The central problem in TB-500 research is attribution, not a shortage of thymosin β4 literature: search results, product copy, and secondary summaries routinely file full-length thymosin β4 findings under the shorter name without disclosing that the tested molecules differ. This guide gives the registry identifiers that separate the two, keeps every reported figure attached to its model and species, and sets out the controls a fragment study needs. It provides no dosing, administration, or blend guidance.
- TB-500 is locked here to seven residues, written
Ac-LKKTETQand acetylated at the N-terminus. - The fragment is CAS 885340-08-9, formula
C38H68N10O14, molecular weight 889.0 g/mol; the parent protein is CAS 77591-33-4,C212H350N56O78S, 4,963 g/mol. - Full-length human thymosin β4 contains 43 amino acids; TB-500 is not the complete parent peptide.
- A 2012 analytical paper directly identified Ac-LKKTETQ in a product called TB-500.
- Most wound, cardiac, ligament, corneal, and human trial papers in the legacy source set tested full-length thymosin β4.
- An active-site relationship is a biological rationale, not proof that the fragment reproduces every parent-protein effect.
- TB-500 has no FDA, EMA, NMPA, MHRA, PMDA, TGA or Health Canada approval anywhere globally, and WADA lists it as prohibited in sport.
- Sequence, N-terminal acetylation, mass, purity, counterion, lot, matrix, and matched controls must be documented for fragment-specific work.
What Is TB-500?
TB-500 is the name used here for the N-terminally acetylated seven-residue sequence Ac-LKKTETQ — leucine, two lysines, threonine, glutamate, threonine and glutamine, with an acetyl group on the N-terminus. It corresponds to residues 17–23 within human thymosin β4, but it is not full-length thymosin β4. That category boundary is the foundation for every claim on this page.
The sequence alone is not a complete reagent specification, and “thymosin beta-4 fragment” without a sequence is too ambiguous for reproducible work. The rest of the required record is set out under study controls below.
Reagent Identity: Sequence, CAS, Formula and Mass
TB-500 and its parent protein carry different CAS numbers, different molecular formulas, and masses differing by more than a factor of five.
| Property | TB-500 (fragment) | Thymosin β4 (parent protein) |
|---|---|---|
| Sequence | Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln (Ac-LKKTETQ), 7 residues, N-acetylated | 43 residues, including the N-terminal Ser-Asp-Lys-Pro (Ac-SDKP) tetrapeptide the fragment does not contain |
| Position in the parent | Residues 17–23, the central actin-binding domain | Complete peptide |
| CAS number | 885340-08-9 | 77591-33-4 |
| Molecular formula | C38H68N10O14 | C212H350N56O78S |
| Molecular weight | 889.0 g/mol | 4,963 g/mol |
| PubChem CID | 62707662 | 45382195 |
| Form supplied as a reagent | Lyophilized powder, acetate salt | Not supplied by Apex Laboratory |
Identifiers and masses above come from the PubChem compound records for CAS 885340-08-9 (CID 62707662) and CAS 77591-33-4 (CID 45382195). The mass gap is the practical control: an identity check landing near 889 Da is consistent with the acetylated heptapeptide, while a result near 4,963 Da is the 43-residue parent protein.
How Was the TB-500 Identity Established?
Esposito and colleagues analyzed a product called TB-500 using high-performance liquid chromatography and high-resolution mass spectrometry. They identified the active content as the N-terminally acetylated 17–23 fragment of human thymosin β4, Ac-LKKTETQ, and synthesized the same fragment for analytical characterization (PMID 22962027).
That paper is direct evidence for chemical identity in the product analyzed. It is not an efficacy trial, and it reports no quantitative endpoint — a detection-method study is not designed to produce one. Its deliverable is a chemical assignment: the acetylated 17–23 heptapeptide, whose 889.0 Da mass separates it from the ~4,963 Da parent protein. It answers what material was detected, not what that material does.
TB-500 Versus Full-Length Thymosin β4
| Feature | TB-500 in this guide | Full-length thymosin β4 |
|---|---|---|
| Identity | N-acetylated residues 17–23 | Complete human β-thymosin peptide |
| Length | 7 residues | 43 residues |
| Direct source strength | Analytical identity and detection literature | Extensive structural, cell, animal, formulation, and limited clinical literature |
| Claim rule | Use only fragment-specific evidence | Keep outcomes labeled as parent-protein or formulation evidence |
What Does the Actin-Binding Motif Establish?
