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

Hierarchical Two-Dimensional Layered Double Hydroxide Coated Polydopamine Nanocarriers for Combined Chemodynamic and Photothermal Tumor Therapy

The combination of chemodynamic therapy (CDT) and photothermal therapy (PTT) has proven to be successful in combating the challenges associated with cancer therapy. A combination of these therapies can maximize the benefits of each therapeutic modality through endogenous reduction-oxidation (redox) reaction and external laser power induction. In the current work, we have designed a copper-aluminum layered double hydroxide (CuAl-LDH) loaded doxorubicin (DOX) by a co-precipitation method; the surface was coated with polydopamine (PDA). The synthesized CuAl-LDH@DOX@PDA nanocarrier (NC) served as a Fenton-like catalyst with photothermal properties. It is well known that metal ion incorporated NCs can induce intracellular depletion of reduced glutathione (GSH) levels along with the reduction of Cu2+ to Cu+. The Cu+ ions in turn react with DOX leading to the generation of intracellular hydrogen peroxide (H2O2) molecules to produce the highly toxic hydroxyl radicals (•OH) through a Fenton-like reaction. The enhanced absorption of CuAl@DOX@PDA at 810 nm, greatly improved the photothermal efficiency in comparison with bare CuAl-LDH and CuAl-LDH@DOX. In vitro studies revealed the tremendous CDT/PTT efficacy of CuAl@DOX@PDA in suppressing A549 cancer cells. Furthermore, reactive oxygen species (ROS) assays and intracellular levels of various ROS cascade biomolecules support our findings in the efficient destruction of cancer cells through synergistic CDT/PTT therapy.

Effects of β-HgS on cell viability and intracellular oxidative stress in PC-12 cells

Traditional Tibetan medicines containing β-HgS have been used to treat chronic ailments for thousands of years. The effects were studied of β-HgS on cell viability and intracellular oxidative stress in PC-12 cells.

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.

Oxidative stress in the oral cavity: sources and pathological outcomes

Oxidative stress (OS), an imbalance in the oxidant-antioxidant equilibrium, is thought to be involved in the development of many seemingly unrelated diseases. Oral cavity tissues are a unique environment constantly exposed to internal and external compounds and material hazards as almost no other part of the human body. Some of the compounds are capable of generating OS. Here, the main groups of endogenous as well as exogenous OS sources are presented, followed by their oxidative effect on the salivary contents and function. The oxidative mechanisms in oral cells and their pathologic influence are also discussed.

Effects of dental methacrylates on oxygen consumption and redox status of human pulp cells

Several studies have already demonstrated that the incomplete polymerization of resin-based dental materials causes the release of monomers which might affect cell metabolism. The aim of this study was to investigate the effects of triethylene glycol dimethacrylate, 1,4-butanediol dimethacrylate, urethane dimethacrylate, and 2-hydroxyethyl methacrylate on (1) cellular energy metabolism, evaluating oxygen consumption rate, glucose consumption, glucose 6-phosphate dehydrogenase activity, and lactate production, and (2) cellular redox status, through the evaluation of glutathione concentration and of the activities of enzymes regulating glutathione metabolism. Methods. Human pulp cells were used and oxygen consumption was measured by means of a Clark electrode. Moreover, reactive oxygen species production was quantified. Enzymatic activity and glucose and lactate concentrations were determined through a specific kit. Results. Triethylene glycol dimethacrylate, 1,4-butanediol dimethacrylate, and 2-hydroxyethyl methacrylate induced a decrease in oxygen consumption rate, an enhancement of glucose consumption, and lactate production, whilst glucose 6-phosphate dehydrogenase and glutathione reductase activity were not significantly modified. Moreover, the monomers induced an increase of reactive oxygen species production with a consequent increase of superoxide dismutase and catalase enzymatic activities. A depletion of both reduced and total glutathione was also observed. Conclusion. The obtained results indicate that dental monomers might alter energy metabolism and glutathione redox balance in human pulp cells.

