TB-500

Research · TB-500

Overview

TB-500 designates a synthetic, N-terminally acetylated seven-residue sequence, Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln (Ac-LKKTETQ), corresponding to residues 17-23 of thymosin beta-4, a 43-residue actin-sequestering protein abundant in platelets and most nucleated cells. The name originated in veterinary products, and analytical work has confirmed Ac-LKKTETQ as their principal constituent. The term is sometimes applied loosely to full-length thymosin beta-4, so identity should be confirmed analytically by mass spectrometry. Most mechanistic and clinical literature describes the full-length protein rather than the fragment, a distinction relevant when interpreting data.

Mechanism of action

The 17-23 region lies within the central actin-binding motif of thymosin beta-4, which binds monomeric G-actin in a 1:1 complex and regulates the cellular pool available for filament assembly, influencing cell migration. Full-length thymosin beta-4 also reportedly engages integrin-linked kinase and Akt signaling and is the precursor of Ac-SDKP, an N-terminal four-residue fragment released by protease cleavage with anti-fibrotic activity. Because Ac-SDKP derives from residues 1-4, it cannot be generated from TB-500; whether the isolated fragment reproduces the full protein's signaling activity has not been established.

Key research findings

1. 01

   Full-length thymosin beta-4 has been characterized in preclinical cardiac, corneal, dermal, and renal injury models and in early-phase clinical studies of ophthalmic formulations.

2. 02

   Doping-control laboratories have synthesized Ac-LKKTETQ and developed liquid chromatography-mass spectrometry methods to detect it and its metabolites in equine and human matrices.

3. 03

   In vitro and rat studies have characterized the fragment's metabolic products, and a 2026 rat Achilles tendon study reported histological and biomechanical endpoints.

4. 04

   Controlled human data specific to the fragment are absent, and it is listed on the World Anti-Doping Agency prohibited list.

Published references

• 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 et al. — J Chromatogr A, 2012 · PMID: 23084823

• 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 et al. — Drug Test Anal, 2012 · PMID: 22962027

The information above is derived from published preclinical and clinical research. It is provided for educational purposes only and does not constitute medical advice, diagnosis, or treatment recommendations.