Special Section on Mechanistic and Translational Research on Transporters in Toxicology Perfluorinated Carboxylic Acids with Increasing Carbon Chain Lengths Upregulate Amino Acid Transporters and Modulate Compensatory Response of Xenobiotic Transporters in HepaRG Cells S

Perfluorinated carboxylic acids (PFCAs) are widespread environmental pollutants for which human exposure has been documented. PFCAs at high doses are known to regulate xenobiotic transporters partly through peroxisome proliferator-activated receptor alpha (PPAR a ) and constitutive androstane receptor (CAR) in rodent models. Less is known regarding how various PFCAs at a lower concentration modulate transporters for endogenous substrates, such as amino acids in human hepatocytes. Such studies are of particular importance because amino acids are involved in chemical detoxification, and their transport system may serve as a promising therapeutic target for structurally similar xenobiotics. The focus of this study was to further elucidate how PFCAs modulate transporters involved in intermediary metabolism and xenobiotic biotransformation. We tested the hepatic transcriptomicresponseofHepaRGcellsexposedto45 l Mofperfluor-ooctanoic acid, perfluorononanoic acid, or perfluorodecanoic acid in triplicates for 24 hours (vehicle: 0.1% DMSO), as well as the prototypical ligands for PPAR a (WY-14643, 45 l M) and CAR (6-(4-chlorophenyl) imidazo[2,1-b][1,3]thiazole-5-carbaldehyde O-(3,4-dichlorobenzyl)oxime [CITCO], 2 l M). PFCAs with increasing carbon chain lengths (C8-C10) regulated more liver genes, with amino acid metabolism and transport ranked among the top enriched pathways and PFDA ranked as the most potent PFCA tested. Genes encoding amino acid transporters, which are essential for protein synthesis, were novel inducible targets by all three PFCAs, suggesting a potentially protective mechanism to reduce further toxic insults. None of the transporter regulations appeared to be through PPAR a or CAR but potential involvement of nuclear factor erythroid 2-related factor 2 is noted for all 3 PFCAs. In conclusion, PFCAs with increasing carbon chain lengths up-regulate amino acid transport-ersandmodulatexenobiotictransporterstolimitfurthertoxicexposures inHepaRGcells. All PFCAs were also predicted to significantly modulate the PXR-signaling. perfluorooctanoic acid and PFNA were predicted to inhibit HIF1A (note: PFDA was also predicted to significantly modulate the HIF1A signaling). Regarding the transporters, NRF2 was predicted to be altered by all three PFCAs to regulate the transporter mRNAs. PFNA and PFDA were predicted to activate upstream regulators involved in xenobiotic biotransformation, signaling molecule regulation, and lipid sensing and metabolism (AHR, ESR1, PGR, and PPARG) to regulate the transporter mRNAs. Therefore, we hypothesize that key transcription factors, such as ATF4 and NRF2 play critical roles in regulating downstream signatures of xenobiotic, carbohydrates, and amino acid metabolism from PFCAs. Several categories of transporters were differentially regulated, including an up-regulation in many amino acid transporters and several xenobiotic efflux transporters, as well as a down-regulation of several xenobiotic and BA uptake transporters, with PFDA having the most potent effect.