Evaluation of Streptococcus mutans adhesion to fluoride varnishes and subsequent change in biofilm accumulation and acidogenicity

Objectives

The aim of this study was to evaluate Streptococcus mutans adhesion to fluoride varnishes and subsequent change in biofilm accumulation and acidogenicity.

Methods

After producing fluoride varnish-coated hydroxyapatite discs using Fluor Protector (FP), Bifluorid 12 (BIF), Cavity Shield (CASH), or Flor-Opal Varnish White (FO), S. mutans biofilms were formed on the discs. To assess S. mutans adhesion to the discs, 4-h-old biofilms were analysed. To investigate the change in biofilm accumulation during subsequent biofilm formation, the biomass, colony forming units (CFU), and water-insoluble extracellular polysaccharides (EP) of 46-, 70-, and 94-h-old biofilms were analysed. To investigate the change in acidogenicity, pH values of the culture medium were determined during the experimental period. The amount of fluoride in the culture medium was also determined during the experimental period.

Results

BIF, CASH, and FO affected S. mutans adhesion (67–98% reduction) and subsequent biofilm accumulation in 46-, 70-, and 94-h-old biofilms. However, the reducing effect of the fluoride varnishes on the biomass, CFU count, water-insoluble EP amount, and acid production rate of the biofilms decreased as the biofilm age increased. These results may be related to the fluoride-release pattern of the fluoride varnishes. Of the fluoride varnishes tested, FO showed the highest reducing effect against the bacterial adhesion and subsequent biofilm accumulation.

Conclusions

Our findings suggest that if the results of these experiments are extrapolable to the in vivo situation, then reduced clinical benefit of using fluoride varnishes may occur with time.

Clinical significance

Fluoride varnish application can affect cariogenic biofilm formation but the anti-biofilm activity may be reduced with time.     

Gold nanoclusters as prospective carriers and detectors of pramipexole

Pramipexole (PPX) is known in the treatment of Parkinson''s disease and restless legs syndrome. We carried out a theoretical investigation on pramipexole–Au cluster interactions for the applications of drug delivery and detection. Three Au_N clusters with sizes N = 6, 8 and 20 were used as reactant models to simulate the metallic nanostructured surfaces. Quantum chemical computations were performed in both gas phase and aqueous environments using density functional theory (DFT) with the PBE functional and the cc-pVDZ-PP/cc-pVTZ basis set. The PPX drug is mainly adsorbed on gold clusters via its nitrogen atom of the thiazole ring with binding energies of ca. −22 to −28 kcal mol⁻¹ in vacuum and ca. −18 to −24 kcal mol⁻¹ in aqueous solution. In addition to such Au–N covalent bonding, the metal–drug interactions are further stabilized by electrostatic effects, namely hydrogen-bond NH⋯Au contributions. Surface-enhanced Raman scattering (SERS) of PPX adsorbed on the Au surfaces and its desorption process were also examined. In comparison to Au₈, both Au₆ and Au₂₀ clusters undergo a shorter recovery time and a larger change of energy gap, being possibly conducive to electrical conversion, thus signaling for detection of the drug. A chemical enhancement mechanism for SERS procedure was again established in view of the formation of nonconventional hydrogen interactions Au⋯H–N. The binding of PPX to a gold cluster is expected to be reversible and triggered by the presence of cysteine residues in protein matrices or lower-shifted alteration of environment pH. These findings would encourage either further theoretical probes to reach more accurate views on the efficiency of pramipexole–Au interactions, or experimental attempts to build appropriate gold nanostructures for practical trials, harnessing their potentiality for applications.

Gold clusters as prospective carriers and detectors of pramipexole.     

Enhancing the chloramphenicol sensing performance of Cu–MoS2 nanocomposite-based electrochemical nanosensors: roles of phase composition and copper loading amount

The rational design of nanomaterials for electrochemical nanosensors from the perspective of structure–property–performance relationships is a key factor in improving the analytical performance toward residual antibiotics in food. We have investigated the effects of the crystalline phase and copper loading amount on the detection performance of Cu–MoS₂ nanocomposite-based electrochemical sensors for the antibiotic chloramphenicol (CAP). The phase composition and copper loading amount on the MoS₂ nanosheets can be controlled using a facile electrochemical method. Cu and Cu₂O nanoparticle-based electrochemical sensors showed a higher CAP electrochemical sensing performance as compared to CuO nanoparticles due to their higher electrocatalytic activity and conductivity. Moreover, the design of Cu–MoS₂ nanocomposites with appropriate copper loading amounts could significantly improve their electrochemical responses for CAP. Under optimized conditions, Cu–MoS₂ nanocomposite-based electrochemical nanosensor showed a remarkable sensing performance for CAP with an electrochemical sensitivity of 1.74 μA μM⁻¹ cm⁻² and a detection limit of 0.19 μM in the detection range from 0.5–50 μM. These findings provide deeper insight into the effects of nanoelectrode designs on the analytical performance of electrochemical nanosensors.

In this work, we clarify the roles of phase composition and copper loading amount on the CAP sensing performance of Cu–MoS₂ nanocomposite-based electrochemical nanosensors.     

The radical scavenging activity of muriolide in physiological environments: mechanistic and kinetic insights into double processes

Muriolide (MO) is a natural lactone that was isolated from Ranunculus muricatus. This compound exhibited good antioxidant activity in some experiments; however, the radical scavenging activity of MO in physiological environments has not been studied yet. In this study, the reaction between hydroperoxyl radical and MO was investigated in physiological environments by using density functional theory (DFT) calculations. It was found that MO exhibits excellent antiradical activity in water at physiological pH (k = 1.05 × 10⁸ M⁻¹ s⁻¹) by the single electron transfer mechanism of the anion state. However, the activity in lipid media is moderate with k = 2.54 × 10⁴ M⁻¹ s⁻¹ and is defined by the formal hydrogen transfer pathway. The antiradical reactions can occur in double processes; however, the first reaction may define the HOO˙ radical scavenging activity of MO. Compared with typical natural antioxidants, the antiradical activity of MO against HOO˙ radicals is slightly lower than Trolox in pentyl ethanoate. However, the activity of MO is approximately 808 times faster than that of the reference in aqueous solution. Thus, the data suggest that MO is a promising natural radical scavenger in the physiological environment.

Muriolide, which is a natural lactone that was isolated from Ranunculus muricatus, is a promising natural radical scavenger in the physiological environment.