Inhibition of in vitro mineralization by aluminum in a clonal osteoblastlike cell line, MC3T3-E1

Preparation, characterization and in vitro osteoblast growth of waste-derived biomaterials

Preparation, characterization and in vitro osteoblast growth of beer bagasse derived biomaterial.

Comparison of fetal and adult marrow stromal cells in osteogenesis with and without glucocorticoids

To better understand the potential use of fetal marrow stromal cells (MSCs) in bone tissue engineering, we compared the ability of these cells with those of adult MSCs with respect to osteoblasts differentiation in the presence or absence of glucocorticoids. Cells were grown for 3-4 weeks in basal medium or supplemented with 100 nM dexamethasone (DEX, a synthetic glucocorticoid analog) or with 50 microM L-ascorbate and 10 mM glycerol-2-phosphate (AS+GP) or with AS+GP+DEX. At various time points in culture, the following parameters were compared between fetal and adult MSCs: cell morphology, cell proliferation, alkaline phosphatase activity, calcium (45Ca) uptake, von Kossa staining, and glucocorticoids receptor expression were analyzed. Compared with adult MSCs, fetal cells showed a less dramatic change to cuboidal morphology in DEX-containing media. Fetal MSCs in all media conditions showed higher proliferation rates and lower alkaline phosphatase activities (p < 0.001) than adult cells. Both fetal and adult MSCs responded similarly in DEX-containing media with respect to suppressing cell proliferation, stimulating alkaline phosphatase activity, and consistently accumulating calcium (usually higher in fetal cells) with subsequent formation of mineralized matrix when compared with cells cultured in AS+GP. Our findings further implicate the requirement of glucocorticoids in osteogenesis. In conclusion, compared with adult MSCs, fetal cells showed greater ability in sustaining cell proliferation and calcium uptake suggesting that they may be useful for bone tissue repair.

Sensitivity of bone to glucocorticoids

Glucocorticoids are used widely in a range of medical specialities, but their main limitation is an adverse impact on bone. Although physicians are increasingly aware of these deleterious effects, the marked variation in susceptibility between individuals makes it difficult to predict who will develop skeletal complications with these drugs. Although the mechanisms underlying the adverse effects on bone remain unclear, the most important effect appears to be a rapid and substantial decrease in bone formation. This review will examine recent studies that quantify the risk of fracture with glucocorticoids, the mechanisms that underlie this increase in risk and the potential basis for differences in individual sensitivity. An important determinant of glucocorticoid sensitivity appears to be the presence of glucocorticoid-metabolizing enzymes within osteoblasts and this may enable improved estimates of risk and generate new approaches to the development of bone-sparing anti-inflammatory drugs.

Normal matrix mineralization induced by strontium ranelate in MC3T3-E1 osteogenic cells

There is growing evidence that strontium ranelate (SR; S12911-2, PROTELOS; Institut de Recherches Internationales Servier, Courbevoie, France), a compound containing 2 atoms of stable strontium (Sr), influences bone cells and bone metabolism in vitro and in vivo. We previously reported that SR increases bone mass in rats and mice by stimulating bone formation and inhibiting bone resorption. We also showed that short-term treatment with SR enhances osteoblastic cell recruitment and function in short-term rat calvaria cultures. Because Sr incorporates into the bone matrix, it was of interest to determine whether SR may affect matrix mineralization in long-term culture. To this goal, osteogenic mouse calvaria-derived MC3T3-E1 osteoblastic cells were cultured for up to 14 days in the presence of ascorbic acid and phosphate to induce matrix formation and mineralization. Matrix formation was determined by incorporation of tritiated proline during collagen synthesis. Matrix mineralization was quantified by measuring the number and surface of mineralized nodules using a digital image analyzer. In this model, 1,25(OH)2 vitamin D (1 nmol/L) used as internal control, increased alkaline phosphatase (ALP) activity, an early osteoblast marker, on days 4, 10, and 14 of culture. Treatment with SR (1 mmol/L Sr(2+)) increased ALP activity at days 4 and 14 of culture. SR also increased collagen synthesis at days 4 and 10 of culture. In contrast, 1,25(OH)2 vitamin D (1 nmol/L) inhibited collagen synthesis at 4 to 14 days of culture. Long-term treatment with SR (0.1 to 1 mmol/L Sr(2+)) dose dependently increased Sr concentration into the calcified nodules, but did not alter matrix mineralization in long-term culture, as shown by the ratio of the surface of mineralized nodules to the number of mineralized nodules on day 14 of culture. These results show that long-term treatment with SR increases collagenous matrix formation by MC3T3-E1 osteoblasts without inducing deleterious effect on matrix mineralization.

