Key Takeaways
- •TB-500 and Thymosin Beta-4 are not the same thing. Almost every published study is of Thymosin Beta-4, the natural 43-residue protein; TB-500 is the synthetic material supplied for research.
- •Material sold as TB-500 is described elsewhere as at least three different molecules: full-length Tbeta4, the seven-residue fragment Ac-LKKTETQ at about 889 Da, and the tetrapeptide Ac-SDKP. Check the sequence and mass on the certificate against what a paper actually studied.
- •Volta's certificate identifies its vial as the heptapeptide Ac-LKKTETQ, by an MS/MS transition whose precursor only that molecule can produce.
- •The molecular mechanism under study is actin sequestration. Tbeta4 binds monomeric G-actin and holds it out of filament assembly. It is not a growth factor and has no known dedicated receptor.
- •Several foundational papers on Tbeta4 have been retracted or carry expressions of concern. Check any mechanistic claim back to its primary source.
- •No Thymosin Beta-4 product is approved for any use in Canada or the United States.
Summary
The first thing to settle is what the name refers to. TB-500 is a synthetic peptide supplied for laboratory research; Thymosin Beta-4 is the naturally occurring 43-residue protein whose central actin-binding region it reproduces, and essentially the whole published literature is about the latter. Different suppliers and papers use the name TB-500 for at least three different molecules with different masses, so a figure quoted for one does not carry over to another.
At the molecular level Tbeta4 is an actin-sequestering peptide. It binds free G-actin in a one-to-one complex and keeps it out of filament assembly, which is a different kind of activity from a growth factor binding a receptor. The seven-residue fragment corresponds to the region of the protein that makes that actin contact.
The literature carries two cautions. Several foundational papers have been retracted or flagged, so any mechanistic claim needs checking back to source. And no Thymosin Beta-4 product has been approved for any use.
What TB-500 Is
TB-500 is a synthetic peptide corresponding to the central actin-binding region of Thymosin Beta-4 (Tbeta4), a protein present in human and animal cells. The two are not the same thing, and the distinction carries most of the weight when reading this literature: almost every published study describes Thymosin Beta-4 itself, while TB-500 is the synthetic material supplied for laboratory research.
Thymosin Beta-4 is the most abundant beta-thymosin in human tissue, present at high concentration in blood platelets among other cell types, and is encoded by the TMSB4X gene. It acts principally as an actin-sequestering peptide.
Volta supplies TB-500 as a lyophilised research material, and the batch certificate for the 10mg vial identifies which molecule that is. Report COA-2026-SC-02807 (SideChain Analytics, 27 September 2026) confirms identity by the MRM transition 445.3 to 241.2. A precursor at 445.3 is the doubly protonated Ac-LKKTETQ heptapeptide, monoisotopic mass near 888.5 g/mol; no charge state of the 4,963 g/mol full-length protein lands there. So the vial holds the seven-residue actin-binding fragment, measured at 99.5 percent chromatographic purity with 11.19 mg of net peptide against a 10 mg label claim. The product specification table carries the same figures: CAS 885340-08-9, C38H68N10O14, 889.0 g/mol. The full specification and the measured batch purity are on the TB-500 product page.
A note on conflicting identity claims. Material sold as "TB-500" is described in the wider literature and by other suppliers as at least three different molecules: full-length Thymosin Beta-4, the seven-residue actin-binding fragment Ac-LKKTETQ at roughly 889 Da, and the N-terminal tetrapeptide Ac-SDKP. They are not interchangeable, and published figures for one do not transfer to another. Check the sequence and mass on the certificate against what a paper actually studied before relying on it. For why a matching mass alone does not prove the sequence, see what proves a sequence.
Molecular Mechanisms Under Study
All of the following comes from biochemical, cell-culture and animal-model work. None of it describes an effect in humans.
- G-actin sequestration. Thymosin Beta-4 binds monomeric G-actin and prevents its polymerisation into F-actin filaments, buffering the pool of unpolymerised actin a cell holds. The LKKTETQ region is the part of the protein that makes that contact.
- Cytokine and transcription-factor readouts. Cell-culture work reports reduced expression of TNF-alpha and IL-1beta, and changes consistent with downregulation of NF-kappaB signalling, in treated cell lines.
- Matrix metalloproteinase expression. Some studies report upregulation of matrix metalloproteinases and downregulation of their tissue inhibitors in cultured cells.
- Endothelial cell migration. Endothelial cell-culture assays report increased migration, which is consistent with an actin-cytoskeleton mechanism.
These are molecular and cellular observations under investigation, and they are specific to the cell types in which they were measured.
How the Literature Was Produced
The Tbeta4 literature spans dermal and corneal injury models (rodent and rabbit), myocardial ischaemia models (rodent), central and peripheral nerve injury models (rodent), and cell-culture work in fibroblasts and microglial lines. Its weight is limited by how it was produced rather than by the questions it asked:
- Retractions and expressions of concern. Several foundational papers on Thymosin Beta-4 have been retracted or have received expressions of concern over data integrity and reproducibility. Any mechanistic claim traced back to that body of work needs the primary source checked before it is relied on.
- Limited replication. The nerve-model and cell-senescence results originate from a small number of laboratories.
- Inconsistent study conditions. Preclinical studies use widely differing amounts, routes and durations, which makes cross-study comparison unreliable.
- Short observation windows. Many studies report only days-to-weeks measurements.
- Antibody response is uncharacterised. Tbeta4 is an endogenous protein, and whether a synthetic fragment provokes an antibody response in a model has not been characterised.
- The molecule studied is usually not TB-500. Most of this work used full-length Tbeta4, so it describes a 43-residue protein rather than the seven-residue fragment.
Regulatory Status
RegeneRx Biopharmaceuticals developed Thymosin Beta-4 candidates and ran a Phase I study around 2009 to 2011. That programme did not continue to approval. No Thymosin Beta-4 product is approved for any indication in Canada or the United States, and describing that work as current or ongoing would be wrong by roughly fifteen years. No registered clinical trial of the TB-500 heptapeptide was identified.
This material is supplied for laboratory research only and is not for human or veterinary use.
Research Status
| Attribute | Detail |
|---|---|
| Evidence base | Biochemical, cell-culture and animal-model work, almost all on full-length Thymosin Beta-4 |
| Regulatory status | Not approved for human or veterinary use in any jurisdiction |
| Principal molecular mechanism | G-actin sequestration |
| Supplied as | Lyophilised powder, Ac-LKKTETQ heptapeptide, C₃₈H₆₈N₁₀O₁₄, 889.0 g/mol, CAS 885340-08-9 |
For how to read the analytical documentation that accompanies a vial, see How to Read a Certificate of Analysis and the Quality & Testing page. The compound hub at TB-500 carries the vial sizes, batch certificates and handling notes.
Corrected 18 October 2026: this article previously described TB-500 as another name for Thymosin Beta-4 and as naturally occurring, presented a discontinued clinical programme as current, and carried a figure from a human study that has been removed.
Corrected 29 October 2026: the research status table described the vial as the 43-residue sequence, contradicting the certificate quoted above. It now gives the heptapeptide's formula, mass and CAS number.
Consolidated 18 October 2026: merged with four further TB-500 and Thymosin Beta-4 articles. Their identity claims were not carried across: between them they described TB-500 as four mutually exclusive molecules, three of those descriptions were wrong, and two carried molecular formulae that do not match the molecule they named.
