Causes of oxidative stress in the pre- and perinatal period

Oxidative stress may be defined as an imbalance between pro-oxidant and antioxidant forces resulting in an overall pro-oxidant insult. Pregnancy is a physiological state accompanied by a high energy demand of many bodily functions and an increased oxygen requirement. Because of the increased intake and utilization of oxygen, augmented levels of oxidative stress would be expected. Arguments for a role of oxidative stress/oxidative lipid derivatives in the pathogenesis of preeclampsia are documented in many papers and evidence continues to accumulate that oxidative stress is a mediator of endothelial dysfunction and thus contributes to the cardiovascular complications of preeclampsia. Also other conditions, such as toxic substance exposure, smoking and asphyxia likewise induce oxidative stress. The oxidized lipid products generated as a consequence of these conditions are highly reactive and cause damage to cells and cell membranes. Thus, increased oxidative stress accompanied by reduced endogenous defences may play a role in the pathogenesis of a number of diseases in the newborn.

Allopregnanolone attenuates N-methyl-D-aspartate-induced excitotoxicity and apoptosis in the human NT2 cell line in culture

Progesterone modulates gamma-aminobutyric acid and excitatory amino acid neurotransmitter systems and has neuroprotective properties in models of hypoxia-ischemia. This study examined the in vitro effects of allopregnanolone, the active progesterone metabolite, in models of N-methyl-D-aspartate (NMDA)-induced necrosis and apoptosis. Cultured NT2 neurons were exposed to 1 mM NMDA. Lactate dehydrogenase (LDH) release was measured 24 h later. NMDA at a concentration of 1 mM produced a 39 +/- 19% release of total LDH. Exposure to 10 microM allopregnanolone prior to NMDA exposure reduced LDH release by 51% (P = 0.0028). NMDA stimulated apoptotic cell changes defined by terminal dUTP nick-end labeling (TUNEL) and 5,5', 6,6'-tetrachloro-1,1,3,3'-tetra ethlybenzimidazolycarbocyanide iodide staining were reduced to baseline values by both 10 microM allopregnanolone and 100 microM MK-801. Pretreatment with allopregnanolone (0-10 microM) reduced the percentage of TUNEL-positive cells in a dose-dependent manner (EC(50) = 2.7 +/- 0.1 nM). Physiologic concentrations of allopregnanolone provided protection against both necrotic and apoptotic injury induced by NMDA excitotoxicity.

Acute neuronal injury after hypoxia is influenced by the reoxygenation mode in juvenile hippocampal slice cultures

In neonates asphyxia is usually followed by hyperoxia due to resuscitation procedures. In order to study whether hyperoxic reoxygenation might cause additional cell injury we subjected organotypic hippocampal slice cultures of juvenile rats to normoxic or hyperoxic reoxygenation (19 or 85% oxygen, respectively) following hypoxia (3% oxygen) for 30, 60, and 120 min. Cell injury was quantified by lactate dehydrogenase (LDH) release and propidium iodide (PI) fluorescence 1 h after end of the reoxygenation period. In both experimental groups, LDH activity was significantly enhanced by hypoxia as compared to normoxic controls. However, hyperoxic reoxygenation caused a larger increase in LDH activity than normoxic reoxygenation (e.g., by a factor of 1.60 vs. 1.29 following 120 min hypoxia). PI fluorescence increased after hypoxia in all principal cell layers of the hippocampus but again showed a larger enhancement after hyperoxic reoxygenation as compared to normoxic reoxygenation (e.g., by a factor of 3.9 vs. 1.7 for CA1 and 120 min of hypoxia). After normoxic reoxygenation, PI fluorescence intensity was lower in the dentate gyrus as compared to CA1 and CA3, while it reached similar values like CA1 after high oxygen supply. In conclusion, juvenile hippocampal slice cultures subjected to hyperoxic reoxygenation display a greater amount of acute neuronal injury than slice cultures undergoing normoxic reoxygenation.

