Dual role of nitric oxide in focal cerebral ischemia

Candidate neuroinflammatory markers of cerebral autoregulation dysfunction in human acute brain injury

The loss of cerebral autoregulation (CA) is a common and detrimental secondary injury mechanism following acute brain injury and has been associated with worse morbidity and mortality. However patient outcomes have not as yet been conclusively proven to have improved as a result of CA-directed therapy. While CA monitoring has been used to modify CPP targets, this approach cannot work if the impairment of CA is not simply related to CPP but involves other underlying mechanisms and triggers, which at present are largely unknown. Neuroinflammation, particularly inflammation affecting the cerebral vasculature, is an important cascade that occurs following acute injury. We hypothesise that disturbances to the cerebral vasculature can affect the regulation of CBF, and hence the vascular inflammatory pathways could be a putative mechanism that causes CA dysfunction. This review provides a brief overview of CA, and its impairment following brain injury. We discuss candidate vascular and endothelial markers and what is known about their link to disturbance of the CBF and autoregulation. We focus on human traumatic brain injury (TBI) and subarachnoid haemorrhage (SAH), with supporting evidence from animal work and applicability to wider neurologic diseases.

Neurovascular coupling protects neurons against hypoxic injury via inhibition of potassium currents by generation of nitric oxide in direct neuron and endothelium cocultures

This study examined the effect of neuron-endothelial coupling on the survival of neurons after ischemia and the possible mechanism underlying that effect. Whole-cell patch-clamp experiments were performed on cortical neurons cultured alone or directly cocultured with brain microvascular endothelial cells (BMEC). Propidium iodide (PI) and NeuN staining were performed to examine neuronal death following oxygen and glucose deprivation (OGD). We found that the neuronal transient outward potassium currents (I_A) decreased in the coculture system, whereas the outward delayed-rectifier potassium currents (I_K) did not. Sodium nitroprusside, a NO donor, enhanced BMEC-induced I_A inhibition and nitro-l-arginine methylester, a NOS inhibitor, partially prevented this inhibition. Moreover, the neurons directly cocultured with BMEC showed more resistance to OGD-induced injury compared with the neurons cultured alone, and that neuroprotective effect was abolished by treatment with NS5806, an activator of the I_A. These results indicate that vascular endothelial cells assist neurons to prevent hypoxic injury via inhibiting neuronal I_A by production of NO in the direct neuron-BMEC coculture system. These results further provide direct evidence of functional coupling between neurons and vascular endothelial cells. This study clearly demonstrates that vascular endothelial cells play beneficial roles in the pathophysiological processes of neurons after hypoxic injury, suggesting that the improvement of neurovascular coupling or functional remodeling may become an important therapeutic target for preventing brain injury.

Post-ischaemic silencing of p66Shc reduces ischaemia/reperfusion brain injury and its expression correlates to clinical outcome in stroke

AIM

Constitutive genetic deletion of the adaptor protein p66(Shc) was shown to protect from ischaemia/reperfusion injury. Here, we aimed at understanding the molecular mechanisms underlying this effect in stroke and studied p66(Shc) gene regulation in human ischaemic stroke.

METHODS AND RESULTS

Ischaemia/reperfusion brain injury was induced by performing a transient middle cerebral artery occlusion surgery on wild-type mice. After the ischaemic episode and upon reperfusion, small interfering RNA targeting p66(Shc) was injected intravenously. We observed that post-ischaemic p66(Shc) knockdown preserved blood-brain barrier integrity that resulted in improved stroke outcome, as identified by smaller lesion volumes, decreased neurological deficits, and increased survival. Experiments on primary human brain microvascular endothelial cells demonstrated that silencing of the adaptor protein p66(Shc) preserves claudin-5 protein levels during hypoxia/reoxygenation by reducing nicotinamide adenine dinucleotide phosphate oxidase activity and reactive oxygen species production. Further, we found that in peripheral blood monocytes of acute ischaemic stroke patients p66(Shc) gene expression is transiently increased and that this increase correlates with short-term neurological outcome.

CONCLUSION

Post-ischaemic silencing of p66(Shc) upon reperfusion improves stroke outcome in mice while the expression of p66(Shc) gene correlates with short-term outcome in patients with ischaemic stroke.

Oxidative Stress and the Use of Antioxidants in Stroke

Transient or permanent interruption of cerebral blood flow by occlusion of a cerebral artery gives rise to an ischaemic stroke leading to irreversible damage or dysfunction to the cells within the affected tissue along with permanent or reversible neurological deficit. Extensive research has identified excitotoxicity, oxidative stress, inflammation and cell death as key contributory pathways underlying lesion progression. The cornerstone of treatment for acute ischaemic stroke remains reperfusion therapy with recombinant tissue plasminogen activator (rt-PA). The downstream sequelae of events resulting from spontaneous or pharmacological reperfusion lead to an imbalance in the production of harmful reactive oxygen species (ROS) over endogenous anti-oxidant protection strategies. As such, anti-oxidant therapy has long been investigated as a means to reduce the extent of injury resulting from ischaemic stroke with varying degrees of success. Here we discuss the production and source of these ROS and the various strategies employed to modulate levels. These strategies broadly attempt to inhibit ROS production or increase scavenging or degradation of ROS. While early clinical studies have failed to translate success from bench to bedside, the combination of anti-oxidants with existing thrombolytics or novel neuroprotectants may represent an avenue worthy of clinical investigation. Clearly, there is a pressing need to identify new therapeutic alternatives for the vast majority of patients who are not eligible to receive rt-PA for this debilitating and devastating disease.

Hypoxic ischemic brain injury: Potential therapeutic interventions for the future

Perinatal hypoxic-ischemic brain injury is a common problem with potentially devastating impact on neurodevelopmental outcomes. While therapeutic hypothermia, the first available treatment for this disease, reduces the risk of death or major neurodevelopmental disability, the risk of major neurologic morbidity following HI remains significant. Basic research has identified cellular mechanisms that mediate neuronal death. This article reviews the cellular processes induced that lead to brain injury following HI, and identify treatments currently under investigation for potential translation to clinical trials.

Rac1-mediated effects of HMG-CoA reductase inhibitors (statins) in cardiovascular disease

SIGNIFICANCE

HMG-CoA reductase inhibitors (statins) lower serum cholesterol concentrations and are beneficial in the primary and secondary prevention of coronary heart disease. The positive clinical effects have only partially been reproduced with other lipid-lowering interventions suggesting potential statin effects in addition to cholesterol lowering. In experimental models, direct beneficial cardiovascular effects that are mediated by the inhibition of isoprenoids have been documented, which serve as lipid attachments for intracellular signaling molecules such as small Rho guanosine triphosphate-binding proteins, whose membrane localization and function are dependent on isoprenylation.

