Published · 10 references
TB-500 vs Thymosin Beta-4
TB-500 is a seven-residue fragment of Thymosin Beta-4, corresponding to its residues 17 to 23; most published research associated with TB-500 used the full 43-residue peptide, not the fragment.
Structure at a glance
Thymosin Beta-4 · 43 residues
TB-500 · 7 residues
Ac: N-terminal acetyl group. Letters are one-letter amino acid codes.
Drawn from the product database. Each measure's bars share one scale.
| Property | TB-500 | Thymosin Beta-4 |
|---|---|---|
| What it is | A synthetic seven-residue peptide corresponding to residues 17 to 23 of Thymosin Beta-4. | A 43-residue peptide found across most human tissues; the material supplied is made by solid-phase synthesis. |
| How they relate | TB-500 is a fragment of Thymosin Beta-4. It corresponds to residues 17 to 23 of the parent, with an acetyl group added on residue 17, and carries under a fifth of the parent's mass. | |
| CAS number | 885340-08-9 | 77591-33-4 |
| Also known as | TB500 | Tβ4, TB4 |
| Molecular formula | C38H68N10O14 | C212H350N56O78S |
| Molecular weight | 889.02 g/mol | 4963.44 g/mol |
| Sequence | Ac-LKKTETQ | Ac-SDKPDMAEIEKFDKSKLKKTETQEKNPLPSKETIEQEKQAGES |
| Target | No target established for TB-500, which contains the actin-binding motif of Thymosin Beta-4.[1] | Monomeric G-actin. Thymosin Beta-4 is the principal protein sequestering it inside cells, a role reviewed in 2005.[2] |
| Evidence base | Cell-culture and explant assays tested a peptide with its seven-residue sequence.[1] An aged-mouse study tested a synthetic peptide with that sequence.[3] Attributed activity not directly determined with TB-500 itself in animal or human studies, in the literature reviewed for it. | Human trials over two decades of clinical development; most of what has read out has failed. Three later trials in one indication randomized 1,618 patients, and none has a peer-reviewed publication. |
| Regulatory status | The FDA has not approved TB-500 for human use. | No marketing application has ever been submitted to the FDA, in any formulation. An orphan drug designation was granted in one indication, and a second is associated with another program; a designation is not a marketing authorization. |
| Compared head-to-head? | Not with this form: a peptide with TB-500's seven-residue sequence was compared with Thymosin Beta-4 in cell-culture and explant assays.[1] A synthetic peptide with that sequence was compared with it in aged mice.[3] No comparison of TB-500 with Thymosin Beta-4 found in PubMed (searched October 2026).[4] | |
| Handling difference | Thymosin Beta-4 contains a methionine, which oxidizes on air exposure; TB-500 contains none. | |
| Where they get confused | Other suppliers sometimes apply the name TB-500 to the full-length peptide. In a 2026 briefing document, the FDA stated that the two are not the same substance.[5] | |
How TB-500 and Thymosin Beta-4 differ
TB-500 and Thymosin Beta-4 are not the same molecule. Thymosin Beta-4 is a 43-residue peptide found across most human tissues. TB-500 is a seven-residue peptide corresponding to its residues 17 to 23. High-resolution mass spectrometry of commercial TB-500 identified it as the N-terminally acetylated 17 to 23 fragment of human Thymosin Beta-4.[6] TB-500 is a research-market designation rather than a formal pharmacological name. In a 2026 briefing document, the FDA stated that the two are not the same substance.[5]
In the literature reviewed for TB-500, most studies used full-length Thymosin Beta-4 rather than the fragment, and only the actin-binding-domain studies used a peptide with TB-500's sequence. Much of that foundational work comes from a relatively small number of groups, and the proposed mechanisms are not fully resolved. None of the clinical evidence in the literature reviewed for Thymosin Beta-4 was generated with the fragment. Evidence generated with Thymosin Beta-4 should not be assumed to transfer to TB-500, or the reverse.
TB-500 contains the actin-binding motif of Thymosin Beta-4.[1] Van Troys and colleagues mapped actin binding using full-length Thymosin Beta-4 variants, not isolated fragments.[7] Binding depended on two separate regions: an N-terminal segment and that motif.[7] The study did not test the isolated motif, so its affinity on its own cannot be read from it.
A peptide with TB-500's seven-residue sequence was tested in cell-culture and explant assays.[1] A synthetic peptide with the same sequence was also tested in aged mice.[3] TB-500 supplies that sequence in N-acetylated form. In the literature reviewed for TB-500, the activity attributed to it is largely extrapolated from Thymosin Beta-4 biology. That attributed activity has not been directly determined using the synthetic TB-500 peptide in animal or human studies. A 2010 review assigned other activities, in cell and animal work, to separate N-terminal peptides of Thymosin Beta-4.[8] Neither N-terminal region is present in TB-500.
