Toxicology
Definition:
Toxicology is the study of the
adverse effects of chemical,
physical or biological agents on
living organisms and the
ecosystem, including the
prevention and amelioration of
such adverse effects. (Society
of Toxicology)
http://www.toxicology.org/
Toxicology: The study of adverse effects
of xenobiotics.
~ Xenobiotics: From the Greek xeno (févo)
for “foreign” and bios (Bioc) for “life’’).
_ This discipline actually has its roots In
the ancient art of poisoning.
~ Now its scope is much broader.
scope of Toxicology:
branches
Different
Biomedical:
® Mechanisms
of actions
® Effects of exposure
® Understanding biological responses through
model toxic compounds
Public Health:
® Recognition and identification of hazards
® Occupational exposure
® Development and use of pesticides
scope of Toxicology:
Branches
Different
Regulatory:
© Development of exposure standards
® Detection methods
Environmental:
® Chemical effects on plants, animals &
ecosystems
Clinical:
© Development of antidotes & treatments
® Recognition of exposure
scope of Toxicology:
got here
How we
- Toxicology, like other disciplines, is a
mixture of science, art & creative thinking
® Science: The observational and data-
gathering phase.
scope of Toxicology:
got here
How we
® Art: Utilization of the data to predict outcomes
in humans
studies.
based on /n vitro and in vivo
® Creative Thinking: Determining the next
hypothesis and how to design experiments to
actually answer the questions posed.
scope of Toxicology:
got here
How we
_ It is important to note that facts are
different from predictions.
' Facts have been proven; predictions are
based on probabilities. They don’t have
equal value, in terms of scientific weight.
_ Toxicologists need to be careful when
talking to the public to make sure they
don't confuse the two!
Historical background
Toxicology dates to the earliest humans
Poisons played an important role in the history
of mankind. In most cases, poisoning is caused
by people's negative characteristics
They may either be lack of information or
ignorance, carelessness, untidiness, and, at
worst, anger that may lead to cases of deliberate
poisoning
History of Toxicology—
Antiquity
Humans have a long history of using
poisons
® Hemlock (Greek capital punishment)
® Aconite (Chinese poison arrows)
Milestones
® Dioscorides—Greek physician who classified
poisons for Nero. He included descriptions and
drawings. This was a standard text for 1600
ere
| ge
History of Toxicology—
Antiquity
| Toxicology during this time, however,
mainly focused on poisoning (Suicide,
state-sanctioned & personal usage...)
_ This knowledge also lead to antidotes.
© Emetics (e€upetikoc)—Agent to induce
vomiting following poisonings
Most known historical persons dealing
with toxicology
- Dioscorides : first classification of poisons, use
of emetics in treatment
- Paracelsus : ,All substances are poisons; there
is none which is not a poison. The right dose
differentiates a poison from a remedy.”
- a physician — alchemist; set the basics of
pharmacology, toxicology and
therapeutics; investigated the
dose-response relation
History of Toxicology—
Antiquity
King Mithridates VI of Pontus—
Experimented on criminals and himself!
® He would drink a poison cock-tail (36
ingredients!) to prevent political enemies from
being able to poison him.
History of Toxicology—
Antiquity
| Poisonings were so rampant in Rome, a
law was enacted in 82BC. It made
poisoning illegal, and later extended to
careless dispensers of drugs (an early
regulatory effort!)
History of Toxicology—Middle
A eX-3—
_ Maimonides—Concept of
bioavailability: Based on the forms of
toxicants, or what one eats/drinks
before ingestion, the chemical can be
more or less readily available in the
body.
® Milk, butter and cream could delay
intestinal absorption (due to the fat
content)
© Full stomach also delays absorption
History of Toxicology—Middle
A eX-3| The poisoner, in Renaissance Italy, was
an integral part of society.
® Toffana—Woman who sold arsenic-laced
cosmetics
® Hieronyma Spara—Provided ‘services’ to
local young soon-to-be widows.
History of Toxicology—Middle
Vedoy
Catherine de Medici—Systematic study of the
effects of poisons in the sick and poor to
make sure the correct concoction was
delivered to her ‘customers’.
© Noted the following:
> Rapidity of the toxic response (onset
of action)
) Effectiveness of the compound “
ney)
> Degree and specificity of belies le
of action)
©
Complaints
of victims
(clinical
signs
an r symptor 1)
History of Toxicology—Age
Enlightenment
of
| The age of Paracelsus (1493-1541 )—
Responsible for the most famous saying
in all of toxicology:
| All substances are poisons; there is
none which is not a poison. The right
dose differentiates a poison from a
remedy.
