Neonatal cerebral hypoxia-ischemia: involvement of FAK-dependent pathway

Focal adhesion kinase (FAK) is a non-receptor tyrosine kinase thought to play a major role in transducing extracellular matrix (ECM)-derived survival signals into cells. Thus, modulation of FAK activity may affect the linkage between ECM and signaling cascade to which it is connected and may participate in a variety of pathological settings. In the present study, we investigated the effect of neonatal cerebral hypoxia-ischemia (HI) on levels and tyrosine phosphorylation of focal adhesion kinase and the interaction of this enzyme with Src protein tyrosine kinase and adapter protein p130Cas, involved in FAK-mediated signaling pathway. The total amount of focal adhesion kinase as well as its phosphorylated form declined substantially to about 50% of the control between 24 and 48 h after the insult. Concomitantly a decreased association of FAK with its investigated molecular partners, Src kinase and p130Cas protein has been observed. This early response to brain hypoxia-ischemia was attenuated during prolonged recovery with almost complete return to control values at 7 days. These data are indicative of an involvement of FAK-dependent signaling pathway in the evolution of HI-induced neuronal degeneration.

Inducible nitric oxide synthase in long-term intermittent hypoxia: hypersomnolence and brain injury

RATIONALE

Long-term intermittent hypoxia (LTIH) exposure in adult mice, modeling oxygenation patterns of moderate-severe obstructive sleep apnea, results in lasting hypersomnolence and is associated with nitration and oxidation injuries in many brain regions, including wake-active regions.

OBJECTIVES

We sought to determine if LTIH activates inducible nitric oxide synthase (iNOS) in sleep/wake regions, and if this source of NO contributes to the LTIH-induced proinflammatory gene response, oxidative injury, and wake impairments.

METHODS

Mice with genetic absence of iNOS activity and wild-type control animals were exposed to 6 weeks of long-term hypoxia/reoxygenation before behavioral state recordings, molecular and biochemical assays, and a pharmacologic intervention.

MEASUREMENTS AND MAIN RESULTS

Two weeks after recovery from hypoxia/reoxygenation exposures, wild-type mice showed increased iNOS activity in representative wake-active regions, increased sleep times, and shortened sleep latencies. Mutant mice, with higher baseline sleep times, showed no effect of long-term hypoxia/reoxygenation on sleep time latencies and were resistant to hypoxia/reoxygenation increases in lipid peroxidation and proinflammatory gene responses (tumor necrosis factor alpha and cyclooxygenase 2). Inhibition of iNOS after long-term hypoxia/reoxygenation in wild-type mice was effective in reversing the proinflammatory gene response.

CONCLUSIONS

These data support a critical role for iNOS activity in the development of LTIH wake impairments, lipid peroxidation, and proinflammatory responses in wake-active brain regions, and suggest a potential role for inducible NO inhibition in protection from proinflammatory responses, oxidative injury, and residual hypersomnolence in obstructive sleep apnea.

Fos expression in the suprachiasmatic nucleus in rats following high altitude exposure

INTRODUCTION

Disturbances of circadian rhythms occur at high altitude. We examined the suprachiasmatic nucleus (SCN), considered to be the biological clock in mammals that regulates circadian rhythmicity, in adult rats following an exposure to simulated high altitude.

METHODS

Male adult Wistar rats weighing 250 g were exposed to an altitude of 8000 m in an altitude chamber, following which they were sacrificed at various time intervals ranging from 45 min to 3 d. Normal rats of similar weight kept outside the chamber were used as controls. Sections of hypothalamus containing the suprachiasmatic nucleus were processed immunohistochemically for expression of Fos, neuronal nitric oxide synthase (nNOS), and endothelial nitric oxide synthase (eNOS).

RESULTS

At 45 min, 4 h, and 24 h following the altitude exposure, a large number of Fos-positive neurons were detected as compared with the control rats in which occasional Fos-positive neurons were observed. Increased expression of nNOS and eNOS was also observed at 45 min and 4 h following the altitude exposure.

CONCLUSIONS

It is suggested that the neuronal activation indicated by upregulated expression of Fos and nitric oxide (NO) generated by nNOS may be involved in the disturbed circadian rhythms of the cardiovascular system (e.g., heart rate and BP), hormone secretion, and sleep-wake cycle which occur frequently during sojourns to high altitude. Increased eNOS expression also indicates excess production of NO, which may be involved in vasodialation and increased blood flow to the SCN following the exposure and may also be involved in modulating the circadian rhythms at high altitude.

Cyclooxygenase-mediated generation of free radicals during hypoxia in the cerebral cortex of newborn piglets

Previous studies have demonstrated that free radicals are formed under hypoxic conditions in newborn piglet brain. To test the hypothesis that the cyclooxygenase pathway serves as a source of free radical generation during hypoxia studies were performed on 24 piglets divided into four groups. Six saline (group 3) and six indomethacin treated (group 4) were exposed to hypoxia (FiO2 0.05-0.07) for 60 min. Cerebral hypoxia was documented biochemically by determination of ATP and phosphocreatine. Fluorescent compounds and conjugated dienes were determined as indices of lipid peroxidation. Free radical formation was determined by using n-tert butyl phenyl nitrone (PBN) as a spin trap agent and measuring spin adduct formation in duplicate using a Varian E-109 spectrometer. Groups 1 and 2 (normoxic) showed no spin adduct formation. Group 3 showed a significant increase in spin adduct formation compared to normoxia (372+/-125 vs. 63+/-15, P<0.001). Hypoxic animals pretreated with indomethacin had a spin adduct level of 197+/-132 and were similar to normoxic animals. ATP/PCr levels were the same in groups 3 and 4 denoting the same degree of cerebral hypoxia in all hypoxic animals. Conjugated dienes increased significantly during hypoxia as compared to normoxia (0.142+/-0.017 vs. 0.0+/-0.0) and were decreased insignificantly with indomethacin treatment. Fluorescent compounds were not significantly different among the four groups. Na+,K+-ATPase activity decreased during hypoxia but was not preserved in hypoxic animals pretreated with indomethacin. These data provide direct evidence of the presence of free radicals during hypoxia and the contribution of cyclooxygenase metabolism to their formation.

