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心脏毒性的严重限制。我们以成年大鼠心肌细胞为工作模型的初步结果表明，这一机制可以解释阿霉素产生的活性氧物种如何在不造成严重氧化损伤的情况下引发肌纤维变性。具体地说，1)我们观察到阿霉素在心肌线粒体中的直接积聚和随后活的心肌细胞内氧化的增加，2)观察到阿霉素的应用与蛋白激酶C epsilon亚型从胞浆重新分布到肌原纤维有关，以及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的周期性中断。基于这些数据，我们提出了以下事件序列：阿霉素在心肌线粒体中迅速积累；然后它通过形成超氧化物和与过渡金属的药物络合物启动脂质过氧化；尽管脂质过氧化程度很小，没有发生明显的膜损伤，但它导致磷脂酶的激活；脂肪酶随后释放包括花生四烯酸在内的几个第二信使，激活特定的蛋白激酶C亚型；然后，该激酶启动肌纤维变性。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转位与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转位是否是改变心肌细胞肌纤维组织和细胞收缩能力的先决条件；3)揭示磷脂酶A2在阿霉素诱导的激酶激活和随之而来的肌纤维组织和收缩能力变化中的作用。拟议的实验旨在揭示活性氧物种参与蒽环类药物诱导的心肌病的明确途径。这些研究还将提供有关激酶参与肌丝退化以及活性氧物种与信号转导途径之间相互作用的新信息。

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.