Interaction between Hexametaphosphate, Other Active Ingredients of Toothpastes, and Erosion-Abrasion in Enamel in vitro.

Sodium hexametaphosphate (HMP) as toothpaste additive is claimed to reduce erosive tooth wear and to stabilize stannous ions. However, little is known about the impact of concentration and its interactions with fluoride (F) or stannous+fluoride ions (F/Sn) on enamel erosion and erosion-abrasion. In a 10 day cyclic in vitro erosion-abrasion model, 320 flat human enamel specimens were divided into ten groups (n = 32 each) and daily subjected to six erosive challenges (0.5% citric acid, 2 min) and two toothpaste suspension applications (2 min, 1:3 F-free toothpaste:mineral-salt solution, 0.23% sodium gluconate). Half of specimens per group were additionally brushed twice/day (200 g, 15 s) during suspension immersion. Nine suspensions contained HMP (0.25%, 1.75%, 3.25%), either on its own or combined with F (373 ppm F-) or F/Sn (800 ppm Sn2+, 373 ppm F-). One suspension contained sodium gluconate only (NegContr). After 10 days, specimens' surfaces were analysed with profilometry, energy dispersive X-ray spectroscopy, and scanning electron microscopy. Tissue loss (µm, mean ± standard deviation) in NegContr was 10.9 ± 2.0 (erosion), 22.2 ± 1.6 (erosion-abrasion). Under erosive conditions, only 0.25% HMP in any combination and 1.75% HMP with F/Sn reduced loss significantly (-28% to -54%); 3.25% HMP without F and F/Sn increased loss significantly (+35%). With additional abrasion, no suspension reduced loss significantly compared to NegContr, instead, in groups without F and F/Sn or with 3.25% HMP loss was increased (+15% to +30%). Conclusively, at higher concentrations, HMP increased erosive tooth wear and seemed to reduce anti-erosive effects of fluoride and stannous ions.

Towards unravelling biological mechanisms behind radiation-induced oral mucositis via mass spectrometry-based proteomics.

Objective: Head and neck cancer (HNC) accounts for almost 890,000 new cases per year. Radiotherapy (RT) is used to treat the majority of these patients. A common side-effect of RT is the onset of oral mucositis, which decreases the quality of life and represents the major dose-limiting factor in RT. To understand the origin of oral mucositis, the biological mechanisms post-ionizing radiation (IR) need to be clarified. Such knowledge is valuable to develop new treatment targets for oral mucositis and markers for the early identification of "at-risk" patients. Methods: Primary keratinocytes from healthy volunteers were biopsied, irradiated in vitro (0 and 6 Gy), and subjected to mass spectrometry-based analyses 96 h after irradiation. Web-based tools were used to predict triggered biological pathways. The results were validated in the OKF6 cell culture model. Immunoblotting and mRNA validation was performed and cytokines present in cell culture media post-IR were quantified. Results: Mass spectrometry-based proteomics identified 5879 proteins in primary keratinocytes and 4597 proteins in OKF6 cells. Amongst them, 212 proteins in primary keratinocytes and 169 proteins in OKF6 cells were differentially abundant 96 h after 6 Gy irradiation compared to sham-irradiated controls. In silico pathway enrichment analysis predicted interferon (IFN) response and DNA strand elongation pathways as mostly affected pathways in both cell systems. Immunoblot validations showed a decrease in minichromosome maintenance (MCM) complex proteins 2-7 and an increase in IFN-associated proteins STAT1 and ISG15. In line with affected IFN signalling, mRNA levels of IFNß and interleukin 6 (IL-6) increased significantly following irradiation and also levels of secreted IL-1ß, IL-6, IP-10, and ISG15 were elevated. Conclusion: This study has investigated biological mechanisms in keratinocytes post-in vitro ionizing radiation. A common radiation signature in keratinocytes was identified. The role of IFN response in keratinocytes along with increased levels of pro-inflammatory cytokines and proteins could hint towards a possible mechanism for oral mucositis.

Early senescence and production of senescence-associated cytokines are major determinants of radioresistance in head-and-neck squamous cell carcinoma.

