Oxidation-specific epitopes are important targets of innate immunity

During the oxidation of LDL, a central pathophysiological component of atherogenesis, a wide variety of chemical and physical changes occur leading to the generation of oxidation-specific neoepitopes. These epitopes are not only immunogenic, leading to adaptive humoral responses, but are also a prominent target of multiple arcs of innate immunity. The pattern recognition receptors (PRRs) of innate immunity are germ line encoded, conserved by natural selection, and bind to pathogen-associated molecular patterns (PAMPs) common on multiple structures. However, it is not intuitive as to why they should recognize oxidation-specific neoepitopes. Yet it is clear that multiple macrophage scavenger receptors, which are classic PRRs, recognize oxidation-specific epitopes, such as those found on oxidized LDL (OxLDL). Other innate proteins, such as C-reactive protein, also bind to OxLDL. Natural antibodies (NAbs), the humoral arc of innate immunity, provide a nonredundant role in the first line of defence against pathogens, but are also believed to provide important homeostatic house-keeping functions against self-antigens. Our work demonstrates that oxidation-specific epitopes, as found on OxLDL, are a major target of NAbs. In this review, we will discuss the specific example of the prototypic NAb T15/E06, which is increased in atherosclerotic mice and mediates atheroprotection, and discuss the potential role of NAbs in atherogenesis, and in inflammation in general. We also review data that oxidation-specific epitopes are generated whenever cells undergo programmed cell death, forming a common set of PAMPs recognized by oxidation-specific PRRs on macrophages, NAbs and innate proteins. We present the hypothesis that oxidation-specific epitopes on apoptotic cells exerted evolutionary pressure for the conservation of these PRRs and also serve to maintain the expansion of a substantial proportion of NAbs directed to these stress-induced self-antigens.

Persistent superconductivity in ultrathin Pb films: a scanning tunneling spectroscopy study

By using a low temperature scanning tunneling microscope we have probed the superconducting energy gap of epitaxially grown Pb films as a function of the layer thickness in an ultrathin regime (5-18 ML). The layer-dependent energy gap and transition temperature (Tc) show persistent quantum oscillations down to the lowest thickness without any sign of suppression. Moreover, by comparison with the quantum-well states measured above Tc and the theoretical calculations, we found that the Tc oscillation correlates directly with the density of states oscillation at E(F) . The oscillation is manifested by the phase matching of the Fermi wavelength and the layer thickness, resulting in a bilayer periodicity modulated by a longer wavelength quantum beat.

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.

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.

Hydrogenation-induced insulating state in the intermetallic compound LaMg2Ni

Hydrogenation-induced metal-semiconductor transitions usually occur in simple systems based on rare earths and/or magnesium, accompanied by major reconstructions of the metal host (atom shifts >2 A). We report on the first such transition in a quaternary system based on a transition element. Metallic LaMg2Ni absorbs hydrogen near ambient conditions, forming the nonmetallic hydride LaMg2NiH7 which has a nearly unchanged metal host structure (atom shifts <0.7 A). The transition is induced by a charge transfer of conduction electrons into tetrahedral [NiH4]4- complexes having closed-shell electron configurations.

Demonstration of different modes of cell death upon herpes simplex virus 1 infection in different types of oral cells

The effects of Herpes simplex virus 1 (HSV-1) infection on five different types of oral cancerous cells (neck metastasis of gingival carcinoma (GNM) cells and tongue squamous cells of carcinoma (TSCCa) and non-cancerous cells (buccal mucosal fibroblasts (BF), gingival fibroblasts (GF), oral submucosal fibrosis cells (OSF)) and one type of non-oral cancerous cells (KB cells) were investigated. In HSV-1-infected cells the cell viability, CPE, viral antigens accumulation, caspase-3 activity, annexin V binding and DNA fragmentation were estimated. Three different forms or pathways of cell death were considered: apoptosis (the presence or rise of caspase-3 activity, DNA fragmentation and annexin V binding), slow cell death (the presence or rise of DNA fragmentation, the absence or decline of caspase-3 activity and annexin V binding), and necrosis (the absence of decline of caspase-3 activity, DNA fragmentation and annexin V binding). The viability of all cell types, except for KB cells, was reduced by the infection. CPE and viral antigens data demonstrated that all six types of cells could be infected with HSV-1. Upon HSV-1 infection there occurred (i) a classical apoptosis in GF cells, (ii) apoptosis in the early phase of infection and necrosis in the late phase of infection in GNM and TSCCa cells, (iii) slow cell death followed by necrosis in BF and OSF cells (however, these cells showed a different type of CPE), (iv) a classical slow cell death in KB cells. It is hypothesized that HSV-1 infection has a potential to induce several distinct pathways leading to cell death or several forms of cell death. Moreover, more than one pathway may be involved in the death of particular cell type. As HSV-1 was demonstrated to infect different oral and non-oral cells and cause different pathways or forms of cell death, the safety of using HSV-1 as a vector for gene therapy should be re-considered.

