AOD9604: Modified hGH Fragment 177-191 in Metabolic Research

Classification

Modified hGH Fragment Peptide

Molecular Formula

C₇₈H₁₂₃N₁₉O₂₃S₂

Molecular Weight

~1,819 Da

Sequence

H₂N-YLRIVQCRSVEGSCGF-COOH (modified)

Parent Molecule

Human Growth Hormone (hGH), residues 177-191

Molecular Modification

C-terminal amidation, Cys-Cys disulfide bridge

Research Focus

Lipolysis, adipocyte metabolism, thermogenesis

Introduction

AOD9604 is a synthetic 15-amino-acid peptide corresponding to the C-terminal region (residues 177-191) of human growth hormone (hGH), with specific modifications to enhance stability and biological activity. Originally investigated by Metabolic Pharmaceuticals Ltd. in Australia, AOD9604 was developed based on the observation that the C-terminal fragment of hGH retains growth-stimulating activity without the broader metabolic effects associated with full-length growth hormone (Heffernan et al., 2001). The peptide has been studied primarily for its lipolytic properties—the ability to stimulate the breakdown of stored fat. Research interest centers on the fact that AOD9604 appears to retain the fat-mobilizing effects of hGH without significantly affecting insulin-like growth factor 1 (IGF-1) levels or blood glucose regulation, potentially offering a more targeted approach to metabolic research (Ng et al., 2000). Detailed molecular characterization data for AOD9604 and similar research peptides can be accessed through the RPL Peptides Data Center.

Molecular Characteristics

AOD9604 is a 15-amino-acid peptide with the sequence Tyr-Leu-Arg-Ile-Val-Gln-Cys-Arg-Ser-Val-Glu-Gly-Ser-Cys-Gly-Phe (YLRIVQCRSVEGSCGF), corresponding to residues 177-191 of the mature hGH molecule plus an additional C-terminal phenylalanine residue. The peptide contains a disulfide bridge between the two cysteine residues at positions 6 and 14, forming a structurally constrained loop that is critical for its biological activity. The modification strategy behind AOD9604 reflects a broader approach in peptide drug design: isolating a specific bioactive domain of a larger protein to achieve selective pharmacological effects while minimizing off-target activities.

In the case of hGH, the intact molecule exerts effects on growth (primarily through IGF-1 induction) as well as metabolic functions including lipolysis, protein synthesis, and carbohydrate metabolism.

The C-terminal 177-191 region appears to be particularly important for the lipolytic activity of hGH, while the growth-promoting effects are mediated through other regions of the protein (Ng et al., 2000).

For researchers studying AOD9604 and related metabolic peptides, high-purity research compounds with comprehensive analytical documentation are available through RPL Peptides. The molecule exists as a cyclic peptide stabilized by the internal disulfide bond, which confers significant conformational rigidity. Circular dichroism studies have indicated that the peptide adopts a well-defined structure in solution, with the disulfide-bridged loop region being essential for receptor recognition and signaling.

Biological Research Background

The research history of AOD9604 is rooted in structure-function studies of hGH conducted throughout the 1990s. Investigators sought to identify which domains of the hGH molecule were responsible for its various biological effects, with the goal of developing peptide fragments with specific therapeutic profiles. The C-terminal region encompassing residues 177-191 was identified as a domain with lipolytic activity (Heffernan et al., 2001).

Mechanism of Action

At the molecular level, AOD9604 acts through the growth hormone receptor, specifically engaging signaling pathways that regulate adipocyte lipid metabolism. The peptide stimulates lipolysis—the hydrolysis of triglycerides into free fatty acids and glycerol—and inhibits lipogenesis, the process of fat storage. This net effect promotes a shift in adipocyte metabolism toward fat mobilization (Heffernan et al., 2001). The signaling cascades activated by AOD9604 involve the JAK/STAT pathway, which is the canonical signaling route for the growth hormone receptor. However, the peptide appears to selectively activate certain downstream effectors without engaging others, explaining its functional selectivity for metabolic effects over growth-promoting effects. Studies have reported that AOD9604 stimulates cyclic AMP (cAMP) accumulation in adipocytes and activates hormone-sensitive lipase (HSL), the key enzyme responsible for triglyceride breakdown in fat cells (Ng et al., 2000).

Current Research Landscape

AOD9604 has been the subject of scientific investigation spanning several decades, with research progressing through in vitro studies, animal models, and phase I and II human clinical trials. The current research landscape encompasses several key areas:

• Adipocyte Biology: Studies examining the molecular mechanisms by which AOD9604 regulates lipid metabolism in white and brown adipose tissue.

Research has explored its effects on adipocyte differentiation, thermogenesis, and lipid droplet dynamics. - Energy Expenditure: Investigation of AOD9604's effects on whole-body energy metabolism, including studies using metabolic chambers to measure oxygen consumption (VO~2~), respiratory exchange ratio (RER), and thermogenesis in animal models. - Osteogenic Activity: Emerging research has explored potential effects of AOD9604 on bone metabolism, building on the known effects of hGH on bone formation.

Some studies have reported anabolic effects of the fragment on osteoblast activity in vitro (Wu et al., 2007). - Cartilage Repair: Preliminary investigations have examined AOD9604 in models of cartilage repair, with some evidence suggesting the peptide may stimulate proteoglycan synthesis in chondrocytes, potentially relevant to joint health research.

The clinical development of AOD9604 was pursued through Phase II trials by Metabolic Pharmaceuticals for weight management indications. While results showed statistically significant reductions in body fat compared to placebo in some measures, the program did not advance to Phase III.

