Oxidation of saxitoxin: detection and biological activity of its reaction products.

We characterized the oxidation products of saxitoxin by high-performance liquid chromatography and thin-layer chromatography. We observed several changes in the saxitoxin and neosaxitoxin chromatographic profile, as well as changes in the biological activities of the saxitoxin oxidized product. Toxins were heated in the presence of oxidizing agent, and at least five oxidation products were detected. Spectrophotometric measurements with Folin-Ciocalteau reagent confirmed the formation of these oxidation products. The excitation maximum of each of the oxidized components was determined by spectrophotofluorometry scans, and differed from the parent compound. The oxidized saxitoxin inhibited 3H-saxitoxin binding to neuroblastoma-glioma hybrid cells (NG108-15) to a lesser extent than saxitoxin, and had no toxic effect in mice. Formation of oxidation products suggests the possible, non-enzymatic transformation of saxitoxin and neosaxitoxin.