ABSTRACT
In this study, the effects of the light/dark cycle, hormone replacement therapy (HRT), and nocturnal melatonin supplementation on osteogenic markers and serum melatonin levels were examined in a blind mouse model (MMTV-Neu transgenic mice). Melatonin levels in this mouse strain (FVB/N) with retinal degeneration (rd-/-) fluctuate in a diurnal manner, suggesting that these mice, although blind, still perceive light. Real-time RT-PCR analyses demonstrated that Runx2, Bmp2, Bmp6, Bglap, and Per2 mRNA levels coincide with melatonin levels. The effect of chronic HRT (0.5 mg 17ß-estradiol + 50 mg progesterone in 1800 kcal of diet) alone and in combination with melatonin (15 mg/L drinking water) on bone quality and density was also assessed by histomorphometry and microcomputed tomography, respectively. Bone density was significantly increased (P < 0.05) after 1 yr of treatment with the individual therapies, HRT (22% increase) and nocturnal melatonin (20% increase) compared to control. Hormone replacement therapy alone also increased surface bone, decreased trabecular space, and decreased the number of osteoclasts without affecting osteoblast numbers compared to the control group (P < 0.05). Chronic HRT + melatonin therapy did not significantly increase bone density, even though this combination significantly increased Bglap mRNA levels. These data suggest that the endogenous melatonin rhythm modulates markers important to bone physiology. Hormone replacement therapy with or without nocturnal melatonin in cycling mice produces unique effects on bone markers and bone density. The effects of these therapies alone and combined may improve bone health in women in perimenopause and with low nocturnal melatonin levels from too little sleep, too much light, or age.
Subject(s)
Bone Density Conservation Agents/administration & dosage , Bone and Bones/drug effects , Circadian Rhythm/drug effects , Estradiol/administration & dosage , Estrogen Replacement Therapy , Melatonin/administration & dosage , Photoperiod , Progesterone/administration & dosage , Animals , Bone Density/drug effects , Bone Density/radiation effects , Bone Morphogenetic Protein 2/genetics , Bone Morphogenetic Protein 2/metabolism , Bone Morphogenetic Protein 6/genetics , Bone Morphogenetic Protein 6/metabolism , Bone and Bones/diagnostic imaging , Bone and Bones/metabolism , Bone and Bones/radiation effects , Circadian Rhythm/genetics , Circadian Rhythm/radiation effects , Core Binding Factor Alpha 1 Subunit/genetics , Core Binding Factor Alpha 1 Subunit/metabolism , Drug Administration Schedule , Drug Therapy, Combination , Female , Gene Expression Regulation/drug effects , Gene Expression Regulation/radiation effects , Mammary Tumor Virus, Mouse/genetics , Melatonin/blood , Mice , Mice, Transgenic , Osteocalcin/genetics , Osteocalcin/metabolism , Period Circadian Proteins/genetics , Period Circadian Proteins/metabolism , RNA, Messenger/metabolism , Receptor, ErbB-2/genetics , Receptor, ErbB-2/metabolism , Time Factors , X-Ray MicrotomographyABSTRACT
BACKGROUND: The association of DDT (dichlorodiphenyltrichloroethane) with breast cancer is controversial, but animal studies directly linking DDT to risk are lacking. Concerns with DDT reside in its environmental persistence, bioaccumulation in breast adipose tissue, and endocrine-disrupting actions. Whereas most attention has been focused on estrogenic congeners, we tested the cancer-inducing potential of the antiandrogen, p,p´-DDE [1,1-dichloro-2,2-bis(p-chlorophenyl) ethylene], the most prevalent and persistent DDT metabolite. OBJECTIVES: We aimed to determine whether developmental exposure to p,p´-DDE stored in adipose tissue surrounding the cancer-prone mammary epithelium of MMTV-Neu mice influences tumor development. METHODS: For localized delivery, Elvax 40P pellets containing p,p´-DDE were implanted into the mammary fat pads of prepubertal female mice. We compared mammary tumor development with p,p´-DDE with development in response to its estrogenic isomer, o,p´-DDE [1,1-dichloro-2-(o-chlorophenyl)-2-(p-chlorophenyl) ethylene], and a mixture of both isomers. RESULTS: p,p´-DDE implants significantly accelerated mammary tumor onset compared with vehicle Elvax implants. o,p´-DDE had similar results, but only at ≤ 10 months of age. Lipid-adjusted levels of p,p´-DDE in mammary adipose tissue and serum in young mice were within the ranges of human exposure, whereas concentrations in aged mice were low to undetectable. Exposure to a 2:1 ratio of p,p´-DDE:o,p´-DDE did not result in the younger latency observed with the individual isomers. CONCLUSIONS: p,p´-DDE exposure at concentrations relevant to human exposure accelerates mammary carcinogenesis in mice, possibly through hormonal and/or other actions. These data suggest that DDE exposure would promote, but not cause, mammary tumorigenesis. Developmental exposure in immature mammary tissue continues to affect tumor onset even after p,p´-DDE levels have declined. Future studies are needed to determine whether early exposure to p,p´-DDE correspondingly predisposes women to early-onset breast cancer.
