Lecture 2: Dose Response Curves and Bioassays

Question 1

_____: is the intrinsic toxic properties of a toxicant
or toxicant mixture

Answer 1

hazard

Question 2

_____: is the probability of an adverse outcome based on the exposure to the
hazardous toxicant(s)

Answer 2

risk

Question 3

T/F: Our perception of risk is often different than the truth

Answer 3

true! because we don’t differentiate between hazard/risk… like people are more afraid of plane crashes than car crashes

Question 4

how do government regulations try to manage risks?

Answer 4

Governmental regulations try to manage the risks, either by reducing the hazard
(i.e., banning toxicants) or reducing the risks (decreasing the probability of an
adverse outcome)

Question 5

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

Answer 5

Risk assessment

Question 6

______ = process by which policy actions are chosen to control hazards

Answer 6

Risk management

Question 7

what are the four key steps of risk assessment?

Answer 7

hazard identification
dose-response assessment
exposure assessment
risk characterization

Question 8

_______:
Do the chemicals/agents cause — or have the potential to cause —
adverse health effects?

Answer 8

hazard identification

Question 9

how do we perform hazard identification? what tests can we use?

Answer 9

using epidemiology data, which is highly correlative

in vitro tests

structure activity modelling

animal bioassays

Question 10

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

Answer 10

Epidemiology

Question 11

what is the main trouble with correlations?

Answer 11

Lots of things change together but may be completely unrelated… correlation does not equal causation!!!

Question 12

when we use in vitro tests to identify hazards, what are we actually testing?

Answer 12

how cell cultures respond to exposure

Question 13

why are Henrietta Lack’s cells so important in medical research?

Answer 13

she had an immortal cell line! so we can use them for various tests and never lose them! they were crucial for developing a polio vaccine

Question 14

how do we use structure activity modelling to identify hazard?

Answer 14

does a chemical look like a known toxicant!

this is a computerized method, where we look for structural similarities

Question 15

how do we prove causation with bioassays when looking to identify hazard?

Answer 15

animals can show cause/effect relationship, can be done in vivo

Question 16

A ______ is a quantitative estimation of the effect of a biologically active chemical, measured via some biological response under standardized conditions

Answer 16

bioassay

Question 17

T/F: Bioassays are usually in a controlled laboratory setting, but sometimes done under
“natural” conditions (to mimic environmental conditions)

Answer 17

true!

Question 18

what four types of mammals are used for bioassays?

Answer 18

rats, mice, guinea pigs, monkeys

Question 19

what five types of fish are used for bioassays?

Answer 19

goldfish, fathead minnows, Japanese medaka, rainbow trout, zebrafish

Question 20

what three types of invertebrates are used for bioassays?

Answer 20

water fleas (cladocerans), amphipods, bivalves

Question 21

what are the three goals of toxicity testing?

Answer 21

1. Determine the range of doses over which the
   toxic responses are produced.
2. Identify the nature of the responses to a toxicant.
3. Extrapolate these results for risk assessment analyses

Question 22

Determine of the most sensitive species or life stage for a bunch of organisms.

Compare effects of different toxicants on a single organism.

Compare effects of other environmental factors that modify the effects of the toxicant.
- temperature.
- air quality.

Determine the maximum level of a toxicant that may occur in the environment without causing biological change.

these are all examples of uses of bioassays in _________

Answer 22

ecotoxicology

Question 23

who is responsible for setting and maintaining standards for the ethical use and care of
animals in science in Canada since 1968?

Answer 23

CCAC: Canadian Council on Animal Care

Question 24

what are the three R’s that Russel and Burch defined in 1959, which guide scientists on the ethical use of animals?

