Ronald D. Thomas

BIOCHEMICAL AND MOLECULAR CHANGES AT THE CELLULAR LEVEL IN RESPONSE TO EXPOSURE TO ENVIRONMENTAL ESTROGEN-LIKE CHEMICALS

Estrogen-like chemicals are unique compared to nonestrogenic xenobiotics, because in addition to their chemical properties, the estrogenic property of these compounds allows them to act like sex hormones. Whether weak or strong, the estrogenic response of a chemical, if not overcome, will add extra estrogenic burden to the system. At elevated doses, natural estrogens and environmental estrogen-like chemicals are known to produce adverse effects. The source of extra or elevated concentration of estrogen could be either endogenous or exogenous. The potential of exposure for humans and animals to environmental estrogen-like chemicals is high. Only a limited number of estrogen-like compounds, such as diethylstilbestrol (DES), bisphenol A, nonylphenol, polychlorinated biphenyls (PCBs), and dichlorodiphenyltrichloroethane (DDT), have been used to assess the biochemical and molecular changes at the cellular level. Among them, DES is the most extensively studied estrogen-like chemical, and therefore this article is focused mainly on DES-related observations. In addition to estrogenic effects, environmental estrogen-like chemicals produce multiple and multitype genetic and/or nongenetic hits. Exposure of Syrian hamsters to stilbene estrogen (DES) produces several changes in the nuclei of target organ for carcinogenesis (kidney): (1) Products of nuclear redox reactions of DES modify transcription regulating proteins and DNA; (2) transcription is inhibited; (3) tyrosine phosphorylation of nuclear proteins, including RNA polymerase II, p53, and nuclear insulin-like growth factor-1 receptor, is altered; and (4) DNA repair gene DNA polymerase beta transcripts are decreased and mutated. Exposure of Noble rats to DES also produces several changes in the mammary gland: proliferative activity is drastically altered; the cell cycle of mammary epithelial cells is perturbed; telomeric length is attenuated; etc. It appears that some other estrogenic compounds, such as bisphenol A and nonylphenol, may also follow a similar pattern of effects to DES, because we have recently shown that these compounds alter cell cycle kinetics, produce telomeric associations, and produce chromosomal aberrations. Like DES, bisphenol A after metabolic activation is capable of binding to DNA. However, it should be noted that a particular or multitype hit(s) will depend upon the nature of the environmental estrogen-like chemical. The role of individual attack leading to a particular change is not clear at this stage. Consequences of these multitypes of attack on the nuclei of cells could be (1) nuclear toxicity/cell death; (2) repair of all the hits and then acting as normal cells; or (3) sustaining most of the hits and acting as unstable cells. Proliferation of the last type of cell is expected to result in transformed cells.

Diallyl sulfide inhibits diethylstilbestrol induced DNA damage in human breast epithelial cells (MCF-10A)

Breast cancer is the second leading cause of cancer deaths in women in the United States. Diethylstilbestrol (DES) is a synthetic estrogen that has been shown to cause cancer in animals and humans, altering cell viability as well as inducing DNA damage. Diallyl sulfide (DAS) is a garlic organosulfide that has been shown to inhibit both the initiation and promotion phases of cancer in vivo and in vitro, as well as reduce the risk of cancer in epidemiological studies. MCF-10A cells, regarded as a normal breast epithelial cell line, were treated with varying concentrations of DES, DAS or various dose combinations of DES and DAS concomitantly, and assessed for cell viability, DNA strand breaks, and lipid peroxidation. DES (10μM) in combination with 1, 10, or 100μM DAS resulted in a 31%, 34%, or 36% respective increase in cell viability compared to the DES treatment alone, after 24h. At the same time point, 1, 10, and 100μM DAS were all effective in significantly reducing DES (100μM)-induced strand breaks to near that of the vehicle control. Additionally, 1μM DAS was effective in significantly reducing DES (100μM)-induced lipid peroxidation after 3h. The results of this research suggest that DAS is effective in recovering cell viability, attenuating DNA strand breaks, and decreasing lipid peroxidation in MCF-10A cells.