AOD9604: A Modified hGH Fragment Studied for Lipolytic Activity

Research summary. AOD9604 is a synthetic hexadecapeptide derived from the C-terminal lipolytic domain of human growth hormone (hGH), specifically residues 177–191, with an added N-terminal tyrosine to improve stability. It was originally developed as an anti-obesity candidate by Metabolic Pharmaceuticals in Australia. The molecule retains hGH's reported effects on fat mobilisation while lacking its growth-promoting and insulin-counterregulatory activities.

Molecular profile

• Sequence: Tyr-Leu-Arg-Ile-Val-Gln-Cys-Arg-Ser-Val-Glu-Gly-Ser-Cys-Gly-Phe (intramolecular Cys7–Cys15 disulfide bond)
• Molecular formula: C₇₈H₁₂₃N₂₃O₂₃S₂
• Molecular weight: ~1815.1 g/mol
• PubChem CID: 16131447
• CAS Number: 386264-39-7

The peptide preserves the disulfide-bridged loop that, in the parent hGH molecule, has been mapped to lipolytic activity. By isolating this domain, AOD9604 was designed to dissociate fat-mobilising activity from the receptor-mediated effects on IGF-1 secretion, glucose handling, and somatic growth.

Mechanism of action

The mechanistic story for AOD9604 is incomplete and has evolved over time. Early work proposed that the molecule acts on the β3-adrenergic receptor pathway in adipocytes to upregulate lipolysis and oxidative metabolism. Subsequent studies in β3-adrenergic-receptor knockout mice, however, demonstrated that AOD9604-induced fat loss persists in the absence of this receptor — implying that additional, as-yet-uncharacterised pathways are involved. Proposed contributors include direct effects on hormone-sensitive lipase, modulation of mitochondrial fatty-acid oxidation, and possible adipocyte-selective apoptotic signalling.

Notably, unlike full-length hGH, AOD9604 does not appear to elevate IGF-1 levels or induce insulin resistance in animal models, which has been a primary rationale for its continued investigation as a research tool for studying lipolysis-specific signalling.

Preclinical research highlights

Lipolysis in obese rodent models. Early studies by Ng, Heffernan, and colleagues at Monash University demonstrated that hGH fragment 177–191 and its analogues, including AOD9604, increased lipolytic rates in adipose tissue from genetically obese mice (ob/ob) and reduced body fat without affecting longitudinal growth. These reports established the proof-of-concept that the lipolytic domain of hGH could be biologically separated from its other endocrine actions [1].

Adipocyte studies. In isolated rat adipocytes, AOD9604 has been reported to enhance basal lipolysis and inhibit lipogenesis from labelled glucose substrates. Effects appear dose-dependent within a narrow concentration window characteristic of peptide-mediated GPCR-adjacent signalling.

Cartilage and joint research. A separate line of investigation has examined AOD9604 in rodent models of osteoarthritis, where intra-articular injection has been associated with reductions in cartilage degeneration scores and inflammatory markers in surgically induced joint injury. The mechanism is not well characterised; proposed contributors include modulation of chondrocyte metabolism and effects on extracellular matrix turnover.

Cardiovascular and metabolic models. Limited rodent data suggest that AOD9604 may exert effects on cardiac substrate utilisation and lipid handling distinct from its effects on adipose tissue. These observations remain preliminary.

Regulatory context

AOD9604 has been the subject of human clinical trials, including a Phase 2b study in obese adults conducted by Metabolic Pharmaceuticals. The compound did not achieve regulatory approval as an anti-obesity therapeutic. In 2014, the U.S. FDA granted AOD9604 GRAS (Generally Recognized As Safe) self-affirmed status for use as a food ingredient by certain commercial parties — a designation that is unrelated to therapeutic approval and does not constitute endorsement of pharmacological claims.

The World Anti-Doping Agency lists growth hormone fragments, including AOD9604, as prohibited substances under category S2 (peptide hormones, growth factors, related substances and mimetics).

Current research status

AOD9604 remains an investigational research peptide in the academic and preclinical research context. It is studied primarily as a tool compound for investigating:

• Lipolysis-specific hGH signalling decoupled from IGF-1 axis effects
• Mechanisms of adipocyte fat mobilisation independent of β3-adrenergic signalling
• Local musculoskeletal applications, particularly in chondrocyte and cartilage metabolism research

The mechanistic ambiguity of AOD9604 — particularly the unresolved question of which receptor or receptors mediate its reported effects — continues to limit its development as a therapeutic candidate but also keeps it of interest as a probe for studying lipolytic signalling.

Key takeaways for researchers

• AOD9604 is a 16-amino-acid synthetic fragment of the C-terminal lipolytic region of hGH.
• It is reported to promote lipolysis without engaging IGF-1 secretion or growth-promoting hGH actions.
• The β3-adrenergic receptor was an early hypothesised mediator but has been shown not to be required.
• Despite Phase 2 human trials, AOD9604 has not received regulatory approval as a therapeutic, and is listed on the WADA Prohibited List.

References

1. Ng FM, Sun J, Sharma L, Libinaki R, Jiang WJ, Gianello R. Metabolic studies of a synthetic lipolytic domain (AOD9604) of human growth hormone. Hormone Research. 2000;53(6):274–278.

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This article is provided for educational and research purposes only. AOD9604 is a research peptide. It is not an approved drug or therapeutic agent and is not intended for human consumption, diagnosis, treatment, cure, or prevention of any disease or condition. AOD9604 is listed by the World Anti-Doping Agency as a prohibited substance. All work involving this peptide should be conducted by qualified personnel within an appropriate research setting and in compliance with applicable institutional and regulatory requirements.