RESUMEN
There is increasing evidence that alkylating agent exposure may increase large bowel cancer risk and factors which either alter such exposure or its effects may modify risk. Hence, in a cross-sectional study of 78 patients with colorectal disease, we have examined whether (i) metabolic genotypes (GSTT1, GSTM1, CYP2D6, CYP2E1) are associated with O(6)-methyldeoxyguanosine (O(6)-MedG) levels, O(6)-alkylguanine-DNA alkyltransferase (ATase) activity or K-ras mutations, and (ii) there was an association between ATase activity and O(6)-MedG levels. Patients with colon tumours and who were homozygous GSTT1(*)2 genotype carriers were more likely than patients who expressed GSTT1 to have their DNA alkylated (83 versus 32%, P=0.03) and to have higher O(6)-MedG levels (0.178+/-0.374 versus 0.016+/-0.023 micromol O(6)-MedG/mol dG, P=0.04) in normal, but not tumour, DNA. No such association was observed between the GSTT1 genotype and the frequency of DNA alkylation or O(6)-MedG levels in patients with benign colon disease or rectal tumours. Patients with colon tumours or benign colon disease who were CYP2D6-poor metabolisers had higher ATase activity in normal tissue than patients who were CYP2D6 extensive metabolisers or CYP2D6 heterozygotes. Patients with the CYP2E1 Dra cd genotype were less likely to have a K-ras mutation: of 55 patients with the wild-type CYP2E1 genotype (dd), 23 had K-ras mutations, whereas none of the 7 individuals with cd genotype had a K-ras mutation (P=0.04). No other associations were observed between GSTT1, GSTM1, CYP2D6 and CYP2E1 Pst genotypes and adduct levels, ATase activity or mutational status. O(6)-MedG levels were not associated with ATase activity in either normal or tumour tissue. However, in 15 patients for whom both normal and tumour DNA contained detectable O(6)-MedG levels, there was a strong positive association between the normal DNA/tumour DNA adduct ratio and the normal tissue/tumour tissue ATase ratio (r(2)=0.66, P=0.001). These results indicate that host factors can affect levels both of the biologically effective dose arising from methylating agent exposure and of a susceptibility factor, the DNA repair phenotype.
Asunto(s)
Neoplasias Colorrectales/enzimología , Citocromo P-450 CYP2D6/genética , Reparación del ADN , ADN de Neoplasias/metabolismo , Glutatión Transferasa/genética , Guanina/metabolismo , O(6)-Metilguanina-ADN Metiltransferasa/metabolismo , Adenosina Trifosfatasas/metabolismo , Anciano , Alquilación , Neoplasias Colorrectales/genética , Estudios Transversales , Femenino , Predisposición Genética a la Enfermedad , Genotipo , Glutatión Transferasa/metabolismo , Guanina/análogos & derivados , Humanos , Masculino , Persona de Mediana Edad , Mutación , Proteínas Proto-Oncogénicas p21(ras)/metabolismoRESUMEN
OBJECTIVE: To determine whether there are specific cytochrome P450 (CYP2) alleles that increase susceptibility to scleroderma in individuals who have been exposed to organic solvents. METHODS: CYP alleles at 2 loci, 2E1 and 2C19, were compared in 7 patients who had developed scleroderma after exposure to solvents versus 71 patients with scleroderma without solvent exposure ("sporadic" disease) and 106 population controls. RESULTS: The 2E1*3 allele was found in 2 of the 7 patients who had been exposed to organic solvents, with a greater frequency than occurred in either the disease controls or the population controls (odds ratio [95% confidence interval] 9.1 [1.5-59.1] and 10.2 [1.8-62.2], respectively). All 7 patients with solvent exposure carried the 2C19EM genotype, compared with 89% of patients with sporadic scleroderma. CONCLUSION: Our results suggest that alleles at CYP loci may be involved in increasing susceptibility to scleroderma among subjects who have been exposed to organic solvents.
Asunto(s)
Sistema Enzimático del Citocromo P-450/genética , Susceptibilidad a Enfermedades/inducido químicamente , Esclerodermia Sistémica/inducido químicamente , Solventes/efectos adversos , Estudios de Casos y Controles , Exposición a Riesgos Ambientales/efectos adversos , Humanos , Polimorfismo GenéticoAsunto(s)
Polaridad Celular/genética , Hígado/citología , Animales , Carcinógenos/toxicidad , Comunicación Celular/efectos de los fármacos , Comunicación Celular/genética , Polaridad Celular/efectos de los fármacos , Regulación hacia Abajo , Citometría de Flujo , Uniones Comunicantes/efectos de los fármacos , Uniones Comunicantes/genética , Hígado/efectos de los fármacos , Microscopía Electrónica , Peso Molecular , RatasRESUMEN
Phenobarbitone (PB) produced a dose- and time-dependent decrease in gap junctional intercellular communication (GJIC) (up to 25.0 +/- 5.3% inhibition) in rat hepatocyte couplets (4 h cultures). The effect was reversible and independent of protein synthesis. This inhibition was exacerbated (to 53.3 +/- 5.4% inhibition) by depletion of intracellular glutathione following pretreatment with diethylmaleate (0.5 microM, 15 min). Inhibition was also significantly enhanced by addition of the cytochrome P450 inhibitors SKF 525A (25 microM) and metyrapone (20 nM). In contrast, hepatocyte couplets derived from rats pretreated with PB (0.1% w/v in drinking water) for up to 28 days were fully functional regarding GJIC and were found to be refractory to the effects of PB added in vitro. This, coupled with the lack of effect of p-hydroxy-PB, suggests that an active metabolite of PB is not involved in the inhibition of GJIC which may, instead, be through an oxidative stress, which is prevented by glutathione.