Quantitative comparison of immunohistochemical staining intensity in tissues fixed in formalin and Histochoice

A new method for the sampling and preservation of placental specimens in low-resource settings for the identification of P. falciparum and analysis of nucleic acids

Collection, preservation, and shipment of histological specimens in low-resource settings is challenging. We present a novel method that achieved excellent preservation of placental specimens from rural Mali by using formalin fixation, ethanol dehydration, and long-term storage in a solar-powered freezer. Sample preservation success was 92%, permitting evaluation of current and past malaria infection, anemia, placental maturity, and inflammation. Using RNAscope® hybridization we were able to visualize cell-specific gene expression patterns in the formalin-fixed paraffin-embedded (FFPE) specimens. Additionally, our method entailed mirrored sampling from the two cut faces of a cotyledon, one for the FFPE workflows and the other for storage in RNAlater™ and RNA-seq.

Processing and Sectioning Undecalcified Murine Bone Specimens

Preparation of mineralized tissue specimens for bone-specific staining encompasses a critical sequence of histological techniques that provides visualization of tissue and cellular morphology. Bone specimens are fixed in 10% neutral buffered formalin (NBF), dehydrated in graded ethanol (EtOH) solutions (and optionally cleared in xylene), infiltrated and embedded in polymethyl methacrylate (methyl methacrylate or MMA), classically sliced into 4-10 micrometer (μm) sections, and stained with bone-specific histological stains such as von Kossa (with either nuclear fast red solution counterstain or MacNeal's tetrachrome counterstain), modified Goldner's trichrome, Alizarin Red S, Safranin O, and tartrate-resistant acid phosphatase (TRAP) stain. Here, we describe the tissue processing of mineralized mouse bones from dissection to staining for histological analysis by light microscopy.

Effects of short and long-term alcohol-based fixation on Sprague-Dawley rat tissue morphology, protein and nucleic acid preservation

Safety concerns on the toxic and carcinogenic effects of formalin exposure have drawn increasing attention to the search for alternative low risk fixatives for processing tissue specimens in laboratories worldwide. Alcohol-based fixatives are considered some of the most promising alternatives. We evaluated the performance of alcohol-fixed paraffin-embedded (AFPE) samples from Sprague-Dawley (SD) rats analyzing tissue morphology, protein and nucleic acid preservation after short and extremely long fixation times (up to 7 years), using formalin-fixed paraffin-embedded (FFPE) samples as a comparator fixative. Following short and long-term alcohol fixation, tissue morphology and cellular details in tissues, evaluated by scoring stained sections (Hematoxylin-Eosin and Mallory's trichrome), were optimally preserved if compared to formalin fixation. Immunoreactivity of proteins (Ki67, CD3, PAX5, CD68), evaluated by immunohistochemistry, showed satisfactory results when the fixation period did not exceed 1 year. Finally, we confirm the superiority of alcohol fixation compared to formalin, in terms of quantity of nucleic acid extracted from paraffin blocks, even after an extremely long time of alcohol fixation. Our results confirm that alcohol fixation is a suitable and safe alternative to formalin for pathological evaluations. There is a need for standardization of formalin-free methods and harmonization of diagnosis in pathology department worldwide.

Tissue fixation and the effect of molecular fixatives on downstream staining procedures

It is impossible to underplay the importance of fixation in histopathology. Whether the scientist is interested in the extraction of information on lipids, proteins, RNA or DNA, fixation is critical to this extraction. This review aims to give a brief overview of the current “state of play” in fixation and focus on the effect fixation, and particularly the effect of the newer brand of “molecular fixatives” have on morphology, histochemistry, immunohistochemistry and RNA/DNA analysis. A methodology incorporating the creation of a fixation tissue microarray for the study of the effect of fixation on histochemistry is detailed.

Tips and techniques for processing and sectioning undecalcified murine bone specimens

Preparation of mineralized tissue specimens for bone-specific staining encompasses a critical sequence of histological techniques that provides visualization of tissue and cellular morphology. Bone specimens are fixed in 10 % neutral-buffered formalin, dehydrated in graded ethanol (EtOH) solutions (and optionally cleared in xylene), infiltrated and embedded in polymethyl methacrylate (methyl methacrylate), classically sliced into 4-10 micrometer (μm) sections, and stained with bone-specific histological stains such as von Kossa (with either nuclear fast red solution counterstain or MacNeal's tetrachrome counterstain), modified Goldner's trichrome, and alizarin red S stain. Here, we describe the tissue processing of mineralized mouse bones from dissection to staining for histological analysis by light microscopy.

