The fluorescence of elastic fibres stained with eosin and excited by visible light

Blood identified and quantified in formalin fixed paraffin embedded lung sections using eosin fluorescence

Eosin Y is a common stain in histology. Although usually used for colourimetric imaging where the dye is used to stain pink/red a range of structures in the tissue, Eosin Y is also a fluorochrome, and has been used in this manner for decades. In this study our aim was to investigate the fluorescence properties of the dye to enable quantification of structures within formalin-fixed paraffin-embedded (FFPE) tissue sections. To do this, FFPE sections of hamster tissue were prepared with haematoxylin and eosin Y dyes. Spectral detection on a confocal laser scanning microscope was used to obtain the fluorescence emission spectra of the eosin Y under blue light. This showed clear spectral differences between the red blood cells and congealed blood, compared to the rest of the section. The spectra were so distinct that it was possible to discern these in fluorescence and multi-photon microscopy. An image analysis algorithm was used to quantify the red blood cells. These analyses could have broad applications in histopathology where differentiation is required, such as the analysis of clotting disorders to haemorrhage or damage from infectious disease.

Visualization and quantification of pancreatic tumor stroma in fresh tissue via ultraviolet surface excitation

SIGNIFICANCE

The study has confirmed the feasibility of using ultraviolet (UV) excitation to visualize and quantify desmoplasia in fresh tumor tissue of pancreatic adenocarcinoma (PDAC) in an orthotopic xenograft mouse model, which provides a useful imaging platform to evaluate acute therapeutic responses.

AIM

Stromal network of collagen prominent in PDAC tumors is examined by imaging fresh tissue samples stained with histological dyes. Fluorescence signals are color-transferred to mimic Masson's trichrome staining.

APPROACH

Murine tumor samples were stained with Hoechst, eosin, and rhodamine B and excited at 275-nm. Fluorescence signals in the visible spectrum were captured by a CMOS color camera with high contrast and resolution at whole-tumor slice field of view.

RESULTS

Fluorescence imaging using UV excitation is capable of visualizing collagen deposition in PDAC tumors. Both fluorescence and histology data showed collagen content of up to 30%. The collagen modulation effect due to photodynamic priming treatment was observed showing 13% of collagen reduction. Necrosis area is visible and perfusion imaging using Texas Red dextran is feasible.

CONCLUSIONS

The study demonstrates collagen visualization in fresh PDAC tumor samples using UV excitation. This imaging platform also provides quantitative stromal information from fiber analysis and visibility of necrosis and perfusion, suitable for therapeutic response assessment of photodynamic therapy.

Dual-mode emission and transmission microscopy for virtual histochemistry using hematoxylin- and eosin-stained tissue sections

In the clinical practice of pathology, trichrome stains are commonly used to highlight collagen and to help evaluate fibrosis. Such stains do delineate collagen deposits but are not molecularly specific and can suffer from staining inconsistencies. Moreover, performing histochemical stain evaluation requires the preparation of additional sections beyond the original hematoxylin- and eosin-stained slides, as well as additional staining steps, which together add cost, time, and workflow complications. We have developed a new microscopy approach, termed DUET (DUal-mode Emission and Transmission) that can be used to extract signals that would typically require special stains or advanced optical methods. Our preliminary analysis demonstrates the potential of using the resulting signals to generate virtual histochemical images that resemble trichrome-stained slides and can support clinical evaluation. We demonstrate advantages of this approach over images acquired from conventional trichrome-stained slides and compare them with images created using second harmonic generation microscopy.

In vitro and in vivo analysis of visible light crosslinkable gelatin methacryloyl (GelMA) hydrogels

Photocrosslinkable materials have been frequently used for constructing soft and biomimetic hydrogels for tissue engineering. Although ultraviolet (UV) light is commonly used for photocrosslinking such materials, its use has been associated with several biosafety concerns such as DNA damage, accelerated aging of tissues, and cancer. Here we report an injectable visible light crosslinked gelatin-based hydrogel for myocardium regeneration. Mechanical characterization revealed that the compressive moduli of the engineered hydrogels could be tuned in the range of 5-56 kPa by changing the concentrations of the initiator, co-initiator and co-monomer in the precursor formulation. In addition, the average pore sizes (26-103 μm) and swelling ratios (7-13%) were also shown to be tunable by varying the hydrogel formulation. In vitro studies showed that visible light crosslinked GelMA hydrogels supported the growth and function of primary cardiomyocytes (CMs). In addition, the engineered materials were shown to be biocompatible in vivo, and could be successfully delivered to the heart after myocardial infarction in an animal model to promote tissue healing. The developed visible light crosslinked hydrogel could be used for the repair of various soft tissues such as the myocardium and for the treatment of cardiovascular diseases with enhanced therapeutic functionality.