Full-length thymosin β4 binds actin monomers. Cross-linking placed its contacts across the whole monomer: Lys-3 of thymosin β4 to Glu-167 of actin, Lys-18 to the actin N-terminal acidic cluster, and Lys-38 to Gln-41, with the C-terminal half held in an extended conformation. That study reports no quantitative outcome of the effect-size kind — its result is a contact map, not a treatment effect (PMID 9153421).
β-Thymosins are characterised as the main intracellular G-actin-sequestering peptides of most vertebrate cells, binding with a dissociation constant in the micromolar range that permits fast association and release; the review reports no quantitative endpoint for any repair outcome (PMID 17468232).
A second review maps activity onto discrete sequence blocks: a 4-residue N-terminal Ac-SDKP site linked to blocking inflammation and fibrosis, a 15-residue N-terminal site linked to cell survival, and the 7-residue LKKTETQ central actin-binding domain at residues 17–23 linked to angiogenesis, wound healing and cell migration. Being a narrative synthesis, it too reports no quantitative endpoint (PMID 20179146). That mapping is mechanistic rationale for studying fragments. It does not prove that Ac-LKKTETQ has the same affinity, kinetics, stability, localization, or in-vivo effects as the complete molecule.
An Evidence-Attribution Map for TB-500
| Evidence lane | Representative source | What it supports | What it does not support |
|---|---|---|---|
| Direct fragment identity | Esposito et al., 2012 | TB-500 product content identified as Ac-LKKTETQ | Biological or clinical efficacy |
| Short-sequence rationale | Sosne et al., 2010 | Active-site research within thymosin β4 | Equivalence between TB-500 and the parent |
| Parent-protein mechanism | Safer et al., 1997 | Full-length thymosin β4–actin structural context | Fragment binding or activity without direct testing |
| Parent-protein preclinical | Wound, cardiac, ligament studies | Outcomes for full-length thymosin β4 in stated models | TB-500 outcomes |
| Parent-protein clinical formulation | Ophthalmic phase II trials | Protocol-specific results for a defined full-length formulation | Safety or efficacy of an RUO TB-500 vial |
What the Full-Length Thymosin β4 Literature Found
Full-length thymosin β4 studies are useful background when labeled correctly, and labeling them correctly means keeping their numbers attached. In a rat full-thickness dermal wound model, topical or intraperitoneal thymosin β4 increased reepithelialization by 42% over saline controls at 4 days and by as much as 61% at 7 days, and treated wounds contracted at least 11% more than controls by day 7. The same report found that as little as 10 pg of thymosin β4 stimulated keratinocyte migration 2–3-fold over medium alone in a Boyden-chamber assay (PMID 10469335). Every one of those figures is rat or rat-derived-cell data for the 43-residue protein.
Mouse dermal wound work raised MMP-2 and MMP-9 expression several-fold over control on day 2 after wounding, with cell-specific increases in MMP-1, -2 and -9 across cultured keratinocytes, endothelial cells and fibroblasts. That study also localised the responsible region: the central actin-binding domain, amino acids 17–23, carried all of the metalloproteinase-inducing activity (PMID 16607611). This is the closest the retained set comes to fragment-relevant biology, and it is still domain mapping inside the parent protein, not a test of the acetylated free heptapeptide.
In cardiac work, thymosin β4 formed a functional complex with PINCH and integrin-linked kinase that activated Akt; after coronary artery ligation in mice, treatment raised ILK and Akt activity in the heart, enhanced early myocyte survival and improved cardiac function. The abstract reports no quantitative endpoint for the magnitude of that functional improvement (PMID 15565145). A rat medial-collateral-ligament transection study placed 1 µg of thymosin β4 in 100 µL of fibrin sealant into the ligament gap and assessed healing at 4 weeks, reporting evenly spaced collagen-fibre bundles, significantly increased fibril diameters, and significantly better biomechanics than in untreated rats (PMID 23523891).
