Abstract
The 35th Annual Society of
Historical Perspective: Milestones in Toxicology
From Beginning of Civilization
Toxicology is arguably the oldest scientific discipline, as the earliest humans had to recognize which plants, nuts, or fruits were safe to eat. More than likely through illnesses, and even possibly death, they soon recognized harmful and beneficial consequences associated with taking foreign materials into their bodies. From these early and basic observations, the concept involving the division of chemicals into two categories of beneficial and harmful chemicals evolved and has persisted to the present day. Technically, there is no strict line of demarcation to describe or distinguish beneficial or harmful chemicals, and the degrees of harmfulness and safeness appear to lie in the dose of the chemical, thereby making this concept the hinge pin of modern toxicology that is the dose makes the poison. All chemicals can cause toxic effects in large enough amounts, and humans are exposed to chemicals both deliberately and inadvertently. Most exposure of humans to chemicals is via naturally occurring compounds consumed in the diet from food plants.
Many of the Earliest Practitioners of Toxicology Were Women
It has been alleged that Lucrezia Borgia, daughter of Rodrigo Lenzuoli Borgia or Pope Alexander VI, who specialized in “faith-based” poisoning, was an early Italian who helped develop poisoning into a simple but fine art. It is said that the Borgias selected and laid down rare poisons in their cellars with as much thought as they had given to selecting and preserving their vintage wines. It is historically rumored that the Borgias served poisonous wine to members of the papal court, wealthy guests, suitors, and even family members, to their demise, to increase their wealth and power (Hayes and Kruger 2014). Lucrezia and her family members could all be considered early food toxicologists. Another early practitioner of toxicology was Catherine de Medici of Florence and Queen Consort of France. She tested and carefully studied the effects of various toxic concoctions on the poor and sick, noting the onset of action and symptoms that occurred (Knecht 1998), and could by today’s standards be considered an early experimental toxicologist. Goeie Mie (Good Mary) of Leiden, the Netherlands, was alleged to have poisoned at least 102 friends (27 died) and relatives between 1867 and 1884, distributing arsenic trioxide in hot milk to her victims after opening life insurance policies in their names (Gaute and Odell 1991). She would have been considered an early forensic toxicologist. Catherine Deshayes or “La Voisin” would be thought of as an early economic toxicologist because of her propensity to trade in selling poisons to wives who wished to rid themselves of their husbands (Ramsland 2005).
Historical Examples of Poisoning
Examples of historical cases of poisoning include Joseph Stalin, leader of the former Soviet Union, who reportedly died of brain hemorrhage. It has been suggested that he could have been poisoned, possibly by the Politburo who allegedly gave him warfarin (Hayes and Kruger 2014). It is reported that the U.S. Central Intelligence Agency (CIA) made attempts on the life of the Cuban dictator Fidel Castro by attempting to give him botulinum-laced pills in his food or drinks (http://www.edwardjayepstein.com/archived/castro.htm). More recently, in the history of high-profile poisonings, evidence suggests Viktor Yushchenko, the former Ukrainian President, was poisoned with dioxin (a polychlorinated dibenzodioxin) in an attempt to remove him from office. Another suspected casualty of poisoning is Napoleon Bonaparte who died in exile on the island of St. Helena in 1821. British doctors performed an autopsy and found evidence of stomach cancer, and this was given as the cause of his death. However, in the 1960s, unusually high levels of arsenic were reported in Napoleon’s hair. Arsenic was present in the drinking water, hair cream, and even the wallpaper in his cottage. It is historically rumored that Napoleon’s associate the Comte de Montholon, who was in charge of his food and wine, poisoned him slowly, first with arsenic and then with other medications (Weider, Forshufvud, and Forshufvud 1995).
From Killers to Healers: Toxicology Evolves, but Poisonings Still Occur
Over the years, there have been several cases of human exposures to chemicals that have led to devastating outcomes and in some instances death. In 2008, one such case of worldwide poisoning was the exposure of hundreds of thousands of Chinese children to melamine-contaminated milk, with ensuing kidney stones, kidney failure, and death in some of the children exposed (Xin and Stone 2008; Yang and Batlle 2008; Chiu 2008). Melamine was found in tainted pet food a year earlier with hundreds of thousands of dogs and cats being exposed (Dobson et al. 2008).
