MOLECULAR MECHANISMS OF ENVIRONMENTAL TOXINS BSCI 273 Fall 2004

COURSE SYLLABUS Professor Wallace M. LeStourgeon [email protected] Office (Biological Sciences Bldg 5269) Phone (2-2588)

Introduction: Course rationale.

The fundamental problem: The earth is 4.57 billion years old. While bipedal primates have existed for 4-6 million years, until about 4000 BC, modern primates (humans) existed in small dispersed groups probably rarely exceeding a few thousand individuals. In the past 200 years (a hiccup in geological time) the human population has entered an exponential growth phase.

In 1650, about 500 million humans inhabited the earth. In the following 200 years the population doubled to 1 billion. The population doubled to 2 billion between 1850 and 1930 and again to 4 billion by 1975. Today there are about 6,177,607,223 humans on the planet and this number is increasing at a rate of 3 people per second or about 95 million each year. Y6B occurred October 12, 1999. 95 million new people each year corresponds to more than eleven new New York cities per year. By 2050 nine billion people will inhabit the earth. At no time in earth’s history has a single species so dominated the biosphere. More importantly, we now move mountains, redirects rivers, farms desserts and rain forests, and alters atmospheric chemistry on a global scale. 2000

Human Population Growth 5

4

3 Population (Billions) 2

The Plague 1

8000 BC 4000 BC 3000 BC 1000 BC 0 AD 1000 AD 2000

In the ascent of mankind, an inescapable fact of social development is that economic growth is directly proportional to and therefore encourages population growth. This is the major reason our borders have been open to immigrants for the past 20 years. Modern cultures do not know how to uncouple economic growth from population growth nor can they change the basic elements of human behavior that fuel the engine for economic growth. We are motivated by our egos, misguided values, and greed to acquire wealth far beyond our personal needs (yachts, 5000 sq.ft. homes, etc).

As the current inhabitants of space ship Earth, we are motivated to understand the biological problems arising from high population density due to the severity of its consequences. For example: As a result of human activity, in the last 30 years the atmospheric CO2 concentration has increased more than 11%. Microbubbles in the Greenland ice cap demonstrate that CO2 concentrations were stable for many thousands of years (at 280 ppm) until about 1800. In 1957 [CO2] was 315 ppm and today it is 362 ppm. Fossil fuel combustion alone now adds over 6 billion metric tons of CO2 annually to the atmosphere. Of equal significance, human activities now fix nitrogen from the atmosphere at a rate near 100 million metric tons per year. It is estimated that in 1940 human activities fixed almost no nitrogen and that half of all the nitrogen ever fixed by human activities has occurred since 1980. Ultimately, CO2 - and nitrous oxide (N2O)-induced earth warming (the green house effect) will limit human population growth through land and food crop loss. The preceding two decades were back to back the warmest decades in recorded history.

Toxic environments limit population growth through many mechanisms: In addition to human- induced atmospheric alterations, until the early 1940’s organic compounds with covalently bound halogen (chlorine, fluorine, bromine) were exceedingly rare on the earth’s surface (some environmentalists argue that, “God knew better than to link chlorine to a benzene ring”). Today these compounds are the most abundant of all man made molecules (type and amount). In the United States, the concentration of chlorocarbons and flame retardants in normal human breast milk is so high that it can not (based on EPA guidelines) be sold in stores for human consumption. In the past 20 years halogenated hydrocarbons are alone responsible for a 10% depletion of atmospheric ozone (O3). This chemical activity may limit population growth because released chlorine, fluorine, bromine (and nitrous oxide) act as never-ending cyclical catalysts. While we often hear of increased cancer due to UV irradiation, the population-limiting effect of ozone depletion (enhanced UV irradiation) will actually be due to the loss of plant and animal life.

A classic means of limiting population growth is shortened life span. Today, in industrialized countries, one man in two will be diagnosed with cancer in his lifetime and this “age-independent” incidence continues to increase. At this writing, one in eight women will develop breast cancer alone. Without question, more than 98% of all human cancers result from chemical-induced somatic mutations in the genes that regulate the cell cycle (oncogenes). Interestingly, the “cause” of cancer was deduced in the 1950s as was its increase in incidence. Today, the general public is completely unaware of the 50% cancer incidence rate, and that 98% of all cancers are caused by mutagens in the environment. The first convincing evidence for cancers environmental etiology was seen in the acquisition of local cancer incidence rates by immigrants. Today, unequivocal evidence that 98% of all cancers are caused by environmental mutagens, has come from our ability to identify the mutated oncogenes in an individuals cancerous cells and compare them to the same genes in neighboring normal cells . We often hear that today, humans are living longer than ever. This is false. Humans have no greater life span potential today than a 5 thousand years ago (probably less). “”Longevity” (the average age at death for a population group) has increased in the past 50 years but this is entirely due to antibiotics and better diagnostic procedures.

