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Ricky Woofter,¹ M-Yasmine Bottein Dechraoui,¹ Ian Garthwaite,² Neale R. Towers,² Christopher J. Gordon,³ José Córdova,⁴ and John S. Ramsdell¹

¹Marine Biotoxins Program, Center for Coastal Environmental Health and Biomolecular Research, National Oceanic and Atmospheric Administration, National Ocean Service, Charleston, South Carolina, USA; ²Toxinology, Food Science, AgResearch Ruakura, Hamilton, New Zealand; ³Neurotoxicology Division, National Health and Environmental Effects Research Laboratory, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina, USA; ⁴Fundación Ciencia Para La Vida, Santiago, Chile

Abstract
We developed a radioimmunoassay (RIA) using a sheep anti-brevetoxin antiserum to evaluate detection of brevetoxin on blood collection cards from mice treated with the brevetoxin congener PbTx-3. The RIA has high affinity for PbTx-3 [half-maximal effective concentration (EC₅₀) ± SE = 1.2 ± 0.2 nM ; n = 10] and recognizes both type 1 and type 2 brevetoxins, but not ciguatoxin. Direct comparison of the RIA with a radiolabeled [³H]-PbTx-3 receptor-binding assay (RBA) revealed excellent sensitivity, congener selectivity, and minimal interference from blood matrix. We first analyzed blood samples from an acute time course exposure, using a maximal nonlethal dose [180 µg/kg body weight (bw) ] for 0.5, 1, 2, 4, and 24 hr. Mean blood brevetoxin levels were 36 nM at 30 min and stayed above 20 nM during the 1-4 hr time points. We next analyzed blood brevetoxin levels after longer exposure (0.5, 1, 2, 3, 4, or 7 days) . Mean blood brevetoxin levels were 26.0 nM at 0.5 days, decreased to 8.2 nM at 1.0 day, and maintained a significant level (p < 0.05) of 1.3 nM at day 2. We next determined the lowest measurable dose using increasing concentrations of PbTx-3 (10-300 µg/kg bw) . Analysis of the blood samples at 60 min revealed a linear relationship between administered and internal doses (r² = 0.993) . All doses of brevetoxin administered were detectable at 1 hr, with significant levels found for the lowest administered dose of 10 µg/kg bw--a dose that was 10-fold lower than the lowest observable effect level. This RIA provides an optimal first-tier detection of brevetoxin from blood collection cards and, used in combination with the RBA and liquid chromatography-mass spectrometry, should provide a complete panel of methods to biomonitor brevetoxin exposure. Key words: blood, brevetoxin, radioimmunoassay. Environ Health Perspect 111:1595-1600 (2003) . doi:10.1289/ehp.6166 available via http://dx.doi.org/ [Online 2 July 2003]