BASIC PRINCIPLES

Sho’im Hidayat

Industrial Toxicology

INTRODUCTION

What is Toxicology ?- Traditional : the science of poisons- The study of adverse health effects of chemicals

or physical agents on living organism

What is Industrial toxicology ?Industrial toxicoloy is the science of poisons whereby is used, produced or byproduced in industry

History :Ancient time (1500 BC): Have recognized the use of plants and animal poisons extracts

for hunting or warfare : hemlock, opium, arrow poisons, certain metal

With time : Poisons become widely used and with great sophistication

Victims : Socrates, Cleopatra, Claudius

Renaissance & Enlightenment :Fundamental concept of toxicology began to take place

(Paracelcus, 1500 AD and Orfila, 1800 AD)

Paracelcus :- Specific chemical actually responsible for toxicity of the plant

and animal poison- His famous statement : dose–response relationship

All substance are poisons; there is none which is not a poison. The right dose differentiates a poison and a remedy.

Orfila :- Often referred as founder of toxicology - Prepared a systematic correlation between chemical and

biological properties of poisons- Demonstrates effect of poison in specific organ by autopsy

Basic Toxicology Terminology There are varies in terminology :

toxicanttoxinpoisontoxic agenttoxic substancetoxic chemical

Toxic agent :Anything can produce an adverse biological effect (chemical : cyanide; physical : radiation; biological: snake venom)Not included : infected by microorganism

Biological toxin :Chemical excreted by microorganism which is

the basis of toxicityEx : tetanus toxin (neurotoxin), produced by Clostridium tetani

Toxic material : Doesn’t consist of an exact chemical Ex : asbestos (fiber and other chemical)

Organic toxin : Substance originally derived from living organism

(named organic) Contain carbon, large molecule

Inorganic toxin : Specific chemical not derived from living organism

(mineral) Generally small molecule, consist of few atoms

Xenobiotic : Foreign substance taken in to the body

xeno = foreign

Xenobiotics may produce :- beneficial effects (such as pharmaceuticals) - toxic effect (such as lead)

Systemic toxin : Effects is in the entire body or many organs rather

than a specific organ Ex : potassium cyanide, it effects virtually every cell and organ

Organ toxin : Effects only in specific cell or organ (target organ or

target tissue), not producing damage to the body as a whole

Ex : Benzene blood forming tissue Lead CNS, kidney, hematopoietic system)

DOSE and DOSE-RESPONSE• Dose : The amount of a substance administered at one time• Parameter needed : number of dose, frequency, total time period

Ex : - 650 mg Tylenol as single dose - 500 mg Penicillin every 8 hours for 10 days - 10 mg DDT per day for 90 days

Type of DosesExposure doseExternal dose*)

the amount of a xenobiotic encountered in the environment

Absorbed doseInternal dose*)Effective dose*)

the actual amount of the exposed dose that enter the body

Administered dose the quantity administered usually orally or by injection

Total dose The sum all individual doses

Dose Unit : mg/kg/day

Environmental exposure unit are expressed as the amount of a xenobiotic in a unit of the media

Examples :• mg/liter (mg/l) for liquid• mg/gram (mg/g) for solids• mg/cubic meter (mg/m3) for air

Smaller unit : µg/ml; ppm; ppb; ppt

Dose Response RelationshipCorrelates : exposure and spectrum of effectsIn general, higher dose more severe the response(Based on observed data from animal, human clinic or cell

study)

Knowladge of dose-response relationship :- Establish causality- Establisth the lowest dose where the induce effect

occur- Determines the rate which the injury build-up

(slope)

Dose-response curve : sigmoid

• The point at which toxicity first appear threshold dose level

• At that point the ability of the body to detoxify a xenobiotic or repair toxic injury has been exeeded.

• For most organs there is a reserve capacity so that loss of some organ function does not cause decreased performance

• For example, the development of cirrhosis in the liver may not result in a clinical effect until over 50% of the liver has been replaced by fibrous tissue.

