PM_2.5-Bound Organophosphate Flame Retardants in Hong Kong: Occurrence, Origins, and Source-Specific Health Risks

Organophosphate flame retardants (OPFRs) are emerging organic pollutants in PM2.5, which have caused significant public health concerns in recent years, given their potential carcinogenic and neurotoxic effects. However, studies on the sources, occurrence, and health risk assessment of PM2.5-bound OPFRs in Hong Kong are lacking. To address this knowledge gap, we characterized 13 OPFRs in one-year PM2.5 samples using gas chromatography–atmospheric pressure chemical ionization tandem mass spectrometry. Our findings showed that OPFRs were present at a median concentration of 4978 pg m–3 (ranging from 1924 to 8481 pg m–3), with chlorinated OPFRs dominating and accounting for 82.7% of the total OPFRs. Using characteristic source markers and positive matrix factorization, we identified one secondary formation and five primary sources of OPFRs. Over 94.0% of PM2.5-bound OPFRs in Hong Kong were primarily emitted, with plastic processing and waste disposal being the leading source (61.0%), followed by marine vessels (14.1%). The contributions of these two sources to OPFRs were more pronounced on days influenced by local pollution emissions (91.9%) than on days affected by regional pollution (44.2%). Our assessment of health risks associated with human exposure to PM2.5-bound OPFRs indicated a low-risk level. However, further source-specific health risk assessment revealed relatively high noncarcinogenic and carcinogenic risks from chlorinated OPFRs emitted from plastic processing and waste disposal, suggesting a need for more stringent emission control of OPFRs from these sources in Hong Kong

Dual Quinone Tagging for MALDI-TOF Mass Spectrometric Quantitation of Cysteine-Containing Peptide

A dual quinone tagging strategy is designed for quantitation of cysteine-containing peptide (CCP) with MALDI-TOF mass spectrometry. The quinone compounds can rapidly and specifically bind to the thiol group of cysteine residues by a Michael addition reaction, which is used to identify both CCP and the number of cysteine residues in CCP through the direct observation of untagged and tagged products. After reduced with DL-dithiothreitol, the intramolecular disulfide bond can also be identified. Using benzoquinone (BQ) and methyl-<i>p</i>-benzoquinone (MBQ) as dual tags and a peptide with an amino acid sequence of SSDQFRPDDCT (C-pep1) as a model target, respectively, the quantitation strategy is performed through the intensity ratio of MBQ-tagged C-pep1 to BQ-tagged C-pep1 as the internal standard. The logarithm value of the intensity ratio is proportional to C-pep1 concentration in a range from 5.0 to 5000 nM. The limit of detection is as low as 2.0 nM. The proposed methodology provides a novel tool for rapid characterization, identification, and quantitation of biomolecules containing thiol reactive sites and has a promising application in the large-scale detection and analysis of cysteine-containing biomolecules

Matrix Interference-Free Method for the Analysis of Small Molecules by Using Negative Ion Laser Desorption/Ionization on Graphene Flakes

This work presents a new approach for the analysis of small molecules with direct negative ion laser desorption/ionization (LDI) on graphene flakes. A series of matrix interference-free mass spectra were obtained for the analysis of a wide range of small molecules including peptides, amino acids, fatty acids, as well as nucleosides and nucleotides. The mixture of analytes and graphene flakes suspension were directly pipetted onto a sample plate for LDI-time-of-flight mass spectrometry (TOFMS) analysis. Deprotonated monomeric species [M−H]− ions were homogeneously obtained on uniform graphene flakes film when negative ion mode was applied. In positive ion mode, the analytes were detected in form of multiple adduct ions such as sodium adduct [M+Na]+, potassium adduct [M+K]+, double sodium adduct [M+2Na−H]+, double potassium adduct [M+2K−H]+, as well as sodium and potassium mixed adduct [M+Na+K−H]+. Better sensitivity and reproducibility were achieved in negative ion mode compared to positive ion mode. It is believed that the new method of matrix interference-free negative ion LDI on graphene flakes may be expanded for LDI-MS analysis of various small molecules

Spatial Lipidomics Reveals Lipid Changes in the Cotyledon and Plumule of Mung Bean Seeds during Germination

Seed germination is a vital process in plant development involving dynamic biochemical transformations such as lipid metabolism. However, the spatial distribution and dynamic changes of lipids in different seed compartments during germination are poorly understood. In this study, we employed liquid chromatography/mass spectrometry (LC/MS)-based lipidomics and MALDI mass spectrometry imaging (MSI) to investigate lipid changes occurring in the cotyledon and plumule of mung bean seeds during germination. Lipidomic data revealed that the germination process reduced the levels of many glycerolipids (e.g., triglyceride) and phosphatidylglycerols (e.g., phosphatidylcholine) while increased the levels of lysophospholipids (e.g., lysophosphatidylcholine) in both the cotyledon and plumule. Sphingolipids (e.g., sphingomyelin) displayed altered levels solely in the plumule. Sterol levels increased in the cotyledon but decreased in the plumule. Further imaging results revealed that MALDI–MSI could serve as a supplement and validate LC–MS data. These findings enhance our understanding of the metabolic processes underlying seedling development, with potential implications for crop improvement and seed quality control

