Quantitation of Glutathione by Quinoline-5, 8-Dione-Based Tag Strategy Using MALDI Mass Spectrometry

In the present work, we developed an UV-absorptive and highly reactive tag aromatic molecule, quinoline-5,8-dione (QLD), for robust quantitative analysis of GSH by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. The QLD could react with GSH with high efficiency at room temperature, and the resultant QLD-GSH conjugate could be readily detected by MALDI MS without interferences. By using the QLD tag, the detection limit of GSH was lowered to 10 fmol μL^-1, which was four orders of magnitude higher than that detected without using the QLD tag. Furthermore, accurate quantitative measurements of GSH in solution were successfully demonstrated by using glutamic acid-cysteine-alanine (ECA) as an internal standard. By properly adjusting the ECA concentrations, the intensity ratio value of QLD-tagged GSH (QLD-GSH) to QLD-tagged ECA (QLD-ECA) displayed a good linearity with GSH concentrations in a broad range from 4 to 4000 μM. Finally, the GSH level in HeLa cell lysates was also successfully detected, and the results are consistent with that obtained by a colorimetric assay. In summary, the proposed QLD-based tag method should be a rapid, cost-/time-effective, and sensitive new method for quantitative determination of GSH by MALDI MS. Graphical Abstract.