Nitric oxide synthase and intermittent hypoxia-induced spatial learning deficits in the rat

Intermittent hypoxia (IH) during sleep induces significant neurobehavioral deficits in the rat. Since nitric oxide (NO) has been implicated in ischemia-reperfusion-related pathophysiological consequences, the temporal effects of IH (alternating 21% and 10% O(2) every 90 s) and sustained hypoxia (SH; 10% O(2)) during sleep for up to 14 days on the induction of nitric oxide synthase (NOS) isoforms in the brain were examined in the cortex of Sprague-Dawley rats. No significant changes of endothelial NOS (eNOS) and neuronal NOS (nNOS) occurred over time with either IH or SH. Similarly, inducible NOS (iNOS) was not affected by SH. However, increased expression and activity of iNOS were observed on days 1 and 3 of IH (P < 0.01 vs. control; n = 12/group) and were followed by a return to basal levels on days 7 and 14. Furthermore, IH-mediated neurobehavioral deficits in the water maze were significantly attenuated in iNOS knockout mice. We conclude that IH is associated with a time-dependent induction of iNOS and that the increased expression of iNOS may play a critical role in the early pathophysiological events leading to IH-mediated neurobehavioral deficits.

Effect of hypoxia on protein phosphatase 2A activity, subcellular distribution and expression in cerebral cortex of newborn piglets

Protein phosphatase (PP) 2A (PP2A), a major serine/threonine phosphatase highly active in the brain, is known to regulate programmed cell death by different mechanisms including downregulation of Ca++/calmodulin-dependent kinase IV (CaMK IV). Previous studies have shown that CaMK IV activity is increased following cerebral hypoxia. In the present study, we tested the hypothesis that PP2A activity and expression in neuronal nuclei are decreased following hypoxia in newborn piglets. PP and PP2A activities were determined in cerebral subcellular fractions spectrophotometrically using a serine phosphopeptide in the presence or absence of microcystine. The activity of CaMK IV in neuronal nuclei was determined by 33P-incorporation into syntide 2 in the presence or absence of either 1 mM EGTA or 0.8 mM CaCl2 and 1 mM calmodulin. The expressions of PP2A and CaMK IV were measured using Western blot. Following hypoxia, nuclear Ca++-dependent kinase IV activity increased two-fold (P<0.001), whereas PP2A and PP activities significantly decreased (P<0.05) in the neuronal nuclei and membranes but not in the cytosol (P=NS). The distribution of the activity of PP2A was 60% in the cytosol, 35% in membranes and 5% in the neuronal nuclei. The expression of PP2A protein showed a 14% increase and for CaMK IV protein a 100% increase during hypoxia. We propose that due to the decreased activity of PP and PP2A following hypoxia in the neuronal nuclei there is a shift in the balance of the phosphorylation/dephosphorylation system toward increased phosphorylated state thereby increasing activity of the nuclear CaMK IV, modulator of programmed cell death. Since there is only slight increase in the PP2A protein expression, we conclude that the changes observed in the activity of PP2A are due to hypoxia-induced modification of the enzyme itself. We also provide evidence that PP2A is a potential regulator of CaMK IV during hypoxia.

Effect of hypoxia on protein tyrosine kinase activity in cortical membranes of newborn piglets—the role of nitric oxide

