Presentation on theme: "Endocrinology Biology 595EN October 2003 Endocrine Disruptors Kenneth L. Campbell Professor of Biology University of Massachusetts at Boston."— Presentation transcript:
Endocrinology Biology 595EN October 2003 Endocrine Disruptors Kenneth L. Campbell Professor of Biology University of Massachusetts at Boston
This presentation is made possible by a grant entitled “Shortcourses in Endocrinology at Minority Undergraduate Institutions” from the National Institute of General Medical Sciences (NIGMS) to The Minority Affairs Committee of the Endocrine Society
What is an Endocrine Distruptor? Any chemical agent in the environment that can alter normal endocrine system actions leading to deleterious effects on an organism or its progeny. Disruptors may act directly or indirectly. Direct acting disruptors are usually hormone agonists or antagonists that interfere with hormone actions on target cells. Indirect acting disruptors alter hormone dynamics in circulation, change hormone metabolism, or interfere with hormone regulation.
Useful References 1. Silent Spring. R. Carson. 1962. 2. Our Stolen Future. T. Colborn, D. Dumanoski, J.P. Myers. 1996. 3. Our Stolen Future - an activist website 4. Hormonally Active Agents in the Environment. National Research Council. National Academy Press: Washington, D.C. 1999. 5. Endocrine and Hormonal Toxicology. P.W. Harvey, K.C. Rush, A. Cockburn. John Wiley & Sons Ltd.: Chichester, UK. 1999. 6. Generations at Risk: Reproductive Health and the Environment. T. Schettler, G. Solomon, M. Valenti, A. Huddle. The MIT Press: Cambridge, MA. 1999. 7. Hormonal Chaos: The Scientific and Social Origins of the Environmental Endocrine Hypothesis. S. Krimsky. Johns Hopkins University Press: Baltimore, MD. 2000.
Timeline for Endocrine Disruptors 1874 DDT synthesized 1881 PCB synthesized 1930-77 Widespread PCB use in transformers & as cutting oils 1938 DES synthesized 1942-72 Widespread DDT application in malaria control & agriculture 1941-54 FDA & USDA: DES approved for use in humans & animals 1959 DES produces cancer in experimental animals 1962 Publication of Silent Spring by Rachel Carson 1972 EPA bans DDT, FDA warnings on DES in pregnant women 1977 EPA bans PCBs 1979-95 Meetings & publications on estrogens in the environment 1995 EPA endocrine disruptor workshop; NAS/NRC panel meets 1996 Our Stolen Future, Colborn, Dumanoski & Myers, published; FQPA passed & Safe Drinking Water Act amended 1998 International Conference on Endocrine Disruptors, Kyoto 1999 NRC report, Hormonally Active Agents in the Environment
What are endocrine systems for? Endocrine Functions Maintain Internal Homeostasis Support Cell Growth Coordinate Development Coordinate Reproduction Facilitate Responses to External Stimuli
What are the elements of an endocrine system? Sender = Sending Cell Signal = Hormone Nondestructive Medium = Serum & Hormone Binders Selective Receiver = Receptor Protein Transducer = Transducer Proteins & 2º Messengers Amplifier = Transducer/Effector Enzymes Effector = Effector Proteins Response = Cellular Response (2º hormones)
What kinds of hormone are there? Known Hormonal Classes Proteins & peptides Lipids (steroids, eicosanoids) Amino acid derived (thyronines, neurotransmitters) Gases (NO, CO) chemcases.com/olestra/ images/insulin.jpg chem.pdx.edu/~wamserc/ ChemWorkshops/ gifs/W25_1.gif website.lineone.net/~dave.cushman/ epinephrine.gif
What is a hormone receptor? Hormone Receptors are cellular proteins that bind with high affinity to hormones & are altered in shape & function by binding; they exist in limited numbers. Binding to hormone is noncovalent & reversible. Hormone binding will alter binding to other cellular proteins & may activate any receptor protein enzyme actions.
What are the main types of receptors? Membrane Receptors Imbedded in target cell membrane; integral proteins/ glycoproteins; penetrate through membrane For protein & charged hormones (peptides or neurotransmitters) 3 major groups: Serpentine = 7 transmembrane domains, Growth factor/cytokine = 1 transmembrane domain, Ion channels Nuclear Receptors Nuclear proteins that usually act in pairs & bind to specific Hormone Recognition Elements (HREs) = sequences on the DNA in the promoter regions of target genes For small, hydrophobic molecules (steroids, thyroid hormones)
Cross your eyes, relax, & see if you can see how 2 molecules of steroid receptor, green & yellow, interact with a specific sequence, SRE, in DNA. Receptors for steroids, T 3, retinoids, vitamin D, & aryl hydrocarbons all work this way.