RECENT ADVANCES

Rac1 GTPase is an established master regulator of cell motility through the cortical actin reorganization and of reactive oxygen species generation through the regulation of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity.

CRITICAL ISSUES

Observations in cells, animals, and humans have implicated the activation of Rac1 GTPase as a key component of cardiovascular pathologies, including the endothelial dysfunction, cardiac hypertrophy and fibrosis, atrial fibrillation, stroke, hypertension, and chronic kidney disease. However, the underlying signal transduction remains incompletely understood.

FUTURE DIRECTIONS

Based on the recent advance made in Rac1 research in the cardiovascular system by using mouse models with transgenic overexpression of activated Rac1 or conditional knockout, as well as Rac1-specific small molecule inhibitor NSC 23766, the improved understanding of the Rac1-mediated effects statins may help to identify novel therapeutic targets and strategies.

Prolonged exposure to isoflurane ameliorates infarction severity in the rat pup model of neonatal hypoxia-ischemia

The neonatal hypoxia-ischemia rat model referred to as the Rice-Vannucci model is extensively used to study perinatal hypoxia-ischemia and child brain injury. One of the major weaknesses of this model is its inconsistency of brain infarction among animals. We hypothesize that the inconsistency of infarction is caused by prolonged operation time and therefore isoflurane exposure. Neonatal hypoxia-ischemia was induced in postnatal days 7 and 10 rat pups by unilateral right common carotid ligation followed by 2.5 h of hypoxia (8% oxygen). The incision-to-ligation (ITL) was defined as the amount of time from initial incision (4 min after 2% isoflurane exposure) to completion of carotid ligation (at which point isoflurane exposure was also terminated). In the first part of the study, the ITL of each group was designated to be 5, 13, and 21 min. In the second part of the study, the ITL is designated to 4 min; however, continued isoflurane was used to make 5, 13, and 21 min isoflurane exposure for each group. Percentages of brain infarction were assessed at 48 h following surgery. Motor deficits were accessed by Rotarod test. Marked brain infarction was observed in the 5-min ITL group and a decrease of brain infarction observed in the 13-and 21-min groups (P<0.05). In the second part of the study, marked brain infarction was observed in the 5-min isoflurane exposure group, and a decrease of brain infarction was observed in each of the 13- and 21-min isoflurane exposure groups (P<0.05). Similar tendencies were observed in Rotarod tests than 5-min ITL and 5-min isoflurane groups showed more marked deficits (P<0.05). This study demonstrated that brain infarction inconsistency of the neonatal hypoxia-ischemia rat pup model is related to the operation time. The observed time-dependent decrease of brain infarction is correlated to the isoflurane exposure time. Shorter operation and isoflurane exposure improves this model consistency of brain infarction and motor deficits.

Ginsenjilinol, a new protopanaxatriol-type saponin with inhibitory activity on LPS-activated NO production in macrophage RAW 264.7 cells from the roots and rhizomes of Panax ginseng

One new dammarane triterpene saponin named ginsenjilinol (1) was isolated from the roots and rhizomes of Panax ginseng C.A. Mey., together with two known saponins ginsenoside Rf (2) and ginsenoside Re5 ( = panajaponol A, 3). Based on IR, HR-ESI-MS, and 1D as well as 2D NMR ((1)H-(1)H COSY, NOESY, HSQC, and HMBC) spectral data, the chemical structure of the new saponin was elucidated as 3β,12β,20S,26-tetrahydroxydammar-24E-en-6α-O-β-d-glucopyranosyl-(1 → 2)-O-β-d-glucopyranoside. The ability of the isolated saponins to inhibit nitric oxide production by lipopolysaccharide-activated RAW 264.7 cells was also assayed. All of the isolated saponins exhibited the significant activity in a concentration-dependent manner at concentrations of 60-200 μM with the half maximal inhibitory concentration (IC50) values of 70.96 ± 2.05 μM for 1, 74.14 ± 2.65 μM for 2, and 79.83 ± 1.78 μM for 3, respectively, whereas indomethacin had an IC50 of 63.75 ± 3.33 μM as a positive control drug.

Hypothermia decreases cerebrospinal fluid asymmetric dimethylarginine levels in children with traumatic brain injury

OBJECTIVES

Pathological increases in asymmetric dimethylarginine, an endogenous nitric oxide synthase inhibitor, have been implicated in endothelial dysfunction and vascular diseases. Reduced nitric oxide early after traumatic brain injury may contribute to hypoperfusion. Currently, methods to quantify asymmetric dimethylarginine in the cerebrospinal fluid have not been fully explored. We aimed to develop and validate a method to determine asymmetric dimethylarginine in the cerebrospinal fluid of a pediatric traumatic brain injury population and to use this method to assess the effects of 1) traumatic brain injury and 2) therapeutic hypothermia on this mediator.

DESIGN, SETTING, AND PATIENTS

An ancillary study to a prospective, phase II randomized clinical trial of early hypothermia in a tertiary care pediatric intensive care unit for children with Traumatic brain injury admitted to Children's Hospital of Pittsburgh.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

A UPLC-MS/MS method was developed and validated to quantitate asymmetric dimethylarginine. A total of 56 samples collected over 3 days with injury onset were analyzed from the cerebrospinal fluid of consented therapeutic hypothermia (n = 9) and normothermia (n = 10) children. Children undergoing diagnostic lumbar puncture (n = 5) were enrolled as controls. Asymmetric dimethylarginine was present at a quantifiable level in all samples. Mean asymmetric dimethylarginine levels were significantly increased in normothermic Traumatic brain injury children compared with that in control (0.19 ± 0.08 µmol/L and 0.11 ± 0.02 µmol/L, respectively, p = 0.01), and hypothermic children had significantly reduced mean asymmetric dimethylarginine levels (0.11 ± 0.05 µmol/L) vs. normothermic (p = 0.03) measured on day 3. Patient demographics including age, gender, and nitric oxide levels (measured as nitrite and nitrate using liquid chromatography coupled with Griess reaction) did not significantly differ between normothermia and hypothermia groups. Also, nitric oxide levels did not correlate with asymmetric dimethylarginine concentrations.

CONCLUSIONS

Asymmetric dimethylarginine levels were significantly increased in the cerebrospinal fluid of traumatic brain injury children. Early hypothermia attenuated this increase. The implications of attenuated asymmetric dimethylarginine on nitric oxide synthases activity and regional cerebral blood flow after traumatic brain injury by therapeutic hypothermia deserve future study.

