Protective Effects And Mechanisms Of Isosteviol On Isoprenaline-induced Adult Rat Myocardial Hypertrophy

Myocardial hypertrophy is a compensatory response on stimulus, such as hormones,cytokines and pressure overload. However, on the constant stimulation, the hypertrophy will develop to a decompensation state, which will fianlly lead to heart failure. Therefore, it is of great significance to explore the pathogenesis of cardiac hypertrophy and seek potent drugs to prevent and treat hypertrophy in cardiovascular field.Isosteviol, a beyerane diterpene, is an isoform of steviol obtained by acid hydrolysis of stevioside. STVNa is the sodium form of isosteviol with higher solubility. Isosteviol was demonstrated to have heart protective effects, such as anti-ischemia, anti-arrhythmia,improvement of cardiac contractility in previous studies. However, the anti-hypertrophy effect of isosteviol has not been studied so far.We established effective and stable isoprenaline-induced adult rat myocardial hypertrophy model to study the effects and mechanisms of STVNa on hypertrophy.1. A new isolation method of adult rat ventricular cells was modified to get high viability and yield of cardiac myocytes. 5 μM isoprenaline(Iso) was applied to induce hypertrophy for 24 h.Compared with control group, 5 μM Iso significantly increased cell surface area from 1.00 to1.39 ± 0.02(relative value, P < 0.05) and increased expression of BNP, the bio-marker of hypertrophy from 1.00 ± 0.18 to 2.35 ± 0.18(relative value, P < 0.05). STVNa showed inhibition effects on cardiac hypertrophy at different concentrations. Compared with Iso treated group, 5 μM,10 μM,20 μM STVNa significantly decreased cell surface area from1.39 ± 0.02 to 1.17 ± 0.01, 1.14 ± 0.01, 1.13 ± 0.01(relative value, P < 0.05).2. To further explore the underlying mechanism of anti-hypertrophy effect of STVNa on cardiac myocytes, following studies were conducted.(1) We found that STVNa is a potential ROS scavenger and shows protective effect of mitochondrial. Compared with control group, Iso significantly increased ROS from 1.00 ±0.06 to 2.03 ± 0.11(relative value, P < 0.01) and decreased mitochondrial membrane potential from 2.47 ± 0.18 to 1.51 ± 0.04(relative value, P < 0.05). 5 μM STVNa significantly attenuated ROS production from 2.03 ± 0.11 to 1.32 ± 0.07(relative value, P < 0.05)and restored mitochondrial membrane potential from 1.51 ± 0.04 to 1.85 ± 0.09(relative value, P< 0.05).(2) We also found that STVNa can improve calcium handling and increase contractility of hypertrophied cardiac myocytes. Compared with control group, Iso significantly increased cytoplasm calcium, prolonged calcium uptaking time and decreased contractility of cardiac myocytes. 5 μM STVNa can inhibit calcium overload and increase contractility of cardiac cells significantly.In conclusion, STVNa has protective effects on isoprenaline-induced cardiac hypertrophy and can increase contractility of hypertrophied cardiac myocytes, the mechanisms of which are related to scavenge intracellular excessive ROS, inhibit calcium overload and improve the uptaking rate of calcium.