Mammary Epithelial DNA Research Articles

Abstract 1477: Acrylamide exposure in obesity enhances mammary epithelial DNA damage via the activity of its metabolite, glycidamide, and increased oxidative stress

Abstract Obesity is a world-wide epidemic, with 39% of adults considered overweight and 13% obese, and rates are rising. Obese women are at greater risk for developing breast cancer than lean women, however the mechanisms of how obesity increases breast cancer risk are not well understood. There is also limited knowledge on how environmental toxins may interact with obesity to promote breast cancer. Acrylamide, a probable carcinogen, is a biproduct in starchy foods cooked at high temperatures, which are prevalent in the obesity-inducing Western diet. Acrylamide is metabolized by the CYP2E1 enzyme into the epoxide, glycidamide, which is known to induce DNA damage. CYP2E1 activity is elevated in obesity, which could enhance DNA damage in obese individuals. Acrylamide exposure is associated with an increased risk of breast cancer in epidemiologic studies, but the evidence has been contradictory. To investigate how acrylamide impacts DNA damage in the obese mammary gland, three-week-old FVB female mice were randomized to receive a low-fat (LFD; 16% kcal from fat) or high-fat diet (HFD; 60% kcal from fat) and either 0.7 mM acrylamide water or control water. HFD-fed mice gained significantly more weight than LFD-fed mice, and exposure to acrylamide did not impact weight gain compared to respective controls. Mammary epithelial cells from acrylamide-treated mice had increased DNA damage compared to controls measured by COMET assays, with the highest DNA damage present in epithelial cells from obese acrylamide-treated mice. Mammary epithelial cells from acrylamide-treated mice also had enhanced oxidative DNA damage, measured by 8-OHdG adducts, and an additive effect was observed between acrylamide exposure and obesity. To investigate the impact of acrylamide in vitro, COMMA-D mammary epithelial cells were treated with vehicle, 9.8 µM acrylamide, or 0.5 mM glycidamide for 24 hours, then COMET assays and immunohistochemistry for markers of DNA damage were performed. COMMA-D cells treated with acrylamide-metabolite glycidamide showed significantly increased double strand DNA breaks compared to vehicle-treated cells, however acrylamide-treated cells did not. Interestingly, acrylamide-treated cells demonstrated significantly higher levels of intracellular reactive oxygen species compared to both glycidamide and vehicle-treated cells. These studies suggest acrylamide exposure enhances DNA damage in mammary epithelial cells via conversion to the genotoxic metabolite glycidamide and through generation of oxidative stress, which is exacerbated by obese conditions. These studies suggest that long-term acrylamide exposure through foods common in the Western diet may enhance DNA damage in mammary epithelial cells, potentially enhancing obesity-induced breast cancer risk. Citation Format: Brenna Walton, Lisa Arendt. Acrylamide exposure in obesity enhances mammary epithelial DNA damage via the activity of its metabolite, glycidamide, and increased oxidative stress [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1477.

Effects of DMBA Preparation on DMBA-Induced Rat Mammary Carcinogenesis

We compared two protocols for 7,12-dimethylbenz[ a ]anthracene (DMBA)-induced mammary carcinogenesis. DMBA (20 mg/ml) was prepared at room temperature or at 60°C and administered by gavage to 50-day-old Sprague-Dawley rats. Two days post-DMBA, mammary epithelial DNA was 32 P-postlabeled. At 12 weeks post-DMBA, tumor DNA was screened for H- ras codon 61 mutations using an enriched polymerase chain reaction (EPCR). The number of in situ carcinomas (3.0 - 2.7 vs. 2.5 - 2.7), invasive carcinomas (1.1 - 1.6 vs. 0.6 - 0.8), and H- ras codon 61 mutations (34 - 13% vs. 23 - 13%) were statistically not different ( p = 0.05) between the groups. The relative adduct levels in mammary organoids were significantly ( p h 0.001) greater in the 60°C (568 - 158) than the room temperature (150 - 130) group. While DMBA-DNA adduct levels differed significantly between these protocols, this did not correlate with significant differences in tumor pathologies or H- ras codon 61 mutations.

DNA adduct formation and persistence in rat tissues following exposure to the mammary carcinogen dibenzo[a,l]pyrene.

Dibenzo[a,l]pyrene (DBP), an environmentally significant polycyclic aromatic hydrocarbon (PAH), is one of the most potent carcinogens with greater carcinogenicity in rodent mammary glands and skin than 7,12-dimethylbenz[a]anthracene or benzo[a]pyrene, respectively. In this study, we have examined the formation and persistence of stable DNA adducts in rats administered a carcinogenic intramammillary (i.m.) dose of DBP (0.25 micromol/gland). 32P-post-labeling analysis of mammary epithelial DNA 6 h, and 2, 5 and 14 days post-treatment produced one major (approximately 30%) and at least six minor adducts. Non-target tissue DNA (lung, heart, bladder and pancreas) also showed essentially the same adduct pattern as did mammary DNA, except liver which resulted in four additional adduct spots. The mammary DNA was most adducted (2640 +/- 532 adducts/10(9) nucleotides) on day 5 while the other tissue DNAs had 10- to 65-fold lower adduct levels (lung > liver > heart > bladder > pancreas). Adduct levels continued to increase at all time points examined for all tissues, except mammary tissue which showed a decline ( approximately 40%) on day 14. Chromatographic comparison with adducts formed in vitro by reaction of syn- and anti-DBP-11, 12-diol-13,14-epoxides (DBPDEs) with DNA and individual nucleotides indicated that the in vivo adducts were deoxyadenosine- and deoxyguanosine-derived, formed by interaction with both the anti- and syn-isomers; the adenine-derived adducts comprised 60-75% of the total adducts. However, the liver-specific DNA adducts (nos 8-11) were not derived from any of the DBPDE isomers. Our data show: (i) significantly higher DBP-DNA adduction in mammary tissue as compared with non-target tissues, which is consistent with its mammary carcinogenicity; (ii) adenine is highly reactive towards DBP metabolites as has been observed for many other PAHs; and (iii) the peak binding of DBP with DNA was shifted beyond 14 days for the non-target tissues by i.m. route of exposure.

