Neobavaisoflavone stimulates osteogenesis via p38-mediated up-regulation of transcription factors and osteoid genes expression in MC3T3-E1 cells

Neobavaisoflavone (NBIF) is an isoflavone isolated from Psoralea corylifolia L, a plant claimed to have osteogenic activity and used to treat bone fractures, osteomalacia and osteoporosis. The present results showed that NBIF concentration-dependently promoted osteogenesis in MC3T3-E1cells, demonstrated by notable enhancement of alkaline phosphatase (ALP) activity, increase of bone-specific matrix proteins expression including type I collagen (Col-I), osteocalcin (OCN) and bone sialoprotein (BSP), and formation of bone nodules. However, cell proliferation in the presence of NBIF was not affected. Results also demonstrated that NBIF up-regulated the expression of runt-related transcription factor 2 (Runx2) and Osterix (Osx), the bone-specific transcription factors participating in regulation of bone marker genes expression. Application of p38 inhibitor SB203580 repressed not only NBIF-induced activation of ALP, the expression of Col-I, OCN and BSP, but also the matrix proteins mineralization. Western blot analysis further revealed that NBIF increased the phosphorylated level of p38 concentration-dependently. Additionally, inhibition of p38 abolished the stimulatory effect of NBIF on the expression of Runx2 and Osx. Taken together, the osteogenic activity of NBIF might probably act through activation of p38-dependent signaling pathway to up-regulate the mRNA levels of Runx2 and Osx then stimulate bone matrix proteins expression. The beneficial effect of NBIF on mineralization demonstrated that NBIF represented as an active component existed in P. corylifolia and might be a potential anabolic agent to treat bone loss-associated diseases.

[Effect of vitamin K on bone material properties]

Collagen cross-links are determinants of bone quality. Because vitamin K is thought to ameliorate bone quality, we summarized the literature regarding the effect of vitamin K such as menatetorenone (MK-4) on bone matrix property in the review. MK-4 seems to stimulate the osteoblastic activity. This results in the increase in collagen accumulation and lysyl oxidase controlled enzymatic cross-links in bone. Furthermore, vitamin K stimulates the secretion of collagen binding protein regulating proper fibrillogenesis such as leucine-rich repeat protein (tsukushi). This kinds of non-collagenous proteins induced by the treatment of vitamin K may also affect proper collagen cross-link formation and show the favorable effect on bone material quality.

Physiology of bone

Bone serves three main physiological functions. Its mechanical nature provides support for locomotion and offers protection to vulnerable internal organs, it forms a reservoir for storage of calcium and phosphate in the body, and it provides an environment for bone marrow and for the development of haematopoietic cells. The traditional view of a passive tissue responding to hormonal and dietary influences has changed over the past half century to one of a dynamic adaptive tissue responding to mechanical demands. This chapter gathers together some recent advances in bone physiology and molecular cell biology and discusses the potential application of the bone's functional adaptation to loading in enhancing bone strength during childhood and adolescence.

Phosphatase actions at the site of appositional mineralization in bisphosphonate-affected bones of the rat

Tissue-nonspecific alkaline phosphatase (TNSALP) and Ca-ATPase are known to play roles in bone mineralization, but how these enzymes contribute to appositional mineralization has been illusive. Here we examined the active sites of these enzymes in appositional mineralization using the bones of young rats being administered with 1-hydroxyethylidene-1,1-bisphosphonate (HEBP) for 5 days. The doses of HEBP totally abolished mineralization of newly formed bone matrix except in matrix vesicles (MVs), and hence allowed precise localization of MVs and phosphatase reactions within non-mineralized extracellular matrix. Intense TNSALP and ATPase reactions were confirmed along the limited portions of osteoblast membranes where intimate cell-cell contacts were maintained. Diffuse reactions of these enzymes were throughout the osteoid implicating efflux of TNSALP and ATPase molecules into extracellular matrix from the osteoblast membranes. Phosphatase reactions associated with MVs varied both in intensity and location among the individual vesicles; newly formed MVs were almost free of reactions but appeared to gain those activities later in the osteoid. These data suggest that TNSALP and ATPase are released from the osteoblast membrane and later integrated into MVs within the osteoid. The osteoblasts may thus regulate appositional mineralization of bone from a distance at least in part by providing phosphatases via MVs.

Functional involvement of PHOSPHO1 in matrix vesicle-mediated skeletal mineralization

PHOSPHO1 is a phosphatase highly expressed in bone. We studied its functional involvement in mineralization through the use of novel small molecule inhibitors. PHOSPHO1 expression was present within matrix vesicles, and inhibition of enzyme action caused a decrease in the ability of matrix vesicles to calcify.

INTRODUCTION

The novel phosphatase, PHOSPHO1, belongs to the haloacid dehalogenase superfamily of hydrolases and is capable of cleaving phosphoethanolamine (PEA) and phosphocholine to generate inorganic phosphate. Our aims in this study were to examine the expression of PHOSPHO1 in murine mineralizing cells and matrix vesicles (MV) and to screen a series of small-molecule PHOSPHO1-specific inhibitors for their ability to pharmacologically inhibit the first step of MV-mediated mineralization.

MATERIALS AND METHODS

q-PCR and immunohistochemistry were used to study the expression and localization profiles of PHOSPHO1. Inhibitors of PHOSPHO1's PEA hydrolase activity were discovered using high-throughput screening of commercially available chemical libraries. To asses the efficacy of these inhibitors to inhibit MV mineralization, MVs were isolated from TNAP-deficient (Akp2(-/-)) osteoblasts and induced to calcify in their presence.

RESULTS

q-PCR revealed a 120-fold higher level of PHOSPHO1 expression in bone compared with a range of soft tissues. The enzyme was immunolocalized to the early hypertrophic chondrocytes of the growth plate and to osteoblasts of trabecular surfaces and infilling primary osteons of cortical bone. Isolated MVs also contained PHOSPHO1. PEA hydrolase activity was observed in sonicated MVs from Akp2(-/-) osteoblasts but not intact MVs. Inhibitors to PHOSPHO1 were identified and characterized. Lansoprazole and SCH202676 inhibited the mineralization of MVs from Akp2(-/-) osteoblasts by 56.8% and 70.7%, respectively.

CONCLUSIONS

The results show that PHOSPHO1 localization is restricted to mineralizing regions of bone and growth plate and that the enzyme present within MVs is in an active state, inhibition of which decreases the capacity of MVs to mineralize. These data further support our hypothesis that PHOSPHO1 plays a role in the initiation of matrix mineralization.

Effects of hydrogen peroxide (H2O2) on alkaline phosphatase activity and matrix mineralization of odontoblast and osteoblast cell lines

Hydrogen peroxide (H(2)O(2)), an oxidizing agent, has been widely used as a disinfectant. Recently, because of its reactive properties, H(2)O(2) has also been used as a tooth bleaching agent in dental care. This is a cause for concern because of adverse biological effects on the soft and hard tissues of the oral environment. To investigate the influence of H(2)O(2) on odontoblasts, the cells producing dentin in the pulp, we assessed cellular viability, generation of reactive oxygen species (ROS), alkaline phosphatase (ALP) activity, and nodule formation of an odontoblastic cell line (MDPC-23) after treatment with H(2)O(2), and compared those with the effects on preosteoblastic MC3T3-E1 cells. Cytotoxic effects of H(2)O(2) began to appear at 0.3 mmol/L in both MDPC-23 and MC3T3-E1 cells. At that concentration, the accumulation of intracellular ROS was confirmed by a fluorescent probe, DCFH-DA. Although more ROS were detected in MDPC-23, the increasing pattern and rate are similar between the two cells. When the cells were treated with H(2)O(2) at concentrations below 0.3 mmol/L, MDPC-23 displayed a significant increase in ALP activity and mineralized bone matrix, while MC3T3-E1 cells showed adverse effects of H(2)O(2). It is known that ROS are generally harmful by-products of aerobic life and represent the primary cause of aging and numerous diseases. These data, however, suggest that ROS can induce in vitro cell differentiation, and that they play a more complex role in cell physiology than simply causing oxidative damage.