More than 63,000 chemical compounds are commonly used in the U.S. today. No information exists on the biological effects of more than 50,000 of these chemicals and about 1,000 new chemicals per year are waived into common use without testing for their effects on human and environmental health. The EPAs latest Toxics Release Inventory shows that more than 23,000 industrial facilities in the US alone release 3.2 billion pounds of known toxic pollutants into the air, soil and waterways per year. This figure is derived from voluntary reports by only the largest corporations on just 300 or so chemicals. Estimates of the US’ total yearly emission of toxic chemicals from all sources, legal and illegal, are in the neighborhood of 22.5 billion pounds. The intent of the Clean Water Act enacted in 1972 was “zero discharge” of known toxic agents. In response to powerful financial concerns and a sympathetic administration, this act has been quietly gutted by Congress during the past 3 years. Interestingly, the voluntary consumption of pharmaceutical compounds and recreational drugs are major culprits in the etiology of human cancer.

Limiting population growth by decreased fertility and potency. In comparison to their fathers at the same age, today in certain industrialized areas and in farming areas where atrazine is widely used, young males produce half as much normal sperm and this appears to be associated with decreased libido and sexual potency in young men. Apparently related to sperm decline in humans and domestic animals is: the early onset of puberty in females, the unprecedented increase in testicular, prostate, and breast cancer, the production of eggs in the testes of male trout harvested from rivers near cities, and undeveloped male genitals in reptiles of the Florida everglades. A wide variety of man made molecules are now known to possess both estrogenic and androgenic activity.

What to do? While the mechanisms mentioned above will ultimately slow population growth, the quality of life will be miserable by today’s standards for many generations. In order to identify the most significant health threats that exist naturally in our environment and that arise from human activities and high population densities, we must understand the molecular mechanisms of all environmental toxins. In other words, how xenobiotic (foreign to life, or non-biological) compounds act to interfere with normal biochemical processes at the cellular, organismal, and ecosystem levels. With this knowledge we can identify those substances that must be strictly avoided and with this knowledge we may be able to develop antidotes and strategies to minimize the effects of environmental toxins. If all the numerous human cancers could be cured with a simple painless biochemical/genetic therapy would we fear environmental carcinogens? Would it be fair to the animals that must exist in increasing volumes of human waist but that can not be so treated? With knowledge, we can objectively address these and many other questions. With knowledge we can strive to safeguard our own health and, hopefully with knowledge, we can educate our peers in an objective manner. Herein lies the rationale for BSCI 273.

Course Objectives: In order to understand the molecular mechanisms of action of environmental toxins it is first necessary to identify their subcellular targets (i.e. the cellular receptors or macromolecules that are bound by the toxic agent). Secondly it is important to understand the forces that direct binding specificity and that determine binding affinity. With this information in hand it is often possible to identify the metabolic pathway involved and to predict the physiological magnitude of the toxic effect. This semester we will study the toxicology of a representative number of xenobiotic agents. While detailed biochemical information is available for only a few of the thousands of environmental chemicals, we often can make good predictions as to a new molecules toxicity and mode of action by comparing its molecular structure and chemical properties to those of well characterized molecules.

It is not an objective of this course to berate industry or industrialists. We will; however, on several occasions consider the conflicting positions of “industrial conservatives” and “environmental conservatives”. We will also consider examples of overt directed efforts to misinform the public in an effort to continue the manufacture and distribution of environmental toxins (i.e., lead, pesticides, alcohol, nicotine, formaldehyde, and many others). The adage “caveat emptor” is as valid today as in the past. However, in the past this advice applied to a single individual. Today it applies to mankind. These discussions will constitute the Science and Society component of the course.

Some important incidentals: There is no textbook for this course. All lectures will be PowerPoint presentations and hard copies of each presentation will be handed out in class and posted on the internet. During the last half of the semester original research articles, and review articles on specific subjects will be studied. Much of the basic information presented this semester can be found in the reference list at the end of this syllabus.

Course Grade: The course grade will be based on two hour examinations, a 6-10 page term paper and 15 minute in-class presentation, and a final examination. The paper and presentation will count as one hour examination (22% of course grade). Regarding the paper/presentation each student in consultation with the professor may select either a specific environmental toxin, class of toxins, or toxicological phenomenon for detailed study (history, rationale for production, use, distribution, toxicology, and politics). The final exam will comprise one-third of the course grade and it will be comprehensive. LECTURE TOPICS, READING ASSIGNMENTS AND IMPORTANT DATES

August

Wed. 25 Introduction, Course Objectives, The Fundamental Problem (population and greed) Fri. 27 The absorption, distribution, biotransformation, and elimination of chemical compounds. Mon. 30 Biotransformation, Cytochrome P450 and first pass, and phase I and II bioactivation.