Alternative low-symmetry structure for 13-atom metal clusters

The atomic geometry, electronic structure, and magnetic moment of 4d transition-metal clusters with 13 atoms are studied by pseudopotential density-functional calculations. We find a new buckled biplanar structure with a C(2v) symmetry stabilized by enhanced s-d hybridization. It has a lower energy than the close-packed icosahedral or cuboctahedral structure for elements with more than half-filled d shells. The magnetic moments of this buckled biplanar structure are found to be smaller than those of the icosahedral structure and closer to available experimental results.

Thermal stability and electronic structure of atomically uniform Pb films on Si(111)

Atomically uniform Pb films are successfully prepared on Si(111), despite a large lattice mismatch. Angle-resolved photoemission measurements of the electronic structure show layer-resolved quantum well states which can be correlated with dramatic variations in thermal stability. The odd film thicknesses N = 5, 7, and 9 monolayers show sharp quantum well states. The even film thicknesses N = 6 and 8 do not, but are much more stable than the odd film thicknesses. This correlation is discussed in terms of a total energy calculation and Friedel-like oscillations in properties.

Quantum confinement and electronic properties of silicon nanowires

We investigate the structural, electronic, and optical properties of hydrogen-passivated silicon nanowires along [110] and [111] directions with diameter d up to 4.2 nm from first principles. The size and orientation dependence of the band gap is investigated and the local-density gap is corrected with the GW approximation. Quantum confinement becomes significant for d<2.2 nm, where the dielectric function exhibits strong anisotropy and new low-energy absorption peaks start to appear in the imaginary part of the dielectric function for polarization along the wire axis.

Cytotoxic effects of gingival retraction cords on human gingival fibroblasts in vitro

The objective of this study was to determine the cytocompatibility of three different extracts of gingival retraction cords and to compare the cytotoxic effect of these materials on human gingival fibroblasts. Gingival retraction cords impregnated with aluminium sulphate (Gingi-Aid), dl-adrenaline HCl (Gingi-Pak) and non-drug-impregnated cord (Gingi-Plain) were eluted with culture medium for 10 min and 24 h. Cytotoxicity was judged using a tetrazolium bromide reduction assay. Our data demonstrated that gingival retraction cords applied alone almost completely inhibited cell viability (P < 0.05). In addition, the results also showed that the eluates from aluminium sulphate-impregnated cord, dl-adrenaline HCl-impregnated cord and non-drug-impregnated cord were cytotoxic to primary human gingival fibroblast cultures (P < 0.05). The cell viability of incubation of gingival fibroblasts containing 10-min eluates of aluminium sulphate, dl-adrenaline HCl and non-drug-impregnated cord was 61, 21 and 70%, respectively. The cell viability of incubation of gingival fibroblasts containing 24 h eluates of aluminium sulphate, dl-adrenaline HCl and non-drug-impregnated cord was 68, 58 and 72%, respectively. It was found that dl-adrenaline HCl-impregnated gingival retraction cord was the most toxic gingival retraction cord among the materials tested in all cultures (P < 0.05). The cytotoxicity decreased in an order of dl-adrenaline HCl-impregnated cord > aluminium sulphate-impregnated cord > non-drug-impregnated cord. The extent or degree of the cytotoxicity depended on the materials tested. Gingival retraction cords have significant potential for gingival toxicity. Careful management of gingiva retraction cords would lower the risk of potential gingival tissue damage during clinical application procedure and thus increase the success of prosthodontic procedures.

Activation of p53 signalling in acetylsalicylic acid-induced apoptosis in OC2 human oral cancer cells

BACKGROUND

Nonsteroidal anti-inflammatory drugs (NSAIDs) such as acetylsalicylic acid (ASA, aspirin) are well known chemotherapeutic agents of cancers; however, the signalling molecules involved remain unclear. The aim of this study was to investigate the possible existence of a putative p53-dependent pathway underlying the ASA-induced apoptosis in OC2 cells, a human oral cancer cell line.

