The effect of various fixatives on the preservation of acid glycosaminoglycans in tissues

Histochemical studies of the extracellular matrix of human articular cartilage--a review

OBJECTIVE

This paper reviews the histochemistry of the extracellular matrix of human articular cartilage. No systematic review of histochemical knowledge and techniques in the study of articular cartilage has been published previously.

METHODS AND RESULTS

Literature was searched in the Winspirs Medline database from 1960 to 2000. Only techniques applicable for bright field or polarization microscopy were considered. Unless otherwise noted, all applies to hyaline cartilage. The most widely used fixatives are adequate for routine staining of proteins, but proteoglycan fixation is problematic, and no one fixative can be recommended. Proteoglycan can be stained reliably but it is problematic that, at low substrate concentrations, these methods are not stoichiometric. Collagen can be stained efficiently, although attempts to differentiate collagen types have not been successful.

CONCLUSIONS

Detailed studies of fixation and staining procedures should be carried out and standards for cartilage sampling, handling and evaluation agreed upon if results from different laboratories are to be compared.

In situ compressive stiffness, biochemical composition, and structural integrity of articular cartilage of the human knee joint

OBJECTIVE

Reduction of compressive stiffness of articular cartilage has been reported as one of the first signs of cartilage degeneration. For the measurement of in situ compressive stiffness, a hand-held indentation probe has recently been developed and baseline data for macroscopically normal knee joint cartilage were provided. However, the histological stage of degeneration of the measured cartilage was not known. The purpose of this study was to investigate whether there is a relationship between the in situ measured compressive stiffness, the histological stage of degeneration, and the biochemical composition of articular cartilage.

DESIGN

Instantaneous compressive stiffness was measured for the articular cartilage of 24 human cadaver knees. Additionally, biochemical composition (total proteoglycan and collagen content) and histological appearance (according to the Mankin score) were assessed for each measurement location.

RESULTS

Despite visually normal surfaces, various histological signs of degeneration were present. A high correlation between Mankin score and cartilage stiffness was observed for the lateral patellar groove (R(2)=0.81), the medial (R(2)=0.83) and the lateral femoral condyle (R(2)=0.71), whereas a moderate correlation was found for the medial patellar groove (R(2)=0.44). No correlation was observed between biochemical composition and cartilage compressive stiffness.

CONCLUSIONS

Our results are in agreement with others and show that the instantaneous compressive stiffness is primarily dependent on the integrity of the extracellular matrix, and not on the content of the major cartilage constituents. The high correlation between stiffness and Mankin score in mild osteoarthrosis suggests that the stage of cartilage degeneration can be assessed quantitatively with the hand-held indentation probe. Moderate and severe case of osteoarthrosis remains to be investigated.

Fluorometric determination of DNA in cartilage of various species

A sensitive, modified 3,5-diaminobenzoic acid (DABA), fluorometric DNA assay was developed and compared to mithramycin and ethidium bromide assays in determining the DNA content of dense connective tissues including: Swarm rat chondrosarcoma, rabbit, dog, monkey, and most importantly, adult human articular cartilage. In the more cellular cartilages, the three methods gave equivalent results. However, in the relatively acellular human cartilage, the DABA method was shown to be superior. Both the mithramycin and ethidium bromide gave falsely high values compared to the DABA method, which by subtraction after DNase digestion approached the DABA value. The latter was completely DNase sensitive. With the DABA method, the DNA content of human cartilage can be obtained on less than 5 mg wet weight of fresh, alcohol-fixed, or lyophilized material. While the DNA can also be released by digestion with papain or protease from Streptomyces griseus, proteinase K was preferable. The comparison of literature values for other fluorometric and spectrophotometric assays of human cartilage suggest these methods overestimate human articular cartilage DNA concentrations, whereas the DABA values were in line with those predicted from previous morphometric analysis. Thus, the modified method represents an improvement in DNA analysis of dense connective tissues.

Evaluation of multiphase implants for repair of focal osteochondral defects in goats

