Evaluation of the osteoclastic population in iliac crest biopsies from 36 normal subjects: a histoenzymologic and histomorphometric study

Interest of Bone Histomorphometry in Bone Pathophysiology Investigation: Foundation, Present, and Future

Despite the development of non-invasive methods, bone histomorphometry remains the only method to analyze bone at the tissue and cell levels. Quantitative analysis of transiliac bone sections requires strict methodologic conditions but since its foundation more 60 years ago, this methodology has progressed. Our purpose was to review the evolution of bone histomorphometry over the years and its contribution to the knowledge of bone tissue metabolism under normal and pathological conditions and the understanding of the action mechanisms of therapeutic drugs in humans. The two main applications of bone histomorphometry are the diagnosis of bone diseases and research. It is warranted for the diagnosis of mineralization defects as in osteomalacia, of other causes of osteoporosis as bone mastocytosis, or the classification of renal osteodystrophy. Bone biopsies are required in clinical trials to evaluate the safety and mechanism of action of new therapeutic agents and were applied to anti-osteoporotic agents such as bisphosphonates and denosumab, an anti-RANKL, which induces a marked reduction of the bone turnover with a consequent elongation of the mineralization period. In contrast, an increased bone turnover with an extension of the formation site is observed with teriparatide. Romosozumab, an anti-sclerostin, has a dual effect with an early increased formation and reduced resorption. Bone histomorphometric studies allow us to understand the mechanism of coupling between formation and resorption and to evaluate the respective role of bone modeling and remodeling. The adaptation of new image analysis techniques will help bone biopsy analysis in the future.

Quantitative histomorphometric analysis of halved iliac crest bone biopsies yield comparable ROD diagnosis as full 7.5mm wide samples

BACKGROUND AND OBJECTIVES

Histomorphometric analysis of a transiliac bone biopsy is the gold standard for the diagnosis of renal osteodystrophy (ROD). This procedure is costly, invasive and usually performed with a trephine with an internal diameter of 7.5 mm. Our objective was to evaluate the accuracy of ROD diagnosis on halved histological bone sections to determine if they are comparable to the standard 7.5 mm samples.

DESIGN

We included 68 bone biopsies performed in CKD patients for diagnostic purposes with a 7.5 mm diameter trephine. Quantitative histomorphometric analysis of the whole bone samples was performed including assessment of bone mineralization, turnover and volume. Each histological section (representing the whole 7.5 mm diameter biopsy) was then divided lengthwise in two hemisections (representing the 3.5 mm diameter biopsy). Histomorphometric analysis was repeated this time on the two hemibiopsies for each sample, blinded from initial results. Diagnoses were classified as osteitis fibrosa, adynamic bone disease, mixed uremic bone disease, osteomalacia or other. Correlations between the whole sample and the hemibiopsies for each parameter were studied. Concordance between the various bone parameters and final ROD diagnosis obtained from the whole section versus the two hemi sections was evaluated.

RESULTS

Highly significant correlations were found between parameters measured on the whole section and the corresponding hemisections, with r coefficient of 0.98 for osteoid surface and thickness and bone formation rate, 0.97 for osteoclast surface, and 0.96 for bone volume (p < 0.001). Final diagnosis was in full accordance between the whole biopsy and the two corresponding hemi-biopsies in 91% of cases.

CONCLUSIONS

Accurate diagnosis of ROD type was obtained by evaluation of bone surface areas of 3 mm diameter. These data suggest that small invasive bone biopsies might provide accurate ROD diagnostics while decreasing both invasiveness and cost of the procedure.

From histology to micro-CT: Measuring and modeling resorption cavities and their relation to bone competence

The process of bone remodelling plays an essential role in the emergence and maintenance of bone geometry and its internal structure. Osteoclasts are one of the three main bone cell types that play a crucial role in the bone remodelling cycle. At the microstructural level, osteoclasts create bone deficits by eroding resorption cavities. Understanding how these cavities impair the mechanical quality of the bone is not only relevant in quantifying the impact of resorption cavities in healthy bone and normal aging, but maybe even more so in quantifying their role in metabolic bone diseases. Metabolic bone diseases and their treatment are both known to affect the bone remodelling cycle; hence, the bone mechanical competence can and will be affected. However, the current knowledge of the precise dimensions of these cavities and their effect on bone competence is rather limited. This is not surprising considering the difficulties in deriving three-dimensional (3D) properties from two-dimensional (2D) histological sections. The measurement difficulties are reflected in the evaluation of how resorption cavities affect bone competence. Although detailed 3D models are generally being used to quantify the mechanical impact of the cavities, the representation of the cavities themselves has basically been limited to simplified shapes and averaged cavity properties. Qualitatively, these models indicate that cavity size and location are important, and that the effect of cavities is larger than can be expected from simple bone loss. In summary, the dimensions of osteoclast resorption cavities were until recently estimated from 2D measures; hence, a careful interpretation of resorption cavity dimensions is necessary. More effort needs to go into correctly quantifying resorption cavities using modern 3D imaging techniques like micro-computed tomography (micro-CT) and synchrotron radiation CT. Osteoclast resorption cavities affect bone competence. The structure-function relationships have been analysed using computational models that, on one hand, provide rather detailed information on trabecular bone structure, but on the other incorporate rather crude assumptions on cavity dimensions. The use of high-resolution representations and parametric descriptions could be potential routes to improve the quantitative fidelity of these models.

