# Frequently asked questions — Thymosin Beta-4 and TB-500 > Direct answers, with citations, to the questions readers ask most often about TB-500 and Thymosin Beta-4 — how the fragment relates to the parent, what the brain and wound-healing research actually shows, the porcine cardiac negative, WADA status, and the regulatory record. Direct, cited, and slightly warmer than the research pages. The citations link to the primary papers. ## Foundations **What exactly is TB-500, and how is it different from full-length Thymosin Beta-4?** TB-500 is a synthetic, N-acetylated 7-amino-acid peptide with the sequence Ac-Leu-Lys-Lys-Thr-Glu-Thr-Gln-OH. The seven residues correspond to positions 17–23 of the parent peptide, full-length human Thymosin Beta-4 (Tβ4), which is a 43-amino-acid intracellular peptide encoded by the X-chromosome gene TMSB4X. TB-500 contains the conserved LKKTET hexapeptide motif that mediates G-actin binding, which is the structural reason the fragment retains in-vitro affinity for monomeric actin. It does not contain the rest of the parent molecule. Virtually every peer-reviewed preclinical study, every published human pharmacokinetic dataset, and every registered clinical trial uses the 43-AA full-length Tβ4, not the 7-AA synthetic fragment [11][12][13]. The two are routinely treated as interchangeable in commercial literature; in the peer-reviewed literature they are not. **How does the parent peptide Thymosin Beta-4 actually work?** The primary mechanism is 1:1 sequestration of monomeric G-actin through a central α-helix containing the LKKTET motif, which holds G-actin in a polymerization-incompetent state and creates a mobilizable reservoir for rapid actin remodeling [16]. Secondary mechanisms include prolyl-oligopeptidase cleavage of Tβ4 to release the N-terminal tetrapeptide AcSDKP, which has its own antifibrotic and pro-angiogenic activity [20]; direct binding of NF-κB RelA/p65 and suppression of TNF-α-driven IL-8 transcription; upregulation of angiopoietin-1 and downregulation of angiopoietin-2 in endothelium and Schwann cells [3]; reactivation of adult cardiac epicardial progenitor cells [16]; and EGFR-driven oligodendrocyte progenitor differentiation in demyelinating CNS injury [2]. A 2025 microneedle study added Vsig4 and IL22Rα2 to the known target list [18]. ## Brain and nervous system **What does the research say about Tβ4 in traumatic brain injury?** In rats with controlled cortical impact TBI, recombinant human Tβ4 administered intraperitoneally at 6 mg/kg starting 24 hours after injury and continuing every three days for four additional doses reduced hippocampal CA3 neuronal loss, increased BrdU-positive proliferating cells and new oligodendrocytes in the injured cortex and hippocampus, and produced durable sensorimotor and spatial-learning recovery through day 90 [1]. The 24-hour start is meaningful: the molecule appears to act on recovery rather than as a classical acute neuroprotectant. **What about stroke?** A single 3.75 mg/kg IV dose of Tβ4 administered 24 hours after embolic middle-cerebral-artery occlusion in adult rats produced durable adhesive-removal and modified Neurological Severity Score improvements from day 14 through day 56, with no change in infarct volume [5]. The pattern mirrors TBI — neurorestorative rather than neuroprotective. **Has Tβ4 been studied in multiple sclerosis models?** Yes. In experimental autoimmune encephalomyelitis and cuprizone-diet demyelination mouse models, daily IP Tβ4 increased oligodendrocyte progenitor proliferation and the density of mature myelinating oligodendrocytes through an EGFR-dependent program. New mature-OL density correlated with EAE clinical score recovery at r = 0.73 (p < 0.05) [2]. The work supports remyelination, not just protection against demyelination. **What about Alzheimer's?** Two lines of evidence. In 12.5-month-old APP/PS1 mice challenged with systemic LPS, 5 mg/kg IV Tβ4 prevented LPS-induced amyloid plaque accumulation and attenuated sickness behavior [6]. In 2025, Zeng and colleagues used familial-AD iPSC-derived cerebral organoids to show that 0.5 μg/mL Tβ4 increased neuronal density and lowered intracellular Aβ; in parallel, AAV-driven TMSB4X overexpression in 5xFAD mouse cortex rescued neuronal hyperexcitability [7]. The combined organoid-and-mouse identification of Tβ4 as an AD intervention target is recent and exploratory. ## Cardiac and the rodent-to-large-mammal gap **Was Thymosin Beta-4 ever shown to repair adult hearts?** In mice, yes. Smart and colleagues' 2007 Nature paper established that IP Tβ4 at 150 μg every three days mobilized adult mouse epicardial progenitor cells, restored their multipotent capacity, and produced new coronary-vessel formation in injured hearts [16]. The work grounded the cardiac-repair clinical hypothesis behind the RGN-352 program. **What happened in pigs?** The rodent signal did not translate. Wei and colleagues, in a 2016 randomized 24-animal study, administered 150 μg/kg IV bolus plus maintenance to pigs before or after a closed-chest 90-minute ischemia / 24-hour reperfusion myocardial-injury protocol. Global infarct size measured by TTC and MRI was not reduced versus vehicle [23]. The Phase II human cardiac trial that the rodent work motivated — RGN-352 (NCT01311518), designed for ~75 patients at 450 mg or 1,200 mg IV daily x 3 then weekly x 4 — has been listed as Withdrawn since September 2021. **Why is this relevant to TB-500?** It is the most concrete published illustration that Tβ4 biology, no matter how robust in rodents, does not necessarily translate to large mammals on every endpoint. The cardiac translation gap is the reason any honest reading of this literature distinguishes 'rodent signal' from 'eventual human therapeutic.' ## Wound healing and the eye **What is the strongest human-efficacy signal in the Tβ4 program?