Nitric oxide is involved in ischemia-induced apoptosis in brain: a study in neuronal nitric oxide synthase null mice

Subacute Elevation of Plasma Level of Caspase-Cleaved Cytokeratin-18 is Associated with Hemorrhagic Transformation and Functional Outcome in Ischemic Stroke

BACKGROUND

Caspase-cleaved cytokeratin-18 (CCCK-18) is an apoptosis marker. Here, we analyzed the relationship between plasma level of CCCK-18 in the acute and subacute stage of ischemic stroke and early and late functional outcome. Besides, correlation among CCCK-18 and complications, such as hemorrhagic transformation (HT) were also explored.

METHODS

Plasma concentration of CCCK-18 was investigated in 54 patients at admission and poststroke 72 hours. HT was evaluated by CT scans on 24 poststroke hours. Outcome measures were assessed by modified Rankin scale at hospital discharge and 6-month later. Receiver operating characteristics (ROC) analysis was used to determine the best cut-off values of CCCK-18 as a predictor of unfavorable functional outcome.

RESULTS

Significantly elevated CCCK-18 level was observed at 72 hours after onset of stroke, in nonsurviving compared to surviving patients (331 ± 191 ng/L versus 251 ± 164 ng/L, P = .01). Based on ROC analysis, the cut-off value of plasma CCCK-18 levels >223 ng/L at 72 poststroke hours predicted 6-month unfavorable stroke outcome with a sensitivity of 84.4% and a specificity of 77.3% (area under the curve: .851, 95% confidence interval = .745-.955, P < .001). The rate of complications such as HT and in-hospital infection was significantly higher in patients presented with a plasma CCCK-18 level above the cut-off value.

CONCLUSIONS

The association between high serum CCCK-18 levels and unfavorable early and late stroke outcome in an unselected study population was first described here. Besides, the apoptosis marker CCCK-18 might be a predictor of further complication such as HT and in-hospital infection.

Adenovirus-mediated eNOS expression augments liver injury after ischemia/reperfusion in mice

Hepatic ischemia/reperfusion (l/R) injury continues to be a critical problem. The role of nitric oxide in liver I/R injury is still controversial. This study examines the effect of endothelial nitric oxide synthase (eNOS) over-expression on hepatic function following I/R. Adenovirus expressing human eNOS (Ad-eNOS) was administered by tail vein injection into C57BL/6 mice. Control mice received either adenovirus expressing LacZ or vehicle only. Sixty minutes of total hepatic ischemia was performed 3 days after adenovirus treatment, and mice were sacrificed after 6 or 24 hrs of reperfusion to assess hepatic injury. eNOS over expression caused increased liver injury as evidenced by elevated AST and ALT levels and decreased hepatic ATP content. While necrosis was not pervasive in any group, TUNEL demonstrated significantly increased apoptosis in Ad-eNOS infected livers. Western blotting demonstrated increased levels of protein nitration and upregulation of the pro-apoptotic proteins bax and p53. Our data suggest that over-expression of eNOS is detrimental in the setting of hepatic I/R.

Pergolide protects CA1 neurons from apoptosis in a gerbil model of global cerebral ischemia

OBJECTIVE

To investigate the effects of dopamine (DA) receptor agonists and antagonists on neuronal apoptosis in hippocampal CA1 region after forebrain ischemia/reperfusion (I/R) injury in gerbils.

METHODS

Gerbil forebrain ischemia was induced by occluding bilateral carotid arteries for 5 minutes. The open field test, hematoxylin-eosin staining and in situ terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) methods were used 1, 3 and 7 days after reperfusion. Western blot was used to examine the phosphorylation of c-Jun.

RESULTS

Pergolide could significantly reduce the habituation impairments of ischemic gerbils, increase the number of normal neurons and reduce the number of apoptotic neurons in hippocampal CA1 region after reperfusion. SKF38393, SCH23390 and spiperone had no effects on these changes in this transient I/R injury model. Furthermore, pergolide can significantly reduce the phosphorylation of c-Jun induced by transient forebrain ischemia.

Protective functions of taurine against experimental stroke through depressing mitochondria-mediated cell death in rats

Taurine, an abundant amino acid in the nervous system, is reported to reduce ischemic brain injury in a dose-dependent manner. This study was designed to investigate whether taurine protected brain against experimental stroke through affecting mitochondria-mediated cell death pathway. Rats were subjected to 2-h ischemia by intraluminal filament, and then reperfused for 22 h. It was confirmed again that taurine (50 mg/kg) administered intravenously 1 h after ischemia markedly improved neurological function and decreased infarct volume at 22 h after reperfusion. In vehicle-treated rats, the levels of intracellular ATP and the levels of cytosolic and mitochondrial Bcl-xL in the penumbra and core were markedly reduced, while the levels of cytosolic Bax in the core and mitochondrial Bax in the penumbra and core were enhanced significantly. There was a decrease in cytochrome C in mitochondria and an increase in cytochrome C in the cytosol of the penumbra and core. These changes were reversed by taurine. Furthermore, taurine inhibited the activation of calpain and caspase-3, reduced the degradation of αII-spectrin, and attenuated the necrotic and apoptotic cell death in the penumbra and core. These data demonstrated that preserving the mitochondrial function and blocking the mitochondria-mediated cell death pathway may be one mechanism of taurine's action against brain ischemia.

