[THE INFLUENCE OF THE MELATONIN ON THE CORRELATION BETWEEN THE INTENSITY OF THE ACCUMULATION OF THE OXIDATI-VE-MODIFIED PROTEINS CONTENT, ACTIVITY OF THE ANTIOXIDANT ENZYMES AND THE STATE OF PROTEOLYSIS IN THE BASAL NUCLEI OF THE BRAIN UNDER THE ACUTE HYPOXIA]

The effect of melatonin on the correlation between the intensity of the accumulation of the oxidative-modified protein content, activity of the antioxidant enzymes and the state of proteoly-sis in the basal nuclei (the nucleus caudatus, globus pallidus, nucleus accumbens, amigdaloid complex) of the brain under the conditions of acute hypoxia has been studied. Under the conditions of acute hypoxia in the basal nuclei an intensification of the protein peroxidation processes is observed, the activity of the antioxidant enzymes decreases, the intensity of the proteolysis increases. The injection of melatonin in a dose of 1 mg per kg of the body mass before the modeling of acute hypoxia results in the decreasing of protein peroxidation, increasing of the antioxidant enzyme activity and normalization of the parameters of proteolysis.

Nitric oxide synthase in hypoxic or ischemic brain injury

Abstract Hypoxic or ischemic stress causes many serious brain injuries, including stroke and neonatal hypoxia ischemia encephalopathy. During brain hypoxia ischemia processes, nitric oxide (NO) may play either a neurotoxic or a neuroprotective role, depending upon factors such as the NO synthase (NOS) isoform, the cell type by which NO is produced, and the temporal stage after the onset of the hypoxic ischemic brain injury. Excessive NO production can be neurotoxic, leading to cascade reactions of excitotoxicity, inflammation, apoptosis, and deteriorating primary brain injury. In contrast, NO produced by endothelial NOS plays a neuroprotective role by maintaining cerebral blood flow and preventing neuronal injury, as well as inhibiting platelet and leukocyte adhesion. Sometimes, NO-derived inducible NOS and neuronal NOS in special areas may also play neuroprotective roles. Therefore, this review summarizes the different roles and the regulation of the three NOS isoforms in hypoxic or ischemic brain injury as revealed in research in recent years, focusing on the neurotoxic role of the three NOS isoforms involved in mechanisms of hypoxic or ischemic brain injury.

[ROLE OF CASPASE-3 IN REGULATION OF THE CONTENT OF THE AMYLOID-DEGRADING NEUROPEPTIDASE NEPRILYSIN IN THE CORTEX OF RATS AFTER HYPOXIA]

Analysis of the effect of a caspase-3 inhibitor on the content of the amyloid-degrading neuropeptidase neprilysin (NEP) in the cortex of rats subjected to prenatal hypoxia (7% O2, 3 h) on the 14-th day of the embryonic development (E14) was performed. It was found that rats subjected to prenatal hypoxia on days 20-30 after birth have an increased content and activity of caspase-3 with reduced levels of NEP and of the C-terminal fragment of the amyloid precursor protein (AICD) regulating NEP expression. In hypoxic animals 3 days after a single injection of a caspase inhibitor (i. v., Ac-DEVD-CHO, P20) the content of AICD and NEP was found to be increased up to the levels observed in control rats. The data obtained suggest that the increase of caspase-3 enzyme activity could affect NEP expression via proteolytic degradation of its transcription factor AICD. These data for the first time demonstrate the role of caspases in AICD-dependent regulation of NEP production in the brain of mammals under hypoxic conditions.

Temporal Changes in Caspase-1 and Caspase-8 Activities Following Brain Hypoxia With and Without Src kinase Inhibition in a Piglet Animal Model

The Src family kinases are a family of intracellular, non-receptor tyrosine kinases that are involved in a variety of cellular functions including the regulation of inflammation and apoptosis after brain hypoxia. Caspase-1 (C1) activates IL-1β through the formation of complex structures, the inflammasomes, while caspase-8 (C8) is part of the extrinsic apoptotic pathway. C8 has been found to directly activate the production of IL-1β. Previously, we observed that C1 and IL-1β are increased in the acute phase after hypoxia in the brain of piglets, but they follow a different pattern long term, with C1 remaining activated throughout the period of observation, while IL-1β returning to baseline at 15 days. Src kinase inhibition ameliorated the activation of C1 and IL-1β early, but did not appear to have any effect long term. Prompted by these findings, we assessed the changes that occur over time (1 h and 15 days) in C1 and C8 activities after brain hypoxia as well as the effect of pretreatment with a Src kinase inhibitor, PP2 on these biochemical markers. Enzymatic activities were determined by spectrophotometry with measurements of C1 and C8 in each cytosolic brain sample (N = 4 in each group). We found that C1 and C8 activities increase in the acute phase following hypoxia in the brain of newborn piglets, with C8 relatively more than C1 (C8/C1 ratio increased from 2:1 as baseline to 3:1 in hypoxia). Fifteen days after hypoxia C8/C1 ratio decreased to about 1:1. In piglets that were pretreated with a Src kinase selective inhibitor (PP2) and then subjected to hypoxia, the C8/C1 ratio early increase was not observed. Immediately after hypoxia C8 and C1 follow a similar pattern of increase while long term this appears to dissociate. We propose that following this experimental methodology, the previously observed IL-1β production after hypoxia might be associated with C8 rather than C1 and that Src kinase is involved in the above process.

