Tetracycline labeling of bone in vivo

Bone-Targeted Nanoparticle Drug Delivery System: An Emerging Strategy for Bone-Related Disease

Targeted delivery by either systemic or local targeting of therapeutics to the bone is an attractive treatment for various bone metabolism diseases such as osteoporosis, osteoarthritis, osteosarcoma, osteomyelitis, etc. To overcome the limitations of direct drug delivery, the combination of bone-targeted agents with nanotechnology has the opportunity to provide a more effective therapeutic approach, where engineered nanoparticles cause the drug to accumulate in the bone, thereby improving efficacy and minimizing side effects. Here, we summarize the current advances in systemic or local bone-targeting approaches and nanosystem applications in bone diseases, which may provide new insights into nanocarrier-delivered drugs for the targeted treatment of bone diseases. We envision that novel drug delivery carriers developed based on nanotechnology will be a potential vehicle for the treatment of currently incurable bone diseases and are expected to be translated into clinical applications.

YAP and TAZ Promote Periosteal Osteoblast Precursor Expansion and Differentiation for Fracture Repair

In response to bone fracture, periosteal progenitor cells proliferate, expand, and differentiate to form cartilage and bone in the fracture callus. These cellular functions require the coordinated activation of multiple transcriptional programs, and the transcriptional regulators Yes-associated protein (YAP) and transcriptional co-activator with PDZ-binding motif (TAZ) regulate osteochondroprogenitor activation during endochondral bone development. However, recent observations raise important distinctions between the signaling mechanisms used to control bone morphogenesis and repair. Here, we tested the hypothesis that YAP and TAZ regulate osteochondroprogenitor activation during endochondral bone fracture healing in mice. Constitutive YAP and/or TAZ deletion from Osterix-expressing cells impaired both cartilage callus formation and subsequent mineralization. However, this could be explained either by direct defects in osteochondroprogenitor differentiation after fracture or by developmental deficiencies in the progenitor cell pool before fracture. Consistent with the second possibility, we found that developmental YAP/TAZ deletion produced long bones with impaired periosteal thickness and cellularity. Therefore, to remove the contributions of developmental history, we next generated adult onset-inducible knockout mice (using Osx-Cre^tetOff ) in which YAP and TAZ were deleted before fracture but after normal development. Adult onset-induced YAP/TAZ deletion had no effect on cartilaginous callus formation but impaired bone formation at 14 days post-fracture (dpf). Earlier, at 4 dpf, adult onset-induced YAP/TAZ deletion impaired the proliferation and expansion of osteoblast precursor cells located in the shoulder of the callus. Further, activated periosteal cells isolated from this region at 4 dpf exhibited impaired osteogenic differentiation in vitro upon YAP/TAZ deletion. Finally, confirming the effects on osteoblast function in vivo, adult onset-induced YAP/TAZ deletion impaired bone formation in the callus shoulder at 7 dpf before the initiation of endochondral ossification. Together, these data show that YAP and TAZ promote the expansion and differentiation of periosteal osteoblast precursors to accelerate bone fracture healing. © 2020 American Society for Bone and Mineral Research (ASBMR).

Drug Delivery Based on Nanotechnology for Target Bone Disease

Bone diseases are a serious problem in modern human life. With the coming acceleration of global population ageing, this problem will become more and more serious. Due to the specific physiological characteristics and local microenvironment of bone tissue, it is difficult to deliver drugs to the lesion site. Therefore, the traditional orthopedic medicine scheme has the disadvantages of high drug frequency, large dose and relatively strong side effects. How to target deliver drugs to the bone tissue or even target cells is the focus of the development of new drugs. Nano drug delivery system with a targeting group can realize precise delivery of orthopedic drugs and effectively reduce the systemic toxicity. In addition, the application of bone tissue engineering scaffolds and biomedical materials to realize in situ drug delivery also are research hotspot. In this article, we briefly review the application of nanotechnology in targeted therapies for bone diseases.

In vivo Labeling of Bone Microdamage in an Animal Model of Type 1 Diabetes Mellitus

Type 1 diabetes mellitus (DM1) is linked to a decrease in bone strength. Bone strength entails both bone mineral density and bone quality. Limited data are available regarding diabetes-induced microdamage, which can severely influence bone quality. This study has investigated bone microdamage as a measure of bone quality in an animal model of DM1. Microdamage in the neck of the femur was labelled in vivo using multiple fluorochromes at 4, 12 and 24 weeks after the onset of DM1. Microcracks were quantified and their morphology analyzed using microscopy techniques. The mean length of microcracks at 24 weeks, and crack numerical and surface densities were significantly higher (p < 0.05) 4 weeks after the onset of DM1 when compared with control. Diffuse damage density was highest at 12 weeks after the onset of DM1. The arrangement of the collagen fibrils became progressively more irregular from 4 to 24 weeks of DM. This is the first study to analyze microdamage in vivo at different time points of DM1. DM1is associated with microcracks from the early stage, however bone microstructure shows toughening mechanisms that arrest their growth but disease progression further deteriorates bone quality resulting in longer microcracks which may increase fracture risk.