Ferulic acid inhibits nitric oxide-induced apoptosis by enhancing GABA(B1) receptor expression in transient focal cerebral ischemia in rats

AIM

Ferulic acid (4-hydroxy-3-methoxycinnamic acid, FA) provides neuroprotection against apoptosis in a transient middle cerebral artery occlusion (MCAo) model. This study was to further investigate the anti-apoptotic effect of FA during reperfusion after cerebral ischemia.

METHODS

Rats were subjected to 90 min of cerebral ischemia followed by 3 or 24 h of reperfusion after which they were sacrificed.

RESULTS

Intravenous FA (100 mg/kg) administered immediately after middle cerebral artery occlusion (MCAo) or 2 h after reperfusion effectively abrogated the elevation of postsynaptic density-95 (PSD-95), neuronal nitric oxide synthase (nNOS), inducible nitric oxide synthase (iNOS), nitrotyrosine, and cleaved caspase-3 levels as well as apoptosis in the ischemic cortex at 24 h of reperfusion. FA further inhibited Bax translocation, cytochrome c release, and p38 mitogen-activated protein (MAP) kinase phosphorylation. Moreover, FA enhanced the expression of gamma-aminobutyric acid type B receptor subunit 1 (GABA(B1)) in the ischemic cortex at 3 and 24 h of reperfusion. In addition, nitrotyrosine-positive cells colocalized with cleaved caspase-3-positive cells, and phospho-p38 MAP kinase-positive cells colocalized with nitrotyrosine- and Bax-positive cells, indicating a positive relationship among the expression of nitrotyrosine, phospho-p38 MAP kinase, Bax, and cleaved caspase-3. The mutually exclusive expression of GABA(B1) and nitrotyrosine revealed that there is a negative correlation between GABA(B1) and nitrotyrosine expression profiles. Additionally, pretreatment with saclofen, a GABA(B) receptor antagonist, abolished the neuroprotection of FA against nitric oxide (NO)-induced apoptosis.

CONCLUSION

FA significantly enhances GABA(B1) receptor expression at early reperfusion and thereby provides neuroprotection against p38 MAP kinase-mediated NO-induced apoptosis at 24 h of reperfusion.

Cornel iridoid glycoside inhibits inflammation and apoptosis in brains of rats with focal cerebral ischemia

The capacity of cornel iridoid glycoside (CIG) to suppress the manifestations of ischemic stroke was investigated. CIG was administered to rats by the intragastric route once daily for 7 days. Focal cerebral ischemia was induced by 2 h of middle cerebral artery occlusion followed by 24 h of reperfusion. In non-treated rats large infarct areas were observed within 24 h of reperfusion. Examination of the ischemic cerebral cortex revealed microglia and astrocyte activation, increased interleukin-1beta (IL-1 beta) and tumor necrosis factor-alpha (TNF-alpha) concentrations, increased DNA fragmentation in the ischemia penumbra, elevated Bax expression, increased caspase-3 cleavage, and decreased Bcl-2 expression. Pretreatment with CIG decreased the infarct area, DNA fragmentation, IL-1beta and TNF-alpha concentrations, microglia and astrocyte activation, Bax expression, and caspase-3 cleavage while increasing Bcl-2 expression. CIG exerts anti-neuroinflammatory and anti-apoptotic effects which should prove beneficial for prevention or treatment of stroke.

Concise route to the chiral pyrrolidine core of selective inhibitors of neuronal nitric oxide

2-(((3R,4R)-4-(Allyloxy)-1-benzylpyrrolidin-3-yl)methyl)-6-(2,5-dimethyl-1H-pyrrol-1-yl)-4-methylpyridine (2), a key intermediate for the preparation of novel neuronal nitric oxide synthase (nNOS) inhibitors, is synthesized using diisopropyl (R)-(+)-malate as the starting material. The key steps involve a Frater-Seebach diastereoselective alkylation and a fast intramolecular cyclization.

Neuroinflammation and MMPs: potential therapeutic targets in neonatal hypoxic-ischemic injury

Exposure to hypoxic-ischemic insults during the neonatal or perinatal developmental periods produces various forms of pathology. Injuries that occur in response to these events often manifest as severe cognitive and/or motor disturbances over time. Due to difficulties regarding the early diagnosis and treatment of hypoxic-ischemic injury, there is a growing need for effective therapies that can be delivered at delayed time points. Much of the research into mechanisms of neural injury has focused on molecular targets associated with excitotoxicity and free oxygen radicals. Despite repeated success in animal models, these compounds have failed to show efficacy in clinical trials. Increasing evidence indicates that hypoxic-ischemic injury in the neonate is progressive, and the resulting neuropathies are linked to the activation of neuroinflammatory processes that occur in response to the initial wave of cell death. Understanding this latter response, therefore, will be critical in the development of novel therapies to block the progression of the injury. In this review, we summarize emerging concepts from rodent models concerning the regulation of various cytokines, chemokines, and matrix metalloproteinases in response to ischemia, and the various ways in which the delayed neuroinflammatory response may contribute to the progressive nature of neonatal hypoxic-ischemic injury in rat. Finally, we discuss data that supports the potential to target these neuroinflammatory signals at clinically relevant time points.