MATERIALS AND METHODS

The methyl tetrazolium (MTT) assay was employed to quantify differences in cell viability. DNA ladder formation on agarose electrophoresis was used as apoptosis assay. The expression levels of several master regulatory molecules controlling various signal pathways were monitored using the immunoblotting techniques. Flow cytometry was used to confirm the effect of ASA on cell cycle. Patterns of changes in expression were scanned and analyzed using the NIH image 1.56 software (NIH, Bethesda, MD, USA). All the data were analyzed by ANOVA.

RESULTS

Acetylsalicylic acid reduced cell viability and presence of internucleosomal DNA fragmentation. In the meanwhile, phosphorylation of p53 at serine 15, accumulation of p53 and increased the expression of its downstream target genes, p21 and Bax induced by ASA. The expression of cyclooxygenase-2 was suppressed. Disruption of p53-murine double minute-2 (MDM2) complex formation resulted in increasing the expression of MDM2 60-kDa cleavage fragment. Inhibited the activation of p42/p44 mitogen-activated protein kinase (MAPK) by PD98059, a specific inhibitor of extracellular regulatory kinase (ERK), significantly decreased cell viability and enhanced the expression of p53 induced by ASA. The result of the cell-cycle analysis showed that ASA and PD98059 induced the cell cycle arrested at the G0/G1 phase and resulted in apoptosis.

CONCLUSION

Nonsteroidal anti-inflammatory drug-inhibited cyclooxygenase is not the only or even the most important mechanism of inhibition. Our study presents evidences that activation of p53 signalling involved in apoptosis induced by ASA. Furthermore, the apoptotic effect was enhanced by blocking the activation of p42/p44 MAPK in response to treatment with ASA, thus indicating a negative role for p42/p44 MAPK.

Alternating layer and island growth of Pb on Si by spontaneous quantum phase separation

Real-time in situ x-ray studies of continuous Pb deposition on Si(111)-(7x7) at 180 K reveal an unusual growth behavior. A wetting layer forms first to cover the entire surface. Then islands of a fairly uniform height of about five monolayers form on top of the wetting layer and grow to fill the surface. The growth then switches to a layer-by-layer mode upon further deposition. This behavior of alternating layer and island growth can be attributed to spontaneous quantum phase separation based on a first-principles calculation of the system energy.

Immunohistochemical localization of cyclooxygenase-2 in radicular cysts

AIM

The purpose of this study was to investigate the expression of cyclooxygenase-2 (COX-2) in radicular cysts.

METHODOLOGY

Thirty biopsy specimens of radicular cysts were examined using immunohistochemistry. A peroxidase-labelled streptavidin-biotin technique was used for identification of the COX-2. Fisher's exact test (two-tail) was used for statistical analysis of the results.

RESULTS

The result demonstrated that COX-2 expression was significantly higher in radicular cysts with higher levels of inflammatory infiltrates. COX-2 stain was detected in the lining epithelium, subepithelial fibroblasts, macrophages and endothelial cells in all specimens.

CONCLUSIONS

COX-2 expression is significantly higher in radicular cysts. COX-2 may play an important role in the pathogenesis of radicular cysts.

Electron-hole coupling and the charge density wave transition in TiSe2

Angle-resolved photoemission is employed to measure the band structure of TiSe2 in order to clarify the nature of the ( 2 x 2 x 2) charge density wave transition. The results show a very small indirect gap in the normal phase transforming into a larger indirect gap at a different location in the Brillouin zone. Fermi surface topology is irrelevant in this case. Instead, electron-hole coupling together with a novel indirect Jahn-Teller effect drives the transition.

Modulation of calcium balance in tilapia larvae (Oreochromis mossambicus) acclimated to low-calcium environments

This study examined how developing fish larvae regulate their Ca2+ balance for acclimation to low ambient Ca2+. Calcium balance in newly hatched larvae was examined individually. Developing larvae not only increased Ca2+ influx but also decreased Ca2+ efflux when they were acclimated to low-Ca2+ environments. After acclimation for 8 days, the influx and efflux of the low-Ca2+ (0.02 mM) group were about 106% and 43%, respectively, compared to those of the high-Ca2+ (1.0 mM) group. Sensitivity and response to low-Ca2+ environments are age-dependent. Upon acute exposure to low Ca2+. newly hatched (H0) larvae increased both Ca2+ influx (from 24% to 67% of high-Ca2+) and net uptake (from 5% to 69%) within 64 h, while 3-day-posthatching (H3) larvae managed to reach the levels of the control within 38 h. Declining Ca2+ efflux in H3 larvae occurred 14 h after exposure, much faster than those in H0 larvae (38 h). It is suggested that modulation of Ca2+-balance mechanisms in developing larvae is dependent upon the levels of Ca2+ in the larval body.