Structure and quantification of microvascularisation within mouse long bones: what and how should we measure?

Bone marrow vascularisation is involved in both remodeling and hematopoïesis. Challenged mouse models often require imaging and quantitative assessment of blood vessels and bone cell activities for a better understanding of the role of the vascular system. In this study we compared images of mouse hind limb long bone vascularisation after infusion of either barium sulfate or lead chromate-loaded silicon. The images were then analyzed through histology as well as low-resolution and synchrotron-radiation microtomography. We show that barium sulfate infusion provides the best vessel images and furthermore, that it is compatible with staining procedures used in bone histomorphometry and CD31 immunohistochemistry. Bone marrow vascularisation displays large structural and spatial distribution heterogeneity, including large lobular clusters of sinusoids and an unexpectedly substantial amount of capillaries in the adipocytes-rich distal third of the tibia. For an unbiased assessment of bone vascular development/changes, these features must be taken into account. We describe the conditions under which the quantification of microvascularisation on histological sections of barium-infused long bones is reproducible, as applied to seven-month-old male C57/Bl6J and mixed CD1/129Sv/J mice, and we propose a nomenclature for the histological parameters measured. Finally, we validate our technique by studying the effect of ovariectomy on mouse tibial vascular density.

Fractal analysis of mandibular trabecular bone: optimal tile sizes for the tile counting method

Purpose

This study was performed to determine the optimal tile size for the fractal dimension of the mandibular trabecular bone using a tile counting method.

Materials and Methods

Digital intraoral radiographic images were obtained at the mandibular angle, molar, premolar, and incisor regions of 29 human dry mandibles. After preprocessing, the parameters representing morphometric characteristics of the trabecular bone were calculated. The fractal dimensions of the processed images were analyzed in various tile sizes by the tile counting method.

Results

The optimal range of tile size was 0.132 mm to 0.396 mm for the fractal dimension using the tile counting method. The sizes were closely related to the morphometric parameters.

Conclusion

The fractal dimension of mandibular trabecular bone, as calculated with the tile counting method, can be best characterized with a range of tile sizes from 0.132 to 0.396 mm.

Catabolic properties of microdissected human endosteal bone lining cells

Bone lining cells cover > 80% of endosteal surfaces of human cancellous bone. Current research assigns to them a dual role: (1) as a biological membrane regulating exchange of substrates between the bone fluid compartment and the extracellular fluid of bone marrow and (2) as a signaling link between the osteocytic network as mechanical receptor and the osteoclastic cell pool for local induction of bone resorption. Furthermore, a catabolic role has been considered. We therefore examined the presence of matrix-metalloproteinases (MMPs) and their physiological tissue inhibitors (TIMPs) as putative proteolytic elements. Firstly, human cancellous bone from 60 patients was examined by immunofluorescence with antibodies against MMPs and TIMPs. Secondly, we applied laser-assisted microdissection (LMD) to isolate bone lining cells from frozen sections of human trabecular bone. mRNA analysis was performed using a single-cell PCR protocol. Three laser microdissection systems were tested: the new generation of Leica LMD and P.A.L.M. laser pressure catapulting (LPC) were compared to P.A.L.M. laser microdissection and micromanipulation (LMM). In a few pooled cell profiles, mRNA of MMP13, MMP14, TIMP1, and CBFA-1 was clearly detected. By immunofluorescence MMP13 and -14 as well as TIMP1 and -2 were strongly present in lining cells, while MMP2, TIMP3, and TIMP4 showed weak or negative signals. Although the functional impact of these enzymatic components remains open, there is additional evidence for a catabolic function of lining cells. The new diode-laser microdissection with LMD and LPC proved to be especially suitable to gain new insights into the properties of bone lining cells.

