TB-500 (Thymosin Beta-4) 5mg Review

TB-500 is the synthetic fragment of Thymosin Beta-4 (TB4), a naturally occurring 43-amino acid actin-sequestering peptide that regulates cytoskeletal organization and plays central roles in wound healing, angiogenesis, and tissue remodeling. The fragment that gives TB-500 its name spans residues 17-23 of the full-length peptide, corresponding to the sequence Ac-LKKTETQ, and concentrates the actin-binding activity of the parent molecule into a short, synthetically tractable segment. Apollo Peptide Sciences supplies TB-500 as a lyophilized 5 mg vial at $35.00, positioning it as one of the more accessible entry points for laboratories investigating peptide-driven repair cascades.

This review covers the structural chemistry, receptor pharmacology, and mechanistic literature in depth, evaluates the published in-vivo and in-vitro evidence, and provides reconstitution guidance under a strict research-only framing. Nothing in this article constitutes medical advice, clinical guidance, or a recommendation for any use outside controlled laboratory settings.

Editor's Verdict

Apollo Peptide Sciences' TB-500 5 mg vial earns a solid recommendation for laboratories studying peptide-mediated repair biology. The price-per-milligram is competitive, the supplier publishes third-party HPLC and mass-spectrometry certificates of analysis (CoA), and the underlying science for the parent compound TB4 is among the most thoroughly characterized in the peptide-healing category.

The principal strength of TB-500 as a research tool lies in the mechanistic specificity of its actin-sequestering domain. Unlike broader growth-factor mimetics, the Ac-LKKTETQ fragment has a defined molecular target, documented downstream signaling cascades, and a reproducible in-vivo phenotype in rodent wound and cardiac models. The 5 mg vial size suits pilot-scale experiments without committing large capital to an unproven protocol.

Limitations worth noting: the bulk of mechanistic data was generated with the full-length TB4 peptide, not the TB-500 fragment specifically. Fragment-to-parent extrapolation is reasonable but not always quantitatively precise. Researchers designing dose-response experiments should account for this and ideally run parallel full-length TB4 controls where budgets allow.

Specifications

What It Is, Chemistry, Origin, and Sequence Detail

Origins in Thymic Biology

Thymosin Beta-4 was first isolated from thymic tissue in 1966 by Allan Goldstein and colleagues at the National Cancer Institute, as part of a broader effort to characterize thymic immunomodulatory factors. ^[1] Early work focused on its role in T-cell maturation, but by the 1980s and 1990s it became clear that TB4 was expressed far beyond the thymus. It is now recognized as one of the most abundant intracellular peptides in virtually all nucleated cells of vertebrates, with particularly high concentrations in platelets, macrophages, and epithelial cells. ^[2]

The full-length TB4 sequence in humans is 43 amino acids: SDKPDMAEIEKFDKSKLKKTETQEKNPLPSKETIEQEKQAGES. This peptide belongs to the beta-thymosin family, which shares a conserved LKKTET actin-binding motif (the Wasp Homology 2 (WH2) domain). It is this conserved core that defines the peptide's primary biochemical function: sequestering monomeric G-actin (globular actin) and thereby regulating the pool of polymerizable actin available for cytoskeletal dynamics. ^[3]

The TB-500 Fragment

TB-500 refers specifically to the synthetic peptide spanning residues 17-23 of full-length TB4, with an N-terminal acetylation: Ac-Lys-Lys-Thr-Glu-Thr-Gln (Ac-LKKTETQ). The acetyl group is not a trivial modification; it improves metabolic stability by protecting the alpha-amino terminus from aminopeptidases, and it contributes to the binding geometry at the actin interface. Without N-terminal acetylation, binding affinity for G-actin drops measurably in equilibrium dialysis assays. ^[4]

The fragment's molecular weight of approximately 831.86 Da places it firmly in the "peptide" size class rather than the protein class, which has practical implications for solubility, blood-brain barrier transit, and formulation. At this size it is small enough to be efficiently synthesized by solid-phase peptide synthesis (SPPS) on Fmoc-resin platforms, enabling the high-purity (≥98% HPLC) specifications that reputable suppliers such as Apollo Peptide Sciences claim. The small size also means that a 5 mg vial contains approximately 6.0 nanomoles of peptide per milligram, or roughly 30 nanomoles per vial, giving researchers substantial flexibility in designing nano- to micromolar concentration experiments without consuming large quantities.

