GLP-1 peptides explained: single, dual, triple agonists

GLP-1 (glucagon-like peptide-1) is a gut hormone that the body releases after a meal. It belongs to the incretin hormones, a group of peptides that increase insulin release when blood glucose rises. In its natural form, GLP-1 survives in the blood for only about two minutes. Synthetic analogues solve this problem and have become the basis of a whole class of research peptides and approved medicines. This guide explains what GLP-1 does, how the related hormones GIP and glucagon fit in, and what the terms single, dual and triple agonist mean.

What is GLP-1 and where does it come from?

GLP-1 is cut out of a larger precursor protein called proglucagon. Specialised cells in the gut lining, the L cells, produce it. Most L cells sit in the lower small intestine and the colon. When nutrients reach these cells, they release GLP-1 into the blood within minutes.

The active form of the hormone is a chain of 30 or 31 amino acids, written as GLP-1(7-36) amide or GLP-1(7-37). It binds to the GLP-1 receptor, a class B G protein-coupled receptor. This receptor is found on the insulin-producing beta cells of the pancreas, in several regions of the brain, in the stomach, in the heart and in other tissues. A detailed review of GLP-1 biology by Daniel Drucker (2018) in Cell Metabolism describes the main effects that follow receptor activation:

• Insulin release: GLP-1 increases insulin secretion, but only when glucose is elevated

• Glucagon suppression: it reduces glucagon output from the alpha cells of the pancreas

• Gastric emptying: it slows the movement of food from the stomach into the intestine

• Appetite signalling: it acts on neurons in the hypothalamus and brainstem that regulate food intake

The glucose-dependent nature of the insulin effect is important. GLP-1 does not force insulin release when blood sugar is normal, which is one reason the receptor became an attractive drug target.

Why native GLP-1 has a two minute half-life

Native GLP-1 is a poor drug candidate. An enzyme called dipeptidyl peptidase-4 (DPP-4) cuts off the first two amino acids of the peptide almost immediately after release. The cut happens after the alanine at position 8. The shortened fragment no longer activates the receptor. Together with rapid kidney clearance, this gives native GLP-1 a plasma half-life of about one to two minutes.

Peptide chemists use three main modifications to make GLP-1 analogues last longer. The review by Knudsen and Lau (2019) in Frontiers in Endocrinology describes how these tools were applied to liraglutide and semaglutide:

• DPP-4 resistance: the alanine at position 8 is replaced, for example with aminoisobutyric acid (Aib). DPP-4 can no longer cut the chain.

• Fatty acid chains: a lipid chain is attached to a lysine side chain through a short linker. Liraglutide carries a C16 fatty acid, semaglutide a C18 fatty diacid.

• Albumin binding: the fatty acid binds reversibly to albumin, the most abundant protein in blood. The bound peptide is protected from enzymes and from kidney filtration, and it is released slowly.

The result is a dramatic change in half-life. Liraglutide reaches about 13 hours, which allows once-daily dosing in the approved medicine. Semaglutide reaches about one week, as reported by Lau et al. (2015) in the Journal of Medicinal Chemistry. The same principles are used in the dual and triple agonists described below.

GLP-1 vs GIP vs glucagon: the three receptor classes

GLP-1 is one of three related hormones that share a similar structure and signal through related receptors. Understanding the differences explains why newer peptides target more than one receptor at a time.

• GLP-1 receptor: activated by GLP-1 from the L cells. Main effects are glucose-dependent insulin release, slower gastric emptying and reduced appetite signalling.

• GIP receptor: activated by glucose-dependent insulinotropic polypeptide. GIP is released by K cells in the upper small intestine. It also increases insulin release after a meal and acts on fat tissue and on the brain. The review by Müller et al. (2019) in Molecular Metabolism discusses how GIP receptor signalling adds to the effects of GLP-1 in animal models.

• Glucagon receptor: activated by glucagon from the alpha cells of the pancreas. Glucagon raises blood glucose by releasing stored glucose from the liver and increases energy expenditure. On its own, this would be unwanted. In combination with GLP-1 receptor activity, the glucose-raising effect is balanced by the insulin effect.

All three receptors belong to the same class B family of G protein-coupled receptors. This structural similarity is what makes it possible to design one peptide that fits more than one receptor. For a wider overview of compounds in this area, see our collection of GLP-1 and weight management peptides.

Single, dual and triple agonists explained

An agonist is a molecule that activates a receptor. The terms single, dual and triple refer to how many of the three receptors a peptide activates.

Single agonists: semaglutide and liraglutide

Single agonists act on the GLP-1 receptor only. Liraglutide is a 97 percent match to native GLP-1 with one amino acid change and a C16 fatty acid. Semaglutide adds the Aib substitution at position 8 and a longer C18 diacid chain. In the STEP 1 trial (Wilding et al., 2021, New England Journal of Medicine), 1,961 adults with overweight or obesity received once-weekly semaglutide 2.4 mg or placebo for 68 weeks. Mean body weight change was minus 14.9 percent with semaglutide and minus 2.4 percent with placebo.

