The CCI model we used causes cortical tissue loss. Traditionally, the target for neuroprotective treatment of TBI is to reduce the lesion volume.39,40 A major limitation of neuroprotection strategies is the short time window between injury and treatment. In the vast majority of preclinical TBI studies, the treatment compounds provide neuroprotection only when administered early (usually several hours after brain injury).11 The administration of a compound early in the clinical setting is not practical.41 The neuroprotective effects demonstrated in rodents may diminish if the treatment compounds are given in the clinical setting beyond the short neuroprotective window. We are able to stimulate recovery of neurological function without altering the lesion volume, which has also been demonstrated in our experimental studies of stroke,19,42,43 and is in essence, enhancement of neurorecovery.19 The extended 24-hour window for treatment which improves neurological recovery, without altering CCI cortical volume, is a major benefit of the neurorestorative therapy. Recently, we evaluated the efficacy of delayed Tβ4 treatment on spatial learning and sensorimotor functional recovery in rats after TBI induced by CCI.34 Briefly, TBI rats received Tβ4 at a dose of 6 mg/kg or a vehicle (saline) administered i.p. starting at 24 hours after injury and then every third day for 2 weeks. The dose of Tβ4 was selected based on our previous studies in animal models of stroke and EAE.25,27 Tβ4 did not alter lesion volume (14.2 ± 3.9% for saline treatment vs. 15.7 ± 3.6% for Tβ4 treatment). TBI caused neuronal cell loss in the ipsilateral CA3 and DG examined 35 days after injury compared to sham controls. Tβ4 treatment initiated 24 hours post injury significantly reduced cell loss in these two regions compared to saline controls. Tβ4-treated TBI rats showed significant improvement in spatial learning (MWM test) and sensorimotor (mNSS test) functional recovery compared to the saline-treated TBI rats.34
Treated cells were washed with PBS and cytosolic protein extracts were prepared using 1X cell lysis buffer (Santa Cruz Biotechnology, CA) supplemented with protease inhibitor cocktail. Protein concentrations were determined using the Bradford assay (Bio-Rad, CA, USA) as per the manufacturer's protocol. Aliquots of protein lysates were separated on sodium dodecyl sulfate–10% polyacrylamide gels and Western blotting was performed. The proteins were transferred onto a polyvinylidene difluoride membrane (Bio-Rad, CA, USA) in transfer buffer (20 mm Tris, 150 mm glycine, 20% methanol, pH 8.0; TBS-T) at 4°C and 100 V for 1 hour. The membrane was blocked with 5% dry milk in TBS-T for 1 hour at room temperature and incubated with primary antibodies (1:1000) and horseradish peroxidase (HRP)-conjugated secondary antibodies. Protein bands were detected using an enhanced chemiluminescence (ECL) system (Amersham Biosciences, Backinghamshire, UK).
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.
TB-500 is a synthetic fraction of the protein thymosin beta-4, which is present in virtually all human and animal cells. The main purpose of this peptide is to promote healing. It also promotes creation of new blood and muscle cells. The healing effects of TB-500 have been observed in tendons, ligaments, muscle, skin, heart, and the eyes. Thymosin beta-4 is naturally produced in higher concentration where tissue has been damaged. This peptide is also a very potent anti-inflamatory agent.
Thymosin beta 4 accelerated skin wound healing in a rat model of a full thickness wound where the epithelial layer was destroyed. When Tb4 was applied topically to the wound or injected into the animal, epithelial layer restoration in the wound was increased 42% by day four and 61% by day seven, after treatment, compared to untreated. Furthermore, Tb4 stimulated collagen deposition in the wound and angiogenesis. Tb4 accelerated keratinocyte migration, resulting in the wound contracting by more than 11%, compared to untreated wounds, to close the skin gap in the wound. An analysis of skin sections (histological observations) showed that the Tb4 treated wounds healed faster than the untreated. Proof of accelerated cell migration was also seen in vitro, where Tb4 increased keratinocyte migration two to three fold, within four to five hours after treatment, compared to untreated keratinocytes.
Beta thymosins are a family of proteins which have in common a sequence of about 40 amino acids similar to the small protein thymosin β4. They are found almost exclusively in multicellular animals. Thymosin β4 was originally obtained from the thymus in company with several other small proteins which although named collectively "thymosins" are now known to be structurally and genetically unrelated and present in many different animal tissues.
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.[40] This reaction occurs both in nervous tissue and in the liver.[41] 5-HTP crosses the blood–brain barrier,[42] while 5-HT does not. Excess 5-HTP, especially when administered with vitamin B6, is thought to be metabolized and excreted.[43][44]