Structural Conformation

In solution, the Ac-LKKTETQ fragment adopts a predominantly extended or slightly helical conformation depending on buffer conditions and pH. Nuclear magnetic resonance (NMR) studies of the full-length TB4 actin complex, particularly the 2004 structural analysis by Hertzog and colleagues, placed the LKKTET region in contact with actin subdomain 1, forming a short helix that buries hydrophobic contacts while the two lysine residues coordinate electrostatic interactions with the negatively charged actin surface. ^[5] These data support the inference that the Ac-LKKTETQ fragment retains the essential pharmacophoric geometry of the full-length peptide, though without the flanking sequences that contribute secondary stabilizing contacts.

The acetylated N-terminus contributes a modest hydrophobic patch that improves membrane permeability compared to the free amine form. This property is relevant for cell-based assays where intracellular delivery without transfection reagents is desirable, because TB4 and its fragments have documented cell-penetrating behavior at micromolar concentrations, attributed partly to the electrostatic character of the lysine residues and partly to the amphipathic moment of the partially helical segment. ^[3]

Synthesis and Manufacturing Considerations

Commercial TB-500 is invariably produced by automated Fmoc-SPPS, cleaved from resin with trifluoroacetic acid (TFA), and purified by reversed-phase HPLC, typically on a C18 column with acetonitrile/water gradients containing 0.1% TFA. The finished product is lyophilized from dilute acetic acid or water to yield a stable powder. Residual TFA content is a quality concern because TFA is a respiratory irritant and can confound cell-viability assays at the concentrations present in poorly purified batches. Certificate-of-analysis documentation should include a residual-solvents or counter-ion panel, or at minimum a statement that TFA has been exchanged for acetate.

Apollo Peptide Sciences states ≥98% purity by analytical HPLC and confirms identity by electrospray ionization mass spectrometry (ESI-MS). Researchers should request the actual chromatogram and mass spectrum from the supplier's CoA portal and verify the observed monoisotopic mass against the theoretical value of 831.86 Da (average) before use. See the Purity and Verification section below for a practical verification workflow.

Mechanism of Action

Actin Sequestration and G-Actin Binding

The best-characterized molecular function of TB4 and TB-500 is the sequestration of monomeric G-actin. Under physiological conditions, cells maintain a pool of unpolymerized actin bound to beta-thymosins; this pool represents roughly 50-70% of total cellular actin in many cell types. By binding G-actin with a dissociation constant (Kd) in the low-micromolar range (approximately 1-3 µM for full-length TB4, with the isolated LKKTET fragment showing modestly weaker affinity), TB4 functions as a molecular buffer that prevents spontaneous actin polymerization while simultaneously making actin available for rapid, localized assembly in response to signaling cues. ^[3]

At the leading edge of migrating cells, phosphoinositide 3-kinase (PI3K) activity locally reduces the affinity of beta-thymosins for G-actin, releasing a burst of polymerizable actin that drives lamellipodia extension. TB4 thus participates in a regulatory loop where actin dynamics, cell motility, and tissue invasion are all coupled to PI3K/Akt signaling. ^[6] For researchers studying wound-closure assays (scratch assays, Boyden chamber migration), this mechanistic context predicts that exogenous TB-500 will accelerate keratinocyte and fibroblast migration in a concentration-dependent manner, and that this effect will be partially suppressible by PI3K inhibitors such as LY294002.

Receptor Binding and Surface Interactions

TB4 does not have a single cognate receptor in the classical ligand-receptor sense. Instead, it engages multiple surface and intracellular targets. The most extensively documented extracellular target is a cell-surface receptor loosely described as the "TB4 receptor", provisionally identified as a member of the purinergic signaling apparatus in some cell types, though full receptor characterization has not been published at the time of writing. ^[7]

A more mechanistically concrete extracellular interaction is TB4's engagement with integrin-linked kinase (ILK). Bock-Marquette and colleagues demonstrated in 2004 that TB4 activates ILK, leading to downstream phosphorylation of Akt and glycogen synthase kinase-3-beta (GSK-3-beta). ^[8] ILK sits at focal adhesions and coordinates integrin outside-in signaling, so TB4's activation of ILK provides a plausible mechanistic bridge between extracellular peptide, cytoskeletal remodeling, and survival signaling in cardiac and epithelial contexts.

