The GARD™skin assay: Investigation of the applicability domain for metals.

New approach methodologies (NAMs) for hazard identification of skin sensitizing chemicals were adopted as test guidelines by the OECD during the last decade. These alternatives to animal models align to individual key events (KE) in the adverse outcome pathway (AOP) for skin sensitization for which the molecular initiating event (MIE) is covalent binding to proteins. As it currently stands, the AOP does not include mechanistic events of sensitization by metals, and limited information is available on whether NAMs accurately predict the sensitization potential of such molecules, which have been proposed to act via alternative mechanisms to organic chemicals.

Joint effects of heterogeneous estrogenic chemicals in the E-screen--exploring the applicability of concentration addition.

In the last few years, significant advances have been made toward understanding the joint action of endocrine disrupting chemicals (EDCs). A number of studies have demonstrated that the combined effects of different types of EDCs (e.g.

Detection of DNA strand breaks and oxidized DNA bases at the single-cell level resulting from exposure to estradiol and hydroxylated metabolites.

Long-term exposure to steroidal estrogens is a key factor contributing to increases in the risk of developing breast cancer. Proposed mechanisms include receptor-activated increases in the rate of cell proliferation leading to the accumulation of genetic damage resulting from reading errors, and the production of DNA damage by species arising from metabolism of 17beta-estradiol (E2) resulting in mutations. In support of the second mechanism, catechol metabolites of E2 induce DNA damage in vitro.

Deviation from additivity with estrogenic mixtures containing 4-nonylphenol and 4-tert-octylphenol detected in the E-SCREEN assay.

An intriguing deviation from expected additivity is reported with mixtures containing 17beta-estradiol, 17alpha-ethinylestradiol, genistein, bisphenol A, 4-nonylphenol, and 4-tert-octylphenol. The effect of these chemicals on the proliferation of estrogen-dependent MCF-7 human breast cancer cells (the E-SCREEN) was measured. Data variance-component analyses, carried out to optimize the assay for mixture studies, showed that between-experiment variability was the dominant source of data variation.

Combining xenoestrogens at levels below individual no-observed-effect concentrations dramatically enhances steroid hormone action.

The low potency of many man-made estrogenic chemicals, so-called xenoestrogens, has been used to suggest that risks arising from exposure to individual chemicals are negligible. Another argument used to dismiss concerns of health effects is that endogenous steroidal estrogens are too potent for xenoestrogens to contribute significantly to estrogenic effects. Using a yeast reporter gene assay with the human estrogen receptoralpha, we tested these ideas experimentally by assessing the ability of a combination of 11 xenoestrogens to affect the actions of 17ss-estradiol.

Something from "nothing"--eight weak estrogenic chemicals combined at concentrations below NOECs produce significant mixture effects.

We tested whether multicomponent mixtures of xenoestrogens would produce significant effects when each component was combined at concentrations below its individual NOEC or EC01 level. The estrogenic effects of eight chemicals of environmental relevance, including hydroxylated PCBs, benzophenones, parabenes, bisphenol A, and genistein, were recorded using a recombinant yeast estrogen screen (YES). To ensure that no chemical contributed disproportionately to the overall combination effect, a mixture was prepared at a mixture ratio proportional to the potency of each individual component.