May 5, 2005
A Message from Iain Kerr - Biomarkers & Whales
In the January 1979 issue of National Geographic magazine, Ocean Alliance President Dr Roger Payne said, "Pollution has replaced the harpoon as a mortal threat to whales and in its own way can be far more deadly".
This quote ultimately lead to the Voyage of the Odyssey, whose mission over the last 5 years has been to establish
the first-ever, baseline data set on the concentrations, distributions and effects of Persistent Organic Pollutants (POPs) throughout the world's oceans.
Alas while the above sentence makes the science sound simple - it is not. As a non-scientist I have tried to give an overview of just the toxicology work below (we also do bioacoustic, genetic, stable isotope and animal behavior studies along with an award winning education and conservation program).
Ultimately we would like to know what toxicants an animal has been exposed to and what are the potential effects to the animal to this exposure?
To simplify explaining this whole process I find it useful to think of the human body at its most basic level; as a biological machine - the aspect of that machine that most interests us here is the bodies response to compounds that it takes in, whether through ingestion or absorption through the skin or lungs.
90% of the time when we take in compounds the first step in making use of or discarding these compounds is a response by our bodies at a cellular level - cells respond to the presence of these compounds by making enzymes.
The creation of enzymes or an enzymatic response is what we look for and measure - we call these chemical responses - biomarkers.
One of our primary goals then is measure the body's response to things that it takes in by looking at these biomarkers. We use biomarkers because they are easily identifiable stable compounds that react in a predictable measurable way when they come in contact with other compounds - compounds that otherwise may or may not be easy to measure.
Typically biomarkers stay in the body even when the compounds that they have responded to have left the body through such processes as metabolism or excretion.
A key component for the success of the Voyage of the Odyssey toxicology program was to develop a biomarker (in whales) that:
a) Would be indicative of EXPOSURE to contaminants (molecular consequences)
b) Develop a biomarker demonstrating EFFECTS of an animal's exposure to contaminants (physiological consequences).
Because females can pass on their toxic load to their offspring and because some species may be more sensitive to toxicants than others, just looking at the levels of pollutants carried in blubber would not tell us the whole picture (even though it is an important part of the picture).
When we first started the voyage, biomarkers (for exposure) had been demonstrated in other animals but never in whales.
To review the basic biology of a cell:
The nucleus in a cell consists of genes - genes consist of strings of nucleotides (DNA) carrying information - (think of a necklace of information beads) all genetic information (genes) are packed up into chromosomes inside the nucleus.
The nucleus sits in the middle of a cytoplasm bath, consisting of a number of different "cellular machines" that make an animal run (chemically speaking) - for our work we only concern ourselves with one type of cellular machine - called organelles.
A notable success stemming from the voyage data analysis is that
we have demonstrated that proteins are being created as part of an enzymatic response to pollutants that the animal is being exposed to. Consequently the amount of a certain protein we find in the cell correlates directly with the exposure to Persistent Organic Pollutant's the animal has received - So we established a valid biomarker for exposure utilizing proteins.
The next step was to look for a way to make this test more sensitive - to do this we had to ask the question - how does the cell create proteins?
When the cell wants to create proteins, there is a process inside the nucleus whereby gene info is transcribed into RNA molecules (directly corresponding to each specific gene) - these RNA molecules are then transported outside the nucleus into the cells cytoplasm - cellular machines or organelles in the cytoplasm then create proteins based on the info from the RNA molecules.
So, in a cell, if genes carry the genetic info from the nucleus into the cytoplasm (info that the cell needs to create our protein biomarkers) then to make our test more sensitive we would want to look at the genes and not the proteins they create.
If we know that the amount of the protein biomarker is indicative of exposure to pollutants (and we have proved that it is) and if we know that the RNA copy of the gene is used to create the protein biomarker, then we can add one level of sensitivity to the experiment by ignoring the protein (constructed from gene info) and just look at the gene.
Or to put it another way: until now we have been looking at the amount of protein in the cytoplasm (that we have demonstrated is created in a response to exposure to pollutants) - now we can look at the RNA molecules (that have come from a copy of the original gene) that build these proteins to determine response to exposure to pollutants.
Now that we understand the process - what have we actually done:
- We demonstrated the validity of the cytochrome P450 1A1 enzyme as a biomarker of exposure (and molecular effects) in cetaceans (study published in Toxicological Sciences 80, 268-275 in August 2004). In simple terms, the protein level of this enzyme is directly proportional to the levels of pollutants present in the whale tissue examined.
- In this study, we also pioneered a technique whereby the experiment can be performed with a small sample of skin tissue that can be collected from a living whale in a minimally invasive way.
- We successfully established the genetic identity of this enzyme - (as mentioned above every gene is made of a string of nucleotides, so we identified (cloned) the positions of every nucleotide in the necklace - 1600 in the case of P450 1A1).
- With this under our belt we are able to increase the sensitivity of our biomarker test by detecting the amount of the cytochrome P450 1A1 enzyme at the gene level (by measuring the RNA that creates the protein - the levels of which we had been looking at previously). This one step level in increased sensitivity means we can now detect even smaller molecular effects of pollutants and at earlier stages, two essential criteria for whale (and other wildlife) conservation.
- We are well underway in the cloning (gene identification) of another biomarker, the cytochrome P450 1B1 enzyme. It has been demonstrated that this biomarker is more effective (sensitive) than the cytochrome P450 1A1 enzyme in terrestrial mammals but it had not been studied in any marine mammals.
We expect that this work / process will also have benefits to a number of different species, including humans.
This is very exciting for the future since it is now being suggested that many of the compounds of concern to us are not carcinogenic when they enter our body - BUT - it is our body's enzymatic response that makes them carcinogenic. It is also being suggested that low chronic exposure over time is far worse than intermittent high exposure.
To sum up and review the fundamentals as to why we are doing this:
Marine mammals can accumulate environmental contaminants in their blubber at concentrations known to be harmful to laboratory animals.
Unfortunately there is still limited understanding of the effects of such contaminant loads in whales.
The challenges pertaining to toxicological research on protected species are many and include ethical, logistical, legal and financial limitations.
Beyond collecting a base line data set on the distribution and concentrations of POP's in the worlds oceans, and beyond our on the ground education conservation initiatives, Ocean Alliance is becoming a leader in marine mammal toxicology by successfully pioneering protocols for investigating the toxic effects of marine pollutants in minimally invasive ways that are suitable for the study of these (and hopefully) other animals.
The Voyage of the Odyssey is, in 2005, creating the foundation of scientific reference (through new methods and materials) for future studies by marine biologists locally, regionally and globally.
Log written by Iain Kerr.