Qom University of Medical Sciences Journal

Introduction
Cadmium (Cd) is a toxic non-essential transition metal that poses a health risk for both human and animals. It naturally exists in the environment as a pollutant that is derived from agricultural and industrial sources [1]. It has a long biological half-life of 20–40 years in humans, and is accumulated in the body for a considerable period of time. Getting in chronic exposure of Cd in low doses can also alter the microscopic structures of tissues, particularly in the liver, kidney, brain, pancreas, intestine, and reproductive organs due to increased content of Cd in these tissues. Because of over-production of oxygen active species, the continuous encounter with Cd causes the increase of oxidative stress in cellular levels and degrades antioxidant defensive mechanisms [2]. Given that the Cd causes lipid peroxidation, increases Malondialdehyde (MDA), and reduces total oxidative capacity (TAC) by producing free radicals, it can lead to infertility and damage of the intracellular defensive system. Studies have shown that infertile men most probably have lower antioxidant capacity than fertile men.
Aerobic exercises are considered as an effective method to improve several undesirable outcomes of health; however, their results have been remained challenging in the reproductive health. It has been proved that moderate exercise is useful for preventing primary and secondary diseases including cardiovascular diseases, type II diabetes, metabolic syndrome, and neurodegenerative diseases, such as Alzheimer’s. This study aims to determine the effect of a period of endurance exercise on MDA level and TAC of testicular tissue in adult male rats with Cd-induced infertility.
Methods
This is an experimental study. Samples were 32 mature and healthy male Wistar rats with a mean weight of 250±30 g and age of 12 weeks. They were purchased from the Tehran Pasteur Institute and kept in the animal laboratory of Islamic Azad University, Qom Branch, at a temperature of 22 2 C °, a humidity of 55±4%, and a 12:12 light-dark circle. All rats had free access to food and water. They were randomly divided into four groups of 8: Control group, Exercise group, Cd group, and Cd+exercise group. To be infertile, the rats received 3 mg/kg body weight of Cd (diluted with distilled water) by gavage. All steps of maintenance and killing were performed according to the instructions of experiments on laboratory animals. To adapt to new environment, the rats were placed in the laboratory conditions for 2 weeks. They were placed on a rodent treadmill to become familiar with the exercise. Endurance exercise was then performed at five sessions per week for five weeks. The exercise protocol included running on a treadmill at a speed of 27 m/min. First session was performed for 16 minutes; one minute was then added to the time daily reaching 30 minutes per session. In order for the obtained adaptations to remain unchanged, the intensity of exercise was kept constant in the fourth and fifth weeks. Rats were anesthetized with diethyl ether 48 hours after the last exercise session. The testicles and epididymis were removed by making an incision in the posterior abdominal area and then transferred to the laboratory to measure their MDA and TAC.
Shapiro-Wilk and Levene’s tests were used to determine the normality of data distribution and the equality of variances, respectively. One-way analysis of variance (ANOVA) followed by the Least Significant Difference (LSD) post hoc test was used to evaluate the differences in the variables between the study groups. All analyses were performed in SPSS software, version 24. The significance level was set at 0.05.
Results
The results of one-way ANOVA showed a significant difference among the four study groups in MDA (P=0.045). The results of LSD post hoc test showed that this difference was significant between control and Cd+exercise groups (P=0.03) and between Cd and Cd+exercise groups (P=0.02). The results of one-way ANOVA also showed a significant difference among the four study groups in TAC (P =0.032). This difference was significant between Cd and control groups (P=0.012), and between Cd and exercise groups (P=0.036). In this study, the levels of MDA and TAC enzymes significantly increased in the exercise group compared to the control group (P<0.05).
Discussion
Moderate-intensity endurance exercise in this study caused a significant increase in the TAC and MDA of testicular tissue in rats with Cd-induced infertility. Therefore, it can be said that regular moderate-intensity endurance exercise can make the body more resistant to oxidative stress. Physical activity improves antioxidant activities and reduces lipid peroxidation level both in adult and in aged people [5] The antioxidant defense system of the body consists of enzymatic antioxidants (e.g., superoxide dismutase, catalase, and glutathione peroxidase) and non-enzymatic antioxidants (e.g., Coenzyme Q10, glutathione, uric acid, lipoic acid, bilirubin). Reactive oxygen species (ROS) generation caused by exercise leads to increased activity of enzymatic antioxidants which increases resistance to wide range of oxidative stress-related diseases including cardiovascular diseases, acquired neurodegenerative disorders (Alzheimer’s and Parkinson’s disease), asthma, diabetes and mitochondrial myopathies. Chronic exposure to high levels of ROS can lead to impairment of cellular functions and cause macromolecule damage, apoptosis, and necrosis. Regular exercise causes compatibility in TAC and protection of cells against the harmful effects of oxidative stress; hence, can prevent cell damage. According to the results, it can be concluded that regular moderate-intensity endurance exercise can make the body more resistant to oxidative stress and can increase the TAC of testicular tissue in rats with Cd-induced infertility.
Ethical Considerations
Compliance with ethical guidelines
This article is taken from the Master's thesis of Sports Physiology, which was conducted at the Islamic Azad University, Qom Branch. All ethical principles approved by University of Qom. (Ethics Code: IR.QOM.REC.1399.023).
Funding
This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Authors contributions
All authors contributed equally in preparing all parts of the research.
Conflicts of interest
The authors declared no conflict of interest.
Acknowledgements
We are grateful for the cooperation of the laboratory personnel of Islamic Azad University, Qom Branch, who helped us in conducting this research, and also to Dr. Hamid Amini, who was present as the second guide in the thesis.