Aerobic exercise training protects against endothelial dysfunction by increasing nitric oxide and hydrogen peroxide production in LDL receptor-deficient mice
© The Author(s) 2016
Received: 2 May 2016
Accepted: 11 July 2016
Published: 19 July 2016
Endothelial dysfunction associated with hypercholesterolemia is an early event in atherosclerosis characterized by redox imbalance associated with high superoxide production and reduced nitric oxide (NO) and hydrogen peroxide (H2O2) production. Aerobic exercise training (AET) has been demonstrated to ameliorate atherosclerotic lesions and oxidative stress in advanced atherosclerosis. However, whether AET protects against the early mechanisms of endothelial dysfunction in familial hypercholesterolemia remains unclear. This study investigated the effects of AET on endothelial dysfunction and vascular redox status in the aortas of LDL receptor knockout mice (LDLr−/−), a genetic model of familial hypercholesterolemia.
Twelve-week-old C57BL/6J (WT) and LDLr−/− mice were divided into sedentary and exercised (AET on a treadmill 1 h/5 × per week) groups for 4 weeks. Changes in lipid profiles, endothelial function, and aortic NO, H2O2 and superoxide production were examined.
Total cholesterol and triglycerides were increased in sedentary and exercised LDLr−/− mice. Endothelium-dependent relaxation induced by acetylcholine was impaired in aortas of sedentary LDLr−/− mice but not in the exercised group. Inhibition of NO synthase (NOS) activity or H2O2 decomposition by catalase abolished the differences in the acetylcholine response between the animals. No changes were noted in the relaxation response induced by NO donor sodium nitroprusside or H2O2. Neuronal NOS expression and endothelial NOS phosphorylation (Ser1177), as well as NO and H2O2 production, were reduced in aortas of sedentary LDLr−/− mice and restored by AET. Incubation with apocynin increased acetylcholine-induced relaxation in sedentary, but not exercised LDLr−/− mice, suggesting a minor participation of NADPH oxidase in the endothelium-dependent relaxation after AET. Consistent with these findings, Nox2 expression and superoxide production were reduced in the aortas of exercised compared to sedentary LDLr−/− mice. Furthermore, the aortas of sedentary LDLr−/− mice showed reduced expression of superoxide dismutase (SOD) isoforms and minor participation of Cu/Zn-dependent SODs in acetylcholine-induced, endothelium-dependent relaxation, abnormalities that were partially attenuated in exercised LDLr−/− mice.
The data gathered by this study suggest AET as a potential non-pharmacological therapy in the prevention of very early endothelial dysfunction and redox imbalance in familial hypercholesterolemia via increases in NO bioavailability and H2O2 production.
KeywordsAerobic exercise training LDL receptor-deficient mice Familial hypercholesterolemia Endothelial dysfunction Nitric oxide synthase Hydrogen peroxide Superoxide dismutase
Familial hypercholesterolemia (FH) is a genetic disorder characterized by high concentrations of low-density lipoprotein (LDL), resulting in premature development of atherosclerosis and its vascular complications . Endothelial dysfunction has been described as an important early marker of atherosclerosis preceding atheroma formation and is characterized by impaired vasodilatation . Therefore, non-pharmacological strategies preventing the onset of endothelial dysfunction may protect against the acceleration of atherosclerosis in FH.
LDL receptor knockout (LDLr−/−) mice are a genetic model of hypercholesterolemia that mimics human FH . It is accepted that LDLr−/− mice fed a chow diet develop small lesions in the aortic root and impaired endothelium-dependent relaxation in the thoracic aorta [4, 5], despite lacking atherosclerotic plaques throughout the descending aorta [6–8]. In this model of genetic hypercholesterolemia, endothelial dysfunction is associated with impaired hydrogen peroxide (H2O2) production . Similar to the effects of endothelial NOS (eNOS)-derived nitric oxide (NO), H2O2 production by neuronal nitric oxide synthase (nNOS) contributes to endothelium-dependent relaxation in the mouse aorta . Furthermore, increased NADPH oxidase Nox2-derived superoxide anion production, together with a reduction in NO bioavailability, is often found to contribute to the development of atherosclerosis in humans and experimental models [10–12]. Thus, reactive oxygen species (ROS) participate in the pathogenesis of atherosclerotic disease via multiple pathways.
It is well established that aerobic exercise training (AET) promotes vascular beneficial effects, mitigating the risk of cardiovascular disease . AET has been demonstrated to improve oxidative stress and endothelium-dependent relaxation, delaying the progression of vascular injury in atherosclerosis-prone model apolipoprotein E knockout mice (ApoE−/−) fed a high-fat and cholesterol diet [11, 13]. Atherogenic diets are often associated with metabolic disorders, including obesity and type 2 diabetes. Previous studies have demonstrated that treadmill AET improves endothelial dependent-relaxation , oxidative stress , NO release and nNOS expression  in obese non-atherosclerosis-prone rats. However, the potential beneficial effects of AET in the early stages of atherosclerosis, independent of atherogenic diet-induced confounding factors, are unclear. Recently, Langbein et al.  demonstrated that voluntary physical activity was not able to improve endothelial dysfunction in aortas from LDLr−/− mice fed a standard or high-fat diet. However, it is still unknown whether or not an AET program can modulate endothelial function and vascular redox status in aortas from LDLr−/− mice.
