Vanadyl(IV) complexes with saccharides. Bioactivity in osteoblast-like cells in culture

Complexes of vanadyl(IV) with 4 monosaccharides and 5 disaccharides were tested in 2 osteoblast-like cell lines (MC3T3E1 and UMR106). Many complexes caused stimulation of UMR106 proliferation (120% basal) in the range of 2.5 to 25 micromol/L. In the nontransformed osteoblasts, some vanadyl-saccharide complexes stimulated the mitogenesis (115% basal) in the same range of concentration. The glucose and sucrose complexes were the most efficient inhibitory agents (65% and 88% of inhibition vs. basal, respectively) for tumoral cells at 100 micromol/L. The galactose and turanose complexes exerted a similar effect in the nontransformed osteoblasts. On the other hand, all the complexes promoted the phosphorylation of the extracellular regulated kinases (ERKs). All together, these results indicate that the stimulation of ERKs is not the only factor that plays a role in the proliferative effects of vanadium derivatives since some compounds were inhibitory proliferating agents. Cell differentiation was evaluated by alkaline phosphatase specific activity and collagen synthesis in UMR106 cells. All the complexes inhibited alkaline phosphatase activity, with galactose complex as the most effective compound (IC50 = 43 micromol/L). The complex with the trehalose TreVO was the most effective agent to stimulate collagen synthesis (142% basal) and glucose consumption (132% basal). A cytosolic tyrosine protein kinase and the kinase-3 of glycogen synthase seem to be involved in the stimulation of glucose consumption by vanadium derivatives. In this series, only TreVO gathered the characteristics of a good insulin mimetic and osteogenic drug. In addition, this complex was a good promoting agent of nontransformed osteoblast proliferation, whereas it inhibited tumoral osteoblasts. GluVO, the complex with glucose, was also more toxic for tumoral than for nontransformed cells. These 2 vanadium derivatives are good potential antitumoral drugs. All the results suggest that the biological effects of vanadium compounds are a complex phenomenon influenced by the complexation, the dose, and the nature of the ligands and the cells.     

Osteogenic activity of vanadyl(IV)-ascorbate complex: evaluation of its mechanism of action

We have previously shown that different vanadium(IV) complexes regulate osteoblastic growth. Since vanadium compounds are accumulated in vivo in bone, they may affect bone turnover. The development of vanadium complexes with different ligands could be an alternative strategy of use in skeletal tissue engineering. In this study, we have investigated the osteogenic properties of a vanadyl(IV)-ascorbate (VOAsc) complex, as well as its possible mechanisms of action, on two osteoblastic cell lines in culture. VOAsc (2.5-25 microM) significantly stimulated osteoblastic proliferation (113-125% basal, p<0.01) in UMR106 cells, but not in the MC3T3E1 cell line. VOAsc (5-100 micrioM) dose-dependently stimulated type-I collagen production (107-156% basal) in osteoblasts. After 3 weeks of culture, 5-25 microM VOAsc increased the formation of nodules of mineralization in MC3T3E1 cells (7.7-20-fold control, p<0.001). VOAsc (50-100 microM) significantly stimulated apoptosis in both cell lines (170-230% basal, p<0.02-0.002), but did not affect reactive oxygen species production. The complex inhibited alkaline and neutral phosphatases from osteoblastic extracts with semi-maximal effect at 10 microM doses. VOAsc induced the activation and redistribution of P-ERK in a time- and dose-dependent manner. Inhibitors of the mitogen activated protein kinases (MAPK) pathway (PD98059 and UO126) partially blocked the VOAsc-enhanced osteoblastic proliferation and collagen production. In addition, wortmanin, a PI-3-K inhibitor and type-L channel blocker nifedipine also partially abrogated these effects of VOAsc on osteoblasts. Our in vitro results suggest that this vanadyl(IV)-ascorbate complex could be a useful pharmacological tool for bone tissue regeneration.     

