In vitro effects of metal ions on cellular metabolism and the correlation between these effects and the uptake of the ions

Impact of Metal Ions on Cellular Functions: A Focus on Mesenchymal Stem/Stromal Cell Differentiation

Metals play a crucial role in the human body, especially as ions in metalloproteins. Essential metals, such as calcium, iron, and zinc are crucial for various physiological functions, but their interactions within biological networks are complex and not fully understood. Mesenchymal stem/stromal cells (MSCs) are essential for tissue regeneration due to their ability to differentiate into various cell types. This review article addresses the effects of physiological and unphysiological, but not directly toxic, metal ion concentrations, particularly concerning MSCs. Overloading or unbalancing of metal ion concentrations can significantly impair the function and differentiation capacity of MSCs. In addition, excessive or unbalanced metal ion concentrations can lead to oxidative stress, which can affect viability or inflammation. Data on the effects of metal ions on MSC differentiation are limited and often contradictory. Future research should, therefore, aim to clarify the mechanisms by which metal ions affect MSC differentiation, focusing on aspects such as metal ion interactions, ion concentrations, exposure duration, and other environmental conditions. Understanding these interactions could ultimately improve the design of biomaterials and implants to promote MSC-mediated tissue regeneration. It could also lead to the development of innovative therapeutic strategies in regenerative medicine.

Corrosion behavior of high nitrogen nickel-free austenitic stainless steel in the presence of artificial saliva and Streptococcus mutans

High nitrogen nickel-free austenitic stainless steels (HNSs) have great potentials to be used in dentistry owing to its exceptional mechanical properties, high corrosion resistance, and biocompatibility. In this study, HNSs with nitrogen of 0.88 wt% and 1.08 wt% displayed much lower maximum pit depths than 316L stainless steel (SS) after 21 d of immersion in abiotic artificial saliva (2.2 μm and 1.7 μm vs. 4.5 μm). Microbiologically influenced corrosion (MIC) evaluations revealed that Streptococcus mutans biofilms led to much severer corrosion of 316L SS than HNSs. Corrosion current densities of HNSs were two orders of magnitude lower than that of 316L SS after incubation of 7 d (37.5 nA/cm² and 29.9 nA/cm² vs. 5.63 μA/cm²). The pitting potentials of HNSs were at least 550 mV higher than that of 316L SS in the presence of S. mutans, confirming the better MIC resistance of HNSs. Cytotoxicity assay confirmed that HNSs were not toxic to MC3T3-E1 cells and allowed better sessile cell growth on them than on 316L SS. It can be concluded that HNSs are more suitable dental materials than the conventional 316L SS.

Assessment of Antimicrobic, Antivirotic and Cytotoxic Potential of Alginate Beads Cross-Linked by Bivalent Ions for Vaginal Administration

Antimicrobial agent abuse poses a serious threat for future pharmacotherapy, including vaginal administration. The solution can be found in simple polymeric systems with inherent antimicrobial properties without the need to incorporate drugs, for instance alginate beads cross-linked by bivalent ions. The main goal of the presented study was to provide improvement on the well-documented cytotoxicity of Cu²⁺ cross-linked alginate. Alginate beads were prepared by external ionotropic gelation by cross-linking with Cu²⁺, Ca²⁺ and Zn²⁺ ions, separately and in mixtures. Morphological properties, swelling capacity, ion release and efficacy against the most common vaginal pathogens (C. albicans, E. coli, E. faecalis and virus strain—human herpesvirus type 1) were evaluated. The prepared particles (particle size 1455.68 ± 18.71–1756.31 ± 16.58 µm) had very good sphericity (0.86 ± 0.04–0.97 ± 0.06). In mixture samples, Cu²⁺ hampered second ion loading, and was also released incompletely (18.75–44.8%) compared to the single ion Cu²⁺ sample (71.4%). Efficacy against the selected pathogens was confirmed in almost all samples. Although anticipating otherwise, ion mixture samples did not show betterment over a Cu²⁺ cross-linked sample in cytotoxicity–pathogen efficacy relation. However, the desired improvement was found in a single ion Zn²⁺ sample whose minimal inhibition concentrations against the pathogens (0.6–6.12 mM) were close to, or in the same mathematical order as, its toxic concentration of 50 (1.891 mM). In summary, these findings combined with alginate’s biocompatibility and biodegradability give the combination solid potential in antimicrobial use.

