Role of nitric oxide after brain ischaemia

Leukaemia inhibitory factor stimulates proliferation of olfactory neuronal progenitors via inducible nitric oxide synthase

Neurogenesis continues in the adult brain and in the adult olfactory epithelium. The cytokine, leukaemia inhibitory factor and nitric oxide are both known to stimulate neuronal progenitor cell proliferation in the olfactory epithelium after injury. Our aim here was to determine whether these observations are independent, specifically, whether leukaemia inhibitory factor triggers neural precursor proliferation via the inducible nitric oxide synthase pathway. We evaluated the effects of leukaemia inhibitory factor on inducible form of nitric oxide synthase (iNOS) expression, and cell proliferation in olfactory epithelial cell cultures and olfactory neurosphere-derived cells. Leukaemia inhibitory factor induced expression of iNOS and increased cell proliferation. An iNOS inhibitor and an anti-leukaemia inhibitory factor receptor blocking antibody inhibited leukaemia inhibitory factor-induced cell proliferation, an effect that was reversed by a NO donor. Altogether, the results strongly suggest that leukaemia inhibitory factor induces iNOS expression, increasing nitric oxide levels, to stimulate proliferation of olfactory neural precursor cells. This finding sheds light on neuronal regeneration occurring after injury of the olfactory epithelium.

Losartan, an angiotensin II type 1 receptor blocker, ameliorates cerebral ischemia-reperfusion injury via PI3K/Akt-mediated eNOS phosphorylation

Angiotensin (Ang) II type 1 receptor blockers (ARBs) have been shown to protect against cerebral ischemia-reperfusion (I/R) injury. However, the mechanism by which ARBs protect brain ischemia injury is still unclear. The aims of this study were to investigate the effects of losartan, an ARB, on the phosphorylation of endothelial nitric oxide synthase (eNOS) in response to focal brain I/R and to determine whether the neuroprotective phosphatidylinositol-3-kinase (PI3K)-Akt signaling pathway is involved. Normotensive Wistar rats were pretreated for 14 days with 5mg/kg losartan, then subjected to middle cerebral artery occlusion for 2h followed by reperfusion (MCAO-R). Our results showed that losartan reduced infarct volumes and improved neurobehavioral outcomes in rats subjected to MCAO-R. Losartan pretreatment significantly suppressed an increase in inducible nitric oxide synthase (iNOS) and sustained normal levels of eNOS expression 24h after MCAO-R injury. Phosphorylated eNOS and Akt levels were much lower than those in the sham group at 24h after MCAO-R, suggesting that losartan pretreatment significantly preserved eNOS phosphorylation in response to the activated Akt. Moreover, blockade of PI3K activity by wortmannin, totally abolished losartan-induced eNOS phosphorylation, providing the first evidence that losartan stimulates eNOS phosphorylation through PI3K/Akt signaling in the MCAO-R rat model. Our findings provide a mechanistic basis underlying the benefits of using selective ARBs, such as losartan, in the treatment of cerebrovascular disease.

Resveratrol preconditioning modulates inflammatory response in the rat hippocampus following global cerebral ischemia

Considerable evidence has been accumulated to suggests that blocking the inflammatory reaction promotes neuroprotection and shows therapeutic potential for clinical treatment of ischemic brain injury. Consequently, anti-inflammatory therapies are being explored for prevention and treatment of these diseases. Induction of brain tolerance against ischemia by pretreatment with resveratrol has been found to influence expression of different molecules. It remains unclear, however, whether and how resveratrol preconditioning changes expression of inflammatory mediators after subsequent global cerebral ischemia/reperfusion (I/R). Therefore, we investigated the effect of resveratrol pretreatment on NF-κB inflammatory cascade, COX-2, iNOS and JNK levels in experimental I/R. Adult male rats were subjected to 10 min of four-vessel occlusion and sacrificed at selected post-ischemic time points. Resveratrol (30 mg/kg) pretreatment was injected intraperitoneally 7 days prior to I/R induction. We found that resveratrol treatment before insult remarkably reduced astroglial and microglial activation at 7 days after I/R. It greatly attenuated I/R-induced NF-κB and JNK activation with decreased COX-2 and iNOS production. In conclusion, the neuroprotection of resveratrol preconditioning may be due in part to the suppression of the inflammatory response via regulation of NF-κB, COX-2 and iNOS induced by I/R. JNK was also suggested to play a protective role through in neuroprotection of resveratrol, which may also be contributing to reduction in neuroinflammation. The study adds to a growing literature that resveratrol can have important anti-inflammatory actions in the brain.

Knock out of neuronal nitric oxide synthase exacerbates intestinal ischemia/reperfusion injury in mice

Recent investigation of the intestine following ischemia and reperfusion (I/R) has revealed that nitric oxide synthase (NOS) neurons are more strongly affected than other neuron types. This implies that NO originating from NOS neurons contributes to neuronal damage. However, there is also evidence of the neuroprotective effects of NO. In this study, we compared the effects of I/R on the intestines of neuronal NOS knockout (nNOS(-/-)) mice and wild-type mice. I/R caused histological damage to the mucosa and muscle and infiltration of neutrophils into the external muscle layers. Damage to the mucosa and muscle was more severe and greater infiltration by neutrophils occurred in the first 24 h in nNOS(-/-) mice. Immunohistochemistry for the contractile protein, α-smooth muscle actin, was used to evaluate muscle damage. Smooth muscle actin occurred in the majority of smooth muscle cells in the external musculature of normal mice but was absent from most cells and was reduced in the cytoplasm of other cells following I/R. The loss was greater in nNOS(-/-) mice. Basal contractile activity of the longitudinal muscle and contractile responses to nerve stimulation or a muscarinic agonist were reduced in regions subjected to I/R and the effects were greater in nNOS(-/-) mice. Reductions in responsiveness also occurred in regions of operated mice not subjected to I/R. This is attributed to post-operative ileus that is not significantly affected by knockout of nNOS. The results indicate that deleterious effects are greater in regions subjected to I/R in mice lacking nNOS compared with normal mice, implying that NO produced by nNOS has protective effects that outweigh any damaging effect of this free radical produced by enteric neurons.

Exaggerated neutrophil-mediated reperfusion injury after ischemic stroke in a rodent model of type 2 diabetes

OBJECTIVE

We tested the hypothesis that both chronic and acute inflammatory processes contribute to worse reperfusion injury and stroke outcome in an experimental model of T2DM.

MATERIALS AND METHODS

Twelve- to thirteen-week-old male Zucker Diabetic Fatty (ZDF) rats vs. Zucker Lean Controls (ZLC) rats were tested at baseline and after middle cerebral artery occlusion (ischemia) and reperfusion (I-R). Neutrophil adhesion to the cerebral microcirculation, neutrophil expression of CD11b, infarction size, edema, neurologic function, sICAM, and cerebral expression of neutrophil-endothelial inflammatory genes were measured.

RESULTS

At baseline, CD11b and sICAM were significantly increased in ZDF vs. ZLC animals (p < 0.05). After I-R, significantly more neutrophil adhesion and cell aggregates were observed in ZDF vs. ZLC (p < 0.05); infarction size, edema, and neurologic function were significantly worse in ZDF vs. ZLC (p < 0.05). CD11b and sICAM-1 remained significantly increased in ZDFs (p < 0.05), and cerebral expression of IL-1β, GRO/KC, E-selectin, and sICAM were significantly induced in ZDF, but not ZLC groups (p < 0.05) after 2.5 hours of reperfusion.