The government of Nigeria implemented tighter controls on chemical imports after 84 children between the ages of 2 months and 7 years died after consuming a tainted teething syrup, “My Pikin” (Okuonghae et al. 1992). Authorities believe diethylene glycol (component of antifreeze) was wrongly labeled as propylene glycol, a chemical generally recognized as safe for use in food and medicine, which was smuggled into Nigeria before being purchased by a Lagos-based company, which has since been shut down. To prevent future incidents, The National Agency for Food and Drug Administration and Control (NAFDAC) required all propylene glycol imports from India and China to be certified by the agency’s independent analysts in India and China before shipment and to be recertified upon entry into Nigeria. The first case was discovered on November 3 with symptoms including diarrhea, vomiting, fever, convulsions, and an inability to pass urine.
Diethylene glycol was used as a cheap replacement for the sweetener glycerin in cough syrup and more than 100 people, mostly children, died in Panama (http://www.cdc.gov/mmwr/preview/mmwrhtml/mm5848a2.htm). In addition to the United States and Panama, diethylene glycol–tainted toothpaste was found in Australia, the Dominican Republic, Costa Rica, Honduras, and Nicaragua (http://www.nytimes.com/2007/06/02/us/02toothpaste.html?_r=0).
In 2009, 121 of the 287 children under 14 years of age in Longyan, China, had high blood lead levels (http://www.nytimes.com/2009/09/28/world/asia/28china.html). A smelting plant closed after more than 600 children were found to have lead poisoning; and in another case, 800 children living near a zinc and lead smelting plant were found to have high blood lead levels. In the United States, the Food and Drug Administration (FDA) has a limit of 0.5 µg/dl in products intended for infants and children and has banned the use of lead-soldered food cans.
Each year in the United States, 310,000 one- to five-year-old children are found to have unsafe levels of lead in their blood due to exposure to lead through dust and other sources (https://www.cdc.gov/nceh/lead/data/). Just recently, Virginia Tech University researchers brought proof of high lead levels in Flint, Michigan, water to public attention in September 2015, performing water tests in more than 250 Flint homes. Lead levels were high enough, up to 38 μg/dl, to warrant urgent government action (https://www.rt.com/usa/327363-flint-children-blood-lead-water/); however, in a similar problem with Washington, DC’s tap water a little over a decade ago, hundreds of homes were found to have stratospheric lead levels of 300 parts per billion (ppb) or more (Guidotti et al. 2007).
New Sweden, Maine, made national headlines in 2003 when a man poisoned the coffee urn with arsenic at the local Lutheran church, sickening 15 parishioners and killing 1 (http://www.nytimes.com/2003/05/09/us/poison-mystery-widens-after-a-suicide-note.html). Five days later, a church member, Daniel Bondeson, was found after apparently shooting himself and supposedly leaving a suicide note confessing to having something to do with the poisoning, but the note has never been released to the press or even to his sister.
China has a 150-ppb arsenic limit in foods such as rice. Rice grown in the United States has an average 260 ppb of arsenic; however, a 100-ppb action level has been proposed for inorganic arsenic in infant rice cereal (http://www.philrice.gov.ph/phl-rice-safe-from-arsenic/).
The U.S. Food and Drug Act, also known as the “Wiley Act,” was passed in 1906 in response to the exponential growth of American counterfeiters of patented medicine(s). The most notorious scheme involved importing empty bottles and filling them with phony concoctions and affixing fake labels from well-respected European companies. Harvey Wiley, a chief chemist of the Division of Chemistry (later Bureau of Chemistry), U.S. Department of Agriculture (USDA), Washington, DC, was a strong advocate for this act, hence, the nickname the Wiley Act. Wiley was also known as the “Crusading Chemist” and “Father” of the Pure Food and Drugs Act. Wiley’s department was responsible for examining food and drugs for “misbranding” or “adulteration,” and he used these newly found regulatory powers to pursue aggressive action toward the manufacturers of foods with chemical additives. His department later came under scrutiny and the Bureau of Chemistry’s powers were quickly checked by judicial decisions that focused and defined the bureau’s powers and set standards to be achieved for proof of fraudulent intent. In 1927, the regulatory Bureau of Chemistry was reorganized under a new USDA group, the Food, Drug, and Insecticide Organization. In 1930, the name was changed to the FDA (http://www.fda.gov/AboutFDA/WhatWeDo/History/Milestones/default.htm).
