Studies On The Protective Effect Of Nicorandil On Cardiac Hypertrophy And Its Mechanism

Cardiac hypertrophy, the prelude of heart failure, could increase the incidence rates of cardiac arrhythmia, myocardial infarction and sudden death, which was generally accepted as an independent risk factor of cardiovascular disease. Nicorandil was an ATP-sensitive potassium channel opener with a calcium blocking effect. It was confirmed that nicorandil could not only increase coronary blood, decrease oxygen consumption, but also reduce preload and afterload of heart, in the meanwhile, without accompanying tachycardia reflexly. With the techniques of immunology, electro- physiology and molecular biology, we studied the effects and its mechanism of nicorandil on cardiac hypertrophy through mice and rats in vivo and guinea pig papillary muscles in vitro. To clarify the mechanism of its action, we investigated the degree of reactive oxidative damages, energy metabolism, action potential, cell apoptosis,intracellular calcium overload and related gene expression in myocardial tissue of cardiac hypertrophy when given nicorandil.Part I The effects of nicorandil on cardiac hypertrophy1. Protective effects of nicorandil on cardiac hypertrophy induced by isoproterenol in miceIn this study, cardiac hypertrophy of mice was induced by continuous subcutaneous administration of isoproterenol (2mg·kg-1). The cardiac indexes, morphological changes, the survival time by close normobaric hypoxia, the activities of superoxide dismutase(SOD), glutathione peroxidase (GSH-Px) and the content of malondialdehyde (MDA) were determined. The results showed that nicorandil remarkably reduced the cardiac indexes, obviously prolonged the survival time of mice in the close normobaric hypoxia (P<0.05 or P<0.01)and significantly increased the activities of SOD,GSH-Px and decreased the content of MDA in mice, especially in middle and high dose(P<0.05 or P<0.01).2. Protective effects of nicorandil on cardiac hypertrophy induced by L-thyroxine in rats.Cardiac hypertrophy of rats was established by administration of ip L-thyroxine. The activities of superoxide dismutase (SOD), the content of malondialdehyde (MDA), Na+,K+-ATPase and Ca2+-ATPase in the mitochondria of cardiac tissue were determined. Glibenclamide, a blocker of the ATP-sensitive potassium channel, was used to examine the changed effects of nicorandil on cardiac hypertrophy. The results showed that nicorandil significantly increased the activities of SOD,Na+,K+-ATPase, Ca2+-ATPase (P<0.01) and decreased the content of MDA (P<0.05 or P<0.01)in the mitochondria of cardiac tissue.PartⅡThe action mechanism of nicorandil on preventing cardiac hypertrophy1. Effects of nicorandil on the action potential of cardiac tissue in guinea pig papillary muscles.The action potential of isolated guinea pig papillary muscles was determined by the standard microelectrode technique. Effects of nicorandil on the action potential and the action of glibenclamide, a blocker of the ATP-sensitive potassium channel, on nicorandil were observed. Under the different concentration (0.3,1,3,10,30μmol?L-1)of nicorandil, the effects of nicorandil on APA,APD50 and APD90 were examined. The whole procedure was duplicated after adding glibenclamide. The results showed that nicorandil could shorten APD50 and APD90 in a concentration dependent manner, especially on APD90(P<0.01), with little effect on APA. The shortening rates of APD50 and APD90 significantly decreased ( P<0.01 ) after using glibenclamide, which indicated that glibenclamide could remarkably attenuate the above effects of nicorandil on APD50 and APD90.2. Effects of nicorandil on cell apoptosis in myocardial tissue of cardiac hypertrophy Cardiac hypertrophy was established by administration of ip L-thyroxine. Expression of Fas and Bcl-2 protein was measured by the technique of immuno- histochemistry. The results indicated that nicorandil could obviously reduce the expression of Fas protein(P<0.01)and enhance the expression of Bcl-2 protein(P<0.05 or P<0.01). Furthermore, when glibenclamide, a blocker of the ATP- sensitive potassium channel, was also used in the meanwhile, compared with using corresponding nicorandil, the expression of Fas protein was remarkably increased (P<0.01)while the expression of Bcl-2 significantly decreased(P<0.01).3. Effects of nicorandil on the expression of c-fos,c-jun and TGF-β1 in myocardial tissue of cardiac hypertrophy.Effect of nicorandil on the activity of calcineurin(CaN) in myocardial tissue of cardiac hypertrophy was determined. Expression of c-fos, c-jun and TGF-β1 was examined by semiquantitative reverse transcription polymerase chain reaction (RT-PCR); TGF-β1 protein levels were measured by enzyme-linked immunosorbent assay (ELISA). The results showed that nicorandil significantly decreased the activity of CaN(P<0.01), nicorandil could induce mRNA expression of c-fos,c-jun and TGF-β1 (P<0.05orP<0.01) and decrease protein expression of TGF-β1 (P<0.01). Glibenclamide could reverse the above effects of nicorandil(P<0.05 or P<0.01). In conclusion:1. Nicorandil relieves cardiac hypertrophy induced by isoproterenol in mice. Nicorandil can protect cardiac tissue, which may be involved in inhibiting lipid peroxidation and eliminating oxygen free radical.2. Nicorandil can prevent cardiac hypertrophy induced by L-thy, which may be related to inhibiting lipid peroxidation in the mitochondria of myocytes and ameliorating energy metabolism.3. Nicorandil can shorten APD50 and APD90 in a concentration dependent manner. Glibenclamide can remarkably reverse the above effects of nicorandil, which indicate that its mechanism may be in correlation with opening potassium channel.4. Nicorandil can remarkably reduce the expression of Fas protein and enhance the expression of Bcl-2 protein, which indicate that nicorandil can inhibit cell apoptosis of hypertrophic myocardial.5. Nicorandil can decrease the activity of CaN, depress mRNA expression of c-fos,c-jun and TGF-β1 and reduce protein expression of TGF-β1 in myocardial tissue of cardiac hypertrophy. Glibenclamide can remarkably attenuate the above effects of nicorandil, which indicate that nicorandil can depress related gene expression by opening KATP channel.