Search PubMed⌕ Search

Biomedical subjects

A Boyde

Publications and source records attributed to A Boyde.

At least 73 records · Page 4Linked to original sources
PubMed1995

Mineral density quantitation of the human cortical iliac crest by backscattered electron image analysis: variations with age, sex, and degree of osteoarthritis.

Bone samples from the rim of the iliac crest were obtained at autopsy from 59 patients aged 23 to 75 years, of whom 10 men and 10 women aged 50-75 years had osteoarthritis diagnosed by hand X-rays. An equal number in the same age group and 10 men and 9 women aged less than 50 years were without osteoarthritis. After embedding the bone in PMMA, the blocks were cut, polished, and coated with carbon. The fractions of bone falling within four consecutive bands of signal level were derived from digital backscattered electron imaging. Normal males had more low and medium density bone and normal females more very high density phase tissue proportionately. In both male and female osteoarthritis cases, low and medium fractions were low. The very high density fraction was mainly calcified fibrocartilage; when it was excluded from the calculations, the low, medium, and high phases occurred equally in normal males but increased stepwise in normal females and in osteoarthritis cases of both sexes. The results suggest a lower rate of bone renewal in females than males, and in male osteoarthritis subjects than normal males. An increased proportion of bone of high density would reduce the quality of the bone by increasing its stiffness.

Adult↗
PubMed1995

Effects of ethanol on bone cells in vitro resulting in increased resorption.

Abuse of alcohol has been found to be an important risk factor for fractures and osteoporosis, and tissue culture experiments have indicated that low concentrations of ethanol can affect bone formation and resorption. This study investigated direct effects of ethanol on bone cells using an in vitro resorption assay. Osteoclasts from long bones of 19-day prehatch chicks were seeded onto slices of dentine and cultured with control medium alone, or medium containing 0.001%, 0.01% or 0.1% ethanol, at 37 degrees C with 5% CO2 for 24 h before being removed. The volumes and areas of resorption pits made in the dentine were measured using confocal laser reflection microscopy (Lasertech 1LM21 system) and the pits counted. An increase in the pit numbers and mean pit areas, volumes and volume/area ratios was observed with 0.001% and 0.01% ethanol, with a dose-related, bell-shaped curve of resorption. Greatest mean volume resorbed per pit (p < 0.05), mean area resorbed per pit (p < 0.01) and number of pits was at 0.01% ethanol. Volume/area (mean depth) per pit was greatest at 0.001% ethanol (p < 0.05). This study has shown that ethanol, even at blood concentrations experienced by the social drinker, has an immediate direct effect on bone cells in vitro, resulting in increased resorption by osteoclasts.

Animals↗
PubMed1994

Correlated alkaline phosphatase histochemistry and quantitative backscattered electron imaging in the study of rat incisor ameloblasts and enamel mineralization.

The different functional conditions of pre-ameloblasts, secretory ameloblasts, and maturation ameloblasts in 9 day rat incisors were recognized using high resolution light microscopic alkaline phosphatase histochemistry: Digital backscattered electron imaging was performed using the block surfaces from which thin sections were taken for histochemical study. It was possible to correlate exact locations in histochemical sections with positions in the block face at all stages of enamel mineralization from early secretion through late maturation. The first steep increase in the rate of mineralization of completed enamel matrix occurs after the first transition from smooth ended ameloblasts to ruffle ended ameloblasts. In the 9 day rat incisors used for this purpose, there are only two smooth to ruffle cyclical transitions, and the width of successional smooth ended bands of ameloblasts in the maturation cycling process is always narrow. Nevertheless, there seems to be a good correlation between mineralization increase and the acquisition of the high alkaline phosphatase activity in the deeply enfolded distal cytoplasm of the ruffle-ended maturation stage ameloblasts.

Alkaline Phosphatase↗
PubMed1994

Effects of medium acidification by alteration of carbon dioxide or bicarbonate concentrations on the resorptive activity of rat osteoclasts.

