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Research use only
· 7 min read
The name is doing a lot of work it cannot support. "HGH Fragment 176-191" appears on vendor pages alongside study data that overwhelmingly concerns a different molecule entirely - AOD9604, a tyrosine-modified analogue that shares a C-terminal lineage but is structurally distinct. Getting that distinction wrong on a catalogue page is not a minor editorial slip; it is a misattribution of published findings to the wrong chemical entity. This reference covers what the verified identifiers actually describe, where AOD9604 fits in the record, what each published study examined, and how to handle the material at the bench. Kovalabs supplies HGH Fragment 176-191 strictly as a laboratory research reagent - not for human or veterinary use. Everything below describes what published studies investigated, not any human use or outcome.
| Compound | HGH Fragment 176-191 (somatotropin 176-191) |
|---|---|
| Synonyms | Somatotropin (176-191); HGH (176-191); growth-hormone C-terminal fragment |
| Class / origin | C-terminal fragment of human growth hormone (16-residue peptide) |
| Molecular formula | C78H123N23O22S2 (free base) |
| Molecular weight | 1799.1 g/mol (free base) |
| CAS number | 66004-57-7 |
| PubChem CID | 16131230 |
| Structural feature | One intramolecular cysteine-cysteine disulfide bond |
| Classification | Research use only; not for human or veterinary use |
HGH Fragment 176-191 corresponds to residues 176-191 of human growth hormone (somatotropin). The CAS-anchored free-base record gives a 16-residue peptide with the sequence Phe-Leu-Arg-Ile-Val-Gln-Cys-Arg-Ser-Val-Glu-Gly-Ser-Cys-Gly-Phe, containing a single intramolecular cysteine-cysteine disulfide bond that closes a small ring within the peptide. The verified free-base identifier set is: PubChem CID 16131230 (named Somatotropin (176-191) / HGH (176-191)), CAS 66004-57-7, molecular formula C78H123N23O22S2, and molecular weight 1799.1 g/mol. These figures were adversarially cross-checked: CAS 66004-57-7 resolves to CID 16131230 through PubChem's CAS-to-CID resolver, and the formula and weight are mutually consistent with that CAS-anchored record.
There is a second PubChem record worth knowing about. CID 172966176 also carries the name HGH Fragment 176-191, but it is the acetate salt form (formula C80H127N23O24S2, weight near 1859 g/mol - the free base plus one acetic acid). The two records describe the same peptide in different forms, not a contradiction. A third figure - 1817.12 - circulates on some vendor pages for a tyrosine-led variant; it does not match the CAS-anchored free-base record and is not adopted here. Only the verified free-base identifiers appear in the Key facts table above.
The structural relationship between HGH Fragment 176-191 and AOD9604 must be stated precisely, because most of the literature attached to this compound name actually concerns the latter. Cox HD et al. (Drug Test Anal, 2014; PMID 25208511; DOI 10.1002/dta.1715) define AOD9604 in the peer-reviewed analytical chemistry record as a peptide consisting of residues 177-191 of human growth hormone with an additional tyrosine at the N-terminus. That makes it structurally distinct from the unmodified 176-191 fragment on two counts: it spans 177-191 rather than 176-191, and it carries an extra N-terminal tyrosine the unmodified fragment does not. AOD9604 findings cannot be presented as characterising HGH Fragment 176-191; doing so is scientifically incorrect and a misbranding risk. Every study entry below is labelled with the exact molecule it examined.
| Property | HGH Fragment 176-191 (unmodified) | AOD9604 (modified analogue) |
|---|---|---|
| Peptide origin | Human growth hormone residues 176-191 | Human growth hormone residues 177-191 |
| N-terminal modification | None (sequence begins Phe) | Additional tyrosine residue at the N-terminus |
| Residue count | 16-residue peptide | Modified 15-residue fragment plus N-terminal Tyr |
| Identity status | The unmodified fragment | A distinct, structurally modified molecule |
| Body of published in-vivo / clinical study | Minimal in its own right | Carries almost all published animal and trial literature |
| Defining reference | PubChem CID 16131230 / CAS 66004-57-7 | PMID 25208511 (structural definition) |
The most detailed published characterisation of a molecule in this class was conducted in an anti-doping context and concerns AOD9604. Cox HD et al. (Drug Test Anal, 2014; PMID 25208511; DOI 10.1002/dta.1715) incubated AOD9604 in human serum and urine and developed a solid-phase-extraction LC-MS/MS detection method. The named endpoints were the limit of detection of the parent peptide in urine; the method's linearity, precision, specificity and recovery; and the identification and relative stability of six candidate metabolites, including a metabolite fragment with the sequence CRSVEGSCG. This is an analytical and metabolism-characterisation study; it named no biological-activity endpoint, and no effect is asserted here. It is also the same record that defines AOD9604's structure relative to the 176-191 / 177-191 fragment.
