Degradation of glucagon-like peptide-1 by human plasma in vitro yields an N-terminally truncated peptide that is a major endogenous metabolite in vivo.
The metabolism of glucagon-like peptide-1 (GLP-1) has not been studied in detail, but it is known to be rapidly cleared from the circulation. Measurement by RIA is hampered by the fact that most antisera are side-viewing or C-terminally directed, and recognize both intact GLP-1 and biologically inactive. N-terminally truncated fragments. Using high pressure liquid chromatography in combination with RIAs, methodology allowing specific determination of both intact GLP-1 and its metabolites was developed. Human plasma was shown to degrade GLP-1-(7-36)amide, forming an N-terminally truncated peptide with a t1/2 of 20.4 +/- 1.4 min at 37 C (n = 6). This was unaffected by EDTA or aprotinin. Inhibitors of dipeptidyl peptidase-IV or low temperature (4 C) completely prevented formation of the metabolite, which was confirmed to be GLP-1-(9-36)amide by mass spectrometry and sequence analysis. High pressure liquid chromatography revealed the concentration of GLP-1-(9-36)amide to be 53.5 +/- 13.7% of the concentration of endogenous intact GLP-1 in the fasted state, which increased to 130.8 +/- 10.0% (P < 0.01; n = 6) 1 h postprandially. Metabolism at the C-terminus was not observed. This study suggests that dipeptidyl peptidase-IV is the primary mechanism for GLP-1 degradation in human plasma in vitro and may have a role in inactivating the peptide in vivo.
Deacon
C F
CF
Department of Medical Physiology, Panum Institute, University of Copenhagen, Denmark.
Johnsen
A H
AH
Holst
J J
JJ
D002851:Chromatography, High Pressure Liquid; D005260:Female; D005934:Glucagon / Q000097:blood / Q000378:metabolism*; D052216:Glucagon-Like Peptide 1; D006801:Humans; D008297:Male; D010446:Peptide Fragments / Q000097:blood / Q000378:metabolism*; D011498:Protein Precursors / Q000097:blood / Q000378:metabolism*
D010446:Peptide Fragments; D011498:Protein Precursors; D052216:Glucagon-Like Peptide 1; D005934:Glucagon