Little is known about the extracellular conditions or factors that stimulate mature osteoclasts to resorb mineralized tissues. Isolated mammalian osteoclasts are strongly stimulated by protons in HEPES-buffered culture media in the absence of CO2 and HCO3-, but it has been reported that cell-mediated Ca2+ release from bone organ cultures is increased only when media are acidified by reduction of HCO3- concentrations, and not by increasing PCO2 (considered models of metabolic and respiratory acidosis, respectively). We investigated this question using disaggregated rat osteoclasts cultured on dentin slices for 24 h. The number of pits resorbed per osteoclast was stimulated in media acidified by manipulation of either HCO3- or CO2 concentrations. In experiments in which incubator CO2 was varied, resorption was almost abolished in the presence of 2.5% CO2 at pH 7.61 but increased in a stepwise manner up to 1.3 pits per osteoclast when dentin slices were cultured with 10% CO2 at pH 6.97. The depths and widths of pits, measured using a confocal laser reflection microscope, also tended to increase with increasing CO2 and decreasing pH. However, in experiments where pH was lowered by reducing medium HCO3-, pit size decreased, partially offsetting the increased number of pits resorbed per osteoclast. These findings suggest that rat osteoclasts may be more sensitive to stimulation by CO2 acidosis than by HCO3- acidosis, at least in the short term, and may possibly reflect local regulatory processes in bone.

Acid Phosphatase↗
PubMed1994

Inhibition of bone resorption by selective inactivators of cysteine proteinases.

Inactivators of cysteine proteinases (CPs) were tested as inhibitors of bone resorption in vitro and in vivo. The following four CP inactivators were tested: Ep475, a compound with low membrane permeability which inhibits cathepsins B, L, S, H, and calpain; Ep453, the membrane-permeant prodrug of Ep475; CA074, a compound with low membrane permeability which selectively inactivates cathepsin B; and CA074Me, the membrane-permeant prodrug of CA074. The test systems consisted of 1) monitoring the release of radioisotope from prelabelled mouse calvarial explants and 2) assessing the extent of bone resorption in an isolated osteoclast assay using confocal laser microscopy. Ep453, Ep475, and CA074Me inhibited both stimulated and basal bone resorption in vitro while CA074 was without effect; the inhibition was reversible and dose dependent. None of the inhibitors affected protein synthesis, DNA synthesis, the PTH-enhanced secretion of beta-glucuronidase, and N-acetyl-beta-glucosaminidase, or the spontaneous release of lactate dehydrogenase. Ep453, Ep475, and CA074Me dose-dependently inhibited the resorptive activity of isolated rat osteoclasts cultured on bone slices with a maximal effect at 50 microM. The number of resorption pits and their mean volume was reduced, whilst the mean surface area remained unaffected. Again, CA074 was without effect. Ep453, Ep475, and CA074Me, but not CA074, when administered subcutaneously at a dose of 60 micrograms/g body weight inhibited bone resorption in vivo as measured by an in vivo/in vitro assay, by about 20%. This study demonstrates that cathepsins B, L, and/or S are involved in bone resorption in vitro and in vivo. Whilst cathepsin L and/or S act extracellularly, and possibly intracellularly, cathepsin B mediates its effects intracellularly perhaps through the activation of other proteinases involved in subosteoclastic collagen degradation.

Animals↗
PubMed1994

Deciduous enamel defects in low-birth-weight children: correlated X-ray microtomographic and backscattered electron imaging study of hypoplasia and hypomineralization.

Enamel does not remodel, and disturbances occurring during development may remain in the tooth as a permanent record of the upset. Mineralization in prenatal and postnatal deciduous enamel was studied in the shed deciduous incisors of low-birth-weight (LBW: < 2kg) children. The specific objective was to gain further insight into the mechanism of formation of developmental defects of enamel. Sections at a resolution of 22-40 microns were reconstructed using X-ray microtomography (microCT) giving absolute measurements of linear absorption coefficient for AgK alpha radiation. Detail to ca. 1 micron resolution was obtained using automated, digital backscattered electron (BSE) imaging of PMMA-embedded material. Matching the histograms of BSE and microCT images made possible the calibration of the mean atomic number-dependent signal in the BSE images. The comparison of abnormal, affected enamel regions and post-recovery, normal, unaffected regions could be made in the same teeth, since these zones were easily recognized from the distribution of hypoplasia and hypomineralization. The microCT values, converted to calculated mineral densities, ranged from 2.3 g cm-3 to 2.6 g cm-3 in LBW hypoplastic, and between 2.65 and 2.78 g cm-3 in control primary enamel and post-defect, post-natal LBW enamel. Hypoplasia with or without minimal hypomineralization indicated recovery of the ameloblasts in the maturation phase. Disturbance during late matrix formation and early maturation resulted in hypoplasia and hypomineralization.

Child, Preschool↗
PubMed1994

Simulation of bone resorption-repair coupling in vitro.

