Mutagenicity of aflatoxins related to their metabolism and carcinogenic potential.

Abstract

Aflatoxins and their animal biotransformation products were screened for carcinogenic potential using the Ames' in vitro microbial detection system for carcinogens as bacterial mutagens [B. N. Ames et aL (1973) Proc (1). The four naturally occurring AFs, aflatoxins B1 (AFB1), B2 (AFB2), G1 (AFG1), and G2 (AFG2), when administered as mixtures, were a potent class of animal hepatocarcinogens (2-6). They have been also associated with neoplastic formations in tissues and organs other than the liver (3,(6)(7)(8)(9).Tests with rats (10) and rainbow trout (11) have revealed that AFB1 is a potent hepatocarcinogen; AFG1 is also considerably carcinogenic, but AFB2 and AFG2 possess much lower activity. Recent studies on the metabolism of AFB1 have resulted in the isolation and identification of numerous metabolites, all of minor structural variations but significantly different biological activity relative to the parent compound (12).Among these metabolites, aflatoxins Q, (AFQ1), M1 (AFM1), Bk (AFBa), and P1 (AFP1), aflatoxicol (AFL), and aflatoxicol H1 (AFLH1) (Table 1) are the biotransformation products of AFB1 when the latter is incubated with liver preparations and a NADPH-generating system (13-17). Since evidence has indicated that AFB1 requires metabolic activation for its toxic, mutagenic, and/or carcinogenic activity (18)(19)(20)(21)(22), the toxicity of each metabolite has been of great interest in the search for the active molecular species. Attempts have been made to correlate the relative activity of the different metabolic pathways and the variations in the species susceptibility to aflatoxicosis (16,23 (24,25). The analysis of the known major AF metabolites in our study permits an observation of the structureactivity relationships as related to the carcinogenic potential of the AFs. MATERIALS AND METHODSChemicals are obtained as follows: AFBI, AFG1, AFB2, and AFG2 were purchased from Makor Chemicals, Ltd., Jerusalem, Israel. AFM1, AFQ1, and AFH1 were prepared by biotransformation of AFB1 using monkey liver homogenates (14, 17). AFL was prepared by a similar biotransformation method to be published elsewhere. AFB2k and AFGk were chemically synthesized from AFB1 with dilute acid (27). AFP1 was a chemically synthesized product kindly provided by G. N. Wogan, Massachusetts Institute of Technology, Cambridge, Mass. The purity and identity of all AFs was checked by fluorodensitometric analysis of thin-layer chromatography plates and mass spectrometry. In addition, AFQ1, AFM1, AFH1, and AFB2k were checked by high-pressure liquid chromatography (28). All biochemicals, NADP+, glucose 6-phosphate, histidine, and biotin, were purchased from Sigma Chemicals, St. Louis, Mo.The bacterial tester strain, Salmonella typhimurium strain TA 98 (21), was the generous gift of B. N. Ames, University of California, Berkeley. The bacteria were stored and grown as outlined by McCann et al. (21). The hepatic S-9 enzyme preparation was prepared from Charles River male white rats (200-250 g) and utilized according to procedur...

In vivo covalent binding of aflatoxin B1 and aflatoxin M1 to liver DNA of rat, mouse and pig

“…The difference between AFB 1 and AFM 1 in hepatoma incidence in the trout was found to be of a factor of 4 [9], the difference in the Salmonella/ microsome mutagenicity testwas about 30: 1 in one report [24] and about 3 : 1 in another [25]. The rate data on carcinogenicity in the rat cannot be used for a quantitative comparison of the two compounds [11,12].…”

Identification of the principal aflatoxin B1-DNA adduct formed in vivo in rat liver.

“…This represents approximately 100% of the activity originally present in the nucleic acids. Compounds eluting in fractions [3][4][5][6][7][8][9][10][11] during the wash phase represent 23.7% of the total 3H activity. The radioactive compounds contained in these fractions have not been identi- fied but it is suspected that these peaks contain polar AFB1 deoxyribo-and ribonucleotide derivatives.…”

“…The rat, rainbow trout and duck are among the most susceptible to its toxic effects. AFB1 is also a potent hepatocarcinogen in these species (1) and is a potent mutagen in mammalian and bacterial cells (2)(3)(4). Epidemiological investigations in several human populations have revealed an association of increased incidences of hepatocellular carcinoma with increasing dietary contamination by AFB1 (5).…”

Validation of a lateral flow test (MRLAFMQ) for the detection of aflatoxin M1at 50 ng l−1in raw commingled milk

“…When mould growth occurs on feeds or grains, aflatoxin B 1 could be produced. Aflatoxin B 1 is the most toxic aflatoxin and a potent hepatocarcinogen (Wogan 1966;Carnaghan 1967;Wong & Hsieh 1976). Feeds and grains are generally screened in a range of 2 µg kg -1 aflatoxin B 1 for European Union (EU) Regulation No.…”