Influence of poisonous metals on bone metabolism. III. The effect of cadmium on bone resorption in tissue culture

Cadmium in bone cement induces necrosis and decreases the viability of residual osteosarcoma cells: A xenograft study

OBJECTIVE

The aim of this study was to show whether local application of cadmium-impregnated bone cement can induce apoptosis and decrease the viability of residual osteosarcoma (OS) cells in nude mice.

METHODS

K7M2 tumorigenic OS cell line was cultivated in vitro. The xenograft tumor model was formed by subcutaneously adding the tumor cells to athymic nude mice. Tumor was formed within 1 month. Then, mice were randomly assigned to five groups, each containing seven nude mice: control (group 1), wide resection (group 2), intralesional resection (group 3), intralesional resection + bone cement (group 4), and intralesional resection + cadmium embedded in bone cement (group 5). Tumor resection with 1 cm surgical margins was performed in the wide resection group. In intralesional resection groups, tumor tissue was resected with positive margins aiming to leave 15 mm3 of macroscopic tumor tissue. In group 3, the defect was left empty; groups 4 and 5 received bone cements prepared with saline and cadmium solutions, respectively. After the resection, mice were observed for 15 days and sacrificed. Next, surgical resection sites were evaluated histopathologically in each group.

RESULTS

Recurrent tumor was formed in all mice in the wide resection group, and apparent progression of residual tumor was observed in groups 3 and 4. On the contrary, only a thin layer of residual tumor was observed around the bone cement in group 5. Histological evaluation revealed remarkable necrosis in group 5 and lowest viability compared to other groups. No systemic toxic effect related to cadmium was observed.

CONCLUSION

Our data suggest that local application of cadmium in bone cement has a significant potential to increase tumor necrosis and decrease the viability of residual OS cells.

Cadmium osteotoxicity in experimental animals: mechanisms and relationship to human exposures

Extensive epidemiological studies have recently demonstrated increased cadmium exposure correlating significantly with decreased bone mineral density and increased fracture incidence in humans at lower exposure levels than ever before evaluated. Studies in experimental animals have addressed whether very low concentrations of dietary cadmium can negatively impact the skeleton. This overview evaluates results in experimental animals regarding mechanisms of action on bone and the application of these results to humans. Results demonstrate that long-term dietary exposures in rats, at levels corresponding to environmental exposures in humans, result in increased skeletal fragility and decreased mineral density. Cadmium-induced demineralization begins soon after exposure, within 24 h of an oral dose to mice. In bone culture systems, cadmium at low concentrations acts directly on bone cells to cause both decreases in bone formation and increases in bone resorption, independent of its effects on kidney, intestine, or circulating hormone concentrations. Results from gene expression microarray and gene knock-out mouse models provide insight into mechanisms by which cadmium may affect bone. Application of the results to humans is considered with respect to cigarette smoke exposure pathways and direct vs. indirect effects of cadmium. Clearly, understanding the mechanism(s) by which cadmium causes bone loss in experimental animals will provide insight into its diverse effects in humans. Preventing bone loss is critical to maintaining an active, independent lifestyle, particularly among elderly persons. Identifying environmental factors such as cadmium that contribute to increased fractures in humans is an important undertaking and a first step to prevention.

Involvement of mitogen-activated protein kinases and protein kinase C in cadmium-induced prostaglandin E2 production in primary mouse osteoblastic cells

