Nano-flow SQUAD LC-HRAM enables ultrasensitive bile acid quantitation and discovery

SQUAD bile acids — Nano-flow SQUAD LC-HRAM enables ultrasensitive bile acid quantitation and discovery

Significance of the topic:

Many bile acids occur at very low concentrations in biological matrices yet play central roles in host metabolism, immune signaling, and host–microbiome interactions. Improving analytical sensitivity for bile acids expands the ability to quantify low-abundance species, detect disease-associated signatures, and simultaneously support untargeted metabolomics for biomarker discovery and mechanistic studies.

Study goals and overview:

This work developed and evaluated a Simultaneous Quantitation and Discovery (SQUAD) workflow combining nano-flow liquid chromatography (0.5 µL/min) with high-resolution accurate-mass (HRAM) detection to (1) achieve ultrasensitive targeted quantitation of a 12‑compound bile acid panel, and (2) perform untargeted metabolomics discovery from the same dataset. The approach was benchmarked against conventional analytical flow rates (100 and 300 µL/min) and applied as a proof-of-principle to human plasma from Crohn's disease patients and healthy controls (n = 6 per group).

Materials and methods (sample handling and study design):

- Target panel: 12 bile acids (including DCA, GCA, GCDCA, GDCA, LCA, MCA, TCA, TLCA, TDCA, TUDCA, UDCA, CA).
- Sample preparation: plasma protein precipitation with methanol prior to LC‑MS analysis.
- Comparative flows: nano-flow LC at 0.5 µL/min versus conventional analytical flows at 100 and 300 µL/min.
- Quantitative evaluation: calibration standards to determine limits of quantitation (LOQs) and dynamic range; targeted quantitation of selected bile acids in plasma.
- Discovery analysis: untargeted metabolomics processing and statistical annotation performed with Thermo Scientific Compound Discoverer and multivariate analyses to compare disease and control groups.

Instrumentation used:

- Vanquish Neo UHPLC System operated in nano-flow mode (0.5 µL/min).
- Orbitrap Excedion Pro hybrid mass spectrometer (high-resolution accurate mass detection).
- Software: Compound Discoverer for untargeted data processing and statistical analysis.

Main results and discussion:

- Sensitivity gain: Nano-flow operation substantially improved detection sensitivity for the bile acid panel relative to conventional flows. LOQs as low as 0.001 fmol on-column were achieved for some analytes, with sensitivity improvements ranging from ~2-fold up to >200-fold depending on the compound. For example, GCDCA LOQ decreased to ~0.0109 fmol on-column at 0.5 µL/min, representing roughly ~180-fold greater sensitivity compared with higher flow rates.

- Robust targeted performance: The SQUAD workflow produced robust quantitation across a wide dynamic range for the 12 bile acids, enabling reliable measurement of low-abundance species in complex plasma matrices.

- Discovery outcomes: The same nano-flow LC-HRAM dataset supported untargeted metabolomics. Multivariate analysis separated Crohn's disease and control plasma samples, and metabolic differences consistent with inflammation were identified, including reductions in several polyunsaturated fatty acids (arachidonic acid, DHA, dihomo-γ-linolenic acid, linoleic acid) and elevations in inflammatory mediators such as leukotriene B4 and prostaglandin E2.

- Biological application: Targeted quantitation of TUDCA, TDCA, and GCDCA in the Crohn's disease cohort demonstrated method suitability for clinical research samples. In this pilot cohort (n = 6 per group), differences in bile acid levels did not reach statistical significance, but the method reliably measured low‑abundance analytes and revealed disease-associated metabolic trends.

Benefits and practical applications of the method:

- Combined targeted and untargeted capabilities: One LC‑MS acquisition supports both ultrasensitive quantitation and discovery metabolomics, maximizing information obtained from limited sample material.
- Enhanced sensitivity: Lower LOQs enable detection and quantitation of trace bile acids that are otherwise undetectable using conventional analytical-flow methods, supporting biomarker research and mechanistic studies in inflammation, metabolic disease, and microbiome research.
- Applicability to complex matrices: The workflow demonstrated robust performance in human plasma, indicating suitability for translational and clinical research sample sets.

Limitations and considerations:

- Cohort size and statistical power: The pilot biological study was small (n = 6 per group), limiting the ability to draw definitive clinical conclusions; larger cohorts and validation studies are required.
- Operational requirements: Nano-flow LC and nanospray HRAM MS demand specialized hardware, careful method development, and maintenance to ensure stable electrospray and reproducible performance; throughput may be lower than analytical-flow setups.

Future trends and potential applications:

- Clinical validation and larger cohorts: Scaling the approach to larger, well-characterized cohorts could validate bile acid and lipid mediator biomarkers for IBD and other diseases.
- Integration with targeted panels and panels expansion: Combining nano-flow SQUAD with broader targeted assays could expand coverage of conjugated and microbially derived bile acids and related metabolites.
- Automation and robustness improvements: Advances in nano-flow hardware and autosampler designs could increase robustness and throughput, making ultrasensitive workflows more routine in applied laboratories.
- Multi-omics and mechanistic studies: The high sensitivity supports linking bile acid profiles to microbiome composition, host lipid signaling, and pharmacometabolomics in preclinical and clinical studies.

Conclusions:

The nano-flow SQUAD LC-HRAM workflow implemented on the Vanquish Neo UHPLC and Orbitrap Excedion Pro MS achieved marked sensitivity improvements for bile acid quantitation (LOQs down to 0.001 fmol on-column and up to >200-fold gains versus conventional flows). The single-run combination of targeted quantitation and untargeted discovery proved effective in plasma, enabling detection of inflammation-associated lipid mediator changes in a Crohn's disease pilot cohort. The method offers substantial potential for sensitive biomarker measurement and metabolomics discovery, pending further validation in larger studies.

References:

- Harlan R, Amer B, Grim C, Deshpande RR, Reisdorph N, Doenges K, Armstrong M, Bird SS. Nano-flow SQUAD LC-HRAM enables ultrasensitive bile acid quantitation and discovery. Thermo Fisher Scientific / University of Colorado. Scientific poster PO004822-2026-EN. 2026.