AOD-9604: The hGH Fragment 176-191 in the Research Literature

Research-use-only context. This article summarizes published third-party scientific literature and laboratory practice. It is not medical advice, not a therapeutic or performance claim, and not a usage guide. US Prime Peptides products are supplied strictly for in vitro laboratory research and are not for human or veterinary use.

This article explains what AOD-9604 is at the sequence level, how a Monash University program on growth hormone fragments produced it, what the rodent and tissue studies actually measured, what happened in the Australian clinical program, what the developer's GRAS self-affirmation does and does not mean, and what a certificate of analysis should show for a disulfide-bridged 16-residue peptide.

AOD-9604 is the C-terminal 177-191 fragment of human growth hormone with an added tyrosine

AOD-9604 is a 16-residue synthetic peptide, Tyr-Leu-Arg-Ile-Val-Gln-Cys-Arg-Ser-Val-Glu-Gly-Ser-Cys-Gly-Phe, consisting of residues 177 to 191 of the 191-residue human growth hormone (hGH) sequence with one extra tyrosine on the N-terminus. The two cysteines, which correspond to Cys182 and Cys189 of hGH, are joined by a disulfide bond, so the peptide is a small loop with short tails. Its formula is C₇₈H₁₂₃N₂₃O₂₃S₂, average mass about 1,815 daltons, CAS 221231-10-3, PubChem CID 71300630.

The naming in the literature is layered. "hGH 177-191" is the unmodified fragment. "AOD9401" was the Monash group's code for a synthetic version of that fragment. "AOD9604" is the tyrosine-extended version, with the added residue commonly included to permit radiolabelling. The compound is also written "hGH fragment 176-191," which is the same loop counted from one residue earlier. "AOD" stood for "anti-obesity drug" in the developer's nomenclature, a label that reflects a corporate program, not an established property. The molecule has no sequence relationship to the secretagogues covered in Sermorelin (GHRH 1-29); it is a piece of growth hormone itself, not a releasing factor.

The fragment came out of decades of work on which parts of growth hormone do what

The C-terminal region of hGH was studied as a functional domain long before AOD-9604 existed. Frank Ng's laboratory at Monash University in Melbourne spent the late 1970s and 1980s dissecting hGH into synthetic part-sequences and measuring which fragments reproduced which actions of the whole hormone in rat tissue. In 1993, Wu and Ng reported in Biochemistry and Molecular Biology International that the synthetic fragment hGH 177-191 showed antilipogenic activity matching that of intact hGH in rat adipose tissue, but no significant lipolytic effect when glycerol release from epididymal fat pads was measured. Their reading was that the antilipogenic domain of hGH sits in the C-terminal region and that the hormone's main effect on lipid handling is at the level of lipogenesis.

The same year, Wijaya and Ng reported in the same journal that hGH 177-191 reduced basal and insulin-stimulated 2-deoxyglucose uptake in adipocytes isolated from genetically obese Zucker rats, and that at equimolar concentrations the fragment was more potent than the intact hormone. The key feature of this early literature is its model system: isolated rat fat pads and isolated rat adipocytes, with enzyme activity, glycerol release and sugar uptake as endpoints. These are tissue measurements. They are not statements about what the peptide does in a person.

What the 2000-2001 rodent studies measured

Three papers from the Monash group in 2000 and 2001 form the core of the AOD-9604 evidence base, and all three are rodent or ex vivo tissue studies. Ng and colleagues reported in the Journal of Molecular Endocrinology in 2000 that synthetic AOD9401 stimulated hormone-sensitive lipase and inhibited acetyl-CoA carboxylase in isolated rat adipose tissue, mimicked the effect of intact hGH on diacylglycerol release in adipocytes, and that over 20 days in obese Zucker rats the average adipocyte diameter fell from 110 to 80 micrometres. Unlike hGH, the fragment did not induce insulin resistance or glucose intolerance in those animals.

In Hormone Research the same year, Ng and colleagues reported that AOD9604 given by the oral route to obese Zucker rats over 19 days reduced cumulative body-weight gain relative to controls (15.8 versus 35.6 g), that adipose tissue from those animals showed increased lipolytic activity, and that euglycemic clamp measurements showed no adverse effect on insulin sensitivity.