Erk pathways negatively regulate matrix mineralization

Skeletal mineralization is an important step regulating the mechanical properties of the calcified tissues, but molecular events underlying mineralization still remain elusive. We examined the role of extracellular signal-regulated kinase (Erk) pathways in matrix mineralization of osteogenic cells both in vitro and in vivo. Matrix mineralization by preosteocytic MLO-A5 cells and osteoblastic MC3T3-E1 cells was increased by either PD98059 Mek inhibitor treatment or adenovirus vector-mediated dominant negative Ras (Ras(DN)) expression and was suppressed by Erk activation by platelet-derived growth factor (PDGF) treatment or constitutively active Mek1 (Mek(CA)) expression. Administration of adenovirus vectors carrying Ras(DN) gene onto the calvaria of 1-day-old mice increased the mineralization of the tissues, while that of the Mek(CA) adenovirus suppressed it. These results suggest that the Erk pathway is a negative regulator of the matrix mineralization both in vitro and in vivo.

Proteolytic enzymes in skeletal development: histochemical methods adapted to the study of matrix lysis during the transformation of a "cartilage model" into bone

The replacement of a "cartilage model" by definitive bone is characterized by a series of localized excavations of the cartilage which are eventually followed by bone deposition. Each excavation requires lysis of cartilage components (defined here as the breakdown of a peptide bond) and their eventual resorption (defined here as microscopical visible cartilage loss). More precisely we have proposed that the lysis is affected by proteases capable of breaking down the main proteoglycan "aggrecan" and the main fibril element, "type II collagen". Four approaches combining biochemical, immunologic and microscopic techniques have been adapted to test this hypothesis. Each is applied to the rat tibial head's "cartilage model" where proteases have been shown to be major contributors to secondary ossification center formation. The approaches have been found both effective and distinct as cartilage resorbing enzymes have not only been identified but also detected in situ before and after activation. Achieved overall is an understanding of when, where and how specified proteases contribute to tissue component lyses. While the focus resides on the in situ proteolysis of cartilage, three of the approaches could be translated without change to other tissues, whereas one may require tissue specific adjustments before use.

The expression of matrix metalloproteinase-13 and osteocalcin in mouse osteoblasts is related to osteoblastic differentiation and is modulated by 1,25-dihydroxyvitamin D3 and thyroid hormones

Matrix metalloproteinase-13 (MMP-13), is a key protein of bone matrix degradation, and is highly expressed by osteoblasts. We used the osteoblast-like MC3T3-E1 cell line and compared the stimulatory effects of the bone resorptive agents 1,25-dihydroxyvitamin D3 (1,25-(OH)(2)D(3)) 3,3',5-triido-L-thyronine (T3) on the expression of MMP-13 mRNA. We showed that the stimulatory effects were time and dose dependent, and were also transduced to the protein level, with 1,25-(OH)(2)D(3)being more potent.MMP-13 expression in different mouse cells and its localization within developing bone from the onset of osteogenesis were also investigated. 1,25-(OH)(2)D(3)- and T3-regulated osteocalcin (Osc) expression in mouse osteoblasts was compared to hormonal effects on MMP-13 expression and activity. Here we show divergent and common roles of 1,25-(OH)(2)D(3)and T3 action on the expression of these marker proteins, depending on the stage of cell differentiation. In addition, we propose a role for MMP-13 in the bone collar of developing long bones. The results could help to more precisely characterize hormonal regulation in the developmental sequence of osteoblasts.

Metabolic activation stimulates acid secretion and expression of matrix degrading proteases in human osteoblasts

BACKGROUND

Both cellular and matrix components of healthy bone are permanently renewed in a balanced homoeostasis. Osteoclastic bone resorption involves the expression of vacuolar-type ATPase proton pumps (vATPase) on the outer cell membrane and the secretion of matrix degrading proteases. Osteoblasts modulate the deposition of bone mineral components and secrete extracellular matrix proteins.

OBJECTIVES

To investigate the ability of osteoblasts and osteosarcoma to secrete acid and express matrix degrading proteases upon metabolic activation. To examine also the potential contribution of vATPases to proton secretion expressed on osteoblasts.

METHODS

Osteoblasts were isolated from trabecular bone and characterised by reverse transcriptase-polymerase chain reaction and immunohistochemistry. Proton secretion was analysed by a cytosensor microphysiometer.

RESULTS

Osteoblasts not only express matrix degrading proteases upon stimulation with tumour necrosis factor or with phorbol ester but they also secrete protons upon activation. Proton secretion by osteoblasts is associated partially with proton pump ATPases.

CONCLUSION

These data suggest that, in addition to monocyte derived osteoclasts, cytokine activated mesenchymal osteoblasts and osteosarcoma cells may contribute to the acidic milieu required for bone degradation.

Matrix metalloproteinases and their inhibitors in bone remodelling following distraction osteogenesis of the sheep mandible

AIM

Matrix metalloproteinases (MMPs), together with their tissue inhibitors (TIMPs), are responsible for the controlled degradation of collagen and other matrix substrates in bone and other tissues. This study evaluated the expression of MMPs and TIMPs in bony remodelling in a bilateral sheep mandible model up to 12 months following lengthening by distraction osteogenesis.

METHODOLOGY

Sheep mandibles were harvested 3, 6, 9 or 12 months following lengthening by bilateral mandibular distraction (1 mm/day for 20 days). Undistracted sheep mandibles were used as controls. The tissues underwent routine histology and immunohistochemical staining with monoclonal antibodies specific to MMPs 1-3 and TIMP-1, 2. Matrix and cell staining was assessed using a semi-quantitative analysis.

RESULTS

Matrix metalloproteinases and their tissue inhibitors (TIMPs) expression levels were marked at 3 months and decreased thereafter becoming similar to undistracted controls by 12 months. The histologic development of mature lamellar cortical bone was similar to undistracted controls by 9 months following distraction.

CONCLUSIONS

A temporal expression of MMPs and TIMPs was found in distraction osteogenesis. MMPs and TIMPS may, in part, reflect the state of bony remodelling following mandibular lengthening by distraction osteogenesis. Matrix metalloproteinases and TIMP expression were comparable to undistracted controls by 12 months, suggesting that equilibrium had been achieved and that bony relapse is unlikely.

Ultrastructural changes in osteocytes in microgravity conditions

We examined the histology and morphometry of biosamples (biopsies) of the iliac crest of monkeys, flown 14 days aboard the "Bion-11", using electron microscopy. We found, that some young osteocytes take part in the activation of collagen protein biosynthesis in the adaptive remodeling process of the bone tissue to microgravity conditions. Osteocyte lacunae filled with collagen fibrils; this correlates with fibrotic osteoblast reorganization in such zones. The osteolytic activity in mature osteocytes is intensified. As a result of osteocyte destruction, the quantity of empty osteocytic lacunae in the bone tissue increases.

