Transcriptomic points of departure for 6PPD-Quinone derived from human Caco-2 and HepG2 cells.

N-(1,3-Dimethyl butyl)-N'-phenyl-phenylenediamine-quinone (6ppd-quinone) is of emerging concern due to its widespread presence and toxicity to aquatic species. The chemical has been detected in human biofluids though little is known about its effects on human tissues. The objective of this study was to increase understanding of 6ppd-quinone's potential human health effects by deriving transcriptomic points of departure (tPOD) values in two human cell lines using the TPD-seq workflow. An EC20 for cytotoxicity was calculated for Caco-2 (104 μg/L) but not for HepG2 cells. Even in the absence of cytotoxicity, tPOD values (20th gene, 10th percentile, mode) were calculated in Caco-2 (6.5-25 μg/L) and HepG2 (0.36-35 μg/L) cells. These ranges capture values from 16 statistical and bioinformatic tests that examined mapping methods (CLC and Deplexer), algorithms (Limma and DESeq2), and filters (log2FC and BMR). The most common and sensitive genes with calculable benchmark doses (BMDs) in Caco-2 (DPF2, CD44, PGAP1, GDF15, H4C16) and HepG2 (SLC5A3, DKK1, ARG2, PHLDA1, TM4SF1) cells are listed. Pathway BMDs were also calculated for Caco-2 (systemic lupus erythematosus, 9.7-18 μg/L; alcoholism, 9.7-20 μg/L; viral carcinogenesis, 9.3-18.1 μg/L), and HepG2 (metabolic pathways, 50-60 μg/L) cells. These findings highlight TPD-seq as an efficient workflow to yield quantitative and mechanistic data relevant for human health risk assessment.