Exposure-dose-response of Tellina deltoidalis to metal-contaminated estuarine sediments: 1. Cadmium spiked sediments

Cadmium is a ubiquitous environmental metal contaminant with an affinity for biological membranes; it can enter cells by facilitated transport and it binds therein to various biomolecules and affects membrane system function. The relationship between cadmium exposure, dose and response was investigated in the benthic, deposit feeding, marine bivalve Tellina deltoidalis, using 28 day microcosm spiked cadmium exposures. Tissue cadmium reached steady state with the exposure concentration. Half the accumulated cadmium was detoxified and with increased exposure more was converted into metal rich granules. Most biologically active cadmium was in the mitochondrial fraction, with up to 7320-fold cadmium increases in exposed organisms. Cadmium exposed T. deltoidalis generally had reduced glutathione peroxidase enzyme activity. An increase in total glutathione concentrations, due to a build up of oxidised glutathione, was indicated by the reduced to oxidised glutathione ratio. All cadmium exposed T. deltoidalis had reduced total antioxidant capacity that corresponded with increased lipid peroxidation, lysosomal destabilisation and micronuclei frequency. Clear exposure-dose-response relationships have been demonstrated for T. deltoidalis exposed to cadmium-spiked sediments, supporting this organism's suitability for laboratory or in situ evaluation of sediment cadmium toxicity.

Lipid peroxides and glutathione status in human progenitor mononuclear (U937) cells following exposure to low doses of nickel and copper

Effects of Cu(2+), Ni(2+) or Cu(2+) + Ni(2+) on lipid peroxide and glutathione (GSH) levels in U937 cells were investigated. Cells were treated with 0, 5, 10, and 20 µM of Cu(2+) and/or Ni(2+) and H(2)O(2) (0.01 mM) and incubated for 24 hours at 37°C. Lipid peroxides were measured by the thiobarbituric acid assay (TBA). GSH intracellular levels were assayed by the GSH assay kit from EMD/Calbiochem (San Diego, California, USA). Cu(2+) or Ni(2+) significantly (P < 0.01) increased lipid peroxides in a dose-dependent manner, compared to controls. The effect was more pronounced for Cu(2+), compared to the Ni(2+)-treated samples. Cu(2+) + Ni(2+) increased lipid peroxides in a significant (P < 0.001), dose-dependent manner, compared to Cu(2+) or Ni(2+) alone (i.e., ratio of 2.5:1-fold for combined versus single treatments, respectively). Cu(2+) or Ni(2+) significantly decreased GSH levels in U937 cells, with the effect being pronounced for Cu(2+). Cu(2+) + Ni(2+) metal ions significantly (P < 0.001) depleted cells of GSH in a dose-dependent manner. Ethylene diamine tetraacetic acid (EDTA) at 50 or 100 µM moderately reduced the Cu(2+)- or Ni(2+)-induced effects on GSH levels. Interestingly, GSH levels generally decreased to half (except for the combined metal dose of 20 µM at 100 µM EDTA) of its level at the highest metal concentration tested for both the single or combined treatments. In conclusion, multiple exposures of cells to metal ions may be lethal to cells, compared to their single treatments.

Zinc, cadmium and nickel increase the activation of NF-κB and the release of cytokines from THP-1 monocytic cells

The sustained activation of the transcription factor nuclear factor κB (NF-κB) by metal-activated signalling pathways can lead to chronic inflammatory processes and related diseases, including carcinogenesis. The aim of the present work was to clarify the effect of zinc, nickel and cadmium on NF-κB activation in the THP-1 human monocytic leukemia cell line. The production of the NF-κB downstream pro-inflammatory mediators tumor necrosis factor (TNF)-α and interleukin (IL)-1β, IL-6 and IL-8 was also evaluated due to their important roles in the pathogenesis of chronic inflammatory and autoimmune diseases and, ultimately, in the development of cancer. The results obtained demonstrated that zinc, nickel and cadmium significantly activate NF-κB, and the release of the chemokine IL-8. Cadmium also induced the release of TNF-α and IL-6 in THP-1 monocytic cells, which may indicate some potential to induce deleterious effects through this pathway.

Effects of metal ions on fibroblasts and spiral ganglion cells

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

Effects of 1,4-butanediol dimethacrylate and urethane dimethacrylate on HL-60 cell metabolism

The polymerization of methacrylic monomers present in dental composite resins never reaches completion and therefore the leakage of residual monomers into the oral cavity and into biological fluids can cause local and systemic adverse effects. This work was carried out to study the in vitro biochemical interactions of urethane dimethacrylate and 1,4-butanediol dimethacrylate monomers with HL-60 cells, a cell line assumed as an experimental model for simulating granulocyte behaviour. Our main finding was that both monomers induce cell differentiation at toxic concentrations and that cytotoxicity seems to be caused by alterations of glucose metabolism arising from mitochondrial dysfunction rather than from oxidative stress, which could not be altogether verified under our experimental conditions. Our study could be considered as a useful approach to investigate the biochemical mechanisms that contribute to the cytotoxicity of methacrylate compounds and it underlines the importance of assessing such parameters for testing biocompatibility in order to promote the development of better and safer dental materials.