[Experimental therapy approaches for ischemic stroke]

In Germany, as in most other industrialized countries, ischemic stroke is the leading cause of disability and the third leading cause of death. As the incidence of ischemic stroke increases with age it is expected that this problem will become even more urgent in an aging society. Despite significant research efforts on the clinical as well as on the experimental level, treatment of ischemic stroke is still based on general intensive care measures and on reperfusion therapy with recombinant tissue plasminogen activator (rtPA); however, rtPA is not suitable for a wide range of patients and is restricted to a therapeutic window of 4.5 h due to an increasing risk of bleeding. Accordingly, novel therapeutic options for ischemic stroke are urgently need. The current review discusses novel experimental therapeutic principles for ischemic stroke which may have clinical potential. The main topics are neuroprotection and strategies addressing the immune system.

A self-propelling cycle mediated by reactive oxide species and nitric oxide exists in LPS-activated microglia

It has been widely accepted that microglia, the innate immune cells in the brain, can be chronically activated in response to neuron death, fuelling a self-renewing cycle of microglial activation followed by further neuron damage (reactive microgliosis), which has been considered as the main reason responsible for the progressive nature of neurodegenerative diseases. In the present study, it was found that LPS (lipopolysaccharide) significantly induced the activation of N9 microglia, and the increase of NO level induced by pretreatment of LPS could last after the removal of LPS. The culture medium of activated microglia significantly decreased the viability of rat primary cortical neuron. These results can be blocked by the antioxidant N-acetylcysteine (NAC) and nicotinamide adenine dinucleotide phosphate reduced (NADPH) oxidase inhibitor diphenyleneiodonium sulfate (DPI), suggesting that intracellular reactive oxide species (iROS) released from the activated microglial cells may continue to further activate microglia. Next, it was shown that the iROS level increased rapidly after the LPS treatment in microglia cells followed by the NO production through the regulation of iNOS (inducible nitric oxide synthase) expression. The increase of iROS could be reversed by gp91phox (the critical and catalytic subunit of NADPH oxidase) siRNA. Moreover, NO released from sodium nitroprusside (SNP) was able to increase the iROS production of N9 microglia by regulating of the activity and the expression of NADPH oxidase. In conclusion, our research suggests for the first time that there may exist a self-propelling cycle in microglial cells possibly mediated by iROS and NO when they become activated by LPS. It may be responsible partially for the ongoing microglial activation and the progressive nature of neurodegenerative diseases.

Modulation of ionotropic glutamate receptors and Acid-sensing ion channels by nitric oxide

Ionotropic glutamate receptors (iGluR) are ligand-gated ion channels and are densely expressed in broad areas of mammalian brains. Like iGluRs, acid-sensing ion channels (ASIC) are ligand (H⁺)-gated channels and are enriched in brain cells and peripheral sensory neurons. Both ion channels are enriched at excitatory synaptic sites, functionally coupled to each other, and subject to the modulation by a variety of signaling molecules. Central among them is a gasotransmitter, nitric oxide (NO). Available data show that NO activity-dependently modulates iGluRs and ASICs via either a direct or an indirect pathway. The former involves a NO-based and cGMP-independent post-translational modification (S-nitrosylation) of extracellular cysteine residues in channel subunits or channel-interacting proteins. The latter is achieved by NO activation of soluble guanylyl cyclase, which in turn triggers an intracellular cGMP-sensitive cascade to indirectly modulate iGluRs and ASICs. The NO modification is usually dynamic and reversible. Modified channels undergo significant, interrelated changes in biochemistry and electrophysiology. Since NO synthesis is enhanced in various neurological disorders, the NO modulation of iGluRs and ASICs is believed to be directly linked to the pathogenesis of these disorders. This review summarizes the direct and indirect modifications of iGluRs and ASICs by NO and analyzes the role of the NO-iGluR and NO-ASIC coupling in cell signaling and in the pathogenesis of certain related neurological diseases.

Endothelium-derived hyperpolarizing factor in the brain: influence of sex, vessel size and disease state

The endothelial layer of cells lining the intimal surface of blood vessels is essential for vascular function. The endothelium releases multiple vasodilator and protective factors, including nitric oxide, prostacyclin and endothelium-derived hyperpolarizing factor; an imbalance in these factors predisposes individuals to vascular diseases such as stroke. These factors are differentially regulated by vessel size, sex hormones and disease state, therefore playing differential roles in different tissues following vascular injury. In particular, the endothelium-derived hyperpolarizing factor candidate termed epoxyeicosatrienoic acid, plays a prominent role in microvessel function, especially after ischemia, thereby making this signaling pathway an attractive target for therapy in vascular disease, including stroke.

Beneficial effects of combination of valsartan and amlodipine on salt-induced brain injury in hypertensive rats

The optimum antihypertensive treatment for prevention of hypertensive stroke has yet to be elucidated. This study was undertaken to examine the benefit of a combination of valsartan, an angiotensin II type 1 (AT1) receptor blocker, and amlodipine, a calcium channel blocker, in prevention of high-salt-induced brain injury in hypertensive rats. High-salt-loaded stroke-prone spontaneously hypertensive rats (SHRSPs) were given 1) vehicle, 2) valsartan (2 mg/kg/day), 3) amlodipine (2 mg/kg/day), or 4) a combination of valsartan and amlodipine for 4 weeks. The effects on brain injury were compared between all groups. High-salt loading in SHRSPs caused the reduction of cerebral blood flow (CBF), cerebral hypoxia, white matter lesions, glial activation, AT1 receptor up-regulation, endothelial nitric-oxide synthase (eNOS) uncoupling, inducible nitric-oxide synthase induction, and nitroxidative stress. Valsartan, independently of blood pressure, enhanced the protective effects of amlodipine against brain injury, white matter lesions, and glial activation in salt-loaded SHRSPs. These beneficial effects of valsartan added to amlodipine were associated with an additive improvement in CBF and brain hypoxia because of an additive improvement in cerebral arteriolar remodeling and vascular endothelial dysfunction. Furthermore, valsartan added to amlodipine enhanced the attenuation of cerebral nitroxidative stress through an additive suppression of eNOS uncoupling. Valsartan, independently of blood pressure, augmented the protective effects of amlodipine against brain injury in salt-loaded hypertensive rats through an improvement in brain circulation attributed to nitroxidative stress. Our results suggest that the combination of valsartan and amlodipine may be a promising strategy for the prevention of salt-related brain injury in hypertensive patients.

