TB-500

What TB-500 is

TB-500 is a lab-made peptide, a short chain of amino acids (the building blocks of protein). It copies the active part of a natural protein called Thymosin Beta-4, or Tβ4. Most of the research was done on Tβ4 itself, in animals and in cells in a dish. The only finished human trials tested a Tβ4 eye drop. Nobody has compared TB-500 with Tβ4 side by side.

Tβ4 has 43 amino acids and weighs 4.9 kDa. Nearly every kind of mammal cell contains it. Within the beta-thymosin family, no other member is as plentiful. Blood platelets and wound fluid hold especially large amounts. Allan Goldstein and his team at the Albert Einstein College of Medicine first pulled it out of cow thymus tissue in the 1960s and 1970s [22].

TB-500 matches the working region of Tβ4. At its center is a stretch called 17LKKTETQ23. This stretch grabs actin, a protein that cells use to hold their shape and to move. It is the main reason Tβ4 makes cells move and helps wounds heal. Papers often swap the two names as if they meant the same thing. They do not. TB-500 is a man-made piece. Tβ4 is the whole protein that the body makes.

Early work on Tβ4 looked at how T-cells, a type of immune cell, mature, and at immune function. Over the last three decades, scientists found that it does much more. It holds single actin units in reserve. It helps cells move. It helps new blood vessels grow, a process called angiogenesis. It calms inflammation. It also wakes up progenitor cells, which are early cells that can turn into other cell types [1], [3]. For these reasons it has been tested in animals and cells for skin wounds, heart repair, brain and nerve injury, organ scarring (fibrosis) and eye disease.

As of April 2026, the only finished randomized controlled trials in people are in eye care. RGN-259 is an eye drop that holds 0.1% Tβ4. It went through Phase II and Phase III trials for dry eye and for neurotrophic keratopathy, a disease of the cornea, the clear front of the eye [7], [8]. Every other use is still at the animal and cell stage. The FDA, the EMA and the MHRA have not approved TB-500 for any medical use.

How much research there is

There is a large body of Tβ4 work from many labs. Human trials exist for eye disease only. Very little was done on the TB-500 fragment itself.

Question	Answer
Published studies	A large Tβ4 literature. This guide cites 23 key studies.
What was tested	Rats and mice, cells in a dish, protein structure, and people in eye trials only
People studied	Eye care only: a Phase II dry eye trial (72 subjects) and a Phase III neurotrophic keratopathy trial
Checked by other labs	Strong. Several separate groups: Sosne, Bock-Marquette, Smart/Riley, Xiong/Chopp, Philp, Hinkel
Where the work comes from	At least 6 independent groups in the USA, UK and Germany
How the body handles it	Little data. No full human profile for TB-500
Human trials outside the eye	None. Heart, brain, skin, and muscle and bone findings all come from animals and cells
TB-500 compared with Tβ4	Never compared directly. Most papers used whole Tβ4, not the fragment

Compared with some other research peptides, Tβ4 has one clear strength. Many separate labs have added to the findings. It also has two papers in Nature [9], [10] and a finished Phase III trial [7]. That level of care is not common in peptide research.

How it might work

Scientists have found several linked ways that Tβ4 and TB-500 could act. These come mostly from animals, cells in a dish and studies of protein structure.

Actin and cell movement

In mammal cells, Tβ4 is the main protein that holds single actin units in reserve. In 1992, Weber, Nachmias and Safer found that it binds to loose actin units, called G-actin. That stops them from linking up on their own into F-actin threads [1]. In 2004, Hertzog and colleagues reported the structure in the journal Cell. Tβ4 has two helices, or coiled sections. One binds the barbed face of actin and the other binds the pointed face. Both ends of the unit end up capped [2].

The result is a pool of unlinked actin. A cell can draw on it fast, in a controlled way, when it needs to move. Tβ4 makes cells move but does not change how much they multiply. Classic growth factors work in a different way. The active stretch (17LKKTETQ23) gets several cell types moving [3], [20]:

• endothelial cells, which line blood vessels
• keratinocytes, the main cells of the outer skin
• cells on the surface of the cornea
• heart progenitor cells
• stem cells in hair follicles

New blood vessels

Tβ4 helps blood vessels form in more than one way. In 2007, Smart and colleagues published a well-known study in Nature. They showed that the heart’s own vessels, the coronary vessels, cannot develop without Tβ4. It caused outgrowth from resting pieces of adult epicardium, the outer layer of the heart. Those cells then turned into endothelial cells, smooth muscle cells and fibroblasts, the cells that build connective tissue [10].

