Nitric oxide-mediated Ca++-influx in neuronal nuclei and cortical synaptosomes of normoxic and hypoxic newborn piglets

Hypercapnia Causes Injury of the Cerebral Cortex and Cognitive Deficits in Newborn Piglets

In critically ill newborns, exposure to hypercapnia (HC) is common and often accepted in neonatal intensive care units to prevent severe lung injury. However, as a "safe" range of arterial partial pressure of carbon dioxide levels in neonates has not been established, the potential impact of HC on the neurodevelopmental outcomes in these newborns remains a matter of concern. Here, in a newborn Yorkshire piglet model of either sex, we show that acute exposure to HC induced persistent cortical neuronal injury, associated cognitive and learning deficits, and long-term suppression of cortical electroencephalogram frequencies. HC induced a transient energy failure in cortical neurons, a persistent dysregulation of calcium-dependent proapoptotic signaling in the cerebral cortex, and activation of the apoptotic cascade, leading to nuclear deoxyribonucleic acid fragmentation. While neither 1 h of HC nor the rapid normalization of HC was associated with changes in cortical bioenergetics, rapid resuscitation resulted in a delayed onset of synaptosomal membrane lipid peroxidation, suggesting a dissociation between energy failure and the occurrence of synaptosomal lipid peroxidation. Even short durations of HC triggered biochemical responses at the subcellular level of the cortical neurons resulting in altered cortical activity and impaired neurobehavior. The deleterious effects of HC on the developing brain should be carefully considered as crucial elements of clinical decisions in the neonatal intensive care unit.

Computational analysis of cortical neuronal excitotoxicity in a large animal model of neonatal brain injury

BACKGROUND

Neonatal hypoxic brain injury is a major cause of intellectual and developmental disability. Hypoxia causes neuronal dysfunction and death in the developing cerebral cortex due to excitotoxic Ca²⁺-influx. In the translational piglet model of hypoxic encephalopathy, we have previously shown that hypoxia overactivates Ca²⁺/Calmodulin (CaM) signaling via Sarcoma (Src) kinase in cortical neurons, resulting in overexpression of proapoptotic genes. However, identifying the exact relationship between alterations in neuronal Ca²⁺-influx, molecular determinants of cell death, and the degree of hypoxia in a dynamic system represents a significant challenge.

METHODS

We used experimental and computational methods to identify molecular events critical to the onset of excitotoxicity-induced apoptosis in the cerebral cortex of newborn piglets. We used 2-3-day-old piglets (normoxic [Nx], hypoxic [Hx], and hypoxic + Src-inhibitor-treatment [Hx+PP2] groups) for biochemical analysis of ATP production, Ca²⁺-influx, and Ca²⁺/CaM-dependent protein kinase kinase 2 (CaMKK2) expression. We then used SimBiology to build a computational model of the Ca²⁺/CaM-Src-kinase signaling cascade, simulating Nx, Hx, and Hx+PP2 conditions. To evaluate our model, we used Sobol variance decomposition, multiparametric global sensitivity analysis, and parameter scanning.

RESULTS

Our model captures important molecular trends caused by hypoxia in the piglet brain. Incorporating the action of Src kinase inhibitor PP2 further validated our model and enabled predictive analysis of the effect of hypoxia on CaMKK2. We determined the impact of a feedback loop related to Src phosphorylation of NMDA receptors and activation kinetics of CaMKII. We also identified distinct modes of signaling wherein Ca²⁺ level alterations following Src kinase inhibition may not be a linear predictor of changes in Bax expression. Importantly, our model indicates that while pharmacological pre-treatment significantly reduces the onset of abnormal Ca²⁺-influx, there exists a window of intervention after hypoxia during which targeted modulation of Src-NMDAR interaction kinetics in combination with PP2 administration can reduce Ca²⁺-influx and Bax expression to similar levels as pre-treatment.

CONCLUSIONS

Our model identifies new dynamics of critical components in the Ca²⁺/CaM-Src signaling pathway leading to neuronal injury and provides a feasible framework for drug efficacy studies in translational models of neonatal brain injury for the prevention of intellectual and developmental disabilities.

Beneficial effects of asiaticoside on cognitive deficits in senescence-accelerated mice

The effect of asiaticoside isolated from Hydrocotyle sibthorpioides (AHS) on the promotion of cognition in senescence-accelerated mice (SAMP) was evaluated. Six-month old male SAMP8 mice were orally administered 20, 40 or 80 mg/kg AHS daily for three months. SAMR1 mice were used as a "normal aging" control. The results showed that treatment with AHS significantly improved learning and memory abilities in behavioral tests. AHS-treated mice showed higher antioxidant enzyme activity and lower lipid oxidation in serum compared with untreated SAMP8 mice. Mechanistically, studies showed that AHS markedly reduced the content and deposition of β-amyloid peptide (Aβ) by inhibiting the expression of mRNA for amyloid protein precursor, β-site amyloid cleaving enzyme-1 and cathepsin B and promoting the expression of mRNA for neprilysin and insulin degrading enzyme. In addition, AHS significantly increased the expression of plasticity-related proteins including postsynaptic density-95, phosphor-N-methyl-D-aspartate receptor 1, phospho-calcium-calmodulin dependent kinase II, phospho-protein kinase A Catalyticβ subunit, protein kinase Cγ subunit, phospho-CREB and brain derived neurotrophic factor. Furthermore, AHS increased the levels of acetylcholine (Ach), but decreased cholinesterase (AchE) activity. These results demonstrated that AHS administration may prevent spatial learning and memory decline by scavenging free radicals, up-regulating the activity of antioxidant enzymes, decreasing the level of Aβ, ameliorating dysfunction in synaptic plasticity, and reversing abnormal changes in Ach level and AchE activity. Thus, AHS should be developed as a new drug to prevent age-related cognitive deficits.

Mechanism of CaM kinase IV activation during hypoxia in neuronal nuclei of the cerebral cortex of newborn piglets: the role of Src kinase

The present study aims to investigate the mechanism of CaM kinase IV activation during hypoxia and tests the hypothesis that hypoxia-induced increased activity of CaM kinase IV is due to Src kinase mediated increased tyrosine phosphorylation of calmodulin and CaM kinase IV in neuronal nuclei of the cerebral cortex of newborn piglets. Piglets were divided into normoxic (Nx, n = 5), hypoxic (Hx, F(i)O(2) of 0.07 for 1 h, n = 5) and hypoxic-pretreated with Src kinase inhibitor PP2 (Hx-Srci, n = 5) groups. Src inhibitor was administered (1.0 mg/kg, I.V.) 30 min prior to hypoxia. Neuronal nuclei were isolated and purified, and tyrosine phosphorylation of calmodulin (Tyr(99)) and CaM kinase IV determined by Western blot using anti-phospho-(pTyr(99))-calmodulin, anti-pTyrosine and anti-CaM kinase IV antibodies. The activity of CaM kinase IV and its consequence the phosphorylation of CREB protein at Ser(133) were determined. Hypoxia resulted in increased tyrosine phosphorylation of calmodulin at Tyr(99), tyrosine phosphorylation of CaM kinase IV, activity of CaM kinase IV and phosphorylation of CREB protein at Ser(133). The data show that administration of Src kinase inhibitor PP2 prevented the hypoxia-induced increased tyrosine phosphorylation of calmodulin (Tyr(99)) and tyrosine phosphorylation of CaM.kinase IV as well as the activity of CaM kinase IV and CREB phosphorylation at Ser(133). We conclude that the mechanism of hypoxia-induced increased activation of CaM kinase IV is mediated by Src kinase-dependent tyrosine phosphorylation of the enzyme and its activator calmodulin. We propose that Tyr(99) phosphorylated calmodulin, as compared to non-phosphorylated, binds with a higher affinity at the calmodulin binding site (rich in basic amino acids) of CaM kinase IV leading to increased activation of CaM kinase IV. Similarly, tyrosine phosphorylated CaM kinase IV binds its substrate with a higher affinity and thus increased tyrosine phosphorylation leads to increased activation of CaM kinase IV resulting in increased CREB phosphorylation that triggers increased transcription of proapoptotic proteins that initiate hypoxic neuronal death.

