Muneyoshi Yamazaki

Tumor necrosis factor alpha (TNF-alpha)-induced prostaglandin E2 release is mediated by the activation of cyclooxygenase-2 (COX-2) transcription via NFkappaB in human gingival fibroblasts.

Nuclear factor kappaB (NFκB) is a transcription factor and plays a key role in the expression of several genes involved in the inflammatory process. Cyclooxygenase (COX) is the key regulatory enzyme of the prostaglandin/eicosanoid synthetic pathway. COX-2 is a highly inducible enzyme by proinflammatory cytokines, of which gene expression is regulated by NFκB. TNF-α is a pro-inflammatory cytokine. In this paper, we investigated the involvement of NFκB on TNF-α-mediated prostaglandin E2 (PGE2) release and COX-2 gene expression in human gingival fibroblasts (HGF). TNF-α- induced PGE2 release and COX-2 mRNA accumulation in a time- and concentration-dependent manner in HGF. The results of transient transfection assays using a chimeric construct of the human COX-2 promoter (nts –1432 ∼ +59) ligated to a luciferase reporter gene indicated that TNF-α stimulated the transcriptional activity ∼ 1.4-fold. Gel mobility shift assays with a radiolabelled COX-2-NFκB oligonucleotide (nts –223 to –214) revealed an increase in the binding of nuclear proteins from TNF-α-stimulated HGF. The COX-2-NFκB DNA-protein complex disappeared after treatment with pyrrolidine dithiocarbamate (PDTC; an antioxidant) or herbimycin A (a tyrosine kinase inhibitor). PDTC and herbimycin A attenuated TNF-α-stimulated PGE2 release. These results suggest that NFκB transcription factor is a key regulator of COX-2 expression in TNF-α-induced PGE2 production, which is mediated through a tyrosine kinase pathway in HGF.

Generation of Free Radicals and/or Active Oxygen by Light or Laser Irradiation of Hydrogen Peroxide or Sodium Hypochlorite

Generation of free radical and/or active oxygen by light or laser irradiation of hydrogen peroxide (H2O2) or sodium hypochlorite (NaClO), which have been used for tooth whitening or root canal irrigation, was investigated using electron spin resonance spectroscopy combined with a spin-trapping technique. When H2O2 was exposed to light or laser radiation, the amount of hydroxyl radical generated changed according to the concentration of H2O2 and irradiation time. The amount of 5,5-dimethyl-1-pyrrolidone-(2)-oxyl-(1) (DMPO-X) also changed in accordance with irradiation time. The amounts of hydroxyl radical generated from H2O2 after irradiation were in the order: plasma lamp > halogen lamp > He-Ne laser > Yellow He-Ne laser. On the other hand, the amounts of DMPO-X generated from NaClO after irradiation were in the order: plasma lamp > Yellow He-Ne laser > halogen lamp > He-Ne laser.

Activation of NFκB is necessary for IL-1β-induced cyclooxygenase-2 (COX-2) expression in human gingival fibroblasts

The immediate-early cyclooxygenase-2 (COX-2) gene encodes an inducible prostaglandin synthase enzyme which is implicated in inflammatory and proliferative diseases. COX-2 is highly induced during cell activation by various factors, including mitogens, hormones and cytokines. Since pro-inflammatory cytokine IL-1β has been shown to induce prostaglandin E2 (PGE2) release in human gingival fibroblasts (HGF), here we analyzed the effect of IL-1β on the expression of COX-2 and the activation of NFκB in HGF. Northern hybridization analysis revealed that IL-1β (200 pg/ml) increased the expression of COX-2 mRNA in HGF. The effect of IL-1β was abrogated by herbimycin A, a protein tyrosine kinase inhibitor, and enhanced by orthovanadate, a protein tyrosine phosphatase inhibitor. IL-1β-induced PGE2 release was blocked by the tyrosine kinase inhibitor and increased by the tyrosine phosphatase inhibitor. The results of transient transfection assays using chimeric constructs of the human COX-2 promoter (nt -1432 ~ +59) ligated to a luciferase reporter gene indicated that IL-1β stimulated the transcriptional activity ~ 1.5-fold. Gel mobility shift assays with a radiolabelled COX-2-NFκB oligonucleotide (nts -223 to -214) revealed an increase in the binding of nuclear proteins from IL-1β-stimulated HGF. This increase of DNA-protein complex formation induced by IL-1β was blocked by herbimycin A and another tyrosine kinase inhibitor, genistein. These results suggest that NFκB is an important transcription factor for IL-1β-induced COX-2 gene expression, and is involved in inducing COX-2 gene transcription through tyrosine phosphorylation in HGF.

Stimulatory effect of laser irradiation on calcified nodule formation in human dental pulp fibroblasts.

