Cerebroprotective effects of aminoguanidine in a rodent model of stroke

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.

The Polyamine Spermine Potentiates the Propagation of Negatively Charged Molecules through the Astrocytic Syncytium

The interest in astrocytes, the silent brain cells that accumulate polyamines (PAs), is growing. PAs exert anti-inflammatory, antioxidant, antidepressant, neuroprotective, and other beneficial effects, including increasing longevity in vivo. Unlike neurons, astrocytes are extensively coupled to others via connexin (Cx) gap junctions (GJs). Although there are striking modulatory effects of PAs on neuronal receptors and channels, PA regulation of the astrocytic GJs is not well understood. We studied GJ-propagation using molecules of different (i) electrical charge, (ii) structure, and (iii) molecular weight. Loading single astrocytes with patch pipettes containing membrane-impermeable dyes, we observed that (i) even small molecules do not easily permeate astrocytic GJs, (ii) the ratio of the charge to weight of these molecules is the key determinant of GJ permeation, (iii) the PA spermine (SPM) induced the propagation of negatively charged molecules via GJs, (iv) while no effects were observed on propagation of macromolecules with net-zero charge. The GJ uncoupler carbenoxolone (CBX) blocked such propagation. Taken together, these findings indicate that SPM is essential for astrocytic GJ communication and selectively facilitates intracellular propagation via GJs for negatively charged molecules through glial syncytium.

Inducible nitric oxide synthase: Regulation, structure, and inhibition

A considerable number of human diseases have an inflammatory component, and a key mediator of immune activation and inflammation is inducible nitric oxide synthase (iNOS), which produces nitric oxide (NO) from l-arginine. Overexpressed or dysregulated iNOS has been implicated in numerous pathologies including sepsis, cancer, neurodegeneration, and various types of pain. Extensive knowledge has been accumulated about the roles iNOS plays in different tissues and organs. Additionally, X-ray crystal and cryogenic electron microscopy structures have shed new insights on the structure and regulation of this enzyme. Many potent iNOS inhibitors with high selectivity over related NOS isoforms, neuronal NOS, and endothelial NOS, have been discovered, and these drugs have shown promise in animal models of endotoxemia, inflammatory and neuropathic pain, arthritis, and other disorders. A major issue in iNOS inhibitor development is that promising results in animal studies have not translated to humans; there are no iNOS inhibitors approved for human use. In addition to assay limitations, both the dual modalities of iNOS and NO in disease states (ie, protective vs harmful effects) and the different roles and localizations of NOS isoforms create challenges for therapeutic intervention. This review summarizes the structure, function, and regulation of iNOS, with focus on the development of iNOS inhibitors (historical and recent). A better understanding of iNOS' complex functions is necessary before specific drug candidates can be identified for classical indications such as sepsis, heart failure, and pain; however, newer promising indications for iNOS inhibition, such as depression, neurodegenerative disorders, and epilepsy, have been discovered.

An Evidence-Based Review of Related Metabolites and Metabolic Network Research on Cerebral Ischemia

In recent years, metabolomics analyses have been widely applied to cerebral ischemia research. This paper introduces the latest proceedings of metabolomics research on cerebral ischemia. The main techniques, models, animals, and biomarkers of cerebral ischemia will be discussed. With analysis help from the MBRole website and the KEGG database, the altered metabolites in rat cerebral ischemia were used for metabolic pathway enrichment analyses. Our results identify the main metabolic pathways that are related to cerebral ischemia and further construct a metabolic network. These results will provide useful information for elucidating the pathogenesis of cerebral ischemia, as well as the discovery of cerebral ischemia biomarkers.

Inhibition of autophagy and glycolysis by nitric oxide during hypoxia-reoxygenation impairs cellular bioenergetics and promotes cell death in primary neurons

Excessive nitric oxide (NO) production is known to damage mitochondrial proteins and the autophagy repair pathway and so can potentially contribute to neurotoxicity. Accordingly, we hypothesized that protection against protein damage from reactive oxygen and nitrogen species under conditions of low oxygen by the autophagy pathway in neurons would be impaired by NO and enhance bioenergetic dysfunction. Rat primary cortical neurons had the same basal cellular respiration in hypoxia as in normoxia, whereas NO-exposed cells exhibited a gradual decrease in mitochondrial respiration in hypoxia. Upon reoxygenation, the respiration in NO-treated cells did not recover to prehypoxic levels. Hypoxia-reoxygenation in the presence of NO was associated with inhibition of autophagy, and the inability to recover during reoxygenation was exacerbated by an inhibitor of autophagy, 3-methyladenine. The effects of hypoxia could be recapitulated by inhibiting glycolytic flux under normoxic conditions. Under both normoxic and hypoxic conditions NO exposure induced immediate stimulation of glycolysis, but prolonged NO exposure, associated with irreversible inhibition of mitochondrial respiration in hypoxia, inhibited glycolysis. Importantly, we found that NO inhibited basal respiration under normoxic conditions only when glucose was absent from the medium or glycolysis was inhibited by 2-deoxy-d-glucose, revealing a novel NO-dependent mechanism for the inhibition of mitochondrial respiration that is modulated by glycolysis. Taken together these data suggest an oxygen-dependent interaction between mitochondrial respiration, glycolysis, and autophagy in protecting neuronal cells exposed to NO. Importantly, they indicate that mitochondrial dysfunction is intimately linked to a failure of glycolytic flux induced by exposure to NO. In addition, these studies provide new insights into the understanding of how autophagy and NO may play interactive roles in neuroinflammation-induced cellular damage, which is pertinent to our understanding of the pathology of neurodegenerative diseases in which excessive NO is generated.