The effects of indomethacin on caspases, glutathione level and lipid peroxidation in the newborn rats with hypoxic-ischemic cerebral injury

Activation of phospholipase A(2), degradation of membrane phospholipids resulting in tissue accumulation of arachidonic acid, and the activation of cyclooxygenase that leads to the formation of prostaglandin and free radicals may occur after hypoxic-ischemic damage. The aim of this study was to investigate the effects of indomethacin, a nonselective cyclooxygenase inhibitor, on caspase activity, glutathione levels and lipid peroxidation in newborn rats with hypoxic-ischemic encephalopathy. The effects of indomethacin were evaluated by measuring caspase-3 and caspase-8 activities and glutathione levels. Lipid peroxidation was evaluated by measuring concentrations of malondialdehyde in rat brains. Seven-day-old rat pups with the Levine-Rice model of hypoxic-ischemic cerebral injury were randomly divided into three study groups. In the indomethacin-treated group, rats were administered three doses of indomethacin, at a dose of 2 mg/kg every 12 h. Sham and the hypoxic-ischemic group of rats were given physiologic saline. The sham group underwent all surgical procedures except for arterial ligation. After 72 hours, the rats were decapitated and brain tissues were evaluated. Caspase-3 and caspase-8 activities and glutathione and malondialdehyde levels were evaluated in all groups. There was an obvious decrease in caspase-3 and caspase-8 activities and depleted glutathione levels were reversed in the indomethacin-treated group compared to the hypoxic-ischemia group (p<0.001). As indomethacin was unable to prevent lipid peroxidation, malondialdehyde concentrations increased to ischemia-induced levels. In conclusion, indomethacin administration after hypoxic-ischemic encephalopathy injury has a neuroprotective effect since it inhibits caspase activity and reverses the depletion of glutathione. However, it also aggravates lipid peroxidation-induced ischemia.

Mechanism of increased tyrosine (Tyr(99)) phosphorylation of calmodulin during hypoxia in the cerebral cortex of newborn piglets: the role of nNOS-derived nitric oxide

The present study aims to investigate the mechanism of calmodulin modification during hypoxia and tests the hypothesis that hypoxia-induced increase in Tyr(99) phosphorylation of calmodulin in the cerebral cortex of newborn piglets is mediated by NO derived from nNOS. Fifteen piglets were divided into normoxic (Nx, n = 5), hypoxic (Hx, F(i)O(2) of 0.07 for 1 h, n = 5) and hypoxic-pretreated with nNOSi (Hx-nNOSi, n = 5) groups. nNOS inhibitor I (selectivity >2,500 vs. eNOS and >500 vs. iNOS) was administered (0.4 mg/kg, I.V.) 30 min prior to hypoxia. Cortical membranes were isolated and tyrosine phosphorylation (Tyr(99) and total) of calmodulin determined by Western blot using anti-phospho-(pTyr(99))-calmodulin and anti-pTyr antibodies. Protein bands were detected by enhanced chemiluminescence, analyzed by densitometry and expressed as absorbance. The pTyr(99) calmodulin (ODxmm(2)) was 78.55 +/- 10.76 in Nx, 165.05 +/- 12.26 in Hx (P < 0.05 vs. Nx) and 96.97 +/- 13.18 in Hx-nNOSi (P < 0.05 vs. Hx, P = NS vs. Nx). Expression of total tyrosine phosphorylated calmodulin was 69.24 +/- 13.69 in Nx, 156.17 +/- 16.34 in Hx (P < 0.05 vs. Nx) and 74.18 +/- 3.9 in Hx-nNOSi (P < 0.05 vs. Hx, P = NS vs. Nx). The data show that administration of nNOS inhibitor prevented the hypoxia-induced increased Tyr(99) phosphorylation of calmodulin. Total tyrosine phosphorylation of calmodulin was similar to Tyr(99) phosphorylation. We conclude that the mechanism of hypoxia-induced modification (Tyr(99) phosphorylation) of calmodulin is mediated by NO derived from nNOS. We speculate that Tyr(99) phosphorylated calmodulin, as compared to non-phosphorylated, binds with a higher affinity at the calmodulin binding site of nNOS leading to increased activation of nNOS and increased generation of NO.

Plasticity and injury in the developing brain

The child's brain is more malleable or plastic than that of adults and this accounts for the ability of children to learn new skills quickly or recovery from brain injuries. Several mechanisms contribute to this ability including overproduction and deletion of neurons and synapses, and activity-dependent stabilization of synapses. The molecular mechanisms for activity-dependent synaptic plasticity are being discovered and this is leading to a better understanding of the pathogenesis of several disorders including neurofibromatosis, tuberous sclerosis, Fragile X syndrome and Rett syndrome. Many of the same pathways involved in synaptic plasticity, such as glutamate-mediated excitation, can also mediate brain injury when the brain is exposed to stress or energy failure such as hypoxia-ischemia. Recent evidence indicates that cell death pathways activated by injury differ between males and females. This new information about the molecular pathways involved in brain plasticity and injury are leading to insights that will provide better therapies for pediatric neurological disorders.

Antioxidant therapy and neuroprotection in the newborn

Injury to the perinatal brain is a leading cause of childhood mortality and lifelong disability. Despite recent improvements in neonatal care, no effective treatment for perinatal brain lesions is available. The newborn, especially if preterm, is highly prone to oxidative stress (OS) and to the toxic effect of free radicals (FRs). At birth, the newborn is exposed to a relatively hyperoxic environment caused by an increased oxygen bioavailability with greatly enhanced generation of FRs. Additional sources (e.g., inflammation, hypoxia, ischemia, glutamate and free iron release) occur, magnifying OS. In the preterm baby, the perinatal transition is accompanied by the immaturity of the antioxidant systems and the reduced ability to induce efficient homeostatic mechanisms designed to control overproduction of cell-damaging FRs. Improved understanding of the pathophysiological mechanism involved in perinatal brain lesions helps to identify potential targets for neuroprotective interventions, and the knowledge of these mechanisms has enabled scientists to develop new therapeutic strategies that have confirmed their neuroprotective effects in animal studies. Considering the growing role of OS in preterm newborn morbidity in respect to the higher risk of FR damage in these babies, erythropoietin, allopurinol, melatonin and hypothermia demonstrate great promise as potential neuroprotectans. This article provides an overview of the pathogenesis of FR-mediated diseases of the newborn and the antioxidant strategies now tested in order to reduce OS and its damaging effects.

Ameliorative effects of lotus seedpod proanthocyanidins on cognitive deficits and oxidative damage in senescence-accelerated mice

We investigated the effects of lotus seedpod proanthocyanidins (LSPC) administration by oral gavage for 3 months on body weight, learning and memory deficits using Y-maze test, oxidative stress and antioxidative enzyme activity in brain and serum of the senescence-accelerated mice (SAMP8) and the senescence-resistant mice (SAMR1). Mice of each group were weighed weekly. Brain was obtained from SAMP8 and SAMR1 (the control mouse for SAMP8) at 6 months of age and serum was available from SAMP8 and SAMR1 at 3, 4, 5 and 6 months of age. The results of body weight showed that 90mg/kg LSPC administration significantly increased body weight at 5.5 and 6 months of age in SAMP8 when compared with control SAMP8 of the same age. Y-maze test indicated that learning and memory abilities of mice were deteriorated significantly at 6 months of age in SAMP8 compared with age-matched SAMR1, but were remarkably improved after LSPC (60, 90, 120mg/kg body weight) administration beginning at 3 months of ages. Malondialdehyde (MDA), nitric oxide (NO) and nitric oxide synthase (NOS) exhibited significant increases mostly at 5 and 6 months of age in SAMP8. Glutathione (GSH), glutathione peroxidase (GPx) and superoxide dismutase (SOD) activities decreased significantly mostly at 5 and 6 months of age in SAMP8. LSPC (60, 90, 120mg/kg body weight) administration beginning at 3 months of ages decreased MDA, NO content and lowered NOS activity in the brain and serum of SAMP8. Furthermore, LSPC significantly increased GSH level and augmented GPx, SOD activity in the brain and serum of SAMP8. These results suggest that an age-related increase in brain tissue vulnerability to oxidation and deterioration in learning and memory abilities in SAM that can be modified by LSPC, most likely through the ability of LSPC to scavenge oxygen free radicals and to stimulate antioxidant enzyme activity.

Mechanism of Ca2+-influx and Ca2+/calmodulin-dependent protein kinase IV activity during in utero hypoxia in cerebral cortical neuronal nuclei of the guinea pig fetus at term

