# TB-500: Research Literature on the Thymosin Beta-4 Synthetic Fragment > TB-500 (Ac-LKKTETQ) has been studied in wound healing, tendon repair, cardiac protection, hair follicle activation, and neurological recovery across two decades of preclinical research. A cited literature digest. A botanical reading room for the peer-reviewed record on TB-500, the synthetic Ac-LKKTETQ fragment of Thymosin Beta-4 — citing every quantitative claim. ## The short version TB-500 is a short synthetic peptide — seven amino acids, sequence Ac-LKKTETQ — taken from the actin-binding region of a protein your body already makes called Thymosin Beta-4. In animal studies, it has been looked at for wound healing, tendon and ligament repair, heart protection after injury, hair follicle activation, and neurological recovery. The parent protein has been tested in humans in two Phase I safety trials; the TB-500 fragment itself has not completed any controlled human trial for any condition. It is not FDA-approved. It is prohibited in competitive sport by WADA. The pages here gather what the peer-reviewed record actually says about each of those areas — with the species, doses, and limitations named plainly. For what people outside of research settings report experiencing, the [effects page](/effects) covers that separately. ## What Is the TB-500 Peptide? TB-500 is a synthetic heptapeptide — seven amino acids, sequence Ac-LKKTETQ — derived from residues 17 through 23 of Thymosin Beta-4, a 43-amino-acid endogenous signaling protein found in virtually every nucleated human cell. The acetylated N-terminus distinguishes TB-500 from the parent protein's native sequence. Molecular weight: 887 daltons. Thymosin Beta-4 itself was isolated from calf thymus in the early 1970s; its wound-healing properties were being characterized in rodent models by the late 1990s. The synthetic fragment designated TB-500 entered anti-doping literature in 2012, when Ho et al. validated an LC-MS/MS method for its detection in equine urine and plasma at detection limits of 0.01 ng/mL [12]. The research literature uses TB-500 and Thymosin Beta-4 (Tβ4) interchangeably in many contexts. This site covers both: findings on the full 43-amino-acid protein are noted where relevant; findings specifically on the 7-residue synthetic fragment are identified as such. The two are mechanistically related but not pharmacokinetically equivalent. In rodent wound models, Thymosin Beta-4 increased wound re-epithelialization by 42% at 4 days and 61% at 7 days post-wounding, with treated tissue contracting at least 11% more than controls and showing elevated collagen deposition and angiogenesis [2]. The active-region peptide — the sequence that TB-500 preserves — accelerated wound closure in both diabetic (db/db) and aged mice when applied topically [1]. These are the foundational observations that established the field. TB-500 is not FDA-approved for any human indication. It is a research compound. The Phase I human studies that exist in this literature evaluated full-length recombinant Thymosin Beta-4 — not the synthetic fragment — in intravenous administration contexts [9, 10]. That distinction matters and this site maintains it throughout. ## What Does TB-500 Do in Preclinical Studies? The primary mechanism is G-actin sequestration. TB-500 (and the full Thymosin Beta-4 protein) binds monomeric G-actin in a 1:1 stoichiometric ratio, modulating how much actin is available for cytoskeletal polymerization. That single interaction generates a cascade: cells become more motile, actin-based cytoskeletal rearrangements accelerate migration, and angiogenesis is upregulated via VEGFR2 signaling. The downstream effects documented in preclinical models include: - Wound closure and re-epithelialization acceleration [1, 2] - Medial collateral ligament repair with histologically and biomechanically improved collagen architecture [3] - Cardiac cardiomyocyte survival and improved post-infarct function via ILK/Akt activation [4, 5] - Hair follicle stem cell activation in the bulge region at nanomolar concentrations [6] - Myoblast chemotaxis following muscle injury [15] - Neuroprotective angiogenesis in rat traumatic brain injury models [8] - Anti-fibrotic activity in liver and cardiac tissue [5, 14] Across these findings, the consistent thread is cell migration. TB-500 promotes it in wound keratinocytes, ligament fibroblasts, cardiomyocytes, myoblasts, and hair follicle stem cells. Angiogenesis — new blood vessel formation via VEGFR2 — follows cell migration and is a secondary but critical effect in models where oxygen and nutrient delivery to injured tissue limits healing speed. For a detailed mechanism summary, see [TB-500 mechanism of action](/research#mechanism). ## Is TB-500 a Steroid? No. TB-500 is a synthetic peptide — a short amino acid chain. It shares no structural, mechanistic, or pharmacological class with anabolic steroids. Steroids are lipid-soluble molecules derived from cholesterol; they act on nuclear androgen, estrogen, or glucocorticoid receptors. TB-500 is a water-soluble heptapeptide; it acts on actin cytoskeletal dynamics and cell-surface signaling pathways. The confusion occasionally arises from the compound's association with performance-related research. TB-500 is classified by WADA under S2 (Peptide Hormones, Growth Factors, Related Substances, and Mimetics) — the peptide category, not the anabolic steroid category — and is prohibited at all times as a non-Specified Substance carrying a maximum four-year sanction. ## What Does TB-500 Stand For? The TB-500 designation refers to Thymosin Beta-500 — a naming convention used in early peptide research and anti-doping contexts for the synthetic heptapeptide fragment corresponding to amino acids 17–23 of Thymosin Beta-4. The '500' element appeared in early peptide-synthesis literature to distinguish the fragment from the parent protein (Thymosin Beta-4, or TB4). In current research publications, the compound is more precisely identified by its sequence designation: N-acetyl-LKKTETQ, or Ac-LKKTETQ. The full research record — including its relationship to the parent protein and findings on both — is covered across this site. See the [frequently asked questions about TB-500](/faq) for more definitional context. ## The Research Record in Summary Twenty-one primary-source findings form the backbone of this literature digest. The strongest quantitative results: **Wound healing**: Thymosin Beta-4 at doses as low as 10 picograms increased wound re-epithelialization by 42% (day 4) and 61% (day 7) in rats; the active-fragment heptapeptide accelerated closure in diabetic and aged mouse models [1, 2]. **Ligament repair**: 1 µg of Thymosin Beta-4 administered via fibrin sealant to rat medial collateral ligament injury produced histologically uniform, biomechanically superior healing at 4 weeks compared to controls [3]. **Cardiac protection**: Two independent murine myocardial infarction studies showed cardiomyocyte survival improvement, reduced fibrosis, and improved cardiac function via ILK/Akt pathway activation and mitophagy promotion [4, 5]. **Hair follicles**: Nanomolar concentrations activated quiescent bulge-region hair follicle stem cells in rat and mouse models, stimulating keratinocyte migration and MMP-2 secretion [6]. **Human Phase I (full-length Tβ4)**: Two Phase I randomized trials — one in 40 healthy US volunteers (doses 42–1260 mg IV), one in 40 healthy Chinese volunteers — reported no dose-limiting toxicities, dose-proportional pharmacokinetics, and no accumulation on repeat dosing [9, 10]. **2024–2025 additions**: Zebrafish Mauthner axon regeneration via G-actin polymerization facilitation [19]; tandem tTB4 showing superior corneal wound healing over native TB4 [20]; Tβ4 attenuating NAFLD liver inflammation via M2 macrophage polarization at 12 mg/kg/day IP [21]. The full literature is organized in [TB-500 references and citations](/references). --- A literature digest of peer-reviewed findings — not a clinic, not a prescription, not a vendor.