publications

2026

1. TBD

   Understanding Long COVID (LC) in Frontline and Essential Workers (FEWs) through Proteomic Profiling: A Longitudinal Cohort Study

   Tuo Liu, Danielle Stea, Shawn C Beitel, and 3 more authors

   BMC-Medicine, in prep, 2026

   DOI
2. PLoS ONE

   Unveiling Post-Vaccination Proteomic Signatures in Infection-Naïve Individuals Associated with Omicron Breakthrough Infections

   Yiwen Liu, Eric Lu, Katherine D. Ellingson, and 6 more authors

   PLoS ONE, 2026

   DOI
3. IJHEH

   Differential Metabolic Profile by Training Fire Exposure in Female Firefighters

   Tuo Liu, James Hollister, Krystal J. Kern, and 15 more authors

   International Journal of Hygiene and Environmental Health, 2026

   DOI
4. CEHR

   Extreme Heat Exposure During Pregnancy and Birth Outcomes: A Review of Epidemiological Evidence and Policy Implications

   Rebecca Ramos, Paulina L. Ramirez, Rietta S. Wagoner, and 7 more authors

   Current Environmental Health Reports, peer review, 2026

   DOI
5. BR

   A Life-Course View of Bone Health Through Bone Mineral Density: Metabolomic Insights in Adolescents, Young Adults, and Older Adults

   Tuo Liu, Zhenjiang Li, Douglas I. Walker, and 10 more authors

   Bone Research, peer review, 2026

   DOI
6. JBMR

   Per- and polyfluoroalkyl Substances (PFAS) and Bone Health in Older Hispanic Adults on US-Mexico Border

   Tuo Liu, Zhenjiang Li, Douglas I. Walker, and 8 more authors

   Journal of Bone and Mineral Research, peer review, 2026

   DOI
7. EI

   Metabolic effects of wood smoke: evidence from in vivo and in vitro in reference to firefighters

   Riley D. Hellinger, Tuo Liu, Weiguo Han, and 8 more authors

   Environmental International, under development, 2026

   DOI

2025

1. Metabolomics

   Differential metabolic profiles by Hispanic ethnicity among male Tucson firefighters

   Tuo Liu, Melissa A. Furlong, Justin M Snider, and 10 more authors

   Metabolomics, 2025

   Abs DOI

   Introduction Firefighters face regular exposure to known and probable human carcinogens, such as polycyclic aromatic hydrocarbons (PAHs), benzene, and formaldehyde, leading to an increased risk of various cancers compared to the general population. Hispanic and black firefighters are at increased risk of additional cancers not elevated in non-Hispanic white firefighters, yet biological pathways underlying these differences are unknown. Objectives The study objectives were to evaluate differences in the urinary metabolome between Hispanic and non-Hispanic firefighters, pre-and post-fireground exposure. Methods To investigate the metabolic patterns, we employed a comprehensive metabolomics pipeline that leveraged liquid chromatography coupled with high-resolution mass spectrometry. We applied linear mixed effects regression to identify the differential metabolites at an FDR < 0.05 among 19 Hispanic and 81 non-Hispanic firefighters. We also performed overrepresentation analysis using Mummichog to identify enriched pathways at FDR < 0.05. Results Out of 175 features in HILIC(−) mode and 1847 features in RP(+) mode, we found 26 and 276 differential urinary features, respectively, when comparing Hispanic and non-Hispanic firefighters. We noted pathway enrichment in tryptophan and galactose metabolism. However, post-exposure, we did not observe differences in the metabolomic response by ethnicity despite differing fireground exposures. Conclusion Dysregulation in the tryptophan and galactose pathway is an important contributor to cancer risks and may explain the increased cancer risk among Hispanic firefighters. Supplementary Information The online version contains supplementary material available at 10.1007/s11306-024-02198-9.

