[Therapeutic hypothermia reduced brain damage on rats after cardiopulmonary resuscitation by activating III-type PI3K pathway to increase autophagy].

OBJECTIVE: To investigate the effect of III-type phosphatidylinositide 3 kinase (PI3K) pathway adjusting autophagy on brain damage mechanism after cardiopulmonary resuscitation (CPR) and hypothermia treatment.

METHODS: The asphyxia induce cardiac arrest-CPR model was reproduced on healthy male Sprague-Dawley (SD) rats. Sixty rats after restoration of spontaneous circulation (ROSC) were randomly divided into normothermia group, therapeutic hypothermia group and PI3K inhibitor 3-methyl adenine (3-MA) pretreatment group, differentiated by 24 hours and 48 hours after ROSC. Each group had 10 rats at each time point. The anal temperature in the normothermia group was maintained at (37.0±0.2) centigrade, and the rats in the hypothermia group were given cooling treatment immediately after ROSC, and the target rectal temperature was 32-34 centigrade. In the 3-MA pretreatment group, 10 mmol/L 3-MA 5 μL was injected into the ventricle 20 minutes before asphyxia, and other groups were given the same amount of normal saline. Ten rats without CPR were included in Sham group only received anesthesia and catheterization. The rats were sacrificed at 24 hours and 48 hours after ROSC respectively, and the brain tissues were harvested, the brain water content (BWC) was measured by dry-wet weight method. Western Blot was used to determine the autophagy related proteins Beclin-1 and microtubule-associated protein 1 light chain 3 (LC3), apoptosis related proteins Bcl-2 and caspase-3, and the III-type PI3K pathway proteins Vps34 and Atg14. Ultrastructural changes in brain tissue were observed with transmission electron microscope. Neurological deficit scores (NDS) was obtained in each group at 48 hours after ROSC.

RESULTS: Compared with Sham group, the cortex at 24 hours after ROSC in normothermic group showed obvious edema, apoptosis and autophagy began to appear under transmission electron microscope, and the expressions of autophagy, apoptosis and III- type PI3K-related proteins in brain tissue were significantly increased in a time-dependent manner, and the neurological function at 48 hours after ROSC was significantly damaged. After hypothermia intervention, brain edema of rats was significantly reduced, no obvious apoptosis was found, but autophagy was increased, the expressions of autophagy-related proteins Vps34, Atg14 and III-type PI3K-related proteins Beclin-1 and LC3 at 48 hours after ROSC were further higher than those of normothermic group (Vps34/GAPDH: 0.25±0.03 vs. 0.15±0.04, Atg14/GAPDH: 0.12±0.03 vs. 0.05±0.04, Beclin-1/GAPDH: 0.060±0.002 vs. 0.018±0.002, LC3 -II/GAPDH: 0.160±0.010 vs. 0.050±0.010, all P < 0.05), the expressions of apoptosis related proteins Bcl-2 and caspase-3 were significantly lowered (Bcl-2/GAPDH: 0.05±0.03 vs. 0.20±0.04, caspase-3/GAPDH: 0.050±0.002 vs. 0.140±0.015, both P < 0.05), neurological function was significantly improved (NDS: 157±85 vs. 343±198, P < 0.05). Pretreatment with 3-MA inhibited the protective effect of hypothermia on brain tissues. The expressions of Vps34, Atg14, Beclin-1 and LC3 in brain tissues at 48 hours after ROSC in 3-MA pretreatment group was significantly lower than those in the hypothermia group (Vps34/GAPDH: 0.18±0.03 vs. 0.25±0.03, Atg14/GAPDH: 0.07±0.04 vs. 0.12±0.03, Beclin-1/GAPDH: 0.015±0.003 vs. 0.060±0.002, LC3-II/GAPDH: 0.045±0.030 vs. 0.160±0.010, all P < 0.05), the expressions of Bcl-2 and caspase-3 were significantly increased (Bcl-2/GAPDH: 0.15±0.04 vs. 0.05±0.03, caspase-3/GAPDH: 0.120±0.015 vs. 0.050±0.002, both P < 0.05), and NDS score was significantly increased (341±208 vs. 157±85, P < 0.05).

CONCLUSIONS: Hypothermia treatment reduced brain edema and ameliorated brain function after CPR, which might be related to increase autophagy and inhibit apoptosis adjustment by activating III-type PI3K pathway.