Involvement of neuronal nitric oxide synthase in ongoing fetal brain injury following near-term rabbit hypoxia-ischemia

Neuronal nitric oxide synthase (nNOS) and nitric oxide (NO) are implicated in neuronal injury following acute hypoxia-ischemia (HI). Our hypothesis was that NO from nNOS is responsible for ongoing mitochondrial dysfunction in near-term fetal HI. Recently, we synthesized new selective nNOS inhibitors that prevent the cerebral palsy phenotype in our animal model. We tested the efficacy of a selective nNOS inhibitor (JI-8) in fetal brains after in utero HI in our rabbit model. Brain slices at 29 days gestation were obtained after in utero HI, and immediately cultured in medium containing JI-8 or saline for 3-6 days. Mitochondrial membrane integrity and function were determined by flow cytometry using rhodamine 123 and JC-1, and cell death by using propidium iodide. JI-8 decreased NO production in brain slices and also showed significant preservation of mitochondrial function at both 3 and 6 days (p < 0.05) when compared with saline and inducible NOS inhibitor 1400W. There was no difference in cell death. In conclusion, nNOS is involved in ongoing mitochondrial dysfunction after in utero HI. The subacute brain slice model could be a tool for studying the mechanisms involved in ongoing neuronal injury, and for rapidly assessing potential neuroprotectants.

Basic Science Review Section: Statin Therapy—Part II: Clinical Considerations for Cardiovascular Disease

3-Hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors, commonly known as statins, are the medical treatment of choice for hypercholesterolemia. In addition to achieving a therapeutic decrease in serum cholesterol levels, statin therapy appears to promote pleiotropic effects that are independent of changes in serum cholesterol. These cholesterol lowering and pleiotropic effects are beneficial not only for the coronary circulation, but for the myocardium and peripheral arterial system as well. Patients receiving statin therapy must be carefully monitored, however, as statins potentially have harmful side effects and drug interactions. This article is part II of a 2-part review, and it focuses on the clinical aspects of statin therapy in cardiovascular disease.

Synergistic effect of melatonin on exercise-induced neuronal reconstruction and functional recovery in a spinal cord injury animal model

Nitric oxide (NO) may aggravate neuronal damage after spinal cord injury (SCI). We hypothesized that NO produced by inducible nitric oxide synthase (iNOS) accelerates secondary damage to spinal tissue, which may be reversed by the neuroprotectant, melatonin. This study investigated the effects of combination therapy with melatonin (10 mg/kg) and exercise (10 m/min) on recovery from SCI caused by contusion. We examined locomotor recovery, iNOS gene expression, autophagic and apoptotic signaling, including Beclin-1, LC3, p53 and IKKalpha protein expression and histological alterations in the ventral horn of the spinal cord. Melatonin in combination with exercise resulted in significantly increased hindlimb movement (P < 0.05), a reduced level of iNOS mRNA (P < 0.05) and more motor neurons in the ventral horn, versus control SCI and SCI plus exercise alone, with no effect on the other signaling molecules examined. This study shows that combined therapy with melatonin and exercise reduces the degree of secondary damage associated with SCI in rats and supports the possible use of melatonin in combination with exercise to reduce the side effects related to exercise-induced fatigue and impairment.

Oxidative stress mediates hippocampal neuron death in rats after lithium-pilocarpine-induced status epilepticus

Oxidative stress, which is defined as the over-production of free radicals, can dramatically alter neuronal function and has been linked to status epilepticus (SE). The pathological process and underlying mechanisms involved in the oxidative stress during SE are still not fully clear. In the current study, SE was induced in rats by lithium-pilocarpine administration. Our data show that hippocampal neuron death occurs at 6h and is sustained for 7 days after SE. The production of nitric oxide (NO) started to increase at 30 min and was evident at 6h and 7 days after SE, which coincided with increased expression of neuronal nitric oxide synthase (nNOS), inducible nitric oxide synthase (iNOS) and malondialdehyde (MDA) after SE, whereas, activated caspase-3 prominently appeared at 7 days after SE. Further, FK506, an immunosuppressant, partially rescued the neuron death and attenuated the expression of NO, nNOS, iNOS, MDA and activated caspase-3. Taken together, our study indicates that oxidative stress mediated hippocampal neuron death occurs prior to caspase-3 activation and that FK506 plays an important role in protecting hippocampal neurons during status epilepticus.

Blockade of peroxynitrite-induced neural stem cell death in the acutely injured spinal cord by drug-releasing polymer

Therapeutic impact of neural stem cells (NSCs) for acute spinal cord injury (SCI) has been limited by the rapid loss of donor cells. Neuroinflammation is likely the cause. As there are close temporal-spatial correlations between the inducible nitric oxide (NO) synthase expression and the donor NSC death after neurotrauma, we reasoned that NO-associated radical species might be the inflammatory effectors which eliminate NSC grafts and kill host neurons. To test this hypothesis, human NSCs (hNSCs: 5 x 10(4) to 2 x 10(6) per milliliter) were treated in vitro with "plain" medium, 20 microM glutamate, or donors of NO and peroxynitrite (ONOO(-); 100 and 400 microM of spermine or DETA NONOate, and SIN-1, respectively). hNSC apoptosis primarily resulted from SIN-1 treatment, showing ONOO(-)-triggered protein nitration and the activation of p38 MAPK, cytochrome c release, and caspases. Therefore, cell death following post-SCI (p.i.) NO surge may be mediated through conversion of NO into ONOO(-). We subsequently examined such causal relationship in a rat model of dual penetrating SCI using a retrievable design of poly-lactic-co-glycolic acid (PLGA) scaffold seeded with hNSCs that was shielded by drug-releasing polymer. Besides confirming the ONOO(-)-induced cell death signaling, we demonstrated that cotransplantation of PLGA film embedded with ONOO(-) scavenger, manganese (III) tetrakis (4-benzoic acid) porphyrin, or uric acid (1 micromol per film), markedly protected hNSCs 24 hours p.i. (total: n = 10). Our findings may provide a bioengineering approach for investigating mechanisms underlying the host microenvironment and donor NSC interaction and help formulate strategies for enhancing graft and host cell survival after SCI.

Inhaled nitric oxide and neuroprotection in preterm infants

Although inhaled nitric oxide-mediated decreases in chronic lung disease and severe intraventricular hemorrhage/periventricular leukomalacia undoubtedly contribute to improved neurodevelopmental outcomes, inhaled nitric oxide has an independent neuroprotective effect. Although these data are encouraging, additional studies are required before recommending the routine use of inhaled nitric oxide for neuroprotection in preterm infants.

Nitric oxide: new evidence for novel therapeutic indications

BACKGROUND

Nitric oxide (NO) deficiency is implicated in many pathophysiological processes in mammals. NO is a ubiquitous molecule involved in multiple cellular functions. Uncontrolled or inappropriate production of NO may lead to several disease states including septic shock, rheumatoid and inflammatory arthropathies, and expansion of cerebral damage after stroke. However, to date, there are no therapeutic agents available that can overcome these conditions. Similarly, underproduction of NO by NO synthase or enhanced breakdown of NO also leads to diseases such as hypertension, ischemic conditions, pre-eclampsia, premature delivery, among others. NO donor therapies are indicated in these conditions.

