On the mechanisms of bone resorption. The action of parathyroid hormone on the excretion and synthesis of lysosomal enzymes and on the extracellular release of acid by bone cells

Destruction of Hassall's corpuscles by macrophages in the sheep thymus

The dissolution of Hassall's corpuscles by macrophages has been demonstrated in the sheep thymus. The findings indicate that enlarged Hassall's corpuscles are rapidly broken down by macrophages at the end of gestation or immediately after birth and replaced by newly formed corpuscles, and that these cyclic changes in Hassall's corpuscles persist, under normal physiological conditions, throughout life.

Fate of mineralized and demineralized osseous implants in cranial defects

We have evaluated the fate of mineralized osseous implants placed into cranial defects in rats. By 2 weeks, 100% of the defects that had been filled with demineralized bone powder (DBP, 75-250 micrometer) showed bony repair as judged by histomorphometric analysis and incorporation of 45Ca. The DBP was not appreciably resorbed but rather was amalgamated within the new bone. Histomorphometric evaluation of osteo-genesis induced by equal masses of demineralized bone powders of various particle sizes (less than 75, 75-250, 250-450 micrometer) revealed that the smaller particles induced more bone per field than did the larger particles. In contrast, mineralized bone powder (BP) was completely resorbed by 3 weeks, without bony repair of the cranial defect. These specimens contained large multinucleated cells within 7 days and completely resorbed by 3 weeks. It is concluded that (a) demineralized bone powder predictably induces a osteogenic healing of cranial defects, (b) demineralized bone powder is not appreciably resorbed prior to bone induction, (c) the extent of bone induction is a function of the surface area of the demineralized bone implant, and (d) mineralized bone powder undergoes obligatory resorption.

Calcium lysosomes in rachitic and vitamin D3 replete chick duodenal absorptive cells

Calcium-containing lysomes were described in a previous communication in this series (Davis et al., 1979). Their potential role in intestinal calcium uptake and transcellular transports was hypothesized. To further this notion, the effects of a rachitogenic diet and vitamin D3 repletion were investigated. Intestinal absorptive cells from chicks maintained on a vitamin D deficient diet were characterized by decreased numbers of supranuclear calcium lysosomes. In contrast, intestinal cells from chicks given vitamin D3 (cholecalciferol) subsequent to the rachitogenic diet showed numerous large compound supranuclear calcium lysosomes. Since other steroid hormones are known to effect lysosomes, it is tempting to speculate that vitamin D, itself a steroid hormone, may activate lysosomes which themselves might be involved in calcium homeostatic mechanisms.

Effects of inhibition of microtubule assembly on bone mineral release and enzyme release by human breast cancer cells

When supernates from the established human breast cancer cell line MCF-7 were applied to fetal rat long bones that had been labeled with 45Ca and devitalized to remove endogenous bone cells, mineral was released from the bones. The release of bone mineral by MCF-7 supernates was associated with increased basal release of hydrolytic enzyme activity by the tumor cells. The basal release of lysosomal enzymes and collagenolytic activity by MCF-7 cells with approximately twice that of mouse 3T3 cells, which did not cause mineral release by the fetal rat bones. Release of hydrolytic enzymes and bone mineral-releasing activity was increased by colchicine and vinblastine, drugs that inhibit microtubule assembly, but not affected by lumicolchicine. Time-course experiments performed on MCF-7 cells with or without colchicine showed that release of cathepsin D and collagenolytic activity was associated more closely with release of bone mineral and degradation of bone matrix than was the release of N-acetylglucosaminidase. The release of previously incorporated [3H]proline from the bones exposed to MCF-7 cell cultures was more closely associated with release of collagenolytic activity by MCF-7 cells than with release of cathepsin D or N-acetylglucosaminidase. These data suggest that breast cancer-mediated bone resorption in vitro is positively correlated with release of hydrolytic enzymes by the tumor cells, and release of these enzymes is enhanced by disassembly of microtubules.

Inhibition of bone resorption in culture by inhibitors of thiol proteinases

Leupeptin, antipain, tosyl-lysylchloromethane (Tos-Lys-CH2Cl) and benzyloxy-carbonylphenylalanylalanyldiazomethane (Z-Phe-Ala-CHN2) inhibit reversibly the resorption induced by parathyroid hormone or heparin in cultured mouse bones. Leupeptin and antipain do not affect collagenase production and activity or the enhanced secretion of beta-glucuronidase induced by the bone-resorbing agents. They might thus act by a direct (extracellular?) inhibition of lysosomal thiol proteinases.

