TB-500 Fragment

TB-500 Fragment should mean unmodified LKKTETQ, a seven-amino-acid region of thymosin beta-4. It is chemically distinct from acetylated LKKTETQ sold as TB-500 and from full-length thymosin beta-4. Human injury outcomes for the exact fragment were not found.

unmodified LKKTETQ thymosin beta-4 fragment

Sequence LKKTETQ
Unmodified seven-residue fragment
Different from Ac-LKKTETQ and full-length Tβ4
No credible exact-fragment human trial identified

Which fragment is this page about?

Unmodified LKKTETQ is distinct from Ac-LKKTETQ, full-length 43-amino-acid thymosin beta-4, and the shorter Ac-LKKTE metabolite. Each has a separate evidence record.

Keep the molecules separate
Name	Identity	Direct human outcome evidence
TB-500 Fragment	LKKTETQ	No study in the cited records
TB-500	Usually Ac-LKKTETQ	No credible study in the cited records
Thymosin beta-4	Full 43-amino-acid protein	Human topical programs exist, but are adjacent
Ac-LKKTE	Shorter metabolite	Cell work, not human treatment

Structure study · LKKTETQ region

Biochemistry study

Safer D et al. Journal of Biological Chemistry, 1991.

Biochemical mapping identified the LKKTET sequence within thymosin beta-4 as part of its actin-binding region. This supports a structural role inside the full protein, not a clinical effect of injected free LKKTETQ.

Participants / model: Purified proteins and biochemical systems
Treatment: Thymosin beta-4 sequence mapping
Study design: Biochemical binding study

Read the original source

TB-500 · acetylated fragment is different

Analytical chemistry study

Ho ENM et al. Journal of Chromatography A, 2012.

The analyzed TB-500 material was acetylated LKKTETQ. Adding an N-terminal acetyl group creates a different chemical entity from unmodified LKKTETQ.

Participants / model: Equine analytical samples
Treatment: Detection of Ac-LKKTETQ
Study design: Mass-spectrometry method

Read the original source

Metabolite study · not intact LKKTETQ

Analytical and cell study

Wang J et al. Drug Testing and Analysis, 2024.

The study examined the shorter metabolite Ac-LKKTE and reported in-vitro wound-related activity. It does not test intact unmodified LKKTETQ in people.

Participants / model: Analytical and cell systems
Treatment: Ac-LKKTE metabolite
Study design: Metabolite characterization and in-vitro study

Read the original source

Has unmodified LKKTETQ been tested in people?

The cited PubMed and ClinicalTrials.gov records contain no credible administered-human trial of exact unmodified LKKTETQ. Human full-length thymosin beta-4 studies do not answer this question.

Can full-length thymosin beta-4 trials be used here?

Cleaving a seven-residue sequence from a 43-amino-acid protein changes structure, exposure, tissue distribution, and degradation. Full-length thymosin beta-4 trials do not establish the fragment's pharmacokinetics, efficacy, or safety.

Structure study · LKKTETQ region

Biochemistry study

Safer D et al. Journal of Biological Chemistry, 1991.

Biochemical mapping identified the LKKTET sequence within thymosin beta-4 as part of its actin-binding region. This supports a structural role inside the full protein, not a clinical effect of injected free LKKTETQ.

Participants / model: Purified proteins and biochemical systems
Treatment: Thymosin beta-4 sequence mapping
Study design: Biochemical binding study

Read the original source

ClinicalTrials.gov · no credible exact trial

Trial registrations

ClinicalTrials.gov.

ClinicalTrials.gov lists no credible administered-human trial of unmodified LKKTETQ under the exact name or sequence. The TB-500 Hudson record explicitly describes itself as fictional and is excluded as a registry artifact.

Read the original source

FDA safety page · no human exposure data

FDA safety communication

U.S. Food and Drug Administration.

FDA states that it had not identified human exposure data for drug products containing thymosin beta-4 fragment and cites immunogenicity, impurity, and API-characterization concerns.

Study design: Agency safety summary

Read the original source

What direct evidence supports LKKTETQ?

The sequence maps to an actin-binding region, and an LKKTETQ-domain peptide promoted wound repair in mice. The cited studies do not establish a tendon, ligament, muscle, or skin benefit in people.

The shorter Ac-LKKTE metabolite also has in-vitro work, but it cannot be treated as a clinical result for intact LKKTETQ.

Structure study · LKKTETQ region

Biochemistry study

Safer D et al. Journal of Biological Chemistry, 1991.

Biochemical mapping identified the LKKTET sequence within thymosin beta-4 as part of its actin-binding region. This supports a structural role inside the full protein, not a clinical effect of injected free LKKTETQ.

Participants / model: Purified proteins and biochemical systems
Treatment: Thymosin beta-4 sequence mapping
Study design: Biochemical binding study

Read the original source

Mouse wounds · fragment-domain activity

Animal study

Philp D et al. Wound Repair and Regeneration, 2003.

Full-length thymosin beta-4 and a synthetic peptide containing its LKKTETQ actin-binding domain promoted dermal repair in diabetic and aged mice. The result does not supply human efficacy, pharmacokinetics, or a validated injection regimen.