Oxidative stress as a component of chromium-induced cytotoxicity in rat calvarial osteoblasts

It has been documented that medical prosthetic alloys release metal ions into surrounding tissues and cause cytotoxicity, but the mechanisms remain undefined. In that regard the cellular oxidative stress may be a common pathway in cellular responses to metal ions. The objective of this study was to approach the hypothesis that oxidative stress mediates chromium-induced cytotoxicity in rat calvarial osteoblasts. Osteoblasts were exposed to different concentrations of Cr6+ or Cr3+ (5-20 microM) in the presence or absence of the antioxidant N-acetyl-cysteine (NAC; 1-5 mM). Cellular viability, differentiation, and intracellular ultrastructural alterations were evaluated by MTT assay, alkaline phosphatase (ALP) activity assay, and transmission electron microscopy. Cellular oxidative stress was evaluated by intracellular reactive oxygen species (ROS) production. ROS production was monitored by the oxidation-sensitive fluorescent probe 2'7'-dichlorofluorescin diacetate (DCFH-DA). A time- and concentration- dependent increased cytotoxicity, time-dependent increased intracellular ROS production were indicated on exposure to Cr6+. Pretreatment of osteoblasts with 1-5 mM NAC afforded dose-dependent cytoprotective effects against Cr6+-induced cytotoxicity in osteoblasts. NAC decreased the level of intracellular ROS induced by Cr6+, too. While Cr3+ and NAC did not have any significant effects on osteoblasts (5-20 microM). These results suggest that oxidative stress is involved in Cr6+-induced cytotoxicity in osteoblasts, and NAC can provide protection for osteoblasts against Cr6+-induced oxidative stress. Cr3+ (5-20 microM) have no significant cytotoxicity in osteoblasts based on the results of this study.

Alterations of energy metabolism and glutathione levels of HL-60 cells induced by methacrylates present in composite resins

OBJECTIVES

Methacrylic compounds such as 2-hydroxyethyl methacrylate (HEMA), triethylene glycol dimethacrylate (TEGDMA) and bisphenol A glycerolate (1 glycerol/phenol) dimethacrylate (Bis-GMA) are largely present in auto- or photopolymerizable composite resins. Since the polymerization reaction is never complete, these molecules are released into the oral cavity tissues and biological fluids where they could cause local adverse effects. The aim of this work was to verify the hypothesis that the biological effects of HEMA, TEGDMA and Bis-GMA - at a non-cytotoxic concentration - depend on the interaction with mitochondria and exert consequent alterations of energy metabolism, GSH levels and the related pathways in human promyelocytic cell line (HL-60).

METHODS

The biological effects of methacrylic monomers were determined by analyzing the following parameters: GSH concentration, glucose-6-phosphate dehydrogenase (G6PDH) and glutathione reductase (GR) activity, oxygen and glucose consumption and lactate production along with cell differentiation and proliferation.

RESULTS

All monomers induced both cellular differentiation and decrease in oxygen consumption. Cells treated with TEGDMA and Bis-GMA showed a significant enhancement of glucose consumption and lactate production. TEGDMA and HEMA induced GSH depletion stimulating G6PDH and GR activity.

CONCLUSIONS

All the monomers under study affect the metabolism of HL-60 cells and show differentiating activity. Since alterations in cellular metabolism occurred at compound concentrations well below cytotoxic levels, the changes in energy metabolism and glutathione redox balance could be considered as potential mechanisms for inducing clinical and sub-clinical adverse effects and thus providing useful parameters when testing biocompatibility of dental materials.

