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.

Prediction of drug-induced catalepsy based on dopamine D1, D2, and muscarinic acetylcholine receptor occupancies

It is known that catalepsy serves as an experimental animal model of parkinsonism. In this study, the relationship between in vivo dopamine D1 and D2 receptor occupancies and catalepsy was investigated to predict the intensity of catalepsy induced by drugs that bind to D1 and D2 receptors nonselectively. 3H-SCH23390 and 3H-raclopride were used for the labeling of D1 and D2 receptors, respectively. The ternary complex model consisting of agonist or antagonist, receptor, and transducer was developed, and the dynamic parameters were determined. After coadministration of SCH23390 and nemonapride, catalepsy was stronger than sum of the values predicted by single administration of each drug, and it was intensified synergistically. This finding suggested the existence of interaction between D1 and D2 receptors, and the necessity for constructing the model including this interaction. To examine the validity of this model, catalepsy and in vivo dopamine receptor occupancy were measured after administration of drugs that induce or have a possibility to induce parkinsonism (haloperidol, flunarizine, manidipine, oxatomide, hydroxyzine, meclizine, and homochlorcycilzine). All of the tested drugs blocked both dopamine D1 and D2 receptors. Intensity of catalepsy was predicted with this dynamic model and was compared with the observed values. In contrast with haloperidol, flunarizine, manidipine, and oxatomide (which induced catalepsy), hydroxyzine, meclizine, and homochlorcyclizine failed to induce catalepsy. Intensities of catalepsy predicted with this dynamic model considering the interaction between D1 and D2 receptors overestimated the observed values, suggesting that these drugs have catalepsy-reducing properties as well. Because muscarinic acetylcholine (mACh) receptor antagonists inhibit the induction of catalepsy, the anticholinergic activities of the drugs were investigated. After SCH23390, nemonapride and scopolamine were administered simultaneously; catalepsy and in vivo mACh receptor occupancy were measured to evaluate quantitatively the anticholinergic activity. Relationship between mACh receptor occupancy and change in catalepsy was used as the measure of catalepsy-reducing effects of the drugs. Measurement of in vivo mACh receptor occupancy revealed a significant blockade of mACh receptor by all of the tested drugs except for haloperidol. The predicted values of catalepsy, when corrected for the mACh receptor-related reduction, approached the observed values. This finding indicates the possibility that mACh receptor antagonism of drugs may contribute to the reduction of catalepsy. In conclusion, the dynamic model considering D1, D2, and mACh receptor occupancies and synergism between D1 and D2 receptors may be useful for quantitative prediction of drug-induced catalepsy.

[Tissue distribution of methylsulfonyl metabolites derived from Kanechlor 400 in mice]

Kanechlor 400, which caused the "Yusho disease", was i.p. administered to mice and methylsulfonyl (MeSO2) metabolites were investigated with respect to the concentration in liver and lung during 28 days after the administration. Major components were 3- and 4-MeSO2 derivatives from seven PCBs (IUPAC no. #31, #49, #64, #70, #101, #110, #132). In the liver, similar concentration ratio of 3- and 4-MeSO2 derivatives was observed, whereas seven 4-MeSO2 derivatives were selectively retained in the lung. Methylsulfone metabolites of triCB (#31) were rapidly formed and eliminated. The highest concentration of the metabolites in the lung was 4-MeSO2-2, 2', 4', 5-tetraCB. Concentration ratio of MeSO2-CBs to residual PCBs was 1:2.1 in the liver whereas 4.6:1 in the lung 28 days after the administration.

[The condition of PCBs and PCDFs in the blood of Yusho patients 20 years after the onset]

Blood samples of Yusho and control persons were analyzed for individual congeners of PCDDs, PCDFs, and PCBs by high resolution GC/MS. Concentrations of 2,3,4,7,8-penta-CDF, 1,2,3,4,7,8-hexa-CDF and 2,3,3',4,4',5-hexa-CB in Yusho blood were up to 56 times higher than the corresponding concentrations in the control blood. These high concentrations have persisted for 23 years after the incident. Concentrations of 3,3',4,4',5-penta-CB and 2,3',4,4',5-penta-CB in some Yusho blood were lower than the control blood. In Yusho blood, 2,3,4,7,8-penta-CDF contributed the highest toxicity (TEQ 77-248 ppt in lipid) among the congeners determined and toxic contribution of PCDFs was very large (41-77%) in the chlorinated pollutants. Thirty PCB congeners were identified in the blood of Yusho patients in 1996 by GC/MS. The average total PCB concentration in Yusho blood were 4.9 times higher than that of the controls. Characteristic PCB congeners in Yusho patients were 2,2',3,4,4',5-hexa-CB, 2,3,3',4,4',5-hexa-CB and 2,3,3',4,4',5'-hexa-CB and their concentration ratios to the controls were 8-19.