[Participation of metabotropic glutamate receptors of the brain in mechanizms of hypoxic signaling]

Group I of metabotropic glutamate receptors (ImGluRs) are a family of G-protein-coupled receptors which activate a multitude of signaling pathways important for modulating neuronal excitability and synaptic plasticity as well as anti- and prosurvival pathways initiated by hypoxia. However these functions are still not complete and sometimes controversial. The present work is a review of data concerning involvement of ImGluRs in mechanisms of cell response to hypoxia. We also present original data demonstrating their participation in forming pathogenic and adaptogenic intracellular events, appearing in rat neocortex during a day after severe or moderate hypobaric hypoxia, respectively. Ca2+ responses to ImGluRs stimulation in survival cortical slices and expression of ImGluRs, IP3Rs and PLCbeta1 in immunolabelled cortical preparations were estimated for these two different hypoxic models.

Differential expression of pro-inflammatory cytokines, endothelin-1 and nitric oxide synthases in the rat carotid body exposed to intermittent hypoxia

The enhanced carotid body (CB) chemosensory response to hypoxia induced by chronic intermittent hypoxia (CIH) has been attributed to oxidative stress, which is expected to increase the expression of chemosensory modulators including chemoexcitatory pro-inflammatory cytokines in the CB. Accordingly, we studied the time-course of the changes in the immunohistological expression of TNF-α, IL-1β, IL-6, ET-1, iNOS, eNOS and 3-nitrotyrosine in the CB, along with the progression of enhanced CB chemosensory responses to acute hypoxia in male Sprague-Dawley rats exposed to CIH (5%O₂, 12 times/h per 8h) for 7, 14 and 21 days. Exposure to CIH for 7 days resulted in a sustained potentiation of CB chemosensory responses to acute hypoxia, which persisted until 21 days of CIH. The chemosensory potentiation was paralleled by an increased 3-nitrotyrosine expression in the CB. On the contrary, CIH produced a transient 2-fold increase of ET-1 immunoreactivity at 7 days, a decrease in eNOS immunoreactivity, and a delayed but progressive increase of TNF-α, IL-1β and iNOS immunoreactivity, which was not associated with changes in systemic plasma levels or immune cell invasion within the CB. Thus, present results suggest that the local expression of chemosensory modulators and pro-inflammatory cytokines in the CB may have different temporal contribution to the CB chemosensory potentiation induced by CIH.

Physostigmine Reverses Cognitive Dysfunction Caused by Moderate Hypoxia in Adult Mice

BACKGROUND

Cognitive changes associated with moderate hypoxia in rodents may result from the diminished functioning of central cholinergic neurotransmission. We designed this study to examine whether treatment with physostigmine (PHY), an acetylcholinesterase inhibitor, could improve the impairment of working memory after hypoxic hypoxia.

METHODS

We randomized 90 Swiss Webster, 30-35 g mice (6-8 wks) to three hypoxia groups at fraction of inspired oxygen, FiO2 = 0.10 (1. no treatment; 2. PHY 0.1 mg/kg intraperitoneally administered immediately before; or 3. after hypoxia), or to two room air groups (given either no treatment or PHY after an insult). An object recognition test was used to assess short-term memory function. The object recognition test exploits the tendency of mice to prefer exploring novel objects in an environment when a familiar object is also present. During the 15 min training trial, two identical objects were placed in two defined sites of the box. During the test trial performed 1 h later, one of the objects was replaced by a new object with a different shape. The time spent exploring the two objects was automatically recorded by a video camera and associated software. The performance was analyzed with ANOVA, followed by post hoc comparisons using the Newman-Keuls test when appropriate. P values <0.05 were considered significant.

RESULTS

Untreated mice subjected to hypoxia at Fio2 = 0.1 spent significantly less time exploring a novel object on testing day 1 than did untreated mice breathing room air. Performance of the mice subjected to hypoxia, who received physostigmine after, but not before, the insult did not differ from the control group.

