GLP-1, GIP and Glucagon Receptor Pharmacology: Mono-, Dual- and Triple-Agonist Peptides Compared

• ·Semaglutide is a selective GLP-1 receptor agonist. Tirzepatide activates the GIP and GLP-1 receptors. Retatrutide activates the GIP, GLP-1 and glucagon receptors.[1][2][3]
• ·Tirzepatide is "imbalanced": it favors the GIP receptor, and at the GLP-1 receptor it shows biased signaling toward cAMP over β-arrestin recruitment.[2]
• ·All three carry a fatty-acid modification for albumin binding and an extended half-life.
• ·For in vitro work, potency at each receptor, signaling bias and receptor internalization are separate measurements and should be assayed separately.

All three targets are class B G protein-coupled receptors that signal primarily through Gαs and cAMP.

• ·GLP-1 receptor (GLP-1R). Expressed in pancreatic β-cells, brainstem and hypothalamic nuclei, and the gastrointestinal tract. Activation enhances glucose-dependent insulin secretion and slows gastric emptying.
• ·GIP receptor (GIPR). Expressed in β-cells, adipose tissue and the central nervous system. Its role in energy balance is still debated, which makes GIPR agonism a scientifically interesting component of dual and triple agonists.
• ·Glucagon receptor (GCGR). Expressed mainly in liver. Activation increases hepatic glucose output, but also drives lipid oxidation and energy expenditure.

Research Material

Semaglutide is a GLP-1 analog with an amino-acid substitution that protects against DPP-4 cleavage and a C18 fatty diacid side chain for albumin binding.[6] It acts at GLP-1R alone. Its clinical program, including the STEP 1 obesity trial in the New England Journal of Medicine, provides the reference dataset for the mono-agonist class.[1][4]

The research-supply side is covered in semaglutide in the US.

Amino Acid Sequence

Chemical Structure

Tirzepatide is a 39-amino-acid peptide based on the GIP sequence, with a C20 fatty diacid moiety.[7] Willard and colleagues characterized it as imbalanced, with GIPR potency comparable to native GIP but weaker GLP-1R potency than native GLP-1.[2]

At GLP-1R they also found signaling bias: tirzepatide drove cAMP generation more effectively than β-arrestin recruitment, and produced less receptor internalization than native GLP-1.[2] The authors proposed that this bias, together with the imbalance toward GIPR, may help account for its efficacy despite lower potency at the GLP-1 receptor; in their islet experiments β-arrestin1 limited the insulin response to GLP-1 but not to tirzepatide.[2] SURMOUNT-1 in the New England Journal of Medicine is the key obesity trial.[5]

Amino Acid Sequence

Chemical Structure

Retatrutide adds glucagon receptor activity. Coskun and colleagues reported greater potency than native GIP at the human GIP receptor and lower potency than the native ligands at GLP-1R and GCGR, with its GLP-1R and GCGR activity balanced against each other.[3] The glucagon component is hypothesized to contribute to energy expenditure and hepatic fat reduction; in obese mice the authors attributed part of the weight loss to GCGR-mediated increases in energy expenditure.[3]

The phase 3 program is covered in retatrutide and the TRIUMPH phase 3 readouts, and the dual-against-triple comparison in retatrutide vs tirzepatide.

Amino Acid Sequence

Chemical Structure

• ·Semaglutide. Receptors: GLP-1R. Backbone: GLP-1. Half-life extension: fatty diacid, albumin binding. Notable pharmacology: selective. US status: FDA-approved (as branded products).
• ·Tirzepatide. Receptors: GIPR and GLP-1R. Backbone: GIP. Half-life extension: fatty diacid, albumin binding. Notable pharmacology: imbalanced toward GIPR, cAMP-biased at GLP-1R.[2] US status: FDA-approved (as branded products).
• ·Retatrutide. Receptors: GIPR, GLP-1R and GCGR. Backbone: GIP. Half-life extension: fatty diacid, albumin binding. Notable pharmacology: GIPR-favoring, with lower and balanced GLP-1R and GCGR activity.[3] US status: investigational.

• ·Express each receptor separately. HEK293 or CHO lines stably expressing human GLP-1R, GIPR or GCGR allow clean potency comparisons.
• ·Measure cAMP and β-arrestin independently. Bias can only be seen when both pathways are quantified against a reference agonist.
• ·Include native ligands as references for each receptor: GLP-1(7-36)amide, GIP(1-42) and glucagon.
• ·Watch albumin in the medium. Fatty-acid-modified peptides bind albumin, which shifts apparent potency. Run assays with defined albumin concentrations and report them.
• ·Use measured peptide content for concentrations, not the label mass. See HPLC purity vs net peptide content; the Peptide Calculator converts a measured mass into stock concentration and molarity.

Every lot of all three compounds is tested by Janoshik Analytical before sale, and each certificate is published as the laboratory reported it, verifiable on Janoshik's own site. The current certificates are below, one per compound. Purity and measured content are separate numbers, and the second is the one to build assay concentrations on. Every lot is listed on the certificates of analysis page.

Published Certificate

Select strength

10mg30mg60mg65mg

Batch

TIRZ-CA-26A-01

Purity (HPLC)

99.634%

Measured content

11.42 mglabeled 10 mg

Laboratory

Janoshik

Verify on the lab’s own databaseAll published certificates

Published Certificate

Select strength

10mg20mg40mg50mg

Batch

RETA-CA-26E-01

Purity (HPLC)

99.637%

Measured content

11.76 mglabeled 10 mg

Laboratory

Janoshik

Verify on the lab’s own databaseAll published certificates

Published Certificate

Batch

SEMA-CA-26C-01

Purity (HPLC)

99.504%

Measured content

11.27 mglabeled 10 mg

Laboratory

Janoshik

Verify on the lab’s own databaseAll published certificates

Available at Eppix Labs

Tirzepatide

10mg · 30mg · 60mg · 65mg

Every batch tested by an independent laboratory, with the certificate published before sale.

From $39.99 USDIn stock