TB-500: what the research on thymosin beta-4 and its fragment covers

In short: TB-500 is a name used for two materials: full-length thymosin beta-4, a 43-amino-acid protein, and a synthetic seven-residue fragment of it (Ac-LKKTETQ). Human trials have used only the full protein; research on the fragment is cell, animal and analytical work. In Australia, the TGA names TB-500 as an unapproved peptide product, not included in the ARTG.

Most writing about TB-500 blends two different bodies of research: studies of thymosin beta-4, the full 43-residue protein, and studies of the short fragment that anti-doping chemists first identified under the TB-500 name. This review keeps them apart. For a side-by-side comparison of the two molecules, see TB-500 vs thymosin beta-4. For the other peptide in this cluster, see our review of the BPC-157 research.

Key facts

The TB-500 that Certified Research Peptides supplies is full-length thymosin beta-4 acetate, according to our supplier’s specification. The identifiers below are for that protein; the fragment is listed separately.

Name and synonyms	TB-500 (market name); thymosin beta-4 acetate; Tβ4; Fx; timbetasin 1
Sequence and length	Ac-SDKPDMAEIEKFDKSKLKKTETQEKNPLPSKETIEQEKQAGES, 43 amino acids, acetylated N-terminal serine 2
Molecular formula	C212H350N56O78S (peptide, excluding acetate counter-ions) 1
Molecular weight	4,963 g/mol (peptide, excluding acetate counter-ions) 1
CAS number	77591-33-4 1
PubChem CID	16132341
UniProt	P62328 (human thymosin beta-4) 2
Compound class	Actin-sequestering protein of the beta-thymosin family
Fragment also sold as TB-500	Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln-OH (Ac-LKKTETQ), residues 17 to 23; C38H68N10O14; 889.0 g/mol; CAS 885340-08-9; PubChem CID 62707662 3
Evidence base	Full-length Tβ4: cell, animal and human trials. Fragment: cell, animal and analytical studies
WADA status	Prohibited at all times, section S2.3: “Thymosin-β4 and its derivatives e.g. TB-500” (2026 list) 4
TGA status	Named in the TGA safety advisory of 13 April 2026 as an unapproved peptide product, meaning goods not included in the Australian Register of Therapeutic Goods (ARTG) 5

What is TB-500?

TB-500 is a market name used for two different materials: full-length thymosin beta-4, a protein found in most mammalian cells, and a synthetic peptide built from its actin-binding region.

The TB-500 that Certified Research Peptides supplies is the full-length protein, thymosin beta-4 acetate (43 residues), according to our supplier’s specification. The acetate is a counter-ion, a small charged molecule paired with the peptide’s charged groups, explained in our post on acetate and TFA salts.

The fragment definition comes from anti-doping laboratories. In 2012, Esposito et al. analysed a product sold as TB-500 using high-performance liquid chromatography with high-resolution mass spectrometry, and identified the N-terminally acetylated 17 to 23 fragment of human thymosin beta-4, Ac-LKKTETQ 6. The same year, Ho et al. described TB-500 as a veterinary preparation whose key ingredient was LKKTETQ with artificial acetylation of the N-terminus (the starting end of the peptide chain) 7. PubChem records TB-500 under that seven-residue structure 3.

Outside that literature, the name is used for both molecules. Delcourt et al. analysed products sold online as TB500 and TB1000 and reported in 2023 that their contents were not consistently in line with earlier descriptions 8. In 2025, the same group wrote that doping-control laboratories had found numerous online products claiming to contain either the acetylated fragment or full-length thymosin beta-4 9, and a 2026 rat study described the TB-500 it tested as “synthetic thymosin beta-4” 10. Any study, product or certificate labelled TB-500 therefore needs checking for which molecule it actually describes.

How is TB-500 structured?

Full-length thymosin beta-4 is a single chain of 43 amino acid residues with an acetylated N-terminus (the starting end of the chain), while the fragment matches seven residues from its middle.

The full protein. The gene product starts with a methionine that is removed, and the first retained residue, serine, is acetylated 2. UniProt annotates the whole chain as a disordered region, meaning it has no fixed folded shape on its own 2. Its molecular weight is 4,963 g/mol 1.

