Cyclosporine A as a potential neuroprotective agent: a study of prolonged hypothermic circulatory arrest in a chronic porcine model

Evaluation of cyclosporine a as a cardio- and neuroprotective agent after cardiopulmonary resuscitation in a rat model

The immunosuppressant drug cyclosporine A (CsA) is a direct inhibitor of the mitochondrial permeability transition pore, which is the common end point of many pathways of ischemic preconditioning and postconditioning. We studied the neuroprotective and cardioprotective effect of CsA after cardiac arrest (CA) in a rat model of cardiopulmonary resuscitation. After institutional approval by the Governmental Animal Care Committee, 83 rats were subjected to 6 min of CA and were randomly and investigator-blinded allocated either to placebo (n = 15) or interventional group (n = 15; 10-mg/kg body weight CsA intravenously) after restoration of spontaneous circulation (ROSC). Before CA (baseline) as well as 1 h and 3 h after ROSC, continuous measurement of stroke volume, left ventricular ejection fraction, preload adjusted maximum power, and end diastolic volume was performed using a conductance catheter. One day, 3 days, and 7 days after ROSC, neurological outcome was evaluated by a tape removal test. After 7 days of reperfusion, coronal brain sections were analyzed by counting Nissl-positive (i.e., viable) neurons and terminal deoxynucleotidyl transferase dUTP nick end labeling positive (i.e., apoptotic) cells. Animals treated with CsA had a higher stroke volume (96 [93; 107] μL vs. 78 [73; 94] μL; P = 0.02), higher ejection fraction (58% [51%; 63%] vs. 42% [35%; 51%]; P = 0.002), and higher preload adjusted maximum power (4.8 [3.9; 6.1] vs. 2.3 [2.0; 2.6] mW/μL; P < 0.001). End diastolic volume remained stable in the CsA group 3 h after ROSC in comparison to baseline (160 [143; 181] μL vs. 157 [148; 192] μL; P = 0.56), whereas it increased in the placebo group (169 [153; 221] μL vs. 156 [138; 166] μL, P = 0.05). More neurons survived after administration of CsA (2.5 [1.6; 4.9] vs. 0.7 [0.4; 1.4]; P = 0.005). Compared to placebo-treated animals, the time in the tape removal test 7 days after ROSC was reduced by half in the CsA group without reaching statistical significance (26 [22; 51] vs. placebo 53 [38; 56] s; P = 0.13). Cyclosporine A treatment neither affected the number of terminal deoxynucleotidyl transferase dUTP nick end labeling-positive cells nor the survival rate. Pharmacological postconditioning with CsA after successful cardiopulmonary resuscitation attenuates myocardial dysfunction and reduces neuronal damage.

Neuroprotective strategies and neuroprognostication after cardiac arrest

Neurocognitive disturbances are common among survivors of cardiac arrest (CA). Although initial management of CA, including bystander cardiopulmonary resuscitation, optimal chest compression, and early defibrillation, has been implemented continuously over the last years, few therapeutic interventions are available to minimize or attenuate the extent of brain injury occurring after the return of spontaneous circulation. In this review, we discuss several promising drugs that could provide some potential benefits for neurological recovery after CA. Most of these drugs have been investigated exclusively in experimental CA models and only limited clinical data are available. Further research, which also considers combined neuroprotective strategies that target multiple pathways involved in the pathophysiology of postanoxic brain injury, is certainly needed to demonstrate the effectiveness of these interventions in this setting. Moreover, the evaluation of neurological prognosis of comatose patients after CA remains an important challenge that requires the accurate use of several tools. As most patients with CA are currently treated with targeted temperature management (TTM), combined with sedative drug therapy, especially during the hypothermic phase, the reliability of neurological examination in evaluating these patients is delayed to 72-96 h after admission. Thus, additional tests, including electrophysiological examinations, brain imaging and biomarkers, have been largely implemented to evaluate earlier the extent of brain damage in these patients.

