The effects of voluntary complex and regular wheel running exercises on the levels of 8-oxoguanine DNA glycosylase, semaphorin 3B, H2O2, and apoptosis in the hippocampus of diabetic rats

چکیده مقاله

Purpose: One of the most frequent complications associated with diabetes mellitus is apoptosis within the brain which can lead to cognitive disorders. Exercise is considered the best non-pharmacological approach to reduce the severity and extent of cell death through poorly-understood mechanisms. The aim of this study was to investigate the effects of voluntary complex and regular wheel running on the levels of 8-oxoguanine DNA glycosylase (OGG1), semaphorin 3B (sema3B), hydrogen peroxide (H2O2), and apoptosis in the hippocampus of diabetic rats. Methods: 48 Wistar male rats were randomly divided into 6 groups: healthy control (C), diabetes control (D), regular wheel running + diabetes (RWD), complex wheel running + diabetes (CWD), healthy regular wheel running (RW), and healthy complex wheel running (CW). The diabetic rat model was produced by intraperitoneal injection of streptozotocin (STZ). The protocol encompassed a 4-week voluntary running training regimen on regular and complex wheel running apparatus. The rats were sacrificed 48 hr after the last training session. To measure the protein concentrations within the hippocampus, ELISA has been utilized. One-way ANOVA was used to compare the groups. Results: There were no significant differences in OGG1 protein levels between the groups. H2O2 level in the D group was significantly higher than the C group (p = .002), while this in RWD and CWD groups was considerably lower than the D group (p = .002 and p = .003, respectively). In the D group, the levels of apoptosis and Sema3B were significantly (p = .001 and p = .007, respectively) higher than C, RWD (p = .001, p = .0001, respectively), and CWD groups (p = .001, p = .006, respectively). Nevertheless, there were not any significant differences between RWD and CWD groups. 2 of 10  |     FAZELZADEH et al. 1 | INTRODUCTION Diabetes mellitus is a chronic and progressive metabolic disorder, and the complications associated with it account for 2.2% of all deaths in the world. Oxidative stress, an imbalance between production and detoxification of oxygen or nitrogen free radicals, contributes to the onset and progression of diabetes (Rains & Jain, 2011). It has been shown that free radicals increase the risk of diabetes-related disorders such as endothelial dysfunction, cardiomyopathy, retinopathy, nephropathy, and neuropathy in diabetic patients (Zatalia & Sanusi, 2013). Diabetes causes neuronal apoptosis in the brain through several mechanisms, including oxidative stress, inhibition of caspases, disturbance in the expression of apoptotic regulator genes, as well as mitochondrial dysfunction. Any abnormalities within the apoptotic pathway may cause pathological conditions such as neurodegenerative diseases (Radi et al., 2014). Within the brain, the hippocampus is particularly susceptible to certain clinical conditions such as ischemia, stress, and diabetes leading to neurophysiological, structural, and molecular changes in this region. There have been studies showing a reduction in memory and learning capabilities following diabetes (Boulton et al., 2005). Nuclear and mitochondrial DNA are the main targets of free radicals leading to cell death and apoptosis. 8-hydroxy-2′-deoxyguanosine (8-OHdG) is the most commonly considered biomarker of oxidative DNA damage, as it represents 5% of total oxidized bases in DNA and therefore can be easily detected (Helbock et al., 1999). The mutagenic base, 8-OHdG, is a consequence of oxidative stress by hydroxyl radicals attacking 2'-deoxyguanosine (dG) resulting in a hydroxyl moiety replacing the hydrogen atom (Van Remmen et al., 2003). The level of 8-OHdG is remarkably increased in diabetic patients, and also in a rat model of diabetes (Nishikawa et al., 2003). Base excision repair (BE) is the major repair system for oxidative base damage, and this system is particularly crucial in neurons because of their high oxygen metabolism rate (Jeppesen et al., 2011). OGG1 is among the enzymes in this repair system that plays important roles. The OGG1 gene is located on short arm of chromosome 3 and encodes 8-hydroxyguanine glycosylase, an enzyme which catalyzes the excision of 8-OHdG (Zou et al., 2016). It has been reported that overexpression of cellular hydrogen peroxide (H2O2) decreases the expression and activity of the OGG1 enzyme, compromising its ability in protecting DNA (Kim et al., 2014). Induction of type I diabetes in rats has been shown to decrease OGG1 activity leading to higher risks of DNA damage in kidney cortical cells (Simone et al., 2008). It has been demonstrated that axon-guiding molecules, especially semaphorins, play critical roles in the formation of the vascular network as well as induction of apoptosis in neurons (Neufeld & Kessler, 2008; Shirvan et al., 1999). The biological form of this molecule in vertebrates is class 3 semaphorin (Neufeld & Kessler, 2008). One of the subunits of class 3 semaphorin, Sema3B, has been particularly known for its role in the induction of apoptosis within nerve cells in certain pathological conditions, and thus its up-regulation induces apoptosis and suppression of cancerous tumors (Shirvan et al., 1999). It has been reported that Sema3A is highly expressed in patients with diabetic nephropathy, which can lead to apoptosis within kidney podocytes, and thereby accelerating disease progression (Aggarwal et al., 2015). As a result, we hypothesized that there is an increased level of Sema3B and a decreased level of OGG1 in diabetic patients, which would increase the extent of apoptosis in the brain. Therefore, restoring the levels of these two molecules through exercise as a safe and non-pharmacological approach might potentially decrease the adverse effects of diabetes on the brain. Although there are several contradictory studies concerning the effects of exercise on antioxidant enzyme activities, exercise can indeed improve brain functions by balancing oxidation–regeneration processes through increasing resistance against oxidative stress and accelerating the recovery from its detrimental effects (Devi & Kiran, 2004; Radak et al., 2007). It has been shown that even highly intensive exercises are unlikely to cause significant oxidative damage to DNA (Ogonovszky, Berkes, et al., 2005). It has been reported that regular exercise reduces the accumulation of 8-OHdG in the hippocampus (Mahjoub et al., 2016). This is while, the production of moderate amounts of 8-OHdG is important for neurogenesis (Walton et al., 2012). Exercise has been shown to be able to modulate the activity of DNA repair enzymes, especially OGG1 and uracil DNA glycosylase (UDG), thereby reducing 8-OHdG accumulation and mutation in skeletal muscle cells (Sallam & Laher, 2016). Similarly, Bo et al. (2014) have shown that performing prolonged treadmill running exercise restores the impaired activity of OGG1 and the mitochondrial antioxidant enzymes within the hippocampus in rats model of Alzheimer`s disease (Bo et al., 2014). Although there are reports about the positive effects of treadmill running and swimming exercises on the base excision repair system, and OGG1 and UDG enzymes, there are not enough studies investigating the effects of voluntary wheel running on the levels of OGG1 and UDG enzymes (Sallam & Laher, 2016). Wheel running is a type of endurance exercise resembling the normal physical activity in rats and humans, with minimal Conclusion: The increased levels of Sema3B, H2O2, and apoptosis within the hippocampus associated with diabetes could be noticeably restored by both types of voluntary wheel running protocols.