D tier · weak
The heptapeptide has a genuine, independently replicated preclinical record in rodent wound-repair models and a defined molecular target in monomeric actin, but no human interventional trial has evaluated it and it is routinely conflated with the full 43-residue thymosin beta-4 protein.
tb-500 fragment
TB-500, as characterised in the analytical chemistry literature, is the N-terminally acetylated 17-23 fragment of thymosin beta-4 - the seven-residue LKKTETQ actin-binding motif rather than the intact 43-residue protein. Rodent studies report improved dermal wound repair and angiogenesis attributable to this motif, but no published human interventional trial has evaluated the fragment.
// we supply this one
available as a research reagent
≥ 99% HPLC · lyophilised powder · batch certificate published. Grade D above is our own and is not adjusted because we stock it.
the explanation
Thymosin beta-4 is a natural 43-piece protein involved in tissue repair, and TB-500 is only the seven-piece section that grabs the cell's internal scaffolding. Animal wound-healing studies on that short piece look promising, but it has never been tested in a published human trial.
regulatory status
Not approved in any jurisdiction; established anti-doping target
The fragment holds no marketing authorisation anywhere and is not a recognised medicine. It is a well-established doping-control target, with dedicated LC-MS methods published for TB-500 in equine urine and plasma from 2012 and in in-vitro and rat matrices from 2024, and it appears in multi-analyte doping screening panels for synthetic peptides. It is chemically and pharmacologically distinct from full-length thymosin beta-4, which has its own separate research and development history that should not be treated as evidence for the fragment.
how it works · proposed mechanism
The peptide's only well-defined molecular action is binding monomeric actin through the motif that it reproduces.
G-actin sequestration motif
LKKTETQ is the actin-binding domain of thymosin beta-4, which within the intact protein sequesters monomeric G-actin and buffers the pool available for filament assembly. Isolating this motif is the stated rationale for using the fragment as a minimal active unit.
Cytoskeletal remodelling and migration
Through its effects on actin dynamics the motif is proposed to promote cell migration, a prerequisite for re-epithelialisation and angiogenesis during wound repair. Sosne and colleagues mapped several biological activities of thymosin beta-4 onto short peptide sequences including this one.
Fragment is not Tβ4
Full-length thymosin beta-4 is 43 residues with functions extending well beyond actin binding, and analytical work confirms that TB-500 preparations contain only the acetylated 17-23 fragment. Evidence generated with intact thymosin beta-4 therefore does not automatically apply to the heptapeptide.
what’s reported
evidence shape
6 sourcesThe composition of the cited literature by study type. This describes the shape of the evidence, not its quality — and it does not by itself set the grade.
⚠ the catch
Most material presented as TB-500 evidence in fact describes full-length thymosin beta-4, a 43-residue protein with a separate research history, while the marketed fragment reproduces only seven of those residues. A 2026 Sports Medicine review of unapproved musculoskeletal peptides concludes that favourable tissue-repair outcomes in animal models are not matched by rigorous human safety data.
key published findings
- Rodent: Philp et al. (Wound Repair Regen 2003) reported that thymosin beta-4 and a synthetic peptide containing its actin-binding domain both promoted dermal wound repair in db/db diabetic mice and in aged mice.
- In vitro and mechanistic: Sosne et al. (FASEB J 2010) defined biological activities of thymosin beta-4 - including angiogenesis and wound healing - by mapping them to short peptide sequences, identifying LKKTETQ as an active site.
- Human cells (in vitro): Shah et al. (Expert Opin Biol Ther 2018) reported that thymosin beta-4 inhibits PDGF-BB-induced activation, proliferation and migration of human hepatic stellate cells via its actin-binding domain.
- Analytical (product identity): Esposito et al. (Drug Test Anal 2012;4:733-738) synthesised and characterised the N-terminally acetylated 17-23 fragment of thymosin beta-4 and identified it as the constituent of TB-500, establishing that the marketed product is the heptapeptide and not the intact protein.
- Literature audit: a PubMed search for LKKTETQ returns only preclinical studies, analytical chemistry and equine doping-control methodology, with no human interventional trial of the fragment appearing in the indexed literature.
limitations of the evidence
- No human interventional data, no human pharmacokinetics, and no published half-life exist for the fragment.
- Several key rodent studies administered full-length thymosin beta-4 alongside or instead of the isolated motif, so the fragment's independent contribution is not cleanly separated from the parent protein's.
- Product composition has proven variable enough that analytical work on seized and commercial preparations was required to establish what TB-500 actually contains.
documented safety signals
- No published human safety data for the fragment; the 2026 Sports Medicine review of unapproved peptide therapies states that rigorous human safety data for this class are scarce despite favourable animal results.
- Theoretical concern arising from the mechanism itself: a peptide that promotes actin-dependent cell migration and angiogenesis has unquantified effects on unwanted cell migration, and no long-term study in any species addresses this.
identity
| full name | Thymosin beta-4 actin-binding fragment (Tβ4 17-23, LKKTETQ) |
| category | Growth Hormone |
| modality | peptide |
| formula | C36H66N10O13 |
| molar mass | 847 g/mol |
| sequence | LKKTETQ |
laboratory handling
| storage | Supplied as a lyophilised powder; research peptide is generally stored desiccated at -20 °C and protected from light. |
| solubility | Freely soluble in water - a short, highly polar peptide with two lysines, no hydrophobic core and no cysteines. |
| co-studied with | No published study evaluates the fragment in combination with any other compound, and evidence generated with full-length thymosin beta-4 should not be transferred to it. |
Handling information describes laboratory practice for a research reagent. It is not a preparation guide for use in humans.
the receipts
6 citedDrug Testing and Analysis 4(9):733-738 · 2012 · peer-reviewed
Journal of Chromatography A 1265:57-69 · 2012 · peer-reviewed
Sports Medicine · 2026 · review
Wound Repair and Regeneration · 2003 · preclinical
FASEB Journal · 2010 · preclinical
Expert Opinion on Biological Therapy 18(sup1):177-184 · 2018 · preclinical
others in Growth Hormone