Multiple ciguatoxins present in Indian Ocean reef fish

Area of Science:

• Marine Biology
• Analytical Chemistry
• Toxicology

Background:

• Ciguatoxins (CTXs) are potent marine toxins responsible for ciguatera fish poisoning.
• The diversity and origin of CTXs in different oceanic regions remain incompletely understood.
• Lutjanus sebae (red emperor) is a known accumulator of marine toxins.

Purpose of the Study:

• To identify and characterize ciguatoxins present in a highly toxic red emperor fish from the Indian Ocean.
• To compare the properties and relative potencies of identified Indian Ocean ciguatoxins (I-CTXs) with known Pacific (P-CTX) and Caribbean (C-CTX) analogs.
• To investigate the potential precursors and biotransformation pathways of I-CTXs in fish.

Main Methods:

• Optimized gradient reversed-phase high-performance liquid chromatography electrospray ionization mass spectrometry (LC/MS) for toxin separation and detection.
• A [3H]-brevetoxin binding assay (RLB) was used to quantify toxin potency.
• Accurate mass analysis was employed to determine the molecular masses of identified ciguatoxins.

Main Results:

• Four ciguatoxins were identified: two major toxins (I-CTX-1 and I-CTX-2) at 1140.6 Da and two minor toxins (I-CTX-3 and I-CTX-4) at 1156.6 Da.
• I-CTX-1 and I-CTX-2 exhibited indistinguishable masses from Caribbean C-CTX-1 and possessed approximately 60% the potency of Pacific P-CTX-1.
• I-CTX-3 and I-CTX-4 were less potent (approx. 20% of P-CTX-1), and unlike other CTXs, I-CTX-1 and -2 did not show interconversion under acidic conditions or during storage.

Conclusions:

• The study identified novel ciguatoxins in the Indian Ocean, expanding the known diversity of these marine toxins.
• I-CTX-1 and I-CTX-2 likely originate from separate dinoflagellate precursors.
• Oxidative biotransformation in fish may lead to the formation of less potent I-CTX-3 and I-CTX-4 from I-CTX-1 and -2.