Sildenafil mediates blood-flow redistribution and neuroprotection after neonatal hypoxia-ischemia

The potential therapeutic effect of phosphodiesterase 5 inhibitors in the acute ischemic stroke (AIS)

Acute ischemic stroke (AIS) is a focal neurological disorder that accounts for 85% of all stroke types, due to occlusion of cerebral arteries by thrombosis and emboli. AIS is also developed due to cerebral hemodynamic abnormality. AIS is associated with the development of neuroinflammation which increases the severity of AIS. Phosphodiesterase enzyme (PDEs) inhibitors have neuro-restorative and neuroprotective effects against the development of AIS through modulation of the cerebral cyclic adenosine monophosphate (cAMP)/cyclic guanosine monophosphate (cGMP)/nitric oxide (NO) pathway. PDE5 inhibitors through mitigation of neuroinflammation may decrease the risk of long-term AIS-induced complications. PDE5 inhibitors may affect the hemodynamic properties and coagulation pathway which are associated with thrombotic complications in AIS. PDE5 inhibitors reduce activation of the pro-coagulant pathway and improve the microcirculatory level in patients with hemodynamic disturbances in AIS. PDE5 inhibitors mainly tadalafil and sildenafil improve clinical outcomes in AIS patients through the regulation of cerebral perfusion and cerebral blood flow (CBF). PDE5 inhibitors reduced thrombomodulin, P-selectin, and tissue plasminogen activator. Herein, PDE5 inhibitors may reduce activation of the pro-coagulant pathway and improve the microcirculatory level in patients with hemodynamic disturbances in AIS. In conclusion, PDE5 inhibitors may have potential roles in the management of AIS through modulation of CBF, cAMP/cGMP/NO pathway, neuroinflammation, and inflammatory signaling pathways. Preclinical and clinical studies are recommended in this regard.

Feasibility and Safety of Sildenafil to Repair Brain Injury Secondary to Birth Asphyxia (SANE-01): A Randomized, Double-blind, Placebo-controlled Phase Ib Clinical Trial

OBJECTIVE

To test feasibility and safety of administering sildenafil in neonates with neonatal encephalopathy (NE), developing brain injury despite therapeutic hypothermia (TH).

STUDY DESIGN

We performed a randomized, double-blind, placebo-controlled phase Ib clinical trial between 2016 and 2019 in neonates with moderate or severe NE, displaying brain injury on day-2 magnetic resonance imaging (MRI) despite TH. Neonates were randomized (2:1) to 7-day sildenafil or placebo (2 mg/kg/dose enterally every 12 hours, 14 doses). Outcomes included feasibility and safety (primary outcomes), pharmacokinetics (secondary), and day-30 neuroimaging and 18-month neurodevelopment assessments (exploratory).

RESULTS

Of the 24 enrolled neonates, 8 were randomized to sildenafil and 3 to placebo. A mild decrease in blood pressure was reported in 2 of the 8 neonates after initial dose, but not with subsequent doses. Sildenafil plasma steady-state concentration was rapidly reached, but decreased after TH discontinuation. Twelve percent of neonates (1/8) neonates died in the sildenafil group and 0% (0/3) in the placebo group. Among surviving neonates, partial recovery of injury, fewer cystic lesions, and less brain volume loss on day-30 magnetic resonance imaging were noted in 71% (5/7) of the sildenafil group and in 0% (0/3) of the placebo group. The rate of death or survival to 18 months with severe neurodevelopmental impairment was 57% (4/7) in the sildenafil group and 100% (3/3) in the placebo group.

CONCLUSIONS

Sildenafil was safe and well-absorbed in neonates with NE treated with TH. Optimal dosing needs to be established. Evaluation of a larger number of neonates through subsequent phases II and III trials is required to establish efficacy.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.govNCT02812433.

Synergistic effect of sildenafil combined with controlled hypothermia to alleviate microglial activation after neonatal hypoxia-ischemia in rats

BACKGROUND AND PURPOSE

The only validated treatment to prevent brain damage associated with hypoxia-ischemia (HI) encephalopathy of the newborn is controlled hypothermia with limited benefits. Additional putative neuroprotective drug candidates include sildenafil citrate, a phosphodiesterase-type 5 inhibitor. The main objective of this preclinical study is to assess its ability to reduce HI-induced neuroinflammation, in particular through its potential effect on microglial activation.

METHODS

HI was induced in P10 Sprague-Dawley rats by unilateral carotid permanent artery occlusion and hypoxia (HI) and treated by either hypothermia (HT) alone, Sildenafil (Sild) alone or combined treatment (SildHT). Lesion size and glial activation were analyzed by immunohistochemistry, qRT-PCR, and proteomic analyses performed at P13.

RESULTS

None of the treatments was associated with a significant early reduction in lesion size 72h after HI, despite significant changes in tissue loss distribution. Significant reductions in both Iba1 + (within the ipsilateral hemisphere) and GFAP + cells (within the ipsilateral hippocampus) were observed in SildHT group, but not in the other treatment groups. In microglia-sorted cells, pro-inflammatory markers, i.e. Il1b, Il6, Nos2, and CD86 were significantly downregulated in SildHT treatment group only. These changes were restricted to the ipsilateral hemisphere, were not evidenced in sorted astrocytes, and were not sex dependent. Proteomic analyses in sorted microglia refined the pro-inflammatory effect of HI and confirmed a biologically relevant impact of SildHT on specific molecular pathways including genes related to neutrophilic functions.

CONCLUSIONS

Our findings suggest that Sildenafil combined with controlled hypothermia produces maximum effect in mitigating microglial activation induced by HI through complex proteomic regulation. The reduction of neuroinflammation induced by Sildenafil may represent an interesting therapeutic strategy for neonatal neuroprotection.

Cardiac Dysfunction in Neonatal HIE Is Associated with Increased Mortality and Brain Injury by MRI

OBJECTIVE

Describe the association between cardiac dysfunction and death or moderate-to-severe abnormalities on brain magnetic resonance imaging (MRI) in neonates undergoing therapeutic hypothermia for hypoxic ischemic encephalopathy (HIE).

STUDY DESIGN

Retrospective study in neonates with moderate or severe HIE undergoing therapeutic hypothermia between 2008 and 2017. Primary outcome was death or moderate-to-severe brain injury using the Barkovich score. Conventional and speckle-tracking echocardiography measures were extracted from available echocardiograms to quantify right (RV) and left (LV) ventricular functions.

RESULTS

A total of 166 newborns underwent therapeutic hypothermia of which 53 (36.5%) had echocardiography performed. Ten (19%) died prior to hospital discharge, and 11 (26%) had moderate-to-severe brain injury. There was no difference in chronologic age at echocardiography between the normal and adverse outcome groups (22 [±19] vs. 28 [±21] hours, p = 0.35). Cardiac findings in newborns with abnormal outcome included lower systolic and diastolic blood pressure (BP) at echocardiography (p = 0.004) and decreased tricuspid annular plane systolic excursion (a marker of RV systolic function; p = 0.01), while the ratio of systolic pulmonary artery (PA) pressure to systolic BP indicated isosystemic pressures (>2/3 systemic) in both groups. A multilogistic regression analysis, adjusting for weight and seizure status, indicated an association between abnormal outcome and LV function by longitudinal strain, as well as by ejection fraction.

CONCLUSION

Newborns who died or had moderate-to-severe brain injury had a higher incidence of cardiac dysfunction but similar PA pressures when compared with those who survived with mild or no MRI abnormalities.

KEY POINTS

· Newborns with HIE with functional LV/RV dysfunction are at risk for death or brain injury.. · All neonates with HIE had elevated pulmonary pressure, but neonates with poor outcome had RV dysfunction.. · When evaluating newborns with HIE by echocardiography, beyond estimation of pulmonary pressure, it is important to assess biventricular function..

