Lecture 3: Chemical toxicology - Lunds universitet Courses/Riskkursen...Lecture 3: Chemical...

Environmental issues and hazards in the chemical research laboratory

Richard Johnsson

Lecture 3: Chemical toxicology

normal spider web

normal spider web spider treated with marijuana

O

OHH

normal spider web spider treated with LSD

HN

N

O N

normal spider web spider treated with...

normal spider web spider treated with...caffeine (coffee)

N

NO

O

N

N

Lecture 3 - outline1. Introduction2. Toxicological concepts3. Toxicity4. Acute toxicity5. Toxicological testing6. Uptake and distribution of chemicals7. Metabolism - Phase I8. Metabolism - Phase II9. Excretion10.Electrophiles11.Examples (reference only)

1. Introduction

• What is a poison? Alle Ding sind Gi!, und nichts ohn Gi!; allein die Dosis macht, da ein Ding kein Gi! ist.

! All things are poison and nothing is without poison, only the dose permits something not to be poisonous.

Paracelsus, 1538

1. Introduction

• What is a poison? Alle Ding sind Gi!, und nichts ohn Gi!; allein die Dosis macht, da ein Ding kein Gi! ist.

! All things are poison and nothing is without poison, only the dose permits something not to be poisonous.

Paracelsus, 1538

! ! more than 1 liter of water each hour gives serious problems....

1. IntroductionCompoun d Lethal dose

Ethanol 700 g

Salt 300 g

Acetyl salicylic acid 100 g

D D T 8 g

Strycnine 150 mg

Nicotine 100 mg

Arsenic (III) oxide 100 mg

Tetrodotox in 10 mg

Dimethyl mercury 0,1 mg

2,3,7,8-tetrachlorodibenzodioxin e 0,1 mg

Botulinum toxin 0,001 mg

OCOOH

O

N

N

CCl3

Cl Cl

NO

N

H

O

H

H

O

OCl

Cl

Cl

Cl

As2O3

NaCl

CH3-Hg-CH3

OH

etanol

2. Toxicological conceptsa) Acute or chronic effects

Acute effects are observed immediately or shortly after an exposure at one single occasion or multiple doses within 24 h.

Subacute effects means exposure during less than 1 month

Subchronic means exposure over 1-3 months

Chronic effects are the result of a continous exposure during at least 3 months

Time

2. Toxicological conceptsa) Acute or chronic effects

example:

acute effect: narcotic

chronic effect: leukemia

2. Toxicological conceptsb) Reversible or irreversible effects

Reversible effects disappear if the exposure stops

-example: narcotic effect of solvents

Irreversible effects never disappear

-example: damages to nerves, tumors

2. Toxicological conceptsc) Local or systemic effects

Local effects are observed on the part of the body that first came in contact with the chemical

example: acid burns

Systemic effects require tha the chemical is uptaken and distributed to the target organ

Target organs: central nervous systemcirculatory systemthe liverthe kidneysthe lungsthe skin

musclesbones

often

rarely

2. Toxicological conceptsd) Total effect

It is difficult to estimate the total effect of a mixture of chemicals!

2. Toxicological conceptsd) Total effectIndependent effect - two compounds are toxic independent of each other! ! ! ! 2 + 2 = 2Additive effect - the total effect is the sum of the the two independent effects example: toluene + xylene!! 2 + 2 = 4

Synergistic effect - the united effect is stronger than the additive effect example: ethanol + carbon tetrachloride 2 + 2 = 8

Potentiating effect - one of the compounds is not toxic in itself but enhance the effect of another compound ! ! 0 + 2 = 4example: 2-propanol + carbon tetrachloride

Antagonistic effect - one compound opposes the effect of another 2 + 2 = 1-functional: one raise blood pressure and one lowers it -chemical: two compounds neutralize each other -dispositional: one compound lowers the uptake of another -receptoric: the two compounds bind to the same receptor

It is difficult to estimate the total effect of a mixture of chemicals!

3. Toxicitya) Physical state

The purity of a compound is important to evaluate the toxicity (impurities can have very strong effects)

The physical state of a compound cam influence the toxicity: -vapor or aerosols are easily uptakne by the lungs -some solids are not easily dissolved and thus not toxic -finely ground arsenic oxide is much more toxic compared to granlulates -solution can be uptaken by the skin

example: mercury

3. Toxicityb) Exposure

The route of exposure is very important for the toxicity

intravenous (ivn) - injected in a vein

inhalated (ihl)

intraperitoneal (ipr) - injected in the peritoneal cavity subcutaneous (scu) - injected into the skin

oral (orl) - swallowed

dermal (d) - applied on the skin

3. Toxicityb) Exposure

3. Toxicityc) The victim

-Species-related differences

human???