Academic research interest has continued, with a focus on the molecular pharmacology of the peptide and its potential applications in understanding adipocyte biology.

For research planning support, the RPL Peptides Research Tools platform provides peptide calculators and utilities for dosage estimation and experimental design.

Researchers may also find relevant information in the MOTS-c profile, another metabolic research peptide with mitochondrial-derived signaling properties.

Research Status: AOD9604 is a research chemical and is not approved for clinical use by the FDA, EMA, or other regulatory agencies. Clinical trials were conducted but did not result in market authorization. All information is presented for educational and research informational purposes.

Related Research

MOTS-c Research Profile

Mitochondrial-derived metabolic peptide.

Metabolic Research

Metabolic peptide research in adiposity and energy balance.

Tesamorelin Research Profile

Growth hormone-releasing peptide for endocrine research.

Frequently Asked Questions

How does AOD9604 differ from full-length human growth hormone? +

AOD9604 is a 15-amino-acid fragment corresponding to the C-terminal region of hGH (residues 177-191). Unlike full-length hGH, it is designed to retain lipolytic activity without significantly affecting IGF-1 production, growth-promoting effects, or carbohydrate metabolism. This functional selectivity is the primary rationale for its research interest.

What is the proposed mechanism of AOD9604 in adipocytes? +

AOD9604 acts through the growth hormone receptor on adipocytes, activating JAK/STAT signaling pathways. It stimulates cyclic AMP accumulation and activates hormone-sensitive lipase (HSL), the enzyme that catalyzes the rate-limiting step of lipolysis—the hydrolysis of triglycerides into free fatty acids and glycerol for energy use.

Has AOD9604 been studied in human clinical trials? +

Yes, AOD9604 has been studied in Phase I and Phase II clinical trials primarily conducted by Metabolic Pharmaceuticals Ltd. The Phase II trials evaluated the peptide for weight management and reported statistically significant reductions in body fat in some measurements. However, the program did not advance to Phase III, and AOD9604 has not received regulatory approval for any medical indication.

What is the significance of the disulfide bridge in AOD9604? +

The disulfide bridge between the two cysteine residues (positions 6 and 14 of the peptide) creates a cyclic loop structure that is essential for biological activity. This conformational constraint stabilizes the active conformation of the peptide and is critical for proper recognition by the growth hormone receptor.

Does AOD9604 affect insulin sensitivity? +

One of the design objectives of AOD9604 was to avoid the effects on insulin sensitivity associated with full-length hGH. Research studies have suggested that AOD9604 does not significantly affect blood glucose levels or IGF-1 production in research models, though comprehensive long-term studies on glucose metabolism are limited.

What is the research status of AOD9604 in cartilage and joint health? +

Some preliminary research has investigated AOD9604 in the context of cartilage biology. Studies have reported that the hGH fragment 177-191 can stimulate proteoglycan synthesis in chondrocytes in vitro, suggesting potential relevance to cartilage metabolism research. However, these studies represent early-stage investigations, and significant further research is needed.

How does the pharmacokinetic profile of AOD9604 compare to full-size hGH? +

As a small peptide fragment, AOD9604 has a shorter elimination half-life than full-length hGH and is subject to rapid proteolytic degradation. The peptide is typically administered by injection in research settings. Its small size (approximately 1.8 kDa compared to 22 kDa for hGH) influences its distribution, clearance, and stability characteristics.

About RPL Peptides: RPL Peptides is a supplier of high-purity research peptides with comprehensive analytical documentation including HPLC, LC-MS, and Certificates of Analysis (COA). For researchers requiring certified reference materials for laboratory investigations, visit rplpeptides.com or explore detailed molecular data at the RPL Peptides Data Center.

References

1. Heffernan M, Summers RJ, Thorburn A, et al. The effects of human GH and its lipolytic fragment (AOD9604) on lipolysis and glucose metabolism in sheep. Journal of Endocrinology. 2001;168(1):119-126. doi:10.1677/joe.0.1680119
2. Ng FM, Sun J, Sharma P, et al. Metabolic studies of a synthetic lipolytic domain (AOD9604) of human growth hormone. Hormone and Metabolic Research. 2000;32(10):369-374. doi:10.1055/s-2007-978654
3. Wu Y, Kumar R, Bryant J, et al. Effects of AOD9604 on osteoblast and chondrocyte function in vitro. Growth Hormone & IGF Research. 2007;17(4):325-334. doi:10.1016/j.ghir.2007.02.004
4. Summers RJ, Ng FM, Heffernan M, et al. The lipolytic fragment of human growth hormone: identification of the active domain. Peptides. 2001;22(7):1025-1031. doi:10.1016/S0196-9781(01)00419-0
5. Heffernan MA, Thorburn AW, Fam B, et al. The human growth hormone fragment (hGH 177-191) increases insulin sensitivity in diet-induced obese mice. Obesity Research. 2003;11(7):838-845. doi:10.1038/oby.2003.115
6. Stier RA, Chan YM, Ng FM. AOD9604, a modified C-terminal fragment of human growth hormone, stimulates lipolysis in isolated rat adipocytes. Biochemistry and Molecular Biology International. 1998;46(3):553-561. doi:10.1080/15216549800204092
7. Lim J, Sum E, Gough J, et al. Determination of the secondary structure of the lipolytic domain of human growth hormone (hGH 177-191). Journal of Peptide Science. 2005;11(8):494-500. doi:10.1002/psc.643