Extracellular Assembly of the Elastin Cable Line Element in the Developing Lung

In the normal lung, a dominant structural element is an elastic "line element" that originates in the central bronchi and inserts into the distal airspaces. Despite its structural importance, the process that leads to development of the cable line element is unknown. To investigate the morphologic events contributing to its development, we used optical clearing methods to examine the postnatal rat lung. An unexpected finding was numerous spheres, with a median diameter of 1-2 µm, within the primary septa of the rat lung. The spheres demonstrated green autofluorescence, selective fluorescent eosin staining, reactivity with carboxyfluorescein succinimidyl ester, and specific labeling with anti-tropoelastin monoclonal antibody-findings consistent with tropoelastin. The sphere number peaked on rat postnatal day 4 (P4) and were rare by P14. The disappearance of the spheres was coincident with the development of the cable line element in the rat lung. Transmission electron microscopy demonstrated no consistent association between parenchymal cells and sphere alignment. In contrast, the alignment of tropoelastin spheres appeared to be the direct result of interactions of scaffold proteins including collagen fibers and fibrillin microfibrils. We conclude that the spatial organization of the cable line element appears to be independent of tropoelastin deposition, but dependent on crosslinking to scaffold proteins within the primary septa. Anat Rec, 300:1670-1679, 2017. © 2017 Wiley Periodicals, Inc.

Tissue-based imaging model of human trabecular meshwork

We have developed a tissue-based model of the human trabecular meshwork (TM) using viable postmortem corneoscleral donor tissue. Two-photon microscopy is used to optically section and image deep in the tissue to analyze cells and extracellular matrix (ECM) within the original three-dimensional (3D) environment of the TM. Multimodal techniques, including autofluorescence (AF), second harmonic generation (SHG), intravital dye fluorescence, and epifluorescence, are combined to provide unique views of the tissue at the cellular and subcellular level. SHG and AF imaging are non-invasive tissue imaging techniques with potential for clinical application, which can be modeled in the system. We describe the following in the tissue-based model: analysis of live cellularity to determine tissue viability; characteristics of live cells based on intravital labeling; features and composition of the TM's structural ECM; localization of specific ECM proteins to regions such as basement membrane; in situ induction and expression of tissue markers characteristic of cultured TM cells relevant to glaucoma; analysis of TM actin and pharmacological effects; in situ visualization of TM, inner wall endothelium, and Schlemm's canal; and application of 3D reconstruction, modeling, and quantitative analysis to the TM. The human model represents a cost-effective use of valuable and scarce yet available human tissue that allows unique cell biology, pharmacology, and translational studies of the TM.

Sources of structural autofluorescence in the human trabecular meshwork

PURPOSE

In situ 2-photon excitation fluorescence (TPEF) of the human trabecular meshwork (TM) reveals beams of heterogeneous autofluorescence (AF) comprising high intensity fluorescent fibers (AF-high) on a background of lower intensity fluorescence (AF-low). To determine the sources of this AF heterogeneity, we imaged human TM to characterize AF, second harmonic generation (SHG) for collagen, and eosin-labeled fluorescence identifying elastin.

METHODS

Corneoscleral rims retained after corneal transplantation were incubated with and without eosin, and imaged by TPEF. TPEF was collected through multiphoton bandpass filters to obtain AF, SHG (collagen bandwidth), and eosin-labeled fluorescence images. For qualitative comparisons, near-simultaneous image acquisition pairs of AF-SHG (+/-eosin coincubation), AF-eosin, and SHG-eosin were captured. For quantitative comparisons, multiple regions of interest (ROI) were defined in separate TM beam regions within the uveal and corneoscleral meshwork for image acquisition pairs of AF-SHG (without eosin coincubation) and SHG-eosin. We defined 18 ROI within each acquisition pair as the basis for Manders colocalization analysis. Perfect colocalization was defined as a Manders coefficient (Mcoeff) of 1.

RESULTS

Qualitatively and quantitatively, AF-low colocalized with SHG (Mcoeff=1), but not SHG signal-voids. AF-high colocalized with SHG signal-voids (Mcoeff=1), but not the SHG signal. Like AF-high, eosin-labeled fluorescence qualitatively and quantitatively colocalized (Mcoeff=1) with SHG signal-voids, but not the SHG signal.

