Procyanidin C1
Procyanidin C1 (PCC1), trimeric proanthocyanidin from grape seed
Written by Aaron CuhaReviewed Sep 2026
Also known as: PCC1, Grape seed procyanidin C1
A grape seed polyphenol reported in 2021 to kill senescent cells and extend lifespan in old mice. That paper has carried an Editorial Expression of Concern since March 2026, and there is no human evidence for the isolated compound.
Overview
Procyanidin C1 is a trimeric proanthocyanidin found in grape seed extract. The 2021 Nature Metabolism paper that put it on the map reported a concentration-dependent double action: at low concentrations it suppressed the senescence-associated secretory phenotype, and at higher concentrations it selectively killed senescent cells. In mice it depleted senescent cells in a treatment-damaged tumour microenvironment, and intermittent dosing of irradiated, senescent-cell-implanted or naturally aged old mice alleviated physical dysfunction and prolonged survival.
In March 2026 Nature Metabolism published an Editorial Expression of Concern on that paper. The notice was verified live in the PubMed record and explicitly references the 2021 article. The indexed record carries no explanatory text, so the reason for the concern cannot be established from it. An Expression of Concern is not a retraction, and it is not a finding that the results are wrong; it is a signal from the journal that readers should not rely on the paper while the matter is examined. The mouse lifespan claim for procyanidin C1 rests on that single paper.
Other groups have published mouse work using procyanidin C1 as a senolytic tool: alleviation of age-related retinal decline in naturally aged mice, and reduced renal fibrosis after ureteral obstruction by promoting apoptosis of senescent tubular cells. Both are mouse studies and neither is a lifespan study. There is no human evidence for isolated procyanidin C1: no trial, no pharmacokinetic study, no registered study. No senolytic has improved a clinical outcome in a randomised trial in humans, and procyanidin C1 has not been given to a person in a published study.
Mechanism of action
Reported in cultured cells and mice: at low concentrations procyanidin C1 suppresses senescence-associated secretory factors, acting as a senomorphic; at higher concentrations it induces apoptosis in senescent cells, acting as a senolytic. The concentration dependence is the central claim and it comes from the paper now under Editorial Expression of Concern. Nothing has been characterised in humans.
Human evidence
None. No human has been given isolated procyanidin C1 in a published study, no pharmacokinetic data exist, and no trial is registered.
What this does not tell you: With no human dosing data there is no way to know what plasma concentration a grape seed supplement produces, let alone whether it approaches the concentrations used in mouse experiments. The distinction the mouse work depends on, senomorphic at low concentration and senolytic at higher, would be meaningless without knowing where a human dose lands.
Reading the research record
The status of the foundational paper is the most important fact on this page. Nature Metabolism issued an Editorial Expression of Concern on the 2021 procyanidin C1 lifespan paper in March 2026, and the mouse lifespan claim has no independent replication. Procyanidin C1 should not be described as a validated senolytic while that stands.
The two later mouse papers, in retina and kidney, used procyanidin C1 as a senolytic tool and reported organ-level effects. They do not test lifespan and they do not resolve the concern about the 2021 paper. Grape seed extract is an unpatentable botanical, so no sponsor has a commercial reason to fund human trials, and none are registered; that is an economic explanation for the empty human record, not a reason to assume a positive result waiting to be found.
The evidence, charted
Fig. 1 · evidence composition
0of 4 citations (0%) are in people
Counted from the citation list on this page. The Human count is the same number shown in the badge at the top. Both understate any literature larger than the sources we cite.
Fig. 2 · evidence over time
Evidence spans 4 distinct years, 2021 to 2026, counted from the citation list on this page.
Fig. 3 · legal status at a glance
US
Not approved
UK
Approved
AU
Not approved
CA
Not approved
Approved in 1 of 4, prescription route in 0, not approved in 3. A jurisdiction's classification is a regulatory fact, not a verdict on the science; see Legal status below for the full text and any notes.
Fig. 4 · dose response
No human dose response curve exists
We draw this figure where the data supports it. For this compound in humans it does not, so the panel stays empty rather than borrowing an animal curve and implying it transfers.
Key studies & citations
- Animal2021
The flavonoid procyanidin C1 has senotherapeutic activity and increases lifespan in mice
Mouse and cultured cells. Low concentrations suppressed the senescence-associated secretory phenotype; higher concentrations killed senescent cells. Intermittent dosing of old mice alleviated physical dysfunction and prolonged survival. This paper is subject to an Editorial Expression of Concern issued in March 2026.
Nature Metabolism - Review2026
Editorial Expression of Concern: The flavonoid procyanidin C1 has senotherapeutic activity and increases lifespan in mice
Editorial Expression of Concern published March 2026, verified live and explicitly referencing the 2021 paper. The indexed record carries no explanatory text, so the specific reason cannot be established from it. This is a flag, not a retraction.
Nature Metabolism - Animal2024
Senolytic and senomorphic agent procyanidin C1 alleviates structural and functional decline in the aged retina
Naturally aged mice. Long-term procyanidin C1 treatment reduced retinal senescent cell burden and ameliorated age-related structural and functional decline in the retina, characterised by single-cell RNA sequencing. Mouse, no lifespan endpoint.
Proceedings of the National Academy of Sciences - Animal2025
Senolytic procyanidin C1 alleviates renal fibrosis by promoting apoptosis of senescent renal tubular epithelial cells
Mouse ureteral obstruction model, with senescent tubular cells also observed in obstructed human kidney tissue. Procyanidin C1 reduced senescent tubular cells and renal fibrosis in the mice. The human component is tissue observation, not treatment.
FASEB Journal
Frequently asked questions
Does procyanidin C1 extend lifespan?
One 2021 mouse paper reported prolonged survival in old mice. That paper has been under an Editorial Expression of Concern from the journal since March 2026, it has not been independently replicated, and there is no human lifespan evidence for any senolytic.
What is an Editorial Expression of Concern?
A notice from the journal telling readers that questions have been raised about a paper and that they should not rely on it while those are examined. It is not a retraction and it does not establish that the results are wrong. In this case the indexed notice gives no reason, so the reason is not publicly verifiable.
Is taking grape seed extract the same as taking procyanidin C1?
No. Grape seed extract contains procyanidin C1 among many other polyphenols at amounts that vary by product. No study has measured what blood level of procyanidin C1 a supplement produces in a person.