Infrared Laser Desorption and Electrospray Ionisation of Non‐Covalent Protein Complexes: Generation of Intact, Multiply Charged Species

We present a novel method enabling the infrared laser desorption and electrospray ionisation (ESI) of protein complexes in their native state. Using this method, we demonstrate the surprising generation of intact, multiply charged ions of myoglobin, non-covalent haemoglobin complex, and intact immunoglobulin G antibody in their native states. The observation of a surviving population of intact non-covalent complexes is characteristic of the low internal energy build-up experienced during both laser desorption from solution and subsequent ionisation. Compared to conventional nano-ESI, this approach yielded slightly lower average charge states suggesting additional maintenance of tertiary structure during desorption and ionisation, and is more tolerant to salts enabling simpler sample purification procedures. This approach may enable the development of high-throughput native-MS methods capable of analysing the composition and sequence of multiple macromolecular samples per minute

A novel dual ionization modality source for infrared laser ablation post-ionization mass spectrometry imaging to study fungicide metabolism and transport

We present a novel probe design for ambient laser-based mass spectrometry imaging combining electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) in a single probe, compatible with a commercial laser ablation electrospray ionization (LAESI) instrument. Here we describe the probe design considerations and features, as well as an in-house developed data processing routine designed to extract accurate mass spectrometry imaging data from ambient laser ablation post-ionization experiments. We characterize the probe performance in both APCI and ESI mode on a selection of compounds and show improved pixel-to-pixel repeatability for LA-APCI as compared to LAESI. We apply the dual ionization probe in APCI mode in a time series experiment to monitor agrochemicals on tomato plants. We investigate the translocation of fungicide isotianil and one of its metabolites, anthranilonitrile, by mass spectrometry imaging over a period of two weeks after application on a leaf surface. LA-APCI-MSI shows translocation of anthranilonitrile from treated leaves towards non-treated leaves. In summary, we demonstrate that LA-APCI imaging is a valuable addition to the ambient mass spectrometry toolbox, with particular advantages for imaging experiments across a variety of compounds

Novel cerebrospinal fluid biomarkers of glucose transporter type 1 deficiency syndrome: Implications beyond the brain's energy deficit

We used next-generation metabolic screening to identify new biomarkers for improved diagnosis and pathophysiological understanding of glucose transporter type 1 deficiency syndrome (GLUT1DS), comparing metabolic cerebrospinal fluid (CSF) profiles from 12 patients to those of 116 controls. This confirmed decreased CSF glucose and lactate levels in patients with GLUT1DS and increased glutamine at group level. We identified three novel biomarkers significantly decreased in patients, namely gluconic + galactonic acid, xylose-α1-3-glucose, and xylose-α1-3-xylose-α1-3-glucose, of which the latter two have not previously been identified in body fluids. CSF concentrations of gluconic + galactonic acid may be reduced as these metabolites could serve as alternative substrates for the pentose phosphate pathway. Xylose-α1-3-glucose and xylose-α1-3-xylose-α1-3-glucose may originate from glycosylated proteins; their decreased levels are hypothetically the consequence of insufficient glucose, one of two substrates for O-glucosylation. Since many proteins are O-glucosylated, this deficiency may affect cellular processes and thus contribute to GLUT1DS pathophysiology. The novel CSF biomarkers have the potential to improve the biochemical diagnosis of GLUT1DS. Our findings imply that brain glucose deficiency in GLUT1DS may cause disruptions at the cellular level that go beyond energy metabolism, underlining the importance of developing treatment strategies that directly target cerebral glucose uptake

Infrared Laser Desorption and Electrospray Ionisation of Non‐Covalent Protein Complexes: Generation of Intact, Multiply Charged Species

