The effect of hyperglycemia on cerebral metabolism during hypoxia-ischemia in the immature rat

Blood and Brain Metabolites after Cerebral Ischemia

The study of an organism's response to cerebral ischemia at different levels is essential to understanding the mechanism of the injury and protection. A great interest is devoted to finding the links between quantitative metabolic changes and post-ischemic damage. This work aims to summarize the outcomes of the most studied metabolites in brain tissue-lactate, glutamine, GABA (4-aminobutyric acid), glutamate, and NAA (N-acetyl aspartate)-regarding their biological function in physiological conditions and their role after cerebral ischemia/reperfusion. We focused on ischemic damage and post-ischemic recovery in both experimental-including our results-as well as clinical studies. We discuss the role of blood glucose in view of the diverse impact of hyperglycemia, whether experimentally induced, caused by insulin resistance, or developed as a stress response to the cerebral ischemic event. Additionally, based on our and other studies, we analyze and critically discuss post-ischemic alterations in energy metabolites and the elevation of blood ketone bodies observed in the studies on rodents. To complete the schema, we discuss alterations in blood plasma circulating amino acids after cerebral ischemia. So far, no fundamental brain or blood metabolite(s) has been recognized as a relevant biological marker with the feasibility to determine the post-ischemic outcome or extent of ischemic damage. However, studies from our group on rats subjected to protective ischemic preconditioning showed that these animals did not develop post-ischemic hyperglycemia and manifested a decreased metabolic infringement and faster metabolomic recovery. The metabolomic approach is an additional tool for understanding damaging and/or restorative processes within the affected brain region reflected in the blood to uncover the response of the whole organism via interorgan metabolic communications to the stressful cerebral ischemic challenge.

A Novel 5-Chloro-N-phenyl-1H-indole-2-carboxamide Derivative as Brain-Type Glycogen Phosphorylase Inhibitor: Potential Therapeutic Effect on Cerebral Ischemia

Brain-type glycogen phosphorylase inhibitors are potential new drugs for treating ischemic brain injury. In our previous study, we reported compound 1 as a novel brain-type glycogen phosphorylase inhibitor with cardioprotective properties. We also found that compound 1 has high blood–brain barrier permeability through the ADMET prediction website. In this study, we deeply analyzed the protective effect of compound 1 on hypoxic-ischemic brain injury, finding that compound 1 could alleviate the hypoxia/reoxygenation (H/R) injury of astrocytes by improving cell viability and reducing LDH leakage rate, intracellular glucose content, and post-ischemic ROS level. At the same time, compound 1 could reduce the level of ATP in brain cells after ischemia, improve cellular energy metabolism, downregulate the degree of extracellular acidification, and improve metabolic acidosis. It could also increase the level of mitochondrial aerobic energy metabolism during brain cell reperfusion, reduce anaerobic glycolysis, and inhibit apoptosis and the expression of apoptosis-related proteins. The above results indicated that compound 1 is involved in the regulation of glucose metabolism, can control cell apoptosis, and has protective and potential therapeutic effects on cerebral ischemia-reperfusion injury, which provides a new reference and possibility for the development of novel drugs for the treatment of ischemic brain injury.

Effects of antenatal dexamethasone and hyperglycemia on cardiovascular adaptation to asphyxia in preterm fetal sheep

Antenatal glucocorticoids improve outcomes among premature infants but are associated with hyperglycemia, which can exacerbate hypoxic-ischemic injury. It is still unclear how antenatal glucocorticoids or hyperglycemia modulate fetal cardiovascular adaptations to severe asphyxia. In this study, preterm fetal sheep received either saline or 12 mg im maternal dexamethasone, followed 4 h later by complete umbilical cord occlusion (UCO) for 25 min. An additional cohort of fetuses received titrated glucose infusions followed 4 h later by UCO to control for the possibility that hyperglycemia contributed to the cardiovascular effects of dexamethasone. Fetuses were studied for 7 days after UCO. Maternal dexamethasone was associated with fetal hyperglycemia (P < 0.001), increased arterial pressure (P < 0.001), and reduced femoral (P < 0.005) and carotid (P < 0.05) vascular conductance before UCO. UCO was associated with bradycardia, femoral vasoconstriction, and transient hypertension. For the first 5 min of UCO, fetal blood pressure in the dexamethasone-asphyxia group was greater than saline-asphyxia (P < 0.001). However, the relative increase in arterial pressure was not different from saline-asphyxia. Fetal heart rate and femoral vascular conductance fell to similar nadirs in both saline and dexamethasone-asphyxia groups. Dexamethasone did not affect the progressive decline in femoral vascular tone or arterial pressure during continuing UCO. By contrast, there were no effects of glucose infusions on the response to UCO. In summary, maternal dexamethasone but not fetal hyperglycemia increased fetal arterial pressure before and for the first 5 min of prolonged UCO but did not augment the cardiovascular adaptations to acute asphyxia.

Targeting Sentinel Proteins and Extrasynaptic Glutamate Receptors: a Therapeutic Strategy for Preventing the Effects Elicited by Perinatal Asphyxia?

Perinatal asphyxia (PA) is a relevant cause of death at the time of labour, and when survival is stabilised, associated with short- and long-term developmental disabilities, requiring inordinate care by health systems and families. Its prevalence is high (1 to 10/1000 live births) worldwide. At present, there are few therapeutic options, apart from hypothermia, that regrettably provides only limited protection if applied shortly after the insult.PA implies a primary and a secondary insult. The primary insult relates to the lack of oxygen, and the secondary one to the oxidative stress triggered by re-oxygenation, formation of reactive oxygen (ROS) and reactive nitrogen (RNS) species, and overactivation of glutamate receptors and mitochondrial deficiencies. PA induces overactivation of a number of sentinel proteins, including hypoxia-induced factor-1α (HIF-1α) and the genome-protecting poly(ADP-ribose) polymerase-1 (PARP-1). Upon activation, PARP-1 consumes high amounts of ATP at a time when this metabolite is scarce, worsening in turn the energy crisis elicited by asphyxia. The energy crisis also impairs ATP-dependent transport, including glutamate re-uptake by astroglia. Nicotinamide, a PARP-1 inhibitor, protects against the metabolic cascade elicited by the primary stage, avoiding NAD+ exhaustion and the energetic crisis. Upon re-oxygenation, however, oxidative stress leads to nuclear translocation of the NF-κB subunit p65, overexpression of the pro-inflammatory cytokines IL-1β and TNF-α, and glutamate-excitotoxicity, due to impairment of glial-glutamate transport, extracellular glutamate overflow, and overactivation of NMDA receptors, mainly of the extrasynaptic type. This leads to calcium influx, mitochondrial impairment, and inactivation of antioxidant enzymes, increasing further the activity of pro-oxidant enzymes, thereby making the surviving neonate vulnerable to recurrent metabolic insults whenever oxidative stress is involved. Here, we discuss evidence showing that (i) inhibition of PARP-1 overactivation by nicotinamide and (ii) inhibition of extrasynaptic NMDA receptor overactivation by memantine can prevent the short- and long-term consequences of PA. These hypotheses have been evaluated in a rat preclinical model of PA, aiming to identify the metabolic cascades responsible for the long-term consequences induced by the insult, also assessing postnatal vulnerability to recurrent oxidative insults. Thus, we present and discuss evidence demonstrating that PA induces long-term changes in metabolic pathways related to energy and oxidative stress, priming vulnerability of cells with both the neuronal and the glial phenotype. The effects induced by PA are region dependent, the substantia nigra being particularly prone to cell death. The issue of short- and long-term consequences of PA provides a framework for addressing a fundamental issue referred to plasticity of the CNS, since the perinatal insult triggers a domino-like sequence of events making the developing individual vulnerable to recurrent adverse conditions, decreasing his/her coping repertoire because of a relevant insult occurring at birth.