Previous studies have shown that cerebral hypoxia results in increased tyrosine phosphorylation of cerebral cortical cell membrane proteins as well as nuclear membrane anti-apoptotic protein, Bcl-2. The present study tests the hypothesis that hypoxia results in increased protein tyrosine kinase activity in cortical cell membranes of newborn piglets and that the inhibition of neuronal NOS by administration of 7-nitroindazole sodium salt (7-NINA), a selective inhibitor of nitric oxide synthase (NOS), will prevent the hypoxia-induced increase in protein tyrosine kinase activity. To test this hypothesis, protein tyrosine kinase activity was determined in cerebral cortical membranes of 2- to 4-day-old newborn piglets divided into normoxic (n=6), hypoxic (n=5) and 7-NINA-treated hypoxic (n=5) (7-NINA, 1mg/kg, i.p., prior to hypoxia) groups. Tissue hypoxia was achieved by exposing the animals to an FiO(2) of 0.07 for 60 min and was documented biochemically by determining tissue ATP and phosphocreatine (PCr) levels. Cortical P(2) membranes were isolated and protein tyrosine kinase activity determined by (33)P incorporation into a specific peptide substrate for 15 min at 37 degrees C in a medium containing 100 mM HEPES, pH 7.0, 1mM EDTA, 125 mM MgCl(2), 25 mM MnCl(2), 2mM DTT, 0.2 mM sodium orthovanadate, 2mM EGTA, 150 microM tyrosine kinase peptide substrate [Lys 19] cdc2(6-20)-NH(2), (33)P-ATP, and 10 microg of membrane protein. Protein tyrosine kinase activity was determined by the difference between (33)P incorporation in the presence and absence of specific peptide substrate and expressed as pmol/mg protein/h. The ATP values in the normoxic, hypoxic and 7-NINA-treated hypoxic animals were ATP: 4.57+/-0.45 micromol/g, 1.29+/-0.23 micromol/g (p<0.05 versus normoxic) and 1.50+/-0.14 micromol/g brain (p<0.05 versus normoxic), respectively. The PCr values in the normoxic, hypoxic and 7-NINA-treated hypoxic animals were: 3.77+/-0.36 micromol/g, 0.77+/-0.13 micromol/g (p<0.05 versus normoxic) and 1.02+/-0.24 micromol/g brain (p<0.05 versus normoxic), respectively. Protein tyrosine kinase activity in the normoxic, hypoxic and the 7-NINA-treated groups was 378+/-77 pmol/mg protein/h, 854+/-169 pmol/mg protein/h (p<0.05 versus normoxic) and 464+/-129 pmol/mg protein/h (p<0.05 versus hypoxic), respectively. The data show that cerebral tissue hypoxia results in increased protein tyrosin kinase activity in cortical membranes of newborn piglets and pretreatment with 7-NINA prevents the hypoxia-induced increase in protein tyrosine kinase activity. We conclude that the hypoxia-induced increase in protein tyrosine kinase activity is NO-mediated. We propose that the hypoxia-induced increase in protein tyrosine kinase activity leading to increased phosphorylation of Bcl-2 is a critical link to hypoxic neuronal injury pathway.

Hypoxia induces caspase-9 and caspase-3 activation without neuronal death in gerbil brains

To investigate the in vivo apoptotic machinery in oxygen deprived brain, we examined the expression of caspase-9 and caspase-3 in the hippocampus of Mongolian gerbils subjected to either transient hypoxia (4% O2 for 6 min) or forebrain ischemia (10 min bilateral carotid artery occlusion) followed by 8 h to 7 days of reoxygenation or blood recirculation. Apoptotic death was characterized by isolating hippocampal genomic DNA and analysing DNA fragmentation as well as histological studies including TUNEL assay and toluidine blue staining of brain sections. The results showed that both hypoxic and ischemic gerbil brains exhibited an increase in caspase-9 and caspase-3 gene expression. However, no cell damage was detectable following hypoxia, while marked DNA fragmentation and extensive cell death was observed following ischemia. Moreover, although hypoxia did not lead to cell death, both hypoxia and ischemia were associated with cleavage of procaspase-9 and procaspase-3 and increases in their activities as well as cleavage of poly(ADP-ribose) polymerase-1 (PARP-1), a major caspase-3 substrate. These results indicate that, in vivo, even late apoptotic events such as caspase activation and PARP-1 cleavage in hypoxic brains do not necessarily induce an irreversible commitment to apoptotic neuronal death.

ATP and cytochrome c-dependent inhibition of caspase-9 activity in the cerebral cortex of newborn piglets

The present study investigates the mechanism of activation of caspase-9 during hypoxia and tests the hypothesis that ATP and cytochrome c regulate the activity of caspase-9 in the cerebral cortex of newborn piglets. Cerebral tissue hypoxia was documented by decreased levels of high energy phosphates, ATP and phosphocreatine (PCr). Cytosolic fractions were prepared from cerebral cortices and passed through a G50 column, to remove endogenous ATP and cytochrome c. Caspase-9 activity was determined spectrofluorometrically using a specific fluorogenic substrate for caspase-9 at increasing concentrations of ATP (0-1.0 mM) or cytochrome c (0-3.0 microM). Caspase-9 activity (nmol/mg protein/h) was 1.26 +/- 0.15 in the normoxic and 2.13 +/- 0.14 in the hypoxic group (P < 0.05). The enzyme activity was inhibited by ATP or cytochrome c in both normoxic and hypoxic groups. The IC50 for ATP and cytochrome c increased 5-fold and 1.5-fold, respectively, following hypoxia, suggesting a hypoxia-induced modification of the ATP and cytochrome binding sites. The data demonstrate that ATP (1 mM) and cytochrome c (3.0 microM) inhibit caspase-9 activity by approximately 70%. On the basis of these observations, we propose a new and novel concept that the caspase-9 activity remains inhibited under the normoxic conditions and during hypoxia the decrease in ATP and decreases in the affinity for ATP and cytochrome c release the inhibitory block to activate the enzyme. Results of ATP- and cytochrome c-dependent inhibition of purified caspase-9 human recombinant show that the inhibitory effect by ATP and cytochrome c does not require Apaf-1. To our knowledge, this is a completely new concept and a new mechanism of regulation of caspase-9 activity that may lead to hypoxia-induced programmed cell death.

[The effect of posthypoxic hypothermia for lactate dehydrogenase activity in brain cortex and blood serum of 14-days-old rats]

OBJECTIVE

The effect of various degrees of hypobaric hypoxia and consequent hypothermia on lactate dehydrogenase (E.C.1.1.1.27) activity in blood serum and brain cortex in 14 day-old rats was investigated.

DESIGN

Experimental study.

SETTING

Institute of Physiology, 1st Med. Faculty, Charles University, Prague.