History of Toxicology—Age
Enlightenment
of
- Paracelsus focused on the importance of
the ‘toxicon’—a primary toxic agent and a
single chemical entity.
_ This was in contrast to previous schools of
thought that included the concept of
patel este
History of Toxicology—Age
Enlightenment
of
® Experimentation is essential in the
examination of responses.
© There is a difference between the therapeutic
and toxic properties.
® The above are not easily determined, except
by dose.
® It is possible to ascertain a degree of
specificity of chemicals and their therapeutic
or toxic effects.
History of Toxicology—Age
Enlightenment
of
Seminal texts:
® On the Miners’ Sickness and other Diseases
of Miners (1567) by Paracelsus
© Included treatment and prevention strategies
® Discourse on the Diseases of Workers (1700)
by Bernardino Ramazzini
© Set the standard for occupational medicine.
© Also included information about miners,
midwives, printers, weavers and potters.
History of Toxicology—Age
Enlightenment
of
Major developments:
® 1775—Role of soot in scrotal cancer in
chimney sweeps (due to polyaromatic
hydrocarbons)
® 1825—Synthesis of phosgene and
mustard gas (chemical warfare)
® 1880—Boom in organic chemical
synthesis led to over 10,000 new
compounds (no industry testing for
toxicity)
History of Toxicology—Age
Enlightenment
of
Major developments:
® Orfila (1787-1853): Introduced the use of
autopsy material to toxicology to provide
legal proof of poisoning.
® Magendie (1783-1885): Detailed the
absorption and distribution of various
compounds in the body.
Modern
Toxicology
Toxicologists must understand aspects of
biology, chemistry and metabolism.
© They tend to function as detectives who must
utilize many clues.
Initial growth in the field spurred by need to
explain deaths occurring after administration
of ether, chloroform and carbonic acid in
iatrogenic deaths.
© latrogenic: From the Greek tatros (1atpoc) for doctor
Modern
Toxicology
1890s-1900s
© Discovery of vital amines (vitamins) led to
the wide-spread usage of bioassays to
determine whether these new chemicals
were beneficial.
® Development of neurotoxicity field due to the
production of bootleg liquor by-products
(methanol & lead).
® Toxicology of metals due to the production
of ‘the bomb’.
Modern
Toxicology
Post World War Il
® Discovery of organophosphates (OPs) as
cholinesterase inhibitors.
© Today used as non-bioaccumulating pesticides
Production of quinine as an antimalarial.
® Based on derivative of chincona bark
© First use of non-human primates
Discovery of mixed-function oxidases
(MFQs)
© Prelude to latter work on P450s
Modern
Toxicology
Two major discoveries (1948):
® Paper chromatography for chemical
separation.
® Use of blood and urine for testing
presence of various chemical
metabolites (biomarkers).
Modern
Toxicology
Formalization of the experimental program
for the testing of food, drug and cosmetic
safety in 1955.
® Updated by the FDA in 1982.
® Basically states that any chemical found to be
carcinogenic in lab animals or humans cannot
be added to the US food supply.
Modern
Toxicology
_ Toxicology and Applied
Pharmacology started around 1958—
First journal dedicated to toxicology.
|
Textbook of Toxicology published in
1959.
_ Society of Toxicology (SOT) founded
in 1965.
Modern
Toxicology
Major events in the 1960s:
® Thalidomide babies
® Silent Spring by Rachel Carson
® Equipment for detecting parts per billion (ppb)
® Genetic assays for point mutations (Ames
assay)
Currently
Now a unique and separate discipline
® Offered at many graduate schools
® “Surprisingly, courses in toxicology are
now being offered in several liberal arts
undergraduate schools as part of their
biology and chemistry curricula.” (p 10)
om
Famous poisonings and poisoners
The King Mithridates Eupator (1st century BC)
Is said to have taken small doses of 36 poisons to build tolerance
against them. When his son sent assassins to murder him, he
attempted suicide by poison but the poison had no effect on him,
and he had one of his servants kill him by the spear. This is where
immunity from poison got its name of mithridatism.
- The principle of addiction:
The organism already responds during resorption, mainly at the
level of intestinal wall, and reduces the penetration of exogenous
substances from the gastrointestinal tract to blood
As part of adaptation, the organism enhances the capacity of
detoxification processes
The organism incorporates the poison into its biochemical
processes, and the poison then becomes part of those processes.
lf the regular intake of the poison is interrupted,
the so-called withdrawal syndrome evolves
Examples of addictive substances are arsenic
(arsenic used to be given to horses as a stimulant,
but interrupting the supply may have led even to
the death of the horse), NaCl, morphine, some plant
toxins
socrates
One of the greatest ancient philosophers was
executed by a solution of the hemlock plant
(Conium maculatum) in 399 BC.
