What is TB-500 (Thymosin Beta-4)?
TB-500 is a synthetic 17–23 fragment of thymosin beta-4, a research peptide studied in animal and in vitro models of cell migration, angiogenesis and tissue repair. This page summarises the mechanism, the models used and
TB-500 is the common research name for a synthetic peptide corresponding to the 17–23 fragment of thymosin beta-4 (Tβ4), the actin-binding protein also known as TMSB4X. It is classed as a synthetic fragment peptide, not the full-length parent protein, and it is supplied for laboratory research use only. The evidence block available here does not give a sequence, molecular formula or molecular weight for the fragment, so none is stated on this page. The one identifier the evidence does provide is a registry record: a Phase 1/2 trial of TB-500 versus placebo in adults with stable atherosclerotic cardiovascular disease (ASCVD), with exploratory endpoints assessing vascular function and inflammation biomarkers [1].
The work around this fragment centres on actin sequestration and the downstream actin–cytoskeletal signalling that governs cell migration, and on the angiogenic and anti-inflammatory pathways that follow from it.
Research Studies
TB-500 and actin binding in cell-free and in vitro systems
Thymosin beta-4 is defined in the literature by its actin-binding behaviour, and the 17–23 fragment is the region most often used when that behaviour is studied in isolation. In cell-free and cultured-cell systems, the fragment has been used as a tool to probe actin monomer sequestration and the availability of actin for polymerisation. These are in vitro observations. They describe a biochemical interaction, not a physiological outcome in a living organism, and they do not by themselves establish that the same interaction produces a measurable effect when the peptide is administered to an animal or a human.
TB-500 and cell migration in cultured cells
Because actin dynamics sit directly upstream of cell motility, the fragment has been applied in in vitro migration assays — scratch-wound and transwell formats are the usual models — where the readout is the rate at which a monolayer closes or the number of cells crossing a membrane. Findings in these assays are reported for cultured cell populations, typically endothelial or fibroblast lines. The limitation is structural: a migration assay measures the behaviour of cells on plastic or on a coated membrane, and it cannot speak to migration in a whole tissue, where matrix, perfusion and immune cell populations all contribute.
TB-500 and angiogenesis in animal models
Angiogenesis — the formation of new capillary structures — is the mechanism most frequently attached to this fragment in animal work. The models used are typically rodent, with readouts such as capillary density on histological sections, tube-formation assays in cultured endothelial cells, and expression of angiogenic markers. Where an effect on vessel formation has been reported, it has been reported in animal models. Animal findings of this kind are hypothesis-generating. They do not establish that the same angiogenic response occurs in humans, and they do not establish a clinical benefit in any population.
TB-500 and tissue repair in animal models
A parallel body of animal work examines the fragment in wound and tissue-injury models, with endpoints such as time to wound closure, tensile strength of repaired tissue, and histological scoring of regeneration. These studies are conducted in rodents and, in some cases, in larger animal species. The population in which any repair effect has been observed is therefore the animal model population, not humans. Species differences in peptide clearance, receptor distribution and immune response are large enough that animal repair data cannot be read across to human outcomes.
TB-500 and inflammation markers in animal models
Several animal studies report changes in inflammatory markers — cytokine concentrations in serum or tissue homogenate, and inflammatory cell infiltration on histology — following administration of the fragment. The direction and size of these changes vary between models and between injury types. As with the angiogenesis and repair work, the observations belong to animal models, and the markers measured are surrogate endpoints rather than clinical events.
TB-500 and vascular function in adults with stable ASCVD
The only human data point in the evidence available here is a registry record for a Phase 1/2 trial of TB-500 versus placebo in adults with stable atherosclerotic cardiovascular disease [1]. The record describes the study as evaluating safety and tolerability, with exploratory endpoints assessing vascular function and inflammation biomarkers. Two features of that record matter for how the evidence should be read. First, the primary objective is safety and tolerability, not efficacy. Second, the vascular and inflammatory endpoints are labelled exploratory, which means they are not powered to support a conclusion about effect. No results are given in the evidence block, so no result is reported here.
TB-500 and the parent protein, thymosin beta-4
TB-500 is a fragment, and the distinction from full-length thymosin beta-4 is not cosmetic. The parent protein carries additional domains and a different half-life and distribution profile. Findings attributed to thymosin beta-4 in the literature cannot be assumed to apply to the 17–23 fragment, and findings attributed to the fragment cannot be assumed to apply to the parent. The table below sets out the comparison as the evidence allows it.
| Attribute | TB-500 (17–23 fragment) | Thymosin beta-4 (full-length) |
|---|---|---|
| Class | Synthetic fragment peptide | Endogenous actin-binding protein |
| Relationship | Corresponds to residues 17–23 of the parent | Parent sequence |
| Sequence, formula, molecular weight | Not given in the evidence available here | Not given in the evidence available here |
| Human trial record in this evidence block | Phase 1/2, stable ASCVD, safety and tolerability primary, exploratory vascular and inflammation biomarkers [1] | None in this evidence block |
| Evidence tier for mechanism claims | In vitro and animal models; one human safety record [1] | Not addressed by this evidence block |
TB-500 and the limits of the current evidence
Three limits apply to everything above. The mechanistic work — actin binding, migration, angiogenesis, repair, inflammation — is in vitro or animal-only, and the populations in which those effects were observed are cultured cell lines and animal models. The single human record is a safety and tolerability study with exploratory secondary endpoints, and no results from it are available in this evidence block [1]. And the fragment is not the parent protein, so the two cannot be used interchangeably when reading the literature. Anyone working with this material should treat the mechanism as established in model systems and the human picture as unresolved.
If you are reading this for personal health reasons
This material is sold for laboratory research use only, and it is not a consumer product. We do not provide dosing information, medical guidance or any recommendation about use in a person. If you are considering a compound for yourself, speak to a licensed clinician.
Sources
- [1] TB-500 (Thymosin Beta 4 17-23 Fragment) for Cardiovascular Biomarkers in Stable ASCVD — ClinicalTrials.gov