Regulation of thyrotropin receptor gene expression in 3T3-L1 adipose cells is distinct from its regulation in FRTL-5 thyroid cells

We previously have demonstrated that rat adipose tissue expresses TSH receptor (TSHR) messenger RNAs (mRNAs) at levels approaching those detected in the thyroid. Furthermore, we recently reported that TSHR mRNA is detected in fibroblast-like 3T3-L1 cells after their hormone-induced differentiation into adipocytes. TSH induces cAMP formation and lipolysis in differentiated 3T3-L1 cells. We now show that, in Northern blot analyses, TSH-induced down-regulation of TSHR mRNA levels, which can be duplicated by forskolin and dibutylyl cAMP, i.e. which is cAMP-mediated. We also have demonstrated that a beta-adrenergic stimulant, which stimulates cAMP formation in adipocytes, induces a down-regulation of TSHR mRNA levels in 3T3-L1 adipocytes. Nuclear run-on assays show that the ability of TSH/cAMP to decrease TSHR mRNA levels in 3T3-L1 cells reflects transcriptional regulation. This report also demonstrates that TSHR gene expression in 3T3-L1 adipocytes is regulated in a manner distinct from that observed in thyroid cells. Thus, in fully differentiated 3T3-L1 adipocytes, TSH-induced down-regulation of TSHR mRNA levels is evident within 1 h and is near maximum within 4 h after addition of TSH. A transient increase of TSHR gene expression, which has been demonstrated in FRTL-5 thyroid cells, was not observed in 3T3-L1 adipocytes. The down-regulation of TSHR gene expression induced by TSH/cAMP in 3T3-L1 cells is cycloheximide-insensitive, suggesting that continuous protein synthesis is not required for this process. In contrast, the down-regulation of TSHR gene expression observed in FRTL-5 cells is sensitive to cycloheximide. In both FRTL-5 thyroid cells and 3T3-L1 adipocytes, insulin or serum increased TSHR mRNA levels. Although insulin or serum was required for the TSH-induced down-regulation of TSHR mRNA levels in FRTL-5 thyroid cells, neither insulin nor serum was required for TSHR down-regulation in 3T3-L1 adipocytes. These findings demonstrate that TSH/cAMP regulates TSHR mRNA levels in adipocytes via a regulatory system distinct from that used in FRTL-5 cells. This report further demonstrates that adipose cells do not express thyroid transcription factor-1, which interacts with the TSHR promoter region in FRTL-5 cells, and that 3T3-L1 nuclear extracts exhibit a different binding activity to the cAMP-response element-like element in the TSHR promoter region compared with extracts from FRTL-5 cells.

Socioeconomic factors and dental caries in developing countries: a cross-national study

The purpose of the present study was to analyze statistically correlations between socioeconomic factors and the prevalence of dental caries in developing countries. The DMFT index, which evaluates the incidence of dental caries, showed a positive correlation (P < 0.01) with several socioeconomic factors, such as life expectancy, adult literacy rate, school attendance rate, population employed in the service sector, population aged 15-64 years, and urban population. According to multiple regression analysis, population aged 15-64 years, population employed in the service sector, and urban population were the most influential independent socioeconomic variables, in descending order, with a regression coefficient of 0.635 and a coefficient of determination of 0.404 (P < 0.001). This finding suggests that the prevalence of dental caries in developing countries increases with the degree of urbanization.

