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1.
Environ Mol Mutagen ; 60(2): 100-121, 2019 03.
Artículo en Inglés | MEDLINE | ID: mdl-30536466

RESUMEN

The interpretation and significance of DNA adduct data, their causal relationship to mutations, and their role in risk assessment have been debated for many years. An extended effort to identify key questions and collect relevant data to address them was focused on the ubiquitous low MW N7-alkyl/hydroxyalkylguanine adducts. Several academic, governmental, and industrial laboratories collaborated to gather new data aimed at better understanding the role and potential impact of these adducts in quantifiable genotoxic events (gene mutations/micronucleus). This review summarizes and evaluates the status of dose-response data for DNA adducts and mutations from recent experimental work with standard mutagenic agents and ethylene oxide and propylene oxide, and the importance for risk assessment. This body of evidence demonstrates that small N7-alkyl/hydroxyalkylguanine adducts are not pro-mutagenic and, therefore, adduct formation alone is not adequate evidence to support a mutagenic mode of action. Quantitative methods for dose-response analysis and derivation of thresholds, benchmark dose (BMD), or other points-of-departure (POD) for genotoxic events are now available. Integration of such analyses of genetox data is necessary to properly assess any role for DNA adducts in risk assessment. Regulatory acceptance and application of these insights remain key challenges that only the regulatory community can address by applying the many learnings from recent research. The necessary tools, such as BMDs and PODs, and the example datasets, are now available and sufficiently mature for use by the regulatory community. Environ. Mol. Mutagen. 60: 100-121, 2019. © 2018 The Authors. Environmental and Molecular Mutagenesis published by Wiley Periodicals, Inc. on behalf of Environmental Mutagen Society.


Asunto(s)
Aductos de ADN/genética , Mutagénesis/efectos de los fármacos , Mutación/efectos de los fármacos , Aductos de ADN/química , Aductos de ADN/efectos de los fármacos , Daño del ADN/efectos de los fármacos , Compuestos Epoxi/toxicidad , Óxido de Etileno/toxicidad , Humanos , Peso Molecular , Mutagénesis/genética , Mutágenos/toxicidad , Mutación/genética , Medición de Riesgo
2.
Cancer Chemother Pharmacol ; 69(3): 665-77, 2012 Mar.
Artículo en Inglés | MEDLINE | ID: mdl-21968950

RESUMEN

PURPOSE: To characterize the cellular action mechanism of Debio 0507, we compared the major DNA adducts formed by Debio 0507- and oxaliplatin-treated HCT116 human colon carcinoma cells by a combination of inductively coupled plasma mass spectrometry (ICP-MS) and ultraperformance liquid chromatography mass spectrometry (UPLC-MS/MS). METHODS: HCT116 cells were treated with IC(50) doses of Debio 0507 or oxaliplatin for 3 days. Total cellular Pt-DNA adducts were determined by ICP-MS. The DNA was digested, and the major Pt-DNA adducts formed by both drugs were characterized by UPLC/MS/MS essentially as described previously for cisplatin (Baskerville-Abraham et al. in Chem Res Toxicol 22:905-912, 2009). RESULTS: The Pt level/deoxynucleotide was 7.4/10(4) for DNA from Debio 0507-treated cells and 5.5/10(4) for oxaliplatin-treated cells following a 3-day treatment at the IC(50) for each drug. UPLC-MS/MS in the positive ion mode confirmed the major Pt-DNA adducts formed by both drugs were dach-Pt-d(GpG) (904.2 m/z â†’ 610 m/z and 904.2 m/z â†’ 459 m/z) and dach-Pt-d(ApG) (888.2 m/z â†’ 594 m/z and 888.2 m/z â†’ 459 m/z). CONCLUSIONS: These data show that the major DNA adducts formed by Debio 0507 are the dach-Pt-d(GpG) and dach-Pt-d(ApG) adducts and at equitoxic doses Debio 0507 and oxaliplatin form similar levels of dach-Pt-d(GpG) and dach-Pt-d(ApG) adducts. This suggests that the action mechanisms of Debio 0507 and oxaliplatin are similar at a cellular level.


Asunto(s)
Antineoplásicos/farmacología , Aductos de ADN/metabolismo , Nucleótidos de Desoxiadenina/metabolismo , Desoxiguanosina/metabolismo , Fosfatos de Dinucleósidos/metabolismo , Compuestos Organoplatinos/farmacología , Antineoplásicos/química , Antineoplásicos/metabolismo , Técnicas de Cultivo de Célula , Cromatografía Líquida de Alta Presión , Aductos de ADN/química , Nucleótidos de Desoxiadenina/química , Desoxiguanosina/química , Fosfatos de Dinucleósidos/química , Células HCT116 , Humanos , Compuestos Organoplatinos/química , Compuestos Organoplatinos/metabolismo , Oxaliplatino , Espectrometría de Masas en Tándem
3.
Inhal Toxicol ; 20(13): 1125-43, 2008 Oct.
Artículo en Inglés | MEDLINE | ID: mdl-18800271

RESUMEN

Gasoline engine emissions are a ubiquitous source of exposure to complex mixtures of particulate matter (PM) and non-PM pollutants; yet their health hazards have received little study in comparison with those of diesel emissions. As a component of the National Environmental Respiratory Center (NERC) multipollutant research program, F344 and SHR rats and A/J, C57BL/6, and BALBc mice were exposed 6 h/day, 7 days/week for 1 week to 6 months to exhaust from 1996 General Motors 4.3-L engines burning national average fuel on a simulated urban operating cycle. Exposure groups included whole exhaust diluted 1:10, 1:15, or 1:90, filtered exhaust at the 1:10 dilution, or clean air controls. Evaluations included organ weight, histopathology, hematology, serum chemistry, bronchoalveolar lavage, cardiac electrophysiology, micronuclei in circulating cells, DNA methylation and oxidative injury, clearance of Pseudomonas aeruginosa from the lung, and development of respiratory allergic responses to ovalbumin. Among the 120 outcome variables, only 20 demonstrated significant exposure effects. Several statistically significant effects appeared isolated and were not supported by related variables. The most coherent and consistent effects were those related to increased red blood cells, interpreted as likely to have resulted from exposure to 13-107 ppm carbon monoxide. Other effects supported by multiple variables included mild lung irritation and depression of oxidant production by alveolar macrophages. The lowest exposure level caused no significant effects. Because only 6 of the 20 significant effects appeared to be substantially reversed by PM filtration, the majority of effects were apparently caused by non-PM components of exhaust.