Heffernan and colleagues addressed mechanism in Endocrinology in 2001 using beta₃-adrenergic receptor knock-out mice. Both hGH and AOD9604 increased beta₃-AR mRNA in adipose tissue of obese mice to levels seen in lean animals, and the chronic changes in body weight and lipolysis seen in wild-type mice were absent in the knock-outs. In an acute experiment, however, AOD9604 still raised energy expenditure and fat oxidation in knock-out mice. The authors' conclusion was that the fragment's lipolytic actions are not mediated directly through the beta₃-AR, although both compounds increase its expression. That nuance is often lost in secondary summaries that simply call AOD-9604 a "beta-3 agonist."

The Australian clinical program ended in 2007, and GRAS self-affirmation is not drug approval

AOD-9604 is not an approved drug in the United States or anywhere else, and its clinical development program was discontinued. Metabolic Pharmaceuticals, a Melbourne company spun out of the Monash work, took AOD-9604 through early- and mid-phase human trials during the 2000s. The program was stopped in 2007 after later-phase results did not meet their efficacy endpoints. The trials were conducted under investigational protocols with pharmaceutical-grade material; their existence says nothing about a research vial.

In 2014 the developer announced that AOD-9604 had achieved "self-affirmed GRAS" status in the United States. This phrase is easily misread. GRAS ("generally recognized as safe") is a food-ingredient concept under the Federal Food, Drug, and Cosmetic Act. A self-affirmed GRAS determination is a conclusion reached by a panel of experts convened by the company itself; it is not an FDA review, not an FDA "no questions" letter, and not an approval of any kind. It concerns use as a food ingredient and has no bearing on drug status. Since then, FDA has placed AOD-9604 in Category 2 of its list of bulk drug substances nominated for use in compounding under section 503A, the category for substances the agency has identified as raising significant safety risks, in its 2023 updates. The compound is also named explicitly in class S2 of the WADA Prohibited List under "growth hormone fragments," alongside hGH 176-191. See FDA Status of Common Research Peptides: A Reference Table and The WADA Prohibited List and Peptides.

The anti-doping and seizure literature is the best modern chemistry on the molecule

Because AOD-9604 is prohibited in sport, the most rigorous recent analytical work on it comes from anti-doping and regulatory laboratories rather than from biology groups. Cox and colleagues at the Sports Medicine Research and Testing Laboratory in Salt Lake City reported in Drug Testing and Analysis in 2015 a validated solid-phase extraction method for the peptide in urine with a limit of detection of 50 pg/mL. After incubating AOD9604 in serum and urine they identified six potential breakdown products, and quantification in serum showed that one, the loop fragment Cys-Arg-Ser-Val-Glu-Gly-Ser-Cys-Gly, was considerably more stable than the parent or the other fragments.

That stability pattern is chemically sensible. Exopeptidases trim the linear tails, but the disulfide-closed loop resists further cleavage until the bridge is reduced. The same paper noted that the peptide had recently been identified in confiscated vials in the United States. Vanhee and colleagues at the Belgian Scientific Institute of Public Health reported a parallel case in the same journal in 2014, describing the identification and characterization of AOD9604 in an unknown preparation seized by Belgian authorities. Both reports show that a laboratory receiving a vial labelled AOD-9604 should expect to confirm identity by mass spectrometry rather than by label.

What a certificate should show for a disulfide-bridged 16-mer

For AOD-9604, the critical certificate lines are the observed mass, which must reflect the closed disulfide, and a purity trace that can show cysteine-related impurities. The oxidized (bridged) peptide is two daltons lighter than the fully reduced form, so an observed monoisotopic mass should match the bridged calculation, and a certificate that quotes the reduced mass is either reporting an unbridged product or a calculation error. Mass spectrometry does not distinguish the correct intramolecular bridge from an intermolecular one, so a dimer peak at twice the mass on the HPLC trace is worth looking for. Disulfide scrambling and cysteine oxidation to sulfonic acid are the two likely degradation routes; see Aliquots, Freeze-Thaw Cycles, and Oxidation.

