Analysis of bone composition at the microscopic level

Regional differences in architecture and mineralization of developing mandibular bone

The goal of this study was to investigate the mutual relationship between architecture and mineralization during early development of the pig mandible. These factors are considered to define the balance between the requirements for bone growth on the one hand and for load bearing on the other. Architecture and mineralization were examined using micro-CT, whereas the mineral composition was assessed spectrophotometrically in groups of fetal and newborn pigs. The development of the condyle coincided with a reorganization of bone elements without an increase in bone volume fraction, but with an increase in mineralization and a change in mineral composition. In the corpus, the bone volume fraction and mineralization increased simultaneously with a restructuring of the bone elements and a change in mineral composition. The growth of the condyle was reflected by regional differences in architecture and mineralization. The anterior and inferior regions were characterized by a more dense bone structure and a higher mineralization as compared to posterior and superior regions, respectively. In the corpus, growth was mainly indicated by differences between buccal and lingual plates as well as between anterior, middle, and posterior regions characterized by a more compact structure and higher mineralization in the lingual and middle regions. In conclusion, the architecture and mineralization in the condyle and corpus started to deviate early during development toward their destiny as trabecular and cortical bone, respectively. These results were compatible with those obtained with mineral composition analysis. Regional differences within condyle and corpus reflected known developmental growth directions.

Atomic force microscopy and nanoindentation characterization of human lamellar bone prepared by microtome sectioning and mechanical polishing technique

Surface topography, microstructure, and micromechanical properties of human lamellar bone were characterized by atomic force microscopy and nanoindentation. The lamellar bone surfaces were prepared by two different methods: microtome sectioning and mechanical polishing. The lamellar bone surfaces prepared by mechanical polishing revealed that thin lamellae formed depressions approximately 200 nm deep, whereas the surfaces prepared by microtome sectioning were flat. Atomic force microscopy surface topographic images at higher magnification showed differences between thick and thin lamellae in polished samples, but these differences were less pronounced in microtomed samples. Roughness measurements confirmed that there was a significant difference between thick (21.0 nm) and thin lamellae (8.3 nm) in polished samples (p < 0.001). The difference in surface roughness between thick (13.9 nm) and thin lamellae (12.7 nm) in microtomed sample was statistically insignificant (p = 0.74). Higher elastic modulus values were observed for thick lamella in microtomed samples compared with that of thin lamellae, whereas measured elastic modulus differences between thick and thin lamellae in polished samples were found to be statistically insignificant.

Intravascular stents: a new technique for tissue processing for histology, immunohistochemistry, and transmission electron microscopy

BACKGROUND

Study of the vascular response to stent implantation has been hampered by difficulties in sectioning metal and tissue without distortion of the tissue stent interface. The metal is often removed before histochemical processing, causing a loss of arterial architecture. Histological and immunohistochemical sections should be 5 microns with an intact tissue stent interface.

OBJECTIVES

To identify the most suitable cutting and grinding equipment, embedding resin, and slides for producing thin sections of stented arteries with the stent wires in situ for histological, immunohistochemical, and transmission electron microscopic (TEM) analyses.

METHODS

20 balloon stainless steel stents were implanted in the coronary arteries of 10 pigs. Twenty eight days later the stented arterial segments were excised, formalin fixed, embedded in five different resins (Epon 812, LR white, T9100, T8100, and JB4), and sectioned with two different high speed saws and a grinder for histological, immunohistochemical, and TEM analyses. Five stented human arteries were obtained at necropsy and processed using the best of the reported methods.

RESULTS

The Isomet precision saw and grinder/polisher unit reliably produced 5 microns sections with most embedding resins; minimum section thickness with the horizontal saw was 400 microns. Resin T8100, a glycol methacrylate, enabled satisfactory sectioning, grinding, and histological (toluidine blue, haematoxylin and eosin, and trichromatic and polychromatic stains) and immunohistochemical analyses (alpha smooth muscle actin, von Willebrand factor, vimentin, proliferating cell nuclear antigen, and CD68 (mac 387)). T9100 and T8100 embedded stented sections were suitable for ultrastructural examination with TEM. Stented human arterial sections showed preserved arterial architecture with the struts in situ.