Dual Ion Releasing Nanoparticles for Modulating Osteogenic Cellular Microenvironment of Human Mesenchymal Stem Cells

In this study we developed a dual therapeutic metal ion-releasing nanoparticle for advanced osteogenic differentiation of stem cells. In order to enhance the osteogenic differentiation of human mesenchymal stem cells (hMSCs) and induce angiogenesis, zinc (Zn) and iron (Fe) were synthesized together into a nanoparticle with a pH-sensitive degradation property. Zn and Fe were loaded within the nanoparticles to promote early osteogenic gene expression and to induce angiogenic paracrine factor secretion for hMSCs. In vitro studies revealed that treating an optimized concentration of our zinc-based iron oxide nanoparticles to hMSCs delivered Zn and Fe ion in a controlled release manner and supported osteogenic gene expression (RUNX2 and alkaline phosphatase) with improved vascular endothelial growth factor secretion. Simultaneous intracellular release of Zn and Fe ions through the endocytosis of the nanoparticles further modulated the mild reactive oxygen species generation level in hMSCs without cytotoxicity and thus improved the osteogenic capacity of the stem cells. Current results suggest that our dual ion releasing nanoparticles might provide a promising platform for future biomedical applications.

Cationic Substitutions in Hydroxyapatite: Current Status of the Derived Biofunctional Effects and Their In Vitro Interrogation Methods

High-performance bioceramics are required for preventing failure and prolonging the life-time of bone grafting scaffolds and osseous implants. The proper identification and development of materials with extended functionalities addressing socio-economic needs and health problems constitute important and critical steps at the heart of clinical research. Recent findings in the realm of ion-substituted hydroxyapatite (HA) could pave the road towards significant developments in biomedicine, with an emphasis on a new generation of orthopaedic and dentistry applications, since such bioceramics are able to mimic the structural, compositional and mechanical properties of the bone mineral phase. In fact, the fascinating ability of the HA crystalline lattice to allow for the substitution of calcium ions with a plethora of cationic species has been widely explored in the recent period, with consequent modifications of its physical and chemical features, as well as its functional mechanical and in vitro and in vivo biological performance. A comprehensive inventory of the progresses achieved so far is both opportune and of paramount importance, in order to not only gather and summarize information, but to also allow fellow researchers to compare with ease and filter the best solutions for the cation substitution of HA-based materials and enable the development of multi-functional biomedical designs. The review surveys preparation and synthesis methods, pinpoints all the explored cation dopants, and discloses the full application range of substituted HA. Special attention is dedicated to the antimicrobial efficiency spectrum and cytotoxic trade-off concentration values for various cell lines, highlighting new prophylactic routes for the prevention of implant failure. Importantly, the current in vitro biological tests (widely employed to unveil the biological performance of HA-based materials), and their ability to mimic the in vivo biological interactions, are also critically assessed. Future perspectives are discussed, and a series of recommendations are underlined.

A mineral layer as an effective binder to achieve strong bonding between a hydrogel and a solid titanium substrate

This study has developed an effective strategy to bind a hydrogel with solid titanium by forming a CaCO₃ layer at their interface.

Building an experimental model of the human body with non-physiological parameters

New advances in engineering and biomedical technology have enabled recent efforts to capture essential aspects of human physiology in microscale, in-vitro systems. The application of these advances to experimentally model complex processes in an integrated platform - commonly called a 'human-on-a-chip (HOC)' - requires that relevant compartments and parameters be sized correctly relative to each other and to the system as a whole. Empirical observation, theoretical treatments of resource distribution systems and natural experiments can all be used to inform rational design of such a system, but technical and fundamental challenges (e.g. small system blood volumes and context-dependent cell metabolism, respectively) pose substantial, unaddressed obstacles. Here, we put forth two fundamental principles for HOC design: inducing in-vivo-like cellular metabolic rates is necessary and may be accomplished in-vitro by limiting O₂ availability and that the effects of increased blood volumes on drug concentration can be mitigated through pharmacokinetics-based treatments of solute distribution. Combining these principles with natural observation and engineering workarounds, we derive a complete set of design criteria for a practically realizable, physiologically faithful, five-organ millionth-scale (× 10^-6) microfluidic model of the human body.

Metallic ions released from stainless steel, nickel-free, and titanium orthodontic alloys: toxicity and DNA damage

INTRODUCTION

The aims of this study were to determine the amounts of metallic ions that stainless steel, nickel-free, and titanium alloys release to a culture medium, and to evaluate the cellular viability and DNA damage of cultivated human fibroblasts with those mediums.

METHODS

The metals were extracted from 10 samples (each consisting of 4 buccal tubes and 20 brackets) of the 3 orthodontic alloys that were submerged for 30 days in minimum essential medium. Next, the determination of metals was performed by using inductively coupled plasma mass spectrometry, cellular viability was assessed by using the tetrazolium reduction assay (MTT assay) (3-[4,5-dimethylthiazol-2-yl]-2, 5-diphenyltetrazolium bromide), and DNA damage was determined with the Comet assay. The metals measured in all the samples were Ti(47), Cr(52), Mn(55), Co(59), Ni(60), Mo(92), Fe(56), Cu(63), Zn(66), As(75), Se(78), Cd(111), and Pb(208).

