Lecture 3: Dose Response

Question 1

Hazard

Answer 1

as defined in North America, is the intrinsic toxic properties of a toxicant or toxicant mixture.

• Everything is toxic everything is a hazard- Dose is important
• Whatever the compound is- copper etc
• Referring to the toxic properties of that compound

Question 2

Risk

Answer 2

is the probability of an adverse outcome(biological response we are looking for) based on the exposure to the hazardous toxicant(s).

Question 3

Ex of a risk

Answer 3

Smoking: cigarette smoke is a hazard. If you do not smoke, the risk of adverse outcomes from inhaling tobacco smoke is much less for you

Illicit drugs are an example too (heroin, fentanyl, bath salts).
- If you dont take drugs the risk of adverse outcomes is low

Ivermectin for COVID symptoms
- Ivermectin; Deworming for animals

Question 4

i

Answer 4

Our perception of risk is often different than the truth
– General public doesn’t always understand probability – Think of shark attacks; very low risk of shark attacks but as a society we have trouble understanding the probability behind this

Question 5

How do governments manage risks?

Answer 5

Governmental regulations try to manage the risks, either by reducing the hazard (i.e., banning toxicants, legacy pollutants is an ex of this) or reducing the risks (decreasing the probability of an adverse outcome, wearing masks social distancing ).

Question 6

Risk assessment

Answer 6

characterization of the probability of potentially adverse health effects from human (or other animals!) exposures to hazardous agents.

• Identify compound and see if it can actually have some sort of adverse effect
• What concentrations lead to these affects
• How long do we need to be exposed to get these effects
• Types of exposures

Question 7

What are the 1st steps taken to figure out if a toxicant is harmful

Answer 7

Standard hazard identification and dose response assessments are usually 1st things you do when trying to figure out if a toxicant is actually harmful

Question 8

Risk management

Answer 8

process by which policy actions are chosen to control hazards.

Policy for helping general public

Question 9

Hazard Identification

Answer 9

Do the chemicals/agents cause — or have the potential to cause adverse health affects?

We need to identify what are potential hazards

Question 10

How are determined?

Answer 10

Epidemiology data (highly correlative)

Epidemiology- studies the patterns, causes, and effects of health and disease conditions in defined populations.

Can ask question like: does living close to a nuclear power plant increase your risk of developing cancer? Is living in Wpg more statistically likely to have a certain disease?(This stuff is highly correlative)

Often the best we can do for human studies…
We don’t do human testing so this is best we can do

Question 11

Epidemiology

Answer 11

studies the patterns, causes, and effects of health and disease conditions in defined populations.

Question 12

correlation

Answer 12

A “real” correlation is a statistical test that tells you whether two variables are changing together.

do not say “correlation” unless you have the stats to back it up!

This is NOT a cause and effect relationship! Correlation does not indicate causation!

-correlation is just telling us if 2 variables are changing in the same way

Positive- x and y both increase
Negative- x increases and y decreases

Question 13

What is the trouble with correlations?.

Answer 13

spurious correlations)
• Lots of things change together but may be completely unrelated(Lots of things are correlated but not related- no cause-and-effect relationship )

• Saying some vaccines cause autism is equally ridiculous
• As temp goes up the number of pirates decrease- no way are these 2 things are related – not a cause and effect but forms a nice negative relationship

Question 14

What is another way to do hazard identification?

Answer 14

In vitro tests (e.g., test how cell cultures respond to exposure) – e.g., HeLa cells

Henrietta Lack’s cells – her cells are immortal.
The same cell line has continued for decades
An immortal cell line, used A LOT in medical research
Crucial for developing a polio vaccine.

Question 15

Give an ex of cell lines grown in lab

Answer 15

Hormones receptors in a cell are well conserved across a species and a cell line they can be grown in a lab and exposed to certain compounds and see if they are bound to certain receptors and see if that lead to a change in gene expression

Question 16

What are 2 other ways to do hazard identification?

Answer 16

Structure activity modeling (do chemical look like a known toxicant?)

