Formaldehyde substitute fixatives. Analysis of macroscopy, morphologic analysis, and immunohistochemical analysis

Rapid in-solution preparation of somatic and meiotic plant cell nuclei for high-quality 3D immunoFISH and immunoFISH-GISH

BACKGROUND

Though multicolour labelling methods allow the routine detection of a wide range of fluorescent (immuno)probe types in molecular cytogenetics, combined applications for the simultaneous in situ detection of proteins and nucleic acids are still sporadic in plant cell biology. A major bottleneck has been the availability of high-quality plant nuclei with a balance between preservation of 3D ultrastructure and maintaining immunoreactivity. The aim of this study was to develop a quick and reliable procedure to prepare plant nuclei suitable for various combinations of immunolabelling and fluorescence in situ hybridisation methods (immunoFISH-GISH).

RESULTS

The mechanical removal of the cell wall and cytoplasm, instead of enzymatic degradation, resulted in a gentle, yet effective, cell permeabilisation. Rather than manually releasing the nuclei from the fixed tissues, the procedure involves in-solution cell handling throughout the fixation and the preparation steps as ended with pipetting the pure nuclei suspension onto microscope slides. The optimisation of several critical steps is described in detail. Finally, the procedure is shown to be compatible with immunolabelling, FISH and GISH as well as their simultaneous combinations.

CONCLUSION

A simple plant cell nuclei preparation procedure was developed for combined immunolabelling-in situ hybridisation methods. The main and critical elements of the procedure are: a short period of fixation, incorporation of detergents to facilitate the fixation of tissues and the penetration of probes, tissue grinding to eliminate unwanted cell components, and an optimal buffer to handle nuclei. The procedure is time efficient and is easily transferable without prior expertise.

Molecular Phylogenetic Analysis of Paracoccidioides Species Complex Present in Paracoccidioidomycosis Patient Tissue Samples

Paracoccidioidomycosis (PCM) is the main and most prevalent systemic mycosis in Latin America, that until recently, it was believed to be caused only by Paracoccidioides brasiliensis (P. brasiliensis). In 2006, researchers described three cryptic species: S1, PS2, PS3, and later, another one, PS4. In 2009, Paracoccidioides lutzii (Pb01-like) was described, and in 2017, a new nomenclature was proposed for the different agents: P. brasiliensis (S1), P. americana (PS2), P. restrepiensis (PS3), and P. venezuelensis (PS4). These species are not uniformly distributed throughout Latin America and, knowing that more than one cryptic species could coexist in some regions, we aimed to identify those species in patients’ biopsy samples for a better understanding of the distribution and occurrence of these recently described species in Botucatu region. The Hospital of Medical School of Botucatu—UNESP, which is a PCM study pole, is located in São Paulo State mid-west region and is classified as a PCM endemic area. Genotyping analyses of clinical specimens from these patients that have been diagnosed and treated in our Hospital could favor a possible correlation between genetic groups and mycological and clinical characteristics. For this, molecular techniques to differentiate Paracoccidioides species in these biopsies, such as DNA extraction, PCR, and sequencing of three target genes (ITS, CHS2, and ARF) were conducted. All the sequences were analyzed at BLAST to testify the presence of P. brasiliensis. The phylogenetic trees were constructed using Mega 7.0 software and showed that 100% of our positive samples were from S1 cryptic species, therefore P. brasiliensis. This is important data, demonstrating the predominance of this species in the São Paulo State region.

Automated variable power cold microwave tissue processing: A novel universal tissue processing protocol without using formaldehyde and xylene

The tissue processing technique is used to preserve the biological structure of tissue samples harvested from biopsy as closely as possible to their in vivo state for the diagnoses and study of disease on the cellular level. This process includes fixation, dehydration, clearing, paraffin infiltration. The protocol follows paraffin block embedding, microtome slicing, staining, and microscope slide studying. Tissue processing is a time-sensitive task as histopathologists must rapidly prevent the decomposition of tissue samples and promptly provide diagnoses on time. However, there are different tissue processing protocols for processing tissues with different types and sizes. Fatty tissues and tissues thicker than 1.5 mm are more susceptible to human errors when choosing a proper tissue processing protocol when preparing separate batches of tissues. In this research, a novel automated variable power cold microwave tissue processor was developed using a universal tissue processing protocol (processing time of 97 min) to simultaneously process all tissue types up to 4 mm in thickness. The tissue processor operated with a relatively smaller number of reagents without formaldehyde or xylene. These materials cause severe health and safety issues for humans and the environment. The quality of healthy and diseased processed tissues (sizes 1×1×1 to 24×15×4 mm) of fatty, thyroid, breast, placenta, skin, prostate, stomach, and bladder was examined under a light microscope by defining MAS (morphology, artifacts, and staining) criteria for evaluating cellular details, tissue arrangement, tissue integrity, stain uptake, and visual distinction of a tissue structure in light microscopy. It was found that the new tissue processor has successfully processed both healthy and diseased fatty and nonfatty tissue samples, while all tissue samples also met MAS criteria. Light microscopy showed outstanding integrity and arrangement in the tissue structures with an excellent visual distinction.

