PwPepwise

TB-500 / Thymosin Beta-4

Healing & Recovery

a.k.a. Tβ4

Actin-binding peptide

TB-500 is a synthetic peptide fragment derived from Thymosin Beta-4 (Tβ4).

§Dosing at a glance

2 protocols · from the research
What it's forDoseHow oftenHowFor how long
into a vein (Cardiac / STEMI)450 mgOnce dailyIntravenousInjected directly into a vein.—
Topical Ophthalmic5 mcgTwice dailyTopicalApplied on the skin.—

Approximate values pulled from the research — double-check before dosing.

§01Summary

TB-500 is a synthetic peptide fragment derived from Thymosin Beta-4 (Tβ4), a naturally occurring 43-amino-acid protein found throughout the body in high concentrations17. In the body, Tβ4 plays a fundamental role in regulating actin — the protein that forms the structural scaffolding of cells and drives cell movement, a process essential for tissue repair and wound healing15,16. By controlling how actin monomers are assembled into filaments, Tβ4 helps coordinate cell migration, new blood vessel formation, and the inflammatory response following injury13,18.

In preclinical research, Tβ4 has been reported to accelerate corneal wound healing and reduce inflammation following injury18, and preliminary evidence suggests it may support cardiac recovery following heart attack when administered early after reperfusion2. Human trials are actively investigating its potential in cardiovascular repair, wound healing conditions such as pressure ulcers and epidermolysis bullosa, and ophthalmic applications including dry eye and corneal repair3,4,5,8. Endogenous Tβ4 is upregulated in hepatocellular carcinoma tissue and has been shown to enhance HCC cell motility in vitro10 — a biological relationship that ongoing clinical research will help characterize. The human evidence base for therapeutic TB-500 is actively developing, with multiple registered trials and emerging peer-reviewed data.

This is the layperson summary. Mechanism, dosing, the evidence base, and the published literature are in the sections below — every claim links to its source.

§02In depth

Thymosin Beta-4 is a 43-amino-acid, 4,982 Da polypeptide with a blocked N-terminal acetyl group and an isoelectric point of 5.1, whose complete primary structure was first established from bovine thymic tissue17. Its defining biochemical function is the stoichiometric sequestration of globular actin (G-actin) monomers: Tβ4 forms a 1:1 complex with G-actin at an affinity of approximately Kd 0.7–1 µM, inhibiting both actin polymerization and nucleotide exchange on the actin monomer15,20. At least 50% of unpolymerized actin in resting human platelets is complexed with Tβ4, underscoring its physiological dominance in actin monomer buffering15.

The relationship between Tβ4 and profilin defines a key regulatory axis for actin dynamics. While Tβ4 maintains an ATP-ADP-actin equilibrium by blocking nucleotide dissociation from sequestered monomers, profilin catalytically promotes nucleotide exchange to regenerate ATP-actin, which polymerizes preferentially at barbed filament ends16. Even low concentrations of profilin can overcome the inhibitory effects of high concentrations of Tβ4, driving net actin assembly fueled by the thermodynamic irreversibility of ATP hydrolysis during polymerization13. This competitive interplay enables cells to rapidly toggle between cytoskeletal quiescence and directed filament growth — a mechanism central to cell migration, wound closure, angiogenesis, and tissue remodeling.

Beyond actin dynamics, Tβ4 exerts immunomodulatory and neuroendocrine effects. In corneal injury models, topical Tβ4 reduced expression of IL-1β, MIP-1α, MIP-1β, MIP-2, and MCP-1 alongside promotion of epithelial healing, indicating downstream suppression of pro-inflammatory cytokine and chemokine signaling18. In cardiac ischemia-reperfusion contexts, the cardioprotective mechanism has been linked to activation of the ErbB2/Raf1 signaling pathway with suppression of cardiomyocyte apoptosis; pharmacological ErbB2 inhibition abolished rhTB4's protective effects in murine models, confirming pathway dependency2. An early neuroendocrine role was identified when synthetic Tβ4 was shown to stimulate LHRF release from rat hypothalamic tissue and subsequent LH release from sequentially superfused pituitary tissue — an effect not shared by thymosin alpha-1 — suggesting peptide-specific receptor interactions within the hypothalamic-pituitary axis19.

TB-500, the synthetic fragment corresponding to residues 17–23 of full-length Tβ4, represents a distinct pharmacological entity12. While it shares some biological activities attributed to the parent peptide, the mechanistic and pharmacokinetic equivalence of the fragment versus the full 43-amino-acid sequence has not been fully characterized in published peer-reviewed literature. Notably, global and cardiac-specific genetic knockout of Tβ4 in mice produces no detectable developmental or functional cardiac phenotype9, indicating that the pharmacological effects of exogenous Tβ4 administration operate through mechanisms beyond simple endogenous replacement — a distinction important for interpreting both therapeutic potential and safety.

