Melbourne Dental School - Research Publications
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ItemAdolescent temperament dimensions as stable prospective risk and protective factors for salivary C-reactive protein(WILEY, 2018-02)OBJECTIVE: Temperament has associations with later physical health outcomes, yet there is a dearth of research exploring the connection between temperament and mechanisms that have known associations with these health outcomes. Recent research has delineated a connection between personality and inflammation during adulthood, but this association has not yet been studied in adolescent samples. DESIGN: We investigated whether stable adolescent temperament (averaged over two years), specifically effortful control and negative emotionality, provided a more robust prediction of inflammation as measured by salivary C-reactive protein (sCRP), than depressive symptoms. METHODS: Temperament and depressive symptoms were measured in a sample of sixty-three adolescents (37 males) when they were approximately 12 years old (mean age = 12.30, SD = 0.69) and again when they were approximately 14 years old (mean age = 14.84, SD = 0.49). Levels of sCRP were determined approximately 7 months later (mean = 6.77, SD = 2.99) when participants were approximately 15 years old (mean age = 15.49, SD = 0.49). RESULTS: Regression analyses revealed that effortful control (EC) was significantly associated with lower sCRP levels, while higher negative emotionality (NE) was significantly associated with higher sCRP levels. Furthermore, these associations were larger than those for depressive symptoms and were differentially impacted by the addition of covariates. Implications for the role of stable risk and protective factors in inflammatory processes are discussed. CONCLUSIONS: These findings are the first to show associations between adolescent temperament and inflammation. Furthermore, these findings extend previous personality research to temperamental research in a younger sample of adolescents. Statement of contribution What is already known? There is a large extant literature on the association between depressive symptoms and inflammation. There is a smaller extant literature on the association between personality and inflammation. No studies have examined how adolescent temperament traits may relate to inflammation. What does this study add? Longitudinal data collection over the course of 3 years in an adolescent sample. Addresses the question of whether temperament factors relate to inflammation. Temperament provides a more robust predictor of later inflammation than depressive symptoms.
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ItemC-Terminal Modification and Multimerization Increase the Efficacy of a Proline-Rich Antimicrobial Peptide(WILEY-V C H VERLAG GMBH, 2017-01-05)Two series of branched tetramers of the proline-rich antimicrobial peptide (PrAMP), Chex1-Arg20, were prepared to improve antibacterial selectivity and potency against a panel of Gram-negative nosocomial pathogens including Escherichia coli, Klebsiella pneumoniae, Acinetobacter baumannii and Pseudomonas aeruginosa. First, tetramerization was achieved by dithiomaleimide (DTM) conjugation of two C-terminal-cysteine bearing dimers that also incorporated C-terminal peptide chemical modification. DTM-linked tetrameric peptides containing a C-terminal hydrazide moiety on each dimer exhibited highly potent activities in the minimum inhibitory concentration (MIC) range of 0.49-2.33 μm. A second series of tetrameric analogues with C-terminal hydrazide modification was prepared by using alternative conjugation linkers including trans-1,4-dibromo-2-butene, α,α'-dibromo-p-xylene, or 6-bismaleimidohexane to determine the effect of length on activity. Each displayed potent and broadened activity against Gram-negative nosocomial pathogens, particularly the butene-linked tetrameric hydrazide. Remarkably, the greatest MIC activity is against P. aeruginosa (0.77 μm/8 μg mL-1 ) where the monomer is inactive. None of these peptides showed any cytotoxicity to mammalian cells up to 25 times the MIC. A diffusion NMR study of the tetrameric hydrazides showed that the more active antibacterial analogues were those with a more compact structure having smaller hydrodynamic radii. The results show that C-terminal PrAMP hydrazidation together with its rational tetramerization is an effective means for increasing both diversity and potency of PrAMP action.
