Systemic hyperthermia induces ischemic brain injury in neonatal mice with ligated carotid artery and jugular vein

Subtypes and Mechanistic Advances of Extracorporeal Membrane Oxygenation-Related Acute Brain Injury

Extracorporeal membrane oxygenation (ECMO) is a frequently used mechanical cardiopulmonary support for rescuing critically ill patients for whom conventional medical therapies have failed. However, ECMO is associated with several complications, such as acute kidney injury, hemorrhage, thromboembolism, and acute brain injury (ABI). Among these, ABI, particularly intracranial hemorrhage (ICH) and infarction, is recognized as the primary cause of mortality during ECMO support. Furthermore, survivors often suffer significant long-term morbidities, including neurocognitive impairments, motor disturbances, and behavioral problems. This review provides a comprehensive overview of the different subtypes of ECMO-related ABI and the updated advance mechanisms, which could be helpful for the early diagnosis and potential neuromonitoring of ECMO-related ABI.

Thermal conditions during neonatal anoxia affect the endogenous level of brain-derived neurotrophic factor

Anoxia during delivery is a complication that can disturb infant brain development leading to various types of neurological disorders. Our studies have shown that increased body temperature of newborn rats of both sexes intensifies the postanoxic oxidative stress and prevents triggering the endogenous adaptive response such as HIF-1α activation. Currently, brain-derived neurotrophic factor-BDNF is considered to be a modulator of neuronal plasticity. In the developing brain, mature BDNF and its precursor exhibit prosurvival action through the TrkB receptor and proapoptotic functions binding to p75^NTR , respectively. The aim of our experiments was to check the effects of body temperature on the postanoxic level of BDNF and on the expression of its receptors as well as on the marker of apoptosis-caspase-3 in the rat brain. Two-day-old Wistar Han rats (male/female ratio, 1:1) were exposed to anoxia in 100% nitrogen atmosphere for 10 min in different thermal conditions, which allowed them to regulate their rectal temperature at the following levels: normothermic-33°C; hyperthermic-37°C; and extremely hyperthermic-39°C. Thermal conditions during neonatal anoxia affected the level of proBDNF, BDNF as well as their receptors and caspase-3 in the forebrain. The increased BDNF protein level followed by decreased caspase-3 protein level was probably dependent on body temperature under anoxic conditions and was observed only in rats maintaining decreased body temperature. The positive effect of BDNF was not observed under hyperthermic conditions. Moreover, BDNF level changes correlated with body temperature probably affected the learning and spatial memory in juvenile rats.

Intracellular Staphylococcus aureus Control by Virulent Bacteriophages within MAC-T Bovine Mammary Epithelial Cells

Bacteriophages (phages) are known to effectively kill extracellular multiplying bacteria. The present study demonstrated that phages penetrated bovine mammary epithelial cells and cleared intracellular Staphylococcus aureus in a time-dependent manner. In particular, phage vB_SauM_JS25 reached the nucleus within 3 h postincubation. The phages had an endocytotic efficiency of 12%. This ability to kill intracellular host bacteria suggests the utility of phage-based therapies and may protect patients from recurrent infection and treatment failure.

Hyperthermia, inflammation, and perinatal brain injury

Hyperthermia at the time of or following a hypoxic-ischemic insult has been associated with adverse neurodevelopmental outcome. Moreover, an elevation in temperature during labor has been associated with a variety of other adverse neurologic sequelae such as neonatal seizures, encephalopathy, stroke, and cerebral palsy. These outcomes may be secondary to a number of deleterious effects of hyperthermia including an increase in cellular metabolic rate and cerebral blood flow alteration, release of excitotoxic products such as free radicals and glutamate, and hemostatic changes. There is also an association between chorioamnionitis at the time of delivery and cerebral palsy, which is thought to be secondary to cytokine-mediated injury. We review experimental and human studies demonstrating a link between hyperthermia and perinatal brain injury.