Search for an endogenous collagenase in chicken endochondral bone matrix vesicles

While isolating matrix vesicles from avian endochondral bone, collagenase activity was discovered unexpectedly. The question was raised whether this collagenase activity was endogenous or if it was due to the bacterial collagenase used to release the matrix vesicles from bone. In related experiments done, collagen partially degraded by collagenase mineralized better than undegraded collagen. This study would then attempt to show if an endogenous collagenase is found, whether it facilitates collagen mineralization by allowing better access for matrix vesicles by the "nicking" of collagen. From this two-month study evidence was found that an endogenous collagenase as well as a gelatinase was present on matrix vesicles. SDS gel electrophoresis and zymography were used to determine the presence of collagenases in purified matrix vesicle fractions. Western blots with antibodies to bacterial collagenase, matrix metallo-proteinases 13 (MMP-13), an endogenous collagenase, and MMP-2, an endogenous gelatinase, were also done to determine the presence of an endogenous collagenase. Another facet was added to this study to determine if contamination by exogenous collagenase during matrix vesicle isolation could be removed. From the final Western blots done, it was verified that even after exhaustive washings of the column and centrifugation, purified matrix vesicles contained contaminating bacterial collagenase. Due to the research completed, the matrix vesicle isolation protocol was changed from using bacterial collagenase to a trypsin isolation method to prevent any exogenous collagenase contamination.

Calcified microspheres as biological entities and their isolation from bone

Calcified microspheres, about 1 microm in diameter, appear at sites of bone formation where they invest the collagenous matrix, become confluent and disappear. Evidence that the particle boundaries are not lost with compaction but merely deformed is supported in section by the granular histochemical staining of the inorganic phase for bone salt, lipid, fibronectin and acid phosphatase in osteomalacic, acid-etched and normal human bone. Their persistence as discrete objects is confirmed by the application of methods for their isolation from the collagenous matrix of immature mouse calvarium and mature bovine femur. Five methods have been used to extract them and include (i) biochemical, (ii) chemical, (iii) mechanical, (iv) pyrogenous and (v) biological separation. Under the optical microscope, all isolates consisted of similar discrete objects and bridged assemblies, whose birefringence varied with treatment. After decalcification, their organic 'ghosts' remained. Each isolated microsphere had a complex substructure of clusters of non-collagenous calcified filaments surrounding a less dense centre. The filaments were 5 nm in diameter with a 5 nm periodicity and regular fine interfilamentous connections. It is concluded that the microspheres are independent, complex, pervasive and central to the containment (i.e. packaging) of calcium phosphate in bone. Their extraction will enable further analysis.

Association of matrix acid and alkaline phosphatases with mineralization of cartilage and endochondral bone

The activities of acid and alkaline phosphatases were localized by enzyme histochemistry in the chondroepiphyses of 5 week old rabbits. Using paraformaldehyde-lysine-periodate as fixative, the activity of acid phosphatase was particularly well preserved and could be demonstrated not only in osteoclasts, but also in chondrocytes as well as in the cartilage and early endochondral matrices. The acid phosphatase in the chondrocytes and the matrix was tartrate-resistant, but inhibited by 2 mM sodium fluoride, whereas for osteoclasts 50-100 mM sodium fluoride were required for inhibition. Simultaneous localisation of both acid and alkaline phosphatase activities was possible in tissue that had been fixed in 85% ethanol and processed immediately. In the growth plates of the secondary ossification centre and the physis, there was a sequential localisation of the two phosphatases associated with chondrocyte maturation. The matrix surrounding immature epiphyseal chondrocytes or resting/proliferating growth plate chondrocytes contained weak acid phosphatase activity. Maturing chondrocytes were positive for alkaline phosphatase which spread to the matrix in the pre-mineralizing zone, in a pattern that was consistent with the known location of matrix vesicles. The region of strong alkaline phosphatase activity was the precise region where acid phosphatase activity was reduced. With the onset of cartilage calcification, alkaline phosphatase activity disappeared, but strong acid phosphatase activity was found in close association with the early mineral deposition. Acid phosphatase activity was also present in the matrix of the endochondral bone, but was only found in early spicules which had recently mineralised. The results suggest that alkaline phosphatase activity is required in preparation of mineralization, whereas acid phosphatase activity might have a contributory role during the early progression of mineral formation.

Cysteine proteinases and matrix metalloproteinases play distinct roles in the subosteoclastic resorption zone

Digestion of calvarial bone by osteoclasts depends on the activity of cysteine proteinases and matrix metalloproteinases (MMPs). It is unknown, however, whether these enzymes act simultaneously or in a certain (time) sequence. In the present study, this was investigated by culturing mouse calvarial bone explants for various time intervals in the presence or absence of selective low molecular weight inhibitors of cysteine proteinases (E-64, Z-Phe-Tyr(O-t-Bu)CHN2 or CA074[Me]) and MMPs (CI-1, CT1166, or RP59794). The explants were morphometrically analyzed at the electron microscopic level. All proteinase inhibitors induced large areas of nondigested demineralized bone matrix adjacent to the ruffled border of actively resorbing osteoclasts. The appearance of these areas proved to be time dependent. In the presence of the cysteine proteinase inhibitors, a maximal surface area of demineralized bone was seen between 4 and 8 h of culturing, whereas the metalloproteinase inhibitors had their maximal effect at a later time interval (between 16 and 24 h). Because different inhibitors of each of the two classes of proteolytic enzymes had the same effects, our data strongly suggest that cysteine proteinases attack the bone matrix prior to digestion by MMPs. In line with the view that a sequence may exist were differences in the amount of proteoglycans (shown with the selective dye cuprolinic blue) in the subosteoclastic demineralized areas induced by the inhibitors. In the presence of the cysteine proteinase inhibitor, relatively high levels of cuprolinic blue precipitates were found, whereas this was less following inhibition of metalloproteinases. These data suggested that cysteine proteinases are important for digestion of noncollagenous proteins. We propose the following sequence in the digestion of calvarial bone by osteoclasts: after attachment of the cell to the mineralized surface an area with a low pH is created which results in dissolution of the mineral, then cysteine proteinases, active at such a low pH, digest part of the bone matrix, and finally, when the pH has increased somewhat, MMPs exert their activity.

Spaceflight has compartment- and gene-specific effects on mRNA levels for bone matrix proteins in rat femur

In the present study, we evaluated the possibility that the abnormal bone matrix produced during spaceflight may be associated with reduced expression of bone matrix protein genes. To test this possibility, we investigated the effects of a 14-day spaceflight (SLS-2 experiment) on steady-state mRNA levels for glyceraldehyde-3-phosphate dehydrogenase (GAPDH), osteocalcin, osteonectin, and prepro-alpha(1) subunit of type I collagen in the major bone compartments of rat femur. There were pronounced site-specific differences in the steady-state levels of expression of the mRNAs for the three bone matrix proteins and GAPDH in normal weight-bearing rats, and these relationships were altered after spaceflight. Specifically, spaceflight resulted in decreases in mRNA levels for GAPDH (decreased in proximal metaphysis), osteocalcin (decreased in proximal metaphysis), osteonectin (decreased in proximal and distal metaphysis), and collagen (decreased in proximal and distal metaphysis) compared with ground controls. There were no changes in mRNA levels for matrix proteins or GAPDH in the shaft and distal epiphysis. These results demonstrate that spaceflight leads to site- and gene-specific decreases in mRNA levels for bone matrix proteins. These findings are consistent with the hypothesis that spaceflight-induced decreases in bone formation are caused by concomitant decreases in expression of genes for bone matrix proteins.

