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TB-500

Also identified as Ac-LKKTETQ, Thymosin β4 fragment, Tβ4 17-23

Acetylated thymosin beta-4 fragment (Ac-LKKTETQ)

Sequence: Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln

Molecular weight
889
Molecular formula
C38H68N10O14
CAS
885340-08-9
Published studies reviewed
4

FOR RESEARCH USE ONLY. NOT FOR HUMAN OR VETERINARY USE. NOT FOR HUMAN CONSUMPTION.

Compounds described on this site are supplied solely for laboratory research. They are not offered for human or veterinary use or for clinical use, and they are not intended to diagnose, mitigate, cure or prevent any disease.

TB-500 is the acetylated seven-residue fragment Ac-LKKTETQ, corresponding to positions 17 to 23 of thymosin beta-4; it is not the full-length 43-residue peptide, whose studies are kept on a separate page. Of the four publications reviewed, three come from drug-testing laboratories that identified the fragment in TB-500 preparations and tracked it and its breakdown products in horses and rats, and the fourth is a cell study of the actin-binding motif whose abstract does not say whether its peptide was acetylated. No human study of the fragment was found, and whether full-length findings apply to it is not established.

At a glance

Also identified as
Ac-LKKTETQ, Thymosin β4 fragment, Tβ4 17-23
Class
Acetylated thymosin beta-4 fragment (Ac-LKKTETQ)
Target or mechanism
Actin (the thymosin beta-4 actin-binding site, residues 17 to 23)
Evidence types represented
in vitro, animal
Published studies reviewed
4
Last reviewed
2026-09-21

Overview

TB-500 is an acetylated seven-residue fragment, Ac-LKKTETQ, taken from the 43-residue peptide thymosin beta-4. The seven residues correspond to positions 17 to 23 of that peptide.

It is not thymosin beta-4. The two have different registry numbers, different molecular formulas and different masses, and the published human studies of the full-length peptide are recorded on its own page, not here. Whether a finding about the full-length peptide applies to this fragment is an open question that nothing published establishes, which is why the two records are kept apart.

Most of what has been published on this exact material is analytical. Three of the four publications below come from drug-testing laboratories: they identified Ac-LKKTETQ in supplied TB-500 preparations, measured it and its breakdown products in horses and in rats, and set out how it is detected. The fourth is a laboratory study of the seven-residue actin-binding motif itself, and it carries an identity flag — its abstract does not state whether the peptide it used was acetylated.

No human study of this fragment is recorded here, because this project found none.

Mechanism under investigation

TB-500
  • Actin (the thymosin beta-4 actin-binding site, residues 17 to 23)

One analytical publication describes the segment LKKTETQ as the actin-binding site within thymosin beta-4. One laboratory study of that seven-residue motif reports it as essential for the parent peptide's angiogenic activity in cell and vessel-sprouting assays — but that study's material is flagged here, because its abstract does not state whether the peptide was acetylated, and acetylation is what distinguishes this material. No publication recorded here establishes what the acetylated fragment does in a living animal.

Scope of the published work

Areas investigated
  • Structural identification in supplied preparations
  • Doping-control detection
  • Metabolism
  • Endothelial cell migration and vessel sprouting in vitro
Models used
  • Mass-spectrometric analysis of preparations
  • Equine urine and plasma
  • Rat metabolism study
  • Human serum and enzyme incubations
  • Endothelial cell and chick aortic-arch assays

Every figure on this page was recorded in an analytical, animal or cell-based study, using material prepared for that study. It is not the research material PepGenex supplies and no result here transfers to it, or to a person.

Limitations

Evidence represented on this page: in vitro and animal. No human research is represented. The page reviews 4 published studies, and each figure is reported for the study that published it; results are not pooled across studies. 1 of these publications carries a note on whether it studied this exact material.

Common questions

What is TB-500?

TB-500 is an acetylated seven-residue fragment, Ac-LKKTETQ, taken from the 43-residue peptide thymosin beta-4.

How does TB-500 work, according to the published research?

One analytical publication describes the segment LKKTETQ as the actin-binding site within thymosin beta-4. One laboratory study of that seven-residue motif reports it as essential for the parent peptide's angiogenic activity in cell and vessel-sprouting assays — but that study's material is flagged here, because its abstract does not state whether the peptide was acetylated, and acetylation is what distinguishes this material. No publication recorded here establishes what the acetylated fragment does in a living animal.