Dynamic simulation of three dimensional architectural and mechanical alterations in human trabecular bone during menopause

A three dimensional (3D) computational simulation of dynamic process of trabecular bone remodeling was developed with all the parameters derived from physiological and clinical data. Contributions of the microstructural bone formation deficits: trabecular plate perforations, trabecular rod breakages, and isolated bone fragments, to the rapid bone loss and disruption of trabecular microarchitecture during menopause were studied. Eighteen human trabecular bone samples from femoral neck (FN) and spine were scanned using a micro computed tomography (microCT) system. Bone resorption and formation were simulated as a computational cycle corresponding to 40-day resorption/160-day formation. Resorption cavities were randomly created over the bone surface according to the activation frequency, which was strictly based on clinical data. Every resorption cavity was refilled during formation unless it caused trabecular plate perforation, trabecular rod breakage or isolated fragments. A 20-year-period starting 5 years before and ending 15 years after menopause was simulated for each specimen. Elastic moduli, standard and individual trabeculae segmentation (ITS)-based morphological parameters were evaluated for each simulated 3D image. For both spine and FN groups, the time courses of predicted bone loss pattern by microstructural bone formation deficits were fairly consistent with the clinical measurements. The percentage of bone loss due to trabecular plate perforation, trabecular rod breakage, and isolated bone fragments were 73.2%, 18.9% and 7.9% at the simulated 15 years after menopause. The ITS-based plate fraction (pBV/BV), mean plate surface area (pTb.S), plate number density (pTb.N), and mean rod thickness (rTb.Th) decreased while rod fraction (rBV/BV) and rod number density (rTb.N) increased after the simulated menopause. The dynamic bone remodeling simulation based on microstructural bone formation deficits predicted the time course of menopausal bone loss pattern of spine and FN. Microstructural plate perforation could be the primary cause of menopausal trabecular bone loss. The combined effect of trabeculae perforation, breakage, and isolated fragments resulted in fewer and smaller trabecular plates and more but thinner trabecular rods.

Bone changes in myelofibrosis with myeloid metaplasia: a histomorphometric and microcomputed tomographic study

Myelofibrosis with myeloid metaplasia (MMM) is a clonal disorder of the haematopoietic stem cell which can be associated with marrow fibrosis and/or osteosclerosis. Because bone progenitors and mature bone cells are influenced by the marrow microenvironment, cellular and tissular changes were assessed by histomorphometry in MMM. Thirteen patients, with a clinical proven MMM, had a bone biopsy of the iliac crest with double tetracycline labelling and osteoclast count. Histomorphometry was done at the 2D level (bone volume, osteoid parameters, bone histodynamic parameters and osteoclast count) and 3D level by microcomputed tomography. All patients had clusters of abnormal megakaryocytes in bone marrow. Newly apposed bone packets were observed in 12 patients and corresponded to an increased thickness of some bone units with new lamellae or focal areas of woven bone anchored on the pre-existing trabeculae. Osteoid parameters were unchanged, only bone formation rate appeared considerably increased in seven patients. There was a net tendency for decrease in osteoclast number and conversion of trabecular pillars into plates. An uncoupling of bone remodelling was evidenced with an increased life-span of osteoblasts associated with a normal/reduced osteoclast activity. A very complex network of factors is candidate to explain bone changes observed in MMM.

Activation of p38 MAPK is a key step in tumor necrosis factor-mediated inflammatory bone destruction

OBJECTIVE

To investigate whether activation of p38 MAPK is a crucial signaling factor in inflammatory bone destruction mediated by tumor necrosis factor (TNF). Mice overexpressing TNF were treated with 2 different inhibitors of p38 MAPK, and the effect of this treatment on joint inflammation and structural damage was assessed.

METHODS

Human TNF-transgenic mice received systemic treatment with 2 different p38 MAPK inhibitors (RO4399247 and AVE8677). Treatment was started at the time of symptom onset and lasted for 6 weeks. Mice were assessed for clinical signs of arthritis, bone erosion, and cartilage damage. In addition, the effect of these inhibitors on osteoclast generation in vitro and in vivo was assessed.

