title: Characterization of in vitro oxidative and conjugative metabolic pathways for brevetoxin (PbTx-2).
abstract: Brevetoxins are potent marine toxins produced by the dinoflagellate Karenia brevis, the causative organism of Florida red tides. An in vitro metabolism of PbTx-2 was performed using purified cDNA-expressed rat liver cytochrome P-450 (CYP) enzymes and freshly isolated rat hepatocytes. The metabolic activities of six CYP enzymes, CYP1A2, CYP2A2, CYP2C11, CYP2D1, CYP2E1, and CYP3A1, were examined by incubation with PbTx-2 for up to 4 h in the presence of a NADPH-generating system. Further identification of the metabolites produced by CYP1A2 and CYP3A1 was preformed using high performance liquid chromatography-mass spectrometry (LC/MS). Both CYP1A2 and CYP3A1 metabolized PbTx-2 to PbTx-3 (MH+: m/z 897), PbTx-9 (MH+: m/z 899), and a newly recorded diol brevetoxin-2 metabolite (MH+: m/z 929). CYP3A1 also produced a considerably higher amount of BTX-B5 (MH+: m/z 911). Subsequent incubation of PbTx-2 with rat hepatocytes produced additional phase 1 metabolites of MH+: m/z 911, 913, 915, 917, and 931, indicating a CYP-catalyzed epoxidation at H-ring (C27,C28-double bond) and a subsequent A-ring hydrolysis of PbTx-2 metabolic products. A conjugation metabolism was identified by the production of a glutathione-brevetoxin conjugate (MH+: m/z 1222) and a cysteine-brevetoxin conjugate (MH+: m/z 1018). Structures of the new metabolites are postulated, and a likely CYP-catalyzed metabolism pathway of PbTx-2 metabolism are discussed.
authors.affiliation: Marine Biotoxins Program, Center for Coastal Environmental Health and Biomedical Research, NOAA/National Ocean Service, 219 Fort Johnson Road, Charleston, South Carolina 29412, USA.
authors.forename: Faisal F Y
authors.initials: FF
authors.lastname: Radwan
authors.forename: John S
authors.initials: JS
authors.lastname: Ramsdell
mesh_terms: D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases / Q000378:metabolism*; D002478:Cells, Cultured; D002851:Chromatography, High Pressure Liquid; D004141:Dinoflagellida; D022781:Hepatocytes / Q000187:drug effects / Q000201:enzymology*; D008297:Male; D008387:Marine Toxins / Q000378:metabolism* / Q000633:toxicity; D050217:Metabolic Detoxication, Phase II; D010084:Oxidation-Reduction; D035964:Oxocins; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D008387:Marine Toxins; D035964:Oxocins; C051732:Ptychodiscus brevis T2 toxin; D001189:Aryl Hydrocarbon Hydroxylases