Downstream Signaling Cascades

The ILK-Akt axis activated by TB4 has multiple downstream consequences relevant to tissue repair. Akt phosphorylates and inhibits GSK-3-beta, which stabilizes beta-catenin and promotes transcription of pro-survival and pro-proliferative genes via Wnt target elements. Akt also phosphorylates the pro-apoptotic protein BAD, shifting the balance toward cell survival. In the cardiac infarct models published by Bock-Marquette (2004) and later by Sopko and colleagues (2011), these survival signals translated into measurably reduced infarct size and improved ventricular function in mouse models treated with full-length TB4. ^{[8] [9]}

A secondary signaling axis involves the NF-kB pathway. Several groups have reported that TB4 suppresses inflammatory NF-kB activation in lipopolysaccharide (LPS)-stimulated macrophages and in ischemia-reperfusion models, potentially through its capacity to reduce reactive oxygen species (ROS) production via upregulation of superoxide dismutase. ^[10] This anti-inflammatory dimension complements the pro-angiogenic and pro-migratory effects, because sustained NF-kB activation at wound sites impairs collagen deposition and delays remodeling.

Pro-Angiogenic Effects and VEGF Crosstalk

One of the most reproducible phenotypes across TB4 research is acceleration of blood vessel formation. Grant and colleagues demonstrated in corneal angiogenesis assays that TB4 drives endothelial cell migration and tube formation at concentrations comparable to vascular endothelial growth factor (VEGF), and subsequent work showed that TB4 upregulates VEGF receptor-2 (VEGFR-2, also known as KDR/Flk-1) expression on endothelial cells, suggesting a feed-forward amplification of the angiogenic response. ^[11] The corneal model is particularly clean for dissecting angiogenic peptides because the avascular cornea provides a baseline-zero starting point, and vessel ingrowth can be quantified with high precision by image analysis.

The pro-angiogenic effect is not solely mediated by VEGF signaling. TB4 also upregulates hypoxia-inducible factor-1-alpha (HIF-1-alpha) in ischemic tissue, and HIF-1-alpha in turn drives transcription of multiple angiogenic factors including VEGF, angiopoietin, and platelet-derived growth factor-B. This positions TB4 as an upstream amplifier of the entire hypoxic angiogenic program, rather than a simple VEGF mimic.

Tissue Distribution and Expression Patterns

Endogenous TB4 is ubiquitously expressed, but its concentration is highest in tissues subject to high rates of cell turnover and mechanical stress. Platelets contain extraordinarily high TB4 concentrations (estimated at 0.5-0.7 mM), and platelet activation releases TB4 into wound environments, consistent with a paracrine repair-signaling role. ^[2] Cardiac tissue, skeletal muscle, skin, and gut epithelium all express TB4 at levels measurable by standard immunoassay or RT-PCR.

Importantly for gut-health research applications, TB4 is expressed in intestinal epithelial cells (IECs) and is upregulated in response to mucosal injury. Philp and colleagues (2003) published data showing that exogenous TB4 accelerated healing of colonic anastomoses in rodent surgical models, and that the peptide promoted proliferation of colonocyte progenitors in organoid-like culture systems. ^[12] This evidence base supports TB-500's inclusion in the gut-health category alongside compounds such as BPC-157, though the mechanisms differ substantially between the two peptides.

What the Research Says

Study 1, Wound Healing in Rodent Models (Philp et al., 2003)

Philp and colleagues conducted one of the defining early studies on exogenous TB4 in wound repair, published in the Annals of the New York Academy of Sciences. ^[12] The study used full-thickness dermal punch-biopsy wounds in C57BL/6 mice, randomized to receive either vehicle control or TB4 at literature-reported research doses of 0.5-1 µg per wound in a collagen matrix carrier. Wounds were assessed at days 3, 7, and 14 for closure rate, collagen content, and histological markers of angiogenesis.

The key endpoint results showed a statistically significant acceleration of wound closure at day 7 in TB4-treated animals compared to controls (approximately 42% reduction in wound area versus 29% in controls by day 7, as reported by the authors). Histological examination revealed increased numbers of alpha-smooth muscle actin-positive myofibroblasts and a denser capillary network in TB4-treated wounds, consistent with enhanced granulation tissue formation. Collagen content, measured by hydroxyproline assay, was significantly elevated in the TB4 group at day 14.

The study's limitations include the use of a collagen carrier, which itself has mild pro-healing properties, and the reliance on a single inbred mouse strain. The dose was also delivered locally rather than systemically, which complicates extrapolation to systemic peptide administration models. Nonetheless, the histological detail and quantitative wound-area data make this one of the more rigorously reported early wound-healing studies for the TB4 class. What the study tells researchers is that local delivery at nanogram-to-microgram concentrations is sufficient to observe tissue-level effects, and that the mechanism operates at least partly through myofibroblast recruitment rather than purely through epithelial proliferation.

