The dental monomer hydroxyethyl methacrylate (HEMA) counteracts lipopolysaccharide-induced IL-1β release-Possible role of glutathione

The cadmium tolerance enhancement through regulating glutathione conferred by vacuolar compartmentalization in Aspergillus sydowii

Aspergillus was found to be a vital hyperaccumulation species for heavy metal removal with admirable tolerance capacity. But the potential tolerance mechanism has not been completely studied. This study quantified the amounts of total cadmium (Cd), Cd2+, glutathione (GSH), and reactive oxygen species (ROS) in the protoplasts and vacuoles of mycelium. We modulated GSH synthesis using buthionine sulfoximine (BSO) and 2-oxothiazolidine-4-carboxylic acid (OTC) to investigate the subcellular regulatory mechanisms of GSH in the accumulation of Cd. The results confirmed that GSH plays a crucial role in vacuolar compartmentalization under Cd stress. GSH and GSSG as a redox buffer to keep the cellular redox state in balance and GSH as a metal chelating agent to reduce toxicity. When regulating the decreased GSH content with BSO, and increased GSH content with OTC, the system of Cd-GSH-ROS can change accordingly, this also supported that vacuolar compartmentalization is a detoxification strategy that can modulate the transport and storage of substances inside and outside the vacuole reasonably. Interestingly, GSH tended to be distributed in the cytoplasm, the battleground of redox takes place in the cytoplasm but not in the vacuole. These finding potentially has implications for the understanding of tolerance behavior and detoxification mechanisms of cells. In the future bioremediation of Cd in soil, the efficiency of soil remediation can be improved by developing organisms with high GSH production capacity.

L-glutathione 1% promotes neuroprotection of nitrergic neurons and reduces the oxidative stress in the jejunum of rats with Walker-256-bearing tumor

AIMS

Our main goals were to investigate the effects of L-glutathione (1%) treatment in Walker-256 tumor-bearing rats by analyzing immunoreactive neurons (IR), responsive to the nNOS enzyme and 3-Nitrotyrosine, in their jejunum myenteric plexus. Moreover, the oxidative state and inflammatory process in these animals were investigated.

METHODS

Four experimental groups were utilized: control (C), control treated with L-glutathione (CGT), Walker-256 tumor-bearing rats (TW), and Walker-256 tumor-bearing rats treated with L-glutathione (TWGT). After 14 days of tumor inoculation, the jejunum was collected for immunohistochemical techniques and assessment of oxidative status. Plasma was collected to evaluate oxidative status and measure cytokines.

RESULTS

The TW group exhibited a decrease of reduced glutathione in their jejunum, which was prevented in the L-glutathione treated TWGT group. TW animals presented pronounced oxidative stress by increasing levels of lipoperoxidation in their jejunum and malondialdehyde in their plasma; however, the L-glutathione treatment in TWGT group was not able to avoid it. The total antioxidant capacity was altered in groups TW and TWGT, yet the last one had a better index in their plasma. The IL-10, and TNF-α levels increased in TWGT animals. The nNOS-IR neuron density decreased in the jejunum myenteric plexus of the TW group, which was avoided in the TWGT group. The nNOS +3-Nitrotyrosine neurons quantification did not show significative alterations.

CONCLUSION

The treatment with L-glutathione (1%) imposed an important defense to some parameters of oxidative stress induced by TW-256, leading to neuroprotection to the loss in the nNOS-IR neuron density.

Influence of HEMA on LPS- and LTA-stimulated IL-6 release from human dental pulp cells

OBJECTIVE

Dental pulp cells interact with immunogenic components such as LPS (lipopolysaccharide) or LTA (lipoteichoic acid) released from microorganisms in carious lesions. In the present investigation, the formation of the pro-inflammatory cytokines TNFα and IL-6 in LPS- or LTA-stimulated cells from the dental pulp interface and pulp fibroblasts was analyzed in the presence of the resin monomer 2-hydroxyethyl methacrylate (HEMA) under varying cellular redox conditions.

METHOD

Human pulp fibroblasts (HPC) or cells from the dental pulp interface expressing an odontoblast phenotype (hOD-1) were exposed to LTA, LPS or HEMA for 1 h or 24 h. Redox homeostasis was modified by the prooxidant BSO (L-buthionine sulfoximine) or the antioxidant NAC (N-acetyl cysteine). Formation of TNFα or IL-6 was analyzed by ELISA, and cell survival was determined by a crystal violet assay. Statistical analyses were performed using the Mann-Whitney-U-test.