Temperature dependence of cerebral blood flow for isolated regions of the brain during selective cerebral perfusion in pigs

BACKGROUND

Hypothermic circulatory arrest (HCA) and antegrade selective cerebral perfusion (ASCP) are utilized for cerebral protection during aortic surgery. However, no consensus exists regarding optimal ASCP-temperature showing a tendency toward higher values during the last years. This study investigates regional changes of cerebral blood flow (CBF) during ASCP at two temperatures.

METHODS

In this blinded study, 20 pigs (35 to 37 kg) were randomized to two groups. Animals were cooled to 10 minutes of HCA followed by 60 minutes of ASCP. Afterward the animals were perfused at 25 degrees C and 30 degrees C according to the study group. Fluorescent microspheres were injected at seven time points during the experiment to calculate total and regional CBF. Hemodynamics, cerebrovascular resistance (CVR) and cerebral metabolic rate of oxygen (CMRO(2)) were assessed. Tissue samples from the cortex, cerebellum, hippocampus, and pons were taken for microsphere count.

RESULTS

The CBF and CMRO(2) decreased significantly (p < 0.002) during cooling in both groups; it was significantly higher throughout ASCP in the 30 degrees C versus the 25 degrees C group (p = 0.0001). These findings were similar among all brain regions, certainly at different levels. The CBF increased significantly (p = 0.002) during the early period of ASCP for analyzed regions and decreased significantly (p = 0.034) below baseline after 60 minutes of ASCP, reaching critical levels in the hippocampus and neocortex. The hippocampus turned out to have the lowest CBF, while the pons showed the highest CBF. Thirty minutes and more ASCP provides less CBF compared with baseline values at both temperatures.

CONCLUSIONS

Antegrade selective cerebral perfusion improves CBF in all regions of the brain for a limited time. Our study characterizes the brain specific hierarchy of blood flow during ASCP. These dynamics are highly relevant for clinical strategies of perfusion.

Optimizing selective cerebral perfusion: deleterious effects of high perfusion pressures

OBJECTIVE

Selective cerebral perfusion is a proven adjunct to hypothermia for neuroprotection in complex aortic surgery. The ideal conditions for the provision of selective cerebral perfusion, however, including optimal perfusion pressure, remain unknown. We investigated the effects of various perfusion pressures during selective cerebral perfusion on cerebral physiology and outcome in a long-term porcine model.

METHODS

Thirty piglets (26.3 +/- 1.4 kg), cooled to 20 degrees C on cardiopulmonary bypass with alpha-stat pH management (mean hematocrit 23.6%), were randomly assigned to 90 minutes of selective cerebral perfusion at a pressure of 50 (group A), 70 (group B), or 90 (group C) mm Hg. With fluorescent microspheres and sagittal sinus sampling, cerebral blood flow and cerebral oxygen metabolism were assessed at baseline, after cooling, at two points during selective cerebral perfusion, and for 2 hours after cardiopulmonary bypass. Visual evoked potentials were monitored during recovery. Neurobehavioral scores were assessed blindly from standardized videotaped sessions for 7 postoperative days.

RESULTS

Cerebral blood flow during selective cerebral perfusion was significantly increased by higher-pressure perfusion (P = .04), although all groups sustained similar levels of cerebral oxygen metabolism during selective cerebral perfusion (P = .88). After the end of cardiopulmonary bypass, the cerebral oxygen metabolism increased to above baseline in all groups, with the highest levels seen in group C (P = .06). Intracranial pressure was significantly higher during selective cerebral perfusion in group C (P = .0002); visual evoked potentials did not differ among groups. Neurobehavioral scores were significantly better in group A (P = .0002).

CONCLUSION

Selective cerebral perfusion at 50 mm Hg provides neuroprotection superior to that at higher pressures. The increased cerebral blood flow with higher-pressure selective cerebral perfusion is associated with cerebral injury, reflected by high post-cardiopulmonary bypass cerebral oxygen metabolism and poorer neurobehavioral recovery.

Avoidance of hemodilution during selective cerebral perfusion enhances neurobehavioral outcome in a survival porcine model

INTRODUCTION

The ideal hematocrit (HCT) level during hypothermic selective cerebral perfusion (SCP)--to ensure adequate oxygen delivery without excessive perfusion--has not yet been determined.

