Procyanidin C1

Procyanidin C1 (PCC1) is a B-type proanthocyanidin trimer composed of three (2R,3R)-(-)-epicatechin units joined by two successive (4beta to 8)-interflavan bonds, with molecular formula C45H38O18 and molecular weight 866.77 g/mol. The compound is a polyphenolic constituent of grape seed extract (GSE), cocoa, cinnamon bark, unripe apple peel, and pine bark, and was first structurally characterized in the 1980s as part of the broader oligomeric proanthocyanidin (OPC) family originally described by Masquelier in 1947. PCC1 remained a minor analytical curiosity within the proanthocyanidin literature until 2021, when a landmark screening study by Xu, Fu, and colleagues, published in Nature Metabolism, identified PCC1 as a potent and selective senotherapeutic agent capable of extending healthspan and lifespan in aged mice through dual-mode activity on senescent cells [1]. At low concentrations (below approximately 50 micromolar), PCC1 acts as a senomorphic agent, suppressing the production of pro-inflammatory senescence-associated secretory phenotype (SASP) factors through inhibition of NF-kappaB signaling without inducing senescent cell death. At higher concentrations (above approximately 100 micromolar), PCC1 transitions to a senolytic mode, selectively inducing apoptosis in senescent cells through a reactive oxygen species (ROS)-dependent mitochondrial dysfunction pathway involving the p53-Puma/Noxa axis, while sparing proliferating and quiescent non-senescent cells. This concentration-dependent functional switch distinguishes PCC1 from most other characterized senolytic agents and provides a pharmacological basis for dose-titrated senotherapeutic intervention.

The 2021 Nature Metabolism study demonstrated that intermittent administration of PCC1 (20 mg/kg intraperitoneally, biweekly for two months) to aged C57BL/6J mice reduced senescent cell burden across multiple tissues, attenuated age-related physical dysfunction, and extended median remaining lifespan by approximately 64 percent compared to vehicle-treated controls, with no observed systemic toxicity [1]. Subsequent preclinical studies have expanded the evidence base substantially. Zhu, Huang, and colleagues (2024) demonstrated that PCC1 alleviates structural and functional decline in the aged mouse retina through combined senolytic and senomorphic mechanisms [2]. Gan and colleagues (2025) reported that PCC1 alleviates renal fibrosis by promoting apoptosis of senescent renal tubular epithelial cells [3]. Additional preclinical evidence supports activity against skin fibrosis through EGFR inhibition and TGF-beta/SMAD pathway suppression [4], neuroprotection through Nrf2/HO-1 signaling activation [5], endothelial nitric oxide production through PI3K/Akt-dependent eNOS phosphorylation [6], insulin sensitization in adipocytes through AKT-eNOS pathway activation [7], and colon cancer growth inhibition through miR-501-3p/HIGD1A axis modulation [8]. Single-cell profiling has revealed broad geroprotective effects on the hematopoietic immune system, including restoration of B cell and hematopoietic stem cell populations and suppression of senescence-associated inflammatory markers [9].

Pharmacokinetically, PCC1 shares the absorption limitations characteristic of oligomeric proanthocyanidins: oral bioavailability of trimeric procyanidins is low, with the majority of ingested material reaching the colon intact where it is degraded by gut microbiota into phenylvalerolactones, phenylvaleric acids, and smaller phenolic acid metabolites. Phytosomal formulations have demonstrated 2- to 3-fold improvements in gastrointestinal absorption efficiency. No completed Phase 1 or Phase 2 clinical trials of purified PCC1 have been published as of the most recent monograph revision, though preliminary findings from phytosomal PCC1 formulations have shown reductions in senescence markers in peripheral blood mononuclear cells from elderly individuals. The compound is not approved by any regulatory authority for therapeutic use. It is available as a research-grade preparation from multiple chemical suppliers at greater than 95 percent purity by HPLC. This monograph documents the chemistry, natural sourcing, dual-mode senotherapeutic pharmacology, pharmacokinetics, preclinical evidence base across aging, fibrotic, neurodegenerative, metabolic, and oncologic indications, sourcing and quality verification, reconstitution and handling, stack-interaction considerations, adverse-event signal, and a structured comparative assessment of five senolytic candidates against PCC1 on five competency standards.