RESULTS

Both p38 MAPK inhibitors significantly reduced clinical signs of TNF-mediated arthritis. This was attributable to reducing synovial inflammation by 50% without affecting the cellular composition of the infiltrate. Synovial expression of interleukin-1 and RANKL was reduced upon p38 MAPK blockade, and activation of the molecular target MAPK-activated protein kinase 2 (MAPKAP-2) was also inhibited. Proteoglycan loss of articular cartilage was reduced by 50%, although p38 MAPK inhibition did not change matrix molecule synthesis by cultivated chondrocytes. Importantly, bone loss was almost completely prevented by p38 MAPK inhibition. The numbers of synovial osteoclasts and precursors were dramatically reduced, and both p38 MAPK inhibitors also inhibited in vitro osteoclastogenesis at micromolar concentrations and blocked activation of MAPKAP-2 as well as differentiation markers in cultured osteoclast precursors.

CONCLUSION

These results suggest the major importance of p38 MAPK for TNF-mediated inflammatory bone destruction in arthritis and suggest that inhibition of p38 MAPK might be an important tool for reducing structural damage in rheumatoid arthritis.

First inventory of resorption lacunae on rods and plates of trabecular bone as observed by scanning electron microscopy

In the present study a novel systematic distribution scheme of resorption lacunae (RL) was applied using scanning electron microscopy. RL, classified as either reticulate patch resorption lacunae (RPR) or as longitudinally extended resorption lacunae (LER) [11, were analyzed and quantified according to their localizations on rods (middle, nodes or both) and plates (central or peripheral) in standardized segments from the femoral head of 24 Caucasian subjects without bone disease. Age and gender variations were explored. No clear gender-related distribution pattern could be detected on plates. On rods of males, however, the distribution of RL tended to be higher at the nodes, but seemed to be more prevalent in the middle or extended from the middle to the nodes of rods in females. Certain other non-conclusive tendencies in relation to age, gender, type of RL and localization were observed.

Ability of osteoclast formation from peripheral monocytes using anti-fusion regulatory protein-1/CD98/4F2 monoclonal antibodies in patients with osteoporosis

We investigated the difference in osteoclast formation between patients with osteoporosis and two healthy control groups by inducing it from peripheral blood monocytes with use of anti-fusion regulatory protein- monoclonal antibody. The group of patients with osteoporosis consisted of 35 women and excluded secondary osteoporosis, and the control groups consisted of 12 young healthy volunteers (control I) or 10 individuals age-matched to the patients with osteoporosis (control II). Osteoclast formation declined with age between the two control groups, but this decline was not significant. Fusion rate and the mean number of nuclei in osteoclasts were significantly less in the patients with osteoporosis than in the young or age-matched controls. It was clearly demonstrated that the ability of monocytes to fuse declines significantly in patients with osteoporosis.

Fractal properties of cancellous bone of the iliac crest in vertebral crush fracture

Fractal analysis is a method for describing complex shapes, including the cancellous structure of bone. It describes the surface texture and form of individual trabecular profiles and the overall cancellous structure. Sixty-four postmenopausal women with symptoms of back pain were referred for investigation for osteoporosis. The patients were divided into two groups for comparison: vertebral crush fracture (n = 31, mean age 68.58 +/- 6.47 years), and no vertebral crush fracture (n = 33, mean age 63.36 +/- 7.21 years). Cores of cancellous bone, 3 mm in diameter, were taken from the iliac crest and sectioned. A box-counting method implemented on an image analyzer was used to measure the fractal dimension. Three fractal dimensions describing trabecular surface texture (fractal 1), trabecular shape (fractal 2), and trabecular arrangement (fractal 3) were measured, indicating that cancellous bone has sectional self-similarity. Conventional histomorphometry was also performed on the samples. The results show that fractal 2 is significantly lower in the vertebral crush fracture group than in the nonfracture group (1.15 +/- 0.10 < 1.23 +/- 0.090, p < 0.0013). The histomorphometric analysis shows that bone surface total volume (p < 0.0002), trabecular number (p < 0.0001), and osteoid surface bone surface (p < 0.028) are significantly lower in the fracture group than the nonfracture group. Eroded surface/bone surface (p < 0.056) follows this trend, whereas trabecular separation (p < 0.001) is significantly higher in the fracture group than in the nonfracture group. Fractal 1 and fractal 3 were not significantly different between study groups. The fractal dimension detects changes in the cancellous architecture and gives information about iliac bone transformation in postmenopausal women with vertebral fracture.

