Biological effects of Ni(II) on monocytes and macrophages in normal and hyperglycemic environments.

Corrosion and release of nickel ions from biomedical alloys are well documented, but little is still known about the effects of released nickel ions on cellular function with recurrent inflammatory challenges. Evidence suggests Ni(II) ions amplify LPS-induced secretion of several pro-inflammatory cytokines from monocytes. Exacerbating the inflammatory response, hyperglycemic conditions also affect monocytic function. This study investigated how Ni(II) and hyperglycemic conditions, both singly and in combination, alter monocyte proliferation, mitochondrial activity, inflammatory responses, and differentiation. Results showed that Ni(II) did not affect proliferation, but decreased mitochondrial activity in monocytic-cells and macrophages under normal conditions. However, hyperglycemic conditions negated the toxicity seen with Ni(II) exposure. Cytokine secretion in response to LPS was variable, with little effect on IL6 secretion, but significantly increased secretion of IL1ß at intermediate Ni(II) concentrations. Hyperglycemic conditions did not alter these results significantly. Finally, exposure to eluants from nickel-based commercial alloys caused enhanced IL1ß secretion from PMA-treated cells. These data suggest that corrosion products from nickel-containing dental alloys increased Ni(II)-induced changes in cytokine secretion by monocytes and macrophages. By better defining the effects of Ni(II) at these lower, biomedically relevant concentrations, we improve understanding of the biomedical alloy risk in the context of dental inflammation. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 106A:2433-2439, 2018.

Cytotoxicity of endodontic sealers after one year of aging in vitro.

The in vitro cytotoxic response to endodontic sealers was assessed for one year. AH-Plus (AHP), Epiphany (EPH), EndoRez (ER), Guttaflow (GF), InnoEndo (IN), and Pulp Canal Sealer (PCS) were exposed to mouse osteoblasts and human monocytes after curing, 52 weeks of aging, and after resurfacing post-aging; cellular response was estimated by succinate dehydrogenase (SDH) activity. The effect of materials on TNFα secretion from activated (LPS) and inactivated monocytes also was measured. Cell responses were compared with ANOVA and Tukey post hoc analysis (α = 0.05). Initially, all materials except GF suppressed osteoblastic SDH activity compared with Teflon (Tf) controls. SDH activity in cells exposed to some aged sealers improved significantly; but IN and ER remained cytotoxic. When aged materials were resurfaced then tested, AHP, ER, GF, and IN did not change. EPH and PCS were more toxic. Monocytes responded similarly to the osteoblasts. No endodontic sealer activated monocytic TNFα secretion (p > 0.05 vs. -LPS Tf-controls). LPS-activated monocytes exposed to unresurfaced AHP and IN significantly suppressed TNFα secretion. When activated monocytes were exposed to the resurfaced sealers, differential suppression of TNFα secretion was observed for three of the four sealers tested (EPH, IN, and PCS). The results suggest that long-term aging may be a useful adjunct to in vitro assessment of these materials.

Dysregulation of monocytic cytokine secretion by endodontic sealers.

Recent studies have reported that sealers may alter the secretion of specific cytokines from THP1 monocytic cells in vitro. In this study, a cytokine array was used to determine if endodontic sealers changed secretion of 42 cytokines. White mineral trioxide aggregate (WMTA), MTA preparation (CS), AH-Plus (AHP), and Pulp Canal Sealer (PCS) were mixed, allowed to set for 72 h, then "aged" in buffered-saline for 12 weeks. Aged specimens were placed in direct contact with THP1 for 72 h and their cytotoxicity (MTT assay) was assessed. Materials that were not severely toxic were then exposed to THP1 with or without lipolysaccharide (LPS), and the culture medium was assayed for cytokine secretion. Secretion of cytokines was quantified using infrared scanning (Odyssey(®)); replicate pairs were averaged. PCS severely suppressed MTT activity and was not assessed for its influence on cytokine secretion. WMTA, CS, and AHP induced a broad-based increase in cytokine secretion (>20% vs. Teflon controls), but AHP induced the greatest increase (>100% in 17 of 42 cytokines). The effects of the sealers on LPS-activated THP1 were biphasic, with some increases and decreases cytokine secretion of >20%, but few larger effects. This work shows endodontic sealers may alter the secretion of a broad cross section of cytokines from monocytic cells.