Hypoxia-induced cell death and changes in hypoxia-inducible factor-1 activity in PC12 cells upon exposure to nerve growth factor

The transcription factor hypoxia-inducible factor-1 (HIF-1) strongly contributes to the expression of adaptive genes under hypoxic conditions. In addition, HIF-1 has been implicated in the regulation of delayed neuronal cell death. Suspension-grown and adherent PC12 cells treated with NGF were used as an experimental model for studying the relationship between hypoxia-induced cell death and activation of HIF-1. Cell damage was assessed by flow cytometry of double-stained (Annexin V and propidiumiodide) cells, and by analysis of the overall death parameters LDH and mitochondrial dehydrogenase. In parallel, cells were transfected with a control and a three-hypoxia-responsive-elements (HRE)-containing vector and HIF-1-driven luciferase activity was determined. Exposure of NGF-treated PC12 cells to hypoxia resulted in a higher cell death rate when compared to untreated controls. PC12 cells exposed for 2 days to NGF exhibited a decrease of HIF-1 activity up to a factor of ten. This decrease may contribute to the enhanced hypoxia-induced cell death via reduced expression of HIF-1alpha-regulated genes responsible for adaptation to hypoxia, like those for glucose transport proteins and enzymes of the glycolytic chain. The decrease in HIF-1 activity and the increase in hypoxia sensitivity may suggest that NGF act as an hierarchically organized signaling molecule.

Altered expression and phosphorylation of N-methyl-D-aspartate receptors in piglet striatum after hypoxia-ischemia

The mechanisms for the profound degeneration of striatal neurons after hypoxia-ischemia in newborns are not understood. We hypothesized that this striatal neurodegeneration is related to N-methyl-D-aspartate (NMDA) receptor-mediated excitotoxicity. Using a 1-week-old piglet model of hypoxia-ischemia, we evaluated whether the expression and phosphorylation of NMDA receptor subunits in striatum are modified with severity of evolving neuronal injury after hypoxia-ischemia. Protein levels of NR1, phosphorylated NR1 897serine, NR2A and NR2B in striatum were measured by immunoblotting after piglets underwent hypoxic-asphyxic cardiac arrest, cardiopulmonary resuscitation, and recovery for 3, 6, 12 or 24 h. In membrane fractions isolated from total striatum, mean NR1 and NR2A levels did not change significantly with time after hypoxia-ischemia compared to control; however, the levels of both NR1 and phosphorylated NR1 897serine correlated with neuronal injury in putamen, with higher levels associated with greater neuronal injury in individual animals. NR2B levels were increased at 24 h after hypoxia-ischemia. Astrocyte expression of NR2B was prominent after hypoxia-ischemia. We conclude that NMDA receptors are changed in striatum after neonatal hypoxia-ischemia and that abnormal NMDA receptor potentiation through increased NR1 phosphorylation may participate in the mechanisms of striatal neuron degeneration after hypoxia-ischemia.

The role of glutamate receptor maturation in perinatal seizures and brain injury

The perinatal age window is characterized by vulnerability to age-specific patterns of injury. Hypoxia/ischemia occurs in a number of settings both in term and preterm neonates, yet the patterns of response appear dependent upon the age of the infant. In the preterm neonate, hypoxic/ischemic insults result in selective white matter injury, termed periventricular leukomalacia (PVL), with little or no cortical pathology. However, in term babies, hypoxic encephalopathy is the most common cause of seizures, and also can result in cortical infarction. Extracellular glutamate accumulates in the setting of hypoxia/ischemia, and excess activation of glutamate receptors has been implicated in hypoxic/ischemic cellular death. Glutamate receptors are developmentally regulated in both neuronal and glial cells within the brain. Using rodent models, we have shown that hypoxia/ischemia results in selective white matter injury in postnatal day (P) seven rat pups, while hypoxia causes seizures in P10-12 rats, but not at younger or older ages. We have further demonstrated that antagonists of the alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) glutamate receptor subtype block white matter injury at P7 and seizures at P10. We have shown that AMPA receptors are relatively overexpressed in oligodendrocytes (OLs) within white matter at P7 and in neurons in cortex and hippocampus at P10. Hence maturational patterns of glutamate receptor expression correlate with age-specific regional susceptibility to injury to hypoxia/ischemia. While glutamate receptor blockade represents a rational strategy in the treatment of perinatal hypoxic/ischemic brain injury, it is unclear what role variations in their expression play in normal development and plasticity. Further investigation of patterns of glutamate receptor subunit expression in human brain and in experimental animal models is necessary to determine potential age specific strategies as well as adverse effects.

Seizure-associated brain injury in term newborns with perinatal asphyxia

BACKGROUND

There is controversy over whether seizures, the most common manifestation of neonatal brain injury, may themselves damage the developing brain.

OBJECTIVE

To determine if neonatal seizures are independently associated with brain injury in newborns with perinatal asphyxia.

METHODS

Ninety term neonates were studied with MRI and single-voxel (1)H-MRS on median day of life 6 (range 1 to 13 days). The severity of MR abnormality in the (1)H-MRS regions of interest was scored using a validated scale. Seizure severity was scored based on seizure frequency and duration, EEG findings, and anticonvulsant administration. Multivariable linear regression tested the independent association of seizure severity with impaired cerebral metabolism measured by lactate/choline and compromised neuronal integrity measured by N-acetylaspartate/choline in both regions.