The effect of dibutyryl cyclic AMP and PGE2 on lysosomal enzyme release and lactate production in relation to bone resorption in vitro

The effect of dibutyryl cyclic AMP (dbc AMP) and PGE2 on the content and release of lysosomal and non-lysosomal enzymes was studied in a bone organ culture system using half calvaria from 6-7 day-old mice. In parallel the effect of dbc AMP and PGE2 on the release of calcium (Ca2+) and inorganic phosphate (Pi), glucose consumption and lactate production was also followed. DbcAMP (2.5 X 10(-4) M) decreased the release of beta-glucuronidase, beta-N-acetyl-glucosaminidase, acid phosphatase, Ca2+ and Pi during the first day of culture. During the 3rd and 4th day of dbcAMP increased all these parameters. In contrast no changes in the release of lactate dehydrogenase (LDH) and alanine aminotransferase (ALAT) were seen. Glucose consumption and lactate production was not stimulated by dbcAMP until the 3rd and 4th day. On the other hand, PGE2 (10(-7) M) stimulated the release of beta-glucuronidase, beta-N-acetylglucosaminidase, Ca2+ and Pi as well as glucose consumption and lactate production already after 24 h and this stimulation was maintained throughout the culture period. No effect by PGE2 on the release of LDH and ALAT was registered. The activities of LDH in the bone explants after 96 h of culture were significantly augmented by both dbcAMP and PGE2. It is concluded that bone resorption stimulated by dbcAMP and PGE2, is associated lysosomal enzyme release and lactate production.

Relationship between bone resorption and lysosomal enzyme release as demonstrated by the effect of 1 alpha-hydroxy-vitamin D-3 in an organ culture system

The effect of 1 alpha-hydroxy-vitamin D-3 on the release of calcium (40Ca, 45Ca), inorganic phosphate and lysosomal enzymes, on glucose consumption and lactate production was studied in a bone organ culture system using half calvaria from 6--7-day-old mice. 1 alpha-Hydroxy-vitamin D-3 stimulated the mobilization of minerals and increased the release of beta-glucuronidase, beta-N-acetylglucosaminidase and acid phosphatase, while no effect on the release of lactate dehydrogenase was seen. 1 alpha-Hydroxy-vitamin D-3 also caused a significant increase in the total activities of acid phosphatase in the bones after culture, indicating increased enzyme synthesis. The stimulatory effect on the release of Pi and beta-glucuronidase was also obtained after a temporary exposure to 1 alpha-hydroxy-vitamin D-3. The stimulation by 1 alpha-hydroxy-vitamin D-3 on the release of Ca2+, Pi and beta-glucuronidase was suppressed by a protein synthesis inhibitor, cycloheximide. No effect by 1 alpha-hydroxy-vitamin D-3 on glucose consumption and lactate production was registered, suggesting that increased mineral mobilization does not require increased lactate production. It is concluded that although the data in the present paper do not prove a cause-and-effect relationship between lysosomal enzyme release and bone resorption, they give further support to the concept that the processes are intimately associated.

Influence of diphenylhydantoin on lysosomal enzyme release during bone resorption in vitro

The effect of diphenylhydantoin (DPH) on the release of lysosomal enzymes during resorption of cultured mouse calvarial bone was studied. The enzyme activities of beta-glucuronidase and beta-galactosidase in the culture medium was taken as indicators for lysosomal enzyme release. In concentrations 50 micrograms/ml or higher, DPH inhibited the release of beta-glucuronidase and beta-galactosidase in parallel with bone resorption as indicated by reduced release of 45Ca, Ca2+, Pi and hydroxyproline. The release of the cytosolic enzyme lactate dehydrogenase was not influenced by concentrations of DPH up to 50 micrograms/ml but higher concentrations caused an increased release indicating cell injury. When bone resorption was stimulated by prostaglandin E2, DPH (50 micrograms/ml) also reduced the mobilization of bone mineral and the release of beta-glucuronidase without influencing the release of lactate dehydrogenase. It is suggested that DPH by interfering with cellular release processes reduces the resorption of bone.

Normal osteoclast number and function in rat pups lacking parathyroid hormone

In parathyroidectomized suckling rats, bone modeling and the number and activity of cells in the osteoclast population are normal. These findings are at variance with observations in older animals and suggest that factors other than parathyroid hormone influence osteoclast formation and function in the neonate.

