L6: Molecular Effects & Biomarkers Flashcards
Biomarkers
biochemical, physiological, morphological, histological measures used to imply exposure to or effect of contaminant
- Often used as early warning
- Can be used to assess effective remediation of site
What makes an effective and ideal biomarker? (8)
- Measurable b/f adverse consequences occur at higher levels of organization
- Measurement should be rapid, inexpensive, easy enough for widespread use
- Amenable to quality assurance procedures
- Specific to single contaminant or class of contaminants
- Shows concentration-effect (dose-response) relationship w contaminant
- Applicable to broad range of species
- Linked to effect at higher level of organization
- Other influences on biomarker are understood (temp, sex)
Enzymes (metabolize contaminants and biomolecules, make them more hydrophilic) induced when:
There is exposure to contaminant
Occurs in tissues
- In contact w contaminant (lung, intestine, skin, liver)
- Important for detoxification (liver, kidney)
Contaminant binds to receptor and leads to enzyme production
2 commonly used Cytochrome P-450s
1) Aryl hydrocarbon hydroxylase (AHH): hydroxylation of benzo[a]pyrene
2) Ethoxyresorufin O-deethylase (EROD): deethylation of ethoxyresorufin
Induction of P-450 enzymes
Influenced by:
ambient temp, types of contaminant & conc, species, body weight, sex
Are harlequin ducks still exposed to oils from Exxon Valdez spill?
Many birds, mammals and fish died
Oil slow to degrade in colder enviro
Lots of PAHs from oil accumulate in sediments
Harlequin ducks feed on invertebrates that live in shallow sediments
Duck livers had elevated P-450 (EROD) in oiled areas in 1998
Still exposed to elevated PAHs in 2005?
Ducks in Prince William Sound still exposed to high level of oils, EROD still higher in these ducks than unoiled areas
Metallothionein (MT)
Small, thiol rich pr that strongly binds many divalent metals (Cd, Zn, Cu, Hg)
Induced in response to these metals, used as biomarker
MT involved in uptake, compartmentalization, sequestration, excretion of essential and non-essential metals
Sequester metals away from sites of toxic actin, toxicity occurs when MT all used up
Found in bacteria, fungi, invertebrates, vertebrates (including humans)
Occur in several diff tissues –liver, kidney, lung/gills, intestine
Stress Proteins
Cells have pr protection system, protects other pr from damage from contaminants, heat, UV
Protect other pr from being denatured or help refold pr that have been denatured
Induced by agents that have proteotoxicity
Used as biomarker of general stress response
Oxidative Stress
damage to biomolecules from free oxyradicals (includes hydrogen peroxide, hydroxyl radicals), damage proteins, lipids, DNA
Where do oxyradicals come from?
Produced during aerobic metabolism
Photooxidation of chemicals (UV light)
Metabolism of chemicals
How do organisms cope w oxyradicals?
1) Use or produce antioxidants that react w oxyradicals (vitamin E and C, B-carotene, GSH)
2) Produce enzymes that reduce oxyradicals (SOD, CAT)
3 Consequences of Oxidative Stress
Lipid peroxidation
- Leads to loss of membrane fluidity, then alters activity of membrane pr and permeability
Protein oxidation
- Changes structure and function
- Can lead to loss of enzyme activity
- Affects receptor activity
DNA oxidation
- Leads to strand breaks and mutations
- Increase risk of cancers
Contaminants can increase oxidative stress by
- Interfering w normal mech of coping w oxyradicals (infer w enzymes that reduce oxyradicals)
- May also form oxyradicals themselves
Biomarkers of oxidative stress are:
- Changes in antioxidant pools (decrease of GSH=biomarker)
- Elevated levels of oxidative stress enzymes
- Catalase, SOD, GSH peroxidase
Antioxidant enzymes
response to reduce effects of oxyradicals