Azithromycin and Sildenafil May Have Protective Effects on Retinal Ganglion Cells via Different Pathways: Study in a Rodent Microbead Model

Decreased blood flow to the optic nerve (ON) and neuroinflammation are suggested to play an important role in the pathophysiology of glaucoma. This study investigated the potential neuroprotective effect of azithromycin, an anti-inflammatory macrolide, and sildenafil, a selective phosphodiesterase-5 inhibitor, on retinal ganglion cell survival in a glaucoma model, which was induced by microbead injection into the right anterior chamber of 50 wild-type (WT) and 30 transgenic toll-like receptor 4 knockout (TLR4KO) mice. Treatment groups included intraperitoneal azithromycin 0.1 mL (1 mg/0.1 mL), intravitreal sildenafil 3 µL, or intraperitoneal sildenafil 0.1 mL (0.24 μg/3 µL). Left eyes served as controls. Microbead injection increased intraocular pressure (IOP), which peaked on day 7 in all groups and on day 14 in azithromycin-treated mice. Furthermore, the retinas and ON of microbead-injected eyes showed a trend of increased expression of inflammatory- and apoptosis-related genes, mainly in WT and to a lesser extent in TLR4KO mice. Azithromycin reduced the BAX/BCL2 ratio, TGFβ, and TNFα levels in the ON and CD45 expression in WT retina. Sildenafil activated TNFα-mediated pathways. Both azithromycin and sildenafil exerted a neuroprotective effect in WT and TLR4KO mice with microbead-induced glaucoma, albeit via different pathways, without affecting IOP. The relatively low apoptotic effect observed in microbead-injected TLR4KO mice suggests a role of inflammation in glaucomatous damage.

Inhaled Nitric Oxide Promotes Angiogenesis in the Rodent Developing Brain

Inhaled nitric oxide (iNO) is a therapy used in neonates with pulmonary hypertension. Some evidence of its neuroprotective properties has been reported in both mature and immature brains subjected to injury. NO is a key mediator of the VEGF pathway, and angiogenesis may be involved in the reduced vulnerability to injury of white matter and the cortex conferred by iNO. Here, we report the effect of iNO on angiogenesis in the developing brain and its potential effectors. We found that iNO promotes angiogenesis in the developing white matter and cortex during a critical window in P14 rat pups. This shift in the developmental program of brain angiogenesis was not related to a regulation of NO synthases by exogenous NO exposure, nor the VEGF pathway or other angiogenic factors. The effects of iNO on brain angiogenesis were found to be mimicked by circulating nitrate/nitrite, suggesting that these carriers may play a role in transporting NO to the brain. Finally, our data show that the soluble guanylate cyclase/cGMP signaling pathway is likely to be involved in the pro-angiogenetic effect of iNO through thrombospondin-1, a glycoprotein of the extracellular matrix, inhibiting soluble guanylate cyclase through CD42 and CD36. In conclusion, this study provides new insights into the biological basis of the effect of iNO in the developing brain.

3D doppler ultrasound imaging of cerebral blood flow for assessment of neonatal hypoxic-ischemic brain injury in mice

Cerebral blood flow (CBF) acutely reduces in neonatal hypoxic-ischemic encephalopathy (HIE). Clinic studies have reported that severe CBF impairment can predict HIE outcomes in neonates. Herein, the present study uses a non-invasive 3D ultrasound imaging approach to evaluate the changes of CBF after HI insult, and explores the correlation between CBF alterations and HI-induced brain infarct in mouse pups. The neonatal HI brain injury was induced in postnatal day 7 mouse pups using the Rice-Vannucci model. Non-invasive 3D ultrasound imaging was conducted to image CBF changes with multiple frequencies on mouse pups before common carotid artery (CCA) ligation, immediately after ligation, and 0 or 24 hours after HI. Vascularity ratio of the ipsilateral hemisphere was acutely reduced after unilateral ligation of the CCA alone or in combination with hypoxia, and partially restored at 24 hours after HI. Moreover, regression analysis showed that the vascularity ratio of ipsilateral hemisphere was moderately correlated with brain infarct size 24 hours after HI, indicating that CBF reduction contributes to of HI brain injury. To further verify the association between CBF and HI-induced brain injury, a neuropeptide C-type natriuretic peptide (CNP) or PBS was intranasally administrated to the brain of mouse pups one hour after HI insult. Brain infarction, CBF imaging and long-term neurobehavioral tests were conducted. The result showed that intranasal administration of CNP preserved ipsilateral CBF, reduced the infarct size, and improved neurological function after HI brain injury. Our findings suggest that CBF alteration is an indicator for neonatal HI brain injury, and 3D ultrasound imaging is a useful non-invasive approach for assessment of HI brain injury in mouse model.

Neonatal hypoxia ischemia redistributes L1 cell adhesion molecule into rat cerebellar lipid rafts

BACKGROUND

Hypoxic-ischemic encephalopathy (HIE) is a devastating disease with lifelong disabilities. Hypothermia is currently the only treatment. At term, the neonatal cerebellum may be particularly vulnerable to the effects of HIE. At this time, many developmental processes depend on lipid raft function. These microdomains of the plasma membrane are critical for cellular signaling and axon extension. We hypothesized that HIE alters the protein content of lipid rafts in the cerebellum.

METHODS

Postnatal day (PN) 10 animals, considered human term equivalent, underwent hypoxic-ischemic (HI) injury by a right carotid artery ligation followed by hypoxia. For some animals, LPS was administered on PN7, and hypothermia (HT) was conducted for 4 h post-hypoxia. Lipid rafts were isolated from the right and left cerebella. The percent of total L1 cell adhesion molecule in lipid rafts was determined 4 and 72 h after hypoxia.

RESULTS

No sex differences were found. HI alone caused significant increases in the percent of L1 in lipid rafts which persisted until 72 h in the right but not the left cerebellum. A small but significant effect of LPS was detected in the left cerebellum 72 h after HI. Hypothermia had no effect.

CONCLUSIONS

Lipid rafts may be a new target for interventions of HIE.

IMPACT

This article investigates the effect of neonatal exposure to hypoxic-ischemic encephalopathy (HIE) on the distribution of membrane proteins in the cerebellum. This article explores the effectiveness of hypothermia as a prevention for the harmful effects of HIE on membrane protein distribution. This article shows an area of potential detriment secondary to HIE that persists with current treatments, and explores ideas for new treatments.

The Role of Sildenafil in Treating Brain Injuries in Adults and Neonates

Sildenafil is a recognized treatment for patients suffering from erectile dysfunction and pulmonary hypertension. However, new evidence suggests that it may have a neuroprotective and a neurorestorative role in the central nervous system of both adults and neonates. Phosphodiesterase type 5-the target of sildenafil-is distributed in many cells throughout the body, including neurons and glial cells. This study is a comprehensive review of the demonstrated effects of sildenafil on the brain with respect to its function, extent of injury, neurons, neuroinflammation, myelination, and cerebral vessels.

Phosphodiesterase-5 Inhibitor Attenuates Anxious Phenotypes and Movement Disorder Induced by Mild Ischemic Stroke in Rats

Objective

Patients with mild ischemic stroke experience various sequela and residual symptoms, such as anxious behavior and deficits in movement. Few approaches have been proved to be effective and safe therapeutic approaches for patients with mild ischemic stroke by acute stroke. Sildenafil (SIL), a phosphodiesterase-5 inhibitor (PDE5i), is a known remedy for neurodegenerative disorders and vascular dementia through its angiogenesis and neurogenesis effects. In this study, we investigated the efficacy of PDE5i in the emotional and behavioral abnormalities in rats with mild ischemic stroke.

Methods

We divided the rats into four groups as follows (n=20, respectively) : group 1, naïve; group 2, middle cerebral artery occlusion (MCAo30); group 3, MCAo30+SIL-pre; and group 4, MCAo30+SIL-post. In the case of drug administration groups, single dose of PDE5i (sildenafil citrate, 20 mg/kg) was given at 30-minute before and after reperfusion of MCAo in rats. After surgery, we investigated and confirmed the therapeutic effect of sildenafil on histology, immunofluorescence, behavioral assays and neural oscillations.

Results

Sildenafil alleviated a neuronal loss and reduced the infarction volume. And results of behavior task and immunofluorescence shown possibility that anti-inflammation process and improve motor deficits sildenafil treatment after mild ischemic stroke. Furthermore, sildenafil treatment attenuated the alteration of theta-frequency rhythm in the CA1 region of the hippocampus, a known neural oscillatory marker for anxiety disorder in rodents, induced by mild ischemic stroke.