Comparison of Fixation Methods for the Detection of Claudin 1 and E-Cadherin in Breast Cancer Cell Lines by Immunofluorescence

The tight junction membrane protein claudin 1 and the adherens junction protein E-cadherin play critical roles in cell-cell communication and in cell signaling. As a result, their protein levels and distribution in cancer have been a focus of cancer researchers in recent years. The loss of sensitivity to contact inhibition and the establishment of invasive properties in cancer are thought to be a result of the mislocalization of these membrane proteins to the cytoplasm. However, reports on their distribution and levels have been inconsistent. It is therefore critical that the techniques used to determine the cellular localization of these proteins be both consistent and reliable. This study was undertaken to determine the optimal fixation method, methanol or formalin, for the detection of claudin 1 and E-cadherin by immunofluorescence in five different human breast cancer cell lines. Both methods exhibited staining of the cell membrane and cytoplasm, but the strongest and most distinct signals were obtained using methanol fixation. Interestingly, cell-specific differences were also observed that appeared to be associated with levels of claudin 1 and E-cadherin as seen by Western blotting. Therefore, when evaluating cellular localization of the junction proteins claudin 1 and E-cadherin, expression level and cell type differences must be considered.

The effect of conventional preservatives on spicule length of Heligmosomoides bakeri (Nematoda, Heligmosomidae)

Nematode spicules vary in shape and size even between closely related species and, therefore, constitute key characters in nematode taxonomy for distinguishing between species. Spicules are seldom measured on fresh specimens, but rather at some time after extraction from culled hosts and after a period of preservation of the worms in chemical fixatives or by freezing. We carried out two experiments to assess the effects of freezing in Hanks' balanced salt solution, 70% or 80% ethanol and 10% formalin (both of the latter at room temperature and after storage at -80°C) on spicule length of Heligmosomoides bakeri at two time intervals after extraction from mice (Experiment 1, one and four weeks; Experiment 2, one and four months). In Experiment 1, no significant differences were detected, although there was some variation between treatments and over time. In Experiment 2, spicule length varied significantly between treatments and over time, the greatest shrinkage being in 80% ethanol and the least in 10% formalin. However, overall variation in spicule length was very limited, accounting for no more than 5.03% change in length over time and 4.95% between treatments at any of the periods of assessment. Therefore, while whole nematodes can shrivel and shrink in preservatives, making many measurements unreliable, our data indicated that spicule lengths are very little changed by preservation techniques over time, and so spicule length remains as a reliable taxonomic character.

Comparison of the Benzanthrone Luminophores: They Are Not Equal for Rapid Examination of Parafasciolopsis fasciolaemorpha (Trematoda: Digenea)

Luminescent derivatives of benzanthrone are becoming more useful based on their light-absorbing and fluorescent-emitting properties. Our previous studies showed that luminescent staining properties of the same benzanthrone dye differ for variable parasite samples. Therefore, two types of benzanthrone dyes were prepared. One has a strongly basic amidine group and a halogen atom, and the other has an amide moiety and a tertiary amine group. Trematoda Parafasciolopsis fasciolaemorpha is a liver fluke of a moose (Alces alces) and has a significant influence on the health and abundance of the moose population. Staining protocols for parasite P. fasciolaemorpha specific organ or organ systems imaging are mostly time-consuming and labor-intensive. The study aimed to compare the fixation technique and the staining protocol by synthesized benzanthrone luminescent dyes to determine detailed morphology, anatomical arrangement of the organ systems and gross organization of the muscle layers of P. fasciolaemorpha using confocal laser scanning microscopy. Luminophores were tested for samples fixed in different fixatives. Developed dyes and staining protocol resulting in imaging of all parts of trematode without additional sample preparation procedures, which usually are required for parasite examination. Obtained results confirmed that the most qualitative results could be reached using 3-N-(2-piperidinylacetamido)benzanthrone dye which has amide moiety and a tertiary amine group. Based on obtained results, 3-N-(2-piperidinylacetamido)benzanthrone gave more qualitative parasite visualization than 2-bromo-3-N-(N′,N′-dimethylformamidino)benzanthrone.

Comparison of histological and computed tomographic measurements of pig lung bronchi

Aim

Light microscopy is used as template in the evaluation and further development of medical imaging methods. Tissue shrinkage caused by histological processing is known to influence lung tissue dimensions. In diagnosis of COPD, computed tomography (CT) is widely used for automated airway measurement. The aim of this study was to compare histological and computed tomographic measurements of pig lung bronchi.

Methods

Airway measurements of pig lungs were performed after freezing under controlled inflation pressure in a liquid nitrogen bath. The wall thickness of seven bronchi was measured via Micro-CT and CT using the integral-based method (IBM) and the full-width-at-half-maximum method (FWHM) automatically and histologically on frozen and paraffin sections. Statistical analysis was performed using the Wilcoxon test, Pearson's correlation coefficient with a significance level at p<0.05, scatter plots and Bland–Altman plots.

Results

Bronchial wall thickness was smallest in frozen sections (median 0.71 mm) followed by paraffin sections (median 0.75 mm), Micro-CT (median 0.84 mm), and CT measurements using IBM (median 0.68 mm) and FWHM (median 1.69 mm). Statistically significant differences were found among all tested groups (p<0.05) except for CT IBM and paraffin and frozen sections and Micro-CT. There was high correlation between all parameters with statistical significance (p<0.05).

