AOD-9604: Growth Hormone Fragment 176-191 Research

AOD-9604 is a synthetic peptide corresponding to amino acids 176-191 of human growth hormone (hGH), with a tyrosine residue added at the N-terminus. The resulting 16-amino acid sequence retains the lipolytic (fat-mobilizing) activity attributed to the C-terminal region of hGH while lacking the growth-promoting and diabetogenic effects associated with the full hormone.

The compound was developed by Frank Ng and colleagues at Monash University in Australia during the 1990s. The research rationale was straightforward: full-length growth hormone stimulates lipolysis but also promotes insulin resistance, fluid retention, and tissue growth. By isolating the C-terminal fragment responsible for lipolytic signaling, researchers aimed to study fat metabolism independently of these confounding effects.

AOD-9604 has a molecular weight of approximately 1,815.08 Da. It does not bind to the classical growth hormone receptor (GHR) and does not stimulate IGF-1 production, distinguishing its mechanism from full-length GH.

AOD-9604 stimulates lipolysis through a mechanism that is distinct from classical GH receptor signaling.

**Beta-3 adrenergic-like pathway:** In adipocyte models, AOD-9604 stimulates lipolysis via a pathway that involves beta-3 adrenergic receptor signaling. It increases cyclic AMP (cAMP) levels in adipocytes and activates hormone-sensitive lipase (HSL), the enzyme responsible for hydrolyzing stored triglycerides into free fatty acids and glycerol. This pathway is the same one engaged by catecholamines and beta-adrenergic agonists.

**Anti-lipogenic activity:** Beyond stimulating fat breakdown, AOD-9604 inhibits lipogenesis — the synthesis of new fatty acids from non-lipid precursors. In rodent adipose tissue preparations, the compound reduced incorporation of radiolabeled acetate into fatty acids, indicating suppression of de novo lipogenesis.

**No GHR binding:** Unlike full-length growth hormone, AOD-9604 does not bind the growth hormone receptor and does not activate the JAK2-STAT5 signaling cascade responsible for GH's growth-promoting and IGF-1-stimulating effects. This was confirmed by receptor binding assays and the absence of IGF-1 elevation in animal studies.

**No effect on glucose metabolism:** In preclinical studies, AOD-9604 did not alter glucose tolerance or insulin sensitivity, addressing one of the primary concerns with full-length GH — its tendency to induce insulin resistance at supraphysiological levels.

AOD-9604 has been studied in both in-vitro adipocyte systems and in-vivo rodent models.

The unmodified hGH fragment 176-191 (without the N-terminal tyrosine) also exists as a research compound. The key differences are:

**AOD-9604** includes an additional tyrosine at the N-terminus, which was added during development to improve stability and bioactivity. The tyrosine provides a site for potential phosphorylation and may enhance the peptide's interaction with its target pathway. Most published preclinical data uses this modified form.

**hGH 176-191** is the native sequence without modification. It has some lipolytic activity but is generally less potent than AOD-9604 in comparative studies. It also has a shorter half-life due to increased susceptibility to aminopeptidase degradation at the unprotected N-terminus.

For research purposes, AOD-9604 is the preferred form unless the study specifically requires the native, unmodified sequence. The larger body of published literature uses AOD-9604, making it easier to compare results across studies.

Practical guidance for AOD-9604 research:

**Reconstitution:** Dissolve in bacteriostatic water or sterile saline. AOD-9604 reconstitutes readily at concentrations up to 5 mg/mL. The solution should be clear and colorless.

**In-vitro concentrations:** Lipolytic effects in isolated adipocytes are observed at 0.1-10 micromolar. Glycerol release assays (colorimetric or fluorometric) are the standard readout for lipolytic activity. Include isoproterenol as a positive control for beta-adrenergic stimulated lipolysis.

**In-vivo protocols:** Published rodent studies use 200-500 mcg/kg/day administered intraperitoneally. Chronic protocols (4-8 weeks) are typical for body composition endpoints. Measure body weight, fat mass (by DEXA or MRI), food intake, and plasma IGF-1 (to confirm absence of GH receptor activation).

**Storage:** Lyophilized AOD-9604 is stable at -20°C for up to 24 months. Reconstituted solutions should be stored at 2-8°C and used within 21 days. The peptide is relatively stable in solution due to the lack of oxidation-sensitive residues in the hGH 176-191 sequence.

*All materials are for research use only.*