@article{gorr_rider_wang_olmstead_leblanc_2006, title={A candidate juvenoid hormone receptor cis-element in the Daphnia magna hb2 hemoglobin gene promoter}, volume={247}, ISSN={["0303-7207"]}, DOI={10.1016/j.mce.2005.11.022}, abstractNote={Hemoglobin levels are significantly elevated in the crustacean Daphnia magna by juvenoid hormones. The present study was undertaken to identify the specific globin (hb) genes that are induced by juvenoids and to identify putative juvenoid response elements (JREs) that may mediate this induction. Gene product of globin 2 (hb2), but not globin 1 and globin 3, was robustly elevated following juvenoid treatment of daphnids. A candidate JRE, located in the promoter of hb2, bound activated factor(s) in response to juvenoid treatment of daphnids. This hormone-induced protein:JRE interaction was robust when daphnids were reared at high oxygen tension but was inhibited when daphnids were reared under low pO2, implying that hypoxia might act to disrupt juvenoid-mediated endocrine signaling. The candidate JRE consists of a steroid/retinoid-response element-like core adjacent to a 5′ AT-rich extension and thus bears resemblance to response elements that bind monomeric nuclear receptors. The induction of hb2 mRNA levels by juvenoid treatment occurred rapidly (within 4 h of exposure) and was not attenuated by treatment of daphnids with cycloheximide. In contrast, cycloheximide treatment did block hormone-mediated elevations in hemoglobin protein levels. Thus, induction of hb2 by juvenoids was not dependent upon the synthesis of secondary transcription factors that bound the JRE but was likely due to activation of the gene directly by the juvenoid-receptor complex. Affinity pull-down experiments with nuclear proteins extracted from juvenoid-treated daphnids using the JRE as bait yielded a 52 kDa candidate for a monomeric nuclear receptor in D. magna that may mediate the regulatory activity of juvenoids.}, number={1-2}, journal={MOLECULAR AND CELLULAR ENDOCRINOLOGY}, author={Gorr, TA and Rider, CV and Wang, HY and Olmstead, AW and LeBlanc, GA}, year={2006}, month={Mar}, pages={91–102} }
 @article{olmstead_leblanc_2005, title={Joint action of polycyclic aromatic hydrocarbons: Predictive modeling of sublethal toxicity}, volume={75}, ISSN={["1879-1514"]}, DOI={10.1016/j.aquatox.2005.08.007}, abstractNote={Polycyclic aromatic hydrocarbons (PAHs) typically contaminate the environment as complex assemblages of different chemical compounds. Modeling approaches provide a means of estimating the toxicity of these PAH mixtures. In the present study, we tested the hypothesis that the joint effects of four PAHs: pyrene, phenanthrene, fluoranthene and naphthalene, on the growth rate of the crustacean Daphnia magna during sub-chronic exposure could be accurately predicted using a mathematical algorithm for concentration addition based upon the assumption that these PAHs impact growth by a common mode of action. Assessment of the individual toxicity of the four PAHs confirmed that these compounds elicited the common effect of retarding growth of daphnids at concentrations below those that were lethal to the organisms. Using the experimentally derived toxicity parameters for the individual chemicals, the toxicity of multiple mixtures of these four PAHs was modeled. These mixtures were based on concentrations reported in the environment and on equi-toxic concentrations. The effects of over 140 combinations of four mixture formulations on the growth rate of daphnids were experimentally determined and compared to model predictions. The concentration addition models tended to over predict the joint toxicity of these PAH mixtures and experimental data was better represented by an alternative model based upon the concept of independent joint action. Mixtures at environmentally relevant concentrations were predicted and experimentally demonstrated to have no effect on daphnid growth rates. Results indicate that PAHs elicit toxicity to daphnids by multiple mechanisms and demonstrate an appropriate modeling approach to assess the toxicity of these mixtures.}, number={3}, journal={AQUATIC TOXICOLOGY}, author={Olmstead, AW and LeBlanc, GA}, year={2005}, month={Nov}, pages={253–262} }
 @article{rider_gorr_olmstead_wasilak_leblanc_2005, title={Stress signaling: coregulation of hemoglobin and male sex determination through a terpenoid signaling pathway in a crustacean}, volume={208}, ISSN={["1477-9145"]}, DOI={10.1242/jeb.01343}, abstractNote={SUMMARY}, number={1}, journal={JOURNAL OF EXPERIMENTAL BIOLOGY}, author={Rider, CV and Gorr, TA and Olmstead, AW and Wasilak, BA and Leblanc, GA}, year={2005}, month={Jan}, pages={15–23} }