Conclusion

PDE5i as effective therapeutic agents for anxiety and movement disorders and provide robust preclinical evidence to support the development and use of PDE5i for the treatment of mild ischemic stroke residual disorders.

Sildenafil improves hippocampal brain injuries and restores neuronal development after neonatal hypoxia-ischemia in male rat pups

The hippocampus is a fundamental structure of the brain that plays an important role in neurodevelopment and is very sensitive to hypoxia-ischemia (HI). The purpose of this study was to investigate the effects of sildenafil on neonatal hippocampal brain injuries resulting from HI, and on neuronal development in this context. HI was induced in male Long-Evans rat pups at postnatal day 10 (P10) by a left common carotid ligation followed by a 2-h exposure to 8% oxygen. Rat pups were randomized to vehicle or sildenafil given orally twice daily for 7 days starting 12 h after HI. Hematoxylin and eosin staining was performed at P30 to measure the surface of the hippocampus; immunohistochemistry was performed to stain neurons, oligodendrocytes, and glial cells in the hippocampus. Western blots of the hippocampus were performed at P12, P17, and P30 to study the expression of neuronal markers and mTOR pathway. HI caused significant hippocampal atrophy and a significant reduction of the number of mature neurons, and induced reactive astrocytosis and microgliosis in the hippocampus. HI increased apoptosis and caused significant dysregulation of the normal neuronal development program. Treatment with sildenafil preserved the gross morphology of the hippocampus, reverted the number of mature neurons to levels comparable to sham rats, significantly increased both the immature and mature oligodendrocytes, and significantly reduced the number of microglia and astrocytes. Sildenafil also decreased apoptosis and reestablished the normal progression of post-natal neuronal development. The PI3K/Akt/mTOR pathway, whose activity was decreased after HI in the hippocampus, and restored after sildenafil treatment, may be involved. Sildenafil may have both neuroprotective and neurorestorative properties in the neonatal hippocampus following HI.

Sildenafil-Mediated Neuroprotection from Adult to Neonatal Brain Injury: Evidence, Mechanisms, and Future Translation

Cerebral stroke, traumatic brain injury, and hypoxic ischemic encephalopathy are among the most frequently occurring brain injuries. A complex pathogenesis, characterized by a synergistic interaction between alterations of the cerebrovascular system, cell death, and inflammation, is at the basis of the brain damage that leads to behavioral and neurodevelopmental disabilities in affected subjects. Sildenafil is a selective inhibitor of the enzyme phosphodiesterase 5 (PDE5) that is able to cross the blood-brain barrier. Preclinical data suggest that sildenafil may be a good candidate for the prevention or repair of brain injury in both adults and neonates. The aim of this review is to summarize the evidence supporting the neuroprotective action of sildenafil and discuss the possible benefits of the association of sildenafil with current therapeutic strategies.

Therapies for neonatal encephalopathy: Targeting the latent, secondary and tertiary phases of evolving brain injury

In term and near-term neonates with neonatal encephalopathy, therapeutic hypothermia protocols are well established. The current focus is on how to improve outcomes further and the challenge is to find safe and complementary therapies that confer additional protection, regeneration or repair in addition to cooling. Following hypoxia-ischemia, brain injury evolves over three main phases (latent, secondary and tertiary), each with a different brain energy, perfusion, neurochemical and inflammatory milieu. While therapeutic hypothermia has targeted the latent and secondary phase, we now need therapies that cover the continuum of brain injury that spans hours, days, weeks and months after the initial event. Most agents have several therapeutic actions but can be broadly classified under a predominant action (e.g., free radical scavenging, anti-apoptotic, anti-inflammatory, neuroregeneration, and vascular effects). Promising early/secondary phase therapies include Allopurinol, Azithromycin, Exendin-4, Magnesium, Melatonin, Noble gases and Sildenafil. Tertiary phase agents include Erythropoietin, Stem cells and others. We review a selection of promising therapeutic agents on the translational pipeline and suggest a framework for neuroprotection and neurorestoration that targets the evolving injury.

Role of Sirtuin-1 in Neonatal Hypoxic-Ischemic Encephalopathy and Its Underlying Mechanism

BACKGROUND Neonatal hypoxic-ischemic encephalopathy (HIE) is a dreaded disease and one of the leading causes of severe neurological dysfunction in neonates. The present study explored the functions of Sirtuin-1 (SIRT1) in neonatal HIE. MATERIAL AND METHODS A HIE neonatal rat model was generated to determine SIRT1 levels in brain tissues. Cell apoptosis and cell viability were analyzed by flow cytometry and MTT assay. qRT-PCR and Western blot analysis were used to assess gene mRNA and protein levels. Subsequently, the effect of SIRT1 on HIE was investigated in vitro by constructing an oxygen-glucose deprivation (OGD) cell model. RESULTS The effective construction of the HIE rat model was confirmed by the enhanced brain cell apoptosis and the increased expression of HIE-related molecular markers, including S100 calcium-binding protein B (S100B) and neuron-specific enolase (NSE). SIRT1 expression was downregulated in HIE rat brain tissues. These findings indicated that SIRT1 was downregulated in neuronal cells subjected to OGD. In addition, enhanced cell viability and reduced cell apoptosis were observed, suggesting that SIRT1 overexpression relieved OGD-induced neuronal cell injury. Transfection with SIRT1-siRNA further increased OGD-induced neuronal cell injury, evidenced by decreased cell viability and enhanced cell apoptosis. Finally, SIRT1 overexpression significantly downregulated p-p65 protein expression. CONCLUSIONS Our findings revealed that SIRT1 may be a novel and promising therapy target for HIE treatment.

Differentiation of human neuroblastoma cell line IMR-32 by sildenafil and its newly discovered analogue IS00384

Sildenafil, a phosphodiesterase-5 inhibitor is FDA approved drug against erectile dysfunction. It is currently undergoing many clinical trials, alone or in combinations against different diseases. Treatment of neural progenitor cells with sildenafil is known to regulate their basal cGMP levels and enhance neurogenesis and differentiation. cGMP as well as cAMP are known to play a central role in the maintenance, repair and remodelling of the nervous system. In the present study, we report the neurodifferentiation property of sildenafil in neuroblastoma cancer cell line IMR-32. Sildenafil was found to induce the formation of neurite outgrowths that were found expressing neuronal markers, such as NeuN, NF-H and βIII tubulin. IS00384, a recently discovered PDE5 inhibitor by our laboratory, was also found to induce neurodifferentiation of IMR-32 cells. The effect of IS00384 on differentiation was even more profound than sildenafil. Both the compounds were found to elevate and activate the Guanine nucleotide exchange factor C3G, which is a regulator of differentiation in IMR-32 cells. They were also found to elevate the levels of cGMP and activate the AMPK-ACC and PI3K-Akt signalling pathways. These pathways are known to play important role in cytoskeletal rearrangements necessary for differentiation. This study highlights the role of phosphodiesterases-5 in neurodifferentiation and use of sildenafil and IS00384 as small molecule tools to study the process of cellular differentiation.

Blast-induced tinnitus: Animal models

Blast-induced tinnitus is a prevalent problem among military personnel and veterans, as blast-related trauma damages the vulnerable microstructures within the cochlea, impacts auditory and non-auditory brain structures, and causes tinnitus and other disorders. Thus far, there is no effective treatment of blast-induced tinnitus due to an incomplete understanding of its underlying mechanisms, necessitating development of reliable animal models. This article focuses on recent animal studies using behavioral, electrophysiological, imaging, and pharmacological tools. The mechanisms underlying blast-induced tinnitus are largely similar to those underlying noise-induced tinnitus: increased spontaneous firing rates, bursting, and neurosynchrony, Mn++ accumulation, and elevated excitatory synaptic transmission. The differences mainly lie in the data variability and time course. Noise trauma-induced tinnitus mainly originates from direct peripheral deafferentation at the cochlea, and its etiology subsequently develops along the ascending auditory pathways. Blast trauma-induced tinnitus, on the other hand, results from simultaneous impact on both the peripheral and central auditory systems, and the resultant maladaptive neuroplasticity may also be related to the additional traumatic brain injury. Consequently, the neural correlates of blast-induced tinnitus have different time courses and less uniform manifestations of its neural correlates.

