Induction of cytochrome P4501A by binary mixtures of polychlorinated biphenyls (PCBs) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in liver cell lines from rat and trout

The induction of ethoxyresorufin-o-deethylase (EROD) activity by binary combinations of 2,3,7,X-tetrachlorodibenzo-p-dioxin (TCDD) and seven polychlorinated biphenyls (PCBs) was examined in liver cell lines from rat (H4IIE) and rainbow trout (RTL-W1). The non-ortho PCBs were 77, 81, 126, and 169; the mono-ortho PCBs were 105, 118, and 156. Binary combinations yielded less-than-additive interactions more commonly with RTL-W1 than with H4IIE. In RTL-W1, less-than-additive behaviour was observed at mono-ortho PCB/TCDD ratios of greater than 10000 to I and at non-ortho PCB/TCDD ratios of greater than 80 to 1. In H4IIE, less-than-additive interactions were observed at mono-ortho PCB/TCDD ratios of greater than 20000 to I, but only additive interactions were seen between TCDD and non-ortho PCBs. With both cell lines, greater-than-additive interactions were not found. These results imply that bioassays with these cell lines could lead to lower TCDD-equivalent concentrations than would be determined by chemical analysis. (C) 1998 Elsevier Science B.V. All rights reserved.