 @article{wang_olmstead_li_leblanc_2005, title={The screening of chemicals for juvenoid-related endocrine activity using the water flea Daphnia magna}, volume={74}, ISSN={["1879-1514"]}, DOI={10.1016/j.aquatox.2005.05.010}, abstractNote={U.S. Environmental Protection Agency is charged with developing a screening and testing paradigm for detecting endocrine toxicity of chemicals that are subject to regulation under the Food Quality Protection and the Safe Drinking Water Acts. In this study, we developed and evaluated a screening assay that could be employed to detect juvenoid-related endocrine-modulating activity in an invertebrate species. Juvenoid activity, anti-juvenoid activity, and juvenoid potentiator activity of chemicals was assessed using the water flea Daphnia magna. Male sex determination is under the regulatory control of juvenoid hormone, presumably methyl farnesoate, and this endpoint was used to detect juvenoid modulating activity of chemicals. Eighteen chemicals were evaluated for juvenoid agonist activity. Positive responses were detected with the juvenoid hormones methyl farnesoate and juvenile hormone III along with the insect growth regulating insecticides pyriproxyfen, fenoxycarb, and methoprene. Weak juvenoid activity also was detected with the cyclodiene insecticide dieldrin. Assays performed repetitively with compounds that gave either strong positive, weak positive, or negative response were 100% consistent indicating that the assay is not prone to false positive or negative responses. Five candidate chemicals were evaluated for anti-juvenoid activity and none registered positive. Four chemicals (all trans-retinoic acid, methoprene, kinoprene, bisphenol A) also were evaluated for their ability to potentiate the activity of methyl farnesoate. All registered positive. Results demonstrate that an in vivo assay with a crustacean species customarily employed in toxicity testing can be used to effectively screen chemicals for juvenoid-modulating activity.}, number={3}, journal={AQUATIC TOXICOLOGY}, author={Wang, HY and Olmstead, AW and Li, H and LeBlanc, GA}, year={2005}, month={Sep}, pages={193–204} }
 @article{olmstead_leblanc_2005, title={Toxicity Assessment of Environmentally Relevant Pollutant Mixtures Using a Heuristic Model}, volume={1}, ISSN={["1551-3793"]}, DOI={10.1897/ieam_2004-005r.1}, abstractNote={Abstract}, number={2}, journal={INTEGRATED ENVIRONMENTAL ASSESSMENT AND MANAGEMENT}, author={Olmstead, Allen W. and LeBlanc, Gerald A.}, year={2005}, month={Apr}, pages={114–122} }
 @misc{leblanc_olmstead_2004, title={Evaluating the toxicity of chemical mixtures}, volume={112}, ISSN={["0091-6765"]}, DOI={10.1289/ehp.112-a729}, abstractNote={Vol. 112, No. 13 PerspectivesOpen AccessEvaluating the Toxicity of Chemical Mixtures Gerald A. LeBlanc and Allen W. Olmstead Gerald A. LeBlanc Search for more papers by this author and Allen W. Olmstead Search for more papers by this author Published:1 September 2004https://doi.org/10.1289/ehp.112-a729Cited by:8AboutSectionsPDF ToolsDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InReddit Tinwell and Ashby (2004) provided a detailed evaluation of the joint action of a mixture of estrogenic chemicals using the immature rat uterotrophic assay. The researchers demonstrated that a mixture of estrogenic chemicals in which each individual chemical was present in the mixture at levels approximating the no observed effect level (NOEL) elicited a measurable response. This work advances our understanding of the toxicity of endocrine-active substances, and Tinwell and Ashby are to be commended for providing detailed results of their experiments suitable for evaluation by others.The analysis of the data, however, stopped short of providing insights into the joint action of mixtures of endocrine disruptors. Tinwell and Ashby (2004) proposed three avenues for the analysis of the joint action of chemicals. The first, a simple addition-of-effects approach, is overly simplistic and unrealistic, as demonstrated by the authors. The second, graphic isobole analysis, was rejected by the authors for any mixture in excess of three chemicals. We concur that isobole analysis poses limitations for more complex mixtures of chemicals. The third, concentration addition, was