CONCLUSION

Moderate hypoxia impairs rodents' performance in a working memory task. It appears that changes are transient, because the cognitive functioning of the mice returned to the baseline level 7 days after treatment. Postinsult administration of PHY prevented deterioration of cognitive function. An increased level of acetylcholine in the central nervous system may be responsible for the improved performance of the hypoxia-treated mice.

Neuronal Cyclooxygenase-2 Activity and Prostaglandins PGE2, PGD2, and PGF2α Exacerbate Hypoxic Neuronal Injury in Neuron-enriched Primary Culture

Cyclooxygenase-2 (COX-2) activity has been implicated in the pathogenesis of cerebral ischemia. To determine whether COX-2 activity within the neuron itself exacerbates hypoxic neuronal injury, neuron-enriched cultures were subjected to anoxia. Treatment with COX-2 selective antagonists decreased cell death. Neurons cultured from homozygous COX-2 gene disrupted mice were resistant to hypoxia compared to those of heterozygotes. Infection of primary neurons with AAV expressing COX-2 exacerbated cell death compared to neurons infected with enhanced green fluorescent protein (EGFP) control vector. Addition of PGE2, PGD2 or PGF2 alpha to the medium exacerbated injury, suggesting that the deleterious effects of COX-2 overexpression in hypoxia could be mediated by direct receptor mediated effects of prostaglandins. Overexpression of COX-2 did not increase expression of cyclin D1 or phosphoretinoblastoma protein (pRb), or cleavage of caspase 3 suggesting that this cell cycle mechanism does not mediate COX-2 toxicity in this model.

Neuron-specific phosphorylation of c-Jun N-terminal kinase increased in the brain of hypoxic preconditioned mice

Accumulated studies have suggested that mitogen-activated protein kinase (MAPK) play a pivotal role in the development of cerebral hypoxic preconditioning (HPC). By using our "auto-hypoxia"-induced HPC mouse model, we have reported increased phosphorylation level of p38 MAPK, and decreased phosphorylation and protein expression levels of extracellular signal regulated kinases 1/2 (ERK1/2) in the brain of HPC mice. In the current study, we investigated the involvement of c-Jun N-terminal kinase (JNK) in the brain of HPC mice. By using Western blot analysis, we found that the phosphorylation levels of JNK at Thr183 and Tyr185 sites (phospho-Thr183/Tyr185 JNK), but not its protein expression, increased significantly (p<0.05, n=6 for each group) both in the hippocampus and frontal cortex of early (H1-H4) and delayed (H5 and H6) HPC mice than that of the normoxic group (H0, n=6). Similarly, enhanced phospho-Thr183/Tyr185 JNK was also observed by immunostaining in the hippocampus and frontal cortex of mice following series of hypoxic exposures (H3 and H6). In addition, we found that phospho-Thr183/Tyr185 JNK predominantly co-localized with a neuron-specific protein, neurogranin, in both the hippocampus and frontal cortex of HPC mice (H3) by using double-labeled immunofluorescence. These results suggest that the increased neuron-specific phosphorylation of JNK at Thr183/Tyr185, not protein expression, might be involved in the development of cerebral HPC of mice.

Manganese superoxide dismutase protects mouse cortical neurons from chronic intermittent hypoxia-mediated oxidative damage

Obstructive sleep apnea (OSA) syndrome has been recognized as a highly prevalent public health problem and is associated with major neurobehavioral morbidity. Chronic intermittent hypoxia (CIH), a major pathological component of OSA, increases oxidative damage to the brain cortex and decreases neurocognitive function in rodent models resembling human OSA. We employed in vitro and in vivo approaches to identify the specific phases and subcellular compartments in which enhanced reactive oxygen species (ROS) are generated during CIH. In addition, we utilized the cell culture and animal models to analyze the consequences of enhanced production of ROS on cortical neuronal cell damage and neurocognitive dysfunction. In a primary cortical neuron culture system, we demonstrated that the transition phase from hypoxia to normoxia (NOX) during CIH generates more ROS than the transition phase from NOX to hypoxia or hypoxia alone, all of which generate more ROS than NOX. Using selective inhibitors of the major pathways underlying ROS generation in the cell membrane, cytosol, and mitochondria, we showed that the mitochondria are the predominant source of enhanced ROS generation during CIH in mouse cortical neuronal cells. Furthermore, in both cell culture and transgenic mice, we demonstrated that overexpression of MnSOD-decreased CIH-mediated cortical neuronal apoptosis, and reduced spatial learning deficits measured with the Morris water maze assay. Together, the data from the in vitro and in vivo experiments indicate that CIH-mediated mitochondrial oxidative stress may play a major role in the neuronal cell loss and neurocognitive dysfunction in OSA. Thus, therapeutic strategies aiming at reducing ROS generation from mitochondria may improve the neurobehavioral morbidity in OSA.

