Detoxification pathways of the free radical superoxide anion, provided by tissue metabolism, and the reactive species hydrogen peroxide, forming other less toxic compounds. The effects of HPA on increase or decrease enzymatic activities are showed by cycled+and -, respectively. Regular exercise in HPA rats maintain normal values of catalase and glutathione peroxidase activities (boxed =). These reactions are considered the main enzymatic antioxidant system essential to avoid oxidative stress 

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... confirmation of normality of data and homogeneity of variances, the statistical analyses were performed by Student ’ s t -test or two-way ANOVA followed by the Tukey test for multiple comparisons using the Statistical Package for the Social Sciences (SPSS) software in a PC-compatible computer. A value of p < 0.05 was considered to be statistically significant. We measured the glycogen content of soleus muscles to verify if 14-day regular exercise was effective, in other words, to check the oxidative impact of the training conducted. The exercised groups showed increased levels of muscle glycogen content (t (38) =4.78; p <0.001; n =20 per group) comparing to the sedentary groups (Sed 1.57±0.34 mg/g tissue; and Exe 2.22±0.47 mg/g tissue), showing a peripheral adaptation caused by the aerobic exercise, as was expected. The measurement of lipid peroxidation and antioxidant enzyme activities were carried out to verify oxidative stress parameters in the brain of rats subjected to HPA model under regular exercise. Representing the products of lipid peroxidation, TBA-RS content (Fig. 1) was increased by the HPA condition and this oxidative change was prevented by the regular exercise (F (3,36) =10.46, p <0.001). Regarding antioxidant enzymatic defense, we measured the activities of SOD, CAT and GPx, three important enzymes that act in detoxification of superoxide and hydrogen peroxide. Figure 2 shows that SOD activity was increased by HPA model, while regular exercise was able to avoid this alteration (F (3,36) = 12.35, p <0.001). CAT (Fig. 3) and GPx (Fig. 4) activities were reduced by HPA and these activities were restored in the regular exercised group (F (3,28) =9.18, p <0.001 and F (3,28) = 8.59, p <0.001, respectively). No statistical differences were found comparing ExeSAL groups to control values (SedSAL group) for all oxidative stress parameters analyzed. HPA has been associated to oxidative stress (Sierra et al. 1998; Hagen et al. 2002; Artuch et al. 2004; Moraes et al. 2010), although its mechanisms are not completely understood. The moderate but continuous increase of phenylalanine levels appears to be harmful even after maturation of the central nervous system of PKU patients (Huijbregts et al. 2002; Sitta et al. 2009), highlighting the need for concomitants strategies additionally to the restricted dietary treatment. Animal studies of HPA (Hagen et al. 2002; Moraes et al. 2010) have shown increased oxidative stress due to decreased activity of enzymes responsible for detoxifying reactive substances in cells. Similar results were also observed in PKU patients and may be related with the impairments of mental health reported (Gassio et al. 2008). Free radicals and reactive species are normally produced by cell respiration, mainly in the mitochondria, by process of oxidative phosphorylation, but also by various cytosolic enzymes (Balaban et al. 2005). The exercise is certainly a great stressor, increasing the production of free radicals and reactive species in whole body. Sympathoadrenal stimula- tion triggers a series of reactions to provide energy substrate to active muscles, increasing energy demand and cellular respiration. However, regular and systematic physical exercise can leads to adaptation of the organism, improving peripheral (Pinho et al. 2006) and central aspects (Warburton et al. 2006; Salim et al. 2010). Daily physical training in a treadmill for 14 days has already been described as neuroprotector in rats (Scopel et al. 2006; Cechetti et al. 2008). In addition, this protocol was effective to increase the peripheral oxidative metabolism, as sug- gested by the highest levels of muscle glycogen content of the exercised rats (Pinho et al. 2006). Scopel et al. (2006) reported that regular exercise, at correct intensity and load that can provide adaptations, enables the achievement of favorable effects including improvement of the antioxidant system after training. Reactive species formed repeatedly at each exercise session are capable of generating positive adaptations in the antioxidant system of these individuals, facilitating the handling of reactive species at rest and submaximal activities (Powers and Jackson 2008). Thus, individuals who exercise regularly will be able to deal better with the reactive species normally