LEAP2: Complete Research Profile — The Endogenous Ghrelin Receptor Antagonist, Liver-Derived Satiety Signal, and Counter-Regulator of Ghrelin Action (2026)

# LEAP2: Complete Research Profile — The Endogenous Ghrelin Receptor Antagonist, Liver-Derived Satiety Signal, and Counter-Regulator of Ghrelin Action (2026)

When ghrelin was discovered in 1999 as the endogenous ligand for the growth hormone secretagogue receptor (GHSR-1a), it was celebrated as the first identified "hunger hormone" — rising before meals and falling after eating, signaling to the hypothalamus to increase food intake and stimulate GH release. For nearly two decades, the ghrelin-GHSR-1a axis was viewed primarily through this monocular lens: ghrelin activates GHSR-1a, downstream effects follow. What was missing was the counter-signal — the endogenous GHSR antagonist that would rise during the fed state to dampen ghrelin-driven hunger and complete the push-pull circuit. In 2018, that counter-signal was identified: LEAP2 (liver-expressed antimicrobial peptide 2).

The discovery that a peptide originally characterized as an antimicrobial compound was actually a major metabolic regulator — and a GHSR-1a antagonist/inverse agonist — represents one of the most unexpected revelations in metabolic peptide biology of the last decade.

Background: Ghrelin and GHSR-1a

To understand LEAP2's significance, context on the ghrelin system is essential.

Ghrelin (acylated ghrelin; des-acyl ghrelin is inactive at GHSR-1a) is a 28-amino acid peptide produced primarily by oxyntic cells in the gastric fundus. Its key metabolic properties:

• •Plasma ghrelin peaks before meals (preprandially) and falls rapidly after eating
• •Falls with increasing body weight (paradoxically lower in obesity)
• •Potently stimulates GH release from the anterior pituitary
• •Increases food intake and adiposity when administered centrally or peripherally
• •Requires n-octanoyl acylation at Ser³ (added by GOAT enzyme) for GHSR-1a binding

GHSR-1a has the unusual property of high constitutive activity — it signals even without ligand at ~50% of maximal capacity. This constitutive activity contributes to tonic GH secretion and basal appetite drive independent of circulating ghrelin levels.

Before LEAP2's discovery, the known GHSR pharmacology included ghrelin (full agonist) and a variety of synthetic antagonists/inverse agonists developed for research, but no endogenous antagonist had been identified.

Discovery of LEAP2 as a GHSR Antagonist (2018)

The Antimicrobial Peptide Background

LEAP2 was originally described in 2002 as a liver-expressed antimicrobial peptide isolated from human blood ultrafiltrate. Its name derives from Liver-Expressed Antimicrobial Peptide 2 — a companion to LEAP1, which turned out to be hepcidin, the master regulator of systemic iron homeostasis. Unlike hepcidin/LEAP1, LEAP2's original antimicrobial characterization did not reveal major physiological functions, and it remained relatively obscure for over 15 years.

The 2018 Cell Metabolism Breakthrough

In 2018, Ge and colleagues published in Cell Metabolism the landmark discovery that LEAP2 is an endogenous antagonist and inverse agonist of GHSR-1a. Key findings:

1. LEAP2 binds GHSR-1a with nanomolar affinity

2. LEAP2 blocks ghrelin-induced GHSR-1a activation (functional antagonism)

3. LEAP2 suppresses GHSR-1a constitutive activity (inverse agonist property — reducing even baseline signaling)

4. Circulating LEAP2 levels rise with feeding and fall with fasting — the mirror image of ghrelin

5. LEAP2 administration reduces food intake and GH release in mice

6. Neutralization of endogenous LEAP2 (with antibody) increases food intake and body weight

This discovery fundamentally reframed GHSR-1a pharmacology from a "ghrelin-only" receptor to a push-pull system with both an endogenous agonist (ghrelin) and an endogenous antagonist (LEAP2).

Molecular Biology: LEAP2 Structure and Processing

Gene and Preproprotein

LEAP2 is encoded by the LEAP2 gene (also called AGAP5 in some databases). The gene product is a 77-amino acid preproprotein:

• •Signal peptide (residues 1-21): directs secretion
• •Propeptide region
• •Mature LEAP2 (residues ~30-77): the ~40-amino acid circulating form

The mature form of LEAP2 contains:

• •Two disulfide bonds (four Cys residues)
• •An N-terminal domain critical for GHSR-1a interaction
• •The C-terminal region less important for receptor binding

Active Fragment: LEAP2(1-14)

Structure-activity studies identified that the N-terminal 14 amino acids of mature LEAP2 [LEAP2(1-14)] are sufficient for GHSR-1a antagonism. This N-terminal fragment:

• •Retains full GHSR-1a binding affinity
• •Blocks ghrelin-stimulated Ca²⁺ release and cAMP changes
• •Is more amenable to chemical synthesis and pharmacokinetic optimization than full-length LEAP2
• •Has been used as the primary research tool in mechanistic in vitro studies

The identification of a 14-amino acid active fragment considerably simplifies LEAP2-based pharmacology compared to working with the full 40-aa mature peptide.

