The effect of cellular age on zinc levels in untreated and zinc-treated human diploid fibroblasts

In vitro evaluation of novel titania-containing borate bioactive glass scaffolds

Titanium-containing borate bioactive glass scaffolds (0, 5, 15, and 20 mol %, identified as BRT0, BRT1, BRT3, and BRT4) with a microstructure similar to that of human trabecular bone were prepared and evaluated in vitro for potential bone loss applications in revision total knee arthroplasty (rTKA). Methyl thiazolyl tetrazolium (MTT) cell viability assays of scaffold ion release extracts revealed that BRT0 scaffolds (0 mol % titanium) inhibited cell proliferation and activity at day 14. At day 30, all scaffold extracts decreased cell proliferation and activity significantly. However, live/dead cell assay results demonstrated that degradation products from all the scaffolds had no inhibitory effect on cell viability. Significant bactericidal efficacies of BRT3 extracts against Escherishia coli (Gram-negative) and BRT1 extracts against Staphylococcus aureus and Staphylococcus epidermidis (both Gram-positive bacteria) were demonstrated. Finally, evaluation of the cell/bioactive glass surface interactions showed well-spread cells on the surface of the BRT3 glass discs and BRT1 and BRT3 scaffolds, when compared to BRT0 and BRT4 scaffolds. The results indicate that by changing the Ti⁴⁺ :B³⁺ ratio, the ion release and consequently cell proliferation could be improved. in vitro results in this study demonstrate that BRT3 scaffolds could be a promising candidate for addressing bone loss in rTKAs; however, in vivo studies would be required to evaluate the effect of a dynamic environment on the cell and tissue response to the fabricated scaffolds.

In Vitro Cytotoxicity of Zinc Fructoborate, a Novel Zinc-Boron Active Natural Complex

In recent years, the role of zinc in biological systems has been a subject of intense research. Zinc is required for multiple metabolic processes as a structural, regulatory, or catalytic ion. The objective of this study, was to assess the toxicity profile of a newly synthesized zinc-boron molecule on cultured cells. Zinc fructoborate, at different levels of concentration, was tested for its impact on the Vero kidney cell line (ATCC® CCL-81™) using the MTT assay. The compound exhibited a low cytotoxic effect on the cell line. Thus, our study demonstrates that the zinc fructoborate could become a promising dietary supplement molecule.

Heparan sulfate phage display antibodies recognise epitopes defined by a combination of sugar sequence and cation binding

Phage display antibodies are widely used to follow heparan sulfate (HS) expression in tissues and cells. We demonstrate by ELISA, that cations alter phage display antibody binding profiles to HS and this is mediated by changes in polysaccharide conformation, demonstrated by circular dichroism spectroscopy. Native HS structures, expressed on the cell surfaces of neuroblastoma and fibroblast cells, also exhibited altered antibody binding profiles following exposure to low mM concentrations of these cations. Phage display antibodies recognise conformationally-defined HS epitopes, rather than sequence alone, as has been assumed, and resemble proteins in being sensitive to changes in both charge distribution and conformation following binding of cations to HS polysaccharides.

Effect of zinc supplementation on resistance of cultured human skin fibroblasts toward oxidant stress

In purified system zinc has been shown to have an antioxidant role. Its effects on the resistance of cultured cells towards oxidative stress in vitro were examined. Diploid human skin fibroblasts were grown for 21 d in culture media (RPMI 1640 containing 15% fetal calf serum) added with different zinc (Zn) concentrations (100, 125, and 150 microM as Zinc chlorur ZnCl2). In comparison, cell controls were grown in standard culture media (6.5 microM Zn). The intracellular zinc levels of treated fibroblasts increased from 3- to 7-fold (2330 +/- 120 ng/mg protein in 150-microM Zn-treated cells versus 331 +/- 21 ng/mg protein in control cells). The intracellular copper increased 3- fold whereas the iron content slightly but not significantly decreased. The index of basal lipid peroxidation measured as thiobarbituric acid reactants (TBARs) of zinc-supplemented cells was lower than that of non zinc supplemented controls (0.89 mumol/g protein in 150 microM Zn-treated cells versus 1.59 mumol/g protein in controls). At these high doses of zinc, fibroblasts expressed lower antioxidant metalloenzymes activities. Diminished TBARs in Zn treated cells tends to support that Zn acts protectively against free radical mediated damage. However when the cells were challenged with extracellular oxidant stresses mediated by hypoxanthine/xanthine oxidase or hydrogen peroxide (H2O2), an increased toxicity in Zn-supplemented cells was observed. When we applied an intracellular oxidative stress as UV-B or UV-A radiation, Zn-treated fibroblasts were more resistant than cells grown in normal medium. If Zn has shown antioxidant effect in some in vitro or in vivo systems our observations clearly demonstrate that this role is not mediated by antioxidant metalloenzymes.

