Consecutive in vivo measurement of nitric oxide in transient forebrain ischemic rat under normothermia and hypothermia

Role of Nitric Oxide and Protein S-Nitrosylation in Ischemia-Reperfusion Injury

Ischemia-reperfusion injury (IRI) is a process in which damage is induced in hypoxic tissue when oxygen supply is resumed after ischemia. During IRI, restoration of reduced nitric oxide (NO) levels may alleviate reperfusion injury in ischemic organs. The protective mechanism of NO is due to anti-inflammatory effects, antioxidant effects, and the regulation of cell signaling pathways. On the other hand, it is generally known that S-nitrosylation (SNO) mediates the detrimental or protective effect of NO depending on the action of the nitrosylated target protein, and this is also applied in the IRI process. In this review, the effect of each change of NO and SNO during the IRI process was investigated.

Nitrite Protects Neurons Against Hypoxic Damage Through S-nitrosylation of Caspase-6

Aims: The coordination of neurons to execute brain functions requires plenty of oxygen. Thus, it is not surprising that the chronic hypoxia resulting from chronic obstructive pulmonary diseases (COPD) can cause neuronal damage. Injury in the cortex can give rise to anxiety and cognitive dysfunction. This study investigated what causes hypoxia-induced neuronal injury and what strategies might be used to protect neurons against such damage. Results: This study found that hypoxia in primary cortical neurons caused neurite retraction, a caspase-6-dependent process. The hypoxic stress activated caspase-6 within the neurite, leading to microtubule disassembly and neurite retraction. The effect of hypoxia on caspase-6 activation, microtubule disassembly, and neurite retraction was alleviated by nitrite treatment. The protective role of nitrite was further supported by the observation that the active-site Cys146 of caspase-6 was S-nitrosylated in hypoxic neuro-2a cells treated with nitrite. We further validated the beneficial effect of nitrite on neuronal function against hypoxic stress in vivo. Using the wild-type or Apo E^-/- mice exposed to chronic hypoxia as a model, we demonstrated that supplementing drinking water with nitrite suppressed active caspase-6 in the cortex of the brain, concomitant with the prevention of hypoxia-induced anxiety in the animals. Innovation: These results are the first evidence of a new pathway for the activation of caspase-6 and the first to indicate that nitrite can protect neurons against chronic hypoxic insult. Conclusion: Our findings suggest that nitrite holds great potential for the treatment of diseases such as COPD associated with hypoxia-induced neuronal injury.

Cerebroprotective Effect against Cerebral Ischemia of the Combined Extract of Oryza sativa and Anethum graveolens in Metabolic Syndrome Rats

The novel strategy against ischemic stroke in metabolic syndrome (MetS) targeting at oxidative stress and inflammation has gained attention due to the limitation of the current therapy. Due to the antioxidant and anti-inflammation of the combined extract of Oryza sativa and Anethum graveolens, the cerebroprotective effect against cerebral ischemia in MetS condition has been focused. Since no data were available, this study was set up to determine the effects of the combined extract of Oryza sativa L. and Anethum graveolens Linn. against ischemic stroke in the animal model of metabolic syndrome. The possible underlying mechanism was also further investigated. Male Wistar rats (180-220 g) were fed with high-carbohydrate high-fat diet (HCHF diet) to induce metabolic syndrome-like condition. Then, MetS rats were subjected to reperfusion injury at the right middle cerebral artery. The combined extract of O. sativa and A. graveolens (OA extract) at doses of 0.5, 5, and 50 mg/kg BW was fed once daily for 21 days. Neurological assessment was performed every 7 days throughout the experimental period. At the end of study, brain infarction volume, neuron and glial fibrillary acidic protein- (GFAP-) positive cell density, the oxidative stress status, the expressions of proinflammatory cytokines (NF-κB, IL-6), and eNOS in the cortical area together with the expression of VCAM-1 and the histological changes of common carotid artery were determined. It was found that OA extract decreased brain infarction, neurological score, oxidative stress status, and inflammatory mediators but increased eNOS expression in the cortical area; the increased VCAM-1 and intima-media thickness together with the reduction of lumen diameter of common carotid artery of MetS eats with MCAO were also mitigated by OA extract. These data suggest the cerebroprotective effect of OA, and the underlying mechanism may occur partly via the improvement of oxidative stress status, inflammation, and brain blood supply.

