The association between the regulation of L-lactic acid content in skeletal muscle cell involved in MCT and the mechanism of the drug-induced rhabdmyolysis

首先，我们以大鼠和人类骨骼肌为模型，研究了MCT异构体是否有助于L6和RD细胞中l -乳酸的运输。我们得出结论，在L6和RD细胞中，单羧酸转运蛋白（MCT） 1负责l -乳酸摄取，而l -乳酸外排是由MCT4介导的。另一方面，包括HMG-CoA还原酶抑制剂、他汀类药物在内的单羧酸类药物对mct介导的l -乳酸转运系统的影响尚未阐明。因此，我们研究了他汀类药物对MCT介导的l -乳酸转运的影响与他汀类药物诱导的细胞内酸化之间的关系。亲脂性他汀、西伐他汀、辛伐他汀酸、氟伐他汀、阿托伐他汀、洛伐他汀酸、匹伐他汀以浓度依赖的方式减少活细胞数量，引起剧烈的形态变化和DNA断裂。此外，亲脂性他汀类药物诱导的细胞凋亡与细胞内酸化和caspase-9和-3/7活化有关。为了阐明他汀类药物诱导细胞内酸化的机制，我们研究了他汀类药物对L6和RD细胞MCT4介导的l -乳酸外排的影响。亲脂性他汀类药物抑制L6和RD细胞MCT4介导的l -乳酸外排。另一方面，亲水性他汀类药物、瑞舒伐他汀和普伐他汀对l -乳酸外排无影响。此外，我们建立了转染MCT4的细胞系，以阐明l -乳酸的转运机制以及他汀类药物对该转运系统的影响。亲脂性他汀类药物显著抑制转染MCT4细胞中MCT4介导的l -乳酸转运。相反，亲水他汀类药物对这一转运系统几乎没有影响。接下来，我们试图确定抑制他汀类药物引起的肌病的化合物。碳酸氢盐在临床上用于治疗乳酸酸中毒，并参与细胞pH调节（碱化）。由于西伐他汀诱导的细胞凋亡与细胞内酸化有关，因此我们研究了碳酸氢盐诱导的他汀诱导的细胞凋亡的改善。碳酸氢盐抑制cerivastatin诱导的pH改变、caspase激活、形态学改变以及RD和L6细胞活力降低。此外，在体内研究中，碳酸氢盐阻止了cervastatin引起的CPK水平升高。这些体外和体内研究的结果支持补充碳酸氢盐可以防止他汀类药物引起的肌肉损伤。少

Firstly, we investigated whether MCT isoform contribute to the transport of L-lactic acid in L6 and RD cells as a model of rat and human skeletal muscle. We concluded that monocarboxylate transporter (MCT) 1 is responsible for L-lactic acid uptake and L-lactic acid efflux is mediated by MCT4 in L6 and RD cells. On the other hand, the effects of monocarboxylate dugs including HMG-CoA reductase inhibitors, statins, on MCT-mediated L-lactic acid transport system have not been elucidated. Therefore, we examined that the association between the effect of statins on L-lactic acid transport mediated by MCT and statins-induced intracellular acidification. Lipophilic satins, cerivastatin, simvastatin acid, fluvastatin, atorvastatin, lovastatin acid, pitavastatin reduced the number of viable cells and caused dramatic morphological changes and DNA fragmentation in a concentration- dependent manner. Moreover, lipophilic statins-induced apoptosis was associated with intracellular acidification and … More caspase-9 and -3/7 activation.To clarify the mechanism of statins-induced intracellular acidification, we examined the effect of statins on the efflux of L-lactic acid mediated by MCT4 from L6 and RD cells. Lipophilic statins inhibited the L-lactic acid efflux mediated by MCT4 from L6 and RD cells. On the other hand, hydrophilic statins, rosuvastatin and pravastatin had no effect on the efflux of L-lactic acid. Moreover, we established an MCT4 transfected cell line and to clarify the transport mechanism of L-lactic acid and the effects of statins on this transport system. Lipophilic statins significantly inhibited MCT4-mediated L-lactic acid transport in MCT4 transfected cells. On the contrary, hydrophilic statins had little effect on this transport system.Next, we tried to identify the compound suppressing statins-induced myopathy. Bicarbonate is clinically used for treatment of lactic acidosis and is involved in cellular pH regulation (alkalization). Since cerivastatin-induced apoptosis was associated with intracellular acidification, we therefore examined bicarbonate-induced improvement of statin-induced apoptosis. Bicarbonate suppressed cerivastatin-induced pH alteration, caspase activation, morphological change and reduction of RD and L6 cell viability. Moreover, bicarbonate prevented CPK levels increased by cerivastatin in vivo study. These results from in vitro and in vivo studies support that bicarbonate supplementation prevented statin-induced muscle damage. Less