Screening Metabolic Biomarkers in KRAS Mutated Mouse Acinar and Human Pancreatic Cancer Cells via Single-Cell Mass Spectrometry.

Pancreatic cancer is a highly aggressive and rapidly progressing disease, often diagnosed in advanced stages due to the absence of early noticeable symptoms. The KRAS mutation is a hallmark of pancreatic cancer, yet the underlying mechanisms driving pancreatic carcinogenesis remain elusive. Cancer cells display significant metabolic heterogeneity, which is relevant to the pathogenesis of cancer. Population measurements may obscure information about the metabolic heterogeneity among cancer cells. Therefore, it is crucial to analyze metabolites at the single-cell level to gain a more comprehensive understanding of metabolic heterogeneity. In this study, we employed a 3D-printed ionization source for metabolite analysis in both mice and human pancreatic cancer cells at the single-cell level. Using advanced machine learning algorithms and mass spectral feature selection, we successfully identified 23 distinct metabolites that are statistically significantly different in KRAS mutant human pancreatic cancer cells and mouse acinar cells bearing the oncogenic KRAS mutation. These metabolites encompass a variety of chemical classes, including organic nitrogen compounds, organic acids and derivatives, organoheterocyclic compounds, benzenoids, and lipids. These findings shed light on the metabolic remodeling associated with KRAS-driven pancreatic cancer initiation and indicate that the identified metabolites hold promise as potential diagnostic markers for early detection in pancreatic cancer patients.

Mass Spectrometry Reveals High Levels of Hydrogen Peroxide in Pancreatic Cancer Cells.

Reactive oxygen species (ROS) are critical for many cellular functions, and dysregulation of ROS involves the development of multiple types of tumors, including pancreatic cancer. However, ROS have been grouped into a single biochemical entity for a long time, and the specific roles of certain types of ROS in tumor cells (e.g., pancreatic ductal adenocarcinoma (PDAC)) have not been systematically investigated. In this work, a highly sensitive and accurate mass spectrometry-based method was applied to study PDAC cells of humans and of genetically modified animals. The results show that the oncogenic KRAS mutation promotes the accumulation of hydrogen peroxide (H2 O2 ) rather than superoxide or hydroxyl radicals in pancreatic cancer cells. We further identified that the enriched H2 O2 modifies cellular metabolites and promotes the survival of pancreatic cancer cells. These findings highlight the specific roles of H2 O2 in pancreatic cancer development, which may provide new directions for pancreatic cancer therapy.

Development of a 3D-Printed Ionization Source for Single-Cell Analysis.

Understanding the physiologies and pathologies of diseases requires a thorough understanding of metabolic heterogeneity in cells. This technical note presents a 3D printing technology for manufacturing an ionization source that is specially adapted for mass spectrometry-based single-cell analysis. This all-in-one 3D-printed electrospray ionization source integrates the sample introduction, metabolite extraction, and ionization into one device, simplifying the process of single-cell analysis and improving the reproducibility of the measurement. We successfully used it for high-throughput analysis of three types of cancer cells (around 17 cells/min) and used the t-distributed stochastic neighbor embedding algorithm to distinguish different cell types based on detected metabolites. By simply adjusting the printing parameters of the 3D-printed ionization source, it can be applied to cells with different sizes. The proposed 3D-printed ionization source promises to open new possibilities for single-cell analysis.

Structural Studies of a Stapled Peptide with Native Ion Mobility-Mass Spectrometry and Transition Metal Ion Förster Resonance Energy Transfer in the Gas Phase.

Native mass spectrometry has emerged as an important tool for gas-phase structural biology. However, the conformations that a biomolecular ion adopts in the gas phase can differ from those found in solution. Herein, we report a synergistic, native ion mobility-mass spectrometry (IM-MS) and transition metal ion Förster resonance energy transfer (tmFRET)-based approach to probe the gas-phase ion structures of a nonstapled peptide (nsp; Ac-CAARAAHAAAHARARA-NH2) and a stapled peptide (sp; Ac-CXARAXHAAAHARARA-NH2). The stapled peptide contains a single hydrocarbon chain connecting the peptide backbone in the i and i + 4 positions via a Grubbs ring-closure metathesis. Fluorescence lifetime measurements indicated that the Cu-bound complexes of carboxyrhodamine 6g (crh6g)-labeled stapled peptide (sp-crh6g) had a shorter donor-acceptor distance (rDA) than the labeled nonstapled peptide (nsp-crh6g). Experimental collision cross-section (CCS) values were then determined by native IM-MS, which could separate the conformations of Cu-bound complexes of nsp-crh6g and sp-crh6g. Finally, the experimental CCS (i.e., shape) and rDA (i.e., distance) values were used as constraints for computational studies, which unambiguously revealed how a staple reduces the elongation of the peptide ions in the gas phase. This study demonstrates the superiority of combining native IM-MS, tmFRET, and computational studies to investigate the structure of biomolecular ions.

Hybrid Ionization Source Combining Nanoelectrospray and Dielectric Barrier Discharge Ionization for the Simultaneous Detection of Polar and Nonpolar Compounds in Single Cells.