CONCLUSION

This study identified the optimal methods for embedding, sawing, grinding, and slide mounting of stented arteries to achieve 5 microns sections with an intact tissue metal interface, excellent surface qualities, histological and immunohistochemical staining properties, and suitability for TEM examination. The technique is applicable to experimental and clinical specimens.

Chemical and structural characterization of the mineral phase from cortical and trabecular bone

X-ray diffraction, infrared spectroscopy and chemical investigations have been carried out on the inorganic phases from rat cortical and trabecular bone. Although both inorganic phases consist of poorly crystalline B carbonated apatite, several significant differences have been observed. In particular, trabecular bone apatite displays reduced crystallite sizes, Ca/P molar ratio, and carbonate content, and exhibits a greater extent of thermal conversion into beta-tricalcium phosphate than cortical bone apatite. These differences can be related to the different extents of collagen posttranslational modifications exhibited by the two types of bone, in agreement with their different biological functions.

Structural evaluation of human and sheep bone and comparison with synthetic hydroxyapatite by FT-Raman spectroscopy

The composition of whole human and sheep cortical bone tissue, and of a synthetic hydroxyapatite (P120), were compared using Fourier transform Raman (FT-Raman) spectroscopy. Deproteination procedures to remove the bulk of the collagen present in bone tissue allowed isolation of the mineral phase. A comparison of the spectra obtained from both whole and deproteinated bone with those of synthetic hydroxyapatite showed direct correlation only in the region of 952 cm-1 (symmetric P-O mode). In contrast, human and sheep bone were very closely matched in both, the organic and inorganic structures. The results demonstrate that deproteination of bone is not a necessary precursor to obtain spectral information.

Calcium density measurement in histological samples of trabecular bone of normal subjects: relationship with aging

It is well-known that bone volume decreases with age both in normal subjects and particularly in osteoporotic patients. It is not well demonstrated, however, whether bone loss is associated with changes in the composition of bone tissue and especially with altered concentration of mineral elements. To verify whether calcium density changes with aging, autoptic specimens, of iliac crest trabecular bone from 20 normal subjects between 21 and 66 years, 10 males and 10 females were analyzed by using a new method which allows the measurement of calcium density in a non-destructive way, on entire histologic sections of the bone. Bone specimens were embedded in araidite and tissue sections, about 3 microm thick and 4x4 mm size, were mounted onto polyvinyl acetate films and analyzed by PIXE (proton induced X-ray emission) using the CISE setup for calcium content determination. The same bone tissue sections were then mounted on glass slides, stained with the Von Kossa method and the volume of calcified bone was measured with a semiautomatic image analyzer (Videoplan). 3 to 4 sections from each subject were analyzed and the values of calcium concentration were derived in microg/microl. Similar values of calcium density were found in males and females (535.6+77.1 and 539.2+74.1 microg/microl, respectively). No significant correlation between calcium density and age was observed either in all cases (r=0.0925) or in males (r=-0.0687) and in females (r=0.2676) separately. The unchanged calcium density during aging obtained by combining PIXE and histomorphometric techniques demonstrates that the skeletal calcium reduction observed in old age and probably during osteoporosis, is mainly due to the decrease of bone volume.

Studies on EDTA extracts and collagenase digests from osteoporotic cancellous bone of the femoral head

Using EDTA extraction and collagenase digestion, cancellous bone of the femoral heads from 10 normal and 9 osteoporotic subjects were analyzed for their contents of collagen, sialoprotein, proteoglycan and carbohydrate. The percentage of extracted matrix proteins of the osteoporotic bone in EDTA was significantly decreased, as was the collagenase-resistant fraction (p less than 0.05). The sialic acid level in osteoporotic bone matrix was lower than in controls (p less than 0.05). The alterations found in bone matrix constituents in osteoporotic bone relative to controls suggest that in osteoporosis and fractures, not only bone mass changes, but also bone quality changes play a role in bone strength.