Previously we showed that following hypoxia there is an increase in nuclear Ca(2+)-influx and Ca(2+)/calmodulin-dependent protein kinase IV activity (CaMK IV) in the cerebral cortex of term guinea pig fetus. The present study tests the hypothesis that clonidine administration will prevent hypoxia-induced increased neuronal nuclear Ca(2+)-influx and increased CaMK IV activity, by blocking high-affinity Ca(2+)-ATPase. Studies were conducted in 18 pregnant guinea pigs at term, normoxia (Nx, n=6), hypoxia (Hx, n=6) and clonidine with Hx (Hx+Clo, n=6). The pregnant guinea pig was exposed to a decreased FiO(2) of 0.07 for 60 min. Clonidine, an imidazoline inhibitor of high-affinity Ca(2+)-ATPase, was administered 12.5 microg/kg IP 30 min prior to hypoxia. Hypoxia was determined biochemically by ATP and phosphocreatine (PCr) levels. Nuclei were isolated and ATP-dependent (45)Ca(2+)-influx was determined. CaMK IV activity was determined by (33)P-incorporation into syntide 2 for 2 min at 37 degrees C in a medium containing 50mM HEPES (pH 7.5), 2mM DTT, 40muM syntide 2, 0.2mM (33)P-ATP, 10mM magnesium acetate, 5 microM PKI 5-24, 2 microM PKC 19-36 inhibitor peptides, 1 microM microcystine LR, 200 microM sodium orthovanadate and either 1mM EGTA (for CaMK IV-independent activity) or 0.8mM CaCl(2) and 1mM calmodulin (for total activity). ATP (mumoles/gbrain) values were significantly different in the Nx (4.62+/-0.2), Hx (1.65+/-0.2, p<0.05 vs. Nx), and Hx+Clo (1.92+/-0.6, p<0.05 vs. Nx). PCr (mumoles/g brain) values in the Nx (3.9+/-0.1), Hx (1.10+/-0.3, p<0.05 vs. Nx), and Hx+Clo (1.14+/-0.3, p<0.05 vs. Nx). There was a significant difference between nuclear Ca(2+)-influx (pmoles/mg protein/min) in Nx (3.98+/-0.4), Hx (10.38+/-0.7, p<0.05 vs. Nx), and Hx+Clo (7.35+/-0.9, p<0.05 vs. Nx, p<0.05 vs. Hx), and CaM KIV (pmoles/mg protein/min) in Nx (1314.00+/-195.4), Hx (2315.14+/-148.5, p<0.05 vs. Nx), and Hx+Clo (1686.75+/-154.3, p<0.05 vs. Nx, p<0.05 vs. Hx). We conclude that the mechanism of hypoxia-induced increased nuclear Ca(2+)-influx is mediated by high-affinity Ca(2+)-ATPase and that CaMK IV activity is nuclear Ca(2+)-influx-dependent. We speculate that hypoxia-induced alteration of high-affinity Ca(2+)-ATPase is a key step that triggers nuclear Ca(2+)-influx, leading to CREB protein-mediated increased expression of apoptotic proteins and hypoxic neuronal death.

Cerebral palsy

Cerebral palsy (CP) is a group of disorders of movement and posture resulting from nonprogressive disturbances of the fetal or neonatal brain. More than 80% of cases of CP in term infants originate in the prenatal period; in premature infants, both prenatal or postnatal causes contribute. The most prevalent pathological lesion seen in CP is periventricular white matter injury (PWMI) resulting from vulnerability of the immature oligodendrocytes (pre-OLs) before 32 wk of gestation. PWMI is responsible for the spastic diplegia form of CP and a spectrum of cognitive and behavioral disorders. Oxidative stress and excitotoxicity resulting from excessive stimulation of ionotropic glutamate receptors on preOLs are the most prominent molecular mechanisms for PWMI. Asphyxia around the time of birth in term infants accounts for less than 15% of CP in developed countries but the incidence is higher in underdeveloped areas. Asphyxia causes a different pattern of brain injury and CP than is seen after preterm injuries. This type of CP is associated with the clinical syndrome of hypoxic-ischemic encephalopathy shortly after the insult, and the cortex, basal ganglia, and brainstem are selectively vulnerable to injury. Experimental models indicate that neurons in the neonatal brain are more likely to die by delayed apoptosis extending over days to weeks than those in the adult brain. Neurons die by glutamate-mediated excitotoxicity involving downstream caspase-dependent and caspase-independent cell death pathways. Recent reports indicate that males and females preferentially utilize different pathways. Clinical trials indicate that mild hypothermia reduces death or disability in term infants following asphyxia and basic research suggests that this approach might be combined with pharmacological strategies in the future.

Differential expression of apoptotic proteins following hypoxia-induced CREB phosphorylation in the cerebral cortex of newborn piglets

The present study investigates the correlation between the hypoxia-induced phosphorylation of cyclic AMP response element binding protein and the expression of apoptotic proteins (proapoptotic proteins Bax and Bad and antiapoptotic proteins Bcl-2 and Bcl-xl) during hypoxia in the cerebral cortex of newborn piglets. Piglets were divided into normoxic (Nx) and hypoxic (Hx, FiO(2)=0.06 for 1 h) groups. Cerebral tissue hypoxia was documented by ATP and phosphocreatine (PCr) levels. Ser(133) phosphorylation of cyclic AMP response element binding (CREB) protein was determined by Western blot analysis using a specific anti-phosphorylated Ser(133)-CREB protein antibody. The expression of apoptotic proteins was determined by using specific anti-Bax, anti-Bad, anti-Bcl-2 and anti-Bcl-xl antibodies. ATP and PCr values (mumoles/g brain) in Hx were significantly different from Nx (ATP: 4.40 +/- 0.39 in Nx vs. 1.19 +/- 0.44 in Hx, P<0.05 vs. Nx; PCr: 3.60 +/- 0.40 in Nx vs. 0.70 +/- 0.31 in Hx, P<0.05 vs. Nx). Ser(133) phosphorylated CREB protein (OD x mm(2)) was 74.55 +/- 4.75 in Nx and 127.13 +/- 19.36 in Hx (P<0.05 vs. Nx). The expression of proapoptotic proteins Bax and Bad increased and strongly correlated with the increase in CREB protein phosphorylation (correlation coefficient r=0.82 and r=0.85, respectively). The expression of antiapoptotic proteins Bcl-2 and Bcl-xl did not show correlation with CREB protein phosphorylation. We conclude that cerebral hypoxia results in differential regulation of CREB protein-mediated expression of proapoptotic and antiapoptotic proteins in the cerebral cortex of newborn piglets. We propose that the increased expression of proapoptotic vs antiapoptotic genes will lead to an increased potential for apoptotic programmed cell death in the Hx newborn brain.

Effect of hyperoxia on cortical neuronal nuclear function and programmed cell death mechanisms

There is growing concern over detrimental neurologic effects to human newborns caused by increased inspired oxygen concentrations. We hypothesize that hyperoxia (FiO(2)>0.95) results in increased high-affinity Ca(2+)-ATPase activity, Ca(2+)-influx, and proapoptotic protein expression in cortical neuronal nuclei of newborn piglets. Neuronal cerebral energy metabolism was documented by determining ATP and phosphocreatine levels. Neuronal nuclear conjugated dienes and fluorescent compounds were measured as indices of lipid peroxidation. High-affinity Ca(2+)-ATPase activity and ATP-dependent Ca(2+)-influx were determined to document neuronal nuclear membrane function. Hyperoxia resulted in increases in lipid peroxidation, high-affinity Ca(2+)-ATPase activity, ATP-dependent Ca(2+)-influx, and Bax/Bcl-2 ratio in the cortical neuronal nuclei of newborn piglets. We conclude that hyperoxia results in modification of neuronal nuclear membrane function leading to increased nuclear Ca(2+)-influx, and propose that hyperoxia-induced increases in intranuclear Ca(2+) activates the Ca(2+)/calmodulin-dependent protein kinase pathway, triggering increased CREB protein-mediated apoptotic protein expression in hyperoxic neurons.

Mechanism of Ca(2+)/calmodulin-dependent protein kinase IV activation and of cyclic AMP response element binding protein phosphorylation during hypoxia in the cerebral cortex of newborn piglets

Previously we showed that hypoxia results in increased neuronal nuclear Ca(2+) influx, Ca(2+)/calmodulin-dependent protein kinase IV activity (CaM KIV) and phosphorylation of c-AMP response element binding (CREB) protein. The aim of the present study was to understand the importance of neuronal nuclear Ca(2+) in the role of CaM KIV activation and CREB protein phosphorylation associated with hypoxia. To accomplish this the present study tests the hypothesis that clonidine administration will block increased nuclear Ca(2+) influx by inhibiting high affinity Ca(2+)/ATPase and prevent increased CaM KIV activity and CREB phosphorylation in the neuronal nuclei of the cerebral cortex of hypoxic newborn piglets. To accomplish this piglets were divided in three groups: normoxic, hypoxic, and hypoxic-treated with clonidine. The piglets that were in the Hx+Cl group received clonidine 5 min prior to hypoxia. Cerebral tissue hypoxia was confirmed biochemically by tissue levels of ATP and phosphocreatine (PCr). The data show that clonidine prevents hypoxia-induced increase in CaM KIV activity and CREB protein phosphorylation. We conclude that the mechanism of hypoxia-induced activation of CaM KIV and CREB phosphorylation is nuclear Ca(2+) influx mediated. We speculate that nuclear Ca(2+) influx is a key step that triggers CREB mediated transcription of apoptotic proteins and hypoxic mediated neuronal death.

Characterization of transcriptional regulation of neurogranin by nitric oxide and the role of neurogranin in SNP-induced cell death: implication of neurogranin in an increased neuronal susceptibility to oxidative stress

Neurogranin (Ng), a calmodulin (CaM)-binding protein kinase C (PKC) substrate, regulates the availability of Ca²⁺/CaM complex and modulates the homeostasis of intracellular calcium in neurons. Previous work showed Ng oxidation by NO donor induces increase in [Ca²⁺]_i. The current study demonstrated that the gene transcription of Ng could be up-regulated by various nitric oxide (NO) donors via a NO-soluble guanylyl cyclase (sGC)-mediated pathway. Furthermore, ectopic expression of neuronal nitric oxide synthase (nNOS) in human embryonic kidney 293 cells (HEK 293) exhibited a nNOS-concentration-dependent biphasic regulatory effect on Ng gene transcription. One of the NO donors, sodium nitroprusside (SNP), however, induced cell death of neuroblastoma Neuro-2a cells. The potency of SNP-induced cell death was shown to be higher in Neuro-2a cells expressing recombinant Ng, as compared with Neuro-2a control cells without Ng expression in cell viability and apoptosis assays. Single-cell fluorescence imaging and site-directed mutagenesis studies suggest that Ng promotes SNP-induced cell death through an amplification of calcium-mediated signaling, which requires the interaction between CaM and IQ motif of Ng. Increased neuronal susceptibility rendered by Ng in response to pathophysiological NO production is suggested to be involved in the selective vulnerability of neurons to oxidative insults in the CNS.

