Characterization of new fluorogenic substrates for the rapid and sensitive assay of cathepsin E and cathepsin D

Cathepsin E and cathepsin D are two major intracellular aspartic proteinases implicated in the physiological and pathological degradation of intra- and extracellular proteins. In this study, we designed and constructed highly sensitive synthetic decapeptide substrates for assays of cathepsins E and D based on the known sequence specificities of their cleavage sites. These substrates contain a highly fluorescent (7-methoxycoumarin-4-yl)acetyl (MOCAc) moiety and a quenching 2,4-dinitrophenyl (Dnp) group. When the Phe-Phe bond is cleaved, the fluorescence at an excitation wavelength of 328 nm and emission wavelength of 393 increases due to diminished quenching resulting from the separation of the fluorescent and quenching moieties. The first substrate, MOCAc-Gly-Lys-Pro-Ile-Leu-Phe-Phe-Arg-Le u-Lys(Dnp)gamma-NH2, in which the Lys-Pro combination at positions P5 and P4 was designed for specific interaction with cathepsin E, is hydrolyzed equally well by cathepsins E and D (kcat/Km = 10.9 microM(-1) x s(-1) for cathepsin E and 15.6 microM(-1) x s(-1) for cathepsin D). A very acidic pH optimum o was obtained for both enzymes. The second substrate, MOCAc-Gly-Lys-Pro-Ile-Ile-Phe-Phe-Arg-Le u-Lys(Dnp)gamma-NH2, in which the isoleucine residue at position P2 was meant to increase the specificity for cathepsin E, is also hydrolyzed equally by both enzymes (kcat/Km = 12.2 microM(-1) x s(-1) for cathepsin E and 16.3 microM(-1) x s(-1) for cathepsin D). The kcat/Km values for both substrates are greater than those for the best substrates for cathepsins E and D described so far. Unfortunately, each substrate shows little discrimination between cathepsin E and cathepsin D, suggesting that amino acids at positions far from the cleavage site are important for discrimination between the two enzymes. However, in combination with aspartic proteinase inhibitors, such as pepstatin A and Ascaris pepsin inhibitor, these substrates enable a rapid and sensitive determination of the precise levels of cathepsins E and D in crude cell extracts of various tissues and cells. Thus these substrates represent a potentially valuable tool for routine assays and for mechanistic studies on cathepsins E and D.

A predominant apoptotic death pathway of neuronal PC12 cells induced by activated microglia is displaced by a non-apoptotic death pathway following blockage of caspase-3-dependent cascade

Activated microglia have been implicated in the regulation of neuronal cell death. However, the biochemical mechanism for neuronal death triggered by activated microglia is still unclear. When treated with activated microglia, neuronal PC12 cells undergo apoptosis accompanied by caspase-3-like protease activation and DNA fragmentation. Apoptotic bodies formed were subsequently phagocytosed by neighboring activated microglia. Pretreatment of the cells with the caspase-3-like protease inhibitor N-acetyl-Asp-Glu-Val-Asp-aldehyde did not reverse this cell death. Although Bcl-2 overexpression in the cells caused the inhibition of caspase-3-like protease activity and DNA fragmentation and the effective interference of apoptosis induced by deprivation of trophic factors, it could not suppress the activated microglia-induced neuronal death. At the electron microscopic level, degenerating cells with high levels of Bcl-2 were characterized by slightly condensed chromatins forming irregular-shaped masses, severely disintegrated perikarya, and marked vacuolation. Various protease inhibitors tested did not inhibit this cell death, whereas the radical oxygen species scavenger N-acetyl-L-cysteine significantly suppressed this death. Altogether, our study provides an alternative death pathway for the activated microglia-induced neuronal death by blockage of the caspase-3 protease cascade.

[An epidemiologic examination on the prevalence of the periodontal diseases and oral pigmentation in Yusho patients in 1998]

An epidemiologic examination was carried out to reveal the prevalence of the periodontal diseases and oral pigmentation in patients with Yusho 30 years after PCBs exposure. The results obtained were as follows. 1) 69 patients out of 71 patients with Yusho, who were measured periodontal pocket depth using Ramfjord' methods, had at least one tooth with periodontal pocket deeper than 3 mm. Similarly, 241 teeth out of a total 348 examined teeth showed periodontal pocket with more than 3 mm depth. 2) Oral pigmentation was observed in 46 out of 79 patients with Yusho. In this study, gingival pigmentation was most predominant among oral pigmentation. In addition, it is of particular interest that oral pigmentation tended to be observed at a much higher frequency in younger patients with Yusho.