• Edcs are very common, mimic estrogen
• This can be because they have structural similarities that allow them to bind to the estrogen receptor (BPA has similar structure to estrogen)
• If they can bind to the estrogen receptor they can mimic the same effect of 17 beta estradiol(functional estrogen in the body)

Testing (bioassay) data -use organism to see if the compounds elicit a biological effect
- Animal testing

Question 17

bioassay experiments

Answer 17

One way to prove causation

Can be done on live animals (in vivo)

Question 18

What is a bioassay?

Answer 18

a quantitative estimation of the intensity or concentration of a biologically active chemical, measured via some biological response under standardized conditions. (how much of a compound we need to be exposed to, to elicit a biological response)

Question 19

What is a very important thing that needs to be done when conducting bioassays?

Answer 19

Very important thing is it is done under standardized conditions, if we want to be able to make comparisons between different species , toxicants we need to make sure the methodology is the same then we can make direct comparisons if not done in exact same conditions then you cant compare

Question 20

Where are bioassays done?

Answer 20

are usually done in a controlled laboratory setting (controlled environment)but they are sometimes done under “natural” conditions (to mimic environmental conditions).

Question 21

Give a basic description of how bioassays are conducted

Answer 21

Basically we expose animals to toxicants and measure what the effect is in a controlled setting.

Metaphorical and literal lab rats…

Main things that’s done for hazard identification and risk assessment

Question 22

List common animals used in bioassays

Answer 22

mammals- rats, mice, guinea pigs, monkeys

fish- goldfish, fathead minnows, japanese medaka, rainbow trout, zebrafish

invertebrates- cladocerans (water fleas , daphnia), amphipods, oysters

Question 23

Describe why fish are used for toxicity testing

Answer 23

zebrafish; model species for many things, used in developmental studies because vertebrates’ function very similarly to humans, many of our hormones and cell functions are the same (toxicological tests can be done on fish and they will be relevant to humans)

Question 24

Invertebrate testing__________

Answer 24

is for looking at effects of environment

Question 25

What are the goals of toxicity testing?

Answer 25

1. Determine the range of doses over which the toxic responses are produced.
2. Identify the nature of the responses to a toxicant. (figure out what type of biological responses will occur once exposed to these toxicants)
3. Extrapolate these results for risk assessment analyses for human exposure.

Question 26

What are the uses of bioassays in environmental toxicology?

Answer 26

1. Determine of the most sensitive species or life stage for a bunch of organisms.
2. Compare effects of different toxicants on a single organism.
   - Daphnia- model species
3. Compare effects of other environmental factors that modify the effects of the toxicant.
   - temperature
   - air quality
4. Determine the maximum level of a toxicant that may occur in the environment without causing biological change. (max concentration that doesn’t actually lead to a biological effect)

Question 27

Dose-Response assessments

Answer 27

quantify the relationships between the exposure concentration (i.e., the dose) and a defined endpoint (i.e., the response).

• Often represented graphically – a dose-response curve
• Fundamental concept in toxicology
• Often the first step in toxicity testing

Question 28

Endpoints

Answer 28

can be whatever we are most interested in measuring (e.g., molecular, enzymatic, organismal, etc.)

• endpoint; changes in expression of genes, changes in hormone level, animal dying)

Question 29

adverse outcome pathways

Answer 29

So many steps along the way and any of those steps could be incorporated into a dose response relationship

Question 30

i

Answer 30

We find out something is hazardous start off by doing this dose response relationships usually using mortality as the end point

RMBR: A dose response curve can be produced using whatever endpoint we are interested in

Question 31

What do we mean by dose?