Potential involvement of calcium and nitric oxide in protective effects of puerarin on oxygen-glucose deprivation in cultured hippocampal neurons

The aim of this study was to clarify the mechanisms underlying neuroprotection of puerarin (Pur) against cerebral hypoxia-ischemia. Primary hippocampal cultures were prepared from 2-day-old Sprague-Dawley rats. After 8 days in vitro, the cultures subjected to 3h oxygen/glucose deprivation (OGD). Flow cytometric analysis of annexin-V and propidium iodide (PI) labeling cells found that apoptosis and necrosis were significantly reduced in the cultured hippocampal neurons by addition of Pur during 3h OGD and for the following 24h. Pur (40 and 100 microM) also attenuated glutamate (Glu) induced neuronal damage, suppressing apoptosis and necrosis induced by Glu of 0.5mM. Furthermore, the changes in intracellular Ca(2+) and generation of nitric oxide (NO) were measured by confocal laser scanning microscopy with Fluo-3, a Ca(2+) probe, and diaminofluorescein diacetate (DAF DA), a NO probe, respectively. In agreement with the results from flow cytometric analysis, Pur (40 and 100 microM) markedly slowed down OGD-induced Ca(2+) influx and lowered the intracellular Ca(2+) peak. Meanwhile, NO synthesis induced by OGD was significantly inhibited by Pur. Our findings suggest that Pur can ameliorate hippocampal neuronal death induced by OGD in vitro. The protective effects of Pur are associated with inhibiting the action of glutaminergic transmitter, intracellular Ca(2+) elevation and neuronal NO synthesis.

Systemic inflammation induces apoptosis with variable vulnerability of different brain regions

During severe sepsis several immunological defence mechanisms initiate a cascade of inflammatory events leading to multi-organ failure including septic encephalopathy and ultimately death. To assess the reaction and participation of parenchymal brain cells during endotoxaemia, the present study evaluates micro- and astroglial activation, expression of the inducible nitric oxide synthase (iNOS) pro- and antiapoptotic protein levels Bax and Bcl-2, and apoptosis. Male Wistar rats received 10 mg/kg lipopolysaccharide (LPS) or vehicle intraperitoneally and were sacrificed for brain collection at 4, 8 or 24 h after induction of experimental sepsis. One group of animals received 10 mg/kg of the NOS inhibitor N-monomethyl-L-arginine (L-NMMA) intraperitoneally 1 day before and during the experiment. Immunohistochemical evaluation revealed a sepsis-induced, time-dependent increase in the immunoreactivity of iNOS, glial fibrillary acidic protein (GFAP) and activated microglia (ED-1), paralleled by a time-dependent increase of apoptotic brain cells marked by terminal deoxynucleotidyl transferase-mediated dUTP-nick end labeling (TUNEL), an increase of Bax-positive cells and a decrease of Bcl-2-positive cells. Evaluation of different brain regions revealed that the hippocampus is the most vulnerable region during experimental sepsis. iNOS-inhibition with L-NMMA significantly reduced the number of apoptotic cells in hippocampus, midbrain and cerebellum. In addition, it reduced the increase of the proapoptotic protein Bax in all examined brain regions and reduced the decrease of Bcl-2-positive cells in the hippocampus. We therefore conclude, that peripheral inflammation leads to a profound glial activation, the generation of nitric oxide and changes of Bax and Bcl-2 protein regulation critical for apoptosis.

The many faces of nitric oxide in schizophrenia. A review

Intense research has been conducted in an effort to identify specific biological markers of schizophrenia. The gas nitric oxide (NO) is one of the most important signaling molecules involved in a plethora of cellular events that take place in the cardiovascular, immune and nervous systems of animals. This survey aims to demonstrate that NO and its metabolites play important roles in schizophrenia and have a significant influence on our understanding of the development, progression and treatment of the disease. Special emphasis is given to the impact of NO metabolism on processes known to be disturbed in schizophrenia (i.e., cell migration, formation of synapses, NMDA receptor mediated neurotransmission, membrane pathology and cognitive abilities). However, when comparing data on the NO metabolism in the brain tissue and body fluids of schizophrenics with those obtained from patients with other neurological and psychiatric diseases, it becomes clear that alterations of NO metabolism are not unique to, or indicative of, schizophrenia. Thus, NO and its metabolites are not suitable diagnostic tools to distinguish schizophrenia from psychically healthy control cases or from other brain disorders.

VEGF protects brain against focal ischemia without increasing blood--brain permeability when administered intracerebroventricularly

Delayed administration of vascular endothelial growth factor (VEGF) promotes functional recovery after focal cerebral ischemia. However, early intravenous injection of VEGF increases blood-brain barrier (BBB) leakage, hemorrhagic transformation and infarct volume whereas its application to cortical surface is neuroprotective. We have investigated whether or not early intracerebroventricular administration of VEGF could replicate the neuroprotective effect observed with topical application and the mechanism of action of this protection. Mice were subjected to 90 mins middle cerebral artery (MCA) occlusion and 24 h of reperfusion. Vascular endothelial growth factor (8 ng, intracerebroventricular) was administered 1 or 3 h after reperfusion. Compared with the vehicle-treated (intracerebroventricular) group, VEGF decreased the infarct volume along with BBB leakage in both treatment groups. Neurologic disability scores improved in parallel to the changes in infarct volume. Independently of the decrease in infarct size, VEGF also reduced the number of TUNEL-positive apoptotic neurons. Phospo-Akt levels were significantly higher in ischemic hemispheres of the VEGF-treated mice. Contrary to intracerebroventricular route, intravenous administration of VEGF (15 microg/kg) enhanced the infarct volume as previously reported for the rat. In conclusion, single intracerebroventricular injection of VEGF protects brain against ischemia without adversely affecting BBB permeability, and has a relatively long therapeutic time window. This early neuroprotective action, observed well before recovery-promoting actions such as angiogenesis, possibly involves activation of the PI-3-Akt pathway.