PIXE technique for calcium analysis of human bone

The determination of calcium content in human bone tissue is very useful in metabolic diseases of bone, such as renal osteodystrophy, osteoporosis, hyperparathyroidism, and osteomalacia of diverse etiology. The PIXE technique allows calcium to be directly determined in bioptic tissue sections properly, sampled for histological optical and/or electron microscopy examination.Bone semithin sections (3 μm thick, 4×4 mm(2) dimensions), cut by ultramicrotome and deposited onto polyvinyl acetate films, underwent PIXE analysis using the CISE set-up. Histomorphometric (after standard staining), evaluation of calcified bone volume (CBV) in absolute value allows calcium density to be determined. A total of nine bone biopsies were analyzed (three sections each) obtaining values ranging between 352 and 482, with an average value of 421.5±15.3 (M±SE) μg/μL, in good agreement with literature data (obtained by AAS technique on dissected bone samples).The aim of this paper is to emphasize the usefulness, of combined PIXE and histomorphometric techniques for the study of calcium content in bone tissue in both healthy and diseased bones.

Biological characterization of human bone tumors. V. Zonal characterization of osteosarcoma: topological biochemical analysis correlated with morphology

Human osteosarcoma specimens were sliced in a cryomicrotome under strict morphological guidance. Serial sections of ten 10 micron slices each were collected in two groups according to morphologic criteria, one containing mostly undifferentiated tumor tissue, the other predominantly well-differentiated tumor tissue. The two series were analysed chemically for alkaline phosphatase (APase) acid phosphatase (acPase), beta-glucuronidase and proteolytic activities; protein, phosphorus, hydroxyproline, hexosamine, water and collagen contents were also determined. Four different types of osteosarcoma were studied: case 1 was a highly malignant osteoblastic osteosarcoma, case 2 a small cell sclerosing osteosarcoma case 3 a well-differentiated osteosarcoma, and case 4 a highly malignant anaplastic osteosarcoma. The types of cases 1, 2 and 3 are known as osteoid-forming tumors. In their less well differentiated areas APase activity was about twice as high as in better differentiated osteosarcoma. In contrast, no APase was found in the wholly undifferentiated areas of case 4, while the enzyme showed a marked increase in the areas of incipient differentiation of this tumor. The matrix of tumors differs with regard to collagen and hexosamine contents, in accordance with the general state of differentiation. In general, increasing hexosamine contents together with decreasing hydroxyproline contents will reflect the anaplastic, dedifferentiated osteosarcoma. Calcification evident in the better differentiated areas of osteosarcoma is indicated by the phosphorus content, highest in case 2, with cases 3, 1, and 4 following in sequential order.

Biological characterization of human bone tumors. IV. Combined biochemical and histological analyses of different osteosarcomas

A new technique was applied to the study of human osteosarcoma. Ten slices of 10 micron were cut serially from 2 X 2 X 6 mm shock frozen blocks of human osteosarcoma for chemical analysis. Before and after each series of 10 slices, one slice of 10 micron was separated for morphological analysis. Four different types of osteosarcoma were investigated: Case 1 was an atypical osteoblastic osteosarcoma, case 2 a small cell sclerosing osteosarcoma, case 3 a well-differentiated parosteal osteosarcoma grade I, and case 4 a highly malignant anaplastic osteosarcoma. Alkaline phosphatase, acid phosphatase, beta-glucuronidase and proteolytic activities were analysed as well as matrix collagen and hexosamine, phosphorus (Pi and Po), protein, DNA, and water content. In accordance with the morphology, the obtained data illustrate the great heterogeneity of osteosarcomas. Although case 1, 2 and 3 all represent calcifying types of the tumor, characteristic differences exist with regard to the matrix and the degree of calcification. In contrast to these three, case 4 presents a noncalcified type of osteosarcoma whose matrix contains relatively high amounts of hexosamine and low amounts of collagen, whereas DNA and water contents are high. The data from the analysis of osteosarcoma were compared with previous results from the calf epiphyseal growth plate in order to define differences and similarities between the formation of tumor bone and the physiological formation of hard tissue.