Synthesis, characterization, antitumoral and osteogenic activities of quercetin vanadyl(IV) complexes

The development of new vanadium derivatives with organic ligands, which improve the beneficial actions (insulin-mimetic, antitumoral) and decrease the toxic effects, is of great interest. A good candidate for the generation of a new vanadium compound is the flavonoid quercetin because of its own anticarcinogenic effect. The complex [VO(Quer)₂EtOH] _n (QuerVO) has been synthesized and characterized by means of different spectroscopic techniques (UV–vis, Fourier transform IR, electron paramagnetic resonance) and its magnetic and stability properties. The inhibitory effect on bovine alkaline phosphatase (ALP) activity has been tested for the free ligand, the complex as well as for the vanadyl(IV) (comparative purposes). The biological activity of the complex on the proliferation of two osteoblast-like cells in culture, a normal one (MC3T3E1) and a tumoral one (UMR106), has been compared with that of the vanadyl(IV) cation and quercetin. The differentiation osteoblast markers ALP specific activity and collagen synthesis have been also tested. In addition, the effect of QuerVO on the activation of the extracellular regulated kinase (ERK) pathway is reported. The bone antitumoral effect of quercetin alone was established with the cell proliferation assays (it inhibits the proliferation of the tumoral cells and does not exert any effect on the normal osteoblasts). Moreover, the complex exerts osteogenic effects since it stimulates the type I collagen production and is a weak inhibitory agent upon ALP activity. Finally, QuerVO stimulated the ERK phosphorylation in a dose–response manner and this activation seems to be involved as one of the possible mechanisms for the biological effects of the complex.     

Spectroscopic Characterization of an Oxovanadium(IV) Complex of Oxodiacetic Acid and o-Phenanthroline. Bioactivity on Osteoblast-Like Cells in Culture

The oxovanadium(IV) complex of oxodiacetic acid (H(2)ODA) and o-phenanthroline of stoichiometry [VO(ODA)(ophen)]·1.5H(2)O, which presents the interesting tridentate OOO coordination, was thoroughly characterized by infrared, Raman, and electronic spectroscopies. The biological activity of the complex on the cell proliferation was tested on osteoblast-like cells (MC3T3E1 osteoblastic mouse calvaria-derived cells and UMR106 rat osteosarcoma-derived cells) in culture. The complex caused inhibition of cellular proliferation in both osteoblast cell lines in culture, but the cytotoxicity was stronger in the normal (MC3T3E1) than in the tumoral (UMR106) osteoblasts.     

Spectroscopic Characterization of a VO<Superscript>2+</Superscript> Complex of Oxodiacetic Acid and its Bioactivity on Osteoblast-like Cells in Culture

The oxovanadium(IV) complex of oxodiacetic acid (H₂oda) of stoichiometry [VO(oda)(H₂O)₂], which presents an unprecedented tridentate OOO coordination, was thoroughly characterized by infrared, Raman, electronic, and electron paramagnetic resonance spectroscopies. The biological activity of the complex on the cell proliferation and differentiation was tested on osteoblast-like cells (MC3T3E1 osteoblastic mouse calvaria-derived cells and UMR106 rat osteosarcoma-derived cells) in culture. The complex caused inhibition of cellular proliferation in both osteoblast-like cells in culture, but the cytotoxicity was stronger in the normal (MC3T3E1) than in the tumoral (UMR106) osteoblasts. The effect of the complex in cell differentiation was tested through the specific activity of alkaline phosphatase of the UMR106 cells because they expressed a high activity of this enzyme. What occurs with other vanadium compounds [VO(oda)(H₂O)₂] is an inhibitory agent of osteoblast differentiation.     

