In vitro Toxicology and Biomedicine, Dept inaugurated by the Doerenkamp-Zbinden Foundation, University of Konstanz, Konstanz, Germany.
Konstanz Research School Chemical Biology (KoRS-CB), University of Konstanz, Konstanz, Germany.
ALTEX. 2019;36(1):154-160. doi: 10.14573/altex.1901031.
Some laboratory issues are taken for granted as they seem to be simple and not worth much thought. This applies to "concentrations of a chemical tested for bioactivity/toxicity". Can there be any issue about weighing a compound, diluting it in culture medium and calculating the final mass (or particle number)-to-volume ratio? We discuss here some basic concepts about concentrations and their units, addressing also differences between "dose" and "concentration". The problem of calculated nominal concentrations not necessarily corresponding to local concentrations (relevant for biological effects of a chemical) is highlighted. We present and exemplify different concentration measures, for instance those relying on weight, volume, or particle number of the test compound in a given volume; we also include normalizations to the mass, protein content, or cell number of the reference system. Interconversion is discussed as a major, often unresolved, issue. We put this into the context of the overall objective of defining concentrations, i.e., the determination of threshold values of bioactivity (e.g., an EC50). As standard approach for data display, the negative decadic logarithm of the molar concentrations (-log(M)) is recommended here, but arguments are also presented for exceptions from such a rule. These basic definitions are meant as a foundation for follow-up articles that examine the concepts of nominal, free, and intracellular concentrations to provide guidance on how to relate in vitro concentrations to in vivo doses by in vitro-to-in vivo extrapolation (IVIVE) in order to advance the use of new approach methods (NAM) in regulatory decision making.
一些实验室问题被认为是理所当然的，因为它们看起来很简单，不值得过多思考。这适用于“测试生物活性/毒性的化学物质的浓度”。称重化合物、在培养基中稀释它并计算最终质量（或粒子数）与体积比，会有什么问题吗？在这里，我们讨论了一些关于浓度及其单位的基本概念，还涉及了“剂量”和“浓度”之间的差异。计算的名义浓度不一定对应于局部浓度（与化学物质的生物效应有关）的问题被强调了。我们提出并举例说明了不同的浓度度量，例如依赖于给定体积中测试化合物的重量、体积或粒子数的度量；我们还包括了对参考系统的质量、蛋白质含量或细胞数的归一化。相互转换是一个主要的、经常未解决的问题，我们将其放入定义浓度的总体目标的背景中，即确定生物活性的阈值值（例如，EC50）。作为数据显示的标准方法，这里推荐使用摩尔浓度的负十进制对数（-log(M)），但也提出了例外情况的论据。这些基本定义是为后续文章提供的基础，这些文章将检查名义浓度、游离浓度和细胞内浓度的概念，以指导如何通过体外-体内外推法（IVIVE）将体外浓度与体内剂量联系起来，从而推进在监管决策中使用新方法。