Answer 31

We tend to give the same amount of substance per unit of body weight in bioassays (and pharmaceutical drug tests) (standardize the amount )

The same amount of a toxicant can have a greater effect on smaller individuals or organisms
• give 80 mg of a toxicant to an 80 kg adult…a dose of 1mg/kg
give 80 mg to a 8 kg child… that child is dosed at 10 mg/kg (dose is 10x times higher)
- Size becomes important when looking at how much dose an individual receives

• This is why we standardize doses to body weight when studying organisms!
Always want to make sure we are all taking same dose
Do this to make data comparable

Question 32

Acute exposure

Answer 32

means different things to different people…

– Physiologists: acute is minutes to hours

– Toxicologists: acute is hours to days (i.e., 24-96 hrs) • Acute toxicity tests for aquatic organisms are often exposures for days

Tend to lead to higher concentrations that lead to adverse outcomes when comparing with chronic exposures

Question 33

Chronic exposure

Answer 33

means different things to different people… - - Physiologists: chronic is weeks to months – Toxicologists: chronic is months to years

Question 34

lethal concentration (LC50) or lethal dose (LD50).

Answer 34

If we did an acute toxicity test and measured what concentration would kill (endpoint) 50% of the individuals in 96 hrs.-

Question 35

Graded dose-response relationships

Answer 35

use a continuous variable and occur in a single individual. They are characterized by a dose- related increase in the severity of the response. (effects of the same person for diff concentration)

• Examples:
– enzyme inhibition (pictured)
– changes in blood hormone levels

Question 36

Quantal dose–response relationships

Answer 36

occur in a “population” (effects over many people, different concentrations affecting diff individuals)

At a given dose, an individual in the population is classified as either a “responder” or a “non-responder”.

Question 37

Why are Duration and Frequency of exposure VERY important for understanding the response in a test?

Answer 37

Duration and Frequency of exposure VERY important for understanding the response in a test.
This is why we must clearly state how long an individual was exposed to a toxicant (our bodies have a remarkable ability to handle acute exposures we can get exposed to things and recover from them easily but if exposed to them over a chronic period that can start to lead to adverse outcomes)- the dose we need to receive to have that adverse outcome is usually lower over a chronic exposure compared to an acute exposure

Question 38

What is usually used as the end point

Answer 38

endpoint is mortality (easy to quantify…)

Count how many individuals die (i.e., respond) in your experiment at a given concentration

Example of a quantal dose-response relationship

Question 39

What does the dose response curve look like

Answer 39

Curve is often sigmoidal

Question 40

What can dose-response curves be used for?

Answer 40

Can use dose-response curves to compare relative toxicity of toxicants.
We must use the same test conditions and test species for this to be comparable.

Answer 41

UNLESS YOU SEE SOMETHING INDICATING A DIFFERENT METRIC WAS USED FOR COMPARING TOXICITY THEN YOU CAN ASSUME LD50 WAS USED

Question 42

Which is more toxic a compound with a high LD50 or low LD50?

Answer 42

compound that has the lowest LD50 is considered more toxic

THE EXPERIMENTAL CONDIITONS NEED TO BE STANDARDIZED IN ORDER TO BE COMPARABLE

Question 43

What are dose response curves and LD50s used for?

Answer 43

DOSE RESPONSE AND LD50S ARE USED TO COMPARE THE RELATIVE TOXICITY BETWEEN DIFFERENT COMPOUNDS

Question 44

What do Dose-Response curves change based on?

Answer 44

will change based on “route of exposure”

– Injection(right into blood reaches target tissue faster), Inhalation (breathing in picked up by the lungs and circulating body), Ingestion(broken down by stomach absorbed by intestine broken down by liver then general circulation), Dermal (in order of effectiveness)

The speed of the response is related to how quickly a toxicant can get into the bloodstream.

Question 45

what is the rule of thumb for route of exposure

Answer 45

The faster the compound can get into your blood and start circulating in your body the faster it can reach its target tissues and the faster it can elicit its effect

RULE OF THUMB: THE FASTER SOMETHING CAN GET INTO GENERAL CIRCULATION, THE FASTER IT WILL LEAD TO SOME EFFECT (DIRECT INJECTION INTO BLOOD CAN LEAD TO A LOWER LD50 BECAUSE ITS GETTING INTO GENERAL CIRCULATION FASTER