Biological effects of a complex of vanadium(V) with salicylaldehyde semicarbazone in osteoblasts in culture: Mechanism of action

Vanadium compounds display important pharmacological actions in vivo and in vitro systems. Semicarbazones are versatile ligands with therapeutic effects. Herein, we report the effects of V^VO₂(salicylaldehydesemicarbazone) (V(V)-Salsem) on two osteoblast cell lines in culture (MC3T3-E1 and UMR106). V(V)-Salsem inhibited cell proliferation in a dose response manner. At 100 μM, the complex caused an inhibition of ca. 48% and 38% for the normal and the tumoral osteoblasts, respectively (p < 0.001). This inhibition could be partially reversed to 35% and 28% by NAC (N-acetylcysteine) and a mixture of vitamins E and C. Changes in cell proliferation correlated with morphological alterations and the disruption of actin cytoskeleton fibers. The complex also enhanced the level of ROS (reactive oxygen species) up to ca. 100% over basal in both cell lines. Activation of ERK signalling cascade was also observed. These events led to apoptosis (up to 44% in MC3T3-E1 and 33% in UMR106 cells). Scavengers of ROS and inhibitors of ERK cascade allowed to elucidate the mechanisms involved in the cytotoxicity. In conclusion, V(V)-Salsem displayed cytotoxic effects on osteoblasts in culture through the production of free radicals and the activation of ERK cascade. These mechanisms triggered the apoptotic events that conveyed to cell death.     

Synthesis, characterization, and biological activity of oxovanadium(IV) complexes with polyalcohols

Oxovanadium(IV) complexes of the polyalcohols sorbitol, galactitol, and mannitol, of stoichiometry Na(2)[VO(L)(2)].H(2)O, were obtained from aqueous alkaline solutions. They were characterized by elemental analysis, infrared and UV-vis spectroscopies, thermoanalytical (thermogravimetric and differential thermal analysis) data, and magnetic susceptibility measurements. The biological activities of the complexes on the proliferation, differentiation, and glucose consumption were tested on osteoblast-like cells (MC3T3E1 osteoblastic mouse calvaria-derived cells and UMR106 rat osteosarcoma-derived cells) in culture. The three complexes exerted a biphasic effect on cell proliferation, being slight stimulating agents at low concentrations and inhibitory in the range of 25-100 microM. All the complexes inhibited cell differentiation in tumor osteoblasts. Their effects on glucose consumption were also discussed. The free ligands did not show any effect on the studied biological parameters.     

Dinuclear copper(II) complexes with valsartan. Synthesis, characterization and cytotoxicity

Two novel dinuclear complexes involving the antihypertensive drug valsartan and copper(II) ion have been prepared in water and DMSO. The complex compositions were determined as: [Cu(vals)(H₂O)₃]₂.6H₂O and [Cu(vals)(H₂O)₂DMSO]₂.2H₂O. They were thoroughly characterized by elemental and thermal analysis, spectrophotometric titrations and UV-visible, diffuse reflectance, FTIR, Raman and EPR spectroscopies. No effect of the ligand on two tested osteoblastic cell lines in culture (one normal MC3T3E1 and one tumoral UMR106) was observed in concentrations up to 100 μM. Higher concentrations of Valsartan are required to induce cytotoxicity in both cell lines. The antiproliferative effect of the tested complex ([Cu(vals)(H₂O)₃]₂.6H₂O) in a dose-response manner, was higher in the UMR106 osteoblastic cell line than that of the MC3T3E1 normal line at concentrations ≥ 100 μM. Morphological alterations are in accordance with proliferative observations.     

Antioxidant,DNA cleavage,and cellular effects of silibinin and a new oxovanadium(IV)/silibinin complex

A new complex of the oxovanadium(IV) cation with the flavolignan silibinin has been synthesized and characterized. Vanadium compounds show interesting biological and pharmacological properties and some of them display antitumoral actions. Flavonoids are part of a larger group of antioxidant compounds called polyphenols which may inhibit the proliferation and growth of cancer cells. The antioxidant and antitumoral effects of silibinin and its oxovanadium(IV) complex were investigated. Silibinin acted as a very strong antioxidant and its complexation with oxovanadium(IV) improved this behavior. Besides, the generation of reactive oxygen species (ROS) by this compound was favored in tumoral (UMR106) cells and correlated with the deleterious behavior in the proliferation of this cell line. Conversely, silibinin did not exert any effect on the proliferation of normal osteoblasts (MC3T3E1). The cytotoxic action and ROS generation of the oxovanadium(IV) complex was more effective in tumoral cells. This behavior was not consistent with cleaving DNA of plasmid DNA pA1 because no significant cleaving activity was observed in both cases. These results suggest that the main deleterious mechanisms may take place through cytotoxic effects more than genotoxic actions. A comparison with our own findings on the behavior of other flavonoids and their vanadyl(IV) complex has also been performed.     