Anti-fibrotic cardio protective efficacy of aminoguanidine against streptozotocin induced cardiac fibrosis and high glucose induced collagen up regulation in cardiac fibroblasts

This study mainly focuses on cardio protective anti-fibrotic activity of aminoguanidine against streptozotocin induced cardiac fibrosis and high glucose induced collagen accumulation in cardiac fibroblasts. Dysregulation of matrix metalloproteinase especially 2 and 9 were considered to be responsible for the abnormal collagen deposition, which resulting improper cardiac contractile function in diabetic mice. Mice received a single dose of streptozotocin (100 mg/kg) through tail vein to induce diabetes. Normal and diabetic mice received aminoguanidine orally (100 mg/kg/day) throughout the study period of 8 weeks. Cardiac fibroblasts cultured and exposed to high glucose, aminoguanidine and both for 48 h. Collagen quantitatively estimated in both in vivo and in vitro models. Altered structural changes were studied using the Masson tri-chrome staining, TEM images of cardiac sections. Increased collagen and metalloproteinase activities were confirmed using gelatin zymography, western blotting and gene expression studies. The exact mechanism responsible for high glucose induced collagen up regulation in diabetic heart was incompletely understood. From this above in vivo and in vitro results, we conclude that, the cardio protective anti fibrotic activity of amino guanidine was mainly attributed by exhibiting the inhibitory efficacy against streptozotocin and high glucose induced collagen accumulation probably by inhibiting high glucose altered metalloproteinase-2 and -9 activities.

Reactive oxygen species and inhibitors of inflammatory enzymes, NADPH oxidase, and iNOS in experimental models of Parkinson's disease

Reactive oxygen species (ROSs) are emerging as important players in the etiology of neurodegenerative disorders including Parkinson's disease (PD). Out of several ROS-generating systems, the inflammatory enzymes nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and inducible nitric oxide synthase (iNOS) were believed to play major roles. Mounting evidence suggests that activation of NADPH oxidase and the expression of iNOS are directly linked to the generation of highly reactive ROS which affects various cellular components and preferentially damage midbrain dopaminergic neurons in PD. Therefore, appropriate management or inhibition of ROS generated by these enzymes may represent a therapeutic target to reduce neuronal degeneration seen in PD. Here, we have summarized recently developed agents and patents claimed as inhibitors of NADPH oxidase and iNOS enzymes in experimental models of PD.

Harmful and beneficial effects of inflammation after spinal cord injury: potential therapeutic implications

Spinal cord injury (SCI) results in immediate damage followed by a secondary phase of tissue damage that occurs over a period of several weeks. The mechanisms underlying this secondary damage are multiple and not fully understood. A number of studies suggest that the local inflammatory response in the spinal cord that occurs after SCI contributes importantly to secondary damage. This response is mediated by cells normally found in the central nervous system (CNS) as well as infiltrating leukocytes. While the inflammatory response mediated by these cells is required for efficient clearance of tissue debris, and promotes wound healing and tissue repair, they also release various factors that can be detrimental to neurons, glia, axons, and myelin. In this chapter we provide an overview of the inflammatory response at the cell and molecular level after SCI, and review the current state of knowledge about its contribution to tissue damage and repair. Additionally, we discuss how some of this work is leading to the development and testing of drugs that modulate inflammation to treat acute SCI in humans.

Intraperitoneal aminoguanidine improves sciatic nerve ischemia-reperfusion injury in male sprague-dawley rats

The present work was designed to investigate the potential protective effects of post-ischemic treatment with aminoguanidine (AG) on sciatic nerve ischemia/reperfusion (I/R) injury in rat. Seventy-two rats were divided into 12 groups (n = 6). We used ischemia model in these groups by occluding the right common iliac and femoral arteries for 3 h with a silk suture 6-0 using slipknot technique. Treatment groups (2, 4, 6, 8, 10, and 12) received 150 mg/kg AG intraperitoneally 24 h after induction of ischemia. After certain time intervals of reperfusion (2, 4, 7, 14, and 28 days), the function of the hind limb was assessed using behavioral scores based on gait, racing reflex, toe spread, pinch sensitivity, paw position, and grasp. After euthanasia, sciatic nerves were removed at the end of reperfusion times and sections were cut at 5 μm, then were stained for light microscopy studies and graded for ischemic fiber degeneration (IFD), edema, and apoptosis. Maximal behavioral deficit occurred at 7 days of reperfusion. The comparison of behavioral score pertaining to the control and AG groups revealed significant differences and showed also a better time course in recovery (P < 0.05). Other than 3 and 4 groups, the amount of edema in AG treatment groups showed significant differences compared with control groups (P < 0.05). IFD was also significantly decreased in the AG treatment groups than controls. Most importantly, I/R-induced apoptosis were improved significantly on the 4th, 7(th), and 14th days of reperfusion in AG-treated groups compared to controls. In conclusion, our findings suggest that post-ischemic administration of AG exhibits protective effect against sciatic nerve I/R injury.

