Yoshihisa Kato

Induction of hepatic microsomal drug-metabolizing enzymes by methylsulphonyl metabolites of polychlorinated biphenyl congeners in rats

The effect of methylsulphonyl (MeSO2) metabolites of 2,3,4,5-tetrachlorobiphenyl (tetraCB) (IU-70), 2,2,3,4,5-pentachlorobiphenyl (pentaCB) (IU-87), 2,2,4,5,5-pentaCB (IU-101) and 2,2,3,4,5,5-hexachlorobiphenyl (hexaCB) (IU-141), on the hepatic microsomal drug-metabolizing enzyme system was investigated in rats. The administration of 3-MeSO2-2,3,4,5-tetraCB (10 mumol/kg), 3-MeSO2-2,2,3,4,5-pentaCB (0.5 mumol/kg), 3-MeSO2-2,2,4,5,5-pentaCB (0.5 mumol/kg) and 3-MeSO2-2,2,3,4,5,5-hexaCB (2 mumol/kg) to rats significantly increased the contents of cytochromes P-450 and b5 and the activities of aminopyrine N-demethylase, 7-ethoxycoumarin O-deethylase and benzo[a]pyrene hydroxylase. From these results, it is suggested that the 3-MeSO2 derivatives studied are possibly potent phenobarbital-like inducers of microsomal drug-metabolizing enzymes. On the other hand, 4-MeSO2-2,3,4,5-tetraCB, 4-MeSO2-2,2,3,4,5-pentaCB, 4-MeSO2-2,2,4,5,5-pentaCB and 4-MeSO2-2,2,3,4,5,5-hexaCB had almost no effect on both cytochrome contents and these enzyme activities. After 96 h, following administration of 2,3,4,5-tetraCB, 2,2,3,4,5-pentaCB, 2,2,4,5,5-pentaCB and 2,2,3,4,5,5-hexaCB (342 mumol/kg each), significant increases in contents of these two cytochromes and in activities of these enzymes were observed. The relationship between liver concentrations of 3-MeSO2-PCBs after administration of four PCB congeners and that after administration of their 3-MeSO2 derivatives, and increases in the contents of both cytochromes and activities of drug-metabolizing enzyme suggests that the 3-MeSO2 metabolites derived from PCBs studied play an important role in the induction of the drug-metabolizing enzymes by the parent PCB congeners.

Reduction of thyroid hormone levels by methylsulfonyl metabolites of polychlorinated biphenyl congeners in rats

Abstract Male Sprague-Dawley rats received four consecutive intraperitoneal doses of four kinds of methylsulfonyl (MeSO2) metabolites of polychlorinated biphenyl (PCB) congeners: 3-MeSO2-2,2′,3′,4′,5,6-hexachlorobiphenyl (3-MeSO2-CB132); 3-MeSO2-2,2′,3′,4′, 5,5′-hexachlorobiphenyl (3-MeSO2-CB141); 3-MeSO2-2,2′,4′,5,5′,6-hexachlorobiphenyl (3-MeSO2-CB149) and 4-MeSO2-2,2′,4′,5,5′,6-hexachlorobiphenyl (4-MeSO2-CB149). The congeners were major MeSO2-PCBs determined in human milk, liver and adipose tissue, and the aim was to determine their effect on thyroid hormone levels. All four tested MeSO2 metabolites (20 μmol/kg once daily for 4 days) reduced serum total thyroxine levels by 22–44% at a much lower dose than phenobarbital (PB; 431 μmol/kg once daily for 4 days) on days 2, 3, 4 and 7 after the final doses. Total triiodothyronine levels were reduced 37% by treatment with 4-MeSO2-CB149 at day 7. A 30% increase in thyroid weight was produced by 3-MeSO2-CB141 treatment. Total cytochrome P450 content was increased by 3-MeSO2-CB132, 3-MeSO2-CB141 and 3-MeSO2-CB149, but not by 4-MeSO2-CB149. Thus, it is likely that the 3-MeSO2-hexachlorobiphenyls and 4-MeSO2-CB149 could influence the thyroid hormone metabolism by different mechanism(s). The results show that tested 3- and 4-MeSO2 metabolites of PCB congeners reduce thyroid hormone levels much more than PB in rats. Our finding suggests that the metabolites may act as endocrine-disrupters.

