategy for preventing endothelial dysfunction, attenuating NIH, and improving AVF patency in patients with kidney disease.

Endothelial Piezo1 sustains muscle capillary density and contributes to physical activity

Piezo1 forms mechanically activated nonselective cation channels that contribute to endothelial response to fluid flow. Here we reveal an important role in the control of capillary density. Conditional endothelial cell-specific deletion of Piezo1 in adult mice depressed physical performance. Muscle microvascular endothelial cell apoptosis and capillary rarefaction were evident and sufficient to account for the effect on performance. There was selective upregulation of thrombospondin-2 (TSP2), an inducer of endothelial cell apoptosis, with no effect on TSP1, a related important player in muscle physiology. TSP2 was poorly expressed in muscle endothelial cells but robustly expressed in muscle pericytes, in which nitric oxide (NO) repressed the Tsp2 gene without an effect on Tsp1. In endothelial cells, Piezo1 was required for normal expression of endothelial NO synthase. The data suggest an endothelial cell-pericyte partnership of muscle in which endothelial Piezo1 senses blood flow to sustain capillary density and thereby maintain physical capability.

Remote Ischemic Conditioning: A Potential Treatment for Chronic Cerebral Hypoperfusion

BACKGROUND

Chronic cerebral hypoperfusion (CCH) is a clinical syndrome, which is characterized by significantly decreased cerebral blood flow (CBF). CCH is a common consequence of cerebrovascular and cardiovascular diseases and the elderly. CCH results in a series of pathological damages, increasing cell death, autophagy dysfunction, amyloid β (Aβ) peptide accumulation, blood-brain barrier (BBB) disruption, and endothelial damage, which are found in CCH models. In addition, CCH is a prominent risk factor of cognitive impairment, such as vascular dementia, and CCH contributes to the occurrence and development of Alzheimer's disease. Therefore, the treatment of patients with CCH is of great value. It has been confirmed that remote ischemic conditioning (RIC) is a safe, promising treatment for acute and chronic cerebrovascular diseases. RIC significantly increases CBF in both CCH models and patients, inhibits neuronal apoptosis, reduces Aβ deposition, protects BBB integrity and endothelial function, alleviates neuroinflammation, improves cognitive impairment, and exerts neuroprotection.

SUMMARY

With the development of animal models, the pathophysiological mechanisms of CCH and RIC are increasingly revealed. Key Messages: We discuss the mechanisms related to hypoperfusion in the brain and explore the potential treatment of RIC for CCH to promote its transformation and application in humans.

Endothelial Nitric Oxide Synthase-Deficient Mice: A Model of Spontaneous Cerebral Small-Vessel Disease

Age-related cerebral small-vessel disease (CSVD) is a major cause of stroke and dementia. Despite a widespread acceptance of small-vessel arteriopathy, lacunar infarction, diffuse white matter injury, and cognitive impairment as four cardinal features of CSVD, a unifying pathologic mechanism of CSVD remains elusive. Herein, we introduce partial endothelial nitric oxide synthase (eNOS)-deficient mice as a model of age-dependent, spontaneous CSVD. These mice developed cerebral hypoperfusion and blood-brain barrier leakage at a young age, which progressively worsened with advanced age. Their brains exhibited elevated oxidative stress, astrogliosis, cerebral amyloid angiopathy, microbleeds, microinfarction, and white matter pathology. Partial eNOS-deficient mice developed gait disturbances at middle age, and hippocampus-dependent memory deficits at older ages. These mice also showed enhanced expression of bone morphogenetic protein 4 (BMP4) in brain pericytes before myelin loss and white matter pathology. Because BMP4 signaling not only promotes astrogliogenesis but also blocks oligodendrocyte differentiation, we posit that paracrine actions of BMP4, localized within the neurovascular unit, promote white matter disorganization and neurodegeneration. These observations point to BMP4 signaling pathway in the aging brain vasculature as a potential therapeutic target. Finally, because studies in partial eNOS-deficient mice corroborated recent clinical evidence that blood-brain barrier disruption is a primary cause of white matter pathology, the mechanism of impaired nitric oxide signaling-mediated CSVD warrants further investigation.

Soluble Interleukin-6 Receptor Regulates Interleukin-6-Dependent Vascular Remodeling in Long-Distance Runners

Little is known about the effects of training load on exercise-induced plasma increase of interleukin-6 (IL-6) and soluble IL-6 receptor (sIL-6R) and their relationship with vascular remodeling. We sought to evaluate the role of sIL 6R as a regulator of IL-6-induced vascular remodeling. Forty-four male marathon runners were recruited and allocated into two groups: low-training (LT, <100 km/week) and high-training (HT, ≥100 km/week), 22 athletes per group. Twenty-one sedentary participants were used as reference. IL-6, sIL-6R and sgp130 levels were measured in plasma samples obtained before and immediately after finishing a marathon (42.2-km). Aortic diameter was measured by echocardiography. The inhibitory effect of sIL-6R on IL-6-induced VSMC migration was assessed using cultured A7r5 VSMCs. Basal plasma IL-6 and sIL-6R levels were similar among sedentary and athlete groups. Plasma IL-6 and sIL-6R levels were elevated after the marathon, and HT athletes had higher post-race plasma sIL-6R, but not IL-6, level than LT athletes. No changes in sgp130 plasma levels were found in LT and HT groups before and after running the marathon. Athletes had a more dilated ascending aorta and aortic root than sedentary participants with no differences between HT and LT athletes. However, a positive correlation between ascending aorta diameter and plasma IL-6 levels corrected by training load and years of training was observed. IL-6 could be responsible for aorta dilation because IL-6 stimulated VSMC migration in vitro, an effect that is inhibited by sIL-6R. However, IL-6 did not modify cell proliferation, collagen type I and contractile protein of VSMC. Our results suggest that exercise induces vascular remodeling. A possible association with IL-6 is proposed. Because sIL-6R inhibits IL-6-induced VSMC migration, a possible mechanism to regulate IL-6-dependent VSMC migration is also proposed.

DL-3-n-butylphthalide Increases Collateriogenesis and Functional Recovery after Focal Ischemic Stroke in Mice

Recent evidence indicates that collateral circulation is critical for the outcome of ischemic stroke. DL-3-n-butylphthalide (NBP), a synthesized compound based on an extract from seeds of celery Apium graveolens Linn, has been used as a therapeutic drug, showing multiple neuroprotective and regenerative activities. A potential effect of NBP on collateral arterial regulation is unknown. We examined the effects of NBP on arteriogenesis of collateral arteries in vitro and a mouse ischemic stroke model. In cultures of mouse iPS cell-derived vascular progenitors, NBP (10 μM) significantly increased α-smooth muscle actin (αSMA)/CD-31 co-labeled cells and the expression of newly formed vasculature marker PDGFRα. A sensorimotor cortex ischemia was induced in transgenic mice expressing αSMA-GFP that allowed direct observation of arterial vasculatures in brain regions. NBP (80 mg/kg) was intranasally delivered 1 hr after stroke and once daily for 14 days. To label proliferating cells, 5-Bromo-2’-deoxyuridine (BrdU, 50 mg/kg, i.p.) was administrated every day from 3 days after stroke. Western blotting of peri-infarct tissue detected increased expressions of VEGF, Ang-1 and reduced nNOS level in NBP-treated mice. The NBP treatment significantly increased αSMA/BrdU co-labeled cells, the diameter of ipsilateral collaterals, and arterial area in ischemic and peri-infarct regions examined 14 days after stroke. Examined 3 days after stroke, NBP prevented functional deficits in the cylinder test and corner test. The NBP treatment of 14 days improved the local cerebral blood flow (LCBF) and functional performance in multiple tests. Thus, NBP promotes collateriogenesis, short and long-term structural and functional improvements after ischemic stroke.