Extracellular spermine exacerbates ischemic neuronal injury through sensitization of ASIC1a channels to extracellular acidosis

Ischemic brain injury is a major problem associated with stroke. It has been increasingly recognized that acid-sensing ion channels (ASICs) contribute significantly to ischemic neuronal damage, but the underlying mechanism has remained elusive. Here, we show that extracellular spermine, one of the endogenous polyamines, exacerbates ischemic neuronal injury through sensitization of ASIC1a channels to extracellular acidosis. Pharmacological blockade of ASIC1a or deletion of the ASIC1 gene greatly reduces the enhancing effect of spermine in ischemic neuronal damage both in cultures of dissociated neurons and in a mouse model of focal ischemia. Mechanistically, spermine profoundly reduces desensitization of ASIC1a by slowing down desensitization in the open state, shifting steady-state desensitization to more acidic pH, and accelerating recovery between repeated periods of acid stimulation. Spermine-mediated potentiation of ASIC1a activity is occluded by PcTX1 (psalmotoxin 1), a specific ASIC1a inhibitor binding to its extracellular domain. Functionally, the enhanced channel activity is accompanied by increased acid-induced neuronal membrane depolarization and cytoplasmic Ca(2+) overload, which may partially explain the exacerbated neuronal damage caused by spermine. More importantly, blocking endogenous spermine synthesis significantly attenuates ischemic brain injury mediated by ASIC1a but not that by NMDA receptors. Thus, extracellular spermine contributes significantly to ischemic neuronal injury through enhancing ASIC1a activity. Our data suggest new neuroprotective strategies for stroke patients via inhibition of polyamine synthesis and subsequent spermine-ASIC interaction.

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.

Drug interactions

Drugs for allergy are often taken in combination with other drugs, either to treat allergy or other conditions. In common with many pharmaceuticals, most such drugs are subject to metabolism by P450 enzymes and to transmembrane transport. This gives rise to considerable potential for drug-drug interactions, to which must be added consideration of drug-diet interactions. The potential for metabolism-based drug interactions is increasingly being taken into account during drug development, using a variety of in silico and in vitro approaches. Prediction of transporter-based interactions is not as advanced. The clinical importance of a drug interaction will depend upon a number of factors, and it is important to address concerns quantitatively, taking into account the therapeutic index of the compound.

The role of polyamine metabolism in neuronal injury following cerebral ischemia

Stroke is a leading cause of morbidity and mortality in the US, with secondary damage following the initial insult contributing significantly to overall poor outcome. Prior investigations have shown that the metabolism of certain polyamines such as spermine, spermidine, and putrescine are elevated in ischemic parenchyma, resulting in an increase in their metabolite concentration. Polyamine metabolites tend to be cytotoxic, leading to neuronal injury in the penumbra following stroke and expansion of the area of infarcted tissue. Although the precise mechanism is unclear, the presence of reactive aldehydes produced through polyamine metabolism, such as 3-aminopropanal and acrolein, have been shown to correlate with the incidence of cerebral vasospasm, disruption of oxidative metabolism and mitochondrial functioning, and disturbance of cellular calcium ion channels. Regulation of the polyamine metabolic pathway, therefore, may have the potential to limit injury following cerebral ischemia. To this end, we review this pathway in detail with an emphasis on clinical applicability.

Neuronal RAGE expression modulates severity of injury following transient focal cerebral ischemia

Inflammation has a significant role in the neurological injury that follows stroke. The receptor for advanced-glycation end products (RAGE) is a multiligand member of the immunoglobulin superfamily that has been implicated in multiple neuronal and inflammatory stress processes. To directly test the role of neuronal RAGE in stroke, we employed two cohorts of transgenic mice, one over-expressing full-length functional human RAGE in neurons, and the other a human RAGE transgene in which deletion of the cytoplasmic domain of the receptor in neurons suppresses signal transduction stimulated by ligands (referred to as dominant negative or DN-RAGE). We found a statistically significant increase in stroke volume in the RAGE over-expressing cohort compared to normal controls, and a trend towards decreased stroke volume in the DN RAGE cohort. These results indicate that RAGE signaling directly contributes to pathology in cerebral ischemia.

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.

Structural and functional recovery elicited by combined putrescine and aminoguanidine treatment after aspirative lesion of the fimbria-fornix and overlying cortex in the adult rat

Damage to the adult CNS often causes permanent deficits. Based on a lesion model of septohippocampal pathway aspiration in the rat, we attempted to promote neuronal cell survival and post-traumatic recovery by using a pharmacological treatment combining aminoguanidine and putrescine (AGP). The functional recovery was followed over 15 weeks before morphological analysis. AGP treatment produced a persistent attenuation (approximately 50%) of the lesion-induced hyperactivity, a reduction (approximately 60%) in the sensorimotor impairments and an improved performance in the water-maze task which did not, however, rely upon improved memory capabilities. AGP weakened the lesion-induced decrease in ChAT-positive neurons in the medial septum and the extent of thalamic retrograde necrosis (by approximately 30% in each case) and resulted in a partial cholinergic reinnervation of the dentate gyrus. These promising results support the idea that coadministration of putrescine and aminoguanidine might become a potent way to foster structural and functional recovery (or compensation) in the adult mammalian CNS after injury.

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.

Decreased focal inflammatory response by G-CSF may improve stroke outcome after transient middle cerebral artery occlusion in rats

Recent studies have shown that administration of granulocyte colony-stimulating factor (G-CSF) is neuroprotective. However, the precise mechanisms of the neuroprotective effect of G-CSF are not entirely known. We carried out 90-min transient middle cerebral occlusion (tMCAO) of rats. The rats were injected with vehicle or G-CSF (50 mug/kg) immediately after reperfusion and sacrificed 8, 24, or 72 hr later. 2,3,5-Triphenyltetrazolium chloride (TTC) staining was carried out using brain sections of 72 hr, and immunohistochemistry was carried out with those of 8, 24, and 72 hr. TTC-staining showed a significant reduction of infarct volume in the G-CSF-treated group (**P < 0.01). Immunohistochemistry showed a significant decrease of the number of cells expressing tumor necrosis factor-alpha (TNF-alpha) at 8-72 hr, transforming growth factor-beta (TGF-beta) and inducible nitric oxide synthase (iNOS) at 24 and 72 hr after tMCAO in the peri-ischemic area (*P < 0.05 each). Our data suggest that the suppression of inflammatory cytokines and iNOS expression may be one mechanism of neuroprotection by G-CSF.