RESULTS

The cellular viability of the cultured fibroblasts incubated for 7 days with minimum essential medium, with the stainless steel alloy submerged, was close to 0%. Moreover, high concentrations of titanium, chromium, manganese, cobalt, nickel, molybdenum, iron, copper, and zinc were detected. The nickel-free alloy released lower amounts of ions to the medium. The greatest damage in the cellular DNA, measured as the olive moment, was also produced by the stainless steel alloy followed by the nickel-free alloy. Conversely, the titanium alloy had an increased cellular viability and did not damage the cellular DNA, as compared with the control values.

CONCLUSIONS

The titanium brackets and tubes are the most biocompatible of the 3 alloys studied.

Effects of metal ions on fibroblasts and spiral ganglion cells

Degeneration of spiral ganglion cells (SGC) after deafness and fibrous tissue growth around the electrode carrier after cochlear implantation are two of the major challenges in current cochlear implant research. Metal ions are known to possess antimicrobial and antiproliferative potential. The use of metal ions could therefore provide a way to reduce tissue growth around the electrode array after cochlear implantation. Here, we report on in vitro experiments with different concentrations of metal salts with antiproliferative and toxic effects on fibroblasts, PC-12 cells, and freshly isolated spiral ganglion cells, the target cells for electrical stimulation by a cochlear implant. Standard cell lines (NIH/3T3 and L-929 fibroblasts and PC-12 cells) and freshly isolated SGC were incubated with concentrations of metal ions between 0.3 μmol/liter and 10 mmol/liter for 48 hr. Cell survival was investigated by neutral red uptake, CellQuantiBlue assay, or counting of stained surviving neurons. Silver ions exhibited distinct thresholds for proliferating and confluent cells. For zinc ions, the effective concentration was lower for fibroblasts than for PC-12 cells. SGC showed comparable thresholds for reduced cell survival not only for silver and zinc ions but also for copper(II) ions, indicating that these ions might be promising for reducing tissue growth on the surface of CI electrode arrays. These effects were also observed when combinations of two of these ions were investigated.

Ag and Ag/N2 plasma modification of polyethylene for the enhancement of antibacterial properties and cell growth/proliferation

Polyethylene (PE) is one of the most common materials used for medical implants. However, it usually possesses low biocompatibility and insufficient antibacterial properties. In the work described here, plasma immersion ion implantation (PIII) is employed to implant silver into PE to enhance both its antibacterial properties and its biocompatibility. Our results show that Ag PIII can give rise to excellent antibacterial properties and induces the formation of functional groups such as C-O and C=C. These C-O and C=C groups on the modified surface can trigger the growth of the human fetal osteoblastic cell line (hFOB). Furthermore, combining N(2) and Ag PIII prolongs the antibacterial effects, but nitrogen-containing functional groups such as C-N and C=N created by N(2) co-PIII negatively impact proliferation of hFOB on the surface. According to our experimental investigation on cell proliferation, functional groups such as C-N and C=N created by nitrogen PIII are disadvantageous to cell growth whereas the C-O and C=C groups benefit cell growth. Both the antibacterial activity and biocompatibility of PE can be enhanced by means of the proper plasma surface treatment.

Scanning Electrochemical Microscopy. 58. Application of a Micropipet-Supported ITIES Tip To Detect Ag+ and Study Its Effect on Fibroblast Cells

We report the use of a micropipet-supported ITIES (interface between two immiscible electrolyte solutions, also called a liquid/liquid (L/L) or water/oil (W/O) interface) as a scanning electrochemical microscopy (SECM) tip to detect silver ion and explore Ag+ toxicity in living cells. A 1,2-dichloroethane solution containing a commercially available calixarene-based Ag+ ionophore (IV) was injected into a micrometer-size glass pipet to construct an Ag+-selective SECM tip. The local Ag+ concentration, down to the micromolar level, in the vicinity of living fibroblast cells, was monitored by SECM approach curves and through imaging of the uptake and efflux of Ag+ by living fibroblast cells in real time. The results show that several stages of interaction between Ag+ and fibroblast cells exist. Since a number of biological processes of cells are involved with non-redox-active ions, the work presented here provides a new way to explore cell metabolism, drug delivery, and toxicity assessment by SECM.

The use of three-dimensional oral mucosa cell cultures to assess the toxicity of soldered and welded wires

