Prolonged deep hypothermic circulatory arrest in rats can be achieved without cognitive deficits

Reduction of Serious Adverse Events Demanding Study Exclusion in Model Development: Extracorporeal Life Support Resuscitation of Ventricular Fibrillation Cardiac Arrest in Rats

Extracorporeal life support is a promising concept for selected patients in refractory cardiogenic shock and for advanced life support of persistent ventricular fibrillation cardiac arrest. Animal models of ventricular fibrillation cardiac arrest could help to investigate new treatment strategies for successful resuscitation. Associated procedural pitfalls in establishing a rat model of extracorporeal life support resuscitation need to be replaced, refined, reduced, and reported.Anesthetized male Sprague-Dawley rats (350-600 g) (n = 126) underwent cardiac arrest induced with a pacing catheter placed into the right ventricle via a jugular cannula. Rats were resuscitated with extracorporeal life support, mechanical ventilation, defibrillation, and medication. Catheter and cannula explantation was performed if restoration of spontaneous circulation was achieved. All observed serious adverse events (SAEs) occurring in each of the experimental phases were analyzed.Restoration of spontaneous circulation could be achieved in 68 of 126 rats (54%); SAEs were observed in 76 (60%) experiments. Experimental procedures related SAEs were 62 (82%) and avoidable human errors were 14 (18%). The most common serious adverse events were caused by insertion or explantation of the venous bypass cannula and resulted in lethal bleeding, cannula dislocation, or air embolism.Establishing an extracorporeal life support model in rats has confronted us with technical challenges. Even advancements in small animal critical care management over the years delivered by an experienced team and technical modifications were not able to totally avoid such serious adverse events. Replacement, refinement, and reduction reports of serious adverse events demanding study exclusions to avoid animal resources are missing and are presented hereby.

Inhibition of microRNA-29c protects the brain in a rat model of prolonged hypothermic circulatory arrest

OBJECTIVE

We sought to investigate the cerebroprotection of a novel microRNA mechanism by targeting peroxisome proliferator-activated receptor gamma coactivator 1-alpha in a rat model of prolonged deep hypothermia circulatory arrest.

METHODS

The right carotid artery and jugular vein of male Sprague-Dawley rats were cannulated for cardiopulmonary bypass. Circulatory arrest was conducted for 60 minutes when the pericranial temperature was cooled to 18°C. The sham group received the surgical procedure without cardiopulmonary bypass and deep hypothermia circulatory arrest; the deep hypothermia circulatory arrest group received cardiopulmonary bypass and deep hypothermia circulatory arrest; lentivirus control vector or lentiviral vector containing antagomiR-29c was given to the deep hypothermia circulatory arrest + vector group or the deep hypothermia circulatory arrest + antagomiR-29c group by intracerebroventricular administration 5 days before cardiopulmonary bypass (n = 8, for each of the 4 groups). Neurologic function was evaluated by the modified hole board test and beam balance task during 14 postoperative days. Expressions of caspase-3, peroxisome proliferator-activated receptor gamma coactivator 1-alpha, and miR-29c in the hippocampus were measured by Western blot and quantitative reverse transcription polymerase chain reaction. Malondialdehyde was measured using the Malondialdehyde Assay Kit (Beyotime, Jiangsu, China).

RESULTS

Pretreatment with antagomiR-29c significantly decreased the expression of microRNA-29c and increased the expression of peroxisome proliferator-activated receptor gamma coactivator 1-alpha in the hippocampus (P < .05 vs deep hypothermia circulatory arrest group). The level of malondialdehyde in the hippocampus was lower in the deep hypothermia circulatory arrest + antagomiR-29c group (P < .05 vs deep hypothermia circulatory arrest group). The neurologic functions were markedly protected in rats pretreated with antagomiR-29c as evidenced by improvement of vestibulomotor and cognitive performance during the early postoperative period. In the deep hypothermia circulatory arrest + antagomiR-29c group, histologic scores of the hippocampus were improved and the level of caspase-3 in the hippocampus was lower (P < .05 vs deep hypothermia circulatory arrest group).