We present a novel method enabling the infrared laser desorption and electrospray ionisation (ESI) of protein complexes in their native state. Using this method, we demonstrate the surprising generation of intact, multiply charged ions of myoglobin, non-covalent haemoglobin complex, and intact immunoglobulin G antibody in their native states. The observation of a surviving population of intact non-covalent complexes is characteristic of the low internal energy build-up experienced during both laser desorption from solution and subsequent ionisation. Compared to conventional nano-ESI, this approach yielded slightly lower average charge states suggesting additional maintenance of tertiary structure during desorption and ionisation, and is more tolerant to salts enabling simpler sample purification procedures. This approach may enable the development of high-throughput native-MS methods capable of analysing the composition and sequence of multiple macromolecular samples per minute

Visualizing molecular distributions for biomaterials applications with mass spectrometry imaging: a review

Mass spectrometry imaging (MSI) is a rapidly emerging field that is continually finding applications in new and exciting areas. The ability of MSI to measure the spatial distribution of molecules at or near the surface of complex substrates makes it an ideal candidate for many applications, including those in the sphere of materials chemistry. Continual development and optimization of both ionization sources and analyzer technologies have resulted in a wide array of MSI tools available, both commercially available and custom-built, with each configuration possessing inherent strengths and limitations. Despite the unique potential of MSI over other chemical imaging methods, their potential and application to (bio) materials science remains in our view a largely underexplored avenue. This review will discuss these techniques enabling high parallel molecular detection, focusing on those with reported uses in (bio) materials chemistry applications and highlighted with select applications. Different technologies are presented in three main sections; secondary ion mass spectrometry (SIMS) imaging, matrix-assisted laser desorption ionization (MALDI) MSI, and emerging MSI technologies with potential for biomaterial analysis. The first two sections (SIMS and MALDI) discuss well-established methods that are continually evolving both in technological advancements and in experimental versatility. In the third section, relatively new and versatile technologies capable of performing measurements under ambient conditions will be introduced, with reported applications in materials chemistry or potential applications discussed. The aim of this review is to provide a concise resource for those interested in utilizing MSI for applications such as biomimetic materials, biological/synthetic material interfaces, polymer formulation and bulk property characterization, as well as the spatial and chemical distributions of nanoparticles, or any other molecular imaging application requiring broad chemical speciation.</p

A novel dual ionization modality source for infrared laser ablation post-ionization mass spectrometry imaging to study fungicide metabolism and transport

We present a novel probe design for ambient laser-based mass spectrometry imaging combining electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) in a single probe, compatible with a commercial laser ablation electrospray ionization (LAESI) instrument. Here we describe the probe design considerations and features, as well as an in-house developed data processing routine designed to extract accurate mass spectrometry imaging data from ambient laser ablation post-ionization experiments. We characterize the probe performance in both APCI and ESI mode on a selection of compounds and show improved pixel-to-pixel repeatability for LA-APCI as compared to LAESI. We apply the dual ionization probe in APCI mode in a time series experiment to monitor agrochemicals on tomato plants. We investigate the translocation of fungicide isotianil and one of its metabolites, anthranilonitrile, by mass spectrometry imaging over a period of two weeks after application on a leaf surface. LA-APCI-MSI shows translocation of anthranilonitrile from treated leaves towards non-treated leaves. In summary, we demonstrate that LA-APCI imaging is a valuable addition to the ambient mass spectrometry toolbox, with particular advantages for imaging experiments across a variety of compounds

Synthesis, radiolabeling and preclinical evaluation of a [11C]GMOM derivative as PET radiotracer for the ion channel of the N-methyl-D-aspartate receptor

