MEDICAL DISCLAIMER: Educational research guidelines only. Lyophilized peptides are investigational chemical compounds and are NOT approved for human consumption, diagnosis, or therapy. Consult a licensed physician before any research application.
B7-33 Dosage Chart, Schedule & Reconstitution Protocol
Quickstart Highlights
B7-33 is a 27-amino-acid single-chain relaxin-2 mimetic and the first functionally selective ('biased') agonist of the relaxin receptor RXFP1. Derived from the B-chain (B7–B33) of H2 relaxin with its cysteines replaced by serine, it preferentially drives anti-fibrotic pERK1/2 and MMP-2 signalling — partly via RXFP1–AT2R heterodimers — while largely avoiding relaxin's cAMP-linked vascular and proliferative effects (PMID 30155023). In rodent models of cardiac, pulmonary and vascular fibrosis it matched relaxin's anti-scarring potency and, after myocardial infarction at 0.25 mg/kg, roughly halved infarct size (PMID 32295457). It is dosed parenterally in research, usually by osmotic-minipump infusion because its in-vitro serum half-life is only ~6 minutes (PMID 37047588). B7-33 has never been tested in humans, has no validated human dose, and is not approved by the FDA or EMA — it is sold for laboratory research only. The subcutaneous reconstitution figures here are an educational reference, not medical advice.
Reconstitute: Add 2 mL bacteriostatic water → 2.5 mg/mL concentration.
Typical dose: No validated human dose; ~0.25 mg/kg/day SC (preclinical)
Easy measuring: At 2.5 mg/mL, 1 unit = 0.01 mL = 0.0250 mg (25 mcg) on a U-100 insulin syringe.
Storage: Lyophilized powder stored frozen at −20 °C or colder, protected from light and moisture. Because B7-33 is an unprotected linear peptide that degrades rapidly in solution, reconstituted material should be kept refrigerated at 2–8 °C and used within about 1–2 weeks, or aliquoted and frozen at −20 °C to minimize freeze–thaw cycles.
Half-life: ~6 minutes in vitro (serum); in-vivo even shorter, so studies use continuous osmotic-minipump infusion. A lipidated analogue (L-B7-33) reaches ~60 min in vitro.
Route: Parenteral in research — subcutaneous, intraperitoneal or intranasal, frequently by continuous infusion. Not oral, never given to humans; the SC reconstitution here is a measurement reference only.
Status: Not FDA- or EMA-approved; no human clinical trials. Research/educational use only (CAS 1818415-56-3). This page is not medical advice.
About B7-33
B7-33 is a single-chain relaxin-2 mimetic and the first reported functionally selective ("biased") agonist of the relaxin receptor RXFP1. It reproduces relaxin's anti-fibrotic signalling (pERK1/2 and MMP induction) while largely avoiding the cAMP-linked vascular and proliferative effects of the full hormone [1]. It has only ever been studied in cells and animals; there is no validated human B7-33 dosage and the compound has never been tested in a clinical trial.\n\nIn published work the peptide is given parenterally — subcutaneously, intraperitoneally or intranasally — and very often through an implanted osmotic minipump rather than bolus injection, because its in-vitro serum half-life is only about 6 minutes [3][5]. The headline preclinical figure is roughly 0.25 mg/kg/day; after myocardial infarction one study dosed 0.25 mg/kg subcutaneously at reperfusion and then twice daily [3][4]. The subcutaneous reconstitution numbers below are an educational measurement reference built around that twice-daily research pattern, not a recommended human protocol.\n\nThis guide models a 5 mg vial reconstituted with 2.0 mL of bacteriostatic water (2.5 mg/mL), so doses land cleanly on a U-100 insulin syringe: 250 mcg ≈ 10 units, 500 mcg ≈ 20 units, and 1000 mcg ≈ 40 units. These illustrative per-injection amounts are provided only so the math is concrete; they are not derived from any human dose-finding study.\n\nFrequency: Twice daily subcutaneously in this educational model, reflecting the short half-life and the twice-daily regimen used in the myocardial-infarction study [3]. B7-33 is not FDA- or EMA-approved and is presented here for research and educational purposes only.