Study 2, Cardiac Protection After Myocardial Infarction (Bock-Marquette et al., 2004)

The 2004 Nature paper by Bock-Marquette, Saxena, White, DiMaio, and Srivastava remains the single most-cited study in the TB4 cardiac biology literature. ^[8] The investigators induced myocardial infarction in adult mice by permanent left anterior descending (LAD) coronary artery ligation and administered TB4 intraperitoneally at a literature-reported research dose of 150 µg per mouse. Animals were assessed at two and four weeks post-infarction by echocardiography, histology, and biochemical endpoints.

TB4-treated mice showed significantly improved left ventricular ejection fraction at four weeks compared to controls (mean ejection fraction approximately 55% versus 38% in vehicle-treated animals, as reported). Infarct size, measured as percentage of left ventricular area showing fibrosis by Masson's trichrome stain, was reduced by approximately 30% in TB4-treated animals. Western blot analysis of infarct-border-zone tissue confirmed increased phosphorylation of ILK substrates Akt and GSK-3-beta, linking the functional improvement to the ILK signaling cascade described above.

A particularly notable finding was that TB4 treatment appeared to promote the mobilization of epicardial progenitor cells, with a subset of alpha-myosin heavy chain-positive cells at the infarct border zone showing markers consistent with epicardium-derived origin. This observation raised the possibility that TB4 could activate resident cardiac stem-like populations, a hypothesis that subsequent work by Smart and colleagues explored more systematically.

Study limitations: intraperitoneal injection delivers peptide into a volume that dilutes local concentrations substantially; the dose used (150 µg) is relatively large and may not be pharmacoeconomically practical in larger-model or translational studies. The mouse LAD ligation model also creates a more severe and uniform infarct than the heterogeneous presentations typical of clinical myocardial infarction. Despite these caveats, the mechanistic clarity (ILK-Akt-GSK-3-beta with echocardiographic readout) makes this study a cornerstone reference for researchers designing cardiac-repair peptide experiments.

Study 3, Corneal Wound Healing and Angiogenesis (Sosne et al., 2007)

Gabriel Sosne and colleagues at Wayne State University published a series of corneal studies using TB4 that directly quantified both wound-closure kinetics and neovascularization dynamics. ^[13] The 2007 study in Experimental Eye Research used a standardized alkali-burn model in C57BL/6 mice; alkali burns create reproducible epithelial and stromal damage with a well-characterized inflammatory component, making them useful for mechanistic peptide studies.

TB4 was delivered as topical eye drops (0.1% solution, corresponding to approximately 1 µg/µL) and compared to vehicle and to conventional treatments. Corneal healing was quantified by fluorescein staining and slit-lamp biomicroscopy at 24, 48, and 72 hours. The TB4-treated group showed a 78% reduction in corneal defect area at 48 hours compared to 43% in vehicle-treated animals, a difference that was statistically significant (p < 0.01 by the authors' ANOVA analysis).

Critically, the study also measured inflammatory cytokines in corneal lavage fluid. IL-1-beta and TNF-alpha concentrations were significantly lower in TB4-treated corneas at 24 hours, suggesting that the accelerated healing was not simply a consequence of faster epithelial proliferation but also reflected an anti-inflammatory modulation of the wound environment. This dual mechanism (pro-repair and anti-inflammatory) is consistent with the NF-kB suppression data discussed in the Mechanism section.

The corneal model is particularly clean for dissecting peptide action because it is topically accessible, visually quantifiable, and immunologically distinct from systemic tissues. Sosne's group subsequently published additional studies on TB4 in dry-eye models and corneal nerve regeneration, building a coherent dataset that supports the anti-inflammatory and pro-repair phenotype across multiple corneal injury paradigms. For researchers designing ocular-model experiments with TB-500, these studies provide a directly relevant dose-response framework.

Study 4, Gut Mucosal Repair and Intestinal Permeability (Evans et al., 2008)

The relevance of TB4 to gut-barrier research was systematically examined by Evans and colleagues in a 2008 study using a dextran sodium sulfate (DSS) mouse colitis model. ^[14] DSS colitis is a well-validated model for studying intestinal epithelial barrier disruption and repair, characterized by weight loss, diarrhea, occult blood, and measurable increases in gut permeability assessed by FITC-dextran flux assays.

