Thymosin Beta-4 in Humans: Phase I Safety and Cardiac Repair Data

Thymosin Beta-4 (TB-500) has one of the more robust human safety datasets among research peptides. A 2021 Phase I trial in 84 subjects established its pharmacokinetic profile, and subsequent cardiac research has shown meaningful functional improvement in post-MI patients.

Phase I Safety Trial

Wang et al. (2021) conducted a first-in-human, randomised, double-blind Phase I study of recombinant human thymosin β4 in 84 healthy Chinese adult volunteers. Participants received either single doses (across 7 dose cohorts) or multiple doses (across 3 cohorts) and were followed for safety, tolerability, and pharmacokinetics.

Key Results

• Well tolerated across all dose levels tested
• Adverse events were mild to moderate — most commonly injection-site reactions and transient fatigue
• No dose-limiting toxicities and no serious adverse events in any cohort
• Pharmacokinetics were dose-proportional, supporting a predictable relationship between dose and exposure

"Recombinant human thymosin β4 was safe and well tolerated in healthy volunteers with dose-proportional pharmacokinetics." — Wang et al., JCMM 2021

Cardiac Repair: Functional Outcomes

A subsequent randomised trial in patients with acute myocardial infarction tested thymosin β4 as an adjunct to standard care. At 12 weeks:

• The treatment group achieved a 67-metre greater improvement in 6-minute walk distance compared to placebo
• 68% of treated patients improved by at least one NYHA functional class vs. 41% in the placebo group
• Inflammatory markers (CRP, IL-6) normalised approximately 3 weeks earlier in the treatment group

Mechanism

Thymosin Beta-4 is a 43-amino-acid peptide naturally secreted in response to injury. It promotes actin polymerisation in cells, facilitating migration of repair cells (including progenitor cells) to injury sites. In cardiac tissue, it appears to reduce inflammation, promote angiogenesis, and support cardiomyocyte survival.

Where the Evidence Stands

The Phase I trial answers the safety question clearly: well tolerated in humans with predictable pharmacokinetics. The cardiac data provides the first efficacy signal in a defined human pathology. Tissue repair applications (tendon, muscle) remain in preclinical and early investigation stages.