Delayed treatment with aminoguanidine decreases focal cerebral ischemic damage and enhances neurologic recovery in rats

Small molecule inhibiting microglial nitric oxide release could become a potential treatment for neuroinflammation

Microglia are the immune effector cells of the central nervous system (CNS) and react to pathologic events with a complex process including the release of nitric oxide (NO). NO is a free radical, which is toxic for all cells at high concentrations. To target an exaggerated NO release, we tested a library of 16 544 chemical compounds for their effect on lipopolysaccharide (LPS)-induced NO release in cell line and primary neonatal microglia. We identified a compound (C1) which significantly reduced NO release in a dose-dependent manner, with a low IC50 (252 nM) and no toxic side effects in vitro or in vivo. Target finding strategies such as in silico modelling and mass spectroscopy hint towards a direct interaction between C1 and the nitric oxide synthase making C1 a great candidate for specific intra-cellular interaction with the NO producing machinery.

Plant polyphenols in the treatment of age-associated diseases: revealing the pleiotropic effects of icariin by network analysis

Polyphenols are a broad class of compounds. Some are ingested in substantial quantities from nutritional sources, more are produced by medicinal plants, and some of them are taken as drugs. It is becoming clear, that a single polyphenol is impacting several cellular pathways. Thus, a network approach is becoming feasible, describing the interaction of a single polyphenol with cellular networks. Here we have selected icariin to draw a prototypic network of icariin activities. Icariin appears to be a promising drug to treat major age-related diseases, like neurodegeneration, memory and depressive disorders, chronic inflammation, diabetes, and osteoporosis. It interacts with several relevant pathways, like PDE, TGF-ß, MAPK, PPAR, NOS, IGF, Sirtuin, and others. Such networks will be useful to future comparative studies of complex effects of polyphenols.

Capacity of HSYA to inhibit nitrotyrosine formation induced by focal ischemic brain injury

Peroxynitrite-mediated protein tyrosine nitration represents a crucial pathogenic mechanism of stroke. Hydroxysafflor yellow A (HSYA) is the most important active component of the safflower plant. Here we assess the neuroprotective efficacy of HSYA and investigate the mechanism through anti-nitrative pathway. Rats were subjected to 60-min ischemia followed by reperfusion. HSYA (2.5-10mg/kg) was injected at 1h after ischemia onset. Other groups received HSYA (10mg/kg) treatment at 3-9h after onset. Infarct volume, brain edema, and neurological score were evaluated at 24h after ischemia. Nitrotyrosine and inducible NO synthase (iNOS) expression, as well as NO level (nitrate/nitrite) in ischemic cortex was examined within 24h after ischemia. The ability of HSYA to scavenge peroxynitrite was evaluated in vitro. Infarct volume was significantly decreased by HSYA (P<0.05), with a therapeutic window of 3h after ischemia at dose of 10mg/kg. HSYA treatment also reduced brain edema and improved neurological score (P<0.05). Nitrotyrosine formation was dose- and time-dependently inhibited by HSYA. The time window of HSYA in decreasing protein tyrosine nitration paralleled its action in infarct volume. HSYA also greatly reduced iNOS expression and NO content at 24h after ischemia, suggesting prevention of peroxynitrite generation from iNOS. In vitro, HSYA blocked authentic peroxynitrite-induced tyrosine nitration in bovine serum albumin and primary cortical neurons. Collectively, our results indicated that post-ischemic HSYA treatment attenuates brain ischemic injury which is at least partially due to reducing nitrotyrosine formation, possibly by the combined mechanism of its peroxynitrite scavenging ability and its reduction in iNOS production.

Therapeutic window of taurine against experimental stroke in rats

The dose-dependent protection of taurine against experimental stroke has been demonstrated previously. The objective of this study was to investigate the therapeutic window of taurine against experimental stroke, and the effects of delayed administration of taurine on inflammatory reaction in a rat model of stroke. Rats received 2-h ischemia by intraluminal filament, and then reperfused. Taurine (50 mg/kg) was administered intravenously 4 h, 8 h, 10 h, or 12 h after ischemia. The neurologic scores and the infarct volumes were evaluated 24 h after ischemia. Then, the effect of administration of taurine at 8 h after ischemia on the neutrophil infiltration in ischemic region was determined. Treatment with taurine 4 h or 8 h after ischemia significantly improved the neurologic function, and decreased the infarct volumes 24 h after ischemia. However, administration of taurine at 10 h or 12 h after ischemia had no significant neuroprotection. Further, taurine administered at 8 h after ischemia markedly reduced myeloperoxidase activity and attenuated neutrophil infiltration in ischemic region. Our data suggest that the therapeutic window of taurine against experimental stroke is of at least 8 h, and suppressing the neutrophil infiltration may be one of the mechanisms of delayed administration of taurine against experimental stroke.

Aminoguanidine administration ameliorates hippocampal damage after middle cerebral artery occlusion in rat

The effects of a selective inducible nitric oxide synthase inhibitor aminoguanidine (AG) on neuronal cells survival in hippocampal CA1 region after middle cerebral artery occlusion (MCAO) were examined. Transient focal cerebral ischemia was induced in rats by 60 or 90 min of MCAO, followed by 7 days of reperfusion. AG treatment (150 mg/kg i.p.) significantly reduced total infarct volumes: by 70% after 90 min MCAO and by 95% after 60 min MCAO, compared with saline-treated ischemic group. The number of degenerating neurons in hippocampal CA1 region was also markedly lower in aminoguanidine-treated ischemic groups compared to ischemic groups without AG-treatment. The number of iNOS-positive cells significantly increased in the hippocampal CA1 region of ischemic animals, whereas it was reduced in AG-treated rats. Our findings demonstrate that aminoguanidine decreases ischemic brain damage and improves neurological recovery after transient focal ischemia induced by MCAO.

Mitochondrial dysfunction: a potential link between neuroinflammation and neurodegeneration?

Dysfunctional mitochondria are thought to play a cardinal role in the pathogenesis of various neurological disorders, such as multiple sclerosis, Alzheimer's disease, Parkinson's disease and stroke. In addition, neuroinflammation is a common denominator of these diseases. Both mitochondrial dysfunction and neuroinflammatory processes lead to increased production of reactive oxygen species (ROS) which are detrimental to neurons. Therefore, neuroinflammation is increasingly recognized to contribute to processes underlying neurodegeneration. Here we describe the involvement of mitochondrial (dys)function in various neurological disorders and discuss the putative link between mitochondrial function and neuroinflammation.

Distinct pattern of microglial response, cyclooxygenase-2, and inducible nitric oxide synthase expression in the aged rat brain after excitotoxic damage

Microglial and inflammatory responses to acute damage in aging are still poorly understood, although the aged brain responds differently to injury, showing poor lesion outcome. In this study, excitotoxicity was induced by intrastriatal injection of N-methyl-D-aspartate in adult (3-4 months) and aged (22-24 months) rats. Cryostat brain sections were processed for the analysis of microglial response by lectin histochemistry and cyclooxygenase 2 (COX2) and inducible nitric oxide synthase (iNOS) expression by immunohistochemistry and confocal analysis. Aged injured animals showed more widespread area of microglial response at 12 hr postlesion (hpl) and greater microglia/macrophage density at 3 days postlesion (dpl). However, aged reactive microglia showed prevalence of ramified morphologies and fewer amoeboid/round forms. Aged injured animals presented a diminished area of COX2 expression, but a significantly larger density of COX2(+) cells, with higher numbers of COX2(+) neurons during the first 24 hpl and COX2(+) microglia/macrophages later. In contrast, the amount of COX2(+) neutrophils was diminished in the aged. iNOS was more rapidly induced in the aged injured striatum, with higher cell density at 12 hpl, when expression was mainly neuronal. From 1 dpl, both the iNOS(+) area and the density of iNOS(+) cells were reduced in the aged, with lower numbers of iNOS(+) neurons, microglia/macrophages, neutrophils, and astrocytes. In conclusion, excitotoxic damage in aging induces a distinct pattern of microglia/macrophage response and expression of inflammatory enzymes, which may account for the changes in lesion outcome in the aged, and highlight the importance of using aged animals for the study of acute age-related insults.

