LAUSR

A number of new C-11 hydroxyl metabolites (so-called M-toxins) of paralytic shellfish toxins (PSTs) have been discovered in contaminated shellfish, and trace amounts have also been detected in some strains of PST-producing microalgae. To investigate the chemical conversion and stability of M-toxins, mussel extracts were purified with solid-phase extraction cartridges (Oasis HLB) and Bio-gel P-2 resin columns, and four partially purified M-toxin fractions were stored at different temperatures (-20℃, 4℃, 20℃) and pH values (3, 4, 5). The concentrations and profiles of M-toxins in these fractions were analyzed using LC-MS/MS for 27 weeks. Results further confirmed the chemical conversion pathway M1→M3→M5, and determined for the first time two new transformation pathways: M2→M4→M6 and neosaxitoxin (NEO)→M10. The half-lives of M1, M2, M4 and M10 were calculated using a first-order degradation kinetics model, which indicated that the degradation of all M-toxins was dependent on temperature and pH, increasing with rising temperature and pH. Compared to M4 and M10, M1 was more sensitive to temperature, followed by M2. Results suggest that M-toxins should be maintained at low temperature (-20℃) and low pH (3) for their prolonged storage. M-toxins were less stable than all the common analogues of PSTs, which may be beneficial for shellfish to achieve rapid detoxification through transformation of PSTs to M-toxins. These new findings are of significance as they enable further understanding of the metabolism of PSTs and their detoxification mechanisms in contaminated shellfish.