Question 1

What is Ac-SDKP and where does it come from?

Accepted Answer

Ac-SDKP (N-acetyl-seryl-aspartyl-lysyl-proline) is a naturally occurring tetrapeptide found in human blood at low nanomolar concentrations. It is produced by enzymatic cleavage of thymosin beta-4, a 43-amino acid protein present in virtually all nucleated cells. The enzyme prolyl oligopeptidase (POP) cleaves thymosin beta-4 to release Ac-SDKP from its N-terminal region. The peptide is then degraded by angiotensin-converting enzyme (ACE), which hydrolyzes the Asp-Lys bond. This balance of production and degradation maintains steady-state Ac-SDKP levels in the circulation.

Question 2

How does Ac-SDKP relate to thymosin beta-4 and TB-500?

Accepted Answer

Ac-SDKP is a tetrapeptide fragment corresponding to the first four amino acids of thymosin beta-4 (with an acetylated N-terminus). While thymosin beta-4 is a 43-amino acid protein with multiple functional domains including actin-binding activity, Ac-SDKP is specifically the anti-fibrotic fragment released by enzymatic processing. TB-500 is a synthetic peptide corresponding to the actin-binding domain (amino acids 17-23) of thymosin beta-4 — a different region of the same parent molecule. Ac-SDKP and TB-500 therefore represent distinct functional fragments of thymosin beta-4 with different biological activities: Ac-SDKP is primarily anti-fibrotic and anti-inflammatory, while TB-500 primarily promotes cell migration through actin dynamics.

Question 3

Do ACE inhibitors raise Ac-SDKP levels?

Accepted Answer

Yes. Since ACE is the primary enzyme responsible for degrading Ac-SDKP in the circulation, ACE inhibitor drugs (captopril, enalapril, ramipril, lisinopril, etc.) block this degradation and raise plasma Ac-SDKP concentrations approximately 4-5 fold. This is clinically significant because some researchers propose that the anti-fibrotic and organ-protective benefits of ACE inhibitors — which go beyond what would be expected from blood pressure reduction alone — may be partially mediated through Ac-SDKP accumulation. A landmark 2008 study demonstrated that blocking Ac-SDKP with a specific antibody abolished the anti-fibrotic benefit of ACE inhibition in a diabetic nephropathy model.

Question 4

What is the evidence for Ac-SDKP in cardiac fibrosis?

Accepted Answer

The cardiac anti-fibrotic evidence for Ac-SDKP is well-replicated in preclinical models. In aldosterone/salt-induced cardiac fibrosis, Ac-SDKP infusion reduced left ventricular collagen fraction by approximately 50% without affecting blood pressure. In angiotensin II-induced cardiac fibrosis, Ac-SDKP both prevented fibrosis development and reversed established fibrosis. The mechanism involves direct inhibition of cardiac fibroblast proliferation, suppression of fibroblast-to-myofibroblast differentiation, and reduction of inflammatory cell infiltration. However, all cardiac evidence is from rodent models — no human clinical trial has tested Ac-SDKP as a standalone treatment for cardiac fibrosis.

Question 5

Can Ac-SDKP help with kidney fibrosis?

Accepted Answer

Preclinical evidence for renal anti-fibrotic effects is substantial. In the unilateral ureteral obstruction model (the standard experimental model for kidney fibrosis), Ac-SDKP reduced tubular damage, collagen deposition, and the epithelial-to-mesenchymal transition that drives fibrosis progression. In the remnant kidney model, it reduced macrophage infiltration and TGF-beta expression. Most notably, in diabetic nephropathy models, the anti-fibrotic benefit of ACE inhibitors was shown to be partially dependent on Ac-SDKP accumulation. These findings suggest that Ac-SDKP is a physiologically relevant endogenous anti-fibrotic peptide in the kidney, but human trials are needed to confirm therapeutic potential.

Question 6

Why is Ac-SDKP difficult to use as a drug?