Radicals produced by blue-light–resin interactions alter the redox status of THP1 human monocytes

Resin composites are widely used in dentistry, and are polymerized in situ using a blue-light activated, free-radical polymerization mechanism. Blue light (400-500nm) is used to activate camphoroquinone (CQ), which decomposes to form free radicals that are stabilized by dimethyl-p-toludine (DMPT). CQ and DMPT are applied near tooth pulpal tissues and are irradiated during restorative procedures, suggesting that pulpal cells are exposed to free radicals. Because glutathione is a major component of the cellular redox management system, we tested the hypothesis that blue light irradiation would shift cellular glutathione redox balance of cells exposed to CQ and DMPT. We also measured NFkappaB activation, a redox-sensitive transcription factor that regulates inflammatory responses and glutathione synthetic enzyme levels. THP1 human monocytes were exposed to sublethal levels of CQ (0.4 mM) or DMPT (1.0 mM), with or without blue light exposure (25 J/cm(2)) from a quartz-tungsten-halogen source. The ratio of reduced to oxidized glutathione was measured using as assay based on 5,5'-dithio-bis(2-nitrobenszoic acid). NFkappaB transactivation was measured by transfection of an NFkappaB-containing plasmid linked to a luciferase reporter. Our results showed that blue light, CQ, or DMPT alone had no significant effect on cellular glutathione redox balance, but that the combination of these agents induced a marked oxidative bias, and reduced total glutathione levels up to 50%. On the other hand, light, CQ, and DMPT alone or in combination suppressed NFkappaB transactivation by >70%. Our results suggest that CQ and DMPT pose risks to pulpal tissues with or without blue light irradiation, and that multiple, interacting mechanisms shape the response to these agents.

Protection of platinum-DNA adduct formation and reversal of cisplatin resistance by anti-MRP2 hammerhead ribozymes in human cancer cells

Resistance to platinum-containing antineoplastic drugs is the major limitation in their clinical use. To elucidate the role of the ABC transporter MRP2 in platinum drug resistance, its expression was analyzed in human cisplatin-resistant cell lines: the ovarian carcinoma line A2780RCIS, the adrenocortical carcinoma line D43/86RCIS and the melanoma line MeWoCIS1. All these cells showed overexpression of MRP2. For reversal of platinum resistance, 2 anti-MRP2 hammerhead ribozymes were introduced into A2780RCIS cells. Both ribozymes showed gene-silencing activities and reversed the drug-resistant phenotype. Moreover, formation of platinum-induced intrastrand cross-links was measured in DNA. The level of DNA platination corresponded inversely to the level of MRP2 expression and was accompanied by increased caspase-3-dependent apoptosis. Kinetics of formation and elimination of platinum-DNA adducts suggest that the DNA repair capacity was not altered; the decrease in platinum-DNA adduct formation was rather a reflection of the protecting activity of MRP2. In conclusion, functional inhibition of MRP2 might be a promising strategy in the reversal of resistance to platinum-based anticancer drugs. This was reflected by the specific inhibition of MRP2 by ribozyme technology, indicating that this gene therapeutic approach may be applicable as a specific means to overcome platinum resistance in human neoplasms.

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.

ROS formation and glutathione levels in human oral fibroblasts exposed to TEGDMA and camphorquinone

Glutathione (GSH) is important for the self-protection of cells against oxidative stress and toxic xenobiotics, whereas reactive oxygen species (ROS) at elevated concentrations may cause detrimental alterations of cell membranes, DNA, and other cellular structures. The present investigation addressed the effects of triethylene-glycoldimethacrylate (TEGDMA) and camphorquinone (CQ) on glutathione metabolism and the formation of ROS in oral cells. Primary human pulp fibroblasts were exposed to various concentrations of TEGDMA and CQ (0.1-5 mM). Subsequently, GSH concentration and ROS formation were analyzed with the use of the monobromobimane assay (GSH) and 2',7'-dichlorofluorescein diacetate (DCFH-DA) (ROS). The endogenous ROS hydrogen peroxide (H2O2) was used as a positive control (0.02-2 mM). TEGDMA significantly decreased GSH at concentrations between 0.5 and 5 mM (p<0.05), but did not elevate ROS levels. Contrary, CQ increased ROS formation at concentrations>or=1 mM, but had only a moderate effect on GSH at the highest test concentration. Hydrogen peroxide increased ROS and simultaneously decreased GSH at concentrations of >or=0.2 mM. These data show that the investigated substances may cause cell damage due to various mechanisms, GSH decrease and/or ROS increase. As a consequence, TEGDMA and CQ released into an aqueous environment from resinous materials might interact, thus generating significant cytotoxic effects even at low concentrations.

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.

