Abstract
Accurate quantification of plasma glucagon levels in humans is necessary for understanding the physiological and pathological importance of glucagon. Although several immunoassays for glucagon are available, they provide inconsistent glucagon values owing to cross-reactivity of the antibodies with peptides other than glucagon. To overcome this limitation, we developed a novel method to measure glucagon levels by a liquid chromatography (LC)-high-resolution mass spectrometry (HRMS) assay via parallel reaction monitoring (PRM) without immunoaffinity enrichment. Using stable isotope-labeled glucagon as an internal standard and 200 μL of plasma, the lower limit of quantification was 0.5 pM. This method was applied to measure plasma glucagon levels during the oral glucose tolerance test (OGTT) and meal tolerance test (MTT) in healthy volunteers, and its results were compared with those of sandwich enzyme-linked immunosorbent assay (ELISA) and radioimmunoassay (RIA). During the OGTT, this method showed significant suppression of plasma glucagon levels, and similar patterns were observed with sandwich ELISA and RIA. In contrast, during the MTT, plasma glucagon levels were slightly elevated according to the LC-MS/MS and sandwich ELISA results and were reduced according to RIA results. Our newly developed LC-MS/MS method overcomes a lack of specificity among currently available immunoassays for glucagon and may contribute to a better understanding of the importance of glucagon.
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Abbreviations
- CV:
-
Coefficient of variation
- ESI:
-
Electrospray ionization
- HRMS:
-
High-resolution mass spectrometry
- IS:
-
Internal standard
- LLOQ:
-
Lower limit of quantification
- MTT:
-
Meal tolerance test
- OGTT:
-
Oral glucose tolerance test
- PP:
-
Protein precipitation
- PRM:
-
Parallel reaction monitoring
- RE:
-
Relative error
- SPE:
-
Solid-phase extraction
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Acknowledgements
We are grateful to the members of Thermo Fisher Scientific and to T. Murase, S. Yamashita, and H. Hashimoto for their fruitful discussions and technical support. We also thank the members of the Kitamura Laboratory for the discussion of the data.
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All participants gave oral and written consent. The study was approved by the Ethics Committee of Gunma University and was conducted in accordance with the Declaration of Helsinki.
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Miyachi, A., Kobayashi, M., Mieno, E. et al. Accurate analytical method for human plasma glucagon levels using liquid chromatography-high resolution mass spectrometry: comparison with commercially available immunoassays. Anal Bioanal Chem 409, 5911–5918 (2017). https://doi.org/10.1007/s00216-017-0534-0
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DOI: https://doi.org/10.1007/s00216-017-0534-0