The body breaks a small piece off the front end of Tβ4, called the N-terminal. The piece is named Ac-SDKP (acetyl-seryl-aspartyl-lysyl-proline). It strongly drives both the first forming of heart vessels and the growth of new ones. This effect comes from endothelial cells moving, through actin changes and pathways tied to VEGF, a growth signal for blood vessels. Compounds such as BPC-157 grow vessels through nitric oxide instead, which is a separate route [10], [17].

Inflammation

Tβ4 lowers inflammation mainly by holding back NFkappaB, a protein that turns on inflammation genes. It keeps NFkappaB from moving into the cell nucleus and lowers its activity. Sosne and colleagues (2002, 2007) tested this in corneal injury models. Tβ4 turned down inflammation signals, including IL-1β and several chemokines. Fewer polymorphonuclear leukocytes, a kind of white blood cell, moved into the injured site [5], [6].

Some other repair peptides control inflammation through brain chemicals. Tβ4 uses the NFkappaB route. Because the routes differ, their protective effects in injured tissue may not overlap.

Cell survival (ILK and Akt)

In a 2004 paper in Nature, Bock-Marquette and colleagues showed that Tβ4 turns on integrin-linked kinase (ILK). ILK then turns on the Akt pathway, also called protein kinase B [9]. This chain of signals helps cells stay alive. It blocks apoptosis, the process by which cells destroy themselves. It gives one explanation for how Tβ4 protects the heart.

Wei and colleagues (2012) added to this. They found that Tβ4 shields heart muscle cells from oxidative stress. It raised antioxidant enzymes (Cu/Zn-SOD and catalase) and genes that block apoptosis. So the heart protection goes beyond ILK and Akt alone [12].

Scarring (Ac-SDKP)

Most of Tβ4’s power against fibrosis sits in Ac-SDKP, the front-end piece. Kleinman and Sosne (2023) reviewed the evidence. Ac-SDKP stopped fibroblasts from multiplying. It reduced fibrosis in models of the heart, lung, kidney and liver. It did this mainly by getting in the way of a signal chain called TGF-β/Smad [17].

What stands out is that a breakdown product does this job, not the parent peptide. Tβ4 may act through several active pieces, and each piece may behave like a different drug.

Waking up progenitor cells

Tβ4 can restart adult progenitor cells that have gone quiet. This is one of its most unusual traits. Smart and colleagues (2007) showed that it restored pluripotency, the power to become many cell types, in adult epicardial cells. The cells went on to form endothelial cells, smooth muscle cells and fibroblasts. All three are needed for heart repair [10].

Philp and colleagues (2004) looked at hair follicles. Tβ4 moved stem cells and their first daughter cells down to the bottom of the follicle. There the cells matured and the matrix around them was rebuilt. Three pathways were involved: MMP-2, PI3K/AKT and Wnt/β-catenin [20].

What the studies found

Every study here was peer reviewed and is listed in PubMed unless noted. Most used animals or cells in a dish. The only finished human trials are the eye trials.

Skin wounds

Skin repair was one of the first uses tested.

• Full-thickness wounds in rats: Malinda and colleagues (1999) gave Tβ4 on the skin or into the abdomen. Compared with saline, regrowth of the skin surface was 42% higher at 4 days and 61% higher at 7 days after wounding. Treated wounds also shrank 11% more, laid down more collagen and grew more blood vessels [3].
• Diabetic and old mice: Philp and colleagues (2003) found faster wound repair in db/db diabetic mice and in aged mice. Both are cases where the body heals poorly [4].

These results marked Tβ4 as a strong aid to skin repair in animals. It works by moving cells, not by making them multiply. That sets it apart from the usual growth factor approach.

Cornea and eye

Eye care is the furthest along, with finished Phase II and Phase III trials in people.

• Alkali burn of the cornea in mice: Sosne and colleagues (2002) put Tβ4 on the eye, 5 µg twice daily. The corneal surface grew back faster at every time point. At 7 days, fewer polymorphonuclear leukocytes had moved in. mRNA levels of IL-1β and several chemokines were lower [5].
• How it calms the eye: Sosne and colleagues (2007) worked across several corneal injury models. Tβ4 made the surface cells of the cornea move, not multiply. It cut NFkappaB activity and its movement into the nucleus, and it lowered inflammation signals [6].
• Phase II trial in dry eye (72 subjects): Sosne and Ousler (2015) compared RGN-259 with the same drop minus the drug. At day 56, the RGN-259 group had 35.1% less eye discomfort and 59.1% less total corneal fluorescein staining. The tear film took longer to break up, and tear volume rose. The drop was well tolerated, with no safety concerns [8].
• Phase III trial in neurotrophic keratopathy (SEER-1): Sosne and colleagues (2022) reported significant gains in eye discomfort, dryness and the feeling of something in the eye. Disease stage on the Mackie scale improved at days 29, 36 and 43. They saw no significant side effects. At day 43, two weeks after treatment stopped, no defects had come back in the treated group. The one person who responded to placebo relapsed [7].

