Yasuyoshi Sayato

Disinfection by-products in the chlorination of organic nitrogen compounds : By-products from kynurenine

Volatile by-products in the chlorination of 3 humic acids as naturally-occurring substances and 37 nitrogen compounds normally found in excrement were analyzed, and as result kynurenine, a urinary metabolite of tryptophan was found a suitable model compound for dichloroacetonitrile-forming precursors. Possible pathways for the formation of chlorination by-products from kynurenine were also proposed by identification and kinetic properties of by-products decomposed further from each product.

Mutagenicity of adsorbates to a copper-phthalocyanine derivative recovered from municipal river water

Blue cotton, bearing a covalently bound copper-phthalocyanine derivative capable of adsorbing polycyclic aromatic hydrocarbons (PAHs) over 3 rings, was applied to recover mutagens from the Katsura River which is a tributary of the Yodo River. The Ames Salmonella/microsome assay with TA98 and TA100 of the blue cotton concentrate recovered from the river water demonstrated indirect mutagenicity toward TA98. The subfractions separated by Sephadex G-25 gel chromatography also showed direct mutagenicity in strains YG1021 and YG1024, the nitroreductase- and O-acetyltransferase-overproducing derivatives of TA98; this activity was greatly increased by the addition of S9 mix, especially in YG1024. However, these subfractions were less mutagenic with TA98NR or TA98/1,8-DNP6, regardless of whether S9 mix was present or not. The behaviors of these mutagenic activities therefore suggested that frameshift mutagens of both directly mutagenic nitroarenes and indirectly mutagenic aminoarenes were present in the blue cotton concentrate from the river water.

Mutagenicity of products formed by ozonation of naphthoresorcinol in aqueous solutions

The mutagenicity of products formed by ozonation of naphthoresorcinol in aqueous solution was assayed with Salmonella typhimurium strains TA97, TA98, TA100, TA102 and TA104 in the presence and absence of S9 mix from phenobarbital- and 5,6-benzoflavone-induced rat liver. Ozonated naphthoresorcinol was mutagenic in TA97, TA98, TA100 and TA104 without S9 mix. By the addition of S9 mix, the mutagenic activity of ozonated naphthoresorcinol was markedly suppressed in TA98 and TA100, but became positive in TA102. High-performance liquid chromatography (HPLC) after derivatization to 2,4-dinitrophenylhydrazones demonstrated the formation of glyoxal as an ozonation product of naphthoresorcinol. Ion chromatographic technique also demonstrated the formation of o-phthalic acid, muconic acid, maleic acid, mesoxalic acid, glyoxylic acid and oxalic acid as ozonation products. The mutagenicity assays of these identified products with five Salmonella showed that glyoxal and glyoxylic acid were directly mutagenic; the former in TA100, TA102 and TA104, the latter in TA97, TA100 and TA104. In the presence of S9 mix, glyoxylic acid gave a positive response of mutagenicity for TA102. The experimental evidence supported that glyoxal and glyoxylic acid may contribute to the mutagenicity of ozonated naphthoresorcinol.

Mechanisms of selenium methylation and toxicity in mice treated with selenocystine

Abstractu2002Mechanisms of selenium methylation and toxicity were investigated in the liver of ICR male mice treated with selenocystine. To elucidate the selenium methylation mechanism, animals received a single oral administration of selenocystine (Se-Cys; 5, 10, 20, 30, 40, or 50u2005mg/kg). In the liver, both accumulation of total selenium and production of trimethylselenonium (TMSe) as the end-product of methylation were increased by the dose of Se-Cys. A negative correlation was found between production of TMSe and level of S-adenosylmethionine (SAM) as methyl donor. The relationship between Se-Cys toxicity and selenium methylation was determined by giving mice repeated oral administration of Se-Cys (10 or 20u2005mg/kg) for 10 days. The animals exposed only to the high dose showed a significant rise of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) activities in plasma. Urinary total selenium increased with Se-Cys dose. TMSe content in urine represented 85% of total selenium at the low dose and 25% at the high dose. The potential of Se-methylation and activity of methionine adenosyltransferase, the enzyme responsible for SAM synthesis, and the level of SAM in the liver were determined. The high dose resulted in inactivation of Se-methylation and decrease in SAM level due to the inhibition of methionine adenosyltransferase activity. To learn whether hepatic toxicity is induced by depressing selenium methylation ability, mice were injected intraperitoneally with periodate-oxidized adenosine (100u2005μmol/kg), a known potent inhibitor of the SAM-dependent methyltransferase, at 30u2005min before oral treatment of Se-Cys (10, 20, or 50u2005mg/kg). Liver toxicity induced by selenocystine was enhanced by inhibition of selenium methylation. These results suggest that TMSe was produced by SAM-dependent methyltransferases, which are identical with those involved in the methylation of inorganic selenium compounds such as selenite, in the liver of mice orally administered Se-Cys. Depression of selenium methylation ability resulting from inactivation of methionine adenosyltransferase and Se-methylation via enzymic reaction was also found in mice following repeated oral administration of a toxic dose of Se-Cys. The excess selenides accumulating during the depression of selenium methylation ability may be involved in the liver toxicity caused by Se-Cys.

