Exercise prevents cardiometabolic alterations induced by chronic use of glucocorticoids

Abstracts

FUNDAMENTO: Cronicamente, os glicocorticóides induzem alterações cardiometabólicas adversas, incluindo resistência à insulina, diabete, dislipidemia, esteatose hepática e hipertensão arterial. OBJETIVOS: Avaliar o efeito da prática regular de exercício físico aeróbio sobre as alterações cardiometabólicas induzidas por administração crônica de dexametasona (Dex - 0,5 mg/kg/dia i.p) em ratos. MÉTODOS: Ratos Wistar machos (n = 24) foram divididos em quatro grupos: Grupo controle; Grupo treinado; Grupo tratado com Dex e Grupo tratado com Dex e treinado. O treinamento físico (iniciado 72 horas após a primeira dose de Dex) foi realizado 3 vezes por semana, até o final do tratamento. Ao final desse período, realizaram-se as seguintes avaliações bioquímicas: glicemia em jejum, teste de tolerância à glicose e análise do perfil lipídico no sangue que incluiu colesterol total (CT), LDL-c, HDL-c, VLDL-c e triglicerídeos (TG). O peso do músculo gastrocnêmio, análise histopatológica do fígado e os índices cardiometabólicos (CT/HDL-c, LDL-c/HDL-c e TG/HDL-c) também foram avaliados. RESULTADOS: Observou-se hiperglicemia, menor tolerância à glicose, elevação do CT, LDL-c, VLDL-c e TG, diminuição do HDL-c, presença de esteatose hepática, hipotrofia muscular e elevação dos índices CT/HDL-c, LDL-c/HDL-c e TG/HDL-c nos animais tratados com Dex. O exercício físico reduziu a hiperglicemia, melhorou a tolerância à glicose, reduziu a dislipidemia e preveniu a esteatose hepática , a hipotrofia muscular e reduziu os índices CT/HDL-c, LDL-c/HDL-c e TG/HDL-c. Entretanto, não houve efeito significante do treinamento físico sobre o HDL-c. CONCLUSÃO: O exercício físico aeróbio tem efeito protetor contra as alterações cardiometabólicas induzidas pelo uso crônico de glicocorticóides.

Exercício físico; glicocorticóide; resistência à insulina; colesterol; dislipidemia; dexametasona

FUNDAMENTO: Crónicamente, los glucocorticoides inducen alteraciones cardiometabólicas adversas, incluyendo resistencia a la insulina, diabetes, dislipidemia, esteatosis hepática e hipertensión arterial. OBJETIVOS: Evaluar el efecto de la práctica regular de ejercicio físico aeróbico sobre las alteraciones cardiometabólicas inducidas por administración crónica de dexametasona (Dex - 0,5 mg/kg/día i.p) en ratones. MÉTODOS: Se dividieron ratones Wistar machos (n = 24) en cuatro grupos: Grupo control; Grupo entrenado; Grupo tratado con Dex y Grupo tratado con Dex y entrenado. El entrenamiento físico (iniciado 72 horas después de la primera dosis de Dex) se realizó 3 veces por semana, hasta el final del tratamiento. Al final de ese período, se realizaron las siguientes evaluaciones bioquímicas: glicemia en ayunas, test de tolerancia a la glucosa y análisis del perfil lipídico en sangre que incluyó colesterol total (CT), LDL-c, HDL-c, VLDL-c y triglicéridos (TG). También se evaluaron, el peso del músculo gastrocnemio, análisis histopatológico del hígado y los índices cardiometabólicos (CT/HDL-c, LDL-c/HDL-c y TG/HDL-c). RESULTADOS: Se observó hiperglicemia, menor tolerancia a la glucosa, elevación de CT, LDL-c, VLDL-c y TG, disminución del HDL-c, presencia de esteatosis hepática, hipotrofia muscular y elevación de los índices CT/HDL-c, LDL-c/HDL-c y TG/HDL-c en los animales tratados con Dex. El ejercicio físico redujo la hiperglicemia, mejoró la tolerancia a la glucosa, redujo la dislipidemia y previno la esteatosis hepática, la hipotrofia muscular y redujo los índices CT/HDL-c, LDL-c/ HDL-c ye TG/HDL-c. Con todo, no hubo efecto significativo del entrenamiento físico sobre el HDL-c. CONCLUSIÓN: El ejercicio físico aeróbico tiene efecto protector con las alteraciones cardiometabólicas inducidas por el uso crónico de glucocorticoides.

