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Biomedical subjects

N Nemoto

Publications and source records attributed to N Nemoto.

At least 109 records · Page 6Linked to original sources
PubMed1990

Acquisition of aryl hydrocarbon hydroxylase inducibility by aromatic hydrocarbons in monolayer-cultured hepatocytes from nonresponsive mouse strains.

The expression of P1450 and P3450 genes isolated from C57BL26 mouse liver in mouse hepatocytes from responsive (BALB/c, C3H/He, C57BL/6, and CBA) and nonresponsive (AKR, DBA/2, NZB, and NZW) strains in primary culture after exposure to aromatic hydrocarbons was investigated with respect to aryl hydrocarbon hydroxylase (AHH) activity and corresponding P450 transcript levels. Constitutive AHH activity in all strains decreased with an increasing culture period. The AHH activity of cells treated with either benz(a)anthracene, benzo(a)pyrene, 3-methylcholanthrene, or TCDD continuously or 24 h before harvesting was measured during observation periods for up to 5 days. Slight induction of AHH activity by benz(a)anthracene, benzo(a)pyrene, and 3-methylcholanthrene was observed in hepatocytes from the CBA and C3H/He strains during the first half of the observation period, followed by a steep increase thereafter. Enzyme activities in hepatocytes from BALB/c mice were the same as or lower than the control values during the first half of the observation period, and in the C57BL/6 mouse high levels of AHH activities were observed even during this period. AHH activities in hepatocytes from the AKR, DBA/2, NZB, and NZW mice after treatment with aromatic hydrocarbons were lower than control levels during the first half of the observation period; however, significant induction was observed thereafter. P450 transcripts including both P1450 and P3450 RNA species were detected when the treatment was started during the early incubation period, whereas only P1450 RNA was found at the later periods. The amounts of P1450 transcript also correlated well with AHH activity, higher levels being found after starting treatment with benz(a)anthracene at day 3 or 4 than at day 1. Our observations indicate that, although AHH induction was genetically determined in each strain, activity can be induced in hepatocytes of so-called nonresponsive as well as responsive mouse strains by treatment with aromatic hydrocarbons after transfer of the cells to primary culture.

Animals↗
PubMed1989

Proline-dependent expression of aryl hydrocarbon hydroxylase in C57BL/6 mouse hepatocytes in primary culture.

Induction of aryl hydrocarbon hydroxylase (AHH) was studied in mouse hepatocytes in primary culture and compared with that in rat hepatocytes. Enzyme activity in hepatocytes from C57BL/6 mice was found to increase dose dependently after treatment with benz(a)anthracene. However, the induction was strictly dependent on culture medium. Although appreciable levels of AHH activity were inducible in Sprague-Dawley rat hepatocytes cultivated in either Dulbecco's minimal essential medium (DMEM) or Waymouth's medium, C57BL/6 mouse cells cultivated in DMEM responded to the inducer only very slightly, whereas those in Waymouth's or Ham's F-12 medium demonstrated a marked increase. Proline, but not glutamic acid or cysteine, all of which were lacking in DMEM but present in Waymouth's and Ham's F-12 medium, restored the potential for response to the cells in DMEM. While increased amounts of P450 mRNA in C57BL/6 cells cultivated in DMEM were transient and decreased after a peak observed at 24 h, levels of mRNA in Waymouth continued to demonstrate an increase at 48 h. Addition of proline to mouse hepatocytes in DMEM increased the generation of transcripts without, however, influencing the decrease observed from 24 h to 48 h. Timing of treatment with benz(a)anthracene and incubation in Waymouth greatly influenced the eventual AHH activity. Thus, while enzyme activities measured at 48 h were in the same range after treatment with benz(a)anthracene for either the whole period or only for the initial 24 h, and prominent induction was observed with cells in Waymouth for 24 to 48 h regardless of whether they were at first cultivated in DMEM or Waymouth, levels remained low if the cells were incubated in DMEM during the 24- to 48-h period. These observations suggest that induction of AHH in mouse hepatocytes is regulated by both transcriptional and posttranscriptional events and that proline-dependent events are required for expression of the enzyme activity.

Animals↗
PubMed1988

Immunohistochemical detection of anti-(+/-)-trans-7,8-dihydroxy-9,10-epoxy-7,8,9,10-tetrahydrobenzo(a)p yrene-bound adduct in nuclei of cultured HeLa cells and mouse lung tissue.