We previously reported that cadmium (Cd) induced prostaglandin E2 (PGE2) biosynthesis through the activation of cytosolic phospholipase A2 (cPLA2) and induction of cyclooxygenase 2 (COX-2) in primary mouse osteoblastic cells. In the present study, we further investigated the mechanism of PGE2 production by Cd focusing on the main mitogen-activated protein kinase (MAPK) subfamilies that mediate prostaglandin synthesis, extracellular signal-regulated kinase (ERK1/2 MAPK), c-jun-amino-terminal kinase (JNK MAPK) and p38 MAPK, and protein kinase C (PKC) which is activated by Cd in several kinds of cells. Cd at 2 microM and above stimulated PGE2 production in osteoblastic cells and its production was inhibited by the kinase-specific inhibitors PD98059, SB203580, curcumin, and calphostin C. Calphostin C also inhibited the production of PGE2 by phorbol 12-myristate 13-acetate (PMA), which is a potent activator of PKC. PD98059 inhibited PGE2 production stimulated by PMA as well as Cd, indicating that activation of PKC by ERK1/2 MAPK was necessary for Cd-stimulated PGE2 production. Moreover, Cd stimulated the phosphorylation of these three MAPKs, and inhibition of the phosphorylation of ERK1/2 MAPK by calphostin C was also observed. On the other hand, Cd was found to phosphorylate cPLA2 and the phosphorylation was inhibited by PD98059, indicating that cPLA2 was activated by Cd through ERK1/2 MAPK and released arachidonic acid (AA), a substrate of COX-2, from membranous phospholipids. From these results, it was suggested that activation of each of the ERK1/2, p38, and JNK MAPK cascades in addition to that of PKC and cPLA2 played an important role in the Cd-stimulated biosynthesis of PGE2 in mouse osteoblastic cells.

Microarray analysis of changes in bone cell gene expression early after cadmium gavage in mice

We developed an in vivo model for cadmium-induced bone loss in which mice excrete bone mineral in feces beginning 8 h after cadmium gavage. Female mice of three strains [CF1, MTN (metallothionein-wild-type), and MT1,2KO (MT1,2-deficient)] were placed on a low-calcium diet for 2 weeks. Each mouse was gavaged with 200 microg Cd or vehicle only. Fecal calcium was monitored daily for 9 days, beginning 4 days before cadmium gavage, to document the bone response. For CF1 mice, bones were taken from four groups: +/- Cd, 2 h after Cd and +/- Cd, 4 h after Cd. MTN and MT1,2KO strains had two groups each: +/-Cd, 4 h after Cd. PolyA+ RNA preparations from marrow-free shafts of femura and tibiae of each +/- Cd pair were submitted to Incyte Genomics for microarray analysis. Fecal Ca results showed that bone calcium excreted after cadmium differed for the three mouse strains: CF1, 0.24 +/- 0.08 mg; MTN, 0.92 +/- 0.22 mg; and MT1,2KO, 1.7 +/- 0.4 mg. Gene array results showed that nearly all arrayed genes were unaffected by cadmium. However, MT1 and MT2 had Cd+/Cd- expression ratios >1 in all four groups, while all ratios for MT3 were essentially 1, showing specificity. Both probes for MAPK 14 (p38 MAPK) had expression ratios >1, while no other MAPK responded to cadmium. Vacuolar proton pump ATPase and integrin alpha v (osteoclast genes), transferrin receptor, and src-like adaptor protein genes were stimulated by Cd; other src-related genes were unaffected. Genes for bone formation, stress response, growth factors, and signaling molecules showed little or no response to cadmium. Results support the hypothesis that Cd stimulates bone demineralization via a p38 MAPK pathway involving osteoclast activation.

Urinary cadmium excretion is correlated with calcaneal bone mass in Japanese women living in an urban area

Nine hundred eight women aged 40-88 years living in a non-Cd-polluted area in Japan were analyzed for urinary cadmium (Cd), N-acetyl-beta-D-glucosaminidase (NAG) activity, beta(2)-microglobulin (B2MG) concentration, and for the stiffness index (STIFF) of calcaneal bone using an ultrasound method. The urinary Cd in the subjects, with a mean and range of 2.87 and 0.25-11.4 microg/g creatinine, respectively, showed a significant correlation with NAG but not with B2MG. STIFF was significantly inversely correlated with urinary Cd, and the association remained significant after adjusting for age, body weight, and menstrual status, suggesting a significant effect of Cd on the bone loss in these subjects without signs of Cd-induced kidney damage. A two-fold increase in urinary Cd was accompanied by a decrease in STIFF corresponding to a 1.7-year rise in age. These results emphasize the need for reassessment of the significance of Cd exposure in the general Japanese population.