RESULTS

Nitroglycerin and nitrates (NO donors) have been used as therapeutic agents for the past century, particularly to treat vascular disease, and the only significant adverse effects are headaches. NO donors are highly cost-effective and have beneficial effects in multiple body systems. When the body cannot generate NO via NO synthase or due to rapid turnover leading to inadequate amounts of NO available for biological homeostasis, administration of exogenous NO, or prolongation of the actions of endogenous NO, are practical ways to supplement NO.

CONCLUSION

Recipients of such therapy include patients with angina pectoris, coronary artery disease, hypertension, osteoporosis, gastrointestinal motility disorders, pregnancy-related disorders including premature delivery, pre-eclampsia, vulvodynia, and erectile dysfunction in men. Postmenopausal NO deficiency is rectified with hormone replacement therapy, which enhances local production of NO. Declining local NO production secondary to estrogen deficiency in postmenopausal women and perhaps in older men could be one of the reasons for age-related increased incidences of cardiovascular events and sexual dysfunction. Thus, in addition to supplementation of NO compounds in acute situations like alleviating angina and erectile dysfunction, chronic NO therapy is cost-effective in decreasing cardiovascular events, and improving the urogenital system and skeletal health.

Nitric oxide in the injured spinal cord: synthases cross-talk, oxidative stress and inflammation

Nitric oxide (NO) is a unique informational molecule involved in a variety of physiological processes in the central nervous system (SNS). It has been demonstrated that it can exert both protective and detrimental effects in several diseases states of the CNS, including spinal cord injury (SCI). The effects of NO on the spinal cord depend on several factors such as: concentration of produced NO, activity of different synthase isoforms, cellular source of production and time of release. Basically, it has been shown that low NO concentrations may play a role in physiologic processes, whereas large amounts of NO may be detrimental by increasing oxidative stress. However, this does not explain all the discrepancies evidenced studying the effects of NO in SCI models. The analysis of the different synthase isoforms, of their temporal profile of activation and cellular source has shed light on this topic. Two post-injury time intervals can be defined with reference to the NO production: immediately after injury and several hours-to-days later. The initial immediate peak of NO production after injury is due to the up-regulation of the neuronal NO synthase (nNOS) in resident spinal cord cells. The late peak is due primarily to the activity of inducible NOS (nNOS) produced by inflammatory infiltrating cells. High NO levels produced by up-regulated nNOS and iNOS are neurotoxic; the down-regulation of nNOS corresponds temporally to the expression of iNOS. On the bases of the evidence, therapeutic approaches should be aimed: (1) to reduce the NO-elicited damage by inhibition of specific synthases according to the temporal profile of activation; (2) by maintaining physiologic amount of NO to keep the induction of iNOS.

Simvastatin and atorvastatin improve behavioral outcome, reduce hippocampal degeneration, and improve cerebral blood flow after experimental traumatic brain injury

The treatment of traumatic brain injury (TBI) remains limited, and aside from surgical hematoma evacuation, clinical management is largely supportive and directed toward management of cerebral edema and intracranial hypertension. Secondary neuronal injury caused by ischemia and the development of cerebral edema may occur in the subacute phase, with intracranial pressures often peaking in the first several days following injury. Because inflammation contributes significantly to the pathophysiology of cerebral ischemia and endothelial dysfunction underlies the development of cerebral edema, therapeutic strategies that target the post-traumatic inflammatory cascade and reduce endothelial dysfunction hold enormous potential to improve clinical outcomes after TBI. Statins inhibit inflammation by suppressing inflammatory cytokine release, and by interfering with multiple steps of leukocyte recruitment and migration into the CNS. In this study, we demonstrate that treatment with atorvastatin and simvastatin markedly reduced functional neurological deficits after traumatic brain injury in mice. These effects were accompanied by histological reduction in degenerating hippocampal neurons and suppression of inflammatory cytokine mRNA expression in brain parenchyma. Furthermore, statin treatment improved cerebral hemodynamics following head injury. Thus, the administration of statins may represent a viable therapeutic strategy in the acute treatment of closed head injury.

Cellular and molecular pathways of ischemic neuronal death

Three routes have been identified triggering neuronal death under physiological and pathological conditions. Excess activation of ionotropic glutamate receptors cause influx and accumulation of Ca2+ and Na+ that result in rapid swelling and subsequent neuronal death within a few hours. The second route is caused by oxidative stress due to accumulation of reactive oxygen and nitrogen species. Apoptosis or programmed cell death that often occurs during developmental process has been coined as additional route to pathological neuronal death in the mature nervous system. Evidence is being accumulated that excitotoxicity, oxidative stress, and apoptosis propagate through distinctive and mutually exclusive signal transduction pathway and contribute to neuronal loss following hypoxic-ischemic brain injury. Thus, the therapeutic intervention of hypoxic-ischemic neuronal injury should be aimed to prevent excitotoxicity, oxidative stress, and apoptosis in a concerted way.

Neuroprotective Effect of Simvastatin in Stroke: A Comparison Between Adult and Neonatal Rat Models of Cerebral Ischemia

Statins, the most widely used lipid lowering drugs, have been demonstrated to play a protective role in stroke. Animal studies confirmed the observations obtained in clinical trials and provided additional data on the putative mechanism/s of action underlying this beneficial effect. We have shown that simvastatin reduced the size of the infarct to a different extend, according to the animal model used. Indeed, in the rat neonatal model of hypoxia/ischemia simvastatin affords protection only when is administered before the ischemic insult. In contrast, in adult rats bearing middle cerebral artery occlusion, simvastatin exerted its beneficial effect on brain injury when injected for 3 days either before or after induction of ischemia. Studies carried out to determine the therapeutic window of simvastatin demonstrated that the protective effect is observed after a single dose and when the drug is administered within 3-6 hours after ischemia. Simvastatin-dependent activation of eNOS has been claimed to be one of the main mechanisms responsible for neuroprotection. This hypothesis is confirmed in the adult animal model where eNOS is activated by either pre- or post- simvastatin treatment but is not supported by the data obtained in the neonate where eNOS activity is not affected by drug treatment. These observations suggest that the protective effect of simvastatin on stroke may be mediated by multiple mechanisms as can be expected by its pleiotropic effects.