METHODS

Twenty pigs (26.0+/-2.6 kg) were randomized to low or high HCT management. The cardiopulmonary bypass (CPB) circuit was primed with crystalloid in the low HCT group (21+/-1%), and with donor blood in the high HCT group (30+/-1%). Pigs were cooled to 20 degrees C and SCP was carried out for 90 min. During rewarming, whole blood was added in the low HCT group and crystalloid in the high HCT group to produce equivalent HCT levels by the end of the procedure. Using fluorescent microspheres and sagittal sinus sampling, cerebral blood flow (CBF) and oxygen metabolism (CMRO2) were assessed at baseline, after cooling, at two points during SCP (30 and 90 min), and at 15 min and 2 h post-CPB. In addition, a range of physiological and metabolic parameters, including intracranial pressure (ICP), were recorded throughout the procedure. The animals' behavior was videotaped and assessed blindly for 7 days postoperatively (maximum score=5).

RESULTS

HCT levels were equivalent at baseline, 2 h post-CPB, and at sacrifice, but significantly different (p<0.0001) during cooling and SCP. Mean arterial pressure, pH and pCO2, and CMRO2 were equivalent between groups throughout. ICP was similar in the two groups throughout cooling, SCP, and rewarming, but was significantly higher in the low HCT animals after the termination of CPB. CBF was similar at baseline, but thereafter markedly higher in the low HCT group. Neurobehavioral performance was significantly better in the high HCT animals (median score 3.5 vs 4.5 on day 3, and 4.5 vs 4.75 on day 7, p=0.003).

CONCLUSIONS

Higher HCT levels for SCP produced a significantly superior functional outcome, suggesting that the higher CBF with a lower HCT may be injurious, possibly because of an increased embolic load.

Perfusing the Cold Brain: Optimal Neuroprotection for Aortic Surgery

BACKGROUND

Selective cerebral perfusion (SCP) may enhance the neuroprotective benefits of hypothermia during aortic surgery. However, despite its widespread adoption, there is no consensus regarding optimal implementation of SCP. We used a survival porcine model to explore the physiologic characteristics and behavioral benefits of various protocols involving hypothermic circulatory arrest (HCA) and SCP.

METHODS

Thirty pigs (26.3 +/- 1.4 kg), cooled to 15 degrees C on cardiopulmonary bypass, using alpha-stat pH management (mean hematocrit 30%), were randomly allocated to differing brain protection strategies: 90 minutes of HCA (group A); 30 minutes of HCA, then 60 minutes of SCP (group B); or 90 minutes of SCP (group C). Using fluorescent microspheres and sagittal sinus sampling, cerebral blood flow (CBF [mL x 100g(-1) x min(-1)]) and cerebral metabolic rate for oxygen (CMRO2 [mL x 100g(-1) x min(-1)]) were assessed at baseline, after cooling, during SCP (where applicable), and for 2 hours after cardiopulmonary bypass. Neurobehavioral scores were assessed blindly from standardized videotaped sessions for 7 days postoperatively.

RESULTS

Cerebral blood flow was significantly higher (p = 0.0001) during SCP (60 and 90 minutes) if preceded by HCA. The CMRO2 was also significantly higher in group B versus group C (p = 0.016) at 60 minutes. The CMRO2 in all three groups rebounded promptly toward baseline after weaning from cardiopulmonary bypass. Postoperative neurobehavioral scores were significantly worse in group A.

CONCLUSIONS

Continuous SCP provides the best brain protection overall. However, an initial period of HCA does not seem to impair late outcome; perhaps the elevated CBF and CMRO2 observed reflect a beneficial cerebral response to a recoverable insult. Clearly, 90 minutes of HCA induces permanent brain injury, even in this carefully controlled setting.

Mitochondria as key components of the stress response

The exquisitely orchestrated adaptive response to stressors that challenge the homeostasis of the cell and organism involves important changes in mitochondrial function. A complex signaling network enables mitochondria to sense internal milieu or environmental changes and to adjust their bioenergetic, thermogenic, oxidative and/or apoptotic responses accordingly, aiming at re-establishment of homeostasis. Mitochondrial dysfunction is increasingly recognized as a key component in both acute and chronic allostatic states, although the extent of its role in the pathogenesis of such conditions remains controversial. Genetic and environmental factors that determine mitochondrial function might contribute to the significant variation of the stress response. Understanding the often reciprocal interplay between stress mediators and mitochondrial function is likely to help identify potential therapeutic targets for many stress and mitochondria-related pathologies.