Differentiation of rat preadipocytes is accompanied by expression of thyrotropin receptors

To investigate the regulation of expression of the TSH receptor (TSHR) in extrathyroidal tissues, the level of TSHR messenger RNA (mRNA) and TSH-dependent signal transduction were determined in isolated rat adipocytes and cultured preadipocytes. The epididymal, sc, and perirenal, but not the interscapular brown adipose tissues, possessed TSHR mRNA and increased cAMP responses to TSH and were thus used as the source of preadipocytes. Morphological analysis revealed that the combination of insulin and T3 most effectively caused the differentiation of rat preadipocytes. These differentiated preadipocytes exhibited increased cAMP production in response to TSH. The addition of FCS to the culture medium inhibited the differentiation of rat preadipocytes as well as TSH-stimulated production of cAMP. The stimulation of differentiation was associated with an increased expression of TSHR mRNA levels, whereas the inhibition of differentiation was associated with a decreased expression of TSHR mRNA, as detected by Northern blot analysis. The results indicate that the expression and function of the TSHR in cultured rat preadipocytes are closely related to cellular differentiation. Cultured rat preadipocytes appear to provide a useful system for studying the mechanism of extrathyroidal expression of TSHR.

Functional expression of thyrotropin receptor in differentiated 3T3-L1 cells: a possible model cell line of extrathyroidal expression of thyrotropin receptor

Thyrotropin receptor (TSHR) in extrathyroidal tissue, especially fat tissue, is supposed to have important roles in the development of extrathyroidal manifestations of Graves' disease. However, the molecular mechanism of TSHR expression is not known. Expression of TSHR mRNA and TSH-dependent cAMP production were observed in differentiated but not in undifferentiated 3T3-L1 cells. Maximal expression was obtained when the cells were differentiated in the presence of insulin, dexamethasone, and isobutylmethylxanthine (IBMX). Dexamethasone and IBMX were indispensable for the first three days. On the other hand, after day 4, insulin was indispensable for the expression of TSHR. 3T3-L1 cell is the first non-thyroidal cell line reported that expresses TSHR and whose expression can be induced. 3T3-L1 cell can be a good model to investigate the mechanism of expression of TSHR and extrathyroidal manifestations of Graves' disease.

Catalepsy induced by manidipine, a calcium channel blocker, in mice

Manidipine, a calcium channel blocker, is a piperazine derivative similar to flunarizine or cinnarizine, which are known to induce parkinsonism. Since it has been reported that manidipine can worsen parkinsonian symptoms in a patient with Parkinson's disease, we have evaluated catalepsy in manidipine-treated mice and compared this with flunarizine-and haloperidol-induced catalepsy. The minimum dose at which manidipine induced catalepsy was 200 times higher than that of haloperidol whereas for flunarizine, the minimum dose was 50 times higher than that for haloperidol. Manidipine, flunarizine and haloperidol occupied both dopamine D1 and D2 receptors and D2-receptor occupancy was higher than D1-receptor occupancy. These results suggest that the blockade of dopamine D1 and D2 receptors by drugs and the drug-induced catalepsy are related to the structure (piperazinyl substituent) of the drugs.

A case of calcification of the cervical ligamentum flavum

We report a case of cervical myelopathy caused by the calcification of the cervical ligamentum flavum. A 42-year-old woman with gait disturbance and an episode of dysuria was transferred to our hospital on June 30, 1994. Neurological examination revealed only a mild right hemiparesis. A plain neck X-ray and a tomogram revealed a nodular calcification in the posterior part of the spinal canal at the level of C5/6. Three dimensional computed tomography clearly demonstrated that the mass consisted of three nodular structures on the vertebral lamina. Magnetic resonance images demonstrated severe compression of the spinal cord by the mass whose intensity was low. The mass was removed en bloc together with the ligamentum flavum and C5 and C6 lamina. The mass showed no continuity to the dura mater. The calcification was confined within the ligament. The patient's neurological deficits were resolved two weeks after the surgery. X-ray diffraction study demonstrated the component of the mass was found to be pure hydroxyapatite. Clinical features of calcification of the ligamentum flavum are reviewed from 85 reported cases including ours, and the difference between this calcification and the ossification of the ligament is emphasized. Calcification of the ligamentum flaum is a distinct clinical entity.

Cloning and nucleotide sequence of the inulin fructotransferase (DFA I-producing) gene of Arthrobacter globiformis S14-3

A gene encoding an inulin fructotransferase (DFA I-producing) [EC 2.4.1.200] from Arthrobacter globiformis S14-3 was cloned and the nucleotides sequenced, for the first time. The sequence indicated that the native enzyme protein is composed of 392 amino acid residues. The native enzyme is an extracellar enzyme produced in the culture supernatant of A. globiformis S14-3, but the nucleotide sequence of the gene lacks a sequence for signal peptide for secretion. The 1.5-kb DNA fragment encoding the gene was found to produce the active enzyme in the culture supernatant of an E. coli clone, under the control of the lac promoter of pUC119.

