Thymosin Beta-4

TB4 (full-length)

Thymosin Beta-4 (TB4 (full-length)) is a healing & recovery research compound. Full-length actin-sequestering peptide (TB-500 is its active fragment) — drives cell migration, angiogenesis, and tissue/cardiac repair.

How Thymosin Beta-4 works

Full-length actin-sequestering peptide (TB-500 is its active fragment) — drives cell migration, angiogenesis, and tissue/cardiac repair.

Proposed benefits

Researched for soft-tissue and gut repair, reduced inflammation, angiogenesis and faster recovery from injury.

Where to get Thymosin Beta-4

The evidence for Thymosin Beta-4

Graded by what exists behind each claim.

✅ Clinically validated

• The parent protein TB-500 is a fragment of, and it reached phase 2 in humans — RegeneRx ran trials in dry eye disease and in venous stasis and pressure ulcers. The dry-eye program reported improvement in signs and symptoms; the wound program showed acceleration of healing in some cohorts. Neither reached approval and development stalled on funding rather than on a safety finding.

📊 Correlative data

• Used interchangeably with TB-500 in practice, though they are not the same molecule — the full 43-amino-acid protein versus the active fragment. Reported experience is indistinguishable, which is unsurprising given the fragment carries the actin-binding domain that does the work.

🧪 Theoretical / extrapolated

• An actin-sequestering protein present in most cells and elevated at wound sites. It promotes cell migration, angiogenesis and downregulation of inflammatory cytokines — a broader mechanism than the fragment alone.
• The same pro-migratory, pro-angiogenic activity carries the same unanswerable long-term question as every repair peptide here.

How to read these tiers: they say how much human evidence exists, not how well something works — and ✗ flags harm, never a disappointing trial. How the evidence tiers work →

What Thymosin Beta-4 actually does

This page is about the intact 43-residue protein, and the reason it needs its own page is that the fragment sold as TB-500 is missing the half of the molecule that does the anti-inflammatory work. Mature thymosin beta-4 is Ac-Ser-Asp-Lys-Pro-Asp-Met-Ala-Glu-Ile-Glu-Lys-Phe-Asp-Lys-Ser-Lys-Leu-Lys-Lys-Thr-Glu-Thr-Gln-Glu-Lys-Asn-Pro-Leu-Pro-Ser-Lys-Glu-Thr-Ile-Glu-Gln-Glu-Lys-Gln-Ala-Gly-Glu-Ser, acetylated at the N-terminus. Run it through this site’s peptide chemistry: 4,963.5 Da, isoelectric point 4.50, net charge about −3.0 at blood pH. A polyanion, and an intrinsically disordered one — it has no fixed fold in solution and acquires structure on binding.

The site map, which is the single most useful published fact about this protein. Its activities are assigned to distinct short sequences, not to the molecule as a whole Sosne 2010:

• The amino-terminal 4 residues, Ac-SDKP — blocks inflammation and reduces fibrosis.
• A 15-residue amino-terminal site that includes Ac-SDKP — promotes cell survival and blocks apoptosis.
• The central actin-binding domain, residues 17–23 plus the glutamine at 24 — promotes angiogenesis, wound healing and cell migration.
• Further sites, not yet localized — antimicrobial activity, and induction of laminin-5, matrix metalloproteinases, TGF-beta, zyxin, terminal deoxynucleotidyl transferase and angiogenesis-related proteins, plus activation of ILK/PINCH/Akt signaling.

Now the mechanism nobody in this market has ever put on a page. Ac-SDKP is not simply a region of the protein — it is a released product. Prolyl oligopeptidase hydrolyzes thymosin beta-4 to generate Ac-SDKP, and that axis is the accepted route by which this protein exerts antifibrotic effects in liver, kidney, heart and lung Wang 2022. The chemistry is exactly what the sequence predicts: prolyl oligopeptidase cuts on the carboxyl side of proline, residue 4 of thymosin beta-4 is a proline, and the cut at Pro4–Asp5 releases the acetylated tetrapeptide intact.