Participants / model: Diabetic and aged mice with dermal wounds
Treatment: Full-length thymosin beta-4 or LKKTETQ-domain peptide
Study design: Controlled animal study

Read the original source

What is known about safety?

The cited evidence does not provide an adequate administered-human safety record for exact LKKTETQ. Pharmacokinetics, repeated exposure, immune reactions, pregnancy, interactions, and the safety of injected market products remain unknown.

Identity: acetylated, unmodified, full-length, and metabolite forms may be mislabeled or conflated.
Injection quality: sterility, endotoxin, concentration, aggregation, and degradation are product-specific risks.
Repair signaling: mouse cell migration and angiogenesis findings do not quantify cancer or vascular risk in people.

FDA safety page · no human exposure data

FDA safety communication

U.S. Food and Drug Administration.

FDA states that it had not identified human exposure data for drug products containing thymosin beta-4 fragment and cites immunogenicity, impurity, and API-characterization concerns.

Study design: Agency safety summary

Read the original source

ClinicalTrials.gov · no credible exact trial

Trial registrations

ClinicalTrials.gov.

ClinicalTrials.gov lists no credible administered-human trial of unmodified LKKTETQ under the exact name or sequence. The TB-500 Hudson record explicitly describes itself as fictional and is excluded as a registry artifact.

Read the original source

Is TB-500 Fragment approved?

No FDA-approved LKKTETQ product or dosing label appears in the cited US records. FDA lists safety concerns for thymosin beta-4 fragment, and WADA prohibits thymosin beta-4 derivatives for covered athletes.

FDA safety page · no human exposure data

FDA safety communication

U.S. Food and Drug Administration.

FDA states that it had not identified human exposure data for drug products containing thymosin beta-4 fragment and cites immunogenicity, impurity, and API-characterization concerns.

Study design: Agency safety summary

Read the original source

WADA 2026 · Tβ4 derivatives

Sports rule

World Anti-Doping Agency, effective 1 January 2026.

Thymosin beta-4 and its derivatives are prohibited under S2 for athletes covered by the Code.

Study design: Binding sport rule for covered athletes

Read the original source

Studies and sources

Structure study · LKKTETQ region

Biochemistry study

Safer D et al. Journal of Biological Chemistry, 1991.

Biochemical mapping identified the LKKTET sequence within thymosin beta-4 as part of its actin-binding region. This supports a structural role inside the full protein, not a clinical effect of injected free LKKTETQ.

Participants / model: Purified proteins and biochemical systems
Treatment: Thymosin beta-4 sequence mapping
Study design: Biochemical binding study

Read the original source

Mouse wounds · fragment-domain activity

Animal study

Philp D et al. Wound Repair and Regeneration, 2003.

Full-length thymosin beta-4 and a synthetic peptide containing its LKKTETQ actin-binding domain promoted dermal repair in diabetic and aged mice. The result does not supply human efficacy, pharmacokinetics, or a validated injection regimen.

Participants / model: Diabetic and aged mice with dermal wounds
Treatment: Full-length thymosin beta-4 or LKKTETQ-domain peptide
Study design: Controlled animal study

Read the original source

TB-500 · acetylated fragment is different

Analytical chemistry study

Ho ENM et al. Journal of Chromatography A, 2012.

The analyzed TB-500 material was acetylated LKKTETQ. Adding an N-terminal acetyl group creates a different chemical entity from unmodified LKKTETQ.

Participants / model: Equine analytical samples
Treatment: Detection of Ac-LKKTETQ
Study design: Mass-spectrometry method

Read the original source

Metabolite study · not intact LKKTETQ

Analytical and cell study

Wang J et al. Drug Testing and Analysis, 2024.

The study examined the shorter metabolite Ac-LKKTE and reported in-vitro wound-related activity. It does not test intact unmodified LKKTETQ in people.

Participants / model: Analytical and cell systems
Treatment: Ac-LKKTE metabolite
Study design: Metabolite characterization and in-vitro study

Read the original source

ClinicalTrials.gov · no credible exact trial

Trial registrations

ClinicalTrials.gov.

ClinicalTrials.gov lists no credible administered-human trial of unmodified LKKTETQ under the exact name or sequence. The TB-500 Hudson record explicitly describes itself as fictional and is excluded as a registry artifact.

Read the original source

FDA safety page · no human exposure data

FDA safety communication

U.S. Food and Drug Administration.

FDA states that it had not identified human exposure data for drug products containing thymosin beta-4 fragment and cites immunogenicity, impurity, and API-characterization concerns.

Study design: Agency safety summary

Read the original source

WADA 2026 · Tβ4 derivatives

Sports rule

World Anti-Doping Agency, effective 1 January 2026.

Thymosin beta-4 and its derivatives are prohibited under S2 for athletes covered by the Code.

Study design: Binding sport rule for covered athletes

Read the original source

Why is TB-500 Fragment in C tier?

The C grade reflects mouse wound-repair evidence for an LKKTETQ-domain peptide. No administered-human study establishes the efficacy or safety of injected unmodified LKKTETQ, and results from other thymosin beta-4 forms do not transfer to it.