In the normal adult human skeleton, new bone formation by osteoblasts restores the contours of bone surfaces following osteoclastic bone resorption, but the evidence for resorption-repair coupling remains circumstantial. To investigate whether sites of prior resorption, more than the surrounding unresorbed surface, attract osteoblasts or stimulate them to proliferate or make new matrix, we developed a simple in vitro system in which resorption-repair coupling occurs. Resorption pits were produced in mammalian dentine or bone slabs by culturing chick bone-derived cells on them for 2-3 days. The chick cells were swept off and the substrata reseeded with rat calvarial osteoblastic cells, which make bone nodules in vitro, for periods of up to 8 weeks. Cell positions and new bone formation were investigated by ordinary light microscopy, fluorescence and reflection confocal laser microscopy, and SEM, in stained and unstained samples. There was no evidence that the osteoblasts were especially attracted to, or influenced by, the sites of resorption in dentine or bone before cell confluence was reached. Bone formation was identified by light microscopy by the accumulation of matrix, staining with alizarin and calcein and by von Kossa's method, and confirmed by scanning electron microscopy (SEM) by using backscattered electron (BSE) and transmitted electron imaging of unembedded samples and BSE imaging of micro-milled embedded material. These new bone patches were located initially in the resorption pits. The model in vitro system may throw new light on the factors that control resorption-repair coupling in the mineralised tissues in vivo.

Animals↗
PubMed1994

Three-dimensional photographic study of cancellous bone in human fourth lumbar vertebral bodies.

In an analysis of the 3D architecture of cancellous bone, two-dimensional techniques are of limited value. A simple technique employing stereophotographs of whole sections of lumbar vertebrate made possible a detailed description of the 3D structure of the normal fourth lumbar vertebral body and its changes with ageing and osteoporosis. Parallax measurements were used to calculate the real lengths of horizontal trabeculae. The bone presented a continuous spectrum of microstructure, from a honeycomb of tubes, to plates and braces and, finally, fragile rods. A distinct pattern was produced in osteoporotic samples by the removal of horizontal and selected vertical trabeculae followed by a thickening of the remaining vertical trabeculae in the peripheral regions. Very long, thin horizontal trabeculae were formed in all three zones (superior, middle and inferior) during this process. The observation of porotic architecture in intact specimens points to the inadequacy of the clinical criterion of the occurrence of a fracture in judging the osteoporotic state.

Adult↗
PubMed1994

The effect of 3-amino-1-hydroxypropylidene-1,1-bisphosphonate (ADP) on the resorptive function of osteoclasts of known nuclear number.

Bisphosphonates (BP) are known to suppress osteoclastic resorption in vivo and in vitro, but doubt persists as to how, and the effect of BP on the resorptive capability of osteoclasts of known nuclear number is unknown. We aimed to find whether the addition of 3-amino-1-hydroxypropylidene-1,1- bisphosphonate (APD) changed the nuclear profile of an osteoclast population in vitro, and to measure the resorptive efficiency of individually characterized osteoclasts in the presence and absence of the BP. Prehatch chick bone cells were cultured for 24 hours on slices of dentine in medium with or without added APD at 10(-6) M or 10(-8) M, or in control medium on dentine presoaked with 10(-6) M APD for 48 hours. Total pit counts, and pit depths, areas and volumes for pits made by osteoclasts of known nuclear number, were found using confocal video-rate laser reflection microscopy and 3-D image analysis software. APD in the medium inhibited resorption and reduced the volume, area, and depth resorbed per nucleus per chick osteoclast. The nuclear number distribution did not shift significantly, suggesting that no preferential effect arose from the APD affecting one size of cell more than another. The large reduction found in pit numbers, depths, areas, and volumes in the APD dentine-pretreated group supports previous views that BP released during resorption act as metabolic inhibitors, altering protein synthesis by the cell. Larger cells made larger pits, but resorptive efficiency was similar for different cell sizes within the control or APD-treated groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Investigation of the early mineralisation on collagen in dentine of rat incisors by quantitative electron spectroscopic diffraction (ESD).