The eye data are the strongest human evidence for Tβ4 so far. RGN-259 has not yet received full FDA approval.

Heart

Two well-known papers in Nature made Tβ4 a major subject in heart research.

• Heart attack in mice: Bock-Marquette and colleagues (2004) tied off the LAD artery for good, then gave Tβ4. Ejection fraction, a measure of how well the heart pumps, was better at 14 and 28 days after surgery. Scar volume was smaller at 28 days. More heart muscle cells survived early on, through ILK and a more active Akt pathway [9].
• Progenitor cells in mice: Smart and colleagues (2007) found that coronary vessels need Tβ4 to develop. It drew outgrowth from resting adult epicardial tissue and restored pluripotency. The cells became endothelial cells, smooth muscle cells and fibroblasts [10].
• Reviewed by another group: Hinkel and colleagues (2012), a separate group in Munich, reviewed how Tβ4 protects the heart after ischemic injury, which is damage from lost blood flow. Their paper is a review, not a new experiment. It describes Tβ4 growing new vessels, lowering inflammation by holding back NFkappaB, and helping heart muscle cells and vessel lining cells survive [11].
• Oxidative stress: Wei and colleagues (2012) showed that Tβ4 guards heart muscle cells by raising Cu/Zn-SOD, catalase and genes that block apoptosis [12].

These results look promising. Still, nobody has run a heart trial in people with Tβ4 or TB-500.

Brain and nerves

Most of this work comes from the Chopp and Xiong group at Henry Ford Hospital in Detroit.

• Traumatic brain injury in rats: Xiong and colleagues (2011) found that Tβ4 significantly cut cell loss in the hippocampus, a memory center. The injured cortex and hippocampus grew more blood vessels and more new neurons. Area CA3 made more oligodendrocytes, the cells that insulate nerve fibers. The rats recovered more movement and sensation and did better at spatial learning [13].
• Treatment delayed by 6 hours in rats: Xiong and colleagues (2012) waited 6 hours after the injury before treating. Tβ4 still significantly improved spatial learning and the recovery of movement and sensation. The damaged area of cortex shrank by 20 to 30%, depending on dose, at 6 mg/kg and 30 mg/kg. Fewer hippocampal cells died and more new neurons formed [14].
• Stroke models (a review): Morris and colleagues (2018) reviewed the evidence. Tβ4 helped the brain, spinal cord and outer nerves adapt, and helped nerves and vessels rebuild together. It raised the growth of vessels, neurons, oligodendrocytes, and the long fibers of nerve cells called neurites and axons [15].
• Multiple sclerosis model (EAE in mice): Zhang and colleagues (2009) used experimental autoimmune encephalomyelitis. Treated mice had better nerve function. This points to a possible role in autoimmune nerve disease, not only in sudden injury [16].

The 6-hour window in the 2012 study matters, since many nerve-protecting agents must be given almost at once. Even so, all of this evidence comes from animals. No human brain or nerve trial has been run.

Organ scarring

Tβ4 acts against fibrosis mainly through Ac-SDKP, its N-terminal breakdown product.

• Several organs (a review): Kleinman and Sosne (2023) reviewed studies in heart, lung, kidney and liver models. Ac-SDKP held back fibrosis and the multiplying of fibroblasts, mostly by blocking TGF-β/Smad signals [17].
• Liver in mice: Shah and colleagues (2018) injured the liver with ethanol and LPS. Tβ4 prevented oxidative stress, inflammation and fibrosis. It lowered TGF-β receptor-II and kept hepatic stellate cells, the liver’s scar-forming cells, from switching on [18].
• Kidney (a review): Vasilopoulou and colleagues (2018) reported that added Tβ4 or Ac-SDKP helped in a range of kidney disease models. Inflammation and fibrosis fell, and the endothelial and epithelial cell layers were restored [19].

Hair

• Follicle activation in mice: Philp and colleagues (2004) showed that Tβ4 sped up hair growth. Stem cells and their first daughter cells moved to the bottom of the follicle, matured, and rebuilt the matrix around them. The effect ran through MMP-2, PI3K/AKT and Wnt/β-catenin [20].
• Stem cells in mice: Philp and colleagues (2007) confirmed that the hair growth comes from stem cells moving and maturing, not multiplying. More blood vessel growth also helped the hair cycle shift phases [21].