The controlled in-vivo work below examined the AOD9604 analogue, not the unmodified fragment - a distinction carried through each entry. Study design and endpoint names only are reported; no result, effect size, or benefit is stated or implied.
Foundational animal pharmacology (AOD9604). Ng FM et al. (Horm Res, 2000; PMID 11146367; DOI 10.1159/000053183) administered a daily oral dose of the C-terminal-fragment analogue versus control in a genetic obesity rat model over 19 days, with a euglycaemic-clamp sub-study. Named endpoints: a pre-specified body-mass measure; an adipose-tissue metabolic-activity assay; and insulin sensitivity measured by the euglycaemic clamp. The disease-model endpoints are named generically for compliance.
Receptor-pathway mechanism study (AOD9604). Heffernan M et al. (Endocrinology, 2001; PMID 11713213; DOI 10.1210/endo.142.12.8522) ran a controlled chronic-administration study in obesity-model mice and in beta-3-adrenergic-receptor knock-out mice versus wild-type, comparing intact human growth hormone and the fragment, plus an acute energy-expenditure experiment. Named endpoints: a body-mass measure; an adipose-content measure; beta-3-adrenergic-receptor mRNA expression level; a lipid-metabolism-sensitivity assay; and acute energy expenditure and a substrate-oxidation measure. The disease-model metabolic endpoints are named generically for compliance.
Comparative animal and in-vitro receptor study (AOD9604). Heffernan MA et al. (Int J Obes Relat Metab Disord, 2001; PMID 11673763; DOI 10.1038/sj.ijo.0801740) ran a 14-day controlled study in obesity-model (ob/ob) and lean C57BL/6J mice using mini-osmotic pumps (human growth hormone, AOD9604, or saline) with indirect calorimetry, paired with in-vitro assays in BaF-B03 cells transfected with the human growth-hormone receptor. Named endpoints: a body-mass measure; resting energy expenditure; a substrate-oxidation rate; glucose oxidation rate; plasma glucose, insulin and glycerol; and, in vitro, 125I-human-growth-hormone receptor binding and cell proliferation. The disease-model endpoints are named generically for compliance.
Joint-cartilage model (AOD9604, intra-articular route). Kwon DR and Park GY (Ann Clin Lab Sci, 2015; PMID 26275694) used a collagenase-induced knee osteoarthritis rabbit model (n=32) with four weekly ultrasound-guided intra-articular injection groups (saline; hyaluronic acid; AOD9604; AOD9604 plus hyaluronic acid) over 4-7 weeks. Named endpoints: gross morphological cartilage-degeneration score; histopathological score; and duration of lameness.
Human safety and tolerability synthesis (AOD9604, the distinct analogue). The human-trial record concerns AOD9604 under a former clinical-development programme and does not describe any use of the research compound supplied here. A peer-reviewed synthesis (not PubMed-indexed) by Stier H, Vos E and Kenley D (J Endocrinol Metab, 2013; DOI 10.4021/jem157w) covers six randomized, double-blind, placebo-controlled human trials conducted in the 2001-2006 development period: three acute dose-escalation studies, one multiple-dose study, and two longer studies. Named safety measures: serum IGF-1 concentration; oral glucose tolerance test; anti-AOD9604 antibody titres; physical examination, vital signs, laboratory parameters and ECG; and recorded adverse events. Only the trial designs and the names of the monitored parameters are reported; no tolerability outcome is asserted.
Secondary and unconfirmed records. One further human study of AOD9604 (the distinct analogue) is recorded in an institutional research-output record as a randomized, double-blind, placebo-controlled, multicentre Phase-2-stage trial. Its design specified a pre-specified primary efficacy endpoint over the treatment period, with glucose tolerance among the secondary measures. The primary endpoint is described generically for compliance; no result is stated or implied. Because an exact journal, volume, pages and DOI could not be independently verified from a primary index, no DOI is asserted and this entry is listed here rather than alongside the PMID-anchored records.
A direct query of the ClinicalTrials.gov API (v2) for AOD9604 returned no registered study records. The relevant trials largely predate mandatory registration, which is the likely reason no NCT record is retrievable. No NCT identifier is asserted.
These entries are listed as research context, not as findings a reader should expect.
Form. The free-base peptide (CID 16131230, CAS 66004-57-7) has formula C78H123N23O22S2 and molecular weight 1799.1 g/mol. The common solid form is the acetate salt (CID 172966176), typically supplied as a lyophilised powder.
