NOS Evaluations in Human Dental Pulp-Capping with MTA and Calcium-Hydroxide

The aim of this study is to compare mineral trioxide aggregate (MTA) with calcium hydroxide when used as pulp-capping material in human teeth. 40 teeth were divided into groups based on clinical diagnosis: healthy and hyperaemic. The teeth were pulp capped with MTA and calcium hydroxide. We localized the eNOS and iNOS by immunohistochemistry, tested their mRNA expression by RT-PCR and protein levels by western blots. The evaluation of the samples was based on the cell inflammatory response and on the pulp tissue organization. In particular, evaluation of eNOS and iNOS differences between the various groups and the cellular evolution after the first 7 days from the treatment, and at a distance of 28 days. Our results suggest that there are differences in localization and expression between eNOS and iNOS in dental pulp. Our study has helped us to better understand the effects that calcium hydroxide and MTA have on pulp tissue.

Cementum and Dentin in Hypophosphatasia

Hypophosphatasia (HPP) often leads to premature loss of deciduous teeth, due to disturbed cementum formation. We addressed the question to what extent cementum and dentin are similarly affected. To this end, we compared teeth from children with HPP with those from matched controls and analyzed them microscopically and chemically. It was observed that both acellular and cellular cementum formation was affected. For dentin, however, no differences in mineral content were recorded. To explain the dissimilar effects on cementum and dentin in HPP, we assessed pyrophosphate (an inhibitor of mineralization) and the expression/activity of enzymes related to pyrophosphate metabolism in both the periodontal ligament and the pulp of normal teeth. Expression of nucleotide pyrophosphatase phosphodiesterase 1 (NPP1) in pulp proved to be significantly lower than in the periodontal ligament. Also, the activity of NPP1 was less in pulp, as was the concentration of pyrophosphate. Our findings suggest that mineralization of dentin is less likely to be under the influence of the inhibitory action of pyrophosphate than mineralization of cementum.

Painful Tooth Stimulation Elevates Matrix Metalloproteinase-8 Levels Locally in Human Gingival Crevicular Fluid

Recent studies have demonstrated that pulpal pain can induce neurogenic inflammatory reactions in gingiva and the expression of pro-inflammatory neuropeptides in gingival crevicular fluid (GCF). Neuropeptides co-ordinate the activity of immuno-effector cells and may influence the secretion of matrix metalloproteinase (MMP)-8, the major tissue-destructive protease in GCF. With this background, we studied whether experimental pulpal pain can trigger changes in GCF MMP-8 levels. The molecular forms of MMP-8 in the GCF of stimulated and non-stimulated teeth were analyzed by Western immunoblot, and MMP-8 levels by quantitative immunofluorometric assay. Painful stimulation of the upper incisor provoked significant elevations in GCF MMP-8 levels of the stimulated tooth. Western immunoblot revealed elevations in both neutrophil- and mesenchymal-type MMP-8 isoforms. At the same time, the GCF MMP-8 levels of the non-stimulated teeth were not changed. Analysis of these data indicated that pulpal pain can induce local elevations in MMP-8 levels in GCF.

Urethane dimethacrylate induces cytotoxicity and regulates cyclooxygenase-2, hemeoxygenase and carboxylesterase expression in human dental pulp cells

The toxic effect of urethane dimethacrylate (UDMA), a major dental resin monomer, on human dental pulp is not fully clear. In this study, we investigated the influence of UDMA on the cytotoxicity, cell cycle distribution, apoptosis and related gene expression of dental pulp cells. The role of reactive oxygen species, hemeoxygenase-1 (HO-1) and carboxylesterase (CES) in UDMA cytotoxicity, was evaluated. UDMA induced morphological changes of pulp cells and decreased cell viability by 29-49% at concentrations of 0.1-0.35 mM. UDMA induced G0/G1, G2/M cell cycle arrest and apoptosis. The expression of cdc2, cyclinB1 and cdc25C was inhibited by UDMA. Moreover, UDMA stimulated COX-2, HO-1 and CES2 mRNA expression of pulp cells. The cytotoxicity of UDMA was attenuated by N-acetyl-l-cysteine, catalase and esterase, but was enhanced by Zn-protoporphyrin (HO-1 inhibitor), BNPP (CES inhibitor) and loperamide (CES2 inhibitor). Exposure of UDMA may potentially induce the inflammation and toxicity of dental pulp. These findings are important for understanding the clinical response of human pulp to resin monomers after operative restoration and pulp capping, and also provide clues for improvement of dental materials.

Copper-zinc superoxide dismutase activity in dental pulp after dental preparation

The superoxide dismutases (SODs) are the major enzymatic defence mechanism against toxic reactive oxygen species generated during normal oxidative metabolism and during the respiratory burst associated with inflammation. To further clarify the potential role of copper-zinc (Cu/Zn)-SOD during inflammation of pulp tissue in humans, the aim was to determine whether significant changes in Cu/Zn-SOD activity occur in healthy dental pulp after dental preparation. The condition of the pulp was assessed using clinical and radiographic evaluation. Thirty systemically healthy patients were the source of the pulp tissue, which was collected by longitudinally grooving and splitting teeth that were matched between the control dental pulp and the prepared tooth (test) dental pulp. Cu/Zn-SOD activity was determined through spectrophotometric methods, with Mann-Whitney tests used to assess the significance of the differences between the groups. The Cu/Zn-SOD activity was 168.2+/-46.4 mU.mg−1 total protein (range: 96-212 mU.mg−1) in the control group, and 328.2+/-84.2 mU.mg−1 total protein (range: 280-420 mU.mg−1) in the test group. The difference between the groups was statistically significant, at P <0.001. These results demonstrate a potential role for Cu/Zn-SOD during dental pulp inflammation in humans after dental preparation.

Endodontic-orthodontic relationships: expression of no synthase in human dental pulp during orthodontic tooth movement

Inflamed human pulp tissue presents an increase in the level of nitric oxide synthase (NOS). The aim of this study is to verify the presence of NOS in human pulp of teeth that are subject to orthodontic force. 20 healthy subjects, wearers of fixed braces on the upper arch, were selected. An open coil-spring in NiTi was applied on the upper premolar test tooth (TT); the controlateral control tooth (CCT) was subjected to orthodontic treatment but not to the further force of the open coil-spring; the antagonist control tooth (ACT) did not undergo any orthodontic treatment. Pulps were taken from test, contralateral control and antagonist control teeth immediately after the extractions which were done at 15 and 30 days from the start of application of the orthodontic force. The pulp tissue was analyzed through immunohistochemical and molecular biology examinations. The results showed tooth pulps subject to orthodontic treatment were very inflamed in the first 15 days with high levels of iNOS and low levels of eNOS; after 30 days a decrease of the inflammation and an increase of the pulp vascularization were observed together with a reduction of iNOS and an increase of eNOS respectively.

Phosphate increases bone morphogenetic protein-2 expression through cAMP-dependent protein kinase and ERK1/2 pathways in human dental pulp cells

Extracellular phosphate (Pi) is known to play a key role in promoting osteoblastic differentiation by altering gene expression and cellular function. Importantly, it may be possible to use this knowledge as a means to deliver Pi to local sites to regenerate mineralized tissues associated with the oral cavity. Therefore, we determined the ability of Pi to regulate differentiation of pulp cells toward an odontoblast phenotype and further determined if this was in part due to an increase in the expression of bone morphogenetic protein (BMP)-2, a crucial regulator of mineralization. Results showed that Pi increased BMP-2 expression at both mRNA and protein level and BMP-2 promoter activity. Signaling inhibitors revealed that increased BMP-2 expression was dependent on cAMP/protein kinase A but not the protein kinase C signaling pathway. Treatment with 8-Br-cAMP, a cell-permeable analog of cAMP, enhanced Pi-mediated BMP-2 expression, but treatment with 8-Br-cAMP alone did not increase BMP-2, suggesting that cAMP is indispensable but not sufficient for Pi-mediated BMP-2 expression. Pi activated ERK1/2, and treatment with PD98059, an ERK1/2 inhibitor, suppressed Pi-mediated BMP-2 increase, indicating a requirement for activation of ERK1/2. ERK1/2 pathway may operate independently of cAMP-dependent signaling because MDL12,330A, an adenylate cyclase inhibitor, did not inhibit phosphorylation of ERK1/2 in response to Pi. Pulp cells expressed the sodium-dependent Pi transporter (NaPi) III type, but not NaPi-I type or NaPi-II type. Pi-mediated BMP-2 increase was inhibited in the presence of phosphonoformic acid, an inhibitor not only of NaPi transport but also of crystal nucleation. Furthermore, a similar inhibition was observed in the presence of pyrophosphate, a mineralization inhibitor. These findings demonstrate, for the first time, that Pi regulates BMP-2 expression via cAMP/protein kinase A and ERK1/2 pathways in human dental pulp cells.

