In vitro reaction of macrophages to metal ions from dental biomaterials

Deciphering platinum dissolution in neural stimulation electrodes: Electrochemistry or biology?

Platinum (Pt) is the metal of choice for electrodes in implantable neural prostheses like the cochlear implants, deep brain stimulating devices, and brain-computer interfacing technologies. However, it is well known since the 1970s that Pt dissolution occurs with electrical stimulation. More recent clinical and in vivo studies have shown signs of corrosion in explanted electrode arrays and the presence of Pt-containing particulates in tissue samples. The process of degradation and release of metallic ions and particles can significantly impact on device performance. Moreover, the effects of Pt dissolution products on tissue health and function are still largely unknown. This is due to the highly complex chemistry underlying the dissolution process and the difficulty in decoupling electrical and chemical effects on biological responses. Understanding the mechanisms and effects of Pt dissolution proves challenging as the dissolution process can be influenced by electrical, chemical, physical, and biological factors, all of them highly variable between experimental settings. By evaluating comprehensive findings on Pt dissolution mechanisms reported in the fuel cell field, this review presents a critical analysis of the possible mechanisms that drive Pt dissolution in neural stimulation in vitro and in vivo. Stimulation parameters, such as aggregate charge, charge density, and electrochemical potential can all impact the levels of dissolved Pt. However, chemical factors such as electrolyte types, dissolved gases, and pH can all influence dissolution, confounding the findings of in vitro studies with multiple variables. Biological factors, such as proteins, have been documented to exhibit a mitigating effect on the dissolution process. Other biological factors like cells and fibro-proliferative responses, such as fibrosis and gliosis, impact on electrode properties and are suspected to impact on Pt dissolution. However, the relationship between electrical properties of stimulating electrodes and Pt dissolution remains contentious. Host responses to Pt degradation products are also controversial due to the unknown chemistry of Pt compounds formed and the lack of understanding of Pt distribution in clinical scenarios. The cytotoxicity of Pt produced via electrical stimulation appears similar to Pt-based compounds, including hexachloroplatinates and chemotherapeutic agents like cisplatin. While the levels of Pt produced under clinical and acute stimulation regimes were typically an order of magnitude lower than toxic concentrations observed in vitro, further research is needed to accurately assess the mass balance and type of Pt produced during long-term stimulation and its impact on tissue response. Finally, approaches to mitigating the dissolution process are reviewed. A wide variety of approaches, including stimulation strategies, coating electrode materials, and surface modification techniques to avoid excess charge during stimulation and minimise tissue response, may ultimately support long-term and safe operation of neural stimulating devices.

Phosphate Starvation by Energy Metabolism Disturbance in Candida albicansvip1Δ/Δ Induces Lipid Droplet Accumulation and Cell Membrane Damage

Phosphorus in the form of phosphate (Pi) is an essential element for metabolic processes, including lipid metabolism. In yeast, the inositol polyphosphate kinase vip1 mediated synthesis of inositol heptakisphosphate (IP₇) regulates the phosphate-responsive (PHO) signaling pathway, which plays an important role in response to Pi stress. The role of vip1 in Pi stress and lipid metabolism of Candida albicans has not yet been studied. We found that when vip1Δ/Δ was grown in glucose medium, if Pi was supplemented in the medium or mitochondrial Pi transporter was overexpressed in the strain, the lipid droplet (LD) content was reduced and membrane damage was alleviated. However, further studies showed that neither the addition of Pi nor the overexpression of the Pi transporter affected the energy balance of vip1Δ/Δ. In addition, the LD content of vip1Δ/Δ grown in Pi limitation medium PNMC was lower than that grown in SC, and the metabolic activity of vip1Δ/Δ grown in PNMC was also lower than that grown in SC medium. This suggests that the increase in Pi demand by a high energy metabolic rate is the cause of LD accumulation in vip1Δ/Δ. In addition, in the vip1Δ/Δ strains, the core transcription factor PHO4 in the PHO pathway was transported to the vacuole and degraded, which reduced the pathway activity. However, this does not mean that knocking out vip1 completely blocks the activation of the PHO pathway, because the LD content of vip1Δ/Δ grown in the medium with β-glycerol phosphate as the Pi source was significantly reduced. In summary, the increased Pi demand and the decreased PHO pathway activity in vip1Δ/Δ ultimately lead to LD accumulation and cell membrane damage.

Development and Validation of Conditions for Extracting Flavonoids Content and Evaluation of Antioxidant and Cytoprotective Activities from Bougainvillea x buttiana Bracteas (var. Rose)

In this study the effect of the ethanol concentration of Bougainvillea x buttiana extracts on the flavonoids content, and its antioxidant and cytoprotective activities in vitro were determined and compared. For the elucidation of the chemical constituents, the high-performance liquid chromatography method (HPLC) was used, and verification of the antioxidant activity was carried out using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical method. The cytoprotective effects of extracts were determined by exposure to hydrogen peroxide. The HPLC analysis showed the presence of rutin, quercetin-3-glucoside and quercetin rhamnoside. Among the extracts investigated the best recuperation of the rutin content was observed in extracts with 80% ethanol (83 ± 5 mg/mL). The amounts of rutin present in all extracts contribute to the antioxidant capacity and the IC50 was 427.49 (0%), 275.41 (50%), 271.61 (80%), and 272.14 (100%) µg/mL. The lowest percentage of viability was found in the cultures exposed to 100% ethanol (92%). In cultures exposed to hydrogen peroxide the percentages of protection were 25%, 33%, 78%, and 65% for cultures treated for 72 h at 0%, 50%, 80%, and 100% ethanol, respectively. The ethanolic extract of B. x buttiana was confirmed to have high rutin content with potent antioxidant activity, low cytotoxic and strong cytoprotective effects.

Ti(C, N) as Barrier Coatings

Metals and their alloys are materials that have long been used in stomatological prosthetics and orthodontics. The side effects of their application include reactions of the body such as allergies. Their source can be corrosion products as well as metal ions released in the corrosion process, which penetrate the surrounding tissue. In order to prevent the harming effect of metal alloys, intensive research has been performed to purify metal prosthetic restorations by way of modifying their surface. The study presents the investigation results of Ti(C, N)-type coatings applied to alloy Ni–Cr by means of the magnetronic method. Five coatings differing in the nitrogen and carbon content were investigated. The studies included the determination of the coatings’ chemical composition, construction, as well as the amount of ions released into the environment: distilled water, 0.9% NaCl and artificial saliva. The performed investigations showed that, in reference to an alloy without a coating, each coating constitutes a barrier reducing the amount of ions transferred into the examined solutions. So, Ti(C, N)-type coatings can be considered for biomedical applications as protective coatings of non-precious metal alloys.

A superfusion apparatus for ex vivo human eye irritation investigations

A superfusion apparatus (SA) was developed to maintain isolated human corneas ex vivo under conditions which mimic the natural eye environment in vivo, including controlled temperature, tear flow and intraocular pressure. The SA was designed, developed and tested for use in ophthalmic pre-clinical research and to test new pharmaceutical formulations. Corneas undergo an equilibration process in the new physiological environment for one day. The test was then initiated by the application of the test substance, incubation, and temporal assessment of corneal damage using various parameters. The effects of mild and severe irritant concentrations of NaOH (2% and 8%, respectively) on corneal opacity, swelling and epithelial integrity were studied, and the inflammatory status assessed using F4/80 and MPO as macrophages and neutrophils markers, respectively. The SA was then used to test new artificial tear formulations supplemented with silver ions as an active constituent, showing different degrees of inflammatory responses as indicated by the migration of MPO and F4/80 positive cells towards the epithelium. The human cornea superfusion apparatus was proposed as a model for acute eye irritation research.

