Immediate-early gene expression in ovine brain after cardiopulmonary bypass and hypothermic circulatory arrest

Therapeutic hypothermia in the intensive cardiac care unit

Therapeutic hypothermia has demonstrated to improve both survival and neurological outcome in patients who experienced an out-of-hospital cardiac arrest. Nevertheless, many aspects of its clinical application are still controversial. Current guidelines recommend to cool patients who survive a cardiac arrest due to either ventricular fibrillation or ventricular tachycardia, whereas the beneficial effect of lowering body temperature in nonshockable rhythms is still questionable due to the lack of randomized controlled trial involving this subgroup of patients. Although therapeutic hypothermia is often begun before hospital arrival, the optimal time to start cooling is still a matter of debate. Furthermore, different methods are available to low body temperature, but no direct comparisons are available to establish which device performs better than others, and a combination of external and endovascular cooling is usually preferred. The present review is aimed at summarizing the available evidence supporting the use in clinical practice of mild hypothermia in comatose survivors from cardiac arrest and at evaluating its adverse events and their treatment.

Therapeutic hypothermia after cardiopulmonary resuscitation

Full cerebral recovery after cardiopulmonary resuscitation is still a rare event. Unfortunately, up to now, no specific and outcome-improving therapy was available after such events. From several cases it is known that low body and brain temperature during a cardiocirculatory arrest improves the neurological outcome following these events. As it is not possible in acute events to induce hypothermia beforehand, whether cooling after the insult could also be protective was evaluated. After animal studies in the 1990s and first clinical pilot trials of mild therapeutic and induced hypothermia, two randomized trials of hypothermic therapy after successful resuscitation after cardiac arrest were conducted. These studies demonstrated that hypothermia after cardiac arrest could improve neurological outcome as well as overall mortality.

The influence of deep hypothermic global brain ischemia on EEG in a new rat model

OBJECTIVES

Neurological complications following deep hypothermic circulatory arrest (DHCA) occur between t 4% ≈ 25%. However, the cerebral injury mechanisms are still not well understood due to a lack of a practical and simple animal model. We aimed to establish a rodent deep hypothermic global brain ischemia (DHGBI) model, which can be used to elucidate these mechanisms in future studies.

DESIGN

30 Sprague-Dawley rats were divided randomly into three groups: the carotid occlusion DHGBI group, the internal carotid shunt DHGBI group, and the sham operation group. We validated the model in terms of electroencephalogram (EEG) and regional cerebral blood flow (rCBF). All rats were sacrificed for analysis of brain moisture capacity after 24 hours.

RESULTS

In the internal carotid shunt DHGBI group the EEG activity was suppressed to "flat-line" and the relative power of the α and θ frequency bands was decreased (p < 0.05). However, in the carotid occlusion DHGBI group we only observed the relative power of the α frequency band depressed (p < 0.05). The rCBF was significantly decreased in all groups. In the internal carotid shunt DHGBI group the rCBF was significantly reduced to 4.27 ± 2.75%, and was lower than the other two groups (p < 0.05). The result of brain moisture capacity was consistent with the EEG and rCBF observations.

CONCLUSIONS

The current study presents a novel cerebral recovery model of DHCA in the rat. This experimental model may be suitable to further elucidate the mechanisms associated with adverse cerebral outcomes after DHCA and to investigate potential neuroprotective strategies.

The significance of protein S-100B testing in cardiac arrest patients

Cardiac arrest often represents the first expression of an underlying cardiac disease. Despite advances in neurocritical care, the neurological assessment of cardiac arrest patients relies on clinical, instrumental and biochemical parameters. The clinical significance of S-100 calcium binding protein B (S-100B) has substantially increased throughout several areas of clinical neuroscience, but reliable evidences attest it can be used as a reliable and early predictor of poor physiological and cognitive neurological outcomes after cardiac arrest.

Animal models of cardiopulmonary bypass: development, applications, and impact

Neurologic and neurocognitive complications after cardiac surgery have been reported repeatedly. To better understand its etiology and design protective strategies, small animal models have been developed. This study describes the development of a survival rat cardiopulmonary bypass (CPB) model, along with the introduction of an appropriately sized oxygenator. This model led the way for even more complicated models with CPB, facilitating full cardiac arrest with anterograde cardioplegia administration, air embolization, and deep hypothermic circulatory arrest. In addition, the results of several of those rat CPB studies are summarized and their preclinical relevance is pointed out.