Nuclear Ca(++)-influx, Ca (++)/calmodulin-dependent protein kinase IV activity and CREB protein phosphorylation during post-hypoxic reoxygenation in neuronal nuclei of newborn piglets: the role of nitric oxide

The present study tests the hypothesis that post-hypoxic reoxygenation results in an nitric oxide (NO)-mediated increase in nuclear Ca(++)-influx, increased calmodulin kinase (CaM kinase) IV activity, and increased Ser(133) phosphorylation of cyclic AMP response element binding (CREB) protein in neuronal nuclei of the cerebral cortex of newborn piglets. Piglets were divided into normoxic (Nx), hypoxic (Hx, FiO(2) = 0.07 for 1 h), hypoxic with 6 h reoxygenation (Hx + reox), and Hx + reox injected with 7-nitroindazole sodium salt (7-NINA), a nNOS inhibitor, immediately after hypoxia (Hx + 7-NINA). Cerebral tissue hypoxia was documented by ATP and phosphocreatine (PCr) levels. Nuclear Ca(++)-influx was determined using (45)Ca(++) and CaM kinase IV activity determined by (33)P-incorporation into syntide-2. Ser(133) phosphorylation of CREB protein was determined by Western blot analysis using a specific anti-phosphorylated Ser(133)-CREB protein antibody. ATP and PCr values in Hx, Hx + reox, and Hx + 7-NINA were significantly different from Nx (P < 0.05 versus Nx). Ca(++)-influx (pmoles/mg protein/min) was 3.79 +/- 0.91 in Nx; 11.81 +/- 2.54 in Hx (P < 0.05 versus Nx), 16.55 +/- 3.55 in Hx + reox (P < 0.05 versus Nx), and 12.40 +/- 2.93 in Hx + 7-NINA (P = NS versus Hx). CaM kinase IV activity (pmoles/mg protein/min) was 1,220 +/- 76 in Nx, 2,403 +/- 254 in Hx (P < 0.05 versus Nx), 1,971 +/- 147 in Hx + reox (P < 0.05 versus Hx), and 1,939 +/- 125 Hx + 7-NINA (P < 0.05 versus Hx). Ser(133) phosphorylated CREB protein expression (OD x mm(2)) was 87 +/- 2 in Nx, 203 +/- 24 in Hx (P < 0.05 versus Nx), 186 +/- 23 in Hx + reox (P < 0.05 Nx, P = NS versus Hx), and 128 +/- 10 in Hx + 7-NINA (P < 0.05 versus Hx and Hx + reox). The results show that post-Hx administration of 7-NINA prevents the increased nuclear Ca(++)-influx and CREB protein phosphorylation at Ser(133) during reox. We conclude that post-Hx increase in nuclear Ca(++)-influx leading to increased phosphorylation of CREB protein is mediated by NO derived from nNOS. However, hypoxia-induced increase in CaM Kinase IV activity decreased during the post-Hx reox. We propose that hypoxia-induced increase in CaM Kinase IV activity leads to increased phosphorylation of CREB protein and transcription of proapoptotic genes during post-Hx reox resulting in Hx neuronal death.

Increased neuronal nuclear calcium influx in neonatal seizures

We hypothesized that neonatal seizures lead to increased Ca(2+) influx (nCa(2+)I) in neuronal nuclei of newborn rats and that such increase is nitric-oxide mediated. Neuronal nuclear (45)Ca(2+) influx (nCa(2+)I) was measured in neuronal nuclei of 25 10-day-old male rat-pups newborn brains. They were divided into five groups (n = 5/group). (I) control; (II) hypoxia without seizures; (III) hypoxia with seizures; (IV) kainate, 2 mg/kg intraperitoneal (i.p.)-induced seizures and (V) 7-nitroindazole (7-NINA), 1 mg/kg i.p. pretreated, kainate-induced seizures. nCa(2+)I was significantly (P < 0.05) increased following hypoxia or seizures (hypoxic- or kainate-induced). Post-hypoxic seizures further enhanced nCa(2+)I increase induced by hypoxia (P < 0.05). 7-NINA abated the nCa(2+)I increase induced by kainate. We conclude that (1) kainate or hypoxia-induced seizures in newborn rats modify the neuronal nuclear membrane function, resulting in increased nCa(2+)I, (2) seizures exacerbate the hypoxia-induced increased nCa(2+)I incurred after hypoxia and (3) intranuclear calcium surges during kainate-induced neonatal seizures are nitric oxide-mediated.

Effects of magnesium sulfate administration during hypoxia on Ca(2+) influx and IP(3) receptor modification in cerebral cortical neuronal nuclei of newborn piglets

Magnesium is a non-competitive antagonist of the NMDA receptor. Hypoxic insults to the brain are associated with a significant increase in the intranuclear Ca(2+) due to altered nuclear membrane Ca(2+) influx mechanisms including hypoxia-induced modifications of nuclear membrane IP(3) receptors. In this study we have examined the effects of magnesium sulfate administration to newborn piglets subjected to normoxia and severe hypoxia. The animals were randomly divided into normoxic (n=4), hypoxic (n=4) and magnesium sulfate treated hypoxic (n=4) groups. Hypoxia was confirmed biochemically by measuring ATP and phosphocreatine (PCr) levels in the brain tissue. Intranuclear Ca(2+) influx was assessed by measuring (45)Ca(2+) uptake. Results show a significant (P<0.05) decrease in ATP and PCr levels in hypoxic group in comparison with normoxia. On the other hand magnesium-treated hypoxic group showed a significantly (P<0.05) higher ATP and PCr in comparison with the hypoxic group. Intranuclear Ca(2+) was significantly (P<0.05) higher in the hypoxic group in comparison with both normoxic and magnesium-treated hypoxic groups. In addition results show that magnesium prevented hypoxia-induced modification of the IP(3) receptor. Magnesium treatment significantly reduced the hypoxia-induced increase in the number of receptors (reduced B(max) --P<0.05-treated hypoxia vs. hypoxia and normoxia), and reversed the receptor affinity (reduced dissociation coefficient-K(d)--P<0.05-treated hypoxia vs. normoxia). The results demonstrate that the administration of magnesium sulfate prior to hypoxia prevents the hypoxia-induced increase in intranuclear Ca(2+) and IP(3) receptor modifications. We conclude that Mg(2+ )administration prevents hypoxia-induced modification of neuronal nuclear membrane function that leads to intranuclear Ca(2+)-dependent transcription of apoptotic proteins leading to hypoxic neuronal programmed cell death.

Effects of magnesium sulfate administration during hypoxia on CaM kinase IV and protein tyrosine kinase activities in the cerebral cortex of newborn piglets

The present study tested the hypothesis that magnesium sulfate administration prior to hypoxia prevents hypoxia-induced increase in Ca(2+)/Calmodulin-dependent-kinase (CaM Kinase) IV and Protein Tyrosine Kinase (PTK ) activities. Animals were randomly divided into normoxic (Nx), hypoxic (Hx) and magnesium-pretreated hypoxic (Mg(2+)-Hx) groups. Cerebral hypoxia was confirmed biochemically by measuring ATP and phosphocreatine (PCr) levels. CaM Kinase IV and PTK activities were determined in Nx, Hx and Mg(2+)-Hx newborn piglets. There was a significant difference between CaM kinase IV activity (pmoles/mg protein/min) in Nx (270 +/- 49), Mg(2+)-Hx (317 +/- 82) and Hx (574 +/- 41, P < 0.05 vs. Nx and Mg(2+)-Hx) groups. Similarly, there was a significant difference between Protein Tyrosine Kinase activity (pmoles/mg protein/h) in normoxic (378 +/- 68), Mg(2+)-Hx (455 +/- 67) and Hx (922 +/- 66, P < 0.05 vs. Nx and Mg(2+)-Hx ) groups. We conclude that magnesium sulfate administration prior to hypoxia prevents hypoxia-induced increase in CaM Kinase IV and Protein Tyrosine Kinase activities. We propose that by blocking the NMDA receptor ion-channel mediated Ca(2+)-flux, magnesium sulfate administration inhibits the Ca(2+)/calmodulin-dependent activation of CaMKIV and prevents the generation of nitric oxide free radicals and the subsequent increase in PTK activity. As a result, phosphorylation of CREB and Bcl-2 family of proteins is prevented leading to prevention of programmed cell death.