Cyclic nucleotide phosphodiesterases (PDEs) and endothelial function in ischaemic stroke. A review

BACKGROUND

Endothelial dysfunction is a hallmark of cerebrovascular disease, including ischemic stroke. Modulating endothelial signalling by cyclic nucleotides, cAMP and cGMP, is a potential therapeutic target in stroke. Inhibitors of the cyclic nucleotide degrading phosphodiesterase (PDE) enzymes may restore cerebral endothelial function. Current knowledge on PDE distribution and function in cerebral endothelial cells is sparse. This review explores data on PDE distribution and effects of PDEi in cerebral endothelial cells and identifies which PDEs are potential treatment targets in stroke.

METHOD

We performed a systematic search of electronic databases (Medline and Embase). Our search terms were cerebral ischaemia, cerebral endothelial cells, cyclic nucleotide, phosphodiesterase and phosphodiesterase inhibitors.

RESULTS

We found 23 publications which described effects of selective inhibitors of only three PDE families on endothelial function in ischemic stroke. PDE3 inhibitors (PDE3i) (11 publications) and PDE4 inhibitors (PDE4i) (3 publications) showed anti-inflammatory, anti-apoptotic or pro-angiogenic effects. PDE3i also reduced leucocyte infiltration and MMP-9 expression. Both PDE3i and PDE4i increased expression of tight junction proteins and protected the blood-brain barrier. PDE5 inhibitors (PDE5i) (6 publications) reduced inflammation and apoptosis. In preclinical models, PDE5i enhanced cGMP/NO signalling associated with microvascular angiogenesis, increased cerebral blood flow and improved functional recovery. Non-specific PDEi (3 publications) had mainly anti-inflammatory effects.

CONCLUSION

This review demonstrates that non-selective and selective PDEi of PDE3, PDE4 and PDE5 modulated endothelial function in cerebral ischemic stroke by regulating processes involved in vascular repair and neuroprotection and thus reduced cell death and inflammation. Of note, they promoted angiogenesis, microcirculation and improved functional recovery; all are important in stroke prevention and recovery, and effects should be further evaluated in humans.

Comparison of sildenafil, fluoxetine and its co-administration against chronic constriction injury induced neuropathic pain in rats: An influential additive effect

Current drug treatment available for neuropathic pain (NP) provides meager and partial pain relief due to incomplete efficacy and dose-dependent adverse effect. Hence, combination therapy can provide prolongation in analgesic effect with milder side effects. The present investigation aimed at observing the effects of sildenafil (SD) on Fluoxetine (FLX) in attenuation of chronic constriction injury (CCI) induced NP in rats. CCI was achieved in rats by placing four loose ligations around the sciatic nerve and rats were received respective treatments on SD and FLX till 14 days further behaviors parameters like heat hyperalgesia and allodynia, pin prick and acetone drop test were executed in order to access thermal, mechanical and cold allodynia, respectively, on a predetermined time interval. On the 21st day the animals were sacrificed for determination of total protein, myeloperoxidase activity in the adjoining muscular tissues while glutathione and TNF-α in the sciatic nerve. Co-administration of SD + FLX + CCI gave the pronounced effect that was superior over individual responses of SD and FLX in all behavioral as well as biochemical parameters. It was observed that attenuation in the altered behavioral pattern of CCI induced rats was modified prominently from 3rd day only in a group of rats treated with SD + FLX + CCI. The whole study was finally supported by histopathological results. Finally, it was concluded that SD produces an additive effect when given with FLX in attenuation of NP may be due to elevation in the level of intracellular concentrations of cyclic guanosine monophosphate which further causes downregulation of calcium channel.

PKM2 Involved in Neuronal Apoptosis on Hypoxic-ischemic Encephalopathy in Neonatal Rats

Pyruvate Kinase isozymes M2 (PKM2) is a glycolytic enzyme involved in glycolysis that decarboxylates phosphoenolpyruvate to pyruvate and generates ATP. PKM2 also plays a significant role in tumor growth, in cell division, angiogenesis, apoptosis and metastasis. In this study, we have investigated the role of PKM2 in cortical neurons which suffered hypoxic-ischemic encephalopathy (HIE) in newborn rats. Immunohistochemistry and Western blot analysis revealed the protein expression of PKM2 peaking at 24 h after HIE. Double immunofluorescence labeling showed that PKM2 was mainly located in the neurons of the ipsilateral cerebral cortex, not in astrocytes or microglia. The increased level of active caspase-3 and the decreased level of phosphorylated AKT (p-AKT) were consistent with the PKM2 expression. TUNEL staining assay showed that PKM2 may participate in neuronal apoptosis in the rat ipsilateral cerebral cortex. Silencing of PKM2 in primary cultures of cortical neurons using a specific siRNA reduced the expression of active caspase-3 and upregulated p-AKT expression. Taken together, the results indicate that PKM2 may be involved in neuronal apoptosis after HIE by a mechanism dependent on the inactivation of p-AKT.

Increased bioavailability of cyclic guanylate monophosphate prevents retinal ganglion cell degeneration

The nitric oxide - guanylyl cyclase-1 - cyclic guanylate monophosphate (NO-GC-1-cGMP) pathway has emerged as a potential pathogenic mechanism for glaucoma, a common intraocular pressure (IOP)-related optic neuropathy characterized by the degeneration of retinal ganglion cells (RGCs) and their axons in the optic nerve. NO activates GC-1 to increase cGMP levels, which are lowered by cGMP-specific phosphodiesterase (PDE) activity. This pathway appears to play a role in both the regulation of IOP, where reduced cGMP levels in mice leads to elevated IOP and subsequent RGC degeneration. Here, we investigated whether potentiation of cGMP signaling could protect RGCs from glaucomatous degeneration. We administered the PDE5 inhibitor tadalafil orally (10 mg/kg/day) in murine models of two forms of glaucoma - primary open angle glaucoma (POAG; GC-1^-/- mice) and primary angle-closure glaucoma (PACG; Microbead Occlusion Model) - and measured RGC viability at both the soma and axon level. To determine the direct effect of increased cGMP on RGCs in vitro, we treated axotomized whole retina and primary RGC cultures with the cGMP analogue 8-Br-cGMP. Tadalafil treatment increased plasma cGMP levels in both models, but did not alter IOP or mean arterial pressure. Nonetheless, tadalafil treatment prevented degeneration of RGC soma and axons in both disease models. Treatment of whole, axotomized retina and primary RGC cultures with 8-Br-cGMP markedly attenuated both necrotic and apoptotic cell death pathways in RGCs. Our findings suggest that enhancement of the NO-GC-1-cGMP pathway protects the RGC body and axon in murine models of POAG and PACG, and that enhanced signaling through this pathway may serve as a novel glaucoma treatment, acting independently of IOP.

The nitric oxide-guanylate cyclase pathway and glaucoma

Glaucoma is a prevalent optic neuropathy characterized by the progressive dysfunction and loss of retinal ganglion cells (RGCs) and their optic nerve axons, which leads to irreversible visual field loss. Multiple risk factors for the disease have been identified, but elevated intraocular pressure (IOP) remains the primary risk factor amenable to treatment. Reducing IOP however does not always prevent glaucomatous neurodegeneration, and many patients progress with the disease despite having IOP in the normal range. There is increasing evidence that nitric oxide (NO) is a direct regulator of IOP and that dysfunction of the NO-Guanylate Cyclase (GC) pathway is associated with glaucoma incidence. NO has shown promise as a novel therapeutic with targeted effects that: 1) lower IOP; 2) increase ocular blood flow; and 3) confer neuroprotection. The various effects of NO in the eye appear to be mediated through the activation of the GC- guanosine 3:5'-cyclic monophosphate (cGMP) pathway and its effect on downstream targets, such as protein kinases and Ca²⁺ channels. Although NO-donor compounds are promising as therapeutics for IOP regulation, they may not be ideal to harness the neuroprotective potential of NO signaling. Here we review evidence that supports direct targeting of GC as a novel pleiotrophic treatment for the disease, without the need for direct NO application. The identification and targeting of other factors that contribute to glaucoma would be beneficial to patients, particularly those that do not respond well to IOP-dependent interventions.

