Neuroprotective mechanism of autophagy in bradykinin postconditioning after cardiac arrest in rats

Abstract

To explore the protective effects of bradykinin postconditioning on cardiopulmonary resuscitation (CPR) rats, and to assess the underlying mechanisms. Forty-eight adult male Sprague-Dawley (SD) rats were randomly divided into four groups according to random number table: Sham operation group, cardiac arrest (CA) group, bradykinin treatment (BK) group, and AMP-activated protein kinase (AMPK) inhibitor Compound C+ bradykinin treatment (CP+BK) group, finally, 8 rats in each group were taken for follow-up experiment. CA was induced by asphyxia. Rats in the Sham group received arteriovenous catheterization, endotracheal intubation, and mechanical ventilation, without CA. Compound C (250 μg/kg) was intraperitoneally injected in CP+BK group 30 minutes before CA, and the same volume of dimethyl sulfoxide (DMSO) was given in the remaining groups. Bradykinin (150 μg/kg) was intraperitoneally injected in BK group and CP+BK group 48 hours after restoration of spontaneous circulation (ROSC), and same volume of saline was given in the remaining groups. The neural function of rats in each group was evaluated with neurological deficit score (NDS) 72 hours after ROSC. Microtubule-associated protein light chain 3 (LC3) and p62 expressions were detected by immunohistochemistry, autophagosomes were observed by transmission electron microscopy, and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling method (TUNEL) assay was used to assess apoptosis. Compared with the Sham group, the NDS was decreased (60.75±5.80 vs. 80.00±0.00, P < 0.01), the expression levels of LC3 and p62 elevated [LC3 (A value): 1.04±0.64 vs. 0.40±0.14, p62 (A value): 2.75±0.57 vs. 0.36±0.12, both P < 0.05], the number of autophagosomes and apoptotic cells increased in the CA group [(39.00±8.00)% vs. (3.87±1.90)%, P < 0.05]. Compared with the CA group, the NDS (67.75±6.32 vs. 60.75±5.80, P < 0.05), the expression of LC3 (A value: 1.60±0.34 vs. 1.04±0.64, P < 0.05), and the number of autophagosomes increased in the BK group, while the expression of p62 and the rate of apoptotic cells reduced [p62 (A value): 1.51±0.32 vs. 2.75±0.57, apoptotic cells rate: (23.03±1.91)% vs. (39.00±8.00)%, both P < 0.05]. Compared with the BK group, the NDS (59.00±8.19 vs. 67.75±6.32, P < 0.05), the expression of LC3 (A value: 0.62±0.41 vs. 1.60±0.34, P < 0.05) and the number of autophagosomes declined in the CP+BK group, while the expression of p62 and the rate of apoptotic cells elevated [p62 (A value): 3.50±0.47 vs. 1.51±0.32, apoptotic cells rate: (44.53±10.15)% vs. (23.03±1.91)%, both P < 0.05]. Bradykinin postconditioning played a neuroprotective role in CPR rats by activating autophagy and reducing apoptosis.