RESULTS

Clinical seizures occurred in 33 of 90 infants (37%). Seizure severity was associated with increased lactate/choline in both the intervascular boundary zone (p < 0.001) and the basal nuclei (p = 0.011) when controlling for potential confounders of MRI abnormalities and amount of resuscitation at birth. Each increase in seizure score was independently associated with a 21% increase in lactate/choline in the intervascular boundary zone (95% CI, 5.1-38.2%) and a 15% increase in the basal nuclei (95% CI, 0.1-31.7%). Seizure severity was independently associated with diminished N-acetylaspartate/choline in the intervascular boundary zone (p = 0.034).

CONCLUSION

The severity of seizures in human newborns with perinatal asphyxia is independently associated with brain injury and is not limited to structural damage detectable by MRI.

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

Previous studies have shown that hypoxia results in the generation of nitric oxide (NO) free radicals in the cerebral cortex of newborn animals. The present study tested the hypothesis that NO increases Ca++-influx in neuronal nuclei as well as N-methyl-D aspartate (NMDA) receptor-mediated Ca++-influx in cortical synaptosomes of newborn piglets. Studies were performed in five normoxic (Nx) and 6 hypoxic (Hx) newborn piglets. Cerebral tissue hypoxia was documented by determining the levels of ATP and phosphocreatine (PCr). 45Ca++ -influx was determined in the presence of sodium nitroprusside (SNP, 10 microM), a NO donor, and peroxynitrite (10 microM). In the Hx group, ATP levels decreased to 1.40+or-0.69 vs 4.27+or-0.80 micromoles/g brain in the Nx group (P<0.05). Similarly, PCr levels decreased to 0.91+or-0.57 vs 3.40+or-0.99 micromoles/g brain (P<0.001). Nuclear 45Ca++-influx increased from 3.57+or-1.46 pmoles/mg protein in Nx nuclei to 8.64+or-3.50 in Hx nuclei (P<0.05). SNP increased neuronal nuclear Ca++ influx in the Nx from 3.57+or-1.46 to 5.47+or-2.52 pmoles/mg protein (P<0.05) but did not affect Ca++ influx in the Hx group (8.64+or-3.50 vs. 10.17+or-4.00 pmoles/mg protein). The level of Ca++ influx in the presence of SNP in Nx nuclei was similar to that seen in Hx nuclei alone. Peroxynitrite did not affect nuclear Ca++-influx in either Nx or Hx group. Synaptosomal Ca++-influx in the presence of glu + gly was 40+or-11 pmoles/mg protein in the Nx group and 80+or-16 pmoles/mg protein in the Hx group (P<0.05). Both SNP and peroxynitrite increased Ca++ influx in Nx and Hx synaptosomes. These results show that hypoxia results in increased nuclear and synaptosomal Ca++-influx. Further, the data demonstrate that NO increases intranuclear as well as intrasynaptosomal Ca++-influx and suggest that during hypoxia, the increase in intranuclear and intraynaptosomal Ca++ is NO-mediated. We propose that NO-mediated modification (by nitrosylation/nitration) of nuclear membrane high affinity Ca++-ATPase and neuronal membrane NMDA receptor, resulting in increased intranuclear and intracellular Ca++ influx, are potential NO-mediated mechanisms of Hx neuronal injury.

Caspase-3 activation and caspase-like proteolytic activity in human perinatal hypoxic-ischemic brain injury

Human perinatal hypoxic-ischemic brain injury is an important cause of death and morbidity. One relatively common pattern of perinatal injury involves selective neuronal death in the ventral gray matter of the pons and in the subiculum of the hippocampal formation, classically termed 'pontosubicular neuronal necrosis' (PSN). The vulnerable neurons undergo karyorrhectic condensation of their nuclear chromatin and exhibit in situ end labeling for DNA fragmentation, leading to the recent reclassification of cell death in PSN as apoptotic. Caspase activation plays a central role in apoptosis and caspase-3 appears to be an especially important effector enzyme in neuronal apoptosis. In this study we performed immunohistochemistry on brain sections from six postmortem cases of PSN using two polyclonal antisera; CM1, a specific marker of caspase-3 activation, and fractin, which specifically recognizes a neoepitope at a caspase cleavage site in actin, and is therefore a marker of caspase-like proteolytic activity. Numerous CM1- and fractin-immunolabeled neurons were seen in the nuclei pontis and subiculum in each case, and the great majority showed karyorrhectic morphology. The immunostaining involved the nuclei and cytoplasm of these cells and the proximal portions at least of their neuritic processes. Some neurons exhibited a more extensive pattern of dendritic fractin labeling. Frequent CM1- and fractin-immunoreactive axonal segments were also seen. The identification of caspase-3 activation and caspase-like proteolytic activity in PSN cases in this study suggests that caspase inhibitors may potentially have a therapeutic neuroprotective role in human perinatal hypoxic-ischemic brain injury.