Is acid phosphatase activity present in bone matrix at sites of endochondral ossification in rabbit fracture callus?

It has been suggested that acid phosphatase activity is present in newly formed bone matrix at sites of endochondral ossification in rabbit fracture calluses. Because acid phosphatases are usually found intracellularly, it was decided to test this possibility more rigorously. Tissue from 10- and 14-day healing rabbit fractures was subjected to a series of critical tests for acid phosphatases with a pH optimum of 5.0. Fluoride, tartrate and molybdate were used as potential inhibitors of acid phosphatase activity. The effects of several counterstaining protocols were also investigated. A fluoride- and tartrate-resistant acid phosphatase is located in osteoclasts and mononuclear phagocytes. Diffuse staining of the bone matrix is seen, but it is dependent upon the length of incubation in the substrate medium and the distance from the acid phosphatase-reacting cells. It is concluded that the coloration of the bone matrix is probably caused by diffusion of the dye and reaction product and is, therefore, artifactual.

Variability of embryonic development among three inbred strains of mice

We examined the relationships between litter size, embryonic growth, days of gestation, onset and duration of morphological stages and development of the first arch skeleton in three inbred strains of mice--C57BL/6, CBA/J and C3H/He. Detailed embryonic staging was based on craniofacial development between 11 and 18 days of gestation. Considerable intra- and interlitter variation of morphological stages of embryonic development exists in all three inbred strains. The relationship of morphological stages to days of gestation reveals that each stage has a different duration, being shortest at Theiler's stage 18 and longest at stage 21 in all three inbred strains. Embryos of CBA/J mice tend to reach each stage later than do embryos of the other two strains, i.e., morphological development is slowest in CBA/J. The greatest length, a measurement of embryonic growth, increases at a constant rate during gestation in all three strains. In C57BL/6 and CBA/J, more embryos tend to be implanted in the right horn of the uterus than in the left, whereas in C3H/He an even number of embryos tends to be implanted in both horns. Timing of the development of Meckel's cartilage differs between the three inbred strains: both condensation and onset of matrix deposition begin one stage earlier in C57BL/6 than in CBA/J and C3H/He. On the other hand, alkaline phosphatase, one of the earliest markers for bone development, is expressed at the same time in all three inbred strains. Differences in timing of skeletal development between the strains may be attributed in part to the genealogical closeness OF CBA/J and C3H/He mice.

The migration of purified osteoclasts through collagen is inhibited by matrix metalloproteinase inhibitors

The most obvious proteolytic event controlled by the osteoclast is bone matrix removal in the resorption compartment. Here, however, we investigated whether matrix metalloproteinase (MMP) activity of the osteoclast might be involved in its migration to its future bone resorption site. We seeded either nonpurified or purified osteoclasts onto either uncoated or collagen-coated dentine slices and cultured them in the presence or absence of specific MMP inhibitors. When nonpurified osteoclasts were cultured on uncoated dentine, MMP inhibitors did not prevent pit formation, as previously reported. However, when collagen-coated dentine was used, pit formation was strongly inhibited by MMP inhibitors. The same results were obtained when performing these experiments with purified osteoclasts, thus demonstrating the ability of osteoclasts by themselves to migrate through collagen via an MMP-dependent pathway. This demonstration was confirmed by using collagen-coated invasion chambers. In addition, the invasions were not, or only slightly, inhibited by inhibitors of serine proteinases, cysteine proteinases, and carbonic anhydrase, though the latter two are well established bone resorption inhibitors that strongly inhibited pit formation. It is concluded that osteoclasts can migrate through collagen in the absence of other cells and that this migration relies on MMP activity, whereas other enzymes typically required for bone removal in the resorption compartment are not essential for migration. Some of the osteoclast MMPs might thus be relevant to the migratory/invasive activity of the osteoclast, rather than to its bone resorptive activity itself.

[Investigation on matrix degrading enzymes of lumbar intervertebral discs]

Changes in the macromolecular matrix of the intervertebral disc may predispose to biomechanical failure of the disc. Such changes would involve extracellular enzymes capable of altering the collagen and proteoglycan of the disc matrix. In this study, tritium-labeled type I collagen was used as a substrate to estimate the activity of collagenase in the discs of 41 cases of lumbar disc protrusion (LDP) patients by surgical intervention. The annulus fibrous (AF) and nucleus pulposus (NP) were measured separately. 34 normal discs harvested by autopsy acted as controls. For estimation of relative neutral proteinase content of 6 normal and 16 degenerated lumbar discs, polyacrylamide gelelectrophoresis (PAGE), heat-denatured collagen as a substrate, and photo-density scanning with peak area autocalculating system were adopted. The results presented that both AF and NP of the normal discs had a similar lower collagenolytic activity and a very limited activity of neutral proteinase, while the degenerated discs showed a higher activity, especially in the degenerated NP. The extruded type of LDP got a higher collagenolytic activity in NP than that of the prolapsed LDP. The fact showed that the matrix degrading enzymes play a very important role in the process of lumbar disc degeneration. The difference of disc degeneration is the biochemical basis of different clinical types of LDP. Matrix degrading enzyme system is a very complexed multienzymatic system. Other neutral proteinases may join this system besides the collagenase.

New aspects of endochondral ossification in the chick: chondrocyte apoptosis, bone formation by former chondrocytes, and acid phosphatase activity in the endochondral bone matrix

A detailed histological study of the growth plates from 9- to 20-day-old embryonic chick long bones was carried out with the aim of clarifying the long-debated question of the fate of the hypertrophic chondrocytes. Since resorption in chick bones does not occur synchronously across the plate as it does in mammals, specialized regions develop and the fate of the chondrocyte depends on its location within the growth plate. Where resorption took place, as at the sites of primary vascular invasion or at the main cartilage/marrow interface, chondrocytes underwent apoptosis before the lacunae were opened. In addition, spontaneous apoptosis of chondrocytes occurred at apparently random sites throughout all stages of chondrocyte differentiation. In older chick bones, a thick layer of endochondral bone matrix covered the cartilage edge. This consisted of type I collagen and the typical noncollagenous bone proteins but, in addition, contained tartrate-resistant acid phosphatase in the mineralized matrix. Where such matrix temporarily protected the subjacent cartilage from resorption, chondrocytes differentiated to bone-forming cells and deposited bone matrix inside their lacunae. At sites of first endochondral bone formation, some chondrocytes underwent an asymmetric cell division resulting in one daughter cell which underwent apoptosis, while the other cell remained viable and re-entered the cell cycle. This provided further support for the notion that chondrocytes as well as marrow stromal cells give rise to endochondral osteoblasts.

