toxicology introduction

د.شامل هاشم ألنعيمي

MBchB ,M Sc, PhD

Assistant Professor

Dept. of Pharmacology
College of Medicine

General Principles of Toxicology

Historical Perspective

“...the appearance of disease in human populations is influenced by the quality of air, water, and food; the topography of the land; and general living habits.”

The ancient-Greek physician Hippocrates in his treatise Air, Water and Places 400 BC

Swiss physician Paracelsus (1493-1541)

credited with being “the father of modern toxicology”

“All substances are poisons: there is none which is not a poison. The right dose differentiates a poison from a remedy.”

What is Toxicology?

• Old definition: the basic science of poisons

• New Definition: the study of the adverse effects of chemical agents on biological systems

• The ultimate goal is to increase our understanding of how chemicals affect human health.

The Dose Makes the Poison!

• An apparently non-toxic chemical can be toxic at high doses. (Too much of a good thing can be bad!).

• Highly toxic chemicals can be life saving when given in appropriate doses.(Poisons are not harmful at a sufficiently low dose)

Did you know that....

About 4 million toxic exposures annually

• Fewer than 1% of overdose patients that reach the hospital result in fatality

• But 13-35% mortality if arrive in deep coma


• One fourth of suicide attempts are via drugs

Leading causes of pharmaceutical death

• Analgesics
• Tricyclic antidepressants
• Sedative/hypnotics
• Stimulants and street drugs
• Cardiovascular drugs
• Alcohols

Toxicology Terms

The term “toxicant” refers to toxic substances that are produced by or are a by product of human-made activities.

• The term “toxin” refers to toxic substances that are produced naturally.

• A toxic symptom is any feeling or sign indicating the presence of a poison in the system.

• Toxic effects refers to the health effects that occur due to exposure to a toxic substance.

• LD50:

The amount (dose) of a chemical which produces death in 50% of population of test animals to which it is administered by any of a variety of methods.


Normally expressed as milligrams of substance per kilogram of animal body weight (mg/kg)

Toxicology Terms

Toxicity - The adverse effects that a chemical may produce.

Dose - The amount of a chemical that gains access to the body (mg/kg)

Adverse effects
• any change from an organism’s normal state
• dependent upon the concentration of active compound at
the target site for a sufficient time.

Hazard – is a chemical substance, physical agent, or biological agent that can harm the health of people

Exposure – Exposure means Contact with a hazard

• Exposure Frequency – how often
• Exposure Duration – how long
• Exposure Concentration – how much

Risk = Hazard X Exposure


Toxicants
• Heavy Metals
• Solvents and Vapors
• Radiation and Radioactive Materials
• Dioxin/Furans
• Pesticides

Exposure

Duration and frequency are important components of exposure and contribute to dose.
• Single exposure:
Acute exposure - less than 24 hours
• Repeated exposures are classified as:
• Subacute - repeated for up to 30 days
• Subchronic - repeated for 30-90 days
• Chronic -repeated for over 90 days

Mechanisms of Toxicity

1. Interfere with O2 transport or tissue utilization of oxygen (example cyanide, CO)
2. Affect CNS (example cocaine, sedatives)
3. Affect ANS (example organophosphates)
4. Affect lungs (example paraquat)
5. Affect cardiovascular system(example TCA, Ca++channel blockers)
6. Direct local damage (example acids, bases)
7. Delayed effects on liver or kidneys (example acetaminophen, metals)


Dose - Response Curve
Dose-Response Relationship: As the dose of a toxicant increases, so does the response.

What is a Response?