Cytotoxic response of three cell lines exposed in vitro to dental endodontic sealers.

The in vitro cytotoxicity of five endodontic sealers was measured >8-12 weeks using L929 mouse fibroblasts, osteoblastic cells (ROS) 17/2.8 rat osteoblasts, and MC3T3-E1 mouse osteoblasts. Discs (n = 6) of AH-plus Jet (AHP), two versions of Endo Rez (ER, ERx), Epiphany (EPH), and Pulp Canal Sealer (PCS) were prepared. The sealers and Teflon (Tf, negative control) were placed in direct contact with cells after immersion in phosphate-buffered saline for 1-12 wk. Cellular succinate dehydrogenase (SDH) activity was estimated using the MTT method (3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, a yellow tetrazole), and activities were normalized to Teflon® controls. The cellular responses to the materials were compared using analysis of variance with Tukey posthoc analyses (α = 0.05). Initially, all sealers suppressed normalized SDH activity of L929 fibroblasts by >90%. After 12 weeks of immersion in saline, AHP exhibited the SDH activity above Tf (120%), followed by ERx (78%), ER (58%), PCS (38%), and EPH (28%), all statistically distinct (p < 0.05). In general, the three cell lines responded similarly to the sealers. However, AHP caused unique responses: ROS cells were significantly (p < 0.05) less sensitive initially, and AHP was severely cytotoxic to MC3T3 cells (<35% of Tf) through 8 weeks. The data suggest that with "aging" in saline, current endodontic sealers decrease in in vitro cytotoxicity at different rates.

Cytotoxicity, calcium release, and pH changes generated by novel calcium phosphate cement formulations.

Few published studies describe the biological properties of calcium phosphate cements (CPCs) for dental applications. We measured several biologically relevant properties of 3 CPCs over an extended (8 wk) interval. Monocalcium phosphate, calcium oxide, and synthetic hydroxyapatite were combined with either modified polyacrylic acid, light-activated modified polyalkenoic acid, or 35% w/w polymethyl vinyl ether maleic acid to obtain Types I, II, and III CPCs, respectively. Set cements were placed in direct contact with L929 fibroblasts for up to 8 weeks. Media Ca(+2) and pH were determined by atomic absorption spectroscopy and pH electrode respectively. Cell mitochondrial function was measured by MTT assay. Type I cements suppressed mitochondrial activity > 90% (vs. Teflon controls), but significantly (p < 0.05) improved to control levels over 8 weeks. Type II cements suppressed mitochondrial activity > 90% at all times. Type III cements elevated mitochondrial activity significantly after 7 wks. The pH profiles approached neutrality by 24 h, and all cements released calcium into the storage medium at all periods (24 h - 8 wk). We concluded that several types of cements had long-term biological profiles that show promise for dental applications.

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.

Inflammatory suppression by endodontic sealers after aging 12 weeks In vitro.

Dental endodontic sealers are in intimate contact with tissues around the root apex (periapical area) for extended periods. New endodontic sealers have been developed in the past decade, but the biological responses to many new products are not well documented. In this study, we assessed in vitro monocytic cytotoxic and inflammatory responses to several contemporary endodontic sealers. AH-Plus (AH), Pulp Canal Sealer (PC), Epiphany (EPH), Endo-Rez (ER), and an experimental Endo-Rez (ERx) were initially placed in buffered-saline for 12 weeks to simulate in vivo use. After "aging," specimens were placed in direct contact with THP1 monocytes for 72 h and their cytotoxicity (mitochondrial response; MTT) or ability to trigger or suppress cytokine secretion (ELISA; TNFalpha, IL1beta, IL=6; +/- lipopolysaccharide (LPS) exposure) were measured relative to Teflon (Tf) negative controls. Cellular responses among conditions were compared with ANOVA and Tukey post-hoc analysis (alpha = 0.05). Two of the five sealers, EPH and PC, still suppressed cell mitochondrial activity by 70% or more after 12 weeks of conditioning in saline. No sealer alone activated monocytic TNFalpha, IL1beta, or IL6 secretion (p > 0.05 vs. +LPS controls). When THP1 were activated by LPS after exposure to the sealers, differential suppression of TNFalpha, IL1beta, and IL6 secretion was observed for two of the five sealers tested. (EPH and PC) This data suggest that common endodontic sealers do not activate monocytic TNFalpha, IL1beta, and IL6 secretion in vitro by themselves, but degradation products of the sealers may suppress activation of monocytes.