So thymosin beta-4 is, in part, a pro-drug for its own N-terminal tetrapeptide. That reframes the whole comparison with the fragment: TB-500 is residues 17–23, it contains no proline at position 4 because it contains no position 4, and no amount of prolyl oligopeptidase will produce Ac-SDKP from it. The antifibrotic and anti-apoptotic activities are not merely absent from the fragment — they are structurally unreachable from it.

The actin half, and why the intact protein has the complete determinant. Thymosin beta-4 binds G-actin 1:1 and prevents its polymerization by sequestration. A variant missing residues 17–23 shows no interaction with G-actin at all, and replacing lysines 14, 16, 18 and 19 with alanine yields a complex 15 times less stable Zoubek 2007. Two of those four lysines sit outside 17–23. The intact protein carries all four; the fragment carries half of them.

Cell, rodent, human — and where it stops

Step one, protein biochemistry. Purified G-actin against bacterially expressed thymosin beta-4 variants, with deletion and point-mutant arms Zoubek 2007. This is the cleanest evidence the molecule has and it is about binding, not healing.

Step two, in rodents, in the one study that ran the protein and the fragment side by side. Thymosin beta-4 and a synthetic peptide containing its actin-binding domain both promoted dermal wound repair in db/db diabetic mice and in aged mice Philp 2003. Note what the design does and does not settle: both worked in a skin wound treated locally. It is not a head-to-head at equal molarity, it is not a fibrosis model, and a dermal wound in an impaired-healing mouse is where the actin-binding arm should look best and the antifibrotic arm should be least visible.

Step three, humans, topically, on the ocular surface, twice. The first: 9 patients with severe dry eye, RGN-259 at 0.1% or vehicle, 6 times daily for 28 days with follow-up to day 56, across 2 US sites — 12 treated eyes against 6 control eyes. At day 56, ocular discomfort fell 35.1% against control (P = 0.0141) and total corneal fluorescein staining fell 59.1% (P = 0.0108) Sosne 2015.

The second is larger and repays careful reading. A single-center, double-masked, placebo-controlled phase 2 in 72 subjects randomized 1:1 to 0.1% thymosin beta-4 or placebo for 28 days, using the controlled adverse environment model, with 6 visits across 32 days. The prespecified primary endpoints were ocular discomfort scores and INFERIOR corneal staining at day 29. What is reported: day 28 controlled-adverse-environment discomfort down 27% versus placebo (P = 0.0244), central corneal staining improved (P = 0.0075) and superior corneal staining improved (P = 0.0210), with no adverse events Sosne 2015. The prespecified inferior-staining result is not among the significant ones reported. Two of the three staining regions that are reported are regions the protocol did not nominate. That is not fraud and it is not nothing; it is the difference between a hit and a subgroup, and it is invisible unless you read the endpoint list.

Step four, humans, topically, on a wound — a study that is usually cited as a result and is not one. The venous ulcer paper describes a double-blind, placebo-controlled, dose-escalation design: 72 patients, 24 per group, 10 sites across Italy and Poland, randomized 3:1, treated for 84 days with 14 days of follow-up, primary efficacy the proportion achieving complete ulcer closure at day 84. At the time of publication, 21 patients had been enrolled in the first group at the lower dose Guarnera 2007. It is a protocol description with an enrolment update, not an outcome.

Step five, humans, systemically, once, and it is intravenous. A first-in-human phase 1 of recombinant human thymosin beta-4: 54 healthy Chinese volunteers across 7 single-dose cohorts at 0.05, 0.25, 0.5, 2.0, 5.0, 12.5 and 25.0 micrograms per kilogram intravenously, then 30 further subjects dosed daily for 10 days at 0.5, 2.0 and 5.0 micrograms per kilogram. Cmax and AUC rose with dose, terminal clearance was consistent across dose groups, there was no obvious accumulation over 10 days, adverse events were mild to moderate, and there were no dose-limiting toxicities and no serious adverse events Wang 2021.

