TB-500

Overview

TB-500 is a synthetic N-acetylated heptapeptide (Ac-LKKTETQ) corresponding to amino acids 17–23 of thymosin β4, the actin-binding region of the native 43-residue protein. Despite widespread vendor labeling, TB-500 is NOT identical to full-length thymosin β4 (Tβ4); it is a short 7-amino-acid fragment. It is sold as a research chemical, is not FDA-approved for any human indication, and is banned by WADA.

Mechanism of Action

Native thymosin β4 is the principal G-actin–sequestering peptide in mammalian cells, regulating cytoskeletal dynamics and cell migration. Preclinically Tβ4 promotes endothelial and epithelial cell migration, angiogenesis, ILK/Akt survival signaling, and downregulation of pro-inflammatory cytokines. The TB-500 fragment retains the actin-binding motif, but whether it fully reproduces Tβ4's activity in humans has not been established.

Research Summary

Animal studies of full-length Tβ4 show accelerated dermal wound reepithelialization, increased angiogenesis, improved cardiac function after ischemic injury, and corneal healing. The short Ac-LKKTETQ peptide sold as TB-500 was characterized analytically in the anti-doping literature as a substance with suspected doping potential; controlled human efficacy trials of injected TB-500 do not exist. Full-length synthetic Tβ4 (RGN-259, RegeneRx/HLB Therapeutics) has been evaluated in Phase II/III ophthalmic trials for dry eye disease and neurotrophic keratopathy with mixed results (one Phase III NK trial met healing endpoints, a later European Phase III missed its primary endpoint).

Dosing Information

Reported Side Effects

• Injection site reactions
• Headache and lethargy reported anecdotally
• Theoretical risk of promoting growth of occult tumors via angiogenesis and cell migration (not established in humans)
• Unknown long-term safety profile in humans

Labs to monitor before & during your TB-500 protocol

These biomarkers are commonly tracked to assess response and safety. Run baseline labs before starting, mid-cycle labs halfway through, and post-cycle labs 1–2 weeks after the final dose.

Commonly Stacked With

Research References

• Malinda KM, et al. Thymosin beta4 accelerates wound healing. FASEB J / J Invest Dermatol. 1999. PMID 10469335.
• Bock-Marquette I, et al. Thymosin beta4 activates ILK and promotes cardiac cell migration, survival and repair. Nature. 2004;432(7016):466-472. PMID 15565145.
• Sosne G, Kleinman HK. Primary mechanisms of thymosin β4 repair activity in dry eye disorders and other tissue injuries. 2015. PMID 26241398.
• Esposito S, et al. Synthesis and characterization of the N-terminal acetylated 17-23 fragment of thymosin beta 4 identified in TB-500. 2012. PMID 22962027.