Perivascular nitric oxide and superoxide in neonatal cerebral hypoxia-ischemia

Role of NADPH Oxidases in Stroke Recovery

Stroke is one of the most significant causes of death and long-term disability globally. Overproduction of reactive oxygen species by NADPH oxidase (NOX) plays an important role in exacerbating oxidative stress and causing neuronal damage after a stroke. There is growing evidence that NOX inhibition prevents ischemic injury and that the role of NOX in brain damage or recovery depends on specific post-stroke phases. In addition to studies on post-stroke neuroprotection by NOX inhibition, recent reports have also demonstrated the role of NOX in stroke recovery, a critical process for brain adaptation and functional reorganization after a stroke. Therefore, in this review, we investigated the role of NOX in stroke recovery with the aim of integrating preclinical findings into potential therapeutic strategies to improve stroke recovery.

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.

Tetrahydrobiopterin treatment in phenylketonuria: A repurposing approach

In phenylketonuria (PKU) patients, early diagnosis by neonatal screening and immediate institution of a phenylalanine-restricted diet can prevent severe intellectual impairment. Nevertheless, outcome remains suboptimal in some patients asking for additional treatment strategies. Tetrahydrobiopterin (BH4 ) could be one of those treatment options, as it may not only increase residual phenylalanine hydroxylase activity in BH4 -responsive PKU patients, but possibly also directly improves neurocognitive functioning in both BH4 -responsive and BH4 -unresponsive PKU patients. In the present review, we aim to further define the theoretical working mechanisms by which BH4 might directly influence neurocognitive functioning in PKU having passed the blood-brain barrier. Further research should investigate which of these mechanisms are actually involved, and should contribute to the development of an optimal BH4 treatment regimen to directly improve neurocognitive functioning in PKU. Such possible repurposing approach of BH4 treatment in PKU may improve neuropsychological outcome and mental health in both BH4 -responsive and BH4 -unresponsive PKU patients.

Therapies that enhance pulmonary vascular NO-signaling in the neonate

There are several pulmonary hypertensive diseases that affect the neonatal population, including persistent pulmonary hypertension of the newborn (PPHN) and bronchopulmonary dysplasia (BPD)-associated pulmonary hypertension (PH). While the indication for inhaled nitric oxide (iNO) use is for late-preterm and term neonates with PPHN, there is a suboptimal response to this pulmonary vasodilator in ~40% of patients. Additionally, there are no FDA-approved treatments for BPD-associated PH or for preterm infants with PH. Therefore, investigating mechanisms that alter the nitric oxide-signaling pathway has been at the forefront of pulmonary vascular biology research. In this review, we will discuss the various mechanistic pathways that have been targets in neonatal PH, including NO precursors, soluble guanylate cyclase modulators, phosphodiesterase inhibitors and antioxidants. We will review their role in enhancing NO-signaling at the bench, in animal models, as well as highlight their role in the treatment of neonates with PH.

Usefulness of Intravenous Sodium Nitrite During Resuscitation for the Treatment of Out-of-Hospital Cardiac Arrest

It is hypothesized that intravenous (IV) sodium nitrite given during resuscitation of out-of-hospital cardiac arrest (OHCA) will improve survival. We performed a phase 1 open-label study of IV sodium nitrite given during resuscitation of 120 patents with OHCA from ventricular fibrillation or nonventricular fibrillation initial rhythms by Seattle Fire Department paramedics. A total of 59 patients received 25 mg (low) and 61 patients received 60 mg (high) of sodium nitrite during resuscitation from OHCA. Treatment effects were compared between high- and low-dose nitrite groups, and all patients in a concurrent local Emergency Medical Services registry of OHCA. Whole blood nitrite levels were measured in 97 patients. The rate of return of spontaneous circulation (48% vs 49%), rearrest in the field (15% vs 25%), use of norepinephrine (12% vs 12%), first systolic blood pressure (124 ± 32 vs 125 ± 38 mm Hg), survival to discharge (23.7% vs 16.4%), and neurologically favorable survival (18.6% vs 11.5%) were not significantly different in the low and high nitrite groups. There were no significant differences in these outcomes among patients who received IV nitrite compared with concurrent registry controls. We estimate that 60 mg achieves whole blood nitrite levels of 22 to 38 μM 10 minutes after administration, whereas 25 mg achieves a level of 9 to 16 μM 10 minutes after delivery. In conclusion, administration of IV nitrite is feasible and appears to be safe in patients with OHCA, permitting subsequent evaluation of the effectiveness of IV nitrite for the treatment of OHCA.

Efficacy of Novel Carbon Nanoparticle Antioxidant Therapy in a Severe Model of Reversible Middle Cerebral Artery Stroke in Acutely Hyperglycemic Rats

INTRODUCTION

While oxidative stress can be measured during transient cerebral ischemia, antioxidant therapies for ischemic stroke have been clinically unsuccessful. Many antioxidants are limited in their range and/or capacity for quenching radicals and can generate toxic intermediates overwhelming depleted endogenous protection. We developed a new antioxidant class, 40 nm × 2 nm carbon nanoparticles, hydrophilic carbon clusters, conjugated to poly(ethylene glycol) termed PEG-HCCs. These particles are high-capacity superoxide dismutase mimics, are effective against hydroxyl radical, and restore the balance between nitric oxide and superoxide in the vasculature. Here, we report the effects of PEG-HCCs administered during reperfusion after transient middle cerebral artery occlusion (tMCAO) by suture in the rat under hyperglycemic conditions. Hyperglycemia occurs in one-third of stroke patients and worsens clinical outcome. In animal models, this worsening occurs largely by accelerating elaboration of reactive oxygen species (ROS) during reperfusion.