Aldehyde load in ischemia-reperfusion brain injury: neuroprotection by neutralization of reactive aldehydes with phenelzine

In ongoing studies of the neuroprotective properties of monoamine oxidase inhibitors, we found that phenelzine provided robust neuroprotection in the gerbil model of transient forebrain ischemia, with drug administration delayed up to 3 h post reperfusion. Since ischemia-reperfusion brain injury is associated with large increases in the concentrations of reactive aldehydes in the penumbra area, we investigated if the hydrazine function of phenelzine was capable of sequestering reactive aldehydes. Both aminoaldehydes and acrolein are generated from the metabolism of polyamines to putrescine by polyamine oxidase. These toxic aldehydes in turn compromise mitochondrial and lysosomal integrity and initiate apoptosis and necrosis. Previous studies have demonstrated that pharmacological neutralization of reactive aldehydes via the formation of thioacetal derivatives results in significant neuroprotection in ischemia-reperfusion injury, in both focal and global ischemia models. In our studies of acrolein and 3-aminopropanal toxicity, using an immortalized retinal cell line, we found that aldehyde sequestration with phenelzine was neuroprotective. The neuroprotection observed with phenelzine is in agreement with previous studies of aldehyde sequestering agents in the treatment of ischemia-reperfusion brain injury and supports the concept that "aldehyde load" is a major factor in the delayed cell losses of the ischemic penumbra.

Polyamine and aminoguanidine treatments to promote structural and functional recovery in the adult mammalian brain after injury: a brief literature review and preliminary data about their combined administration

The regeneration potential of the adult mammalian central nervous system (CNS) is very modest, due to, among other factors, the presence of either a glial scar, or myelin-associated regeneration inhibitors such as Nogo-A, MAG and OMgp, which all interact with the same receptor (NgR). After a brief review of the key proteins (Rho and PKC) implicated in NgR-mediated signalling cascades, we will tackle the implications of cAMP and Arginase I in overcoming myelin growth-inhibitory influence, and then will focus on the effects of polyamines and aminoguanidine to propose (and to briefly support this proposal by our own preliminary data) that their association might be a potent way to enable functionally-relevant regeneration in the adult mammalian CNS.

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.

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.

Lack of iNOS induction in a severe model of transient focal cerebral ischemia in rats

Calcium-independent nitric oxide synthase (NOS) activity has been reported in ischemic brains and usually attributed to the inducible isoform, iNOS. Because calcium-independent mechanisms have recently been shown to regulate the constitutive calcium-dependent NOS, we proposed to confirm the presence of iNOS activity in our model of transient focal cerebral ischemia in rats. Our initial results showed that, in our model, ischemia induced an important increase in brain calcium concentration. Consequently, the determination of calcium-independent NOS activity required a higher concentration of calcium chelator than classically used in the NOS assay. In these conditions, calcium-independent NOS activity was not observed after ischemia. Moreover, our ischemia was associated with neither iNOS protein expression, measured by Western blotting, nor increased NO production, evaluated by its metabolites (nitrate/nitrite). Our results demonstrate that iNOS activity may be overestimated due to increased brain calcium concentration in ischemic conditions and also that iNOS is not systematically induced after cerebral ischemia.

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.

Perioperative Plasma Concentrations of Stable Nitric Oxide Products Are Predictive of Cognitive Dysfunction After Laparoscopic Cholecystectomy

In this study our objectives were to determine the incidence of postoperative cognitive dysfunction (POCD) after laparoscopic cholecystectomy under sevoflurane anesthesia in patients aged >40 and <85 yr and to examine the associations between plasma concentrations of i) S-100beta protein and ii) stable nitric oxide (NO) products and POCD in this clinical setting. Neuropsychological tests were performed on 42 ASA physical status I-II patients the day before, and 4 days and 6 wk after surgery. Patient spouses (n = 13) were studied as controls. Cognitive dysfunction was defined as deficit in one or more cognitive domain(s). Serial measurements of serum concentrations of S-100beta protein and plasma concentrations of stable NO products (nitrate/nitrite, NOx) were performed perioperatively. Four days after surgery, new cognitive deficit was present in 16 (40%) patients and in 1 (7%) control subject (P = 0.01). Six weeks postoperatively, new cognitive deficit was present in 21 (53%) patients and 3 (23%) control subjects (P = 0.03). Compared with the "no deficit" group, patients who demonstrated a new cognitive deficit 4 days postoperatively had larger plasma NOx at each perioperative time point (P < 0.05 for each time point). Serum S-100beta protein concentrations were similar in the 2 groups. In conclusion, preoperative (and postoperative) plasma concentrations of stable NO products (but not S-100beta) are associated with early POCD. The former represents a potential biochemical predictor of POCD.

