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B7-33 Guide & Dosage Chart

A single-chain relaxin analog studied for fibrosis.

Routesubcutaneous
B7-33 — Dosage chart
Every row cited
GoalDoseFrequencyDurationEvidenceSource
Cardioprotection / anti-fibrotic in cardiomyopathy (preclinical) 0.25 mg 1x/day 7 days (days 7-14 post-injury) Preclinical PMID 36753958
Anti-fibrotic in established cardiomyopathy via oral nanoparticle conjugate (SPION-B7-33) 0.025 mcg 1x/72h 4 weeks (days 14-42 post-injury) Preclinical PMID 41382190
Vasoprotection / endothelium-dependent relaxation (acute bolus, preclinical) 13.3 mcg single dose per trial Preclinical PMID 28478069
Prevention of endothelial dysfunction ex vivo (preeclampsia model) 15–30 mcg single dose per trial Preclinical PMID 28478069
For research and educational use only. Not medical advice.

What is B7-33?

B7-33 is a synthetic peptide designed to mimic part of a natural hormone called relaxin-2. Relaxin is a hormone your body makes — it's best known for loosening ligaments during pregnancy, but it also plays a big role in reducing scar tissue (fibrosis) and protecting blood vessels. The problem? Natural relaxin has a complicated two-chain structure with three internal bonds, making it expensive and tricky to produce in the lab.[5]

Scientists solved that problem by stripping the molecule down to just the essential working piece — the B-chain — and engineering it into a single, simpler strand called B7-33.[5] Think of it like taking a complicated two-part tool and redesigning it as a single, sleeker instrument that does the same key job. The result is a molecule that's far easier and cheaper to synthesize while still activating the same receptor — called RXFP1 (relaxin family peptide receptor 1).[3]

Important note: B7-33 is a research compound studied in preclinical (animal and cell) models. It is not approved for human use, and nothing here constitutes medical advice.

How B7-33 Works

Your cells have locks called receptors. B7-33 fits into the RXFP1 lock — the same one relaxin uses — and turns on a specific signaling pathway inside the cell involving proteins called ERK 1/2 (extracellular signal-regulated kinases).[2] This is called functionally selective activation: B7-33 doesn't trigger every signal relaxin does, just a targeted subset.

Here's the plain-language version: imagine the receptor as a smart thermostat with many programs. Full relaxin runs all the programs. B7-33 runs just the anti-scarring and vessel-protecting programs — potentially with fewer unwanted side effects.

That targeted ERK 1/2 signal tells cells to calm down the production of excess collagen (the protein that forms scar tissue) and to protect the lining of blood vessels.[2][3]

What the Research Shows

Heart protection and anti-fibrosis after cardiac injury

In a mouse model of heart attack (ischemia-reperfusion injury), B7-33 treatment significantly reduced infarct size — the dead heart tissue area — from roughly 45% of the heart wall down to about 22%.[2] It also preserved how well the heart squeezed (fractional shortening), an important measure of heart function.[2] In cell studies, B7-33 reduced a stress marker called GRP78, suggesting it protects heart muscle cells from a type of cellular stress that occurs during and after a heart attack.[2]

Cardiomyopathy model: faster than a standard drug

In a mouse model of cardiomyopathy (drug-induced heart muscle disease), B7-33 reduced left ventricular fibrosis, calmed inflammation, reversed heart muscle cell enlargement (hypertrophy), and restored blood vessel density — matching the effects of the full relaxin hormone.[3] Compared to perindopril, a widely used ACE inhibitor heart drug, B7-33 reduced fibrosis more rapidly and also tackled hypertrophy — something perindopril failed to do in this model.[3]

Protecting blood vessels

In rat experiments, a single injection of B7-33 enhanced the ability of the mesenteric artery (a gut-supplying blood vessel) to relax in response to bradykinin — a natural vessel-dilating signal.[1] It did this by boosting a mechanism called endothelium-derived hyperpolarization.[1] In a preeclampsia model (a dangerous pregnancy complication involving blood vessel problems), B7-33 prevented the development of endothelial dysfunction when blood vessels were exposed to harmful placental signals.[1]

Reducing scar tissue around implanted devices

When B7-33 was loaded into a biodegradable PLGA polymer coating on implanted devices and placed under mouse skin, the thickness of the fibrotic capsule that formed around the implant was reduced by nearly 50% over six weeks.[4] This matters for medical devices like biosensors and implants, which often get walled off by scar tissue.

Cancer-related fibrosis (emerging research)

A 2025 study engineered nanovesicles carrying B7-33 (alongside anti-angiogenic components) to tackle the dense fibrous tissue that shields bile duct tumors (cholangiocarcinoma) from treatment. The B7-33-carrying nanovesicles disrupted the feedback loop between cancer-associated fibroblasts and tumor blood vessel growth.[6] This is early-stage work, but it shows how B7-33's anti-fibrotic action is being explored beyond heart disease.