METHODS

PEG-HCCs were studied for their protective ability against hydrogen peroxide in b.End3 brain endothelial cell line and E17 primary cortical neuron cultures. In vivo, hyperglycemia was induced by streptozotocin injection 2 days before tMCAO. 58 Male Sprague-Dawley rats were analyzed. They were injected IV with PBS or PEG-HCCs (4 mg/kg 2×) at the time of recanalization after either 90- or 120-min occlusion. Rats were survived for up to 3 days, and infarct volume characteristics and neurological functional outcome (modified Bederson Score) were assessed.

RESULTS

PEG-HCCs were protective against hydrogen peroxide in both culture models. In vivo improvement was found after PEG-HCCs with 90-min ischemia with reduction in infarct size (42%), hemisphere swelling (46%), hemorrhage score (53%), and improvement in Bederson score (70%) (p = 0.068-0.001). Early high mortality in the 2-h in the PBS control group precluded detailed analysis, but a trend was found in improvement in all factors, e.g., reduction in infarct volume (48%; p = 0.034) and a 56% improvement in Bederson score (p = 0.055) with PEG-HCCs.

CONCLUSION

This nano-antioxidant showed some improvement in several outcome measures in a severe model of tMCAO when administered at a clinically relevant time point. Long-term studies and additional models are required to assess potential for clinical use, especially for patients hyperglycemic at the time of their stroke, as these patients have the worst outcomes.

Neonatal hypoxic ischemic encephalopathy: an update on disease pathogenesis and treatment

INTRODUCTION

Hypoxic ischemic encephalopathy (HIE) is the most important reason for morbidity and mortality in term-born infants. Understanding pathophysiology of the brain damage is essential for the early detection of patients with high risk for HIE and development of strategies for their treatments. Areas covered: This review discusses pathophysiology of the neonatal HIE and its treatment options, including hypothermia, melatonin, allopurinol, topiramate, erythropoietin, N-acetylcyctein, magnesium sulphate and xenon. Expert commentary: Several clinical studies have been performed in order to decrease the risk of brain injury due to difficulties in the early diagnosis and treatment, and to develop strategies for better long-term outcomes. Although currently standard treatment methods include therapeutic hypothermia for neonates with moderate to severe HIE, new supportive options are needed to enhance neuroprotective effects of the hypothermia, which should aim to reduce production of the free radicals and to have anti-inflammatory and anti-apoptotic actions.

Notch signaling in cerebrovascular diseases (Review)

The Notch signaling pathway is a crucial regulator of numerous fundamental cellular processes. Increasing evidence suggests that Notch signaling is involved in inflammation and oxidative stress, and thus in the progress of cerebrovascular diseases. In addition, Notch signaling in cerebrovascular diseases is associated with apoptosis, angiogenesis and the function of blood-brain barrier. Despite the contradictory results obtained to date as to whether Notch signaling is harmful or beneficial, the regulation of Notch signaling may provide a novel strategy for the treatment of cerebrovascular diseases.

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.

A novel dual NO-donating oxime and c-Jun N-terminal kinase inhibitor protects against cerebral ischemia-reperfusion injury in mice

The c-Jun N-terminal kinase (JNK) has been shown to be an important regulator of neuronal cell death. Previously, we synthesized the sodium salt of 11H-indeno[1,2-b]quinoxalin-11-one (IQ-1S) and demonstrated that it was a high-affinity inhibitor of the JNK family. In the present work, we found that IQ-1S could release nitric oxide (NO) during its enzymatic metabolism by liver microsomes. Moreover, serum nitrite/nitrate concentration in mice increased after intraperitoneal injection of IQ-1S. Because of these dual actions as JNK inhibitor and NO-donor, the therapeutic potential of IQ-1S was evaluated in an animal stroke model. We subjected wild-type C57BL6 mice to focal ischemia (30min) with subsequent reperfusion (48h). Mice were treated with IQ-1S (25mg/kg) suspended in 10% solutol or with vehicle alone 30min before and 24h after middle cerebral artery (MCA) occlusion (MCAO). Using laser-Doppler flowmetry, we monitored cerebral blood flow (CBF) above the MCA during 30min of MCAO provoked by a filament and during the first 30min of subsequent reperfusion. In mice treated with IQ-1S, ischemic and reperfusion values of CBF were not different from vehicle-treated mice. However, IQ-1S treated mice demonstrated markedly reduced neurological deficit and infarct volumes as compared with vehicle-treated mice after 48h of reperfusion. Our results indicate that the novel JNK inhibitor releases NO during its oxidoreductive bioconversion and improves stroke outcome in a mouse model of cerebral reperfusion. We conclude that IQ-1S is a promising dual functional agent for the treatment of cerebral ischemia and reperfusion injury.

Neuroprotective agents for neonatal hypoxic-ischemic brain injury

Hypoxic-ischemic (H-I) brain injury in newborns is a major cause of morbidity and mortality that claims thousands of lives each year. In this review, we summarize the promising neuroprotective agents tested on animal models and pilot clinical studies of neonatal H-I brain injury according to the different phases of the disease. These agents target various phases of injury including the early phase of excitotoxicity, oxidative stress and apoptosis as well as late-phase inflammatory reaction and neural repair. We analyze the cell survival and cell death pathways modified by these agents in neonatal H-I brain injury. We aim to 'build a bridge' between animal trials of neuroprotective agents and potential candidate treatments for future clinical applications against H-I encephalopathy.