deemed impractical by Tinwell and Ashby due to the requirement of detailed characterization of the concentration–response relationship of each chemical within the mixture. We agree that analysis of mixtures toxicity using concentration addition requires an understanding of the toxicity of the individual constituents within a mixture. However, we disagree that such a data requirement should discourage efforts to model and predict toxicity of chemical mixtures using this approach. Results reported by Tinwell and Ashby (2004), along with published data cited by the authors, provided sufficient information on the toxicity of the individual chemicals for us to accurately model the joint action of the mixture based upon concentration addition.The authors’ recommendation that toxicity of chemical mixtures be directly assessed on a case-by-case basis (Tinwell and Ashby 2004) would provide a Band-Aid but not a cure to the dilemma of characterizing the hazards of chemical mixtures. Chemical mixtures are ever varying with respect to constituents and to concentrations of those constituents. Granted, the individual toxicity of many, if not most, chemicals has not been adequately evaluated to provide the concentration–response information required for the joint evaluation of toxicity. Rather than avoid such endeavors, the scientific community should mobilize to generate such data; the data should be made available in the public domain; and, alternative approaches (i.e., in vitro analyses of ligand–receptor interactions) should be explored as means to rapidly generate surrogate data for use in mixtures toxicity assessments. Thanks to the efforts of investigators such as Tinwell and Ashby, who are generous with the data they have generated, a growing database exists for estrogenic chemicals. Hopefully, key agencies (i.e., the National Institute of Environmental Health Sciences, the U.S. Environmental Protection Agency) will take the initiative to generate public-domain databases on chemicals harboring other mechanisms of toxicity. With such data resources, we may someday have the ability to routinely model the toxicity of chemical mixtures.ReferencesTinwell H, Ashby J. 2004. Sensitivity of the immature rat uterotrophic assay to mixtures of estrogens. Environ Health Perspect 112:575-58215064164. Link, Google ScholarFiguresReferencesRelatedDetailsCited By Shaw J, Moore M, Readman J, Mou Z, Langston W, Lowe D, Frickers P, Al-Moosawi L, Pascoe C and Beesley A (2019) Oxidative stress, lysosomal damage and dysfunctional autophagy in molluscan hepatopancreas (digestive gland) induced by chemical contaminants, Marine Environmental Research, 10.1016/j.marenvres.2019.104825, (104825), Online publication date: 1-Oct-2019. Moore M, Wedderburn R, Clarke K, McFadzen I, Lowe D and Readman J (2018) Emergent synergistic lysosomal toxicity of chemical mixtures in molluscan blood cells (hemocytes), Environmental Pollution, 10.1016/j.envpol.2018.01.019, 235, (1006-1014), Online publication date: 1-Apr-2018. Dawson D, Genco N, Bensinger H, Guinn D, Il’Giovine Z, Wayne Schultz T and Pöch G (2012) Evaluation of an asymmetry parameter for curve-fitting in single-chemical and mixture toxicity assessment, Toxicology, 10.1016/j.tox.2011.12.006, 292:2-3, (156-161), Online publication date: 1-Feb-2012. Cao Z, Shafer T, Crofton K, Gennings C and Murray T (2011) Additivity of Pyrethroid Actions on Sodium Influx in Cerebrocortical Neurons in Primary Culture, Environmental Health Perspectives, 119:9, (1239-1246), Online publication date: 1-Sep-2011.Miller M, Crofton K, Rice D and Zoeller R (2009) Thyroid-Disrupting Chemicals: Interpreting Upstream Biomarkers of Adverse Outcomes, Environmental Health Perspectives, 117:7, (1033-1041), Online publication date: 1-Jul-2009.Wolansky M, Gennings C, DeVito M and Crofton K (2009) Evidence for Dose-Additive Effects of Pyrethroids on Motor Activity in Rats, Environmental Health Perspectives, 117:10, (1563-1570), Online publication date: 1-Oct-2009. Crofton K (2008) Thyroid disrupting chemicals: mechanisms and mixtures, International Journal of Andrology, 10.1111/j.1365-2605.2007.00857.x, 31:2, (209-223), Online publication date: 1-Apr-2008. Crofton K, Craft E, Hedge J, Gennings C, Simmons J, Carchman R, Carter W and DeVito M (2005) Thyroid-Hormone–Disrupting Chemicals: Evidence for Dose-Dependent Additivity or Synergism, Environmental Health Perspectives, 113:11, (1549-1554), Online publication date: 1-Nov-2005. Vol. 