Hari K. Bhat

Exposure to estrogens is suggested to be a risk factor in human breast cancer development. The mechanisms underlying estrogen‐induced cancer have not been fully elucidated. Both estrogen receptor (ER)‐mediated proliferative processes and ER‐independent generation of oxidative stress are suggested to play important roles in estrogen‐induced breast carcinogenesis. In the current study, we investigated the role of oxidative stress in breast carcinogenesis using the ACI rat model of mammary tumorigenesis. Female ACI rats were treated with 17β‐estradiol (E₂), butylated hydroxyanisole (BHA), or a combination of E₂ + BHA for up to 240 days. Cotreatment of rats with E₂ + BHA reduced estrogen‐induced breast tumor development with tumor incidence of 24%, a significant decrease relative to E₂ where tumor incidence was 82%. Proliferative changes in the breast tissue of E₂ + BHA‐treated animals were similar to those observed in E₂‐treated animals. Tissue levels of 8‐isoprostane, a marker of oxidant stress, as well as the activities of antioxidant enzymes including glutathione peroxidase, superoxide dismutase, and catalase were quantified in the breast tissues of rats treated with E₂ + BHA and compared to activity levels found in E₂‐treated animals and respective age‐matched controls. Cotreatment with BHA inhibited E₂‐mediated increases in 8‐isoprostane levels as well as activities of antioxidant enzymes. In summary, these data suggest that estrogen‐mediated oxidant stress plays a critical role in the development of estrogen‐dependent breast cancers and BHA inhibits E₂‐dependent breast carcinogenesis by decreasing oxidant stress. © 2009 Wiley Periodicals, Inc. J Biochem Mol Toxicol 23:202–211, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/jbt.20281

The mechanisms underlying the pathogenesis of estrogen-induced breast carcinogenesis remain unclear. The present study investigated the roles of estrogen metabolism and oxidative stress in estrogen-mediated mammary carcinogenesis in vivo . Female August Copenhagen Irish (ACI) rats were treated with 17β-estradiol (E ₂ ), the antioxidant vitamin C, the estrogen metabolic inhibitor α-naphthoflavone (ANF), or cotreated with E ₂ + vitamin C or E ₂ + ANF for up to 8 months. E ₂ (3 mg) was administered as an subcutaneous implant, ANF was given via diet (0.2%) and vitamin C (1%) was added to drinking water. At necropsy, breast tumor incidence in the E ₂ , E ₂ + vitamin C and E ₂ + ANF groups was 82, 29 and 0%, respectively. Vitamin C and ANF attenuated E ₂ -induced alterations in oxidative stress markers in breast tissue, including 8-iso-prostane F _2α formation and changes in the activities of antioxidant enzymes superoxide dismutase and glutathione peroxidase. Quantification of 2-hydroxyestradiol (2-OHE ₂ ) and 4-hydroxyestradiol (4-OHE ₂ ) formation in breast tissue confirmed that ANF inhibited 4-hydroxylation of E ₂ and decreased formation of the highly carcinogenic 4-OHE ₂ . These results demonstrate that antioxidant vitamin C reduces the incidence of estrogen-induced mammary tumors, increases tumor latency and decreases oxidative stress in vivo . Further, our data indicate that ANF completely abrogates breast cancer development in ACI rats. The present study is the first to demonstrate the inhibition of breast carcinogenesis by antioxidant vitamin C or the estrogen metabolic inhibitor ANF in an animal model of estrogen-induced mammary carcinogenesis. Taken together, these results suggest that E ₂ metabolism and oxidant stress are critically involved in estrogen-induced breast carcinogenesis.

CYP19 and PPARγ are two genes expressed in the placental trophoblast that are important to placental function and are disrupted by phthalate exposure in other cell types. Measurement of the mRNA of these two genes in human placental tissue by quantitative real-time polymerase chain reaction (qPCR) offers a source of potential biomarkers for use in epidemiologic research. We report on methodologic challenges to be considered in study design.

