(10) Feb 11.pdf
Transcript of (10) Feb 11.pdf
Biomarkers
Biochemical, physiological or histological changes
in organisms that are can be used to estimate either
exposure to chemicals or resultant effects
Behavioural changes??
Current emphasis is on Early Warning indicators of
stress at higher levels of organization
- individual
- population
- community
Two most relevant biomonitoring tools are relevant to:
1) Detoxification or adaptive responses
2) Reproductive effects
Biomarkers
A special type of endpoint
van der Oost R, Beyer J, Vermeulen NPE. 2003 Fish bioaccumulation and biomarkers in environmental risk assessment: a review. Environmental Toxicology and Pharmacology 13(2):57-149.
Advantages of Biomarkers
1) Rapid results
2) Subpopulation can be sampled
- vs. large scale population # monitoring
3) most yield info regarding actual toxic
mechanisms
Disadvantages of Biomarkers
1) Predicative capabilities are tenuous
2) Limited by data regarding “normal”
levels
3) lack of understanding by public and
funders
Criteria for Effective Biomarkers
1) General Specificity
Does the marker respond to one chemical
or is it a general indicator of stress?
Specific markers are more useful for
determining exposure to specific chemicals
but general markers are better for overall
health assessment.
2) Sensitivity
How sensitive is the marker in responding
to stress compared with traditional
measures of health? Eg. Condition Factor
Are there more sensitive biomarkers avail.
that are more predictive than the proposed
marker?
Criteria Cont’d
3) Biological Specificity
Is the marker responsive in just one type of
organisms or can it be used in other species?
Eg. MFO enzymes re not applicable to
molluscs since they metabolize organics
by a separate pathway (MFOs- Consider Later)
4) Interpretation
Can the results easily be interpreted? Are
they easily separated from natural
variation?
5) Timeline
The marker has to respond in a reasonably
short timeframe to be useful as a predictive
tool.
Criteria Cont’d
6) Permanence of Response
Is the response reversible? Is so, how
quickly?
Reversible = useful for establishing cause
and effect (eg. plasma ions)
Permanent = useful for establishing
exposure (eg. cancer)
7) Variability
Does the marker respond similarly in
individuals? What is the range of the
response? How does it compare to
natural variability of the parameter?
2 sources of variability
a) Physiological
Depends on the range of biological
responses exhibited by organisms.
b) Environmental
Variability due to the effects of
external factors. Eg. Ambient temp.
7) Variability cont’d
Criteria Cont’d
8) Linkage to higher levels of organization
Have to be able to answer “So what?”
question.
In early stages of development these
may be less clear…….
Criteria Cont’d
9) Applicability to the Field
Collection techniques, sample prep, and
even interpretation must be easily
transferred.
10) Validation in the Field
Ideally, the marker should have been
tested in wild populations.
11) Methodologies
Important to consider the analytical ease
and cost of using the biomarker and to
note the precision of the assay
(Precision = analytical reproducibility)
1) MFO Enzymes
Mixed Function Oxidases or Mixed Funtion
Oxygenases also called CYP1A (Cytochrome P450
Family 1A)
Group of enzymes that metabolize several different
endogenous and exogenous compounds
10 Different Families in Mammals, >3
in fish and birds
Eg. Fatty acids, steroids, lipids, alcohol
and some contaminants
Activity expressed constitutively at a very low level
Found to respond to coplanar organochlorines
Coplanar Organochlorines
1) PCBs (Polychlorinated Biphenyls)
Cl
Cl
Cl
Cl
Ortho Position
- Cl here does not
favour co-planarity
Binding to Ah Binding to Ah Receptor Receptor
Induction of MFO Enzymes
Binding of Coplanar Organochlorines
To the Ah-Receptor
Translocation
to nucleus
Binding to gene
responsive element
MFO Enzymes As Biomarkers
Data available for variability due to:
sex, season, reproductive cycle,
temperature, handling stress,
dietary effects
BUT………
Links between MFO induction and population
level effects still weak.
Some evidence to suggest induction
is linked to inhibited reproduction, slower
growth and impaired reproduction.
2) Metallothionein
Low molecular weight protein (6-7 kDaltons) with
high cysteine content (30%)
Binds Group IB and IIB metals
Metallothionein cont’d
Each domain can bind different metals at one time
Affinity in the order:
Hg>Ag=Cu>Cd>Zn
But stoichiometry
7 for Hg, Cd, Zn
12 for Cu
12, 17 or 18 for Ag
Found in many aquatic organisms and all
vertebrates studied thus far…..also some inverts
Metallothionein cont’d
Also thought to function in the regulation of
toxicity of metals
2 lines of evidence:
1) Induced tolerance
- organisms pre-exposed to low
concentrations of metals have
greater tolerance for subsequent
exposures
2) Genetic Manipulations
- organisms with inhibited or
enhanced MTN expression have
either greater or lesser susceptibility
to metal toxicity
Metallothionein cont’d
Spillover Hypothesis:
Toxic effects of certain metals begins only
after the binding capacity of MTN is
exceeded.
At that point toxic metals “spill over” to
interact toxically with cellular constituents
Metallothionein cont’d
Other factors affecting MTN:
1) Physiological
developmental state, dietary Zn,
starvation, stress
Reproduction
[MTN] declines just prior to
spawning in fish and returns to
basal levels after spawning
Thought to be due to Zn
requirements to synthesize VTG
Metallothionein cont’d
Other factors affecting MTN:
1) Environmental
- metals
- arthritis, diabetes
- endotoxin
- epinephrine, glucocorticoids
- vitaminC, retinoic acid
- capture stress
- oxidative stress