TESIS FICOTOXINAS MARINAS EVA FONFRIA

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The IC50 values obtained for 13-desmethyl C spirolide in the different shellfish
matrixes were very close to the IC50 obtained in buffer (PBS-BT). However, the IC50
values obtained with GYM showed more variability and were less close to controls
than 13-desmethyl C spirolide. The higher variability of the GYM IC50 can be related
to the use of a logarithmic fit instead of a four-parameter fit, since a slight variation
in the x axis will yield a higher concentration variation due to the logarithmic scale.
Nevertheless, there are other factors that could be increasing the variability such as
possible interactions between toxins and matrixes.
For 13-desmethyl C spirolide the results obtained in extracts from the four mollusk
species have an acceptable variability and accuracy. The coefficient of variation
(CV) of measurements using this assay in samples contaminated post-extraction with
a 200 nM concentration of toxin is lower than 14%. This concentration of the
spirolide is equivalent to a concentration in shellfish meat of 276 µg/Kg. Regarding
the accuracy of the fluorescence polarization assay, a full evaluation would need
more experiments with different laboratories and operators involved. However, in
these preliminary data the calculated concentrations of 13-desmethyl C spirolide in
contaminated extract with a 200 nM concentration differ less than 10% from that
concentration in mussels and clams, and around 20% in cockles and scallops. GYM
measurements present more variability and less accuracy than the spirolide. The
cause of this variation is unknown at the moment, although as we mentioned above
several factors could be responsible. Because the spirolides have a higher toxicity
than the GYM it is preferable that the method yields better results with the more
dangerous of both molecules.
The extraction method presented in this work was optimized for spirolides based on
their solubility in organic solvents. The recovery rates of 13-desmethyl C spirolide
are actually higher than 85% for the four species tested. Not surprisingly, the method
also extracts GYM. However, in this case as well, the variability of the recovery rates
is higher than for the spirolide, showing good recoveries for clam, cockle, and
scallop, but considerably lower for mussels. Differences between GYM and 13-
desmethyl C spirolide in the recovery rates are probably related to slight differences
in the physicochemical properties due to their chemical structure, while differences