Biotransformation of Mycotoxins in the Reconstituted Cytochrome P-450 System

1985 JSM Mycotoxins  
Metabolic transformation of ochratoxin A (OA) and emodin (EM) was investigated in the microsomal and reconstituted cytochrome P-450 systems of the rat liver. In the microsomal system, OA was transformed into 4 (R)-and 4 (S)-4-hydroxy-OAs, and 3methylcholanthrene (3 MC) as well as PCB enhanced the microsomal hydroxylation of OA to 4 (R)-4-hydroxy-OA. In the reconstituted cytochrome P-450 system, cytochrome P-450 II-a (maximal CO-differential spectrum at 448.0 nm and high-spin form), fractionated
more » ... from PCB-microsomes, selectively catalyzed the hydroxylation of OA and EM into 4 (R)-4-hydroxy-OA and 2-hydroxy-EM, respectively. In the preceding papers, we reported that AFBI was biotransformed into DNA-binding form (s) and a hydroxylated metabolite, AFM1, in the reconstituted cytochrome P-450 system composed of cytochrome P-450 s, NADPH-cytochrome C reductase (f pr), deoxycholate, and others, and that the activation of AFBI into DNA-binding form (s) and the hydroxylation to AFM1 were selectively catalyzed by cytochrome P-450 I-a (maximal CO-differential sepectrum at 450.0 nm and low-spin form) and cytochrome P.450 II-a (448.0 nm and high-spin form), respectively. The hepatic microsomes derived from rats transformed emodin (EM; 1, 3, 8-trihydroxy-6-methylanthraquinone) into at least 10 anthraquinoid metabolites, and among these metabolites 2-hydroxy-EM (1, 2, 3, 8-tetrahydroxy-6-methyl-anthraquinone) is a direct-acting mutagen in Ames assay. In order to characterize the role of cytochrome P.450 isozymes in metabolic transformation of mycotoxins, we described the biotransformation of ochratoxin A (OA) and EM in the reconstituted cytochrome P.450 system. Materials and Methods Mycotoxins: OA and EM were isolated from Aspergillus ochraceus and rhubarb, respectively. Standard 4(R)-and 4 (S)-4-hydroxy-OAs were kindly gifted by Dr. Stormer (University of Oslo). Enzymes and assay : Microsomes were prepared from the livers of rats, and cytochrome P.450 s were fractionated from the livers of PCB (Kane chlore 400)-induced rats. In the microsomal system, potassium phosphate buffer (pH 7.2) 100 pmoles, MgCl2 2.5 pmoles, NADP 2.5 pmoles, glucose-6-phosphate (G-6-P) 5 pmoles, G-6-P dehydrogenase 1 unit, microsomal protein 2-3 mg, and OA 0.125 or EM 37 pmoles, in total volume of 1.0 ml, were incubated at 37°C for 20-60 min. In the
doi:10.2520/myco1975.1985.22_28 fatcat:baffzjaxxra27cuvjnm7j62zxq