Solid-phase extraction clean-up of ciguatoxin-contaminated coral fish extracts for use in the mouse bioassay

Abstract

Florisil solid-phase extraction (SPE) cartridges were used for purifying ciguatoxin (CTX)-contaminated coral fish extracts, with the aim of removing extracted lipid but retaining optimal level of CTXs in the purified fractions. The CTX-containing fraction (target fraction) in fish ether extract was isolated and purified by eluting through a commercially available Florisil cartridge with hexane–acetone–methanol solvent mixtures of increasing polarity (hexane–acetone (4:1, v/v) < acetone–methanol (7:3, v/v) < 100% methanol). Application of Florisil SPE using acetone–methanol (7:3, v/v) condition facilitated the separation of 4.2 ± 0.4 mg (mean ± standard error of the mean (SEM)) of purified target fraction from 20 mg ether extract with good retention of CTXs. The mouse bioassay was used to demonstrate that the average CTX recovery of the target fraction from CTX-spiked samples was 75.8% ± 3.3%, which was significantly increased by 96.7% ± 15% when compared with CTX recovery from ether extracts (44.8% ± 5.2%) without performing SPE purification. Over 70% of non-target lipids were removed in which no CTX toxicity was found. Moreover, the target fractions of both CTX-spiked and naturally CTX-contaminated samples gave more prominent toxic responses of hypothermia and/or induced more rapid death of the mice. The use of acetone–methanol (7:3, v/v) condition in the elution could significantly improve overall recovery of CTXs, while minimizing the possible interferences of lipid matrix from co-extractants on mice.

Keywords:

• ciguatera fish poisoning
• ciguatoxin recovery
• Florisil
• mouse bioassay
• solid-phase extraction

Acknowledgements

The authors are indebted to the Director of Health, Dr P. Y. Lam, for permission to publish this paper and are particularly grateful to the anonymous donor for supplying the ciguatoxin-contaminated coral fish samples. Declaration: All commercial products and trade names mentioned in this paper do not represent any suggestion or endorsement for use by the authors’ department.