Pleiotropic effects of statins

Statins are potent inhibitors of cholesterol biosynthesis. In clinical trials, statins are beneficial in the primary and secondary prevention of coronary heart disease. However, the overall benefits observed with statins appear to be greater than what might be expected from changes in lipid levels alone, suggesting effects beyond cholesterol lowering. Indeed, recent studies indicate that some of the cholesterol-independent or "pleiotropic" effects of statins involve improving endothelial function, enhancing the stability of atherosclerotic plaques, decreasing oxidative stress and inflammation, and inhibiting the thrombogenic response. Furthermore, statins have beneficial extrahepatic effects on the immune system, CNS, and bone. Many of these pleiotropic effects are mediated by inhibition of isoprenoids, which serve as lipid attachments for intracellular signaling molecules. In particular, inhibition of small GTP-binding proteins, Rho, Ras, and Rac, whose proper membrane localization and function are dependent on isoprenylation, may play an important role in mediating the pleiotropic effects of statins.

Induction of iNOS restricts functional activity of both eNOS and nNOS in pig cerebral artery

The aim of the study was to investigate the effect of iNOS expression on eNOS and nNOS functional activity in porcine cerebral arteries. iNOS was induced in pig basilar arteries using lipopolysaccharide (LPS). Arteries expressing iNOS generated NO and relaxed when challenged with L-arginine (30 microM), an effect that was reduced by treatment with dexamethasone (coincubated with LPS) and prevented by the iNOS inhibitor 1400 W (administered 10 min prior to precontraction). eNOS was activated by A23187 and was found to be impaired in arteries that had iNOS induced (A23187 1 microM relaxation: control 110+/-8%, LPS-treated 50+/-16% ; p<0.05, N=5-6). This was due mainly to reduced formation of NO by A23187 (NO concentration in response to A23187 1 microM: control 25+/-6 nM, LPS-treated 0.8+/-1.2 nM; p<0.001, N=5-6), in addition to a small reduction in the vasodilator response to the NO-donors NOC-22 and SIN-1. Cerebral vasodilation produced by stimulation of intramural nitrergic nerves was impaired in arteries that had iNOS induced, and this was reversed by 1400 W (control 23+/-4% relaxation, LPS-treated 11+/-1% relaxation, LPS plus 1400 W 10 microM treated 25+/-2% relaxation; p<0.01 for control versus LPS, N=6). It is concluded that the induction of iNOS in cerebral arteries reduces NO-mediated vasodilation initiated by eNOS and by nNOS, primarily by modulation of NO formation.

Role of nitric oxide after brain ischaemia

Ischaemic stroke is the second or third leading cause of death in developed countries. In the last two decades substantial research and efforts have been made to understand the biochemical mechanisms involved in brain damage and to develop new treatments. The evidence suggests that nitric oxide (NO) can exert both protective and deleterious effects depending on factors such as the NOS isoform and the cell type by which NO is produced or the temporal stage after the onset of the ischaemic brain injury. Immediately after brain ischaemia, NO release from eNOS is protective mainly by promoting vasodilation; however, after ischaemia develops, NO produced by overactivation of nNOS and, later, NO release by de novo expression of iNOS contribute to the brain damage. This review article summarizes experimental and clinical data supporting the dual role of NO in brain ischaemia and the mechanisms by which NO is regulated after brain ischaemia. We also review NO-based therapeutic strategies for stroke treatment, not only those directly linked with the NO pathway such as NO donors and NOS inhibitors but also those partially related like statins, aspirin or lubeluzole.

Nitric oxide in traumatic brain injury

Nitric oxide (NO) is a gaseous chemical messenger which has functions in the brain in a variety of broad physiological processes, including control of cerebral blood flow, interneuronal communications, synaptic plasticity, memory formation, receptor functions, intracellular signal transmission, and release of neurotransmitters. As might be expected from the numerous and complex roles that NO normally has, it can have both beneficial and detrimental effects in disease states, including traumatic brain injury. There are two periods of time after injury when NO accumulates in the brain, immediately after injury and then again several hours-days later. The initial immediate peak in NO after injury is probably due to the activity of endothelial NOS and neuronal NOS. Pre-injury treatment with 7-nitroindazole, which probably inhibits this immediate increase in NO by neuronal NOS, is effective in improving neurological outcome in some models of traumatic brain injury (TBI). After the initial peak in NO, there can be a period of relative deficiency in NO. This period of low NO levels is associated with a low cerebral blood flow (CBF). Administration of L-arginine at this early time improves CBF, and outcome in many models. The late peak in NO after traumatic injury is probably due primarily to the activity of inducible NOS. Inhibition of inducible NOS has neuroprotective effects in most models.

Molecular mechanisms of neuroprotective action of immunosuppressants--facts and hypotheses

Cyclosporin A (CsA) and FK506 (Tacrolimus) are short polypeptides which block the activation of lymphocytes and other immune system cells. Immunosuppressants exert neuroprotective and neurotrophic action in traumatic brain injury, sciatic nerve injury, focal and global ischemia in animals. Their neuroprotective actions are not understood and many hypotheses have been formed to explain such effects. We discuss a role of drug target--calcineurin in neuroprotective action of immunosuppressants. Protein dephosphorylation by calcineurin plays an important role in neuronal signal transduction due to its ability to regulate the activity of ion channels, glutamate release, and synaptic plasticity. In vitro FK506 protects cortex neurons from NMDA-induced death, augments NOS phosphorylation inhibiting its activity and NO synthesis. However, in vivo experiments demonstrated that FK506 in neuroprotective doses did not block excitotoxic cell death nor did it alter NO production during ischemia/reperfusion. Tissue damage in ischemia is the result of a complex pathophysiological cascade, which comprises a variety of distinct pathological events. Resident non-neuronal brain cells respond rapidly to neuronal cell death and may have both deleterious and useful role in neuronal damage. There is increasing evidence that reactive gliosis and post-ischemic inflammation involving microglia contribute to ischemic damage. We have demonstrated that FK506 modulates hypertrophic/proliferative responses and proinflammatory cytokine expression in astrocytes and microglia in vitro and in focal transient brain ischemia. Our findings suggest that astrocytes and microglia are direct targets of FK506 and modulation of glial response and inflammation is a possible mechanism of FK506-mediated neuroprotection in ischemia.