Low hematocrit worsens cerebral injury after prolonged hypothermic circulatory arrest in rats

PURPOSE

This study tests the hypothesis that low hematocrit (Hct) worsens cerebral injury after prolonged hypothermic circulatory arrest (HCA) in rats, and the mechanism involves variable expression of the genes C-Fos, Bcl-2 and Bax.

METHODS

A rat HCA model was developed, and 40 animals were randomly assigned to four groups: Sham (sham) group, or Hct groups of Hct 10%, Hct 20% and Hct 30%. After 90 min of HCA at 18 degrees C, physiologic variables were recorded and brain morphological changes were evaluated with light and electron microscopy. Expressions of C-Fos, Bcl-2, Bax in various brain areas were measured by the reverse transcriptase polymerase chain reaction and standard immunohistochemistry techniques.

RESULTS

The number of injured neurons in the hippocampus CA1 and parietal cortex in the Hct 10% group (CA1: 11.44 +/- 2.52; cortex: 13.65 +/- 2.31) exceeded the mean number of injured neurons in the Hct 20% group (CA1: 8.29 +/- 1.31; cortex: 10.68 +/- 1.24; P < 0.05) and the Hct 30% group. Mean mitochondrial injury scores were greatest at lower Hct levels, while the expression of C-Fos and Bax were highest in the Hct 10% group and lowest in the Hct30% group (P < 0.05). In contrast, the expression of the Bcl-2 mRNA was greatest in the Hct 30% group (P < 0.05).

CONCLUSION

Low Hct worsens cerebral injury after prolonged HCA and CPB in rats, which may relate in part to the variable expression of the genes C-Fos, Bcl-2 and Bax.

Antioxidant enzyme gene transfer for ischemic diseases

The balance of redox is pivotal for normal function and integrity of tissues. Ischemic insults occur as results of a variety of conditions, leading to an accumulation of reactive oxygen species (ROS) and an imbalanced redox status in the tissues. The oxidant stress may activate signaling mechanisms provoking more toxic events, and eventually cause tissue damage. Therefore, treatments with antioxidants, free radical scavengers and their mimetics, as well as gene transfer approaches to overexpress antioxidant genes represent potential therapeutic options to correct the redox imbalance. Among them, antioxidant gene transfer may enhance the production of antioxidant scavengers, and has been employed to experimentally prevent or treat ischemic injury in cardiovascular, pulmonary, hepatic, intestinal, central nervous or other systems in animal models. With improvements in vector systems and delivery approaches, innovative antioxidant gene therapy has conferred better outcomes for myocardial infarction, reduced restenosis after coronary angioplasty, improved the quality and function of liver grafts, as well as outcome of intestinal and cerebral ischemic attacks. However, it is crucial to be mindful that like other therapeutic armentarium, the efficacy of antioxidant gene transfer requires extensive preclinical investigation before it can be used in patients, and that it may have unanticipated short- or long-term adverse effects. Thus, it is critical to balance between the therapeutic benefits and potential risks, to develop disease-specific antioxidant gene transfer strategies, to deliver the therapy with an optimal time window and in a safe manner. This review attempts to provide the rationale, the most effective approaches and the potential hurdles of available antioxidant gene transfer approaches for ischemic injury in various organs, as well as the possible directions of future preclinical and clinical investigations of this highly promising therapeutic modality.

Brain function after resuscitation from cardiac arrest

PURPOSE OF REVIEW

In industrial countries the incidence of cardiac arrest is still increasing. Almost 80% of cardiac arrest survivors remains in coma for varying lengths of time and full cerebral recovery is still a rare event. After successful cardiopulmonary resuscitation, cerebral recirculation disturbances and complex metabolic postreflow derangements lead to death of vulnerable neurons with further deterioration of cerebral outcome. This article discusses recent research efforts on the pathophysiology of brain injury caused by cardiac arrest and reviews the beneficial effect of therapeutic hypothermia on neurologic outcome along with the recent approach to prognosticate long-term outcome by electrophysiologic techniques and molecular markers of brain injury.

