B7-33

What it is

B7-33 is an experimental peptide designed as a simplified, single-chain analogue of relaxin — a natural hormone known for relaxing blood vessels and, importantly, for anti-fibrotic (anti-scarring) effects. Native relaxin is a two-chain hormone that is difficult to manufacture; B7-33 was engineered to keep its key anti-fibrotic activity in a smaller, more practical molecule.¹

It is discussed mainly in the context of reducing tissue fibrosis. The most important thing to understand is that this is early-stage laboratory science, not a validated treatment.

How it works

B7-33 is designed to act through the relaxin receptor pathway (notably RXFP1) in a way that biases signalling toward anti-fibrotic effects — reducing the activation of cells that lay down scar tissue and limiting excess collagen build-up — while aiming to minimise unwanted blood-pressure-lowering activity.²

This selective, “biased agonist” design is scientifically interesting, but its real-world behaviour in humans is entirely unstudied.

What the evidence shows

Laboratory and animal studies

The evidence base is entirely preclinical. In cell and animal models, B7-33 has been reported to reduce fibrosis in tissues such as the heart, lung and kidney.^2,3 These findings are promising at the model level and are the basis for continued research interest.

Human studies

There are no published human clinical trials of B7-33. No benefit, dose or safety profile has been established in people. The honest summary is early animal-model promise with zero human evidence.

Dosages reported in the literature

Informational only. There is no validated human dosing for B7-33. The note below reflects only the research context. It is not a recommendation or a prescription.

Because no human trials have been performed, there is no dose range that can be considered safe or effective for people.

Safety & side effects

There are no human safety data for B7-33. Its risk profile in people is simply unknown. Because it acts on relaxin signalling, which affects blood vessels and tissue remodelling, unanticipated effects cannot be ruled out.

As an experimental research chemical, any material sold as “B7-33” also carries significant concerns about identity, purity and dose accuracy.

Legal & regulatory status

B7-33 is not approved by the FDA or any other regulator for any use. It is an experimental compound sold only as an unapproved research peptide.⁴ Rules differ by country and change over time.

References

1. 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. Chemical Science. 2016;7(6):3805-3819. [PMID 30155023, doi:10.1039/c5sc04754d]
2. 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. Chemical Science. 2016;7(6):3805-3819. [PMID 30155023, doi:10.1039/c5sc04754d]
3. Hossain MA, et al. A single-chain derivative of the relaxin hormone is a functionally selective agonist of the G protein-coupled receptor, RXFP1. Chemical Science. 2016;7(6):3805-3819 (efficacy in three rodent models of heart/lung fibrosis). Additional: Devarakonda T, Mauro AG, Guzman G, Hovsepian S, Cain C, Das A, Praveen P, Hossain MA, Salloum FN. B7-33, a Functionally Selective Relaxin Receptor 1 Agonist, Attenuates Myocardial Infarction-Related Adverse Cardiac Remodeling in Mice. J Am Heart Assoc. 2020;9(9):e015748. [PMID 30155023, PMID 32295457, doi:10.1161/JAHA.119.015748]
4. U.S. Food and Drug Administration. Certain Bulk Drug Substances for Use in Compounding that May Present Significant Safety Risks. FDA, Human Drug Compounding. [fda.gov]