Research overview
"TB-500 Fragment" is a trade name, not a scientific one. It most likely means Ac-LKKTETQ, a synthetic seven-amino-acid peptide copying residues 17 to 23 of thymosin beta-4 (the protein's central actin-binding site) with an acetyl group added at the start. This is the sequence anti-doping laboratories identified in the original veterinary product called TB-500. However, other pieces of the 43-amino-acid protein are also called thymosin beta-4 fragments, such as Ac-SDKP (residues 1 to 4) and the end piece AGES, and each has its own research. Check the product specifications for the sequence supplied.
For LKKTETQ, the evidence is from cells and animals. In endothelial cell migration and blood-vessel sprouting assays it matched full-length thymosin beta-4 (Philp et al., FASEB J 2003), and in a study of skin wounds in aged mice it gave results similar to the full protein. Doping-control studies have traced how the acetylated peptide is broken down in horses and rats; in a fibroblast scratch test, its breakdown product Ac-LKKTE showed activity while the parent peptide did not (Rahaman et al., 2024). No human studies have been published, and its stability, safety and human relevance are not known. Supplied for laboratory research use only.
Mechanism of action
Ac-LKKTETQ copies the central actin-binding site of thymosin beta-4 (residues 17 to 23). In the full protein, this site helps hold single actin units in reserve, which controls the building of actin filaments that cells use to move and change shape. In cell studies the seven-amino-acid peptide matched the full protein in tests of endothelial cell migration and blood-vessel sprouting, and it blocked cells from sticking to thymosin beta-4 (Philp et al., 2003), but whether the short peptide binds actin inside cells in the same way has not been established. Evidence comes from cell and mouse studies only.
