AOD-9604 is a modified sixteen-residue analogue of the terminal region of human growth hormone, developed initially to investigate lipid metabolism and obesity. It consists of hGH residues 177–191 with an additional tyrosine at the beginning. Rodent experiments found metabolic activity, and a sponsor-associated human publication reported monitored safety findings across six trials. The obesity programme nevertheless ended after the larger efficacy study failed its primary endpoint. Later development under the name LAT8881 moved into pain research, where a placebo-controlled neuropathic-pain trial was also negative on its principal comparison. These outcomes define the clinical evidence more clearly than the broad description “fat-loss fragment.”
Overview
AOD-9604, commonly written AOD9604 in the literature, has the sequence Tyr-Leu-Arg-Ile-Val-Gln-Cys-Arg-Ser-Val-Glu-Gly-Ser-Cys-Gly-Phe, with a disulfide bridge between its two cysteines. The original LAT8881 protocol identifies this sequence and states that the compound was called AOD9604 during its obesity development. The same document links the later investigational name to the earlier peptide core.
Molecular profile
Forms and derivatives
LAT8881
The later investigational name for the Tyr-hGH177–191 core formerly developed as AOD9604. Pain-study formulations, populations and outcomes remain identified separately from the obesity trials.
AOD9604 acetate
The acetate salt shares the active peptide moiety while requiring its own complete form and quality characterization. FDA evaluated free base and acetate separately.
LAT9991 and photoaffinity material
An active metabolite and a modified metabolite probe used in the LanCL1 investigation. Their assay findings remain labeled to the tested material.
Native hGH176–191 and hGH177–191
Related native terminal sequences. Native176–191 begins with phenylalanine; native177–191 is shorter. Their results require direct material identification.
The native hGH176–191 segment begins with phenylalanine. AOD9604 replaces that starting position with tyrosine, producing Tyr-hGH177–191. The shorter native hGH177–191 sequence and older preparations such as AOD9401 also require distinct labels. AOD9604 free base and acetate share an active peptide moiety, while salt composition and formulation affect the complete material description. FDA’s 2024 evaluation specifically addressed confusion between free base and acetate in compounding nominations.
Uses and research areas
The original programme asked whether a small GH-related domain could influence lipid metabolism without reproducing the complete hormone’s GH-receptor and IGF-I response. Obese rats and mice supplied weight, adipose-tissue and insulin-sensitivity measurements. Human development then tested oral products for obesity and monitored GH-related safety variables.
Other experiments explored local treatment in induced rabbit osteoarthritis and, later, oral LAT8881 in neuropathic pain. These indications depend on different tissue biology, routes and endpoints. The rabbit joint results, human weight programme and pain trial should therefore be evaluated as separate interventions even though they share a peptide core. Ng et al., Kwon and Park, EU trial results
Mechanism of action
An excised and modified GH fragment lacks the full protein architecture required for the usual GH-receptor activation process. The human safety programme monitored IGF-I specifically because intact GH can raise it. AOD9604 did not produce a significant rise relative to placebo under those trial conditions, consistent with the earlier receptor and proliferation experiments discussed in the report. Stier, Vos and Kenley
The mouse metabolic work implicated adaptation of the beta-adrenergic system. After chronic treatment, AOD9604 increased beta3-adrenergic-receptor RNA in adipose tissue. The chronic weight and lipolysis changes were absent in mice lacking that receptor, while acute increases in energy expenditure and fat oxidation still occurred in the knockout animals. This pattern supports a contribution of beta3-dependent physiology to chronic responses, while leaving room for another initiating mechanism. Heffernan et al.
Later pain research identified LanCL1, a protein involved in neuronal sensitization, as an experimental target. The 2026 study by Spanswick and colleagues combined rodent behavior, nerve recordings and ex-vivo spinal-cord experiments. Target isolation used a photoaffinity conjugate of an active metabolite, and LanCL1 knockdown blocked LAT8881 activity. The experiment connects a particular neural target to preclinical pain responses; the metabolite probe and parent peptide remain distinct materials within that investigation.
Pharmacokinetics
Moré and Kenley reported nonclinical metabolism using several preparations and assays. AOD9604 spiked into rat plasma at room temperature underwent sequential removal of amino-terminal residues, with an approximate four-minute disappearance half-life in that in-vitro system. The report also described rapid clearance after intravenous administration in pigs, with an approximate three-minute half-life. Those measurements belong to different models.