Increased motor neuron resilience by small molecule compounds that regulate IGF-II expression

The selective vulnerability of motor neurons in amyotrophic lateral sclerosis (ALS) is evident by sparing of a few subpopulations during this fast progressing and debilitating degenerative disease. By studying the gene expression profile of resilient vs. vulnerable motor neuron populations we can gain insight in what biomolecules and pathways may contribute to the resilience and vulnerability. Several genes have been found to be differentially expressed in the vulnerable motor neurons of the cervical spinal cord as compared to the spared motor neurons in CNIII/IV. One gene that is differentially expressed and present at higher levels in less vulnerable motor neurons is insulin-like growth factor II (IGF-II). The motor neuron protective effect of IGF-II has been demonstrated both in vitro and in SOD1 transgenic mice. Here, we have screened a library of small molecule compounds and identified inducers of IGF-II mRNA and protein expression. Several identified compounds significantly protected motor neurons from glutamate excitotoxicity in vitro. One of the compounds, vardenafil, resulted in a complete motor neuron protection, an effect that was reversed by blocking receptors of IGF-II. When administered to naïve rats vardenafil was present in the cerebrospinal fluid and increased IGF-II mRNA expression in the spinal cord. When administered to SOD1 transgenic mice, there was a significant delay in motor symptom onset and prolonged survival. Vardenafil also increased IGF-II mRNA and protein levels in motor neurons derived from healthy subject and ALS patient iPSCs, activated a human IGF-II promoter and improved survival of ALS-patient derived motor neurons in culture. Our findings suggest that modulation of genes differentially expressed in vulnerable and resilient motor neurons may be a useful therapeutic approach for motor neuron disease.

Icariside II, a PDE5 inhibitor from Epimedium brevicornum, promotes neuron-like pheochromocytoma PC12 cell proliferation via activating NO/cGMP/PKG pathway

Icariside II (ICS II), a phosphodiesterase 5 inhibitor (PDE 5-I), is a major ingredient of Epimedium brevicornum, with wide spectrum of neuroprotective properties. However, little is known about the potential beneficial effect of ICS II on neuronal cell proliferation, and its possible underlying mechanism remains still unclear. We hypothesized that the beneficial effect of ICS II on neuron-like highly differentiated rat pheochromocytoma (PC12) cell proliferation is correlated with the nitric oxide (NO) signaling pathway and its upstream of PI3K/AKT pathway. PC12 cells were treated with ICS II alone or together with L-NMMA, H89, KT-5823, and/or LY294002 (the inhibitor of NOS, PKA, PKG, PI3K, respectively). It was found that ICS II concentration-dependently promoted PC12 cells proliferation, and cell cycle analysis showed that the proportion of ICS II-treated PC12 cells in S phase was higher than that of control. Moreover, ICS II at the appropriate concentration (100 μM) not only increased nNOS expression, NO production, but also enhanced cGMP content and PKG activity. The addition of L-NMMA and KT-5 823 significantly inhibited the effects of ICS II on nNOS expression, NO production and PKG activity. Furthermore, LY294002 significantly decreased p-AKT level, NOS activity, NO production and nNOS expression, but it did not affect iNOS expression. These findings demonstrate that the beneficial effect of ICS II on neuronal cell proliferation, and its possible underlying mechanisms are, at least partly, through activating AKT/nNOS/NO/cGMP/PKG signaling pathway.

Phosphodiesterase 5 inhibition as a therapeutic target for ischemic stroke: A systematic review of preclinical studies

Phosphodiesterase 5 inhibitors (PDE5i), such as sildenafil (Viagra®) are widely used for erectile dysfunction and pulmonary hypertension. Preclinical studies suggest that PDE5i may improve functional outcome following ischemic stroke. In this systematic review we aimed to evaluate the effects of selective PDE5i in animal models of brain ischaemia. A systematic search in Medline, Embase, and The Cochrane Library was performed including studies in English assessing the effects of selective PDE5i. 32 publications were included describing outcome in 3646 animals. Neuroprotective effects of PDE5i were dependent on the NO-cGMP-PKG-pathway. These included reduced neuronal apoptosis (n=3 studies), oxidative stress (n=5), and neuroinflammation (n=2). PDE5i increased angiogenesis and elevated regional cerebral blood flow in the ischemic penumbra, and improved functional recovery. Some studies found that PDE5i treatment reduced lesion volume (n=9), others found no effect (n=9). Treatment was effective when administered within 24h post-ischemia, though treatment delayed to seven days improved outcome in one study. This review demonstrates both neuroprotective and neurorestorative effects of PDE5i in animal models of stroke, though the specific underlying signaling pathways relating to PDE5 inhibition and cGMP may remain serendipitous in some studies. There is currently limited evidence on the effects of selective PDE5i in human stroke patients, hence translation of preclinical results into clinical trials may be warranted.

Therapeutic hypothermia in infants with hypoxic-ischemic encephalopathy and reversible persistent pulmonary hypertension: short-term hospital outcomes

AIM

Neonatal hypoxic ischemic encephalopathy (HIE) patients are at times accompanied by persistent pulmonary hypertension (PPHN), which is by itself another risk factor of adverse outcomes. We aimed to assess the outcome of therapeutic hypothermia (TH) in these patients whom we managed to reverse the shunt flow, as they are expected to be at much higher risk of adverse neurodevelopmental outcome.

METHODS

We reviewed the medical records of 116 HIE infants (13 with PPHN and 103 without PPHN) who underwent TH between 2012 and 2016. We analyzed the short-term hospital outcomes and brain study results (electroencephalogram and magnetic resonance imaging) of TH in these patients.

RESULTS

While infants with PPHN were significantly more likely to be outborn or have meconium aspiration syndrome, and required a longer duration of inotrope and intensive care support, electroencephalographic and brain magnetic resonance findings did not significantly differ according to PPHN status.

CONCLUSION

Based on our study, the hospital outcomes of infants with HIE accompanied by reversible PPHN who underwent TH were in general not significantly graver than those not accompanied by PPHN. Our results suggest that undergoing TH may be more beneficial in HIE infants with PPHN and the risks for possible adverse effects may not be as so high.

Phosphodiesterase Inhibitors as a Therapeutic Approach to Neuroprotection and Repair

A wide diversity of perturbations of the central nervous system (CNS) result in structural damage to the neuroarchitecture and cellular defects, which in turn are accompanied by neurological dysfunction and abortive endogenous neurorepair. Altering intracellular signaling pathways involved in inflammation and immune regulation, neural cell death, axon plasticity and remyelination has shown therapeutic benefit in experimental models of neurological disease and trauma. The second messengers, cyclic adenosine monophosphate (cyclic AMP) and cyclic guanosine monophosphate (cyclic GMP), are two such intracellular signaling targets, the elevation of which has produced beneficial cellular effects within a range of CNS pathologies. The only known negative regulators of cyclic nucleotides are a family of enzymes called phosphodiesterases (PDEs) that hydrolyze cyclic nucleotides into adenosine monophosphate (AMP) or guanylate monophosphate (GMP). Herein, we discuss the structure and physiological function as well as the roles PDEs play in pathological processes of the diseased or injured CNS. Further we review the approaches that have been employed therapeutically in experimental paradigms to block PDE expression or activity and in turn elevate cyclic nucleotide levels to mediate neuroprotection or neurorepair as well as discuss both the translational pathway and current limitations in moving new PDE-targeted therapies to the clinic.

Effect of chronic administration of sildenafil citrate (Viagra) on the histology of the retina and optic nerve of adult male rat

BACKGROUND

Abnormal vision has been reported by 3% of patients treated with sildenafil citrate (Viagra). Although many men use Viagra for an extended period for treatment of erectile dysfunction, the implications of the long term-daily use of it on the retina and optic nerve are unclear.

AIM OF THE WORK

To investigate the effect of chronic daily use of sildenafil citrate in a dose equivalent to men preferred therapeutic dose on the histology of the retina and optic nerve of adult male rat.

