Research Peptide · For laboratory research use only
Also known as Thymosin Beta-4, TB4
TB-500 is a name used for synthetic thymosin beta-4 supplied for research. Thymosin beta-4 is a 43-residue, N-terminally acetylated peptide and one of the main G-actin sequestering molecules in cells: in 1991 it was shown to be identical to Fx, a platelet peptide that forms a 1:1 complex with actin monomers and inhibits their polymerisation1.
The name is not used consistently. Doping-control laboratories identified the key ingredient of a veterinary product sold as TB-500 as Ac-LKKTETQ, the N-acetylated 17-23 fragment of thymosin beta-4 that corresponds to its actin-binding region6,7, while other studies use TB-500 to mean synthetic thymosin beta-48. The identity of the supplied material is given on the batch Certificate of Analysis.
As described in the research literature
As described in the research literature, the founding observation for thymosin beta-4 is actin sequestration: the purified peptide binds monomeric actin stoichiometrically and inhibits salt-induced polymerisation1. In vitro, it acted as a chemoattractant for human umbilical vein endothelial cells, accelerated their migration into scratch wounds and increased matrix metalloproteinase production2.
In embryonic and postnatal cardiomyocytes, thymosin beta-4 was reported to form a functional complex with PINCH and integrin-linked kinase (ILK), leading to activation of the survival kinase Akt; ILK and Akt activity were raised in mouse hearts after coronary artery ligation4. Later work in mice found it essential for coronary vessel development and reported that it stimulated outgrowth and differentiation from quiescent adult epicardial explants, with its cleavage product Ac-SDKP enhancing endothelial differentiation5.
What published studies have examined
Protein sequencing and actin polymerisation assays established the identity of thymosin beta-4 with the actin-sequestering peptide Fx1. Boyden chamber, scratch wound and Matrigel plug assays examined endothelial cell migration2.
A rat full-thickness wound model examined re-epithelialisation, wound contraction, collagen deposition and angiogenesis with thymosin beta-4, alongside keratinocyte migration in Boyden chamber assays3.
Sources [3]
Cardiomyocyte migration and survival in culture and cardiac function after coronary artery ligation were examined in mice4. Thymosin beta-4 knockdown and adult epicardial explant studies examined coronary vessel development and neovascularisation5.
A 2026 rat study of Achilles tendon transection and repair compared TB-500 (described as synthetic thymosin beta-4), BPC-157 and their combination using load to failure, histological scoring and collagen type I and III immunohistochemistry8.
Sources [8]
Analytical laboratories detected and synthesised Ac-LKKTETQ found in a TB-500 product6, and developed LC-MS methods to detect it and its metabolites in equine urine and plasma7.
Thymosin beta 4 and Fx, an actin-sequestering peptide, are indistinguishable.
Safer D, Elzinga M, Nachmias VT The Journal of Biological Chemistry, 1991.
Thymosin beta 4 stimulates directional migration of human umbilical vein endothelial cells.
Malinda KM, Goldstein AL, Kleinman HK The FASEB Journal, 1997.
Thymosin beta4 accelerates wound healing.
Malinda KM, Sidhu GS, Mani H, et al. The Journal of Investigative Dermatology, 1999.
Thymosin beta4 activates integrin-linked kinase and promotes cardiac cell migration, survival and cardiac repair.
Bock-Marquette I, Saxena A, White MD, et al. Nature, 2004.
Thymosin beta4 induces adult epicardial progenitor mobilization and neovascularization.
Smart N, Risebro CA, Melville AA, et al. Nature, 2007.
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.
Esposito S, Deventer K, Goeman J, et al. Drug Testing and Analysis, 2012.
Doping control analysis of TB-500, a synthetic version of an active region of thymosin β₄, in equine urine and plasma by liquid chromatography-mass spectrometry.
Ho EN, Kwok WH, Lau MY, et al. Journal of Chromatography A, 2012.
Effects of BPC-157 and TB-500 on Achilles tendon healing in rats: A histopathological and biomechanical study.
Biçer O, Adanir O, Güleryüz Y, et al. Joint Diseases and Related Surgery, 2026.
This page is provided for research and educational reference only. It does not constitute medical advice, dosing guidance, or a recommendation for use. All compounds are strictly for laboratory and in-vitro research purposes.