Identification of polycyclic aromatic hydrocarbons in mutagenic adsorbates to a copper-phthalocyanine derivative recovered from municipal river water.

A study was made to identify polycyclic aromatic hydrocarbons (PAHs) in the mutagenic adsorbate to blue cotton recovered from the water of the Katsura River which is a tributary of the Yodo River, a typical municipal river. As blue cotton bears a covalently bound copper-phthalocyanine derivative which can adsorb PAHs over 3 rings, PAHs in the adsorbate were separated into 4 fractions (I-IV) by Sephadex LH-20 gel chromatography. Fractions III and IV showed high direct and indirect frameshift mutagenicity in strains YG1021 and YG1024, the nitroreductase- and O-acetyltransferase-overproducing derivatives of TA98, especially in YG1024 with S9 mix, whereas these fractions showed less mutagenicity in TA98NR or TA98/1,8-DNP6. These results suggest that mutagenic nitroarenes and aminoarenes are present in both fractions. The retention times of some peaks separated from both fractions using high performance liquid chromatography (HPLC) with a fluorescence detector were identical with those of authentic PAHs. Gas chromatography-mass spectrometry of some HPLC fractions demonstrated that anthraquinone, azulene derivative, quinoline derivative, chrysene and benzo[b]fluoranthene are probably contained in these fractions.

Identification and metabolism of selenocysteine-glutathione selenenyl sulfide (CySeSG) in small intestine of mice orally exposed to selenocystine

Abstractu2002This investigation was carried out to elucidate the chemical form of selenium-containing metabolite in small intestine of ICR male mice orally administered selenocystine (CySeSeCy). The metabolite in intestinal cytosol of mice treated with CySeSeCy (50u2004mg/kg) was identified as selenocysteine-glutathione selenenyl sulfide (CySeSG) by high performance liquid chromatography using a gel filtration and reversed phase column. Hydrogen selenide formation was caused as a result of the anaerobic reaction between the CySeSG and liver cytosol containing selenocysteine β-lyase, which specifically acts on selenocysteine (CySeH). Effects of GSH or glutathione reductase on hydrogen selenide formation from CySeSG reacted with the liver cytosol were examined. The CySeSG was nonenzymatically reduced to CySeH by excess GSH in the liver cytosol. It was also recognized that CySeSG was enzymatically reduced to CySeH by glutathione reductase in the presence of NADPH. These results indicate that the chemical form of this metabolite is CySeSG, which has a molecular weight of 473, the CySeSG is then reduced by excess GSH and/or gluta- thione reductase yielding CySeH, which is decomposed by selenocysteine β-lyase to hydrogen selenide. CySeSG may be a stable precursor of hydrogen selenide in animals.

Characteristics of mutagenesis by glyoxal in Salmonella typhimurium: contribution of singlet oxygen.

The characteristics of mutagenesis by glyoxal in Salmonella tester strains TA100 and TA104, and particularly a possible role of active oxygen species, were investigated. Glyoxal was converted into a non-mutagenic chemical with glutathione (GSH) by glyoxalase I, and the mutagenic activity was enhanced by the depletion of intracellular GSH. Glyoxal caused the reduction of nitro blue tetrazolium, which was suppressed by the addition of 2,5-diphenylfuran, superoxide dismutase (SOD) and catalase (CAT), scavengers of singlet oxygen (1O2), superoxide radical (O2-) and hydrogen peroxide (H2O2), respectively. However, only the 1O2 scavenger almost completely suppressed the mutagenic activity of glyoxal. Mutagenicity assays using strains pretreated with N,N-diethyldithiocarbamate of a SOD inhibitor and strains with low levels of SOD and CAT indicated that the mutagenesis by glyoxal was independent of intracellular levels of SOD and CAT, though glyoxal itself repressed them. Therefore, all the results suggest that 1O2 formed from glyoxal is related to its mutagenesis, but that neither O2- nor H2O2 is intracellularly predominantly related to it. The action of glyoxal against SOD and CAT, and the formation of glyoxal adducts with amino acids as their components are also discussed.

