Department of Food Chemistry, Technology and Biotechnology, Gdansk University of Technology, Gdansk, Poland.
Department of Physical Chemistry, Gdansk University of Technology, Gdansk, Poland.
Redox Biol. 2018 Jul;17:355-366. doi: 10.1016/j.redox.2018.05.005. Epub 2018 May 14.
Redox homeostasis involves factors that ensure proper function of cells. The excess reactive oxygen species (ROS) leads to oxidative stress and increased risk of oxidative damage to cellular components. In contrast, upon reductive stress, insufficient ROS abundance may result in faulty cell signalling. It may be expected that dietary antioxidants, depending on their standard reduction potentials (E°), will affect both scenarios. In our study, for the first time, we systematically tested the relationship among E°, chemical properties, and biological effects in HT29 cells for a series of structurally different catechins and a major endogenous antioxidant - glutathione (GSH), at both physiological and dietary concentrations. Among chemical antioxidant activity tests, the strongest correlation with E° was seen using a DPPH assay. The values of E° were also highly correlated with cellular antioxidant activity (CAA) values determined in HT29 cells. Our results indicated that physiological concentrations (1-10 µM) of tested catechins stabilized the redox status of cells, which was not exhibited at higher concentrations. This stabilization of redox homeostasis was mirrored by constant, dose and E° independent CAA values, uninhibited growth of HT29 cells, modulation of hydrogen peroxide-induced DNA damage, as well as effects at the genomic level, where either up-regulation of three redox-related genes (ALB, CCL5, and HSPA1A) out of 84 in the array (1 µM) or no effect (10 µM) was observed for catechins. Higher catechin concentrations (over 10 µM) increased CAA values in a dose- and E°-dependent manner, caused cell growth inhibition, but surprisingly did not protect HT29 cells against reactive oxygen species (ROS)-induced DNA fragmentation. In conclusion, dose-dependent effects of dietary antioxidants and biological functions potentially modulated by them may become deregulated upon exposure to excessive doses.
氧化还原平衡涉及到确保细胞正常功能的因素。过量的活性氧（ROS）会导致氧化应激，增加细胞成分发生氧化损伤的风险。相反，在还原性应激下，ROS 含量不足可能导致细胞信号传递错误。可以预期，根据其标准还原电位（E°），膳食抗氧化剂将影响这两种情况。在我们的研究中，我们首次系统地测试了一系列结构不同的儿茶素和主要内源性抗氧化剂 - 谷胱甘肽（GSH）在 HT29 细胞中的 E°、化学性质和生物学效应之间的关系，在生理和膳食浓度下进行。在化学抗氧化活性测试中，与 E°相关性最强的是 DPPH 测定法。E°值也与在 HT29 细胞中测定的细胞抗氧化活性（CAA）值高度相关。我们的结果表明，测试儿茶素的生理浓度（1-10µM）稳定了细胞的氧化还原状态，而在更高浓度下则没有表现出这种作用。这种氧化还原平衡的稳定反映在恒定的、剂量和 E°独立的 CAA 值上，HT29 细胞不受抑制的生长，调节过氧化氢诱导的 DNA 损伤，以及基因组水平的影响，其中儿茶素观察到 84 个基因（ALB、CCL5 和 HSPA1A）中 3 个与氧化还原相关的基因（ALB、CCL5 和 HSPA1A）中的 1 个（1µM）上调或无影响（10µM）。更高的儿茶素浓度（超过 10µM）以剂量和 E°依赖的方式增加 CAA 值，导致细胞生长抑制，但令人惊讶的是，儿茶素不能保护 HT29 细胞免受活性氧（ROS）诱导的 DNA 片段化。总之，膳食抗氧化剂的剂量依赖性作用及其潜在调节的生物学功能可能会在暴露于过量剂量时失去调节。