Functional deterioration of endothelial nitric oxide synthase after focal cerebral ischemia

Endothelial nitric oxide synthase (eNOS) dysfunction is related to secondary injury and lesion expansion after cerebral ischemia. To date, there are few reports about postischemic alterations in the eNOS regulatory system. The purpose of the present study was to clarify eNOS expression, Ser1177 phosphorylation, and monomer formation after cerebral ischemia. Male Wistar rats were subjected to transient focal cerebral ischemia. Endothelial nitric oxide synthase messenger RNA (mRNA) and protein expression increased ≈ 8-fold in the ischemic lesion. In the middle cerebral artery core, eNOS-Ser1177 phosphorylation increased 6 hours after ischemia; however, there was an approximately 90% decrease in eNOS-Ser1177 phosphorylation observed 24 hours after ischemia that continued until at least 7 days after ischemia. Endothelial nitric oxide synthase monomer formation also increased 24 and 48 hours after ischemia (P<0.05), and protein nitration progressed in parallel with monomerization. To assess the effect of a neuroprotective agent on eNOS dysfunction, we evaluated the effect of fasudil, a Rho-kinase inhibitor, on eNOS phosphorylation and dimerization. Postischemic treatment with fasudil suppressed lesion expansion and dephosphorylation and monomer formation of eNOS. In conclusion, functional deterioration of eNOS progressed after cerebral ischemia. Rho-kinase inhibitors can reduce ischemic lesion expansion as well as eNOS dysfunction in the ischemic brain.

Nitric oxide: considerations for the treatment of ischemic stroke

Some 40 years ago it was recognized by Furchgott and colleagues that the endothelium releases a vasodilator, endothelium-derived relaxing factor (EDRF). Later on, several groups identified EDRF to be a gas, nitric oxide (NO). Since then, NO was identified as one of the most versatile and unique molecules in animal and human biology. Nitric oxide mediates a plethora of physiological functions, for example, maintenance of vascular tone and inflammation. Apart from these physiological functions, NO is also involved in the pathophysiology of various disorders, specifically those in which regulation of blood flow and inflammation has a key role. The aim of the current review is to summarize the role of NO in cerebral ischemia, the most common cause of stroke.

General versus specific actions of mild-moderate hypothermia in attenuating cerebral ischemic damage

Mild or moderate hypothermia is generally thought to block all changes in signaling events that are detrimental to ischemic brain, including ATP depletion, glutamate release, Ca(2+) mobilization, anoxic depolarization, free radical generation, inflammation, blood-brain barrier permeability, necrotic, and apoptotic pathways. However, the effects and mechanisms of hypothermia are, in fact, variable. We emphasize that, even in the laboratory, hypothermic protection is limited. In certain models of permanent focal ischemia, hypothermia may not protect at all. In cases where hypothermia reduces infarct, some studies have overemphasized its ability to maintain cerebral blood flow and ATP levels, and to prevent anoxic depolarization, glutamate release during ischemia. Instead, hypothermia may protect against ischemia by regulating cascades that occur after reperfusion, including blood-brain barrier permeability and the changes in gene and protein expressions associated with necrotic and apoptotic pathways. Hypothermia not only blocks multiple damaging cascades after stroke, but also selectively upregulates some protective genes. However, most of these mechanisms are addressed in models with intraischemic hypothermia; much less information is available in models with postischemic hypothermia. Moreover, although it has been confirmed that mild hypothermia is clinically feasible for acute focal stroke treatment, no definite beneficial effect has been reported yet. This lack of clinical protection may result from suboptimal criteria for patient entrance into clinical trials. To facilitate clinical translation, future efforts in the laboratory should focus more on the protective mechanisms of postischemic hypothermia, as well as on the effects of sex, age and rewarming during reperfusion on hypothermic protection.

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.