Threshold :

• Shape and slope important for predicting the toxicity of substance

• Some / every substance may has a different type of the curve

Dose estimates of toxic effect : LD50

LD50 20 mg/kg, rat, oral, 5%

Effective doses (ED) : Indicate the effectiveness of a substance

Toxic doses (TDs) : Indicates doses that cause adverse toxic effects

Therapeutic Index (TI) : compare the therapeutically effective dose to the toxic dose

NOAEL and LOAELNo Observed Adverse Effect LevelLow Observed Adverse Effect Level

TOXIC EFFECTS

Toxicity : complex process; dose is the most important influencing factor

Xenobiotic :- originally toxic- after metabolized

Toxicity :- adverse cellular- biochemical - macromolecular change

Examples :

• Cell replacement, such as fibrosis• Damage to an enzym system• Disruption of protein synthesis• Production of reactive chemicals in cell• DNA damage

Indirectly :• Modification of an essential biochemical function• Interference with nutrition• Alteration of physiological mechanisme

Factors influencing toxicity :

• Form and innate chemical activity• Dosage, especially dose-time relationship• Exposure route• Species• Age• Sex• Ability to be absorbed• Metabolisme• Distribution within the body• Excretion• Presence of other chemicals

FormExamples : - methyl mercury – mercury vapour (element)

- Cr3+ - Cr6+

InnateExamples : HCN cytohrome oxidase hypoxia

Nicotin cholinergic receptor paralysis

Dosage Toxicant : Acute toxicity : Chronic toxicity : Ethanol CNS depressant liver cirrhosis Arsenic GIT damage skin / liver damage

Exposure Route :- Ingested chemicals : intestine liver

distributed- Inhaled chemicals : blood circulation whole

body

Liver : the most active organ for chemicals inactivation Frequenly : diff. target organ for diff. exp. route

Selective toxicity : Differences in toxicity between two species

- an insectcide is lethal to insect, not to human- antibiotics lethal for microorganisme, nontoxic to

human

Age :- parathion is more toxic to young animals- nitrosamines are more carcinogenis to newborne

or young animals

Sex :- male rats 10 x more sensitive to liver damage from

DDT- female rats 2x more sensitive to parathion

Ability to be absorbed :- ethanol is readily absorbed from GIT but poorly

absorbed through the skin- organic mercury is readily absorbed from GIT, but

inorganic mercury is not

Metabolism = biotransformation Is a major factor in determining toxicity

- detoxification (bioinactivation) : process by which a xenobiotic is converted to a less toxic form water soluble

- bioactivation : process by which a xnobiotic may be converted to more reactive or toxic form.

Distribution : Determine the sites where toxicity occur. Depend on how the lipid-solubility

Excretion :Another major factor affecting the toxicityExcretory organ : kidney, GIT, lung. Sometime

also : sweat, tears, milk

Presence of other chemicalsAntagonism, additivity, potentiation, synergism

SYSTEMIC EFFECTS

Toxic effects occur at multiple sites, including : - acute toxicity- subchronic toxicity- chronic toxicity- carcinogenicity- developmental toxicity- genetic toxicity (somatic cells)

• Acute toxicity– occurs almost immediatly (h / d) after exposure– Usually single dose at large dose– Examples : Methyl isocyanat accident in Bophal India

• Subchronic toxicity– Results from repeated exposure for several weeks or

months

• Chronic toxicity– Represents cumulative damage to specific organ system

and takes many months or years to become a recognizible clinical disease

– Ex : cirrhosis in alcoholics, chronis bronchitis in long-term cigarrete smokers, pulmonary fibrosis in coal miners

• Carcinogenicity– Complex multistages of abnormal cell growth

and differentiation– Need : initiator, promoter – Mutation results initial neoplastic

transformation of cellular gene• Developmental toxicity

– An adverse effect on developing embryo or fetus

– Involving : embryolethality, embryotoxicity, terratogenicity

• Genetic toxicity– Results from damage to DNA and altered

genetic expression mutagenesis– 3 types of genetic change : gene mutation,

chromosome abberation, aneploidy / polyploidy

Organ specific toxicity

Type of organ specific toxic effect are :- blood / cardiovasculer toxicity- dermal / occular toxicity- genetic (germ cell) toxicity- hepatotoxicity- immunotoxicity- nephrotoxicity- reproductive toxicity- respiratory toxicity