Electron microscope study of bone lesion in cholesteatoma otitis

Biopsy specimens were obtained at ear surgery of patients with cholesteatoma otitis and were studied by electron microscopy. The osseous tissue decalcified in EDTA demonstrated degradation of collagen matrix as well as extensive degeneration of bone cells. The surface of the eroded bone was found to be in direct contact with the subepithelial connective tissue or the granulation, but not with the keratinizing squamous epithelium of matrix. These results indicate that the bone destruction by cholesteatoma is of non-osteoclastic type and lend support to the view that the keratinizing squamous epithelium do not participate in bone destruction. One the ultrastructural basis, the inflammatory process in the soft tissue adjacent to bone and extensive degeneration of bone cells are considered as cardinal factors for bone destruction in this disease.

Free radicals and inflammation: superoxide-dependent activation of a neutrophil chemotactic factor in plasma

The intravenous administration of superoxide dismutase (superoxide:superoxide oxidoreductase, EC 1.15.1.1) to animals with induced inflammation suppresses the inflammatory response and inhibits leukocyte infiltration into the challenged site, suggesting that neutrophil-generated superoxide reacts with an extracellular precursor to generate a substance chemotactic for neutrophils. Plasma exposed to superoxide in vitro becomes potently chemotactic. The appearance of chemotactic activity is inhibited by superoxide dismutase but not by catalase. The chemotactic factor does not stimulate superoxide production or degranulation in neurtrophils. Intradermal injection of superoxide-treated plasma or of a superoxide-generating system causes heavy infiltration of neutrophils to the injection site but does not cause overt signs of inflammation. The chemotactic factor consists of a chloroform-extractable component bound to serum albumin. The superoxide-dependent chemotactic factor appears to play a major role in communication in neutrophil-mediated inflammatory events. Prevention of production of this factor appears to be the major anti-inflammatory action of superoxide dismutase.

Release of lysosomal hydrolases from bone explants affected by dental plaque

Lysosomal hydrolases as indicators of plaque-induced bone resorption in tissue culture were studied. Fetal rat bones cultured in a synthetic medium containing sonicated and filtrated human dental plaque were used as bones to be resorbed. Acid phosphatase and beta-glucuronidase were found to be the most suitable enzymes for studying the degradation rate of bone cell lysosomes. When dental plaque is used as a resorbing agent, special attention has to be paid to the fact that plaque extract contains similar lysosomal hydrolase activity. Plaque hydrolases in the present study were quite stable in culture medium. No significant adsorption of enzymes by fetal rat bones occurred while remarkable adsorption by synthetic hydroxyapatite was found. The present results indicate that dental plaque is able to release lysosomal hydrolases from bone explants. This release corresponds to the degree of resorption measured by 45Ca release from bones.

Metabolic aspects of bone resorption in calcium-deficient lactating rats

Lactating female rats were fed diets containing 1.0, 0.1, or 0.04% Ca for 21 days. Fat-free dry weight, ash weight, calcium and phosphorus content of the humerus, plasma calcium levels, and bone acid and alkaline phosphatase activities were compared to those of nonlactating rats fed the same diets. Bone, plasma, and urinary cAMP levels were also studied. Dietary calcium deficiency and/or lactation caused significant loss of bone mass from experimental animals. Urinary cAMP levels reflecting increased parathyroid activity were elevated by the stresses of lactation and calcium deficiency over those of control animals. Plasma and bone levels of cAMP were not different. Bone alkaline and acid phosphatase activities were affected only by the most extreme stress. The results demonstrated that the calcium-deficient lactating rat is an excellent model for bone resorption studies.

Indomethacin inhibits bone resorption and lysosomal enzyme release from bone in organ culture

The effect of indomethacin on bone resorption was studied in an organ culture system, using calvarial bones from 6--7-day-old mice. It was found that indomethacin inhibited spontaneous bone resorption, as estimated by decreased release of 45Ca, Ca2+ and Pi. Indomethacin reduced the release of beta-glucuronidase, beta-galactosidase and beta-N-acetylglucosaminidase, diminished glucose consumption and lactate production, but showed no effect on the release of lactate dehydrogenase. No inhibitory effect of indomethacin on the release of 45Ca stimulated by parathyroid hormone, prostaglandin E2 or 1 alpha(OH)D3 could be registered. 5,8,11,14-eicosatetraynoic acid, an inhibitor of both cyclo- and lipoxygenase pathway of arachidonate metabolism, reduced the spontaneous release of 45Ca, whereas the selective lipoxygenase inhibitor 5,8,11-eicosatriynoic acid was without effect. The results presented indicate that indomethacin may have an inhibitory effect upon the osteoclasts, probably by decreased metabolism of arachidonic acid via the cyclo-oxygenase pathway. A possible relationship between this finding and the pathogenesis of rapid destruction of articular bone in osteoarthritic patients treated with indomethacin is discussed.

