Effects of methylsulphonyl polychlorinated biphenyl homologues and 7,8-benzoflavone on aryl hydrocarbon hydroxylase activity.

First, we investigated the effects of eleven methylsulphonyl polychlorinated biphenyl (MSF-PCB) homologues at 1.5 micrograms/ml and 7,8-benzoflavone (ANF) at 1.4 micrograms/ml on 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD, 15 ng/ml)-induced aryl hydrocarbon hydroxylase (AHH) activity of cultured human lymphoblastoid cells and the following results were obtained. 1) The relative AHH activity (TCDD-induced AHH activity treated with each of the MSF-PCB compounds or ANF/the enzyme activity treated with acetone, %) of the ANF-treated culture was the smallest value (about 9%). 2) Among MSF-PCB homologues, 3-MSF-4,5,3',4'- and 4-MSF-3,5,3',4'-tetrachlorobiphenyls (TCBs) showed the highest inhibition and their relative enzyme activities were about 20%. 3) In the rest of MSF-PCB compounds, the relative AHH activities were as follows: 4-MSF-3,5,3',4',5'-pentachlorobiphenyl (PenCB); 37%, 3-MSF-4,5,2',3',4'-PenCB; 50%, 3-MSF-4,5,2',3'-TCB, 3-MSF-4,5,2',3',4',5'-hexachlorobiphenyl and 3-MSF-4,5,6,2',3',4',5'-heptachlorobiphenyl; 60 to 64%, 4-MSF-2,5,2',3',4'-PenCB; 77%, 3-MSF-2,5,3',4'-TCB; 88%, 4-MSF-2,5,2',5'-TCB; 93% and 3-MSF-4,5,3',4',5'-PenCB rather enhanced the TCDD-induced enzyme activity. Second, we prepared the hepatic microsomes of BALB/c (Ah responsive) and AKR/J (Ah nonresponsive) strains of mice after the treatment of olive oil (as control), 3-methylcholanthrene (MC, 42 mg/kg, once) and TCDD (20 micrograms/kg, 6 times, once every other week) in order to examine the effects of 3-MSF-4,5,3',4'-TCB (1.5 to 45 micrograms/ml) and ANF (1.4 to 42 micrograms/ml) on the respective hepatic microsomal AHH activities.(ABSTRACT TRUNCATED AT 250 WORDS)