DIUTHAME enables matrix-free mass spectrometry imaging of frozen tissue sections

RATIONALE

A recently developed matrix-free laser desorption/ionization method, DIUTHAME (desorption ionization using through-hole alumina membrane), was examined for the feasibility of mass spectrometry imaging (MSI) applied to frozen tissue sections. The permeation behavior of DIUTHAME is potentially useful for MSI as positional information may not be distorted during the extraction of analytes from a sample.

METHODS

The through-hole porous alumina membranes used in the DIUTHAME chips were fabricated by wet anodization, were 5 μm thick, and had the desired values of 200 nm through-hole diameter and 50% open aperture ratio. Mouse brain frozen tissue sections on indium tin oxide (ITO)-coated slides were covered using the DIUTHAME chips and were subjected to MSI experiments in commercial time-of-flight mass spectrometers equipped with solid-state UV lasers after thawing and drying without matrix application.

RESULT

Mass spectra and mass images were successfully obtained from the frozen tissue sections using DIUTHAME as the ionization method. The mass spectra contained rich peaks in the phospholipid mass range free from the chemical background owing to there being no matrix-derived peaks in that range. DIUTHAME-MSI delivered high-quality mass images that reflected the anatomy of the brain tissue.

CONCLUSIONS

Analytes can be extracted from frozen tissue by capillary action of the through-holes in DIUTHAME and moisture contained in the tissue without distorting positional information of the analytes. The sample preparation for frozen tissue sections in DIUTHAME-MSI is simple, requiring no specialized skills or dedicated apparatus for matrix application. DIUTHAME can facilitate MSI at a low mass, as there is no interference from matrix-derived peaks, and should provide high-quality, reproducible mass images more easily than MALDI-MSI.

Laser Capture Microdissection on Frozen Sections for Extraction of High-Quality Nucleic Acids

Many cancers harbor a large fraction of nonmalignant stromal cells intermixed with neoplastic tumor cells. While single-cell transcriptional profiling methods have begun to address the need to distinguish biological programs in different cell types, such methods do not enable the analysis of spatial information available through histopathological examination. Laser capture microdissection offers a means to separate cellular samples based on morphological criteria. We present here an optimized method to retrieve intact RNA from laser capture microdissected tissue samples, using pancreatic ductal adenocarcinoma as an example, in order to separately profile tumor epithelial and stromal compartments. This method may also be applied to nonmalignant tissues to isolate cellular samples from any morphologically identifiable structure.

Optimization of sample cooling temperature for redox cryo-imaging

Cryo-imaging techniques have been widely used to measure the metabolic state of tissues by capturing reduced nicotinamide adenine dinucleotide (NADH) and flavin adenine dinucleotide (FAD) autofluorescence. However, NADH and FAD fluorescence is sensitive to changes in temperature, which may result in unreliable redox ratio calculations. Here, the relationship between the measured redox ratio and sample surface temperature was analyzed using a standard phantom solution and biological tissues. The results indicated that a temperature < - 100°C was a suitable cryo-imaging temperature window in which redox ratio measuring was immune to temperature fluctuations. These results may serve as a reference for designing and optimizing redox cryo-imaging experiments for quantitatively mapping the metabolic state of biological samples.

[Rapid frozen sections in neuropathology]

Neuropathological evaluation of frozen sections requires a) special expertise in neuropathological specimen assessment and neurooncology as well as b) a trustful and open communication culture with the neurosurgeons. In addition to frozen sections, cytological examinations of smear and touch preparations as supporting methods are available to reach a correct diagnosis: these additional methods should therefore be performed whenever possible. Besides evaluation of biopsy specimens, appraisal of resection specimens and resection margin controls are of high clinical relevance. In the case of diffusely infiltrating central nervous system (CNS) neoplasms, in particular gliomas, resection margin control is often not feasible in contrast to other types of solid tumor.

A procedure for tissue freezing and processing applicable to both intra-operative frozen section diagnosis and tissue banking in surgical pathology

Different methods for snap freezing surgical human tissue specimens exist. At pathology institutes with higher work loads, solid carbon dioxide, freezing sprays, and cryostat freezing are commonly used as coolants for diagnosing frozen tissue sections, whereas for tissue banking, liquid nitrogen or isopentane cooled with liquid nitrogen is preferred. Freezing tissues for diagnostic and research purposes are therefore often time consuming, laborious, even hazardous, and not user friendly. In tissue banks, frozen tissue samples are stored in cryovials, capsules, cryomolds, or cryocassettes. Tissues are additionally embedded using freezing media or wrapped in plastic bags or aluminum foils to prevent desiccation. The latter method aggravates enormously further tissue handling and processing. Here, we describe an isopentane-based workflow which concurrently facilitates tissue freezing and processing for both routine intra-operative frozen section and tissue banking and satisfies the qualitative demands of pathologists, cancer researchers, laboratory technicians, and tissue bankers.

