Caffeic acid improves cell viability and protects against DNA damage: involvement of reactive oxygen species and extracellular signal-regulated kinase

Hormesis is an adaptive response to a variety of oxidative stresses that renders cells resistant to harmful doses of stressing agents. Caffeic acid (CaA) is an important antioxidant that has protective effects against DNA damage caused by reactive oxygen species (ROS). However, whether CaA-induced protection is a hormetic effect remains unknown, as is the molecular mechanism that is involved. We found that a low concentration (10 μM) of CaA increased human liver L-02 cell viability, attenuated hydrogen peroxide (H2O2)-mediated decreases in cell viability, and decreased the extent of H2O2-induced DNA double-strand breaks (DSBs). In L-02 cells exposed to H2O2, CaA treatment reduced ROS levels, which might have played a protective role. CaA also activated the extracellular signal-regulated kinase (ERK) signal pathway in a time-dependent manner. Inhibition of ERK by its inhibitor U0126 or by its specific small interfering RNA (siRNA) blocked the CaA-induced improvement in cell viability and the protective effects against H2O2-mediated DNA damage. This study adds to the understanding of the antioxidant effects of CaA by identifying a novel molecular mechanism of enhanced cell viability and protection against DNA damage.

毒物兴奋效应（hormesis）是一类针对多种氧化应激的适应性应答，可使细胞对有害剂量的应激原产生抗性。咖啡酸（Caffeic acid, CaA）是一类重要的抗氧化剂，可对活性氧（reactive oxygen species, ROS）诱导的DNA损伤发挥保护作用。然而，咖啡酸诱导的保护作用是否属于毒物兴奋效应，其背后的分子机制尚不清楚。本研究发现，低浓度（10 μM）的咖啡酸可提升人肝脏L-02细胞的存活率，减轻过氧化氢（hydrogen peroxide, H₂O₂）介导的细胞存活率下降，并降低过氧化氢诱导的DNA双链断裂（DNA double-strand breaks, DSBs）程度。在暴露于过氧化氢的L-02细胞中，咖啡酸处理可降低活性氧水平，这可能是其发挥保护作用的关键途径之一。咖啡酸还可通过时间依赖性方式激活细胞外调节蛋白激酶（extracellular signal-regulated kinase, ERK）信号通路。通过ERK抑制剂U0126或其特异性小干扰RNA（small interfering RNA, siRNA）抑制ERK活性，可阻断咖啡酸诱导的细胞存活率提升以及其对抗过氧化氢介导的DNA损伤的保护作用。本研究通过阐明一条提升细胞存活率、抵御DNA损伤的新型分子机制，加深了人们对咖啡酸抗氧化作用的认知。