Delayed rFGF21 Administration Improves Cerebrovascular Remodeling and White Matter Repair After Focal Stroke in Diabetic Mice

Type 2 diabetes mellitus (T2DM) is a major comorbidity exacerbating ischemic brain injury and impairing post-stroke recovery. Our previous study suggested that recombinant human fibroblast growth factor (rFGF) 21 might be a potent therapeutic targeting multiple aspects of pathophysiology in T2DM stroke. This study aims to evaluate the potential effects of rFGF21 on cerebrovascular remodeling after T2DM stroke. Permanent distal middle cerebral artery occlusion was performed in heterozygous non-diabetic db/ + and homozygous diabetic db/db mice. Daily rFGF21 administration was initiated 1 week after stroke induction and maintained for up to 2 weeks thereafter. Multiple markers associated with post-stroke recovery, including angiogenesis, oligodendrogenesis, white matter integrity, and neurogenesis, were assessed up to 3 weeks after stroke. Our results showed an impairment in post-stroke vascular remodeling under T2DM condition, reflected by the decreased expression of trophic factors in brain microvessels and impairments of angiogenesis. The defected cerebrovascular remodeling was accompanied by the decreased oligodendrogenesis and neurogenesis. However, delayed rFGF21 administration normalized post-stroke hyperglycemia and improved neurological outcomes, which may partially be via the promotion of pro-angiogenic trophic factor expression in brain microvessels and cerebrovascular remodeling. The better cerebrovascular remodeling may also contribute to oligodendrogenesis, white matter integrity, and neurogenesis after T2DM stroke. Therefore, delayed rFGF21 administration may improve neurological outcomes in T2DM stroke mice, at least in part by normalizing the metabolic abnormalities and promoting cerebrovascular remodeling and white matter repair.

Nitric Oxide-Dependent Pathways as Critical Factors in the Consequences and Recovery after Brain Ischemic Hypoxia

Brain ischemia is one of the leading causes of disability and mortality worldwide. Nitric oxide (NO^•), a molecule that is involved in the regulation of proper blood flow, vasodilation, neuronal and glial activity constitutes the crucial factor that contributes to the development of pathological changes after stroke. One of the early consequences of a sudden interruption in the cerebral blood flow is the massive production of reactive oxygen and nitrogen species (ROS/RNS) in neurons due to NO^• synthase uncoupling, which leads to neurotoxicity. Progression of apoptotic or necrotic neuronal damage activates reactive astrocytes and attracts microglia or lymphocytes to migrate to place of inflammation. Those inflammatory cells start to produce large amounts of inflammatory proteins, including pathological, inducible form of NOS (iNOS), which generates nitrosative stress that further contributes to brain tissue damage, forming vicious circle of detrimental processes in the late stage of ischemia. S-nitrosylation, hypoxia-inducible factor 1α (HIF-1α) and HIF-1α-dependent genes activated in reactive astrocytes play essential roles in this process. The review summarizes the roles of NO^•-dependent pathways in the early and late aftermath of stroke and treatments based on the stimulation or inhibition of particular NO^• synthases and the stabilization of HIF-1α activity.

Increasing O-GlcNAcylation is neuroprotective in young and aged brains after ischemic stroke

Spliced X-box binding protein-1 (XBP1s) together with the hexosamine biosynthetic pathway (HBP) and O-GlcNAcylation forms the XBP1s/HBP/O-GlcNAc axis. Our previous studies have provided evidence that activation of this axis is neuroprotective after ischemic stroke and critically, ischemia-induced O-GlcNAcylation is impaired in the aged brain. However, the XBP1s' neuroprotective role and its link to O-GlcNAcylation in stroke, as well as the therapeutic potential of targeting this axis in stroke, have not been well established. Moreover, the mechanisms underlying this age-related impairment of O-GlcNAcylation induction after brain ischemia remain completely unknown. In this study, using transient ischemic stroke models, we first demonstrated that neuron-specific overexpression of Xbp1s improved outcome, and pharmacologically boosting O-GlcNAcylation with thiamet-G reversed worse outcome observed in neuron-specific Xbp1 knockout mice. We further showed that thiamet-G treatment improved long-term functional recovery in both young and aged animals after transient ischemic stroke. Mechanistically, using an analytic approach developed here, we discovered that availability of UDP-GlcNAc was compromised in the aged brain, which may constitute a novel mechanism responsible for the impaired O-GlcNAcylation activation in the aged brain after ischemia. Finally, based on this new mechanistic finding, we evaluated and confirmed the therapeutic effects of glucosamine treatment in young and aged animals using both transient and permanent stroke models. Our data together support that increasing O-GlcNAcylation is a promising strategy in stroke therapy.

Role of Interleukin-6 in Vascular Health and Disease

IL-6 is usually described as a pleiotropic cytokine produced in response to tissue injury or infection. As a pro-inflammatory cytokine, IL-6 activates innate and adaptative immune responses. IL-6 is released in the innate immune response by leukocytes as well as stromal cells upon pattern recognition receptor activation. IL-6 then recruits immune cells and triggers B and T cell response. Dysregulated IL-6 activity is associated with pathologies involving chronic inflammation and autoimmunity, including atherosclerosis. However, IL-6 is also produced and released under beneficial conditions, such as exercise, where IL-6 is associated with the anti-inflammatory and metabolic effects coupled with physical adaptation to intense training. Exercise-associated IL-6 acts on adipose tissue to induce lipogenesis and on arteries to induce adaptative vascular remodeling. These divergent actions could be explained by complex signaling networks. Classical IL-6 signaling involves a membrane-bound IL-6 receptor and glycoprotein 130 (gp130), while trans-signaling relies on a soluble version of IL-6R (sIL-6R) and membrane-bound gp130. Trans-signaling, but not the classical pathway, is regulated by soluble gp130. In this review, we discuss the similarities and differences in IL-6 cytokine and myokine signaling to explain the differential and opposite effects of this protein during inflammation and exercise, with a special focus on the vascular system.

Endogenous THBD (Thrombomodulin) Mediates Angiogenesis in the Ischemic Brain—Brief Report

Objective:

THBD (thrombomodulin) is part of the anticoagulant protein C-system that acts at the endothelium and is involved in anti-inflammatory and barrier-stabilizing processes. A recombinant soluble form of THBD was shown to have protective effects in different organs, but how the endogenous THBD is regulated during ischemia, particularly in the brain is not known to date. The aim of this study was to investigate the role of THBD, especially in brain endothelial cells, during ischemic stroke.

Approach and Results:

To induce ischemic brain damage, we occluded the middle cerebral artery of mice. We found an increased endothelial expression of Thbd in the peri-infarct area, whereas in the core of the ischemic tissue Thbd expression was decreased compared with the contralateral side. We generated a novel Cre/loxP-based mouse line that allows for the inducible deletion of Thbd specifically in brain endothelial cells, which worsened stroke outcome 48 hours after middle cerebral artery occlusion. Unexpectedly, we found no signs of increased coagulation, thrombosis, or inflammation in the brain but decreased vessel diameters and impaired angiogenesis in the peri-infarct area that led to a reduced overall vessel length 1 week after stroke induction.

Conclusions:

Endogenous THBD acts as a protective factor in the brain during ischemic stroke and enhances vessel diameter and proliferation. These previously unknown properties of THBD could offer new opportunities to affect vessel function after ischemia and thereby improve stroke outcome.