The added N-terminal tyrosine gives the peptide a usable UV chromophore at 275 to 280 nm, which makes net peptide content by absorbance straightforward if the extinction coefficient is stated. The counter-ion (acetate or trifluoroacetate) should be declared because it changes the fraction of the label mass that is peptide. For general guidance on reading each line, see How to Read a Peptide Certificate of Analysis, Line by Line.

US Prime Peptides posts lot-matched certificates before purchase for AOD-9604 5 mg and AOD-9604 10 mg, each covering identity by mass spectrometry, HPLC purity, net peptide content, endotoxin, sterility and heavy metals, with an independent third-party report. The label mass is the lyophilized fill and should be read against the content line.

Frequently Asked Questions

What is AOD-9604 made from?

It is a synthetic copy of residues 177 to 191 of human growth hormone with an extra tyrosine at the N-terminus, 16 residues in all, closed into a loop by a disulfide bond between its two cysteines. It is made by solid-phase synthesis, not extracted from growth hormone.

Is AOD-9604 approved by the FDA?

No. AOD-9604 is not an approved drug in the United States or any other country. Its Australian clinical program was discontinued in 2007. The developer's 2014 "self-affirmed GRAS" claim is a company-convened food-ingredient conclusion, not an FDA review or approval, and in 2023 FDA placed the substance in Category 2 of its 503A bulk substances list.

Does AOD-9604 act through the beta-3 adrenergic receptor?

Not directly, according to the 2001 Endocrinology study. In beta₃-AR knock-out mice the chronic effects on body weight and lipolysis were absent, but the fragment still raised energy expenditure acutely. The authors concluded the fragment increases beta₃-AR expression without acting through it directly.

Why is AOD-9604 on the WADA Prohibited List?

WADA lists "growth hormone fragments," naming AOD-9604 and hGH 176-191, under class S2 (peptide hormones, growth factors and related substances). Anti-doping laboratories have published urine detection methods for the peptide and its stable loop fragment Cys-Arg-Ser-Val-Glu-Gly-Ser-Cys-Gly.

Citations

1. Wu Z, Ng FM. Antilipogenic action of synthetic C-terminal sequence 177-191 of human growth hormone. Biochem Mol Biol Int. 1993;30:187-196. PMID 8358331
2. Wijaya E, Ng FM. Effect of an antilipogenic fragment of human growth hormone on glucose transport in rat adipocytes. Biochem Mol Biol Int. 1993;31:543-552. PMID 8118430
3. Ng FM, Jiang WJ, Gianello R, Pitt S, Roupas P. Molecular and cellular actions of a structural domain of human growth hormone (AOD9401) on lipid metabolism in Zucker fatty rats. J Mol Endocrinol. 2000;25:287-298. PMID 11116208
4. Ng FM, Sun J, Sharma L, Libinaka R, Jiang WJ, Gianello R. Metabolic studies of a synthetic lipolytic domain (AOD9604) of human growth hormone. Horm Res. 2000;53:274-278. PMID 11146367
5. Heffernan M, Summers RJ, Thorburn A, et al. The effects of human GH and its lipolytic fragment (AOD9604) on lipid metabolism following chronic treatment in obese mice and beta(3)-AR knock-out mice. Endocrinology. 2001;142:5182-5189. PMID 11713213
6. Vanhee C, Moens G, Deconinck E, De Beer JO. Identification and characterization of peptide drugs in unknown pharmaceutical preparations seized by the Belgian authorities: case report on AOD9604. Drug Test Anal. 2014;6:964-968. PMID 24976118
7. Cox HD, Smeal SJ, Hughes CM, Cox JE, Eichner D. Detection and in vitro metabolism of AOD9604. Drug Test Anal. 2015;7:31-38. PMID 25208511

This article is for laboratory research reference only. US Prime Peptides products are supplied strictly for in vitro research. Not for human consumption.

Compliance Notice: US Prime Peptides products are supplied strictly for laboratory and academic research purposes only. They are not intended for human or veterinary consumption, diagnosis, treatment, or prevention of any disease. All content on this page is educational in nature and does not constitute medical advice or product claims. Researchers are responsible for handling these compounds in accordance with their institution’s safety protocols and applicable laws.