Reproducibility of organ-level effects in repeat dose animal studies

Abstract

This work estimates benchmarks for new approach method (NAM)performance in predictingorgan-level effects in repeat dose studies of adult animals based on variability in replicate animal studies. Treatment-related effect values from theToxicityReference database (v2.1)for weight, gross, or histopathological changes in the adrenal gland, liver, kidney, spleen, stomach, and thyroid were used. Rates of chemical concordance among organ-level findings in replicate studies, definedbyrepeated chemical only, chemical and species, or chemical and study type, were calculated. Concordancewas 39–88%, depending on organ, and was highest within species.Variance in treatment-related effect values, including lowest effect level (LEL) values and benchmark dose (BMD) valueswhen available, was calculated by organ. Multilinear regression modeling,usingstudy descriptorsof organ-level effect values as covariates, was used to estimate total variance, mean square error(MSE), and root residual mean square error (RMSE). MSE values, interpreted as estimates of unexplained variance, suggeststudydescriptorsaccountedfor52–69% of totalvariance inorgan-levelLELs.RMSE ranged from0.41 to 0.68 log10-mg/kg/day. Differences between organ-level effects from chronic (CHR) and subchronic (SUB) dosing regimens were also quantified. Odds ratios indicated CHR organ effects were unlikely if the SUB study was negative. Mean differences of CHR - SUB organ-level LELs ranged from − 0.38 to − 0.19 log10mg/kg/day; the magnitudes of these mean differences were less than RMSE for replicate studies. Finally, in vitro to in vivo extrapolation (IVIVE) was employed to compare bioactive concentrations from in vitro NAMs for kidney and liver to LELs. The observed mean difference between LELs and mean IVIVE dose predictions approached 0.5 log10-mg/kg/day, but differences by chemical ranged widely. Overall, variability in repeat dose organ-level effects suggests expectations for quantitative accuracy of NAM prediction of LELs should be at least ± 1 log10-mg/kg/day, with qualitative accuracy not exceeding 70%.