Effects of hypothermia on Ca2+ /calmodulin-dependent protein kinase II and cell autophagy in brain tissues after cardiac arrest and cardiopulmonary resuscitation in swine

Abstract

Objective To evaluate the effects of hypothermia on Ca2+ /calmodulin-dependent protein kinase Ⅱ (CaMKⅡ) and cell autophagy in brain tissues after cardiac arrest and cardiopulmonary resuscitation (CA-CPR) in swine. Methods Twenty-one healthy male white swine, weighing 33-40 kg, were divided into 3 groups using a random number table method: sham operation group (group S, n=5), CA-CPR group (n=8) and hypothermia group (group H, n=8). The experimental model of CA-CPR was established in CA-CPR and H groups.The Swan-Ganz catheters were placed in the right femoral artery and vein to monitor the pressure of thoracic aorta and right atrium and body temperature and to collect blood samples.A pacing catheter was advanced from the right external jugular vein into the right ventricle.Ventricular fibrillation was induced by using a 1 mA alternating current through the pacing catheter.Once ventricular fibrillation was successfully induced, mechanical ventilation was discontinued for 8 min, and then CPR was initiated.Epinephrine 20 μg/kg was intravenously injected at 2.5 min of CPR, followed by repetition once every 3 min.Defibrillation was delivered at 5 min of CPR, and then spontaneous circulation was evaluated.If the spontaneous circulation was not restored, CPR was immediately resumed for 2 min, and then defibrillation was delivered again.Mechanical ventilation was continued for 30 h after successful CPR.At 5 min after successful resuscitation, body temperature was decreased to 33 ℃ by using a cooling blanket, then maintained at 33 ℃ until 24 h after resuscitation, and finally increased at a rate of 1 ℃/h for 5 h in group H. The temperature was maintained at a normal level of 37.5-38.5 ℃ with the aid of a cooling blanket in S and CA-CPR groups.At 1, 6, 12, 24 and 30 h after resuscitation (T1-5), blood samples were collected from the femoral vein for measurement of the concentration of neuron specific enolase (NSE) and S100β protein in serum by enzyme-linked immunosorbent assay.Five animals in each group were then sacrificed, and brains were removed to determine the expression of CaMKⅡ, microtubule-associated protein 1 light chain 3 Ⅱ (LC3Ⅱ) and p62 in cerebral cortex by Western blot.Neurological deficit score was evaluated in the remaining three swine at 48, 72 and 96 h after resuscitation (T6-8) in CA-CPR and H groups. Results Compared with group S, the concentrations of NSE and S100β protein in serum were significantly increased at T1-5, the expression of CaMKⅡ and LC3Ⅱ in cerebral cortex was up-regulated, and the expression of p62 in cerebral cortex was down-regulated in CA-CPR and H groups (P<0.05). Compared with group CA-CPR, the concentrations of NSE and S100β protein in serum were significantly decreased at T3-5, the neurological deficit score was decreased at T6-8, the expression of CaMKⅡ and LC3Ⅱ in cerebral cortex was down-regulated, and the expression of p62 in cerebral cortex was up-regulated in group H (P<0.05). Conclusion The mechanism by which hypothermia alleviates brain injury after CA-CPR may be related to inhibiting CaMKⅡ activation and reducing cell autophagy in brain tissues of swine. Key words: Hypothermia, induced; Heart arrest; Cardiopulmonary resuscitation; Reperfusion injury; Brain; Ca2+ /calmodulin-dependent protein kinase Ⅱ; Autophagy