B7-33
Relaxin-2 Analog · Anti-Fibrotic & Cardiovascular
B7-33 is a single-chain peptide analog of human relaxin-2 that selectively activates the relaxin family peptide receptor 1 (RXFP1). Unlike native relaxin-2, which requires a complex two-chain A/B structure connected by disulfide bonds, B7-33 achieves RXFP1 activation with a much simpler single-chain design. This makes it significantly easier and more cost-effective to synthesize. Preclinical research demonstrates potent anti-fibrotic, vasodilatory, and cardioprotective properties, positioning B7-33 as a promising therapeutic candidate for fibrotic diseases, heart failure, and vascular dysfunction.
Overview
B7-33 is a single-chain peptide analog of human relaxin-2 that selectively activates the relaxin family peptide receptor 1 (RXFP1). Unlike native relaxin-2, which requires a complex two-chain A/B structure connected by disulfide bonds, B7-33 achieves RXFP1 activation with a much simpler single-chain design. This makes it significantly easier and more cost-effective to synthesize. Preclinical research demonstrates potent anti-fibrotic, vasodilatory, and cardioprotective properties, positioning B7-33 as a promising therapeutic candidate for fibrotic diseases, heart failure, and vascular dysfunction.
Selectively activates RXFP1, the primary receptor for relaxin-2, triggering downstream signaling cascades that inhibit fibroblast activation and collagen deposition, promote extracellular matrix remodeling via increased matrix metalloproteinase (MMP) activity, enhance nitric oxide-mediated vasodilation, and reduce inflammatory cytokine expression. B7-33 appears to preferentially engage pERK1/2 signaling pathways while showing reduced cAMP activation compared to native relaxin-2, suggesting biased agonism at RXFP1.
Research indications
What the compound has been studied for, grouped by body system. Effect size is the reported magnitude where it was measured — not a recommendation.
Reduces myocardial fibrosis and collagen deposition, attenuating adverse cardiac remodeling in preclinical heart failure models.
Enhances nitric oxide-mediated vasodilation, reducing vascular resistance and improving blood flow in preclinical studies.
Demonstrates cardioprotective effects in animal models of heart failure, improving cardiac function and reducing fibrotic burden.
Inhibits fibroblast differentiation into myofibroblasts and reduces extracellular matrix deposition in multiple organ systems.
Shows protective effects against kidney fibrosis progression in preclinical disease models.
A large effect in a weak study and a small effect in a strong one are different things. Effect size is never evidence of use in people.
- Class
- Single-chain peptide
- Molecular weight
- 4000 Da
- Typical dose
- 100-250mcg
- Frequency
- Once daily
- Cycle length
- 4-8 weeks (preclinical extrapolation)
- Storage
- Lyophilized: freezer long-term. Reconstituted: 2-8 C for up to 28 days
Molecular data
- Type
- Single-chain peptide
- Molecular weight
- 4000 Da
Dosing reference
Doses reported in the literature and by suppliers. These are a record of what has been used in research — reference, never instruction.
| Context | Route | Amount | Frequency |
|---|---|---|---|
| Anti-fibrotic / Cardiovascular support | SubQ | 100-250 mcg | 1x daily |
Interactions
Potential synergistic effects for cardiac protection; both target complementary pathways involved in cardiac remodeling and fibrosis.
No known negative interactions; different mechanisms of action with complementary tissue-repair and anti-fibrotic properties.
Quality checklist
- ✓White to off-white lyophilized powder
- ✓Clear solution after reconstitution with no particles
- ✓Intact vacuum seal on vial
- !Slight clumping that dissolves with gentle swirling (may occur from shipping)
- ×Discolored or wet powder indicating degradation
- ×Cloudy solution, visible particles, or precipitates after reconstitution
- ×Broken or missing vacuum seal
What to expect
Safety
- Injection site reactions (redness, mild irritation)
- Potential transient hypotension due to vasodilatory effects
- Persistent or symptomatic hypotension (dizziness, lightheadedness, fainting)
- Severe injection site reactions or signs of infection
- Allergic reactions (rash, swelling, difficulty breathing)
- Pre-existing hypotension or conditions exacerbated by vasodilation
- Pregnancy or breastfeeding (no safety data available)
- Concurrent use of potent antihypertensive agents without medical supervision
- No human safety data exists -- all protocols are extrapolated from preclinical research
FAQ
Why is B7-33 easier to synthesize than native relaxin-2?
B7-33 is a single-chain peptide analog that retains RXFP1 activation while avoiding native relaxin-2's complex two-chain A/B structure connected by disulfide bonds. This simplified single-chain design is significantly easier and more cost-effective to synthesize while achieving equivalent biological activity.
What are the cardiovascular benefits of B7-33 compared to other compounds?
B7-33 reduces myocardial fibrosis, enhances vasodilation through nitric oxide pathway, and demonstrates cardioprotective effects in heart failure models. These anti-fibrotic and vasoprotective properties position it for potential use in cardiac remodeling, though all current data is preclinical.
Can B7-33 cause dangerous drops in blood pressure like other vasodilators?
Preclinical research suggests transient hypotension due to vasodilatory effects is possible. Users may experience symptomatic hypotension including dizziness or lightheadedness. Those with pre-existing hypotension or on antihypertensive medications must be cautious. No human data exists on hypotension incidence or management.
Is B7-33 safe in pregnancy given its anti-fibrotic effects?
No. B7-33 is teratogenic and contraindicated in pregnancy or potential pregnancy. The mechanisms affecting tissue remodeling and fibroblast function create theoretical teratogenic risk. No safety data exists for pregnant or breastfeeding women.
References
- 1A single-chain peptide derived from the relaxin B-chain selectively activates RXFP1Hossain, M.A., et al. · Chemical Science · 2016
Identified B7-33 as a single-chain relaxin analog that selectively activates RXFP1, demonstrating that a simplified single-chain peptide can replicate key signaling functions of native two-chain relaxin-2.
reviewPubMed 28058093 ↗ - 2B7-33 replicates the vasoprotective effects of relaxin in mouse models of cardiovascular diseaseMarshall, S.A., et al. · Annals of the New York Academy of Sciences · 2017
B7-33 replicated the vasoprotective and anti-fibrotic effects of native relaxin in mouse models, reducing vascular stiffness and improving cardiovascular outcomes.
animalPubMed 28500779 ↗ - 3The role of relaxin and its receptor (RXFP1) in the pathogenesis and treatment of fibrotic diseasesSamuel, C.S., et al. · Molecular and Cellular Endocrinology · 2017
Reviews the anti-fibrotic mechanisms of relaxin/RXFP1 signaling, including inhibition of TGF-beta-driven fibroblast activation and collagen synthesis, with implications for simplified analogs like B7-33.
in-vitroPubMed 27838392 ↗ - 4The relaxin receptor as a therapeutic target -- perspectives from evolution and drug targetingBathgate, R.A.D., et al. · Pharmacology & Therapeutics · 2018
Comprehensive review of RXFP1 as a drug target, discussing relaxin-2 and analogs including B7-33 for cardiovascular, fibrotic, and reproductive indications.
reviewPubMed 29378218 ↗ - 5The single-chain relaxin mimetic, B7-33, maintains anti-fibrotic activity in liver and kidney fibrosis modelsHossain, M.A., et al. · British Journal of Pharmacology · 2020
B7-33 reduced fibrosis markers in both liver and kidney fibrosis models, demonstrating organ-protective anti-fibrotic effects comparable to native relaxin-2 despite its simplified structure.
reviewPubMed 31789427 ↗