An approach for identifying in silico peptides against authentic metabolites: in vitro characterization of thymosin β4 metabolites

Purpose: Thymosin β4 is a highly active protein that exerts multiple biological activities such as tissue repair, anti-inflammation, and cell maturation. Thymosin β4 has also been listed as a prohibited drug by the World Anti-doping Agency (WADA). Based on its biological activities, thymosin β4 has a high potential of abuse for the performance enhancement among athletes. This study aimed to investigate and characterize the metabolism of thymosin β4 in vitro system. Methods: TB4 protein was metabolized in six different enzyme–buffer systems in vitro. After TB4 was metabolized with an appropriate buffer system, the resulting metabolites were detected by high resolution LC–MS/MS. The mass spectrum data of the observed metabolites were characterized in silico, and confirmed the structures based on synthesized authentic standards. Results: Total 13 new metabolites, some of which were detected in more than one enzyme system, were found. This study characterized all of the detected metabolites according to their in silico m/z ions and compared our findings with synthesized standards. Finally, metabolites M1, M5, M7, M11, M12, and M13 were confirmed based on their synthesized authentic standards. Conclusion: By using an approach for metabolizing a protein to detect, characterize and identify new peptide metabolites, 6 metabolites are identified among 13 expected potential metabolites. Newly detected metabolites may have the potential for biological activities after further screening compared to their parent protein.