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In research, TB-500, the name for a short lab-made peptide copied from one small part of the protein thymosin beta-4, has been studied for how it breaks down and whether it moves skin cells in a dish [G2, G3, G5]. Material labelled TB-500 has also been tested in one rat tendon study [G9]. Most of the research covered here was done on the full thymosin beta-4 protein, not on the TB-500 fragment: in lab studies of how cells move, and in animal models of skin and eye wounds, heart damage and hair growth [G1, G6, G7, G8, G12].
What is TB-500?
Amino acids are the building blocks of proteins, and a peptide is a short chain of them. Thymosin beta-4 (Tβ4) is a natural protein 43 amino acids long, found in nearly all cells and body fluids [G1, G2]. One of its jobs is holding on to actin, the protein that forms a cell's internal scaffolding, so the cell can control when that scaffolding is built [G1, G2]. One review calls it "the major actin-sequestering molecule in eukaryotic cells" [G2].
TB-500 is much smaller. A 2012 analytical-chemistry study examined material sold as TB-500 and, using mass spectrometry (a method that identifies molecules by their mass), identified a seven-amino-acid peptide in it [G3]. That peptide is LKKTETQ, the stretch at positions 17 to 23 of human Tβ4, with an acetyl group (a small chemical cap) added to one end. It is written Ac-LKKTETQ [G3].
Is TB-500 the same as thymosin beta-4?
TB-500 and thymosin beta-4 are different molecules. TB-500 has 7 of Tβ4's 43 amino acids, and its acetyl cap means it is not identical even to the matching stretch of the natural protein [G2, G3, G5]. The stretch it copies is the part of Tβ4 that binds actin [G1, G2].
So there are three molecules in this research: the full protein, the uncapped LKKTETQ fragment, and TB-500 (Ac-LKKTETQ). The table below labels each finding with the molecule its paper tested.
What is TB-500 used for?
In research, TB-500 has mainly been studied in two ways:
- How it breaks down, and whether it or its breakdown products move skin cells in a dish [G5].
- One 2026 rat study of a cut Achilles tendon that was surgically repaired, using material the authors labelled TB-500. At four weeks, that group had a higher maximum load before the tendon failed than controls, and lower Bonar and Movin scores (scales where lower means more organised tendon tissue) [G9].
A 2024 paper noted that the reported functions of the protein's active stretch, such as actin binding and activity in skin-wound models, belonged to "its unacetylated form, LKKTETQ", and that "the biological effects of TB-500… have not been documented" [G5].
Full Tβ4 has been studied in lab assays of cell movement and blood-vessel sprouting [G1], and in animal models of skin wounds in rats [G6], eye (cornea) injury in mice [G7], heart damage in mice [G8] and hair follicles in rats and mice [G12].
TB-500 and thymosin beta-4 research at a glance
| Area | Molecule studied | What researchers looked at | Models | How strong the evidence is |
|---|---|---|---|---|
| Actin binding and cell movement | Full Tβ4, and the LKKTETQ fragment [G1, G2] | Whether the actin-binding stretch alone moved vessel-lining cells and sprouted vessels like the whole protein | Human endothelial (vessel-lining) cells; chick aortic arches | Lab (cell and tissue) studies |
| Breakdown and skin-cell activity | TB-500 (Ac-LKKTETQ) and its breakdown products [G5] | Which pieces TB-500 broke into, and whether each moved skin cells to close a scratch in a dish | Human serum, enzyme systems, rat urine, fibroblasts (connective-tissue cells) | One lab study using rat samples |
| Skin-wound models | Full Tβ4 [G6] | Skin regrowth over the wound, wound contraction, collagen and new vessels, against saline controls | Rats | Animal studies |
| Eye (cornea) models | Full Tβ4 [G7] | Regrowth of the corneal surface after a chemical burn, and inflammation markers | Mice | Animal studies |
| Heart models | Full Tβ4 [G8] | Heart-cell movement and survival, and heart-function measures after an induced heart attack | Mouse heart tissue and cells; mice | Lab and animal studies |
| Hair-follicle models | Full Tβ4 [G12] | Hair growth, and how follicle stem cells moved and matured | Rats and mice; rat follicle cells | Lab and animal studies |
| Tendon model | Material labelled TB-500; sequence, supplier and purity not stated [G9] | Tendon strength and tissue organisation four weeks after a cut tendon was surgically repaired | 32 rats, 4 per group for each measure | One small animal study |
| Human trials | Full Tβ4 [G10, G11] | Trial designs only (one phase 2, one phase 3) | People: 73 in one trial, 18 in the other | Two randomised, placebo-controlled trials |
How is it thought to work?
Actin sequestering (full Tβ4). Inside a cell, actin exists as single units (G-actin) that can join into long filaments. Tβ4 is "regarded as the main G-actin sequestering peptide" [G1]. Sequestering here means binding those single units and holding them back from joining filaments. In Philp and colleagues' assays, a seven-amino-acid actin-binding motif of Tβ4 was the part required for endothelial-cell movement and vessel sprouting, and adding free actin blocked cell attachment and sprouting [G1].