CONCLUSION

Both sides of the neutrophil-endothelial interface appear to be primed prior to I-R, and remain significantly more activated during I-R in an experimental model of T2DM. Consequently, reperfusion injury appears to play a significant role in poor stroke outcome in T2DM.

Anti-inflammatory properties and pharmacological induction of Hsp70 after brain injury

The 70-kDa heat shock protein (Hsp70) is thought to protect the brain from a variety of insults. Although the mechanism has been largely limited to its chaperone functions, recent work indicates that Hsp70 also modulates inflammatory pathways. Brain injury and ischemia are associated with an immune response that is largely innate. Hsp70 appears to suppress this response and lead to improved neurological outcome. However, most of this work has relied on the use of genetic mutant models or Hsp70 overexpression using gene transfer or heat stress, thus limiting its translational utility. A few compounds have been studied by various disciplines which, through their ability to inhibit Hsp90, can cause induction of Hsp70. The investigation of Hsp70-inducing pharmacological compounds has obvious clinical implications in terms of potential therapies to mitigate neuroinflammation and lead to neuroprotection from stroke or traumatic brain injury. This review will focus on the inflammation modulating properties of Hsp70, and the current literature surrounding the pharmacological induction in acute neurological injury models with comments on potential applications at the clinical level.

Association of NOS3 tag polymorphisms with hypoxic-ischemic encephalopathy

Aim

To test the association of NOS3 gene with hypoxic-ischemic encephalopathy (HIE).

Methods

The study included 110 unrelated term or preterm born children (69 boys and 41 girls) with HIE and 128 term and preterm born children (60 boys and 68 girls) without any neurological problems after the second year of life. Children with perinatal HIE fulfilled the diagnostic criteria for perinatal asphyxia. All children were admitted to the Clinical Hospital Split between 1992 and 2008. We analyzed 6 tagging single nucleotide polymorphisms (SNP) within NOS3 gene (rs3918186, rs3918188, rs1800783, rs1808593, rs3918227, rs1799983), in addition to previously confirmed NOS3-associated SNP rs1800779. Genotyping was conducted using real-time polymerase chain reaction (PCR). Association analyses were performed according to allelic and genotypic distribution.

Results

Allelic test did not show any SNP association with HIE. SNP rs1808593 showed genotype association (P = 0.008) and rs1800783-rs1800779 TG haplotype showed an association with HIE (P < 0.001). The study had 80% statistical power to detect (α = 0.05) an effect with odds ratio (OR) = 2.07 for rs3918186, OR = 1.69 for rs3918188, OR = 1.70 for rs1800783, OR = 1.80 for rs1808593, OR = 2.10 for rs3918227, OR = 1.68 for rs1800779, and OR = 1.76 for rs1799983, assuming an additive model.

Conclusion

Despite the limited number of HIE patients, we observed genotypic and haplotype associations of NOS3 polymorphisms with HIE.

(S)-ZJM-289, a nitric oxide-releasing derivative of 3-n-butylphthalide, protects against ischemic neuronal injury by attenuating mitochondrial dysfunction and associated cell death

Pharmacological compounds that release nitric oxide (NO) have been recognized as the potential therapeutic agents for acute stroke. (S)-ZJM-289 is a novel NO-releasing derivative of 3-n-butylphthalide (NBP) with enhanced anti-platelet and anti-thrombotic actions. The present study was performed to investigate the neuroprotective effects and related mechanisms of (S)-ZJM-289 on ischemic neuronal injury in vitro and in vivo. Primary cortical neuronal cultures were exposured to oxygen-glucose deprivation followed by recovery (OGD/R), a model of ischemia-like injury, and treated with (S)-ZJM-289 before OGD. In vitro results showed that (S)-ZJM-289 attenuated OGD/R-induced neuronal injury, which was associated with the maintenance of mitochondrial integrity and function by alleviating intracellular calcium overload and reactive oxygen species (ROS) accumulation, preventing mitochondrial membrane depolarization and preserving respiratory chain complexes activities. Moreover, (S)-ZJM-289 treatment suppressed mitochondrial release of cytochrome c (cyt c) and nuclear translocation of apoptosis-inducing factor (AIF), thereby blocking mitochondria-mediated cell death, which may be partially mediated by up-regulation of Hsp70. The neuroprotection by (S)-ZJM-289 was also studied using a model of middle cerebral artery occlusion (MCAO). Oral administration of (S)-ZJM-289 at the onset of reperfusion for 3d significantly reduced the brain infarct size, improved neurological deficit and prevented neuronal loss and apoptosis. In current study, (S)-ZJM-289 appears to be more potent in ischemic neuroprotection than NBP, in particular at the lower doses, which may be due to the synergistic action of NBP and NO. These findings point to that (S)-ZJM-289 could be an attractive alternative to NBP in preventing the process of ischemia/reperfusion (I/R) injury.

Age-specific eNOS polymorphisms in moyamoya disease

OBJECTIVE

We conducted a case-control study to investigate whether polymorphisms in eNOS are related to the age-specific onset of moyamoya disease.

MATERIALS AND METHODS

Ninety-three Korean patients [mean age, 23.0 ± 16.1 years; 59 female (63.4%) and 34 male (36.6%)] with moyamoya disease were consecutively recruited for this study. Three hundred twenty-eight healthy subjects [mean age, 27.7 ± 16.2 years; 217 female (66.2%), 111 male (33.8%)] were consecutively included in the control group. The subjects were divided into pediatric (< 20 years) and adult (≥ 20 years) groups. We further divided the moyamoya group into ischemic and hemorrhagic groups based on clinical and MRI findings. The frequencies and distributions of four eNOS polymorphisms (eNOS -922A>G, -786T>C, 4a4b, and 894G>T) were assessed in pediatric and adult patients with moyamoya disease and compared to the frequencies and distribution in the control group.

RESULTS

No differences in eNOS polymorphisms were observed between control and moyamoya disease group. However, we found that the 4a4b sequences was less frequent in the adult group (p = 0.029). Compared to the control group, there were differences in the haplotype distribution of the study group, specifically the A-4b-G haplotype, which was seen more frequently in the adult patient group.

CONCLUSION

Our results suggest that pediatric and adult-onset moyamoya disease have different genetic backgrounds. These genetic differences can affect age-specific clinical characteristics, such as cerebral ischemia and hemorrhage.

Melatonin treatment following stroke induction modulates L-arginine metabolism

The efficacy of melatonin treatment in experimental stroke has been established. Some of the neuroprotective properties have been attributed to its anti-oxidant and anti-inflammatory effects. Nitric oxide synthases (NOS) and cyclooxygenases (COX) are considered to have a significant role in the inflammatory milieu occurring in acute stroke. While previous reports have shown that pretreatment with melatonin in a stroke model can modulate NOS isoforms, the effect of post-treatment with melatonin on l-arginine metabolism has not been investigated. This study initially examined the effect of melatonin (1 nm-1 mm) on l-arginine metabolism pathways in human fibrosarcoma fibroblasts (HT-1080) fibroblasts. Evidence of neuroprotection with melatonin was evaluated in rats subjected to middle cerebral artery occlusion (MCAO). Animals were treated with three daily doses of 5 mg/kg i.p., starting 1 hr after the onset of ischemia. Constitutive NOS activity but not expression was significantly increased by in vitro exposure (72 hr) to melatonin. In addition, melatonin treatment increased arginase activity by increasing arginase II expression. In vivo studies showed that melatonin treatment after MCAO significantly inhibited inducible NOS activity and attenuated expression of the inducible isoform, resulting in decreased total NOS activity and tissue nitrite levels. COX activity was significantly reduced with melatonin treatment. The neuroprotective anti-inflammatory effects of melatonin were consistent with the substantial reduction in infarct volume throughout the cortex and striatum and recovery of mitochondrial enzyme activities. The evidence presented here suggests that modulation of l-arginine metabolism by melatonin make it a valuable neuroprotective therapy for stroke.

