TB-500 (Thymosin Beta-4) — Research Product Overview

**Disclaimer:** This product overview is provided strictly for in-vitro and preclinical research use. [TB-500](/catalog/tb-500) is not approved by the FDA for human use, is not a drug, food, or cosmetic, and nothing in this document constitutes medical advice or a recommendation for human administration. Materials are sold to qualified research professionals for laboratory investigation only.

Overview

TB-500 is the synthetic research designation most commonly applied to thymosin beta-4 (Tβ4), a 43-amino-acid peptide originally isolated from calf thymus tissue by Allan Goldstein and colleagues at George Washington University in the 1960s. Tβ4 is one of the most abundant intracellular peptides in mammalian cells, present at especially high concentrations in platelets, wound fluid, and developing cardiac tissue. Its dual role as a G-actin sequestering protein and an extracellular signaling molecule for cell migration, angiogenesis, and anti-inflammatory responses has made it a sustained focus of regenerative-medicine research. Compared to most regenerative peptides — including the closely studied BPC-157 — Tβ4's sustained intracellular presence at micromolar concentrations across nearly every tissue makes its biology unusually well-anchored in baseline physiology rather than in pharmacological perturbation.

Some commercial preparations marketed as "TB-500" correspond to a short fragment containing the actin-binding motif (around residues 17–23, sequence LKKTETQ) rather than the full 43-amino-acid peptide; researchers should always confirm with the COA which sequence has been supplied.

Sequence and Structural Notes

• Full Tβ4 sequence (43 aa): Ac-SDKPDMAEIEKFDKSKLKKTETQEKNPLPSKETIEQEKQAGES
• Single-letter code: SDKPDMAEIEKFDKSKLKKTETQEKNPLPSKETIEQEKQAGES
• Molecular weight: ~4963 Da (acetylated form; ~4921 Da non-acetylated)
• N-terminus: acetylated (native modification)
• Actin-binding domain: central residues 17–23, core motif LKKTETQ
• Secondary structure: largely intrinsically disordered in solution; adopts partial α-helical structure upon actin binding

The native peptide is acetylated at its N-terminus, which is essential for stability and for several extracellular activities. Researchers comparing acetylated full-length material against shorter "actin-binding fragment" preparations should expect different solubility, half-life, and bioactivity profiles.

Mechanism of Action (Summary)

1. G-actin sequestration — binds monomeric actin 1:1 (Kd ~0.7 µM), maintaining the unpolymerized pool available for rapid cytoskeletal reorganization.
2. ILK / Akt signaling — extracellular Tβ4 activates integrin-linked kinase, which in turn activates Akt/PKB to drive cell survival, migration, and proliferation.
3. Pro-angiogenic activity — promotes endothelial migration, tube formation, and VEGF/MMP upregulation.
4. Epicardial progenitor reactivation — in adult cardiac tissue, Tβ4 induces epithelial-to-mesenchymal transition of quiescent epicardial cells, generating Wt1+/Tbx18+ progenitors.
5. Anti-inflammatory effects — reduces NF-κB nuclear translocation and decreases IL-1β, TNF-α, and IL-8 production in injured tissue.

Preclinical Research Summary

Bock-Marquette et al. (2004, *Nature*) showed that intraperitoneal Tβ4 after experimental myocardial infarction in mice improved left-ventricular ejection fraction, reduced cardiomyocyte apoptosis, and increased peri-infarct vascularity. Smart et al. (2007, *Nature*) extended this work by demonstrating reactivation of adult epicardial progenitor cells. Sosne and colleagues have published extensively on corneal wound healing, demonstrating accelerated re-epithelialization and reduced inflammation. Malinda et al. (1999) demonstrated accelerated dermal wound healing in aged mice. RegeneRx Biopharmaceuticals has advanced Tβ4 (designated RGN-259) into clinical trials for several ophthalmic indications.

Comparator Peptides and Molecules

The most natural comparator for TB-500 is BPC-157. Although both peptides are routinely co-prescribed in research stacks, their mechanisms diverge sharply: BPC-157 is a 15-mer pentadecapeptide that engages migration through the FAK-paxillin axis and angiogenesis through VEGF/eNOS signaling, while Tβ4 is a 43-mer intrinsically disordered peptide whose primary intracellular function is G-actin sequestration (Kd ~0.7 µM) and whose extracellular activity propagates through ILK/Akt and a separate pro-angiogenic cascade involving MMPs and endothelial progenitor mobilization. The detailed contrast is treated in the BPC-157 vs TB-500 comparison article and in the broader BPC-157 vs TB-500 overview.

Within the thymosin family itself, TB-500 (Tβ4) shares the WLVK actin-binding motif with thymosin β-10 and β-15, which are similarly intrinsically disordered but expressed in different tissues — Tβ10 in developing brain, Tβ15 in tumor cell lines associated with metastatic phenotypes. Sosne's corneal-injury work has occasionally compared Tβ4 to substance P and to PEDF as ocular regenerative comparators. Researchers exploring multi-mechanism repair stacks should also consult the BPC-157/TB-500 blend overview and the contrasting matrix-remodeling profile of GHK-Cu. For broader signaling context, Tβ4's extracellular activity sits at the intersection of the growth-hormone axis and integrin-linked kinase pathways relevant to many regenerative peptides.