produced. TBA-RS are a known marker of lipid peroxidation, assessing the products of this process such as malondialde- hyde. Concerning PKU model, the findings of this study showed increase damage to lipids in the brain related to high phenylalanine levels, as was expected (Martinez-Cruz et al. 2002; Moraes et al. 2010). Moreover, regular exercise prevented the increase of TBA-RS in the HPA group. Interestingly, while some authors have found decreased levels of lipid peroxidation in total brain (Coelho et al. 2010) and specific brain areas (Husain and Somani 1998), Aksu et al. (2009) did not find any change in this parameter analyzing different brain areas. All these previous studies were conducted with healthy animals that had exercised for about two months, but using distinct intensities. It seems that the protocol chosen for training influences the adaptation obtained, thus, it is necessary to generate a particular stimuli to achieve a specific adaptation. Hence, the protocol may be responsible for some different results that have been showed in the literature about exercise effects (Radak et al. 2007). The activity of SOD was increased only in sedentary HPA group comparing to control, which probably may represent an adaptation to enhanced levels of superoxide. Physical exercise did not alter this activity in both exercised groups, probably keeping the consumption capacity of superoxide. Some authors (Somani et al. 1995; Coelho et al. 2010) found increased activity of SOD in response to physical training in healthy animals, depending of brain areas. Gomez-Cabrera et al. (2008) also found an increase in the expression of SOD in response to physical training achieved by exercising at moderate intensity but not by exhaustive sessions of exercise. Although SOD is an antioxidant enzyme, which represents an important protection of the cells from damage caused by superoxide anion, its increased activity produces hydrogen peroxide, another reactive species that has to be handled by CAT and GPx. The reduction in activities of CAT and GPx caused by HPA has already been demonstrated (Hagen et al. 2002; Moraes et al. 2010), although the mechanisms are not yet completely clear. These enzymes act converting the hydrogen peroxide, which was probably increased by the increased SOD activity, in water and oxygen. CAT and GPx are especially important for the maintenance of hydrogen peroxide degradation, once this toxic metabolite is one of the main reactive species that leads to imbalance in oxidative system (Halliwell and Gutteridge 2007). In addition, Baud et al. (2004) found that these enzymes act together in a cooperative way in the central nervous system, avoiding the increase of their shared harmful substrate. Taking together, the increase of SOD activity along with the decrease of CAT and GPx activities observed in sedentary HPA rats was prevented in exercised HPA group (Fig. 5). Thus, we can speculate that exercise may avoid the destination of hydrogen peroxide producing hydroxyl radical, which would react with lipids of cell membranes and myelin sheath, as observed in the reduced levels of TBA-RS found when the HPA rats were exercised comparing to sedentary group. In this study, the stimuli provided by a 14-day aerobic training were not able to change any oxidative stress parameter which can be seen comparing exercised saline group (ExeSAL) to values of sedentary rats (SedSAL). Although muscle glycogen content was increased, the stimulus of the physical exercise per se was not sufficient to modify the antioxidant system in the brain of healthy rats. On the other hand, the alterations on oxidative stress parameters observed in HPA sedentary rats were prevented by exercise. It can be hypothesized that regular exercise of only 14 days was not able to improve the antioxidant system above the normal condition, but can avoid the decrease found in a pathological condition, as HPA. We cannot rule out that other parameters of oxidative stress not measured in this work were improved by exercise and so helped to maintain oxidative status at normal levels in HPA rats. In addition, these effects may depend on individual characteristics, resulting in different optimal doses of exercise for each subject. Thereby, the HPA condition showed a greater responsiveness to the benefits provided by regular exercise than healthy rats (saline groups). The study of new therapeutic strategies additionally to the dietary approach may be very helpful for the PKU patient. This study has shown that regular exercise was effective to prevent alterations of some parameters of oxidative stress found in the HPA condition in rats. More studies are necessary to verify the effects of exercise in this pathological condition and the possible benefits using this strategy to contribute to prevent the oxidative stress status in ...