Neuroprotective effect of selective antegrade cerebral perfusion during prolonged deep hypothermic circulatory arrest: Cerebral metabolism evidence in a pig model

Objective:

The aim of this study was to elucidate the mechanism of cerebral injury and to evaluate selective antegrade cerebral perfusion (SACP) as a superior neuroprotective strategy for prolonged deep hypothermic circulatory arrest (DHCA).

Methods:

Twelve pigs (6–8-week old) were randomly assigned to DHCA alone (n=6) and DHCA with SACP (n=6) at 18°C for 80 min groups. Serum S100 was determined using an immunoassay analyzer. The concentrations of cerebral dialysate glucose, lactate, pyruvate, glycerol, and glutamate were measured using a microdialysis analyzer.

Results:

Compared with a peak at T4 (after 60 min of rewarming) in the DHCA group, the serum S100 in the SACP group was significantly lower throughout the study. The DHCA group was susceptible to significant increases in the levels of lactate, glycerol, and glutamate and the ratio of lactate/pyruvate as well as decreases in the level of glucose. These microdialysis variables showed only minor changes in the SACP group. There was a positive correlation between cerebral lactate and intracranial pressure during reperfusion in the DHCA group. However, the apoptosis index and C-FOS protein levels were lower in the SACP group.

Conclusion:

Metabolic dysfunction is involved in the mechanism of cerebral injury. SACP is a superior neuroprotective strategy for both mild and prolonged DHCA.

Reduced PLP2 expression increases ER-stress-induced neuronal apoptosis and risk for adverse neurological outcomes after hypoxia ischemia injury

Both genetic and environmental factors contribute to the development of intellectual disability (ID). Previously, we identified a promoter variant (-113C>A) in PLP2 (proteolipid protein 2) that results in an ∼4-fold reduction of transcript and protein and is overly represented in males with X-linked ID (XLID). The functional connection between reduced PLP2 expression and increased risk to XLID is unknown. To investigate the pathophysiological mechanisms, we studied a Plp2-loss-of-function murine model and fibroblasts from XLID patients hemizygous for PLP2-(-113C>A). We found that Plp2-deficient mouse embryonic fibroblast and human fibroblasts carrying PLP2-(-113C>A) have similarly defective endoplasmic reticulum (ER) trafficking, increased basal ER stress and exaggerated susceptibility to inducers of ER stress. Plp2-deficient mice show increased neuronal death to ER stress and hypoxia in vitro and in a neonatal hypoxia-ischemia model in vivo. Finally, we provide evidence that up-regulation of PLP2 directly promotes resistance to ER stressors. Results of our studies support the hypothesis that reduced PLP2 expression increase susceptibility of neurons to environmental ER stressors such as hypoxia and ischemia and that increased apoptosis and neuronal death contribute to the risks to ID in humans.

A New Technique for Collection of Cerebrospinal Fluid in Rat Pups

BACKGROUND

Neuroprotective strategies to prevent or decrease brain injury in hypoxic ischemic newborns are one of the main research lines in neonatology. Animal models have been used to assess the efficiency of new therapeutic strategies. Brain damage biomarkers in cerebrospinal fluid (CSF) are frequently used to evaluate the outcome at the bedside. Despite the importance of this approach in clinical practice, there are many difficulties in using it in small animals. The aim of this paper was to describe a new technique for collecting CSF in rat pups. Furthermore the reference values of S100β protein levels, commonly used in common clinical practice, were analyzed in animals between 7 to 12 days.

METHODS

42 Wistar rat pups aged 7 to 12 days were used. CSF was obtained by direct puncture of the cisterna magna with a 24-gauge needle. S100β protein levels were determined with enzyme-linked immunosorbent assay (ELISA).

RESULTS

CSF was successfully obtained in 96% of the cases, with an average amount of 21.28 μl (5–40 μl). Normal values for S100β were described. HI animals presented higher S100β values than controls.

CONCLUSIONS

A simple, reproducible technique for CSF collection in rat pups has been described. This new method will allow study of brain injury biomarkers in newborn hypoxic ischemic animal models.

Hyperglycemia accentuates and ketonemia attenuates hypoglycemia-induced neuronal injury in the developing rat brain

BACKGROUND

Prolonged hypoglycemia leads to brain injury, despite treatment with 10% dextrose. Whether induction of hyperglycemia or ketonemia achieves better neuroprotection is unknown. Hyperglycemia is neuroprotective in other brain injuries during development; however, it worsens hypoglycemia-induced injury in the adult brain via poly(ADP-ribose)polymerase-1 (PARP-1) overactivation.

METHODS

Three-week-old rats were subjected to insulin-induced hypoglycemia and treated with 10% dextrose or 50% dextrose. Neuronal injury, PARP-1, and brain-derived neurotrophic factor (BDNF) III/TrkB/p75(NTR) expressions were determined. In the second experiment, ketonemia was induced by administering β-hydroxybutyrate during hypoglycemia and its effect on neuronal injury was compared with those conventionally treated using 10% dextrose.

RESULTS

Both 10 and 50% dextrose administration led to hyperglycemia (50% dextrose > 10% dextrose). Compared with the 10% dextrose group, neuronal injury was greater in the 50% dextrose group and was accompanied by PARP-1 overactivation. BDNF III and p75(NTR), but not TrkBFL, mRNA expressions were upregulated. Neuronal injury was less severe in the rats subjected to ketonemia, compared with those conventionally treated using 10% dextrose.

CONCLUSION

Hyperglycemia accentuated hypoglycemia-induced neuronal injury, likely via PARP-1 overactivation. Although BDNF was upregulated, it was not neuroprotective and potentially exaggerated injury by binding to p75(NTR) receptor. Conversely, ketonemia during hypoglycemia attenuated neuronal injury.

A novel algorithm in the management of hypoglycemia in newborns

Study Objective. To evaluate the safety of a new protocol in comparison to the standard protocol for managing hypoglycemia in neonates. Methods. Open label RCT-pilot study. Neonates admitted to NICU with hypoglycemia and requiring intravenous fluids were included. Fifty-seven eligible neonates were randomly allocated to either intervention group (starting fluids with 10% dextrose and increments of 1.5%) or standard protocol group (GIR of 6 mg/kg/min with increments of 2 mg/kg/min) till control of hypoglycemia. Primary outcome of the study was to know proportion of infants with subsequent hypoglycemia and hyperglycemia after enrolment. Results. The initial GIR (6 ± 0 mg/kg/min versus 4.8 ± 1.4 mg/kg/min, P < 0.001), the mean maximum GIR (6.7 ± 1.6 mg/kg/min versus 5.6 ± 2 mg/kg/min, P = 0.03), the maximum concentration of glucose infused (13.8 ± 2.9% versus 10.9 ± 1.9%, P < 0.001), and the total amount of glucose infused were significantly lower in the intervention group. The mean maximum blood sugar was significantly higher (129 ± 57 mg/dL versus 87 ± 30 mg/dL, P = 0.001) and there was a trend towards high proportion of infants with Hyperglycemia in the standard protocol group (n = 10, 39% versus n = 5, 16%, P = 0.07). The median difference between the highest and the lowest recorded sugar for any infant was significantly higher in the standard protocol group (median 93 mg/dL, IQR 52 to 147 mg/dL versus median 50 mg/dL, IQR 38 to 62.5 mg/dL, P = 0.03). Conclusion. A new and novel algorithm in the management of hypoglycemia in neonates is as safe as the standard protocol and requires further testing before routine implementation.

Early antioxidant treatment and delayed hypothermia after hypoxia-ischemia have no additive neuroprotection in newborn pigs

BACKGROUND

The implementation and clinical efficacy of hypothermia in neonatal hypoxic-ischemic (HI) encephalopathy are limited, in part, by the delay in instituting hypothermia and access to equipment. In a piglet model of HI, half of the neurons in putamen already showed ischemic cytopathology by 6 hours of recovery. We tested the hypothesis that treatment with the superoxide dismutase-catalase mimetic EUK-134 at 30 minutes of recovery provides additive neuronal protection when combined with 1 day of whole-body hypothermia implemented 4 hours after resuscitation.