The effect of zinc supply on cadmium-induced changes in the tibia of rats

It has been determined that zinc supplementation (240 microg Zn/ml) during (for 12 weeks) or after (for 2 weeks) cadmium exposure (50 microg Cd/ml for 12 weeks) can prevent the accumulation and toxic action of Cd in the tibia of rats. The exposure to Cd led to disturbances in bone metabolism reflected by changes in the chemical composition of bone and decreased bone mineral density (osteomalacian changes). The Zn supply in conditions of Cd intoxication completely prevented the Cd-induced increase in percentage of water content and decrease in tibia ash weight, ash weight/dry weight, non-org. comp./org. comp., Zn content and concentration. Moreover, Zn partly protected from the decrease in Ca concentration and content, percentage of non-organic components content, Ca/wet weight, Ca/ash weight and Ca/dry weight. Zn administered after Cd exposure partly, but not completely, protected from Cd-induced decrease in percentage of non-organic components content, Ca/wet weight as well as Ca content and concentration. This protective effect on bone was most evident when Zn was administered during Cd exposure. But Zn, independently of the manner of its administration, did not prevent Cd accumulation in the tibia. Our results suggest that Zn supply in conditions of simultaneous exposure can prevent Cd-induced bone loss to some extent, and used after Cd treatment can give therapeutic benefits.

Evidence that E-cadherin may be a target for cadmium toxicity in epithelial cells

E-cadherin is a Ca(2+)-dependent cell adhesion molecule that plays an important role in the development and maintenance of epithelial polarity and barrier function. This commentary describes the results of recent studies showing that the environmental pollutant Cd(2+) can damage the E-cadherin-dependent junctions between many types of epithelial cells and reviews the evidence indicating that this effect results from the direct interaction of Cd(2+) with the E-cadherin molecule. In addition, the implications of these findings with respect to the mechanisms of Cd(2+) toxicity in specific target organs such as lung, kidney, bone, and the vascular endothelium are discussed.

Effects of cadmium on bone: an in vivo model for the early response

Cadmium (Cd) exposure induces bone resorption in vitro and in vivo that can lead to low bone mass and increased incidence of fracture. We have developed an animal model for following the early skeletal response to Cd. A low-calcium (but not calcium-deficient) diet is used to increase gastrointestinal absorption of calcium so that the endogenous fecal calcium excretion is essentially the total fecal calcium excretion. The bone response is followed by quantitation of stable fecal calcium and does not require a radioactive label. After mice were adjusted to a low-calcium diet, Cd was administered by a single gavage and fecal calcium was monitored to determine the magnitude of the calcium release from bone. Fecal calcium excretion (microg Ca/hr; mean +/- SE) remained at the background level for 8 hr (13.6 +/- 1.8, n = 18) but increased during the 8- to 24-hr and 24- to 56-hr collection periods (43.8 +/- 6.8, n = 12; 50.75 +/- 3.7, n = 6, respectively). The bone response was transient and dropped to nearly background levels during the 56- to 104-hr collection period. Blood calcium levels were normal throughout the time course. Bone resorption occurred at Cd levels of 7.9 +/- 0.7 microg/liter blood (mean +/- SE, n = 6), which is in the range of occupational exposure levels. The transient nature of the bone response contrasted to the slow but continuing rise observed in blood Cd levels. These results suggest that a threshold level of Cd is required for a bone response but that chronic levels of Cd in blood do not necessarily indicate the occurrence of continuous active bone resorption. This model can be used to probe early gene changes (prior to the bone response) that may be occurring in response to Cd exposure.