Effect of 7-nitroindazole sodium on the cellular distribution of neuronal nitric oxide synthase in the cerebral cortex of hypoxic newborn piglets

Cerebral hypoxia results in generation of nitric oxide (NO) free radicals by Ca(++)-dependent activation of neuronal nitric oxide synthase (nNOS). The present study tests the hypothesis that the hypoxia-induced increased expression of nNOS in cortical neurons is mediated by NO. To test this hypothesis the cellular distribution of nNOS was determined immunohistochemically in the cerebral cortex of hypoxic newborn piglets with and without prior exposure to the selective nNOS inhibitor 7-nitroindazole sodium (7-NINA). Studies were conducted in newborn piglets, divided into normoxic (n = 6), normoxic treated with 7-NINA (n = 6), hypoxic (n = 6) and hypoxic pretreated with 7-NINA (n = 6). Hypoxia was induced by lowering the FiO(2) to 0.05-0.07 for 1 h. Cerebral tissue hypoxia was documented by decrease of ATP and phosphocreatine levels in both the hypoxic and 7-NINA pretreated hypoxic groups (P < 0.01). An increase in the number of nNOS immunoreactive neurons was observed in the frontal and parietal cortex of the hypoxic as compared to the normoxic groups (P < 0.05) which was attenuated by pretreatment with 7-NINA (P < 0.05 versus hypoxic). 7-NINA affected neither the cerebral energy metabolism nor the cellular distribution of nNOS in the cerebral cortex of normoxic animals. We conclude that nNOS expression in cortical neurons of hypoxic newborn piglets is NO-mediated. We speculate that nNOS inhibition by 7-NINA will protect against hypoxia-induced NO-mediated neuronal death.

Effect of nitric oxide synthase inhibition during post-hypoxic reoxygenation on Bax and Bcl-2 protein expression and DNA fragmentation in neuronal nuclei of newborn piglets

Previous studies have shown that cerebral tissue hypoxia results in increased generation of oxygen-free radicals including nitric oxide (NO), expression of the proapoptotic protein Bax and fragmentation of nuclear DNA. The present study tests the hypothesis that post-hypoxic reoxygenation for 6 h following hypoxia (FiO2=0.06 for 1 h) results in continued hypoxia-induced, NO-mediated expression of the Bax protein and nuclear DNA fragmentation in the cerebral cortex of newborn piglets. Piglets were divided into normoxic (Nx), hypoxic (Hx, FiO2=0.06 for 1 h), hypoxic with 6 h reoxygenation (Hx+reox) and hypoxic with 6 h reoxygenation injected with 7-nitroindazole sodium salt (7-NINA), a selective nNOS inhibitor, immediately after hypoxia (Hx+7-NINA). Cerebral tissue hypoxia was documented by levels of ATP and phosphocreatine (PCr). Bax and Bcl-2 were analyzed by Western blot and DNA fragmentation was determined by agarose gel electrophoresis. ATP and PCr values in Hx, Hx+reox and Hx+7-NINA were significantly different from Nx (P<0.05 vs. Nx). Bax protein (ODxmm2) was 128.9+/-38.7 in Nx; 223.6+/-45.8 in Hx (P<0.05 vs. Nx); 340.5+/-73.2 in Hx+reox (P<0.05 vs. Nx, Hx and Hx+7-NINA); and 202.2+/-34.8 in Hx+7-NINA (P=NS vs. Hx). Bcl-2 protein (ODxmm2) was 14.9+/-2.7 in Nx, 12.4+/-2.1 in Hx, (P<0.05 vs. Nx), 15.7+/-3.8 in Hx+reox, (P<0.05 vs. Hx) and 13.1+/-2.2 in Hx+7-NINA (P=NS among groups). Nuclear DNA fragmentation (ODxmm2) was 147+/-15 in Nx; 797+/-84 in Hx (P<0.05 vs. Nx); 1134+/-127 in Hx+reox (P<0.05 vs. Nx, Hx and Hx+7-NINA); and 778+/-146 in Hx+7-NINA (P=NS vs. Hx, P<0.05 vs. Hx+reox). The results show that post-hypoxic reoxygenation results in increased expression of Bax protein without affecting Bcl-2 protein and increased fragmentation of nuclear DNA, which are prevented by 7-NINA. We conclude that during post-hypoxic reoxygenation the increase in Bax protein expression and fragmentation of nuclear DNA are mediated by NO derived from nNOS. We propose that in addition to NO-mediated nuclear DNA damage, the hypoxia-induced increased ratio of Bax/Bcl-2 protein will lead to caspase-activated cascade of hypoxic neuronal death during post-hypoxic reoxygenation.

Hypoxia-induced Bax and Bcl-2 protein expression, caspase-9 activation, DNA fragmentation, and lipid peroxidation in mitochondria of the cerebral cortex of newborn piglets: the role of nitric oxide

The present study tests the hypothesis that cerebral hypoxia results in increased ratio of Bax/Bcl-2, activation of caspase-9, lipid peroxidation, and DNA fragmentation in mitochondria of the cerebral cortex of newborn piglets and that the inhibition of nitric oxide synthase by N-nitro-L-arginine during hypoxia will prevent the events leading to mitochondrial DNA fragmentation. To test this hypothesis, six piglets, 3-5 days old, were divided into three groups: normoxic (n=5), hypoxic (n=5), and hypoxic-nitric oxide synthase (n=4). Hypoxic animals were exposed to a FiO2 of 0.6 for 60 min. Nitric oxide synthase (40 mg/kg) was infused over 60 min prior to hypoxia. Tissue hypoxia was confirmed by measuring levels of ATP and phosphocreatine. Cerebral cortical tissue mitochondria were isolated and purified using a discontinuous ficoll gradient. Mitochondrial Bax and Bcl-2 proteins were determined by Western blot. Caspase-9 activity in mitochondria was determined spectro-fluorometrically using fluorogenic substrate for caspase-9. Fluorescent compounds, an index of mitochondrial membrane lipid peroxidation, were determined spectrofluorometrically. Mitochondrial DNA was isolated and separated by electrophoresis on 1% agarose gel and stained with ethidium bromide. ATP levels (micromol/g brain) were 4.52+/-0.34 in normoxic, 1.18+/-0.29 in hypoxic (P<0.05) and 1.00+/-0.26 in hypoxic-nitric oxide synthase animals (P<0.05 vs. normoxic). Phosphocreatine levels (micromol/g brain) were 3.61+/-0.33 in normoxic, 0.70+/-0.20 in hypoxic (P<0.05 vs. normoxic) and 0.57+/-0.14 in hypoxic-nitric oxide synthase animals (P<0.05 vs. normoxic, P=NS vs. hypoxic). Bax density in mitochondrial membranes was 160+/-28 in normoxic and 324+/-65 in hypoxic (P<0.001 vs. normoxic). Bcl-2 density mitochondria was 96+/-18 in normoxic and 98+/-20 in hypoxic (P=NS vs. normoxic). Mitochondrial caspase-9 activity (nmol/mg protein/h) was 1.32+/-0.23 in normoxic and 2.25+/-0.24 in hypoxic (P<0.01 vs. normoxic). Levels of fluorescent compounds (microg of quinine sulfate/g protein) were 12.48+/-4.13 in normoxic and 37.92+/-7.62 in hypoxic (P=0.003 vs. normoxic). Densities (ODxmm2) of low molecular weight DNA fragments were 143+/-38 in normoxic, 365+/-152 in hypoxic, (P<0.05 vs. normoxic) and 163+/-25 in hypoxic-nitric oxide synthase animals (P<0.05 vs. hypoxic, P=NS vs. normoxic). The data demonstrate that hypoxia results in increased mitochondrial proapoptotic protein Bax, increased mitochondrial caspase-9 activity, increased mitochondrial lipid peroxidation, and increased fragmentation of DNA in mitochondria of the cerebral cortex of newborn piglets. The administration of a nitric oxide synthase inhibitor, nitric oxide synthase, prior to hypoxia prevented fragmentation of mitochondrial DNA, indicating that the hypoxia-induced mitochondrial DNA fragmentation is NO-mediated. We propose that NO free radicals generated during hypoxia lead to NO-mediated altered expression of Bax leading to increased ratio of pro-apoptotic/anti-apoptotic protein resulting in modification of mitochondrial membrane, and subsequently Ca2+-influx and fragmentation of mitochondrial DNA.