Expression and Regulation: The Liver-Gut-Brain Axis

Primary Source: The Liver

LEAP2 is predominantly produced in the liver, which secretes LEAP2 into portal and systemic circulation. This hepatic origin positions LEAP2 as a genuine endocrine signal — a liver-derived hormone that communicates nutritional status to the brain through circulating levels.

The liver's role in monitoring metabolic state (it receives nutrient-rich portal blood directly from the gut) makes it a logical source for a postprandial satiety signal. As glucose and nutrients flood the portal vein after a meal, hepatic LEAP2 production increases.

Secondary Expression Sites

LEAP2 is also expressed in:

• •Small intestine (enteroendocrine cells)
• •Kidney
• •Brain (at lower levels)

Gut-derived LEAP2 may act locally on vagal afferents and enteric neurons expressing GHSR-1a, contributing to meal-induced satiety independent of systemic circulation.

Regulation of LEAP2 Expression

Fasting: LEAP2 plasma levels fall significantly (by 50-70% in rodents) during a 24-hour fast — concordant with ghrelin rising during fasting. The combined effect: low LEAP2 + high ghrelin = maximal GHSR-1a activation → strong hunger drive.

Feeding/Glucose: LEAP2 rises within 30-60 minutes of food consumption or glucose administration. The rise is rapid and meal-proportional.

High-fat diet/Obesity: In diet-induced obese (DIO) mice and in human obesity, plasma LEAP2 is elevated relative to lean controls — potentially a compensatory mechanism to counteract elevated ghrelin-like signaling in the context of overnutrition.

Fasting state in obesity: The normal LEAP2 decline with fasting appears blunted in obese states, which may contribute to impaired hunger suppression.

Exercise: Acute aerobic exercise reduces plasma LEAP2, mirroring exercise-induced ghrelin increases — potentially contributing to post-exercise appetite effects.

Bariatric surgery: Roux-en-Y gastric bypass and sleeve gastrectomy produce complex changes in LEAP2 that vary by time post-surgery and study. Some reports show early post-operative reduction (related to caloric restriction), while others show eventual normalization or reconfiguration of the LEAP2/ghrelin ratio.

Mechanism of GHSR-1a Antagonism

Binding Site

LEAP2 and ghrelin compete for overlapping binding sites on GHSR-1a, though their specific contact points differ:

• •Ghrelin binds primarily to transmembrane helices TM3, TM6, and TM7 of GHSR-1a, with the octanoyl-Ser³ inserting into a hydrophobic binding pocket
• •LEAP2 contacts the extracellular loops (ECL2, ECL3) and upper transmembrane regions
• •The two binding sites are overlapping but not identical, consistent with competitive antagonism kinetics

This binding mode means LEAP2 can block ghrelin access and suppress constitutive GHSR-1a activity — the inverse agonist property.

Inverse Agonism at GHSR-1a

GHSR-1a's high constitutive activity (~50% of maximum) means that even without ghrelin, the receptor signals actively. This contributes to:

• •Tonic GH pulsatility
• •Baseline appetite drive
• •Homeostatic set-point for body weight

LEAP2's inverse agonism at GHSR-1a means it reduces signaling below the constitutive baseline — a more complete suppression than simple competitive antagonism would provide. This property makes LEAP2 potentially useful as a research tool to probe the contribution of constitutive GHSR-1a activity to baseline physiology.

Downstream Pharmacology

LEAP2-mediated GHSR-1a blockade reduces:

• •Growth hormone release: LEAP2 reduces pulsatile GH secretion from pituitary somatotrophs
• •Food intake: Central and peripheral LEAP2 reduces meal size and caloric intake in rodent models
• •Body weight: Chronic LEAP2 treatment in DIO mice reduces body weight gain
• •Blood glucose: LEAP2 may modulate glycemia through GHSR-1a on pancreatic islets (GHSR-1a is expressed on alpha cells)

LEAP2 and the GHSR-1a Pharmacological Landscape

The ghrelin receptor system now has a substantially richer pharmacological landscape than pre-2018:

The push-pull architecture is now clearer: the post-prandial state is characterized by rising LEAP2 + falling ghrelin — a dual mechanism ensuring GHSR-1a is robustly suppressed after meals, reducing hunger and GH drive.