Changes at the focus of experimental ischemic stroke treated with neuroprotective agents

The aim of the present work was to compare the morphological changes occurring at the focus of experimental ischemic stroke treated with agents of the neurotrophic group (alpha-GPC, cerebrolysin), an agent with nootropic properties (piracetam), and a mixed-action agent (vinpocetine). Experiments were performed on 18 rats. Transient cerebral circulatory lesions (acute ischemia) were produced in the right hemisphere by clipping the stem of the innominate artery for 40 min. Light microscopic and electron microscopic studies were performed on fragments of cerebral cortex, brainstem, and cerebellum. Use of alpha-GPC and cerebrolysin increased the tolerance of neurons to ischemic damage and slowed the execution of the cell death program. Intracellular changes were seen and were interpreted as adaptive and reparative: these included folding of the nuclear membrane, abundance of polyribosomes, and endoplasmic reticulum and Golgi complex hypertrophy. These agents preserved the structures of the nuclear membranes and major cellular organelles. When piracetam and vinpocetine were used, all morphological measures indicated inadequate energy provision for repair processes in the acute stage of ischemic stroke. Morphological signs of functional tension of cerebral cortex neurons were seen, with gliocytes in different stages of apoptosis, along with the phenomenon of incomplete separation of gliocytes during proliferation, pathological changes to myelin and non-myelinated fibers, and abnormalities in synapse structure.

Effect of aminoguanidine on post-ischemic brain edema in transient model of focal cerebral ischemia

Previous experimental studies have shown that aminoguanidine (AG) is beneficial in the late phase of cerebral ischemia. Recently, it has been reported that AG reduces cerebral edema in traumatic brain injury. However, the effects of AG on post-ischemic cerebral edema and blood-brain barrier (BBB) permeability are not clear. Under chloral hydrate anesthesia, transient focal cerebral ischemia was induced in rats by 60 min of middle cerebral artery occlusion (MCAO), followed by 23 h of reperfusion. Saline as vehicle or AG at the doses of 75, 150 and 300 mg/kg, i.p., was administered at the beginning or at 1 or 3 h after induction of ischemia. Subsequently, 24 h after MCAO brain edema, BBB permeability and infarct volume were evaluated. Administration of AG (150 mg/kg) at the beginning or at 1 or 3 h after MCAO, significantly reduced cerebral edema (P<0.001), while AG at the doses of 75 and 300 mg/kg had no effect. Moreover, treatment with AG (150 mg/kg) significantly reduces Evans Blue extravasation by 48% into ischemic brain compared to the saline group (P<0.001). Additionally, AG at the doses of 75 and 150 mg/kg significantly reduces cortical and striatal infarct volumes (P<0.001), while AG at the dose of 300 mg/kg did not change striatal infarct volumes (P>0.05). Our findings show that AG significantly reduced post-ischemic increase of brain edema with a 3-h therapeutic window in the transient model of focal cerebral ischemia. Moreover, it seems that at least part of the anti-edematous effects of AG is due to decrease of BBB disruption.

The nitric oxide donor LA 419 decreases brain damage in a focal ischemia model

Stroke affects a large number of people, especially in developed countries, but treatment options are limited. Over the years, it has become clear that nitric oxide (NO) plays a major role in this pathology and that treatments that either reduce or increase NO presence may provide an alternative route for reducing the sequelae of brain ischemia. The NO donor LA 419 previously has been shown to protect the brain tissue from ischemic damage in an experimental model of global brain ischemia. Here we study whether this holds true for focal ischemia, a condition closer to the more common form of human stroke. Ischemia was induced in rats by a stereotaxic injection of endothelin-1, a potent vasoconstrictor, in the striatum. Seven days after the injection, magnetic resonance imaging (MRI) found a significant elevation in apparent diffusion coefficient (ADC) in the injected striatum of untreated rats, due to ischemia-induced vascular edema. Animals that received LA 419 prior to injection with endothelin-1 showed an ADC undistinguishable from the contralateral striatum or from the striatum of rats not treated with LA 419. In addition, immunohistochemistry with antibodies against neuronal nitric oxide synthase (nNOS), inducible NOS (iNOS), and nitrotyrosine showed a marked increase in the expression of these markers of NO production following ischemic treatment that was dampened by treatment with LA 419. In summary, our results clearly show that the NO donor LA 419 may be a useful compound for the prevention and/or treatment of focal brain ischemia.

Oxidative stress in immature brain after traumatic brain injury

High oxygen demand along with the abundance of readily oxidizable substrates yielding productive oxidative metabolism are required for the normal function of the brain. This necessitates the existence of the complex and multicomponent antioxidant system in the brain for protection against oxidative damage. However, during development, individual components of the antioxidant system are not equally expressed and not always sufficient to fulfill their tasks in a coordinated way. As a result, the developing brain may be more vulnerable to oxidative insults than the adult brain. Traumatic brain injury is one of the damaging acute impacts that challenge the brain antioxidant reserves by exposing them to a number of decompartmentalized prooxidant molecules. This review focuses on the sources and assessment of oxidative stress and the link between oxidative stress and cell death pathways in the immature brain after experimental and clinical traumatic brain injury.

Distribution of inducible nitric oxide synthase and cell proliferation in rat brain after transient middle cerebral artery occlusion

Nitric oxide (NO) can be neuroprotective or neurotoxic during cerebral ischemia, depending on the NO synthase (NOS) isoform involved. In addition to neurotoxic effect in ischemic brain, inducible NOS (iNOS) also adversely affect ischemic outcome by blocking neurogenesis. In the present study, therefore, we studied the chronological and spatial change of the distribution of iNOS and cell proliferation in subventricular zone (SVZ) after transient focal cerebral ischemia. After 90 min of transient middle cerebral artery occlusion (tMCAO), iNOS-positive cells decreased in the ischemic core at 1 to 21 days, and increased in the ipsilateral periischemic area at 1 and 3 days. 5-Bromodeoxyuridine (BrdU)-positive cells appeared in the ischemic core at 3 to 21 days, appeared in the periischemic area at 3 and 7 days, and increased in the ipsilateral SVZ at 7 days. ED-1-positive cells appeared in the ischemic core at 3 to 21 days, and some of them were double positive with BrdU or iNOS, but the majority were BrdU-negative. The present study suggests that astrocytes are born within the periischemic area at early stage after tMCAO and migrate from SVZ into periischemic area at later stage, and that time-dependent and spatial changes of iNOS expression may be involved in the proliferation and differentiation of adult neurogenesis after focal cerebral ischemia.

Aminoguanidine inhibits caspase-3 and calpain activation without affecting microglial activation following neonatal transient cerebral ischemia

Microglial cells, the resident macrophages of the CNS, can be both beneficial and detrimental to the brain. These cells play a central role as mediators of neuroinflammation associated with many neurodegenerative states, including cerebral ischemia. Because microglial cells are both a major source of inducible nitric oxide synthase (iNOS)/nitric oxide (NO) production locally in the injured brain and are activated by NO-mediated injury, we tested whether iNOS inhibition reduces microglial activation and ischemic injury in a neonatal focal ischemia-reperfusion model. Post-natal day 7 rats were subjected to a 2 h transient middle cerebral artery (MCA) occlusion. Pups with confirmed injury on diffusion-weighted magnetic resonance imaging (MRI) during occlusion were administered 300 mg/kg/dose aminoguanidine (AG) or vehicle at 0, 4 and 18 h after reperfusion, and animals were killed at 24 or 72 h post-reperfusion. The effect of AG on microglial activation as judged by the acquisition of ED1 immunoreactivity and proliferation of ED1-positive cells, on activation of cell death pathways and on injury volume, was determined. The study shows that while AG attenuates caspase 3 and calpain activation in the injured tissue, treatment does not affect the rapidly occurring activation and proliferation of microglia following transient MCA occlusion in the immature rat, or reduce injury size.

Role of gastric oxidative stress and nitric oxide in formation of hemorrhagic erosion in rats with ischemic brain

AIM: To investigate the role of gastric oxidative stress and nitric oxide (NO) in the formation of gastric hemorrhagic erosion and their protection by drugs in rats with ischemic brain.