What Is Toxicology?
Paracelsus and the Concept of Dose
Paracelsus, born Philippus Aureolus Theophrastus Bombastus von Hohenheim, is credited as the founder of toxicology. His premise of poisons was that “All things are poison, and nothing is without poison; only the dose permits something not to be poisonous.” Simply stated, “The dose makes the poison.”
Traditionally, the study of poisons was centered on the inherent capacity of a chemical or compound to produce injury. Today, toxicology is more safety-driven, and modern toxicology uses chemicals as tools to understand molecular/cellular biology. One basic function of toxicology is to assess the likelihood of occurrence of adverse effects (qualitative): Is a chemical or compound safe? This is hazard identification. Also, toxicology studies the nature and mode of action of adverse effects (quantitative). At what concentration is it safe? This is known as dose–response assessment or hazard characterization.
Toxicology affects us every day. The purpose of toxicology is to provide workers a safe working environment and to ensure consumers’ products are safe to use as specified and under foreseeable misuse. Another area of toxicology is the environment or ecotoxicology, which is concerned with the quality of the air, water (surface and ground), soil, and bedrock, and aquatic wildlife (fresh and salt) and terrestrial organisms (flora and fauna). Toxicology provides information to risk managers about the nature and severity of effects on human health and the environment, as it relates to specific exposures. Ecotoxicology often drives remediation site cleanups. There are approximately 6,000,000 known chemicals: approximately 100,000 currently in use worldwide and 500 new chemicals being added annually. There is limited information available on many of these chemicals, which has spawned in the European Union regulations such as the formation of the Registration, Evaluation, and Authorization of Chemicals (REACH), which enforces enterprises that manufacture large volumes of chemicals to register those chemicals in a central database. Risk assessment involves hazard identification, dose–response, exposure, and risk characterization. Risk is defined as hazard times exposure.
Primer on Toxicology
Dose Matters
The key points of toxicology are (1) dose matters (and so does timing), (2) people differ, and (3) things change (Mitchell et al. 2004). When we explore the concept of dose, there are poisons such as botulinum toxin A (0.00001 mg/kg) that can be poisonous, yet this toxin can also heal.
Conversely, botulinum toxin is a poison that can heal. In its purified form (type A), it was the first bacterial toxin to be used as a medicine. In 1989, the FDA licensed Oculinum for treating 2 eye conditions characterized by excessive muscle contractions: blepharospasm (tic or twitch of eyelid) and strabismus (eyes not properly aligned). As a medicine, type A toxin can be used to control certain conditions marked by involuntary muscle contractions and can block muscle contractions. The toxin binds to nerve endings at the point where the nerves join muscles and blocks release of acetylcholine, thereby blocking muscle contractions. Another beneficial effect of botulinum toxin is its use in cosmetic applications, such as Botox and Botox Cosmetic (botulinum toxin A). Another is its use in the treatment of patients with cervical (neck) dystonia and to reduce the severity of abnormal head position and neck pain associated with cervical (neck) dystonia. Other applications of botulinum toxin include severe primary axillary hyperhidrosis (excessive sweating), achalasia (failure of the lower esophageal sphincter to relax), neuropathies, migraine and other headache disorders, although the evidence is conflicting in this indication, and overactive bladder and benign prostatic hyperplasia.
