TB-500

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Snapshot

Chemistry and make-up

This is the single most important identity trap in the repair category, so it gets covered in depth.

“TB-500” is a market name, not a defined chemical entity. It is used loosely for two very different molecules:

1. The short synthetic fragment Ac-LKKTETQ (Tβ4 residues 17-23, N-terminally acetylated). This 7-residue peptide carries the actin-binding motif (the LKKTETQ tetrapeptide region) that is thought to drive cell migration. Acetylated it runs at roughly 889 g/mol; the bare heptapeptide is ~847 g/mol (PubChem CID 10169788, C36H66N10O13) [B]. 2. The full-length 43-amino-acid Thymosin beta-4, N-terminally acetylated, formula C212H350N56O78S, MW ~4963, PubChem CID 45382195 (verified via PubChem REST, 2026-07-30) [B]. This is the actual endogenous molecule studied in the peer-reviewed Tβ4 literature and in RegeneRx’s clinical trials.

The practical problem: much of the “TB-500” sold to the research market is in fact full acetylated Tβ4, while much of the published human/clinical evidence is on full Tβ4 rather than the short fragment. Vendors then borrow Tβ4 trial data to sell a 7-aa fragment, or ship full Tβ4 under a fragment name and price. Either way the label alone does not tell you which molecule is in the vial, and the two differ by more than 5x in molecular weight, so a “10 mg” vial contains a very different molar amount depending on which it is.

Because of this, the CoA must state the actual amino-acid sequence and the MS observed mass (expected vs found), not just “TB-500”. A purity-only CoA is worthless here: 98% pure of *what*? An MS peak near 889 Da tells you it is the fragment; a peak near 4963 Da tells you it is full Tβ4. AxYn’s spec should demand sequence + MS, and should reject any CoA that names only “TB-500”. Tβ4 contains one methionine (the single sulphur in the formula) and no cysteine, so there are no disulphide bridges; oxidation of that methionine is a plausible degradation product to watch on MS.

What it is studied for (evidence)

• Mechanism (preclinical [A]): Tβ4 is the major intracellular G-actin-sequestering peptide; it regulates actin polymerisation and thereby cell migration, and promotes angiogenesis, endothelial cell migration, and down-modulation of inflammation. The LKKTETQ region mediates the actin interaction. It accelerates wound repair in dermal, corneal and cardiac animal models (Nature Sci Rep 2018, RGN-259) [A].
• Established (for full Tβ4, not the fragment): consistent animal wound-healing and cytoprotection data, plus human ophthalmic trial data. RGN-259 (0.1% Tβ4 eye drops) improved signs and symptoms of severe dry eye in a randomised placebo-controlled Phase 2 (PubMed 25826322; Phase 2 CAE model, PubMed 26056426) and showed benefit in neurotrophic keratopathy in a Phase 3 (PMC9820614) [A]. Note these are topical ocular results, not systemic injectable tendon/muscle results.
• Emerging / thin / preclinical only: the systemic “injury recovery” use that the research market sells TB-500 for (tendon, ligament, muscle, cardiac repair by injection) rests on animal models and mechanism, not completed human efficacy trials. Cardiac Tβ4 work has reached early human safety stages only.
• Marketing claims vs data: vendor and community pages present the short Ac-LKKTETQ fragment as interchangeable with full Tβ4 and cite Tβ4 trial data for it. The fragment has far less direct evidence than the full protein, and no completed human efficacy trial supports systemic injectable use of either for musculoskeletal repair. Treat “heals injuries in humans” and any dosing protocol as unsupported.
• Human clinical status: full Tβ4 (RGN-259) has completed Phase 2/3 ophthalmic trials with orphan designation but no FDA marketing approval; no approved systemic product exists for the fragment or the full protein.