Structure-dependent induction of CYP2B1/2 by 3-methylsulfonyl metabolites of polychlorinated biphenyl congeners in rats.

The effects of eleven 3-methylsulfonyl (3-MeSO(2))-metabolites of polychlorinated biphenyl (PCB) congeners (which were reported to remain in Swedish mothers milk and Japanese Yusho patients tissues) and their two structurally similar 3-MeSO(2)-PCBs on the hepatic drug-metabolizing enzyme activities were compared with those of phenobarbital (PB) and 3-methylcholanthrene (3-MC).The induction profile of the drug-metabolizing enzymes, CYP2B1 and CYP2B2 in the hepatic microsomes of rats treated with nine 3-MeSO(2) derivatives, namely 3-MeSO(2)-2,4,5-trichlorobiphenyl, 3-MeSO(2)-2,2,4,5-tetrachlorobiphenyl (3-MeSO(2)-2,2,4,5-tetraCB), 3-MeSO(2)-2,2,5,5-tetraCB, 3-MeSO(2)-2,3,4,5-tetraCB, 3-MeSO(2)-2,2,3,4,5-pentachlorobiphenyl (3-MeSO(2)-2,2,3,4,5-pentaCB), 3-MeSO(2)-2,2,4,5,5-pentaCB, 3-MeSO(2)-2,2,3,4,5,5-hexachlorobiphenyl (3-MeSO(2)-2,2,3,4,5,5-hexaCB), 3-MeSO(2)-2,2,3,4,5,6-hexaCB and 3-MeSO(2)-2,2,4,5,5,6-hexaCB, was similar to that of rats treated with PB, but was different from that of rats treated with 3-MC. These findings indicate that 3-MeSO(2) metabolites derived from nine PCBs are PB-type inducers of microsomal drug-metabolizing enzymes. The relative inducing potencies of 3-MeSO(2) derivatives on the hepatic drug-metabolizing enzyme activities differed with the extent of chlorination and the positions of chlorine substituent on the phenyl rings. The results of present study show that the structure-CYP2B1/2 induction relationship exists for the 3-MeSO(2) derivatives studied. The inducing abilities of 3-MeSO(2)-2,2,4,5-tetraCB and 3-MeSO(2)-2,2,4,5,5-pentaCB (2 μmol/kg) on the content of cytochrome P450 were higher than those of 2,3,4,4,5-pentaCB (mono-ortho-substituted PCB) (80 μmol/kg), 3,3,4,4-tetraCB (coplanar PCB) (80 μmol/kg) and 3,3,4,4,5-pentaCB (coplanar PCB) (0.5 μmol/kg). The inducing effects of the administration of 3-MeSO(2)-2,2,4,5-tetraCB and 3-MeSO(2)-2,2,4,5,5-pentaCB at 2 μmol/kg on the contents of total cytochrome P450, CYP2B1 and CYP2B2 corresponded to those of PB at 431 μmol/kg twice at a 24 h interval. It is noticeable that 3-MeSO(2)-2,2,4,5-tetraCB and 3-MeSO(2)-2,2,4,5,5-pentaCB have highly potent PB-type inducing activity on drug-metabolizing enzyme systems.

Binding characteristics of naftopidil and α1-adrenoceptor antagonists to prostatic α-adrenoceptors in benign prostatic hypertrophy

Abstract Binding properties of naftopidil and α 1 -adrenoceptor antagonists to α-adrenoceptors in prostates from benign prostatic hypertrophy (BPH) were characterized by radioreceptor assays usinh [ 3 H]prazosin and [ 3 ]- rauwolscine. Specific binding of [ 3 H]prazosin and [ 3 H] rauwolscine in human prostatic membranes was saturable and of high affinity, and it showed a pharmacological specificiwhich characterized α 1 and α 2 - adrenoceptors, respectively. Naftopidil and several α 1 antagonists competed for prostatic [ 3 H]prazosin binding in order: R-(-)-YM-12617 >prazosin>bonazosin>terazosin>naftopidil>urapidil, and the inhibitory effect (Ki = 11.6 nM) of naftopidil was 10 to 45 times less potent than quinazoline derivatives such as prazosin, bunazosin and terazosin. The potencies of these antagonists in competing for [ 3 H]prazosin binding sites in human prostates correlated well with their pharmacological potencies (pA 2 ). Scatchard analysis indicated that the decrease of prostatic [ 3 H]prazosin binding by naftopidil was due to a marked increase in the Kd value without a change in the Bmax value. The inhibition of prostatic [ 3 H]prazosin binding by naftopidil was reversible. Naftopidil also inhibited prostatic [ 3 H]rauwolscine binding (Ki = 70.0 nM). Thus, it is suggested that naftopidil antagonizes α 1 -adrenoceptors in human prostates in a competitive and reversible manner.