METHODS

Anesthetized piglets were subjected to 40 minutes of hypoxia (10% inspired oxygen) followed by 7 minutes of airway occlusion and resuscitation. Body temperature was maintained at 38.5°C in normothermic groups and at 34°C in hypothermic groups. All groups were mechanically ventilated, sedated, and received muscle relaxants during the first day of recovery. Neuropathology was assessed by profile and stereological cell-counting methods.

RESULTS

At 10 days of recovery, neuronal viability in putamen of a normothermic group treated with saline vehicle was reduced to 17% ± 6% (±95% confidence interval) of the value in a sham-operated control group (100% ± 15%). Intravenous infusion of EUK-134 (2.5 mg/kg at 30 minutes of recovery + 1.25 mg/kg/h until 4 hours of recovery) with normothermic recovery resulted in 40% ± 12% viable neurons in putamen. Treatment with saline vehicle followed by delayed hypothermia resulted in partial protection (46% ± 15%). Combining early EUK-134 treatment with delayed hypothermia also produced partial protection (47% ± 18%) that was not significantly greater than single treatment with EUK-134 (confidence interval of difference: -15% to 29%) or delayed hypothermia (-16% to 19%). Furthermore, no additive neuroprotection was detected in caudate nucleus or parasagittal neocortex, where neuronal loss was less severe.

CONCLUSIONS

We conclude that early treatment with this antioxidant does not substantially enhance the therapeutic benefit of delayed hypothermia in protecting highly vulnerable neurons in HI-insulted newborns, possibly because basal ganglia neurons are already undergoing irreversible cell death signaling by the time EUK-134 is administered or because this compound and hypothermia attenuate similar mechanisms of injury.

Programmed Necrosis: A Prominent Mechanism of Cell Death following Neonatal Brain Injury

Despite the introduction of therapeutic hypothermia, neonatal hypoxic ischemic (HI) brain injury remains a common cause of developmental disability. Development of rational adjuvant therapies to hypothermia requires understanding of the pathways of cell death and survival modulated by HI. The conceptualization of the apoptosis-necrosis “continuum” in neonatal brain injury predicts mechanistic interactions between cell death and hydrid forms of cell death such as programmed or regulated necrosis. Many of the components of the signaling pathway regulating programmed necrosis have been studied previously in models of neonatal HI. In some of these investigations, they participate as part of the apoptotic pathways demonstrating clear overlap of programmed death pathways. Receptor interacting protein (RIP)-1 is at the crossroads between types of cellular death and survival and RIP-1 kinase activity triggers formation of the necrosome (in complex with RIP-3) leading to programmed necrosis. Neuroprotection afforded by the blockade of RIP-1 kinase following neonatal HI suggests a role for programmed necrosis in the HI injury to the developing brain. Here, we briefly review the state of the knowledge about the mechanisms behind programmed necrosis in neonatal brain injury recognizing that a significant proportion of these data derive from experiments in cultured cell and some from in vivo adult animal models. There are still more questions than answers, yet the fascinating new perspectives provided by the understanding of programmed necrosis in the developing brain may lay the foundation for new therapies for neonatal HI.

Systemic effects of whole-body cooling to 35 °C, 33.5 °C, and 30 °C in a piglet model of perinatal asphyxia: implications for therapeutic hypothermia

INTRODUCTION

The precise temperature for optimal neuroprotection in infants with neonatal encephalopathy is unclear. Our aim was to assess systemic effects of whole-body cooling to 35 °C, 33.5 °C, and 30 °C in a piglet model of perinatal asphyxia.

METHODS

Twenty-eight anesthetized male piglets aged <24 h underwent hypoxia-ischemia (HI) and were randomized to normothermia or cooling to rectal temperature (Trec) 35 °C, 33.5 °C, or 30 °C during 2-26 h after insult (n = 7 in each group). HR, MABP, and Trec were recorded continuously.

RESULTS

Five animals cooled to 30 °C had fatal cardiac arrests. During 30 °C cooling, heart rate (HR) was lower vs. normothermia (P < 0.001). Although mean arterial blood pressure (MABP) did not vary between groups, more fluid boluses were needed at 30 °C than at normothermia (P < 0.02); dopamine use was higher at 30 °C than at normothermia or 35 °C (P = 0.005 and P = 0.02, respectively). Base deficit was increased at 30 °C at 12, 24, and 36 h vs. all other groups (P < 0.05), pH was acidotic at 36 h vs. normothermia (P = 0.04), and blood glucose was higher for the 30 °C group at 12 h vs. the normothermia and 35 °C groups (P < 0.05). Potassium was lower at 12 h in the 30 °C group vs. the 33.5 °C and 35 °C groups. There was no difference in cortisol level between groups.

DISCUSSION

Cooling to 30 °C led to metabolic derangement and more cardiac arrests and deaths than cooling to 33.5 °C or 35 °C. Inadvertent overcooling should be avoided.

Distribution of pH changes in mouse neonatal hypoxic-ischaemic insult

We assessed the distribution in brain pH after neonatal hypoxic-ischaemic insult and its correlation with local injury. Postnatal day 7 mice were injected with neutral red and underwent left carotid occlusion and exposure to 8% oxygen. Images captured from the cut surface of snap-frozen brain were used to calculate the pH from the blue-green absorbance ratios. Carotid occlusion alone had no effect, but combined with hypoxia caused rapid, biphasic pH decline, with the first plateau at 15-30 min, and the second at 60-90 min. The ipsilateral dorsal cortex, hippocampus, striatum and thalamus were most affected. Contralateral pH initially showed only 30% of the ipsilateral decline, becoming more acidotic with increasing duration. Systemic blood analysis revealed, compared with hypoxia alone, that combined insult caused a 63% decrease in blood glucose (1.3 ± 0.2 mM), a 2-fold increase in circulating lactate (17.7 ± 2.9 mM), a reduction in CO(2) to 1.9 ± 0.1 kPa and a drop in pH (7.26 ± 0.06). Re-oxygenation resulted in the normalisation of systemic changes, as well as a global alkaline rebound in brain pH at 4-6 h. A topographic comparison of brain injury showed only a partial correlation with pH changes, with the severest injury occurring in the ipsilateral hippocampus and sparing acidic parts of the contralateral cortex.

Excitatory action of GABA on immature neurons is not due to absence of ketone bodies metabolites or other energy substrates

Brain slices incubated with glucose have provided most of our knowledge on cellular, synaptic, and network driven mechanisms. It has been recently suggested that γ-aminobutyric acid (GABA) excites neonatal neurons in conventional glucose-perfused slices but not when ketone bodies metabolites, pyruvate, and/or lactate are added, suggesting that the excitatory actions of GABA are due to energy deprivation when glucose is the sole energy source. In this article, we review the vast number of studies that show that slices are not energy deprived in glucose-containing medium, and that addition of other energy substrates at physiologic concentrations does not alter the excitatory actions of GABA on neonatal neurons. In contrast, lactate, like other weak acids, can produce an intracellular acidification that will cause a reduction of intracellular chloride and a shift of GABA actions. The effects of high concentrations of lactate, and particularly of pyruvate (4-5 mm), as used are relevant primarily to pathologic conditions; these concentrations not being found in the brain in normal "control" conditions. Slices in glucose-containing medium may not be ideal, but additional energy substrates neither correspond to physiologic conditions nor alter GABA actions. In keeping with extensive observations in a wide range of animal species and brain structures, GABA depolarizes immature neurons and the reduction of the intracellular concentration of chloride ([Cl(-)](i)) is a basic property of brain maturation that has been preserved throughout evolution. In addition, this developmental sequence has important clinical implications, notably concerning the higher incidence of seizures early in life and their long-lasting deleterious sequels. Immature neurons have difficulties exporting chloride that accumulates during seizures, leading to permanent increase of [Cl(-)](i) that converts the inhibitory actions of GABA to excitatory and hampers the efficacy of GABA-acting antiepileptic drugs.