Transient middle cerebral artery occlusion and reperfusion alters inducible NOS expression within the ventrolateral medulla and modulates cardiovascular function during static exercise

A major cause of stroke is cerebral ischemia in regions supplied by the middle cerebral artery (MCA). In this study, we hypothesized that compromised cardiovascular function during static exercise may involve altered expression of inducible NOS (iNOS) protein within the rostral ventrolateral medulla (RVLM) and caudal ventrolateral medulla (CVLM). We compared cardiovascular responses and iNOS protein expression within the left and right sides of both RVLM and CVLM in sham-operated rats and in rats with a 90 min left-sided MCA occlusion (MCAO) followed by 24 h of reperfusion. Increases in blood pressure during a static muscle contraction were attenuated in MCAO rats compared with sham-operated rats. Also, iNOS expression within the left RVLM was augmented compared with the right RVLM in MCAO rats and compared with both RVLM quadrants in sham-operated rats. In contrast, compared with sham-operated rats and the right CVLM of MCAO rats, iNOS expression was attenuated in the left CVLM in left-sided MCAO rats. These data suggest that the attenuation of pressor responses during static exercise in MCAO rats involves overexpression of iNOS within the ipsilateral RVLM and attenuation in iNOS within the ipsilateral CVLM. Differential expression of iNOS within the medulla plays a role in mediating cardiovascular responses during static exercise following stroke.

The role of aspirin in childhood tuberculous meningitis

Arterial stroke is the main cause of poor outcome in childhood tuberculous meningitis. Aspirin has an antithrombotic action at low dose and anti-ischemic and anti-inflammatory properties, which are dose-related. The aim of the study was to explore the possible benefits of aspirin in children with tuberculous meningitis. A total of 146 consecutive children with a diagnosis of probable tuberculous meningitis were studied. Patients were randomized into 3 groups: (1) placebo group, (2) low-dose aspirin group, and (3) high-dose aspirin group. Twenty-nine additional patients who received aspirin before admission were excluded from the randomized study, but continued on low-dose aspirin. Aspirin, irrespective of dose, did not show any significant benefit regarding morbidity (hemiparesis and developmental outcome) and mortality. Aspirin was well tolerated, but 1 death was probably related to aspirin. The fact that the outcome of the high-dose aspirin group compared favorably with the other treatment groups despite younger age and more severe neurological involvement at baseline needs further investigation.

RNA interference-produced autoregulation of inducible nitric oxide synthase expression

Vector-mediated delivery of short-hairpin RNA (shRNA) to regulate gene expression holds a great therapeutic promise. We hypothesize that gene expression can be autoregulated with RNA interference. We used inducible nitric oxide synthase (iNOS) as a gene model to test this hypothesis. Lipopolysaccharide dose-dependently increased iNOS in rat aortic smooth muscle cells and the nitrite production from these cells. These increases were attenuated in cells transfected with plasmids containing code for iNOS shRNA whose expression was controlled by an iNOS promoter. The production of shRNA was lipopolysaccharide dose-dependent. The lipopolysaccharide-induced iNOS expression in rat C6 glioma cells also was attenuated by transfection with plasmids containing the iNOS shRNA code. These results provide proof-of-concept evidence for using RNA interference technique to achieve autoregulation of gene expression.

Cerebroprotection by angiotensin-(1-7) in endothelin-1-induced ischaemic stroke

Activation of angiotensin-converting enzyme 2 (ACE2), production of angiotensin-(1-7) [Ang-(1-7)] and stimulation of the Ang-(1-7) receptor Mas exert beneficial actions in various peripheral cardiovascular diseases, largely through opposition of the deleterious effects of angiotensin II via its type 1 receptor. Here we considered the possibility that Ang-(1-7) may exert beneficial effects against CNS damage and neurological deficits produced by cerebral ischaemic stroke. We determined the effects of central administration of Ang-(1-7) or pharmacological activation of ACE2 on the cerebral damage and behavioural deficits elicited by endothelin-1 (ET-1)-induced middle cerebral artery occlusion (MCAO), a model of cerebral ischaemia. The results of the present study demonstrated that intracerebroventricular infusion of either Ang-(1-7) or an ACE2 activator, diminazine aceturate (DIZE), prior to and following ET-1-induced MCAO significantly attenuated the cerebral infarct size and neurological deficits measured 72 h after the insult. These beneficial actions of Ang-(1-7) and DIZE were reversed by co-intracerebroventricular administration of the Mas receptor inhibitor, A-779. Neither the Ang-(1-7) nor the DIZE treatments altered the reduction in cerebral blood flow elicited by ET-1. Lastly, intracerebroventricular administration of Ang-(1-7) significantly reduced the increase in inducible nitric oxide synthase mRNA expression within the cerebral infarct that occurs following ET-1-induced MCAO. This is the first demonstration of cerebroprotective properties of the ACE2-Ang-(1-7)-Mas axis during ischaemic stroke, and suggests that the mechanism of the Ang-(1-7) protective action includes blunting of inducible nitric oxide synthase expression.

Neuroprotective effect of guanosine against glutamate-induced cell death in rat hippocampal slices is mediated by the phosphatidylinositol-3 kinase/Akt/ glycogen synthase kinase 3β pathway activation and inducible nitric oxide synthase inhibition

Excitotoxicity and cell death induced by glutamate are involved in many neurodegenerative disorders. We have previously demonstrated that excitotoxicity induced by millimolar concentrations of glutamate in hippocampal slices involves apoptotic features and glutamate-induced glutamate release. Guanosine, an endogenous guanine nucleoside, prevents excitotoxicity by its ability to modulate glutamate transport. In this study, we have evaluated the neuroprotective effect of guanosine against glutamate-induced toxicity in hippocampal slices and the mechanism involved in such an effect. We have found that guanosine (100 μM) was neuroprotective against 1 mM glutamate-induced cell death through the inhibition of glutamate release induced by glutamate. Guanosine also induced the phosphorylation and, thus, activation of protein kinase B (PKB/Akt), a downstream target of phosphatidylinositol-3 kinase (PI3K), as well as phosphorylation of glycogen synthase kinase 3β, which has been reported to be inactivated by Akt after phosphorylation at Ser9. Glutamate treated hippocampal slices showed increased inducible nitric oxide synthase (iNOS) expression that was prevented by guanosine. Slices preincubated with SNAP (an NO donor), inhibited the protective effect of guanosine. LY294002 (30 μM), a PI3K inhibitor, attenuated guanosine-induced neuroprotection, guanosine prevention of glutamate release, and guanosine-induced GSK3β(Ser9) phosphorylation but not guanosine reduction of glutamate-induced iNOS expression. Taken together, the results of this study show that guanosine protects hippocampal slices by a mechanism that involves the PI3K/Akt/GSK3β(Ser9) pathway and prevention of glutamate-induced glutamate release. Furthermore, guanosine also reduces glutamate-induced iNOS by a PI3K/Akt-independent mechanism.

