This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Gurtoo, H. L. Articles by Dave, C. V. Search for Related Content PubMed PubMed Citation Articles by Gurtoo, H. L. Articles by Dave, C. V.

In Vitro Metabolic Conversion of Aflatoxins and Benzo(a)pyrene to Nucleic Acid-binding Metabolites¹

Department of Experimental Therapeutics, Grace Cancer Drug Center, Roswell Park Memorial Institute, New York State Department of Health, Buffalo, New York 14203

An aflatoxin B₁ metabolite was found to become covalently bound to rat liver RNA and calf thymus DNA in vitro, and it formed complexes with increased spectral absorbance in the 360 nm region. The formation of such complexes was reduced nicotinamide adenine dinucleotide phosphate and microsome dependent, was inhibited by ß-diethylaminoethyl diphenylpropylacetate-HCl, and by CO and N₂, when the latter were used to replace the gas phase of the incubations. The formation of the complexes was enhanced about 2-fold with microsomes from phenobarbital-treated rats but not from 3-methylcholanthrene-treated rats. More binding was observed with DNA than with RNA. Denatured DNA was about 70% as effective as native DNA. Nucleic acids from various sources showed the following order of binding potency: DNA from Micrococcus luteus > DNA from calf thymus = DNA from rat liver > RNA from rat liver > transfer RNA from rat liver. In the presence of reduced nicotinamide adenine dinucleotide phosphate and microsomes from phenobarbital-treated rats, aflatoxin G₁ was also converted into metabolite(s) that became covalently bound to nucleic acids and formed complexes with increased spectral absorbances in the 360 nm region: this reaction was also inhibited by ß-diethylaminoethyl diphenylpropylacetate-HCl. Under the same conditions, aflatoxin B₂, aflatoxin G₂, aflatoxin B_2a, and "Compound 11," which lack a C2-C3 double bond, did not show any noticeable binding to either DNA or RNA. These data strongly support the concept that the microsomal mixed-function oxygenase-catalyzed oxidation of the C2-C3 double bond of aflatoxins is a prerequisite for the formation of nucleic acid-binding metabolites.

Microsomes from untreated, phenobarbital-treated, and 3-methylcholanthrene-treated rats were compared in vitro for their ability to catalyze the formation of DNA-binding metabolites from aflatoxin B₁ and benzo(a)pyrene. In assays involving benzo(a)pyrene, microsomes from 3-methylcholanthrene-treated rats were 12- and 5-fold more active than microsomes from untreated and phenobarbital-treated rats, respectively. This is in contrast to the results obtained with aflatoxin B₁ and suggests that different enzymes in the hepatic microsomal mixed-function oxygenase complex are involved in the generation of reactive metabolites from various polycyclic hydrocarbons.

¹ Supported in part by Core Program Grant CA-13038, General Research Support Grant Allocation RR-05648-08, and American Cancer Society Allocation IN-54-M5.

Received 7/22/74. Accepted 10/25/74.

This article has been cited by other articles:

				D. M. Kuhn and M. A. Ghannoum Indoor Mold, Toxigenic Fungi, and Stachybotrys chartarum: Infectious Disease Perspective Clin. Microbiol. Rev., January 1, 2003; 16(1): 144 - 172. [Abstract] [Full Text] [PDF]