OnePin Peptide Library · Cardiovascular
B7-33
B7-33 Relaxin Analog
B7-33 is a single-chain peptide analog of human relaxin-2 (H2 relaxin), engineered as a 25-amino-acid linear peptide derived from the B-chain of native relaxin. Native relaxin is a two-chain disulfide-linked hormone produced primarily during pregnancy that mediates connective tissue remodeling, vasodilation, and anti-fibrotic signaling via the relaxin family peptide receptor 1 (RXFP1). B7-33 retains anti-fibrotic and pro-angiogenic activity but discards the cAMP-coupled vasodilatory and reproductive endocrine actions of full relaxin, producing a more focused therapeutic profile.
Inject any time of day. Reconstitute with bacteriostatic water. The 25-amino-acid linear peptide is more stable than disulfide-linked native relaxin - tolerates standard handling. Daily dosing is the typical research-community pattern given the relatively short half-life.
Start here. Every protocol below is ordered lowest-first. Begin at the smallest effective dose, hold about a week to assess tolerance, and step up only if needed.
How it works
B7-33 is a structurally simplified relaxin-2 analog that retains the binding affinity for relaxin family peptide receptor 1 (RXFP1) but produces biased signaling - favoring the ERK1/2 / TGF-β-antagonist / anti-fibrotic pathway over the cAMP-coupled vasodilatory and reproductive pathways of full-length relaxin.
RXFP1 Activation
B7-33 binds RXFP1, a G-protein coupled receptor expressed on cardiac fibroblasts, vascular smooth muscle, kidney mesangial cells, lung interstitial cells, and other connective tissue compartments.
Anti-Fibrotic Signaling
B7-33 activates downstream pathways that antagonize TGF-β-driven fibroblast activation, reduce collagen I/III deposition, and promote matrix metalloproteinase (MMP) expression - net reducing extracellular matrix accumulation in chronically inflamed tissues.
Biased Agonism
Unlike full relaxin-2 (or serelaxin), B7-33 produces minimal cAMP elevation and minimal vasodilation. This eliminates the rapid hemodynamic effects (and side effects) of native relaxin while preserving the slower-onset structural anti-fibrotic action.
Pro-Angiogenic
B7-33 maintains relaxin's pro-angiogenic effects via VEGF pathway signaling - useful in cardiac and renal repair contexts where neovascularization supports healing.
Linear Peptide Stability
25-amino-acid linear peptide without the disulfide bridges of native relaxin - simpler synthesis and more stable in storage. No Met or Cys residues - chemistry-compatible with copper-conjugated peptides like GHK-Cu.
What to expect
Week 1-4: minimal subjective effect. Anti-fibrotic action is silent at the cellular level.
Week 4-8: rodent-model fibrotic burden reductions emerge. Human translational data unavailable.
Week 8-12+: peak theoretical anti-fibrotic effect. Without imaging or biomarker monitoring, clinical effect in off-label use is hard to assess.
Evidence
Interactions & stacking
What's safe to combine, and what belongs in a separate pin.
Keep separate
Side effects & safety
Commonly reported
- Injection site reaction (mild)
- Possible mild headache (early doses)
- Possible mild orthostatic dizziness (rare with biased agonist)
Less common & notes
- Bleeding-related events (theoretical - relaxin pathway intersects vascular biology, but biased agonism should reduce this risk vs full relaxin).
- Allergic reaction to peptide or formulation.
- Long-term safety unknown - no human exposure beyond research-chemical community use.
- Reproductive system effects in females theoretically possible but reduced by biased signaling.
- The full-relaxin Phase 3 failure (RELAX-AHF-2) is a cautionary translational signal even though B7-33 is mechanistically distinct.
Pharmacokinetics
Storage. Lyophilized vial: refrigerate (2-8°C / 36-46°F) or freeze (-20°C) for long-term storage. After reconstitution with bacteriostatic water: refrigerate, use within 21-28 days. The linear peptide structure (no disulfides) is relatively stable. Light-sensitive. Discard if cloudy, discolored, or contains particulates.
Regulatory status
Not FDA-approved for any indication. Has not entered human clinical trials. All evidence is rodent preclinical. Available only as a research chemical from peptide-supply vendors. WADA prohibited under class S2 (peptide hormones, growth factors, related substances). Sale for human use is prohibited by FDA regulation. The related compound serelaxin (recombinant relaxin-2) reached Phase 3 for acute heart failure but failed (RELAX-AHF-2) and was withdrawn from development.
Put it to work
Calculate, log & track
Open B7-33 straight into OnePin with your vial and dose pre-filled, then let it handle the syringe math and remind you before the vial runs out.
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The guide & community
The complete B7-33 walkthrough, real protocol discussion and coaching live inside the BlessUp community on Skool.
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