TB-500 is the synthetic Ac-LKKTETQ fragment of thymosin beta-4, studied for actin binding, cell migration, and angiogenesis.

TB-500, in one line, then the caveat that governs the rest

TB-500 is the synthetic, N-acetylated heptapeptide Ac-LKKTETQ — residues 17–23 of the 43-amino-acid protein thymosin beta-4 (Tβ4), and the conserved actin-binding motif of the beta-thymosins. Molecular weight: ~889 Da. Formula: C38H68N10O14. The fragment is supplied as a research and veterinary-context peptide; it is not an FDA-approved drug.

One distinction governs everything below. In commerce and in the anti-doping literature, "TB-500" means this 7-amino-acid fragment. But the overwhelming majority of efficacy studies — cardiac, neurological, wound-healing, hair-follicle — were run with full-length recombinant or synthetic Tβ4 (~4963 Da), not the heptapeptide ^[5]. It is not established that the isolated 7-mer reproduces the parent protein's effects at the doses peptide research uses. This site flags that gap wherever a finding rests on full-length Tβ4, and it is the single most important thing to carry forward.

The actin mechanism is the part that is genuinely the fragment's own. The LKKTETQ motif binds monomeric (G-) actin 1:1, capping both ends of the monomer to hold a buffered pool of unpolymerized actin — a structure resolved by X-ray crystallography of a gelsolin-domain-1–Tβ4 hybrid bound to actin at 2 Å ^[1]. That actin-sequestration step is the hub from which the rest of the thymosin beta-4 parent protein signaling network fans out: cell migration, angiogenesis, cardiomyocyte survival, anti-inflammatory and anti-fibrotic branches. Three decades of work map that graph well in animals. What it does not yet contain is a completed controlled human trial of the fragment itself.

TB-500 peptide: what the research describes

The TB-500 peptide is the actin-binding core of a regulatory protein, lifted out and sold on its own. Where the parent protein Tβ4 is a ubiquitous intracellular actin-sequestering peptide present in nearly all human cells and released by platelets and macrophages at sites of injury, the Ac-LKKTETQ fragment is a synthetic construct — not an endogenous species ^[5].

That matters for how the evidence reads. A consolidated mechanism review describes Tβ4 binding actin, promoting cell mobilization and migration, decreasing myofibroblast number (and so reducing scar formation), limiting apoptosis and inflammation after injury, and promoting angiogenesis — the rationale that carried Tβ4 into clinical trials for dermal wounds, corneal injury, and heart and CNS repair ^[5]. The fragment carries the actin-binding motif at the center of that picture, which is why it is marketed under the parent protein's story. Whether the heptapeptide alone delivers the same downstream effects in vivo is the open question the literature has not closed.

What is TB-500?

TB-500 is the synthetic N-acetylated heptapeptide Ac-LKKTETQ — residues 17–23, the actin-binding motif, of the 43-amino-acid protein thymosin beta-4. Most published efficacy data are on full-length Tβ4 (~4963 Da), not the 7-mer (~889 Da), so the two are easily conflated in marketing ^[5]. The fragment itself is a research and veterinary-context substance with no approved human indication.

What does TB-500 stand for?

TB is a thymosin-beta designation. TB-500 denotes the LKKTETQ actin-binding fragment of thymosin beta-4, supplied as a research and veterinary peptide. The number is a product designation, not a chemical one; the molecule is most precisely named by its sequence, Ac-LKKTETQ, and by its origin as Tβ4 residues 17–23 ^[1].

What is TB-500 used for in research?

In research it is studied for tissue repair, cell migration, and angiogenesis, and — as full-length Tβ4 — for cardiac, neurological, and hair-follicle endpoints in animal models ^[5]. None of these is an approved human use. Read the TB-500 angiogenesis research page for the dealt lens, and the research page for the tissue-repair and mechanism record.

Thymosin beta-4: the parent protein behind TB-500

Thymosin beta-4 is the body's principal G-actin-sequestering peptide: a 43-residue protein (gene TMSB4X; human UniProt P62328) found in nearly all human cells, released by platelets and macrophages at injury sites. The LKKTETQ segment that TB-500 reproduces is its actin-binding core ^[5]. Everything the fragment is sold to do traces back to this protein's biology.

Thymosin beta-4 has the human evidence the fragment lacks. In a randomized, placebo-controlled Phase 1 study, synthetic Tβ4 given intravenously to 40 healthy volunteers — single dose then daily for 14 days at 42, 140, 420, or 1260 mg — was well tolerated, with only infrequent mild-to-moderate adverse events, no dose-limiting toxicities, and no serious adverse events; pharmacokinetics were dose-proportional, with half-life increasing with dose ^[6]. A clinical-grade topical ophthalmic formulation (RGN-259) has been studied in dry-eye and corneal-healing trials. None of that human work is the 7-mer.

There is also a piece of Tβ4 biology that the fragment does not carry: Ac-SDKP, an N-terminal cleavage product of full-length Tβ4 with its own anti-fibrotic and angiogenic activity, comes from the protein's N-terminus — not from the C-terminal-region LKKTETQ fragment ^[5]. So even where full-length Tβ4 shows an effect, part of that effect can belong to a metabolite the heptapeptide never produces. The distinction is not pedantry; it is the difference between the data and the marketing.

What the literature genuinely establishes — and what it does not

Three results are about as solid as this field gets, and all three are worth stating plainly. The 1:1 actin-sequestration mechanism is resolved at the structural level ^[1]. In a rat full-thickness wound model, topical or intraperitoneal Tβ4 increased re-epithelialization by 42% at 4 days and up to 61% at 7 days versus saline, with increased contraction, collagen, and angiogenesis ^[3]. And the IV Phase 1 study established that full-length Tβ4 was tolerated to 1260 mg in healthy volunteers ^[6].

What the literature does not contain is equally clear. There are no completed controlled clinical trials of the TB-500 heptapeptide for any indication ^[10]. A 2026 Sports Medicine review of approved and unapproved musculoskeletal peptides places TB-500 among the unapproved compounds with animal-model promise but scarce human safety data and no regulatory approval ^[10]. The same review lists TB-500 and BPC-157 together in that unapproved category — neither carries the human efficacy record its marketing implies.

The rest of this console is organized around that honest split: TB-500 angiogenesis research for the dealt vascular lens, the research page for mechanism and tissue repair, TB-500 dosage in research for the animal mg/kg ranges and the human IV figures, and TB-500 legal status for the FDA 503A standing and how compounded access actually works.