Mariko Tachikawa

Metabolic methylation is a possible genotoxicity-enhancing process of inorganic arsenics

To elucidate if the metabolic methylation participates in the induction of inorganic arsenic-responsible genetic damage, arsenite (ARS) and its methylated metabolites, methanearsonic acid (MMAA) and dimethylarsinic acid (DMAA), were comparatively assayed for the induction of DNA damage by determining DNA repair synthesis using polymerization inhibitors such as aphidicolin (aph) and hydroxyurea (HU). When human alveolar epithelial type II (L-132) cells in culture were exposed to either one of these three arsenic compounds, DNA single-strand breaks resulting from the inhibition of repair polymerization were remarkably produced by exposure to DMAA at 5 to 100 microM, while not by that to ARS and MMAA even at 100 microM. Furthermore, a bromodeoxyuridine (BrdrU)-photolysis assay indicated that the induction of DNA repair synthesis was observed only in the case of exposure to DMAA. When L-132 cells were exposed to 100 microM MMAA in the presence of 10 mM S-adenosyl-L-methionine (SAM), which is a well-known methyl-group donor in metabolic methylation of arsenics, DNA repair synthesis was induced along with an increase in the amount of dimethylarsenic in the cells. These results indicate that metabolic methylation of inorganic arsenics to dimethylarsenics is predominantly involved in the induction of DNA damage.

Oxidative DNA damage following exposure to dimethylarsinous iodide: the formation of cis-thymine glycol.

The purpose of the present study was to elucidate the genotoxic mechanism of trivalent dimethylated arsenic, particularly the induction mechanism of oxidative stress in nuclear bases. Cis-thymine glycol was used as a biomarker of DNA oxidation damage. The treatment of thymine with dimethylarsinous iodide (DMI), a model compound of dimethylarsinous acid, induced the formation of cis-thymine glycol. This oxidative damage was induced via the production of dimethylated arsenic peroxide, but not via the production of superoxide anion or hydrogen peroxide. Trivalent dimethylated arsenic may thus play an important role in arsenic carcinogenesis through the induction of oxidative base damage.

Studies on the Disinfection and Removal of Biofilms by Ozone Water Using an Artificial Microbial Biofilm System

Abstract Inactivation rates of the biofilms of P. fluorescence and P. aeruginosa established on a small slide glass in ozone water (0.9–3.2 mg/L, 1–20 min) were determined in a batch or flow-through system. The effects of ozone water on the biofilm matrices were defined clearly in situ by confocal laser scanning microscopy. These results indicate that ozone is an effective biocide against biofilms and it can remove exopolysaccharides in the biofilm matrices. However, the effective concentration of ozone for disinfection of biofilms varied with the biofilms formed, mainly due to reactions of ozone with constituents of the biofilms.

Differences between freshwater and seawater killifish (Oryzias latipes) in the accumulation and elimination of pentachlorophenol

Freshwater and seawater acclimated (FWA and SWA) killifish (Oryzias latipes) were exposed to pentachlorophenol (PCP) for 3–10 days. Uptake and clearance rates of FWA and SWA killifish were determined. The estimated bioaccumulation factors (BCF) of PCP for FWA and SWA killifish were 1680 and 370, respectively. The smaller uptake rate and faster clearance rate resulted in the lower BCF for SWA killifish. Fresh- and seawater killifish excreted the PCP metabolites, the glucuronide and sulfate conjugates of PCP; the major metabolite of freshwater killifish was PCP sulfate; for seawater acclimated fish, it was PCP glucuronide. The greater excretion of PCP glucuronide by seawater killifish may be responsible for the rapid elimination of PCP. PCP accumulation in killifish decreased with higher pH levels in both freshwater and seawater environments, but these differences were less than the effect of salinity. The results indicate that salinity can affect the accumulation and elimination of environmental pollutants in killifish.

Effects of isocyanuric acid on the monochlorodimedone chlorinating rates with free chlorine and ammonia chloramine in water.