AGE-R3/galectin-3 expression in osteoblast-like cells: Regulation by AGEs

The accumulation of irreversible advanced glycation endproducts (AGEs) on long-lived proteins, and the interaction of AGEs with cellular receptors such as AGE-R3/galectin-3 and RAGE, are considered to be key events in the development of long-term complications of diabetes mellitus, Alzheimer's disease, uremia and ageing. The aim of this study was to investigate the expression and sub-cellular distribution of galectin-3, as well as its possible modulation by AGEs, in MC3T3E1 mouse calvaria-derived osteoblasts and in UMR 106 rat osteosarcoma cells. Both osteoblastic lines were cultured either with control bovine serum albumin (BSA) or with AGEs-BSA for 48 h. Cells were evaluated for galectin-3 expression by fixing and immunofluorescent microscopic analysis; or Western blot analysis of whole cell extracts, sub-cellular fractions and culture media. Both cell lines express 30 kDa (monomeric) galectin-3, although expression was about 15-fold lower in the UMR106 osteosarcoma cells. Dimeric (70 kDa) galectin-3 was additionally observed in the UMR106 cells. Immunofluorescent analysis of galectin-3 distribution showed a diffuse cytoplasmic and strong nuclear pattern in MC3T3E1 osteoblasts, and a patchy cytoplasmic pattern in UMR106 cells. Western blot analysis for both cell lines showed that galectin-3 was mainly found in the cytoplasm and in minor amounts in the microsomal fraction, while considerable amounts were secreted into the culture media. Exposure to 100-200 microg/mL AGEs-BSA increased the cellular content of 30 kDa galectin-3 (20-25% for MC3T3E1 and 35-70% for UMR106 versus control BSA, p < 0.05), and decreased the culture media levels of galectin-3 (10-20% for MC3T3E1 and for UMR106 versus control BSA, p < 0.05). These results confirm the expression of galectin-3 in osteoblastic cells, and suggest different levels and sub-cellular distribution of this protein in transformed versus non-transformed osteoblasts. Osteoblastic exposure to AGEs alters their expression and secretion of galectin-3, which could have significant consequences on osteoblast metabolism and thus on bone turnover.     

Effect of vanadium compounds on the lipid organization of liposomes and cell membranes

The influence of vanadate on the adsorption properties of Merocyanine 540 (MC540) to UMR cells was studied by means of specrofluorometry. An increment in the fluorescence was observed in the osteoblasts incubated with 0.1 mM vanadate. This effect could be interpreted in terms of vanadate inhibitory effects on aminotraslocase activity. However, vanadate promotes a similar behavior to that found in UMR 106 cells when it was added to lipid vesicles composed of phosphatidylcholine. The effect of vanadium in different oxidation states, such as vanadate(V) and vanadyl(IV) on lipid membrane properties was examined in large unilamellar vesicles by means of spectrofluorometry employing different probes. Merocyanine 540 and 1,6-diphenylhexatriene were used in order to sense the changes at interfacial and hydrophobic core of membranes, respectively. In contrast to vanadate, vanadyl decreased the fluorescence of MC540. Both vanadium compounds slightly perturbed the hydrocarbon core. The results can be interpreted by the specific adsorption of both compounds on the polar head groups of phospholipid and suggest a possible influence of vanadium compounds on the lipid organization of cell membranes.     