Altered endothelial nitric oxide synthesis in preterm and small for gestational age infants

BACKGROUND

Preterm infants are often exposed to neuronal and endothelial damage. The aim of the present study was to investigate the correlation between endothelial dysfunction and neuronal injury in preterm infants.

METHODS

We compared serum nitric oxide (NO), endothelial nitric oxide synthase (eNOS) and neuron-specific enolase (NSE) concentrations in 33 moderate preterm (MP) and 47 late preterm (LP) infants using standard ELISA. Each group was classified as appropriate for gestational age (AGA) or small for gestational age (SGA).

RESULTS

Compared to the AGA infants, the SGA infants had higher NO on day 1 (MP: mean, 72.3 ng/mL, range, 50.9-99.5 ng/mL vs 52.2 ng/mL, range, 28.1-68.2 ng/mL, P < 0.05; LP: mean, 58.4 ng/mL, range, 25.7-66.4 ng/mL vs 43.7 ng/mL, range, 21.2-60.6 ng/mL, P < 0.05), lower eNOS concentration on day 3 in the MP group (mean, 5.8 IU/mL, range, 1.2-7.9 IU/mL vs 8.9 IU/mL, range, 4.2-14.6 IU/mL, P < 0.05), and on day 1 in the LP group (mean, 5.5 IU/mL, range, 1.5-8.1 IU/mL vs 7.7 IU/mL, range, 4.4-13.8 IU/mL, P < 0.05). The NO/eNOS ratio was higher in SGA infants compared with the AGA subgroups (MP: mean, 13.8, range, 9.9-20.2 vs mean, 9.9, range, 4.7-13.1, P < 0.05; LP: mean, 12.2, range, 9.2-19.9 vs mean, 9.9, range, 5.4-14.4, P < 0.05). AGA infants had lower NSE concentration compared with the SGA infants on day 1 in the LP group (mean, 27.4 ng/mL, range, 20-43 ng/mL vs mean, 40.89 ng/mL, range, 34-51 ng/mL, P < 0.05). A positive correlation was found between NO/eNOS ratio and NSE concentration (r = 0.75, P < 0.05 and r = 0.64, P < 0.05 on days 1 and 3, respectively).

CONCLUSION

High NO concentration in the context of low eNOS activity suggests a possible role of NO in the development of neuronal injury in SGA infants.

Ischemic postconditioning in cerebral ischemia: Differences between the immature and mature brain?

Ischemic postconditioning (postC), defined as serial mechanical interruptions of blood flow at reperfusion, effectively reduces myocardial infarct size in all species tested so far, including humans. In the brain, ischemic postC leads to controversial results regardless of variations in factors such as onset time of beginning, the duration of ischemia and/or reperfusion, and the number of cycles of occlusion/reperfusion. Thus, many major issues remain to be resolved regarding its protective effects. Future studies should aim to identify the parameters that yield the strongest protection, as well as to understand why the efficacy of ischemic postC differs between models. This review will focus on initial hemodynamic changes and their consequences, and on specific features such as NO-dependent vascular tone and/or prolonged acidosis in cerebral ischemia-reperfusion in order to better understand the dynamics of ischemic postC in the developing brain.

A time course of NADPH-oxidase up-regulation and endothelial nitric oxide synthase activation in the hippocampus following neurotrauma

Nicotinamide adenine dinucleotide phosphate oxidase (NADPH-oxidase; NOX) is a complex enzyme responsible for increased levels of reactive oxygen species (ROS), superoxide (O2(•-)). NOX-derived O2(•-) is a key player in oxidative stress and inflammation-mediated multiple secondary injury cascades (SIC) following traumatic brain injury (TBI). The O2(•-) reacts with nitric oxide (NO), produces various reactive nitrogen species (RNS), and contributes to apoptotic cell death. Following a unilateral cortical contusion, young adult rats were killed at various times postinjury (1, 3, 6, 12, 24, 48, 72, and 96 h). Fresh tissue from the hippocampus was analyzed for NOX activity, and level of O2(•-). In addition we evaluated the translocation of cytosolic NOX proteins (p67(Phox), p47(Phox), and p40(Phox)) to the membrane, along with total NO and the activation (phosphorylation) of endothelial nitric oxide synthase (p-eNOS). Results show that both enzymes and levels of O2(•-) and NO have time-dependent injury effects in the hippocampus. Translocation of cytosolic NOX proteins into membrane, NOX activity, and O2(•-) were also increased in a time-dependent fashion. Both NOX activity and O2(•-) were increased at 6 h. Levels of p-eNOS increased within 1h, with significant elevation of NO at 12h post-TBI. Levels of NO failed to show a significant association with p-eNOS, but did associate with O2(•-). NOX up-regulation strongly associated with both the levels of O2(•-) and the total NO. The initial 12 h post-TBI are very important as a possible window of opportunity to interrupt SIC. It may be important to selectively target the translocation of cytosolic subunits for the modulation of NOX function.