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 post-hypoxic MgSO(4) administration in utero on Ca(2+)-influx and Ca(2+)/calmodulin kinase IV activity in cortical neuronal nuclei

Previously we have demonstrated that in utero hypoxia results in increased nuclear Ca(2+)-influx and increased CaM kinase IV activity in neuronal nuclei of the guinea pig fetus. The present study tests the hypothesis that maternal treatment with magnesium sulfate (MgSO(4)) following in utero hypoxia will attenuate the hypoxia-induced increase in Ca(2+)-influx and CaM kinase IV activity in neuronal nuclei of the fetal guinea pig brain during recovery. Pregnant guinea pigs at 60 days of gestation were divided into four groups: normoxic (Nx=5), hypoxic (Hx, n=4), untreated post-hypoxic 24h recovery (Rec, n=8) and Mg(2+)-treated post-hypoxic 24h recovery (Mg(2+)-Rec, n=8). Maternal hypoxia was induced by decreasing FiO(2) to 8% for 1h. Recovery groups received either saline or 300 mg/kg MgSO(4) (i.p.) followed by 100mg/kg/h i.p. for 4h. Fetal cerebral tissue hypoxia was documented by ATP and phosphcreatine (PCr) levels. Neuronal nuclei were isolated and nuclear Ca(2+)-influx as well as CaM kinase activity was determined. Nuclear Ca(2+) influx (pmol/mg protein) was 4.84+/-0.83 in Nx, 12.50+/-2.97 (p<0.05) in Hx, 7.83+/-1.78 in Rec group (p<0.05 versus Nx and Hx) and 5.02+/-1.77 in Mg(2+)-Rec group (p<0.05 versus Rec group, p<0.05 versus Hx, p=NS versus Nx). CaM kinase IV activity (pmol/mg protein/min) was 1197+/-62 in Nx, 2524+/-132 (p<0.05 versus Nx) in Hx, 1830+/-141 (p<0.05 versus Nx and Hx) in Rec and 1938+/-118 in Mg(2+)-Rec group (p<0.05 versus Hx and Nx, p=n.s. versus Rec). The data show that MgSO(4) administration following in utero hypoxia prevents hypoxia-induced increase in neuronal nuclear Ca(2+)-influx but has no effect on CaM kinase activity in the guinea pig fetus during recovery. We conclude that post-hypoxic administration of Mg(2+) prevents hypoxia-induced modification of neuronal nuclear membrane function.

Effects of acupuncturing Tsusanli (ST36) on expression of nitric oxide synthase in hypothalamus and adrenal gland in rats with cold stress ulcer

AIM: To study the protective effect of acupuncturing Tsusanli (S_T36) on cold stress ulcer, and the expression of nitric oxide synthase (NOS) in hypothalamus and adrenal gland.

METHODS: Ulcer index in rats and RT-PCR were used to study the protective effect of acupuncture on cold stress ulcer, and the expression of NOS in hypothalamus and adrenal gland. Images were analyzed with semi-quantitative method.

RESULTS: The ulcer index significantly decreased in rats with stress ulcer. Plasma cortisol concentration was up regulated during cold stress, which could be depressed by pre-acupuncture. The expression of NOS1 in hypothalamus increased after acupuncture. The increased expression of NOS2 was related with stress ulcer, which could be decreased by acupuncture. The expression of NOS3 in hypothalamus was similar to NOS2, but the effect of acupuncture was limited. The expression of NOS2 and NOS3 in adrenal gland increased after cold stress, only the expression of NOS1 could be repressed with acupuncture. There was no NOS2 expression in adrenal gland in rats with stress ulcer.

CONCLUSION: The protective effect of acupuncturing Tsusanli (S_T36) on the expression of NOS in hypothalamus and adrenal gland can be achieved.

Hypoxia modifies nuclear calcium uptake pathways in the cerebral cortex of the guinea-pig fetus

Nuclear Ca2+ signals are thought to play a critical role in the initiation and progression of programmed cell death. The present study tests the hypothesis that hypoxia alters nuclear Ca2+ transport pathways and leads to an increase in nuclear Ca(2+)-influx in cerebral cortical neuronal nuclei. To test this hypothesis the effect of tissue hypoxia on high affinity Ca(2+)-ATPase activity and the binding characteristics of inositol 1,4,5-triphosphate (IP3) and inositol 1,3,4,5-tetrakisphosphate (IP4) receptors were studied in neuronal nuclei from the cerebral cortex of guinea-pig fetuses. Results show increased high-affinity Ca(2+)-ATPase activity (nmol/mg protein/h) in the hypoxic group 969.7+/-79 as compared with 602.4+/-90.9 in the normoxic group, P<0.05. The number of IP3 receptors (Bmax, fmol/mg protein) increased from 61+/-21 in the normoxic group to 164+/-49 in the hypoxic group, P<0.05. K(d) values did not change following hypoxia. In contrast, IP4 receptor Bmax (fmol/mg protein) and K(d) (nM) values increased from 360+/-32 in the normoxic group to 626+/-136 in the hypoxic group (P<0.001) and, from 26+/-1 in the normoxic group to 61+/-9 in the hypoxic group (P<0.001), respectively. 45Ca(2+)-influx (pmol/mg protein) significantly increased from 6.3+/-1.9 in the normoxic group to 10.9+/-1.1 the hypoxic group (P<0.001). The data show that hypoxia modifies nuclear Ca2+ transport pathways and results in increased nuclear Ca(2+)-influx. We speculate that hypoxia increases nuclear Ca2+ uptake from the cytoplasm to the nucleoplasm, resulting in increased transcription of proapoptotic genes and subsequent activation of programmed cell death pathways.

Effect of hypoxia on the expression of pro- and anti-apoptotic proteins in neuronal nuclei of the guinea pig fetus during gestation

The present study investigates the expression of apoptotic proteins Bax, Bad, Bcl-2, and Bcl-xl following hypoxia in the cerebral cortex of the guinea pig fetus as a function of gestational age. Normoxic (Nx, n = 6) and hypoxic (Hx, n = 6) guinea pig fetuses at 35 and 60 days gestation were studied. Bax expression (OD X mm(2)) was 96.9 +/- 9.5 (Nx 35 days), 116.5 +/- 8.3 (Hx 35 days), P < 0.05 and 116.2 +/- 3.4 (Nx 60 days, 144.6 +/- 11.7 (Hx 60 days), P < 0.05. Bad expression (OD X mm(2)) was 78.6 +/- 2.6 (Nx 35 days), 102.9 +/- 5.8 (Hx 35 days), P < 0.05 and 101.5 +/- 4.3 (Nx 60 days), 139.8 +/- 7.9 (Hx 60 days), P < 0.05 vs. Nx 60 days, also significantly higher from preterm hypoxia P < 0.007. Expression of Bcl-2 (OD X mm(2)) was 27.4 +/- 2.0 (Nx 35 days), 28.0 +/- 2.4 (Hx 35 days), and 27.4 +/- 2.7 (Nx 60 days), 29.7 +/- 2.3 (Hx 60 days). Expression of Bcl-xl (OD X mm(2)) was 51.0 +/- 4.4 (Nx 35 days), 46.1 +/- 8.0 (Hx 35 days) and 50.0 +/- 1.4 (Nx 60 days), 54.9 +/- 7.4 (Hx 60 days). Hypoxia resulted in increased expression of the proapoptotic proteins Bax and Bad by 20% and 30% in the preterm as compared to 24% and 38% at term, without altering the expression of anti-apoptotic proteins Bcl-2 and Bcl-xl. We conclude that the hypoxia-induced increased expression of Bax and Bad is greater at term compared to preterm. Furthermore, the hypoxia-induced increase in proapoptotic as compared to antiapoptotic proteins at term will accelerate the ongoing active process of programmed cell death at term compared to preterm gestation.

Effect of hypoxia on the expression and activity of mitogen-activated protein (MAP) kinase-phosphatase-1 (MKP-1) and MKP-3 in neuronal nuclei of newborn piglets: the role of nitric oxide

Mitogen-activated protein kinase-1 (MAPK-1) and MAPK-3 regulate survival and programmed cell death of neurons under stress conditions. The activity of MAPK-1 and MAPK-3 is regulated by dual specificity phosphatases: MKP-1 and MKP-3. In previous studies, we have shown that cerebral hypoxia results in increased activation of MAPK-1 and MAPK-3. Furthermore, we have shown that the hypoxia-induced activation of MAPK is nitric oxide (NO)-mediated. The present study tested the hypothesis that hypoxia results in altered expression and activity of MKP-1 and MKP-3 in neuronal nuclei and the administration of 7-nitro-indazole (7-NINA; 1 mg/kg, 60 min prior to hypoxia), a selective nNOS inhibitor, will prevent the hypoxia-induced alteration in the expression and activity of MKP-1 and MKP-3. To test this hypothesis expression and activity of MKP-1 and MKP-3 were determined in neuronal nuclei of normoxic (Nx; n=5), hypoxic (Hx; n=5) and 7-NINA-pretreated-hypoxic (7-NINA-Hx; n=5). Hypoxia was achieved by exposing the animals to an FiO2 of 0.07 for 60 min. Cerebral tissue hypoxia was documented biochemically by determining ATP and phosphocreatine levels. Neuronal nuclei were isolated using discontinuous sucrose gradient centrifugation and purified. Nuclear proteins were analyzed by Western blot using specific antibodies for MKP-1 and MKP-3 (Santa Cruz, CA, USA). The protein band density was determined by imaging densitometry and expressed as OD x mm2. The density of MKP-1 was 61.57+/-5.68, 155.86+/-44.02 and 69.88+/-25.54 in the Nx, Hx and 7-NINA-Hx groups, respectively (P<0.05, ANOVA). Similarly, the density of MKP-3 was 66.46+/-5.88, 172.04+/-33.10 and 116.88+/-14.66 in the Nx, Hx and 7-NINA-Hx groups, respectively (P<0.05, ANOVA). The data show an increased expression of MKP-1 and MKP-3 during hypoxia in neuronal nuclei of newborn piglets and the administration of 7-NINA, an nNOS inhibitor, prevented the hypoxia-induced increased expression of MKP-1 and MKP-3. The activity of MKP-1 (pmol/min) was 176.17+/-16.95 in Nx, 97.56+/-10.64 in Hx and 130+/-14.42 in the 7-NINA-Hx groups, respectively (P<0.05, ANOVA). Similarly the activity of MKP-3 was 104.11+/-12.17 in Nx, 36.29+/-16.88 in Hx and 77.89+/-20.18 in the 7-NINA groups, respectively (P<0.05, ANOVA). The results demonstrate that cerebral hypoxia results in increased expression of MKP-1 and MKP-3 expression that was prevented by the administration of 7-NINA. In contrast, hypoxia resulted in decreased activity of MKP-1 and MKP-3 that was prevented by the administration of a nNOS inhibitor. We conclude that hypoxia-induced decrease in MKP-1 and MKP-3 activity is not due to altered expression but due to NO-mediated modification of the cysteine residue at the active site of these dual specificity phosphatases, a mechanism of their inactivation that leads to activation of MAP kinases.

