Hypothesis

A timed-release, butyrate-hyperproducing engineered probiotic administered at the onset of the biological night will restore hippocampal Per2/Bmal1 transcriptional rhythm, dampen microglial inflammasome activation, and improve episodic memory in older adults.

Mechanistic Rationale

Butyrate acts as a histone deacetylase (HDAC) inhibitor, increasing acetylation of histone H3 at clock gene promoters and enhancing the transcriptional activity of the BMAL1:CLOCK complex. In microglia, HDAC3 inhibition shifts the balance toward an anti‑inflammatory phenotype by reducing NF‑κB driven IL‑1β transcription while boosting Per2 expression, thereby reinforcing the cellular circadian firewall. Delivery of butyrate in a phase‑specific manner (early night) aligns peak intestinal concentrations with the rising phase of peripheral clock genes, amplifying the entrainment signal to the suprachiasmatic nucleus via vagal afferents and circulating metabolites.

Testable Predictions

1. Participants receiving the chronobiotic will show a ≥20 % increase in the amplitude of salivary melatonin and cortisol rhythms after 4 weeks.
2. Hippocampal‑targeted PET imaging (or CSF biomarkers) will reveal elevated Per2 mRNA levels relative to baseline.
3. Pro‑inflammatory cytokines (IL‑1β, TNF‑α) in plasma will decrease by ≥15 %.
4. Composite memory scores (e.g., RBANS delayed recall) will improve by ≥10 % compared with placebo.

Experimental Design

A double‑blind, placebo‑controlled, parallel‑group trial with 120 adults aged 65‑80, stratified by baseline actigraphy‑measured circadian robustness. Intervention: daily oral capsule containing 10⁹ CFU of an engineered Bifidobacterium strain that secretes butyrate in a pH‑dependent, timed‑release coating designed to dissolve at ileal pH (~7.4) corresponding to early night. Control: identical capsule with wild‑type strain. Duration: 8 weeks. Outcomes collected at baseline, week 4, and week 8: saliva melatonin/cortisol curves (every 2 h over 24 h), plasma cytokines, CSF or blood‑derived Per2 expression (via qPCR on PBMCs as peripheral proxy), actigraphy, and cognitive battery.

Potential Outcomes and Falsifiability

If the chronobiotic fails to raise melatonin/cortisol amplitude, does not elevate Per2 expression, and does not improve memory relative to placebo, the hypothesis that timed butyrate delivery restores brain clock function to confer cognitive benefit is falsified. Conversely, a concordant improvement across circadian, inflammatory, and cognitive measures would support the mechanistic link and justify larger scale trials.