Conclusions

Significant differences in airway measurement were found among the different methods. The absolute measurements with CT IBM were closest to the histological results followed by Micro-CT, whereas CT FWHM demonstrated a distinct divergence from the other groups.

Automated measurement techniques advance diagnosis of lung diseases. Pig bronchi wall size varies between Micro-CT, CT IBM, CT FWHM and histology. CT IBM is closest to histological results, followed by Micro-CT. CT FWHM differs highly from all other groups.https://bit.ly/3iRXSrv

Clinical validation of full genotyping CLART® HPV4S assay on SurePath and ThinPrep collected screening samples according to the international guidelines for human papillomavirus test requirements for cervical screening

Background

To ensure the highest quality of human papillomavirus (HPV) testing in primary cervical cancer screening, novel HPV assays must be evaluated in accordance with the international guidelines. Furthermore, HPV assay with genotyping capabilities are becoming increasingly important in triage of HPV positive women in primary HPV screening. Here we evaluate a full genotyping HPV assay intended for primary screening.

Methods

The CLART® HPV4S (CLART4S) assay is a newly developed full-genotyping assay detecting 14 oncogenic (16, 18, 31, 33, 35, 39, 45, 51, 52, 56, 58, 59, 66, 68) and two non-oncogenic HPV genotypes (6, 11). It was evaluated using SurePath and ThinPrep screening samples collected from the Danish and Swedish cervical cancer screening programs, respectively. For calculation of sensitivity, 81 SurePath and 80 ThinPrep samples with confirmed ≥CIN2 were assessed. For clinical specificity analysis, 1184 SurePath and 1169 ThinPrep samples from women with <CIN2 histology were assessed. Sensitivity and specificity of the CLART4S assay was compared to an established reference test; the MGP-PCR (Modified General Primers GP5+/6+ with genotyping using Luminex). Inter and intra laboratory reproducibility of the assay was assessed using 540 SurePath and 520 ThinPrep samples, respectively. The genotype concordance between CLART4S and MGP-PCR was also assessed.

Results

In SurePath samples, the sensitivity of CLART4S was 0.90 (MGP-PCR =0.93) and the specificity was 0.91 (MGP-PCR = 0.91); In ThinPrep samples the sensitivity of CLART4S was 0.98 (MGP-PCR = 1.00) and specificity was 0.94 (MGP-PCR =0.87). The CLART4S was shown to be non-inferior to that of MGP-PCR for both sensitivity (p = 0.002; p = 0.01) and specificity (p = 0.01; p = 0.00) in SurePath and ThinPrep samples, respectively. Intra-laboratory reproducibility and inter-laboratory agreement was met for both media types. The individual genotype concordance between CLART4S and MGP-PCR was good agreement for almost all 14 HPV genotypes in both media types.

Conclusions

The CLART4S assay was proved non-inferior to the comparator assay MGP-PCR for both sensitivity and specificity using SurePath and ThinPrep cervical cancer screening samples from the Danish and Swedish screening programs, respectively. This is the first study to demonstrate clinical validation of a full-genotyping HPV assay conducted in parallel on both SurePath and ThinPrep collected samples.

Clinical and Analytical Performance of the BD Onclarity HPV Assay with SurePath Screening Samples from the Danish Cervical Screening Program Using the VALGENT Framework

The Validation of HPV Genotyping Tests (VALGENT) framework is an international cooperation designed to evaluate human papillomavirus (HPV) assays with genotyping capabilities.

The Validation of HPV Genotyping Tests (VALGENT) framework is an international cooperation designed to evaluate human papillomavirus (HPV) assays with genotyping capabilities. Here, we assessed the performance of the BD Onclarity assay using Danish SurePath cervical screening samples collected under the fourth VALGENT installment, consisting of 998 consecutive samples from a screening population and 297 enriched samples with abnormal cytology (100 with atypical squamous cells of undetermined significance [ASCUS], 100 with low-grade squamous intraepithelial lesions [LSIL], and 97 with high-grade squamous intraepithelial lesions [HSIL]). The Onclarity assay detects six HPV genotypes individually (genotypes 16, 18, 31, 45, 51, and 52) and eight genotypes in three bulks (genotypes 33 and 58; genotypes 56, 59, and 66; and genotypes 35, 39, and 68). The clinical performance of the Onclarity assay for the detection of cervical intraepithelial neoplasia of grade 2 or worse (≥CIN2) and of two consecutive cytology outcomes negative for intraepithelial lesion or malignancy (2×NILM) was assessed relative to that of the GP5+/6+ PCR-enzyme immunoassay (GP-EIA) by a noninferiority test. The relative sensitivity for ≥CIN2 was 1.00 (95% confidence interval [CI], 0.97 to 1.04), and the relative specificity for 2×NILM was 1.04 (95% CI, 1.02 to 1.06). The Onclarity assay was found to be noninferior to the GP-EIA in terms of both sensitivity (P = 0.0006) and specificity (P < 0.0001). The type-specific performance of the Onclarity assay was also assessed, using the GP5+/6+ PCR with Luminex genotyping (GP-LMNX) as the comparator. The Onclarity assay showed good concordance for almost all HPV genotype groups. A stability analysis of SurePath samples was also performed, where a SurePath aliquot was stored refrigerated for 7 months and the internal control of the Onclarity assay was used as a marker for cellularity. The threshold cycle (C_T) value was the same (24.8) in the first and second Onclarity runs, showing that a SurePath sample can be stored refrigerated for 7 months and still remain a valid test specimen.