MATERIAL & METHODS

Eighteen adult male Wistar rats were equally divided into three groups. Group I: control. Group II: treated with sildenafil citrate orally (10mg/kg/day) for 8 weeks. Group III (withdrawal): treated as group II and then left for 4 weeks without treatment. Specimens from the retina and optic nerve were processed for light and electron microscopy.

RESULTS

In sildenafil citrate treated group, the retina and optic nerve revealed vacuolations and congested blood capillaries with apoptotic endothelial and pericytic cells, and thickened basal lamina. Caspase-3 (apoptotic marker) and CD31 (endothelial marker) expression increased. Glial cells revealed morphological changes: Müller cells lost their processes, activated microglia, astrocytic clasmatodendrosis, degenerated oligodendrocytes surrounded by disintegrated myelin sheathes of the optic nerve fibers. The retina and optic nerve of the withdrawal group revealed less vacuolations and congestion, and partial recovery of the glial cells.

CONCLUSION

Chronic treatment with sildenafil citrate (Viagra) caused toxic effect on the structure of the retina and optic nerve of the rat. Partial recovery was observed after drug withdrawal.

Sildenafil Improves Brain Injury Recovery following Term Neonatal Hypoxia-Ischemia in Male Rat Pups

Term asphyxiated newborns remain at risk of developing brain injury despite available neuropreventive therapies such as hypothermia. Neurorestorative treatments may be an alternative. This study investigated the effect of sildenafil on brain injury induced by neonatal hypoxia-ischemia (HI) at term-equivalent age. Neonatal HI was induced in male Long-Evans rat pups at postnatal day 10 (P10) by left common carotid ligation followed by a 2-hour exposure to 8% oxygen; sham-operated rat pups served as the control. Both groups were randomized to oral sildenafil or vehicle twice daily for 7 consecutive days. Gait analysis was performed on P27. At P30, the rats were sacrificed, and their brains were extracted. The surfaces of both hemispheres were measured on hematoxylin and eosin-stained brain sections. Mature neurons and endothelial cells were quantified near the infarct boundary zone using immunohistochemistry. HI caused significant gait impairment and a reduction in the size of the left hemisphere. Treatment with sildenafil led to an improvement in the neurological deficits as measured by gait analysis, as well as an improvement in the size of the left hemisphere. Sildenafil, especially at higher doses, also caused a significant increase in the number of neurons near the infarct boundary zone. In conclusion, sildenafil administered after neonatal HI may improve brain injury recovery by promoting neuronal populations.

Pharmacokinetic investigation of sildenafil using positron emission tomography and determination of its effect on cerebrospinal fluid cGMP levels

Sildenafil (Viagra) is a selective inhibitor of phosphodiesterase type 5 (PDE5), which degrades cyclic guanosine monophosphate to the linear nucleotide. Sildenafil is acutely used in erectile dysfunction and chronically in pulmonary hypertension. Evidence in the last decade shows that sildenafil may have potential as a therapeutic option for Alzheimer's disease or other neurodegenerative disorders. The purpose of this work was to explore whether sildenafil crosses the blood-brain barrier. Pharmacokinetic properties of sildenafil in rodents were investigated using (11) C-radiolabeling followed by in vivo positron emission tomography (PET) and ex vivo tissue dissection and gamma counting. PET results in rats suggest penetration into the central nervous system. Ex vivo data in perfused animals suggest that trapping of [(11) C]sildenafil within the cerebral vascular endothelium limits accumulation in the central nervous system parenchyma. Peroral sildenafil administration to Macaca fascicularis and subsequent chemical analysis of plasma and cerebrospinal fluid (CSF) using liquid chromatography coupled with tandem mass spectrometry showed that drug content in the CSF was high enough to achieve PDE5 inhibition, which was also demonstrated by the significant increases in CSF cyclic guanosine monophosphate levels. Central actions of sildenafil include both relaxation of the cerebral vasculature and inhibition of PDE5 in neurons and glia. This central action of sildenafil may underlie its efficacy in neuroprotection models, and may justify the continued search for a PDE5 ligand suitable for PET imaging. Sildenafil interacts with phosphodiesterase type 5 (PDE5) expressed in the endothelium and/or smooth muscle cells of brain vessels and also crosses the blood-brain barrier to interact with PDE5 expressed in brain cells. At therapeutic doses, the concentration of sildenafil in the cerebrospinal fluid (CSF) is high enough to inhibit PDE5 in the neural cells (neurons and glia). In turn, the concentration of cGMP likely increases in parenchymal cells and, as shown in this report, in the CSF. Read the Editorial Highlight for this article on page 220. Cover Image for this issue: doi: 10.1111/jnc.13302.

Sildenafil (Viagra(®)) prevents and restores LPS-induced inflammation in astrocytes

Astrocytes are effectively involved in the pathophysiological processes in the central nervous system (CNS) and may contribute to or protect against development of inflammatory and degenerative diseases. Sildenafil is a potent and selective phosphodiesterase-5 (PDE-5) inhibitor, which induces cyclic GMP accumulation. However, the mechanisms of actions on glial cells are not clear. The aim of the present work is to evaluate the role of sildenafil in lipopolysaccharide (LPS)-stimulated astrocytes. The cytoskeleton integrity and Ca(2+) waves were assessed as indicators of inflammatory state. Two main groups were done: (A) one prevention and (B) one restoration. Each of these groups: A1: control; A2: LPS for 24h; A3: sildenafil 1 or 10μM for 4h and then sildenafil 1 or 10μM+LPS for 24h. B1: control; B2: LPS for 24h; B3: LPS for 24h and then LPS+sildenafil 1 or 10μM for 24h. Cytoskeleton integrity was analyzed through GFAP immunolabeling and actin labeling with an Alexa 488-conjugated phalloidin probe. Calcium responses were assessed through a Ca(2+)-sensitive fluorophore Fura-2/AM. The results show that both preventive and restorative treatments with sildenafil (in both concentrations) reduced the Ca(2+) responses in intensity and induced a more organized actin fiber pattern, compared to LPS treated cells. This work demonstrated for the first time that astrocytes are a key part of the sildenafil protective effects in the CNS.

Alterations in the corticotropin-releasing hormone (CRH) neurocircuitry: Insights into post stroke functional impairments

Although it is well accepted that changes in the regulation of the hypothalamic-pituitary adrenal (HPA) axis may increase susceptibility to affective disorders in the general population, this link has been less examined in stroke patients. Yet, the bidirectional association between depression and cardiovascular disease is strong, and stress increases vulnerability to stroke. Corticotropin-releasing hormone (CRH) is the central stress hormone of the HPA axis pathway and acts by binding to CRH receptors (CRHR) 1 and 2, which are located in several stress-related brain regions. Evidence from clinical and animal studies suggests a role for CRH in the neurobiological basis of depression and ischemic brain injury. Given its importance in the regulation of the neuroendocrine, autonomic, and behavioral correlates of adaptation and maladaptation to stress, CRH is likely associated in the pathophysiology of post stroke emotional impairments. The goals of this review article are to examine the clinical and experimental data describing (1) that CRH regulates the molecular signaling brain circuit underlying anxiety- and depression-like behaviors, (2) the influence of CRH and other stress markers in the pathophysiology of post stroke emotional and cognitive impairments, and (3) context and site specific interactions of CRH and BDNF as a basis for the development of novel therapeutic targets. This review addresses how the production and release of the neuropeptide CRH within the various regions of the mesocorticolimbic system influences emotional and cognitive behaviors with a look into its role in psychiatric disorders post stroke.