Ejercicio físico; glucocorticoide; esistencia a la insulina; colesterol; dislipidemia; dexametasona

ORIGINAL ARTICLE

^IDepartamento de Fisioterapia, Centro de Ciências da Saúde, Universidade de Fortaleza, CE, Brasil

^IIDepartamento de Ciências Farmacêuticas, Centro de Ciências da Saúde, Universidade de Fortaleza, CE, Brasil

^IIIDepartamento de Ciências da Nutrição, Centro de Ciências da Saúde, Universidade de Fortaleza, CE, Brasil

^IVFaculdade de Medicina, Centro de Ciências da Saúde, Universidade de Fortaleza, Fortaleza, CE, Brasil

Mailing Address

SUMMARY

BACKGROUND: Chronically, glucocorticoids induce adverse cardiometabolic alterations including insulin resistance, diabetes, dyslipidemia, liver steatosis and arterial hypertension.

OBJECTIVES: To evaluate the effect of regular practice of aerobic exercise on cardiometabolic alterations induced by chronic administration of dexamethasone (Dex - 0.5 mg/kg/day ip) in rats.

METHODS: Male Wistar rats (n = 24) were divided in four groups: Control group; Trained group; Treated with Dex group and Treated with Dex and trained group. The exercise training (initiated 72 hours after the first dose of Dex) was carried out three times a week until the end of the treatment. At the end of this period, the following biochemical assessments were performed: fasting glycemia, oral glucose tolerance test and analysis of the blood lipid profile that included total cholesterol (TC), LDL-c, HDL-c, VLDL-c and triglycerides (TG). The weight of the gastrocnemius muscle, the histopathological analysis of the liver and cardiometabolic indices (TC/HDL-c, LDL-c/HDL-c and TG/HDL-c) were also performed.

RESULTS: Hyperglycemia, lower glucose tolerance, increased TC, LDL-c, VLDL-c, TG, CT/HDL-c, LDL-c/HDL-c and TG/HDL-c, decreased HDL-c, presence of liver steatosis and muscular hypotrophy were observed in the animals treated with Dex. The exercise training reduced hyperglycemia, improved glucose tolerance, decreased dyslipidemia and prevented liver steatosis, muscular hypotrophy and reduced CT/HDL-c, LDL-c/HDL-c and TG/HDL-c ratios. However, there was no significant effect on HDL-c.

CONCLUSION: The aerobic exercise training have a protective effect against the cardiometabolic alterations induced by the chronic use of glucocorticoids.

Key words: Exercise, glucocorticoid, insulin resistance, cholesterol, dyslipidemia, dexamethasone.

Introduction

Glucocorticoids (GCs) are corticosteroids, substances derived from cholesterol, synthesized and secreted by the adrenal glands¹. The GCs are hormones that act on the transcriptional control of genes involved in the regulation of metabolic, cardiovascular and immunological functions¹. This effect is processed through the nuclear glucocorticoid receptor (GR), which is activated, transiently, only after the exposition of the cells to the GCs^1,2.

The term "glucocorticoid" is due to the action of these substances on the carbohydrate metabolism. In the skeletal muscle, the GCs cause insulin resistance resulting in a lower uptake of blood glucose and reduced glycogen synthesis¹. In this tissue, protein synthesis inhibition and increased protein catabolism are also observed, which result in muscular hypotrophy¹. The amino acids mobilized from the muscular tissue are used in liver gluconeogenesis¹. Together, the insulin resistance and increased gluconeogenesis result in hyperglycemia¹.

In the 1950s, the discovery of the potent anti-inflammatory effect of the GCs led to their prescription in the treatment of chronic rheumatic diseases³. Currently, the synthetic GCs are broadly used in the treatment of autoimmune diseases and in the prevention of allograft rejection^4,5. However, the chronic use of GCs is associated to several adverse cardiometabolic effects^6,7. As in Cushing's syndrome, caused by elevated levels of blood cortisol, the chronic use of GCs causes insulin resistance, diabetes, dyslipidemia and arterial hypertension⁸. If left untreated, Cushing's syndrome may result in death by cardiovascular disease^6,8.

The GCs would have a role in the physiopathology of the metabolic or plurimetabolic syndrome. Recently, it was demonstrated that the elevated gene expression of GR in the skeletal muscle is associated to lower insulin sensitivity⁹. Additionally, the 11-beta-hydroxysteroid dehydrogenase, which converts cortisone (inactive GC) into cortisol (biologically active GC), has also been implicated in the development of obesity, insulin resistance and type 2 diabetes¹⁰. Rats chronically treated with dexamethasone (a synthetic GC) have been used in the experimental study of the metabolic syndrome. These animals present insulin resistance, hypercholesterolemia, hypertriglyceridemia, non-alcoholic fatty liver disease (liver steatosis), endothelial dysfunction and arterial hypertension⁷. Clinical directives on the treatment and prevention of atherosclerosis¹¹ acknowledge the cardiometabolic risk caused by the chronic use of GCs and stimulate lifestyle changes as a strategy to promote cardiovascular health.

