Estudo das alterações vasculares em modelo murino de obesidade induzida por dieta hiperglicídica e avaliação da eficácia do treinamento físico de intensidade moderada

Abstract

Obesity is an important risk factor for many cardiovascular diseases such as hypertension, atherosclerosis and diabetes. Under this condition, the adipose tissue inflammation contributes to the development of vascular alterations and intensifies the related pathophysiological stages of these diseases. The practice of physical activity as prevention of vascular changes associated with obesity is widely recommended although there is no consensus of its long-term benefits. The aim of this study was to investigate the impact of physical training on vascular and metabolic changes induced by a high-carbohydrate diet. Methods: C57BL/6J mice (12 weeks) were randomly assigned into four groups: untrained + standard diet (SC); untrained + high-carbohydrate diet (SD); trained + standard diet (EC) and trained + high-carbohydrate diet (ED). The animals were fed either standard chow or with high-carbohydrate diet that was enriched with condensed milk and sugar, during eight weeks. Simultaneously, low intensity exercise training (60% of maximal speed of maximal exercise test) was performed on a motor treadmill five days/week. We assessed body weight, perivascular, mesenteric, testis and retroperitoneal fats. Metabolic, inflammatory and hormonal parameters were evaluated using specific commercial kits. Vascular reactivity in aortic and mesenteric arteries rings was assessed in an organ bath using isometric transducers. Systolic blood pressure and heart rate were measured by tail pletismography. Protein expressions of the iNOS, eNOS, COX-2, receptor-1 to TNF, the p65 subunit of NFκB were assessed by Western blot. The basal production of nitric oxide in the aorta was estimated by indirect dosage with diaminonaphthalene and by fluorescence microscopy using DAF-FM probe to NO. Results: High-carbohydrate diet induced an increase of visceral fat, and of the concentrations of total cholesterol, especially LDL fraction, insulin, leptin. The obese mice showed increased pro-inflammatory cytokines production on themesenteric adipose tissue, epididymal and retroperitoneal. It is also observed a raise of TNFα in the obese animal serum. The periaortic adipose tissue of animals showed no change in TNFα and MCP-1 secretion profile. Physical training reduced weight gain, fat deposits, and concentrations of cholesterol and LDL in the ED group. It also prevented the increase of cytokine production in the serum and adipose tissue, and prevented the raise of insulin and leptin-induced highcarbohydrate diet. There was no change in serum concentrations of glucose, fatty acids and triglycerides, glucose tolerance test, blood pressure, heart rate among the four experimental groups. Data from vascular reactivity showed a contractile dysfunction, characterized by decreased response to phenylephrine in the aorta of animals SD compared to animals SC. This difference was endotheliumdependent and reverted by the pre-treatment with L-NAME (300µM) or with LNIL (10µM). The exercise was unable to restore the contractile response induced by diet (ED group). These results suggest that the dysfunction is dependent on the increased production of NO by inducible isoform of nitric oxide synthase. The aorta of the ED group’s animals also showed increased expression of the iNOS, receptor for TNF-1, and basal NO production. In the mesenteric artery of obese sedentary group, we found a vascular dysfunction characterized by increased contractile response to phenylephrine and decreased vasorelaxation response to acetylcholine. These alterations were prevented by exercise training. The mesenteric hypercontractility of SD group also was restored by the pre-treatment with ibuprofen (10μM) or with celecoxib (10μM), or with the TP receptor antagonist (SQ29548, 10μM). These results suggest that the pathway of COX-2 and contractile prostanoids production were stimulated in the SD mesenteric artery by high-carbohydrate diet. The mesenteric artery of obese animals showed higher expression of COX-2, receptor-1 for TNF and p65 subunit of NFκB. These increase was prevented by physical training. In the animals with deletion of the iNOS and in the animals with acute silencing of iNOS, both of them fed with the high-carbohydrate diet, we have not observed the vascular dysfunction. In conclusion: Obese animals showed vascular and metabolic changes similar to those observed in obese human beings, such as increased visceral adipose tissue, increased circulating levels of cholesterol and LDL, and vascular changes that vary depending on the vascular bed. The vascular dysfunction, both in the aorta and in the mesenteric artery, was related to the alterations induced by proinflammatory cytokines arising from the surrouding adipose tissue and bloodstream. These cytokines led to the activation of the TNF α/ TNFα receptor1 / NFκB, with consequent expression of target genes of this pathway, such as iNOS and COX-2. The physical training was able to prevent the onset of contractile and endothelial dysfunction of mesenteric artery and improves metabolic parameters, probably by reducing the pro-inflammatory state found in obese animals. These results show the efficacy of exercise as therapy in preventing the deleterious effects of obesity.