Biomedical subjects

Z Schwartz

Publications and source records attributed to Z Schwartz.

At least 181 records · Page 10Linked to original sources

PubMed1994

Gender dependent effects of testosterone and 17 beta-estradiol on bone growth and modelling in young mice.

This study examined the effects of estrogen (17 beta-estradiol) and testosterone on the growth of long bones in male and female mice, with and without gonadectomy. Weight and nose-to-tail length were determined at 3 weeks of age at time of gonadectomy, 7 days later at the onset of hormone therapy, and throughout the treatment period. Gonadectomized mice exhibited an initial weight gain during the pretreatment period but length was unaffected. Hormone treatment altered weight gain in surgical and intact animals in a gender- and hormone-dependent manner. Estradiol enhanced weight gain in intact mice, but inhibited weight gain in ovariectomized mice. Lower doses of estradiol increased weight gain in orchiectomized mice at early time points. Testosterone increased weight in intact females and males, but not in gonadectomized mice. Estradiol increased nose-to-tail length in intact females at early time points, but inhibited length in ovariectomized females at later times, and it decreased length in intact males. Testosterone increased length in normal females and normal males. Serum Ca was unaffected by ovariectomy, but orchiectomy resulted in decreased levels. Estradiol reduced serum Ca in gonadectomized animals; serum Ca was increased by estradiol treatment in intact females. Changes in tibial bone weight, ash weight and mineral composition, and relative sizes of epiphyseal and metaphyseal bone were gender-, gonadectomy- and hormone-specific. Bone weight was greater in ovariectomized mice. Ash weight per bone was comparable, but there was an increase in Ca and P content with ovariectomy. Estradiol increased bone weight, ash content, and bone Ca and P in ovariectomized and intact females. Orchiectomy alone did not alter bone weight, ash content, or Ca and P, but orchiectomized mice were sensitive to estradiol; all parameters were increased in the orchiectomized animals treated with estradiol. Analysis of the ash content and Ca and P per mg bone, rather than per bone, demonstrated estradiol and testosterone alter net bone formation, but not the amount of mineral per unit bone. Ovariectomy increased hypertrophic cartilage. While estradiol did not alter tibial area in ovariectomized mice, it caused an increase in intact females. The total amount of growth plate cartilage in ovariectomized animals was decreased by estradiol to levels typical of intact animals due to a greater decrease in the hypertrophic cartilage in the ovariectomized mice, as well as a greater increase in metaphyseal bone area. Testosterone had no effect on these parameters in the females. Orchiectomy decreased the amount of growth plate cartilage, but increased the hypertrophic zone.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1994

Gender-related effects of vitamin D metabolites on cartilage and bone.

Sex steroid hormones are known to have gender-dependent effects on bone and cartilage in vivo and in vitro. To investigate whether this is a general property of steroids, or is specific to the sex steroid hormones, we examined whether the effects on bone of 1,25-(OH)2D3 and 24,25(OH)2D3, the two active metabolites of vitamin D, are also gender-dependent. One-month-old male and female rats were treated for 1 month with various doses of 1,25-(OH)2D3, 24,25-(OH)2D3, or a combination of both metabolites. The direct effects of both metabolites on the skeleton of the treated animals were similar in male and female rats. 24,25-(OH)2D3 alone or in combination with 1,25-(OH)2D3 increased bone calcium and phosphorus, while 1,25-(OH)2D3 slightly decreased bone mineral content. 24,25-(OH)2D3 also enhanced the differentiation of cartilage in the growth plate, increasing the size of the hypertrophic zone. In addition, an increased metaphyseal bone volume was observed following 24,25-(OH)2D3 treatment in rats of both sexes, but not with 1,25-(OH)2D3. Vitamin D metabolites affected the weight gain of the experimental animals in a gender-dependent manner; 1,25-(OH)2D3 increased weight gain of male rats and 24,25-(OH)2D3 decreased weight gain of female rats. In addition, 1,25-(OH)2D3 increased bone weight and ash weight in male animals. These gender-dependent effects of vitamin D metabolites may occur indirectly via effects of sex steroid hormones, the latter being a sex-related effect.

