[Effects of autophagy on myocardial injury in rats with common bile duct ligation].

Abstract

Objective: To investigate the impact of autophagy on cardiac tissue injury following common bile duct ligation (CBDL) in rats.

Methods: Twenty-four SPF grade healthy adult male Sprague-Dawley (SD) rats were randomly divided into four groups, with 6 rats in each group. The sham-operated (Sham) group underwent only dissection of the common bile duct without ligation. The CBDL group underwent CBDL to simulate jaundice-induced myocardial injury. The autophagy inhibitor 3-methyladenine (3-MA)+CBDL group was intraperitoneally injected with 15 mg/kg 3-MA 2 hours before modeling, and then injected once every other day. The CBDL+autophagy enhancer rapamycin (Rapa) group was intraperitoneally injected with Rapa 1 mg/kg 0.5 hour after modeling, and then injected once every other day. The rats in each group were sacrificed 2 weeks after surgery, and blood was taken from the inferior vena cava. Serum total bilirubin (TBil), alanine transaminase (ALT), aspartate transaminase (AST), lactate dehydrogenase (LDH), and MB isoenzyme of creatine kinase (CK-MB) were detected by using a fully automated animal biochemical analyzer. Serum oxidative stress marker superoxide dismutase (SOD) activity and malondialdehyde (MDA) content were detected by colorimetric assay. The heart tissues of rats were taken and pathological changes were observed under a light microscope after hematoxylin-eosin (HE) staining. Transmission electron microscope was used to observe autophagosomes after double staining with uranyl acetate and lead citrate. The expressions of autophagy-related proteins were detected using Western blotting.

Results: Compared with the Sham group, the serum SOD activity of rats in the CBDL group was significantly decreased, while the serum MDA, TBil, ALT, AST, LDH, and CK-MB were significantly increased; the expressions of autophagy-related proteins Beclin-1 and microtubule-associated protein 1 light chain 3-II/I (LC3-II/I) were significantly increased, and p62 protein expression was significantly decreased. Autophagosomes were seen under electron microscopy in the CBDL group, and cardiac histopathological morphology showed focal necrosis in the myocardium as well as infiltration of inflammatory cells, dilatation of small interstitial blood vessels, and myocardial fiber degeneration. Compared with the CBDL group, cardiac tissue injury in rats was attenuated by pretreatment with the autophagy inhibitor 3-MA, with a decrease in inflammatory cell infiltration in myocardial tissue, a reduction in interstitial vasodilatation, and a decrease in the area of myocardial fibrosis; a decrease in the number of autophagosomes by electron microscopy; and a further rise in the viability of serum TBil, ALT, and AST [TBil (μmol/L): 184.40±6.74 vs. 120.70±16.93, ALT (U/L): 501.10±62.18 vs. 178.80±22.30, AST (U/L): 806.50±76.92 vs. 275.50±55.81, all P < 0.01], as well as a decrease in the levels of serum SOD, MDA, LDH, and CK-MB [SOD (kU/L): 85.00±5.29 vs. 107.50±7.86, MDA (μmol/L): 10.72±0.93 vs. 15.06±1.88, LDH (U/L): 387.40±119.50 vs. 831.30±84.35, CK-MB (U/L): 320.10±14.04 vs. 814.70±75.66, all P < 0.05]. The expressions of the autophagy-related proteins Beclin-1 and LC3-II/I in cardiac tissues were significantly decreased [Beclin-1 protein (Beclin-1/GAPDH): 0.67±0.04 vs. 0.89±0.01, LC3-II/I ratio: 0.93±0.03 vs. 1.09±0.01, both P < 0.01], and p62 protein expression was significantly increased (p62/GAPDH: 0.99±0.01 vs. 0.60±0.01, P < 0.01). In contrast, compared with the CBDL group, after administration of the autophagy enhancer Rapa, the rats showed increased cardiac tissue injury, increased inflammatory cell infiltration in myocardial tissues, increased interstitial vasodilatation, and increased area of myocardial fibrosis; an increase in autophagosomes was seen by electron microscopy; the change tendency of serum biochemical indicators and proteins in myocardial tissues were opposite with autophagy inhibition group with a decrease in serum TBil, ALT, and AST [TBil (μmol/L): 22.00±3.21 vs. 120.70±16.93, ALT (U/L): 72.13±5.97 vs. 178.80±22.30, AST (U/L): 135.20±12.95 vs. 275.50±55.81, all P < 0.05], as well as a increase in the levels of serum SOD, MDA, LDH, and CK-MB [SOD (kU/L): 208.00±2.65 vs. 107.50±7.86, MDA (μmol/L): 20.38±0.40 vs. 15.06±1.88, LDH (U/L): 1 268.00±210.90 vs. 831.30±84.35, CK-MB (U/L): 1 150.00±158.70 vs. 814.70±75.66, all P < 0.05]. The protein expressions of Beclin-1 and LC3-II/I in cardiac tissues were significantly increased [Beclin-1 protein (Beclin-1/GAPDH): 0.96±0.01 vs. 0.89±0.01, LC3-II/I ratio: 1.19±0.01 vs. 1.09±0.01, both P < 0.05], and p62 protein expression was significantly decreased (p62/GAPDH: 0.19±0.02 vs. 0.60±0.01, P < 0.01).

Conclusions: Activation of autophagy in CBDL rats led to myocardial tissue injury and reduced cardiac function. Inhibition of autophagy improved cardiac tissue injury in CBDL rats, while increasing autophagy exacerbated myocardial tissue injury.