In vivo electrochemical measurement of nitric oxide in corpus cavernosum penis

A wealth of pharmacological studies suggest that nitric oxide (NO) generated in the corpus cavernosum is a main molecular mediator of penile erection. However, the physiological levels of NO in the corpora and their possible changes during penile erection have remained unknown for want of suitable methodologies. We have adapted a voltammetric procedure, derived from Malinski's method, for assessing NO levels in the penis in vivo. Differential normal pulse voltammetry with carbon fiber electrodes (30 microm) coated with a polymeric porphyrin and Nafion was used to measure the NO oxidation current in the corpora cavernosa of urethane-anesthetized rats. The intracavernous pressure was monitored simultaneously. A NO oxidation peak was consistently detected at approximately 650 mV both in NO solutions and in the corpora in vivo. The changes in the NO signals observed in vitro were consistent with the concentration values measured by chemiluminescence. The NO signal recorded in vivo increased following cavernous nerve stimulation and was greatly decreased by intracavernous injections of several inhibitors of the neuronal and endothelial NO synthase isoenzymes. Such results agree with our previous studies using this methodology and substantiate further its validity for monitoring the physiological changes in NO levels in the penis.

Severe cerebral blood flow reduction inhibits nitric oxide synthesis

The purpose of this study was to investigate the relationship between cerebral blood flow (CBF) and nitric oxide (NO) synthesis using a rat model of transient forebrain ischemia of varying severity. Forebrain ischemia was induced for 30 min by occlusion of the bilateral common carotid arteries without hemorrhagic hypotension. The production of NO end-products (nitrite and nitrate) was measured by in vivo microdialysis, and CBF by the hydrogen clearance technique. Ischemia induced NO synthesis, although the increase in the quantity of NO end-products was not remarkable during the ischemic period but became prominent after reperfusion. Such increases were abolished by Nomega-nitro-L-arginine methyl ester (L-NAME), although 7-nitroindazole (7-NI) appeared to have only slight effects. The production of NO end-products during ischemia increased when the CBF during ischemia was less than 60 mL/100 g/min. In animals in which the CBF during ischemia was higher than 22.7 mL/100 g/min, the production of NO end-products increased gradually after the induction of ischemia and reached a peak during the reperfusion period, whereas in other animals in which the CBF during ischemia fell below 22.7 mL/100 g/min, the NO end-products decreased during ischemia and increased transiently after reperfusion. These results suggest that the increase in NO end-products is NO synthase (NOS)-dependent and that most of the increase is derived from endothelial NOS. It is also suggested that NO synthesis during ischemia is closely related to CBF, and that severe CBF reduction may inhibit NO synthesis.

Dynamics of nitric oxide during simulated ischaemia-reperfusion in rat striatal slices measured using an intrinsic biosensor, soluble guanylyl cyclase

Nitric oxide (NO) may act as a toxin in several neuropathologies, including the brain damage resulting from cerebral ischaemia. Rat striatal slices were used to determine the mechanism of enhanced NO release following simulated ischaemia and, for estimating the NO concentrations, the activity of guanylyl cyclase served as a biosensor. Exposure of the slices for 10 min to an oxygen- and glucose-free medium caused a 70% fall in cGMP levels. On recovery, cGMP increased 2-fold above basal, where it remained for 40 min before declining. The pattern of changes matched those of cGMP or NO oxidation products measured during and after brain ischaemia in vivo. The increase observed during the recovery period was blocked by inhibition of NO synthase or NMDA receptors and was curtailed by tetrodotoxin, implying that it was caused by glutamate release leading to activation of the NMDA receptor-NO synthase pathway. Calibration of the cGMP levels against NO-stimulated guanylyl cyclase yielded a basal NO concentration of 0.6 nm. The peak NO concentration achieved on recovery from simulated ischaemia was estimated as 0.8 nm. These values are compatible with the low micromolar concentrations of NO oxidation products (chiefly nitrate) found by microdialysis in vivo, providing the NO inactivation rate (forming nitrate) is accounted for. NO at a concentration around 1 nm is unlikely to be toxic to cells. However, if the NO inactivation mechanism were to fail (as it can) the NO production rate normally providing only subnanomolar NO could readily generate toxic (microM) NO concentrations.

Measurement of nitric oxide and brain tissue oxygen tension in patients after severe subarachnoid hemorrhage

OBJECTIVE

Nitric oxide (NO), one of the most powerful endogenous vasodilators, is thought to play a major role in the development of delayed vasospasm in patients with subarachnoid hemorrhage (SAH). However, the role of the production of cerebral NO in patients with SAH is not known. In other SAH studies, NO metabolites such as nitrite and nitrate have been demonstrated to be decreased in cerebrospinal fluid and in plasma.