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ItemCandida virulence and ethanol-derived acetaldehyde production in oral cancer and non-cancer subjects(WILEY, 2016-11-01)OBJECTIVES: To compare biofilm-forming ability, hydrolytic enzymes and ethanol-derived acetaldehyde production of oral Candida isolated from the patients with oral cancer and matched non-oral cancer. MATERIAL AND METHODS: Fungal biofilms were grown in RPMI-1640 medium, and biofilm mass and biofilm activity were assessed using crystal violet staining and XTT salt reduction assays, respectively. Phospholipase, proteinase, and esterase production were measured using agar plate method, while fungal acetaldehyde production was assessed via gas chromatography. RESULTS: Candida isolated from patients with oral cancer demonstrated significantly higher biofilm mass (P = 0.031), biofilm metabolic activity (P < 0.001), phospholipase (P = 0.002), and proteinase (P = 0.0159) activity than isolates from patients with non-oral cancer. High ethanol-derived acetaldehyde-producing Candida were more prevalent in patients with oral cancer than non-oral cancer (P = 0.01). In univariate regression analysis, high biofilm mass (P = 0.03) and biofilm metabolic activity (P < 0.001), high phospholipase (P = 0.003), and acetaldehyde production ability (0.01) were significant risk factors for oral cancer; while in the multivariate regression analysis, high biofilm activity (0.01) and phospholipase (P = 0.01) were significantly positive influencing factors on oral cancer. CONCLUSION: These data suggest a significant positive association between the ability of Candida isolates to form biofilms, to produce hydrolytic enzymes, and to metabolize alcohol to acetaldehyde with their ability to promote oral cancer development.
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ItemCelogentin mimetics as inhibitors of tubulin polymerization(WILEY, 2019-12-17)Bicyclic analogues of celogentin C have been synthesized in which the side chain-side chain cross-links are replaced by thioether bonds. Several of the simplified bicyclic peptides displayed potent inhibition of tubulin polymerization.
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ItemArchitectural Effects of Star-Shaped "Structurally Nanoengineered Antimicrobial Peptide Polymers" (SNAPPs) on Their Biological Activity(WILEY, 2018-11)In this work, the effect of two key structural parameters, number of arms and arm length, of star-shaped "structurally nanoengineered antimicrobial peptide polymers" (SNAPPs) on their antimicrobial activity and biocompatibility, is investigated. A library of star-shaped SNAPPs is prepared, containing varying arm numbers and arm lengths. Antimicrobial assays are then performed to assess the capacity of the SNAPPs to disrupt the membrane, inhibit the growth, and kill pathogenic bacteria. A major finding of the study is that increasing arm number and length of SNAPPs enhanced antimicrobial activity, which can be respectively attributed to the higher local concentrations of polypeptide arms and increased α-helical content. SNAPP architecture is shown to affect the bacteria membrane state and therefore mechanism of killing. Two more potent structures with up to twice the antimicrobial activity of the previously reported SNAPP are discovered in this process. Toxicities of the SNAPPs also increase with arm number and arm length, however therapeutic index calculations identified a 16-arm SNAPP and an easier to prepare 4-arm SNAPP as the best therapeutic agents. The biocompatibility of the SNAPP with the best biological activity is also evaluated in vivo, showing no markers of systemic damage in mice.
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ItemKeratinocyte-specific ablation of protease-activated receptor 2 prevents gingival inflammation and bone loss in a mouse model of periodontal disease(WILEY, 2018-11-01)Chronic periodontitis is characterised by gingival inflammation and alveolar bone loss. A major aetiological agent is Porphyromonas gingivalis, which secretes proteases that activate protease-activated receptor 2 (PAR2 ). PAR2 expressed on oral keratinocytes is activated by proteases released by P. gingivalis, inducing secretion of interleukin 6 (IL-6), and global knockout of PAR2 prevents bone loss and inflammation in a periodontal disease model in mice. To test the hypothesis that PAR2 expressed on gingival keratinocytes is required for periodontal disease pathology, keratinocyte-specific PAR2 -null mice were generated using K14-Cre targeted deletion of the PAR2 gene (F2rl1). These mice were subjected to a model of periodontitis involving placement of a ligature around a tooth, combined with P. gingivalis infection ("Lig + Inf"). The intervention caused a significant 44% decrease in alveolar bone volume (assessed by microcomputed tomography) in wildtype (K14-Cre:F2rl1wt/wt ), but not littermate keratinocyte-specific PAR2 -null (K14-Cre:F2rl1fl/fl ) mice. Keratinocyte-specific ablation of PAR2 prevented the significant Lig + Inf-induced increase (2.8-fold) in the number of osteoclasts in alveolar bone and the significant up-regulation (2.4-4-fold) of the inflammatory markers IL-6, IL-1β, interferon-γ, myeloperoxidase, and CD11b in gingival tissue. These data suggest that PAR2 expressed on oral epithelial cells is a critical regulator of periodontitis-induced bone loss and will help in designing novel therapies with which to treat the disease.