September

Wed. 1 The mechanism of action of xenobiotic compounds – Receptors, ligands, binding affinities and specificity, binding assays. Fri. 3 Receptor-activated pathways and ligand-receptor interactions. Mon. 6 Principles of toxicology - the dose response relationship. Wed. 8 Chemical carcinogens - types and mechanisms - risk assessment. Fri. 10 Risk assessment continued. Mon. 13 Chemicals acting at synaptic and neuroeffector junctions. The sympathetic and parasympathetic nervous systems. Wed. 15 Continued. Fri. 17 Neurotransmission - axonal conduction, chemical blockade and specific toxins and pesticides. Mon. 20 Cholinergic transmission Wed. 22 Adrenergic transmission and desensitization Fri. 24 Chemicals that interfere with acetylcholinesterase, organophosphates and other pesticides Mon. 27 Test I Wed. 29 Heavy metals defined, environmental sources, contaminant levels

October

Fri. 1 Heavy metals: mechanisms of toxicity Mon. 4 DNA repair enzymes, polymerases, and tumor suppressor denaturation (heavy metal mutagenesis) Wed. 6 Air pollutants, solvents. Fri. 8 Solvents continued. Mon. 11 Pesticides Wed. 13 Pesticides continued. Fri. 15 Endocrine disrupters. Mon. 18 Fall Break Wed. 20 Xenobiotics, immunotoxins, and autoimmune disease. Fri. 22 Autoimmune disease continued. Mon. 25 Mutagenic pharmaceuticals. Wed. 27 Test Fri. 29 Cell cycle controls.

November

Mon. 1 Mechanisms of chemical carcinogens. Wed. 3 Assays for chemical carcinogens. Fri. 5 Chemical carcinogens continued. Mon. 8 Who gets cancer, genetic polymorphisms. Wed. 10 Polymorphisms continued. Fri. 12 TBA Mon. 15 Film Wed. 17 Film Fri. 19 TBA

Mon. 22-Fri. 26 Thanksgiving holidays Mon. 29 Group presentations begin

December

Wed 1 and Friday 3, Presentations Continue Mon 6 Last class day and last presentation, course overview, information for final exam.

Final Exam: Friday, December 17 @ 9:00 A.M.

References: Mechanistic Toxicology. Urs A. Boelsterli. Taylor and Francis Group. London and New York, 2003 Essentials of Toxicology (Casarett and Doull’s). Curtis D. Klaassen and John B. Watkins III, eds. McGraw-Hill, 2003 Guide to Cytochromes P450 (Structure and Function). David F. V. Lewis. Taylor and Francis Group, London. 2001 Reactive Oxygen Metabolites, Chemistry and Medial Consequences. Manfred K. Eberhardt. CRC Press 2000 Principles of Biochemical Toxicology (3rd Ed.). John Timbrell. Taylor and Francis Press. 2000 Environmental Toxicology and Chemistry. Donald G. Crosby. Oxford University Press. New York 1998 Pathology of Environmental and Occupational Disease. John E. Craighead. Mosby-Year Book, Inc. St. Louis. 1995 Molecular Toxicology. P. David Joseph. Oxford University Press, New York, N.Y. 1997 Disposition of Toxic Drugs and Chemicals in Man. (4th Ed.). Baselt & Carvey, eds. Chemical Toxicology Institute, Foster City, CA. 1995 Perspectives in Environmental Chemistry. D.L. Macalady, Oxford University Press, Inc. New York. 1998 Goodman and Gilman’s The Pharmacological Basis of Therapeutics. J.G. Hardman and Lee E. Limbird editors in chief. Ninth Edition. McGraw-Hill. 1996 Medical Toxicology. Matthew J. Ellenhorn. Williams and Wilkins, Baltimore. 1997 Handbook of Carcinogenic Potency and Genotoxicity Databases. L.S. Gold and E. Zeiger, eds. CRC Press, New York. 1997 Origins of Human Cancer. H.H. Hiatt, J.D. Watson, J. A. Winsten, eds. Cold Spring Harbor Press. Cold Spring Harbor, N. Y. 1977 Clinical Management of Poisoning and Drug Overdose. Second Edition. L. M. Haddad and J. F. Winchester, eds. W.B. Saunders Co. Philadelphia 1990 Toxic Deception. D. Fagin and M. Lavelle. Birch Lane Press. 1996 Fertility on The Brink. The National Wildlife Federation, Washington D.C., 1994 Cancer at a Crossroads: A Report to Congress for the Nation. National Cancer Advisory Board. 1994 The Environmental Safety Guide: Hazardous Chemical Waste Management - Guide for Vanderbilt Personnel. Department of Institutional Safety. Environmental Safety Section. 1994