ABSTRACT
The carcinogenic mycotoxin aflatoxin B(1) (AFB(1)) induces 8-hydroxy-2'-deoxyguanosine (8-OHdG) formation in mouse lung, an effect that can be prevented by treatment with polyethylene glycol-conjugated catalase (PEG-CAT). G-->T transversion mutation in K-ras, an early event in AFB(1)-induced mouse lung carcinogenesis, is thought to result from AFB(1)-8,9-exo-epoxide binding to DNA to form AFB(1)-N(7)-guanine, but may also result from formation of 8-OHdG. Therefore, oxidative DNA damage may be important in AFB(1) carcinogenicity. The objective of this study was to determine whether PEG-CAT would prevent AFB(1) tumorigenicity. Mouse lung tumorigenesis was assessed following treatment of female A/J mice with 300 kU/kg PEG-CAT ip and/or 50 mg/kg AFB(1). Mice were killed 7 months post-treatment and tumors greater than 1 mm in diameter were excised. Unexpectedly, the mean number of tumors per mouse in the PEG-CAT+AFB(1) group (8.81+/-3.64, n=47) was greater than that of the group treated with AFB(1) alone (7.05+/-3.45, n=42) (P<0.05). The tumors obtained from mice treated with PEG-CAT+AFB(1) were larger than those from mice treated with AFB(1) alone (P<0.05). There was no difference in K-ras exon 1 mutation spectrum or in the histological diagnosis of tumors between AFB(1) and PEG-CAT+AFB(1) groups (P>0.05). In vitro incubation with mouse liver catalase (CAT) resulted in conversion of [(3)H]AFB(1) into a DNA-binding species, a possible explanation for the results observed in vivo. These results demonstrate that PEG-CAT is not protective against AFB(1) carcinogenicity in mouse lung despite preventing DNA oxidation.
Subject(s)
Aflatoxin B1/antagonists & inhibitors , Carcinogens/antagonists & inhibitors , Catalase/pharmacology , Lung Neoplasms/chemically induced , Lung Neoplasms/prevention & control , Aflatoxin B1/metabolism , Aflatoxin B1/toxicity , Animals , Biotransformation , Carcinogens/metabolism , Carcinogens/toxicity , Catalase/administration & dosage , DNA Damage/drug effects , DNA, Neoplasm/biosynthesis , DNA, Neoplasm/genetics , Data Interpretation, Statistical , Excipients , Female , Genes, ras/drug effects , Genes, ras/genetics , Liver/enzymology , Liver/metabolism , Mice , Mice, Inbred A , Mutation/drug effects , Polyethylene Glycols , Polymorphism, Single-Stranded Conformational , Reverse Transcriptase Polymerase Chain ReactionABSTRACT
Aflatoxin B(1) (AFB(1)) is a mycotoxin produced by some strains of Aspergillus and is a recognized pulmonary and hepatic carcinogen. The most widely accepted mechanism of AFB(1) carcinogenicity involves bioactivation to AFB(1)-8,9-exo-epoxide and binding to DNA to form AFB(1)-N(7)-guanine. Another potential cause of DNA damage is AFB(1)-mediated stimulation of reactive oxygen species formation, leading to oxidation of DNA bases. The objective of this study was to determine the ability of AFB(1) to cause oxidative DNA damage in lung cell types of the A/J mouse. The formation of 8-hydroxy-2'-deoxyguanosine (8-OHdG) in freshly isolated mouse lung alveolar macrophages, alveolar type II cells, and nonciliated bronchial epithelial (Clara) cells was assessed by high-performance liquid chromatography with electrochemical detection. An approximately 3-fold increase in 8-OHdG formation occurred in both alveolar macrophage and Clara cell preparations isolated from A/J mice 2 h following treatment with a single tumorigenic dose of 50 mg/kg AFB(1) ip (n = 3, p < 0.05). Prior treatment with 300 kU/kg polyethylene glycol-conjugated catalase prevented the AFB(1)-induced increase in 8-OHdG levels in all mouse lung cell preparations (n = 3, p < 0.05). These results support the possibility that oxidative DNA damage in mouse lung cells contributes to AFB(1) carcinogenicity.
