P21 is a synthetic hexadecapeptide reported to activate telomerase and promote telomere lengthening in cell culture and animal models. It is positioned as a complement to epitalon (the better-characterised hTERT activator in the QSC catalog) — both target telomere maintenance, but through sequences that may engage different aspects of the hTERT/hTERC complex. The evidence base for P21 is more limited than epitalon, but it provides a second telomerase-activating compound for comparative longevity research and for exploring whether additive telomere maintenance effects are achievable by combining two mechanistically distinct telomerase activators. Research applications: cellular senescence, telomere length assay development, hTERT activation pathway mapping.
16 aa
Hexadecapeptide
hTERT
Telomerase catalytic subunit
Telomere
Primary endpoint
Epitalon analog
Complementary tool
≥99%
Purity
P21 — Specifications
Property
Value
CAS
N/A — synthetic telomerase-activating peptide
Formula
Hexadecapeptide — 16 aa
MW
~1850 Da
Half-life
Short
Class
Short telomerase-activating peptide — longevity research
Purity
≥99% HPLC verified
COA
Janoshik independent third-party
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Mechanism of Action — P21
P21 telomerase activation mechanism:
hTERT expression: P21 is reported to upregulate hTERT (the catalytic subunit of telomerase) at the transcriptional level in cell culture models
Telomerase activity: TRAP assay shows increased telomerase activity in P21-treated cells vs vehicle
Telomere length maintenance: qPCR telomere length assays show modest telomere length preservation in P21-treated aged cells vs controls
P21 vs Epitalon — honest comparison for longevity researchers
Epitalon (Ala-Glu-Asp-Gly tetrapeptide) has 20+ years of published data from Khavinson et al., characterised hTERT activation mechanism, and in vivo lifespan extension data in multiple rodent models. P21 has a smaller, more recent, and less independently replicated evidence base. For established telomere research, epitalon is the primary tool. P21 adds value as a second independent telomerase activator for parallel-arm comparison.
Key Research Studies & Data
Study
Model
Finding
Limited published literature — primarily cell culture
WI-38 human fibroblasts
Telomerase activity increase by TRAP assay; modest telomere length preservation vs vehicle
Comparison with epitalon
Parallel cell culture arms
Both increase telomerase activity; P21 data less robust — useful as comparative second compound
In vivo data
Sparse — primarily preclinical observations
Limited to anecdotal preclinical reports; no peer-reviewed controlled animal lifespan data published as of 2025
Research Protocols — P21
Protocol 1: Telomerase activity (TRAP assay)
P21 0.1-10 µM in WI-38 or IMR-90 human fibroblasts × 72hr. TRAP assay (PCR-based telomerase activity), telomere length qPCR (T/S ratio), hTERT mRNA (qPCR), hTERT protein (WB). Run parallel epitalon arm for direct comparison.
Protocol 2: Replicative senescence delay
P21 1 µM in serial passage WI-38 fibroblasts — treat every 3 passages. Count population doublings to senescence (SA-b-gal threshold). Compare vs epitalon, vehicle, and positive control (TA-65).
P21 1 µM + epitalon 1 µM vs either alone in aged fibroblasts. TRAP, T/S ratio, SA-b-gal, proliferation (BrdU). Tests additive vs synergistic vs no additional effect.
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Frequently Asked Questions
What is P21 peptide?
P21 is a synthetic hexadecapeptide reported to activate telomerase (hTERT) and promote telomere length maintenance in cell culture. Used as a complementary compound to epitalon for comparative telomerase activation research.
How does P21 compare to epitalon for telomere research?
Epitalon has a substantially larger and better-replicated evidence base spanning 20+ years of Khavinson publications, characterised hTERT activation, and in vivo rodent lifespan data. P21 has more limited published data. For established telomere research, epitalon is the primary compound; P21 adds value as a second independent activator.
What is the TRAP assay?
TRAP (Telomeric Repeat Amplification Protocol) measures telomerase enzyme activity by assessing its ability to add TTAGGG repeats to an oligonucleotide substrate, which is then PCR-amplified. Standard cell culture assay for measuring telomerase activation by peptides.
Can P21 and epitalon be combined?
Combining two mechanistically distinct hTERT activators is a valid research question. Whether P21 + epitalon produces additive, synergistic, or no additional telomerase activation vs either alone is an open experimental question that the P21 + epitalon combination protocol addresses.
What formats does QSC supply P21 in?
QSC supplies P21 as lyophilised research vials, ≥99% purity HPLC verified with Janoshik COA. Ships from domestic warehouses in USA, EU, UK, Canada, and Australia.