METHODS: Male Wistar rats were deprived of food for 24 h. Under chloral hydrate (300 mg/kg) anesthesia, bilateral carotid artery ligation was performed. The pylorus and carotid esophagus of the rats were also ligated. The stomachs were then irrigated for 3 h with either normal saline or simulated gastric juice containing 100 mmol/L HCl plus 17.4 mmol/L pepsin and 54 mmol/L NaCl. Rats were killed and stomachs were dissected. Gastric mucosa and gastric contents were harvested. The rat brain was dissected for the examination of ischemia by triphenyltetrazolium chloride staining method. Changes in gastric ulcerogenic parameters, such as decreased mucosal glutathione level as well as enhanced gastric acid back-diffusion, mucosal lipid peroxide generation, histamine concentration, luminal hemoglobin content and mucosal erosion in gastric samples, were measured.

RESULTS: Bilateral carotid artery ligation produced severe brain ischemia (BI) in rats. An exacerbation of various ulcerogenic parameters and mucosal hemorrhagic erosions were observed in these rats. The exacerbated ulcerogenic parameters were significantly (P < 0.05) attenuated by antioxidants, such as exogenous glutathione and allopurinol. These gastric parameters were also improved by intraperitoneal aminoguanidine (100 mg/kg) but were aggravated by N^G-nitro-L-arginine-methyl ester (L-NAME: 25 mg/kg). Intraperitoneal L-arginine (0-500 mg/kg) dose-dependently attenuated BI-induced aggravation of ulcerogenic parameters and hemorrhagic erosions that were reversed by L-NAME.

CONCLUSION: BI could produce hemorrhagic erosions through gastric oxidative stress and activation of arginine-nitric oxide pathway.

Neuroprotective effects of indomethacin and aminoguanidine in the newborn rats with hypoxic-ischemic cerebral injury

Nitric oxide (NO) and prostaglandins (PG) play important roles in delayed mechanisms of brain injury. While NO disrupts oxidative metabolism, prostaglandins are responsible for free radical attack in reperfusion interval. Relatively little is known about neuroprotection exerted at this level in perinatal models. The aim of this study was to investigate the effect of indomethacin and aminoguanidine on endogenous inducible nitric oxide synthase (iNOS) biosynthesis and neuroprotection in the newborn rats with hypoxic ischemic cerebral injury.Seven-day old rat pups with model of hypoxic-ischemic cerebral injury were randomly divided into four study groups. Group C (n=18; served as a control) pups were given physiologic saline (SF). Group I (n=18) pups were treated with indomethacin at a dose of 0,2 mg/kg per 12 h. Group A (n=20) pups were treated with aminoguanidine at a dose of 300 mg/kg per 8 h. Administration of drugs and SF were begun half an hour after hypoxic-ischemic insult in these groups. Group I+A (n=18) pups were treated with indomethacin at a single dose of 0.2 mg/kg 1 h before hypoxia-ischemia followed by aminoguanidine as in group A. Drugs and SF were administered for three consecutive days. On the tenth day, rat pups were decapitated and coronal sections at the level of dorsal hippocampal region of brains were evaluated. In the histopathologic examination; the mean infarcted area in group I+A was significantly lower than the control group (P<0.05). Although there was no statistically significant difference between treatment groups in terms of iNOS expression, the risk of iNOS expression was 7 times less for group I (CI: 1.6-30.8, P=0.01), 19.8 times less for group A (CI: 3.8-104, P=0.001) and 12.3 times less for group I+A (CI: 2.5-59, P=0.002) compared to group C. In conclusion, only indomethacin administration before hypoxic ischemia and followed by aminoguanidine was more effective to reduce infarct area, but we did not find any difference between treatment groups and control group for iNOS expression. So we suggest that this neuroprotection may not be related to depression of iNOS expression.

The effect of i.v. L-NG methylarginine hydrochloride (L-NMMA: 546C88) on basal and acetazolamide (Diamox) induced changes of blood velocity in cerebral arteries and regional cerebral blood flow in man

The aim of this study was to estimate the effect of Nitric Oxide synthase (NOS)-inhibition (L-NMMA) on the diameter of the middle cerebral artery (MCA) and on regional cerebral blood flow (rCBF). Furthermore, to assess the effect of L-NMMA on acetazolamide induced increases in MCA blood velocity (Vmean) and rCBF. In an open crossover design 12 healthy subjects attended the laboratory twice. The first day 6 mg/kg L-LNMMA i.v. over 15 min preceded 1 g acetazolamide i.v. over 5 min. Eight days later only acetazolamide was given. V(mean) in MCA was determined with transcranial Doppler (TCD) and rCBF with Xe-133 inhalation SPECT at baseline, after L-NMMA and 25 and 55 min after acetazolamide infusion. After L-NMMA the decrease in rCBF(MCA) was 6.8% (+/- 7.4) (P < 0.019, n = 12), whereas V(mean) was not affected (P = 0.83, n = 8). The change in MCA diameter was estimated to - 1.3% (P = 0.44, n = 8). L-NMMA did not affect acetazolamide increases in Vmean (P = 0.67, n = 8) nor rCBF (P = 0.29, n = 12). The percentage increase of V(mean) was 1.5 times that of rCBF (n = 8). Our data suggest that the basal tone of human cerebral arterioles but not of conduit arteries is NO-dependent. The action of acetazolamide in man is not NO-dependent.

Modulation of prostaglandin biosynthesis by nitric oxide and nitric oxide donors

The biosynthesis and release of nitric oxide (NO) and prostaglandins (PGs) share a number of similarities. Two major forms of nitric-oxide synthase (NOS) and cyclooxygenase (COX) enzymes have been identified to date. Under normal circumstances, the constitutive isoforms of these enzymes (constitutive NOS and COX-1) are found in virtually all organs. Their presence accounts for the regulation of several important physiological effects (e.g. antiplatelet activity, vasodilation, and cytoprotection). On the other hand, in inflammatory setting, the inducible isoforms of these enzymes (inducible NOS and COX-2) are detected in a variety of cells, resulting in the production of large amounts of proinflammatory and cytotoxic NO and PGs. The release of NO and PGs by the inducible isoforms of NOS and COX has been associated with the pathological roles of these mediators in disease states as evidenced by the use of selective inhibitors. An important link between the NOS and COX pathways was made in 1993 by Salvemini and coworkers when they demonstrated that the enhanced release of PGs, which follows inflammatory mechanisms, was nearly entirely driven by NO. Such studies raised the possibility that COX enzymes represent important endogenous "receptor" targets for modulating the multifaceted roles of NO. Since then, numerous papers have been published extending the observation across various cellular systems and animal models of disease. Furthermore, other studies have highlighted the importance of such interaction in physiology as well as in the mechanism of action of drugs such as organic nitrates. More importantly, mechanistic studies of how NO switches on/off the PG/COX pathway have been undertaken and additional pathways through which NO modulates prostaglandin production unraveled. On the other hand, NO donors conjugated with COX inhibitors have recently found new interest in the understanding of NO/COX reciprocal interaction and potential clinical use. The purpose of this article is to cover the advances which have occurred over the years, and in particular, to summarize experimental data that outline how the discovery that NO modulates prostaglandin production has impacted and extended our understanding of these two systems in physiopathological events.

Nitric oxide synthase inhibitors in experimental ischemic stroke and their effects on infarct size and cerebral blood flow: a systematic review

Nitric oxide produced by the neuronal or inducible isoform of nitric oxide synthase (nNOS, iNOS) is detrimental in acute ischemic stroke (IS), whereas that derived from the endothelial isoform is beneficial. However, experimental studies with nitric oxide synthase inhibitors have given conflicting results. Relevant studies were found from searches of EMBASE, PubMed, and reference lists; of 456 references found, 73 studies involving 2321 animals were included. Data on the effects of NOS inhibition on lesion volume (mm3, %) and cerebral blood flow (CBF; %, ml * min(-1) * g(-1)) were analyzed using the Cochrane Review Manager software. NOS inhibitors reduced total infarct volume in models of permanent (standardized mean difference (SMD) -0.56, 95% confidence interval (95% CI) -0.86, -0.26) and transient (SMD -0.99, 95% CI -1.25, -0.72) ischemia. Cortical CBF was reduced in models of permanent but not transient ischemia. When assessed by type of inhibitor, total lesion volume was reduced in permanent models by nNOS and iNOS inhibitors, but not by nonselective inhibitors. All types of NOS inhibitors reduced infarct volume in transient models. NOS inhibition may have negative effects on CBF but further studies are required. Selective nNOS and iNOS inhibitors are candidate treatments for acute IS.

