RESUMEN
DNA repair is a critical process in protecting cellular genetic information from mutation. Nucleotide excision repair (NER) is a mechanism by which cells correct DNA damage caused by agents that form bulky covalent adducts and UV photoproducts such as thymine dimers and 6-4 photoproduct. NER, sometimes called dark repair, is generally accepted as being low in fish compared to mammals. This study was designed to quantitate NER in two related catfish species that have known differential sensitivities to liver carcinomas. The original hypothesis was that the more cancer resistant species, channel catfish (Ictalurus punctatus), would have more efficient DNA repair compared to the more sensitive brown bullhead (Ameriurus nebulosus). In order to measure NER, primary cultured hepatocytes of both species were exposed to UV light (10-40 J/m2) and collected at 0, 24, 48 and 72 h after exposure. Total DNA was extracted from the cells and incubated with T4 endonuclease V. Using alkaline gel electrophoresis, endonuclease sensitive sites (ESS) were quantified. Results from the ESS assay indicated there was a UV dose-response increase in thymine dimers from 0 to 40 J/m2. However, no repair (decrease in number of ESS) occurred in either fish species over a 72-h time period. When cells were exposed to photoreactivating fluorescent light, repair was detected. These studies highlight the difficulty of measuring NER in fish and are consistent with the low levels of NER reported by other researchers in fish.
Asunto(s)
Reparación del ADN , Hepatocitos/efectos de la radiación , Ictaluridae/genética , Rayos Ultravioleta/efectos adversos , Proteínas Virales , Animales , Técnicas de Cultivo de Célula , Desoxirribodipirimidina Fotoliasa/farmacología , Desoxirribonucleasa (Dímero de Pirimidina) , Relación Dosis-Respuesta en la Radiación , Endodesoxirribonucleasas/farmacología , Masculino , Dímeros de Pirimidina/efectos de la radiación , Factores de TiempoRESUMEN
Reproductive toxicity studies have historically centered on post-fertilization events. A thorough assessment of reproductive hazards to an organism should include all aspects of its life cycle. Cadmium is a teratogenic and carcinogenic heavy metal that occurs naturally in the environment but is also released anthropogenically. The effect of cadmium administration on oocyte development in Xenopus laevis was studied. Adult female Xenopus were injected in the dorsal lymph sac with cadmium chloride (CdCl2) at doses of 0.5, 0.75, 1.0, 3.0 or 5.0 mg/kg every other day for 21 days. Significant adverse effects of Cd on oocyte development were observed. The percentage of oocytes at all stages of oogenesis was decreased while the population of atretic oocytes increased dramatically (P < 0.0001). Numerous oocytes exhibited a speckled or mottled appearance and the incidence of completely atretic oocyte follicles increased. The observations indicate that Cd has the potential to significantly disrupt oogenesis and that examination of developing gametes may be a useful parameter for assessing the influence of environmental contaminants on reproductive capacity.
Asunto(s)
Cadmio/toxicidad , Oogénesis/efectos de los fármacos , Xenopus laevis/fisiología , Animales , Cadmio/análisis , Gonadotropina Coriónica/farmacología , Femenino , Hígado/anatomía & histología , Masculino , Oocitos/química , Tamaño de los Órganos/efectos de los fármacos , Ovario/anatomía & histología , Ovario/química , Bazo/anatomía & histologíaRESUMEN
Differential susceptibility of polycyclic aromatic hydrocarbon (PAH)-mediated liver cancer exists in two related species of Ictalurid catfish. Two hypotheses are addressed in this study to explain this difference. Specifically, the relatively insensitive channel catfish 1) do not produce mutagenic PAH metabolites, and/or 2) they more quickly eliminate PAHs due to greater Phase II enzyme activities than the more sensitive brown bullhead. Livers and bile were collected from each species 6, 24, 72, and 168 h after a single 10 mg/kg i.p. benzo(a)pyrene (BaP) exposure. BaP treatment had no significant effect on cytosolic 1-chloro-2,4-dinitrobenzene or ethacrynic acid (EA)-glutathione-S:- transferase (GST) and cis-stilbene oxide-microsomal epoxide hydrolase (EH) activities of either species. Channel catfish EH and GST activities were 1.2-fold higher than brown bullhead activities (p = 0.058 and p < 0.002, respectively). HPLC-APCI-MS of extracted bile and bile enzymatically digested to detect glucuronyl transferase (GT), GST, and sulfotransferase (ST) conjugated metabolites indicated no species differences in elimination or profiles of total biliary metabolites. GT conjugates predominated; ST and GST conjugates were minimal. BaP-diones accounted for the majority of metabolites in both species. Overall, these results indicated that brown bullhead preferentially formed BaP-7,8-dihydrodiol, a precursor to the DNA-reactive BaP-7, 8-dihydrodiol-9,10-epoxide (BPDE), which may be linked to the increased PAH susceptibility in this species.