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性心脏毒性的严重限制。我们的初步结果使用成年大鼠心肌细胞作为工作模型，已经为机制提供了证据，可以解释阿霉素产生的活性氧如何引起肌纤维变性而不引起严重的氧化损伤。具体来说，1)我们直接观察了阿霉素在心脏线粒体中的积累以及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 epsilon异构体从细胞质到肌原纤维的重新分布有关，3)检测到肌动蛋白染色的周期性在肌细胞反复暴露于临床相关药物浓度后被破坏。基于这些数据，我们提出以下事件顺序：阿霉素在心脏线粒体中迅速积累；然后通过形成超氧化物和与过渡金属的药物配合物引发脂质过氧化；脂质过氧化程度虽小，未发生明显的膜损伤，但可导致磷脂酶活化；脂肪酶随后释放几个第二信使，包括花生四烯酸，激活特定的蛋白激酶C异构体；激酶随后引发肌原纤维变性。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与自由基形成增加之间的因果关系；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改变的先决条件；3)揭示磷脂酶A2在阿霉素诱导的激酶活化和随后的肌纤维组织和收缩性变化中的作用。本实验旨在揭示活性氧参与蒽环类药物引起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变性和活性氧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.