The functional significance of the second extracellular loop of thyrotropin receptor in thyrotropin- and thyroid stimulating antibody-dependent signal transduction

In order to determine the functional significance of the extracellular loop of human thyrotropin receptor (hTSHR), two peptides composed of eight amino acids were inserted into hTSHR by ligating synthetic oligonucleotides into +1811 NCol site of hTSHR cDNA. Mutant hTSHR cDNAs which encode a hydrophobic peptide (ATVLVVPM) and a hydrophilic peptide (GTTRTVAM) between +572 Met and +573 Asp were transfected into Chinese hamster ovary (CHO) cells to develop F-cell lines and R-cell lines, respectively. Of the resulting cloned cell lines, F-29 and R-9 were shown to express mutant hTSHs at the protein level by Western blotting and at the mRNA level by reverse transcription-polymerase chain reaction (RT-PCR). We show that neither thyrotropin (TSH) nor IgGs from patients with Graves' disease stimulated cAMP production by F-29 and R-9 cells. 125I-TSH binding study revealed that F-29 and R-9 cells do not bind TSH. Our data demonstrate that the mutations impaired TSH-binding and incapacitated the cells from responding to TSH. The evidence suggests that the second extracellular loop of hTSHR has an important role in TSH and thyroid stimulating antibody (TSAb)-dependent signal transduction.

Cloning and functional expression of a thyrotropin receptor cDNA from rat fat cells

Thyrotropin receptor (TSH-R) has been thought to be thyroid-specific, but, by Northern blot analysis, we found that rat adipose tissue expressed TSH-R mRNAs in amounts approaching those in the thyroid. To investigate the function of TSH-R from adipose tissue, we screened a rat fat cell lambda gt11 cDNA library for TSH-R sequences using a 32P-labeled rat thyroid TSH-R cDNA as a probe. Among 10(6) plaques, we obtained four positive clones. Sequencing of these cDNAs has revealed that two of them (F alpha and F beta) contained both initiation and termination codons. Comparison of F alpha with the thyroid TSH-R cDNA sequence revealed that F alpha was almost identical to the thyroid TSH-R, except that nucleotides 1041 and 1277 were changed from A to G and from C to T, respectively. In contrast, we found that F beta contained 21 novel nucleotides between nucleotides 467 and 468 of the thyroid TSH-R cDNA, encoding an additional 7 amino acids. However, when we prepared mRNA from adipose tissue and transcribed it into cDNA, we failed to amplify the F beta type of TSH-R cDNA by polymerase chain reaction, suggesting that F beta mRNAs are rare in the tissue. We then ligated F cDNAs into pSG5 and transfected them with pSV2-neo into Chinese hamster ovary (CHO)-K1 cells. TSH stimulated cAMP formation in CHO-F alpha cells in a manner similar to that in CHO cells transfected with thyroid TSH-R cDNA. In contrast, no increase of cAMP was observed in CHO-F beta cells. IgG from patients with Graves' disease (n = 4) showed thyroid-stimulating antibody activity only in CHO-F alpha cells (1288-4582%). In addition, CHO-F alpha cells and CHO cells transfected with thyroid TSH-R showed similar 125I-TSH binding activity. These results indicate that the fat cell expresses high levels of a TSH-R whose function is indistinguishable from that in the thyroid and suggest that the TSH-R autoantibody plays an important role in the pathogenesis of the extrathyroidal manifestations of Graves' disease.

Effect of 2, 3, 4, 7, 8-pentachlorodibenzofuran and its analogues on induction of sister chromatid exchanges in cultured human lymphocytes

