Investigating the mode of action for liver toxicity and wasting-like responses produced by high dose exposures to longer chain perfluoroacid substances (PFAS) using high throughput transcriptomics

Single doses of perfluoro-n-decanoic acid (PFDA) cause wasting, a progressive loss of 30 to 50% body weight, increasing liver/body weight ratios, and death within several weeks (Olson and Andersen, 1983). Repeat high doses of perfluorooctane sulfonate (PFOS) produce a subset of these responses in rats and monkeys. The mode of action (MOA) of these wasting-like syndromes is not clear, nor is it understood if these responses are limited to a subset of perfluoroacid substances (PFAS) or a common response to high dose exposure with a larger number of PFAS. To identify pathway perturbations in liver caused by PFAS, we analyzed published in vitro gene expression studies from human primary liver spheroids treated with various PFAS for treatment times up to 14 days (Rowan-Carroll et al., 2021). With treatment times of 10 to 14 days, longer-chain PFAS compounds, specifically PFOS, perfluorodecane sulfonate (PFDS) and higher doses of perfluorooctanoic acid (PFOA), downregulated large numbers of genes in pathways for steroid metabolism, fatty acid metabolism and biological oxidations. Shorter chain PFAS compounds upregulated genes in pathways for fatty acid metabolism. Although PFDA was more toxic and could only be examined at 1-day of treatment, it also downregulated genes for lipid metabolism, steroid metabolism, and biological oxidations. Shorter chain PFAS, both carboxylic and sulfonic acids, did not lead to downregulation of pathways for fatty acid or steroid metabolism. TCDD is also known to cause wasting responses in rodents and humans. In intact rats, high dose responses of longer chain PFAS produce downregulation of batteries of genes associated with fatty acid oxidation and lipogenesis similar to those seen with TCDD. Based on our results, when combined with other literature, we propose that the longer-chain PFAS impair lipogenic pathways through inhibitory interactions between PPAR{beta}, PPAR and PPAR{gamma}.