Rabbit IgG against anti-BP-DE-modified calf thymus DNA was characterized and utilized for detection of adducts formed in cultured HeLa cells treated with anti-BP-DE or in lung tissues from mice given BP. Four weekly treatments with 1 mg of the modified (1.2% of total nucleotides) DNA were used to raise the rabbit antiserum, which even at 10(6)-fold dilution clearly recognized adducts in an ELISA. The detection limit was 25 fmol of anti-BP-DE adduct with 10(3)-fold diluted IgG fraction. The IgG did not cross-react with BP, BP tetraol, guanine, or 7-methyl-guanine, and only slightly with the syn form of BP-DE, (+/-)-4,5-dihydrobenzo(a)-pyrene-4,5-epoxide, aflatoxin B1, and N-methyl-N-nitrosourea-modified DNA. Although syn-BP-DE-modified DNA inhibited the reaction between IgG and anti-BP-DE adduct, the inhibition rate was low, not correlating with the numbers of modified bases. Essentially similar values for level of bound adducts in HeLa cells treated with anti-BP-DE were generated by both ELISA and associated radioactivity derived from anti-3H-BP-DE. Immunohistochemical detection of adduct formation was dependent on the amounts of anti-BP-DE added to the culture medium of HeLa cells. Similar positive binding was obtained in mouse lung alveolar cell nuclei after intragastric administration of BP. These observations indicate that the prepared IgG is highly specific for anti-BP-DE-modified DNA and that should prove useful for detection of adducts formed in tissue samples exposed to anti-BP-DE or BP.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗
PubMed1988

Elevation of polycyclic aromatic hydrocarbon-inducible aryl hydrocarbon hydroxylase activity in rat hepatocytes in primary culture by inhibitors of poly(ADP-ribose) polymerase.

Induction of aryl hydrocarbon hydroxylase (AHH) activity was studied in primary cultures of rat hepatocytes. AHH activity was induced by treatment with benz[a]anthracene and combined treatment with cycloheximide for an initial short period during the induction enhanced benz[a]anthracene-inducible AHH activity. The enhancement was correlated to amounts of cytochrome P-450 RNA, indicating that cycloheximide treatment increased transcription of benz[a]anthracene-inducible cytochrome P-450 gene species. 3-Methoxybenzamide and 3-aminobenzamide, known to be physiologically specific inhibitors for poly(ADP-ribose) polymerase, but not the structurally related non-inhibitor, 3-aminobenzoic acid, also increased benz[a]anthracene-induced AHH activity. In addition, 3-methoxybenzamide was found to further increase the enhancing effects of cycloheximide on benz[a]anthracene induction of AHH. The effects of poly(ADP-ribose) polymerase inhibitors were not mediated by reduction of cyclic nucleotide phosphodiesterase activity. This was in clear contrast to the situation with the xanthine derivative, aminophylline, which also brought about a similar enhancement of AHH induction by benz[a]anthracene. The results suggest the participation of poly(ADP-ribose) in the regulation of expression of benz[a]anthracene-inducible cytochrome P-450 genes.

Aminophylline↗
PubMed1987

Nucleotide sequence comparison of the predicted first exonic region of goldfish ras gene between normal and neoplastic tissues.

The first exonic and its flanking regions of a ras-related gene in cultured erythrophoroma cells and normal liver of goldfish (Carassius auratus) were sequenced and their sequences compared. The two samples demonstrated identical sequences for the Alu I fragment of 245 nucleotides, of which 70 nucleotides might correspond to the 5'-upstream segment and 64 to the first intervening sequence, indicating that the predicted exonic region encodes from the 1st to the 37th amino acids from the N-terminal of mammalian ras protein. The length of the predicted first exon of goldfish was the same as that of mammals. There was a 5 nucleotide difference in this exonic region (length 111 nucleotides) from another previously determined ras-related sequence of normal goldfish. This difference was much smaller than that between any two of the three mammalian ras genes. Enhanced expression of ras gene was observed in erythrophoroma cells, although it was uncertain which ras gene was responsible for generation of the observed RNA.

Animals↗
PubMed1987

O6-methylguanine DNA methyltransferase activity in liver from various fish species.