Therapeutic potential of breakers of advanced glycation end product-protein crosslinks

Long-lived structural proteins, collagen and elastin, undergo continual non-enzymatic crosslinking during aging and in diabetic individuals. This abnormal protein crosslinking is mediated by advanced glycation end products (AGEs) generated by non-enzymatic glycosylation of proteins by glucose. The AGE-derived protein crosslinking of structural proteins contributes to the complications of long-term diabetes such as nephropathy, retinopathy, and neuropathy. AGE-crosslinks have also been implicated in age-related cardiovascular diseases. Potential treatment strategies for these AGE-derived complications include prevention of AGE-formation and breaking of the existing AGE-crosslinks. The therapeutic potential of the AGE-inhibitor, pimagedine (aminoguanidine), has been extensively investigated in animal models and in Phase 3 clinical trials. This review presents the pre-clinical and clinical studies using ALT-711, a highly potent AGE-crosslink breaker that has the ability to reverse already-formed AGE-crosslinks. Oral administration of ALT-711 has resulted in a rapid improvement in the elasticity of stiffened myocardium in experimental animals. Topical administration of ALT-711 was effective in improving the skin hydration of aged rats. The therapeutic potential of crosslink breakers for cardiovascular complications and dermatological alterations associated with aging and diabetes is discussed.

Evaluation of MCAO stroke models in normotensive rats: standardized neocortical infarction by the 3VO technique

The temporary three-vessel occlusion (3VO) technique with a surgical approach for middle cerebral artery (MCA) produces consistent cerebral infarction in the neocortex in normotensive rats. The intraluminal thread-occlusion technique with an endovascular approach targeting the MCA occlusion (MCAO) is more widely used since it does not require complicated intracranial procedures. The aim of this study was to review the methods/models for MCAO stroke in normotensive rats and to evaluate a 3VO stroke model that provides consistent degrees and variance of cortical stroke injury for additional discussion. First, we analyzed a model with modified temporary 3VO technique requiring less complicated procedures than the temporary 3VO model, i.e., temporary occlusion of the bilateral common carotid arteries (CCAs) superimposed on a permanent occlusion of the MCA, in Sprague-Dawley rats or C57BL/6J mice. In the microvascular tissue (cerebral) perfusion study, significant reductions in regional cerebral perfusion during the 3VO accompanied a rapid return to baseline after release of the CCAs, showing that the technique induces temporary focal ischemia. The average sizes and variances of the neocortical infarction in this model, together with those in the other normotensive rat models caused by the 3VO technique in the literature, indicated a standard size and variance of infarcted lesion in the control groups relative to the specific ischemic period. However, stroke injuries in the neocortex induced by the thread occlusion technique showed greater variability with less consistent lesion sizes. Inclusion/exclusion criteria to avoid inappropriate cases with too mild (no/faint infarction) or too great (huge/fatal infarction) severity in the ischemic injury may differ between laboratories in the thread occlusion model.

Mechanisms of salt-sensitive hypertension: role of renal medullary inducible nitric oxide synthase

The goal of this study was to determine the role of renal medullary inducible nitric oxide synthase (iNOS) in the arterial pressure, renal hemodynamic, and renal excretory changes that occur in Dahl/Rapp salt-resistant (R) and salt-sensitive (S) rats during high Na intake. Forty R and S rats, equipped with indwelling arterial, venous, and renal medullary catheters, were subjected to high (8%) Na intake, and selective iNOS inhibition was achieved with continuous intravenous or renal medullary interstitial infusion of aminoguanidine (AG; 3.075 mg. kg(-1). h(-1)). After 5 days of AG, mean arterial pressure increased to 132 +/- 2% control in the S rats with high Na intake and intramedullary AG compared with 121 +/- 4% control (P < 0.05) in the S rats with high Na intake alone and 121 +/- 2% control (P < 0.05) in the S rats with high Na intake and intravenous AG. AG did not change arterial pressure in R rats. AG also caused little change in renal hemodynamics, urinary Na, or H(2)O excretion or ACh-induced aortic vasorelaxation in R or S rats. The data suggest that during high Na intake, nitric oxide produced by renal medullary iNOS helps to prevent excessive increases in arterial pressure in the Dahl S rat but not the R rat.

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.

Neuroprotection in cerebral ischemia by neutralization of 3-aminopropanal

Cerebral ischemia stimulates increased activity of polyamine oxidase, a ubiquitous enzyme that catabolizes polyamines to produce 3-aminopropanal. 3-Aminopropanal is a reactive aldehyde that mediates progressive neuronal necrosis and glial apoptosis. Here we report that increased levels of 3-aminopropanal-modified protein levels in humans after aneurysmal subarachnoid hemorrhage correlate with the degree of cerebral injury as measured by admission Hunt/Hess grade. In vitro screening of clinically approved drugs reveals that N-2-mercaptopropionyl glycine (N-2-MPG), an agent clinically approved for prevention of renal stones in patients with cysteinuria, significantly inhibits the cytotoxicity of 3-aminopropanal. N-2-MPG reacts with 3-aminopropanal to yield a nontoxic thioacetal adduct, as confirmed by electrospray ionization mass spectroscopy. Administration of N-2-MPG in clinically relevant doses to rats significantly reduces cerebral 3-aminopropanal-modified protein immunoreactivity and infarct volume in a standardized model of middle cerebral artery occlusion, even when the agent is administered after the onset of ischemia. These results implicate 3-aminopropanal as a therapeutic target for cerebral ischemia.

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.