Biomaterial-assisted local and systemic delivery of bioactive agents for bone repair

Although bone tissues possess an intrinsic capacity for repair, there are cases where bone healing is either impaired or insufficient, such as fracture non-union, osteoporosis, osteomyelitis, and cancers. In these cases, treatments like surgical interventions are used, either alone or in combination with bioactive agents, to promote tissue repair and manage associated clinical complications. Improving the efficacy of bioactive agents often requires carriers, with biomaterials being a pivotal player. In this review, we discuss the role of biomaterials in realizing the local and systemic delivery of biomolecules to the bone tissue. The versatility of biomaterials enables design of carriers with the desired loading efficiency, release profile, and on-demand delivery. Besides local administration, systemic administration of drugs is necessary to combat diseases like osteoporosis, warranting bone-targeting drug delivery systems. Thus, chemical moieties with the affinity towards bone extracellular matrix components like apatite minerals have been widely utilized to create bone-targeting carriers with better biodistribution, which cannot be achieved by the drugs alone. Bone-targeting carriers combined with the desired drugs or bioactive agents have been extensively investigated to enhance bone healing while minimizing off-target effects. Herein, these advancements in the field have been systematically reviewed. STATEMENT OF SIGNIFICANCE: Drug delivery is imperative when surgical interventions are not sufficient to address various bone diseases/defects. Biomaterial-assisted delivery systems have been designed to provide drugs with the desired loading efficiency, sustained release, and on-demand delivery to enhance bone healing. By surveying recent advances in the field, this review outlines the design of biomaterials as carriers for the local and systemic delivery of bioactive agents to the bone tissue. Particularly, biomaterials that bear chemical moieties with affinity to bone are attractive, as they can present the desired bioactive agents to the bone tissue efficiently and thus enhance the drug efficacy for bone repair.

Recent advances in functional nanostructured materials for bone-related diseases

Bone-related diseases seriously threaten people's health and research studies have been dedicated towards searching for new and effective treatment methods. Nanotechnologies have opened up a new field in recent decades and nanostructured materials, which exist in a variety of forms, are considered to be promising materials in this field. This article reviews the most recent progress in the development of nanostructured materials for bone-related diseases, including osteoporosis, osteoarthritis, bone metastasis, osteomyelitis, myeloma, and bone defects. We highlight the advantages and functions of nanostructured materials, including sustained release, bone targeting, scaffolding in bone tissue engineering, etc., in bone-related diseases. We also include the remaining challenges of these emerging materials.

Drug delivery systems functionalized with bone mineral seeking agents for bone targeted therapeutics

The systemic administration of drugs to treat bone diseases is often associated with poor uptake of the drug in the targeted tissue, potential systemic toxicity and suboptimal efficacy. In order to overcome these limitations, many micro- and nano-sized drug carriers have been developed for the treatment of bone pathologies that exhibit specific affinity for bone. Drug carriers can be functionalized with bone mineral seekers (BMS), creating a targeted drug delivery system (DDS) which is able to bind to bone and release therapeutics directly at the site of interest. This class of advanced DDS is of tremendous interest due to their strong affinity to bone, with great expectation to treat life-threatening bone disorders such as osteomyelitis, osteosarcoma or even osteoporosis. In this review, we first explain the mechanisms behind the affinity of several well-known BMS to bone, and then we present several effective approaches allowing the incorporation BMS into advanced DDS. Finally, we report the therapeutic applications of BMS based DDS under development or already established. Understanding the mechanisms behind the biological activity of recently developed BMS and their integration into advanced therapeutic delivery systems are essential prerequisites for further development of bone-targeting therapies with optimal efficacy.

Human tooth-derived biomaterial as a graft substitute for hard tissue regeneration

Aim: The present study was conducted to evaluate the efficacy of human dentine grafts for new bone augmentation. Materials & methods: Dentine grafts (demineralized dentine matrix [DDM] and mineralized dentine matrix [MDM]) were prepared and implanted in rats. Tetracycline was administered twice. Paraffin and resin sections were prepared from the harvested grafts and stained respectively with hematoxylin and eosin (in addition to tartrate acid phosphatase for osteoclasts) and Villanueva. The new bone formation (bone thickness, mineral apposition rate and the bone formation rate) was analyzed in tetracycline-labeled resin sections. Results & conclusion: DDM grafts implanted in bone were better able to augment the bone compared to MDM grafts. However, both MDM and DDM failed to induce new bone in ectopic site, they could be considered as alternative autograft substitutes after protocol optimization.

Bmp2 and Bmp4 accelerate alveolar bone development

Alveolar bone remodeling is a continuous process that takes place during development and in response to various physiological and pathological stimuli. However, detailed knowledge regarding the underlying mechanisms involved in alveolar bone development is still lacking. This study aims at improving our understanding of alveolar bone formation and the role of bone morphogenetic proteins (Bmps) in this process. Mice at embryonic (E) day 13.5 to postnatal (PN) day 15.5 were selected to observe the process of alveolar bone development. Alveolar bone development was found to be morphologically observable at E14.5. Molar teeth isolated from mice at PN7.5 were pretreated with Bmp2, Bmp4, Noggin, or BSA, and grafted subcutaneously into mice. The subcutaneously implanted tooth germs formed alveolar bone indicating the role of the dental follicle in alveolar bone development. Alveolar bone formation was increased after pretreatment with Bmp2 and Bmp4, but not with Noggin. Gene expression levels in dental follicle cells from murine molars were also determined by real-time RT-PCR. The expression levels of Runx2, Bsp, and Ocn were significantly higher in dental follicle cells cultured with Bmp2 or Bmp4, and significantly lower in those cultured with Noggin when compared with that of the BSA controls. Our results suggest that the dental follicle participates in alveolar bone formation and Bmp2/4 appears to accelerate alveolar bone development.