Fractal properties of subchondral cancellous bone in severe osteoarthritis of the hip

Primary osteoarthritis of the hip results in changes to the architecture of subchondral cancellous bone. These changes in architecture occur through the action of osteoclasts and osteoblasts in selectively removing and adding bone. The quantitative description of the bone architecture helps in understanding the etiology of primary osteoarthritis. Fractal analysis is a method for describing complex shapes, which is expressed numerically as the fractal dimension. A box counting method was used, where the perimeter of binary profiles of cancellous bone samples was measured for different box sizes. The fractal dimension was the absolute value of the slope of the straight line segments from the plot of the log number of boxes versus the log box size. Cancellous bone samples from two subchondral regions, superior and inferomedial, to the fovea were analyzed from primary severe osteoarthritic specimens taken following total hip replacement surgery (n = 19, aged 51-80 years) and autopsy controls (n = 25, aged 18-90 years). There were three straight line segments identified on the log-log plot, for each subject, indicating a fractal dimension over three different ranges of scale. The results show that in the superior region there is a highly significant difference between the groups (p < 0.0001) for fractal 1 and pivot point 2. The histomorphometry shows significant differences for bone volume/total volume, bone surface/total volume, trabecular separation, and osteoid surface/total volume between groups. In the inferomedial region fractal 1 and fractal 2 are significantly different. For the histomorphometry, trabecular thickness and eroded surface/total volume are significantly different between the groups. The pivot points, i.e., the box size at which the fractal dimension changes, were of similar magnitude to the trabecular thickness and trabecular separation. These data suggest that the fractal geometry analysis of cancellous bone identifies architectural features not easily recognized by conventional bone histomorphometry. The fractal dimension is a descriptor of bone structure which simplifies the description of a complex structure and enables changes in cancellous bone architecture, due to disease, to be identified.

Tartrate-resistant acid phosphate activity as osteoclastic marker: sensitivity of cytochemical assessment and serum assay in comparison with standardized osteoclast histomorphometry

Tartrate-resistant acid phosphatase (TRAP) activity is regarded as an important cytochemical marker of osteoclasts; its concentration in serum is utilized as a biochemical marker of osteoclast function and degree of bone resorption. This study was carried out to assess the sensitivity of TRAP activity both as a cytochemical marker in histological sections and as a biochemical marker in serum in comparison with the standardized histomorphometric variables of osteoclasts. To this end we investigated 24 patients (21 women, 3 men; 60 +/- 17 years of age) affected with various metabolic bone diseases. Osteoclast surface (OcS/BS) and osteoclast number (OcN/BS) were evaluated by standardized histomorphometry in iliac crest biopsies. On the basis of TRAP cytochemical activity, TRAP-positive osteoclast surface (TRAP + OcS/BS) and number (TRAP + OcN/BS) were measured. TRAP-positive cells adjacent to bone and showing one nucleus or no nuclei at all in the plane of section were included in the counts as osteoclasts. Serum TRAP activity was determined by spectrophotometric assay. Values of OcS/BS and OcN/BS were much lower than those of TRAP + OcS/BS (-50%) and TRAP + OcN/BS (-60%), respectively. Correlations between OcS/BS and TRAP + OcS/BS, and between OcN/BS and TRAP + OcN/BS, were highly significant. Serum TRAP was significantly correlated with OcS/BS, OcN/BS, and TRAP + OcN/BS. These correlations, however, were rather low. Moreover, serum TRAP did not correlate with TRAP + OcS/BS. From these results, the conclusion can be drawn that while TRAP activity is confirmed as a valid cytochemical marker for identification of osteoclasts, serum TRAP activity is an osteoclastic marker of weak sensitivity. This may be due to known factors, such as synthesis of the enzyme not being unique to osteoclasts, enzyme instability, and the presence of inhibitors in serum. Mononucleated osteoclasts do not significantly influence the serum enzyme levels.

Osteoclast cytomorphometry in patients with femoral neck fracture

In patients with femoral neck fracture, nutritional deficiencies have been shown to be common. A low calcium diet and/or a reduced vitamin D intake have been suspected to cause secondary hyperparathyroidism responsible for increased bone turn over and bone loss. Parathyroid hormone (PTH) levels are increased in these patients, data which are in accordance with the pronounced changes observed on bone biopsies reflecting a true hyperparathyroidism. We have used a cytomorphometrical approach to characterize PTH-induced changes on the osteoclastic population. Osteoclasts were detected histochemically (by tartrate resistant acid phosphatase staining) on bone biopsies from 10 control subjects, 8 patients with primary hyperparathyroidism and 10 patients with a femoral neck fracture of osteoporotic origin. The maximum Feret's diameter of each osteoclast (Oc.Le) was determined with a semiautomatic image analyzer. In all groups, the frequency distribution of Oc.Le appeared positively skewed. In both hip fractured patients and primary hyperparathyroid patients, the mode of the distribution was higher (25-30 microns) than in controls (20-25 microns). When graphically converted on a probability graph, the osteoclastic populations appeared homogeneous and well described by a lognormal distribution in the three groups. However, osteoclasts appeared similarly enlarged in the groups of patients with primary hyperparathyroidism and with femoral neck fracture. PTH has been shown to increase both the recruitment of mononucleated precursors and their fusion into larger osteoclasts than controls. In the present study, a cytomorphometric method appeared able to identify the border line hyperparathyroidism in the hip fractured patients.

