Best Practice & Research Clinical Endocrinology & Metabolism
2Immunoassays for the incretin hormones GIP and GLP-1
Section snippets
Measurement of proglucagon-derived peptides
The proglucagon (PG) gene is expressed in the pancreatic α-cells, the intestinal L-cells and in the brain.1, 2 Following the cloning of the gene in 19835, it was discovered that the way in which it is processed differs in a tissue-specific way, giving rise to a number of peptides which are secreted in parallel (Fig. 1). In the pancreatic α-cells, cleavage by prohormone convertase (PC) 26 gives rise to glicentin-related pancreatic peptide (GRPP) and glucagon, corresponding to PG (1–30) and PG
Measurement of preproGIP-derived peptides
The immunological determination of GIP concentrations generally does not present the same difficulties as GLP-1 since the processing pattern of GIP is much less complicated (Fig. 2). GIP is derived by proteolytic processing of the 153-residue precursor, preproGIP, which is expressed in the intestinal K-cells, and consists of three domains.29 The 42-amino-acid-long GIP is flanked at either side by an N-terminal domain, which contains the signal peptide, and a C-terminal domain. Cleavage by PC
Practical considerations
It is noteworthy that a comparison of incretin hormone levels determined in earlier studies with those reported in more recent publications shows that there is a clear trend for the measured concentrations to have become lower with time. Part of the explanation is that the interference from cross-reacting peptides has been eliminated (or at least reduced) by the selection of antisera directed against well-defined epitopes, based upon the better understanding of the processing patterns of the
Conclusions
The determination of incretin hormone concentrations by immunological methods is complicated because the processing of the precursor molecules and subsequent degradation of the products in the plasma give rise to a plethora of related peptides which can cross-react to varying degrees with the assays being used.
It is also worthy of comment that commercially available antisera and assay kits are, in general, poorly characterised, and, in many cases, the epitope which is being detected is
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2023, Metabolism: Clinical and ExperimentalCitation Excerpt :Because of the importance of antisera directed against specific GLP-1 epitopes, the majority of studies employ a well-defined radioimmunoassay [27]. Commercially available antisera and assay kits are often poorly characterised which limits the certainty of which GLP-1 isoforms are detected [28]. As a result, commercially available assays tend to exhibit varying specificity [29], which suggests the type of assay may influence the quantified difference in GLP-1 secretion between individuals with and without T2D.
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2022, Metabolism: Clinical and ExperimentalCitation Excerpt :Accordingly, the Millipore Total GLP-1 ELISA Kit should be suitable for studies aiming to assess the secretory response of GLP-1 to specific interventions in clinical settings [50]. To further improve the specificity and sensitivity, Deacon et al. recommended an ethanol extraction step before formal test in order to reduce non-specific interference [51]; And Perakakis et al. reported novel GLP-1 ELISA assays from Ansh labs that a uniquely designed solid phase extraction plate could eliminate the risk of detecting other proglucagon-derived peptides, which makes the assays attain higher specificity to GLP-1 [52]. Several limitations should be noted while interpreting our findings.
Oxyntomodulin: Actions and role in diabetes
2018, PeptidesCitation Excerpt :There were no reported side effects, such as itching or restlessness. In rodents, its effects on food intake were abolished by exendin-4 [9–39] and absent in GLP-1R knockout mice [42]. The effect on energy expenditure, however, was not affected and may thus be due to activation of the glucagon receptor [69].
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2017, Nutrition, Metabolism and Cardiovascular DiseasesMeasurement of the incretin hormones: Glucagon-like peptide-1 and glucose-dependent insulinotropic peptide
2015, Journal of Diabetes and its ComplicationsCitation Excerpt :A low secretory rate is responsible for this, but rapid post-secretory degradation of the peptides and the existence of several peptide isoforms complicate analyses further. In addition, there are inter-species differences with respect to the molecular forms, requiring special attention, and finally there is often unspecific interference by substances present in biological fluids (Deacon & Holst, 2009). In the following, we will discuss current methods for quantification of GIP and GLP-1.