A Protein Phosphatase 2A-Based Assay to Detect Okadaic Acids and Microcystins

Abstract

Okadaic acids (OAs) are causative agents of diarrhetic shellfish poisoning, produced by the dinoflagellates Dinophysis spp. and Prorocentrum spp. Microcystins (MCs) are cyclic heptapeptide hepatotoxins produced by some cyanobacteria genera, including Microcystis spp. Traditionally, toxicity detection and quantification of these natural toxins were performed using a mouse bioassay (MBA); however, this is no longer widely employed owing to its lack of accuracy, sensitivity, and with regard to animal welfare. Therefore, alternative toxicity analyses have been developed based on MCs’ and OAs’ specific inhibition of protein phosphatase 2A (PP2A), using p-nitrophenylphosphate (p-NPP) as a substrate. The assay is simple, inexpensive, ready for use on site, and can be applied to several samples at once. For OA detection, this assay method is appropriate for widespread application as a substitute for MBA, as evidenced by its alignment with the oral toxicity of MBA. In this review, we summarize the structure and function of PP2A, the inhibitory activities of OAs and MCs against PP2A, and the practical applications of the PP2A assay, with the aim of improving understanding of the PP2A assay as an OAs and MCs detection and quantification method, as well as its suitability for screening before confirmatory chemical analysis.