Two randomized, placebo-controlled phase 2 trials tested a 0.1% thymosin β4 ophthalmic solution (RGN-259) in dry-eye disease. A 9-patient multicentre trial dosing 6 times daily for 28 days reported, at day 56, a 35.1% reduction in ocular discomfort in treated eyes versus vehicle control (P = 0.0141) and a 59.1% reduction in total corneal fluorescein staining (P = 0.0108) (PMID 25826322). A larger 72-subject controlled-adverse-environment trial missed both of its primary endpoints at visit 5; among secondary findings it reported a 27% reduction in day-28 discomfort scores versus placebo (P = 0.0244) and improved central and superior corneal staining (P = 0.0075 and P = 0.0210) (PMID 26056426). Both trials tested the complete parent peptide in a defined ophthalmic formulation under an investigational protocol. Neither tested TB-500, and the second is a reminder that the human record here includes a missed primary endpoint.
Additional Reported Findings
A wider set of parent-protein studies sits behind that summary. Each claim-map row names the tested compound, the model and species, the endpoint, the reported result, and the source. Every row is full-length thymosin β4 (Tβ4) or a genetic manipulation of it; none tested Ac-LKKTETQ.
| Compound | Model and species | Endpoint | Reported result | Source |
|---|---|---|---|---|
| Tβ4 | Limited proteolysis and tritium exchange; purified actin monomers, in vitro | Proteolysis at actin Gly-46 | >12-fold faster for MgATP-actin when Tβ4 is bound | PMID 10777749 |
| Tβ4 | FRET and calorimetry; purified actin monomers, in vitro | Probe distances within actin | Gln-41↔Cys-374 +2 Å; εATP↔Lys-61 −1.9 Å; no quantitative outcome beyond those shifts | PMID 16272441 |
| Tβ4 overexpression | Stable lines vs vector control; NIH 3T3 fibroblasts (mouse), in vitro | Cytoskeletal and adhesion proteins | G-actin and F-actin each ~2-fold higher, so the ratio held constant; vinculin ~3-fold | PMID 9331222 |
| Tβ4 | Coronary artery ring sprouting; HUVEC (human) and artery explant, in vitro | Vessel area via branching | Doubled with as little as 100 ng of synthetic Tβ4 | PMID 14517430 |
| Tβ4 | TNF-α-stimulated inflammation; human corneal epithelial cells, in vitro | Nuclear NF-κB p65 | Level, activity and phosphorylation significantly decreased; no quantitative outcome given | PMID 17254567 |
| Tβ4 | TNF-α with PINCH-1 and ILK; human cells, in vitro | NF-κB activation and IL-8 transcription | Both inhibited, independently of G-actin binding; no quantitative outcome given | PMID 21343177 |
| Tβ4 and its sulphoxide | Injured skeletal muscle and C2C12 assays; mouse, in vivo and in vitro | Myoblast chemotaxis and wound closure | Both significantly accelerated; no quantitative outcome given | PMID 20880960 |
| Tβ4 | Collagen–chitosan hydrogel after LAD ligation; rat myocardium, in vivo | Tissue loss after infarction | 13 ± 4% vs 58 ± 3% untreated and 30 ± 8% with Tβ4-free hydrogel; more mature vessels (P < 0.0001) | PMID 22817626 |
| Tβ4 | EPC pretreatment and transplantation; human EPC in vitro, rat heart in vivo | VEGF secretion and tube formation | Both increased and abolished by a VEGF-neutralising antibody; no quantitative outcome given | PMID 29956769 |
| Tβ4 overexpression | Critical-limb-ischaemia model; mouse in vivo, HUVEC in vitro | Ang2, Tie2, VEGFA and CD31 | All increased via Notch/NF-κB and reversed by DAPT and BMS; no quantitative outcome given | PMID 32945357 |
| Tβ4 | Follicle bulge stem cells; rat vibrissa keratinocytes in vitro, rats and mice in vivo | Hair growth and MMP-2 | Both increased; no quantitative outcome given | PMID 14657002 |
| Tβ4 overexpression and knockout | Epidermis-specific and global lines; mouse, in vivo | MMP-2, VEGF, β-catenin and Lef-1 | Raised in overexpressers and sharply reduced in knockouts; no quantitative outcome given | PMID 27130465 |
Three legacy sources are deliberately not carried here: two 2007 symposium papers restating datasets already cited above (the mouse coronary-ligation experiment and the hair-growth programme) and a 2005 narrative review superseded by the 2007 β-thymosins review. The 1997 endothelial-migration paper stays with the guides that own endothelial-migration intent.