METHODS

In this study, a microdialysis probe was used, along with a multiparameter sensor, to measure NO metabolites, brain tissue oxygen tension, brain tissue carbon dioxide tension, and pH in the cortex of patients with severe SAH who were at risk for developing secondary brain damage and vasospasm. NO metabolites, glucose, and lactate were analyzed in the dialysates to determine the time course of NO metabolite changes and to test the interrelationship between the analytes and clinical variables.

RESULTS

Brain tissue oxygen tension was strongly correlated to dialysate nitrate and nitrite (r2 = 0.326; P < 0.001); however, no correlation was noted between brain tissue oxygen tension and NO metabolites in cerebrospinal fluid (r2 = 0.018; P = 0.734). No significant correlation between NO production, brain tissue carbon dioxide tension, and dialysate glucose and lactate was observed.

CONCLUSION

Cerebral ischemia and compromised substrate delivery are often responsible for high morbidity rates and poor outcomes after SAH. The relationship between brain tissue oxygen and cerebral NO metabolites that we demonstrate suggests that substrate delivery and NO are linked in the pathophysiology of vasospasm after SAH.

Glial reaction in the hippocampus after global cardiogenic ischemia

Many experimental surgerical procedures have been perfomed in the analyse of the phenomenon of brain trophism and plasticity, however undesirable intercorrence can occour leading to specific changes in the results that should be taken into attention. To study this issue we have promoted a transient cardiogenic interruption of the blood flow together with a transient occlusion of the bilateral common carotid arteries (2VO) in rats and analysed the state of activation of astrocyte and microglia by means of the glial fibrillary acidic protein (GFAP) and OX42 immunohistochemistry, respectively. Rats were submitted to incomplete global cerebral ischemia (IGCI) by occlusion of the bilateral carotid arteries for 30 minutes. During the IGCI surgical, some rats received a higher dose of the chloral hydrate anaesthesia which promoted a cardiogenic interruption of the blood flow (CIBF) for a period of 10 minutes followed by and prompt reperfusion. During that period, animals were submited to a cardiac massage and ventilated. Sham operation were made in control animals. Rats were killed and their brains processed 14 days after the surgery. The animals that have received a IGCI showed a slight astroglial and microglial reaction in all subfields of the hippocampal formation, however the animal submitted to CIBF showed a massive infiltration of the reactive astrocyte and microglia in CA1 subfield. This results demonstrated that a transient occlusion of the bilateral common carotid arteries leads to activation of glial cells in the hippocampus, however this response can be remarkable changed in animal developing a transient systemic hypoperfusion during surgery. Thus, an accurated monitoration of the hemodinamic condition of the animal has to be done in experimental models of brain ischemia and the results have to be analysed in view of this aspect.

Oxygen-sensing microdialysis probe for in vivo use

Electrochemical conditions were optimized to allow the metal tube used for the shaft of commercial microdialysis (MD) probes to be coated with gold. In in vitro tests with phosphate-buffered Ringer's solution using double differential pulse amperometry (DDPA), the gold-coated shafts were capable of specifically measuring the reduction of oxygen and the oxidation of ascorbic acid in the presence of high concentrations of potentially interfering endogenous substances. By using fixed-potential amperometry (FPA), the gold-plated shaft also measured oxygen with minimal interference from high concentrations of potentially interfering endogenous substances. Concentric design MD probes were constructed that used a metal shaft (O.D = 0.4 mm), fused silica inlet and outlet tubes, and a 1.5 mm dialyzing membrane (O.D = 0.2 mm). A 0.5-0.7 mm gold collar was electroplated onto the metal shaft approximately 0.5 mm above the dialyzing membrane. The nongold outer surface of the MD probe was coated with an insulating polymer. In vivo tests demonstrated that DDPA was not suitable for use with this gold microdialyzing electrode (GMDE). However, brain oxygen levels were satisfactorily measured using FPA. In urethane-anesthetized rats, the reduction current to oxygen in the striatum was increased by brief (1 min) inhalation of O2 or CO2 and decreased by inhalation of N2. Transient application of noxious stimuli (foot pinch) increased cerebral O2, whereas bilateral carotid artery occlusion and death decreased striatal O2. The responses of the GMDE were indistinguishable from the reduction current simultaneously measured from a conventional carbon fiber electrode implanted adjacent to the gold-plated area of the MD shaft. Basal levels of striatal O(2) were 20 +/- 5 microM (n = 4) for the GMDE and 30 +/- 11 microM (n = 3) for the carbon fiber. The GMDE was robust and could be used for at least three animals. This technique can be used to provide information about the oxygen status of the tissue adjacent to the dialyzing membrane without the need for implantation of an additional electrode.