Neuronal nitric oxide synthase inhibition prevents cerebral palsy following hypoxia-ischemia in fetal rabbits: comparison between JI-8 and 7-nitroindazole

Cerebral palsy and death are serious consequences of perinatal hypoxia-ischemia (HI). Important concepts can now be tested using an animal model of cerebral palsy. We have previously shown that reactive oxygen and nitrogen species are produced in antenatal HI. A novel class of neuronal nitric oxide synthase (nNOS) inhibitors have been designed, and they ameliorate postnatal motor deficits when administered prior to the hypoxic-ischemic insult. This study asks how the new class of inhibitors, using JI-8 (K(i) for nNOS: 0.014 μM) as a representative, compare with the frequently used nNOS inhibitor 7-nitroindazole (7-NI; K(i): 0.09 ± 0.024 μM). A theoretical dose equivalent to 75 K(i) of JI-8 or equimolar 7-NI was administered to pregnant rabbit dams 30 min prior to and immediately after 40 min of uterine ischemia at 22 days gestation (70% term). JI-8 treatment resulted in a significant decrease in NOS activity (39%) in fetal brain homogenates acutely after HI, without affecting maternal blood pressure and heart rate. JI-8 treatment resulted in 33 normal kits, 2 moderately and 13 severely affected kits and 5 stillbirths, compared with 8 normal, 3 moderately affected and 5 severely affected kits and 10 stillbirths in the 7-NI group. In terms of neurobehavioral outcome, 7-NI was not different from saline treatment, while JI-8 was superior to saline and 7-NI in its protective effect (p < 0.05). In the surviving kits, JI-8 significantly improved the locomotion score over both saline and 7-NI scores. JI-8 was also significantly superior to saline in preserving smell, muscle tone and righting reflex function, but 7-NI did not show significant improvement. Furthermore, a 100-fold increase in the dose (15.75 μmol/kg) of 7-NI significantly decreased systolic blood pressure in the dam, while JI-8 did not. The new class of inhibitors such as JI-8 shows promise in the prevention of cerebral palsy and is superior to the previously more commonly used nNOS inhibitor.

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.

Altered expression of inducible nitric oxide synthase after sciatic nerve injury in rat

Nitric oxide is known to contribute to neuronal damage as well as to peripheral neuronal regeneration following injury. Sciatic nerve injury is a common and serious complication of intramuscular injections. In order to ascertain the role of inducible nitric oxide synthase (iNOS) in the injured sciatic nerve, we studied the expression of this enzyme by RT-PCR and immunohistochemistry, in a rat model of sciatic nerve injury. In sham-operated control rats iNOS expression was undetectable by immunohistochemistry and its mRNA level was also very low. In contrast, in the experimental group that was subjected to sciatic nerve injury, both mRNA and protein of iNOS were found to be significantly elevated. The protein level of iNOS, as revealed by positive immunostaining, peaked at 7 days post-surgery followed by a decrease. Similarly, the iNOS mRNA levels remained elevated at 1, 3, 7 days but declined to very low level by day 21, after surgery. This study indicates that the increased expression of iNOS after sciatic nerve injury in rats may contribute to nerve regeneration. Thus our results suggest that excessive expression of iNOS after nerve injury is not conducive to nerve regeneration.

Chondroitin sulfate reduces cell death of rat hippocampal slices subjected to oxygen and glucose deprivation by inhibiting p38, NFκB and iNOS

The glycosaminoglycan chondroitin sulfate (CS) is a major constituent of the extracellular matrix of the central nervous system where it can constitute part of the perineuronal nets. Constituents of the perineuronal nets are gaining interest because they have modulatory actions on their neighbouring neurons. In this study we have investigated if CS could afford protection in an acute in vitro ischemia/reoxygenation model by using isolated hippocampal slices subjected to 60min oxygen and glucose deprivation (OGD) followed by 120min reoxygenation (OGD/Reox). In this toxicity model, CS afforded protection of rat hippocampal slices measured as a reduction of lactate dehydrogenase (LDH) release; maximum protection (70% reduction of LDH) was obtained at the concentration of 3mM. To evaluate the intracellular signaling pathways implicated in the protective effect of CS, we first analysed the participation of the mitogen-activated protein kinases (MAPKs) p38 and ERK1/2 by western blot. OGD/Reox induced the phosphorylation of p38 and dephosphorylation of ERK1/2; however, CS only inhibited p38 but had no effect on ERK1/2. Furthermore, OGD/Reox-induced translocation of p65 to the nucleus was prevented in CS treated hippocampal slices. Finally, CS inhibited iNOS induction caused by OGD/Reox and thereby nitric oxide (NO) production measured as a reduction in DAF-2 DA fluorescence. In conclusion, the protective effect of CS in hippocampal slices subjected to OGD/Reox can be related to a modulatory action of the local immune response by a mechanism that implies inhibition of p38, NFκB, iNOS and the production of NO.

Betulinic acid protects against cerebral ischemia-reperfusion injury in mice by reducing oxidative and nitrosative stress

Increased production of reactive oxygen and nitrogen species following cerebral ischemia-reperfusion is a major cause for neuronal injury. In hypercholesterolemic apolipoprotein E knockout (ApoE-KO) mice, 2h of middle cerebral artery (MCA) occlusion followed by 22h of reperfusion led to an enhanced expression of NADPH oxidase subunits (NOX2, NOX4 and p22phox) and isoforms of nitric oxide synthase (neuronal nNOS and inducible iNOS) in the ischemic hemisphere compared with the non-ischemic contralateral hemisphere. This was associated with elevated levels of 3-nitrotyrosine, an indicator of peroxynitrite-mediated oxidative protein modification. Pre-treatment with betulinic acid (50mg/kg/day for 7days via gavage) prior MCA occlusion prevented the ischemia reperfusion-induced upregulation of NOX2, nNOS and iNOS. In parallel, betulinic acid reduced the levels of 3-nitrotyrosine. In addition, treatment with betulinic acid enhanced the expression of endothelial eNOS in the non-ischemic hemispheres. Finally, betulinic acid reduced infarct volume and ameliorated the neurological deficit in this mouse stroke model. In conclusion, betulinic acid protects against cerebral ischemia-reperfusion injury in mice. This is likely to result from a reduction of oxidative stress (by downregulation of NOX2) and nitrosative stress (by reduction of nNOS and iNOS), and an enhancement of blood flow (by upregulation of eNOS).

Hesperidin pre-treatment attenuates NO-mediated cerebral ischemic reperfusion injury and memory dysfunction

The present study was designed to explore the mechanism of hesperidin action via the nitric oxide pathway in the protection against ischemic reperfusion cerebral injury-induced memory dysfunction. Male Wistar rats (200-220 g) were subjected to bilateral carotid artery occlusion for 30 min followed by 24 h reperfusion. Hesperidin (50 and 100 mg/kg, po) pretreatment was given for 7 days before animals were subjected to cerebral I/R injury. Various behavioral tests (rotarod performance and memory retention), biochemical parameters (lipid peroxidation, nitrite concentration, glutathione levels, superoxide dismutase activity and catalase activity), mitochondrial complex enzyme dysfunctions (complex I, II, III and IV) and histopathological alterations were subsequently assessed in hippocampus. Seven days of hesperidin (50 and 100 mg/kg) treatment significantly improved neurobehavioral alterations (delayed fall off time and increased memory retention), oxidative defense and mitochondrial complex enzyme activities in hippocampus compared to control (I/R) animals. In addition, hesperidin treatment significantly attenuated histopathological alterations compared to control (I/R) animals. L-arginine (100 mg/kg) pretreatment attenuated the protective effect of the lower dose of hesperidin on memory behavior, biochemical and mitochondrial dysfunction compared with hesperidin alone. However, L-NAME pretreatment significantly potentiated the protective effect of hesperidin. The present study suggests that the L-arginine-NO signaling pathway is involved in the protective effect of hesperidin against cerebral I/R-induced memory dysfunction and biochemical alterations in rats.