Dental adhesive compounds alter glutathione levels but not glutathione redox balance in human THP-1 monocytic cells

The use of hydrophilic dental monomers in dentin bonding agents has vastly improved resin-dentin bond strengths, but incomplete polymerization of these monomers and their leaching into adjacent (pulpal) oral tissues has raised concerns about their biocompatibility. The sublethal effects of these resins are virtually unknown, but their electrophilic nature led to the hypothesis that they may alter cellular oxidative stress pathways. Glutathione balance between reduced (GSH) and oxidized (GSSG) is a major mechanism by which cells maintain redox balance and was therefore the focus of the current investigation. THP-1 human monocytic cells were exposed to hydroxyethyl methacrylate (HEMA), benzoyl peroxide (BPO), camphorquinone (CQ), or triethyelene glycol dimethacrylate (TEGDMA) for 24 h at sublethal doses, then GSH and GSSG levels were measured by means of Ellman's method adapted for cell culture. The results indicate that these dental resin compounds act at least partly via oxidative stress by increasing GSH levels at sublethal concentrations. However, the GSH-GSSG ratio was relatively unaffected. Only BPO altered the GSH-GSSG ratio at 24 h, again at sublethal levels (7.5-15 micromol/L). The results support the hypothesis that resin monomers act, at least in part, via oxidative stress, and that oxidative-stress pathways should be one focus of future investigations of monomer biocompatibility.

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.

Effect of TEGDMA on the intracellular glutathione concentration of human gingival fibroblasts

Previous studies revealed that primarily small and relatively hydrophilic comonomers, such as TEGDMA, leach out of resin-based restorative materials into aqueous media. Subsequently, these compounds may cause detrimental reactions with intracellular metabolic systems. The present experiments attempted to elucidate the interactions of TEGDMA with the important intracellular reducing agent glutathione (GSH). The influence of various concentrations of TEGDMA (0.5-7.5 mM) on viability and intracellular GSH concentration of primary human gingival fibroblasts was determined by means of a fluorescence assay (monobromobimane) performed in microtiter plates. Cells were treated with TEDGMA between 2 and 24 h. The incubation of fibroblasts with TEGDMA even at subtoxic concentrations quickly decreased the intracellular glutathione level to 30-50% of controls within the first 2-6 hours. However, no simultaneous adverse effect on cell viability was found. Longer incubation periods up to 24 h caused a regulatory reincrease at TEGDMA concentrations <or= 2.5 mM, whereas higher concentrations resulted in a continuous depletion of glutathione concentration concomitant with a significant decrease of cell viability. Because glutathione plays an important role in protection and detoxification processes as well in the regulation of cell death, the early and extensive depletion of the intracellular glutathione pool due to TEGDMA may significantly contribute to the cytotoxic potency of this compound.

Regulation of LPS induced IL-12 production by IFN-gamma and IL-4 through intracellular glutathione status in human alveolar macrophages

Interleukin-12 (IL-12) is secreted from monocytes and macrophages; it exerts pleiotropic effects on T cells and natural killer (NK) cells, and stimulates interferon-gamma (IFN-gamma) secretion. Glutathione tripeptide regulates the intracellular redox status and other aspects of cell physiology. We examined whether IFN-gamma and IL-4 affect the balance between intracellular reduced glutathione (GSH) and oxidized (GSSG) glutathione, as this may affect IL-12 production in human alveolar macrophages (AM). We used both AM from healthy non-smokers obtained by bronchoalveolar lavage and the monocytic THP-1 cell line in this study. Incubation of AM for 2 h with the GSH precursor N-acetylcysteine (NAC) increased the intracellular GSH/GSSG ratio, and enhanced lipopolysaccharide (LPS)-induced IL-12 secretion by AM. In THP-1 cells, NAC increased the GSH/GSSG ratio and the expression of LPS-induced IL-12 mRNA, whereas L-buthionine-[S,R]-sulphoximine (BSO) decreased these. NAC and BSO offset their own effects on the intracellular GSH/GSSG ratio and the expression of LPS-induced IL-12 mRNA. Furthermore, exposure of AM to the helper T cell type 1 (Th1) cytokine IFN-gamma or the helper T cell type 2 (Th2) cytokine IL-4 for 72 h increased and decreased the GSH/GSSG ratio, respectively. Lipopolysaccharide (LPS)-induced secretion of IL-12 in AM was enhanced by IFN-gamma but inhibited by IL-4. These results suggest that IFN-gamma and IL-4 oppositely affect the GSH/GSSG balance, which may regulate IL-12 secretion from AM in response to LPS.