Gap junctional intercellular communication (GJIC) is the major pathway of intercellular signal transduction, and is thus important for normal cell growth and function. Recent studies have revealed a global distribution of some perfluorinated organic compounds, especially perfluorooctane sulfonic acid (PFOS) in the environment. Because other perfluoroalkanes had been shown to inhibit GJIC, the effects of PFOS and related sulfonated fluorochemicals on GJIC were studied using a rat liver epithelial cell line (WB-F344) and a dolphin kidney epithelial cell line (CDK). In vivo effects on GJIC were studied in Sprague-Dawley rats orally exposed to PFOS for 3 days or 3 weeks. Effects on GJIC were measured using the scrape loading dye technique. PFOS, perfluorooctane sulfonamide (PFOSA), and perfluorohexane sulfonic acid (PFHA) were found to inhibit GJIC in a dose-dependent fashion, and this inhibition occurred rapidly and was reversible. Perfluorobutane sulfonic acid (PFBS) showed no significant effects on GJIC within the concentration range tested. A structure activity relationship was established among all 4 tested compounds, indicating that the inhibitory effect was determined by the length of fluorinated tail and not by the nature of the functional group. The results of the studies of the 2 cell lines and the in vivo exposure were comparable, suggesting that the inhibitory effects of the selected perfluorinated compounds on GJIC were neither species- nor tissue-specific and can occur both in vitro and in vivo.

Perfluorinated fatty acids (PFFAs), such as perfluorooctanoic acid (PFOA) and perfluorodecanoic acid (PFDA), are known peroxisome proliferators and hepatocarcinogens. A causal link between an increase in the oxidative stress by peroxisomes and tumor promotion has been proposed to explain the hepatocarcinogenicity of PFOA and PFDA. However, the down‐regulation of gap junctional intercellular communication (GJIC) has also been linked to the tumor‐promoting properties of many carcinogens. Therefore, the effect of PFFAs on GJIC in WB‐rat liver epithelial cells was determined. The chain length of the PFFAs tested for an effect on GJIC ranged from 2 to 10, 16 and 18 carbons. Carbon lengths of 7 to 10 inhibited GJIC in a dose–response fashion, whereas carbon lengths of 2 to 5, 16 and 18 did not appreciably inhibit GJIC. Inhibition occurred within 15 min and was reversible, with total recovery from inhibition occurring within 30 min after the removal of the compound from the growth medium. This short time of inhibition suggests that GJIC was modified at the post‐translational level. Also, this short time period was not long enough for peroxisome proliferation. The post‐translational modification of the gap junction proteins was not a consequence of altered phosphorylation as determined by Western blot analysis. Perfluorooctanesulfonic acid also inhibited GJIC in a dose–response fashion similar to PFDA, indicating that the determining factor of inhibition was probably the fluorinated tail, which required 7–10 carbons. Our results suggest that PFFAs could potentially act as hepatocarcinogens at the level of gap junctions in addition to or instead of through peroxisome proliferation.Int. J. Cancer 78:491–495, 1998.

Cell to cell communication via gap junctions is essential in the maintenance of the homeostatic balance of multicellular organisms. Aberrant intercellular gap junctional communication (GJIC) has been implicated in tumor promotion, neuropathy and teratogenesis. Oxidative stress has also been implicated in similar pathologies such as cancer. We report a potential link between oxidative stress and GJIC. Hydrogen peroxide, a known tumor promoter, inhibited GJIC in WB-F344 rat liver epithelial cells with an I50 value of 200 microM. Inhibition of GJIC by H2O2 was reversible as indicated by the complete recovery of GJIC with the removal of H2O2 via a change of fresh media. Free radical scavengers, such as t-butyl alcohol, propylgallate, and Trolox, did not prevent the inhibition of GJIC by H2O2, which indicated that the effects of H2O2 on GJIC was probably not a consequence of aqueous free radical damage. The depletion of intracellular GSH reversed the inhibitory effect of H2O2 on GJIC. The treatment of glutathione-sufficient cells with H2O2 resulted in the hyperphosphorylation of connexin43, which is the basic subunit of the hexameric gap junction protein, as determined by Western blot analysis. TPA, a well-known tumor promoter, also inhibits GJIC via hyperphosphorylation of GJIC, which is a result of protein kinase-C activation. However, H2O2 also induced hyperphosphorylation in GSH-deficient cells that had normal rates of GJIC. Therefore, the mechanism of GJIC inhibition must be different from the TPA-pathway and involves GSH.