TB-500 vs Thymosin Beta-4: Fragment or Full Protein?

Thymosin beta-4 is a natural 43-amino-acid protein found in almost every cell, where it holds actin, the protein cells use to move and change shape. TB-500, as identified by doping-control laboratories, is a synthetic seven-amino-acid peptide, Ac-LKKTETQ: residues 17 to 23 of thymosin beta-4, its actin-binding site, with an acetyl group added to the front. They are related but not the same molecule. The fragment keeps the part of the protein linked to cell migration and new blood vessels; the human clinical trials were all run on the full protein. Here is what each is, what the research shows for each, and why the names get mixed up.

Findings

• Thymosin beta-4 has 43 amino acids, a molecular weight of 4982 and an acetylated N-terminus, from its 1981 sequencing in calf thymus.
• Laboratories in Ghent and Hong Kong found that the key ingredient of TB-500 is LKKTETQ with an artificial N-terminal acetyl group, the actin-binding region of thymosin beta-4 (2012). A reference supplier lists its formula weight as 889.0.
• The seven-amino-acid actin-binding motif showed near-identical activity to the whole protein in endothelial migration and vessel sprouting assays at about 50 nM (2003).
• Full-length thymosin beta-4 has phase 1 and phase 2 human trials, including 73 patients with venous ulcers and 72 with dry eye; we found no published human trial of the seven-residue fragment.

What is thymosin beta-4?

Thymosin beta-4 was isolated from calf thymus and sequenced in 1981: 43 amino acids, a molecular weight of 4982 and an N-terminus blocked by an acetyl group (Low et al., PNAS, 1981). It was first thought of as a thymic hormone. A decade later, a peptide that holds most of the unpolymerised actin in human platelets turned out to have an identical sequence; it forms a one-to-one complex with single actin molecules and stops them assembling into filaments (Safer et al., J Biol Chem, 1991). It is now regarded as the main actin-sequestering molecule in mammalian cells (Philp et al., FASEB J, 2003), and as a repair molecule released by platelets at the site of injury (Treadwell et al., Ann N Y Acad Sci, 2012).

Its active sites

Different stretches of the protein carry different jobs. A 2010 review describes an N-terminal site containing Ac-SDKP that promotes cell survival, and a short central sequence, LKKTETQ, that promotes blood vessel growth, wound healing and cell migration (Sosne et al., FASEB J, 2010). The N-terminal Ac-SDKP end appears to carry most of the protein’s anti-fibrotic activity, preventing and even reversing fibrosis in animal models of liver, lung, heart and kidney disease (Kleinman et al., Int Immunopharmacol, 2023). Actin sequestering itself needs the front of the molecule: fragments covering residues 13 to 43 and 24 to 43 did not block actin polymerisation (Hannappel and Wartenberg, Biol Chem Hoppe Seyler, 1993); the 17 to 23 fragment alone was not tested in that assay.

What is TB-500?

TB-500 first drew scientific attention as a doping concern in horse racing. In 2012 the doping-control laboratory at Ghent University analysed TB-500 by high-resolution mass spectrometry, identified its active content as Ac-LKKTETQ, the N-terminal acetylated 17 to 23 fragment of human thymosin beta-4, and confirmed the structure by synthesising the peptide (Esposito et al., Drug Test Anal, 2012). The Hong Kong Jockey Club’s racing laboratory described TB-500 the same year as a veterinary preparation whose key ingredient is LKKTETQ with artificial acetylation of the N-terminus, and built a test that detected it and its breakdown products in the urine and plasma of horses given a single dose (Ho et al., J Chromatogr A, 2012). Cayman Chemical, a research reagent supplier, lists TB-500 as Ac-LKKTETQ-OH with a formula weight of 889.0.

Why the names get mixed up

The two names are often used as if they were one compound. A 2026 rat tendon study refers to “synthetic thymosin beta-4 (TB-500)” (Biçer et al., Jt Dis Relat Surg, 2026), while a 2026 primer for sports medicine physicians lists “TB-4 and its derivative TB-500” separately (Mayfield et al., Am J Sports Med, 2026). The practical check is molecular weight: full-length thymosin beta-4 sits near 4,980, the acetylated seven-residue fragment near 889. A certificate of analysis that reports the measured mass shows which one a vial holds.