O6-Methylguanine DNA methyltransferase (O6-MT) is considered to play an important role in the repair of alkylating carcinogen-induced lesions in a wide range of mammalian species. Fish are used widely in cancer research, one advantage being their high sensitivity to a variety of alkylating agents. To throw light on the mechanisms of DNA repair in the hitherto uninvestigated fish group, O6-MT activity was measured in liver from eight fish species belonging to six classes. Levels of O6-MT activity comparable with mouse values were found in liver of Japanese medaka (Oryzias latipes). Relatively low, but appreciable, levels of O6-MT activity were also observed in the other seven species examined. No adaptive increase in enzyme activity could be established in liver of rainbow trout following chronic dimethylnitrosamine pretreatment.

Animals↗
PubMed1987

Inter-individual variations of arylhydrocarbon-hydroxylase activity in cultured human epidermal and dermal cells.

Arylhydrocarbon hydroxylase (AHH) activity was determined in cultured human epidermal and dermal cells with and without induction by benz[a]anthracene (BA). Large inter-individual variations were found in the basal and induced AHH activities and the induction ratio. The average basal AHH activity of 29 epidermal cultures in primary culture was 3.9 units (SD, 4.2; range, 0-16.3) (one unit was defined as 1 pmol of 3-hydroxybenzo[a]pyrene formed/mg protein/hr). AHH activity was induced time- and dose-dependently by BA. The average AHH activity induced by treatment with 13 microM BA for 24 hr was 97.4 units (SD, 69.4; range, 2.7-216.9). The induction ratio ranged from 0.6 to 262.0, but in the majority of cultures (15 of 27 cultures, 55%) it was less than 30. The mean induction ratio and SD was 51.1 +/- 63.0. The frequency distributions of basal AHH activity and the induction ratio were asymmetrical with a right tail. No correlation was found between the AHH activity or induction ratio and the age or sex of the donors or their residential district. The basal and induced AHH activities of dermal fibroblasts were both lower than those of epidermal cells; the average basal AHH level of 14 cultures was 1.5 units (SD, 1.4; range, 0-5.2), while the average induced AHH activity was 9.6 units (SD, 6.3; range 0-23.5). The induction ratio of dermal fibroblasts was lower than that of epidermal cells, the mean and SD being 7.5 +/- 7.4 (range, 1.9-27.0). There was no correlation between the AHH activities or induction ratios in epidermal and dermal cells isolated from the same donors.

Adolescent↗
PubMed1986

Marked activation of benzo[a]pyrene to protein-binding forms in the presence of unsaturated fatty acids and heme-compounds.

In vitro activation of benzo[a]pyrene to protein-binding forms was investigated with the following two systems: (1) various fractions of human and rat blood had a potential of activating benzo[a]pyrene to forms binding to proteins in the presence of linoleic or arachidonic acid. Red blood cells activated much more benzo[a]pyrene than platelets or lymphocytes. Variation in the individual activity of the respective cell types and the relative activity between cells from different individual donors was observed; and (2) more prominent activation of benzo[a]pyrene was observed with a simplified system, in which a combination of unsaturated fatty acid, i.e., linoleic or arachidonic acid, and heme-compounds resulted in activation of benzo[a]pyrene. Although the binding of benzo[a]pyrene to bovine serum albumin did increase with incubation time, an initial rapid reaction within the first few minutes after addition of the substrates was followed by very much reduced rates of binding thereafter. Hematin and hemin could be utilized for the activation of benzo[a]pyrene, but biliverdin, hematoporphyrin and protoporphyrin IX could not. The present results suggest a possible role for unsaturated fatty acids and heme-compounds in the activation of benzo[a]pyrene in vivo.

7,8-Dihydro-7,8-dihydroxybenzo(a)pyrene 9,10-oxide↗
PubMed1986

Extensive sequence homology of the goldfish ras gene to mammalian ras genes.