Contemporary methacrylate resin-based root canal sealers exhibit different degrees of ex vivo cytotoxicity when cured in their self-cured mode.

The cytotoxicity of four methacrylate resin-based sealers was investigated by the 3-(4,5-dimethyl-thiazoyl)-2,5-diphenyl-tetrazolium bromide assay, which measures cell viability by assessing its succinate dehydrogenase activity. The sealers were polymerized in the self-cured mode to simulate the setting condition upon their extrusion into periradicular tissues. Disks were prepared from EndoREZ (Ultradent, South Jordan, UT), RealSeal (SybronEndo, Orange, CA), MetaSEAL (Parkell, Farmington, NY), and RealSeal SE (SybronEndo) together with positive and negative controls. After setting, they were placed in direct contact with rat osteosarcoma (ROS 17/2.8) cells and for 5 succeeding weeks after immersing in simulated body fluid (SBF). All sealers exhibited severe toxicity initially (week 0). EndoREZ and RealSeal remained severely toxic after five cycles of SBF immersion. Toxicity of the two self-etching resin-based sealers MetaSEAL and RealSeal SE decreased gradually over time. Transmission electron microscopy of cells exposed to RealSeal SE showed variable degrees of cell injury that reflect its toxicity status. Cells with intact mitochondria were identifiable after the sealer became noncytotoxic at week 5.

In vitro cytotoxicity evaluation of a self-adhesive, methacrylate resin-based root canal sealer.

This study compared the cytotoxicity of MetaSEAL (Parkell Inc, Farmington, NY), a methacrylate resin-based sealer with an epoxy resin-based (AH Plus Jet; Dentsply Caulk, Milford, DE) and a zinc oxide-eugenol-based sealer (Pulp Canal Sealer; SybronEndo, Orange, CA). Five-millimeter diameter disks prepared from the respective sealer and disks prepared from Teflon (negative control) and polymethyl methacrylate (positive control) were placed in direct contact with a rat osteosarcoma (ROS) 17/2.8 rat osteoblast-like cell line at six intervals after setting completely at 72 hours and for 5 succeeding weeks after the disks were immersed in simulated body fluid. Succinate dehydrogenase activity was evaluated by using 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyl tetrazolium bromide assay. All sealers exhibited severe toxicity at 72 hours, after which toxicity decreased gradually over the experimental period except for Pulp Canal Sealer, which remained severely toxic. MetaSEAL was more toxic than AH Plus Jet during the first week. Both were similar to the toxicity profile of the positive control after the first week, which was probably diffusion controlled.

Brushing-induced surface roughness of nickel-, palladium-, and gold-based dental casting alloys.

STATEMENT OF PROBLEM: Alloys with high nickel content have been increasingly used for dental prostheses. These alloys have excellent hardness, elastic modulus, and strength, yet have high corrosion rates when exposed to chemical or physical forces that are common intraorally. PURPOSE: The purpose of the current study was to measure the susceptibility of several types of nickel-based alloys to brushing abrasion relative to gold- and palladium-based alloys. MATERIAL AND METHODS: Au-Pt, Au-Pd, Pd-Ag, Ni-Cr, and Ni-Cr-Be dental alloys were brushed with a toothbrush (Oral-B Soft) and toothpaste (Ultrabrite) in a linear brushing machine, then the surface roughness was measured by profilometry (R(a), R(v), R(p)). Specimens (n=4) were brushed for 48 hours in a saline solution (pH 7). The effect of brushing was determined using 2-sided t tests (alpha=.05), and roughness among alloys postbrushing was compared using 1-way ANOVA with Tukey post hoc analyses (alpha=.05). RESULTS: All polished alloy surfaces (before brushing) had roughnesses of 1 microm (R(a)). Ni-Cr alloys without Be had a postbrushing surface roughness of 0.25 microm (R(a)). Postbrushing roughness of all other alloys ranged from 0.1-0.25 microm (R(a)). R(v) and R(p) values behaved similarly to R(a) values for all alloys. CONCLUSIONS: Although they have many excellent mechanical properties, Ni-Cr-Be alloys may be prone to degradation from brushing.

