New Screen for Shellfish Poisoning

Dinophysis_acuminata
Dinophysis acuminata, a species of OA-producing algae

About 300  species can cause algal blooms, and a quarter of them are able to produce toxins. Among these are the okadaic acid group toxins(OA) made by some marine dinoflagellates. They are found in contaminated shellfish, and the maximum permitted level (MPL) is 160 μg OA equivalents/ kg shellfish meat ( 160 parts per billion).

okadaic acid
Okadaic acid and derivatives, a group of toxins from the dinoflagellate genera Dinophysis and Prorocentrum . From http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3917280/

OA has long been linked to severe diarrhea, but two years ago a Spanish review study highlighted its role as a neurotoxin and a cancer promoter. Okadaic acid has an intricate mechanism of action. Most (but not all) of its more recently discovered effects are due to its inhibition of protein phosphatase enzymes and its consequences. For example, when okadaic acid inhibits such enzymes, tau proteins bond to too many phosphate groups. Since such proteins play a role in memory in the hippocampus, not surprisingly, rats lose cognitive function when the acid is microinjected into their brains, where it causes an Alzheimer’s like-pathology.

Recently, a new test-strip (lateral flow immunoassay or LFIA ) has been developed to detect the presence of okadaic acid toxins. LFIA is cheaper than mass spectrometry-chromatography, and LFIA does not rely on animal testing. After coming across an explanation of its mechanism in the Economist, I drew something simple to illustrate the clever design behind these strips, the fruit of research led by Waqass Jawaid, of Queen’s University in Belfast.

okadaic!I contacted one of the coauthors  (Julie Meneely) to make sure my illustration was adequate, and she was kind enough to promptly look at it and let me know that it was an accurate portrayal. The sample—see adjacent diagram— flows through three regions on the strip. The first region contains mobile antibodies capable of bonding to okadoic acid(OA). The second region will bind to the antibody only if it did not already bond with OA. Finally, the third region binds to the antibody regardless of whether it’s holding OA. In other words, it serves as a control, making sure that the antibody has indeed migrated down the strip.

okadaic2

The next illustration reveals how a safe sample will produce two red zones. Being free of the toxin it is capable of binding to the antibody. But a contaminated shellfish sample’s OA occupies the site in the antibody meant to interact with the 2nd zone. Once the group migrates to the second area, no additional bonding occurs and no red color band shows up on the middle part of the strip.

The frequency of algal blooms has increased in the Great Lakes and in other regions of the world.  And since the toxins are more harmful than previously imagined, this convenient test will hopefully encourage citizens, lawmakers, the seafood and agricultural industries to lower the phosphate and nitrate concentrations in our waterways. They are, after all, the promoters of algal growth.

 

 

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