The fragment. Ac-LKKTETQ matches positions 17 to 23 of the mature protein, with an acetyl group on the leucine and a free acid at the glutamine end 3. Inside the protein, leucine 17 carries no acetyl group, so this acetylation is a synthetic addition 7. Its molecular weight is 889.0 g/mol 3, about 18% of the full protein’s.

Two features of the full protein explain why the 17 to 23 segment was singled out:

• It sits in the actin-binding site. Van Troys et al. mapped the site in 1996 using chemically synthesised variants of the full protein. They reported two separate parts that contact actin: an N-terminal segment (residues 1 to 16) that needs to coil into an alpha-helix, and a six-residue motif at residues 17 to 22 11.
• It carries activity in some assays. A 2010 review by Sosne et al. describes LKKTETQ as the central actin-binding domain associated with cell migration and blood-vessel formation in experimental models, and lists other active sites elsewhere in the protein, such as the N-terminal tetrapeptide Ac-SDKP 12.

Illustration: a seven-bead chain beside a longer chain, representing a peptide fragment and its parent protein. Not an exact structure.

What mechanisms have researchers studied?

Research on mechanism has centred on actin binding and on signalling linked to cell migration, mostly using full-length thymosin beta-4 and, in fewer studies, the unacetylated LKKTETQ sequence.

• Actin sequestration. Safer et al. reported in 1991 that Fx, the main peptide bound to unpolymerised actin in human platelets, was identical to Tβ4. It formed a one-to-one complex with actin monomers (G-actin) and inhibited their assembly into filaments 13. Actin filaments form much of a cell’s internal scaffolding, which is why actin-binding proteins are studied in cell movement.
• The motif and endothelial cells. In a 2003 cell and tissue study, Philp et al. reported that Tβ4 and its seven-residue actin-binding motif showed near-identical activity in migration assays with human umbilical vein endothelial cells and in vessel sprouting from chick aortic arches. Peptides missing any part of the motif were inactive, and adding soluble actin inhibited the activity 14.
• ILK and Akt signalling. In 2004, Bock-Marquette et al. reported that full-length Tβ4 formed a complex with PINCH and integrin-linked kinase (ILK), leading to activation of Akt, a kinase involved in cell survival, in cultured heart cells and in mice 15.
• Stellate cell signalling. Shah et al. reported in 2018 that the 17 to 23 peptide, but not a 1 to 15 peptide, blunted Akt phosphorylation and markers of activation in human hepatic stellate cells, liver cells central to fibrosis 16.
• Metabolites. Rahaman et al. studied acetylated TB-500 itself in 2024. They reported that only one breakdown product, Ac-LKKTE, showed significant activity compared with control in a fibroblast wound assay, and suggested that earlier reported activity might come from that metabolite rather than the parent peptide 17.

What does the published research include?

The literature falls into three groups: studies of full-length Tβ4 (cell, animal and human), studies of the unacetylated LKKTETQ sequence (cell and animal), and studies of acetylated TB-500 itself (mostly analytical and metabolic work).