24,25-Dihydroxyvitamin D 3↗

PubMed1994

Gender-specific, maturation-dependent effects of testosterone on chondrocytes in culture.

This study examined the effects of testosterone on chondrocytes in vitro in order to determine whether the effects of testosterone were dependent on the stage of chondrocyte maturation and gender specific. Cells derived from male or female rat costochondral growth zone and resting zone cartilage were used as the cell culture model. [3H]Thymidine incorporation, cell number, alkaline phosphatase specific activity, and percent collagen production were used as indicators. Alkaline phosphatase specific activity in matrix vesicles and plasma membranes isolated from male and female chondrocyte cultures was measured to determine which membrane fraction was targeted by the hormone. The role of fetal bovine serum in the culture medium was also addressed. The results demonstrated that testosterone decreases cell number and [3H]thymidine incorporation in male chondrocytes, suggesting that it may promote differentiation of these cells. Alkaline phosphatase specific activity is stimulated in growth zone cells, with no effect on resting zone cells. The increase in enzyme activity is targeted to the matrix vesicles. Cells cultured in serum-free medium exhibit a dose-dependent inhibition of alkaline phosphatase activity when cultured with testosterone, even in the presence of phenol red. Testosterone-dependent stimulation of enzyme activity is seen only in the presence of serum, suggesting that serum factors are also necessary. Testosterone increased the percent collagen production in male cells only, regardless of the cartilage zone of origin. The results of this study indicate that the effects of testosterone are dependent on the time of exposure, presence of serum, and sex and stage of maturation of the chondrocytes. Testosterone-dependent stimulation of alkaline phosphatase specific activity is targeted to matrix vesicles.

Alkaline Phosphatase↗

PubMed1994

Evidence for receptors specific for 17 beta-estradiol and testosterone in chondrocyte cultures.

Recently, sex hormones were shown to stimulate chondrocyte differentiation and matrix protein synthesis in vitro in a sex-specific and maturation-dependent manner. The aim of the present study was to determine whether cytosolic receptors in these cells would specifically bind 17 beta-estradiol and testosterone, and if so, whether binding was gender- and maturation-dependent. Confluent, fourth passage cultures of cells derived from male or female rat costochondral growth zone and resting zone cartilage were homogenized and specific binding of 17 beta-estradiol or testosterone measured in the cytosolic fraction. Scatchard analysis indicated the presence of a high-affinity 17 beta-estradiol receptor (Kd = 4.5 to 8.7 x 10(-11) M), with low binding capacity (3.9 to 11.2 fmol/mg protein). Chondrocytes from female rats were found to have a significantly greater binding capacity for 17 beta-estradiol than chondrocytes from male rats. However, cells from both sexes had binding capacities that were independent of cell maturation. A high-affinity testosterone receptor (Kd = 4.3 to 6.3 x 10(-11) M) with low binding capacity (4.1 to 5.9 fmol/mg protein) was found in both males and females, but no difference in binding capacity was noted, either as a function of gender or stage of cell maturation. Immunohistochemistry using antibodies against 17 beta-estradiol and testosterone and the 17 beta-estradiol nuclear receptor (D-75) confirmed that 17 beta-estradiol and testosterone receptors were present in chondrocytes from both male and female rats. These data demonstrate that chondrocytes from growth zone and resting zone cartilage are capable of binding both 17 beta-estradiol and testosterone. This suggests that these hormones mediate their direct effects on chondrocytes via receptors specific for their appropriate ligand. The sex-specific effects of 17 beta-estradiol may be due to differences in receptor number between chondrocytes derived from female and male rats. In contrast, the sex-specific effects of testosterone may be regulated at the post receptor level since no differences in binding capacity were found between males and females.

