GENERAL TOXICOLOGY

Aconitum wolf plaqueAconitum lycoctonum

LD 1 – 5 mg

HemlockConium maculatum

LD 150 - 300 mg

Red yewTaxus baccata

Ricinus communis

Oil tree

Castor seeds contain 40-70% oil and about 20% of proteins, including ricin, which represents one of the sharpest plant poisons. Ricin causes agglutinations of red blood cells, can damage the liver, kidney and spleen. Poisoning is manifested burning in the mouth, vomiting, diarrhea, intestinal colic, headache, weakness, etc.

Possible misuse of ricin for terrorist attack (easy isolation).

General Definitions

Paracelsus (1493-1541) :All substances are poisons; there is none which is not poison. The right dose differentiates a poison and a remedy.(As2O3 400 mg, NaCl 250 g, destilled water 15 l)

Poison: Any chemical capable of producing a deleterious response in a biological system, seriously injuring function or producing deathToxicology : The study of the adverse effects of chemicals on living organisms.Toxicologists : Trained to examine the nature of these effects and to assess the probability of their occurrence.

Overview of toxicology1. Biological systems are resistant to the toxic effect of

chemicals (lethal dose : ethanol=10g/kg, CdCl2= 225 mg/kg, TCDD=0.05 mg/kg)

2. Attempt of the body to protect itself from chemical exposure -Defense mechanisms :

a) Barriers to absorption of chemicals (skin, gut)b) Barriers to distribution of chemicals to critical organs

(blood-brain barrier, plasma protein binding, storage in fat, uptake by kidney and liver for elimination)

c) Excretion of chemicals by urine, feces and liverd) Biotransformatione) Detoxication of chemicals (electrophilic chemicals,

reactive oxygen species, intracel.binding protein)

f) Repair of macromolecules (oxidative injury –8OHdG)

g) Apoptosis

h) Cell proliferation

i) Reflex physiological function

j) Alter Gene Expression

Mechanisms by which chemicals cause toxic effects

a) Toxic effects produced by : parent chemical, reactive metabolite, reactive oxygen species

b) Toxicant interaction with macromolecules

c) Organ differences (kidney-concentrate chemical for excretion,

liver - high amount of drug metabolizing enzymes)

d) Subcellular sites of toxicity (nucleus, mitochondria,ER, lysosome, peroxisome,cytoplasm)

e) Intra-organ differences (liver – centrilobular versus periportal,

kidney – proximal tubule and loop)

f) Age (fetus and newborn)

Factors controlling target organ toxicity

1. Route of exposure

2. Distribution in the body

3. Metabolism

4. Excretion

5. Sensitization

Liver toxicity

Main defence against toxic agents - great detoxifying capability

Toxicity is predominantly associated with lipid-soluble agents Direct liver injury (alcoholic type, Reye´s Syndrome type,

toxic metabolite production, heavy metal damage) Immune mediation of toxic liver injury (hepatocytic injury, bile

duct injury) Chronic hepatotoxicity and neoplasia (vinyl chloride,

nitrosamines, aflatoxin, hormones, polyhalogenated polycyclic hydrocarbons)

Chemical Exposure

A. Acute : single exposureAcute toxicity expressed as lethal dose – LD50B. Subacute : less than 1 monthC. Subchronic : 1 – 3 monthsD. Chronic : more than 3 months

The effect can be acute, chronic, and late. In thelate effect is long period of latency (at this time theexposure is not condition). Incidence of symptomsalso in a few years (cancer).

Dose – response curves

Regardless of how a drug effect occurs—through binding or chemical interaction—the concentration of the drug at the site of action controls the effect. However, response to concentration may be complex and is often nonlinear. The relationship between the drug dose, regardless of route used, and the drug concentration at the cellular level is even more complex.

Dose-response data are typically graphed with the dose or dose function (eg, log10 dose) on the x-axis and the measured effect (response) on the y-axis. Because a drug effect is a function of dose and time, such a graph depicts the dose-response relationship independent of time. Measured effects are frequently recorded as maxima at time of peak effect or under steady-state conditions (eg, during continuous IV infusion). Drug effects may be quantified at the level of molecule, cell, tissue, organ, organ system, or organism.

Fig. 1 Hypothetical dose-response curve.Features of this curve :potency (location of curve along the dose axis), maximal efficacy or ceiling effect (greatest attainable response), and slope (change in response per unit dose)

Fig. 2 Comparison of dose-response curves.

Drug X has greater biologic activity per dosing equivalent and is thus more potent than drug Y or Z. Drugs X and Z have equal efficacy, indicated by their maximal attainable response (ceiling effect). Drug Y is more potent than drug Z, but its maximal efficacy is lower.

Classification of Toxicants

Compound LD50 (mg/kg) Toxicity

Ethanol 10,000 slightly

NaCl 4,000 moderately

Phenobarbital

150 very toxic

Strychnine 2 Super toxic

Nicotine 1

TCDD 0.001

Botulinus 0.00001

THRESHOLD vs NON-THRESHOLD EFFECTS

Most Toxic effects are considered threshold

Cancer is usually considered a non-threshold effect

Effects

1. Substances irritating mucose and skin (acids, bases, oxidants).2. Substances with narcotic effect (volatile solvents as

benzen, toluene, CCl4, C2H2Cl4, inhalation anaesthetics) which are soluble in membranes, slow down

transmission of nervous impulse.3. Substances inhibiting transfer of oxygen and electrons

(interaction with hemoglobin – CO, NO) Substances changing hemoglobin to methemoglobin (hemiglobin) Fe2+to Fe3+ - nitrites and chlorates4. Substances inhibiting enzymes: ions of heavy metals (Pb2+, Hg2+, Cd2+)

Glossary Mutagen – A chemical agent or type of radiation such as

X-rays, cosmic rays, UV rays that causes mutations. Mutation - A gene mutation is a permanent change in

the DNA sequence that makes up a gene. Mutations range in size from a single DNA building block (DNA base) to a large segment of a chromosome.

