pH-Targeted Resveratrol Nanoparticles Selectively Activate SIRT1 in Senescent Immune Cells to Deacetylate Key Inflammatory Substrates and Dampen SASP

Hypothesis

Delivering resveratrol via pH-responsive β‑cyclodextrin nanoparticles that release cargo at lysosomal pH (≈5) will produce a selective, measurable increase in SIRT1‑dependent deacetylation of native protein substrates (p53‑Lys382 and NF‑κB‑p65‑Lys310) specifically in senescent immune cells, leading to a reduction in the senescence‑associated secretory phenotype (SASP). In contrast, free resveratrol or non‑targeted nanoparticle formulations will not achieve this effect because (i) the assay‑artifact‑driven SIRT1 activation observed with fluorogenic substrates is absent in native contexts, and (ii) resveratrol’s antioxidant activity can inhibit SIRT1 under oxidative conditions unless confined to the acidic lysosomal compartment where its redox state favors deacetylation.

Mechanistic Rationale

1. Lysosomal enrichment of senescent immune cells – Senescent macrophages and T‑cells exhibit heightened lysosomal biogenesis and acidic pH as part of the autophagy‑lysosome axis that sustains the SASP [4]. A pH‑triggered nanoparticle therefore concentrates resveratrol precisely where senescent immune cells are most active.
2. Conformational SIRT1 activation in acidic microenvironments – Resveratrol binds SIRT1 and stabilizes an active conformation that enhances deacetylation of substrates bearing negatively charged groups (e.g., phospho‑ or acetyl‑lysine) when the local pH promotes protonation of catalytic residues. This environment mimics the lysosomal lumen, potentially bypassing the need for fluorophore‑induced artifacts seen in vitro [1,2].
3. Decoupling deacetylation from antioxidant noise – At lysosomal pH, resveratrol’s phenol groups are less prone to radical scavenging, reducing competing redox reactions that can obscure SIRT1 activity in standard assays. Thus, any observed deacetylation of native substrates can be attributed to direct enzymatic modulation rather than indirect ROS scavenging.
4. Substrate specificity toward inflammatory regulators – p53‑Lys382 deacetylation promotes p53‑dependent cell‑cycle arrest without triggering apoptosis, while NF‑κB‑p65‑Lys310 deacetylation directly attenuates transcriptional drive of IL‑6, IL‑8, and MCP‑1, core SASP components [6,7]. Targeted SIRT1 activation should therefore shift the senescence program from a pro‑inflammatory to a more quiescent state.

Experimental Design (Testable & Falsifiable)

• Cell model: Human peripheral blood mononuclear cells (PBMCs) induced to senescence via low‑dose etoposide or replicative exhaustion; confirm senescence by SA‑β‑gal, p16^INK4a^ elevation, and SASP cytokine secretion.
• Treatment groups: (a) Free resveratrol (10 µM), (b) Non‑targeted β‑CD‑liposome resveratrol (equivalent resveratrol dose), (c) pH‑responsive β‑CD nanoparticle resveratrol (same dose), (d) Vehicle control. Include a SIRT1 inhibitor (sirtinol) arm for each to confirm specificity.
• Readout: After 24 h, isolate senescent immune cells (CD14^+CD16^- monocytes or CD8^+CD28^- T cells) via flow sorting. Perform targeted parallel reaction monitoring (PRM) mass spectrometry to quantify acetylation status of p53‑Lys382 and NF‑κB‑p65‑Lys310 on endogenous proteins (no fluorophore tags). Simultaneously measure SASP cytokines (IL‑6, IL‑8, MCP‑1) in supernatants by ELISA.
• Expected outcome: Group (c) shows a ≥2‑fold increase in deacetylation of both substrates relative to control, accompanied by a ≥30 % reduction in SASP cytokines. Groups (a) and (b) show no significant change in native substrate acetylation despite comparable total cellular resveratrol levels (verified by LC‑MS). SIRTinol co‑treatment abolishes the deacetylation and SASP suppression, confirming SIRT1 dependence.

Falsifiability Criteria

The hypothesis is falsified if:

1. pH‑targeted nanoparticles fail to produce a statistically significant increase in deacetylation of p53‑Lys382 or NF‑κB‑p65‑Lys310 compared with free resveratrol or non‑targeted carriers, or
2. Any observed deacetylation does not correlate with reduced SASP secretion, or
3. SIRTinol does not reverse the deacetylation/SASP effects, indicating off‑target mechanisms.

Significance

Confirming this hypothesis would reshape the view of polyphenol interventions in immunosenescence: it would demonstrate that pharmacokinetic targeting, not merely antioxidant capacity, enables genuine SIRT1 signaling in the very immune cells that drive aging. It would also provide a mechanistic bridge between lysosomal biology, sirtuin enzymology, and inflammaging, offering a clear translational path for nanoparticle‑based gerotherapeutics.