# TB-500: Research Overview — Prime Peptide Labs > A literature summary of TB-500 (Ac-LKKTETQ), a synthetic fragment of thymosin beta-4 studied for tissue repair. Covers the fragment-versus-full-protein distinction, actin biology, and key safety signals. Seven amino acids holding the actin-binding motif of thymosin beta-4 — but most of the healing evidence comes from the full parent protein, not the fragment itself. ## The short version TB-500 is a small synthetic peptide — just seven amino acids — with the sequence Ac-LKKTETQ. That stretch is the *actin-binding* piece of a larger natural protein called thymosin beta-4. Actin is part of the internal skeleton cells use to hold their shape and crawl toward a wound, so the parent protein is closely tied to cell movement, healing, and new blood-vessel growth [10]. The single most important thing to understand about TB-500 is a naming gap. In research commerce and anti-doping labs, "TB-500" means the short seven-amino-acid fragment. But most of the published *efficacy* research was done with the full-length parent protein, which is roughly five times larger [8]. It is not established that the small fragment reproduces what the whole protein does. TB-500 is not an approved medicine, it is banned in sport, and this page reports doses only as they were studied — never as advice. ## What it is TB-500 is a synthetic, N-terminally acetylated heptapeptide with the sequence Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln. The `LKKTETQ` motif corresponds to residues 17-23 of thymosin beta-4 (Tβ4), a 43-amino-acid protein, and it is the conserved *actin-binding* region of the beta-thymosin family. The size difference matters throughout: the fragment sold as TB-500 weighs about 889 daltons, while full-length Tβ4 is about 4,963 daltons. Wherever a study below used the full protein rather than the 7-mer, this page flags it, because that is precisely where TB-500 marketing borrows a much larger molecule's data [8]. ## How it works Full-length thymosin beta-4 is the body's major intracellular *G-actin sequestering* peptide. "G-actin" is the free, monomeric form of actin; "sequestering" means Tβ4 grabs and holds those individual units so they are not assembled into filaments until needed. A 2-angstrom X-ray crystal structure of a gelsolin-Tβ4 hybrid bound to actin established that Tβ4 forms a 1:1 complex with G-actin and caps both ends of the monomer, preventing polymerization — the structural basis for its actin-buffering role [12]. Why does that matter for repair? By regulating the actin skeleton, Tβ4 and the LKKTETQ motif it contains are associated with faster cell migration, new blood-vessel growth, anti-inflammatory signaling, reduced scar-forming myofibroblasts, and recruitment of progenitor cells — a consolidated mechanism reviewed across dermal-wound, corneal, heart, and CNS models [10]. Whether the isolated seven-amino-acid fragment reproduces all of that at the doses used in peptide research has not been shown in controlled human trials [10]. ## What the research shows *Structural and mechanistic basis.* The crystallography work pinned down the 1:1 actin-capping mechanism [12], and a multi-model review consolidated Tβ4's actin-binding, pro-migratory, anti-scarring, anti-inflammatory, and angiogenic activities as the rationale for clinical development in dermal wounds, corneal injury, and heart and CNS repair [10]. *Human safety data (full-length protein).* In a randomized, placebo-controlled Phase 1 study, synthetic thymosin beta-4 was given intravenously to 40 healthy volunteers — a single dose then daily for 14 days at 42, 140, 420, or 1260 mg. It was well tolerated, with only infrequent mild-to-moderate adverse events, no dose-limiting toxicities, no serious adverse events, and dose-proportional pharmacokinetics [11]. This used full-length Tβ4, not the TB-500 fragment. *Animal dose-response.* In male Wistar rats with an embolic stroke model, intraperitoneal thymosin beta-4 at 2 mg/kg and 12 mg/kg (starting 24 hours after stroke, then every three days) improved neurological function significantly through day 56, while 18 mg/kg gave no significant benefit — a non-monotonic result in which more was not better [9]. *Field-level review.* A 2026 Sports Medicine narrative review listing TB-500 and BPC-157 among unapproved peptides for musculoskeletal injury and athletic performance concluded that favorable animal-model results have not been matched by rigorous human safety data, and that these compounds operate largely outside regulatory oversight [8]. ## Reported effects, cautions & safety The cautions for TB-500 are unusually concrete: - *Identity confusion.* Because "TB-500" is the fragment but most efficacy data are from full-length Tβ4, efficacy claims for the fragment in humans are unproven [8]. No completed controlled clinical trials of the TB-500 fragment exist for any indication. - *Tumor angiogenesis signal.* Thymosin beta-4 is overexpressed in several cancers (including pancreatic and colorectal) and is implicated in metastasis and tumor blood-vessel growth. The same pro-migratory, pro-angiogenic properties that may aid repair could, in theory, support tumor progression [10]. - *Mixed preclinical results.* In dystrophin-deficient mice, chronic Tβ4 increased regenerating fibers but did not improve muscle strength, cardiac function, or fibrosis, and systemic Tβ4 failed to reduce myocardial ischemia-reperfusion injury in a pig study [8][10]. - *Non-monotonic dosing.* The rat stroke study's finding that 18 mg/kg helped less than 12 mg/kg undermines community "loading" rationales — higher dose is not necessarily more effective [9]. - *Regulatory.* TB-500 is prohibited in sport by WADA and is a prescription medicine in some jurisdictions; it has been encountered as a designer doping agent in racehorses, prompting dedicated detection assays [8]. ## Where it fits in recovery research TB-500 occupies a specific niche here: a compound whose *mechanism* — actin regulation driving cell migration — is well described at the protein level, but whose *evidence as the actual marketed fragment* is the thinnest of the three [8]. Where [GHK-Cu](/ghk-cu) leads with matrix-building and human topical data and [BPC-157](/bpc-157) leads with angiogenesis and a deep animal record, TB-500's story is really thymosin beta-4's story, borrowed. That makes it the clearest case study in why this field rewards careful reading. See how it stacks up on the [comparison page](/compare). ![TB-500 actin-binding heptapeptide fragment and filament structure in cold azure graphite](/images/tb-500.webp) --- A plain-language reading desk for recovery-peptide research — citations on every claim, no products, no prescriptions.