Rodent models in bone-related research: the relevance of calvarial defects in the assessment of bone regeneration strategies

In vivo research with animal models has been a preferred experimental system in bone-related biomedical research since, by approximation, it allows relevant data gathering regarding physiological and pathological conditions that could be of use to establish more effective clinical interventions. Animal models, and more specifically rodent models, have been extensively used and have contributed greatly to the development and establishment of a wide range of translational approaches aiming to regenerate the bone tissue. In this regard, the calvarial defect model has found great application in basic and applied research, nonetheless the controversial rationalization for the use of critical size defects - defects that are unable to report spontaneous healing - or subcritical size defects in the proposed applications. Accordingly, this work aims to review the advantages and limitations of the use of rodent models in biomedical bone-related research, emphasizing the problematic issues of the use of calvarial critical and subcritical size defects. Additionally, surgical protocols for the establishment of both defects in rat calvarial bone, as well as the description and exemplification of the most frequently used techniques to access the bone tissue repair, are portrayed.

The Effect of Residual Calcium in Decalcified Freeze-dried Bone Allograft in a Critical-sized Defect in the Rattus norvegicus Calvarium

Demineralized freeze-dried bone allograft (DFDBA), a widely used graft material in periodontal regenerative procedures, is processed with hydrochloric acid in the attempt to expose proteins located within the bone matrixes that are capable of inducing new bone formation. However, the degree of DFDBA demineralization varies between tissue banks, which may have an effect on clinical regeneration. This study uses the critical-sized defect (CSD) model to evaluate the wound-healing response to the residual calcium of donor bone. If the percentage of residual calcium in a graft were demonstrated to significantly enhance wound healing, then periodontal patients may benefit from further standardization of human-allograft processing. Sixty adult, male, Harlan Sprague-Dawley rats (Rattus norvegicus) were randomly and equally divided into 4 test groups (ie, DFDBA at 1%, 2%, and 3% to 6% residual calcium levels and FDBA at 23% residual calcium) and a control group (no allograft). An 8-mm-diameter craniotomy was made in the rat calvarium, and polytetrafluoroethylene membranes with pore sizes of 0.50 μm were placed intracranially and ectocranially. Treatment materials were carefully placed into the CSD with a new sterilized dental amalgam carrier. Tetracycline hydrochloride was injected intraperitoneally for labeling new bone growth, and animals were euthanized 12 weeks postsurgery. As a result, histomorphometric bone fill at 12 weeks showed a statistically significant increase in the 2% DFDBA group as compared to all other groups. The authors conclude that a 2% residual calcium level in human DFDBA appears to significantly (P ≤ .05) enhance osseous wound healing in the rat calvarium.

Evaluation of a novel alloplast for osseous regeneration in the rat calvarial model

BACKGROUND

Alloplasts are inert foreign bodies acting as osteoconductive space maintainers during osseous wound healing. They may also function as carriers for growth factors that are known to enhance neovascularization and osteoinduction; human recombinant transforming growth factor beta (rhTGF-beta1) is one such factor. The purpose of this study was to evaluate di-vinyl styrene beads (DVSb) and rhTGF-beta1 effects on osseous regeneration in the rat calvaria critical-sized defect model.

METHODS

Di-vinyl styrene beads (DVSb) with and without rhTGF-beta1 were placed between gelfilm membranes in a critical-sized defect in the rat (Rattus norvegicus) calvaria. Actual bone fill; percentage bone fill; bone formation rate (BFR); and mineralization at 3, 6, and 12 weeks postsurgery were measured using densitometry, histomorphometry, scanning electron microscopy (SEM), and vital staining with tetracycline-HCl.

RESULTS

Mean radiographic density and percentage fill were statistically greater for DVSb treatment groups as compared with controls (P < or = 0.05). BFR was consistently between 3 and 7 microm per day for all groups; alloplast group BFR was significantly greater than controls or the rhTGF-beta1 groups at 6 weeks (P < or = 0.05); however, at 3 and 12 weeks, the control BFR was greater than treatment groups (P < or = 0.05). Membranes often collapsed and little bone fill or mineralization occurred in defects without DVSb. Mineralization appeared to occur adjacent to the alloplast by 12 weeks in the histologic and SEM sections. While DVSb fibrous attachment occurred in some specimens, there was no evidence of an inflammatory response.

CONCLUSION

Di-vinyl styrene beads, with or without rhTGF-beta1, significantly enhance bone regeneration in the rat calvaria defect model.

Bioabsorbable poly-L-lactic acid cages for lumbar interbody fusion: three-year follow-up radiographic, histologic, and histomorphometric analysis in goats

STUDY DESIGN

Long-term evaluation was performed for bioabsorbable poly-L-lactic acid cages in a goat interbody fusion model.

OBJECTIVE

To assess the radiographic, histologic, and histomorphometric characteristics of poly-L-lactic acid cages during 3 years of follow-up evaluation.