Downregulation of nitric oxide by electroacupuncture against hypoxic‑ischemic brain damage in rats via nuclear factor‑κB/neuronal nitric oxide synthase

The present study aimed to investigate the role of nitric oxide (NO) against perinatal hypoxic‑ischemic brain damage (HIBD) in rats by electroacupuncture (EA) and to examine its potential neuroprotective mechanism. NO content, the number of positive cells, neuronal nitric oxide synthase (nNOS) and nuclear factor‑κB (NF‑κB) in rat cortex cells were determined. The results demonstrated that treatment with EA significantly downregulated the NO content in the cortex cells (*P<0.05, **P<0.01, compared with the control groups) and alleviated cell damage in the cortex of rats with HIBD. The activator, S‑adenosyl‑L‑methionine and the inhibitor, hydroxylamine of cystathionine‑β‑synthase (CBS), aggravated and remitted the hypoxic damage in the cortex cells, respectively. In addition, treatment with EA significantly downregulated the expression of nNOS and NF‑κB in the rat cortex cells (*P<0.05, **P<0.01, compared with the control groups). The results also indicated that treatment with EA downregulated the NO content of cortical cells against HIBD via the NF‑κB/nNOS pathway and further implied that the hydrogen sulfide/CBS system may be involved in the process. The present study provided a significant reference for the prevention and treatment of HIBD using the EA technique and also described a novel protective mechanism.

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

BACKGROUND AND PURPOSE

The best conceivable treatment for hypoxia-ischemia (HI) is the restoration of blood flow to the hypoxic-ischemic region(s). Our objective was to examine whether boosting NO-cGMP signaling using sildenafil citrate, a phosphodiesterase-type 5 inhibitor, could modify cerebral blood flow and reduce lesions in the developing brain.

METHODS

HI was induced in P7 Sprague-Dawley rats by unilateral carotid artery occlusion and hypoxia, and followed by either PBS or sildenafil. Blood-flow velocities were measured by ultrasound imaging with sequential Doppler recordings to evaluate collateral recruitment. Cell death, blood-brain barrier integrity, and glial activation were analyzed by immunohistochemistry. Motor behavior was evaluated using an open-field device adapted to neonatal animals.

RESULTS

Sildenafil citrate (10 mg/kg) induced collateral patency, reduced terminal dUTP nick-end labeling-positive cells, reactive astrogliosis, and macrophage/microglial activation at 72 hours and 7 days post-HI. Sildenafil also reduced the number of terminal dUTP nick-end labeling-positive endothelial cells within lesion site. Seven days after HI and sildenafil treatment, tissue loss was significantly reduced, and animals recovered motor coordination.

CONCLUSIONS

Our findings strongly indicate that sildenafil citrate treatment, associated with a significant increase in cerebral blood flow, reduces HI damage and improves motor locomotion in neonatal rats. Sildenafil may represent an interesting therapeutic strategy for neonatal neuroprotection.

Ca²⁺/calmodulin-dependent protein kinase II contributes to hypoxic ischemic cell death in neonatal hippocampal slice cultures

We have recently shown that p38MAP kinase (p38MAPK) stimulates ROS generation via the activation of NADPH oxidase during neonatal hypoxia-ischemia (HI) brain injury. However, how p38MAPK is activated during HI remains unresolved and was the focus of this study. Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) plays a key role in brain synapse development, neural transduction and synaptic plasticity. Here we show that CaMKII activity is stimulated in rat hippocampal slice culture exposed to oxygen glucose deprivation (OGD) to mimic the condition of HI. Further, the elevation of CaMKII activity, correlated with enhanced p38MAPK activity, increased superoxide generation from NADPH oxidase as well as necrotic and apoptotic cell death. All of these events were prevented when CaMKII activity was inhibited with KN93. In a neonatal rat model of HI, KN93 also reduced brain injury. Our results suggest that CaMKII activation contributes to the oxidative stress associated with neural cell death after HI.

Baicalin's Therapeutic Time Window of Neuroprotection during Transient Focal Cerebral Ischemia and Its Antioxidative Effects In Vitro and In Vivo

We investigated the effects of baicalin on an ischemia-reperfusion-induced brain injury model in rats and its antioxidative activities in vitro and in vivo. An ischemia-reperfusion injury of the brain via a middle cerebral artery occlusion (MCAO) was induced in rats. Baicalin was injected at different time points (0, 2, 4, and 6 h) after the MCAO was induced. Baicalin can improve neurological function and significantly decrease brain infarction within a time window of 4 h. Moreover, baicalin was able to reduce cell apoptosis and had the strong antioxidative effect of reducing reactive oxygen species production and malondialdehyde generation. In contrast, baicalin interfered with superoxide dismutase and nicotinamide adenine dinucleotide 2′-phosphate oxidase activities. Moreover, baicalin also exhibited strong neuroprotective effects against H₂O₂-mediated injury and improved the SOD activity of neurons. Furthermore, baicalin demonstrated good scavenging of hydroxyl radicals, superoxide anions, and DPPH radicals and exerted an additional effect of inhibiting xanthine oxidase. Baicalin showed beneficial effects against MCAO-induced injury within a 4 h time window, and its antioxidative effects both in vitro and in vivo may partly elucidate its mechanism of action.

Perioperative central nervous system injury in neonates

Anaesthetic-induced developmental neurotoxicity (AIDN) has been clearly established in laboratory animal models. The possibility of neurotoxicity during uneventful anaesthetic procedures in human neonates or infants has led to serious questions about the safety of paediatric anaesthesia. However, the applicability of animal data to clinical anaesthesia practice remains uncertain. The spectre of cerebral injury due to cerebral hypoperfusion, metabolic derangements, coexisting disease, and surgery itself further muddles the picture. Given the potential magnitude of the public health importance of this issue, the clinician should be cognisant of the literature and ongoing investigations on AIDN, and raise awareness of the risks of both surgery and anaesthesia.