Enhanced oxidative stress in iNOS-deficient mice after traumatic brain injury: support for a neuroprotective role of iNOS

Studies in experimental traumatic brain injury (TBI) suggest both deleterious and protective effects of inducible nitric oxide synthase (iNOS). Early after injury, iNOS may be detrimental via formation of peroxynitrite and iNOS inhibitors are protective. In contrast, we reported impaired long-term functional outcome after TBI in iNOS knockout (ko) versus wild-type (wt) mice. To elucidate potential neuroprotective and neurotoxic mechanisms for iNOS, we studied nitric oxide formation by electron paramagnetic resonance (EPR) spectroscopy using diethyldithiocarbamate-iron (DETC-Fe) as a spin trap and markers of nitrosative (S-nitrosothiol (RSNO, Fluorescent assay); nitrotyrosine (3NT, ELISA)) and oxidative stress (ascorbate, HPLC) at 72 h after controlled cortical impact (CCI) in iNOS ko and wt and in uninjured iNOS ko and wt mice. 3NT immunostaining with macrophage and myeloperoxidase (MPO) dual labeling was also assessed in brain sections. Brain DETC-Fe-NO low-temperature EPR signal intensity was approximately 2-fold greater in wt versus iNOS ko at 72 h after CCI. Ascorbate levels decreased in injured hemisphere in wt and iNOS ko versus uninjured -this decrease was more pronounced in iNOS ko. In wt mice, RSNO and 3NT levels were increased after CCI versus uninjured (50% and 400%, respectively, P < 0.05). RSNO levels were not increased in iNOS ko after CCI. Nitrotyrosine levels increased after CCI in wt and ko versus respective uninjured -this increase was more pronounced in wt (2.34 +/- 0.95 versus 1.27 +/- 0.49 pmol/mg protein, P < 0.05). Increased 3NT immunoreactivity was detected in wt versus iNOS ko at 72 h after CCI, and colocalized with macrophage marker and MPO. Our data support a role for iNOS-derived NO as an endogenous antioxidant after CCI. iNOS also contributes protein nitrosylation and nitration. Colocalization of 3NT with macrophages and MPO suggests generation of nitrating agents by macrophages and/or phagocytosis of nitrated proteins.

Interaction between inducible nitric oxide synthase and poly(ADP-ribose) polymerase in focal ischemic brain injury

BACKGROUND AND PURPOSE

Overactivation of the DNA repair enzyme poly(ADP-ribose) polymerase (PARP) contributes to ischemic brain injury. Because PARP upregulates proinflammatory genes, we investigated whether inducible nitric oxide synthase (iNOS), a gene involved in the deleterious effects of postischemic inflammation, participates in the mechanisms by which PARP activation contributes to cerebral ischemic injury.

METHODS

The middle cerebral artery (MCA) was occluded in mice for 20 minutes using an intravascular filament, and injury volume was measured 72 hours later in Nissl-stained brain sections. mRNA expression was assessed in the postischemic brain by the quantitative "real-time" polymerase chain reaction.

RESULTS

The PARP inhibitor PJ34 reduced infarct volume and attenuated postischemic iNOS mRNA upregulation by 72%. To determine whether iNOS contributes to the toxicity of PARP, the iNOS inhibitor aminoguanidine was co-administered with PARP inhibitors. Unexpectedly, co-administration of PARP and iNOS inhibitors, or treatment of iNOS-null mice with PARP inhibitors, abrogated the protective effect afforded by iNOS or PARP inhibition alone. The loss of neuroprotection was associated with upregulation of the inflammatory genes iNOS, intercellular adhesion molecule-1, and gp91(phox).

CONCLUSIONS

The results suggest that iNOS expression contributes to the deleterious effects exerted by PARP activation in cerebral ischemia. However, iNOS activity is required for the protective effect of PARP inhibition and, conversely, PARP activity must be present for iNOS inhibition to be effective. The findings unveil a previously unrecognized deleterious interaction between iNOS and PARP that is relevant to the development of combination therapies for ischemic stroke.

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.

Relationship between S100β and GFAP expression in astrocytes during infarction and glial scar formation after mild transient ischemia

The expression of astrocyte marker proteins (S100beta and GFAP) during infarction and glial scar formation after transient middle cerebral artery (MCA) occlusion was examined using double immunostaining. S100beta immunoreactivity markedly decreased in the core of the injured area when observed immediately after reperfusion and did not increase again. In the periphery, however, S100beta expression increased, showing that S100beta synthesis was up-regulated. S100beta+/iNOS+ astrocytes in the periphery were observed from day 1, when small infarct areas were detectable, up to day 5, when infarct expansion had almost ended. TUNEL+ cells in the periphery were present from days 1 to 5. S100beta+/TUNEL+ cells were observed centrally and around the periphery of the injured area, predicting that cell death contributes to the increase of S100beta concentration in the injured area. Our results suggest that (1) higher concentration of S100beta in the extracellular space due to S100beta leakage from damaged astrocytes leads to up-regulation of S100beta synthesis and induction of inducible nitric oxide synthase (iNOS) synthesis in astrocytes, contributing to infarct expansion that results in DNA damage or cell death via NO and ROS production, and (2) GFAP, but not S100beta, is a main contributor to glial scar formation. On day 1 postreperfusion, the microdiascopic images of the injured areas from the unstained thick sections or the areas detected by S100beta immunoreactivity were larger than those of the infarct areas detected by hematoxylin--eosin (HE)-staining. The difference between these sizes might be useful to predict infarct expansion.

D-JNKI1, a Cell-Penetrating c-Jun-N-Terminal Kinase Inhibitor, Protects Against Cell Death in Severe Cerebral Ischemia

BACKGROUND AND PURPOSE

In 2 models of severe ischemic injury, we have evaluated the neuroprotective action of D-JNKI1, a cell-penetrating and protease-resistant peptide selectively inhibiting the c-Jun-N-terminal kinase (JNK).

METHODS

Hippocampal slices from newborn rats were subjected to oxygen (5%) and glucose (1 mmol/L) deprivation for 30 minutes. Cell death was evaluated with propidium iodide, and the evoked potential responses were recorded in the CA1 region after stimulation in CA3. Male ICR-CD1 mice were subjected to permanent endoluminal "suture" middle cerebral artery occlusion (MCAo). The lesion size was determined after 24 hours by triphenyl-tetrazolium chloride staining, and neurological scores and rotarod treadmill performance were used to evaluate the neurological outcome.

RESULTS

In vitro, D-JNKI administration 6 hours after oxygen glucose deprivation reduced cell death at 24 hours from 21%+/-8% (n=10) to 5%+/-3% (n=7, P<0.01). This protective effect was still seen at 48 hours, paralleled by an improved amplitude of the evoked potential response. In vivo in the mouse, D-JNKI1 administration 3 hours after ischemia significantly reduced the infarct volume from 162+/-27 mm(3) (n=14) to 85+/-27 mm(3) (n=9, P<0.001). The functional outcome was also improved.

CONCLUSIONS

JNK inhibition prevents cell death induced by oxygen and glucose deprivation in hippocampal slice cultures in vitro and by permanent suture MCAo in vivo. D-JNKI1 is a powerful neuroprotectant in models of both mild and severe cerebral ischemia, with an extended therapeutic window. Further investigations are needed to identify the relevant JNK target(s) mediating ischemic neuronal death.

Post-ischemic delayed expression of hepatocyte growth factor and c-Met in mouse brain following focal cerebral ischemia

We investigated long-term changes in the expression of protein and mRNA of hepatocyte growth factor (HGF) and its receptor c-Met in mouse brain after permanent occlusion of the middle cerebral artery, by using immunohistochemistry and quantitative reverse transcription-polymerase chain reaction. HGF-immunopositive cells were observed in the periinfarct region from 4 days after occlusion, peaking at 14-28 days. The area containing HGF-immunopositive cells continued to expand until 28 days after occlusion. c-Met-immunopositive cells were observed exclusively at the periinfarct region at 7 and 14 days after occlusion. At 28 days after occlusion, there were many c-Met-immunopositive cells in the widespread periinfarct region. Triple immunohistochemical staining by using confocal laser scanning microscopy (CLSM) demonstrated that most of the HGF-immunopositive cells were localized to reactive astrocytes. The c-Met-immunopositive cells were also localized to reactive astrocytes. HGF mRNA was upregulated exclusively in the periinfarct region at 14 days. c-Met mRNA was upregulated in the periinfarct region from as late as 28 days after occlusion. Thus, HGF and c-Met show delayed expression in the periinfarct region at both protein and mRNA levels after induction of ischemia. Because HGF was recently shown to play critical roles in angiogenesis and neurotrophic activities, the temporal profiles of their expression may imply the involvement of HGF in the process of post-ischemic brain tissue repair.

