DNA damage in breast epithelial cells: detection by the single-cell gel (comet) assay and induction by human mammary lipid extracts.

The presence of DNA damage in primary cultures of human mammary epithelial cells (HMECs), and the ability of extracts of human mammary lipid to cause such damage, has been investigated. Lipid extracts, prepared by a solid-phase procedure, and HMECs were obtained from breast tissue removed from healthy women (ages 18-50 years) who were resident in the UK and undergoing elective reduction mammoplasties. DNA single strand breaks (SSBs) were detected using the single-cell gel assay (comet assay) with alkaline electrophoresis (pH 12.3) and quantified by measuring comet tail length (CTL) (microm). Untreated HMECs and HMECs incubated (30 min, 37 degrees C) with a mammary lipid extract, with or without DNA-repair inhibitors hydroxyurea (HU) and cytosine arabinoside (ara-C), were examined. Ionizing radiation was used as a positive control. An active lipid extract gave a linear dose-response over the range 2.0-12.2 g equivalents. When MCL-5 cells, a line of metabolically-competent human lymphoblastoid cells, were used to compare the DNA-damaging properties of lipid extracts from six different donors, significant interindividual variations (median CTLs were 15.0, 53.5, 32.5, <4.0, <4.0 and 77.5 microm respectively) were observed. In eight subjects, the donors' HMECs were examined both before and after treatment with extracts of that donor's own lipid. Pre-existing DNA damage was detected in untreated HMECs from some donors (median CTLs 22.0-37.5 microm) that was not present in others (median CTLs 4.0-11.5 microm), and increases in CTL could be induced by incubation with the matching lipid extract (8 g equivalent) in more than half (five out of eight) the subjects examined (median CTL up to 111.0 microm). There was a tendency for the most active lipid extracts to be those obtained from donors whose HMECs also contained the most pre-existing DNA SSBs. The results of this pilot study may prove to be significant in relation to the initiation of breast cancer.