Toxic effect of palladium on embryonic development of zebrafish

Since palladium (Pd) is now increasingly used in modern industry, it progressively accumulates in the environment, especially in aquatic ecosystem. The potential toxicity of Pd has therefore caused extensive concern worldwidely. In the present study, we investigated the toxic effect of Pd on zebrafish development. Acute Pd exposure significantly decreased both the survival rate (LC50: 292.6 μg/L, viz. 2.75 μM) and hatching rate (IC50: 181.5 μg/L, viz. 1.71 μM) of zebrafish during embryonic development. The most common developmental defect observed in Pd treated embryos is pericardiac edema, which occurs in a dose-dependent manner. Whole mount immunostaining and histological studies revealed that Pd exposure would produce the elongated, string-like heart. The heartbeat rate of zebrafish embryos was also decreased after Pd exposure. Consistently, mRNA expression levels of several cardiac-related genes were affected by Pd, suggesting a potential molecular mechanism of Pd-induced cardiac malformation of zebrafish embryo. Moreover, similar to other metals, Pd exposure resulted in the elevated expression of general metal-inducible genes. It was also found that the expression of several antioxidant enzymes was significantly down-regulated in the presence of Pd. Taken together, our study investigated the effects of Pd on zebrafish embryonic development and its potential molecular mechanisms, paving the way for the full understanding of Pd toxicity.

In vitro age dependent response of macrophages to micro and nano titanium dioxide particles

As a result of corrosion, microparticles (MP) and/or nanoparticles (NP) can be released from the metallic implants surface into the bioenvironment. The biological response to these particles depends not only on the physico-chemical properties of the particles but also on host factors, such as age. Macrophages have attracted wide concern in biomedicine. The aim of this investigation was to study the age related biological response of macrophages to TiO2 -MP and NP in vitro. Alveolar macrophages (AM) obtained from young and senescent rats were cultured and exposed to TiO2 -MP and NP. Cell metabolism, superoxide anion (O2 (-) ) and nitric oxide (NO) generation, and cytokine release (IL-6, TNFα, IL-10) were measured. Cell metabolism was not affected by particle exposure. O2 (-) and NO generation increased in a dose dependent manner. A marked increase on IL-6 release was found in the young-AM subpopulation exposed to TiO2 -MP. Conversely, both particle sizes induced a dose dependent release of TNFα in senescent-AM. Only the highest concentration of TiO2 -particles caused a significant increase in IL-10 release in AM-cultures. These observations lend strong support to the suggestion that cellular response of macrophages to TiO2 -particles is age dependent. The biological effect of the particles would seem to be more deleterious in the senescent age-group.

Differential regulation of intracellular factors mediating cell cycle, DNA repair and inflammation following exposure to silver nanoparticles in human cells

Background

Investigating the cellular and molecular signatures in eukaryotic cells following exposure to nanoparticles will further our understanding on the mechanisms mediating nanoparticle induced effects. This study illustrates the molecular effects of silver nanoparticles (Ag-np) in normal human lung cells, IMR-90 and human brain cancer cells, U251 with emphasis on gene expression, induction of inflammatory mediators and the interaction of Ag-np with cytosolic proteins.

Results

We report that silver nanoparticles are capable of adsorbing cytosolic proteins on their surface that may influence the function of intracellular factors. Gene and protein expression profiles of Ag-np exposed cells revealed up regulation of many DNA damage response genes such as Gadd 45 in both the cell types and ATR in cancer cells. Moreover, down regulation of genes necessary for cell cycle progression (cyclin B and cyclin E) and DNA damage response/repair (XRCC1 and 3, FEN1, RAD51C, RPA1) was observed in both the cell lines. Double strand DNA damage was observed in a dose dependant manner as evidenced in γH2AX foci assay. There was a down regulation of p53 and PCNA in treated cells. Cancer cells in particular showed a concentration dependant increase in phosphorylated p53 accompanied by the cleavage of caspase 3 and PARP. Our results demonstrate the involvement of NFκB and MAP kinase pathway in response to Ag-np exposure. Up regulation of pro-inflammatory cytokines such as interleukins (IL-8, IL-6), macrophage colony stimulating factor, macrophage inflammatory protein in fibroblasts following Ag-np exposure were also observed.

Conclusion

In summary, Ag-np can modulate gene expression and protein functions in IMR-90 cells and U251 cells, leading to defective DNA repair, proliferation arrest and inflammatory response. The observed changes could also be due to its capability to adsorb cytosolic proteins on its surface.

Peroxotitanates for biodelivery of metals

Metal-based drugs are largely undeveloped in pharmacology. One limiting factor is the systemic toxicity of metal-based compounds. A solid-phase, sequestratable delivery agent for local delivery of metals could reduce systemic toxicity, facilitating new drug development in this nascent area. Amorphous peroxotitanates (APT) are ion-exchange materials with high affinity for several heavy metal ions and have been proposed to deliver or sequester metal ions in biological contexts. In the current study, we tested a hypothesis that APTs are able to deliver metals or metal compounds to cells. We exposed fibroblasts (L929) or monocytes (THP1) to metal-APT materials for 72 h in vitro and then measured cellular mitochondrial activity (SDH-MTT method) to assess the biological impact of the metal-APT materials versus metals or APT alone. APT alone did not significantly affect cellular mitochondrial activity, but all metal-APT materials suppressed the mitochondrial activity of fibroblasts (by 30-65% of controls). The concentration of metal-APT materials required to suppress cellular mitochondrial activity was below that required for metals alone, suggesting that simple extracellular release of the metals from the metal-APT materials was not the primary mechanism of mitochondrial suppression. In contrast to fibroblasts, no metal-APT material had a measurable effect on THP1 monocyte mitochondrial activity, despite potent suppression by metals alone. This latter result suggested that "biodelivery" by metal-APT materials may be cell type-specific. Therefore, it appears that APTs are plausible solid-phase delivery agents of metals or metal compounds to some types of cells for potential therapeutic effect.

Patterns of bone loss around teeth restored with endodontic posts

OBJECTIVES

This retrospective study described the pattern of bone loss around teeth with endodontic posts in periodontitis patients, and compared it with contra-lateral teeth without posts.

MATERIAL AND METHODS

From full-mouth radiographic surveys of 146 periodontitis patients (> or =35 years), 194 roots with endodontic posts and contra-laterals without posts were selected. Upper molars, pre-molars with two posts and roots of lower molars with two posts were excluded. Technical parameters of the post space preparation, endodontic and restorative status were evaluated. The level of alveolar bone measured in millimetre from the cemento-enamel junction (CEJ)/restoration margin and the pattern of bone loss (angular/horizontal) were evaluated on both mesial and distal aspects of roots with posts and contra-laterals, but not on the furcal areas of lower molars.

RESULTS

The distance from the bone level to the CEJ/restoration margin was similar for teeth with posts and contra-laterals. However, teeth with posts had more angular defects mesially (18.8%versus 7.3%) as compared with their contra-laterals without posts. The defects around teeth with posts appeared to be typical in the sense that their apical level approximated the tip of the endodontic post.

CONCLUSION

In periodontitis patients, teeth restored by an endodontic post had angular bony defects on the mesial aspect more frequently in comparison with their contra-laterals.

Cytotoxicity of Silver Solder Employed in Orthodontics

Objective: To test the null hypothesis that the silver soldering employed in orthodontics is not cytotoxic for fibroblasts.

Materials and Methods: This in vitro study was performed using a culture of mice fibroblasts (lineage NIH/3T3), divided into four groups (n = 10 each): control, negative control (stainless steel archwire), positive control (amalgam disks), and test group (silver soldering). After cell culture in complete Dulbecco modified eagle medium and achievement of confluence in 80%, the suspension was added to the plates of 24 wells containing the specimens and incubated in an oven at 37°C for 24 hours. The plates were analyzed on an inverted light microscope, photomicrographs were obtained, and the results were recorded as response rates based on modifications of the parameters of Stanford according to the size of the diffusion halo of the toxic substance and quantity of cell lysis.