Safety

In human trials

• RGN-259, the 0.1% Tβ4 eye drop, was well tolerated in the Phase II trial (72 subjects) and the Phase III trial. No significant side effects were reported [7], [8].
• No safety concerns came up for use in the eye over several dosing periods.

In animals

• Generally well tolerated in several species, at many doses, and by several routes.
• No published study has reported acute toxicity.
• Tβ4 given to the whole body in heart, brain and skin models caused no notable side effects.

What is not known

• Cancer risk. Some tumors make extra Tβ4, including pancreatic cancer, hepatocellular carcinoma and colorectal cancer. Nobody has shown that Tβ4 causes them [23]. Because it grows blood vessels, there is a concern in theory that it could feed a tumor’s blood supply and help it spread. The link seems to depend on the setting. In multiple myeloma, lower Tβ4 goes with a worse outlook.
• Long-term use. There is no long-term safety data for Tβ4 or TB-500 given to the whole body. The only such data are for the eye.
• Fragment or whole protein. The RGN-259 safety data are for whole Tβ4 in an eye drop. They cannot be assumed to hold for the TB-500 fragment given to the whole body.
• Dose and handling. The best dose for whole-body use in people has not been worked out. Data are thin on the half-life of added Tβ4 or TB-500, on how much reaches the blood, on where it goes, and on how it is broken down.
• Drug interactions. No formal studies have been done.
• Pregnancy and development. No reproductive or developmental toxicity data have been published.

Legal status in the US

• Not FDA approved. TB-500 has no approval for medical use from the FDA. The same is true of the EMA in Europe and the MHRA in the UK. RGN-259, the Tβ4 eye drop, has been through clinical trials but does not yet have full approval from any of the three.
• Banned in sport. The World Anti-Doping Agency (WADA) bans Thymosin Beta-4 and its derivatives, TB-500 included, at all times. Its Prohibited List names them under class S2, which covers peptide hormones, growth factors, related substances and mimetics. It classes them as non-Specified Substances. They are grouped with agents that affect how muscle, tendon or ligament protein is built or broken down, blood vessel growth, and the capacity to regenerate. In at least one doping case, the athlete was ruled ineligible for four years.
• Research use. Suppliers label it for laboratory research use only, not for human use.

Limits of the research

1. TB-500 and Tβ4 are different things. Most papers used whole Thymosin Beta-4, not the man-made TB-500 fragment. Studies that compare the two directly are missing. Nobody can assume they act the same in the body, and TB-500 may not work as well as whole Tβ4, or may work differently.
2. Outside the eye, it is all animals and cells. The heart, brain, skin and fibrosis results look promising. But no human trial has been run for any of them. Animal results may not carry over to people.
3. Only eye use has been tested in people. The Phase II and Phase III data are for RGN-259, a 0.1% Tβ4 drop put on the eye for corneal disease. They do not support whole-body TB-500 for anything else.
4. Cancer risk is not settled. Several tumor types make extra Tβ4, and its effect on blood vessel growth is a concern in theory. Nobody knows if adding it from outside raises cancer risk [23].
5. Handling by the body is poorly understood. There is no full human profile for TB-500 or for Tβ4 given to the whole body. Little is known about half-life, uptake into the blood, spread through the body or breakdown.
6. Doses do not translate. Animal studies used varying doses, such as 6 to 30 mg/kg in brain injury models [14], and varying routes. No evidence exists for a best human dose for any use.

Many labs have shown that Tβ4 helps animals heal, and an eye drop has passed human trials. TB-500 itself has barely been tested, and never in a human trial.

References

Selected peer-reviewed references. Ordered chronologically.

