After over 500 bottlenose dolphins washed ashore during a decade of Florida red tides, puzzled scientists measured little to no brevetoxin in them. An unusual mortality event occurred in 2004 leaving 100 dolphins dead after gorging on menhaden. We analyzed dolphin stomachs finding high levels of brevetoxin in the menhaden; the toxin measured was too low to kill dolphins. We are studying how brevetoxin hybrid “conjugate” molecules escape detection while still threatening humans and animals.
Why We Care
We are concerned about the threat brevetoxin conjugates (toxins attached to other molecules) pose to coastal residents including humans, bottlenose dolphins and other animals such as manatees, sea turtles and birds. Conjugates of brevetoxin could hide the true amount of toxicity associated with brevetoxin or even change to different types of brevetoxins that elude detection. Furthermore, the toxin might react with and mutate DNA, a known cause of cancer in response to toxins, threatening humans who are most commonly exposed to brevetoxin by inhalation of released aerosols from wave action during red tides.
What We Did
We conducted experimental studies to document what happens to brevetoxin when it comes in contact with animals. We added the reactive form of brevetoxin to liver cells to see how the toxin is transformed when it contacts the primary organ animals use for detoxification. The toxin was converted into a wide array of rarely seen metabolites. We examined and confirmed brevetoxin formed conjugates and damaged DNA in the lung of laboratory rats. Since not all forms of DNA damage lead to mutations we examined this potential using the Ames mutagenicity test (a test to assess the mutagenic potential of a chemical). When brevetoxin and other reaction products showed no evidence of mutagenic potential, we focused on testing understanding the toxicity of amino acid and fatty acid brevetoxin conjugates to exposed animals.
With colleagues in New Zealand we prepared amino acid and fatty acid brevetoxin conjugates for toxicity testing, and amino acid conjugates and fatty acid conjugates behaved much like the common forms of brevetoxins. We determined that brevetoxin conjugates to free amino acids and several different amino acids when part of a larger protein molecule.
What We Found
We discovered a wide variety of brevetoxin metabolites never before seen. We found that brevetoxin:
- attacks and fragments DNA,
- attaches on much larger blood proteins and,
- has much greater toxic potency and evades common detection methods when attached to fatty acids.
We disseminated these findings through official press releases, scientific articles in the public health and ecological journals, articles in the lay press and formal presentations to societies of scientists and managers working to mitigate the effects of harmful algal blooms.
We are now examining the details of how the brevetoxin conjugates enter the body as a toxic meal: how readily they are absorbed into the blood stream and distributed into tissues. Using models we will be able to better define the true exposure risk of brevetoxins. Identification of where the toxins distribute after being absorbed from ingestion will identify yet other routes to brevetoxin toxicity.