Study	Study type	Model	What was measured	Reported finding
Safer, 1991	Biochemical study	Peptide purified from human platelets; muscle actin	Sequence; binding to actin monomers	Fx was identical to Tβ4, formed a 1:1 complex with actin monomers and inhibited polymerisation
Malinda, 1999	Animal and cell study	Rat full-thickness wound model; keratinocyte migration assay	Re-epithelialisation (regrowth of the surface cell layer), wound contraction, collagen, vessel formation	Full-length Tβ4 increased re-epithelialisation by 42% over saline at day 4 and by up to 61% at day 7, with increased collagen deposition and angiogenesis
Philp, 2003a	Cell and ex vivo study	Human umbilical vein endothelial cells; chick aortic arches	Migration, adhesion, vessel sprouting	Tβ4 and its seven-residue actin-binding motif had near-identical activity; peptides lacking part of the motif were inactive
Philp, 2003b	Animal study	Full-thickness dermal wounds in db/db mice (a genetically diabetic strain) and 26-month-old mice	Wound contraction, collagen deposition, keratinocyte migration	The synthetic peptide LKKTETQ produced repair in aged mice comparable to that seen with full-length Tβ4
Bock-Marquette, 2004	Cell and animal study	Embryonic and postnatal cardiomyocytes; mouse coronary artery ligation	Cell migration and survival; ILK and Akt activity; cardiac function	Tβ4 formed a complex with PINCH and ILK and activated Akt; treated mice had greater early myocyte survival and better cardiac function after ligation
Shah, 2018	Cell study	Primary human hepatic stellate cells exposed to PDGF-BB	Activation markers, Akt phosphorylation, proliferation, migration	The 17 to 23 peptide, but not the 1 to 15 peptide, inhibited PDGF-BB-induced increases in PDGFβ receptor, α-SMA and collagen 1
Rahaman, 2024	Analytical, cell and rat study	Human serum, enzyme systems and rat urine; cultured fibroblasts	Metabolites of Ac-LKKTETQ; cytotoxicity; fibroblast wound assay	Ac-LK was the main metabolite in rats and Ac-LKK was detected for up to 72 hours; no cytotoxicity was found; only Ac-LKKTE showed significant activity in the wound assay
Biçer, 2026	Animal study	Rat Achilles tendon transection and repair, eight rats per group	Maximum load to failure; Bonar and Movin histology scores; collagen types I and III	The TB-500 group had significantly higher load to failure and lower total Bonar and Movin scores than controls; combining it with BPC-157 showed no additive effect
Ruff, 2010	Phase 1 randomised, placebo-controlled trial	40 healthy volunteers given synthetic full-length Tβ4	Adverse events; pharmacokinetics	Adverse events were infrequent and mild or moderate in intensity, with no serious adverse events reported
Wang, 2021	Phase 1 randomised, double-blind trial	84 healthy volunteers given recombinant full-length Tβ4	Adverse events; pharmacokinetics; anti-drug antibodies	Adverse events were mild to moderate, with no serious adverse events; no obvious accumulation on repeated exposure

Three points about this table matter for interpretation. First, only Rahaman et al. clearly tested acetylated Ac-LKKTETQ; Philp and Shah used the unacetylated sequence. Second, the Biçer abstract describes its TB-500 as “synthetic thymosin beta-4 (TB-500)” without giving a sequence, so it is unclear which molecule was used 10. Third, every human study in the table used the full protein. Trials of a Tβ4 formulation (RGN-259) in dry eye and neurotrophic keratopathy, a disorder of the corneal surface, have also been published 22, 23.

Our guide to reading a peptide study explains how much weight cell, animal and human evidence can each carry.

What are the limits of the evidence?

The main limit is that research published under the TB-500 name covers at least three different molecules, and the acetylated fragment, the molecule the analytical literature calls TB-500, has the least biological data.

• One name, several molecules. Findings on full-length Tβ4, on unacetylated LKKTETQ and on acetylated Ac-LKKTETQ cannot be assumed to transfer from one to another. Rahaman et al. found the acetylated parent itself inactive in their wound assay, with activity only in one metabolite 17.
• No human data for the fragment. We found no published human trial results for Ac-LKKTETQ in Europe PMC or ClinicalTrials.gov on 28 September 2026 24. Human trials exist only for full-length Tβ4 20, 21, 22.
• Small, early animal studies. The 2026 rat tendon study used eight animals per group and described itself as exploratory 10.
• Overlapping authorship. Much of the early work linking Tβ4 and its actin-binding motif to repair models came from overlapping author groups: HK Kleinman is an author on 14, 18, 19 and 23, and AL Goldstein on 12, 18 and 19. Independent replication of the fragment work is limited.
• Uncertain product contents. Analyses of products sold as TB-500 have not consistently matched their descriptions 8, 9.
• Reviews reach the same view. A 2026 narrative review of peptides used in sports medicine, which covered both Tβ4 and TB-500, concluded that many unapproved peptides show tissue repair outcomes in animal models but that rigorous human safety data are scarce 25.