1. Weber A, Nachmias VT, Pennise CR, Pring M, Safer D. (1992). Interaction of thymosin beta 4 with muscle and platelet actin: implications for actin sequestration in resting platelets. Biochemistry, 31(27), 6179–6185. PMID: 1627561
2. Hertzog M, van Heijenoort C, Didry D, et al. (2004). The beta-thymosin/WH2 domain: structural basis for the switch from inhibition to promotion of actin assembly. Cell, 117(5), 611–623. PMID: 15163409
3. Malinda KM, Sidhu GS, Mani H, et al. (1999). Thymosin beta4 accelerates wound healing. Journal of Investigative Dermatology, 113(3), 364–368. PMID: 10469335
4. Philp D, Badamchian M, Scheremeta B, et al. (2003). Thymosin beta 4 promotes dermal wound repair in db/db diabetic mice and in aged mice. Wound Repair and Regeneration, 11(1), 19–24. PMID: 12581423
5. Sosne G, Szliter EA, Barrett R, et al. (2002). Thymosin beta 4 promotes corneal wound healing and decreases inflammation in vivo following alkali injury. Experimental Eye Research, 74(2), 293–299. PMID: 11950239
6. Sosne G, Qiu P, Goldstein AL, Wheater M. (2007). Thymosin beta 4: A novel corneal wound healing and anti-inflammatory agent. Clinical Ophthalmology, 1(3), 201–207. PMC: PMC2701135
7. Sosne G, Dunn SP, Kim C. (2022). 0.1% RGN-259 (Thymosin β4) 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, 24(1), 554. PMID: 36613994
8. Sosne G, Ousler GW. (2015). Thymosin beta 4 ophthalmic solution for dry eye: a randomized, placebo-controlled, Phase II clinical trial. Clinical Ophthalmology, 9, 877–884. PMC: PMC4445951
9. 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, 432(7016), 466–472. PMID: 15565145
10. Smart N, Risebro CA, Melville AAD, et al. (2007). Thymosin beta4 induces adult epicardial progenitor mobilization and neovascularization. Nature, 445, 177–182. DOI: 10.1038/nature05383
11. Hinkel R, Trenkwalder T, Kupatt C. (2012). Molecular and cellular mechanisms of thymosin β4-mediated cardioprotection. Annals of the New York Academy of Sciences, 1269, 102–109. PMID: 23045977
12. Wei C, Kumar S, Kim IK, Gupta S. (2012). Thymosin beta 4 Protects Cardiomyocytes from Oxidative Stress by Targeting Anti-Oxidative Enzymes and Anti-Apoptotic Genes. PLoS ONE, 7(8), e42586. PMID: 22880044
13. Xiong Y, Mahmood A, Zhang Y, et al. (2011). Treatment of traumatic brain injury with thymosin beta4 in rats. Journal of Neurosurgery, 114(1), 102–115. PMC: PMC2962722
14. Xiong Y, Zhang Y, Mahmood A, Meng Y, Qu C, Chopp M. (2012). Neuroprotective and neurorestorative effects of thymosin beta4 treatment initiated 6 hours after traumatic brain injury in rats. Journal of Neurosurgery, 116(5), 1081–1092. PMID: 22324420
15. Morris DC, Zhang ZG, Chopp M. (2018). Thymosin β4 for the treatment of acute stroke: neurorestorative or neuroprotective? Expert Opinion on Biological Therapy, 18(sup1), 149–158. PMID: 30063858. PMC: PMC6481613
16. Zhang J, Zhang ZG, Morris D, et al. (2009). Neurological Functional Recovery After Thymosin Beta4 Treatment in Mice with Experimental Auto Encephalomyelitis. Neuroscience, 164(4), 1887–1893. PMC: PMC2784109
17. Kleinman HK, Sosne G. (2023). Thymosin β4 and the anti-fibrotic switch. International Immunopharmacology, 115, 109628. PMID: 36580759
18. Shah R, Reyes-Gordillo K, Arellanes-Robledo J, et al. (2018). Thymosin Beta4 Prevents Oxidative Stress, Inflammation, and Fibrosis in Ethanol- and LPS-Induced Liver Injury in Mice. Oxidative Medicine and Cellular Longevity, 2018, 9630175. PMC: PMC6079392
19. Vasilopoulou E, Riley PR, Long DA. (2018). Thymosin-beta4: A key modifier of renal disease. Expert Opinion on Biological Therapy, 18(sup1), 187–194. PMID: 29727205
20. Philp D, Nguyen M, Scheremeta B, et al. (2004). Thymosin beta4 increases hair growth by activation of hair follicle stem cells. FASEB Journal, 18(2), 385–387. PMID: 14657002
21. Philp D, St-Surin S, Cha HJ, et al. (2007). Thymosin beta 4 induces hair growth via stem cell migration and differentiation. Journal of Investigative Dermatology, 127(11), 2555–2562. PMID: 17947589
22. Goldstein AL. (2007). History of the discovery of the thymosins. Annals of the New York Academy of Sciences, 1112, 1–13. PMID: 17600284
23. Sribenja S, Wongkham S, Wongkham C, Yao Q, Chen C. (2013). Roles and mechanisms of β-thymosins in cell migration and cancer metastasis: an update. Cancer Investigation, 31(2), 103–110. PMID: 23320791