Libin Xu
· Associate Professor, Medicinal ChemistryUniversity of Washington · Medicinal Chemistry Graduate Program
Active 1998–2024
About
Dr. Libin Xu is an Associate Professor in the Department of Medicinal Chemistry at the School of Pharmacy. His research focuses on mechanisms and products of lipid oxidation, cholesterol biosynthesis disorders such as Smith-Lemli-Opitz syndrome, and the effects of drugs on lipid metabolism. His lab employs mass spectrometry-based lipidomics and analytical techniques to study lipid metabolism in neurodevelopment, human diseases, and bacterial pathogens. Dr. Xu's work aims to develop interventions to ameliorate or reverse adverse effects caused by disrupted lipid homeostasis and oxidized lipids, as well as strategies to combat antibiotic resistance through understanding lipid metabolism in bacteria. He has a background in organic chemistry, with postdoctoral training at Vanderbilt University expanding his research into lipid peroxidation chemistry and biology. Dr. Xu has received several awards, including the NIH Pathway to Independence Award from NICHD in 2012, the Young Investigator Award from the Society for Free Radical Biology and Medicine in 2011, and multiple faculty innovation funds from the School of Pharmacy. His research contributions include elucidating lipid oxidation mechanisms, developing novel lipid analysis methodologies, and investigating the role of lipids in neurodevelopment, infectious diseases, and environmental health.
Research topics
- Chemistry
- Computer Science
- Biology
- Chromatography
- Machine Learning
- Biochemistry
- Pharmacology
- Genetics
- Data Mining
- Microbiology
- Medicine
- Physiology
- Environmental health
- Biotechnology
- Immunology
- Business
- Internal medicine
- Environmental chemistry
- Pathology
- Organic chemistry
- Biological system
- Computational biology
Selected publications
Environmental Science & Technology · 2024 · 21 citations
Senior authorCorresponding- Chemistry
- Chromatography
- Environmental chemistry
), and MS/MS spectra for 19 parent QACs and 81 QAC metabolites. Using this database, we confidently identified 13 parent QACs and 35 metabolites in de-identified human fecal samples. This is the first study to integrate in vitro metabolite biosynthesis with LC-IM-MS/MS for the simultaneous monitoring of parent QACs and their metabolites in humans.
Quaternary Ammonium Compounds: A Chemical Class of Emerging Concern
Environmental Science & Technology · 2023 · 322 citations
- Business
- Environmental health
- Biotechnology
Quaternary ammonium compounds (QACs), a large class of chemicals that includes high production volume substances, have been used for decades as antimicrobials, preservatives, and antistatic agents and for other functions in cleaning, disinfecting, personal care products, and durable consumer goods. QAC use has accelerated in response to the COVID-19 pandemic and the banning of 19 antimicrobials from several personal care products by the US Food and Drug Administration in 2016. Studies conducted before and after the onset of the pandemic indicate increased human exposure to QACs. Environmental releases of these chemicals have also increased. Emerging information on adverse environmental and human health impacts of QACs is motivating a reconsideration of the risks and benefits across the life cycle of their production, use, and disposal. This work presents a critical review of the literature and scientific perspective developed by a multidisciplinary, multi-institutional team of authors from academia, governmental, and nonprofit organizations. The review evaluates currently available information on the ecological and human health profile of QACs and identifies multiple areas of potential concern. Adverse ecological effects include acute and chronic toxicity to susceptible aquatic organisms, with concentrations of some QACs approaching levels of concern. Suspected or known adverse health outcomes include dermal and respiratory effects, developmental and reproductive toxicity, disruption of metabolic function such as lipid homeostasis, and impairment of mitochondrial function. QACs' role in antimicrobial resistance has also been demonstrated. In the US regulatory system, how a QAC is managed depends on how it is used, for example in pesticides or personal care products. This can result in the same QACs receiving different degrees of scrutiny depending on the use and the agency regulating it. Further, the US Environmental Protection Agency's current method of grouping QACs based on structure, first proposed in 1988, is insufficient to address the wide range of QAC chemistries, potential toxicities, and exposure scenarios. Consequently, exposures to common mixtures of QACs and from multiple sources remain largely unassessed. Some restrictions on the use of QACs have been implemented in the US and elsewhere, primarily focused on personal care products. Assessing the risks posed by QACs is hampered by their vast structural diversity and a lack of quantitative data on exposure and toxicity for the majority of these compounds. This review identifies important data gaps and provides research and policy recommendations for preserving the utility of QAC chemistries while also seeking to limit adverse environmental and human health effects.
Toxicology Reports · 2021 · 135 citations
- Physiology
- Immunology
- Medicine
Humans are frequently exposed to Quaternary Ammonium Compounds (QACs). QACs are ubiquitously used in medical settings, restaurants, and homes as cleaners and disinfectants. Despite their prevalence, nothing is known about the health effects associated with chronic low-level exposure. Chronic QAC toxicity, only recently identified in mice, resulted in developmental, reproductive, and immune dysfunction. Cell based studies indicate increased inflammation, decreased mitochondrial function, and disruption of cholesterol synthesis. If these findings translate to human toxicity, multiple physiological processes could be affected. This study tested whether QAC concentrations could be detected in the blood of 43 human volunteers, and whether QAC concentrations influenced markers of inflammation, mitochondrial function, and cholesterol synthesis. QAC concentrations were detected in 80 % of study participants. Blood QACs were associated with increase in inflammatory cytokines, decreased mitochondrial function, and disruption of cholesterol homeostasis in a dose dependent manner. This is the first study to measure QACs in human blood, and also the first to demonstrate statistically significant relationships between blood QAC and meaningful health related biomarkers. Additionally, the results are timely in light of the increased QAC disinfectant exposure occurring due to the SARS-CoV-2 pandemic. MAIN FINDINGS: This study found that 80 % of study participants contained QACs in their blood; and that markers of inflammation, mitochondrial function, and sterol homeostasis varied with blood QAC concentration.