Evaluation of fixation methods for demonstration of Neoparamoeba perurans infection in Atlantic salmon, Salmo salar L., gills

Formaldehyde-based fixatives are generally employed in histopathology despite some significant disadvantages associated with their usage. Formaldehyde fixes tissue by covalently cross-linking proteins, a process known to mask epitopes which in turn can reduce the intensity of immunohistochemical stains widely used in disease diagnostics. Additionally, formaldehyde fixation greatly limits the ability to recover DNA and mRNA from fixed specimens to the detriment of further downstream molecular analyses. Amoebic gill disease (AGD) has been reliably diagnosed from histological examination of gills although complementary methods such as in situ hybridization (ISH) and polymerase chain reaction (PCR) are required to confirm the presence of Neoparamoeba perurans, the causative agent of AGD. As molecular techniques are becoming more prevalent for pathogen identification, there is a need to adapt specimen collection and preservation so that both histology and molecular biology can be used to diagnose the same sample. This study used a general approach to evaluate five different fixatives for Atlantic salmon, Salmo salar L., gills. Neutral-buffered formalin and seawater Davidson's, formaldehyde-based fixatives commonly used in fish histopathology, were compared to formalin-free commercial fixatives PAXgene®, HistoChoice™MB* and RNAlater™. Each fixative was assessed by a suite of analyses used to demonstrate AGD including routine histochemical stains, immunohistochemical stains, ISH and DNA extraction followed by PCR. All five fixatives were suitable for histological examination of Atlantic salmon gills, with seawater Davidson's providing the best quality histopathology results. Of the fixatives evaluated seawater Davidson's and PAXgene® were shown to be the most compatible with molecular biology techniques. They both provided good DNA recovery, quantity and integrity, from fixed and embedded specimens. The capacity to preserve tissue and cellular morphology in addition to allowing molecular analyses of the same specimens makes seawater Davidson's and PAXgene® appear to be the best fixation methods for diagnosis and research on AGD in Atlantic salmon gills.

Extraction of nucleic acids from ancient formalin- and ethanol-preserved specimens of the tapeworm Bertiella studeri: which method works best?

In this study we show that intact DNA can be recovered from both alcohol- and formalin-preserved specimens of the parasitic tapeworm Bertiella studeri for >1 yr after the original fixation and can be successfully amplified and quantified using real-time polymerase chain reaction (RT-PCR). Three different DNA extraction techniques on formalin- and alcohol-fixed material were evaluated to determine which is best suited for obtaining DNA of sufficient yield and purity to be used in downstream applications such as RT-PCR. These techniques included a first organic extraction procedure with an extensive washing step based on a glycine-containing buffer, a second organic extraction procedure that omits the glycine-containing buffer and halves the number of washes in organic solvents, and a third procedure that involves the use of a silica-based DNA binding column from Qiagen(©). The quality of extracted DNA was first examined by agarose gel electrophoresis and ethidium bromide staining and the concentrations were evaluated by OD260. We then used an RT-PCR Applied Biosystems TaqMan® Fluorogenic 5' Nuclease Gene Expression Assay based on the detection of a universal eukaryotic 18S rRNA gene sequence to evaluate the efficiency of the 3 methods. Here we report that, first, the use of a silica column-based DNA extraction technique results in the maximum yield of DNA, on average 55% higher than for the organic extraction methods; second, the use of glycine as a formaldehyde-binding agent in the washing buffer does not necessarily result in a better DNA yield and; third, specimens preserved in ethanol result in significantly higher yields of amplifiable DNA than do specimens preserved in formalin. We, therefore, strongly recommend the use of ethanol as the appropriate fixative if specimens are to be used for molecular work. This is the first report of DNA extraction from preserved specimens of Bertiella studeri.

Validation of a postfixation tissue storage and transport medium to preserve histopathology and molecular pathology analyses (total and phosphoactivated proteins, and FISH)

Tumor biomarker studies are integral to oncology clinical trials but may yield artifactual results owing to variation in sample procurement and processing. Ethanol, 70% vol/vol, was validated as a sample transport medium using markers of the PI3K/Akt/mTOR pathway. BT474 tumor xenografts were excised and slices were immediately placed into formaldehyde and fixed for 24 hours. Fixed tissue slices were immediately processed into paraffin or transferred to 70% vol/vol ethanol and stored at room temperature for 1, 2, and 4 weeks before further processing. Freshly cut tissue sections were evaluated for pAKT(S473), HER2, pHER-2(Y1248), pS6(S235/236), and pS6(S240/244), Ki-67, and HER2 by fluorescence in situ hybridization and stained with H&E and Masson trichrome. No significant changes were observed when comparing samples stored in 70% ethanol for up to 4 weeks with immediately processed tissue. Ethanol, 70% vol/vol, provides a safe storage medium for formaldehyde-fixed tumor tissue, facilitating sample transport during multicenter clinical trials.