CONCLUSIONS

Inhibition of miR-29c attenuates neurologic injuries induced by prolonged deep hypothermia circulatory arrest through a peroxisome proliferator-activated receptor gamma coactivator 1-alpha pathway.

Microglial depletion using intrahippocampal injection of liposome-encapsulated clodronate in prolonged hypothermic cardiac arrest in rats

Trauma patients who suffer cardiac arrest (CA) from exsanguination rarely survive. Emergency preservation and resuscitation using hypothermia was developed to buy time for resuscitative surgery and delayed resuscitation with cardiopulmonary bypass (CPB), but intact survival is limited by neuronal death associated with microglial proliferation and activation. Pharmacological modulation of microglia may improve outcome following CA. Systemic injection of liposome-encapsulated clodronate (LEC) depletes macrophages. To test the hypothesis that intrahippocampal injection of LEC would attenuate local microglial proliferation after CA in rats, we administered LEC or PBS into the right or left hippocampus, respectively. After rapid exsanguination and 6min no-flow, hypothermia was induced by ice-cold (IC) or room-temperature (RT) flush. Total duration of CA was 20min. Pre-treatment (IC, RTpre) and post-treatment (RTpost) groups were studied, along with shams (cannulation only) and CPB controls. On day 7, shams and CPB groups showed neither neuronal death nor microglial activation. In contrast, the number of microglia in hippocampus in each individual group (IC, RTpre, RTpost) was decreased with LEC vs. PBS by ∼34-46% (P<0.05). Microglial proliferation was attenuated in the IC vs. RT groups (P<0.05). Neuronal death did not differ between hemispheres or IC vs. RT groups. Thus, intrahippocampal injection of LEC attenuated microglial proliferation by ∼40%, but did not alter neuronal death. This suggests that microglia may not play a pivotal role in mediating neuronal death in prolonged hypothermic CA. This novel strategy provides us with a tool to study the specific effects of microglia in hypothermic CA.

Fluoro jade-C staining in the assessment of brain injury after deep hypothermia circulatory arrest

OBJECTIVE

To evaluate the efficacy of Fluoro Jade-C staining (FJC) in the assessment of brain injury after deep hypothermia circulatory arrest (DHCA).

METHODS

Six healthy adult miniature male pigs underwent DHCA, the rectal temperature was down to 18°C, circulation was stopped , circulatory arrest was maintained for 60 minutes. On postoperative day 1, perfusion-fixation was performed on brain tissue. Cerebral cortex, hippocampus, cerebellum were taken for sampling. FJC, hematoxylin-eosin staining (HE), nissl staining (NISSL), terminal deoxynucleotidyl transferase biotin-dUTP nick end labeling (TUNEL) were performed to detect the histological and pathological changes. Histological scores of all slices were ranked. Comparison between the FJC and other techniques was done by analysis of variance (ANOVA) according to histological scores.

RESULTS

All animals survived the operation. On the cerebral cortex, in comparison of FJC between HE, NISSL and TUNEL, the p value was 0.90, 0.40, 0.16 respectively (p>0.05). On the hippocampus, the comparison of FJC with HE, NISSL and TUNEL had a p value of 0.12, 0.23, 0.62 respectively (p>0.05). On the cerebellum, in comparing FJC with HE, NISSL and TUNEL, the p value was 0.96, 0.77, 0.96 respectively (p>0.05). On representative regions, the results of FJC were in accordance with that of TUNEL, NISSL and HE. Furthermore, ascertainment of brain injury is easier with FJC.

CONCLUSION

FJC is a reliable and convenient method to assess brain injury after DHCA.