What is TB-500’s regulatory and anti-doping status in Australia?

The TGA names TB-500 as an unapproved peptide product, and it is prohibited in sport.

• TGA advisory. The TGA safety advisory of 13 April 2026 names TB-500 as an example of an unapproved peptide product, meaning goods not included in the Australian Register of Therapeutic Goods (ARTG). It says these products have not been evaluated by the TGA for safety, quality or effectiveness 5.
• Anti-doping. The WADA 2026 Prohibited List names “Thymosin-β4 and its derivatives e.g. TB-500” under section S2.3, growth factors and growth factor modulators, prohibited at all times 4. Our anti-doping status guide sets out the status of related compounds, and Sport Integrity Australia is the national authority.

How is TB-500 characterised in the lab?

TB-500 is characterised by mass spectrometry for identity and by high-performance liquid chromatography (HPLC) for purity, the same pair of methods anti-doping laboratories used to define it.

Identity. The monoisotopic mass of full-length Tβ4, calculated from the most common isotope of each element, is 4,960.49 Da, and that of the fragment Ac-LKKTETQ is 888.49 Da 1, 3. A mass spectrometry identity test therefore shows at once which molecule a sample labelled TB-500 contains, which is how a batch of full-length thymosin beta-4 acetate is told apart from the fragment. Esposito et al. used high-resolution Orbitrap mass spectrometry for this 6, and Ho et al. and Kwok et al. built liquid chromatography-mass spectrometry methods that also detect its metabolites 7, 26.

Purity. HPLC separates the main peptide from related impurities, such as truncated or incompletely deprotected sequences from synthesis. Our explainer on HPLC purity covers what the percentage does and does not tell you.

Handling in analysis. Peptides can stick to lab surfaces. In 2017, Judák et al. measured how much TB-500 was recovered from different glass and plastic consumables, and reported that expensive low-binding materials were not better in every case 27.

Illustration: an HPLC system and chromatogram of the kind used to assess peptide purity.

For how these results appear on a report, see how to read a peptide certificate of analysis. Our own batch reports are on the certificates of analysis page, and any report can be checked on the verification page.

Frequently asked questions

Is TB-500 the same as thymosin beta-4?

Not always. In anti-doping research, TB-500 is a synthetic seven-residue fragment, Ac-LKKTETQ, matching residues 17 to 23 of thymosin beta-4 with an added acetyl group (Esposito et al., 2012). The name is also used for the full 43-residue protein (Biçer et al., 2026), and the TB-500 we supply is full-length thymosin beta-4 acetate. Our comparison of TB-500 and thymosin beta-4 covers the differences.

What is the molecular formula and weight of TB-500?

It depends on the material. Full-length thymosin beta-4, the form we supply, has the formula C212H350N56O78S and a molecular weight of 4,963 g/mol, CAS 77591-33-4 (PubChem CID 16132341). The fragment Ac-LKKTETQ has the formula C38H68N10O14 and a molecular weight of 889.0 g/mol, CAS 885340-08-9 (PubChem CID 62707662). Both values exclude counter-ions such as acetate.

Has TB-500 been studied in humans?

We found no published human trial results for the acetylated fragment Ac-LKKTETQ in Europe PMC or ClinicalTrials.gov, searched on 28 September 2026. Published human studies involve full-length thymosin beta-4, including phase 1 trials in healthy volunteers (Ruff et al., 2010; Wang et al., 2021). Research on the fragment itself remains cell, animal and analytical work, as described in our guide to reading a peptide study.

Is TB-500 on the WADA Prohibited List?

Yes. The WADA 2026 Prohibited List names “Thymosin-β4 and its derivatives e.g. TB-500” in section S2.3, growth factors and growth factor modulators, which are prohibited at all times (WADA, 2026). Anti-doping laboratories have published detection methods for the fragment and its metabolites (Ho et al., 2012). Our anti-doping status guide covers related compounds.

How is the identity of a TB-500 sample confirmed?