Rho-kinase inhibition acutely augments blood flow in focal cerebral ischemia via endothelial mechanisms

Rho-kinase is a serine threonine kinase that increases vasomotor tone via its effects on both endothelium and smooth muscle. Rho-kinase inhibition reduces cerebral infarct size in wild type, but not endothelial nitric oxide synthase deficient (eNOS-/-) mice. The mechanism may be related to Rho-kinase activation under hypoxic/ischemic conditions and impaired vasodilation because of downregulation of eNOS activity. To further implicate Rho-kinase in impaired vascular relaxation during hypoxia/ischemia, we exposed isolated vessels from rat and mouse to 60 mins of hypoxia, and showed that hypoxia reversibly abolished acetylcholine-induced eNOS-dependent relaxation, and that Rho-kinase inhibitor hydroxyfasudil partially preserved this relaxation during hypoxia. We, therefore, hypothesized that if hypoxia-induced Rho-kinase activation acutely impairs vasodilation in ischemic cortex, in vivo, then Rho-kinase inhibitors would acutely augment cerebral blood flow (CBF) as a mechanism by which they reduce infarct size. To test this, we studied the acute cerebral hemodynamic effects of Rho-kinase inhibitors in ischemic core and penumbra during distal middle cerebral artery occlusion (dMCAO) in wild-type and eNOS-/- mice using laser speckle flowmetry. When administered 60 mins before or immediately after dMCAO, Rho-kinase inhibitors hydroxyfasudil and Y-27632 reduced the area of severely ischemic cortex. However, hydroxyfasudil did not reduce the area of CBF deficit in eNOS-/- mice, suggesting that its effect on CBF within the ischemic cortex is primarily endothelium-dependent, and not mediated by its direct vasodilator effect on vascular smooth muscle. Our results suggest that Rho-kinase negatively regulates eNOS activity in acutely ischemic brain, thereby worsening the CBF deficit. Therefore, rapid nontranscriptional upregulation of eNOS activity by small molecule inhibitors of Rho-kinase may be a viable therapeutic approach in acute stroke.

Hypoxia inducible factor prolyl 4-hydroxylase enzymes: center stage in the battle against hypoxia, metabolic compromise and oxidative stress

Studies of adaptive mechanisms to hypoxia led to the discovery of the transcription factor called hypoxia inducible factor (HIF). HIF is a ubiquitously expressed, heterodimeric transcription factor that regulates a cassette of genes that can provide compensation for hypoxia, metabolic compromise, and oxidative stress including erythropoietin, vascular endothelial growth factor, or glycolytic enzymes. Diseases associated with oxygen deprivation and consequent metabolic compromise such as stroke or Alzheimer's disease may result from inadequate engagement of adaptive signaling pathways that culminate in HIF activation. The discovery that HIF stability and activation are governed by a family of dioxygenases called HIF prolyl 4 hydroxylases (PHDs) identified a new target to augment the transcriptional activity of HIF and thus the adaptive machinery that governs neuroprotection. PHDs lose activity when cells are deprived of oxygen, iron or 2-oxoglutarate. Inhibition of PHD activity triggers the cellular homeostatic response to oxygen and glucose deprivation by stabilizing HIF and other proteins. Herein, we discuss the possible role of PHDs in regulation of both HIF-dependent and -independent cell survival pathways in the nervous system with particular attention to the co-substrate requirements for these enzymes. The emergence of neuroprotective therapies that modulate genes capable of combating metabolic compromise is an affirmation of elegant studies done by John Blass and colleagues over the past five decades implicating altered metabolism in neurodegeneration.

Inhibition of the myosin light chain kinase prevents hypoxia-induced blood-brain barrier disruption

Increased mortality after stroke is associated with development of brain edema. The aim of the present study was to examine the contribution of endothelial myosin light chain (MLC) phosphorylation to hypoxia-induced blood-brain barrier (BBB) opening. Measurements of trans-endothelial electrical resistance (TEER) were performed to analyse BBB integrity in an in vitro co-culture model (bovine brain microvascular endothelial cells (BEC) and rat astrocytes). Brain fluid content was analysed in rats after stroke induction using a two-vein occlusion model. Dihydroethidium was used to monitor intracellular generation of reactive oxygen species (ROS) in BEC. MLC phosphorylation was detected using immunohistochemistry and immunoblot analysis. Hypoxia caused a decrease of TEER values by more than 40%, which was prevented by inhibition of the MLC-kinase (ML-7, 10 micromol/L). In addition, ML-7 significantly reduced the brain fluid content in vivo after stroke. The NAD(P)H-oxidase inhibitor apocynin (500 micromol/L) prevented the hypoxia-induced TEER decrease. Hypoxia-dependent ROS generation was completely abolished by apocynin. Furthermore, ML-7 and apocynin blocked hypoxia-dependent phosphorylation of MLC. Our data demonstrate that hypoxia causes a breakdown of the BBB in vitro and in vivo involving ROS and the contractile machinery.

