| Proanthocyanidins (PACs; condensed tannins) = oligomeric/polymeric flavan-3-ols (e.g., catechin/epicatechin units); abundant in grape seed, cocoa, cranberry, apple skin, pine bark. Degree of polymerization (DP) influences bioactivity and absorption.
Primary mechanisms (conceptual rank):
1) Redox modulation → direct ROS scavenging + metal chelation (Fe²⁺/Cu²⁺).
2) NRF2 activation → endogenous antioxidant enzymes (HO-1, NQO1, GCLC).
3) Anti-inflammatory signaling → ↓ NF-κB / ↓ COX-2 / ↓ cytokines.
4) Anti-proliferative / pro-apoptotic signaling in cancer (MAPK, PI3K/Akt modulation; dose-dependent).
5) Anti-angiogenic / anti-metastatic effects (VEGF, MMPs; model-dependent).
PK / bioavailability: monomers/low-DP oligomers absorbed; higher-DP polymers poorly absorbed but metabolized by gut microbiota to phenolic acids; plasma parent PAC levels modest vs many in-vitro studies.
In-vitro vs systemic exposure: many cancer studies use ≥10–100 µM equivalents; achievable circulating levels typically lower and largely conjugated/metabolite-driven.
Clinical evidence status: strongest human data in vascular/cardiometabolic endpoints; oncology evidence largely preclinical/adjunct.
Polyphenols found in cranberry, blueberry, and grape seeds.
Proanthocyanidin B2 (PB2) is a type of dimer flavonoid that is found in grape seed, pine bark, wine, and tea leaves [17]. PB2 has been shown to possess various bioactivities, including anti-oxidant, anti-inflammation, and anti-obesity activities, and it has also shown efficacy in the treatment of cancer, cardiovascular disease, type 2 diabetes, ulcerative colitis, as well as acute liver injury.
PKM2 is the target of proanthocyanidin B2
PB2 also suppressed glucose uptake and lactate levels via the direct inhibition of the key glycolytic enzyme, PKM2.
Proanthocyanidins (PACs) — Cancer-Relevant Pathways
| Rank |
Pathway / Axis |
Cancer Cells |
Normal Cells |
TSF |
Primary Effect |
Notes / Interpretation |
| 1 |
ROS tone / redox balance |
↓ (low–mod dose); ↑ (high concentration only) |
↓ |
P→R |
Antioxidant; metal chelation |
Catechol-rich structure scavenges radicals; pro-oxidant shift reported at high doses in tumors (model-dependent). |
| 2 |
NRF2 axis |
↑ (context-dependent) |
↑ |
R→G |
Endogenous antioxidant induction |
↑ HO-1/NQO1; protective in normal tissue; may support tumor stress resistance (context-dependent). |
| 3 |
NF-κB / inflammatory signaling |
↓ |
↓ |
R→G |
Anti-inflammatory |
Reduces cytokines, COX-2; anti-tumor microenvironment effect plausible. |
| 4 |
PI3K/Akt / MAPK pathways |
↓ proliferation (model-dependent) |
↔ |
R→G |
Growth signaling attenuation |
Observed in breast, colon, prostate models; dose and DP dependent. |
| 5 |
Apoptosis (caspase activation) |
↑ (dose-dependent) |
↔ / ↓ |
R→G |
Pro-apoptotic signaling |
Mitochondrial depolarization reported; often supra-physiologic exposure. |
| 6 |
Angiogenesis (VEGF) |
↓ (preclinical) |
↔ |
G |
Anti-angiogenic |
↓ VEGF expression in models; human oncologic data limited. |
| 7 |
Ferroptosis axis |
↓ (anti-lipid-ROS bias) |
↓ |
P→R |
Lipid peroxidation inhibition |
Strong antioxidant property may counter ferroptotic strategies (context-dependent). |
| 8 |
Clinical Translation Constraint |
— |
— |
— |
Bioavailability & dose gap |
High-DP PACs poorly absorbed; many in-vitro doses exceed realistic plasma exposure; adjunct role most plausible. |
TSF Legend: P: 0–30 min | R: 30 min–3 hr | G: >3 hr
Proanthocyanidins (PACs) — Alzheimer’s Disease–Relevant Axes
| Rank |
Pathway / Axis |
Cells (neurons/glia) |
TSF |
Primary Effect |
Notes / Interpretation |
| 1 |
Lipid peroxidation / neuronal ROS |
↓ |
P |
Neuroprotective antioxidant |
Reduces oxidative damage markers in models; aligns with AD oxidative stress hypothesis. |
| 2 |
NRF2 activation |
↑ |
R→G |
Endogenous antioxidant upregulation |
Supports neuronal resilience; mostly preclinical evidence. |
| 3 |
Neuroinflammation (NF-κB) |
↓ |
R→G |
Microglial modulation |
Reduced cytokine production in animal models. |
| 4 |
Aβ aggregation / toxicity |
↓ (preclinical) |
G |
Interference with amyloid aggregation |
Reported inhibition of Aβ fibrillization in vitro; human data limited. |
| 5 |
BDNF / synaptic plasticity |
↑ (model-dependent) |
G |
Neurotrophic signaling |
Observed in flavanol-rich cocoa/grape extract studies; translation to PAC isolates unclear. |
| 6 |
Clinical Translation Constraint |
— |
— |
Dietary-level evidence |
Human trials mostly use flavanol-rich extracts; cognitive effects modest and stage-dependent. |
TSF Legend: P: 0–30 min | R: 30 min–3 hr | G: >3 hr
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