We have investigated the in vitro metabolism of algal toxins using enzyme preparations from blue mussels (Mytilus edulis) and Wistar rats. Microsomal and cytosolic fractions from the digestive gland of blue mussels were prepared by differential centrifugation. Cell suspensions of primary hepatocytes were isolated from rat livers by collagenase perfusion.
Incubation of purified pectenotoxin-2 (PTX-2) with the supernatant from ultra-centrifuged blue mussel hepatopancreas homogenate caused rapid conversion to pectenotoxin-2 seco acid (PTX-2 SA). The blue mussel homogenate hydrolysed PTX-2 with a half-life of 15 minutes in analytical-scale experiments and PTX-2SA was the only observable product.1
Rapid conversion of PTX-2 was also observed during incubation with suspensions of rat hepatocytes, with observed half-lives ranging from 8 to 14 minutes. LC-MS analysis revealed the formation of two major and several minor oxidised pectenotoxin metabolites, none of which had retention times corresponding to PTX-1. Preliminary LC-MS studies indicate that both of the major analogues resulted from insertion of an oxygen atom into C-19–C-24 or C-44, and that no significant conversion to seco acids had occurred. The low oral toxicity of some PTXs1 may be related to this rapid oxidative metabolism. Further characterisation of the metabolites by LC-MS is under way.
The in vitro metabolism of other algal toxins is also being investigated and preliminary results will be reported.
1Miles CO et al. Isolation of pectenotoxin-2 from Dinophysis acuta and its conversion to pectenotoxin-2 seco acid, and preliminary assessment of their acute toxicities. Toxicon 2004, 43, 1-9.
