Characterization of polar brevetoxin derivatives isolated from Karenia brevis cultures and natural blooms

Several novel brevetoxin derivatives were isolated and identified in Karenia brevis cultures and natural blooms by using solid phase extraction (SPE) and LC/MS(MS) techniques. These analogs were more polar compared with previously described brevetoxins, and were poorly extractable by conventional non-polar solvent (chloroform) partitioning. Brevetoxin analogs were structurally confirmed as hydrolyzed (open A-ring) forms of brevetoxins PbTx-1, PbTx-7, PbTx-2, and PbTx-3, and of oxidized PbTx-1 and PbTx-2. Some of these open A-ring derivatives were in greater abundance than their non-hydrolyzed counterparts. All were in much greater abundance in bloom water filtrate compared with cell-rich fractions. Open A-ring compounds were cytotoxic in mouse neuroblastoma (N2a) cell assay. In the K. brevis bloom-exposed Eastern oyster, brevetoxin metabolites with opened A rings were identified (e.g., open-ring cysteine-PbTx conjugates), contributing to their overall toxin burden.