A liquid chromatography-mass spectrometry assay for quantification of Exendin[9-39] in human plasma

Exendin[9-39] is a glucagon-like peptide-1 receptor (GLP-R) antagonist and a potential therapeutic drug for treatment of congenital hyperinsulism by lowering insulin concentration in plasma. A specific and sensitive LC-MS/MS method was validated for quantification of Exendin[9-39] in human plasma. Exendin[9-39] and the stable isopically labeled internal standard eluted at 9.2 min and were analyzed by single reaction monitoring (SRM) of the transitions m/z 842.9→991.8 and 848.2→998.8, respectively. The calibration curve was linear in the range 15-1260 ng/mL with a limit of detection of 1.3 ng/mL. The CVs of the standards were 2.7-13.1% within-run and 3.1-13.2% between-run. The matrix effect was >100% and the SPE recovery was 98.4±12.9%. In absence of protease inhibitors, short-term stability at room temperature was only one hour. Accordingly, samples were kept on ice and sample processing was kept below 1h. Human plasma samples from a clinical pilot study in which Exendin[9-39] was administered intravenously were analyzed and concentrations up to 600 ng/mL were reported Plasma samples from the study were stored at -80 °C with internal standard and successfully reanalyzed after 12 months.