Hypercalcemia complicating childhood malignancies: a report of seven cases with some pathophysiological considerations

A group of seven children with different malignant processes presenting with hypercalcemia was studied. Bone destruction, diffuse metabolic abnormalities, abnormal acid-base homeostasis and recurrent hypercalcemia characterized these patients. A different mechanism leading to the production of hypercalcemia and/or bone destruction by cancer cells is considered. The results of this report suggest that parathyroid hormone production (P.T.H.) by the parathyroid glands is normal and that ectopic secretion of PTH or PTH-like material is negligible in these cases.

Low-calcium/high-phosphorus rickets in rats. II. Osteoclast changes

Weanling rats were given a low Ca (0.003%)/high P (0.64%) diet with and without vitamin D for periods up to 6 weeks. An ultrastructural examination of selected areas of the proximal tibial metaphysis was carried out to study osteoclasts and their relation to calcified and uncalcified bone tissue. Osteoclasts were seen with ruffled borders adjacent to unmineralized osteoid or with their processes penetrating small patches of calcified osteoid tissue. In both cases the calcified bone margin had a 'frayed edge', suggesting that osteoclasts are capable of chemical demineralization, as well as phagocytic action. In a few cases, osteoblasts were seen adjoining osteoid seams with underlying calcified bone exhibiting frayed edges indicative of demineralization. Osteoclastic intranuclear inclusion bodies similar to those found in experimental lead poisoning were observed. It was considered that the presence of a frayed, calcified bone margin at a considerable distance from the osteoclast supports the proposition that the initial action of this cell is to demineralize calcified bone.

Bone resorption in chronic otitis media

Bone resorption is an important aspect of chronic otitis media contributing to many complications of this disease. It is postulated that the mechanism of this localized destructive process is chemical in origin. Collagenase, lysosomal enzymes, prostaglandins, and other cell mediators are thought to induce bone resorption, but the site of action and cellular origin of these substances remains unclear. In this report, we demonstrate the location and attempt to delineate the cellular origin of two enzymes, collagenase and the lysosomal enzyme acid phosphatase in guinea pig temporal bones and human ossicles from ears containing chronic otitis media. Tissue localization of these enzymes identifies sites of active bone resorption and demonstrates the cells initiating this process. Using immunohistochemical and immunocytochemical techniques, collagenase was seen surrounding mononuclear inflammatory cells of granulation tissue at bone resorbing margins and at the periphery of osteocyte lacunae adjacent to resorbing areas. Electron microscopic data suggests that collagenase is an extracellular enzyme foun at the periphery of osteocytes. In addition, abundant acid phosphatase activity was seen in the same cells that exhibited collagenase staining, lending credence to the destructive function of these cells. The chronic inflammatory reaction found in chronic otitis media appears to activate bone destruction through the dynamic activity of mononuclear inflammatory cells and stimulates bone cells to increase their destructive biochemical functions.

Morphology of osteoclasts in resorbing fetal rat bone explants: effects of PTH and AIF in vitro

Osteoclastic bone resorption was studied using 45Ca-labeled fetal rat bones cultured in the presence of parathyroid hormone (PTH) and an anti-invasion factor (AIF) derived from bovine hyaline cartilage which is enriched in a collagenase inhibitor. The specific morphological expressions of osteoclasts cultured in PTH and AIF were observed in both light and electron microscopy and analyzed cytometrically. Stimulation of bone resorption with PTH revealed significant increases in the numbers and activity of osteoclasts, whereas bones cultured in the presence of AIF showed significant decreases in numbers of osteoclasts and altered cell features including the loss of osteoclast contact with bone surfaces. These structural modifications were evaluated with 45Ca release data derived from matched-pair explants of fetal rat bones, revealing the existence of a relationship between resorptive states of the cultured bones and morphological expressions of osteoclastic activity.

A calcitonin-like action of prostaglandin E1

The pharmacological effects of PGE1 (6 and 9 days, 2-1,250 micrograms/kg per day subcutaneously) upon the growth and the bone resorption of mammals were studied using the proximal tibia and upper incisor of immature rats along with lead acetate as a time marker, and upon the serum calcium and inorganic phosphorus levels. The following results were obtained. 1. PGE1 hardly affected the body weight or the weight of organs of the rats but apparently inhibited the longitudinal growth of proximal tibia in a dose related manner. 2. PGE1 clearly inhibited not only the longitudinal growth (incisor growth) but also the appositional growth (dentin formation) of incisal dentin. 3. The grade of the inhibitory effect on the growth was in the order of bone growth greater than dentin formation greater than incisor growth. 4. The occurrence of osteoporosis due to a low calcium diet was inhibited by the simultaneous administration of PGE1, the mechanism being considered to be mainly due to the inhibitory effect on the bone resorption. 5. PGE1 lowered the level of serum calcium and the lowering effect was not observed in the thyro-parathyroidectomized rat. From the facts that the above effects were exactly the same as those of calcitonin (1), the possibility that the subcutaneous injection of PGE1 may induce a calcitonin-like action, a part of which may dependent on the calcitonin secretion is suggested.

