Effect of edaravone, a novel free radical scavenger, supplemented to cardioplegia on myocardial function after cardioplegic arrest: in vitro study of isolated rat heart.

Cardioplegic arrest has been the main mechanism of myocardial protection during open-heart surgery; however, it causes myocardial injury during ischemia-reperfusion. Free radical scavengers are widely known to attenuate ischemia-reperfusion injury in various settings. We investigated the effects of edaravone, a novel free radical scavenger that was originally used for cerebral protection, on myocardial function during ischemia-reperfusion after cardioplegic arrest. Rat hearts were excised and perfused using Langendorff apparatus. The hearts were cardioplegically arrested for 90 min using St. Thomas' Hospital cardioplegic solution (ST solution) at 4 degrees C every 45 min and then reperfused for 20 min. The hearts were divided into 4 groups (n = 13 in each group). In Group ST, the hearts were arrested using the ST solution alone. In Groups L, M, and H, the hearts were arrested using the ST solution supplemented with a low-dose (1 microM), moderate dose (10 microM), and high dose (100 microM) of edaravone, respectively. Left ventricular function (+dp/dt (max)) and the levels of the cardiac enzymes released were measured before and after cardioplegic arrest. At the end of the study, the water content and the tissue oxidative stress (8-hydroxy-2'-deoxyguanosine) of the heart were measured. During reperfusion, the edaravone-treated groups showed a greater functional recovery with regard to the +dp/dt (max) (P < 0.05). The lactate level was the lowest (P < 0.01) in Group M. The water content of the hearts in the edaravone-treated groups was significantly lower (P < 0.05) than that in Group ST. Oxidative stress was significantly lower (P < 0.01) in the edaravone-treated hearts than in Group ST, and it was the lowest in Group M. The addition of edaravone to the cardioplegic solution ameliorates the impairment in myocardial function by reducing the oxidative stress after cardioplegic arrest. In this study, the maximum improvement in the myocardial function was achieved by addition of a moderate dose (10 microM) of edaravone.

Does the beta2-agonist clenbuterol help to maintain myocardial potential to recover during mechanical unloading?

OBJECTIVE: Chronic mechanical unloading induces left ventricular (LV) atrophy, which may impair functional recovery during support with an LV-assist device. Clenbuterol, a beta2-adrenergic receptor (AR) agonist, is known to induce myocardial hypertrophy and might prevent LV atrophy during LV unloading. Furthermore, beta2-AR stimulation is reported to improve Ca2+ handling and contribute to antiapoptosis. However, there is little information on the effects of clenbuterol during LV unloading. METHODS AND RESULTS: We investigated LV atrophy and function after LV unloading produced by heterotopic heart transplantation in isogenic rats. After transplantation, rats were randomized to 1 of 2 groups (n=10 each). The clenbuterol group received 2 mg.kg(-1).d(-1) of the drug for 2 weeks; the control group received normal saline. The weight of unloaded control hearts was 48% less than that of host hearts after 2 weeks of unloading. Clenbuterol significantly increased the weight of the host hearts but did not prevent unloading-induced LV atrophy. Papillary muscles were isolated and stimulated, and there was no difference in developed tension between the 2 groups. However, the inotropic response to the beta-AR agonist isoproterenol significantly improved in the clenbuterol group. The mRNA expression of myocardial sarco(endo)plasmic reticulum Ca2+-ATPase 2a (SERCA2a) and fetal gene shift (myosin heavy chain [MHC] mRNA isozyme) was also significantly improved by clenbuterol treatment. There was no difference in beta1-AR mRNA expression between the 2 groups. In contrast, beta2-AR mRNA was significantly decreased in the clenbuterol-treated, unloaded heart. This indicates that clenbuterol may downregulate beta2-ARs. In the evaluation of apoptosis, mRNA expression of caspase-3, which is the central pathway for apoptosis, tended to be better in the clenbuterol group. CONCLUSIONS: During complete LV unloading, clenbuterol did not prevent myocardial atrophy but improved gene expression (SERCA2a, beta-MHC) and beta-adrenergic responsiveness and potentially prevented myocardial apoptosis. However, chronic administration of clenbuterol may be associated with downregulation of beta2-ARs.

Heterotopic transplantation of the failing rat heart as a model of left ventricular mechanical unloading toward recovery.

The left ventricular assist device (LVAD) is usually used in patients with end-stage heart failure as a bridge to transplantation. Recently, some studies have reported functional recovery with the use of an LVAD, although the mechanisms responsible for recovery are not fully understood. We investigated the functional recovery of the infarcted, failing rat heart in response to mechanical unloading after heterotopic transplantation. Heart failure was induced in Lewis rats by ligating the left anterior descending artery. After 4 weeks, the infarcted hearts were harvested and heterotopically transplanted. The transplanted infarcted heart was removed after 2 weeks of unloading and examined for hypertrophy and fibrosis, as well as for mRNA levels encoding for brain natriuretic peptide, sarco(endo)plasmic reticulum Ca(2+)-ATPase2a (SERCA2a), and beta1- and beta2-adrenergic receptors. Normal and infarcted rats without transplantation served as control animals. The infarcted heart was hypertrophied as evidenced by an increase in heart weight and myocyte diameter. After unloading the infarcted heart for 2 weeks, there was a decrease in heart weight and myocyte diameter. However, the percentage of myocardial fibrosis increased after unloading. The mRNA expression of brain natriuretic peptide and the beta2-adrenergic receptor significantly improved after mechanical unloading. The levels of SERCA2a mRNA tended to increase after unloading. In conclusion, unloading the failing, infarcted heart can help normalize left ventricular hypertrophy and cardiac gene expression. This unloading model appears to partially mimic the conditions of hemodynamic support with an LVAD in heart failure patients and potentially offers insights into the mechanisms of functional recovery.

Taurine prevents myocardial ischemia/reperfusion-induced oxidative stress and apoptosis in prolonged hypothermic rat heart preservation.

Taurine (2-aminoethanesulfonic acid) is a potent antioxidant and inhibits cell apoptosis in ischemic reperfusion injury. In this study we evaluated whether addition of taurine to St. Thomas' cardioplegic solution enhances its myocardial protective effects in prolonged hypothermic heart preservation in rats. Hearts isolated from male Sprague-Dawley rats were mounted on a Langendorff apparatus to estimate baseline cardiac function, then arrested and stored in St. Thomas' cardioplegic solution, with taurine (10 mM; taurine group, n = 8) or without taurine (control group, n = 8), for 6 h at 4 degrees C. After storage, the hearts were reperfused and heart rate (HR), coronary flow (CF), left ventricular developed pressure (LVP), and positive maximum left ventricular developing pressure (max LV dp/dt) were measured. The LV tissue was examined immunohistochemically for determining DNA oxidative stress and cell apoptosis. Compared with control groups, recovery of LVP (P < 0.001), max LV dp/dt (P < 0.001), and coronary flow (P < 0.001) were significantly enhanced, whereas glutamic oxaloacetic transaminase (P < 0.01), lactate dehydrogenase (P < 0.05), creatine phosphate kinase (P < 0.01), 8-hydroxy-2'-deoxyguanosine index (P < 0.01), caspase-3 mRNA expression (P < 0.05), and percentage of TUNEL-positive cardiomyocytes (P < 0.05) were reduced in the taurine group. Addition of taurine to St. Thomas' cardioplegic solution improved cardiac function recovery for prolonged hypothermic rat heart preservation by suppressing DNA oxidative stress and cell apoptosis.