The regular physical activity is an important non-pharmacological resource in the management of the cardiometabolic risk¹¹. Exercise increases uptake and oxidation of glucose and fatty acids from the blood^12,13, improve insulin signaling^13,14, increase the activity and expression of transporters and enzymes that regulate the glucose and fatty acid metabolism^14,15, promotes mitochondrial biogenesis¹² and improves endothelium-dependent vasodilation in skeletal muscle¹⁶.

However, scientific evidence on the effect of exercise training on cardiometabolic alterations caused by the chronic use of GCs is scarce in the literature. In the present study, the impact of aerobic exercise training upon cardiometabolic parameters in long-term glucocorticoid-treated rats was investigated.

Methods

Ethical aspects

The present study was approved by the Committee of Ethics in Animal Research of Medicine School of Federal University of Ceará. All animals received humane care in compliance with the Ethical Principles of the Brazilian College of Animal Experimentation (COBEA) and according to the rules established by the Guide for the Care and Use of Laboratory Animals (Institute of Laboratory Animal Resources, National Academy of Sciences, Washington, D. C. 1996).

Animals

Male albino Wistar rats (Rattus norvegicus alvinus, Rodentia, Mammalia), aged 5 months and weighing between 230 and 250 g were studied. The animals were fed a standard rodent chow (Purina^®, Cargill Incorporated, Monsanto do Brasil Ltda) and received water ad libitum. They were housed in groups of three per cage, maintained on a 12-hour light-dark cycle and ambient temperature of 23 ± 2 ºC.

Experimental design

The animals (n = 24) were randomly distributed in four groups: Control group (comprising sedentary rats that were not treated with GC; n = 6); Trained group (comprising rats submitted to physical training only; n = 6); Treated group (comprising sedentary rats treated with GC; n = 6); Treated and trained group (comprising rats treated with GC and submitted to the physical training; n = 6).

At the end of the study, the following biochemical analyses were performed in blood: fasting glycemia, oral glucose tolerance test (OGTT), serum levels of total cholesterol (TC), low-density lipoprotein cholesterol (LDL-c), high density lipoprotein cholesterol (HDL-c), very-low density lipoprotein cholesterol (VLDL-c) and triglycerides (TG). The body weight was monitored weekly throughout the study. At the end of the study, the gastrocnemius muscle weight was determined and the liver was used for slide preparation and posterior histopathological analysis.

The following cardiometabolic parameters were also assessed: Castelli's atherogenic ratios (CT/HDL-c) I and II (LDL-c/HDL-c), and the TG/HDL-c ratio. Castelli's ratios are used for the analysis of coronary risk in the presence of cardiovascular risk factors¹⁷. The TG/HDL-c ratio is associated to the cardiovascular risk conferred by the insulin resistance¹⁸.

Glucocorticoid therapy experimental protocol

The animals were treated with dexamethasone (Dex - 0.5 mg/kg/day ip) (Decadron^®, Prodome, Brazil), for one month, always at the same time of the day. This dose results in insulin resistance after seven days¹⁹.

Progressive exercise stress test

Previously, a progressive stress test was carried out in the animals submitted to the physical training. The test was carried out in a Rota Rod Treadmill (model 7700, Ugo Basile^®, Milan, Italy). After the period of adaptation to the equipment, suggested by the manufacturer, a personalized protocol was applied, with an initial velocity of 3 rotations per minute (rpm) and 3 rpm increments every 3 minutes (Table 1). This protocol presents good reproducibility (R/ Square = 0.96). The test was carried out until exhaustion set in and the fatigue criterion used was that of three falls during a 100-second interval²⁰. The maximum velocity attained by the animals during the test was recorded and expressed as an arithmetic mean. The characteristics of the equipment and of the animals' responses to the progressive stress test are shown in Figure 1.

Exercise training protocol

The aerobic exercise training was carried out 3 times a week, always at the same time of the day (7:00 p.m) until the end of the glucocorticoid treatment. The intensity of the exercise was 60% of the maximum velocity attained by the animals during the exercise stress test, being the exercise training protocol considered as moderate intensity. Before reaching the training velocity, the animals were submitted to low-velocity warming-up (2 rpm), for 6 minutes. The exercise duration was 60 minutes and the first session was carried out 72 hours after the first Dex dose.

Body weight monitoring

The body weight was monitored through weekly measurements and the first one was carried out before the first Dex dose.

Measurement of blood glycemia and oral glucose tolerance test (OGTT)

Seventy-two hours after the last exercise session, the animals were submitted to a 12-hour fasting period and then were anesthetized with sodium pentobarbital (40 mg/kg i.p.; Nembutal^®, Abbot Laboratories, Abbot Park, Illinois, USA). A surgical incision was made on the posterior paw and the femoral vein was located. A blood specimen (300 µl) was collected for blood glycemia measurement, which was performed with a digital glucosimeter (Accu-Check Active^®; Roche Diagnostic System, Branchburg, NJ, USA). The OGTT was carried out after the oral administration of glucose (1 g/kg of body weight) by gavage. New blood specimens were collected after 30, 60 and 120 minutes.