Interactions between inducible nitric oxide synthase and cyclooxygenase-2 in response to ischaemia-reperfusion of rabbit bladder

OBJECTIVE

To investigate the interactions between inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) in response to ischaemia-reperfusion (I/R) of rabbit bladder.

MATERIALS AND METHODS

Rabbit bladders were exposed to 2 h of ischaemia by bilaterally clamping the major arteries entering the bladder and then a subsequent 36 h of reperfusion (I/R) with or without intraperitoneal administration of a selective iNOS inhibitor n-(3-(amynomethyl)benzyl)acetamidine (1400W) or a selective COX-2 inhibitor NS-398 given 1 h before killing. The bladder tissues were processed for isometric tension experiments, enzymatic NOS activitiy, tissue contents of nitrite/nitrate (NO(X) ), cyclic guanosine monophosphate (cGMP) and COX activity determined by prostaglandin E(2) (PGE(2) ) production.

RESULTS

iNOS and constitutive NOS (cNOS) activities, NO(X) and PGE(2) contents in the bladder tissues at 36 h after reperfusion were significantly higher than those in the sham group with no significant increase in cGMP. Treatment with 1400W abrogated the increases in iNOS activity and NO(X) as well as PGE(2) without changing cNOS activity. In the tension experiments, a NOS substrate, l-arginine, induced detrusor contraction only in the I/R group, which was inhibited by 1400W or NS-398 but not by a selective soluble guanylate cyclase inhibitor 1H-[1,2,4] oxadiazole[4,3-a]quinoxalin-1-one (ODQ). 8-Br-cGMP induced detrusor relaxation in the sham and I/R groups. Also, l-arginine increased NO(X) and PGE(2) in the bladder tissues only in the I/R group, which were inhibited by pretreatment with 1400W. While, l-arginine increased cGMP contents in the I/R group and this increase was suppressed by ODQ but not by 1400W.

CONCLUSION

These results show that NO derived from an up-regulation of iNOS after I/R increases COX-2-derived PG via a cGMP-independent mechanism. NO-mediated activation of COX-2 may be an important mechanism for the modulation of bladder function after I/R injury.

Methylene blue protects the cortical blood-brain barrier against ischemia/reperfusion-induced disruptions

OBJECTIVES

To investigate the effects of cardiac arrest and the reperfusion syndrome on blood-brain barrier permeability and evaluate whether methylene blue counteracts blood-brain barrier disruption in a pig model of controlled cardiopulmonary resuscitation.

DESIGN

Randomized, prospective, laboratory animal study.

SETTING

University-affiliated research laboratory.

SUBJECTS

Forty-five piglets.

INTERVENTIONS

Forty-five anesthetized piglets were subjected to cardiac arrest alone or 12-min cardiac arrest followed by 8 mins cardiopulmonary resuscitation. The first group (n = 16) was used to evaluate blood-brain barrier disruptions after untreated cerebral ischemia after 0, 15, or 30 mins after untreated cardiac arrest. The other two groups received either an infusion of saline (n = 10) or infusion of saline with methylene blue (n = 12) 1 min after the start of cardiopulmonary resuscitation and continued 50 mins after return of spontaneous circulation. In these groups, brains were removed for immunohistological analyses at 30, 60, and 180 mins after return of spontaneous circulation.

MEASUREMENTS AND MAIN RESULTS

An increase of injured neurons and albumin immunoreactivity was demonstrated with increasing duration of ischemia/reperfusion. Less blood-brain barrier disruption was observed in subjects receiving methylene blue as demonstrated by decreased albumin leakage (p < .01), water content (p < .05), and neuronal injury (p < .01). Methylene blue treatment reduced cerebral tissue nitrite/nitrate content (p < .05) and the number of inducible and neuronal nitric oxide synthase-activated cortical cells during administration (p < .01). Meanwhile, the number of cortical endothelial nitric oxide synthase-activated cells increased over time (p < .001).

CONCLUSION

Cerebral tissue water content, blood-brain barrier permeability and neurologic injury were increased early in reperfusion after cardiac arrest. Methylene blue exerted neuroprotective effects against the brain damage associated with the ischemia/reperfusion injury and ameliorated the blood-brain barrier disruption by decreasing nitric oxide metabolites.

The contribution of L-arginine to the neurotoxicity of recombinant tissue plasminogen activator following cerebral ischemia: a review of rtPA neurotoxicity

Alteplase is the only drug licensed for acute ischemic stroke, and in this formulation, the thrombolytic agent recombinant tissue plasminogen activator (rtPA) is stabilized in a solution of L-arginine. Improved functional outcomes after alteplase administration have been shown in clinical trials, along with improved histological and behavioral measures in experimental models of embolic stroke. However, in animal models of mechanically induced ischemia, alteplase can exacerbate ischemic damage. We have systematically reviewed the literature of both rtPA and L-arginine administration in mechanical focal ischemia. The rtPA worsens ischemic damage under certain conditions, whereas L-arginine can have both beneficial and deleterious effects dependent on the time of administration. The interaction between rtPA and L-arginine may be leading to the production of nitric oxide, which can cause direct neurotoxicity, altered cerebral blood flow, and disruption of the neurovascular unit. We suggest that alternative formulations of rtPA, in the absence of L-arginine, would provide new insight into rtPA neurotoxicity, and have the potential to offer more efficacious thrombolytic therapy for ischemic stroke patients.

Regulation of endothelial nitric oxide synthase by agmatine after transient global cerebral ischemia in rat brain

Nitric oxide (NO) production by endothelial nitric oxide synthase (eNOS) plays a protective role in cerebral ischemia by maintaining vascular permeability, whereas NO derived from neuronal and inducible NOS is neurotoxic and can participate in neuronal damage occurring in ischemia. Matrix metalloproteinases (MMPs) are up-regulated by ischemic injury and degrade the basement membrane if brain vessels to promote cell death and tissue injury. We previously reported that agmatine, synthesized from L-arginine by arginine decarboxylase (ADC) which is expressed in endothelial cells, has shown a direct increased eNOS expression and decreased MMPs expression in bEnd3 cells. But, there are few reports about the regulation of eNOS by agmatine in ischemic animal model. In the present study, we examined the expression of eNOS and MMPs by agmatine treatment after transient global ischemia in vivo. Global ischemia was induced with four vessel occlusion (4-VO) and agmatine (100 mg/kg) was administered intraperitoneally at the onset of reperfusion. The animals were euthanized at 6 and 24 hours after global ischemia and prepared for other analysis. Global ischemia led severe neuronal damage in the rat hippocampus and cerebral cortex, but agmatine treatment protected neurons from ischemic injury. Moreover, the level and expression of eNOS was increased by agmatine treatment, whereas inducible NOS (iNOS) and MMP-9 protein expressions were decreased in the brain. These results suggest that agmatine protects microvessels in the brain by activation eNOS as well as reduces extracellular matrix degradation during the early phase of ischemic insult.

Regulation of endothelial nitric oxide synthase by agmatine after transient global cerebral ischemia in rat brain

Nitric oxide (NO) production by endothelial nitric oxide synthase (eNOS) plays a protective role in cerebral ischemia by maintaining vascular permeability, whereas NO derived from neuronal and inducible NOS is neurotoxic and can participate in neuronal damage occurring in ischemia. Matrix metalloproteinases (MMPs) are up-regulated by ischemic injury and degrade the basement membrane if brain vessels to promote cell death and tissue injury. We previously reported that agmatine, synthesized from L-arginine by arginine decarboxylase (ADC) which is expressed in endothelial cells, has shown a direct increased eNOS expression and decreased MMPs expression in bEnd3 cells. But, there are few reports about the regulation of eNOS by agmatine in ischemic animal model. In the present study, we examined the expression of eNOS and MMPs by agmatine treatment after transient global ischemia in vivo. Global ischemia was induced with four vessel occlusion (4-VO) and agmatine (100 mg/kg) was administered intraperitoneally at the onset of reperfusion. The animals were euthanized at 6 and 24 hours after global ischemia and prepared for other analysis. Global ischemia led severe neuronal damage in the rat hippocampus and cerebral cortex, but agmatine treatment protected neurons from ischemic injury. Moreover, the level and expression of eNOS was increased by agmatine treatment, whereas inducible NOS (iNOS) and MMP-9 protein expressions were decreased in the brain. These results suggest that agmatine protects microvessels in the brain by activation eNOS as well as reduces extracellular matrix degradation during the early phase of ischemic insult.