Rotation cryotomy: medical and scientific value of a new serial sectioning procedure

Preparation of thin serial sections for comparative macromorphologic investigations has always represented a grave technical problem, especially in the case of regions in which bone as well as soft tissue are to be documented within their natural relations to each other in any desired sectional plane. Non-decalcified specimens up to the size of a whole cadaver are embedded in physiologic medium, precisely positioned, and deep-frozen to a specimen-ice block. A newly developed device, working on the basis of blades rotating at high speed, allows quick, successive removal of sections from the surface of the specimen block, with a thickness of each section infinitely variable between 0.1 and 5 mm. Following each cut, the new surface of the block can be documented photographically or on videotape for macromorphologic evaluation. So far more than 1,000 human, animal, and botanical specimens have been sectioned and evaluated with this method. In none of the cases were specimens damaged. Furthermore, any desired sectional plane could be adjusted: consequently a definite correlation between these sections and previous sonography, magnetic resonance (MR), or computed tomography (CT) images could be established. As serial cryosectioning becomes available to a far wider circle of medical and natural scientists, high-quality results should be obtained at lower costs.

A new modification for preparing tissue blocks for cryostat sectioning

A modification of the Carter method for preparing tissue blocks for cryostat sectioning is presented. One problem with the Carter method is that tissue edges occasionally freeze above the plane of the smooth cryostat disk. My modification avoids this problem by gradual liquid nitrogen cooling of the disk. This enables all tissue edges to be applied to the smooth disk surface until freeze adherence occurs.

Histochemical representation of regional ATP in the brain using a firefly luciferase-immobilized membrane in a multilayer film format

The enzymatic bioluminescence of firefly luciferase has been used in sensitive pictorial assays of ATP. We describe a method using a membrane with immobilized luciferase in a multilayer film format for the histochemical representation of brain ATP content. The multilayer film consisted of a transparent support, a reagent layer, and a pigment layer. The reagent layer contained all necessary reagents, including immobilized luciferase. The pigment layer was effective for high image resolution. An unfixed slice of frozen brain 16 microns thick was placed on the film. The chemical energy of brain ATP was converted into luminescent energy in the reagent layer and the bioluminescence emitted was recorded photographically with high spatial resolution. A close linear relationship was obtained between the optical density of the bioluminescent images and logarithmic plots of the brain ATP content. With this film, the regional ATP content in fine anatomical structures of gerbil brains was clearly demonstrated in both physiological and pathological states.

A rapid method for processing very large numbers of tissue sections for immunohistochemical hybridoma screening

A hybridoma screening format which facilitates the processing of thousands of tissue sections for immunohistochemical analysis is described. The method utilizes sterile replica transfers of monoclonal antibody-containing test supernatants from 96-well culture plates to tissue sections mounted in appropriately sized 8 X 12 arrays, and is extremely rapid and inexpensive.

Frozen sections of bone biopsies in metabolic and other bone diseases

Frozen sections of bone trephine and needle biopsies can be satisfactorily cut in a standard cryostat and, when stained with haematoxylin and eosin, they enable a rapid diagnosis to be made in a wide range of metabolic bone disorders including Paget's disease, osteoporosis, osteomalacia, hyperparathyroidism and renal osteodystrophy. Neoplastic disease of bone may also be diagnosed using the same technique. A tissue diagnosis can be established within an hour of the biopsy being taken, instead of the 1-3 weeks required for resin section diagnosis, with a consequent potential saving in further costly biochemical and radiological investigations, a possible shortening of the patient's stay in hospital and earlier initiation of correct treatment. The method is quick, reliable and highly cost-effective; it is of particular value in laboratories with insufficient workload to justify the expenditure on specialized microtomes and reagents for resin embedding.

A comparison of subcellular element concentrations in frozen-dried, plastic-embedded, dry-cut sections and frozen-dried cryosections

Biological X-ray microanalysis of diffusible elements within cellular and subcellular compartments requires preparation methods to retain electrolytes in the compartments they occupied in vivo. X-ray microanalysis of frozen-dried, plastic-embedded samples has been used to quantitate electrolytes at the cellular level. We have compared the subcellular elemental distribution in dry cut sections from such samples with that in ultrathin frozen-dried cryosections. Rat pancreases were quench-frozen onto a helium-vapor-cooled copper block. Cryosections were cut at 130-150 K, transferred using a Gatan cold stage, frozen-dried in the column and analysed at 190 K. Tissue fragments were frozen-dried at 190 K, and cut on a dry knife at 293 K. Both samples provided images permitting unambiguous identification of all major compartments except the Golgi complex. Intracellular potassium-to-sodium ratios obtained on frozen-dried plastic-embedded sections were lower than for cryosections (e.g. 1.77 in basal cytoplasm in plastic sections as compared to 4.34 for cryosections) and varied with the pre-embedding procedure (e.g. 1.77 in formaldehyde-fixed as compared to 2.87 in osmium-fixed plastic sections). Potassium gradients between adjacent organelles were large in cryosections and insignificant in plastic-embedded material. Higher cytoplasmic phosphorus, potassium and sulfur concentrations were observed in cryosections. Therefore, a redistribution of electrolytes and covalently bound elements occurred subcellularly in the plastic sections. Calcium was quantifiable in most organelles in cryosections but the plastic lowered sensitivity too much to permit routine calcium quantification. We conclude that in our hands frozen-dried, plastic-embedded samples were compromised and provided lower sensitivity than cryosections.(ABSTRACT TRUNCATED AT 250 WORDS)