Occupational exposure to airborne formaldehyde in hospital: setting an automatic sampling system, comparing different monitoring methods and applying them to assess exposure

BACKGROUND

In recent years, under-vacuum sealing (UVS) and containers with formalin encapsulated in the lid have been proposed for the reduction of occupational exposure to airborne formaldehyde (FA) in healthcare environments.

OBJECTIVES

We are presenting a study focused on the assessment of FA in hospitals: an automatic sampling system was set, different sampling devices were compared, and the concentration of FA was assessed, following its use in different scenarios.

METHODS

Three different devices for sampling/measuring FA were compared. They are based on: 1. silica gel cartridges impregnated with 2,4-dinitrophenylhydrazine (2,4-DNPH); 2. SPME® fiber using O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine; 3. direct reading commercial instrumentation. Three typical scenarios using FA were investigated: operating theatres where small biopsies are soaked into closed-circuit system 4% FA containers, secretariat of pathology laboratories during the registration of biopsies and pathology laboratories during the filling procedure by UVS and the slicing of biopsies.

RESULTS

The automatic sampling system allowed short-, long-, and in continuous-sampling time to measure airborne FA. Different sampling devices provided comparable results when tested to assess FA concentration ranging from 0.020-0.320 ppm in a test chamber, although  the devices based on 2,4-DNPH were  the best in terms of sensitivity and accuracy. The results of 246 samples showed that the FA concentration was less than 0.04 ppm in 91% of the measurements.

CONCLUSIONS

The automatic methods efficiently allow sampling and measurement of FA in hospital settings. When using safe practices, the concentration of FA is well below occupational limit values.

PreservCyt Is an Optimal Fixative that Permits Cytologic and Molecular Analyses of Vitreoretinal Lymphoma Biopsies

Purpose: Vitreoretinal lymphoma (VRL) is a potentially fatal intraocular malignancy. Diagnosis is hampered by poor preservation of morphology and DNA/RNA integrity, which precludes adjunctive molecular analysis. We aimed to determine the optimum fixative protocol for VRL biopsies that permits cytology, IHC/flow cytometry and molecular analyses.Methods: Six fixatives were compared on cultured Pfeiffer cells used as a cellular model. Cells were fixed and evaluated on cellular morphology, antibody staining, DNA/RNA amount and integrity. VRL clinical cases were used as validation and proof-of-concept.Results: PreservCyt was the best fixative for preserving cellular morphology and high-quality RNA/DNA from vitreous fluid biopsies. Cells from clinical VRL cases fixed with PreservCyt showed adequate cellular morphology and IHC positivity. Sufficient DNA was obtained for IgH clonality and MYD88 mutation detection using remnant cytological fluid.Conclusions: PreservCyt maintains good morphology and RNA/DNA integrity suggesting that it is a suitable fixative for VRL diagnosis and molecular analysis.

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 expansion of lung bronchi due to tissue processing for histology - A comparative analysis of paraffin versus frozen sections in a pig model

AIM

Tissue shrinking due to fixation and processing is well known. However, the degree of shrinking varies significantly with the tissue type as well as the processing method and is not well studied in various tissues. In daily pathological routine workflow, histological specimens from frozen and paraffin sections are performed from the same tissue. In the present study we compared the thickness of bronchus walls obtained from paraffin and frozen sections.

METHODS

Pig lungs were frozen in ventilated condition in liquid nitrogen and 36 bronchi were isolated after dissection. Frozen sections of 5 μm thickness were performed and the remaining tissue was fixed and embedded in paraffin after fixation in 4% formalin. Frozen and paraffin sections from the same cutting edge were analysed after haematoxylin and eosin staining by measuring the wall thickness of the bronchi using high power fields of 400-fold magnification. In each bronchus 40 measurements were implemented at different wall positions distributed over the entire wall area. Summed up, in each group 1440 wall measurements were performed in total. Statistical analysis was conducted using the Wilcoxon test and t-test as well as Pearson's correlation coefficient with a significance level at P < 0.05.

RESULTS

The bronchial wall thickness was significantly (p < 0.001) smaller in frozen sections (median: 0.50 mm; min: 0.37 mm; max: 0.97 mm) compared to paraffin sections (median: 0.58 mm; min: 0.35 mm; max: 1.06 mm). The median difference between paraffin and frozen sections was 0.05 mm (min: -0.11 mm; max: 0.22 mm). The wall thickness ratio of both groups was as follows: frozen/paraffin section = 0.8609, thus yielding a difference between paraffin and frozen of 13.91%. High correlation was found between wall thickness measurements on paraffin and frozen sections (R = 0.87, p < 0.001).

