TB-500
Also known as: Thymosin Beta-4 fragment, Tβ4 fragment, TB4 fragment, LKKTETQ, Thymosin Beta-4 Fragment (17–23)
6 notable studies · 7 references
TLDR
TB-500 is a synthetic fragment derived from Thymosin Beta-4 that is studied for tissue repair, cell migration, angiogenesis, and inflammatory processes, but much of the evidence commonly attributed to TB-500 actually comes from full-length Tβ4 and direct human evidence for TB-500 itself is currently lacking.
Research Supports
- The LKKTETQ fragment itself has been investigated for actin-related biological activity in experimental systems
- Related full-length Thymosin Beta-4 research has examined wound repair, cell migration, and angiogenesis
- Related full-length Thymosin Beta-4 research has examined corneal repair and inflammation
- No published human-administration studies of TB-500 itself have been identified (FDA, 2026)
Observations Reported in Research
- FDA's 2026 review found no articles in which TB-500 was administered to humans
- Full-length Tβ4 (not TB-500) accelerated corneal re-epithelialization and reduced inflammatory-cell infiltration in mouse models (Sosne et al., 2001, 2002)
- Full-length Tβ4 (not TB-500) showed no dose-limiting toxicity in a first-in-human IV Phase I study (2021)
- A topical full-length Tβ4 (not TB-500) trial in 73 venous-ulcer patients suggested accelerated healing at one concentration (2010)
These are brief summaries of what the referenced research examined or reported — not conclusions about safety or effectiveness, and not medical advice. See Notable Studies and Sources & References below for the full context and citations.
At a Glance
Classification: Synthetic peptide fragment derived from Thymosin Beta-4; investigational research peptide
TB-500 is a synthetic peptide fragment derived from a region of Thymosin Beta-4 (Tβ4), a naturally occurring 43-amino-acid peptide involved in actin regulation, cell migration, inflammation, angiogenesis, and tissue repair. TB-500 is frequently described online simply as “Thymosin Beta-4,” but that terminology can substantially overstate its evidence base. Full-length Tβ4 has been studied extensively in cells and animals and has also reached human clinical trials, including studies of chronic wounds and corneal injury. TB-500 itself has a much thinner evidence base. FDA's 2026 review reported finding no articles in which TB-500 was administered to humans. That distinction is essential when evaluating claims about TB-500.
What Is TB-500?
TB-500 is a short synthetic peptide associated with a biologically active region of Thymosin Beta-4. Thymosin Beta-4 is a naturally occurring 43-amino-acid peptide found widely in mammalian tissues and cells. One of its best-established biological functions is binding monomeric G-actin, making it an important regulator of the cellular actin cytoskeleton. Tβ4 has also been investigated for effects involving cell migration, angiogenesis, inflammation, apoptosis, and tissue repair. Research attempting to identify smaller active regions of Tβ4 led to interest in the amino-acid sequence LKKTETQ, corresponding to residues 17–23 of the full peptide. TB-500 is associated with this fragment. The distinction matters because reducing a 43-amino-acid peptide to a seven-amino-acid fragment can substantially alter its pharmacology. Results obtained with full-length Tβ4 therefore cannot automatically be attributed to TB-500. FDA emphasized this problem in its 2026 evaluation, noting that publications submitted in support of TB-500 included studies involving Tβ4 rather than actual compounded TB-500 and that it found no published human-administration studies of TB-500 itself.
What Are Researchers Studying?
Cell migration and tissue repair
Thymosin Beta-4 has been extensively investigated for its ability to influence cell migration and wound repair. The LKKTETQ region associated with TB-500 has been investigated as one possible biologically active portion of the larger Tβ4 molecule. Preclinical findings involving the fragment have contributed to interest in TB-500 as a tissue-repair research compound. However, much of the broader wound-healing literature concerns full-length Tβ4 rather than TB-500.
