Hypothesis

We hypothesize that administering indole-3-propionic acid (IPA) in alignment with the host's peripheral circadian timing restores microbial rhythmicity, strengthens gut barrier function, and re-synchronizes mitochondrial bioenergetics, thereby attenuating age-related damage across multiple SENS categories.

Mechanistic Rationale

Circadian disruption desynchronizes gut microbiota oscillations, reducing short-chain fatty acid (SCFA) producers and compromising epigenetic stability via diminished butyrate-mediated HDAC inhibition Butyrate HDAC inhibition and epigenetic stability. This loss of SCFA producers also weakens gut barrier integrity, facilitating microbial translocation and inflammaging Loss of SCFA producers compromises gut barrier. IPA, a tryptophan-derived indole, exhibits potent antioxidant properties and preserves intestinal epithelial tight junctions independent of SCFA pathways. We propose that IPA acts as a chronobiotic cue: its rhythmic release from entrained microbiota feeds back to reinforce host peripheral clocks, particularly in liver and muscle, where circadian genes regulate mitochondrial fission/fusion and autophagy flux Muscle cells contain circadian clocks. By stabilizing microbiota-host clock coupling, IPA improves NAD+ salvage pathways, enhances SIRT1 activity, and restores rhythmic mitophagy, counteracting mitochondrial dysfunction Circadian disruption desynchronizes gut microbiota rhythms.

Additionally, IPA’s anti-inflammatory action reduces NF‑κB signaling, lowering circulating cytokines that otherwise blunt clock gene expression in adipocytes and hepatocytes. This creates a positive feedback loop: improved clock function drives timed IPA production, which further stabilizes the microbiome, breaking the cycle of inflammaging and metabolic decline seen in shift workers Shift work biological age acceleration. BMI mediates 36‑53 % of the association between night‑shift work and biological age acceleration, suggesting that metabolic improvements via IPA could directly mitigate this pathway BMI mediates night shift work and biological age acceleration.

Testable Predictions

1. In aged mice subjected to chronic jet‑lag, timed IPA administration (delivered at ZT6) will restore fecal microbiota rhythmicity (measured by 16S rRNA sequencing) to resemble that of young, ad libitum‑fed controls.
2. Treated mice will show increased colonic butyrate levels and elevated tight‑junction protein (occludin, ZO‑1) expression relative to jet‑lag controls receiving vehicle.
3. Liver and skeletal muscle biopsies will reveal restored circadian expression of Bmal1, Clock, and mitochondrial genes (Pgc‑1α, Sirt3) and improved mitochondrial respiration (Seahorse assay).
4. Treated animals will exhibit delayed onset of age‑related phenotypes: reduced frailty index, preserved grip strength, and lower epigenetic age (Horvath mouse clock) compared with untreated jet‑lag peers.
5. In a human crossover trial, night‑shift workers receiving timed IPA (evening dose) will demonstrate decreased plasma IL‑6 and TNF‑α, improved nocturnal melatonin amplitude, and a reduction in DunedinPACE epigenetic acceleration score after 8 weeks.

Experimental Design

Animal model: C57BL/6 mice, 18 months old, exposed to 8‑hour advancing light‑dark shifts twice weekly for 12 weeks. Groups: (1) sham‑shift + vehicle, (2) jet‑lag + vehicle, (3) jet‑lag + timed IPA (10 mg/kg oral gavage at ZT6), (4) jet‑lag + constant IPA (same total dose split across 24 h). Measurements taken every 4 h over 48 h at study end.

Human trial: 60 night‑shift healthcare workers, randomized to timed IPA (5 mg at 20:00) or placebo for 8 weeks, with a 4‑week washout and crossover. Primary outcomes: nocturnal melatonin rhythm (salivary melatonin AUC), peripheral inflammatory cytokines, and change in epigenetic age acceleration.

If timed IPA rescues circadian‑microbiota synchrony and mitigates aging biomarkers, the hypothesis will be supported; failure to observe these effects would falsify the proposed mechanism.