Complex formation of heterocyclic amines with porphyrins: its use in detection and prevention

Abstract

Porphyrins can suppress mutagenicity of heterocyclic amines. We have shown using the Ames Salmonella test that the mutagenicity of heterocyclic amines is efficiently inhibited by addition of hemin, the red blood porphyrin, in the assay mixture. In this suppression, hemin acts in two ways; inhibition of metabolic activation and suppression of the mutagenicity in the metabolically activated heterocyclic amines. In both of these actions, a complex formation between the porphyrin molecule and the planar molecules of heterocyclic amines seems to play a role. Complex formation and its use in detecting heterocyclic amines in various samples can be seen in the case for copper phthalocyanine, a blue pigment with a porphyrin-like structure. Cellulose bearing copper phthalocyanine trisulfonate as ligand was found to be a selective adsorbent for polycyclic compounds. This adsorbent, named blue cotton/blue rayon, adsorbs polycyclics in aqueous media by forming complexes on the ligand molecules, and releases the adsorbed compounds in organic solvents, such as in methanol plus a small amount of ammonia. The ease in manipulation and its high efficiency have made the blue cotton/blue rayon technique a means now widely used in detecting heterocyclic amines and other polycyclic mutagens in crude samples such as food, urine, and even river water. Chlorophyll, a green plant porphyrin, is another example. Chlorophyll and its stable form, chlorophyllin, have been shown to be inhibitory against the mutagenicity of heterocyclic amines. We have prepared Sepharose-supported chlorophyllin and have shown that heterocyclic amines are adsorbable to this ligand in a reversible fashion. Complex formation between chlorophyllin and heterocyclic amines is also suggested from spectrophotometric studies. A preliminary in vivo study has shown that chlorophyllin is effective in diminishing the cooked beef-derived urinary mutagenicity in humans.