TB-500 fragment 17-13 10mg

▎TB-500 fragment(17-13) Structure

▎TB-500 fragment(17-13) Research

Molecular Background

TB-500 fragment (17–23) is an N-terminally acetylated heptapeptide with the sequence Ac-LKKTETQ, corresponding to residues 17–23 of thymosin beta-4 (Tβ4). PubChem lists TB-500 under CID 62707662, with the molecular formula C38H68N10O14 and a molecular weight of approximately 889.0 g/mol. This seven-amino-acid fragment is chemically distinct from full-length Tβ4, which contains 43 amino acids.[6]

Research Progress

Khandoker Asiqur Rahaman and colleagues developed a UHPLC-Q-Exactive Orbitrap MS/MS method for the simultaneous analysis of TB-500 (Ac-LKKTETQ) and its metabolites in in vitro systems and rat urine. Diabetes was examined in human serum, enzyme preparations, and samples from rats exposed to TB-500, while fibroblast assays were used to compare cytotoxicity and wound-closure responses. The authors identified Ac-LK as the major early metabolite and Ac-LKK as a metabolite detectable for a longer period. No cytotoxicity was reported for the parent peptide or the tested metabolites under the assay conditions. In the wound-closure experiment, the parent TB-500 did not show a significant difference from control, whereas Ac-LKKTE did.[2]

Fig1. Chromatographic identification of TB-500 and its metabolites using authentic synthetic standards in the cited analytical study.[2]

In a subsequent study, Khandoker Asiqur Rahaman and colleagues further examined Ac-LK, the major metabolite generated from TB-500 in their metabolic studies. The investigators compared TB-500 and Ac-LK using SARS-CoV-2 main-protease assays, endothelial-cell uptake and functional assays, proteomic analysis, and a mouse wound model. Under the experimental conditions, Ac-LK showed stronger Mpro inhibition than the parent peptide and differences in endothelial-cell migration, barrier-related measurements, hypoxia/reoxygenation-associated responses, proteomic pathways, and wound measurements. The authors proposed that formation of Ac-LK may contribute to some biological responses associated with TB-500, while also noting that further studies using metabolically stable analogues or selective inhibition of peptide degradation would be required for definitive validation of the proposed peptide-prodrug mechanism.[1]

Fig2. Identification of Ac-LK as a major metabolite generated from TB-500 in the cited study.[1]
The source figure shows the structures and molecular masses of acetylated TB-500 (Ac-LKKTETQ) and non-acetylated LKKTETQ, LC-MS/MS measurements after cellular incubation, the reported metabolite series, and characterization of Ac-LK. Complete analytical conditions are reported in the original publication.[1]

Janina Wyczółkowska and colleagues investigated full-length thymosin beta-4 and several Tβ4-derived peptides in murine peritoneal mast cells and the human HMC-1 mast-cell line. The authors reported concentration-dependent mediator release after exposure to Tβ4 and observed that peptides corresponding to Tβ4 residues 16–38 and 17–23 also produced mediator release under the conditions tested. Their findings suggested involvement of the LKKTET actin-binding motif in the mast-cell response. The 17–23 peptide in this study was a Tβ4-derived sequence and the publication did not establish equivalence between that material and the N-terminally acetylated TB-500 form Ac-LKKTETQ.[3]

Fig3. Mast-cell exocytosis measurements reported after exposure to full-length Tβ4 and Tβ4-derived peptides in the cited study.[3]
The source figure compares β-hexosaminidase release from HMC-1 cells exposed to Tβ4, AcSDKP, Tβ4 residues 16–38, tuftsin, and the Tβ4 17–23 peptide. Statistical methods and complete experimental conditions are reported in the original publication.[3]

Simone Esposito and colleagues reported the detection and identification of the N-terminally acetylated 17–23 fragment of human thymosin beta-4 (Ac-LKKTETQ) in a TB-500 sample using high-resolution mass spectrometry coupled with liquid chromatography. The same fragment was synthesized by solid-phase peptide synthesis, and the authors proposed an analytical strategy for detecting Ac-LKKTETQ in plasma and urine using liquid chromatography coupled with triple-quadrupole mass spectrometry. This work was an analytical identification study and did not evaluate clinical efficacy or safety.[4]

Pan D. Y. and colleagues reviewed published work concerning TB-500 and Tβ4-related fragments, including animal studies examining hair-follicle and hair-growth-related endpoints. Because this publication is a secondary review and the cited experiments involve different Tβ4-derived materials and animal models, these observations should not be treated as direct independent evidence for Ac-LKKTETQ itself.[5]

Research Limitations

Direct biological evidence for the N-terminally acetylated TB-500 fragment Ac-LKKTETQ remains limited. The 2024 metabolism study found that the parent TB-500 did not produce a significant wound-closure response in the fibroblast assay, whereas the metabolite Ac-LKKTE did.[2] The 2026 study focused substantially on Ac-LK, another metabolite, and the authors described the proposed peptide-prodrug mechanism as requiring additional mechanistic validation.[1] Results obtained with full-length Tβ4, non-acetylated LKKTETQ, other Tβ4-derived fragments, or individual metabolites should therefore not be treated as interchangeable with Ac-LKKTETQ.

FDA currently lists thymosin beta-4 fragment (LKKTETQ), also known as TB-500, among bulk substances for which compounded products may present significant safety risks. FDA notes potential immunogenicity concerns for certain routes because of aggregation and peptide-related impurities and states that it has not identified human exposure data for drug products containing the thymosin beta-4 fragment.[7] These regulatory observations do not characterize a COCER Peptides laboratory research material, but they limit any extrapolation of the preclinical and analytical literature to human use.

COCER Peptides presents TB-500 fragment (17–23) solely for laboratory research and analytical use. It is not intended for human or veterinary use. This material is not an FDA-approved drug product. The research described above summarizes findings reported in third-party publications and is not a statement of clinical efficacy, safety, diagnosis, treatment, prevention, or an instruction for use.

▎Relevant Citations

References

[1] Rahaman K A, Mukim M S I, Hasan M L, et al. Functional Characterization of N-acetyl-l-Leucyl-l-Lysine Supports a Peptide Prodrug Mechanism for TB-500[J]. Biomaterials Research, 2026,30:0418.

DOI:10.34133/bmr.0418.

[2] Rahaman K A, Muresan A R, Min H, et al. Simultaneous quantification of TB-500 and its metabolites in in-vitro experiments and rats by UHPLC-Q-Exactive orbitrap MS/MS and their screening by wound healing activities in-vitro[J]. Journal of Chromatography B, 2024,1235:124033.

DOI:10.1016/j.jchromb.2024.124033.

[3] Wyczółkowska J, Walczak-Drzewiecka A, Wagner W, et al. Thymosin beta4 and thymosin beta4-derived peptides induce mast cell exocytosis[J]. Peptides, 2007,28(4):752-759.

DOI:10.1016/j.peptides.2007.01.004.

[4] Esposito S, Deventer K, Goeman J, et al. 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[J]. Drug Testing and Analysis, 2012,4(9):733-738.

DOI:https://doi.org/10.1002/dta.1402.

[5] Pan D Y, Xu L Y, Li E M. Post-translational modification of TB-500 and its functional regulation[J]. Chemistry of Life, 2021,41(4):734-740.

DOI:10.13488/j.smhx.20200532.

[6] NCBI PubChem. TB-500. PubChem CID 62707662.

[7] U.S. Food and Drug Administration. Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks: Thymosin beta-4, fragment (LKKTETQ), also known as TB-500.

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