TB-500

What it is

TB-500 is the trade name for synthetic peptides related to thymosin beta-4 (Tβ4), a 43-amino-acid protein abundant in many human cells. Esposito et al. (2012) analyzed a product sold as TB-500 and identified its active content as Ac-LKKTETQ, the acetylated 17–23 fragment of human Tβ4, a seven-amino-acid stretch that contains the protein's actin-binding motif; products sold under the name vary by seller, with some described as this fragment, others as different fragments or as full-length Tβ4. Nearly all published research, including the human eye-drop trials run by RegeneRx, used full-length Tβ4 rather than the fragment, and that distinction runs through the evidence below.

Mechanism of action

Full-length Tβ4 is best known as a protein that binds and holds monomeric actin inside cells, and most proposed repair mechanisms come from animal and cell studies of the full protein. Bock-Marquette et al. (2004) reported that Tβ4 formed a complex with PINCH and integrin-linked kinase (ILK) that activated the survival kinase Akt, and that in mice after coronary artery ligation it raised ILK and Akt activity in the heart and supported early heart-muscle cell survival. Malinda et al. (1999) observed more collagen deposition and new vessel growth in Tβ4-treated rat skin wounds. The link to TB-500 runs through the actin-binding region: Philp et al. (2003) found that a seven-amino-acid actin-binding motif was essential for Tβ4's vessel-promoting activity, and that a short peptide containing it matched the full protein in endothelial cell migration and aortic sprouting assays. Whether an injected fragment reproduces the full protein's other actions in living animals or people has not been established.

What it’s most studied for

Research on full-length Tβ4 has examined tissue repair in several organs: skin wounds in rats, the cornea and ocular surface, and heart muscle after experimental myocardial infarction in mice. RegeneRx Biopharmaceuticals took the full protein into human trials as an eye drop (RGN-259) for dry eye and neurotrophic keratopathy, and as a topical gel (RGN-137) studied in venous stasis and pressure ulcers. The fragment sold as TB-500 has a much thinner literature of its own: chemical analyses of what commercial products contain, laboratory work on the actin-binding motif, and a small number of animal studies, including a 2026 rat Achilles tendon study. Interest in TB-500 for musculoskeletal injury recovery, in horse racing and in human sport, has run well ahead of that evidence.

Notable findings

Each finding carries the species or population it was observed in and the dose that study used. Doses are reported as research context, exactly as published. They are not guidance.

Study quality

No published controlled human study has tested TB-500 itself. Most of the research cited for it was done on full-length Tβ4, a larger molecule, in rats, mice and cell culture. Evidence specific to the fragment is limited to cell and tissue assays of the actin-binding motif (Philp et al. 2003) and a 2026 rat tendon study of 32 animals that its authors called preliminary. Human data exist only for full-length Tβ4 applied to the eye, in small trials sponsored by the company developing it: the SEER-1 phase 3 trial analyzed 18 patients and missed statistical significance on its primary endpoint, and a phase 2 dry eye trial enrolled nine (Sosne et al. 2015). Those trials reported no significant adverse effects, but topical eye drops say little about the safety of injected peptides. Because sellers apply the name TB-500 to different molecules, results from Tβ4 studies cannot be assumed to transfer to any given product.

On the research desk

Recent records on TB-500 from the Alpha Helix research feed, each with its evidence tier and citation.

• Recombinant human thymosin beta-4 ameliorates experimental colitis and intestinal fibrosis through suppression of mineralocorticoid receptor signalling2026-05-30 · 42606759
• Reparative outcomes in corneal infection: linking adjunctive thymosin beta-4 treatment to nerve regeneration and visual function2026-03-28 · 42283548

References

1. 1
   Esposito S, Deventer K, Goeman J, et al. (2012). 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. PMID 22962027
2. 2
   Philp D, Huff T, Gho YS, et al. (2003). The actin binding site on thymosin beta4 promotes angiogenesis. FASEB Journal.
3. 3
   Malinda KM, Sidhu GS, Mani H, et al. (1999). Thymosin beta4 accelerates wound healing. Journal of Investigative Dermatology. PMID 10469335
4. 4
   Bock-Marquette I, Saxena A, White MD, et al. (2004). Thymosin beta4 activates integrin-linked kinase and promotes cardiac cell migration, survival and cardiac repair. Nature. PMID 15565145
5. 5
   Biçer O, Adanir O, Güleryüz Y, et al. (2026). Effects of BPC-157 and TB-500 on Achilles tendon healing in rats: a histopathological and biomechanical study. Joint Diseases and Related Surgery. PMID 42542926
6. 6
   Sosne G, et al. (2023). 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. International Journal of Molecular Sciences. DOI 10.3390/ijms24010554
7. 7
   Sosne G, Dunn SP, Kim C (2015). Thymosin β4 significantly improves signs and symptoms of severe dry eye in a phase 2 randomized trial. Cornea. PMID 25826322
8. 8
   US Food and Drug Administration, Pharmacy Compounding Advisory Committee (2026). July 23-24, 2026 Meeting of the Pharmacy Compounding Advisory Committee: votes on nominated bulk drug substances for the 503A list. U.S. Food and Drug Administration.