Mutagenesis, Vol. 15, No. 2, 149-154,
March 2000
© 2000 UK Environmental Mutagen Society/Oxford University Press
Pathways of heterocyclic amine activation in the breast: DNA adducts of 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) formed by peroxidases and in human mammary epithelial cells and fibroblasts
Institute of Cancer Research, Haddow Laboratories, Cotswold Road, Sutton, Surrey SM2 5NG, UK
Most human mammary carcinomas originate in the epithelial cells of the breast ducts. A potential role of heterocyclic amines (HAs) in the aetiology of this disease has led us to investigate peroxidase-catalysed and stromal (non-epithelial) activation of the HA 2-amino-3-methylimidazo[4,5-f]quinoline (IQ), which may subsequently lead to DNA damage in the adjacent human mammary epithelial cells (HMECs). HAs are formed when proteinaceous foods are cooked at high temperature and some, but not all, can cause mammary tumours in rats. Myeloperoxidase (MPO) and lactoperoxidase (LPO) are peroxidase enzymes present in breast secretions. 32P-post-labelling analysis showed that IQ–DNA adducts were formed after co-incubation of IQ (500 µM) with calf thymus DNA, hydrogen peroxide and either bovine LPO or horseradish peroxidase (HRP). The major HRP-mediated IQ–DNA adduct co-migrated on TLC and HPLC with the major adduct formed in HMECs, suggesting a common reactive intermediate (nitrenium ion). IQ–DNA adducts were also formed in extracellular DNA when phorbol myristate acetate-stimulated neutrophils (which activate IQ via MPO) were co-incubated with IQ (500 µM) and extracellular plasmid (4 ± 1 adducts/108 nucleotides) or calf thymus DNA (6 ± 2). Mean adduct formation was five to seven times greater in neutrophil DNA (31 ± 20). Primary cultures of human mammary fibroblasts or epithelial cells isolated from reduction mammoplasty tissues (n = 4 individuals) were incubated with IQ (500 µM) and formed 2.5 and 14.8 adducts/108 nucleotides (mean values), respectively. Our results indicate the possible contribution of stromal cells and breast peroxidases to the metabolic activation of carcinogens in the mammary gland.
1 To whom correspondence should be addressed. Tel: +1 181 643 8901; Fax: +1 181 770 7290; Email: andyw{at}icr.ac.uk
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