Fatty acid receptor Gpr40 mediates neuromicrovascular degeneration induced by transarachidonic acids in rodents

OBJECTIVE

Nitro-oxidative stress exerts a significant role in the genesis of hypoxic-ischemic (HI) brain injury. We previously reported that the ω-6 long chain fatty acids, transarachidonic acids (TAAs), which are nitrative stress-induced nonenzymatically generated arachidonic acid derivatives, trigger selective microvascular endothelial cell death in neonatal neural tissue. The primary molecular target of TAAs remains unidentified. GPR40 is a G protein-coupled receptor activated by long chain fatty acids, including ω-6; it is highly expressed in brain, but its functions in this tissue are largely unknown. We hypothesized that TAAs play a significant role in neonatal HI-induced cerebral microvascular degeneration through GPR40 activation.

APPROACH AND RESULTS

Within 24 hours of a HI insult to postnatal day 7 rat pups, a cerebral infarct and a 40% decrease in cerebrovascular density was observed. These effects were associated with an increase in nitrative stress markers (3-nitrotyrosine immunoreactivity and TAA levels) and were reduced by treatment with nitric oxide synthase inhibitor. GPR40 was expressed in rat pup brain microvasculature. In vitro, in GPR40-expressing human embryonic kidney (HEK)-293 cells, [(14)C]-14E-AA (radiolabeled TAA) bound specifically, and TAA induced calcium transients, extracellular signal-regulated kinase 1/2 phosphorylation, and proapoptotic thrombospondin-1 expression. In vivo, intracerebroventricular injection of TAAs triggered thrombospondin-1 expression and cerebral microvascular degeneration in wild-type mice, but not in GPR40-null congeners. Additionally, HI-induced neurovascular degeneration and cerebral infarct were decreased in GPR40-null mice.

CONCLUSIONS

GPR40 emerges as the first identified G protein-coupled receptor conveying actions of nonenzymatically generated nitro-oxidative products, specifically TAAs, and is involved in (neonatal) HI encephalopathy.

Neuroprotective therapies after perinatal hypoxic-ischemic brain injury

Hypoxic-ischemic (HI) brain injury is one of the main causes of disabilities in term-born infants. It is the result of a deprivation of oxygen and glucose in the neural tissue. As one of the most important causes of brain damage in the newborn period, the neonatal HI event is a devastating condition that can lead to long-term neurological deficits or even death. The pattern of this injury occurs in two phases, the first one is a primary energy failure related to the HI event and the second phase is an energy failure that takes place some hours later. Injuries that occur in response to these events are often manifested as severe cognitive and motor disturbances over time. Due to difficulties regarding the early diagnosis and treatment of HI injury, there is an increasing need to find effective therapies as new opportunities for the reduction of brain damage and its long term effects. Some of these therapies are focused on prevention of the production of reactive oxygen species, anti-inflammatory effects, anti-apoptotic interventions and in a later stage, the stimulation of neurotrophic properties in the neonatal brain which could be targeted to promote neuronal and oligodendrocyte regeneration.

Dynamic spatio-temporal imaging of early reflow in a neonatal rat stroke model

The aim of the study was to better understand blood-flow changes in large arteries and microvessels during the first 15 minutes of reflow in a P7 rat model of arterial occlusion. Blood-flow changes were monitored by using ultrasound imaging with sequential Doppler recordings in internal carotid arteries (ICAs) and basilar trunk. Relative cerebral blood flow (rCBF) changes were obtained by using laser speckle Doppler monitoring. Tissue perfusion was measured with [(14)C]-iodoantipyrine autoradiography. Cerebral energy metabolism was evaluated by mitochondrial oxygen consumption. Gradual increase in mean blood-flow velocities illustrated a gradual perfusion during early reflow in both ICAs. On ischemia, the middle cerebral artery (MCA) territory presented a residual perfusion, whereas the caudal territory remained normally perfused. On reflow, speckle images showed a caudorostral propagation of reperfusion through anastomotic connections, and a reduced perfusion in the MCA territory. Autoradiography highlighted the caudorostral gradient, and persistent perfusion in ventral and medial regions. These blood-flow changes were accompanied by mitochondrial respiration impairment in the ipsilateral cortex. Collectively, these data indicate the presence of a primary collateral pathway through the circle of Willis, providing an immediate diversion of blood flow toward ischemic regions, and secondary efficient cortical anastomoses in the immature rat brain.

Ischemic postconditioning fails to protect against neonatal cerebral stroke

The lack of efficient neuroprotective strategies for neonatal stroke could be ascribed to pathogenic ischemic processes differentiating adults and neonates. We explored this hypothesis using a rat model of neonatal ischemia induced by permanent occlusion of the left distal middle cerebral artery combined with 50 min of occlusion of both common carotid arteries (CCA). Postconditioning was performed by repetitive brief release and occlusion (30 s, 1 and/or 5 min) of CCA after 50 min of CCA occlusion. Alternative reperfusion was generated by controlled release of the bilateral CCA occlusion. Blood-flow velocities in the left internal carotid artery were measured using color-coded pulsed Doppler ultrasound imaging. Cortical perfusion was measured using laser Doppler. Cerebrovascular vasoreactivity was evaluated after inhalation with the hypercapnic gas or inhaled nitric oxide (NO). Whatever the type of serial mechanical interruptions of blood flow at reperfusion, postconditioning did not reduce infarct volume after 72 hours. A gradual perfusion was found during early re-flow both in the left internal carotid artery and in the cortical penumbra. The absence of acute hyperemia during early CCA re-flow, and the lack of NO-dependent vasoreactivity in P7 rat brain could in part explain the inefficiency of ischemic postconditioning after ischemia-reperfusion.