Deeper Preclinical Breakdown

Bock-Marquette et al. 2004 (*Nature* 432, PMID 15378064) used a permanent LAD-ligation mouse MI model. Tβ4 was administered as an intracardiac injection (400 µg) immediately after coronary occlusion plus systemic IP injection (150 µg) every other day. At 4 weeks, treated animals showed approximately 60% improvement in cardiac function by ejection fraction, reduced infarct scar size, and significantly increased numbers of epicardium-derived cells in the peri-infarct zone. Mechanistic follow-up demonstrated ILK activation as the proximal signaling event upstream of Akt phosphorylation. Limitations include the supraphysiological dosing relative to endogenous tissue levels and the lack of dose-response characterization in the original paper.

Smart et al. 2007 (*Nature* 445, PMID 17581592) extended the cardiac repair story by examining adult epicardial progenitors. Mice received Tβ4 by intraperitoneal injection at 150 µg every other day for 7 days, after which Wt1+/Tbx18+ epicardial cells were profiled. The treatment reactivated an embryonic-like epicardial program, generating progenitors capable of differentiation into endothelial and smooth muscle lineages. The study introduced the now-canonical concept that Tβ4 can re-engage developmental progenitor programs in adult tissue, an idea that has propagated into spinal cord, retinal, and dermal regeneration work.

Goldstein 2012 (*Annals NY Acad Sci* 1269, "Thymosin β4: a multi-functional regenerative peptide") consolidated the dermal, corneal, cardiac, and CNS work into a coherent multi-system framework, and remains the standard reference review. Sosne's 2016 *FEBS Letters* corneal series demonstrated reduced PMN infiltration and MMP-9 normalization at 0.1% topical Tβ4 in alkali-burn rabbit eyes; this work supports the clinical-stage RGN-259 ophthalmic program. The principal limitation across these studies is the difficulty of measuring intracellular versus extracellular Tβ4 pools separately — most assays cannot distinguish administered material from the large endogenous reservoir.

Formulation Considerations

TB-500 is supplied as a lyophilized powder, typically 2 mg or 5 mg per vial, produced by either solid-phase synthesis (yielding the 43-mer) or by chemical synthesis of the actin-binding fragment (residues 17–23, LKKTETQ). Researchers should always confirm the supplied sequence against the COA, since fragment and full-length material differ substantially in solubility, half-life, and bioactivity. Native Tβ4 is acetylated at the N-terminus, and this modification should be verified by mass spectrometry on the COA.

Reconstitution typically uses bacteriostatic water for injection (0.9% benzyl alcohol). The peptide is highly water-soluble due to its intrinsic disorder and high concentration of charged residues, but harsh acidic buffers can hydrolyze the long backbone and should be avoided. Lyophilized stability is at least 24 months at -20 °C; reconstituted stability is shorter than for BPC-157 (7–14 days at 2–8 °C). Common impurities visible on a COA include des-acetyl species at the N-terminus, oxidized methionine variants, and truncation fragments from incomplete coupling. For protocol depth see the peptide reconstitution guide, peptide storage stability, and peptide solubility guide.

Research-Context Dosing Ranges

In rodent cardiac models, intraperitoneal doses of 150–400 µg per mouse (approximately 6–16 mg/kg) every other day have been used. Corneal-injury studies have used 0.1% topical drops applied multiple times daily. In-vitro endothelial tube formation and migration assays typically use 100 ng/mL to 10 µg/mL Tβ4. Equine veterinary research has used parenteral doses on the order of 2–4 mg per animal weekly. No human dosing is implied or recommended. The peptide is on the WADA prohibited list 2026 for sport contexts.

Common Research Applications

• In-vitro endothelial tube-formation and Boyden chamber migration assays
• Rodent corneal alkali-burn and dry-eye models
• LAD-ligation myocardial infarction models in mice and rats
• Dermal punch-biopsy and excisional wound models, particularly in aged or diabetic animals
• Comparative tissue-repair studies versus BPC-157 — see BPC-157 vs TB-500

Handling, Reconstitution, and Storage

• Form supplied: white lyophilized powder, typically 2 mg or 5 mg per vial
• Reconstitution: bacteriostatic water for injection or sterile water; the peptide is highly water-soluble
• Working concentration: 0.5–2 mg/mL typical for cell-culture work
• Lyophilized stability: ≥24 months at -20 °C, desiccated and protected from light
• Reconstituted stability: up to 14 days at 2–8 °C; aliquot and store at -20 °C or -80 °C for longer term
• Avoid: repeated freeze-thaw cycles; full-length Tβ4 is more freeze-thaw sensitive than the short BPC-157 peptide

See the peptide reconstitution guide for detailed protocol.

Lab Specifications

• [HPLC](/research/glossary#hplc) purity target: ≥98.0% by RP-HPLC at 220 nm
• Identity confirmation: ESI-MS or MALDI-TOF, observed mass within ±2 Da of theoretical
• Acetate content: <15% w/w
• Endotoxin: <1 EU/mg for cell-culture grade
• N-terminal acetylation: confirmed by mass spectrometry (full-length only)
• Water content: <8% by Karl Fischer

For COA interpretation see how to read a peptide COA and understanding peptide purity.

Cross-References

Related Viking Labs research:

• BPC-157 vs TB-500 comparison
• Product overview: BPC-157
• Product overview: BPC/TB blend
• Product overview: GHK-Cu
• Peptides longevity research 2026
• Research peptide buying guide

Summary

Thymosin beta-4 occupies a unique niche in the regenerative peptide landscape because of its dual intracellular and extracellular functions. The cardiac repair literature, particularly the demonstrations of epicardial progenitor reactivation, remains among the most provocative in regenerative medicine. Researchers should pay careful attention to whether their material represents the full 43-amino-acid acetylated peptide or a shorter actin-binding fragment, because biological activity, pharmacokinetics, and dose-response characteristics differ substantially.

*This document is provided for research and educational purposes only. Viking Labs does not sell products intended for human consumption.*