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TB-500

TB-500 (Thymosin Beta-4): An Actin-Sequestering Peptide Studied in Tissue Repair

Research summary. Thymosin beta-4 (TB-500) is a 43-amino-acid peptide present in essentially all mammalian cells, where it is the most abundant member of the beta-thymosin family. Its primary biochemical function is sequestration of monomeric G-actin — TB-500 maintains a large pool of unpolymerised actin available for rapid cytoskeletal reorganisation. This actin-sequestering function underlies its reported roles in cell migration, wound healing, angiogenesis, and tissue regeneration. The "TB-500" preparation supplied for research is structurally identical to or closely matches endogenous thymosin beta-4 and is widely studied across cardiac, dermal, ocular, and musculoskeletal tissue-repair models. WADA prohibits TB-500 in competitive sport.

Molecular profile

  • Sequence: Ac-Ser-Asp-Lys-Pro-Asp-Met-Ala-Glu-Ile-Glu-Lys-Phe-Asp-Lys-Ser-Lys-Leu-Lys-Lys-Thr-Glu-Thr-Gln-Glu-Lys-Asn-Pro-Leu-Pro-Ser-Lys-Glu-Thr-Ile-Glu-Gln-Glu-Lys-Gln-Ala-Gly-Glu-Ser
  • Molecular formula: C₂₁₂H₃₅₀N₅₆O₇₈S
  • Molecular weight: ~4963.4 g/mol
  • PubChem CID: 16132341
  • Class: Beta-thymosin family; actin-sequestering peptide
  • Synonyms: Thymosin beta-4; TMSB4X gene product; TB-500
  • WADA status: Prohibited substance under the World Anti-Doping Agency Code (S2 class)

Mechanism of action

TB-500's biological activity is grounded in actin-cytoskeleton biology and downstream tissue-remodelling pathways:

  • G-actin sequestration. The N-terminal region of TB-500 binds monomeric (G-)actin in a 1:1 stoichiometry, maintaining a sequestered pool that buffers against premature polymerisation. This pool is rapidly mobilised during cell migration and cytoskeletal remodelling.
  • Promotion of cell migration. By regulating the G-actin / F-actin balance, TB-500 supports cell migration in fibroblasts, endothelial cells, keratinocytes, and cardiac progenitors.
  • Angiogenesis. Reported across multiple models; the underlying mechanism involves both direct effects on endothelial-cell migration and modulation of pro-angiogenic gene expression.
  • Anti-inflammatory and antioxidant effects. Reported reductions in inflammatory cytokine expression and reductions in oxidative-stress markers in injured tissue.
  • N-terminal AcSDKP fragment. Proteolytic cleavage of TB-500 releases the tetrapeptide N-acetyl-Ser-Asp-Lys-Pro (AcSDKP), itself biologically active as a haematopoietic-stem-cell-modulating and anti-fibrotic peptide.

Preclinical and clinical research highlights

Cardiac repair. Foundational rodent post-infarction work (Bock-Marquette et al., Nature 2004) reported that TB-500 administration after myocardial infarction reduced cardiomyocyte apoptosis, supported epicardial-progenitor migration to injury sites, and improved cardiac function relative to vehicle controls. Subsequent work has extended these observations across multiple cardiac-injury models.

Dermal wound healing. Multiple rodent studies have reported accelerated wound closure, reduced scarring, increased angiogenesis, and increased keratinocyte and fibroblast migration in TB-500-treated wounds.

Ocular surface healing. Topical TB-500 (RGN-259) has been evaluated in dry-eye disease and corneal-injury models, with reported acceleration of corneal-epithelial healing.

Musculoskeletal injury. Rodent muscle-injury and tendon-injury studies have reported faster recovery and improved tissue-architecture endpoints with TB-500 administration.

Human safety and tolerance. A Phase 1 human study (Ruff et al., 2010) reported intravenous TB-500 administration up to high cumulative doses without dose-related toxicity, supporting subsequent indication-specific clinical work.

Limited human efficacy data. Despite extensive preclinical literature, TB-500 has not achieved FDA approval for any indication.

Current research status

TB-500 / thymosin beta-4 is an investigational research peptide. It is not approved by the FDA for any indication. It is prohibited under the WADA Code for use in competitive sport.

For research-supplier contexts, TB-500 is supplied as a research-grade investigational peptide and is not intended for self-administration.

Key takeaways for researchers

  • TB-500 / thymosin beta-4 is a 43-amino-acid actin-sequestering peptide present in essentially all mammalian cells.
  • The mechanism centres on G-actin sequestration and cytoskeletal-remodelling support, with downstream effects on cell migration, angiogenesis, and tissue repair.
  • Reported preclinical effects include accelerated cardiac, dermal, ocular, and musculoskeletal-tissue repair.
  • TB-500 is not FDA-approved and is prohibited by WADA in competitive sport.
  • The proteolytic fragment AcSDKP is itself biologically active and contributes to some reported TB-500 effects.

References

  1. Bock-Marquette I, Saxena A, White MD, Dimaio JM, Srivastava D. Thymosin beta4 activates integrin-linked kinase and promotes cardiac cell migration, survival and cardiac repair. Nature. 2004;432(7016):466–472.
  2. Goldstein AL, Hannappel E, Sosne G, Kleinman HK. Thymosin β4: a multi-functional regenerative peptide. Basic properties and clinical applications. Expert Opin Biol Ther. 2012;12(1):37–51.

This article is provided for educational and research purposes only. TB-500 / thymosin beta-4 is a research peptide. It is not an approved drug or therapeutic agent and is not intended for human consumption, diagnosis, treatment, cure, or prevention of any disease or condition. TB-500 is prohibited by the World Anti-Doping Agency in competitive sport. All work involving this peptide should be conducted by qualified personnel within an appropriate research setting and in compliance with applicable institutional and regulatory requirements.

TB-500 | BonesLabs