Correction of defective interdomain interaction within ryanodine receptor by antioxidant is a new therapeutic strategy against heart failure.

BACKGROUND: Defective interdomain interaction within the ryanodine receptor (RyR2) seems to play a key role in the pathogenesis of heart failure, as shown in recent studies. In the present study we investigated the effect of oxidative stress on the interdomain interaction, its outcome in the cardiac function in heart failure, and the possibility of preventing the problem with antioxidants. METHODS AND RESULTS: Sarcoplasmic reticulum (SR) vesicles were isolated from dog left ventricular (LV) muscle (normal or rapid ventricular pacing for 4 weeks with or without the antioxidant edaravone). In the edaravone-treated paced dogs (EV+), but not in the untreated paced dogs (EV-), normal cardiac function was restored almost completely. In the SR vesicles isolated from the EV-, oxidative stress of the RyR2 (reduction in the number of free thiols) was severe, but it was negligible in EV+. The oxidative stress of the RyR2 destabilized interdomain interactions within the RyR2 (EV-), but its effect was reversed in EV+. Abnormal Ca2+ leak through the RyR2 was found in EV- but not in EV+. The amount of the RyR2-bound FKBP12.6 was less in EV- than in normal dogs, whereas it was restored almost to a normal amount in EV+. The NO donor 3-morpholinosydnonimine (SIN-1) reproduced, in normal SR, several abnormal features seen in failing SR, such as defective interdomain interaction and abnormal Ca2+ leak. Both cell shortening and Ca2+ transients were impaired by SIN-1 in isolated normal myocytes, mimicking the pathophysiological conditions in failing myocytes. Incubation of failing myocytes with edaravone restored the normal properties. CONCLUSIONS: During the development of heart failure, edaravone ameliorated the defective interdomain interaction of the RyR2. This prevented Ca2+ leak and LV remodeling, leading to an improvement of cardiac function and an attenuation of LV remodeling.

Chronic effects of ethanol on pharmacokinetics and left ventricular systolic function in rats.

BACKGROUND: Observational clinical studies have demonstrated that there is a U-shaped relationship between ethanol consumption and all-cause mortality or risk of ischemic stroke. Although the exact cause of the U-shaped relationship is unclear, the pharmacokinetics of ethanol during the time course of chronic intake of ethanol may be involved, in relation to its cardiotoxic effects. The present study has assessed the cause of the U-shaped relationship between the ethanol consumption and left ventricular (LV) systolic dysfunction in a pharmacokinetic way. METHODS: Male Wistar rats were paired, and either ethanol or control liquid diet was chronically administered for 7 weeks. Then, these rats were subdivided into 3 groups: control liquid-diet-fed rats [EtOH (-)], 3 g/dL ethanol liquid-diet-fed rats (3%EtOH), and 5 g/dL ethanol liquid-diet-fed rats (5%EtOH). Ethanol's cardiotoxicity on LV systolic function was investigated by echocardiography. Ethanol concentration in blood, ethanol pharmacokinetics, and hepatic alcohol dehydrogenase (ADH) activity were evaluated simultaneously. RESULTS: The 5%EtOH group revealed LV systolic dysfunction, associated with a higher ethanol concentration in blood, and lower hepatic ADH activity than the EtOH (-) group; however, the 3%EtOH group did not show LV systolic dysfunction. During the acute ethanol stress, LV systolic dysfunction appeared in both EtOH (-) and 5%EtOH groups, with a higher ethanol concentration in blood and lower hepatic ADH activity than the 3%EtOH group. The 3%EtOH group showed a higher ethanol washout rate, less time-integral of ethanol concentration, and shorter mean residence time of ethanol in blood than the EtOH (-) or 5%EtOH group. CONCLUSIONS: The U-shaped relationship between chronic ethanol consumption and LV systolic dysfunction may be closely related to the pharmacokinetic characteristics of ethanol in blood, which depends on the quantity of chronically drinking alcohol.

AT1 receptor antagonist restores cardiac ryanodine receptor function, rendering isoproterenol-induced failing heart less susceptible to Ca2+ -leak induced by oxidative stress.

BACKGROUND: The Ca(2+) regulatory proteins in the sarcoplasmic reticulum (SR) play a key role in the pathogenesis of heart failure. In the present study the effect of chronic beta-receptor-stimulation on cardiac and SR functions was assessed, with or without angiotensin-II receptor antagonist treatment recently reported to have anti-beta-adrenergic activity. METHODS AND RESULTS: Rats were treated with isoproterenol with (+) or without (-) candesartan (CAN) and then SR vesicles were isolated from the left ventricular muscle. Both Ca(2+)-uptake and the amount of SR Ca(2+)-ATPase were significantly lower in the CAN (-) group than in the shams, but those were almost normally restored in the CAN (+). Although the level of the protein kinase A (PKA)-phosphorylation of the SR Ca(2+) release channel, known as the ryanodine receptor (RyR2), was elevated in the CAN (-), no Ca(2+)-leak was detected. However, SIN-1 (O(2) (-) donor) induced Ca(2+)-leak in the CAN (-) at a 10-fold lower dose than in the sham and CAN (+). In cardiomyocytes, SIN-1 decreased cell shortening and the peak Ca(2+) transient and prolonged time from peak to 70% decline in CAN (-), again at 10-fold lower dose than in the sham and CAN (+). CONCLUSION: Chronic beta-receptor-stimulation did not induce any Ca(2+)-leak from the SR, whereas Ca(2+)-leak was easily induced when oxidative stress was applied to the PKA-phosphorylated RyR2. Candesartan not only improved Ca(2+)-uptake, but also prevented PKA-phosphorylation, rendering the SR less susceptible to Ca(2+)-leak.