TB-500
TB-500 and protein fragments — Peptide R Lab
Removing most of a protein raises questions that its surviving motif cannot answer alone.
Ac-LKKTETQ and thymosin beta-4
TB-500 names a synthetic, N-acetylated seven-amino-acid fragment: Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln-OH, abbreviated Ac-LKKTETQ. It corresponds to residues 17-23 of the 43-amino-acid protein thymosin beta-4 and contains its actin-binding motif.
Isolating a short active region is an enticing idea to me. The review of thymosin beta-4 biology describes cell movement, tissue repair and blood-vessel growth across a substantial body of research. Most of that efficacy work used full-length thymosin beta-4. The fragment’s own human efficacy and pharmacokinetics remain unestablished.
A structure with actin
The structural study of a thymosin beta-4 hybrid bound to actin used a gelsolin-domain-1–thymosin beta-4 hybrid. It showed a 1:1 complex with globular actin, capping both ends of the actin monomer and preventing assembly into filaments. That is a concrete explanation for how the larger protein can buffer the actin available to a moving cell.
The preparation matters here. A structure made with a hybrid gives molecular information about actin binding; it leaves the isolated TB-500 fragment’s clinical behaviour open. Describing how actin is held is a substantial achievement, I think. The fragment’s own exposure and outcome data remain a separate job.
Thymosin beta-4 animal outcomes
In a full-thickness wound experiment in rats, full-length thymosin beta-4 increased re-epithelialization by 42% at 4 days and up to 61% at 7 days versus saline. Collagen deposition, wound contraction and angiogenesis also increased. Re-epithelialization is the replacement of a wound’s surface covering.
In mouse cardiac experiments, the same larger protein promoted cell migration and survival through PINCH–ILK–Akt signaling and improved cardiac function after coronary-artery ligation. The rat stroke dose-response study complicates an easy dose-response story: 2 and 12 mg/kg improved neurological function, while 18 mg/kg gave no significant benefit. These amounts describe that animal experiment.
I take the variation seriously. A result can depend on the model, measured endpoint and preparation; a general recovery claim erases all three.
Thymosin beta-4 Phase 1 safety
The randomized Phase 1 intravenous safety trial enrolled 40 healthy volunteers and tested full-length synthetic thymosin beta-4. It was well tolerated, with infrequent mild-to-moderate adverse events, no dose-limiting toxicities and no serious adverse events. Half-life increased with dose.
That last finding interests me alongside BPC-157’s animal metabolism paper. Time in the body needs to be measured for the actual material and conditions. This trial provides a human safety and pharmacokinetic record for the larger protein. No completed controlled human trial establishes safety or benefit for the TB-500 heptapeptide.
TB-500 safety and anecdotes
People describe faster soft-tissue recovery and easier movement, as well as local reactions, tiredness, headache, nausea and mood changes. Those are anecdotal reports, not clinical evidence. I cannot infer repaired tissue from a report of feeling more mobile.
The 2026 review of unapproved musculoskeletal peptides describes scarce rigorous human safety data and potential for serious harm. Blood-vessel growth and cell migration raise a theoretical cancer concern; bleeding, surgery, pregnancy, breastfeeding and use in young people also remain unresolved precautions rather than measured human risks for this fragment.
TB-500 has no FDA approval and is WADA-prohibited at all times. On FDA’s page current as of April 22, 2026, it appears among withdrawn nominations after earlier Category 2 placement, with FDA’s safety concerns retained. Withdrawal establishes neither approval nor Category 1 placement. Research-labelled material and patient-specific prescription care have distinct requirements. Neither supplies a completed human efficacy trial of the fragment.