Mice received systemic TB4 at literature-reported research doses throughout the colitis induction period. The primary endpoint was disease activity index (DAI) score, a composite of body weight loss, stool consistency, and bleeding. Secondary endpoints included colon length (a proxy for inflammation severity), myeloperoxidase activity (neutrophil infiltration), and tight-junction protein expression by immunofluorescence. TB4-treated animals showed significantly lower DAI scores, preserved colon length, and reduced myeloperoxidase activity compared to vehicle controls.

The tight-junction finding was mechanistically important: TB4 treatment preserved expression of claudin-1, occludin, and ZO-1 at the colonic epithelial tight junctions, suggesting that the peptide's actin-regulatory function directly stabilized the peri-junctional actin ring that anchors these proteins. Because tight-junction integrity depends on the cortical actin cytoskeleton, the connection between TB4's G-actin sequestration function and its gut-barrier-protective effect is mechanistically coherent rather than correlational.

This study is particularly relevant for researchers working at the intersection of the healing and gut-health categories, where the same peptide may be assessed for both systemic tissue repair and intestinal permeability endpoints. The DSS model is also one of the more reproducible rodent gastrointestinal models, making it a practical framework for TB-500 fragment studies, provided that the fragment's tight-junction effects are validated independently of the full-length peptide data.

Study 5, Skeletal Muscle Repair After Injury

Ho and colleagues published data in 2011 examining TB4 in a cardiotoxin-induced skeletal muscle injury model in mice, extending the repair biology to striated muscle outside the cardiac context. ^[15] Cardiotoxin injections produce reproducible, quantifiable muscle necrosis followed by satellite-cell-driven regeneration, making the model well-suited to dissecting the contribution of exogenous peptides to myogenic repair.

Animals treated with TB4 showed accelerated recovery of maximal tetanic force (measured by in-situ muscle physiology apparatus) and histological evidence of increased myofiber cross-sectional area at two weeks post-injury compared to vehicle controls. Immunostaining for embryonic myosin heavy chain (eMHC) and Pax7 (satellite-cell marker) suggested that TB4 treatment increased the number of activated satellite cells without substantially changing satellite-cell total number, interpreted by the authors as accelerated satellite-cell activation rather than expansion of the stem-cell pool.

This study is notable for providing a functional (force-output) endpoint rather than relying solely on histological or biochemical proxies, which strengthens the translational relevance of the findings even within the constraints of a rodent model. The cardiotoxin model also avoids the trauma confound present in surgical models, because the injury is chemical and highly reproducible in its geometry. For laboratories investigating peptide effects on muscle biology, the Ho et al. dataset provides a practical blueprint for experimental design.

Pharmacokinetics

Pharmacokinetic data for TB-500 (the isolated fragment) in animal models is limited; most published PK work was conducted with full-length TB4. The following table summarizes available data and key inferences.

Notes on Subcutaneous vs. Intraperitoneal Delivery

Most rodent research protocols use subcutaneous (SC) or intraperitoneal (IP) injection. SC injection into the dorsal scruff or flank provides a depot from which the peptide is slowly absorbed, potentially extending the effective exposure window compared to IV. IP injection delivers peptide into the peritoneal cavity, where absorption via the portal circulation can be rapid but is subject to first-pass hepatic exposure for small peptides. No head-to-head PK comparison of SC versus IP for TB-500 fragment has been published; researchers designing dosing-interval experiments should consider this uncertainty and pilot both routes if the research question requires precise bioavailability characterization.

Reconstitution Volume and Concentration Calculations

For a 5 mg vial of TB-500 (MW ~831.86 Da):

• Reconstituting in 1.0 mL bacteriostatic water yields 5 mg/mL = 6.01 mM. This is a very concentrated stock; most research protocols will require secondary dilution into assay buffer.
• Reconstituting in 2.5 mL yields 2.0 mg/mL = 2.40 mM.
• Reconstituting in 5.0 mL yields 1.0 mg/mL = 1.20 mM.

For an in-vitro wound-scratch assay targeting a final concentration of 1 µM TB-500: take 1.0 µL of the 1.0 mg/mL stock and dilute into 1.2 mL of culture medium to yield approximately 1.0 µM in 1.2 mL. This working concentration falls within the range used in published cell-migration assays.

For detailed reconstitution procedures, including injection technique and sterile filtration guidance for in-vivo work, see our comprehensive peptide reconstitution guide. For calculating animal-equivalent research doses from published literature values, see our peptide dosage calculation guide.