Accepted Answer

The primary pharmacokinetic challenge is Ac-SDKP's extremely short plasma half-life of approximately 4-5 minutes, due to rapid degradation by ACE. In rodent studies, this was overcome by continuous infusion via subcutaneously implanted osmotic minipumps — a delivery method impractical for routine human use. Potential solutions being investigated include sustained-release formulations, POP-resistant or ACE-resistant peptide analogs with extended half-lives, and indirect elevation of endogenous Ac-SDKP through ACE inhibitor therapy or POP activators. The short half-life is the main reason Ac-SDKP has not progressed to human clinical trials despite two decades of consistent preclinical anti-fibrotic data.

Question 7

What is the difference between Ac-SDKP and goralatide?

Accepted Answer

Goralatide (also called seraspenide) is another name for Ac-SDKP, used primarily in the hematology literature. Early research on this peptide focused on its ability to inhibit hematopoietic stem cell proliferation — it was found to reversibly block the entry of pluripotent stem cells into S-phase of the cell cycle, providing a protective effect during chemotherapy. This hematoprotective activity was the original focus of Ac-SDKP research before the anti-fibrotic effects were discovered. The names goralatide and seraspenide are the same molecule as Ac-SDKP.

Question 8

Does Ac-SDKP have anti-inflammatory effects?

Accepted Answer

Yes. Beyond its direct anti-fibrotic activity, Ac-SDKP has well-documented anti-inflammatory properties. It modulates macrophage polarization, shifting macrophages away from the pro-inflammatory and pro-fibrotic phenotype. It reduces infiltration of inflammatory cells (macrophages, T-cells) into damaged tissues. It suppresses production of inflammatory cytokines including TNF-alpha, IL-1beta, and monocyte chemoattractant protein-1 (MCP-1). These anti-inflammatory effects are mechanistically linked to its anti-fibrotic activity, since chronic inflammation is a key driver of fibrosis progression in most organs.

Question 9

Is Ac-SDKP safe? What are the known side effects?

Accepted Answer

Ac-SDKP is an endogenous peptide naturally circulating in human blood, which provides a baseline safety signal. In preclinical studies using chronic infusion over weeks, no significant toxicity has been reported. The peptide does not appear to affect blood pressure at anti-fibrotic doses. Its hematoprotective activity (reversible inhibition of stem cell proliferation) was originally considered for clinical use to protect bone marrow during chemotherapy, and Phase I trials of goralatide in the 1990s did not reveal major safety concerns. However, comprehensive toxicology data from modern controlled studies is limited, and long-term safety in humans at pharmacological doses has not been established.

Question 10

Can Ac-SDKP promote angiogenesis and wound healing?

Accepted Answer

Yes. In addition to its anti-fibrotic and anti-inflammatory properties, Ac-SDKP has demonstrated proangiogenic activity. It stimulates endothelial cell proliferation and migration, promotes capillary tube formation in vitro, and enhances blood vessel density in ischemic tissues in vivo. This angiogenic effect is mediated through FGF-dependent signaling pathways. The combination of anti-fibrotic, anti-inflammatory, and proangiogenic activities makes Ac-SDKP theoretically attractive for wound healing applications where fibrosis (scarring) and insufficient blood supply are limiting factors. However, the extremely short half-life limits practical wound healing applications without a sustained-release delivery system.

Origin / Manufacturer	Synthetic (solid-phase peptide synthesis) / Endogenous (derived from thymosin beta-4 by prolyl oligopeptidase cleavage)
Active Components	Ac-SDKP tetrapeptide (N-acetyl-seryl-aspartyl-lysyl-proline)
Storage	Store lyophilized at −20°C; reconstituted at 2–8°C, protect from light
Shelf Life	24 months (lyophilized)
Form Factor	Lyophilized powder for reconstitution

Ac-SDKP (Thymosin Beta-4 Fragment)

Specifications

Clinical Evidence

Frequently Asked Questions

Sources & References

Related Peptides

BPC-157

GHK-Cu (Copper Tripeptide-1)

TB-500 (Thymosin β4 Fragment)

Thymosin Beta-4