[Analysis of Ciguatoxins in the Spotted Knifejaw, Oplegnathus punctatus from the Waters of Japan].

Ciguatera fish poisoning (CFP) is recognized as the most frequent seafood poisoning due to the consumption of fish containing the principal toxins, ciguatoxins (CTXs). In Japan, CFP events have been reported annually from Okinawa and Amami Islands, locating subtropical regions. In addition, there have been reported several outbreaks due to consumption of the fish caught from the Pacific coast of the Mainland and they were often caused by the matured spotted knifejaw, Oplegnathus punctatus. As part of our research on CFP in Japan, we investigated CTXs analysis by LC-MS/MS on 176 individuals of O. punctatus (weight: 100-6,350 g, standard length: 13-60 cm) from the coast of the Mainland (Honshu, Shikoku, and Kyushu), Amami, Okinawa, and Ogasawara (Bonin) Islands. CTXs were detected from only two specimens collected from Okinawa. Total CTXs levels of the two specimens were at 0.014 and 0.040 µg/kg, respectively, exceeding FDA guidance level at 0.01 µg CTX1B equivalent/kg. However, they might be little risk of CFP because consuming over 1.5 kg of flesh is needed to develop intoxication. The toxins consisted of CTX1B analogs including CTX1B, 52-epi-54-deoxyCTX1B, CTX4A, and CTX4B, and no CTX3C analogs, supporting the finding that ciguatoxic fishes in Okinawan Waters containing only CTX1B analogs.

Determination of toxins involved in ciguatera fish poisoning in the Pacific by LC/MS.

Ciguatera fish poisoning is the most extensive and difficult to control of the seafood poisonings. To facilitate monitoring of fish toxicity, toxin profiles were investigated by an LC/MS/MS method using 14 reference toxins on eight representative species of fish collected in four different areas of the Pacific. Snappers and groupers from Okinawa contained ciguatoxin-1B (CTX1B) and two deoxy congeners at variable but species-specific ratios, while red snapper, Lutjanus bohar, from Minamitorishima, and amberjack, Seriola dumerili, from Hawaii, contained both CTX1B-type and CTX3C-type toxins. Spotted knifejaw, Oplegnathus punctatus, from Okinawan waters, contained mainly CTX4A and CTX4B, but the same species caught at Miyazaki was contaminated primarily with the CTX3C-type toxins. Otherwise, the toxin profiles were consistently species-specific in fish collected from various locations around Okinawa over 20 years. The LC/MS/MS and mouse bioassay results agreed well, indicating the LC/MS/MS method is a promising alternative to the mouse bioassay. Pure CTX1B and CTX3C were prepared for use in future LC/MS/MS analysis.

Isolation of 6-deoxytetrodotoxin from the pufferfish, Takifugu pardalis, and a comparison of the effects of the C-6 and C-11 hydroxy groups of tetrodotoxin on its activity.

Identification of new tetrodotoxin (TTX, 1) analogues would be significant in the elucidation of its biosynthetic pathway and a study of its structure-activity relationships. In this study, a new TTX analogue, 6-deoxyTTX (2), was isolated from the ovary of the pufferfish, Takifugu pardalis, and the structure was determined using spectroscopic methods. Compound 2 was also identified in other marine animals, Nassarius snail and blue-ringed octopuses, using LC-MS. Furthermore, we investigated the voltage-gated sodium channel blocking activity of 2 by examination of the inhibitory activities to cytotoxicity induced by ouabain and veratridine in mouse neuroblastoma cells (Neuro-2a). The activities were then compared with those of 1, 11-deoxyTTX (3), and 6,11-dideoxyTTX (4). The EC50 value for 2 was estimated to be 6.5±2.2 nM, approximately 3-fold larger than that of 1 (2.1±0.6 nM) and approximately 20-fold smaller than that of 3. These results suggested that contribution of the C-6 hydroxy group to the activity is less than that of the C-11 hydroxy group.

[Toxin profiles in fish implicated in ciguatera fish poisoning in Amami and Kakeroma Islands, Kagoshima Prefecture, Japan].

Ciguatoxins (CTXs) responsible for ciguatera fish poisoning (CFP) in Amami Islands, Kagoshima, Japan in 2008 were determined by LC-MS/MS analysis. Ciguatoxin-1B (CTX1B), 54-deoxyCTX1B, and 52-epi-54-deoxyCTX1B were detected in Variola louti and Lutjanus monostigma. The toxin profile distinctly differed from that of a CFP-related fish from Miyazaki, which mainly contained ciguatoxin-3C type toxins. Toxin profiles were species-specific, as observed in fish from Okinawa. The LC-MS/MS and mouse bioassay (MBA) methods produced comparable data, though 54-deoxyCTX1B was not taken into consideration owing to the lack of toxicity data. To improve assessment, toxicity data for this compound are needed. A reef fish caught on the same occasion and judged nontoxic by MBA (<0.025 MU/g) was found to contain low levels of CTX, indicating a potential risk for CFP.