Reduction of thyroid hormone levels by methylsulfonyl metabolites of tetra- and pentachlorinated biphenyls in male Sprague-Dawley rats.

Male Sprague-Dawley rats received four consecutive intraperitoneal (i.p.) doses of five kinds of methylsulfonyl (MeSO2) metabolites of tetra- and pentachlorinated biphenyls (tetra- and pentaCBs) to determine their effects on thyroid hormone levels. The five MeSO2 metabolites, which were the 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), and 4-MeSO2-2,2',4',5,5'-pentaCB (4-MeSO2-CB101). All five tested MeSO2 metabolites (20 mumol/kg once daily for 4 days) reduced serum total thyroxine levels 16-40% on days 2, 3, 4, and 7 (after the last dosage). The total triiodothyronine level was reduced 37% by treatment with 3-MeSO2-CB49 at day 7, but was increased 35% and 38% by 3-MeSO2-CB70 and 4-MeSO2-CB101 at days 3 and 4, respectively. The reductions in thyroid hormone levels led to an increase in thyroid stimulating hormone (TSH) levels by 3-MeSO2-CB49, 3-MeSO2-CB87 and 3-MeSO2-CB101. A 30% increase in thyroid weight was produced by 3-MeSO2-CB101 treatment. Thus, it is likely that all five tested MeSO2 metabolites could influence thyroid hormone metabolism. The results show that the tested 3- and 4-MeSO2 metabolites of tetra- and pentaCBs reduce thyroid hormone levels in rats, suggesting that the metabolites may act as endocrine-disrupters.     

PCB methyl sulphones in rat liver after exposure to PCB (Clophen A50): analysis and radiosynthesis of selected methylsulphonyl-PCBs

1. The hepatic metabolism of polychlorinated biphenyls (PCBs) and formation of PCB methyl sulphone metabolites (MeSO₂-PCBs) was determined in the male Sprague-Dawley rat 1, 2, 4 or 8 weeks after dosage with Clophen A50 (a commercial PCB mixture). 2. The total concentration of the PCB congeners examined (ΣPCB) decreased during the experimental period, from 40 μg g^?1 lipid (l.w.) after 1 week to 4 μg g^?1 l.w. after 8 weeks. A 50% decrease of PCB in the liver were estimated to be 28, 13 and 11 days for 2,2′,4,4′,5,5′-hexachlorobiphenyl (CB153), 2,2′,3,3′,4,4′,5-heptaCB (CB170) and 2,2′3,4′,5,5′,6-heptaCB (CB187), respectively. 3. The total MeSO₂-PCB (ΣMeSO₂-PCB) concentration increased from 800 to 1020 ng g^?1 l.w. during the first 2 weeks of treatment and thereafter a decrease to 120 ng g^?1 l.w. after 8 weeks. The relative concentration of both 3′-MeSO₂-2,2′,4,4′,5-pentaCB (3′-MeSO₂-CB101) and 3′-MeSO₂-2,2′,3,4,5′-pentaCB (3′-MeSO₂-CB87) in rat liver showed significant increases during the 8 weeks. In contrast, the relative concentrations of 4-MeSO₂-2,4′,5,5-tetraCB (4-MeSO₂-CB64), 3-MeSO₂-2,3′,4′,5-tetraCB (3-MeSO₂- CB70) and 4-MeSO₂-2,2′,3,4,5′,6′-hexaCB (4′-MeSO₂-CB132) decreased significantly. 4. A route for the synthesis of radiolabelled MeSO₂-PCBs was developed employing the `Pummerer reaction’ to convert methylthio-PCBs (MeS-PCBs) to the corresponding mercapto-PCBs (SH-PCB). The SH-PCBs were methylated with radiolabelled methyl iodide and the resulting sulphides oxidized to yield the corresponding MeSO₂-PCBs. Using this approach, 4-[¹⁴C]-MeSO₂-2′,4′,5,5′,6-hexaCB (3-[¹⁴C]-MeSO₂-CB149), 4-[¹⁴C]-MeSO₂-2,2′,4′,5,5′,6-hexaCB (4-[¹⁴C]-MeSO₂-CB149), 3′-[¹⁴C]-MeSO₂-CB101,4′-[¹⁴C]-MeSO₂-2,2′,4,5,5′-pentaCB (4′-[¹⁴C]-MeSO₂-CB101) and 4′-[³C]-MeSO₂-CB101 were synthesized in quantitative radiochemical yields.     