112, No. 13 September 2004Metrics About Article Metrics Publication History Originally published1 September 2004Published in print1 September 2004 Financial disclosuresPDF download License information EHP is an open-access journal published with support from the National Institute of Environmental Health Sciences, National Institutes of Health. All content is public domain unless otherwise noted. Note to readers with disabilities EHP strives to ensure that all journal content is accessible to all readers. However, some figures and Supplemental Material published in EHP articles may not conform to 508 standards due to the complexity of the information being presented. If you need assistance accessing journal content, please contact [email protected]. Our staff will work with you to assess and meet your accessibility needs within 3 working days.}, number={13}, journal={ENVIRONMENTAL HEALTH PERSPECTIVES}, author={LeBlanc, GA and Olmstead, AW}, year={2004}, month={Sep}, pages={A729–A730} }
 @article{thompson_young_edens_olmstead_leblanc_hodgson_roe_2004, title={Non-target toxicology of a new mosquito larvicide, trypsin modulating oostatic factor}, volume={80}, ISSN={["1095-9939"]}, DOI={10.1016/j.pestbp.2004.06.009}, abstractNote={Trypsin modulating oostatic factor (TMOF), a peptide hormone originally isolated from the ovaries of adult Aedes aegypti, is currently under commercial development as a new pesticide chemistry with a novel mode of action for the control of larval mosquitoes. The objective of the current research is to evaluate potential risks of the use of TMOF as an insecticide on non-target organisms. TMOF (YDPAP6) was degraded in vitro (as determined by HPLC and LC/MS) to DPAP6, PAP6, and then AP6 by leucine aminopeptidase, a pancreatic enzyme found in the digestive system of vertebrates. The rate of degradation of TMOF and PAP6 was significantly greater than that of DPAP6, while no metabolism of AP6 was found. TMOF technical insecticide was produced on a commercial scale by recombinant yeast (heat-killed before application). The technical TMOF when administered in a single dose by gavage to male and female mice at 2000 mg dry weight/kg body weight produced no negative effects as compared to controls up to 12 days after treatment. When male and female mallard ducks were treated by gavage with 1250 mg dry weight of technical TMOF/kg body weight each day for 5 days, again no toxic effects were noted through 35 days after the last treatment. TMOF technical insecticide was also applied to the shaved skin of male and female rabbits at the rate of 2000 mg/kg for 1–2 days, with no effect. The end point observations in these in vivo experiments were mortality; changes in growth rate, behavior, body structure, and color; and possible lesions observed during necropsy. Finally, Daphnia incubated with technical TMOF in rearing water at the level of 1.0 × 106 yeast cells/ml (10 mg/ml) also demonstrated no negative effects on mortality, growth, molting, time to first brood, and production of viable neonates. It appears from these studies that TMOF can be degraded by vertebrate digestive proteases and technical TMOF is not toxic to the non-target organisms examined.}, number={3}, journal={PESTICIDE BIOCHEMISTRY AND PHYSIOLOGY}, author={Thompson, DM and Young, HP and Edens, FW and Olmstead, AW and LeBlanc, GA and Hodgson, E and Roe, RM}, year={2004}, month={Nov}, pages={131–142} }
 @article{olmstead_leblanc_2003, title={Insecticidal juvenile hormone analogs stimulate the production of male offspring in the crustacean Daphnia magna}, volume={111}, ISSN={["0091-6765"]}, DOI={10.1289/ehp.5982}, abstractNote={Juvenile hormone analogs (JHAs) represent a class of insecticides that were designed specifically to disrupt endocrine-regulated processes relatively unique to insects. Recently we demonstrated that the crustacean juvenoid hormone methyl farnesoate programs oocytes of the crustacean Daphnia magna to develop into males. We hypothesized that insecticidal JHAs might mimic the action of methyl farnesoate, producing altered sex ratios of offspring. Daphnids were exposed chronically (3 weeks) to sublethal concentrations of methyl farnesoate, the JHA pyriproxyfen, and several nonjuvenoid chemicals to discern whether excess male offspring production is a generic response to stress or a specific response to juvenoid hormones. Only methyl farnesoate and pyriproxyfen increased the percentage of males produced by exposed maternal