RESUMO
Oesophageal cancer is one of the most common and lethal malignancies in the world. Despite many efforts, treatment is still ineffective for most cases; thus, the development of preventive strategies is crucial for decreasing the burden presented by this disease. Environmental factors, particularly nitrosamines, are thought to be involved in the genesis of oesophageal tumours, and knowledge about the expression of enzymes capable of activating pre-carcinogens in human oesophagus is very important for the development of preventive measures. We analysed the expression of CYP1A1, CYP1A2, CYP2A6/2A7, CYP2E1 and CYP3A4 mRNA in oesophageal mucosa of 50 patients by semi-quantitative RT-PCR. In five patients, who suffered from squamous cell carcinoma, we measured Nnitrosodimethylamine and N-nitrosodiethylamine metabolism in normal and tumorous tissue. CYP2A6/2A7 mRNA was expressed in 61% and CYP2E1 mRNA in 96% of the patients, but in the latter a lower degree of inter-individual variation was observed. These enzymes were expressed either in the distal or middle portions of the oesophagus of 90% of the patients. CYP1A1, CYP1A2 and CYP3A4 mRNA expression was not detected in any portion of the oesophagus. Oesophageal microsomes activated N-nitrosodimethylamine with a low degree of inter-individual variation and microsomes prepared from the tumour of a patient who strongly expressed CYP2A6/2A7 mRNA activated N-nitrosodiethylamine. We conclude that the human oesophagus expresses CYP2A6/2A7 and CYP2E1 and can activate nitrosamines. Notably, the expression of these enzymes is preferentially localized to the most common sites where tumours arise.
Assuntos
Hidrocarboneto de Aril Hidroxilases , Citocromo P-450 CYP2E1/biossíntese , Sistema Enzimático do Citocromo P-450/biossíntese , Esôfago/enzimologia , Oxigenases de Função Mista/biossíntese , Mucosa Bucal/enzimologia , Alquilantes/metabolismo , Carcinoma de Células Escamosas/enzimologia , Citocromo P-450 CYP2A6 , Família 2 do Citocromo P450 , Dietilnitrosamina/metabolismo , Dimetilnitrosamina/metabolismo , Humanos , Microssomos/enzimologia , Neoplasias Bucais/enzimologia , RNA Mensageiro/metabolismo , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Fatores de TempoRESUMO
In previous studies from our laboratory we reported the presence in highly purified liver nuclei, free of contamination with other organelles, of an ethanol metabolizing system (NEMS) able to lead to acetaldehyde and 1-hydroxyethyl free radicals (1HEt). In the present study we tested whether this NEMS is inducible by chronic alcohol administration to rats and whether these nuclei also have increased ability to bioactivate N-nitrosodimethylamine (NDMA). Sprague Dawley male rats (125-150g) were fed with a nutritionally adequate liquid diet containing alcohol to provide 36% of total energy (standard Lieber-De Carli rat diet), for 28 days. Controls received an isocaloric diet without alcohol. Animals were sacrificed, livers were excised and microsomes and purified nuclear fractions were prepared. Both microsomes and nuclei from treated animals had significantly increased ability compared to controls, to biotransform ethanol to acetaldehyde using NADPH as cofactor under an air atmosphere. Both organelles also exhibited significantly increased capacity compared to controls, to bioactivate NDMA to formaldehyde and to reactive metabolites that bind covalently to proteins. Nuclear preparations from control animals were also able to metabolize NDMA to formaldehyde and reactive metabolites. Results indicate that liver nuclei may have a CYP2E1 able to bioactivate both NDMA and EtOH and that these processes are being induced by chronic alcohol drinking. The bioactivation of these xenobiotics to reactive metabolites in the neighborhood of nuclear proteins and DNA might have significant toxicological implications.