Immunocytochemical study of cathepsin L and rat salivary cystatin-3 in rat osteoclasts treated with E-64 in vivo

The localization of cathepsin L and rat salivary cystatin-3 (RSC-3) in rat osteoclasts (rat femoral and alveolar bones) treated with or without E-64 (control) was examined immunocytochemically. In osteoclasts pretreated with E-64, immunoreactivity for cathepsin L was very weak extracellularly compared to that in the control osteoclasts. However, it was strong intracellularly. The localization of RSC-3 was unclear in the control osteoclasts, while in E-64 treated osteoclasts, both the clear zone and ruffled border areas showed a very strong immunoreaction. At the electron-microscopic level, in normal osteoclasts, numerous immunoreaction products for cathepsin L were found extracellularly in the bone matrix under the ruffled border, while few intracellular products were observed. In contrast, in the E-64-treated osteoclasts, only a few immunoreaction products were found extracellularly, while intracellularly cathepsin L was found in numerous endosome-lysosomal vacuoles. In the immunoreaction for RSC-3, the cytoplasm of the ruffled border was positive, and the tips of the RSC-3-positive ruffled border appeared to enter deeply into the bone matrix. Intracellularly, the granular reaction products of RSC-3 were found in the vacuoles (probably autophagolysosomes). Thus, in E-64-treated osteoclasts, inhibition of the extracellular release of cathepsin L was demonstrated. In addition, intralysosomal accumulation of RSC-3 and deep penetration of the RSC-3-positive ruffled border into the bone matrix were found. These findings suggest that RSC-3 is associated with the inhibition of cathepsin L in both the lysosomes (in the osteoclasts) and bone matrix.

Stage-specific expression patterns of alkaline phosphatase during development of the first arch skeleton in inbred C57BL/6 mouse embryos

Timing and pattern of expression of alkaline phosphatase was examined during early differentiation of the 1st arch skeleton in inbred C57BL/6 mice. Embryos were recovered between 10 and 18 d of gestation and staged using a detailed staging table of craniofacial development prior to histochemical examination. Expression of alkaline phosphatase is initiated at stage 20.2 in the plasma membrane of mesenchymal cells in the distal region of the first arch. Expression is strongest in osteoid (unmineralised bone matrix) and presumptive periosteum at stage 21.32. Mineralisation begins at stage E23. Expression is present in the mineralised bone matrix. Secondary cartilages form in the condylar and angular processes by stage M24. The cartilaginous cells and surrounding cells in the processes are all alkaline phosphatase-positive and surrounded by the common periosteum, suggesting that progenitor cells of the processes, dentary ramus and secondary cartilages all originate from a common pool. Nonhypertrophied chondrocytes of Meckel's cartilage express alkaline phosphatase at stage M23. Expression in these chondrocytes is preceded by the expression in their adjacent perichondrium. This is true of chondrocytes in all other cranial cartilages examined. 3-D reconstruction of expression in Meckel's cartilage also revealed that the chondrocytes of Meckel's cartilage which express alkaline phosphatase and the matrix of which undergoes mineralisation are those surrounded by the alkaline phosphatase-positive dentary ramus. By stage 25, coincident with mineralisation in the distal section of Meckel's cartilage, most chondrocytes are strongly positive. The perichondria of malleus and incus cartilages express alkaline phosphatase at stage M24. Nonhypertrophied chondrocytes along these perichondria also express alkaline phosphatase. Superficial and deep cells in the dental laminae of incisor and 1st molar teeth become alkaline phosphatase-positive at the bud stage, stages 21.16 and 21.32, respectively. Dental papillae are negative until stage M24 when alkaline phosphatase expression begins in the dental papillae and follicles of the incisor teeth and the dental follicles of the 1st molar teeth. The dental papillae of the 1st molar teeth express alkaline phosphatase at stage 25. Expression in the dental papillae and follicles appears to coincide with cellular differentiation of follicle from papilla. The presumptive squamosal, ectotympanic and gonial membrane bones, lingual oral epithelial cells connected to the dental laminae of the incisor teeth, hair follicle papillae and sheath and surrounding dermis all express alkaline phosphatase in a stage-specific manner.

Biochemical evidence for altered subchondral bone collagen metabolism in osteoarthritis of the hip

Osteoarthritis (OA) of the hip is invariably viewed as a disease primarily affecting the articular cartilage. Data presented in this report, however, demonstrate changes in the metabolic activity of the underlying trabecular bone tissue, the processes of which may represent a significant factor in the pathogenesis of hip OA. Trabecular bone tissue from OA subjects expressed significantly more matrix metalloproteinase (MMP)-2 (gelatinase A, 72 kDa type IV collagenase) when compared to age-matched osteoporotic (OP) and normal bone tissue. Alkaline phosphatase was also significantly elevated in OA bone tissue. The combination of increased MMP-2 and alkaline phosphatase indicates heightened collagen turnover in the subchondral bone compartment of osteoarthritic hips. The data obtained from this study warrant a closer investigation into the significance of these changes in OA and emphasize the multifactorial elements of the whole joint in the whole joint in the overall disease process.

Matrix metalloproteinases are obligatory for the migration of preosteoclasts to the developing marrow cavity of primitive long bones

A key event in bone resorption is the recruitment of osteoclasts to future resorption sites. We follow here the migration of preosteoclasts from the periosteum to the developing marrow cavity of fetal mouse metatarsals in culture, and investigate the role of proteinases and demineralization in this migration. Our approach consisted in testing inhibitors of proteinases and demineralization on the migration kinetics. Migration was monitored by histomorphometry and the (pre)osteoclasts were identified by their tartrate resistant acid phosphatase (TRAP) activity. At the time of explantation, TRAP+ cells (all mononucleated) are detected only in the periosteum, and the core of the diaphysis (future marrow cavity) consist of calcified cartilage. Upon culture, TRAP+ cells (differentiating progressively into multinucleated osteoclasts) migrate through a seam of osteoid and a very thin and discontinuous layer of mineral, invade the calcified cartilage and transform it into a “marrow' cavity; despite the passage of maturing osteoclasts, the osteoid develops into a bone collar. The migration of TRAP+ cells is completely prevented by matrix metalloproteinase (MMP) inhibitors, but not by a cysteine proteinase inhibitor, an inhibitor of carbonic anhydrase, or a bisphosphonate. The latter three drugs inhibit, however, the resorptive activity of mature osteoclasts at least as efficiently as do the MMP inhibitors, as assessed in cultures of calvariae and radii. Furthermore, in situ hybridizations reveal the expression of 2 MMPs, gelatinase B (MMP-9 or 92 kDa type IV collagenase) in (pre)osteoclasts, and interstitial collagenase (MMP-13) in hypertrophic chondrocytes. It is concluded that only MMPs appear obligatory for the migration of (pre)osteoclasts, and that this role is distinct from the one MMPs may play in the subosteoclastic resorption compartment. We propose that this new role of MMPs is a major component of the mechanism that determines where and when the osteoclasts will attack the bone.

Herniated cervical intervertebral discs spontaneously produce matrix metalloproteinases, nitric oxide, interleukin-6, and prostaglandin E2

STUDY DESIGN

Herniated cervical disc specimens were obtained from patients undergoing surgical discectomy for persistent radiculopathy and cultured in vitro to determine whether various biochemical agents were being produced.

OBJECTIVES

Our hypothesis is that biochemical mediators of inflammation and tissue degradation play a role in cervical intervertebral disc degeneration and in the pathophysiology of cervical radiculopathy.

SUMMARY OF BACKGROUND DATA

Neck pain with or without radiculopathy is a common clinical problem, but the etiology of neck pain and the exact pathophysiology of radiculopathy remain uncertain. We have previously reported the production of various biochemical agents by herniated lumbar disc specimens in vitro. Because of a lack of such studies in the literature with respect to the cervical spine, the purpose of this study was to determine whether similar biochemical agents of inflammation and tissue degradation were being produced by herniated cervical disc specimens.