Collagenase, procollagenase and bone resorption. Effects of heparin, parathyroid hormone and calcitonin

1. The addition of heparin to the culture fluid of mouse tibiae or calvaria did not cause any significant resorption of bone collagen or mineral. However, heparin (or analogue sulfated polyanions), enhanced greatly the amount of latent, trypsin-activatable collagenase (i.e. procollagenase) released by the bones in the medium without influencing that of directly active collagenase which was always very low. Heparin appeared to act by increasing the production of the enzyme which is immediately excreted. Procollagenase and collagenase are not stored in bone tissue, even under conditions where it is in active resorption. 2. Parathyroid hormone induced in the explants a resorption of both mineral and collagen that was inhibited by calcitonin. These hormones, however, had no influence on the release of procollagenase or collagenase either in the presence or in the absence of heparin. 3. Once activated, bone collagenase digested the collagen of the bone explants, and more extensively after their demineralization. Thus the latent collagenase that accumulates around non-resorbing bones has to be considered as a precursor, (and not as a residue), of active enzyme. 4. Active collagenase added to incipient cultures of bones disappeared with a half-life of 24 h. The lost enzyme could, however, not be reactivated by trypsin and thus was not transformed into latent procollagenase.

Interaction of 24,25-dihydroxyvitamin D3 and parathyroid hormone on bone enzymes in vitro

The in vitro effects of vitamin D3 metabolites, parathyroid extract (PTE), purified parathyroid hormone (bPTH), vitamin A, and heparin on acid and alkaline phosphatases in rat or mouse calvaria in culture were investigated. Results show that: (a) when compared to values found in half calvaria incubated for 24 h in control medium, the bone acid and alkaline phosphatase content is significantly higher in paired halves incubated with PTE (L USP/ml), bPTH (4 x 10(-8)M), heparin (5 USP/ml), vitamin A (23 USP/ml), 25-(OH)D3 (2.5 x 10(-11) to 2.5 x 10(-8)M), 24,25-(OH)2D3, and 1,25-(OH)2D3 (2.5 x 10(-12) to 2.5 x 10(-7M); (b) the presence of 24,25-(OH)2D3 at low concentrations in the incubation medium decreases significantly the PTE, bPTH, vitamin A, or heparin induced stimulation of the phosphatase activities. This interaction is also observed when measuring beta glucuronidase and glucose-6-phosphatase activities and 45Ca release from previously labeled mouse calvaria; (c) a similar activity could not be found with 1,25-(OH)2D3 suggesting that 24,25-(OH)2D3 may have a specific role in bone metabolism.

Effect of mithramycin on bone beta-glucuronidase and resorption

Mithramycin suppresses bone resorption. Its effect on the synthesis and release of beta-glucuronidase (a referent for lysosomal enzymes) in mouse calvarial explants was studied in an in vitro culture system. A newly described medium (designated as KT medium) was introduced in this specific study. Mithramycin initially inhibited the release of beta-glucuronidase into the medium and resulted in an ultimate accumulation of this enzyme in the bone. These results suggest that inhibition of bone resorption by mithramycin may be attributed to interference in release of lysosomal enzymes from bone cells.

The simultaneous release by bone explants in culture and the parallel activation of procollagenase and of a latent neutral proteinase that degrades cartilage proteoglycans and denatured collagen

1. A latent neutral proteinase was found in culture media of mouse bone explants. Its accumulation during the cultures is closely parallel to that of procollagenase; both require the presence of heparin in the media. 2. Latent neutral proteinase was activated by several treatments of the media known to activate procollagenase, such as limited proteolysis by trypsin, chymotrypsin, plasmin or kallikrein, dialysis against 3 M-NaSCN at 4 degrees C and prolonged preincubation at 25 degrees C. Its activation often followed that of the procollagenase present in the same media. 3. Activation of neutral proteinase (as does that of procollagenase) by trypsin or plasmin involved two successive steps: the activation of a latent endogenous activator present in the media followed by the activation of neutral proteinase itself by that activator. 4. The proteinase degrades cartilage proteoglycans, denatured collagen (Azocoll) and casein at neutral pH; it is inhibited by EDTA, cysteine or serum. Collagenase is not inhibited by casein or Azocoll and is less resistant to heat or to trypsin than is the proteinase. Partial separation of the two enzymes was achieved by gel filtration of the media but not by fractional (NH4)2SO4 precipitation, by ion exchange or by affinity chromatography on Sepharose-collagen. These fractionations did not activate latent enzymes. 5. Trypsin activation decreases the molecular weight of both latent enzymes (60 000-70 000) by 20 000-30 000, as determined by gel filtration of media after removal of heparin. 6. The latency of both enzymes could be due either to a zymogen or to an enzyme-inhibitor complex. A thermostable inhibitor of both enzymes was found in some media. However, combinations of either enzyme with that inhibitor were not reactivated by trypsin, indicating that this inhibitor is unlikely to be the cause of the latency.