Animals↗

PubMed1993

Effects of hydroxyapatite implants on primary mineralization during rat tibial healing: biochemical and morphometric analyses.

The effect of 40- to 60-mesh hydroxyapatite (HA) granules (Calcitek, Inc., Carlsbad, CA) on the process of primary mineralization during bone healing was examined following insertion of the HA granules into rat tibial bone after marrow ablation. Response to HA was assessed by monitoring morphometric and biochemical changes in matrix vesicles, which are extracellular organelles associated with initial calcification. Following insertion of HA, matrix vesicle-enriched membranes (MVEMs) were isolated from the tissue adjacent to the implant and from the endosteum of the contralateral limb at 3, 6, 14, and 21 days and from a nonimplanted control group (t = 0). MVEM alkaline phosphatase- and phospholipase A2-specific activities were increased on days 6 (peak) and 14; phosphatidylserine content was also elevated on days 6 and 14 (peak). Comparable changes were seen in the contralateral limb but at lesser magnitudes. Morphological changes were observed as well. The number of matrix vesicles/micron2 matrix increased on days 6 (peak) and 14. The mean diameter of the matrix vesicles was elevated on days 6 (peak), 14, and 21. Mean distance from the calcifying front increased on day 6 but was decreased on days 14 and 21. These results indicated that HA behaves like bone-bonding implants in that there is a stimulation of matrix vesicle enzymes, increased phosphatidylserine content, and increase numbers of matrix vesicles. However, the increases occur only after 6 days postimplantation, indicating a delay in response when compared to normal healing. This delay is confirmed by the morphometric measurements. HA causes a reduction in the response associated with marrow ablation. In addition, the effects of HA are comparable locally and systemically but with different intensity. These observations suggest that osteogenic cells are able to compensate for the inhibitory effects of HA and primary calcification involves normal matrix vesicle production and maturation, if somewhat delayed and reduced in magnitude. The ability to support primary mineral formation may contribute to the successful bonding of HA with surrounding osseous tissue.

Alkaline Phosphatase↗

PubMed1993

Diagnostic tools and biologic models for studying osteoporosis and oral bone loss: tissue sampling.

Study of oral tissues to understand the mechanisms of osteoporosis and oral bone loss includes histologic, biochemical, and molecular assessments of the tissue itself, as well as in vivo analysis of the biology of resident cells. Tissue sampling is limited by the nature of the defect and the use of appropriate controls (contralateral site vs same site, different subjects vs repeated measures of the same sites). Experimental parameters may include histomorphometrics, histochemistry, immunohistochemistry, and in situ hybridization. Molecular and biochemical technology also can be used to study the tissue in vivo. The presence of mineral is a confounding variable. To understand the underlying mechanisms of oral bone loss, cell culture is a powerful tool. The location in the oral cavity, the type of tissue (periosteum/cortical bone/trabecular bone), and the presence of pathology (periodontal disease) affect the biology of the cultured cells. Enzymatic release of cells from their extracellular matrix yields heterogeneous cell populations. Migratory cells from explant cultures are more homogeneous but less differentiated. Fibroblastic and bacterial contamination may be problems. Although cell culture data must be considered in the context of the intact tissue, the potential exists for developing bone cell function tests with diagnostic use in the treatment of bone disease.

Alveolar Bone Loss↗

PubMed1993

Sex-dependent effects of 17-beta-estradiol on chondrocyte differentiation in culture.

