麻痹性贝类毒素在栉孔扇贝体内的代谢轮廓

Metabolic profile of paralytic shellfish toxin in scallop Chlamys farreri

将栉孔扇贝(Chlamys farreri)直接暴露于产毒藻,通过比较各组织器官中毒素的蓄积及代谢转化特征,研究麻痹性贝类毒素(Paralytic Shellfish Toxins,PSTs)在栉孔扇贝体内危害形成的过程。结果显示,分布于中国的一株塔玛亚历山大藻(Alexandrium tamarense,AT5-3株),其生长及产毒性状稳定,产毒能力强,主要成分为Gonyautoxins-1&-4(GTX1&4),单细胞产毒能力为7.95 fmol/cell;栉孔扇贝对该产毒藻具有较强摄食能力及PSTs蓄积能力,总体蓄积效率达到84.4%,最高蓄积浓度为1903μg STX eq./kg,不同组织蓄积能力由高到低依次为内脏团、性腺、外套膜、闭壳肌;内脏团对PSTs的代谢能力也最强,是该毒素在栉孔扇贝体内蓄积代谢的靶器官;此外,栉孔扇贝对PSTs表现出较强的生物转化能力,主要转化途径为:N-磺酰胺甲酰基类毒素(N-Sulfocarbamoylgonyautoxin-2,C1)→膝沟藻毒素(Gonyautxins-2,GTX2)/脱氨甲酰基类毒素(Decarbamoylgonyautoxins-2,dc GTX2),N-磺酰胺甲酰基类毒素(N-Sulfocarbamoylgonyautoxin-3,C2)→膝沟藻毒素(Gonyautxins-3,GTX3)。本研究中,栉孔扇贝对PSTs总体呈现出迅速蓄积和缓慢代谢的特点,同时,GTX1&4和NEO等高毒成分所占比例较高,造成扇贝中PSTs毒性和风险性均显著升高。本研究有助于科学评估PSTs危害的形成机制,为系统监控我国PSTs风险性提供科学支撑。

Paralytic shellfish toxins （PSTs） are potent neurotoxins produced by a variety of marine dinoflagellates, such as Gymnodinium, Alexandrium and Pyrodinium. PSTs can accumulate and be passed into the food chain through the filter feeding of toxin-producing algae by bivalve mollusks. The consumption of contaminated shell- fish can cause poisoning in humans, with symptoms including nausea, vomiting, diarrhea, numbness or tingling in the extremities, and even death as a result of respiratory failure. A. tamarense is widely distributed along the coast of China, and often forms large algal blooms in the waters surrounding Nanhuangcheng Island, the Zhoushan area, and the port city of Xiamen. Many controlled in vivo feeding experiments with shellfish have investigated the accumulation and fate of PSTs toxins in the marine food web. Comparative studies of PST profiles often found significant differences between the causative dinoflagellates and contaminated bivalve mollusks, thus indicating active metabolism of the toxin in some shellfish. The scallops Patinopecten yessoensis and Chlamys nipponensis are known to become much more toxic for consumption than mussels grown under the same environmental conditions, and several months are required until the toxicity drops to an acceptably safe level. Conversely, levels of toxicity in the short-necked clam and oysters are generally low, and the toxicity can decline as quickly as in the mussel. The metabolic interconversion of incorporated toxins achieved by enzymatic and chemical reactions in the tissues of bivalves, and different uptake and depuration kinetics of the individual toxins, may each contribute to differ- ences in the PST profiles. In this study, we exposed scallop directly to toxin-producing algae in order to characterize the formation of PSTs in Chlamys farreri. Furthermore, we followed PST accumulation and metabolic biotransformation in different organs of the scallop using liquid chromatography coupled with tandem mass spectrometry （LC-MS/MS）. The results showed that the AT5-3 strain ofAlexandrium tamarense in separate areas of the South China Sea were sta- ble both in their growth and toxin production. The composition of the toxin consisted mainly of gonyautoxin- 1 and -4, with a cell toxin-production of 7.95 fmol/cell. Rapid accumulation of the PST was observed, while total accumulation efficiency reached 84.4%. The highest accumulation concentration was 1903 μg STX.2HCl-eq/kg. The toxin-accumulation ability of the different tissues was ordered as viscera〉gonad〉pallium〉muscle. Moreover, the viscera showed the strongest PST metabolic ability and was also the target organ. In addition, the proportion of PST in bivalves differed from the profile of the dinoflagellate that produces the toxins. Chlamys farreri has a strong ability to perform biological transformation. The main transformation pathway was： N-sulfocarbamoylgonyautoxin-2 （C1） → gonyautxin-2 （GTX2）/decarbamoylgonyautoxin-2 （dcGTX2）, and N-sulfocarbamoylgony- autoxin-3 （C2） → gonyautxin-3 （GTX3）. In this experiment, Chlamys farreri showed characteristically rapid PST-accumulation and slow PST-metabolism; meanwhile the high ratio of the toxin component GTX1 and 4 and NEO resulted in significantly increased risk of PSTs in this scallop. This study contributes to the scientific evaluation of the formation mechanisms of PSTs, thereby providing scientific support for the monitoring of PSTs in China.