Increased cardiomyocyte apoptosis following ischemia and reperfusion in diet‐induced hypercholesterolemia: Relation to Bcl‐2 and bax proteins and caspase‐3 activity

Abstract

It has been reported that apoptosis is a significant contributor to myocardial cell death as a result of reperfusion injury. However, whether the extent of cardiomyocyte apoptosis following ischemia and reperfusion varies in different pathophysiological backgrounds is still uncertain. In this study, we examined whether hypercholesterolemia increases the extent of myocardial reperfusion injury by aggravating cardiomyocyte apoptosis and the effects of hypercholesterolemia on the expression of Bcl-2 and Bax proteins and the activation of caspase-3. Twenty-eight male New Zealand white rabbits were fed standard chow (control, n = 14) or chow supplemented with 10% cholesterol (hypercholesterolemic, n = 14) for 8 wk. Anesthetized rabbits were then subjected to 30 min of left circumflex artery occlusion followed by 4 h of reperfusion. Apoptosis was identified as "DNA ladders" by gel electrophoresis and confirmed histologically using the terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) assay. The infarct size (% of risk region) was significantly greater in hypercholesterolemic rabbits than in controls (39 +/- 6 vs. 23 +/- 2%, P = 0.02). Very few TUNEL-positive cardiomyocytes could be identified in the nonischemic regions in both groups, consistent with an absence of DNA laddering. In contrast, TUNEL-positive cardiomyocytes were significantly displayed in the ischemic, nonnecrotic myocardium, and DNA ladder occurred in all animals. The percentage of TUNEL-positive cardiomyocytes in the ischemic nonnecrotic myocardium was significantly higher in hypercholesterolemic rabbits compared with controls (40 +/- 5 vs. 17 +/- 11%, P < 0.001). Western blot analysis showed that, in the nonischemic myocardium, hypercholesterolemic rabbits exhibited an approximately 50% increase in the expression of Bcl-2 (P < 0.05), but not Bax, than control rabbits. However, compared with controls, hypercholesterolemic rabbits exhibited a more pronounced decrease in the expression of Bcl-2 (42 +/- 4 vs. 26 +/- 2%, P < 0.01) and a similar extent of increase in the expression of Bax in the ischemic myocardium. Furthermore, hypercholesterolemic rabbits were associated with a markedly increased activation of caspase-3 within the ischemic myocardium compared to control rabbits. This study demonstrates that although hypercholesterolemia is associated with an increased myocardial Bcl-2/Bax ratio at baseline, it still significantly exacerbates cardiac reperfusion injury, not only by increasing the infarct size but also by increasing the extent of cardiomyocyte apoptosis.

Taurine Attenuates Hepatic and Cardiac Damage and Apoptosis in Rabbits Fed a High-Fat Diet

“…The present work, reported that hypercholesterolemi induces apoptosis in cardiomyocytes through the activation of caspase-3. This was in agreement with the previous findings of Wang et al (2002) who reported that experimental hyperlipidemia induced by a high cholesterol diet (10%) increased infarct size and apoptotic cell death. The present results confirmed this report and demonstrated that a moderate hypercholesterolemia (2% cholesterol diet for 8 weeks) also increased myocardial apoptosis.…”

Intermedin protects against myocardial ischemia-reperfusion injury in hyperlipidemia rats

“…Several studies conducted in rodent models have suggested that myocardial ischemia/reperfusion (MI/R) injury in the setting of hyperlipidemia may result in more myocardial necrosis and apoptosis compared with non-hyperlipidemia animals (Wang et al, 2002;Osipov et al, 2009). For patients with a first MI condition, hyperlipidemia has been reported to have a detrimental effect on ventricular function with a more pronounced deterioration; but if treated with lipid-lowering agents before MI, myocardial infarct size can be significantly reduced both in patients and experimental animals (Wang et al, 1998;Aronow et al, 2008).…”

Pharmacological preconditioning and postconditioning with nicorandil attenuates ischemia/reperfusion-induced myocardial necrosis and apoptosis in hypercholesterolemic rats

“…Various studies have demonstrated that the myocardia of patients with hypercholesterolemia are more vulnerable to I/R-induced myocardial injury (10)(11)(12)(13)(14)(15) Nicorandil is a hybrid agent with two distinct mechanisms of pharmacological action; it opens KATP channels, thereby dilating peripheral and coronary resistance arterioles, in addition to activating sGC through its nitrate-like effect, which increases cyclic guanosine monophosphate (cGMP) levels and subsequently dilates the systemic veins and epicardial coronary arteries. Therefore, nicorandil increases coronary blood flow, reduces preload and afterload, and exerts an anti-anginal effect (19).…”

“…Following 30 min of reperfusion, the hearts were homogenized in radioimmunoprecipitation assay lysis buffer (Beyotime Institute of Biotechnology, Shanghai, China) prior to protein quantification using the BCA method (11). Equal quantities of protein from each sample were then separated by SDS-PAGE and transferred onto polyvinylidene difluoride-plus membranes (Bio-Rad Laboratories, Inc., Hercules, CA, USA).…”

“…One important factor is that the animal studies were performed on healthy animals, whereas humans who are treated with cardioprotective agents tend to have various co-morbidities, such as hypercholesterolemia, diabetes, obesity and aging, which may modify the myocardial responses to I/R and cardioprotective agents (7)(8)(9). Hypercholesterolemia is commonly found in patients with cardiovascular disease and is considered to be a risk factor (10), as previous studies have shown that patients with a hypercholesterolemic myocardium are vulnerable to I/R injury (10)(11)(12)(13)(14)(15). Previous studies have demonstrated that this vulnerability may be associated with the following: Increased expression of proapoptotic proteins, decreased expression of prosurvival proteins, increased myocardial inflammatory responses and oxidative/nitrative stress, inhibition of nitric oxide (NO) synthesis, and the impaired opening of mitochondrial adenosine triphosphate-sensitive potassium (mitoKATP) channels, in response to myocardial I/R (10-15).…”