Hiroaki Kuroki

Thyroid hormonal activity of the flame retardants tetrabromobisphenol A and tetrachlorobisphenol A

The thyroid hormonal-disrupting activity of the flame retardants tetrabromobisphenol A (TBBPA) and tetrachlorobisphenol A (TCBPA) was examined and compared with that of bisphenol A, a typical estrogenic xenobiotic. TBBPA and TCBPA, halogenated derivatives of bisphenol A, markedly inhibited the binding of triiodothyronine (T(3); 1 x 10(-10) M) to thyroid hormone receptor in the concentration range of 1 x 10(-6) to 1 x 10(-4) M, but bisphenol A did not. The thyroid hormonal activity of TBBPA and TCBPA was also examined using rat pituitary cell line GH3 cells, which grow and release growth hormone (GH) depending on thyroid hormone. TBBPA and TCBPA enhanced the proliferation of GH3 cells and stimulated their production of GH in the concentration range of 1 x 10(-6) to 1 x 10(-4) M, while bisphenol A was inactive. TBBPA, TCBPA, and bisphenol A did not show antagonistic action, i.e., these compounds did not inhibit the hormonal activity of T(3) to induce growth and GH production of GH3 cells. TBBPA and TCBPA, as well as bisphenol A, enhanced the proliferation of MtT/E-2 cells, whose growth is estrogen-dependent. These results suggest that TBBPA and TCBPA act as thyroid hormone agonists, as well as estrogens.

Elimination of polychlorinated dibenzofurans (PCDFs) and polychlorinated biphenyls (PCBs) from human blood in the Yusho and Yu-Cheng rice oil poisonings

The pharmacokinetics of polychlorinated dibenzofurans (PCDFs) and polychlorinated biphenyls (PCBs) in humans was studied by monitoring the blood concentrations of individuals who ingested a contaminated rice oil in Japan (yusho) in 1968 and in Taiwan (yu-cheng) in 1979. Sixteen yusho patients were followed from 1982 to 1990 and three yu-cheng individuals from 1980 to 1989. From the three yucheng patients, blood lipid values for the two persistent toxic congeners, 2,3,4,7,8-pentachlorodibenzofuran (PnCDF) and 1,2,3,4,7,8-hexachlorodibenzofuran (HxCDF), varied from 50 μg/kg at first sampling to about 1 μg/kg at last sampling corresponding to half-lives for elimination (t1/2) of 2-21/2 years. The blood lipid values for the same PCDF congeners in yusho patients varied from 5 μg/kg down to 0.1 μg/kg. The calculated t1/2 were more variable with median values closer to 10 years. Planar PCBs #126 and #169 were present at lower concentrations than the PCDFs. For seven of the other PCB congeners, half-lives for elimination in the yu-cheng individuals varied from 1.2 up to 4.6 yr depending on the degree of chlorination. For the yusho patients, the elimination for the PCBs was longer. These results show that clearance of the toxic PCDFs and PCBs in humans is non-linear with faster elimination at higher exposure followed by slower decreases as background levels are approached. Such a clearance pattern can best be explained by a two compartment liver and fat pharmacokinetic model.

Inductive effect on hepatic enzymes and acute toxicity of individual polychlorinated dibenzofuran congeners in rats

Abstract Toxicological assessment of 13 individual polychlorinated dibenzofurans (PCDFs) with varying chlorine substitutions was made in young male Wistar rats. All the 9 congeners having at least three chlorine atoms in the ring positions at 2, 3, 7 and 8, such as 1,2,7,8-, 2,3,6,7-, and 2,3,7,8-tetrachlorodibenzofurans (TCDFs), 1,2,3,7,8-, 1,2,6,7,8-, 2,3,4,7,8-pentachlorodibenzofurans (PenCDFs), 1,2,3,4,6,7- and 1,2,3,4,7,8-hexachlorodibenzofurans (HCDFs), exhibited a typical 3-methylcholanthrene (MC)-type induction, i.e., a marked increase in activity of aryl hydrocarbon hydroxylase (AHH) and DT-diaphorase in the liver. The most potent congeners were 2,3,7,8-TCDF and 2,3,4,7,8-PenCDF, both of which significantly induced the AHH and DT-diaphorase even at a single dose of 1 μg/kg. On the contrary, the congeners having two or less chlorine atoms in the lateral ring positions, such as 2,8-dichlorodibenzofuran, 1,3,6,7- and 1,3,6,8-TCDFs, and 1,2,4,6,8-PenCDF, did not show any inductive effect on these hepatic enzymes at the single dose of 5 or 10 mg/kg. All the MC-type PCDFs except for 1,2,7,8-TCDF caused a marked atrophy of the thymus and a hypertrophy of the liver in rats, while no toxic signs were observed in animals treated with the congeners lacking the MC-type inducing ability. The ranking of toxic potencies of the MC-type PCDFs coincided well with their inducing abilities. The hepatic disposition of the congeners varied markedly. For example, 2,3,7,8-TCDF and 2,3,4,7,8-PenCDF showed an equipotent toxicity, however, the hepatic concentration of PenCDF was about 20-fold higher than that of TCDF. These results clearly indicate that the acute toxicity of PCDF congeners is well correlated with their MC-type inducibility, but not with their hepatic distribution.