What does the fragment keep?

The strongest evidence that the fragment carries real activity comes from an NIH team that compared natural thymosin beta-4, proteolytic fragments and synthetic peptides. The seven-amino-acid actin-binding motif was essential for the protein’s effect on blood vessels: full protein and motif showed near-identical activity at about 50 nM in endothelial migration and chick aortic sprouting assays, while peptides missing any part of the motif were inactive, and the motif blocked cell adhesion to the full protein (Philp et al., 2003). Given the active sites above, the fragment covers the migration and vessel-growth site and leaves out the Ac-SDKP end linked to anti-fibrotic and cell-survival effects.

In the 2026 rat Achilles study, the TB-500 group showed a statistically significant gain in maximum load to failure and lower tendon-damage scores than controls at four weeks (Biçer et al., 2026); that paper’s naming means it does not settle which form was used.

What does the human research show?

Every human trial in this family used full-length synthetic thymosin beta-4. Forty healthy volunteers in four dose cohorts received it intravenously, once and then daily for 14 days, with no dose-limiting toxicity or serious adverse events (Ruff et al., Ann N Y Acad Sci, 2010). A double-blind, placebo-controlled phase 2 trial at eight European sites randomised 73 patients with venous leg ulcers to topical thymosin beta-4, with safety comparable to placebo and signs of faster healing at the 0.03% strength (Guarnera et al., Ann N Y Acad Sci, 2010). Across that and a pressure-ulcer trial, patients who healed did so almost a month sooner (Treadwell et al., 2012).

In the eye, six of nine patients with geographic neurotrophic corneal defects showed dramatic healing under compassionate use (Dunn et al., Ann N Y Acad Sci, 2010). A phase II dry-eye trial randomised 72 people to 0.1% thymosin beta-4 eye drops or placebo for 28 days; its two primary endpoints were not met, while discomfort in the challenge chamber fell 27% against placebo on day 28 and corneal staining improved, with no adverse events (Sosne and Ousler, Clin Ophthalmol, 2015). The repair trials are covered in TB-500 and thymosin beta-4: the repair research.

How do TB-500 and thymosin beta-4 compare side by side?

Question	TB-500	Thymosin beta-4
What is it?	Synthetic fragment, Ac-LKKTETQ	Natural protein in almost all cells
Size	7 amino acids, formula weight 889.0	43 amino acids, molecular weight 4982
Main research areas	Cell migration, vessel growth, doping control	Wound and corneal healing, cardiac repair, fibrosis
Mechanism focus	Actin-binding motif only	Actin sequestering plus Ac-SDKP and other sites
Human evidence	None published that we found	Phase 1 and phase 2 trials
Forms we supply	10 mg vial, nasal spray, blends	Not listed separately

Which one fits which research question?

• Endothelial migration and vessel sprouting: TB-500, since the motif matched the full protein in those assays.
• Anti-fibrotic or cell-survival effects: full-length thymosin beta-4 or Ac-SDKP; the fragment does not contain that end.
• Reproducing the human ulcer, eye or volunteer trials: full-length thymosin beta-4, the form those trials used.
• Combination work with BPC-157: TB-500, as in the BPC-157 vs TB-500 comparison and the Wolverine stack.

How is TB-500 supplied?

TB-500 comes as a 10 mg lyophilised vial and the ready-mixed TB-500 Nasal Spray, metered at 0.175 mL per press. It is also in the BPC-157 + TB-500 blend, GLOW and KLOW. Vials are reconstituted with bacteriostatic water, and storage windows are in how long TB-500 lasts. Certificates of analysis are on the lab reports page, buying notes are in Buy TB-500 in Canada, and every order ships from within Canada.

Frequently asked questions

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

No. Thymosin beta-4 is a natural 43-amino-acid protein. Doping-control laboratories identified the key ingredient of TB-500 as Ac-LKKTETQ, a synthetic acetylated copy of residues 17 to 23 of that protein, its actin-binding site. Some papers still use the name TB-500 for full-length synthetic thymosin beta-4.

