Caribbean ciguatoxin (C-CTX) reference materials: feasibility studies for calibration solutions and fish tissue...

Ciguatera poisoning (CP) is the most prevalent marine toxin illness globally and disproportionately affects tropical and subtropical regions that rely on fish as a major food source. It is a global concern due to fish importation, tourism in endemic regions, and changes to ocean temperatures leading to the spread of the causative microorganisms into non-endemic regions. CP is caused by the consumption of fish contaminated with ciguatoxins, a class of lipophilic, ladder-framed polyether marine toxins that cause a combination of gastrointestinal, neurological, and cardiovascular symptoms. A major constraint in ciguatoxin analysis is the lack of reference materials (RMs), especially for Caribbean ciguatoxins. Caribbean ciguatoxin-5 (C-CTX5) was isolated from Gambierdiscus silvae and quantitated by qNMR. The purified C-CTX5 was accurately diluted and used to prepare a small batch calibration solution RM at a concentration of 0.5 µg/mL. The solution was shown to be homogeneous and demonstrated good stability over 28 days at temperatures up to 23 °C. A matrix reference material was prepared using fish tissue (Sphyraena barracuda) naturally incurred with C-CTX1, with concentrations estimated using the C-CTX5 calibration solution. The fish matrix RM was homogeneous, and C-CTX1 remained stable at temperatures up to 4 °C for 28 days. At temperatures above 4 °C, a time-dependent decrease in measured C-CTX1 concentration was observed. Addition of antibiotics and an antioxidant stabilizer was shown to improve both the stability of the fish matrix and measured C-CTX1 content. These successful feasibility studies establish processes for the development of large-scale C-CTX reference materials, which are essential to ensure accurate measurements for both research and regulatory frameworks.