Cadmium perturbs calcium homeostasis in rat osteosarcoma (ROS 17/2.8) cells; a possible role for protein kinase C

The mechanism of the toxic effects of Cd2+ on bone cell function is not completely understood at this time. This study was designed to characterize the effect of Cd2+ on Ca2+ metabolism in ROS 17/2.8 cells. Cells were labeled with (45)Ca (1.87 mM Ca) for 20 h in the presence of 0.01, 0.1, or 1.0 microM Cd2+ and kinetic parameters were determined from (45)Ca efflux curves. Three kinetic compartments described the intracellular metabolism of (45)Ca. Cd2+ (0.01 microM) caused an approximate 9 x increase in Ca2+ flux across the plasma membrane and a decrease in the most rapidly exchanging intracellular Ca2+ compartment (S1). However, there was no change in total cell Ca2+, indicating an increased cycling of Ca2+ across the plasma membrane. Flux between S1 and the intermediate Ca2+ compartment (S2) was also increased and S2 increased significantly. All Cd2+ induced changes in Ca2+ homeostasis were obliterated by concurrent treatment with 0.1 microM calphostin C (CC), a potent protein kinase C (PKC) inhibitor. This data suggests that Cd2+ perturbs Ca2+ metabolism via a PKC dependent process.

The effect of cadmium on cytosolic free calcium, protein kinase C, and collagen synthesis in rat osteosarcoma (ROS 17/2.8) cells

Cadmium affects normal bone growth but the mechanisms of Cd2+ toxicity are not fully understood. Calcium is an integral component of bone growth and a second messenger necessary for the actions of calciotropic hormones. Ca2+ activates protein kinase C (PKC), and PKC is a mediator of [Ca2+]1 and mediator of collagen synthesis in osteoblastic cells. Therefore, PKC is a possible loci of Cd2+ effects on Ca2+ metabolism and Ca(2+)-regulated processes. This work was conducted to determine the effect of Cd2+ on cytosolic free Ca2+ ([Ca2+]i) levels, characterize the activation and/or inhibition of PKC by Cd2+ and Ca2+, and measure the effect of Cd2+ on collagen synthesis in ROS 17/2.8 cells. Cells were treated for 120 min with Cd2+ (0 to 30 microM) and [Ca2+]i was measured. Basal [Ca2+]i was 132 nM and the maximal increase to 268 nM occurred in the presence of 5 microM Cd2+. Treatment with 1 or 5 microM Cd2+ caused an increase in [Ca2+]i at 40 min with return to basal levels at 120 min of treatment. Pretreatment (24 hr) with 0.1 microM calphostin C (CC), a PKC inhibitor, produced no change in [Ca2+]i and prevented any rise in [Ca2+]i in response to Cd2+. Free Cd2+ activates PKC with an activation constant of 7.5 X 10(-11) M, while Ca2+ activates PKC with an activation constant of 3.6 X 10(-7) M. Cd2+ also caused a dose-dependent decrease in collagen synthesis, a PKC-mediated process. These data suggest that Cd2+ affects Ca2+ metabolism and Ca(2+)-mediated processes via unwarranted PKC activation as demonstrated by Cd2+ perturbation of collagen synthesis.

Characterisation of the effects of cadmium on the release of calcium and on the activity of some enzymes from neonatal mouse calvaria in culture

Exposure to cadmium (Cd) causes skeletal impairments, such as osteoporosis and osteomalacia, in many mammalian species, including humans. There is, however, some controversy about the mechanism of action of these Cd-induced skeletal effects, although both a direct influence on bone cells and effects that are secondary to renal damage caused by the metal have been demonstrated. In the present study, we cultured calvarial bones from neonatal mice and exposed them to Cd to study the effects of the metal on calcium release and on the activity of some enzymes of importance for bone resorption and bone formation. Cd dose-dependently stimulated calcium release from the bones. Maximal release was noted at Cd concentrations of 0.4-0.8 microM, which was similar to the level of release in the presence of maximal stimulatory concentrations of parathyroid hormone (10 nM) and prostaglandin E2 (10 microM). Cykloheximide (1 microM) inhibited calcium release elicited by Cd, prostaglandin E2 and parathyroid hormone. Cd-induced calcium release was linearly increased from 24 to 72 hr of culture. Production of prostaglandin E2 by the bone specimens was dose-dependently stimulated by Cd and inhibited by 1 microM indomethacin. Cd-induced calcium release was inhibited by acetazolamide (100 microM), indomethacin (1 microM) and ibuprofen (10 microM). Prostaglandin E2-stimulated calcium release was not inhibited by indomethacin. Exposure to 32 microM Cd, present during a 48-hr incubation period, significantly decreased prostaglandin E2-stimulated calcium release from 38.9% to 29.8%. Calcium release induced by parathyroid hormone was more sensitive to inhibition by the metal (i.e., Cd concentrations of 0.2 and 32 microM decreased the release from 37.7% to 31% and 19%, respectively). Cd present in the culture medium during a 48-hr incubation dose-dependently inhibited the activity of alkaline phosphatase and tartrate-resistant acid phosphatase in the bones but did not influence the activity of carbonic anhydrase. We conclude that Cd has a direct stimulatory effect on bone resorption, and this effect is dependent on prostaglandin production and also on protein synthesis. On the other hand, Cd also has an inhibitory effect on bone resorption (i.e., resorption is inhibited by higher concentrations of the metal). Moreover, Cd may impair bone formation by impeding the activity of alkaline phosphatase.

