Brain oxygen and metabolism is dependent on the rate of low-flow cardiopulmonary bypass following circulatory arrest in newborn piglets

Early Impairment of Cerebral Bioenergetics After Cardiopulmonary Bypass in Neonatal Swine

Objectives: We previously demonstrated cerebral mitochondrial dysfunction in neonatal swine immediately following a period of full-flow cardiopulmonary bypass (CPB). The extent to which this dysfunction persists in the postoperative period and its correlation with other markers of cerebral bioenergetic failure and injury is unknown. We utilized a neonatal swine model to investigate the early evolution of mitochondrial function and cerebral bioenergetic failure after CPB. Methods: Twenty piglets (mean weight 4.4 ± 0.5 kg) underwent 3 h of CPB at 34 °C via cervical cannulation and were followed for 8, 12, 18, or 24 h (n = 5 per group). Markers of brain tissue damage (glycerol) and bioenergetic dysfunction (lactate to pyruvate ratio) were continuously measured in cerebral microdialysate samples. Control animals (n = 3, mean weight 4.1 ± 1.2 kg) did not undergo cannulation or CPB. Brain tissue was extracted immediately after euthanasia to obtain ex-vivo cortical mitochondrial respiration and frequency of cortical microglial nodules (indicative of cerebral microinfarctions) via neuropathology. Results: Both the lactate to pyruvate ratio (P < .0001) and glycerol levels (P = .01) increased in cerebral microdialysate within 8 h after CPB. At 24 h post-CPB, cortical mitochondrial respiration was significantly decreased compared with controls (P = .046). The presence of microglial nodules increased throughout the study period (24 h) (P = .01, R2 = 0.9). Conclusion: CPB results in impaired cerebral bioenergetics that persist for at least 24 h. During this period of bioenergetic impairment, there may be increased susceptibility to secondary injury related to alterations in metabolic delivery or demand, such as hypoglycemia, seizures, and decreased cerebral blood flow.

Impact of G-CSF on expressions of Egr-1 and VEGF in acute ischemic cerebral injury

The aim of the present study was to investigate the protective effect of granulocyte colony-stimulating factor (G-CSF) on acute ischemic cerebral injury, and its mechanism through the impact of G-CSF on early growth response-1 (Egr-1) and vascular endothelial growth factor (VEGF) expressions. Male Sprague-Dawley (SD) rats were divided them into three groups, i.e., the sham, model and G-CSF groups to measure the effect of G-CSF on the volume of cerebral infarction and level of lactate dehydrogenase (LDH) in rats. Hematoxylin and eosin (H&E) staining method was performed for histopathological examination. Reverse transcription-polymerase chain reaction (RT-PCR) and western blot analysis were used to detect the mRNA and protein expressions of Egr-1 and VEGF in different groups. Furthermore, Statistical Product and Service Solutions (SPSS) 17.0 software was applied to detect the differences in the expression of Egr-1 and VEGF between the two groups. Compared with the sham group, we found that the volume of cerebral infarction and LDH content in the model group were significantly elevated. By contrast, in the model group, those indicators in the G-CSF group were obviously decreased. H&E staining results also showed that G-CSF could decrease the necrotic area in cerebral infarction and the incidence of inflammation, and sustain the integrity of the molecular structure. Immunofluorescence staining results revealed that the protein expressions of Egr-1 and VEGF in the model group were all significantly decreased, while those in the G-CSF group were remarkably elevated. RT-PCR and western blot analysis revealed that the mRNA and protein expressions of Egr-1 and VEGF in the model group were decreased obviously, but those in the G-CSF group were elevated significantly, and the differences between the two groups showed statistical significance (P<0.05). G-CSF manifests a significant protective effect on the acute ischemic cerebral injury, which may be realized through its effect on the expressions of Egr-1 and VEGF.

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.

Effect of granulocyte-colony stimulating factor on expression of selected proteins involved in regulation of apoptosis in the brain of newborn piglets after cardiopulmonary bypass and deep hypothermic circulatory arrest

OBJECTIVE

The study objective was to investigate the effect of granulocyte-colony stimulating factor on the expression of proteins that regulate apoptosis in newborn piglet brain after cardiopulmonary bypass and deep hypothermic circulatory arrest.

METHODS

The newborn piglets were assigned to 3 groups: (1) deep hypothermic circulatory arrest (30 minutes of deep hypothermic circulatory arrest, 1 hour of low-flow cardiopulmonary bypass); (2) deep hypothermic circulatory arrest with prior injection of granulocyte-colony stimulating factor (17 μg/kg 2 hours before cardiopulmonary bypass); and (3) sham-operated. After 2 hours of post-bypass recovery, the frontal cortex, striatum, and hippocampus were dissected. The expression of proteins was measured by gel electrophoresis or protein arrays. Data are presented in arbitrary units. Statistical analysis was performed using 1-way analysis of variance.