Determination of drugs and drug metabolites by ion mobility-mass spectrometry: A review
Analytica Chimica Acta · 2021 · 60 citations
Senior authorCorresponding- Chemistry
- Chromatography
- Pharmacology
Analytical Chemistry · 2020 · 148 citations
Senior authorCorresponding- Data Mining
- Computer Science
- Chemistry
Identification of unknowns is a bottleneck for large-scale untargeted analyses like metabolomics or drug metabolite identification. Ion mobility-mass spectrometry (IM-MS) provides rapid two-dimensional separation of ions based on their mobility through a neutral buffer gas. The mobility of an ion is related to its collision cross section (CCS) with the buffer gas, a physical property that is determined by the size and shape of the ion. This structural dependency makes CCS a promising characteristic for compound identification, but this utility is limited by the availability of high-quality reference CCS values. CCS prediction using machine learning (ML) has recently shown promise in the field, but accurate and broadly applicable models are still lacking. Here we present a novel ML approach that employs a comprehensive collection of CCS values covering a wide range of chemical space. Using this diverse database, we identified the structural characteristics, represented by molecular quantum numbers (MQNs), that contribute to variance in CCS and assessed the performance of a variety of ML algorithms in predicting CCS. We found that by breaking down the chemical structural diversity using unsupervised clustering based on the MQNs, specific and accurate prediction models for each cluster can be trained, which showed superior performance than a single model trained with all data. Using this approach, we have robustly trained and characterized a CCS prediction model with high accuracy on diverse chemical structures. An all-in-one web interface (https://CCSbase.net) was built for querying the CCS database and accessing the predictive model to support unknown compound identifications.
Clinical Microbiology and Infection · 2020 · 42 citations
Senior authorCorresponding- Microbiology
- Biology
- Genetics
Analytical Chemistry · 2020 · 59 citations
Senior authorCorresponding- Computer Science
- Chemistry
- Chromatography
strains that are resistant to various antimicrobials.
Journal of Antimicrobial Chemotherapy · 2020 · 13 citations
- Biology
- Microbiology
- Genetics
OBJECTIVES: Tedizolid is an oxazolidinone antimicrobial with activity against Gram-positive bacteria, including MRSA. Tedizolid resistance is uncommon and tedizolid's capacity to select for cross-resistance to other antimicrobials is incompletely understood. The objective of this study was to further explore the phenotypic and genetic basis of tedizolid resistance in MRSA. METHODS: We selected for tedizolid resistance in an MRSA laboratory strain, N315, by serial passage until an isolate with an MIC ≥1 log2 dilution above the breakpoint for resistance (≥2 mg/L) was recovered. This isolate was subjected to WGS and susceptibility to a panel of related and unrelated antimicrobials was tested in order to determine cross-resistance. Homology modelling was performed to evaluate the potential impact of the mutation on target protein function. RESULTS: After 10 days of serial passage we recovered a phenotypically stable mutant with a tedizolid MIC of 4 mg/L. WGS revealed only one single nucleotide variant (A1345G) in rpoB, corresponding to amino acid substitution D449N. MICs of linezolid, chloramphenicol, retapamulin and quinupristin/dalfopristin increased by ≥2 log2 dilutions, suggesting the emergence of the so-called 'PhLOPSa' resistance phenotype. Susceptibility to other drugs, including rifampicin, was largely unchanged. Homology models revealed that the mutated residue of RNA polymerase would be unlikely to directly affect oxazolidinone action. CONCLUSIONS: To the best of our knowledge, this is the first time that an rpoB mutation has been implicated in resistance to PhLOPSa antimicrobials. The mechanism of resistance remains unclear, but is likely indirect, involving σ-factor binding or other alterations in transcriptional regulation.
Recent grants
7-Dehydrocholesterol-derived oxysterols in SLOS: role and therapy
NIH · $745k · 2014–2017
Oxysterols in SLOS Neurodevelopment: Pathological Role and Therapy
NIH · $1.9M · 2017–2023
NIH · $3.5M · 2018–2028
7-Dehydrocholesterol-derived oxysterols in SLOS: role and therapy
NIH · $215k · 2012–2015
Mechanisms of Peroxyl Radical Addition Reactions
NSF · $486k · 2017–2022
Frequent coauthors
- 48 shared
Ned A. Porter
Vanderbilt University
- 32 shared
Kelly M. Hines
University of Georgia
- 26 shared
Rutan Zhang
University of Washington
- 23 shared
Ryan P. Seguin
University of Washington
- 23 shared
Željka Korade
University of Nebraska Medical Center
- 21 shared
César A. Arias
Universidad El Bosque
- 18 shared
Dylan H. Ross
University of Washington
- 18 shared
Steven J. Fliesler
University at Buffalo, State University of New York
Education
Ph.D., Organic Chemistry
Vanderbilt University
B.S., Chemistry
University of Illinois at Chicago
B.S.
Nankai University
Awards & honors
- NIH Pathway to Independence Award from NICHD (2012)
- Young Investigator Award from the Society for Free Radical B…
- Inaugural recipient of the School of Pharmacy Faculty Innova…
- School of Pharmacy Faculty Innovation Fund (2020)
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