Effect of powder grinding on hydroxyapatite formation in a polymeric calcium phosphate cement prepared from tetracalcium phosphate and poly(methyl vinyl ether-maleic acid)

The primary aim of this study was to determine if cements based on poly(methyl vinyl ether-maleic acid) (PMVE-Ma) and tetracalcium phosphate resulted in hydroxyapatite formation. In addition, the mechanical strength of this type of polymeric calcium phosphate cement was evaluated. Cements were prepared by mixing, in a powder/liquid mass ratio of 3.0, an aqueous solution of PMVE-Ma (mass fraction = 25%) and tetracalcium phosphate powders ground for various periods of time. The tetracalcium phosphate powders and set cements were characterized by means of X-ray powder diffraction and scanning electron microscopy. Mechanical strengths of the cements were tested 24 h after mixing. Prolonged grinding of tetracalcium phosphate powder decreased particle size and/or crystallite size and increased lattice distortion. This enhanced the reactivity of the tetracalcium phosphate powder and elevated the extent of crosslinking between PMVE-Ma molecules, resulting in improved mechanical strength. Hydroxyapatite formation was detected in the cement prepared with the most finely ground tetracalcium phosphate powder. The conversion of residual tetracalcium phosphate particles to more thermodynamically stable hydroxyapatite crystals will reduce the solubility of the polymeric cement and increase its biocompatibility.

Limited and selective localization of the lysosomal membrane glycoproteins LGP85 and LGP96 in rat osteoclasts

Monospecific antibodies against two major glycoproteins of rat lysosomal membranes with apparent molecular masses of 96 and 85 kDa, termed LGP96 and LGP85, respectively, were used as probes to determine the expression and distribution of lysosomal membranes in rat osteoclasts. At the light microscopic level, the preferential immunoreactivity for both proteins was found at high levels at the side facing bone of actively bone-resorbing osteoclasts. Osteoclasts detached from bone surface were devoid of immunoreactivity for each protein. At the electron microscopic level, both proteins were exclusively confined to the apical plasma membrane at the ruffled border of active osteoclasts with well-developed ruffled border membrane. No immunolabeling for both proteins was observed in the basolateral membrane and the clear zone of bone-resorbing osteoclasts. The plasma membrane of preosteoclasts and post- and/or resting osteoclasts showed little or no reactivity against these two antibodies. The results indicate that lysosomal membrane glycoproteins are actively synthesized in active osteoclasts, rapidly transported to the ruffled border area, and contribute to the formation and maintenance of the acidic resorption lacuna of osteoclasts.

Expression of growth/differentiation factor 11, a new member of the BMP/TGFbeta superfamily during mouse embryogenesis

We have cloned and characterized a new member of the bone morphogenetic protein/transforming growth factor beta (BMP/TGFbeta) superfamily, growth differentiation factor 11 (Gdf11), from rat incisor pulp RNA by reverse transcription-polymerase chain reaction using degenerate primers. The mature carboxyl-terminal domain encoded by Gdf11 is most closely related to Gdf8, being 90% identical to the mouse gene. Northern blot analysis revealed Gdf11 is expressed in adult dental pulp and brain. In situ hybridization of sections and whole-mount embryos demonstrated Gdf11 is first strongly expressed in restricted domains at 8.5 days post coitus (dpc) when it is highest in the tail bud. At 10.5 dpc, it is expressed in the branchial arches, limb bud, tail bud and posterior dorsal neural tube. Later, it is expressed in terminally-differentiated odontoblasts, the nasal epithelium, retina and specific regions of the brain.