  • Using naturally occurring thymosin beta-4, proteolytic fragments and synthetic peptides, reports that a seven-amino-acid actin-binding motif of thymosin beta-4 is essential for the parent peptide's angiogenic activity. (Philp et al., 2003, PMID 14500546)

What has published research on TB-500 found, and what are its limits?

This page records 4 publications, reporting laboratory (in vitro) work in 4, animal work in 2. Each is listed with its identifier under References.

No human study is represented on this page.

Evidence represented on this page: in vitro and animal.

No human research is represented.

The page reviews 4 published studies, and each figure is reported for the study that published it; results are not pooled across studies.

1 of these publications carries a note on whether it studied this exact material.

Every figure on this page was recorded in an analytical, animal or cell-based study, using material prepared for that study. It is not the research material PepGenex supplies and no result here transfers to it, or to a person.

Is TB-500 approved by the U.S. FDA?

This page cites no FDA approval record for TB-500; PepGenex Science states a U.S. regulatory status only where a sourced record exists.

PepGenex research materials are not FDA approved and are not for human or veterinary use.

What risks have published studies of TB-500 reported?

No human study is recorded on this page, so it reports no adverse events in people. Laboratory and animal findings are not a measure of risk in people.

Published research

Grouped by the kind of study. Select one to narrow what is shown below.

Laboratory (in vitro)(2)

Laboratory (in vitro)

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.

Esposito S, Deventer K, Goeman J, Van der Eycken J, Van Eenoo P., Drug Testing and Analysis, 2012;4(9):733-738

published

  • Reports the detection and identification of the N-terminal acetylated 17-23 fragment of human thymosin beta-4 — Ac-LKKTETQ — in the formulation TB-500, by high-performance liquid chromatography with high-resolution mass spectrometry on an Orbitrap Exactive instrument.
  • Ac-LKKTETQ was also prepared by solid-phase peptide synthesis, and an analytical strategy was proposed for its detection in plasma and urine by liquid chromatography with low-resolution triple-quadrupole mass spectrometry.
Context

What the published work on this exact material establishes is chemical: which peptide is in a TB-500 preparation, how it is detected, and what it breaks down into in horses, rats and serum. Those are real findings, and they are not findings about what the fragment does in a body.

View publication →
Laboratory (in vitro)

The actin binding site on thymosin beta4 promotes angiogenesis.

Philp D, Huff T, Gho YS, Hannappel E, Kleinman HK., FASEB Journal, 2003;17(14):2103-2105

published

Material identity not established. This study used a seven-residue actin-binding motif of thymosin beta-4 alongside the full-length peptide and proteolytic fragments. Its abstract does not state whether that synthetic peptide was acetylated at the N-terminus — and N-terminal acetylation is precisely what distinguishes TB-500 from the bare motif. Whether the material studied here is this material is therefore not established.

  • Using naturally occurring thymosin beta-4, proteolytic fragments and synthetic peptides, reports that a seven-amino-acid actin-binding motif of thymosin beta-4 is essential for the parent peptide's angiogenic activity.
  • In migration assays with human umbilical vein endothelial cells and vessel-sprouting assays using chick aortic arches, thymosin beta-4 and the actin-binding motif displayed near-identical activity at about 50 nM, whereas peptides lacking any portion of the actin motif were inactive. Adhesion to thymosin beta-4 was blocked by the seven-amino-acid peptide, and the adhesion and sprouting activity of thymosin beta-4 was inhibited by 5 to 50 nM soluble actin.
Limitations

The laboratory study of the actin-binding motif is flagged for identity: its abstract does not say whether the peptide it used was acetylated, and acetylation is what makes this material what it is. Separately, the large body of work on full-length thymosin beta-4 is about a 43-residue peptide, not this seven-residue one, and is recorded on that peptide's own page.

View publication →

Preclinical (animal)(2)

Laboratory (in vitro)Preclinical (animal)

Rahaman et al., 2024 (title withheld on this site; see the publication record)

Rahaman KA, Muresan AR, Min H, Son J, Han HS, Kang MJ, Kwon OS., Journal of Chromatography B, 2024;1235:124033

published

Metabolism of TB-500 was studied in human serum, in several in-vitro enzyme systems, and in urine from rats given TB-500, with simultaneous quantification of the parent peptide and its metabolites by UHPLC-Q-Exactive orbitrap mass spectrometry. The biological activity of the metabolites was compared with that of the parent in fibroblasts, using cytotoxicity and scratch (cell-migration) assays.