Theory and practice of combining coagulant fixation and microwave histoprocessing

The German, F. Blum, introduced formalin as a fixative in 1893. Formalin rapidly became popular for hardening and preserving gross human and animal specimens. As a result, microscopy for diagnostic pathology by combining paraffin embedding and formalin fixation was developed. Alcohol-based fixatives have coagulation of proteins as their main preservative effect. Because there is no cross-linking, immunostaining is not compromised, and DNA and RNA is not damaged. Ethyl alcohol was used by Dutch scientists of the 18th century, but was replaced by the cheaper formalin. Addition of low molecular weight polyethylene glycol (PEG) optimized the coagulant fixative, Kryofix. The polyethylene glycol prevents excessive hardening and enhances the speed of coagulation of proteins. Kryofix was used on a large scale for skin biopsies in Leiden between 1987 and 2001. DNA preservation by the formulated coagulant fixative, BoonFix, is related to the concentration of ethyl alcohol, PEG and acetic acid. BoonFix has been used since 2004 in Leiden for over 40,000 diagnostic skin biopsies and more than 100,000 cervical samples. A literature review and three decades of experience with coagulant, formalin-free fixatives in pathology suggest that when health authorities realize that formalin invalidates expensive tests, it might eventually be eliminated legislatively from diagnostic pathology. Finally, coagulant fixation is optimal for microwave histoprocessing where ethyl alcohol is followed by isopropanol.

The use of Histochoice for histological examination of articular and growth plate cartilages, intervertebral disc and meniscus

Histochoice is a proprietary nontoxic, non-cross-linking fixative designed by the manufacturer to replace formaldehyde based fixation protocols. We compared Histochoice and formalin fixation for several cartilaginous tissues including, articular and growth plate cartilage, meniscus and intervertebral disc. The tissues were stained with general histology stains including toluidine blue for tissue proteoglycans, picrosirius red to evaluate collagenous organization, and hematoxylin and eosin to assess cell morphology. The chondroitin sulfate and heparin sulfate substituted proteoglycans aggrecan and perlecan were also immunolocalized in some of the tissues to provide a comparison. Histochoice did not fix deep into the tissue blocks resulting in focal loss of aggrecan and other matrix components from the more central regions of the blocks. This was evident in toluidine blue stained sections of immature tibial articular cartilage where loss of glycosaminoglycan was significant in Histochoice fixed tissues. Histochoice fixation worked well, however, in the aggrecan and perlecan immunohistology applications where its non-cross-linking traits were conducive to epitope retrieval and identification by primary antibodies to extracellular matrix components.

Histomorphologic assessment of formalin substitute fixatives for diagnostic surgical pathology

CONTEXT

In 1987, the Formaldehyde Standard became law in the United States, alerting laboratory workers to the potential carcinogenicity of formaldehyde. As a result, a variety of proprietary fixatives were developed for use in surgical pathology.

OBJECTIVE

To assess histomorphology with different formalin substitute fixatives.

DESIGN

Four experienced board-certified surgical pathologists examined 7 specimens (hepatocellular carcinoma, ovarian sex cord/stromal tumor, myxoid liposarcoma, uterine endometrioid adenocarcinoma, splenic follicular hyperplasia, infiltrating mammary carcinoma, and cecal signet ring carcinoma) fixed with formalin and 5 proprietary fixatives advertised as formalin replacements. In a blind study, the pathologists rated cellular outlines, cytoplasmic detail, nuclear detail, erythrocyte integrity, lymphocyte integrity, overall morphology, and overall staining in each case.

RESULTS

Formalin received the highest overall morphology and staining scores, followed by Glyo-Fixx, STF-Streck, Omnifix, Histochoice, and Histofix. Formalin also received the highest scores in cellular outline and erythrocyte integrity. Individually, some fixatives performed better in different areas than others. Glyo-Fixx performed as well as formalin for overall morphology and provided highest nuclear detail and lymphocyte appearance scores. Omnifix II gave best results for cytoplasmic detail.