The polyamine oxidase inactivator MDL 72527

Polyamine oxidase is a FAD-dependent amine oxidase, which is constitutively expressed in nearly all tissues of the vertebrate organism. In 1985, N1,N4-bis(2,3-butadienyl)-1,4-butanediamine (MDL 72527) was designed as a selective enzyme-activated irreversible inhibitor of polyamine oxidase (EC 1.5.3.11). It inactivates, at micromolar concentration and time-dependently, the enzyme in cells, as well as in all organs of experimental animals, without inhibiting other enzymes of polyamine metabolism. MDL 72527 served during nearly two decades as a unique tool in the elucidation of the physiological roles of polyamine oxidase. The compound has anticancer and contragestational effects, and it improves the anticancer effect of the ornithine decarboxylase inactivator (D,L)-2-(difluoromethyl)ornithine (DFMO). Profound depletion of the polyamine pools of tumour cells and effects on different components of the immune defence system are responsible for the anticancer effects of MDL 72527/DFMO combinations. Recently a direct cytotoxic effect of MDL 72527 at concentrations above those required for polyamine oxidase inactivation was observed. The induction of apoptosis by MDL 72527 was ascribed to its lysosomotropic properties. Therapeutic potentials of the apoptotic effect of MDL 72527 need to be explored. Polyamine oxidase is the last enzyme of the polyamine interconversion pathway that awaits the detailed elucidation of its structure and regulation. MDL 72527 should be useful as a lead in the development of inactivators which are selective for the isoforms of polyamine oxidase. Isozyme-selective inhibitors will give more profound insights into and reveal a diversity of specific functions of polyamine oxidase.

Therapeutic potential of AGE inhibitors and breakers of AGE protein cross-links

Glucose and other reducing sugars react non-enzymatically with proteins leading to the formation of advanced glycosylation end products (AGEs) and AGE-derived protein cross-linking. Formation of AGEs is a normal physiological process, which is accelerated under the hyperglycaemic condition in diabetes. Under normal conditions, AGEs build up slowly and accumulate as one ages. Numerous studies have indicated that AGEs contribute to the pathological events leading to diabetic complications, such as age-related diseases, including nephropathy, retinopathy, vasculopathy and neuropathy. Potential therapeutic approaches to prevent these complications include pharmacological inhibition of AGE formation and disruption of pre-formed AGE-protein cross-links. Studies using animal models and preliminary clinical trials have shown the ability of the AGE-inhibitor, pimagedine and the cross-link breaker, ALT-711, to reduce the severity of pathologies of advanced glycosylation. These agents offer potential treatments for glucose-derived complications of diabetes and ageing.

Effect of chronic aminoguanidine treatment on age-related glycation, glycoxidation, and collagen cross-linking in the Fischer 344 rat

Aminoguanidine (AG) is an inhibitor of protein modification by the advanced Maillard reaction. We evaluated its effects in preventing age-related collagen cross-linking, glycation, and glycoxidation in Fischer 344 rats by administering the drug in their drinking water at 1 g/l from the time they were 6 months until they were 24 months of age. Body weight and food and water consumption were consistently recorded throughout the study. Plasma glucose was measured by the glucose oxidase method, and collagen cross-linking was assessed by tail tendon break time (TBT) in urea. Glycation (furosine) and glycoxidation (pentosidine and carboxymethyllysine) were assessed by high-performance liquid chromatography in acid hydrolysates of skin and tendon collagen. Water consumption dramatically increased (p <.0001) after 20 months of age and was accelerated in the control versus AG-treated rats (p <.0001). Plasma glucose increased approximately 20% at age 19 months in both groups (p <.0001). TBT, glycation, and glycoxidation all increased significantly (p <.0001) with age. However, except for a modest decrease of TBT at all ages that approached significance (p =.077), AG had no effect on collagen glycation or glycoxidation. These results are important because they suggest that alpha,beta-dicarbonyl compounds that can be trapped by aminoguanidine do not play a major role in collagen aging in the rat. Instead, post-Amadori pathways involving oxidative or nonoxidative fragmentation of the Amadori product emerge as the more likely mechanism of collagen cross-linking in aging.

Neuroprotective effect of aminoguanidine on transient focal ischaemia in the rat brain

Using serial magnetic resonance imaging we have evaluated the effectiveness of aminoguanidine (AG) as a neuroprotective agent in a rat model of transient middle cerebral artery occlusion (MCAO). Because aminoguanidine's neuroprotective properties have primarily been ascribed to its action as iNOS inhibitor, we also performed a biochemical analysis of nitric oxide metabolites and NOS isoforms in our model of ischaemia. Daily injections of AG (100 mg/kg) or saline, were started at 6 h after the occlusion and the effects of this treatment on lesion progression monitored by T(2)-weighted MRI at 6 (pre-treatment scan), 24 and 72 h. Measurements of lesion volumes showed that between 6 and 72 h post-MCAO, lesion growth was slower in AG-treated rats than in control rats. This difference was most pronounced between 24 and 72 h post-MCAO when AG halted the lesion volume expansion observed in control rats. Measurements of plasma NOx (nitrite plus nitrate) at 0, 24, 48 and 72 h after MCAO, showed that NO levels did not differ significantly between the AG- and saline-treated groups at any time-point. Moreover, NOS activity assays revealed that no iNOS activity was present in any of the brains tested and that constitutive neuronal NOS activity was similar across the two hemispheres between both groups. The absence of iNOS protein in the ischaemic and contralateral hemispheres at 48 and 72 h after MCAO (control group only) was confirmed by Western blot analysis. These results suggest that AG treatment reduces the rate of growth of ischaemic lesions, perhaps preserving the functioning of perifocal neurons. Our observations contradict suggestions that high levels of NO generated by iNOS are partially responsible for exacerbating the neuronal damage in the postischaemic phase of MCAO. Although this does not rule out a role for AG as a neuroprotective agent via its ability to inhibit iNOS, these findings indicate that neuroprotective actions of AG may also be mediated via other cellular targets.