Influence of aluminum on the regulation of PTH- and 1,25(OH)2D3-dependent pathways in the rat osteosarcoma cell line ROS 17/2.8

The role of hormonal status in the development of aluminum (Al)-dependent renal osteodystrophy, which is characterized by reduced bone matrix deposition, still remains largely unknown. To address this question, we used the osteoblast-like osteosarcoma cell line ROS 17/2.8 to evaluate the role of Al on parathyroid hormone (PTH)- and 1,25-dihydroxyvitamin D3 (1,25(OH)2D3)-dependent activities in these cells. Al (1 microM) caused an inhibition of basal and 1,25(OH)2D3-induced alkaline phosphatase, but only at low doses (< 1 nM) of the steroid. Al partly inhibited basal osteocalcin (OC) secretion in ROS cells (p < 0.001), and the dose-dependent increase in 1,25(OH)2D3-induced OC release by these cells was also reduced by 1 microM Al at low concentrations of the steroid (< or = 1 nM), whereas high doses of 1,25(OH)2D3 (> or = 5 nM) totally prevented the inhibiting effects of Al. Al also had strong inhibitory actions on PTH-dependent cAMP production by ROS cells over the concentration range tested (0.5-50 nM). This inhibitory action of Al was also observed for PTH-related peptide- (PTHrp, 50 nM) but not for Isoproterenol-dependent (100 nM) cAMP formation. To evaluate more fully the mechanism of this inhibition of cAMP formation, we investigated the effect of Al on toxin-modulated, G protein-dependent regulation of cAMP formation and on the activation of adenylate cyclase by Forskolin. Cholera toxin (CT, 10 micrograms/ml), applied to cells for 4 h prior to PTH challenge, enhanced cAMP production about 2-fold above PTH alone (p < 0.001), a process that was further stimulated by Al. Pertussis toxin (PT, 1 microgram/ml, 4 h) did not modify basal PTH-dependent cAMP formation by ROS cells. However, PT treatment prevented the inhibitory effect of Al on cAMP formation by these cells (p < 0.025). The stimulation of adenylate cyclase by Forskolin (0.1 and 1 microM), which bypasses G protein regulation, was not modified by Al, indicating that Al does not affect adenylate cyclase directly. Northern blot analysis of PTH receptor mRNA levels showed that Al did not modify PTH receptor message in ROS cells. Likewise, Western blot analyses of G protein subunits showed that Al did not significantly alter Gs alpha subunit levels, in accordance with the results obtained for cAMP-dependent formation in response to CT. In contrast, Gi alpha-1 and Gi alpha-2 subunits were decreased by Al treatment, consistent with PT-restricted increases in cAMP formation in Al-treated ROS cells. Taken together, these results suggest that Al has multiple actions in osteoblast-like ROS cells. The effects of Al are modulated by hormonal control of the pathways investigated. Al affects 1,25(OH)2D3-regulated functions only when this steroid is low. Al has large inhibitory effects on PTH- and PTHrp-dependent cAMP formation. This last feature is related to the ability of Al to alter the G protein transducing pathway for PTH/PTHrp-dependent formation of cAMP since it does not affect adenylate cyclase activity directly and does not affect the PTH receptor message level. Thus, Al has stronger deleterious effects in osteoblast-like cells with an already compromised 1,25(OH)2D3 status and can modulate specifically PTH/PTHrp-mediated cAMP formation at the postreceptor level.

Lipid oxidation products have opposite effects on calcifying vascular cell and bone cell differentiation. A possible explanation for the paradox of arterial calcification in osteoporotic patients

Atherosclerotic calcification and osteoporosis often coexist in patients, yielding formation of bone mineral in vascular walls and its simultaneous loss from bone. To assess the potential role of lipoproteins in both processes, we examined the effects of minimally oxidized low-density lipoprotein (MM-LDL) and several other lipid oxidation products on calcifying vascular cells (CVCs) and bone-derived preosteoblasts MC3T3-E1. In CVCs, MM-LDL but not native LDL inhibited proliferation, caused a dose-dependent increase in alkaline phosphatase activity, which is a marker of osteoblastic differentiation, and induced the formation of extensive areas of calcification. Similar to MM-LDL, oxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine (ox-PAPC) and the isoprostane 8-iso prostaglandin E2 but not PAPC or isoprostane 8-iso prostaglandin F2 alpha induced alkaline phosphatase activity and differentiation of CVCs. In contrast, MM-LDL and the above oxidized lipids inhibited differentiation of the MC3T3-E1 bone cells, as evidenced by their stimulatory effect on proliferation and their inhibitory effect on the induction of alkaline phosphatase and calcium uptake. These results suggest that specific oxidized lipids may be the common factors underlying the pathogenesis of both atherosclerotic calcification and osteoporosis.