RESULTS

Secretion of TNFα was not detected in LPS- or LTA-stimulated HPC or hOD-1, and IL-6 was not found after a short exposure (1 h). After a 24 h exposure, LPS induced a 3-fold increase in IL-6 formation in HPC, while LTA stimulated IL-6 release about 20-fold. Likewise, LTA was more effective than LPS in hOD-1 stimulating IL-6 levels about 50-fold. HEMA inhibited the LPS- and LTA-induced IL-6 release, and this effect was enhanced by BSO but counteracted by NAC in both cell types. IL-6 release was independent of cell survival rates.

CONCLUSIONS

The protective immune response in odontoblasts and pulp fibroblasts is impaired by monomers such as HEMA through the disturbance of the redox homeostasis.

Redox regulation of immunity and the role of small molecular weight thiols

It is thought that excessive production of reactive oxygen species (ROS) can be a causal component in many diseases, some of which have an inflammatory component. This led to an oversimplification whereby ROS are seen as inflammatory and antioxidants anti-inflammatory. This paper aims at reviewing some of the literature on thiols in host defense. The review will first summarize the mechanisms by which we survive infections by pathogens. Then we will consider how the redox field evolved from the concept of oxidative stress to that of redox regulation and how it intersects the field of innate immunity. A third section will analyze how an oversimplified oxidative stress theory of disease led to a hypothesis on the role of ROS and glutathione (GSH) in immunity, respectively as pro- and anti-inflammatory mediators. Finally, we will discuss some recent research and how to think out of the box of that oversimplification and link the role of thiols in redox regulation to the mechanisms by which we survive an infection outlined in the first section.

HEMA-induced oxidative stress inhibits NF-κB nuclear translocation and TNF release from LTA- and LPS-stimulated immunocompetent cells

OBJECTIVE

The release of inflammatory cytokines from antigen-stimulated cells of the immune system is inhibited by resin monomers such as 2-hydroxyethyl methacrylate (HEMA). Although the formation of oxidative stress in cells exposed to HEMA is firmly established, the mechanism behind the inhibited cytokine secretion is only partly known. The present investigation presents evidence regarding the role of HEMA-induced oxidative stress in the secretion of the pro-inflammatory cytokine TNFα from cells exposed to the antigens LTA (lipoteichoic acid) or LPS (lipopolysaccharide) of cariogenic microorganisms using BSO (L-buthionine sulfoximine) or NAC (N-acetyl cysteine) to inhibit or stabilize the amounts of the antioxidant glutathione.

METHOD

RAW264.7 mouse macrophages were treated with LTA, LPS or HEMA in the presence of BSO or NAC for 1h or 24h. Secretion of TNFα from cell cultures was analyzed by ELISA, and the formation of reactive oxygen (ROS) or nitrogen species (RNS) was determined by flow cytometry. Protein expression was detected by Western blotting.

RESULTS

The release of TNFα in both LTA- and LPS-exposed cells was decreased by HEMA, and this concentration-dependent inhibitory effect was amplified by BSO or NAC. LTA- and LPS-stimulated expression of the redox-sensitive transcription factor NF-αB (p65) in cell nuclei decreased in the presence of HEMA because the translocation of p65 from the cytosol was prevented by oxidative stress specifically increased by the monomer.

CONCLUSIONS

A disturbance of the cellular redox balance, particularly induced by HEMA, is a crucial factor in the inhibition of LTA- and LPS-stimulated signalling pathways leading to TNFα secretion.

In vitro effects of dental monomer exposure - Dependence on the cell culture model

Methacrylate monomers are major components of resin-based biomaterials. The polymerization of these materials is never complete, and methacrylates leaking from cured materials cause exposure of patients. Only some selected methacrylates have thoroughly been tested for possible interaction with living cells. In the current study, we compared the effects of 2-hydroxyethyl-methacrylate (HEMA; a carefully studied methacrylate) and hydroxypropyl-methacrylate (HPMA; a scarcely investigated methacrylate). Five cell lines differing in both source and cell type were used. The cells were exposed to methacrylates (1-8 mM). Cell viability, cell death, glutathione levels, reactive oxygen species (ROS), and cell growth pattern were measured. Both methacrylates reduced cell viability, and glutathione depletion was observed in all cell lines. The cell death pattern varied among the cell lines. The ROS levels and cell growth pattern also differed between the cell lines after exposure to methacrylate monomers. No difference between HEMA and HPMA exposures were observed in any of the cell lines. The variation between cell lines shows that the measured methacrylate toxicity depends heavily on the test system chosen. Further, the conformity between HEMA and HPMA effects suggests that the two methacrylates similarly affect living cells.