METHODS

14 day-old rats (Wistar of our own breed) were exposed to mild hypobaric hypoxia (corresponding to altitude of 7000 m, pO2 = 8.6 kPa, BP = 41.2 kPa, lasting 20 min) or strong hypobaric hypoxia (corresponding to altitude of 9000 m, pO2 = 6.4 kPa, BP = 30.7 kPa, lasting 30 min). Just after hypoxic stress the animals were killed by decapitation and on cooled block the grey cortical matter was removed. Blood serum samples as well as brain cortex homogenates were immediately incubated in three variously tempered media (38 degrees Celsius = control values, 30 degrees Celsius and 22 degrees Celsius = hypothermic conditions). The incubation was over (30 min.), and the lactate dehydrogenase (LDH) activity was followed using the Lachema test.

RESULTS

The LDH activity was influenced by mild hypobaric hypoxia (7000 m) neither in blood serum nor in brain cortex. Also the values of LDH activities registered in normo or in hypothermic conditions were not different as compared with control values. The strong hypoxia (9000 m) evokes in brain cortex homogenates simultaneously with normothermia and posthypoxic hypothermia (30 degrees Celsius) significant increase of LDH activity. In blood serum the strong hypoxia increased the LDH activity; in subsequent hypothermic condition (22 degrees Celsius) the LDH activity was more lowered.

CONCLUSION

The LDH activity in brain cortex as well as in blood serum of young rats (Wistar) seems to be resistent to mild hypoxia (7000 m) as well to hypothermic conditions. The strong hypoxia (9000 m) evokes quite different responses: in brain cortex the LDH activities in hypothermic conditions are higher, in blood serum lower as compared with control values (14 day-old rats stressed by hypoxia only). In control measurements the lowering temperature decreases the mentioned enzyme activity in brain cortex; in blood serum no significant differences could be found.

Nitric oxide-mediated alterations of protein tyrosine phosphatase activity and expression during hypoxia in the cerebral cortex of newborn piglets

The present study tested the hypothesis that the hypoxia-induced decrease in protein tyrosine phosphatase (PTP) activity in the membranes and increased activity and expression of PTPs (PTP-1B, PTP-SH1 and 2) in the cytosol of the cerebral cortex of newborn piglets are mediated by nitric oxide (NO). To test this hypothesis, PTP activity in cell membranes and activity and expression were measured in the cytosol of normoxic (Nx, n = 5), hypoxic (Hx, n = 5), and 7-nitro-indazole sodium salt (7-NINA), a selective inhibitor of neuronal nitric oxide synthase (nNOS), pretreated hypoxic (7-NINA+Hx, n = 6) newborn piglets. PTP activity in cortical cell membranes was lower in the Hx group as compared to the Nx group and this decrease was prevented in the 7-NINA+Hx group. The density of cytosolic PTP-1B, cytosolic PTP-SH1 and PTP-SH2 was increased in the Hx group and this increase was prevented in the 7-NINA+Hx group. Immunohistochemistry results show an increased immunoreactivity to PTP-1B in the Hx as compared to Nx animals. The data show that pretreatment with 7-NINA, a selective inhibitor of nNOS, prevents the hypoxia-induced decrease in PTP activity in membranes. nNOS inhibition also prevented the hypoxia-induced increase in PTP activity and expression in cytosol, and therefore we conclude that modification of PTP during hypoxia is NO-mediated.

Hypoxia-induced ischemic tolerance in neonatal rat brain involves enhanced ERK1/2 signaling

Hypoxic preconditioning (HP) 24 h before hypoxic-ischemic (HI) injury confers significant neuroprotection in neonatal rat brain. Recent studies have shown that the mitogen-activated protein kinase (MAPK) and phosphatidylinositol-3-kinase (PI3K) intracellular signaling pathways play a role in the induction of tolerance to ischemic injury in heart and brain. To study the role of MAPK (ERK1/2, JNK, p38MAPK) and PI3K/Akt/GSK3beta signaling pathways in hypoxia-induced ischemic tolerance, we examined the brains of newborn rats at different time points after exposure to sublethal hypoxia (8% O(2) for 3 h). Immunoblot analysis showed that HP had no effect on the levels of phosphorylated Akt, GSK3beta, JNK and p38MAPK. In contrast, significantly increased levels of phosphorylated ERK1/2 were observed 0.5 h after HP. Double immunofluorescence staining showed that hypoxia-induced ERK1/2 phosphorylation was found mainly in microvessels throughout the brain and in astrocytes in white matter tracts. Inhibition of hypoxia-induced ERK1/2 pathway with intracerebral administration of U0126 significantly attenuated the neuroprotection afforded by HP against HI injury. These findings suggest that activation of ERK1/2 signaling may contribute to hypoxia-induced tolerance in neonatal rat brain in part by preserving vascular and white matter integrity after HI.

