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 DNA damage arising from dietary exposure to heterocyclic amines can modify cell genomes and thereby affect future organ function. To determine enzymes responsible for heterocyclic amine processing in mammalian tissues, we performed studies to measure genotoxic activation of the N-hydroxy form of 2-amino-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 enzymes from newborn and adult rat heart, liver, spleen, kidney, brain, lung, and skeletal muscle. The resultant enzyme-specific DNA adduct formation was quantified via (32)P-postlabeling techniques. In biochemical assays with rat tissue cytosolic proteins, O-acetyltransferases were the enzymes most responsible for N-hydroxy-PhIP (N-OH-PhIP) activation. Compared to O-acetyltransferase activation, there was significantly less kinase activity and even lesser amounts of sulfotransferase activity. Proyl-tRNA synthetase activation of N-OH-PhIP was not detected. Comparing newborn rat tissues, the highest 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 observed for whole newborn heart. This tissue specificity suggests that neonatal cardiac myocytes might be at greater risk for damage from dietary heterocyclic amine mutagens than some other cell types. However, cytosolic enzymes from adult rat tissues exhibited a different O-acetyltransferase activation profile, such that liver > muscle > spleen > kidney > lung > brain > heart. These results demonstrated that enzymes involved in catalyzing PhIP-DNA adduct formation varied substantially in activity between tissues and in some tissues, changed significantly during development and aging. The results further suggest that O-acetyltransferases are the primary activators of N-OH-PhIP in rat tissues.
Dubuisson
J G.
JG
Department of Biochemistry and Molecular Biology, College of Medicine, University of South Alabama, 36688-0002, Mobile, Alabama, USA
Murph
W S.
WS
Griffin
S R.
SR
Gaubatz
J W.
JW