1. Introduction
Prooxidant-Antioxidant Balance (PAB) results from the dynamic balance established under homeostasis between the production and release of free radicals. A change in the balance between the production of Reactive Oxygen Species (ROS) and the antioxidant system can induce oxidative stress [1]. Oxidative stress has been reported to cause DNA damage and apoptosis, leading to cardiovascular disease [2].
Evidence shows that aerobic exercise reduces oxidative stress by adapting to the antioxidant systems [6]. A study on middle-aged women with obesity showed that 12 weeks of aerobic exercise can lead to an improvement in the oxidant/antioxidant process in the body due to reducing the serum concentration of Malondialdehyde (MDA) and increasing the antioxidant capacity [9]. However, 8 weeks of high-intensity interval training had no effect on the total antioxidant capacity and MDA in the liver tissue of male Wistar rats [10].
Due to the potential role of tribulus terrestris extract and regular exercise in preventing oxidative stress, the present study aims to investigate the effect 8 weeks of aerobic exercise and consumption of tribulus terrestris extract on the oxidative stress markers in the heart tissue of male rats poisoned with Hydrogen Peroxide (H2O2).

2. Materials and Methods
This experimental study was conducted in 2019 on male Wistar rats in the animal house of Islamic Azad University of Central Tehran Branch in Iran.
Samples were 42 male Wistar rats randomly divided into seven groups. 
All groups received H2O2 (100 mg/kg/body weight) for 14 days intraperitoneally [15]. Rats in supplementation groups received hydroalcoholic extracts of tribulus terrestris (5 and 10 mg per day) by gavage [16]. Aerobic exercise was performed on a treadmill at a speed of 23 m/min for eight weeks, 5 days per week, each for 30 min [17]. After the last exercise session, heart tissue of rats was collected and the concentration of oxidative stress markers was then measured by ELISA method.

3. Results
Tribulus terrestris extract and combination of tribulus terrestris extract and aerobic training led to significant increase in levels of O6-methylguanine-DNA-methyl transferase, PAB, and cytochrome C oxidase, and a significant decrease in adenosine triphosphate and MDA levels in the heart tissue of rats compared to the control group poisoned with H2O2 (P<0.05).

4. Conclusion
The findings of this study were consistent with the results of Carraro et al., [7], Siu et al., [8] and Hejazi et al. [9]. The reasons for oxidative stress and destruction of cellular DNA following aerobic exercise includes increased intracellular responses, reaction of various body tissues to oxidative stress produced during exercise, and catabolism of synthetic components of proteins and cell defense mechanism [23]. Moderate-intensity aerobic exercise can have a protective effect against these damages by strengthening and activating the body’s antioxidant and immune systems [24].
Tribulus terrestris has considerable effect on the treatment of various heart diseases including coronary heart disease, myocardial infarction, and atherosclerosis. It protects the heart against ischemic injury by activating protein kinase C [27]. It contains components such as flavonoids, polyphenols, vitamins E and C that have antioxidant properties. The compounds in this plant purify various ROS such as superoxide anion (O2-) and hydroxyl radical (OH) [28]. Therefore, it is possible that the extract of tribulus terrestris protected against free radical damage in the heart tissue of rats in our study due to its compounds.
It seems that regular aerobic exercise along with consumption of various doses of tribulus terrestris extract is a moderating factor in mitochondrial biogenesis and is effective in reducing DNA damage in the heart tissue. Lower dosage of tribulus terrestris extract has more benefits.

Suggestions
It is recommended to use aerobic exercise combined with supplementation of tribulus terrestris extract for its cardiac benefits.

Limitations
There were some limitations in the present study due to study on animals. We did not measure other oxidative stress markers in the heart tissue of rats. Examining the effect of different doses of tribulus terrestris extract on the heart tissue after exercise can help better explain and interpret the results. 

Ethical Considerations
Compliance with ethical guidelines
This study was approved by the Ethics Committee of the Islamic Azad University-Marvdasht Branch (Code: IR.IAU.M.REC.1398.028).

Funding
The paper was extracted from the PhD. dissertation of the first authorat the Department of Exercise Physiology, Central Tehran Branch, Islamic Azad University, Tehran, Iran.

Authors' contributions
All authors contributed equally in preparing this article.

Conflicts of interest
The authors declare no conflict of interest. 

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