Therefore, in the present study, we investigated the effect of treadmill AET on impaired endothelium-induced relaxation in LDLr−/− mice, focusing on the effects of vascular production of the superoxide anion, NO, and H2O2.
All experimental protocols were approved (protocol number: 3420-1) by the Ethics Committee on Animal Use of the University of Campinas (CEUA-UNICAMP, Campinas-SP, Brazil) and conformed to the ethical principles for animal experimentation adopted by the Brazilian Society of Laboratory Animal Science (SBCAL/COBEA). LDL receptor knockout (LDLr−/−) mice and wild-type (WT) mice (C57BL/6J) were purchased from the Jackson Laboratory; the strains are now maintained by breeding in the Multidisciplinary Center for Biological Research (CEMIB) of UNICAMP with genotypic control. The mice were housed at a constant room temperature (22–24 °C) and light cycle (12:12 h light:dark). All mice were fed a chow diet. Food and water were provided ad libitum to all animals.
WT and LDLr−/− mice (12-week-old) were divided into four experimental groups: sedentary WT (WT S, n = 20) and exercised WT (WT Ex, n = 20) and sedentary LDLr−/− (LDLr−/− S, n = 20) and exercised LDLr−/− (LDLr−/− Ex, n = 20). The sample size was defined based on the variability of the different analyzes using the GraphPad Statmate version 2.0.
Aerobic exercise protocol
Animals were trained on a treadmill with individual lanes designed for small animals, without electrical stimulation (Gesan, Sao Paulo-SP, Brazil). One week before starting the AET program, the mice were subjected to a treadmill adaptation protocol in an attempt to minimize potential stress; this consisted of daily runs beginning at 10 m/min for 10 min on the first day and was progressively increased to 10 m/min for 30 min. Only the animals that adapted to the treadmill were used in the present study. After 4 days of adaptation, the intensity of the exercise training was determined according to an acute incremental exercise test on the treadmill , where the intensity of exercise was increased by 3.3 m/min (5–38.3 m/min) every 3 min at a 0 % gradient until the point of exhaustion (defined as an inability to maintain running speed). The maximal speed was used to calculate the percentage corresponding to moderate intensity (60–70 % of maximal speed). At the beginning of the training program, the duration and speed started at 10 m/min for 30 min and were progressively increased to 60 min at a speed of 15.0–16.6 m/min, 5 days/week for 4 weeks, at a 0 % gradient. All animals were trained between 7:00 and 10:00 a.m.
To evaluate the effectiveness of the training program, sedentary and exercised mice were subjected to an acute incremental exercise test on the treadmill during the last week of the study. This test provided the total distance, total time, and maximal speed run for each animal.
Serum biochemical analysis
At the end of the training protocol, 48 h after the last exercise session and after 12 h of fasting, blood samples were collected from the tail vein and blood glucose was measured using a hand-held glucometer (Accu-Chek Advantage, Roche Diagnostics, Sao Paulo, Brazil). Immediately thereafter, the mice were anesthetized (5 g/kg urethane, i.p.), and blood samples were obtained by cardiac puncture and centrifuged (8000g, for 15 min); serum supernatants were subsequently collected for biochemical analysis. Total cholesterol (CHOL) and triglyceride (TG) levels were measured using standard commercial kits (Chod-Pap, Roche Diagnostic GmbH, Mannheim, Germany); the absorbance for CHOL and TG was measured at 492 nm.
Vascular reactivity study
Thoracic aortas were cut into segments (2 mm in length), free of adipose and connective tissue, and then mounted in an isolated tissue chamber containing Krebs-Henseleit solution (in mM: 118 NaCl, 4.7 KCl, 25 NaHCO3, 2.5 CaCl2-2H2O, 1.2 KH2PO4, 1.2 MgSO4-7H2O, 11 glucose, and 0.01 EDTA) and gassed with 95 % O2 and 5 % CO2. The rings were maintained at a resting tension of 0.5 g at 37 °C, pH = 7.4, as previously described . Isometric tension was recorded using an isometric force transducer (MLT0420, ADInstruments, Sydney, Australia) connected to an acquisition PowerLab 8/30 system for tension recordings (LabChart 7, ADInstruments). After a 60 min equilibration period, the aortic rings were exposed to 125 mM KCl to determine the maximal tension. After washout, relaxation concentration–response curves to acetylcholine (ACh, 1 nM–30 µM, Sigma-Aldrich, Saint Louis, MO, USA), NO-donor sodium nitroprusside (10 pM–3 µM, Sigma-Aldrich, Saint Louis, MO, USA), or exogenous H2O2 (1 µM–3 mM, Sigma-Aldrich, Saint Louis, MO, USA) were generated for the aortic rings contracted with U46619 (Enzo Life Sciences, Farmingdale, NY, USA) until 50–70 % of maximum contraction with 125 mM KCl was reached. Some aortic rings were incubated for 30 min with the nonselective NOS inhibitor N-nitro-l-arginine methyl ester (L-NAME, 100 µM, Sigma-Aldrich, Saint Louis, MO, USA), the NADPH oxidase inhibitor apocynin (30 µM, Sigma-Aldrich, Saint Louis, MO, USA), the SOD inhibitor diethyldithiocarbamate (DETCA, 1 mM, Sigma-Aldrich, Saint Louis, MO, USA), the nNOS inhibitor 7-nitroindazole (7-NI, 100 µM, Sigma-Aldrich, Saint Louis, MO, USA), or catalase (800 U/ml, Sigma-Aldrich, Saint Louis, MO, USA) before the relaxation response curves to ACh were generated.
