[Effects of pretreatment with metoprolol on cardiomyocyte apoptosis and caspase-8 activation after coronary microembolization in rats].

OBJECTIVE: To investigate the effects of metoprolol on cardiomyocyte apoptosis and caspase-8 activation after coronary microembolization(CME) in rats. METHODS: Adult rats were randomly assigned into CME group (intraventricular injection of 3000 microspheres with 42 µm in diameter), sham-operated group (0.1 ml saline) and CME plus metoprolol group (pretreatment with 3 bolus metoprolol 2.5 mg/kg intravenous injection at 10 minutes interval at 30 minutes before microspheres injection, n = 15, each group). Cardiac function was evaluated by echocardiography at 6 hours post various treatments. Cardiomyocyte apoptosis was detected with TUNEL staining and the expression of caspase-3 and caspase-8 was detected with Western blot analysis. RESULTS: Compared with sham-operated group, LVEF (72.68% ± 3.26% vs. 82.64% ± 3.43%, P < 0.05), fractional shortening (FS) (37.46% ± 2.38% vs. 42.85% ± 3.25%) and cardiac output (CO) [(0.101 ± 0.006) L/min vs. (0.162 ± 0.008) L/min] were significantly reduced while left ventricular end-diastolic diameter (LVEDd) [(6.22 ± 0.17) mm vs. (5.18 ± 0.43) mm] was significantly increased in CME group (all P < 0.05). Cardiac function [LVEF:73.94% ± 4.22%, FS:38.53% ± 2.03%, CO:(0.120 ± 0.012) L/min, LVEDd:(6.18 ± 0.27) mm] was similar in CME plus metoprolol group compared to CME group (all P > 0.05). The cardiomyocytes apoptosis rates (3.19% ± 1.23% vs. 0.18% ± 0.10%) and the levels of activated caspase-3 and caspase-8 proteins were significantly increased in CME group than in sham-operated group (all P < 0.05). The cardiomyocyte apoptosis rate (1.32% ± 0.28%) and the levels of activated caspase-3 and caspase-8 proteins were significantly lower in CME plus metoprolol group than in CME group (all P < 0.05). CONCLUSIONS: Metoprolol pretreatment reduced post-CME myocardial apoptosis possibly through downregulating death receptor-mediated apoptotic pathway.

Effect of metoprolol on myocardial apoptosis and caspase-9 activation after coronary microembolization in rats.

OBJECTIVE: To explore the effect of metoprolol on myocardial apoptosis and caspase-9 activation after coronary microembolization (CME) in rats. METHODS: Forty rats were randomly divided into four groups (n=10 each): a sham operation (control) group, CME plus saline (CME) group, CME plus metoprolol (metoprolol) group and caspase-9 inhibitor Z-LEHD-FMK (ZLF) group. CME was induced by injecting 3000 polyethylene microspheres (42 µm diameter) into the left ventricle during a 10 s occlusion of the ascending aorta. Echocardiography, terminal deoxynucleotidyl transferase dUTP nick end labelling and Western blotting were used to evaluate cardiac function, apoptosis and activation of caspase-9/caspase-3, respectively, 6 h after CME. RESULTS: The echocardiographic parameters of left ventricular function were significantly decreased in the CME group compared with the control group (P<0.05); however, the metoprolol group and ZLF group showed significantly improved cardiac function compared with CME alone (P<0.05). Compared with the control group, the myocardial apoptosis rate and the levels of activated caspase-9 and -3 increased significantly in the CME group (P<0.05). Again, these effects were ameliorated by metoprolol and ZLF (P<0.05). CONCLUSIONS: The present study demonstrates that metoprolol and ZLF can protect the rat myocardium during CME by inhibiting apoptosis and improving cardiac function, likely by inhibiting apoptosis/ mitochondrial apoptotic pathway. These results suggest that antiapoptotic therapies may be useful in treating CME.

Effect of metoprolol on myocardial apoptosis after coronary microembolization in rats.