SUMMARY OF BACKGROUND DATA

Failed cage fusions may be related to cage design and material in addition to the surgical technique used. To overcome material-related complications and to explore the potential benefits of bioabsorbable cages, poly-L-lactic acid cages have been designed.

METHODS

For this study, 36 Dutch milk goats underwent a lumbar interbody fusion procedure (L3-L4). Two types of custom-made cage devices were impacted with bone graft and implanted: poly-L-lactic acid cages (n = 30) and titanium cages (n = 6). Sequential harvesting of surgically managed motion segments (intervals: 3, 6, 12, 24, and 36 months) was performed for analysis.

RESULTS

In poly-L-lactic acid specimens, permanent interbody fusion could be achieved within 6 months after surgery with maintenance of cage height. Titanium specimens showed no interbody fusion within this period. Radiographic follow-up evaluation (6-36 months) showed interbody fusion in 86% (19/22) of poly-L-lactic acid specimens, as compared with 33% (2/6) of titanium specimens. After 36 months of implantation, in one half of the specimens, poly-L-lactic acid cages were completely absorbed. Bone histomorphometry showed complete bone remodeling after 2 years of follow-up evaluation. During the study period, no local or distant adverse histologic effects were observed.

CONCLUSIONS

The current study showed that poly-L-lactic acid cage devices are feasible for lumbar interbody fusion. New poly-L-lactic acid cages designed for clinical practice might be a viable alternative to current nonabsorbable cage devices.

Resorbable cages for spinal fusion: an experimental goat model

OBJECT

A biomechanical cadaveric study and an in vivo monosegmental spinal fusion study were performed to evaluate a novel bioresorbable poly(L-lactic acid) (PLLA) cage.

METHODS

The yield strength of a spinal segment was chosen as the main design parameter for the resorbable cages to be used in a goat model. In a 3-year in vivo study the authors found fusion to be significantly faster and more complete when using PLLA cages compared to titanium cages with the same dimensions. In the PLLA group, the intervertebral grafting height did not change and bone remodeling within the cage was completed 2 years after implantation. In terms of degradation of the PLLA, similar features were observed in vivo and in vitro.

CONCLUSIONS

Degradation was almost completed 3 years after implantation. Tissue reaction was mild during the 3-year period.

Resorbable cages for spinal fusion: an experimental goat model

A biomechanical cadaver study and an in vivo monosegmental spinal fusion study were performed to evaluate a novel bioresorbable poly-L-lactic acid (PLLA) cage. The yield strength of a spinal segment was chosen as the main design parameter for the resorbable cages to be used in a goat model. A 3-year in vivo study revealed a significantly faster and more complete fusion using PLLA cages as compared to titanium cages with the same dimensions. In the PLLA group, the intervertebral grafting height did not change and bone remodeling within the cage was completed 2 years after implantation. In terms of degradation of the PLLA, similar features were observed in vivo and in vitro. Degradation was almost completed 3 years after implantation. Tissue reaction was mild during the 3-year period.

Evaluation of pluronic polyols as carriers for grafting materials: study in rat calvaria defects

BACKGROUND

Pluronic polyols are a family of non-ionic surfactants currently used as drug carriers for antibiotic, anti-inflammatory, and anti-neoplastic agents. Therapeutic administration of non-ionic surface-active agents is known to facilitate early collagen synthesis and microcirculation, thus promoting wound healing. The purpose of this study was to determine the in vivo effects of pluronic polyols combined with either an allograft or an alloplast on the healing of critical-sized calvarial defects.

METHODS

One hundred fifty (150) adult (95 to 105 days old) male Sprague-Dawley rats weighing between 375 and 425 g were randomly and evenly assigned to each of 15 separate treatment groups and anesthetized, and 8 mm calvarial critical-sized defects were created. Pluronic F-68 (F-68) or pluronic F-127 (F-127) was administered either topically or systemically and in conjuction with demineralized bone powder (DBP), tricalcium phosphate (TCP), or non-grafted controls. Pluronic polyols are easily mixed with either DBP or TCP to improve handling ease. Calvaria were harvested at 12 weeks postsurgery and evaluated histomorphometrically, by contact radiography with subsequent densitometric analysis, through energy spectrometry utilizing a scanning electron microscope, and by fluorescent microscopy.

RESULTS

There was a significant difference in the percentage of bone fill among the control, TCP, and DBP only groups, P <0.05. The only significant difference within any of these groups was between the TCP control and TCP plus systemic F-127, P<0.05.

CONCLUSIONS

Although there were isolated differences, the overall trend was that the pluronic polyol and the mode of administration did not result in a significant change in bone wound healing as measured by the percentage of bone fill. Pluronic polyols may be considered as carriers for osseous graft materials.

Vital staining of bone in stable, retrieved femoral surface replacement prostheses: a microscopic study of undecalcified ground sections

We used vital staining with tetracycline to detect viability of bone at the bone-cement interface in 11 stable ICLH femoral surface replacement prostheses that were retrieved at revision surgery for acetabular loosening. The resected femoral heads were processed for undecalcified ground sections with the prostheses in situ. All sections showed direct bone-to-cement contacts. Bone in direct contact with or close to the cement sometimes showed an abnormal staining, indicating that the bone was not fully mineralized. Areas with fluorescence were observed within all femoral heads but never in direct bone-to-cement contact. From this study, we conclude that the mechanical stability of these cemented femoral surface replacement prostheses depends mainly on the original bone present at the time of primary operation.