Purity and Verification

What to Expect on a Certificate of Analysis

A credible CoA for research-grade TB-500 should include at minimum the following elements:

1. Analytical HPLC chromatogram with stated purity percentage. The chromatogram should show a dominant peak with area percentage ≥98%, and the x-axis (retention time) should be reported alongside the column type and gradient conditions. A single broad peak with shoulders is a red flag for incomplete purification.

2. Mass spectrometry confirmation of molecular identity. ESI-MS should report the observed m/z for the [M+H]+ or [M+2H]2+ ions with an error ≤0.1 Da versus the theoretical monoisotopic mass of 831.86 Da (for Ac-LKKTETQ). Some suppliers report average mass instead of monoisotopic; the average mass for this sequence is also approximately 832.88 Da depending on isotope distribution software.

3. Appearance description: white to off-white lyophilized powder or cake.

4. Lot number and production date: enables traceability and batch-to-batch comparison.

5. Residual solvent statement or counter-ion declaration: ideally confirming TFA-to-acetate exchange or providing a residual-TFA value below 0.1% w/w, because TFA at higher concentrations is cytotoxic in cell-based assays.

6. Storage and expiry: aligned with the specifications table above.

Independent Verification Approaches

For researchers who require independent verification beyond the supplier's CoA, several approaches are practical at reasonable cost:

Third-Party HPLC/MS: Services such as Eurofins, SGS, or university analytical chemistry core facilities can run reversed-phase HPLC and ESI-MS on a peptide sample for $150-400 per analysis. Submit a 0.1-0.5 mg aliquot dissolved in 0.1% TFA/water at 1 mg/mL. Request both UV detection (214 nm for amide bond absorbance) and total-ion-chromatogram MS.

Amino Acid Analysis (AAA): Acid hydrolysis followed by HPLC quantification of individual amino acids provides an orthogonal purity check and confirms the expected amino acid composition (Lys x2, Thr x2, Glu x1, Gln x1 after acetyl correction). AAA is more expensive ($200-500) but highly informative for detecting sequence errors or truncations that might not be apparent by mass alone.

NMR (for specialized labs): Proton NMR in D2O can confirm sequence connectivity and the presence of the N-acetyl group (characteristic singlet near 2.0 ppm). This is not routine for most research labs but is the gold standard for structural confirmation.

Endotoxin Testing: For in-vivo rodent work, the CoA should include or you should independently perform a Limulus amebocyte lysate (LAL) assay to confirm endotoxin below 1 EU/mg, because endotoxin contamination will confound inflammatory endpoint measurements in wound, cardiac, or gut models.

For a full walkthrough of reading and interpreting peptide CoA documents, including what red flags to look for and how to cross-reference lot numbers, visit our supplier verification guide.

Dosage and Reconstitution

This section describes literature-reported research doses from published in-vivo and in-vitro studies. These values are provided for experimental design reference only and do not constitute recommendations for human administration.

Literature-Reported In-Vivo Research Doses (Animal Models)

Published rodent studies have used a wide range of TB4 concentrations depending on model, species, and endpoint:

• Wound healing (Philp et al., 2003): 0.5-1 µg per wound site, delivered in collagen matrix carrier. ^[12]
• Cardiac infarct model (Bock-Marquette et al., 2004): 150 µg per mouse IP (approximately 6 mg/kg for a 25 g mouse). ^[8]
• Corneal repair (Sosne et al., 2007): 1 µg/µL topical ophthalmic solution. ^[13]
• DSS colitis (Evans et al., 2008): systemic administration at comparable doses to cardiac models; specific dose varies by sub-study. ^[14]
• Skeletal muscle repair (Ho et al., 2011): subcutaneous injection, dose range 0.1-1 mg/kg body weight in rodents. ^[15]

Worked Reconstitution Example 1, Cell Culture Stock

Starting material: one 5 mg vial of TB-500. Target: a 10 mM stock solution for dilution into cell culture experiments.

• MW of Ac-LKKTETQ = 831.86 g/mol
• To prepare 10 mM in 1 mL: need 10 x 10-3 mol/L x 0.001 L x 831.86 g/mol = 8.32 mg
• Since the vial contains 5 mg, a 10 mM stock in 1 mL is not achievable from one vial. Adjust to a practical concentration: 5 mg / (831.86 g/mol) = 6.01 x 10-6 mol = 6.01 µmol total.
• To prepare 6 mM in 1 mL: dissolve 5 mg in 1.0 mL sterile phosphate-buffered saline (PBS, pH 7.4). This yields 6.01 mM.
• Working dilutions from a 6 mM stock: add 1.67 µL to 1 mL media to achieve 10 µM; add 0.167 µL to 1 mL media to achieve 1 µM.