This study examined the effects of 17-beta-estradiol (E2) on chondrocyte differentiation in vitro. Cells derived from male or female rat costochondral growth zone and resting zone cartilage were used to determine whether the effects of E2 were dependent on the stage of chondrocyte maturation and whether they were sex-specific. [3H]-Thymidine incorporation, cell number, alkaline phosphatase specific activity, and percent collagen production were used as indicators of differentiation. Alkaline phosphatase specific activity in matrix vesicles and plasma membranes isolated from female chondrocyte cultures was measured to determine which membrane fraction was targeted by the hormone. Specificity of the E2 effects was assessed using 17-alpha-estradiol. The role of fetal bovine serum and phenol red in the culture medium was also addressed. The results demonstrated that E2 decreases cell number and [3H]-thymidine incorporation in female chondrocytes, indicating that it promotes differentiation of these cells. Alkaline phosphatase specific activity is stimulated in both growth zone and resting zone cells, but the effect is greater in the less mature resting zone chondrocytes. The increase in enzyme activity is targeted to the matrix vesicles in both cell types, but the fold increase is greater in the growth zone cells. In male chondrocytes, there was a decrease in [3H]-thymidine incorporation at high E2 concentrations in resting zone cells at the earliest time point examined (12 hours) and a slight stimulation in alkaline phosphatase activity in growth zone cells at 24 hours. Cells cultured in serum-free medium exhibited a dose-dependent inhibition in alkaline phosphatase activity when cultured with E2, even in the presence of phenol red. E2-dependent stimulation of enzyme activity is seen only in the presence of serum, suggesting that serum factors are also necessary. E2 increased percent collagen production in female cells only; the magnitude of the effect was greatest in the resting zone chondrocyte cultures. The results of this study indicate that the effects of E2 are dependent on time of exposure, presence of serum, and the sex and state of maturation of the chondrocytes. E2-dependent stimulation of alkaline phosphatase specific activity is targeted to matrix vesicles.

Alkaline Phosphatase↗

PubMed1993

Maturation-dependent regulation of protein kinase C activity by vitamin D3 metabolites in chondrocyte cultures.

Vitamin D3 metabolites regulate the differentiation of chondrocytes isolated from the growth zone or resting zone of rat costochondral cartilage. Since some of the direct membrane effects of vitamin D metabolites are nongenomic, we hypothesized that protein kinase C (PKC) plays a role in signal transduction for these chondrocyte differentiation factors and that the regulation of PKC by the vitamin D metabolites is cell maturation dependent. Confluent, fourth passage cultures of growth zone and resting zone chondrocytes were treated with vitamin D3 metabolites for up to 24 h, lysed, and cell extracts assayed for kinase activity using a specific PKC substrate peptide. The addition of 1,25-(OH)2D3 to growth zone cell cultures resulted in a rapid dose-dependent stimulation of PKC, significant at 10(-9)-10(-7) M, beginning at 3 min and sustained until 90 min; 1,25-(OH)2D3 had no effect on PKC activity in resting zone chondrocyte cultures. The addition of 24,25-(OH)2D3 to resting zone cultures showed a slower PKC activation, with significant stimulation seen at 90-360 min for 10(-8)-10(-7) M 24,25-(OH)2D3. However, 24,25-(OH)2D3 had no effect on PKC activity in growth zone cell cultures at all times and concentrations examined. The specificity of PKC stimulation by the vitamin D3 metabolites was verified using a specific pseudosubstrate region peptide inhibitor, which reduced PKC activity when included in the reaction mixture. Pretreatment of the cultures with U73, 122, a phospholipase C inhibitor, decreased 1,25-(OH)2D3-stimulated PKC activity but had no effect upon 24,25-(OH)2D3-induced activity. The tyrosine kinase inhibitor, genistein, did not inhibit the PKC response in either vitamin D3 metabolites-treated culture. Neither actinomycin D nor cycloheximide affected 1,25-(OH)2D3-induced PKC activity in growth zone chondrocyte cultures, while both compounds inhibited 24,25-(OH)2D3-induced activity in resting zone chondrocyte cultures. The results of this study indicate that vitamin D metabolites stimulate PKC activity in a metabolite- and cell-maturation-specific manner. Effects of 1,25-(OH)2D3 appear to be nongenomic, whereas the effects of 24,25-(OH)2D3 probably involve a genomic mechanism.

24,25-Dihydroxyvitamin D 3↗

PubMed1993

Direct effects of transforming growth factor-beta on chondrocytes are modulated by vitamin D metabolites in a cell maturation-specific manner.

