Persistent neurochemical changes in neonatal piglets after hypoxia–ischemia and resuscitation with 100%, 21% or 18% oxygen

Practical oxygen therapy for newborn piglets

Aims: To evaluate the effect of a novel method of practical oxygen therapy on physiological parameters related to survival, weaning weight and preweaning mortality of neonatal piglets under commercial farm conditions. Methods: Piglets from hyperprolific sows born with signs of asphyxia, (n = 109; <6 on a score of respiration, meconium staining and activity) or very low birth weight (VLBW; n = 112; <1.05 kg) were selected for the study. Approximately half of each group (n = 55 VLBW piglets and n = 57 piglets with asphyxia) received 100% oxygen immediately after birth using a specially designed facemask for 45 seconds (VLBW) or 1 minute (asphyxiated). Physiological parameters (peripheral blood oxygen saturation (SpO₂) blood glucose concentration and rectal temperature) were measured before oxygen treatment 5 minutes after birth (SpO₂) and 24 hours later (SpO₂, blood glucose concentration, temperature). Weight at birth, at 24 hours and at 21 days of age, preweaning mortality, and estimated colostrum intake were also recorded. Results: A significant treatment effect on SpO₂ was observed (p = 0.013 and p < 0.001 for VLBW and asphyxiated piglets respectively). VLBW and asphyxiated piglets that received oxygen treatment had higher SpO₂ after treatment (measured 5 minutes after birth, 97.7 and 97.8% respectively) compared to immediately after birth (93.3 and 86.8% respectively) while untreated piglets showed no variation. Blood glucose concentrations increased in all piglets between birth and 24 hours of age (p = 0.003 and p < 0.001 for asphyxiated and VLBW piglets respectively) and this was higher in asphyxiated piglets that received oxygen than those that did not (5.6 (SE 0.2) mmol/L; p < 0.05). Estimated colostrum intake was higher in asphyxiated (401.6 (SD 24.4) g/kg) and VLBW (374.9 (SE 23.4 g/kg) piglets that received oxygen than those that did not (273.2 (SE 24.1) g/kg; p < 0.001 and 249.0 (SE 22.5) g/kg; p < 0.001 respectively). Similarly weight at weaning was higher in asphyxiated (5.8 (SE 0.2) kg) and VLBW (4.9 (SE 0.2) kg) piglets that received oxygen therapy than control animals (4.9 (SE 0.2) kg; = 0.005 and 4.1 (SE 0.2) kg; p = 0.008 respectively). Furthermore, oxygen treatment markedly reduced preweaning mortality from 9/52 (17%) untreated to 1/57 (1.7%) oxygen-treated piglets suffering asphyxia at birth (p = 0.006). Conclusions: Oxygen therapy improves physiological and productive parameters in piglets born with signs of asphyxia or VLBW. The incorporation of this strategy as part of the farrowing routine enhances the advantages of rearing hyperprolific sows.

Gradually increased oxygen administration promoted survival after hemorrhagic shock

Gradually increased oxygen administration (GIOA) seems promising in hemorrhagic shock. However, the effects of GIOA on survival remain unclear, and details of GIOA are to be identified. After the induction of hemorrhagic shock, the rats were randomized into five groups (n = 9): normoxic group (Normo), hyperoxic group (Hypero), normoxic to hyperoxic group (GIOA1), long-time hypoxemic to hyperoxic group (GIOA2), and short-time hypoxemic to hyperoxic group (GIOA3). Survival was recorded for 96 h, plasma alanine transaminase, oxidative stress, hemodynamics, and blood gas were measured. The mean survival time of the GIOA3 was significantly longer than that of the Normo, Hypero, and GIOA2. Plasma alanine transaminase levels were significantly lower in the Normo, GIOA1, and GIOA3 compared to the Hypero and GIOA2 at 2 h post-resuscitation (PR). Plasma 3-nitrotyrosine levels at 2 h PR were significantly lower in the GIOA2 and GIOA3 compared to the Normo and Hypero. Central venous oxygen saturation at 2 h PR in the GIOA3 was significantly higher than the Normo; however, no significant difference was observed between GIOA1 and Normo. Besides, at 2 h PR, mean arterial pressure in the GIOA3 was significantly higher than the GIOA2; however, no significant difference was observed between GIOA1 and GIOA2. (1) GIOA could significantly prolong survival time compared to normoxemic resuscitation and hyperoxic resuscitation; (2) early moments of GIOA are critical to the benefits; and (3) hypoxemia at onset of resuscitation may be imperative, more works are needed to determine the optimal initial oxygen concentration of GIOA.