High-turnover periprosthetic bone remodeling and immature bone formation around loose cemented total hip joints

Aseptic loosening and periprosthetic osteolysis are the major problems awaiting solution in total hip surgery. The clinical investigation focused on the analysis of periprosthetic bone remodeling to clarify one important key event in the cascade of periprosthetic connective tissue weakening and osteolysis around loose artificial hip joints. Twelve acetabular bone samples adjacent to granulomatous synovial-like membrane of loose hip prosthesis were retrieved at revision surgery and processed for Villanueva bone staining for morphological observation and bone histomorphometric analysis. Eight well-fixed bony samples were used as control. Although osteoclastic surface and eroded surface by osteoclasts were evident in the periprosthetic bone from loose hip joints (p = 0.003 and p = 0.027), increased osteoid/low-mineralized bone matrix (p < 0.001) and osteoid width (p < 0.001) also were significant findings in structural analysis. In addition, not only elevated mineral apposition rate (MAR; p = 0.044) but also increased mineralizing surface (p = 0.044) and bone formation rate (BFR; p = 0.002) in loose periprosthetic bones were shown in dynamic data analysis. These results were confirmed by precise morphological observation by confocal laser scanning microscopy. Active coupling of bone formation and resorption and increased osteocytes with abundant bone canalicular projections were found in combined with the presence of immature bone matrices (osteoid and low-mineralized bone areas) in periprosthetic bones from loose hip joints. These results indicated that active osteoclastic bone resorption and/or defective bone formation are coupled with monocyte/macrophage-mediated foreign body-type granuloma in the synovial-like interface membrane of loose hip joints. Thus, this unique high-turnover periprosthetic bone remodeling with bad bone quality probably is caused by the result of cellular host response combined with inappropriate cyclic mechanical loading. The fragile periprosthetic bone may contribute to hip prosthesis loosening.

Hypermineralized lamellae below the bone surface: a quantitative microradiographic study

Hypermineralized lamellae similar to interstitial resting lines were identified by microradiography beneath haversian, endocortical, and trabecular resting surfaces in 42 subjects aged 18-96 years. In cross-sectioned osteons, this hypermineralized lamella appeared as a circle showing the same high microdensity as the inner margin of the haversian canal. Bone tissue separating this circle and the margin was more mineralized than the peripheral lamellae of the osteon. In the tibia, 13.7 +/- 0.9% (Mean +/- SE) of Haversian canals exhibited a hypermineralized circle, localized at a distance of 20 +/- 0.4 microns from the canal wall. The scalloped haversian canals, different from osteoclastic resorption cavities, represented 9.9 +/- 0.7% of the haversian canals. There was a significant correlation between both types of haversian canals. Therefore, hypermineralized lamellae can appear at the end of bone apposition, whatever the bone surface. Their high mineral content may secondarily lead to an increased brittleness of the most superficial lamellae and even to their disaggregation.

Surgical treatment of induced peri-implantitis in the micro pig: clinical and histological analysis

The purpose of this pilot study was to determine if lost osseous support adjacent to root form implants could be regenerated using a guided tissue regeneration technique. Three fixtures were placed in each edentulous mandibular bicuspid region of two micro pigs. A total of 6 fixtures were placed in each pig. Due to the presence of a pathologic condition, which was in no way related to the research, the results of one pig were not evaluated. Following osseointegration, peri-implantitis were induced by the use of ligatures and a soft diet. Three modalities of treatment were performed. Utilizing a surgical flap approach, one third of the fixtures (one per quadrant) were covered with expanded polytetrafluoroethylene (ePTFE) membrane and submerged under the soft tissue complex. The second group of fixtures were submerged under the soft tissue complex with no ePTFE membrane. The control fixtures along with their abutments were debrided and remained non-submerged. All fixtures were debrided using an air-abrasive polishing system. The osseous defects around the fixtures were measured from a fixed reference point at the time of surgery and after obtaining block sections.(ABSTRACT TRUNCATED AT 250 WORDS)

Bone formation periods studied with triple tetracycline labels in women with postmenopausal osteoporosis

In adult cancellous bone, cyclic remodeling occurs in discrete locations (BMUs, or basic multicellular units). Some aspects of these remodeling cycles are still not clear. Only about half the osteoid surface normally has tetracycline labels; the remainder is thought to be immature or in a resting phase. This study was designed to test the assumption that pauses occur during the bone formation periods. Iliac crest bone biopsies were performed in 84 women with postmenopausal osteoporosis. The subjects were given three tetracycline labels; the middle label had a distinctive color. The osteoid surface was 10 +/- 6% of the bone surface; the range was 0.6-24.4%. The mineralizing surface was 42 +/- 26% of the osteoid surface. Immature osteoid was 7.6 +/- 5.3% of the osteoid surface. There were no BMUs with the first and third tetracycline label but without the middle demeclocycline label. The expected length of double 1-3 label, based on an assumption that unlabeled mature osteoid was temporarily in a resting phase, was significantly higher than the observed length (68 +/- 77 microns/mm2 tissue area versus 0, p < 0.0001). The mean active formation period was 77 +/- 16 days calculated by standard methods but was only 55 +/- 26 days when calculated by label escape (p < 0.001). The correlation coefficient between these two methods was only modest (r = 0.27, p < 0.01). The failure to find any double 1-3 labels despite abundant triple labels provides strong evidence against the presence of pauses in bone mineralization between 3 and 34 days.(ABSTRACT TRUNCATED AT 250 WORDS)