Three-dimensional tissue engineering-based Dentin/Pulp tissue analogue as advanced biocompatibility evaluation tool of dental restorative materials

OBJECTIVE

Two-dimensional (2D) in vitro models have been extensively utilized for cytotoxicity assessment of dental materials, but with certain limitations in terms of direct in vitro-in vivo extrapolation (IVIVE). Three-dimensional (3D) models seem more appropriate, recapitulating the structure of human tissues. This study established a 3D dentin/pulp analogue, as advanced cytotoxicity assessment tool of dental restorative materials (DentCytoTool).

METHODS

DentCytoTool comprised two compartments: the upper, representing the dentin component, with a layer of odontoblast-like cells expanded on microporous membrane of a cell culture insert and covered by a treated dentin matrix; and the lower, representing a pulp analogue, incorporating HUVEC/SCAP co-cultures into collagen I/fibrin hydrogels. Representative resinous monomers (HEMA: 1-8mM; TEGDMA: 0.5-5mM) and bacterial components (LPS: 1μg/ml) were applied into the construct. Cytotoxicity was assessed by MTT and LDH assays, live/dead staining and real-time PCR for odontogenesis- and angiogenesis-related markers.

RESULTS

DentCytoTool supported cell viability and promoted capillary-like network formation inside the pulp analogue. LPS induced expression of odontogenesis-related markers (RUNX2, ALP, DSPP) without compromising viability of the odontoblast-like cells, while co-treatment with LPS and resin monomers induced cytotoxic effects (live/dead staining, MTT and LDH assays) in cells of both upper and lower compartments and reduced expression angiogenesis-related markers (VEGF, VEGFR2, ANGPT-1, Tie-2, PECAM-1) in a concentration- and time- dependent manner. LPS treatment aggravated TEGDMA-induced and -in certain concentrations (2-4mM)- HEMA-induced cytotoxicity.

SIGNIFICANCE

DentCytoTool represents a promising tissue-engineering-based cytotoxicity assessment tool, providing more insight into the mechanistic aspects of interactions of dental materials to the dentin/pulp complex.

Establishing a macrophage model with relevance for oral methacrylate monomer exposures: Attenuated Staphylococcus aureus-induced cytokine release from human macrophages

BACKGROUND

Leakage of unpolymerized methacrylate monomers after placement of methacrylate-containing polymeric dental materials leads to human exposure. Based on studies using murine macrophages and LPS from Escherichia coli (E. coli), dental monomers like 2-hydroxyethyl methacrylate (HEMA) are known to inhibit lipopolysaccharide (LPS) induced cytokine release. The aim of this study was to establish a model system with relevance for human oral monomer exposure using exposure to live gram-positive bacteria, and to confirm the HEMA-induced effects on cytokine release in this model.

METHODS

The human THP-1 monocyte cell line was differentiated to macrophages using phorbol 12-myristate 13-acetate (PMA), before exposure to 0.5-2mM HEMA and live Staphylococcus aureus (S. aureus) in various multiplicity of infections (MOI). Cytokine release and cytotoxicity were determined after (i) 2-24h pre-exposure to HEMA followed by 2-4h S. aureus exposure and (ii) 2-4h simultaneous exposure. The 24h pre-exposure regime was also tested in primary human airway macrophages and for phagocytosis of S. aureus in THP-1 macrophages.

RESULTS

HEMA attenuated the cytokine release more strongly in the pre-exposure than combined exposure regime, with a maximal reduction of 95% in the S. aureus-induced cytokine release. A MOI of 0.1 (corresponding to a bacteria-macrophage ratio of 1:10) was determined to be optimal in the THP-1 macrophages as it induced sufficient cytokine release and negligible cytotoxicity. Attenuated release of S. aureus-induced interleukin (IL)-1β after HEMA exposure was confirmed in primary airway macrophages, while HEMA increased the phagocytosis of S. aureus in THP-1 cells.

CONCLUSION

The model was successfully established and attenuated bacteria-induced cytokine release after HEMA exposure confirmed.

Therapeutic Role of a Cysteine Precursor, OTC, in Ischemic Stroke Is Mediated by Improved Proteostasis in Mice