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.

Effect of neuronal nitric oxide synthase inhibition on CA2+/calmodulin kinase kinase and CA2+/calmodulin kinase IV activity during hypoxia in cortical nuclei of newborn piglets

The present study tests the hypothesis that cerebral tissue hypoxia results in increased Ca(2+)/calmodulin (CaM) kinase kinase activity and that the administration of nitric oxide synthase inhibitors (N-nitro-l-arginine [NNLA], or 7-nitroindazole sodium [7-NINA]) prior to the onset of hypoxia will prevent the hypoxia-induced increase in the enzyme activity. To test this hypothesis, CaM kinase kinase and CaM kinase IV activities were determined in normoxic, hypoxic, NNLA-treated hypoxic, and 7-NINA-treated hypoxic piglets. Hypoxia was induced (FiO(2)=0.05-0.08x1 h) and confirmed biochemically by tissue levels of ATP and phosphocreatine. CaM kinase kinase activity was determined in a medium containing protein kinase and phosphatase inhibitors, calmodulin, and a specifically designed CaM kinase kinase target peptide. CaM kinase IV activity was determined by (33)P-incorporation into syntide-2 in a buffer containing protein kinase and phosphatase inhibitors. Compared with normoxic animals, ATP and phosphocreatine levels were significantly lower in all hypoxic piglets whether or not pretreated with nitric oxide synthase inhibitors. There was a significant difference among CaM kinase kinase activity (pmol/mg protein/min) in normoxic (76.84+/-14.1), hypoxic (138.86+/-18.2, P<0.05 vs normoxia), NNLA-pretreated hypoxic (91.34+/-19.3; P=NS vs normoxia, P<0.05 vs hypoxia) and 7-NINA-pretreated hypoxic animals (100.12+/-23.3; P=NS vs normoxia, P<0.05 vs hypoxia). There was a significant difference among CaM kinase IV activity (pmol/mg protein/min) in normoxia (1270.80+/-126.1), hypoxia (2680.80+/-136.7; P<0.05 vs normoxia), NNLA-pretreated hypoxia (1666.00+/-154.8; P<0.05 vs normoxia, P<0.05 vs hypoxia), and 7-NINA-pretreated hypoxic (1712.9+/-231.5; P=NS vs normoxia, P<0.05 vs hypoxia). We conclude that the hypoxia-induced increase in CaM kinase kinase and CaM kinase IV activity is mediated by neuronal NOS-derived NO.

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.

Inositol tetrakisphosphate (IP4)- and inositol triphosphate (IP3)-dependent Ca2+ influx in cortical neuronal nuclei of newborn piglets following graded hypoxia

Previous studies have shown that hypoxia results in a modification of the binding characteristics of the neuronal nuclear membrane inositol tetrakisphosphate (IP4) and inositol triphosphate (IP3) receptors. The present study tests the hypothesis that hypoxia-induced modification of the IP4 and IP3 receptors results in increased IP4 and IP3 dependent Ca2+ influx in neuronal nuclei as a function of the degree of cerebral tissue hypoxia in newborn piglets. Studies were performed in piglets, 3-5 days old, divided into normoxic (N = 5) and hypoxic (N = 6) groups. The hypoxic group was exposed to decreased FiO2 ranging from 0.15 to 0.05 for 1 h. Brain tissue hypoxia was documented biochemically by determining ATP and phosphocreatine (PCr) levels. Neuronal nuclei were isolated and 45Ca2+ influx was determined in a medium containing 50 mM Tris buffer (pH 7.4), neuronal nuclei (150 microg protein), 1 microM 45Ca2+, with or without 10 microM IP4 or IP3. In normoxic and hypoxic groups, ATP levels were 4.27 +/- 0.80 and 1.40 +/- 0.69 micromoles/g brain, respectively, P < .001 (ranging from 4.78 to 0.82). PCr levels were 3.40 +/- 0.99 and 0.91 +/- 0.57 micromoles/g brain, respectively, P < .001 (raning from 4.07 to 0.60). During hypoxia, IP4-dependent intranuclear 45Ca2+ influx increased from 3.39 +/- 0.64 in normoxic nuclei to 13.30 +/- 2.18 pM/mg protein in hypoxic nuclei (P < .01). There was an inverse correlation between the 45Ca2+ influx in neuronal nuclei and the levels of cerebral tissue ATP (r = 0.83) and PCr (r = 0.85). Similarly, IP3-dependent intranuclear 45Ca2+ influx increased from 2.26 +/- 0.38 pmoles/mg protein in normoxic nuclei to 11.12 +/- 1.65 pmoles/mg protein in hypoxic nuclei and showed an inverse correlation between 45Ca2+ influx in neuronal nuclei and the levels of cerebral tissue ATP (r = 0.86) and PCr (r = 0.71). The data demonstrate that there is an IP4- as well as IP3-dependent increase in nuclear Ca2+ influx with increasing cerebral tissue hypoxia, suggesting a hypoxia-induced modification of the nuclear membrane IP4 and IP3 receptors. We propose that there is a specific level of tissue hypoxia that results in a critical increase of intranuclear Ca2+ that leads to altered transcription of apoptotic genes and activation of nuclear endonucleases resulting in hypoxia-induced programmed neuronal death.

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

Nuclear mechanisms of hypoxic cerebral injury in the newborn

In early studies, we demonstrated that cerebral tissue hypoxia leads to N-methyl-D-aspartate receptor modification and results in increased intracellular Ca2+. Our subsequent studies have demonstrated an alteration in nuclear Ca2+ influx mechanisms and an increase in the nuclear Ca2+ influx after hypoxia. The hypoxia induced nuclear Ca2+ influx increase correlated in a curvilinear function with the increase in the degree of cerebral tissue hypoxia. The activity of nuclear membrane high-affinity Ca2+-ATPase also increased with the increase in cerebral hypoxia. The expression of the proapototic protein Bax increased as an inverse function with cerebral tissue ATP and phosphocreatine concentrations. However,the expression of the antiapoptotic protein Bcl-2 did not increase after hypoxia. Cerebral tissue hypoxia also led to the activation of caspases 3, 8, and 9. Furthermore, our studies demonstrated that the fragmentation of neuronal genomic DNA increased with increase in degree of cerebral tissue hypoxia. Studies presented in this article elucidate nuclear Ca2+ influx and nuclear Ca2+-mediated mechanisms, including signal transduction, apoptotic gene transcription,caspase activation, and nuclear DNA fragmentation, that result in hypoxic neuronal injury in the newborn brain.

