BPC-157 vs TB-500

BPC-157

BPC-157 is a synthetic 15-residue peptide whose sequence was taken from a larger protein reported in human gastric juice. That parent protein, named body protection compound, is described mainly in the papers of the group that reported it, and the peptide is known almost entirely through its own studies. Most published work comes from that single research group and is in rodents, covering models of tendon, ligament, muscle and bone injury, lesions of the stomach and intestine, and some nervous-system models. Human data are very limited, consisting of a few small reports rather than controlled trials. Independent replication outside the originating group is limited.

TB-500

TB-500 is a synthetic seven-residue peptide, Ac-LKKTETQ, matching residues 17 to 23 of the 43-residue actin-binding protein thymosin β4. The stretch it copies lies in the central actin-binding region of thymosin β4; the N-terminal acetyl cap is a synthetic addition, since that position is internal in the native protein. The name is sometimes applied loosely to full-length thymosin β4, and the two should be kept apart: they differ in length, in mass (about 0.9 kDa against about 5 kDa) and in which parts of the parent protein they contain. Most published research concerns the full-length protein, examined in cell culture and in rodent models of skin, cardiac and corneal injury. Work on the fragment alone is far thinner, and it cannot be assumed to share the properties described for the whole protein.

How BPC-157 acts

No receptor for BPC-157 has been identified. Rodent and cell studies have reported changes in several signalling systems, most often the nitric oxide system, VEGF receptor 2 signalling in endothelial cells, and the FAK–paxillin pathway in cultured tendon fibroblasts. Other papers describe interactions with dopamine and serotonin systems in animal models. Several studies have also examined growth-factor and early-response gene expression in injured tissue. Because many of these findings come from a small number of laboratories, using different models, the mechanism is best regarded as unsettled rather than as a known pathway.

How TB-500 acts

Full-length thymosin β4 binds monomeric G-actin in a one-to-one complex and is a major actin-sequestering protein in many cell types, holding actin in unpolymerised form. Structural studies place the LKKTET motif, shared with the WH2 family of actin-binding domains, at the centre of that contact, flanked by N-terminal and C-terminal segments that also touch actin. A small number of cell studies have reported that the isolated fragment affects endothelial cell migration, but how closely it reproduces the actin binding of the whole protein is not well established. Other activities attributed to thymosin β4 map elsewhere: the N-terminal tetrapeptide Ac-SDKP is released by enzymatic cleavage and has been studied separately.

The records side by side

• Type: BPC-157, Pentadecapeptide; TB-500, Heptapeptide (thymosin β4 fragment)
• Length: BPC-157, 15 amino acids; TB-500, 7 amino acids
• Molecular weight: BPC-157, 1419.5 g/mol; TB-500, 889.0 g/mol
• Molecular formula: BPC-157, C62H98N16O22; TB-500, C38H68N10O14

Reading a comparison

A comparison places two records side by side; it does not merge them. Each description above is drawn from that compound's own record, and the two were not necessarily characterised by the same methods, at the same time, or to the same level of detail. Before comparing any attribute, it is worth establishing that both records describe the substance you think they describe — names are not identifiers, and two entries sharing a name can differ in salt form, stereochemistry or the convention used to state a mass. Where a figure carries no method beside it, the comparison is between two reported numbers rather than between two measurements.