Comparative effect of cadmium on osteoblastic cells and osteoclastic cells

Cadmium(Cd) has been thought to disturb the bone metabolism directly. The mechanism for the bone lesion is unknown, however. To examine the effects of cadmium on bone metabolism, we compared its effects on osteoblasts and osteoclasts in vitro. We used an established cell line, MC3T3-E1, as osteoblasts and tartrate resistant acid phosphatase (TRACP)-positive multi-nucleated cells (MNC) formed by a bone marrow culture system as osteoclasts. Alkaline phosphatase (ALP) activity was decreased by 10(-7) M Cd and DNA content and hydroxyproline content of osteoblastic cells were decreased by 10(-5) M Cd. Cadmium at 10(-7) M inhibited the osteoclastic cell formation from mouse bone marrow in the presence of 10(-8) M 1 alpha, 25(OH)2 vitamin D3. A 100-fold higher concentration of zinc(Zn) simultaneously added to the cadmium-containing medium prevented the toxicity of cadmium to osteoclastic cells as observed in the culture of osteoblastic cells. These results indicate that both bone formation and bone resorption are inhibited by cadmium. The responses of osteoclasts and osteoblasts to cadmium in this culture system were the same and the responses of cadmium-damaged osteoblasts and osteoclasts to zinc were also similar. These results suggest that another mechanism by which cadmium could cause bone damage should be considered in addition to the specific induction of osteoclastic cells by Cd.

Stimulative effects of cadmium on bone resorption in neonatal parietal bone resorption

Effects of cadmium on bone resorption were investigated using neonatal mouse parietal bone culture system. Cadmium at 0.5 microM and above stimulated hydroxyproline release as well as 45Ca release. As cadmium-stimulated bone resorption was inhibited by calcitonin, bone resorption induced by cadmium is osteoclast-mediated bone resorption. CI-1, collagenase inhibitor, depressed cadmium-stimulated bone resorption in a dose-dependent manner. Osteoblasts are also involved in cadmium-induced bone resorption. Indomethacin-inhibited cadmium-stimulated bone resorption and cadmium-treated bones released prostaglandin E2 to a greater extent than untreated bones. Cadmium-stimulated bone resorption was shown to be dependent on the production of prostaglandin E2. 3-Isobutyl-1-methylxanthine potentiated cadmium-stimulated bone resorption and verapamil depressed it. It is possible that an increase in levels of cAMP and calcium ion in bone cells is involved in cadmium-induced bone resorption. From these results, cadmium was found to stimulate osteoclast-mediated bone resorption which is dependent on prostaglandin E2. Second messengers in cadmium-induced bone resorption may be cAMP and calcium ion.