We have been already contaminated with various chemicals including highly toxic organochlorine compounds such as 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD), 2, 3, 4, 7, 8-pentachlorodibenzofuran (PenCDF) and 3, 4, 5, 3', 4'-pentachlorobiphenyl (Co-PenCB). In this study, in order to evaluate the genotoxicity of the three chemicals, we have examined their effects on the induction of sister chromatid exchanges (SCEs), which has been frequently utilized as an indicator of biological and genetic damage due to exposure to carcinogens or mutagens, in cultured human lymphocytes in the absence or presence of 7, 8-benzoflavone (ANF) and the following results were obtained. 1) TCDD, PenCDF and Co-PenCB significantly increased the frequency of SCEs with almost the same dose-dependent manner in terms of the concentration of TCDD toxic equivalent. 2) 8 x 10(-5) MANF significantly enhanced the frequency of SCEs and the simultaneous treatment of ANF and either of TCDD, PenCDF or Co-PenCB seemed to exert an additive effect as SCEs inducer. 3) TCDD, PenCDF and Co-PenCB were considered to be very potent inducers of SCEs, because their 50% effective concentration in SCEs enhancement were only 5 to 10 times higher than the level of the adipose tissue in healthy Japanese, namely, 70ppt as TCDD. Consequently, the respective TCDD toxic equivalency factors of 0.5 and 0.2 for PenCDF and Co-PenCB seemed to be reasonable so far as the induction of SCEs was employed as an indicator of the genotoxic potency.(ABSTRACT TRUNCATED AT 250 WORDS)

[Change of PCDF and PCB concentrations in the blood of Yucheng and Yusho patients for 25 years]

The blood samples of 3 Yucheng patients collected 6-7 times from 1980 to 1993 and 5 Yusho patients collected 6-8 times from 1982 to 1993 were analyzed for congeners of polychlorinated dibenzofurans (PCDF) and polychlorinated biphenyls (PCB) by high resolution gas chromatography-mass spectrometry and gas chromatography-electron capture detection. In the blood of Yucheng patients, the high concentrations of 3 PCDF congeners, 2,3',4, 4',5-penta-CB and 5 PCB congeners were eliminated at half-lives of 2.4-2.9, 1.7 and 4.1-6.1 years, respectively, while in Yusho patients, 14 years after the incident, their half-lives were converted to longer times as observed 3.2-13.4, 24.0 and 13.7-34.2 years, respectively. In the same Yucheng and Yusho patients, the half-lives of the 5 PCB congeners were about twice longer than those of the 3 PCDF congeners. PCBs are more retainable than PCDFs in human blood.

[Tissue retention of hydroxy and methylsulfonyl metabolites of 2, 2', 4, 4'-tetrachlorobiphenyl in rats]

Previously, we have identified a large number of methylsulfonyl metabolites in tissues of mink treated with Clophen A50. Most of them were found to be derived from CBs with a 2, 5-dichlorophenyl or a 2, 3, 6-trichlorophenyl ring. It is further necessary to investigate if CBs with a 2, 4-dichlorophenyl ring could be biotransformed to the sulfur-containing metabolites in animals. In the present study, 2, 2', 4, 4'-tetrachlorobiphenyl (TCB) was administered i.p. to rats, and liver, lung, kidney, adipose tissue and blood were analyzed for the unchanged CB and its metabolites. Both hydroxy and methylsulfonyl metabolites were detected in all tissues analyzed. Major metabolites were identified as 3-OH-2, 2', 4, 4'-TCB, 5-5-OH-2, 2', 4, 4'-TCB, 5-MeSO(2)-2, 2', 4, 4'-TCB and 6-MeSO(2)-2, 2', 4, 4'-TCB. Total level of the four metabolites was estimated to be 1.5 micrograms/g wet weight in the liver, corresponding to similar level of the unchanged CB. The concentration ratios of 3-OH- to 5-OH-TCB and 5-MeSO2- to 6-MeSO(2)-TCB were about 2:3 and 2:1, respectively, in liver and kidney. These results indicate that CBs with a 2, 4-dichlorophenyl ring can provide both hydroxy and methylsulfonyl metabolites that are retainable in tissues of rats.

Influence of five methylsulphonyl PCB congeners on frequency of micronucleated cells in cultured human lymphocytes by cytokinesis block method