Blood lipid profile assessment

The serum lipid levels were measured by spectrophotometry according to the instructions and recommendations of the National Cholesterol Education Program (NCEP)²¹. The fasting animals were euthanized by cervical displacement and immediately after it, a heart puncture was performed to collect blood samples, which were stored in ice. The serum was obtained by centrifuging at 2500 rpm, for 20 minutes, at 4°C. The biochemical analyses were carried out by spectrophotometry. A wavelength of 500 nm was used to measure the TC levels, according to the manufacturer's instructions (Kit Colesterol Liquiform, Labtest Diagnóstica, Lagoa Santa, MG, Brazil). The TG measurement was carried out using the kit Triglicerides Liquiform (Labtest Diagnóstica, Lagoa Santa, MG, Brazil) and a wavelength of 510 nm. The measurement of the HDL-c was carried out with the kit HDL LE (Labtest Diagnóstica, Lagoa Santa, MG, Brazil) and a wavelength of 600 nm. The levels of LDL-c and VLDL-c were calculated using Friedewald equation²².

Friedewald equation = [LDL-C = CT - (HDL-C + TG/5)]

Skeletal muscle weight determination

After euthanization, the gastrocnemius muscle was surgically removed and the proximal and distal insertions were preserved. The weight of the skeletal muscle was measured with a precision scale (model 750 SW - OHAUS Corp., Pine Brook, NJ, USA). The gastrocnemius muscle was chosen for the study of the effect of Dex on protein metabolism as it presents a large number of fast contraction fibers, considering that these fibers are more susceptible to the catabolic action of GCs²³. As the animals had similar weights and were of similar ages, we chose the non-normalization of the skeletal muscle weight variable.

Histopathological analysis

The liver was removed before the heart puncture and was immediately fixed in a 10% formaldehyde solution. After the material was paraffin-embedded, histological slides were prepared using hematoxylin and eosin (HE) stain. The histopathological analysis was performed by optical microscopy (Nikon E800, Nikon USA, Melville, NY, USA).

Statistical analysis

The data were expressed as means ± standard error (SEM) and the comparison between the groups was carried out by one-way Analysis of Variance (ANOVA) statistical test combined with Tukey-Kramer post-test. The level of significance was set at p < 0.05.

Results

Exercise training decrease hyperglycemia and improve glucose tolerance in rats treated with glucocorticoid

After 4 weeks, the animals treated with a daily dose of Dex presented hyperglycemia when compared to the control group (181.25 ± 12 mg/dl vs. 85 ± 10 mg/dl; p < 0.05). The exercise training reduced this increase in glycemia by approximately 47%. Among the animals that received GC, the glycemia was lower in the trained animals, when compared to the sedentary ones (140.67 ± 10 mg/dl vs. 181.25 ± 12 mg/dl; p < 0.05). However, the training protocol used in the study was not effective in preventing the glycemia increase in relation to controls (140.67 ± 10 mg/dl vs. 85 ± 10 mg/dl; p < 0.05). There was no effect of the exercise training on the glycemia levels of the animals that did not received Dex. The fasting blood glycemia of the study groups is shown in Figure 2A.

The treatment with Dex altered the glycemic response to the OGTT. The sedentary animals presented higher glycemic levels at 30, 60 and 120 minutes when compared to the control group, which represents lower glucose tolerance. The animals submitted to exercise training concomitantly with Dex treatment presented a glycemic response similar to that of the control group. The exercise training had no effect on the glucose tolerance in the animals that were not treated with Dex. The OGTT data are shown in Figure 2B.

Effect of exercise training on body weight and lipid profile of the rats treated with glucocorticoid

The chronic administration of Dex induced dyslipidemia characterized by hypercholesterolemia, hypertriglyceridemia and decreased serum levels of HDL-c, when compared to the control group. We also observed an increase in the LDL-c and VLDL-c levels in sedentary animals treated with GC.

The exercise training was effective in preventing hypercholesterolemia (TC, LDL-c and VLDL-c) and hypertriglyceridemia induced by the chronic administration of Dex. However, the exercise had no significant effect on serum levels of HDL-c (p > 0.05). The exercise training also reduced the TG and VLDL-c levels in the animals that were not treated with GC.

In parallel to the improvement in the dyslipidemia condition, the animals treated with Dex and trained presented higher weight loss when compared to the control group and the sedentary animals. The exercise training also reduced the body weight in the untreated animals. The treated sedentary animals showed weight gain after 7 days of treatment and subsequently, they presented a progressive decrease of this variable. The blood TC and lipoprotein levels are shown in Figure 3. The behavior of body weight and blood TG levels are shown in Figure 4.