Quick Protocol Navigation
Reconstitution Instruction & Mixing Step-by-Step
Lyophilized powder must be reconstituted carefully. Agitating peptide chains can shear disulfide bonds and render the peptide biologically inert.
Draw 2.0 mL of bacteriostatic water into a sterile syringe (this yields a 2.5 mg/mL solution from a 5 mg vial, i.e. 25 mcg per insulin-syringe unit).
Inject the water slowly down the inner glass wall of the vial; do not spray it directly onto the powder, and never shake — agitation can fragment this fragile linear peptide.
Swirl gently and let the vial sit until the solution is completely clear; if particulate or cloudiness persists, discard rather than inject.
Refrigerate at 2–8 °C and draw the units for your chosen research reference (250 mcg ≈ 10 units, 500 mcg ≈ 20 units, 1000 mcg ≈ 40 units on a U-100 syringe); for longer storage, aliquot and freeze at −20 °C.
Educational note: B7-33 has a very short half-life and in studies was usually infused continuously via osmotic minipump rather than bolus-injected. For the subcutaneous model here, swab the site, inject slowly, and rotate sites — recognising that bolus dosing does not reproduce the steady exposure used in the source research.
Interactive B7-33 Syringe Calculator
Currently visualizing the 5 mg vial reconstituted with 2 mL bacteriostatic water. Adjust the target dose to dynamically render syringe units.
Reconstitution Calculation: 5mg dry powder in 2mL water yields 2.50 mg/mL. To evaluate a 250mcg dose, pull to 10.0 units (10 syringe ticks).
U-100 Syringe Representation
Educational reference visual. Assumes standard U-100 insulin syringe where 1.0 mL volume = 100 units.
Titration & Dose Escalation Schedules
| Phase | Dose per injection | Units (per injection) |
|---|---|---|
| Low research reference (~250 mcg/injection) | 250 mcg | 10 units (0.10 mL) |
| Mid research reference (~500 mcg/injection) | 500 mcg | 20 units (0.20 mL) |
| Upper illustrative reference (~1000 mcg/injection) | 1000 mcg (1 mg) | 40 units (0.40 mL) |
Administration guidelines: Refer to guidelines | 2 mL Reconstitution
Research Supplies Quantity Planner
Scientific mathematical planning of syringes, bacteriostatic water and dry vials needed for extended research blocks using the 5 mg vial.
Peptide Vials (B7-33, 5 mg each):
- check8 weeks at 250 mcg twice daily (0.5 mg/day) ≈ 28 mg ≈ 6 vials
- check12 weeks at 500 mcg twice daily (1 mg/day) ≈ 84 mg ≈ 17 vials
- check16 weeks at 1000 mcg twice daily (2 mg/day) ≈ 224 mg ≈ 45 vials — the high count reflects the short half-life and why studies infuse rather than bolus-inject
Insulin Syringes (U-100):
- checkTwice-daily dosing: 14 syringes per week
- check8 weeks ≈ 112 syringes; 12 weeks ≈ 168 syringes
- check16 weeks ≈ 224 syringes; keep spares for misdraws on a fragile peptide
Bacteriostatic Water (30 mL bottles): Use 2 mL per 5 mg vial for reconstitution.