Changes in reactive oxygen species (ROS) production in rat brain during global perinatal asphyxia: an ESR study

A large body of evidence suggests that the production of reactive oxygen species (ROS) can play an important role in ischemic neuronal injury. However any studies has been performed in hypoxic conditions. In the present experiments we studied using electron spin resonance (ESR) techniques the ROS release in neostriatum of newborn rats subjected to acute perinatal asphyxia (PA) followed by various periods of reoxygenation. Pregnant rats' uteri still containing foetuses were taken out and subjected to PA by immersion in a 37 degrees C water bath during the following periods of time: 5, 10, 15, 19 and 20 min. After performing PA, animals were recovered and ROS measured after 0, 5, 15, 30 or 60 min of reoxygenation. Then, pups were sacrificed, their neostriatum removed and homogenised with N-tert.-butyl-alpha-phenylnitrone (PBN) and diethylenetriamine-pentacetic acid (DPTA) in phosphate-buffered saline (PBS) and the formed complexes were extracted with ethyl acetate an analysed using an X-band ESR spectrometer. A significant release of ROS was detected at 19 and 20 min of PA after 5 min of reoxygenation. These data provide strong evidence that ROS could be involved in neuronal damage during PA.

5-HT acting on 5-HT(1/2) receptors does not participate in the in vitro hypoxic respiratory depression

The involvement of serotoninergic mechanisms in the central respiratory depression produced by hypoxia was studied in the newborn rat brainstem-spinal cord preparation. The respiratory frequency measured by the C4 ventral root activity was recorded. 5-HT (30 microM) superfusion elicited a rapid increase in respiratory frequency, prevented by a treatment with methysergide (a 5-HT(1/2) receptor antagonist) (40 microM). To investigate the possible participation of 5-HT in hypoxic respiratory depression, this concentration of methysergide was added to the bathing medium during hypoxia. Methysergide did not modify the decrease in respiratory frequency produced by hypoxia. In order to ensure that other 5-HT subtype receptors were not involved in hypoxic respiratory depression, 5-HT was added to the bath during hypoxic-methysergide tests; no effect on respiratory frequency was observed. These results suggest that in the newborn rat brainstem-spinal cord preparation, serotoninergic mechanisms are not involved in the elaboration of the in vitro respiratory response to hypoxia.

Attenuation of hypoxia-ischemia-induced monocyte chemoattractant protein-1 expression in brain of neonatal mice deficient in interleukin-1 converting enzyme

Interleukin-1beta (IL-1beta) upregulates expression of the chemokine monocyte chemoattractant protein-1 (MCP-1) in many experimental models. In neonatal rodent brain, hypoxia-ischemia rapidly stimulates expression of this chemokine, although the role of IL-1beta in regulating this response is unknown. Interleukin-1 converting enzyme (ICE) is a cysteine protease that cleaves inactive pro-IL-1beta to generate mature IL-1beta. Neonatal mice with a homozygous deletion of ICE (ICE -/-) are resistant to moderate, but not to severe cerebral hypoxic-ischemic insults, relative to their wild-type controls. We hypothesized that their resistance to moderate hypoxic-ischemic insults is mediated by suppression of the acute inflammatory response to brain injury in the absence of IL-1beta, and that hypoxia-ischemia induced MCP-1 expression would be attenuated in ICE -/- animals. To test this hypothesis, paired litters of 9-10-day-old ICE -/- and wild-type mice underwent right carotid ligation, followed by 40, 70 or 120 min exposure to 10% O2 and ischemia-induced changes in MCP-1 mRNA and protein were compared, using a semi-quantitative reverse-transcription polymerase chain reaction assay and an ELISA, respectively. With a lesioning protocol that elicits minimal injury in wild-types (ligation+40 min 10% O2), there was an attenuation of hypoxia-ischemia-induced MCP-1 production at 8 h post-hypoxia; in contrast, in animals that underwent longer periods of hypoxia-ischemia the magnitude of injury-induced induced MCP-1 production did not differ between wild-type and ICE -/- animals. These results demonstrate both that the acute inflammatory response to hypoxia-ischemia is attenuated in ICE -/- animals, and also that hypoxic-ischemic brain injury stimulates MCP-1 expression even in the absence of IL-1beta activity.

