TB-500 (Thymosin Beta-4 Fragment): Actin-Binding Peptide Research Data

What Is TB-500?

TB-500 is the marketed name for a synthetic short-fragment peptide derived from the active region of Thymosin Beta-4 (Tβ4), the principal intracellular G-actin-sequestering peptide in mammalian cells. Native human Tβ4 is a 43-amino-acid acidic peptide with a reference molecular weight of 4,963.4 g/mol and CAS number 77591-33-4.^[1] The "TB-500" label dates to early veterinary horse-racing literature where a Tβ4-derived fragment was studied as a research tool for soft-tissue repair, and the name has persisted in the research-peptide market.

Two things are worth being precise about up front. First, TB-500 is defined by FDA and the anti-doping literature as Ac-LKKTETQ (Tβ4 residues 17–23, 889 g/mol), a seven-residue fragment that keeps the central actin-binding motif but not the N-terminal AcSDKP sequence; products sold under the name vary, and some contain or claim full-length Tβ4 (about 4,963 g/mol), so a vial's COA mass is what identifies its contents.^{[8][9][11][12][13]} Second, full-length Tβ4 used in clinical-grade work (notably the RegeneRx RGN-259 ophthalmic) is a defined recombinant or synthetic 4,963.4 g/mol peptide manufactured under cGMP conditions and is regulatorily distinct from research-grade TB-500 vials.^[3]

For a research reader, the practical takeaway is that TB-500 is best understood as a Tβ4-derived fragment research tool rather than a finished clinical product. Most of the actin-biology, cell-migration, and wound-healing work it is associated with used full-length Tβ4, and the biological effects of TB-500 itself have not been documented.^[14]

Mechanism of Action: Actin Binding, Cell Migration & Angiogenesis

Tβ4 is described in the cell-biology literature as the most abundant member of the β-thymosin family in mammalian cells and the principal sequestering peptide for monomeric G-actin. The peptide binds G-actin in a 1:1 stoichiometric complex, maintains a cytoplasmic G-actin pool, and modulates the equilibrium between G-actin and filamentous F-actin during cytoskeletal remodelling.^[1] Three functional consequences are repeatedly cited:

• Cell migration. By regulating local G-actin availability, Tβ4 modulates lamellipodial protrusion, fibroblast migration, and keratinocyte sheet movement — the classical building blocks of wound re-epithelialisation.^[1]
• Angiogenesis. Multiple in-vitro and rodent studies report that Tβ4 promotes endothelial cell migration, tube formation, and collateral vessel growth in ischaemic tissue. The angiogenic phenotype is one of the better-replicated preclinical signals in the Tβ4 literature.^[2]
• Anti-inflammatory and anti-apoptotic signalling. Tβ4 has been shown to reduce inflammatory cytokine output and to lower apoptotic indices in cardiac and corneal injury models, an effect attributed in part to downstream Akt and ILK signalling.^[2]

A distinct mechanistic strand involves the N-terminal tetrapeptide N-acetyl-Ser-Asp-Lys-Pro (AcSDKP). AcSDKP is released enzymatically from the Tβ4 N-terminus and is itself a separately characterised bioactive peptide: it is an endogenous regulator of haematopoietic stem-cell cycling, an anti-fibrotic agent in renal and cardiac models, and a substrate for angiotensin-converting enzyme (ACE), which catalyses its degradation.^[5] When a research reader encounters "TB-500" claims that span actin biology, anti-fibrotic effects, and stem-cell mobilisation, that breadth is borrowed from full-length Tβ4: AcSDKP is Tβ4 residues 1–4 and is not part of the TB-500 sequence, so its anti-fibrotic and haematopoietic findings do not transfer to TB-500.

What this gives the field is a believable, multi-pathway sketch for full-length Tβ4 — G-actin sequestration by the intact protein plus anti-fibrotic and haematopoietic signalling by its AcSDKP fragment — rather than a single-receptor pharmacology. For TB-500 itself the record is thinner: activity has been reported for the unacetylated heptapeptide LKKTETQ, but the biological effects of TB-500 have not been documented, and in a 2024 fibroblast assay only its metabolite Ac-LKKTE, not the parent peptide, showed significant wound-healing activity.^[14]

Preclinical Evidence: Cardiac Repair, Ophthalmology, and Wound Healing

Three preclinical signal sets dominate the modern Tβ4 / TB-500 literature.

