Characterization of rat liver microsomal and hepatocytal metabolites of brevetoxins by liquid chromatography-electrospray tandem mass spectrometry

• Published in: Analytical and bioanalytical chemistry 2005-09, Vol.383 (1), p.67-75
• Main Authors: Wang, Weiqun, Hua, Yousheng, Wang, Guangdi, Cole, Richard B
• Format: Article
• Language: English
• Subjects: Animals; Brevetoxin; Chromatography, Liquid - methods; Electrospray; Hepatocytes - chemistry; Hepatocytes - metabolism; Hydrolysis; LC-MS; Marine Toxins - analysis; Marine Toxins - metabolism; mass spectrometry; Metabolite; Microsomes, Liver - chemistry; Microsomes, Liver - metabolism; Molecular Structure; Molecular Weight; Oxocins - analysis; Oxocins - metabolism; Rats; Red tide; Spectrometry, Mass, Electrospray Ionization - methods
• ISSN: 1618-2642; 1618-2650
• DOI: 10.1007/s00216-005-3323-0

Brevetoxins are natural neurotoxins that are produced by “red tide” algae. This class of compounds can cause neurotoxic shellfish poisoning and other health problems. Brevetoxin-2 is the most abundant among the nine brevetoxins that have been characterized, whereas brevetoxin-1 is the most toxic. In this study, brevetoxin-1 and brevetoxin-2 were incubated with rat liver hepatocytes and rat liver microsomes, respectively. After clean-up steps were taken to remove the proteins, samples were analyzed by liquid chromatography (LC) coupled with electrospray mass spectrometry (LC-MS). After incubation of brevetoxin-1, two metabolites were found: brevetoxin-1-M1 (molecular weight = 900 Da), and brevetoxin-1-M2 (molecular weight = 884 Da). The increase in molecular weight combined with evidence from tandem mass spectrometry showing an increased tendency for loss of water molecules, along with considerations of established precedents for chemical transformations led to the conclusion that brevetoxin-1-M1 was formed by converting one double bond in the E or F ring of brevetoxin-1 into a diol. The second metabolite (brevetoxin-1-M2) is proposed to be a hydrolysis product of brevetoxin-1 involving opening of the lactone ring with the addition of a water molecule. The incubation study of the other starting compound, brevetoxin-2, found two metabolites in the LC-ES-MS selected ion chromatogram. Brevetoxin-2-M1 (molecular weight = 912 Da) gave a large [M-H]- peak at m/z 911, and its product ion mass spectrum allowed the deduction that this metabolite was the hydrolysis product of brevetoxin-2 involving conversion of the lactone to a carboxylic acid and an alcohol. The second metabolite (brevetoxin-2-M2, molecular weight = 896 Da) was deduced to have the same structure as that of brevetoxin-3 based on identical chromatographic retention times and similar mass spectra as those obtained for a brevetoxin-3 standard.