Prenatal auditory enrichment with species-specific calls and sitar music modulates expression of Bcl-2 and Bax to alter programmed cell death in developing chick auditory nuclei

Postnatal auditory stimulation influences early perceptual learning. Previously we reported morphological effects of prenatal auditory stimulation by species-specific and sitar musical sounds on the chick brainstem auditory nuclei-nucleus magnocellularis and nucleus laminaris. At hatching, these two nuclei of auditory enriched embryos showed higher neuronal numbers, amongst other morphological changes. There were also increases in synaptophysin and syntaxin1 expressions in the sound enriched groups and modulation of the developmental expression of transcription factors c-Fos and c-Jun. We hypothesized that prenatal auditory enrichment may have reduced embryonic apoptosis in these nuclei with possible alteration of molecular mechanisms enhancing the postsynaptic neuron's ability to survive. In the present study, therefore, we examined apoptotic cell death by TUNEL technique and Bcl-2 expression using immunohistochemistry and immunoblotting. In the controls, a peak percentage in the TUNEL-positive cells was noted in the auditory nuclei at embryonic day 12, which was reduced at embryonic day 16. Bcl-2 immunoreactivity decreased from embryonic day 8 to embryonic day 12 overlapping the period of embryonic cell death in these nuclei. The stimulated groups, however, showed fewer apoptotic neurons and higher Bcl-2 level than that in the controls. On the other hand, Bax immunohistochemistry showed correlated reverse changes compared to Bcl-2 expression. Thus prenatal extra-acoustic stimulation appears to alter Bcl-2 and Bax expression to support cell survival and differentiation, thereby augmenting the development of auditory nuclei.

Role of mast cells in hepatic remodeling during cholestasis and its resolution: relevance to regulation of apoptosis

BACKGROUND/AIMS

Mast cells are thought to be related to fibrogenesis, but recent studies have shown that fibrosis of the liver can be induced even in mast cell-deficient rats. To clarify the significance of mast cell accumulation in cholestatic liver diseases, the relations between such accumulation, bile ductule proliferation and apoptosis of biliary epithelial cells were examined in the rats during cholestasis and its resolution.

METHODS

Cholestasis and its resolution were induced in rats by common bile duct ligation and spontaneous recanalization, respectively. The extent of bile ductule proliferation and the numbers of mast cells and apoptotic biliary epithelial cells were estimated quantitatively in liver sections.

RESULTS

Recanalization of the ligated common bile duct led to an abrupt and transient increase in the number of mast cells, although the number of proliferated bile ductules decreased rapidly. The number of apoptotic biliary epithelial cells of the proliferated bile ductules increased rapidly and transiently, and the change paralleled that of the mast cells.

CONCLUSIONS

Mast cells accumulating in the portal triads during cholestasis and its resolution may relate to the reduction of proliferated bile ductules, i.e., in hepatic remodeling, through the induction of apoptosis of biliary epithelial cells.

Age-related alteration of activity and gene expression of endothelial nitric oxide synthase in different parts of the brain in rats

Nitric oxide (NO) plays important roles in aging and neurodegeneration. Our previous results indicated that aging differently affects NOS isoforms. Expression of nNOS mRNA was lower while iNOS was absent at any age. However, total NO synthesis increased in aged cerebral cortex and cerebellum as a consequence of changes of nNOS phosphorylation state. The question arise how aging influences activity and expression of eNOS in different parts of adult and aged brain. The levels of eNOS mRNA, protein and activity were measured using RT-PCR, immuno- and radiochemical methods, respectively. Our studies indicated that after inhibition of nNOS with 7-nitroindazole (7-NI) NO synthesis is lower in all parts of aged brain comparing to adults. However, eNOS activity significantly decreases only in cerebellum. The expression of eNOS determined on mRNA level was enhanced in all investigated aged brain parts to 140-190% of adult value and the data were statistically significant for cerebral cortex and cerebellum. The higher level of mRNA is probably the adaptive response to lower NOS activity. However, the Western-blot signal of eNOS protein was unchanged in aged brain parts comparing to adults suggesting age-related disturbances of protein synthesis and its function. It is also possible that a post-translational modification of the enzyme occurs in the aged rat brain. The lower eNOS activity in aged brain may significantly affects the signal transduction processes on the pathway NO/cGMP/PKG.

Nitric oxide and cerebral ischemic preconditioning

Nitric oxide (NO) is an important mediator of cerebral blood flow and metabolism. As a vasodilator, NO regulates cerebral blood flow, and couples regional brain perfusion with metabolic activity. Following cerebral ischemia, NO levels rise significantly due to activation of neuronal nitric oxide synthase by NMDA receptor mediated calcium entry. Depending on its tissue and enzymatic source, NO may be protective or toxic. This article reviews the effects of NO following cerebral ischemia, the signaling pathways through which NO acts, and its potential roles in cerebral ischemic preconditioning.