Intracerebral microdialysis and its clinical application: a review

In vivo intracerebral microdialysis is an important neurochemical technique that has been used extensively in the experimental setting. Relatively recently, techniques have been developed to utilize this method in human subjects. The past decade has seen the advent of clinical investigations utilizing in vivo microdialysis in a number of neuropathological states. This review summarizes the principles of in vivo microdialysis techniques, as applied to humans, while discussing the significance of recent investigations for future clinical development.

Subacute but not acute generation of nitric oxide in focal cerebral ischemia

BACKGROUND AND PURPOSE

Excessive release of nitric oxide (NO) has been implicated in the pathophysiology of neurodegeneration in ischemic stroke. We compared intracerebral release of indicators of NO generation at the acute and subacute stages of transient focal cerebral ischemia.

METHODS

In vivo microdialysis in the rat striatum was performed at the acute (first hours) and subacute (after 24 or 48 hours) stages of cerebral ischemia or sham operation to monitor intracerebral release of the stable NO metabolites nitrite and nitrate.

RESULTS

Whereas only a nonsignificant trend toward increased release of these NO metabolites was evidenced in acute cerebral ischemia, a significant NO generation was observed subacutely, 48 hours after induction of cerebral ischemia. Aminoguanidine, a selective inhibitor of inducible NO synthase, suppressed this delayed release of nitrite and nitrate.

CONCLUSIONS

Whereas these observations do not support a major NO generation in acute cerebral ischemia, they indicate an inducible NO synthase-dependent NO generation predominantly at the subacute phase of ischemic neurodegeneration. Therefore, NO generation may play a pathophysiological role in delayed ischemic neurodegeneration.

Different nitric oxide synthase inhibitors cause rapid and differential alterations in the ligand-binding capacity of transmitter receptors in the rat cerebral cortex

Inhibitors of nitric oxide (NO) synthesis reduce postlesional neuronal death during reperfusion injury by reducing the NO-mediated increase in excitatory neurotransmitter-release. The protective effects of various NO-synthase (NOS) inhibitors differ due to their isoform selectivity. The effects of NO-mediated excessive neurotransmitter supply are transmitted via specific neurotransmitter receptors expressed by the target cells. We report changes in the ligand-binding of different excitatory and inhibitory neurotransmitter-receptors studied by in vitro receptor autoradiography after in vivo-application of NOS-inhibitors. Since the constitutively expressed neuronal NOS-I is area-specifically distributed within the rat cortex, numerous cortical areas were studied in non-lesioned rats, in order to analyze the area-specific effects of NOS-inhibitors. The results showed that the NOS-I-specific inhibitor 7-nitroindazole increased binding of 3H-muscimol, 3H-pirenzepine and 3H-kainate, whereas the less isoform-specific, general NOS-inhibitor L-nitroarginine increased binding of 3H-muscimol and 3H-AMPA in most cortical areas, leaving 3H-kainate binding almost unchanged. The water soluble L-nitroarginine-methylester caused similar effects to those of L-nitroarginine which changed over a period of chronic treatment. The inhibitory GABAA-receptors were increased after NOS-inhibition in most cortical areas, whereas binding of 3H-Oxotremorine-M (acetylcholine receptors), 3H-MK-801 (NMDA-receptors) and 3H-AMPA (AMPA receptors) was affected differently among the cortical areas. Strongest alterations of ligand-binding capacity after administration of NOS-inhibitors were seen in cortical areas known to contain the highest packing densities of NOS-I-positive interneurons such as the piriform and entorhinal cortices, indicating that, in normal animals, neurotransmission and probably cognitive information processing would be affected by the pharmacological modulation of nitric oxide production.