Identity is confirmed by mass spectrometry, which measures the molecule’s mass. Full-length thymosin beta-4 has a monoisotopic mass of 4,960.49 Da (PubChem), while the fragment Ac-LKKTETQ is 888.49 Da (PubChem), so a single measurement shows which is present. Purity is assessed separately by HPLC. Batch reports that show both results are published on our certificates of analysis page.

References

1. PubChem. Timbetasin (thymosin beta-4), Compound CID 16132341. National Center for Biotechnology Information. https://pubchem.ncbi.nlm.nih.gov/compound/16132341, accessed 28 September 2026. [chemical database]
2. UniProt. P62328, Thymosin beta-4 (TMSB4X), human. https://www.uniprot.org/uniprotkb/P62328/entry, accessed 28 September 2026. [protein database]
3. PubChem. TB500, Compound CID 62707662. National Center for Biotechnology Information. https://pubchem.ncbi.nlm.nih.gov/compound/62707662, accessed 28 September 2026. [chemical database]
4. World Anti-Doping Agency. Prohibited List 2026, section S2.3. https://www.wada-ama.org/en/prohibited-list, accessed 28 September 2026. [regulatory document]
5. Therapeutic Goods Administration. Understanding your responsibilities when importing, compounding and supplying unapproved peptide products (safety advisory, 13 April 2026). https://www.tga.gov.au/safety/safety-monitoring-and-information/safety-alerts/understanding-your-responsibilities-when-importing-compounding-and-supplying-unapproved-peptide-products, accessed 28 September 2026. [regulatory advisory]
6. Esposito S, Esposito S, Deventer K, 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):733-738. doi:10.1002/dta.1402. PMID: 22962027. [analytical study]
7. Ho EN, Kwok WH, Lau MY, 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. doi:10.1016/j.chroma.2012.09.043. PMID: 23084823. [analytical study, equine samples]
8. Delcourt V, Garcia P, Chabot B, et al. TB500/TB1000 and SGF1000: A scientific approach for a better understanding of misbranded and adulterated drugs. Drug Test Anal. 2023;15(4):458-464. doi:10.1002/dta.3421. PMID: 36482504. [product analysis, short communication]
9. Delcourt V, Garcia P, Chabot B, et al. Equine Doping Controls of Thymosin β 4: A Population Study and Strategy for Misuse Detection. Drug Test Anal. 2025;17(7):1071-1077. doi:10.1002/dta.3806. PMID: 39314109. [analytical and population study, equine samples]
10. Biçer O, Adanir O, Güleryüz Y, 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. doi:10.52312/jdrs.2026.2951. PMID: 42542926. [rodent study]
11. Van Troys M, Dewitte D, Goethals M, et al. The actin binding site of thymosin beta 4 mapped by mutational analysis. EMBO J. 1996;15(2):201-210. doi:10.1002/j.1460-2075.1996.tb00350.x. PMID: 8617195. PMCID: PMC449934. [biochemical study]
12. Sosne G, Qiu P, Goldstein AL, et al. Biological activities of thymosin beta4 defined by active sites in short peptide sequences. FASEB J. 2010;24(7):2144-2151. doi:10.1096/fj.09-142307. PMID: 20179146. [narrative review]
13. Safer D, Elzinga M, Nachmias VT. Thymosin beta 4 and Fx, an actin-sequestering peptide, are indistinguishable. J Biol Chem. 1991;266(7):4029-4032. doi:10.1016/s0021-9258(20)64278-8. PMID: 1999398. [biochemical study]
14. Philp D, Huff T, Gho YS, et al. The actin binding site on thymosin beta4 promotes angiogenesis. FASEB J. 2003;17(14):2103-2105. doi:10.1096/fj.03-0121fje. PMID: 14500546. [cell and ex vivo study]