Neuron-specific phosphorylation of mitogen- and stress-activated protein kinase-1 involved in cerebral hypoxic preconditioning of mice

Studies have demonstrated the involvement of mitogen-activated protein kinase (MAPK) cascade pathways in the development of cerebral ischemic/hypoxic preconditioning (I/HPC). However, the role of mitogen- and stress-activated protein kinase 1 (MSK1), an important downstream kinase of MAPK signaling pathways, in cerebral I/HPC is unclear. By using Western blot and immunostaining methods, we applied our unique "autohypoxia"-induced I/HPC mouse model to investigate the effects of repetitive hypoxic exposure (H0-H6, n=6 for each group) on phosphorylation and protein expression levels of MSK1 in the brain of mice. We found that the levels of phosphorylation on threonine 645 (Thr645) and serine 375 (Ser375) of MSK1, but not the protein expression, increased significantly both in hippocampus and in cortex of mice from H1-H6 groups (P<0.05) over that of the normoxic group (H0, n=6). Similarly, enhanced phosphorylations on Thr645 and Ser375 of MSK1 were also observed by immunostaining in both the cortex and the hippocampus of mice following three series of hypoxic exposures (H3). In addition, we found by using double-immunofluorescence labeling that phosphorylated Thr645-MSK1 colocalized with a neuron-specific protein, neurogranin, in both cortex and hippocampus of I/HPC mice (H3). These results suggest that the increased neuron-specific phosphorylation of MSK1 on Thr645 and Ser375, not protein expression, might be involved in the development of cerebral I/HPC in mice.

Dynamics of hepatic enzyme activity following birth asphyxia

AIM

To investigate: 1) the occurrence of hypoxic hepatitis in full-term infants after birth asphyxia, 2) the temporal enzyme pattern in asphyxiated newborn infants, and 3) whether the degree of hypoxic hepatitis, as reflected by the rise in aminotransferase, correlates with the severity of the asphyxia and CNS symptomatology.

METHODS

Serum aminotransferases, lactate dehydrogenase, gamma-glutamyl transferase, total and conjugated bilirubin, cholinesterase activity, albumin, international normalized ratio (INR), and nucleated red blood cell count were prospectively measured in full-term asphyxiated newborn infants (n=26). Samples were collected three times during the first 72 h and once between days 6 and 12 after birth. Samples from healthy newborns (n=56), collected 24-172 h after birth, served as controls.

RESULTS

In 12 of the 26 asphyxiated infants, a serum alanine aminotransferase (S-ALAT) pattern compatible with hypoxic hepatitis was found. Five infants showed increased S-ALAT activity but with a different pattern. Similar patterns were seen in serum aspartate aminotransferase (S-ASAT). S-ALAT and -ASAT concentrations 0-72 h after birth correlated significantly with severity of hypoxic-ischaemic encephalopathy.

CONCLUSION

Birth asphyxia can induce an enzyme pattern in serum compatible to hypoxic hepatitis. There seems to be a correlation between aminotransferases in serum and the extent of CNS injury.

Prediction of neurological outcome after cardiopulmonary resuscitation by serial determination of serum neuron-specific enolase

AIMS

Data on the diagnostic accuracy of neuron-specific enolase (NSE) as marker of hypoxic brain damage are conflicting. The purpose of this prospective observational cohort study was to explore the prognostic value of serum NSE after cardiopulmonary resuscitation (CPR) and to define the most sensitive cutoff value with a specificity of 100% for the prediction of persistent coma.

METHODS AND RESULTS

Serum NSE concentrations were serially determined in 227 consecutive unconscious patients after CPR who were classified according to the best Glasgow-Pittsburgh cerebral performance categories (CPC, 1-4) achieved within 6 months follow-up. Sixteen patients were excluded due to incomplete NSE data and 34 due to death under analgesia sedation. The prevalence of poor neurological outcome (persistent coma, CPC 4) in our 177 analysed patients was 33%. At a specificity of 100%, a peak NSE concentration above 80 ng/mL predicted persistent coma with a sensitivity of 63%, a positive predictive value of 100%, a negative predictive value of 84%, and a predictive accuracy of 88%.

CONCLUSION

A peak serum NSE concentration exceeding 80 ng/mL is a highly specific but only moderately sensitive marker for a poor neurological outcome after CPR.