The angiotensin II type 1-receptor blocker candesartan increases cerebral blood flow, reduces infarct size, and improves neurologic outcome after transient cerebral ischemia in rats

The goal of the present study was to test the impact of administration time of the angiotensin II type 1-receptor blocker candesartan on cerebral blood flow (CBF), infarct size, and neuroscore in transient cerebral ischemia. Therefore, 1-hour middle cerebral artery occlusion (MCAO) was followed by reperfusion. Rats received 0.5-mg/kg candesartan intravenously 2 hours before MCAO (pretreatment), 24 hours after MCAO, every 24 hours after MCAO, or 2 hours before and every 24 hours after MCAO. Infarct size (mm3) and a neuroscore at day 7 were compared with controls. CBF was quantified by radiolabeled microspheres and laser-Doppler flowmetry. Compared with controls (95 +/- 8), infarct size in candesartan-treated groups was smaller (59 +/- 5, 68 +/- 10, 28 +/- 3, and 15 +/- 3, respectively; P<0.05). Although there was no difference in neuroscore between pretreatment and controls (1.55 +/- 0.18, 1.80 +/- 0.13), other treatment regimens resulted in improved neuroscores (1.33 +/- 0.16, 1.11 +/- 0.11, 0.73 +/- 0.15; P<0.05). CBF in pretreated animals at 0.5 hours after MCAO was significantly higher than in controls (0.58 +/- 0.09 mL x g(-1) x min(-1) and 44% +/- 7% of baseline compared with 0.49 +/- 0.06 mL x g(-1) x min(-1) and 37% +/- 6%, microspheres and laser-Doppler flowmetry; P<0.05). Thus, candesartan reduces infarct size even if administered only during reperfusion. Apart from pretreatment, other treatment regimens result in significantly improved neuroscores. In the acute phase of cerebral ischemia, candesartan increases CBF.

Nuclear factor-kappaB contributes to infarction after permanent focal ischemia

BACKGROUND AND PURPOSE

Activation of transcription factor nuclear factor-kappaB (NF-kappaB) may induce expression of either proinflammatory/apoptotic genes or antiapoptotic genes. Because a considerable number of middle cerebral artery occlusions (MCAOs) in humans are not associated with reperfusion during the first 24 hours, the role of NF-kappaB after permanent MCAO (pMCAO) was investigated.

METHODS

Mice transgenic for a NF-kappaB-driven beta-globin reporter were exposed to pMCAO, and the expression of the reporter gene was quantified with real-time polymerase chain reaction. Mice lacking the p50 subunit of NF-kappaB and wild-type controls were exposed to pMCAO with or without treatment with pyrrolidinedithiocarbamate (PDTC), an NF-kappaB inhibitor. Brain sections of human stroke patients were immunostained for the activated NF-kappaB.

RESULTS

pMCAO increased NF-kappaB transcriptional activity to 260% (36.9+/-4.5 compared with 14.4+/-2.6; n=10; P<0.01) in the brain; this NF-kappaB activation was completely blocked by PDTC (17.2+/-2.6; n=9; P<0.05). In p50-/- mice, pMCAO resulted in 41% (18+/-3.2 mm3; n=12) smaller infarcts compared with wild-type controls (32.9+/-3.8 mm3; n=9; P<0.05), which was comparable to the protection achieved with PDTC in wild-type mice (19.6+/-4.2 mm3; n=8). Pro-DTC, a PDTC analogue that does not cross the blood-brain barrier, had no effect, even though Pro-DTC and PDTC were equally protective in vitro. During the first 2 days of human stroke, NF-kappaB was activated in neurons in the penumbral areas.

CONCLUSIONS

NF-kappaB is induced in neurons during human stroke, and activation of NF-kappaB in the brain may contribute to infarction in pMCAO.

Dual role of Fcgamma receptor in transient focal cerebral ischemia in mice

BACKGROUND AND PURPOSE

Cerebral ischemia/reperfusion injury is associated with the development of inflammatory response, including pathological contributions by vascular leukocytes and endogenous microglia. Expression of Fc receptors (FcRs) on macrophages and microglia is thought to be involved in the inflammatory cascade. The present study assessed the role of FcgammaR in ischemia/reperfusion injury, using FcgammaR knockout (FcgammaR-/-) mice and bone marrow chimera FcgammaR-/- mice, which express enhanced green fluorescent protein (EGFP).

METHODS

Mice underwent occlusion of the middle cerebral artery for 60 minutes, followed by reperfusion. Infarct volume and mortality were calculated at several time points after ischemia. To clarify the function and distribution of microglia/macrophages, immunohistochemical staining and immunoblotting of ionized calcium-binding adapter molecule 1 (Iba-1), inducible nitric oxide synthase, and nitrotyrosine were performed.

RESULTS

FcgammaR-/- mice showed significantly reduced mortality (20%) and smaller infarcts (19.7+/-3.63 versus 33.28+/-7.98 mm3; P<0.001) than wild-type (WT) mice at 72 hours after reperfusion. Western blotting revealed that microglial activation (P<0.002) and induction of inducible nitric oxide synthase (P<0.005) were reduced in FcgammaR-/- mice compared with WT mice. At 7 days after reperfusion, sections double-immunostained for EGFP and Iba-1 showed less activation and migration of EGFP-positive bone marrow-derived macrophages in FcgammaR-/- chimera mice than in WT mice.

CONCLUSIONS

Our results demonstrated that the neuroprotective effect of FcgammaR deficiency in our model may be primarily attributed to the suppression of activation and infiltration of inflammatory cells.

Aminoguanidine downregulates expression of cytokine-induced Fas and inducible nitric oxide synthase but not cytokine-enhanced surface antigens of rat islet cells

Autoimmune beta-cell destruction occurs directly by cell-mediated cytotoxicity or indirectly by cytokines released from infiltrating lymphocytes. Cytokines (IL-1beta/IFN-gamma) modify or induce expression of MHC antigens and ICAM-1 on beta-cells which can lead to an improved binding of T-lymphocytes to beta-cells and finally to an enhanced cell-mediated cytotoxicity. Cytokines also induce Fas-expression and inducible nitric oxide synthase (iNOS) causing generation of nitric oxide (NO) which is toxic for beta-cells. The iNOS inhibitor aminoguanidine (AG) delays diabetes onset, but does not reduce diabetes incidence. We wanted to know whether AG inhibits cytokine-induced expression of Fas, MHC antigens and ICAM-1 on beta-cells of LEW.1W and BB/OK rat islets after culture with IL-1beta/IFN-gamma. NO was completely inhibited by 5.0 mmol/L AG while 0.5 mmol/L had no inhibitory effect. AG downregulated Fas-expression on the surface of beta-cells. Cytokine-induced/enhanced expression of MHC class-II and ICAM-1 was not affected by any AG concentration. AG syngergistically increased cytokine-induced enhancement of MHC class-I antigen density. AG possibly blocks the indirect pathway of beta-cell damage in vivo due to inhibition of Fas and iNOS and improves direct cell-mediated cytotoxicity due to drastic increased MHC class-I expression. Inhibition of only one pathway of beta-cell destruction is not sufficient to prevent diabetes.

The involvement of glucose metabolism in the regulation of inducible nitric oxide synthase gene expression in glial cells: possible role of glucose-6-phosphate dehydrogenase and CCAAT/enhancing binding protein

In rat glial cells the lipopolysaccharide (LPS)-induced inducible nitric oxide synthase (iNOS) gene expression was enhanced by extracellular glucose concentration in a dose-dependent manner. On the other hand, 2-deoxy-d-glucose decreased the LPS-induced iNOS gene expression even in the presence of glucose (6 gm/l), suggesting that glucose metabolism is linked to the regulation of iNOS gene expression. The intracellular NADPH/NADP+ directly correlated with the extracellular glucose concentration, and the reduction of NADPH generation via a block of glucose-6-phosphate dehydrogenase (G6PD) by treatment with dehydroepiandrosterone or the antisense DNA oligomer of G6PD mRNA resulted in the inhibition of iNOS gene expression. Gel shift assays showed that CAAT/enhancing binding protein (C/EBP), rather than AP-1 or NF-kappaB, correlated better with a glucose-dependent increase in iNOS gene expression. The induction of C/EBP DNA binding activity by LPS and glucose was attributable mainly to the increase in C/EBP-delta protein. The cotransfection with wild-type C/EBP-delta increased the iNOS promoter activity to the level achieved with a higher glucose concentration in the presence of LPS. Therefore, our results suggest that C/EBP-delta may be a critical mediator in glucose-mediated regulation of iNOS gene expression.