The obstacles, one at a time. (1) Every efficacy result in a human is topical, to an eye surface or an open ulcer, where the protein is applied directly to the tissue it acts on and systemic pharmacokinetics are irrelevant Sosne 2015 Sosne 2015. (2) The one systemic human study is intravenous, at micrograms per kilogram, with safety as its endpoint Wang 2021. (3) No human has received full-length thymosin beta-4 subcutaneously in a published study, which is the route every buyer uses. (4) The dose gap is large and runs the wrong way: the highest single human exposure ever given was 25.0 micrograms per kilogram, about 1.75 mg in a 70 kg adult, intravenously, under monitoring — this site’s card lists 2 to 5 mg subcutaneously. (5) The antifibrotic mechanism runs through a released metabolite Wang 2022 that no human study has ever measured after dosing.

Thymosin Beta-4 pharmacokinetics — how much of it actually gets in

The card says roughly 30 to 60 minutes, and unusually for this catalog there is real human pharmacokinetic data behind the question.

What was measured. Intravenous dosing across 0.05 to 25.0 micrograms per kilogram produced Cmax and AUC that rose with dose, with terminal clearance consistent across dose groups and no obvious accumulation after 10 days of daily administration Wang 2021. Linear kinetics with no accumulation on daily dosing is exactly the profile a short half-life predicts.

What clears it, and the arithmetic that makes it fast. The protein is 4,963.5 Da and carries a net charge of about −3.0. The glomerulus passes molecules well below its roughly 60 kDa cut-off freely, and 5 kDa is more than ten times under it. Nothing holds this protein in the vascular compartment: no acyl chain, no albumin binding, no Fc. It is filtered. On top of that it is an enzymatic substrate by design — prolyl oligopeptidase cuts it to Ac-SDKP Wang 2022.

The N-terminal acetyl is the one piece of protection it has. Aminopeptidase N attacks free N-terminal amines and is abundant on the vascular endothelium a subcutaneous dose must cross. Mature thymosin beta-4 is acetylated, so that route is closed — which is also why the Ac-SDKP that comes off it is acetylated and therefore itself resistant at that end.

And the fact that makes ‘half-life’ the wrong question for this molecule. Its principal degradation product is pharmacologically active: Ac-SDKP is the antifibrotic arm of the whole axis Wang 2022. Clearance of the parent is therefore not loss of effect; it is conversion. Every other peptide on this site degrades into inert fragments, and reasoning about this one as though it does is a category error. Note the corollary, and treat it as a hypothesis rather than a finding: Ac-SDKP has its own clearance enzyme in the wider physiology literature, and none of the papers read for this page tests what happens to it when that enzyme is inhibited — which is a plausible and entirely unstudied interaction for anybody on a blood-pressure medicine.

The oral barrier. Absolute. A 43-residue polyanion swallowed meets gastric acid, pancreatic endopeptidases and brush-border peptidases, and the charge rules out passive absorption. There is no published oral bioavailability figure for it in any species.

The routes, ranked by what is actually known. Topical to a mucosal surface has two human efficacy studies Sosne 2015 Sosne 2015; intravenous has one human pharmacokinetic study Wang 2021; subcutaneous, the route everyone uses, has none, so its absorption rate, bioavailability and time to peak are unmeasured for this molecule.

What would have to be true, and how you would know it was not

Four predictions. The first has an ambiguous direction on purpose, because the molecule genuinely points both ways on the same marker.