Gamma glutamyl transpeptidase is a dynamic indicator of endothelial response to stroke

Gamma glutamyl transpeptidase (gammaGT) is enriched at the apical surface of the cerebral capillaries that constitute the blood-brain barrier (BBB). This study tested the effects of hypoxia and inflammation on gammaGT activity in mice after stroke induced by transient cerebral artery occlusion (tMCAO) and in cultured cerebral microvessel endothelial cells. In microvessel-enriched preparations from mice after tMCAO, gammaGT activity was higher than in the sham controls in both ipsilateral and contralateral hemispheres from 12 h to 5 days after stroke, but lower at later time points (10-15 days). To identify the roles of different cytotoxic and stimulatory signals in this event, we further studied the dynamic changes of gammaGT activity in rat brain endothelial (RBE4) cells. Tumor necrosis factor alpha and lipopolyssachride significantly increased gammaGT activity in a time-dependent manner, an effect not seen after re-oxygenation. Such endothelial activation correlated with reduced total cellular ATP production. Thus, hypoxia and inflammatory stimulation appeared to have opposite effects on endothelial function. With the co-existence of inflammation and hypoxia in the brain after ischemic stroke, dynamic changes of gammaGT activity reflect evolving changes of endothelial function.

Nitric oxide-mediated mechanism of neuronal nitric oxide synthase and inducible nitric oxide synthase expression during hypoxia in the cerebral cortex of newborn piglets

Previously, we have shown that hypoxia results in increased generation of nitric oxide free radicals in the cerebral cortex of newborn piglets that may be due to up-regulation of nitric oxide synthases, neuronal nitric oxide synthase and inducible nitric oxide synthase. The present study tests the hypothesis that hypoxia results in increased expression of neuronal nitric oxide synthase and inducible nitric oxide synthase in the cerebral cortex of newborn piglets and that the increased expression is nitric oxide-mediated. Newborn piglets, 2-4 days old, were divided to normoxic (n=4), hypoxic (n=4) and hypoxic-treated with 7-nitro-indazole-sodium salt, a selective neuronal nitric oxide synthase inhibitor (hypoxic-7-nitro-indazole-sodium salt, n=6, 1 mg/kg, 60 min prior to hypoxia). Piglets were anesthetized, ventilated and exposed to an FiO2 of 0.21 or 0.07 for 60 min. Cerebral tissue hypoxia was documented biochemically by determining ATP and phosphocreatine. The expression of neuronal nitric oxide synthase and inducible nitric oxide synthase was determined by Western blot using specific antibodies for neuronal nitric oxide synthase and inducible nitric oxide synthase. Protein bands were detected by enhanced chemiluminescence, analyzed by imaging densitometry and the protein band density expressed as absorbance (OD x mm(2)). The density of neuronal nitric oxide synthase in the normoxic, hypoxic and hypoxic-7-nitro-indazole-sodium salt groups was: 41.56+/-4.27 in normoxic, 61.82+/-3.57 in hypoxic (P<0.05) and 47.80+/-1.56 in hypoxic-7-nitro-indazole-sodium salt groups (P=NS vs normoxic), respectively. Similarly, the density of inducible nitric oxide synthase in the normoxic, hypoxic and hypoxic-7-nitro-indazole-sodium salt groups was: 105.21+/-9.09, 157.71+/-13.33 (P<0.05 vx normoxic), 117.84+/-10.32 (p=NS vx normoxic), respectively. The data show that hypoxia results in increased expression of neuronal nitric oxide synthase and inducible nitric oxide synthase proteins in the cerebral cortex of newborn piglets and that the hypoxia-induced increased expression is prevented by the administration of 7-nitro-indazole-sodium salt. Furthermore, the neuronal nitric oxide synthase inhibition prevented the inducible nitric oxide synthase expression for a period of 7 days after hypoxia. Since administration of 7-nitro-indazole-sodium salt prevents nitric oxide generation by inhibiting neuronal nitric oxide synthase, we conclude that the hypoxia-induced increased expression of neuronal nitric oxide synthase and inducible nitric oxide synthase is mediated by neuronal nitric oxide synthase derived nitric oxide. We speculate that during hypoxia nitric oxide-mediated up-regulation of nitric oxide synthases will continue the perpetual cycle of nitric oxide generation-->NOS up-regulation-->nitric oxide generation resulting in hypoxic neuronal death.