- check8 weeks (~6 vials) ≈ 12 mL ≈ 1 bottle
- check12 weeks (~17 vials) ≈ 34 mL ≈ 2 bottles
- check16 weeks (~45 vials) ≈ 90 mL ≈ 3 bottles
Alcohol Swabs:
- check1-2 swabs per dose (vial top + injection site), 14 doses per week
- check8 weeks ≈ 110-220 swabs; 12 weeks ≈ 170-340 swabs
- check16 weeks ≈ 220-450 swabs; keep extras for re-swabbing multi-use vials
Mechanism of Action (MOA)
B7-33 is a single-chain peptide corresponding to the B7–B33 region of the human H2 relaxin B-chain (about 27 residues, ~2,986 Da, CAS 1818415-56-3). In native relaxin two disulfide-linked chains are required for full activity; the B7-33 design removes the A-chain entirely and substitutes the two B-chain cysteines with serine, leaving a linear, non-aggregating peptide that is far simpler and cheaper to make than recombinant serelaxin [1][6].\n\nIts defining property is functional selectivity, or "biased agonism," at relaxin family peptide receptor 1 (RXFP1), a class A G-protein-coupled receptor. Full-length relaxin couples RXFP1 strongly to adenylate cyclase, raising cAMP — the arm associated with vasodilation, cell proliferation and some of relaxin's growth-promoting effects. B7-33 instead is a weak cAMP activator but, in fibroblasts and other cells that natively express RXFP1, potently and efficaciously phosphorylates ERK1/2 [1]. The downstream anti-fibrotic program runs through RXFP1 forming a heterodimer with the angiotensin II type-2 receptor (AT2R), which biases signalling toward pERK1/2 and induction of the collagen-degrading enzyme matrix metalloproteinase-2 (MMP-2), reducing interstitial collagen deposition [1]. Critically, unlike native relaxin, B7-33 did not promote prostate tumour growth in vivo, which the authors attribute to its avoidance of the proliferative cAMP arm [1].\n\nPharmacokinetics are the compound's main liability. As an unstructured linear peptide with no disulfide constraint, B7-33 is rapidly cleaved by serum proteases: its measured in-vitro serum half-life is only about 6 minutes, and its in-vivo half-life is expected to be even shorter than relaxin's [5]. There is no published human pharmacokinetic, bioavailability or oral-absorption data because the peptide has never been administered to humans. This short exposure is why preclinical investigators almost always delivered B7-33 by continuous subcutaneous or intraperitoneal infusion through implanted osmotic minipumps, or by repeated daily/twice-daily injection, rather than relying on a single bolus [3][4]. Medicinal-chemistry efforts have since added a palmitoyl fatty-acid/PEG handle (the lipidated analogue "L-B7-33"), extending the in-vitro half-life roughly ten-fold to about 60 minutes without losing RXFP1 activity, and parallel work on truncated and minimal derivatives continues to optimise potency and stability [5][7].\n\nMechanistically, then, B7-33 behaves as a relaxin "anti-scarring" pharmacophore: it engages the same receptor as the hormone but routes signalling toward tissue-remodelling and away from vascular/proliferative outputs, with vasoprotective endothelial effects (enhanced bradykinin-mediated, endothelium-dependent relaxation) also retained in rat vessels [2]. The route used in research is parenteral, not oral; the subcutaneous reconstitution scheme on this page is an educational measurement convention used across this site and does not correspond to any approved or clinically validated delivery method [6].
Clinical Trial Efficacy Highlights
- starThere are no human clinical trials of B7-33; all efficacy evidence is preclinical (cell and rodent), so none of the findings below establish human efficacy, safety or dosing.
- starHossain and colleagues (Chemical Science, 2016) first reported B7-33 as the only known functionally selective agonist of RXFP1, showing it weakly activates cAMP but potently phosphorylates ERK1/2 in native RXFP1-expressing cells, prevents or reverses fibrosis in three rodent models of heart and lung disease with potency similar to H2 relaxin, and — unlike relaxin — does not promote prostate tumour growth in vivo [1].
- starIn the same body of work, the anti-fibrotic mechanism was traced to RXFP1–angiotensin II type-2 receptor (AT2R) heterodimers driving pERK1/2 and matrix metalloproteinase-2 expression, linking biased signalling directly to collagen breakdown [1].
- starMarshall and colleagues (European Journal of Pharmacology, 2017) showed in male Wistar rats that B7-33 replicated the rapid vasoprotective actions of serelaxin, selectively enhancing bradykinin-mediated, endothelium-dependent relaxation in mesenteric arteries via increased endothelium-derived hyperpolarization — supporting it as a lower-cost alternative to the two-chain hormone [2].
- starDevarakonda and colleagues (Journal of the American Heart Association, 2020) gave mice B7-33 at 0.25 mg/kg subcutaneously at the onset of reperfusion and continued twice-daily dosing; B7-33 roughly halved infarct size (about 22% vs 45% in controls) and preserved cardiac function by reducing cardiomyocyte death and endoplasmic-reticulum stress [3].
