A synthetic fragment of a protein found throughout the body. Research began with the question of what that protein was doing there.
TB-500
TB-500 is a synthetic peptide corresponding to the actin-binding region of thymosin beta-4, a naturally occurring 43-amino-acid protein and the most abundant beta-thymosin in the human body. Thymosin beta-4 is present in essentially every nucleated cell type and circulates in plasma at measurable concentrations. The two are frequently discussed together, but they are not the same molecule: the full-length protein carries the complete sequence, while TB-500 carries only the actin-binding motif.
The best-characterised biochemical role of thymosin beta-4 is the regulation of actin, the cytoskeletal protein cells use to change shape and migrate, by sequestering monomeric G-actin. X-ray crystallography resolved the one-to-one complex with actin, making this one of the more firmly established mechanisms among compounds in this category. Most of the wider literature follows from that single mechanism.
Thymosin beta-4 was isolated and characterised from the 1960s onward, with sustained contributions from multiple independent research groups through the 1990s and 2000s. Cell and animal models have examined roles in cell migration, angiogenesis and tissue remodelling. The distinction matters when reading the literature: the great majority of published work concerns the full-length protein rather than the fragment, and the systemic regenerative research remains largely preclinical.
Thymosin beta-4 and its derivatives, including TB-500, appear on the World Anti-Doping Agency Prohibited List and have done since 2012. Anyone subject to anti-doping testing should treat that as disqualifying.