ANTHRACYCLINE CARDIOTOXICITY--OXIDATIVE STRESS

阿霉素及其衍生物是已知的最有效的抗癌药物之一。不幸的是，它们的治疗效果受到剂量累积的心脏毒性的严重限制。我们使用成年大鼠心肌细胞作为工作模型的初步结果显示了机制的证据，该机制可以解释多柔比星产生的活性氧如何引起肌原纤维变性，同时不引起严重的氧化损伤。 具体而言，1）我们直接观察到阿霉素在心肌线粒体中的积累和随后在活心肌细胞中细胞内氧化的增加，2）观察到阿霉素给药与蛋白激酶C β亚型从胞质溶胶到肌原纤维的再分布有关，3）检测到肌细胞重复暴露于临床相关药物浓度后肌动蛋白染色周期性的破坏。 基于这些数据，我们提出了以下事件顺序：阿霉素在心肌线粒体中迅速积累，然后通过形成超氧化物和过渡金属的药物络合物引发脂质过氧化，尽管脂质过氧化程度很小，没有明显的膜损伤发生，但它导致磷脂酶的激活;脂肪酶于是释放几个第二信使，包括花生四烯酸，激活特定的蛋白激酶C同种型;激酶然后启动肌原纤维变性。为了支持上述假设，我们的目标是：1）建立观察到的阿霉素诱导的激酶易位和增加的自由基形成之间的因果关系; 2）确定阿霉素诱导的自由基和/或蛋白激酶C易位是否是肌细胞肌原纤维组织和细胞收缩性变化的先决条件; 3）揭示磷脂酶A2在阿霉素诱导的激酶活化及随后的肌原纤维组织和收缩性变化中的作用。所提出的实验旨在揭示活性氧参与蒽环类药物诱导的心肌病的明确途径。 这些研究还将为肌丝变性中激酶的参与以及活性氧与信号转导通路之间的相互作用提供新的信息。

Doxorubicin and its derivatives are among the most potent anticancer drugs known. Unfortunately their therapeutic efficacy is severely restricted by a dose-accumulated cardiotoxicity. Our preliminary results using adult rat cardiomyocytes as a working model, have shown evidence for the mechanism which could explain how reactive oxygen species generated by doxorubicin provoke myofibrillar degeneration while not causing severe oxidative damage. Specifically, 1) we visualized directly doxorubicin accumulation in cardiac mitochondria and subsequent increase in intracellular oxidation in living cardiomyocytes, 2) observed that doxorubicin administration is associated with redistribution of the protein kinase C epsilon isoform from cytosol to myofibrils, and 3) detected disruption of the periodicity of actin staining after repetitive exposure of myocytes to clinically relevant drug concentrations. Based on these data we propose the following sequence of events: doxorubicin rapidly accumulates in cardiac mitochondria; it then initiates lipid peroxidation via formation of superoxide and drug complexes with transition metals; and although the degree of lipid peroxidation is small and no significant membrane damage occurs, it leads to the activation of phospholipases; lipase thereupon release several second messengers, including arachidonic acid, activating a specific protein kinase C isoform; the kinase then initiates myofibrillar degeneration. To support the above hypothesis we aim to 1) establish a causal relationship between observed doxorubicin-induced kinase translocation and increased free radical formation; 2) to determine whether doxorubicin-induced free radicals and/or protein kinase C translocation are prerequisites for changes in myocyte myofibrillar organization and cell contractility; 3) to uncover role of phospholipase A2 in doxorubicin-induced activation of kinase and ensuing changes in myofibrillar organization and contractility. The proposed experiments aim to reveal explicit pathways through which reactive oxygen species are involved in anthracycline- induced cardiomyopathy. The studies will also provide new information about kinases involvement in myofilament degeneration and interaction between reactive oxygen species and signal transduction pathways.