1. TGF-beta 1 — and which way it moves is the experiment. The intact protein induces TGF-beta among its gene targets Sosne 2010, while its released metabolite Ac-SDKP is antifibrotic Wang 2022 and antifibrotic activity in this axis classically runs through suppressing TGF-beta signaling. So the parent and the product push the same marker in opposite directions, and nobody has ever measured which wins in a person. Draw TGF beta-1 at baseline and at 8 weeks, from the same laboratory, with the same collection tube — platelet activation during clotting releases TGF-beta and will dominate a sloppy draw. Either direction is informative; no movement says the systemic dose is doing nothing.

2. hs-CRP is the marker that should separate this from the fragment. The anti-inflammatory activity of this biology is assigned to the N-terminal Ac-SDKP site Sosne 2010, which the 43-residue protein has and the 7-residue fragment does not. Draw hs-CRP and an ESR at baseline and at 8 weeks. This is the cleanest available test of the pro-drug argument at the top of this page: an anti-inflammatory signal on the intact protein and none on the fragment would be the first human evidence that the N-terminal sites matter clinically.

3. At the doses people use, nothing systemic will move, and that cuts against the compound. The highest single systemic dose ever given to a human in a registered study was 25.0 micrograms per kilogram intravenously with no efficacy endpoint attached Wang 2021, and there is no subcutaneous human pharmacokinetic data at all. Draw a CBC and a CMP at baseline and 8 weeks and expect flat lines. If something moves, the first hypothesis is something else in the stack, not this.

4. What to watch, and the honest read-out for the injury people actually buy it for. What to watch: a single numeric pain-on-loading score for one named movement, recorded at the same time of day, plus range of motion measured the same way each week. How long before it means anything: six weeks minimum per arm — tendon and ligament adapt more slowly than muscle, and the human efficacy studies for this protein needed 28 days of six-times-daily dosing on a surface it was applied directly to Sosne 2015. What will fool you: the rehabilitation program almost everyone starts in the same week, and the natural history of a chronic tendinopathy, which improves on its own over months.

What nobody has tested yet

Five experiments. The first is the one that would settle whether this molecule is what its own mechanism says it is.

1. Nobody has measured plasma Ac-SDKP after a dose of thymosin beta-4 in a human. The antifibrotic mechanism of this whole axis is prolyl-oligopeptidase release of Ac-SDKP Wang 2022. Ac-SDKP is measurable in plasma by immunoassay and has been for decades. One timed-sample series after a single subcutaneous dose would show whether the conversion actually happens at the doses people use, and it has never been reported.

2. Nobody has run intact protein against Ac-SDKP against LKKTETQ, at equal molarity, in the model where the human data already exists. The ocular-surface studies Sosne 2015 Sosne 2015 give a validated read-out with published effect sizes. Adding two arms — the N-terminal tetrapeptide and the actin-binding heptapeptide — to that exact protocol would allocate the effect between the two halves of the molecule for the first time. The reagents are commercial and the design is already written.

3. Nobody has given full-length thymosin beta-4 subcutaneously to a human in a published study. Not once, at any dose. The only systemic route ever studied is intravenous Wang 2021, and subcutaneous absorption of a 5 kDa polyanion is not a formality — it goes by lymphatic uptake, which is slow and variable and would give this molecule a completely different concentration–time profile from the intravenous one.

4. The prespecified endpoint of the largest ocular trial has never been reported. Inferior corneal staining at day 29 was a primary endpoint of a 72-subject randomized trial and does not appear among the reported significant findings Sosne 2015. The number exists in a dataset. Publishing it would cost nothing and would tell the field whether the effect is regional or general.

5. Nobody has asked whether prolyl oligopeptidase activity predicts who responds. If the antifibrotic arm depends on enzymatic conversion Wang 2022, then people differ in how much of it they perform, and that is measurable in serum. It is the obvious responder-stratification experiment for this molecule and no version of it has been run in any species.

Thymosin Beta-4 — its own safety story, not its class's

The class block on this page is the shared repair-peptide warning about angiogenesis. On the intact protein the concern is different from the one that applies to the fragment, and it is worth stating precisely.