The aim of the present study was to determine whether there is a difference in toxicity and loss of viability of three-dimensional (3D) reconstructed human oral epithelium (RHOE) cell cultures induced by point-welded (PW), laser-welded (LW), and silver-soldered (SiS) orthodontic wires. Three types of soldered stainless steel (SS) wires: PW, LW, and SiS were prepared (n = 3) and subjected to multiple end-point analysis (MEA). Six pieces were cut from each wire. Each piece was placed on the triplicate cell cultures (RHOE model based on TR 146 cells). After 24 hours of topical exposure, the cell cultures were cut and stained with haematoxylin/eosin. Toxicity was assessed by evaluating the morphological changes and classifying these as mild, moderate, or severe. The in vitro cell cultures were subjected to a 3-(4,5-dimethylthiazol-2-yl)2,5-diphenyl tetrazolium bromide (MTT) assay in order to quantify viability. Copper wires served as the control to determine severe toxicity and native cell cultures were used as a baseline. Untreated SS wire (0.9 mm) was included for comparison with the welded wires. Histological evaluation with respect to toxicity and measurement of viability in the 3D cell cultures showed no severe toxicity or loss of viability for any of the wires. The morphological ranking of the tested wires from mild to severe toxicity was: SS = PW = LW < SiS. MTT tests revealed the following mean viability values: native cell line (negative control) 98.1 per cent, SS 96.8 per cent, PW 95.5 per cent, LW 95.5 per cent, SiS 85.7 per cent, and copper wires (positive control) 51.2 per cent. Relative comparison between the different welding techniques tested on RHOE revealed, however, that LW and PW wires induced less toxicity/loss of viability compared with SiS wires.

Effects of soluble metals on human peri-implant cells

Despite reports associating tissue necrosis with implant failure, the degree to which processes, such as metal toxicity, negatively impact implant performance is unknown. We evaluated representative human peri-implant cells (i.e., osteoblasts, fibroblasts, and lymphocytes) when challenged by Al+3, Co+2, Cr+3, Fe+3, Mo+5, Ni+2, and V+3 chloride solutions (and Na+2 as a control) over a wide range of concentrations (0.01-10.0 mM). Cell responses were measured using proliferation assays, viability assays, and microscopic cell morphology assessments. Differential effects were found to be less a function of the cell type than of the composition and concentration of metal challenge. No preferential immunosuppression was demonstrated. Below 0.01 mM, no metal was toxic. The most toxic metals (i.e., Co, Ni, and V) reduced proliferation (IC50), and viability (LC50) and cell morphology of osteoblasts, fibroblasts, and lymphocytes by <50% at challenge concentrations <1 mM. All other metals tested required >5 mM to exact the same responses. Below 1 mM, these toxic metals also induced alterations in all cell morphology consisting of loss of filopodia or lamellipodia or changes in cell shape. Metals that were toxic at clinically relevant concentrations (less than previously reported values in peri-implant tissues/fluids) include Co (0.6 mM), Ni (0.8 mM), V (0.5 mM) for lymphocytes and Co (0.8 mM), V (0.3 mM), Al (1-5 mM), Fe (1-5 mM) for fibroblasts, and Co (0.8 mM), Ni (0.7 mM), V (0.1 mM) for osteoblasts. Only Co and V were toxic in vitro at concentrations below that detected in vivo in synovial fluid (V at 0.1 mM and Co at 0.8 mM for fibroblasts, and V at 0.4 mM and Co at 0.8 mM on osteoblasts). Thus, soluble Co and V released from Co- and Ti-based alloys, respectively, could be implicated as the most likely to mediate cell toxicity in the periprosthetic milieu.

Interfacial kinetics of titanium- and cobalt-based implant alloys in human serum: metal release and biofilm formation

The biocompatibility of metallic implant surfaces is governed in large part by the interfacial kinetics associated with metal release and protein binding. The kinetics of metal release from, and protein binding to, cobalt- and titanium-based implant alloys in human serum were investigated by (1). measuring the temporal release of Cr and Ti into serum from Co-Cr-Mo (ASTM F-75) and Ti implant alloys (Ti-6Al-4V: ASTM F136, and commercially pure Ti, cpTi: ASTM F67), respectively; (2). examining the composition of human serum proteins adsorbed onto the surfaces of Co- and Ti-based implant alloys; and (3). identifying the serum proteins associated with the binding of soluble Cr and Ti degradation products. Analysis of metal dissolution kinetics found that Cr was released from Co-based implant alloy at an order of magnitude higher than Ti was released from Ti-based implant alloys. Serum became saturated with soluble CR and Ti at levels as high as 3250 ng/mL Ti from cpTi; 3750 ng/mL Ti from Ti-6Al-4V; and 35400 ng/mL Cr from Co-Cr-Mo degradation. The observation that human serum binds more released metal from Co-based alloy dissolution was consistent with the observed differences in biofilm composition between the two alloys, where additional serum protein(s) of approximately approximately 140 (kDa) molecular weight were detected on Co-based implant alloy surfaces. However, both Cr and Ti released from Co- and Ti-based alloys exhibited a bimodal binding pattern to both low molecular weight serum protein(s) (<32 kDa), and to higher molecular weight protein(s) in the 180-250 kDa range. Identification of metal alloy-dependent biofilm compositions and dissolution products provides the basis for understanding the bioavailability and bioreactivity of these implant alloys and their degradation products.

Sublethal, 2-week exposures of dental material components alter TNF-alpha secretion of THP-1 monocytes

OBJECTIVES

The aim of this study was to investigate the hypothesis that dental material components alter cytokine secretion from monocytes if applied for several weeks at sublethal doses. The current study significantly extended exposure times of monocytes to the components over times published in previous studies. These exposure times approached the estimated average life span of monocytes in the bloodstream.