RECENT FINDINGS

Recent experimental studies have brought new insights to the pathophysiology of secondary postischemic anoxic encephalopathy demonstrating a time-dependent cerebral oxidative injury, increased neuronal expression, and activation of apoptosis-inducing death receptors and altered gene expression with long-term changes in the molecular phenotype of neurons. Recently, nuclear MR imaging and MR spectroscopic studies assessing cerebral circulatory recovery demonstrated the precise time course of cerebral reperfusion after cardiac arrest. Therapeutic hypothermia has been shown to improve brain function after resuscitation from cardiac arrest and has been introduced recently as beneficial therapy in ventricular fibrillation cardiac arrest.

SUMMARY

Electrophysiologic techniques and molecular markers of brain injury allow the accurate assessment and prognostication of long-term outcome in cardiac arrest survivors. In particular, somatosensory evoked potentials have been identified as the method with the highest prognostic reliability. A recent systematic review of 18 studies analyzed the predictive ability of somatosensory evoked potentials performed early after onset of coma and found that absence of cortical somatosensory evoked potentials identify patients not returning from anoxic coma with a specificity of 100%.

Increased Transcription Factor Expression and Permeability of the Blood Brain Barrier Associated With Cardiopulmonary Bypass in Lambs

BACKGROUND

The pathophysiology of neurocognitive dysfunction and developmental delay after cardiopulmonary bypass (CPB) in infants is not known. It is known that head trauma, stroke, and seizures cause dysfunction of the blood brain barrier (BBB) that is associated with increased inducible transcription factor gene expression in the cells of the barrier. The purpose of this study was to determine the effects of CPB and hypothermic circulatory arrest on expression of the transcription factor FOS and the function of the BBB in an infant animal model.

METHODS

Infant lambs (n = 36; 10-12 days) were exposed to 0, 15, 30, 60, or 120 minutes of normothermic (38 degrees C) CPB or 2 hours of hypothermic circulatory arrest at 16 degrees C. After terminating bypass 15 animals had their brains perfusion-fixed and removed for immunohistochemical analysis of expression of the transcription factor FOS. The other animals were perfused with fluorescent albumin to visualize the brain microvasculature. Brain sections were analyzed with a laser scanning confocal microscope.

RESULTS

Control animals (n = 6, sham operated and cannulated) exhibited normal vasculature with negligible leakage and no FOS protein expression in neurons or endothelial cells anywhere in the brain. Significant FOS expression in barrier-associated structures including the blood vessels, choroid plexus, and ependyma but not neurons occurred at all times on bypass. CPB caused leakage of fluorescent albumin from blood vessels in all animals. Two hours of normothermic CPB (n = 4) caused significant (p < 0.01) leakage in the cerebellum, cortex, hippocampus, and corpus callosum. Animals exposed to circulatory arrest experienced severe leakage throughout the brain (p < 0.001) and FOS expression in all cells.

CONCLUSIONS

These experiments indicate that the BBB is dysfunctional after all time points on normothermic CPB, BBB dysfunction is worsened by hypothermic circulatory arrest, and BBB dysfunction is associated with intense molecular activity within the barrier-forming cells. Dysfunction of the BBB may contribute to neurologic complications after heart surgery.

Differential expression of neuronal fos protein after cold water drowning and controlled rewarming

BACKGROUND

Cardiopulmonary bypass has often been applied to revive victims of cold water drowning. The success of resuscitative efforts in patients who have sustained severe hypothermia is largely determined by neurologic outcomes. Measurement of Fos, the protein product of the immediate-early gene c-fos, is a marker of cerebral injury.

STUDY DESIGN

Twenty-eight infant lambs were sedated and ventilated. Group 1 lambs were immersed in a cold water bath for 2 hours (17.3 +/- 2.7 degrees C). Group 2 lambs were placed on normothermic cardiopulmonary bypass for 2 hours (37.7 degrees +/- 0.7 degrees C). Group 3 lambs were immersed in a cold water bath for 2 hours (17.6 degrees +/- 2.4 degrees C), and then rewarmed for a period of 2 hours on cardiopulmonary bypass (37.0 degrees +/- 0.6 degrees C). The lambs were euthanized and immunohistochemical analysis for neuronal Fos was performed.

RESULTS

There was significant induction of Fos-labeled nuclear profiles (cells/1130 microm(2)) in group 3 in the hippocampal regions and dentate gyrus compared with groups 1 and 2 (p < 0.001).

CONCLUSION

Isolated exposure to either hypothermia or cardiopulmonary bypass results in minimal expression of neuronal Fos; the significant induction of Fos in the group 3 animals may represent an ischemic-reperfusion phenomenon. Modifications of rewarming techniques that minimize Fos expression may improve neurologic outcomes in victims of cold water drowning.

