A research digest · Thymosin beta-4 fragment
TB-500 is the synthetic thymosin beta-4 fragment, read against what the recent repair research actually shows.
Ac-LKKTETQ is seven amino acids of a 43-residue protein. Most of the efficacy data is the protein, not the fragment, and zero controlled human trials of the fragment have been completed — so we print the headline and its health together.
TB-500, stated precisely
TB-500 is the synthetic, N-acetylated heptapeptide Ac-LKKTETQ — seven amino acids (Leu-Lys-Lys-Thr-Glu-Thr-Gln) corresponding to residues 17–23 of thymosin beta-4, the actin-binding core of that 43-residue protein [1]. That single sentence carries the most important caveat on this site: the molecule sold and tracked in the anti-doping literature as TB-500 is the ~889 Da fragment, while nearly every efficacy study cited below used full-length thymosin beta-4 (~4963 Da) [6]. It is not established that the isolated 7-mer reproduces the parent protein's effects at the doses used in peptide research.
Thymosin beta-4 itself 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]. The LKKTETQ motif in TB-500 is its actin-binding region. We read the literature on that basis throughout: where a finding used the full protein, we say so; where it used the fragment, we say that too. This is the actin-binding mechanism of TB-500, and it is the spine of everything else.
The honest summary is short. The mechanism is well-characterized. The tissue-repair signals in animal models are real and, in places, large. The human record is thin and confined to the parent protein, the fragment has no completed controlled trial, and a genuine tumor/angiogenesis safety question sits underneath the repair story. Each of those is set out in its own panel below, cited to source.
TB-500 as a Research Peptide: Sequence and Identity
The TB-500 peptide is a defined chemical object: Ac-LKKTETQ, molecular formula C38H68N10O14, molecular weight ~889.02 Da. It is a synthetic construct, not an endogenous species — the body makes the full 43-residue thymosin beta-4, not the isolated heptapeptide. In commerce and in veterinary contexts the same fragment also appears under the designation TB1000; the number is a product label, not a chemical descriptor.
Why the identity matters for reading the evidence: a short acetylated 7-mer and a 4963 Da protein are different molecules with different stability, distribution, and downstream biology. The full protein generates Ac-SDKP, an N-terminal cleavage product with its own anti-fibrotic and angiogenic activity — and that fragment is not produced by the C-terminal-region TB-500 sequence [5]. So when a marketing claim leans on a thymosin beta-4 study, it is borrowing data from a larger molecule. We keep the two labelled apart on every page.
The parent protein's biology is genuinely well-mapped. X-ray crystallography of a gelsolin-domain-1–thymosin beta-4 hybrid bound to actin, resolved to 2 Å, established that thymosin beta-4 forms a 1:1 complex with monomeric (G-) actin and sequesters it by capping both ends, preventing polymerization [1]. That is the structural anchor for the whole beta-thymosin family — and it is the part of the TB-500 story that is fully confirmed.
What the record establishes — and what it does not
Confirmed: the actin-sequestration structure (1:1 G-actin capping) [1]; accelerated re-epithelialization in animal wounds, where full-length thymosin beta-4 raised re-epithelialization by 42% at four days and up to 61% at seven days versus saline [3]; and a randomized, placebo-controlled Phase 1 IV safety study in which synthetic thymosin beta-4 was well tolerated up to 1260 mg with no dose-limiting toxicities [6]. Those are the genuinely-on-the-record findings.
Preclinical only: cardiac survival signaling via PINCH–ILK–Akt in mice [2]; dose-dependent neurological improvement after rat embolic stroke [4]; and the 2021–2026 thymosin beta-4 work — scaffold-released cardiac repair, inhaled-protein pulmonary fibrosis, zebrafish axon regeneration, an NAFLD inflammation study, and a 2025 engineered tandem corneal peptide. These are the latest thymosin beta-4 research signals, and they are animal or in-vitro.
Outright gaps: there are zero completed controlled clinical trials of the TB-500 heptapeptide for any indication [6]. There is no validated human pharmacokinetic half-life for the fragment. And a 2026 Sports Medicine review lists TB-500 among unapproved musculoskeletal peptides with scarce rigorous human safety data and potential for serious harm. The honest record is the findings and the gaps, read together.
Three common questions, answered up front
The full question set lives on the TB-500 side effects and safety signals page. Three definitional ones belong here.