Nitric Oxide in Dental Pulp Tissue: From Molecular Understanding to Clinical Application in Regenerative Endodontic Procedures

Nitric oxide (NO), which is synthesized by the enzyme NO synthase (NOS), is a versatile endogenous molecule with multiple biological effects on many tissues and organs. In dental pulp tissue, NO has been found to play multifaceted roles in regulating physiological activities, inflammation processes, and tissue repair events, such as cell proliferation, neuronal degeneration, angiogenesis, and odontoblastic differentiation. However, there is a deficiency of detailed discussion on the NO-mediated interactions between inflammation and reparative/regenerative responses in wounded dental pulp tissue, which is a central determinant of ultimate clinical outcomes. Thus, the purpose of this review is to outline the current molecular understanding on the roles of Janus-faced molecule NO in dental pulp physiology, inflammation, and reparative activities. Based on this knowledge, advanced physicochemical techniques designed to manipulate the therapeutic potential of NOS and NO production in endodontic regeneration procedures are further discussed. Impact statement The interaction between inflammation and reparative/regenerative responses is very important for regenerative endodontic procedures, which are biologically based approaches intended to replace damaged tissues. Inside dental pulp tissue, endogenous nitric oxide (NO) is generated mainly by immunocompetent cells and dental pulp cells and mediates not only inflammatory/immune activities but also signaling cascades that regulate tissue repair and reconstruction, indicating its involvement in both tissue destruction and regeneration. Thus, it is feasible that NO acts as one of the indicators and modulators in dental pulp repair or regeneration under physiological and pathological conditions.

Transdermal delivery of glyceryl trinitrate: clinical applications in acute stroke

Introduction: Glyceryl trinitrate (GTN), a nitric oxide donor, is a candidate treatment for the management of acute stroke with hemodynamic and potential reperfusion and neuroprotective effects.Areas covered: Here we discuss the evidence to date from clinical trials and present and future possibilities for the clinical application of transdermal GTN in acute stroke. When administered as a transdermal patch during the acute and subacute phases after stroke, GTN was safe, lowered blood pressure, maintained cerebral blood flow, and did not induce cerebral steal or alter functional outcome. However, when given within the hyperacute phase (<6 h of stroke onset), GTN reduced death and dependency, death, disability, cognitive impairment, and mood disturbance, and improved quality of life. However, in a large prehospital trial with treatment within 4 h, GTN did not influence clinical outcomes.Expert opinion: Transdermal GTN is an easy to administer BP-lowering therapy, which is safe when given after 2 h of stroke onset, may improve outcome when initiated within 2-6 h, but should be avoided (outside of a clinical trial) in the ultra-acute period within 2 h of stroke onset. Further research needs to investigate the mechanisms of benefit or harm in ultra/hyperacute stroke patients.

Rehmannioside A attenuates cognitive deficits in rats with vascular dementia (VD) through suppressing oxidative stress, inflammation and apoptosis

Vascular dementia (VD) is a degenerative cerebrovascular disorder, leading to progressive decline of cognitive abilities and memory. Rehmannioside A (ReA) is isolated from Rehmanniae Radix, which exhibits protective role against various diseases. The present study was performed to calculate the possible neuroprotective effects of ReA on VD. Here, the morris water maze (MWM) test and electrophysiological recordings indicated that ReA reduced cognitive deficits. Additionally, through hematoxylin and eosin (H&E) and Nissl staining, ReA attenuated the histological alterations of hippocampus in rats with VD. ReA group significantly reduced oxidative stress, inflammatory response and apoptosis in the hippocampus of rats with VD, which was linked to the activation of nuclear erythroid related factor-2 (Nrf2), while the inactivation of nuclear factor-κB (NF-κB) and Caspase-3. Further, the anti-oxidative, anti-inflammatory and anti-apoptosis abilities of ReA were confirmed in cells stimulated by hydrogen peroxide. Overall, the results above demonstrated the protective effects of ReA against cognitive deficits and indicated the potential value of ReA in the therapy of VD in future.

Ac2-26 ameliorates lung ischemia-reperfusion injury via the eNOS pathway

BACKGROUND

Lung ischemia-reperfusion injury (LIRI) is a major complication after lung transplantation. Annexin A1 (AnxA1) ameliorates inflammation in various injured organs. This study aimed to determine the effects and mechanism of AnxA1 on LIRI after lung transplantation.

METHODS

Thirty-two rats were randomized into sham, saline, Ac2-26 and Ac2-26/L groups. Rats in the saline, Ac2-26 and Ac2-26/L groups underwent left lung transplantation and received saline, Ac2-26, and Ac2-26/L-NIO, respectively. After 24 h of reperfusion, serum and transplanted lung tissues were examined.

RESULTS

The partial pressure of oxygen (PaO₂) was increased in the Ac2-26 group compared to that in the saline group but was decreased by L-NIO treatment. In the Ac2-26 group, the wet-to-dry (W/D) weight ratios, total protein concentrations, proinflammatory factors and inducible nitric oxide synthase levels were notably decreased, but the concentrations of anti-inflammatory factors and endothelial nitric oxide synthase levels were significantly increased. Ac2-26 attenuated histological injury and cell apoptosis, and this improvement was reversed by L-NIO.

CONCLUSIONS

Ac2-26 reduced LIRI and improved alveoli-capillary permeability by inhibiting oxygen stress, inflammation and apoptosis. The protective effect of Ac2-26 on LIRI largely depended on the endothelial nitric oxide synthase pathway.

Impaired Cognitive Performance in Endothelial Nitric Oxide Synthase Knockout Mice After Ischemic Stroke: A Pilot Study

OBJECTIVES

Cognitive dysfunction and dementia are common following ischemic stroke. Endothelial nitric oxide synthase (eNOS) has been found to play an important role in neurologic function and cognition. The purpose of the present study was to assess the specific role of eNOS in cognitive performance after stroke.

DESIGN

Male wild-type and mice lacking eNOS (eNOS) underwent middle cerebral artery occlusion or sham-surgery. Primary outcomes were repeated measures of neurologic score, limb asymmetry, sensory/motor function, and spatial memory/learning assessed at intervals up to 28 days postsurgery. Group differences in brain microglia activation and infiltration and levels of interferon-gamma were examined.

RESULTS

There was no genotype × surgery interaction effect on the pattern of change in neurologic score, limb asymmetry, or sensory motor function across the 28 days postsurgery. In the Morris water maze, eNOS-/- middle cerebral artery occlusion mice displayed learning and memory deficits not evident in wild-type middle cerebral artery occlusion mice. Poorer spatial memory and learning in eNOS-/- middle cerebral artery occlusion mice was associated with a reduction in the number of activated microglia in the striatum on the lesion side and decreased brain tissue levels of interferon-gamma.

CONCLUSIONS

This study's data support a role for eNOS in cognitive performance after stroke. This finding may lead to the development of novel interventions to treat poststroke cognitive deficits.