METHODS

Human THP-1 monocytes were exposed to 2-hydroxyethylmethacrylate (HEMA, 0-1.2mmol/l), triethyleneglycoldimethacrylate (TEGDMA, 0-0.75mmol/l), Hg(2+) (0-2 micromol/l), or Ni(2+) (0-20 micromol/l) for 2 weeks. The cells were then collected and additionally incubated for 24h, with or without bacterial lipopolysaccharide (LPS), a common component of dental plaque. TNF-alpha secretion from THP-1 was determined using by enzyme-linked immunosorbent assay.

RESULTS

None of the dental material components induced TNF-alpha from THP-1 by themselves, but LPS alone strongly induced TNF-alpha secretion as expected. HEMA and TEGDMA significantly suppressed (40-70%) TNF-alpha secretion from cells stimulated with LPS. Hg(2+) at 2.0 micromol/l doubled TNF-alpha secretion from THP-1s stimulated with LPS over LPS alone. Ni(2+) did not significantly affect TNF-alpha secretion, with or without LPS exposure. Significance. The results in this study suggest that sublethal, 2-week exposures of some dental material components may alter TNF-alpha secretion from THP-1 monocytes when the cells are challenged. These alterations may influence the biological response of tissues to materials in an inflammatory intraoral environment.

Effect of subtoxic concentrations of metal ions on NFkappaB activation in THP-1 human monocytes

THP-1 human monocytes and human peripheral blood monocytes have altered inflammatory cytokine secretion profiles after exposure to a variety of metal ions known to be released from biomaterials. Transcriptional regulation of these cytokines often involves activation of the transcription factor NFkappaB. The present study was designed to determine whether metal ion treatment of monocytes results in changes in levels of activated NFkappaB. THP-1 cells were grown in suspension in the presence of sublethal concentrations of ions of Ag(+), Co(2+), Cu(2+), Hg(2+), Ni(2+), and Pd(2+). After 24 h of exposure to metal ions, the cells were harvested, counted, and the nuclear proteins extracted. Electrophoretic mobility shift assays were performed using a (32)P-ATP end-labeled oligonucleotide consensus sequence for the NFkappaB transcription factor. DNA/protein complexes were quantified by phosphorimage analysis and compared by ANOVA (Tukey, alpha = 0.05). Exposure of THP-1 cells to 100 microM of Pd(2+) caused a significant increase in activated NFkappaB (p < 0.05) whereas treatment with 5 microM of Ag(+) resulted in significantly decreased levels of nuclear NFkappaB (p < 0.05). No other metal ions tested caused a significant change in basal levels of nuclear NFkappaB (Co(2+), Hg(2+), Ni(2+), and Cu(2+)). However, exposure to 50 microM of Cu(2+) resulted in a reproducible, though not significant, increase in nuclear NFkappaB levels. These results indicate that inflammatory responses to some metal ions may be influenced by NFkappaB-mediated transcriptional regulation.

Metal ions alter lipopolysaccharide-induced NFκB binding in monocytes

Metals are components of a variety of biomaterials used in orthopedic and dental appliances; however, their biocompatibility with the surrounding tissues is not completely understood. Monocytes are important immune cells that respond to inflammatory stimuli by rapidly producing a variety of inflammatory proteins. Regulation of this response often involves activation of the transcription factor NF kappa B. The current study was designed to determine whether monocyte activation of NF kappa B in response to bacterial lipopolysaccharide (LPS) is affected by pretreatment with metal ions. Concentrations of metal ions that affected cell number after 24 h of exposure were first determined. Then THP-1 human monocytes were cultured for 2 h in media containing metal ions at concentrations below levels that altered cell growth. Parallel cultures were treated with 10 microg/mL Escherichia coli LPS, and all samples were cultured an additional 2 h. Nuclear proteins were extracted and normalized amounts were incubated with [(32)P]-end-labeled NF kappa B consensus oligonucleotide. NF kappa B-DNA complexes were identified and quantified by electrophoretic mobility shift analysis. The extent of NF kappa B-DNA complex formation after metal ion pretreatment with or without LPS induction was compared to no treatment or LPS-only treated controls. Finally, LPS-induced IL1 beta secretion was measured from palladium-treated and control cells. Concentrations were identified for each metal ion (Ag(+), Co(2+), Cu(2+), Hg(2+), Ni(2+), and Pd(2+)) that did not reduce cell number after 24 h of exposure (ranging from 5 microM for Ag(+) and Hg(2+) to 200 microM for Ni(2+)). Exposures of 2 h at these concentrations did not alter cell morphology, staining with trypan blue, or cell number. LPS exposure had no effect on cell number with or without metal ions after 2 h. When metal treatment alone was assessed, none of the metal ions had a significant effect on NF kappa B-DNA binding. However, pretreatment with Co(2+), Ni(2+), Ag(1+), Hg(2+), and Pd(2+) significantly decreased NF kappa B-DNA binding by 40-70% versus LPS alone. Only Cu(2+) had no effect on LPS-induced NF kappa B-DNA complex formation. Pd(2+) lowered, but did not abolish, IL1 beta secretion at concentrations comparable to those that altered NF kappa B-DNA binding. These results suggest that many commonly used metals alter monocyte function at concentrations that are not overtly toxic, and that protein levels controlled in part by NF kappa B also may be altered.

