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Glucagon-like peptide-1 (GLP-1) is a gut hormone which plays an essential role in insulin secretion and glucose homeostasis1. While GLP-1 has become central to many metabolic disease research programs, various GLP-1 ELISA kits currently available on the market have been failing to meet the needs of researchers1-5. Therefore, measuring total and active levels of GLP-1 is difficult for many labs2-4. Experiments testing the assay characteristics of commercially available ELISA kits often demonstrate three challenges with GLP-1 assays.  As a result, ALPCO developed the STELLUX® Chemi Active GLP-1 (7-36) amide ELISA to provide an accurate solution to the challenges with measuring GLP-1.

Although GLP-1 has been studied for more than 30 years1, researchers note that accurate measurement of the incretin hormone is limited by the tools available to labs2,3,4. The following three challenges with measuring GLP-1 create many obstacles within the diabetes and obesity research community which can hinder further advancement in therapies.

One of the challenges with measuring GLP-1 is the variability among GLP-1 assays from different manufacturers and between lots of the same assay2,3. High variability in GLP-1 assays is problematic because not only is it difficult to obtain precise and accurate GLP-1 measurements within the same laboratory, it is also difficult to compare results across laboratories. Researchers at the University of Copenhagen clearly demonstrated high GLP-1 assay variability. Bak, et al2 tested the specificity, sensitivity, and precision of ten commercially available active and total GLP-1 assays. The testing performed clearly demonstrates that the different GLP-1 assays are not standardized. Moreover, this study showed the tremendous inter-lot variability of GLP-1 assays, even from a single manufacturer. The variability displayed by the GLP-1 kits examined by Bak, et al2 is a problem because it limits the ability of researchers to compare results between studies or against results from their own study over time. In turn, this can likely hamper diabetes and obesity research progress.

Another challenge researchers can face when measuring GLP-1 is the inadequate sensitivity provided by commercially available assays2. GLP-1 is an extremely labile analyte and because it circulates in the body, it is rapidly degraded by dipeptidyl peptidase 4 (DPP-4)1,2,3,5. Ultimately, only 10-15% of the originally secreted active GLP-1 reaches peripheral organs2. Overall, research indicates that the typical physiological levels of active GLP-1 are 0-15 pmol/L2 and those of total GLP-1 are 5-80 pmol/L2. When performing fasted vs. fed studies, levels are in the single digit pM levels. Therefore, it is imperative that an assay be able to accurately and precisely measure extremely low levels of circulating active GLP-1. Bak, et al2 discovered through accuracy and precision testing that several of the GLP-1 assays (total and active) fail to be sensitive enough despite the advertised assay characteristics. Researchers should be very careful when selecting a GLP-1 ELISA - to ensure the selected kit can properly detect the chosen form of GLP-1 in their samples2. Using kits that fail to accurately and precisely detect GLP-1 can lead to increased costs for a research project, false positive and/or negative values, and inability to compare data from previously conducted studies.

A third problem when measuring GLP-1 is that some kits require excessive sample volumes to attain any reasonable sensitivity and yield “real” values. The large sample size needed to run some GLP-1 assays can be a heavy burden on research groups when there isn’t enough sample for them to measure either multiple analytes (rodent models) or pre- and post-prandial GLP-1 levels. Half of the GLP-1 assays tested by Bak, et al2 require a sample volume of 100 µL or more per single well determination. Some of the kits tested with high sample volume were not able to detect any form of GLP-1. The assays that did yield GLP-1 values demonstrated poor recovery, indicating inaccuracy. For the GLP-1 kits requiring sample volume less than 100 µL, the lot-to-lot variability was noted as being extremely high2.

It is difficult for many labs to accurately and precisely measure active GLP-1 (7-36) amide. To address the challenges with measuring GLP-1, ALPCO developed a new GLP-1 assay specifically designed to determine the biologically active form of GLP-1 found in circulation, active GLP-1 (7-36) amide. The STELLUX® Chemi Active GLP-1 (7-36) amide ELISA utilizes chemiluminescence to provide labs with high sensitivity and specificity, a broad range, and a very low sample volume. Additionally, ALPCO’s assay is flexible and validated for mouse, rat, and human samples.

Extensive research performed by Bak, et al2 demonstrates three challenges with measuring GLP-1 using commercially available assays. These challenges include high GLP-1 assay variability, insufficient assay sensitivity, and excessive assay sample volume requirements. Due to these three challenges, researchers should use caution when selecting the right GLP-1 kit2. ALPCO developed its STELLUX® Chemi Active GLP-1 (7-36) amide ELISA to confront these issues and provide researchers with an accurate solution to the challenges with measuring GLP-1.  

References

1. Tian L and Jin T (2016). The incretin hormone GLP-1 and mechanisms underlying its secretion. J Diabetes. J Diabetes. 2016 Nov;8(6):753-765. PMID: 27287542.
2. Bak, et al (2014). Specificity and sensitivity of commercially available assays for glucagon-like-peptide-1 (GLP-1): implications for GLP-1 measurements in clinical trials. Diabetes Obes Metab; 16(11):1155-64. PMID: 25041349.
3. Yabe, et al (2012). Comparison of incretin immunoassays with or without plasma extraction: Incretin secretion in Japanese patients with type 2 diabetes. J Diabetes Investig. 2012 Feb 20; 3(1):70-79. PMID: 24843548.
4. Lee, et al (2016). Multiplexed Quantification of Proglucagon-Derived Peptides by Immunoaffinity Enrichment and Tandem Mass Spectrometry after a Meal Tolerance Test. Clin Chem. 2016 Jan;62(1):227-35. PMID: 26430077.
5. Wewer Albrechtsen, et al (2015). Stability of glucagon-like peptide 1 and glucagon in human plasma. Endocrine Connections, 4:50-57. PMID: 25596009.