Overweight worsens apoptosis, neuroinflammation and blood-brain barrier damage after hypoxic ischemia in neonatal brain through JNK hyperactivation

BACKGROUND

Apoptosis, neuroinflammation and blood-brain barrier (BBB) damage affect the susceptibility of the developing brain to hypoxic-ischemic (HI) insults. c-Jun N-terminal kinase (JNK) is an important mediator of insulin resistance in obesity. We hypothesized that neonatal overweight aggravates HI brain damage through JNK hyperactivation-mediated upregulation of neuronal apoptosis, neuroinflammation and BBB leakage in rat pups.

METHODS

Overweight (OF) pups were established by reducing the litter size to 6, and control (NF) pups by keeping the litter size at 12 from postnatal (P) day 1 before HI on P7. Immunohistochemistry and immunoblotting were used to determine the TUNEL-(+) cells and BBB damage, cleaved caspase-3 and poly (ADP-ribose) polymerase (PARP), and phospho-JNK and phospho-BimEL levels. Immunofluorescence was performed to determine the cellular distribution of phospho-JNK.

RESULTS

Compared with NF pups, OF pups had a significantly heavier body-weight and greater fat deposition on P7. Compared with the NF-HI group, the OF-HI group showed significant increases of TUNEL-(+) cells, cleaved levels of caspase-3 and PARP, and ED1-(+) activated microglia and BBB damage in the cortex 24 hours post-HI. Immunofluorescence of the OF-HI pups showed that activated-caspase 3 expression was found mainly in NeuN-(+) neurons and RECA1-(+) vascular endothelial cells 24 hours post-HI. The OF-HI group also had prolonged escape latency in the Morris water maze test and greater brain-volume loss compared with the NF-HI group when assessed at adulthood. Phospho-JNK and phospho-BimEL levels were higher in OF-HI pups than in NF-HI pups immediately post-HI. JNK activation in OF-HI pups was mainly expressed in neurons, microglia and vascular endothelial cells. Inhibiting JNK activity by AS601245 caused more attenuation of cleaved caspase-3 and PARP, a greater reduction of microglial activation and BBB damage post-HI, and significantly reduced brain damage in OF-HI than in NF-HI pups.

CONCLUSIONS

Neonatal overweight increased HI-induced neuronal apoptosis, microglial activation and BBB damage, and aggravated HI brain damage in rat pups through JNK hyperactivation.

Neonatal fluid management

Perioperative fluid management in paediatrics has been the subject of many controversies in recent years, but fluid management in the neonatal period has not been considered in most reviews and guidelines. The literature regarding neonatal fluid management mainly appears in the paediatric textbooks and few recent data are available, except for resuscitation and fluid loading during shock and major surgery. In the context of anaesthesia, many neonates requiring surgery within the first month of life have organ malformation and/or dysfunction. This article aims at reviewing basic physiological considerations important for neonatal fluid management and mainly focusses on fluid maintenance and replacement during surgery.

Treatment of the term newborn with brain injury: simplicity as the mother of invention

Neonatal brain injury remains a common cause of developmental disability, despite tremendously enhanced obstetrical and neonatal care. The timing of brain injury occurs throughout gestation, labor, and delivery, providing an evolving form of brain injury and a moving target for therapeutic intervention. Nonetheless, markedly improved methods are available to identify those infants injured at birth, via clinical presentation with neonatal encephalopathy and neuroimaging techniques. Postischemic hypothermia has been shown to be of tremendous clinical promise in several completed and ongoing trials. As part of this approach to the treatment of the newborn, other parameters of physiologic homeostasis can and should be attended to, with strong animal and clinical evidence that their correction will have dramatic influence on the outcome of the newborn infant. This review addresses aspects of newborn care to which we can direct our attention currently, and which should result in a safe and efficacious improvement in the prognosis of the newborn with neonatal encephalopathy.

Association between intraoperative and early postoperative glucose levels and adverse outcomes after complex congenital heart surgery

BACKGROUND

This study sought to determine whether associations exist between perioperative glucose exposure, prolonged hospitalization, and morbid events after complex congenital heart surgery.

METHODS AND RESULTS

Metrics of glucose control, including average, peak, minimum, and SD of glucose levels, and duration of hyperglycemia were determined intraoperatively and for 72 hours after surgery for 378 consecutive high-risk cardiac surgical patients. Multivariable regression analyses were used to determine relationships between these metrics of glucose control, hospital length of stay, and a composite morbidity-mortality outcome after controlling for multiple variables known to influence early outcomes after congenital heart surgery. Intraoperatively, a minimum glucose <or=75 mg/dL was associated with greater adjusted odds of reaching the composite morbidity-mortality end point (odds ratio [OR], 3.10; 95% confidence interval [CI], 1.49 to 6.48), but other metrics of glucose control were not associated with the composite end point or length of stay. Greater duration of hyperglycemia (glucose >126 mg/dL) during the 72 postoperative hours was associated with longer duration of hospitalization (P<0.001). In the 72 hours after surgery, average glucose <110 mg/dL (OR, 7.30; 95% CI, 1.95 to 27.25) or >143 mg/dL (OR, 5.21; 95% CI, 1.37 to 19.89), minimum glucose <or=75 mg/dL (OR, 2.85; 95% CI, 1.38 to 5.88), and peak glucose level >or=250 mg/dL (OR, 2.55; 95% CI, 1.20 to 5.43) were all associated with greater adjusted odds of reaching the composite morbidity-mortality end point.

CONCLUSIONS

In children undergoing complex congenital heart surgery, the optimal postoperative glucose range may be 110 to 126 mg/dL. Randomized trials of strict glycemic control achieved with insulin infusions in this patient population are warranted.

Bioenergetics of cerebral ischemia: a cellular perspective

In cerebral ischemia survival of neurons, astrocytes, oligodendrocytes and endothelial cells is threatened during energy deprivation and/or following re-supply of oxygen and glucose. After a brief summary of characteristics of different cells types, emphasizing the dependence of all on oxidative metabolism, the bioenergetics of focal and global ischemia is discussed, distinguishing between events during energy deprivation and subsequent recovery attempt after re-circulation. Gray and white matter ischemia are described separately, and distinctions are made between mature and immature brains. Next comes a description of bioenergetics in individual cell types in culture during oxygen/glucose deprivation or exposure to metabolic inhibitors and following re-establishment of normal aerated conditions. Due to their expression of NMDA and non-NMDA receptors neurons and oligodendrocytes are exquisitely sensitive to excitotoxicity by glutamate, which reaches high extracellular concentrations in ischemic brain for several reasons, including failing astrocytic uptake. Excitotoxicity kills brain cells by energetic exhaustion (due to Na(+) extrusion after channel-mediated entry) combined with mitochondrial Ca(2+)-mediated injury and formation of reactive oxygen species. Many (but not all) astrocytes survive energy deprivation for extended periods, but after return to aerated conditions they are vulnerable to mitochondrial damage by cytoplasmic/mitochondrial Ca(2+) overload and to NAD(+) deficiency. Ca(2+) overload is established by reversal of Na(+)/Ca(2+) exchangers following Na(+) accumulation during Na(+)-K(+)-Cl(-) cotransporter stimulation or pH regulation, compensating for excessive acid production. NAD(+) deficiency inhibits glycolysis and eventually oxidative metabolism, secondary to poly(ADP-ribose)polymerase (PARP) activity following DNA damage. Hyperglycemia can be beneficial for neurons but increases astrocytic death due to enhanced acidosis.