Effects of hyperglycemia or hypoglycemia on brain cell membrane function and energy metabolism during the immediate reoxygenation-reperfusion period after acute transient global hypoxia-ischemia in the newborn piglet

This study was done to determine the effects of hyperglycemia or hypoglycemia on brain cell membrane function and energy metabolism during the immediate reoxygenation-reperfusion period after hypoxia-ischemia (HI). Forty-five newborn piglets were divided randomly into four experimental groups: normoxia control (NC, n=9); HI/reoxygenation-reperfusion (RR) control (HC, n=11); HI/RR hyperglycemia (HE, n=12); and HI/RR hypoglycemia (HO, n=13) group. Animals were subjected to transient HI for 30 min followed by 2 h of RR. Cerebral HI was induced by temporary but complete occlusion of bilateral common carotid arteries with surgical clips and simultaneous breathing with 8% oxygen. Glucose was unregulated in HC group, and controlled by modified glucose clamp technique immediately after HI in HE (350 mg/dl) and HO (50 mg/dl) groups. During HI, heart rate, base deficit, glucose and lactate level in the blood and cerebrospinal fluid increased, and arterial pH, oxygen saturation and blood pressure decreased significantly in HC, HE and HO groups. During RR, these abnormalities returned to normal values, but lactic acidosis persisted especially in HO group. Cerebral Na(+),K(+)-ATPase activity decreased, and lipid peroxidation products increased significantly in HC group than in NC group, and these abnormalities were significantly aggravated in HE, but not in HO, group. Brain ATP and phosphocreatine levels in HE group were significantly reduced compared to the corresponding values in NC, HC and HO groups. In summary, hyperglycemia, but not hypoglycemia immediately after HI interfered with the recovery of brain cell membrane function and energy metabolism. These findings suggest that post-hypoxic-ischemic hyperglycemia is not beneficial and might even be harmful in neonatal hypoxic-ischemic encephalopathy.

Neonatal asphyxia in rats: acute effects on cerebral kynurenine metabolism

Two tryptophan metabolites, the anti-excitotoxic N-methyl-D-aspartate (NMDA) receptor antagonist kynurenic acid (KYNA) and the free radical generator 3-hydroxykynurenine (3-HK), have been proposed to influence neuronal viability in the mammalian brain. In rats, the brain content of both KYNA and 3-HK decreases immediately after birth, possibly to ensure normal postnatal functioning of NMDA receptors. Because complications of birth asphyxia have been suggested to be associated with anomalous NMDA receptor function, we examined the acute effects of an asphyctic insult on the brain levels of KYNA and 3-HK in neonatal rats. Asphyxia was induced in animals delivered by cesarean section on the last day of gestation, using the procedure introduced by Bjelke et al. (Brain Res 543: 1-9, 1991). KYNA and 3-HK levels were determined in the brain at seven time points between 10 min and 24 h after asphyxia. Up to 6 h, asphyxia caused 160-267% increases in KYNA levels. In the same tissues, 3-HK levels decreased (significantly at five of the seven time points), demonstrating an asphyxia-induced shift in kynurenine pathway metabolism toward the neuroprotectant KYNA. This shift might constitute the brain's attempt to counter the ill effects of birth asphyxia. Furthermore, the transient increase in the brain KYNA/3-HK ratio in these animals might be causally related to the well-documented detrimental long-term effects of asphyxia.

Glutamate in cerebral tissue of asphyxiated neonates during the first week of life demonstrated in vivo using proton magnetic resonance spectroscopy

We tested the hypothesis that glutamate (Glx) levels as demonstrated by proton magnetic resonance spectroscopy ((1)H-MRS) are elevated in brain tissue of neonates with severe hypoxic-ischemic encephalopathy (HIE). Studies were performed in 26 neonates (median gestational age 40.5 weeks, range 36.7-42.4 weeks; median birth weight 3,360 g, range 2,180-4,200 g). The median postnatal age at the time of testing was 2.5 days (range 1-7 days). HIE was scored according to Sarnat as grade I (n = 4), grade II (n = 15) or grade III (n = 7). Results for neonates with mild to moderate HIE (group 1) were compared to those with severe HIE (group 2). After magnetic resonance imaging, (1)H-MRS was performed in a single volume of interest including the basal ganglia. An echo time of 31 ms was used. After curve-fitting procedures, peak area ratios of different brain metabolites were calculated. The median total Glx/N-acetylaspartate ratio was 1.21 (range 0.64-3.25) in group 1 versus 1.55 (range 1.10-2.75) in group 2 (p = 0.035). The median total Glx/choline ratio was 1.33 (range 0.71-2.52) in group 1 versus 2.14 (range 1.21-3.55) in group 2 (p = 0.019). We concluded that during the first days of life, Glx was elevated in the basal ganglia of neonates with severe HIE.