Deep hypothermia attenuates microglial proliferation independent of neuronal death after prolonged cardiac arrest in rats

INTRODUCTION

Conventional resuscitation of exsanguination cardiac arrest (CA) victims is generally unsuccessful. Emergency preservation and resuscitation is a novel approach that uses an aortic flush to induce deep hypothermia during CA, followed by delayed resuscitation with cardiopulmonary bypass. Minocycline has been shown to be neuroprotective across a number of brain injury models via attenuating microglial activation. We hypothesized that deep hypothermia and minocycline would attenuate neuronal death and microglial activation and improve outcome after exsanguination CA in rats.

METHODS

Using isoflurane anesthesia, rats were subjected to a lethal hemorrhagic shock. After 5 min of no flow, hypothermia was induced with an aortic flush. Three groups were studied: ice-cold (IC) flush, room-temperature (RT) flush, and RT flush followed by minocycline treatment (RT-M). After 20 min of CA, resuscitation was achieved via cardiopulmonary bypass. Survival, Overall Performance Category (1 = normal, 5 = death), Neurologic Deficit Score (0%-10% = normal, 100% = max deficit), neuronal death (Fluoro-Jade C), and microglial proliferation (Iba1 immunostaining) in hippocampus were assessed at 72 h.

RESULTS

Rats in the IC group had lower tympanic temperature during CA versus other groups (IC, 20.9 degrees C +/- 1.3 degrees C; RT, 28.4 degrees C +/- 0.6 degrees C; RT-M, 28.3 degrees C +/- 0.7 degrees C; P < 0.001). Although survival was similar in all groups (RT, 6/9; IC, 6/7; RT-M, 6/11), neurological outcome was better in the IC group versus other groups (Overall Performance Category: IC, 1 +/- 1; RT, 3 +/- 1; RT-M, 2 +/- 1; P < 0.05; Neurologic Deficit Score: IC, 8% +/- 9%; RT, 55% +/- 19%; RT-M, 27% +/- 16%; P < 0.05). Histological damage assessed in survivors showed selective neuronal death in CA1 and dentate gyrus, similar in all groups (P = 0.15). In contrast, microglial proliferation was attenuated in the IC group versus all other groups (P < 0.01).

CONCLUSIONS

Deeper levels of hypothermia induced by the IC versus RT flush resulted in better neurological outcome in survivors. Surprisingly, deep hypothermia attenuated microglial activation but not hippocampal neuronal death. Minocycline had modest benefit on neurologic outcome in survivors but did not attenuate microglial activation in brain. Our findings suggest a novel effect of deep hypothermia on microglial proliferation during exsanguination CA.

Perioperative hypothermia: use and therapeutic implications

Perioperative cerebral ischemic insults are common in some surgical procedures. The notion that induced hypothermia can be employed to improve outcome in surgical patients has persisted for six decades. Its principal application has been in the context of cardiothoracic and neurosurgery. Mild (32-35 degrees C) and moderate (26-31 degrees C) hypothermia have been utilized for numerous procedures involving the heart, but intensive research has found little or no benefit to outcome. This may, in part, be attributable to confounding effects associated with rewarming and lack of understanding of the mechanisms of injury. Evidence of efficacy of mild hypothermia is absent for cerebral aneurysm clipping and carotid endarterectomy. Deep hypothermia (18-25 degrees C) during circulatory arrest has been practiced in the repair of congenital heart disease, adult thoracic aortas, and giant intracranial aneurysms. There is little doubt of the protective efficacy of deep hypothermia, but continued efforts to refine its application may serve to enhance its utility. Recent evidence that mild hypothermia is efficacious in out-of-hospital cardiac arrest has implications for patients incurring anoxic or global ischemic brain insults during anesthesia and surgery, or perioperatively. Advances in preclinical models of ischemic/anoxic injury and cardiopulmonary bypass that allow definition of optimal cooling strategies and study of cellular and subcellular events during perioperative ischemia can add to our understanding of mechanisms of hypothermia efficacy and provide a rationale basis for its implementation in humans.