METHODS

Eighteen herniated cervical discs were obtained from 15 patients undergoing anterior disc surgery. The specimens were cultured and incubated for 72 hours, and the media were subsequently collected for biochemical analysis. Biochemical assays for matrix metalloproteinases, nitric oxide, prostaglandin E2, and a variety of cytokines were performed. As a control group, six cervical discs specimens were obtained from three patients undergoing anterior surgery for traumatic burst fractures, and similar biochemical analyses were performed.

RESULTS

The culture media from the herniated cervical disc specimens showed increased levels of matrix metalloproteinase activity compared with the control discs. Similarly, the levels of nitric oxide, prostaglandin E2, and interleukin-6 were significantly higher in the herniated disc specimens compared with the control discs. Interleukin-1 alpha, interleukin-1 beta, tumor necrosis factor-alpha, interleukin-1 receptor antagonist protein, and substance P were not detected in the culture media of the herniated or control discs.

CONCLUSIONS

Herniated cervical disc specimens were making spontaneously increased amounts of matrix metalloproteinases, nitric oxide, prostaglandin E2, and interleukin-6. These results were similar to those obtained in herniated lumbar disc specimens that we have previously reported. These products may be intimately involved in the biochemistry of disc degeneration and the pathophysiology of radiculopathy.

Osteosarcoma hybrids can preferentially target alkaline phosphatase activity to matrix vesicles: evidence for independent membrane biogenesis

Alkaline phosphatase is the marker enzyme for matrix vesicles, extracellular organelles that play a major role in primary bone formation and calcification. Recently, we developed osteosarcoma x fibrosarcoma hybrids in which alkaline phosphatase expression was greatly reduced, a phenomenon known as extinction. In the present study, we used to cell hybrids, LTA-1 and LTA-5, constructed from a human osteoblast-like osteosarcoma. TE85, and a mouse fibrosarcoma, La-t-, to examine the differential distribution of alkaline phosphatase between matrix vesicles and the plasma membrane, postulated to be the parent membrane from which matrix vesicles are derived. While alkaline phosphatase in plasma membranes was extinguished, enzyme activity in matrix vesicles from LTA-1 hybrid cells was 34.2% of that present in matrix vesicles from the TE85 parent cells and 200 times that found in La-t- matrix vesicles. Matrix vesicles from LTA-5 had alkaline phosphatase levels similar to La-t-. When other membrane enzymes (phospholipase A2, 5'-nucleotidase, and Na+/K+ ATPase) were examined, hybrid matrix vesicle and plasma membrane levels were similar to those of TE85 and significantly higher than in La-t- membrane fractions. Northern analysis detected mRNA for alkaline phosphatase in TE85 cells, but not in the hybrids or La-t- cells. In contrast, reverse transcription-polymerase chain reaction (RT-PCR) revealed alkaline phosphatase mRNA in the hybrid cells, but at very low levels. Taken together, the data indicate that regulation of plasma membrane and matrix vesicle alkaline phosphatase is independent and suggest that matrix vesicle biogenesis is independent and distinct from that of plasma membrane biogenesis. Analysis of 1B- and 1L-type alkaline phosphatase mRNA by RT-PCR showed that alternate promoter usage of the alkaline phosphatase gene was not responsible for the differential localization of this enzyme in matrix vesicle. Thus, it is likely that matrix vesicle and plasma membrane alkaline phosphatase are regulated differently at a post-transcriptional level.

Voluntary exercise increases osteogenetic activity in rat bones

The purpose of this study was to investigate the effect of voluntary exercise on osteoinductive activity in rat bone. Sprague-Dawley male and female rats were allowed to exercise freely by running on a treadmill or kept as controls without exercise for 53 days. Decalcified humeral diaphyses from experimental and control rats were implanted intraperitoneally into host rats and harvested after 33 days. A significant increase in bone formation was confirmed in the implanted bone matrices from the running group in comparison with those from control animals by soft X-ray photography and determination of alkaline phosphatase activity and mineral content. Alkaline phosphatase activity in bone and serum was increased by exercise in both male and female animals. The results suggest that osteoinductive activity in the bone was probably due to increased levels of bone morphogenetic protein following voluntary exercise.

Alendronate modulates osteogenesis of human osteoblastic cells in vitro

The bisphosphonates, which are carbon-substituted pyrophosphates, have been studied extensively both in vivo and in vitro to elucidate their effects on bone tissues and cells. However, because these agents were shown to have a potent inhibitory effect on bone resorption, the majority of studies have focused on only this aspect of bone metabolism. There appears to be less information regarding the direct effect of bisphosphonates on bone formation, so thus we undertook experiments to investigate the effects of bisphosphonates, especially alendronate, on the mineralization and matrix protein synthesis of human osteoblastic cells in vitro. The data show that the bisphosphonates, alendronate, etidronate and pamidronate, suppressed 1,25-dihydroxycholecalciferol (1,25(OH)2D3)-stimulated mineralization of human osteoblastic cells at high concentrations, while relatively lower concentrations of alendronate and etidronate potentiated mineralization of the cells in the presence of 1,25(OH)2D3. The potentiation of mineralization with alendronate was accompanied by increased synthesis of bone matrix proteins, osteocalcin and collagen, and the mRNA of pro alpha(I) collagen. These findings show that in addition to their well-known effects on bone resorption, bisphosphonates have significant and direct effects on osteogenesis in osteoblasts in vitro. The actual mechanism remains to be further investigated.

Immunolocalization of complement C1s and matrix metalloproteinase 9 (92kDa gelatinase/type IV collagenase) in the primary ossification center of the human femur

The first component of complement C1s has been shown to degrade type I and type II collagens (Yamaguchi et al. 1990), the latter of which is a major constituent of the cartilage matrix. In order to understand the physiological roles of C1s in cartilage resorption, the expression of C1s was examined by immunohistochemistry in the primary ossification center where the matrix is removed and replaced by bone marrow. Hypertrophic chondrocytes, endothelium and hematogenous elements in the capillary buds were intensely stained by a monoclonal antibody against C1s. Matrix metalloproteinase 9 (MMP-9, 92kDa gelatinase/type IV collagenase) was also immunolocalized in hypertrophic chondrocytes, mesenchymal cells in the primitive bone marrow and the cartilage matrix adjacent to the marrow. In addition, C1s was found to activate the zymogen of MMP-9. These observations suggest that C1s and MMP-9 coordinately participate in matrix degradation in cartilage.

Allosteric modulation by ATP, calcium and magnesium ions of rat osseous plate alkaline phosphatase

Alkaline phosphatase from rat osseous plate is allosterically modulated by ATP, calcium and magnesium at pH 7.5. At pH 9.4, the hydrolysis of ATP and PNPP follows Michaelis-Menten kinetics with K0.5 values of 154 microM and 42 microM, respectively. However, at pH 7.5 both substrates exhibit more complex saturation curves, while only ATP exhibited site-site interactions. Ca(2+)-ATP and Mg(2+)-ATP were effective substrates for the enzyme, while the specific activity of the enzyme for the hydrolysis of ATP at pH 7.5 was 800-900 U/mg and was independent of the ion species. ATP, but not PNPP, was hydrolyzed slowly in the absence of metal ions with a specific activity of 140 U/mg. These data demonstrate that in vitro and at pH 7.5 rat osseous plate alkaline phosphatase is an active calcium or magnesium-activated ATPase.