[Biochemical parameters predictive of neuronal damage in childhood]

INTRODUCTION

Hypoxemia, hypoxia and ischemia may induce deletereous effects on both metabolism and cellular structure, particularly at neuronal level. Early estimation of the potential severity of an acute cerebral hypoxic ischemic injury or other pathological conditions would be useful on making preventive or therapeutic decisions. On the basis of the physiopathological mechanisms involved in the brain damage related to hypoxic ischemic encephalopathy of the newborn, a number of metabolic parameters had been studied in the aim to provide an early and reliable marker of tissue injury for both diagnostic and prognostic purposes.

OBJECTIVE

To provide a current revision about the diagnostic and prognostic value of various biochemical parameters determined in different body fluids and studied in the last years, the attention focusing in the hypoxic ischemic encephalopathy of the newborn. Design. For methodological purposes the exposition is structured in the following sections: 1. creatine kinase isoenzymes; 2. lactate; 3. lactate dehydrogenase, aspartate aminotransferase and hidroxybutirate dehydrogenase; 4. excitatory amino acids; 5. glial fibrillary acidic protein; 6. cytokines; 7. neuron specific enolase; 8. oxypurines; 9. cyclic adenosine monophosphate; 10. Others.

CONCLUSIONS

The current role of the above mentioned biochemical parameters as predictors of brain damage and the future perspectives on this topic are discussed.

Comparison between hypothermia and glutamate antagonism treatments on the immediate outcome of perinatal asphyxia

This study investigated the influence of temperature or glutamate antagonism on the immediate outcome of perinatal asphyxia. Perinatal asphyxia was produced by water immersion of fetus-containing uterus horns removed by cesarean section from ready to deliver rats. The uterus horns were kept in a water bath for different time periods, before the pups were delivered and stimulated to breathe. After delivery, the pups were assessed for behavior and for systemic glutamate, aspartate, lactate and pyruvate levels measured with in vivo microdialysis, or ex vivo for energy-rich phosphates, including adenosine triphosphate (ATP), in brain, heart and kidney. In a series of experiments, asphyxia was initiated in a water bath at 37 degrees C, before the pup-containing uterus horns were moved for different time intervals to a 15 degrees C bath. In another series of experiments, the mothers were treated with N-methyl-D-aspartate (NMDA) antagonist, dizocilpine (MK-801), or alpha-amino-3-hydroxy-methylisoxazole-4-propionic acid (AMPA) antagonist,2,3-dihydroxy-6-nitro-7-sulfamoyl benzo(f) quinoxalin NBQX) 1 h before hysterectomy and asphyxia at 37 degrees C. The rate of survival rapidly decreased following exposure to more than 16 min of asphyxia, and no survival could be observed after 22 min of asphyxia. An LD50 was estimated to occur at approximately 19 min of asphyxia. The outcome was paralleled by a decrease in ATP in kidney, followed by a decrease in heart and brain. A maximal decrease in ATP was observed after 20 min of asphyxia in all tissues. Systemic microdialysis revealed that glutamate, aspartate and pyruvate levels were increased with a peak after 5 min of asphyxia. In contrast, lactate levels increased along with the length of the insult. Survival was increased when the pup-containing uterus horns were moved from a 37 degrees C to a 15 degrees C bath, at 15 min of asphyxia (the LD50 was thus increased to 30 min). If the shift occurred at 10 or 5 min of asphyxia, the LD50 increased to 80 or 110 min, respectively. The effect of glutamate antagonism was minor compared to hypothermia; the best effect (an increase in the LD50 to approximately 22 min) was observed after combining AMPA and NMDA antagonists.

Effect of temperature on postanoxic, potentially neurotoxic changes of plasma pH and free iron level in newborn rats

In asphyxiated newborns, iron, released from heme and ferritin and deposited in the brain, contributes to neurodegeneration. Because hypothermia provides neuroprotection, newborn mammals, showing reduced body temperature, might avoid iron-mediated neurotoxicity. However, hypothermia leads to acidosis, which induces hyperferremia. Therefore, we decided to study the effects of body temperature on plasma pH and iron levels in newborn rats exposed to a critical anoxia. Rectal temperature was kept at 33 degrees C (typical of neonates), reduced by 2 degrees C, or elevated to a level typical of healthy (37 degrees C) or febrile (39 degrees C) adults. Arterial blood samples were collected at 0, 10, 20, 30, and 120 min postanoxia. Control samples were obtained from normoxic, temperature-matched neonates. Anoxia tolerance time decreased progressively at rectal temperatures exceeding 33 degrees C. Neither pH nor plasma iron were significantly affected by anoxia at 33 degrees C. Although hypothermia (31 degrees C) resulted in acidosis in normoxic rats, both pH and iron levels were hardly influenced by anoxia. However, acidosis and hyperferremia, proportional to body temperature, developed at 37 and 39 degrees C. In conclusion, reduced body temperature is likely to protect asphyxiated newborns against iron-mediated brain injury.