Improvement of quality of life after surgery on the thoracic aorta: effect of antegrade cerebral perfusion and short duration of deep hypothermic circulatory arrest

BACKGROUND

We have recently demonstrated that the use of deep hypothermic circulatory arrest (DHCA) during surgery for acute type A aortic dissections or thoracic aortic aneurysms adversely affect mid-term quality of life (QoL). The aim of this study is to assess the impact of DHCA duration and the potential effects of antegrade cerebral perfusion (ACP) on mid-term QoL.

METHODS AND RESULTS

Between January 1994 and December 2002, 363 patients underwent surgery of the thoracic aorta with the use of DHCA at our institution. One hundred seventy-six (48.5%) presented with acute type A dissections and 187 (51.5%) presented with aortic aneurysms. ACP was used in 41 (11.3%) cases. All in-hospital data were assessed and a follow-up was performed in all survivors after 2.4+/-1.2 years. QoL was analyzed with the Short-Form 36 Health Survey Questionnaire (SF-36). In-hospital mortality was 8.6%. In comparison with patients having undergone DHCA <20 minutes, averaged QoL score was significantly decreased in patients with DHCA between 20 and 34 minutes (95.6+/-12.8 versus 81.9+/-15.7; P<0.01) and >35 minutes (61.8+/-18.3; P<0.01). Averaged QoL score was significantly better with the use of ACP, independently of the duration of DHCA.

CONCLUSIONS

DHCA duration >20 minutes, and especially >35 minutes, adversely affects mid-term QoL in patients undergoing surgery of the thoracic aorta. The use of ACP, however, improved averaged QoL score at each time period and allows DHCA to be extended up to 30 minutes, without impairment in mid-term QoL.

Use of a Maze to Detect Cognitive Dysfunction in a Porcine Model of Hypothermic Circulatory Arrest

BACKGROUND

Hypothermic circulatory arrest (HCA) can result in cognitive impairment not reflected by histopathology or gross neurologic observation. We tested the sensitivity of two multi-room maze tasks in detecting cerebral dysfunction after HCA in pigs.

METHODS

Twenty-seven pigs were studied, divided between two tasks. 13 underwent 90 minutes HCA at 20 degrees C and were trained from postoperative day (POD) 7; 14 were unoperated controls. The maze includes a holding area, 8 rooms, and a center hallway. One piece of apple is placed in each baited room on each of 10 days of learning evaluation. After a pig enters a room, doors to all other rooms close, and the pig must return to the holding area. In task 1, 6 of 8 rooms were baited, and each day's session ended when each baited room had been entered, or after 20 trials. In task 2, initially only the right- or left-sided rooms were baited. Pigs were evaluated each day until they entered 4 baited rooms, or for 15 trials; the process was then repeated, baiting the other side.

RESULTS

Intraoperative physiology and postoperative recovery showed no differences between task 1 or 2 pigs. Task 1 did not distinguish between control and HCA groups (p = 0.5), but task 2 revealed significantly (p = 0.04) better learning in controls.

CONCLUSIONS

The significantly poorer performance of pigs after HCA suggests that the reversal of baited rooms in task 2 provides the sensitivity to detect cognitive dysfunction. The maze is a promising tool to investigate in pigs the mild cerebral damage often seen after HCA.

Blockade of the extracellular signal-regulated kinase pathway by U0126 attenuates neuronal damage following circulatory arrest

OBJECTIVES

The extracellular signal-regulated kinase pathway of the mitogen-activated protein kinase signal transduction cascade has been implicated in the neuronal and endothelial dysfunction witnessed following cerebral ischemia-reperfusion injury. Extracellular signal-regulated kinase is activated by mitogen-activated protein kinase/extracellular signal-regulated kinase 1/2. We evaluated the ability of a mitogen-activated protein kinase/extracellular signal-regulated kinase 1/2-specific inhibitor (U0126) to block extracellular signal-regulated kinase activation and mitigate ischemic neuronal damage in a model of deep hypothermic circulatory arrest.