Kinetic properties of osseous plate alkaline phosphatase from diabetic rats

1. Increased levels of bone alkaline phosphatase activity were observed in diabetic rats. These animals exhibited impaired bone development without concomitant alterations of the sequence of cellular transformations. 2. Alkaline phosphatase activity was delayed in diabetic rats but the kinetic parameters for the hydrolysis of p-Nitrophenylphosphate (PNPP) were virtually the same observed for controls (N = 1.2 and K0.5 = 43 microM). 3. Alkaline phosphatase from diabetic rats had a better affinity (K0.5 = 38 microM) for magnesium ions than controls (K0.5 = 91 microM). 4. Zinc ions affected alkaline phosphatase activity from control and diabetic rats in the same way (K0.5 = 10 microM).

Cysteine-proteinase localization in osteoclasts: an immunocytochemical study

Cysteine-proteinases such as cathepsin B and G were localized in rat osteoclasts, by an indirect protein A-immunogold labeling technique, on post-embedded ultrathin sections. In osteoclasts, specific immunogold labeling of both anti-cathepsin B and G was localized in Golgi vesicles, lysosomes, pale vacuoles of various sizes, and the extracellular canals of ruffled borders; no immunoreactivity was seen in the cytoplasmic matrix, mitochondria, cisterns of the rough endoplasmic reticulum, or nuclei. The presence of immunolabeling of cathepsins in osteoclasts and in the subosteoclastic compartment suggests that these enzymes are involved in the extracellular degradation of collagen and other non-collagenous bone matrix proteins.

Influence of an intermittent compressive force on matrix protein expression by ROS 17/2.8 cells, with selective stimulation of osteopontin

The purpose of this study was to determine the response of bone cells to physical stress. Intermittent compressive force (ICF) was applied to 13 kPa to subconfluent ROS 17/2.8 cells at 18 cycles/min. After 48 h of this application, the cells were labelled with [35S]-methionine or [32PO4]. Application of ICF over this time did not alter the synthesis of type I collagen, fibronectin or bone SPARC (osteonectin) compared to that of control cells. However, the activity of alkaline phosphatase was increased 1.5-fold, and the synthesis of a 32PO4-labelled, 75-kDa phosphoprotein, recognized as osteopontin by immunoprecipitation with specific antibodies, was increased 1.4-fold. Also, an increase in osteopontin mRNA starting within 12h of ICF application was observed. The selective increase in osteopontin expression associated with ICF may be important in the remodelling of bone tissues during growth and development and in response to functional forces.

Modulation of matrix vesicle enzyme activity and phosphatidylserine content by ceramic implant materials during endosteal bone healing

This study examined effects of bone bonding and nonbonding implants on parameters associated with matrix vesicle-mediated primary bone formation, matrix vesicle alkaline phosphatase and phospholipase A2 specific activities, and phosphatidylserine content. Tibia marrow ablation followed by implantation of KG-Cera, Mina 13 (bonding), KGy-213, or M 8/1 (nonbonding) was used as the experimental model. Postsurgery, matrix vesicle-enriched microsomes (MVEM) were isolated from implanted and contralateral limbs. MVEM alkaline phosphatase and phospholipase A2 were stimulated adjacent to bonding implants with similar, though reduced, effects contralaterally. Alkaline phosphatase exhibited slight stimulation in nonbonding tissue; phospholipase A2 was inhibited or unchanged in treated and contralateral limbs. Phosphatidylserine content of MVEM was differentially affected by the implant materials. Thus, MVEM are modulated by implant materials locally and systemically. The data demonstrate that the model is a biologically relevant diagnostic for assessing the tissue/implant interface, primary calcification is affected by implant materials, and implant-specific effects are detected in the contralateral unimplanted limb.

Immunolocalization of alkaline phosphatase in osteoblasts and matrix vesicles of human fetal bone

A monoclonal antibody raised against alkaline phosphatase (ALP) of human osteosarcoma was used to localize this enzyme in human fetal bone tissue. For light microscopy, the presence of alkaline phosphatase in osteoblasts and osteocytes was demonstrated by use of an avidin-biotin immunoperoxidase procedure. Electron microscopic immunolocalization was accomplished with an indirect immunoperoxidase method which revealed a concentration of the enzyme on matrix vesicle and osteoblast plasma membranes. In addition, many vesicular protrusions arising from areas of plasma membrane on the lateral surfaces of adjacent osteoblasts were strongly immunolabeled. Immunostaining for ALP was absent in vesicles which contained fine crystallites. Alkaline-phosphatase-rich matrix vesicles may play a significant role in the mineralization of the extracellular matrix.

Effect of a pulsing electromagnetic field on demineralized bone-matrix-induced bone formation in a bony defect in the premaxilla of rats

A 2-mm non-healing bony defect was prepared in the premaxilla of male Wistar rats weighing about 180 g as a simulation of an alveolar cleft, for determination of whether a pulsing electromagnetic field (PEMF) could promote regeneration of bone induced by demineralized bone matrix (DBM). The defect was either treated with 7 mg DBM or was left as a non-grafted control. The rats were exposed to a PEMF with a frequency of 100 Hz, a 10-ms-wide burst with 100 microseconds-wide quasi-rectangular pulses, repeating at 15 Hz, and magnetic field strength of 1.5-1.8 G. Alkaline phosphatase activity increased significantly from day 7 in the DBM-graft-plus-PEMF group and from day 10 in the DBM-graft group, reaching a maximum on day 14. A greater-than-two-fold rise in alkaline phosphatase activity and a three-fold rise in the amount of 45Ca incorporation in the DBM-graft-plus-PEMF group were attained compared with those of the DBM-graft group. The DBM-graft-plus-PEMF group produced more bone with almost complete osseous bridging in the defect sites than did the group treated with DBM only on day 35. The findings indicate that PEMF had an enhancing effect on the bone-inductive properties of the DBM through the stimulation of osteoblast differentiation induced by DBM.

A histochemical study of acid phosphatases in medullary bone matrix and osteoclasts in laying Japanese quail

Acid phosphatase activity in medullary bone matrix and osteoclasts of laying Japanese quail was examined histochemically. To avoid nonspecific staining, the reactivity of the enzyme was evaluated using both the azo dye method and the lead salt method and nonembedded thick sections and resin-embedded thin sections. The pH of the incubation medium was also varied from the acid range (pH 5.0 and 6.5) to the alkaline range (pH 8.5). Medullary bone osteoclasts contain both tartrate-resistant acid phosphatase (TRAP) activity and fluoride-resistant acid phosphatase (FRAP) activity, and no significant difference in intensity was detected between active and inactive osteoclasts. The entire matrix of medullary bone was positive for tartrate-resistant, fluoride-sensitive acid phosphatase activity. No reaction product was observed in sections incubated in substrate-free and pH 8.5 media. The results demonstrate the existence of FRAP in medullary bone osteoclasts and suggest that medullary bone matrix includes TRAP throughout the matrix.

An active neutral metalloproteinase bound to the insoluble collagen in the mineralized phase matrix of adult rat calvaria

Two kinds of proteinases were found in the mineralized phase matrix of 24-week-old rat calvaria by means of enzymography using gelatin as a substrate. One proteinase was a neutral thiol 58kD proteinase as shown in a previous paper [2]. The other was a neutral metalloproteinase that had a molecular mass of 56kD and was detected only when calcium (Ca) ions were added to the incubation buffer. It is believed that the 56kD proteinase is bound to the insoluble collagen of the bone matrix, as it is solubilized by 4 M guanidine HC1 solution from the insoluble collagen fraction, when prepared by removing extractable proteins of the mineralized phase matrix. The insoluble collagen fraction could also be solubilized and prepared as gelatin by heating at 65 degrees C for 5 minutes. The gelatin was then incubated at 37 degrees C without further treatment and became degraded without an activation of 4-aminophenylmercuric acetate (APMA). This nonactivated degradation was enhanced by adding Ca ions. These results suggest that the 56kD metalloproteinase bound to the insoluble collagen of bone matrix is in an active form and may participate in the rapid degradation of collagen during bone resorption. As partially purified 56kD metalloproteinase degraded cartilage type proteoglycan, but not type I, IV, and V collagens, it is possibly related to the degradation of proteoglycans before it binds to collagen fibers during bone formation.