Histological study of periapical tissue healing in the rat molar after retrofilling with various materials

We histologically examined the effects on the periapical tissue of various dental filling materials applied as retrofillings in rats and compared them with those of amalgam. The 4-META-TBB resin Superbond and the light-cured composite resin produced the least severe inflammatory reaction, with the greatest amount of new bone. In these specimens, regeneration of a part of the periodontal ligament was also observed. These results indicate that these materials might be very biocompatible and thus foster the natural regeneration of the periapical tissue.

Transforming growth factor-beta superfamily members expressed in rat incisor pulp

The transforming growth factor (TGF)-beta superfamily comprises more than 35 structurally related genes that have been implicated in embryonic induction and morphogenesis. Different superfamily members may have distinct regulatory roles in tooth development and maintenance. Degenerate primer sets derived from the highly conserved carboxy terminal region of the TGF-beta superfamily were used for reverse transcriptase polymerase with poly(A)+ RNA from the rat incisor pulp as a template. TGF-beta superfamily members expressed in the pulp with known potential to differentiate into odontoblasts and to form dentine were identified. Nucleotide-sequence analysis of the amplified cDNAs identified those encoding activin-betaB; bone morphogenic protein (BMP)-2, -4, -7 and -8; growth/differentiation factor (GDF)-1, -5 and -6; and glial cell line-derived neurotrophic factor. In addition, Northern blot analysis detected TGF-beta1 -beta2 and -beta3; activin-betaA; BMP-6 and GDF-7 mRNA transcripts in the pulp. Coordinated expression of TGF-beta superfamily members in pulp may be critical in tooth development and repair.

Expression of TGF-beta superfamily receptors in dental pulp

Transforming growth factor-beta (TGF-beta) superfamily members and their cell-surface receptors may play inductive and/or regulatory roles in tooth development and repair. It will be important to identify the complete set of TGF-beta superfamily receptors, to examine their temporal and spatial localization during tooth development, and to elucidate the cascade of molecular events of tooth formation induced by the TGF-beta superfamily. In this report, we have cloned the cDNAs encoding potential receptors for TGF-beta superfamily members in rat incisor pulp and bovine adult pulp which are regarded as embryonic and adult pulp, respectively. We analyzed poly (A)+ RNA from rat incisor pulp and bovine adult pulp by reverse-transcriptase/polymerase chain-reaction (RT-PCR), using a degenerate primers corresponding to the most conserved amino acid sequences in the intracellular serine/threonine kinase of type I or type II like kinase-1 (ALK-1), ALK-2, ALK-3 (bone morphogenetic protein receptor type IA, BMPR-IA), ALK-4 (B1), ALK-5, ALK-6 (BMPR-IB), and BMPR-II (BMP type II receptor) was found to be in dental pulp. Northern blot analysis further detected TGF-beta type II receptor (T beta R-II) mRNA transcript in addition to the above-identified receptors. These results provide the first evidence of multiple type I and type II receptors for TGF-beta s, activins, and BMPs expressed in embryonic and adult pulp, implicating diverse function in tooth development and pulp tissue repair.

Temporal changes in expression of transforming growth factor-beta superfamily members and their receptors during bovine preodontoblast differentiation in vitro

Transforming growth factor (TGF)-beta superfamily members and their receptors play a part in the differentiation of pulp cells into odontoblasts during reparative dentinogenesis. Bovine primary pulp-cell culture has been used as an in vitro model for proliferation and differentiation of pulp cells into preodontoblasts. To explore the molecular cascade of odontoblast differentiation, Northern blot analyses and reverse transcriptase polymerase chain reaction were here used to investigate the expression patterns of the genes for TGF-beta superfamily members: TGF-beta 1, namely bone morphogenetic protein (BMP)-4, BMP-7, activin-beta A and activin-beta B, and their type I and type II receptors, namely activin receptor-like kinase (ALK)-2 (ActR-I), ALK-3 (BMPR-IA), ALK-4 (ActR-IB), ALK-5 (T beta R-I), BMPR-II and T beta R-II, during differentiation of pulp cells into preodontoblasts in bovine adult pulp-cell culture. TGF-beta 1 and BMP-4 mRNAs were expressed from day 14 when matrix formation increased. BMP-7 mRNA was expressed only on day 28 when osteocalcin appeared. ALK-2 mRNA was increased from the beginning of the culture. ALK-3 and ALK-5 mRNAs first decreased on day 14 and increased again on day 21. T beta R-II and BMPR-II mRNAs were almost constant. These results suggest that the differentiation of pulp cells into preodontoblasts may be regulated by changes in the temporally coordinated expression pattern of TGF-beta superfamily members and their receptors, including up-regulation of transcription of TGF-beta 1, BMP-4, BMP-7, ALK-2, ALK-3, and ALK-5.

