Early regional response of apoptotic activity in newborn piglet brain following hypoxia and ischemia

Hippocampal mitogen-activated protein kinase activation is associated with intermittent hypoxia in a rat model of obstructive sleep apnea syndrome

Obstructive sleep apnea syndrome (OSAS), characterized by intermittent hypoxia/re-oxygenation, may impair the cerebral system. Although mitogen-activated protein kinase (MAPK) signaling was observed to have a key role in hypoxia-induced brain injury, the intracellular events and their underlying mechanisms for intermittent hypoxia/re-oxygenation-associated damage to hippocamal MAPKs, including extracellular signal-regulated kinase (ERK)1/2, P38MAPK and c-Jun N-terminal kinase (JNK) remain to be elucidated and require further investigation. A total of five rats in each sub-group were exposed to intermittent hypoxia or continued hypoxia for 2, 4, 6 or 8 weeks. Histological, immunohistochemical and biological analyses were performed to assess nerve cell injury in the hippocampus. Surviving CA1 pyramidal cells were identified by hematoxylin and eosin staining. The levels of phosphorylated ERK1/2, P38MAPK and JNK were detected by western blotting. B-cell lymphoma 2 (Bcl-2) and Bcl-2-associated X protein (Bax) in neural cells were examined by immunohistochemistry. The malondialdehyde (MDA) contents and superoxide dismutase (SOD) activities were measured by thiobarbituric acid and xanthine oxidation methods, respectively. Under continued hypoxia, the levels of phospho-ERK1/2 peaked at the fourth week and then declined, whereas phospho-P38MAPK and JNK were detected only in the late stages. By contrast, under intermittent hypoxia, ERK1/2, P38MAPK and JNK were activated at all time-points assessed (2, 4, 6 and 8 weeks). The levels of phospho-ERK1/2, P38MAPK and JNK were all higher in the intermittent hypoxia groups than those in the corresponding continued hypoxia groups. Bcl-2 was mainly increased and reached the highest level at six weeks in the continued hypoxia group. Of note, Bcl-2 rapidly increased to the peak level at four weeks, followed by a decrease to the lowest level at the eighth week in the intermittent hypoxia group. Bax was generally increased at the late stages under continued hypoxia, but increased at all time-points under the intermittent hypoxia conditions. The two types of hypoxia induced an increase in the MDA content, but a decrease in SOD activity. Marked changes in these two parameters coupled with markedly reduced surviving cells in the hippocampus in a time-dependent manner were observed in the intermittent hypoxia group in comparison with the continued hypoxia group. OSAS-induced intermittent hypoxia markedly activated the MAPK signaling pathways, which were triggered by oxidative stress, leading to abnormal expression of downstream Bcl-2 and Bax, and a severe loss of neural cells in the hippocampus.

Light-addressable measurement of in vivo tissue oxygenation in an unanesthetized zebrafish embryo via phase-based phosphorescence lifetime detection

We have developed a digital light modulation system that utilizes a modified commercial projector equipped with a laser diode as a light source for quantitative measurements of in vivo tissue oxygenation in an unanesthetized zebrafish embryo via phase-based phosphorescence lifetime detection. The oxygen-sensitive phosphorescent probe (Oxyphor G4) was first inoculated into the bloodstream of 48 h post-fertilization (48 hpf) zebrafish embryos via the circulation valley to rapidly disperse probes throughout the embryo. The unanesthetized zebrafish embryo was introduced into the microfluidic device and immobilized on its lateral side by using a pneumatically actuated membrane. By controlling the illumination pattern on the digital micromirror device in the projector, the modulated excitation light can be spatially projected to illuminate arbitrarily-shaped regions of tissue of interest for in vivo oxygen measurements. We have successfully measured in vivo oxygen changes in the cardiac region and cardinal vein of a 48 hpf zebrafish embryo that experience hypoxia and subsequent normoxic conditions. Our proposed platform provides the potential for the real-time investigation of oxygen distribution in tissue microvasculature that relates to physiological stimulation and diseases in a developing organism.

Reoxygenation of asphyxiated newborn piglets: administration of 100% oxygen causes significantly higher apoptosis in cortical neurons, as compared to 21%

OBJECTIVE

Evaluation of neuronal changes in an animal experimental model of normocapnic hypoxia- reoxygenation.

MATERIALS AND METHODS

Fifty male piglets were the study subjects; normocapnic hypoxia was induced in 40 piglets and ten were sham-operated (controls). When bradycardia and/or severe hypotension occurred, reoxygenation was initiated. Animals were allocated in 4 groups according to the oxygen concentration, they were resuscitated with 18%, 21%, 40%, and 100% O2. Persisting asystole despite 10 minutes of cardiopulmonary resuscitation and return of spontaneous circulation were the endpoints of the experiment. Surviving animals were euthanized and brain cortex samples were collected, hematoxylin and eosin-stained, and examined for apoptotic bodies observing 10 consecutive high power fields.

