Oxyntomodulin

Overview

Oxyntomodulin (OXM) is a 37-amino acid peptide hormone derived from the proglucagon precursor by post-translational processing in intestinal L-cells. The name "oxyntomodulin" reflects its originally identified activity: modulation of oxyntic (acid-secreting) gastric cells. It corresponds to residues 33-69 of proglucagon — which is equivalent to the entire glucagon sequence (29 aa) plus a C-terminal octapeptide extension.

The pharmacological significance of OXM lies in its dual receptor agonism: unlike pure glucagon (which is selective for the glucagon receptor, GCGR) or GLP-1 (which is selective for the GLP-1 receptor, GLP1R), OXM activates both receptors. This dual activity combines two complementary metabolic effects:

• GLP1R activation: Insulinotropic, glucagonostatic, delays gastric emptying, reduces food intake (like semaglutide and liraglutide)
• GCGR activation: Increases hepatic glucose output (potentially unwanted) but also increases resting energy expenditure and promotes lipolysis (potentially beneficial for weight loss)

The net effect of OXM in vivo is weight loss with improved glycemic control — a profile that has made it the conceptual template for a generation of synthetic dual agonist peptides including tirzepatide (GLP-1 + GIP), retatrutide (GLP-1 + GIP + glucagon triple agonist), cotadutide (GLP-1 + glucagon dual agonist), and others that have become major areas of metabolic drug development.

OXM was isolated from porcine jejunoileum in the late 1970s by Lars-Inge Larsson and colleagues and by Grégoire Bataille's laboratory. It was long considered one of the "enteroglucagons" — a loose term for glucagon-like intestinal peptides identified by cross-reactivity with glucagon antibodies. Only after proglucagon gene cloning revealed the full set of mature products did OXM's specific identity and sequence become clear.

Structure/Sequence

Human Oxyntomodulin: HSQGTFTSDYSKYLDSRRAQDFVQWLMNTKRNRNNIA

• Length: 37 amino acids
• Molecular weight: ~4,448 g/mol
• Gene: GCG (glucagon/proglucagon, chromosome 2q24.2)
• Source: Intestinal L-cells (distal small intestine and colon)
• Position in proglucagon: Residues 33-69 of 180-aa preproglucagon

Relationship to Glucagon

OXM = Glucagon (residues 33-61 of proglucagon, 29 aa) + C-terminal octapeptide (KRNRNNIA, residues 62-69 of proglucagon). The octapeptide extension is called the "intervening peptide 1" (IP-1) and is cleaved off in α-cells to release pure glucagon; in L-cells, the extension is retained, producing OXM.

Receptor Binding

• GLP-1 receptor: ~100-fold lower affinity than GLP-1
• Glucagon receptor: ~10-fold lower affinity than glucagon
• Combined activity: At physiological concentrations, OXM produces modest activation of both receptors, generating the distinctive dual profile

Species Conservation

The core glucagon sequence is highly conserved; the C-terminal octapeptide extension shows some variation across species.

Mechanism of Action

Dual Receptor Activation

OXM binds and activates:

• GLP-1 receptor (GLP1R): Gs-coupled, stimulates cAMP, glucose-dependent insulin secretion, gastric emptying delay, appetite suppression
• Glucagon receptor (GCGR): Gs-coupled, stimulates cAMP in liver and adipose tissue, promotes glycogenolysis, lipolysis, energy expenditure

Appetite Suppression

• Reduces food intake when administered peripherally or centrally
• Effects mediated through GLP1R in arcuate nucleus and area postrema
• Delays gastric emptying
• Human studies show appetite reduction and weight loss

Energy Expenditure

• Increases resting energy expenditure
• GCGR-mediated effects on mitochondrial biogenesis and thermogenesis
• Promotes lipolysis in adipose tissue
• Together with appetite suppression, produces net weight loss exceeding pure GLP-1 agonists in some models

Glycemic Control

• Insulinotropic (via GLP1R): glucose-dependent insulin release
• Glucagonostatic effects through GLP1R partially offset the direct GCGR-mediated hepatic glucose output
• Net effect: improved glycemic control
• This balance is the theoretical basis for dual-agonist drug design

Cardiovascular Effects

• GLP1R activation: vasodilation, reduced blood pressure
• GCGR activation: positive inotropy
• Combined effects vary by dose and duration

Gastric Acid

• Original "oxyntomodulin" activity: modulates gastric acid secretion
• Inhibits meal-stimulated gastric acid through GLP1R

Postprandial Release

• Released from L-cells along with GLP-1, GLP-2, and PYY
• Nutrient-stimulated release peaking 30-60 minutes postprandially
• Rapidly degraded by DPP-4 and neprilysin
• Plasma half-life ~5-10 minutes

Research Summary

Common Discussion Topics

1. Template for dual agonist drug class — OXM's natural combination of GLP-1 and glucagon receptor activation has been the conceptual and chemical starting point for a major class of synthetic metabolic peptides. Cotadutide (MEDI0382) is a direct OXM-inspired dual agonist; tirzepatide is a GLP-1/GIP dual agonist; retatrutide adds glucagon receptor activation to a GLP-1/GIP scaffold.

2. Glucagon receptor rehabilitation — Historically, glucagon receptor activation was viewed as undesirable for metabolic disease because of glycemia elevation. OXM demonstrated that combined GLP1R/GCGR activation could be beneficial, rehabilitating the glucagon receptor as a drug target and driving interest in carefully balanced multi-agonists.

3. L-cell origin and co-secretion — OXM is released from intestinal L-cells along with GLP-1, GLP-2, PYY, and other post-prandial peptides. The L-cell is a central hub for nutrient-sensing and gut-brain signaling, making its secretory products collectively of major metabolic interest.

4. Balance of receptor activity — The therapeutic value of OXM and its analogs depends on the precise ratio of GLP1R to GCGR activation. Too much GCGR drives hyperglycemia; too little and the energy expenditure benefit is lost. Medicinal chemistry has optimized these ratios extensively.

5. DPP-4 vulnerability — Like native GLP-1, OXM is rapidly cleaved by DPP-4, limiting its in vivo half-life. Analogs with DPP-4 resistance (via N-methylation, Aib substitution, or acylation-based albumin binding) extend half-life sufficiently for weekly or longer dosing.

Related Compounds

• Glucagon — shorter proglucagon-derived peptide
• Semaglutide — GLP-1 receptor agonist
• Liraglutide — earlier GLP-1 receptor agonist
• GLP-2 — co-secreted intestinal proglucagon product
• Peptide YY — co-secreted L-cell peptide
• Retatrutide — triple agonist with glucagon receptor component