Environ Sci Technol. 2020 Feb 4;54(3):1431-1442. doi: 10.1021/acs.est.9b07478. Epub 2020 Jan 13.
Excessive oxidative stress has been recognized as an important cause of the adverse health effects associated with exposure to ambient particulate matter (PM). Transition metals (TMs) (e.g., iron (Fe) and copper (Cu)) are known catalysts in the formation of reactive oxygen species (ROS) in surrogate lung fluid containing antioxidants. Humic-like substances (HULIS), extracted from atmospheric aerosols, retain the compositional complexity of real-world samples. It contains mixtures of organics that chelate TMs and was used in this work to examine the roles of atmospheric organics in affecting ROS formation and antioxidant depletion by TMs. Two types of metal-binding organics known to be present in HULIS, oxygen-containing (i.e., carboxylic acids) and reduced-nitrogen-containing organics (i.e., imidazoles), were first investigated for their effects on the ascorbic acid depletion (denoted as OP) and hydroxyl radical formation (denoted as OP) from both Fe(II) and Cu(II) in phosphate buffered saline (pH 7.40) containing ascorbic acid. Our results show that carboxylic acids enhance the OP and OP by TMs while imidazoles suppress them. Similar experiments using three HULIS samples with distinctly different chemical compositions revealed complexity in metal-organics interactions. While ambient HULIS showed negligible impacts, two biomass burning source HULIS samples from rice straw and sugar cane leaf burning displayed unambiguous suppression or enhancement effects on OP and OP by TMs. The effect was metal-specific and source HULIS-specific. The distinct behaviors of the three HULIS types can be explained by their different chemical compositions, for example, outstanding higher level of alkaloid compounds (e.g., imidazoles) in rice straw burning HULIS was consistent with the suppression effect exerted by this source of HULIS. In addition, we found OP and OP are well-correlated while the proportion of OP/OP by Cu is noticeably lower than that by Fe, indicating varying sensitivity of the metals to different OP end points. Our work highlights the importance and complexity of metal-organics interactions and the advantages of comeasurements of ROS generation and antioxidant depletion when assessing oxidative stress elicited by atmospheric PM.
过度的氧化应激已被认为是暴露于环境颗粒物（PM）相关不良健康影响的一个重要原因。过渡金属（TMs）（例如铁（Fe）和铜（Cu））是在含有抗氧化剂的替代肺液中形成活性氧物种（ROS）的已知催化剂。从大气气溶胶中提取的类腐殖质物质（HULIS）保留了实际样品的组成复杂性。它包含与 TMs 螯合的有机物混合物，并且在这项工作中被用来研究大气有机物在影响 TMs 引起的 ROS 形成和抗氧化剂消耗中的作用。首先研究了两种类型的已知存在于 HULIS 中的金属结合有机物，含氧（即羧酸）和含还原氮的有机物（即咪唑），以研究它们对 pH 为 7.40 的磷酸盐缓冲盐水（含抗坏血酸）中 Fe（II）和 Cu（II）的抗坏血酸消耗（表示为 OP）和羟基自由基形成（表示为 OP）的影响。我们的结果表明，羧酸增强了 TMs 的 OP 和 OP，而咪唑则抑制了它们。使用三种具有明显不同化学成分的 HULIS 样品进行的类似实验揭示了金属有机物相互作用的复杂性。虽然环境 HULIS 几乎没有影响，但来自稻草和甘蔗叶燃烧的两种生物质燃烧源 HULIS 样品对 TMs 的 OP 和 OP 表现出明确的抑制或增强作用。这种影响是金属特异性和源 HULIS 特异性的。三种 HULIS 类型的明显行为可以通过它们不同的化学成分来解释，例如，稻草燃烧 HULIS 中突出的高水平生物碱化合物（例如咪唑）与该来源 HULIS 施加的抑制作用一致。此外，我们发现 OP 和 OP 呈良好相关性，而 Cu 的 OP/OP 比例明显低于 Fe，这表明金属对不同 OP 终点的敏感性不同。我们的工作强调了金属有机物相互作用的重要性和复杂性，以及在评估大气 PM 引起的氧化应激时同时测量 ROS 生成和抗氧化剂消耗的优势。
