ABC | Volume 115, Nº1, July 2020

Original Article Silva-Bertani et al. Mechanism of decreased heart collagen I in obesity Arq Bras Cardiol. 2020; 115(1):61-70 Myocardial protein levels of collagen type I, TIMP-1, TIMP- 2, and leptin Figure 2 reveals that obesity promoted a reduction in protein levels of collagen type I, TIMP-1 and TIMP-2; however, there was an increase in leptin protein levels in the obese group compared to the control group. Myocardial MMP-2 activity Figure 3 shows the identification of two weak bands of degradation corresponding to MMP-2 in electrophoresis gel: inactive MMP-2 (pro-MMP-2) with a molecular weight of approximately 72 kDa and active MMP-2 with a molecular weight of approximately 64 kDa. Between the two bands mentioned, it was possible to identify the strong band of MMP- 2 intermediate degradation. There was a significant increase in MMP-2 in the obese animals. Linear association between cardiac variables Table 3 reveals that there was a significant correlation between the decrease in collagen type I and increased MMP- 2 activity, as well as between the elevation of MMP-2 activity and leptin. Moreover, a correlation was observed between the increase in MMP-2 and the decrease in TIMP-1 and -2, as well as between decreased TIMP-1 and increased leptin protein levels. There was no significant correlation between decreased TIMP-2 and increased leptin. Discussion This study aimed to investigate whether a reduction in collagen type I is associated with increased MMP-2 activity and elevated levels of leptin in the myocardium of obese rats. The main results confirmed this hypothesis. The continuous feeding of a high-fat diet was effective to promote obesity in 34 weeks, given that the rats showed higher levels of body and fat weight and AI compared to rats fed a standard diet; these data are in agreement with other studies. 27,28 The major causes of obesity are a more abundant supply of food, higher intake of energy-dense, palatable food, and reduction in energy expenditure. The high-fat diet used in the current study was rich in mono- and polyunsaturated fatty acids with an energy content of 3.65 kcal/g, while the standard diet fed to the control group consisted of 2.95 kcal/g, generating a difference of 24% in caloric content. Authors have shown that consumption of a high-fat diet promotes less satiety and thus increased food intake. 29 These data differ from our results since the obese animals ate a lower amount of food and calories compared to control. However, feed efficiency was higher in obese rats, likely due to the thermic effect of food. Dietary fat requires less energy (2% – 3%) to be metabolized, and the excessive fat is thus easily deposited in the form of triglycerides in adipocytes, resulting in obesity. 30 Several studies have reported some comorbidities related to experimental obesity, 29,31,32 such as glucose intolerance, insulin resistance, dyslipidemia, hyperinsulinemia, hyperleptinemia, and arterial hypertension. In the present study, the obese animals exhibited higher AUC in the oral glucose tolerance test and higher serum insulin levels than controls, indicating that obesity promoted glucose intolerance and hyperinsulinemia. Glucose intolerance, associated with increased serum insulin, indicated that obese rats presented resistance to the action of insulin. These results are further supported by the increased HOMA-IR in obese rats. All these findings are in accordance with previous reports that used rats fed a high unsaturated fat diet. 13,27,28,33 Different studies Table 1 – Animal general characteristics Variables Groups Control (n = 20) Obese (n = 21) p value IBW (g) 151 ± 11 151 ± 11 0.290 FBW (g) 480 ± 51 534 ± 58 0.009 Epididymal fat (g) 9.3 ± 2.3 14.2 ± 3.4 < 0.001 Epididymal fat/100gFBW 1.9 ± 0.5 2.7 ± 0.6 < 0.001 Retroperitoneal fat (g) 10.5 ± 3.3 21.7 ± 5.9 < 0.001 Retroperitoneal fat/100gFBW 2.2 ± 0.7 4.1 ± 1.1 < 0.001 Visceral fat (g) 6.3 ± 1.4 11.2 ± 4.2 < 0.001 Visceral fat/100gFBW 1.3 ± 0.3 2.1 ± 0.8 < 0.001 BF (g) 26.1 ± 6.2 47.2 ± 12.3 < 0.001 Adiposity index 5.6 ± 0.9 8.8 ± 1.6 < 0.001 Food consumption (g/day) 22.8 ± 2.1 17.0 ± 2.3 < 0.001 Caloric intake (kcal) 67.4 ± 6.3 62.1 ± 8.2 0.03 Feeding efficiency (%) 2.1 ± 0.2 2.7 ± 0.2 < 0.001 Values are means ± SD. IBW: initial body weight; FBW: final body weight; BF: body fat. Student’s t-test. 64