Enhanced Neurogenesis and Collaterogenesis by Sodium Danshensu Treatment After Focal Cerebral Ischemia in Mice

Ischemic stroke remains a serious threat to human life. There are limited effective therapies for the treatment of stroke. We have previously demonstrated that angiogenesis and neurogenesis in the brain play an important role in functional recovery following ischemic stroke. Recent studies indicate that increased arteriogenesis and collateral circulation are determining factors for restoring reperfusion and outcomes of stroke patients. Danshensu, the Salvia miltiorrhiza root extract, is used in treatments of various human ischemic events in traditional Chinese medicine. Its therapeutic mechanism, however, is not well clarified. Due to its proposed effect on angiogenesis and arteriogenesis, we hypothesized that danshensu could benefit stroke recovery through stimulating neurogenesis and collaterogenesis in the post-ischemia brain. Focal ischemic stroke targeting the right sensorimotor cortex was induced in wild-type C57BL6 mice and transgenic mice expressing green fluorescent protein (GFP) to label smooth muscle cells of brain arteries. Sodium danshensu (SDS, 700 mg/kg) was administered intraperitoneally (i.p.) 10 min after stroke and once daily until animals were sacrificed. To label proliferating cells, 5-bromo-2′-deoxyuridine (BrdU; 50 mg/kg, i.p.) was administered, starting on day 3 after ischemia and continued once daily until sacrifice. At 14 days after stroke, SDS significantly increased the expression of vascular endothelial growth factor (VEGF), stromal-derived factor-1 (SDF-1), brain-derived neurotrophic factor (BDNF), and endothelial nitric oxide synthase (eNOS) in the peri-infarct region. SDS-treated animals showed increased number of doublecortin (DCX)-positive cells. Greater numbers of proliferating endothelial cells and smooth muscle cells were detected in SDS-treated mice 21 days after stroke in comparison with vehicle controls. The number of newly formed neurons labeled by NeuN and BrdU antibodies increased in SDS-treated mice 28 days after stroke. SDS significantly increased the newly formed arteries and the diameter of collateral arteries, leading to enhanced local cerebral blood flow recovery after stroke. These results suggest that systemic sodium danshensu treatment shows significant regenerative effects in the post-ischemic brain, which may benefit long-term functional recovery from ischemic stroke.

Effect of Yokukansan on Nitric Oxide Production and Hydroxyl Radical Metabolism During Cerebral Ischemia and Reperfusion in Mice

BACKGROUND

The purpose of this study was to investigate the effects of yokukansan on forebrain ischemia. Because we can measure nitric oxide production and hydroxyl radical metabolism continuously, we investigated the effect of yokukansan on nitric oxide production and hydroxyl radical metabolism in cerebral ischemia and reperfusion.

METHODS

Yokukansan (300 mg per kg per day) was mixed into feed and given to 16 mice for 10days. Sixteen additional mice received normal feed (control). Nitric oxide production and hydroxyl radical metabolism were continuously monitored using the salicylate trapping method. Forebrain ischemia was producedin all mice by occluding the common carotid artery bilaterally for 10minutes. Levels of the nitric oxide metabolites nitrite and nitrate were determined using the Griess reaction. Survival rates of hippocampal CA1 neurons were calculated and 8-hydroxydeoxyguanosine-immunopositive cells were counted to evaluate the oxidative stress in hippocampal CA1 neurons 72hours after the start of reperfusion.

RESULTS

Arterial blood pressure and regional cerebral blood flow were not significantly different between the 2 groups. The level of nitrate was significantly higher in the yokukansan group than in the control group during ischemia and reperfusion. Levels of 2,3- and 2,5-dihydroxybenzoic acid were significantly lower in the yokukansan group than in the control group during ischemia and reperfusion. Although survival rates in the CA1 did not differ significantly, there were fewer 8-hydroxydeoxyguanosine-immunopositive cells in animals that had received yokukansan than in control animals.

CONCLUSIONS

These data suggest that yokukansan exerts reducing hydroxyl radicals in cerebral ischemic injury.

Functional and pharmacological analysis of agmatine administration in different cerebral ischemia animal models

Agmatine (AgM, 100 mg/kg i.p.) effect was tested in parallel at two animal models of cerebral ischemia - rat MCAO model (60'/24 h, 60'/48 h, 90'/24 h, 90'/48 h) and gerbil global ischemia (10') model, administrated 5 min after reperfusion. Aim was to evaluate AgM effect on functional outcome 24 and 48 h after MCAO on neurological and sensor-motor function, and coordination in rats. AgM administration significantly reduced infarct volume, improved neurological score and improved post-ischemic oxidative status. Results of behavioral tests (cylinder test, beam walking test, and adhesive removal test) have shown very effective functional recovery after AgM administration. Efficiency of AgM administration in gerbils was observed in forebrain cortex, striatum, hippocampus, and cerebellum at the level of each examined oxidative stress parameter (nitric oxide level, superoxide production, superoxide dismutase activity, and index of lipid peroxidation) measured in four different time points starting at 3 h up to 48 h after reperfusion. The highest levels were obtained 6 h after the insult. The most sensitive oxidative stress parameter to AgM was nitric oxide. Additionally, we performed pharmacological analysis of AgM on rat isolated common carotid arteries. The findings imply that mixed population of potassium channels located on the smooth muscle cells was involved in common carotid artery response to AgM, with predominance of inward rectifying K⁺ channels. In our comparative experimental approach, judged by behavioral, biochemical, as well as pharmacological data, the AgM administration showed an effective reduction of ischemic neurological damage and oxidative stress, hence indicating a direction towards improving post-stroke recovery.

Development of a reactive oxygen species-sensitive nitric oxide synthase inhibitor for the treatment of ischemic stroke

Ischemic stroke is caused by a blockage of cerebral blood flow resulting in neuronal and glial hypoxia leading to inflammatory and reactive oxygen species (ROS)-mediated cell death. Nitric oxide (NO) formed by NO synthase (NOS) is known to be protective in ischemic stroke, however NOS has been shown to 'uncouple' under oxidative conditions to instead produce ROS. Nitrones are antioxidant molecules that are shown to trap ROS to then decompose and release NO. In this study, the nitrone 5 was designed such that its decomposition product is a NOS inhibitor, 6, effectively leading to NOS inhibition specifically at the site of ROS production. The ability of 5 to spin-trap radicals and decompose to 6 was observed using EPR and LC-MS/MS. The pro-drug concept was tested in vitro by measuring cell viability and 6 formation in SH-SY5Y cells subjected to oxygen glucose deprivation (OGD). 5 was found to be more efficacious and more potent than PBN, and was able to increase phospho-Akt while reducing nitrotyrosine and cleaved caspase-3 levels. 6 treatment, but not 5, was found to decrease NO production in LPS-stimulated microglia. Doppler flowmetry on anesthetized mice showed increased cerebral blood flow upon intravenous administration of 1mg/kg of 5, but a return to baseline upon administration of 10mg/kg, likely due to its dual nature of antioxidant/NO-donor and NOS-inhibition. Mice treated with 5 after permanent ischemia exhibited a >30% reduction in infarct volume, and higher formation of 6 in ischemic tissue resulting in region specific effects limited to the infarct area.

Endothelial nitric oxide synthase inhibition triggers inflammatory responses in the brain of male rats exposed to ischemia-reperfusion injury

Nitric oxide (NO) derived from endothelial NO synthase (eNOS) plays a role in preserving and maintaining the brain's microcirculation, inhibiting platelet aggregation, leukocyte adhesion, and migration. Inhibition of eNOS activity results in exacerbation of neuronal injury after ischemia by triggering diverse cellular mechanisms, including inflammatory responses. To examine the relative contribution of eNOS in stroke-induced neuroinflammation, we analyzed the effects of systemic treatment with l-N-(1-iminoethyl)ornithine (L-NIO), a relatively selective eNOS inhibitor, on the expression of MiR-155-5p, a key mediator of innate immunity regulation and endothelial dysfunction, in the cortex of male rats subjected to transient middle cerebral artery occlusion (tMCAo) followed by 24 hr of reperfusion. Inducible NO synthase (iNOS) and interleukin-10 (IL-10) mRNA expression were evaluated by real-time polymerase chain reaction in cortical homogenates and in resident and infiltrating immune cells isolated from ischemic cortex. These latter cells were also analyzed for their expression of CD40, a marker of M1 polarization of microglia/macrophages.tMCAo produced a significant elevation of miR155-5p and iNOS expression in the ischemic cortex as compared with sham surgery. eNOS inhibition by L-NIO treatment further elevated the cortical expression of these inflammatory mediators, while not affecting IL-10 mRNA levels. Interestingly, modulation of iNOS occurred in resident and infiltrating immune cells of the ischemic hemisphere. Accordingly, L-NIO induced a significant increase in the percentage of CD40⁺ events in CD68⁺ microglia/macrophages of the ischemic cortex as compared with vehicle-injected animals. These findings demonstrate that inflammatory responses may underlie the detrimental effects due to pharmacological inhibition of eNOS in cerebral ischemia.