Results: The results revealed a maximum response rate for the silver soldering group, as well as severe inhibition of cell proliferation and growth, more round cells with mostly darkened and granular aspects, suggesting lysis with cell death. A similar response was seen in the positive control group.

Conclusion: The hypothesis is rejected. The silver soldering used in orthodontics represents a highly cytotoxic material for the cells analyzed.

Airborne particulate matter, platinum group elements and human health: a review of recent evidence

Environmental concentrations of the platinum group elements (PGE) platinum (Pt), palladium (Pd) and rhodium (Rh) have been on the rise, due largely to the use of automobile catalytic converters which employ these metals as exhaust catalysts. It has generally been assumed that the health risks associated with environmental exposures to PGE are minimal. More recent studies on PGE toxicity, environmental bioavailability and concentrations in biologically relevant media indicate however that environmental exposures to these metals may indeed pose a health risk, especially at a chronic, subclinical level. The purpose of this paper is to review the most recent evidence and provide an up-to-date assessment of the risks related to environmental exposures of PGE, particularly in airborne particulate matter (PM). This review concludes that these metals may pose a greater health risk than once thought for several reasons. First, emitted PGE may be easily mobilised and solubilised by various compounds commonly present in the environment, thereby enhancing their bioavailability. Second, PGE may be transformed into more toxic species upon uptake by organisms. The presence of chloride in lung fluids, for instance, may lead to the formation of halogenated PGE complexes that have a greater potential to induce cellular damage. Third, a significant proportion of PGE found in airborne PM is present in the fine fraction that been found to be associated with increases in morbidity and mortality. PGE are also a concern to the extent that they contribute to the suite of metals found in fine PM suspected of eliciting a variety of health effects, especially in vulnerable populations. All these factors highlight the need to monitor environmental levels of PGE and continue research on their bioavailability, behaviour, speciation and associated toxicity to enable us to better assess their potential to elicit health effects in humans.

Ni(II) ions dysregulate cytokine secretion from human monocytes

Nickel-containing alloys are used in dentistry because of their low cost, but poor corrosion behavior increases their risk of causing adverse biological responses. Intraorally, nickel-containing alloys accumulate bacterial plaque that triggers periodontal inflammation via toxins such as lipopolysaccharide (LPS). Recent evidence suggests that in monocytes, Ni(II) amplifies LPS-induced secretion of several cytokines that mediate periodontal destruction. Thus, we investigated the effects of Ni(II), with or without LPS, on the secretion of a broader array of cytokines from monocytes. We then measured monocytic expression of two proteins, Nrf2 and thioredoxin-1 (Trx1), that influence the regulation of cytokine secretion. Cytokine arrays were used to measure the effects of 0-50 microM Ni(II) on cytokine secretion from human THP1 monocytes, with or without LPS activation. Immunoblots were used to estimate Nrf2 and Trx1 levels. Our results indicate that both Ni(II) alone and Ni(II) with LPS have broad-based effects on cytokine secretion. Ni(II) increased Nrf2 levels by threefold, and LPS amplified the effects of Ni(II) by 10-fold. Trx1 levels did not change under any condition tested. Our results suggest that Ni(II)-induced changes in cytokine secretion by monocytes are diverse and may be influenced by Nrf2 but are not likely influenced by changes in whole-cell Trx1 levels.

The influence of Ni(II) on surface antigen expression in murine macrophages

Biomedical alloys may release nickel ions during corrosion phenomena and, in addition to their interaction with oral tissues, these ions may also influence characteristic properties of the immune system cells. The aim of this study was to evaluate the effect of nickel chloride on the expression of functionally distinct surface antigens in murine RAW macrophages. The expression of the surface antigens CD14, CD40, MHC class I, MHC class II, CD80, CD86, CD54 was analyzed by flow cytometry. The bacterial endotoxin lipopolysaccharide (LPS) was used as a positive control to induce antigen expression. Cells were stimulated with NiCl(2) (0.1 and 0.5mm) in the presence and absence of LPS (0.1 or 25 microg/ml). After exposure periods of 6, 24 and 48 h, LPS caused a time- and dose-dependent increase in the expression of all surface antigens. CD14 expression was up-regulated by 0.1 microg/ml LPS by about 10-fold after 24h and 100-fold after 48 h. After 48 h, NiCl(2) alone up-regulated the expression of all surface antigens between 2- and 4-fold, while in cells stimulated by LPS, 0.1mm NiCl(2) was effective only on CD14, CD40 and MHC class I. Moreover, 0.5mm NiCl(2) even inhibited the LPS-induced expression of all surface antigens, except for CD54, which was still significantly up-regulated. These results show that nickel chloride is able to induce an up-regulation of surface antigen expression, but a high concentration may impair essential functions of macrophages stimulated by LPS.

Antimicrobial efficacy and ocular cell toxicity from silver nanoparticles

Silver in various forms has long been recognized for antimicrobial properties, both in biomedical devices and in eyes. However, soluble drugs used on the ocular surface are rapidly cleared through tear ducts and eventually ingested, resulting in decreased efficacy of the drug on its target tissue and potential concern for systemic side effects. Silver nanoparticles were studied as a source of anti-microbial silver for possible controlled-release contact lens controlled delivery formulations. Silver ion release over a period of several weeks from nanoparticle sources of various sizes and doses in vitro was evaluated in vitro against Pseudomonas aeruginosa strain PA01. Mammalian cell viability and cytokine expression in response to silver nanoparticle exposure is evaluated using corneal epithelial cells and eye-associated macrophages cultured in vitro in serum-free media. Minimal microcidal and cell toxic effects were observed for several silver nanoparticle suspensions and aqueous extraction times for bulk total silver concentrations commensurate with comparative silver ion (e.g., Ag(+) ((aq))) toxicity. This indicates that (1) silver particles themselves are not microcidal under conditions tested, and (2) insufficient silver ion is generated from these particles at these loadings to produce observable biological effects in these in vitro assays. If dosing allows substantially increased silver particle loading in the lens, the bactericidal efficacy of silver nanoparticles in vitro is one possible approach to limiting bacterial colonization problems associated with extended-wear contact lenses.

In vitro biological effects of sodium titanate materials

Monosodium titanate (MST) particles effectively bind specific metals and are therefore promising compounds for delivery or sequestration of metals in biological contexts. Yet, the biological properties of MST are largely unexplored. Our previous study showed that the cytotoxicity of these compounds was mild, but the nature of the dose response curves suggested that residual titanates in culture may have interfered with the assay. In the current study, we assessed the importance of these artifacts, and extended our previous results using fibroblasts for biological evaluation. We also assessed the biological response to a new type of titanate (referred to as amorphous peroxo-titanate or APT) that shows more promising metal binding properties than MST.

METHODS

The degree of titanate-induced interference in the MTT (mitochondrial activity assay) was estimated by means of cell-free assays with and without a final centrifugation step to remove residual titanate particulate. Cytotoxic responses to titanates were assessed by measuring succinate dehydrogenase activity (by MTT) in THP1 monocytes or L929 fibroblasts after 24-72 h exposures. Monocytic activation by APT was assessed by TNFalpha secretion (ELISA) from monocytes with or without lipopolysaccharide (LPS) activation.

RESULTS

We confirmed that residual titanate particulates may alter the SDH activity assay, but that this effect is eliminated by adding a final centrifugation step to the standard MTT procedure. Addition of MST or APT at concentrations up to 100 mg/L altered succinate dehydrogenase activity by < 25% in both monocytes and fibroblasts. Fibroblasts displayed time-dependent adaptation to the MST. APT did not trigger TNFalpha secretion or modulate LPS-induced TNFalpha secretion from monocytes.