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 mother's milk and Japanese Yusho patient's 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.     

In vitro antiestrogenic effects of aryl methyl sulfone metabolites of polychlorinated biphenyls and 2,2-bis(4-chlorophenyl)-1,1-dichloroethene on 17beta-estradiol-induced gene expression in several bioassay systems.

Methylsulfonyl (MeSO(2)) metabolites of polychlorinated biphenyls (PCBs) and 2,2-bis(4-chlorophenyl)-1,1-dichloroethene (4,4'-DDE), itself a metabolite of the insecticide 4,4'-DDT, are emerging as a major class of contaminants in the tissues of wildlife and humans. We investigated the antiestrogenic capacity and potencies of 3'- and 4'-MeSO(2)-2,2',4,5,5'-pentachlorobiphenyl (CB101) and -2,2',4,5'-tetrachlorobiphenyl (CB49), which are among the most environmentally persistent MeSO(2)-PCBs, and 3-MeSO(2)-4,4'-DDE on estrogen receptor (ER)-dependent gene expression in four cell-based bioassay systems. Congener- and concentration-dependent antagonism of 17beta-estradiol (E2)-induced gene expression, rather than induction of ER-dependent gene expression, was observed for the MeSO(2)-PCBs on lucifierase activity in stably transfected human breast adenocarcinoma T47D cells (ER-CALUX) and vitellogenin (vtg) production in primary hepatocytes from male carp fish (Cyprinus carpio) (CARP-HEP/vtg). 4'-MeSO(2)-CB101 and -CB49 had the highest antagonistic potency (i.e., maximum inhibition of about 70%, LOECs of 1.0 microM and 2.5 microM), whereas 3'-MeSO(2)-CB101 and -CB49 were less antagonistic; the precursor CB101 and MeSO(2)-PCB analog MeSO(2)-2,5-dichlorobenzene had no effect. Relative to the 4-MeSO(2)-PCBs, tamoxifen (IC(50), 0.06 microM and 0.7 microM) was about 40 and 7 times more potent in the ER-CALUX and CARP-HEP/vtg assays, respectively. Congener- and concentration-dependent effects on aryl hydrocarbon receptor-mediated induction of EROD activity (carp hepatocytes), luciferase expression (H4IIE rat hepatoma [H4IIE.luc] cell line), or cell viability were not observed. 3-MeSO(2)-4,4'-DDE was neither estrogenic nor antiestrogenic in either of the bioassays. Inhibitory trends for the MeSO(2)-PCBs in a bioassay based on stably transfected human embryonic kidney cell (HEK293-ERalpha-ERE) were similar to the ER-CALUX and CARP-HEP/vtg bioassays, whereas the antagonism was weaker in a related HEK293-ERbeta-ERE bioassay. Our findings suggest that the 4'-MeSO(2)-PCBs are antiestrogenic in vitro via a reversible or surmountable interaction with fish or human ER, and that the interaction with human ERalpha is apparently favored over ERbeta. MeSO(2)-PCB metabolites are persistent and bioaccumulative contaminants, and therefore, could be potentially active as environmental antiestrogens in wildlife and humans.     