Effect of exercise training on skeletal muscle hypotrophy induced by glucocorticoid

The animals treated with Dex presented lower gastrocnemius muscle weight when compared to the control group (0.8 ± 0.07 g vs. 1.23 ± 0.03 g; p < 0.05). The exercise training prevented the muscular hypotrophy in the animals chronically treated with GC. Among the treated animals, those submitted to the exercise training did not present a significant difference in gastrocnemius weight when compared to the control group (1.25 ± 0.03 g vs. 1.23 ± 0.03 g; p > 0.05). When compared to the control group, the weight of the gastrocnemius muscle was also higher in the trained animals that were not treated with Dex (1.53 ± 0.06 g vs. 1.23 ± 0.03 g; p < 0.05).

Chronic effect of the glucocorticoid and physical exercise on the liver

The histopathological analysis of the liver in the animals treated with GC showed the presence of lipid vacuolization in the hepatocytes, which morphologically characterizes the non-alcoholic fatty liver disease (liver steatosis). The exercise training prevented this liver alteration. The liver histopathological analysis is shown in Figure 5.

Chronic effect of the glucocorticoid and physical exercise on the cardiometabolic parameters

The sedentary animals submitted to the chronic treatment with Dex presented higher cardiometabolic risk in comparison to controls. An increase in Castelli's ratio I and II and the TG/HDL-c was verified. Regarding the treated and trained animals, they presented lower values of all these ratios, when compared to sedentary animals. The data regarding the effect of the GC and exercise training on the cardiometabolic risk are shown in Figure 6.

Discussion

Dexamethasone (Dex) has been broadly used as an experimental model for the study of the metabolic syndrome, because one of its main adverse effects is insulin resistance⁷. According to some authors^1,7 rats treated with Dex present decreased glucose uptake stimulated by insulin in the skeletal muscle and fat tissue, whereas in the liver, there was a reversion of gluconeogenesis suppression. A permissive effect to the action of lipolytic hormones (adrenaline, noradrenaline and growth hormone) was observed in the fat tissue, resulting in the increased hydrolysis of triglycerides, release of fatty acids into the blood (substances that induce oxidative stress and endothelial dysfunction) and glycerol for liver gluconeogenesis^1,7,24. The peripheral insulin resistance and the increased gluconeogenesis mediated by GCs cause persistent hyperglycemia, diabetes, dyslipidemia and arterial hypertension due to endothelial dysfunction⁷.

In the present study, the chronic administration of Dex to rats resulted in hyperglycemia, decreased glucose tolerance, hypercholesterolemia, hypertriglyceridemia and decreased serum HDL-c levels, and induced liver steatosis and muscular hypotrophy. The cardiometabolic risk indices were also higher in these animals, when compared to the control group.

The data of the present study are in accordance with those described by Severino et al⁷. The main contribution of the present study was to demonstrate that the cardiometabolic alterations induced by the chronic use of GCs can be reduced and/or prevented by the regular practice of aerobic exercise. In the present study, the aerobic exercise training decreased hyperglycemia, prevented hypercholesterolemia, hypertriglyceridemia, the increase in cardiometabolic indices, the liver steatosis and muscular hypotrophy in rats chronically treated with Dex. However, exercise trainig had no effect on the serum HDL-c levels.

In the skeletal muscle tissue, the GCs inhibit the glucose uptake stimulated by insulin^7,14,25. In the skeletal muscle of rats treated with Dex, there is inhibition of phosphatidylinositol-3-kinase (PI3K)²⁵. The PI3K is involved in the activation mechanism of the translocation of the Glucose Transporter Isoform 4 (GLUT4) to the sarcolemma after the insulin stimulus, mainly, in the postprandial period^25,26. The treatment with GCs also decreases the synthesis of glycogen in this tissue^1,25,26.

The contraction is a powerful stimulus capable of increasing the blood glucose uptake in the skeletal muscle¹². The muscle contraction activates the translocation of GLUT4 to the sarcolemma through a signaling pathway independent from the activation of PI3K, that is, through a cascade of signal transduction events independent from insulin signaling²⁵. Ruzzin and Jensen²⁵ demonstrated that the increase in the glucose uptake mediated by the muscle contraction is preserved in rats chronically treated with Dex, whereas the insulin-induced uptake is impaired. Some authors^13,14,25,27 demonstrated that insulin sensitivity in the skeletal muscle also increases after the physical exercise. According to Howlett et al²⁷, the muscle contraction increases the phosphorylation of insulin receptor substrate-2 (IRS-2), an alternative pathway in insulin signaling. There is also a higher phosphorylation in protein-kinase serine B (PKB or AKT), important for the activation of the GLUT4 translocation to the sarcolemma²⁸.