Beta-glycerophosphate accelerates calcification in cultured bovine vascular smooth muscle cells

Calcification is a common feature of advanced atherosclerotic lesions and is being reemphasized as a clinically significant element of vascular disease. However, the scarcity of in vitro models of vascular calcification preclude studying its molecular and cellular mechanism. In the present study, we describe an in vitro calcification in which diffuse calcification can be induced by culturing bovine vascular smooth muscle cells (BVSMC) in the presence of beta-glycerophosphate, ascorbic acid, and insulin in a manner analogous to in vitro mineralization by osteoblasts. Calcification was confirmed by von Kossa staining and 45Ca accumulation. Factor analysis revealed that beta-glycerophosphate is the most important factor for this calcification process, suggesting that alkaline phosphatase (ALP) may be involved. As predicted, high levels of ALP expression were detected by ALP assay and Northern blot analysis. Functional significance of ALP was confirmed by demonstrating that levamisole, a specific inhibitor of ALP, inhibited BVSMC calcification in a dose-dependent manner. Bisphosphonates such as etidronate and pamidronate potently inhibited BVSMC calcification, suggesting that hydroxyapatite formation may be involved. Importantly, expression of osteopontin mRNA was dramatically increased in calcified BVSMC compared with uncalcified control cells. These data suggest that beta-glycerophosphate can induce diffuse calcification by an ALP-dependent mechanism and that this in vitro calcification system is useful for analyzing the molecular and cellular mechanisms of vascular calcification.

Role of endogenous PGE2 in osteoblastic functions of a clonal osteoblast-like cell, MC3T3-E1

MC3T3-E1 cells actively synthesized and released prostaglandin E2 (PGE2) during culture. PGE2 release was minimal on day 9 and gradually increased with culture up to day 27. DNA content gradually increased until day 27. Alkaline phosphatase (ALP) activity increased up to day 15 and decreased thereafter. In contrast to the decrease in ALP activity, calcium accumulation increased rapidly after day 21, possibly due to mineralization by the cells. Indomethacin, a cyclooxygenase inhibitor, blocked PGE2 production completely at concentrations higher than 0.3 mumol/L. In the presence of indomethacin (3 mumol/L), DNA content was slightly decreased on day 27. Furthermore, ALP activity on day 15 was greater than that of the control and this high activity was maintained until day 27. However, calcium accumulation was not affected by the addition of indomethacin. These results suggest that endogenous PGE2 down-regulates ALP activity and slightly stimulates the proliferation of MC3T3-E1 cells as an autocrine mediator, although it does not directly influence the cells' mineralizing activity.

Distinct proliferative and differentiated stages of murine MC3T3-E1 cells in culture: an in vitro model of osteoblast development

We examine clonal murine calvarial MC3T3-E1 cells to determine if they exhibit a developmental sequence similar to osteoblasts in bone tissue, namely, proliferation of undifferentiated osteoblast precursors followed by postmitotic expression of differentiated osteoblast phenotype. During the initial phase of developmental (days 1-9 of culture), MC3T3-E1 cells actively replicate, as evidenced by the high rates of DNA synthesis and progressive increase in cell number, but maintain a fusiform appearance, fail to express alkaline phosphatase, and do not accumulate mineralized extracellular collagenous matrix, consistent with immature osteoblasts. By day 9 the cultures display cuboidal morphology, attain confluence, and undergo growth arrest. Downregulation of replication is associated with expression of osteoblast functions, including production of alkaline phosphatase, processing of procollagens to collagens, and incremental deposition of a collagenous extracellular matrix. Mineralization of extracellular matrix, which begins approximately 16 days after culture, marks the final phase of osteoblast phenotypic development. Expression of alkaline phosphatase and mineralization is time but not density dependent. Type I collagen synthesis and collagen accumulation are uncoupled in the developing osteoblast. Although collagen synthesis and message expression peaks at day 3 in immature cells, extracellular matrix accumulation is minimal. Instead, matrix accumulates maximally after 7 days of culture as collagen biosynthesis is diminishing. Thus, extracellular matrix formation is a function of mature osteoblasts. Ascorbate and beta-glycerol phosphate are both essential for the expression of osteoblast phenotype as assessed by alkaline phosphatase and mineralization of extracellular matrix. Ascorbate does not stimulate type I collagen gene expression in MC3T3-E1 cells, but it is absolutely required for deposition of collagen in the extracellular matrix. Ascorbate also induces alkaline phosphatase activity in mature cells but not in immature cells. beta-glycerol phosphate displays synergistic actions with ascorbate to further stimulate collagen accumulation and alkaline phosphatase activity in postmitotic, differentiated osteoblast-like cells. Mineralization of mature cultures requires the presence of beta-glycerol phosphate. Thus, MC3T3-E1 cells display a time-dependent and sequential expression of osteoblast characteristics analogous to in vivo bone formation. The developmental sequence associated with MC3T3-E1 differentiation should provide a useful model to study the signals that mediate the switch between proliferation and differentiation in bone cells, as well as provide a renewable culture system to examine the molecular mechanism of osteoblast maturation and the formation of bone-like extracellular matrix.