[An epidemiologic examination on the prevalence of the periodontal diseases and oral pigmentation in Yusho patients in 1996]

An epidemiologic examination was carried out to reveal the prevalence of the periodontal diseases and oral pigmentation in patients with Yusho 28 years after PCB exposure. The results obtained were as follows. 1) 162 teeth out of a total of 309 examined teeth had a periodontal pocket deeper than 3 mm, although 32 teeth out of 162 teeth had a periodontal pocket deeper than 4 mm. 2) Oral pigmentation was observed in 47 out of 82 patients with Yusho. It was particularly noteworthy that gingival pigmentation was observed at a much higher frequency in younger patients while pigmentation of the buccal mucosa, the lips or the palate was observed at a much higher frequency in older patients.

Biochemical properties of the monomeric mutant of human cathepsin E expressed in Chinese hamster ovary cells: comparison with dimeric forms of the natural and recombinant cathepsin E

Cathepsin E (CE) is the only known aspartic proteinase that exists as a homodimer consisting of two fully catalytically active monomers, which are covalently bound by a disulfide bond between two cysteine residues at the NH2-terminal region (Cys43 in human pro-CE). To understand the physiological significance of the dimer formation, the monomeric mutant of human CE was constructed by site-directed mutagenesis (Cys43 ->Ser43) and expressed in Chinese hamster ovary (CHO) cells. Immunolocalization of the mutant protein at both the light and electron microscopic levels revealed the monomeric CE to be associated predominantly with the endoplasmic reticulum and the non-lysosomal endocytic organelles. The cellular localization of the monomeric protein was compatible with that of the wild-type (dimeric form) of recombinant human CE expressed in the same cells. The monomeric protein was generated primarily as the 46-kDa pro-CE with a high-mannose-type oligosaccharide chain in the cells. In addition to the maximal activation at around pH 3.5, a substantial proportion of the monomeric pro-CE was converted to the mature form by incubation at pH 7 and 37 degrees C for 5 min. In contrast, the dimeric pro-CE was scarcely activated by treatment at pH7. Although catalytic properties of the in vitro-activated monomeric CE appeared to be indistinguishable from those of the dimeric forms of natural and recombinant CE, the monomeric form was more unstable to pH and temperature changes than these dimeric forms. These results indicate that the dimerization of CE is not necessarily required for proper folding to express activity, correct intracellular localization and carbohydrate modification, but that it may be essential to structurally stabilize the molecule in vivo.

Specific immunocytochemical localization of cathepsin E at the ruffled border membrane of active osteoclasts

The immunocytochemical localization of cathepsin E, a non-lysosomal aspartic proteinase, was investigated in rat osteoclasts using the monospecific antibody to this protein. At the light-microscopic level, the preferential immunoreactivity for cathepsin E was found at high levels in active osteoclasts in the physiological bone modeling process. Neighboring osteoblastic cells were devoid of its immunoreactivity. At the electron-microscopic level, cathepsin E was exclusively confined to the apical plasma membrane at the ruffled border of active osteoclasts and the eroded bone surface. Cathepsin E was also concentrated in some endocytotic vacuoles of various sizes in the vicinity of the ruffled border membrane, some of which appeared to be secondary lysosomes containing the phagocytosed materials. These results strongly suggest that this enzyme is involved both in the extracellular degradation of the bone organic matrix and in the intracellular breakdown of the ingested substances in osteoclasts.