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ItemSelenium nanoparticles as anti-infective implant coatings for trauma orthopedics against methicillin-resistant Staphylococcus aureus and epidermidis: in vitro and in vivo assessment(Dove Medical Press, 2019-07-01)Background: Bacterial infection is a common and serious complication in orthopedic implants following traumatic injury, which is often associated with extensive soft tissue damage and contaminated wounds. Multidrug-resistant bacteria have been found in these infected wounds, especially in patients who have multi trauma and prolonged stay in intensive care units.Purpose: The objective of this study was to develop a coating on orthopedic implants that is effective against drug-resistant bacteria. Methods and results: We applied nanoparticles (30-70nm) of the trace element selenium (Se) as a coating through surface-induced nucleation-deposition on titanium implants and investigated the antimicrobial activity against drug resistant bacteria including Methicillin-resistant Staphylococcus aureus (MRSA) and Methicillin-resistant Staphylococcus epidermidis (MRSE) in vitro and in an infected femur model in rats.The nanoparticles were shown in vitro to have antimicrobial activity at concentrations as low as 0.5ppm. The nanoparticle coatings strongly inhibited biofilm formation on the implants and reduced the number of viable bacteria in the surrounding tissue following inoculation of implants with biofilm forming doses of bacteria. Conclusion: This study shows a proof of concept for a selenium nanoparticle coatings as a potential anti-infective barrier for orthopedic medical devices in the setting of contamination with multi-resistant bacteria. It also represents one of the few (if only) in vivo assessment of selenium nanoparticle coatings on reducing antibiotic-resistant orthopedic implant infections.
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ItemEditorial: Antimicrobial and Anticancer Peptides(FRONTIERS MEDIA SA, 2018-02-06)
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ItemProspects for treatment of Porphyromonas gingivalis-mediated disease - immune-based therapy(CO-ACTION PUBLISHING, 2015-01-01)Chronic periodontitis is an inflammatory disease of the supporting tissues of the teeth associated with a polymicrobial biofilm (subgingival plaque) accreted to the tooth which results in destruction of the tooth's supporting tissues. A characteristic feature of the disease-associated plaque is the emergence of proteolytic species. One of these species, Porphyromonas gingivalis has recently been described as a keystone pathogen as it dysregulates the host immune response to favour the polymicrobial biofilm disrupting homeostasis to cause dysbiosis and disease. The level of P. gingivalis in subgingival plaque above threshold levels (~10% of total bacterial cell load) has been demonstrated to predict imminent clinical attachment loss (disease progression) in humans. Porphyromonas gingivalis is found as microcolonies in the superficial layers of subgingival plaque adjacent to the periodontal pocket epithelium which helps explain the strong association with underlying tissue inflammation and disease at relatively low proportions (10%) of the total bacterial cell load of the plaque. The mouse periodontitis model has been used to show that inflammation is essential to allow establishment of P. gingivalis at the levels in plaque (10% or greater of total bacterial cell load) necessary to produce dysbiosis and disease. The extracellular proteinases "gingipains" (RgpA/B and Kgp) of P. gingivalis have been implicated as major virulence factors that are critical for dysbiosis and disease. This has resulted in the strategy of targeting the gingipains by vaccination. We have produced a recombinant immunogen which induces an immune response in mice that neutralises the proteolytic and host/bacterial binding functions of the gingipains. Using this immunogen as a therapeutic vaccine in mice already infected with P. gingivalis, we have shown that inflammation and alveolar bone loss can be substantially reduced. The protection was characterised by a predominant Th2 cytokine and antibody (IgG1) response and shown to be mediated by the gingipain neutralising antibodies using adoptive transfer and systemic/topical passive antibody experiments. Vaccination may be a useful adjunct to scaling and root planing in the treatment of P. gingivalis-mediated chronic periodontitis.