The lungs and blood of Yusho patients and healthy Japanese people have already been contaminated with methylsulphonyl polychlorinated biphenyls (MSF-PCBs) at relatively high concentration. Therefore, we should give due attention to their biological and toxicological effects to man. In this study, in order to mainly evaluate non-S-dependent genotoxicity of five MSF-PCB congeners, namely, 3-MSF-4, 5, 3', 4'-tetrachlorobiphenyl (TCB), 3-MSF-4, 5, 2', 3'-TCB, 3-MSF-2, 5, 2', 4', 5'-pentachlorobiphenyl (PenCB), 4-MSF-2, 5, 2', 3', 4'-PenCB and 4-MSF-2, 5, 2', 3', 5', 6'-hexachlorobiphenyl (HCB). We have examined their effects on the induction of micronucleated cells, which has been frequently used to estimate the dose of ionizing radiation and truly radiomimetic, non-S-dependent, clastogens, in cultured human lymphocytes in the absence or presence of 2, 3, 4, 7, 8-pentachlorodibenzofuran (PenCDF), 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD) or 3, 4, 5, 3', 4'-pentachlorobiphenyl (Co-PenCB). The following results were obtained. 1) 4 x 10(-5) M7, 8-benzoflavone (ANF) significantly enhanced the frequency of micronucleated cells and all of the five MSF-PCB congeners failed to induce the formation of micronucleated cells at doses of 5.2 to 9.6 ppm, which were about 35,000 times higher than the concentrations in the lungs and adipose tissue of healthy Japanese people.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

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.

Desensitization to somatostatin analogue (Octreotide) observed in a patient with acromegaly

We encountered a 33-year-old female patient with a pituitary growth hormone (GH)-secreting macroadenoma. The patient was treated with somatostatin analogue (Octreotide) in combination with bromocriptine for 2 months before a transsphenoidal adenomectomy was carried out. Octreotide (300-800 micrograms/day) in combination with bromocriptine was effective in reducing the size of the adenoma by 36%, but produced only a marginal decrease in serum GH. After the operation, bromocriptine alone (15 mg/day) did not lower the level of GH which was produced by residual adenoma tissue. When octreotide (200 micrograms/day) was resumed along with the bromocriptine one year after the operation, it effectively lowered serum GH for 6 months. Thereafter, octreotide therapy became ineffective with a concomitant rise in serum GH and somatomedin C, which was not accompanied by an increase in tumor size. This was a rare case of acromegaly that showed desensitization to octreotide after long-term treatment.

Desensitization and internalization of a thyrotrophin receptor lacking the cytoplasmic carboxy-terminal region

To understand the functional significance of the carboxy-terminal half of the intracellular region of the human TSH receptor (hTSHR), a mutant hTSHR lacking amino acids from the carboxy-terminal to His726 was constructed. Wild type hTSHR cDNA and truncated hTSHR cDNA were subcloned into a eukaryotic expression vector, pRc/CMV, and transfected into Chinese hamster ovary cells to obtain cell lines which stably expressed hTSHRs at high levels. This allowed us to observe highly efficient coupling of hTSHR and adenylyl cyclase as well as desensitization and internalization of hTSHR. Despite the differences in potential phosphorylation sites and internalization signals, dose-dependent stimulation of adenylyl cyclase by TSH, TSH-dependent desensitization and the rate of hTSHR internalization were similar for wild type and truncated hTSHRs. We conclude that the carboxy-terminal half of the intracellular region of hTSHR does not have a major functional role in TSH-dependent signal transduction.

Structure of the rat thyroid transcription factor-1 (TTF-1) gene

TTF-1 is a homeodomain-containing thyroid transcription factor which activates the genes of thyroid specific protein, thyroglobulin, thyroid peroxidase and thyrotropin receptor. We have cloned the TTF-1 gene from rat liver genomic library, and the exon/intron organization and the structure of the 5' flanking region were determined. The clone contained the 5.2 kbp upstream sequence from translation initiation site, and we found that the gene has a single intron in the coding sequence. We found in the 5' flanking region the TTF-1 binding consensus sequence, CTCAAGC, at -175 to -169, which overlaps the consensus sequence of CAAT box, DNase I foot print analysis has revealed that the region is protected by nuclear extract from thyroid cells but not by the extract from the liver, suggesting that expression of the TTF-1 gene is autoregulated by TTF-1.

[The structure and function of the extracellular domain of human thyrotropin receptor]

Since the molecular cloning of human TSH receptor (TSHR), much efforts have been focused on determining the TSH or TSAb binding sites. Despite many conflicting data, there seems to be a consensus that TSH binds to the various parts of the extracellular domain of TSHR discontinuously. However, following questions are not yet answered 1) Is the binding to extracellular domain of TSHR sufficient to the signal transduction? 2) Is there any contribution of the extracellular loops to TSH binding? Using TSHR mutated at the first or the second extracellular loops, we propose that the extracellular loops are important for TSH binding and signal transduction.