The earliest crystallites in dentine appear as chains of "dots" in ultra-thin sections viewed by transmission electron microscopy. These dots rapidly coalesce along the longitudinal directions of the collagen microfibrils to form needle-like structures that coalesce preferentially in lateral directions to form ribbon-like or plate-like crystallites. This morphological interpretation is supported by line-scans of the corresponding zero-loss filtered electron spectroscopic diffraction patterns, which demonstrate the crystalline structure of the dentine mineral (apatite). The intensity ratio of the Debye-Scherrer rings of the characteristic Bragg-reflections (002 to 300, together with 1 or 2 unresolved reflections) shows a maximum in the region of early chain-like and needle-like crystallites, decreasing with maturation of the dentine mineral to the ribbon-plate-like crystallites. Detailed investigations using line-scans of the zero-loss filtered electron spectroscopic diffraction patterns through the dentine zone show that the intensity ratio found near the mineralisation front is repeated 3-5 times at distances of about 10-20 microns. This may represent a circadian pattern of mineralisation corresponding to light microscopically visible incremental lines in dentine.

Animals↗
PubMed1994

Questions of quality and quantity--a morphological view of bone biology.

The quality of bone may be as important as its quantity, influencing bone strength and turnover. Using quantitative BSE (backscattered electron) imaging, we have found changes in the mineral density of bone with age, the proportion of denser bone increasing, and discontinuities occurring in the mineral phase between packets of bone. SEM of resorptive fields showed that severing of trabeculae occurs with deep, vertical excavations; their thinning is by long, narrow, resorption grooves extending from node to node. Grooved regions may become deeper, undercut and burrowing. In vitro, we showed that larger osteoclasts made larger pits. However, the volume of tissue resorbed per nucleus did not increase, and could decrease. Interactions between osteoclasts and autologous osteoblastic cells were observed by time-lapse video microscopy in vitro. Message-mediated contact behaviour, dependent upon the state of activation of both cell types, resulted in changes in the territory of the responding cell. The numbers and sizes of gap junctions between rat parietal bone cells in situ were investigated using confocal fluorescence and reflection microscopy and polyclonal antisera to connexin-43 peptides. The junctions reached approximately 1.3 microns in diameter, with 0.2 microns as the limit of detection. The extent of connectivity and communication may also affect bone quality.

Animals↗
PubMed1993

Novel method for stereo imaging in light microscopy at high magnifications.

A new method for realizing direct stereoscopic (3D) views of thick microscopic sections employs multiple oblique illuminating beams and a single objective lens. Excellent 3D images are obtained in the higher magnification range, where conventional stereo microscopes no longer function. Using conventional microscope optics, significant increases in depth of focus and sharpness are demonstrated.

Alzheimer Disease↗
PubMed1993

The incidence and size of gap junctions between the bone cells in rat calvaria.

Polyclonal antisera to synthetic peptides matching sequences on the cytoplasmic regions of connexin-43, a gap junction protein first identified in rat heart, have been used to immunolabel gap junctions in the calvarial bone, maintained intact as in vivo, of 1- to 2-week-old rats. The specimens were examined in reflection and fluorescence modes by scanning laser confocal microscopy, and the numbers of gap junctions and their sizes estimated. The mean number of connexin-43 immunolabelled junctions per osteoblast (n = 65) was 15.3 (SD +/- 4.5). The mean length of 227 junctions, selected for the sharpness of the image of the fluorescent spot, was 0.67 micron (SD +/- 0.18; range 0.37-1.29 microns) and their mean area 0.26 micron2 (SD +/- 0.145; range 0.075-0.93 micron2); these probably fell within the upper half of the total size range. Gap junctions were detected between preosteoblasts, osteoblasts, osteocytes and chondrocytes, and between these juxtaposed cell types. In addition, connexin-43 immunolabelled junctions were found between some osteoclasts and overlying mononuclear cells at active sites of resorption.

Animals↗
PubMed1993

Functional associations between collagen fibre orientation and locomotor strain direction in cortical bone of the equine radius.

A novel technique for determining the collagen fibre orientation pattern of cross-sections of cortical bone was used to study mid-diaphyseal sections from the equine radius. Several in vivo strain gauge studies have demonstrated that this bone is loaded in bending during locomotion in such a way that the cranial cortex is consistently subjected to longitudinal tensile strains and the caudal cortex to longitudinal compressive strains. Twenty-three radii from 17 horses were studied. All the bones obtained from adult horses exhibited a consistent pattern of collagen fibre orientation across the cortex. The cranial cortex, subjected to intermittent tension, and the lateral and medial cortices, through which the neutral axis passes, contained predominantly longitudinally oriented collagen fibres. The caudal cortex, subjected to longitudinal compression during life, contained predominantly oblique/transverse collagen. This pattern was less evident in bones from foals. Microscopic analysis of the bones studied showed that primary lamellar bone was composed of predominantly longitudinal collagen fibres, irrespective of cortex. However, there was a strong relationship between cortical location and fibre orientation within remodelled bone. Secondary osteons which formed in the caudal (compressive) cortex contained predominantly oblique/transverse collagen, while those which formed elsewhere contained longitudinal collagen. This observation explained the developmental appearance of the characteristic macroscopic pattern of collagen fibre orientation across the whole cortex in the adult. These findings provide evidence for the existence of a relationship between the mechanical function of a bone with its architecture, and now demonstrate that it extends to the molecular level.