The presence of open dentinal tubules affects the biological properties of dental pulp cells ex vivo

To investigate the effects of open dentinal tubules on the morphological and functional characteristics of dental pulp cells. Morphological changes in human dental pulp cells that were seeded onto dentin discs with open dentinal tubules were investigated on days 1, 2, 4, and 10 of culture using scanning electron microscopy and fluorescence microscopy. Samples collected on days 1, 3, 6, 8, and 10 of culture were evaluated for cell proliferation rate and alkaline phosphatase activity. Cultured human dental pulp cells developed a columnar or polygonal morphology and monopolar cytoplasmic processes that extended into the dentinal tubules. The cells formed a multilayer and secreted an extracellular matrix onto the cell surface. Scanning electron microscopy and fluorescence microscopy revealed polarized organization of odontoblasts. Cells seeded onto dentin discs proliferated minimally but showed high levels of ALP activity. Dental pulp cells seeded onto treated dentin discs develop an odontoblastlike phenotype, which may be a potential alternative for use in experimental research on dentinogenesis.

Monoamine oxidase and semicarbazide sensitive amine oxidase activities in normal and inflamed human dental pulp

BACKGROUND

Human dental pulp contains monoamine oxidase (MAO) and semicarbazide sensitive amine oxidase (SSAO). In other tissues SSAO is involved in oxidative stress and inflammation, but the role of MAO and SSAO in human pulp and changes of their activities in reversible pulpitis still remains poorly understood.

MATERIAL/METHODS

We investigated MAO labeling with mechanism-based inhibitor [3H]pargyline activities of MAO A, MAO B, and SSAO in healthy and inflamed human dental pulp.

RESULTS

Incubation of human dental pulp homogenates with [3H]pargyline caused MAO labeling. MAO activity assayed with 100 microM [14C]5HT or 10 microM [14C]PEA was sensitive to selective inhibitors of MAO A and MAO B, respectively. MAO activity with 50 microM [14C]PEA was partially inhibited by clorgyline, and total inhibition was achieved only by the combination of clorgyline and semicarbazide, suggesting the presence of SSAO. Inflammation of the dental pulp was accompanied by a significant decrease in MAO labeling, MAO B (but not MAO A) activity and the increase in SSAO activity.

CONCLUSIONS

The results of the present study suggest that the increase of dental pulp SSAO activity contributes to the development of inflammation in the dental pulp. The decrease in MAO B activity and lack of significant changes in MAO A activity may be associated with an anti-inflammatory response - inflamed pulp MAO A still effectively deaminates the inflammatory mediator 5HT, whereas inhibition of MAO B could result in some decrease of hydrogen peroxide generation, essential for the tissue damage in inflammation.

Hypoxia induces expression and activation of AMPK in rat dental pulp cells

AMP-activated protein kinase (AMPK) is a stress-responsive enzyme involved in cell adaptation to an energy crisis. We hypothesized that hypoxia suppresses oxidative phosphorylation and ATP production, resulting in AMPK activation to protect cells. We investigated the effects of hypoxia on cell proliferation, the expression of AMPK and hypoxia-inducible factor 1alpha (HIF-1alpha), the activation of AMPK, and the relationship between AMPK and HIF-1alpha expression in rat dental pulp RPC-C2A cells. AMPK in the cells was composed of catalytic alpha1, and regulatory beta1 and gamma1 subunit isoforms. Cell proliferation was initially suppressed under hypoxia, but it increased thereafter, together with an increase in the expression of AMPK and HIF-1alpha, and the activation of AMPK. Down-regulation of AMPKalpha1 by siRNA inhibited cell proliferation under both normoxia and hypoxia, revealing that AMPK induction and activation were required for cell proliferation, although HIF-1alpha expression under hypoxia was not affected.

Odontogenic capability: bone marrow stromal stem cells versus dental pulp stem cells

BACKGROUND INFORMATION

Although adult bone-marrow-derived cell populations have been used to make teeth when recombined with embryonic oral epithelium, the differences between dental and non-dental stem-cell-mediated odontogenesis remain an open question.

RESULTS

STRO-1(+) (stromal precursor cell marker) DPSCs (dental pulp stem cells) and BMSSCs (bone marrow stromal stem cells) were isolated from rat dental pulp and bone marrow respectively by magnetic-activated cell-sorting techniques. Their odontogenic capacity was compared under the same inductive microenvironment produced by ABCs (apical bud cells) from 2-day-old rat incisors. Co-cultured DPSCs/ABCs in vitro showed more active odontogenic differentiation ability than mixed BMSSCs/ABCs, as indicated by the accelerated matrix mineralization, up-regulated alkaline phosphatase activity, cell-cycle modification, and the expression of tooth-specific proteins and genes. After cultured for 14 days in the renal capsules of rat hosts, recombined DPSC/ABC pellets formed typical tooth-shaped tissues with balanced amelogenesis and dentinogenesis, whereas BMSSC/ABC recombinants developed into atypical dentin-pulp complexes without enamel formation. DPSC and BMSSC pellets in vivo produced osteodentin-like structures and fibrous connective tissues respectively.

CONCLUSIONS

DPSCs presented more striking odontogenic capability than BMSSCs under the induction of postnatal ABCs. This report provides critical insights into the selection of candidate cells for tooth regeneration between dental and non-dental stem cell populations.

Differential signalling pathways involved in cholinoceptor-dependent stimulation of nitric oxide isoforms in dental pulp

AIM

To investigate the role of muscarinic acetylcholine receptor (mAChR) subtype activity in the regulation of endothelial- (e) and neuronal- (n) nitric oxide synthase (NOS) expression and activity.

METHODOLOGY

Rat dental pulp tissue was used throughout the study. The e-nos and n-nos mRNA levels were specifically measured using reverse transcriptase polymerase chain reaction procedures that involve simultaneous co-amplification of both target cDNA and a reference template with a single set of primers. NOS activity was measured by the production of [U-(14)C]-citrulline from [U-(14)C]-arginine.

RESULTS

Stimulation of M(1)/M(2) and M(3)/M(4) mAChRs with pilocarpine caused an increase in e-nos and n-nos mRNA levels and NOS activity in the dental pulp. The specific mAChR subtype antagonists, L-NMMA, l-NIO and N(2)-propyl-L-arginine but not aminoguanidine attenuated all these effects. Inhibitors of phospholipase C (PLC), protein kinase C (PKC) and calcium/calmodulin (CaM) prevented the pilocarpine-dependent increase in n-nos and e-nos mRNA levels and NOS activity.

CONCLUSIONS

Activation of mAChR subtypes stimulated NOS activity by increasing the production of NO through e-nos and n-nos gene expression and NOS activity. The mechanism appears to occur secondarily to stimulation of CaM and PKC enzymatic activity.

Elevated expression of Cu, Zn-SOD and Mn-SOD mRNA in inflamed dental pulp tissue

AIM

To determine the mRNA expression levels of copper-zinc superoxide dismutase (Cu, Zn-SOD) and manganese SOD (Mn-SOD) in healthy and inflamed human dental pulp tissue.

