TB-500

What it is

Thymosin beta-4 (Tbeta4) is a naturally occurring 43-amino-acid actin-sequestering peptide. In research it has been studied for tissue repair: dermal and corneal wound healing, cardiac protection after a heart attack, and dry eye. The clinical and animal-study evidence is built almost entirely on the full-length 43-amino-acid peptide (drug codes RGN-259 for the eye and RGN-352 for systemic/cardiac use). The product sold in research markets as "TB-500" is marketed as the actin-binding fragment of Tbeta4 (often centred on the Ac-LKKTETQ sequence) and is not the molecule used in the published peer-reviewed efficacy studies below. There are essentially no controlled efficacy trials on the isolated "TB-500" fragment itself, so the evidence here is for full-length thymosin beta-4.

How studies used it

How solid the evidence is

Honest assessment. (1) Molecule mismatch: every study below tested full-length 43-amino-acid thymosin beta-4 (RGN-259 / RGN-352), NOT the "TB-500" fragment sold in research markets. There is essentially no controlled efficacy literature on the isolated TB-500 fragment, so applying these results to TB-500 is an extrapolation, not direct evidence. (2) Most efficacy data are animal (mouse, rat, pig) or in vitro; only the dry-eye work is human. (3) The human evidence is thin and ophthalmic-only: the strongest human study here (PMID 25826322) is a phase 2 RCT with just 9 patients, statistically significant for dry-eye signs/symptoms but very small; later larger phase 3 dry-eye programs for RGN-259 have produced mixed results and at least one missed its primary endpoint, so eye benefit is not firmly established. (4) Negative data exist and matter: the pig ischemia-reperfusion study (PMID 27199757) was a well-controlled large-animal trial that found NO cardioprotection at 6 mg/kg IV and showed dose-related vascular and clotting effects; this contradicts the positive small-rodent cardiac findings. (5) Cardiac benefit in mice (PMID 25015963) comes from a single research group's rodent model and has not translated to large animals or humans. (6) Dosing across studies is inconsistent and route-dependent: systemic rodent doses range from 1.6 mg/kg/day (IP infusion) to 5 mg/kg (intradermal) to 6 mg/kg IV (pig); topical ocular and wound doses are absolute microgram amounts that cannot be converted to mg/kg. (7) Several abstracts report direction of effect without numeric magnitudes (PMID 25230158, 25015963), and the foundational rat wound paper (PMID 10469335) did not report per-animal dose or body weight. Overall: mechanistically plausible repair peptide with reproducible wound and corneal signals in animals, one small positive human eye trial, but a documented negative large-animal cardiac trial, no human systemic outcome data, and no validated standardized human dosing protocol.

Sources

• Peng H, Xu J, Yang XP, Dai X, Peterson EL, Carretero OA, Rhaleb NE. Thymosin-beta4 prevents cardiac rupture and improves cardiac function in mice with myocardial infarction. Am J Physiol Heart Circ Physiol. 2014.(PMID 25015963)
• Stark C, et al. Systemic Dosing of Thymosin Beta 4 before and after Ischemia Does Not Attenuate Global Myocardial Ischemia-Reperfusion Injury in Pigs. Front Pharmacol. 2016.(PMID 27199757)
• Sosne G, Dunn SP, Kim C. Thymosin beta4 significantly improves signs and symptoms of severe dry eye in a phase 2 randomized trial. Cornea. 2015.(PMID 25826322)
• Sosne G, Szliter EA, Barrett R, Kernacki KA, Kleinman H, Hazlett LD. Thymosin beta 4 promotes corneal wound healing and decreases inflammation in vivo following alkali injury. Exp Eye Res. 2002.(PMID 11950239)
• Kim S, Kwon J. Thymosin beta 4 improves dermal burn wound healing via downregulation of receptor of advanced glycation end products in db/db mice. Biochim Biophys Acta. 2014.(PMID 25230158)
• Malinda KM, Sidhu GS, Mani H, Banaudha K, Maheshwari RK, Goldstein AL, Kleinman HK. Thymosin beta4 accelerates wound healing. J Invest Dermatol. 1999.(PMID 10469335)
• Bock-Marquette I, Saxena A, White MD, Dimaio JM, Srivastava D. Thymosin beta4 activates integrin-linked kinase and promotes cardiac cell migration, survival and cardiac repair. Nature. 2004 (foundational cardiac mechanism paper; dosing not in abstract).(PMID 15565145)