In Vitro Effects of Methylsulfonyl Polychlorinated Biphenyls and 7,8‐Benzoflavone on Aryl Hydrocarbon Hydroxylase Activity in Human Lymphoblastoid Cells

The effects of 11 isomers of methylsulfonyl polychlorinated biphenyls (MSF‐PCBs) on the aryl hydrocarbon hydroxylase (AHH) activity were examined at a fixed dose of 1.5 μg/ml by using cultured lymphoblastoid cells. One of the isomers 3‐MSF‐3′,4,4′,5‐tetraCB, as well as 4‐MSF‐3,3′,4′,5‐tetraCB and 4‐MSF‐3,3′,4′,5,5′‐pentaCB, effectively reduced the AHH activity when added to the culture medium, especially that previously treated with 2,3,7,8‐tetrachlorodibenzo‐p‐dioxin (TCDD) to induce the AHH activity. However, the inhibitory potencies exerted by the above three MSF‐PCB compounds were smaller than that by 7,8‐benzoflavone (BNF). When added to the culture medium simultaneously with TCDD or 3‐methylcholanthrene (MC), 3‐MSF‐3′,4,4′,5‐tetraCB blocked the enhancement of the AHH activity by TCDD but did not that by MC. This is in contrast to BNF which blocked the increases due to both TCDD and MC. On the other hand, 3‐MSF‐3′,4,4′,5‐tetraCB added directly to the reaction mixture for the TCDD‐induced AHH activity showed little influence, while BNF decreased the same activity. These results imply that the effect of 3‐MSF‐3′,4,4′,5‐tetraCB on the AHH activity is different from that of BNF. 1990 Nordic Pharmacological Society