Collagen type I prevents glyoxal-induced apoptosis in osteoblastic cells cultured on titanium alloy

Advanced glycation end products (AGEs) irreversibly cross-link proteins with sugars and accumulate at a higher age and in diabetes, processes which can interfere with the integration of implants into the tissue. Glyoxal is a highly reactive glycating agent involved in the formation of AGEs and is known to induce apoptosis, as revealed by the upregulation of caspase-3 and fractin (caspase-3 being a key enzyme activated during the late stage of apoptosis and fractin being a caspase-cleaved actin fragment). In this study, we investigated the influence of collagen type I coating on the cytotoxic effect of glyoxal on rat calvarial osteoblastic cells and on human osteosarcoma cells (Saos-2) grown on titanium alloy, Ti6Al4V. Activation of caspase-3 and fractin was measured by counting immunohistochemically stained cells and by flow cytometry with propidium iodide (detection of the apoptosis indicating a sub-G1 peak). Our results showed an increased number of apoptotic osteoblasts after incubation with glyoxal on Ti6Al4V discs. However, the number of apoptotic cells on collagen-coated titanium was significantly smaller than on uncoated titanium after the same treatment. The present findings demonstrate that osteoblasts treated with glyoxal undergo apoptosis, whereas collagen type I coating of titanium alloys (used for implants) has an antiapoptotic function.

Apoptotic and Necrotic Death Mechanisms Are Concomitantly Activated in the Same Cell After Cerebral Ischemia

BACKGROUND AND PURPOSE

Both necrotic and apoptotic cell death mechanisms are activated after cerebral ischemia. However, whether they are concomitantly active in the same cell or in discrete cell populations is not known.

METHODS

We investigated activation of both pathways at the cellular level in mice brains subjected to transient or permanent focal ischemia.

RESULTS

Four hours after ischemia, diffuse cathepsin-B spillage into cytoplasm, suggesting lysosomal leakage, was observed within neurons immunoreactive for the active form of caspase-3 (p20). Ischemic neurons with a leaky plasma membrane (positive for propidium iodide) were colabeled with caspase-cleaved actin fragment and exhibited TUNEL-positive nuclei having apoptotic morphology. At 72 hours, up to 27% of cells with caspase activity displayed morphological features suggestive of secondary necrosis.

CONCLUSIONS

These data, demonstrating an early and concurrent increase in caspase-3 and cathepsin-B activities followed by appearance of caspase-cleavage products, DNA fragmentation, and membrane disintegration, suggest that subroutines of necrotic and apoptotic cell death are concomitantly activated in ischemic neurons and that the dominant cell death phenotype is determined by the relative speed of each process.

Heparin-binding epidermal growth factor-like growth factor and intestinal ischemia-reperfusion injury

Intestinal ischemia/reperfusion (I/R) injury affects patients of different ages, especially premature babies and the elderly. The outcome after intestinal I/R is often dismal, which may be attributed to loss of the barrier and immune functions of the intestines, as well as development of secondary injury in remote organs. The available treatment for advanced gut ischemia mandates extensive resection, which may cause growth retardation in infants and nutritional problems in the elderly. Throughout the past decade we have been investigating the potential therapeutic role of heparin-binding epidermal growth factor-like factor (HB-EGF) in intestinal I/R. The mitogenic and chemoattractant functions of HB-EGF formed the initial rationale for our investigations. In addition, HB-EGF is a potent antiapoptotic protein that enables cells and tissues exposed to different apoptotic stimuli to survive hypoxic, oxidative, and nutritional stresses. HB-EGF is known to have a vital role in wound healing and postischemic regeneration in different organs. In the current review, we summarize the results of our findings of the beneficial effects of HB-EGF in intestinal I/R, supported by additional evidence from the literature and an explanation of different possible mechanisms of its actions. Collectively, the data strongly suggest a potential therapeutic role for the use of HB-EGF to treat intestinal ischemic diseases such as I/R and necrotizing enterocolitis.

Biphasic modulation by nitric oxide of caspase activation due to malonate injection in rat striatum

The present study examined caspase activation and its modulation by nitric oxide (NO) in a model of oxidative stress induced by injection of malonate (3 micromol), a mitochondrial toxin, into rat striatum. Caspase-3-like enzymatic activity was maximal 6 h after malonate while NO production evaluated by its metabolites nitrites and nitrates was increased at 3 h. The neuronal NO-synthase inhibitor 7-nitroindazole reduced malonate induced-NO production by 50% at 25 mg/kg and enhanced by 32% caspase activation. This result suggests that a moderate production of NO potentiates caspase activation, an effect counterbalanced by NO itself at higher concentrations. Accordingly, complete inhibition of NO production by 7-nitroindazole at 50 mg/kg did not modify malonate-induced caspase activity. Thus NO production by the neuronal isoform of NO-synthase is not the major event leading to caspase activation due to malonate. However, NO seems to have pro- and anti-caspase effects that neutralize each other.

