Immunoprecipitation and liquid chromatographic-mass spectrometric determination of the peptide glucose-dependent insulinotropic polypeptides GIP(1-42) and GIP(3-42) from human plasma samples - New sensitive method to analyzephysiological concentrations of peptide hormones

The gastrointestinal peptide glucose-dependent insulinotropic polypeptide ( GIP(1-42)) is one of the incretin hormones regulating glucose-induced insul in secretion from the endocrine pancreas. GIP(1-42) is a substrate of the c irculating enzyme dipeptidyl peptidase IV, which removes the N-terminal pep tide Tyr-Ala resulting in the inactive polypeptide GIP(3-42). Hither to exi sting immunoassays do not enable a separate quantification of active and in active forms, respectively. Therefore, we developed a highly specific and s ensitive LC-MS assay for the identification and quantification of GIP(1-42) and GIP(3-42). Total GIP was inummoprecipitated from crude plasma samples using a C-terminally directed antibody. Thus, peptides were purified and co ncentrated prior to LC-MS analysis. The present immunoprecipitation-LC-MS a ssay enables the quantification of active and inactive GIP over a concentra tion range from 5 to 350 pmol/l in human plasma samples. Since this range c overs the basal and postprandial levels of GIP, the method is applicable to the determination of concentration changes and changes in the ratio of act ive and inactive forms of GIP in human plasma. (C) 2001 Elsevier Science B. V. All rights reserved.