Effects of systemic aluminum on the resolution of a uremic and dietary phosphorus-dependent model of uremic osteomalacia in rats

We have developed a model of osteomalacia that is dependent on both uremia and the feeding of a diet low in phosphorus and that can be reversed by subsequent dietary phosphorus repletion. The objectives for this study were to use this model to investigate the role of aluminum (Al) in both the induction and resolution of osteomalacia. Adult male Sprague-Dawley rats were five-sixths nephrectomized and fed either low or normal dietary phosphorus, both with and without intraperitoneal Al injections. Uremic rats fed low phosphorus developed osteomalacia characterized by increased osteoid surface, volume, and thickness and osteoid maturation time and decreased mineralizing surface. Al-treated uremic rats fed low phosphorus were similarly affected, developing increased osteoid volume and thickness and osteoid maturation time and decreased osteoblastic surface, mineralizing surface, and bone formation rate. In addition, they had a significantly increased Al-positive surface. Al-treated uremic rats fed normal phosphorus had only increased osteoid thickness and aluminum-positive surface and decreased osteoblastic surface. Osteomalacic rats continuously treated with Al during the induction and phosphorus repletion stages had increased growth plate thickness, osteoid volume and thickness, and Al-positive surface and decreased osteoblastic and mineralizing surface. Mineralization in these rats was impaired to such a degree that no detectable double labels were present. Osteomalacic rats treated with Al during the induction phase but not during phosphorus repletion had increased osteoid surface and volume and Al-positive surface and decreased osteoblastic and mineralizing surface. Double labels were not detectable in these rats, either.(ABSTRACT TRUNCATED AT 250 WORDS)

Stimulation by 1,25-dihydroxyvitamin D3 of in vitro mineralization induced by osteoblast-like MC3T3-E1 cells

Although vitamin D is essential for mineralization of bone, it is as yet unclear whether vitamin D has a direct stimulatory effect on the bone mineralization process. In the present study, the effect of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] on in vitro mineralization mediated by osteoblast-like MC3T3-E1 cells was examined. MC3T3-E1 cells continued to grow after they reached confluency, and DNA content and alkaline phosphatase activity increased linearly until about 16 days of culture, whereas 45Ca accumulation into cell and matrix layer remained low. After this period, DNA content plateaued, and 45Ca accumulation increased sharply. Histological examination by von Kossa staining revealed that calcium was accumulated into extracellular matrix. In addition, needle-shaped mineral crystals similar to hydroxyapatite crystals could be demonstrated in between collagen fibrils by electron microscopy. Thus, MC3T3-E1 cells differentiate in vitro into cells with osteoblastic phenotype and exhibit mineralization. When MC3T3-E1 cells were treated with 1,25(OH)2D3 at this stage of culture, there was a dose-dependent stimulation of 45Ca accumulation by 1,25(OH)2D3, and a significant stimulation of 45Ca accumulation was observed with 3 x 10(-10) M 1,25(OH)2D3. Although 1,25(OH)2D3 enhanced alkaline phosphatase activity and collagen synthesis at the early phase of culture, it did not affect any of these parameters at the late phase when 1,25(OH)2D3 stimulated mineralization. Neither 24,25-dihydroxyvitamin D3 nor human PTH(1-34) affected mineralization in the presence or absence of 1,25(OH)2D3. These results demonstrate that 1,25(OH)2D3 stimulates matrix mineralization induced by osteoblastic MC3T3-E1 cells, and are consistent with the possibility that 1,25(OH)2D3 has a direct stimulatory effect on bone mineralization process.(ABSTRACT TRUNCATED AT 250 WORDS)