** RGN-259, the 0.1% Tβ4 ophthalmic solution. In a randomized, placebo-controlled, double-masked Phase III trial of 18 patients with neurotrophic keratopathy (NCT02600429), complete corneal healing at day 29 was observed in 60% of treated patients versus 12.5% of placebo (p = 0.066), with statistically significant healing at day 43 (p = 0.036) and durable benefit two weeks after stopping treatment [13]. It is the most rigorous published efficacy signal in the entire Tβ4 development program. The same RGN-259 formulation missed the prespecified primary endpoints in Phase III ARISE-3 dry-eye disease. **Does Tβ4 actually accelerate wound healing in animals?** In the foundational mouse alkali corneal-burn study, topical Tβ4 at 5 μg BID accelerated re-epithelialization at every measured time point and reduced corneal IL-1β, KC, and MIP-2 chemokine mRNA [14]. In rats, full-thickness dermal wounds close faster with topical dimeric Tβ4 than with equimolar monomeric Tβ4 [15]; an engineered tandem-repeat construct of the actin-binding region (the same LKKTET class as TB-500) accelerated corneal-epithelium closure beyond monomeric Tβ4 in 2024 [17]. The most active 2024–2025 work is in delivery platforms: dissolvable microneedles loaded with 248 μg Tβ4 per patch [18], and HAMA/PLMA hydrogels loaded with stem-cell exosomes overexpressing Tβ4 in diabetic mouse wounds [19]. ## Safety, pharmacokinetics, and regulation **What is the half-life of TB-500?** There is no peer-reviewed human pharmacokinetic study of the synthetic 7-amino-acid TB-500 fragment. The widely circulated '2–3 hour half-life' figure traces to vendor materials and should be treated as low-confidence [22]. For the 43-AA recombinant parent peptide, both Phase I cohorts (Ruff 2010 at 42–1,260 mg IV in US volunteers; Wang 2021 at 0.05–25 μg/kg IV in Chinese volunteers) reported biphasic plasma decline with rapid distribution and terminal exposure over hours, with dose-proportional Cmax and AUC and no accumulation [11][12]. **Has TB-500 ever been in a human clinical trial?** No registered human clinical trial of the synthetic 7-amino-acid TB-500 fragment has been published. The entire published human safety and efficacy record is for the 43-amino-acid recombinant parent peptide. The two are not interchangeable in the peer-reviewed literature, no matter how often they are treated as such in commercial materials. **Is TB-500 banned in sport?** Yes. The World Anti-Doping Agency prohibits TB-500 and its parent class at all times under S2 (Peptide Hormones, Growth Factors, Related Substances and Mimetics) and the catch-all S0 (Non-Approved Substances) of the WADA Prohibited List in the current code year. Athlete sanctions have been issued, including a four-year ineligibility for a Canadian athlete in a non-analytical positive case involving BPC-157 and TB-500. Equine doping-control LC-MS detection methods for intact TB-500 and its metabolites are published [22]. **Why is TB-500 associated with horse racing?** The analytical chemistry was built there first. Esposito and colleagues published the validated LC-MS method for detecting intact TB-500 and its metabolites in equine urine and plasma after IV administration in 2012; horse-racing was the historical regulated domain in which TB-500 first emerged as a controlled substance [22]. Human anti-doping testing for the synthetic fragment is downstream of that equine analytical work. ## Context and unresolved questions **Is Thymosin Beta-4 always anti-fibrotic?** No. In a 2023 CCl4 mouse model, conditional deletion of Tβ4 in hepatic stellate cells REDUCED αSMA+ activated HSC density and ameliorated liver fibrosis — direct evidence that Tβ4 plays a pro-fibrotic role in the hepatic compartment, opposite to its anti-fibrotic role in heart, kidney, and lung [21]. Tβ4 biology is context-dependent and is not universally regenerative. Anyone framing it that way is reading the literature selectively. **What is AcSDKP and why does it matter?** AcSDKP — N-acetyl-Ser-Asp-Lys-Pro, also known as Goralatide — is an N-terminal tetrapeptide enzymatically cleaved from full-length Tβ4 by prolyl-oligopeptidase. It carries its own antifibrotic and pro-angiogenic activity through TGF-β1 / Smad suppression and is cleared almost exclusively by the N-terminal active site of angiotensin-converting enzyme. ACE-inhibitor therapy elevates endogenous AcSDKP, which is a recurring theme in cardiorenal Tβ4 / AcSDKP work [20]. Whether the synthetic 7-amino-acid TB-500 fragment can be cleaved by prolyl-oligopeptidase to liberate AcSDKP at all is mechanistically unresolved. This matters because AcSDKP carries a meaningful share of the downstream activity that the literature attributes to 'Tβ4.' **What are the main risks and unknowns with research-chemical TB-500?** Three categories. First, manufacturing: research-chemical TB-500 is sold without GMP manufacturing, lot-release testing, endotoxin control, or sterility assurance. Purity, microbial contamination, and immunogenicity risks dwarf the peptide's pharmacology in unregulated use. Second, mechanistic translation: the 7-amino-acid synthetic fragment retains G-actin binding in vitro, but whether it recapitulates Tβ4's downstream signaling — AcSDKP release, PINCH-ILK-Akt assembly, progenitor mobilization — has not been resolved in the peer-reviewed literature. Third, indirect inference: most of what is 'known' about TB-500 is inferred from the parent molecule's literature. The inferential bridge is plausible but unverified for most endpoints. --- An independent editorial reading of the peer-reviewed literature — not a clinic, not a vendor, not a recommendation.