In addition to increasing the translocation of GLUT4 to the sarcolemma, the contraction also increases the gene expression of GLUT4 in the skeletal muscle²⁹. Thus, the trained skeletal muscle uptakes more glucose due to a higher gene expression and larger amount of GLUT4 in the sarcolemma and through the increase in insulin sensitivity.

Exercise training is an effective non-pharmacological resource in the treatment of insulin resistance and promotes glycemic control in animals with insulin resistance induced by obesity²⁹. The evidence generated by the present study reinforce the indication of aerobic exercise as treatment for insulin resistance induced by GCs. To date, no study had demonstrated this effect, which has a very significant clinical relevance.

In addition to insulin resistance in peripheral tissues, the increased liver gluconeogenesis and the augmented blood mobilization of muscle amino acids have an important role in hyperglycemia caused by the chronic use of GCs¹. The stimulation of the muscular protein synthesis can favor the glycemic control through the decreased release of amino acids for the liver gluconeogenesis. According to LaPier²³, the practice of endurance exercise is an effective resource in the prevention of muscular hypotrophy induced by GCs. The protocol of exercise training used in the present study is characterized by strength and aerobic resistance exercise, as the animals were exercised during 60 minutes at a constant velocity and needed to overcome the force of gravity to keep them on the equipment. It was also demonstrated that the physical training prevented the muscular hypotrophy and improved the glycemic control in the animals chronically treated with Dex.

In the present study, the aerobic exercise also decreased the secondary dyslipidemia induced by the chronic use of GC. The increase in the oxidation of fatty acids during the aerobic exercise has been well demonstrated. During contractions in the skeletal muscle, the increase in the concentrations of adenosine monophosphate (AMP) and the decrease in the concentrations of creatine phosphate lead to the activation of the AMP-activated protein kinase (AMPK)¹². The AMPK phosphorilates and inhibits the acetyl-CoA-carboxylase and, consequently, reduces the concentrations of malonyl-CoA, an allosteric inhibitor of carnitine palmitoyltransferase 1 (CPT1)¹². That increases the long-chain fatty acids oxidation within the mitochondria^12,15. The exercise training also promotes the mitochondrial biogenesis and increases the expression of transporters and enzymes that regulate fatty acid oxidation in the skeletal muscle¹⁵. In our experimental model, the exercise training decreased dyslipidemia and lipid accumulation in the liver. Similar results were observed by Severino et al⁷ in response to the treatment with metformin (a potential AMPK activating drug) in rats chronically treated with Dex.

Alterations in the lipid metabolism are accompanied by changes in body weight. Clinically, weight gain is observed in patients with Cushing's syndrome and in those submitted to chronic treatment with GCs^1,6,8. This is due to the stimulating effect of GCs in the hypothalamic appetite regulation center¹. Differently from what is observed in humans, there is a decrease in body weight in animal models. As in the present study, Severino et al⁷ also demonstrated a weight decrease in rats treated with Dex. That is probably due to the intense lipolysis caused by the insulin resistance in the fat tissue and the permissive effect of GCs on the lipolytic action of adrenaline and noradrenaline¹. The lower uptake of glucose caused by the insulin resistance in the skeletal muscle leads to a preference of oxidation of fatty acids in this tissue³⁰. Venkatesan et al³⁰ demonstrated that the administration of etomoxir, an inhibitor of CPT1, inhibits the oxidation of fatty acids in the skeletal muscle, with a consequent increase in the concentrations of free fatty acids in the blood, decreasing hyperglycemia and hyperinsulinemia in rats treated with Dex. Therefore, the increase in the bioavailability of fatty acids in the blood caused by the increase in lipolysis stimulates the oxidation of these energetic substrates in the skeletal muscle^30-32.

The improvement in the lipid metabolism in response to the exercise training is accompanied by a decrease in body weight. The animals treated with Dex and trained presented the highest weight loss when compared to the sedentary animals. Such fact can be attributed to the increased oxidation potential of fatty acids in the muscles of trained animals and also to the permissive effect of GCs on the lipolytic action of adrenaline and noradrenaline, of which plasma concentrations are elevated during the exercise¹. The oxidation of fatty acids during the exercise depends on the bioavailability of these substrates in blood, activation of AMPK and the content of transporters and enzymes involved in the oxidation of these lipids in the skeletal muscle^31,33.