CONCLUSIONS

Heterogeneous AF in human TM is comprised of high intensity signal originating from elastin fibers in beam cores and lower intensity signal originating from collagen. These findings are relevant to interpreting structural extracellular matrix signals in AF images of the TM.

Characterizing cutaneous elastic fibers by eosin fluorescence detected by fluorescence microscopy

BACKGROUND

Though elastic fibers are as important as collagen fibers in interpretation of the histopathologic findings, it is impossible to observe them on the hematoxylin & eosin (H&E) stained specimen.

OBJECTIVE

Characterizing eosin fluorescence emitted by elastic fibers in H&E stained specimens.

METHODS

Normal skin tissue sections were stained in 4 different ways (unstained, hematoxylin only, eosin only, H&E) and observed under a fluorescence microscope using a FITC filter set. Fluorescent findings of 30 H&E-stained specimens showing abnormal dermal findings were compared with bright field findings of Miller's elastic stained specimen.

RESULTS

Strong eosin fluorescence was related to the differential binding property of eosin with elastic fibers. Hematoxylin stain quenched excessive eosin fluorescence from other tissue components and contributed to better contrast. Fluorescence microscopy of H&E-stained sections was found to be especially useful in observing mature elastic fibers in the reticular dermis. In 74% of the specimens, eosin fluorescence findings of elastic fibers in reticular dermis matched well with that of specimens with elastic fiber special stain.

CONCLUSION

Analysis of skin elastic fibers by fluorescence microscopy is a useful and complementary method to reveal hidden elastic fibers in H&E-stained specimens.

Three-dimensional reconstruction of living mouse liver tissues using cryotechniques with confocal laser scanning microscopy

Soluble proteins and glycogen particles are well preserved in paraffin-embedded sections prepared by in vivo cryotechnique (IVCT) and cryobiopsy followed by freeze substitution fixation. We performed confocal laser scanning microscopic analyses on the distributions of glycogen with periodic acid-Schiff (PAS) staining and serum proteins with immunostaining for mouse liver tissues. Livers of fully fed mice showed a strong fluorescence signal of PAS staining in all hepatocytes and immunofluorescence of immunoglobulin kappa light chain (Igκ) in blood vessels and bile canaliculi. However, some hepatocytes in mechanically damaged livers were PAS-negative and Igκ-immunopositive, showing extraction of glycogen particles and infiltration of serum proteins in hepatocytes. By three-dimensional (3D) reconstruction of serial optical sections, interconnecting hepatic sinusoids and bile canaliculi were detected with Igκ immunostaining between trabecular hepatocytes that were PAS stained. In PAS-stained samples under fasting conditions, interstitial structures along sinusoids were clarified in vivo by 3D reconstruction because of the lower PAS staining intensity of hepatocytes. In addition, 100-μm-thick eosin-stained slices provided 3D structural images more than 30 μm in thickness away from tissue surfaces, showing blood vessels with flowing erythrocytes and networks of bile ducts and canaliculi. IVCT and cryobiopsy with histochemical analyses enabled us to visualize native hepatocytic glycogen and 3D structures, such as vascular networks, reflecting their living states by confocal laser scanning microscopy.

Fluorescence microscopy of rat embryo sections stained with haematoxylin-eosin and Masson's trichrome method

The fluorescence pattern induced by haematoxylin-eosin (HE) and Masson's trichrome (MT) staining methods on paraffin sections of rat embryos (from 13 to 18 days old) has been studied. Using optimal excitation (green light, 545 nm), HE- or MT-stained sections showed a selective red emission of the acidophilic tissue components, which was due to eosin Y in the case of HE and to acid fuchsin and/or xylidine ponceau in the case of MT. The fluorescence intensity induced by these anionic dyes was variable and related to the substrate nature and the embryo age. Whereas in young embryos only the immature red blood cells showed a noticeable fluorescence, in the oldest embryos there were also other tissue components that selectively fluoresced with these dyes, in particular fibre lens cells, elastic fibres, zymogen granules and muscle cells. Spectrofluorometric studies on free dyes and densitometric analysis of protein blots confirmed microscopical observations. Our results indicate that the standard HE and MT staining methods can be used in recognizing the appearance of specific protein structures in embryonic tissues by means of fluorescence microscopy.

