1. What is the difference between an internal and external dose?
Nina - internal: what has been absorbed by body, conc in blood/urine, dont know external
external: measure in air/water/food that could lead to human exposure, never sure this is actual
exposure level of individual/group of ppl, dont know how much filtered out by body,. easy to
2. What is the difference between inhalation and intratracheal instillation of
nanoparticles, and how could these animal experiments result in different toxicity for the
Ed: Inhalation is from the surrounding environment - similar to what Nina said above, it is the
external environment which makes the concentration impossible to figure out (that the specimen
will receive). Intratracheal instillation is a very controlled method to ensure that the dose
reaching the specimens lung is known. these experimental results will vary as the
concentration being injected through instillation maybe higher than if the animal were to inhale it
(if it inhales any).
Also, intratracheal may omit some extra translocation routes (olfactory bulb in nose goes
straight to brain), + having your agent dispersed in air may induce extra chemical modification -
3. Explain how non-cancerous substances result in a threshold below which there
doesnt seem to be any adverse effects observed.
The bodys defence(s) will be able to remove an amount of the foreign substances naturally.
Examples are such as the cilia in ones lungs that will actively remove foreign substances that
have enter the trachea. Therefore, below the threshold, the body would actually be able to
remove these foreign substances.
4. What is it about the subjects that react to very low doses of materials?
Nina: susceptible subgroup
Andrew: Certain species have a tumor suppressing gene inactivated that leads to greater
5. What is an LD50?
- The dose required to kill 50% of the tested population within a specified time period.
6. How is determining a LOAEL different than determining an LD50? The lowest-observed-adverse-effect level is the lowest concentration or amount of a
substance found by experiment/observation which causes an adverse alteration of morphology,
function, capacity, growth, development or life span of a target organism distinguished from
normal organisms of the same species under defined conditions of exposure.
- For LOAEL, must have a concentration tested that shows the effects with another that shows
that the substance is safe. At LD50, the death rate is 50%
LOAEL is strictly an empirical/experimental dose. I think LD50 can technically be extrapolated -
7. Since nanoparticles translocate, explain how this process could occur.
Nina - particles not detected by macrophage in lungs could translocate thru alveolar membranes
into general circulation and into vital organs
8. Explain genotoxicity, mutagenicity, and carcinogenity and the different tests done to
Genotoxicity: damage to DNA which can cause mutation (and potentially tumour initiation) if not
Mutagenicity: permanent alteration to DNA (happens after replication cycle), there is a wrong
base inserted or a base is added or removed
Ames test - assay where you starve to cultures of excessive nutrient. Then expose one to
mutagen. Incubate, if mutagenics then many colonys will form due to mutations. - vic
Carcinogenicity: damage to genetic information leads to tumor formation (multistage process
with initiation, promotion and progression)
How to identify a genotoxin: If there is a DNA damage but no breaks, can treat with repair
enzymes that cleave at the site of damage, then look at the DNA migration using Comet Assay
(Single Cell Gel Electrophoresis). In Comet Assay, broken DNA strands migrate more readily
than tightly coiled DNA.
Comet Assay: The image analysis mea stronger the signal from the migrated DNA the
more damage there is present. The overall structure resembles a comet (hence "comet assay")
with a circular head corresponding to the undamaged DNA that remains in the cavity and a tail
of damaged DNA. The brighter and longer the tail, the higher the level of damage.
9. Specifically how a transition A to G mutation occurs? Can someone explain this?
Mutations associated with SWCNTs
the main difference between the two sets of base pairs is the number of hydrogen bonds and
the length of the pair. If G is damaged it can bind improperly and link to T instead of C, which
will cause A to appear when the strand containing T is replicated.
Damon: Oxidation can cause a guanine to be replaced by an adenine. The result can be an
AGU codon instead of GGU, leading to glycine instead of serine in transcribed protein.
10. What is the difference between a point and frameshift mutation?
Ippy: A point mutation changes one nucleotide, ends up probably only one amino acid will get
coded differently. Can screw up your protein folding. Possible that it becomes silent, since
multiple codons can code for the same amino acid, causing no overall change. A frameshift
mutation is the addition (or subtraction) of a nucleotide, ends up changing everything from that
point onwards along the DNA strand. Very likely to screw up your entire protein.
11. Carbon nanotubes are known to cause oxidative stress. Explain what this means and
show reactions that could be implicated.
Oxidative stress means that a lot of OH free radicals are produced; this can lead to DNA strands
breaking, protein oxidation, lipid peroxidation
12. Explain how some substances, such as arsenic, are known human carcinogens but
are not mutagens.
Many mutagens are also carcinogens, but some carcinogens are not mutagens. Examples of
carcinogens that are not mutagens include alcohol and estrogen. These are thought to promote
cancers through their stimulating effect on the rate of cell mitosis. Faster rates of mitosis increasingly leave fewer opportunities for repair enzymes to repair damaged DNA during DNA
replication, increasing the likelihood of a genetic mistake. A mistake made during mitosis can
lead to the daughter cells' receiving the wrong number of chromosomes, which leads to
aneuploidy and may lead to cancer
Carcinogenic promoter? + Chromosomal effects? carcinogen benzene, As, dioxin,
Non-genotoxic carcinogens: agents that increase the rates of tumor formation by promoting cell
Initiated cell expands into a visible tumor (benign lesion)
Can be reversible; promoter is affecting gene expression by binding to certain
Promoter inhibits apoptosis
Formation of a malignant tumor
Increased growth rates
Suppressed contact inhibition
Irreversible mutation of a benign lesion
Progressor inhibits DNA repair mechanisms
13. Explain what the octanol-water partition coefficient tells you about how the
nanoparticles interact with animals/humans.
Octanol simulates lipids (body fat) so basically how much will be taken into the lipids compared
to what will stay in aqueous solution. Has to do primarily with bioaccumulation and translation
through cells (dermal exposure)
High K_OW = partitions into lipids, so high bioaccumulation (long term biomagnification risk)
High K_AW = highly volatile, risk of aerosol exposure (acute dose risk)
Exposure Assessment and Risk:
1. List the nanomaterial physical properties generally thought to be important with
respect to human toxicity.
Nina - surface area, size, size distribution, particle number, dry/dissolved in media, shape
(length), aggregation state, chemical composition, surface coating, reactivity, purity
Added: charge, radical generating ability, catalytic activity
2. Define acute and chronic exposure
acute is single exposure, chronic is consistent exposure.
Acute is exposure that occurs over a period of less than 24 hours. Chronic is exposure that
occurs over a period of time greater than three months