§04Evidence & efficacy

Evidence base
332Studies
144Human
75Animal

Tβ4 demonstrates consistent pro-healing and anti-inflammatory activity in preclinical models. In a murine corneal alkali burn model, topical TB4 accelerated corneal re-epithelialization at all measured time points and significantly reduced polymorphonuclear leukocyte infiltration at Day 7, alongside multi-fold reductions in IL-1β, MIP-1α, MIP-1β, MIP-2, and MCP-1 mRNA expression18. In murine cardiac ischemia-reperfusion models, rhTB4 administered for 7 days has been reported to reduce infarct size, prevent cardiac dysfunction, reduce fibrosis at 28 days, and suppress cardiomyocyte apoptosis via ErbB2/Raf1 signaling pathway activation2.

In human studies, rhTB4 may reduce myocardial infarct size when administered shortly after reperfusion2. A Phase IIc RCT evaluating NL005 in STEMI patients is currently underway, using cardiac MRI infarct sizing as a primary endpoint and long-term cardiac recovery at Day 360 as a secondary objective1. In ophthalmic applications, human RCTs of Tβ4 eye drops for dry eye, diabetic corneal wound healing, and ocular surface defects are part of an active clinical development program7,8,11. Wound healing indications including pressure ulcers and epidermolysis bullosa have been investigated in registered RCTs3,4, with the human evidence base actively developing. Tβ4 serves as a superior diagnostic biomarker for hepatocellular carcinoma compared to AFP (AUROC 0.908 vs. 0.712)10, reflecting a distinct biological role in oncological contexts.

§05Safety

Across the available evidence, Thymosin Beta-4 and its derivatives appear generally well tolerated in the settings studied to date. In a preclinical murine corneal alkali burn model, topical TB4 at 5 mcg twice daily produced no reported adverse events or local irritation18. Global and cardiac-specific Tβ4 knockout mice developed normally with no detectable adverse phenotypes under baseline conditions, suggesting that modulation of endogenous Tβ4 is not inherently harmful in animals9. In the 96-patient human cardiac trial, no explicit adverse events or safety concerns were described in the published abstract2.

Human Phase 1 pharmacokinetic and safety data from intravenous administration are in active development: a registered Phase 1 healthy-volunteer IV dose-escalation trial was designed to characterize the tolerability and PK profile of intravenous Tβ4 across ascending single and multiple doses6, with formal published results still emerging. Registered cardiovascular trials have evaluated intravenous doses as high as 1200 mg in acutely ill STEMI patients5, and safety monitoring in the NL005 Phase IIc trial includes daily blood draws, ECGs during the first week, and follow-up assessments through Day 3601.

Endogenous Tβ4 is upregulated in hepatocellular carcinoma tissue and has been shown to enhance HCC cell motility in vitro10 — a biological relationship that ongoing clinical research will help characterize.

§06History

Thymosin Beta-4 was first identified as a component of thymosin fraction 5 — a thymic extract studied extensively from the 1960s onward for its immunomodulatory properties. Its complete 43-amino-acid primary sequence was established in 1981 from bovine thymus, where it was characterized as a thymic hormone capable of inducing terminal deoxynucleotidyl transferase (TdT) activity in murine thymocytes, pointing to a role in early T-lymphocyte maturation17. In the same year, Tβ4 was shown to stimulate LHRF secretion from rat hypothalamic tissue, revealing an unexpected neuroendocrine dimension19.

A paradigm shift occurred in the early 1990s when Tβ4 was independently identified as biochemically identical to 'Fx,' a platelet-derived actin-sequestering peptide15, and subsequent work established its role as a major regulator of actin monomer dynamics in concert with profilin13,16. This reframed Tβ4 as a cytoskeletal regulator rather than primarily a thymic hormone, providing a mechanistic foundation for its tissue-repair and wound-healing properties.

RegeneRx Biopharmaceuticals advanced Tβ4 into clinical development in the 2000s, registering multiple Phase 1 and Phase 2 RCTs across wound healing (pressure ulcers4, epidermolysis bullosa3), cardiovascular repair5, and ophthalmic applications6,7,8. ReGenTree subsequently developed RGN-259, a 0.1% Tβ4 ophthalmic solution for dry eye disease8. Preclinical corneal healing data generated in the early 2000s18 supported this ophthalmic program. Cardioprotective research culminated in a published 96-patient human trial2 and an ongoing Phase IIc RCT by Beijing Northland Biotech1. The TB-500 fragment (residues 17–23) has entered early Phase 1 cardiovascular investigation12, representing the current frontier of clinical development.

§07References