Nitric oxide donors (nitrates), L-arginine, or nitric oxide synthase inhibitors for acute stroke

BACKGROUND

Nitric oxide (NO) has multiple effects that may be beneficial in acute stroke, including lowering blood pressure, and promoting reperfusion and cytoprotection. Some forms of nitric oxide synthase inhibition (NOS-I) may also be beneficial. However, high concentrations of NO are likely to be toxic to brain tissue. This is an update of a Cochrane review first published in 1998, and last updated in 2002.

OBJECTIVES

To assess the safety and efficacy of NO donors, L-arginine, and NOS-I in people with acute stroke.

SEARCH METHODS

We searched the Cochrane Stroke Group Trials Register (last searched 6 February 2017), MEDLINE (1966 to June 2016), Embase (1980 to June 2016), ISI Science Citation Indexes (1981 to June 2016), Stroke Trials Registry (searched June 2016), International Standard Randomised Controlled Trial Number (ISRCTN) (searched June 2016), Clinical Trials registry (searched June 2016), and International Clinical Trials Registry Platform (ICTRP) (searched June 2016). Previously, we had contacted drug companies and researchers in the field.

SELECTION CRITERIA

Randomised controlled trials comparing nitric oxide donors, L-arginine, or NOS-I versus placebo or open control in people within one week of onset of confirmed stroke.

DATA COLLECTION AND ANALYSIS

Two review authors independently applied the inclusion criteria, assessed trial quality and risk of bias, and extracted data. The review authors cross-checked data and resolved issues through discussion. We obtained published and unpublished data, as available. Data were reported as mean difference (MD) or odds ratio (OR) with 95% confidence intervals (CI).

MAIN RESULTS

We included five completed trials, involving 4197 participants; all tested transdermal glyceryl trinitrate (GTN), an NO donor. The assessed risk of bias was low across the included studies; one study was double-blind, one open-label and three were single-blind. All included studies had blinded outcome assessment. Overall, GTN did not improve the primary outcome of death or dependency at the end of trial (modified Rankin Scale (mRS) > 2, OR 0.97, 95% CI 0.86 to 1.10, 4195 participants, high-quality evidence). GTN did not improve secondary outcomes, including death (OR 0.78, 95% CI 0.40 to 1.50) and quality of life (MD -0.01, 95% CI -0.17 to 0.15) at the end of trial overall (high-quality evidence). Systolic/diastolic blood pressure (BP) was lower in people treated with GTN (MD -7.2 mmHg (95% CI -8.6 to -5.9) and MD -3.3 (95% CI -4.2 to -2.5) respectively) and heart rate was higher (MD 2.0 beats per minute (95% CI 1.1 to 2.9)). Headache was more common in those randomised to GTN (OR 2.37, 95% CI 1.55 to 3.62). We did not find any trials assessing other nitrates, L-arginine, or NOS-I.

AUTHORS' CONCLUSIONS

There is currently insufficient evidence to recommend the use of NO donors, L-arginine or NOS-I in acute stroke, and only one drug (GTN) has been assessed. In people with acute stroke, GTN reduces blood pressure, increases heart rate and headache, but does not alter clinical outcome (all based on high-quality evidence).

Combined l-citrulline and glutathione administration prevents neuronal cell death following transient brain ischemia

We previously reported that oral l-citrulline (l-Cit) administration antagonizes neuronal cell death in hippocampus following transient brain ischemia and that oral glutathione (GSH) administration prevents neuronal death through antioxidant activity. Here, we tested potential synergy of combined l-Cit and GSH administration in protection against neuronal death following cerebral ischemia. One day after a 20-min bilateral common carotid artery occlusion (BCCAO), mice were orally administered l-Cit or GSH alone (at 40 or 100mg/kgp.o.) or both (at 40mg/kgp.o. each) daily for 10days. The combination, but not l-Cit or GSH alone at 40mg/kgp.o., significantly prevented neuronal death in the hippocampal CA1 region in BCCAO mice. Consistently, combined l-Cit and GSH administration improved memory-related behavioral deficits observed in BCCAO mice. Combination treatment also significantly rescued reduced endothelial nitric oxide synthase (eNOS) protein levels and antagonized eNOS S-glutathionylation seen following BCCAO ischemia. Recovery of eNOS activity was confirmed by in vivo NO production in hippocampus of BCCAO mice. Taken together, combined administration of l-Cit with GSH rescues eNOS function, thereby inhibiting delayed neuronal death in hippocampus.

Optimizing the host substrate environment for cardiac angiogenesis, arteriogenesis, and myogenesis

INTRODUCTION

The diseased host milieu, such as endothelial dysfunction (ED), decreased NO bioavailability, and ischemic/inflammatory post-MI environment, hamper the clinical success of existing cardiac regenerative therapies. Area covered: In this article, current strategies including pharmacological and nonpharmacological approaches for improving the diseased host milieu are reviewed. Specifically, the authors provide focus on: i) the mechanism of ED in patients with cardiovascular diseases, ii) the current results of ED improving strategies in pre-clinical and clinical studies, and iii) the use of biomaterials as a novel modulator in damaged post-MI environment. Expert opinion: Adjunct therapies which improve host endothelial function have demonstrated promising outcomes, potentially overcoming disappointing results of cell therapy in human studies. In the future, elucidation of the interactions between the host tissue and therapeutic agents, as well as downstream signaling pathways, will be the next challenges in enhancing regenerative therapy. More careful investigations are also required to establish these agents' safety and efficacy for wide usage in humans.

Therapeutic Potential of Transdermal Glyceryl Trinitrate in the Management of Acute Stroke

The nitric oxide donor, glyceryl trinitrate (GTN), is a candidate treatment for the management of acute stroke with haemodynamic and potential reperfusion and neuroprotective effects. When administered as a transdermal patch during the acute and subacute phases after stroke, GTN was safe, lowered blood pressure, maintained cerebral blood flow, and did not induce cerebral steal or alter functional outcome. However, when given within 6 h of stroke onset, GTN reduced death and dependency (odds ratio 0.52; 95% confidence interval 0.34-0.78), death, disability, cognitive impairment and mood disturbance, and improved quality of life (data from two trials, n = 312). In a pooled analysis of four studies (n = 186), GTN reduced between-visit systolic blood pressure variability over days 1-7 compared with no GTN (mean difference -2.09; 95% confidence interval -3.83 to -0.35; p = 0.019). The efficacy of GTN given in the ultra-acute/pre-hospital setting is currently being assessed and, if found to be beneficial, the implications for hyperacute stroke practice are significant. Here, we discuss the evidence to date, potential mechanisms of action and future possibilities, including unanswered questions, for the therapeutic potential of GTN in acute stroke.

Nitric Oxide and Hydrogen Sulfide Regulation of Ischemic Vascular Remodeling

Blockage or restriction of blood flow through conduit arteries results in tissue ischemia downstream of the disturbed area. Local tissues can adapt to this challenge by stimulating vascular remodeling through angiogenesis and arteriogenesis thereby restoring blood perfusion and removal of wastes. Multiple molecular mechanisms of vascular remodeling during ischemia have been identified and extensively studied. However, therapeutic benefits from these findings and insights are limited due to the complexity of various signaling networks and a lack of understanding central metabolic regulators governing these responses. The gasotransmitters NO and H2 S have emerged as master regulators that influence multiple molecular targets necessary for ischemic vascular remodeling. In this review, we discuss how NO and H2 S are individually regulated under ischemia, what their roles are in angiogenesis and arteriogenesis, and how their interaction controls ischemic vascular remodeling.