Results of Disruptions Inability to maintain homeostasis Altered growth & development Altered responses to external stimuli Altered behavior Suppressed gametogenesis Elevated gestational losses Embryonic malformation Induced neoplasia or carcinogenesis
Agonist, Antagonist, Mixed Activity Relative Affinities for Receptors of the Insulin Family to Family Members NGF (only)NGF Relaxin >NGF >Proinsulin > IGF >>Insulin (~0)Relaxin IGF II = IGF I >>Insulin ~ ProinsulinIGF II IGF I > IGF II >Insulin ~ ProinsulinIGF I Insulin >Proinsulin (10%) >IGF II >IGF I >>Relaxin(~0) Insulin Relative AffinitiesReceptor Hormones & receptors co-evolve. It is common to have several hormone receptors demonstrate varying affinity for the same hormone. It is also common for one hormone to have some affinity for several different receptor types. Promiscuity often occurs with opioids & steroids. Progestins can bind glucocorticoid receptors. Clomiphene binds estrogen receptors & demonstrates mixed anti-estrogenic & estrogenic actions. Cyproterone acetate is a progestin & anti-androgen. TCDD is an anti-estrogen & thyroid agonist.
Basis for Endocrine Pathology of Direct Disruptors = Interference with Hormone Synthesis & Action Synthetic enzyme inhibitor Agonist or antagonist binding to receptor Alteration of normal dose-response relationships www.pharmacist.com/images/ estrogen_molecule.gif 17β-Estradiol www.ac-nantes.fr/peda/ disc/scphy/dochtml/3ieme/ch ouroug/images/molecule.gif Diethylstilbesterol
Biologically available (free) hormone levels vary due to: Changes in synthesis Changes in secretion Changes in degradation Changes in binding proteins Age Gender Developmental stage Reproductive status Stage of temporal rhythm so…, alterations at any process or stage changes free hormone levels.
www.fst.rdg.ac.uk/courses/ fs916/lect5/l5b.gif Hormone Transport or Secretion Kinetics users.rcn.com/jkimball.ma.ultranet/Biolog yPages/H/hypothalamic_feedback.gif Feedback loops, Neural controls Mechanisms for Indirect Endocrine Disruption Involve Modification of: www.nurse-prescriber.co.uk/ education/visual_lib/pp18.jpg Enterohepatic Metabolism
Detoxification Pathways Modified from D.J. Liska, The Detoxification Enzyme Systems, www.thorne.com/altmedrev/ fulltext/detox3-3.html.
Human Sperm Suppression From the Study of Scottish Male Reproductive Health www.link.med.ed.ac.uk/ HEW/repro/default.htm
Disruption of Sex Determination Stages sensitive to hormonally active agents
Penoscrotal type hypospadias www.vghtpe.gov.tw/~peds/ lecture/pedsintr/73.jpg www.ourstolenfuture.org/Images/graphs/ hypospadias.jpg Are Endocrine Disruptors Causal?
*SAX TOXICITY EVALUATION: THR: Poison by intraperitoneal and subcutaneous routes. Moderately toxic by ingestion and other routes. A human carcinogen and teratogen by many routes. It causes skin, liver and lung tumors in exposed humans as well as uterine and other reproductive system tumors in the female offspring of exposed women. An experimental carcinogen, neoplastigen, tumorigen and teratogen by various routes. A transplacental carcinogen. Glandular system effects by skin contact. Human reproductive effects by ingestion. Implicated in male impotence and enlargement of male breasts. Other experimental reproductive effects. Mutagenic data. Diethylstilbestrol New Jersey Department of Health and Senior Services Cancer Hazard * Bis (2-Ethylhexyl) Phthalate may be a CARCINOGEN in humans. It has been shown to cause liver cancer in animals… Reproductive Hazard * Bis (2-Ethylhexyl) Phthalate may be a TERATOGEN in humans since it has been shown to be a teratogen in animals. * Bis (2-Ethylhexyl) Phthalate may damage the testes... Bis (2-ethylhexyl) phthalate
Impacts on Cancer Rates Breast Cancer Risks. Reference group (R) vs quartiles of dieldrin exposure (adapted from Høyer et al. 1998 in Our Stolen Future Website: www.ourstolen future.org/ Images/graphs/breast%20 cancer%20dieldrin%20risk.jpg). Vertical bars = 95% confidence interval. Dose response is significant (p = 0.01). www.link.med.ed.ac.uk/ HEW/repro/default.htm
Conclusions Endocrine disruptors or hormonally active agents have been with us for millennia as elements of plants and cooking. The new abundance of synthetic compounds has unleashed a wave of new challenges to our physiology, including the endocrine system. The impacts are as pleiotropic as endocrine actions are. Not surprisingly they involve altered reproductive success, growth, and cancer risks because of endocrine controls or inputs in these processes. Due care will help minimize impacts, but some increased risks are here permanently.