Cytotoxicity of resin-, zinc oxide-eugenol-, and calcium hydroxide-based root canal sealers on human periodontal ligament cells and permanent V79 cells

AIM

The purpose of this study was to determine the cytotoxicity of three different types of root canal sealer on human periodontal ligament (PDL) cells and a permanent hamster cell line (V79 cells).

METHODOLOGY

Set specimens from two resin based sealers (AH26 and AHPlus), three zinc oxide-eugenol-based sealers (Canals, Endomethasone and N2) and one calcium hydroxide-based sealer (Sealapex) were eluted with culture medium for 1, 2, 3 and 7 days. Cytotoxicity was judged using tetrazolium bromide reduction assay on human primary PDL cells and V79 cells derived from a Chinese hamster.

RESULTS

The results showed that elutes from resin-based, zinc oxide-eugenol-based, and calcium hydroxide-based sealers were cytotoxic to primary human PDL cultures and V79 cells. Calcium hydroxide-based sealer was the least toxic sealer amongst the chemicals tested in both cultures. The cytotoxic response decreased in an order of N2 > Endomethasone > AH26 > AHplus > Canals > Sealapex.

CONCLUSIONS

The sensitivity of toxicity depended on the materials tested and the cell culture system used. Thus, the use of both permanent and primary cells is recommended for screening of the cytotoxic effects of root canal sealers. In addition, the results confirmed that root canal sealers constantly dissolve when exposed to an aqueous environment for extended periods, possibly causing moderate or severe cytotoxic reactions. Use of calcium hydroxide-based material as a root canal sealer initially may result in a more favourable response to periradicular tissues.

Antimicrobial activity of four root canal sealers against endodontic pathogens

The antibacterial effects of various types of widely used endodontic sealers have not been compared systematically on facultative or obligate anaerobic endodontic pathogens. The aim of this study was to evaluate the antimicrobial properties of four commonly used endodontic sealers: two epoxy-resin-based sealers (AH26, AH plus), one zinc-oxide eugenol-based sealer (N2), and one calcium hydroxide-based sealer (Sealapex). The testing microbes were four facultative anaerobic species (Streptococcus mutans, Streptococcus sanguis, Escherichia coli, and Staphylococcus aureus) and four obligate anaerobic species (Porphyromonas gingivalis, Porphyromonas endodontalis, Fusobacterium nucleatum, and Prevotella intermedia). The freshly mixed sealers were placed into the prepared wells of agar plates inoculated with the test microorganisms. After varying periods of incubation (2 days for facultative anaerobic species and 7 days for obligate anaerobic species), the zones of growth inhibition were observed and measured. All the sealers were distinctly different from each other in their antimicrobial activity. The sealers showed different inhibitory effects depending on the types and bacterial strains. N2 containing formaldehyde and eugenol proved to be the most effective against the microorganisms. The extreme antimicrobial potency of this root canal sealer must be weighted against its pronounced tissue toxic effect.

The correlation between alteration of p16 gene and clinical status in oral squamous cell carcinoma

The purpose of the study was to evaluate the presence of alteration of the tumor suppressor gene p16 and to correlate these changes with the clinical status of the patients in oral squamous cell carcinoma. Forty-eight oral squamous cell carcinomas were included in the analyses. Deletion analysis was performed by the polymerase chain reaction (PCR). Mutation analysis was restricted to exon 1 and exon 2 of the p16 gene, previously shown to have a high incidence of mutations. The sequences containing exon 1 and exon 2 were amplified by PCR and screened with a single-strand conformation polymorphism (SSCP) technique. Samples showing band shifts in SSCP were sequenced by PCR direct sequencing. Western blots were used to detect the protein expression of the p16 gene, and the results were evaluated with regard to their biological relevance in correlation with clinicopathological factors. Seven (14.6%) deletions were found; 5 (10.4%) mutations were discovered and located in different codons; 26 (54%) specimens had no p16 protein expression; in 11 specimens with p16 deletion or mutation, p16 protein could not be detected. One mutation was non-sense. The p16 gene alterations showed no relationship with location and clinical stage of cancer; however, a close relationship between p16 alterations and cancer metastasis to neck lymph node was found. The alteration rate gradually elevated from well to poorly differentiated grades. We perceive two results. First, the alterations of the p16 gene are common in oral squamous cell carcinoma. Second, the alterations of the p16 gene may attribute to the metastatic behavior or histological grade of cancer cells.

