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Updated: Mar 16, 2026
Homogeneous Time-resolved Förster Resonance Energy Transfer-based Assay for Detection of Insulin Secretion
Published on: May 10, 2018
A stable isotope method for in vivo assessment of human insulin synthesis and secretion
Sjaam Jainandunsing1, Joram N I van Miert1, Trinet Rietveld1
1Department of Internal Medicine, Erasmus MC - University Medical Center Rotterdam, Room Na512, PO Box 2040, 3000 CA, Rotterdam, The Netherlands.
Insights
Newly synthesized insulin accounts for 20% of total secretion during an oral glucose tolerance test (OGTT). This stable isotope tracer method can assess in vivo beta cell function, distinguishing between readily available and newly made insulin.
Area of Science:
- Endocrinology
- Metabolic Research
- Biochemistry
Background:
- Beta cells release stored insulin rapidly upon glucose increase.
- Prolonged glucose stimulation triggers newly synthesized insulin secretion.
- Quantifying newly synthesized insulin in vivo is crucial for understanding beta cell dynamics.
Purpose of the Study:
- To develop an in vivo method for measuring the ratio of readily available to newly synthesized insulin in humans.
- To label and quantify newly synthesized insulin secretion following a glucose challenge.
Main Methods:
- Administered a stable isotope tracer (13C leucine) before a 75g oral glucose tolerance test (OGTT).
- Collected blood and urine samples frequently over 210 minutes to measure C-peptide.
- Utilized stable isotope enrichment of de novo C-peptide to assess newly synthesized insulin contribution.
Main Results:
- Newly synthesized insulin comprised approximately 20% of total insulin secretion during the OGTT.
- Isotope enrichment patterns indicated newly synthesized insulin contributes to the late phase of secretion.
- De novo C-peptide levels negatively correlated with early plasma insulin and glucose AUC.
Conclusions:
- A stable isotope technique combined with OGTT successfully measured newly synthesized insulin in healthy individuals.
- This novel method shows promise for developing a direct in vivo beta cell function test.
- The findings provide insights into the dynamic nature of insulin secretion.
Aims:
In vitro, beta cells immediately secrete stored but readily releasable insulin in response to a rise of glucose. During a prolonged insulin response, this is followed by newly synthesized insulin. Our aim was to develop an in vivo test to determine the ratio between readily available and newly synthesized insulin after a stimulus in humans by labelling newly synthesized insulin.
Methods:
A stable isotope tracer of 1.0 g 13C leucine with C-peptide as target peptide was administered 45 min prior to 75 g glucose load of a frequently blood sampled 210-min oral glucose tolerance test (OGTT). Our OGTT also encompassed collection of urine, which has a high content of C-peptide. Prior, the optimal conditions under which the tracer 13C leucine was administered for enrichment of (pre) proinsulin were established. Also, techniques to obtain urinary C-peptide under highly purified circumstances were set up. Our main outcome measure was the stable isotope enrichment of de novo C-peptide, which we related to early plasma insulin and glucose AUC. Twelve healthy Caucasian individuals (M4F8, age 41.8 ± 2.3, BMI 28.3 ± 1.7) with normal glucose tolerance underwent our OGTT.
Results:
We found that during a 75-g OGTT, newly synthesized insulin contributed approximately 20 % of total insulin secretion. The pattern of isotope enrichment obtained by collecting multiple urine voids was suggestive that the newly synthesized insulin contributes to the late phase of insulin secretion. De novo C-peptide correlated negatively with both early plasma insulin AUC (r = -0.629, P = 0.028) and early plasma glucose AUC (r = -0.605, P = 0.037).
Conclusions:
With stable isotope technique added to OGTT, we were able to measure newly synthesized insulin in healthy individuals. This new technique holds the promise that it is feasible to develop a direct in vivo beta cell function test.