Histomorphometric study of trabecular bone remodeling during condylar process fracture healing in the growing period: experimental study

Trabecular bone remodeling during condylar fracture healing in the growing period was analyzed by histomorphometry with a synchronous system. Data from the study showed displacement of the fractured condyle was compensated by the changes in remodeling ascribed to the pubertal spurt of growth, and that such remodeling still continued even after clinical healing. The regional acceleratory phenomenon, evolved to potentiate tissue healing, was observed 1 week after induction of the fracture. Mesenchymal cells were presumably modulated into chondroblasts that promoted endochondral ossification. It was concluded that trabecular bone remodeling plays an important role in healing of condylar fractures during the growth period.

Normal bone particles are preferentially resorbed in the presence of osteocalcin-deficient bone particles in vivo

In an in vivo model of osteoclastic bone resorption, we previously showed that osteocalcin-deficient bone particles (BPs), derived from warfarin-treated rats, were resorbed 50% as well as normal BPs and that they recruited fewer osteoclastic cells with decreased tartrate-resistant acid phosphatase (TRAP) activity. In order to determine the specificity of the resorption response, we evaluated the fate of implanted mixtures of normal and osteocalcin-deficient BPs. Normal and warfarin-treated donor rats were prelabeled in vivo with oxytetracycline to permit identification of BPs from either source. Normal, osteocalcin-deficient, and 50:50 mixtures of BPs (either labeled or unlabeled) were implanted into normal rats and recovered 12 days later for enzymatic (TRAP) and nondecalcified histomorphometric analyses. The incorporated oxytetracycline had no significant effect on resorption of bone particles. The recovered osteocalcin-deficient BPs were surrounded by fewer osteoclastic cells, were resorbed less, and contained less extractable TRAP activity than normal BPs. In mixed BP implants with normal and osteocalcin-deficient BPs, each type of bone particle elicited the same tissue response as when implanted separately. Remarkably, the different particles evoked dissimilar osteoclastic responses and were resorbed to different extents, even when adjacent within the same implant. These data suggest that osteocalcin may act as a substrate signal for resorption and that osteocalcin in the normal BPs does not influence the cellular response to adjacent osteocalcin-deficient BPs.

A systemic acceleratory phenomenon (SAP) accompanies the regional acceleratory phenomenon (RAP) during healing of a bone defect in the rat

The rate of remodeling in the region of a bone defect exceeds normal tissue activity. It was Frost who described this reaction as a regional acceleratory phenomenon (RAP). We investigated the local healing process with rats with a burr hole defect (1.2 mm in diameter) in the left tibia. We differentiated an initial phase of bone formation followed by a phase of predominant resorption. To determine whether this regional enhancement of bone formation would result in a systemic impact on bone metabolism, we analyzed both tibiae and femora and the fourth lumbar vertebra. On day 7 both femora of rats with the tibial defect showed a significant increase in computerized x-ray density, dry weight, ash weight, and Ca2+ content. Both tibiae and the fourth lumbar vertebra showed a significant increase in mineralizing surface, mineral apposition rate, and bone formation rate. Because of these results we conclude that a systemic acceleratory phenomenon (SAP) accompanies the RAP. SAP affects only the cancellous, but not the cortical bone compartment. SAP is associated closely with the occurrence of woven bone during the formation phase of the healing process. Thus we assume that woven bone formation plays a pivotal role in the mediation of SAP.

A model of osteon closure in cortical bone

A model of osteon closure is presented that incorporates some physiologic features of cortical bone remodeling, such as matrix synthesizing activity of osteoblasts, their burial as osteocytes, and elimination of cells. A simplified version of the model assumes a constant osteoblast activity throughout radial closure. An extended version allows for variable osteoblasts activity and is based on Lee's law of radial closure kinetics. The model calculations (extended model) show that both in humans and beagle dogs osteoblast activity steadily decreases during radial closure of the osteon. The potential of the model is also illustrated by calculating the dynamic change of the geometrical shape of the closing cone and the time dependence of the osteoid seam width, number of osteoblasts and bone formation rate in the closing cone.

Fluorochrome labelling in Roman period skeletons from Dakhleh Oasis, Egypt

A histological aging study of femoral midshafts in a late Roman period sample from the Dakhleh Oasis, Egypt, showed discrete fluorochrome labelling. The fluorochrome is yellow-green in colour and fluoresces at a wavelength of 525 nm. The labelling occurs at the mineralization fronts and is so distinct that several histomorphometric measurements were made. The percent labelled surface values ranged from 6.03% to 59.34%, and the mean distance between labels ranged from 13.57 to 20.63 microns. Teeth from several individuals were also labelled within the enamel matrix. Comparisons were made between the patterns of fluorescent labelling from this population and from patients treated with interval and continuous dosages of tetracycline. The results collectively indicate that the fluorochrome is most likely tetracycline that made its way into the bone (in vivo) via stored grain contaminated by Streptomycetes. The labelling was differential, much like that of the patient on interval doses of tetracycline, so it is argued that the tetracycline was ingested occasionally, probably on a seasonal basis. The lack of bone infection in the adults (n = 29) suggests that the tetracycline may have provided some antibiotic protection in this population.