Nitric oxide-mediated activation of extracellular signal-regulated kinase (ERK) and c-jun N-terminal kinase (JNK) during hypoxia in cerebral cortical nuclei of newborn piglets

Previous studies have shown that mitogen-activated protein kinases, such as extracellular signal-related kinase (ERK) and c-Jun N-terminal kinase (JNK), mediate signal transduction from cell surface receptors to the nucleus and phosphorylate anti-apoptotic proteins thereby regulating programmed cell death. The present study tests the hypotheses that hypoxia activates ERK and JNK in neuronal nuclei of newborn piglets and the hypoxia-induced activation of ERK and JNK is mediated by nitric oxide (NO). Activated ERK and JNK were assessed by determining phosphorylated ERK and JNK using immunoblotting in six normoxic (Nx) and 10 hypoxic (Hx) and five N-nitro-L-arginine (a NOS inhibitor, 40 mg/kg,) -pretreated hypoxic (N-nitro-L-arginine [NNLA]-Hx) 3-5 day old piglets. Hypoxia was induced by decreasing inspired oxygen from 21% to 7% for 60 min. Cerebral tissue hypoxia was documented biochemically by determining the tissue levels of ATP and phosphocreatine (PCr). Cortical neuronal nuclei were isolated and the nuclear protein was analyzed for activated ERK and JNK using anti-phosphorylated ERK and JNK antibodies. Protein bands were detected using enhanced chemiluminescence method and analyzed by imaging densitometry. Protein density was expressed as absorbance ODxmm(2). ATP levels were 4.57+/-0.45 micromoles/g brain in the Nx group, 1.29+/-0.23 micromoles/g brain in the Hx group (P<0.05 vs Nx) and 1.50+/-0.14 micromoles/g brain in the NNLA-Hx group (P<0.05 vs Nx). PCr levels were 3.77+/-0.36 micromoles/g brain in the Nx group, 0.77+/-0.13 micromoles/g brain in the hypoxic group (P<0.05) and 1.02+/-0.24 in the NNLA-Hx group (P<0.05 vs Nx). Density of phosphorylated ERK protein was 170.5+/-53.7 ODxmm(2) in the Nx group as compared with 419.6+/-63.9 ODxmm(2) in the hypoxic group (P<0.001 vs Nx) and 270.0+/-28.7 in the NNLA-Hx group (P<0.002 vs Hx). Density of phosphorylated JNK protein was 172.8+/-42.8 ODxmm(2) in the normoxic group as compared with 364.6+/-60.1 ODxmm(2) in the Hx group (P<0.002) and 254.8+/-24.8 in the NNLA-Hx group (P<0.002 vs Hx). The data demonstrate increased phosphorylation of ERK and JNK during hypoxia indicating that hypoxia results in activation of ERK and JNK in neuronal nuclei of newborn piglets. The administration of NNLA, a NOS inhibitor, prevented the hypoxia-induced phosphorylation of ERK and JNK indicating that the hypoxia-induced activation of ERK and JNK in the cerebral cortical nuclei of newborn piglets is NO-mediated

Green tea polyphenol (−)-epigallocatechin gallate attenuates the neuronal NADPH-d/nNOS expression in the nodose ganglion of acute hypoxic rats

Recent studies have shown that (-)-epigallocatechin gallate (EGCG), one of the green tea polyphenols, has a potent antioxidant property. Nitric oxide (NO) plays an important role in the neuropathogenesis induced by brain ischemia/reperfusion and hypoxia. This study aimed to explore the potential neuroprotective effect of EGCG on the ganglionic neurons of the nodose ganglion (NG) in acute hypoxic rats. Thus, the young adult rats were pretreated with EGCG (10, 25, or 50 mg/kg, i.p.) 30 min before they were exposed to the altitude chamber at 10,000 m with the partial pressure of oxygen set at the level of 0.27 atm (pO2=43 Torr) for 4 h. All the animals examined were allowed to survive for 3, 7, and 14 successive days, respectively, except for those animals sacrificed immediately following hypoxic exposure. Nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) histochemistry and neuronal nitric oxide synthase (nNOS) immunohistochemistry were carried out to detect the neuronal NADPH-d/nNOS expression in the NG. The present results show a significant increase in the expression of NADPH-d/nNOS reactivity in neurons of the NG at various time intervals following hypoxia. However, the hypoxia-induced increase in NADPH-d/nNOS expression was significantly depressed only in the hypoxic rats treated with high dosages of EGCG (25 or 50 mg/kg). These data suggest that EGCG may attenuate the oxidative stress following acute hypoxia.

Intermittent hypoxia induces time-dependent changes in the protein kinase B signaling pathway in the hippocampal CA1 region of the rat

Intermittent hypoxia (IH) during sleep induces temporally defined increases in apoptosis within vulnerable brain regions such as the hippocampal CA1 region in rats. Protein kinase B (AKT) has emerged as major signal transduction protein underlying inhibition of apoptosis and consequent increases in cell survival. Sprague Dawley adult male rats were exposed during sleep to IH or to normoxia (RA) for periods ranging from 0 to 30 days, and expression of total and phosphorylated AKT, of forkhead family members FKHR and FKHRL1, and of glycogen synthase kinase 3beta (GSK3beta) was assessed. Decreases in phosphorylation occurred as early as 1 h IH exposure, reached a nadir at 6 h-3 days, and then progressively returned to baseline levels at 14-30 days. Phosphorylated AKT and GSK3beta were intensely expressed and highly colocalized within neuronal cells (Neu-N positive) in the CA1 region. Thus, IH induces time-dependent biphasic changes in AKT survival pathways within the CA1 region that are temporally correlated with the initial increases and subsequent decreases in neuronal apoptosis.