Characterization of hepatic microsomal cytochrome P-450 from rats treated with methylsulphonyl metabolites of polychlorinated biphenyl congeners

The inducing potency of 3-methylsulphonyl(MeSO2)-2,2,4,5,5-pentachlorobiphenyl (pentaCB), which was one of the major MeSO2 metabolites of polychlorinated biphenyls (PCBs) present in seal blubber, on the hepatic drug metabolizing enzyme activities was examined in comparison with that of the parent compound and phenobarbital (PB). The inducing fashion of the above enzymes and changes in the contents of PB-inducible P-450 forms by 2,3,4,5-tetrachlorobiphenyl (tetraCB) (IU-70), 2,2,3,4,5-pentaCB (IU-87), 2,2,4,5,5-pentaCB (IU-101) and 2,2,3,4,5,5-hexachlorobiphenyl (hexaCB) (IU-141), and their MeSO2 metabolites were investigated in rats. Administration at various doses (0.2-1.0 mumol/kg) of 3-MeSO2-2,2,4,5,5-pentaCB produced nearly dose-related increases in the hepatic concentration of this methyl sulphone, in the contents of cytochromes P-450 and b5, and in activities of aminopyrine N-demethylase, 7-ethoxycoumarin O-deethylase and benzo[a]pyrene hydroxylase of liver microsomes. Major PB-inducible forms, CYP2B1, CYP2B2, CYP3A2 and CYP2C6 were induced with four PCBs (342 mumol/kg) and their 3-MeSO2 metabolites (0.5-10 mumol/kg), indicating that 3-MeSO2 metabolites were strong PB-type inducers of hepatic drug-metabolizing enzymes. 3-MeSO2-2,2,4,5,5-pentaCB was an especially strong inducer. On the other hand, four PB-inducible forms of cytochrome P-450 were not induced with the 4-MeSO2 isomers. The relation between liver concentrations of the corresponding 3-MeSO2 derivatives and induction of four PB-inducible forms of cytochrome P-450 after administration of four PCBs and their 3-MeSO2 derivatives further confirmed that the 3-MeSO2 metabolites played an important role in the induction which parent PCB congeners caused on the hepatic drug-metabolizing enzyme system.

Inhibition of cell-cell communication by methylsulfonyl metabolites of polychlorinated biphenyl congeners in rat liver epithelial IAR 20 cells

The effects of three polychlorinated biphenyl (PCB) congeners and their six methylsulfonyl (MeSO2)-metabolites on cell communication have been investigated in the scrape-loading/dye-transfer assay in IAR 20 rat liver epithelial cells. The results demonstrated that at non-cytotoxic concentrations 2,2′,4′,5-tetrachlorobiphenyl,u200a2,2′,4′,5,5′-pentachlorobiphenylu2009(2,2′,4′,5,5′-pentaCB), 2,2′,4′,5,5′,6-hexachlorobiphenyl (2,2′,4′,5,5′, 6-hexaCB), and their 3- and 4-MeSO2 derivatives completely inhibited the cell communication within 1u2009h. 4-MeSO2-2,2′,4′,5,5′-pentaCB and 4-MeSO2-2,2′,4′,5, 5′,6-hexaCB appeared to inhibit the cell communication at slightly lower concentration than their parental PCB congeners and 3-MeSO2 derivatives. The results show that 3- and 4-MeSO2 derivatives of the PCB congeners tested inhibit gap junction intercellular communication at about the same potency as their parental compounds. Since inhibition of cell communication is often observed after treatment with many tumor promoters, our findings suggest that the metabolites may also act as tumor promoters.