Effects of Oxygen Concentrations on Postresuscitation Myocardial Oxidative Stress and Myocardial Function in a Rat Model of Cardiopulmonary Resuscitation

OBJECTIVE

Lipid peroxidation induced by free-radical species plays a prominent role in myocardial injury following ischemia and reperfusion. However, there is a lack of data in different oxygen concentrations on myocardial lipid peroxidation during the early phase of reperfusion. In this study, we investigated whether ventilation with medium or normal concentration of oxygen would decrease the severity of myocardial lipid peroxidation and postresuscitation myocardial dysfunction.

DESIGN

Prospective, randomized, controlled experimental study.

SETTING

University-affiliated animal research institution.

SUBJECTS

Sixty-three healthy male Sprague-Dawley rats.

INTERVENTIONS

Animals were randomized into three groups: 1) 100% group, 2) 50% group, and 3) 21% group. Ventricular fibrillation was induced and untreated for 8 minutes, and defibrillation was attempted after 8 minutes of cardiopulmonary resuscitation. Ventilation with 100%, 50%, or 21% oxygen was initiated in all groups during cardiopulmonary resuscitation and 1 hour following the return of spontaneous circulation. Normoxic ventilation was maintained thereafter.

MEASUREMENTS AND MAIN RESULTS

Myocardial function, including ejection fraction and myocardial performance index, were measured at baseline, 4, or 72 hours after resuscitation. Blood samples were drawn at baseline, 15 minutes, 1, 4, or 72 hours after resuscitation for the measurements of blood gas or biomarkers. Significantly better myocardial function and longer duration of survival were observed in the 50% group. Compared with the 21% and 100% groups, a mild hyperoxia and greater oxygen extraction with lower 8-iso-prostaglandin F2α were observed in the 50% group. Pearson correlation analysis confirmed that 8-iso-prostaglandin F2α was positively correlated with myocardial performance index at 4 hours postresuscitation.

CONCLUSIONS

In a rat model of cardiac arrest and resuscitation, ventilation with 50% inspired oxygen during early postischemic reperfusion phase contributed to a decreased lipid peroxidation and a better myocardial function and duration of survival.

Preclinical Models of Encephalopathy of Prematurity

Encephalopathy of prematurity (EoP) encompasses the central nervous system (CNS) abnormalities associated with injury from preterm birth. Although rapid progress is being made, limited understanding exists of how cellular and molecular CNS injury from early birth manifests as the myriad of neurological deficits in children who are born preterm. More importantly, this lack of direct insight into the pathogenesis of these deficits hinders both our ability to diagnose those infants who are at risk in real time and could potentially benefit from treatment and our ability to develop more effective interventions. Current barriers to clarifying the pathophysiology, developmental trajectory, injury timing, and evolution include preclinical animal models that only partially recapitulate the molecular, cellular, histological, and functional abnormalities observed in the mature CNS following EoP. Inflammation from hypoxic-ischemic and/or infectious injury induced in utero in lower mammals, or actual prenatal delivery of more phylogenetically advanced mammals, are likely to be the most clinically relevant EOP models, facilitating translation to benefit infants. Injury timing, type, severity, and pathophysiology need to be optimized to address the specific hypothesis being tested. Functional assays of the mature animal following perinatal injury to mimic EoP should ideally test for the array of neurological deficits commonly observed in preterm infants, including gait, seizure threshold and cognitive and behavioral abnormalities. Here, we review the merits of various preclinical models, identify gaps in knowledge that warrant further study and consider challenges that animal researchers may face in embarking on these studies. While no one model system is perfect, insights relevant to the clinical problem can be gained with interpretation of experimental results within the context of inherent limitations of the chosen model system. Collectively, optimal use of multiple models will address a major challenge facing the field today - to identify the type and severity of CNS injury these vulnerable infants suffer in a safe and timely manner, such that emerging neurointerventions can be tailored to specifically address individual reparative needs.

An experimental model of neonatal normocapnic hypoxia and resuscitation in Landrace/Large White piglets

OBJECTIVE

The aim of this study is to describe and evaluate an experimental model of neonatal normocapnic hypoxia and resuscitation.

METHODS

Ten male Landrace/Large White neonatal piglets were studied. Following anaesthesia and intubation, the animals were mechanically ventilated. Surgical procedures included catheterization of the right internal jugular vein and the carotid artery. After stabilization with 21% O(2), normocapnic hypoxia was induced by decreasing the inspired O(2) to 6-8%. When piglets developed bradycardia (heart rate < 60 beats/min), reoxygenation was initiated by administering 21% O(2). Arterial blood samples were taken during baseline, hypoxia and reoxygenation in order to measure interleukine-6 and interleukine-8.

