# TB-500: What the Research Shows — and What It Doesn't

> TB-500 is a synthetic heptapeptide studied in wound healing, tendon repair, and cardiac protection models. This digest covers the preclinical record, the safety gaps, and the WADA status — all cited.

## What TB-500 is, and what the preclinical record shows

TB-500 is a synthetic heptapeptide — seven amino acids, sequence Ac-LKKTETQ — corresponding to positions 17 through 23 of Thymosin Beta-4 (Tβ4), the primary G-actin-sequestering protein in mammalian cells [1]. The compound weighs 796.9 daltons and is N-terminally acetylated, which confers some resistance to proteolytic degradation.

The preclinical record is substantial. Tβ4 and its active fragment have been studied in full-thickness wound models, transected ligament models, myocardial infarction models, traumatic brain injury protocols, and skeletal muscle injury preparations — across at least four species, in more than two dozen peer-reviewed papers [21].

The short summary: in animal models, the compound accelerates tissue repair, promotes new blood vessel formation, reduces inflammatory markers, and supports cell survival in ischemic conditions. The longer summary is that no published Phase I pharmacokinetic or safety trial for injectable TB-500 (Ac-LKKTETQ) in humans exists. Every injected human use of this compound occurs outside a regulated clinical framework [20].

## Thymosin Beta-4 and TB-500: The Relationship Explained

Thymosin Beta-4 (Tβ4) is a 43-amino-acid endogenous protein. TB-500 is only the central 7-amino-acid fragment of Tβ4. The LKKTETQ sequence at positions 17–23 contains the actin-binding domain responsible for Tβ4's wound-healing and matrix metalloproteinase induction activity.

This distinction matters for reading the safety literature. Most mechanistic and clinical data covers the full Tβ4 protein. The only published Phase I human trial used intravenous full-length recombinant Tβ4, not the TB-500 fragment [16]. A Phase II dry-eye trial found a favorable safety profile with only 5.6% treatment-emergent events versus 13.9% on placebo [23]. Both datasets cover the parent protein; neither applies directly to injected TB-500.

## What is TB-500? The three findings the literature consistently shows

**Tissue repair acceleration.** In rat full-thickness wound models, Tβ4 increased reepithelialization by 42% at day 4 and up to 61% at day 7 vs. saline controls [3]. Local delivery of 1 µg Tβ4 to surgically transected rat MCLs produced superior biomechanical properties and improved collagen organization at four weeks [9].

**Angiogenesis and cardiovascular activity.** At 5.37 mg/kg IP in Sprague-Dawley rats following coronary artery occlusion, Tβ4 reduced infarct size by 43% at 28 days [6]. In rat TBI models (30 mg/kg IP), sensorimotor recovery improved and cortical lesion volume decreased [7].

**Immune modulation.** At 12 mg/kg/day IP for 4 weeks in NAFLD mice, Tβ4 shifted macrophages from M1 to M2 phenotype, reducing TNF-alpha and IL-1beta [22].

## The open questions this site does not hide

TB-500 promotes angiogenesis via VEGF upregulation — the same vascularization pathway exploited by tumors. In mouse melanoma models, Tβ4 overexpression produced 4.3 times more lung metastases and 4.4-fold greater tumor blood vessel formation [12]. In human colon cancer tissue, Tβ4 stabilizes HIF-1alpha, directly inducing VEGF expression [13]. In human pancreatic cancer cell lines, Tβ4 was overexpressed 3.7–4.5-fold [14].

No human study has confirmed that exogenous TB-500 causes cancer. No study rules it out.

Beyond the cancer question: the FDA designated TB-500 a Category 2 bulk drug substance. WADA prohibits TB-500 in competitive sport. A Canadian athlete received a 4-year ineligibility for a non-analytical positive involving TB-500 [18]. A 2023 analytical study found that internet-marketed TB500/TB1000 products are inconsistent in composition [17].

## References

[1] Philp D, Scheremeta B, Sibliss K, et al. Thymosin beta4 promotes matrix metalloproteinase expression during wound repair. Journal of Cellular Physiology. 2006;208(1):84-92. DOI: 10.1002/jcp.20650

[2] Philp D, et al. Thymosin beta 4 and a synthetic peptide containing its actin-binding domain promote dermal wound repair in db/db diabetic mice and in aged mice. Wound Repair and Regeneration. 2003;11(1):19-24.

[3] Malinda KM, et al. Thymosin beta4 accelerates wound healing. Journal of Investigative Dermatology. 1999;113(3):364-368.

[6] Bao W, et al. Cardioprotection by systemic dosing of thymosin beta four following ischemic myocardial injury. Frontiers in Pharmacology. 2013;4:149.

[7] Xiong Y, et al. Neuroprotective and neurorestorative effects of thymosin beta4 treatment following TBI in rats. Journal of Neurosurgery. 2012;116(5):1081-1092.

[9] Xu B, et al. Thymosin β4 enhances the healing of medial collateral ligament injury in rat. Regulatory Peptides. 2013;184:1-5.

[12] Cha HJ, Jeong MJ, Kleinman HK. Role of thymosin beta4 in tumor metastasis and angiogenesis. J Natl Cancer Inst. 2003;95(22):1674-1680.

[13] Jo JO, et al. Thymosin β4 induces VEGF expression in a HIF-1α-dependent manner. Biochim Biophys Acta. 2010;1803(11):1244-1251.

[14] Zhang Y, et al. Thymosin Beta 4 is Overexpressed in Human Pancreatic Cancer Cells. Cancer Biology and Therapy. 2007;7(3):419-423.

[16] Wang X, et al. A first-in-human, phase I study of recombinant human thymosin β4 in healthy Chinese volunteers. J Cell Mol Med. 2021;25(17):8390-8399.

[17] Delcourt V, et al. TB500/TB1000 and SGF1000: misbranded and adulterated drugs. Drug Testing and Analysis. 2023;15(3):282-293.

[18] Barton C, et al. Doping control analysis of TB-500 in equine urine and plasma. Drug Testing and Analysis. 2013;5(9-10):819-827.

[20] Mendias CL, Awan TM. Safety and Efficacy of Approved and Unapproved Peptide Therapies. Sports Medicine. 2026.

[21] Philp D, Kleinman HK. Animal studies with thymosin beta, a multifunctional tissue repair peptide. Ann NY Acad Sci. 2010;1194:81-86.

[22] Zhu Z, et al. Thymosin β4 Regulates Tissue Inflammatory Response in Mouse NAFLD. J Inflammation Research. 2025;18:5483-5498.

[23] Sosne G, Ousler GW. Thymosin beta 4 ophthalmic solution for dry eye: Phase II clinical trial. Clinical Ophthalmology. 2015;9:863-869.

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Peer-reviewed findings on TB-500, read warmly and honestly — the evidence gaps are noted alongside the findings, and no clinic sits behind this page.