Concentration- and composition-dependent effects of metal ions on human MG-63 osteoblasts

Metal debris from implants has been shown to alter the function of osteoblasts in cell cultures. Its remains unclear, however, if specific forms of released ionic metals are involved in the pathogenesis of periprosthetic osteolysis. We evaluated the relative effects of ionic forms of implant metals by treating human osteoblast-like MG-63 osteosarcoma cells with eight concentrations (0.001-10.0 mM) of Cr(+3), Mo(+5), Al(+3), Ta(+5), Co(+2), Ni(+2), Fe(+3), Cu(+2), Mn(+2), Mg(+2), Na(+2), and V(+3) chloride solutions. The results demonstrated that the metal ions differentially affected osteoblast proliferation, viability, type-I collagen gene expression, and cytokine release. The metal ions were ranked in order from least to most toxic (based on a 50% reduction in viability) as follows: Na < Cr < Mg < Mo < Al < Ta < Co < Ni < Fe < Cu < Mn < V. Metal-induced decreases in osteoblast proliferation were similar in ranking. Nontoxic concentrations of metals had no effect on procollagen alpha1[I] gene expression; only at toxic concentrations did metals produce a decrease in gene expression. The most toxic metals (V, Mn, Fe, and Ni) were also the only metals found to induce IL-6 secretion on a per cell basis (of the cytokines tested, interleukin 6 (IL-6), interleukin beta 1 (IL-1beta), transforming growth factor beta 1 (TGF-beta1), and tumor necrosis factor alpha (TNF-alpha), only IL-6 was detectable in the culture medium after 48 h for any metal at any concentration). Less toxic metals (e.g., Co and Cr) had little effect on IL-6 release, even at high concentrations. In general, metal ions reduced osteoblast function (i.e., proliferation and collagen gene expression) in proportion to the degree of toxicity. These results support the hypothesis that adverse local cellular responses (particularly necrotic responses) associated with metal debris from implanted metallic devices may be due in part to metal ions released from implants or from particulate debris.

Cytotoxicity of orthodontic bands, brackets and archwires in vitro

OBJECTIVES

In orthodontic therapy, different materials are used and subjected to a damp oral environment, which can modify their properties. In order to evaluate the biocompatibility of metallic and non-metallic orthodontic appliances their in vitro cytotoxicity has been measured.

METHODS

Twenty-eight new and nine clinically used materials, including brackets, molar bands and archwires were used. The metallic materials were made of stainless steel, gold-plated steel, pure titanium, nickel-titanium, titanium-molybdenum and silver-based soldering alloy. The non-metallic materials were in polycarbonates and ceramics. After a release period of the material in the culture medium (0.1 mg/ml) for 3 and 14 days, the viability of fibroblasts L929 cultivated with this medium was compared to negative control with MTT assay.

RESULTS

The results showed the non-cytotoxicity of the materials. The metallic and non-metallic materials were similar in terms of cytotoxicity. The cytotoxicity of clinically used samples was equivalent to that of the same non-used samples, except a cytotoxic sample, at 14 days, corresponding to a soldered and clinically used molar band. The 3 day results were different from the 14 day results in six cases out of 37.

SIGNIFICANCE

In spite of the presence of one cytotoxic sample, the orthodontic materials can be considered as non cytotoxic. However, the practitioner should pay attention to the composition and the polish of soldering silver-based alloys containing copper and zinc in order to limit cytotoxic ion release. The cytotoxicity of the used sample related to ion release might be related to some clinical sub-acute effects related with orthodontic materials, thus a long term release period may be suitable to evaluate in vitro the sub-acute clinical effects of alloys.