The use of biodegradable scaffolds for articular cartilage repair has been investigated by numerous researchers. The objective of this screening study was to examine how the mechanical and physical properties of four multiphase implants can affect the cartilage healing response. Multiphase implant prototypes were prepared using poly(D,L)lactide-co-glycolide as the base material. PGA fibers (FR), 45S5 Bioglass (BG) and medical grade calcium sulfate (MGCS) were used as additives to vary stiffness and chemical properties. Osteochondral defects (3 mm dia. and 4 mm in depth) were created bilaterally in the medial femoral condyle (high-weight bearing) and the distal medial portion of the patellar groove (low-weight bearing) of 16 Spanish goats. Half of the implants were loaded with autologous costochondral chondrocytes. Defect sites (total n = 64, 4 sites/treatment) were randomly treated and allowed to heal for 16 weeks, fully weight bearing. At euthanasia, gross evaluations and biomechanical testing were conducted. Histological sections of the defect sites were stained with H and E, Safranin O/Fast Green or processed to analyze collagen architecture. Sections were semi-quantitatively scored for repair tissue structure. Qualitative evaluations showed that all groups had a high percentage of hyaline cartilage and good bony restoration, with new tissue integrating well with the native cartilage. Gross and histology scoring indicated a significantly higher score for defect healing in the condyle than in the patellar groove, but no difference in healing for implant types or addition/omission of cells was found. This investigation demonstrates that focal, osteochondral defects in caprine distal femurs treated with various implant constructs were repaired with hyaline-like cartilage and good underlying bone. The multiphase implants show potential for treatment of osteochondral defects and long-term studies need to be undertaken to confirm the longevity of the regenerated tissue.

Method of histomorphometric assessment of glycosaminoglycans in articular cartilage

A method of image analysis has been developed for use in the semiquantitative histomorphometric assessment of glycosaminoglycans in articular cartilage stained with safranin O. The reliability of the methodology is reported along with its application to the assessment of articular cartilage in a model of osteoarthritis, i.e., transection of the anterior cruciate ligament in rabbits. With this system, specimens of normal and osteoarthritic articular cartilage were assessed histomorphometrically for the following parameters: total cartilage area, percentage of safranin O stained area, mean gray scale (average stain intensity), and gray scale index (the relative total amount of glycosaminoglycans). Reproducibility was established for 12 specimens of normal cartilage and found to have a SD of less than 8% of the mean for each parameter that was measured. Image analysis of osteoarthritic cartilage revealed each of the parameters, except for average stain intensity, to be significantly lower than that in control cartilage.

Effect of aqueous and nonaqueous fixatives on the quantitative estimation of collagen-proteoglycan interaction in tissue sections

The present study was designed to assess the influence of aqueous and nonaqueous fixatives on the quantitative estimation of collagen-proteoglycan interaction in tissue sections. Tissues containing different collagen types and distinct sulfated proteoglycan classes were isolated from pig costal cartilage, human skin, and the inner muscular layer of dog small intestine and fixed using aqueous or nonaqueous methods. The results showed that the best fixation method was exposure to paraformaldehyde gas. When using aqueous fixatives, proteoglycans were lost to different degrees among the various tissues analyzed, reflecting differences in chemical properties of proteoglycan classes and/or in their interactions with other matrix components such as collagen.

The biological reality of the interlacunar network in the embryonic, cartilaginous, skeleton: a thiazine dye/absolute ethanol/LR White resin protocol for visualizing the network with minimal tissue shrinkage

Third toe phalanges of chicks aged 8-13 days in ovo and 7-day post-natal rat femoral growth plate were examined to determine whether the interlacunar network (IN), a structure with no lipoprotein membrane component or cytoplasmic organelles, is a genuine component of young growth cartilage. In chick phalanges dehydrated by 70% (v/v) ethanol and LR White resin, variable metachromatic staining of the interlacunar network by toluidine blue and red staining by picro-Sirius red indicate the presence of glycosaminoglycans and collagen. The network in phalanges dehydrated by 80% (v/v) ethanol appears little different; however, the network is much less widely detectable in phalanges dehydrated by 90% (v/v) ethanol and, after dehydration by absolute ethanol, is almost completely undetectable. In contrast, when the young cartilage is permeated by a thiazine dye such as toluidine blue, using a solution of dye in the aldehyde fixative, the network is widely detectable, following dehydration by absolute ethanol, both in chick phalanges and in rat growth plate. Comparison of projected areas shows that the extent to which whole chick feet are found to have shrunk, by the time that they are photographed under LR White resin, is determined principally by the extent of dehydration, by 70% (v/v) or absolute ethanol; post-shrinkage areas are 33% or 35% of areas measured in buffer for 70% (v/v) ethanol/LR White resin and 71% or 75% for absolute ethanol/LR White resin (the higher value in each is for the toluidine blue treatment). The network is thus present in radically shrunk tissue, but, significantly, is also fully represented in tissue shrunk by only a conventional margin and is therefore not produced as an artefact by exceptional tissue shrinkage as has been suggested.

