Study of the effects of Acetyl L-carnitine on ischemia/reperfusion-induced arrhythmias and infarct size in isolated rat heart

Abstract

Introduction: Acetyl-L-carnitine (ALC) is an ester of the trimethylated amino acid, L-carnitine, and is synthesized in the human brain, liver, and kidney by the enzyme ALC transferase. ALC facilitates the uptake of acetyl CoA into the mitochondria during fatty acid oxidation, enhances acetylcholine production, and stimulates protein and membrane phospholipids synthesis. ALC, similar in structure to acetylcholine, also exerts a cholinomimetic effect. ALC plays a major role in normal mitochondrial function, being a transport molecule for free fatty acids and an important acetyl-group donor in high-energy metabolism and free fatty acid beta-oxidation. Its main body stores are in skeletal and cardiac muscle. It is found along with free plasma L-carnitine and other acyl-esters of varying chain length and has been claimed to be superior to normal L-carnitine in terms of bioavailability. This study aimed to examine whether ALC was able to reduce cardiac arrhythmias and myocardial infarction size in ischemic-reperfused isolated rat heart.

Method & materials : Male Wistar rats weighing 270-330 g were used in this study. The rats were pretreated with intraperitoneal (ip) injection of 300 IU heparin then anaesthetized by sodium pentobarbital (60 mg/kg, ip). The hearts were excised rapidly and mounted on a non-recirculating langendorff apparatus under 100 mmHg pressure at 37 °C and perfused throughout the experiments with modified Krebs-Henseleit (K/H) solution which was previously equilibrated with 95% O2 - 5% CO2. A fluid filled balloon introduced into the left ventricle and inflated to give a preload of 8–10 mmHg . After 20 min stabilization, the hearts subjected to 30 min regional ischemia followed by 120 min reperfusion. In control group (n=8-10), the hearts perfused only by normal K/H solution throughout the experiment, while in the treatment groups (4 groups, n=8-10 in each group), they were perfused during I/R with enriched K/H solution with 0.375, 0.75, 1.5 and 3 mM of ALC, respectively. Induction of regional ischemia achieved by temporary occlusion of left anterior descending (LAD) coronary artery followed by 120 min reperfusion. An epicardial ECG was recorded by a polygraph during the experiment. Based on the Lambeth conventions, the ECGs were analyzed to determine the total number of ventricular ectopic beats (VEBs), the number of beats occurring as ventricular tachycardia (VT), and the incidence and duration of VT and ventricular fibrillation (VF) during ischemia and the first 30 min of reperfusion time. At the end of reperfusion, Evans blue solution was infused to stain the non-ischemic area. Then the hearts were cut into slices, incubated by 1% Triphenyltetrazolium chloride solution, and fixed in formalin. The infarct size was determined by using a computerized planimetry package.

Results: During ischemia, all used concentrations of ALC decreased number and duration of ischemic ventricular tachycardia (VT) and number of ventricular ectopic beats (VEBs) versus the control group (p<0.01). ALC reduced the incidence of total ventricular fibrillation (VF) and the time spent for reversible VF (p<0.05). In addition, incidence of VT was significantly reduced only by 3 mM (p<0.05). At the reperfusion phase, duration of VT showed significant reduction by lower concentrations (p<0.05). Moreover, ALC (0.375, 1.5 and 3 mM) reduced the incidence of total VF from 80% (control) to 25%, 50% and 38%, respectively (p<0.05). In the control group, infarct size was 23±3.1%, however, ALC (0.375, 0.75, 1.5 and 3 mM) reduced infarct size to 8.7±2.3 (p<0.01), 5.3±1.4 (p<0.0001), 12±4.1 (p<0.05) and 8±2.9% (p<0.01).

Conclusions: By considering of the results, it may be concluded that ALC has protective effects against cardiac ischemia-reperfusion injuries as reduction of infarct size and arrhythmias in isolated rat heart. Stimulation of glucose oxidation via activation of PDH, and then reducing lactate production, reduction of fatty acid metabolites in the myocytes and antioxidant effect by ALC may have important roles in this condition.