Nitric oxide pros and cons: The role of L-arginine, a nitric oxide precursor, and idebenone, a coenzyme-Q analogue in ameliorating cerebral hypoxia in rat

Evidence exists that nitric oxide (NO) may mediate both protective and pathological responses during brain hypoxia (HP). Reactive oxygen species have also been implicated in the pathophysiological response of the brain tissues to HP. Therefore, this study investigated whether a NO precursor, l-arginine (l-arg), a free radical scavenger, idebenone (ID), and their combination would reduce neurological injury resulting from hemic hypoxia (HP) in rats. Adult male Wistar albino rats were injected with sodium nitrite (60 mg/kg, s.c.) to establish hemic hypoxia. ID (100 mg kg(-1), i.p.) and/or l-arg (100 mg kg(-1), i.p.) were administrated 24 and 1h prior to sodium nitrite intoxication, respectively. Hypoxia significantly decreased hemoglobin concentration, while significantly increased serum lactate dehydrogenase (LDH), creatine phosphokinase (CPK), total nitrate/nitrite, sialic, and uric acids concentrations. Moreover, brain lipid peroxides were significantly enhanced, while reduced glutathione, l-ascorbic acids, adenosine triphosphate (ATP) contents, and the activities of catalase and superoxide dismutase, were significantly reduced in the brain tissue. Pretreatment with either ID or l-arg altered the majority of the above-mentioned biochemical changes in hypoxic rats. Additionally, the combination of these two agents significantly reduced injury marker enzyme activities as well as serum sialic, and uric acids level (P>0.05 vs. control). Moreover, this combination exerted a synergistic antioxidant effect by blocking the induction of lipid peroxidation, preserving brain energy (ATP) content, and greatly reducing the hypoxic alterations in brain enzymatic and non-enzymatic antioxidants. Histopathological examination of the brain tissue supported these biochemical findings. This study showed that ID and l-arg were capable of reducing neurological injury following HP in rat, and support the idea of the usefulness of l-arg and ID as prophylaxis from hypoxic brain injury.

Normobaric hyperoxia delays and attenuates early nitric oxide production in focal cerebral ischemic rats

Overproduction of neuronal nitric oxide synthase (nNOS)-derived NO is detrimental during cerebral ischemia. Normobaric hyperoxia (NBO) has been shown to be neuroprotective, extending the therapeutic time window for ischemic stroke, but the mechanism is not fully understood. In the present study, using a rat model of ischemic stroke, we investigated the effect of early NBO treatment on neuronal NO production. Male Sprague-Dawley rats were given normoxia (30% O(2)) or NBO (95% O(2)) during 10, 30, 60 or 90min filament occlusion of the middle cerebral artery. NO(x)(-) (nitrite plus nitrate) and 3-nitrotyrosine were measured in the ischemic cortex. Ischemia caused a rapid increase in the production of NO(x)(-), with a peak at 10min after ischemia onset, then gradually declining to the baseline level at 60min. NBO treatment delayed the NO(x)(-) production peak to 30min and attenuated the total amount of NO(x)(-). Ischemia also increased 3-nitrotyrosine formation, which was significantly reduced by NBO treatment. Inhibition of nNOS by pre-treatment with 7-nitroindazole had similar effect as NBO treatment on NO(x)(-) and 3-nitrotyrosine production, and when combined with NBO, no further reduction in NO production was observed. Furthermore, NBO treatment significantly decreased brain infarct volume. Taken together, our findings demonstrate that delaying and attenuating the early NO release from nNOS may be an important mechanism accounting for NBO's neuroprotection.

Statins: multiple neuroprotective mechanisms in neurodegenerative diseases

Statins have been widely used for the treatment of a variety of conditions beyond their original role in lowering cholesterol. Since statins have relatively few side effects, they have been recognized as useful medicine to ameliorate neurodegenerative disorders. Current studies on the applications of statins have demonstrated their neuroprotective and clinical significance among neurodegenerative diseases like cerebral ischemic stroke, vascular dementia, Alzheimer's disease, and Parkinson's disease, though the neuroprotective mechanisms are not completely understood. This review will discuss recent development in the use of statins in slowing down the progression of these neurodegenerative diseases. It will summarize the potential mechanisms for statin-mediated neuroprotective effects in neurodegenerative diseases. In detail, this review discuss the roles of statins in lowering cholesterol, reducing reactive oxygen species, impairing β-amyloid production and serum apolipoprotein E levels, enhancing the levels of endothelial nitric oxide synthase and cerebral blood flow, and modulating cognitive related receptors and matrix metalloproteases. Finally, different alterations of various receptors in brain regions following statin treatment and their correlations with cognitive dysfunction in Parkinson's disease will also be reviewed, as well as the potential for therapy in ameliorating the progression of Parkinson's disease. This article is part of a Special Issue entitled "Interaction between repair, disease, & inflammation."

The dynamic detection of NO during stroke and reperfusion in vivo

PURPOSE

Nitric oxide (NO) has been implicated as a mediator of synaptic transmission and a pathological factor in stroke/reperfusion. The purpose of this study was to detect the change of NO concentration in rat hippocampus during global cerebral ischemia and reperfusion in vivo and to reveal effects of different NO synthases (NOS).

METHOD

In the present study, the real-time record of NO levels in rat hippocampus was obtained by using a NO sensor during the global cerebral ischemia and the initial stage of reperfusion. The effects of two inhibitors of NOS on NO concentration were also observed. The two inhibitors were respectively administrated intravenously at the onset of reperfusion and 1 hour later.

RESULTS

The change of the NO concentration in the initial stage of reperfusion was 0.768 +/- 0.029 microM. 7-nitroindazole (7-NI, inhibitor of nNOS) had a strong inhibitive effect on NO synthesis at both time points, while 1400W dihydrochloride (1400W, inhibitor of iNOS) had no significant effect on the NO synthesis.

CONCLUSIONS

The in vivo detection revealed the real dynamic change of NO concentration, which is much more reliable than the in vitro method. The results showed that, during the initial stage of reperfusion, NO biosynthesis was mainly in an nNOS-dependent manner. Thus, the toxicity of NO in this process had a close relationship with the activity of nNOS but not iNOS.

Sex differences in cerebral injury after severe haemorrhage and ventricular fibrillation in pigs

BACKGROUND

Experimental studies of haemorrhagic shock have documented a superior haemodynamic response and a better outcome in female animals as compared with male controls. Such sexual dimorphism has, nevertheless, not been reported after circulatory arrest that follows exsanguination and shock. We aimed to study differences in cerebral injury markers after exsanguination cardiac arrest in pre-pubertal piglets. The hypothesis was that cerebral injury is less extensive in female animals, and that this difference is independent of sexual hormones or choice of resuscitative fluid.