Localization of metallic ions with gingival fibroblast subcellular fractions

Nickel-based alloys have been in use since the 1930s; however, there are concerns regarding the release of metal ions (Be(+2), Cr(+6), Cr(+3), Ni(+2), Mo(+6)) from these alloys into surrounding tissues. Therefore, the objective of this study was to determine the cellular location and accumulation of ions using atomic absorption spectroscopy and correlate location with the cytotoxic, morphologic, and ultrastructural evaluations reported previously. Human gingival fibroblasts were exposed to the metal ions for 72 h. Controlled atomic absorption spectroscopy studies were used to determine the intracellular location of these ions reported as parts per million metal ions per milligram protein. Enzymatic markers were shown to correspond to the appropriate fraction indicating success in fractionation of the gingival fibroblasts. These results correspond with the cytotoxic, morphologic, and ultrastructural alterations reported previously for fibroblasts exposed to these ions. The highest concentration of beryllium ions occurred in the low-density molecule fraction, where lipofuscin granules were found, which has been shown to contain metal ions. The highest concentrations of hexavalent chromium ions occurred in the plasma membrane and nuclear fractions followed by the mitochondria fraction, which is supported by the ions' ability to oxidize to trivalent chromium accumulating at the membrane as well as the alterations in nuclear and mitochondrial function. For trivalent chromium, the highest concentrations occurred in the low-density molecule and the plasma membrane fractions, which correlates with the ions' inability to readily cross membranes. The highest concentration of molybdenum ions occurred in the plasma membrane fraction correlating with alterations in membrane morphology and increased numbers of myelin figures. The highest concentration of nickel ions was associated with the cytosol fraction where lipid droplets seen in the transmission electron micrographs were located. The current study demonstrates that a successful subcellular fractionation was obtained on gingival fibroblasts and that the location of metallic ions within the fractions correlated with cellular alterations reported previously.

Lack of effects of hydrocortisone pretreatment on zinc-induced changes in protein assemble

Inhalational zinc intoxication may lead to the development of acute respiratory distress syndrome (ARDS). Pharmacological treatment of ARDS is based on glucocorticoids, while the efficiency of glucocorticoid treatment is discussed controversially. Glucocorticoid pretreatment of lung cell lines is known to cause disparate effects with regard to zinc susceptibility. Both substances are known to each interact with protein metabolism. In the present study, zinc effects were examined on hydrocortisone (HC)-pretreated lung cell lines by detection of content and synthesis of different proteins after two-dimensional (2D) gel electrophoresis. (1) In HC- pretreated fibroblast-like 11Lu and alveolar epithelial L2 cells, no zinc-mediated changes after silver staining of 2D gels were seen. Few differences occurred in HC-pretreated alveolar epithelial A549 cells that might be explained by the appearance of heat shock proteins (hsp) after zinc exposure. (2) In autoradiographs after 35S-Met incorporation only in 11Lu cells, small differences occurred after HC treatment as compared to controls without HC. (3) All cell lines tested demonstrated the same zinc-mediated changes in autoradiographs with a nearly complete loss of synthesized proteins and an appearance of a few new spots. These changes were reversible in all cell lines after washing out of external zinc. The new spots were transiently expressed for a few hours after zinc exposure. (4) The overall effect of HC pretreatment was rather unimpressive. The virtual lack of major effects does not support the hypothesis that a gross interaction between glucocorticoids and zinc at the cellular protein synthesis level would be an important mechanism of influence in zinc-induced lung injury.

An investigation of fibroblast mitochondria enzyme activity and respiration in response to metallic ions released from dental alloys

Most cellular functions evaluated for biocompatibility are high-energy processes such as proliferation and therefore are not usually affected before a decrease in energy production is observed. Several studies have shown that metabolic functions are altered at much lower concentrations than several normally used biocompatibility tests such as viability. Therefore, the purpose of this study was to provide an in-depth evaluation of metallic ion effects on mitochondria function and thereby biocompatibility. These studies evaluated the mitochondrial function of human gingival fibroblasts exposed to the salt solutions of ions released from nickel-based dental alloys, particularly beryllium (Be(2+)), chromium (Cr(6+) and Cr(3+)), nickel (Ni(2+)), and molybdenum (Mo(6+)). Mitochondrial function was examined by NADH:CoQ reductase activity, succinate dehydrogenase activity, and oxygen consumption.

Generic tendency of metal salt cytotoxicity for six cell lines

Systematic cytotoxicity evaluation of various metallic elements may contribute to the development of new metallic biomaterials with superior biocompatibility. It is generally reported that the cytotoxicity of a chemical differs with cell lines. However, our previous study revealed a high correlation in the cytotoxicity of 43 metal salts between two murine cell lines. If there is any generic tendency toward metal salt cytotoxicity for many kinds of cells, that information is helpful for the determination of the chemical composition of new metallic biomaterials that are expected to have lower cytotoxicity. In this study, the cytotoxicity of 12 metal salts was evaluated using four cell lines, and the results were compared, including those for two other cell lines obtained in our previous study. A metal salt concentration that reduced cell viability to 50% of that without any metal salt (IC(50)) was used as an index to compare the metal salt cytotoxicity between cell lines. The correlation was statistically proved by the IC(50)s of 12 metal salts among these cell lines (p < 0.01), suggesting the existence of a generic tendency to metal salt cytotoxicity beyond cell lines. The metal salt order of toxicity from the highest was K(2)Cr(2)O(7), AgNO(3), VCl(3), SbCl(3), CuCl(2), CoCl(2), NiCl(2), ZnCl(2), Cr(NO(3))(3), FeCl(3), TiCl(4), and Al(NO(3))(3). The sensitivity for metal salt cytotoxicity differed with cell lines; IMR-32 had the highest sensitivity among the six cell lines.