Lactate dehydrogenase isoenzymes in matrix vesicles (review)

Matrix vesicles (MV) isolated from mineralizing tissues contain high alkaline phosphatase (ALPase) activities associated with the membrane; this may be because MV originate from the plasma membrane of chondrocytes. Previous studies in our laboratory demonstrated that lactate dehydrogenase (LDH) isoenzymes, which appeared to be derived from chondrocytes cytosol, were located in MV of the epiphyseal growth plate of young-rabbit leg bones [1]. In the epiphyseal cartilage, alkaline phosphatase (ALPase) is enriched in the growth zone, whereas it is rarely detected in the resting zone, suggesting that MV containing ALPase are not present in the resting zone. In recent study, we divided the epiphyseal cartilages of young-rat rib bones into the growth zone and the resting zone, followed by the isolation of MV after collagenase digestion. MV containing ALPase and LDH were found in the growth zone, and surprisingly, vesicles containing LDH without ALPase were found in the resting zone [2]. The function of LDH-containing vesicles without ALPase is unknown at the present. However, these findings might accelerate the studies on cell-mediated calcification, because (1) LDH could be a marker enzyme of these vesicles, (2) LDH is found to be a specific cytosolic enzyme which is enfolded in these vesicles, suggesting that an unknown mechanism for the specific uptake of the cytosolic enzyme might be present.

Presence and specific concentration of carbonic anhydrase II in matrix vesicles

Matrix vesicles were isolated from the epiphyseal growth plates of normal weanling rats, and the presence of carbonic anhydrase II was demonstrated by Western blotting and ultrastructural immunolocalization using the immunogold technique. Total carbonic anhydrase activity was assayed and showed a statistically significant increase in matrix vesicles as compared to normal rat chondrocytes derived from the same growth plates. These results are the first to establish the presence of carbonic anhydrase in matrix vesicles.

Extracellular alkaline phosphatase activity in mineralizing matrices of cartilage and bone: ultrastructural localization using a cerium-based method

The ultrastructural localization of alkaline phosphatase (A1P) activity has been demonstrated in epiphyseal growth cartilage and metaphyseal bone of rats. Epiphyso-metaphyseal specimens were decalcified with EDTA and treated with MgCl2 to regenerate the enzymatic activity before incubation in a medium containing beta-glycerophosphate, MgCl2 and CeCl3. A1P activity was present on the outer surface of the plasmamembrane of maturing and hypertrophic chondrocytes and of osteoblasts. Moreover, the reaction product was present in chondrocyte lacunae, in matrix vesicles, and in cartilage matrix, as well as among uncalcified collagen fibrils of osteoid tissue in bone. The intensity of reaction was the lowest, or completely lacking, where the degree of matrix calcification was the highest. These results suggest that alkaline phosphatase is transported from the cells into the cartilage and bone matrix by its association with matrix vesicles and plasmamembrane components, and that its activity in cartilage and bone matrix is inhibited as it is incorporated in the mineral substance.

In vivo regulation of matrix vesicle concentration and enzyme activity during primary bone formation

In vivo regulation of matrix vesicles (MV) during primary bone formation was examined using tibial marrow ablation in rats as the experimental model. The effects of bone-bonding and nonbonding implants on the number of MV/micron 2 of matrix and the alkaline phosphatase (ALPase) and phospholipase A2 (PA2) activities of MV-enriched microsomes (MVEM) isolated from the healing bone were studied. MV concentration, ALPase, and PA2 were increased by bone-bonding implants by day 3 post-surgery; a similar effect was seen in the contralateral limb, but at a lower magnitude. Nonbonding implants had no effect at day 3 and decreased MV concentration and PA2 activity at later time points; the same behavior was observed in the contralateral limb. These results demonstrate that MVs are influenced in a differential manner by implant materials, both locally and systemically, and can be regulated during primary mineralization.

Stimulation of matrix vesicle enzyme activity in osteoblast-like cells by 1,25(OH)2D3 and transforming growth factor beta (TGF beta)

After demonstrating the presence of matrix vesicles in three osteosarcoma cell lines, MG-63, ROS 17/2.8 and MC-3T3-E1, we sought to determine whether two major enzymes localized to matrix vesicles, alkaline phosphatase and phospholipase A2, could be regulated by 1,25(OH)2D3 and/or TGF beta. Intravesicular calcification is probably dependent on these two enzymes. Alkaline phosphatase is essential for hydrolysis of phosphate-containing substrates and phospholipase A2 hydrolyzes diacylphosphatides in a calcium-mediated manner at lipid-aqueous interfaces leading to changes in membrane fluidity and possibly breakdown of the matrix vesicle. The 1,25(OH)2D3 induced increase of alkaline phosphatase in bone cells is localized to the matrix vesicle. TGF beta also increased alkaline phosphatase activity in two of the cell lines, MG-63 and ROS 17/2.8 but to a greater degree than 1,25(OH)2D3. Matrix vesicle alkaline phosphatase activity exhibited a greater response than that in the plasma membrane. TGF beta increased phospholipase A2 activity in both matrix vesicles and plasma membranes, therefore, no targeting was observed with respect to this enzyme. When TGF beta was combined with 1,25(OH)2D3, 1,25(OH)2D3 had no effect on phospholipase A2 and did not interfere with TGF beta stimulation of phospholipase A2 activity. When 1,25(OH)2D3 and TGF beta were combined, a tremendous synergy was observed in alkaline phosphatase specific activity in both plasma membranes and matrix vesicles with targeting to matrix vesicles. Therefore, TGF beta not only plays an important role in matrix formation and differentiation, but works in conjunction with 1,25(OH)2D3 to greatly potentiate the effects seen with 1,25(OH)2D3 alone.

Matrix vesicle enzyme activity in endosteal bone following implantation of bonding and non-bonding implant materials

The effect of bone bonding (KGy-Cera) and non-bone bonding (KGy-213) implant materials on primary mineralization was examined in endosteal bone repair following marrow ablation. Comparisons were made to determine implant effect on concentration and biochemical parameters of matrix vesicles, as contrasted to vesicles in normal bone healing. Matrix vesicle number was determined by high-resolution computerized morphometric analysis, and implant effect on the specific activity of alkaline phosphatase and phospholipase A2 was measured. Bone responses differed according to the composition of the implant material. The bone bonding implant in this study stimulated matrix vesicle formation, alkaline phosphatase specific activity, and, to a lesser extent, phospholipase A2 activity. The effect of the non-bonding implant on healing bone was of suppression of enzyme specific activities and reduced matrix vesicle production. The results indicate that the bone bonding implant material (KGy-Cera) promotes the initiation of primary mineralization, whereas failure of the KGy-213 to bond may be related to toxic materials that leach from the implant and inhibit the normal sequence of events in the mineralization cascade. The results also demonstrate that the implant materials alter the healing process distal to the injury site. Changes observed in the contralateral control limb mimic the changes observed in the injured limb, but at lower magnitude.