Histomorphometric evaluation of stress shielding in mandibular continuity defects treated with rigid fixation plates and bone grafts

Histomorphometric techniques were used to evaluate the stress shielding effect in bilateral bone grafts in 4 Macaca fascicularis monkeys. Bilateral continuity defects were created and grafted by replacing the resected portion of the mandible and iliac crest bone into the defect area. Both sides were plated with rigid internal fixation plates. Three months after bone grafting, the plate was removed from one side while the other plate was left in place. The animals were sacrificed at 1, 4, 6, and 8 months after plate removal and the grafted areas removed for histomorphometric analysis. This study documents decreased bone volume as well as smaller interlabel width on the plated side, suggesting a stress shielding effect as a result of the rigid internal fixation plate.

The effect of fluoride on bone histology in postmenopausal osteoporosis depends on adequate fluoride absorption and retention

Forty-one women with idiopathic postmenopausal osteoporosis have been followed for 2 years after initiation of sodium fluoride at 40-50 mg/day, given together with a daily calcium supplement of 1 gram and vitamin D2, at 50,000 IU weekly. Histological and histomorphometric analyses were done on bone biopsies taken prior to and after 1 year of treatment (mean 1.25 +/- 0.35 years). Thirty patients (74%) developed the histological fluoride effect of hyperosteoidosis, while the remaining 11 patients (26%) had no change from pretreatment biopsies. Hyperosteoidosis was based on increased values for osteoid volume and/or thickened osteoid with greater than 3 lamellar bands. Based on previously reported findings, this histological evidence of hypersoteoidosis within 12-18 months of initiation of therapy provides a useful predictor of ultimate satisfactory fluoride response in terms of bone mineral accretion. No increases in bone mass (measured by neutron activation analysis) were observed at the time of the posttreatment biopsy but, according to this previous work, increases are anticipated over a further 2-3 years of treatment. Factors affecting the development of hyperosteoidosis were analyzed. Hyperosteoidosis was associated with a significantly higher dose of sodium fluoride and a significantly higher level of bone fluoride retention but without significant increase in fasting serum fluoride. Results suggest that fluoride retention depends not only on fluoride dose but also on body size, renal function, and intestinal absorptions of calcium and fluoride. There were no differences in the initial investigations between patients with and without hyperosteoidosis, with respect to age, years of postmenopause, estrogen use, initial biochemistry, or initial bone histology.(ABSTRACT TRUNCATED AT 250 WORDS)

An organ culture system designed to study interaction of fetal rat calvaria with human head and neck squamous cell carcinoma

The development of permanent cell lines of human head and neck squamous cell carcinoma in culture has enabled these cell lines to be used to investigate the interaction of the tumor cells with bone. After the squamous carcinoma lines on fetal rat skulls were implanted the explants with their added tumor were maintained in long-term tissue culture by use of the procedures developed for growing these tumor cells. Results confirm direct interaction with the bone by the malignant cells. Specific surface and cytoplasmic markers have been demonstrated by use of monoclonal antibodies against the tumor cells. Furthermore, tumor angiogenesis without the addition of any endogenous endothelial components has been verified. Investigations into the degree of bone infiltration and susceptibility of these interacting tumor cells to various factors, radiation therapy, and chemotherapeutic agents have been carried out. The establishment of a model system for bony invasion by squamous cell carcinoma of the head and neck permits the investigation of the mechanism of tumor invasion and the study of various potential treatment modalities.

Treatment of denervation/disuse osteoporosis in the rat with a capacitively coupled electrical signal: effects on bone formation and bone resorption

Utilizing a sciatic neurectomy model of disuse osteoporosis, the effects on rates of bone formation and bone resorption were examined when a capacitively coupled electrical signal was applied to the denervated tibia in the rat. It was found that a low-voltage, symmetrical sine wave, 60-kHz, capacitively coupled signal had no significant effect on the amount of bone resorption occurring in denervated right tibiae in rats previously labeled with [3H]tetracycline. This was true whether the signal was applied while osteoporosis was developing (prevention of osteoporosis) or after it had been established (treatment of osteoporosis). If a similar capacitively coupled signal was applied to rats in which osteoporosis was well established, and the rats were labeled with [3H]tetracycline daily during a 12-day treatment period, it was found that there was statistically significant enhancement of the amount of new bone formation (increased [3H]tetracycline incorporation) in the tibiae that received the signal as compared with that of the controls. These results indicate that prevention or amelioration of disuse osteoporosis that occurs with a capacitively coupled electrical signal is due not to a change in the rate of bone resorption, but to an increase in the rate of bone formation.

