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.硝基烷烃（nitroparaffins）——硝基甲烷（nitromethane, NM）、硝基乙烷（nitroethane, NE）与1-硝基丙烷（1-nitropropane, 1NP）的毒理学特征仍未被完全阐明。这导致学界不得不依赖交叉外推法，将NM的致癌性数据外推至NE与1NP，尽管此类外推的有效性尚不明确。本研究以原代大鼠肝细胞为模型，探究了NM、NE与1NP的浓度依赖性转录调控效应，以明确其细胞影响与毒性作用机制。我们评估了细胞毒性、差异基因表达及通路富集情况，并应用体外-体内外推法（in vitro to in vivo extrapolation, IVIVE）估算系统生物利用度与清除速率。研究观察到，NM与NE在3 mM浓度下即产生细胞毒性，而1NP在最高10 mM浓度下均未表现出细胞毒性。转录组分析显示，三种化合物的差异表达基因与富集通路的重叠度极低。其中，NE引发的转录应答范围最广，而NM与1NP的调控效应更为有限。体外-体内外推法进一步表明三种化合物的系统生物利用度与清除速率存在显著差异，提示其毒代动力学特征各不相同。综上，本研究结果证实，仅依靠结构相似性无法预测化合物具有可比的毒理学行为。每种硝基烷烃均表现出独特的分子活性与毒代动力学特征，这意味着该类化合物的交叉外推需同时验证其生物活性与毒代动力学特征的一致性，而目前NM、NE与1NP之间尚不具备此类一致性。因此，依赖将NM的毒理学数据外推至NE或1NP的做法可能会歪曲健康风险评估结果，且具有重要的监管意义。