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.

The state of systemic circulation, collapsed or preserved defines the need for hyperoxic or normoxic resuscitation in neonatal mice with hypoxia-ischemia

BACKGROUND

The return of spontaneous circulation (ROSC) is a primary goal of resuscitation. For neonatal resuscitation the International Liaison Committee on Resuscitation (ILCOR) recommends oxygen concentrations ranging from 21% to 100%.

AIMS AND METHODS

This study (a) compared the efficacy of resuscitation with room air (RA) or 100% O(2) in achieving ROSC in 46 neonatal mice with circulatory collapse induced by lethal hypoxia-ischemia (HI) and (b) determined whether re-oxygenation with RA or 100% O(2) alters the extent of HI cerebral injury in mice with preserved systemic circulation (n=31). We also compared changes in generation of reactive oxygen species (ROS) in cerebral mitochondria in response to re-oxygenation with RA or 100% O(2).

RESULT

In HI-mice with collapsed circulation re-oxygenation with 100% O(2) versus RA resulted in significantly greater rate of ROSC. In HI-mice with preserved systemic circulation and regional (unilateral) cerebral ischemia the restoration of cerebral blood flow was significantly faster upon re-oxygenation with 100% O(2), than RA. However, no difference in the extent of brain injury was detected. Regardless of the mode of re-oxygenation, reperfusion in these mice was associated with markedly accelerated ROS production in brain mitochondria.

CONCLUSION

In murine HI associated with circulatory collapse the resuscitation limited to re-oxygenation with 100% O(2) is superior to the use of RA in achievement of the ROSC. However, in HI-mice with preserved systemic circulation hyperoxic re-oxygenation has no benefit over the normoxic brain recovery.

Mitochondrial dysfunction contributes to alveolar developmental arrest in hyperoxia-exposed mice

This study investigated whether mitochondrial dysfunction contributes to alveolar developmental arrest in a mouse model of bronchopulmonary dysplasia (BPD). To induce BPD, 3-day-old mice were exposed to 75% O2. Mice were studied at two time points of hyperoxia (72 h or 2 wk) and after 3 weeks of recovery in room air (RA). A separate cohort of mice was exposed to pyridaben, a complex-I (C-I) inhibitor, for 72 hours or 2 weeks. Alveolarization was quantified by radial alveolar count and mean linear intercept methods. Pulmonary mitochondrial function was defined by respiration rates, ATP-production rate, and C-I activity. At 72 hours, hyperoxic mice demonstrated significant inhibition of C-I activity, reduced respiration and ATP production rates, and significantly decreased radial alveolar count compared with controls. Exposure to pyridaben for 72 hours, as expected, caused significant inhibition of C-I and ADP-phosphorylating respiration. Similar to hyperoxic littermates, these pyridaben-exposed mice exhibited significantly delayed alveolarization compared with controls. At 2 weeks of exposure to hyperoxia or pyridaben, mitochondrial respiration was inhibited and associated with alveolar developmental arrest. However, after 3 weeks of recovery from hyperoxia or 2 weeks after 72 hours of exposure to pyridaben alveolarization significantly improved. In addition, there was marked normalization of C-I and mitochondrial respiration. The degree of hyperoxia-induced pulmonary simplification and recovery strongly (r(2) = 0.76) correlated with C-I activity in lung mitochondria. Thus, the arrest of alveolar development induced by either hyperoxia or direct inhibition of mitochondrial oxidative phosphorylation indicates that bioenergetic failure to maintain normal alveolar development is one of the fundamental mechanisms responsible for BPD.