Neuroprotection during cardiac surgery

Cardiac surgery continues to be associated with significant adverse cerebral outcomes, ranging from stroke to cognitive decline. The underlying mechanism of the associated cerebral injury is incompletely understood but is believed to be primarily caused by cerebral embolism and hypoperfusion, exacerbated by ischemia/reperfusion injury. Extensive research has been undertaken in an attempt to minimize the incidence of perioperative cerebral injury, and both pharmacological and nonpharmacological strategies have been investigated. Although many agents demonstrated promise in preclinical studies, there is currently insufficient evidence from clinical trials to recommend the routine administration of any pharmacological agents for neuroprotection during cardiac surgery. The nonpharmacological strategies that can be recommended on the basis of evidence include transesophageal echocardiography and epiaortic ultrasound-guided assessment of the atheromatous ascending aorta with appropriate modification of cannulation, clamping or anastomotic technique and optimal temperature management. Large-scale randomized controlled trials are still required to address further the issues of optimal pH management, glycemic control, blood pressure management and hematocrit during cardiopulmonary bypass. Past, present and future directions in the field of neuroprotection in cardiac surgery will be discussed.

The effects of hyperglycemia on ischemic cell change and reactive neuronal change in neonatal rat brain following transient forebrain ischemia

To examine the effects of hyperglycemia on a transient ischemia in the neonatal brain, neuropathological and biochemical evaluations were performed. In 10-day-old rats, brain ischemia was induced by permanent occlusion of the right external and internal carotid and subclavian arteries and the clamping of the left external and internal carotid arteries for 2h. The peritoneal injection of a 50% glucose solution (0.10 ml/15 g weight) 5 min before the induction of brain ischemia increased the plasma glucose concentration to 20-25 mmol/l during ischemia. It preserved brain tissue glucose levels at 1h of ischemia in the glucose-treated group, while tissue glucose was exhausted in the saline-injected group. Tissue lactate concentrations increased slightly at the end of the ischemic insult (6.7 mmol/kg) in the saline-injected group and remarkably (18.7 mmol/kg) in the glucose-treated group. Two distinct forms of ischemic neuronal change were found in this study: ischemic cell change and reactive neuronal change. A quantitative neuropathological assessment indicated that hyperglycemia significantly reduced the volume of ischemic cell change in the neocortex from 85% to 33%, but not that of reactive neuronal change (from 5.5% to 2.4%). These results indicated that hyperglycemia attenuated ischemic cell change, but not reactive neuronal change, in the neonatal rat brain and suggested that it reduced ischemic cell change probably because of reserved brain glucose.

Neuroprotection during cardiac surgery

Cerebral injury following cardiac surgery continues to be a significant source of morbidity and mortality after cardiac surgery. A spectrum of injuries ranging from subtle neurocognitive dysfunction to fatal strokes are caused by a complex series of multifactorial mechanisms. Protecting the brain from these injuries has focused on intervening on each of the various etiologic factors. Although numerous studies have focused on a pharmacologic solution, more success has been found with nonpharmacologic strategies, including optimal temperature management and reducing emboli generation.

Sustained neocortical neurogenesis after neonatal hypoxic/ischemic injury

OBJECTIVE

Neocortical neurons are sensitive to hypoxic-ischemic (H-I) injuries at term and their demise contributes to neurological disorders. Here we tested the hypothesis that the subventricular zone of the immature brain regenerates neocortical neurons, and that this response is sustained.

METHODS

Systemic injections of 5-bromo-2'-deoxyuridine (BrdU) and intraventricular injections of replication-deficient retroviruses were used to label newly born cells, and confocal microscopy after immunofluorescence was used to phenotype the new cells from several days to several months after perinatal H-I in the postnatal day 6 rat. Quantitative polymerase chain reaction was used to evaluate chemoattractants, growth factors, and receptors.

RESULTS

Robust production of new neocortical neurons after perinatal H-I occurs. These new neurons are descendants of the subventricular zone, and they colonize the cell-sparse columns produced by the injury to the neocortex. These columns are populated by reactive astrocytes and microglia. Surprisingly, this neuronogenesis is sustained for months. Molecular analyses demonstrated increased neocortical production of insulin-like growth factor-1 and monocyte chemoattractant factor-1 (but statistically insignificant production of erythropoietin, brain-derived neurotrophic factor, glial-derived neurotrophic factor, and transforming growth factor-alpha).

INTERPRETATION

The young nervous system has long been known to possess a greater capacity to recover from injury than the adult system. Our data indicate that H-I injury in the neonatal brain initiates an enduring regenerative response from the subventricular zone. These data suggest that additional mechanisms than those previously surmised contribute to the remarkable ability of the immature brain to recover from injury.

Glucose management during and after intensive delivery room resuscitation

Hypoxic-ischemic encephalopathy remains a major cause of morbidity and mortality in preterm and full-term infants. Experimental data from animal studies suggest that interventions that improve survival of injured neurons and prevent delayed neuronal loss may decrease hypoxic ischemic brain injury. Considerable attention has focused on optimizing management of newborns in the period immediately after resuscitation from perinatal asphyxia to minimize delayed neuronal death. The evidence regarding the role of glucose in modifying post-asphyxia brain injury and resuscitation was reviewed to better define optimal glucose management after perinatal asphyxia and resuscitation.

The role of glucose in brain injury following the combination of lipopolysaccharide or lipoteichoic acid and hypoxia-ischemia in neonatal rats

We have previously shown that lipopolysaccharide (LPS) sensitizes the immature rat brain to subsequent hypoxic-ischemic (HI) injury; however, the underlying mechanisms remain unclear. In this study, we examined the role of glucose in the sensitizing effects of LPS and lipoteichoic acid (LTA) in combination with HI in 7-day-old rats. LPS/HI resulted in hypoglycemia which lasted 24 h and lactate levels were increased from 6 to 10 h after LPS administration. LPS/HI induced severe brain injury, which persisted 2 weeks after LPS/HI. Administration of glucose to LPS-treated animals with HI reduced brain injury in the cerebral cortex and hippocampus, while striatal damage remained. LTA/HI did not affect blood glucose, lactate or brain injury. In conclusion, enhanced blood glucose levels during HI after LPS administration conferred protection in some brain regions but not in the striatum, suggesting that alterations in glucose can only partly explain the sensitizing effect of LPS.

Energy metabolism in mammalian brain during development

Production of energy for the maintenance of ionic disequilibria necessary for generation and transmission of nerve impulses is one of the primary functions of the brain. This review attempts to link the plethora of information on the maturation of the central nervous system with the ontogeny of ATP metabolism, placing special emphasis on variations that occur during development in different brain regions and across the mammalian species. It correlates morphological events and markers with biochemical changes in activities of enzymes and pathways that participate in the production of ATP. The paper also evaluates alterations in energy levels as a function of age and, based on the tenet that ATP synthesis and utilization cannot be considered in isolation, investigates maturational profiles of the key processes that utilize energy. Finally, an attempt is made to assess the relevance of currently available animal models to improvement of our understanding of the etiopathology of various disease states in the human infant. This is deemed essential for the development and testing of novel strategies for prevention and treatment of several severe neurological deficits.

Effects of exogenous glucose on brain ischemia in ovine fetuses

We examined the effects of prolonged moderate hyperglycemia with and without an additional rapid glucose injection on ischemic brain injury in the fetus. Twenty-five ewes (117-124 d of gestation) were assigned to one of four groups: 1) glucose-infused fetuses exposed to 30 min of carotid artery occlusion followed by 48 h of reperfusion (I/R-Glu, n = 8); 2) glucose-infused plus rapid glucose injection given 100 min before 30 min of occlusion followed by 48 h of reperfusion (I/R-GluR, n = 4); 3) placebo-infused exposed to 30 min of occlusion and 48 h of reperfusion (I/R-PL, n = 8); and 4) glucose-infused sham occlusion and 48 h of sham reperfusion (control, n = 5). After baseline measurements, fetuses were infused with glucose (9-16 mg/kg/min) for 48 h before and after carotid occlusion or sham treatment. The I/R-PL group received 0.9% NaCl. Brain pathologic outcome was determined. Serial sections stained with Luxol fast blue-hematoxylin and eosin were scored for white matter, cerebral cortical, and hippocampal lesions. These areas received graded pathologic scores of 0 to 5, reflecting the amount of injury, where 0 = 0%, 1 = 1-25%, 2 = 26-50%, 3 = 51-75%, 4 = 76-95%, and 5 = 96-100% of the area damaged. Comparisons of the pathologic scores for cerebral cortex (CC), white matter (WM), and hippocampus (H) demonstrated that the I/R-GluR (CC: 4.56 +/- 0.11, WM: 4.50 +/- 0.11, H: 3.44 +/- 0.48, mean +/- SEM) had more (p < 0.05) damage than the I/R-Glu (CC: 2.46 +/- 0.47, WM: 1.97 +/- 0.37, H: 1.81 +/- 0.36) and control (CC: 1.12 +/- 0.13, WM: 0.82 +/- 0.34, H: 0.80 +/- 0.34) groups. The pathologic scores in the I/R-Glu were (p < 0.05) greater than the control, but not the I/R-PL (CC: 2.12 +/- 0.35, WM: 2.20 +/- 0.44, H: 1.59 +/- 0.41) group. We conclude that exposure to prolonged moderate hyperglycemia before ischemia and during reperfusion does not affect the extent of brain injury, but exposure to an additional acute increase in plasma glucose concentration before ischemia is extremely detrimental to the fetal brain.