Chondrocytes in the endochondral differentiation pathway produce transforming growth factor-beta (TGF-beta) and response to this growth factor both in vitro and in vivo. To clarify the role that cell maturation state plays in the response, we used a well characterized chondrocyte cell culture model which compares cartilage cells at two different stages of maturation. Confluent fourth passage cultures of rat costochondral resting zone and growth zone cartilage cells were incubated with recombinant human (rh) TGF-beta-1 for 24, 48, or 72 h, and the effect on cell number and [3H]thymidine incorporation was observed. To assess whether TGF-beta regulates chondrocyte differentiation to a calcifying cartilage phenotype, cells were incubated for 24 h with TGF-beta, and the specific activities of alkaline phosphatase and phospholipase A2, two enzymes associated with calcification, were assayed in isolated plasma membranes and matrix vesicles. Alkaline phosphatase-specific activity was also measured in the cell layer. Modulation of TGF-beta action by vitamin D metabolites, also known to regulate endochondral differentiation, was examined. The ability of the chondrocytes to produce latent TGF-beta was assayed. The results show that: 1) quiescent chondrocytes at two stages of endochondral maturation respond to rhTGF-beta-1 by increasing [3H]thymidine incorporation; 2) growth zone cells exhibit no increase in cell number over a 72-h incubation with TGF-beta, whereas resting zone cells exhibit a dose-dependent increase in cell number at 72 h; 3) nonquiescent cells exhibit an increase in alkaline phosphatase-specific activity at 24 h; 4) the effects on this membrane enzyme are comparable in the plasma membranes and matrix vesicles, but the net effect is greater in the extracellular organelle due to the intrinsically higher levels of activity; 5) although differentiation is promoted in resting zone cells, it is limited in the growth zone cells by inhibition of phospholipase A2 activity; and 6) there is a synergistic enhancement of resting zone chondrocyte differentiation when cells are exposed to rhTGF-beta-1 and 24,25-dihydroxyvitamin D3.

24,25-Dihydroxyvitamin D 3↗

PubMed1993

Specific beta estradiol binding in cartilage and serum from young mice and rats is age dependent.

Various studies have shown a direct effect of beta estradiol on cartilage and bone. Such effects point to the possibility that specific receptors to estradiol exist in the growth plate cartilage as well as in bone. 3H-estradiol specific binding (EB) was therefore investigated in the supernatant of cartilage homogenates from the epiphyses and ribs of young growing mice and rats. High levels of EB were observed in the cytosol fraction of cartilage homogenates in the late fetal stage and in young rats and mice. The EB levels decreased gradually from late fetal stage up to 14 days of age in both groups of animals independent of their sex. Nuclear binding of 3H estradiol was also demonstrated by autoradiography in the chondrocytes of proliferating and hypertrophic zones. Estradiol binding was inhibited by high doses of unlabelled beta-estradiol, but not by alpha estradiol. Binding was also inhibited by tamoxifen and DES but not by testosterone. High levels of estradiol binding (EBS) were also observed in serum from young animals, but not in animals 2 months of age or older. Study of estradiol binding in cartilage and in serum of rats of the same age showed a significant difference in estradiol binding between these two systems. The difference in estradiol binding between serum and cartilage was seen in the response to inhibitors, Scatchard analysis, and temperature dependence. The results of our study imply that there are specific receptors for 17 beta estradiol in growth plate cartilage; they originate from chondrocytes, and their amount decreases with age. The effects of estradiol on endochondral bone growth seems therefore to be receptor mediated.

Aging↗

PubMed1993

Response of bone and cartilage cells to biomaterials in vivo and in vitro.