Assuntos
Núcleo Celular/metabolismo , Citocromo P-450 CYP2E1/metabolismo , Dimetilnitrosamina/metabolismo , Etanol/metabolismo , Fígado/metabolismo , N-Metilaspartato/metabolismo , Acetaldeído/metabolismo , Animais , Biotransformação , Isótopos de Carbono , Núcleo Celular/enzimologia , Doença Crônica , DNA/metabolismo , Dieta , Etanol/farmacocinética , Formaldeído/metabolismo , Metabolismo dos Lipídeos , Masculino , Microssomos Hepáticos/metabolismo , NADP/metabolismo , Ratos , Ratos Sprague-DawleyAssuntos
Animais , Feminino , Masculino , Cobaias , Cricetinae , Camundongos , Ratos , Dietilnitrosamina/toxicidade , Dimetilnitrosamina/toxicidade , Neoplasias Hepáticas Experimentais/induzido quimicamente , Dieta , Dietilnitrosamina/administração & dosagem , Dietilnitrosamina/metabolismo , Dimetilnitrosamina/administração & dosagem , Dimetilnitrosamina/metabolismo , Modelos Animais de Doenças , Suscetibilidade a Doenças , Gerbillinae , Ratos Endogâmicos BUF , Ratos Wistar , Fatores de TempoAssuntos
Gravidez , Lactente , Cricetinae , Humanos , Animais , Feminino , Neoplasias Pulmonares/etiologia , Nitrosaminas/metabolismo , Tabagismo/complicações , Carcinógenos/efeitos adversos , Dimetilnitrosamina/metabolismo , DNA/metabolismo , Neoplasias Laríngeas , Neoplasias Pulmonares/epidemiologia , Neoplasias Pulmonares/etiologia , Menopausa/efeitos dos fármacos , Nitrosaminas/efeitos adversos , Neoplasias Ovarianas/etiologia , Neoplasias Ovarianas/metabolismo , Ovário/enzimologia , Ovário/metabolismo , Placenta/efeitos adversos , Fumar/história , Nicotiana , Poluição por Fumaça de Tabaco/efeitos adversos , Neoplasias da LínguaAssuntos
Gravidez , Lactente , Cricetinae , Humanos , Animais , Feminino , Tabagismo/complicações , Neoplasias Pulmonares/etiologia , Nitrosaminas/metabolismo , Nitrosaminas/efeitos adversos , Tabagismo/história , Poluição por Fumaça de Tabaco/efeitos adversos , Nicotiana , Dimetilnitrosamina/metabolismo , Neoplasias Pulmonares/epidemiologia , Neoplasias Pulmonares/etiologia , Neoplasias da Língua , Neoplasias Laríngeas , Ovário/metabolismo , Ovário/enzimologia , Carcinógenos/efeitos adversos , DNA/metabolismo , Menopausa/efeitos dos fármacos , Neoplasias Ovarianas/metabolismo , Neoplasias Ovarianas/etiologia , Placenta/efeitos adversosRESUMO
N-Nitrosodimethylamine (NDMA) was metabolized by ovarian slices of noninbred Sprague-Dawley rats (200-250 g body wt, to CO2 and to reactive metabolites that bind covalently to nucleic acids. That ability was about 10 or 5 times smaller than the one observed in liver slices, respectively. Both ovarian microsomes and mitochondria were able to biotransform NDMA to formaldehyde and to reactive metabolites that bind covalently to proteins. Formaldehyde formation by microsomes was significantly higher than that by ovarian mitochondria but of the same order of magnitude. Ability to lead to covalent binding to proteins in microsomes was not significantly different from that in the respective mitochondrial fraction. DNA isolated from ovarian slices activating NDMA revealed the presence of the altered bases 7-methylguanine (7-MeGua) and O6-methylguanine (O6-MeGua) resulting from NDMA reactive metabolites' attack. Results suggest potential, mutagenic, carcinogenic and reproductive risks derived from women's exposure to NDMA present in tobacco smoke, food, beverages, workplace or other environmental sources.
