Hypothesis: Timed NAD+ supplementation disrupts the SASP‑CD38‑NAD+ sink and prevents resistance to intermittent senolytics

Core idea Intermittent dasatinib + quercetin (D+Q) clears senescent cells but triggers a compensatory SASP surge that up‑regulates CD38 in neighboring cells, draining NAD+ and blunting SIRT1 activity. This NAD+ depletion creates a microenvironment that protects residual senescent cells and drives resistance observed at week 4. Supplying an NAD+ precursor (e.g., nicotinamide riboside, NR) during the SASP peak window should replenish NAD+, sustain SIRT1‑mediated deacetylation of p53 and FOXO, and thereby enhance senolytic‑induced apoptosis while blocking the CD38‑driven sink.

Mechanistic rationale

1. SASP factors (IL‑6, IL‑8, MCP‑1) induce CD38 expression via STAT1/STAT2 signaling [4].
2. CD38 hydrolyzes NAD+ to ADP‑ribose, lowering intracellular NAD+ and reducing SIRT1 deacetylase activity [5].
3. Low NAD+ shifts the balance toward a pro‑survival senescent phenotype by decreasing p53 acetylation and increasing NF‑κB activity, which sustains SASP production.
4. Intermittent D+Q creates a pulsatile SASP peak (max at ~day 3 post‑dose) that coincides with the window when NAD+ levels are lowest; providing NR at this moment restores NAD+, reactivates SIRT1, and promotes senescent cell clearance.

Testable predictions

• In aged mice treated with intermittent D+Q alone, NAD+ in spleen and liver drops ~30 % at day 4 post‑dose and returns to baseline by day 7.
• Co‑administration of NR (300 mg/kg) 2 h after each D+Q dose will maintain NAD+ > 90 % of baseline throughout the dosing cycle.
• Mice receiving D+Q + NR will show a ≥ 2‑fold increase in senolytic‑induced apoptosis (caspase‑3+ senescent cells) compared with D+Q alone at day 4.
• Consequently, p16^INK4a^+ cell burden will be reduced by an additional 40 % relative to D+Q alone, and functional readouts (grip strength, treadmill endurance) will improve by ≥ 15 % after four cycles.
• If NAD+ supplementation is given outside the SASP peak (e.g., 24 h after D+Q), no additive benefit will be observed, falsifying the timing‑dependence claim.

Experimental design (mouse)

1. Groups (n = 10 per group): vehicle, D+Q alone (5 mg/kg dasatinib + 50 mg/kg quercetin, i.p., 1 day on/7 days off), NR alone (300 mg/kg oral daily), D+Q + NR (NR given 2 h post‑D+Q), D+Q + NR‑delayed (NR given 24 h post‑D+Q).
2. Treat for four cycles (28 days).
3. Measure NAD+ levels (LC‑MS) in blood, liver, spleen at 0, 2, 4, 8, 24 h after each dose.
4. Quantify senescent cells via p16^INK4a^ immunohistochemistry and SASP cytokines (ELISA).
5. Assess apoptosis (cleaved caspase‑3) in p16^+ cells.
6. Perform functional tests (grip strength, rotarod, treadmill) at baseline and end.

Falsifiability If NAD+ levels do not rise with NR co‑administration, or if senolytic‑induced apoptosis and functional gains are not superior to D+Q alone, the hypothesis is refuted. Likewise, if delayed NR provides equal benefit, the timing‑specific mechanism is unsupported.

Translational implication A biomarker‑driven protocol—baseline high SASP score → intermittent D+Q + NAD+ booster timed to SASP peak—could convert the modest, variable responses seen in human trials into consistent functional improvement, directly addressing the heterogeneity and resistance problems highlighted in recent senolytic research [1,2]