Benchmark Dose Modeling of In Vitro Genotoxicity Data: a Reanalysis

Abstract

The methods of applied genetic toxicology are changing from qualitative hazard identification to quantitative risk assessment. Recently, quantitative analysis with point of departure (PoD) metrics and benchmark dose (BMD) modeling have been applied to in vitro genotoxicity data. Two software packages are commonly used for BMD analysis. In previous studies, we performed quantitative dose-response analysis by using the PROAST software to quantitatively evaluate the mutagenicity of four piperidine nitroxides with various substituent groups on the 4-position of the piperidine ring and six cigarette whole smoke solutions (WSSs) prepared by bubbling machine-generated whole smoke. In the present study, we reanalyzed the obtained genotoxicity data by using the EPA's BMD software (BMDS) to evaluate the inter-platform quantitative agreement of the estimates of genotoxic potency. We calculated the BMDs for 10%, 50%, and 100% (i.e., a two-fold increase), and 200% increases over the concurrent vehicle controls to achieve better discrimination of the dose-responses, along with their BMDLs (the lower 95% confidence interval of the BMD) and BMDUs (the upper 95% confidence interval of the BMD). The BMD values and rankings estimated in this study by using the EPA's BMDS were reasonably similar to those calculated in our previous studies by using PROAST. These results indicated that both software packages were suitable for dose-response analysis using the mouse lymphoma assay and that the BMD modeling results from these software packages produced comparable rank orders of the mutagenic potency.

Keywords: Benchmark dose; In vitro genotoxicity; Mouse lymphoma assay; Quantitative analysis.

Fig. 1

Quantitative analysis of the mutagenic dose-responses induced by four piperidine nitroxides (A) and six WSSs (B). The original dose-response data were published previously (22,23), and the BMD₁₀, BMDL₁₀, and BMDU₁₀ were calculated by using the EPA’s BMD software. The indication of exponential or power shows the model used for the calculation. The bars represent the calculated 95% confidence interval of each MF.

Fig. 2

A comparison of BMD values for WSSs in the mouse lymphoma assay. The BMDs (BMD₁₀, BMD₅₀, BMD₁₀₀, and BMD₂₀₀) estimates producing a 10%, 50%, 100%, or 200% increase over the background frequency were calculated using the selected models in the BMDS (A, B, C, and D). The bars represent the calculated 95% confidence interval (CI) for each value. The lower and upper limits derived from the BMD estimates were used to differentiate between the responses based on non-overlapping confidence intervals.