Asunto(s)
Gasolina/efectos adversos , Estado de Salud , Exposición por Inhalación/efectos adversos , Emisiones de Vehículos , Animales , Daño del ADN/efectos de los fármacos , Daño del ADN/fisiología , Femenino , Masculino , Ratones , Ratones Endogámicos BALB C , Ratones Endogámicos C57BL , Material Particulado/administración & dosificación , Material Particulado/efectos adversos , Ratas , Ratas Endogámicas F344 , Ratas Endogámicas SHR
4.
Regul Toxicol Pharmacol ; 51(1): 53-65, 2008 Jun.
Artículo en Inglés | MEDLINE | ID: mdl-18367300

RESUMEN

Nitrapyrin has been registered as a nitrogen stabilizer in the United States for many years based on a robust set of regulatory data. These data demonstrated that nitrapyrin was not genotoxic and that there were no tumors elicited in rats or mice that were relevant for human risk assessment. A repeat carcinogenicity study in B6C3F1 mice, conducted at two substantially higher-dose levels (0, 125 or 250 mg/kg/day) than the original study (0, 5, 25 or 75 mg/kg/day) identified liver, stomach, epididymal and Harderian gland tumors. In order to assess the relevance of these findings for human risk assessment, a Scientific Advisory Group (SAG) examined relevant microscopic changes in these tissues and also evaluated genotoxicity and mechanistic data. The SAG determined that the maximum tolerated dose had been exceeded in mice given 125 or 250 mg/kg/day, based on 26-33% decreased body weight gains (males-250 mg/kg/day), hepatocellular necrosis and compensatory hepatocellular proliferation (males and females-125 and 250 mg/kg/day). The SAG believed that the increased incidences of hepatocellular foci of alteration and hepatocellular neoplasms represented an epigenetic response to hepatocellular necrosis and increased mitogenesis. Increased incidences of proliferative lesions in the forestomach mucosa were likely secondary to the irritant effects of nitrapyrin. Neither the liver nor forestomach effects were interpreted to be a direct carcinogenic effect. Higher incidences of Harderian gland adenomas (females) and undifferentiated sarcomas in the epididymis represented normal biological variations in incidence and were unrelated to nitrapyrin. Therefore, it was the SAG's opinion that nitrapyrin exposure that does not produce target organ toxicity in exposed individuals would not be expected to increase the risk of cancer.


Asunto(s)
Carcinógenos/toxicidad , Carcinoma Hepatocelular/inducido químicamente , Neoplasias Hepáticas/inducido químicamente , Picolinas/toxicidad , Administración Oral , Animales , Peso Corporal/efectos de los fármacos , Pruebas de Carcinogenicidad , Carcinógenos/clasificación , Carcinoma Hepatocelular/patología , Proliferación Celular/efectos de los fármacos , Consenso , Relación Dosis-Respuesta a Droga , Epigénesis Genética , Hepatocitos/efectos de los fármacos , Hepatocitos/patología , Neoplasias Hepáticas/patología , Ratones , Ratones Endogámicos , Picolinas/clasificación , Medición de Riesgo
5.
Kidney Int ; 71(3): 266-71, 2007 Feb.
Artículo en Inglés | MEDLINE | ID: mdl-17149371

RESUMEN

Endogenous creatinine clearance (Ccr) is widely accepted as an estimate of glomerular filtration rate (GFR), the best overall biomarker of kidney function. However, current common methods of measuring creatinine are not sensitive enough for mouse plasma. Accordingly, we here report a new method of measuring creatinine by liquid chromatography tandem mass spectrometry (LC-MS/MS) using deuterated [2H3]-creatinine as an internal standard. The assay requires 10 microl or less of plasma or urine, and is eight times more sensitive than high-performance liquid chromatography. The reproducibility of the assay of replicates is approximately +/-10%. The plasma creatinine levels of wild type male C57BL/6J mice obtained by LC-MS/MS are 0.076+/-0.002 mg/dl (n=65). To estimate daily urinary creatinine excretion for calculating Ccr, we collected urine from mice housed in metabolic cages, and combined this with washes from the cage internal surfaces. Creatinine in the wash varies from 4 to 67% of the total daily urinary creatinine excretion (typically approximately 400 microg/day). Ccr obtained by LC-MS/MS was 329+/-17 microl/min, which is indistinguishable from GFR measured by using fluorescein isothiocyanate-inulin. The LC-MS/MS method is sensitive, specific, simple, fast, and inexpensive; it is suitable for estimating GFR in conscious mice or other small animals. As it allows repeated measurements in the same animals, it facilitates detection of subtle differences or changes in renal function.


Asunto(s)
Cromatografía Liquida/métodos , Creatinina/sangre , Creatinina/orina , Tasa de Filtración Glomerular , Espectrometría de Masas en Tándem/métodos , Animales , Ratones , Ratones Endogámicos C57BL
6.
Carcinogenesis ; 26(9): 1573-80, 2005 Sep.
Artículo en Inglés | MEDLINE | ID: mdl-15888494

RESUMEN

1,3-Butadiene (BD) is a confirmed rodent carcinogen and a suspect human carcinogen that forms mutagenic epoxide metabolites during biotransformation. Species differences in the roles of individual DNA reactive intermediates in BD mutagenicity and carcinogenicity are not completely understood. Evidence suggests that 1,2:3,4-diepoxybutane (DEB) is responsible for the mutagenic effect induced by exposures to low concentrations of BD in mice and that metabolites of 3-butene-1,2-diol (BD-diol) are involved in the mutagenicity at high exposures in both mice and rats. Two reactive metabolites, 3,4-epoxy-1,2-butanediol (EB-diol) and hydroxymethylvinyl ketone (HMVK), are formed during the biotransformation of BD-diol and could potentially be involved in BD-diol associated mutagenicity. To examine the role of EB-diol in BD-diol mutagenicity we have evaluated the dosimetry of N7-(2,3,4-trihydroxybutyl)guanine (THB-Gua) and N-(2,3,4-trihydroxybutyl)valine (THB-Val) in female B6C3F1 mice and female F344 rats exposed by inhalation to 0, 6, 18 and 36 p.p.m. BD-diol for 4 weeks (6 h/day x 5 days/week). Results showed higher levels of both THB-Gua and THB-Val in mice than in rats. An evaluation of THB-Gua adducts showed virtually no differences between liver and lung for either species, suggesting that EB-diol is stable and is freely circulated. The data also indicated that THB adduct formation began to plateau around 18 p.p.m. in both species. Most importantly, the shape of the dose-response curve for THB adduct formation mimicked the one observed for hypoxanthine-guanine phosphoribosyltransferase (Hprt) mutation frequency. This showed that THB adducts, which are not thought to be responsible for causing the mutations, are good quantitative indicators of mutagenicity in rodents exposed to BD-diol. Although the potential contribution of HMVK still needs to be evaluated, the data suggest that EB-diol is responsible, at least in part, for BD-diol associated mutagenicity in rodents.