Comparison of Neuroprotective Effect of Bevacizumab and Sildenafil following Induction of Stroke in a Mouse Model

To evaluate the effect of bevacizumab and sildenafil on stroke parameters in a mouse model, middle cerebral artery occlusion was induced in male C57Bl/6 mice using an intra-arterial filament method. The filament was removed after 60 minutes, and the mice were immediately given a single intraperitoneal injection of saline, bevacizumab, or sildenafil. An additional group of mice (n = 7) received bevacizumab 6 h after MCAO induction. The mice were euthanized 24 hours later and evaluated for infarct area and brain edema using triphenyltetrazolium chloride staining and ImageJ. In the saline-treated mice (n = 16), total stroke volume was 19.20 ± 6.38 mm³, mean penumbra area was 4.5 ± 2.03 mm³, and hemispheric asymmetry was 106.5%. Corresponding values in the bevacizumab group (n = 19) were 17.79 ± 5.80 mm³, 7.3 ± 3.5 mm³, and 108.6%; in the delayed (6 h) bevacizumab injected mice (n = 7) they were 9.80 ± 8.00 mm³, 2.4 ± 2.0 mm³, and 98.2%; and in the sildenafil group (n = 16) they were 18.42 ± 5.41 mm³, 5.7 ± 2.02 mm³, and 109.9%. The bevacizumab group had a significantly larger mean penumbra area when given immediately and smaller total stroke area in both groups than the saline- (p = 0.03) and sildenafil-treated (p = 0.003) groups. Only delayed bevacizumab group had reduced edema. Bevacizumab, injected immediately or delayed after injury, exerts a neuroprotective/salvage effect, whereas immediate treatment with sildenafil does not. Inflammation may play a role in the neuroprotective effect.

Sildenafil, a cyclic GMP phosphodiesterase inhibitor, induces microglial modulation after focal ischemia in the neonatal mouse brain

BACKGROUND

Perinatal ischemic stroke is the most frequent form of cerebral infarction in neonates; however, evidence-based treatments are currently lacking. We have previously demonstrated a beneficial effect of sildenafil citrate, a PDE-5 inhibitor, on stroke lesion size in neonatal rat pups. The present study investigated the effects of sildenafil in a neonatal mouse stroke model on (1) hemodynamic changes and (2) regulation of astrocyte/microglia-mediated neuroinflammation.

METHODS

Ischemia was induced in C57Bl/6 mice on postnatal (P) day 9 by permanent middle cerebral artery occlusion (pMCAo), and followed by either PBS or sildenafil intraperitoneal (i.p.) injections. Blood flow (BF) velocities were measured by ultrasound imaging with sequential Doppler recordings and laser speckle contrast imaging. Animals were euthanized, and brain tissues were obtained at 72 h or 8 days after pMCAo. Expression of M1- and M2-like microglia/macrophage markers were analyzed.

RESULTS

Although sildenafil (10 mg/kg) treatment potently increased cGMP concentrations, it did not influence early collateral recruitment nor did it reduce mean infarct volumes 72 h after pMCAo. Nevertheless, it provided a significant dose-dependent reduction of mean lesion extent 8 days after pMCAo. Suggesting a mechanism involving modulation of the inflammatory response, sildenafil significantly decreased microglial density at 72 h and 8 days after pMCAo. Gene expression profiles indicated that sildenafil treatment also modulates M1- (ptgs2, CD32 and CD86) and M2-like (CD206, Arg-1 and Lgals3) microglia/macrophages in the late phase after pMCAo. Accordingly, the number of COX-2(+) microglia/macrophages significantly increased in the penumbra at 72 h after pMCAo but was significantly decreased 8 days after ischemia in sildenafil-treated animals.

CONCLUSIONS

Our findings argue that anti-inflammatory effects of sildenafil may provide protection against lesion extension in the late phase after pMCAo in neonatal mice. We propose that sildenafil treatment could represent a potential strategy for neonatal ischemic stroke treatment/recovery.

Oxymatrine attenuated hypoxic-ischemic brain damage in neonatal rats via improving antioxidant enzyme activities and inhibiting cell death

Oxymatrine (OMT), an active constituent of Chinese herb Sophora flavescens Ait, has been proved to possess anti-tumor, anti-oxidant, anti-inflammatory, and anti-apoptotic activities. Previous study has demonstrated that OMT had protective roles on multiple in vitro and in vivo brain injury models including regulation of apoptosis-related proteins caspase-3, Bax and Bcl-2. In this study, we investigated whether this protective effect could apply to neonatal hypoxic-ischemic brain damage. Seven-day-old Sprague-Dawley rats were treated with the left carotid artery ligation followed by exposure to 8% oxygen (balanced with nitrogen) for 2.5 h at 37 °C. In sham group rats, neither ligation nor hypoxia was performed. After two successive days intraperitoneal injection with OMT (30, 60 and 120 mg/kg), Nimodipine (1 mg/kg), and saline, brain infarct volume was estimated, histomorphology changes were performed by hematoxylin-eosin (HE) staining as well as electron microscopy. In addition, the activities of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), catalase (CAT), and total antioxidant capacity (T-AOC), as well as production of malondialdehyde (MDA) were assayed in ipsilateral hemisphere homogenates to evaluate the redox status after hypoxic-ischemic. Expression of apoptosis-related proteins Caspase-3, Bax and Bcl-2 in brain were analyzed by western-blot analysis and immunofluorescence. Administration of OMT significantly decreased brain infarct volume and the percentage of injured cells, and ameliorated histopathology and morphological injury as well. Furthermore, OMT obviously increased the activities of SOD, GSH-Px, CAT and T-AOC, and decreased MDA content. Western-blot analysis showed a marked decrease in Caspase-3 expression and increase in the ratio of Bcl-2/Bax after OMT (120 mg/kg) post-treatment as compared with hypoxic-ischemic group. These results suggest that OMT exerts a neuroprotective effect against hypoxic-ischemic brain damage in neonatal rats, which is likely to be mediated through increasing anti-oxidant enzyme activities and inhibiting cell death.

NF-κB Upregulates Type 5 Phosphodiesterase in N9 Microglial Cells: Inhibition by Sildenafil and Yonkenafil

Our previous studies showed that the phosphodiesterase-5 (PDE5) inhibitor sildenafil inhibited the microglial activation induced by lipopolysaccharide (LPS). However, whether yonkenafil, a novel PDE5 inhibitor, also inhibits microglial activation and the underlying mechanism of inhibition remain elusive. Here we found that yonkenafil significantly suppressed the production of NO, interleukin-1β (IL-1β), and tumor necrosis factor-α (TNF-α) and the protein expression of inducible NO synthase (iNOS) induced by LPS in microglial cells in a concentration-dependent manner. Knockdown of PDE5 inhibits NO and iNOS protein expression in LPS-stimulated N9 microglia. Moreover, we observed that the nuclear factor-κB (NF-κB) transcriptionally upregulated PDE5 expression, which was inhibited by sildenafil and yonkenafil in LPS-stimulated N9 microglia. Therefore, sildenafil and yonkenafil may exert their inhibitory effects on microglial activation by reducing the expression of PDE5. Furthermore, sildenafil and yonkenafil increased the cyclic guanosine monophosphate (cGMP) level in N9 microglia, and 8-Br-cGMP, an analogue of cGMP, downregulates extracellular signal-regulated kinases 1 and 2 (ERK1/2)/the NF-κB pathway, suggesting that sildenafil and yonkenafil inhibit microglial activation by decreasing PDE5 expression and increasing the cGMP level. Importantly, sildenafil and yonkenafil significantly alleviated the death of SH-SY5Y neuroblastoma cells and primary cortical neurons induced by the conditioned medium from activated microglia. Together, these findings position PDE5 as a potential therapy target for the treatment of neuroinflammation accompanied by microglial activation.

Pathophysiology and neuroprotection of global and focal perinatal brain injury: lessons from animal models

BACKGROUND

Arterial ischemic stroke occurs more frequently in term newborns than in the elderly, and brain immaturity affects mechanisms of ischemic injury and recovery. The susceptibility to injury of the brain was assumed to be lower in the perinatal period as compared with childhood. This concept was recently challenged by clinical studies showing marked motor disabilities after stroke in neonates, with the severity of motor and cortical sensory deficits similar in both perinatal and childhood ischemic stroke. Our understanding of the triggers and the pathophysiological mechanisms of perinatal stroke has greatly improved in recent years, but many factors remain incompletely understood.

METHODS

In this review, we focus on the pathophysiology of perinatal stroke and on therapeutic strategies that can protect the immature brain from the consequences of stroke by targeting inflammation and brain microenvironment.

RESULTS

Studies in neonatal rodent models of cerebral ischemia have suggested a potential role for soluble inflammatory molecules as important modulators of injury and recovery. A great effort is underway to investigate neuroprotective molecules based on our increasing understanding of the pathophysiology.

