Ciguatoxins (CTXs) are potent neurotoxins which accumulate in seafood and cause ciguatera poisoning, a leading cause of seafood borne illness throughout the world. CTX precursors are produced by the harmful alga, Gambierdiscus spp., and are subsequently transferred throughout marine food webs, undergoing metabolic biotransformations that produce several structurally and toxicologically related derivatives. Identifying CTX biotransformation pathways is a key step towards predicting the fate of CTXs in seafood species and toxicological effects in humans. Although CTX biotransformation has long been theorized, support for its occurrence is largely based on the distribution of Pacific CTX (P-CTX) derivatives across marine species and limited evidence from experiments on P-CTX metabolism. However, no information currently exists on the biotransformation pathways of Caribbean CTXs (C-CTX) in fish or humans, leaving a gap in our understanding of C-CTX ecotoxicological fate. In this study, we investigated the biotransformation of C-CTX -1/-2 across several fish and mammalian species through in vitro metabolism assays focused on Phase I (CYP) functionalization and Phase II (UGT) conjugation reactions. Using UHPLC-HRMS(/MS) to aid in the tentative identification of potential C-CTX biotransformation products, we observed two glucuronide products of C-CTX-1/-2 forming in incubations with fish, but not mammalian, microsomes. Chemical reduction experiments confirmed that the metabolites were comprised of four distinct glucuronide products with the sugar attached at two separate sites on C-CTX-1/-2, and excluded the C-56 hydroxyl group as the conjugation site. Glucuronidation is a novel biotransformation pathway for CTXs and this work provides the first evidence of C-CTX biotransformation reported thus far. Yet, its occurrence across all fish species tested indicates that it could be a prevalent detoxification mechanism in marine organisms, with differing capabilities across fish potentially contributing variable fish toxicities in ciguatera endemic regions. The absence of glucuronidation observed here for both rat and human microsomes suggests that alternate biotransformation pathways may dominate in mammals or higher vertebrates, and may underlie human sensitivity to C-CTX poisoning.

First report of in vitro glucuronidation of Caribbean ciguatoxins in reef fish using UHPLC-HRMS(/MS): Implications for ciguatera poisoning

ACS Fall 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.