Asunto(s)
Aductos de ADN , Glicoles/toxicidad , Hemoglobinas/metabolismo , Animales , ADN/efectos de los fármacos , ADN/aislamiento & purificación , Femenino , Cromatografía de Gases y Espectrometría de Masas , Hígado/efectos de los fármacos , Pulmón/efectos de los fármacos , Ratones , Ratones Endogámicos , Ratas , Ratas Endogámicas F344 , Especificidad de la Especie , Valina/análogos & derivados
7.
Chem Biol Interact ; 135-136: 343-61, 2001 Jun 01.
Artículo en Inglés | MEDLINE | ID: mdl-11397400

RESUMEN

A study was conducted to test the hypothesis that repeated low level exposures to 1,3-butadiene (BD), approaching the OSHA occupational threshold for this chemical, produce a significant mutagenic response in mice. Female B6C3F1 mice (4-5 weeks of age) were exposed by inhalation for 2 weeks (6 h/day, 5 days/week) to 0 or 3 ppm BD, and then necropsied at 4 weeks after the cessation of exposures to measure the frequency of mutations (MF) at the Hprt locus using the T-lymphocyte clonal assay. At necropsy, T cells were isolated from spleen and cultured in the presence of mitogen, growth factors, and a selection agent. Cells were scored for growth on days 8-9 after plating to determine cloning efficiencies (CEs) and Hprt MFs. There was a marginal but significant reduction in the growth of splenic T cells from mice exposed to 3 ppm (n=27) compared with control mice (n=24) (P=0.004), suggesting the occurrence of BD-induced cytotoxicity at this low exposure concentration. In addition, the average Hprt MF in mice exposed to 3 ppm BD [1.54+/-0.82 (S.D.)x10(-6)] was significantly increased by 1.6-fold over the average control value of 0.96+/-0.51 (S.D.)x10(-6) (P=0.004). Comparisons of these data to earlier Hprt mutagenicity studies of mice exposed to high concentrations of BD (where significant mutagenic but not cytotoxic effects were observed) indicate that the ability to detect the cytotoxic and mutagenic responses of T cells to low levels of BD was enhanced by using a much larger sample size than usual for both the control and treatment groups. Additional analyses of the quantitative relationships between CE and MF demonstrated that CE had no significant effect upon MF values in sham-exposed control mice or mice exposed to low-level BD. Furthermore, the approaches for assessing the impact of CE and clonality on Hprt MFs in these control and BD-exposed mice were applied with the same rigor as in in vivo Hprt mutagenicity studies in human children. The overall study results support the conclusion that short-term low-level BD exposure is mutagenic in the mouse.


Asunto(s)
Butadienos/toxicidad , Hipoxantina Fosforribosiltransferasa/genética , Mutágenos/toxicidad , Linfocitos T/efectos de los fármacos , Administración por Inhalación , Animales , Butadienos/administración & dosificación , Pruebas de Carcinogenicidad , Carcinógenos/administración & dosificación , Carcinógenos/toxicidad , Ensayo de Unidades Formadoras de Colonias , Relación Dosis-Respuesta a Droga , Femenino , Neoplasias Pulmonares/inducido químicamente , Ratones , Pruebas de Mutagenicidad , Mutágenos/administración & dosificación , Linfocitos T/enzimología
8.
Chem Biol Interact ; 135-136: 387-403, 2001 Jun 01.
Artículo en Inglés | MEDLINE | ID: mdl-11397403

RESUMEN

The purpose of this paper is to review what we know about various biomarkers of butadiene in animal, human and in vitro studies, and to draw inferences from these data that impact on the accurate assessment of human risks for cancer. Studies comparing the DNA and hemoglobin adducts of butadiene with exposure, metabolism and genotoxicity have provided a great deal of insight that is applicable to biologically based risk assessment. First, the DNA and hemoglobin adduct data strongly support the conclusion that 3,4-epoxy-1,2-butanediol is the major electrophile available for binding to these macromolecules. Biomarker studies have also provided insight into the possibility of a sensitive population associated with the GSTT1 null genotype. While it is clear that lymphocytes from GSTT1 null individuals are more sensitive for the induction of sister chromatid exchanges (SCE) following in vitro exposure to 1,2,3,4-diepoxybutane, there was no such increase in SCE or other biomarkers of genotoxicity in workers exposed to 1-3 p.p.m. butadiene, regardless of GST genotype. The globin adduct data also demonstrate that there is roughly a tenfold range for interindividual differences in the metabolism of butadiene. This type of analysis represents an excellent means for providing scientific data for this critical determinant. Another useful application of hemoglobin adducts in risk assessment was demonstrated by regressing data for various endpoints for genotoxicity against that individual's biologically effective dose, thereby providing an independent mechanism for evaluation that excludes any possible confounding by inappropriate controls. Finally, biomarker studies have identified critical gaps in our knowledge that are needed for the accurate assessment of butadiene. Most notable of these is the lack of diepoxide-specific biomarkers in mice, rats and humans.


Asunto(s)
Butadienos/toxicidad , Aductos de ADN/efectos de los fármacos , Hemoglobinas/efectos de los fármacos , Animales , Biomarcadores , Butadienos/química , Butadienos/metabolismo , Aductos de ADN/química , Aductos de ADN/metabolismo , Hemoglobinas/química , Hemoglobinas/metabolismo , Humanos , Técnicas In Vitro , Mutágenos/química , Mutágenos/metabolismo , Mutágenos/toxicidad , Medición de Riesgo
9.
Chem Biol Interact ; 135-136: 429-53, 2001 Jun 01.
Artículo en Inglés | MEDLINE | ID: mdl-11397405