METHODS

Piglets underwent normal flow cardiopulmonary bypass (control, n = 4), deep hypothermic circulatory arrest (n = 6), and deep hypothermic circulatory arrest with U0126 (n = 5) at 20 degrees C for 60 minutes. The deep hypothermic circulatory arrest with U0126 group was given 200 microg/kg of U0126 45 minutes prior to initiation of bypass followed by 100 microg/kg at reperfusion. Following 24 hours of post-cardiopulmonary bypass recovery, brains were harvested. Eleven distinct cortical regions were evaluated for neuronal damage using hematoxylin and eosin staining. A section of ischemic cortex was further evaluated by immunohistochemistry with rabbit polyclonal antibody against phosphorylated extracellular signal-regulated kinase 1/2.

RESULTS

The deep hypothermic circulatory arrest and deep hypothermic circulatory arrest with U0126 groups displayed diffuse ischemic changes. However, the deep hypothermic circulatory arrest with U0126 group possessed significantly lower neuronal damage scores in the right frontal watershed zone of cerebral cortex, basal ganglia, and thalamus (P < or =.05) and an overall trend toward neuroprotection versus the deep hypothermic circulatory arrest group. This neuroprotection was accompanied by nearly complete blockade of phosphorylated extracellular signal-regulated kinase in the cerebral vascular endothelium.

CONCLUSIONS

In this experimental model of deep hypothermic circulatory arrest, U0126 blocked extracellular signal-regulated kinase activation and provided a significant neuroprotective effect. These results support targeting of the extracellular signal-regulated kinase pathway for inhibition as a novel therapeutic approach to mitigate neuronal damage following deep hypothermic circulatory arrest.

Cerebral physiology and outcome after hypothermic circulatory arrest followed by selective cerebral perfusion

BACKGROUND

This study explored the impact of an interval of hypothermic circulatory arrest (HCA) preceding selective cerebral perfusion (SCP) on cerebral physiology and outcome. This protocol allows use of SCP during aortic surgery without the threat of embolization inherent in balloon catheterization of often severely atherosclerotic cerebral vessels.

METHODS

In this blinded study, 30 pigs (20 to 22 kg) were randomized after cooling to 20 degrees C. Pigs in the HCA-CPB group (n = 10) underwent 30 minutes of HCA followed by 60 minutes of total body perfusion (CPB); HCA-SCP pigs (n = 10) underwent 30 minutes of HCA followed by 60 minutes of SCP, and SCP pigs (n = 10) had 90 minutes of SCP without prior HCA. Fluorescent microspheres enabled calculation of cerebral blood flow during perfusion and recovery. Hemodynamics, intracranial pressure, cerebrovascular resistance, and cerebral oxygen consumption were also monitored. Daily behavioral scores were obtained for 7 days postoperatively.

RESULTS

In all groups, cerebral oxygen consumption fell significantly with cooling (p < 0.0001), remained low during perfusion, and rebounded promptly with rewarming; cerebral oxygen consumption was significantly (p = 0.027) greater during SCP than during HCA-CPB. Cerebral blood flow was significantly higher throughout SCP in the HCA-SCP group (p < 0.0001) than with CPB. Cerebrovascular resistance during SCP and HCA-SCP was significantly lower (p = 0.036) than during CPB. Behavioral scores were significantly better with SCP than with HCA-CPB throughout recovery, but did not differ between SCP and HCA-SCP.

CONCLUSIONS

This study suggests that a short period of HCA preceding SCP provides global cerebral protection comparable to continuous SCP, implying that in clinical practice, a short period of HCA to reduce risk of embolization will not compromise the superior cerebral protection provided by SCP.

Cyclosporin A reduces delayed motor neuron death after spinal cord ischemia in rabbits

BACKGROUND

Spinal cord ischemia has varied etiologies, and in some cases, may develop into paraplegia. This is attributable to the vulnerability of spinal motor neurons to ischemia. We evaluated the potential of the immunosuppressant cyclosporin A for treatment of spinal motor neuron damage caused by ischemia.

