Hypothesis

Chronic non‑steroidal anti‑inflammatory drug (NSAID) use exacerbates age‑related increases in ileal ASBT expression, leading to exaggerated conjugated primary bile acid (CPBA) accumulation in serum and brain, which accelerates neuroinflammation and cognitive decline.

Mechanistic Rationale

1. Aging elevates intestinal ASBT – In aged rodents, glucocorticoid receptor (GR)‑mediated transactivation boosts ASBT expression and protein levels, driving heightened CPBA uptake despite reduced hepatic CYP7A1 activity [1](2).
2. NSAIDs compromise the intestinal barrier – Chronic NSAID ingestion increases epithelial permeability, facilitating bacterial translocation and endotoxin (LPS) influx, which triggers hepatic inflammation and a systemic rise in glucocorticoids.
3. Feed‑forward loop – Elevated glucocorticoids further activate intestinal GR, amplifying ASBT expression beyond age‑related baseline. More CPBA is absorbed, raising circulating and brain CPBA levels (especially taurocholic acid) [1].
4. Bile acid‑driven neurotoxicity – Brain CPBA accumulation disrupts microglial homeostasis, promotes oxidative stress, and exacerbates tau pathology, while altered FXR/TGR5 signaling skews immune responses toward a pro‑inflammatory state.
5. Outcome – The combined effect of age‑driven ASBT upregulation and NSAID‑induced barrier leak creates a vicious cycle that accelerates cognitive decline beyond what aging alone would produce.

Testable Predictions

• Prediction 1: In aged mice, chronic NSAID treatment will increase ileal ASBT mRNA and protein levels ≥2‑fold compared with vehicle‑treated aged controls.
• Prediction 2: NSAID‑treated aged mice will exhibit higher serum and brain CPBA concentrations (particularly taurocholate) and elevated serum ammonia relative to untreated aged mice.
• Prediction 3: These biochemical changes will correlate with worsened performance in hippocampal‑dependent memory tasks (e.g., Morris water maze) and increased markers of neuroinflammation (Iba1+, GFAP+, IL‑1β).
• Prediction 4: Co‑administration of a GR antagonist (e.g., mifepristone) or intestinal‑specific ASBT knock‑down will blunt NSAID‑induced CPBA accumulation and rescue cognitive deficits.

Experimental Approach

1. Animal model: Use 18‑month-old male and female C57BL/6 mice; administer ibuprofen (50 mg/kg/day, p.o.) or vehicle for 8 weeks.
2. Groups: (a) Vehicle‑aged, (b) NSAID‑aged, (c) NSAID + GR antagonist, (d) NSAID + ileal‑specific ASBT shRNA (AAV‑mediated).
3. Readouts: qPCR/Western blot for ileal ASBT; LC‑MS serum/brain CPBA profiling; serum ammonia; intestinal permeability assay (FITC‑dextran); behavioral testing; immunohistochemistry for microglial activation and cytokine ELISA.
4. Statistical plan: Two‑way ANOVA (treatment × sex) with post‑hoc Tukey; n = 10 per group to achieve 80 % power for detecting a 30 % difference in brain taurocholate.

Potential Implications

If validated, this hypothesis would reframe NSAIDs—not merely as analgesics but as potential gerontogens that hijack an endogenous longevity signal (pain‑activated stress pathways) and convert it into a driver of brain aging. It would suggest that preserving transient, low‑intensity pain signaling (or selectively blocking GR‑ASBT axis in the gut) could mitigate the pro‑aging collateral damage of chronic analgesic use, opening avenues for interventions that balance pain relief with preservation of homeostatic stress responses.