  • Ac-LK was the primary metabolite, present at the highest concentration in rats over the 0-to-6-hour interval, and Ac-LKK was a longer-lasting metabolite, detected up to 72 hours.
  • No cytotoxicity was found for the parent peptide or its metabolites. In the fibroblast scratch (cell-migration) assay, only the metabolite Ac-LKKTE differed significantly from the control — the parent compound did not. The authors state that the biological effects of TB-500 itself have not been documented, and that activity attributed to it in the literature may instead be due to the metabolite Ac-LKKTE.
Limitations

The one publication that compared the parent peptide against its own breakdown products in a cell assay found the parent did not separate from the control; a shorter metabolite did. The authors' own conclusion is that activity reported for this compound may belong to that metabolite rather than to the compound.

View publication →
Laboratory (in vitro)Preclinical (animal)

Doping control analysis of TB-500, a synthetic version of an active region of thymosin β₄, in equine urine and plasma by liquid chromatography-mass spectrometry.

Ho EN, Kwok WH, Lau MY, Wong AS, Wan TS, Lam KK, Schiff PJ, Stewart BD., Journal of Chromatography A, 2012;1265:57-69

published

  • States that the key ingredient of the veterinary preparation TB-500 is the peptide LKKTETQ with artificial acetylation of the N-terminus, and that the segment at positions 17 to 23 is the active site within thymosin beta-4 responsible for actin binding.
  • A method was developed for the simultaneous detection of N-acetylated LKKTETQ and its metabolites in equine urine and plasma. The parent peptide could be detected and confirmed at 0.02 ng/mL in equine plasma and 0.01 ng/mL in equine urine.
  • The method confirmed the presence of N-acetylated LKKTETQ and its metabolites in urine and plasma collected from horses after a single dose of TB-500. The authors state this is, to their knowledge, the first identification of TB-500 and its metabolites in samples collected from horses afterwards.
Context

What the published work on this exact material establishes is chemical: which peptide is in a TB-500 preparation, how it is detected, and what it breaks down into in horses, rats and serum. Those are real findings, and they are not findings about what the fragment does in a body.

View publication →

Compared with related compounds

Classification, structure, recorded targets, evidence types and FDA status only, each read from the two compounds' own pages. These comparisons do not compare study results.

TB-500 and Thymosin beta-4

Parent and fragment: TB-500 is a seven-residue acetylated fragment of the 43-residue thymosin beta-4. They are different molecules.

TB-500Thymosin beta-4
ClassificationAcetylated thymosin beta-4 fragment (Ac-LKKTETQ)43-residue actin-binding peptide
StructureSequence Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln; formula C38H68N10O14Not recorded on its page
Targets recordedActin (the thymosin beta-4 actin-binding site, residues 17 to 23)G-actin (actin monomers)
Evidence types representedin vitro, animalin vitro, human
Status with the U.S. FDANot shown (no Drugs@FDA application record verified for this page)Not shown (no Drugs@FDA application record verified for this page)

References

Published studies reviewed (4)

  1. 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. — Esposito S, Deventer K, Goeman J, Van der Eycken J, Van Eenoo P., Drug Testing and Analysis, 2012;4(9):733-738
    DOI 10.1002/dta.1402 · PMID 22962027
  2. Doping control analysis of TB-500, a synthetic version of an active region of thymosin β₄, in equine urine and plasma by liquid chromatography-mass spectrometry. — Ho EN, Kwok WH, Lau MY, Wong AS, Wan TS, Lam KK, Schiff PJ, Stewart BD., Journal of Chromatography A, 2012;1265:57-69
    DOI 10.1016/j.chroma.2012.09.043 · PMID 23084823
  3. Rahaman et al., 2024 (title withheld on this site; see the publication record) — Rahaman KA, Muresan AR, Min H, Son J, Han HS, Kang MJ, Kwon OS., Journal of Chromatography B, 2024;1235:124033
    DOI 10.1016/j.jchromb.2024.124033 · PMID 38382158
  4. The actin binding site on thymosin beta4 promotes angiogenesis. — Philp D, Huff T, Gho YS, Hannappel E, Kleinman HK., FASEB Journal, 2003;17(14):2103-2105
    DOI 10.1096/fj.03-0121fje · PMID 14500546

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