Activation of the Nrf2-regulated antioxidant cell response inhibits HEMA-induced oxidative stress and supports cell viability.
Oxidative stress due to increased formation of reactive oxygen species (ROS) in target cells of dental resin monomers like 2-hydroxyethyl methacrylate (HEMA) is a major mechanism underlying the disturbance of vital cell functions including mineralization and differentiation, responses of the innate immune system, and the induction of cell death via apoptosis. Although a shift in the equilibrium between cell viability and apoptosis is related to the non-enzymatic antioxidant glutathione (GSH) in HEMA-exposed cells, the major mechanisms of adaptive antioxidant cell responses to maintain cellular redox homeostasis are still unknown. The present study provides insight into the induction of a communicating network of pathways under the control of the redox-sensitive transcription factor Nrf2, a major transcriptional activator of genes coding for enzymatic antioxidants. Here, oxidative stress was indicated by DCF fluorescence in cells after a short exposure (1 h) to HEMA, while DHR123 fluorescence significantly increased about 1.8-fold after a long exposure period (24 h) showing the formation of hydrogen peroxide (H2O2). The corresponding expression of Nrf2 was activated immediately after HEMA exposure (1 h) and remained constant up to 24 h. Nrf2-regulated expression of enzymes of the glutathione metabolism (glutathione peroxidase 1/2, glutathione reductase) decreased in HEMA-exposed cells as a result of GSH depletion, and superoxide dismutase expression was downregulated after H2O2 overproduction. However, the expression of Nrf2-controlled enzymatic antioxidants (catalase, peroxiredoxin, thioredoxin 1, thioredoxin reductase, heme oxygenase-1) and the NADPH-regenerating system (glucose 6-phosphate dehydrogenase, transaldolase) was increased. Phenolic tert-butylhydroquinone (tBHQ), a classic inducer of the Nrf2 pathway, reduced oxidative stress and protected cells from HEMA-induced cell death through a shift in the number of cells in necrosis to apoptosis. The expression of Nrf2 and related enzymatic antioxidants downstream was enhanced by tBHQ in parallel. In conclusion, this investigation expanded the detailed understanding of the underlying mechanisms of HEMA-induced oxidative stress, and highlighted the cross-talk and interdependence between various Nrf2-regulated antioxidant pathways as a major adaptive cell response. The current results demonstrate that modulation of the Nrf2-mediated cellular defense response is an effective means for manipulating the sensitivity of cells to dental resin monomers.
Department of Operative Dentistry and Periodontology, University Hospital Regensburg, University of Regensburg, D-93042 Regensburg, Germany; Department of Pharmacy, University "G. d'Annunzio" Chieti-Pescara, Via dei Vestini 31, 66100 Chieti, Italy.
Marialucia
M
Gallorini
Department of Operative Dentistry and Periodontology, University Hospital Regensburg, University of Regensburg, D-93042 Regensburg, Germany.
Christine
C
Petzel
Department of Operative Dentistry and Periodontology, University Hospital Regensburg, University of Regensburg, D-93042 Regensburg, Germany.
Carola
C
Bolay
Department of Operative Dentistry and Periodontology, University Hospital Regensburg, University of Regensburg, D-93042 Regensburg, Germany.
Karl-Anton
KA
Hiller
Department of Pharmacy, University "G. d'Annunzio" Chieti-Pescara, Via dei Vestini 31, 66100 Chieti, Italy.
Amelia
A
Cataldi
Department of Operative Dentistry and Periodontology, University Hospital Regensburg, University of Regensburg, D-93042 Regensburg, Germany.
Wolfgang
W
Buchalla
Department of Operative Dentistry and Periodontology, University Hospital Regensburg, University of Regensburg, D-93042 Regensburg, Germany.
Stephanie
S
Krifka
Department of Operative Dentistry and Periodontology, University Hospital Regensburg, University of Regensburg, D-93042 Regensburg, Germany. Electronic address: helmut.schweikl@klinik.uni-regensburg.de.
Helmut
H
Schweikl
D000818:Animals; D000975:Antioxidants / Q000737:chemistry*; D017209:Apoptosis; D002470:Cell Survival; D005978:Glutathione / Q000737:chemistry; D005979:Glutathione Peroxidase / Q000378:metabolism; D005980:Glutathione Reductase / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000737:chemistry; D008264:Macrophages / Q000166:cytology* / Q000378:metabolism; D008689:Methacrylates / Q000737:chemistry*; D051379:Mice; D051267:NF-E2-Related Factor 2 / Q000378:metabolism*; D009336:Necrosis; D010084:Oxidation-Reduction; D018384:Oxidative Stress; D000067996:RAW 264.7 Cells; D017382:Reactive Oxygen Species / Q000378:metabolism; D015533:Transcriptional Activation
D000975:Antioxidants; D008689:Methacrylates; D051267:NF-E2-Related Factor 2; C495636:Nfe2l2 protein, mouse; D017382:Reactive Oxygen Species; C005044:hydroxyethyl methacrylate; D006861:Hydrogen Peroxide; D005979:Glutathione Peroxidase; D005980:Glutathione Reductase; D005978:Glutathione
Antioxidant protein; Apoptosis; HEMA; Nrf2; Reactive oxygen species; Resin monomer