Role of nitric oxide in the secondary expansion of a cortical brain lesion from cold injury

We have investigated the role of nitric oxide (NO) as mediator of the secondary growth of a traumatic cortical necrosis. For this purpose, a highly standardized focal lesion of the brain was induced in 46 Sprague-Dawley rats by cold injury. Twenty-four hours later--the timepoint of maximal lesion spread--the animals were sacrificed and brains were removed for histomorphometry of the maximal necrosis area and volume. The animals were divided into five experimental groups. Group I received the NO donor L-arginine as i.v. bolus 10 min prior to trauma (300 mg/kg body weight; n = 10) and a second bolus of the same dosage intraperitoneally 1 h after trauma. Group II (n = 10)--serving as control of group I--was infused with an i.v. bolus of 1 mL/kg isotonic saline 10 min prior to and a subsequent bolus i.p. 1 h after trauma. Group III (n = 8) received 100 mg/kg b.w. of the inducible NOS (iNOS) inhibitor aminoguanidine (AG) 1 h before and 8 h after trauma by intraperitoneal route. Group IV was administered with the nitric oxide synthase (NOS) inhibitor N(G)-nitro-L-arginine (L-NNA; 100 mg/kg b.w., i.p.; n = 8); group V--the controls of group III and IV--was administered with isotonic saline (1 mL/kg b.w. i.p.; n = 10) 1 h before and 8 h after trauma. In the control group with i.v./i.p. sham treatment (II), the focal lesion led to a cortical necrosis with a maximum area of 3.1 +/- 0.3 mm2 and a lesion volume of 5.7 +/- 0.5 mm3 at 24 h after trauma. In animals with administration of L-arginine, the focal lesion had a maximum area of 3.1 +/- 0.3 mm2 and a volume of 5.3 +/- 0.5 mm3. Hence, the NO donor did not affect the secondary growth of necrosis. Animals with i.p. sham treatment (group V) had a maximal lesion area of 3.6 +/- 0.2 mm2 and lesion volume of 6.2 +/- 0.4 mm3. Administration of aminoguanidine afforded significant attenuation of the lesion growth. Accordingly, the maximal area of necrosis spread only to 2.8 +/- 0.2 mm2 with a volume of 4.5 +/- 0.5 mm3, respectively, at 24 h after trauma (p < 0.01 vs group V). On the other hand, administration of L-NNA did not influence the maximal lesion area (3.7 +/- 0.2 mm2) or lesion volume (6.5 +/- 0.5 mm3) evolving at 24 h after trauma. Thus, neither the enhancement of the formation of NO by L-arginine nor gross inhibition of the synthesis of NO by L-NNA did affect the secondary spread of the necrosis from a focal trauma. The marked attenuation of the posttraumatic necrosis growth by the iNOS inhibitor aminoguanidine strongly indicates an important role of iNOS product in this phenomenon. These findings, thus, demonstrate that the expansion of a primary necrotic focal lesion is a secondary process which can be therapeutically inhibited. Thereby, the growth of a focal tissue necrosis from trauma is clearly identified as a manifestation of secondary brain damage. This information is deemed important for the better understanding of the pathophysiology of traumatic brain injury and for the targeted development of specific treatment modalities.

Can we identify genes for susceptibility to diabetic microangiopathies using stroke-prone spontaneously hypertensive rat models?

The aortic biochemical properties are reported to be altered in stroke-prone spontaneously hypertensive rats (SHR-SPs) as a result not only of the accelerated accumulation of advanced glycation end products (AGEs) in thoracic aortae but also of primary defects. There is a growing body of evidence that reactive oxygen species (ROS) are involved in the formation of AGEs. We propose here a novel hypothesis that SHR-SPs are the strain that genetically produce more ROS generations. Since ROS formations and AGE accumulations play central roles in the pathogenesis of diabetic microvascular complications, SHR-SPs might be more susceptible to vascular complications when induced to be diabetic. To reveal new genes involved in susceptibility to diabetic microangiopathies through the study of these animal models might be a valuable strategy to develop novel therapeutic approaches.

Mechanisms of salt-sensitive hypertension: role of inducible nitric oxide synthase

The goal of this study was to determine the role of inducible nitric oxide synthase (iNOS) in the arterial pressure, renal hemodynamic, renal excretory, and hormonal changes that occur in Dahl/Rapp salt-resistant (R) and salt-sensitive (S) rats during changes in Na intake. Thirty-two R and S rats, equipped with indwelling arterial and venous catheters, were subjected to low (0.87 mmol/day) or high (20.6 mmol/day) Na intake, and selective iNOS inhibition was achieved with intravenous aminoguanidine (AG, 12.3 mg. kg(-1). h(-1)). After 5 days of AG, mean arterial pressure increased to 121 +/- 3% control in the R-high Na AG rats compared with 98 +/- 1% control (P < 0.05) in the R-high Na alone rats, and S-high Na rats increased their arterial pressure to 123 +/- 3% control compared with 110 +/- 2% control (P < 0.05) in S-high Na alone rats. AG caused no significant changes in renal hemodynamics, urinary Na or H(2)O excretion, plasma renin activity, or cerebellar Ca-dependent NOS activity. The data suggest that nitric oxide produced by iNOS normally helps to prevent salt-sensitive hypertension in the Dahl R rat and decreases salt sensitivity in the Dahl S rat.