In vivo and in vitro models have been developed to study the bone/material interface. The in vivo model exploits the osteogenesis that accompanies marrow ablation of the rat tibia and uses morphological and biochemical changes in extracellular organelles, called matrix vesicles, as markers of the healing process. Matrix vesicles, which are associated with primary bone formation and calcification, are produced by osteoblasts and are sensitive to cellular and environmental regulation. In bone adjacent to bone-bonding implants, matrix vesicle number increases, as does its alkaline phosphatase activity. In bone adjacent to nonbonding materials, matrix vesicle activity is inhibited. The materials exert systemic effects which can also be studied by use of matrix vesicles. Cell models are needed in order for the specificity of the cellular response to the material to be understood. By the use of culture plates sputter-coated with implant materials, the response of cells can be studied under controlled conditions. Comparison of the response of costochondral chondrocytes at two stages of endochondral development demonstrates that the effects of various materials are surface- and cell-maturation-dependent. Cells cultured on Ti exhibited increased alkaline-phosphatase-specific activity, whereas those cultured on Al2O3 have decreased enzyme activity.

Alkaline Phosphatase↗

PubMed1993

Uptake and biodistribution of technetium-99m-MD32P during rat tibial bone repair.

The present study was carried out in order to test the hypothesis that intravenously injected Tc-MDP separates into its technetium and methylene diphosphonate components in the bone, and that the technetium is preferentially taken-up by the newly-formed osteoid, while the methylene diphosphonate is taken up by the forming mineral. Uptake of Tc-MDP was studied in a rat model of primary bone formation following tibial bone marrow ablation. Each of five radiopharmaceuticals (99mTCO4, 99mTc-MDP, Tc-MD32P, 99mTc-MD32P or MD32P) was injected and their uptake was followed in the whole bone as well as in the organic and inorganic phases of the bone. Irrespective of the radionuclides injected, 99mTc was always taken-up preferentially by the organic phase, while the 32P was preferentially taken-up by the inorganic phase. When 99mTcO4 was injected, it was not taken up by the bone at all. These results indicate that the increased incorporation of 99mTc, when administered as 99mTc-MDP during bone healing, reflects an enhancement in the formation of the organic matrix and not of the calcification process. The study also suggests that the 99mTc-MDP dissociates into its technetium and methylene diphosphonate moieties, which are then adsorbed onto the organic and inorganic phases respectively.

Animals↗

PubMed1992

1,25-(OH)2D3 and 24,25-(OH)2D3 regulation of arachidonic acid turnover in chondrocyte cultures is cell maturation-specific and may involve direct effects on phospholipase A2.

Previous studies have shown that 1,25-(OH)2D3 stimulates phospholipase A2 (PA2) activity in growth zone chondrocytes (GC), but has no effect on the resting zone chondrocyte (RC) enzyme activity. 24,25-(OH)2D3 inhibits the RC enzyme but has no effect on the GC. This study examined whether the vitamin D metabolites affect arachidonic acid turnover in their contra-target cell populations. Incorporation and release of [14C]arachidonate was measured at various times following addition of hormone. Acylation and reacylation were measured independently by incubating with p-chloromercuribenzoate. The results demonstrated that 1,25-(OH)2D3 has no effect on arachidonic acid turnover in RC, but stimulates turnover in GC. In contrast, 24,25-(OH)2D3 stimulates arachidonic acid turnover in RC, but inhibits both incorporation and release in GC. To determine whether direct interaction with PA2 is one mechanism by which 1,25-(OH)2D3 and 24,25-(OH)2D3 regulate arachidonic acid release, snake venom (Niger niger) PA2 was incubated with the vitamin D metabolites. Enzyme specific activity was inhibited by 24,25-(OH)2D3 and stimulated by 1,25-(OH)2D3 in a time- and dose-dependent manner. These results suggest that at least part of the direct effect of vitamin D3 metabolites on cell membranes may be related to changes in PA2 activity. The regulation is related to the stage of differentiation of the target cell population. Changes in fatty acid acylation and reacylation may be one mode of vitamin D3 action in cartilage.

24,25-Dihydroxyvitamin D 3↗

PubMed1992

Effects of combining transforming growth factor beta and 1,25-dihydroxyvitamin D3 on differentiation of a human osteosarcoma (MG-63).