Poison hemlock (Conium maculatum) grows
on rubbish heaps. It contains the alkaloid
coniine (most of the alkaloids are in fruit).
The onset of toxic effects is in 20 — 30 minutes. The
death is most frequently caused by the cessation of
tells at full consciousness and before cardiac
ela ots)
Coniine isa curare-like poison, such alkaloids block the
transmission of stimuli from motor nerve endings to
Striated muscles, which subsequent leads to muscle
paralysis. The paralysis progresses from the lower limbs
upwards to respiratory muscles, and when these
muscles are paralyzed, the victim dies of asphyxia. The
brain is not affected and the victim retains
consciousness.
In the Middle Ages, many of the greatest
poisoners were women
The best known of them were Catherine de
Medici and Lucrezia Borgia (a daughter of
Pope Alexander VI.)
Catherine had a cabinet full of different
poisons at home, and she made the use of
yy,
ay
poisons a standard political tool. She was the = ge Medici
wife of the French king Henry II, and later
became Queen of France. She tried to
prevent any weakening of the royal family's
political power.
In Italy, an infamous poisoner was a woman
named Tofana, who made her mark by her
arsenic-containing cosmetics ("Aqua Tofana’").
Lucrezia
Borgia
There are also many examples of the use of poison in more recent
alii)ay,
In World War 2, German generals had a glass poison capsule
(containing e.g. potassium cyanide) set in one of the tooth under a
removable crown
A case from a very recently past is that of the Ukrainian president
Yushchenko, who was poisoned by dioxin (which left typical
symptoms of acne on his face)
Descriptions of animal poisoning also abound.
There have also been many cases of food poisoning:
- Minamata Disease (Japan, 1950s — 1960s) This was a case of
methylmercury poisoning of both people and animals. A chemical
factory dumped its mercury-containing waste to the Minamata Bay for
dozens of years. Inorganic mercury in mercury compounds that
accumulated in sediments on the bay bed began to transform to
methylmercury (the most toxic form of mercury) under the action of
bacteria. Methylmercury penetrated to the food chain of the aquatic
environment, |.e. fish and subsequently to man. People (mostly
fishermen) suffered of central nervous system disorders, loss of
hearing and speech disturbance. Several cases of limb paralysis and
severe mental disorders were also reported. Children were born with
defects. Several dozen people die.
- Poisoning of people in Irag in 1960s. Poisoning was caused
because seed wheat was mistaken for food wheat. The wheat
had been treated with phenylmercurychloride-based fungicidal
agent. Although exported as seed, the wheat was eventually by
mistake used as food wheat.
- Itai-ltai Disease (the ouch-ouch disease) In the 1950, Japan
witnessed mass poisoned of its citizens with rice heavily
contaminated with cadmium. The source of cadmium were ore
dumps from which cadmium was washed by rainwater to the
river. The name of the disease came from characteristic painful
screams of the victims who suffered severe pain in the joints and
the lower part of spine.
- The oil disease (Yusho) In 1968 about 1600 people in Japan
were poisoned by rice oil contaminated with polychlorinated
biphenyls (PCB) during the manufacturing process. The PCB
leaked into edible oil from corroded pipes of the cooling system.
The main symptoms of the poisoning were impaired immunity
(people died of common infectious diseases — flu, pneumonia —
rather than of PCB poisoning), damage to the nervous system,
hyperkeratosis, hyperpigmentation, etc.