CONCLUSION

In this review, we provide a comprehensive summary of new insights concerning pathophysiology of focal and global perinatal brain injury and their implications for new therapeutic approaches.

In vivo Monitoring of Cerebral Hemodynamics in the Immature Rat: Effects of Hypoxia-Ischemia and Hypothermia

BACKGROUND

Neonatal hypoxic-ischemic (HI) encephalopathy occurs in 1-4 per 1,000 live term births and can cause devastating neurodevelopmental disabilities. Currently, therapeutic hypothermia (TH) is the only treatment with proven efficacy. Since TH is associated with decreased cerebral metabolism and cerebral blood flow (CBF), it is important to assess CBF at the bedside. Diffuse correlation spectroscopy (DCS) has emerged as a promising optical modality to noninvasively assess an index of CBF (CBFi) in both humans and animals. In this initial descriptive study, we employ DCS to monitor the evolution of CBFi following HI with or without TH in immature rats. We investigate potential relationships between CBF and subsequent cerebral damage.

METHODS

HI was induced on postnatal day 10 or 11 rat pups by right common carotid artery ligation followed by 60-70 min hypoxia (8% oxygen). After HI, the pups recovered for 4 h under hypothermia (HI-TH group, n = 23) or normothermia (HI-N group, n = 23). Bilateral measurements of hemispheric CBFi were made with DCS in unanesthetized animals at baseline, before HI, and 0, 1, 2, 3, 4, 5, and 24 h after HI. The animals were sacrificed at either 1 or 4 weeks, and brain injury was scored on an ordinal scale of 0-5 (0 = no injury).

RESULTS

Carotid ligation caused moderate bilateral decreases in CBFi. Following HI, an initial hyperemia was observed that was more prominent in the contralateral hemisphere. After initiation of TH, CBFi dropped significantly below baseline levels and remained reduced for the duration of TH. In contrast, CBFi in the HI-N group was not significantly decreased from baseline levels. Reductions in CBFi after 4 h of TH were not associated with reduced damage at 1 or 4 weeks. However, elevated ipsilateral CBFi and ipsilateral-to-contralateral CBFi ratios at 24 h were associated with worse outcome at 1 week after HI.

CONCLUSIONS

Both HI and TH alter CBFi, with significant differences in CBFi between hypothermic and normothermic groups after HI. CBFi may be a useful biomarker of subsequent cerebral damage.

Impact of inhaled nitric oxide on white matter damage in growth-restricted neonatal rats

BACKGROUND

Fetal growth restriction is the second leading cause of perinatal morbidity and mortality, and neonates with intrauterine growth retardation (IUGR) have increased neurocognitive and neuropsychiatric morbidity. These neurocognitive impairments are mainly related to injury of the developing brain associated with IUGR. Growing evidence from preclinical models of brain injury in both adult and neonatal rodents supports the view that nitric oxide can promote neuroprotection.

METHODS

In a model of IUGR induced by protracted gestational hypoxia leading to diffuse white matter injury, we subjected neonatal rats to low dose (5 ppm) but long-lasting (7 d) exposure to inhaled NO (iNO). We used a combination of techniques, including immunohistochemistry, quantitative PCR, and cognitive assessment, to assess neuroprotection.

RESULTS

Antenatal hypoxia-induced IUGR was associated with severe neuroinflammation and delayed myelination. iNO exposure during the first postnatal week significantly attenuated cell death and microglial activation, enhanced oligodendroglial proliferation and finally improved myelination. Remarkably, iNO was associated with the specific upregulation of P27kip1, which initiates oligodendrocytic differentiation. Finally, iNO counteracted the deleterious effects of hypoxia on learning abilities.

CONCLUSION

This study provides new evidence that iNO could be effective in preventing brain damage and/or enhancing repair of the developing brain.

Increased Brain Perfusion Persists over the First Month of Life in Term Asphyxiated Newborns Treated with Hypothermia: Does it Reflect Activated Angiogenesis?

Many asphyxiated newborns still develop brain injury despite hypothermia therapy. The development of brain injury in these newborns has been related partly to brain perfusion abnormalities. The purposes of this study were to assess brain hyperperfusion over the first month of life in term asphyxiated newborns and to search for some histopathological clues indicating whether this hyperperfusion may be related to activated angiogenesis following asphyxia. In this prospective cohort study, regional cerebral blood flow was measured in term asphyxiated newborns treated with hypothermia around day 10 of life and around 1 month of life using magnetic resonance imaging (MRI) and arterial spin labeling. A total of 32 MRI scans were obtained from 24 term newborns. Asphyxiated newborns treated with hypothermia displayed an increased cerebral blood flow in the injured brain areas around day 10 of life and up to 1 month of life. In addition, we looked at the histopathological clues in a human asphyxiated newborn and in a rat model of neonatal encephalopathy. Vascular endothelial growth factor (VEGF) was expressed in the injured brain of an asphyxiated newborn treated with hypothermia in the first days of life and of rat pups 24-48 h after the hypoxic-ischemic event, and the endothelial cell count increased in the injured cortex of the pups 7 and 11 days after hypoxia-ischemia. Our data showed that the hyperperfusion measured by imaging persisted in the injured areas up to 1 month of life and that angiogenesis was activated in the injured brain of asphyxiated newborns.

The role of the nitric oxide pathway in brain injury and its treatment--from bench to bedside

Nitric oxide (NO) is a key signalling molecule in the regulation of cerebral blood flow. This review summarises current evidence regarding the role of NO in the regulation of cerebral blood flow at rest, under physiological conditions, and after brain injury, focusing on subarachnoid haemorrhage, traumatic brain injury, and ischaemic stroke and following cardiac arrest. We also review the role of NO in the response to hypoxic insult in the developing brain. NO depletion in ischaemic brain tissue plays a pivotal role in the development of subsequent morbidity and mortality through microcirculatory disturbance and disordered blood flow regulation. NO derived from endothelial nitric oxide synthase (eNOS) appears to have neuroprotective properties. However NO derived from inducible nitric oxide synthase (iNOS) may have neurotoxic effects. Cerebral NO donor agents, for example sodium nitrite, appear to replicate the effects of eNOS derived NO, and therefore have neuroprotective properties. This is true in both the adult and immature brain. We conclude that these agents should be further investigated as targeted pharmacotherapy to protect against secondary brain injury.

The roles of methylenetetrahydrofolate reductase 677C>T and 1298A>C polymorphisms in moyamoya disease patients

PURPOSE

The methylenetetrahydrofolate reductase (MTHFR) 677C>T and 1298A>C polymorphisms, which are associated with hyperhomocysteinemia and nitric oxide (NO) deficiency (which is related to atherothrombosis and cerebral ischemia), have not been studied in moyamoya disease. A case-control study was performed to investigate whether the MTHFR 677C>T and 1298A>C polymorphisms contribute to moyamoya disease (MMD).

METHODS

One hundred and seven Korean patients with MMD (mean age, 20.85 ± 15.89 years; 66.4 % female) and 232 healthy control subjects (mean age, 23.99 ± 16.16 years; 56.8 % female) were included. Genotyping for the MTHFR 677C>T and 1298A>C polymorphisms and measurements of homocysteine, folate, vitamin B12, and NO in the cerebrospinal fluid (CSF) were performed. The statistical analysis was performed by multivariate linear regression and logistic regression.

RESULT

The MTHFR 677CT+TT genotype frequency was significantly increased with early-onset MMD (<10 years) compared with late-onset MMD (≥10 years) (adjusted odds ratio, 3.392; 95 % confidence interval, 1.294-8.893, P = 0.013). The MTHFR 677C-1298C/677T-1298A diplotype (1.71 ± 1.23 arbitrary units) presented significantly lower NO levels in the CSF compared with the 677C-1298A/677C-1298A diplotype (11.40 ± 12.24 arbitrary units).

CONCLUSION

The MTHFR 677C>T and 1298A>C polymorphisms have restricted roles in the Korean MMD population. Therefore, further studies involving larger and more heterogeneous cohorts are needed to extend our understanding of the influence of polymorphisms in MTHFR and other thrombophilic genes on MMD.