In vitro cytotoxic response to lithium disilicate dental ceramics.

OBJECTIVES: The use of lithium disilicate dental ceramics is increasing in dentistry and previous reports have suggested that they may have greater biological risks than previously thought. We tested a hypothesis that composition and processing influence the biological properties of these ceramics. METHODS: The cytotoxicity of two machined and three pressed lithium disilicate materials (n=6) were tested in vitro using mouse fibroblasts in direct contact with the materials for 72h. Cellular response was estimated by mitochondrial succinate dehydrogenase activity (MTT method). Mitochondrial activity was expressed as a percentage of Teflon controls, then compared to Teflon using 2-sided t-tests (alpha=0.05). Polished materials were aged in artificial saliva and tested for cytotoxicity periodically over 6 weeks, then were repolished (320grit SiC paper), aged and tested again for 4 weeks. RESULTS: All materials significantly (50-70%) suppressed cellular mitochondrial activity in the initial week, but suppression decreased by 25-30% over the next 2 weeks. In weeks 4 and 6 some materials exhibited a cytotoxic 'relapse' of 10-20%. The cytotoxic response was no different for machined or pressed materials, but the presence of ZnO had at least an association with longer-term cytotoxicity and relapse. Repolishing to 320grit did not increase cytotoxicity significantly. SIGNIFICANCE: Our results suggest that lithium disilicates are not biologically inert, and that many have a similar cytotoxicity dynamic regardless of small differences in composition or processing.

Effect of mercury(II) on Nrf2, thioredoxin reductase-1 and thioredoxin-1 in human monocytes.

OBJECTIVES: Human blood levels of mercury are commonly 10nM, but may transiently reach 50-75nM after dental amalgam placement or removal. Controversy persists about the use of mercury because the effects of these 'trace' levels of mercury are not clear. Concentrations of mercury > or =5000nM unequivocally alter redox balance in blood cells including monocytes. In the current study, we tested a hypothesis that concentrations of mercury <100nM altered levels and activities of key proteins that maintain monocytic redox balance. METHODS: Human THP1 monocytes were exposed to 10-75nM of Hg(II) for 6-72h, with or without activation by lipopolysaccharide (LPS). The redox management proteins Nrf2 and thioredoxin-1 (Trx1) were separated by electrophoresis, then quantified by immunoblotting. The activity of the seleno-enzyme thioredoxin reductase (TrxR1), important in maintaining Trx1 redox balance, was measured by cell-free and cell-dependent assays. RESULTS: Concentrations of Hg(II) between 10-75nM increased Nrf2 levels (3.5-4.5 fold) and decreased Trx1 levels (2-3 fold), but these changes persisted <24h. Hg(II) potently inhibited (at concentrations of 5-50nM) TrxR1 activity in both cell-free and intracellular assays. Furthermore, Hg(II) transiently amplified LPS-induced Nrf2 levels by 2-3 fold and limited LPS-induced decreases in Trx1. All effects of Hg(II) were mitigated by pre-adding N-acetyl-cysteine (NAC) or sodium selenide (Na2SeO3), supplements of cellular thiols and selenols, respectively. SIGNIFICANCE: Our results suggest that nanomolar concentrations of Hg(II) transiently alter cellular redox balance in monocytes that trigger changes in Nrf2 and Trx1 levels. These changes indicate that monocytes have a capacity to adapt to trace concentrations of Hg(II) that are introduced into the bloodstream after dental amalgam procedures or fish consumption. The ability of monocytes to adapt suggests that low levels of mercury exposure from dental amalgam may not overtly compromise monocyte function.

Initial in vitro biological response to contemporary endodontic sealers.

The objective of this study was to evaluate the cytotoxicity of three endodontic sealers (AH Plus/Maillefer-Dentsply, Epiphany/Pentron, GuttaFlow, Coltene-Whaledent). Materials were mixed according to the manufacturer instructions and packed into Teflon molds (10 x 1 mm). For cytotoxicity testing (MTT method), the specimens were placed in contact with cultured cells, then evaluated at two subsequent time points (24 or 72 h). In addition to testing the mixed materials, 5 microl of primer liquid (GuttaFlow and Epiphany) and resin solvents (HEMA, ethanol, sterile water, or acetone) were added directly in culture for 24 and 72 h. The results showed that most materials pose significant cytotoxic risks and that cytotoxicity generally increased with time. At 72 h, GuttaFlow became significantly less toxic than AH Plus, Epiphany sealer, and Resilon. The current results support the need to continue to develop better endodontic sealers that combine the excellent sealing and bonding properties of resins with acceptable biological properties for endodontic applications.