- starAlam and colleagues (Biomedicine & Pharmacotherapy, 2023) treated isoprenaline-induced cardiomyopathy in mice with B7-33 0.25 mg/kg/day subcutaneously (a molecular-weight-corrected equivalent of relaxin 0.5 mg/kg/day) from days 7–14; B7-33 equalled relaxin in reducing left-ventricular fibrosis, inflammation and hypertrophy and restoring vascular density, and reduced fibrosis more completely than the ACE inhibitor perindopril (1 mg/kg/day) [4].
- starPraveen and colleagues (International Journal of Molecular Sciences, 2023) quantified B7-33's in-vitro serum half-life at about 6 minutes and demonstrated that a lipidated derivative (L-B7-33) extended it roughly ten-fold to ~60 minutes while retaining RXFP1 activity — work explicitly framed as preclinical optimisation ahead of any future in-vivo PK/PD studies [5].
- starReviews of single-chain relaxin agonists position B7-33 as a proof-of-concept biased RXFP1 ligand whose therapeutic translation still depends on overcoming its short half-life and on generating in-vivo pharmacokinetic and human safety data that do not yet exist [6][7].
Side Effects & Tolerability Profile
Clinical subjects transiently report mild side effects. Slowly escalating the titration dose represents the single most effective intervention to limit side effects.
- warningHuman safety is unknown: B7-33 has never been administered to people, so there are no clinical data on adverse effects, tolerability, immunogenicity or long-term risk. Everything below is inferred from preclinical work and peptide pharmacology.
- warningBecause it is an injected foreign peptide, plausible parenteral effects include injection-site irritation, redness or swelling, and the theoretical risk of an immune/anti-drug-antibody response with repeated dosing — none of which have been formally characterised for B7-33.
- warningIts extremely short in-vitro serum half-life (~6 minutes) means bolus subcutaneous injection delivers only brief exposure; the source studies used continuous osmotic-minipump infusion, so simple injection may not reproduce — and could unpredictably alter — the effects reported in animals [3][5].
- warningB7-33 retains vasoprotective, vasorelaxant activity in rodent vessels [2]; by analogy to relaxin, blood-pressure or haemodynamic effects are conceivable, though no human cardiovascular data exist.
- warningAs an RXFP1 agonist active in reproductive and vascular tissue, use in pregnancy, in people trying to conceive, or with cardiovascular disease cannot be considered safe; relaxin-family signalling has not been validated for safety in these settings with this molecule.
- warningNo drug–drug interaction studies exist. Combining B7-33 with antifibrotics, RAAS-modulating agents (e.g. ACE inhibitors), or other vasoactive compounds is entirely unstudied and should be regarded as experimental.
- warningPurity and identity of research-grade material vary by supplier; an unstable linear peptide is prone to degradation and aggregation, so contaminants and degradation products are a real practical hazard.
- warningRegulatory/research status: B7-33 is NOT approved by the FDA, EMA or any regulator, is not a medicine or dietary supplement, and is sold only for in-vitro/laboratory research. This page is educational and is not medical advice or an endorsement of human use.
Subcutaneous Injection Technique
Most research peptides require subcutaneous injection into fatty tissue. Never inject directly into a blood vessel or deep muscle tissue unless clinically detailed.
1. Site Selection
Common locations include the abdomen (2 inches from navel), outer upper arms, or thighs.
2. Sanitization
Thoroughly clean the selected site, stopper and vial top using 70% isopropyl alcohol prep swabs.
3. Angle & Push
Pinch the skin and insert the needle at a 45 to 90-degree angle. Depress plunger smoothly.
4. Site Rotation
Rotate injection sites continuously to avoid lipodystrophy or tissue scarring.
Frequently Asked Questions
What is the typical B7-33 dosage?expand_more
There is no established human B7-33 dosage — it has never been given to people in a clinical trial, so no safe or effective human dose exists. The most-cited preclinical figure is about 0.25 mg/kg/day subcutaneously in mice; after myocardial infarction one study used 0.25 mg/kg subcutaneously at reperfusion followed by twice-daily dosing, and a related heart-failure model used 0.5 mg/kg/day in rats. In those studies the peptide was usually delivered by continuous osmotic-minipump infusion rather than bolus injection. The per-injection micrograms shown on this page (about 250–1000 mcg) are an educational measurement reference only, not a recommended human protocol.
