TB4-FRAG
Also known as: Thymosin Beta-4 Fragment, Ac-SDKP, Acetyl-N-Ser-Asp-Lys-Pro
TB4-FRAG (Ac-SDKP) is a tetrapeptide fragment of Thymosin Beta-4. It has been studied for anti-fibrotic and cardioprotective effects.
Key Findings at a Glance
- •TB4-FRAG is naturally degraded by angiotensin-converting enzyme, which means ACE inhibitor medications unexpectedly raise its levels, potentially contributing to those drugs' cardioprotective benefits.
- •TB4-FRAG protects bone marrow stem cells during chemotherapy by inducing reversible cell cycle arrest in the quiescent G0 phase, shielding them from cytotoxic drugs that target dividing cells.
- •In cardiac fibrosis models, TB4-FRAG reduces collagen deposition by 40 to 60 percent through direct suppression of TGF-beta signaling, the master driver of pathological scarring.
- •Despite being only four amino acids derived from the 43 amino acid Thymosin Beta-4, TB4-FRAG has distinct anti-fibrotic and hematopoietic activities not shared by its parent molecule.
TB4-FRAG Overview & Molecular Profile
TB4-FRAG is the N-terminal tetrapeptide fragment of Thymosin Beta-4 (sequence: Ac-SDKP), naturally released by prolyl oligopeptidase cleavage and present in human plasma at nanomolar concentrations. ACE is the primary degradation enzyme, so ACE inhibitors like lisinopril raise endogenous Ac-SDKP 4–5-fold, potentially explaining some of their cardioprotective effects. Research focuses on anti-fibrosis with 40–60% collagen reduction in cardiac, pulmonary, and renal fibrosis models, hematopoietic stem cell G0 arrest for chemotherapy protection, and TGF-β pathway suppression distinct from parent TB-500.
Mechanism of Action: Gene Activation & Angiogenesis
Ac-SDKP inhibits the proliferation of pluripotent hematopoietic stem cells, protecting them during chemotherapy. It also has anti-fibrotic effects, inhibiting collagen synthesis and fibroblast proliferation. The peptide is degraded by ACE, explaining why ACE inhibitors increase its levels.
Research-Observed Effects
Anti-fibrotic Activity
Research demonstrates TB4-FRAG's (Ac-SDKP) potent anti-fibrotic properties through inhibition of collagen synthesis, reduction of fibroblast proliferation, and prevention of myofibroblast transformation, making it a critical research compound for understanding and treating fibrotic diseases. Studies have documented 40-60% reductions in collagen deposition in various tissue fibrosis models including cardiac, pulmonary, renal, and hepatic fibrosis, with effects mediated through suppression of transforming growth factor-beta (TGF-β) signaling pathways that drive fibrotic remodeling. The peptide inhibits fibroblast DNA synthesis and cell cycle progression, preventing the excessive proliferation of connective tissue cells that leads to pathological scarring and organ dysfunction. Research shows Ac-SDKP reduces expression of fibrotic markers including alpha-smooth muscle actin, collagen types I and III, and fibronectin in treated tissues, indicating comprehensive suppression of the fibrotic program at the molecular level. Studies demonstrate that endogenous Ac-SDKP levels are naturally elevated by ACE inhibitor medications, suggesting this anti-fibrotic peptide may mediate some of the beneficial effects of these commonly prescribed cardiovascular drugs beyond blood pressure control. These anti-fibrotic properties have significant implications for treating pulmonary fibrosis, preventing post-myocardial infarction cardiac remodeling, addressing renal fibrosis in chronic kidney disease, and developing peptide-based therapies for fibrotic conditions that lack effective treatments.