Dual agonists: tirzepatide

Tirzepatide is a 39 amino acid peptide that activates both the GIP receptor and the GLP-1 receptor. Coskun et al. (2018) in Molecular Metabolism describe its discovery. The sequence is based on native GIP, with changes that add GLP-1 receptor activity, plus a C20 fatty diacid for albumin binding. Its half-life is about five days. In the SURMOUNT-1 trial (Jastreboff et al., 2022, New England Journal of Medicine), 2,539 adults received tirzepatide 5 mg, 10 mg or 15 mg once weekly or placebo for 72 weeks. Mean body weight changes were minus 15.0 percent, minus 19.5 percent and minus 20.9 percent for the three doses, compared with minus 3.1 percent for placebo.

Triple agonists: retatrutide

Retatrutide goes one step further and activates the GIP, GLP-1 and glucagon receptors. Coskun et al. (2022) in Cell Metabolism report that the peptide is also built on a GIP backbone with a C20 fatty diacid and has a half-life of about six days. The phase 2 trial by Jastreboff et al. (2023) in the New England Journal of Medicine enrolled 338 adults with obesity for 48 weeks. Mean weight change at 48 weeks was minus 8.7 percent (1 mg), minus 17.1 percent (4 mg group), minus 22.8 percent (8 mg group) and minus 24.2 percent (12 mg group), compared with minus 2.1 percent for placebo. Retatrutide is in phase 3 trials and is not an approved medicine.

Comparison table: receptor targets and half-life

Half-life values are taken from the discovery papers listed in the sources. They describe the pharmaceutical reference compounds, not research grade material.

GLP-1 research compounds: GLP-2T and GLP-3RT

The compounds in our catalogue are research peptides, not pharmaceutical products. GLP-2T is a dual agonist research compound designed around the GIP and GLP-1 receptor profile. GLP-3RT is a triple agonist research compound designed around the GIP, GLP-1 and glucagon receptor profile. Both are supplied as lyophilised powder in vial sizes from 10 mg to 40 mg, each with a certificate of analysis (COA) for the batch.

Points to keep in mind when working with these compounds:

• They are made by chemical peptide synthesis for in vitro and preclinical research.

• They are not the branded medicines and have not passed any clinical trial programme.

• The COA documents identity and purity of the batch, which is the basis for any experimental work.

• Lyophilised powder is stored at minus 20 °C and dissolved in a sterile solvent before use. The steps are described in our guide on how to reconstitute peptides.

Regulatory status of GLP-1 peptides

The regulatory picture is split in two. On one side are approved medicines. Liraglutide, semaglutide and tirzepatide are authorised by the FDA and the EMA for defined indications, with product information published for each, for example the EMA page on tirzepatide (Mounjaro). Retatrutide has not been approved anywhere.

On the other side are research compounds such as GLP-2T and GLP-3RT. These are not approved for any medical use. They are sold as research chemicals for laboratory use only and are not intended for human or veterinary use.

In sport, GLP-1, GIP and glucagon receptor agonists are not named on the current WADA Prohibited List. The list is updated every year, and athletes who are subject to anti-doping rules should check the latest version before making any assumption.

Frequently asked questions about GLP-1 peptides

Sources

• Drucker DJ (2018). Mechanisms of action and therapeutic application of glucagon-like peptide-1. Cell Metabolism 27(4), 740-756. doi:10.1016/j.cmet.2018.03.001

• Müller TD, Finan B, Bloom SR, et al. (2019). Glucagon-like peptide 1 (GLP-1). Molecular Metabolism 30, 72-130. doi:10.1016/j.molmet.2019.09.010

• Knudsen LB, Lau J (2019). The discovery and development of liraglutide and semaglutide. Frontiers in Endocrinology 10, 155. doi:10.3389/fendo.2019.00155

• Lau J, Bloch P, Schäffer L, et al. (2015). Discovery of the once-weekly glucagon-like peptide-1 (GLP-1) analogue semaglutide. Journal of Medicinal Chemistry 58(18), 7370-7380. doi:10.1021/acs.jmedchem.5b00726

• Wilding JPH, Batterham RL, Calanna S, et al. (2021). Once-weekly semaglutide in adults with overweight or obesity. New England Journal of Medicine 384, 989-1002. doi:10.1056/NEJMoa2032183

• Coskun T, Sloop KW, Loghin C, et al. (2018). LY3298176, a novel dual GIP and GLP-1 receptor agonist for the treatment of type 2 diabetes mellitus: from discovery to clinical proof of concept. Molecular Metabolism 18, 3-14. doi:10.1016/j.molmet.2018.09.009

• Jastreboff AM, Aronne LJ, Ahmad NN, et al. (2022). Tirzepatide once weekly for the treatment of obesity. New England Journal of Medicine 387(3), 205-216. doi:10.1056/NEJMoa2206038

• Coskun T, Urva S, Roell WC, et al. (2022). LY3437943, a novel triple glucagon, GIP, and GLP-1 receptor agonist for glycemic control and weight loss: from discovery to clinical proof of concept. Cell Metabolism 34(9), 1234-1247. doi:10.1016/j.cmet.2022.07.013

• Jastreboff AM, Kaplan LM, Frías JP, et al. (2023). Triple-hormone-receptor agonist retatrutide for obesity: a phase 2 trial. New England Journal of Medicine 389(6), 514-526. doi:10.1056/NEJMoa2301972

• European Medicines Agency. Mounjaro (tirzepatide) EPAR. ema.europa.eu

This article summarises published research for information only. It is not medical advice. All products on this site are sold for laboratory research use only and are not intended for human or veterinary use.