Toxicity Characterisation of Gambierdiscus Species from the Canary Islands

Abstract

In the last decade, several outbreaks of ciguatera fish poisoning (CFP) have been reported in the Canary Islands (central northeast Atlantic Ocean), confirming ciguatera as an emerging alimentary risk in this region. Five Gambierdiscus species, G. australes, G. excentricus, G. silvae, G. carolinianus and G. caribaeus, have been detected in macrophytes from this area and are known to produce the ciguatoxins (CTXs) that cause CFP. A characterization of the toxicity of these species is the first step in identifying locations in the Canary Islands at risk of CFP. Therefore, in this study the toxicity of 63 strains of these five Gambierdiscus species were analysed using the erythrocyte lysis assay to evaluate their maitotoxin (MTX) content. In addition, 20 of the strains were also analysed in a neuroblastoma Neuro-2a (N2a) cytotoxicity assay to determine their CTX-like toxicity. The results allowed the different species to be grouped according to their ratios of CTX-like and MTX-like toxicity. MTX-like toxicity was especially high in G. excentricus and G. australes but much lower in the other species and lowest in G. silvae. CTX-like toxicity was highest in G. excentricus, which produced the toxin in amounts ranging between 128.2 ± 25.68 and 510.6 ± 134.2 fg CTX1B equivalents (eq) cell−1 (mean ± SD). In the other species, CTX concentrations were as follows: G. carolinianus (100.84 ± 18.05 fg CTX1B eq cell−1), G. australes (31.1 ± 0.56 to 107.16 ± 21.88 fg CTX1B eq cell−1), G. silvae (12.19 ± 0.62 to 76.79 ± 4.97 fg CTX1B eq cell−1) and G. caribaeus (<LOD to 90.37 ± 15.89 fg CTX1B eq cell−1). Unlike the similar CTX-like toxicity of G. australes and G. silvae strains from different locations, G. excentricus and G. caribaeus differed considerably according to the origin of the strain. These differences emphasise the importance of species identification to assess the regional risk of CFP.

Characterization of maitotoxin‐4 (MTX4) using electrospray positive mode ionization high‐resolution mass spectrometry and UV spectroscopy

“…Recent studies revealed that G. excentricus is one of the most toxic species known to date for production of both ciguatoxins (CTXs) and maitotoxins (MTXs) 3–7 . CTXs are the main known causative agents of CP 8 .…”

“…CTXs are the main known causative agents of CP 8 . Although they have very low oral potency, 7,9 MTXs are very toxic following intraperitoneal injection 10 and feeding studies by Kohli et al 11 in laboratory‐controlled conditions have shown they may accumulate in fish muscle. To date, six MTX congeners have been described: maitotoxin (MTX), 10,12–14 maitotoxin‐2 (MTX2), 15 maitotoxin‐3 (MTX3) 16 and maitotoxin‐4 (MTX4), 17 as well as two further mono‐sulfated analogues of MTX 18 .…”

Epibenthic Harmful Marine Dinoflagellates from Fuerteventura (Canary Islands), with Special Reference to the Ciguatoxin-Producing Gambierdiscus

“…For this reason, in order to assess the potential risk of CFP occurrence it is necessary to know the specific diversity and distribution of Gambierdiscus in the region as well as the CTXs and MTXs contained by each one. G. excentricus displays the highest content of CTXs so far [23,24,50] and its CTX-like toxicity has been comparable to that of G. polynesiensis, the predominant CTX producer in the South Pacific, a ciguatera endemic region. In contrast to the consistent toxicity characteristics of G. excentricus, analyses of G. australes have yielded variable results depending on the strains and their origins [24,30,85,86].…”

“…Although highly toxic, MTXs do not induce CFP because of their low oral potency and inability to accumulate in the muscle tissue of fish [83,84]. It has very recently been reported that different species of Gambierdiscus contain different proportions of the two types of toxins and therefore a very different toxic potential [23,24,85]. For this reason, in order to assess the potential risk of CFP occurrence it is necessary to know the specific diversity and distribution of Gambierdiscus in the region as well as the CTXs and MTXs contained by each one.…”

“…Subsequent studies demonstrated high variability in the toxic potential among species. Higher toxicity has been reported, for example for G. polynesiensis in the Pacific [21][22][23], and G. excentricus in Caribbean Sea and the Canary Islands, in comparison with other species in the same regions [23,24]. This emphasizes the need for implementing adequate methodologies for the unequivocal identification of species in these genera, as well as for their quantification.…”