Oxyresveratrol and resveratrol are potent antioxidants and free radical scavengers: effect on nitrosative and oxidative stress derived from microglial cells

Hydroxystilbenes are naturally occurring polyphenols with protective effects against reactive oxygen and nitrogen species (ROS/RNS). Here, we investigated oxyresveratrol (OXY), which is contained in high amounts in mulberry wood, in comparison to the antioxidant resveratrol (RES). We found that OXY is a more effective scavenger for 2,2-diphenyl-1-picryl-hydrazyl (DPPH, 100 microM) used as a general free radical model, compared to RES or trans-4-hydroxystilbene (IC(50)=28.9, 38.5, and 39.6 microM, respectively). When primary glial cell cultures were loaded with the ROS/RNS-sensitive fluorochrome 2,7-dichlorodihydrofluorescein, the lowest rise in the fluorescence signal after H(2)O(2) exposure was seen when the cells were pretreated with OXY. Using 4,5-diaminofluorescein (DAF-2) to monitor free nitric oxide levels (7.7 microM NO) in a spectrofluorimetric cell-free assay, we found again that OXY (at 5 microM) is a more effective scavenger. Accordingly, cultures of the murine microglial cell line N9 and primary mixed glial cultures were used to test the drug effects of NO production upon expression of the inducible isoform of nitric oxide synthase (iNOS). We found that both compounds considerably diminished NO (nitrite) levels, RES more effectively than OXY (IC(50)=22.36 and 45.31 microM). RES but not OXY down-regulated the expression of iNOS protein, but both did not alter iNOS activity. Furthermore, OXY displayed a generally lower cytotoxicity than RES. The radical and ROS scavenging properties, as well as the lower cytotoxicity towards microglia and the known good water solubility suggest OXY as a potential protectant against ROS/RNS.

The induction and detection in vitro of iNOS in the porcine basilar artery

The expression of iNOS in vascular tissues has an adverse effect on vascular responses to vasoconstrictors and NO-mediated vasodilators. The development of a simple method for detecting the iNOS expression by functional means would be extremely useful. Here we describe a method for inducing iNOS in the porcine basilar artery followed by the detection of iNOS protein by immunocytochemical means and the characterisation of functional responses to U46619 and L-arginine. Porcine basilar arteries were treated with LPS (1, 10 and 100 microg/ml) for between 5 and 18 h at 37 degrees C. Inducible NOS protein was expressed in a concentration-dependent manner in the endothelial and smooth muscle cells after 5 h and persisted for 18 h. Vessels treated with LPS showed a time-dependent reduction in contractile function in response to U46619 (10 nM) reaching significance at the 18-h time point. Moreover, a similar time-dependent increase in the vasodilator response to exogenously applied L-arginine (30 microM) was observed at both 5- and 18-h time points. These effects of LPS at the 18-h time point were prevented by the incubation of vessels with dexamethasone (100 microM) in addition to LPS. The vasodilator response to L-arginine was prevented with the incubation with and in the presence of the inhibitor of inducible NOS, 1400W (10 microM) in addition to LPS. These results show that iNOS protein can be expressed in porcine cerebral arteries and that the iNOS is functional. The assessment of contractile function and responses to L-arginine using single concentrations is a rapid and effective method for establishing whether functional iNOS is present in porcine cerebral arteries.

Changes in brain amino acids and nitric oxide after melatonin administration in rats with pentylenetetrazole-induced seizures

We examined the effect of melatonin on brain levels of amino acids and nitric oxide (NO) after pentylenetetrazole (PTZ)-induced seizures in rats. Animals were treated with melatonin (10-160 mg/kg, i.p.) 30 min before PTZ administration (100 mg/kg, s.c.), and were killed 3 hr later. At the dose of 80 mg/kg, melatonin significantly increased the latency (5.7-12.7 min) and decreased the duration (31.2-18.4 s) of the first seizure, reducing PTZ induced mortality from 87.5 to 25%. After kill, brains were removed and neurotransmitters and nitrite levels measured in prefrontal cortex (PF), parieto-temporal cortex (PF), striatum (ST), hippocampus (HP) and brain stem (BS) by high performance liquid chromatography. PTZ treatment increased glutamine levels in all brain areas studied, without changes in glutamate, gamma-amino butyric acid (GABA) and glycine. Aspartate and taurine increased in PF and PT and in HS and PT, respectively. Melatonin administration displayed a dose-dependent effect. At doses of 10-40 mg/kg, melatonin counteracted the PTZ-induced glutamine increase and reduced both glutamate and aspartate levels in the studied areas, with minor changes in GABA and glycine content. At doses of 80 and 160 mg/kg, the levels of glutamine, and glutamate, and to a lesser extent aspartate increased, whereas serine levels did not change. These two doses of melatonin also increased taurine, GABA and glycine in most brain areas studied. Treatment with melatonin (40-160 mg/kg) significantly decreased nitrite content in PT cortex, ST and BS areas of epileptic rats, without changes in the other brain regions. The results suggest that the anticonvulsant property of melatonin involves a modulation of both brain amino acids and NO production.

Effect of 7-nitroindazole on bilirubin-induced changes in brain cell membrane function and energy metabolism in newborn piglets

We evaluated the effects of 7-nitroindazole, a selective neuronal nitric oxide synthetase (nNOS) inhibitor, on bilirubin-induced alterations in brain cell membrane function and energy metabolism in the newborn piglets. The decreased cerebral cortical cell membrane Na(+),K(+)-ATPase activity and increased lipid peroxidation products, indicative of bilirubin-induced brain damage, were significantly attenuated by 7-nitroindazole treatment. 7-Nitroindazole also significantly improved the bilirubin-induced reduction in both brain ATP and phosphocreatine levels, decreased blood-to-brain glucose ratio and increased brain lactate level. In summary, 7-nitroindazole significantly attenuated the bilirubin-induced alterations in brain cell membrane function and energy metabolism in the newborn piglet. These findings suggest that nitric oxide produced by nNOS is involved in mediating or facilitating bilirubin-induced cerebral dysfunction.

Is neuroprotective efficacy of nNOS inhibitor 7-NI dependent on ischemic intracellular pH?

The purpose of this study was to test the hypothesis that the efficacy of 7-nitroindazole (7-NI), a selective neuronal nitric oxide (NO) synthase (NOS) inhibitor, is pH dependent in vivo during focal cerebral ischemia. Wistar rats underwent 2 h of focal cerebral ischemia under 1% halothane anesthesia. 7-NI, 10 and 100 mg/kg in 0.1 ml/kg DMSO, was administered 30 min before occlusion. Ischemic brain acidosis was manipulated by altering serum glucose concentrations. Confirmation of the effects of these serum glucose manipulations on brain intracellular pH (pH(i)) was confirmed in a group of acute experiments utilizing umbelliferone fluorescence. The animals were euthanized at 72 h for histology. 7-NI significantly (P < 0.05) reduced infarction volume in both the normoglycemic by 93.3% and hyperglycemic animals by 27.5%. In the moderate hypoglycemic animals, the reduction in infarction volume did not reach significance because moderate hypoglycemia in itself dramatically reduced infarction volume. We hypothesize that a mechanism to explain the published discrepancies on the effects of neuronal NOS inhibitors in vivo may be due to the effects by differences in ischemic brain acidosis on the production of NO.

