TB-500

TB-500 is the synthetic acetylated fragment corresponding to residues 17-23 of thymosin beta-4 (LKKTETQ), supplied as a lyophilised powder. It is frequently conflated with full-length thymosin beta-4, a 43-residue peptide, and the two are not the same material: the literature on the full-length protein cannot be transferred to the fragment without stating that substitution explicitly. Identity of laboratory material is confirmed by mass spectrometry against the calculated mass and purity by reversed-phase HPLC with a stated gradient. Values published on this record are transcribed from the supplier specification sheet and batch certificate of analysis.

Thymosin beta-4 was isolated from thymic tissue in the 1980s and characterised as an actin-sequestering protein present in most mammalian cell types. The LKKTETQ motif was subsequently identified as the actin-binding region, and short synthetic fragments containing that motif were investigated as simplified experimental probes. The full-length protein progressed into clinical investigation for ophthalmic and dermal indications; the seven-residue fragment did not follow it into that regulatory pathway, and its record remains preclinical.

The distinction between protein and fragment shaped the evidence base in a way that persists today. Investment followed the full-length protein into formal clinical development, generating registered trials, published pharmacokinetics and regulatory-grade safety data. The fragment attracted attention through a different route, as an inexpensive synthetic material referenced in secondary sources that borrow the parent protein's clinical credentials. When reading any summary of this compound, the first question to ask is which of the two molecules the cited study actually used.

Published work centres on actin sequestration and cytoskeletal dynamics: the motif binds G-actin and modulates polymerisation in cell-free and cell-culture systems. Downstream observations in animal models include reports of altered endothelial cell migration, angiogenic sprouting in explant assays, and modified inflammatory cell profiles in injured tissue. Studies in cardiac injury models examined myocyte survival and epicardial cell activation. These are mechanistic observations in defined systems and describe assay endpoints, not established outcomes in intact organisms.

Actin binding by the LKKTETQ motif is well established biochemically and has been demonstrated across independent laboratories using structural and biophysical methods. The role of full-length thymosin beta-4 as an intracellular actin buffer is uncontroversial. Cell-migration effects in culture have been reproduced by more than one group. Analytical characterisation of the synthetic fragment is straightforward: it is short, easily resolved by HPLC and unambiguous by mass spectrometry.

Structural work on the interaction between the actin-binding motif and G-actin has been performed using crystallography and solution methods by laboratories studying cytoskeletal biology for reasons unrelated to any therapeutic claim, which makes it unusually reliable within this catalogue. The biology of the parent protein is likewise established in mainstream cell biology rather than in a niche literature.

There are no completed randomised controlled human trials of the fragment for any indication. The clinical literature that exists concerns the full-length 43-residue protein, and applying it to the seven-residue fragment is an unsupported extrapolation. Animal studies are typically small, use induced injury models, and report short follow-up. Dose-response relationships are poorly characterised, and several frequently cited effects rest on single papers that have not been independently replicated. Pharmacokinetic data for the fragment in any species are sparse, and plasma stability of a short unprotected peptide is a known limitation that much of the enthusiastic secondary literature ignores. Treat the fragment's efficacy record as preliminary.

There is also a labelling problem specific to this material. Because the full-length protein and the short fragment are marketed under overlapping names, and because some suppliers list the fragment while shipping a differently modified analogue, mass-spectrometric identity confirmation on the batch certificate is not a formality here — it is the only practical protection against receiving a different molecule from the one the literature describes. Purity figures do not address identity. A certificate that reports 99 percent purity without an identity method has established that the vial contains one predominant substance, not which substance it is.

Store the lyophilised solid as stated in the storage conditions on this record, protected from light and moisture, and equilibrate the sealed vial to ambient temperature before opening. Short peptides of this class are sensitive to repeated freeze-thaw cycles once in solution and to prolonged ambient exposure. Handling here refers to laboratory containment and analytical handling of the material as supplied; no preparation or administration procedure is provided.

Peptides of this length are straightforward to resolve chromatographically, so a supplier has no technical excuse for a certificate lacking a stated method. Where documentation for a seven-residue peptide is vague, the reasonable inference concerns the supplier's documentation practice rather than the difficulty of the analysis.

Indexed citations appear in the literature section below, each verified by PMID and linked to its PubMed record. Analytical basis for the specification values is described in testing methodology; documentation expectations for incoming batches are set out in sourcing standards. Related records are listed in the compound index.