Effect of neuronal nitric oxide synthase inhibition on caspase-9 activity during hypoxia in the cerebral cortex of newborn piglets

Previous studies have shown that cerebral hypoxia results in increased activity of caspase-9, a key initiator of programmed cell death. We have also shown increased nitric oxide (NO) free radical generation during hypoxia in the cerebral cortex of newborn piglets. The present study tests the hypothesis that hypoxia-induced increase in caspase-9 activity in the cerebral cortex of newborn piglets is mediated by NO derived from neuronal nitric oxide synthase (nNOS). To test this hypothesis, cytosolic caspase-9 activity was determined in 15 newborn piglets divided into three groups: normoxic (Nx, n=5), hypoxic (Hx, n=5), and Hx pretreated with 7-nitroindazole sodium salt (7-NINA), a selective nNOS inhibitor, 1mg/kg, i.p., 1h prior to hypoxia (Hx+7NI, n=5). The hypoxic piglets were exposed to an FiO(2) of 0.06 for 1h. Tissue hypoxia was documented by ATP and phosphocreatinine (PCr) levels. The cytosolic fraction was obtained from the cerebral cortical tissue following centrifugation at 100,000 x g for 1h and caspase-9 activity was assayed using Ac-Leu-Glu-His-Asp-amino-4-methyl coumarin, a specific fluorogenic substrate for caspase-9. Caspase-9 activity was determined spectroflourometrically at 460 nm using 380 nm as excitation wavelength. ATP levels (micromol/g brain) were 4.35+/-0.21 in the Nx 1.43+/-0.28 in the Hx (p<0.05 versus Nx), and 1.73+/-0.33 in the Hx+7-NINA group (p<0.05 versus Nx, p=NS versus Hx). PCr levels (micromol/g brain) were 3.80+/-0.26 in the Nx, 0.96+/-0.20 in the Hx (p<0.05 versus Nx), and 1.09+/-0.39 in the Hx+7 NINA group (p<0.05 versus Nx, p=NS versus Hx). Cytosolic caspase-9 activity (nmol/mg protein/h), increased from 1.27+/-0.15 in the Nx to 2.13+/-0.14 in the Hx (p<0.05 versus Nx) compared to 1.10+/-0.21 in the Hx+7-NINA group (p<0.05 versus Hx, p=NS versus Nx). Caspase-3 activity (nmol/mg protein/h) also increased from 9.39+/-0.73 in Nx to 18.94+/-3.64 in Hx (p<0.05 versus Nx) compared to 8.04+/-1.05 in the Hx+7-NINA group (p<0.05 versus Hx, p=NS versus Nx). The data show that administration of 7-NINA, an nNOS inhibitor, prevented the hypoxia-induced increase in caspase-9 activity that leads to increase in caspase-3 activity. Since nNOS inhibition blocked the increase in caspase-9 activity during hypoxia, we conclude that hypoxia-induced increase in caspase-9 activity is mediated by nNOS derived NO. We propose that the NO generated during hypoxia leads to activation of caspase-9 and results in initiation of caspase-cascade-dependent hypoxic neuronal death.

Neuroprotective effect of the stearic acid against oxidative stress via phosphatidylinositol 3-kinase pathway

Stearic acid is a long-chain saturated fatty acid consisting of 18 carbon atoms without double bonds. In the present study, we reported the neuroprotective effects and mechanism of stearic acid on cortical or hippocampal slices insulted by oxygen-glucose deprivation, NMDA or hydrogen peroxide (H(2)O(2)) in vitro. Different types of models of brain slice injury in vitro were developed by 10 min of oxygen/glucose deprivation, 0.5 mM NMDA or 2 mM H(2)O(2), respectively. After 30 min of preincubation with stearic acid (3-30 microM), cortical or hippocampal slices were subjected to oxygen-glucose deprivation, NMDA or H(2)O(2). Then the tissue activities were evaluated by using the 2,3,5-triphenyltetrazolium chloride (TTC) method. Population spikes were recorded in randomly selected hippocampal slices. Stearic acid (3-30 microM) dose-dependently protected brain slices from oxygen-glucose deprivation, NMDA and H(2)O(2) insults. Its neuroprotective effect against H(2)O(2) insults can be completely blocked by wortmannin (inhibitor of PI3K) and partially blocked by H7 (inhibitor of PKC) or genistein (inhibitor of TPK). Treatment of cortical or hippocampal slices with 30 microM stearic acid resulted in a significant increase in PI3K activity at 5, 10, 30 and 60 min. These observations reveal that stearic acid can protect cortical or hippocampal slices against injury induced by oxygen-glucose deprivation, NMDA or H(2)O(2), and its neuroprotective effects are via phosphatidylinositol 3-kinase dependent mechanism.

