Effects of intermittent fasting and high-intensity interval training on cardiac remodeling and myocardial sestrins and AMP-activated protein kinase expression in healthy rats

Abstract Introduction Intermittent fasting (IF) and high-intensity interval training (HIIT) are non-pharmacological interventions with potential cardioprotective effects. The mechanisms underlying the cardiac changes induced by IF and HIIT are not fully understood. There is evidence that sestrins, a family of stress-responsive proteins, and AMP-activated protein kinase (AMPK), a fuel sensor, play an important role in cardioprotective mechanisms. Purpose To evaluate the influence of IF and HIIT on cardiac remodeling and myocardial sestrins and AMPK expression in healthy rats. Methods Male Wistar rats (n=60) were divided into Control (C), IF, HIIT (T), and IF + HIIT (TIF) groups. C and T were fed daily with ad libitum standard chow; IF and TIF received ad libitum chow every other day. T and TIF were submitted to a HIIT protocol on a treadmill. After 12 weeks, the rats were submitted to echocardiogram and maximal exercise test. The following variables were assessed: cardiomyocyte cross-sectional area and interstitial collagen fraction (histology), myocardial myosin heavy chain isoforms distribution (electrophoresis), DNA fragmentation (ELISA), metalloproteinase-2 activity (zymography), protein carbonyl levels (spectrophotometry), and sestrins 1 and 2 and AMPK (total and phosphorylated forms) protein expression (Western blot). Statistical analysis: ANOVA and Tukey. Results Exercise tolerance was higher in T and TIF than in C and IF, respectively. Left ventricular (LV) diastolic and systolic diameters, diastolic LV posterior wall thickness, and left atrium diameter were lower in IF than in C and TIF; left atrium diameter was lower in TIF than in T. LV endocardial fractional shortening did not differ between groups; LV posterior wall shortening velocity was higher in TIF than in T (C 40.4±4.2; IF 42.7±4.4; T 40.2±3.7; TIF 43.2±3.7 mm/s). Isovolumetric relaxation time normalized to R-R interval was lower in T than in C. E/E' ratio was lower in T than in C and TIF (C 19.5±2.2; IF 17.4±2.2; T 15.2±2.8; TIF 18.7±3.5). LV and total heart weight, in absolute values and normalized to tibia length, were lower in IF than in C and TIF. Cardiomyocyte cross-sectional area was lower in IF and TIF than in C and T, respectively. Interstitial collagen fraction was higher in T than in C and TIF. DNA fragmentation levels and metalloproteinase-2 activity did not differ between groups. The alpha-to-beta myosin heavy chain isoforms ratio was higher in IF than in C. Myocardial protein carbonylation (C 2.7±0.6; IF 5.4±2.0; T 3.2±1.3; TIF 3.0±1.1 mmol/mg protein) was higher in IF than in C and TIF. Protein expression of sestrins 1 and 2 was similar between groups. Phosphorylated-to-total AMPK ratio (C 1.37±0.78; IF 0.57±0.32; T 1.70±0.86; TIF 1.31±0.47 arbitrary units) was lower in IF than in C and TIF. Conclusion IF and HIIT promote cardiac alterations which are associated with changes in myocardial AMPK expression, but not with sestrins in healthy rats.