Cancer is the second leading cause of death worldwide. Although great advancements have been made in the treatment and control of cancer progression, significant deficiencies and room for improvement remain. A number of undesired side effects sometimes occur during chemotherapy. Natural therapies, such as the use of plant-derived products in cancer treatment, may reduce adverse side effects. Currently, a few plant products are being used to treat cancer. However, a myriad of many plant products exist that have shown very promising anti-cancer properties in vitro, but have yet to be evaluated in humans. Further study is required to determine the efficacy of these plant products in treating cancers in humans. This review will focus on the various plant-derived chemical compounds that have, in recent years, shown promise as anticancer agents and will outline their potential mechanism of action.

Phytoestrogens display an array of pharmacologic properties, and in recent years investigation of their potential as anticancer agents has increased dramatically. In this article we review the published literature related to phytoestrogens and breast ...

Methylmercury (MeHg) is a highly toxic compound that successfully traverses the blood brain barrier with deleterious effects to the central nervous system. Exposure is generally through the ingestion of contaminated fish. Two well-known disastrous exposures to methylmercury occurred in Japan in the 1950s and in Iraq in the 1970s. Acute methylmercury exposures such as these resulted in parasthesia, ataxia, and narrowing of the visual field. Exposures in utero resulted in microcephaly, cerebropalsy, seizures, and mental retardation. Since the developing fetus as well as the neonate are particularly vulnerable, the study of chronic low-dose exposures in utero which may result in developmental delays has become increasingly of interest. The known neurotoxic mechanisms are multifactorial. Methylmercury inhibits protein synthesis by post-transcriptionally interfering with chain elongation resulting from inhibition of aminoacyl-tRNA synthetase enzymes. Abnormalities in protein phosphorylation, critical to intercellular communication, were found both in vitro and in vivo. Methylmercury's high affinity for tubulin sulfhydryl groups was implicated in the disruption of microtubules. The resulting interference with tubulin polymerization can negatively affect cell proliferation and migration. Methylmercury altered neurotransmitter functions by stimulating spontaneous transmitter release and inhibiting glutamate uptake resulting in excitotoxicity. Methylmercury disrupted Ca²⁺ homeostasis by increasing intracellular concentrations of this ion. Methylmercury may overwhelm the cell's natural protective mechanisms provided by glutathione, metallothioneins, and heat shock protein, thereby producing the generation of reactive oxygen species (ROS). The resulting oxidative stress produced damage to cellular membranes through lipid peroxidation as well as damage to a variety of vital cellular macromolecules. The observed protective effect of antioxidants supports the critical role of oxidative stress in neurotoxicity. Though much has already been discerned regarding the various mechanisms involved in methylmercury-induced neurotoxicity, the interplay between these modes and whether or not they occur sequentially or synchronously has yet to be determined. Attention in this review is focused on oxidative stress since recent studies suggests that oxidative stress may be the initiating event from which other modes of cellular damage originate.

An efficient and effective method for quantification of small amounts of nucleic acids contained within a sample specimen would be an important diagnostic tool for determining the content of mitochondrial DNA (mtDNA) in situations where the depletion thereof may be a contributing factor to the exhibited pathology phenotype. This study compares two quantification assays for calculating the total mtDNA molecule number per nanogram of total genomic DNA isolated from human blood, through the amplification of a 613‐bp region on the mtDNA molecule. In one case, the mtDNA copy number was calculated by standard competitive polymerase chain reaction (PCR) technique that involves co‐amplification of target DNA with various dilutions of a nonhomologous internal competitor that has the same primer binding sites as the target sequence, and subsequent determination of an equivalence point of target and competitor concentrations. In the second method, the calculation of copy number involved extrapolation from the fluorescence versus copy number standard curve generated by real‐time PCR using various dilutions of the target amplicon sequence. While the mtDNA copy number was comparable using the two methods (4.92 ± 1.01 × 10⁴ molecules/ng total genomic DNA using competitive PCR vs 4.90 ± 0.84 × 10⁴ molecules/ng total genomic DNA using real‐time PCR), both inter‐ and intraexperimental variance were significantly lower using the real‐time PCR analysis. On the basis of reproducibility, assay complexity, and overall efficiency, including the time requirement and number of PCR reactions necessary for the analysis of a single sample, we recommend the real‐time PCR quantification method described here, as its versatility and effectiveness will undoubtedly be of great use in various kinds of research related to mitochondrial DNA damage‐ and depletion‐associated disorders. © 2004 Wiley Periodicals, Inc. J Biochem Mol Toxicol 18:180–186, 2004 Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/jbt.20024