METHODOLOGY

Sixteen patients with symptomatic irreversible pulpitis (eight females and eight males) were selected for study. Normal healthy pulps were removed from extracted mandibular third molar teeth from 10 systemically healthy individuals (six females and four males). QRT-PCR analysis of Cu, Zn-SOD and Mn-SOD mRNA expression was carried out in 16 cases of irreversible pulpitis and in 10 cases of systemically healthy donors. The Shapiro-Wilk's test was used to test the normality of data, whereas the Mann-Whitney U-test was used to evaluate the significance of the differences between groups. Differences in the expression levels were considered to be statistically significant for P-values <0.05.

RESULTS

A significant increase (P < 0.05) occurred in both Cu, Zn-SOD and Mn-SOD mRNA expression in cases of irreversible pulpitis. The increase in Mn-SOD level was significantly higher (P < 0.05) than the change observed for Cu, Zn-SOD.

CONCLUSIONS

The development of pulpitis is associated with elevated transcription of both Cu, Zn-SOD and Mn-SOD; pulp tissue inflammation generated higher Mn-SOD transcription compared with Cu, Zn-SOD.

The role of matrix metalloproteinases in the oral environment

This review focuses specifically on matrix metalloproteinases (MMPs) and their role in physiological and pathological extracellular matrix (ECM) remodeling and degradation processes in the oral environment. A group of enzymes capable of degrading almost all ECM proteins, MMPs contribute to both normal and pathological tissue remodeling. The expression of different MMPs may be upregulated in pathological conditions such as inflammation and tumor invasion. The balance between activated MMPs and tissue inhibitors of metalloproteinases (TIMPs) controls the extent of ECM remodeling. Prior to mineralization, MMPs may participate in the organization of enamel and dentin organic matrix, or they may regulate mineralization by controlling the proteoglycan turnover. There is evidence indicating that MMPs could be involved in the etiology of enamel fluorosis and amelogenesis imperfecta. They seem to play a part in dentinal caries progression, since they have a crucial role in dentin collagen breakdown in caries lesions. MMPs have been identified in pulpal and periapical inflammation and are strongly correlated with periodontal diseases, since they are the major players in collagen breakdown during periodontal tissue destruction. The use of MMP inhibitors could help the prevention and treatment of many MMP-related oral diseases.

Sequential expression of endothelial nitric oxide synthase, inducible nitric oxide synthase, and nitrotyrosine in odontoblasts and pulp cells during dentin repair after tooth preparation in rat molars

Nitric oxide (NO) stimulates osteoblast differentiation, but whether NO contributes to odontoblast differentiation during dentin repair is unknown. By using reverse transcription/polymerase chain reaction and immunostaining, we investigated the gene expression and/or immunolocalization of endothelial NO synthase (eNOS), inducible NOS (iNOS), and nitrotyrosine (a biomarker for NO-derived peroxinitrite), and alkaline phosphatase (ALP) and osteocalcin (early and terminal differentiation markers of odontoblasts, respectively) in dental pulp tissue after rat tooth preparation. At the early stage (1-3 days) post-preparation, markedly increased expression of iNOS and nitrotyrosine was found in odontoblasts and pulp cells beneath the cavity, whereas eNOS expression was significantly decreased. ALP mRNA expression was significantly increased after 1 day but decreased after 3 days, whereas ALP activity was weak in the dentin-pulp interface under the cavity after 1 day but strong after 3 days. Osteocalcin mRNA expression was significantly increased at this stage. At 7 days post-preparation, tertiary dentin was formed under the cavity. All the molecules studied were expressed at control levels in odontoblasts/pulp cells beneath the cavity. These findings show that abundant NO is released from odontoblasts and pulp cells at an early stage after tooth preparation and indicate that, after tooth preparation, the up-regulation of iNOS and nitrotyrosine in odontoblasts is synchronized with increased cellular expression of ALP and osteocalcin. Therefore, the NO synthesized by iNOS after tooth preparation probably participates in regulating odontoblast differentiation during tertiary dentinogenesis.

Co-expression of cyclooxygenase-2 and vascular endothelial growth factor in inflamed human pulp: an immunohistochemical study

Recent data from the medical literature indicates that cyclooxygenase-2 (COX-2) plays a key role in the production of vascular endothelial growth factor (VEGF), a glycoprotein that has the ability to increase the permeability of blood vessels and to induce angiogenesis. This study was undertaken to investigate the immunohistological co-expression of COX-2 and VEGF in inflamed human pulp, in conjunction with the expression of CD34, a transmembrane glycoprotein expressed in endothelial cells. Pulp tissue of extracted carious human third molars with a recent history of spontaneous pain were collected and processed for immunostaining of COX-2, VEGF, and CD34 using the biotin-streptoavidin method. Healthy pulp samples served as controls. COX-2 expression was not observed in healthy pulps, whereas all inflamed pulps demonstrated COX-2-expressing cells. Similarly, VEGF was not expressed in normal pulp tissue, but was strongly positive in inflamed pulps. CD34 was expressed in the endothelium of both normal and inflamed pulp tissues. Co-expression of COX-2 and VEGF in all consecutive sections of inflamed pulps could be suggestive of a possible release of VEGF via a COX-2-dependent pathway.

Lipopolysaccharide stimulates histamine-forming enzyme (histidine decarboxylase) activity in murine dental pulp and gingiva

To examine the potential role of the histamine-forming enzyme, histidine decarboxylase (HDC), in oral inflammation and disease, we studied HDC activity in oral tissue after induction by bacterial agents. Following injection of E. coli-derived lipopolysaccharide (LPS) into mice, we measured the quantitative changes in HDC activity over time in dental pulp and gingiva. Oral tissue taken from individual mice was insufficient for detecting precise HDC activity, thus, we combined dental pulp or gingival tissues from four mice and assayed them over the course of 24 h. Our results indicate that LPS stimulated marked elevations of HDC activity in dental pulp and gingiva. This increase reached a maximum at 6 h after LPS injection and remained detectable at for least 24 h. Since mast cells are known to produce histamine through a difference mechanism than HDC induction, we compared LPS-induced HDC activity in dental pulp and gingiva to that in ear skin (a tissue rich in mast cells) and liver (a tissues lacking in mast cells). LPS also induced a marked increase in the HDC activity in liver and ear skin at 6 h after LPS injection. By contrast, saline injection had no effect on the HDC activity in any of the four tissues, although basal levels of HDC activity in ear skin was markedly higher than basal HDC activity in the other three kinds of tissues. Still, the relative increase in LPS-induced HDC activity in dental pulp and gingiva were much greater than that in ear skin. Since liver are devoid of mast cells and ear skin is considered the tissue richest in mast cells, the differences in HDC activity between tissues indicates that histamine induced by LPS may be produced by cells other than mast cells through another mechanism of action. These results also suggest that histamine produced in oral tissues in response to bacterial agents such as LPS could be involved in development of pulpitis or gingivitis (periodontitis), the most common diseases in the dental clinic, and that efforts to inhibit HDC activity, which elevates histamine levels in oral tissues, might offer the basis for novel treatment strategies.

The effects of tumor necrosis factor-alpha, interleukin-1beta, interleukin-6, and transforming growth factor-beta1 on pulp fibroblast mediated collagen degradation

Dental pulp destruction is believed to be regulated, in part, by the matrix metalloproteinases (MMPs) and tissue inhibitors of MMPs (TIMPs). Cytokines are believed to be important in the pathogenesis of pulpitis. This study examined the effects that TNF-alpha, IL-1beta, IL-6, and TGF-beta1 have on the collagen degradation mediated by pulp fibroblasts utilizing a cell-mediated collagen degradation assay. Reverse transcriptase-polymerase chain reaction, Western blot analyses, and zymography were utilized to examine multiple MMPs and TIMPs. The collagen degradation mediated by these cells was stimulated by these cytokines. TNF-alpha, IL-1beta, and IL-6 increased the mRNA and/or protein expression of MMP-1, MMP-2, and MMP-3. TGF-beta1 decreased MMP-1 mRNA expression, while only slightly affecting the MMP-2 and MMP-3 mRNA and/or protein. These cytokines did not affect the expression of TIMP-1 or TIMP-2. These results suggest that these cytokines affect pulp destruction, in part, by differentially regulating the MMPs and TIMPs.