Antioxidant carbon particles improve cerebrovascular dysfunction following traumatic brain injury

Injury to the neurovasculature is a feature of brain injury and must be addressed to maximize opportunity for improvement. Cerebrovascular dysfunction, manifested by reduction in cerebral blood flow (CBF), is a key factor that worsens outcome after traumatic brain injury (TBI), most notably under conditions of hypotension. We report here that a new class of antioxidants, poly(ethylene glycol)-functionalized hydrophilic carbon clusters (PEG-HCCs), which are nontoxic carbon particles, rapidly restore CBF in a mild TBI/hypotension/resuscitation rat model when administered during resuscitation--a clinically relevant time point. Along with restoration of CBF, there is a concomitant normalization of superoxide and nitric oxide levels. Given the role of poor CBF in determining outcome, this finding is of major importance for improving patient health under clinically relevant conditions during resuscitative care, and it has direct implications for the current TBI/hypotension war-fighter victims in the Afghanistan and Middle East theaters. The results also have relevancy in other related acute circumstances such as stroke and organ transplantation.

Targeting NOX enzymes in the central nervous system: therapeutic opportunities

Among the pathogenic mechanisms underlying central nervous system (CNS) diseases, oxidative stress is almost invariably described. For this reason, numerous attempts have been made to decrease reactive oxygen species (ROS) with the administration of antioxidants as potential therapies for CNS disorders. However, such treatments have always failed in clinical trials. Targeting specific sources of reactive oxygen species in the CNS (e.g. NOX enzymes) represents an alternative promising option. Indeed, NOX enzymes are major generators of ROS, which regulate progression of CNS disorders as diverse as amyotrophic lateral sclerosis, schizophrenia, Alzheimer disease, Parkinson disease, and stroke. On the other hand, in autoimmune demyelinating diseases, ROS generated by NOX enzymes are protective, presumably by dampening the specific immune response. In this review, we discuss the possibility of developing therapeutics targeting NADPH oxidase (NOX) enzymes for the treatment of different CNS pathologies. Specific compounds able to modulate the activation of NOX enzymes, and the consequent production of ROS, could fill the need for disease-modifying drugs for many incurable CNS pathologies.

Role of endothelial nitric oxide in cerebrovascular regulation

Endothelial nitric oxide (NO) plays important roles in the vascular system. Animal models that show vascular dysfunction demonstrate the protective role of endothelial NO dependent pathways. This review focuses on the role of endothelial NO in the regulation of cerebral blood flow and vascular tone. We will discuss the importance of NO in cerebrovascular function using animal models with altered endothelial NO production under normal, ischemic and reperfusion conditions, as well as in hyperoxia. Pharmacological and genetic manipulations of the endothelial NO system demonstrate the essential roles of endothelial NO synthase in maintenance of vascular tone and cerebral perfusion under normal and pathological conditions.

Cerebral blood flow during reperfusion predicts later brain damage in a mouse and a rat model of neonatal hypoxic-ischemic encephalopathy

Children with severe neonatal hypoxic-ischemic encephalopathy (HIE) die or develop life-long neurological impairments such as cerebral palsy and mental retardation. Decreased regional cerebral blood flow (CBF) is believed to be the predominant factor that determines the level of tissue injury in the immature brain. However, the spatio-temporal profiles of CBF after neonatal HIE are not well understood. CB17 mouse and Wistar rat pups were exposed to a unilateral hypoxic-ischemic (HI) insult at eight or seven days of age. Laser speckle imaging sequentially measured the cortical surface CBF before the hypoxic exposure and until 24h after the hypoxic exposure. Seven days after the HI insult, brain damage was morphologically assessed by measuring the hemispheric volumes and by semi-quantitative scoring for neuropathologic injury. The mean CBF on the ipsilateral hemisphere in mice decreased after carotid artery ligation. After the end of hypoxic insult (i.e., the reperfusion phase), the mean CBF level gradually rose and nearly attained its pre-surgery level by 9h of reperfusion. It then decreased. The degree of reduced CBF during reperfusion was well correlated with the degree of later morphological brain damage. The correlation was the strongest when the CBF was measured in the ischemic core region at 24h of reperfusion in mice (R²=0.89). A similar trend in results was found in rats. These results suggest that the CBF level during reperfusion may be a useful predictive factor for later brain damage in immature mice. This may enable optimizing brain damage for detail analyses.

Oxygen resuscitation after hypoxia ischemia stimulates prostaglandin pathway in rat cortex

Exposure to hypoxia and hyperoxia in a rodent model of perinatal ischemia results in delayed cell death and inflammation. Hyperoxia increases oxidative stress that can trigger inflammatory cascades, neutrophil activation, and brain microvascular injury. Here we show that 100% oxygen resuscitation in our rodent model of perinatal ischemia increases cortical COX-2 protein levels, S-nitrosylated COX-2cys526, PGE2, iNOS and 5-LOX, all components of the prostaglandin and leukotriene inflammatory pathway.