The purpose of the present study was to investigate the effect of laser irradiation on calcified nodule formation in human dental pulp (HDP) cells. HDP cells were irradiated once with a Ga-Al-As laser for 5 and 10 min, and calcified nodule formation was determined by von Kossa staining. The laser irradiation increased the number of calcified nodules in a time-dependent manner. The activity of alkaline phosphatase and production of collagen and osteocalcin in conditioned medium were measured. Both were higher in the irradiated group than in the nonirradiated group. These results suggested that formation of calcified nodules in HDP cells, as well as in alkaline phosphatase activity, the production of collagen and osteocalcin were enhanced by laser irradiation.

Lipid Peroxidation as a Possible Cause of Benzoyl Peroxide Toxicity in Rabbit Dental Pulp—A Microsomal Lipid Peroxidation in vitro

The toxicity of composite resin on rabbit dental pulp was investigated biochemically. A microsomal fraction of rabbit dental pulp was incubated with each of the components of composite resins, and the formation of peroxide was determined by the thiobarbituric acid reaction. Benzoyl peroxide (BPO), the most widely used catalyst, was the most effective on peroxidation, but monomers were not. Cations such as Cu2+ or Fe2+ were required for acceleration of this reaction. Authentic polyunsaturated fatty acids and phospholipids were extensively converted into their peroxides by BPO, but amino acids and carbohydrates were not. Among the active oxygens, hydroxyl radicals were thought to be responsible for BPO-dependent peroxidation. The results presented in this paper indicate that the lipid portion of the cells may be attacked by hydroxyl radicals produced by BPO and copper or iron. Therefore, BPO is considered to be the major factor responsible for the toxicity of composite resins.

Stimulation of interleukin-6 production in human dental pulp cells by peptidoglycans from Lactobacillus casei

Interleukin-6 (IL-6), which is a multifunctional cytokine, has an important role in acute and chronic inflammation. The peptidoglycan (PG) was purified from Lactobacillus casei, which was a Gram-positive bacteria frequently isolated from deep carious lesions and suspected to be a pathogen of pulpitis. In this study, the effects of PG on the production of IL-6 in human dental pulp cells were examined. PG stimulated IL-6 production in a time- and dose-dependent manner. Reverse transcriptase-polymerase chain reaction experiments showed that the increase was dependent on the enhancement of IL-6 mRNA levels. These findings suggest that Gram-positive bacteria, such as L. casei, from carious lesions, might be involved in developing pulpitis through the stimulation of IL-6 production.

Effect of the application of dentin primers and a dentin bonding agent on the adhesion between the resin-modified glass-ionomer cement and dentin

OBJECTIVES This study was designed to evaluate the influence of the application of dentin primer and/or dentin bonding agent on the adhesion of a resin-modified glass-ionomer cement to dentin. METHODS Bovine dentin was pretreated with Dentin Conditioner or EDTA 3-2 solution, primed by an experimental dentin primer, and applied with a dentin bonding agent. A resin-modified glass-ionomer cement, Fuji II LC, was then adhered to the dentin. The tensile bond strength between the light-cured glass-ionomer cement and the pretreated dentin was measured. The components of the experimental dentin primers were 2-hydroxyethyl methacrylate (HEMA), glyceryl methacrylate (GM) and a water-soluble photo-polymerization initiator, 2-hydroxy-3-(3,4-dimethyl-9-oxo-9H-thioxanthen-2-yloxy)-N,N, N-trimethyl-1- propanaminium chloride (OTX). Significant differences in the data were examined by an analysis of variance and Scheffes test for multiple comparisons between the means at p = 0.05. RESULTS A significantly higher mean bond strength between the Fuji II LC and dentin was obtained by EDTA 3-2 pretreatment, QTX/GM priming, and LB Bond application. This value was comparable with that obtained with the resin composite system. Scanning electron microscopy observation showed the formation of a hybrid layer with a thickness of 1-1.5 microns. SIGNIFICANCE The data obtained in this investigation suggest that the adhesion of Fuji II LC to dentin is closer to that provided by a resin composite system than to that of conventional glass-ionomer cements.

