Shin Dong Yeok, Kim Gi Young, Li Wei, Choi Byung Tae, Kim Nam Deuk, Kang Ho Sung, Choi Yung Hyun
Department of Biochemistry, Dongeui University College of Oriental Medicine, Busan 614-052, South Korea.
Biomed Pharmacother. 2009 Feb;63(2):86-94. doi: 10.1016/j.biopha.2008.08.001. Epub 2008 Aug 30.
Platycodon D is a major constituent of triterpene saponins found in the root of Platycodon grandiflorum, Platycodi Radix, which is widely used in traditional Oriental medicine for the treatment of many chronic inflammatory diseases. The results of previous studies have shown that this compound has in vitro growth-inhibitory activity in human cancer cells, however, the mechanism by which this action occurs is poorly understood. In this study, we examined the effects of platycodon D on the production of reactive oxygen species (ROS) and evaluated the association of these effects with apoptotic tumor cell death using a human leukemic U937 cell line. The results of this study demonstrate that platycodon D mediates ROS production, and that this mediation is followed by a decrease in mitochondrial membrane potential (MMP, DJm), activation of caspase-3, and cleavage of poly (ADP-ribose) polymerase (PARP). Both the cytotoxic effects and apoptotic characteristics induced by platycodon D treatment were significantly inhibited by z-DEVD-fmk, a caspase-3 inhibitor, which demonstrates the important role that caspase-3 plays in the observed cytotoxic effect. Additionally, the transcription factor early growth response-1 (Egr-1) gene was transcriptionally activated and the levels of non-steroidal anti-inflammatory drug (NSAID)-activated gene-1 (NAG-1) protein were elevated in platycodon D-treatedU937 cells. However, the quenching of ROS generation in response to treatment with a ROS scavenger, N-acetyl-L-cysteine, reversed the platycodon D-induced apoptosis effects via inhibition of Egr-1 activation, ROS production, MMP collapse, and the subsequent activation of caspase-3. Although further studies are needed to demonstrate that increased expression of Egr-1 by platycodon D leads directly to NAG-1 induction and subsequent apoptosis, our observations clearly indicate that ROS induced through Egr-1 activation are involved in the early molecular events involved in the platycodon D-induced apoptotic pathway.
桔梗皂苷D是桔梗（桔梗科植物桔梗的根）中发现的三萜皂苷的主要成分，桔梗在传统东方医学中广泛用于治疗多种慢性炎症性疾病。先前研究结果表明，该化合物在体外对人癌细胞具有生长抑制活性，然而，这种作用发生的机制尚不清楚。在本研究中，我们使用人白血病U937细胞系研究了桔梗皂苷D对活性氧（ROS）产生的影响，并评估了这些影响与凋亡性肿瘤细胞死亡的关联。本研究结果表明，桔梗皂苷D介导ROS产生，随后线粒体膜电位（MMP，ΔΨm）降低、半胱天冬酶-3激活以及聚（ADP-核糖）聚合酶（PARP）裂解。桔梗皂苷D处理诱导的细胞毒性作用和凋亡特征均被半胱天冬酶-3抑制剂z-DEVD-fmk显著抑制，这表明半胱天冬酶-3在观察到的细胞毒性作用中起重要作用。此外，在桔梗皂苷D处理的U937细胞中，转录因子早期生长反应-1（Egr-1）基因被转录激活，非甾体抗炎药（NSAID）激活基因-1（NAG-1）蛋白水平升高。然而，用ROS清除剂N-乙酰-L-半胱氨酸处理后ROS生成的淬灭通过抑制Egr-1激活、ROS产生、MMP崩溃以及随后的半胱天冬酶-3激活，逆转了桔梗皂苷D诱导的凋亡作用。尽管需要进一步研究来证明桔梗皂苷D引起的Egr-1表达增加直接导致NAG-1诱导和随后的凋亡，但我们的观察结果清楚地表明，通过Egr-1激活诱导的ROS参与了桔梗皂苷D诱导的凋亡途径中的早期分子事件。
