Letter: Mechanism of tissue component staining by osmium tetroxide

Multimodal Imaging of Chemically Fixed Cells in Preparation for NanoSIMS

In this work, we have employed time-of-flight secondary ion mass spectrometry (ToF-SIMS) to image chemically fixed adrenal cells prepared for transmission electron microscopy (TEM) and subsequent high-spatial-resolution NanoSIMS imaging. The sample fixation methodology preserves cell morphology, allows analysis in the ultrahigh vacuum environment, and reduces topographic artifacts, thus making these samples particularly favorable for ToF-SIMS analysis. ToF-SIMS imaging enables us to determine the chemistry and preservation capabilities of the chemical fixation as well as to locate specific ion species from OsO4. The OsO4 species have been localized in lysosomes of cortical cells, a type of adrenal cell present in the culture. NanoSIMS imaging of the (190)Os(16)O(-) ion species in cortical cells reveals the same localization as a wide range of OsO4 ions shown with ToF-SIMS. Even though we did not use during NanoSIMS imaging the exact OsxOy(-) ion species discovered with ToF-SIMS, ToF-SIMS allowed us to define the specific subcellular features in a high spatial resolution imaging mode. This study demonstrates the possibility for application of ToF-SIMS as a screening tool to optimize high-resolution imaging with NanoSIMS, which could replace TEM for localization in ultrahigh resolution imaging analyses.

The use of nano-computed tomography to enhance musculoskeletal research

Advances in computed tomography (CT) imaging are opening new avenues toward more precise characterization and quantification of connective tissue microarchitecture. In the last two decades, micro-computed tomography (microCT) has significantly augmented destructive methods for the 3D micro-analysis of tissue structure, primarily in the bone research field. Recently, microCT has been employed in combination with contrast agents to generate contrast-enhanced images of soft tissues that are otherwise difficult to visualize due to their native radiodensity. More recent advances in CT technology have enabled ultra-high resolution imaging by utilizing a more powerful nano-focused X-ray source, such as that found in nano-computed tomography (nanoCT) systems. NanoCT imaging has facilitated the expansion of musculoskeletal research by reducing acquisition time and significantly expanding the range of samples that can be imaged in terms of size, age and tissue-type (bone, muscle, tendon, cartilage, vessels and adipose tissue). We present the application and early results of nanoCT imaging in various tissue types and how this ultra-high resolution imaging modality is capable of characterizing microstructures at levels of details previously not possible. Contrast-enhanced imaging techniques to enable soft-tissue visualization and characterization are also outlined.

Osmium assay in fixatives and stained rat tissues by means of acid and o,o′-dihydroxo substituted monoazo dyes and some flavonoids

New simple, rapid and accurate spectrophotometric techniques for osmium assays in fixatives and stained tissues have been elaborated using acid (Tropaeolin O, Tropaeolin OOO-I, Tropaeolin OOO-II, Orange G), o,o′-dihydroxo substituted azo dyes (Eriochrome Blue Black R, Acid Chrome Dark-Blue, Eriochrome Black T) and flavonoids (morin, quercetin, luteolin). Methods are based on sensitive osmium(IV) reactions with reagents and the formation of stable coloured compounds. Tolerance ratios of main matrix components of histological specimens during Os(IV) spectrophotometric determination with reagents has been established. Results of osmium determination in fixatives and fixed tissues, obtained by means of different reagents, appeared to be sufficiently similar, although effects of matrix components differ. The accuracy of spectrophotometric osmium assay in fixatives with azo dyes has been confirmed with voltammetric investigations. Results obtained from osmium uptake by rat gum tissues are valuable for clinical testing of dental drugs, indicating the influence of drug treatment on the gums.

Chemical analysis of osmium tetroxide staining in adipose tissue using imaging ToF-SIMS

Osmium tetroxide (OsO4) is a commonly used stain for unsaturated lipids in electron and optical microscopy of cells and tissues. In this work, the localization of osmium oxide and specific lipids was independently monitored in mouse adipose tissue by using time-of-flight secondary ion mass spectrometry with Bi cluster primary ions. Substance-specific ion images recorded after OsO4 staining showed that unsaturated C18 fatty acids were colocalized with osmium oxide, corroborating the view that osmium tetroxide binds to unsaturated lipids. In contrast, saturated fatty acids (C14, C16 and C18) and also unsaturated C16 fatty acids show largely complementary localizations to osmium oxide. Furthermore, the distributions of saturated and unsaturated diglycerides are consistent with the specific binding of osmium oxide to unsaturated C18 fatty acids. The abundance of ions, characteristic of phospholipids and proteins, is strongly decreased as a result of the osmium staining, suggesting that a large fraction of these compounds are removed from the tissue during this step, while ions related to fatty acids, di- and triglycerides remain strong after osmium staining. Ethanol dehydration after osmium staining results in more homogeneous distributions of osmium oxide and unsaturated lipids. This work provides detailed insight into the specific binding of osmium oxide to different lipids.

Osmium tetroxide/p-phenylenediamine staining of nucleoli and Balbiani Rings in Chironomus salivary glands

This paper deals with the application of the osmium tetroxide fixation followed by p-phenylenediamine treatment to salivary gland cells from Chironomus larvae. After this procedure, cytoplasm, nucleoli and Balbiani rings show a high degree of staining both in light and electron microscopy, while chromatin remains unstained. Ethanol fixation followed by osmium tetroxide/p-phenylenediamine does not modify the above mentioned staining pattern. Under these conditions, extractive procedures for lipids do not affect the osmiophilia of nucleoli and Balbiani rings, while RNase or trichloroacetic acid treatment decreaes the staining degree of these structures. In osmium tetroxide/p-phenylenediamine treated salivary glands, the highest contrast within nuclei is seen to occur in the pars granulosa from normal or segregated nucleoli, as well as in Balbiani ring granules, which appear either as hollow granules or with a bipartite or horseshoe-like structure.