Targeted expression of a dominant negative epidermal growth factor receptor in the mammary gland of transgenic mice inhibits pubertal mammary duct development.

The epidermal growth factor (EGF) system has been thought to play an important role in normal mammary development and carcinogenesis. To study the role of the EGF receptor (EGFR) in mammary development, we developed a transgenic mouse model in which a C-terminal truncated mouse EGFR (EGFR-TR) was expressed in the mouse mammary epithelium under the control of the mouse mammary tumor virus long terminal repeat. The EGFR-TR lacks most of the cytoplasmic domain of the receptor, including the entire protein tyrosine kinase domain. In cultured cells, we show that it acts in a dominant negative manner in EGF-signaled EGFR autophosphorylation. Several lines of mice were characterized and shown to express the transgene at the mRNA and protein levels not only in the mammary gland but also in the salivary glands, epididymis, and prostate. In postpubertal virgin female mice, the expression of the EGFR-TR in the mammary glands was greater than the expression of the endogenous wild type EGFR. In these virgin mice, inhibition in mammary ductal development and a decrease of mammary epithelial DNA synthesis were observed beginning at 5-6 weeks. The inhibition of duct development was most apparent by 15-16 weeks, resulting in a significant defect in ductal branching and outgrowth and an apparent overall decrease in the size of the mammary glands. However, during pregnancy, expression of the endogenous wild type EGFR was markedly increased relative to the EGFR-TR and, at this stage, normal presecretory alveoli developed from the hypoplastic duct tree. Postpartum, normal lactation occurred. Despite EGFR-TR expression in other tissues, no morphological abnormalities were observed. This model demonstrates that the EGFR-TR behaves as a dominant negative regulator of the EGFR system in vivo and that the EGFR system plays an important role in mammary ductal development.

Tissue distribution of DNA adducts in rats treated by intramammillary injection with dibenzo[ a,l]pyrene, 7,12-dimethylbenz[ a]anthracene and benzo[ a]pyrene

Dibenzo[ a,l]pyrene (DBP) has recently emerged as a potent environmental carcinogen having greater carcinogenicity in the rat mammary epithelial glands than 7,12-dimethylbenz[ a]anthracene (DMBA), previously considered to be the most potent mammary carcinogen and benzo[ a]pyrene (BP), a ubiquitous environmental carcinogen. Previous studies on the tumor-initiating potential of DBP, DMBA, and BP demonstrated that DBP was 2.5 times more potent in inducing the tumors in mouse skin and rat mammary glands than DMBA; BP was a weak mammary carcinogen in these animals. The present study was designed to investigate if the significantly increased mammary carcinogenicity of DBP over DMBA and BP was related to increased DNA adduction at the target site. Female Sprague–Dawley rats were treated by intramammillary injection with an equimolar dose of 0.25 μmol/gland of DBP, DMBA, and BP at the 3rd, 4th and 5th mammary glands on both sides. 32P-Postlabeling analysis of mammary epithelial DNA of rats treated with DBP produced two major (nos. 3 and 6) and at least 5 minor adducts. DMBA treatment resulted in one major and 4 minor DNA adducts while BP produced one major and two minor adducts. Quantitation of the adduct radioactivity revealed that DNA adduction was 6- and 9-fold greater in DBP-treated animals than in BP- and DMBA-treated animals, respectively. The adduct levels per 10 9 nucleotides in mammary epithelial cells for DBP, BP and DMBA were in the following descending order: 1828±378, 300±45 and 207±72, respectively. Tissue distribution of DNA adducts in non-target organs following DBP treatment showed similar adduct pattern as found in the mammary epithelial cells except the liver, which resulted in 4 additional adduct spots; vehicle-treated tissue DNA processed in parallel did not show any detectable adducts. DMBA- and BP–DNA adduct patterns in various tissues were similar to that found in mammary epithelial cells, however, significant quantitative differences were found; BP–DNA adducts were undetectable in the pancreas and bladder. Quantitation of adduct radioactivity showed a 15- to 60-fold lower DBP-DNA adduction in these tissues than the levels found in the mammary tissue; similarly 5–20 and 30–100 times lower DNA adduction was found following treatment with DMBA and BP, respectively. The significantly increased binding of DBP to the mammary epithelial DNA over BP and DMBA is in concordance with its known higher mutagenicity and tumorigenicity.