Disulfide integrity. The molecule contains a single intramolecular cysteine-cysteine disulfide bond. Reduction of that bond changes the molecule, so reducing conditions and reducing agents should be avoided in any workflow where the intact ring is required. This is the kind of detail that does not make it onto a short spec sheet, and it is precisely where a verified certificate of analysis earns its place in the workflow: a vial that says intact disulfide is not the same as a vial that has one.
Storage. Standard small-peptide practice applies: store the lyophilised powder cold and protected from moisture and light. For longer-term storage the powder is generally held frozen.
Reconstitution as a bench procedure. Dissolve the lyophilised material in an appropriate laboratory solvent suitable for the intended assay, allow gentle dissolution without vigorous agitation, then aliquot to minimise freeze-thaw cycles. The reconstituted solution should be used within a defined working window appropriate for the analytical method. This is not a preparation method for any use in humans or animals. See the reconstitution guide for handling specifics.
For completeness at the GH-axis bench: researchers cross-referencing the growth-hormone secretagogue literature may also consult the AOD-9604 page, which covers the distinct tyrosine-modified analogue and its own identifier set, and the GH-axis research category for related compounds in the same molecular neighbourhood.
Tier one is solid: the chemistry is verified. CAS 66004-57-7 resolves to PubChem CID 16131230, with formula C78H123N23O22S2 and a free-base weight of 1799.1 g/mol, an unmodified 16-residue C-terminal fragment of human growth hormone carrying one cysteine-cysteine disulfide. The identity is well established. Tier two is shakier and belongs mostly to a different molecule: the in-vitro and animal mechanism work (PMID 11146367, 11713213, 11673763, 26275694) examined the AOD9604 analogue, not the unmodified fragment, and a cell in a dish is not a person. Tier three is the weakest: the human record is confined to AOD9604 under a former development programme, and almost nothing characterises the unmodified fragment itself. It is not a licensed medicine, and it has not been shown to produce defined outcomes in humans. Curiosity is warranted; certainty is not.
HGH Fragment 176-191 supplied by Kovalabs is a laboratory research chemical intended for in-vitro and laboratory research use only. It is not a medicinal product and is not for human or veterinary use, ingestion, or administration. No statement in this reference constitutes a medicinal, therapeutic, efficacy, or human-outcome claim. The published studies referenced are described solely by their design and the names of their measured endpoints, with no result or benefit asserted, and the dominant in-vivo and clinical record concerns the distinct analogue AOD9604. Researchers are responsible for compliance with all applicable laws, institutional approvals, and safe-handling requirements. See the research disclaimer for full terms.
No. HGH Fragment 176-191 is the unmodified 16-residue C-terminal fragment of human growth hormone (residues 176-191). AOD9604 is a distinct, modified analogue: according to PubMed it spans residues 177-191 and carries an additional tyrosine at the N-terminus (PMID 25208511; DOI 10.1002/dta.1715). They are not interchangeable, and AOD9604 findings should not be presented as characterising the unmodified fragment.
The verified free-base identifier set is PubChem CID 16131230, CAS 66004-57-7, molecular formula C78H123N23O22S2, and molecular weight 1799.1 g/mol. These were adversarially cross-checked: the CAS resolves to that CID, and the formula and weight are mutually consistent. The acetate salt form is a separate record (CID 172966176, weight near 1859 g/mol).
Those figures describe different forms or variants. A weight near 1859 g/mol corresponds to the acetate salt (free base plus one acetic acid, CID 172966176). A value of 1817.12 circulates on some vendor pages for a tyrosine-led variant; it does not match the CAS-anchored free-base record, so it is not adopted here. The figure reported in this reference, 1799.1 g/mol, is the verified free-base weight.
The controlled in-vivo studies examined the AOD9604 analogue. Their designs included an oral 19-day rat study with a euglycaemic clamp (PMID 11146367), a beta-3-adrenergic-receptor knock-out mouse study (PMID 11713213), a 14-day osmotic-pump mouse study with in-vitro receptor assays (PMID 11673763), and a rabbit intra-articular joint-cartilage model (PMID 26275694). Only those study designs and the names of their measured endpoints are reported here; no result or benefit is stated.
Standard small-peptide practice for research use only. Store the lyophilised powder cold, protected from moisture and light, and frozen for longer-term storage. Dissolve in an appropriate laboratory solvent, allow gentle dissolution, then aliquot to minimise freeze-thaw cycles. The molecule contains one cysteine-cysteine disulfide, so avoid reducing agents where the intact ring is required. See the linked reconstitution guide.
No. It is supplied strictly for in-vitro and laboratory research use only. It is not a medicine and is not for human or veterinary use, ingestion, or administration. Nothing in this reference constitutes a medicinal, therapeutic, or efficacy claim.