A dose-response study of nitric oxide synthase inhibition in different vascular beds in man

BACKGROUND AND OBJECTIVE

Nitric oxide (NO) is an almost ubiquitous messenger molecule and is implicated in several disorders. NG monomethyl L-arginine ( L-NMMA:546C88) is an inhibitor of all three NO synthases (NOS), the enzymes that catalyse the production of NO. The present study was performed to evaluate the dose-response relation of L-NMMA to improve the design and interpretation of studies in migraine sufferers and other diseases.

METHODS

In a double-blind, placebo-controlled, cross-over design, six healthy volunteers were randomised to receive three different doses of L-NMMA (0.3 mg/kg, 1 mg/kg, 3 mg/kg) or placebo (5% dextrose) intravenously (iv) over 5 min on four different days. On a fifth study day, in an open design, the same subjects received L-NMMA in the dose 6 mg/kg iv over 15 min. The effect of L-NMMA on the maximal mean blood velocity (Vmean) in the middle cerebral artery (MCA) (transcranial Doppler), the luminal diameter of the radial artery (high-frequency ultrasound), mean arterial blood pressure (MAP), heart rate and electrocardiogram were repeatedly followed every 5 min until 60 min after start of the infusion, then every 15 min during the following hour, and at 3 h and 4 h.

RESULTS

Inhibition of NOS had no effect on Vmean in MCA or on the diameter of the radial artery, but MAP increased and heart rate decreased dose dependently. With a dose of 6-mg/kg L-NMMA infused over a 15-min period, the maximum MAP increase was 20% 20 min after the start of L-NMMA infusion. The maximum decrease of heart rate was 24% 15 min after start of the L-NMMA infusion.

CONCLUSION

L-NMMA in a dose that caused marked changes in systemic blood pressure and heart rate had no effect on cerebral and radial arteries in man.

Inhibition of nNOS and iNOS following hypoxia-ischaemia improves long-term outcome but does not influence the inflammatory response in the neonatal rat brain

In this study, we tested the hypothesis that combined inhibition of nNOS and iNOS will reduce neuronal damage and the inflammatory response induced by perinatal hypoxia-ischaemia (HI). In 12-day-old rats, HI was induced by right carotid artery occlusion followed by 90 min of 8% O2. Immediately upon reoxygenation, the rats were treated with NOS inhibitors (n = 24) or placebo (n = 24). Neuropathology was scored at 6 weeks after HI on a 4-point scale (n = 12 per group). The expression of heat shock protein 70 (HSP70) and mRNA expression for cytokines were measured 12 h after HI (n = 12 per group). Histopathological analysis showed that the ipsilateral hemisphere in the NOS inhibition group was less damaged than in the placebo group (p < 0.05). HI induced a significant increase in HSP70 levels (p < 0.05) in the ipsilateral hemispheres, which tended to be lower in the NOS inhibition group (p = 0.07). HI induced an increase in mRNA expression for IL-1beta, TNF-alpha and TNF-beta, but there was no difference between the ipsi- and contralateral hemispheres. Combined inhibition of nNOS and iNOS did not induce any change in cytokine expression. We conclude that the long-term neuroprotective effects of combined nNOS and iNOS inhibition were not achieved by an altered cytokine response.

N-Acetyl cysteine protects against injury in a rat model of focal cerebral ischemia

Ischemic cerebrovascular disease (stroke) is one of the leading causes of death and long-time disability. Ischemia/reperfusion to any organ triggers a complex series of biochemical events, which affect the structure and function of every organelle and subcellular system of the affected cells. The purpose of this study was to investigate the therapeutic efficacy of N-acetyl cysteine (NAC), a precursor of glutathione and a potent antioxidant, to attenuate ischemia/reperfusion injury to brain tissue caused by a focal cerebral ischemia model in rats. A total of 27 male Sprague-Dawley rats weighing 250-300 g were used in this study. Focal cerebral ischemia (45 min) was induced in anesthetized rats by occluding the middle cerebral artery (MCA) with an intra-luminal suture through the internal carotid artery. The rats were scored post-reperfusion for neurological deficits. They were then sacrificed after 24 h of reperfusion and infarct volume in the brain was assessed by 2,3,5-triphenyl tetrazolium chloride (TTC). Brain sections were immunostained for tumor necrosis factor (TNF-alpha) and inducible nitric oxide synthase (iNOS). Animals treated with NAC showed a 49.7% (S.E.M.=1.25) reduction in brain infarct volume and 50% (S.E.M.=0.48) reduction in the neurological evaluation score as compared to the untreated animals. NAC treatment also blocked the ischemia/reperfusion-induced expression of tumor necrosis factor and inducible nitric oxide synthase. The data suggest that pre-administration of NAC attenuates cerebral ischemia and reperfusion injury in this brain ischemia model. This protective effect may be as a result of suppression of TNF-alpha and iNOS.

The potential of nitric oxide therapeutics in stroke

The therapeutic modulation of the nitric oxide (NO) system has generated considerable interest as a new way for managing many disease processes. In stroke, a useful strategy is to increase NO availability and thereby exploit its beneficial antiplatelet, antiatherosclerotic, haemodynamic and neuroprotective properties. Pharmacologically, this can be achieved by providing NO substrate, using NO donors or by upregulating nitric oxide synthase. Alternatively, one can reduce NO availability by inhibiting NO synthase and thereby limiting its pro-inflammatory and neurotoxic properties. This article reviews developments in NO-related therapeutics for treatment of stroke, with a particular emphasis on compounds that are in the clinical research and development pipeline. Although the routine use of NO therapeutics for the prevention or treatment of stroke cannot currently be recommended, we are evidently at an exciting stage in their pharmacological development. Definitive randomised controlled trials in stroke patients are required as a matter of urgency.

Aspirin inhibits p44/42 mitogen-activated protein kinase and is protective against hypoxia/reoxygenation neuronal damage

BACKGROUND AND PURPOSE

Acetylsalicylic acid (ASA) is preventive against stroke and protects against focal brain ischemia in rats. We studied the mechanisms of the manner in which ASA provides neuroprotection against hypoxia/reoxygenation (H/R) injury.

METHODS

Spinal cord cultures exposed to 20 hours of hypoxia followed by reoxygenation were treated with a vehicle, ASA or inhibitors of inducible nitric oxide synthase (iNOS), mitogen-activated protein kinases p38 MAPK and ERK1/2, or an N-methyl-d-aspartic acid (NMDA) receptor antagonist. Cell viability was assessed by LDH release measurement and cell counts. Prostaglandin production was measured by enzyme immunoassay, MAPK signaling by immunoblotting, and DNA binding of nuclear factor-kappaB (NF-kappaB) and activating protein-1 (AP-1) by electrophoretic mobility shift assay.

RESULTS

One to 3 mmol/L ASA inhibited H/R-induced neuronal death when present during H/R but not when administered only for the reoxygenation period. Prostaglandin E2 production was very low and was not altered by ASA. The AP-1 and NF-kappaB DNA binding activities increased after H/R. ASA increased the H/R-induced AP-1 binding but had no effect on NF-kappaB binding. H/R induced a sustained ERK1/2 activation followed by neuronal death, whereas no changes in p38 or c-Jun N-terminal kinase were detected. ASA strongly inhibited this ERK1/2 activation. PD98059, an ERK1/2 inhibitor, was also neuroprotective, prevented H/R-induced ERK1/2 activation, and had no effect on NF-kappaB binding activity. Inhibition of NMDA receptors, iNOS, or p38 MAPK did not provide neuroprotection.

CONCLUSIONS

Inhibition of the sustained activation of ERK1/2 may partially contribute to neuroprotection achieved by ASA against H/R injury.

