B7-33 – 6MG

What Is B7-33?

H2-relaxin is a naturally occurring, endogenous protein compound, which was synthetically mimicked and named the “B7-33” peptide. The H2-relaxin protein class comprises relaxin, H3-relaxin, insulin-like peptide-3, and insulin-like peptide-5. All these proteins have been suggested to exhibit a variety of biological actions, including possibly affecting genetic functions and the reproductive, musculoskeletal, and cardiovascular systems.⁽²⁾ Considered structurally similar to H2-relaxin, the synthetic equivalent B7-33 may possess anti-fibrotic potential.

There are four different receptors that these naturally produced relaxin proteins are speculated to bind with, namely RXFP-1, RXFP-2, RXFP-3, and RXFP-4. Each receptor has a different action, as outlined below:⁽²⁾

• RXFP-1 receptor is suggested to influence sperm motility
• RXFP-2 receptor appears to impact testicular development
• RXFP-3 receptor may play a role in circadian rhythm and sleep cycle regulation
• RXFP-4 receptor has shown indications of affecting hunger hormone signaling cycles

Due to the variety of receptors involved and a wide range of biological impact, extensive research has been conducted on the relaxin protein and its analogs, such as the B7-33 peptide, to fully understand their potential.

 

How Is B7-33 Thought to Work?

B7-33 is a singular chain peptide, a smaller analogous derivative of the endogenous relaxin protein.⁽³⁾ Typically, the relaxin peptide comprises four components – a signal peptide, B chain, C chain, and COOH terminal. Several studies were conducted initially to replicate these peptide structures, however the researchers reported that results indicated it being highly insoluble and inactive. After extensive subsequent research, scientists modified the structure by producing a B chain and elongating the COOH terminal, thereby forming the first-ever soluble analog – B7-33 peptide – in 2016.⁽³⁾

Besides the structural difference, the peptide has other variations from the endogenous protein. B7-33 peptide has been suggested to act via the pERK pathway instead of the cAMP pathway. The pERK pathway is a signaling route within cells that may affect cell function, often related to cell growth and survival. In contrast, the cAMP pathway involves different cellular activities primarily related to energy balance and metabolism. H2-relaxin has been suggested to produce antifibrotic potential via the cAMP pathway, which may stimulate tumor formation.⁽¹⁾ Furthermore, the peptide may have a strong affinity towards the RXFP-1 receptors. The peptide appears to bind with these RXFP-1 receptors, stimulating the pERK pathway, which then may lead to increased synthesis of MMP-2 matrix metalloproteinase chemicals. MMP-2 is an enzyme that breaks down proteins and plays a crucial role in tissue remodeling and repair. These chemicals then possibly inhibit the scarring of tissues, thereby preventing fibrosis.⁽¹⁾ Fibrosis is considered the formation of excess fibrous connective tissue in an organ or tissue in a reparative or reactive process, which is associated with a loss of function.

 

Specifications

Name	B7-33
Other known names	(B7-33)H2, H2 relaxin B-chain analog, GTPL9321
Molecular formula	C131H228N40O37S
Molecular weight	2987.75 g/mol
Synthesis	Solid-phase peptide synthesis, US
Form	Lyophilized powder
Amount per vial	6 mg
Storage	−20 °C, dry, protected from light
SKU	P-B733-6

 

What Does Research Show About B7-33?

How May B7-33 Affect Blood Vessels?

Key finding: In male lab models, a single bolus of B7-33 selectively enhanced bradykinin-mediated endothelium-dependent relaxation of the mesenteric artery three hours later by increasing endothelium-derived hyperpolarization; in isolated mesenteric arteries, B7-33 prevented the endothelial dysfunction induced by placental trophoblast-conditioned media.⁽⁴⁾

This 2017 study⁽⁴⁾ was conducted on male Wistar rat models where their tails were presented with a control compound (which was sodium acetate), H2 relaxin, or B7-33 peptide. After three hours, these rats were examined for their vascular functions, mainly in the mesenteric artery, renal artery, and abdominal aorta. While the results were not as promising in the renal artery and abdominal aorta, B7-33 and H2 relaxin exhibited potential vasodilatory properties in the mesenteric artery. Thus, the results suggest that both B7-33 and serelaxin may preferentially augment bradykinin-induced endothelium-dependent relaxation, particularly emphasizing the mesenteric artery in rats. This augmentation appears to be linked to enhanced endothelium-derived hyperpolarization.

