Magnetic bead-based peptide extraction methodology for tissue imaging

Targeted Energy Metabolomics Combined with Spatial Metabolomics Study on the Efficacy of Guhong Injection Against Cerebral Ischemia Reperfusion

Optimizing the metabolic phenotype to improve cerebral function is critical for treatment of cerebral ischemia-reperfusion (I/R) injury. Guhong injection (GHI), which comprised safflower extract and aceglutamide, is widely prescribed in Chinese medicine for the treatment of cerebrovascular diseases. In this study, a combination of LC-QQQ-MS and MALDI-MSI were utilized to explore tissue-specific metabolic alterations in the brain of I/R, as well as to evaluate the therapeutic effect of GHI. Pharmacological evaluation demonstrated that GHI can significantly improve infarction rate, neurological deficit, cerebral blood flow, and neuronal damage in I/R rats. Based on LC-QQQ-MS, 23 energy metabolites were found to be significantly altered in the I/R group compared to the sham group (P < 0.05). After GHI treatment, 12 metabolites, including G6P, TPP, NAD, citrate, succinate, malate, ATP, GTP, GDP, ADP, NADP, and FMN showed a significant tendency of returning to baseline values (P < 0.05). Based on MALDI-MSI, 4 metabolites in glycolysis and TCA, 4 metabolites in nucleic acid metabolism, 4 amino acid metabolites, and 6 metabolites were discovered and compared between the different groups in the four special regions of cortex, hippocampus, hypothalamus, and striatum. Parts of these were found to have significant changes after I/R in the special brain region, and were regulated by GHI. The study provides comprehensive and detailed information for specific metabolic reprogramming of brain tissue in rats with I/R, and the therapeutic effect of GHI. Schema describing the discovery strategies of integrated LC-MS and MALDI-MSI to identify cerebral ischemia reperfusion metabolic reprogramming and GHI therapeutic effects.

Food allergen analysis: A review of current gaps and the potential to fill them by matrix-assisted laser desorption/ionization

Food allergy remains a public health, business, and regulatory challenge. Risk analysis (RA) and risk management (RM) of food allergens are of great importance and analysis for food allergens is necessary for both. The current workhorse techniques for allergen analysis (enzyme linked immunosorbent assay [ELISA] and real-time polymerase chain reaction) exhibit recognized challenges including variable and antibody specific responses and detection of species DNA rather than allergen protein, respectively. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) enables protein identification, with potential for multiplex analysis and traceability to the System of International units (SI), aiding global measurement standardization. In this review, recent literature has been systematically reviewed to assess progress in LC-MS/MS and define the potential and benefits of matrix-assisted laser desorption/ionization-time-of-flight MS (MALDI-ToF-MS) technology for allergen analysis. MALDI-ToF-MS of initially intact protein is already applied to verify in silico-derived peptide sequences for LC-MS/MS analysis. We describe the origins of MALDI and its future perspectives, including affinity bead-assisted assays coupled to MALDI. Based on the proliferation of reliable and reproducible MALDI-based clinical applications, the technique should emulate the detection capability (sensitivity) of established allergen detection techniques, whilst reducing technical support and having equivalent multiplexing potential to competing techniques, for example, LC-MS/MS and ELISA. Although unlikely to offer inherent SI traceability, MALDI-based allergen analysis will complement existing MS approaches for allergens. Affinity bead-MALDI appears capable of higher throughput at lower cost per sample than almost any existing technique, enabling repeated sub-sampling as a way to reduce representative sampling issues.