RESULTS

Nine out of ten animals were successfully resuscitated (one of these required chest compressions and a dose of adrenaline) and one died despite resuscitation efforts. After returning to baseline haemodynamic values, euthanasia was performed using thiopental overdose.

CONCLUSIONS

Haemodynamic fluctuations at baseline, during normocapnic hypoxia and reoxygenation in Landrace/Large White piglets are comparable to that in human neonates, making the breed a favorable model of human neonatal hypoxia investigation.

Mild hypoxemia during initial reperfusion alleviates the severity of secondary energy failure and protects brain in neonatal mice with hypoxic-ischemic injury

Reperfusion triggers an oxidative stress. We hypothesized that mild hypoxemia in reperfusion attenuates oxidative brain injury following hypoxia-ischemia (HI). In neonatal HI-mice, the reperfusion was initiated by reoxygenation with room air (RA) followed by the exposure to 100%, 21%, 18%, 15% oxygen for 60 minutes. Systemic oxygen saturation (SaO(2)), cerebral blood flow (CBF), brain mitochondrial respiration and permeability transition pore (mPTP) opening, markers of oxidative injury, and cerebral infarcts were assessed. Compared with RA-littermates, HI-mice exposed to 18% oxygen exhibited significantly decreased infarct volume, oxidative injury in the brain mitochondria and tissue. This was coupled with improved mitochondrial tolerance to mPTP opening. Oxygen saturation maintained during reperfusion at 85% to 95% was associated (r=0.57) with the best neurologic outcome. Exposure to 100% or 15% oxygen significantly exacerbated brain injury and oxidative stress. Compared with RA-mice, hyperoxia dramatically increased reperfusion CBF, but exposure to 15% oxygen significantly reduced CBF to values observed during the HI-insult. Mild hypoxemia during initial reperfusion alleviates the severity of HI-brain injury by limiting the reperfusion-driven oxidative stress to the mitochondria and mPTP opening. This suggests that at the initial stage of reperfusion, a slightly decreased systemic oxygenation (SaO(2) 85% to 95%) may be beneficial for infants with birth asphyxia.

Decreased GABAB receptor function in the cerebellum and brain stem of hypoxic neonatal rats: role of glucose, oxygen and epinephrine resuscitation

Background-

Hypoxia during the first week of life can induce neuronal death in vulnerable brain regions usually associated with an impairment of cognitive function that can be detected later in life. The neurobiological changes mediated through neurotransmitters and other signaling molecules associated with neonatal hypoxia are an important aspect in establishing a proper neonatal care.

Methods-

The present study evaluated total GABA, GABA_B receptor alterations, gene expression changes in GABA_B receptor and glutamate decarboxylase in the cerebellum and brain stem of hypoxic neonatal rats and the resuscitation groups with glucose, oxygen and epinephrine. Radiolabelled GABA and baclofen were used for receptor studies of GABA and GABA_B receptors respectively and Real Time PCR analysis using specific probes for GABA_B receptor and GAD mRNA was done for gene expression studies.

Results-

The adaptive response of the body to hypoxic stress resulted in a reduction in total GABA and GABA_B receptors along with decreased GABA_B receptor and GAD gene expression in the cerebellum and brain stem. Hypoxic rats supplemented with glucose alone and with oxygen showed a reversal of the receptor alterations and changes in GAD. Resuscitation with oxygen alone and epinephrine was less effective in reversing the receptor alterations.

Conclusions-

Being a source of immediate energy, glucose can reduce the ATP-depletion-induced changes in GABA and oxygenation, which helps in encountering hypoxia. The present study suggests that reduction in the GABA_B receptors functional regulation during hypoxia plays an important role in central nervous system damage. Resuscitation with glucose alone and glucose and oxygen to hypoxic neonatal rats helps in protecting the brain from severe hypoxic damage.