Hypoxia-induced modification of the inositol triphosphate receptor in neuronal nuclei of newborn piglets: role of nitric oxide

Previous studies have shown that hypoxia results in increased Ca2+ influx in neuronal nuclei and generation of nitric oxide (NO) free radicals in the cerebral cortical tissue of newborn piglets. The present study tests the hypothesis that hypoxia results in modification of the inositol triphosphate (IP3) receptor characteristics in neuronal nuclei and that the hypoxia-induced modification of the IP3 receptor is NO mediated. Studies were performed in piglets, 3-5 days old, divided into normoxic (n = 5), hypoxic (n = 5), and NO synthase (NOS) inhibitor N-nitro-L-arginine (NNLA)-treated hypoxic (n = 5) groups. The NNLA-treated hypoxic group received an infusion of NNLA (40 mg/kg) over 1 hr prior to hypoxic exposure. The hypoxia was induced by lowering the FiO2 to 0.05-0.07 for 1 hr. Brain tissue hypoxia was documented biochemically by determining ATP and phosphocreatine (PCr) levels. Neuronal nuclei were isolated from the cerebral cortical tissue, and IP3 receptor binding was performed in a medium containing 50 mM HEPES (pH 8.0), 2 mM EDTA, 3H-IP3 (7.5-100 nM), and 100 microg nuclear protein. Nonspecific binding was determined in the presence of 10 microM unlabelled IP3. The IP3 receptor characteristics Bmax (number of receptor sites) and Kd (dissociation constant) were determined. In normoxic, hypoxic, and NNLA-hypoxic groups, ATP levels were 4.46 +/- 0.35, 1.52 +/- 0.10 (P <.05 vs. normoxic), and 1.96 +/- 0.33 micromoles/g brain, respectively (P <.05 vs. normoxic). PCr levels were 3.75 +/- 0.35, 0.87 +/- 0.09 (P <.05 vs. normoxic), and 1.31 +/- 0.10 micromoles/g brain, respectively (P <.05 vs. normoxic). IP3 receptor binding characteristics in normoxic nuclear membranes showed that the Bmax value was 150.0 +/- 14.1 pmoles/mg protein compared with 239.3 +/- 13.6 pmoles/mg protein in the hypoxic group (P <.05). In the NNLA-treated hypoxic group, the Bmax value was 159.0 +/- 42.6 pmoles/mg protein (P <.05 vs. hypoxic a, P = NS vs. normoxic). Similarly, the Kd was 25.2 +/- 0.28 nM in the normoxic group, 44.6 +/- 5.4 nM in the hypoxic group (P <.05), and 28.1 +/- 6.4 nM in the NNLA-treated hypoxic group. (P <.05 vs. hypoxic and P = NS vs. normoxic). The results show that hypoxia results in increased Bmax and Kd values for the IP3 receptor. Furthermore, the data demonstrate that administration of NNLA prior to hypoxia prevents the hypoxia-induced modification of the IP3 receptor in neuronal nuclei of newborn piglets. Because NNLA inhibits NOS and prevents generation of NO, we conclude that the mechanism of hypoxia-induced modification of the neuronal nuclear membrane IP3 receptor is NO mediated. We propose that NO-mediated modification of the IP3 receptor during hypoxia may lead to increased intranuclear Ca2+, resulting in altered transcription of apoptotic genes and activation of cascades of hypoxia-induced programmed neuronal death.

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.

Hypoxia-induced Ca2+-influx in cerebral cortical neuronal nuclei of newborn piglets

The present study was designed to investigate the effect of hypoxia on nuclear calcium-influx in the cerebral cortex of newborn piglets. Anesthetized and ventilated newborn piglets divided into normoxic (n=4) and hypoxic groups with varying degrees of tissue hypoxia (n=10) were studied. Nuclear Ca(2+)-influx was determined using (45)Ca(2+) and plotted against ATP and phosphocreatine levels. The plots were analyzed by non-linear regression (exponential) analysis that showed a curvilinear relationship (r=0.92 for ATP and r=0.88 for phosphocreatine). These data suggest a threshold at which there is a sudden increase in the nuclear calcium-influx that then continues to increase with further decrease in the ATP and phosphocreatine levels. The results demonstrate an increase in the nuclear Ca(2+)-influx during hypoxia in newborn piglets and that this increase correlates in a curvilinear fashion with the increase in the degree of cerebral tissue hypoxia. We propose that the hypoxia-induced increase in intranuclear Ca(2+) is due to altered nuclear membrane Ca(2+)-influx mechanisms and will lead to Ca(2+)-mediated alteration of apoptotic gene expression as well as Ca(2+)-dependent activation of endonucleases that result in DNA fragmentation and subsequent programmed neuronal cell death.

Phosphorylation of cAMP response element binding (CREB) protein during hypoxia in cerebral cortex of newborn piglets and the effect of nitric oxide synthase inhibition

Previous studies have shown that hypoxia results in increased phosphorylation of CREB protein that mediates gene expression including that of the pro-apoptotic gene bax. We also have shown that hypoxia-induced expression of Bax protein is prevented by blocking nitric oxide synthase (NOS). The present study tests the hypothesis that inhibition of NOS by N-nitro-L-arginine (NNLA) will prevent the hypoxia-induced increased phosphorylation of CREB protein in neuronal nuclei of newborn piglets. To test this hypothesis, phosphorylation of CREB protein was assessed by immunoblotting neuronal nuclear proteins from five normoxic (Nx), 10 hypoxic (Hx) and five Hx-NNLA-treated 3-5-day-old piglets. NNLA (40 mg/kg) or saline was infused over 60 min prior to induction of hypoxia. Hypoxia was achieved by reducing the FiO(2) (0.15 to 0.05) for 60 min and documented biochemically by ATP and phosphocreatine (PCr) levels. Neuronal nuclei were isolated using discontinuous sucrose gradient centrifugation and purified. Nuclear proteins were separated on 12% sodium dodecylsulfate-polyacrylamide gel electrophoresis, transferred to nitrocellulose membranes, reacted with anti-phosphorylated CREB protein antibody and conjugated with horseradish peroxidase antibody. Protein bands were detected using the enhanced chemiluminescence method and quantitated by imaging densitometry. Protein density was expressed as absorbance (OD)xmm(2). ATP levels (micromol/g brain) were 4.3+/-0.6 in the Nx group, 1.3+/-0.5 in the Hx group (P<0.001) and 1.1+/-0.2 in the Hx-NNLA group (P<0.001 vs. Nx and Hx). Similarly, PCr levels (micromol/g brain) were 3.8+/-0.6 in the Nx group, 0.7+/-0.2 in the Hx group (P<0.001) and 0.6+/-0.1 in the Hx-NNLA group (P<0.001 vs. Nx and Hx). Density of phosphorylated CREB protein (ODxmm(2)) was 134.2+/-52.4 in the Nx group compared to 746.0+/-76.8 in the Hx group (P<0.05) and 491.1+/-40.9 in the Hx-NNLA group (P<0.05 Hx). The data show that NOS inhibition attenuates the hypoxia-induced increase in CREB protein phosphorylation in the cerebral cortex of newborn piglets.

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.

Nitric oxide-mediated expression of Bax protein and DNA fragmentation during hypoxia in neuronal nuclei from newborn piglets

The present study tests the hypothesis that nitric oxide mediates the hypoxia-induced increase in expression of Bax and in DNA fragmentation in the cerebral cortex of newborn piglets, and that administration of N-nitro-L-arginine (NNLA), a nitric oxide synthase inhibitor, will prevent a change in hypoxia-induced expression of apoptotic genes and DNA damage. Piglets were assigned to normoxic, hypoxic, or NNLA-pretreated hypoxic groups. Cerebral tissue hypoxia was documented biochemically by measuring ATP and phosphocreatine (PCr) levels. Cerebral cortical neuronal nuclei were isolated and nuclear proteins were separated electrophoretically and probed with specific antibodies against Bcl-2 or Bax proteins. Neuronal nuclear DNA from normoxic, hypoxic, and NNLA-pretreated hypoxic animals was isolated, separated by electrophoresis on 1% agarose gel and stained with ethidium bromide. Cerebral hypoxia resulted in an increase in nuclear membrane Bax protein levels from 121.33+/-47.7 optical density (OD)xmm(2) in normoxic to 273.67+/-67.3 ODxmm(2) in hypoxic group (P<0.05 vs. normoxic), but levels in NNLA-pretreated hypoxic group were 155.78+/-48.3 ODxmm(2) (P<0.05 vs. hypoxic, P=NS vs. normoxic). Similarly, cerebral hypoxia resulted in the density of DNA fragments increasing from 1530.3+/-309.8 OD/mm(2) in the normoxic group to 5383.3+/-775 OD/mm(2) in the hypoxic group (P<0.05), while levels in NNLA-pretreated hypoxic group were 3574.0+/-952 OD/mm(2) (P<0.05 compared to hypoxic and normoxic groups). The data show that NNLA-pretreatment prevents the hypoxia-induced increase in Bax expression and DNA fragmentation demonstrating that the hypoxia-induced Bax gene expression and the DNA fragmentation are NO-mediated.

Effect of hypoxia on caspase-3, -8, and -9 activity and expression in the cerebral cortex of newborn piglets

Caspases play an important role in programmed cell death. Caspase-3 is a key executioner of apoptosis, whose activation is mediated by the initiator caspases, caspase-8 and caspase-9. The present study tested the hypothesis that cerebral hypoxia results in increased activation and expression of caspases-3, -8, and -9 in the cytosolic fraction of the cerebral cortex of newborn piglets. To test this hypothesis the activity and expression of caspases-3, -8, and -9 were determined in newborn piglets divided into normoxic and hypoxic groups. Caspase activity was determined spectrofluorometrically using enzyme specific substrates. The expression of caspase protein was assessed by Western blot analysis using enzyme specific antibody. Caspases-3, -8, and -9 activity and expression was significantly higher in the hypoxic group than in the normoxic group. These results demonstrate that hypoxia induces activation and increased expression of both the initiator caspases and the executioner caspase in the cerebral cortex of newborn piglets. We conclude that hypoxia results in stimulation of both the pathways of caspase-3 activation.