Contribution of central nervous system endothelial nitric oxide synthase to neurohumoral activation in heart failure rats

Neurohumoral activation, a hallmark in heart failure (HF), is linked to the progression and mortality of HF patients. Thus, elucidating its precise underlying mechanisms is of critical importance. Other than its classic peripheral vasodilatory actions, the gas NO is a pivotal neurotransmitter in the central nervous system control of the circulation. While accumulating evidence supports a contribution of blunted NO function to neurohumoral activation in HF, the precise cellular sources, and NO synthase (NOS) isoforms involved, remain unknown. Here, we used a multidisciplinary approach to study the expression, cellular distribution, and functional relevance of the endothelial NOS isoform within the hypothalamic paraventricular nucleus in sham and HF rats. Our results show high expression of endothelial NOS in the paraventricular nucleus (mostly confined to astroglial cells), which contributes to constitutive NO bioavailability, as well as tonic inhibition of presympathetic neuronal activity and sympathoexcitatory outflow from the paraventricular nucleus. A diminished endothelial NOS expression and endothelial NOS-derived NO availability were found in the paraventricular nucleus of HF rats, resulting, in turn, in blunted NO inhibitory actions on neuronal activity and sympathoexcitatory outflow. Taken together, our study supports blunted central nervous system endothelial NOS-derived NO as a pathophysiological mechanism underlying neurohumoral activation in HF.

Pharmacological neuroprotection after perinatal hypoxic-ischemic brain injury

Perinatal hypoxia-ischemia (HI) is an important cause of neonatal brain injury. Recent progress in the search for neuroprotective compounds has provided us with several promising drugs to reduce perinatal HI-induced brain injury. In the early stage (first 6 hours after birth) therapies are concentrated on prevention of the production of reactive oxygen species or free radicals (xanthine-oxidase-, nitric oxide synthase-, and prostaglandin inhibition), anti-inflammatory effects (erythropoietin, melatonin, Xenon) and anti-apoptotic interventions (nuclear factor kappa B- and c-jun N-terminal kinase inhibition); in a later stage stimulation of neurotrophic properties in the neonatal brain (erythropoietin, growth factors) can be targeted to promote neuronal and oligodendrocyte regeneration. Combination of pharmacological means of treatment with moderate hypothermia, which is accepted now as a meaningful therapy, is probably the next step in clinical treatment to fight post-asphyxial brain damage. Further studies should be directed at a more rational use of therapies by determining the optimal time and dose to inhibit the different potentially destructive molecular pathways or to enhance endogenous repair while at the same time avoiding adverse effects of the drugs used.

Short- and long-term behavioral effects of exposure to 21%, 40% and 100% oxygen after perinatal hypoxia-ischemia in the rat

Until recently, supplementation with 100% oxygen was standard therapy for newborns who required resuscitation at birth or suffered later hypoxic-ischemic events. Exposure to high concentrations of oxygen, however, may worsen oxidative stress induced by ischemic injury. In this study we investigated the short- and long-term behavioral outcomes in rats that had undergone hypoxic-ischemic brain injury on postnatal day 7, followed by 2h exposure to 21%, 40%, or 100% oxygen, compared to normal controls. There were no differences in the development of walking, head lifting and righting reflexes from postnatal days 9 to 15. Cliff avoidance showed some abnormal responses in the H21 animals. From postnatal days 28 to 56, three tests of sensorimotor coordination were performed weekly: ledged tapered beam, cylinder, and bilateral tactile stimulation. The ledged tapered beam test without prior training of animals was sensitive to injury, but did not distinguish between treatment groups. The cylinder test showed a greater use of the unimpaired limb in female 21% and 40% oxygen groups compared to controls. Performance in both cylinder and the beam tests showed a correlation with the degree of brain injury. The bilateral tactile stimulation test showed that the male 21% oxygen groups had worse sensory asymmetry than male 40% or 100% oxygen groups, but was not statistically significantly different from controls. We thus found a minor benefit to post-hypoxia-ischemic treatment with 100% and 40% oxygen compared to 21% in one test of early motor skills. Our results for long-term sensorimotor behavior, however, showed conflicting results, however, as males treated with 40% or 100% oxygen had less sensory asymmetry (better performance) in the bilateral tactile stimulation test than males treated with 21% oxygen, while females had impaired motor performance in the cylinder test with both 21% and 40% oxygen.

Nitroxyl in the central nervous system

Nitroxyl (HNO) is the one-electron-reduced and protonated congener of nitric oxide (NO). Compared to NO, it is far more reactive with thiol groups either in proteins or in small antioxidant molecules either converting those into sulfinamides or inducing disulfide bond formation. HNO might mediate cytoprotective changes of protein function through thiol modifications. However, HNO is a strong oxidant that in vitro reacts with glutathione to form glutathione disulfide and glutathione sulfinamide. The resulting oxidative stress might aggravate tissue damage in inflammatory diseases. In this review, we will summarize the current knowledge of how exogenous HNO affects the central nervous system, especially nerve cells and glia in health and disease. Unlike most other organs, the brain is separated from the circulation by the blood-brain barrier, which limits access of many pharmacological compounds. Given that, we will review what is known about the ability of currently used HNO donors to cross the blood-brain barrier. Moreover, considering that the physiology and composition of the brain has unique properties, for example, expression of brain-specific enzymes like neuronal NO synthase, its high iron content, and increased energy metabolism, we will discuss possible sources of endogenous HNO in the brain.