Altered trabecular architecture induced by corticosteroids: a bone histomorphometric study

Prolonged corticosteroid (CS) therapy induces osteoporosis and fractures. Osteoporosis is characterized at the histomorphometric level by reduced bone volume (BV/TV) and disruption of the three-dimensional (3D) trabecular architecture. Several stereological methods have been proposed to characterize these alterations: measurements of trabecular thickness and trabecular number, star volumes, interconnectivity index (ICI) of the bone marrow spaces, and trabecular bone pattern factor (TBP(f)). These methods were computerized with a single program running on an image analyzer to evaluate the bone changes in a series of iliac biopsies performed on 31 male patients. All of them were asthmatic and had received CS for a long period of time. BV/TV was reduced when compared with age-matched controls. In the CS-treated population, exponential relationships were obtained between bone volume and the different connectivity parameters. The various methods used to measure connectivity were well correlated. When the population was divided into two groups (BV/TV greater or less than an 11% threshold), the architectural disturbances were found to imply two mechanisms. A progressive decline in trabecular thickness was noted in both groups versus controls. Trabecular perforations were not established in the group with BV/TV> 11% with the star volume or ICI, although some alterations were detected by trabecular bone pattern factor measurement. However, perforations were revealed in the group with BV/TV < 11% by all the different methods. Perforations seemed to occur when the trabecular thickness was below 70 mu m. This strongly suggests that bone histomorphometry should take into consideration bone volume in combination with detailed 3D descriptors of the trabecular architecture. Several histological methods need to be used in combination to appreciate the 3D architecture of trabecular bone.

Alveolar bone turnover in male rats: site- and age-specific changes

BACKGROUND

This study compares alveolar bone turnover adjacent to distally drifting maxillary first molar teeth of rapidly and slowly growing rats.

METHODS

Two groups of forty male rats (1 and 3 months) were sacrificed. Sera were analyzed for acid (AcP), alkaline (AlkP), and tartrate-resistant acid phosphatase (TRAP). Bone histomophometry was done on parasagittal sections of maxillary molars. Molar drift was quantified cephalometrically.

RESULTS

Distal surface contained more osteoclasts and higher osteoclast percents than mesials at both ages (P < 0.001). There were also more osteoclasts on the distals of the older rats as compared to the young (P < 0.001). Osteoblast percents were higher (P < 0.001) in the older rats on both surfaces. Mesials had higher double-labeled surface, MAR and BFR than distals in the younger rats (P < 0.001). The younger rats had higher (P < 0.001) AlkP, AcP, and TRAP. There were no age-specific differences in rate of molar drift. A model of rate of molar drift (P < 0.0015) containing bone formation measures accounts for 54.9% of the variability.

CONCLUSIONS

We conclude that the bone turnover dynamics adjacent to maxillary first molars represent predominantly remodeling on the distal in both groups and modeling on the mesial only in the young rats, that distal molar tooth drift reflects alveolar bone turnover, and that alveolar bone manifests the marked reduction in bone cell activity that occurs in the rat skeleton after 8 weeks but that this reduction is compensated by recruitment or maintenance of more bone cells at these sites.

Effects of tiludronate on bone loss in paraplegic patients

Immobilization secondary to spinal cord injury is associated with a marked and rapid atrophy of trabecular bone (disuse osteoporosis). This is due to an early increase of osteoclastic bone resorption associated with a pronounced decreased osteoblastic bone formation. Bisphosphonates are antiosteoclastic compounds and they have been effective in preventing disuse osteoporosis. However, some of them also depress osteoblastic activity and may impair the mineralization process. Tiludronate was shown effective in reducing bone resorption in several metabolic bone diseases without inducing mineralization defects. Twenty paraplegic patients (6 females and 14 males) were randomly assigned to three groups: 6 patients entered the placebo group; 7 patients received tiludronate 200 mg/day; and 7 received 400 mg/day. Histomorphometric analysis was performed on transiliac bone biopsies before and after 3 months treatment. An insignificant decrease of bone volume was observed in the placebo group and the 200 mg group. In patients receiving 400 mg/day, a slight increase was noted. Osteoid parameters changed nonsignificantly in three groups although the 400 mg group exhibited a slight tendency to decrease osteoid volume and thickness. Eroded surfaces increased in all groups. The number of osteoclasts (identified histochemically by TRAP staining) increased in the placebo group but decreased in groups receiving tiludronate. Tiludronate appears effective in reducing bone resorption without impairing bone formation in a manner that preserved bone mass and bone cell coupling.

