In Plain English:
B7-33 is a 27-amino-acid synthetic peptide derived from the B-chain of human relaxin-2 — one half of the two-chain relaxin hormone. Relaxin is a natural peptide that helps soften connective tissue during pregnancy, but native relaxin requires complex multi-step synthesis and has off-target effects. B7-33 was engineered to keep the beneficial 'anti-scarring' signal while being far simpler and cheaper to make. In preclinical studies it reduced scar tissue (fibrosis) in the heart, lungs, and kidneys, and halved infarct size in heart-attack models — all without the tumor-promoting effect seen with full relaxin.
Research Maturity
Preclinical (Studied in 40+ published papers since 2016+ Studies)
Focus
Anti-Fibrotic Signaling
Cardiovascular Research
Origin
Synthetic single-chain analog; sequence derived from the B-chain (residues 7–33 + C-terminal KRSL extension) of endogenous human relaxin-2 (H2 relaxin), with Cys→Ser substitutions at positions 11 and 23.
Mechanism
Biased agonist at RXFP1 (relaxin family peptide receptor 1). Preferentially activates the pERK1/2 pathway via RXFP1–angiotensin II type 2 receptor (AT2R) heterodimers, upregulating matrix metalloproteinase-2 (MMP-2) to degrade excess collagen. Does not appreciably activate the cAMP/PKA arm of RXFP1 — the pathway linked to native relaxin's tumor-promoting activity.
Outcome
Collagen deposition, interstitial fibrosis, myofibroblast markers (α-SMA), MMP-2 activity, cardiomyocyte viability, infarct size, left ventricular end-diastolic pressure.