Immunohistochemical staining for chondroitin sulphate and keratan sulphate. An evaluation of two monoclonal antibodies

Immunohistochemical staining with commercially available antibodies against chondroitin sulphate (clone CS-56) and keratan sulphate (clone 1/20/5-D-4) was compared with two conventional histochemical methods for the demonstration of glycosaminoglycans, namely Alcian Blue with varying pH and critical electrolyte concentrations, and a modified PAS stain. The antibodies were tested on sections from both frozen and fixed, paraffin embedded human material from umbilical cord, skin, and bronchus. The results showed immunostaining to function equally well on frozen and routine sections, and to be superior to Alcian Blue and PAS with regard to morphological detail. Thus, reactivity with anti-chondroitin sulphate was demonstrated in vessel walls, in small nerves, in the basal membrane zone of the skin, in perichondrium, and in and around chondrocytes. Reactivity with anti-keratan sulphate occurred in chondroid matrix and in perichondrial tissue; however, some cells of the bronchial epithelium and mucous glands also exhibited positivity.

The reaction of acridine orange with proteoglycans in the articular cartilage of the rat

Acridine Orange in concentrations from 0.01% to 0.2% was added to the first fixative solution in order to stain vibratome sections and small blocks of the articular cartilage of 2 month old rats. The interterritorial matrix of the radial or deep zone (zone 3) was examined. It contained reaction products with different morphology depending on the specimens used. In vibratome sections filaments were seen arranged in a homogenous pattern and changing in size with the concentration of the dye: diluted solutions produced finer filaments than concentrated ones. In contrast, in tissue blocks the staining pattern was not altered by different concentrations of Acridine Orange. However, with increase of the distance from the surface of the specimens the size of the filaments gradually decreased and formed a finer network. Since after preincubation with chondroitin ABC lyase only minute reaction products remained, an interaction of the dye with the sulphated glycosaminoglycans of the proteoglycans in the articular cartilage is suggested. The experiments show that by using mainly monocationic monomers of Acridine Orange the proteoglycans can be stained in a more expanded state than with polycationic dye polymers.

Biocompatibility of hydroxyapatite ceramic: response of chondrocytes in a test system using low temperature scanning electron microscopy

An investigation is described of R37W, one of a number of porous ceramics being developed for maxillofacial surgery and the restoration of periodontal bone defects. Sensitive and precise methods are needed to assess the biocompatibility of these new materials. Mammalian chondrocytes are known to form colonies on and within porous ceramics; therefore, the tissue formed has been evaluated to gauge the response of these proliferating mesenchymal cells to the hydroxyapatite. Cell colonies, grown on R37W, have been rapidly frozen at -210 degrees C (63K) in nitrogen slush and examined by low temperature scanning electron microscopy (SEM). This method enables unfixed, fully hydrated cells to be viewed in detail and demonstrates the three-dimensional surface structure of chondrocytes in a life-like state. Features such as complex pericellular fenestrations and papilliform surface processes are believed to indicate cell viability and normality: they are not detectable by the light microscopy and SEM of fixed, dehydrated preparations. This recently recognized fine structure, together with the determination of rates of increase of cell numbers and histochemical and immunological tests of cell synthetic and secretory behaviour, provides a new guide to biocompatibility. It is concluded that the low temperature SEM of chondrocytes grown on ceramics is a valuable addition to the procedures available for the testing of hard materials before their adoption in oral surgery.

Alcian blue staining of glycosaminoglycans in embryonic material: effect of different fixatives

Glycosaminoglycans are important components of the extracellular matrix of developing embryos where they are found in the form of proteoglycans. Alcian Blue staining of tissue sections is the technique most commonly used for demonstrating their distribution. Glycosaminoglycans have a high solubility in water, and are easily lost from the tissue during processing, even if non-aqueous fixatives have been used. Formalin and Carnoy's fluid are the most frequently used fixatives, and the addition of cetyl pyridinium chloride has been recommended to reduce glycan solubility. Using sections of day-10 rat embryos containing developing head and heart (both known to be rich in glycosaminoglycans) the effects of ten fixatives have been investigated with and without cetyl pyridinium chloride on the preservation of Alcian Blue-stainable material (at pH 2.5) and tissue structure. The most useful fixatives were Karnovsky's and Sainte-Marie's. Both gave a strong and reproducible staining pattern of the extracellular polyanionic material. Sainte-Marie's gave better preservation of tissue structure, allowing the demonstration of cell-matrix interrelationships; Karnovsky's gave a better contrast between extracellular and intracellular staining, which is particularly useful at lower magnifications. Cetyl pyridinium chloride is a detergent. Transmission electron microscope observations showed that it causes cell membrane disruption and vesicle formation, which at the light microscopic level, would cause cell membrane-associated glycosaminoglycans to appear as stained strands wholly within the extracellular domain. Therefore the use of cetyl pyridinium chloride is inadvisable where a distinction between surface-related and extracellular glycosaminoglycans is desirable. It has the further disadvantage of enhancing cytoplasmic and nuclear polyanionic material, thus decreasing the differential staining intensity of intracellular and extracellular domains.