-Sex-related differences! there are usually differences between males! and females

-Age-related differences! in general, infants (undeveloped systems) and! old people (poor immune system) are more! sensitive to toxic chemicals


-Individual-related differences!

a) Dose-response relationships

4. Acute toxicity

Number of deaths (%)!

log Dose log Dose

Sum of deaths (%)

LD50

4. Acute toxicitya) Dose-response relationships

!LD50 -the dose that will kill 50% of the exposed individualsLD10 -the dose that will kill 10% of the exposed individualsLDlow -the lowest dose known to cause deathLC50 -the concentration (mg/m3) that will kill 50% of the exposed individualsTDx -the dose that will give a toxic effect in X% of the exposed individuals

ex. LD50 = 25 mg/kg (or, rat)

economical and ethical issues (more than 100 animals for a normal test)

4. Acute toxicityb) specific toxicity

!

4. Acute toxicityc) non-specific toxicity -the toxicity is dependent on the lipophilicity

!

logP

toxicity

4. Acute toxicityd) selective toxicity -the toxicity is selective to one species or one organ example: penicillin, DDT!

5. Toxicological testing

!

5. Toxicological testingRisk assesment! -Comparison of the effects on different organisms (animals, cells....)

and men

! -Dose-response relationships

! -Weighing the risks against use, pleasure etc

!

5. Toxicological testingRisk assesment

!

6. Uptake and distributionuptake

distribution

excretion

gastro-intestinal

tract

skin lungs intravenous other(mucous

membranes)

faeces urine exhaled air secretion

circulatory system

liver

gall

kidney lung

bladder

portal vein

glands interstitial liquid

fat bone other tissue

6.1 By the skin

epidermis

dermis

blood vessels

Uptake of chemicals by the skin depends on:-the general condition (brusies etc)-the thickness (arms thin, palms thick) -the water content of the epidermis (gloves)

Many compounds enter easily by the skin (dichloromethane, methanol)

DMSO increase the permeability for other compounds (used in veterinary medicine)

6. Uptake and distribution

6.2 By the gastro-intestinal tract

mechanical degradation

chemical degradation

pH = 2

enzymatic degradation bacterial

degradation

Total surface 300 m2 (a tennis court)


6.2 By the gastro-intestinal tractThe absorption takes place in villi

Toxic compounds sometimes fit into transport systems

examples:

Some compounds pass through the system

example:

-thallium and cobalt fit into the iron transporter

-lead fit into the calcium transporter

-elemental mercury


6.3 By the lungs-100 m2 (a badminton court)-the exchange takes place in the alveoli where the distance between the blood and the air is only 1 μm


6.3 By the lungsAerosols are particles or droplets that are sufficientlysmall to hover in the air! Dust (solid particles)! Fume (particles formed by combustion)! Smoke (particles formed by combustion of! organic material)! Fog, mist (liquid droplets)! Smog (particles from car exhausts)


6.3 By the lungs

The uptake is dependent on size-small particles (< 1 μm) goes down in the alveoli and cancause e.g. silicosis or asbestosis-bigger particles are stopped in the mucus membranesand transported by the mucociliary escalator:


6.3 By the lungs

-Hydrophilic gases are usually absorbed by the mucusmembranes

-Very reactive gases (HCl, NH3, SO2) are irritating andblocks respiration and can therefore not be inhaled inlarger quantities

-Chemicals with intermediate reactivity and lipophilicity(phosgene, ozone, isocyanates) can be inhaled and giveinjuries at all levels in the lungsThey harm the epithelial cells (by lipid peroxidation) so thatthese are leaking fluid - pulmonary oedema (internaldrowning) which takes up to 48 h to develop


6.4 Bioaccumulation

Chemicals that are relatively stable and not rapidly converted may be absorbed by another organism that feeds on the first. (biomagnification)

example: polyhalogenated aromatic hydrocarbons (PCB)

Chemicals can be concentrated in organisms (bioconcentration) for example in fat


uptake

distribution

excretion

gastro-intestinal

tract

skin lungs intravenous other(mucous

membranes)

faeces urine exhaled air secretion

circulatory system

liver

gall

kidney lung

bladder

portal vein

glands interstitial liquid

fat bone other tissue


6.5 AccumulationAbsorbed compounds are distributed by the blood but aresometimes accumulated in target organs.

Brain, nerves, fatty tissue: lipophilic compounds

Bones: inorganic lead, barium, strontium, fluorine, tin

Liver: mercury vapour, manganese, organic lead

Kidneys: cadmium, mercury

Thyroid gland: iodine

Hair: Arsenic


6.6 Biological barriersThe endothelial cells of the blood capillaries in the brain are held together and are surrounded by glial cells. This makes the passage of compounds difficult and constitute the blood-brain barrier.

Problem: elemental mercury is lipophilic enough to pass the blood-brain barrier. If it is oxidized to Hg2+ it will not get out again...

The placenta regulates the flow of chemicals to the fetus


7. Metabolism - Phase I

Properties suitable for excretion of toxic compounds:

Is the compound useful in the normal metabolism?