Metallothionein expression and stress responses in aging human diploid fibroblasts

Metallothioneins (MTs) are low molecular weight proteins with a high cysteine content that are inducible by heavy metals and by other conditions of environmental stress. This laboratory was investigated in human diploid fibroblasts the induction of MTs by cadmium and by dexamethasone, and the induction of heat shock proteins, as models for age-related changes in gene expression that reflect the ability of old cells to respond to environmental stress. Old cells were more sensitive to the toxic effects of CdCl2 in the concentration range 100-175 microM. Analysis of 35S-cysteine-labelled cell extracts by polyacrylamide gel electrophoresis and fluorography showed that in the absence of any inducer, old cells have a 3.7-fold increase over young cells in the basal level of MT. The rate and extent of induction of MT by CdCl2 was reduced in old cells: Exposure of old cells to 100 microM CdCl2 for 18 h resulted in MT levels about 33% of the amount in young cells. Northern blot analysis showed that the changes in MT protein levels occurred in parallel with changes in mRNA levels, which implicates transcriptional control as the origin of these aging changes. These young/old differences in MT synthesis were maintained in density-arrested cultures, indicating that the aging changes were not due to differences in the cell cycle status of these cell populations. The rate and extent of induction of a 68-kDa heat shock protein were also reduced in old cells, which showed an increase in basal, uninduced level of this protein similar to MT. In contrast, old cells retained the ability to synthesize MTs in response to dexamethasone at a rate similar to that in young cells.

Cultured human skin fibroblasts absorb 65Zn. Optimization of the method and study of the mechanisms involved

The radioactive isotope 65Zn was used to study the incorporation of zinc by cultured human skin fibroblasts. The development of the method for studying cell uptake of 65Zn in a minimal synthetic medium is presented. Kinetics carried out on control cultures up to 240 min indicated that zinc uptake occurred in three phases, the first being the most rapid. Temperature and pH affect zinc uptake, in favor of an active transport process. In addition, the rate of incorporation is considerably decreased during the first phases after adding potassium cyanide, during the last phases after adding sodium iodoacetate, and during all the phases if dithioerythritol is used. A hypothesis is therefore proposed according to which several types of mechanisms would be involved in zinc uptake by fibroblasts. At least a part of these mechanisms is energy-dependent.

Cytotoxicity of zinc in vitro

The effect of zinc ions on B16 mouse melanoma lines, HeLa cells and I-221 epithelial cells was investigated in vitro in order to ascertain whether sensitivity to Zn2+ is a general feature of cells in vitro and in an attempt to elucidate the mechanism(s) of zinc cytotoxicity. The proliferation of B16, HeLa and I-221 cell lines was inhibited by 1.25 x 10(-4), 1.50 x 10(-4) and 1.50 x 10(-4) mol/l Zn2+, respectively. The free radical scavengers, methimazole and ethanol, did not suppress the toxicity of Zn2+, neither did superoxide dismutase or catalase. The addition of the chelating agent EDTA reduced the zinc cytotoxicity. It was possible to suppress the cytotoxicity of zinc by increasing the concentration of either Fe2+ or Ca2+ but not Mg2+, which suggests that a prerequisite for the toxic action of zinc is entry into cells using channels that are shared with iron or calcium. This view was supported by experiments in which transferrin intensified the cytotoxic action of zinc in serum-free medium. Another agent facilitating zinc transport, prostaglandin E2, inhibited the proliferation of the B16 melanoma cell line. There were no conspicuous differences in zinc toxicity to pigmented and unpigmented cells. The toxic effect of zinc in the cell systems studied exceeded that of iron, copper, manganese and cobalt in the same concentration range. In vitro, Zn2+ should be regarded as a dangerous cation.