雪卡毒素在珊瑚鱼的转化及累积

Ciguatera fish poisoning (CFP) is one of the most common non-bacterial food intoxication caused by consumption of coral reef fishes contaminated by ciguatoxins (CTXs). The demand for coral reef fishes in Chinese food market has increased rapidly, and therefore part of the coral reef fishes have to be imported from island nations in the South Pacific Ocean such as the Republic of Kiribati. In the past decades, around 430 cases of CFP have been recorded and it affected more than 2000 people. Since 1958, the food chain hypothesis has been suggested to explain the origin of CTXs and the cause of CFP. According to this hypothesis, CTXs are biotransformation products of gambiertoxins (GTXs) that are produced by benthic dinoflagellates such as Gambierdiscus toxicus. Herbivorous fishes grazing on macroalgae also ingest the associated epiphytic dinoflagellates and their toxins, and these fishes are then in turn preyed upon by carnivorous fishes; the fishes oxidize GTXs to CTXs, which then bioaccumulate and biomagnify up the food chain. Recently, our research group have proven that feeding habits can be one of the important factors governing the composition of CTXs in coral reef fishes. Yet, there is limited studies focusing on ability and mechanism of CTX biotransformation in coral reef fishes. Also, information on the biotransformation of less toxic precursor CTXs to more toxic biotransformation products in human is not available, but this may increase the associated health risk to human who has consumed coral reef fishes contaminated by a variety of CTXs, including precursor CTXs. With the development of an analytical method using ultra-high performance liquid chromatography - tandom mass spectrometry (UPLC-MS/MS), the present study aims to examine the biotransformation and bioaccumulation of CTX precursors in coral reef fishes. Levels of six ciguatoxins, including P-CTX-4A, P-CTX-4B, P-CTX-3C, P-CTX-1, P-CTX-2 and P-CTX-3 will be determined in various tissues such as muscle, liver, brain, intestine, heart, bile, blood in the experimental animals as a function of time. The results of the present study can provide important insight on (1) species-specific variations in capacity of biotransformation and bioaccumulation of CTXs and their precursors in fishes at different trophic levels; (2) roles of various coral reef fishes governing formation, distribution and fates of CTXs in marine food web; and (3) effective management of fishery resources and human health risk in relation to the control of CFP.

雪卡鱼类中毒是全球最常见的一种非细菌性海产中毒，主要是由食用含雪卡毒素的珊瑚礁鱼类引致。我国民众对珊瑚鱼的需求庞大，每年还会从南太平洋岛国大量进口各种珊瑚鱼。近十多年来有详细数据记载的雪卡鱼类中毒事件有430多起，2000余人中毒。而雪卡毒素在鱼体的转化及累积机制到现阶段还未有深入详细的研究证明，由于脂溶性毒素可否通过长期低剂量的摄入在人体内富集并转化成毒性更强的P-CTX-1, P-CTX-2 和P-CTX-3还是未知数。因此，本项目拟以精确定量六种雪卡毒素并通过毒素暴露实验研究不同食性珊瑚鱼体内雪卡毒素及其前体物质水平随时间的变化趁势；揭示珊瑚鱼对雪卡毒素吸收、分布、转化、累积及排泄的规律。从而探索不同食性层次珊瑚鱼的转化及累积部位、机制与效率，以揭示珊瑚鱼对雪卡毒素在食物链中的形成及分布所扮演的角色，并证明Randall食物链假说，为珊瑚鱼资源的有效管理及人类的健康风险评估提供依据。

本项目成功建立了以固相萃取结合高效液相色谱-电喷雾串联质谱(LC-MS/MS)同时测定含毒底栖纲比甲藻及珊瑚鱼鱼肉中的5种太平洋雪卡毒素(P-CTX-1、P-CTX-2、P-CTX¬3、P-CTX-3C及P-CTX-4B)的痕量检测方法。利用显微注射法或喂食法将雪卡毒素作用于药物代谢动力学及药物效应动力学的典型珊瑚鱼样本[包括海水青鳉鱼(杂食性)及点带石斑鱼(肉食性)]上，经雪卡毒素暴露24h后，结果表明雪卡毒素已被迅速吸收。暴露于0.26 ng/g 和 0.52 ng/g浓度下的海水青鳉鱼其心率呈现不同程度下降，并产生异常的泳动行为；0.26 ng/g 暴露96h后的海水青鳉鱼死亡率显著上升。雪卡毒素对点带石斑鱼的生长速率、食欲、呼吸率及其泳动行为产生不利影响；高剂量(0.6 ng/g 和 1.5 ng/g)暴露30天后，会致使点带石斑鱼体重减轻、呼吸率降低、身体弯曲及失去平衡的异常泳动行为。经暴露后的鱼体，雪卡毒素能有效的转移至内脏、头部、肢体；且连续暴露雪卡毒素后总累积的毒素量与单次注射相同毒素量所导致的死亡率相近，推断P-CTXs具有较大的生物累积潜力。本研究为探讨雪卡毒素对珊瑚鱼的吸收、累积及毒理反应的规律奠定了坚实的工作基础。项目资助发表SCI论文1篇，核心论文1篇，待发表两篇。项目投入经费27万元，支出24.872928万元，各项支出基本与预算相符。剩余经费2.27072万元，剩余经费计划用于本项目研究后续支出。