Decreased phosphorylation and protein expression of ERK1/2 in the brain of hypoxic preconditioned mice

Accumulated reports have suggested that activation of protein kinase C (PKC) isoforms may involve the activation of extracellular signal-regulated kinases 1/2 (ERK1/2) in the neuronal response to hypoxic stimuli. We have previously demonstrated that the membrane translocation or activation of conventional PKC (cPKC) betaII, gamma and novel PKC (nPKC) epsilon are increased in the early phase of cerebral hypoxic preconditioning in mice. However, the role of ERK1/2 in the development of cerebral hypoxic preconditioning is unclear. In the current study, we used Western blot analysis to investigate the effects of repetitive hypoxic exposure (H0-H6, n=6 for each group) on the levels of phosphorylation and protein expression of ERK1/2 in the frontal cortex and the whole hippocampus of mice. We found that the levels of phosphorylated ERK1/2, not protein expression of ERK1/2, decreased significantly in both cortex and hippocampus of the early hypoxic preconditioned mice (H1-H4), when compared to that of the normoxic group (p<0.05). In addition, a significant decrease (p<0.05) in the ERK1/2 protein expression, not the phosphorylated form of ERK1/2, was found both in the frontal cortex and hippocampus of mice followed hypoxia with previous hypoxia (H5 and H6). These results suggest that the decreased phosphorylation and downregulation of protein expression of ERK1/2 might be involved in the development of hypoxic preconditioning.

[Effects of taurine and zinc on activity of NOS and expression of nNOS in cerebral cortex of acute hypoxic mice]

OBJECTIVE

To explore the effect of taurine and zinc on vigor of nitric oxide synthase (NOS) and the expression level of neuronal nitric oxide synthase (nNOS) in the cerebral cortex of acute hypoxic mice and the their neuroprotective effects.

METHODS

Model of acute hypoxic mice was duplicated, NADPH-d histochemistry and nNOS immunohistochemistry were used to investigate the changes of NOS in different groups.

RESULTS

Compared with the NS group, the anoxia endurance of the zinc sulfate group was increased 33.06%, while that of the taurine and zinc sulfate group was increased 26.83% than that of the zinc sulfate group (P < 0.05). Compared with the NS group, the number of NADPH-d positive neurons and nNOS positive neurons in cerebral cortex of zinc sulfate group were significantly decreased, while those of the taurine and zinc sulfate group were significantly decreased than the zinc sulfate group (P < 0.05).

CONCLUSION

Both taurine and zinc could prolong the anoxia endurance, perhaps they might play an important role in decreasing the level of nitric oxide synthase to protect the brain against hypoxic damage.

Aging affects but does not eliminate the enzymatic antioxidative response to hypoxia/reoxygenation in cerebral cortex

The effect of aging on basal and hypoxia/reoxygenation levels of both oxidative stress (protein carbonyl and TBARS) and antioxidative-enzyme activity (Cu/Zn-SOD; Mn-SOD; Catalase, CAT; Se-independent and Se-dependent glutathione peroxidase, GPX; glutathione transferase, GST and glutathione reductase, GR) has been studied in the cerebral cortex of adult and old rats. Oxidative stress markers increased with aging and show an age-dependent post-hypoxic response. Moreover, aging caused either no change (GST, GR and CAT) or an increase (Se-GPX, Cu/Zn-SOD, Mn-SOD) in the basal activity of the enzymes analysed. Only Se-independent GPX activity decreases. However, we detected an age-dependent response of SODs to the hypoxic injury. The early and sustained Cu/Zn-SOD activity rise in adult animals became late and weak in aged animals. Meanwhile, aging slowed the Mn-SOD post-hypoxic response although this activity was consistently higher in aged rats. Aging eliminated the post-hypoxic CAT response, but, perhaps offset by increased GPX activity, did not affect the GST response and slightly reduced post-hypoxic GR activity. In conclusion, aging rise basal ROS production, does not diminish or even increase the antioxidative-enzyme activity, and may slow but does not usually eliminate the enzymatic antioxidant response to the increased post-hypoxic ROS generation.

Cellular levels of TrkB and MAPK in the neuroprotective role of BDNF for embryonic rat cortical neurons against hypoxia in vitro

Intrauterine asphyxia often results in neonatal loss or mental retardation. Brain-derived neurotrophic factor (BDNF) has been shown to be a protective agent against hypoxic damage to neurons. To understand the signaling mechanism underling the neuroprotective function of BDNF and to find therapeutic interventions for intrauterine asphyxia, we utilized an immunofluorescent technique to measure the intracellular levels of tyrosine kinase B (TrkB), phosphorylated TrkB, and the mitogen-activated protein kinase (MAPK) in the rat embryonic cortical neurons cultured in hypoxic conditions with and without BDNF pretreatment. The results showed that the fluorescent intensity of TrkB and phosphorylated TrkB in the cytoplasm and the fluorescent intensity of MARK in both cytoplasma and nucleus of the neurons were significantly increased in the presence of BDNF. The results indicate that the neuroprotective function of BDNF against hypoxia-induced neurotoxicity requires the participation of TrkB and is transduced via the Ras-MAPK signaling pathway.