An ultrastructural study of osmiophilia in the human rectum

Rectal biopsies from subjects with a normal rectum and from patients with various forms of inflammatory bowel disease were studied by the prolonged osmication technique. No consistent ultrastructural differences were observed between these groups, but there were striking differences between individual epithelial cells in the same biopsy and between the epithelium and the cells of the lamina propria. The Golgi apparatus was demonstrated occasionally in the epithelium, often in endothelium. Endoplasmic reticulum, perinuclear cisterna and mitochondria were variably outlined. In plasma cells, there were striking differences in osmiophilia. The underlying mechanism of the different staining patterns is not clear. The findings do not appear to help in the differential diagnosis of inflammatory bowel disease nor to shed any new light on their underlying pathogenic mechanisms.

The chemical nature of osmium tetroxide fixation and staining of membranes by x-ray photoelectron spectroscopy

X-ray photoelectron spectroscopy was used to determine the oxidation states of osmium compounds present in erythrocyte ghost preparations and related systems treated with osmium tetroxide. Osmium tetroxide and cholesterol, codeposited at -100 degrees C, began to react at -70 degrees C, and Os(VI) was formed. Similarly, Os(VI) was detected for the known cholesterol-osmate ester prepared and purified chemically. However, osmium tetroxide applied in phosphate buffer (pH 7.2) gave rise to large proportions of Os(IV) and Os(III) species in addition to Os(VI) compounds. Egg phosphatidylcholine likewise produced a mixture of Os(VI), Os(IV), and Os(III), but dipalmitoyl phosphatidylcholine failed to give significant amounts of osmium containing products under identical conditions. Glutaraldehyde gave a mixture of compounds with the same osmium oxidation states when allowed to react with aqueous osmium tetroxide. Unfixed and glutaraldehyde-fixed erythrocyte ghosts also produced mixtures of Ss(VI), Os(IV) and Os(III) under conditions identical to those of normal tissue processing. Additionally, the mixture of adducts initially formed by treatment with osmium tetroxide was further reduced by dehydration of the tissue with ethanol, rpesulting in a final mixture which was 50-60% Os(III). The results support a scheme for the reaction os osmium tetroxide with tissues in which the initial reaction site is the double bonds of unsaturated lipids to form Os(VI) derivatives. Subsequent hydrolysis and further reduction yield complexes of Os(IV) and Os(III). A mixture of these three states is present in membrane specimens during microscopic observation. Os(VI) and Os(IV) could be present as osmate esters and osmium dioxide, respectively; Os(III) could be present as an oxo- or amino complex(es). The photoelectron spectrum of intact erythrocyte ghosts can be synthesized from the spectra of phospholipid and cholesterol only, suggesting the predominance of the reaction with lipids in the fixation process.

Ultrahistochemical study on the ruthenium red surface staining. I. Processes which give rise to electron-dense marker

The cell coat picture effect which is usually obtained with the conventional RR method, that is with the RR/OsO4 coupled reaction, is investigated. In this first paper, each of conceivable events which might take place between RR, OSO4 and cell surface membrane is discussed or studied. Various tests are carried out on ascites Ehrlich carcinoma cells and Zajdela ascites hepatoma cells treated with numerous chemical reagents, as also on a few pure proteins. The set of data supports the concept that the staining pattern is due to the combination in surface membranes of RR with a "colloidal-like" form of OsO2. The latter might occur during the formation of stable cyclic osmic acid diesters between OsO4 and membrane unsaturated lipids. A possibility by which the resulting marker is though also to be in a "colloidal-like" state is put forward. A next report will deal with this problem.

Glycogen, its chemistry and morphological appearance in the electron microscope. III. Identification of the tissue ligands involved in the glycogen contrast staining reaction with the osmium (VI)--iron(II) complex

By application of appropriate blocking reactions (acetylation, de-amination, methylation and NaHSO3-treatment) it is demonstrated that the tissue ligands involved in the selective glycogen contrast staining reaction with the OsVI. FeII complex (known to be present in the combination K2OsO4K4Fe(CN)6) are the glycogen C2-C3 di-hydroxyl groups. Deliberate conversion of the diols into di-aldehydes and (di-)carboxyl groups by the application of specific oxidative agents followed by application of the OsVI. FeII-complex results morphologically in identical selective contrast staining of glycogen. By applying appropriate blocking reactions to such pre-oxidized aldehyde fixed glycogen, evidence is accumulated that K2OSO4 and K3Fe(CN)6 are unable to oxidize diols, whereas OSO4 and H2O2 are able to convert diols into carboxyl groups. From these results it is concluded that in the combination K2OSO4K4Fe(CN)6 the OsVI.FeII complex reacts with unchanged diols in the glycogen, whereas the OSO4 in the combination OSO4K3Fe(CN)6 can potentially create carbocyl groups in the aldehyde-fixed glycogen. The addition of urea to the two glycogen contrasting combinations (K2OSO4K4Fe(CN)6 or OSO4K3Fe(CN)6), also emphasizes that, although morphologically both combinations produce identical contrast stained glycogen, chemically the contrast staining is apparently obtained in a different way, as urea prevented the contrast formation in the glycogen by the combination K2OsO4Fe(CN)L, but not by the combination OSO4K3F e(CN)6.