The degree and spectra of responses depend upon the dose and the organism

• molecular, cellular, organ, or organism level

• Local or Systemic
• Reversible or Irreversible
• Immediate or Delayed
• Graded or Quantal

Route of Exposure

Ingestions account for 79% of exposures
• 7% dermal
• 6% ophthalmologic
• 5% inhalations
• 3% stings and bites
• 0.3% injection
Typical Effectiveness of Route of Exposure:
iv > inhale > ip > im > ingest > topical


What toxicologists do?
Most toxicologists work to develop a mechanistic
understanding of how chemicals affect living systems:
• Develop safer chemical products
• Develop safer drugs
• Determine risks for chemical exposures
• Develop treatments for chemical exposures
• Teach ( e.g. other toxicologists, graduate students)

Risk: the probability that harm will occur under specified conditions

Safety: the probability that harm will not occur under
specified conditions

Areas of toxicology (fields of specialty)

Mechanistic toxicologists study how a chemical
causes toxic effects by investigating its absorption,
distribution, and excretion. They often work in
academic settings or private industries and develop
antidotes.


Descriptive toxicologists evaluate the toxicity of
drugs, foods, and other products. They often perform
experiments in a pharmaceutical or academic setting.

Clinical toxicologists usually are physicians or

veterinarians interested in the prevention, diagnosis,
and treatment of poisoning cases.

They have specialized training in emergency medicine and poison management.

Areas of toxicology (fields of specialty)
Forensic toxicologists study the application of toxicology to the law. They uses chemical analysis to determine the cause and circumstances of death in a postmortem investigation.

Environmental toxicologists study the effects of pollutants on organisms, populations, ecosystems, and the biosphere.

Regulatory toxicologists use scientific data to decide how to protect humans and animals from excessive risk.

Types of toxic effect

A wide variety of effects:
• Allergic agents: itching, rashes, sneezing, watery eyes.
• Asphyxiants: cause displacement of oxygen and thus suffocation.
• Irritants: cause pulmonary edema (fluid in the lungs) when inhaled at high concentrations and rashes when spilled onto the skin.
• Necrotic agents – cause cell death.
• Carcinogens, mutagens and teratogens: Cancer, mutations, and deformed embryos result from chronic exposure to low levels
• Systemic poisons – can have an adverse effect on the whole body when taken internally.


Adverse Effect
Not all organs are affected equally
• greater susceptibility of the target organ
• higher concentration of active compound
Liver: high blood flow, oxidative reactions
Kidney: high blood flow, concentrates chemicals
Lung: high blood flow, site of exposure
Neurons: oxygen dependent, irreversible damage
Myocardium: oxygen dependent
Bone marrow, intestinal mucosa: rapid divide

Types of Toxic Effects

Death - arsenic, cyanide
Organ Damage - ozone, lead
Mutagenesis - UV light
Carcinogenesis - benzene, asbestos
Teratogenesis - thalidomide

Mechanisms of Toxic Effects

Adverse effects can occur at the level of the molecule, cell, organ, or organism
Molecular level: chemical can interact with: Proteins / Lipids / DNA
Cellular level: chemical can
• interfere with receptor-ligand binding
• interfere with membrane function
• interfere with cellular energy production
• bind to biomolecules
• Agitate homeostasis


Types of Interactions
Additive effects: (1+1 = 2)
Synergism: one contaminant enhances the effect of another (1+1 = 3)
Antagonism: one contaminant reduces the effect of another
Tolerance
state of decreased responsiveness to a toxic effect of a chemical, resulting from previous exposure
- dispositional tolerance; a decreased amount of drug reaching the site
- cellular; reduced responsiveness of a tissue

Individual Susceptibility

There can be 10-30 fold difference in response to a toxicant in a population!
Genetics species, strain variation, interindividual variations
Gender (gasoline nephrotox in male mice only)
Age
• underdeveloped excretory mechanisms
• underdeveloped biotransformation enzymes
• underdeveloped blood-brain barrier
• body fat
Nutritional status
Health conditions
Previous or Concurrent Exposures


Toxicology helps create a safer world ...

Toxicology is a fascinating science that makes

biology and chemistry interesting and relevant.

• Understanding HOW (i.e. mechanism) something

produces a toxic effect can lead to new ways of
preventing or treating chemically-related diseases.

• Many diseases are the result of an interaction

between our genetics (individual variability) and
chemicals in our environment.

• Toxicology provides an interesting and exciting way

to apply science to important problems of social,
environmental, and public health significance.