The effects of diphosphonates on the growth and glycolysis of connective-tissue cells in culture

1. The effects of two diphosphonates (compounds containing a P-C-P bond), disodium dichloromethanediphosphonate and disodium 1-hydroxyethane-1,1-diphosphonate, on the metabolism of cultured rat calvaria cells, rabbit ear cartilage cells and rat skin fibroblasts were investigated. 2. The diphosphonates had no effect on the growth of cartilage cells and on the exponential growth of the calvaria cells and the fibroblasts. However, dichloromethanediphosphonate stopped the growth of the calvaria cells and the fibroblasts after the beginning of confluence, whereas the untreated cells were still growing to a certain extent. This inhibition was dose-dependent. After the drug was withdrawn, the cells recovered slowly. 1-Hydroxyethane-1,1-diphosphonate had no detectable effect on the growth of any of the cell types studied. Both diphosphonates decreased the cloning efficiency of calvaria cells and fibroblasts. 3. The K+ content of cartilage, calvaria and skin cells was diminished only by the highest (0.25 mM) concentration of dichloromethanediphosphonate. 4. Radioactive dichloromethanediphosphonate and 1-hydroxyethane-1,1-diphosphonate were taken up linearly with time for at least 48 h by calvaria cells and fibroblasts. The diphosphonate concentration in the cells depended on its concentration in the medium. 5. Both diphosphonates, in a dose-dependent fashion, markedly inhibited glycolysis, dichloromethanediphosphonate being more effective than 1-hydroxyethane-1,1-diphosphonate, at drug doses that had no effect on cell growth or cellular K+ content. Calvaria cells were much more sensitive than cartilage cells. When cartilage cells were cultured in an N2 atmosphere, these effects on glucose and lactate metabolism disappeared. 6. As increased acid production appears to be associated with resorption of bone, this decrease in lactate may explain why diphosphonates are effective inhibitors of bone resorption in vivo.

The polymorphonuclear leukocyte

Polymorphonuclear leukocytes (PMNs) are one of the main sources of enzymes responsible for tissue damage in inflammatory processes. These enzymes are stored in two types of cytoplasmic granules. Azurophil granules contain lysosomal hydrolases, neutral serine proteinases, and bactericidal elements (myeloperoxidase and lysozyme). Specific granules contain collagenase, lysozyme and lactoferrin but lack lysosomal hydrolases. PMNs store all four classes of tissue proteinases, carboxyl, thiol and serine proteinases in the azurophil granules, and metallo proteinases in the specific granules. Three serine proteinases have been identified, elastase, cathepsin G and a third enzyme, which together account for a large proportion of the protein of the azurophil granules. In the course of phagocytic events, all these enzymes are released extracellularly. The neutral proteinases degrade proteoglycans and collagen. In vitro, they stimulate B-lymphocytes, which suggests that they may have immuno-potentiating activity when they are released at sites of chronic inflammation.

[Paget's disease of bone: ultrastructure and cytogenesis of osteoclasts (author's transl)]

The cytogenesis of giant osteoclasts in Paget's disease of bone was studied by means of electron microscopy. 26 iliac crest biopsies were made and divided for light and electron microscopic investigation. A special procedure was used for electron microscopic preparation of bone without previous decalcification. Paget osteoclasts are characterized by their high content of nuclei. Several nuclei may show paracrystalline inclusions pointing to a possible virus infection of these cells. Giant osteoclasts have an increased mobility and a high resorptive activity, manifest by the dissection of bone fragments from endosteal bone surfaces. Cell membrane interdigitations between mononuclear cells and osteoclasts occur as a morphologic concomitant of cell fusion. Frequent occurence of such cell membrane contacts seem to indicate an increased tendency to cell fusion among the mononuclear precursors of Paget-osteoclasts. Precursor cells are located in the pericapillary region, and morphologically resemble pericytes. The assumption of an increased rate of cell fusion amoungst the precursor cells of osteoclasts might explain the development of giant osteoclasts in this disease. Further studies of the paracrystalline nuclear inclusions of Paget-osteoclasts are necessary to determine whether this process can be considered to be a cytopathogenic effect of virus infection.