Brain fatty acids in perinatal asphyxia

In hypoxic or ischemic states the release of fatty acids is proposed to have several harmful effects on brain structure and function. We therefore decided to study brain FFA in a simple, clinically related animal model resembling intrauterine perinatal asphyxia (PA). Cerebral blood flow (CBF), brain fatty acids (C14:0, C16:1, C16:0, C18:1, C1 8:0, sigma C), plasma glucose, lactate, beta-hydroxybutyrate (beta-OHB), non-esterified fatty acids (NEFA) and insulin were determined in PA and compared to the normoxic state. Brain C 14:0 FFA were not significantly different from normoxic rats. Brain FFA C 16:0 were comparable between groups but significantly decreased at 20 min of PA. C 18:0 FFA showed a trend to increase with the length of PA reaching significance at 10 min of asphyxia only and were declining at 20 min, however, not significantly. Brain C 16:1 and C 18:1 FFA concentrations were comparable between groups. The parameters cerebral blood flow, glucose and lactate showed a stepwise and significant increase with the length of PA, whereas beta-HOB, NEFA and insulin showed no changes. CBF, glucose and lactate showed a strong association whereas other parameters failed to correlate with each other. Only inconsistent trends of increased brain FFA were found and the association between brain glucose and brain FFA could be ruled out. Although CBF was manifold and significantly elevated in PA, brain FFA pattern suggests that the increase of CBF is obviously not mediated by brain FFA. We conclude that FFA may not be involved in the early phase-pathogenesis of PA.

Resuscitation with room air instead of 100% oxygen prevents oxidative stress in moderately asphyxiated term neonates

BACKGROUND

Traditionally, asphyxiated newborn infants have been ventilated using 100% oxygen. However, a recent multinational trial has shown that the use of room air was just as efficient as pure oxygen in securing the survival of severely asphyxiated newborn infants. Oxidative stress markers in moderately asphyxiated term newborn infants resuscitated with either 100% oxygen or room air have been studied for the first time in this work.

METHODS

Eligible term neonates with perinatal asphyxia were randomly resuscitated with either room air or 100% oxygen. The clinical parameters recorded were those of the Apgar score at 1, 5, and 10 minutes, the time of onset of the first cry, and the time of onset of the sustained pattern of respiration. In addition, reduced and oxidized glutathione concentrations and antioxidant enzyme activities (superoxide dismutase, catalase, and glutathione peroxidase) were determined in blood from the umbilical artery during delivery and in peripheral blood at 72 hours and at 4 weeks' postnatal age.

RESULTS

Our results show that the room-air resuscitated (RAR) group needed significantly less time to first cry than the group resuscitated with 100% oxygen (1.2 +/- 0.6 minutes vs 1.7 +/- 0.5). Moreover, the RAR group needed less time undergoing ventilation to achieve a sustained respiratory pattern than the group resuscitated with pure oxygen (4.6 +/- 0.7 vs 7.5 +/- 1.8 minutes). The reduced-to-oxidized-glutathione ratio, which is an accurate index of oxidative stress, of the RAR group (53 +/- 9) at 28 days of postnatal life showed no differences with the control nonasphyxiated group (50 +/- 12). However, the reduced-to-oxidized-glutathione ratio of the 100% oxygen-resuscitated group (OxR) (15 +/- 5) was significantly lower and revealed protracted oxidative stress. Furthermore, the activities of superoxide dismutase and catalase in erythrocytes were 69% and 78% higher, respectively, in the OxR group than in the control group at 28 days of postnatal life. Thus, this shows that these antioxidant enzymes, although higher than in controls, could not cope with the ongoing generation of free radicals in the OxR group. However, there were no differences in antioxidant enzyme activities between the RAR group and the control group at this stage.