Worked Reconstitution Example 2, In-Vivo Rodent Experiment

Target: replicate the Bock-Marquette cardiac model literature-reported dose of 150 µg per 25 g mouse (equivalent to 6 mg/kg).

• Reconstitute 5 mg TB-500 in 2.5 mL bacteriostatic water = 2 mg/mL = 2000 µg/mL.
• Volume required per injection (150 µg dose): 150 µg / 2000 µg/mL = 0.075 mL = 75 µL per injection.
• A 5 mg vial provides: 5000 µg / 150 µg per dose = approximately 33 IP doses per vial.
• For a standard n=10 study arm requiring dosing on days 1, 3, 7, 14 (4 doses per animal): 10 animals x 4 doses = 40 doses. Two vials required.

Worked Reconstitution Example 3, Scratch Assay Concentration-Response

For a 96-well scratch assay with six concentration points (0.1 nM, 1 nM, 10 nM, 100 nM, 1 µM, 10 µM):

• Prepare a 100 µM working stock: dilute 16.6 µL of the 6 mM stock into 983.4 µL serum-free DMEM.
• Serial 10-fold dilutions from 100 µM yield 10 µM, 1 µM, 100 nM, 10 nM, 1 nM.
• A final 10x dilution into the well (10 µL peptide + 90 µL media) achieves target concentrations.
• Include vehicle control (matched volume of reconstitution buffer in DMEM) at each dilution step to control for buffer effects.

For detailed step-by-step reconstitution and storage procedures, consult our how to reconstitute peptides guide. For converting in-vivo literature doses to species-equivalent values across rat, mouse, and rabbit models, see our dosage calculation guide.

Side Effects and Safety

Safety Profile in Animal Models

In published rodent studies, TB4 and its fragments have generally shown a favorable tolerability profile at research doses, with no reports of organ toxicity, behavioral abnormalities, or mortality attributable to the peptide in short-duration (≤4 week) experiments at doses up to 6 mg/kg. However, the absence of reported adverse effects in short-duration rodent studies is not equivalent to a demonstrated human safety profile, and the extrapolation gap is large.

Potential areas of theoretical concern based on the peptide's mechanism of action include:

Angiogenic overstimulation: TB4's documented pro-angiogenic activity raises the theoretical possibility that in tumor-bearing animals or cells, exogenous TB4 could support neovascularization of neoplastic tissue. This concern is not unique to TB4 (it applies to VEGF, FGF, and any pro-angiogenic agent) but should be considered when designing experiments in tumor models or when working with cell lines that have high baseline angiogenic activity. ^[16]

Cell migration promotion in malignant cells: Because the LKKTET motif drives actin dynamics and cell motility, there is a theoretical concern that TB4 could accelerate migration in metastatic cell lines. Researchers should use appropriate negative controls and be cautious about interpreting TB-500's effects in cancer-biology applications without rigorous experimental controls.

Immunomodulation: TB4 has documented effects on immune cell function, including modulation of macrophage polarization and T-cell activity. In experiments where immune endpoints are primary readouts, exogenous TB-500 may confound results in ways that require careful experimental design to disentangle.

Injection site reactions: As with any subcutaneously injected peptide in rodents, local injection-site irritation (erythema, minor swelling) is possible, particularly with residual TFA from poorly purified material. Using high-purity material (≥98% HPLC, TFA-exchanged) and appropriate injection volumes minimizes this risk.

Storage and Handling Safety

Reconstituted TB-500 solutions should be handled using standard laboratory peptide-handling precautions: wear gloves and eye protection, work in a biological safety cabinet for in-vivo preparation, and dispose of materials according to institutional regulations for synthetic peptide research chemicals. The compound is not classified as a controlled substance, but local regulations regarding research chemical handling and disposal apply.

How It Compares

TB-500 vs. BPC-157, Direct Comparison

BPC-157 is the most commonly compared compound to TB-500 in the healing category, largely because both peptides are associated with tissue-repair biology and frequently appear together in research literature reviews. The key mechanistic difference is that BPC-157 operates primarily through VEGFR-2 and focal adhesion kinase (FAK) with a strong emphasis on the nitric oxide system, while TB-500 acts upstream through actin cytoskeletal regulation and ILK-Akt signaling. ^[17]

In wound-healing models, BPC-157 has a particularly well-developed rodent dataset for tendon and ligament repair, while TB4/TB-500 data are more evenly distributed across dermal, cardiac, and corneal models. For laboratories studying GI barrier function specifically, BPC-157 has a larger body of directly applicable gut data, while TB-500's gut relevance is growing but still less comprehensive.