Patterns of cerebral inflammatory response in a rabbit model of intrauterine infection-mediated brain lesion

Although the fetal inflammatory response syndrome seems crucial to the association between intrauterine infection and white matter disease in human preterm infants, the underlying mechanisms remain unclear. Using our previously described rabbit model of cerebral cell death in the white matter and hippocampus induced by intrauterine Escherichia coli infection, we investigated inflammatory and astroglial responses in placenta and brain tissues, in correlation with cell death distribution. Brains and placentas were studied 12, 24, or 48 h following intrauterine inoculation of E. coli or saline (groups G12, G24, and G48). Diffuse monocyte-macrophage infiltrates positive for inducible nitric oxide synthase (i-NOS) were significantly more marked in G24 and G48 placentas than in controls. In the G48 fetuses with both diffuse cell death and focal periventricular white matter cysts mimicking cystic periventricular leukomalacia, a strong rabbit macrophage and inducible nitric oxide synthase immunostaining was observed at the border of these cystic lesions. In contrast, in the fetuses with only diffuse and significant cell death, no inflammatory or astroglial responses were detected in the white matter or hippocampus. Cell death was accompanied by i-NOS immunostaining in the hippocampus but not the white matter. Hippocampal cells positive for i-NOS usually displayed a neuronal phenotype. In this model, focal white matter cysts are accompanied by a robust inflammatory response, and diffuse cell death, which may mimic the white matter and hippocampal damage seen in very and extremely pre-term infants, occur in the absence of a detectable brain inflammatory response.

Combined nimodipine and citicoline reduce infarct size, attenuate apoptosis and increase bcl-2 expression after focal cerebral ischemia

Cerebral ischemia triggers a multitude of pathophysiological and biochemical events that separately affect the evolution of focal ischemia and, therefore, stroke treatment should logically employ all known neuroprotective agents. We hypothesized that a treatment combining nimodipine and citicoline might have a potential neuroprotective effect. To assess this idea, Sprague-Dawley rats underwent transient bilateral common carotid artery ligation with simultaneous middle cerebral artery occlusion for 60 min. Four treatment groups were established. Animals received either: a) saline (control group); b) intracarotid nimodipine infusion during 30 min in the ischemia-reperfusion (nimodipine group); c) i.p. postischemic citicoline injections once daily for 7 days (citicoline group); or d) intracarotid nimodipine bolus during ischemia-reperfusion plus i.p. postichemic citicoline injections (combination group). They were killed after either 7 or 3 days after reperfusion. In the first case, the volume of the infarcted tissue was studied by a stereological procedure and in the second case, in situ end-labeling of nuclear DNA fragmentation (TUNEL) and Bcl-2 expression were employed to determine the level of apoptosis. The infarct volume was significantly reduced in both the nimodipine and the citicoline treatment groups after 7 days of reperfusion; combination of both drugs produced an additive effect. After 3 days of reperfusion, the number of Bcl-2-positive neurons was significantly increased while that of TUNEL-positive cells significantly decreased at the infarct border in the combined-treatment animals. Our findings demonstrate a neuroprotective effect from an acute single dose of nimodipine during ischemia-reperfusion and prolonged post-ischemic treatment with citicoline in a model of focal cerebral ischemia. These results suggest that a possible mechanism of neuroprotective action would be mediated by increased Bcl-2 expression and decreased apoptosis within the boundary zone of the infarct together with neutralization of the ischemia-reperfusion injury.

Antioxidant nutrients and hypoxia/ischemia brain injury in rodents

Cerebral ischemia and recirculation cause delayed neuronal death in rodents, such as Mongolian gerbils and stroke-prone spontaneously hypertensive rats (SHRSP), which were used as an experimental stroke model. It was documented that an enhanced nitric oxide production, the occurrence of apoptosis, and an attenuated redox regulatory system contribute to the development of delayed neuronal death. Many studies have suggested the beneficial antioxidant effects of antioxidant nutrients such as vitamin E, green tea extract, ginkgo biloba extract, resveratrol and niacin in cerebral ischemia and recirculation brain injury. These results are important in light of an attenuation of the deleterious consequences of oxidative stress in ischemia and recirculation injury.

Is the cell death in mesial temporal sclerosis apoptotic?

PURPOSE

Mesial temporal sclerosis (MTS) is characterized by neuronal loss in the hippocampus. Studies on experimental models and patients with intractable epilepsy suggest that apoptosis may be involved in neuronal death induced by recurrent seizures.

METHODS

We searched evidence for apoptotic cell death in temporal lobes resected from drug-resistant epilepsy patients with MTS by using the terminal deoxynucleotidyl transferase (TdT) and digoxigenin-11-dUTP (TUNEL) method and immunohistochemistry for Bcl-2, Bax, and caspase-cleaved actin fragment, fractin. The temporal lobe specimens were obtained from 15 patients (six women and nine men; mean age, 29 +/- 8 years).

RESULTS

Unlike that in normal adult brain, we observed Bcl-2 immunoreactivity in some of the remaining neurons dispersed throughout the hippocampus proper as well as in most of the reactive astroglia. Bax immunopositivity was increased in almost all neurons. Fractin immunostaining, an indicator of caspase activity, was detected in approximately 10% of these neurons. Despite increased Bax expression and activation of caspases, we could not find evidence for DNA fragmentation by TUNEL staining. We also could not detect typical apoptotic changes in nuclear morphology by Hoechst-33258 or hematoxylin counterstaining.

CONCLUSIONS

These data suggest that either apoptosis is not involved in cell loss in MTS, or a very slow rate of cell demise may have precluded detecting TUNEL-positive neurons dying through apoptosis. Increased Bax expression and activation of caspases support the latter possibility.