Bone histomorphometry in 50 normal Tunisian subjects

Quantitative bone histomorphometry was done on undecalcified sections of iliac crest bone specimens obtained at autopsy from 50 normal subjects (24 males and 26 females). The following parameters were measured: cortical thickness (Ct.Th), trabecular bone volume (BV/TV), trabecular number (Tb.N), trabecular thickness (Tb.Th), osteoid volume (OV/BV), osteoid surfaces (OS/BS), osteoid thickness (O.Th) and eroded surfaces (ES/BS). There was a significant age-related decrease in BV/TV in both sexes which followed a x3 polynomial regression. A significant decrease of Tb.Th was noted in males after the fifth decade. In males, bone loss was 1.5% per decade, but in females it was 0.36% before menopausal period and 2% after. Other parameters were unrelated to age and sex.

A new method for measuring cancellous bone erosion depth: application to the cellular mechanisms of bone loss in postmenopausal osteoporosis

We have devised a new method for measurement of final depth of erosion in cancellous bone with an intra-individual precision of 4.3% and applied it to determine the mechanism of continuing reduction in trabecular thickness after menopause. Mean erosion depth (SD) was 40.8 (2.0) microns in 10 healthy postmenopausal women and 41.4 (2.1) microns in 10 age-matched patients with postmenopausal osteoporosis; the difference was not statistically significant. In contrast, wall thickness, using a method based on density differences between new and old bone, was 39.5 (2.0) microns in the normal subjects and 35.3 (2.0) microns in the patients with osteoporosis (p less than 0.0001). The balance per remodeling cycle (delta BMU) was -1.34 (2.49) microns in the normal subjects and -6.11 (1.95) microns in the patients with osteoporosis. This difference was also highly significant (p less than 0.001). Indirect estimations of erosion depth and delta BMU, based on the fall in trabecular thickness from an assumed premenopausal value of 147 microns and the number of remodeling cycles accumulated since menopause, agreed closely with the measured values. Erosion depth measured by the Eriksen method also showed no significant difference between the two groups, but because the values were substantially higher delta BMU was improbably high in both groups, did not differ significantly between groups, and was inconsistent with the observed difference in trabecular thickness.(ABSTRACT TRUNCATED AT 250 WORDS)

Age-related changes in resorption cavity characteristics in human trabecular bone

The depth of resorption cavities in trabecular bone is an important determinant of bone structure and has implications relevant to the cellular pathophysiology of bone loss in osteoporosis. However, assessment of resorption depth has proved difficult and few data are available; in this study we report age-related changes in iliac crest trabecular bone obtained from 41 normal healthy subjects (21 female, 20 male) aged 22-80 years. Using 8-microns undecalcified sections stained with toluidine blue, resorption cavities were quantitatively assessed by a computerized technique in which the eroded bone surface is reconstructed and measurements made interactively. Maximum and mean cavity depth showed no significant correlation with age in either sex. The absolute length of eroded surface was unrelated to age but the eroded surface/BS (%) and the number of cavities/BS (/mm) showed a significant positive correlation with age (r = 0.384 and 0.386 respectively, p less than 0.05). No significant correlation was found between age and either cavity area or density. These results suggest that increased resorption depth does not contribute to age-related bone loss, although the possibility that deeper resorption cavities occur which result in trabecular penetration and are therefore unrecognizable cannot be discounted. The age-related increase in eroded surface/BS (%) reflects a decreased available trabecular surface and/or increased number of cavities rather than a greater surface length of individual cavities; alternatively it may indicate an increased resorption period. No evidence of increased resorption depth at the time of the menopause was found in this study.