Hypoxia-induced modification of poly (ADP-ribose) polymerase and dna polymerase beta activity in cerebral cortical nuclei of newborn piglets: role of nitric oxide

Previous studies have shown that poly (ADP-ribose) polymerase (PARP) and DNA polymerase beta, nuclear enzymes, are associated with cell replication and DNA repair. The present study tests the hypothesis that hypoxia results in increased PARP and DNA polymerase activity in cerebral cortical neuronal nuclei to repair the hypoxia-induced damage to genomic DNA. Studies were conducted in 13 anesthetized and ventilated newborn piglets (age 3-5 days) divided into normoxic (n=5) and hypoxic (n=8) groups. Hypoxia was induced by decreasing inspired oxygen from 21% to 7% for 60 min. Cerebral tissue hypoxia was documented biochemically by determining the tissue levels of ATP and phosphocreatine (PCr). Following isolation of the cortical neuronal nuclei, the activity of PARP and DNA polymerase beta was determined. During hypoxia, the tissue ATP level decreased by 73% from 4.12+/-0.67 micromol/g brain to 1.12+/-0.34 micromol/g brain, and PCr decreased by 78% from 4.14+/-0.68-0.90+/-0.20 micromol/g brain. In hypoxic neuronal nuclei, PARP activity significantly increased from 5.88+/-0.51 pmol NAD/mg protein/h in normoxic nuclei to 10.04+/-2.02 (P=0.001). PARP activity inversely correlated with tissue ATP (r=0.78) and PCr levels (r=0.81). Administration of N-nitro-L-arginine prior to hypoxia decreased the hypoxia-induced increase in PARP activity by 67%. Endogenous DNA polymerase beta activity increased from 0.96+/-0.13 in normoxic nuclei to 1.39+/-0.18 nmol/mg protein/h in hypoxic nuclei (P<0.005). DNA polymerase beta activity in the presence of exogenous template increased from 1.54+/-0.14 in the normoxic to 2.42+/-0.26 nmol/mg protein/h in the hypoxic group (P<0.005). DNA polymerase beta activity in the presence or absence of template inversely correlated with the tissue ATP (r=0.95 and 0.84, respectively) and PCr levels (r=0.93 and 0.77, respectively). These results demonstrate that the activity of PARP and DNA polymerase beta enzymes increase with the increase in degree of cerebral tissue hypoxia. Furthermore, the results demonstrate a direct correlation between the PARP and the DNA polymerase beta activity. We conclude that tissue hypoxia results in increased PARP and DNA polymerase beta activities indicating activation of DNA repair mechanisms that may result in potential neuronal recovery following hypoxia and the hypoxia-induced increase in PARP activity is NO-mediated.

Matrix metalloproteinase-9 expression in post-hypoxic human brain capillary endothelial cells: H2O2 as a trigger and NF-kappaB as a signal transducer

The haemorrhagic transformation in ischemic stroke involves disruption of the integrity of the microvascular beds, partially based on the action of matrix metalloproteinases (MMPs). The objective of the present study was to evaluate the contribution of microvascular endothelial cells from human brain (HBECs) to MMPs' expression and regulation under conditions relevant to brain ischemia. MMPs and their inhibitors were examined with zymography, Western-blotting, ELISA and MMP-activity assay in cultured HBECs. Four-hour hypoxia (pO(2)=60 mmHg) elevated the level of MMP-9 in the supernatant of the HBECs and this early response required collagen-matrix. Active oxygen species sustained the increased MMP-9 activity for at least 24 h. In the post-hypoxic period 20 micro mol/L H(2)O(2) caused a 6-fold increase in the specific activity of MMP-9 over the normoxic cells and a comparable effect was exerted by thrombin (50 nmol/L) and leukocyte elastase (10 nmol/L). The role of NF-kappaB, a redox-state sensitive transcription factor, was evaluated with immunofluorescence confocal microscopy and immunoblotting of nuclear and cytoplasmic extracts. The oxidative stress-dependent MMP-9 induction was accompanied by a significant increase in the NF-kappaB localized in the nuclei and these responses were blunted with a proteasome inhibitor (MG132). Consequently, according to our in vitro data HBECs are a source of MMP-9, which is under the control of triggers relevant to the ischemic/reperfused brain (reactive oxygen species, thrombus and inflammation related proteases) and this regulation is partially based on NF-kappaB activation. The reported regulation of endothelium-derived MMP-9 supports its potential involvement in the post-hypoxic disturbances of the cerebral microcirculation.

Hypoxic induction of caspase-11/caspase-1/interleukin-1beta in brain microglia

Caspase-11 is an inducible protease that plays an important role in both inflammation and apoptosis. Inflammatory stimuli induce and activate caspase-11, which is required for the activation of caspase-1 or interleukin-1beta (IL-1beta) converting enzyme (ICE). Caspase-1 in turn mediates the maturation of proinflammatory cytokines such as IL-1beta, which is one of the crucial mediators of neurodegeneration in the central nervous system. Here, we report that hypoxic exposure of cultured brain microglia (BV-2 mouse microglia cells and rat primary microglial cultures) induces expression and activation of caspase-11, which is accompanied by activation of caspase-1 and secretion of mature IL-1beta and IL-18. Hypoxic induction of caspase-11 was observed in both mRNA and protein levels, and was mediated through p38 mitogen-activated protein kinase pathway. Transient global ischemia in rats also induced caspase-11 expression and IL-1beta production in hippocampus supporting our in vitro findings. Caspase-11-expressing cells in hippocampus were morphologically identified as microglia. Taken together, our results indicate that hypoxia induces a sequential event-caspase-11 induction, caspase-1 activation, and IL-1beta release-in brain microglia, and point out the importance of initial caspase-11 induction in hypoxia-induced inflammatory activation of microglia.

