An AOP-informed testing strategy to identify chemicals causing
genotoxicity through oxidative DNA damage: case study on
4-nitroquinoline 1-oxide
Abstract
Adverse outcome pathways (AOPs) provide a framework to organize and
weigh evidence linking molecular interactions of toxicants in cells to
outcomes of regulatory concern. Applying this framework facilitates the
interpretation of data produced using new test methods. We used AOP
#296 which describes how oxidative DNA damage leads to mutations and
chromosomal aberrations to develop an integrated testing strategy to
evaluate whether a chemical operates through this pathway. We exposed
human TK6 cells to increasing concentrations of 4-nitroquinoline 1-oxide
(4NQO), a tobacco mimetic that causes oxidative DNA damage, in a
time-series design. We measured oxidative DNA damage and strand breaks
using the high-throughput CometChip assay with and without
formamidopyrimidine DNA glycosylase (Fpg), alongside analyses of
micronucleus (MN) frequency by flow cytometry, and mutations by
error-corrected next-generation sequencing (Duplex Sequencing). Our
analysis shows how these methods can be combined to quantify
4NQO-induced, concentration- and time-dependent increases in: (a)
oxidative DNA damage (occurred early and at lower concentrations than
single strand breaks); (b) strand breaks (remained elevated to 6 hours
post-exposures); (c) MN frequency (at 24 hours); (d) mutation frequency
(at 48 hours); and, (e) C>A transversions consistent with
expected substitutions induced by oxidative DNA lesions. The time-series
shows the repair of oxidative DNA damage with persistent strand breaks
remaining at 6 hours. Overall, we provide an example of an AOP-informed
testing strategy and contribute to quantitative understanding of AOP
#296. We also demonstrate the high value of Duplex Sequencing for
elucidating the mechanisms associated with exposure to oxidative stress
inducers.