Ni(II) activates the Nrf2 signaling pathway in human monocytic cells.

Nickel is a component of biomedical alloys that is released during corrosion and causes inflammation in tissues by as yet unknown mechanisms. Recent data show that Ni(II) at concentrations of 10-50 microM amplifies lipopolysaccharide-triggered, NFkappaB-mediated cytokine secretion from monocytes. In the current study, we tested the hypothesis that Ni(II) amplifies cytokine secretion by activating the Nrf2 antioxidant pathway rather than by enhancing activity of the NFkappaB signaling pathway. Human THP1 monocytes were exposed to Ni(II) concentrations of 10-30 microM for 6-72 h, then immunoblots of whole-cell lysates or cytosolic and nuclear proteins were used to detect changes in Nrf2 or NFkappaB signaling. Our results show that Ni(II) increased (by 1-2 fold) whole-cell Nrf2 levels and nuclear translocation of Nrf2, and amplified lipopolysaccharide (LPS)-induction of Nrf2 (by 3-5 fold), but had no detectable effect on the initial activation or nuclear translocation of NFkappaB. Because Nrf2 target gene products are known regulators of NFkappaB nuclear activity, our results suggest that Ni(II) may affect cytokine secretion indirectly via modulation of the Nrf2 pathway.

Sublethal concentrations of diverse gold compounds inhibit mammalian cytosolic thioredoxin reductase (TrxR1).

UNLABELLED: Thioredoxin reductase (TrxR) reduces thioredoxin (Trx), thereby contributing to cellular redox balance, facilitating the synthesis of deoxy-ribose sugars for DNA synthesis, and regulating redox-sensitive gene expression. Auranofin is a gold compound that potently inhibits TrxR. This inhibition is one suspected mechanism of auranofin's therapeutic benefit in the treatment of rheumatoid arthritis. The use of other gold compounds to treat cancer or inflammatory disease may rely on their ability to inhibit TrxR. In the current study, we tested the hypothesis that a variety of gold compounds may inhibit TrxR. METHODS: We exposed rat-TrxR1 to auranofin, gold sodium thiomalate, sodium aurothiosulfate, triphenyl phosphine gold chloride, or gold acetate, and measured TrxR activity ex vivo. We then compared TrxR1 inhibitory levels of gold compounds to those that inhibited mitochondrial activity of THP1 monocytes and OSC2 epithelial cells, estimated by succinate dehydrogenase activity. RESULTS: All gold compounds inhibited TrxR1 at concentrations ranging from 5 to 4000 nM (50% inhibitory concentration). The oxidation state of gold did not correlate with inhibitory potency, but ligand configuration was important. Au(I)-phosphine compounds (triphenyl phosphine gold chloride and auranofin) were the most potent inhibitors of TrxR. All TrxR1 inhibitory concentrations were sublethal to mitochondrial activity in both THP1 and OSC2 cells. CONCLUSIONS: Diverse types of gold compounds may be effective inhibitors of TrxR1 at concentrations that do not suppress cellular mitochondrial function. Inhibition may be optimized to some degree by altering the ligand configuration of the compounds. These results support future study of a variety of Au compounds for therapeutic development as inhibitors of TrxR1.

Extracellular environment as one mediator of blue light-induced mitochondrial suppression.

