In Vitro Glucuronidation of Caribbean Ciguatoxins in Fish: First Report of Conjugative Ciguatoxin Metabolites

Abstract

Ciguatoxins (CTX) are potent marine neurotoxins, which can bioaccumulate in seafood, causing a severe and prevalent human illness known as ciguatera poisoning (CP). Despite the worldwide impact of ciguatera, effective disease management is hindered by a lack of knowledge regarding the movement and biotransformation of CTX congeners in marine food webs, particularly in the Caribbean and Western Atlantic. In this study we investigated the hepatic biotransformation of C-CTX across several fish and mammalian species through a series of in vitro metabolism assays focused on phase I (CYP P450; functionalization) and phase II (UGT; conjugation) reactions. Using liquid chromatography high-resolution mass spectrometry to explore potential C-CTX metabolites, we observed two glucuronide products of C-CTX-1/-2 and provided additional evidence from high-resolution tandem mass spectrometry to support their identification. 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 not yet reported for CTX or other related polyether phycotoxins, yet its occurrence across all fish species tested suggests that it could be a prevalent and important detoxification mechanism in marine organisms. The absence of glucuronidation observed in this study for both rat and human microsomes suggests that alternate biotransformation pathways may be dominant in higher vertebrates.

Metabolic Hepatic Disorders Caused by Ciguatoxins in Goldfish (Carassius auratus)

“…This alteration has been associated with the isolation of pollutants in liver lipid droplets, degenerative changes in liver tissue, increased detoxification capacity, and glucose-associated modifications in liver metabolism [ 52 , 53 , 54 ]. In a study published by Gwinn et al [ 10 ], it was noted that liver glucuronidation could be an important way to depurate C-CTX1. Moreover, Diniz et al [ 55 ] detected an increase in HSI with the increment of pollutants concentration in goldfish.…”

“…Few studies utilizing genomics and proteomics investigations have been conducted on the impacts of CTX in fish to assess potential biomarkers and resistance mechanisms, mainly involving the CTX1B [ 7 , 9 ]. Regarding C-CTX, less research has been performed except for a recently published study by Gwinn et al [ 10 ], where the first evidence of CTX glucuronidation in fish was proposed, suggesting that it could be a prevalent detoxification mechanism.…”

Ciguatera Fish Poisoning in the Caribbean Sea and Atlantic Ocean: Reconciling the Multiplicity of Ciguatoxins and Analytical Chemistry Approach for Public Health Safety

“…Different rates of depuration, time from initial exposure, and species-specific differences in the ability of P-450 enzymes to generate C-CTX congeners can explain the different toxin profiles found in fish [ 19 , 23 , 38 , 41 , 42 , 45 , 46 , 75 , 89 , 91 , 118 ]. Two glucuronide products of C-CTX-1/-2 were recently identified by Gwinn et al using high-resolution tandem mass spectrometry [ 165 ]. Their 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 the hydroxyl group on carbon C56 was excluded as the conjugation site [ 165 ].…”

Contribution of Mass Spectrometry to the Advances in Risk Characterization of Marine Biotoxins: Towards the Characterization of Metabolites Implied in Human Intoxications

“…Phase-II metabolites of CTXs were recently detected by Gwinn et al [ 92 ]. The in vitro incubation of C-CTX1 and C-CTX2 with liver microsomes of five fish species from the Caribbean Sea and also Atlantic Salmon showed the metabolization of these toxins to glucuronide products.…”

“…On the other hand, GlcA conjugates of C-CTX1 and C-CTX2 were not detected after their incubation with both rat and human mammalian microsomes. Therefore, glucuronidation may be a specific metabolization of fish which might explain the sensitivity of humans after the exposition to C-CTXs [ 92 ].…”