RESULTS

Histological examination of the control group did not show any pathological change. On the contrary, apoptosis of neurons was found in 87.5% of treated animals. When specimens were examined according to the oxygen concentration used for resuscitation, we found marked intergroup variability; a higher percentage of apoptotic neurons was observed in piglets of group 4 (100% oxygen) compared to the others (P=0.001).

CONCLUSIONS

This preliminary data shows that normocapnic hypoxia and reoxygenation in Landrace/Large White piglets resulted in significant histological changes in the brain cortex. The degree of pathological changes in cortical neurons was significantly associated with the oxygen concentration used for reoxygenation, with a higher percentage of apoptotic neurons being observed in piglets reoxygenated with 100% compared to 18% O2 and to 21% O2.

Minocycline attenuates brain tissue levels of TNF-α produced by neurons after prolonged hypothermic cardiac arrest in rats

Neuro-cognitive disabilities are a well-recognized complication of hypothermic circulatory arrest. We and others have reported that prolonged cardiac arrest (CA) produces neuronal death and microglial proliferation and activation that are only partially mitigated by hypothermia. Microglia, and possibly other cells, are suggested to elaborate tumor necrosis factor alpha (TNF-α), which can trigger neuronal death cascades and exacerbate edema after CNS insults. Minocycline is neuroprotective in some brain ischemia models in part by blunting the microglial response. We tested the hypothesis that minocycline would attenuate neuroinflammation as reflected by brain tissue levels of TNF-α after hypothermic CA in rats. Rats were subjected to rapid exsanguination, followed by a 6 min normothermic CA. Hypothermia (30 °C) was then induced by an aortic saline flush. After a total of 20 min CA, resuscitation was achieved via cardiopulmonary bypass (CPB). After 5 min reperfusion, minocycline (90 mg kg−1; n = 6) or vehicle (PBS; n = 6) was given. Hypothermia (34 °C) was maintained for 6 h. Rats were sacrificed at 6 or 24 h. TNF-α was quantified (ELISA) in four brain regions (cerebellum, CEREB; cortex, CTX; hippocampus, HIP; striatum, STRI). Naïve rats (n = 6) and rats subjected to the same anesthesia and CPB but no CA served as controls (n = 6). Immunocytochemistry was used to localize TNF-α. Naïve rats and CPB controls had no detectable TNF-α in any brain region. CA markedly increased brain TNF-α. Regional differences were seen, with the highest TNF-α levels in striatum in CA groups (10-fold higher, P < 0.05 vs. all other brain regions). TNF-α was undetectable at 24 h. Minocycline attenuated TNF-α levels in CTX, HIP and STRI (P < 0.05). TNF-α showed unique co-localization with neurons. In conclusion, we report region-dependent early increases in brain TNF-α levels after prolonged hypothermic CA, with maximal increases in striatum. Surprisingly, TNF-α co-localized in neurons and not microglia. Minocycline attenuated TNF-α by approximately 50% but did not totally ablate its production. That minocycline decreased brain TNF-α levels suggests that it may represent a therapeutic adjunct to hypothermia in CA neuroprotection. University of Pittsburgh IACUC 0809278B-3.

Effects of phentolamine infusion during selective cerebral perfusion in neonatal piglets

BACKGROUND

An optimal selective cerebral perfusion protocol in pediatric cardiac surgery is unknown. Phentolamine is frequently used in pediatric cardiopulmonary bypass. We sought to determine the effects of continuous phentolamine infusion during selective cerebral perfusion.

METHODS

Twenty-seven neonatal piglets (3.38 ± 0.32 kg) were randomly assigned to 3 groups; sham (n = 7, anesthesia alone, no surgery or bypass), control (n = 10, saline infusion), or experimental (n = 10, phentolamine infusion 0.1 mg/kg per hour). Animals underwent 90 minutes of selective cerebral perfusion. Cerebral vascular resistance index (CVRI) and metabolic rate of oxygen (CMRO2) were determined every 15 minutes. Standardized sections of hippocampus, basal ganglia, and neo-cortex were obtained. Tissue samples were stained for caspase-3 and analyzed for positive apoptotic cell count. Data were analyzed with repeated measures and one-way analysis of variance.

RESULTS

The CVRI tended to increase over time in the control group and decrease over time in the experimental group, but difference was not statically significant (0.46 ± 0.24 vs 0.39 ± 0.10 mm Hg × min × kg(2/3)/mL, p = 0.15). Mean CMRO2 was higher in the control group compared with the experimental group (0.90 ± 0.27 vs 0.59 ± 0.12 mLO2/min × kg(2/3), p = 0.005) and decreased over time in both groups. The percentage of caspase-3 positive cells was significantly different among regions (hippocampus = 16.9 ± 8.8; basal ganglia = 14.6 ± 7.5; neocortex = 10.8 ± 6.3; p < 0.0001) but not significantly different among sham (11.8% ± 2.68%), control (14.4% ± 2.24%), and experimental (15.5% ± 2.24%) groups.