Early protective effect of hypothermia in newborn pigs after hyperoxic, but not after normoxic, reoxygenation

Abstract Mild hypothermia can attenuate the development of brain damage after asphyxia. Supplemental oxygen during resuscitation increases generation of reactive oxygen species, compared to room air. It is unknown if supplemental oxygen affects hypothermic neuroprotection. We studied the early effects of hyperoxic reoxygenation and subsequent hypothermia on tissue oxygenation, microcirculation, inflammation and brain damage after global hypoxia. Anesthetized newborn pigs were randomized to control (n=6), or severe global hypoxia (n=46). Three pigs died during hypoxia or reoxygenation. After 20-min reoxygenation with room air (n=22) or 100% oxygen (n=21), pigs were randomized to normothermia (deep rectal temperature 39 degrees C, n=22) or total body cooling (35 degrees C, n=21) for 6.5 h before the experiment was terminated. We demonstrated a differential effect of post-hypoxic hypothermia between animals reoxygenated with 100% oxygen and with room air, with reduced damage only in hypothermic animals reoxygenated with 100% oxygen (P=0.001). Hyperoxic reoxygenation resulted in a significant overshoot in striatal oxygen tension, without affecting microcirculation. Inflammatory response after the insult did not differ between groups. The results indicate an early protective effect of hypothermia which may vary with oxygen level used during reoxygenation.

Vascular dysfunction in cerebrovascular disease: mechanisms and therapeutic intervention

The endothelium plays a crucial role in the control of vascular homoeostasis through maintaining the synthesis of the vasoprotective molecule NO* (nitric oxide). Endothelial dysfunction of cerebral blood vessels, manifested as diminished NO* bioavailability, is a common feature of several vascular-related diseases, including hypertension, hypercholesterolaemia, stroke, subarachnoid haemorrhage and Alzheimer's disease. Over the past several years an enormous amount of research has been devoted to understanding the mechanisms underlying endothelial dysfunction. As such, it has become apparent that, although the diseases associated with impaired NO* function are diverse, the underlying causes are similar. For example, compelling evidence indicates that oxidative stress might be an important mechanism of diminished NO* signalling in diverse models of cardiovascular 'high-risk' states and cerebrovascular disease. Although there are several sources of vascular ROS (reactive oxygen species), the enzyme NADPH oxidase is emerging as a strong candidate for the excessive ROS production that is thought to lead to vascular oxidative stress. The purpose of the present review is to outline some of the mechanisms thought to contribute to endothelial dysfunction in the cerebral vasculature during disease. More specifically, we will highlight current evidence for the involvement of ROS, inflammation, the RhoA/Rho-kinase pathway and amyloid beta-peptides. In addition, we will discuss currently available therapies for improving endothelial function and highlight future therapeutic strategies.

Oxidative stress and its role in the pathogenesis of ischaemic stroke

Stroke is one of the leading causes of mortality and morbidity, with astronomical financial repercussions on health systems worldwide. Ischaemic stroke accounts for approximately 80-85% of all cases and is characterised by the disruption of cerebral blood flow and lack of oxygen to the affected area. Oxidative stress culminates due to an imbalance between pro-oxidants and antioxidants and consequent excessive production of reactive oxygen species. Reactive oxygen species are biphasic, playing a role in normal physiological processes and are also implicated in a number of disease processes, whereby they mediate damage to cell structures, including lipids, membranes, proteins, and DNA. The cerebral vasculature is a major target of oxidative stress playing a critical role in the pathogenesis of ischaemic brain injury following a cerebrovascular attack. Superoxide, the primary reactive oxygen species, and its derivatives have been shown to cause vasodilatation via the opening of potassium channels and altered vascular reactivity, breakdown of the blood-brain barrier and focal destructive lesions in animal models of ischaemic stroke. However, reactive oxygen species are involved in normal physiological processes including cell signalling, induction of mitogenesis, and immune defence. Primarily, this review will focus on the cellular and vascular aspects of reactive oxygen and nitrogen species generation and their role in the pathogenesis of ischaemia-reperfusion phenomena. Secondly, the proposed mechanisms of oxidative stress-related neuronal death will be reflected upon and in summation specific targeted neuroprotective therapies targetting oxidative stress and their role in the pathogenesis of stroke will be discussed.

Mitochondrial mechanisms of cell death and neuroprotection in pediatric ischemic and traumatic brain injury

There are several forms of acute pediatric brain injury, including neonatal asphyxia, pediatric cardiac arrest with global ischemia, and head trauma, that result in devastating, lifelong neurologic impairment. The only clinical intervention that appears neuroprotective is hypothermia initiated soon after the initial injury. Evidence indicates that oxidative stress, mitochondrial dysfunction, and impaired cerebral energy metabolism contribute to the brain cell death that is responsible for much of the poor neurologic outcome from these events. Recent results obtained from both in vitro and animal models of neuronal death in the immature brain point toward several molecular mechanisms that are either induced or promoted by oxidative modification of macromolecules, including consumption of cytosolic and mitochondrial NAD(+) by poly-ADP ribose polymerase, opening of the mitochondrial inner membrane permeability transition pore, and inactivation of key, rate-limiting metabolic enzymes, e.g., the pyruvate dehydrogenase complex. In addition, the relative abundance of pro-apoptotic proteins in immature brains and neurons, and particularly within their mitochondria, predisposes these cells to the intrinsic, mitochondrial pathway of apoptosis, mediated by Bax- or Bak-triggered release of proteins into the cytosol through the mitochondrial outer membrane. Based on these pathways of cell dysfunction and death, several approaches toward neuroprotection are being investigated that show promise toward clinical translation. These strategies include minimizing oxidative stress by avoiding unnecessary hyperoxia, promoting aerobic energy metabolism by repletion of NAD(+) and by providing alternative oxidative fuels, e.g., ketone bodies, directly interfering with apoptotic pathways at the mitochondrial level, and pharmacologic induction of antioxidant and anti-inflammatory gene expression.