DNA damage in human breast milk cells and its induction by 'early' and 'late' milk extracts

Environmental and dietary factors are thought to be significant in breast c ancer aetiology, The alkaline single-cell gel electrophoresis ('Comet') ass ay was used to examine breast milk cells for DNA damage and to measure the activity of extracts of the milk in causing such damage. UK-resident women were recruited as donors (n = 16) and provided 'early' (similar to 4 weeks post-partum) and/or 'late' (similar to 4 months post-partum) milk samples. Cells (79-94% viable, trypan blue exclusion) were either examined immediate ly for DNA damage or were cultured for 1 week prior to treatment with a bre ast milk extract. DNA damage in the form of single-strand breaks was quanti fied as comet tail length (CTL), Cell preparations examined immediately exh ibited interindividual variation in median CTL (range 2.0-40.0 mu m) with o r without the DNA repair inhibitors hydroxyurea (HU) and cytosine arabinosi de (ara-C). DNA damage decreased following culture, suggesting either DNA r epair or death of DNA-damaged cells. Some donors' breast milk extracts indu ced DNA damage in their cultured cells and increases in median CTL were sig nificantly greater with HU/ara-C (range 4.0-72.5 mu m) than without (range 2.5-27.5 mu m), Genotoxicity occurred without cytotoxicity (81-97% viabilit y after treatment). Comparisons between cells and extracts from 'early' and 'late' milk samples did not support the idea of a progressive clearance of genotoxins from mammary lipid during lactation. Donors whose untreated cel ls contained the most DNA damage tended to yield genotoxic breast milk extr acts. Cells isolated from milk activated the rodent mammary carcinogens o - toluidine and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), The r elevance of genotoxic exposures to breast cancer initiation requires furthe r investigation.