Quantification of lactate-dehydrogenase and cell viability in postmortem human dental pulp

Understanding pulp repair and regeneration requires being familiar with this tissue's behavior under extreme conditions, such as postmortem state where an abrupt interruption of tissue blood supply occurs. The purpose of this study was to quantify cell viability and the amount of lactate-dehydrogenase (LDH) expressed in human pulp tissue 6, 12, and 24 hours postmortem to establish how long dental pulp remains viable after death. Pulp samples were obtained from 14 unidentified corpses of people who had received lethal injuries in car accidents or from gunshot wounds; they had at least three caries- and restoration-free incisors. Half of each sample was used for determining cell viability at three different time intervals. The rest of each sample was used for quantifying LDH expression at the same time intervals. Another 14 pulp samples were obtained from live patients' healthy premolars where extraction was indicated for orthodontic reasons to assess normal LDH value in pulp tissue. The results showed cell viability decreasing from 89 to 68 to 41% measured 6, 12, and 24 hours postmortem, respectively. LDH expression in healthy pulps was 246 U/mg pulp weight. Expression increased after death from 249 U/mg at 6 hours to 337 U/mg at 12 hours. LDH expression decreased to 131 U/mg 24 hours postmortem. These findings are valuable in understanding dental pulp survival capability under extreme conditions that may have important clinical significance in terms of repair and regeneration.

Heme oxygenase-1 mediates cytoprotection against nitric oxide-induced cytotoxicity via the cGMP pathway in human pulp cells

OBJECTIVE

This study examined the effects of exogenous nitric oxide (NO) on human pulp cells and the involvement of cyclic 3',5'-monophosphate (cGMP) in pulpal protection induced by heme oxygenase-1 (HO-1) against NO-induced cytotoxicity.

STUDY DESIGN

This study investigated cytotoxicity and HO-1 induction in pulp cells induced by the NO donor S-nitroso-N-acetyl-D,L-penicillamine (SNAP), by using Western blotting and a cell viability assay. It also investigated whether HO-1 contributes to the cytoprotective effect against the cytotoxicity caused by NO and the relationship between HO-1 and cGMP in the signaling pathway.

RESULTS

S-nitroso-N-acetyl-D,L-penicillamine decreased cell viability, but increased HO-1 expression in a concentration- and time-dependent manner in human pulp cells. NO-induced cytotoxicity was inhibited in the presence of hemin (inducer of HO-1), whereas it was enhanced in the presence of zinc protoporphyrin IX (ZnPP IX, HO-1 inhibitor); therefore, the NO-induced cytotoxicity was correlated with HO-1 expression. Pretreatment with a membrane-permeable cGMP analog, 8-bromo-cGMP, restored cell death and enhanced the HO-1 protein expression induced by SNAP. By contrast, 1 mM SNAP inhibited guanylate cyclase in pulp cells pretreated with 1H-[1,2,4]oxadiazole[4,3-alpha]quinoxalin-1-one (ODQ), resulting in marked cytotoxicity.

CONCLUSION

These findings of a link between HO-1, regulated via the cGMP system and NO-induced cytotoxicity in human pulp cells, suggest a protective role for HO-1 in pulpal inflammation.

Interleukin-1 α Alters the Expression of Matrix Metalloproteinases and Collagen Degradation by Pulp Fibroblasts

Matrix metalloproteinases (MMPs) and the tissue inhibitors of MMPs (TIMPs) have been suggested to play a role in dental pulp destruction. This study examined the effects of interleukin (IL)-1 alpha on pulp fibroblasts. The ability of these cells to degrade collagen was determined with or without IL-1 alpha utilizing a cell-mediated collagen degradation assay. Reverse transcriptase-polymerase chain reaction was utilized to examine the mRNA expression of multiple MMPs and TIMPs with and without IL-1 alpha, while Western blot analyses and zymography were utilized to examine their protein expression. The collagen degradation mediated by these cells was stimulated by IL-1 alpha and inhibited by MMP inhibitors. IL-1 alpha increased the mRNA expression of MMP-1 and MMP-3, as well as induced MMP-7. Western blot analyses confirmed these results. IL-1 alpha increased the secreted protein level of TIMP-1, while only slightly affected the level of TIMP-2. These results suggest that IL-1 alpha can induce pulp destruction by differentially regulating MMPs and TIMPs.

p38 mitogen-activated protein kinase and alkaline phosphatase in human dental pulp cells

OBJECTIVE

The objective of this study was to investigate the implication of p38 mitogen-activated protein kinase (MAPK) in mediating alkaline phosphatase (ALPase) activity in human dental pulp cells (HPCs).

STUDY DESIGN

Nuclear translocation of p38 was observed by immunofluorescence in isolated HPCs treated with transforming growth factor beta1 (TGF-beta1). TGF-beta1 was used to examine the interaction between p38 MAPK and Smad pathway. Role of p38 kinase in mediating ALPase activity was determined with SB203580, a specific inhibitor for the p38 pathway. Lipopolysaccharide (LPS) or TGF-beta1 was added to inhibit or increase ALPase activity. Statistical analysis was performed by unpaired t test.

RESULTS

TGF-beta1 induced nuclear translocalization of p38. Blockage of p38 pathway with SB203580 inhibited translocation of Smad2/3 to nuclei. ALPase activity decreased in cells treated with SB203580, in contrast to its vehicle (P < .05). Inhibition on enzyme activity by LPS was exacerbated by SB203580 (P < .05). Treatment with SB203580 before addition of TGF-beta1 also made a significant decrease in ALPase activity (P < .05).

CONCLUSIONS

These results suggest that p38 MAPK is implicated in regulating ALPase activity in HPCs and may interact with Smad pathway.

Examination of the Signal Transduction Pathways Leading to Upregulation of Tissue Type Plasminogen Activator by Interleukin-1α in Human Pulp Cells

Tissue type plasminigen activator (t-PA) is one of the important proteolysis factors in the pathogenesis of pulpal inflammation. However, the mechanisms and signal transduction pathways involved in the production of t-PA in human pulp cells are not fully understood. The purpose of this study was to investigate the t-PA activity in human pulp cells stimulated with various pharmacological agents. IL-1alpha was used to evaluate t-PA activity in human pulp cells using casein zymography and enzyme-linked immunosorbent assay (ELISA). Furthermore, to search possible signal transduction pathways, p38 inhibitor SB203580, MEK inhibitor U0126, and phosphatidylinositaol 3-kinase (PI3K) inhibitor LY294002 were added to test how they modulated the t-PA activity. The main casein secreted by human pulp cells migrated at 70 kDa and represented t-PA. Secretion of t-PA was found to be stimulated with IL-1alpha during 2 day cultured period (p < 0.05). From the results of casein zymography and ELISA, SB203580, U0126, and LY294002 significantly reduced the IL-1alpha-stimulated t-PA production, respectively (p < 0.05). Our findings demonstrated that IL-1alpha enhance t-PA production in human pulp cells, and the signal transduction pathways p38, MEK, and PI3K are involved in the inhibition of t-PA. SB203580, U0126, and LY294002 suppress t-PA activity and may also have important implication for pharmacological intervention.

Examination of the signal transduction pathways leading to upregulation of tissue type plasminogen activator by Porphyromonas endodontalis in human pulp cells

AIM

To investigate the tissue type plasminogen activator (t-PA) activity in human pulp cells stimulated with Porphyromonas endodontalis (P. endodontalis) in the absence or presence of p38 inhibitor SB203580, mitogen-activated protein kinase kinase (MEK) inhibitor U0126 and phosphatidylinositaol 3-kinase (PI3K) inhibitor LY294002.