2. EnvHealth

   Evaluating Urine Metabolic Profiles with Wildland- Urban-Interface (WUI) Fire Exposure: A Comparison with Municipal Structure Fires (MSF)

   Tuo Liu, Melissa A. Furlong, Shawn C. Beitel, and 5 more authors

   Environmental Health, 2025

   Abs DOI

   Firefighters have frequent exposure to carcinogens and an increased risk of cancer. Wildland-urban interface (WUI) fires, which involve both structures and undeveloped wildland fuels, pose unique challenges to the health of firefighters. However, the extent of health risks associated with these fires remains underexplored. This study aims to identify altered urine metabolites and metabolic processes among male firefighters that were associated with WUI fires as compared with municipal structure fires (MSF). Untargeted metabolomic profiling was applied to pre-exposure (baseline) and postfire urine samples collected from firefighters responding to WUI and MSF exposure. Differential analysis was conducted by fitting linear mixed effects regression models on preprocessed ion intensity and exposure status while adjusting for demographic covariates. Differential metabolites by post-exposure status were identified using a false discovery rate (FDR) threshold of <0.05. Enrichment analysis was performed to identify pathways that were significantly perturbed at a Bonferroni adjusted p-value <0.05 level. Eighty-five firefighters contributed paired baseline and post-fire samples from WUI events, and 98 firefighters contributed paired baseline and post-fire samples from MSF events. We performed metabolic profiling on baseline and postfire urine samples from WUI and structure fires using four modes: HILIC(-), HILIC(+), C18(-), and C18(+) and identified metabolites against an in-house library. We identified 244, 297, 320, and 266 level 1 metabolites from the four respective modes. In the statistical analysis, the main model identified a total of 176 differential metabolites from WUI fires. For MSF, the model identified a total of 652 differential metabolites from the four respective modes. Most metabolites with significant changes after a WUI fire also changed significantly after an MSF event. Two pathways were significantly enriched after WUI fires, while seven pathways were significantly enriched after MSF exposure and two pathways overlapped between the two types of fires. Fire exposure induces numerous metabolic perturbations in firefighters that may partially explain their elevated cancer risks. Although individual metabolites changed in a similar fashion across both WUI and MSF, structure fires were associated with an increased number of metabolite changes and some of the altered pathways differed between exposures to WUI fires vs. MSF. These results suggest that exposures to WUI fires and MSF present both common and unique cancer risks for firefighters.

3. EnvRes

   Per- and polyfluoroalkyl Substances (PFAS) and microRNA: an epigenome-wide association study in firefighters

   Melissa A Furlong, Tuo Liu, Alesia Jung, and 4 more authors

   Environmental Research, 2025

   Abs DOI

   The occupation of firefighting is classified as a Group 1 carcinogen. Increased cancer risk among firefighters may be partly attributable to increased occupational exposure to a range of chemicals, including per- and polyfluoroalkyl substances (PFAS). Some PFAS are known and suspect human carcinogens. Investigating epigenetic response to these PFAS exposures in firefighters may help to identify biological pathways of specific cancers, and previously unidentified health outcomes that are associated with PFAS. We therefore investigated the associations of serum PFAS concentrations with miRNA expression in firefighters. Sera collected from 303 firefighters from 6 sites across the USA were analyzed for 9 PFAS along with miRNA expression. Linear regression was used to estimate associations between log PFAS and miRNA expression, with false discovery rate (FDR) set to 0.05 for significance, and an exploratory cutoff of FDR q<0.20. Gene set enrichment analysis (GSEA) was performed using miRTarBase’s miRWalk pathways. Age, race-ethnicity, BMI, fire department, and sex were controlled for in all models. At FDR<0.05, the linear isomer of perfluorooctane sulfonic acid (PFOS) was inversely associated with hsa-miR-128-15p expression (Beta = -0.146, 95% CI -0.216, -0.076). At a relaxed FDR of 0.20, we observed inverse associations for the sum of branched isomers of PFOS with 5 miRNAs (hsa-let-7d-5p, hsa-let-7a-5p, hsa-miR-423-5p, hsa-let-7b-5p, has-mir-629-5p). Several pathways were enriched for multiple PFAS, including those correlated with certain cancers, blood diseases, thyroid disorders, autoimmune disorders, and neurological outcomes. Some PFAS in firefighters were found to be associated with alteration of miRNA consistent with increased risk for a range of chronic diseases.

