Determination of Saxitoxin by Receptor Binding Assay: A New Radiolabeled Kit in Thailand

Abstract

Objective: A receptor binding assay for detection of saxitoxin, a paralytic shellfish poisoning toxin, was formatted for use in a high throughputdetection system using microplate scintillation counting. The RBA technology was transferred from the NOAA National Ocean Service, SC USA, tothe Thailand Institute of Nuclear Technology, which uses a Perkin Elmer Microbeta TriLux 1450 microplate scintillation counter. Methods: Validationof method was performed by participating in the regional inter-laboratory program. The result yielded all parameters within the critical control point(i.e. RSD less than 30%). Results: The slope of the calibration graph = 1.2 + 0.26 (RSD = 21.7%) (criteria = 0.8 - 1.2), half maximal inhibition (IC50)= 3.1 + 0.47 nM (RSD = 15.2%) (criteria = 3.0 nM), dynamic range = 1.2 - 10 nM and the limit of detection (IC80) from graph = 1.2 nM, equivalentto the limit of quantification of 2.57 mg/100 g shellfish. The result of analysis of unknown samples yielded the RSD between assays ranging from 6 -23% and the recovery compared to the expected value ranging from 79 -133%. The application of RBA for determination of PSP in shellfish samplesyielded RSD in assays less than 30% and between assays ranging from 1.4-15.2%. Conclusion: RBA for STX has showed a valuable for rapid,reliable, cost-effective alternative to live animal testing and high throughput screen prior to testing by the conventional mouse bioassay (MBA) and itssuitability for providing an early warning of increasing PSP toxicity when toxin levels are below the MBA limit of detection.Keywords: saxitoxin, receptor binding assay, paralytic shellfish poisoning, tritiumThai Pharm Health Sci J 2010;5(4):287-295§