• Blood & cardiovascular toxicity– Toxicity on circulating blood, bone marrow,

heart– Ex : - hypoxia do to monoxide

- decrease leucocyte do to chloramphenocol - leukemia do to benzene

• Dermal and eye toxicity– Results from direct contact or internal

distribution to the skin– Ex : dermal irritation, dermal corrosion,

hypersensitivity, skin cancer

• Hepatotoxicity– Toxicity to the liver, bile dict and gall bladder

• Immunotoxicity– Toxicity of the immune system– Forms : hypersensitivity (allergic & autoimmunity),

immunodeficiency, uncontrolled proliferation (leukemia & lymphoma),

– Ex : contact dermatitis, systemic lupus erytematosus (SLE)

• Nephrotoxicity– Succeptibility factor of kidney : high volume blood flow

& filtrates amount of toxin– Forms : decrease excrete body waste, inability to

maintain body fluid, decrease to synthesis hormon erythropoietin

• Neurotoxicity– Damage cell of CNS & PNS– Types :

• Neuropathy (neuron injury)• Axonopathy (axon injury)• Demyelination (loss of axon insulation)• Interference with neurotransmitter

• Reproductive toxicity– Male and female– Effects :

• Impotency / decrease of libido• Infertility• Interupted pregnancy• Infant death / childhood mortality• Childhood cancer, etc

• Respiratory toxicity– Upper and lower respiratory tract– Forms :

• Pulmonary irritation• Asthma bronchitis• Reactive airways disease• Emphysema• Allergic alveolitis• Fibrotic lung disease• Pnumoconiosis• Lung cancer

INTERACTIONType of interaction :

The interactions described can be categorized by their chemical or biological mechanisms as follows:– chemical reactions between chemicals– modifications in absorption, metabolism, or

excretion– reactions at binding sites and receptors– physiological changes

Additivity : Tranquilizer + alcohol Two Organophosphate Organochlorine + halogenated solvent

Synergism : Cigaret smoke + asbestor / radon Ethanol + carbontetrachloride Potentiation : Carbontetrachloride (hepatotoxic) + isopropanol

Antagonysme :

TOXIKOKINETCS

1. ABSORPTION2. DISTRIBUTION - STORAGE3. BIOTRANSFORMATION4. EXCRETION

Toxicokinetics determines the severity of toxicity, through :

- duration & concentration of substance at portal of entry

- rate & amount that can be absorbed- distribution in the body & concentration at

specific sites- efficiency of biotransformation & nature of

metabolites.- ability of substance pass through cell membra-

ne & reactivity to specific cell component- the rate and sites of excretion

1. ABSORPTION :Process whereby toxicants gain entrance

into the bodyVaries with specific chemicals and the route

of exposureFactors influencing the absorption :

- route of exposure- concentration of the substance at the site of

contact- biochemical and physical properties of the

substance

Primary route of exposure/absorption :

Diagram how chemicals pass through membrane

How chemicals pass through membrane 1. Passive transfer : simple diffusion

- Difference concentration on opposite sides- Ability of substance to move through small

pores in membrane It is depend on : lipid solubility, molecule size and degree of ionozation

2. Facilitated transfer :- facilitated diffusion- active transport- endocytosis (phagocytosis & pinocytosis)

Large molecules and particles can not enter cell via passive or active mechanism by endocytosis- phagocytosis (cell eating)- pinopcytosis (cell drinking)

Route of entry :1. Respiratory tract The most chemicals in industry absorbed / inhaled via respiratory tract :

- aerosol : dust, fume, mist - gas / vapour

Region : - nasopharyngeal - tracheobronchial - pulmonary

Toxic effect on respiratory tract, caused by:- gas / vapour:

