Impact of oral astringent stimuli on surface charge and morphology of the protein-rich pellicle at the tooth-saliva interphase

The proteinaceous pellicle layer, which develops upon contact with saliva on the surface of teeth, is important for the formation of oral biofilms and for the protection of teeth from abrasion and chemically induced erosion. Astringent food ingredients comprising polyphenols, cationic macromolecules, and multivalent metal salts are known to interact with the pellicle. However, astringent-induced changes in the physicochemical properties of the tooth-saliva interphase are not yet completely understood. Here we provide comprehensive insights into interfacial charging, ultrastructure, thickness, and surface roughness of the pellicles formed on the model substrates silicon oxide (SiO₂), Teflon^® AF, and hydroxyapatite, as well as on bovine enamel before and after incubation with the astringents epigallocatechin gallate, tannic acid, iron(III) salt, lysozyme, and chitosan. Quartz crystal microbalance with dissipation monitoring demonstrated viscous behavior of untreated pellicles formed in vitro on the different materials. Electrokinetic (streaming current) measurements revealed that cationic astringents reverse the charge of native pellicles, whereas polyphenols did not change the charge under physiological pH condition. In addition, transmission electron microscopy and atomic force microscopy showed a concentration-dependent increase in average film thickness and pellicle surface roughness as induced by astringents. These multifaceted alterations of the salivary pellicle may come along with an increase in roughness perceived on the teeth, which is part of the complex sensations of oral astringency.

Oral astringent stimuli alter the enamel pellicle's ultrastructure as revealed by electron microscopy

OBJECTIVES

This electron microscopic study aimed at investigating effects of oral astringent stimuli on the enamel pellicle's morphology.

METHODS

Pellicles were formed in situ within 30min on bovine enamel slabs, fixed to individuals' upper jaw splints. The pellicle-coated specimens were immersed in vitro in seven diverse astringent solutions and subsequently analyzed by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy, as well as transmission electron microscopy (TEM). Four biocompatible astringents, namely the polyphenol epigallocatechin gallate, the metal salt iron(III) sulfate, the basic protein lysozyme, and the aminopolysaccharide chitosan, were additionally applied in situ. After rinsing the oral cavity with these compounds, the pellicle's ultrastructure was imaged by SEM and TEM, respectively. Untreated pellicle samples served as controls.

RESULTS

Exposure to polyphenols and lysozyme induced particularly thicker and electron-denser pellicles in comparison to the control pellicle with similar characteristics in vitro and in situ. In contrast, acidic chitosan and metal salt solutions, respectively, revealed minor pellicle alterations. The incorporation of Fe and Al into the pellicles treated with the corresponding inorganic salts was verified by EDX analysis.

CONCLUSIONS

Astringent-induced pellicle modifications were for the first time visualized by TEM. The ultrastructural alterations of the dental pellicle may partly explain the tooth-roughening effect caused by oral astringent stimuli.

CLINICAL SIGNIFICANCE

Astringents might modify the pellicle's protective properties against dental erosion, attrition, as well as bacterial adhesion, and by this means may influence tooth health. The findings may thus be particularly relevant for preventive dentistry.

Direct Pro-Inflammatory Effect of C-Reactive Protein on Human Pulmonary Artery Endothelial Cells

C-reactive protein (CRP) has a prognostic role in cardiovascular and pulmonary diseases. Recent data suggest its pro-inflammatory effects in atherosclerotic lesion formation. This raises the hypothesis of whether or not CRP has pro-inflammatory effects on pulmonary vasculature by inducing the production of endothelin-1 (ET)-1, a potent vasoconstrictor and proliferative cytokine, and expression of adhesion molecules which could culminate in inflammatory cell recruitment and vascular injury. Human pulmonary artery endothelial cells (HPAECs) were cultured and incubated with 25μg/ml of human recombinant CRP and with interleukin (IL)-1β 10ng/ml, a well-known activator of endothelial cells, which served as a positive control for 24 hours. Expression of vascular cell adhesion molecule (VCAM)-1 and intercellular adhesion molecule (ICAM)-1 was assessed by flow cytometry. Secretion of ET-1 from HPAECs was also evaluated. In this study we show that incubation of HPAECs with human recombinant CRP for 24 hours induced a significant increase in ICAM-1 expression (from 610 to 6553 mean fluorescence intensity, p < 0.005) and VCAM-1 expression (from 212 to 303 mean fluorescence intensity, p < 0.05), as compared to control. Adhesion molecule induction was similar to that observed in endothelial cells activated with IL-1β. Likewise, CRP potentiated the ET-1 production by HPAECs. The levels of ET-1 were significantly higher at 24 hours (control 19.94±3 vs CRP 46.54±18 pg/ml, p < 0.05). In conclusion, this study makes a novel observation that CRP induces expression of adhesion molecules and secretion of ET-1 in HPAECs. Our study provides the first evidence that CRP exerts direct proinflammatory effects on pulmonary artery endothelial cells.