Louvain Drug Research Institute (LDRI), Cellular & Molecular Pharmacology Unit (FACM), Université catholique de Louvain (UCL), Brussels 1200, Belgium; de Duve Institute (DDUV), Cell Biology Unit (CELL), Université catholique de Louvain (UCL), Brussels 1200, Belgium.
Louvain Drug Research Institute (LDRI), Cellular & Molecular Pharmacology Unit (FACM), Université catholique de Louvain (UCL), Brussels 1200, Belgium.
Toxicol Appl Pharmacol. 2018 Aug 1;352:59-67. doi: 10.1016/j.taap.2018.05.014. Epub 2018 May 18.
Saponins exhibit several biological and pharmacological activities, such as antibacterial, anti-inflammatory and anticancer effects. Many studies attribute their activities to their interactions with cholesterol. In this study, we focus on the steroid saponin ginsenoside Rh2, one of the active principles of Panax ginseng root. Some evidence suggests that lipid rafts, defined as nanodomains enriched in cholesterol and sphingolipids, could be involved in the Rh2-induced apoptosis. However, the role of membrane lipids, especially cholesterol, in this process is still poorly understood. Here, we demonstrate that (i) A549, THP-1 and U937 cells are all susceptible to the Rh2-induced apoptosis but to a differential extent and (ii) the cytotoxic effect inversely correlates with the cell membrane cholesterol content. Upon cholesterol depletion via methyl-β-cyclodextrin, those three cells lines become more sensitive to Rh2-induced apoptosis. Then, focusing on the cholesterol-auxotroph U937 cell line, we showed that Rh2 alters plasma membrane fluidity by compacting the hydrophobic core of lipid bilayer (DPH anisotropy) and relaxing the interfacial packaging of the polar head of phospholipids (TMA-DPH anisotropy). The treatment with Rh2 conducts to the dephosphorylation of Akt and the activation of the intrinsic pathway of apoptosis (loss of mitochondrial membrane potential, caspase-9 and -3 activation). All these features are induced faster in cholesterol-depleted cells, which could be explained by faster cell accumulation of Rh2 in these conditions. This work is the first reporting that membrane cholesterol could delay the activity of ginsenoside Rh2, renewing the idea that saponin cytotoxicity is ascribed to an interaction with membrane cholesterol.
皂苷具有多种生物和药理活性，如抗菌、抗炎和抗癌作用。许多研究将其活性归因于它们与胆固醇的相互作用。在这项研究中，我们专注于甾体皂苷人参皂苷 Rh2，它是人参根的有效成分之一。有证据表明，富含胆固醇和鞘脂的脂质筏（定义为纳米域）可能参与 Rh2 诱导的细胞凋亡。然而，该过程中膜脂，特别是胆固醇的作用仍知之甚少。在这里，我们证明（i）A549、THP-1 和 U937 细胞均易受 Rh2 诱导的细胞凋亡影响，但程度不同，（ii）细胞毒性作用与细胞膜胆固醇含量呈负相关。通过甲基-β-环糊精耗竭胆固醇后，这三种细胞系对 Rh2 诱导的细胞凋亡更为敏感。然后，我们专注于胆固醇营养缺陷型 U937 细胞系，表明 Rh2 通过压缩脂质双层的疏水性核心（DPH 各向异性）和放松磷脂极性头部的界面包装（TMA-DPH 各向异性）来改变质膜流动性。Rh2 的处理导致 Akt 的去磷酸化和细胞凋亡的内在途径的激活（线粒体膜电位丧失，caspase-9 和 -3 的激活）。所有这些特征在胆固醇耗尽的细胞中更快地诱导，这可以解释为在这些条件下 Rh2 在细胞中的更快积累。这项工作首次报道了膜胆固醇可能会延迟人参皂苷 Rh2 的活性，这再次表明皂苷的细胞毒性归因于与膜胆固醇的相互作用。
