IRON-CHLOROPHYLLIN-MEDIATED CONVERSION OF 3-HYDROXYAMINO-1-METHYL-5H-PYRIDO[4,3-B]INDOLE (TRP-P-2(NHOH)) INTO ITS NITROSO DERIVATIVE

Early work from our laboratory has shown that the mutagenicity of hete rocyclic amines in Salmonella can be inhibited by hemin and chlorophyl lins. We have speculated that the inhibition is a result of complex fo rmation between heterocyclic amines and the pigments, and the speculat ion has been given a line of experimental evidence. We have now found that ferric-chlorophyllin (Fe-chlorophyllin) can modify the mutagenici ty of 3-hydroxyamino-1-methyl-5H-pyrido[4,3-b]indole (Trp-P-2(NHOH)), a metabolically activated form of 3-amino-1-methyl-5H-pyrido[4,3-b]ind ole (Trp-P-2). The mutagenicity of Trp-P-2(NHOH) in Salmonella typhimu rium TA 98 (without S9) was strongly inhibited by an addition of an eq uimolar Fe-chlorophyllin in the pre-incubation mixture. Fe-chlorophyll in also inhibited the mutagenicity of 2-hydroxyamino-6-methyldipyrido[ 1,2-a:3',2'-d] imidazole (Glu-P-1(NHOH)). A rapid change in the UV spe ctrum of a mixture of Trp-P-2(NHOH) and Fe-chlorophyllin was observed. Analysis by high performance liquid chromatography showed that Trp-P- 2(NHOH) was converted into 3-nitroso-1-methyl-5H-pyrido[4,3-b]indole ( Trp-P-2(NO)), the mutagenic potency of which is a quarter of that of T rp-P-2(NHOH). Furthermore, the mutagenicity of Trp-P-2(NO), in turn, w as inhibited by Fe-chlorophyllin. We conclude that the suppression of the mutagenicity of Trp-P-2(NHOH) is ascribable to the oxidative funct ion of Fe-chlorophyllin, coupled with its ability to form complex form ation with the planar surface of the heterocyclic amine molecules. (C) 1998 Elsevier Science B.V. All rights reserved.