If not, it has to be excreted in order not to be accumulated.

Low molecular weight Exhaled fromthe lungs

metabolism break bonds or converts functional groups




Molecular weight > 500 Excreted with the bile

the compound is conjugated with some endogenous compound





High water solubility Excreted with the urine

functional groups are converted or the compound is conjugated

with polar compounds


Biotransformation is not equal to detoxification!

The metabolism will effect the biological activity of a compound


Summary of important Phase I and Phase II reactions


8. Metabolism - Phase II8.1 Conjugation with sulfate

8.2 Conjugation with glucoronic acid8. Metabolism - Phase II

8.2 Conjugation with glucoronic acidDeconjugation

8. Metabolism - Phase II

8.3 Conjugation with amino acids8. Metabolism - Phase II

8.4 Conjugation with glutathione8. Metabolism - Phase II

9.1 By the lungs-volatile compounds are exhaled by the lungs

9. Excretion of chemicals

9.1 By the lungs-volatile compounds are exhaled by the lungs

9.2 By the liver-The liver metabolize compoundsSome compounds (e.g. mercury) are however excretedby bile which contains amphiphathic compounds suchas cholesterol and bile salts-The liver is the normal excretion way for compoundswith a molecular mass of more than 500 g/mol inhumans (lower for rats)-Compounds excreted by the liver can be uptaken bythe gastro-intestinal tract....


The kidneys is the most important excretion way

Some animals concentrate the urine (e.g. rats)


Milk is the major excretion way for DDT in breast-feeding women!

Cl Cl

ClClCl


• Electrophiles are very reactive and can destroy DNA


OO

smallrings

carbonyl-groups

isothiocyanates

NC

S


• We have a safety system


HO NH

HN

OHNH2

O O

O

OSH

glutation


• We have a safety system• Glutation


HO NH

HN

OHNH2

O O

O

OSH

glutation


• We have a safety system• Glutation


• ...and a warning system• TRPA1


• Isothiocyanates

OOH

HOHO OH

S NOSO3K

sinigrin


• Isothiocyanates

OOH

HOHO OH

S NOSO3K

sinigrin

NC

S

allylisotiocyanat


OOH

HOHO OH

S NOSO3K

sinigrin

NC

S

allylisotiocyanat

• Isothiocyanates


OOH

HOHO OH

S NOSO3K

sinigrin

NC

S

allylisotiocyanat

• Isothiocyanates


NC

S

S

6-metyltiohexyl-isotiocyanat

NC

S

allylisotiocyanat

• Isothiocyanates


• Carbonyl compounds



O

akrolein


kloracetofenon, CN(0.3-1.5 mg/m3)

OCl




OCl



• Carbonyl compounds• Teargas -developed to be irritating but rather safe


OCl


• Small rings• Mustard gas

very strong electrophile that affect the skin, eyesand the lungs







ClS

Clsenapsgas




ClS

Clsenapsgas

ClS

episulfoniumjon





• Mustard gas-0,02 mg can give blisters -severe damage on skin-humidity give worse effects-infections


“further development...”

ClAs

Cl

Cl

ClN

Clkvävesenapsgas

Cl

Lewisit


... but there is hope!

ClN

Clkvävesenapsgas

Cl

O

OHOHHO

OH NCl

Galactose 6-Mustard (G-6-M)

Cl


11. Specific examples11.1 Hexane and heptane

11.2 Benzene11. Specific examples

11.2 Benzene11. Specific examples

11.3 Hydroquinones11. Specific examples

11.4 Toluene11. Specific examples

11.5 Naphthalenes11. Specific examples

11.6 Styrene

good substrate for epoxide hydrolase

11. Specific examples

11.7 PAH (polycyclic aromatic hydrocarbons)

not a good substrate for epoxide hydrolase


11.8 Dichloromethane 11. Specific examples

11.8 Trichloroethylene 11. Specific examples

11.8 Trichloroethylene 11. Specific examples

11.9 Urethane 11. Specific examples

11.10 Acetonitrile 11. Specific examples

11.11 Aromatic amines 11. Specific examples

11.11 Aromatic amines

A-list! B-list!


11.12 Paracetamol

- limited amount of PAPS available for conjugation -more than a few grams a of paracetamol each day can give liver damage


11.13 N,N-dimethyl formamide 11. Specific examples

11.14 Dimethyl sulfoxide 11. Specific examples

11.15 Acidosis pH of the blood must be regulated to 7.35-7.40pH <7 or >8 is lethalthe blood is buffered and we can excrete CO2 in the lungs and acids with the urine


11.15 Acidosis

pKa = 3.8

pKa = 4.8

pKa = 1.2


11.15 Haemoglobin 11. Specific examples

11.16 Fluoroacetic acid 11. Specific examples

11.17 HCN 11. Specific examples

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