1. Introduction

Alzheimer’s Disease (AD) is considered as a global challenge, regarding the increase of old population in developing countries. The AD symptoms and neurodegeneration stimulate the glial cells to secret proinflammatory cytokines. Moreover, the increasing level of the proinflammatory cytokines leads to further production of Aβ42 plaques and other proinflammatory cytokines, through the autocrine and paracrine pathways. Finally, this sequence of changes leads to more neurodegeneration in patients with AD [5]. 

No definite treatment has been defined for AD. However, some treatments decelerate and control the disease processes. It has been shown that physical trainings decrease the damage to the nervous and immune systems, in patients with AD [10]. Also, the use of medicinal plants, such as saffron is proposed as another prevention and treatment [17]. Saffron is used to treat the complications of neurological disorders [25]. Yet, the inflammatory response to saffron remained to be studied in AD.

Interleukin (IL)-17 acts as a central regulator of the inflammatory response in the brain [7]. Also, IL-18 is one of the main regulators of the innate and acquired immune system [8]. The expressions of IL-17 and IL-18 in neurons are positively associated with each other [9]. Studies have reported inconsistent results on the association between aerobic exercise training and the plasma concentrations of IL-17 and IL-18. Aerobic exercise training has led to both increase [12] and decrease [11] in the plasma concentration of IL-17. Besides, studies show that exercise decreases [13] or does not affect [14] the plasma concentration of IL-18. Therefore, the present study aimed to investigate the effect of endurance training and saffron extract on the plasma levels of IL-17 and IL-18, in trimethyltin chloride-induced Alzheimer’s rats.

2. Materials and Methods

The study population included all the male Sprague-Dawley rats in the Animal Care Center of Islamic Azad University, Marvdasht City, Iran. A total number of 32 rats were selected as the study sample, based on the purposive sampling method. All the rats had four weeks of age and 180±20 grams of weight. The selected rats were kept in the laboratory for a week to become adapted to the environment. Next, the AD was induced with the intraperitoneal injection of 80 mg/kg trimethyltin chloride. The Alzheimer’s rats were randomly assigned into four groups: training, saffron extract, saffron extract + training, and control.

The endurance training program included incremental running on the treadmill at a speed of 15 to 20 m/min. The program was performed in 15 to 30 minutes sessions, three sessions per week, for eight weeks. After the completion of the training program, the plasma concentrations of IL-17 and IL-18 were determined using ELISA kits. Then, the two-way ANOVA was conducted to compare the differences in the inflammatory indices. Besides, the statistical analyses were performed with SPSS-23 software.

3. Results

The two-way ANOVA represented that training (P=0.10), saffron extract (P=0.07), and the interaction of training and saffron extract (P=0.06) do not significantly affect the plasma IL-17 levels, in rats. Also, the effect size was calculated; the obtained eta values were 0.20, 0.24, and 0.26 for training, saffron extract, and the interaction of training and saffron extract, respectively (Figure 1).



The two-way ANOVA was also used to compare the differences of IL-18 concentrations in the Alzheimer’s rats. The results showed that training (P=0.68), saffron extract (P=0.84), and the interaction of training and saffron extract (P=0.57) do not significantly affect the plasma IL-18 levels, in rats. Also, the obtained eta values were 0.01, 0.00, and 0.02 for training, saffron extract, and the interaction of training and saffron extract, respectively (Figure 2).


 

4. Discussion

The present results indicated that eight weeks of endurance training, the use of saffron extract, and the interaction of endurance training and saffron extract do not significantly affect the plasma concentrations of IL-17 and IL-18, in Alzheimer’s rats. The reactions of IL-17 and IL-18 have not been determined in the central nervous system. However, it is suggested that physical training leads to the release of cytokines in the bloodstream, and causes systematic effects, such as neuroprotection. Moreover, the high levels of physical activity reduce the chronic inflammation [33]. Energy consumption increases with the levels of physical activity, thus, exercise that expends more energy is likely to have more beneficial effects on the inflammatory condition. In the present study, the inflammatory responses to aerobic exercise may be influenced by the amount of consumed energy. Consuming more energy, longer training programs lead to a significant reduction in the inflammatory responses. Intense exercise releases proinflammatory cytokines, which produce anti-inflammatory cytokines, such as IL-2, IL-6, and IL-10. The consecutive production of proinflammatory and anti-inflammatory cytokines can initiate the production of IL-17 in peripheral blood and skeletal muscles [35]. Furthermore, the increase in anti-inflammatory cytokines may justify the decrease of IL-18 concentration [36].

Saffron has anti-inflammatory effects because it includes flavonoids, tannins, saponins, and crocins [39]. Crocin is ineffective at low doses [41], however, high doses of crocin have improved hippocampal function [42]. The inflammatory effects of saffron may be dose-dependent in Alzheimer’s patients. Also, the saffron’s absorption, effectiveness, and adaptation to exercise have not been confirmed, regarding variables, such as physical function, hematological indicators, and body weight.

The main limitation of the present study was the lack of measurement of other related inflammatory factors. The measurement of inflammatory factors (such as IL-2, IL-6, and IL-10) helps to explain and interpret the results, especially in AD. It is recommended to investigate the oxidative damage indices following the consumption of saffron extract and exercise trainings in Alzheimer’s rats.

5. Conclusion

According to the findings, exercise training and saffron extract do not affect the inflammatory factors, in rats with AD. These results can be caused by the inadequate exercise intervention period. However, manipulating the dose of saffron extract and the consumption period may lead to clear results. Few studies have been conducted on this issue, thus, further research is required to confirm the effect of exercise and saffron extract consumption on inflammatory factors in AD.

Ethical Considerations

Compliance with ethical guidelines

The present study was confirmed by the Ethics Committee of the Biomedical Research of Islamic Azad University, Marvdasht Branch (Ethics Code, IR.IAU.M.REC.1399.011).

Funding

This article has been extracted from the master’s thesis of the first author in the Department of Sport Physiology, Islamic Azad University, Marvdasht Branch, Shiraz, Iran.

Authors' contributions

All authors equally contributed in preparing this paper.

Conflicts of interest

The authors declare no conflict of interest.

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