Reduction of serum thyroxine concentrations by methylsulfonyl metabolites of tetra-, penta- and hexachlorinated biphenyls in male Sprague-Dawley rats.

Male Sprague-Dawley rats received four consecutive intraperitoneal doses of nine methylsulfonyl (MeSO2) metabolites of tetra-, penta- and hexachlorinated biphenyls (tetra-, penta- and hexaCBs) to determine their effects on thyroid hormone levels. Nine MeSO2 metabolites, major MeSO2-PCBs detected in human milk, liver and adipose tissue, were 3-MeSO2-2,2,4,5-tetraCB (3-MeSO2-CB49), 3-MeSO2-2,3,4,5-tetraCB (3-MeSO2-CB70), 3-MeSO2-2,2,3,4,5-pentaCB (3-MeSO2-CB87), 3-MeSO2-2,2,4,5,5-pentaCB (3-MeSO2-CB101), 4-MeSO2-2,2,4,5,5-pentaCB (4-MeSO2-CB101), 3-MeSO2-2,2,3,4,5,6-hexaCB (3-MeSO2-CB132), 3-MeSO2-2,2,3,4,5,5-hexaCB (3-MeSO2-CB141), 3-MeSO2-2,2,4,5,5,6-hexaCB (3-MeSO2-CB149) and 4-MeSO2-2,2,4,5,5,6-hexaCB (4-MeSO2-CB149). All nine MeSO2 metabolites (20 micromol/kg once daily for four days) reduced serum total thyroxine levels (16-44%) at a much lower dose than phenobarbital (431 micromol/kg once daily for four days) on days 2, 3, 4 and 7 after the last dosage. Total triiodothyronine level was reduced 37% by treatments with 3-MeSO2-CB49 and 3-MeSO2-CB149 at day 7, but increased 35% and 38% by 3-MeSO2-CB70 and 4-MeSO2-CB101 at days 3 and 4, respectively. The reductions in thyroxine levels led to an increase in thyroid-stimulating hormone levels by 3-MeSO2-CB49, 3-MeSO2-CB87, 3-MeSO2-CB101, 3-MeSO2-CB132, 3-MeSO2-CB141, 3-MeSO2-CB149 and 4-MeSO2-CB149. A 30% increase in thyroid weight was produced by 3-MeSO2-CB101 and 3-MeSO2-CB141 treatments. Total cytochrome P450 content and the activity of 7-pentoxyrosorufin O-dealkylase were increased by all seven 3-MeSO2-PCBs. 3-MeSO2-CB49, 3-MeSO2-CB87, 3-MeSO2-CB101 and 3-MeSO2-CB132 also increased the activity of 7-ethoxyresorufin O-dealkylase. Thus, it is likely that all nine tested MeSO2 metabolites could influence thyroid hormone metabolism. The results show that tested 3- and 4-MeSO2 metabolites of tetra-, penta- and hexaCBs reduce thyroid hormone levels in rats, suggesting that the metabolites may act as endocrine-disrupters.

The ability to alter the gap junction protein expression outside GST-P positive foci in liver of rats was associated to the tumour promotion potency of different polychlorinated biphenyls

The results demonstrate different modes of action by a dioxin-like polychlorinated biphenyl (PCB 126) and a non dioxin-like PCB (PCB 153) in the alteration of connexin (cx) 26 and cx 32 expression outside GST-P positive foci in liver of female Sprague-Dawley rats, treated according to an initiation-promotion protocol. A decreased relative amount of immunopositive cx 26 and cx 32 spots in the parenchymal cell plasma membranes was observed after treatment with the potent tumour promoters PCB 126 or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). No reduction of cx 26 or cx 32 was noted after administration with the weaker tumour promoters PCB 153 or PCB 118 (PCB 118; both dioxin- and non dioxin-like). Additionally, we found that the down-regulation of connexins also occurred in rats treated with PCB 126 or TCDD without partial hepatectomy and initiation with nitrosodiethylamine. In summary, the results indicate that the ability to reduce the gap junction protein level in liver of rats can be associated to the tumour promotive potency of the different PCB-congeners and TCDD.