TNF-α suppresses bone sialoprotein (BSP) expression in ROS17/2.8 cells

Tumor necrosis factor‐alpha (TNF‐α) is a major mediator of inflammatory responses in many diseases that inhibits bone formation and stimulates bone resorption. To determine molecular mechanisms involved in the suppression of bone formation we have analyzed the effects of TNF‐α on BSP gene expression. Bone sialoprotein (BSP) is a mineralized tissue‐specific protein that appears to function in the initial mineralization of bone. Previous studies have demonstrated that BSP mRNA expression is essentially restricted to fully‐differentiated cells of mineralized connective tissues and that the expression of BSP is developmentally regulated. Treatment of rat osteosarcoma ROS 17/2.8 cells with TNF‐α (10 ng/ml) for 24 h caused a marked reduction in BSP mRNA levels. The addition of antioxidant N‐acetylcysteine (NAC; 20 mM) 30 min prior to stimulation with TNF‐α attenuated the inhibition of BSP mRNA levels. Transient transfection analyses, using chimeric constructs of the rat BSP gene promoter linked to a luciferase reporter gene, revealed that TNF‐α (10 ng/ml) suppressed expression in all constructs, including a short construct (pLUC3; nts −116 to +60), transfected into ROS17/2.8 cells. Further deletion analysis of the BSP promoter showed that a region within nts −84 to −60 was targeted by TNF‐α, the effects which were inhibited by NAC and the tyrosine kinase inhibitor, herbimycin A (HA). Introduction of 2bp mutations in the inverted CCAAT box (ATTGG; nts −50 and −46), a putative cAMP response element (CRE; nts −75 to −68), and a FGF response element (FRE; nts −92 to −85) showed that the TNF‐α effects were mediated by the CRE. These results were supported by gel mobility shift assays, using a radiolabeled double‐stranded CRE oligonucleotide, which revealed decreased binding of a nuclear protein from TNF‐α‐stimulated ROS 17/2.8 cells. Further, the inhibitory effect of TNF‐α on CRE DNA–protein complex was completely abolished by NAC or HA treatment. These studies, therefore, show that TNF‐α suppresses BSP gene transcription through a tyrosine kinase‐dependent pathway that generates reactive oxygen species and that the TNF‐α effects are mediated by a CRE element in the proximal BSP gene promoter. J. Cell. Biochem. 87: 313–323, 2002.

Static magnetic fields-induced bone sialoprotein (BSP) expression is mediated through FGF2 response element and pituitary-specific transcription factor-1 motif

Bone sialoprotein (BSP) is a sulfated and phosphorylated glycoprotein found almost exclusively in mineralized connective tissues. Recent studies on the developmental expression of BSP mRNA and temporo‐spatial appearance of the protein during bone formation in vivo and in vitro have demonstrated that BSP is expressed by differentiated osteoblasts, and that it may function in the initial nucleation of hydroxyapatite crystals in de novo bone formation. Physical forces may play a fundamental role in the regulation of cell function in bone, but little is known about how cells are able to sense mechanical loads and signal transduction. Magnetic fields of sufficient magnitude have been shown to affect various biologic systems at organ, tissue, cellular, and subcellular levels. In the present study, rat osteosarcoma‐derived osteoblast‐like cells, UMR 106, were used to assess the effect of static magnetic fields (SMF) on gene transcription of BSP. In our culture system, application of 300 and 800 Gauss SMF increased BSP mRNA levels after 24 h stimulation. To determine the molecular basis of the transcriptional regulation of BSP gene transcription by SMF, we conducted transient transfection analyses with chimeric constructs of the rat BSP gene promoter linked to a luciferase (LUC) reporter gene. SMF (300 and 800 Gauss) increased expression of the construct (pLUC3; −116 to +60) after 24 h treatment. Further deletion analysis of the BSP promoter showed that a region within nt −116 to −84 was targeted by SMF, the effect of which was inhibited by the tyrosine kinase inhibitor herbimycin A (HA). Mutations (2 bp) were made in an inverted CCAAT box between nt −50 and −46, a cyclicAMP response element (CRE; between nt −75 and −68), a fibroblast growth factor‐2 response element (FRE; −92 to −85), and a pituitary‐specific transcription factor‐1 motif (Pit‐1; nt −111 to −105) within the pLUC3 construct. Transcriptional stimulation by SMF was almost completely abrogated in constructs that included 2‐bp mutations in the FRE and Pit‐1. Binding of nuclear proteins to a radiolabeled FRE was increased and that to a Pit‐1 was decreased in nuclear extracts prepared from SMF‐stimulated UMR 106 cells. Further, the stimulatory and inhibitory effects of SMF on FRE and Pit‐1 DNA‐protein complexes were completely abolished by HA treatment. These studies, therefore, show that SMF increases BSP transcription through a tyrosine kinase‐dependent pathway and that the SMF effects are mediated through juxtaposed FRE and Pit‐1elements in the proximal promoter of the BSP gene.

Effect of nonsteroidal anti-inflammatory drugs on lipid peroxidation by hydroxyl radical

1. Effects of acetaminophen and sodium salicylate on hydoxyl radical elimination were studied using an electron-spin-resonance spin-trapping method. The effects of these agents on lipid peroxidation of the human erythrocyte membrane were also investigated by the thiobarbituric acid method. 2. Acetaminophen and sodium salicylate depressed hydroxyl radical generated by Cu2+/H2O2. 3. Acetaminophen inhibited Cu2+/H2O2-dependent lipid peroxidation; however, sodium salicylate enhanced Cu2+/H2O2-dependent lipid peroxidation.