Molecular features, regulation, and function of monocarboxylate transporters: implications for drug delivery

The diffusion of monocarboxylates such as lactate and pyruvate across the plasma membrane of mammalian cells is facilitated by a family of integral membrane transport proteins, the monocarboxylate transporters (MCTs). Currently, at least eight unique members of the MCT family have been discovered and orthologs to each have been identified in a variety of species. Four MCTs (MCT1-MCT4) have been functionally characterized. Each isoform possesses unique biochemical properties such as kinetic constants and sensitivity to known MCT inhibitors. Several fold changes in the expression of MCTs may be evoked by altered physiological conditions, yet the molecular mechanisms underlying the regulation of MCTs are poorly understood. Post-translational regulation of MCT1 and MCT4 occurs, in part, by interaction with CD147, an accessory protein that is necessary for trafficking, localization, and functional expression of these transporters. Because of the physiological importance of monocarboxylates to the overall maintenance of metabolic homeostasis, the function of MCTs is significant to several pathologies that occur with disease, such as ischemic stroke and cancer. Finally, the expression of MCT1 in the epithelium of the small intestine and colon and in the blood-brain barrier may provide routes for the intestinal and blood to brain transfer of carboxylated pharmaceutical agents and other exogenous monocarboxylates.

Cerebral injury in association with profound iatrogenic hyperglycemia in a neonate

The adverse effect of hyperglycemia on neurological outcome following cerebral ischemia has been established in both experimental and adult human studies. However, there is a paucity of data to assess this risk in the human infant. This case is the first to describe severe and prolonged iatrogenic hyperglycemia in association with ischemia in an infant who sustained a major cerebral lesion. The topography of the predominant cerebral injury, i.e., bilateral parieto-occipital cortex and subcortical white matter, shown by magnetic resonance imaging was similar to that documented in the hypoglycemic infant, suggesting a similarity in regional cerebral vulnerability to altered glucose metabolism. This case extends recognition of the risk of severe hyperglycemia in association with cerebral ischemia to the newborn and suggests also that the posterior cerebral predilection for injury is similar in both hypoglycemia and hyperglycemia.

Energy metabolism, stress hormones and neural recovery from cerebral ischemia/hypoxia

All the advancements in the understanding of the molecular and cellular processes leading to the great investments in developing neuroprotection against cerebral ischemic/hypoxic damage cannot obscure the simple fact that exhaustion of energy supplies is still at the basis of this disorder. Much has been investigated and postulated over the years about the quick collapse of energy metabolism that follows oxygen and glucose deprivation in the brain. Anaerobic glycolysis, recognized as a pathway of paramount importance in keeping energy supplies, although, at bare minimum, has also presented a dilemma-a significant increase in lactate production during ischemia/hypoxia (IH). The dogma of lactate as a useless end product of anaerobic glycolysis and its postulated role as a detrimental player in the demise of the ischemic cell has persisted for the past quarter of a century. This persistence is due to, at least in part, the well-documented phenomenon termed "the glucose paradox of cerebral ischemia," the unexplained aggravation of postischemic neuronal damage by preischemic hyperglycemia. Recent studies have questioned the deleterious effect of lactic acid, while others even have offered the possibility that this monocarboxylate serves as an aerobic energy substrate during recovery from IH. Reviewed here are studies published over the past few years along with some key older papers on the topic of energy metabolism and recovery of neural tissue from IH. New insights gained from both in vitro and in vivo studies on energy metabolism of the ischemic/hypoxic brain should improve our understanding of this key metabolic process and the chances of protecting this organ from the consequences of energy deprivation.

Protective effect of high glucose against ischemia-induced synaptic transmission damage in rat hippocampal slices

Cerebral ischemic damage is an important cause of morbidity and mortality. However, there is conflicting evidence regarding the effect of the extracellular glucose concentration in focal and global ischemic injury. This study was designed to investigate this effect in ischemia-induced synaptic transmission damage in rat hippocampal slices. Slices were superfused with artificial cerebrospinal fluid (ACSF) containing various concentrations of glucose before and after ischemia. The evoked somatic postsynaptic population spike (PS) and dendritic field excitatory postsynaptic potential (fEPSP) were extracellularly recorded in the CA1 stratum pyramidal cell layer and s. radiatum after stimulation of the Schaeffer collaterals, respectively. The glucose concentration in ACSF before and after ischemia determined the duration of ischemia tolerated by synaptic transmission as demonstrated by complete recovery of the somatic PS and dendritic fEPSP. Specifically, the somatic PS and dendritic fEPSP completely recovered following 3, 4, and 5 min of ischemia only when slices were superfused with ACSF containing 4, 10, and 20 mM glucose before and after ischemia, respectively. The latencies of the somatic and dendritic ischemic depolarization (ID) occurrence in the CA1 s. pyramidal cell layer and s. radiatum were significantly longer with 10 than 4 mM glucose in ACSF before ischemia and significantly longer with 20 than 10 mM glucose in ACSF before ischemia. Regardless of the glucose concentration in ACSF before and after ischemia, the somatic PS and dendritic fEPSP only partially recovered when ischemia was terminated at the occurrence of ID. These results indicate that high glucose in ACSF during the period before and after ischemia significantly protects CA1 synaptic transmission against in vitro ischemia-induced damage through postponing the occurrence of ID.

Angiogenic and astroglial responses to vascular endothelial growth factor administration in adult rat brain

The effects of exogenous vascular endothelial growth factor (VEGF) on angiogenesis, blood-brain barrier permeability and astroglial proliferation in the adult rat CNS in situ were investigated. Recombinant human VEGF(165) (25 or 50 ng/ml) was delivered for up to 1 week using either intracerebral osmotic minipumps or less traumatic subdural gelatin sponge placement. By 3 days, VEGF delivery caused significantly increased cerebral angiogenesis (25 ng/ml was most effective) in both experimental models when compared to saline controls; VEGF infusion resulted in a 100% increase in an index of vascular proliferation, and gelatin sponge delivery produced a 65% increase. The blood-brain barrier hallmark endothelial glucose transporter-1 was not present in nascent vascular sprouts. Infusion of VEGF produced extensive protein leakage that persisted after saline-induced permeability was mostly resolved, while gelatin sponge administration caused milder barrier dysfunction. Administration of the angiogenic factor had unexpected proliferative effects on astroglia in both models, resulting in an 80-85% increase in mitotically active astroglia when compared to controls. Immunohistochemical results and semi-quantitative reverse transcriptase-polymerase chain reaction indicated that the VEGF receptors flk-1 and flt-1 were up-regulated in response to the infusion trauma; flt-1 was localized to reactive astroglia, while flk-1 was expressed in vascular endothelium but predominantly in neuronal somata and processes adjacent to the delivery site. mRNA for the VEGF(121), VEGF(165) and VEGF(188) isoforms was also increased after delivery of the recombinant protein. These data show that VEGF application has substantial proliferative effects on CNS endothelium and astroglia and causes up-regulation of its own message. Flt-1 and flk-1 receptor mRNAs and proteins are up-regulated in both vascular and non-vascular cell types following infusion trauma. From these results we suggest that administered VEGF has heretofore unanticipated pleiotrophic effects in the adult CNS.