RESULTS

In the frontal cortex, only Fas ligand expression was significantly lower in the granulocyte-colony stimulating factor group when compared with the deep hypothermic circulatory arrest group. In the hippocampus, granulocyte-colony stimulating factor increased Bcl-2 (54.3 ± 6.4 vs 32.3 ± 2.2, P = .001) and serine/threonine-specific protein kinase (141.4 ± 19 vs 95.9 ± 21.1, P = .047) when compared with deep hypothermic circulatory arrest group. Caspase-3, Bax, Fas, Fas ligand, death receptor 6, and Janus protein tyrosine kinase 2 levels were unchanged. The Bcl-2/Bax ratio was 0.33 for deep hypothermic circulatory arrest group and 0.93 for the granulocyte-colony stimulating factor group (P = .02). In the striatum, when compared with the deep hypothermic circulatory arrest group, the granulocyte-colony stimulating factor group had higher levels of Bcl-2 (50.3 ± 7.4 vs 31.8 ± 3.8, P = .01), serine/threonine-specific protein kinase (132.7 ± 12.3 vs 14 ± 1.34, P = 2.3 × 10(6)), and Janus protein tyrosine kinase 2 (126 ± 17.4 vs 77.9 ± 13.6, P = .011), and lower levels of caspase-3 (12.8 ± 5.0 vs 32.2 ± 11.5, P = .033), Fas (390 ± 31 vs 581 ± 74, P = .038), Fas ligand (20.5 ± 11.5 vs 57.8 ± 15.6, P = .04), and death receptor 6 (57.4 ± 4.4 vs 108.8 ± 13.4, P = .007). The Bcl-2/Bax ratio was 0.25 for deep hypothermic circulatory arrest and 0.44 for the granulocyte-colony stimulating factor groups (P = .046).

CONCLUSIONS

In the piglet model of hypoxic brain injury, granulocyte-colony stimulating factor decreases proapoptotic signaling, particularly in the striatum.

Cerebral metabolism during deep hypothermic circulatory arrest vs moderate hypothermic selective cerebral perfusion in a piglet model: a microdialysis study

BACKGROUND

Few data exist regarding antegrade selective cerebral perfusion (ASCP) and its application in newborn and juvenile patients. Clinical data suggest ASCP alone to be superior to deep hypothermic circulatory arrest (DHCA); however, the effects of moderate hypothermia during ASCP on cerebral metabolism in this patient population are still unclear.

METHODS

After obtaining the approval from animal investigation committee, 16 piglets were randomly assigned to circulatory arrest combined with either ASCP at 27 degrees C or DHCA at 18 degrees C for 90 min. Cerebral oxygen extraction fraction (COEF) from blood as well as cerebral tissue glucose, glycerol, lactate, pyruvate, and the lactate/pyruvate ratio (L/P ratio) by microdialysis were obtained repeatedly.

RESULTS

COEF was lower during cooling and rewarming, respectively, in the DHCA18 group compared to the ASCP27 group (30 +/- 8 vs 56 +/- 13% and 35 +/- 6 vs 58 +/- 7%, respectively). Glucose decreased in both the DHCA18 and ASCP27 groups during the course of cardiopulmonary bypass (CPB), but were higher in the ASCP27 group during ASCP, compared to the DHCA18 group during circulatory arrest (0.7 +/- 0.1 vs 0.2 +/- 0.1 mm.l(-1), P < 0.05). Pyruvate was higher (ASCP27 vs DHCA18: 53 +/- 17 vs 6 +/- 2 microm.l(-1), P < 0.05), and the L/P ratio increased during circulatory arrest in the DHCA18 group, compared to the selective perfusion phase of the ASCP27 group (DHCA18 vs ASCP27: 1891 +/- 1020 vs 70 +/- 28, P < 0.01).

CONCLUSIONS

In this piglet model, both cerebral oxygenation and microdialysis findings suggested a depletion of cerebral energy stores during circulatory arrest in the DHCA18 group, compared to selective cerebral perfusion combined with circulatory arrest in the ASCP27 group.

The effect of hypothermia on neuronal viability following cardiopulmonary bypass and circulatory arrest in newborn piglets

OBJECTIVE

To determine the effect of recovery with mild hypothermia after cardiopulmonary bypass (CPB) and deep hypothermic circulatory arrest (DHCA) on the activity of selected key proteins involved in initiation (Bax, Caspase-3) or inhibition of apoptotic injury (Bcl-2, increased ratio Bcl-2/Bax) in the brain of newborn piglets.

METHODS

The piglets were placed on CPB, cooled with pH-stat management to 18 degrees C, subjected to 30 min of DHCA followed by 1h of low flow at 20 ml/kg/min, rewarmed to 37 degrees C (normothermia) or to 33 degrees C (hypothermia), separated from CPB, and monitored for 6h. Expression of above proteins was measured in striatum, hippocampus and frontal cortex by Western blots. The results are mean for six experiments+/-SEM.

RESULTS

There were no significant differences in Bcl-2 level between normothermic and hypothermic groups. The Bax levels in normothermic group in cortex, hippocampus and striatum were 94+/-9, 136+/-22 and 125+/-34 and decreased in the hypothermic group to 59+/-17 (p=0.028), 70+/-6 (p=0.002) and 48+/-8 (p=0.01). In cortex, hippocampus and striatum Bcl-2/Bax ratio increased from 1.23, 0.79 and 0.88 in normothermia to 1.96, 1.28 and 2.92 in hypothermia. Expression of Caspase-3 was 245+/-39, 202+/-74 and 244+/-31 in cortex, hippocampus and striatum in the normothermic group and this decreased to 146+/-24 (p=0.018), 44+/-16 (p=7 x 10(-7)) and 81+/-16 (p=0.01) in the hypothermic group.

CONCLUSION

In neonatal piglet model of cardiopulmonary bypass with circulatory arrest, mild hypothermia during post bypass recovery provides significant protection from cellular apoptosis, as indicated by lower expression of Bax and Caspase-3 and an increased Bcl-2/Bax ratio. The biggest protection was observed in striatum probably by decreasing of neurotoxicity of striatal dopamine.