Chemical composition of human bone

The mineral and non-collagenous organic components of normal human femoral cortex were examined following powdering, demineralization with EDTA and digestion with bacterial collagenase. The protein, hexose, sialic acid and uronic acid contents of the matrix were determined. Neonatal bone had lower levels of mineral and calcium and higher levels of organic material and sialic acid than adult bone, suggesting increased glycoprotein content in neonatal bone. The soluble non-collagenous matrix of human femoral cortex was examined by gel filtration on Sephadex G100 and by ion-exchange chromatography on DEAE-cellulose. Four fractions were eluted off Sephadex-G100: a large molecular weight fraction, a shoulder on the descending portion of this, both of which contained sialic acid and two smaller molecular weight fractions. The material eluted off DEAE-cellulose was separated into 6 fractions which were similar to those found for beef and rabbit bone matrix. Human bone matrix appeared more resistant to collagenase digestion than beef bone, soluble collagen eluted later off DEAE-cellulose than beef bone; sialic acid gave 3 peaks: a major and two lesser ones. The sialic acid-containing material in the fifth fraction was probably bound to proteoglycan. Rabbit bone has 2 to 3 sialic acid peaks whereas beef bone has one, indicating species differences in cortical bone matrix.

Ca2+-binding glycoprotein in avian bone induced by estrogen

The discovery in calcifying cartilage of a glycoprotein, endowed with high calcium affinity and alkaline phosphatase activity, has prompted the investigation of the presence of this compound in other calcified tissues. From medullary bone, a tissue which is highly mineralized under estrogen stimulus, a glycoprotein has been extracted which had the properties described. Besides the high calcium affinity (KD = 10(-7)M), this protein shows phosphatase activity and rate of hydrolysis of ATP, GTP and pyrophosphate was measured. Analysis of the chemical composition of the matrix of the medullary bone indicates that proteoglycans are present in large amounts. The calcium binding glycoprotein appears to be a compound present in different calcified tissues.

The ulstrastructure of the extracellular phase of bone as observed in frozen thin sections

The fine structure of the extracellular phase of avian medullary bone and embryonic chick femur was examined in thin sections prepared by ultracryotomy and ultramicroincineration. Since contact with solutions was completely avoided, little or no loss or dislocation of mineral constituents could occur. Amorphous bone mineral (ABM) was present in two forms: as 15-30 nm spheres and as a structure-free haze. Removal of all organic material by low temperature ashing left the ABM intact. Crystals were usually associated with the ABM. In newly ossifying regions clusters or nodules of randomly oriented crystals and ABM appeared to coalesce when they reached approximately 1 micron in diameter. In highly calcified regions crystals appeared to be oriented along collagen fibers. ABM did not appear to be associated with collagen. Unmineralized collagen was visible in osteoid after staining with dry OsO4 vapor and it appeared to be diverted around nodules. Structures which resembled matrix vesicles were present. Selected area electron diffraction patterns indicated the presence of hydroxyapatite.

An electron microprobe analysis of osteofluorosis in the rabbit

Osteofluorosis was induced in rabbits by the ingestion of 500 ppm F in their drinking water over a period of 30 days. The tibiae from experimental and control animals were selected for macroscopic, microscopic and microradiographic observation. Transverse sections of 100 mum thickness were prepared for an electron-microprobe analysis to determine Ca, P and F concentrations and to display the topographical distribution of F as revealed by the X-ray image of its Kalpha1 radiation. Variation in amount of periosteal and endosteal deposition was observed along the length of the bone. Changes, including numerous mottled osteones, were seen in the compact zone of bone which had been formed prior to the start of the experiment. The Ca/P ratio appeared to show a variation related to the F concentration.