Phosphatase content of rat calvaria after in vivo administration of vitamin D3 metabolites

The effects of acute or chronic administration of small doses (130 pmol) of 25-hydroxycholecalciferol, 24,25-dihydroxycholecalciferol, and 1,25-dihydroxycholecalciferol on rat calvaria acid and alkaline phosphatase activities were investigated in weanling male albino Wistar rats raised on a vitamin D-deficient, low-calcium diet. The results indicate that each of these active metabolites has a different effect on calvarial phosphatase activities. 25-hydroxycholecalciferol causes a significant increase, and 24,25-dihydroxycholecalciferol a decrease in the enzymatic activity. In animals treated with 1,25-dihydroxycholecalciferol these activities are lower after one injection, but after seven daily doses they are not different from those of ethanol-injected control rats. The observed changes do not seem to be related to changes in serum calcium and/or phosphorus concentrations.

Hormonal responses of bone in a continuous flow cultural system

Calvaria from five-day-old mice incubated in a continuous flow system (10 calvaria per culture chamber with 1 ml volume; flow rate 1ml/hr.). In 24-hour cultures, calvaria showed less resorption than in stationary culture. Short-term responses to PTH and calcitonin were similar to those observed in vivo.

A unifying concept for the role of matrix vesicles and lysosomes in the formal pathogenesis of diseases of connective tissues and blood vessels

The cells of the connective tissues contain lysosomes with enzymes capable of degrading intercellular substances (collagen, elastin, proteoglycans) and release their enzymes in membrane-bound or in free form into their intercellular substance. In this way extracellularly located lysosomes (= matrix lysosomes) can be detected by morphological and enzymatic means as well as by their metal concentrating property. This function of such matrix-lysosomes is in connection with the two step-degradation of the connective tissue and is thought to be the main part for the fibrocytic fibrolysis, chondrocytic chondrolysis, osteocytic osteolysis and myocytic mediolyses in the vessel wall. The cells of the mesenchymal tissues thus control the turnover and transformation of their own ground substance. Inflammatory and immunologic processes are suggested to be superimposed on this lysosomal action. If the lysosomal enzyme system in the connective tissues and the vessel wall gets out of control, the consequences can be dangerous as e.g. in case of relapsing polychondritis and arterial aneurysms. In this enzyme system proteolytic activators as well as proteolytic decomposable inhibitors are present. The corresponding proteolytic processes are of lysosomal nature and are subordinated to other regulatory mechanisms.

The early stages of Wallerian degeneration in the severed optic nerve of the newt (Triturus viridescens)

The initiation of Wallerian degeneration in the severed optic nerve of the newt (Triturus viridescens) was very rapid and intense. Significant degeneration of nonmyelinated axons was observed as early as six hours after lesion (h.a.l.) and was almost complete by 48 h.a.l. Initial degeneration of non-myelinated axons began in "extracellular digestion chambers" formed between burgeoning ependymoglial processes. The remaining fragments and debris were later phagocytized by surrounding ependymoglial processes. Many axons of myelinated fibers have degenerated as early as 6 h.a.l. However, the overall population of myelinated axons degenerates at a much slower rate than nonmyelinated ones, for many of them appear intact as late as 48 h.a.l. Some myelin sheaths show significant signs of degeneration by 6 h.a.l. Indeed, by this time a number of myelinated fibers have completely degenerated leaving only large vacuolated spaces in the nerve parenchyma. Swelling and vacuolization of the sheath are among the earliest signs of myelin degeneration. The ependymoglial cell response to optic nerve lesion is manyfold and dramatic. By 6 h.a.l. there are signs of burgeoning ependymoglial processes which begin to resemble scar formation (gliosis) by 48 h.a.l. The morphological evidence is consistent with the concept of an important phagocytic role of ependymoglial cells during the early stages of optic nerve degeneration.