CONCLUSIONS

Although further in vitro and in vivo assessment is needed, MST and APT exhibit biological properties that are promising for their use as agents to sequester or deliver metals in biological systems.

Biocompatibility of dental casting alloys

Most cast dental restorations are made from alloys or commercially pure titanium (cpTi). Many orthodontic appliances are also fabricated from metallic materials. It has been documented in vitro and in vivo that metallic dental devices release metal ions, mainly due to corrosion. Those metallic components may be locally and systemically distributed and could play a role in the etiology of oral and systemic pathological conditions. The quality and quantity of the released cations depend upon the type of alloy and various corrosion parameters. No general correlation has been observed between alloy nobility and corrosion. However, it has been documented that some Ni-based alloys, such as beryllium-containing Ni alloys, exhibit increased corrosion, specifically at low pH. Further, microparticles are abraded from metallic restorations due to wear. In sufficient quantities, released metal ions-particularly Cu, Ni, Be, and abraded microparticles-can also induce inflammation of the adjacent periodontal tissues and the oral mucosa. While there is also some in vitro evidence that the immune response can be altered by various metal ions, the role of these ions in oral inflammatory diseases such as gingivitis and periodontitis is unknown. Allergic reactions due to metallic dental restorations have been documented. Ni has especially been identified as being highly allergenic. Interestingly, from 34% to 65.5% of the patients who are allergic to Ni are also allergic to Pd. Further, Pd allergy always occurrs with Ni sensitivity. In contrast, no study has been published which supports the hypothesis that dental metallic materials are mutagenic/genotoxic or might be a carcinogenic hazard to man. Taken together, very contradictory data have been documented regarding the local and systemic effects of dental casting alloys and metallic ions released from them. Therefore, it is of critical importance to elucidate the release of cations from metallic dental restorations in the oral environment and to determine the biological interactions of released metal components with oral and systemic tissues.

Gold-induced reactive oxygen species (ROS) do not mediate suppression of monocytic mitochondrial or secretory function

The toxicity of anti-rheumatic gold compounds has limited their use and development, yet both the toxicological and therapeutic actions of these compounds remain unclear. In the current study, we tested the hypothesis that intracellular reactive oxygen species (ROS) induced by Au(I) or Au(III) compounds mediate their ability to suppress mitochondrial activity.

METHODS

Human THP1 monocytes were exposed to HAuCl(4) x 3H(2)O (Au(III)), or the anti-rheumatic compounds auranofin (AF) or gold sodium thiomalate (GSTM) for 6-72 h, after which mitochondrial activity (succinate dehydrogenase) was measured. To assess the role of cellular redox status as a mediator of mitochondrial suppression, monocytes were pre-treated with a pro-oxidant (t-butyl hydroquinone, t-BHQ) or antioxidant (N-acetyl cysteine, NAC ). ROS levels were measured 0-24h post-gold addition to determine their role as mediators of mitochondrial activity suppression.

RESULTS

AF was the most potent inhibitor of mitochondrial activity, followed by Au(III) and GSTM. Only Au(III) induced intracellular ROS; no ROS formation was observed in response to AF or GSTM exposure. Although anti- and pro-oxidants had some effects on mitochondrial suppression of Au compounds, collectively the data do not support redox effects or ROS formation as major mediators of Au-compound mitochondrial suppression.

CONCLUSIONS

Our results do not indicate that ROS and redox effects play major roles in mediating the cytotoxicity of AF, GSTM or Au(III).

Adsorption of biometals to monosodium titanate in biological environments

Monosodium titanate (MST) is an inorganic sorbent/ion exchanger developed for the removal of radionuclides from nuclear wastes. We investigated the ability of MST to bind Cd(II), Hg(II), Au(III), or the Au-organic compound auranofin to establish the utility of MST for applications in environmental decontamination or medical therapy (drug delivery). Adsorption isotherms for MST were determined at pH 7-7.5 in water or phosphate-buffered saline. The extent of metal binding was determined spectroscopically by measuring the concentrations of the metals in solution before and after contact with the MST. Cytotoxic responses to MST were assessed using THP1 monocytes and succinate dehydrogenase activity. Monocytic activation by MST was assessed by TNFalpha secretion (ELISA) with or without lipopolysaccharide (LPS) activation. MST adsorbed Cd(II), Hg(II), and Au(III) under conditions similar to those in physiological systems. MST exhibited the highest affinity for Cd(II) followed by Hg(II) and Au (III). MST (up to 100 mg/L) exhibited only minor (<25% suppression of succinate dehydrogenase) cytotoxicity and did not trigger TNFalpha secretion nor modulate LPS-induced TNFalpha secretion from monocytes. MST exhibits high affinity for biometals with no significant biological liabilities in these introductory studies. MST deserves further scrutiny as a substance with the capacity to decontaminate biological environments or deliver metals or metal compounds for therapeutic applications.

Cytotoxicity of materials used in perforation repair tested using the V79 fibroblast cell line and the granulocyte-macrophage progenitor cells

AIM

To compare the cytotoxicity of materials used to repair perforations using permanent V79 fibroblasts and murine granulocyte-macrophage progenitor cells (CFU-GM).

METHODOLOGY

Set specimens from amalgam, glass-ionomer, SuperEBA, N-Rickert, MTA and gutta-percha were eluted with culture medium for 72 h and their cytotoxicities were assessed by incubating the extracts with V79 and bone marrow-derived progenitors for 24 h and 7 days, respectively. Cytotoxicity on V79 cells was judged using the total nucleic acid content (NAC), neutral red uptake (NRU) and reduction of the tetrazolium salt (MTT). The number of bone marrow CFU-GM colonies determined in clonal cultures stimulated with recombinant murine granulocyte-macrophage colony-stimulating factor was used to assess cytotoxicity to progenitor cells. Statistical analyses were conducted using the one-way analysis of variance and Tukey's test where appropriate.

RESULTS

All materials were cytotoxic in both cell systems; however, CFU-GM was more sensitive to the extracts than V79 cells. A similar rank order of toxicity was observed in V79 cells using the NAC and the MTT assays: glass-ionomer > N-Rickert congruent with SuperEBA > gutta-percha > amalgam congruent with MTA (P < 0.05). In contrast, the NRU test exhibited a lower sensitivity to MTA, gutta-percha and amalgam extracts. In the clonal culture assay, the toxicity was less pronounced in the presence of gutta-percha, SuperEBA and MTA. Similar cellular responses were found by placing the set specimens directly in the clonal culture dishes.

CONCLUSIONS

The sensitivity of toxicity depended on the choice of the endpoint and the cell-culture system. Nevertheless, MTA was ranked as the least cytotoxic cement in both cell systems.

In vivo cytokine secretion and NF-kappaB activation around titanium and copper implants

The early biological response at titanium (Ti), copper (Cu)-coated Ti and sham sites was evaluated in an in vivo rat model. Material surface chemical and topographical properties were characterized using Auger electron spectroscopy, energy dispersive X-ray spectroscopy and interferometry, respectively. The number of leukocytes, cell types and cell viability (release of lactate dehydrogenase) were determined in the implant-interface exudate. The contents of activated nuclear transcription factor NF-kappaB, interleukin-6 (IL-6) and interleukin-10 (IL-10) were determined by enzyme linked immunosorbent assay. An increase in the number of leukocytes, in particular, polymorphonuclear leukocytes, was observed between 12 and 48 h around Cu. A marked decrease of exudate cell viability was found around Cu after 48 h. The total amounts of activated NF-kappaB after 12 h was highest in Ti exudates whereas after 48 h the highest amount of NF-kappaB was detected around Cu. The levels of cytokine IL-6 were consistently high around Cu at both time periods. No differences in IL-10 contents were detected, irrespective of material/sham and time. The results show that materials with different toxicity grades (titanium with low and copper with high toxicity) exhibit early differences in the activation of NF-kappaB, extracellular expression and secretion of mediators, causing major differences in inflammatory cell accumulation and death in vivo.