CONCLUSIONS

The bronchus wall thickness in the frozen section was 14% reduced compared to the paraffin section. In routine pathology as well as in scientific studies these results are of relevance, as airway wall thickness represents a relevant marker for pathological interpretation, especially using CT image techniques.

Probing natural substitute for formalin: Comparing honey, sugar, and jaggery syrup as fixatives

Background:

Since its discovery in 1859, formalin has been considered as the “gold standard” in tissue fixation. As formalin is highly toxic and carcinogenic, the quest for its substitute has started recently. Literature search reveals very sparse studies on natural substitute for formalin. Here, it is an attempt to explore eco-friendly, economical, and readily available natural substance for formalin substitute.

Aim:

The aim of our study was to evaluate the efficacy of natural fixatives such as honey, sugar, jaggery, and water in comparison to the standard fixative used like formalin.

Materials and Methods:

Fresh goat tissues (tongue) were fixed separately with buffered 10% formalin (positive control), honey, sugar syrup, jaggery syrup, and distilled water (negative control). 24 h fixation was done at room temperature followed by conventional processing and routine H and E staining. The stained sections were assessed for cytoplasmic and nuclear detail by three pathologists under light microscope and were graded accordingly.

Results:

The results showed statistically significant differences between jaggery with other natural fixatives for both nuclear details and cytoplasmic staining.

Conclusion:

The preservation of tissue by honey, sugar, and jaggery syrup was comparable to that of formalin. Among the three natural fixatives, jaggery syrup excelled. Hence, it can be considered as an equally effective formalin substitute.

Comparison of efficacy of local anesthetic solution, distilled water and normal saline as emergency fixatives

Context:

Adequate tissue fixation is fundamental to good quality histological sections. Owing to undesirable effects of 10% buffered formalin, its availability in clinics is questionable. Thus, the present study was conducted with a novel approach to fixation, together with the scope of finding fixative properties of more commonly used reagents available at the clinics.

Aims:

The present study was aimed to compare the efficacy of local anesthetic solution, normal saline (NS) and distilled water (DW) with that of 10% neutral-buffered formalin.

Settings and Design:

It is a single-blinded study where histological assessment of fixation was done to assert if the tissues procured were sufficient or insufficient for the clinical diagnosis with/without any problems.

Subjects and Methods:

Forty soft-tissue specimens obtained from 2 goat tongue were used. Tissues each were directly immersed in local anesthesia, DW, NS solution and formalin for 12 and 24 h each and labeled as Group I and Group II, respectively. The sections were evaluated for staining quality and were subjected to statistical analysis.

Statistical Analysis Used:

Kruskal–Wallis test was employed to assess the differences in histological quality scores. Comparison between the tissues of the two groups was estimated with Mann–Whitney U-test. Kappa Statistic was used to measure the interobserver variation.

Results:

There was a significant difference (P ≤ 0.05) in the efficacy of all the three emergency fixatives.

Conclusions:

On the basis of the results obtained, local anesthetic solution can be used as an emergency fixative.

Analysis of the Germinal Center Reaction in Tissue Sections

Germinal centers are short-lived microanatomical compartments with essential roles in adaptive immunity. These lymphoid structures can be identified in secondary lymphoid organs using both flow cytometry and immunohistological analyses, but only the latter provides useful architectural and spatial information. Here we describe how to use immunofluorescence and immunohistochemistry with specific antibodies to precisely highlight the cellular and architectural features of germinal centers, both in human and mouse secondary lymphoid organs, and to study their normal development and disturbance in disease.

Alcohol-based solutions for bovine testicular tissue fixation

Tissue fixation, a central element in histotechnology, is currently performed with chemical compounds potentially harmful for human health and the environment. Therefore, alternative fixatives are being developed, including alcohol-based solutions. We evaluated several ethanol-based mixtures with additives to study fixative penetration rate, tissue volume changes, and morphologic effects in the bovine testis. Fixatives used were Bouin solution, 4% formaldehyde (F4), 70% ethanol (E70), E70 with 1.5% glycerol (E70G), E70 with 5% acetic acid (E70A), E70 with 1.5% glycerol and 5% acetic acid (E70AG), and E70 with 1.5% glycerol, 5% acetic acid, and 1% dimethyl sulfoxide (DMSO; E70AGD). Five-millimeter bovine testicular tissue cubes could be completely penetrated by ethanol-based fixatives and Bouin solution in 2–3 h, whereas F4 required 21 h. Bouin solution produced general tissue shrinkage, whereas the other fixatives (alcohol-based and F4) caused tissue volume expansion. Although Bouin solution is an excellent fixative for testicular tissue, ethanol-based fixatives showed good penetration rates, low tissue shrinkage, and preserved sufficient morphology to allow identification of the stages of the seminiferous epithelium cycle, therefore representing a valid alternative for histotechnology laboratories. Common additives such as acetic acid, glycerol, and DMSO offered marginal benefits for the process of fixation; E70AG showed the best preservation of morphology with excellent nuclear detail, close to that of Bouin solution.