Introduction Presently available PET ligands for the NMDAr ion channel generally suffer from fast metabolism. The purpose of this study was to develop a metabolically more stable ligand for the NMDAr ion channel, taking [11C]GMOM ([11C]1) as the lead compound. Methods [11C]1, its fluoralkyl analogue [18F]PK209 ([18F]2) and the newly synthesized fluorovinyloxy analogue [11C]7b were evaluated ex vivo in male Wistar rats for metabolic stability. In addition, [11C]7b was subjected to a biodistribution study and its affinity (Ki) and lipophilicity (logD7.4) values were determined. Results The addition of a vinyl chain in the fluoromethoxy moiety did not negatively alter the affinity of [11C]7b for the NMDAr, while lipophilicity was increased. Biodistribution studies showed higher uptake of [11C]7b in forebrain regions compared with cerebellum. Pre-treatment with MK-801 decreased the overall brain uptake significantly, but not in a region-specific manner. 45 min after injection 78, 90 and 87% of activity in the brain was due to parent compound for [11C]1, [18F]2 and [11C]7b, respectively. In plasma, 26–31% of activity was due to parent compound. Conclusion Complete substitution of the alpha-carbon increased lipophilicity to more favorable values. Substitution of one or more hydrogens of the alpha-carbon atom in the methoxy moiety improved metabolic stability. In plasma, more parent compound was found for [18F]2 and [11C]7b then for [11C]1, although differences were not significant. At 45 min, significantly more parent [18F]2 and [11C]7b was measured in the brain compared with [11C]1

Synthesis, radiolabeling and evaluation of novel amine guanidine derivatives as potential positron emission tomography tracers for the ion channel of the N-methyl-D-aspartate receptor

The N-Methyl-d-Aspartate receptor (NMDAR) is involved in many neurological and psychiatric disorders including Alzheimer's disease and schizophrenia. The aim of this study was to develop a positron emission tomography (PET) ligand to assess the bio-availability of the NMDAR ion channel in vivo. A series of tri-N-substituted diarylguanidines was synthesized and their in vitro binding affinities for the NMDAR ion channel assessed in rat forebrain membrane fractions. Compounds 21, 23 and 26 were radiolabeled with either carbon-11 or fluorine-18 and ex vivo biodistribution and metabolite studies were performed in Wistar rats. Biodistribution studies showed high uptake especially in prefrontal cortex and lowest uptake in cerebellum. Pre-treatment with MK-801, however, did not decrease uptake of the radiolabeled ligands. In addition, all three ligands showed fast metabolism

Binding characterization of N-(2-chloro-5-thiomethylphenyl)-N′-(3-[ 3 H] 3 methoxy phenyl)-N′-methylguanidine ([ 3 H]GMOM), a non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist

Labeled with carbon-11, N-(2-chloro-5-thiomethylphenyl)-N′-(3-methoxyphenyl)-N′-methylguanidine ([ 11 C]GMOM) is currently the only positron emission tomography (PET) tracer that has shown selectivity for the ion-channel site of N-methyl-D-aspartate (NMDA) receptors in human imaging studies. The present study reports on the selectivity profile and in vitro binding properties of GMOM. The compound was screened on a panel of 80 targets, and labeled with tritium ([ 3 H]GMOM). The binding properties of [ 3 H]GMOM were compared to those of the reference ion-channel ligand [ 3 H](+)-dizocilpine maleate ([ 3 H]MK-801), in a set of concentration-response, homologous and heterologous inhibition, and association kinetics assays, performed with repeatedly washed rat forebrain preparations. GMOM was at least 70-fold more selective for NMDA receptors compared to all other targets examined. In homologous inhibition and concentration-response assays, the binding of [ 3 H]GMOM was regulated by NMDA receptor agonists, albeit in a less prominent manner compared to [ 3 H]MK-801. Scatchard transformation of homologous inhibition data produced concave upward curves for [ 3 H]GMOM and [ 3 H]MK-801. The radioligands showed bi-exponential association kinetics in the presence of 100 μmol L −1 l-glutamate/30 μmol L −1 glycine. [ 3 H]GMOM (3 nmol L −1 and 10 nmol L −1 ) was inhibited with dual affinity by (+)-MK-801, (R,S)-ketamine and memantine, in both presence and absence of agonists. [ 3 H]MK-801 (2 nmol L −1 ) was inhibited in a monophasic manner by GMOM under baseline and combined agonist conditions, with an IC 50 value of ~19 nmol L −1 . The non-linear Scatchard plots, biphasic inhibition by open channel blockers, and bi-exponential kinetics of [ 3 H]GMOM indicate a complex mechanism of interaction with the NMDA receptor ionophore. The implications for quantifying the PET signal of [ 11 C]GMOM are discussed