Abstract: Objective · To investigate the effects of different rewarming rates on neuron autophagy in the rats with therapeutic hypothermia following cardiac arrest and cardiopulmonary resuscitation. Methods · The SD rats were randomized into 4 groups, i.e., sham operation group (Sham group), normothermia group (Normo group), slow rewarming group (SR group) and fast rewarming group (FR group). Except Sham group, the other three groups were given cardiopulmonary resuscitation after the establishment of 5-min asphyxial cardiac arrest model. The rats in Normo group were maintained at (37.0±0.5) ℃ ; SR group and FR group were treated with hypothermia (34 ℃ ) for 4 h, and SR group was rewarmed at 0.5 ℃ /h and FR group was rewarmed at 4 ℃ /h to (37.0±0.5) ℃ . SR+chloroquine group and FR+chloroquine group were isolated from the two rewarming groups, and the rats in these two groups were injected intraperitoneally with chloroquine 10 mg/kg 1 h before operation. Morphological changes of cortical motor neurons were detected by Nissl staining. The expressions of autophagy- and lysosomal-related proteins at corresponding time points, i.e., microtubule-associated protein 1 light chain 3- Ⅱ (LC3- Ⅱ ), lysosome-associated membrane protein 2 (LAMP2), P62, Bcl 2-interacting protein-1 (Beclin1), cathepsin D, and ubiquitin, were examined by Western blotting and immunofluorescence. Results · The expressions of LC3- Ⅱ and Beclin1 increased significantly in SR group 6 h after hypothermia treatment compared to Normo group (both P=0.000). Compared with SR group, FR group showed an obviously lower number of viable cortical neurons (P=0.000), significantly decreased expressions of LAMP2 and cathepsin D (both P=0.000), and increased expressions of ubiquitin (P=0.007) and P62 (P=0.000). Compared with SR group, the expressions of ubiquitin (P=0.000) and P62 (P=0.001) in SR+chloroquine group increased, while the expressions of ubiquitin (P=0.000) and P62 (P=0.007) decreased in FR+chloroquine group compared with FR group. Conclusion · Fast rewarming after therapeutic hypothermia for cardiac arrest and cardiopulmonary resuscitation can lead to neuron lysosomal dysfunction, impaired autophagy flux, and increased neuronal damage; however, slow rewarming activates autophagy and reduces neuronal injury.

Key words: cardiac arrest, hypothermia therapy, rewarming, autophagy, neuron, lysosome