NAD⁺ Boosting via Nicotinamide Riboside Enhances SIRT1-Mediated NLRP3 Deacetylation to Reverse Early Immunosenescence

Hypothesis: Chronic low-grade inflammation drives immunosenescence through NF-κB‑dependent NLRP3 inflammasome activation in myeloid‑derived suppressor cells (MDSCs), which promotes IL‑1β/IL‑18 release and drives CD8⁺ T‑cell exhaustion via TIM‑3 upregulation. We propose that boosting intracellular NAD⁺ with nicotinamide riboside (NR) activates SIRT1, which directly deacetylates the NLRP3 protein, suppressing its oligomerization independent of transcriptional NF‑κB signaling. This post‑translational inhibition reduces inflammasome activity, lowers IL‑1β/IL‑18 secretion, and preserves the TCF‑1⁺PD‑1⁺TIM‑3ˡᵒ precursor T‑cell pool, delaying epigenetic fixation of exhaustion. In aged humans, a short course of NR combined with a low‑dose NLRP3 inhibitor (MCC950) should reversibly restore metabolic fitness in PD‑1⁺TIM‑3⁺ T cells without triggering the epigenetic marks (H3K27ac loss at TCF‑1, Runx3 methylation) that define terminal exhaustion.

Testable predictions

1. Older adults with elevated serum CRP (>2 mg/L) who receive 500 mg NR twice daily for 4 weeks will show increased NAD⁺/NADH ratios in peripheral blood mononuclear cells (PBMCs) and enhanced SIRT1 deacetylase activity.
2. The same cohort will exhibit reduced ASC speck formation and decreased caspase‑1 activity in isolated MDSCs, indicating NLRP3 inflammasome suppression.
3. Serum IL‑1β and IL-18 concentrations will fall by ≥30 % relative to baseline, while IL‑10 rises.
4. Flow cytometry will reveal a rise in the frequency of TCF‑1⁺PD‑1⁺TIM‑3ˡᵒ CD8⁺ T cells (≥15 % increase) and a concomitant drop in TCF‑1⁻PD‑1⁺TIM‑3ʰⁱ cells.
5. AT‑PCR or bisulfite sequencing will show no new gain of H3K27ac loss at the TCF‑1 locus nor increased Runx3 promoter methylation after treatment, indicating avoidance of epigenetic fixation.
6. Adding a low dose of MCC950 (5 mg oral once weekly) to NR will produce additive effects: greater NLRP3 inhibition and larger expansion of the precursor T‑cell pool than either agent alone.

Experimental design A randomized, double‑blind, placebo‑controlled trial enrolling 120 participants aged 65‑80 years with baseline CRP > 2 mg/L. Four arms: (1) placebo, (2) NR alone, (3) MCC950 alone, (4) NR + MCC950. Treatment duration 8 weeks. Primary endpoint: change in the TCF‑1⁺PD‑1⁺TIM‑3ˡᵒ/CD8⁺ T‑cell ratio. Secondary endpoints: PBMC NAD⁺ levels, SIRT1 activity, MDSC inflammasome readouts (ASC specks, caspase‑1), plasma cytokines, and epigenetic markers of T‑cell exhaustion. Safety monitored via liver function, CBC, and adverse event logs.

Mechanistic rationale SIRT1 removes acetyl groups from lysine residues on NLRP3’s NACHT domain, a modification required for NLRP3 oligomerization and inflammasome assembly. By increasing NAD⁺, NR elevates SIRT1 catalytic flux, directly throttling inflammasome signaling downstream of NF‑κB‑driven transcription. This dual hit—lower NF‑κB‑dependent cytokine production plus direct NLRP3 deacetylation—should cut the feed‑forward loop where IL‑1β/IL‑18 reinforces NF‑κB activity in MDSCs. Preserving the TCF‑1⁺ precursor pool delays the metabolic collapse (HK2 degradation) and epigenetic silencing that lock T cells into a terminal state. Therefore, intervening before H3K27ac loss and Runx3 methylation occurs offers a reversible window, addressing the translational gap identified in current literature.

Falsifiability If NR fails to raise NAD⁺ or SIRT1 activity, or if MDSC inflammasome readouts and cytokine levels remain unchanged despite adequate dosing, the hypothesis is refuted. Likewise, absence of an increase in TCF‑1⁺PD‑1⁺TIM‑3ˡᵒ T cells or emergence of new epigenetic exhaustion marks would falsify the proposed mechanism.