Answer 24

replacement, reduction, refinement

Question 25

______: avoid or replace the use of animals - Use in silico or in vitro assays instead - Replace with animal with lower potential for pain - (e.g., C.elegans, Drosophila)

Answer 25

Replacement

Question 26

________: experiments conducted using computer simulations (e.g., models, simulations)

Answer 26

In silico

Question 27

______: working with microorganisms, cells, or biological molecules outside of their normal biological context (cells, tissues, or organoids in petri dishes)

Answer 27

In vitro

Question 28

_______: Use fewer animals to obtain sufficient data to answer the research question (i.e., conduct a power analysis)

Answer 28

Reduction

Question 29

whats another way we can reduce our use of animals in testing?

Answer 29

Can also maximize the information obtained per animal (e.g. one animal can contribute to multiple studies) share animal parts with other researchers!

Question 30

______: modification of husbandry or experimental procedures to minimize the pain and distress experienced by an animal Some examples: - use of anesthesia prior to invasive procedure - increasing the complexity of social and physical environments

Answer 30

Refinement

Question 31

what are the five considerations for experimental design?

Answer 31

test group variables biological replicates carriers controls

Question 32

______: what species, life stage/age class, and sex will be studied? experimental design

Answer 32

Test group

Question 33

_______ variable – What endpoint or biomarker will you measure? _______ variables – Identify all potential variables, and control or vary them appropriately. Can control for variables by keeping them constant, or indirectly by using randomization. experimental design

Answer 33

Response Controlled

Question 34

_______: There is natural variation among individuals. Is the sample size adequate to detect an effect of the treatment? experimental design

Answer 34

Biological replicates

Question 35

_______: used to dissolve hydrophobic compounds that will be used as experimental treatments -examples: DMSO, ethanol, coconut oil are common carriers experimental design

Answer 35

Carriers

Question 36

______: required to compare to treatments to determine if there was an effect. Includes negative controls, positive controls, and carrier controls experimental design

Answer 36

Controls

Question 37

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

Answer 37

Dose-Response

Question 38

how do graphically represent dose-response assessments

Answer 38

by creating a dose-response curve

Question 39

T/F: Endpoints can be whatever we are most interested in measuring (e.g., molecular, enzymatic, organismal, etc.)

Answer 39

true!

Question 40

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

Answer 40

true!

Question 41

T/F: The same amount of a toxicant can have a greater effect on smaller individuals or organisms

Answer 41

true!

Question 42

why do we standardize does to body weight when studying organisms?

Answer 42

because the same amount of a toxicant can have a greater effect on smaller individuals or organisms... we have to account for differences in weight

Question 43

T/F: Duration and Frequency of exposure VERY important for understanding the response in a test.

Answer 43

true!!!

Question 44

what does acute exposure mean to toxicologists?

Answer 44

acute means hours to days Acute toxicity tests for aquatic organisms are often exposures for days

Question 45

what does chronic exposure mean to toxicologists?

Answer 45

months to years

Question 46

T/F: we must CLEARLY state how long an individual was exposed to a toxicant

Answer 46

true! time is super important, as dose and frequency of exposure can change results significantly!

Question 47

______ dose-response relationships use a continuous variable and occur in a single individual. They are characterized by a dose-related increase in the severity of the response

Answer 47

Graded they use a binary response (either yes or no)

Question 48

_____ dose–response relationships occur in a “population” * At a given dose, an individual in the population is classified as either a “responder” or a “non-responder”

Answer 48

Quantal measure % of population with certain binary response

Question 49

why do we often use an endpoint of mortality?

Answer 49

because its easy to quantify! can just count how many individuals die at a given concentration

Question 50

Can we use dose-response curves to compare relative toxicity of toxicants?

Answer 50

yes! but we must use the SAME test conditions and test species to compare results

Question 51

T/F: Toxicants can be ranked based upon their LD50s

Answer 51

true!

Question 52

T/F: Dose-Response curves will change based on “route of exposure”

Answer 52

true! different injections have different levels of effectiveness, based on hoe fast they reach the blood

Question 53

T/F: The speed of the response is related to how quickly a toxicant can get into the bloodstream

Answer 53

true!!

Question 54

what are the four different routes of exposure?