Differential cerebral gene expression during cardiopulmonary bypass in the rat: evidence for apoptosis?

Cardiopulmonary bypass (CPB) is associated with a spectrum of cerebral injuries. The molecular changes in the brain that might contribute to these injuries are not clearly known. We sought to determine whether the expression of apoptotic genes is increased after CPB in the rat. Rats (n = 7) were subjected to 90 min of normothermic CPB. A group of sham-operated rats (n = 7) served as non-CPB controls. After a 3-h post-CPB period of recovery, their brains were removed, homogenized, and processed for messenger RNA (mRNA) extraction. By using a ribonuclease protection assay, the ratios of both pro- and antiapoptotic mRNA (bcl-x, bcl-2, bax, caspase 2, and caspase 3) to the housekeeping glyceraldehyde phosphate dehydrogenase (GAPDH) gene were determined. Additionally, Western immunoblotting was performed to detect the presence of activated caspase 3, a protein central in the apoptotic process. Compared with the non-CPB controls, the CPB group had significantly increased levels of apoptotic/GAPDH mRNA ratios (bcl-x, 0.414 +/- 0.152 CPB versus 0.251 +/- 0.051 non-CPB, P = 0.048; caspase 2, 0.030 +/- 0.014 CPB versus 0.018 +/- 0.005 non-CPB, P = 0.048; bax, 0.106 +/- 0.035 CPB versus 0.066 +/- 0.009 non-CPB, P = 0.009; bcl-2, 0.011 +/- 0.006 CPB versus 0.006 +/- 0.002 non-CPB, P = 0.035). However, no activated caspase 3 protein was detected in either group. Elucidating the molecular biological sequelae of CPB may aid in the understanding of the pathophysiology of cardiac surgery-associated cerebral injury and, in doing so, may be useful in identifying potential therapeutic targets for pharmacologic neuroprotection.

IMPLICATIONS

Cardiopulmonary bypass (CPB) appears to induce transcription of pro- and antiapoptotic genes in the rat brain, but caspase-mediated apoptosis itself does not appear to be activated. Elucidating the molecular biological sequelae of CPB may aid in the understanding of the pathophysiology of cardiac surgery-associated cerebral injury and, in doing so, may be useful in identifying potential therapeutic targets for pharmacologic neuroprotection.

Differential cerebral gene expression during cardiopulmonary bypass in the rat: evidence for apoptosis?

Cardiopulmonary bypass (CPB) is associated with a spectrum of cerebral injuries. The molecular changes in the brain that might contribute to these injuries are not clearly known. We sought to determine whether the expression of apoptotic genes is increased after CPB in the rat. Rats (n = 7) were subjected to 90 min of normothermic CPB. A group of sham-operated rats (n = 7) served as non-CPB controls. After a 3-h post-CPB period of recovery, their brains were removed, homogenized, and processed for messenger RNA (mRNA) extraction. By using a ribonuclease protection assay, the ratios of both pro- and antiapoptotic mRNA (bcl-x, bcl-2, bax, caspase 2, and caspase 3) to the housekeeping glyceraldehyde phosphate dehydrogenase (GAPDH) gene were determined. Additionally, Western immunoblotting was performed to detect the presence of activated caspase 3, a protein central in the apoptotic process. Compared with the non-CPB controls, the CPB group had significantly increased levels of apoptotic/GAPDH mRNA ratios (bcl-x, 0.414 +/- 0.152 CPB versus 0.251 +/- 0.051 non-CPB, P = 0.048; caspase 2, 0.030 +/- 0.014 CPB versus 0.018 +/- 0.005 non-CPB, P = 0.048; bax, 0.106 +/- 0.035 CPB versus 0.066 +/- 0.009 non-CPB, P = 0.009; bcl-2, 0.011 +/- 0.006 CPB versus 0.006 +/- 0.002 non-CPB, P = 0.035). However, no activated caspase 3 protein was detected in either group. Elucidating the molecular biological sequelae of CPB may aid in the understanding of the pathophysiology of cardiac surgery-associated cerebral injury and, in doing so, may be useful in identifying potential therapeutic targets for pharmacologic neuroprotection.

