Ac-SDKP vs Oxytocin

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.

Neuropeptide hormone binding oxytocin receptors throughout brain and body; modulates HPA axis, reduces cortisol, promotes parasympathetic tone

Oxytocin is an endogenous hypothalamic nonapeptide and FDA-approved prescription medication (Pitocin) indicated for initiation and augmentation of labor, management of postpartum uterine atony and hemorrhage, and stimulation of milk letdown in breastfeeding women, acting through peripheral oxytocin receptors in the uterus and mammary gland. Beyond its obstetric and lactation roles, oxytocin functions centrally as a neuromodulator in limbic and cortical circuits involved in social recognition, attachment, trust behavior, and fear regulation, with broadly distributed brain oxytocin receptors mediating effects distinct from its peripheral reproductive actions. A landmark randomized, double-blind trial published in Nature demonstrated that intranasal oxytocin significantly increases trust in humans, and controlled research has subsequently characterized its effects on social attention to facial cues and affective empathy, establishing the central prosocial pharmacology of the peptide in human subjects. Oxytocin is FDA-approved only for its obstetric and lactation indications; intranasal formulations for prosocial, cognitive, or psychiatric applications are investigational, and while the mechanistic rationale is established in healthy-volunteer research, no intranasal oxytocin product has received regulatory approval for any psychiatric or behavioral indication. Intranasal oxytocin in research: studies have administered intranasal oxytocin in doses of 20–40 IU, with 24 IU being the most commonly used dose in human behavioral pharmacology research. This delivery route is studied for the hypothesis that olfactory epithelium absorption provides partial access to the CNS beyond what the blood-brain barrier would permit from systemic routes. Research applications under active investigation include autism spectrum disorder (multiple RCTs examining social cognition outcomes), PTSD (fear extinction augmentation), social anxiety disorder, and borderline personality disorder — none of which has produced a regulatory-ready efficacy signal sufficient for approval as of 2025, though ongoing trial activity is substantial. Oxytocin's anti-inflammatory research profile is also documented — oxytocin receptors are expressed on immune cells and the peptide has been shown to suppress pro-inflammatory cytokine release in preclinical models, an emerging research direction that intersects with gut and systemic inflammation contexts. Telehealth providers and compounding pharmacies offering oxytocin formulations for clinical contexts are listed in the PeptideBase directory.