Western blotting analyses
Protein extracts were obtained from isolated thoracic aortas homogenized in RIPA lysis buffer (Merck Millipore, Billerica, MA, USA) containing phenylmethylsulfonyl fluoride (1 mM PMSF), Na3VO4 (1 mM) and a protease inhibitor cocktail (2 μL/mL PIC). To investigate the eNOS dimer:monomer ratio, aortas were lysed in buffer (50 mmol/L Tris–HCl pH = 8.0; 0.2 % Nonidet P-40; 180 mmol/L NaCl; 0.5 mmol/L EDTA; 25 mmol/L phenylmethylsulphonyl fluoride; 0.1 mmol/L dithiothreitol; and protease inhibitors). Protein samples (40 µg) were electrophoretically separated by SDS-PAGE (4–15 % Mini-Protean TGX, BioRad, CA, USA) at room temperature. To analyze eNOS dimerization, non-boiled samples (50 µg) were resolved by 6 % SDS-PAGE at 4 °C. Next, the proteins were transferred onto polyvinylidene fluoride (PVDF) membranes (GE Healthcare, Little Chalfont, Buckinghamshire, UK) overnight at 4 °C using a Mini Trans-Blot Cell System (Bio-Rad, Hercules, CA, USA), as previously described . The membranes were subsequently blocked for 90 min at room temperature with 5 % albumin in Tris-buffer (10 mM Tris, 100 mM NaCl and 0.1 % Tween 20) and then incubated overnight at 4 °C with the following primary antibodies: anti-eNOS (1:1000; BD Transduction, Franklin Lakes, NJ, USA), anti-p-eNOS Ser1177 (1:500; Cell Signaling), anti-nNOS (1:1000; Santa Cruz Biotechnology, CA, USA), anti-CuZn-SOD (1:1000, Sigma-Aldrich, Saint Louis, MO, USA), anti-Mn-SOD (1:1000, Enzo Life Sciences, Farmingdale, NY, USA), anti-EC-SOD (1:500, Enzo Life Sciences, Farmingdale, NY, USA), anti-Nox2 (1:1000 Millipore, Billerica, MA, USA) and anti-catalase (1:1000, Sigma-Aldrich, Saint Louis, MO, USA).
Membranes containing non-boiled samples were incubated with anti-eNOS (1:750, BD Transduction, Franklin Lakes, NJ, USA). α-actin (primary antibody 1:5000, Abcam, Cambridge, UK) was used to normalize the expression of the evaluated proteins in each sample. After washing with Tris-buffer, the membranes were incubated for 90 min with a peroxidase-conjugated IgG antibody, according to each primary antibody used. Protein expression was detected using the Pierce ECL (Electrochemiluminescence) kit. Western blotting substrate (Thermo Scientific, Rockford, IL, USA) was used for chemiluminescent detection using Image Quant LAS 4000 (GE Healthcare, NY, USA) hardware and software, according to the manufacturer’s instructions. The intensity of the blots was quantified using ImageJ 1.46p software (National Institutes of Health, Bethesda, MD, USA). Next, eNOS dimerization of the dimer (260 kDa) to monomer (130 kDa) ratio was calculated.
NO production was evaluated using the NO-sensitive fluorescent dye 4,5-diaminofluorescein diacetate (DAF-2A), as previously described . Thoracic aortic rings (approximately 3 mm in length) were embedded in a cryoprotectant freezing medium (Tissue-Tek® O.C.T compound 4583, Torrance, CA, USA) to obtain transverse sections (10 μm) using a cryostat. The slices were equilibrated for 10 min in a phosphate buffer (PB 0.1 mM, pH = 7.4) containing CaCl2 (0.45 mM) at 37 °C. Next, DAF-2A (8 μM) was topically applied to the slices, and they were maintained for 30 min in a light-protected humidified chamber. Digital images were obtained using a microscope (Eclipse Ti-S, Nikon, Tokyo, Japan) equipped for epifluorescence with a standard fluorescein filter with a 20 × objective. The images were analyzed using ImageJ 1.46p software by measuring the mean optical density of the fluorescence.
Extracellular H2O2 was detected using Amplex Red . To achieve this, four aortic rings (1.5 mm) were placed in a well of a 96-well dark plate and incubated with Amplex Red (10 μM) and horseradish peroxidase (0.2 U/mL) for 60 min at 37 °C in Krebs–Ringer’s phosphate glucose buffer (in mM: 145 NaCl, 5.7 sodium phosphate, 4.86 KCl, 0.54 CaCl2, 1.22 MgSO4, and 5.5 glucose) protected from light. Fluorescence was detected at 590 nm using an excitation of 530 nm every 5 min for 60 min. H2O2 was expressed as fluorescence per minute. In some experiments, catalase (200 U/mL) was added to the tissue samples.