Other active sites (full Tβ4). The review by Sosne and colleagues maps Ac-SDKP, the protein's first four amino acids, which the literature links to inflammation and fibrosis (scar-tissue build-up), and a 15-amino-acid site at the same end linked to cell survival [G2]. TB-500's seven amino acids do not include these sites [G2, G3].
ILK, PINCH and Akt (full Tβ4, heart cells). Integrin-linked kinase (ILK) and PINCH are proteins at the points where a cell grips its surroundings. Bock-Marquette and colleagues found Tβ4 formed a complex with them, which switched on Akt, an enzyme involved in cell survival [G8]. In mice after an induced heart attack, they measured higher ILK and Akt activity, more early heart-muscle-cell survival and better heart-function scores [G8].
MMP-2 (full Tβ4, hair follicles). MMP-2 is an enzyme that breaks down the material around cells. In isolated rat follicle cells, Tβ4 raised how much MMP-2 was made and released, and the cells moved and matured more [G12]. The follicle cells that express Tβ4 come from the "bulge", a stem-cell niche [G12].
Inflammation signals (full Tβ4, cornea). Chemokines are signals that call white blood cells in. After a corneal burn in mice, researchers measured lower IL-1β and chemokine mRNA from day 1 to day 7, and fewer of one type of white blood cell at day 7 [G7].
How TB-500 breaks down (TB-500). In rat samples, TB-500 broke down mainly into Ac-LK over the first six hours, and Ac-LKK was still detectable at 72 hours [G5]. In the skin-cell scratch assay, only the breakdown product Ac-LKKTE showed significant activity against control, and the authors suggested that activity previously reported for TB-500 "may be due to its metabolite Ac-LKKTE rather than the parent form" [G5].
What kind of studies are these?
Studies come in three broad kinds. Cell studies (in vitro) test a molecule on cells or tissue in a dish. Animal studies use living animals, such as rats or mice, sometimes after a deliberately induced injury. Human trials enrol people under a set plan; the strongest kind is randomised (people are assigned to groups by chance) and placebo-controlled (one group gets an inactive substance for comparison).
Among the studies covered here, the TB-500 evidence is one lab study of breakdown and skin cells [G5] and one small rat study of material labelled TB-500 [G9]. The rat study's authors called the work "exploratory" and listed its limits: one time point, healthy young male rats, no functional assessment, four animals per measure, and no power calculation in advance [G9].
Full Tβ4's evidence covers many cell and animal models [G1, G6, G7, G8, G12], plus two human trials.
Their designs, without outcomes [G10, G11]:
- A phase 2 trial in a skin-wound setting: double-blind and placebo-controlled, with 73 people randomised at eight sites in Italy and Poland [G10].
- A phase 3 trial in an eye-surface setting: randomised, double-masked and placebo-controlled at US sites, with 18 people, 10 in the protein arm and 8 in the placebo arm. Its main measure was complete closure of a surface defect at four weeks [G11].
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Sources
- [G1] Philp D, Huff T, Gho YS, Hannappel E, Kleinman HK. FASEB J. 2003;17:2103–2105. doi:10.1096/fj.03-0121fje. PMID 14500546.
- [G2] Sosne G, Qiu P, Goldstein AL, Wheater M. FASEB J. 2010;24:2144–2151. doi:10.1096/fj.09-142307. PMID 20179146.
- [G3] Esposito S, Esposito S, Deventer K, Goeman J, Van der Eycken J, Van Eenoo P. Drug Test Anal. 2012;4:733–738. doi:10.1002/dta.1402. PMID 22962027.
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- [G6] Malinda KM, Sidhu GS, Mani H, et al. J Invest Dermatol. 1999;113:364–368. doi:10.1046/j.1523-1747.1999.00708.x. PMID 10469335.
- [G7] Sosne G, Szliter EA, Barrett R, et al. Exp Eye Res. 2002;74:293–299. doi:10.1006/exer.2001.1125. PMID 11950239.
- [G8] Bock-Marquette I, Saxena A, White MD, Dimaio JM, Srivastava D. Nature. 2004;432:466–472. doi:10.1038/nature03000. PMID 15565145.
- [G9] Biçer O, Adanir O, Güleryüz Y, et al. Jt Dis Relat Surg. 2026;37(3):822–837. doi:10.52312/jdrs.2026.2951. PMID 42542926.
- [G10] Guarnera G, DeRosa A, Camerini R, et al. Ann N Y Acad Sci. 2010;1194:207–212. doi:10.1111/j.1749-6632.2010.05490.x. PMID 20536470.
- [G11] Sosne G, Kleinman HK, Springs C, et al. Int J Mol Sci. 2022;24(1):554. doi:10.3390/ijms24010554. PMID 36613994. Trial record: https://clinicaltrials.gov/study/NCT02600429
- [G12] Philp D, Nguyen M, Scheremeta B, et al. FASEB J. 2004;18:385–387. doi:10.1096/fj.03-0244fje. PMID 14657002.
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