Answer 54

injection inhalation ingestion dermal

Question 55

T/F: if we look at the frequency distribution, it theoretically fits a normal distribution

Answer 55

true

Question 56

____: effective dose where the drug is doing what we want it to do in 50% of the population

Answer 56

ED50

Question 57

_____: toxic dose where adverse effects start happening in 50% of the population

Answer 57

TD50

Question 58

____: lethal dose in 50% of the population

Answer 58

LD50

Question 59

The ________ (TI) is the ratio of TD50/ED50

Answer 59

therapeutic index

Question 60

what do high values of TI mean?

Answer 60

the drug is relatively safe

Question 61

what do low values of TI mean?

Answer 61

should lead to the rejection of the drug from further clinical testing

Question 62

_____ = the amount required to produce an effect of given intensity

Answer 62

Potency look at x-axis

Question 63

______ = refers to the maximum response achievable

Answer 63

Efficacy look at y-axis

Question 64

NOEC: _______

Answer 64

No Observable Effect Concentration

Question 65

LOEC: ______

Answer 65

Lowest Observable Effect Concentration

Question 66

what is a nominal concentration?

Answer 66

intended conc. we wanted to expose someone to

Question 67

what is a measured concentration?

Answer 67

the conc. we actually measured in the subject

Question 68

T/F: we can report either the nominal or measured concentration, but should specify which one we are reporting

Answer 68

true

Question 69

______: Compounds that are beneficial/stimulatory at low doses, but toxic at high doses

Answer 69

hormesis

Question 70

A _______ refers to an effect of a toxic substance on an organism that does not result in death but still causes harmful or disruptive changes to the organism's normal biological functions.

Answer 70

sublethal response we can conduct subchronic bioassays with lower doses!

Question 71

what are the four reasons we may do a subchronic test?

Answer 71

To provide information on all types of sublethal toxicity (except carcinogenicity) that might occur. – immunotoxicity, neurotoxicity. To establish dose regimens for chronic studies. Provide data which will allow an estimate to be made of the MTD, where there is no significant impairment of growth. To develop biomarkers of exposure (e.g., gene expression, specific enzyme function).

Question 72

what is the MTD?

Answer 72

maximum tolerable dose, where there is no significant impairment of growth... slightly lower dose than lethality

Question 73

what do we observe during a subchronic test? (2)

Answer 73

altered growth rate behavioural changes which we can use to develop biomarkers!

Question 74

what do we observe AFTER a subchronic test? (2)

Answer 74

mass blood chemistry biochemical levels cell membrane permeability enzyme activity organ/tissue damage animals are usually euthanized and sampled against control group

Question 75

For the purpose of this course, a ______ can be described as a cellular or biochemical response to a toxicant that is measurable in a biological system or sample.

Answer 75

biomarker

Question 76

what are five examples of common toxicology biomarkers?

Answer 76

enzyme activity changes in cell receptor amount/activity changes in hormone levels increased/decreased gene expression changes in cell structure

Question 77

Can conduct a ______ bioassay to look at longer-term endpoints like cancer development (up to years)

Answer 77

chronic

Question 78

T/F: U.S. National Academy of Sciences estimates that only 10% of the 80,000 chemicals in commercial use have been tested for toxicity

Answer 78

true! because its not required, there's lack of funds/people/facilities, its EXPENSIVE, difficult to test

Question 79

T/F: Commercial chemicals are considered innocent until proven guilty. Pharmaceuticals are tested though

Answer 79

true

Question 80

if governments don't perform many toxicity tests anymore, who is conducting these tests?

Answer 80

the industries... which def aren't giving super reliable results

Question 81

Rofecoxib (trade name Vioxx) is a non-steroidal anti-inflammatory drug (NSAID) that was produced by Merck Pharmaceuticals starting in 1999. why was it pulled from market?

Answer 81

after taking the drug consistently for 1.5 years, it caused heart failure in some people... in 2004 over half of the heart attacks in the US were from this drug... 44 000 cases were fatal in one year Merck knew this in 2001 when they finally did chronic trials, but hid the information until 2004 this is a prime example of regulatory breakdown