A Fully Integrated Spintip-Based Approach for Sensitive and Quantitative Profiling of Region-Resolved in Vivo Brain Glycoproteome

Region- and cell type-resolved global proteome and specific post-translational modifications (PTMs) profiling of tissues has drawn great attention recently for interpreting the heterogeneous multicellular microenvironment of various in vivo systems. Due to access to low microgram of proteins and low abundance of glycoproteins, spatially resolved glycoproteome analysis of in vivo tissue sections remains challenging. Several glycoproteomics sample preparation strategies were established for processing microgram-level of protein samples, but these strategies were not either fully integrated or directly compatible with tissue samples when considering protein extraction in strong lysis buffers. Moreover, these approaches mainly focused on identification of glycosylation sites, but pay less attention to quantification, all of which limit their applications. Here we designed a fully integrated spintip-based glycoproteomic approach (FISGlyco) which achieves all the steps of glycoprotein enrichment, digestion, deglycosylation, and desalting in single spintip device. Sample loss is significantly reduced, and the total processing time is reduced to 4 h, while detection sensitivity and label-free quantification precision is greatly improved. 607 N-glycosylation sites were successfully identified and quantified from only 5 μg of mouse brain proteins. By seamlessly combining with laser capture microdissection (LCM), the first region-resolved N-glycoproteome profiling of four mouse brain regions, including isocortex, hippocampus, thalamus, and hypothalamus, was achieved, with 1875, 1794, 1801, and 1417 N-glycosites identified, respectively. Our approach could be a generic approach for region and even cell type specific glycoproteome analysis of in vivo tissue sections

Liquid Chromatography/Mass Spectrometry Method for Determination of Perfluorooctane Sulfonyl Fluoride upon Derivatization with Benzylamine

Perfluorooctane sulfonyl fluoride (PFOSF) is a main precursor of environmentally ubiquitous perfluorooctanesulfonate (PFOS), and the quantity released to the environment is substantial. Determination of PFOSF, particularly at low concentrations, presents significant challenges for high-performance liquid chromatography and liquid chromatography/mass spectrometry (LC/MS) analyses due to the lack of chromophore and ionizable functional group, respectively. In this study, a new method was developed by derivatizing PFOSF with benzylamine to allow rapid quantitative analysis by using LC/MS. The method demonstrated good linearity in the range from 2 to 80 ng mL–1 with r2 > 0.994 for the derivatization product while the absolute detection limit was 2.5 pg. Liquid–liquid and liquid–solid extraction procedures were established for analysis of water and soil samples, and recoveries were in the range of 51–128%. In addition, the derivatization was selective for PFOSF, whereas PFOS did not nearly react. The developed simple analytical method with good reproducibility might not only be applied for analysis of PFOSF in the environment but also be applicable for supporting investigations on environmental fate of PFOSF, particularly its environmental and biotransformation to PFOS

Three-Dimensional Mass Spectrometry Imaging Reveals Distributions of Lipids and the Drug Metabolite Associated with the Enhanced Growth of Colon Cancer Cell Spheroids Treated with Triclosan

The application of mass spectrometry imaging (MSI) to explore the responses of cancer cell spheroids (CCS) after treatment of exogenous molecules has attracted growing attention. Increasing studies have utilized MSI to image the two-dimensional distributions of exogenous and endogenous molecules in planar CCS sections. However, because CCS are volumetric and heterogenous, maintaining their three-dimensional (3D) information is essential for acquiring a better understanding of the tumor microenvironment and mechanisms of action of exogenous molecules. Here, an established method of 3D MSI was applied to distinguish the distributions of triclosan sulfate and endogenous lipids in three microregions of colon CCS with an enhanced growth induced by the treatment of triclosan, a common antimicrobial agent. The results of 3D MSI showed that triclosan sulfate gradually accumulated from the periphery to the entire structure of CCS and finally localized in the core region. Spatial lipidomics analysis revealed that the upregulated phosphatidylethanolamine (fold change (FD) = 1.26, p = 0.0021), phosphatidylinositol (FD = 1.17, p = 0.0180), and phosphatidylcholine (FD = 1.22, p = 0.0178) species mainly distributed in the outer proliferative region, while the upregulated sphingomyelin (FD = 1.18, p = 0.024) species tended to distribute in the inner necrotic region. Our results suggest that a competitive mechanism between inhibiting and promoting CCS growth might be responsible for the proliferation of CCS treated with triclosan