RESUMEN

The overall objective of this study was to evaluate a continuum of biomarkers in blood and urine for their sensitivities as indicators of low level occupational exposures to 1,3 butadiene (BD). The study design was largely cross-sectional, with biological samples collected within a short timeframe. Personal 8-h BD exposure measures were made on several occasions over a 60-day period for each potentially exposed worker in order provide maximum accuracy for this independent variable and to accommodate the different expression intervals of the several biomarkers. Co-exposures to styrene, toluene and benzene were also measured. The study included 24 BD monomer production workers (mean BD exposure=0.642 mg/m(3)), 34 polymerization workers (mean BD exposure=1.794 mg/m(3)) and 25 controls (mean BD exposure=0.023 mg/m(3)). The several biomarkers were measured by a consortium of investigators at different locations in the US and Europe. These biomarkers included: (1) metabolic genotypes (CYP2E1, EH, GST M1, GST T1, ADH2, ADH3), determined in Prague and Burlington, VT; (2) urinary M1 and M2 metabolites (1,2-dihydroxy-4-[N-acetylcysteinyl]-butane and 1-hydroxy-2-[N-acetylcysteinyl]-3-butene, respectively), determined in Albuquerque, NM and Leiden; (3) hemoglobin adducts (N-[2-dihydroxy-3-butenyl]valine=HBVal and N-[2,3,4-trihydroxybutyl]valine=THBVal), determined in Amsterdam and Chapel Hill, NC, respectively; (4) HPRT mutations determined by autoradiographic assay in Galveston, TX, with slides re-read in Burlington, VT; (6) hypoxanthine-guanine phosphoribosyltransferase (HPRT) mutations determined by cloning assay in Leiden with mutational spectra characterized in Burlington, VT; (7) sister chromatid exchanges and chromosome aberrations determined by standard methods and FISH analysis in Prague. Urinary M1 and M2 metabolites and HBVal and THBVal hemoglobin adducts were all significantly correlated with BD exposure levels, with adducts being the most highly associated. No significant relationships were observed between BD exposures and HPRT mutations or any of the cytogenetic endpoints, regardless of method of assay.


Asunto(s)
Butadienos/toxicidad , Adulto , Benceno/toxicidad , Biomarcadores/sangre , Biomarcadores/orina , Butadienos/administración & dosificación , Butadienos/farmacocinética , Estudios Transversales , Citogenética , Hemoglobinas/efectos de los fármacos , Humanos , Hipoxantina Fosforribosiltransferasa/genética , Masculino , Mutación , Exposición Profesional , Medición de Riesgo , Estireno/toxicidad , Tolueno/toxicidad
10.
Chem Biol Interact ; 135-136: 455-64, 2001 Jun 01.
Artículo en Inglés | MEDLINE | ID: mdl-11397406

RESUMEN

We examined a spectrum of genotoxic and other outcomes in 41 butadiene-polymer production workers and 38 nonexposed controls, in China, to explore the role of butadiene in human carcinogenesis. Among butadiene-exposed workers, median air exposure was 2 ppm (6-h TWA), due largely to intermittent high-level exposures. Compared to unexposed subjects, butadiene-exposed workers had greater levels of hemoglobin N-(2,3,4-trihydroxybutyl)valine (THBVal) adducts (P<0.0001), and adduct levels tended to correlate, among butadiene-exposed workers, with air measures (P=0.03). Butadiene-exposed workers did not differ, however, from unexposed workers with respect to frequency of uninduced or diepoxybutane-induced sister chromatid exchanges, aneuploidy as measured by fluorescence in situ hybridization of chromosomes 1, 7, 8 and 12, glycophorin A variants or lymphocyte hprt somatic mutation. Also among the exposed, greater THBVal levels were not associated with increases in uninduced sister chromatid exchanges, aneuploidy, glycophorin A, or hprt mutations. Butadiene-exposed workers had greater lymphocyte (P=0.002) and platelet counts (P=0.07) and lymphocytes as a percent of white blood cells were moderately correlated with greater THBVal levels (Spearman's rho=0.32, P=0.07). Among butadiene-exposed workers, several serum cytokines correlated with THBVal adduct levels. Overall, the study demonstrated exposure to butadiene in these workers, by a variety of short-term and long-term measures, but did not show specific genotoxic effects, at the chromosomal or gene levels, related to that exposure.


Asunto(s)
Butadienos/toxicidad , Carcinógenos/toxicidad , Contaminantes Ocupacionales del Aire/análisis , Contaminantes Ocupacionales del Aire/toxicidad , Biomarcadores/análisis , Butadienos/análisis , Carcinógenos/análisis , China , Femenino , Hemoglobinas/química , Hemoglobinas/efectos de los fármacos , Humanos , Masculino , Pruebas de Mutagenicidad , Exposición Profesional , Polímeros/toxicidad , Intercambio de Cromátides Hermanas/efectos de los fármacos
11.
Chem Biol Interact ; 135-136: 675-8, 2001 Jun 01.
Artículo en Inglés | MEDLINE | ID: mdl-11397421

RESUMEN

Hemoglobin adducts were determined as biomarkers of 1,3-butadiene (BD) in 30 workers and 10 controls from an Italian BD plant and in 14 diesel-exposed miners. N-(2,3,4-trihydroxybutyl)valine (THBVal), an N-terminal valine globin adduct of reactive butadiene metabolites, was analyzed by gas chromatography/high resolution mass spectrometry after a modified Edman degradation and further acetylation. The BD exposure for the plant workers was 31 microg/m(3) (personal sampling). Whereas there was no detectable difference in hemoglobin adduct levels (range 17.7-61.4 pmol/g globin) between the total group of exposed and controls, slight but significant differences could be found between two subgroups of workers from different production units as well as one subgroup and controls (P<0.05), between smoking (n=13) and non-smoking exposed workers (n=17; P=0.066) as well as between smoking exposed workers and controls (P=0.055). Adduct levels of the miners (all non-smokers) were in the same range as those of the Italian BD-workers and controls. The internal exposure and strain measured by THBVal levels resulting from a very low occupational BD exposure was in the range of the contribution of moderate smoking.


Asunto(s)
Butadienos/toxicidad , Hemoglobinas/química , Hemoglobinas/efectos de los fármacos , Biomarcadores/sangre , Butadienos/análisis , Gasolina/toxicidad , Hemoglobinas/análisis , Humanos , Italia , Minería , Exposición Profesional
12.
Carcinogenesis ; 22(4): 627-34, 2001 Apr.
Artículo en Inglés | MEDLINE | ID: mdl-11285199