METHODOLOGY

The supernatants of P. endodontalis were used to evaluate t-PA activity in human pulp cells using casein zymography and enzyme-linked immunosorbent assay (ELISA). Furthermore, to search for possible signal transduction pathways, SB203580, U0126 and LY294002 were added to test how they modulated the t-PA activity.

RESULTS

The main casein secreted by human pulp cells migrated at 70 kDa and represented t-PA. Secretion of t-PA was found to be stimulated with P. endodontalis during 2-day cultured period (P < 0.05). From the results of casein zymography and ELISA, SB203580 and U0126 significantly reduced the P. endodontalis stimulated t-PA production respectively (P < 0.05). However, LY294002 lacked the ability to change the P. endodontalis stimulated t-PA production (P > 0.05).

CONCLUSIONS

Porphyromonas endodontalis enhances t-PA production in human pulp cells, and the signal transduction pathways p38 and MEK are involved in the inhibition of t-PA.

Alkaline phosphatase activity in dental pulp of orthodontically treated teeth

INTRODUCTION

The aim of this study was to examine alkaline phosphatase (ALP) activity in the dental pulp of orthodontically treated teeth.

METHODS

Sixteen healthy subjects (mean age 17.0 +/-1.6 years) who required extraction of 4 first premolars for orthodontic reasons participated. One maxillary first premolar subjected to orthodontic force was the test tooth. The contralateral first premolar, bracketed but not subjected to mechanical stress, was the control tooth. After a week of treatment, the first premolars were extracted and the dental pulp removed from the teeth. ALP activity was determined spectrophotometrically and the results expressed as units/liter per milligram of pulp tissue [U/(L x mg)].

RESULTS

ALP activity was 89 +/- 26 U/(L x mg) in the test teeth and 142 +/- 33 U/(L x mg) in the control teeth. The difference between the groups was statistically significant (P < .01).

CONCLUSIONS

Orthodontic treatment can lead to significant early-phase reduction in ALP activity in human dental pulp tissue.

Induction of cyclooxygenase-2 expression in human pulp cells stimulated by dentin bonding agents

OBJECTIVES

Histological investigations have demonstrated that dentin bonding agents can induce pulpal inflammation. However, there is little information on the precise mechanisms about dentin bonding agent-induced pulpal inflammation. Cyclooxygenase-2 (COX-2) is an inducible enzyme believed to be responsible for prostaglandin synthesis at the site of inflammation. The aim of this study was to investigate the effects of dentin bonding agents on the expression of COX-2 in human pulp cells.

STUDY DESIGN

Human pulp cells were cultured from extracted impacted third molars using an explant technique. Patients gave informed consent. The reverse-transcriptase polymerase chain reaction and Western blot assays were used to investigate the effects of cultured human pulp cells exposed to dentin bonding agents. In addition, NS-398 (a selective COX-2 inhibitor) was added to test how it modulated the cytotoxic effects of dentin bonding agents.

RESULTS

The exposure of quiescent human pulp cells to dentin bonding agents resulted in the induction of COX-2 mRNA and protein expression. The expression of COX-2 signals depended on the materials tested. In addition, NS-398 at noncytotoxic dose was not able to prevent dentin bonding agent-induced cytotoxicity (P > .05).

CONCLUSION

The activation of COX-2 expression may be one of the pathogenesis of dentin bonding agent-induced pulpal inflammation. In addition, dentin bonding agent-induced cytotoxicity is not directly via the induction of COX-2 expression.

NO-cGMP signaling molecules in cells of the rat molar dentin-pulp complex

By the formation of cyclic guanosine 3',5'-monophosphate (cGMP), nitric oxide (NO)-sensitive enzyme-soluble guanylate cyclase (sGC) plays a receptor role for NO within the NO-cGMP signaling cascade, which is involved in vasodilatation and neurotransmission. The hypothesis that NO-cGMP signaling molecules modulate cells of the dentin-pulp complex was investigated in rat molars by histochemical, immunohistochemical, immuno-ultrastructural, and organ bath techniques. NO synthase (NOS) I-III, the sGC alpha(2)-subunit/beta(1)-subunit, and cGMP were detected in odontoblasts and blood vessels. NOS I, sGC alpha(2), and cGMP were identified in nerve fibers. Treatment of rat molars with the NO donor NONOate (10(-5) M) increased cGMP staining intensities in blood vessels and odontoblasts, while NO synthase inhibitor L-NAME (10(-4) M) attenuated intensity of the reaction products for cGMP, suggesting an effect of endogenous NO on sGC. These correlations of patterns and alterations of cGMP staining intensities after treatment with the NO donor or NO inhibitor might represent an NO-sGC-cGMP signaling-dependent modulation of odontoblasts, blood vessels, and nerve fibers in the dentin-pulp complex.

Neuropeptide release from dental pulp cells by RgpB via proteinase-activated receptor-2 signaling

Dental pulp inflammation often results from dissemination of periodontitis caused mostly by Porphyromonas gingivalis infection. Calcitonin gene-related peptide and substance P are proinflammatory neuropeptides that increase in inflamed pulp tissue. To study an involvement of the periodontitis pathogen and neuropeptides in pulp inflammation, we investigated human dental pulp cell neuropeptide release by arginine-specific cysteine protease (RgpB), a cysteine proteinase of P. gingivalis, and participating signaling pathways. RgpB induced neuropeptide release from cultured human pulp cells (HPCs) in a proteolytic activity-dependent manner at a range of 12.5-200 nM. HPCs expressed both mRNA and the products of calcitonin gene-related peptide, substance P, and proteinase-activated receptor-2 (PAR-2) that were also found in dental pulp fibroblast-like cells. The PAR-2 agonists, SLIGKV and trypsin, also induced neuropeptide release from HPCs, and HPC PAR-2 gene knockout by transfection of PAR-2 antisense oligonucleotides inhibited significantly the RgpB-elicited neuropeptide release. These results indicated that RgpB-induced neuropeptide release was dependent on PAR-2 activation. The kinase inhibitor profile on the RgpB-neuropeptide release from HPC revealed a new PAR-2 signaling pathway that was mediated by p38 MAPK and activated transcription factor-2 activation, in addition to the PAR-2-p44/42 p38MAPK and -AP-1 pathway. This new RgpB activity suggests a possible link between periodontitis and pulp inflammation, which may be modulated by neuropeptides released in the lesion.

Upregulation of tissue-type plasminogen activator in inflamed human dental pulps

AIM

To compare tissue-type plasminogen activator (t-PA) expression in normal human pulp and inflamed human pulp tissue specimens.

METHODOLOGY

Thirty pulpal tissue specimens (13 normal and 17 inflamed pulps) were obtained from extracted third molars. The levels of t-PA between normal pulp and inflamed pulp tissues were compared using the quantitative reverse-transcriptase polymerase chain reaction analysis. In addition, immunohistochemistry was used to identify the in situ localization of t-PA expression in pulp specimens. Wilcoxon-Mann-Whitney rank sum test was applied for the statistical analysis of the results.

RESULTS

t-PA mRNA gene was found more in inflamed pulps when compared with normal pulp tissue (P<0.05). The results from immunohistochemistry demonstrated that t-PA expression was significantly higher in the inflamed pulp (P=0.025). t-PA stain was detected in the fibroblasts, inflammatory infiltrates and endothelial cells.

CONCLUSIONS

t-PA expression was significantly higher in inflamed pulp tissue. t-PA may play an important role in the pathogenesis of pulpal inflammation.

Copper-zinc superoxide dismutase activity in healthy and inflamed human dental pulp

AIM

To examine copper-zinc superoxide dismutase (Cu, Zn-SOD) activity in clinically healthy and symptomatic human dental pulps.