[An epidemiologic examination on the prevalence of the periodontal diseases and oral pigmentation in Yusho patients]

An epidemiologic examination was carried out to reveal the prevalence of the periodontal diseases and oral pigmentation in Yusho patients 26 years after PCB exposure. The results obtained were as follows. 1) 158 teeth of the total 284 examined teeth had the periodontal pockets deeper than 3 mm and the lower left first molar showed the highest prevalence of the periodontal pocket among the examined six index teeth. There was no definitive difference not only between sexes but also between age groups. However, 42 teeth had the periodontal pockets deeper than 4 mm. 2) Oral pigmentation was observed in 25 Yusho patients (33.8%). Chronological examination revealed that the prevalence of oral pigmentation seemed to be higher in the patients below the age of 49 than in those beyond the age of 50, but there was no definitive difference between sexes. It was of particular interest that the incidence of oral pigmentation appeared to decrease with decrease of the teeth present in number.

Detection of interleukin-1 beta mRNA in rat periapical lesions

Cells expressing interleukin-1 beta (IL-1 beta) mRNA were demonstrated by in situ hybridization in rat periapical lesions. A great number of osteoclasts with significant tartrate-resistant acid phosphatase activity were observed on the bone surfaces, and numerous IL-1 beta mRNA-expressing cells were widely distributed in the periodontal ligaments. IL-1 beta mRNA-expressing cells were mainly observed around the blood vessels in the vicinity of the bone resorption sites and occasionally found near the osteoblasts. Immunohistochemistry and enzyme histochemistry assays showed that IL-1 beta mRNA-expressing cells were not bone cells, but that they had the characteristic features of macrophages. These results suggested that macrophages may contribute to the production of IL-1 beta and play an important role in activation of osteoclastic bone resorption.

Localization of osteopontin in resorption lacunae formed by osteoclast-like cells: a study by a novel monoclonal antibody which recognizes rat osteopontin

The characteristics of a monoclonal antibody produced against osteoclast-like multinucleated cells (MNCs) formed in rat bone marrow cultures were examined immunohistochemically and biochemically. The in vitro immunization was performed using as immunogen the MNCs from rat bone marrow cell culture, which revealed many characteristics of osteoclasts. After screening and cloning of hybridomas, the monoclonal antibody HOK 1 was obtained. This antibody reacted weakly with stromal cells and intensely with both MNCs and their putative migratory traces on culture dishes. Immunofluorescent examination of paraffin sections revealed intense reactivity on the epithelium of the choroid plexus, the ileum and the proximal-convoluted tubules of the kidney, and also on bone cells such as osteocytes, osteoblasts, and osteoclasts. Western blotting using purified rat osteopontin verified that the antigen recognized by HOK 1 was osteopontin. Positive HOK 1 immunoreactivity was further observed in the resorption lacunae formed by a culture of MNCs on human tooth slices and on the surface of osteoclasts. The present data suggested that osteopontin is preferentially present on the resorption lacunae in resorbing calcified matrices and that osteoclasts under a specific state might trap this protein on their cell surface.

A histochemical study of the behavior of macrophages during experimental apical periodontitis in rats

The behavior of macrophages from experimentally induced periapical lesions of rats was studied in paraffin sections using nonspecific esterase and a monoclonal antibody, ED1. Macrophages were seen near the regularly arranged osteoblasts in controls and the detached osteoblasts at the initiation phase of bone resorption. In addition, numerous macrophages were widely distributed throughout the periodontium at the activation phase of bone resorption. On the other hand, macrophages were rarely seen near the bone formation surfaces, but large numbers of macrophages were localized in microabscess at the activation phase of bone formation. It is suggested that macrophages may play an important role in activation of osteoclastic bone resorption and inhibition of complete bone repair in bone remodeling during experimental apical periodontitis.

Expression of membrane alkaline phosphatase activity on gingival fibroblasts in chronic inflammatory periodontal disease

We investigated the expression of membrane alkaline phosphatase (ALP) activity on fibroblasts in inflamed gingiva from 7 patients with adult periodontitis. ALP activity was ultrahistochemically detected by a cerium-based capture method. The degree of ALP activity was estimated by morphometric analysis of the percentage of the perimeter on which ALP reaction product was deposited. Fibroblasts in the non-inflammatory connective tissue were surrounded by bundles of collagen fibrils, and the majority of these fibroblasts showed ALP-negative or weakly ALP-positive reaction. By contrast, fibroblasts in the inflammatory connective tissue were either surrounded by a non-collagenous substance or in contact with inflammatory cells, and the majority of these fibroblasts showed a strong ALP-positive reaction. These results suggest that the expression of membrane ALP activity on gingival fibroblasts is induced by microenvironmental changes associated with the loss of contact between the cells and the extracellular collagenous matrix during inflammatory reactions.