- irritant- aphyxiant

- Dust- nonspecific- specific (fibrogenic, carcinogenic)

Irritant gas / vapour :- NH3, Cl2, HCl, formaldehyde, phosgen, etc.- Inflammatory effect - Sites of effect depend on the water solubility of

the substance

Dust- Deposition at epithel - Inflammatory effect (nonspecific)- Specific effect

Asphyxiant gases :1. Simple asphyxiant

due to decreasing of partial pressure of oxygen in atmosphere

2. Chemical asphyxiant- Monoxide gas (CO) more reactive to haemoglobine

competitive inhibitor- Cyanides gas blocking to cytochrome enzyme

2. Gastrointestinal Tract 3 factors affect absorption :

- type of cell at the specific site- period of time that the substance remain at the site- pH of stomach or intestinal

3. Skin Consist of 3 main layer :

- epidermis- dermis- subcutaneus tissue

- Intact & dry skin is good barrier - Lipid soluble substance more absorbable

DISTRIBUTION

Process whereby an absorbed chemical move away from the site of absorption to other areas of the body

How do chemicals move through the body ?- pass through cell lining of the absorbing organ to the interstitial fluid- leave the interstitial fluid and then :

- entering local tissue cell- entering blood capillaries and blood

circulation system- entering the lymphatic system

If chemicals is in the blood stream, may be :

- excreted- stored- biotransformed into difference chemical (metabolites)- its metabolite may be excreted or stored- the chemicals or its metabolites may

interact with cellular component

Does distribution vary with the route of exposure ?

- Yes it does- GIT liver (here biotransformed)

target organ- skin or inhaled circulation target

organ

Structural barrier to distribution- Blood brain barrier- Placenta- Testes

Organ or tissue differ in amount of chemicals that they receive due to 2 factors :

- volume of blood- presence of special barrier

Storage sites :- adipose tissue : lipid soluble toxicant- bone : Sr, Pb- liver : many substances- kidney- nail, hair

BIOTRANSFORMATION

Process whereby a substance is changed from one chemical to another by a chemical reaction in the body

Results called as metabolites

Metabolites : less toxic (bioinactivation / detoxification) or more toxic (bioactivation)

Chemical Reaction :- By enzymatic reaction- Enzyme as a catalyst - Generally as a complex reaction- Phase 1 : degradation of chemicals

(parent) through oxidation, hydrolysis and reduction, acetylation

- Phase 2 : conjugation

Oxidation :A chemical reaction in which a substance

loses electrons.

Aerobic (need oxygen) or anaerobic (without oxygen)

Examples : oxygenation dehydrogenation

electron transfer

Illustration of oxidation :

Reduction :Chemical reaction in which the substance gain

electronsMost likely to occur with xenobiotic in which

oxygen content is lowReduction can occur across nitrogen-nitrogen

double bond (azo reduction) or on nitro group (NO2)

Amina compound oxidized forming toxic metabolites

Carbon tetrachloride free radicals

Reduction :

Hydrolysis :

Phase 2 reaction : conjugationPhase 1 new intermediate metabolite

that contains a reactive chemical group :- hydroxyl (-OH)- amino (-NH2)- carboxyl (-COOH)

CONJUGATION

Modifier of Biotransformation :- age- genetic variability- enzym inhibition and enzym induction- dose level

EXCRETIONMajor route :

- gastrointestinal tract, sweat and saliva- mother milk, tears and semen- urinary excretion, feces excretion, and

exhaled air (main route of excretion)

Urinary excretion :- primary route of excretion- Nephron : functional unit (about one million per

kidney) : - glomerulus

- proximal tubule - distal tubule

Fecal excretion :- excretion in bile, then enters the intestin- direct excretion into the lumen of GIT- enterohepatic circulation will prolong the

life of xenobiotic in the body

Exhaled air :Main route excretion of volatile liquid

Other route of excretion :• Milk : DDT, polybrominated biphenyl, lead• Saliva • Sweat : cadmium, copper, iron, lead, zinc • Tears, hair, skin