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The advantages of linear concentration-response curves for in vitro bioassays with environmental samples
Citation:
Escher, B., P. Neale, AND Dan Villeneuve. The advantages of linear concentration-response curves for in vitro bioassays with environmental samples. ENVIRONMENTAL TOXICOLOGY AND CHEMISTRY. Society of Environmental Toxicology and Chemistry, Pensacola, FL, 37(9):2273-2280, (2018). https://doi.org/10.1002/etc.4178
Impact/Purpose:
In vitro assays and high-throughput screening (HTS) tools are increasingly being employed as replacements for animal testing, but most concentration-response curves are still evaluated with models developed for animal testing. The current paper proposes a computationally simple method for deriving relative effect potency estimates for environmental samples analyzed using in vitro HTS systems. The proposed method is highly amenable to mixture modeling applications and also avoids a number of problems that are encountered when using other types of curve fitting approaches. The analysis methods offered here should be useful for a wide variety of ORD stakeholders interested in the use of in vitro HTS assays to characterize the pathway-based biological potency of environmental samples.
Description:
There is strong interest in using cell-based assays run in high density (e.g., 96, 384, or even 1536 well) format to screen complex mixtures of contaminants present in environmental samples for biological activities. Statistical approaches are used to estimate and compare the potency of these samples in order to inform environmental decision-making. The current paper proposes a simple, straight-forward, transparent and easily transferrable approach for calculating these potency estimates that take advantage of the large number of dose levels, reduced variability, and precision that are facilitated by robotic pipetting of samples and the use of in cell-based assays as alternatives to whole animal testing. In vitro assays and high-throughput screening (HTS) tools are increasingly being employed as replacements for animal testing, but most concentration-response curves are still evaluated with models developed for animal testing. We argue that application of in vitro assays, particularly reporter gene assays, to environmental samples can benefit from new approaches for concentration-response modelling. First, cytotoxicity often occurs at higher concentrations, especially for weakly acting compounds and in complex environmental mixtures with many components. In these cases, specific effects can be masked by cytotoxicity. Second, for many HTS assays, low effect levels can be precisely quantified due to the low variability of controls in cell-based assays and the opportunity to run many concentrations and replicates when using high density well-plate formats (e.g., 384 or more wells per plate). Hence we recommend focusing concentration-response modelling on the lower portion of the concentration-response curve, which is linear for standard log-normal distributions of effect data. Effect concentrations derived from linear concentration-response models facilitate simple derivation of relative effect potencies and the correct application of mixture toxicity models in the calculation of bioanalytical equivalent concentrations.
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DOI: The advantages of linear concentration-response curves for in vitro bioassays with environmental samples