Determination of benzyl isothiocyanate metabolites in human plasma and urine by LC-ESI-MS/MS after ingestion of nasturtium (Tropaeolum majus L.).

A liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed and validated to determine the concentration of benzyl isothiocyanate (BITC) metabolites in human plasma and urine. In this study, the following BITC metabolites have been considered: BITC-glutathione, BITC-cysteinylglycine, BITC-cysteine, and BITC-N-acetyl-L-cysteine. The assay development included: (1) synthesis of BITC conjugates acting as reference substances; (2) sample preparation based on protein precipitation and solid-phase extraction; (3) development of a quantitative LC-MS/MS method working in the multiple-reaction monitoring mode; (4) validation of the assay; (5) investigation of the stability and the reactivity of BITC conjugates in vitro; (6) application of the method to samples from a human intervention study. The lower limits of quantification were in the range of 21-183 nM depending on analyte and matrix, whereas the average recovery rates from spiked plasma and urine were approximately 85 and 75 %, respectively. BITC conjugates were found to be not stable in alkaline buffered solutions. After consumption of nasturtium, containing 1,000 μM glucotropaeolin, the primary source of BITC, quantifiable levels of BITC-NAC, BITC-Cys, and BITC-CysGly were found in human urine samples. Maximum levels in urine were determined 4 h after the ingestion of nasturtium. With regard to the human plasma samples, all metabolites were determined including individual distributions. The work presented provides a validated LC-MS/MS method for the determination of BITC metabolites and its successful application for the analysis of samples collected in a human intervention study.