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Tier 2 Butyrate Assay Audit — Computational Literature Synthesis (comp-038)

Status: Complete first pass — 2026-05-20. Experiment folder: etc/experiments/comp-038-tier-2-butyrate-assay-audit/. Output: outputs/summary.md.

Question

Is there a Tier 2 butyrate quantification assay — colorimetric, enzymatic, breath-proxy, electrochemical, or other low-cost intermediate method — that can be validated against Tier 3 GC-MS for OE's stool, serum, breath, or culture-supernatant use cases?

Verdict

YELLOW. A ready-to-adopt simple/home colorimetric or breath-based butyrate assay did not surface. Two plausible Tier 2 candidates did surface, but both require full-text/protocol review and paired GC-MS validation before wet-lab adoption:

Candidate Matrix fit Verdict Evidence status
HPLC-UV SCFA + lactate assay for bacterial culture supernatants Culture supernatant / engineered-strain work YELLOW PubMed abstract reports mM-range matrix-matched calibration and use for butyric-acid-producing bacteria; full text and OE spike-recovery still required.
Electrochemical fecal SCFA profiling with ANN deconvolution Stool / fecal SCFA profiling YELLOW Emerging fecal SCFA platform; needs full-text butyrate-specific performance, reference-method correlation, and external validation.
Butyric-acid / SCFA ELISA kits Serum/plasma/vendor-claimed matrices RED-provisional Vendor claims exist, but no PubMed/GC-MS validation surfaced; small-molecule specificity is a major concern.
Breath H2/CH4 Breath RED Broad fermentation/adherence proxy, not butyrate-specific quantification.
Generic free-fatty-acid colorimetric kits Serum/plasma/culture, vendor-dependent RED Representative FFA kit protocol excludes SCFAs including butyric acid.

Why This Matters

The quantification ladder needs a cheap Tier 2 surface between visual/user-facing proxies and Tier 3 GC-MS / HPLC / LC-MS anchors. For microbiome-derived metabolites, that gap is especially painful: the genotype-informed supplement workflow can recommend butyrate-emphasis interventions for ABCG2 Q141K carriers, but it cannot yet verify butyrate delivery with a validated home or community-biolab Tier 2 assay.

comp-038 reframes that gap as two different problems:

  1. Culture-supernatant butyrate from engineered strains: plausible Tier 2-lab path exists via HPLC-UV, with GC-MS as anchor.
  2. Stool/serum/home butyrate exposure: no ready-to-adopt Tier 2 method surfaced; electrochemical fecal SCFA profiling is promising but not production-ready.

Method Summary

The run used the committed query strategy in inputs/query-strategy.json, fetched a PubMed title/abstract snapshot via NCBI E-utilities, then performed five Codex/GPT-5.5 in-session synthesis trajectories from outputs/codex-synthesis-packet.md. The completed run used the local Codex synthesis path and made no OpenRouter model calls.

The evidence gate was intentionally strict: PubMed title/abstract hits can surface candidates, but they cannot justify a GREEN wet-lab recommendation without full-text methods, protocol PDFs, vendor validation documents, or method-comparison data.

Key Results

Result Interpretation
PubMed snapshot: 27 queries / 74 records Enough for a first-pass assay landscape; not a full-text review.
HPLC-UV candidate: PMID 23542733 Best near-term candidate for culture-supernatant butyrate in engineered-strain / fermentation work.
Electrochemical fecal candidate: PMID 42041444 Best stool-specific future direction, but still research-platform grade.
Breath proxy literature Useful for fermentation activity, not butyrate quantification.
Generic FFA colorimetric kits False-friend class; representative protocol excludes acetic, propionic, and butyric acid.

Impact on Experimental Priorities

This does not unlock a home butyrate assay today. It does tighten the next experimental move:

  • Keep GC-MS as the Tier 3 anchor for butyrate.
  • For engineered-strain / culture-supernatant work, run a small paired validation of HPLC-UV against GC-MS using sodium-butyrate standards and OE-relevant culture matrices.
  • For stool work, do a full-text and protocol review of the electrochemical fecal SCFA platform before spending on hardware or adaptation.
  • Do not spend on breath hydrogen/methane or generic FFA colorimetric kits for butyrate quantification.

For validation-experiments.md §1.14, this means the butyrate dose-response arm still needs a Tier 3 analytical anchor if concentration verification becomes load-bearing. HPLC-UV may become a cheaper intermediate check for culture-supernatant development, but not for the cellular dose-response arm without matrix validation.

Limitations

  • PubMed results are title/abstract/citation metadata, not full-text validation.
  • Vendor and patent searches were targeted, not exhaustive.
  • Commercial ELISA claims remain unverified and should not drive spend.
  • No non-English corpus pass was run because this specific scope is analytical-chemistry-heavy and Stage 1 was not sparse; revisit if full-text/vendor follow-up stalls.
  • The N=5 trajectories were performed in one Codex session to avoid OpenRouter spend, not by five independent paid model calls.

Next Step

Run a focused full-text/protocol verification pass on PMID 23542733 and PMID 42041444, plus a vendor protocol audit for any butyric-acid/SCFA ELISA claims. If one candidate survives, design a small paired validation with sodium-butyrate spike/recovery and 10-20 real samples measured by the candidate Tier 2 method plus GC-MS.

Cross-References