What B7-33 Is Being Studied For

  • Cardiac fibrosis and adverse remodeling after heart attack or cardiomyopathy[2][3]
  • Vascular protection and endothelial function[1]
  • Preeclampsia-related endothelial dysfunction[1]
  • Foreign body fibrosis around medical implants[4]
  • Tumor-associated fibrosis in cancer models[6]

How B7-33 Is Dosed in Research

Doses used in preclinical research vary considerably depending on the model and delivery method — from microgram single boluses for acute vascular studies to daily subcutaneous injections over one to two weeks for cardiac fibrosis models, and even ultra-low doses delivered via nanoparticle systems on a multi-day schedule. Because the right reference point depends entirely on the study design being replicated, researchers should consult the dosage chart on this page for a full breakdown of the specific amounts and schedules used across published studies, and use the calculator to work out weight-adjusted amounts where applicable.

Mixing and Storing B7-33

B7-33 is a peptide, which means it comes as a delicate powder that must be handled carefully. For reconstitution, researchers typically dissolve the lyophilized (freeze-dried) powder in a mild buffer — sterile water or a dilute acetic acid solution (such as 20 mM sodium acetate, as used in published studies[1]) is common. Add the solvent slowly down the side of the vial and gently swirl — never shake vigorously, as peptides can break down. Once dissolved, aliquot into smaller portions to avoid repeated freeze-thaw cycles, which degrade the peptide over time. Store unused powder at −20 °C or colder, away from light and moisture. Reconstituted solution should be kept at 4 °C and used promptly, typically within a few days. Always check the supplier's certificate of analysis for purity and specific storage recommendations before beginning any experiment.

Sources

  1. B7-33 replicates the vasoprotective functions of human relaxin-2 (serelaxin). — European journal of pharmacology, 2017. PMID 28478069.
  2. B7-33, a Functionally Selective Relaxin Receptor 1 Agonist, Attenuates Myocardial Infarction-Related Adverse Cardiac Remodeling in Mice. — Journal of the American Heart Association, 2020. PMID 32295457.
  3. The single-chain relaxin mimetic, B7-33, maintains the cardioprotective effects of relaxin and more rapidly reduces left ventricular fibrosis compared to perindopril in an experimental model of cardiomyopathy. — Biomedicine & pharmacotherapy = Biomedecine & pharmacotherapie, 2023. PMID 36753958.
  4. Coatings Releasing the Relaxin Peptide Analogue B7-33 Reduce Fibrotic Encapsulation. — ACS applied materials & interfaces, 2019. PMID 31713411.
  5. Single chain peptide agonists of relaxin receptors. — Molecular and cellular endocrinology, 2019. PMID 30641102.
  6. Dual-functional nanovesicles simultaneously inhibit stromal fibrosis and angiogenesis to suppress cholangiocarcinoma progression. — Journal of nanobiotechnology, 2025. PMID 41430305.

B7-33 FAQ

What is B7-33?
B7-33 is a single-chain synthetic peptide designed to mimic the B-chain of the hormone relaxin-2. It was engineered to be simpler and cheaper to produce than full relaxin while still activating the RXFP1 receptor — the same receptor that natural relaxin targets. It is studied as a research tool for fibrosis and vascular protection, not as a human medicine.[5]
How does B7-33 work?
B7-33 binds to RXFP1, the relaxin receptor, and selectively activates an internal signaling pathway involving ERK 1/2 proteins.[2] This tells cells to reduce collagen overproduction (a driver of scarring) and protect blood vessel linings. It's called 'functionally selective' because it activates only a subset of the signals the full relaxin hormone triggers, potentially offering a more targeted effect.[3]
What is B7-33 used for in research?
Preclinical studies have investigated B7-33 for cardiac fibrosis after heart attack and cardiomyopathy,[2][3] vascular protection including a preeclampsia model,[1] reducing scar tissue around medical implants,[4] and more recently, disrupting fibrosis in bile duct cancer models.[6] All work to date is in animal or cell models — no human clinical use is established.
How is B7-33 dosed in research?
Doses span a wide range depending on the study design: single acute boluses in the low microgram range for vascular studies, daily subcutaneous injections over days to weeks for cardiac fibrosis models, and ultra-low doses via nanoparticle delivery on multi-day intervals.[1][3] See the dosage chart on this page for specific amounts used in each published study, and use the calculator for weight-adjusted figures.
How do you reconstitute B7-33?
B7-33 powder is typically dissolved in sterile water or a mild buffer like 20 mM sodium acetate — consistent with solvent used in published vascular studies.[1] Add solvent gently, swirl (don't shake), aliquot to avoid freeze-thaw cycles, and store unused powder at −20 °C. Reconstituted peptide should be kept at 4 °C and used within a few days. Always follow your supplier's specific guidance.
Is B7-33 safe?
B7-33 is a research compound with no established human safety profile. In preclinical animal studies it has been administered without reported major adverse effects,[2][3] and it was well-tolerated in the vascular bolus studies.[1] However, preclinical tolerability does not predict human safety. B7-33 is strictly for laboratory research use only and should never be self-administered or used outside a controlled research setting.