Chronic hypoxia in development selectively alters the activities of key enzymes of glucose oxidative metabolism in brain regions

The immature brain is more resistant to hypoxia/ischemia than the mature brain. Although chronic hypoxia can induce adaptive-changes on the developing brain, the mechanisms underlying such adaptive changes are poorly understood. To further elucidate some of the adaptive changes during postnatal hypoxia, we determined the activities of four enzymes of glucose oxidative metabolism in eight brain regions of hypoxic and normoxic rats. Litters of Sprague-Dawley rats were put into the hypoxic chamber (oxygen level maintained at 9.5%) with their dams starting on day 3 postnatal (P3). Age-matched normoxic rats were use as control animals. In P10 hypoxic rats, lactate dehydrogenase (LDH) activity in cerebral cortex, striatum, olfactory bulb, hippocampus, hypothalamus, pons and medulla, and cerebellum was significantly increased (by 100%-370%) compared to those in P10 normoxic rats. In P10 hypoxic rats, hexokinase (HK) activity in hypothalamus, hippocampus, olfactory bulb, midbrain, and cerebral cortex was significantly decreased (by 15%-30%). Neither alpha-ketoglutarate dehydrogenase complex (KGDHC, which is believed to have an important role in the regulation of the tricarboxylic acid [TCA] cycle flux) nor citrate synthase (CS) activity was significantly decreased in the eight regions of P10 hypoxic rats compared to those in P10 normoxic rats. In P30 hypoxic rats, LDH activity was only increased in striatum (by 19%), whereas HK activity was only significantly decreased (by 30%) in this region. However, KGDHC activity was significantly decreased in olfactory bulb, hippocampus, hypothalamus, cerebral cortex, and cerebellum (by 20%-40%) in P30 hypoxic rats compared to those in P30 normoxic rats. Similarly, CS activity was decreased, but only in olfactory bulb, hypothalamus, and midbrain (by 9%-21%) in P30 hypoxic rats. Our results suggest that at least some of the mechanisms underlying the hypoxia-induced changes in activities of glycolytic enzymes implicate the upregulation of HIF-1. Moreover, our observation that chronic postnatal hypoxia induces differential effects on brain glycolytic and TCA cycle enzymes may have pathophysiological implications (e.g., decreased in energy metabolism) in childhood diseases (e.g., sudden infant death syndrome) in which hypoxia plays a role.

Postnatal changes in the nitric oxide system of the rat cerebral cortex after hypoxia during delivery

The impact of hypoxia in utero during delivery was correlated with the immunocytochemistry, expression and activity of the neuronal (nNOS) and inducible (iNOS) isoforms of the nitric oxide synthase enzyme as well as with the reactivity and expression of nitrotyrosine as a marker of protein nitration during early postnatal development of the cortex. The expression of nNOS in both normal and hypoxic animals increased during the first few postnatal days, reaching a peak at day P5, but a higher expression was consistently found in hypoxic brain. This expression decreased progressively from P7 to P20, but was more prominent in the hypoxic group. Immunoreactivity for iNOS was also higher in the cortex of the hypoxic rats and was more evident between days P0 and P5, decreasing dramatically between P10 and P20 in both groups of rats. Two nitrated proteins of 52 and 38 kDa, were also identified. Nitration of the 52-kDa protein was more intense in the hypoxic animals than in the controls, increasing from P0 to P7 and then decreasing progressively to P20. The 38-kDa nitrated protein was seen only from P10 to P20, and its expression was more intense in control than in the hypoxic group. These results suggest that the NO system may be involved in neuronal maturation and cortical plasticity over postnatal development. Overproduction of NO in the brain of hypoxic animals may constitute an effort to re-establish normal blood flow and may also trigger a cascade of free-radical reactions, leading to modifications in the cortical plasticity.

Differences in nitric oxide production: a comparison of retinal ganglion cells and retinal glial cells cultured under hypoxic conditions

The aim of this study was to compare the effects of hypoxia on nitric oxide synthase (NOS) expression and the production of NO between isolated retinal ganglion cells (RGCs) and retinal glial cells. Reverse transcription-polymerase chain reaction (RT-PCR) was employed to examine the presence of neuronal NOS mRNA, inducible NOS mRNA, and endothelial NOS mRNAs in the two cell types. RGCs and retinal glial cells were separately cultured under hypoxic (10% O(2)) or control (20% O(2)) conditions. Changes in NOS-mRNA expression were quantified by real-time PCR, and nitrite in the medium was measured up to 96 h of culture. The effects of non-NOS- and iNOS-selective inhibitors on hypoxia-induced release of nitrite in the culture medium were evaluated. RT-PCR revealed the presence of three types of NOSs in the two types of cultured cells. Hypoxic culture conditions significantly changed the expression of all NOS mRNAs in retinal glial cells but not in RGCs. NO production showed significant changes corresponding to those of NOS mRNAs in retinal glial cells but not in RGCs, and both NOS inhibitors significantly reduced hypoxia-induced nitrite release in retinal glial cells. Retinal glial cells but not RGCs may be the major source of NO under hypoxic conditions.