Oxidative stress aggravates brain injury following ischemia/reperfusion (I/R). We previously showed that ubiquilin-1 (Ubqln1), a ubiquitin-like protein, improves proteostasis and protects brains against oxidative stress and I/R-induced brain injury. Here, we demonstrate that a small molecule compound, L-2-oxothiazolidine-4-carboxylic acid (OTC) that functions as a precursor of cysteine, upregulated Ubqln1 and protected cells against oxygen-glucose deprivation-induced cell death in neuronal cultures. Further, the administration of OTC either at 1 h prior to ischemia or 3 h after the reperfusion significantly reduced brain infarct injury and improved behavioral outcomes in a stroke model. Administration of OTC also increased glutathione (GSH) level and decreased superoxide production, oxidized protein, and neuroinflammation levels in the penumbral cortex after I/R in the stroke mice. Furthermore, I/R reduced both Ubqln1 and the glutathione S-transferase protein levels, whereas OTC treatment restored both protein levels, which was associated with reduced ubiquitin-conjugated protein level. Interestingly, in the Ubqln1 knockout (KO) mice, OTC treatment showed reduced neuroprotection and increased ubiquitin-conjugated protein level when compared to the similarly treated non-KO mice following I/R, suggesting that OTC-medicated neuroprotection is, at least partially, Ubqln1-dependent. Thus, OTC is a potential therapeutic agent for stroke and possibly for other neurological disorders and its neuroprotection involves enhanced proteostasis.

Effects of triethylene glycol dimethacrylate and hydroxyethyl methacrylate on macrophage polarization

AIM

To evaluate the effects of hydrophilic dental resin monomers, triethylene glycol dimethacrylate (TEGDMA) and hydroxyethyl methacrylate (HEMA), on the polarization of a human monocyte cell line (THP-1).

METHODOLOGY

THP-1 cells were treated with resin monomers at noncytotoxic concentrations for 48 h and were analysed for CD86 and CD206 expressions using flow cytometry. The cells were stimulated for polarization in the presence of resin monomers (co-treatment) or after treatment with monomers (pre-treatment). CD86 and CD206 mRNA in co-treated cells was evaluated using quantitative real-time polymerase chain reaction. The release of TNF-α and TGF-β by pre-treated and co-treated cells was assessed using enzyme-linked immunosorbent assay. Morphological changes of macrophages during polarization were observed using bright-field microscopy. One-way analysis of variance was used for statistical analysis.

RESULTS

TEGDMA (1 mmol L^-1 ) and HEMA (2 mmol L^-1 ) did not induce CD86 and CD206 expressions in THP-1 cells but rather inhibited their expressions in the co-treated cells. The inhibitory effects also appeared at the transcription level. However, the expression of surface markers was not affected by pre-treatment with resin monomers. The release of TNF-α and TGF-β by M1- and M2-stimulated cells, respectively, was suppressed by co-treatment (P < 0.05). Microscopic studies revealed that co-treatment with resin monomers suppressed polarization-associated morphological changes such as cell volume increase.

CONCLUSIONS

TEGDMA and HEMA inhibited macrophage polarization to both M1 and M2 at the transcription level, and the inhibitory effects disappeared upon the removal of resin monomers from the cell culture.

Functions of transcription factors NF-κB and Nrf2 in the inhibition of LPS-stimulated cytokine release by the resin monomer HEMA

OBJECTIVE

Resin monomers like 2-hydroxyethyl methacrylate (HEMA) interfere with effects induced by stressors such as lipopolysaccharide (LPS) released from cariogenic microorganisms. In this study, mechanisms underlying monomer-induced inhibition of the LPS-stimulated secretion of inflammatory cytokines from immunocompetent cells were investigated.

METHODS

Secretion of pro-inflammatory cytokines TNF-α, IL-6 and the anti-inflammatory IL-10 from RAW264.7 mouse macrophages exposed to LPS and HEMA (0-6-8mM) was determined by ELISA. The formation of reactive oxygen (ROS) and nitrogen species (RNS) was determined by flow cytometry (FACS) after staining of cells with specific fluorescent dyes. Cell viability was analyzed by FACS, and protein expression was detected by Western blotting.

RESULTS

Secretion of TNF-α, IL-6 and IL-10 from LPS-stimulated cells increased after a 24h exposure. A HEMA-induced decrease in cytokine secretion resulted from the inhibition of LPS-stimulated NF-κB activation. Nuclear translocation of NF-κB was inhibited possibly as a result of enhanced levels of hydrogen peroxide (H₂O₂) and nitric oxide (NO) in HEMA-exposed cells. Oxidative stress caused by HEMA-induced formation of H₂O₂ and LPS-stimulated peroxynitrite (ONOO) also enhanced nuclear expression of Nrf2 as the major regulator of redox homeostasis, as well as Nrf2-controlled stress protein HO-1 to inhibit NF-κB activity. HEMA inhibited the LPS-stimulated expression of NOS (nitric oxide synthase) to produce NO but counteracted the expression of Nox2, which forms superoxide anions that combine with NO to peroxynitrite.

CONCLUSIONS

Resin monomers like HEMA inhibit LPS-stimulated NF-κB activation essential for cytokine release as a crucial response of immunocompetent cells of the dental pulp to invading cariogenic pathogens.