RESUMEN

DNA damage induced by quinoid metabolites of pentachlorophenol (PCP), i.e. tetrachloro-1,4-benzoquinone (Cl(4)BQ) and tetrachlorohydroquinone (Cl(4)HQ), was investigated in calf thymus DNA. The (32)P-post-labeling assay revealed four major and several minor adducts (3.5 adducts per 10(5) total nucleotides) that were produced in calf thymus DNA treated with Cl(4)BQ (5 mM). These DNA adducts were chemically stable even after conditions that induce thermal depurination and are unlikely to undergo depurination/depyrimidination to form apurinic/apyrimidinic (AP) sites. In addition, increases in 8-hydroxy-deoxyguanosine (8-HO-dG) (5 8-HO-dG per 10(5) nucleotides) and AP sites (0.5 AP sites per 10(5) nucleotides) were observed in Cl(4)BQ-modified calf thymus DNA. Further investigation indicated that in the presence of Cu(II) and NADPH, low concentrations of Cl(4)BQ (1 microM) induced a doubling of 8-HO-dG (10 8-HO-dG per 10(5) nucleotides) and dramatic increases in AP sites (20 AP sites per 10(5) nucleotides) and DNA single-strand breaks. The types of DNA damage induced by Cl(4)HQ plus Cu(II) were similar to those by Cl(4)BQ plus Cu(II) and NADPH, whereas catalase inhibited the formation of DNA damage. These data suggest that oxidative damage is causally involved in the formation of AP sites. Concentration-dependent increases in 8-HO-dG induced by Cl(4)HQ plus Cu(II) and Cl(4)BQ plus Cu(II) and NADPH were correlated with the formation of AP sites (r(2) = 0.977) with a ratio of 8-HO-dG to AP sites at 1:1.6. The AP site-cleavage assay confirmed that approximately 85% of the AP sites induced by Cl(4)HQ and Cu(II) were detected as 5'-cleaved AP sites. Since hydrogen peroxide alone causes similar DNA damage, these results suggest the involvement of Cu(II) and hydrogen peroxide in the induction of oxidative DNA damage by Cl(4)HQ/Cl(4)BQ. The data demonstrate that PCP quinone and hydroquinone induce direct and oxidative base modifications as well as the formation of 5'-cleaved AP sites in genomic DNA. These lesions may have important implications for PCP clastogenicity and carcinogenicity.


Asunto(s)
Cloranilo , Aductos de ADN/metabolismo , Daño del ADN/efectos de los fármacos , ADN/efectos de los fármacos , Desoxiguanosina/análogos & derivados , Fungicidas Industriales , Hidroquinonas , Mutágenos , Oxígeno/metabolismo , Timo/metabolismo , 8-Hidroxi-2'-Desoxicoguanosina , Animales , Sitios de Unión , Bovinos , Cromatografía Líquida de Alta Presión , Cobre/farmacología , Desoxiguanosina/farmacología , Relación Dosis-Respuesta a Droga , Modelos Químicos , NADP/metabolismo , Purinas/metabolismo , Pirimidinas/metabolismo , Especies Reactivas de Oxígeno , Análisis de Regresión
13.
Carcinogenesis ; 22(4): 635-9, 2001 Apr.
Artículo en Inglés | MEDLINE | ID: mdl-11285200

RESUMEN

DNA damage induced by tetrachlorohydroquinone (Cl(4)HQ), the quinonoid metabolite of pentachlorophenol (PCP), was investigated in human HeLa S3 tumor cells. Formation of one major and two minor DNA adducts in cells treated with Cl(4)HQ (50-300 microM) was detected by (32)P-post-labeling assay and the adducts accumulated over the course of the experiment (0.5-2 h), with total adduct levels estimated to be 3-6 per 10(8) nucleotides. These adducts did not correspond to those derived from calf thymus DNA treated with tetrachloro-1,4-benzoquinone. Results from the apurinic/apyrimidinic (AP) sites assay indicated that the number of AP sites was 2-fold greater in cells exposed to Cl(4)HQ (300 microM) than the corresponding control. Further characterization of the AP sites confirmed that Cl(4)HQ induced predominantly (75%) putrescine-excisable AP sites in HeLa S3 cells. In parallel, the concentration of 8-hydroxy-2'-deoxyguanosine (8-HO-dG) in cells treated with Cl(4)HQ for 0.5 and 2 h was increased 2- and 5-fold, respectively, compared with the control. The extent of oxidative DNA damage induced by Cl(4)HQ was approximately two orders of magnitude greater than those of direct DNA adducts. Overall, it appears that reactive oxygen species mediate the parallel formation of AP sites and 8-HO-dG in HeLa S3 cells following treatment with Cl(4)HQ and that the contribution of depurination/depyrimidination of direct DNA adducts is relatively insignificant compared with the formation of oxidized AP sites. We conclude that putrescine-excisable AP sites represent a major type of ROS-mediated oxidative DNA damage in cellular DNA induced by Cl(4)HQ and may play a role in PCP-induced clastogenicity in mammalian cells.


Asunto(s)
Núcleo Celular/metabolismo , Aductos de ADN , ADN/efectos de los fármacos , Desoxiguanosina/análogos & derivados , Hidroquinonas , Oxígeno/metabolismo , 8-Hidroxi-2'-Desoxicoguanosina , Cromatografía Líquida de Alta Presión , Desoxiguanosina/análisis , Relación Dosis-Respuesta a Droga , Células HeLa , Humanos , Modelos Químicos , Purinas , Putrescina/farmacología , Pirimidinas , Especies Reactivas de Oxígeno , Factores de Tiempo
14.
Toxicol Appl Pharmacol ; 172(2): 83-92, 2001 Apr 15.
Artículo en Inglés | MEDLINE | ID: mdl-11298494

RESUMEN

Octamethylcyclotetrasiloxane (D4) has been described as a phenobarbital-like inducer of hepatic enzymes. Phenobarbital (PB) and phenobarbital-like chemicals induce transient hepatic and thyroid hyperplasia and sustained hypertrophy in rats and mice. The extent to which these processes are involved with D4-induced hepatomegaly is not known. The present study has evaluated the effects of repeated inhalation exposure to D4 vapors on hepatic and thyroid cell proliferation and hypertrophy with respect to time and exposure concentration. Female Fischer 344 rats were exposed via whole body inhalation to 0 ppm D4, 700 ppm D4 vapors (6 h/day; 5 days/week), or 0.05% PB in drinking water over a 4-week period. Incorporation of 5'-bromo-2-deoxyuridine (BrdU) and the abundance of proliferating cell nuclear antigen were used as indicators of cell proliferation. Designated animals from each treatment group were euthanized on study days 6, 13, and 27. The effect of D4 exposure concentration on hepatic cell proliferation was evaluated at 0, 7, 30, 70, 150, 300, or 700 ppm. Liver-to-body weight ratios in animals exposed to 700 ppm D4 were increased 18, 20, and 22% over controls while PB-treated animals showed increases of 33, 27, and 27% over controls on days 6, 13, and 27 respectively. Hepatic incorporation of BrdU following exposure to D4 was highest on day 6 (labeling index = 15-22%) and was at or below control values by day 27. This pattern of transient hyperplasia was observed in all hepatic lobes examined and was similar to the pattern observed following treatment with PB.