Dose matters as does timing. An example of this concept is thalidomide (100+ mg/kg) and its critical timing of exposure. Originally developed as a treatment for insomnia and morning sickness in the 1950s, thalidomide is an oral drug that has been shown to be highly active against myeloma. Many consider thalidomide to be the first new agent with major antimyeloma activity in more than 30 years. Thalidomide has been FDA approved for the treatment of not only myeloma but also erythema nodosum leprosum (treat and prevent skin conditions caused by
Interactions between chemicals and biological systems follow a dose–response relationship. Toxicity is quantified through the dose–response relationship. Individual change in severity of effect with dose is also called a dose–effect relationship. Population change is the proportion of the population responding with dose (people differ). There are different relationships for different effects, and the shape of the dose response curve gives information about population variability and toxicity of the compound. A key concept in toxicology is the quantitative relationship between the concentration of a xenobiotic (foreign chemical) in the body and the magnitude of its biological effect. The magnitude of the effect is usually a function of the amount of xenobiotic a person is exposed to. In any given population, there will be a range of sensitivities to a xenobiotic. It is extremely useful to know what is the average sensitivity of a population to a xenobiotic and what the average dose required to elicit a toxic response will be. This brings us back to the central tenet of toxicology that the dose makes the poison and that dose matters.
People Differ
Classic examples of the fact that people differ include allergies to food (e.g., peanuts and shellfish) and to drugs (e.g., penicillin). Food allergy in the United States and Europe affects approximately 2% to 4% of adults and 4% to 8% of young children. Severe allergenic reactions are relatively rare, with approximately 120,000 emergency room visits with less than 200 fatalities/year. Eight foods (peanuts, milk, wheat, eggs, shellfish, soybeans, crustaceans, and some tree nuts) account for approximately 90% of food allergies (United States); whereas 14 foods are listed as allergenic in Europe, which are regional and include molluscan shellfish, lupine, celery root, mustard and sesame seeds, and sulfites in addition to those outlined for the United States. Even more striking are the differences in the effects of the same chemical on a single individual that may be observed during various stages of life (
Acetaminophen (paracetamol) is metabolized 90% by sulfate or glucuronide conjugation (Phase II). The sulfate pathway predominates in children less than 12 years of age, while adults primarily use the glucuronide pathway. Chloramphenicol (chlornitromycin), an antibiotic for gram-positive/-negative (most anaerobic) organisms, is primarily metabolized by glucuronidation and is a poor substrate for sulfotransferase. Therefore, this antibiotic is extremely toxic to neonates (bone marrow) and is responsible for the “gray baby syndrome” consisting of progressive cyanosis, metabolic acidosis, vasomotor collapse, respiratory difficulty, and death (McIntyre and Choonara 2004).
A key concept in toxicology is the quantitative relationship between the concentration of a xenobiotic in the body and the magnitude of the biological effect it produces. The magnitude of the effect of a xenobiotic is usually a function of the amount of xenobiotic a person is exposed to or that reaches a receptor (i.e., “The Dose Makes the Poison”). In any given population, there will be a range of sensitivities to a xenobiotic. It is extremely useful to know what is the average sensitivity of a population to a xenobiotic, and what the average dose required to elicit a toxic response will be. Population dose–response function focuses on a specific end point made up of many individual dose–response functions. At each dose level, individual members of the population either do or do not respond. There is variation in sensitivity/susceptibility of individuals in the population. One can measure the proportion of population responding at each dose level or the level of the response at each dose level.
Why do we look so different or behave so differently? Why are some more able or more susceptible than others? What makes us unique? Individual genetic makeup (polymorphisms)! Changes in the number and order of genes add variety to the human genome. Inversions, insertions, deletions, and copy number variation all contribute to the individuality of our genetic makeup. The Major Histocompatibility Complex (MHC) is a large genomic region or gene family found in most vertebrates. It is the most gene-dense region of the mammalian genome and plays an important role in the immune system, autoimmunity, and reproductive success. The proteins encoded by the MHC are expressed on the surface of cells in all jawed vertebrates and display both
Allelic variants in aldehyde dehydrogenase-2 (ALDH2) cause decreased ability to clear acetaldehyde and other aldehyde substrates, with homozygous variants (ALDH2*2/2) having no activity and heterozygotes (ALDH2*1/2) having intermediate activity relative to the predominant wild type (ALDH2*1/1). These polymorphisms are associated with increased buildup of acetaldehyde following ethanol ingestion and increased immediate symptoms (flushing syndrome) and long-term cancer risks. The nonfunctional allele is rare in most populations but is common in Asians such that 40% are heterozygotes and 5% are homozygote variants.