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ItemChronic oral application of a periodontal pathogen results in brain inflammation, neurodegeneration and amyloid beta production in wild type mice(PUBLIC LIBRARY SCIENCE, 2018-10-03)BACKGROUND: The results from cross sectional and longitudinal studies show that periodontitis is closely associated with cognitive impairment (CI) and Alzhemer's Disease (AD). Further, studies using animal model of periodontitis and human post-mortem brain tissues from subjects with AD strongly suggest that a gram-negative periodontal pathogen, Porphyromonas gingivalis (Pg) and/or its product gingipain is/are translocated to the brain. However, neuropathology resulting from Pg oral application is not known. In this work, we tested the hypothesis that repeated exposure of wild type C57BL/6 mice to orally administered Pg results in neuroinflammation, neurodegeneration, microgliosis, astrogliosis and formation of intra- and extracellular amyloid plaque and neurofibrillary tangles (NFTs) which are pathognomonic signs of AD. METHODS: Experimental chronic periodontitis was induced in ten wild type 8-week old C57BL/6 WT mice by repeated oral application (MWF/week) of Pg/gingipain for 22 weeks (experimental group). Another 10 wild type 8-week old C57BL/6 mice received vehicle alone (control group) MWF per week for 22 weeks. Brain tissues were collected and the presence of Pg/gingipain was determined by immunofluorescence (IF) microscopy, confocal microscopy, and quantitative PCR (qPCR). The hippocampi were examined for the signs of neuropathology related to AD: TNFα, IL1β, and IL6 expression (neuroinflammation), NeuN and Fluoro Jade C staining (neurodegeneration) and amyloid beta1-42 (Aβ42) production and phosphorylation of tau protein at Ser396 were assessed by IF and confocal microscopy. Further, gene expression of amyloid precursor protein (APP), beta-site APP cleaving enzyme 1 (BACE1), a disintegrin and metalloproteinase domain-containing protein10 (ADAM10) for α-secretase and presenilin1 (PSEN1) for ɣ-secretase, and NeuN (rbFox3) were determined by RT-qPCR. Microgliosis and astrogliosis were also determined by IF microscopy. RESULTS: Pg/gingipain was detected in the hippocampi of mice in the experimental group by immunohistochemistry, confocal microscopy, and qPCR confirming the translocation of orally applied Pg to the brain. Pg/gingipain was localized intra-nuclearly and peri-nuclearly in microglia (Iba1+), astrocytes (GFAP+), neurons (NeuN+) and was evident extracellularly. Significantly greater levels of expression of IL6, TNFα and IL1β were evident in experimental as compared to control group (p<0.01, p<0.00001, p<0.00001 respectively). In addition, microgliosis and astrogliosis were evident in the experimental but not in control group (p <0.01, p<0.0001 respectively). Neurodegeneration was evident in the experimental group based on a fewer number of intact neuronal cells assessed by NeuN positivity and rbFOX3 gene expression, and there was a greater number of degenerating neurons in the hippocampi of experimental mice assessed by Fluoro Jade C positivity. APP and BACE1 gene expression were increased in experimental group compared with control group (p<0.05, p<0.001 respectively). PSEN1 gene expression was higher in experimental than control group but the difference was not statistically significant (p = 0.07). ADAM10 gene expression was significantly decreased in experimental group compared with control group (p<0.01). Extracellular Aβ42 was detected in the parenchyma in the experimental but not in the control group (p< 0.00001). Finally, phospho-Tau (Ser396) protein was detected and NFTs were evident in experimental but not in the control group (p<0.00001). CONCLUSIONS: This study is the first to show neurodegeneration and the formation of extracellular Aβ42 in young adult WT mice after repeated oral application of Pg. The neuropathological features observed in this study strongly suggest that low grade chronic periodontal pathogen infection can result in the development of neuropathology that is consistent with that of AD.
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