Hematopoietic Stem Cell Protection
Research establishes TB4-FRAG as a potent regulator of hematopoietic stem cell proliferation, providing protection of bone marrow stem cells during chemotherapy by inducing reversible cell cycle arrest in the G0 phase where cells are resistant to cytotoxic drug damage. Studies demonstrate that Ac-SDKP reduces chemotherapy-induced myelosuppression by 30-50% in animal models, preserving bone marrow stem cell populations that would otherwise be depleted by rapidly dividing cell-targeting chemotherapy agents. The peptide's mechanism involves selective inhibition of primitive pluripotent stem cells while allowing more differentiated progenitor cells to continue cycling, providing targeted protection at the critical stem cell level. Research shows that this protective effect is reversible, with normal stem cell cycling resuming within 24-48 hours after peptide clearance, allowing for strategic timing of chemotherapy administration to maximize tumor cell killing while minimizing bone marrow damage. Clinical implications include potential for improved chemotherapy tolerance, reduced infection risk from neutropenia, and faster hematologic recovery between treatment cycles. These hematopoietic protection properties have driven research into combination protocols using Ac-SDKP with cytotoxic chemotherapy regimens, strategies for bone marrow preservation in intensive treatment protocols, and understanding the molecular regulation of stem cell quiescence.
Cardiac Remodeling Prevention
Extensive research demonstrates TB4-FRAG's ability to prevent adverse cardiac remodeling following myocardial infarction, reducing left ventricular fibrosis, preserving cardiac function, and improving outcomes in animal models of heart disease. Studies in post-infarction models show 30-50% reductions in scar tissue formation and preserved ejection fraction in Ac-SDKP treated animals compared to controls, with effects attributed to the peptide's anti-fibrotic properties preventing excessive collagen deposition in damaged heart tissue. The peptide reduces collagen accumulation in both the infarct zone and remote myocardium, preventing the global fibrotic remodeling that leads to heart failure progression following cardiac injury. Research demonstrates that Ac-SDKP treatment reduces cardiac stiffness and improves diastolic function, addressing the mechanical consequences of myocardial fibrosis that impair normal heart filling and cardiac output. Studies in hypertensive heart disease models show prevention of left ventricular hypertrophy-associated fibrosis, suggesting applications beyond acute cardiac injury to chronic cardiovascular conditions involving pathological remodeling. These cardiac remodeling prevention properties have significant implications for post-myocardial infarction treatment strategies, heart failure prevention research, and understanding how ACE inhibitors provide cardioprotection through elevation of endogenous Ac-SDKP levels.
Anti-inflammatory Effects
Research documents TB4-FRAG's significant anti-inflammatory properties including reduction of pro-inflammatory cytokine production, decreased macrophage infiltration into damaged tissues, and modulation of inflammatory cell phenotypes toward resolution-promoting states. Studies demonstrate reduced levels of inflammatory markers including TNF-alpha, IL-1beta, and IL-6 in tissues treated with Ac-SDKP, with effects observed in cardiac, pulmonary, and renal inflammation models. The peptide inhibits monocyte/macrophage accumulation in injured tissues and promotes polarization toward the alternatively activated M2 phenotype associated with tissue repair and resolution of inflammation rather than propagation of inflammatory damage. Research shows Ac-SDKP reduces reactive oxygen species production and oxidative stress markers in treated tissues, addressing both the inflammatory and oxidative components of tissue damage. Studies indicate synergistic effects between the anti-inflammatory and anti-fibrotic properties, as chronic inflammation drives fibrotic processes and reducing inflammation prevents the signals that initiate pathological scarring. These anti-inflammatory properties expand the therapeutic implications of TB4-FRAG research beyond fibrosis to include inflammatory diseases, tissue protection during injury, and understanding the relationship between inflammation and fibrotic remodeling.
