Coplanar PCBs enzyme induction

Avians, among other wildlife fauna, first drew the attention of PCB researchers, and induction of microsomal enzymes in pigeon had been measured as early as 1968 [48]. EROD inducing capacity of coplanar PCBs in chicken embryos has been standardized [49]. AHH and EROD activities were measured in black-headed and black-tailed gulls [50], Antarctic penguins and south polar skua. TEFs for birds have been proposed [49]. 

Immunotoxicity of PCDE has been studied in rat and mice [82,88,89], Chu et al. [82] reported that PCDE 184 is immunosuppressive in rats. Immunotoxicity of PCDEs has also been reported in mice [88, 89]. Immunotoxicity of PCDEs correlated with enzyme induction activities in the study of Howie et al. [88], who measured the dose-response suppression of the splenic plaque-forming cell response to sheep red blood cells in Ah-responsive C57BL/6 mice. Immunotoxicity of PCDEs was concluded to be mediated by the Ah-receptor. Of eight PCDE congeners tested, only PCDE 167, did not cause dose-response immunosuppressive effects. PCDEs were >200 times less immunotoxic than 2,3,7,8-TCDD. In contrast to PCBs, non-ortho congeners PCDEs 77 and 126 were less potent than mono-ortho-congeners PCDEs 118 and 156. The potencies followed the order PCDE 156 > PCDE 126 > PCDE 118 > PCDE 77 > PCDE 101>PCDE 153 > PCDE 154. Of PCBs, only non- and mono-orfho-coplanar congeners are immunotoxic [79]. 

Induction of AHH and EROD by PCDEs has also been studied in mice [88,89]. EROD activity in C57BL/6 N mice has been measured for PCDEs 77,101,118,126, 153,154,156,167,206,207,208, and 209 [88,89]. Howie et al. [88] reported that the structure-activity of PCDEs was different to that of PCBs. Coplanar PCDE congeners were less potent than their mono-ortho-analogs and increasing ortho-substitution was less effective in reducing the activity of PCDEs compared to ortho-effects of PCBs. Based on the results of immunotoxicity and induction of enzyme activity of the above PCDEs, Safe [79] proposed a similar TEF value (0.001) to that of mono-ortho-PCBs for non- and mono-ortho-PCDEs. 

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