TB-500 (Fragment 17-23): Thymosin Beta-4 Active Fragment Research Overview

In research peptide markets, "TB-500" refers to a synthetic heptapeptide with the sequence Ac-LKKTETQ — the N-acetylated form of amino acid residues 17 through 23 of the endogenous signaling protein thymosin beta-4 (TB-4). This fragment is commercially distinct from full-length thymosin beta-4, and the distinction matters enormously when evaluating safety and efficacy data: every published human clinical trial investigating thymosin beta-4 has used the full-length 43-amino-acid protein, not this 7-residue fragment. Readers should consult the companion guide on Thymosin Beta-4 (TB-4) for that body of clinical evidence. This guide covers what is specifically known about the fragment sold as TB-500.

What Is TB-500 (Fragment 17-23)?

Thymosin beta-4 is a ubiquitous, highly conserved 43-amino-acid intracellular protein and signaling factor that regulates actin dynamics, cell migration, angiogenesis, and tissue repair. Its central actin-binding domain spans residues 17 through 23, forming the sequence Leu-Lys-Lys-Thr-Glu-Thr-Gln (LKKTETQ). This short stretch is responsible for the G-actin sequestering activity of the full-length protein and has been shown in preclinical experiments to retain several biological activities of the parent protein.

The peptide sold in research markets under the name "TB-500" is Ac-LKKTETQ — the N-acetylated heptapeptide. The molecular weight of this fragment is approximately 889 Da, compared to ~4,963 Da for full-length TB-4. Although the fragment is sometimes described as equivalent to full-length TB-4, these are structurally and pharmacologically distinct compounds. Researchers should verify which form they are working with by reviewing the vendor's certificate of analysis (COA) and amino acid sequence.

The origins of the "TB-500" trade name in research markets appear to trace to equine veterinary use, where anti-doping control analysis has explicitly characterized the compound as the 17-23 fragment. A 2012 doping-control study published in Drug Testing and Analysis confirmed that "TB-500" available in research markets is the synthetic heptapeptide fragment rather than full-length thymosin beta-4.

Mechanism of Action

The LKKTETQ sequence is the actin-binding domain of thymosin beta-4. In-vitro experiments have demonstrated that this fragment can sequester G-actin monomers, inhibit actin polymerization, and stimulate cell migration and angiogenesis, though with lower potency than the full-length protein. Philp et al. (2003) characterized the actin-binding interactions of the 17-23 region and demonstrated that the LKKTETQ fragment promotes angiogenesis in cell-based assays, establishing the mechanistic foundation for the fragment's biological activity.

It is important to understand that full-length TB-4 has additional activities beyond the actin-binding domain — including nuclear localization signals, interactions with ILK (integrin-linked kinase), and effects on cardiac progenitor cell mobilization — that the fragment does not possess. Extrapolating the effects of full-length TB-4 to the 17-23 fragment is not scientifically justified.

What the Research Shows

The peer-reviewed literature on the LKKTETQ fragment specifically is limited. Key findings from published preclinical work include:

Wound healing in diabetic mice (Malinda et al., 2003): The 17-23 fragment and a synthetic peptide containing its actin-binding domain promoted dermal wound repair in diabetic and aged mouse models, though less robustly than full-length TB-4. Angiogenesis (Philp et al., 2003): The fragment stimulated endothelial cell migration and tube formation in in-vitro angiogenesis assays. Equine anti-doping analysis (Cannizzo et al., 2012): This study confirmed the identity of market TB-500 as the fragment and characterized its detection in equine biological matrices — a regulatory, not efficacy, finding. Pro-angiogenic peptides from TB-4 (Bock-Marquette et al., 2012): Demonstrated that TB-4-derived peptides including residues in the 17-23 region have pro-angiogenic activity in vitro.

There are NO published human clinical trials for the TB-500 fragment (Ac-LKKTETQ). The human clinical data — including trials in heart failure (РЕМЕНД / REMENDIN study), ophthalmic dry eye (RegeneRx), and traumatic brain injury — were conducted with full-length thymosin beta-4. Attributing those results to the fragment sold as TB-500 is scientifically unsupported.

Pharmacokinetics

Formal pharmacokinetic data for the Ac-LKKTETQ fragment in mammals are not available in peer-reviewed literature. Inference from general peptide pharmacology and from the catalog entry for TB-500 provides the following approximate parameters:

Half-life: the Pepticker catalog reports approximately 1.5–3 hours in rodent plasma with tissue accumulation potentially prolonging biological effects — this figure is based on manufacturer characterization and is not from a peer-reviewed PK study. Molecular weight: ~889 Da. Administration route: subcutaneous injection is the most common route in research applications. Stability: as a small peptide, Ac-LKKTETQ is subject to plasma proteolysis; the N-acetylation at the N-terminus provides some protection against aminopeptidase degradation relative to the free peptide. Distribution: as a small peptide, it may distribute into tissues more readily than the full-length protein.

Common Research Dose Ranges

Not medical advice. These are ranges reported in research literature, not personalized recommendations. Consult your physician.

No human dose-finding studies exist for the TB-500 fragment. Animal wound-healing models have used topical or intraperitoneal administration of TB-4-related peptides in the microgram-per-day range per kilogram of body weight. Dose ranges circulating in research communities (frequently 2–5 mg per administration) are derived from bodybuilding tradition extrapolated from full-length TB-4 protocols and carry no peer-reviewed validation. The Pepticker catalog entry lists a default research dose of 2.5 mg, which reflects what vendors report, not a clinically validated amount.

Storage and Handling

TB-500 (Ac-LKKTETQ) is supplied as a lyophilized powder. As a small peptide, it is generally more stable than large proteins but still subject to degradation from heat, moisture, and oxidation. Standard handling recommendations: lyophilized powder stored at −20 °C, protected from light; reconstituted solution stored at 2–8 °C and used within 28 days; reconstitution with sterile bacteriostatic water is standard; avoid repeated freeze-thaw cycles. These parameters match the Pepticker catalog entry for TB-500.

What TB-500 (Fragment 17-23) Is NOT

TB-500 is not the same as full-length thymosin beta-4 (TB-4). They are structurally distinct. The human clinical trial data cited by many vendors and advocates — cardiac trials, dry eye trials, wound-healing trials — were conducted with full-length TB-4. Those data cannot be attributed to the 7-residue fragment. (See the companion Thymosin Beta-4 / TB-4 guide for that literature.)

TB-500 has not been tested in human clinical trials as a standalone investigational drug. It has not received regulatory approval in any jurisdiction for human use. It is not a pharmaceutical product. The equine veterinary anti-doping context in which TB-500 appears in the scientific literature is a forensic/regulatory context, not a clinical efficacy context.

References

See citations below. Key sources: Philp et al. 2003 (actin binding and angiogenesis), Malinda et al. 2003 (wound healing with TB-4 peptides), Cannizzo et al. 2012 (doping control analysis confirming TB-500 identity as fragment), Bock-Marquette et al. 2012 (pro-angiogenic TB-4 peptides).