1. Cardiac repair after myocardial infarction

Bock-Marquette and colleagues reported in 2004 that systemic Tβ4 administration after experimental myocardial infarction in mice reduced infarct size, improved cardiac function, and promoted survival of cardiomyocytes through Akt-pathway activation and PINCH-ILK-Akt complex signalling.^[2] Follow-up work from the Riley group has explored Tβ4-driven activation of epicardial-derived progenitor cells and collateral vessel growth in mouse models. The cardiac-repair signal is the most cited single mechanistic story in the Tβ4 literature and the backbone of most "Tβ4 heals tissue" narratives.

2. Ophthalmology and corneal wound healing

Tβ4 promotes corneal epithelial cell migration, suppresses inflammatory infiltrates, and accelerates re-epithelialisation in rabbit and rodent corneal injury models. This preclinical signal is the scientific foundation of the RegeneRx RGN-259 ophthalmic programme — a preservative-free Tβ4 0.1% eye drop developed for dry-eye disease and neurotrophic keratitis — discussed in the next section.^[3]

3. Dermal wound healing and tendon / ligament repair

Tβ4 and Tβ4-derived fragments have been studied in full-thickness skin wound, diabetic wound, and pressure-injury rodent models, with reports of accelerated wound closure, reduced inflammation, and increased neovascularisation. A separate strand of mostly preclinical work in rodent tendon and ligament injury models is the most commonly cited basis for athletic-recovery interest in TB-500, although the human late-stage evidence base in musculoskeletal injury remains absent.^[2]

The honest summary across these signal sets is consistent. Tβ4 produces a reproducible preclinical wound-healing and tissue-repair phenotype across multiple organ systems and multiple independent groups. The translational programme that has actually reached late-stage human trials is the ophthalmic one — and even there, the endpoint record is mixed.

RegeneRx RGN-259 ARISE-1 & ARISE-2 — Ophthalmology Phase 3 Status

The clearest human clinical record for Tβ4 is the RegeneRx Biopharmaceuticals ophthalmic programme. RGN-259 is a preservative-free 0.1% Thymosin Beta-4 eye drop developed for dry-eye disease and, in parallel, for neurotrophic keratitis. The programme spans three Phase 3 dry-eye trials — ARISE-1, ARISE-2, and ARISE-3 — conducted under collaboration with regional partners in the U.S. and Asia.^[3]

The published record is mixed. ARISE-1 reported statistically significant improvement in a subset of sign endpoints (notably central corneal fluorescein staining) and certain symptom endpoints, but did not meet all co-primary endpoints. ARISE-2 produced a comparable pattern: some sign and symptom endpoints reached significance in pooled analyses, others did not. ARISE-3 also did not meet its pre-specified co-primary endpoints; it reached significance on one symptom (ocular grittiness) and, outside the pre-specified endpoints, on central corneal staining in a subpopulation. RegeneRx now names neurotrophic keratitis as its first priority and plans to wait for its Phase 3 neurotrophic keratitis results before starting further dry-eye Phase 3 trials.^[18] As of October 2026, there is no FDA approval for RGN-259, and Thymosin Beta-4 ophthalmic remains investigational in the U.S. market.^[3]

For a research reader, two implications follow. First, the ophthalmic programme is the most rigorous test of Tβ4 in humans to date and the clearest source of pharmacological detail (dose, vehicle, exposure window, endpoint definitions). Second, the mixed endpoint record undercuts any framing that Tβ4 is a finished, validated human therapy — even in the indication where it has been most extensively studied.

TB-500 vs Full-Length Thymosin Beta-4: The Labelling Question

A labelling clarification belongs near the top of any honest TB-500 review. TB-500 is defined by FDA and the anti-doping literature as a synthetic shorter fragment of Tβ4, Ac-LKKTETQ (Tβ4 residues 17–23, 889 g/mol, CAS 885340-08-9), rather than the full 43-amino-acid, 4,963.4 g/mol native protein.^{[4][8][9][11]} The fragment contains the actin-binding region of Tβ4 but not the N-terminal AcSDKP sequence. Products sold under the name vary, however, and some contain or claim full-length Tβ4 (about 4,963 g/mol), so a vial's COA mass is what identifies its contents.^[12][13] FDA's briefing found TB-500 products offered online in sizes of 2–15 mg.^[9] The seven-residue fragment is comparatively easy to synthesise by solid-phase peptide synthesis.

