Research overview
TB-500 is a trade name, not a scientific one, and it is used for two different materials. Anti-doping laboratories found that the original veterinary product sold as TB-500 contained Ac-LKKTETQ, a synthetic copy of residues 17 to 23 of thymosin beta-4 with an acetyl group added at the start (Esposito et al., Drug Test Anal 2012). Some suppliers use the name for synthetic full-length thymosin beta-4, a 43-amino-acid actin-binding protein found in nearly all cells, which this listing is named after. Check the product specifications for the sequence supplied.
Thymosin beta-4 itself has been tested in people by drug developers, in safety studies, phase 2 trials for skin ulcers and phase 2 and 3 trials for eye surface conditions, with mixed results. In a 72-person dry eye trial neither main measure differed from placebo (Sosne et al., Clin Ophthalmol 2015), and in an 18-person phase 3 trial in a corneal condition the difference on the main measure was not statistically clear. TB-500 as sold has no published human trials; its evidence is cell and animal work and doping-control studies. An analysis of products sold online as TB500 found contents did not consistently match their labels. Long-term safety and human relevance are not known. Supplied for laboratory research use only.
Mechanism of action
Thymosin beta-4 is the main protein that binds single actin units (G-actin) inside cells and holds them in reserve, which controls how quickly actin filaments, the scaffolding cells use to move and change shape, are built. Its central actin-binding site is residues 17 to 23 (LKKTETQ), the sequence in the original TB-500 product; in cell assays this short sequence matched the whole protein in tests of endothelial cell migration and blood-vessel sprouting (Philp et al., 2003). Other parts of the protein, such as the starting piece Ac-SDKP, have separate activities in cell and animal studies. This evidence comes from cell and animal work, not people.
