TB-500 vs B7-33
Comprehensive side-by-side comparison of mechanisms, dosing, side effects, and research
TB-500 is a synthetic peptide that copies the active region of thymosin beta-4, a natural protein that controls how cells build and move their internal skeleton. Most TB-500 products reproduce the short LKKTETQ sequence (residues 17 to 23) responsible for binding actin and driving cell migration, which is why it gets marketed for tendon, muscle, and wound repair. Here is the honest part: there are essentially no completed human trials of the TB-500 fragment itself, and almost all the human clinical data is for the full-length thymosin beta-4 molecule, which is related but not the same thing.
Also: B7-33 relaxin, Single-chain relaxin-2 analog
B7-33 is a 27-amino-acid, single-chain peptide cut down from the B-chain of human relaxin-2, the hormone that loosens tissue during pregnancy. Relaxin itself has strong anti-scarring effects but is a complex two-chain molecule that is hard and expensive to make, so an Australian group (Hossain and colleagues, 2016) designed B7-33 as a simpler version. In rodent models it reduced heart and lung fibrosis about as well as full relaxin. It has never been tested in humans.
Key Comparison Insights
- Both peptides belong to the Healing category, suggesting similar primary applications.
Detailed Comparison
| Attribute | TB-500 | B7-33 |
|---|---|---|
| Category | Healing | Healing |
| FDA Status | Not FDA Approved | Not FDA Approved |
| Clinical Status | Pre I II III IV FDA | Pre I II III IV FDA |
| Mechanism of Action | Thymosin beta-4 works by grabbing onto G-actin, the building-block form of actin, and acting as the main reservoir cells use to remodel their cytoskeleton. That control over actin lets cells migrate into wounds, which is the proposed basis for faster tissue repair. The active heptapeptide sequence LKKTETQ is the piece that does the actin binding, and TB-500 is built around it. Beyond cell movement, thymosin beta-4 has shown anti-inflammatory effects and pro-angiogenic activity in lab models. Keep in mind that injecting a short synthetic fragment is not guaranteed to reproduce everything the full protein does, so the mechanism story is borrowed largely from research on the parent molecule. | B7-33 activates RXFP1, the relaxin receptor, but in an unusual way. In cells that naturally carry RXFP1 (like fibroblasts), it preferentially switches on the pERK1/2 pathway rather than the cAMP pathway, which made it the first described functionally selective (biased) RXFP1 agonist. Its anti-fibrotic action runs through RXFP1 paired with the angiotensin II type 2 receptor, increasing MMP-2, an enzyme that breaks down collagen. In other words, it pushes scar tissue to be broken down rather than built up. Two practical caveats: it binds RXFP1 poorly in standard engineered cell lines, so its potency depends heavily on the cell type, and it is short-lived in serum (roughly 6 minutes in lab tests), which is why researchers have tried fatty-acid versions to stretch its half-life. |
| Common Dosing | 2-2.5 mg twice weekly (loading), then 2.5 mg once weekly (maintenance) 2x weekly for 4-6 weeks, then 1x weekly | No established human dose Once to twice daily in mouse studies |
| Administration | Subcutaneous or intramuscular injection | Intraperitoneal or subcutaneous injection (including osmotic minipumps) in rodents |
| Typical Duration | 4-6 weeks loading, then maintenance | 1-2 weeks in most rodent studies |
| Best Time to Take | Morning or evening | No evidence-based timing |
Possible Side Effects May vary by individual |
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| Research Summary | The strongest evidence is preclinical and is mostly about full-length thymosin beta-4, not the TB-500 fragment. Animal studies consistently show accelerated wound healing, reduced scarring, and improved recovery in tendon, skin, and cardiac injury models. On the human side, the biotech company RegeneRx ran the molecule (as RGN-259 eye drops and RGN-352 injection) through actual clinical trials: a placebo-controlled Phase 3 study of RGN-259 in neurotrophic keratopathy reported corneal healing in 6 of 10 treated patients versus 1 of 8 on placebo, and an injectable cardiac program reached Phase 2 before a manufacturing hold. But those programs used full-length thymosin beta-4, not the 7-amino-acid TB-500 fragment sold for research. For the fragment specifically, there are no completed, published human efficacy trials for muscle or tendon repair, and a recently listed cardiovascular biomarker study is early-stage. So: real animal data, real human data for the parent protein, and a near-total gap for TB-500 as sold. | The founding paper (Hossain et al., Chemical Science, 2016) reported that B7-33 prevented or reversed organ fibrosis and dysfunction in three rodent models of heart or lung disease with potency similar to full relaxin-2, and, unlike native relaxin, it did not promote prostate tumor growth in mice. That last point matters because relaxin has been linked to tumor growth. Later mouse work extended the findings: Devarakonda et al. (Journal of the American Heart Association, 2020) gave 0.25 mg/kg twice daily by injection after a heart attack and found smaller infarcts, better heart function, and less fibrosis at 7 days. A 2023 follow-up from the original group confirmed that B7-33 cannot be shortened further without losing receptor binding. Important context: the full hormone (serelaxin) went all the way to a large phase 3 trial in acute heart failure (RELAX-AHF-2) and failed both primary endpoints, a reminder that strong animal anti-fibrotic data in this family have not translated easily to people. For B7-33 itself there are no human studies, no human pharmacokinetics, and no human safety data. |
Frequently Asked Questions: TB-500 vs B7-33
What is the difference between TB-500 and B7-33?
TB-500 is a healing peptide that tb-500 is a synthetic peptide that copies the active region of thymosin beta-4, a natural protein that controls how cells build and move their internal skeleton. most tb-500 products reproduce the short lkktetq sequence (residues 17 to 23) responsible for binding actin and driving cell migration, which is why it gets marketed for tendon, muscle, and wound repair. here is the honest part: there are essentially no completed human trials of the tb-500 fragment itself, and almost all the human clinical data is for the full-length thymosin beta-4 molecule, which is related but not the same thing. B7-33 is a healing peptide that b7-33 is a 27-amino-acid, single-chain peptide cut down from the b-chain of human relaxin-2, the hormone that loosens tissue during pregnancy. relaxin itself has strong anti-scarring effects but is a complex two-chain molecule that is hard and expensive to make, so an australian group (hossain and colleagues, 2016) designed b7-33 as a simpler version. in rodent models it reduced heart and lung fibrosis about as well as full relaxin. it has never been tested in humans. The main differences lie in their mechanisms of action and clinical applications.
Which is better, TB-500 or B7-33?
Neither is universally "better" - the choice depends on your specific goals. TB-500 is typically used for healing purposes, while B7-33 is used for healing. Always consult with a healthcare provider to determine which may be appropriate for your situation.
Can TB-500 and B7-33 be used together?
Some peptide protocols combine multiple compounds for synergistic effects. However, using TB-500 and B7-33 together should only be considered under medical supervision, as both compounds have their own side effect profiles and potential interactions. Research on their combined use may be limited.