الفهرس 
Myocardial Infarction (MI)Only 14 pages are availabe for public view
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Abstract
The present study aimed to investigate the potential cardioprotective effect of methyl palmitate (MP) against isoproterenol (ISO)-induced myocardial infarction (MI) in rats. Moreover, the study aimed to elucidate the underlying molecular mechanisms via studying its effect on different oxidative stress, apoptotic and inflammatory markers. The study was carried out in two consequent phases:
Phase I: Assessment of the cardioprotective dose of MP
Fifty male Sprague Dawley rats were randomized into five groups (n=10). group 1 was considered as a control group, where rats were given corn oil, orally, three times per week on alternative days for 2 weeks. Rats in group 2 were given corn oil, orally, three times per week on alternative days for 2 weeks and then injected with 2 consecutive doses of ISO (85 mg/kg, s.c) on the 13th and 14th days. Rats in groups 3, 4 and 5 were given different doses of MP (75, 150 and 300 mg/kg, respectively, p.o) three times per week on alternative days, then injected with 2 consecutive doses of ISO (85 mg/kg s.c.) on the 13th and 14th days. After 24 hours from the last ISO injection, serum samples were collected from each group, then the rats were sacrificed and heart tissues were isolated.
Studied parameters in phase I
Histopathological examination of heart tissues using Hematoxylin and Eosin (H & E) stain was performed. Serum activities of the cardiac enzymes creatine kinase myocardial band (CK-MB), aspartate aminotransferase (AST) and lactate dehydrogenase (LDH) were detected as well. Additionally, heart index was calculated.The results of the first phase revealed that the injection of the two consecutive ISO doses resulted in the induction of MI, evidenced by the histopathological changes, where the heart sections of the rats showed focal areas of coagulative necrosis in addition to a massive number of inflammatory cells infiltration. The degree of myocardial muscle damage revealed severe necrosis with diffuse inflammatory process. Additionally, ISO significantly elevated the serum activities of the cardiac enzymes CK-MB, AST and LDH as well as the significant increase of the heart index as compared to the control group.
Pretreatment with MP (150 mg/kg) proved a marked cardioprotective effect which was significantly more prominent than the lowest dose (75 mg/kg) while the highest dose (300 mg/kg) did not show more protection than the middle dose. Thus, the dose of (150 mg/kg) was the minimum effective cardioprotective dose which was selected to be used in the second phase of the study.
Phase II: Mechanistic study
For studying the potential cardioprotective mechanisms of the selected dose of MP (150 mg/kg), forty rats were randomized into four groups (ten rats per group) and treated for 2 weeks. group 1 was considered as a control group where rats were given corn oil, orally, three times per week on alternative days for 2 weeks. For group 2, rats were given the selected dose of MP (150 mg/kg, p.o) three times per week on alternative days for 2 weeks. Rats in group 3 were given corn oil, orally, three times per week on alternative days for 2 weeks and then injected with 2 consecutive doses of ISO separated by 24 hours (85 mg/kg, s.c) on the 13th and 14th days. Meanwhile, rats in group 4 were given the selected dose of MP (150 mg/kg, p.o) three times per week on alternative days for 2 weeks and then injected with 2 consecutive doses of ISO (85 mg/kg s.c.) on the 13th and 14th days. Finally, after 24 hours from the last ISO injection, serum samples were collected from each group, then the rats were sacrificed and heart tissues were isolated.
Studied parameters in phase II
The rats were subjected to the electrocardiography (ECG). For the detection of the oxidative stress insults, cardiac content of malondialdehyde (MDA) and reduced glutathione (GSH) as well as cardiac activity of superoxide dismutase (SOD) enzyme were determined. Cardiac content of endothelial nitric oxide synthase enzyme was also detected. In addition, cardiac expression of caspase 3, Bax and Bcl-2 was assessed to detect apoptosis. To assess inflammation, toll like receptor 4 (TLR-4), nuclear factor kappa B (NF-κB), tumor necrosis factor-alpha (TNF-α) and cyclooxygenase-2 (COX-2) were detected as well.
The results of the second phase showed that ISO-intoxication induced a significant tachycardia, inversion of T wave, prolongation of QT and QTc intervals and widening of QRS complex. Moreover, ISO-intoxication showed marked elevation of all oxidative stress and inflammatory markers. Additionally, ISO injection significantly increased the cardiac expression of the pro-apoptotic markers Bax and caspase 3 while markedly ameliorated the anti-apoptotic marker Bcl-2. Furthermore, ISO significantly decreased the cardiac content of eNOS enzyme.
Pretreatment of rats with MP (150 mg/kg) proved a significant cardioprotection against ISO-induced MI evidenced by the significant improvement of the ECG changes, amelioration of the oxidative stress markers and restoring the antioxidant defenses as well as the elevation of eNOS cardiac content. In addition, MP pretreatment diminished the cardiac content of TLR-4 and TNF-α and reduced the expression of NF-κB and COX-2. Finally, MP markedly mitigated the expression of the pro-apoptotic proteins while elevated the expression of the anti-apoptotic protein.
In conclusion, the present study revealed for the first time the cardioprotective role of MP against ISO-induced MI in rats. The main mechanisms underlying this cardioprotective effect are mainly attributed to the abrogation of TLR-4/NF-κB inflammatory pathway, enhancing eNOS cardiac content in addition to the potent antioxidant and anti-apoptotic activities of MP. Accordingly, the pretreatment with MP could provide a new promising solution in MI cases.