Relationship between the number of resorbing cells and the amount resorbed in metabolic bone disorders

The relationship between bone-resorbing cells, assessed by the presence of tartrate-resistant acid phosphatases (TRAP) and morphologic indices of bone resorption, was determined in 29 osteoporotic patients (14 postmenopausal females and 15 males) and 15 dialyzed patients. The number of TRAP-positive cells per unit of cancellous bone area (N.Oc/B.Ar) was higher in dialyzed patients than in those with osteoporosis (16.8 +/- 15.3 versus 4.95 +/- 2.86, p less than 0.05). The amount of bone resorbed at the basic multicellular unit level was estimated by calculating eroded area containing TRAP cells per bone area (E.Ar+/BA). This novel parameter was similar in dialyzed and in osteoporotic patients (41,700 +/- 28,400 versus 32,300 +/- 24,600). In contrast, trabecular spacing (Tb.Sp) was identical in both metabolic bone diseases. Trabecular width (169 +/- 38 versus 127 +/- 32 microns, p less than 0.05) and bone area were higher in dialyzed than in osteoporotic patients. N.Oc/B.Ar was significantly related to E.Ar+/BA in dialyzed (r = 0.76, p less than 0.05) but not in osteoporotic patients. Tb.Sp was significantly correlated to N.Oc/B.Ar and to the number of TRAP-positive cell nuclei per B.Ar (r = 0.44, p less than 0.05) in osteoporotic but not in dialyzed patients. This last result shows that in overt osteoporosis with thin trabeculae, trabecular spacing is related to the number of resorbing cells. In contrast, the spacing of thick trabeculae in dialysis osteodystrophy is not dependent on the number of osteoclasts.

Recruitment of new osteoblasts and osteoclasts is the earliest critical event in the pathogenesis of human multiple myeloma

Considering the special relation of human multiple myeloma (MM) to bones, it is of importance to clarify the early steps of bone involvement in this disease. In this work, using bone histomorphometry (including histoenzymologic and kinetic studies for the first time), we have evaluated the bone remodeling (i.e., bone resorption and bone formation rates) of 16 individuals with early MM in comparison with that of 10 with benign monoclonal gammopathy (BMG) and that of 17 patients with previously untreated overt MM. A significantly increased osteoblastic recruitment was observed in the individuals with early MM when compared with those with BMG (P less than 0.01). A significant (P less than 0.01) increased bone resorption (i.e., eroded surfaces, osteoclast numbers and surfaces) was observed from the early stage of MM in comparison with the BMG status where bone resorption remained within the normal range. At the tissue level, there was no difference in terms of bone resorption between early and overt MM. On the other hand, osteoblast activity was significantly reduced in patients with overt MM (P less than 0.05 by comparison with those with early MM). A significant enhancement of osteoblastic recruitment with an increased generation of new osteoclasts is an early critical event in the pathogenesis of human MM. Of particular importance is the early stimulation of osteoblasts, since these cells produce high amounts of IL-6, a potent myeloma cell growth factor and a critical cytokine for the formation of osteoclasts in the bone marrow.

Micro-osteoclast resorption as a characteristic feature of B-cell malignancies other than multiple myeloma

Multiple myeloma (MM) is characterized by the presence of lytic bone lesion and frequent hypercalcaemia. These are due to an excessive osteoclastic resorption in association with a low bone formation, as demonstrated by bone histomorphometry. Conversely, B-cell malignancies other than MM are rarely associated with lytic bone lesion and/or hypercalcaemia. In this study we have analysed quantitative bone histology in 65 patients with B-cell malignancies other than MM at diagnosis: chronic lymphocytic leukaemia (CLL, n = 20), non-Hodgkin's lymphoma (NHL, n = 25), Waldenström's disease (WD, n = 14), hairy cell leukaemia (HCL, n = 6). Fifty patients presented no clinical evidence of increased bone resorption, including no lytic bone lesions radiologically detectable and/or no hypercalcaemia. 80% of these patients (40/50) had increased bone resorption parameter using quantitative bone histology, including 19/29 (65.5%) patients with CLL or WD and 21/21 (100%) patients with NHL or HCL (P less than 0.01). As a control group, seven patients lacking bone marrow involvement on bone sample presented no excessive bone resorption. However, eight patients presented lytic bone lesions and/or hypercalcaemia. All of these patients had increased resorption parameters with high numbers of osteoclasts per surface trabecular bone (mean = 35.3), as opposed to the patients lacking lytic bone lesions and/or hypercalcaemia (mean = 6.6, n = 28) and to normal individuals (mean +/- SD = 3.8 +/- 1.7 and 6.3 +/- 2.6, respectively before and after 60 years). In all the cases, excessive histologic bone resorption was mediated by mononuclear small osteoclasts (mean osteoclast length +/- SD = 27.3 +/- 4.1 as compared to normal range = 35.0 +/- 1.0, P less than 0.001). In different in vitro models, these small mononuclear osteoclasts are considered as progenitors. These data suggest an abnormal osteoclast differentiation in B-cell malignancies other than MM, probably due to differences in the production of local factors acting on bone remodelling.