Immunohistochemical examination on the localization of macrophages and plasma cells in induced rat periapical lesions

To investigate the role of plasma cells and macrophages in the development of periapical lesions, we immunohistochemically examined the distribution of these inflammatory cells in experimental induced rat periapical lesions after pulpectomy. The number of ED1-positive mononuclear cells increased rapidly, reached a plateau which remained stable between days 10 and 60, and subsequently decreased. Immunoglobulin (Ig)-bearing plasma cells appeared after 60 days, and, of these, IgG-bearing plasma cells were predominant after 90 days. The radiographic and histopathological findings indicated the development of bone destruction at 10 days which continued until 60 days; tissue repair began to take place after 90 days. The results suggested that macrophages had a close relation to bone destruction and that plasma cells might participate in tissue repair rather than the development of periapical lesions.

A novel monoclonal antibody recognizing a unique antigen of rat osteoclasts induced by the calcified matrices

The morphology of osteoclasts, primary cells that resorb bone, is well documented; however, the precise details of their terminal differentiation remains obscure. To date, the only morphological criterion for identifying activated functional osteoclasts has been the presence of ruffled borders. We have developed a rat bone marrow culture system in which osteoclast-like cells formed. These cells fulfilled most of the criteria of osteoclasts, and when they were reseeded on calcified tissue, formed numerous resorption lacunae in vitro. To find an immunological marker for functional osteoclasts, we have used these cells in a functional state as antigens for the preparation of monoclonal antibodies (mAb) that reacted with rat osteoclasts; we obtained mAb Ch1 and Ch2. Interestingly, these mAbs reacted with the marginal portion of authentic osteoclasts, where they attached to the bone surface on frozen sections. The reactivity of Ch1 to rat osteoclasts was more restricted than that of Ch2: Ch1 reacted with few tartrate-resistant acid phosphatase (TRAP)-positive cells on a culture plate. These TRAP-positive cells (including mono- and multinucleated cells) were, however, converted to Ch1-positive cells when they were reseeded on calcified tissues. These findings suggested that the antigen recognized by the Ch1 antibody was induced by some factors of matrix proteins released from calcified tissues.

Implanted bone particles induce osteoclast development in the presence of osteoblast lineage cells

We implanted mineral-containing bone particles (BPs) in rats to investigate the involvement of osteoblast lineage cells in osteoclast development in vivo. BPs were implanted in subcutaneous regions on calvaria or artificial defects of calvaria, with or without adjacent parathyroid glands prepared from other rats. The structural characteristics of multinucleated giant cells (MGCs) induced by the BPs were investigated. The MGCs induced by subcutaneously implanted BPs showed membrane ruffling at the basolateral site, but not at the apical site, regardless of whether parathyroid glands were also implanted. In contrast, the MGCs induced by intraosseously implanted BPs showed the characteristics of osteoclasts, i.e., ruffled borders at the apical sites, clear zone, vacuoles, many mitochondria, and scattered rough endoplasmic reticulum. When BPs and parathyroid glands were implanted in bone defects, the number of MGCs was increased compared to that induced by BPs only. These MGCs showed the typical characteristics of active osteoclasts, including developed ruffled borders and stacks of Golgi succules. The number of osteoclasts was also investigated quantitatively by counting the numbers of MGCs positive and negative for tartrate-resistant acid phosphatase. In intraosseous implantation, MGCs with the characteristics of osteoclasts were observed close to osteoblastic cells characterized by developed rough endoplasmic reticulum. These results indicate that the osteoclasts were not induced solely by the subcutaneously implant BPs, but required osteoblast lineage cells for development.