Attenuation of nitric oxide synthase isoform expression by mild hypothermia after focal cerebral ischemia: variations depending on timing of cooling

OBJECT

In this study the authors examined the influence of mild hypothermia on early expression of nitric oxide synthase (NOS) isoforms and peroxynitrite generation after experimental stroke.

METHODS

In 82 male Sprague-Dawley rats, middle cerebral artery occlusion was performed for 2 hours by using the intraluminal suture model. The rats were maintained at their normal body temperature or exposed to 2 hours of intraischemic or postischemic (2-hour delay) mild hypothermia. Brains were collected 2, 6, and 24 hours after onset of ischemia for immunohistochemical and Western blot analysis of neuronal (n)NOS and inducible (i)NOS expression and peroxynitrite generation.

CONCLUSIONS

Western blots showed significantly increased nNOS and iNOS expression in the ischemic cortex at 2, 6, and 24 hours compared with sham-operated animals. The NOS expression was highest at 24 hours. Postischemic hypothermia attenuated nNOS expression at 6 and 24 hours to a greater extent than intraischemic hypothermia. Intraischemic hypothermia reduced iNOS expression at both 2 and 24 hours, whereas postischemic hypothermia decreased iNOS expression at 24 hours. Results of immunohistochemical studies showed that nNOS colocalized with the neuronal marker MAP-2 at all time points, whereas iNOS was initially localized to vessels, and then localized to activated microglia by 24 hours. Intraischemic but not postischemic hypothermia decreased the number of nitrotyrosine-positive cells in the ischemic cortex at 24 hours. Mild hypothermia significantly but differentially attenuates increases in NOS isoforms, with more robust nNOS suppression when cooling is delayed. This may have important implications for understanding the mechanism of hypothermic neuroprotection and for stroke therapy.

Molecular mechanisms of cerebral ischemia-induced neuronal death

The mode of neuronal death caused by cerebral ischemia and reperfusion appears on the continuum between the poles of catastrophic necrosis and apoptosis: ischemic neurons exhibit many biochemical hallmarks of apoptosis but remain cytologically necrotic. The position on this continuum may be modulated by the severity of the ischemic insult. The ischemia-induced neuronal death is an active process (energy dependent) and is the result of activation of cascades of detrimental biochemical events that include perturbion of calcium homeostasis leading to increased excitotoxicity, malfunction of endoplasmic reticulum and mitochondria, elevation of oxidative stress causing DNA damage, alteration in proapoptotic gene expression, and activation of the effector cysteine proteases (caspases) and endonucleases leading to the final degradation of the genome. In spite of strong evidence showing that brain infarction can be reduced by inhibiting any one of the above biochemical events, such as targeting excitotoxicity, up-regulation of an antiapoptotic gene, or inhibition of a down-stream effector caspase, it is becoming clear that targeting a single gene or factor is not sufficient for stroke therapeutics. An effective neuroprotective therapy is likely to be a cocktail aimed at all of the above detrimental events evoked by cerebral ischemia and the success of such therapeutic intervention relies upon the complete elucidation of pathways and mechanisms of the cerebral ischemia-induced active neuronal death.

Activation of constitutive nitric oxide synthase(s) and absence of inducible isoform in aged rat brain

In this study, the effect of aging on nitric oxide synthases (NOS) was investigated in homogenates and cytosolic fractions from hippocampus, brain cortex and cerebellum of adult, old adult and old Wistar rats (3-4, 14, and 24 months old, respectively). Our results indicate the enhancement of Ca(2+) and calmoduline-dependent NOS activity in all investigated aged brain parts. Significantly higher NOS activity was found in the cerebellum. In the absence of Ca(2+) or in the presence of N-nitro-L-arginine (NNLA) the activity of NOS was absent. Inhibitor of constitutive NOS isoforms which preferentially inhibits neuronal NOS (nNOS), 7-nitroindazole, decreased NOS activity by 60 and 75% in adult and aged brain, respectively. However, using RT-PCR a significantly lower amount of mRNA for nNOS was detected in hippocampus. The ratio of NOS activity to nNOS mRNA was significantly higher in hippocampus and cerebellum of aged brain. No expression of the gene for inducible NOS was observed in adult and aged brain. These results indicate that probably nNOS is responsible for higher NOS activity in aged brain. Our data suggest that alteration of nNOS phosphorylation state may be responsible for the activation of NOS in aged brain. The down-regulation of nNOS mRNA expression may be an adaptive mechanism that protects the brain against excessive NO release.

Suppression of oxidative neuronal damage after transient middle cerebral artery occlusion in mice lacking interleukin-1

Interleukin-1 (IL-1) contributes to ischemic neurodegeneration. However, the mechanisms regulating action of IL-1 are still poorly understood. In order to clear this central issue, mice that were gene deficient in IL-1alpha and beta (IL-1 KO) and wild-type mice were subjected to 1-h transient middle cerebral artery occlusion (tMCAO). Expression levels of IL-1beta and IL-1 receptor I (IL-1RI) were then examined. Generation of peroxynitrite and the expression of mRNAs for nitric oxide synthase (NOS) subtypes were also determined. Immunostaining for IL-1beta was increased from 6 h and peaked at 24 h after tMCAO in the microglia and macrophage. The immunoreactivities of IL-1RI were increased progressively in the microvasculature and neuron-like cells of the ipsilateral hemisphere. Infarct volumes were significantly lower in IL-1 KO mice compared with wild-type mice 48 h after tMCAO (P<0.01). The immunoreactivities of 3-nitro-L-tyrosine were determined in the neurons and microvasculature 24 h after tMCAO and were significantly decreased in the IL-1 KO mice compared to wild-type mice. In addition, expression levels of NOS mRNA in IL-1 KO mice were lower than that measured in wild-type mice. These results indicate that IL-1 is up-regulated and may play a role in neurodegeneration by peroxynitrite production during ischemia.