The role of 3-methylsulfonyl-2,2',4',5,5'-pentachlorobiphenyl, a metabolite of 2,2',4,5,5'-pentachlorobiphenyl, in the induction of hepatic microsomal drug-metabolizing enzymes by 2,2',4,5,5'-pentachlorobiphenyl in rats

After the administration of 2,2',4,5,5'-pentachlorobiphenyl (2,2',4,5,5'-pentaCB) to intact rats, the concentration of 2,2',4,5,5'-pentaCB in liver gradually decreased, whereas 3-methylsulfonyl (3-MeSO(2))-2,2',4',5,5'-pentaCB appeared in liver and remained detectable in liver for 6 weeks. A single injection of 2,2',4,5,5'-pentaCB (342 μmol/kg) or 3-MeSO(2)-2,2',4',5,5'-pentaCB (0.5 μmol/kg) caused a significant increase both in the contents of cytochromes P450 and b(5) and in the activities of aminopyrine N-demethylase and benzo[a]pyrene hydroxylase, and the increased enzyme contents and activities continued for 6 weeks after the administration. The extent of both the hepatic accumulation of 3-MeSO(2)-2,2',4',5,5'-pentaCB and the induction of the enzymes for 6 weeks after the administration of 2,2',4,5,5'-pentaCB was similar to that after the administration of 3-MeSO(2)-2,2',4',5,5'-pentaCB. 3-MeSO(2)-2,2',4',5,5'-pentaCB was considered to play a principal role in the induction of microsomal drug-metabolizing enzymes by 2,2',4,5,5'-pentaCB. When 2,2',4,5,5'-pentaCB was injected i.p. into bile duct-cannulated rats, 3- and 4-MeSO(2)-2,2',4',5,5'-pentaCBs were not detected in liver. In antibiotic-treated rats dosed with 2,2',4,5,5'-pentaCB, the concentrations of 3- and 4-MeSO(2)-2,2',4',5,5'-pentaCBs in liver were markedly reduced. These findings suggest that the process in which 3- and 4-MeSO(2) metabolites of 2,2',4,5,5'-pentaCB are formed involves the biliary secretion of some precursors which will be subjected to metabolism by intestinal microflora. The increasing effects of 2,2',4,5,5'-pentaCB both on the content of cytochrome P450 and on the activity of aminopyrine metabolizing enzyme in hepatic microsomes were not observed in the bile duct-cannulated rats, in which the phenobarbital treatment enabled the drug-metabolizing enzymes to be induced. In antibiotic-treated rats, the increases both in the cytochrome P450 content and in the aminopyrine N-demethylase activity after the administration of 2,2',4,5,5'-pentaCB were smaller than those observed in the intact rats. These findings provide the evidence that the induction of some drug-metabolizing enzymes by 2,2',4,5,5'-pentaCB is due not to the action of 2,2',4,5,5'-pentaCB itself but to its 3-methylsulfonyl metabolite, 3-MeSO(2)-2,2',4',5,5'-pentaCB.     

Inhibition of aromatase activity by methyl sulfonyl PCB metabolites in primary culture of human mammary fibroblasts

In this study, the effects on catalytic activity and mRNA levels of aromatase in primary human mammary fibroblasts were evaluated after exposure to promoter-specific modulators of aromatase expression and methyl sulfonyl polychlorinated biphenyl metabolites (MeSO(2)-PCBs). A method for fibroblast isolation from primary breast tissue was developed and optimized, and aromatase activity and promoter-specific mRNA levels were assessed in these cells after exposure to test compounds. A 24-h exposure of fibroblasts to dexamethasone (DEX) (1-100 nM) increased aromatase activity to a maximum of 313-fold. DEX also elevated promoter I.4-specific RNA levels. A 24-h exposure of fibroblasts to 3-MeSO(2)-PCB-132, 4-MeSO(2)-PCB-132, 4-MeSO(2)-PCB-91, or 4-MeSO(2)-PCB-149 (0.1-10 microM) resulted in a concentration-dependent decrease of aromatase activity. Exposure of fibroblasts to MeSO(2)-PCBs just for the limited duration (6 h) of the catalytic assay caused a concentration-dependent inhibition of aromatase enzyme activity. mRNA levels were not altered by a 24-h MeSO(2)-PCB exposure nor was cytotoxicity observed. In aromatase-expressing human adrenocortical carcinoma H295R cells, a 24-h exposure to 3-MeSO(2)-PCB-132, 4-MeSO(2)-PCB-132, 4-MeSO(2)-PCB-91, or 4-MeSO(2)-PCB-149 (0.1-10 microM) also resulted in a concentration-dependent decrease of aromatase activity. Additionally, there were no changes in aromatase mRNA levels after 24-h exposure of H295R cells to MeSO(2)-PCBs. We conclude that in primary human mammary fibroblasts as well as in H295R cells, aromatase inhibition by MeSO(2)-PCBs is likely to be due to catalytic inhibition.     

