Lecture 2: Dose Response Curves and Bioassays Flashcards
_____: is the intrinsic toxic properties of a toxicant
or toxicant mixture
hazard
_____: is the probability of an adverse outcome based on the exposure to the
hazardous toxicant(s)
risk
T/F: Our perception of risk is often different than the truth
true! because we don’t differentiate between hazard/risk… like people are more afraid of plane crashes than car crashes
how do government regulations try to manage risks?
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)
_______ = characterization of the probability of potentially adverse health effects from human (or other animals!) exposures to hazardous agents
Risk assessment
______ = process by which policy actions are chosen to control hazards
Risk management
what are the four key steps of risk assessment?
hazard identification
dose-response assessment
exposure assessment
risk characterization
_______:
Do the chemicals/agents cause — or have the potential to cause —
adverse health effects?
hazard identification
how do we perform hazard identification? what tests can we use?
using epidemiology data, which is highly correlative
in vitro tests
structure activity modelling
animal bioassays
_______ = studies the patterns, causes, and effects of health and disease conditions in defined populations
Epidemiology
what is the main trouble with correlations?
Lots of things change together but may be completely unrelated… correlation does not equal causation!!!
when we use in vitro tests to identify hazards, what are we actually testing?
how cell cultures respond to exposure
why are Henrietta Lack’s cells so important in medical research?
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
how do we use structure activity modelling to identify hazard?
does a chemical look like a known toxicant!
this is a computerized method, where we look for structural similarities
how do we prove causation with bioassays when looking to identify hazard?
animals can show cause/effect relationship, can be done in vivo
A ______ is a quantitative estimation of the effect of a biologically active chemical, measured via some biological response under standardized conditions
bioassay
T/F: Bioassays are usually in a controlled laboratory setting, but sometimes done under
“natural” conditions (to mimic environmental conditions)
true!
what four types of mammals are used for bioassays?
rats, mice, guinea pigs, monkeys
what five types of fish are used for bioassays?
goldfish, fathead minnows, Japanese medaka, rainbow trout, zebrafish
what three types of invertebrates are used for bioassays?
water fleas (cladocerans), amphipods, bivalves
what are the three goals of toxicity testing?
- Determine the range of doses over which the
toxic responses are produced. - Identify the nature of the responses to a toxicant.
- Extrapolate these results for risk assessment analyses
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 _________
ecotoxicology
who is responsible for setting and maintaining standards for the ethical use and care of
animals in science in Canada since 1968?
CCAC: Canadian Council on Animal Care
what are the three R’s that Russel and Burch defined in 1959, which guide scientists on the ethical use of animals?
replacement, reduction, refinement
______: 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)
Replacement
________: experiments conducted using computer
simulations (e.g., models, simulations)
In silico
______: working with microorganisms, cells, or biological molecules outside
of their normal biological context (cells, tissues, or organoids in petri dishes)
In vitro
_______:
Use fewer animals to obtain sufficient data to answer the research question
(i.e., conduct a power analysis)
Reduction
whats another way we can reduce our use of animals in testing?
Can also maximize the information
obtained per animal (e.g. one animal can
contribute to multiple studies)
share animal parts with other researchers!
______: 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
Refinement
what are the five considerations for experimental design?
test group
variables
biological replicates
carriers
controls
______: what species, life stage/age class, and sex will
be studied?
experimental design
Test group
_______ 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
Response
Controlled
_______: There is natural variation among
individuals. Is the sample size adequate to detect an effect
of the treatment?
experimental design
Biological replicates
_______: used to dissolve hydrophobic compounds that will be used as experimental treatments
-examples: DMSO, ethanol, coconut oil are common carriers
experimental design
Carriers
______: required to compare to treatments to determine if
there was an effect. Includes negative controls, positive
controls, and carrier controls
experimental design
Controls
______ assessments quantify the relationships
between the exposure concentration (i.e., the dose) and a defined endpoint (i.e., the response)
Dose-Response
how do graphically represent dose-response assessments
by creating a dose-response curve
T/F: Endpoints can be whatever we are most interested in measuring (e.g., molecular, enzymatic, organismal, etc.)
true!