Finally, the exercise training could have a beneficial effect on the control of GC-induced arterial hypertension. Although this parameter was not evaluated in the present study, it is believed that the exercise training might have positively influenced the blood pressure control in animals treated with Dex. Dex does not have a significant mineralocorticoid action, but it has a hypertensive effect⁷. It is believed that Dex decreases the expression of nitric oxide synthase (NOS) and impairs the endothelium-dependent vasodilation⁷. This would be caused by the increase in the concentration of free fatty acids in blood, the oxidative stress induction and insulin resistance⁷. Severino et al⁷ demonstrated that rats treated with low Dex doses developed arterial hypertension and that the latter is preceded by insulin resistance and dyslipidemia. Such fact suggests that insulin resistance is an event that precedes the development of hypertension in animals treated with Dex. Therefore, aerobic exercise training improves the insulin sensitivity and could have an effect on the blood pressure control decreasing oxidative stress and improving endothelial dysfunction^16,34.

Conclusion

The present study demonstrated that the regular practice of aerobic exercises decreases hyperglycemia, improves glucose tolerance, reduces secondary dyslipidemia and prevents non-alcoholic fatty liver disease and muscular hypotrophy in rats chronically treated with glucocorticoid. Although no effect of exercise traning was observed on blood levels of HDL-c, it is believed that other protocols can demonstrate, in this experimental model, the already known effect of physical activity on the metabolism of this lipoprotein. The data presented herein suggest the use of aerobic exercise training in the prevention and treatment of cardiometabolic alterations induced by the chronic use of glucocorticoids.

Potential Conflict of Interest

No potential conflict of interest relevant to this article was reported.

Sources of Funding

There were no external funding sources for this study.

Study Association

This study is not associated with any post-graduation program.

