TB-500 is a name used in research and doping-control circles for peptides based on thymosin β4 (Tβ4), a small, highly conserved protein found inside nearly every mammalian cell. Its best-established job is holding actin monomers in reserve, and that role in the cytoskeleton led researchers to examine it in cell migration, blood-vessel formation and tissue-injury models.
The name itself causes confusion, because “TB-500” refers to two different molecules in the literature. This overview explains that distinction first, then covers Tβ4’s structure, the actin biology behind most of the research, the main model systems, and the limits of the evidence.
At a glance
- Class: β-thymosin peptide (thymosin β4)
- Origin: First characterized from calf thymus extracts by Allan Goldstein’s group; later found in most cell types
- Structure (Rogue’s product): full-length, N-terminally acetylated Tβ4, 43 amino acids; C212H350N56O78S; 4963 g/mol; CAS 77591-33-4
- Main research areas: actin sequestration, endothelial cell migration, cardiac and dermal injury models, tendon repair, anti-doping analytics
- Regulatory status: Not FDA approved for any use; WADA S2 (thymosin-β4 and its derivatives, e.g. TB-500)
Structure and origin
Thymosin β4 was first purified from thymosin fraction 5, a calf thymus extract studied by Goldstein’s laboratory for its effects on immune cells, and its amino acid sequence was reported in the early 1980s. The “thymosin” name stuck even after it became clear the peptide is not thymus-specific: Tβ4 is abundant in platelets, white blood cells and many other tissues.
The native molecule is 43 residues long, carries an acetyl group on its N-terminal serine, and contains a single methionine (the one sulfur atom in its formula). In solution it is largely unstructured and adopts a more ordered conformation when bound to actin. Two segments receive the most attention. The N-terminal tetrapeptide Ac-Ser-Asp-Lys-Pro (Ac-SDKP) is released by enzymatic cleavage and is studied in its own right. The motif Leu-Lys-Lys-Thr-Glu-Thr, starting at residue 17, is conserved across the β-thymosin family and forms part of the actin-binding region.
Two meanings of “TB-500”
In doping-control literature, TB-500 is described as a synthetic version of an active region of Tβ4: the acetylated 17–23 fragment, Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln, taken from the actin-binding region. Ho and colleagues developed liquid chromatography–mass spectrometry methods to detect this fragment and its metabolites in horse urine and plasma (Ho et al., 2012). Elsewhere, “TB-500” is used as a label for full-length synthetic Tβ4. The product Rogue Compounds sells is the full 43-residue peptide, with the identifiers listed above, and the batch COA records what was found in the vial.
Mechanism: what the research shows
The core biochemistry is well established. Tβ4 binds monomeric (G-) actin in a 1:1 complex and prevents it from adding to filaments, which lets cells keep a large pool of unpolymerized actin ready for rapid remodeling. Safer and colleagues showed that a platelet actin-sequestering factor called Fx was the same molecule as Tβ4, linking the peptide directly to this function (Safer et al., 1991).
Because cell movement depends on fast actin turnover, later studies asked whether extracellular Tβ4 affects migration. In human umbilical vein endothelial cells (HUVECs), added Tβ4 increased directional migration in chamber assays (Malinda et al., 1997). In mouse heart cells, Tβ4 was associated with formation of a complex with PINCH and integrin-linked kinase (ILK), activation of the survival kinase Akt, and increased cardiomyocyte migration (Bock-Marquette et al., 2004). How an intracellular actin-binding protein exerts effects from outside the cell is still not fully resolved.
Key areas of study
Endothelial migration and angiogenesis
HUVEC migration studies were among the first to suggest an extracellular role for Tβ4 (Malinda et al., 1997). Follow-up work used vessel-formation assays and animal models to study angiogenesis, and this thread remains central to how the peptide is discussed.
Cardiac injury models
In a mouse coronary ligation model, Tβ4 treatment was associated with improved cardiomyocyte survival and cardiac function measures, with the ILK-Akt pathway proposed as the mechanism (Bock-Marquette et al., 2004). This Nature paper drew wide attention to Tβ4 as a research tool in cardiac biology.
Dermal and corneal models
A review of animal work summarized studies in rodent skin wounds, corneal injury and other repair models, where readouts included re-epithelialization, inflammatory cell infiltration and collagen deposition (Philp and Kleinman, 2010).
Tendon
A 2026 rat Achilles tendon study compared TB-500, BPC-157 and the two combined, using histopathology and biomechanical load testing; the authors described their results as exploratory (Biçer et al., 2026).
Analytical detection
Because TB-500 is prohibited in sport, a separate literature focuses on finding it. LC-MS methods for the 17–23 fragment and its metabolites in equine samples are an example (Ho et al., 2012).
What the evidence does not show
- Most functional data come from cell culture and rodent models. They do not establish effects or safety in humans.
- Studies use different molecules under the same name: full-length Tβ4, the 17–23 fragment, or Ac-SDKP. Results for one cannot be assumed for another.
- The extracellular mechanism is incompletely understood; no dedicated cell-surface receptor has been confirmed.
- Tendon data are limited to small, exploratory animal studies.
- Neither TB-500 nor Tβ4 is approved for any medical use.
Regulatory status
Neither TB-500 nor thymosin β4 is approved by the FDA for any use. The World Anti-Doping Agency’s Prohibited List names “thymosin-β4 and its derivatives, e.g. TB-500” under S2 (peptide hormones, growth factors, related substances and mimetics). Rogue Compounds sells it as a research reagent only.
Handling and storage in the lab
Lyophilized Tβ4 should be kept sealed and refrigerated at 2–8°C (36–46°F), protected from light.
Sourcing and documentation
Rogue Compounds has TB-500 made in small batches. Every vial carries a batch number and a QR code that opens the independent U.S. testing lab’s own report for that batch, and the same batch COA is on the product page and in the COA Library.
View TB-500 on Rogue Compounds
References
- Safer D, et al. Thymosin beta 4 and Fx, an actin-sequestering peptide, are indistinguishable. J Biol Chem. 1991;266(7):4029-4032. PMID 1999398
- Malinda KM, et al. Thymosin beta 4 stimulates directional migration of human umbilical vein endothelial cells. FASEB J. 1997;11(6):474-481. PMID 9194528
- Bock-Marquette I, et al. Thymosin beta4 activates integrin-linked kinase and promotes cardiac cell migration, survival and cardiac repair. Nature. 2004;432(7016):466-472. PMID 15565145
- Philp D, Kleinman HK. Animal studies with thymosin beta, a multifunctional tissue repair and regeneration peptide. Ann N Y Acad Sci. 2010;1194:81-86. PMID 20536453
- Ho EN, et al. 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. J Chromatogr A. 2012;1265:57-69. PMID 23084823
- Biçer O, et al. Effects of BPC-157 and TB-500 on Achilles tendon healing in rats: a histopathological and biomechanical study. Jt Dis Relat Surg. 2026;37(3):822-837. PMID 42542926
Research use only. Rogue Compounds products are sold strictly for laboratory research. They are not for human or veterinary use, and nothing in this article is medical advice. The studies cited here describe published research, not this product or any use of it.