Educational Reference · Research-Use-Only
TB-500: Mechanism, Research, and Regulatory Status
A research-grade overview of TB-500 — what it is, how it works at the molecular level, what published studies have shown, and answers to the questions researchers ask most.
Last reviewed 2026-07-28
What is TB-500?
Thymosin beta-4 is the principal intracellular G-actin sequestering peptide in eukaryotic cells. It binds monomeric G-actin in a 1:1 stoichiometry through a conserved actin-binding motif, maintaining a cytoplasmic reservoir of polymerization-competent actin and thereby buffering the G-actin/F-actin equilibrium that governs cytoskeletal remodeling and cell motility. An important identity distinction applies to this compound: peer-reviewed analytical work has characterized the material supplied as TB-500 as the N-terminal acetylated 17-23 fragment of thymosin beta-4 (Ac-LKKTETQ), not the intact 43-residue protein, and essentially all of the biology summarized here was generated with full-length thymosin beta-4.
Beyond its canonical intracellular role, the full-length peptide is released extracellularly at sites of tissue injury, where it has been reported to influence endothelial cell migration, angiogenic tube formation, and inflammatory signaling. In cardiac tissue, Bock-Marquette and colleagues reported that thymosin beta-4 forms a functional complex with PINCH and integrin-linked kinase, activating ILK and downstream Akt signaling. The peptide is unstructured in free solution and adopts partial helical character upon binding actin, a conformational feature typical of the beta-thymosin family.
Its small size and lack of stable tertiary structure make it a substrate for exopeptidase processing, generating shorter fragments including the N-terminal Ac-SDKP tetrapeptide, which has its own documented activity in the literature. Mechanistic work on the isolated 17-23 actin-binding fragment is substantially thinner than for the intact 43-mer.
Research highlights
What published peer-reviewed research and preclinical studies have established about TB-500:
- 01Thymosin beta-4 is described in the literature as the major actin-sequestering molecule in eukaryotic cells (Goldstein 2005).
- 02Bock-Marquette and colleagues reported that thymosin beta-4 forms a complex with PINCH and integrin-linked kinase, resulting in ILK activation in cardiac cells (Nature 2004).
- 03Review literature describes a role for thymosin beta-4 in dermal and corneal wound-healing models (Goldstein 2005; Crockford 2010).
- 04Analytical characterization found the material sold as TB-500 to be the N-terminal acetylated 17-23 fragment of thymosin beta-4, not the intact protein (Esposito 2012).
- 05LC-MS/MS methods for detecting TB-500 in equine urine and plasma have been developed for doping-control purposes (Ho 2012).
- 06UniProt annotates residues 2-5 of the mature chain as the separately bioactive hemoregulatory peptide Ac-SDKP.
Frequently asked questions about TB-500
Is TB-500 the same thing as thymosin beta-4?+
No, and the distinction matters when reading the literature. Thymosin beta-4 is a 43-residue endogenous peptide. Analytical work has characterized the material supplied as TB-500 as the N-terminal acetylated 17-23 fragment (Ac-LKKTETQ), which corresponds to the actin-binding region but lacks the remainder of the sequence, including the separately bioactive N-terminal Ac-SDKP motif. Published findings generated with full-length thymosin beta-4 should not be attributed to the fragment.
What is the proposed mechanism?+
Full-length thymosin beta-4 acts as the principal intracellular G-actin sequestering peptide, binding monomeric actin 1:1 and buffering the G-actin/F-actin equilibrium that governs cytoskeletal remodeling and cell motility. Additional reported activity includes complex formation with PINCH and integrin-linked kinase in cardiac cells. Mechanistic characterization of the isolated 17-23 fragment is considerably more limited.
Are there human clinical trials of TB-500?+
No. No human clinical trial of TB-500 (Ac-LKKTETQ) has been conducted. Human data that is sometimes cited in this context comes from RGN-259, an ophthalmic solution of full-length synthetic thymosin beta-4 studied in dry eye disease — a different molecule in a different formulation and route of administration — and the larger of those Phase 2 studies did not meet its primary endpoints.
