The Pharmacological Problem of Native GLP-1: Degradation, Half-Life and DPP-4

Incretin Historical Guideline Series | Milestone 12

Executive summary

The physiological consolidation of GLP-1 introduced a paradox: the peptide showed relevant biological potency, but limited pharmacological stability. Rapid degradation by dipeptidyl peptidase IV (DPP-4) made native GLP-1 an effective physiological signal, but a difficult molecule to use directly as a sustained systemic drug [1-3].

This milestone documents the transition from physiology to pharmacological engineering: identifying the vulnerability of native GLP-1 enabled two subsequent therapeutic lines: resistant or prolonged GLP-1 analogues/agonists, and DPP-4 inhibitors designed to preserve endogenous incretin activity [4,5].

1. Historical context

By the early 1990s, GLP-1 had already been recognized as a functional incretin with effects on insulin secretion, glucagon and postprandial metabolism. The technical problem was different: biological activity did not guarantee pharmacological utility if the molecule was rapidly inactivated in circulation [2,6].

Mentlein, Gallwitz and Schmidt reported in 1993 that DPP-4 hydrolyzed both GIP and GLP-1(7-36) amide in human serum, establishing a direct connection between incretins and a specific enzymatic degradation pathway [1].

2. Scientific development of the milestone

Deacon, Johnsen and Holst reported in 1995 that degradation of GLP-1 in human plasma yielded an N-terminally truncated peptide, GLP-1(9-36) amide, identified as a relevant endogenous metabolite. The study proposed DPP-4 as a primary mechanism of GLP-1 degradation in human plasma [2].

In the same period, Kieffer, McIntosh and Pederson reinforced the role of DPP-4 in the degradation of both GIP and GLP-1 in vitro and in vivo. This convergence made DPP-4 a logical pharmacological target for preserving incretin activity [3].

Holst later synthesized a central physiological reading: GLP-1 is metabolized and inactivated extremely rapidly by DPP-4, even before fully leaving the intestinal territory, limiting its functional plasma half-life and requiring pharmacological stabilization pathways [6].

3. HMD figure: degradation and loss of exposure

Figure 1. HMD representation of the pharmacological problem of native GLP-1: the receptor was not the primary obstacle; the obstacle was sustained exposure of intact peptide under rapid enzymatic degradation.

4. Documentary sequence

5. HMD chronological table

6. Independent HMD analysis

From the HMD perspective, DPP-4 degradation represents a methodological inflection point. Before this milestone, GLP-1 could be understood as a physiological signal. After this milestone, GLP-1 also had to be understood as a pharmacological design problem: how to preserve a useful signal without losing specificity, duration or tolerability.

The fragility of native GLP-1 does not invalidate its relevance; it explains it. The subsequent evolution of GLP-1 receptor agonists, albumin binding, sequence modification, half-life extension and long-acting formulations responded to the same question: how to convert a brief physiological signal into a sustained therapeutic tool [4,7,8].

7. Two solution routes

Figure 2. HMD synthesis of the two historical solutions to the exposure problem: stabilize the agonist or protect endogenous incretin signaling through DPP-4 inhibition.

8. Relationship with later milestones

This milestone prepares the transition toward clinical GLP-1 receptor agonists. The need to overcome degradation and short half-life explains the development of exenatide, liraglutide, semaglutide and other long-acting agonists, as well as the parallel development of DPP-4 inhibitors [5,8].

References

1. Mentlein R, Gallwitz B, Schmidt WE. Dipeptidyl-peptidase IV hydrolyses gastric inhibitory polypeptide and glucagon-like peptide-1(7-36)amide in human serum. Eur J Biochem. 1993;214(3):829-835. doi:10.1111/j.1432-1033.1993.tb17986.x.

2. Deacon CF, Johnsen AH, Holst JJ. Degradation of glucagon-like peptide-1 in vitro yields an N-terminally truncated peptide which is a major endogenous metabolite in vivo. J Clin Endocrinol Metab. 1995;80(3):952-957. doi:10.1210/jcem.80.3.7883856.

3. Kieffer TJ, McIntosh CHS, Pederson RA. Degradation of glucose-dependent insulinotropic polypeptide and truncated glucagon-like peptide-1 in vitro and in vivo by dipeptidyl peptidase IV. Endocrinology. 1995;136(8):3585-3596. doi:10.1210/endo.136.8.7628397.

4. Gallwitz B, Witt M, Paetzold G, Morys-Wortmann C, Zimmermann B, Eckart K, et al. GLP-1-analogues resistant to degradation by dipeptidyl-peptidase IV in vitro. Regul Pept. 2000;86(1-3):103-111. doi:10.1016/S0167-0115(99)00122-3.

5. Ahrén B. GLP-1 receptor agonists and DPP-4 inhibitors in the treatment of type 2 diabetes. Horm Metab Res. 2004;36(11-12):867-876. doi:10.1055/s-2004-826178.

6. Holst JJ. The physiology of glucagon-like peptide 1. Physiol Rev. 2007;87(4):1409-1439. doi:10.1152/physrev.00034.2006.

7. Drucker DJ. The cardiovascular biology of glucagon-like peptide-1. Cell Metab. 2016;24(1):15-30. doi:10.1016/j.cmet.2016.06.009.

8. Müller TD, Finan B, Bloom SR, D'Alessio D, Drucker DJ, Flatt PR, et al. Glucagon-like peptide 1 (GLP-1). Mol Metab. 2019;30:72-130. doi:10.1016/j.molmet.2019.09.010.