B7-33
Also known as: Relaxin, Relaxin-2, Single-chain Relaxin Peptide, RXFP1 Agonist
Relaxin-2 Analog | Anti-Fibrotic & Cardiovascular
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.
Key benefits
- Potent anti-fibrotic activity across multiple organ systems
- Improved vasodilation and vascular compliance
- Cardioprotective effects and potential to attenuate cardiac remodeling
- Much simpler to synthesize than native two-chain relaxin-2
- Selective RXFP1 agonism with biased signaling profile
- Preclinical efficacy in models of heart failure and fibrosis
Mechanism of action
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.
Molecular data
- Type
- Single-chain peptide
- Half-life
- Not well characterized
Sequence
Single-chain analog of relaxin-2 B-chain
Indications
What the research community uses this compound for, with self-reported effectiveness.
Cardiovascular
Cardiac Fibrosis
EffectiveReduces myocardial fibrosis and collagen deposition, attenuating adverse cardiac remodeling in preclinical heart failure models.
Vasodilation
EffectiveEnhances nitric oxide-mediated vasodilation, reducing vascular resistance and improving blood flow in preclinical studies.
Heart Failure
ModerateDemonstrates cardioprotective effects in animal models of heart failure, improving cardiac function and reducing fibrotic burden.
Anti-Fibrotic
Organ Fibrosis
EffectiveInhibits fibroblast differentiation into myofibroblasts and reduces extracellular matrix deposition in multiple organ systems.
Renal Fibrosis
ModerateShows protective effects against kidney fibrosis progression in preclinical disease models.
Dosing protocols
Common protocols by delivery method. Adjust the curve below to model accumulation in your own cycle.
Injectable
Subcutaneous injection is the primary route studied in preclinical research. Dosing protocols are based on animal model data and have not been validated in human trials.
| Protocol | Dose | Frequency | Route / duration |
|---|---|---|---|
| Anti-fibrotic / Cardiovascular support | 100-250 mcg | 1x daily | SubQ |
Preparation
You will need
- Bacteriostatic water (BAC)
- Insulin syringes (0.5-1 mL)
- Alcohol swabs
- Peptide vial
- Sterile work surface
Steps
- Clean work area and hands thoroughly
- Calculate required BAC water volume using calculator
- Draw BAC water into syringe
- Inject slowly down vial side (not directly onto powder)
- Gently swirl until dissolved (never shake)
- Store in refrigerator, use within 28 days
Work out the water volume and syringe units in the reconstitution calculator →
Interactions
Pairwise interactions with other compounds you might be cycling — the same data behind the cycle builder's safety check.
Telmisartan
SynergisticPotential synergistic effects for cardiac protection; both target complementary pathways involved in cardiac remodeling and fibrosis.
BPC-157
CompatibleNo known negative interactions; different mechanisms of action with complementary tissue-repair and anti-fibrotic properties.
Timeline
Typical week-by-week effects reported in clinical and observational data.
- Week 1-2
Onset of vasodilatory effects; initial anti-fibrotic signaling activation
- Week 2-4
Progressive reduction in fibrotic markers based on preclinical timelines
- Week 4-8
Measurable improvements in tissue fibrosis and cardiovascular parameters in animal models
Safety
Reported adverse effects, contraindications, and what to monitor on cycle.
Common side effects
- Injection site reactions (redness, mild irritation)
- Potential transient hypotension due to vasodilatory effects
Stop signs — stop and seek advice
- Persistent or symptomatic hypotension (dizziness, lightheadedness, fainting)
- Severe injection site reactions or signs of infection
- Allergic reactions (rash, swelling, difficulty breathing)
Contraindications
- 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
Quality checks
What a legitimate product looks like, what should give pause, and what should make you stop.
Good signs
- White to off-white lyophilized powder
- Clear solution after reconstitution with no particles
- Intact vacuum seal on vial
Warning signs
- Slight clumping that dissolves with gentle swirling (may occur from shipping)
Stop signs — don't use
- Discolored or wet powder indicating degradation
- Cloudy solution, visible particles, or precipitates after reconstitution
- Broken or missing vacuum seal
References
Primary literature and clinical-trial data informing this entry.
A single-chain peptide derived from the relaxin B-chain selectively activates RXFP1
Hossain, 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.
The single-chain relaxin mimetic, B7-33, maintains anti-fibrotic activity in liver and kidney fibrosis models
Hossain, 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.
The relaxin receptor as a therapeutic target -- perspectives from evolution and drug targeting
Bathgate, 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.
B7-33 replicates the vasoprotective effects of relaxin in mouse models of cardiovascular disease
Marshall, 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.
The role of relaxin and its receptor (RXFP1) in the pathogenesis and treatment of fibrotic diseases
Samuel, 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.
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