T/F: We tend to give the same amount of substance per unit of body weight in
bioassays (and pharmaceutical drug tests)
true!
T/F: The same amount of a toxicant can have a greater effect on smaller
individuals or organisms
true!
why do we standardize does to body weight when studying organisms?
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
T/F: Duration and Frequency of exposure VERY important for understanding the response in a test.
true!!!
what does acute exposure mean to toxicologists?
acute means hours to days
Acute toxicity tests for aquatic organisms are often exposures for days
what does chronic exposure mean to toxicologists?
months to years
T/F: we must CLEARLY state how long an individual was exposed to a toxicant
true! time is super important, as dose and frequency of exposure can change results significantly!
______ 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
Graded
they use a binary response (either yes or no)
_____ 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”
Quantal
measure % of population with certain binary response
why do we often use an endpoint of mortality?
because its easy to quantify! can just count how many individuals die at a given concentration
Can we use dose-response curves to compare relative
toxicity of toxicants?
yes! but we must use the SAME test conditions and test species to compare results
T/F: Toxicants can be ranked based upon their LD50s
true!
T/F: Dose-Response curves will change based on “route of exposure”
true! different injections have different levels of effectiveness, based on hoe fast they reach the blood
T/F: The speed of the response is related to how quickly a toxicant can
get into the bloodstream
true!!
what are the four different routes of exposure?
injection
inhalation
ingestion
dermal
T/F: if we look at the frequency distribution, it theoretically fits a normal
distribution
true
____: effective dose
where the drug is doing
what we want it to do
in 50% of the population
ED50
_____: toxic dose where
adverse effects start
happening in 50% of the
population
TD50
____: lethal dose in 50%
of the population
LD50
The ________ (TI) is the ratio of TD50/ED50
therapeutic index
what do high values of TI mean?
the drug is relatively safe
what do low values of TI mean?
should lead to the rejection of the drug from further clinical testing
_____ = the amount required to produce an effect of given intensity
Potency
look at x-axis
______ = refers to the maximum response achievable
Efficacy
look at y-axis
NOEC: _______
No Observable Effect Concentration
LOEC: ______
Lowest Observable Effect Concentration
what is a nominal concentration?
intended conc. we wanted to expose someone to
what is a measured concentration?
the conc. we actually measured in the subject
T/F: we can report either the nominal or measured concentration, but should specify which one we are reporting
true
______: Compounds that are beneficial/stimulatory at low doses, but toxic at high doses
hormesis
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.
sublethal response
we can conduct subchronic bioassays with lower doses!
what are the four reasons we may do a subchronic test?
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).
what is the MTD?
maximum tolerable dose, where there is no significant impairment of growth… slightly lower dose than lethality
what do we observe during a subchronic test? (2)
altered growth rate
behavioural changes
which we can use to develop biomarkers!
what do we observe AFTER a subchronic test? (2)
mass
blood chemistry
biochemical levels
cell membrane permeability
enzyme activity
organ/tissue damage
animals are usually euthanized and sampled against control group
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.
biomarker
what are five examples of common toxicology biomarkers?
enzyme activity
changes in cell receptor amount/activity
changes in hormone levels
increased/decreased gene expression
changes in cell structure
Can conduct a ______ bioassay to look at longer-term endpoints like cancer development (up to years)
chronic
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
true!
because its not required, there’s lack of funds/people/facilities, its EXPENSIVE, difficult to test
T/F: Commercial chemicals are considered innocent until proven guilty.
Pharmaceuticals are tested though
true
if governments don’t perform many toxicity tests anymore, who is conducting these tests?
the industries… which def aren’t giving super reliable results
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?
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