Role of oxidative stress in the antitumoral action of a new vanadyl(IV) complex with the flavonoid chrysin in two osteoblast cell lines: relationship with the radical scavenger activity

The new complex [VO(chrysin)₂EtOH]₂ (VOchrys) has been synthesized and thoroughly characterized. Fourier transform IR, UV–vis, diffuse reflectance, and EPR spectroscopies as well as elemental analysis and thermal measurements were performed. In solution, different species could be detected by EPR spectroscopy as a function of the ligand-to-metal ratio. The stoichiometry of the chelate complex formed at pH 5 was also determined by spectrophotometric titrations. Since flavonoids are natural antioxidant compounds, the antioxidant capacity of chrysin and its vanadyl(IV) complex was investigated using different radicals. Chrysin and its complex were not able to diminish the level of superoxide and 1,1-diphenyl-2-picrylhydrazyl radicals to a great extent. In contrast, they were strong scavengers for 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid diammonium salt radical cations and OH· radicals with a greater potency for VOchrys. Taking into account their selective antioxidant properties, we investigated the bioactivity of these compounds in two osteoblast-like cells in culture. Chrysin and VOchrys caused an inhibition of cell proliferation in MC3T3E1 normal osteoblasts and UMR106 tumor cells in a dose-response manner, with a greater effect in the latter cell line. The generation of reactive oxygen species (ROS) was evaluated in both cell lines and a correlation could be established between the antiproliferative effects of chrysin and the increase in the ROS levels. The complex did not generate types of ROS that can be detected by the dihydrorhodamine 123 technique so the antiproliferative effect may be attributed to the formation of other radicals such as superoxide, which is not detected by this probe. The morphological alterations were in agreement with these changes.     

Advanced glycation end-products (AGEs) induce concerted changes in the osteoblastic expression of their receptor RAGE and in the activation of extracellular signal-regulated kinases (ERK)

An increase in the interaction between advanced glycation end-products (AGEs) and their receptor RAGE is believed to contribute to the pathogenesis of chronic complications of Diabetes mellitus, which can include bone alterations such as osteopenia. We have recently found that extracellular AGEs can directly regulate the growth and development of rat osteosarcoma UMR106 cells, and of mouse calvaria-derived MC3T3E1 osteoblasts throughout their successive developmental stages (proliferation, differentiation and mineralisation), possibly by the recognition of AGEs moieties by specific osteoblastic receptors which are present in both cell lines. In the present study we examined the possible expression of RAGE by UMR106 and MC3T3E1 osteoblastic cells, by immunoblot analysis. We also investigated whether short-, medium- or long-term exposure of osteoblasts to extracellular AGEs, could modify their affinity constant and maximal binding for AGEs (by 125I-AGE-BSA binding experiments), their expression of RAGE (by immunoblot analysis) and the activation status of the osteoblastic ERK 1/2 signal transduction mechanism (by immunoblot analysis for ERK and P-ERK). Our results show that both osteoblastic cell lines express readily detectable levels of RAGE. Short-term exposure of phenotypically mature osteoblastic UMR106 cells to AGEs decrease the cellular density of AGE-binding sites while increasing the affinity of these sites for AGEs. This culture condition also dose-dependently increased the expression of RAGE and the activation of ERK. In proliferating MC3T3E1 pre-osteoblasts, 24–72 h exposure to AGEs did not modify expression of RAGE, ERK activation or the cellular density of AGE-binding sites. However, it did change the affinity of these binding sites for AGEs, with both higher- and lower-affinity sites now being apparent. Medium-term (1 week) incubation of differentiated MC3T3E1 osteoblasts with AGEs, induced a simultaneous increase in RAGE expression and in the relative amount of P-ERK. Mineralising MC3T3E1 cultures grown for 3 weeks in the presence of extracellular AGEs showed a decrease both in RAGE and P-ERK expression. These results indicate that, in phenotypically mature osteoblastic cells, changes in ERK activation closely follow the AGEs-induced regulation of RAGE expression. Thus, the AGEs-induced biological effects that we have observed previously in osteoblasts, could be mediated by RAGE in the later stages of development, and mediated by other AGE receptors in the earlier pre-osteoblastic stage.     