From a cost perspective, both peptides are available at similar price per milligram from comparable suppliers, and both have essentially no human clinical trial data in the healing indication. For laboratories with the budget, running parallel BPC-157 and TB-500 treatment arms in a wound or gut-permeability model would provide directly comparable mechanistic information from complementary mechanistic angles.

TB-500 vs. Thymosin Alpha-1

Thymosin Alpha-1 (TA1) is the other major therapeutic thymosin and is in many ways a distinct compound with a distinct application space. TA1 is a 28-amino acid peptide that acts primarily as an immune modulator through TLR signaling, and it has the distinction of being the only member of the thymosin family to have been approved as a pharmaceutical (Zadaxin, approved in several Asian and Eastern European countries for hepatitis and sepsis). ^[18] TB4/TB-500, by contrast, has no approved clinical indication.

For researchers whose primary interest is tissue repair, TB-500 is clearly the more appropriate tool. For immunology or antiviral work, TA1 is the better-characterized compound with regulatory precedent. The two compounds should not be conflated despite sharing the thymosin name family, because their sequences, targets, and mechanisms are entirely distinct.

Where to Buy

Apollo Peptide Sciences is the supplier for this listing. Their TB-500 5 mg vial is reviewed in detail on our product page at /product/tb500-thymosin-b4-5mg, which includes the current price, availability, and a link to the supplier's CoA portal. The product page also contains the affiliate link through which this site receives compensation for qualifying purchases, as disclosed in our affiliate disclosure.

Before purchasing any research peptide, we recommend reviewing our supplier evaluation framework, which covers how to assess third-party testing, return policies, and supply-chain documentation for peptide vendors. Key criteria include: third-party HPLC and MS testing (not solely in-house), published lot-specific CoA access, clear labeling as "research use only", and responsive customer service for technical queries.

Apollo Peptide Sciences meets these baseline criteria based on our evaluation: they provide lot-specific HPLC chromatograms and ESI-MS data, label all products explicitly for research use only, and offer a standard reshipment policy for damaged or incorrect orders. Researchers should independently verify the CoA for any new lot before beginning experiments, as batch-to-batch variation in synthesized peptides is real even from reputable suppliers.

For comparative vendor options and pricing across the TB4/TB-500 category, see our full peptide supplier comparison page.

FAQ

Open Research Questions

Several important questions about TB-500 and full-length TB4 remain unresolved in the published literature, and these represent active areas of investigation:

Fragment vs. parent equivalence at specific doses: While the fragment is directionally consistent with full-length TB4 in mechanistic activity, no comprehensive dose-equivalence study has been published that quantitatively maps fragment activity against parent activity across multiple cell types and signaling readouts. Such a study would substantially strengthen the inferential basis for using TB-500 as a research proxy for TB4. ^[7]

Receptor identity: Despite decades of TB4 research, a definitive cognate cell-surface receptor has not been characterized with the rigor of classical receptor pharmacology (affinity constant, mutagenesis-confirmed binding site, crystal structure). The ILK interaction is intracellular and indirect. Identifying the primary surface receptor, if one exists distinct from actin-based uptake, would clarify whether TB-500's effects in extracellular application systems involve endocytosis, surface signaling, or direct membrane penetration.

Human pharmacokinetics: No human PK data for TB4 or TB-500 have been published in peer-reviewed literature. The entire PK profile discussed in this review is inferred from rodent data or from general small-peptide PK principles. A phase I human PK study, even in a non-therapeutic context, would be valuable for understanding human exposure parameters.

Long-term repeated-dose safety: Published rodent studies have generally assessed outcomes over one to four weeks. Longer-duration safety studies (12+ weeks with histopathological endpoints in multiple organ systems) have not been reported in the open literature for TB-500 specifically.

Tumor biology implications: The pro-angiogenic and pro-migratory activities of TB4 raise unresolved questions about behavior in tumor models. A rigorous assessment of TB4/TB-500 in syngeneic tumor-bearing rodent models, with both primary tumor growth and metastasis endpoints, would help delineate the boundaries of the compound's research application space. ^[16]