The pig work used mass-spectrometric peptide analysis and an immunoassay, and the report discusses both parent material and degradation fragments. Rat tissue-distribution studies used radiolabel, which can follow labeled metabolites after the intact peptide has changed. These assay distinctions make a universal “AOD half-life” misleading. No human concentration curve is supplied here, and the animal estimates are not assigned to an oral or injectable human product.
Research findings
What the animal metabolic studies measured
Ng and colleagues studied oral AOD9604 for nineteen days in genetically obese Zucker rats. Treated animals gained 15.8 ± 0.6 g, compared with 35.6 ± 0.8 g in controls, and their adipose tissue showed increased lipolytic activity. The accompanying uncertainty convention and animal counts are not specified in the abstract. Euglycemic-clamp testing found no adverse insulin-sensitivity effect in this comparison, unlike the intact-GH context. The outcome was reduced weight gain in that genetic obesity model.
The 2001 mouse study followed chronic intraperitoneal treatment for fourteen days in obese mice and included beta3-receptor knockout and wild-type comparisons. Body weight and body fat decreased in the susceptible animals. The contrasting acute and chronic knockout results described above are consequential: a receptor needed for a chronic whole-animal response is not automatically the molecule’s direct binding target.
The obesity programme and its failed larger comparison
The 2013 safety publication consolidated six double-blind, placebo-controlled studies involving 893 participants in its reported safety population. It covered distinct intravenous and oral studies, ranging from single exposure to twenty-four weeks. That number includes comparison participants and different trials; it is not one trial with 893 people treated with AOD9604.
The larger METAOD006 study randomized 502 adults with obesity to oral AOD9604 or placebo, alongside diet and exercise. FDA’s 2024 record reported no significant weight-loss difference and noted the absence of a full published efficacy report providing the needed design and results. The later sponsor protocol states that the primary endpoint was missed and obesity development ended in 2007. This failed efficacy comparison remains central even though the separate safety publication described favorable overall tolerability.
Local joint findings in rabbits
Kwon and Park randomized thirty-two mature New Zealand white rabbits with collagenase-induced knee osteoarthritis to saline, hyaluronic acid, AOD9604 or their combination. Morphological and histological cartilage-damage scores and lameness were assessed eight weeks after induction. Active groups had less damage than saline, and the combined group had the lowest damage scores and shortest lameness period. The combination outperformed either constituent in that model. The preparation was delivered into the joint, and the findings concern induced rabbit disease; a human cartilage-repair claim would need a human joint study.
LAT8881 in patient pain research
The randomized, double-blind neuropathic-pain crossover trial included fifty-three adults, forty-three with diabetic peripheral neuropathy and ten with postherpetic neuralgia. It compared oral LAT8881 and placebo over two four-week periods. The prespecified mixed-model primary analysis used forty-eight completers and found a pain-score difference of −0.14, with a 95% confidence interval of −0.76 to 0.49 and P = 0.67. Secondary denominators differed by endpoint. The main patient comparison did not demonstrate pain relief beyond placebo.
The 2026 LanCL1 paper supplies a later mechanistic rationale: LAT8881 reversed mechanical hypersensitivity in several rodent neuropathic models and altered excitability in nerve and spinal preparations. Effects on inflammatory hypersensitivity and ordinary nociception were limited. These model-specific findings refine the target hypothesis while the patient trial retains its negative outcome.
Safety and tolerability
AOD9604 has no FDA-approved therapeutic indication. Food-use or “GRAS” descriptions do not establish an approved obesity, pain or joint treatment. FDA also identifies concerns about immunogenicity, peptide impurities and incomplete safety information for compounded material. FDA safety assessment
The human safety paper found no significant overall deterioration in glucose-tolerance testing or IGF-I increase, and selected antibody assays were negative. It also recorded a severe chest-tightness event during an intravenous study and a serious diarrhea event during an oral study, both considered possibly related. Some cancer diagnoses in the longer trials were judged unrelated by investigators. The abstract’s broad reassurance should be read alongside the events in the full report. Stier et al.