Systemic inflammation following hind-limb ischemia-reperfusion affects brain in neonatal mice

Antenatal and postnatal infection and inflammation are associated with neurological injury in neonates. However, no direct role for systemic inflammation in mediating neurodamage has been shown. The study was aimed to determine whether systemic inflammation following ischemia-reperfusion (IR) of an organ remotely located from the brain results in cerebral injury. Neonatal mice were subjected to 2 h of hind-limb IR. At 48 h of reperfusion, brains were examined for activation of microglia and caspase-3. Lungs were assessed for pulmonary edema and granulocyte infiltration. The levels of circulating inflammatory mediators were measured at 24 h of reperfusion. In a separate cohort of mice, changes in the cerebral and hind-limb blood flow were measured. All data were compared to that in sham mice. Compared to shams the degree of pulmonary edema in IR mice was 33% (p = 0.04) greater. This was associated with significantly (p = 0.0006) greater granulocytic infiltration and a markedly increased level of circulating cytokines. The brains of these same mice exhibited significantly (p = 0.02) greater numbers of caspase-3-immunopositive cells and activation of microglia compared to sham mice. These data indicate that systemic inflammation following IR in the organ remote from the brain can induce neuroinflammation and cerebral proapoptotic changes.

An isolation method for assessment of brain mitochondria function in neonatal mice with hypoxic-ischemic brain injury

This work was undertaken to develop a method for the isolation of mitochondria from a single cerebral hemisphere in neonatal mice. Mitochondria from the normal mouse brain hemisphere isolated by the proposed method exhibited a good respiratory control ratio of 6.39 +/- 0.53 during glutamate-malate-induced phosphorylating respiration. Electron microscopy showed intact mitochondria. The applicability of this method was tested on mitochondria isolated from naïve mice and their littermates subjected to hypoxic-ischemic insult. Hypoxic-ischemic insult prior to reperfusion resulted in a significant (p < 0.01) inhibition of phosphorylating respiration compared to naïve littermates. This was associated with a profound depletion of the ATP content in the ischemic hemisphere. The expression for Mn superoxide dismutase and cytochrome C (markers for the integrity of the mitochondrial matrix and outer membrane) was determined by Western blot to control for mitochondrial integrity and quantity in the compared samples. Thus, we have developed a method for the isolation of the cerebral mitochondria from a single hemisphere adapted to neonatal mice. This method may serve as a valuable tool to study mitochondrial function in a mouse model of immature brain injury. In addition, the suggested method enables us to examine the mitochondrial functional phenotype in immature mice with a targeted genetic alteration.

Neurogenesis and neuronal commitment following ischemia in a new mouse model for neonatal stroke

Stroke in the neonatal brain is an important cause of neurologic morbidity. To characterize the dynamics of neural progenitor cell proliferation and maturation after survival delays in the neonatal brain following ischemia, we utilized unilateral carotid ligation alone to produce infarcts in postnatal day 12 CD1 mice. We investigated the neurogenesis derived from the sub-ventricular zone and the sub-granular zone of the dentate gyrus subsequent to injury. Newly produced cells were labeled by bromodeoxyuridine at approximately 1 week (P18-20) after the insult by 5 i.p. injections (each 50 mg/kg). Subsequent migration and differentiation of the newborn cells was investigated at postnatal day 40 by immunohistochemistry for molecular neuronal and glial cell-lineage markers and BrdU incorporation. Cresyl violet stain demonstrated massive loss of neurons in the ipsilateral septal hippocampus in the CA3 and CA1 regions associated with atrophy. Total counts of new cells were significantly lowered not only in the ipsilateral injured but also the contralateral uninjured hippocampi and correlated with the lesion induced atrophy. Bilateral percent neuronal commitments in the dentate gyri however, were not significantly different from control. New cell densities in the neocortex and striatum increased bilaterally after neonatal stroke. The predominantly non-neuronal commitment of the SVZ-derived new cells was similar to the percentage of non-neuronal commitment in controls. In conclusion, neurogenesis occurring at 1 week after neonatal ischemia in the model maintained cell-lineage commitment patterns similar to sham controls. However, the total number of hippocampal SGZ-derived new neurons was reduced bilaterally; in contrast, the SVZ-derived neurogenesis was amplified.