Effects of metallic ion toxicity on human gingival fibroblasts morphology

Alloys used as implant materials release metal ions to surrounding tissues. Cytotoxic substances attack at the molecular level, and these effects are reflected in the structure of the cells and organelles. The objective of this study was to evaluate the cellular morphology and ultrastructural changes of cultured human gingival fibroblasts to salt solutions of ions (beryllium (Be+2), chromium (Cr+6 and Cr+3), nickel (Ni+2), molybdenum (Mo+6)) which may be released from nickel-chromium dental alloys. The concentrations chosen were based on previously conducted cell culture studies. Fibroblasts were exposed to the different ion concentrations for 24 or 72 h. Cellular morphology and ultrastructural features were examined using scanning electron microscopy and transmission electron microscopy. Ultrastructural alterations observed included irregular shaped nuclei for cells exposed to hexavalent chromium and nickel, pseudopodia for cells exposed to beryllium and molybdenum, and lipid droplet formation in cells exposed to nickel.

Evaluations of metabolic activities as biocompatibility tools: a study of individual ions' effects on fibroblasts

OBJECTIVES

Nickel-based dental alloys have been in use since 1930. However, there are concerns regarding the release of metal ions from these alloys to surrounding tissues. Cell culture evaluations can be used to address these concerns and to develop a biocompatibility model by providing a more basic understanding of the metabolic response to individual ions released from dental alloys. This study evaluates the metabolic as well as the morphological response of cultured human gingival fibroblasts to salt solutions of ions which may be released from these alloys; beryllium (Be2+), chromium (Cr6+ and Cr3+), nickel (Ni2+), molybdenum (Mo6+).

METHODS

These evaluations include viability, lysosomal activity, oxygen consumption, membrane integrity, DNA synthesis, RNA synthesis, protein synthesis, intracellular ATP levels, and glucose-6-phosphate dehydrogenase activity. The results of all cell culture evaluations are reported as the concentration (ppm) required to cause a significant change from the controls, as determined by Duncan's multiple comparison test at 0.05 significance level.

RESULTS

While Ni2+ ion solutions altered metabolic functions at 3-30 ppm and Cr3+ and Mo6+ both at 10 and 100 ppm, Cr6+ and Be2+ were the most toxic causing cellular alterations at 0.04-12 ppm.

SIGNIFICANCE

These studies indicated that monitoring metabolic activities may be better than the normally used morphology and viability assays for evaluating biocompatibility.

Polysulphone inhibits final differentiation steps of osteogenesis in vitro

Biocompatibility is an important factor in the development of orthopedic implants as well as in the development of new tissue culture devices. Polysulphone has been used for orthopedic implants because of its mechanical properties, ease of sterilization, molding capacity, and biocompatibility. Therefore, polysulphone has been chosen as the prime material for the construction of tissue culture devices to be used for the cultivation of osteogenic cells (preosteoblast-like MN7 cells and primary bone marrow fragments), as well as complete fetal long bone explants under space flight conditions. Whereas polysulphone did not interfere with the proliferation in early stages of bone-forming cells, we show that leachable factors within the polysulphone polymer prevented the final steps of matrix formation as measured by collagen synthesis and matrix mineralization. These data argue against polysulphone as a material for orthopedic implants.

In vitro reaction of macrophages to metal ions from dental biomaterials

OBJECTIVES

This study was conducted to 1) measure the sensitivity of human and mouse macrophages to metal ions which are released from dental biomaterials, 2) compare these sensitivities with those of other cell types in the oral cavity, and 3) determine if metal ions alter the metabolism and synthetic processes of these cells at lower concentrations than are required to lyse the cells. This information will help define the biological risks associated with the release of metal ions into the oral cavity.

METHODS

Macrophages were exposed to a range of concentrations of Ag1+, Au3+, Cu2+, Hg2+, Ni2+, Pd2+, Pt4+, and Zn2+ for 24 h in cell culture. The concentrations which caused a 50% decrease in succinic dehydrogenase (SDH) activity, protein production, and lactate dehydrogenase (LDH) release were measured and compared with these values for fibroblasts and osteoblasts.

RESULTS

Most metal ions caused alteration in SDH activity and protein production at lower concentrations than were required to induce LDH release. There were exceptions to this trend, and the differences were not always statistically significant. Furthermore, although the macrophages sometimes had statistically different sensitivities to metal ions than fibroblasts or osteoblasts, these differences were less than one order of magnitude. Macrophage response to the metal ions was highly dependent on the metal ion and the species of macrophage.

SIGNIFICANCE

Macrophages react adversely to metal ions at similar concentrations as other cell types found in the oral cavity. Furthermore, the concentrations which affect cell metabolism and protein production are generally lower than those which lyse the cells. Thus, non-lethal concentrations of metal ions may alter the secretion of protein inflammatory mediators such as cytokines which direct the inflammatory response in tissues.