Resistance against radio(chemo)therapy-induced cell death is a major determinant of oncological treatment failure and remains a perpetual clinical challenge. The underlying mechanisms are manifold and demand for comprehensive, cancer entity- and subtype-specific examination. In the present study, resistance against radiotherapy was systematically assessed in a panel of human head-and-neck squamous cell carcinoma (HNSCC) cell lines and xenotransplants derived thereof with the overarching aim to extract master regulators and potential candidates for mechanism-based pharmacological targeting. Clonogenic survival data were integrated with molecular and functional data on DNA damage repair and different cell fate decisions. A positive correlation between radioresistance and early induction of HNSCC cell senescence accompanied by NF-κB-dependent production of distinct senescence-associated cytokines, particularly ligands of the CXCR2 chemokine receptor, was identified. Time-lapse microscopy and medium transfer experiments disclosed the non-cell autonomous, paracrine nature of these mechanisms, and pharmacological interference with senescence-associated cytokine production by the NF-κB inhibitor metformin significantly improved radiotherapeutic performance in vitro and in vivo. With regard to clinical relevance, retrospective analyses of TCGA HNSCC data and an in-house HNSCC cohort revealed that elevated expression of CXCR2 and/or its ligands are associated with impaired treatment outcome. Collectively, our study identifies radiation-induced tumor cell senescence and the NF-κB-dependent production of distinct senescence-associated cytokines as critical drivers of radioresistance in HNSCC whose therapeutic targeting in the context of multi-modality treatment approaches should be further examined and may be of particular interest for the subgroup of patients with elevated expression of the CXCR2/ligand axis.

Impact of mucin on the anti-erosive/anti-abrasive efficacy of chitosan and/or F/Sn in enamel in vitro.

The application of stannous ions in combination with fluoride (F/Sn) is one of the central strategies in reducing erosive tooth wear. F/Sn efficacy can be enhanced by adding chitosan, a positively charged biopolymer. For patients with low saliva flow, this efficacy, however, is not sufficient, making further improvement desirable. This could be achieved by combining chitosan with other molecules like mucin, which together might form multilayers. This in-vitro study aimed to investigate the effect of chitosan, mucin, F/Sn and combinations thereof on enamel erosion and erosion-abrasion. Human enamel samples (n = 448, 28 groups) were cyclically eroded or eroded-abraded (10 days; 6 × 2 min erosion and 2 × 15 s/200 g abrasion per day). Samples were treated 2 × 2 min/day with solutions containing either, chitosan (50 or 500 mPas), porcine gastric mucin, F/Sn or combinations thereof after abrasive challenge. Tissue loss was measured profilometrically, interaction between hard tissue and active agents was assessed with energy dispersive spectroscopy and scanning electron microscopy. Chitosan and F/Sn showed the expected effect in reducing tissue loss under erosive and under erosive-abrasive conditions. Neither mucin alone nor the combinations with mucin showed any additional beneficial effect.

Viscosity of chitosan impacts the efficacy of F/Sn containing toothpastes against erosive/abrasive wear in enamel.

OBJECTIVES: Chitosan (Ch) in F/Sn-toothpastes can increase toothpastes' anti-erosive efficacy. Whether efficacy can be further increased by changing chitosan's viscosity was study aim. METHODS: 192 human enamel specimens were assigned to 2 × 6 groups (n = 16 each): Four F/Sn (500 ppm F-, 800 ppm Sn2+) toothpastes with chitosan (0.5 %, viscosity 50, 500, 1000 or 2000 mPas), negative-control (no F/Sn/chitosan), positive-control (F/Sn, no chitosan). The study was conducted in two experiments (E1/E2). Specimens were cyclically demineralised (10 d, 6 × 2 min/d; 0.5 % citric acid); half of groups (E1) was exposed to toothpaste slurries (2 × 2 min/d), the other half was additionally brushed (2 × 15 s/d, E2). Tissue loss (mean ±â€¯SD, µm) was quantified profilometrically. Element analysis (EDX, wt%) on specimen surfaces and on toothpastes' particulate fraction and SEM analysis of specimen surfaces were performed. RESULTS: Tissue loss in negative-controls (E1/E2) was 4.96 ±â€¯1.55/12.76 ±â€¯2.45. Toothpastes with active agents (AA) reduced tissue loss compared to negative-control (p < 0.0001). E1: All AA caused precipitates, being the thickest after Ch500. Chitosan increased carbon retention, not tin retention. E2: Only Ch1000 increased efficacy (-0.97 ±â€¯4.48) compared to positive-control (2.98 ±â€¯1.32; p = 0.05). EDX showed comparable carbon values in all AA; tin content was higher in Ch1000 (6.5 ±â€¯3.4) compared to other AA (range: 3.8 ±â€¯0.3-4.3 ±â€¯1.3). On abrasives, tin adsorption was decreased by all chitosans. SEM revealed minor structural differences. CONCLUSIONS: Chitosan viscosity has impact on efficacy of F/Sn toothpastes. Under erosive/abrasive conditions Ch1000 showed the best protective effect with higher tin retention on surfaces and lower tin absorption by abrasives. CLINICAL SIGNIFICANCE: The biopolymer chitosan shows protective effect against enamel erosion and erosion/abrasion when used in an F/Sn toothpaste with specific viscosity.