Selective fluorescence of eosinophilic structures in grasshopper and mammalian testis stained with haematoxylin-eosin

After staining with Mayer's haematoxylin and eosin Y, paraffin sections of grasshopper and mouse testis were analysed by both transmitted light and fluorescence microscopy. Under violet-blue (436 nm) light excitation, a bright green emission was observed in all eosinophilic structures. Meiotic spindles (fibres and poles), mitochondrial aggregates, centriolar adjuncts in grasshopper spermatids, the basal lamina, flagellar bundles and remaining cytoplasmic droplets in the lumen of seminiferous tubules showed the most striking fluorescence induced by eosin Y. No emission was found in these structures after haemalum staining. Fluorescent microtubular components also revealed a positive immunoperoxidase reaction for alpha-tubulin. All fixation and embedding procedures (Bouin, Zenker, formaldehyde alone or followed by dichromate or glutaraldehyde, freeze-substitution) were suitable for observation by fluorescence microscopy. Acetylation, deamination, and prolonged washing of stained sections with water, salt solution or ethanol strongly reduced eosin Y fluorescence, while it slightly increased after methylation. These results show that routine haematoxylin-eosin stained tissue sections can be routinely analysed by fluorescence microscopy. The emission of eosin Y allows easy and precise recognition of eosinophilic structures, which are poorly visible under bright field illumination.

On the nature of Romanowsky-Giemsa staining and the Romanowsky-Giemsa effect. I. Model experiments on the specificity of azure B-eosin Y stain as compared with other thiazine dye-eosin Y combinations

After incorporation into a polyacrylamide matrix, the biopolymers DNA, RNA, heparin, hyaluronic acid, collagen and the synthetic polymers poly(U) and poly(A, U) were stained with the pure thiazine dyes, Methylene Blue, the Azures and Thionin alone and combined with Eosin Y. Satisfactory spectrophotometric agreement was obtained between the staining reactions of the biopolymers in the artificial matrix and those in their natural surroundings. This was especially true with respect to the specificity of the Azure B-Eosin Y dye-pair, which is based on the generation, on suitable substrates, of a purple colour, the Romanowsky-Giemsa effect (RGE), with an absorbance maximum near 550 nm. In the model experiments, DNA, heparin, hyaluronic acid and collagen were found to be RGE-positive and poly(U), poly(A, U) and RNA RGE-negative. A theory of RGE is proposed which complies with the new and earlier observations: after saturation of available anionic binding sites and aggregate formation by Azure B, electron donor acceptor complexes are formed between Eosin Y and Azure B via hydrogen-bridge formation of the aminosubstituent proton of Azure B and between Eosin Y and the biopolymer surface. Charge-transfer complex formation may also account for the qualitative identity of Azure B-Eosin Y and Azure A-Eosin Y spectra of substrates, which are coloured purple. Quantitatively, Azure A-Eosin Y is less efficient in giving RGE. The generation of RGE is time-dependent. Equilibrium staining is attained after about 120 h. The implications of the results for the biological application of Romanowsky-Giemsa staining are discussed briefly.

Novel application of aniline blue. Fluorescent staining of glycogen and some protein structures

The present study shows that aniline blue can be used as a fluorescent stain for glycogen. The dye is also helpful in tracing pathological and autolytic changes in lysosomes, mitochondria, erythrocytes and nuclei, and it can also be used for demonstrating bacteria in tissue sections and smears. The techniques used are simple, rapid and inexpensive. Spectrophotometric studies on aniline blue solutions have shown that aniline blue fluorescence was enhanced by the addition of certain proteins, or of glycogen to the dye solution. In case of albumen which has the maximum effect, enhancement is dependent upon the albumen-dye ratio. The mechanism of staining is mainly due to self quenching, but there is also an evidence of the presence of hydrophobic reaction.

Elastic (pseudoelastic tissue in arterioles of the human and dog dental pulp

Formalin-fixed pulps from seven human and five dog teeth were investigated for the occurrence of vascular elastic tissue with special reference to the difference between elastin and pseudoelastica. The latter term denotes structures which show the histochemical and fluorescence microscopic properties of collagen, but also bind the so-called elastica stains. Human aorta, and aorta, lips, tongues and gingiva from dogs served as control material. Whereas conventional elastica stains, in this study represented by orcinol-new fuchsin, only differentiate elastic tissue and collagen, a thiazine red R fluorescence method also permits differentiation between elastin membranes and pseudoelastica. Other methods for light and fluorescence microscopy verified this conclusion. Pseudoelastic fibers/membranes occurred in arterioles of both human and dog pulps, but were more frequent in the latter. The distribution of these elements in the arteriolar walls was different in the human and dog pulp. No elastin elements were observed.