CONCLUSIONS

A continuous infusion of phentolamine during selective cerebral perfusion significantly decreases CMRO2 and tends to decrease CVRI when compared with control. At the dose studied and at the time of tissue sampling, phentolamine does not appear to decrease apoptosis during or early after selective cerebral perfusion.

Xanthine oxidase does not contribute to apoptosis after brain hypoxia-ischemia in immature rabbits

Background. The mechanisms involving the initiation of apoptosis after brain hypoxia-ischemia through caspase activation are not fully defined. Oxygen free radicals may be an important mediator of caspase initiation with reactive oxygen species generated by xanthine oxidase (XO) being one potential source. The purpose of this study was to examine the role of XO in apoptosis after global cerebral injury. Methods. Immature rabbits were subjected to 8 minutes hypoxia and 8 minutes ischemia and then 4 hours of reperfusion. In one group (n = 5), the XO substrate xanthine was infused to generate more oxygen free radicals to promote apoptosis while in another (n = 5), the XO inhibitor allopurinol was given to reduce apoptosis by preventing free radical production (n = 5). Control animals (n = 4) received the vehicles. Caspase 3, 8, and 9 enzyme activities were measured in the cerebral cortex, hippocampus, cerebellum, thalamus, and caudate. Results. Administration of xanthine increased (P < 0.05) caspase 3 activity but only in the hippocampus, and pretreatment with allopurinol did not reduce it. No differences (P > 0.05) were found in any other region nor were there any changes in caspases 8 or 9 activities. Conclusion. We conclude that XO is not a major factor in inducing apoptosis after hypoxic-ischemic brain injury.

MicroRNA-210 targets antiapoptotic Bcl-2 expression and mediates hypoxia-induced apoptosis of neuroblastoma cells

MicroRNAs (miRNAs) can regulate cell survival and death by targeting apoptosis-related gene expression. miR-210 is one of the most hypoxia-sensitive miRNAs. In this study, we evaluated the roles of miR-210 in hypoxia-induced insults to neural cells. Treatment of neuro-2a cells with oxygen/glucose deprivation (OGD) induced cell apoptosis in a time-dependent manner. In parallel, OGD time-dependently increased cellular miR-210 levels. Knocking down miR-210 expression using specific antisenses significantly attenuated OGD-induced neural apoptosis. Concurrently, OGD increased hypoxia-inducible factor (HIF)-1α mRNA and protein syntheses. Pretreatment with YC-1, an inhibitor of HIF-1α, reduced OGD-caused cell death. Sequentially, OGD specifically decreased antiapoptotic Bcl-2 mRNA and protein levels in neuro-2a cells. A search by a bioinformatic approach revealed that miR-210-specific binding elements exist in the 3'-untranslated region of Bcl-2 mRNA. Application of miR-210 antisenses simultaneously alleviated OGD-involved inhibition of Bcl-2 mRNA expression. In comparison, overexpression of miR-210 synergistically diminished OGD-caused inhibition of Bcl-2 mRNA expression and consequently induced greater cellular insults. Taken together, this study shows that OGD can induce miR-210 expression through activating HIF-1α. And miR-210 can mediate hypoxia-induced neural apoptosis by targeting Bcl-2.

Effect of hypoxia on expression of selected proteins involved in regulation of apoptotic activity in striatum of newborn piglets

The levels of selected neuroregulatory proteins that inhibit or promote apoptotic cell death were measured in the striatum of piglets subjected to precisely controlled 1 h hypoxic insult followed by 0, 2 and 4 h recovery and compared to sham operated animals. The anti-apoptotic proteins: there were increases in Survivin at 0 (157%, P = 0.031) and 4 h (171%, P = 0.033), in Bcl-XL at 0 (138%, P = 0.028) and 4 h (143%, P = 0.007), in VEGF at 4 h (185%, P = 0.019) and Hsp27 at 2 h (144%, P = 0.05) and 4 h (143%, P = 0.05). The pro-apoptotic proteins: caspases-1 and 7 increased at 4 h (135%, P = 0.05) and (129%, P = 0.038), respectively. Bim increased after 4 h (115%, P = 0.028), Apoptosis Inducing Factor after 2 h (127%, P = 0.048) and Calpain after 4 h (143% of control, P = 0.04). Hypoxia causes increase in levels of both anti- and pro-apoptotic proteins. Their relative activity determines the outcome in terms of cell damage and neuronal deficit.