Vascular Protection
Emerging research indicates TB4-FRAG may provide vascular protection through prevention of neointimal hyperplasia, reduction of vascular smooth muscle cell proliferation, and maintenance of endothelial function in conditions of vascular injury and atherosclerosis. Studies in animal models of vascular injury show reduced intimal thickening following arterial damage when Ac-SDKP levels are elevated, suggesting applications for preventing restenosis after angioplasty and stent placement procedures. The peptide's anti-proliferative effects on smooth muscle cells mirror its inhibitory effects on fibroblasts, preventing the excessive cellular accumulation that leads to vascular occlusion. Research documents improved endothelial-dependent vasodilation in hypertensive animals treated with ACE inhibitors that elevate Ac-SDKP levels, suggesting the peptide may preserve normal vascular function. Studies indicate potential protective effects against atherosclerotic plaque development through combined anti-inflammatory, anti-proliferative, and anti-fibrotic mechanisms. These vascular protection properties have implications for cardiovascular disease prevention research, understanding the protective mechanisms of ACE inhibitor therapy, and developing targeted approaches to prevent vascular remodeling in high-risk patients.
Research Dosing Information
| Route | Dose | Frequency | Notes |
|---|---|---|---|
| Subcutaneous/IV (research) | 0.5–2 mg/day | Per protocol | Preclinical dosing range; no approved human dosing; levels also influenced by ACE inhibitor therapy |
Note: Dosing information is provided for research reference only and is based on published studies using research subjects. This is not a recommendation for any use.
Research Studies & References
Ac-SDKP, a naturally occurring peptide, attenuates cardiac fibrosis
Peng H, Carretero OA, et al. (2003). Hypertension
This foundational study established Ac-SDKP as a potent endogenous anti-fibrotic peptide with significant cardiac protective effects, demonstrating that elevation of this Thymosin Beta-4 fragment prevents pathological collagen accumulation in heart tissue. Researchers used animal models of cardiac fibrosis induced by various stimuli including hypertension, myocardial infarction, and angiotensin II infusion, measuring collagen content, fibroblast activation markers, and cardiac function parameters. Results demonstrated 40-50% reductions in myocardial collagen deposition in animals with elevated Ac-SDKP levels, with parallel improvements in left ventricular compliance and diastolic function. The study identified that Ac-SDKP inhibits fibroblast proliferation and collagen synthesis through TGF-beta pathway modulation, establishing the molecular mechanism for its anti-fibrotic effects. Critically, researchers discovered that ACE (angiotensin-converting enzyme) is the primary degradative enzyme for Ac-SDKP, explaining why ACE inhibitor medications elevate endogenous peptide levels and suggesting this mechanism may contribute to the cardioprotective effects of these commonly prescribed drugs. These findings established Ac-SDKP as a significant endogenous regulator of cardiac fibrosis and opened new research directions into peptide-based approaches for preventing pathological heart remodeling.
Ac-SDKP regulates hematopoietic stem cell quiescence and chemotherapy protection
Azizi M, Bonnet D, et al. (1997). Blood
This seminal study established the mechanism by which Ac-SDKP protects hematopoietic stem cells during chemotherapy, demonstrating that the peptide induces reversible cell cycle arrest specifically in primitive pluripotent stem cells while allowing more differentiated progenitors to continue cycling. Researchers conducted bone marrow transplantation and chemotherapy challenge experiments in animals treated with Ac-SDKP versus controls, measuring stem cell survival, hematologic recovery, and engraftment capacity. Results showed that Ac-SDKP treatment prior to chemotherapy preserved 30-50% more long-term repopulating stem cells compared to controls, with these protected cells maintaining full regenerative capacity following treatment. The study documented that Ac-SDKP specifically arrests cells in the G0/G1 phase of the cell cycle where they are resistant to S-phase specific chemotherapy drugs, providing a mechanistic explanation for the protective effect. Flow cytometry analysis confirmed selective effects on primitive CD34+CD38- stem cell populations with less impact on committed progenitors, demonstrating the peptide's unique targeting of the most critical regenerative cell population. These findings established the scientific basis for using Ac-SDKP to protect bone marrow during intensive chemotherapy regimens and improved understanding of the molecular regulation of stem cell quiescence.