Assuntos
DNA/metabolismo , Dimetilnitrosamina/metabolismo , Ovário/metabolismo , Animais , Sistema Enzimático do Citocromo P-450/fisiologia , Dimetilnitrosamina/toxicidade , Feminino , Formaldeído/metabolismo , Ovário/efeitos dos fármacos , Ligação Proteica , Ratos , Ratos EndogâmicosRESUMO
Outbreaks of liver necrosis and liver hemangiosarcoma were detected in a mink breeding colony in Argentina. Analysis of the Minks' food revealed the presence of 2.6 ppm dimethylnitrosamine (NDMA) in it, apparently as a result of the addition of nitrite as preservative. Previous studies gave evidence of the particular susceptibility of minks to NDMA and other hepatic insults. We have determined several biochemical parameters known to correlate with NDMA hepatotoxic effects and compared them with those in rat liver. NDMA administration to both species resulted in the formation of reactive metabolites able to interact with liver DNA to give N7-methylguanine and O6-methylguanine adducts. Biotransformation of NDMA by liver slices to CO2 was significantly lower in the mink than in the rat, whereas the covalent binding (CB) to nucleic acids was slightly lower than in in the rat. Aminopyrine N-demethylase activity was also significantly less in mink than in rat liver. The CB of NDMA reactive metabolites to microsomal proteins was not significantly lower in mink as compared to the rat, and the same holds true for the biotransformation of NDMA to formaldehyde by microsomal preparations. Results suggest that the high susceptibility of minks to NDMA might be partially due to a decreased ability to detoxicate NDMA but also to a higher intrinsic susceptibility of their liver cells to a given chemical insult.
Assuntos
Dimetilnitrosamina/toxicidade , Neoplasias Hepáticas/induzido quimicamente , Fígado/efeitos dos fármacos , Vison , Animais , Dimetilnitrosamina/metabolismo , Feminino , Formaldeído/metabolismo , Técnicas In Vitro , Fígado/enzimologia , Masculino , Ácidos Nucleicos/metabolismo , Ligação Proteica , Ratos , Ratos Endogâmicos , Especificidade da EspécieRESUMO
Effects of catechin, a plant phenolic flavonoid, and of the commonly used organic solvents dimethyl sulfoxide (DMSO) and ethanol (EtOH) on the microsome-mediated metabolism of two hepatocarcinogens, N-nitrosodimethylamine (NDMA) and aflatoxin B1 (AFB1), are presented. Using hamster liver microsomes as a source of mixed-function oxidases, it was shown that catechin at 0.1-0.2 mM levels had no effect on the oxidation of either carcinogen. However, at 1-5 mM levels it caused a concentration-dependent inhibition (38-70%) of the formation of formaldehyde from NDMA, and at the 5 mM level it caused a 40% inhibition of AFB1-DNA binding. DMSO and EtOH totally inhibited NDMA demethylase activity but had little effect on the binding of AFB1 to DNA. These observations indicate that the mixed-function oxidases (cytochrome P450) essential for the metabolic activation of these carcinogens exhibit different sensitivities to different inhibitors.
Assuntos
Aflatoxinas/metabolismo , Catequina/farmacologia , Dimetil Sulfóxido/farmacologia , Dimetilnitrosamina/metabolismo , Etanol/farmacologia , Microssomos Hepáticos/efeitos dos fármacos , Aflatoxina B1 , Animais , Cricetinae , DNA/metabolismo , Relação Dose-Resposta a Droga , Neoplasias Hepáticas/induzido quimicamente , Microssomos Hepáticos/metabolismoRESUMO
Entre los precursores de la síntesis de la dimetilnitrosamina cancerígena se encuentran los nitratos, nitritos y la trimetilamina (TMA). En el presente trabajo se informan los niveles de estos precursores en 30 muestras de pescado de la especie Haemulon parra Desmarest (ronco), capturadas en la plataforma cubana. Los métodos de análisis empleados fueron: para nitratos y nitritos el recomendado por el Comité Mixto FAO/OMS en 1976 y para la trimetilamina el informado por la FAO en 1969. Los resultados obtenidos (x+ ou - S) expresados en mg/kg fueron: TMA 9,7 + ou - 6,63; NaNO3 11,7 + ou - 8,34 y NaNO2 1,0. Los niveles hallados no parecen representar un riesgo a la salud por la ingestión de estos compuestos, en comparación con otros alimentos, incluyendo otras especies de peces informados en la literatura. La posibilidad de formación de dimetilnitrosamina en las muestras analizadas a partir de los precursores estudiados es muy escasa, dados los bajos contenidos encontrados de TMA, NaNO3 y sobre todo NaNO2