IMPLICATIONS

Cardiopulmonary bypass (CPB) appears to induce transcription of pro- and antiapoptotic genes in the rat brain, but caspase-mediated apoptosis itself does not appear to be activated. Elucidating the molecular biological sequelae of CPB may aid in the understanding of the pathophysiology of cardiac surgery-associated cerebral injury and, in doing so, may be useful in identifying potential therapeutic targets for pharmacologic neuroprotection.

Neurological injury during cardiopulmonary bypass in the rat

Cerebral injury is a well-known complication of cardiac surgery. Investigations of both injury mechanisms and neuroprotective strategies have partially been limited by the lack of an adequate preclinical model of small animal cardiopulmonary bypass (CPB). We sought to determine if neurological injury could be demonstrated in a recovery model of complete CPB in the rat. Rats (n = 5) underwent 45 min of normothermic CPB followed by 24 h of recovery. Compared to sham-operated rats (n = 5), the CPB group showed a worse neurological outcome score (median, 25-75th percentile) compared to controls (5, 4-7 vs 9, 8-9, p = 0.016). This rat model of CPB may allow for the study of CPB-associated neurological injury.

Ischemic preconditioning protects against paraplegia after transient aortic occlusion in the rat

BACKGROUND

Paraplegia can result from operations requiring transient occlusion of the thoracic aorta. A rat model of paraplegia with the characteristics of delayed paraplegia and transient ischemic dysfunction was developed to determine whether ischemic preconditioning (IPC) improved neurologic outcome.

METHODS

Rats underwent balloon occlusion of the upper descending thoracic aorta. One group (2 minute IPC, n = 19) underwent 2 minutes of IPC and a second group (5 minute IPC, n = 19) had 5 minutes of IPC 48 hours before 10 minutes of occlusion. The control group (n = 31) had no IPC prior to 10 minutes of occlusion.

RESULTS

Paraplegia occurred in 68% of the control animals (21 of 31 paraplegic: 6 delayed and 15 immediate paraplegia). Both the 2-minute IPC and 5-minute IPC groups had a decreased incidence of paraplegia when compared to controls (32%, p = 0.011 and 26%, p = 0.009, respectively).

CONCLUSIONS

A rat model of spinal cord ischemia demonstrating both delayed paraplegia and transient ischemic dysfunction was characterized. Both 2-minute and 5-minute periods of IPC were found to protect against paraplegia.

Immediate-early gene expression in ovine brain after hypothermic circulatory arrest: effects of aptiganel

BACKGROUND

Altered gene expression occurs in the brain after global ischemia. We have developed a model to examine the effects of cardiopulmonary bypass and hypothermic circulatory arrest (HCA) on the induction of the immediate-early gene c-fos in the brains of neonatal lambs. We then tested the effects of the noncompetitive N-methyl-D-aspartate antagonist, aptiganel hydrochloride (Cerestat), on c-fos expression and neuronal injury.

METHODS

Neonatal lambs (weight, 4 to 6 kg) anesthetized with isoflurane were supported by cardiopulmonary bypass, subjected to 90 or 120 minutes of HCA at 15 degrees C, and rewarmed on bypass to 38 degrees C. One hour after cardiopulmonary bypass was terminated, the brains were perfusion fixed and removed for in situ hybridization and immunohistochemical analysis. Some animals survived 3 days before their brains were removed to examine for neuronal necrosis. One group of lambs (n = 20) received aptiganel (2.5 mg/kg). A second group (n = 25) received saline vehicle only.

RESULTS

Increasing duration of HCA induced a corresponding increase in c-fos messenger RNA expression throughout the hippocampal formation and cortex. However, Fos protein synthesis peaked after 90 minutes of HCA and decreased significantly (p < 0.01) after 120 minutes of HCA. Aptiganel administration caused a significant decrease in (p < 0.001) c-fos messenger RNA expression and Fos protein synthesis after 90 minutes of HCA and preserved Fos protein synthesis after 120 minutes of HCA. Neuronal necrosis was observed in the brains of vehicle-treated lambs after 120 minutes of HCA but was significantly decreased (p < 0.05) in the lambs given aptiganel.

CONCLUSIONS

These experiments indicate that the transcriptional processes of immediate-early genes remain intact, whereas translational processes are impaired after prolonged HCA. The inability to synthesize Fos proteins after 120 minutes of HCA was associated with neuronal degeneration. Aptiganel preserved translational processes and caused a significant improvement in the neurologic outcome.