Carbohydrate source influences gelatinase production by mouse astrocytes in vitro

Molecular mediators of ischemic brain injury include intercellular adhesion molecule-1 (ICAM-1) and matrix metalloproteinase-9 (MMP-9), involved in the alteration of blood-brain barrier permeability and induced in astroglial cultures by tumor necrosis factor-alpha (TNF-alpha). Hyperglycemia is known to aggravate in vivo ischemic brain damage, while treatment with sorbitol shows benefit in reducing vasogenic brain edema. This study investigated whether a culture medium carbohydrate source could alter the astrocyte production of MMP-9 and ICAM-1 in vitro. The growth of astrocytes in 12.5 mM glucose, 25 mM glucose, or 25 mM sorbitol for 14 days did not alter cellular release of lactate dehydrogenase, uptake of Trypan blue, or surface expression of glial fibrillary acidic protein (GFAP). ICAM-1 levels were similar in astrocytes grown in glucose or sorbitol both under basal conditions and after TNF-alpha stimulation for 48 h. In contrast, levels of proMMP-9 released from astrocytes cultured for 14 days in 25 mM sorbitol reached only 55-28% of those obtained from cultures in 25 mM glucose after stimulation with 1,000 U/ml (P = 0.05) or 5,000 U/ml (P < 0.025) TNF-alpha, respectively. Limiting the duration of pre-stimulation sorbitol exposure to 48 h resulted in lower proMMP-9 levels than in glucose cultures after 5,000, but not 1,000, U/ml TNF-alpha, and differences were not significant when sorbitol exposure was further reduced to 24 h. Incubation in mixed glucose/sorbitol media did not affect the release of proMMP-9. These findings suggest that MMP-9 production may be increased in astrocytes as a consequence of glucose metabolism, which can be avoided by growth in sorbitol alone.

Bench-to-bedside review: a possible resolution of the glucose paradox of cerebral ischemia

The glucose paradox of cerebral ischemia (namely, the aggravation of delayed ischemic neuronal damage by preischemic hyperglycemia) has been promoted as proof that lactic acidosis is a detrimental factor in this brain disorder. Recent studies, both in vitro and in vivo, have demonstrated lactate as an excellent aerobic energy substrate in the brain, and possibly a crucial one immediately postischemia. Moreover, evidence has been presented that refutes the lactic acidosis hypothesis of cerebral ischemia and thus has questioned the traditional explanation given for the glucose paradox. An alternative explanation for the aggravating effect of preischemic hyperglycemia on the postischemic outcome has consequently been offered, according to which glucose loading induces a short-lived elevation in the release of glucocorticoids. When an episode of cerebral ischemia in the rat coincided with glucose-induced elevated levels of corticosterone (CT), the main rodent glucocorticoid, an aggravation of the ischemic outcome was observed. Both the blockade of CT elevation by chemical adrenalectomy with metyrapone or the blockade of CT receptors in the brain with mifepristone (RU486) negated the aggravating effect of preischemic hyperglycemia on the postischemic outcome.

The role of cerebral microdialysis in predicting the outcome after experimental hypothermic circulatory arrest

OBJECTIVE

To evaluate whether and which of the cerebral microdialysis parameters are predictive of postoperative outcome after an experimental 75-min period of hypothermic circulatory arrest (HCA) in a chronic porcine model.

DESIGN

Seventy-four juvenile female pigs underwent a 75-min period of HCA at 20 degrees C. A microdialysis catheter was placed into the cortex gray matter and brain extracellular concentrations of glucose, lactate, glycerol and glutamate were measured throughout the experiment by enzymatic methods using a microdialysis analyzer. Surviving animals were sacrificed on the 7th postoperative day and histopathological examination of the brain was performed.

RESULTS

Brain glucose concentrations were higher in animals that survived (p = 0.017), especially from the 90-min until the 7-h interval after the start of rewarming. The blood venous concentrations of glucose were also higher among survivors, and correlated significantly with the brain glucose levels at 2-h and 4-h intervals after the start of rewarming. Higher concentrations of brain lactate, glycerol and glutamate were observed throughout the study among animals that died postoperatively. Brain glutamate and glycerol concentrations were significantly, negatively correlated with brain glucose concentrations. The lactate/glucose ratio was significantly lower among survivors during the postoperative period (p=0.014). Furthermore, brain glucose concentrations were higher and brain glycerol concentrations lower among the animals that did not develop brain infarction, but such differences did not reach statistical significance.

CONCLUSION

Cerebral microdialysis is a useful tool for cerebral monitoring during experimental HCA. Low brain glucose concentrations and high brain lactate/glucose ratios after HCA are strong predictors of postoperative death. Brain glucose concentrations are negatively correlated with brain glycerol and glutamate concentrations.

Preischemic hyperglycemia-aggravated damage: evidence that lactate utilization is beneficial and glucose-induced corticosterone release is detrimental

Aerobic lactate utilization is crucial for recovery of neuronal function posthypoxia in vitro. In vivo models of cerebral ischemia pose a conceptual challenge when compared to in vitro models. First, the glucose paradox of cerebral ischemia, namely, the aggravation of delayed neuronal damage by preischemic hyperglycemia, cannot be reproduced in vitro. Second, in vitro elevated glucose levels protect against ischemic (hypoxic) damage, an outcome that has seldom been reproduced in vivo. Employing a rat model of cardiac-arrest-induced transient global cerebral ischemia (TGI), we found that hyperglycemic conditions, when induced 120-240 min pre-TGI, significantly reduced post-TGI neuronal damage as compared to normoglycemic conditions. In contrast, hyperglycemia, when induced 15-60 min pre-TGI, significantly aggravated post-TGI neuronal damage. Brain lactate levels in rats loaded with glucose either 15 min or 120 min pre-TGI were significantly and equally higher than those of control, saline-injected rats. The beneficial effect of 120 min pre-TGI glucose loading was abolished by lactate transport inhibition. A significant increase in blood corticosterone (CT) levels was observed upon glucose loading that peaked at 15-30 min and returned to baseline levels by 60-120 min. When rats loaded with glucose 15 min pre-TGI were treated with metyrapone, a CT synthesis inhibitor, a significantly lower degree of delayed neuronal damage in comparison to both untreated, 15 min glucose-loaded rats and normoglycemic, control rats was observed. Thus, although elevated levels of brain lactate cannot explain the glucose paradox of cerebral ischemia, hyperglycemia-induced, short-lived elevation in CT blood levels could. More importantly, lactate appears to play a crucial role in improving postischemic outcome.

Glucose and the ischemic brain: a sour grape or a sweet treat?

The lactic acidosis hypothesis of cerebral ischemia has relied on a single finding to support its main postulate: pre-ischemic hyperglycemia-aggravated ischemic brain damage. Although this finding is by no means the proof that the lactic acidosis hypothesis desperately needs, the premise of the hypothesis has been employed in hospitals around the world. A better understanding of some of the processes involved in elevating blood glucose levels pre-ischemia and their influence on the ischemic brain is now available. This understanding offers a unique opportunity to re-examine old dogmas and propose new ideas, in the form of an alternative hypothesis to explain 'the glucose paradox of cerebral ischemia'.