BACKGROUND: Coronary microembolization (CME) is a serious complication following percutaneous coronary intervention (PCI) in patients with acute coronary syndromes. The use of metoprolol before PCI can significantly protect ischemic myocardium from myocardial damage, but the function of metoprolol in the treatment of CME is not entirely clear. This study was to explore the effect and significance of metoprolol on myocardial apoptosis and caspase-3 activation after CME in rats. METHODS: Thirty rats were randomly divided into three groups including sham-operation (control group), CME plus saline (CME group), CME plus metoprolol (metoprolol group), 10 rats for each group. The CME group was induced by injecting 3 000 polyethylene microspheres (42 µm) into the left ventricle during a 10-second occlusion of the ascending aorta; the control group was injected with physiological saline instead of microembolization ball; the metoprolol or saline group was given three intravenous bolus injections before CME. Echocardiography, TUNEL staining, and Western blotting were used to evaluate cardiac function, proportion of apoptotic cells and activation of caspase-3 respectively at 6 hours after operation. RESULTS: Echocardiographic parameters displayed that the metoprolol group improved cardiac function significantly compared with the CME group (P<0.05). The myocardial apoptotic rate of the CME group as well as the contents of activated caspase-3 increased significantly (P<0.05), both of which were ameliorated significantly by metoprolol treatment (P<0.05). CONCLUSIONS: This study demonstrates that metoprolol can protect the myocardium during CME in rats by inhibiting apoptosis and improving cardiac function. These results suggest that the inhibition of apoptosis can be a potential therapeutic strategy for the treatment of CME.

Coronary microembolization induced myocardial contractile dysfunction and tumor necrosis factor-α mRNA expression partly inhibited by SB203580 through a p38 mitogen-activated protein kinase pathway.

BACKGROUND: The microemboli produced during spontaneous plaque rupture and ulceration and during coronary intervention will reduce coronary reserve and cause cardiac dysfunction. It is though that inflammation caused by the microinfarction induced by the microembolization may play an essential role. It is known that the activation of p38 mitogen-activated protein kinases (MAPK) in both infected and non-infected inflammation in myocardium may cause a contractile dysfunction. But the relation between the activation of p38 MAPK and microembolization is still unknown. METHODS: Sprague-Dawley rats were randomly divided into three groups: Sham group, coronary microembolization (CME) group and SB203580 group (n = 10 per group). CME rats were produced by injection of 42 µm microspheres into the left ventricle with occlusion of the ascending aorta. SB203580, a p38 MAPK inhibitor, was injected into the femoral vein after the injection of microspheres to make the SB203580 group. Left ventricular ejection fraction (LVEF) was determined by echocardiography. The protein concentration of P38 MAPK in the myocardium was assessed by Western blotting. The relative expression of mRNA for tumor necrosis factor (TNF)-α was assessed by the technique of semi-quantitative polymerase chain reaction amplification. RESULTS: LVEF was depressed at three hours up to 12 hours in the CME group. Increased p38 MAPK activity and TNF-α mRNA expression were observed in the CME group. The administration of SB203580 partly inhibited p38 MAPK activity, but did not fully depress the TNF-α expression, and partly preserved cardiac contractile function. CONCLUSIONS: p38 MAPK is significantly activated by CME and the inhibition of p38 MAPK can partly depress the TNF-α expression and preserve cardiac contractile function.

The role of ERK1/2 signaling pathway in coronary microembolization-induced rat myocardial inflammation and injury.