To understand better, the researchers reported an additional study⁽⁴⁾ carried out in female rat models experimentally induced with endothelial dysfunction. These mice were then either given B7-33 or H2 relaxin. Following the study, the researchers suggested that both compounds may have helped combat and prevent the further spread of endothelial dysfunction in mice. These results suggest that B7-33 has the potential to replicate the vasoprotective action of H2 relaxin and thereby protect blood vessels from further damage.

What Does Research Suggest About Preeclampsia?

Preeclampsia is a pregnancy ailment characterized by increased hypertension in mothers and decreased fetal weight. This cell culture study⁽⁵⁾ was conducted to understand the potential of B7-33 peptide in pregnant female models of preeclampsia. A cell culture of cytotrophoblasts (CTBs) was used. Cytotrophoblasts are the cells found in the inner cellular layer of the embryo. These cells were given either control compound, a marinobufagenin steroid, or glucose for two days. Following this preparation, some of these cells were given either a relaxin antagonist, or the B7-33 compound. Upon examination, the cells given B7-33 peptide appeared to exhibit an upregulation of the vascular endothelial growth factor, VEGF. Cells that were given relaxin antagonists exhibited apparent reduced VEGF concentration. VEGF is thought to stimulate the proliferation and migration of endothelial cells, which line the interior surfaces of blood vessels. By potentially enhancing these processes, VEGF may play a vital role in forming new vascular structures, essential for supplying tissues with oxygen and nutrients, especially during rapid growth or healing periods. VEGF’s actions are primarily mediated through two tyrosine kinase receptors, VEGFR-1 and VEGFR-2, located on the surface of endothelial cells. The binding of VEGF to these receptors is thought to trigger a cascade of signaling pathways that could lead to endothelial cell proliferation, migration, and survival.

How May B7-33 Reduce Fibrosis?

Key finding: B7-33, a B-chain-only analog of H2 relaxin, bound the RXFP1 receptor and preferentially activated pERK over cAMP signaling; it prevented or reversed organ fibrosis in three lab models of heart or lung disease with a potency similar to H2 relaxin and, unlike H2 relaxin, did not promote prostate tumor growth.⁽¹⁾

Studies⁽⁶⁾⁽⁷⁾ examined a strain of the H2 relaxin protein, which increased heart rate and reportedly stimulated the spread of carcinogenic cells via the cAMP pathway. In the study, researchers sought a derivative that might produce anti-fibrotic action without cAMP activation. When the peptide was exposed in mice with myocardial infarction, it was reported to result in almost 50% reduction in cardiac tissue fibrosis.⁽¹⁾

Furthermore, a study⁽¹⁾ was also conducted in mice with prostate diseases. These mice were presented with two different concentrations of B7-33 peptide. At both concentrations, the results were the same, suggesting the compound might reduce fibrosis without promoting the spread of prostate tumors. This finding indicates the peptide may have the potential to act via the pERK pathway rather than via cAMP activation. The designation “pERK” refers to the phosphorylated state of extracellular signal-regulated kinase (ERK). The activation pathway initiates when a growth factor interacts with its corresponding receptor on the cellular surface. This interaction then induces a sequence of phosphorylation events, transmitting the signal through a network of intermediary proteins, such as RAF and MEK (MAPK/ERK kinase). Ultimately, this will result in the phosphorylation and subsequent activation of ERK. Following activation, ERK translocates to the nucleus where it may phosphorylate various transcription factors, potentially leading to changes in gene expression that might influence cellular processes, including division and differentiation.

