Since its first production in 1947, perfluorooctanoic acid (PFOA) has been applied in extensive industrial fields, including the manufacture of fabrics, leather, floor waxes, waxed papers, electric wires, fire-fighting foam, nonstick frying pans, outdoor clothing, and plastics. In addition, it has been known that per- and poly-fluorinated chemicals can form PFOA and related compounds which show the half-lives of decades in the ecosystem and the environment (Washington et al., 2015). Thus, PFOA was categorized as “the forever chemical”, and recent evidence suggested that PFOA was detected globally in environmental sources, such as drinking water, soil, air, and household dust (Gustafsson et al., 2022). Furthermore, Houde et al. (Houde et al., 2006) reviewed that the level of poly-fluoroalkyl substances increased significantly in samples derived from the biological system during the second half of the 20th century. Therefore, the potential health effects have attracted great concern of many researchers for a long time, and it was classified as a Group 1 carcinogen by the International Agency for Research on Cancer in November 2023 (Zahm et al., 2024).

Harmonized cell signaling and balance between cell proliferation and apoptosis are essential to maintain cellular homeostasis against environmental stress, and the cell membrane functions as the first defense line. Meanwhile, PFOA consists of the head group which is hydrophilic together the tail group which is hydrophobic, linking to possible interference between lipid bilayers followed by organelle damage. A study demonstrated that PFOA-induced hepatomegaly was associated with inhibited gap-junctional intercellular communication, depending on the activation of the extracellular receptor kinase and phosphatidylcholine-specific phospholipase C (Upham et al., 2009). In addition, PFOA, known as a peroxisome proliferator, decreased cytochrome oxidase activity and increased the mitochondrial DNA copy number in the liver of rats administered at a 100 mg/kg dose for 3 days (Berthiaume and Wallace, 2002). Furthermore, Du et al. (Du et al., 2023) recently suggested that non-toxic levels of PFOA significantly inhibited the expression of transcription factors and the activation of cyclic adenosine monophosphate which are upregulated by thyroid-stimulating hormone (TSH) in rat thyroid cells. In addition, as exposed for 48 h, the TSH receptor gene level was downregulated, its N-glycosylation was impaired, and increased ER stress and decreased ER mass were observed in a concentration-dependent manner.

The liver's epithelial cells should be regenerated efficiently along with the proliferation of hepatocytes and biliary cells to restore damaged liver tissue (Gadd et al., 2020). Meanwhile, in another study using PFOA, we found that a 6-month repeated oral dose of PFOA via oral for 6 months reduced the density of cells constituting the liver tissue (under review). Therefore, we hypothesized that PFOA might affect epithelial proliferation. Furthermore, a cohort analysis of the relationship between levels of eight perfluoroalkyl substances in early pregnancy and sporadic first-trimester miscarriage suggested that only PFOA showed a consistent dose-response association with miscarriage (Wikstrom et al., 2021). Therefore, we here tried to identify a toxic mechanism of PFOA using HeLa Chang liver epithelial cells established by contaminating HeLa (American Type Culture Collection, Manassas, VA, USA).