The relationship between bone apposition rate and vitamin D activity in phosphate-deficient rats

In rats, phosphorus deficiency (P-) has been shown previously to stimulate the linear bone apposition rate (BAR) and this P- effect is dependent on adequate intake of vitamin D. To investigate further the relative importance of the vitamin D3 metabolites, 1,25(OH)2D3, 24,25(OH)2D3, and 25(OH)D3, in BAR stimulation, we studied, in P- rats, the relationships between BAR and plasma levels of these three vitamin D3 metabolites following vitamin D3 deprivation. Three groups of rats were placed on diets differing only in phosphorus (P) and vitamin D3(D3) content, with one group diet deficient in both P and D3, one diet, P-, D3 replete, and one diet both P and D3 replete. Plasma levels of the three vitamin D3 metabolites, plasma Ca and P, isotopic Ca absorption and BAR measurements were carried out at 1, 3, and 5 weeks after onset of the test diets. In P-, D3 replete rats, both plasma levels of 1,25(OH)2D3 and BAR were increased throughout the 1 to 5 week study period, while 25(OH)D3 and 24,25(OH)2D3 levels were not significantly different from P and D3 replete controls. In P-, D3 restricted rats, BAR was decreased by one week, prior to any reduction in plasma levels of 25(OH)D3 and 24,25(OH)2D3 and while plasma 1,25(OH)2D3 levels were still well above control values. In this P- rat model, the vitamin D dependent BAR stimulation does not appear to be directly related to alterations in the plasma levels of 1,25(OH)2D3, 24,25(OH)2D3, or 25(OH)D3.

Metabolic bone disease in a patient on long-term total parenteral nutrition: a case report with review of literature

A 38-yr-old woman with Crohn's disease and short bowel on home total parenteral nutrition was studied. Metabolic bone assessments were done prospectively. Daily total parenteral nutrition included 500 IU vitamin D2, 6 to 8 mmol calcium, 10 to 15 mmol phosphorus, 12 to 16 mmol magnesium, and trace elements including zinc, cooper, and chromium. After 6 months, while asymptomatic, chemistries and x-rays were normal. Calcium bone index was 0.79. The bone biopsy showed mild hyperkinetic picture. At 26 months, she had a spontaneous rib fracture and bone pains in the hands and lower back. Chemistries were normal except that calcium bone index was 0.75. Bone biopsy showed mild osteomalacia. Vitamin D2 was withdrawn for 2 months and then restarted at 1000 IU/wk. She improved symptomatically for 4 months, but then developed rib fractures, and the bone pains recurred. After 48 months, chemistries were normal, except that the calcium bone index was 0.57 and bone biopsy showed regression of osteomalacia toward normal. Vitamin D2 was now withdrawn for 6 months, resulting in loss of bone pain. Vitamin D2 may produce a metabolic bone disease, requiring prolonged withdrawal for improvement.

Evidence of sequential remodeling in rat trabecular bone: morphology, dynamic histomorphometry, and changes during skeletal maturation

The occurrence of a sequential bone remodeling activity, similar to what is observed in human bone, is demonstrated in rat trabecular bone at the level of the secondary spongiosa. A complete dynamic histomorphometric analysis of the remodeling activity, using undecalcified sections and double fluorescent labels, has consequently been performed in young adults (220 g, 8 weeks old) and in more mature animals (320 g, 12 weeks old). The results showed that, despite a similar trabecular bone volume, younger animals had a five times higher bone formation rate and five times more osteoclasts than more mature animals. The higher bone formation rate was due in part to a threefold higher extent of double-labeled trabecular bone surface and in part to a 1.5-fold faster mineralization rate. These results therefore demonstrate a marked slowing down of bone turnover during skeletal maturation in the rat. The values obtained in this study have been compared with measurements made in other parts of the skeleton in the same species (Vignery and Baron 1978, 1980b; Tran Van et al., 1982a) or in humans. This comparison indicated that 12-week-old rats had a turnover rate very similar to values observed in iliac crest trabecular bone in adult humans. The rat is therefore a good experimental animal for the study of trabecular bone remodeling but since large variations occur during skeletal maturation, care should be taken in the selection of an age group relevant to the type of questions being asked.

Increased bone apposition in primary hyperparathyroidism: measurements based on short interval tetracycline labeling of bone

Bone biopsies of 23 subjects suffering from primary hyperparathyroidism, which was proven by the demonstration of parathyroid pathology during neck surgery, were studied by morphometric analysis and short interval sequential tetracycline labelling and compared with those of 13 patients without metabolic bone disease. In 19 of these patients, abnormalities were found in the trabecular volume, resorption surface, formation surface, or in various combinations. However, no constant pattern of bone changes was observed. In 4 patients, the bone morphometric parameters were normal. The bone apposition rate, on the other hand, was elevated in all 23 subjects. The rate was re-evaluated in 4 patients 6 wk to 3 mo following successful parathyroid surgery. It fell back within the control range. These findings confirm the observation in experimental animals that parathyroid hormone stimulates bone apposition in vivo and give support to the rationale of using this hormone in the treatment of osteoporosis.

Protective effect on vitamin D2 on bone apposition from the inhibitory action of hydrocortisone in rats

Using the technique of short interval sequential tetracycline labeling, it was documented that the apposition of mineralized bone matrix in adult male Sprague-Dawley rats was inhibited by hydrocortisone. The inhibition occurred as early as six days after the onset of the treatment and was dose dependent over a dose range of 0.62 to 20 mg per kg body weight per day. Vitamin D2 supplements by injection protected bone from this hydrocortisone action. 64 I. U. of vitamin D2 injected daily was able to prevent the inhibition of bone apposition by 20 mg per kg body weight per day of hydrocortisone. The results imply that vitamin D or its metabolites may compete with hydrocortisone in some cellular mechanisms and support the usefulness of vitamin D supplements in the treatment and the prevention of steroid-induced osteoporosis.