Aging↗
PubMed1993

Mechanical implications of collagen fibre orientation in cortical bone of the equine radius.

Mechanical test specimens were prepared from the cranial and caudal cortices of radii from eight horses. These were subjected to destructive tests in either tension or compression. The ultimate stress, elastic modulus and energy absorbed to failure were calculated in either mode of loading. Analysis was performed on the specimens following mechanical testing to determine their density, mineral content, mineral density distribution and histological type. A novel technique was applied to sections from each specimen to quantify the predominant collagen fibre orientation of the bone near the plane of fracture. The collagen map for each bone studied was in agreement with the previously observed pattern of longitudinal orientation in the cranial cortex and more oblique to transverse collagen in the caudal cortex. Bone from the cranial cortex had a significantly higher ultimate tensile stress (UTS) than that from the caudal cortex (160 MPa vs 104 MPa; P < 0.001) though this trend was reversed in compression, the caudal cortex becoming relatively stronger (185 MPa vs 217 MPa; P < 0.01). Bone from the cranial cortex was significantly stiffer than that from the caudal cortex both in tension (22 GPa vs 15 GPa; P < 0.001) and compression (19 GPa vs 15 GPa; P < 0.01). Of all the histo-compositional variables studied, collagen fibre orientation was most closely correlated with mechanical properties, accounting for 71% of variation in ultimate tensile stress and 58% of variation in the elastic modulus. Mineral density and porosity were the only other variables to show any significant correlation with either UTS or elastic modulus. The variations in mechanical properties around the equine radius, which occur in close association with the different collagen fibre orientations, provide maximal safety factors in terms of ultimate stress, yet contribute to greater bending of the bone as it is loaded during locomotion, and thus lower safety factors through the higher strains this engenders.

Animals↗
PubMed1993

Confocal images of marrow stromal (Westen-Bainton) cells.

A cytochemical method was used for imaging a defined subset of marrow stromal cells (alkaline phosphatase-positive reticulum cells, hereinafter referred to as Westen-Bainton cells), which are endowed with membrane-associated alkaline phosphatase. The use of two different types of confocal microscopes was compared: a tandem scanning reflected light microscope and a laser scanning confocal microscope equipped with a 633 nm (helium-neon) laser. Sharp confocal reflection images of the cytochemically stained stromal cells were obtained with both microscopes. Three-dimensional reconstructions were generated with both systems, revealing morphological features of Westen-Bainton cells related to both their actual shape and organization within tissue architecture, which were not otherwise appreciated. The observations were extended to individual cases of bone pathology, and demonstrated the value of confocal microscopy for the investigation of marrow-bone relationships in physiology and disease.

Alkaline Phosphatase↗
PubMed1993

Scanning electron microscopy of human lumbar vertebral trabecular bone surfaces.

Trabecular bone from fourth lumbar vertebral bodies of 30 autopsy subjects (18 male and 12 females, 30-91 years of age) was investigated using surface mode scanning electron microscopy. In the younger individuals, proper coupling of formation and resorption appeared to have maintained both the bone mass and the shape and structural integrity of the trabecular elements. In elderly individuals, including osteoporotics, irregularities and uncoupling of these activities brought about a loss of bone and a disruption of trabecular structure. Distinct resorption patterns (lateral and vertical) are responsible for trabecular thinning and removal of structural elements. Irregularities in the formative process in old age may account for the compensatory thickening and changes in shape and texture of trabecular elements. The mechanisms involved in the occurrence of microfractures and the fate of disconnected elements were also identified. An increased proportion of arrested mineralizing fronts is found in older individuals and in frank osteoporotics. Resorption may occur through osteoid and arrested mineralizing fronts, as well as through resting, fully mineralized surfaces.

Adult↗