Nitroparaffin transcriptional profiles and toxicokinetics support chemical-specific carcinogenicity assessment

The toxicological profiles of nitroparaffins-nitromethane (NM), nitroethane (NE), and 1-nitropropane (1NP)-remain incompletely characterized. This has led to reliance on read-across approaches, extrapolating carcinogenicity data from NM to NE and 1NP, though the validity of such extrapolations is uncertain. In this study, we examined the concentration-dependent transcriptional effects of NM, NE, and 1NP in primary rat hepatocytes to clarify their cellular impact and mechanisms of toxicity. We assessed cytotoxicity, differential gene expression, and pathway enrichment, and applied in vitro to in vivo extrapolation (IVIVE) to estimate systemic bioavailability and clearance rates. Cytotoxicity was observed at 3 mM for NM and NE but not up to 10 mM for 1NP. Transcriptomic profiling revealed minimal overlap in dysregulated genes and enriched pathways among the three compounds. NE elicited the broadest transcriptional response, whereas NM and 1NP showed more limited effects. IVIVE further indicated distinct systemic bioavailability and clearance, suggesting toxicokinetic differences. Taken together, these results demonstrate that structural similarity alone does not predict comparable toxicological behavior. Each nitroparaffin exhibited unique molecular activity and toxicokinetics, indicating that read-across within this class requires demonstrated concordance in both bioactivity and toxicokinetic profiles, which are currently absent for NE, NM and 1NP. Thus, reliance on read-across from NM to NE or 1NP may misrepresent health risks and carries significant regulatory implications.