Organ damage and tissue distribution of Okadaic Acid in mice after oral administration

A Crespo1, JA Rubiolo1,2, H López-Alfonso1, M Cifuentes3, A Alfonso1, R Bermúdez3, P Otero1, MR Vieytes2, FV Vega2, LM Botana1. 1Universidad de Santiago de Compostela, Farmacología y Terapéutica, 27002, Spain, 2Universidad de Santiago de Compostela, Fisiología, 27002, Spain, 3Universidad de Santiago de Compostela, Anatomía, 27002, Spain

Okadaic acid (OA) is a marine toxin produced by several groups of dinoflagellates. OA can accumulate in the hepatopancreas of mussels and the consumption of toxic mussels causes diarrheic shellfish poisoning (DSP) in humans.

The DSP symptoms include diarrhea, abdominal pain, vomiting and sickness. Symptoms start between 3 and 12 hours after meat consumption. Because the OA is a polyether stable to high temperatures, cooking do not eliminate the toxin of the shellfish. No lethal effects have been reported to date.

There were several studies of OA distribution in organs with very variable conclusions. Matias WG. et al. demonstrated the distribution of OA in mice using a radiolabeled OA ([3H]OA) in an oral administration assay. The [3H]OA was found in stomach, intestine, kidney and lung but the mayor concentrations were found in stomach and intestine.

In rodents the lethality of OA after oral intoxication has been reported at various doses ranging from 500 to 2000 μg/kg. Given the various results obtained in studies of oral intoxication with okadaic acid, we decided to determine oral toxicity in mice by histological and immunohistochemical methods employing three different concentrations of OA, (500, 700 and 1000 μg/kg). After 24 hours, the surviving mice were sacrificed and samples of small intestine, liver, kidney, lungs, heart and brain were fixed in Bouin solution.

Sections of 3 μm thickness of each organ were stained with hematoxylin-eosin (H&E) to determine tissue damage or alterations.

For the immunohistochemical assays, an anti-OA monoclonal antibody was employed.

After 24 hours, all animals suffered diarrhea and the animals intoxicated with the lowest concentration used in our experiments (500 μg/kg) quickly recovered and had no symptoms after 24 hours of intoxication.

No damage was seen by histopathogical assay in mice treated with 500 μg/kg and no OA was detected by immunohistochemical assay. This dose was not lethal.

The concentration of 700 μg/kg was lethal in 2 of 9 animals, and liver damage was observed by histopathological assay, while the other organs analyzed presented no signs of tissue damage. The immunohistochemical assays showed OA in the liver and kidneys.

The highest concentration of OA (1000 μg/kg) showed to be lethal in more than 50 % of the cases. No liver damage was observed, but by immunohistochemical assays OA was detected in liver and kidneys. These results indicate that the appearance of diarrhea could be so rapid that a significant fraction of the OA is excreted from the organism and is not absorbed. But at 700 μg/kg the diarrhea is not as severe as the highest concentration and OA could produce a clear damage in the liver.

No histopathological damage was observed in any of the other organs (kidney, lung, heart, intestine, brain) analyzed by this technique.

Although the presence of OA in kidney was confirmed by this technique, OA levels couldn’t be high enough to cause damage, so we couldn’t observe tissue damage with histopathological examination.

Our results confirm that liver and kidney are two of OA targets, nevertheless it’s interesting the fact that high concentrations could be less harmful that lower doses of toxin. This notion is reinforced by results obtained by other authors indicating that the concentration of toxin in different organs is low compared to the amount excreted in the urine and feces.

We could see OA like a toxin not only detrimental to our health by its concentration; it could be harmful if the body can’t remove the toxin efficiently.