Hypothesis

Combining low-dose intermittent rapamycin with NR supplementation will increase brain NAD+ levels more than NR alone by reshaping the gut microbiome to favor conversion of NR to nicotinic acid (NA), a change detectable via magnetic resonance spectroscopy and reflected in a slowed DunedinPACE trajectory.

Mechanistic Rationale

• NR raises circulating NAD+ but depends on gut bacteria to produce NA, which then crosses the blood-brain barrier and boosts cerebral NAD+ NR Raises NAD+ Over 2-Fold More than NMN.
• Rapamycin inhibits mTORC1, altering microbial community structure and increasing taxa that express nicotinamide riboside kinases and NA transporters, as shown in mouse models of immunosuppression.
• Enhanced NA production raises hepatic and neuronal NAD+ via the Preiss-Handler pathway, bypassing the reliance on NRKs that saturate in peripheral tissues.
• Elevated brain NAD+ activates SIRT3 and improves mitochondrial fidelity, a process that should decelerate epigenetic aging pace measured by DunedinPACE, which has high test-retest reliability (ICC >0.90) for quarterly monitoring Biological Age Testing in 2026.

Testable Predictions

1. Participants receiving NR plus rapamycin will show a ≥30% greater increase in brain NAD+ (measured by ^31P-MRS) after 8 weeks compared to NR placebo.
2. Fecal 16S sequencing will reveal a significant rise in Akkomensia and Bacteroides strains correlated with NA production.
3. Plasma NAD+ will not differ significantly between groups, confirming that brain-specific effects are microbiome-mediated.
4. DunedinPACE scores will decline by at least 0.05 units per quarter in the combination group, while NR-only and placebo groups show no change.

Experimental Design

• Design: Randomized, double-blind, placebo-controlled, 2x2 factorial trial (NR vs placebo; rapamycin vs placebo) over 16 weeks.
• Population: 120 healthy adults aged 45-60, stratified by baseline DunedinPACE.
• Interventions: NR 1000 mg daily; rapamycin 3 mg weekly (intermittent); matching placebos.
• Outcomes:
  • Primary: Change in brain NAD+ (MRS) at week 8.
  • Secondary: Fecal microbiome shifts (shotgun metagenomics), plasma NAD+, cytokine panel, quarterly DunedinPACE.
• Analysis: Mixed-effects models testing interaction between NR and rapamycin on brain NAD+ and DunedinPACE slope; mediation analysis to assess whether microbiome NA-producer abundance explains NAD+ changes.

If the interaction is significant and mediated by microbiome shifts, the hypothesis is supported; absence of differential brain NAD+ or microbiome changes falsifies the mechanism.