Asunto(s)
Hepatomegalia/inducido químicamente , Hígado/efectos de los fármacos , Hígado/patología , Fenobarbital/toxicidad , Siloxanos/toxicidad , Animales , Bromodesoxiuridina/metabolismo , ADN/metabolismo , Femenino , Hiperplasia/inducido químicamente , Hipertrofia/inducido químicamente , Exposición por Inhalación , Antígeno Nuclear de Célula en Proliferación/metabolismo , Ratas , Ratas Endogámicas F344
15.
Chem Res Toxicol ; 14(3): 327-34, 2001 Mar.
Artículo en Inglés | MEDLINE | ID: mdl-11258983

RESUMEN

We have previously described an immunoaffinity/gas chromatography/electron capture negative chemical ionization high-resolution mass spectrometry (IA/GC/ECNCI-HRMS) assay for quantitation of the promutagenic DNA adduct N(2),3-ethenoguanine (N(2),3-epsilonGua) in vivo. Here we present an expanded assay that allows simultaneous quantitation of its structural isomer, 1,N(2)-ethenoguanine (1,N(2)-epsilonGua), in the same DNA sample. 1,N(2)-epsilonGua and N(2),3-epsilonGua were purified together from hydrolyzed DNA using two immobilized polyclonal antibodies. GC/ECNCI-HRMS was used to quantitate the 3,5-bis(pentafluorobenzyl) (PFB) derivative of each adduct against an isotopically labeled analogue. Selected ion monitoring was used to detect the [M - 181](-) fragments of 3,5-(PFB)(2)-N(2),3-epsilonGua and 3,5-(PFB)(2)-[(13)C(4),(15)N(2)]-N(2),3-epsilonGua and the [M - 201](-) fragments of 3,5-(PFB)(2)-1,N(2)-epsilonGua and 3,5-(PFB)(2)-[(13)C(3)]-1,N(2)-epsilonGua. The demonstrated limits of quantitation in hydrolyzed DNA were 7.6 fmol of N(2),3-epsilonGua and 15 fmol of 1,N(2)-epsilonGua in approximately 250 microg of DNA, which corresponded to 5.0 N(2),3-epsilonGua and 8.7 1,N(2)-epsilonGua adducts/10(8) unmodified Gua bases, respectively. 1,N(2)-epsilonGua was found to be the predominant ethenoguanine adduct formed in reactions of lipid peroxidation products with DNA. The respective ratios of 1,N(2)-epsilonGua to N(2),3-epsilonGua were 5:1 and 38:1 when calf thymus DNA was treated with ethyl linoleate or 4-hydroxynonenal, respectively, under peroxidizing conditions. Only N(2),3-epsilonGua was detected in DNA treated with the vinyl chloride (VC) metabolite 2-chloroethylene oxide and in hepatocyte DNA from rats exposed to 1100 ppm VC for 4 weeks (6 h/day for 5 days/week). These data suggest that 1,N(2)-epsilonGua plays a minor role relative to N(2),3-epsilonGua in VC-induced carcinogenesis, but that 1,N(2)-epsilonGua may be formed to a larger extent from endogenous oxidative processes.


Asunto(s)
Aductos de ADN/análisis , Guanina/análogos & derivados , Guanina/análisis , Animales , Anticuerpos , Transformación Celular Neoplásica , Cromatografía de Gases y Espectrometría de Masas , Inmunoensayo , Masculino , Oxidación-Reducción , Conejos , Ratas , Ratas Sprague-Dawley , Sensibilidad y Especificidad , Cloruro de Vinilo/efectos adversos , Cloruro de Vinilo/farmacología
16.
Chem Res Toxicol ; 13(12): 1243-50, 2000 Dec.
Artículo en Inglés | MEDLINE | ID: mdl-11123965

RESUMEN

In these studies, we demonstrate that N(2),3-ethenoguanine (N(2), 3-epsilonGua) is formed from lipid peroxidation as well as other oxidative reactions. Ethyl linoleate (EtLA) or 4-hydroxy-2-nonenal (HNE) was reacted with dGuo in the presence of tert-butyl hydroperoxide (t-BuOOH) for 72 h at 50 degrees C. The resulting N(2), 3-epsilonGua was characterized by liquid chromatography/electrospray mass spectroscopy and by gas chromatography/high-resolution mass spectral (GC/HRMS) analysis of its pentafluorobenzyl derivative following immunoaffinity chromatography purification. The amounts of N(2),3-epsilonGua formed were 825 +/- 20 and 1720 +/- 50 N(2), 3-epsilonGua adducts/10(6) normal dGuo bases for EtLA and HNE, respectively, corresponding to 38- and 82-fold increases in the amount of N(2),3-epsilonGua compared to controls containing only t-BuOOH. Controls containing t-BuOOH but no lipid resulted in a >1000-fold increase in the level of N(2),3-epsilonGua over dGuo that was not subjected to incubation. EtLA and HNE, in the presence of t-BuOOH, were reacted with calf thymus DNA at 37 degrees C for 89 h. The amounts of N(2),3-epsilonGua formed in intact ctDNA were 114 +/- 32 and 52.9 +/- 16.7 N(2),3-epsilonGua adducts/10(6) normal dGuo bases for EtLA and HNE, respectively. These compared to 2.02 +/- 0. 17 and 2.05 +/- 0.47 N(2),3-epsilonGua adducts/10(6) normal dGuo bases in control DNA incubated with t-BuOOH, but no lipid. [(13)C(18)]EtLA was reacted with dGuo to determine the extent of direct alkylation by lipid peroxidation byproducts. These reactions resulted in a 89-93% level of incorporation of the (13)C label into N(2),3-epsilonGua when EtLA and dGuo were in equimolar concentrations, when EtLA was in 10-fold molar excess, and when deoxyribose (thymidine) was in 10-fold molar excess. Similar reactions with ctDNA resulted in an 86% level of incorporation of the (13)C label. These data demonstrate that N(2),3-epsilonGua is formed from EtLA and HNE under peroxidizing conditions by direct alkylation. The data also suggest, however, that N(2),3-epsilonGua is also formed by an alternative mechanism that involves some other oxidative reaction which remains unclear.