Apoptotic hair cell death after transient cochlear ischemia in gerbils

The mechanisms of cochlear hair cell death following exposure to transient inner ear ischemia were investigated in gerbils histologically. The animals were subjected to ischemic insult by occluding both vertebral arteries for 15 min. Hoechst 33342 nuclear staining showed that inner hair cells (IHCs) underwent sporadic degeneration via nuclear condensation, which peaked 12 hours after the ischemia. Furthermore, nuclear DNA fragmentation was noted by the terminal deoxynucleotidyl transferase (TdT)-mediated deoxyuridine triphosphate (dUTP)-biotin nick end labeling method. Transmission electron microscopy revealed morphological changes in the IHCs characteristic of apoptosis, including karyopyknosis, chromatin condensation. These findings suggest that apoptotic cell death is the major process in hair cell degeneration in this animal model.

(-)-Epigallocatechin gallate protects against NO stress-induced neuronal damage after ischemia by acting as an anti-oxidant

The present study investigated the effects of (-)-epigallocatechin gallate (EGCG), which is the major component of polyphenol in green tea, on nitric oxide (NO) stress-induced neuronal damage, by monitoring NO mobilizations in the intact rat hippocampus and assaying the viability of cultured rat hippocampal neurons. A 10-min ischemia increased NO (NO(3)(-)/NO(2)(-)) concentrations in the intact rat hippocampus, while EGCG (50 mg/kg i.p.) inhibited the increase by 77% without affecting hippocampal blood flow. The NO donor, sodium nitroprusside (SNP; 50 microM), produced NO (NO(3)(-)/NO(2)(-)), while EGCG inhibited it in a dose-dependent manner at concentrations ranging from 50 to 200 microM. Treatment with SNP (100 microM) reduced the viability of cultured rat hippocampal neurons to 22% of control levels, while EGCG caused it to recover to 51% for 10 microM, 73% for 20 microM, and 70% for 50 microM. Taken together, it appears that EGCG could protect against ischemic neuronal damage by deoxidizing peroxynitrate/peroxynitrite, which is converted to NO radical or hydroxy radical.

Bcl-2-linked apoptosis due to increase in NO synthase in brain of SAMP10

We examined the linkage of nitric oxide (NO)-induced apoptosis to acceleration of brain aging of senescence-accelerated mouse prone 10 (SAMP10). The expression of neuronal nitric oxide synthase (nNOS) increased in the cerebral cortex of the brain of SAMP10 in an age-dependent manner and significantly higher levels of neuronal nitric oxide synthase (nNOS) were observed in both young and old SAMP10 as compared to age-matched controls. Moreover, a lower level of anti-apoptotic protein Bcl-2 and a higher level of pro-apoptotic protein cytochrome c in cytosol were observed in SAMP10 compared to the control. However, there was no significant difference in the expression of pro-apoptotic protein p53 between SAMP10 and the control. Furthermore, terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL)-positive apoptotic cells were more abundant in the cerebral cortex of aged SAMP10 than in the control. The present results suggest that an age-dependent increase of NO by up-regulation of nNOS promotes the Bcl-2-linked apoptosis in the cerebral cortex of SAMP10 and this may cause the acceleration of brain aging of SAMP10.

Chronic daily administration of selegiline and EGb 761 increases brain's resistance to ischemia in mice

Brief cerebral ischemia is reported to cause selective neuronal necrosis, apoptotic cell death, silent infarcts and, when recurrent, cognitive decline. Acute administration of selegiline and EGb 761 have been shown to have anti-apoptotic and neuroprotective effects in experimental ischemia. Their daily use is currently advised to slow down cognitive decline in patients with vascular dementia. Hence, unlike previous studies, we studied the neuroprotective action of chronic daily administration of these drugs in Swiss mice subjected to 30-min middle cerebral artery occlusion and 72 h of reperfusion since this model was reported to induce a slowly evolving infarct with profuse apoptotic cell death. Infarct area was evaluated by H&E staining on coronal brain sections and, apoptotic cells were identified by histological criteria, terminal transferase-mediated d-UTP nick-end labeling (TUNEL) and by immunohistochemical detection of caspase-cleaved actin fragments (fractin). Fifty-one mice received daily intraperitoneal injections of 10 mg/kg selegiline (n=18) or 50 mg/kg EGb 761 (n=17) or equal volume of saline (n=16) for 10-14 days before but not on the day of insult. The infarct volume, number of TUNEL- and fractin-positive cells were significantly reduced in treatment groups by 30, 42 and 51% (selegiline) and, 27, 27 and 29% (EGb 761), respectively. These data suggest that prophylactic use of selegiline and EGb 761 could increase the brain's resistance to mild ischemic injury.