How does it differ from thymosin alpha-1?+
They are unrelated peptides that are frequently confused because of the shared thymosin naming. Thymosin alpha-1 is a 28-residue immunomodulatory peptide with an entirely different sequence, mechanism, and research literature. It is not interchangeable with thymosin beta-4 or its fragments in experimental design.
How should it be stored and reconstituted?+
Store lyophilized material at -20C, desiccated and protected from light, and equilibrate to room temperature before opening to prevent condensation on hygroscopic powder. Reconstitute with sterile or bacteriostatic water using gentle swirling rather than vortexing to limit shear and aggregation. As an unstructured, protease-labile peptide, aliquot working stocks and avoid repeated freeze-thaw cycles.
Why do anti-doping authorities test for it?+
Thymosin beta-4 and its derivatives, including TB-500, fall under WADA Prohibited List section S2 as growth factors, prohibited at all times in and out of competition. Validated LC-MS/MS detection methods have been published for both human and equine testing contexts.
References & sources
Every citation below was resolved against its primary source before publication — each PMID against the PubMed record and each DOI through doi.org. Follow any link to read the paper at the publisher rather than taking our summary on trust.
- [1]Goldstein AL. Thymosin beta4: a new molecular target for antitumor strategies. Trends in Molecular Medicine. 2005. PMID: 16099219 DOI: 10.1016/j.molmed.2005.07.004
- [2]Bock-Marquette I, Saxena A, White MD, Dimaio JM, Srivastava D. Thymosin beta4 activates integrin-linked kinase and promotes cardiac cell migration, survival and cardiac repair. Nature. 2004. PMID: 15565145 DOI: 10.1038/nature03000
- [3]Crockford D, Turjman N, Allan C, Angel J. Thymosin beta4: structure, function, and biological properties supporting current and future clinical applications. Annals of the New York Academy of Sciences. 2010. PMID: 20536467 DOI: 10.1111/j.1749-6632.2010.05492.x
- [4]Esposito S, Deventer K, Goeman J, Van der Eycken J, Van Eenoo P. 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 Testing and Analysis. 2012. PMID: 22962027 DOI: 10.1002/dta.1402
- [5]Ho ENM, Kwok WH, Lau MY, Wong ASY, Wan TSM, Lam KKH, Schiff PJ, Stewart BD. Doping control analysis of TB-500, a synthetic version of an active region of thymosin beta4, in equine urine and plasma by liquid chromatography-mass spectrometry. Journal of Chromatography A. 2012. PMID: 23084823 DOI: 10.1016/j.chroma.2012.09.043
Where this data comes from
- —Citations & trial data: PubMed (NCBI, U.S. National Library of Medicine), Crossref and ClinicalTrials.gov.
- —Chemical identity: PubChem and UniProt. Where sources conflicted, the disputed value is omitted rather than guessed.
- —Regulatory status: U.S. FDA publications and, where applicable, the WADA Prohibited List. Compounding status changes frequently — verify against FDA directly before relying on it.
- —Purity, form and storage are handling and supplier conventions, not literature-derived values. Confirm against the lot-specific certificate of analysis.
Content last reviewed 2026-07-28. Compiled by Veridian Research from the primary literature. This page is an educational reference for laboratory researchers — it is not medical advice, and it describes no human use.
Regulatory status
Neither TB-500 nor full-length thymosin beta-4 is approved by the FDA for any indication, and no thymosin beta-4 product has completed a successful Phase 3 program. Thymosin beta-4 and its derivatives, including TB-500, fall under WADA Prohibited List section S2 (Peptide Hormones, Growth Factors, Related Substances and Mimetics), prohibited at all times both in and out of competition. Compounding status under the FDA 503A bulk drug substances framework has been subject to ongoing review and change; verify against FDA's currently published list rather than any secondary source. Supplied strictly as a research chemical for in vitro and laboratory research use only — not for human or veterinary use, not for diagnostic or therapeutic use.
Research-Use-Only Material
Specifications and certificate of analysis
TB-500 is stocked as a research reagent. Analytical documentation — identity, purity and the lot-specific certificate of analysis — is published on the product record.
View specifications & COA →