Transforming growth factor beta (TGF beta) and 1,25-dihydroxyvitamin D3 (1,25D3), when added simultaneously to a human osteosarcoma cell line, MG-63, induce alkaline phosphatase activity 40-70-fold over basal levels, 6-7-fold over 1,25D3 treatment alone, and 15-20-fold over TGF beta treatment alone. TGF beta and 1,25D3 synergistically increased alkaline phosphatase specific activity in both matrix vesicles and plasma membrane isolated from the cultures, but the specific activity was greater in and targeted to the matrix vesicle fraction. Inhibitor and cleavage studies proved that the enzymatic activity was liver/bone/kidney alkaline phosphatase. Preincubation of MG-63 cells with TGF beta for 30 min before addition of 1,25D3 was sufficient for maximal induction of enzyme activity. Messenger RNA for liver/bone/kidney alkaline phosphatase was increased 2.1-fold with TGF beta, 1.7-fold with 1,25D3, and 4.8-fold with the combination at 72 h. Human alkaline phosphatase protein as detected by radioimmunoassay was stimulated only 6.3-fold over control levels with the combination. This combination of factors was tested for their effect on production of three other osteoblast cell proteins: collagen type I, osteocalcin, and fibronectin. TGF beta inhibited 1,25D3-induced osteocalcin production, whereas both factors were additive for fibronectin and collagen type I production. TGF beta appears to modulate the differentiation effects of 1,25D3 on this human osteoblast-like cell and thereby retain the cell in a non-fully differentiated state.

Alkaline Phosphatase↗

PubMed1992

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.

Alkaline Phosphatase↗

PubMed1992

Matrix vesicles are enriched in metalloproteinases that degrade proteoglycans.

This study examined the presence of extracellular matrix processing enzymes in matrix vesicles produced by rat costochondral resting zone and growth zone chondrocytes in culture. Optimum procedures for the extraction of each enzyme activity were determined. Enzyme activity associated with chondrocyte plasma membrane microsomes was used for comparison. There was a differential distribution of the enzyme activities related to the cartilage zone from which the cells were isolated. Acid and neutral metalloproteinase (TIMP), plasminogen activator, and beta-glucuronidase were highest in the growth zone chondrocyte (GC) membrane fractions when compared with matrix vesicles and plasma membranes isolated from resting zone chondrocyte (RC) cultures. There was a threefold enrichment of total and active acid metalloproteinase in GC matrix vesicles, whereas no enrichment in enzyme activity was observed in RC matrix vesicles. Total and active neutral metalloproteinase were similarly enriched twofold in GC matrix vesicles. TIMP, plasminogen activator, and beta-glucuronidase activities were highest in the plasma membranes of both cell types. No collagenase, lysozyme, or hyaluronidase activity was found in any of the membrane fractions. The data indicate that matrix vesicles are selectively enriched in enzymes which degrade proteoglycans. The highest concentrations of these enzymes are found in matrix vesicles produced by growth zone chondrocytes, suggesting that this may be a mechanism by which the more differentiated cell modulates the matrix for calcification.

Animals↗

PubMed1992

Effect of titanium implants on primary mineralization following 6 and 14 days of rat tibial healing.

The effect of pure commercial titanium implants on the process of primary mineralization was studied. This was examined by insertion of titanium implants into rat tibial bone after ablation. The effects of the titanium were studied through the behaviour of extracellular matrix vesicles (MV). Methods of morphometric analysis at the TEM level were applied. The insertion of titanium implants was followed by an increase in the number of MV as well as vesicular diameter and by a decrease in vesicular distance from the calcified front when compared to normal healing. These results suggest that the process of MV maturation around titanium implants was delayed when compared to normal primary bone formation during bone healing. The delay in mineralization was compensated by an increase in vesicle production, resulting in an enhancement of primary mineralization by the titanium.

Animals↗

PubMed1992

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.

Alkaline Phosphatase↗