Antioxidant effects of the VO(IV) hesperidin complex and its role in cancer chemoprevention

Vanadium compounds are known for a variety of pharmacological properties. Many of them display antitumoral and osteogenic effects in several cell lines. Free radicals induce the development of tumoral processes. Natural polyphenols such as flavonoids have antioxidant properties since they scavenge different free radicals. For these reasons it is interesting to investigate the effects of a new complex generated between the vanadyl(IV) cation and the flavonoid hesperidin. The complex has been synthesized and characterized by physicochemical methods. Spectroscopic analysis revealed a 1:1 stoichiometry of ligand:VO and coordination by deprotonated cis-hydroxyl groups to the disaccharide moiety of the ligand. The complex improves the superoxide dismutase (SOD)-like activity of the ligand, but the scavenging of other radicals tested does not change upon complexation. When tested on two tumoral cell lines in culture (one of them derived from a rat osteosarcoma UMR106 and the other from human colon adenocarcinoma Caco-2), the complex enhanced the antiproliferative effects of the free ligand, and this effect correlated with the morphological alterations toward apoptosis. Also, on the osteoblastic cell line the complex stimulated cell proliferation and collagen type I production at low concentrations. At higher doses the complex behaved as a cytotoxic compound for the osteoblasts.     

Relationship between actions of transforming growth factor (TGF)-β and cell surface expression of its receptors in clonal osteoblastic cells

Various osteoblastic cell lines were examined for the relationship between the presence of cell-surface transforming growth factor (TGF)-β receptors and the synthesis of matrix proteins with their responsiveness to TGF-β. Treatment with TGF-β1 inhibited proliferation and stimulated proteoglycan and fibronectin synthesis in MC3T3-E1 and MG 63 cells. The major proteoglycans synthesized by these cells were decorin and biglycan, and TGF-β1 markedly stimulated the synthesis of decorin in MC3T3-E1 and of biglycan in MG 63 cells. SaOS 2 and UMR 106 cells synthesized barely detectable amounts of decorin or biglycan, and TGF-β1 did not stimulate the synthesis of these proteoglycans. In SaOS 2 cells, however, TGF-β1 enhanced fibronectin synthesis. TGF-β1 did not show any of these effects in UMR 106 cells. Receptor cross-linking studies revealed that only MC3T3-E1 and MG 63 cells had both types I and II signal-transducing receptors for TGF-β in addition to betaglycan. SaOS 2 cells possessed type I but no type II receptor on the cell surface. In contrast, SaOS 2 as well as MC3T3-E1 and MG 63 cells expressed type II receptor mRNA by Northern blot analysis, and cell lysates contained type II receptor by Western blot analysis. Thus, it appears that type II receptor present in SaOS 2 cells is not able to bind TGF-β1 under these conditions. UMR 106 cells with no response to TGF-β1 had neither of the signal-transducing receptors by any of the analyses. These observations using clonal osteoblastic cell lines demonstrate that the ability of osteoblastic cells to synthesize bone matrix proteoglycans is associated with the responsiveness of these cells to TGF-β1, that the responsiveness of osteoblastic cells to TGF-β1 in cell proliferation and proteoglycan synthesis correlates with the presence of both types I and II receptors, and that the effect of TGF-β1 on fibronectin synthesis can develop with little binding of TGF-β1 to type II receptor if type I receptor is present. It is suggested that the combination of cell-surface receptors for TGF-β determines the responsiveness of osteoblastic cells to TGF-β and that changes in cell-surface TGF-β receptors may play a role in the regulation of matrix protein synthesis and bone formation in osteoblasts. © 1995 Wiley-Liss, Inc.     

