Thymosin Beta-4 vs B7-33
Comprehensive side-by-side comparison of mechanisms, dosing, side effects, and research
Also: TB-4, Tβ4
Thymosin beta-4 (Tbeta4) is a small 43 amino acid peptide found in nearly every cell in the body, originally isolated from the thymus. Its main job is binding and sequestering G-actin, the building block of the cell's internal scaffolding, which lets it influence cell movement, wound repair, and tissue regeneration. It is researched heavily for healing of skin, cornea, and heart tissue, but it is not an FDA-approved drug. (The injectable sold as TB-500 is a synthetic fragment marketed as related to Tbeta4, not the full natural peptide.)
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.
- Thymosin Beta-4 has stronger research evidence (Human Trials) compared to B7-33 (Preclinical).
Detailed Comparison
| Attribute | Thymosin Beta-4 | 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 | Tbeta4's core action is binding monomeric G-actin, which regulates how cells assemble and disassemble their cytoskeleton and therefore how they migrate. By controlling actin dynamics it promotes cell migration into wounds, encourages new blood vessel growth (angiogenesis), and dampens inflammation. In injured tissue it acts as a chemoattractant, pulling in cells like endothelial cells, keratinocytes, and stem or progenitor cells to rebuild damaged areas. In the heart specifically, research suggests it can reactivate the epicardium, the heart's outer layer, and support survival of cardiac cells under low-oxygen stress. These are well-supported molecular actions, though translating them into proven clinical treatments is a separate question. | 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 | 2.5-5 mg 2-3x weekly 2-3x weekly | No established human dose Once to twice daily in mouse studies |
| Administration | Subcutaneous injection, topical for eye conditions | Intraperitoneal or subcutaneous injection (including osmotic minipumps) in rodents |
| Typical Duration | 4-8 weeks typical protocol | 1-2 weeks in most rodent studies |
| Best Time to Take | Morning or split doses | No evidence-based timing |
Possible Side Effects May vary by individual |
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| Research Summary | There is genuine peer-reviewed research here, but the human evidence is concentrated in one area: the eye. The ophthalmic formulation RGN-259 (0.1% Tbeta4 eye drops) went through randomized placebo-controlled trials for dry eye and neurotrophic keratopathy, with a phase 2/3 dry eye trial in 317 patients showing significant improvement in corneal staining and ocular discomfort versus vehicle, published in peer-reviewed journals. For the heart, most evidence is preclinical: animal and large-animal studies, including a porcine myocardial infarction model, show Tbeta4 can improve cell engraftment, reduce infarct size, and aid recovery, but a major human cardiac trial program did not deliver an approved drug. Wound healing and hair growth effects are documented mainly in rodents. Across the board, Tbeta4 has a solid molecular story and promising preclinical data, but outside the eye program there are no completed pivotal human trials proving systemic benefit. The widely sold TB-500 research peptide has essentially no controlled human trial data of its own. | 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: Thymosin Beta-4 vs B7-33
What is the difference between Thymosin Beta-4 and B7-33?
Thymosin Beta-4 is a healing peptide that thymosin beta-4 (tbeta4) is a small 43 amino acid peptide found in nearly every cell in the body, originally isolated from the thymus. its main job is binding and sequestering g-actin, the building block of the cell's internal scaffolding, which lets it influence cell movement, wound repair, and tissue regeneration. it is researched heavily for healing of skin, cornea, and heart tissue, but it is not an fda-approved drug. (the injectable sold as tb-500 is a synthetic fragment marketed as related to tbeta4, not the full natural peptide.) 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, Thymosin Beta-4 or B7-33?
Neither is universally "better" - the choice depends on your specific goals. Thymosin Beta-4 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 Thymosin Beta-4 and B7-33 be used together?
Some peptide protocols combine multiple compounds for synergistic effects. However, using Thymosin Beta-4 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.