CONCLUSIONS

There are no apparent clinical disadvantages in using room air for ventilation of asphyxiated neonates rather than 100% oxygen. Furthermore, RAR infants recover more quickly as assessed by Apgar scores, time to the first cry, and the sustained pattern of respiration. In addition, neonates resuscitated with 100% oxygen exhibit biochemical findings reflecting prolonged oxidative stress present even after 4 weeks of postnatal life, which do not appear in the RAR group. Thus, the current accepted recommendations for using 100% oxygen in the resuscitation of asphyxiated newborn infants should be further discussed and investigated.

Perinatal asphyxia: a clinical review, including research with brain hypothermia

Perinatal asphyxia may occur in utero, during labor and delivery, or in the postnatal period. There are numerous causes, and the clinical manifestations vary. Infants who experience mild asphyxia may show no neurologic injury. Severe asphyxia may be fatal in utero, or immediately after birth, with survivors showing extensive neurologic sequelae, with or without cognitive deficits. Mild brain hypothermia appears promising in the prevention of further neurologic damage in encephalopathic infants following asphyxia. Recent research on newborn animal models has focused on the timing, duration, and depth of hypothermia. Promising new research is now under way in nurseries in the U.S. in an attempt to establish clinical protocols for use of hypothermia in human neonates.

Early Neurodegeneration after Hypoxia-Ischemia in Neonatal Rat Is Necrosis while Delayed Neuronal Death Is Apoptosis

We used silver staining to demonstrate neuronal cell body, axonal, and terminal degeneration in brains from p7 rat pups recovered for 0, 1.5, 3, 6, 24, 48, 72 h, and 6 days following hypoxia-ischemia. We found that initial injury is evident in ipsilateral forebrain by 3 h following hypoxia-ischemia, while injury in ventral basal thalamus develops at 24 h. A secondary phase of injury occurs at 48 h in ipsilateral cortex, but not until 6 days in basal ganglia. Initial injury in striatum and cortex is necrosis, but in thalamus the neurodegeneration is primarily apoptosis. Degeneration also occurs in bilateral white matter tracts, and in synaptic terminal fields associated with apoptosis in regions remote from the primary injury. These results show that hypoxia-ischemia in the developing brain causes both early and delayed neurodegeneration in specific systems in which the morphology of neuronal death is determined by time, region, and potentially by patterns of neuronal connectivity.

Effect of graded hypoxia on the high-affinity CPP binding site of the NMDA receptor in the cerebral cortex of newborn piglets

Previous studies have shown that the N-methyl-D-aspartate (NMDA) receptor is modified during hypoxia in the cerebral cortex of newborn piglets. The present study tests the hypothesis that the NMDA receptor 3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid (CPP) high-affinity binding site is modified during hypoxia and that the degree of modification correlates with the progressive decrease in cerebral cellular energy metabolism and increase in lipid peroxidation induced by hypoxia. Studies were conducted in twelve anesthetized, ventilated newborn piglets, five normoxic and seven hypoxic which were exposed to decreased fraction of inspired oxygen (FiO2) to achieve varying phosphocreatine (PCr) levels. 3[H]-CPP binding was performed with CPP concentrations ranging from 0.5 to 1500 nM at 23 degrees C for 40 min in P2 membrane fractions. Brain tissue PCr levels were determined biochemically. Conjugated dienes (CDs) were measured as an index of lipid peroxidation. In the normoxic group, B(max) (receptor number) for the CPP binding site was 329+/-93 fmol/mg protein and Kd (dissociation constant) 137+/-44 nM, the mean PCr value was 2.5+/-0.4 micromol/g brain and the CD level was 0.0 nmol/g brain. As tissue hypoxia worsened, there was a gradual decline in tissue PCr as well as receptor B(max) and K(d) values, and there was an increase in conjugated dienes. Both the receptor B(max) (r=0.90) and Kd (r=0.72) decreased in a linear relationship as PCr decreased. As the levels of CDs increased both the receptor B(max) (r=0.88) and Kd (r=0.68) decreased in a linear fashion. The data show that there is not a critical hypoxic threshold for modification of the CPP binding site of the NMDA receptor, but that modification is coupled to a gradual decrease in brain cell energy metabolism and increase in lipid peroxidation. We speculate that hypoxia-induced modification of the NMDA receptor is mediated not only by changes in the receptor recognition site but also by an alteration of brain cell membrane structure secondary to conjugated diene formation.

[Anoxic encephalopathy of the term neonate and brain hypothermia]

The outcome of term newborns with birth asphyxia and moderate to severe hypoxic ischemic encephalopathy remains very poor. After the primary phase of energy failure during asphyxia, neuronal cell metabolism may deteriorate in a secondary phase of brain injury. The window between these two phases opens the way to potential neuroprotective treatments such as brain cooling. Promising experimental data on controlled hypothermia need to be examined with clinical trials.