Asunto(s)
Aldehídos/química , Guanosina/análogos & derivados , Guanosina/química , Ácidos Linoleicos/química , Peroxidación de Lípido , Mutágenos/química , Animales , Bovinos , Cromatografía Líquida de Alta Presión , Aductos de ADN/química , Cromatografía de Gases y Espectrometría de Masas
17.
Carcinogenesis ; 21(11): 2011-8, 2000 Nov.
Artículo en Inglés | MEDLINE | ID: mdl-11062162

RESUMEN

Propylene oxide (PO) is a relatively weak mutagen that induces nasal tumor formation in rats during long-term inhalation studies at high exposures (> or =300 p.p.m.), concentrations that also cause cytotoxicity and increases in cell proliferation. Direct alkylation of DNA by PO leads mainly to the formation of N:7-(2-hydroxypropyl)guanine (7-HPG). In this study, the accumulation of 7-HPG in tissues of male F344 rats exposed to 500 p. p.m. PO (6 h/day, 5 days/week for 4 weeks) by the inhalation route was measured by gas chromatography-high resolution mass spectrometry (GC-HRMS). In animals killed up to 7 h following the end of the last exposure the levels of 7-HPG (pmol/micromol guanine) in nasal respiratory tissue, nasal olfactory tissue, lung, spleen, liver and testis DNA were 606.2 +/- 53.0, 297.5 +/- 56.5, 69.8 +/- 3.8, 43.0 +/- 3.8, 27.5 +/- 2.4 and 14.2 +/- 0.7, respectively. The amounts of 7-HPG in the same tissues of animals killed 3 days after cessation of exposure were 393.3 +/- 57.0, 222.7 +/- 29.5, 51.5 +/- 1.2, 26.7 +/- 1.0, 18.0 +/- 2.6 and 10.4 +/- 0.1. A comparable rate of disappearance of 7-HPG was found among all tissues. DNA from lymphocytes pooled from four rats killed at the end of the last exposure was found to have 39.6 pmol adduct/micromol guanine. Quantitation of DNA apurinic/apyrimidinic sites, potentially formed after adduct loss by chemical depurination or DNA repair, showed no difference between tissues from control and exposed rats. The level of N:-(2-hydroxypropyl)valine in hemoglobin of exposed rats was also determined using a modified Edman degradation method followed by GC-HRMS analysis. The value obtained was 90.2 +/- 10.3 pmol/mg globin. These data demonstrate that nasal respiratory tissue, which is the target tissue for carcinogenesis, has a much greater level of alkylation of DNA than non-target tissues.


Asunto(s)
Aductos de ADN/análisis , Compuestos Epoxi/toxicidad , Guanina/análogos & derivados , Guanina/análisis , Hemoglobinas/metabolismo , Mutágenos/toxicidad , Valina/análogos & derivados , Valina/análisis , Animales , Ácido Apurínico/metabolismo , Radioisótopos de Carbono , ADN/efectos de los fármacos , ADN/metabolismo , Aductos de ADN/biosíntesis , Compuestos Epoxi/metabolismo , Cromatografía de Gases y Espectrometría de Masas , Guanina/biosíntesis , Hemoglobinas/análisis , Exposición por Inhalación , Masculino , Mutágenos/metabolismo , Radioisótopos de Fósforo , Ratas , Ratas Endogámicas F344 , Salmón , Testículo/química , Valina/biosíntesis
18.
Cancer Res ; 60(17): 4798-803, 2000 Sep 01.
Artículo en Inglés | MEDLINE | ID: mdl-10987289

RESUMEN

It was shown that 4-chloro-6-(2,3-xylidino)-2-pyrimidinylthio acetic acid (Wy-14,643), a potent peroxisome proliferator, caused rapid oxidant-dependent activation of nuclear factor kappaB (NF-kappaB) in Kupffer cells in vivo and activated superoxide production by isolated Kupffer cells. Here, we tested the hypothesis that NADPH oxidase (NADPH OX) is the source of oxidants increased by Wy-14,643. Indeed, both activation of NF-kappaB and increases in cell proliferation due to a single dose of Wy-14,643 (100 mg/kg) were prevented completely when rats were pretreated with diphenyleneiodonium (1 mg/kg), an inhibitor of NADPH OX. p47phox is a critical subunit of NADPH OX; therefore, p47phox knockout mice were used to specifically address the hypothesis of NADPH OX involvement. In livers of wild-type mice, Wy-14,643 activated NF-kappaB, followed by an increase in mRNA for tumor necrosis factor a. Importantly, these changes did not occur in p47phox knockouts. Moreover, when Kupffer cells were treated with Wy-14,643 in vitro, superoxide production was increased in cells from wild-type but not p47phox-null mice. Finally, when mice were fed a Wy-14,643-containing (0.1%) diet for 7 days, the increase in liver weight and cell proliferation caused by Wy-14,643 in wild-type mice was blocked in p47phox-null mice. Combined, these results are consistent with the hypothesis that Wy-14,643 activates NADPH OX, which leads to NF-kappaB-mediated production of mitogens that causes hepatocellular proliferation characteristic of this class of nongenotoxic carcinogens.


Asunto(s)
Carcinógenos/toxicidad , Hígado/efectos de los fármacos , NADPH Oxidasas/metabolismo , Proliferadores de Peroxisomas/toxicidad , Pirimidinas/toxicidad , Superóxidos/toxicidad , Animales , División Celular/efectos de los fármacos , Inhibidores Enzimáticos/farmacología , Femenino , Macrófagos del Hígado/citología , Macrófagos del Hígado/efectos de los fármacos , Macrófagos del Hígado/enzimología , Hígado/citología , Hígado/enzimología , Ratones , Ratones Endogámicos C57BL , Ratones Noqueados , NADPH Oxidasas/antagonistas & inhibidores , FN-kappa B/fisiología , Compuestos Onio/farmacología , Fosfoproteínas/deficiencia , Fosfoproteínas/genética , Fosfoproteínas/metabolismo , ARN Mensajero/biosíntesis , ARN Mensajero/genética , Ratas , Ratas Sprague-Dawley , Superóxidos/antagonistas & inhibidores , Superóxidos/metabolismo , Factor de Necrosis Tumoral alfa/biosíntesis , Factor de Necrosis Tumoral alfa/genética
19.
Res Rep Health Eff Inst ; (92): 191-210; discussion 211-9, 2000 Mar.
Artículo en Inglés | MEDLINE | ID: mdl-10925842