Superoxide anion detection
Hydroethidine was used as an oxidative fluorescent dye . Transverse aortic sections (10 µm) obtained in a cryostat were incubated at 37 °C for 10 min with phosphate buffer. Hydroethidine (5 µM) was topically applied to each tissue section, and the slides were incubated in a light-protected, humidified chamber at 37 °C for 30 min. Some aortic slices were incubated with phosphate buffer containing the membrane-permeable superoxide dismutase (SOD) mimetic Mn(III) tetrakis (1-methyl-4-pyridyl) porphyrin pentachloride (MnTMPyP, 25 µM, Calbiochem, San Diego, CA, USA), apocynin (30 µM, 30 min), or vehicle (deionized water; time controls). Images were obtained using an optical microscope (Eclipse Ti-S, Nikon, Tokyo Japan) equipped with a rhodamine filter and camera (DS-U3, Nikon, Tokyo, Japan), using a 40× objective. The images were analyzed using ImageJ 1.46p software by measuring the mean optical density of the fluorescence.
The results are expressed as the mean ± SEM. Data were analyzed using two-way ANOVA followed by Bonferroni post-test using GraphPad Prism 5.0 software. Values of p < 0.05 were considered statistically significant.
Physical performance, body weight and serum biochemical parameters in sedentary and trained mice
Incremental exercise test performed before (initial) and after (final) 4-week sedentary (S) or exercise-trained (Ex) wild-type (WT) and LDL receptor knockout mice (LDLr−/−)
18 ± 0.5
18 ± 0.9
16 ± 0.6
17 ± 0.7
17 ± 0.6
26 ± 1.2*
17 ± 0.7
26 ± 1.3#
243 ± 10
250 ± 22
208 ± 12
225 ± 15
223 ± 14
459 ± 38*
220 ± 16
486 ± 42#
Max speed (m/min)
24 ± 0.5
25 ± 0.8
22 ± 0.6
23 ± 0.8
23 ± 0.7
31 ± 1.5*
22 ± 0.8
32 ± 1.2#
Body weight and plasma biochemical parameters in sedentary (S) and exercise-trained (Ex) wild-type (WT) and LDLr knockout mice (LDLr−/−)
Initial body weight (g)
25 ± 0.2 (20)
25 ± 0.5 (20)
24 ± 0.6 (20)
24 ± 0.2 (20)
Final body weight (g)
26 ± 0.3 (20)
24 ± 0.4* (20)
26 ± 0.8 (20)
23 ± 0.5# (20)
82 ± 4 (13)
92 ± 6 (9)
262 ± 14* (16)
279 ± 15$ (14)
54 ± 4 (11)
49 ± 6 (7)
151 ± 11* (11)
147 ± 9$ (10)
110 ± 6 (7)
90 ± 5 (7)
114 ± 11 (7)
107 ± 6 (7)
Aerobic exercise training prevented endothelial dysfunction in the thoracic aorta of LDLr−/− mice
Aerobic exercise training improves affected NO and H2O2 production in LDLr−/− mice
To evaluate the participation of H2O2 in endothelium-dependent relaxation, some aortic rings were incubated with catalase, which decomposes H2O2. Catalase reduced the vasodilatory effect of ACh in all groups, abolishing the differences among them (Fig. 2G, H). The Emax graph in Fig. 2I shows that the inhibitory effect of catalase was less prominent in LDLr−/− S than in WT S mice, while no difference was found for LDLr−/− Ex compared with WT Ex mice (Fig. 2I). These data suggest that AET attenuates the effect of H2O2 on vasodilation in LDLr-deficient mice.
Aerobic exercise training reduces the synthesis and increases the degradation of the superoxide anion
This study investigated the protective mechanisms of AET in preventing endothelial dysfunction during the early phase of atherosclerotic disease in LDLr-deficient mice. We found that 4 weeks of AET fully reversed the endothelial vasodilatory dysfunction observed in the aortas of LDLr−/− mice by improving NO bioavailability and H2O2 production. AET increased the phosphorylation of eNOS and aortic expression of nNOS in LDLr−/− mice, suggesting that an up-regulation of the signaling pathways of constitutive isoforms of NOS should be involved in the vascular effects of AET. Furthermore, the improvement of the vascular redox state in exercised-LDLr−/− mice was associated with the up-regulation of the antioxidant defense exerted by SOD and the down-regulation of NADPH oxidase-derived superoxide production. The vascular benefits conferred by AET occurred despite persistent hypercholesterolemia. Therefore, our data revealed that moderate AET may be an effective non-pharmacological therapy for the early prevention of vascular complications of artery disease in FH.
Endothelial dysfunction has been described in the aorta of LDLr-deficient mice fed a standard diet at 12–24 weeks of age [4, 5]. Consistent with the findings of these previous studies, we observed impaired ACh-induced relaxation in the aortas of 16-week-old LDLr−/− mice. Previous studies have demonstrated that long periods of training (12 weeks) reduced preexisting atherosclerotic lesion area in arteries from LDLr−/− mice  and ApoE−/− mice  fed atherogenic diets. Because endothelial dysfunction is an important predictor of atherosclerosis development and future cardiovascular events, we evaluated the effect of AET in controlling this risk factor in a genetic background of hypercholesterolemia.