Targeting Nitric Oxide with Natural Derived Compounds as a Therapeutic Strategy in Vascular Diseases

Within the family of endogenous gasotransmitters, nitric oxide (NO) is the smallest gaseous intercellular messenger involved in the modulation of several processes, such as blood flow and platelet aggregation control, essential to maintain vascular homeostasis. NO is produced by nitric oxide synthases (NOS) and its effects are mediated by cGMP-dependent or cGMP-independent mechanisms. Growing evidence suggests a crosstalk between the NO signaling and the occurrence of oxidative stress in the onset and progression of vascular diseases, such as hypertension, heart failure, ischemia, and stroke. For these reasons, NO is considered as an emerging molecular target for developing therapeutic strategies for cardio- and cerebrovascular pathologies. Several natural derived compounds, such as polyphenols, are now proposed as modulators of NO-mediated pathways. The aim of this review is to highlight the experimental evidence on the involvement of nitric oxide in vascular homeostasis focusing on the therapeutic potential of targeting NO with some natural compounds in patients with vascular diseases.

Neuroprotective Effects of Simvastatin and Cilostazol in L-Methionine-Induced Vascular Dementia in Rats

Vascular dementia (VaD) is a degenerative cerebrovascular disorder that leads to progressive decline in cognitive abilities and memory. Several reports demonstrated that oxidative stress and endothelial dysfunction are principal pathogenic factors in VaD. The present study was constructed to determine the possible neuroprotective effects of simvastatin in comparison with cilostazol in VaD induced by L-methionine in rats. Male Wistar rats were divided into four groups. Group I (control group), group II received L-methionine (1.7 g/kg, p.o.) for 32 days. The remaining two groups received simvastatin (50 mg/kg, p.o.) and cilostazol (100 mg/kg, p.o.), respectively, for 32 days after induction of VaD by L-methionine. Subsequently, rats were tested for cognitive performance using Morris water maze test then sacrificed for biochemical and histopathological assays. L-methionine induced VaD reflected by alterations in rats' behavior as well as the estimated neurotransmitters, acetylcholinesterase activity as well as increased brain oxidative stress and inflammation parallel to histopathological changes in brain tissue. Treatment of rats with simvastatin ameliorated L-methionine-induced behavioral, neurochemical, and histological changes in a manner comparable to cilostazol. Simvastatin may be regarded as a potential therapeutic strategy for the treatment of VaD. To the best of our knowledge, this is the first study to reveal the neuroprotective effects of simvastatin or cilostazol in L-methionine-induced VaD. Graphical Abstract ᅟ.

Multipotent bone marrow stromal cell therapy promotes endogenous cell proliferation following ischemic stroke

Despite extensive research over the years, there still exists some debate as to what constitutes the optimal therapeutic strategy to promote recovery following stroke. Due to the complexity of injured brain pathophysiology, treatment approaches should ideally address numerous factors, ultimately aiming to promote tissue protection, axonal regrowth and functional recovery. This study extends the understanding of the effects of bone marrow stromal cell (BMSC) treatment following experimentally induced ischemic stroke in rats. Focal ischemic brain injury was experimentally induced in rats by placing a preformed clot into the middle cerebral artery. Animals were injected intravenously with BMSCs at 24 h after stroke and were killed 7 days post injury. When administered BMSCs following stroke, the neurological outcome was significantly improved relative to controls. There was an increase in the number of BMSCs labelled with BrdU present in the injured hemisphere of the brain compared to the non-injured side. Furthermore, administration of BMSCs also led to increases in astrocytosis, vascularization and endogenous proliferation. These findings provide insight into the mechanisms of action of BMSC treatment and further argue for the therapeutic potential of BMSCs as an effective treatment following cerebral stroke.

Endothelial nitric oxide synthase: a potential therapeutic target for cerebrovascular diseases

Endothelial nitric oxide (NO) is a significant signaling molecule that regulates cerebral blood flow (CBF), playing a pivotal role in the prevention and treatment of cerebrovascular diseases. However, achieving the expected therapeutic efficacy is difficult using direct administration of NO donors. Therefore, endothelial nitric oxide synthase (eNOS) becomes a potential therapeutic target for cerebrovascular diseases. This review summarizes the current evidence supporting the importance of CBF to cerebrovascular function, and the roles of NO and eNOS in CBF regulation.

Temporal profiles of blood pressure, circulating nitric oxide, and adrenomedullin as predictors of clinical outcome in acute ischemic stroke patients

Stroke remains an important health and social challenge. The present study investigated whether blood pressure (BP) parameters and circulating levels of nitric oxide metabolites (NOx) and adrenomedullin (AM) may predict clinical outcomes of stroke. Patients (n=76) diagnosed with acute ischemic stroke were admitted to the stroke unit and clinical history data and monitored parameters were recorded. Blood plasma was collected at days 1, 2, and 7 to measure NOx and AM levels. Infarct volume, neurological severity [on the National Institutes of Health Stroke Scale (NIHSS)], and functional prognosis (on the Rankin scale) were measured as clinical outcomes. Patients with higher BP had more severe symptoms (NIHSS >3; P<0.01) and BP variability predicted neurological severity and growth of infarct volume. NOx values were significantly lower in stroke patients than in healthy controls (P<0.01). An increase in NOx levels from day 1 to day 2 was beneficial for the patients as measured by NIHSS at 7 days and 3 months, and by Rankin at 3 months [odds ratio (OR), 0.91] whereas a steep increase from day 2 to day 7 was detrimental and associated with an increase in infarct volume (OR, 35.3). AM levels were significantly higher in patients at day 1 and 2 than in healthy individuals (P<0.01) and these levels returned to normal at day 7. Patients with high AM levels at day 2 had significantly higher NIHSS scores measured at day 1 (P<0.05) and 7 (P<0.01). A receiving operating characteristic curve analysis identified that AM levels at day 2 of >522.13 pg/ml predicted increased neurological severity at day 7 (area under the curve=0.721). Multivariate logistic regression indicated that AM levels at day 2 predicted increased neurological severity at 7 days and at 3 months. BP parameters and changing levels for NOx and AM predicted long-term clinical outcomes as measured by infarct volume, neurological severity scale, and functional prognosis.

Partial eNOS deficiency causes spontaneous thrombotic cerebral infarction, amyloid angiopathy and cognitive impairment

Background

Cerebral infarction due to thrombosis leads to the most common type of stroke and a likely cause of age-related cognitive decline and dementia. Endothelial nitric oxide synthase (eNOS) generates NO, which plays a crucial role in maintaining vascular function and exerting an antithrombotic action. Reduced eNOS expression and eNOS polymorphisms have been associated with stroke and Alzheimer’s disease (AD), the most common type of dementia associated with neurovascular dysfunction. However, direct proof of such association is lacking. Since there are no reports of complete eNOS deficiency in humans, we used heterozygous eNOS^+/- mice to mimic partial deficiency of eNOS, and determine its impact on cerebrovascular pathology and perfusion of cerebral vessels.

Results

Combining cerebral angiography with immunohistochemistry, we found thrombotic cerebral infarctions in eNOS^+/- mice as early as 3–6 months of age but not in eNOS^+/+ mice at any age. Remarkably, vascular occlusions in eNOS^+/- mice were found almost exclusively in three areas: temporoparietal and retrosplenial granular cortexes, and hippocampus this distribution precisely matching the hypoperfused areas identified in preclinical AD patients. Moreover, progressive cerebral amyloid angiopaphy (CAA), blood brain barrier (BBB) breakdown, and cognitive impairment were also detected in aged eNOS^+/- mice.