Neuroprotective efficacy of nimesulide against hippocampal neuronal damage following transient forebrain ischemia

Cyclooxygenase-2 is involved in the inflammatory component of the ischemic cascade, playing an important role in the delayed progression of the brain damage. The present study evaluated the pharmacological effects of the selective cyclooxygenase-2 inhibitor nimesulide on delayed neuronal death of hippocampal CA1 neurons following transient global cerebral ischemia in gerbils. Administration of therapeutically relevant doses of nimesulide (3, 6 and 12 mg/kg; i.p.) 30 min before ischemia and at 6, 12, 24, 48 and 72 h after ischemia significantly (P<0.01) reduced hippocampal neuronal damage. Treatment with a single dose of nimesulide given 30 min before ischemia also resulted in a significant increase in the number of healthy neurons in the hippocampal CA1 sector 7 days after ischemia. Of interest is the finding that nimesulide rescued CA1 pyramidal neurons from ischemic death even when treatment was delayed until 24 h after ischemia (34+/-9% protection). Neuroprotective effect of nimesulide is still evident 30 days after the ischemic episode, providing the first experimental evidence that cyclooxygenase-2 inhibitors confer a long-lasting neuroprotection. Oral administration of nimesulide was also able to significantly reduce brain damage, suggesting that protective effects are independent of the route of administration. The present study confirms the ability of cyclooxygenase-2 inhibitors to reduce brain damage induced by cerebral ischemia and indicates that nimesulide can provide protection when administered for up to 24 h post-ischemia.

Effects of aminoguanidine on cerebral ischemia in mice: comparison between mice with and without inducible nitric oxide synthase gene

The expression of inducible nitric oxide synthase (iNOS) is induced in the late stage of cerebral ischemia, and NO produced by iNOS contributes to delays in recovery from brain neuronal damage. To examine the importance of iNOS in the above process, we compared the effects of aminoguanidine (AG), selective iNOS inhibitor, on infarct volume and neurological deficit in iNOS null mice and normal mice subjected to brain ischemia. Neurological deficits in iNOS null mice at 24 h post-ischemia were mild compared with those of normal mice, and did not improve by AG treatment at 96 h post-ischemia. The mean infarct volume of iNOS null mice was smaller than that of normal mice at 96 h post-ischemia, and was not influenced by AG treatment. In contrast, AG reduced the infarct volume in normal mice to levels similar to those of saline-treated iNOS null mice at 96 h post-ischemia. Our results indicated that AG suppresses iNOS activity in mice with brain ischemia to level equivalent to those seen in iNOS knockout mice, confirming that this enzyme is involved in ischemic brain injury.

Inducible nitric oxide synthase expression in the ischemic core and penumbra after transient focal cerebral ischemia in mice

The present observations examined the hypothesis that the iNOS expression in the ischemic penumbra after a transient focal ischemic insult is involved in the recruitment of penumbra into infarction. The middle cerebral artery in mice was occluded for 2 h by an intraluminal filament and then recirculated. The measurement of iNOS activity, iNOS protein formation and NO concentration in the ischemic core and penumbra, and the determination of infarct volume were performed at 6, 12, 24 and 48 h after reperfusion. iNOS protein and iNOS enzymatic activity appeared at 6 h, peaked at 24 h, and declined at 48 h in the penumbra after reperfusion. iNOS protein was not detectable in contralateral area and in sham-operated brains. The time course of iNOS protein, enzymatic activity and NO concentration in the penumbra but not in the core matched the process of infarct maturation. Treatment with iNOS inhibitor aminoguanidine (100 mg.kg(-1), i.p.) at 6 and 12 h after reperfusion inhibited iNOS activity by 88.0 +/- 10.4% and reduced NO concentration by 48.5 +/- 8.3% in the penumbra, and lessened infarct size by 48.8 +/- 7.2%. The iNOS activity and NO level in the core were not affected by the administration of aminoguanidine. These results suggest that iNOS expression in the ischemic penumbra is involved in the recruitment of penumbra into infarction and thereby contributing to the enlargement of infarct.

Effects of underwater sound exposure on neurological function and brain histology

To evaluate the safety of sonar exposure from a neurological perspective, the vulnerability of the central nervous system to underwater exposure with high-intensity, low-frequency sound (HI-LFS) was experimentally examined. Physiological, behavioral and histological parameters were measured in anesthetized, ventilated rats exposed to brief (5 min), underwater HI-LFS. Exposure to 180 dB sound pressure level (SPL) re 1 microPa at 150 Hz (n = 9) did not alter acute cardiovascular physiology (arterial blood pH, pO(2), pCO(2), heart rate, or mean arterial blood pressure) from that found in controls (n = 11). Rats exposed to either 180 dB SPL re 1 microPa at 150 Hz (n = 12) or 194 dB SPL re 1 microPa at 250 Hz (n = 12) exhibited normal cognitive function at 8 and 9 days after sound exposure. Evaluation of neurological motor function revealed a minor deficit 7 days after 180 dB SPL/150 Hz exposure that resolved by 14 days, and no deficits after 194 dB SPL/250 Hz exposure. No overt histological damage was detected in any group. These data suggest that underwater HI-LFS exposure may cause transient, mild motor dysfunction.

Tolerance against ischemic neuronal injury can be induced by volatile anesthetics and is inducible NO synthase dependent

BACKGROUND AND PURPOSE

We tested whether volatile anesthetics induce neuroprotection that is maintained for a prolonged time.

METHODS

Rats were pretreated for 3 hours with 1 minimal anesthetic concentration of isoflurane or halothane in normal air (anesthetic preconditioning [AP]). The animals were subjected to permanent middle cerebral artery occlusion (MCAO) at 0, 12, 24, or 48 hours after AP. Halothane-pretreated animals were subjected to MCAO 24 hours after AP. Histological evaluation of infarct volumes was performed 4 days after MCAO. Cerebral glucose utilization was measured 24 hours after AP with isoflurane. Primary cortical neuronal cultures were exposed to 1.4% isoflurane for 3 hours. Oxygen-glucose deprivation (OGD) was performed 24 hours after AP. Injury was assessed 24 hours later by measuring the release of lactate dehydrogenase into the medium 24 hours after OGD.

RESULTS

Isoflurane anesthesia at 0, 12, and 24 hours before MCAO or halothane anesthesia 24 hours before MCAO significantly reduced infarct volumes (125+/-42 mm3, P=0.024; 118+/-51 mm3, P=0.008; 120+/-49 mm3, P=0.009; and 121+/-48 mm3, P=0.018, respectively) compared with control volumes (180+/-51 mm3). Three hours of isoflurane anesthesia in rats did not have any effect on local or mean cerebral glucose utilization measured 24 hours later. Western blot analysis from cortical extracts of AP-treated animals revealed an increase of the inducible NO synthase (iNOS) protein beginning 6 hours after AP. The iNOS inhibitor aminoguanidine (200 mg/kg IP) eliminated the infarct-sparing effect of AP. In cultured cortical neurons, isoflurane exposure 24 hours before OGD decreased the OGD-induced release of lactate dehydrogenase by 49% (P=0.002).

CONCLUSIONS

Pretreatment with volatile anesthetics induces prolonged neuroprotection in vitro and in vivo, a process in which iNOS seems to be critically involved.

Astrocytic activation and delayed infarct expansion after permanent focal ischemia in rats. Part II: suppression of astrocytic activation by a novel agent (R)-(-)-2-propyloctanoic acid (ONO-2506) leads to mitigation of delayed infarct expansion and early improvement of neurologic deficits

A novel agent, (R)-(-)-2-propyloctanoic acid (ONO-2506), has a unique property in that it modulates functions of activated cultured astrocytes, including pronounced inhibition of S-100beta synthesis. The present study examined whether administration of this agent would mitigate the delayed expansion of infarct volume and the neurologic deficits after permanent middle cerebral artery occlusion (pMCAO) in rats. Daily intravenous administration of ONO-2506 (10 mg/kg) abolished the delayed infarct expansion between 24 and 168 hours after pMCAO, whereas the acute infarct expansion until 24 hours was unaffected. The agent significantly reduced the expression of S-100beta and glial fibrillary acidic protein in the activated astrocytes and the number of terminal deoxynucleotidyl transferase-mediated 2;-deoxyuridine 5;-triphosphate-biotin nick end labeling-positive cells in the periinfarct area. The neurologic deficits were significantly improved, compared with the vehicle-treated groups, as early as 24 hours after the initial administration of ONO-2506. The agent had a wide therapeutic time window of 0 to 48 hours after pMCAO. These results indicate that because of the pharmacologic modulation of astrocytic activation induced by ONO-2506, symptoms can regress whereas delayed expansion of the lesion is arrested. Pharmacologic modulation of astrocytic activation may confer a novel therapeutic strategy against stroke.

