Editorial research dossier — thymosin beta-4 (17-23)
TB-500 is the synthetic Ac-LKKTETQ fragment of thymosin beta-4, read against the published research.
The seven-amino-acid sequence carries thymosin beta-4's actin-binding core. Nearly every efficacy figure below was measured on the full-length protein, not the fragment — this dossier keeps that line visible on every page.
TB-500, in one line and then the asterisk
TB-500 is the synthetic, N-acetylated heptapeptide Ac-LKKTETQ — residues 17 to 23 of thymosin beta-4, the conserved actin-binding region of the beta-thymosins [1]. As a TB-500 peptide it is a short, defined chemical: seven amino acids, a molecular weight near 889 Da, no consistently registered single CAS number under the TB-500 name. That is the entire molecule.
The asterisk is the whole story of this site. In commerce and in anti-doping science, "TB-500" denotes that 7-mer. But the overwhelming majority of efficacy research was conducted with full-length thymosin beta-4 (Tβ4), a 43-residue protein near 4963 Da [5]. The fragment and the protein are not the same construct, and it is not established that the heptapeptide reproduces the parent protein's effects at the doses used in peptide research. Every figure on this site is labelled for which one was actually studied.
This is a research dossier, not a clinic and not a storefront. It summarizes the research evidence on TB-500, the TB-500 anti-inflammatory and anti-fibrotic research, and TB-500 legal status and 503A category, and cites every quantitative claim to a study.
TB-500 peptide: the Ac-LKKTETQ fragment of thymosin beta-4
The parent protein thymosin beta-4 is the body's principal G-actin–sequestering peptide, present in nearly all human cells and released by platelets and macrophages at sites of injury [5]. Its job is structural: it binds monomeric (globular) actin one-to-one, holding a buffered reserve of unpolymerized actin and regulating how the cytoskeleton assembles and how cells move.
The LKKTETQ sequence in TB-500 is the actin-binding core of that protein — a WH2-type motif. X-ray crystallography of a gelsolin-domain-1–Tβ4 hybrid bound to actin, solved at 2 Å, established that thymosin beta-4 forms a 1:1 complex with G-actin and sequesters the monomer by capping both ends to prevent polymerization [1].
What is unresolved is whether the isolated seven-residue motif, lifted out of the protein and acetylated, carries the same activity in a living system. That question — fragment versus full-length — has no controlled human answer.
What TB-500 is studied for
The TB-500 benefits discussed in the literature are, more precisely, the activities of thymosin beta-4 and its actin-binding region in animal and in-vitro models. A consolidating review describes the protein binding actin and promoting cell mobilization and migration, decreasing myofibroblast number to reduce scar formation, limiting apoptosis and inflammation after injury, and promoting angiogenesis — the rationale behind clinical trials in dermal wounds, corneal injury, and heart and CNS repair [5].
The concrete numbers are striking and they are from the full-length protein. 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 [3]. In mice, Tβ4 activated the PINCH–ILK–Akt survival pathway and improved cardiac function after coronary ligation [2]. The same protein has been characterized as an exerkine — a factor released into circulation in response to exercise — which is part of why TB-500 draws recovery interest, even though that interest runs ahead of the fragment data.
The research clusters into a few areas. The earliest and most-replicated is wound and tissue repair: re-epithelialization, contraction, collagen deposition, angiogenesis [3][5]. A second is cardiac repair, where the PINCH–ILK–Akt survival finding drove an attempt at human cardiac development [2]. A third is the TB-500 anti-inflammatory and anti-fibrotic research — NF-κB and IL-8 suppression, pro-resolving pathways, and context-dependent fibrosis effects across liver and corneal models [13][14][15]. A fourth is neurological repair, where the result was strikingly non-monotonic [4].
Those are real, measured effects. They are also, every one of them, effects of the protein — which is why the honest headline stat on this page is the one that reads NONE: there are no completed controlled human trials of the 7-mer for any indication [11]. The body of this site is that reading, kept careful: the research evidence on TB-500 sets out each finding with the molecule it was measured on; the frequently asked questions about TB-500 answer the common questions directly; and TB-500 dosage in the literature reads the doses as study facts, never as a protocol.
How TB-500 works
What is TB-500?
TB-500 is the synthetic N-acetylated heptapeptide Ac-LKKTETQ, corresponding to residues 17–23 of thymosin beta-4 — the actin-binding motif of the parent protein [1]. It is supplied as a research and veterinary-context chemical with no approved human therapeutic indication [11].
What does TB-500 stand for?
TB refers to thymosin beta-4 (Tβ4); "TB-500" is a product and research designation for the synthetic Ac-LKKTETQ fragment of that protein. The number is a label, not a dose or a concentration.
What is TB-500 used for in research?
In animal and in-vitro studies, thymosin beta-4 and its actin-binding region are investigated for wound and tissue repair, cell migration, angiogenesis, cardiac and neurological repair, and anti-fibrotic effects [5]. The fragment is studied largely by analogy to the protein.
How does TB-500 work?
The LKKTETQ motif is thymosin beta-4's actin-binding region. The parent protein binds monomeric (G-) actin 1:1, regulating cytoskeletal dynamics, cell migration, angiogenesis, and survival signaling [1][2]. Whether the isolated 7-mer reproduces these effects at research doses is not established in humans.