Cadmium stimulates prostaglandin E2 synthesis in osteoblast-like cells, MC3T3-E1

The effect of Cd on prostaglandin E2 production in osteoblasts was studied using cloned osteoblast-like cells, MC3T3-E1, which were established from new-born mouse calvaria. Treatment of the cells with Cd caused a dose- (0-10 microM) and time- (0-24 h) dependent increase in the release of prostaglandin E2 from the cells into the culture medium. A lag time of 4 h was required for the onset of the phenomenon. The release of [14C]arachidonic acid from prelabeled cell membrane was little influenced by the Cd treatment, while conversion of [14C]arachidonic acid to prostaglandin E2 by the homogenate of the cells treated with Cd was enhanced as compared to that by untreated cells. The stimulatory effect of Cd on prostaglandin E2 production was abolished in the presence of cycloheximide (100 ng/ml). By Western blot analysis with polyclonal rabbit anti-cyclooxygenase antibody, it was revealed that Cd treatment augmented the amount of immunoreactive cyclooxygenase in the cells. These results strongly suggest that Cd stimulates prostaglandin E2 production through the induction of cyclooxygenase in MC3T3-E1 cells. This effect of Cd may be involved in the mechanisms of Cd-induced bone injury.

Cadmium stimulates prostaglandin E2 production and bone resorption in cultured fetal mouse calvaria

The effect of cadmium on bone resorption was studied using isolated fetal mouse calvaria. Cadmium stimulated bone resorption and PGE2 production in a dose-dependent manner. The minimal concentration of cadmium which stimulated bone resorption was the same as that stimulated prostaglandin E2 production. The stimulatory effects of cadmium (0.5 microM) on bone resorption and prostaglandin E2 production were completely inhibited by indomethacin. Exogenously added PGE2 (100ng/ml) abolished the inhibitory effect of indomethacin on bone resorption stimulated by cadmium. These results strongly indicate that cadmium stimulates bone resorption via prostaglandin E2 mediated mechanism.

Cadmium accelerates bone loss in ovariectomized mice and fetal rat limb bones in culture

Loss of bone mineral after ovariectomy was studied in mice exposed to dietary cadmium at 0.25, 5, or 50 ppm. Results show that dietary cadmium at 50 ppm increased bone mineral loss to a significantly greater extent in ovariectomized mice than in sham-operated controls. These results were obtained from two studies, one in which skeletal calcium content was determined 6 months after ovariectomy and a second in which 45Ca release from 45Ca-prelabeled bones was measured immediately after the start of dietary cadmium exposure. Furthermore, experiments with 45Ca-prelabeled fetal rat limb bones in culture demonstrated that Cd at 10 nM in the medium, a concentration estimated to be in the plasma of mice exposed to 50 ppm dietary Cd, strikingly increased bone resorption, from 27 +/- 2% (mean +/- SEM) 45Ca release in cultures with no added cadmium to 68 +/- 6% release in cultures containing cadmium (n = 4). These in vitro results indicate that cadmium may enhance bone mineral loss by a direct action on bone. Results of the in vivo studies are consistent with a significant role of cadmium in the etiology of Itai-Itai disease among postmenopausal women in Japan and may in part explain the increased risk of postmenopausal osteoporosis among women who smoke.

Interaction of cadmium ions with calcium hydroxyapatite crystals: a possible mechanism contributing to the pathogenesis of cadmium-induced bone diseases

Cadmium ions adsorb onto calcium hydroxyapatite crystals (HA) and are as effective as inorganic pyrophosphate and aluminum ions in retarding the rate of in vitro dissolution of HA. In contrast, cadmium ions have no important retarding effect on the growth of HA, but are built into the crystals, thus making them very resistant to subsequent dissolution. These effects could interfere with bone remodeling, with cadmium protecting normal sites of resorption and thus causing resorption at pathological sites.

Influence of cadmium on the chain dynamics of collagen in rat tail tendon

The molecular mobility of the chain dynamics of collagen was investigated by the thermally stimulated creep method on rat tail tendon after oral administration of cadmium (8 mg.kg-1.day-1) for six weeks. The high resolving power of the technique shows two manifestations of the pseudolathyrogen effect of cadmium: the polar side-chains of collagen, mobile in the immature specimen, which are cross-linked and so immobile in the mature specimen, remain mobile in the cadmium-treated mature specimen. There is also a subsequent decrease in the number of water molecules linked by two hydrogen atoms bound to the tropocollagen molecules. Probably these molecular modifications inhibit mineralization of the organic matrix and so osteogenesis.