Astrocytic activation and delayed infarct expansion after permanent focal ischemia in rats. Part I: enhanced astrocytic synthesis of s-100beta in the periinfarct area precedes delayed infarct expansion

An astrocytic protein S-100beta enhances the expression of inducible nitric oxide synthase in cultured astrocytes at micromolar concentrations, leading to nitric oxide-mediated death of cocultured neurons. The present study examined whether S-100beta production by reactive astrocytes accumulating within the periinfarct area was related to delayed expansion of infarct volume after permanent middle cerebral artery occlusion in the rat. After rapid increases during the initial 24 hours, the increase of infarct volume then decelerated while maintaining the increasing tendency until 168 hours in this model, attaining a significant difference compared with that at 24 hours. In the periinfarct area, the number of reactive astrocytes expressing both S-100 and glial fibrillary acidic protein, the tissue level of S-100beta as measured by the sandwich enzyme-linked immunosolvent assay method using anti-S-100beta monoclonal antibody, and the number of terminal deoxynucleotidyl transferase-mediated 2;-deoxyuridine 5;-triphosphate-biotin nick end labeling-positive cells were significantly increased preceding the delayed expansion of infarct volume. The CSF concentration of S-100beta showed a biphasic increase, presumably reflecting the immediate release from astrocytes within the ischemic core and the subsequent production in reactive astrocytes within the periinfarct area. These results show for the first time that the enhanced synthesis of S-100beta by reactive astrocytes participates in the inflammatory responses within the periinfarct area, which may be related to the occurrence of delayed infarct expansion as a major component of the cytokine network.

Influence of mild hypothermia on inducible nitric oxide synthase expression and reactive nitrogen production in experimental stroke and inflammation

Mild hypothermia is neuroprotective, but the reasons are not well known. Inflammation contributes to ischemic damage; therefore, we examined whether the protection by hypothermia may be attributable to alterations in the inflammation. We examined whether hypothermia might alter the inflammatory cell-associated inducible nitric oxide synthase (iNOS) and subsequent nitric oxide (NO) and peroxynitrite generation in experimental stroke and inflammation. Rats underwent 2 hr of middle cerebral artery occlusion (MCAO). Brain inflammation was modeled by intravenous lipopolysaccharide (LPS) (2 mg/kg) injection. Temperature was maintained at 33 degrees C for 2 hr immediately after MCAO and LPS injection, delayed 2 hr after MCAO or maintained at 38 degrees C. Cultured microglia were activated with LPS and then incubated at 33 or 37 degrees C. Both intraischemic and delayed mild hypothermia attenuated infarct size by 40% (p < 0.05). Immunohistochemistry was performed to identify cell type, iNOS, and peroxynitrite. The majority of iNOS- and peroxynitrite-positive cells were activated microglia-macrophages, and mild hypothermia significantly decreased the numbers of immunoreactive cells at 72 hr by >50% (p < 0.05). After ischemia, mild hypothermia decreased NO production by 40%. Similarly, hypothermia attenuated NO and iNOS in LPS-injected rats, as well as in cultured microglia. Aminoguanidine, an iNOS inhibitor, also attenuated infarct size and NO in ischemic and inflammation models. We conclude that mild hypothermia significantly inhibits the inflammatory response by affecting microglial iNOS-NO generation. Therapies directed against microglia or their activation may be useful in treating stroke.

Peri-ischemic aminoguanidine fails to ameliorate neurologic and histopathologic outcome after transient spinal cord ischemia

Inhibition of neurotoxic events that lead to delayed cellular damage may prevent motor function loss after transient spinal cord ischemia. An important effect of the neuroprotective substance aminoguanidine (AG) is the inhibition of inducible nitric oxide synthase (iNOS), a perpetrator of focal ischemic damage. The authors studied the protective effects of AG on hind limb motor function and histopathologic outcome in an experimental model for spinal cord ischemia, and related these findings to the protein content of iNOS in the spinal cord. Temporary spinal cord ischemia was induced by 28 minutes of infrarenal balloon occlusion of the aorta in 40 anesthetized New Zealand White rabbits. Animals were assigned randomly to two treatments: saline (n = 20) or AG (n = 20; 100 mg/kg intravenously before occlusion). Postoperatively, treatment was continued with subcutaneous injections twice daily (saline or 100 mg/kg AG). Normothermia (38 degrees C) was maintained during ischemia, and rectal temperature was assessed before and after subcutaneous injections. Animals were observed for 96 hours for neurologic evaluation (Tarlov score), and the lumbosacral spinal cord was examined for ischemic damage after perfusion and fixation. Lastly, iNOS protein content was determined using Western blot analysis 48 hours after ischemia in five animals from each group. Neurologic outcome at 96 hours after reperfusion was the same in both groups. The incidence of paraplegia was 67% in the saline-treated group versus 53% in the AG-treated group. No differences in infarction volume, total number of viable motoneurons, or total number of eosinophilic neurons were present between the groups. At 48 hours after reperfusion, iNOS protein content in the spinal cord was increased in one animal in the AG-treated group and in three animals in the control group. The data indicate that peri-ischemic treatment with high-dose AG in rabbits offers no protection against a period of normothermic spinal cord ischemia. There was no conclusive evidence of spinal cord iNOS inhibition after treatment with AG.

N-[3,4-dimethoxycinnamoyl]-anthranilic acid (tranilast) suppresses microglial inducible nitric oxide synthase (iNOS) expression and activity induced by interferon-gamma (IFN-gamma)

1. Microglial cells up-regulate inducible nitric oxide synthase (iNOS) expression in response to various pro-inflammatory stimuli including interferon-gamma (IFN-gamma), allowing for the release of nitric oxide (NO). Tranilast (N-[3,4-dimethoxycinnamoyl]-anthranilic acid) is an antiallergic compound with suppressive effects on the activation of monocytes. 2. Here, we show that N9 murine microglial cells express iNOS mRNA and protein and release nitric oxide into the culture medium in response to IFN-gamma (200 u x ml(-1)) as measured by Northern and Western blot analyses and Griess assay. 3. Exposure to non-toxic doses of tranilast (30-300 microM) leads to a concentration-dependent inhibition of IFN-gamma-induced (200 u x ml(-1)) iNOS mRNA and protein expression. This is paralleled by a suppression of NO-release into the cell culture medium. 4. Inhibition of IFN-gamma-induced iNOS mRNA expression by tranilast is paralleled by an inhibition of nuclear factor-kappaB (NF-kappaB) activation and phosphorylation of inhibitory kappaB (IkappaB) as determined by Western blot analyses and NF-kappaB reporter gene assay. 5. These results suggest that tranilast-mediated suppression of microglial iNOS activity induced by IFN-gamma involves the inhibition of NF-kappaB-dependent iNOS mRNA expression.

Nitric oxide synthases: structure, function and inhibition

This review concentrates on advances in nitric oxide synthase (NOS) structure, function and inhibition made in the last seven years, during which time substantial advances have been made in our understanding of this enzyme family. There is now information on the enzyme structure at all levels from primary (amino acid sequence) to quaternary (dimerization, association with other proteins) structure. The crystal structures of the oxygenase domains of inducible NOS (iNOS) and vascular endothelial NOS (eNOS) allow us to interpret other information in the context of this important part of the enzyme, with its binding sites for iron protoporphyrin IX (haem), biopterin, L-arginine, and the many inhibitors which interact with them. The exact nature of the NOS reaction, its mechanism and its products continue to be sources of controversy. The role of the biopterin cofactor is now becoming clearer, with emerging data implicating one-electron redox cycling as well as the multiple allosteric effects on enzyme activity. Regulation of the NOSs has been described at all levels from gene transcription to covalent modification and allosteric regulation of the enzyme itself. A wide range of NOS inhibitors have been discussed, interacting with the enzyme in diverse ways in terms of site and mechanism of inhibition, time-dependence and selectivity for individual isoforms, although there are many pitfalls and misunderstandings of these aspects. Highly selective inhibitors of iNOS versus eNOS and neuronal NOS have been identified and some of these have potential in the treatment of a range of inflammatory and other conditions in which iNOS has been implicated.