METHODOLOGY

Twenty-five systemically healthy patients, 14 females and 11 males (age: 13.1-34.6 years; mean: 21.7 +/- 6.3), were the source of the pulp tissue. The condition of the pulps was assessed using clinical and radiographic evaluation. The pulp tissue was collected by longitudinally grooving and splitting the teeth (if extracted) or during endodontic treatment, and were age- and sex-matched between the healthy and the irreversible symptomatic pulpitis tissue groups. Cu, Zn-SOD activity was determined through spectrophotometric methods and a Mann-Whitney test assessed the significance of differences between the groups.

RESULTS

The enzyme activities were 144.8 +/- 42.2 and 68.1 +/- 25.0 U mg(-1) in the healthy and irreversible symptomatic pulp tissue, respectively. The difference between the groups was statistically significant (P < 0.001).

CONCLUSIONS

These results demonstrate a potential role for Cu, Zn-SOD during dental pulp inflammation in humans.

Cyclic Amp phosphodiesterase activity in normal and inflamed human dental pulp

Cyclic AMP phosphodiesterase (cAMP PDE) seems to be important in pulp tissues. High levels of cAMP PDE have been demonstrated to be in dental pulp cells. In the present study cAMP PDE activity was analyzed in normal healthy human dental pulps, in reversible pulpitis and in irreversible pulpitis. Enzymatic cAMP PDE control values for normal healthy pulps were 12.14 +/- 3.74 nmols/mg of proteins. In reversible pulpitis the cAMP PDE activity increased almost 2.5 times. In irreversible pulpitis specimens the values increased 4.5 times compared with normal healthy pulps activity. The differences between the groups (control vs. reversible pulpitis and vs. irreversible pulpitis) were statistically significant. These results could point to a role of cAMP PDE in the initial pulp response after injury.

Cyclic GMP phosphodiesterase activity role in normal and inflamed human dental pulp

Cyclic GMP phosphodiesterase (cGMP PDE) plays an important role in pulp tissues. High levels of cGMP PDE are found in dental pulp cells. In the present study cGMP PDE activity was analyzed in normal healthy human dental pulps, in reversible pulpitis and in irreversible pulpitis. Enzymatic cGMP PDE control values for normal healthy pulps were 4.74+/-0.32 nmol/mg of proteins. In reversible pulpitis the cGMP PDE activity increased almost 3 times. In irreversible pulpitis specimens the values increased 4.5 times compared with the normal healthy pulps activity. The differences between the groups (control vs. reversible pulpitis and vs. irreversible pulpitis) were statistically significant. These results point to a role of cGMP PDE in the initial pulp response after injury.

Inhibition of human pulpal gelatinases (MMP-2 and MMP-9) by zinc oxide cements

The interaction between metal ions and the oral environment is a major subject matter in dental research. Matrix metalloproteinases (MMPs) have been implicated in several pathological and physiological processes such as, periodontal tissue destruction, root caries, dentin calcification and pulpal inflammation. The aim of this work was to test the effect of zinc released from zinc oxide-eugenol (ZOE) cements, on the activity of the major pulpal gelatinolytic MMPs. Pulpal explants were cultured overnight in Dulbecco's Modified Eagle Medium and the activity of secreted enzymes was analysed by gelatin zymography in buffer conditioned with diverse ZOE cements. Phenanthroline, a zinc chelator, was used to revert the inhibition of MMPs caused by zinc. The major gelatinolytic proteinases present in the conditioned media were characterized as MMP-2 and MMP-9 by immunoprecipitation. All ZOE cements inhibited MMPs activity, whereas phenanthroline could partially revert the inhibition caused by plain ZOE and Intermediate Restorative Material (IRM).

Nitric oxide synthase in healthy and inflamed human dental pulp

Nitric oxide synthase (NOS) plays a significant role in the pathogenesis of pulpitis. In this study, we hypothesized the existence of endothelial (eNOS) and inducible (iNOS) enzyme isoforms in human dental pulp. Extracted third molar pulps were divided into groups based on clinical diagnosis: healthy, hyperemic, and irreversible pulpitis. We have localized the eNOS and iNOS by immunohistochemistry and have tested their mRNA expression by RT-PCR and protein levels by Western blots. eNOS is present in the endothelial cells and odontoblasts of the healthy pulp, but an elevation of eNOS mRNA and protein levels with a concomitant dilation of vessels was characteristic under pathological conditions. Healthy pulp tissue failed to exhibit any iNOS; however, acute inflammation enhanced the mRNA and protein levels of iNOS, mainly in the leukocytes. There are differences in localization and expression between eNOS and iNOS in healthy and inflamed dental pulp.

Examination of the signal transduction pathways involved in matrix metalloproteinases-2 in human pulp cells

OBJECTIVES

Matrix metalloproteinases (MMPs) play an important role in pulp tissue destruction. However, the mechanisms and signal transduction pathways involved in the production of MMPs in human pulp cells are not fully understood. The purpose of this study was to investigate the gelatinolytic activity in human pulp cells stimulated with various pharmacological agents.

STUDY DESIGN

Human dental pulp cells were cultured using an explant technique obtained from impacted third molars with informed consent of the patients. The effects of p38 inhibitor SB203580, MEK inhibitor U0126, extracellular signal-regulated kinase (ERK) inhibitor PD098059, phosphatidylinositaol 3-kinase (PI3K) inhibitor LY294002, cyclooxygenase-2 (COX-2) inhibitor NS-398, nuclear factor kappa B (NF-kappaB) inhibitor dexamethasone, and tyrosine kinase inhibitor herbimycin A on the production and secretion of MMPs by human pulp cells were determined by gelatin zymography.

RESULTS

The main gelatinase secreted by human pulp cells migrated at 72 kd and represented MMP-2. Minor gelatinolytic bands were also observed at 92 kd regions that correspond to MMP-9. After a 4-day culture period, NS-398, dexamethasone, and herbimycin A were found to depress MMP-2 production (P<.05). The inhibition decreased in an order of dexamethasone >NS-398>herbimycin A. Human pulp cells, however, treated with various pharmacological agents had no effect on the pattern of MMP-9 produced or secreted in either cell extracts or conditioned medium fractions (P>.05).

CONCLUSION

These observations suggest that NS-398, dexamethasone, and herbimycin A can regulate MMP-2 produced by human pulp cells. The signal transduction pathways COX-2, NF-kappaB, and tyrosine kinase may be involved in the production of MMPs.

Aspartate aminotransferase activity in pulp of orthodontically treated teeth

This study examines the aspartate aminotransferase activity in the pulp of orthodontically treated teeth. Seventeen healthy male and female subjects (ages: 14.5-19.6; mean 16.8 +/- 1.6 years) who needed extraction of the maxillary first premolars for orthodontic reasons were enrolled in the study. One randomly chosen maxillary first premolar, included in a straight-wire fixed orthodontic appliance and supporting orthodontic force, was considered as the test tooth. The contralateral first premolar, included in the orthodontic appliance but not subjected to mechanical stress, was used as the control tooth. After a week of treatment, the dental pulp tissues were extracted from both experimental teeth. Aspartate aminotransferase activity was significantly elevated in the test teeth as compared with the control teeth. These results demonstrate that in the early phases of treatment, orthodontic force application to the teeth can lead to significant metabolic changes in the pulp of these teeth.

Proliferation of dental pulp fibroblasts in response to thrombin involves mitogen-activated protein kinase signalling

AIM

To examine the involvement of mitogen-activated protein kinases (MAPK) signalling on thrombin-stimulated human dental pulp fibroblasts (DPF).

METHODOLOGY

Dental pulp fibroblasts were isolated from dental pulp connective tissue of third molars and expanded in vitro. Expression of thrombin receptors was analysed by RT-PCR, and cell proliferation was measured by 3[H]-thymidine incorporation assay. Phosphorylation levels of MAPK were determined by Western blot analysis, and alkaline phosphatase activity was measured to serve as a marker for odontogenic differentiation. Statistical analysis was performed by Student's t-test.

