What Is TB-500 (Thymosin Beta 4)?



TB-500 (a.k.a. thymosin beta-4 or TB-4) is a naturally occurring protein in the human body just like modified GRF 1-29. TB-500 is 43 amino acids in length and plays a critical role in the polymerization of actin, a filament found in most cells and on that is particularly important in muscle cells. TB-500 is currently being investigated for its potential role in reversing liver fibrosis and for its anti-aging effects.


How Does TB-500 Work?


Research suggests that TB-500 is an actin-binding protein. Actin is a primary constitute of the scaffolding (called microfilaments) that gives cells their shape and helps them to maintain the integrity of their membranes. It is also a major component of muscle sarcomeres where it provides the scaffolding against which another protein, myosin, acts. Without actin, there could be no muscle contraction.


Though the exact effects of TB-500 are not perfectly clear, it appears that TB-500 sequesters free actin and holds it within the cell, preventing it from being degraded or lost. TB-500 readily releases actin during polymerization, however. Polymerization is the process by which actin monomers are join to form actin polymers (microfilaments). Microfilaments are the functional form of actin.


TB-500 Effects


Interestingly, research indicates that thymosin beta 4 and most other thymosins play active roles in tissue regeneration. In other words, TB-500 appears to help cells recover after injury. As a result of its tissue-healing properties, TB-500 has been investigated for use in treating bed sores, skin ulcers, and severe conditions that lead to skin erosion. It has also been suggested the thymosin beta 4 may be useful in activating hepatic stellate cells, which are responsible for producing the extracellular structure of the liver. TB-500 may help to reverse or slow the course of liver fibrosis and protect against alcohol-induced liver disease by encouraging extracellular structure formation1,2 .


Thymosin beta 4 is a potent stimulator of muscle cell regrowth. Because muscle sarcomeres contain a great number of actin polymers, they benefit from having a ready supply of actin monomers with which to repair damage. Research in chicken embryos indicates that TB-500 promotes elongation of skeletal muscle cells, resulting in large muscles overall3 . It may be that thymosin beta 4 is capable of increasing muscle cell growth and repair rates.


TB-500 Summary


TB-500 is a natural protein found in the human body and in most vertebrates. Ongoing research suggests that it may be useful in encouraging tissue growth and healing. Current efforts are focusing on liver fibrosis and skeletal muscle repair. There is also some promise for the use of TB-4 in certain lung diseases.




  1. Kim, J. & Jung, Y. Potential role of thymosin Beta 4 in liver fibrosis. Int. J. Mol. Sci.16, 10624-10635 (2015).


  1. Lakshman, M. R. et al. Novel modulators of hepatosteatosis, inflammation and fibrogenesis. Hepatol. Int.8 Suppl 2, 413-420 (2014).


  1. Chankiewitz, V. et al. A thymosin beta15-like peptide promotes intersegmental myotome extension in the chicken embryo. Histochem. Cell Biol.141, 275-287 (2014).

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