Traumatic brain injury (TBI) remains a leading cause of mortality and morbidity worldwide. No effective pharmacological treatments are available for TBI because all Phase II/III TBI clinical trials have failed. This highlights a compelling need to develop effective treatments for TBI. Endogenous neurorestoration occurs in the brain after TBI, including angiogenesis, neurogenesis, synaptogenesis, oligodendrogenesis and axonal remodeling, which may be associated with spontaneous functional recovery after TBI. However, the endogenous neurorestoration following TBI is limited. Treatments amplifying these neurorestorative processes may promote functional recovery after TBI. Thymosin beta4 (Tβ4) is the major G-actin-sequestering molecule in eukaryotic cells. In addition, Tβ4 has other properties including anti-apoptosis and anti-inflammation, promotion of angiogenesis, wound healing, stem/progenitor cell differentiation, and cell migration and survival, which provide the scientific foundation for the corneal, dermal, and cardiac wound repair multicenter clinical trials. Here, we describe Tβ4 as a neuroprotective and neurorestorative candidate for treatment of TBI.
Recently, therapeutic biomolecules such as growth factors provide great potential as an alternative therapeutic approach to traditional periodontal wound healing . However, because of the short half-lives of growth factors and polynucleotides in the body and the necessity to deliver to specific target sites, those medicinal substances do not always exhibit the anticipated therapeutic potency and outcomes . Thus, optimized delivery regimes and well-defined release kinetics appear to be logical prerequisites for safe and efficacious clinical application of biomolecules. For considering the application of Tβ4 in clinical trials, target cells of exogenous Tβ4 should be restricted to cells in the periodontal tissue.
Despite this, Tβ4’s place on the banned-substances list is warranted. It reflects the possibility that the effects of the supplement may manifest as a tangible improvement in athletes. However, any time a journalist flippantly declares it “heals damaged tissue and speeds recovery”, it should be noted that such claims are a harmful distortion of the facts.
Johansson, A., Westberg, L., Sandnabba, K., Jern, P., Salo, B., & Santtila, P. (2012). Associations between oxytocin receptor gene (OXTR) polymorphisms and self-reported aggressive behavior and anger: Interactions with alcohol consumption [Abstract]. Psychoneuroendocrinology 37(9), 1546-56. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/22421562
It was also shown recently that delivery of Fgfs by release from peptide nanofibers, a gradual local delivery system, can increase neovascularization and reduce in-farct size in the ischemic rodent heart (Engel et al., 2006). Related to this, zebrafish have a natural ability to synthesize Fgfs after myocardial injury, a signal that appears to recruit Fgf receptor-expressing epicardial-derived cells toward regenerating muscle (Lepilina et al., 2006). Thus, what has been and what will be discovered about zebrafish heart regeneration is quite likely to illuminate possible strategies for enhancing regeneration in the mammalian heart (see Chapter 14.4).
Friedman, J., Roze, E., Abdenur, J. E., Chang, R., Gasperini, S., Saletti, V., Wali, G. M., Eiroa, H., Neville, B., Felice, A., Parascandalo, R., Zafeiriou, D. I., Arrabal-Fernandez, L., Dill, P., Eichler, F. S., Echenne, B., Gutierrez-Solana, L. G., Hoffmann, G. F., Hyland, K., Kusmierska, K., Tijssen, M. A., Lutz, T., Mazzuca, M., Penzien, J., Poll-The BT, Sykut-Cegielska, J., Szymanska, K., Thony, B., and Blau, N. Sepiapterin reductase deficiency: a treatable mimic of cerebral palsy. Ann Neurol. 2012;71(4):520-530. View abstract.
For this study, one of us, Ben Trumble, followed Tsimane men as they went hunting for food. Typically, Tsimane men set out alone or with a partner in the early morning and search in the forest for prey such as wild pigs, deer, monkeys, or the rare tapir. Following long looping trails they might be gone for eight or nine hours, traveling about six miles (ten kilometers). Ben collected saliva samples throughout the hunt in order to measure changes in men’s hormone levels.
Tβ4 is the major monomeric actin-sequestering peptide in human tissues, and can bind globular actin (G-actin) in a 1:1 ratio and consequently involved in cytoskeletal regulation by inhibiting the polymerization of G-actin into fibrous actin (F-actin) . In addition, Tβ4 is an ubiquitous naturally occurring molecule and is found at concentrations of 1 × 10−5 to 5.6 × 10−1 M in a variety of tissues and cell types, yet, no receptors for the protein have been identified . A recent study suggests that internalization of exogenous Tβ4 is essential for its subsequent cellular functions . Moreover, Tβ4 has been shown to be associated with, wound healing, hair growth, immunomodulation, and angiogenesis [7–9].
The first study to show that Tβ4-promoted tissue repair was a dermal study performed in rats (Malinda et al., 1999). It had previously been found to promote angiogenesis and was reported to be high in platelets (Grant et al., 1995; Hannappel & van Kampen, 1987; Malinda, Goldstein, & Kleinman, 1997; Philp, Huff, Gho, Hannappel, & Kleinman, 2003). Since platelets are the first cells to enter a wound, it was clear that Tβ4 should be tested in dermal wounds in an animal model (Malinda et al., 1997, 1999; Philp, Badamchian, et al., 2003). In the first dermal study using 8 mm full-thickness punch wounds in rats, Tβ4 at 5 μg/50 μL of phosphate-buffered saline was found to accelerate wound closure, increase angiogenesis, and accelerate collagen deposition (Malinda et al., 1999). Tβ4 was only applied at the time of injury and at 48 h since after that the crust had formed. Visible macroscopic improvement was seen in the treated group by day 4. The study also found that Tβ4 promoted keratinocyte migration in vitro with activity in the picogram range. The findings were confirmed in various additional animal models (Table 1) and led to the clinical trials for hard to heal wound in patients as detailed in Table 2.
Such tissue-regenerating properties of thymosin β4 may ultimately contribute to repair of human heart muscle damaged by heart disease and heart attack. In mice, administration of thymosin β4 has been shown to stimulate formation of new heart muscle cells from otherwise inactive precursor cells present in the outer lining of adult hearts, to induce migration of these cells into heart muscle and recruit new blood vessels within the muscle.
5-HTP is decarboxylated to serotonin (5-hydroxytryptamine or 5-HT) by the enzyme aromatic-L-amino-acid decarboxylase with the help of vitamin B6. This reaction occurs both in nervous tissue and in the liver. 5-HTP crosses the blood–brain barrier, while 5-HT does not. Excess 5-HTP, especially when administered with vitamin B6, is thought to be metabolized and excreted.