We cloned ras-related sequences from goldfish genomic libraries constructed as recombinants using the lambda phage. Restriction enzyme mapping of the clones obtained revealed three kinds of ras-related sequences among approximately 350,000 genomic clones. One of these clones was partially sequenced. Comparison with the nucleotide sequences of mammalian ras genes showed that the determined sequences covered the predicted amino acid coding regions and parts of the intervening regions. The predicted amino acid sequences of the cloned ras-related goldfish gene suggested that the coding region is localized separately in DNA, and that its exon-intron boundaries are exactly the same as those of corresponding mammalian genes. The nucleotide and amino acid sequences of the goldfish ras-related gene may have extensive homologies to mammalian p 21 protein. Among the three mammalian ras proteins, the predicted amino acid sequence of the sequenced ras-related goldfish clone is most closely homologous (96%) to the Kirsten ras protein. Differences in the predicted amino acid sequence were greatest in the sequence predicted from the fourth exon; fewer differences were found in the sequence from the third exon, and only slight or no differences were found in the sequence predicted for the first and second exons. The 12th and 61st amino acids from the N-terminal of the protein, which are thought to be critical positions for GTP binding and catalysis, are both conserved in the goldfish protein.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1986

Spontaneous neurinoma in an African lungfish, Protopterus annectens, and DNA repair studies on normal and neoplastic tissues.

Neurinomas developed in an African lungfish (Protopterus annectens), living in an aquarium in Western Japan. The 2 tumors, measuring 7.5 X 9.0 X 6.5 and 13 X 4 X 6 cm, were located on the skin. As shown by light microscopy, tumor cells were composed of spindle-shaped cells with huge pleomorphic nuclei, which were arranged in parallel rows or whorls in interlacing connective tissue. Long-term culture of these tumor cells was achieved in vitro at 25 degrees C with use of conditioned medium over a period of more than 4 months. The nuclear DNA contents of erythrocytes (normal diploids, 2C) and tumor cells dispersed from the fixed tumor tissues were measured by 4',6-diamidino-2-phenylindole hydrochloride-DNA microfluorometry by using mouse cerebellar small granule cells (normal diploids, 2C) as a reference. The 2C value of the lungfish was approximately 28-fold greater than that of the mouse. Furthermore, consistent with the nuclear pleomorphism observed by light microscopy, the nuclear DNA contents of tumor cells showed a wide distribution from hypo-2C to hyper-4C. DNA repair synthesis was measured autoradiographically in organ cultures of the tumor, lung, and skin, exposed to chemical carcinogens or UV radiation. Considerable repair was observed in the tumor and skin cells exposed to 1-methyl-1-nitrosourea (CAS: 684-93-5), N-methyl-N'-nitro-N-nitrosoguanidine (CAS: 70-25-7), or 254-nm or sunlamp UV light. Only traces of repair synthesis were detected in lung exposed to 1-methyl-1-nitrosourea or N-methyl-N'-nitro-N-nitrosoguanidine. 4-Hydroxyaminoquinoline 1-oxide (CAS: 4637-56-3) did not induce repair in any of the three tissues. The observed values for repair, relative to the amount of DNA, were similar to those in other fishes.

4-Hydroxyaminoquinoline-1-oxide↗
PubMed1984

Immunohistochemical localization of nerve growth factor and epidermal growth factor in guinea pig prostate gland.

Prostate glands of adult guinea pigs were stained for nerve growth factor (NGF) and epidermal growth factor (EGF) by immunohistochemical methods. Both NGF and EGF were localized diffusely in the cytoplasm of the glandular epithelial cells, and also in their secretory products. These findings suggest that NGF and EGF are synthesized, stored, and secreted by the glandular epithelial cells of the prostate.

Animals↗
PubMed1984

Activation of 2-amino-6-methyldipyrido[1,2-a:3' ,2' -d]imidazole, a mutagenic pyrolysis product of glutamic acid, to bind to microsomal protein by NADPH-dependent and -independent enzyme systems.