Here, we report for the first time that 4 weeks of a treadmill-based AET program fully prevented the early endothelial dysfunction found in the thoracic aortas of LDLr−/− mice without atherosclerotic plaques. In contrast, Langbein et al.  found that 20 weeks of voluntary running did not ameliorate endothelial dysfunction in LDLr−/− mice fed standard or high-fat diets. Importantly, these authors observed a decrease in mice spontaneous activity over time, which may cause a lack-of-exercise effect on endothelial function. Here, the effectiveness of the training program was confirmed by the significant increases in total time, total distance, and maximal speed reached during the incremental test performed after the 4-week training protocol in WT Ex mice and LDLr−/− Ex mice.
It has been demonstrated that acute aerobic exercise is sufficient to activate eNOS in healthy endothelial cells of the mouse aorta; this effect occurs via a signaling pathway dependent on AMP-activated protein kinase activation (AMPK), resulting in Ser1177 eNOS phosphorylation, without changes in total eNOS expression or in Ser635 and Thr495 eNOS phosphorylation . In the present study, we demonstrated that 4 weeks of AET reversed the reduction in Ser1177 eNOS phosphorylation, normalizing the levels of NO in the aortas of LDLr−/− mice to levels similar to those found in WT animals, without increasing the dimerization of eNOS. A similar mechanism was found in the left internal mammary arteries of 4-week exercise-trained patients with stable coronary artery disease . Reduced eNOS dimerization may not necessarily be associated with eNOS uncoupling as other mechanisms are involved in electron transfer in eNOS domains . Because endothelium-derived NO plays a protective role in the vasculature by inhibiting vascular smooth muscle cell proliferation and by suppressing the adhesion of inflammatory cells and platelets , exercise activates an important protective mechanism against the progression of atherosclerosis in genetic hypercholesterolemia.
eNOS-derived NO and nNOS-derived H2O2 equally contribute to endothelium-dependent vasodilation of the mouse aorta . In young LDLr−/− mice (10 weeks old), increased H2O2 release may compensate for reduced eNOS expression in the aorta . However, nNOS mRNA expression and H2O2 levels decreased with age  or in accelerated atherosclerosis . H2O2 and nNOS are considered antiatherogenic factors [29, 30]. Gene deletion of nNOS in ApoE−/− mice accelerates atherosclerotic plaque formation , while overexpression of Nox4 forming H2O2 reduces the expression of profibrotic and pro inflammatory markers inhibiting vascular remodeling in mice prone to atherosclerosis . We found that reductions in the nNOS and H2O2 components of ACh-induced relaxation of the aorta in 16-week-old LDLr−/− mice were reversed by AET. No changes in relaxation with H2O2 or in the expression of vascular catalase were observed among the strains. Furthermore, AET prevented reductions in H2O2 production and nNOS expression in the aortas of LDLr−/− mice. This finding demonstrates the beneficial effects of AET in the maintenance of endothelial function via the up-regulation of nNOS-derived H2O2 in the genetic background of hypercholesterolemia. However, a limitation of this study is that we cannot exclude that impaired endothelial Nox4 activity/expression leading to a reduction in H2O2 production is involved in the endothelial dysfunction in LDLr−/− mice and modulated by AET.
Recent studies have indicated the beneficial effects of exercise in increasing nNOS signaling in the cardiovascular system. Four weeks of treadmill exercise increased the expression and activity of eNOS and nNOS in the aorta and left ventricle of chronic heart failure rats, respectively . Furthermore, 8 weeks of AET resulted in nNOS overexpression in endothelium-denuded mesenteric arteries, enhancing the participation of nitrergic perivascular innervation in spontaneously hypertensive rats  and obese rats . For the first time, we demonstrated that an AET program can up-regulate the antiatherogenic eNOS-NO and nNOS-H2O2 pathways, which is associated with amelioration of endothelial function in a genetic model of hypercholesterolemia. However, whether or not AET could induce similar vascular signaling pathway in the later stages of atherosclerotic disease is still an opened question.
Reduced formation of H2O2 was associated with increased Nox2 expression in atherosclerosis, but not with Nox1 expression . Judkins et al.  first demonstrated a role for NADPH oxidase Nox2 in enhancing vascular ROS production, thereby reducing NO bioavailability and increasing lesion development in ApoE−/− mice. In addition, we noted up-regulation of Nox2 in the aortas of LDLr−/− S mice. Similarly, inhibition of NADPH oxidase or superoxide anion scavengers reversed endothelial dysfunction and the oxidative stress detected by hydroethidine product fluorescence in the aorta of LDLr−/− S mice, implicating Nox2-derived superoxide in endothelial dysfunction in this hypercholesterolemic strain. Treadmill AET reversed Nox2 up-regulation, as well as enhanced vascular NADPH oxidase-derived superoxide production. Our findings are consistent with the beneficial effects of 10-week AET normalizing Nox2 protein expression in the aortas of type 2 diabetic mice .