Anti-inflammatory effects of Ac-SDKP in organ fibrosis and cardiovascular disease
Rasoul S, Bhagat S, et al. (2020). Peptides
This comprehensive review synthesized recent research on Ac-SDKP's anti-inflammatory properties across multiple organ systems, establishing the peptide's role in modulating inflammatory responses that drive fibrotic disease progression. The authors analyzed studies demonstrating Ac-SDKP reduces macrophage infiltration, suppresses pro-inflammatory cytokine production, and promotes resolution of inflammation in cardiac, pulmonary, renal, and hepatic fibrosis models. Mechanistic analysis revealed that Ac-SDKP affects NF-kappaB signaling, inflammasome activation, and macrophage polarization pathways, providing molecular explanations for its broad anti-inflammatory effects. The review examined the relationship between inflammation and fibrosis, explaining how Ac-SDKP's anti-inflammatory properties prevent the chronic inflammatory signals that initiate and perpetuate fibrotic remodeling. Clinical relevance was discussed in the context of ACE inhibitor therapy, noting that elevated Ac-SDKP levels during treatment may contribute to the anti-inflammatory benefits of these medications beyond blood pressure reduction. These findings established Ac-SDKP as a multi-functional peptide with coordinated anti-inflammatory and anti-fibrotic properties, suggesting therapeutic potential for inflammatory and fibrotic diseases across multiple organ systems.
Frequently Asked Questions
How is TB4-FRAG different from TB-500?
TB4-FRAG (Ac-SDKP; 4 amino acids, ~446 Da) and TB-500 (Thymosin Beta-4 synthetic fragment, ~4963 Da) are derived from the same parent protein but act through completely different mechanisms. Ac-SDKP is cleaved from the N-terminus of TB-4 by prolyl oligopeptidase; it acts primarily as an anti-fibrotic and hematopoietic stem cell protector through TGF-β pathway suppression. TB-500 (representing the full β-thymosin actin-sequestering domain) promotes cell migration and actin polymerization for tissue repair. They do not share receptors, mechanisms, or pharmacological properties despite the naming similarity.
Why do ACE inhibitors increase Ac-SDKP levels?
ACE (angiotensin-converting enzyme) is the principal enzyme that degrades Ac-SDKP, cleaving it at the Asp-Lys bond. When ACE is pharmacologically inhibited by medications like lisinopril or enalapril, Ac-SDKP plasma levels rise 4–5-fold. This accumulation is now considered a potentially significant mechanism underlying ACE inhibitors' cardioprotective effects beyond blood pressure reduction—including the prevention of cardiac fibrosis and left ventricular hypertrophy that these drugs demonstrate in clinical trials. Some researchers propose that the Ac-SDKP elevation from ACE inhibition contributes as much as angiotensin II reduction to the long-term cardiac benefits of this drug class.
How does Ac-SDKP protect bone marrow during chemotherapy?
Ac-SDKP selectively induces G0 (quiescent) cell cycle arrest in pluripotent hematopoietic stem cells (HSCs)—the most primitive bone marrow progenitors. In G0, cells are not synthesizing DNA, making them resistant to S-phase-active chemotherapy agents (alkylating agents, antimetabolites). More differentiated progenitors (which are less critical) are less affected by Ac-SDKP and can continue normal hematopoiesis. Animal studies show 30–50% reductions in chemotherapy-induced myelosuppression with Ac-SDKP pre-treatment. The effect is reversible: when Ac-SDKP levels fall, HSCs resume normal cycling within 24–48 hours. This allows strategic timing: pre-treat with Ac-SDKP, administer chemotherapy (which kills rapidly dividing tumor cells while sparing quiescent HSCs), then withdraw Ac-SDKP to allow marrow recovery.
What fibrotic conditions is Ac-SDKP being studied for?
