Differential Action between Schisandrin A and Schisandrin B in Eliciting an Anti-Inflammatory Action: The Depletion of Reduced Glutathione and the Induction of an Antioxidant Response

Schisandrin A (Sch A) and schisandrin B (Sch B) are active components of Schisandrae Fructus. We compared the biochemical mechanism underlying the anti-inflammatory action of Sch A and Sch B, using cultured lipopolysaccharide (LPS)-stimulated RAW264.7 macrophages and concanavalin (ConA)-stimulated mouse splenocytes. Pre-incubation with Sch A or Sch B produced an anti-inflammatory action in LPS-stimulated RAW264.7 cells, as evidenced by the inhibition of the pro-inflammatory c-Jun N-terminal kinases/p38 kinase/nuclear factor-κB signaling pathway as well as the suppression of various pro-inflammatory cytokines and effectors, with the extent of inhibition by Sch A being more pronounced. The greater activity of Sch A in anti-inflammatory response was associated with a greater decrease in cellular reduced glutathione (GSH) level and a greater increase in glutathione S-transferase activity than corresponding changes produced by Sch B. However, upon incubation, only Sch B resulted in the activation of the nuclear factor (erythroid-derived 2)-like factor 2 and the induction of a significant increase in the expression of thioredoxin (TRX) in RAW264.7 cells. The Sch B-induced increase in TRX expression was associated with the suppression of pro-inflammatory cytokines and effectors in LPS-stimulated macrophages. Studies in a mouse model of inflammation (carrageenan-induced paw edema) indicated that while long-term treatment with either Sch A or Sch B suppressed the extent of paw edema, only acute treatment with Sch A produced a significant degree of inhibition on the inflammatory response. Although only Sch A decreased the cellular GSH level and suppressed the release of pro-inflammatory cytokines and cell proliferation in ConA-simulated splenocytes in vitro, both Sch A and Sch B treatments, while not altering cellular GSH levels, suppressed ConA-stimulated splenocyte proliferation ex vivo. These results suggest that Sch A and Sch B may act differentially on activating GST/ depleting cellular GSH and inducing an antioxidant response involved in their anti-inflammatory actions.五味子素A（Schisandrin A，简称Sch A）与五味子素B（Schisandrin B，简称Sch B）是五味子（Schisandrae Fructus）的活性成分。本研究以体外培养的脂多糖（lipopolysaccharide，缩写LPS）刺激的RAW264.7巨噬细胞及刀豆球蛋白A（concanavalin A，缩写ConA）刺激的小鼠脾淋巴细胞为模型，对比分析二者发挥抗炎作用的生化机制。预先经Sch A或Sch B孵育可在LPS刺激的RAW264.7细胞中产生抗炎效应，具体表现为抑制促炎信号通路c-Jun氨基末端激酶/p38激酶/核因子-κB（nuclear factor-κB，缩写NF-κB）的活化，同时抑制多种促炎细胞因子与效应分子的表达；其中Sch A的抑制效果更为显著。相较于Sch B，Sch A更强的抗炎活性与细胞还原型谷胱甘肽（reduced glutathione，缩写GSH）水平的更大幅度下降以及谷胱甘肽S-转移酶（glutathione S-transferase，缩写GST）活性的更高水平提升密切相关。然而，在孵育过程中，仅Sch B可激活核因子红细胞2相关因子2（nuclear factor erythroid 2-related factor 2，缩写Nrf2），并诱导RAW264.7细胞中硫氧还蛋白（thioredoxin，缩写TRX）的表达显著上调。Sch B诱导的TRX表达上调，与LPS刺激的巨噬细胞中促炎细胞因子及效应分子的抑制作用相关。小鼠炎症模型（角叉菜胶诱导的足肿胀模型）研究显示，尽管长期给予Sch A或Sch B均可抑制足肿胀程度，但仅急性给予Sch A可对炎症反应产生显著的抑制效果。尽管仅Sch A可在体外ConA刺激的脾淋巴细胞中降低细胞GSH水平、抑制促炎细胞因子的释放与细胞增殖，但经Sch A或Sch B处理后，尽管未改变细胞GSH水平，均可在离体条件下抑制ConA刺激的脾淋巴细胞增殖。上述结果表明，Sch A与Sch B可能通过差异化调控GST活化、细胞GSH耗竭以及诱导抗氧化应答，从而发挥其抗炎作用。