High-throughput cell-based bioassays are used for chemical screening and risk assessment. Chemical transformation processes caused by abiotic degradation or metabolization can reduce the chemical concentration or, in some cases, lead to the formation of more toxic transformation products. Unaccounted loss processes may falsify the bioassay results. Capturing the formation and effects of transformation products is important for relating the in vitro effects to in vivo. Reporter gene cell lines are believed to have low metabolic activity, but inducibility of cytochrome P450 (CYP) enzymes has been reported. Baseline toxicity is the minimal toxicity a chemical can have and is caused by the incorporation of the chemical into cell membranes. In the present study, we improved an existing baseline toxicity model based on a newly defined critical membrane burden derived from freely dissolved effect concentrations, which are directly related to the membrane concentration. Experimental effect concentrations of 94 chemicals in three bioassays (AREc32, ARE-bla and GR-bla) were compared with baseline toxicity by calculating the toxic ratio (TR). CYP activities of all cell lines were determined by using fluorescence-based assays. Only ARE-bla showed a low basal CYP activity and inducibility and AREc32 showed a low inducibility. Overall cytotoxicity was similar in all three assays despite the different metabolic activities indicating that chemical metabolism is not relevant for the cytotoxicity of the tested chemicals in these assays. Up to 28 chemicals showed specific cytotoxicity with TR > 10 in the bioassays, but baseline toxicity could explain the effects of the majority of the remaining chemicals. Seven chemicals showed TR < 0.1 indicating inaccurate physicochemical properties or experimental artifacts like chemical precipitation, volatilization, degradation, or other loss processes during the in vitro bioassay. The new baseline model can be used not only to identify specific cytotoxicity mechanisms but also to identify potential problems in the experimental performance or evaluation of the bioassay and thus improve the quality of the bioassay data.

中文翻译：

---

与基线毒性相比，具有不同代谢活性的化学物质对报告基因生物测定的影响


高通量细胞生物测定用于化学筛选和风险评估。由非生物降解或代谢引起的化学转化过程可以降低化学浓度，或者在某些情况下导致形成毒性更大的转化产物。未说明的损失过程可能会伪造生物测定结果。捕获转化产物的形成和效果对于将体外效果与体内效果联系起来非常重要。报告基因细胞系被认为具有低代谢活性，但已报道细胞色素 P450 (CYP) 酶的诱导能力。基线毒性是化学品可能具有的最小毒性，是由化学品掺入细胞膜引起的。在本研究中，我们基于新定义的临界膜负荷改进了现有的基线毒性模型，该临界膜负荷源自自由溶解的效应浓度，与膜浓度直接相关。通过计算毒性比 (TR)，将 94 种化学物质在三种生物测定（AREc32、ARE-bla 和 GR-bla）中的实验效应浓度与基线毒性进行比较。所有细胞系的 CYP 活性均通过基于荧光的测定法测定。仅 ARE-bla 显示出较低的基础 CYP 活性和诱导能力，AREc32 显示出较低的诱导能力。尽管代谢活动不同，这表明化学代谢与这些测定中测试的化学物质的细胞毒性无关，但所有三种测定中的总体细胞毒性相似。在生物测定中，多达 28 种化学物质显示出 TR > 10 的特定细胞毒性，但基线毒性可以解释大多数其余化学物质的影响。七种化学品的 TR < 0。1 表明理化性质不准确或实验假象，如体外生物测定过程中的化学沉淀、挥发、降解或其他损失过程。新的基线模型不仅可用于识别特定的细胞毒性机制，还可用于识别实验性能或生物测定评估中的潜在问题，从而提高生物测定数据的质量。