COVID-19 diagnosis by SARS-CoV-2 Spike protein detection in saliva using an ultrasensitive magneto-assay based on disposable electrochemical sensor

The outbreak of the COVID-19 pandemic, caused by Severe Acute Respiratory Syndrome of Coronavirus 2 (SARS-CoV-2), has fueled the search for diagnostic tests aiming at the control and reduction of the viral transmission. The main technique used for diagnosing the Coronavirus disease (COVID-19) is the reverse transcription-polymerase chain reaction (RT-PCR) technique. However, considering the high number of cases and the underlying limitations of the RT-PCR technique, especially with regard to accessibility and cost of the test, one does not need to overemphasize the need to develop new and less expensive testing techniques that can aid the early diagnosis of the disease. With that in mind, we developed an ultrasensitive magneto-assay using magnetic beads and gold nanoparticles conjugated to human angiotensin-converting enzyme 2 (ACE2) peptide (Gln²⁴-Gln⁴²) for the capturing and detection of SARS-CoV-2 Spike protein in human saliva. The technique applied involved the use of a disposable electrochemical device containing eight screen-printed carbon electrodes which allow the simultaneous analysis of eight samples. The magneto-assay exhibited an ultralow limit of detection of 0.35 ag mL^-1 for the detection of SARS-CoV-2 Spike protein in saliva. The magneto-assay was tested in saliva samples from healthy and SARS-CoV-2-infected individuals. In terms of efficiency, the proposed technique - which presented a sensitivity of 100.0% and specificity of 93.7% for SARS-CoV-2 Spike protein-exhibited great similarity with the RT-PCR technique. The results obtained point to the application potential of this simple, low-cost magneto-assay for saliva-based point-of-care COVID-19 diagnosis.

COVID-19 diagnosis by SARS-CoV-2 Spike protein detection in saliva using an ultrasensitive magneto-assay based on disposable electrochemical sensor

The outbreak of the COVID-19 pandemic, caused by Severe Acute Respiratory Syndrome of Coronavirus 2 (SARS-CoV-2), has fueled the search for diagnostic tests aiming at the control and reduction of the viral transmission. The main technique used for diagnosing the Coronavirus disease (COVID-19) is the reverse transcription-polymerase chain reaction (RT-PCR) technique. However, considering the high number of cases and the underlying limitations of the RT-PCR technique, especially with regard to accessibility and cost of the test, one does not need to overemphasize the need to develop new and less expensive testing techniques that can aid the early diagnosis of the disease. With that in mind, we developed an ultrasensitive magneto-assay using magnetic beads and gold nanoparticles conjugated to human angiotensin-converting enzyme 2 (ACE2) peptide (Gln²⁴-Gln⁴²) for the capturing and detection of SARS-CoV-2 Spike protein in human saliva. The technique applied involved the use of a disposable electrochemical device containing eight screen-printed carbon electrodes which allow the simultaneous analysis of eight samples. The magneto-assay exhibited an ultralow limit of detection of 0.35 ag mL^-1 for the detection of SARS-CoV-2 Spike protein in saliva. The magneto-assay was tested in saliva samples from healthy and SARS-CoV-2-infected individuals. In terms of efficiency, the proposed technique - which presented a sensitivity of 100.0% and specificity of 93.7% for SARS-CoV-2 Spike protein-exhibited great similarity with the RT-PCR technique. The results obtained point to the application potential of this simple, low-cost magneto-assay for saliva-based point-of-care COVID-19 diagnosis.

Electroblotting through Enzymatic Membranes to Enhance Molecular Tissue Imaging

MALDI-TOF mass spectrometry imaging (MSI) is a powerful tool for studying biomolecule localization in tissue. Protein distributions in tissue provide important histological information; however, large proteins exhibit a high limit of detection in MALDI-MS when compared to their corresponding smaller proteolytic peptides. As a result, several techniques have emerged to digest proteins into more detectable peptides for imaging. Digestion is typically accomplished through trypsin deposition on the tissue, but this technique increases the complexity of the tissue microenvironment, which can limit the number of detectable species. This proof-of-principle study explores tryptic tissue digestion during electroblotting through a trypsin-containing membrane. This approach actively extracts and enzymatically digests proteins from mouse brain tissue sections while simultaneously reducing the complexity of the tissue microenvironment (compared to trypsin deposition on the surface) to obtain an increased number of detectable peptide fragments. The method does not greatly compromise spatial location or require expensive devices to uniformly deposit trypsin on tissue. Using electrodigestion through membranes, we detected and tentatively identified several tryptic peptides that were not observed after on-tissue digestion. Moreover, the use of pepsin rather than trypsin in digestion membranes allows extraction and digestion at low pH to detect peptides from a complementary subset of tissue proteins. Future studies will aim to further improve the method, including changing the substrate membrane to increase spatial resolution and the number of detected peptides.

