Cell culture serum alters the uptake and relative potencies of halogenated aromatic hydrocarbons in PLHC-1 cells

Abstract

Cell culture serum has been demonstrated to affect Ah receptor (AHR) expression and function in cell culture models of 2,3,7,8 tetrachlorodibenzo-p-dioxin (TCDD) and polychlorinated biphenyl (PCB) toxicity. Such models are being used with increasing frequency to determine the toxic potencies for these compounds in a variety of species. Accordingly, the ability of serum components to modulate AHR-regulated CYP1A induction was evaluated in the cell line PLHC-1, derived from a hepatocellular carcinoma of the fish Poeciliopsis lucida. PLHC-1 cells grown and treated with TCDD in different media showed differences in the potency of CYP1A induction as measured by the CYP1A-catalyzed ethoxyresorufin-O-deethylase (EROD) activity. Uptake of 3H-TCDD by cells was 2–3-fold greater in serum-free medium than in 10 or 5% calf serum media, demonstrating that the change in potency was due to differences in uptake of TCDD. A similarly increased level of specific TCDD binding by the AHR reflected the greater uptake of TCDD in cells treated in serum-free medium. Three coplanar PCBs also exhibited a greater potency for EROD and CYP1A protein induction in serum-free medium. The magnitude of the effect was greater for the PCBs, and consequently their potencies of induction relative to TCDD are significantly less when treatment occurs in medium with serum than without serum. These results indicate that serum components affect bioavailability of hydrophobic compounds in cell culture studies and can alter toxic equivalency factors determined in vitro. [Supported in part by EPA Grant R823889.]