Handling, format and stability

Supplied lyophilised; reconstituted with bacteriostatic water for research handling (no dosing guidance here). Store lyophilised cold and protected from light; reconstituted peptide is less stable and cold-chain dependent. Full Tβ4, being a 43-mer, is more prone to aggregation and to methionine oxidation than the short fragment, which is one more reason the CoA should report observed mass and appearance. Residual synthesis solvents (TFA) should be characterised.

Regulatory and trade status

• UK/EU RUO: research use only; not an approved medicine. Any healing/treatment claim risks “medicinal product by presentation” classification under the MHRA framework, so keep listings and emails strictly research-use.
• US (bellwether): not FDA-approved for any indication. TB-500 (thymosin beta-4 fragment) sat on the interim 503A Category 2 list; in April 2026 the FDA removed it from Category 2 (the nomination was withdrawn) and referred it to the Pharmacy Compounding Advisory Committee. On 23 July 2026 the PCAC voted 8 to 6 (1 abstention) to recommend TB-500 for the 503A bulks list, against FDA scientific staff’s advice (FDA meeting) [B]. This is an advisory recommendation only, not a rule; formal FDA rulemaking is still required and realistically runs into 2027. Nothing here changes the UK sell-as-RUO position.
• WADA (sport): prohibited at all times. Tβ4 and its fragments (including TB-500 / Ac-LKKTETQ) fall under S2 (Peptide Hormones, Growth Factors, Related Substances and Mimetics), where TB-500 has been listed since 2011; the non-approved status also engages S0. Detectable by LC-MS/MS. Athletes should treat it as banned (WADA Prohibited List; BSCG TB-500 status) [B]. This WADA status is inherited by the Glow and KLOW blends, which contain TB-500.
• Customs: identity ambiguity (fragment vs full Tβ4) is the main trade and QC risk.

Sources

• [A] Thymosin β4 improves severe dry eye, Phase 2 RCT (PubMed 25826322) — https://pubmed.ncbi.nlm.nih.gov/25826322/
• [A] Tβ4 (RGN-259) dry eye Phase 2, CAE model (PubMed 26056426) — https://pubmed.ncbi.nlm.nih.gov/26056426/
• [A] RGN-259 neurotrophic keratopathy Phase 3 (PMC9820614) — https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9820614/
• [A] RGN-259 vs prescription drugs, dry eye model, *Sci Rep* 2018 — https://www.nature.com/articles/s41598-018-28861-5
• [B] PubChem CID 45382195 (full Tβ4, C212H350N56O78S, MW ~4963); CID 10169788 (LKKTETQ heptapeptide) — https://pubchem.ncbi.nlm.nih.gov
• [B] WADA Prohibited List (S2 / S0) — https://www.wada-ama.org/en/prohibited-list
• [B] BSCG, TB-500 status/risks/bans in sport — https://www.bscg.org/blogs/single/tb-500-status-risks-and-bans-in-sport-and-military
• [D] Vendor pages (Biotech Peptides, Path to Peptides, Delta Peptides) — commercial; they conflate fragment with full Tβ4 and publish dosing, which we do not use.

Plain summary

“TB-500” is not one defined molecule: the name is used for both a small 7-amino-acid Thymosin beta-4 fragment (~889 g/mol) and the full 43-amino-acid Thymosin beta-4 protein (~4963 g/mol), and much of what is sold as TB-500 is actually the full protein. The strongest human evidence is for Thymosin beta-4 as an eye drop (dry eye, corneal healing), not for the injectable musculoskeletal repair that the research market promotes, and it is banned in sport (WADA S2). Because a “10 mg” vial means a completely different molar amount depending on which molecule it contains, AxYn’s CoA must state the exact sequence and the MS observed mass, never just “TB-500”.

For laboratory and research use only (RUO). Not for human or veterinary use, not for consumption, and not a medicine. Information is a research summary, not medical advice, and contains no dosing guidance.

For laboratory research use only. Not for human or veterinary use, not for consumption, and not a medicine. This is a research summary, not medical advice, and contains no dosing guidance.