Possible
Topics
Short
Research
Development of early advances in analytic methods
Marsh, 1836: development of method for arsenic analysis
Reinsh, 1841: combined method for separation and analysis of As and Hg
Fresenius, 1845, and von Babo, 1847: development of screening method for general
poisons
Stas-Otto, 1851: extraction and separation of alkaloids
Mitscherlich, 1855: detection and identification of phosphorus
Early mechanistic studies
F. Magendie, 1809: study
strychnine
C. Bernard, 1850: carbon
mechanism of action of
R. Bohm, ca. 1890: active
poisonous mushrooms
of “arrow poisons,’ mechanism of action of emetine and
monoxide combination with hemoglobin, study of
strychnine, site of action of curare
anthelmintics from fern, action of croton oil catharsis,
Possible
Topics
Short
Research
Introduction of new toxicants and antidotes
R.A. Peters, L. A. Stocken, and R. H. S. Thompson, 1945: development of British
Anti Lewisite (BAL) as a relatively specific antidote for arsenic, toxicity of
monofluorocarbon compounds
K. K. Chen, 1934: introduction of modern antidotes (nitrite and thiosulfate) for
cyanide toxicity
C. Voegtlin, 1923: mechanism of action of As and other metals on the SH groups
P. Miller, 1944-1946: introduction and study of DDT
(dichlorodiphenyltrichloroethane) and related insecticide compounds
G. Schrader, 1952: introduction and study of organophosphorus compounds
R. N. Chopra, 1933: indigenous drugs of India
Possible
Topics
Short
Research
Miscellaneous toxicologic studies
R. T. Williams: study of detoxication mechanisms and species variation
A. Rothstein: effects of uranium ion on cell membrane transport
R. A. Kehoe: investigation of acute and chronic effects of lead
A. Vorwald: studies of chronic respiratory disease (beryllium)
H. Hardy: community and industrial poisoning (beryllium)
A. Hamilton: introduction of modern industrial toxicology
H. C. Hodge: toxicology of uranium, fluorides, standards of toxicity
A. Hoffman: introduction of lysergic acid and derivatives, psychotomimetics
R.A. Peters: biochemical lesions, lethal synthesis
A. E. Garrod: inborn errors of metabolism
T. T. Litchfield and F. Wilcoxon: simplified dose-response evaluation
C. J. Bliss: method of probits, calculation of dosage-mortality curves
Methods to evaluate
chemicals
‘)
2)
3)
toxicity of
Based on cases of poisoning, cases studies
(case histories)
Methods for toxicity prediction
Toxicity tests
Up
It is not possible to perform toxicity tests or to
monitor effects of chemical
substances
on
people and most species of animals. For that
reason it is important to learn as much as
possible from individual cases of poisoning, and
that is also the reason why we so often return to
the history of toxicology
2)
There is a relation between the chemical structure of
substances and their biological characteristics. It cannot
be assumed that knowledge of the molecule structure of a
new xenobiotic alone will suffice for an unambiguous
evaluation of biological properties.
On the other hand, it will at least allow for a group
classification. Toxicity prediction may be quite successful if
we are dealing with a series of substances exhibiting
chemical
similarities.
The
relationship
between
the
chemical structure and biological activity is expressed as
Quantitative Structure — Activity Relationship (QSAR).
Computer programmes
are developed for computerassisted toxicity predictions.
But because these predictions may differ from reality, tests
on experimental animals are necessary before a final
decision can be taken. Thanks to prediction processes,
however, the scope of these tests can be minimized (with
a minimum number of experimental animals)
3) Toxicity tests are performed at the level of
cells and tissues (in vitro tests)
organisms
Biocoenoses
- For tests at the level of cells and tissues, primary cell cultures (higher
sensitivity, lower reproducibility) or stable cell cultures (lower sensitivity,
higher reproducibility) are used. Test can be evaluated directly
(numbers of dead cells and extent of cytopathic effects) or indirectly
(evaluations based on physiological reactions of the cells).
- One example is the Neutral Red Test (NRT). It uses the ability of
undamaged lysosomes to incorporate and bind neutral red. After a 20hour period of exposure to the test substance, a neutral red solution is
added,
left there to take effect, then it is drained off and
lysing solution
is added. Undamaged cells are lysed, and the neutral red released is
measured photocolorimetrically.
- The advantage of in vitro tests is their speed, reproducibility, low
financial and time demands. The disadvantage is that in vitro systems
are no substitute for the enzymatic - immune system of the living
organism. In spite of that, in vitro tests are suitable screening tests
before animal experiments.
~
~
- The most frequently performed tests are those at the level of
organisms. They must include all trophic levels, i.e. bacterias,
invertebrates and vertebrates (experiments on fish, birds and
mammals). Methods to be used in such experiments are unified
world-wide by the Organisation for Economic Cooperation and
Development (OECD) and the International Organization for
Standardization (ISO).
- Tests at the level of biocoenoses - these tests are very
expensive and time consuming, they are used in special cases
only. The preparation is applied over a defined area of land and
its effects on soil microorganisms, earthworms, game, birds
etc., are monitored, and its residual concentrations are studied.
Similar methods are used for experiments in the aqueous
environment.
More info:
http://www.portfolio.mvm.ed.ac.uk/studentwebs/session2/group1
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