DNA lesion in rat hepatocytes induced by in vitro and in vivo exposure to glyoxal.

The alkaline elution technique was applied to measure the damage of rat hepatic DNA following exposure to glyoxal. DNA single-strand breaks were induced after exposure of primary-cultured hepatocytes to 0.1-0.6 mg/ml glyoxal for 60 min, while no DNA cross-link was observed. Single-strand breaks were also detected in livers of rats within 2 h following a single oral exposure at 200-1000 mg/kg body weight, and the frequency of the breaks reached a maximum around 9 h after exposure. The breaks were almost fully repaired 24 h after exposure to any dose. However, hardly any DNA lesions were detected in other tissues following exposure to 1000 mg/kg glyoxal. Thus, the present results indicate that glyoxal causes DNA single-strand breaks in rat hepatocytes following in vitro and in vivo exposure.

Subchronic oral toxicity of glyoxal via drinking water in rats

The subchronic oral toxicity of glyoxal via drinking water and the effect on in vivo protein synthesis in tissues following a single treatment with this substance were assessed in Sprague-Dawley male rats. Animals received drinking water containing glyoxal levels of 2000, 4000, and 6000 mg/liter ad libitum for 30, 60, and 90 days in Phase I. In Phase II, the high-dose and control-1 groups fed the diet ad libitum, and a diet-limited control-2 group given the same amount of diet as consumed by the high-dose group were maintained for 90 and 180 days. The study designs included observations of clinical signs, body weights, major organ weights, gross and histopathological examinations, serum clinical chemistry, and biochemical examinations such as glyoxalase activity and glutathione content in selected tissues. Body weight gain and organ weights significantly decreased with dosage. Although consumption of food and water was also depressed in the exposed group, the reduction of body weight gain was greater in the high-dose group than in the diet-limited control 2 group. Histopathological examinations revealed only a slight papillary change in the kidneys from the high-dose group at both 90 and 180 days terminations in Phase II. The induction of both glyoxalase I and II was observed in liver and erythrocytes at 30-day termination of the exposed groups. Serum enzyme and protein levels were significantly reduced by the mid- and/or high-dose exposures. With a single oral high-dose treatment of glyoxal, a great decline in the incorporation of L-[3H]leucine was shown particularly in the liver, and this probably led in part to a reduction in the serum protein levels in rats following subchronic exposure to glyoxal. These data indicated an overall low degree of systemic toxicity to rats exposed subchronically to glyoxal via drinking water.

Toxicity and chemical form of selenium in the liver of mice orally administered selenocystine for 90 days

The subacute oral toxicity of selenocystine and chemical form of selenium in the liver following exposure to this compound were assessed in ICR male mice. Animals were dosed 6 days/week for 30, 60 or 90 days with 0, 5, 10 or 15 mg/kg per day. Body weight gain decreased with dosage. The activities of aspartate aminotransferase and alanine aminotransferase in plasma were significantly elevated at the highest dose level after 60 days and at the two higher dose levels after 90 days of exposure. However, the level of selenium content in the liver was the same at the two higher dosages at both 60 and 90 days of exposure. The subcellular distribution of selenium in the liver from mice treated with selenocystine showed that the major part of the total selenium content, 68.3–72.1%, existed in the cytosolic fraction. Sephadex G-150 chromatograms of liver cytosol of the animals administered selenocystine revealed three selenium-containing fractions which involve glutathione peroxidase (molecular weight 80 000) high molecular (molecular weight 55 000–60 000) and low molecular (molecular weight <10 000) substances. Selenium content and acid-volatile selenium content in the high molecular weight fraction increased with exposure time to selenocystine. Thus, in a subacute toxicity study selenocystine given for 90 days caused hepatic damage in mice, depending on the acid-volatile selenium content in the liver cytosol.