RESUMEN

1,3-Butadiene (BD) is an important chemical used largely in the manufacture of synthetic rubber and thermoplastic resins. In addition, it has been identified in cigarette smoke, automobile exhaust, and gasoline vapor. The objective of this research was to develop highly sensitive and specific assays for the detection and quantitation of hemoglobin adducts of three BD metabolites: 1,2-epoxy-3-butene (BDO), 1,2,3,4-diepoxybutane (BDO2), and 1,2-dihydroxy-3,4-epoxybutane (BDO-diol). We have successfully developed an assay for both N-(2-hydroxy-3-butenyl)valine (HBVal) and N-(2,3,4-trihydroxybutyl)valine (THBVal) in hemoglobin. The six adducts measured were the two diastereomers (isomers I and II) of HBVal and the four diastereomers of THBVal (isomers I through IV, which were eluted as three peaks, 1, 2, and 3). HBVal and THBVal were measured in control and exposed B6C3F1 mice and Sprague-Dawley rats (1,000 ppm BD for 13 weeks at 6 hours/day, 5 days/week). In a second set of animal exposures, total THBVal was determined in B6C3F1 female mice (n = 5) exposed to 1,250 ppm BD for 1, 5, or 10 days (6 hours/day, 5 days/week). THBVal adducts were also monitored in occupationally exposed Chinese workers and nonoccupationally exposed U.S. laboratory workers. This study utilized the modified Edman degradation method of Törnqvist and colleagues (1986). Briefly, the samples were subjected to Edman degradation, Centricon-30 ultrafiltration, washing on C18 columns, and acetylation for isomers of THBVal only, followed by gas chromatography-mass spectrometry (GC-MS) quantitation. For the HBVal assay, an authentic internal standard globin alkylated with [2H6]BDO was used; for the THBVal assay, a synthesized external standard, THB[13C5]Val, was used after Edman degradation. The mean +/- SD amounts of total HBVal measured in exposed mice (in pmol/g globin) were 16,560 +/- 3,910 for female mice (n = 4) and 12,400 +/- 2,030 for male mice (n = 5). The corresponding values for rats were 8,690 +/- 930 for female rats (n = 5) and 5,480 +/- 2,880 for male rats (n = 3). The total amount of THBVal (eluted peaks 1, 2, and 3) in male mice (n = 5) was 78,900 +/- 13,700; and in females (n = 2) was 56,100 +/- 100. In male rats (n = 3), the detected value was 9,650 +/- 1,620 and in females (n = 3) the value was 21,600 +/- 6,780. In control male mice (n = 4), the total level of THBVal isomers was approximately 27 pmol/g globin. In a control male rat, total THBVal was approximately 15 pmol/g globin. In the time course study, the amount of THBVal adducts increased linearly with exposure, resulting in values of 4,200 +/- 830, 19,760 +/- 1,780, and 35,940 +/- 3,460 pmol/g globin following 1, 5, or 10 days of exposure to 1,250 ppm BD, respectively. Detection of HBVal in human samples was difficult due to low concentrations of adducts and a high background in the chromatograms. In a pooled sample from 4 individuals, we performed multiple separations with high-pressure liquid chromatography (HPLC) of the derivatized adducts and detected 4.6 pmol/g globin (that is, 2.7 and 1.9 pmol/g globin for isomers I and II, respectively). We measured the amounts of THBVal in both nonoccupationally exposed U.S. laboratory workers and occupationally exposed workers from a polybutadiene plant in China. The mean total amount of THBVal among the U.S. laboratory workers was 36 +/- 23 pmol/g globin for nonsmokers (n = 7) and 40 +/- 9 for smokers (n = 4), compared with a mean total amount of 39 +/- 13 pmol/g globin in a control set of Chinese workers (n = 25). These control values are overestimations of the true values because the amounts of THBVal in globin samples from other unexposed individuals (15 of 51) were below our limit of detection. BD-exposed Chinese workers had a total amount of 88 +/- 59 pmol/g globin THBVal. The difference between smokers and nonsmokers was not significant, whereas the difference between control and exposed Chinese workers was highly significant (p < 0.001).


Asunto(s)
Biomarcadores , Butadienos/toxicidad , Aductos de ADN , Hemoglobinas/efectos de los fármacos , Mutación , Neoplasias Experimentales/inducido químicamente , Animales , Butadienos/metabolismo , Calibración , Pruebas de Carcinogenicidad , Carcinógenos/metabolismo , Carcinógenos/toxicidad , Femenino , Humanos , Masculino , Ratones , Pruebas de Mutagenicidad , Mutágenos/metabolismo , Mutágenos/toxicidad , Ratas , Ratas Sprague-Dawley , Estándares de Referencia
20.
Chem Res Toxicol ; 13(8): 710-8, 2000 Aug.
Artículo en Inglés | MEDLINE | ID: mdl-10956058

RESUMEN

A possible role for metabolic activation of 2,2',5, 5'-tetrachlorobiphenyl (TCB) to quinonoid metabolites was investigated in vitro in rat liver microsomes and in vivo in male Sprague-Dawley rats. Incubation of TCB with phenobarbital-induced rat liver microsomes resulted in metabolism of TCB to 3-hydroxy-TCB (3-OH-TCB) and 3,4-dihydroxy-TCB (3,4-diOH-TCB), which were further oxidized to form a reactive intermediate that bound to liver proteins. The predominant species observed in the Raney nickel assay for cysteinyl adducts was identified as 3,4-diOH-TCB, consistent with an adduct having the structure 5-cysteinyl-3,6-dichloro-4-(2', 5'-dichlorophenyl)-1,2-benzoquinone. This adduct may arise via the Michael addition of the sulfhydryl group of cysteine to 3, 6-dichloro-4-(2',5'-dichlorophenyl)-1,2-benzoquinone (Cl(4)PhBQ). Metabolism of 3-OH-TCB by phenobarbital-induced microsomes in the presence of either NADPH or cumene hydroperoxide as a cofactor resulted in the formation of adducts. Dose-dependent formation of cysteinyl adducts was observed in liver cytosolic protein from rats treated with a single dose of TCB (0-200 mg/kg) by gavage. By regression analysis, the TCB adducts decayed with a half-life of 2. 03 +/- 0.131 days (mean +/- SE), which is approximately 2.5-fold shorter than the endogenous half-life for liver cytosolic protein in rat liver, suggesting adduct instability. Saturable formation of TCB adducts was observed in liver cytosolic protein of rats receiving multiple doses of TCB over 5 days. The levels of Cl(4)PhBQ-derived adducts were 2.1-fold greater than the estimated steady-state levels predicted by the single-dose treatment [97.7 +/- 13.2 vs 45.7 +/- 3. 73 (pmol/g)/(mg/kg of body weight)], suggesting induction of metabolism. A single cysteinyl adduct, inferred to be 5-cysteinyl-3, 6-dichloro-4-(2',5'-dichlorophenyl)-1,2-benzoquinone, was detected in brain cytosolic protein of rats treated with multiple doses of TCB with levels of 15.2 (pmol/g)/(mg/kg of body weight). Implied involvement of a reactive quinone in the liver and brain of TCB-treated rats supports the idea that quinonoid metabolites may be important contributors to PCB-derived oxidative damage to genomic DNA.


Asunto(s)
Encéfalo/metabolismo , Hígado/metabolismo , Bifenilos Policlorados/metabolismo , Quinonas/metabolismo , Animales , Cisteína/metabolismo , Citosol/metabolismo , Relación Dosis-Respuesta a Droga , Cromatografía de Gases y Espectrometría de Masas , Semivida , Masculino , Microsomas Hepáticos/efectos de los fármacos , Microsomas Hepáticos/metabolismo , Bifenilos Policlorados/farmacología , Unión Proteica/efectos de los fármacos , Ratas , Ratas Sprague-Dawley
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