Is B7-33 FDA approved?expand_more
No. B7-33 is not approved by the FDA, the EMA, or any other regulatory agency for any use. It is not a medicine, not a dietary supplement, and has never advanced into human clinical trials. It exists only as a research compound (CAS 1818415-56-3) sold for laboratory, in-vitro and preclinical animal study. Any human use would be unapproved and unstudied, and this page is provided strictly for education, not as medical advice.
What is the half-life of B7-33?expand_more
B7-33's measured in-vitro serum half-life is only about 6 minutes, because it is an unprotected linear peptide rapidly cleaved by serum proteases; its in-vivo half-life is expected to be even shorter than that of native relaxin. This is why researchers typically infuse it continuously with osmotic minipumps. Medicinal-chemistry work on a lipidated version (L-B7-33) extended the in-vitro half-life roughly ten-fold to about 60 minutes while keeping RXFP1 activity, but that improved analogue is itself still purely experimental.
How is B7-33 reconstituted for research?expand_more
In the educational subcutaneous model used here, a 5 mg vial is reconstituted with 2.0 mL of bacteriostatic water to give 2.5 mg/mL (25 mcg per insulin-syringe unit). Add the water slowly down the vial wall, swirl gently without shaking, and wait until the solution is clear. Because B7-33 is unstable in solution, refrigerate it and use within roughly 1–2 weeks, or aliquot and freeze at −20 °C. At this concentration 250 mcg measures 10 units, 500 mcg measures 20 units, and 1000 mcg measures 40 units on a U-100 syringe.
How does B7-33 differ from relaxin or serelaxin, and can it be stacked?expand_more
B7-33 is a single-chain fragment of relaxin-2's B-chain that acts as a biased RXFP1 agonist: it favours the anti-fibrotic pERK1/2–MMP pathway and largely skips the cAMP signalling of full-length relaxin/serelaxin, and in animals it did not promote tumour growth the way relaxin can. It is also far cheaper to synthesise than two-chain serelaxin. There is no validated stacking protocol — no human data exist on combining B7-33 with other peptides or drugs, and interactions with antifibrotics or cardiovascular agents are entirely unstudied, so any combination should be treated as purely experimental.
Related Guides & Tools
Step-by-step references for reconstituting, measuring, and storing B7-33, plus the universal dosing calculator.
Academic References & Study Citations
Hossain MA, Kocan M, Yao ST, Royce SG, Nair VB, Siwek C, Patil NA, Harrison IP, Rosengren KJ, Selemidis S, Summers RJ, Wade JD, Bathgate RAD, Samuel CS. A single-chain derivative of the relaxin hormone is a functionally selective agonist of the G protein-coupled receptor, RXFP1. Chem Sci. 2016;7(6):3805-3819. View Scientific Paper →
Marshall SA, O'Sullivan K, Ng HH, Bathgate RAD, Parry LJ, Hossain MA, Leo CH. B7-33 replicates the vasoprotective functions of human relaxin-2 (serelaxin). Eur J Pharmacol. 2017 Jul 15;807:190-197. View Scientific Paper →
Devarakonda T, et al. B7-33, a functionally selective relaxin receptor 1 agonist, attenuates myocardial infarction-related adverse cardiac remodeling in mice. J Am Heart Assoc. 2020;9(8):e015748. View Scientific Paper →
Alam F, Gaspari TA, Kemp-Harper BK, et al. 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. Biomed Pharmacother. 2023 Apr;160:114370. View Scientific Paper →
Praveen P, Wang C, Handley TNG, Wu H, Samuel CS, Bathgate RAD, Hossain MA. A lipidated single-B-chain derivative of relaxin exhibits improved in vitro serum stability without altering activity. Int J Mol Sci. 2023;24(7):6616. View Scientific Paper →
Praveen P, et al. Single chain peptide agonists of relaxin receptors. Mol Cell Endocrinol. 2019;487:34-39. View Scientific Paper →
Handley TNG, Praveen P, Tailhades J, Wu H, Bathgate RAD, Hossain MA. Further developments towards a minimal potent derivative of human relaxin-2. Int J Mol Sci. 2023 Aug 11;24(16):12670. View Scientific Paper →