Mercury (II) alters mitochondrial activity of monocytes at sublethal doses via oxidative stress mechanisms

The perennial controversy about the safety of mercury in dental amalgams has adversely affected the availability and the quality of dental care. Chronic Hg(II) blood concentrations above 300 nM are known to alter function of the nervous system and the kidney. However, the effects of blood concentrations of 10 to 75 nM, far more common in the general population, are not clear and mechanisms of any effects are not known. The monocyte is an important potential target of Hg(II) because of its critical role in directing inflammatory and immune responses. In the current study we tested the hypothesis that concentrations of Hg(II) of 10 to 300 nM alter monocyte activity via a redox-dependent mechanism. Mitochondrial activity was used to establish inhibitory concentrations of Hg(II) following 6 to 72 h of exposures to THP1 human monocytic cells. Then subinhibitory concentrations were applied, and total glutathione levels and reactive oxygen species (ROS) were measured. Antioxidants [N-acetyl cysteine, (NAC); Na2SeO3, (Se)] and a pro-oxidant (tert-butylhydroquinone, tBHQ) were used to support the hypothesis that Hg(II) effects were redox-mediated. After 72 h of exposure, 20 microM of Hg(II) inhibited monocytic mitochondrial activity by 50%. NAC mitigated Hg(II)-induced mitochondrial suppression only at concentrations of greater than 10 microM, but Se had few effects on Hg-induced mitochondrial responses. tBHQ significantly enhanced mitochondrial suppression at higher Hg(II) concentrations. Hg(II) concentrations of 75 and 300 nM (0.075 and 0.30 microM, respectively) significantly increased total glutathione levels, and NAC mitigated these increases. Se plus Hg(II) significantly elevated Hg-induced total cellular glutathione levels. Increased ROS levels were not detected in monocytes exposed to mercury. Hg(II) acts in monocytic cells, at least in part, through redox-mediated mechanisms at concentrations below those commonly associated with chronic mercury toxicity, but commonly occurring in the blood of some dental patients.

Au(III), Pd(II), Ni(II), and Hg(II) alter NFκB signaling in THP1 monocytic cells

The transcription factor NFkappaB plays a key role in the tissue inflammatory response. Metal ions released into tissues from biomaterials (e.g., Au, Pd, Ni, Hg) are known to alter the binding of NFkappaB proteins to DNA, thereby modulating the effect of NFkappaB on gene activation and, ultimately, the tissue response to biomaterials. Little is known about the effect of these metals on key signaling steps prior to NFkappaB-DNA binding such as transcription factor activation or nuclear translocation, yet these steps are equally important to modulation of the pathway. Oxidative stress is known to alter NFkappaB proteins and is suspected to play a role in metal-induced NFkappaB signaling modulation. Our aim in the current study was to assess the effects of sublethal levels of Ni, Hg, Pd, and Au ions on NFkappaB activation and nuclear translocation in the monocyte, which is acknowledged as an important orchestrator of the biological response to materials and the pathogenesis of chronic disease. Sublethal concentrations of Au(III), Ni(II), Hg(II), and Pd(II) were added to cultures of human THP1 monocytic cells for 72 h. In parallel cultures, lipopolysaccharide (LPS) was added for the last 30 min to activate the monocytic cells. Then cellular cytoplasmic and nuclear proteins were isolated, separated by electrophoresis, and probed for IkappaBalpha degradation (activation) and NFkappaB p65 translocation. Protein levels were digitally quantified and statistically compared. The levels of reactive oxygen species (ROS) in the monocytic cells were measured as a possible mechanism of metal-induced NFkappaB modulation. Only Au(III) activated IkappaBalpha degradation by itself. Au(III) and Pd(II) enhanced LPS-induced IkappaBalpha degradation, but Hg(II) and Ni(II) suppressed it. Au(III), Ni(II), and Pd(II) activated p65 nuclear translocation without LPS, and all but Ni(II) enhanced LPS-induced translocation. Collectively, the results suggest that these metal ions alter activation and translocation of NFkappaB, each in a unique way at unique concentrations. Furthermore, even when these metals had no overt effects on signaling by themselves, all altered activation of signaling by LPS, suggesting that the biological effects of these metals on monocytic function may only be manifest upon activation. None of the metal ions elevated levels of ROS at 72 h, indicating that ROS were probably not direct modulators of the NFkappaB activation or translocation at this late time point.

Effects of cured dentin bonding materials on human monocyte viability

OBJECTIVES

Dentin Bonding Agents (DBAs) have been proposed as root-end filling materials. This study examined the effect of polymerized DBAs on human monocyte viability.

STUDY DESIGN

Monocytes were directly isolated from peripheral blood and being exposed to cured Scotch bond I (Single Bond) and Prime & Bond in different time intervals (36 and 72 hours). The viability of monocytes was determined by MTT assay.

RESULTS

Viability of the cells was time dependent. There was no significant difference between the effect of 2 DBAs on monocytes.

CONCLUSION

Results indicate that DBAs in polymerized form can alter the viability of monocytes and decrease it within time.

A new austenitic stainless steel with negligible nickel content: an in vitro and in vivo comparative investigation

New nickel (Ni)-reduced stainless-steel metals have recently been developed to avoid sensitivity to Ni. In the present study, an austenitic Ni-reduced SSt named P558 (P558, Böhler, Milan, Italy) was studied in vitro on primary osteoblasts and in vivo after bone implantation in the sheep tibia, and was compared to ISO 5832-9 SSt (SSt) and Ti6Al4V. Cells were cultured directly on P558 and Ti6Al4V. Cells cultured on polystyrene were used as controls. Osteoblast proliferation, viability and synthetic activity were evaluated at 72 h by assaying WST1, alkaline phosphatase activity (ALP), nitric oxide, pro-collagen I (PICP), osteocalcin (OC), transforming growth factor-beta1 (TGFbeta-1) and interleukin-6 (IL-6) after 1.25(OH)2D3 stimulation. Under general anaesthesia, four sheep were submitted for bilateral tibial implantation of P558, SSt and Ti6Al4V rods. In vitro results demonstrated that the effect of P558 on osteoblast viability, PICP, TGF beta-1, tumor necrosis factor-alpha production did not significantly differ from that exerted by Ti6Al4V and controls. Furthermore, P558 enhanced osteoblast differentiation, as confirmed by ALP and OC levels, and reduced IL-6 production. At 26 weeks, the bone-to-implant contact was higher in P558 than in SSt (28%, p<0.005) and Ti6Al4V (4%, p<0.05), and was higher in Ti6Al4V than in SSt (22%, p<0.005). The tested materials did not affect bone microhardness in pre-existing host bone as evidenced by the measurements taken at 1000 microm from the bone-biomaterial interface (F=1.89, ns). At the bone-biomaterial interface the lowest HV value was found for SSt, whereas no differences in HV were observed between materials (F=1.55, ns). The current findings demonstrate P558 biocompatibility both in vitro and in vivo, and osteointegration processes are shown to be significantly improved by P558 as compared to the other materials tested.