Discovery and development of neuronal nitric oxide synthase inhibitors

The role of neuronally derived nitric oxide (NO) in neurotransmission and neural injury remains an area of active investigation. NO generation has been postulated to be involved in the deleterious events surrounding ischemia/reperfusion injury either directly or via the production of more reactive oxidants such as peroxynitrite. In our search for novel therapeutics for the treatment of a variety of neurological diseases including stroke, we have discovered novel, potent, and selective inhibitors of the neuronal nitric oxide synthase (nNOS) isoform. These compounds have proven to be effective in models of ischemia/reperfusion supporting the role of nNOS in these processes. The effects of these compounds as well as additional aspects critical to their development will be presented.

Oxidation of polyamines and brain injury

Several amine oxidases are involved in the metabolism of the natural polyamines putrescine, spermidine, and spermine, and play a role in the regulation of intracellular concentrations, and the elimination of these amines. Since the products of the amine oxidase-catalyzed reactions -- hydrogen peroxide and aminoaldehydes -- are cytotoxic, oxidative degradations of the polyamines have been considered as a cause of apoptotic cell death, among other things in brain injury. Since a generally accepted, unambiguous nomenclature for amine oxidases is missing, considerable confusion exists with regard to the polyamine oxidizing enzymes. Consequently the role of the different amine oxidases in physiological and pathological processes is frequently misunderstood. In the present overview the reactions, which are catalyzed by the different polyamine-oxidizing enzymes are summarized, and their potential role in brain damage is discussed.

Protective effect of aminoguanidine on hypoxic-ischemic brain damage and temporal profile of brain nitric oxide in neonatal rat

Nitric oxide (NO) produced by inducible NO synthase contributes to ischemic brain damage. However, the role of inducible NO synthase-derived NO on neonatal hypoxic-ischemic encephalopathy has not been clarified. We demonstrate here that aminoguanidine, a relatively selective inhibitor of inducible NO synthase, ameliorated neonatal hypoxic-ischemic brain damage and that temporal profiles of NO correlated with the neuroprotective effect of aminoguanidine. Seven-day-old Wister rat pups were subjected to left carotid artery occlusion followed by 2.5 h of hypoxic exposure (8% oxygen). Infarct volumes (cortical and striatal) were assessed 72 h after the onset of hypoxia-ischemia by planimetric analysis of coronal brain slices stained with hematoxylin-eosin. Aminoguanidine (300 mg/kg i.p.), administered once before the onset of hypoxia-ischemia and then three times daily, significantly ameliorated infarct volume (89% reduction in the cerebral cortex and 90% in the striatum; p<0.001). NO metabolites were measured by means of chemiluminescence using an NO analyzer. In controls, there was a significant biphasic increase in NO metabolites in the ligated side at 1 h (during hypoxia) and at 72 h after the onset of hypoxia (p<0.05). Aminoguanidine did not suppress the first peak but significantly reduced the second one (p<0.05), and markedly reduced infarct size in a neonatal ischemic rat model. Suppression of NO production after reperfusion is a likely mechanism of this neuroprotection.

Ischemic cell death in brain neurons

This review is directed at understanding how neuronal death occurs in two distinct insults, global ischemia and focal ischemia. These are the two principal rodent models for human disease. Cell death occurs by a necrotic pathway characterized by either ischemic/homogenizing cell change or edematous cell change. Death also occurs via an apoptotic-like pathway that is characterized, minimally, by DNA laddering and a dependence on caspase activity and, optimally, by those properties, additional characteristic protein and phospholipid changes, and morphological attributes of apoptosis. Death may also occur by autophagocytosis. The cell death process has four major stages. The first, the induction stage, includes several changes initiated by ischemia and reperfusion that are very likely to play major roles in cell death. These include inhibition (and subsequent reactivation) of electron transport, decreased ATP, decreased pH, increased cell Ca(2+), release of glutamate, increased arachidonic acid, and also gene activation leading to cytokine synthesis, synthesis of enzymes involved in free radical production, and accumulation of leukocytes. These changes lead to the activation of five damaging events, termed perpetrators. These are the damaging actions of free radicals and their product peroxynitrite, the actions of the Ca(2+)-dependent protease calpain, the activity of phospholipases, the activity of poly-ADPribose polymerase (PARP), and the activation of the apoptotic pathway. The second stage of cell death involves the long-term changes in macromolecules or key metabolites that are caused by the perpetrators. The third stage of cell death involves long-term damaging effects of these macromolecular and metabolite changes, and of some of the induction processes, on critical cell functions and structures that lead to the defined end stages of cell damage. These targeted functions and structures include the plasmalemma, the mitochondria, the cytoskeleton, protein synthesis, and kinase activities. The fourth stage is the progression to the morphological and biochemical end stages of cell death. Of these four stages, the last two are the least well understood. Quite little is known of how the perpetrators affect the structures and functions and whether and how each of these changes contribute to cell death. According to this description, the key step in ischemic cell death is adequate activation of the perpetrators, and thus a major unifying thread of the review is a consideration of how the changes occurring during and after ischemia, including gene activation and synthesis of new proteins, conspire to produce damaging levels of free radicals and peroxynitrite, to activate calpain and other Ca(2+)-driven processes that are damaging, and to initiate the apoptotic process. Although it is not fully established for all cases, the major driving force for the necrotic cell death process, and very possibly the other processes, appears to be the generation of free radicals and peroxynitrite. Effects of a large number of damaging changes can be explained on the basis of their ability to generate free radicals in early or late stages of damage. Several important issues are defined for future study. These include determining the triggers for apoptosis and autophagocytosis and establishing greater confidence in most of the cellular changes that are hypothesized to be involved in cell death. A very important outstanding issue is identifying the critical functional and structural changes caused by the perpetrators of cell death. These changes are responsible for cell death, and their identity and mechanisms of action are almost completely unknown.