Structure-Activity–Dependent Regulation of Cell Communication by Perfluorinated Fatty Acids using in Vivo and in Vitro Model Systems

Abstract

BackgroundPerfluoroalkanoates, [e.g., perfluorooctanoate (PFOA)], are known peroxisome proliferators that induce hepatomegaly and hepatocarcinogenesis in rodents, and are classic non-genotoxic carcinogens that inhibit in vitro gap-junctional intercellular communication (GJIC). This inhibition of GJIC is known to be a function of perfluorinated carbon lengths ranging from 7 to 10.ObjectivesThe aim of this study was to determine if the inhibition of GJIC by PFOA but not perfluoropentanoate (PFPeA) observed in F344 rat liver cells in vitro also occurs in F344 rats in vivo and to determine mechanisms of PFOA dysregulation of GJIC using in vitro assay systems.MethodsWe used an incision load/dye transfer technique to assess GJIC in livers of rats exposed to PFOA and PFPeA. We used in vitro assays with inhibitors of cell signaling enzymes and antioxidants known to regulate GJIC to identify which enzymes regulated PFOA-induced inhibition of GJIC.ResultsPFOA inhibited GJIC and induced hepatomegaly in rat livers, whereas PFPeA had no effect on either end point. Serum biochemistry of liver enzymes indicated no cytotoxic response to these compounds. In vitro analysis of mitogen-activated protein kinase (MAPK) indicated that PFOA, but not PFPeA, can activate the extracellular receptor kinase (ERK). Inhibition of GJIC, in vitro, by PFOA depended on the activation of both ERK and phosphatidylcholine-specific phospholipase C (PC-PLC) in the dysregulation of GJIC in an oxidative-dependent mechanism.ConclusionsThe in vitro analysis of GJIC, an epigenetic marker of tumor promoters, can also predict the in vivo activity of PFOA, which dysregulated GJIC via ERK and PC-PLC.

Differential toxicity between perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA)

“…Because tumor formation requires loss of homeostasis and many tumor promoters inhibit GJIC, it has been hypothesized that GJIC might play a role in carcinogenesis (Trosko et al, 1998). PFOA has been demonstrated to inhibit GJIC in liver cells in vitro and in vivo (Upham et al, 2009). However, inhibition of GJIC is a widespread phenomenon, and the effect by PFOA was neither species-nor tissue-specific.…”

Per- and polyfluorinated substances in the Nordic Countries

“…Peroxisome induced proliferation and the resulting activation of a nuclear receptor peroxisome proliferator-activated receptor  (PPAR) have also been proposed as a mechanism for tumor induction and for the immune and hormonal changes seen in rodents . Other proposed mechanism for tumor promotion is by inhibition of gap-junctional intercellular communication (GJIC) (Upham et al, 2009). GJIC plays a vital role in maintaining tissue homeostasis, and disruption of gap junction function can lead to diseased states such as tumorigenesis.…”

“…GJIC plays a vital role in maintaining tissue homeostasis, and disruption of gap junction function can lead to diseased states such as tumorigenesis. PFOA was shown to decrease GJIC activity in the liver of rats treated for both acute and long-term dosing (Upham et al, 2009). …”

Methoxychlor and Vinclozolin Induce Rapid Changes in Intercellular and Intracellular Signaling in Liver Progenitor Cells

“…As for many other EDCs, interactions with nuclear sex hormone receptors and their ligand-dependent transcription factor activity (so-called genomic signaling mechanism) have been implicated as the principal molecular mechanism responsible for endocrine disrupting activity of MXC and VIN (Manikkam et al, 2014;Ozgyin et al, 2015;van Ravenzwaay et al, 2013). Although MXC is a weak estrogen receptor (ER) agonist, its hydroxylated metabolites, such as HPTE (2,2-bis-(p-hydroxyphenyl)-1,1,1-trichloroethane), are potent ERa agonists and weak antagonists to both ERß and androgen receptor (AR) (Gaido et al, 2000).…”

“…These effects, which are relevant for transcriptional and epigenetic control of gene expression and normal cell behavior (Trosko, 2011), were studied in a rat liver epithelial cell line WB-F344. This cell line is a well-established in vitro model for assessment of GJIC and mechanistic studies in responses to environmental contaminants (Sovadinova et al, 2015;Upham et al, 2007Upham et al, , 2008, which has been validated by in vivo studies (Sai et al, 2000;Upham et al, 2009) and matches the most extensively used rodent model system, F344 rats, in the National Toxicology Program. Both of these EDCs exhibited dose, time and mechanistic differences on GJIC, MAPKs, and phospholipase C, which were elicited by the parental compounds and occurred independently of ER-or AR-mediated genomic mechanisms.…”