Effects of the nitric oxide donor 3-morpholinosydnonimine (SIN-1) in focal cerebral ischemia dependent on intracellular brain pH

OBJECT

A nitric oxide (NO) donor that has been successfully used in the treatment of myocardial infarction, 3-morpholinosydnonimine (SIN-1), may be a potential neuroprotective agent. Production of NO in brain microsomes is dependent on the pH. The purpose of this study was to determine the efficacy of SIN-1 and its dependence on pH in vivo during periods of focal cerebral ischemia.

METHODS

At 0.1 or 1 mg/kg, SIN-1 was administered to 54 Wistar rats 30 minutes before a 2-hour period of focal cerebral ischemia under moderate hypo-, normo-, and hyperglycemic conditions. Measurements of brain intracellular pH (pHi); regional cortical blood flow, and the redox state of nicotinamide adenine dinucleotide were obtained in three additional animals to confirm the effects of the serum glucose manipulations. The animals were killed at 72 hours after the ischemic period to obtain infarction volumes. Administration of SIN-1 significantly reduced infarction in normoglycemic animals and, to a lesser extent, in hyperglycemic animals, indicating that SIN-1 was less effective under hyperglycemic conditions. At either dose SIN-1 had no significant effect on infarction volume in moderately hypoglycemic animals because moderate hypoglycemia in itself significantly (p < 0.005) reduced infarction volume.

CONCLUSIONS

The NO donor SIN-1 may be a useful intraoperative cerebral protective agent. Furthermore, it is hypothesized that a mechanism that could explain the published discrepancies regarding the effects of NO donors in vivo may be affected by differences in ischemic brain acidosis.

Fluctuation of serum NO(x) concentration at stroke onset in a rat spontaneous stroke model (M-SHRSP). Peroxynitrite formation in brain lesions

Malignant stroke-prone spontaneously hypertensive rats (M-SHRSP) develop hypertension and stroke at earlier ages than do nonmalignant SHRSP. Our previous findings suggested that reactive oxygen species were involved in the development of stroke in this strain. Nitric oxide (NO) which is more released at ischemia, might play a crucial role in stroke development by producing peroxynitrite, a neurotoxic substance. This study investigated whether the development of cerebrovascular lesion in M-SHRSP could be assessed by the fluctuation of serum NO(x) concentration, and whether peroxynitrite is associated with brain damage. Serum NO(x) levels were examined using an automated NO detector. Stroke-onset was temporally assessed according to a known method: changes in body weight, water intake, and neurologic symptoms. Cerebral lesions were confirmed by magnetic resonance imaging (MRI), and Evans blue extravasation at autopsy. MRI taken just after estimated stroke onset disclosed brain lesions. The baseline serum NO(x) level remained at 15-18 micromol/l, but the level gradually increased prior to stroke, and significantly at stroke onset. A marked rise in serum NO(x) occurred subsequently at poststroke. Immunohistochemical staining of nitrotyrosine, a peroxynitrite marker, was detected around vessels, neuronal cells and parenchyma in cerebral lesions. Stroke occurred in 50% of male M-SHRSP at 80 days of age. In conclusion, this study provides the first evidence for fluctuation of serum NO(x) at the onset of spontaneous stroke accompanying the appearance of peroxynitrite in brain lesions. Monitoring serum NO(x) would serve to assess the development of brain lesions at least in spontaneous stroke model.

Nitric oxide synthase expression after human brain contusion

OBJECTIVE

Nitric oxide is a universal mediator of biological effects in the brain, and it has been implicated in the pathophysiological processes of traumatic brain injury. Experimental studies have indicated posttraumatic up-regulation of the three different isoforms of nitric oxide synthase (NOS) (i.e., inducible NOS [iNOS], endothelial NOS, and neuronal NOS) after brain trauma. This study was undertaken to investigate the cellular sources and tissue compartments of nitric oxide produced by human patients undergoing surgical treatment for contusional brain injuries.

METHODS

Contused brain tissue specimens from eight consecutive patients who underwent surgical treatment for brain contusions 3 hours to 5 days after trauma were evaluated in immunohistochemical analyses. Double-staining assays were used to define which cells produced the different isoforms.

RESULTS

Increases in iNOS-positive cells were detectable within 6 hours after trauma, with a peak at 8 to 23 hours. Expression of iNOS after trauma was detected in neurons, macrophages, neutrophils, astrocytes, and oligodendrocytes. The cellular sources of iNOS differed at different times after trauma. No detectable difference in the expression of the neuronal or endothelial isoforms was observed for trauma patients, compared with control subjects.

CONCLUSION

iNOS expression was up-regulated in a time-dependent manner in human brain tissue obtained from patients undergoing surgical treatment for contusional trauma. Our human data largely parallel experimental findings in rats, indicating that such trauma models are relevant for experimental studies and treatment trials.

Statins and ischemic stroke

The 3-hydroxy-3-methylglutaryl (HMG)-CoA reductase inhibitors or statins are potent inhibitors of cholesterol synthesis. Several large clinical trials have demonstrated that these agents reduce serum cholesterol levels and the incidence of cardiovascular diseases. However, overlap and meta-analyses of these clinical trials suggest that the beneficial effects of statins may extend beyond their effects on serum cholesterol levels. Because statins also inhibit the synthesis of isoprenoid intermediates in the cholesterol biosynthetic pathway, they may have pleiotropic effects on the vascular wall. In particular, the ability of statins to decrease the incidence of ischemic stroke highlights some of their non-cholesterol effects since serum cholesterol levels are poorly correlated with the risk for ischemic stroke.

Nitric-oxide-synthase-mediated cyclic guanosine monophosphate production in neonatal rat cerebellar prisms is resistant to calcineurin inhibition

Although the macrolide immunosuppressant tacrolimus (FK506) is neuroprotective in animal models of focal and global cerebral ischaemia, the mechanism of this action is not known. FK506 inhibits the protein phosphatase calcineurin, whose substrates can include nitric oxide synthase (NOS), and the neuroprotective effect of FK506 has been attributed to inhibition of NOS activity. We have examined nitric oxide-mediated cyclic guanosine monophosphate (cGMP) accumulation in neonatal rat cerebellar prisms. As expected, N-methyl-D-aspartate (NMDA) induced a rapid, concentration dependent accumulation of cGMP that was inhibited by the NMDA receptor antagonist dizocilpine (MK801) and the NOS inhibitor L-nitro-arginine methyl ester. Phosphoserine immunopositivity following NMDA exposure was increased in the presence of FK506, confirming inhibition of calcineurin. However, FK506 had no effect on NMDA-stimulated cGMP accumulation. These findings suggest that the neuroprotective effect of FK506 may be mediated by mechanisms other than increased NOS phosphorylation.