Toxicity Dynamics And Toxin Composition Of Nassarius Spp. Along The Coast Of China

Gastropod Nassarius spp. is a kind of favorite seafood to the people living along the coastal regions of China and other Asian countries. However, consumption of gastropod Nassarius spp. caused many poisoning incidents in China in the last several decades, which posed a potent threat on the health and safety of human-beings. Due to the limited information available on the dynamics of toxicity and toxin components in nassariids, it's difficult to develop and implement effective measures to predict and prevent poisoning incidents. To find out the pattern of toxicity dynamics, samples of Nassarius spp. were collected continually from some typical regions, including Lianyungang and Yancheng of Jiangsu Province, Zhoushan and Ningbo of Zhejiang Province, and Ningde, Xiamen and Putian of Fujian Province, where poisoning incidents were frequently reported. The samples were screened with the mouse bioassay method, and analyzed for tetrodotoxins and paralytic shellfish toxins using high performance liquid chromatography (HPLC) and liquid chromatography-mass spectrometry (LC-MS).Based on the results of mouse bioassay, it was found that the proportion of toxic samples collected from Yancheng, Jiangsu Province, was 56% in 2006, and the toxicities varied among 2-5 MU/g tissue. In 2007, there is only 1 toxic sample which was 3.14 MU/g tissue out of the 8 samples collected from the same location. However, samples collected from Lianyungang, Jiangsu Province, in 2007 showed much higher toxicity. The highest toxicity was 846.52 MU/g tissue. During the sampling season, the gastropod toxicity showed an"M"shape fluctuation in Lianyungang, with two peaks of toxicity appeared in late May and July, respectively. In Zhejiang Province, the proportion of toxic samples collected from Ningbo was 25% in 2006, and the toxicities were about 2.5 MU/g tissue. In Zhoushan, however, all samples collected were toxic, and the highest toxicity was 18.4 MU/g tissue. Toxicity of samples peaked in early June and late July during the sampling season. In Fujian province, The proportion of toxic samples collected from Ningde, Xiamen and Putian were 14%, 43%, 20%, respectively. For most of the toxic samples, the toxicities varied among 2-5 MU/g tissue, and the highest toxicity recorded was 16.19 MU/g in a sample collected from Ningde on July 12th. The toxic samples in Putian were mainly found in March, but in the other two sampling sites, toxic samples were found both in March and in a period from June to July. The results indicated that both seasonal factors and geographical factors can affect the dynamics of gastropod toxicity. Furthermore, for most of the regions, the dynamics of the toxicity of samples seemed no correlativity with the average weight of individual.For the samples with high toxicity, no PSP toxins were detected with HPLC. However, tetrodotoxin(TTX) and its analogues, including trideoxy TTX, 4-epi-TTX, anhydro TTX as well as oxoTTX, were detected in all the toxic samples with LC-MS. The profiles of TTX and its analogues in Nassarius spp. from different regions were different. TrideoxyTTX in samples collected from Lianyungang, Jiangsu Province and Zhoushan, Zhejiang Province, was the predominant component, followed by TTX. While in the samples from other regions, TTX was the major toxin,followed by the other analogues of TTX. Studies on anatomical distribution of TTX and its analygues in samples collected from Lianyungang and Zhoushan indicated that the toxin profiles in the muscle, digestive gland and the rest part were roughly the same, with trideoxyTTX as the predominant component. However, in the rest part of samples collected from Zhoushan, TTX content was higher than trideoxyTTX and other analogues. There was no dramatic difference in toxin profile during the sampling season, while variation of toxin content in different tissues could be observed. For most of the time, toxin content in the muscle tissue was the highest, followed by the digestive gland and the rest part.In summary, our results indicated that both seasonal factors and geographical factors could affect the dynamics of snail toxicity. TTX and its analogues were found in all the toxic samples collected from several typical regions along the coast of China. The components of TTX and its analogues were basically the same in samples collected from different locations, with little differences in toxin profiles. Studies on anatomical distribution of TTX and its analogues indicated that the toxin profiles kept relatively constant during the sampling season, despite the varied toxin content. These results suggest that toxic nassariids along the coast of China should have a similar origin of TTX and its analogues. The results will offer a scientific basis for the effective monitoring, prevention and control of the poisoning incidents in China.