TB-500 (Thymosin Beta-4) Research
What is TB-500?
TB-500 is a synthetic form of thymosin beta-4 (TB4), an endogenous human peptide that is made of 43 amino acids and can be found in virtually all cells of the body, especially in platelets and white blood cells [1]. TB4 was first isolated in 1981 by Low and Goldstein from bovine thymus gland extract [2].
The synthetic version, TB-500, has not been approved for human use and is available solely as a research chemical. It was first manufactured in the early 2010s for veterinary use. TB-500 has been used as a doping agent in horse racing and consecutively banned for providing an unfair advantage in that sport [3, 4].
Thymosin beta-4 and its derivatives, including TB-500, are likewise banned by the World Anti-Doping Agency (WADA) and thus prohibited for use by competitive athletes subject to the WADA Code and comparable national and regional regulatory bodies [5].
TB-500 is nonetheless under active research for its potential effects on cell migration and tissue repair, formation of new blood vessels, maturation of stem cells, survival of various cell types, and anti-inflammatory action [1, 6].
TB-500 and thymosin beta-4 have poor oral bioavailability, and thus can only be administered via injections in experimental settings.
Yet, a naturally occurring fragment of thymosin beta-4, called N-acetyl seryl-aspartyl-lysyl-proline (Ac-SDKP), is an orally active peptide thought to possess similar antifibrotic, anti-inflammatory, angiogenic properties, and effects on cell migration and survival [7, 8].
It has been investigated as an inhibitor of hematopoietic stem cell proliferation and a chemoprotective agent [9, 10]. Researchers may find the TB-500 fragment included in innovativeTB-500 capsule formulas intended for tissue repair and recovery.
What Does TB-500 Do?
The mechanisms of action of TB-500 are still under investigation, but scientists already have some insight into the workings of its natural counterpart, thymosin beta-4.
Thymosin beta-4 appears to work as an actin-binding protein that inhibits the polymerization of globular actin (G-actin) into filamentous actin (F-actin) [11, 12]. The process is called actin sequestration and results in upregulated G-actin levels [13].
Actin is a major component of the cellular cytoskeleton that provides structural support to cells and is involved in various cellular processes, including cell motility. Thymosin beta-4 appears to bind with actin primarily (but not only) via its central actin-binding domain (aa 17-23), also known as Ac-LKKTETQ [14].
The prevention of F-actin polymerization by thymosin beta-4 alters the cellular cytoskeleton, which affects the ability of cells to move and change shape. This process has implications for various physiological and pathological processes where cell motility is crucial, such as wound healing, tissue regeneration, and cancer metastasis [15].
In addition, thymosin beta-4 can be found outside of cells (extracellularly) in blood plasma or in wound fluid. Research in blood vessel cells suggests that the application of extracellular thymosin beta-4 may also regulate processes such as cell motility and angiogenesis. It was found to act extracellularly by interacting with cell surface-located ATP synthase enzymes, cellular enzymes involved in the energy production of the cell [16, 17].
Extracellular thymosin beta-4 may also get oxidized in sites of inflammation to thymosin beta-4 sulfoxide, and the latter is thought to have potent anti-inflammatory properties [18].
Thymosin beta-4 may likewise reduce inflammation by increasing the expression of microRNA-146a (miR-146a), thought to decrease the expression of two pro-inflammatory cytokines called L-1 receptor-associated kinase 1 (IRAK1) and tumor necrosis factor receptor-associated factor 6 (TRAF6) [19].
TB-500 for Wound Healing
Due to its potential effects on cell migration, TB-500 has been proposed to facilitate the mobilization and differentiation of progenitor cells, which may speed up the healing of wounds in various tissues, including the skin, blood vessels, and cornea.
Among the few trials conducted in human subjects was a double-blind, placebo-controlled, dose-escalation study involving 73 patients with venous stasis ulcers given local thymosin beta-4 for 84 days.
The trial was conducted across eight European sites, and upon analysis of the results, the researchers reported that the peptide was safe and well-tolerated, with a placebo-comparable safety profile.
Efficacy results from this phase-2 study suggest that a topically administered thymosin beta-4 dose of 0.03% has the potential to accelerate wound healing, having achieved complete wound healing within three months in approximately 25% of patients. It was further reported to decrease the median time to healing by 45% among those whose wounds completely closed [20].
Another phase-2 study examined the effect of thymosin beta-4 as an ophthalmic solution in 72 subjects with moderate to severe dry eye receiving either 0.1% TB4 or a placebo for 28 days.
Damage to the eye cornea related to the dry eye syndrome was measured via corneal staining. The results showed significant improvements in central and superior corneal staining, while no side effects were reported [21].
Similarly, a 56-day phase-2 clinical trial included nine patients with severe dry eye who were treated with either thymosin beta-4 ophthalmic solution or placebo for 28 days, followed by a 28-day follow-up.
At day 56, the six patients taking thymosin beta-4 demonstrated a 35.1% reduction in ocular discomfort compared to a 59.1% reduction in total corneal fluorescein staining compared to the control group [22].
A trial by the same researchers also reported that thymosin beta-4 as an ophthalmic solution was applied to nine patients with chronic nonhealing neurotrophic corneal ulcers and reported that amongst six of the patients who had geographic corneal defects, there was significant healing without neovascularization [23].
1.Goldstein, A. L., Hannappel, E., Sosne, G., & Kleinman, H. K. (2012). Thymosin β4: a multi-functional regenerative peptide. Basic properties and clinical applications. Expert opinion on biological therapy, 12(1), 37–51. https://doi.org/10.1517/14712598.2012.634793
2.Low, T. L., Hu, S. K., & Goldstein, A. L. (1981). Complete amino acid sequence of bovine thymosin beta-4: a thymic hormone that induces terminal deoxynucleotidyl transferase activity in thymocyte populations. Proceedings of the National Academy of Sciences of the United States of America, 78(2), 1162–1166. https://doi.org/10.1073/pnas.78.2.1162
3.Ho, E. N., Kwok, W. H., Lau, M. Y., Wong, A. S., Wan, T. S., Lam, K. K., Schiff, P. J., & Stewart, B. D. (2012). Doping control analysis of TB-500, a synthetic version of an active region of thymosin β₄, in equine urine and plasma by liquid chromatography-mass spectrometry. Journal of chromatography. A, 1265, 57–69. https://doi.org/10.1016/j.chroma.2012.09.043
4.Kwok, W. H., Ho, E. N., Lau, M. Y., Leung, G. N., Wong, A. S., & Wan, T. S. (2013). Doping control analysis of seven bioactive peptides in horse plasma by liquid chromatography-mass spectrometry. Analytical and bioanalytical chemistry, 405(8), 2595–2606. https://doi.org/10.1007/s00216-012-6697-9
5.World Anti-Doping Agency. World Anti-Doping Code International Standard Prohibited List 2022. WADA website. January 1, 2022. Accessed June 2023. https://www.wada-ama.org/sites/default/files/resources/files/2022list_final_en.pdf