Specificity and biological role of cathepsin D

The purity of cathepsin D has been increased from 150 units/mg to over 200 units/mg. Peptides such as Ala-Phe-NH2, His-Phe-NH2 and Phe-Phe were split by impure enzyme and activity was blocked by pepstatin and diazoacetylnorleucine methyl ester. Pure preparations no longer digested these peptides. This points to the presence of a second peptidase activity similar to cathepsin D in specificity and inhibition properties, but distinct from it . Cathepsin D splits the peptides Leu-Phe-NH2, Leu-Tyr-NH2, Ac-Phe-TyrI2, and Ala-Leu-Tyr-Leu upon overnight incubation. More rapid splitting is found with phenyl sulfite, Glu-Ala-Leu-Tyr-Leu-Val, and Bz-Arg-Gly-Phe-Phe-Leu-4-methoxy-beta-naphthylamide. Digestion of bovine hemoglobin and human serum albumin by ruptured rat liver tritosomes was studied over the pH range 2.5-6.5. The combined action of cathepsin D and thiol proteinases accounted for most of the digestion. Cathepsin D accounted for 75% of the hemoglobin digestion at pH 3 and 45% at pH 5. Thiol proteinase accounted for 85% of the albumin digestion at pH 5. The role of cathepsin D in the development of embryonic limbs and skin, in uterine involution, and in cartilage degradation was reviewed. The activity of cathepsin D on cartilage matrix proteoglycans is limited to acid pH values. Human articular cartilage also contains metalloproteases active at pH 4.5 and 5.7.

The actions of parathyroid hormone on bone: relation to bone remodeling and turnover, calcium homeostasis, and metabolic bone diseases. II. PTH and bone cells: bone turnover and plasma calcium regulation

Kinetic and morphologic studies in patients with parathyroid disease, and a wide variety of studies in experimental animals indicate that one major effect of PTH is to increase the proliferation of osteoprogenitor cells into osteoclasts and so to increase bone turnover. PTH stimulates bone cells by increasing cell membrane permeability to calcium and consequently increasing calcium influx and by activating membrane-bound adenyl-cyclase. It is likely that the former event precedes the latter and that calcium is the second messenger and cyclic AMP the third messenger. PTH increases the production by bone cells of lactate, citric and carbonic acids, lysosomal enzymes, collagenase, and hyaluronic acid, some or all of which are concerned in the mechanism of bone resorption. With the exception of lactate which probably comes mainly from osteocytes, the increase in metabolic activity is largely due to the increase in the number of osteoclasts. There is also ultrastructural, biochemical, and biophysical evidence that PTH stimulates existing osteoclasts, but this most likely represents the transformation of inactive cells into an active state, and is a transient and nonsustainable effect. As yet, there is no evidence that either increased osteoprogenitor cell proliferation or increased osteoclast activity is mediated by adenyl-cyclase activation. PTH also acts on the deep osteocyte to cause rapid mobilization of calcium from the zone of hypomineralized metabolically active perilacunar bone. This effect is mediated by adenyl-cyclase activation and is preceded by a slight fall in plasma calcium probably due to the movement of calcium into bone cells. The function of this rapid hypercalcemic response to PTH is correct errors in the prevailing steady-state level of plasma calcium...

A role for adenosine deaminase in human monocyte maturation

The occurrence of a deficiency of adenosine deaminase (ADA) activity in some patients with severe combined immunodeficiency suggests a possible relationship between the activity of ADA and the aberration of the immune system. To help delineate the function of ADA in the immune response we have examined its role in monocyte maturation. When incubated in vitro, peripheral blood monocytes transformed, within 3 days, to macrophagea as assessed by phase-contrast microscopy and an increase in the specific activity of the lysosomal enzyme acid phosphatase. The specific activity of ADA increased as much as ninefold, reaching a peak after the 1st day in culture, while the activities of other enzymes involved in the purine salvage pathway were not altered. Sucrose density ultracentrifugation of extracts prepared immediately after the isolation of monocytes revealed the presence of two forms of ADA with molecular weights of approximately 30,000 and 110,000. The increase in ADA specific activity during monocyte cultivation correlated with an increase in the activity of the smaller molecular species. A specific inhibitor ADA, erythro-9-(2-hydroxy-3-nonyl) adenine, prevented the increase in acid phosphatase activity, as well as the morphological changes associated with the monocyte maturation. These data suggest a role for ADA in monocyte to macrophage maturation. In view of the central role of macrophages in immune function, this observation may relate to the association of combined immunodeficiency and a deficiency of this enzyme.

Export of protein from the osteoclast as studied by electron microscopic autoradiography

The present electron microscopic autoradiographic study includes a quantitative analysis of osteoclasts in vitro using tritiated leucin as a protein tracer. A significant increase in the grain density over the ruffled border and the underlying resportion zone was demonstrated two hours post pulse whereas the grain density of the remaining cytoplasm was relatively constant. This indicates a transport of newly synthesized protein from the osteoclast to the extracellular resorption zone. Earlier histochemical and biochemical experiments suggest that the exported protein may represent lysosomal enzymes to be used in the extracellular bone degradation.