Antigen Masking During Fixation and Embedding, Dissected

Antigen masking in routinely processed tissue is a poorly understood process caused by multiple factors. We sought to dissect the effect on antigenicity of each step of processing by using frozen sections as proxies of the whole tissue. An equivalent extent of antigen masking occurs across variable fixation times at room temperature. Most antigens benefit from longer fixation times (>24 hr) for optimal detection after antigen retrieval (AR; for example, Ki-67, bcl-2, ER). The transfer to a graded alcohol series results in an enhanced staining effect, reproduced by treating the sections with detergents, possibly because of a better access of the polymeric immunohistochemical detection system to tissue structures. A second round of masking occurs upon entering the clearing agent, mostly at the paraffin embedding step. This may depend on the non-freezable water removal. AR fully reverses the masking due both to the fixation time and the paraffin embedding. AR itself destroys some epitopes which do not survive routine processing. Processed frozen sections are a tool to investigate fixation and processing requirements for antigens in routine specimens.

KINFix--A formalin-free non-commercial fixative optimized for histological, immunohistochemical and molecular analyses of neurosurgical tissue specimens

An optimal fixative should ideally combine the advantages of formalin fixation and freezing, allowing for good preservation of histology and molecular components, easy handling and storage, lack of toxicity, and low costs. Most of these criteria are fulfilled by ethanol-based solutions, and due to our good experience with the commercial RCL2 fixative, reflected by our published single-center trial, we initiated a multicenter ring trial. However, during its course, RCL2 was discontinued on the market. Therefore, we created our own agent, KINFix, composed of the same main constituents as RCL2, and employed it in our laboratory with similar results. Here we present our evaluation of the three fixatives formalin, RCL2, and KINFix from the perspective of histopathology as well as nucleic acid and protein analyses in comparison to fresh frozen tissues together with the multicenter ring trial data for RCL2. We observe that RCL2 and KINFix offer comparable histomorphology and superior template for molecular analyses than formalin. Moreover, KINFix as freely available fixative might overcome some of the difficulties related to the commercial agents. Therefore, we conclude that KINFix might be an attractive complement to formalin in tissue processing and advocate its use in neuropathological practice.

The BD Onclarity HPV Assay on Samples Collected in SurePath Medium Meets the International Guidelines for Human Papillomavirus Test Requirements for Cervical Screening

This study describes a validation of the BD Onclarity HPV (Onclarity) assay using the international guidelines for HPV test requirements for cervical cancer screening of women 30 years old and older using Danish SurePath screening samples. The clinical specificity (0.90, 95% confidence interval [CI] = 0.88 to 0.91) and sensitivity (0.97, 95% CI = 0.87 to 1.0) of the Onclarity assay were shown to be not inferior to the reference assay (specificity, 0.90 [95% CI = 0.88 to 0.92]; sensitivity, 0.98 [95% CI = 0.91 to 1.0]). The intralaboratory reproducibility of Onclarity was 97%, with a lower confidence bound of 96% (kappa value, 0.93). The interlaboratory agreement was 97%, with a lower confidence bound of 95% (kappa value, 0.92). The BD Onclarity HPV assay fulfills all the international guidelines for a new HPV test to be used in primarily screening. This is the first clinical validation of a new HPV assay using SurePath screening samples, and thus the Onclarity HPV assay is the first HPV assay to hold an international validation for both SurePath and ThinPrep.

A Buffered Alcohol-Based Fixative for Histomorphologic and Molecular Applications

Formalin-fixed paraffin-embedded (FFPE) tissue is the predominant preparation for diagnostic histopathological evaluation and increasingly the biospecimen on which molecular diagnostics are performed. However, formalin is carcinogenic and results in cross-linking of proteins and nicking and alterations of nucleic acids. Alternative fixatives, including 70% ethanol, improved biomolecular integrity; however, they have yet to replace neutral-buffered formalin (NBF). Herein, we describe the phosphate-buffered ethanol 70% (BE70) fixative. The histomorphology of BE70-fixed tissue is very similar to that of NBF; however, it is a non-cross-linking fixative and lacks the carcinogenic profile of formaldehyde-based fixatives. RNA isolated from tissue fixed in BE70 was of substantially higher quality and quantity than that was recovered from formalin-fixed tissue. Furthermore, the BE70 fixative showed excellent RNA and DNA integrity compared with that of NBF fixative based on real-time polymerase chain reaction analysis results. Immunohistochemical staining was similar for the antigen tested. In conclusion, BE70 is a non-cross-linking fixative that is superior to NBF and 70% ethanol with reference to biomolecule recovery and quality from paraffin-embedded tissue. Additional studies to compare the histomorphologic and immunohistochemical performance and utility in a clinical setting are required.

Detection of alpha human papillomaviruses in archival formalin-fixed, paraffin-embedded (FFPE) tissue specimens

Formalin-fixed, paraffin-embedded (FFPE) tissue specimens stored in pathology departments worldwide are an invaluable source for diagnostic purposes when fresh clinical material is unavailable as well as for retrospective molecular and epidemiological studies, especially when dealing with rare clinical conditions for which prospective collection is not feasible. Accurate detection of HPV infection in these specimens is particularly challenging because nucleic acids are often degraded and therefore, not suitable for amplification of larger fragments of the viral genome or viral gene transcripts. This review provides a brief summary of molecular methods for detecting alpha-HPV DNA/RNA in FFPE tissue specimens. We specifically address the key procedural and environmental factors that have the greatest impact on the quality of nucleic acids extracted from FFPE tissue specimens, and describe some solutions that can be used to increase their integrity and/or amplifiability. Moreover, commonly used methods for HPV DNA/RNA detection in FFPE tissue specimens are presented and discussed, focusing on studies using polymerase chain reaction as an HPV detection method and published after 1999. Finally, we briefly summarize our 22 years of experience with HPV detection in FFPE tissue specimens.

