Effects of an hERG activator, ICA-105574, on electrophysiological properties of canine hearts.

In short QT syndrome, inherited gain-of-function mutations in the human ether a-gogo-related gene (hERG) K(+) channel have been associated with development of fatal arrhythmias. This implies that drugs that activate hERG as a side effect may likewise pose significant arrhythmia risk. hERG activators have been found to have diverse mechanisms of activation, which may reflect their distinct binding sites. Recently, the new hERG activator ICA-105574 was introduced, which disables inactivation of the hERG channel with very high potency. We explored characteristics of this new drug in several experimental models. Patch clamp experiments were used to verify activation of hERG channels by ICA-105574 in human embryonic kidney cells stably-expressing hERG channels. ICA-105574 significantly shortened QT and QTc intervals and monophasic action potential duration (MAP(90)) in Langendorff-perfused guinea-pig hearts. We also administered ICA-105574 to anesthetized dogs while recording ECG and drug plasma concentrations. ICA-105574 (10 mg/kg) significantly shortened QT and QTc intervals, with a free plasma concentration of approximately 1.7 µM at the point of maximal effect. Our data showed that unbound ICA-105574 caused QT shortening in dogs at concentrations comparable to the half maximal effective concentration (EC(50), 0.42 µM) of hERG activation in the patch clamp studies.

Bicarbonate supplementation as a preventive way in statins-induced muscle damage.

PURPOSE: The aim of this study was to evaluate the bicarbonate-induced improvement of statins, cerivastatin, simvastatin acid and lovastatin acid -induced apoptosis using rat myoblast cell line (L6) as a model of in vitro skeletal muscle and of cerivastatin-induced muscle damage in vivo study. METHODS: Statin-induced reduction of cell viability and apoptosis was measured by 3-(4,5-dimethylthiazol-2-yl)2,5-diphenyl tetrazolium bromide (MTT) assay and caspase assay. In vivo, we evaluated plasma creatine phosphokinase (CPK) level in cerivastatin-treated rat. RESULTS: Bicarbonate prevented cerivastatin-, simvastatin- acid and lovastatin acid -induced reduction of cell viability, morphological change and caspase activation in L6 cells. Moreover, in the in vivo study, bicarbonate prevented cerivastatin-induced increase in CPK concentrations. CONCLUSIONS: These results from in vitro and in vivo studies support that bicarbonate supplementation prevented statin-induced muscle damage.

Association between risk of myopathy and cholesterol-lowering effect: a comparison of all statins.

In the present study, we examined the mechanisms underlying the cytotoxicity of pitavastatin, a new statin, and we compared the in vitro potencies of muscle cytotoxicity using a prototypic embryonal rhabdomyosarcoma cell line (RD cells), a typical side effect of statins and compared the cholesterol-lowering effects of statins using Hep G2 hepatoma cells. Pitavastatin reduced the number of viable cells and caused caspase-9 and -3/7 activation in a time- and concentration-dependent manner. The comparison of cytotoxities of statins showed that statins significantly reduced cell viability and markedly enhanced activity of caspase-3/7 in concentration-dependent manner. On the other hand, the effects of hydrophilic statins, pravastatin, rosuvastatin were very weak. The rank order of cytotoxicity was cerivastatin > simvastatin acid> fluvastatin > atorvastatin > lovastatin acid > pitavastatin >> rosuvastatin, pravastatin. Statin-induced cytotoxicity is associated with these partition coefficients. On the other hand, the cholesterol-lowering effect of statins did not correlate with these partition coefficients and cytotoxicity. Thus, it is necessary to consider the association between risk of myopathy and cholesterol-lowering effect of a statin for precise use of statins.

Effect of medium pH on the cytotoxicity of hydrophilic statins.

PURPOSE: The aim of this study was to examine the mechanism of pravastatin- and rosuvastatin-induced cytotoxicity and the relationship between pravastatin- and rosuvastatin-induced cytotoxicity and medium pH using human prototypic embryonal rhabdomyosarcoma cell line (RD) and rat myoblast cell line (L6) as a model of in vitro skeletal muscle. METHODS: Statin-induced reduction of cell viability and apoptosis was measured by 3-(4,5-dimethylthiazol-2-yl)2,5 -diphenyl tetrazolium bromide (MTT) assay and caspase assay. Intracellular accumulation of statins was determined using an HPLC system. RESULTS: Rosuvastatin cytotoxicity, reduction of cell viability, morphological changes and caspase activation at acidic pH (pH 6.8) were significantly greater than those at neutral pH (pH 7.4). Rosuvastatin accumulation at acidic pH was greater than that at pH 7.4. On the other hand, medium pH had no effect on pravastatin accumulation. CONCLUSIONS: Rosuvastatin cytotoxicity at acidic pH is associated with increasing intracellular accumulation of rosuvastatin. On the other hand, medium pH had no effect on cytotoxicity of pravastatin.

Preventive effects of bicarbonate on cerivastatin-induced apoptosis.

Although HMG-CoA reductase inhibitors such as statins are the most widely used cholesterol-lowering agents, there is a risk of myopathy or rhabdmyolysis occurring in patients taking these drugs. It has been reported that a number of lipophilic statins cause apoptosis in various cells, but it is still not clear whether intracellular acidification is involved in statin-induced apoptosis. There have been few studies aimed at identifying compounds that suppress statin-induced myotoxicity. In the present study, we examined the relationship between cerivastatin-induced apoptosis and intracellular acidification and the effect of bicarbonate on cerivastatin-induced apoptosis using an RD cell line as a model of in vitro skeletal muscle. Cerivastatin reduced the number of viable cells and caused dramatic morphological changes and DNA fragmentation in a concentration-dependent manner. Moreover, cerivastatin-induced apoptosis was associated with intracellular acidification and caspase-9 and -3/7 activation. On the other hand, bicarbonate suppressed cerivastatin-induced pH alteration, caspase activation, morphological change and reduction of cell viability. Accordingly, bicarbonate suppressed statin-induced apoptosis. The strategy to combine statins with bicarbonate can lead to reduction in the chance of the severe adverse events including myopathy or rhabdmyolysis.