Ac-SDKP has demonstrated anti-fibrotic efficacy across multiple organ systems in preclinical models: cardiac fibrosis (post-MI remodeling and hypertensive cardiac fibrosis—40–60% collagen reduction), pulmonary fibrosis (bleomycin-induced lung fibrosis models), renal fibrosis (unilateral ureteral obstruction models), and hepatic fibrosis. The common mechanism is TGF-β1 pathway suppression: Ac-SDKP reduces TGF-β1 expression, blocks Smad2/3 phosphorylation, and inhibits myofibroblast differentiation from fibroblasts. Because fibrosis is a terminal pathway common to multiple organ injuries, Ac-SDKP's mechanism is potentially applicable across many conditions.
What is the clinical evidence for TB4-FRAG (Ac-SDKP) in human cardiovascular disease?
TB4-FRAG (Ac-SDKP) has indirect human evidence through the ACE inhibitor observation: ACE inhibitors that raise Ac-SDKP 4–5-fold produce well-documented reductions in cardiac fibrosis and left ventricular hypertrophy in hypertensive heart disease patients—effects that exceed what angiotensin II reduction alone would predict, suggesting the Ac-SDKP elevation contributes. Direct human interventional studies with exogenous Ac-SDKP do not exist as of 2026. The evidence for cardiac benefits comes from: (1) multiple animal models (hypertension models, post-MI models) showing dose-dependent fibrosis reduction; (2) the indirect ACE inhibitor human evidence. Phase I human trials would be needed to establish pharmacokinetics and safety.
What is the relationship between TB4-FRAG and Thymosin Beta-4 (TB-500) naming?
The naming overlap between TB4-FRAG (Ac-SDKP) and TB-500 (Thymosin Beta-4 synthetic fragment) causes significant confusion in the research community. To clarify: (1) Thymosin Beta-4 (TB-4) is a 43-amino-acid protein with multiple functional domains; (2) TB-500 refers to a specific synthetic fragment of TB-4 encompassing the actin-sequestering domain responsible for cell migration effects; (3) TB4-FRAG or Ac-SDKP refers to the N-terminal tetrapeptide Ala-Glu-Asp-Lys that is enzymatically cleaved from TB-4 by prolyl oligopeptidase. These are entirely different molecules with different mechanisms, different receptors, and different research applications—the TB-4 parent protein just happens to contain both active fragments at different termini.
How is Ac-SDKP administered in research and what are its pharmacokinetics?
Ac-SDKP has been studied primarily via continuous subcutaneous infusion using osmotic mini-pumps in animal research (delivering 0.8–1.6 nmol/kg/hr), producing steady-state plasma concentrations in the nanomolar range. As a naturally occurring tetrapeptide, it has a very short plasma half-life (minutes) due to rapid ACE degradation—which is why chronic infusion or repeated injection is needed. In humans, physiological plasma concentrations are approximately 0.1–0.5 nM, rising 4–5-fold with ACE inhibition. Research-grade Ac-SDKP is available for in vitro and animal studies; no standardized human administration protocol exists given the lack of clinical trials.
What is the neuroprotective research status for TB4-FRAG?
Ac-SDKP has shown neuroprotective properties in animal stroke models—reducing inflammatory cytokine production in ischemic brain tissue and preserving peri-infarct neural structure. The anti-inflammatory mechanism (TGF-β pathway modulation, IL-6 and TNF-α suppression) translates to reduced neuroinflammation after injury. Additionally, Ac-SDKP has been shown to promote neural progenitor cell (NPC) differentiation into neurons in vitro. These neurological findings are early-stage and have not been studied in any human neurological context. The cardiac and renal anti-fibrotic applications are more advanced than the neurological research direction.
BPC-157
C62H98N16O22
BPC-157 is a synthetic pentadecapeptide derived from a protective protein found in gastric juice. It has been extensively studied for its potential regenerative and protective properties in various tissue types.
TB-500
C212H350N56O78S
TB-500 is a synthetic version of the naturally occurring peptide Thymosin Beta-4, which plays a crucial role in tissue repair, cell migration, and blood vessel formation in the body.