الفهرس 
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Abstract
Myocardial infarction (MI) is a major cause of both morbidity and mortality worldwide.Myocardial infarction occurs due to coronary artery occlusion, resulting in deprivation of oxygen supply to myocardium, thus providing a serious threat to tissue viability. Cardiomyocytes depend on continuous oxygen and nutrients supply due to the heart’s limited anaerobic metabolism capacity. MI can be diagnosed by chest pain, and elevation of blood enzymes including: creatine kinase myocardial band (CK-MB), aspartate aminotransferase (AST) and lactate dehydrogenase (LDH) and cardiac troponins (cTn). Ischemic heart damage which occurs during MI results in homeostasis imbalancein the heart which leads to a sequential cascade of cellular alterations such as: Oxidative stress, inflammation, Apoptosis, Autophagy and morphological changes. All processes occur within minutes, but progress gradually.
Reactive oxygen species (ROS) formed during oxidative stressassociated with myocardial infarction cases can initiate chain reaction of lipid peroxidation, proteins oxidation and cause DNA damage. Adaptive response will be initiated by the cells to protect themselves against the deleterious effects of ROS. These adaptive systems include: Enzymatic ROS scavengers, superoxide dismutase (SOD), and glutathione peroxidase (GPX). When the oxidant concentration exceeds the cell’s adaptive capacity such as during MI, the cell will exhibit a state of oxidative injury. MI release endogenous signals followed by cascades that finally leading to increasing serum levels of (TNF-α, IL-1β, IL-6. Apoptosis is induced in cardiomyocytes due to a number of factors such as: DNA damage, oxidative stress. Caspases and Bcl-2 families are two main protein familiesthat are involved in apoptosis process. Autophagy is a complex process that can be involved in both cell survival and cell death (dual process). Autophagy normally plays a key role in myocardial structure and function preservation. While in the injured myocardium, the role of autophagy is more complex. Light chain microtubule associated protein -3 (LC3) is synthesized and increased during autophagy, making it a reliable marker of autophagy in cells.
Isoproterenol (ISO): is a non-selectively on β agonist that generates highly cytotoxic free radicals through the autoxidation of catecholamines. It creates potentially fatal arrhythmias, and may possibly create focal MIs of variable size and location.
One of the promising herbs that have a potential protective effect against MI is Nigella Sativa. Thymoquinone (TQ) is the main constituent in Nigella sativa. The active ingredient TQ is considered to have a potent antioxidant and has anti-inflammatory properties it also exhibited nephroprotective, hepatoprotective, and neuroprotective activities.
The present study was conducted to investigate the cardioprotective effect of TQ in MI induced by ISO in rats and understand the possible mechanisms of thymoquinone effects by measuring the markers of oxidative stress, inflammation and apoptosis in the myocardial tissue.
In this study, the rats were randomly assigned into the following six experimental groups (14-16 rats per each group):
group 1: Normal control: the rats of this group received 5% DMSO (1 ml, orally daily) for 21 days and received normal saline (0.5 ml/kg, s.c.) on the 20th and 21st days at a 24 hr interval.
group 2: Thymoquinone (TQ 20) control: the rats of this group received TQ at a dose of 20 mg/kg/day (dissolved in 5% DMSO, orally) for 21 days. On the 20th and 21st days, normal saline was administered (0.5ml/kg, s.c., at a 24hr interval).
group 3: Thymoquinone (TQ 50) control: the rats of this group received TQ at a dose of 50 mg/kg/day (dissolved in 5% DMSO, orally) for 21 days. On the 20th and 21st days, normal saline was administered (0.5ml/kg, s.c., at a 24 hr interval).
group 4: Isoproterenol (ISO): the rats of this group received 5% DMSO
(1 ml, orally daily) for 21 days and received ISO (85mg/kg ,dissolved in 0.5 ml saline, on the 20th and 21st days (at an interval of 24 hr).
group 5: Thymoquinone 20 + Isoproterenol (TQ 20+ISO): the rats of this group received TQ 20mg/kg/day (dissolved in 1ml 5% DMSO, orally) for 21days along with concurrent administration of ISO (85 mg/kg, dissolved in 0.5 ml saline, s.c.) (Ojha et al., 2015) on the 20th and 21st days (at a 24 hr interval).
group 6: Thymoquinone 50 + Isoproterenol (TQ 50+ISO): the rats of this group received TQ 50 mg/kg/day, (dissolved in 1ml 5% DMSO, orally) for 21days along with concurrent administration of ISO (85 mg/kg, dissolved in 0.5ml saline, s.c.) on the 20th and 21st days (at a 24 hr interval).
By the end of the experiment the blood was collected for the measurement of :
- Aspartate aminotransferase (AST)
- Creatine phosphokinase (CK-MB)
- Lactate dehydrogenase (LDH)
- Cardiac troponin I (c Tn I)
The hearts of each group was excised for the measurement of:
- Interleukin 1β (IL-1β) concentration, Interleukin 6 (IL-6) concentration and Tumor necrosis factor-alpha (TNFα) levels concentration.
- Level of malondialdehyde (MDA) level , Reduced glutathione (GSH) concentration and Superoxide dismutase (SOD) activity
- Caspase-3 level
- LC3 light chain 3 level
- Myocardial infarct size using triphenyl tetrazolium chloride (TTC) assay.
- Histopathological examination using H&E and Masson’s trichrome staining
The major results of this study clearly revealed that: both doses of TQ significantly attenuated the injurious effects of ISO on the myocardium, the high dose of TQ (50mg/kg/day) was significantly more effective in ameliorating both the myocardial tissue pathological alterations and the serum diagnostic cardiac markers of MI as compared to the lower dose (20mg/kg/day). TQ possesses a cardioprotective effect against ISO-induced MI in rats. the pretreatment of ISO-administered rats with TQ improved cardiac function, reduced myocardial infarct area, minimized cardiac histopathological changes, decreased elevated myocardial tissue levels of markers of oxidative stress, inflammation, apoptosis and fibrosis and increased the reduced myocardial tissue autophagy in the MI model. Integrating altogether the multiple effects of TQ including antioxidant, anti-inflammatory, anti-apoptosis, antifibrotic and autophagy enhancer effects may explain the marked cardioprotection observed, in the present study, in the TQ-pretreated ISO- administered rats as compared to the saline-pretreated ISO-administered control rats.
There are several new and important insights regarding the efficacy of TQ in cardioprotection against MI, a constantly growing medical and social burden in developed and underdeveloped countries despite significant advances in diagnosis and therapy. First, this study, for the first time, reports the dose dependent cardioprotective effects of TQ in experimentally-induced MI in rats. The changes induced by ISO- administration were ameliorated with TQ pre- and co-treatment in both doses with significantly more obvious amelioration in the high dose (50 mg/kg/day) as compared to the low dose ( 20mg/kg/day). Second, this study, for the first time, demonstrates that treatment with TQ in a high dose could increase the myocardial baseline GSH level adding in direct antioxidant effect to its direct scavenging effect of free radicals, third, TQ exerts antifibrotic effect reducing myocardial fibrosis in the ISO-induced MI model in rats. Fourth, TQ acts as autophagy enhancer modulating the impaired autophagy in the setting of acute MI to prevent further damage from occurring in myocardial cells with subsequent worsening of cardiac function. Further investigations are required for the findings of our study to raise the possibility that TQ may act as a novel promising prophylactic therapy for patients who are at risk of developing MI and to provide cardioprotection against the progression of existent infarction in diagnosed cases.