Trapping of Reactive Metabolites

As a result of advances in LC-MS/MS technology, detecting adducts with nucleophiles, such as GSH, cyanide, methoxylamine, and semicarbazide, is practical (see Fig. 6.3).

6.5.1.1 GSH Conjugates

GSH conjugates are suited for detection of soft electrophiles such as Michael acceptors and epoxides. To screen for GSH conjugates use the following:

• A 129 Da (glutamic acid) neutral loss scan in the positive ion mode on a triple quadrupole mass spectrometer.

• A m/z 272 precursor ion scan in the negative ion mode on a triple quadrupole mass spectrometer (Dieckhaus et al. 2005). This method is described as having low interference.

Detection of GSH conjugates is more selective when using a mixture of regular and stable-labeled GSH (Yan and Caldwell 2004).

6.5.1.2 GSH Analogs

GSH detection by LC-MS/MS is not quantitative, and other trapping analogs, such as [3H]GSH (Thompson et al. 1995) and dansyl-GSH (Gan et al. 2009), are used for this purpose. The limitation of these studies is that the trapped GSH conjugates usually form a small portion of the total GSH conjugates.

In addition, quaternary ammonium GSH analogs produce more-sensitive GSH adducts (Soglia et al. 2006). Note that analogs of GSH are not catalyzed by glutathione S-transferase (GST).

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