Tendon, ligament, and skeletal-muscle injury
TB-500 is commonly associated online with tendon, ligament, and muscle repair. The scientific rationale derives partly from research into Tβ4-mediated cell migration, angiogenesis, inflammatory regulation, and tissue remodeling. Direct evidence for TB-500 itself is considerably more limited than these claims imply, particularly in humans. Human trials demonstrating that TB-500 accelerates tendon, ligament, or muscle healing have not been established.
Actin and cytoskeletal biology
Full-length Thymosin Beta-4 is one of the major actin-sequestering peptides found inside cells. Its interaction with G-actin helps regulate actin polymerization and cellular movement. The LKKTETQ region associated with TB-500 has been investigated for biological activity related to Tβ4, although the fragment does not reproduce every structural or functional property of the complete peptide. This is another reason evidence involving full-length Tβ4 should not automatically be assigned to TB-500.
Angiogenesis
Thymosin Beta-4 has been associated with angiogenesis and endothelial-cell migration in experimental research. Formation of new blood vessels is an important component of tissue repair, and these findings contributed to interest in Tβ4-derived fragments. Angiogenesis is highly context dependent, however, and effects observed with full-length Tβ4 cannot establish equivalent activity or safety for TB-500 in humans.
Inflammation and wound repair
Full-length Tβ4 has demonstrated anti-inflammatory and wound-repair activity in numerous experimental models. Corneal studies, for example, have reported accelerated epithelial repair and reductions in inflammatory-cell infiltration following Tβ4 treatment in animals. Clinical studies have subsequently investigated topical Tβ4 formulations in human wounds and ocular disease. Those findings establish biological and clinical interest in Thymosin Beta-4, not direct evidence for systemic TB-500 administration.
Corneal repair
Corneal wound healing represents one of the most clinically developed areas of full-length Tβ4 research. Early animal studies found enhanced corneal re-epithelialization and reduced inflammation. Compassionate-use reports subsequently described topical Tβ4 treatment in nine patients with chronic neurotrophic corneal epithelial defects. A later randomized, placebo-controlled Phase III study investigated the Tβ4 ophthalmic formulation RGN-259 in neurotrophic keratopathy. These studies are valuable for understanding the parent peptide but should not be presented as clinical trials of TB-500.
How Does It Work?
The mechanism of TB-500 itself is less well characterized than descriptions of the compound online often suggest. Much of the proposed mechanism is extrapolated from full-length Thymosin Beta-4. Tβ4 binds monomeric G-actin and plays an important role in regulation of the actin cytoskeleton. Actin dynamics influence cellular movement, shape, adhesion, and tissue repair. Research involving Tβ4 has additionally implicated processes involving: - Cell migration - Angiogenesis - Inflammatory signaling - Apoptosis - Keratinocyte and endothelial-cell movement - Extracellular-matrix remodeling - Tissue protection The LKKTETQ sequence associated with TB-500 has demonstrated biological activity in experimental systems, which helped motivate development of the fragment. But a seven-amino-acid fragment does not necessarily retain the pharmacokinetics, binding interactions, tissue distribution, or complete biological activity of the 43-amino-acid parent peptide. Accordingly, the mechanism of full-length Tβ4 should not simply be copied onto TB-500.
What Does the Research Show?
Human research
There is an important split in the human evidence. Full-length Thymosin Beta-4 has human clinical evidence. TB-500 itself does not currently have a comparable published human evidence base. For full-length Tβ4: A randomized double-blind study enrolled 73 patients with venous stasis ulcers and evaluated topical Tβ4. The treatment was reported to have a safety profile comparable with placebo, and one concentration showed evidence suggesting accelerated wound healing. Nine patients with chronic nonhealing neurotrophic corneal defects were treated with topical Tβ4 in compassionate-use cases. Six patients with geographic epithelial defects showed substantial healing, while three with punctate defects did not demonstrate comparable changes. A first-in-human randomized Phase I study of recombinant human Tβ4 enrolled healthy volunteers and evaluated single and repeated intravenous administration. Researchers reported predominantly mild-to-moderate adverse events without dose-limiting toxicity or serious adverse events in the study. A randomized Phase III trial also investigated the Tβ4 ophthalmic formulation RGN-259 for neurotrophic keratopathy. None of these studies establishes the safety or effectiveness of TB-500. FDA's 2026 review specifically reported that its literature search found no articles in which TB-500 was administered to humans.
