Tetrodotoxin (TTX), one of the most potent naturally occurring neurotoxins, has been detected in both marine and terrestrial organisms. The marine polyclad flatworm Planocera multitentaculata is known to contain high levels of TTX throughout its life cycle, including in the egg and larval stages. We recently reported that P. multitentaculata from the coastal area of Hayama, Kanagawa, Japan, possesses TTX analogs including 5,6,11-trideoxyTTX, monodeoxyTTXs, dideoxyTTXs, and 11-norTTX-6(S)-ol. It is not known whether all P. multitentaculata occurring in the Japanese archipelago possess major TTX analogs, or whether regional variations in TTX profile exist. In this study, we used high-resolution liquid chromatography–mass spectrometry to investigate the content profile of TTX and its analogs in P. multitentaculata collected from several regions of the Japanese coast. We detected TTX and its major analogs 5,6,11-trideoxyTTX, dideoxyTTXs, monodeoxyTTXs, and 11-norTTX-6(S)-ol in all specimens regardless of the sampling site. In addition, their relative proportions showed a similar pattern. These results suggest that the flatworm may have mechanisms involved in maintaining the proportions of TTX and its analogs in the body. How the toxic flatworms acquire the highly concentrated toxins and maintain the proportions of TTXs is therefore of great interest and further investigation.

河豚毒素 (TTX) 是最有效的天然神经毒素之一，已在海洋和陆地生物中检测到。已知海洋多甲扁虫Planocera multitentaculata在其整个生命周期（包括卵和幼虫阶段）都含有高水平的 TTX。我们最近报道，来自日本神奈川县叶山沿海地区的P. multitentaculata拥有 TTX 类似物，包括 5,6,11-三脱氧TTX、单脱氧TTX、双脱氧TTX 和 11-norTTX-6( S )-ol。目前尚不清楚日本群岛中出现的所有P. multitentaculata是否都具有主要的 TTX 类似物，或者 TTX 特征是否存在区域差异。在本研究中，我们使用高分辨率液相色谱-质谱法研究了从日本海岸几个地区收集的多触手P. multitentaculata中 TTX 及其类似物的含量概况。无论采样地点如何，我们在所有样本中均检测到了 TTX 及其主要类似物 5,6,11-三脱氧TTX、双脱氧TTX、单脱氧TTX 和 11-norTTX-6( S )-ol。此外，它们的相对比例也表现出相似的模式。这些结果表明，扁虫可能具有维持体内 TTX 及其类似物比例的机制。因此，有毒扁虫如何获得高浓度的毒素并维持 TTX 的比例引起了人们的极大兴趣并需要进一步研究。