The conversion of 2-amino-6-methyldipyrido[1,2-a:3' ,2' -d]-imidazole (Glu-P-1), a highly mutagenic principle in a pyrolysate of glutamic acid, to protein-bound metabolites in vitro was examined with microsomes from various tissues of female F344 rats. Addition of NADPH to the incubation mixture containing microsomes and [14C]Glu-P-1 increased the binding of its metabolites to microsomal proteins linearly with time for up to 30 min, while on addition of arachidonic acid the binding increased linearly only for the first 2-4 min of incubation and then levelled off. However, due to the initial rapid binding, addition of arachidonic acid resulted in 6-fold greater binding of metabolites to small intestinal microsomes than addition of NADPH on incubation for 4 min, and with microsomes from liver and colon, arachidonic acid was found to be a better cofactor than NADPH for activation of Glu-P-1. Indomethacin significantly inhibited the increase in binding by arachidonic acid. Additions of linoleic and linolenic acids also increased the binding, but addition of oleic acid had no influence. With hepatic microsomes from 3-methylcholanthrene-treated rats, binding within 4 min after addition of arachidonic acid was greater than that after addition of NADPH and the reverse on further incubation. These findings suggest that prostaglandin synthetase may serve as an alternative enzyme to cytochrome P-450 monooxygenases for conversion of Glu-P-1 to active intermediates in all the rat tissues investigated.

Animals↗
PubMed1984

Arachidonic acid-dependent activation of benzo[a]pyrene to bind to proteins with cytosolic and microsomal fractions from rat liver and lung.

Activation of benzo[a]pyrene to bind to proteins by co-oxidation with prostaglandin synthesis was studied in rat liver and lung microsomes and cytosols. The kinetics of this activation showed a two-phase reaction; a rapid initial reaction for 2-4 min after addition of arachidonic acid and then a slow reaction or a plateau state. The reaction was linear only with low contents of the enzyme proteins, and was slower with more than 1 mg of enzyme per ml of incubation mixture. Other unsaturated fatty acids were also effective in activating benzo[a]pyrene with both microsomes and cytosols. With microsomal proteins linoleic acid was more effective than arachidonic acid, whereas with cytosolic proteins arachidonic acid was the best cofactor. Linolenic acid could also activate benzo[a]pyrene, though less efficiently, but oleic acid had no influence on the binding. Indomethacin did not inhibit the activation, but nordihydroguaiaretic acid and quercetin significantly reduced the binding. Addition of hematin significantly increased the binding. The NADPH-dependent bindings of benzo[a]pyrene to proteins with liver and lung microsomes were one-third and one-twelfth the values after incubation with arachidonic acid. Addition of glutathione or Ca2+ ion reduced the binding significantly. The present results suggest the importance of co-oxidation with lipoxygenase for activation of benzo[a]pyrene and the possible role of both the arachidonic acid cascade system and the NADPH-dependent cytochrome P-450 system in metabolic activation of chemical carcinogens.

Animals↗
PubMed1983

Sister-chromatid exchange induction by indirect mutagens/carcinogens, aryl hydrocarbon hydroxylase activity and benzo[alpha]pyrene metabolism in cultured human hepatoma cells.

2 human hepatoma cell lines (C-HC-4 and C-HC-20), in which aryl hydrocarbon hydroxylase activity was induced with benz[alpha]anthracene in vitro to about 140- and 64-fold of the respective basal levels, yielded an increased frequency of sister-chromatid exchanges (SCEs) when exposed to benzo[alpha]pyrene (BP), 7,12-dimethylbenz[alpha]anthracene and 3-methylcholanthrene in vitro. Analysis of the metabolism of BP by these cells by high-pressure liquid chromatography revealed that both cell lines produced various BP metabolites including the proximate form BP-7,8-dihydrodiol which has been reported to be the most potent inducer of SCEs among the metabolites of BP. In addition, aflatoxin B1 and cyclophosphamide also induced SCEs in these cell lines. The above findings suggest that these cells may be capable of metabolizing a range of indirect mutagens/carcinogens into DNA-active forms. These cells may therefore serve as a useful test system in vitro for the detection of genotoxic agents, without the use of an exogenous activating system.

Aflatoxin B1↗
PubMed1983

Inhibition of benzo[a]pyrene-induced mutagenesis in Chinese hamster V79 cells by hemin and related compounds.

The inhibitory effects of hemin and related compounds on the mutagenicity of benzo[a]pyrene (BP) were investigated in Chinese hamster V79 cells co-cultivated with X-irradiated hamster embryo cells. Mutant V79 cells were selected by their resistance to ouabain. The mutation frequency induced by BP was substantially inhibited dose dependently by hemin. The mutagenicity of BP (1 microgram/ml) on V79 cells was reduced to 6.5% by hemin, 52% by biliverdin, 73% by protoporphyrin and 85% by chlorophyllin at the highest concentration of the compounds tested (15 microM).

Animals↗