Comparison of causal agents in Taiwan and Fukuoka PCB poisonings

INTRODUCTION In 1968, more than 1,500 persons in western Japan were in tox ica ted by consuming a commercial r ice oil contaminated w i th Kanechlor 400 (KC-q00) , a Japanese b rand of po lych lor ina ted b ipheny ls (PCBs) (1 -2 ) . The causal oil was found to contain not only PCBs but also ve ry tox ic po lych lo r i hated d ibenzofurans (PCDFs) (3) and po lych lor ina ted qua te rpheny ls (PCQs) wi th yet unc lar i f ied tox i c i t y (4 -6 ) . In 1979, eleven years a f te r the Japanese inc ident (Yusho ) , a s imi lar mass food poisoning recu r red in the Centra l Taiwan and the pat ients to ta l led neary 2,000. The cooking oil consumed by the pat ients was also contaminated wi th PCBs, PCDFs, and PCQs (7 -9 ) . To fu l l y unders tand the e t io logy of both po ison ings, i t is necessary to inves t iga te i f the two tox ic r ice oi ls used in Japan and Taiwan contain d i f f e ren t components of PCBs and PCDFs, as PCBs and PCDFs consist of many congeners . Above al l , examinat ion of PCDF components is ve ry impor tan t , because some PCDF congeners are much more tox ic than those of PCBs (10) . We analyzed samples of r ice oil which caused the poisoning in Taiwan and the blood from the pat ients for PCB and PCDF congeners and compared these resu l ts w i th those of Japanese cases (3, 11-12). We also est imated the concent ra t ions of PCQs in both the r ice oi ls .

Synthesis and mass spectrometry of some methoxylated PCB

The syntheses of 46 methoxy-polychlorobiphenyls (MeOCBs), containing 3 to 7 chlorine atoms, are described. The MeOCBs were synthesized via the Cadogan diaryl coupling reaction of the appropriate polychloroaniline and polychloroanisole, or via the Ullmann coupling of a polychloroiodobenzene and 4-iodoanisole with subsequent chlorination of the isolated 4-MeOCB product. The synthesized MeOCBs were characterized by electron ionization (EI) mass spectrometry (MS) on an ion trap MS instrument and by EI and negative ion chemical ionization (NICI) on a quadrupole mass spectrometer. Both instruments gave similar El spectra but the fragments were in general more abundant relative to the molecular ion, in the spectra obtained from the ion trap instrument. Characteristic fragmentation patterns were obtained by El for ortho-, meta- and para-MeOCBs, respectively, depending on the position of the MeO-group, with the exception of three meta-substituted MeO-heptaCBs, with a 3-MeO-2,4,6-trichloro-substitution pattern, that gave an abundant [M-15]+-fragment, similar to para-substituted MeOCBs. MS(NICI) of ortho-, meta- and para-MeOCBs did not give any characteristic fragmentation patterns depending on the position of the MeO-group, except for ortho-substituted MeOCBs that showed abundant fragments at [M-36]−. The MS(NICI) gave approximately 10–50 times higher response for MeO-tetraCBs - MeO-heptaCBs than the MS(EI). The ion trap instrument (ITS40) has a somewhat lower detection-limit than the quadrupole MS when operated in the EI-mode.

Characterization of steroid hormone receptor activities in 100 hydroxylated polychlorinated biphenyls, including congeners identified in humans

Hydroxylated polychlorinated biphenyls (OH-PCBs), major metabolites of PCBs, have been reported to act as estrogen receptor α (ERα) agonists or antagonists. However, little concern has been paid to the ability of OH-PCBs to interfere with other steroid hormone receptors such as ERβ, androgen receptor (AR) or glucocorticoid receptor (GR). In this study, we characterized the agonistic and antagonistic activities of available 100 OH-PCBs (39 ortho-, 24 meta-, and 37 para-OH compounds), including some congeners identified in humans, against human ERα/β, AR, and GR using in vitro reporter gene assays. In the ERα assay, 45 and 9 of the 100 OH-PCBs tested showed agonistic and antagonistic activities, respectively. In the ERβ assay, 45 and 6 compounds showed agonistic and antagonistic activities, respectively. In the AR and GR assays, although none of the compounds tested showed agonistic activity, 83 and 30 of the 100 OH-PCBs showed antagonistic activity, respectively. These AR and/or GR antagonistic compounds had various patterns of substituent in the structure, while relatively potent ERα/β agonistic and antagonistic compounds possessed para- and ortho-OH structures, respectively. Three OH-PCBs, predominantly identified in human tissues, showed little ERα/β or AR activities, apart from the weak ERα and/or GR antagonistic activity observed in 4-OH-CB107 and 4-OH-CB187. Taken together, these results suggest that a large number of OH-PCBs might act as agonists and/or antagonists against ERα/β, AR and GR.