Distribution of trace levels of therapeutic gallium in bone as mapped by synchrotron x-ray microscopy

Gallium nitrate, a drug that inhibits calcium release from bone, has been proven a safe and effective treatment for the accelerated bone resorption associated with cancer. Though bone is a target organ for gallium, the kinetics, sites, and effects of gallium accumulation in bone are not known. We have used synchrotron x-ray microscopy to map the distribution of trace levels of gallium in bone. After short-term in vivo administration of gallium nitrate to rats, trace (nanogram) amounts of gallium preferentially localized to the metabolically active regions in the metaphysis as well as the endosteal and periosteal surfaces of diaphyseal bone, regions where new bone formation and modeling were occurring. The amounts measured were well below the levels known to be cytotoxic. Iron and zinc, trace elements normally found in bone, were decreased in amount after in vivo administration of gallium. These studies represent a first step toward understanding the mechanism(s) of action of gallium in bone by suggesting the possible cellular, structural, and elemental "targets" of gallium.

Isolation and characterization of proteoglycans synthesized by mouse osteoblastic cells in culture during the mineralization process

Proteoglycans in mineralized (0.5 M-EDTA/4 M-guanidinium chloride-extractable) and non-mineralized (4 M-guanidinium chloride-extractable) matrices synthesized by a mouse osteoblastic-cell line MC3T3-E1 were characterized at different phases of mineralization in vitro. Cell cultures were labelled with [35S]sulphate and either [3H]glucosamine or 3H-labelled amino acids. At the mineralization phase a large majority of proteoglycans were extracted with 4 M-guanidinium chloride (G extract), and at least five species of labelled proteoglycans were identified; dermatan sulphate proteoglycans (DSPG), apparent Mr approx. 120,000 and 70,000), heparan sulphate proteoglycans (HSPG, apparent Mr approx. 200,000 and 120,000) and DS chains with very little core protein. DSPGs weakly bound to an octyl-Sepharose CL-4B column and HSPGs bound more tightly, whereas DS chains did not bind to the column. Amounts of labelled proteoglycans extracted with 0.5 M-EDTA/4 M-guanidinium chloride (EDTA extract) were much less than those in G extract. Although the predominant species in the EDTA extract were comparable with the DS or DSPGs in the G extract, none of them bound to octyl-Sepharose CL-4B, indicating their lack of hydrophobicity. At the nonmineralizing phase a large chondroitin sulphate proteoglycan (Mr greater than 600,000) was found in the matrix in addition to the five proteoglycan species similar to those at the mineralization phase. Although DS chains at the early phase were similar in size to those at the mineralization phase, the ratio of 2-acetamido-2-deoxy-3-O-(beta-D-gluco-4-enepyranosyluronic acid)-4-O-sulpho-D-galactose to 2-acetamido-2-deoxy-3-O-(beta-D-gluculo-4-enepyranosyluronic acid)-6-O-sulpho-D-galactose was less than that at the mineralization phase. These results agree with those of previous studies performed in vivo and suggest that alteration in the synthesis of proteoglycans is involved in the mineralization process. They also suggest that at the osteoblastic mineralization front proteoglycans undergo partial degradation and lose their hydrophobicity.

Aluminum administration in the rat separately affects the osteoblast and bone mineralization

Aluminum administration in the experimental animal results in osteomalacia as characterized by osteoid accumulation and decreased mineralization. Previous in vivo and in vitro studies have indicated that either aluminum directly inhibits mineralization or is toxic to the osteoblast. In the present study, PTH was continuously infused in rats with aluminum-induced osteomalacia to evaluate whether aluminum administration decreased mineralization without a concomitant decrease in osteoblasts. Four groups of rats were studied: chronic renal failure (CRF); CRF + aluminum (AL); CRF + PTH; and CRF + PTH + AL. Rats were sacrificed 5 and 12 days after aluminum or diluent administration; in the PTH groups, bovine PTH (1-34) was administered at 2 units/h via a subcutaneously implanted Alzet pump. Aluminum administration decreased osteoblast surface, increased osteoid accumulation, and produced a cessation of bone formation. The infusion of PTH alone increased osteoblast surface and bone formation. The simultaneous administration of aluminum and PTH resulted in an osteoblast surface intermediate between aluminum and PTH alone; however, despite a PTH-induced restoration of osteoblast surface, bone formation did not increase. These findings indicate (1) aluminum is toxic to osteoblasts and also directly inhibits mineralization even when osteoblasts are not decreased; (2) PTH is capable of increasing osteoblasts even in the presence of aluminum; and (3) despite a PTH-induced increase in osteoblast surface, mineralization of osteoid was not improved.