The effect of sodium hypochlorite and chlorhexidine on cultured human periodontal ligament cells

OBJECTIVE

The objective of this study was to examine the effects of sodium hypochlorite (NaOCl) and chlorhexidine (CHx) on cultured human periodontal ligament (PDL) cells in vitro.

STUDY DESIGN

The effects of irrigation solutions on human PDL cells were evaluated by propidium iodide fluorescence cytotoxicity assay, protein synthesis assay, and mitochondrial activity.

RESULTS

Both NaOCl and CHx were cytotoxic to human PDL cells in a concentration- and contact time-dependent manner. In addition, CHx inhibited protein synthesis in human PDL cells. Although NaOCl displayed cellular cytotoxicity, it showed no protein inhibition in the PDL cells. Furthermore, both NaOCl and CHx exhibited an inhibitory effect on mitochondrial activity on human PDL cells.

CONCLUSIONS

This study suggests that these irrigation fluids may cause detrimental effects on vital tissues. Its clinical significance, however, needs to be evaluated further because concentration used, exposure time to the agent, and exposure surface area are important factors affecting the resulting effect.

Synergistic effects of nicotine on arecoline-induced cytotoxicity in human buccal mucosal fibroblasts

Areca quid chewing has been linked to oral submucous fibrosis and oral cancer. Arecoline, a major areca nut alkaloid, is considered to be the most important etiologic factor in the areca nut. In order to elucidate the pathobiological effects of arecoline, cytotoxicity assays, cellular glutathione S-transferase (GST) activity and lipid peroxidation assay were employed to investigate cultured human buccal mucosal fibroblasts. To date, there is a large proportion of areca quid chewers who are also smokers. Furthermore, nicotine, the major product of cigarette smoking, was added to test how it modulated the cytotoxicity of arecoline. At a concentration higher than 50 microg/ml, arecoline was shown to be cytotoxic to human buccal fibroblasts in a dose-dependent manner by the alamar blue dye colorimetric assay (P<0.05). In addition, arecoline significantly decreased GST activity in a dose-dependent manner (P<0.05). At concentrations of 100 microg/ml and 400 microg/ml, arecoline reduced GST activity about 21% and 46%, respectively, during a 24 h incubation period. However, arecoline at any test dose did not increase lipid peroxidation in the present human buccal fibroblast test system. The addition of extracellular nicotine acted synergistically on the arecoline-induced cytotoxicity. Arecoline at a concentration of 50 microg/ml caused about 30% of cell death over the 24 h incubation period. However, 2.5 mM nicotine enhanced the cytotoxic response and caused about 50% of cell death on 50 microg/ml arecoline-induced cytotoxicity. Taken together, arecoline may render human buccal mucosal fibroblasts more vulnerable to other reactive agents in cigarettes via GST reduction. The compounds of tobacco products may act synergistically in the pathogenesis of oral mucosal lesions in areca quid chewers. The data presented here may partly explain why patients who combined the habits of areca quid chewing and cigarette smoking are at greater risk of contracting oral cancer.

Adenomatous polyposis coli gene mutation and decreased wild-type p53 protein expression in oral submucous fibrosis: a preliminary investigation

OBJECTIVE

The purpose of this study was to identify the adenomatous polyposis coli (APC) tumor suppressor gene mutation and level of wild-type p53 protein expression in patients with oral submucous fibrosis (OSF).

STUDY DESIGN

Cells from OSF and control subjects were cultured in Dulbecco modified Eagle medium with 10% fetal bovine serum at 37 degrees C. Genomic DNA was extracted from cultured cells and used as a template for polymerase chain reaction amplification of the APC tumor suppressor gene. The presence of wild-type p53 protein in cell lysates of cultured cells was analyzed by Western blot. Data were analyzed by the sign test for nonparametric samples and by analysis of variance.

RESULTS

The results showed that the APC gene of explant cultured cells from OSF patients (8/8) had a CGA-to-GGA transition mutation at codon 498 that resulted in an Arg-to-Gly missense mutation (P <.01). All (8/8) normal HGF cultures revealed expression of the wild-type APC protein. Cells cultured from 7 of 8 OSF patients were also found to have a single nucleotide deletion at nucleotide 1494 that resulted in creating a stop codon (TGA) at codon 504 (P <.01). This created a premature signal for the endpoint of translation and thus resulted in the generation of a truncated protein product that encodes a polypeptide of 503 amino acid residue. It was found that wild- type p53 protein in human gingival fibroblast cell cultures was significantly higher than in OSF cells (P <.01).