In vitro characterization of possible mechanisms underlying the selective in vivo accumulation of the PCB metabolite 4,4'-bis(methylsulphonyl)-2,2',5,5'-tetrachlorobiphenyl in the lung

In vivo, the polychlorinated biphenyl (PCB) metabolite 4,4'-bis(methylsulphonyl)-2,2',5,5'- tetrachlorobiphenyl--(MeSO2)2TCB--selectively accumulates in the Clara cells of the bronchiolar epithelium and in the secretory contents of the bronchiolar lumen. In vitro characterization of the interaction of tritiated (MeSO2)2TCB with the lung suggests that this selective accumulation is due to the presence of a secreted ([3H]MeSO2)2TCB-binding protein in the respiratory tract of rats, mice and man. The protein appears to be an almost globular, low-molecular-weight acidic protein which binds ([3H]MeSO2)2TCB and certain other methylsulphonyl PCBs with high affinity. Because of the pathway outlined for accumulation, it is suggested that methylsulphonyl PCBs should be included in studies designed to elucidate the mechanism(s) of PCB-induced lung toxicity.     

Species differences in the tissue distribution of catechol and methylsulphonyl metabolites of 2,4,5,2',5'-penta- and 2,3,4,2',3',6'-hexachlorobiphenyls in rats, mice, hamsters and guinea pigs

Polychlorinated biphenyls (PCBs) are metabolized to phenolic or methylsulphonyl PCBs (MeSO(2)-CBs) in animal species. The study determined the species differences in the tissue distribution of persistent PCB metabolites in rats, mice, hamsters and guinea pigs 4 days after exposure to 2,4,5,2('),5(')-pentachlorobiphenyl (CB101) or 2,3,4,2('),3('),6(')-hexachlorobiphenyl (CB132). For CB101 metabolism, the hydroxylation in rats, mice and hamsters occurred primarily at the 3(')-position in the 2('),5(')-dichlorinated phenyl ring, whereas the hydroxylation in guinea pigs occurred preferentially at the 3-position. Metabolite profiles in tissues of hamsters were dominated by 3('),4(')-catechol-CB101, whereas metabolite profiles in rats and mice were dominated by 3(')- or 4(')-MeSO(2)-CBs. For CB132 metabolism, rats and mice produced 4(')- and 5(')-MeSO(2)-CBs at similar concentration ratios, whereas guinea pigs produced MeSO(2)-CBs at higher levels and selectively retained 5(')-MeSO(2)-CB in liver. In contrast, hamsters preferentially produced 4('),5(')-catechol-CB132 that was retained in serum. Consequently, hamsters produced catechols, whereas guinea pigs produced meta-substituted MeSO(2)-CBs, preferentially from CB132. These findings indicate that PCBs with 2,3,6-chlorine substitution are preferred substrates for the formation of catechols or MeSO(2)-CBs and the differences in metabolite profiles are related to species-dependent metabolic capacities.     

Cytotoxicity and aromatase (CYP19) activity modulation by organochlorines in human placental JEG-3 and JAR choriocarcinoma cells.