METHODS

Twenty-eight rabbits were randomized into four groups of 7 animals each: group A (cyclosporin A not administered), group B (2.5 mg/kg cyclosporin A), group C (25 mg/kg cyclosporin A), and group S (sham-operated). The spinal cord ischemia model was created by a 15-minute occlusion of the aorta just caudal to a renal artery with a balloon catheter. Administration of cyclosporin A began 30 minutes after restoration of blood flow. The spinal cords were removed after 7-day monitoring of neurologic function. Pathology specimens were prepared, and after staining them with hematoxylin-eosin, viable motor neurons in the ventral spinal cord were counted under light microscopy.

RESULTS

At 7 days after reperfusion, recovery of motor function was seen at varying degrees in groups B and C, whereas all animals in group A continued to exhibit paraplegia. In group C, most of the animals recovered to the baseline level, before creation of the ischemia model. A significant difference in numbers of viable neurons was found in group A (cell count, 10.1 +/- 4.7) and group C (cell count, 22.2 +/- 8.0) (p < 0.05). Higher numbers of viable motor neurons corresponded to a greater recovery of motor function.

CONCLUSIONS

These results suggest that cyclosporin A administration is effective against neuronal damage caused by spinal cord ischemia.

Effects of deep hypothermic circulatory arrest on outcome after resection of ascending aortic aneurysm

BACKGROUND

Aneurysm of the ascending aorta is a common finding especially in patients with aortic valve diseases. The aim of this study was to analyze early and midterm outcome in patients operated on for aneurysm of the ascending aorta with or without the use of deep hypothermic circulatory arrest (DHCA).

METHODS

Between January 1996 and December 2000, 133 of 410 patients with thoracic aortic pathology were operated on for an aortic aneurysm limited mainly to the ascending aorta. Early and midterm outcomes were assessed and quality of life (QOL) evaluated using the Short-Form 36 Health Survey Questionnaire (SF-36).

RESULTS

Sixty patients (group 1) were operated on with DHCA and 73 patients (group 2) without DHCA. In-hospital mortality was identical in both groups (9.6% versus 6.7%; p = not significant) whereas postoperative transient neurologic events were significantly more frequent in group 1 (6.7% versus 0%; p < 0.05). Midterm clinical outcome was not different between groups but QOL showed significant impairment in daily functional physical and emotional activity in group 1 patients compared with group 2 and an age-matched standard population.

CONCLUSIONS

The risk of transient neurologic complications is significantly increased with the use of DHCA and QOL is impaired without benefits in the long-term outcome especially among older patients.

Apoptotic activity is increased in brain cortex infarct after hypothermic circulatory arrest in a porcine model

OBJECTIVE

It has been shown that apoptosis contributes to neuronal cell death after ischemia, and we evaluated the degree of apoptotic activity occurring in brain cortex of pigs after hypothermic circulatory arrest (HCA).

DESIGN

Thirty-one pigs underwent 75 min of HCA at 20 degrees C. Histological examination of the brain was performed, and slides of brain cortex were evaluated for apoptotic activity by the TUNEL method.

RESULTS

Ten animals died during the first postoperative day and 21 survived until the seventh postoperative day. Brain cortex infarcts were found in animals that survived 7 days and these were included in this study. The median histopathological score among animals that died on the first postoperative day was 3.0 (range, 2-4), whereas it was 4.0 (range, 2-4) among survivors (p = 0.019). The apoptotic index was particularly high in the area of the infarct, whereas only a few TUNEL-stained cells were observed in noninfarcted areas. The apoptotic index was nil in all pigs that died in the first postoperative period, whereas it was 2.0 (range, 0-6) among the animals that survived until the seventh postoperative day (p < 0.0001).

CONCLUSION

The apoptotic index was significantly increased in brain cortex infarcts of animals that survived 7 days after HCA, whereas only a few apoptotic cells were observed in noninfarcted areas of these animals as well as in animals that died on the first postoperative day. Further studies are required to elucidate the timing of development of brain infarction after HCA and whether neuroprotective strategies targeting the apoptotic process may mitigate brain damage.