Sublethal concentrations of Au (III), Pd (II), and Ni(II) differentially alter inflammatory cytokine secretion from activated monocytes

Many transition metals have been viewed collectively as nonspecific biological toxins in cells, which has limited investigation into their possible therapeutic effects. In the current study, the effects of Au(III), Ni(II), and Pd(II) on the differential secretion of cytokines from monocytes has been investigated. This is critical to understanding any therapeutic potential of these metals, their allergenicity, or the clinical effects of current metal therapies such as chrysotherapy. Lethal concentrations (defined as > 50% suppression of mitochondrial succinate dehydrogenase (SDH) activity) of metals were determined by dose-response curves with the use of 72 h exposures to human THP-1 monocytes. Then, secretion of TNFalpha, IL1beta, and IL6 were measured after the monocytes were exposed to sublethal concentrations of metals, with or without stimulation by lipopolysaccharide. The concentrations of Au(III), Pd(II), and Ni(II) required to suppress SDH activity by 50% were found to be 255, 270, and 90 microM, respectively. No sublethal concentration of any metal alone caused secretion of the cytokines. However, LPS-induced cytokine secretion was significantly and differentially altered by sublethal concentrations of each metal. Differential responses were highly dependent on metal concentration and involved both suppression and potentiation of the LPS activation. In the case of Ni(II), potentiation of TNFalpha, IL1beta, and IL6 ranged from 200% for TNFalpha to over 1200% for IL6. Metals such as Au(III), Pd(II), and Ni(II) differentially alter cytokine expression from monocytes. These results imply that metals have more specific effects on cell signaling than previously assumed. These results also are important in explaining multiple clinical effects often seen with chrysotherapy, identifying potential new avenues for metal therapy, and understanding the inflammatory effects of metals such as nickel.

Hg2+ and Ni2+ alter induction of heat shock protein-72 in THP-1 human monocytes

The biological liabilities that result from the release of metal ions from biomedical alloys, particularly Ni(2+) and Hg(2+), continue to be a concern. Heat-shock proteins (HSP) are a class of molecular chaperones that may be induced under conditions of cellular stress, including oxidative stress. Our hypothesis was that because Hg(2+) and Ni(2+) alter other cellular stress responses such as glutathione levels and cytokine secretion, these metal ions may alter HSP induction in monocytes, which are key cells in the response of tissues to biomedical alloys. THP-1 monocytes were exposed to sublethal concentrations of Hg(2+) or Ni(2+) for 1 h with or without heat stress (43 degrees C), then allowed to recover at 37 degrees C for 2-6 h. HSP72 was measured using immunoblotting with phosphorimage quantification. Hg(2+) exposures of 2-10 micromol/L induced HSP72 without heat stress. With heat stress, HSP72 levels were altered by Hg(2+) versus heat stress alone. The response depended on the concentration of Hg(2+) and the recovery time. Hg(2+) at 10 micromol/L caused uniformly lower HSP72 levels. Ni(2+) exposures of 20-100 micromol/L did not induce HSP72 without heat stress, but significantly altered heat-induced HSP72 expression, with a significant increase in expression over heat alone at 40 and 100 micromol/L. Results from the current study support the hypothesis that these metal ions can, at concentrations relevant to those released from biomedical alloys, modulate HSP expression in human monocytes. The modulation of HSP expression indicates an early sign of cellular stress that may be important to the overall biological response to biomedical alloys containing and releasing these metal ions.

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.

IL-1alpha, IL-1beta and TNF-alpha secretion during in vivo/ex vivo cellular interactions with titanium and copper

Titanium (Ti) and copper (Cu) were used to evaluate cytokine secretion around materials with different chemical properties. Ti disks were coated with Cu or left uncoated. The disks were inserted subcutaneously in rats for 1, 3, 12, 18, 24 and 48 h. Interleukin-1alpha (IL-1alpha), IL-1beta and tumor necrosis factor-alpha (TNF-alpha) concentrations were measured in vivo around the materials, in sham operated sites, and after ex vivo incubation of surface adherent cells. Ti and Cu revealed distinct cytokine expression patterns. Cu recruited cells showed higher and prolonged release of IL-1alpha than Ti at longer times (>24 h), whereas Ti exhibited a transient IL-1alpha response at earlier periods (<24 h). An early enhanced secretion of TNF-alpha characterized Ti. Low amounts of IL-1beta were found around both materials. Sham site recruited cells produced lower levels of cytokines. The results after ex vivo incubations were similar to those in vivo. This study shows that material chemical properties influence early cytokine production. The Ti-associated transient rise of IL-1alpha and TNF-alpha may be of importance for the early tissue response around biocompatible materials, while a delayed high IL-1alpha expression could be a marker of inflammation induced by toxic materials.

Low-dose, long-term exposures of dental material components alter human monocyte metabolism

The short-term degradation of dental polymers and alloys in biological environments has been well documented, but recent evidence indicates that oral tissues may be chronically exposed to low levels of these released components. The effect of these chronic exposures on the ability of cells to respond to a subsequent challenge is not known. To investigate this idea, we exposed human THP-1 monocytes to sublethal concentrations of HEMA, TEGDMA, Hg(2+), and Ni(2+) for 2 weeks and then assessed the monocytic response to subsequent 24-h challenge with the same components at higher concentrations. Chronic (2 week) exposures of monocytes to HEMA and both metal ions significantly altered monocyte response to short-term (24 h) secondary exposures, even when overt effects of the chronic exposures were not apparent. However, cellular responses were highly variable depending on the material and its concentrations. For TEGDMA, no effects were seen. These results demonstrate that the chronic effects of materials must be considered even when the chronic exposure has no initial overt effect. The effect on cells may only be apparent if the cell is challenged by a secondary exposure.

Relating nickel-induced tissue inflammation to nickel release in vivo

Nickel has a number of adverse biological effects that have made the use of nickel in biomedical implants controversial. Yet information about the distribution of nickel in tissues around nickel-containing implants is scarce. The purpose of the current study was to use a laser ablation technique, combined with inductively coupled mass spectroscopy, to assess the spatial distribution of nickel around nickel-containing implants in vivo. Polyethylene, pure nickel wire, or a nickel-containing alloy (Ni-Cr) were implanted subcutaneously into rats for 7 days. The tissues were analyzed for Ni content and inflammation at 1-mm intervals up to 5 mm away from the implants. The sham surgery sites and the polyethylene caused mild to moderate inflammation 1-2 mm from the implant site with no detectable nickel in the tissue. The nickel wire caused severe inflammation up to 5 mm away from the implant site with necrosis for 1 mm around the implant. Nickel concentrations reached 48 microg/g near the implants, falling exponentially to undetectable levels at 3-4 mm from the implants. The Ni-Cr wire caused inflammation equivalent to polyethylene, with less than 4 microg/g of nickel present in the tissue for 1-2 mm around the implants. The current study showed that the laser-ablation technique was well suited for the analysis of soft tissues for metal-ion content, and that the nickel distribution in tissues correlated well with overt tissue inflammation.

In vitro TNF-α release from THP-1 monocytes in response to dental casting alloys exposed to lipopolysaccharide

STATEMENT OF PROBLEM

Studies have found that lipopolysaccharide (LPS) attaches to and is eluted from dental alloys, but the biologic effects of LPS are not known.

PURPOSE

This study evaluated the ability of dental casting alloys pre-exposed to LPS to activate human monocytes with and without subsequent elution of the LPS.

MATERIAL AND METHODS

Eight types of casting alloys (n = 6 specimens per type) were exposed to LPS (Escherichia coli @ 100 micrograms/mL) for 24 hours. Controls were not exposed to LPS. Teflon (Tf) (+/- LPS) served as the material control. Treated alloys were transferred to THP-1 human monocytes for 24 hours or placed into phosphate-buffered saline (PBS) solution for 120 hours before monocyte exposure. Monocyte activation was assessed by tumor necrosis factor alpha (TNF-alpha) secretion into the medium. Alloys without LPS, with LPS but without PBS elution, and with LPS and elution were compared with ANOVA and Turkey intervals (alpha=.05).

RESULTS

Specimens without LPS exposure but with elution caused no detectable TNF-alpha secretion from monocytes. Specimens without elution into PBS caused low-to-moderate TNF-alpha secretion, indicating a possible false-positive result from the alloy conditioning solution used. After LPS exposure but no elution, high levels of TNF-alpha were found. When alloys were eluted for 120 hours after LPS exposure, there was no detectable TNF-alpha released.