Three-Dimensional Mass Spectrometry Imaging Reveals Distributions of Lipids and the Drug Metabolite Associated with the Enhanced Growth of Colon Cancer Cell Spheroids Treated with Triclosan

The application of mass spectrometry imaging (MSI) to explore the responses of cancer cell spheroids (CCS) after treatment of exogenous molecules has attracted growing attention. Increasing studies have utilized MSI to image the two-dimensional distributions of exogenous and endogenous molecules in planar CCS sections. However, because CCS are volumetric and heterogenous, maintaining their three-dimensional (3D) information is essential for acquiring a better understanding of the tumor microenvironment and mechanisms of action of exogenous molecules. Here, an established method of 3D MSI was applied to distinguish the distributions of triclosan sulfate and endogenous lipids in three microregions of colon CCS with an enhanced growth induced by the treatment of triclosan, a common antimicrobial agent. The results of 3D MSI showed that triclosan sulfate gradually accumulated from the periphery to the entire structure of CCS and finally localized in the core region. Spatial lipidomics analysis revealed that the upregulated phosphatidylethanolamine (fold change (FD) = 1.26, p = 0.0021), phosphatidylinositol (FD = 1.17, p = 0.0180), and phosphatidylcholine (FD = 1.22, p = 0.0178) species mainly distributed in the outer proliferative region, while the upregulated sphingomyelin (FD = 1.18, p = 0.024) species tended to distribute in the inner necrotic region. Our results suggest that a competitive mechanism between inhibiting and promoting CCS growth might be responsible for the proliferation of CCS treated with triclosan

A Fully Integrated Spintip-Based Approach for Sensitive and Quantitative Profiling of Region-Resolved in Vivo Brain Glycoproteome

Region- and cell type-resolved global proteome and specific post-translational modifications (PTMs) profiling of tissues has drawn great attention recently for interpreting the heterogeneous multicellular microenvironment of various in vivo systems. Due to access to low microgram of proteins and low abundance of glycoproteins, spatially resolved glycoproteome analysis of in vivo tissue sections remains challenging. Several glycoproteomics sample preparation strategies were established for processing microgram-level of protein samples, but these strategies were not either fully integrated or directly compatible with tissue samples when considering protein extraction in strong lysis buffers. Moreover, these approaches mainly focused on identification of glycosylation sites, but pay less attention to quantification, all of which limit their applications. Here we designed a fully integrated spintip-based glycoproteomic approach (FISGlyco) which achieves all the steps of glycoprotein enrichment, digestion, deglycosylation, and desalting in single spintip device. Sample loss is significantly reduced, and the total processing time is reduced to 4 h, while detection sensitivity and label-free quantification precision is greatly improved. 607 N-glycosylation sites were successfully identified and quantified from only 5 μg of mouse brain proteins. By seamlessly combining with laser capture microdissection (LCM), the first region-resolved N-glycoproteome profiling of four mouse brain regions, including isocortex, hippocampus, thalamus, and hypothalamus, was achieved, with 1875, 1794, 1801, and 1417 N-glycosites identified, respectively. Our approach could be a generic approach for region and even cell type specific glycoproteome analysis of in vivo tissue sections

Covalent Organic Framework Nanofilm-Based Laser Desorption/Ionization Mass Spectrometry for 5‑Fluorouracil Analysis and Tissue Imaging

Although matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) has become a ubiquitous and effective tool for macromolecules, direct analysis of small molecules by MALDI-MS using conventional organic matrices poses a challenge. Herein, a large-area, uniform, and stable covalent organic framework (COF) nanofilm prepared directly on indium–tin oxide (ITO) glass was first introduced as a substrate for LDI-MS, which showed enhanced sensitivity, no background interference, and high reproducibility in the analysis of diverse small molecules. Taking into account all these merits, an attractive approach of COF nanofilm-based LDI-MS was developed to quantitatively evaluate the pharmacokinetics of 5-fluorouracil (5-FU) in mouse plasma. A good linear relationship (10–20,000 ng/mL) and a low limit of detection (LOD) for 5-FU (∼100 pg/mL) were achieved. In view of the fact that the COF nanofilm was uniform and without the requirement of additional matrix spraying, it was further extended for LDI-MS imaging (LDI-MSI) to visualize the spatial distribution of 5-FU in mouse liver at different interval times after intravenous and intragastric administrations. The results indicated that the decay of 5-FU in mouse liver obtained with the COF nanofilm-based LDI-MSI was consistent with the tendency of 5-FU pharmacokinetics. This work not only offers an alternative solution for LDI-MS/MSI analysis of small molecules but also extends the application fields of COF nanofilm in MS research