organisms. As previously reported with methyl farnesoate, acute exposure (24 hr) to either pyriproxyfen or the JHA methoprene caused oocytes maturing in the ovary to develop into males. We performed experiments to determine whether combined effects of a JHA and methyl farnesoate conformed better to a model of concentration addition (indicative of same mechanism of action) or independent joint action (indicative of different mechanisms of action). Combined effects conformed better to the concentration-addition model, although some synergy, of unknown etiology, was evident between the insecticides and the hormone. These experiments demonstrate that insecticidal JHAs mimic the action of the crustacean juvenoid hormone methyl farnesoate, resulting in the inappropriate production of male offspring. The occurrence of such an effect in the environment could have dire consequences on susceptible crustacean populations.}, number={7}, journal={ENVIRONMENTAL HEALTH PERSPECTIVES}, author={Olmstead, AW and LeBlanc, GA}, year={2003}, month={Jun}, pages={919–924} }
 @article{olmstead_leblanc_2002, title={Juvenoid hormone methyl farnesoate is a sex determinant in the crustacean Daphnia magna}, volume={293}, ISSN={["0022-104X"]}, DOI={10.1002/jez.10162}, abstractNote={Abstract}, number={7}, journal={JOURNAL OF EXPERIMENTAL ZOOLOGY}, author={Olmstead, AW and Leblanc, GA}, year={2002}, month={Dec}, pages={736–739} }
 @article{olmstead_le blanc_2001, title={Low Exposure Concentration Effects of Methoprene on Endocrine-Regulated Processes in the Crustacean Daphnia magna}, volume={62}, ISSN={1096-0929}, url={http://dx.doi.org/10.1093/toxsci/62.2.268}, DOI={10.1093/toxsci/62.2.268}, abstractNote={Methoprene is a growth-regulating insecticide that manifests its toxicity to target organisms by acting as a juvenile hormone agonist. Methoprene similarly may exert toxicity to crustaceans by mimicking or interfering with methyl farnesoate, a crustacean juvenoid. We hypothesized that methoprene interferes with endocrine-regulated processes in crustaceans by several mechanisms involving agonism or antagonism of juvenoid receptor complexes. In the present study, we evaluated this hypothesis, in part, by characterizing and comparing the concentration-response curves for methoprene and several endpoints related to development and reproduction of the crustacean Daphnia magna. Our results demonstrate that methoprene has multiple mechanisms of toxicity and low-exposure concentration effects. Methoprene reduced the growth rate of daphnids with evidence of only a single concentration-response line, having a threshold of 12.6 nM. Molt frequency was reduced by methoprene in a concentration-dependent manner, with a response curve corresponding to a 2-segmented line and thresholds at 4.2 and 0.21 nM. An endpoint related to reproductive maturation, the time of first brood deposition, was also affected by methoprene, with a clear concentration-dependent response and a NOEC of 32 nM. Methoprene reduced fecundity according to a 2-segmented line, with thresholds of 24 and < or =0.18 nM. These results demonstrate that methoprene elicits significant toxicity to endocrine-related processes in the 5-50 nM concentration range. Furthermore, molting and reproduction were impacted at significantly lower methoprene concentrations, with a distinct concentration response and a threshold of < or =0.2 nM. The different concentration-dependent response from that of methoprene could involve agonism or antagonism of various juvenoid receptor configurations.}, number={2}, journal={Toxicological Sciences}, publisher={Oxford University Press (OUP)}, author={Olmstead, A.W. and Le Blanc, G.A}, year={2001}, month={Aug}, pages={268–273} }
 @article{olmstead_leblanc_2001, title={Temporal and quantitative changes in sexual reproductive cycling of the cladoceran Daphnia magna by a juvenile hormone analog}, volume={290}, ISSN={["0022-104X"]}, DOI={10.1002/jez.1044}, abstractNote={Abstract}, number={2}, journal={JOURNAL OF EXPERIMENTAL ZOOLOGY}, author={Olmstead, AW and LeBlanc, GA}, year={2001}, month={Jul}, pages={148–155} }
 @article{olmstead_leblanc_2000, title={Effects of endocrine-active chemicals on the development of sex characteristics of Daphnia magna}, volume={19}, ISSN={["1552-8618"]}, DOI={10.1897/1551-5028(2000)019<2107:EOEACO>2.3.CO;2}, number={8}, journal={ENVIRONMENTAL TOXICOLOGY AND CHEMISTRY}, author={Olmstead, AW and LeBlanc, GA}, year={2000}, month={Aug}, pages={2107–2113} }