METHODS

Thirty-two sexually immature piglets (14 males and 18 females) were subjected to 5 min of haemorrhagic shock followed by 2 min of ventricular fibrillation and 8 min of cardiopulmonary resuscitation, using three resuscitation fluid regimens (whole blood, hypertonic saline and dextran, or acetated Ringers' solution plus whole blood and methylene blue). Haemodynamic values, cellular markers of brain injury and brain histology were studied.

RESULTS

After successful resuscitation, female piglets had significantly greater cerebral cortical blood flow, tended to have lower S-100beta values and a lower cerebral oxygen extraction ratio. Besides, in female animals, systemic and cerebral venous acidosis were mitigated. Female piglets exhibited a significantly smaller increase in neuronal nitric oxide synthase (nNOS) and inducible nitric oxide synthase (iNOS) expression in their cerebral cortex, smaller blood-brain-barrier (BBB) disruption and significantly smaller neuronal injury.

CONCLUSION

After resuscitation from haemorrhagic circulatory arrest, cerebral reperfusion is greater, and BBB permeability and neuronal injury is smaller in female piglets. An increased cerebral cortical iNOS and nNOS expression in males implies a mechanistic relationship with post-resuscitation neuronal injury and warrants further investigation.

Intracellular mechanisms of N-acylethanolamine-mediated neuroprotection in a rat model of stroke

N-acyl ethanolamines (NAEs) are endogenous lipids that are synthesized in response to tissue injury, including ischemia and stroke, suggesting they may exhibit neuroprotective properties. We hypothesized that NAE 16:0 (palmitoylethanolamine) is neuroprotective against ischemia-reperfusion injury in rats, a widely employed model of stroke, and that neuroprotection is mediated through an intracellular mechanism independent of known NAE receptors. Administration of NAE 16:0 from 30 min before to 2 h after stroke significantly reduced cortical and subcortical infarct volume, and correlated with an improvement of the neurological phenotype, as assessed by the neurological deficit score. We here show that NAE 16:0-mediated neuroprotection was independent of cannabinoid (CB1) and vanilloid (VR1) receptor activation, known NAE receptors on the plasma membrane, as determined by inclusion of specific inhibitors. The inclusion of an NAE uptake inhibitor (AM404), however, completely reversed NAE 16:0-mediated neuroprotection, suggesting that NAE 16:0s effects are through an intracellular mechanism. NAE 16:0 produced a significant reduction in the number of cells undergoing apoptosis and reversed ischemia-induced upregulation of several proteins, including inducible nitric oxide synthase and transcription factor NFkappaB. Our findings suggest that NAE 16:0-mediated neuroprotection is due to the reduction of neuronal apoptosis and inflammation in the brain.

Targeting eNOS and beyond: emerging heterogeneity of the role of endothelial Rho proteins in stroke protection

Currently available modalities for the treatment of acute ischemic stroke are aimed at preserving or augmenting cerebral blood flow. Experimental evidence suggests that statins, which show 25-30% reduction of stroke incidence in clinical trials, confer stroke protection by upregulation of eNOS and increasing cerebral blood flow. The upregulation of eNOS by statins is mediated by inhibition of small GTP-binding protein RhoA. Our recent study uncovered a unique role for a Rho-family member Rac1 in stroke protection. Rac1 in endothelium does not affect cerebral blood flow. Instead, inhibition of endothelial Rac1 leads to broad upregulation of the genes relevant to neurovascular protection. Intriguingly, inhibition of endothelial Rac1 enhances neuronal cell survival through endothelium-derived neurotrophic factors, including artemin. This review discusses the emerging therapeutic opportunities to target neurovascular signaling beyond the BBB, with special emphasis on the novel role of endothelial Rac1 in stroke protection.

The reactions of specific neuron types to intestinal ischemia in the guinea pig enteric nervous system

Damage following ischemia and reperfusion (I/R) is common in the intestine and can be caused during abdominal surgery, in several disease states and following intestinal transplantation. Most studies have concentrated on damage to the mucosa, although published evidence also points to effects on neurons. Moreover, alterations of neuronally controlled functions of the intestine persist after I/R. The present study was designed to investigate the time course of damage to neurons and the selectivity of the effect of I/R damage for specific types of enteric neurons. A branch of the superior mesenteric artery supplying the distal ileum of anesthetised guinea pigs was occluded for 1 h and the animals were allowed to recover for 2 h to 4 weeks before tissue was taken for the immunohistochemical localization of markers of specific neuron types in tissues from sham and I/R animals. The dendrites of neurons with nitric oxide synthase (NOS) immunoreactivity, which are inhibitory motor neurons and interneurons, were distorted and swollen by 24 h after I/R and remained enlarged up to 28 days. The total neuron profile areas (cell body plus dendrites) increased by 25%, but the sizes of cell bodies did not change significantly. Neurons of type II morphology (intrinsic primary afferent neurons), revealed by NeuN immunoreactivity, were transiently reduced in cell size, at 24 h and 7 days. These neurons also showed signs of minor cell surface blebbing. Calretinin neurons, many of which are excitatory motor neurons, were unaffected. Thus, this study revealed a selective damage to NOS neurons that was observed at 24 h and persisted up to 4 weeks, without a significant change in the relative numbers of NOS neurons.

Edaravone inhibits DNA peroxidation and neuronal cell death in neonatal hypoxic-ischemic encephalopathy model rat

Neonatal hypoxic-ischemic encephalopathy (HIE) is the most frequent neurologic disease in the perinatal period. Its major cause is oxidative stress, which induces DNA peroxidation and apoptotic neuronal death. We examined 8-hydroxy-2'-deoxyguanosine (8-OHdG) expression to evaluate brain damage in neonatal HIE and the therapeutic effect of edaravone, a free radical scavenger. Using HPLC and immunohistochemistry, the 8-OHdG levels of neonatal HIE model Sprague-Dawley rats that were subjected to left common carotid artery ligation and 2-h hypoxia significantly increased after 24-48 h of hypoxic-ischemic (HI) insult, but decreased after 72 h. Moreover, the number of apoptotic cells with terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling and karyorrhexis significantly increased after 24-72 h of HI insult. In a therapeutic experiment, edaravone was administered i.p. (9 mg/kg) after HI insult every 24 h. Edaravone reduced both the apoptotic neuronal cell number and 8-OHdG expression after 24-48 h of HI. From a double immunofluorescent study, DNA peroxidation occurred in apoptotic neuronal cells with 8-OHdG expression. Edaravone may inhibit the number of apoptotic neuronal cells and 8-OHdG expression within 48 h after HI insult.

Isoform-specific differences in the nitrite reductase activity of nitric oxide synthases under hypoxia

Nitrite (NO(2)(-)) recycling to nitric oxide (NO) is catalysed by a number of enzymes and induces a protective vasodilation effect under hypoxia/ischaemia. In the present work, we tested the in vitro ability of the three NOS (nitric oxide synthase) isoforms to release NO from nitrite under anoxia using electrochemical detection, chemiluminescence and absorption spectroscopy. The release of free NO from anoxic nitrite solutions at 15 muM was specific to the endothelial NOS isoform (eNOS) and did not occur with the neuronal (nNOS) or inducible (iNOS) isoforms. Unlike xanthine oxidase, the eNOS reductase domain did not recycle nitrite to NO, and wild-type eNOS did not reduce nitrate. Our data suggest that structural and, by inference, dynamic differences between nNOS and eNOS in the distal haem side account for eNOS being the only isoform capable of converting nitrite into NO at pH 7.6. In human dermal microvascular endothelial cells under careful control of oxygen tension, the rates of NO formation determined by chemiluminescence were enhanced approximately 3.6- and approximately 8.3-fold under hypoxia (2 p.p.m. O(2)) and anoxia (argon) respectively compared with normoxia ( approximately 22 p.p.m. O(2)) using 10 muM extracellular nitrite. NOS inhibitors inhibited this hypoxic NO release. Our data show that eNOS is unique in that it releases NO under all oxygen levels from normoxia to complete anoxia at physiological micromolar nitrite concentrations. The magnitude of the hypoxic NO release by the endothelial cells suggest that the endothelium could provide an appropriate response to acute episodic ischaemia and may explain the observed eNOS-expression-specific protective effect as a short-term response in animal models of acute hypoxia.