Conclusions

These data provide for the first time the evidence that partial eNOS deficiency results in spontaneous thrombotic cerebral infarctions that increase with age, leading to progressive CAA and cognitive impairments. We thus conclude that eNOS^+/- mouse may represent an ideal model of ischemic stroke to address early and progressive damage in spontaneously-evolving chronic cerebral ischemia and thus, study vascular mechanisms contributing to vascular dementia and AD.

Electronic supplementary material

The online version of this article (doi:10.1186/s13024-015-0020-0) contains supplementary material, which is available to authorized users.

Edaravone's free radical scavenging mechanisms of neuroprotection against cerebral ischemia: review of the literature

Free radicals and oxidative stress play key roles in cerebral ischemic pathogenesis and represent pharmacological targets for treatment. Edaravone (Edv), one of antioxidant agents that have been used in acute ischemic stroke in both clinical settings and animal experiments, exerts neuroprotective effect on ischemic injured brains. This review is aimed to elaborate the latest molecular mechanisms of the neuroprotection of Edv on cerebral ischemia and provide reasonable evidence in its clinical application. It is found that Edv has neuroprotective influence on cerebral ischemia, which is closely related to the facets of scavenging reactive oxygen species (ROS), hydroxyl radical (ċOH) and reactive nitrogen species (RNS). And it is a good antioxidant agent that can be safely used in the treatment of cerebral ischemia and chronic neurodegenerative disorders as well as other ischemia/reperfusion (I/R)-related diseases. The combination of Edv with thrombolytic therapy also can be applied in clinical settings and will be greatly beneficial to patients with stroke.

Hippocampus and nitric oxide

Since it was first identified to play an important role in relaxation of blood vessels, nitric oxide has been demonstrated to regulate many biological processes, especially in the central nervous system. Of the three types of enzymes that produce nitric oxide in humans and rodents, neuronal type is found almost exclusively in the nervous system. This gaseous molecule is a nonclassical neurotransmitter, which maintains the activities of neural cells and regulates the normal functions of brain. It appears to play a role in promoting the transfer of nerve signals from one neuron to another, maintaining the synaptic strength. Meanwhile, nitric oxide is a unique regulator on neurogenesis and synaptogenesis, producing the positive or negative effects upon different signal pathways or cellular origins and locations. Based on its significant roles in neural plasticity, nitric oxide is involved in a number of central nervous diseases, such as ischemia, depression, anxiety, and Alzheimer's disease. Clarifying the profiles of nitric oxide in the brain tissues and its participation in pathophysiological processes opens a new avenue for development of new therapeutic strategies. Thus, this chapter specifies the effects of nitric oxide in the hippocampus, a key structure implicated in the modulation of mood and memories, exhibiting the trend of future research on nitric oxide.

Endothelial nitric oxide synthase regulates white matter changes via the BDNF/TrkB pathway after stroke in mice

Stroke induced white matter (WM) damage is associated with neurological functional deficits, but the underlying mechanisms are not well understood. In this study, we investigate whether endothelial nitric oxide synthase (eNOS) affects WM-damage post-stroke. Adult male wild-type (WT) and eNOS knockout (eNOS(-/-)) mice were subjected to middle cerebral artery occlusion. Functional evaluation, infarct volume measurement, immunostaining and primary cortical cell culture were performed. To obtain insight into the mechanisms underlying the effects of eNOS(-/-) on WM-damage, measurement of eNOS, brain-derived neurotrophic factor (BDNF) and its receptor TrkB in vivo and in vitro were also performed. No significant differences were detected in the infarction volume, myelin density in the ipsilateral striatal WM-bundles and myelin-based protein expression in the cerebral ischemic border between WT and eNOS(-/-) mice. However, eNOS(-/-) mice showed significantly: 1) decreased functional outcome, concurrent with decreases of total axon density and phosphorylated high-molecular weight neurofilament density in the ipsilateral striatal WM-bundles. Correlation analysis showed that axon density is significantly positive correlated with neurological functional outcome; 2) decreased numbers of oligodendrocytes / oligodendrocyte progenitor cells in the ipsilateral striatum; 3) decreased synaptophysin, BDNF and TrkB expression in the ischemic border compared with WT mice after stroke (n = 12/group, p<0.05). Primary cortical cell culture confirmed that the decrease of neuronal neurite outgrowth in the neurons derived from eNOS(-/-) mice is mediated by the reduction of BDNF/TrkB (n = 6/group, p<0.05). Our data show that eNOS plays a critical role in WM-damage after stroke, and eNOS(-/-)-induced decreases in the BDNF/TrkB pathway may contribute to increased WM-damage, and thereby decrease functional outcome.

Anti-Proliferative Effect of an Aqueous Extract of Prunella vulgaris in Vascular Smooth Muscle Cells

The abnormal proliferation of vascular smooth muscle cells (VSMCs) in arterial walls is an important pathogenic factor of vascular disorders such as diabetic atherosclerosis. We have reported the anti-inflammatory effect of an aqueous extract from Prunella vulgaris (APV) in vascular endothelial cell. In the present study, APV exhibited inhibitory effects on high glucose-stimulated VSMC proliferation, migration, and invasion activities, inducing G₁ cell cycle arrest with downregulation of cyclins and CDKs and upregulation of the CKIs, p21^waf1/cip1 and p27^kip1. Furthermore, APV dose dependently suppressed the high glucose-induced matrix metalloproteinase activity. High glucose-induced phosphorylation of ERK, p38 MAPK, was decreased by the pretreatment of APV. NF-κB activation by high glucose was attenuated by APV, as an antioxidant. APV attenuated the high glucose-induced decrease of nuclear factor E2-related factor-2 (Nrf2) translocation and heme oxygenase-1 (HO-1) expression. Intracellular cGMP level was also increased by APV treatment. These results demonstrate that APV may inhibit VSMC proliferation via downregulating ROS/NF-κB /ERK/p38 MAPK pathways. In addition, APV has a beneficial effect by the interaction of Nrf2-mediated NO/cGMP with HO-1, suggesting that Prunella vulgaris may be useful in preventing diabetic atherosclerosis.

Genistein attenuates ischemic oxidative damage and behavioral deficits via eNOS/Nrf2/HO-1 signaling

Global cerebral ischemia, such as occurs following cardiac arrest, can lead to oxidative stress, hippocampal neuronal cell death, and cognitive defects. The current study examined the potential beneficial effect and underlying mechanisms of post-treatment with the naturally occurring isoflavonic phytoestrogen, genistein, which has been implicated to attenuate oxidative stress. Genistein (1 mg kg(-1)) was administered i.v. 5 min after reperfusion in rats subjected to four-vessel global cerebral ischemia (GCI). The results revealed that genistein exerted significant neuroprotection of hippocampal CA1 neurons following GCI, as evidenced by an increase in NeuN-positive neurons and the decrease in TUNEL-positive neurons. Furthermore, genistein treatment also resulted in significantly improved spatial learning and memory as compared to vehicle control animals. The beneficial effects of genistein appear to be mediated by an increase of phosphorylation/activation of eNOS, with subsequent activation of the antioxidant/detoxification Nrf2/Keap1 transcription system. Along these lines, genistein increased keap1 S-nitrosylation, with a corresponding nuclear accumulation and enhanced DNA binding activity of Nrf2. Genistein also enhanced levels of the Nrf2 downstream antioxidant protein, heme oxygenase (HO)-1, as compared to vehicle control groups. In accordance with its induction of Nrf2 activation, genistein exerted a robust attenuation of oxidative DNA damage and lipid peroxidative damage in hippocampal CA1 neurons after GCI, as measured by immunofluorescence staining of the oxidative stress markers, 8-hydroxy-2-deoxyguanosine (8-OHdG) and 4-Hydroxynonenal (4-HNE). Interestingly, the aforementioned effects of genistein were abolished by pretreatment with L-NAME, an inhibitor of eNOS activation. In conclusion, the results of the study demonstrate that low dose genistein can exert significant antioxidant, neuroprotective, and cognitive-enhancing effects in the hippocampal CA1 region following GCI. Mechanistically, the beneficial effects of genistein appear to be mediated by enhanced eNOS phosphorylation/activation and nitric oxide (NO)-mediated thiol modification of Keap1, with subsequent upregulation of the Nrf2/HO-1 antioxidative signaling pathway and a resultant attenuation of oxidative stress.