Short- and long-term behavioral effects of exposure to 21%, 40% and 100% oxygen after perinatal hypoxia-ischemia in the rat

Until recently, supplementation with 100% oxygen was standard therapy for newborns who required resuscitation at birth or suffered later hypoxic-ischemic events. Exposure to high concentrations of oxygen, however, may worsen oxidative stress induced by ischemic injury. In this study we investigated the short- and long-term behavioral outcomes in rats that had undergone hypoxic-ischemic brain injury on postnatal day 7, followed by 2h exposure to 21%, 40%, or 100% oxygen, compared to normal controls. There were no differences in the development of walking, head lifting and righting reflexes from postnatal days 9 to 15. Cliff avoidance showed some abnormal responses in the H21 animals. From postnatal days 28 to 56, three tests of sensorimotor coordination were performed weekly: ledged tapered beam, cylinder, and bilateral tactile stimulation. The ledged tapered beam test without prior training of animals was sensitive to injury, but did not distinguish between treatment groups. The cylinder test showed a greater use of the unimpaired limb in female 21% and 40% oxygen groups compared to controls. Performance in both cylinder and the beam tests showed a correlation with the degree of brain injury. The bilateral tactile stimulation test showed that the male 21% oxygen groups had worse sensory asymmetry than male 40% or 100% oxygen groups, but was not statistically significantly different from controls. We thus found a minor benefit to post-hypoxia-ischemic treatment with 100% and 40% oxygen compared to 21% in one test of early motor skills. Our results for long-term sensorimotor behavior, however, showed conflicting results, however, as males treated with 40% or 100% oxygen had less sensory asymmetry (better performance) in the bilateral tactile stimulation test than males treated with 21% oxygen, while females had impaired motor performance in the cylinder test with both 21% and 40% oxygen.

Prolonged hypoxemia and acidemia in anesthetized pigs: a model for research on extracorporeal organ support in an intensive care setting

PURPOSE

Hypoxemia and acidemia (hypoxemia/acidemia) are serious complications in the critically ill and often occur in unstable patients exposed to extracorporeal organ support. Still, little is known about the biocompatibility interactions of hypoxemia/acidemia with extracorporeal circuits (ECC). Existing animal models often include the release of mediator cascades (sepsis-, lung injury models) or are based on small laboratory animals. We established a porcine model of hypoxemia/acidemia without an underlying disease and further challenged the situation with an extracorporeal circuit (ECC).

METHODS

Hypoxemia/acidemia were induced (3.5 h) and maintained (3 h) in anesthetized pigs (40 kg) by a stepwise reduction in oxygenation, infusion of 0.4 mol.l⁻¹ lactic and hydrochloric acid and by low tidal volume ventilation, targeting an PaO₂ < 70 mmHg, SvO₂ < 65%, pH ~ 7.2. Venovenous hemofiltration (CVVH) operated in recirculation mode without volume exchange was chosen to prove the suitability of the model for studies on ECCs under clinical conditions (ECC group, n=6). Another 6 animals underwent the same protocol except for the CVVH (reference group, n=6).

RESULTS

The median PaO₂ during hypoxemia/acidemia was 62 mmHg, the median SvO₂ was 38%, and the median pH was 7.22. Hypoxemia/acidemia was successfully induced and maintained for 6.5 h in all pigs. CVVH could be performed for 3 h with blood flow rates up to 300 ml.min⁻¹ and filtrate rates up to 60 ml.min⁻¹.

CONCLUSIONS

Our model provides hypoxemia/acidemia with blood gas values comparable to critically ill adult patients for several hours, during which it is possible to perform CVVH. Thus, it enables research on the biocompatibility reactions of extracorporeal circuits under intensive care conditions.

Resuscitation of newborn piglets. short-term influence of FiO2 on matrix metalloproteinases, caspase-3 and BDNF

BACKGROUND

Perinatal hypoxia-ischemia is a major cause of mortality and cerebral morbidity, and using oxygen during newborn resuscitation may further harm the brain. The aim was to examine how supplementary oxygen used for newborn resuscitation would influence early brain tissue injury, cell death and repair processes and the regulation of genes related to apoptosis, neurodegeneration and neuroprotection.

METHODS AND FINDINGS

Anesthetized newborn piglets were subjected to global hypoxia and then randomly assigned to resuscitation with 21%, 40% or 100% O(2) for 30 min and followed for 9 h. An additional group received 100% O(2) for 30 min without preceding hypoxia. The left hemisphere was used for histopathology and immunohistochemistry and the right hemisphere was used for in situ zymography in the corpus striatum; gene expression and the activity of various relevant biofactors were measured in the frontal cortex. There was an increase in the net matrix metalloproteinase gelatinolytic activity in the corpus striatum from piglets resuscitated with 100% oxygen vs. 21%. Hematoxylin-eosin (HE) staining revealed no significant changes. Nine hours after oxygen-assisted resuscitation, caspase-3 expression and activity was increased by 30-40% in the 100% O(2) group (n = 9/10) vs. the 21% O(2) group (n = 10; p<0.04), whereas brain-derived neurotrophic factor (BDNF) activity was decreased by 65% p<0.03.