SOD isoforms represent a major defense against the inactivation of NO and peroxynitrite formation . However, findings related to the expression of SODs in vessels of experimental models of atherosclerosis are controversial. EC-SOD activity and protein expression were found to be increased  or decreased  in ApoE−/− mice, whereas CuZn- and Mn-SOD were not modified . Differences may be due to the type of Western diet and/or the stage of development of the atherosclerotic lesion. In the present study, we noted a reduction in the protein expression of the three isoforms of SOD in the early stages of atherosclerosis in LDLr−/− mice fed a standard diet. Inhibition of Cu–Zn dependent SODs activity (cytoplasmatic CuZn SOD and EC-SOD) with DETCA, a powerful copper chelating agent, exerted a smaller effect on ACh-induced relaxation in LDLr−/− S mice compared with WT S mice. This finding serves as functional proof that down-regulation of Cu-dependent SOD isoforms is a mechanism involved in endothelial dysfunction in genetic hypercholesterolemia.
We observed that 4 weeks of treadmill AET normalized both cytoplasmic and extracellular CuZn-SODs expression, concomitant with normalization of the effects of DETCA on ACh-induced relaxation in the aortas of LDLr-deficient mice. These results demonstrated the up-regulation of CuZn-SODs as a vascular protective mechanism in endothelial dysfunction in hypercholesterolemia. AET has been reported to increase vascular expression of CuZn–SOD in healthy  and obese animals [14, 33]. However, the mechanism by which exercise enhances SOD expression in cardiovascular diseases is not clear, but Fukai et al.  have suggested that increased eNOS-derived NO is a feed-forward mechanism that up-regulates EC-SOD expression in adjacent vascular cells, which in turn increases NO bioavailability.
Taken together, our results suggest that AET improves endothelial dysfunction in the aortas of LDLr-deficient mice via the up-regulation of NO bioavailability and H2O2 production. These effects are associated with the up-regulation of p-eNOS, nNOS, and SOD isoforms and reduced Nox2-derived superoxide anion production. The vasculo-protective effects of 4 weeks of AET were observed in the early stages of atherosclerosis and were independent of changes in the dyslipidemic profile. These data highlight AET as a potential early non-pharmacological therapy for the prevention of endothelial dysfunction and changes in vascular redox status in patients with FH.
aerobic exercise training
5′ adenosine monophosphate-activated protein kinase
analysis of variance
- ApoE−/− :
apolipoprotein E knockout mice
Multidisciplinary Center for Biological Research
- CO2 :
cytoplasmic cupper/zinc-superoxide dismutase
dye 4,5-diaminofluorescein diacetate
extracellular cupper/zinc-superoxide dismutase
- Emax :
maximum vasodilator effect
endothelial nitric oxide synthase
- H2O2 :
- LDLr−/− :
LDL receptor-deficient mice
exercised LDL receptor-deficient mice group
sedentary LDL receptor-deficient mice group
N-nitro-l-arginine methyl ester
mitochondrial manganese-superoxide dismutase
Mn(III) tetrakis (1-methyl-4-pyridyl) porphyrin pentachloride
- NADPH oxidase:
nicotinamide-adenine dinucleotide phosphate oxidase
neuronal nitric oxide synthase
nitric oxide synthase
subunit of NADPH oxidase 1
subunit of NADPH oxidase 2
subunit of NADPH oxidase 4
- O2 :
serine 1177-phosphorylated eNOS
reactive oxygen species
standard error mean
- WT Ex:
exercised wild-type group
- WT S:
sedentary wild-type group
DMG, MHK, and APD conceived and designed the study; DMG and GGD performed experiments; DMG, GGD, MHK, MAD and APD analyzed and interpreted the data; DMG and APD prepared figures and wrote the manuscript; HCFO and MAD examined the manuscript and contributed to the discussion. All authors read and approved the final manuscript.
This work was supported by Grant from Sao Paulo Research Foundation-FAPESP (#10/50323-2) and University of Campinas fund (FAEPX-PAPDIC Program #25810); Ph.D. Scholarship from Coordination for the Improvement of Higher Education Personnel-CAPES (DMG) and Research Fellowship from The Brazilian National Council for Scientific and Technological Development-CNPq (APD and HCFO).
The authors declare that they have no competing interests.
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All experimental protocols were approved (protocol #3420-1) by the Ethics Committee on Animal Use of the University of Campinas (CEUA-UNICAMP, Campinas-SP, Brazil) and conformed to the ethical principles for animal experimentation adopted by the Brazilian Society of Laboratory Animal Science (SBCAL/COBEA).