In situ metabolite and lipid analysis of GluN2D-/- and wild-type mice after ischemic stroke using MALDI MSI

The N-methyl-D-aspartate (NMDA) receptor is a crucial mediator of pathological glutamate-driven excitotoxicity and subsequent neuronal death in acute ischemic stroke. Although the roles of the NMDAR's composite GluN2A-C subunits have been investigated in this phenomenon, the relative importance of the GluN2D subunit has yet to be evaluated. Herein, GluN2D^-/- mice were studied in a model of ischemic stroke using MALDI FT-ICR mass spectrometry imaging to investigate the role of the GluN2D subunit of the NMDA receptor in brain ischemia. GluN2D^-/- mice underwent middle cerebral artery occlusion (MCAO) and brain tissue was subsequently harvested, frozen, and cryosectioned. Tissue sections were analyzed via MALDI FT-ICR mass spectrometry imaging. MALDI analyses revealed increases in several calcium-related species, namely vitamin D metabolites, LysoPC, and several PS species, in wild-type mouse brain tissue when compared to wild type. In addition, GluN2D^-/- mice also displayed an increase in PC, as well as a decrease in DG, suggesting reduced free fatty acid release from brain ischemia. These trends indicate that GluN2D^-/- mice show enhanced rates of neurorecovery and neuroprotection from ischemic strokes compared to wild-type mice. The cause of neuroprotection may be the result of an increase in PGP in knockout mice, contributing to greater cardiolipin synthesis and decreased sensitivity to apoptotic signals. Graphical abstract.

Isolation and characterization of glycosylated neuropeptides

Glycosylation is one of the most ubiquitous and complex post-translational modifications (PTMs). It plays pivotal roles in various biological processes. Studies at the glycopeptide level are typically considered as a downstream work resulting from enzymatic digested glycoproteins. Less attention has been focused on glycosylated endogenous signaling peptides due to their low abundance, structural heterogeneity and the lack of enabling analytical tools. Here, protocols are presented to isolate and characterize glycosylated neuropeptides utilizing nanoflow liquid chromatography coupled with mass spectrometry (LC-MS). We first demonstrate how to extract neuropeptides from raw tissues and perform further separation/cleanup before MS analysis. Then we describe hybrid MS methods for glycosylated neuropeptide profiling and site-specific analysis. We also include recommendations for data analysis to identify glycosylated neuropeptides in crustaceans where a complete neuropeptide database is still lacking. Other strategies and future directions are discussed to provide readers with alternative approaches and further unravel biological complexity rendered by glycosylation.

Recent advances in single-cell analysis by mass spectrometry

Cells are the most basic structural units that play vital roles in the functioning of living organisms. Analysis of the chemical composition and content of a single cell plays a vital role in ensuring precise investigations of cellular metabolism, and is a crucial aspect of lipidomic and proteomic studies. In addition, structural knowledge provides a better understanding of cell behavior as well as the cellular and subcellular mechanisms. However, single-cell analysis can be very challenging due to the very small size of each cell as well as the large variety and extremely low concentrations of substances found in individual cells. On account of its high sensitivity and selectivity, mass spectrometry holds great promise as an effective technique for single-cell analysis. Numerous mass spectrometric techniques have been developed to elucidate the molecular profiles at the cellular level, including electrospray ionization mass spectrometry (ESI-MS), secondary ion mass spectrometry (SIMS), laser-based mass spectrometry and inductively coupled plasma mass spectrometry (ICP-MS). In this review, the recent advances in single-cell analysis by mass spectrometry are summarized. The strategies of different ionization modes to achieve single-cell analysis are classified and discussed in detail.