Interaction between cadmium and copper in relation to the collagen metabolism of embryonic chick bone in tissue culture

To investigate the interaction between Cd and Cu in relation to the content of collagen in bone, femurs obtained from 9-day-old chick embryos were cultivated with a combination of Cd and Cu concentrations of 8.9 microM and below for 4 days. When 2.23 or 4.45 microM Cd was added to the medium containing 4.45 or 8.90 microM Cu, the presence of both Cd and Cu caused a remarkable decrease in collagen synthesis compared with a decrease in collagen synthesis caused by either Cd or Cu alone. The results show that Cd and Cu caused an interactive inhibition of collagen synthesis, which was not due to an increase in collagen degradation by Cd and Cu. At concentrations showing inhibition, Cd caused an increase in Cu content and Cu caused an increase in Cd content. The increase in Cd content was mainly caused by the accumulation of Cd in bone mineral. The increase in Cu content was due to binding to metallothionein-like protein in the cytosol induced by Cd. The relationship between inhibition and the increase in both Cd and Cu was not confirmed after division of the bone into diaphysis and epiphysis. The present study showed that Cu aggravated the bone matrix damage caused by Cd.

The effect of cadmium on the collagen solubility of embryonic chick bone in tissue culture

The effect of cadmium (Cd) on the solubility of bone collagen was examined in cultured tibiae from 9-day chick embryos. The solubility of collagen was not significantly increased by 8.9 microM Cd, but showed a significant increase at 13.4 microM Cd. As the [3H]hydroxyproline (Hyp) formation was inhibited by Cd at 8.9 and 13.4 microM [3H]Hyp formation and collagen solubility were investigated in the presence of 200 microM Fe2+, a metal which is known to prevent the inhibitory effects of Cd on prolyl hydroxylase in vitro. Fe affected neither a decrease in [3H]Hyp formation nor an increase in collagen solubility caused by Cd. This suggests that a Cd-induced increase in collagen solubility may be due to the decrease of lysyl oxidase activity, not to the formation of underhydroxylated collagen. Zn at 48 and 134 microM depressed the Cd-induced increase in collagen solubility, but caused no increase in collagen solubility. Our present and previous results suggest that Zn can protect the disturbance of both the collagen synthesis and the collagen cross linking caused by Cd.

The effect of aluminum on the metabolism of embryonic chick bone in tissue culture

The effect of aluminum (Al) on bone metabolism was assessed in organ cultures of embryonic chick bone. Al of 10(-4)M and above caused an inhibitory effect on mineralization without inhibiting matrix formation and a stimulative effect on demineralization without stimulating matrix degradation. Therefore, Al was shown to influence the mineral metabolism of bone.

In vitro assessment of the toxicity of metal compounds : IV. Disposition of metals in cells: Interactions with membranes, glutathione, metallothionein, and DNA

This review has focused on several parameters related to the delivery of carcinogenic metal compounds to the cell nucleus as a basis for understanding the intermediates formed between metals and cellular components and the effect of these intermediates on DNA structure and function. Emphasis has been placed on metal interactions at the cellular membrane, including lipid peroxidation, metal interactions with glutathione and their relation to membrane injury, and metal effects on the membrane bound enzyme, Na(+)/K(+) ATPase. Metal binding to metallothionein is also considered, particularly as related to transport and utilization of metal ions and to genetic defects in these processes exemplified in Menkes disease. The ability of cadmium to induce the synthesis of metallothionein more strongly than zinc is also discussed in relation to other toxic and carcinogenic metals. The effects of metal ions on purified DNA and RNA polymerase systems are presented with some of the recent studies using biological ligand-metal complexes. This review points out the importance of considering how metals affect in vitro systems when presented as ionic forms or complexed to relevant biological ligands.