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- Vlahos AP, Naka KK, Bechlioulis A, Theoharis P, Vakalis K, Moutzouri E, et al. Endothelial dysfunction, but not structural atherosclerosis, is evident early in children with heterozygous familial hypercholesterolemia. Pediatr Cardiol. 2014;35:63–70.View ArticlePubMedGoogle Scholar
- Vita JA, Keaney JF Jr. Endothelial function: a barometer for cardiovascular risk? Circulation. 2002;106:640–2.View ArticlePubMedGoogle Scholar
- Ishibashi S, Brown MS, Goldstein JL, Gerard RD, Hammer RE, Herz J. Hypercholesterolemia in low density lipoprotein receptor knockout mice and its reversal by adenovirus-mediatedgene delivery. J Clin Invest. 1993;92:883–93.View ArticlePubMedPubMed CentralGoogle Scholar
- Rabelo LA, Cortes SF, Alvarez-Leite JI, Lemos VS. Endothelium dysfunction in LDL receptor knockout mice: a role for H2O2. Br J Pharmacol. 2003;138:1215–20.View ArticlePubMedPubMed CentralGoogle Scholar
- Langbein H, Hofmann A, Brunssen C, Goettsch W, Morawietz H. Impact of high-fat diet and voluntary running on body weight and endothelial function in LDL receptor knockout mice. Atheroscler Suppl. 2015;18:59–66.View ArticlePubMedGoogle Scholar
- Ishibashi S, Goldstein JL, Brown MS, Herz J, Burns DK. Massive xanthomatosis and atherosclerosis in cholesterol-fed low density lipoprotein receptor-negative mice. J Clin Invest. 1994;93:1885–93.View ArticlePubMedPubMed CentralGoogle Scholar
- Moore RE, Kawashiri MA, Kitajima K, Secreto A, Millar JS, Pratico D, et al. Polipoprotein A-I deficiency results in markedly increased atherosclerosis in mice lacking the LDL receptor. Arterioscler Thromb Vasc Biol. 2003;23:1914–20.View ArticlePubMedGoogle Scholar
- Dorighello GG, Rovani JC, Luhman CJ, Paim BA, Raposo HF, Vercesi AE, et al. Food restriction by intermittent fasting induces diabetes and obesity and aggra-vates spontaneous atherosclerosis development in hypercholesterolaemic mice. Br J Nutr. 2014;111:979–86.View ArticlePubMedGoogle Scholar
- Capettini LS, Cortes SF, Lemos VS. Relative contribution of eNOS and nNOS to endothelium-dependent vasodilation in the mouse aorta. Eur J Pharmacol. 2010;643:260–6.View ArticlePubMedGoogle Scholar
- Sorescu D, Weiss D, Lassegue B, Clempus RE, Szöcs K, Sorescu GP, et al. Superoxide production and expression of nox family proteins in human atherosclerosis. Circulation. 2002;105:1429–35.View ArticlePubMedGoogle Scholar
- Laufs U, Wassmann S, Czech T, Münzel T, Eisenhauer M, Böhm M, et al. Physical inactivity increases oxidative stress, endothelial dysfunction, and atherosclerosis. Arterioscler Thromb Vasc Biol. 2005;25:809–14.View ArticlePubMedGoogle Scholar
- Judkins CP, Diep H, Broughton BR, Mast AE, Hooker EU, Miller AA, et al. Direct evidence of a role for Nox2 in superoxide production, reduced nitric oxide bioavailability, and early atherosclerotic plaque formation in ApoE−/− mice. Am J Physiol Heart Circ Physiol. 2010;298:H24–32.View ArticlePubMedGoogle Scholar
- Pellegrin M, Berthelot A, Houdayer C, Gaume V, Deckert V, Laurant P. New insights into the vascular mechanisms underlying the beneficial effect of swimming training on the endothelial vasodilator function in apolipoprotein E-deficient mice. Atherosclerosis. 2007;190:35–42.View ArticlePubMedGoogle Scholar
- de Moraes C, Davel AP, Rossoni LV, Antunes E, Zanesco A. Exercise training improves relaxation response and SOD-1 expression in aortic and mesenter-ic rings from highcaloric diet-fed rats. BMC Physiol. 2008;8:12.View ArticlePubMedPubMed CentralGoogle Scholar
- Li G, Liu JY, Zhang HX, Li Q, Zhang SW. Exercise training attenuates sympathetic activation and oxidative stress in diet-induced obesity. Physiol Res. 2015;64:355–67.PubMedGoogle Scholar
- Sastre E, Caracuel L, Balfagón G, Blanco-Rivero J. Aerobic exercise training increases nitrergic innervation function and decreases sympathetic innervation function in mesenteric artery from rats fed a high-fat diet. J Hypertens. 2015;33:1819–30.View ArticlePubMedGoogle Scholar
- Ferreira JC, Rolim NP, Bartholomeu JB, Gobatto CA, Kokubun E, Brum PC. Maximal lactate steady state in running mice: effect of exercise training. Clin Exp Pharmacol Physiol. 2007;34:760–5.View ArticlePubMedGoogle Scholar
- Davel AP, Ceravolo GS, Wenceslau CF, Carvalho MH, Brum PC, Rossoni LV. Increased vascular contractility and oxidative stress in β2-adrenoceptor knockout mice: the role of NADPH oxidase. J Vasc Res. 2012;49:342–52.View ArticlePubMedGoogle Scholar
- Delbin MA, Davel AP, Couto GK, Araújo GG, Rossoni LV, Antunes E, et al. In-teraction between advanced glycation end products formation and vascular re-sponses in femoral and coronary arteries from exercised diabetic rats. PLoS One. 2012;7:e53318.View ArticlePubMedPubMed CentralGoogle Scholar