Classical phenylketonuria (PKU) is an autosomal recessive disorder, caused by mutations in both alleles of the gene for phenylalanine hydroxylase (PAH), found on chromosome 12. In the body, PAH converts the amino acid phenylalanine to tyrosine, another amino acid. Mutations in both copies of the gene for PAH mean that the enzyme is inactive or is less efficient, and the concentration of phenylalanine in the body can build up to toxic levels. In some cases, mutations in PAH will result in a phenotypically mild form of PKU called hyperphenylalaninemia. Both diseases are the result of a variety of mutations in the PAH locus; in those cases where a patient is heterozygous for 2 mutations of PAH (i.e., each copy of the gene has a different mutation), the milder mutation will predominate. PKU is one of the commonest inherited disorders occurring in approximately 1 in 10,000 babies born in the United States whereby they inherit 2 mutant genes for the enzyme PAH. PAH normally breaks down the amino acid phenylalanine that is in excess of the body’s need for protein synthesis. Both parents must be defective to produce the disease. Test that measure how quickly injection of phenylalanine is removed from blood can distinguish a person who has 1 PKU gene from a person who has none. A person with 1 defective gene is perfectly healthy because the unmutated allele produces enough of the enzyme; however, these heterozygous individuals are “carriers” of the disease. Loss of PAH can result in mental retardation, organ damage, unusual posture, and can, in cases of maternal PKU, severely compromise pregnancy.
Subtle genomic changes known as silent polymorphisms lead to coding-equivalent changes in messenger RNA (mRNA). During translation, these mRNAs yield proteins with identical amino acid sequences but different shapes. In 2007, the NCI showed that a multidrug resistance gene with a single nucleotide, coding-equivalent sequence modification translates into a P-glycoprotein with a different conformation (Kimchi-Sarfaty et al. 2007). They speculate that the difference may result from timing or other subtle changes to the translation process caused by the sequence modification. The work points to a previously unrecognized and potentially profound role of single-nucleotide polymorphisms in health and disease.
The acetylation polymorphism illustrates another genetic polymorphism of a drug-metabolizing enzyme studied in the early era of pharmacogenetics (Grant et al. 1990).
Allelic variation at the
Currently, the importance of these variants in
The emerging field of “Pharmacogenomics” or “Toxicogenomics” offers the potential to identify and protect subsets of people predisposed to toxicity from chemicals or drugs. This approach allows one to identify people with different chemical/drug sensitivity (people differ).
Things Change
Perfumes were an important part of the court life in Ancient Egypt. Cleopatra’s perfume factory was (still is) at the southern end of the Dead Sea. Cleopatra used to drink turpentine (terebinth from
Biotransformation usually decreases the ability, and in turn, the likelihood, of a molecule interacting with a biological system. The probability of potential damage is offset or lowered. Usually, but not always, the process makes the molecule more polar (frequently acidic) and thus more water soluble. As such, the system can more easily remove the molecule via the kidneys (urine) or liver (bile). An example is the enzyme epoxide hydrolase converting ethylene oxide, a chemical with genotoxic and other chronic toxic properties, into the somewhat less toxic ethylene glycol. On occasions, the chemical may be activated and converted into a more dangerous species whereby the body inadvertently poisons itself. For example, chloroform can be converted to phosgene. Phosgene (COCl2), a poisonous gas used as a chemical weapon in World War I, is a highly toxic gas or liquid that is classified as a pulmonary irritant. Exposure to phosgene gas produces delayed onset noncardiogenic pulmonary edema. Exposures to 50 ppm may be rapidly fatal (http://emergency.cdc.gov/agent/phosgene/basics/facts.asp).
Conclusions
In summary, these three axioms (people differ, dose matters and things change [chemicals transform]) help explain why humans respond in varied and often unpredictable ways to a common chemical insult.
Footnotes
Authors’ Contribution
All authors (AH, DD) contributed to conception or design; data acquisition, analysis, or interpretation; drafting the manuscript; and critically revising the manuscript. All authors gave final approval and agreed to be accountable for all aspects of work in ensuring that questions relating to the accuracy or integrity of any part of the work are appropriately investigated and resolved.
Declaration of Conflicting Interests
The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The author(s) received no financial support for the research, authorship, and/or publication of this article.