Toxicity, transfer and depuration of anatoxin-a (cyanobacterial neurotoxin) in medaka fish exposed by single-dose gavage

Abstract

9The proliferations of cyanobacteria are increasingly prevalent in warm and nutrient-enriched 10 waters and occur in many rivers and water bodies due especially to eutrophication. The aim of 11 this work is to study in female medaka fish the toxicity, the transfer and the depuration of the 12 anatoxin-a, a neurotoxin produced by benthic cyanobacterial biofilms. This work will provide 13 answers regarding acute toxicity induced by single gavage by anatoxin-a and to the risks of 14 exposure by ingestion of contaminated fish flesh, considering that data on these aspects remain 15 particularly limited. 16 17The oral LD 50 of a single dose of (±)-anatoxin-a was determined at 11.50 µg.g -1 . First of all, 18lethal dose (100% from 20 µg.g -1 ) provokes rapid respiratory paralysis (in 1-2 min) of the fish 19 inducing the death by asphyxia. Noticeably, no death nor apparent neurotoxicologic effect 20 occurred during the experimentation period for the 45 fish exposed to a single sub-acute dose 21 of (±)-anatoxin-a corresponding to the no observable adverse effect level (NOAEL = 6.67 µg.g -22 1 ). Subsequently, the toxico-kinetics of the (±)-anatoxin-a was observed in the guts, the livers 23 and the muscles of female medaka fish for 10 days. 24In parallel, a protocol for extraction of anatoxin-a has been optimized beforehand by testing 25 3 different solvents on several matrices, the extraction with 75% methanol + 0.1% formic acid 26 appearing to be the most efficient. Anatoxin-a was quantified by high-resolution qTOF mass 27 spectrometry coupled upstream to a UHPLC chromatographic chain. The toxin could not be 28 detected in the liver after 12 h, and in the gut and muscle after 3 days. The mean clearance rates 29 of (±)-anatoxin-a calculated after 12 h are above 58%, 100% and 90% for the guts, the livers 30 and the muscles, respectively. Non-targeted metabolomics investigations performed on the fish 31 liver indicates that the single sub-acute exposure by gavage induces noticeable metabolome 32 dysregulations, including important phospholipid decreases, with an organism recovery period 33 of above 12-24h. Overall, the medaka fish do not appear to accumulate (±)-anatoxin-a and to 34 largely recover after 24h following a single sub-acute oral liquid exposure at the NOAEL. 35 36

Differential influences of (±) anatoxin-a on photolocomotor behavior and gene transcription in larval zebrafish and fathead minnows

“…Rainbow trout immersed in an unspecified enantiomeric mixture of 129-499 µg/L antx-a led to multiple abnormal behaviors after 5 min including irregular/erratic swimming, jaw spasms, air gulping, and difficulty in maintaining equilibrium, though these fish largely recovered by 3 h [32]. Japanese medaka fish exposed to (±) antx-a through oral gavage from 200 to 20,000 µg/kg showed immediate neurotoxic effects including altered opercular movement, abnormal swimming, and muscle rigidity [62]. Since antx-a producing cultures of cyanobacteria may contain other biologically active molecules, studies examining behavioral responses to cyanobacteria were not included in Table 1, but remain necessary to understand behavioral toxicity of antx-a-producing cyanobacterial blooms in aquatic systems [15,16,21,30,[63][64][65].…”