The sponsor-associated nonclinical report described changes in liver mass and glycogen, microscopic spaces called vacuoles in monkey liver cells, and effects on the cell cycle at high concentrations. Its authors considered these findings minor, uncertain or lacking convincing toxicological significance. The neuropathic-pain registry reported no serious events among fifty-one exposed participants in each crossover condition. Its table listed nonserious events only when they met a reporting threshold, so an unlisted event cannot be assumed never to have occurred. Moré and Kenley, EU registry
What the research means
The peptide has biological activity in selected models and a development history that reaches controlled human research. Its animal metabolic effects did not produce a successful larger obesity comparison. The later neuropathic-pain trial also failed its primary placebo comparison, while newer preclinical target work provides a more specific reason for further investigation.
The most useful interpretation keeps three elements connected: exact peptide identity, the tissue and preparation tested, and the outcome obtained. Favorable monitored laboratory findings address selected safety questions. They do not supply the missing weight-loss or pain benefit, and findings for AOD9604 do not settle the native hGH176–191 fragment’s biology.
FAQs
Are AOD9604 and native hGH176–191 the same peptide?
Their first residue differs. AOD9604 is Tyr-hGH177–191, while native176–191 contains phenylalanine at that position. They share much of the terminal sequence, but studies need to be assigned to the exact tested material. LAT8881 protocol
Did human obesity development demonstrate useful weight loss?
The larger placebo-controlled study failed its principal efficacy comparison, and obesity development ended. FDA also noted that the full efficacy design and results were not available in the published medical literature it reviewed. The safety publication addresses another question. FDA transcript
Why does LAT8881 appear in an AOD9604 review?
The original sponsor protocol explicitly links the names and peptide core. Later oral pain development therefore belongs in the parent compound’s account, while its formulations, trial populations and endpoints remain separately described. LAT8881 protocol
What did the neuropathic-pain trial show?
The primary mixed-model comparison did not demonstrate greater pain improvement with LAT8881 than with placebo. The confidence interval included no difference, and the crossover analysis used a specific completer population. The later LanCL1 experiments provide mechanistic interest without changing that patient result. EU results
Does stable IGF-I establish overall safety?
It addresses one monitored endocrine concern. Clinical events, antibodies, glucose regulation, route and product quality contribute additional information. The safety report recorded possibly related chest tightness and diarrhea even while describing favorable aggregate tolerability. Stier et al.
Comparisons and related reading
The native hGH176–191 profile explains the first-residue distinction and its historical glucose-metabolism experiments. Ipamorelin and GHRP-2 provide a different hormone-related strategy by stimulating GH release. Tesamorelin’s indication-specific clinical evidence offers another useful comparison when evaluating how endocrine biology becomes a measured treatment outcome.
References
Oral AOD9604 reduced weight gain and increased adipose lipolytic activity in genetically obese rats.
Chronic and acute beta3-receptor knockout experiments gave different metabolic responses.
A sponsor-associated six-study safety synthesis reports monitored endocrine findings and possibly related events.
A randomized four-group rabbit-joint comparison assessed cartilage-damage scores and lameness.
The sponsor-associated nonclinical synthesis includes degradation assays, pig plasma measurements and liver-related observations.
In the neuropathic-pain crossover trial, LAT8881 did not improve pain more than placebo on the main planned analysis. The number of patients analyzed varied across outcomes.
Rodent behavior, neural recordings and a metabolite-derived probe implicate LanCL1 in neuropathic sensitization.
The sponsor protocol specifies Tyr-hGH177–191, its disulfide, the AOD9604/LAT8881 name link and the failed obesity-development endpoint.
The agency discusses free base versus acetate, negative obesity efficacy and shortcomings in safety and characterization.
The agency identifies substance- and route-specific safety concerns and gaps for compounded peptides.
Glossary
- Lipolysis
- Breakdown of stored fat molecules into smaller components.
- Euglycemic clamp
- An experimental method that controls blood glucose while assessing responses to insulin.
- Beta3-adrenergic receptor
- A receptor involved in metabolic responses to adrenergic signals, particularly in rodent adipose tissue.
- Knockout model
- An animal model in which a specified gene has been disabled.
- IGF-I
- Insulin-like growth factor I, a mediator influenced by GH and metabolic state.
- LanCL1
- Lanthionine synthetase C-like protein 1, an experimental target implicated in neuropathic sensitization.
- Mechanical allodynia
- Pain-related sensitivity to a touch or pressure that ordinarily would not be painful.
- Photoaffinity probe
- A modified molecule activated by light to help isolate its binding partner.
- Immunogenicity
- The ability of a material to provoke an immune response.