OBJECTIVES: The current study tested the hypothesis that the extracellular environment mediates mitochondrial suppression of oral epithelial cells and fibroblasts by blue light. METHODS: We exposed Balb fibroblasts (Balb), normal human epidermal keratinocytes (NHEK), and oral squamous carcinoma cells (OSC2) to blue light (30-120J/cm2) in different cell-culture media and in phosphate buffered saline (PBS). Mitochondrial activity (MTT method) was used to assess cellular response 72 h post-light exposure. Cell-culture media were replaced or supplemented before or after light exposure to assess the variables of exposure time and medium degradation as mediators of blue light-induced effects. RESULTS: Mitochondrial activity of NHEK was not suppressed by exposure to blue light regardless of extracellular conditions. The mitochondrial activity of OSC2 and Balb cells was suppressed most when cells were exposed to light in cell-culture medium (versus PBS). Blue light suppressed mitochondrial activity more when irradiated medium remained in contact with the cells at least 1h, indicating a time-dependence of the medium effects. Neither a replacement nor a supplementation of medium components reduced blue light-induced mitochondrial suppression. SIGNIFICANCE: Our results suggest that tissue environments influence cellular responses to blue light and that these environments should be considered when assessing any biological effects of blue light during the photopolymerization of restorative resins.

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

UNLABELLED: 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).

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.

Isothermal phase transformations of a dental porcelain.

OBJECTIVES: The purpose of this investigation was to determine if the change in the leucite weight fraction during an isothermal heat treatment could be estimated by observing the deformation of PFM strips in a high-heating-rate, computer-controlled bending beam viscometer (BBV). METHODS: Specimens of a commercial body porcelain were fired according to the manufacturer's instructions-50 disk specimens for quantitative X-ray diffraction (XRD) and 100 bimaterial strip specimens for BBV. The XRD specimens were annealed at temperatures between 650 and 1000 degrees C, and leucite weight fraction was measured using an alumina internal standard. The BBV specimens were annealed in the BBV using time-temperature schedules designed to elucidate the leucite crystallization behavior between 700 and 1000 degrees C. Timoshenko's equation for a bimaterial thermostat was used to estimate the change in the thermal expansion of the porcelain near room temperature. Changes in leucite weight fraction were determined from these thermal expansion changes. RESULTS: The means and SDs were compared to values obtained by quantitative XRD. Good agreement was obtained between values of leucite weight fraction derived from beam deformation and those determined by quantitative XRD (p> or =0.45). The anneal sequence showed that the increase in leucite weight fraction at 800 or 900 degrees C is reversible by an anneal at 1000 degrees C. SIGNIFICANCE: The BBV technique yields comparable results to quantitative XRD and provides the opportunity to efficiently monitor porcelain leucite changes nondestructively over multiple heat treatments. This technique could prove useful for testing firing schedules designed to stabilize the leucite content in dental porcelain.

Effect of vascular stent alloys on expression of cellular adhesion molecules by endothelial cells.

OBJECTIVE: Nickel and cobalt ions activate ICAM1 expression on endothelial cells and keratinocytes. Furthermore, these ions are released in vitro and in vivo from the types of alloys used for vascular stents, but the full biological consequences of this release is not known. In the current study, we determined if release of elements from vascular stent alloys that contained nickel and cobalt was sufficient to activate expression of key cellular adhesion molecules (CAMs) by endothelial cells. Expression of these CAMs is a critical step in the long-term inflammatory response to stent materials and possibly to in-stent restenonsis. METHODS: Stainless steel, NiTi, CoCrNi, and NiCr alloys were placed in direct contact with primary human microvascular endothelial cells for 72 hours after preparation at three roughnesses (120, 320, and 1200 grit). Expression of three CAMs--ICAM1, VCAM1, and e-selectin--was assessed using a modified ELISA procedure. Cytotoxicity of the alloys was assessed by measuring succinate dehydrogenase (SDH) activity and total protein content of the cells, and nickel release was measured by atomic absorption spectroscopy. RESULTS: None of the alloys suppressed SDH activity or total cellular protein significantly at any surface roughness, indicating little or no cytotoxicity. Ni release was measurable from all alloys, was greatest from the rougher surfaces, and was significantly different for the different alloy types. NiTi alloys exhibited the lowest nickel release. However, none of the alloys activated expression of the CAMs, regardless of surface roughness or nickel release level. Supplemental experiments using nickel ions alone confirmed that ICAM1 was inducible on the endothelial cells by Ni(II) concentrations above 100 microM. CONCLUSIONS: In this in vitro system, nickel or other elemental release from several common types of stent alloys was not sufficient to activate expression of CAMs on endothelial surfaces. Although these results indicate a low risk for direct activation of endothelial cells by ions released from stent alloys, other mechanisms, such as modulation of CAM expression by monocytes or smooth muscle cells, must be considered before ion-mediated influence on CAM expression can be dismissed.