Screening of Environmental Contaminants for Ecdysteroid Agonist and Antagonist Activity Using the Drosophila Melanogaster Bii Cell in Vitro Assay

Abstract

The B(II) bioassay was developed as a rapid and reliable tool for detecting potential insect growth regulators acting as ecdysteroid receptor (ant)agonists. Based on an ecdysteroid-responsive cell line from Drosophila melanogaster, this microplate assay is ideally suited to the evaluation of environmental contaminants as potential endocrine disrupters. Data are presented for about 80 potential environmental contaminants, including industrial chemicals, pesticides, pharmaceuticals, phytoestrogens, and vertebrate steroids, and are compared with data for known (ant)agonists. Apart from androst-4-ene-3,17-dione (a weak antagonist), vertebrate steroids were inactive at concentrations up to 10(-3) M. The vast majority of xenobiotics also showed no (ant)agonist activity. Among the industrial chemicals, antagonistic activity was observed for bisphenol A median effective concentration (EC50) of 1.0 x 10(-4) M and diethylphthalate (EC50 of 2.0 x 10(-3) M). Some organochlorine compounds also showed weak antagonistic activity, including o,p'-dichlorodiphenyldichloroethylene (DDE), p,p'-DDE, dieldrin, and lindane (EC50 of 3.0 x 10(-5) M). For lindane, bisphenol A, and diethylphthalate, activity is not associated with impurities in the samples and, for lindane and bisphenol A at least, the compounds are able to compete with ecdysteroids for the ligand binding site on the receptor complex, albeit at concentrations very much higher than those found in the environment. The only pharmaceutical showing any detectable antagonist activity was 17alpha-ethynylestradiol. In the context of recent publications on potential endocrine disruption in marine and freshwater arthropods, these findings suggest that, for some compounds (e.g., diethylstilbestrol), ecdysteroid receptor-mediated responses are unlikely to be involved in producing chronic effects. The B(II) assay has a potentially valuable role to play in distinguishing between endocrine-mediated, which normally occur at submicromolar concentrations, and pharmacological effects in insects and crustaceans.

Crustacean Molting: Regulation and Effects of Environmental Toxicants

“…Chemicals with antiecdysteroidal activity include many of the classic estrogen receptor agonists of vertebrate. However, studies with ecdysteroid-responsive insect cells have demonstrated that non-steroidal EcR agonists are rare [62]. The binding of an environmental chemical to the EcR will more likely result in inhibition of ecdysteroid signaling.…”

“…Both of these chemicals may inhibit ecdysteroidsynthesis through this enzyme inhibition. The 4-Nonylphenol is an antagonist of the insect ecdysteroidreceptor in vitro [62]. Bisphenol A was proposed to elicit anti-ecdysteroidal activity through a receptor cross-talk mechanism [71,74].…”

A critical analysis of the biological impacts of plasticizers on wildlife

“…In the D. melanogaster BII cell line, BPA was shown to act as an ecdysteroid antagonist, but only at a high exposure concentration of 22.8 mg l 21 (Dinan et al 2001). Studies combining BPA with other chemicals have shown interactive effects, affecting the number of embryo abnormalities and offspring emergence (Mu et al 2005;Wang et al 2005).…”

Endocrine regulation of the reproduction in crustaceans: Identification of potential targets for toxicants and environmental contaminants

“…For example, male vertebrate sex steroid hormone testosterone (in relatively high concentrations 5-40 µM) interfered with 20-HE signalling in Daphnia magna Straus, 1820 causing abnormal progeny development and prolongation of the first molting (Mu & LeBlanc 2002). Testosterone (Mu & LeBlanc 2002) as well as three estrogens, bisphenol A, diethylphtalate and lindane (Dinan et al (2001), antagonized effects of 20-HE in an insect (Drosophila) in vitro model systems indicating a ligand-competitive mechanism. Similarly, other two xeno-ecdysteroids, strong fytoecdysterone agonist Ponasterone A and synthetic ecdysone agonist bisacylhydrazine RG-102240, are potent lignads for EcR (that heterodimerizes with RXR) in U. pugilator (Wu et al 2004).…”