TB-500 10 mg

The name TB-500 does not resolve to a single molecule, and this page says so rather than picking one. Two chemically distinct materials are sold under it. One is full-length thymosin β4, a 43-residue N-acetylated peptide with a formula of C212H350N56O78S and an average mass near 4963.5 g/mol, registered as CAS 77591-33-4 in its free form and CAS 1346423-89-9 as the acetate salt. The other is the N-acetylated 17-23 fragment, Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln, CAS 885340-08-9, formula C38H68N10O14, average mass near 889.0 g/mol. The two differ by more than five-fold in mass. Janoshik report 222317 identifies the tested sample as TB-500 (TB-4). The report image does not state a sequence, salt form or CAS number; those specifications remain unconfirmed here for the material offered. A sample report does not establish the contents of every vial.

The independent evidence on the name leans toward the fragment. The Global Substance Registration System operated by the United States FDA and NCATS registers TB-500 as a substance in its own right, UNII QHK6Z47GTG, CAS 885340-08-9, with the subunit sequence LKKTETQ, and files the 43-residue peptide under separate records: timbetasin, the international nonproprietary name for the synthetic peptide, UNII 2D5MRE3SSY, CAS 77591-33-4; timbetasin acetate, UNII 945CRJ0XZ0, CAS 1346423-89-9; and native human thymosin β4 carrying its phosphorylation and lysine acetylation, UNII 549LM7U24W, CAS 77642-24-1. Esposito and colleagues analysed a commercial TB-500 formulation by high-performance liquid chromatography coupled to high-resolution Orbitrap mass spectrometry and identified the heptapeptide Ac-LKKTETQ in it (Drug Testing and Analysis, 2012). Some suppliers nonetheless ship the full-length peptide under the same name, which is why identity here is a matter for the certificate of analysis rather than for the product title.

The parent molecule is well characterised. Thymosin β4 is encoded in humans by the TMSB4X gene, UniProt P62328. The translated 44-residue product loses its initiator methionine and the exposed serine at position 2 is acetylated, giving the mature N-terminal sequence Ac-Ser-Asp-Lys-Pro across 43 residues. Safer, Elzinga and Nachmias describe it as an acidic, heat-stable 5 kDa peptide (Journal of Biological Chemistry, 1991), and Philp and colleagues describe it as the most abundant member of the β-thymosin family in mammalian tissue (FASEB Journal, 2003). The chain contains a single methionine, which accounts for the sole sulfur atom in its molecular formula, and no cysteine, so it carries no disulfide bridges. Residues 17 to 23 of the mature chain are LKKTETQ, the actin-binding motif, and that stretch is the fragment from which the smaller material is taken. Material of this type is prepared by solid-phase peptide synthesis or by recombinant expression, then purified by reversed-phase chromatography and lyophilised. Supplied lyophilised for laboratory research use only. Not for human or veterinary consumption.

The biochemical starting point is actin binding. Safer, Elzinga and Nachmias reported that at least 50 percent of the actin in resting human platelets is unpolymerised and that the bulk of it is complexed with a heat-stable, acidic 5 kDa peptide, which they sequenced and found indistinguishable from thymosin β4. In their assays the purified peptide bound stoichiometrically to muscle G-actin, forming a complex identifiable by nondenaturing polyacrylamide gel electrophoresis, and formation of that complex inhibited salt-induced polymerisation of G-actin (Journal of Biological Chemistry, 1991;266(7):4029-4032). This is the property from which the term actin-sequestering derives. Every study summarised below used the full-length 43-residue peptide unless stated otherwise.

Philp and colleagues is the study that links the full-length peptide to the heptapeptide sold under the same TB-500 name. Using naturally occurring thymosin β4, proteolytic fragments and synthetic peptides, they reported that the full-length peptide and the seven amino acid actin-binding motif displayed near-identical activity at approximately 50 nM in human umbilical vein endothelial cell migration assays and in chick aortic arch vessel-sprouting assays, while peptides lacking any portion of the motif were inactive. Adhesion to thymosin β4 was blocked by the seven amino acid peptide, and the adhesion and sprouting activity was inhibited by the addition of 5 to 50 nM soluble actin (FASEB Journal, 2003;17(14):2103-2105).

In dermal models, Malinda and colleagues used a rat full-thickness wound model and reported that reepithelialisation increased by 42 percent over saline controls at 4 days and by as much as 61 percent at 7 days after wounding, with treated wounds contracting at least 11 percent more than controls by day 7. In the same paper, keratinocyte migration in a Boyden chamber assay was stimulated 2 to 3-fold over medium alone after 4 to 5 hours, with as little as 10 pg of peptide added to the assay (Journal of Investigative Dermatology, 1999;113(3):364-368).

A separate strand of work concerns cardiac tissue. Bock-Marquette and colleagues reported that the peptide promoted myocardial and endothelial cell migration in the embryonic heart and retained that property in postnatal cardiomyocytes, and that it formed a functional complex with PINCH and integrin-linked kinase resulting in activation of Akt. Following coronary artery ligation in mice, the authors reported upregulation of integrin-linked kinase and Akt activity in the heart, enhanced early myocyte survival and improved cardiac function (Nature, 2004;432(7016):466-472).

Published human studies concern pharmaceutical formulations of full-length thymosin β4, not the research material offered here. Ruff and colleagues reported an early safety and pharmacokinetic study (2010); Sosne and Ousler reported an ophthalmic study that did not meet its primary endpoints (2015). These studies do not establish the safety, efficacy, dosing or suitability of this product for use in humans or animals. The original references are provided below for evaluation of the research context.