What Does Research Suggest About Implant Coatings?

Key finding: Implants coated with a polymer that slowly released B7-33 developed a fibrotic capsule 49.2% thinner over 6 weeks in lab models than implants without the peptide, and the released B7-33 kept its activity at the RXFP1 receptor.⁽⁸⁾

In one animal study⁽⁸⁾, a peptide-coated device was implanted in murine models. The researchers were curious to see if the peptide might counteract possible fibrotic actions in the mice. As a result of this peptide release from the device coating, the fibrotic capsule around the device was 49.2% thinner over the 6-week duration of the study.

B7-33 peptide is available for research and laboratory purposes only. We offer free shipping in the US for orders over $200. Please review our Terms and Conditions before ordering.

 

Frequently Asked Questions

 

References:

1. Hossain, M. A., Kocan, M., Yao, S. T., Royce, S. G., Nair, V. B., Siwek, C., Patil, N. A., Harrison, I. P., Rosengren, K. J., Selemidis, S., Summers, R. J., Wade, J. D., Bathgate, R. A. D., & Samuel, C. S. (2016). A single-chain derivative of the relaxin hormone is a functionally selective agonist of the G protein-coupled receptor, RXFP1. Chemical science, 7(6), 3805–3819. https://doi.org/10.1039/c5sc04754d
2. Summers, R. J. (2017). Recent progress in the understanding of relaxin family peptides and their receptors. British journal of pharmacology, 174(10), 915–920. https://doi.org/10.1111/bph.13778
3. Patil, N. A., Rosengren, K. J., Separovic, F., Wade, J. D., Bathgate, R. A. D., & Hossain, M. A. (2017). Relaxin family peptides: structure–activity relationship studies. British journal of pharmacology, 174(10), 950–961. https://doi.org/10.1111/bph.13684
4. Marshall, S. A., O’Sullivan, K., Ng, H. H., Bathgate, R. A. D., Parry, L. J., Hossain, M. A., & Leo, C. H. (2017). B7-33 replicates the vasoprotective functions of human relaxin-2 (serelaxin). European journal of pharmacology, 807, 190–197. https://doi.org/10.1016/j.ejphar.2017.05.005
5. Afroze, S. H., et al. (2019). Abstract P3042: Novel peptide B7-33 and its lipidated derivative protect cytotrophoblasts from preeclampsia phenotype in a cellular model of the syndrome. Hypertension, 74(Suppl 1), AP3042. https://doi.org/10.1161/hyp.74.suppl_1.P3042
6. Silvertown, J. D., Ng, J., Sato, T., Summerlee, A. J., & Medin, J. A. (2006). H2 relaxin overexpression increases in vivo prostate xenograft tumor growth and angiogenesis. International journal of cancer, 118(1), 62–73. https://doi.org/10.1002/ijc.21288
7. Feng, S., Agoulnik, I. U., Bogatcheva, N. V., Kamat, A. A., Kwabi-Addo, B., Li, R., Ayala, G., Ittmann, M. M., & Agoulnik, A. I. (2007). Relaxin promotes prostate cancer progression. Clinical cancer research, 13(6), 1695–1702. https://doi.org/10.1158/1078-0432.CCR-06-2492
8. Welch, N. G., Mukherjee, S., Hossain, M. A., Praveen, P., Werkmeister, J. A., Wade, J. D., Bathgate, R. A. D., Winkler, D. A., & Thissen, H. (2019). Coatings releasing the relaxin peptide analogue B7-33 reduce fibrotic encapsulation. ACS applied materials & interfaces, 11(49), 45511–45519. https://doi.org/10.1021/acsami.9b17859

Related reading: B7-33 research: inflammation and fibrosis and B7-33 anti-fibrosis and vasoprotection research.

Last updated Oct 26, 2026 · Scientific review: Dr. Dimitar Marinov, MD, PhD