Expression and localization of a major lysosomal membrane sialoglycoprotein (LGP107) in plasma membranes of rat osteoblasts and osteocytes

The immunocytochemical localization of a major lysosomal membrane sialoglycoprotein with a molecular mass of 107 kDa, which was designated as LGP107, was investigated in osteoblast lineage cells involved in osteoclastic bone resorption using specific polyclonal antibody against LGP107. Osteoclastic bone resorption was induced by transplantation of parathyroid glands. In control experiments, no immunoreaction product for LGP107 was recognized in osteoblasts and osteocytes. Strong immunoreaction products for LGP107 occurred on the plasma membranes in the osteoblasts and osteocytes prior to the appearance of osteoclasts one day after transplantation of the parathyroid glands. Furthermore, two days after induction, strong diaminobenzidine reactions were also observed on the plasma membranes in the osteoblastic cells adjacent to the active osteoclasts. These data suggest that LGP107 in osteoblastic cells and osteocytes may play an important role in cell-recognition and/or cell-adhesion, and that LGP107 may be involved in osteoblastic degradation of the osteoid as well as exposure of the bone surface.

[Production of monoclonal antibodies against osteoclasts of rat]

In mammals, it has been difficult to collect the authentic osteoclasts on a large scale. Recently we established a culture system for forming osteoclast-like multinucleated cells (MNCs) which exhibited many characteristics of osteoclasts. MNCs instead of authentic osteoclasts were used as immunogen to establish the hybridomas which secrete monoclonal antibodies against the osteoclasts by in vitro immunization. We obtained two monoclonal antibodies, HOK 1 and HOK 2. HOK 1 showed intense immunoreactivity with MNCs, mononuclear cells and putative migratory traces of MNCs on the culture dishes, but it had weak reactivity with the stromal cells. HOK 2 also showed strong reactivity with MNCs, mononuclear cells, and the very limited area of the culture dishes just facing to one side of some MNCs. The stromal cells were faintly stained with HOK 2. In th paraffin sections of tibiae, both antibodies intensely stained osteoclasts, osteoblasts and osteocytes. The bone matrix was weakly stained by HOK 2 but not by HOK 1. The present observations indicated that HOK 1 and HOK 2 could recognize the common antigen expressed on cells both involving in the bone formation and resorption. The antigens recognized by HOK 1 and HOK 2 were shown to exist on the putative traces of motile MNCs. These antibodies would be available to investigate the mechanisms of the 'bone remodeling' as a functional marker of bone cells.

Increased synthesis and specific localization of a major lysosomal membrane sialoglycoprotein (LGP107) at the ruffled border membrane of active osteoclasts

The immunocytochemical localization was investigated of a major lysosomal membrane sialoglycoprotein with a molecular mass of 107 kDa, which was designated as LGP107. The study utilized rat osteoclasts with different bone resorbing activity and osteoclast precursors at various stages of differentiation and maturation together with monospecific antibodies to this protein. Despite its localization primarily in lysosomes and endosomes in the other cell types examined, LGP107 was exclusively confined to the apical plasma membrane at the ruffled border of the active osteoclast, where the osteoclast is in contact with the bone surface. The protein was also concentrated in a number of endocytic vacuoles in the vicinity of the ruffled border membrane. However the labeling was not found in the basolateral membranes of the active osteoclast. The ruffled border membrane detached from the bone surface showed a marked decrease in the extent of the immunolabeling. The post- and/or resting osteoclasts, which were located away from the bone surface, were totally devoid of the membraneous localization of LGP107. No definite immunolabeling was found in the immature preosteoclasts. These results indicate that the protein is largely synthesized in the active osteoclast and rapidly translocated to the ruffled border membrane by vectorial vesicle transport. LGP107 is suggested to contribute to the formation and maintenance of the specialized acidic environment for bone resorption.

Biocompatibility of tetracalcium phosphate cement when used as a bone substitute

We evaluated the biocompatibility of tetracalcium phosphate (4CP) cement, made of 4CP powder and 40 wt% copolymer of polyacrylic acid/itaconic acid and 10 wt% citric acid solution. Light and electron microscopic characteristics were studied 3, 10 and 30 d after implantation. Neither inflammation nor foreign-body giant cell reaction was observed in the tissue adjacent to the implanted material. After 30 d, this material was surrounded with newly formed bone. Ultrastructural examination showed that osteogenesis occurred directly on the surface of the material. These findings suggest that this 4CP cement is biocompatible and possesses osteoconductive properties.