In vivo imaging of Nematostella vectensis embryogenesis and late development using fluorescent probes

BACKGROUND

Cnidarians are the closest living relatives to bilaterians and have been instrumental to studying the evolution of bilaterian properties. The cnidarian model, Nematostella vectensis, is a unique system in which embryology and regeneration are both studied, making it an ideal candidate to develop in vivo imaging techniques. Live imaging is the most direct way for quantitative and qualitative assessment of biological phenomena. Actin and tubulin are cytoskeletal proteins universally important for regulating many embryological processes but so far studies in Nematostella primarily focused on the localization of these proteins in fixed embryos.

RESULTS

We used fluorescent probes expressed in vivo to investigate the dynamics of Nematostella development. Lifeact-mTurquoise2, a fluorescent cyan F-actin probe, can be visualized within microvilli along the cellular surface throughout embryonic development and is stable for two months after injection. Co-expression of Lifeact-mTurquoise2 with End-Binding protein1 (EB1) fused to mVenus or tdTomato-NLS allows for the visualization of cell-cycle properties in real time. Utilizing fluorescent probes in vivo helped to identify a concentrated 'flash' of Lifeact-mTurquoise2 around the nucleus, immediately prior to cytokinesis in developing embryos. Moreover, Lifeact-mTurquoise2 expression in adult animals allowed the identification of various cell types as well as cellular boundaries.

CONCLUSION

The methods developed in this manuscript provide an alternative protocol to investigate Nematostella development through in vivo cellular analysis. This study is the first to utilize the highly photo-stable florescent protein mTurquoise2 as a marker for live imaging. Finally, we present a clear methodology for the visualization of minute temporal events during cnidarian development.

Effects of tissue fixation on coherent anti-Stokes Raman scattering images of brain

Coherent anti-Stokes Raman scattering (CARS) microscopy is an emerging multiphoton technique for the label-free histopathology of the central nervous system, by imaging the lipid content within the tissue. In order to apply the technique on standard histology sections, it is important to know the effects of tissue fixation on the CARS image. Here, we report the effects of two common fixation methods, namely with formalin and methanol-acetone, on mouse brain and human glioblastoma tissue. The variations induced by fixation on the CARS contrast and intensity were compared and interpreted using Raman microspectroscopy. The results show that, whenever unfixed cryosections cannot be used, fixation with formalin constitutes an alternative which does not deteriorate substantially the contrast generated by the different brain structures in the CARS image. Fixation with methanol-acetone strongly modifies the tissue lipid content and is therefore incompatible with the CARS imaging.

The innovative safe fixative for histology, histopathology, and immunohistochemistry techniques: "pilot study using shellac alcoholic solution fixative"

The concerns over health and workplace hazards of formalin fixative, joined to its cross-linking of molecular groups that results in suboptimal immunohistochemistry, led us to search for an innovative safe fixative. Shellac is a natural material which is used as a preservative in foods and pharmaceutical industries. This study was undertaken to evaluate the fixation adequacy and staining quality of histopathological specimens fixed in the "shellac alcoholic solution" (SAS), and also to determine the validity of immunohistochemical staining of SAS-fixed material in comparison to those fixed in formalin. Fresh samples from 26 cases from various human tissues were collected at the frozen section room of King Abdulaziz University Hospital, and fixed in SAS fixative or in neutral buffered formaldehyde (NBF) for 12, 18, 24, and 48 h, and processed for paraffin sectioning. Deparaffinized sections were stained with hematoxylin and eosin (H&E) and immunostained for different antigens. The tissues fixed in SAS for >18 h showed best staining quality of H&E comparable to NBF-fixed tissues. Comparison of the immunohistochemical staining of different tissues yielded nearly equivalent readings with good positive nuclear staining quality in both fixatives. These findings support the fixation and preservation adequacy of SAS. Furthermore, it was concluded that the good staining quality obtained with SAS-fixed tissues, which was more or less comparable with the quality obtained with the formalin fixed tissues, supports the validity of this new solution as a good innovative fixative.

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.

When tissue antigens and antibodies get along: revisiting the technical aspects of immunohistochemistry--the red, brown, and blue technique

Once focused mainly on the characterization of neoplasms, immunohistochemistry (IHC) today is used in the investigation of a broad range of disease processes with applications in diagnosis, prognostication, therapeutic decisions to tailor treatment to an individual patient, and investigations into the pathogenesis of disease. This review addresses the technical aspects of immunohistochemistry (and, to a lesser extent, immunocytochemistry) with attention to the antigen-antibody reaction, optimal fixation techniques, tissue processing considerations, antigen retrieval methods, detection systems, selection and use of an autostainer, standardization and validation of IHC tests, preparation of proper tissue and reagent controls, tissue microarrays and other high-throughput systems, quality assurance/quality control measures, interpretation of the IHC reaction, and reporting of results. It is now more important than ever, with these sophisticated applications, to standardize the entire IHC process from tissue collection through interpretation and reporting to minimize variability among laboratories and to facilitate quantification and interlaboratory comparison of IHC results.