Aluminum and chronic renal failure: sources, absorption, transport, and toxicity

In normal subjects the gastrointestinal tract is a relatively impermeable barrier to aluminum with a low fractional absorption rate for this metal ion. Aluminum absorbed from the gastrointestinal tract is normally excreted by the kidneys; in the presence of impaired renal function aluminum is retained and accumulates in body tissues. Aluminum-containing medications are given, by mouth, to patients with chronic renal failure as phosphate-binding agents for the therapeutic control of hyperphosphatemia. Patients with chronic renal failure are also exposed to aluminum in domestic tap-water supplies used either for drinking or, in those on dialysis treatment, in the preparation of their dialysate. In patients with end-stage chronic renal failure, particularly in those on treatment by hemodialysis, the accumulation of aluminum in bone, brain, and other tissues is associated with toxic sequelae. An increased brain content of aluminum appears to be the major etiological factor in the development of a neurological syndrome called either "dialysis encephalopathy" or "dialysis dementia"; an increased bone content causes a specific form of osteomalacia. An excess of aluminum also appears to be an etiological factor in a microcytic, hypochromic anemia that occurs in some patients with chronic renal failure on long-term treatment with hemodialysis. The various mechanisms involved in the toxic phenomena associated with the accumulation of aluminum in body tissues have not been clearly defined but are the subject of extensive investigations.

Inhibitory effects of cadmium on in vitro calcification of a clonal osteogenic cell, MC3T3-E1

To examine an inhibitory mechanism of Cd on bone formation, the effects of Cd on calcification were investigated in a culture of a clonal osteogenic cell line, MC3T3-E1. At 3 days after inoculation, Cd was added to the medium containing 7 mM beta-glycerophosphate, and culture was continued for 8 days. Cd at 1.78 microM and above caused a significant decrease in 45Ca accumulation. The decrease in mineralization by Cd was similar to that in collagen content or alkaline phosphatase (ALP) activity. Histologically, the cell density and the mineralization degree were lower than those of the controls. Ultrastructurally, degenerated cells were observed with undifferentiated cells which had fewer rough-surfaced endoplasmic reticulum and many mitochondria. This suggests that Cd may inhibit the differentiation into osteoblasts as well as the cell function. On the other hand, calcification of cells at 8 days after inoculation was inhibited by Cd at 1.78 microM and above. The decrease in collagen content and ALP activity by Cd was much lower than that in calcification. Cd-treated cells were well differentiated into osteoblasts morphologically, but the mineralization degree was lower than that of the controls. Ultrastructurally, cell damage was not recognized so strongly compared with long-term Cd treatment. The mineralization of osteoblasts was also inhibited by Zn levels which left both collagen content and ALP activity unaffected. From these results, it was suggested that the inhibitory effect of Cd on in vitro calcification of MC3T3-E1 cells may be due to both a depression of cell-mediated calcification and a decrease in physiochemical mineral deposition.

The effects of cadmium, copper or zinc on formation of embryonic chick bone in tissue culture

Femurs from 9-day-old chick embryo were cultivated for 6 days by the roller-tube method in the presence of Cd, Cu or Zn. Cd (5.0 microM and above) and Cu (2.5 microM and above) caused a decrease in collagen content of both diaphysis and epiphysis, mainly due to inhibition of collagen synthesis. In addition, Cd and Cu each showed a tendency to inhibit an increase in Ca content of diaphysis, where intraperiosteal ossification could be observed. Alkaline phosphatase (ALP) activity was decreased by Cd (5.0 microM and above) or Cu (10 microM and above) in diaphysis. On the other hand, Zn at 50 microM and above inhibited an increase in Ca content of the diaphysis with a remarkable elevation of ALP activity in the medium. At this time, Zn did not decrease the collagen content of the diaphysis so strongly. Histological observations revealed that Cd and Cu each decreased both calcified and uncalcified osteoid tissue at 2.5 microM, while Zn at 100 microM decreased calcified tissue but increased uncalcified osteoid tissue. As Zn accumulated particularly in diaphysis and deposited at the edge of calcified tissue, it was suggested that Zn inhibited calcification physicochemically. It was concluded that Cd or Cu would induce bone damage represented by osteoporosis, whereas Zn would induce osteomalacia.