How Much Direct Biological Evidence Exists for TB-500?
Within the current-run verified source set, direct TB-500 evidence establishes analytical identity only. No controlled human therapeutic trial of Ac-LKKTETQ appears in the selected papers, and the biological literature is dominated by full-length thymosin β4. That is a real evidence gap, not a reason to fill the page with parent-protein claims.
A fragment-specific experiment should therefore name its test article and avoid “thymosin β4” as shorthand. If a paper tested the full-length protein, cite it as parent context; if it tested a different short sequence, terminal chemistry, or formulation, retain that exact description; if the material is not adequately characterized, treat identity as unresolved.
Regulatory Status of TB-500 and Thymosin β4
TB-500 — the acetylated heptapeptide Ac-LKKTETQ — holds no FDA, EMA, NMPA, MHRA, PMDA, TGA or Health Canada approval anywhere globally. There is no approved drug product containing it and no approved therapeutic indication for it in any jurisdiction. It is not approved for human or veterinary use, and nothing in this article describes an approved therapy.
Full-length thymosin β4 is likewise unapproved anywhere globally. The 0.1% ophthalmic solution above was studied as an investigational product under a phase 2 protocol, and the larger trial missed its primary endpoints. Investigational status is permission to run a trial, not a marketing authorisation, and it attaches to that formulation and route — not to a research-use-only vial of a seven-residue fragment.
Sport-rule context is a separate question
The World Anti-Doping Agency’s 2026 Prohibited List names TB-500 under peptide hormones, growth factors, related substances, and mimetics. That rule applies to athletes within the anti-doping framework; it is not evidence of therapeutic efficacy, general legal status, or regulatory approval. See the official 2026 WADA list.
Apex Laboratory supplies TB-500 as a chemical reagent for in-vitro and preclinical research only. That is a supplier statement about intended use — a different assertion from regulatory status, and not an approval, a safety determination, or a claim of equivalence to any approved product.
Controls for a TB-500 Fragment Study
Identity comes first: record the exact seven-residue sequence, N-terminal acetylation, C-terminal form, counterion, water content, residual solvents, lot, and concentration basis. Interpret mass-spectrometry evidence against the expected chemical form, and report HPLC purity with its method and detection conditions.
Controls should distinguish the fragment from the parent. Depending on the hypothesis, useful arms include vehicle, untreated, Ac-LKKTETQ, non-acetylated LKKTETQ, full-length thymosin β4, a sequence-scrambled control, and an assay-specific positive control — design examples, not a universal protocol.
Document matrix and stability conditions too: solvent or buffer, pH, ionic strength, protein content, vessel material, temperature, freeze-thaw history, incubation time, and any adsorption control. The mass-spectrometry guide, HPLC purity guide, and COA-reading guide separate identity, purity, and documentation claims.
Research-Material Context
Current vial amount, lot documentation, availability, and fulfillment details belong on the live product record rather than in this evidence guide. Identity and purity documentation does belong here.
The Apex listing specifies research-grade TB-500 as a lyophilized peptide at ≥99% purity by reversed-phase HPLC, with mass-spectrometric identity confirmation and a per-lot certificate of analysis; confirm the current specification against the live listing. A purity figure of that kind describes chromatographic peak area under a stated method. It does not establish sterility, endotoxin status, concentration accuracy, or biological activity, and it says nothing about whether the vial holds the 889.0 Da fragment or the 4,963 Da parent protein — only the mass-spectrometric identity check answers that.
Current TB-500 research-reagent record
Review the live listing for current specifications and documentation. It is a research-use-only listing, not a drug, clinical formulation, or performance protocol.
View the TB-500 research-reagent pageThe tissue-repair research hub maps adjacent topics. The separate BPC-157 versus TB-500 comparison owns direct comparison intent; this guide does not provide a blend, combination, or substitute recommendation.
Frequently Asked Questions
What is TB-500?
TB-500 is the N-terminally acetylated seven-residue sequence Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln, abbreviated Ac-LKKTETQ. It corresponds to residues 17–23 of human thymosin β4.