Carbon-13 nuclear magnetic resonance analysis of formaldehyde free preservatives

Preservation of biomolecules is pivotal in increasingly important molecular diagnostics. Traditionally, formaldehyde is employed for such biomolecular preservation in spite of its carcinogenicity. Moreover, formaldehyde induced cross-linking during fixation is reported to alter structural and functional properties of the preserved biomolecules. Therefore, formaldehyde-free preservatives are advantageous because they are safer for laboratory personnel and they protect the structural and functional integrity of the biomolecules. Streck Cell Preservative and Cell-Free DNA BCT reagents are used as formaldehyde alternative preservatives. However, no studies have been carried out to evaluate formaldehyde concentrations in these preservatives. In this study, we evaluated the free formaldehyde concentrations of these reagents by carbon-13 ((13)C) NMR spectroscopic analysis. Chemically non-invasive NMR analysis is more reliable than the traditional derivatization based techniques in formaldehyde detection. (13)C NMR technique can be used for quantitative measurement by using (13)C NMR-relaxation agents. In this manuscript, we report an optimized NMR analysis method using Gadolinium diethylenetriaminepentaacetate. Additionally the data reported herein provide spectral analyses that indicate Streck Cell Preservative and Cell-Free DNA BCT reagents do not contain detectable free formaldehyde. Therefore, these preservatives are safer alternatives than formaldehyde for laboratory use, which can protect the overall integrity of the biomolecules within preserved samples.

Will PAXgene substitute formalin? A morphological and molecular comparative study using a new fixative system

Aims

In this study we aimed to evaluate this new tissue preservation technique in comparison with formalin fixation and fresh frozen tissue samples.

Methods

12 melanoma biopsy samples were divided and fixed simultaneously with formalin, PAXgene or fresh frozen in liquid nitrogen and analysed with regard to morphology, immunohistochemistry,  DNA and RNA content and quality. Markers of melanocytic differentiation and tumour cell proliferation were used.

Results

Morphology was well preserved in PAXPE samples. However, 5 out of 11 immunohistochemical markers showed significantly lower overall staining and staining intensity with PAXPE tissues in comparison with formalin-fixed, paraffin-embedded (FFPE). Increasing membrane permeability through adding a detergent did proportionally increase staining intensity in PAXPE samples. Amplification of different mRNA amplicons showed a direct relationship with the size of the amplicon with greater template integrity observed in PAXPE samples. Sequencing and mutational analysis of DNA samples were comparable for all the different fixation methods, while the level of DNA fragmentation seemed to be lower in PAXPE compared with FFPE tissues.

Conclusions

The switch from formalin to PAXgene fixation would require a re-evaluation of immunohistochemical markers and staining procedures originally developed for FFPE tissues. Our data demonstrate that PAXPE fixation offers some advantages concerning molecular analysis. However, these advantages would not justify substituting formalin fixation in any routine pathology laboratory.

Evaluation of two commercial and three home-made fixatives for the substitution of formalin: a formaldehyde-free laboratory is possible

BACKGROUND

Formaldehyde (HCHO) is a gas (available as a 37% concentrated solution, stabilized with methanol). The 10% dilution (approximately 4% formaldehyde) has been used as a fixative since the end of the 19th century. Alternative fixatives are also commercially available or may be prepared in-house in laboratories. Statements by the IARC, along with other USA agencies (CalEPA, RoC/NTP) on the carcinogenicity of formaldehyde for humans renders its substitution in Pathology Departments necessary since the annual use of formalin may exceed 3,500 liters for a medium-large laboratory. To achieve a "formalin-free laboratory" we tested straightforward-to-make fixatives along with registered reagents offered as formalin substitutes.

METHODS

More than two hundreds specimens were fixed in parallel with in-laboratory made fixatives PAGA (Polyethylenglycol, ethyl Alcohol, Glycerol, Acetic acid), two zinc-based fixatives (ZBF, Z7), and commercially-available alternatives (RCL2 and CellBlock). Tissue micro arrays were used for morphological and immunohistochemical comparison. Extraction of RNA was carried out to evaluate preservation of nucleic acids.

RESULTS

Differences compared to formalin fixation were evident in alcohol-based fixatives, mainly restricted to higher stain affinity and considerable tissue shrinkage. Conversely, nuclear detail was superior with these alcohol-based formulas compared to formalin or glyoxale-based recipes. RNA extraction was superior for Z7, PAGA and RCL2 with regard to concentration but relatively comparable regarding quality.

CONCLUSIONS

Abolition of the human carcinogen formaldehyde from pathology laboratories is possible even in contexts whereby commercial alternatives to formalin are unavailable or are too expensive for routine use, and aspiration devices are lacking or not adequately serviced. The use of known formulations, possibly with simple and not-noxious ("alimentary grade") constituents, comparable with registered proprietary products, may expand the search for the ideal fixative combining satisfactory morphology with improved preservation of nucleic acids and proteins as well as being easy and safe to dispose of.