Published · Updated · 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 in the laboratory. |
| 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. | Not FDA approved in any formulation. No marketing application for it was identified in the sponsor filings and FDA databases reviewed for it. 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. The literature reviewed for Thymosin Beta-4 reports no serious safety finding from its published human studies. 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. The literature reviewed for TB-500 reports no human safety data.
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
- 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.
- 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.
Related comparisons
BPC-157 vs TB-500
BPC-157 is a 15-residue peptide and TB-500 a seven-residue fragment of Thymosin Beta-4: two different molecules.
Read ComparisonBPC-157 vs Thymosin Beta-4
BPC-157 is a 15-residue peptide and Thymosin Beta-4 a 43-residue member of the beta-thymosin family: two different molecules.
Read ComparisonTB-500 vs Thymosin Alpha-1
TB-500 is a seven-residue fragment of Thymosin Beta-4 and Thymosin Alpha-1 a separate 28-residue peptide: two different molecules.
Read Comparison