Demonstration by X-ray microprobe analysis of relationship between chondrocytes and tertiary surface structure of hyaline articular cartilage

Blocks of hyaline cartilage from the femoral condyles of five young adult beagles dogs were quench-frozen in nitrogen slush at 63 K. The free cartilage surfaces of blocks from three animals were examined in the secondary electron mode; the remaining specimens were cut by cryoultramicrotone (approximately 188 K) tangential to the surface to expose midzone cartilage which was examined in the backscattered electron mode. A random array of gently convex prominences was apparent at the free cartilage surfaces. When X-ray emissions were recorded from tissue immediately below these elevations, the spectra proved to be similar to those derived from midzone chondrocytes. These spectra revealed high count rates for the X-rays characteristic of P and K. By contrast, in areas of free surface remote from these prominences, and in midzone intercellular matrix, larger count rates for the X-rays characteristic of Na, S. Cl and Ca were detected. The evidence supports the hypothesis that the elevations seen on the non-loaded articular cartilage of disarticulated mammalian synovial joints are the surface representations of superficial chondrocytes.

Type II collagen-induced arthritis. A morphologic and biochemical study of articular cartilage

Articular cartilage was obtained from type II collagen-induced arthritic rat joints. Transmission electron microscopy showed a gradual degeneration of chondrocytes, disorganization of the collagenous extracellular matrix, and formation of microscars. Biochemical analyses indicated that type II collagen was the only collagen present and that it was normal in regard to hydroxylation of lysine and glycosylation of hydroxylysine. Analyses of the proteoglycan in the extracellular matrix revealed a 50% loss of chondroitin sulfate and keratan sulfate.

An intercellular network artefact in glycol methacrylate dehydrated neonatal cartilage

A striking network thought to consist of glycosaminoglycan in neonatal cartilage has recently been reported following glycol methacrylate (GMA) dehydration and embedding. This study attempted to learn why the network was not seen in other preparations previously reported. Comparative light and transmission electron microscopy of the network structures was carried out to determine their biological significance. We have shown the networks to be reproducible artefact, attained only following GMA dehydration of glutaraldehyde fixed neonatal cartilage.

Staining of demineralized cartilage. II. Quantitation of articular cartilage proteoglycan after fixation and rapid demineralization

Safranin O in the orthochromatic form stains articular cartilage proteoglycan quantitatively in histological sections of demineralized cartilage. This was shown by scanning microdensitometry of stained sections of undemineralized and demineralized articular cartilage and by biochemical analysis of 35S labelled cartilage subjected to demineralization. In contrast, Alcian Blue staining is affected by unknown factors other than simply the amount of proteoglycan present. Alcoholic formalin fixes articular cartilage proteoglycan more successfully than formol Zenker for subsequent rapid demineralization. Alcoholic formalin does not preserve cellular appearance as well as formol Zenker. Staining of articular cartilage with PAS appears unaffected by demineralization.

Staining of demineralized cartilage. I. Alcoholic versus aqueous demineralization at neutral and acidic pH

Demineralization of cartilage with alcoholic EDTA provides cartilage staining that is no better, as measured by scanning microdensitometry, than that of adequately fixed specimens demineralized with aqueous EDTA. Aqueous EDTA is a faster demineralizing agent than alcoholic EDTA. Certain fixatives can preserve maximal proteoglycan staining in articular cartilage even with subsequent rapid demineralization in formate buffer at pH 3.3. Although alcoholic formalin fixation provided optimum quantitative cartilage staining, cetylpyridinium chloride (CPC) in aqueous buffered formalin improved cellular detail, but CPC partially suppressed matrix staining.

Influence of aqueous fixation on articular surface morphology. A reflected light interference microscope study

Fresh, unfixed temporomandibular fibrous articular surfaces from baboons were examined by reflected light interference microscopy. The appearances, recorded photographically, were compared with those of joints subjected to aqueous fixation in buffered glutaraldehyde and formalin. Fixation caused readily detectable, measureable changes in articular surface morphology. Reflected light interference microscopy is a valuable technique for the demonstration of the effects of fixation on articular surface morphology.