Have TB-500 and Thymosin Beta-4 been compared directly?
A peptide with TB-500's seven-residue sequence matched full-length Thymosin Beta-4 in human umbilical vein endothelial cell migration assays at around 50 nM.[1] That is cell-assay pharmacology, not a ranking for any applied purpose. In chick aortic-arch sprouting, an ex vivo explant assay, the same peptide also matched the parent at around 50 nM.[1] That is an explant measure, not a ranking for any applied purpose. A synthetic peptide with that sequence was compared with Thymosin Beta-4 in an aged-mouse dermal wound model.[3] Results are reported for each compound in that model. A 2006 study compared Thymosin Beta-4 with its residues 17 to 23 for metalloproteinase induction, in a system its abstract does not name.[9] A 2007 study compared the parent with a peptide spanning the same residues for mediator release from mast cells.[10] Neither abstract states whether its 17 to 23 form was N-terminally acetylated, as TB-500 is. No comparison of TB-500 with Thymosin Beta-4 found in PubMed (searched October 2026).[4] That search covers PubMed only.
Read more on each compound
TB-500
Frequently Asked Questions
Is TB-500 the same as Thymosin Beta-4?+−
TB-500 is not the same molecule as Thymosin Beta-4: it is a seven-residue peptide corresponding to residues 17 to 23 of the 43-residue parent. In a 2026 briefing document, the FDA stated that the two are not the same substance. Most published research associated with TB-500 used the full peptide, not the fragment.
Does research on Thymosin Beta-4 apply to TB-500?+−
Evidence generated with Thymosin Beta-4 should not be assumed to transfer to TB-500, or the reverse. None of the clinical evidence reviewed for Thymosin Beta-4 was generated with the fragment.
References
- 1Philp D, Huff T, Gho YS, Hannappel E, Kleinman HK. The actin binding site on thymosin beta4 promotes angiogenesis. FASEB J. 2003;17(14):2103-2105. PMID 14500546
- 2Goldstein AL, Hannappel E, Kleinman HK. Thymosin beta4: actin-sequestering protein moonlights to repair injured tissues. Trends Mol Med. 2005;11(9):421-429. PMID 16099219
- 3Philp D, Badamchian M, Scheremeta B, Nguyen M, Goldstein AL, Kleinman HK. Thymosin beta 4 and a synthetic peptide containing its actin-binding domain promote dermal wound repair in db/db diabetic mice and in aged mice. Wound Repair Regen. 2003;11(1):19-24. PMID 12581423.
- 4PubMed search via NCBI E-utilities, run 3 October 2026; records entered to 2 October 2026. Query: ("TB-500"[tiab] OR "TB500"[tiab] OR "TB 500"[tiab] OR "LKKTETQ"[tiab] OR "Ac-LKKTETQ"[tiab] OR "fragment 17-23"[tiab] OR "17-23 fragment"[tiab] OR "(17-23)"[tiab]) AND ("thymosin beta-4"[tiab] OR "thymosin beta 4"[tiab] OR "thymosin beta4"[tiab] OR "thymosin β4"[tiab] OR "Tβ4"[tiab] OR "Tbeta4"[tiab] OR "timbetasin"[tiab]) AND ("1800/01/01"[edat] : "2026/10/02"[edat]). 15 records; none was a direct comparison of TB-500 with Thymosin Beta-4.
- 5FDA Briefing Document, Pharmacy Compounding Advisory Committee meeting, 23-24 July 2026, memo dated 2026-05-15. FDA evaluation of TB-500 (free base) and TB-500 acetate. fda.gov
- 6Esposito S, Deventer K, Goeman J, Van der Eycken J, Van Eenoo P. Synthesis and characterization of the N-terminal acetylated 17-23 fragment of thymosin beta 4 identified in TB-500, a product suspected to possess doping potential. Drug Test Anal. 2012;4(9):733-738. PMID 22962027.
- 7Van Troys M, Dewitte D, Goethals M, Carlier MF, Vandekerckhove J, Ampe C. The actin binding site of thymosin beta 4 mapped by mutational analysis. EMBO J. 1996;15(2):201-210. PMID 8617195.
- 8Sosne G, Qiu P, Goldstein AL, Wheater M. Biological activities of thymosin beta4 defined by active sites in short peptide sequences. FASEB J. 2010;24(7):2144-2151. PMID 20179146.
- 9Philp D, Scheremeta B, Sibliss K, Zhou M, Fine EL, Nguyen M, Wahl L, Hoffman MP, Kleinman HK. Thymosin beta4 promotes matrix metalloproteinase expression during wound repair. J Cell Physiol. 2006;208(1):195-200. PMID 16607611.
- 10Wyczółkowska J, Walczak-Drzewiecka A, Wagner W, Dastych J. Thymosin beta4 and thymosin beta4-derived peptides induce mast cell exocytosis. Peptides. 2007;28(4):752-759. PMID 17289217.