- Dikalov S, Griendling KK, Harrison DG. Measurement of reactive oxygen species in cardio-vascular studies. Hypertension. 2007;49:717–27.View ArticlePubMedPubMed CentralGoogle Scholar
- Ramachandran S, Penumetcha M, Merchant NK, Santanam N, Rong R, Parthasarathy S. Exercise reduces preexisting atherosclerotic lesions in LDL receptor knockout mice. Atherosclerosis. 2005;178:33–8.View ArticlePubMedGoogle Scholar
- Pellegrin M, Miguet-Alfonsi C, Bouzourene K, Aubert JF, Deckert V, Berthelot A, et al. Long-term exercise stabilizes atherosclerotic plaque in ApoE knockout mice. Med Sci Sports Exerc. 2009;41:2128–35.View ArticlePubMedGoogle Scholar
- Cacicedo JM, Gauthier MS, Lebrasseur NK, Jasuja R, Ruderman NB, Ido Y. Acute exercise activates AMPK and eNOS in the mouse aorta. Am J Physiol Heart Circ Physiol. 2011;301:1255–65.View ArticleGoogle Scholar
- Hambrecht R, Adams V, Erbs S, Linke A, Kränkel N, Shu Y, et al. Regular physical activity improves endothelial function in patients with coronary artery disease by increasing phosphorylation of endothelial nitric oxide synthase. Circulation. 2003;107:3152–8.View ArticlePubMedGoogle Scholar
- Whitsett J, Martásek P, Zhao H, Schauer DW, Hatakeyama K, Kalyanaraman B, et al. Endothelial cell superoxide anion radical generation is not dependent on endothelial nitric oxide synthase-serine 1179 phosphorylation and endothelial nitric oxide synthase dimer/monomer distribution. Free Radic Biol Med. 2006;40:2056–68.View ArticlePubMedGoogle Scholar
- Shimokawa H. Primary endothelial dysfunction: atherosclerosis. J Mol Cell Cardiol. 1999;31:23–37.View ArticlePubMedGoogle Scholar
- Langbein H, Brunssen C, Hofmann A, Cimalla P, Brux M, Bornstein SR, et al. NADPH oxidase 4 protects against development of endothelial dysfunction and atherosclerosis in LDL receptor deficient mice. Eur Heart J. 2016;37:1753–61.View ArticlePubMedGoogle Scholar
- Capettini LS, Cortes SF, Silva JF, Alvarez-Leite JI, Lemos VS. Decreased pro-duction of neuronal NOS-derived hydrogen peroxide contributes to endotelial dysfunction in atherosclerosis. Br J Pharmacol. 2011;164:1738–48.View ArticlePubMedPubMed CentralGoogle Scholar
- Kuhlencordt PJ, Hötten S, Schödel J, Rützel S, Hu K, Widder J, et al. Atheroprotective effects of neuronal nitric oxide synthase in apolipoprotein e knockout mice. Arterioscler Thromb Vasc Biol. 2006;26:1539–44.View ArticlePubMedGoogle Scholar
- Gray SP, Di Marco E, Kennedy K, Chew P, Okabe J, El-Osta A, et al. Reactive Oxygen Species Can Provide Atheroprotection via NOX4-Dependent Inhibition of Inflammation and Vascular Remodeling. Arterioscler Thromb Vasc Biol. 2016;36:295–307.View ArticlePubMedGoogle Scholar
- Ito D, Ito O, Mori N, Cao P, Suda C, Muroya Y, et al. Exercise training upregulates nitric oxide synthases in the kidney of rats with chronic heart failure. Clin Exp Pharmacol Physiol. 2013;40:617–25.View ArticlePubMedGoogle Scholar
- Blanco-Rivero J, Roque FR, Sastre E, Caracuel L, Couto GK, Avendaño MS, et al. Aerobic exercise training increases neuronal nitric oxide release and bioavailability and decreases noradrenaline release in mesenteric artery from spontaneously hypertensive rats. J Hypertens. 2013;31:916–26.View ArticlePubMedGoogle Scholar
- Lee S, Park Y, Dellsperger KC, Zhang C. Exercise training improves endothelial function via adiponectin-dependent and independent pathways in type 2 diabetic mice. Am J Physiol Heart Circ Physiol. 2011;301:H306–14.View ArticlePubMedPubMed CentralGoogle Scholar
- Davis KL, Martin E, Turko IV, Murad F. Novel effects of nitric oxide. Annu Rev Pharmacol Toxicol. 2001;41:203–36.View ArticlePubMedGoogle Scholar
- Fukai T, Galis ZS, Meng XP, Parthasarathy S, Harrison DG. Vascular expression of extracellular superoxide dismutase in atherosclerosis. J Clin Invest. 1998;101:2101–11.View ArticlePubMedPubMed CentralGoogle Scholar
- Wang X, Pu H, Ma C, Jiang T, Wei Q, Zhang C, et al. Adiponectin abates atherosclerosis by reducing oxidative stress. Med Sci Monit. 2014;20:1792–800.View ArticlePubMedPubMed CentralGoogle Scholar
- Rush JW, Turk JR, Laughlin MH. Exercise training regulates SOD-1 and oxidative stress in porcine aortic endothelium. Am J Physiol Heart Circ Physiol. 2003;284:H1378–87.View ArticlePubMedGoogle Scholar
- Fukai T, Siegfried MR, Ushio-Fukai M, Cheng Y, Kojda G, Harrison DG. Regulation of the vascular extracellular superoxide dismutase by nitric oxide and exercise training. J Clin Invest. 2000;105:1631–9.View ArticlePubMedPubMed CentralGoogle Scholar