Lysozyme antigenicity and tissue fixation

The preservation of lysozyme (LZM) antigenicity was studied in paraffin embedded tissue blocks. The reactivity for LZM varied with the type of tissue studied, the fixative used, the osmolarity and pH of the fixative, fixation time and temperature, and the method of dehydration. In both rat and human tissues aqueous fixatives were superior to nonaqueous fixatives in retaining LZM antigenicity. Brief fixation in fixatives of low osmolarity enhanced LZM staining in the parenchymatous tissues but diminished staining in human cartilage; prolonged fixation in fixatives of high osmolarity gave opposite results. Least affected by fixation was the LZM antigenicity in the serous cells of the glands of the respiratory tract. These cells also stained most intensely for LZM of all autopsy material studied.

The histology and in vivo sulphate uptake of epiphyseal cartilage in protein-depleted rats

1. Weanling rats, aged 21 d, given a 40 g casein/kg diet for 25 d were compared with ‘age-matched’ controls given a 200 g casein/kg diet and with ‘weight-matched’ weanling controls.

2. The protein-malnourished rats demonstrated failure of weight gain and linear growth, hypoproteinaemia, hypoalbuminaemia and fatty liver.

3. Autoradiography of the tibia was carried out 24 h after intraperitoneal injection of Na235SO4(0.1, 1.0, 2.0, 5, 10 μCi/g body-weight). Sections of tibia, humerus and costochondral junction were stained by haematoxylin and eosin, resorcin-crystal violet and picro-fuchsin, Alcian Blue at pH 0.1 and pH 2.5, Alcian Blue at pH 5.7 with magnesium chloride (0.1, 0.7, 1.0m), and by Alcian Blue after ovine testicular hyaluronidase (EC3.2.1.35) digestion. The width of the upper tibial epiphysis was measured and the histological and histochemical features of the epiphyses studied.

4. The incorporation of35SO4into the epiphyses of the protein-malnourished animals was markedly reduced. The chondrocytes were small and flattened with frequent pyknotic nuclei. The staining characteristics of the cartilagenous matrix was qualitatively similar in all animals. The epiphyses in malnutrition were found to be thin, all zones being affected. The upper tibial epiphyses (mean±sd; μm) were 202 ±46 for the protein-malnourished animals, 367±52 for age-matched controls and 578±40 for weight-matched controls.

5. The changes found resemble those after hypophysectomy and the possible hormonal factors are discussed.

Topographical distribution of sulphated glycosaminoglycans in human temporomandibular joint disks. A histochemical study of an autopsy material

The distribution of sulphated glycosaminoglycans (GAG's) in the human temporomandibular joint disk and its relationship to sex, age and osteoarthrosis was studied by histochemical methods in autopsy material from 18 individuals. The disks were embedded in paraffin and frontal sections, 5-7 mu thick, were cut at different levels. Two staining methods were used, toluidine blue at pH 0.5 and alcian blue with different concentrations of MgCl2. The two methods gave comparable results. The sulphated GAG's as represented by metachromatic staining with toluidine blue at pH 0.5 and staining with alcian blue in concentrations of MgCl2 above 0.55-M were found in the central load-bearing part of the disks evenly distributed in the medio-lateral direction. The findings from the alcian blue staining method indicated the presence of sulphated GAG's with characteristics similar to chondroitin/dermatan sulphate and keratan sulphate. The latter finding was most frequent in a surface zone )10-100 mu) located mainly in the central part of the disks. In macroscopically thin areas of the disks judged as early osteoarthrosis a significant reduction in the staining of sulphated GAG's could be observed. No age or sex differences were found in the distribution of GAG's, either in normal or in osteoarthrotic disks.

Prolonged methanol fixation of soluble mucosubstances in mucopolysaccharidoses

A simple and efficient method for the demonstration of highly water soluble acid mucosubstances in cold microtone sections is described. It consists of prolonged treatment of cold microtome sections with methanol (for at least 1 h) and subsequent staining with 0.1% azure A in distilled water or in 30% methanol. The procedure is recommended particularly for the bioptical examination of mucopolysaccharidoses.

A new chondrodystrophic mutant in mice. Electron microscopy of normal and abnormal chondrogenesis

The occurrence of a new mutation affecting cartilage and bone in mice is reported. The gene is lethal, shows autosomal recessive inheritance, and has high penetrance. It is not allelic to shorthead and probably not to phocomelia or achondroplasia. It results in a foreshortened face, cleft palate, defective trachea, and shortened long bones with flared metaphyses. Chondrocytes of epiphyseal cartilage from the mutant are not aligned in columns, and there is a decrease in the usual staining of the cartilage matrix. Electron microscope observations show large, wide collagen fibrils with "native" banding in the matrix of mutant cartilage, which are not present in normal cartilage. Possible explanations for the expression of this genetic disorder of cartilage development are put forward.