Poly(ADP-ribose) polymerase as a key player in excitotoxicity and post-ischemic brain damage

Poly(ADP-ribose) polymerases (PARPs) are a group of protein-modifying and nucleotide-polymerizing enzymes able to catalyze the transfer of multiple ADP-ribose units from NAD to substrate proteins. In the human genome, 16 different genes encoding for members of this emerging family of enzymes have been identified. Known family members are PARP-1, PARP-2, PARP-3, vPARP, tankyrase 1 and tankyrase 2, each of them with a possible specific role in cell biology. The most studied member of the family is PARP-1, which is abundantly present in the nucleus and is involved in the maintenance of genomic stability. In pathological conditions, highly reactive radical species may cause DNA damage and PARP-1 hyperactivation. This may lead to necrotic cell death through massive NAD consumption. We show that following middle cerebral artery occlusion, rats treated with PARP inhibitors displayed reduced brain infarct volumes. Similarly, PARP inhibitors reduced neuronal death induced by oxygen-glucose deprivation (OGD) or excitotoxins in primary cultures of murine cortical cells. On the contrary, PARP inhibitors did not attenuate the OGD-induced selective loss of CA1 pyramidal cells in rat organotypic hippocampal slices. In addition, they were not neuroprotective against transient bilateral carotid occlusion in gerbils. We observed that post-ischemic brain damage was predominally necrotic in cultured cortical cells, whereas a caspase-dependent apoptotic process was responsible for the CA1 pyramidal cell loss in hippocampal slices. Hence, it appears reasonable to propose PARP inhibitors as useful therapeutic agents in pathological brain conditions were necrosis predominates.

Serum neuron-specific enolase predicts outcome in post-anoxic coma: a prospective cohort study

OBJECTIVE

The aim of this study was to investigate whether serial serum neuron-specific enolase (NSE) can be used to predict neurological prognosis in patients remaining comatose after cardiopulmonary resuscitation (CPR). DESIGN. Observational cohort study. Clinicians were blinded to NSE results.

SETTING

Eighteen-bed general ICU.

PATIENTS

Comatose patients admitted to the ICU after CPR.

INTERVENTIONS

Serum NSE was measured at admission and daily for 5 days.

MEASUREMENTS AND RESULTS

Patients received full intensive treatment until recovery or until absence of cortical response to somatosensory evoked potentials more than 48 h after CPR proved irreversible coma. Of the 110 patients included (mean GCS at ICU admission 3, range 3--9), 34 regained consciousness, five of whom died in hospital. Seventy-six patients did not regain consciousness, 72 of whom died in hospital. Serum NSE at 24 h and at 48 h after CPR was significantly higher in patients who did not regain consciousness than in patients who regained consciousness (at 24 h: median NSE 29.9 microg/l, range 1.8-250 vs 9.9 microg/l, range 4.5-21.5, P<0.001; at 48 h: median 37.8 microg/l, range 4.4-411 vs 9.5 microg/l, range 6.2-22.4, P= 0.001). No patient with a serum NSE level >25.0 microg/l at any time regained consciousness. Addition of NSE to GCS and somatosensory evoked potentials increased predictability of poor neurological outcome from 64% to 76%.

CONCLUSIONS

High serum NSE levels in comatose patients at 24 h and 48 h after CPR predict a poor neurological outcome. Addition of NSE to GCS and somatosensory evoked potentials increases predictability of neurological outcome.

Nitric oxide-mediated Ca2+/calmodulin-dependent protein kinase IV activity during hypoxia in neuronal nuclei from newborn piglets

The present study tested the hypothesis that hypoxia results in increased Ca(2+)/calmodulin-dependent protein kinase IV (CaM kinase IV) activity and that inhibition of nitric oxide (NO) synthase by N-nitro-L-arginine (NNLA) prevents the hypoxia- induced increase in neuronal nuclear CaM kinase IV activity in newborn piglets. CaM kinase IV activity was determined in normoxic (Nx), hypoxic (Hx), and NNLA-pretreated Hx piglets. Cerebral hypoxia was confirmed biochemically. There was a significant difference between CaM kinase IV activity (pmoles/mg protein/min) in Nx (285.22+/-86.12), Hx (494.77+/-99.79, P<0.05 vs. Nx), and NNLA-pretreated Hx (249.55+/-53.85)(P=NS vs. Nx, P<0.05 vs. Hx) animals. The results demonstrate that the cerebral tissue hypoxia results in an increase in neuronal nuclear CaM kinase IV activity, and the hypoxia-induced increase in CaM kinase IV activity is NO-mediated.

The role of Ca2+/calmodulin-dependent protein kinase II in mechanisms underlying neuronal hyperexcitability induced by repeated, brief exposure to hypoxia or high K+ in rat hippocampal slices

Analysis of extracellular recordings of evoked excitatory postsynaptic potentials and population spikes from rat hippocampal slices has previously revealed that repeated, brief exposures to high extracellular K(+) or to episodes of hypoxia induce a sustained (more than 3 h) hyperexcitability of CA1 pyramidal neurons accompanied with epileptiform activity which was dependent on activation of L-type Ca(2+) channels and N-methyl-D-aspartate receptors. Using in vitro phosphorylation assay we have found the significant increase of Ca(2+)-independent activity of Ca(2+)/calmodulin-dependent protein kinase II in CA1 region of hippocampal slices 60 min after the high extracellular K(+) and 60-80 min after the hypoxic episodes. These data suggest possible involvement of Ca(2+)/calmodulin-dependent protein kinase II in Ca(2+)-dependent mechanisms of the maintenance phase of the observed epileptiform activity.