1. The oncological question here is anti-apoptosis, not angiogenesis. The fragment carries the site credited with angiogenesis and cell migration. The intact protein carries that and a 15-residue N-terminal site credited with promoting cell survival and blocking apoptosis Sosne 2010. Apoptosis is the mechanism by which a damaged cell removes itself, and a molecule with a published anti-apoptotic site is a more specific thing to think about in that context than a molecule that merely encourages vessels. There is no evidence that thymosin beta-4 causes or accelerates cancer in anything, and there is also no study in which it could have been seen: the longest human exposure on record is 10 daily intravenous doses Wang 2021.

2. The dose gap, in the direction people do not expect. Highest single human dose ever given: 25.0 micrograms per kilogram, intravenously, roughly 1.75 mg in a 70 kg adult. Highest repeated dose: 5.0 micrograms per kilogram daily for 10 days Wang 2021. The community protocol on this site’s own card is 2 to 5 mg — up to about 71 micrograms per kilogram, roughly fourteen times the highest repeated dose ever administered under monitoring.

3. The manufacturing problem is specific to the length. The human trials used recombinant human thymosin beta-4 Wang 2021. A 43-residue chain made by stepwise solid-phase synthesis accumulates deletion sequences at every coupling, so a synthetic preparation of this protein carries a class of impurity that a 7-residue fragment simply does not — truncated analogs that co-purify and are invisible to a purity figure quoted as a single percentage.

4. Matrix remodeling is not unambiguously good. Among the genes this protein induces are matrix metalloproteinases Sosne 2010 — the enzymes that degrade extracellular matrix. In a healing wound that is part of remodeling. In a partially healed tendon under load, increasing matrix degradation is not obviously the direction you want, and nobody has measured it in that setting.

5. The safety record, stated fairly. No adverse events in the 72-subject ocular trial Sosne 2015, no dose-limiting toxicities and no serious adverse events across 84 subjects in the phase 1 Wang 2021. That is a genuinely clean record at the doses and durations studied, and those doses are one to two orders of magnitude below the ones in circulation.

Sources read for this page

• Sosne G, et al. Biological activities of thymosin beta4 defined by active sites in short peptide sequences. FASEB Journal 2010 · PMID 20179146
• Wang W, et al. The Role of Tbeta4-POP-Ac-SDKP Axis in Organ Fibrosis. International Journal of Molecular Sciences 2022 · PMID 36362069
• Zoubek RE, Hannappel E. Influence of the N terminus and the actin-binding motif of thymosin beta4 on its interaction with G-actin. Annals of the New York Academy of Sciences 2007 · PMID 17495251
• Philp D, 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 and Regeneration 2003 · PMID 12581423
• Sosne G, et al. Thymosin beta4 significantly improves signs and symptoms of severe dry eye in a phase 2 randomized trial. Cornea 2015 · PMID 25826322
• Sosne G, et al. Thymosin beta 4 ophthalmic solution for dry eye: a randomized, placebo-controlled, Phase II clinical trial conducted using the controlled adverse environment (CAE) model. Clinical Ophthalmology 2015 · PMID 26056426
• Guarnera G, et al. Thymosin beta-4 and venous ulcers: clinical remarks on a European prospective, randomized study on safety, tolerability, and enhancement on healing. Annals of the New York Academy of Sciences 2007 · PMID 17495250
• Wang X, et al. A first-in-human, randomized, double-blind, single- and multiple-dose, phase I study of recombinant human thymosin beta4 in healthy Chinese volunteers. Journal of Cellular and Molecular Medicine 2021 · PMID 34346165

Thymosin Beta-4 — safety, predicted from mechanism

Thymosin Beta-4 — interference & stacking

Bloodwork to run alongside Thymosin Beta-4

Baseline first, then again at 8–12 weeks.

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Thymosin Beta-4 — frequently asked questions

What Thymosin Beta-4 is used for

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