AIM: Inflammation plays an important role in coronary microembolization (CME)-induced myocardial injury. The present study was designed to investigate the role of extracellular signal-regulated kinases 1/2 (ERK1/2) signaling pathway in regulating myocardial inflammation and cardiac function in a rat model of CME. METHODS: Sprague-Dawley rats were randomly divided into three groups: sham-operated group (sham group), CME group and PD98059 group (15 animals per group). CME was produced by injection of 42-µm microspheres into the left ventricle with occlusion of the ascending aorta. Rats in the PD98059 group were injected with PD98059, a specific ERK1/2 inhibitor, 30 min before the CME operation. Western blotting and immunohistochemistry analysis were used to determine the activation of ERK1/2. Echocardiography was employed to evaluate cardiac function. Hematoxylin-eosin staining was performed to assay myocardial inflammation. Expression of TNF-α mRNA was determined by RT-PCR analysis, and activity of NF-κB was assessed by electrophoretic mobility shift assay. RESULTS: CME dramatically induced cardiac dysfunction (left ventricular ejection fraction, LVEF, was 72.97 ± 3.20% in the CME vs. 82.69 ± 3.50% in the sham group, p < 0.05) and local myocardial inflammatory response, both of which were ameliorated significantly by PD98059 (LVEF was 76.46 ± 4.46 and p < 0.05 vs. CME group). When compared to the CME group, PD98059 markedly attenuated the increased phosphorylation of ERK1/2 (0.48 ± 0.11 vs. 0.92 ± 0.10, p < 0.05), expression of TNF-α mRNA (0.42 ± 0.06 vs. 0.94 ± 0.04, p < 0.05) and activity of NF-κB (104.83 ± 13.65 vs. 540.79 ± 24.95, p < 0.05) in CME rat myocardium. CONCLUSIONS: The present study demonstrates a novel role of the ERK1/2 signaling pathway in promoting myocardium inflammation and dysfunction in CME, and suggests that ERK1/2 is a novel potential therapeutic target for CME.

[Myocardial inflammation and injury induced by coronary microembolization in rats: role of ERK1/2 signaling pathway].

OBJECTIVE: To determine the role of extracellular signal-regulated kinases1/2 (ERK1/2) signaling pathway in regulating myocardial inflammation and cardiac function in a rat model of coronary microembolization (CME). METHODS: The Sprague-Dawley rats were randomly divided into three groups: sham-operated group (n = 15), coronary microembolization group (n = 15) and PD98059 group (n = 15). CME model was established by injection of 42 microm microspheres 0.1 ml (3 x 10(4)/ml, 3000)into left ventricle while occluding the ascending aorta. At 30 minutes pre-operation, rats of PD98059 group were injected with PD98059 IV, a specific ERK1/2 inhibitor. Western blot and immunochemical analysis were used to determine the activation and distribution of ERK1/2. Echocardiography was employed to evaluate cardiac functions. The hematoxylin-eosin staining was used to assay myocardial inflammation. Expression of TNF-alpha and MIF mRNA was determined by RT-PCR analysis and activity of NF-kappaB assessed by electrophoretic mobility shift assay. RESULTS: In comparison with sham-operated group, CME increased phosphorylation of ERK1/2 (0.92 +/- 0.10 vs 0.61 +/- 0.04), local myocardial inflammatory cells (455 +/- 16 vs 47 +/- 7), expression of TNF-alpha mRNA (0.94 +/- 0.04 vs 0.60 +/- 0.09) and MIF mRNA(1.30 +/- 0.44 vs 0.63 +/- 0.25) and activity of NF-kappaB (541 +/- 25 vs 311 +/- 65) in myocardium(all P < 0.05). All of these dramatically induced cardiac dysfunction [LVEF (73 +/- 3)% vs (83 +/- 4)%, P < 0.05]. To compare with CME group, treatment of specific ERK1/2 inhibitor PD98059 blocked the activation of ERK1/2 (0.48 +/- 0.11 vs 0.92 +/- 0.10, P < 0.05), decreased inflammatory cells (401 +/- 12 vs 455 +/- 16, P < 0.05), decreased expression of TNF-alpha mRNA (0.42 +/- 0.06 vs 0.94 +/- 0.04, P < 0.05) and suppressed activity of NF-kappaB (105 +/- 14 vs 541 +/- 25, P < 0.05). Most importantly, PD98059 treatment ameliorated cardiac functions dramatically [LVEF (76 +/- 4)% vs (73 +/- 3)%, P < 0.05]. However there was no significant change in the expression of MIF mRNA (1.17 +/- 0.37 vs 1.30 +/- 0.44, P > 0.05). CONCLUSION: The present study demonstrates a novel role of ERK1/2 signaling pathway in promoting myocardial inflammation in CME. And ERK1/2 may be a novel drug target for CME therapy.