CONCLUSION

In this in vitro system as in past studies, LPS appeared to adhere to and elute from the alloys. Monocytes were activated initially but not after elution into PBS for 120 hours. Alloy conditioning solutions may also have an artifactual effect on cytokine release.

Costimulatory molecule expression following exposure to orthopaedic implants wear debris

Patients with long-term orthopedic implants may develop inflammatory reactions due to the accumulation of biomaterial particles both around the implant and in distant organs. The exact impact of these particles on the normal immune cell function still remain relatively unclear. Activation of T-cells following exposure to biomaterial particles is driven by macrophages and requires synergistic signals primed by both antigen presentation and costimulation. The pattern of costimulatory molecule expression (CD80,CD86) was primarily examined using immunohistochemistry on tissue specimens of bone/implant interface membranes taken from sites of bone erosion. Additionally, costimulatory molecule expression was also assessed in the monocytic leukemia cell line U937 following exposure to clinically relevant titanium aluminum vanadium (TiAlV) and stainless steel particles (FeCrNi) cultured in vitro. This study demonstrates the induction and prominent expression of CD86 on almost all macrophage subsets at the bone/implant interface, including fused forms and large multinucleated giant cells (MNGC). In vitro analysis also indicated phagocytosis of metal particles by differentiated U937 caused significant induction of both CD80 and CD86 (p < 0.01), although the expression of CD86 dominated following prolonged exposure. The data presented highlights that CD86 is the predominant costimulatory molecule ligating to the complementary CD28 molecule at the inflammatory lesion of the interface. We propose that the intracellular presence of indigestible implant material, in addition to elevated costimulatory molecule expression, may promote T-cell inflammatory reactions at sites close to and distant from the orthopedic implant.

In vitro effects of zirconia and alumina particles on human blood monocyte-derived macrophages: X-ray microanalysis and flow cytometric studies

The cytocompatibility of two particulate bioceramics, zirconia and alumina, was studied using human blood monocytes driven to differentiate into mature macrophages with granulocyte macrophage-colony-stimulating factor. Changes in individual cell elemental composition, particularly sodium and potassium content, were assessed by X-ray microanalysis of ultrathin freeze-dried sections. Phagocytosis and respiratory burst of macrophages exposed to biomaterial for 7 days were analyzed under flow cytometry using uptake of fluorescent latex beads and 2'7'-dichlorofluorescien diacetate oxidation, respectively. Zirconia and alumina particles were found to decrease the intracellular potassium/sodium ratio (an index of cell vitality) significantly (p<.01) in 7-day-cultured macrophages compared to control cells cultured out of material. Phagocytosis of both ceramic particles by macrophages was followed by a concomitant decrease in cell phagocytic ability (27%) and a marked altered oxidative metabolism (>2 times reduced by zirconia and >5 times reduced by alumina). The present study clearly demonstrates that reduction of the phagocytic capacity of macrophages associated with altered oxidative metabolism caused by biomaterial particles is characterized by changes in intracellular elemental content. Thus, investigation of cellular homeostasis by electron probe microanalysis together with analysis of functional changes may improve estimation of biomaterial cytocompatibility.

Effect of silver, copper, mercury, and nickel ions on cellular proliferation during extended, low-dose exposures

Previous studies have demonstrated and quantified the cytotoxicity of metal ions in vitro, but the data from these reports have been limited to short-term exposures of metal ions to cells (24-72 h). Yet, the longer-term, low-dose effects of metal ions are most relevant to the clinical use of dental and other biomedical alloys. Thus, the purpose of the current study was to assess longer-term effects of ions of silver, copper, mercury, and nickel - four metal ions known to be released from dental alloys - on monocytes. THP-1 human monocytes were exposed to the metal ions for up to 4 weeks. Concentrations of the metal ions were 1-10% of those known to cause cytotoxicity with 24-h exposures. Cellular proliferation and cellular viability were measured weekly. Ag(1+) and Hg(2+) did not alter the percentage of nonviable cells, but Cu(2+) and Ni(2+) increased the nonviable component as a function of metal concentration. These effects were cumulative over the 4 weeks only for Ni(2+). All metal ions caused a significant reduction in cellular proliferation, but the pattern of the effect was unique to each metal ion, and the effects were often not evident until 3 or 4 weeks of exposure. The results of the current study indicate that metal ions released from metallic biomaterials may have adverse biological effects at concentrations lower than previously reported.

A new screening test for toxicity testing of dental materials

OBJECTIVES

The development of a micro plate assay for cytotoxicity testing of dental materials based on a bioassay using brine shrimp larvae (artemia salina) as sensitive organisms.

METHODS

Brine shrimp larvae are commonly used for cytotoxicity assays in pharmacology. These larvae are sensitive to toxic substances. The ratio between dead larvae (no motility) and living larvae (high motility) in comparison to a control without any toxic substances is used to estimate the toxicity of the test solutions. The test materials (Arabesk((R)), Solitaire((R)), Pertac((R)) II, Tetric((R)), Herculite((R)) and the compomer materials Dyract((R)), Hytac((R)), Compoglass((R))) were polymerized and consecutively milled. After incubation of 1g in 4ml distilled water at 37 degrees C for 48h, the solid materials were separated by centrifugation. The solutions were equibrilated with NaCl to a salt content of 25g/l. Aliquots of 200microl were distributed in eight micro wells and 50microl of a artemia salina containing (n=8-14) solution were added to each well. As controls eight wells with 250microl salt solution containing a comparable number of brine shrimp were used. At baseline, after 2, 5, 24 and 48h, the dead shrimp were counted using a stereo microscope. Finally all shrimps were sacrificed using Na-acid (5%) and counted to get the number of shrimps per well.

RESULTS

All compomers and Solitaire caused 100% brine shrimp lethality after 24h and showed significantly (p<0.01, signed rank test) higher toxicities than the remaining composites. With the exception of Pertac II, all composites showed significantly higher toxic values than the control. Pertac II did not show any differences from the controls used.

CONCLUSIONS

This new technique has some advantages for toxicity testing of restorative materials, because it can quickly be carried out at low costs. The disadvantage is the high quantity of material used and the low sensitivity.

Effect of dental metal ions on glutathione levels in THP-1 human monocytes

The release of metal ions from dental restorations has been well established, but the sublethal effects of these ions on oral tissues remain undefined. Metal ions are a potential cause of sublethal oxidative stress in cells. Oxidative stress is known to alter cellular processes which are important in the inflammation of tissues. The presence of oxidative stress is commonly assessed by measuring the oxidized (GSSG) and reduced (GSH) forms of cellular glutathione. Normally, the majority of cellular glutathione exists as GSH and the GSH-GSSG ratio is high. Since monocytes often orchestrate inflammatory responses, oxidative stress in monocytes is important. Our hypothesis for the current work was that metal ions induce oxidative stress in monocytes which is manifested by a lower GSH-GSSG ratio. Human THP-1 monocytes were exposed for 24 h to sublethal concentrations of ions of Ag, Be, Co, Cu, Hg, Ni, Pd, and Zn--all known to be released from dental biomaterials. GSH and GSSG were measured using colorimetric assays. Cu lowered the GSH-GSSG ratio as hypothesized, but the ratio could not be determined for other metals because other metal ions interfered with the GSSG assay. However, a statistically significant (ANOVA/Tukey) increase in GSH per cell was observed upon exposure to Ag (50%), Co (100%), Hg (250%) and Zn (10%). This increase may be indicative of an oxidative stress in its own right. Alterations in GSH levels may be important to how released metal ions alter cytokine secretion from monocytes and other cells which play a role in the inflammatory response to dental biomaterials.

