Ac-SDKP vs Thymosin Beta-4

Inhibits hematopoietic stem cell entry into S-phase. Blocks TGF-β1-mediated fibroblast activation, reducing collagen deposition. Promotes angiogenesis via VEGF upregulation. Regulated in vivo by ACE enzyme.

Ac-SDKP (N-acetyl-seryl-aspartyl-lysyl-proline) is an endogenous tetrapeptide generated from the N-terminus of thymosin beta-4 by the enzyme prolyl oligopeptidase, with further regulation by angiotensin-converting enzyme (ACE), and is characterized by roles in hematopoietic progenitor regulation and anti-fibrotic signaling in renal, cardiac, and vascular tissue. Ac-SDKP inhibits collagen synthesis and fibroblast proliferation, reduces TGF-beta-1-mediated fibrotic signaling, and promotes anti-inflammatory macrophage polarization in preclinical models, suggesting a role in tissue homeostasis downstream of the thymosin beta-4 pathway. Preclinical studies in rodent models of renal fibrosis and systemic lupus erythematosus — predominantly from the NIH-funded Rhaleb and Carretero laboratory at Henry Ford Health — have demonstrated that exogenous Ac-SDKP reduces collagen deposition and inflammatory infiltrate; no human clinical trials have been completed or indexed in PubMed. Ac-SDKP has no FDA approval and no approved indication in any jurisdiction; it is studied as a research compound with a plausible anti-fibrotic mechanism and consistent preclinical evidence, but extrapolation of rodent findings to human therapeutic outcomes has not been validated by any clinical investigation.

Sequesters G-actin monomers via its WH2 domain, regulating actin dynamics and cell migration. Upregulates metalloproteinases and growth factors for tissue remodeling. Promotes cardiomyocyte survival and angiogenesis post-injury.

Thymosin beta-4 (Tb4) is an endogenous 43-amino-acid protein ubiquitously expressed in mammalian tissues, best characterized for its role in G-actin sequestration, cell migration promotion, and tissue repair signaling across multiple organ systems. Tb4 exerts reparative effects by upregulating angiogenesis, modulating inflammation, and generating the anti-fibrotic tetrapeptide Ac-SDKP through enzymatic cleavage; preclinical models in cardiac, renal, and musculoskeletal tissue have demonstrated measurable regenerative outcomes following exogenous administration. Published literature supports anti-fibrotic activity in animal models of renal fibrosis and cardiovascular injury, and the Tb4-Ac-SDKP pathway has been characterized as a plausible target in fibrosis biology; however, clinical translation has been limited, with a Phase 2 cardiac repair trial that did not demonstrate efficacy sufficient to advance to Phase 3. Exogenous thymosin beta-4 has no FDA approval for any indication; it is available only as a research compound, and the substantial gap between preclinical findings and human clinical outcomes represents an important limitation of the current evidence base. Thymosin beta-4 vs TB-500 TB-500 is a commercial label used for synthetic thymosin beta-4 in the peptide research market. The underlying compound is the same 43-amino-acid sequence as endogenous Tb4; "TB-500" originated as a brand name from veterinary product contexts and has since become the predominant research market name for synthetic thymosin beta-4. When research suppliers, athletes, or forum communities reference TB-500, they are referring to synthetic Tb4 — the same compound profiled here. The TB-500 label is commonly associated with injectable research peptide use; the thymosin beta-4 label is associated with the biochemical and medical literature. Some suppliers sell "TB-4 Frag" (the Ac-SDKP tetrapeptide fragment), which is a distinct, smaller molecule derived from enzymatic cleavage of Tb4, not the full-length thymosin beta-4 protein. Thymosin beta-4 dosage in research contexts: Research protocols described in preclinical literature and anecdotal human use reports typically reference doses in the range of 2–5 mg per injection, administered subcutaneously or intramuscularly, with a loading phase of 2–4 injections per week followed by a maintenance phase of 1–2 injections per week. These dosage figures are derived from research compound use and veterinary contexts, not from FDA-approved human clinical protocols — no approved human dosing exists. The Phase 2 cardiac repair trial that administered intravenous Tb4 used significantly different dose and route parameters. Thymosin beta-4 is available only as a research compound; it is not FDA-approved for any human indication and is not available through licensed prescription channels.