Single-cell metabolomics is expected to deliver fast and dynamic information on cell function; therefore, it requires rapid analysis of a wide variety of very small quantities of metabolites in living cells. In this work, a hybrid ionization source that combines nanoelectrospray ionization (nanoESI) and dielectric barrier discharge ionization (DBDI) is proposed for single-cell analysis. A capillary with a 1 µm i.d. tip was inserted into cells for sampling and then directly used as the nanoESI source for ionization of polar metabolites. In addition, a DBDI source was employed as a post-ionization source to improve the ionization of apolar metabolites in cells that are not easily ionized by ESI. By increasing the voltage of the DBDI source from 0 to 3.2 kV, the classes of detected metabolites can be shifted from mostly polar to both polar and apolar to mainly apolar. Plant cells (onion) and human cells (PANC-1) were investigated in this study. After optimization, 50 compounds in onion cells and 40 compounds in PANC-1 cells were observed in ESI mode (3.5 kV) and an additional 49 compounds in onion cells and 73 compounds in PANC-1 cells were detected in ESI (3.5 kV)-DBDI (2.6 kV) hybrid mode. This hybrid ionization source improves the coverage, ionization efficiency, and limit of detection of metabolites with different polarities and could potentially contribute to the fast-growing field of single-cell metabolomics.

High-Throughput Single-Cell Mass Spectrometry Reveals Abnormal Lipid Metabolism in Pancreatic Ductal Adenocarcinoma.

Even populations of clonal cells are heterogeneous, which requires high-throughput analysis methods with single-cell sensitivity. Here, we propose a rapid, label-free single-cell analytical method based on active capillary dielectric barrier discharge ionization mass spectrometry, which can analyze multiple metabolites in single cells at a rate of 38 cells/minute. Multiple cell types (HEK-293T, PANC-1, CFPAC-1, H6c7, HeLa and iBAs) were discriminated successfully. We found evidence for abnormal lipid metabolism in pancreatic cancer cells. We also analyzed gene expression in a cancer genome atlas dataset and found that the mRNA level of a critical enzyme of lipid synthesis (ATP citrate lyase, ACLY) was upregulated in human pancreatic ductal adenocarcinoma (PDAC). Moreover, both an ACLY chemical inhibitor and a siRNA approach targeting ACLY could suppress the viability of PDAC cells. A significant reduction in lipid content in treated cells indicates that ACLY could be a potential target for treating pancreatic cancer.

Rapid analysis of fragrance allergens by dielectric barrier discharge ionization mass spectrometry.

RATIONALE: Fragrances are organic compounds with pleasant odors that are widely used in every aspect of our daily life; some fragrance ingredients can cause allergic reactions. Hence, the qualitative and quantitative analysis of fragrance allergens can prevent consumers coming into contact with these compounds. In this study, we evaluated the ability of a dielectric barrier discharge ionization (DBDI) source for analyzing allergens that occur in fragrances. METHODS: A home-built liquid-infusion device was used to evaporate the liquid samples. An active capillary plasma ionization source, which is based on a dielectric barrier discharge, was used to ionize the analytes. Mass spectra were acquired in positive ion mode with an LTQ Orbitrap mass spectrometer. RESULTS: Seven typical fragrance allergens were analyzed in this study. The limits of detections (LODs) were as low as 0.0001 ppm and a linear dynamic range of 2-3 orders of magnitude was achieved. Allergens in five different perfume products were successfully analyzed and quantified by this method, with analysis times of less than 1 min per sample. CONCLUSIONS: This work introduces a DBDI-MS-based analytical method for detecting and quantifying fragrance allergens. Since DBDI has the advantages of high sensitivity, simple operation and fast analysis time, it is very suitable for the rapid analysis of trace allergens in fragrances, and could easily be used for quality control of consumer products in the cosmetics market.

Disposable Paper-Based Analytical Device for Visual Speciation Analysis of Ag(I) and Silver Nanoparticles (AgNPs).

A disposable, instrument-free, height readout paper-based analytical device (HR-PAD) based on a paper strip inkjet-printed with CdTe quantum dots (QDs) was developed for the sensitive speciation analysis of Ag+ and silver nanoparticles (AgNPs). When the paper strip is immersed into a sample solution, capillary action draws it through the surface and any Ag+ in the solution quenches the fluorescence of CdTe QDs via a cation exchange reaction between Ag+ and the CdTe QDs, with the height of the quenched band being proportional to the concentration of Ag+. In contrast, fluorescence quenching cannot be observed when only AgNPs are present in solution. Thus, the concentration of AgNPs can be obtained by subtracting the Ag+ content from the total silver determined by the HR-PAD after digestion with HNO3. Under optimized conditions, the methodology provides high selectivity, sensitivity, and accuracy for the detection of Ag+ or AgNPs in various samples, even at concentrations as low as 0.05 mg L-1. Precisions of 4.5% and 2.2% RSDs were achieved at concentrations of 1 mg L-1 and 7 mg L-1 of Ag+, respectively. Compared to conventional methods, this approach is inexpensive and user-friendly and eliminates the need for expensive and sophisticated detection instruments. The practicality of the method was demonstrated via the speciation analysis of AgNPs and Ag+ in river water and 12 commercial products with satisfactory results.