CONCLUSION

In this blind study, formalin fixation provided the highest histomorphologic quality for tissue stained with hematoxylin-eosin and examined for diagnostic surgical pathology. Should the use of formalin be discontinued, pathologists will have to familiarize themselves with a different set of microscopic details associated with the replacement fixatives.

HistoChoice as an alternative to formalin fixation of undecalcified bone specimens

We compared histochemical and immunohistochemical staining as well as fluorochrome labeling in murine bone specimens that were fixed with 10% neutral buffered formalin to those fixed with HistoChoice. We showed that sections from undecalcified tibiae fixed for 4 h in HistoChoice resulted in enhanced toluidine blue and Von Kossa histochemical staining compared to formalin fixation. HistoChoice produced comparable or improved staining for alkaline phosphatase. Acid phosphatase localization was better in formalin fixed specimens, but osteoclasts were visualized more easily in HistoChoice fixed specimens. As expected, immunohistochemical labeling was antibody dependent; some antibodies labeled better in HistoChoice fixed specimens while others were better in formalin fixed specimens. Toluidine blue, Von Kossa, and alkaline phosphatase staining of sections fixed for 12 h produced sections that were similar to 4 h fixed sections. Fixation for 12 h preserved acid phosphatase activity better. Increasing fixation to 12 h affected immunolocalization differentially. Bone sialoprotein labeling in HistoChoice fixed specimens was comparable to formalin fixed samples. On the other hand, after 12 h formalin fixation, osteocalcin labeling was comparable to HistoChoice. For most histochemical applications, fixing murine bone specimens for 4 h with HistoChoice yielded superior staining compared to formalin fixation. If immunohistochemical localization is desired, however, individual antibodies must be tested to determine which fixation process retains antigenicity better. In addition, there was no detectable difference in the intensity of fluorochrome labeling using either fixative. Finally, fixation duration did not alter the intensity of labeling.

Expression of somatostatin in the adult and developing mouse kidney

BACKGROUND

Somatostatin (somatotropin release inhibiting factor) (SRIF) has potent antiproliferative and antisecretory actions. In the adult kidney, somatostatin alters renal blood flow, ion transport, and water permeability. While some evidence suggests that SRIF may be produced by adult kidney tubular cells, the specific tubules generating SRIF are unknown. Somatostatin has also been detected in a variety of embryonic tissues, although it has not been described in the developing kidney. Our objective was to determine the expression pattern of SRIF in both the adult and embryonic mouse kidney.

METHODS

We performed reverse transcriptase-polymerase chain reaction (RT-PCR) and immunofluorescence for SRIF in developing and adult mouse kidney tissues. We localized SRIF by dual or serial labeling immunofluorescence with specific markers.

RESULTS

Somatostatin mRNA was present in kidneys throughout embryogenesis and into adulthood. Starting at embryonic day (E) 12.5, SRIF was strongly expressed at the interface of the metanephric mesenchymal cells and the basolateral surfaces of ureteric bud trunks. Starting at E16.5, the staining at the interface was confined to the peripheral ureteric bud trunks and the clefts of newly dividing ureteric bud ampullae. In older embryos, SRIF also appeared in medullary tubules that appeared to be maturing thin descending limbs of Henle. In the adult kidney, SRIF proteins localized exclusively to medullary thin descending limbs of the Henle loop.

CONCLUSION

In embryonic kidneys, SRIF is expressed first at the interface of the metanephric mesenchyme and basolateral ureteric bud and later in maturing thin descending limbs of Henle. Expression in the thin descending limb persists in the adult kidney.

Antibodies that label paraffin-embedded mouse tissues: a collaborative endeavor

Histology and immunohistochemistry are important tools in the study of human diseases and their respective animal models. The study of mouse models has been hampered by the absence of a large set of mouse-specific antibodies adapted to paraffin-embedded tissues. A total of 196 antibodies were tested on paraffin-embedded mouse tissues preserved in five different fixatives (Fekete's acid-alcohol-formalin, 10% neutral buffered formalin, 4% paraformaldehyde, IHC Zinc Fixative, and Bouin's fixative). The antibodies were targeted to proteins of the cytoplasm (n = 100), plasma membrane (n = 48), nucleus (n = 36), extracellular compartment (n = 5), cytoplasm/cell membrane (n = 4), and viral proteins (n = 3). A total of 83 antibodies provided an adequate signal to noise ratio. Of these, adequate labeling required heat-mediated epitope retrieval or enzymatic digestion for 32 and 8 antibodies, respectively. Epitope recognition was best for tissues fixed with Fekete's acid-alcohol-formalin. However, some proteins could be detected only in IHC Zinc Fixative, confirming that there is no single fixative suitable for the preservation of all epitopes. Four of 13 antibodies that failed to label their cellular targets on tissue sections successfully labeled whole-mount tissues, indicating that tissue processing plays an important role in epitope degradation. Regularly updated information on immunohistochemistry of normal and neoplastic mouse tissues is accessible online at (http://tumor.informatics.jax.org); links to antibody suppliers' web sites are provided.