Mutagenesis is a process by which the genetic information of an organism is changed in a stable manner, resulting in a mutation. It may occur spontaneously in nature, or as a result of exposure to mutagens.

Teratogenesis is the production or induction of malformations in an embryo or fetus.

CCH

N

HN O

CH3

O

CCH

N

HN O

CH3

O

dimer thyminu

cytosin

N

N

NH2

HO

N

N

OH

HO

uracil

N

NNH

N

NH2

N

NNH

N

OH

adenin inosin

Mutation - examples

N

NNH

N

OH

H2N

guanin

N

N N

N

OH

H2N

CH3

7-methylguanin

N

NN

N

OH

H2N

CH2CH2OH

7-hydroxyethylguanin

O

OO

O

O

OCH3

N

N

N

N

OH

H2N

OH

aflatoxin B1 - guanin adukt

O

Aflatoxin B1

N

NNH

N

NH2

adenin

N

NNH

N

NH

ethenoadenin

(CH3)2N-NO

CH2CHCl

Chemical carcinogens

1915 – coal tar was applied to test animals (japanese pathologists) – skin cancer

Organic substances – polycyclic aromatic compounds, aromatic amines, chlorinated biphenyls, azo compounds, epoxides, aflatoxins, nitrosoamines, ...

Inorganic substances – arsenic, chromium (VI), cadmium, nickel

metal and polymeric implantates thin layers, fibres, powders asbestos

Mechanisms of effect of chemical carcinogens

Main principle – carcinogen is covalently bound to macromolecule – DNA, proteins, phospholipids, ...

Sometimes the covalent bond is formed with the metabolite of carcinogenic compound (product of biotransformation)

Nitrosamines

They cause tumors in the experimental animals We can find them in cigarette smoke, like

contaminants in preserved foods, and may be formed in the gastrointestinal tract by metabolism of nitrites used as preservatives

Probably metabolized by the P 450 cytochrome system

Metabolically active metabolites can binds to DNA to initiate the tumor response

O

OO

O

O

O CH3

Aflatoxin B1

O

OO

O

O

O CH3

Aflatoxin B1, 2,3 epoxid

O

Benzo(a)pyren Benzo(a)pyren-7,8 epoxid Benzo(a)pyren-7,8 diol-9,10 epoxid

O

OH

HO

O

Aflatoxin

The most potent hepatocarcinogen known and occurs as a by-product of fungal contamination of improperly stored food, notably peanuts

Benzo(a)pyrene – typical example of the polycyclic aromatic hydrocarbons (PAH)

Polycyclic aromatic hydrocarbons – PAHs

Potent atmospheric pollutants. Naphthalene is the simplest PAH. PAHs occur in oil, coal and tar deposits, and also in cooked foods(grilling meats, smoked fishes). They are lipophilic - nonsoluble in water, the larger are less volatile

Also formed by incomplete combustion of carbon-containing fuels (wood, diesel, fat, tobacco)

But they are used also as a raw material for the production of drugs and paints – from gas tar

Benzopyrenes – PAHs toxicity is dependent on exact isomer. The first known carcinogen was Benzo[a]pyrene (found in cigarette smoke). 7 isomers of PAHs have the carcinogenic, mutagenic and teratogenic effects.

Dibenz(a,h)antracenDibenz(a,c)antracen

CH3

CH3

7,12-dimethylbenz(a)antracen

Benzo(a)pyren Benzo(e)pyren

O

O

dibenzodioxin

O

OCl

Cl

Cl

Cl

2,3,7,8-tetrachlodibenzodioxin

O

dibenzofuran

Cl

Cl

ClCl

Cl

polychlorované binenyly

Polychlorinated dibenzodioxins and furanes – PCDD/F

Dioxins are a group of chemically-related compounds that persistent environmental pollutants

Solids, little soluble in water, sorption to scum and plankton, High stability – decomposition by means of UV radiation,

they accumulate in the food chain, mainly in the fatty tissue of animals

PCDD/F are side products of industrial production (e.g. pesticides).

They are most toxic in parallel substitution of positions 2,3,7 and 8 – the most toxic 2,3,7,8- tetrachlorodibenzodioxin TeCDD

Short-term exposure - skin lesions (chloracne), long-term exposure - impairment of immune system, liver tissue, endocrine system and another tissues , TCDD was classified as a „human carcinogen“

O

O

dibenzodioxin

O

OCl

Cl

Cl

Cl

2,3,7,8-tetrachlodibenzodioxin

O

Cl

Cl

Cl

Cl

2,3,7,8-tetrachlordibenzofuranO

dibenzofuranCl

Cl

ClCl

Cl

polychlorované binenyly

Polychlorinated biphenyls - PCBs Belongs to broad family made-man organic chemicals

(chlorinated hydrocarbons) Manufactured from 1929 in USA, banned in 1979 Non-flammability, chemical stability, electric insulating

properties → electrical heat transfer, as plasticizers in paints, plastics and so on

PCBs used in products were chemical mixtures made up of a variety of individual chlorinated biphenyl components (congeners – 207)

PCBs cause cancer and a variety of other adverse effests like effects on the immune system, reproductive system, nervous system and endocrine system

Disposal –PCBs do not readily break down and may remain for long period of time cycling between air, water, and soil.

Disposal is carried out in the blast furnace at high temperature