Animal research
Preclinical research into Thymosin Beta-4 is extensive. Animal studies have examined skin wounds, corneal injuries, cardiovascular injury, inflammation, tissue regeneration, and other forms of cellular and tissue damage. For example, mouse experiments involving alkali-induced corneal injury found that topical Tβ4 accelerated re-epithelialization and reduced inflammatory-cell infiltration compared with controls. Other experiments have examined Tβ4 in dermal healing, including diabetic, aged, and burn models. Research specifically examining the shorter TB-500-associated fragment is substantially less extensive. Animal findings involving full-length Tβ4 can provide biological context for studying TB-500 but should not be treated as direct efficacy evidence for the fragment.
In-vitro research
Cellular research has played an important role in identifying biological activities associated with Thymosin Beta-4 and its fragments. Experiments have examined actin binding, cellular migration, endothelial responses, keratinocyte migration, angiogenesis, inflammatory signaling, and tissue-repair mechanisms. Research into shorter regions of Tβ4 contributed to identification of biologically active sequences including LKKTETQ. These experiments support continued investigation of Tβ4-derived peptides but cannot establish human efficacy or safety for TB-500.
Notable Studies
Thymosin Beta 4 Promotes Corneal Wound Healing and Modulates Inflammatory Mediators In Vivo
animalResearchers investigated Tβ4 in an experimental corneal-injury model. The study reported enhanced corneal wound repair and changes in inflammatory mediators following treatment, contributing to subsequent development of Tβ4 as a potential corneal wound-healing agent.
Limitations: This was animal research involving full-length Tβ4, not TB-500. The results therefore provide background on the parent peptide but cannot establish equivalent activity of the shorter TB-500 fragment.
View publication →Thymosin Beta 4 Promotes Corneal Wound Healing and Decreases Inflammation In Vivo Following Alkali Injury
animalResearchers treated chemically injured mouse corneas with topical Tβ4. Treated corneas demonstrated accelerated re-epithelialization and reduced inflammatory-cell infiltration compared with controls. Researchers also observed reductions in several inflammatory cytokine and chemokine transcripts.
Limitations: The study involved mice and full-length Tβ4. It did not investigate TB-500, systemic administration, human pharmacokinetics, or human clinical outcomes.
View publication →The Effect of Thymosin Treatment of Venous Ulcers
humanResearchers enrolled 73 patients with venous stasis ulcers to investigate topical Tβ4. The reported safety profile was comparable with placebo. Efficacy findings suggested that the 0.03% concentration might accelerate wound healing, particularly among smaller or less severe wounds.
Limitations: The study investigated topical full-length Tβ4, not TB-500. It therefore cannot establish safety, pharmacokinetics, dosing, or wound-healing efficacy for TB-500.
View publication →A First-in-Human, Randomized, Double-Blind, Single- and Multiple-Dose, Phase I Study of Recombinant Human Thymosin β4 in Healthy Chinese Volunteers
humanResearchers evaluated recombinant human Tβ4 administered intravenously to healthy volunteers. The single-dose portion included 54 participants across seven dose cohorts, while 30 participants were enrolled in the multiple-dose portion. Reported adverse events were mild to moderate, with no dose-limiting toxicities or serious adverse events. The study also characterized plasma exposure and pharmacokinetics.
Limitations: This study evaluated recombinant full-length human Tβ4, not TB-500. Safety and pharmacokinetic data from NL005 cannot automatically be transferred to a short synthetic fragment with different structural and pharmaceutical characteristics.