Overexpression of the alpha1B-adrenergic receptor causes apoptotic neurodegeneration: multiple system atrophy

Progress toward elucidating the function of alpha1B-adrenergic receptors (alpha1BARs) in the central nervous system has been constrained by a lack of agonists and antagonists with adequate alpha1B-specificity. We have obviated this constraint by generating transgenic mice engineered to overexpress either wild-type or constitutively active alpha1BARs in tissues that normally express the receptor, including the brain. All transgenic lines showed granulovacular neurodegeneration, beginning in alpha1B-expressing domains of the brain and progressing with age to encompass all areas. The degeneration was apoptotic and did not occur in non-transgenic mice. Correspondingly, transgenic mice showed an age-progressive hindlimb disorder that was parkinsonian-like, as demonstrated by rescue of the dysfunction by 3, 4-dihydroxyphenylalanine and considerable dopaminergic-neuronal degeneration in the substantia nigra. Transgenic mice also had a grand mal seizure disorder accompanied by a corresponding dysplasia and neurodegeneration of the cerebral cortex. Both behavioral phenotypes (locomotor impairment and seizure) could be partially rescued with the alpha1AR antagonist terazosin, indicating that alpha1AR signaling participated directly in the pathology. Our results indicate that overstimulation of alpha1BAR leads to apoptotic neurodegeneration with a corresponding multiple system atrophy indicative of Shy-Drager syndrome, a disease whose etiology is unknown.

Cell, matrix changes and alpha-smooth muscle actin expression in repair of the canine meniscus

Processes in the repair of a crevice in the knee joint meniscus were investigated in 10 dogs. Two 2-mm cylindrical plugs from each medial meniscus were removed, rendered acellular by freezing and thawing, and then reinserted into the meniscus. Dogs were euthanized at intervals of 3-52 weeks after surgery. The crevice between the plug and meniscus at 3 weeks after surgery was filled with a tissue containing alpha-smooth muscle actin-positive cells. One year after surgery, the plug had remodeled and was populated with spindle-shaped and fibrochondrocyte-like cells. The plug had an appearance intermediate between that of hyaline and fibrocartilage at this time, with a seamless integration in sites between the remodeled plug and the surrounding meniscus. alpha-smooth muscle actin-positive cells were concentrated at the interface of the remodeled plug and adjacent meniscus and at the surface of the plug. Therefore, remodeling of both the plug and meniscal tissue and the participation of alpha-smooth muscle actin-positive cells appear essential for integration of the plug into the adjacent meniscal tissue. Cells in the superficial zone of the meniscus seem to be active in the repair process. A change in both the phenotype of the cells and the quality of the matrix toward a more hyaline state appears to be an integral part of the remodeling process in the meniscus.

Fixation and epitope retrieval in diagnostic immunohistochemistry: a concise review with practical considerations

Diagnostic immunohistochemistry (DIHC) is an extremely valuable technological development that has revolutionized the practice of surgical pathology over the past 25 years. Like any laboratory procedure, however, the precise concatenation of methodological details that are used by any given investigator has a major effect on final results. In this overview, the authors consider several of these variables and illustrate how they may be optimized in an effective and efficient approach to quality assurance in the DIHC laboratory. The great majority of this discussion concerns processing factors as they affect paraffin section-based immunohistology because that is still, by far, the most common adjunctive morphologic procedure (AMP) used in hospital pathology. However, information is also presented on elements of tissue processing that affect other analyses as well. The material presented here is a direct reflection of the conjoint experiences of the authors. Although we discuss our preferences regarding many technical aspects of this discipline, we certainly do not mean to imply that ours are the only methods that should be utilized. Nevertheless, it is hoped that they may serve to crystallize basic concepts surrounding fixation, processing, and optimal performance of AMPs.