Full-length Tβ4, by contrast, is the defined 43-residue peptide used in the RegeneRx RGN-259 ophthalmic formulation and in most of the published cardiac and corneal mechanism work. It is the entity to which the CAS reference 77591-33-4 and the 4,963.4 g/mol reference molecular weight apply.^[1]

Two consequences follow for a research reader:

• Literature mapping is not 1:1. Mechanism papers using full-length Tβ4 do not automatically translate to a "TB-500" fragment vial. TB-500 as defined carries the actin-binding motif but not the AcSDKP fragment, so AcSDKP findings from full-length Tβ4 do not transfer to it, and actin-sequestration, receptor and signalling claims should be read with the actual reagent in mind; the biological effects of TB-500 itself have not been documented.^[14]
• COA reading matters. When a per-batch Certificate of Analysis is available, the reported molecular weight shows which molecule the vial holds: about 889 g/mol for the Ac-LKKTETQ fragment, about 4,963 g/mol for full-length Tβ4. The HPLC retention-time data should be cross-checked against that same molecule. Researchers comparing TB-500 vials across suppliers can meet either: anti-doping laboratories have found product contents that were not systematically consistent, and products claiming either the fragment or full-length Tβ4.^[12][13]

This is research-buyer literacy rather than a critique of the molecule. The fragment is biologically interesting on its own terms. Honest framing simply requires being clear about what is in the vial.

Research Format & Storage

For research use, lyophilized TB-500 is supplied as a powder in a sealed vial. The handling notes below describe the format only:

• Storage of the lyophilisate. 2-8°C protected from light and moisture for routine use; -20°C for long-term storage. In warm climates, documented cold-chain handling from arrival to bench-side is important — short ambient excursions during last-mile delivery are the most common stability risk.
• Laboratory preparation. In laboratory work the powder is dissolved in a suitable sterile diluent shortly before use. The appropriate solvent depends on the assay, so preparation follows the laboratory's own validated protocol and the methods of the published study being replicated.

This page provides no human-use dosing or veterinary instructions and is not a clinical-protocol document. Wider storage questions are covered in the peptide stability and storage guide.

What the TB-500 Literature Does Not Yet Give You

Cautious reading of the TB-500 / Tβ4 record requires acknowledging four real gaps:

• No registered Phase 2 or Phase 3 musculoskeletal human trial. A clinicaltrials.gov search at the time of writing did not return a Phase 2 or Phase 3 TB-500 or Tβ4 trial registration for tendon, ligament, muscle, or joint injury. The widely cited soft-tissue repair evidence is animal preclinical work, not late-stage human trial evidence.
• No published human pharmacokinetic profile for the marketed fragment. Human PK data for Tβ4 has been generated inside the RegeneRx ophthalmic programme and a handful of small dermatology studies. The systemic PK profile of the synthetic "TB-500" fragment used in the research-peptide market — distribution, clearance and metabolite profile in humans — is not characterised in the public literature in a way that supports clinical extrapolation.^[5]
• Dose translation is unsupported. Published animal doses do not map cleanly to a human dose with any rigour, and this article makes no attempt to do so. Anyone offering specific TB-500 protocols for humans is going outside the published data.
• Labelling heterogeneity across suppliers. The marketed "TB-500" fragment is not a single uniformly defined entity. Independent third-party analytical confirmation of the fragment composition is the right baseline for serious laboratory work.

These gaps are not arguments against studying TB-500. They are arguments against overselling it.

TB-500 Research-Use Supply & Format

For research use, TB-500 belongs in the category of actin-biology and tissue-repair research peptides. The Remy TB-500 10mg research vial documents the lyophilised format, while the TB-500 20mg research pen separately documents the manufacturer-labelled Ac-LKKTETQ fragment, reference price, out-of-stock state, and targeted-HPLC evidence boundary. The BPC-157 + TB-500 blend vial remains a separate combination format for parallel actin-biology and repair-signalling research.

Material is not framed for human use, not framed for veterinary use, and not framed as a treatment. The wider research catalog comparison sits at /products/, and the COA history sits in the COA library.

For researchers reading this page as a starting point, the most useful adjacent references on this site are the BPC-157 healing peptide review, the KPV tripeptide review, the GHK-Cu copper-peptide review, and — for handling depth — the peptide stability and storage guide.

TB-500 vs BPC-157 vs GHK-Cu — Where the Lanes Differ

Researchers commonly ask how TB-500 positions next to other healing-and-repair research peptides. The three most-compared compounds belong to different families and were investigated in different model systems. The table below summarises that, without claiming clinical interchangeability.

None of these molecules is an approved therapeutic, and none has a peptide-specific late-stage human-trial program of the kind seen with incretin agents. For research framing, the cleanest position is to keep TB-500 in the actin-biology / Tβ4 fragment lane, BPC-157 in the gastric-protein recovery-signalling lane, and GHK-Cu in the skin/copper-remodelling lane. They are not substitutes for each other in a research-design sense.