Changes in monochlorodimedone (MCD) chlorinating rates with free chlorine (mixture of HOCl and OCl-) and ammonia monochloramine (NH2Cl) in water at pH 7 by the addition of isocyanuric acid (H3Cy) were determined at room temperature. Decreases in MCD absorbance at 290nm in equimolar (0.04mM) reactions of MCD and free available chlorine solutions containing H3Cy (0.01-1.60 mM) were recorded in a stopped-flow spectrophotometer. The rates indicate second-order reactions. Since the rate with free chlorine was high (> 7.6 x 10(6) M(-1) s(-1)), the amounts of free chlorine in the solutions could be distinguished from that of chlorinated cyanurates. The chlorinating rates with chlorinated cyanurates decreased with an increase in H3Cy concentrations. Plotting the rates against the molar ratio of chlorine to H3Cy showed a linear correlation and the rates with chlorinated cyanurates (H2ClCy) was estimated at 0.5 x 10(5) M(-1) s(-1). In contrast, the rates with the NH2Cl solution containing H3Cy increased with an increase in H3Cy concentrations, increasing from 1.2 x 10 to 2.7 x 10 M(-1) s(-1) by the addition of 1.55 mM H3Cy. The DPD color development rates (OD512/t1/2/M) with free available chlorine (0.015mM) declined from 1.3 x 10(5) to 0.9 x 10(5)M(-1) by the addition of 0.61 mM H3Cy.

The effects of salinity on pentachlorophenol accumulation and elimination by killifish (Oryzias latipes)

Fresh water and seawater acclimated (FWA and SWA) killifish (Oryzias latipes) were exposed to pentachlorophenol (PCP) at various salinities (1.2–18.7‰). The PCP accumulation in the fish decreased with increase of salinity. As the salinity increased [0‰ (freshwater) −18.6‰], the PCP clearance rate increased from 0.0097 to 0.0170 (h−1). A substantial increase of the clearance rate was observed when the salinity was over 9.3‰. The PCP uptake rate decreased from 20.8 to 10.6 (ml−1 g−1 fish h−1) with the increase of salinity. The uptake rate decreased at a lower salinity (⩽4.7‰). The excretion of PCP glucuronide (PCP-G) increased markedly at the salinity of 9.3‰, although that of PCP sulfate (PCP-S) did not change. The increase of PCP-G excretion may correspond to the increase of clearance rate. Abrupt transfer of FWA and SWA killifish to a PCP solution with a different salinity decreased the PCP accumulation and increased the PCP metabolite excretion with the increase of the salinity. However, the amount of PCP accumulated by FWA was greater than that by SWA killifish.

Methylamine dichloramine may play a role in the process of colorectal disease through architectural and oxidative changes in crypts in mice

AIMS Methylamine dichloramine (CH(3)NCl(2)) produced by neutrophils may promote colon tumors and colitis via architectural and oxidative changes in crypts, which are secretory granulae composed of goblet cells located in the colorectal mucosal layer. We investigated whether CH(3)NCl(2), in comparison with the other reactive oxygen species (ROS) such as H(2)O(2) and HOCl, derived from primed neutrophils in inflammatory sites in the large intestine, is a biogenic factor for the induction of colorectal disease in mice. MAIN METHODS Male ICR-strain mice were administered each oxidant (0.5-0.7 micromol/mouse) by enema under anesthesia. The colorectal tissues were evaluated by histopathological and immunohistochemical analyses. Hemolysis and hemoglobin oxidation by the methylamine chloramines and HOCl were examined by adding them (50-400 microM) to a sheep erythrocyte suspension (1x10(8) cells/ml) and its lysate at pH 7 and 37 degrees C. KEY FINDINGS CH(3)NCl(2) oxidized erythrocyte hemoglobin more effectively than HOCl, indicating it has high cell permeability and selective oxidation ability. CH(3)NCl(2) mainly induced atrophy of crypts at 6 h after administration, while the other ROS tested did not. Furthermore, 4-hydroxy-2-nonenal (4-HNE) showed positive immunostains throughout the mucosal layer, including around the basal regions of atrophied crypts, only with CH(3)NCl(2), while positive immunostains were observed for 3-nitrotyrosine (3-NT) in the atrophied crypts and their surrounding lamina propria in the mucosal layer. SIGNIFICANCE The results suggest that CH(3)NCl(2)derived from primed neutrophils may play the most important role in promoting the development of colon tumor formation and colitis by oxidative stress through its high degree of cell permeability.

A Simple Conversion of Creatinine to Creatol via Creatinine Chloroamine

Creatinine (2-amino-1,5-dihydro-l-methylimidazol-4-one) (1a) was converted in a simple way to creatol (2-amino-1,5-dihydro-5-hydroxy-l-methylimidazol-4-one) (1b) via creatinine chloramine (2-N-chloroamino-1,5-dihydro-l-methylimidazol-4-one) (3a), without using protecting groups. The creatinine chloroamine exists in the 2-N-chloroamino form (3a) in aqueous solution, but in the solid state, X-ray crystal analysis shows that it has the 2-N-chloroimino structure (2-N-chloroimino-1,5-dihydro-1-methylimidazol-4-one) (4a). Related imidazolones have also been prepared and are discussed.