Effect of extreme hypercapnia on hypoxic-ischemic brain damage in the immature rat

To ascertain the effect of extreme hypercapnia on perinatal hypoxic-ischemic brain damage, 7-d-postnatal rats were exposed to unilateral common carotid artery occlusion followed by hypoxia with 8% oxygen combined with 3, 12, or 15% carbon dioxide (CO2) for 2 h at 37 degrees C. Survivors underwent neuropathologic examination at 30 d of postnatal age, and their brains were characterized as follows: 0 = normal; 1 = mild atrophy; 2 = moderate atrophy; 3 = cystic infarct with external dimensions <3 mm; and 4 = cystic infarct with external dimensions >3 mm. The width of the cerebral hemisphere ipsilateral to the carotid artery occlusion also was determined on a posterior coronal section and compared with that of the contralateral hemisphere to ascertain the severity of cerebral atrophy/cavitation. CO2 tensions averaged 5.08, 11.1, and 13.2 kPa in the 3, 12, and 15% CO2-exposed animals, respectively, during hypoxia-ischemia (HI). Neuropathologic results showed that immature rats exposed to 3 and 12% CO2 had similar severities of brain damage. In contrast, rat pups exposed to HI combined with 15% CO2 were significantly more brain damaged than littermates exposed to 3% CO2. Specifically, eight of 14 animals exposed to 15% CO2 showed cystic infarcts (grades 3 and 4), whereas none of 14 littermates exposed to 3% CO2 developed cystic infarcts (p < 0.01). Analyses of coronal width ratios at each CO2 exposure provided results comparable with those of the gross neuropathology scores. Cerebral blood flow (CBF), measured at 90 min of HI, was lowest in those immature rats exposed to 15% CO2 compared with control (p = 0.04), with higher values in those rat pups exposed to 3 and 12% CO2. The findings indicate that 7-d-postnatal rats exposed to HI with superimposed 12% CO2 are neither less nor more brain damaged than littermates exposed to 3% CO(2) (normocapnia). In contrast, animals exposed to 15% CO2 are the most brain damaged of the three groups. Presumably, extreme hypercapnia produces more severe cardiovascular depression than is seen in animals subjected to lesser degrees of hypercapnia; the cardiovascular depression, in turn, leads to greater cerebral ischemia and ultimate brain damage.

Intracellular calcium accumulation during the evolution of hypoxic-ischemic brain damage in the immature rat

An excessive intracellular accumulation of calcium (Ca2+) in neurons and glia has been proposed to represent a major 'final common pathway' for cell death arising from hypoxia-ischemia. To clarify the role of altered calcium flux into the perinatal brain undergoing hypoxic-ischemic damage, 7-day postnatal rats underwent unilateral common carotid artery ligation followed by systemic hypoxia with 8% oxygen. This insult is known to produce brain damage in the form of selective neuronal death or infarction largely limited to the cerebral hemisphere ipsilateral to the arterial occlusion. Either prior to or following hypoxia-ischemia, the rat pups received a s.c. injection of 45CaCl2, and specimens of blood, cerebrospinal fluid (CSF), and brain were obtained for isotopic measurements and the calculation of the extent of brain intracellular radioactivity. During hypoxia-ischemia, there was a modest increase in intracellular Ca2+ radioactivity (+28-47%) in both cerebral hemispheres only after 2 h of hypoxia-ischemia. During recovery from 2 h of hypoxia-ischemia, intracellular Ca2+ accumulated progressively only in the ipsilateral cerebral hemisphere for up to 24 h, during which interval intracellular Ca2+ decreased in the contralateral hemisphere. No such progressive accumulation was noted during recovery in animals previously exposed to only 1 h of hypoxia-ischemia. The results suggest that a disruption of intracellular Ca2+ homeostasis is a major contributing factor in the evolution of perinatal hypoxic-ischemic brain damage. Ca2+ accumulation is a relatively modest and late event during the hypoxic-ischemic phase, and a progressive overload occurs during the recovery phase only if infarction occurs. The question remains as to whether or not the intracellular Ca2+ overload occurring during recovery is a contributor to or a consequence of the ultimate brain damage.

Experimental stroke in the female diabetic, db/db, mouse

Diabetic hyperglycemia increases brain damage after cerebral ischemia in animals and humans, although the underlying mechanisms remain unclear. Gender-linked differences in ischemic tolerance have been described but have not been studied in the context of diabetes. In the current study, we used a model of unilateral common carotid artery ligation, combined with systemic hypoxia, to study the effects of diabetes and gender on hypoxic-ischemic (HI) brain damage in the genetic model of Type II diabetes, the db/db, mouse. Male and female, control and db/db, mice were subjected to right common carotid artery ligation followed by varying periods of hypoxia (8% oxygen/92% nitrogen) to assess mortality, infarct volume, and tissue damage by light microscopic techniques. End-ischemic regional cerebral blood flow (CBF) was determined using [14C] iodoantipyrine autoradiography. Glycolytic and high energy phosphate compounds were measured in blood and brain by enzymatic and fluorometric techniques. Gender and diabetes had significant effects on mortality from HI and extent of brain damage in the survivors. Female mice were more resistant than their male counterparts, such that the severity (mortality and infarction size) in the male diabetics > female diabetics - male controls > female controls. Endischemic CBF and depletion of cerebral high energy reserves were comparable among all groups. Surprisingly, female diabetic mice were more hyperglycemic and demonstrated a greater prolonged lactacidosis than the males; however, they were more resistant to damage. The results suggest a unique pathophysiology of hypoxia-ischemia in the female diabetic brain.

Protein kinase C inhibitors attenuate protective effect of high glucose against hypoxic injury in H9c2 cardiac cells

In this study, we demonstrated that PKC inhibitors significantly attenuated the cardioprotective effect produced by high-glucose (22 mM) treatment for 48 h against hypoxic injury in H9c2 cardiac cells. PKC activators mimicked the cardioprotective effect of high glucose. These results suggest a possible role of PKC activation in high-glucose--induced protection.

Glucose metabolism in the developing brain

As in adults, glucose is the predominant cerebral energy fuel for the fetus and newborn. Studies in experimental animals and humans indicate that cerebral glucose utilization initially is low and increases with maturation with increasing regional heterogeneity. The increases in cerebral glucose utilization with advancing age occurs as a consequence of increasing functional activity and cerebral energy demands. The levels of expression of the 2 primary facilitative glucose transporter proteins in brain, GLUT1 (blood-brain barrier and glia) and GLUT3 (neuronal), display a similar maturational pattern. Alternate cerebral energy fuels, specifically the ketone bodies and lactate, can substitute for glucose, especially during hypoglycemia, thereby protecting the immature brain from potential untoward effects of hypoglycemia. Unlike adults, glucose supplementation during hypoxia-ischemia is protective in the immature brain, whereas hypoglycemia is deleterious. Accordingly, glucose plays a critical role in the developing brain, not only as the primary substrate for energy production but also to allow for normal biosynthetic processes to proceed.

CSF glutamate during hypoxia-ischemia in the immature rat

Cerebrospinal fluid (CSF) glutamate was measured prior to and during the course of cerebral hypoxia-ischemia in the immature rat to estimate its concentration in the extracellular fluid (ECF). A preliminary experiment was conducted using [14C]glutamate injections into immature rat brain, which showed that equilibration between ECF and CSF occurred within 10 min. Seven-day postnatal rats underwent unilateral common carotid artery ligation followed by hypoxia with 8% oxygen for up to 2 h. Brain damage, in the form of selective neuronal necrosis or apoptosis, commences after 60 min, while infarction commences after 90 min of hypoxia-ischemia. During the course of hypoxia-ischemia, CSF was obtained from the cisterna magna and analyzed for glutamate. No statistically significant increases in CSF glutamate occurred until 105 min, at which time the concentration was 240% of control (20 micromol/l). By 120 min, CSF glutamate had increased over twofold above the control value. In rat pups exposed to 1 h of hypoxia-ischemia, no increases in CSF glutamate occurred for up to 6 h of recovery. In animals exposed to 2 h of hypoxia-ischemia, CSF glutamate decreased to the control value by 1 h of recovery, with a secondary rise at 6 h. Accordingly, the increase in CSF, and presumably ECF, glutamate is a late event, which better corresponds temporally to cerebral infarction than to selective neuronal death. The results suggest that glutamate excitotoxicity, although involved in the occurrence of infarction, neither causes or contributes to selected neuronal death. The secondary elevation in CSF glutamate at 6 h of recovery from 2 h of hypoxia-ischemia occurs coincident with the onset of tissue necrosis, seen histologically.