Occurrence and distribution of chlorinated aromatic methylsulfones and sulfoxides in biological samples

Abstract Methylsulfone and methylsulfoxide metabolites of chlorinated benzene (CP), chlorinated biphenyl (PCB) and dichloro(diphenyl)dichloroethene (DDE) were detected in environmental samples as well as human tissues and characterized by gas chromatography/mass spectrometry. The concentrations of PCB-methylsulfones were 9–30 ppb in human tissues, 10 ppb in whale and 4 ppb in rainbow trout, whereas PCB-methylsulfoxides were present in whale and trout at higher levels than in human tissues. CP- and DDE-methylsulfones were detected at lower levels than PCB-methylsulfones. Polychlorinated terphenyl-methylsulfones were also identified in the blood of Yusho patients.

A comparative study of polychlorinated dibenzofurans, polychlorinated biphenyls and 2,3,7,8-tetrachlorodibenzo-p-dioxin on aryl hydrocarbon hydroxylase inducing potency in rats

The aryl hydrocarbon hydroxylase (AHH) inducing potency of toxic chlorinated aromatic hydrocarbons such as polychlorinated dibenzofurans (PCDFs), polychlorinated biphenyls (PCBs) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was studied in the young male Wistar rats. Alternatively, a technical PCDF mixture, 15 individual PCDF isomers or TCDD were administered i.p. in doses of 5 μg/kg; a PCB mixture was given in a dose of 50 mg/kg. The order of AHH inducing ability was TCDD > PCDFs ≫ PCBs in kidney, lung, and liver. In the prostate, thymus, and spleen, only TCDD enhanced the AHH activity. The AHH inducibility in the lung and liver, induced by 15 pure PCDF isomers with varying chlorine substitutions was also examined. Only 2,3,7,8-tetrachlorodibenzofuran (2,3,7,8-tetra-CDF) and 2,3,4,7,8-pentachlorodibenzofurans (2,3,4,7,8-penta-CDF) significantly induced the hepatic AHH activity (4- and 2-fold, respectively), while eight PCDF isomers, including these two, significantly enhanced the pulmonary AHH activity (6- to 30-fold). Taking into account both the potent AHH inducibility and the high bioaccumulation of these compounds, 2,3,7,8-tetra- and 2,3,4,7,8-penta-CDF should be given due attention with regard to environmental-related factors and the possibility of involvement in the etiology of “Yusho” disease.

Synthesis of polychlorinated dibenzofuran isomers and their gas chromatographic profiles

Abstract Fifty-one polychlorinated dibenzofuran (PCDF) isomers were synthesized by the structure specific methods starting from corresponding chlorophenol and chloronitrobenzene or chlorophenol and chlorodiphenyl iodonium salt. Structures of the synthesized PCDF isomers were confirmed by mass spectrometry and proton magnetic resonance spectroscopy. Gas chromatographic retention times and response factors of the PCDF isomers were determined on the fused silica capillary columns of SP-2330 and OV-101.

Selectivity of electron-donor- and electron-acceptor-bonded silica packing materials for hydrophobic environmental contaminants in polar and non-polar eluents

Electron-acceptor-bonded stationary phases, 2-(nitrophenyl)ethylsilyl (NPE) and 3-(p-nitrophenoxy)propylsilyl (NPO), and electron-donor-bonded phases, 3-(N-carbazolyl)propylsilyl (CZP), 2-(1-pyrenyl)ethylsilyl (PYE), and 5-coronenylpentylsilyl (COP), were prepared from silica particles and their selectivities were examined in both polar and non-polar solvents for specific isomers of polychlorodibenzo-p-dioxins (PCDDs), hexachloronaphthalenes (HxCNs) and planar and non-planar polychlorobiphenyl (PCB) congeners. Although no single stationary phase was able to separate all the isomer pairs that are coproduced during the synthesis of the PCDDs and HxCNs, pairs can be separated by selecting a suitable stationary phase and solvent. The separation of mixtures of PCDD isomers were found to be most successful with PYE and NPO phases, which yielded the opposite elution orders for each isomer pair that is produced as a mixture. Similar results were obtained for the HxCN isomers that were separated on PYE and CZP phases. The COP phase provided easier separation of non-ortho-substituted and mono-ortho-substituted PCBs from the other PCBs based on the planarity than PYE phase.