Ability of Ni-containing biomedical alloys to activate monocytes and endothelial cells in vitro

Nickel-containing alloys commonly are used in medical and dental applications that place them into long-term contact with soft tissues. The release of Ni ions from these alloys is disturbing because of the toxic, immunologic, and carcinogenic effects that have been documented for some Ni compounds. In particular, Ni ions in solution recently have been shown to cause expression of inflammatory mediators, such as interleukin-1beta (IL-1beta), tumor necrosis factor-alpha (TNF-alpha), and intercellular adhesion molecules (ICAMs) from keratinocytes, monocytes, and endothelial cells. However, the ability of the solid alloys themselves to induce these inflammatory effects has not been demonstrated. An in vitro system was used to determine if Ni-containing biomedical alloys could cause secretion of either IL-1beta or TNF-alpha from monocytes or expression of ICAMs on endothelial cells. Pure nickel, titanium, and three biomedical alloys-18-8 stainless steel, NiTi, and Rexillium III-were evaluated. First, it was determined whether or not the alloys or pure metals could cause cytotoxicity to THP-1 human monocytes or human microvascular endothelial cells (HMVECs) by measuring the succinic dehydrogenase (SDH) activity of the cells. Then, using identical conditions of exposure, the secretion of IL-1beta or TNF-alpha from monocytes or ICAM-1 expression on the HMVECs was determined. Only pure nickel suppressed (by 48% compared to Teflon controls) the SDH activity of the HMVECs or THP-1 monocytes. No alloy or metal caused the HMVECs to express ICAM-1, but the NiTi alloy caused a significant (ANOVA/Tukey) secretion of IL-1beta from the THP-1 monocytes. Secretion of TNF-alpha induced by NiTi was detectable but not statistically significant. The levels of IL-1beta secretion from monocytes were sufficient to induce ICAM-1 expression on HMVECs. The release of Ni from the NiTi was a logical suspect in causing the IL-1beta secretion by monocytes, but its role was not confirmed since other alloys, such as Rexillium III, released the same quantities of Ni yet did not activate the THP-1 monocytes. Within the limitations of in vitro conditions, our results indicate that NiTi alloys pose a risk of promoting an inflammatory response in soft tissues by activating monocytes. Further study is needed to substantiate this finding in vivo.

Effect of dentin bonding agents on the secretion of inflammatory mediators from macrophages

Dentin bonding agents (DBAs) have been proposed as substitutes for amalgam as root-end filling materials. The current study tested the hypothesis that certain components of DBAs could alter the secretion of cytokines from macrophages. Such alteration would likely be undesirable for healing of the periapical tissues. Human THP-1 macrophages were exposed to 2-hydroxyethyl methacrylate, 4-methacryloxyethyl trimelliate anhydride, bisphenol-gycidylmethacrylate, and urethane dimethacrylate. The secretion of interleukin-1 beta (IL-1 beta) and tumor necrosis factor-alpha (TNF-alpha) were measured with or without challenge by lipopolysaccharide (LPS). Results showed that all DBA components completely suppressed LPS-induced IL-1 beta and TNF-alpha secretion at concentrations that suppressed mitochondrial activity by 50%. In addition, 4-methacryloxyethyl trimelliate anhydride induced secretion of IL-1 beta, but not TNF-alpha, without the LPS challenge. These results indicate that DBA components may alter normal macrophage-directed inflammatory responses if the macrophages are exposed to sufficiently high concentrations of these components.

Effects of dentin bonding agents on macrophage mitochondrial activity

Dentin bonding agents (DBA) have been considered for use as root-end fillings. Previous studies have documented the release of DBA components in vivo and in vitro, but the biological implications are not clear. The macrophage is important in wound healing, and likely to be important in any inflammatory response. Therefore, this study determined the concentrations of the components of DBAs that suppress the mitochondrial activity of human macrophages in vitro. THP-1 macrophages were cultured in the presence of four DBA components (2-hydroxyethyl methacrylate (HEMA), 4-methacryloxyethyl trimellitate anhydride (4-META), bisphenol-glycidylmethacrylate (Bis-GMA), and urethane dimethacrylate (UDMA)) at various concentrations and for varying durations. Residual effects were also measured after the resins were removed. Controls received only the vehicle solution, ethanol or water. THP-1 mitochondrial activity was estimated using the MTT assay, and the 50% toxicity concentrations (TC50) were determined graphically. Resin components suppressed the mitochondrial activity of macrophages at different concentrations (TC50 values for HEMA (10,000 mumol/L), 4-META (3,800 mumol/L), Bis-GMA (130 mumol/L), and UDMA (110 mumol/L) at 24 h, and the effect was time-dependent. Residual effects were observed for all resins.

Techniques to investigate cellular and molecular interactions in the host response to implanted biomaterials

Evaluation of the host response to implanted materials requires systematic, objective investigations of responses at both the cellular and molecular levels. This article explains the basis behind two technologies: antibody and molecular techniques, which will give valuable information when applied to investigations of cells and molecules involved in the host biomaterial interaction. Such investigations are well underway, and a number of groups are now studying well characterised cell markers or molecules to evaluate the host response to biomaterials. Here we outline current technologies for the development of antibodies as tools to study cell markers or molecules, including those for which reagents are not yet available and DNA based technologies, whose continued application should prove an invaluable adjunct to existing approaches. These technologies may be particularly valuable to investigations focusing on newly characterised cytokines, receptors or cell adhesion molecules and subsequently provide a way forward for the production of advanced biomaterials.

Effect of Ni ions on expression of intercellular adhesion molecule 1 by endothelial cells

Previous studies have shown that Ni-based alloys implanted into soft tissues cause an infiltration of inflammatory cells around the implant. This phenomenon is potentially important to dental alloys which are adjacent to oral tissues. To help define the mechanisms by which Ni causes an infiltration of inflammatory cells, we exposed endothelial cells in vitro to Ni ions and measured the expression of intercellular adhesion molecule 1 (ICAM-1). ICAM-1 is known to be involved in the recruitment of inflammatory cells from the bloodstream. We also exposed macrophages to Ni ions to test the hypothesis that Ni might alter cytokine secretion and subsequently cause expression of ICAM-1 on endothelial cells. The results showed that Ni ions could promote the expression of ICAM-1 on endothelial cells, but only at concentrations which were high enough (850 mumol/L for 24 h) to suppress cell metabolic activity. Although we had previous evidence that Ni could cause macrophages to secrete cytokines such as interleukin 1 beta, Ni-exposed macrophage supernatants did not induce expression of ICAM-1 on endothelial cells at concentrations subtoxic to the macrophages (85 mumol/L). At subtoxic concentrations, Ni ions were able to suppress ICAM-1 expression on endothelial cells which were stimulated with lipopolysaccharide. Thus, Ni ions either promoted or suppressed the expression of ICAM-1 depending on their concentration. This dual action of Ni ions may be important in vivo where a gradient of concentrations of released ions is likely to exist around the implanted biomaterial. Further studies are necessary to determine the effect of time of exposure and the molecular mechanisms of increased ICAM-1 expression.

Dental materials: 1995 literature review

This critical review of the published literature on dental materials for the year 1995 has been compiled by the Dental Materials Panel of the United Kingdom. It continues the series of annual reviews started in 1973 and published in the Journal of Dentistry. Emphasis has been placed upon publications which report upon the materials science or clinical performance of the materials. The review has been divided by accepted materials classifications (fissure sealants, glass polyalkenoate cements, resin composites, dentine bonding, dental amalgam, endodontic materials, casting alloys, investment materials, resin-bonded bridges and ceramo-metallic restorations, all ceramic restorations, denture base and soft lining materials, impression materials, dental implants, orthodontic materials and biomechanics). Three hundred and thirty articles published in 68 titles have been reviewed.