Statins: mechanisms of neuroprotection

Clinical trials report that the class of drugs known as statins may be neuroprotective in Alzheimer's and Parkinson's disease, and further trials are currently underway to test whether these drugs are also beneficial in multiple sclerosis and acute stroke treatment. Since statins are well tolerated and have relatively few side effects, they may be considered as viable drugs to ameliorate neurodegenerative diseases. However, the mechanism of their neuroprotective effects is only partly understood. In this article, we review the current data on the neuroprotective effects of statins and their underlying mechanisms. In the first section, we detail the mechanisms by which statins affect cellular signalling. The primary action of statins is to inhibit cellular cholesterol synthesis. However, the cholesterol synthesis pathway also has several by-products, the non-sterol isoprenoids that are also important in cellular functioning. Furthermore, reduced cholesterol levels may deplete the cholesterol-rich membrane domains known as lipid rafts, which in turn could affect cellular signalling. In the second section, we summarize how the effects on signalling translate into general neuroprotective effects through peripheral systems. Statins improve blood-flow, reduce coagulation, modulate the immune system and reduce oxidative damage. The final section deals with the effects of statins on the central nervous system, particularly during Alzheimer's and Parkinson's disease, stroke and multiple sclerosis.

Post-ischemic brain damage: pathophysiology and role of inflammatory mediators

Neuroinflammatory mediators play a crucial role in the pathophysiology of brain ischemia, exerting either deleterious effects on the progression of tissue damage or beneficial roles during recovery and repair. Within hours after the ischemic insult, increased levels of cytokines and chemokines enhance the expression of adhesion molecules on cerebral endothelial cells, facilitating the adhesion and transendothelial migration of circulating neutrophils and monocytes. These cells may accumulate in the capillaries, further impairing cerebral blood flow, or extravasate into the brain parenchyma. Infiltrating leukocytes, as well as resident brain cells, including neurons and glia, may release pro-inflammatory mediators, such as cytokines, chemokines and oxygen/nitrogen free radicals that contribute to the evolution of tissue damage. Moreover, recent studies have highlighted the involvement of matrix metalloproteinases in the propagation and regulation of neuroinflammatory responses to ischemic brain injury. These enzymes cleave protein components of the extracellular matrix such as collagen, proteoglycan and laminin, but also process a number of cell-surface and soluble proteins, including receptors and cytokines such as interleukin-1beta. The present work reviewed the role of neuroinflammatory mediators in the pathophysiology of ischemic brain damage and their potential exploitation as drug targets for the treatment of cerebral ischemia.

Anemia and cerebral outcomes: many questions, fewer answers

A number of clinical studies have associated acute anemia with cerebral injury in perioperative patients. Evidence of such injury has been observed near the currently accepted transfusion threshold (hemoglobin [Hb] concentration, 7-8 g/dL), and well above the threshold for cerebral tissue hypoxia (Hb 3-4 g/dL). However, hypoxic and nonhypoxic mechanisms of anemia-induced cerebral injury have not been clearly elucidated. In addition, protective mechanisms which may minimize cerebral injury during acute anemia have not been well defined. Vasodilatory mechanisms, including nitric oxide (NO), may help to maintain cerebral oxygen delivery during anemia as all three NO synthase (NOS) isoforms (neuronal, endothelial, and inducible NOS) have been shown to be up-regulated in different experimental models of acute hemodilutional anemia. Recent experimental evidence has also demonstrated an increase in an important transcription factor, hypoxia inducible factor (HIF)-1alpha, in the cerebral cortex of anemic rodents at clinically relevant Hb concentrations (Hb 6-7 g/dL). This suggests that cerebral oxygen homeostasis may be in jeopardy during acute anemia. Under hypoxic conditions, cytoplasmic HIF-1alpha degradation is inhibited, thereby allowing it to accumulate, dimerize, and translocate into the nucleus to promote transcription of a number of hypoxic molecules. Many of these molecules, including erythropoietin, vascular endothelial growth factor, and inducible NOS have also been shown to be up-regulated in the anemic brain. In addition, HIF-1alpha transcription can be increased by nonhypoxic mediators including cytokines and vascular hormones. Furthermore, NOS-derived NO may also stabilize HIF-1alpha in the absence of tissue hypoxia. Thus, during anemia, HIF-1alpha has the potential to regulate cerebral cellular responses under both hypoxic and normoxic conditions. Experimental studies have demonstrated that HIF-1alpha may have either neuroprotective or neurotoxic capacity depending on the cell type in which it is up-regulated. In the current review, we characterize these cellular processes to promote a clearer understanding of anemia-induced cerebral injury and protection. Potential mechanisms of anemia-induced injury include cerebral emboli, tissue hypoxia, inflammation, reactive oxygen species generation, and excitotoxicity. Potential mechanisms of cerebral protection include NOS/NO-dependent optimization of cerebral oxygen delivery and cytoprotective mechanisms including HIF-1alpha, erythropoietin, and vascular endothelial growth factor. The overall balance of these activated cellular mechanisms may dictate whether or not their up-regulation leads to cytoprotection or cellular injury during anemia. A clearer understanding of these mechanisms may help us target therapies that will minimize anemia-induced cerebral injury in perioperative patients.

Central administration of angiotensin-(1-7) stimulates nitric oxide release and upregulates the endothelial nitric oxide synthase expression following focal cerebral ischemia/reperfusion in rats

Angiotensin-(1-7) [Ang-(1-7)] is an endogenous peptide of the renin-angiotensin system with several beneficial effects that are often opposite to those attributed to angiotensin II (Ang II). Since there are no data available so far on the role of Ang-(1-7) after cerebral ischemia/reperfusion, in this paper, we investigated the central administration of Ang-(1-7) modulates in vivo the nitric oxide(NO) release and the endothelial NO synthase (eNOS) expression following focal cerebral ischemia/reperfusion in rats. Cerebral ischemia-reperfusion injury was induced by intraluminal thread occlusion of middle cerebral artery in the adult male rats. The levels of NO in ischemic tissues were measured by NO detection kits. Reverse transcription (RT)-PCR and western blot were used to determine messenger RNA (mRNA) and protein levels of the eNOS in ischemic tissues. The cerebral ischemic lesion resulted in a significant increase of NO release at 3 and 6h compared with sham operation group in our model after reperfusion, whereas both medium and high doses Ang-(1-7) markedly enhanced NO levels at 3-24h, and 3-72h after reperfusion, respectively. In addition, NO release increased was significantly induced by high-dose Ang-(1-7) compared with medium-dose Ang-(1-7) at 24-72 h after reperfusion. Medium and high-dose Ang-(1-7) significantly stimulated eNOS activation when compared with artificial cerebrospinal fluid (aCSF) treatment group at 3, 6, 12, 24, and 48h after reperfusion, however, no significant changes in eNOS expression were found between medium and high-dose Ang-(1-7) at different times after the ischemic insult. These findings indicate that medium and high-dose Ang-(1-7) stimulate NO release and upregulate eNOS expression in ischemic tissues following focal cerebral ischemia/reperfusion in rats.