Contribution of heme-propionate side chains to structure and function of myoglobin: chemical approach by artificially created prosthetic groups

The synthesis and spectral and magnetic characterization of VO(2+) complexes with Ibuprofen (2-(4-isobutylphenyl)propionic acid), Naproxen (6-methoxy-alpha-methyl-2-naphthalene acetic acid) and Tolmetin (1-methyl-5-(4-methylbenzoyl)-1H-pyrrole-2-acetic acid) were studied. The complexes [VO(Ibu)(2)] x 5CH(3)OH, [VO(Nap)(2)] x 5CH(3)OH and [VO(Tol)(2)] were obtained from methanolic solutions under nitrogen atmosphere. The biological activities of these complexes on the proliferation of two osteoblast-like cells in culture (MC3T3E1 and UMR106) were compared with that of the vanadyl(IV) cation. The complexes exhibited different effects depending on the concentration and the cellular type, while no effect was observed for their parent drugs.     

Vanadyl and vanadate inhibit Ca2+ transport systems of the adipocyte plasma membrane and endoplasmic reticulum

Vanadate and vanadyl have many insulin-mimetic effects on cellular metabolism and also have been shown to alter cellular Ca2+ fluxes. In this report, vanadate and vanadyl, like insulin, are shown to inhibit the plasma membrane (Ca2+ + Mg2+)-ATPase/Ca2+ transport system as well as Ca2+ transport by endoplasmic reticulum from rat adipocytes. Ca2+ transport by the endoplasmic reticulum was inhibited half-maximally (I50) by vanadate and vanadyl at concentrations of 30 and 33 microM, respectively. Inhibition of the plasma membrane Ca2+ transport by vanadate and vanadyl was less sensitive, with I50 values of 144 and 92 microM, respectively. These I50 values for plasma membrane Ca2+ transport were similar when measured under conditions of calmodulin-stimulated and non-calmodulin-stimulated Ca2+ transport. The predominant effect of both ions on the kinetic parameters of Ca2+ transport was a substantial decrease in the Vmax by 43-46% for both transport systems. An increase in intracellular Ca2+ following the inhibition of the (Ca2+ + Mg2+)-ATPase/Ca2+ pump in the plasma membrane and endoplasmic reticulum by these vanadium ions may result, at least in part, in the observed insulin-mimetic alterations in cellular metabolism.     

Vanadium derivatives act as growth factor — mimetic compounds upon differentiation and proliferation of osteoblast-like UMR106 cells

The effect of different vanadium compounds on proliferation and differentiation was examined in osteoblast-like UMR106 cells. Vanadate increased the cell growth in a biphasic manner, the higher doses inhibiting cell progression. Vanadyl stimulated cell proliferation in a dose-responsive manner. Similar to vanadate, pervanadate increased osteoblast-like cell proliferation in a biphasic manner but no inhibition of growth was observed. Vanadyl and pervanadate were stronger stimulators of cell growth than vanadate. Only vanadate was able to regulate the cell differentiation as measured by cell alkaline phosphatase activity. These results suggest that vanadium derivatives behave like growth factors on osteoblast-like cells and are potential pharmacological tools in the control of cell growth.     

Vitamin A effects on UMR 106 osteosarcoma cells are not mediated by specific cytosolic receptors.

Retinol and retinoic acid at 20 microM altered cell morphology and inhibited cell proliferation of UMR 106 osteosarcoma cells in culture. No specific cytosolic binding proteins for retinol could be detected.     

Interactive regulation of signalling pathways in bone cells: possible modulation of PGE2-stimulated adenylyl cyclase activity by protein kinase C

We have reported previously that tumour-promoting phorbol esters modulate both basal and vasoactive intestinal polypeptide (VIP)-stimulated adenylyl cyclase activity in GH3 (an established pituitary cell line). Here, we probe the receptor and cell specificity of this response. Experiments were performed in the presence of isobutylmethylxanthine. Unlike the response in GH3 cells, the tumour-promoting phorbol ester (tetradecanoyl phorbol acetate (TPA] did not affect either basal adenylyl cyclase activity nor VIP-stimulated activity in the rat osteosarcoma subclones UMR 106-01 and UMR 106-06. In addition, the cyclase responses to parathyroid hormone (PTH), and, in the case of UMR 106-06, to calcitonin were unaffected by tumour-promoting phorbol ester. However, prostaglandin E2-stimulated cyclase activity in both of these subclones was attenuated in a dose-dependent manner.