RESULTS

Dental pulp fibroblasts express the thrombin receptors protease-activated receptor-1 (PAR-1), PAR-3 and PAR-4. Measurement of 3[H]-thymidine incorporation revealed a dose-dependent increase of DNA synthesis in response to thrombin treatment. The thrombin-induced mitogenic activity was decreased by the extracellular signal-regulated protein kinase (ERK) signalling inhibitor PD98059 (P < 0.05), and by SB203580 (P < 0.05), a p38 MAPK inhibitor. Western blot analysis demonstrated increased phosphorylation of ERK in DPF following stimulation with thrombin, while p38 MAPK and c-Jun NH2-terminal kinase (JNK) were not activated. Alkaline phosphatase activity of DPF remained unchanged upon incubation with thrombin.

CONCLUSIONS

These results suggest that signalling via MAPK mediates the mitogenic activity of thrombin on DPF and may thus play a role during the early stages of pulp repair.

IGFs, IGFBPs, IGF-Binding Sites and Biochemical Markers of Bone Metabolism during Differentiation in Human Pulp Fibroblasts

OBJECTIVE

To investigate the role of the insulin-like growth factors (IGF) system during the differentiation of human pulp-derived fibroblasts (HPF).

METHODS

Primary HPF were cultured for 24 days in DMEM medium with IGF-I or IGF-II (50 ng/ml each). Cell growth and morphology, alkaline phosphatase (ALP) activity, the concentration of free deoxypyridinoline (DPD), IGF-I, -II, IGFBP-2 and -3 were studied. The number of (125)I-IGF-I binding sites was estimated by Scatchard analysis.

RESULTS

Light-microscopically visible nodules emerged during differentiation. Simultaneously, the ALP activity increased steadily between days 8 and 24, while the DPD concentration decreased by about 50%. The HPF produced high concentrations of IGF-II (2.00-1.30 microg/10(6) cells) but low IGF-I, IGFBP-2. IGFBP-2 was not changed, IGFBP-3 increased by 65% during differentiation. The number of IGF binding sites increased from 8,500 +/- 55 per cell (day 8) up to 22,000 +/- 570 (day 24).

CONCLUSION

The increasing number of IGF-binding sites accompanied by alterations in the biochemical bone markers during the differentiation of HPF suggests an autocrine/paracrine role for the IGFs in the formation of dentinal hard tissue.

Matrix metalloproteinase-13 (MMP-13, collagenase-3) is highly expressed in human tooth pulp

Matrix metalloproteinases (MMPs) and their specific tissue inhibitors (TIMPs) participate into extracellular matrix degradation in physiological and pathological conditions. We hypothesized that MMP expression in pulp tissue changes in response to caries attack and investigated the gene expression profiles of MMPs and TIMPs in pulp tissue of sound and carious teeth with cDNA microarray. cDNA microarray demonstrated an extremely high MMP-13 (collagenase-3) mRNA expression in pooled pulp samples of sound and carious teeth, with less pronounced expression of MMP-16 (MT3-MMP) and TIMP-1. Real-time quantitative polymerase chain reaction of individual pulp samples revealed a wide range of the MMP-13 expression level between pulp samples with possible downregulation of MMP-13 expression during caries progression. Western blot and immunohistochemical staining confirmed the presence of MMP-13 with no observable differences between sound and carious teeth pulp tissues. The results reveal that MMP-13 is expressed and synthesized in pulp tissue, an interesting feature considering the very limited expression of MMP-13 in normal adult tissues. Further studies with a larger sample size are needed to clarify the changes in MMP-13 expression during caries progression.

Ability of healthy and inflamed human dental pulp to reduce hydrogen peroxide

This study examined the defensive ability of human dental pulp against H2O2 in healthy and reversible and irreversible pulpitis tissues through determination of catalase activity by spectrophotometric methods. Thirty-five systemically healthy patients were donors of the pulp tissue, and pulp conditions were assessed using clinical and X-ray evaluations. Catalase activity was 1.61 +/- 0.23 U mg(-1) protein in the healthy tissues, 2.99 +/- 0.45 U mg(-1) protein in the reversible pulpitis tissues, and 2.44 +/- 467 mU mg(-1) protein in the irreversible pulpitis tissues. All differences between the groups were statistically significant. These results point to a role for catalase during dental pulp inflammation in humans, and therefore demonstrate an inherent biological defense system against reactive oxidants in human dental pulp.

Catalase activity in human healthy and inflamed dental pulps

AIM

To examine the catalase activity in clinically healthy and symptomatic human dental pulps to verify if an active defence system against oxidizing agents is present as a response to bacterial invasion.

METHODOLOGY

Thirty-three systemically healthy patients, 18 females and 15 males (ages: 11.0-25.9 years; mean 18.8 +/- 3.6), were the source of the pulp tissue. The condition of the pulps was assessed using clinical and radiographic evaluations. The specimens were recovered by longitudinally grooving and splitting the teeth (if extracted) or during endodontic treatment, and were matched for age and sex between the healthy and inflamed specimen groups. Catalase activity was determined through spectrophotometric methods.

RESULTS

Enzymatic activity was 1126 +/- 343 and 3074 +/- 698 mU mL(-1) x mg of total protein in the healthy and inflamed pulp tissue specimens, respectively. This difference was statistically significant (P<0.01).

CONCLUSIONS

These results indicate a role for catalase during dental pulp inflammation in humans, and may represent an inherent biological defence system against reactive oxidants of this tissue.

Lactate dehydrogenase isoenzymes in dental pulp of rats according to stage of root development

The objective of this study was to present a classification of the root development stage of female rat molar teeth and to evaluate the variation in the lactate dehydrogenase (LDH) activity and electrophoretic isoenzyme profile according to the stage of root development of the molar teeth. We also studied the LDH activity and isoenzymes of the pulp of incisor teeth. The stage of development of the rat first molar at the age of 15 days and that of the second molar at the age of 18 days was classified as the beginning of root formation. At the age of 15 days, the electrophoretic profile of the isoenzymes for the first molar showed a prevalence of LDH-1 followed by LDH-2. However, for the maxillary second molar there was a prevalence of LDH-4 followed by LDH-1, while for the mandibular second molar LDH-1 predominated followed by LDH-2 and LDH-4. From 18 days of age, the prevalence was always of LDH-1. The electrophoretic profile of LDH isoenzymes from the pulp of the incisor teeth at the ages studied (25 and 60 days) showed the following order of prevalence: LDH-1 > LDH-2 > LDH-3 > LDH-4 > LDH-5. These results suggest that there are variations in the prevalence of the various forms of LDH isoenzymes in the dental pulp of rats according to the developmental stage of the root.

Semicarbazide-sensitive amine oxidases in pig dental pulp

The behaviour of semicarbazide-sensitive amine oxidase (SSAO; E.C. 1.4.3.6) in dental pulp has been studied, with particular reference to the metabolism of 5-hydroxytryptamine (5-HT; serotonin). Kinetic studies using radioactively labelled substrates have confirmed benzylamine, 2-phenylethylamine (PEA) and 5-HT to be substrates for microsomal SSAO from porcine dental pulp. Kinetic substrate-competition studies indicated the presence of two forms of SSAO in dental pulp; one that oxidises benzylamine and PEA but not 5-HT and a second that oxidises 5-HT and PEA but not benzylamine. These two forms also differ in their thermostabilities at 60 and 70 degrees C, although this thermal inactivation is partly reversible.