CONCLUSION

Alterations of the APC and wild-type p53 tumor suppressor genes in OSF may imply a risk for progression to oral cancer.

Quantum Electronic Stability of Atomically Uniform Films

We have studied the structural stability of thin silver films with thicknesses of N = 1 to 15 monolayers, deposited on an Fe(100) substrate. Photoemission spectroscopy results show that films of N = 1, 2, and 5 monolayer thicknesses are structurally stable for temperatures above 800 kelvin, whereas films of other thicknesses are unstable and bifurcate into a film with N +/- 1 monolayer thicknesses at temperatures around 400 kelvin. The results are in agreement with theoretical predictions that consider the electronic energy of the quantum well associated with a particular film thickness as a significant contribution to the film stability.

X-ray studies of phonon softening in tise2

The charge-density-wave transition in TiSe (2), which results in a commensurate (2x2x2) superlattice at temperatures below approximately 200 K, presumably involves softening of a zone-boundary phonon mode. For the first time, this phonon-softening behavior has been examined over a wide temperature range by synchrotron x-ray thermal diffuse scattering.

Cytotoxicity and arecoline mechanisms in human gingival fibroblasts in vitro

Betel nut chewing, like cigarette smoking, is a popular oral habit which impinges on the daily lives of a population of approximately 200 million. People who chew betel nuts have a higher prevalence of periodontal diseases than those who do not. Many of the undesirable effects of betel nuts have been attributed to arecoline, a major component of the particular alkaloid in betel nuts. In this in vitro study, we have focused on the effects of arecoline and the role it could play in periodontal breakdown via its direct effects on human gingival fibroblasts. Human gingival fibroblasts were derived from three healthy individuals undergoing crown-lengthening procedures. We found that arecoline is cytotoxic to human gingival fibroblasts at a concentration higher than 50 micrograms/ml by depleting intracellular thiols and inhibiting mitochondrial activity (P < 0.05). In addition, the cells displayed a marked arrest at G2/M phase in a dose-dependent manner. Repeated and long-term exposure to arecoline could impair the gingival fibroblast functions. As they are cytotoxic, the use of betel nut products in conjunction with periodontal therapy may interfere with optimal healing and/or lead to further periodontal breakdown.

Adverse effects of arecoline and nicotine on human periodontal ligament fibroblasts in vitro

BACKGROUND, AIMS

The habit of betel nut chewing impinges on the daily lives of approximately 200 million people. Betel quid chewers have a higher prevalence of periodontal diseases than non-chewers. This study examined the pathobiological effects of arecoline, a major component of the betel nut alkaloids, on human periodontal ligament fibroblasts (PDLF) in vitro.

METHOD

Cell viability, proliferation, protein synthesis, and cellular thiol levels were used to investigate the effects of human PDLF exposed to arecoline levels of 0 to 200 microg/ml. In addition, nicotine was added to test how it modulated the effects of arecoline.

RESULTS

Arecoline significantly inhibited cell proliferation in a dose-dependent manner. At concentrations of 10 and 30 microg/ml, arecoline suppressed the growth of PDLF by 20% and 50% (p < 0.05), respectively. Arecoline also decreased protein synthesis in a dose-dependent manner during a 24-h culture period. A 100 microg/ ml concentration level of arecoline significantly inhibited protein synthesis to only 50% of that in the untreated control (p < 0.05). Moreover, arecoline significantly depleted intracellular thiols in a dose-dependent manner. At concentrations of 25 microg/ml and 100 microg/ml, arecoline depleted about 18% and 56% of thiols (p < 0.05), respectively. This suggests that arecoline itself might augment the destruction of periodontium associated with betel nut use. Furthermore, the addition of nicotine acted with a synergistic effect on the arecoline-induced cytotoxicity. At a concentration of 60 microg/ml, arecoline suppressed the growth of PDLF by about 33% and 5 mM nicotine enhanced the arecoline-induced cytotoxic response to cause about 66% cell death.

CONCLUSION

During thiol depletion, arecoline may render human PDLF more vulnerable to reactive agents within cigarettes. Taken together, people who combine habits of betel nut chewing with cigarette smoking could be more susceptible to periodontium damage than betel nut chewing alone.