4. Metabolites

   Evaluating Differential Metabolic Profile by Prostate Cancer Risk among Prostate Cancer Patients

   Tuo Liu, Jahnvi Roorkeewal, Melissa Furlong, and 6 more authors

   Metabolites, 2025

   Abs DOI

   Background: Currently there are no clinically validated biomarkers recommended for prostate cancer (PCa) risk stratification other than prostate specific antigen (PSA). Objectives: This study aimed to identify urine metabolites that are associated with presence of high-grade PCa at the time of radical prostatectomy. Methods: Urine samples were collected from patients who underwent radical prostatectomy. High-resolution metabolomics were implemented using mass liquid-chromatography mass spectrometry (LC-MS). To enhance metabolic feature identification, sample extracts were analyzed in two modes, a C18 chromatography [reverse-phase (RP)] and a hydrophilic interaction chromatography (HILIC). Results: This analysis included a total of 22 patients with PCa (10 high-grade and 12 low-grade) and identified 52 differential metabolites, 40 in RP and 12 in HILIC, at p-value 0.05 level. Among these, methyl alpha-aspartyl phenylalaninate was most significantly differentiated, while 3-methylbutanoicacid had the largest difference (slope -3.488). In pathway analysis, the histidine metabolic pathway was significantly enriched with an enrichment factor of 3.5. Our research also identified alterations in vitamins B12, B7 (biotin), B6, and B3 (niacin) pathways. Conclusion: Urine metabolites have the potential to differentiate high-grade from low-grade PCa. Our study also highlights the metabolic reprogramming that occurs as PCa becomes more aggressive.

2023

1. SciRep

   Evaluating changes in firefighter urinary metabolomes after structural fires: an untargeted, high resolution approach

   Melissa A Furlong, Tuo Liu, Justin M Snider, and 12 more authors

   Scientific Reports, 2023

   Abs DOI

   Firefighters have elevated rates of urinary tract cancers and other adverse health outcomes, which may be attributable to environmental occupational exposures. Untargeted metabolomics was applied to characterize this suite of environmental exposures and biological changes in response to occupational firefighting. 200 urine samples from 100 firefighters collected at baseline and two to four hours post-fire were analyzed using untargeted liquid-chromatography and high-resolution mass spectrometry. Changes in metabolite abundance after a fire were estimated with fixed effects linear regression, with false discovery rate (FDR) adjustment. Partial least squares discriminant analysis (PLS-DA) was also used, and variable important projection (VIP) scores were extracted. Systemic changes were evaluated using pathway enrichment for highly discriminating metabolites. Metabolome-wide-association-study (MWAS) identified 268 metabolites associated with firefighting activity at FDR q < 0.05. Of these, 20 were annotated with high confidence, including the amino acids taurine, proline, and betaine; the indoles kynurenic acid and indole-3-acetic acid; the known uremic toxins trimethylamine n-oxide and hippuric acid; and the hormone 7a-hydroxytestosterone. Partial least squares discriminant analysis (PLS-DA) additionally implicated choline, cortisol, and other hormones. Significant pathways included metabolism of urea cycle/amino group, alanine and aspartate, aspartate and asparagine, vitamin b3 (nicotinate and nicotinamide), and arginine and proline. Firefighters show a broad metabolic response to fires, including altered excretion of indole compounds and uremic toxins. Implicated pathways and features, particularly uremic toxins, may be important regulators of firefighter’s increased risk for urinary tract cancers.