# Thymosin Beta-4: The Parent Protein Behind TB-500 (Where the Human Data Sit)

> Thymosin beta-4 is the 43-residue parent protein; TB-500 is its Ac-LKKTETQ fragment. Nearly all human data — the Phase 1 IV study and the ophthalmic RCTs — are on the full protein.

The 43-residue repair protein carries the actin-binding motif TB-500 is cut from — and carries nearly all of the human evidence too.

## Why this page exists

To read TB-500 honestly, you read thymosin beta-4 first. Thymosin beta-4 (Tβ4; gene TMSB4X; UniProt P62328) is a ubiquitous 43-amino-acid peptide, roughly 4,963 Da, that is the body's principal G-actin–sequestering molecule, present in nearly all human cells and released by platelets and macrophages at injury sites [5]. TB-500 is the synthetic Ac-LKKTETQ heptapeptide — residues 17–23 — its actin-binding core, near 889 Da [12].

The practical consequence: when a study says "thymosin beta-4 accelerated wound healing," it used the 43-residue protein, not the 7-mer sold as TB-500 [6]. Nearly all human data — the Phase 1 intravenous safety study and the ophthalmic RCTs — are on the full-length protein [6]. This page collects the parent-protein record so the [how TB-500 works](/research) section can keep the fragment and the protein from being conflated.

## The parent protein's established mechanism

Thymosin beta-4 binds monomeric (G-) actin one-to-one and caps both ends of the monomer, holding a buffered reserve of unpolymerized actin and regulating cytoskeletal assembly and cell motility — established at 2 Å resolution in a gelsolin-domain-1–thymosin beta-4–actin complex [1]. From that buffering role come its reported effects on cell migration, angiogenesis, anti-inflammatory signaling, anti-fibrotic remodeling (fewer myofibroblasts, less scarring), and progenitor-cell recruitment [5].

One mechanistic detail matters for honesty: full-length thymosin beta-4 can be cleaved at its N-terminus to release Ac-SDKP, a separate anti-fibrotic and angiogenic fragment — but Ac-SDKP comes from the N-terminal region and is NOT produced by the C-terminal-region TB-500 heptapeptide [5]. Some effects attributed loosely to "thymosin beta-4" trace to Ac-SDKP, which TB-500 cannot generate.

## The animal record the parent protein carries

The reason marketing for the fragment reaches for the protein is that the protein has the strong animal data. In a rat full-thickness wound model, topical or intraperitoneal thymosin beta-4 increased re-epithelialization by 42% at 4 days and up to 61% at 7 days versus saline, raised wound contraction by at least 11% by day 7, and increased collagen deposition and angiogenesis; as little as 10 pg stimulated keratinocyte migration two- to three-fold in vitro [3]. In mice, thymosin beta-4 activated the PINCH–ILK–Akt survival pathway and improved cardiac function after coronary artery ligation [2]. In rats with embolic stroke, intraperitoneal thymosin beta-4 improved neurological function at 2 and 12 mg/kg but not at the highest 18 mg/kg dose — a non-monotonic result with a modeled optimum near 3.75 mg/kg [4].

The record is honest about its limits, too. In dystrophin-deficient (mdx) mice, chronic thymosin beta-4 increased the number of regenerating fibers but did not improve muscle strength, cardiac function or fibrosis [5], and a porcine study found systemic thymosin beta-4 did not attenuate myocardial ischemia-reperfusion injury [5]. These null and negative results belong to the parent protein; the fragment has no comparable controlled series of its own [6].

## Where the human data actually sit

The human record is full-length thymosin beta-4, and it is modest. A randomized, placebo-controlled Phase 1 study dosed synthetic thymosin beta-4 intravenously in 40 healthy volunteers at 42, 140, 420 and 1260 mg (single dose, then daily for 14 days); it was well tolerated with no dose-limiting toxicities or serious adverse events and dose-proportional pharmacokinetics [6]. Topical thymosin beta-4 ophthalmic solution (RGN-259) improved dry-eye signs and symptoms in a randomized, placebo-controlled trial [7]; a 0.1% RGN-259 formulation promoted corneal healing and integrity [8]; and a dry-eye program was registered on ClinicalTrials.gov [9]. A human acute-MI trial of thymosin beta-4 completed [10]; an early injectable stroke trial was withdrawn [11]. That is the human evidence — for the protein, not the fragment.

## Thymosin beta-4 vs TB-500: the comparison table

The two are best held side by side. Thymosin beta-4 is the 43-residue parent protein (~4,963 Da) carrying nearly all the human and animal efficacy data; TB-500 is the synthetic Ac-LKKTETQ heptapeptide (~889 Da, formula C38H68N10O14) carrying the actin-binding motif but no completed controlled human trial of its own [6][12]. The analytical literature defined TB-500 precisely — the synthesis and characterization of the N-terminal acetylated 17–23 fragment of thymosin beta-4 was published as a doping-control reference [17]. Identity is settled; standalone human efficacy of the fragment is not [6].

## Recent parent-protein research

Thymosin beta-4 research continues on the full-length protein. A 2021 study released thymosin beta-4 from a functionalized self-assembling peptide to activate cardiac cells and promote cardiac repair, demonstrating engineered local delivery [16]. A 2024 study reported thymosin beta-4 improved cutaneous-flap survival in rats and activated Wnt/β-catenin signaling [14]. A 2026 Sports Medicine review placed thymosin beta-4/TB-500 among unapproved peptides with animal-model promise but scarce human safety data and limited regulatory oversight [13].

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A tabbed research binder on TB-500 and thymosin beta-4 — each evidence class filed behind its own divider and cited to source, the fragment kept apart from its parent protein, with no clinic behind the binder and nothing here dispensed or prescribed.