References

• 1. Berne RM, Levy MN, Koeppen MB, Stanton BA. Fisiologia. 5Ş ed. Rio de Janeiro: Elsevier; 2004.
• 2. Beato M, Truss M, Chávez S. Control of transcription by steroid hormones. Ann N Y Acad Sci. 1996; 784: 93-123.
• 3. Hench PS, Kendall EC, Slocumb CH, Polley HF. The effect of a hormone of the adrenal cortex (17-hydroxy-11-dehydrocorticosterone: compound E) and of pituitary adrenocorticotropic hormone on rheumatoid arthritis. Mayo Clin Proc. 1949; 24 (8): 181-97.
• 4. Ward E, Slocumb CH, Polley HF, Kendall EC, Hench PS. Clinical effects of cortisone administered orally to 100 patients with rheumatoid arthritis. Ann Rheum Dis. 1951; 10: 477-84.
• 5. Shih A, Jackson KC 2nd. Role of corticosteroids in palliative care. J Pain Palliat Care Pharmacother. 2007; 21 (4): 69-76.
• 6. Walker BR. Glucocorticoids and cardiovascular disease. Eur J Endocrinol. 2007; 157 (5): 545-59.
• 7. Severino C, Brizzi P, Solinas A, Secchi G, Maioli M, Tonolo G. Low-dose dexamethasone in the rat: a model to study insulin resistance. Am J Physiol Endocrinol Metab. 2002; 283 (2): E367-73.
• 8. Newell-Price J, Bertagna X, Grossman AB, Nieman LK. Cushing's syndrome. Lancet. 2006; 367: 1605-17.
• 9. Whorwood CB, Donovan SJ, Flanagan D, Phillips DI, Byrne CD. Increased glucocorticoid receptor expression in human skeletal muscle cells may contribute to the pathogenesis of the metabolic syndrome. Diabetes. 2002; 51 (4): 1066-75.
• 10. Stulnig TM, Waldhäusl W. 11beta-Hydroxysteroid dehydrogenase Type 1 in obesity and Type 2 diabetes. Diabetologia. 2004; 47 (1): 1-11.
• 11. Sociedade Brasileira de Cardiologia. IV Brazilian Guideline for Dyslipidemia and Atherosclerosis prevention: Department of Atherosclerosis of Brazilian Society of Cardiology. Arq Bras Cardiol. 2007; 88 (Suppl. 1): 2-19.
• 12. Jørgensen SB, Jensen TE, Richter EA. Role of AMPK in skeletal muscle gene adaptation in relation to exercise. Appl Physiol Nutr Metab. 2007; 32 (5): 904-11.
• 13. Wojtaszewski JF, Richter EA. Effects of acute exercise and training on insulin action and sensitivity: focus on molecular mechanisms in muscle. Essays Biochem. 2006; 42: 31-46.
• 14. Daugaard JR, Richter EA. Relationship between muscle fibre composition, glucose transporter protein 4 and exercise training: possible consequences in non-insulin-dependent diabetes mellitus. Acta Physiol Scand. 2001; 171 (3): 267-76.
• 15. Tunstall RJ, Mehan KA, Wadley GD, Collier GR, Bonen A, Hargreaves M, et al. Exercise training increases lipid metabolism gene expression in human skeletal muscle. Am J Physiol Endocrinol Metab. 2002; 283 (1): E66-72.
• 16. Suzuki T, Homma S. Treatment of hypertension and other cardiovascular risk factors in patients with metabolic syndrome. Med Clin North Am. 2007; 91 (6): 1211-23.
• 17. Castelli WP. Cholesterol and lipids in the risk of coronary artery disease - the Framingham Heart Study. Can J Cardiol. 1988; 4: 5A-10A.
• 18. Reaven G. Metabolic syndrome: pathophysiology and implications for management of cardiovascular disease. Circulation. 2002; 106: 286-8.
• 19. Kimura M, Daimon M, Tominaga M, Manaka H, Sasaki H, Kato T. Thiazolidinediones exert different effects on insulin resistance between dexamethasone-treated rats and wistar fatty rats. Endocr J. 2000; 47 (1): 21-8.
• 20. Perez de Alejo JL, Rodriguez Rodriguez G, Flores Miranda R. Ergopanin un producto natural con actividad estimulante y ergogénica. Rev Cubana Plant Med. 1999; 4 (1): 33-5.
• 21. American Academy of Pediatrics. National Cholesterol Education Program: Report of the Expert Panel on Blood Cholesterol Levels in Children and Adolescents. Pediatrics. 1992; 89 (3): 525-84.
• 22. Friedewald WT, Levy RI, Fredrickson DS. Estimation of the concentration of low-density lipoprotein cholesterol in plasma, without use of the preparative ultracentrifuge. Clin Chem. 1972; 18 (6): 499-502.
• 23. LaPier TK. Glucocorticoid-induced muscle atrophy: the role of exercise in treatment and prevention. J Cardiopulm Rehabil. 1997; 17 (2): 76-84.
• 24. Delarue J, Magnan C. Free fatty acids and insulin resistance. Curr Opin Clin Nutr Metab Care. 2007; 10 (2): 142-8.
• 25. Ruzzin J, Jensen J. Contraction activates glucose uptake and glycogen synthase normally in muscles from dexamethasone-treated rats. Am J Physiol Endocrinol Metab. 2005; 289 (2): E241-50.
• 26. Saad MJ, Folli F, Kahn JA, Kahn CR. Modulation of insulin receptor, insulin receptor substrate-1, and phosphatidylinositol 3-kinase in liver and muscle of dexamethasone-treated rats. J Clin Invest. 1993; 92(4): 2065-72.
• 27. Howlett KF, Sakamoto K, Hirshman MF, Aschenbach WG, Dow M, White MF, et al. Insulin signaling after exercise in insulin receptor substrate-2-deficient mice. Diabetes. 2002; 51 (2): 479-83.
• 28. Wojtaszewski JF, Higaki Y, Hirshman MF, Michael MD, Dufresne SD, Kahn CR, et al. Exercise modulates postreceptor insulin signaling and glucose transport in muscle-specific insulin receptor knockout mice. J Clin Invest. 1999; 104 (9): 1257-64.
• 29. Christ CY, Hunt D, Hancock J, Garcia-Macedo R, Mandarino LJ, Ivy JL. Exercise training improves muscle insulin resistance but not insulin receptor signaling in obese Zucker rats. J Appl Physiol. 2002; 92 (2): 736-44.
• 30. Venkatesan N, Lim J, Bouch C, Marciano D, Davidson MB. Dexamethasone-induced impairment in skeletal muscle glucose transport is not reversed by inhibition of free fatty acid oxidation. Metabolism. 1996; 45 (1): 92-100.
• 31. Wolfe RR, Klein S, Carraro F, Weber JM. Role of triglyceride-fatty acid cycle in controlling fat metabolism in humans during and after exercise. Am J Physiol. 1990; 258 (2 Pt 1): E382-9.
• 32. Turcotte LP. Muscle fatty acid uptake during exercise: possible mechanisms. Exerc Sport Sci Rev. 2000; 28 (1): 4-9.
• 33. Kanaley JA, Cryer PE, Jensen MD. Fatty acid kinetic responses to exercise. Effects of obesity, body fat distribution, and energy-restricted diet. J Clin Invest. 1993; 92 (1): 255-61.
• 34. Busija DW, Miller AW, Katakam P, Simandle S, Erdös B. Mechanisms of vascular dysfunction in insulin resistance. Curr Opin Investig Drugs. 2004; 5 (9): 929-35.

Exercise prevents cardiometabolic alterations induced by chronic use of glucocorticoids

Carlos Hermano da Justa Pinheiro^I; Wilson Martins de Sousa Filho^I; Joselito de Oliveira Neto^I; Maria de Jesus Ferreira Marinho^I; Renato Motta Neto^II; Manuela Maria Ramos Lima Smith^III; Carlos Antônio Bruno da Silva^{III, IV}

Publication Dates

• Publication in this collection
  24 Nov 2009
• Date of issue
  Oct 2009

History

• Accepted
  08 Aug 2008
• Reviewed
  03 Aug 2008
• Received
  01 Apr 2008