Cytosolic enzymes from rat tissues that activate the cooked meat mutagen metabolite N-Hydroxyamino-1-methyl-6-phenylimidazo[4,5-b]pyridine (N-OH-PhIP)

Heterocyclic amines are formed during the cooking of foods rich in protein and can be metabolically converted into cytotoxic and mutagenic compounds. These "cooked-food mutagens" constitute a potential health hazard because D NA damage arising from dietary exposure to heterocyclic amines can modify c ell genomes and thereby affect future organ function. To determine enzymes responsible for heterocyclic amine processing in mammalian tissues, we perf ormed studies to measure genotoxic activation of the N-hydroxy form of 2-am ino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP)-a common dietary mutagen . O-Acetyltransferase, sulfotransferase, kinase, and amino-acyl synthetase activities were assayed using substrate-specific reactions and cytosolic en zymes from newborn and adult rat heart, liver, spleen, kidney, brain, lung, and skeletal muscle. The resultant enzyme-specific DNA adduct formation wa s quantified via 32P-postlabeling techniques. In biochemical assays with ra t tissue cytosolic proteins, O-acetyltransferases were the enzymes most res ponsible for N-hydroxy-PhIP (N-OH-PhIP) activation. Compared to O-acetyltra nsferase activation, there was significantly less kinase activity and even lesser amounts of sulfotransferase activity. Proyl-tRNA synthetase activati on of N-OH-PhIP was not detected. Comparing newborn rat tissues, the highes t level of O-acetyltransferase mutagen activation was observed for neonatal heart tissue with activities ranked in the order of heart > kidney > lung > liver > skeletal muscle > brain > spleen. Enzymes from cultured neonatal myocytes displayed high O-acetyltransferase activities, similar to that obs erved for whole newborn heart. This tissue specificity suggests that neonat al cardiac myocytes might be at greater risk for damage from dietary hetero cyclic amine mutagens than some other cell types. However, cytosolic enzyme s from adult rat tissues exhibited a different O-acetyltransferase activati on profile, such that liver > muscle > spleen > kidney > lung > brain > hea rt. These results demonstrated that enzymes involved in catalyzing PhIP-DNA adduct formation varied substantially in activity between tissues and in s ome tissues, changed significantly during development and aging. The result s further suggest that O-acetyltransferases are the primary activators of N -OH-PhIP in rat tissues. (C) 2001 Elsevier Science Inc. All rights reserved .