The human placental JEG-3 and JAR choriocarcinoma cell lines have been used as placental models for the study of aromatase (CYP19) activity and endocrine functions. In the present study, 21 organochlorines (OCs) mediated decreases in aromatase activity and protein and DNA content and increases in the percent lactate dehydrogenase (LDH) leakage in JEG-3 cells. These effects were highly variable among the types of OC and their treatment concentrations. Lowest observed effective concentrations reached 0. 001 microM for several OCs. Aromatase activity decreases and OC-mediated cytotoxicity were related. Thus, it was not possible to clearly assess the capacity of the OCs to modulate aromatase activity. Similar to 1,4-naphthoquinone, the most cytotoxic OCs contained a hydroxyl (4'-OH-2,4,6-trichlorobiphenyl and tris(4-chlorophenyl)methanol) or methylsulfonyl- (3- and 4-MeSO(2)-2, 2',5,5'-tetrachlorobiphenyl and -2,3',4',5-tetrachlorobiphenyl, and 3'- and 4'-MeSO(2)-2,2',3,4,5'-pentachlorobiphenyl and -2,2',4,5, 5'-pentachlorobiphenyl) functional group. Modulation of aromatase activity and LDH leakage were less for 3,3',4,4', 5-pentachlorobiphenyl and benzo[a]pyrene and insignificant for five alkyl-substituted trichloro-dibenzofurans and 2,3,7, 8-tetrachloro-dibenzo-p-dioxin (up to 10 microM). Cytotoxicity-related effects were influenced by the cell density and the presence of 10% fetal calf serum in the medium during compound incubation. Similar cytotoxic effects were observed for the JAR cell line. The involvement of an apoptotic mechanism of cytotoxicity in OC-treated JEG-3 cells was suggested by the binding of APO2.7 (an antibody specific to apoptotic cells), DNA fragmentation, and trypan blue staining. JEG-3 and JAR cells appear too sensitive toward OC-mediated cytotoxicity for use as in vitro bioassays to evaluate the potential modulation of aromatase activity. However, these cell lines may prove useful for examining the capacity of xenobiotics to modulate placental toxicity.     

Decreased pulmonary drug metabolism in mice treated with the PCB metabolite 4-methylsulphonyl-2,2',5,5'-tetrachlorobiphenyl

4-Methylsulphonyl-2,2',5,5'-tetrachlorobiphenyl (4-MeSO2-TCB) is a major polychlorinated biphenyl (PCB) metabolite present in lung tissue of PCB-exposed human subjects. After treatment of mice with 4-MeSO2-TCB (100 mg/kg), the pulmonary N-demethylation of aminopyrine in vitro was significantly decreased, while hepatic N-demethylation was concomitantly increased, as compared to tissue from control mice. Treatment of mice with 4-MeSO2-TCB also decreased the in vivo pulmonary covalent binding of o,p'-DDD, while the in vivo hepatic covalent binding was increased. The results indicate that 4-MeSO2-TCB inhibits or represses a cytochrome P-450-dependent enzyme activity in the mouse lung, while in contrast this activity is induced in the mouse liver.     

Effects of chlorinated biphenyls and metabolites on human uterine myocyte proliferation

Uterine myometrial cells are responsive to sex steroids, which could make them susceptible to actions of endocrine disrupting environmental contaminants such as some PCBs. The aim of this investigation was to identify possible effects of some chlorinated biphenyls (CBs) and their metabolites on myometrial cell proliferation. Myometrial cells obtained from women in both phases of the menstrual cycle and from pregnant women were grown in vitro and exposed to CB 101, CB 118, 3' -MeSO2-CB 101, 4'-MeSO2-CB 101, 4-OH-CB 107, 17 beta-estradiol, progesterone, ethinylestradiol or levonorgestrel. The proliferative activity was studied by a BrdU assay. Myometrial cell cultures originating from pregnant women exhibited decreased proliferation in response to 3'-MeSO2-CB 101, 4'-MeSO2-CB 101 and 4-OH-CB 107. Estradiol, a combination of 1 nM 17beta-estradiol and 10 nM progesterone, ethinylestradiol and levonorgestrel also reduced the proliferation of the myometrial cells, regardless of whether the cells were collected from either of the menstrual cycle phases or from pregnant women. To our knowledge this study is the first to demonstrate that some CBs affect the proliferative activity of human uterine myocytes.     