Is TB-500 the same as full-length thymosin β4?
No. TB-500 is a seven-residue fragment, while full-length human thymosin β4 contains 43 residues. A shared sequence region does not make the fragment and parent peptide biologically equivalent.
What is the exact TB-500 sequence?
The exact sequence used in this guide is Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln, written Ac-LKKTETQ. The Ac prefix records N-terminal acetylation and should not be omitted from the material identity.
What direct evidence identifies TB-500?
Esposito and colleagues used chromatographic and mass-spectrometric methods to identify Ac-LKKTETQ in a product called TB-500. That analytical result establishes identity in the tested product, not biological efficacy.
Can full-length thymosin β4 studies be cited as TB-500 studies?
No. They can be cited as parent-protein context only when the tested material is stated clearly. Wound, cardiac, ligament, corneal, or clinical findings from full-length thymosin β4 do not become fragment evidence.
What controls matter in a TB-500 study?
Document the seven-residue sequence, N-terminal acetylation, C-terminal form, counterion, lot, identity and purity evidence, concentration basis, matrix, stability conditions, matched comparators, contamination controls, and prespecified endpoints.
What is the molecular weight and CAS number of TB-500?
The TB-500 fragment is CAS 885340-08-9, molecular formula C38H68N10O14, molecular weight 889.0 g/mol, PubChem CID 62707662. Full-length thymosin β4 is CAS 77591-33-4, C212H350N56O78S, 4,963 g/mol, CID 45382195. Copy that lists 4,963 g/mol under the TB-500 name has described the parent protein.
Is TB-500 approved by any regulator?
No. TB-500 has no FDA, EMA, NMPA, MHRA, PMDA, TGA or Health Canada approval anywhere globally and no approved therapeutic indication in any jurisdiction. The World Anti-Doping Agency lists it as prohibited in sport, which is an anti-doping rule rather than a statement about efficacy or approval.
What did the thymosin β4 wound-healing studies actually measure?
In a rat full-thickness dermal wound model, thymosin β4 increased reepithelialization by 42% at 4 days and by as much as 61% at 7 days versus saline controls, and treated wounds contracted at least 11% more by day 7. Those are rat data for the 43-residue parent protein, not measurements of Ac-LKKTETQ.
References
- Esposito S, et al. Synthesis and characterization of the N-terminal acetylated 17-23 fragment of thymosin beta 4 identified in TB-500, a product suspected to possess doping potential. Drug Test Anal. 2012;4(9):733-8. PMID: PMID 22962027.
- Sosne G, et al. Biological activities of thymosin beta4 defined by active sites in short peptide sequences. FASEB J. 2010;24(7):2144-51. PMID: PMID 20179146.
- Safer D, et al. Thymosin beta 4 binds actin in an extended conformation and contacts both the barbed and pointed ends. Biochemistry. 1997;36(19):5806-16. PMID: PMID 9153421.
- Hannappel E. beta-Thymosins. Ann N Y Acad Sci. 2007;1112:21-37. PMID: PMID 17468232.
- Malinda KM, et al. Thymosin beta4 accelerates wound healing. J Invest Dermatol. 1999;113(3):364-8. PMID: PMID 10469335.
- Philp D, et al. Thymosin beta4 promotes matrix metalloproteinase expression during wound repair. J Cell Physiol. 2006;208(1):195-200. PMID: PMID 16607611.
- Bock-Marquette I, et al. Thymosin beta4 activates integrin-linked kinase and promotes cardiac cell migration, survival and cardiac repair. Nature. 2004;432(7016):466-72. PMID: PMID 15565145.
- Xu B, et al. Thymosin β4 enhances the healing of medial collateral ligament injury in rat. Regul Pept. 2013;184:1-5. PMID: PMID 23523891.
- Sosne G, et al. Thymosin β4 significantly improves signs and symptoms of severe dry eye in a phase 2 randomized trial. Cornea. 2015;34(5):491-6. PMID: PMID 25826322.
- Sosne G, et al. Thymosin beta 4 ophthalmic solution for dry eye: a randomized, placebo-controlled, Phase II clinical trial conducted using the controlled adverse environment (CAE™) model. Clin Ophthalmol. 2015;9:877-84. PMID: PMID 26056426.