Is TB-500 a fragment of thymosin beta-4?

Yes, as characterised by the Ghent and Hong Kong Jockey Club laboratories in 2012: seven amino acids, LKKTETQ, with an acetyl group added to the N-terminus. A reference supplier lists its formula weight as 889.0, against 4982 for the full protein.

Does the TB-500 fragment work like the full protein?

For endothelial migration and vessel sprouting, the actin-binding motif matched the full protein at about 50 nM in a 2003 NIH study. The fragment does not include the N-terminal Ac-SDKP region, which carries most of thymosin beta-4’s anti-fibrotic activity.

Which has human studies, TB-500 or thymosin beta-4?

Full-length thymosin beta-4: an intravenous safety study in 40 volunteers, a 73-patient venous ulcer trial, eye studies and a 72-person dry-eye trial. We found no published human trial of the seven-residue TB-500 fragment.

Where can I buy TB-500 in Canada?

Vistara Labs supplies TB-500 as a 10 mg lyophilised vial and a ready-mixed nasal spray, and in BPC-157 + TB-500, GLOW and KLOW blends, with certificates of analysis on the lab reports page, shipped from within Canada by Canada Post Xpresspost.

Product details from vistaralabs.ca, October 2026. Sources: Low TL et al. Complete amino acid sequence of bovine thymosin beta 4. Proc Natl Acad Sci U S A. 1981. PMID 6940133. Safer D et al. Thymosin beta 4 and Fx, an actin-sequestering peptide, are indistinguishable. J Biol Chem. 1991. PMID 1999398. Hannappel E, Wartenberg F. Actin-sequestering ability of thymosin beta 4, thymosin beta 4 fragments, and thymosin beta 4-like peptides. Biol Chem Hoppe Seyler. 1993. PMID 8471179. Philp D et al. The actin binding site on thymosin beta4 promotes angiogenesis. FASEB J. 2003. PMID 14500546. Sosne G et al. Biological activities of thymosin beta4 defined by active sites in short peptide sequences. FASEB J. 2010. PMID 20179146. Kleinman HK et al. Thymosin beta4 and the anti-fibrotic switch. Int Immunopharmacol. 2023. PMID 36580759. Esposito S et al. Synthesis and characterization of the N-terminal acetylated 17-23 fragment of thymosin beta 4 identified in TB-500. Drug Test Anal. 2012. PMID 22962027. Ho EN et al. Doping control analysis of TB-500, a synthetic version of an active region of thymosin beta 4, in equine urine and plasma. J Chromatogr A. 2012. PMID 23084823. Cayman Chemical. TB-500 (acetate), product 45081. caymanchem.com. Biçer O et al. Effects of BPC-157 and TB-500 on Achilles tendon healing in rats. Jt Dis Relat Surg. 2026. PMID 42542926. Mayfield CK et al. Injectable peptide therapy: a primer for orthopaedic and sports medicine physicians. Am J Sports Med. 2026. PMID 41476424. Ruff D et al. A randomized, placebo-controlled, single and multiple dose study of intravenous thymosin beta4 in healthy volunteers. Ann N Y Acad Sci. 2010. PMID 20536472. Guarnera G et al. The effect of thymosin treatment of venous ulcers. Ann N Y Acad Sci. 2010. PMID 20536470. Treadwell T et al. The regenerative peptide thymosin beta4 accelerates the rate of dermal healing in preclinical animal models and in patients. Ann N Y Acad Sci. 2012. PMID 23050815. Dunn SP et al. Treatment of chronic nonhealing neurotrophic corneal epithelial defects with thymosin beta4. Ann N Y Acad Sci. 2010. PMID 20536469. Sosne G, Ousler GW. Thymosin beta 4 ophthalmic solution for dry eye: a randomized, placebo-controlled, phase II clinical trial. Clin Ophthalmol. 2015. PMID 26056426.

More on this: Peptides for Injury Recovery: What the Research Shows.