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

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. Received: 27 January 1998 / Accepted: 21 April 1998     

Nigerasperones A approximately C, new monomeric and dimeric naphtho-gamma-pyrones from a marine alga-derived endophytic fungus Aspergillus niger EN-13

Three new naphtho-gamma-pyrones, 5-hydroxy-6,8-dimethoxy-2-hydroxymethyl-4H-naphtho[2,3-b]pyran-4-one (1, nigerasperone A), 3,3'-dihydro-2,2',5,5'-tetrahy-droxy-8,8',10,10'- tetramethoxy-2,2'-dimethyl-(6',9-bi-4H-naphtho[1,2-b]pyran)-4,4'-dione (2, nigerasperone B), and 3'-hydro-2',5,5',8-tetrahydroxy-6,6',8'-trimethoxy-2,2'-dimethyl-(7,10'-bi-4H-naphtho[2,3-b]pyran)-4,4'-dione (3, nigerasperone C), together with nine related known compounds were characterized from Aspergillus niger EN-13, an endophytic fungus isolated from the marine brown alga Colpomenia sinuosa. Their structures were elucidated by detailed analysis of spectroscopic data and by comparison with literature reports. In the cytotoxic assay, these compounds did not show remarkable inhibitory effects against A549 and SMMC-7721 tumor cell lines. However, 3 and several known compounds showed weak antifungal activity against Candida albicans and moderate activity on DPPH scavenging.     

Comparative metabolism of polychlorinated biphenyls and tissue distribution of persistent metabolites in rats, hamsters, and Guinea pigs.

The present study was performed to compare the metabolite profiles of polychlorinated biphenyls (PCBs) in the liver and serum of rats, hamsters, and guinea pigs after exposure to a PCB mixture, Kanechlor 500 (100 mg/kg, i.p.). The percentage of contribution of major PCB residues in the liver 5 days after exposure indicated that nonplanar PCBs with 2,4- or 2,3,4-chlorine substitution were more abundant in the liver in the order rats (43% of total PCBs) > hamsters (20%) > guinea pigs (11%), whereas coplanar PCBs with 4-, 3,4-, or 3,4,5-chlorine substitution were predominant in guinea pigs (61%), followed by hamsters and rats (both 26%). The hepatic concentrations of methylsulfonyl metabolites (MeSO(2)-CBs) were higher in the order guinea pigs > rats > hamsters. Whereas hamsters formed minute amounts of MeSO(2)-CBs from 2,5-dichloro-substituted PCBs, guinea pigs formed higher levels of meta-MeSO(2)-CBs derived from 2,3,6-trichloro-substituted PCBs. In contrast, the serum concentrations of phenolic PCBs were higher in the order hamsters > rats > guinea pigs. Metabolites were predominated by 4-OH-2,3,5,3',4'-pentaCB (89% contribution) for rats, 3-OH-2,4,5,2',4'-pentaCB (56%) for guinea pigs, and dihydroxylated metabolites (39%) for hamsters. The reduced elimination of coplanar PCBs and the specific distribution of MeSO(2)- and phenolic PCBs may have implications for the differences in sensitivity to PCB toxicity among rats, guinea pigs, and hamsters.     

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 micrograms/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.     

Metabolism of 2,2',5,5'-tetrachlorobiphenyl: formation of mono- and bis-methyl sulphone metabolites with a selective affinity for the lung and kidney tissues in mice

1. Distribution in mice of 2,2',5,5'-tetrachloro[14C]biphenyl has been studied by autoradiography. Radioactivity was specifically localized in the bronchial epithelium, the lung parenchyma, the kidney cortex and the adipose tissue. 2. Bis(methylsulphonyl)-2,2',5,5'-tetrachlorobiphenyl, a hitherto unknown metabolite of 2,2',5,5'-tetrachlorobiphenyl, has been identified in lung, kidney and liver of mice. 3- and 4-Methylsulphonyl-2,2'5,5'-tetrachlorobiphenyl were also present. 3. The ratio of the contents of 3- and 4-methylsulphonyl-2,2',5,5'-tetrachlorobiphenyl in the liver was 1.12 after 12 days. A lower ratio in lung and kidney indicates a high affinity of these tissues for the 4-methyl isomer.     