Evidence that methylsulfonyl metabolites of m-dichlorobenzene are causative substances of induction of hepatic microsomal drug-metabolizing enzymes by the parent compound in rats

This study was undertaken to clarify the relationship between the formation of 2,4- and 3,5-dichlorophenyl methyl sulfones, metabolites of m-dichlorobenzene (DCB), and their inducing effect on hepatic microsomal drug-metabolizing enzymes in rats. When m-DCB was injected ip into bile duct-cannulated rats, little or no methyl sulfones were detected in blood, liver, kidneys, adipose tissue, or bile. In the antibiotic-pretreated rats dosed with m-DCB, metabolite concentrations in the blood and the three tissues markedly decreased. These findings suggest that the formation of methylsulfonyl metabolites from m-DCB depends largely upon the metabolism of some precursor(s) excreted in the bile by intestinal microflora. The increasing effects of m-DCB administration on the activities of aminopyrine and aniline metabolizing enzymes and the contents of cytochromes P-450 and b5 in hepatic microsomes were scarcely observed in the bile duct-cannulated and antibiotic-pretreated rats, in which the drug-metabolizing enzymes were able to be induced by phenobarbital treatment. On the other hand, in rats administered 2,4- or 3,5-dichlorophenyl methyl sulfone hepatic distribution of each methyl sulfone was similar to that in intact rats, and the degree of increase of the above four parameters was nearly the same as that in the intact rats. These findings provide evidence that the induction of drug-metabolizing enzymes by m-DCB is not due to the action of m-DCB but is due to its methylsulfonyl metabolites.

The induction of hepatic microsomal UDP-glucuronosyltransferase by the methylsulfonyl metabolites of polychlorinated biphenyl congeners in rats.

The effects of nine methylsulfonyl (MeSO(2)) metabolites of tetra-, penta- and hexachlorinated biphenyls (tetra-, penta- and hexaCBs; 20 micromol/kg once daily for 4 days) on the hepatic microsomal UDP-glucuronosyltransferase (UDP-GT) were investigated in male Sprague-Dawley rats. Each of the seven 3-MeSO(2)-PCBs, 3-MeSO(2)-2, 2,4,5-tetraCB (3-MeSO(2)-CB49), 3-MeSO(2)-2,3,4,5-tetraCB (3-MeSO(2)-CB70), 3-MeSO(2)-2,2,3,4,5-pentaCB (3-MeSO(2)-CB87), 3-MeSO(2)-2,2,4,5,5-pentaCB (3-MeSO(2)-CB101), 3-MeSO(2)-2,2,3, 4,5,6-hexaCB (3-MeSO(2)-CB132), 3-MeSO(2)-2,2,3,4,5,5-hexaCB (3-MeSO(2)-CB141), 3-MeSO(2)-2,2,4,5,5,6-hexaCB (3-MeSO(2)-CB149) and 4-MeSO(2)-2,2,4,5,5-pentaCB (4-MeSO(2)-CB101) increased the activities of UDP-GT toward chloramphenicol, 4-nitrophenol and 4-methylumbelliferone. 4-MeSO(2)-2,2,4,5,5,6-hexaCB (4-MeSO(2)-CB149) increased the activity of UDP-GT toward chloramphenicol (UGT2B1) but not toward 4-nitrophenol (UGT1A6) and 4-methylumbelliferone (UGT1A6). The activity of UDP-GT toward thyroxine (T(4)) significantly increased after the administration of each of the seven 3-MeSO(2)-PCBs and 4-MeSO(2)-CB101. Significant correlation was found between the activity of UDP-GT toward T(4) and serum total T(4) concentration after the administration of each of the MeSO(2) derivatives except 4-MeSO(2)-CB149. In conclusion, seven 3-MeSO(2)-PCBs and 4-MeSO(2)-CB101 induce both UGT2B1 and UGT1A6, and 4-MeSO(2)-CB149 induces UGT 2B1. The results from the present study indicate that increase in the hepatic T(4) glucuronidation after the administration of the seven 3-MeSO(2)-PCBs and 4-MeSO(2)-CB101 possibly because of the induction of both UGT1A1 and UGT1A6 caused the reduction of serum T(4) levels.