LEAP2 in Obesity and Metabolic Disease Research

LEAP2 Levels in Human Obesity

Clinical studies measuring LEAP2 in human cohorts (2019-2024) reveal:

• •Obese individuals have higher circulating LEAP2 compared to lean controls in some studies (potentially compensatory)
• •The LEAP2/ghrelin ratio — rather than either peptide alone — may be the more meaningful biomarker of GHSR-1a drive
• •In patients with type 2 diabetes, LEAP2 patterns differ from non-diabetic obese individuals
• •After caloric restriction and weight loss, LEAP2 decreases while ghrelin increases — theoretically increasing appetite and complicating weight maintenance

Implications for Weight Loss Research

One key insight from LEAP2 research is that the GHSR-1a system is not a simple on/off switch driven by ghrelin alone. The effectiveness of anti-ghrelin strategies for obesity may depend on LEAP2 co-regulation:

• •Very low-calorie diets that dramatically reduce LEAP2 while ghrelin is already low might have less net effect on GHSR-1a activity than predicted from ghrelin alone
• •Understanding LEAP2 dynamics post-bariatric surgery may help explain the differential appetite outcomes of different surgical procedures
• •Pharmacological LEAP2 supplementation or GHSR-1a agonism (paradoxically to probe LEAP2-ghrelin balance) represents potential research directions

GH Research Applications

For researchers studying growth hormone secretion, LEAP2's discovery is pharmacologically significant:

• •LEAP2 blocks GHRP (growth hormone-releasing peptide) stimulation of GHSR-1a, offering a tool to dissect the contribution of GHSR-1a to GH pulsatility
• •Endogenous LEAP2 fluctuations may account for some of the meal-dependent variation in GH pulsatility
• •LEAP2(1-14) provides a selective endogenous-sequence GHSR antagonist for research that was previously unavailable

Research Tools

Current Research Frontiers (2024-2026)

GHSR biased signaling in the context of LEAP2: Whether LEAP2 vs. synthetic antagonists produce different biased signaling profiles at GHSR-1a (β-arrestin vs. G protein bias).

LEAP2/ghrelin ratio as biomarker: Prospective studies evaluating LEAP2/ghrelin ratio as a predictor of appetite regulation, weight regain after diet, and response to GLP-1 agonist therapy.

LEAP2 in anorexia nervosa: Preliminary data suggest markedly elevated ghrelin + markedly reduced LEAP2 in anorexia — a perfect storm for maximal GHSR-1a activation. Whether LEAP2 normalization tracks with recovery is under investigation.

Gut-derived LEAP2: Characterizing the contribution of intestinal vs. hepatic LEAP2 to postprandial satiety, and whether gut LEAP2 acts primarily via vagal GHSR-1a or through portal/systemic circulation.

LEAP2 in GH deficiency: Whether low LEAP2 states could be exploited to enhance endogenous GH pulsatility in GH-deficient conditions without pharmacological GHRP administration.

Exercise and LEAP2: Detailed characterization of exercise-induced LEAP2 changes across different exercise modalities (aerobic vs. resistance) and their impact on post-exercise appetite and GH responses.

Conclusion

LEAP2's discovery as the endogenous GHSR-1a antagonist/inverse agonist completed a circuit that had been assumed complete for 20 years. The ghrelin-GHSR-1a axis is now understood as a balanced push-pull system: ghrelin (stomach-derived, preprandial) drives GHSR-1a activation and hunger, while LEAP2 (liver-derived, postprandial) counteracts this drive — and even suppresses the receptor's constitutive activity. The balance of these two signals — captured as the LEAP2/ghrelin ratio — likely provides a more accurate molecular read of GHSR-1a-driven appetite than either peptide alone.

For researchers studying ghrelin, GH secretion, obesity, or GHSR-1a pharmacology, LEAP2 is an essential component of the research toolkit — both as a pharmacological tool (via LEAP2(1-14) peptide and anti-LEAP2 antibody) and as a biomarker whose dynamics mirror but invert the ghrelin response to nutritional state.

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References

2. Mani BK et al. "LEAP2 changes with body mass and food intake in humans and mice." J Clin Invest 2019;129(9):3909-3923. PMID: 31380808

3. Makris MC et al. "LEAP2: a novel hepatokine with anti-inflammatory and metabolic properties." Curr Mol Med 2022. PMID: 35232345

8. Pradhan G et al. "Ghrelin: much more than a hunger hormone." Curr Opin Clin Nutr Metab Care 2013;16(6):619-624. PMID: 24100676

10. Khatib MN et al. "LEAP2 and ghrelin: two sides of the feeding coin." Peptides 2023;165:171003. PMID: 37098384

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This article is intended for research and educational purposes only (RUO). LEAP2 peptides and related compounds described herein are investigational research tools. No compound discussed in this article has been evaluated by any regulatory authority for safety or efficacy in humans for the applications described. This content does not constitute medical advice, clinical guidance, or endorsement of human use.