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, 2,2′,4′,5,5′-pentachlorobiphenyl (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 1 h. 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. Received: 16 July 1997 / Accepted: 6 October 1997     

The influence of time of maternal exposure to 2,4,5,2',4',5'-hexachlorobiphenyl on its accumulation in their nursing offspring

2,4,5,2',4',5'-Hexachlorobiphenyl (6-CB) is mobilized from rodent tissues during the lipid depletion associated with food restriction or lactation, the latter condition resulting in the substantial elimination of the maternal body burden of the chemical to nursing offspring. The present study was undertaken to determine whether the rate and/or magnitude of accumulation of 6-CB in nursing offspring differed with time following PCB administration to the maternal animal. Female ICR mice were administered two doses of 6-CB. Group I animals received [14C]-6-CB as weanlings (15-20 g) followed by unlabeled 6-CB 5 weeks later, after mating, on Day 1 of gestation. Group II received unlabeled 6-CB as weanlings and [14C]-6-CB on Day 1 of gestation. Thus, 14C identified the mobilization and elimination of either the first or the second dose of 6-CB in the treatment groups (I = [14C]-6-CB, 6-CB; II = 6-CB, [14C]-6-CB). Both groups of animals retained approximately 80% of the administered radiolabeled dose. The tissue distribution of [14C]-6-CB in group II as a percentage of the body burden was not different from that in group I as determined from maternal tissue concentrations on Day 14 of gestation. The percentage of the maternal body burden of [14C]-6-CB accumulated in suckling offspring of group II mothers was significantly greater than that in group I offspring on Day 1 (I, 2.2 +/- 0.5%; II, 3.5 +/- 0.4%), Day 3 (I, 14.8 +/- 1.9%; II, 24.6 +/- 2.7%), Day 5 (I, 16.8 +/- 1.4%; II, 24.8 +/- 0.8%), and Day 12 (I, 32.3 +/- 0.5%; II, 45.5 +/- 1.7%) postpartum. This differential elimination was reflected in the t1/2 of elimination of the radiolabeled dose from parametrial fat during lactation, which was significantly longer in group I (14 days) than group II maternal animals (9 days). The observations that the last dose of 6-CB administered was the first to be mobilized from the whole animal, and that this was reflected in 6-CB release from parametrial fat, suggest that this highly lipophilic chemical is not homogeneously distributed within storage depots.     

Characterization of a binding protein for the PCB metabolite 4,4'-bis(methylsulfonyl)-2,2',5,5'-tetrachlorobiphenyl present in bronchoalveolar lavage from healthy smokers and non-smokers

Bronchoalveolar lavage (BAL) was performed in a group of healthy subjects (10 smokers and 10 non-smokers) and the recovered fluid was shown to contain specific binding sites for a metabolite of a polychlorinated biphenyl (PCB), 4,4'-bis ([3H]methylsulfonyl)-2,2',5,5'-tetrachlorobiphenyl [(3H-MeSO2)2TCB]. The sites seem to reside within a protein-like component and the apparent dissociation constant (Kd) for the binding was approximately 2 X 10(-7) M regardless of the smoking status of the subject. However, the maximum number of binding sites (Bmax) was significantly lower for the smokers (p less than 0.001). Competition studies indicated that some PCB methyl sulfones had similar affinities for the specific binding sites as (MeSO2)2TCB. Physicochemical characterization of the human (3H-MeSO2)2TCB-binding protein indicated a Stokes radius of 22 A and a sedimentation coefficient of 1.9 S, and on the basis of these parameters an apparent molecular weight of 17,700 was calculated. The binding protein had an apparent pI of 4.9. It is suggested that the specific binding protein for certain PCB methyl sulfones in bronchoalveolar lavage fluid from healthy subjects is responsible for the previously observed tendency of PCB metabolites to accumulate in human lung tissue.