Role of N-Nitro-L-Arginine-Methylester as anti-oxidant in transient cerebral ischemia and reperfusion in rats

Background

Previous reports assessing the neuroprotective role of nonselective Nitric Oxide synthase (NOS) inhibitor N-nitro-L-arginine-methylester (L-NAME) following cerebral ischemia/reperfusion are contradictory. The aim of this work was to examine the potential benefits of L-NAME on rats subjected to transient focal cerebral ischemia/reperfusion.

Methods

The study involved 30 adult male Wistar rats divided into three groups 10 rats in each: First group was sham-operated and served as a control, a ischemia/reperfusion (I/R) group of rats infused with 0.9% normal saline intraperitoneally 15 minutes prior to 30 minutes of left common carotid artery (CCA) occlusion and a test group infused with L-NAME intraperitoneally 15 minutes prior to ischemia. Neurobehavioral assessments were evaluated and quantitative assessment of malondialdehyde (MDA), Nitric oxide (NO) metabolites and total antioxidant capacity (TAC) in both serum and the affected cerebral hemisphere were achieved.

Results

Rats’ neurological deficit and TAC were significantly decreased while NO and MDA were significantly increased in the I/R compared with the control group (P < 0.001). Alternatively in the L-NAME group, neurological deficit and TAC were significantly improved while NO and MDA were significantly decreased compared to I/R group (P < 0.001).

Conclusions

L-NAME pretreatment for rats undergoing cerebral ischemia/reperfusion significantly improves neurological deficit while reducing oxidative stress biomarkers in the affected cerebral hemisphere.

A tailed primers protocol to identify the association of eNOS gene variable number of tandem repeats polymorphism with ischemic stroke in Chinese Han population by capillary electrophoresis

Endothelial nitric oxide synthase (eNOS) plays an important role in mediating endothelium-dependent vasodilatation and antithrombotic action and is thus involved in the development of ischemic stroke (IS). Controversial results regarding the association of eNOS gene variable number of tandem repeats (VNTR) polymorphism with IS have been reported by conventional PCR-polyacrylamide gel electrophoresis methods. We aimed to identify any common association of eNOS gene VNTR polymorphism with IS in Chinese Han population by capillary electrophoresis (CE). The VNTR polymorphism of 27 bp within the eNOS intron-4 was determined by CE with specially designed tailed primers in Chinese Han patients with IS (n=457) and matched elderly controls without IS (n=457). Significant differences in BMI, WHR, hypertension, diabetes, smoking, TG, HDL, LDL, LDL, and FBG were observed between cases and controls. The distributions of eNOS VNTR polymorphism were not significantly associated with IS after adjustment for cardiovascular risk factors (OR=1.18, 95% CI: 0.82-1.69). This finding was consistent with the further meta-analysis in Asians. The meta-analysis in Americans demonstrated that 4a/4b+4a/4a genotype was significantly associated with IS risk with an OR of 1.54 (95% CI, 1.09-2.17) compared with the 4b/4b genotype. Our data suggests that BMI, WHR, hypertension, diabetes, smoking, TG, LDL, and FBG may increase the risk of IS. However, eNOS VNTR polymorphism may be not an independent major contributor for IS in Chinese Han population. The VNTR polymorphism might be associated with IS in Americans based on meta-analysis.

Morphological evaluation of the cerebral blood vessels in the late gestation fetal sheep following hypoxia in utero

Hypoxia can significantly contribute to the development of permanent brain injury in the term neonate; however the response of cerebral blood vessels is not well understood. This study aimed to quantitatively measure vascular density and morphology using laminin immunohistochemistry as a marker of blood vessels, and determine the effects of a single, severe bout of hypoxia (umbilical cord occlusion, UCO) late in gestation on the developing cerebrovasculature in fetal sheep. At 124-126 days gestation singleton fetal sheep underwent surgery for implantation of catheters and placement of an inflatable cuff around the umbilical cord. A 10 min UCO or sham UCO (n=5) occurred at 132 days gestation. Fetal brains were collected at 24 h (n=5) or 48 h (n=4) after UCO for vascular density and morphology analysis of laminin immunohistochemistry. 48 h following a single, brief bout of severe hypoxia late in gestation decreased vascular density was seen in the caudate nucleus and no changes in vascular morphology occurred. However closer analysis revealed a significant shift in the frequency of smaller (≤10 μm) to larger (≤100 μm) perimeter blood vessels in periventricular and subcortical white matter. Close examination of the frequency distribution of vascular perimeter highlights that alterations in vascular morphology persist in the near term fetal brain for up to 48 h following a brief (10 min) hypoxia in white but not gray matter. These findings suggest that the near term brain may still be vulnerable to white matter injury following in utero hypoxia.

Nitric oxide: considerations for the treatment of ischemic stroke

Some 40 years ago it was recognized by Furchgott and colleagues that the endothelium releases a vasodilator, endothelium-derived relaxing factor (EDRF). Later on, several groups identified EDRF to be a gas, nitric oxide (NO). Since then, NO was identified as one of the most versatile and unique molecules in animal and human biology. Nitric oxide mediates a plethora of physiological functions, for example, maintenance of vascular tone and inflammation. Apart from these physiological functions, NO is also involved in the pathophysiology of various disorders, specifically those in which regulation of blood flow and inflammation has a key role. The aim of the current review is to summarize the role of NO in cerebral ischemia, the most common cause of stroke.

Proof of concept: endogenous antiangiogenic factors predict the occurrence of symptomatic vasospasm post subarachnoid hemorrhage

BACKGROUND

The pathogenesis of vasospasm (VS) post aneurysmal subarachnoid hemorrhage (SAH) is multifactorial and not completely understood. The authors hypothesize that circulating antiangiogenic factors play an important role in brain injury post SAH and that elevated levels predict the occurrence of symptomatic vasospasm.

METHODS

In this study the authors measured the serum and cerebrospinal fluid (CSF) levels of soluble endoglin (sEng) and soluble fms-like tyrosine kinase 1 (sFlt1) in controls and SAH patients within 48 h of the bleed. Patients were prospectively followed and subcategorized into those with (sVS) and without symptomatic vasospasm (no-sVS).

RESULTS

Compared to healthy controls, SAH patients had higher CSF levels of sEng (0.037 vs. 0.251 ng/ml; P = 0.02) and sFlt1 (0.068 vs. 0.679 ng/ml; P = 0.001). In the subgroup analysis, sVS patients had higher CSF levels of sEng and sFlt1 than no-sVS patients (sEng: 0.380 vs. 0.159 ng/ml, P = 0.02; sFlt1: 1.277 vs. 0.343 ng/ml, P = 0.01). The serum levels of sEng and sFlt1 were not statistically different among the different groups.

CONCLUSIONS

Based on these results the authors conclude that elevated CSF levels of sFlt1 and sEng herald the occurrence of symptomatic VS post SAH.