MALDI Imaging and Structural Analysis of Rat Brain Lipid Negative Ions with 9-Aminoacridine Matrix

Mass spectrometry imaging is of growing interest for chemical mapping of lipids at the surface of tissue sections. Many efforts have been devoted to optimize matrix choice and deposition technique for positive ion mode analyses. The identification of lipid species desorbed from tissue sections in the negative mode can be significantly improved by using 9-aminoacridine together with a robust deposition method, yielding a superior signal-to-noise ratio and thus a better contrast for the ion images in comparison to classical matrices such as α-cyano-4-hydroxycinnamic acid, 2,5-dihydroxybenzoic acid, or 2,4,6-trihydroxyacetophenone. Twenty-eight different lipid species (phosphatidic acids, phosphatidylethanolamines, phosphatidylserines, phosphatidylglycerols, phosphatidylinositols, phosphatidylinositol-phosphates, and sulfatides) were scrutinized on rat brain tissue sections, and systematic MS/MS studies were conducted. It was possible to identify isobaric species differing by their fatty acid chains thanks to the improved sensitivity

Insights into the MALDI Process after Matrix Deposition by Sublimation Using 3D ToF-SIMS Imaging

Imaging mass spectrometry (IMS) has become a powerful tool to characterize the spatial distribution of biomolecules in thin tissue sections. In the case of matrix-assisted laser desorption ionization (MALDI) IMS, homogeneous matrix deposition is critical to produce high-quality ion images, and sublimation in particular has shown to be an excellent matrix deposition method for the imaging of lipids. Matrix deposition by sublimation is, however, a completely solvent-free system, which ought to prevent the mixing of matrix and analytes thought to be necessary for successful MALDI. Using 3D time-of-flight secondary ion imaging mass spectrometry, we have studied the matrix–tissue interface in 3D with high resolution to understand the MALDI process of lipids after matrix deposition by sublimation. There is a strong indication that diffusion is the process by which lipids migrate from the tissue to the matrix layer. We show that triacylglycerols and phospholipids have a delayed migratory trend as compared to diacylglycerols and monoacylglycerols, which is dependent on time and matrix thickness. Additional experiments show that a pure lipid’s capacity to migrate into the matrix is dependent on its fluidity at room temperature. Furthermore, it is shown that cholesterol can only migrate in the presence of a (fluid) lipid and appears to fluidize lipids, which could explain its colocalization with the diacylglycerols and monoacylglycerols in the matrix

Identification of the Environmental Neurotoxins Annonaceous Acetogenins in an Annona cherimolia Mill. Alcoholic Beverage Using HPLC-ESI-LTQ-Orbitrap

Epidemiological and toxicological studies have suggested Annonaceaeous acetogenins to be environmental neurotoxins responsible for sporadic atypical parkinsonism/dementia in tropical areas. These compounds are present in the tropical genus <i>Annona</i> (Annonaceae), known for its fruit-yielding cultivated species such as Annona cherimolia. This species is widely cultivated in South America, Spain, and Portugal and yields acetogenins in its seeds, stems, and roots. The presence of these compounds in the pulp of its fruit and in derived food products is unclear. An innovative and sensitive methodology by HPLC-ESI-LTQ-Orbitrap with postcolumn infusion of lithium iodide was used to identify the presence of low levels of acetogenins in an <i>A. cherimolia</i> Mill. fruit-based commercial alcoholic beverage. More than 80 representatives were detected, and the 31 most intense acetogenins were identified. All together these findings indicate that this species should be considered as a risk factor within the framework of a worldwide problem of food toxicity

Argon Cluster Ion Source Evaluation on Lipid Standards and Rat Brain Tissue Samples

Argon cluster ion sources for sputtering and secondary ion mass spectrometry use projectiles consisting of several hundreds of atoms, accelerated to 10–20 keV, and deposit their kinetic energy within the top few nanometers of the surface. For organic materials, the sputtering yield is high removing material to similar depth. Consequently, the exposed new surface is relatively damage free. It has thus been demonstrated on model samples that it is now really possible to perform dual beam depth profiling experiments in organic materials with this new kind of ion source. Here, this possibility has been tested directly on tissue samples, 14 μm thick rat brain sections, allowing primary ion doses much larger than the so-called static secondary ion mass spectrometry (SIMS) limit and demonstrating the possibility to enhance the sensitivity of time-of-flight (TOF)-SIMS biological imaging. However, the depth analyses have also shown some variations of the chemical composition as a function of depth, particularly for cholesterol, as well as some possible matrix effects due to the presence or absence of this compound

Spectroscopic analysis of non-steatotic hepatocytes on fatty liver.

<p>Spectroscopic analyses were performed on periportal hepatocytes on tissue section from normal or fatty liver. The video image is shown (left panel) with the corresponding averaged IR spectra (right panel) and the chemical imaging of the sum of DAG (middle panel).</p

Assignment of frequency to chemical functions.

<p>From <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0007408#pone.0007408-Dreissig1" target="_blank">[19]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0007408#pone.0007408-Banyay1" target="_blank">[20]</a>.</p

Histological features of steatosis.

<p>Tissue sections of 6 µm thickness were performed on paraffin embedded biopsies from normal liver or from fatty liver and stained with HES (hematoxylin, eosin and safran). Normal hepatic lobule without steatosis (left panel) or fatty liver area exhibiting macrovacuolar and microvesicular steatosis (right panel) are shown. Upper panel: ×100, lower panel: ×400. PT: portal tract, BD: biliary duct, PV: portal vein, HA: hepatic artery, CLV: centrilobular vein, SV: steatotic vacuole.</p

Second derivatives of IR spectra.

<p>Spectra recorded on steatosis or non-steatotic hepatocytes were superimposed (upper panel). Second derivatives of the spectra were calculated and superimposed in the frequency domain 2600–3200 cm⁻¹ (lower panel).</p

History of patients and origin of samples.

<p>History of patients and origin of samples.</p

Analysis of steatosis using synchrotron FTIR microspectroscopy.

<p>A) Optical image of steatotic hepatocytes containing steatotic vesicles (white star) and non-steatotic hepatocytes (black star). B) Averaged IR spectra recorded inside steatotic vesicles (upper spectrum in blue) or on non-steatotic hepatocytes (lower spectrum in red). The band corresponding to olefin (3000–3060 cm⁻¹) is labelled by a black arrow. C) Chemical imaging of some bands on the tissue section.</p