CONCLUSIONS

The use of 100% oxygen for resuscitation resulted in increased potentially harmful proteolytic activities and attenuated BDNF activity when compared with 21%. Although there were no significant changes in short term cell loss, hyperoxia seems to cause an early imbalance between neuroprotective and neurotoxic mechanisms that might compromise the final pathological outcome.

Alterations in cortical GABAB receptors in neonatal rats exposed to hypoxic stress: role of glucose, oxygen, and epinephrine resuscitation

Hypoxia in neonates can cause permanent brain damage by gene and receptor level alterations mediated through changes in neurotransmitters. The present study evaluated GABA(B) receptor alterations, gene expression changes in glutamate decarboxylase and hypoxia-inducible factor 1A in the cerebral cortex of hypoxic neonatal rats and the resuscitation groups with glucose, oxygen, and epinephrine. Under hypoxic stress, a significant decrease in total GABA and GABA(B) receptors, GABA(B) and GAD gene expression was observed in the cerebral cortex, which accounts for the respiratory inhibition. Hypoxia-inducible factor 1A was upregulated under hypoxia to maintain body homeostasis. Hypoxic rats supplemented with glucose alone and with oxygen showed a reversal of the receptor alterations and changes in GAD and HIF-1A to near control. Being a source of immediate energy, glucose can reduce the ATP-depletion-induced changes in GABA and oxygenation, which helps in encountering hypoxia. Resuscitation with oxygen alone and epinephrine was less effective in reversing the receptor alterations. Thus, our study suggests that reduction in the GABA(B) receptors functional regulation during hypoxia plays an important role in cortical damage. Resuscitation with glucose alone and glucose and oxygen to hypoxic neonatal rats helps in protecting the brain from severe hypoxic damage.

Changes in the expression of insulin-like growth factor 1 variants in the postnatal brain development and in neonatal hypoxia-ischaemia

Insulin-like growth factor-1 (IGF-1) is a multifunctional peptide of which numerous isoforms exist. The predominant form, IGF-1Ea is involved in physiological processes while IGF-1Ec (mechano-growth factor, MGF) is expressed in response to a different set of stimuli. We have identified specific changes in the expression patterns of these IGF-1 variants in brain development in normal rats and following neonatal hypoxia-ischaemia (HI). Both IGF-1Ea and IGF-1Ec are expressed during normal postnatal brain development, albeit with highly specific temporal distributions. In contrast, HI produced increased and prolonged expression of the IGF-1Ec isoform only. Importantly, hypoxia alone stimulated the expression of IGF-1Ec as well. Thus, IGF-1Ec may play a role in HI pathology. Neonatal hypoxia-ischaemia occurs in approximately 1:4000-1:10,000 newborns and causes neurological deficits in approximately 75% of those affected. Unfortunately, no specific treatment is available. IGF-1 is known to have neuroprotective activity and its IGF-1Ec variant appears to be an endogenous protective factor in hypoxia-ischaemia. Therefore, IGF-1Ec could potentially be developed into a therapeutic modality for the attenuation or prevention of neuronal damage in this and related disorders.

Metabolic control exerted by the 2-oxoglutarate dehydrogenase reaction: a cross-kingdom comparison of the crossroad between energy production and nitrogen assimilation

Mechanism-based inhibitors and both forward and reverse genetics have proved to be essential tools in revealing roles for specific enzymatic processes in cellular function. Here, we review experimental studies aimed at assessing the impact of OG (2-oxoglutarate) oxidative decarboxylation on basic cellular activities in a number of biological systems. After summarizing the catalytic and regulatory properties of the OGDHC (OG dehydrogenase complex), we describe the evidence that has been accrued on its cellular role. We demonstrate an essential role of this enzyme in metabolic control in a wide range of organisms. Targeting this enzyme in different cells and tissues, mainly by its specific inhibitors, effects changes in a number of basic functions, such as mitochondrial potential, tissue respiration, ROS (reactive oxygen species) production, nitrogen metabolism, glutamate signalling and survival, supporting the notion that the evolutionary conserved reaction of OG degradation is required for metabolic adaptation. In particular, regulation of OGDHC under stress conditions may be essential to overcome glutamate excitotoxicity in neurons or affect the wound response in plants. Thus, apart from its role in producing energy, the flux through OGDHC significantly affects nitrogen assimilation and amino acid metabolism, whereas the side reactions of OGDHC, such as ROS production and the carboligase reaction, have biological functions in signalling and glyoxylate utilization. Our current view on the role of OGDHC reaction in various processes within complex biological systems allows us a far greater fundamental understanding of metabolic regulation and also opens up new opportunities for us to address both biotechnological and medical challenges.