15. Bock-Marquette I, Saxena A, White MD, et al. Thymosin beta4 activates integrin-linked kinase and promotes cardiac cell migration, survival and cardiac repair. Nature. 2004;432(7016):466-472. doi:10.1038/nature03000. PMID: 15565145. [cell and rodent study]
16. Shah R, Reyes-Gordillo K, Rojkind M. Thymosin β4 inhibits PDGF-BB induced activation, proliferation, and migration of human hepatic stellate cells via its actin-binding domain. Expert Opin Biol Ther. 2018;18(sup1):177-184. doi:10.1080/14712598.2018.1478961. PMID: 30063851. PMCID: PMC6748868. [cell study]
17. Rahaman KA, Muresan AR, Min H, et al. Simultaneous quantification of TB-500 and its metabolites in in-vitro experiments and rats by UHPLC-Q-Exactive orbitrap MS/MS and their screening by wound healing activities in-vitro. J Chromatogr B Analyt Technol Biomed Life Sci. 2024;1235:124033. doi:10.1016/j.jchromb.2024.124033. PMID: 38382158. [analytical, cell and rodent study]
18. Malinda KM, Sidhu GS, Mani H, et al. Thymosin beta4 accelerates wound healing. J Invest Dermatol. 1999;113(3):364-368. doi:10.1046/j.1523-1747.1999.00708.x. PMID: 10469335. [rodent and cell study]
19. Philp D, Badamchian M, Scheremeta B, et al. Thymosin beta 4 and a synthetic peptide containing its actin-binding domain promote dermal wound repair in db/db diabetic mice and in aged mice. Wound Repair Regen. 2003;11(1):19-24. doi:10.1046/j.1524-475x.2003.11105.x. PMID: 12581423. [rodent study]
20. Ruff D, Crockford D, Girardi G, et al. A randomized, placebo-controlled, single and multiple dose study of intravenous thymosin beta4 in healthy volunteers. Ann N Y Acad Sci. 2010;1194:223-229. doi:10.1111/j.1749-6632.2010.05474.x. PMID: 20536472. [phase 1 randomised controlled trial]
21. Wang X, Liu L, Qi L, et al. A first-in-human, randomized, double-blind, single- and multiple-dose, phase I study of recombinant human thymosin β4 in healthy Chinese volunteers. J Cell Mol Med. 2021;25(17):8222-8228. doi:10.1111/jcmm.16693. PMID: 34346165. PMCID: PMC8419156. [phase 1 randomised controlled trial]
22. Sosne G, Dunn SP, Kim C. Thymosin β4 significantly improves signs and symptoms of severe dry eye in a phase 2 randomized trial. Cornea. 2015;34(5):491-496. doi:10.1097/ico.0000000000000379. PMID: 25826322. Trial registration: NCT01393132. [phase 2 randomised controlled trial]
23. Sosne G, Kleinman HK, Springs C, et al. 0.1% RGN-259 (Thymosin ß4) Ophthalmic Solution Promotes Healing and Improves Comfort in Neurotrophic Keratopathy Patients in a Randomized, Placebo-Controlled, Double-Masked Phase III Clinical Trial. Int J Mol Sci. 2022;24(1):554. doi:10.3390/ijms24010554. PMID: 36613994. PMCID: PMC9820614. [phase 3 randomised controlled trial]
24. ClinicalTrials.gov. Search results for “thymosin beta 4”. US National Library of Medicine. https://clinicaltrials.gov/search?term=thymosin%20beta%204, accessed 28 September 2026. [trial registry]
25. Mendias CL, Awan TM. Safety and Efficacy of Approved and Unapproved Peptide Therapies for Musculoskeletal Injuries and Athletic Performance. Sports Med. 2026;56(8):1921-1935. doi:10.1007/s40279-026-02437-0. PMID: 41966639. [narrative review]
26. Kwok WH, Ho EN, Lau MY, et al. Doping control analysis of seven bioactive peptides in horse plasma by liquid chromatography-mass spectrometry. Anal Bioanal Chem. 2013;405(8):2595-2606. doi:10.1007/s00216-012-6697-9. PMID: 23318763. [analytical study, equine samples]
27. Judák P, Van Eenoo P, Deventer K. Adsorption effects of the doping relevant peptides Insulin Lispro, Synachten, TB-500 and GHRP 5. Anal Biochem. 2017;537:69-71. doi:10.1016/j.ab.2017.09.003. PMID: 28887173. [analytical study]