Involvement of apoptosis in neurological injury after hypothermic circulatory arrest: a new target for therapeutic intervention?

BACKGROUND

This study was undertaken to evaluate the role of apoptosis in neurological injury after hypothermic circulatory arrest (HCA).

METHODS

Twenty-one pigs (27 to 31 kg) underwent 90 minutes of HCA at 20 degrees C and were electively sacrificed at 6, 24, 48, and 72 hours, and at 7, 10, and 12 days after HCA, and compared with unoperated controls. In addition, 3 animals that had HCA at 10 degrees C, and 3 treated with cyclosporine A (CsA) in conjunction with HCA at 20 degrees C, were examined 72 hours after HCA. After selective perfusion and cryopreservation, all brains were examined to visualize apoptotic DNA fragmentation and chromatin condensation on the same cryosection of the hippocampus: fluorescent in situ end labeling (ISEL) was combined with staining with a nucleic acid-binding cyanine dye (YOYO).

RESULTS

In addition to apoptosis, which was seen at a significantly higher level (p = 0.05) after HCA than in controls, two other characteristic degenerative morphological cell types (not seen in controls) were characterized after HCA. Cell death began 6 hours after HCA and reached its peak at 72 hours, but continued for at least 7 days. Compared with the standard protocol at 20 degrees C, HCA at 10 degrees C and CsA treatment both significantly reduced overall cell death after HCA, but not apoptosis.

CONCLUSIONS

The data establish that significant neuronal apoptosis occurs as a consequence of HCA, but at 20 degrees C, other pathways of cell death, probably including necrosis, predominate. Although preliminary results suggest that the neuroprotective effects of lower temperature and of CsA are not a consequence of blockade of apoptotic pathways, inhibition of apoptosis nevertheless seems promising as a strategy to protect the brain from the subtle neurological injury that is associated with prolonged HCA at clinically relevant temperatures.

Apoptotic cell death in the hippocampus due to prolonged hypothermic circulatory arrest: comparison of cyclosporine A and cycloheximide on neuron survival

OBJECTIVE

To determine whether cyclosporine A (CsA) or cycloheximide (CHX) can reduce neuronal apoptosis in the hippocampus in a chronic animal model of hypothermic circulatory arrest (HCA).

METHODS

Twenty-eight pigs (28-33 kg) underwent 90 min of HCA at 20 degrees C. In a blinded study, animals were randomized to placebo (n=12), 5 mg/kg CsA (n=8), or 1 mg/kg CHX (n=8). After elective sacrifice 7 days postoperatively, brains were perfusion-fixed and the left hippocampus was examined for evidence of neuronal cell death. An in situ double-labeling method was used on cryosections to unequivocally identify apoptotic nuclei by the simultaneous visualization of DNA fragmentation and apoptotic chromatin condensation. Sections were also examined by immunocytochemistry for upregulation of the pro-apoptotic proteins Bax, activated caspase 3, and glyceraldehyde-3-phosphate dehydrogenase.

RESULTS

Apoptotic nuclear degradation was clearly present in the CA1, CA2 and CA3 subregions of the hippocampus after HCA. However, there was also morphological evidence for an accompanying necrotic-like cell death. There was no significant difference between the number of apoptotic nuclei observed in CSA-treated animals, mean value 4.4+/-1.63 SEM or CHX-treated animals, mean value 4.0+/-1.92 SEM, and age-matched control HCA pigs, mean value 4.85+/-1.69 SEM, (P>0.10).

CONCLUSIONS

The data clearly demonstrate apoptotic cell death in pigs after HCA by simultaneously demonstrating in situ end labeling (TUNEL reaction) and apoptotic chromatin condensation using a nucleic acid-binding dye. Since CsA shows promising neuroprotective effects in behavioral studies, and since the peak of HCA-induced apoptosis occurs earlier than 7 days, further studies will be required to determine whether CsA can improve neuronal survival in the first few days after HCA. CHX was not effective in reducing apoptosis in this model.