Expression profile of matrix metalloproteinases (MMPs) and tissue inhibitors of MMPs in mature human odontoblasts and pulp tissue

Previous studies have demonstrated that (at least) matrix metalloproteinase (MMP)-2, -8, -9, -14 and -20 are expressed by human odontoblasts. Here, we analysed the expression of 19 MMPs and their specific tissue inhibitors (TIMP)-1, -2 and -3) -1, -2 and -3 in mature human odontoblasts and pulp tissue. Since MMP-20 is almost exclusively expressed by the dentin-pulp complex cells, we further analysed the effect of transforming growth factor (TGF)-beta1 and bone morphogenetic protein (BMPs)-2 on its expression. Matrix metalloproteinase-9 served as a positive control for growth factor responsiveness. It was found that MMP-1, -2, -9, -10, -11, -13, -14, -15, -16, -17, -19, -20 and -23, in addition to TIMP-1, -2 and -3 were expressed by both odontoblasts and pulp tissue. Neither MMP-3 nor MMP-12 were expressed in odontoblasts or pulp tissue, and MMP-7, -8, -24 and -25 were expressed only in the odontoblasts; MMP-2, -10, -11, -14 and -20 were expressed more abundantly by odontoblasts, whereas pulp tissue expressed more MMP-13 and MMP-17. Transforming growth factor-beta1 (1 ng ml(-1)) and BMP-2 (100 ng ml(-1)) did not markedly affect MMP-20 mRNA expression. In contrast, TGF-beta1 alone and with BMP-2 significantly upregulated MMP-9 mRNA by 2.4-fold and by 2.6-fold, respectively, in odontoblasts, while in pulp tissue no effects could be detected. The wide-scale expression of MMPs and TIMPs by mature human odontoblasts and pulp tissue suggests that they may participate in dentin matrix organization prior to mineralization, and that growth factors may further control dentin matrix modeling by differentially regulating individual MMPs.

Induction of cyclooxygenase-2 mRNA and protein expression in human pulp cells stimulated with black-pigmented bacteroides

Cyclooxygenase-2 (COX-2) is induced after the activation of cells by a variety of proinflammatory agents. Recently, evidence has shown that COX-2 may play a role in the pathogenesis of pulpal inflammation. However, little is known regarding the mechanism of pulpal inflammation at the site of bacterial infection. The purpose of this study was to determine the effects of the supernatants from black-pigmented Bacteroides (Porphyromonas endodontalis, Porphyromonas gingivalis, and Prevotella intermedia) on the COX-2 expression in primary human pulp cells in vitro. Investigations of the time dependence of COX-2 mRNA expression in black-pigmented Bacteroides-treated human pulp cells revealed a rapid accumulation of the transcript, a significant signal first detectable after 1 h of exposure. In addition, black-pigmented Bacteroides also up-regulated COX-2 protein expression in human pulp cells. Data from our in vitro experiment showed that black-pigmented Bacteroides were capable of stimulating COX-2 expression in human pulp cells. These results indicate that black-pigmented Bacteroides species may play an important role in the pathogenesis of pulpal inflammation. The activation of COX-2 may be one of the distinct host degradative pathways in the pathogenesis of microbial-induced pulpal/periapical inflammation.

Proinflammatory cytokines induce cyclooxygenase-2 mRNA and protein expression in human pulp cell cultures

The increased release of prostaglandins (PG) within pulpal tissues is considered to play a pathogenic role during pulpal disease progression. The rate-limiting step in the formation of PG from arachidonic acid is catalyzed by cyclooxygenase (COX). COX-2 is an inducible enzyme believed to be responsible for PG synthesis at site of inflammation. The effect of proinflammatory cytokines on human pulp cells with special reference to COX-2 expression has not been reported earlier. The aim of the present study was to investigate the effects of interleukin (IL)-1alpha and tumor necrosis factor-alpha (TNF-alpha) on the expression of COX-2 mRNA gene and protein in cultured human pulp cells. Investigations of the time dependence of COX-2 mRNA expression in proinflammatory cytokines-treated human pulp cells revealed a rapid accumulation of the transcript, a significant signal first detectable 1 h after exposure. In addition, both IL-1alpha and TNF-alpha up-regulated COX-2 protein expression by human pulp cells. The kinetics of this response showed that COX-2 was detectable in cell lysates as early as 2 h post proinflammatory cytokines challenge and remained elevated throughout the 24-h incubation period. This suggests that one of the pathogenic mechanisms of pulpal inflammation in vivo may be the synthesis of COX-2 by resident cells in response to a proinflammatory cytokines challenge. COX-2 may play an important role in the regulation of prostanoid formation in the pathogenesis of pulpal inflammation. Taken together, we propose that the use of selective COX-2 inhibitors might provide a valuable tool in the control of pulpal inflammation.

Induction of tissue plasminogen activator gene expression by proinflammatory cytokines in human pulp and gingival fibroblasts

Plasminogen activator converts plasminogen to plasmin, and plasmin activates the latent matrix metalloproteinases. Tissue plasminogen activator (t-PA) is one of the important proteolysis factors present in human inflamed tissues. However, few studies reported on the mechanisms of tissue destruction via a t-PA proteolysis pathway in pulpal and periapical diseases. The subsequent reactions leading to pulpal and periapical injury after the induction of proinflammatory cytokines remains to be elucidated. The aim of this study was to investigate the effects of interleukin-1alpha and tumor necrosis factor-alpha on the expression of t-PA mRNA gene in cultured human pulp and gingival fibroblasts. The mRNAs for t-PA were measured by reverse transcription-polymerase chain reaction at 2, 6, and 24 h. The results show that both cytokines induced significantly high levels of t-PA mRNA gene expression in human pulp fibroblasts. The peak of t-PA mRNA levels induced by both proinflammatory cytokines was at the 6-h incubation period. Interleukin-1alpha was found to be more effective in induction of t-PA gene expression than tumor necrosis factor-alpha. In addition, a similar induction pattern was also found in human gingival fibroblasts. These results indicate that proinflammatory cytokines can induce t-PA gene expression and such an effect may partially contribute to the destruction of pulpal and periapical tissues through dysregulated pericellular proteolysis. An understanding of the mechanism could not only further define the role of immune events in pulpal and periapical diseases but also have important implication for pharmacological intervention.

Proliferative ability and alkaline phosphatase activity with in vivo cellular aging in human pulp cells

Little is known about the effect of aging on characteristic functions of pulp cells. When damaged pulp is recovered and mineralized tissue is formed to protect remaining pulp tissue, the general responses of pulp tissue after adequate stimuli (pulp cell proliferation and activation of alkaline phosphatase [ALPase]) are thought to be essential. In this study, we compared proliferative ability and ALPase activity between cultures of human pulp (HP) cells obtained from young and aged donors. The in vitro proliferative lifespan of HP cells from young donors was longer than HP cells from aged donors. Growth rates and ALPase activity of HP cells decreased with increasing donor age. These findings suggest that impaired repair of pulp and dentin in aged patients is partly due to a decrease in the proliferative ability and ALPase activity in aged pulp cells.

Matrix metalloproteinase levels and gelatinolytic activity in clinically healthy and inflamed human dental pulps

The role of matrix metalloproteinases (MMPs) in the breakdown of pulp tissue of teeth with severe caries has not yet been directly elucidated. This study was to determine the levels of selected MMPs and the overall gelatinolytic activity in clinically healthy and inflamed human dental pulps of 29 healthy subjects, aged 10-19 yr. Seventeen pulps were collected from subjects diagnosed with symptomatic pulpitis, and 18 control pulps were obtained from 12 subjects following premolar extraction for orthodontic reasons. The levels of MMP-1, MMP-2, MMP-3 and MMP-9 were determined with enzyme-linked immunosorbent assay. Densitometric analysis of gelatin zymograms was used to assay gelatinolytic activity in pulp supernatants. The MMP-1 levels were below the detection limit for both groups. Levels of MMP-2 and MMP-3 were significantly lower in symptomatic vs. clinically healthy pulps. In contrast, levels of MMP-9 in inflamed pulps were significantly higher than those recorded in clinically normal pulps. The overall gelatinolytic activity was elevated in inflamed pulps compared with healthy counterparts. Further, the gelatinolytic activity was positively correlated with MMP-9 levels. The data obtained suggest a key role of MMP-9 in the breakdown of inflamed human dental pulp tissue.