View publication →0.1% RGN-259 (Thymosin β4) Ophthalmic Solution Promotes Healing and Improves Comfort in Neurotrophic Keratopathy Patients in a Randomized, Placebo-Controlled, Double-Masked Phase III Clinical Trial
humanResearchers investigated RGN-259, a Tβ4 ophthalmic formulation, in patients with neurotrophic keratopathy. The study reported faster epithelial-defect healing and improved ocular comfort with no significant adverse effects identified in the trial.
Limitations: This was an ophthalmic formulation of full-length Tβ4, not TB-500. The publication also reports commercial relationships with companies developing RGN-259, which should be considered when interpreting the findings. Results cannot establish the effects of TB-500 administered through other routes.
View publication →FDA Evaluation of TB-500-Related Bulk Drug Substances for Pharmacy Compounding
animalFDA reviewed available information concerning TB-500 free base and acetate in connection with pharmacy compounding. The agency distinguished TB-500 from full-length Thymosin Beta-4 and reported that its literature search identified no articles in which TB-500 was administered to humans. FDA also identified potential concerns involving immunogenicity, aggregation, peptide-related impurities, and insufficient human safety information.
Limitations: This is a regulatory evidence evaluation rather than a clinical experiment. Absence of identified human exposure data does not itself prove toxicity or lack of biological activity; rather, it demonstrates that adequate evidence needed to characterize human safety and efficacy is missing.
View publication →What We Still Don't Know
Important unresolved questions include: - Whether TB-500 produces clinically meaningful tissue-repair effects in humans - Whether TB-500 actually reproduces the relevant biological effects of full-length Tβ4 - Human pharmacokinetics and bioavailability - Short- and long-term human safety - Immunogenicity - Potential consequences of peptide aggregation or impurities - Whether the LKKTETQ fragment retains the parent peptide's effects on angiogenesis and inflammation in humans - Appropriate pharmaceutical characterization and formulation - Whether effects depend on route of administration - Whether musculoskeletal claims commonly associated with TB-500 translate into measurable human outcomes - How TB-500 differs pharmacologically from other Tβ4-derived fragments - Whether results from full-length Tβ4 clinical trials have any meaningful predictive value for TB-500 FDA currently states that it has not identified human exposure data for drug products containing the TB-500 fragment and lacks sufficient information to determine whether it would cause harm when administered to humans.
Related Compounds
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Sources & References
- Sosne G, Chan CC, Thai K, et al. Thymosin Beta 4 Promotes Corneal Wound Healing and Modulates Inflammatory Mediators In Vivo. Experimental Eye Research. 2001;72(5):605-608. doi:10.1006/exer.2000.0985.
- Sosne G, Szliter EA, Barrett R, Kernacki KA, Kleinman H, Hazlett LD. Thymosin Beta 4 Promotes Corneal Wound Healing and Decreases Inflammation In Vivo Following Alkali Injury. Experimental Eye Research. 2002;74(2):293-299. doi:10.1006/exer.2001.1125.
- Dunn SP, Heidemann DG, Chow CYC, et al. Treatment of Chronic Nonhealing Neurotrophic Corneal Epithelial Defects with Thymosin Beta4. Annals of the New York Academy of Sciences. 2010;1194:199-206. doi:10.1111/j.1749-6632.2010.05471.x.
- The Effect of Thymosin Treatment of Venous Ulcers. Annals of the New York Academy of Sciences. 2010.
- A First-in-Human, Randomized, Double-Blind, Single- and Multiple-Dose, Phase I Study of Recombinant Human Thymosin β4 in Healthy Chinese Volunteers. 2021.
- Sosne G, Kleinman HK, Springs C, et al. 0.1% RGN-259 (Thymosin β4) Ophthalmic Solution Promotes Healing and Improves Comfort in Neurotrophic Keratopathy Patients in a Randomized, Placebo-Controlled, Double-Masked Phase III Clinical Trial. International Journal of Molecular Sciences. 2023;24(1):554.
- U.S. Food and Drug Administration. Evaluation of TB-500 (Thymosin Beta-4 Fragment LKKTETQ) Related Bulk Drug Substances for Use in Compounding. 2026.
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