N-ACETYLTRANSFERASE EXPRESSION AND METABOLIC-ACTIVATION OF THE FOOD-DERIVED HETEROCYCLIC AMINES IN THE HUMAN MAMMARY-GLAND

The heterocyclic amines (HCAs) found in cooked meat are procarcinogens that are metabolically activated by N-hydroxylation followed by O-ace tylation by the N-acetyltransferases NAT1 and NAT2 Despite the importa nce of metabolic activation in HCA carcinogenicity and the finding tha t several HCAs are rodent mammary gland carcinogens, nothing was known about O-acetylation activity in the human mammary gland, The current study examines the expression and catalytic activity of NAT toward the N-hydroxy-HCAs droxyamino-1-methyl-6-phenylimidazo[4,5-b]pyridine (N- hydroxy-PhIP) and 2-hydroxyamino-3-methylimidazo[4,5-f]quinoline (N-hy droxy-IQ) in the human mammary gland, Mammary gland cytosol from 10 wo men and lysates from a primary culture of human mammary epithelial cel ls metabolically activated droxyamino-1-methyl-6-phenylimidazo[4,5-b]p yridine and 2-hydroxyamino-3-methylimidazo[4,5-f]quinoline by NAT-medi ated O-acetyltransferase, as measured by the acetyl CoA-enhanced bindi ng of the N-hydroxylamines to calf thymus DNA ill vitro, N-acetylation of p-aminosalicylic, an activity specific to NAT1, but not N-acetylat ion of sulfamethazine, an activity specific to NAT2, was detected in t he mammary gland cytosols and human mammary epithelial cell lysates. I mmunohistochemical analysis of human mammary gland sections showed pos itive staining for NAT1 protein in the epithelial cells lining the mam mary gland ducts, Reverse transcription-PCR analysis showed that mRNA transcripts for both NAT1 and NAT2 were present in human mammary gland ; however, no NAT2 catalytic activity was detectable, Our data demonst rate for the first time that the human mammary gland is catalytically active toward the metabolic activation of HCA food mutagens, and that this activity is most likely contributed by NAT1 expressed in the duct ular epithelial cells of the mammary gland.