Action of silver nanoparticles towards biological systems: cytotoxicity evaluation using hen's egg test and inhibition of Streptococcus mutans biofilm formation.

This study aimed to evaluate the cytotoxicity and bactericidal properties of four silver nanoparticle (AgNP) colloids and their ability to inhibit Streptococcus mutans biofilm formation on dental enamel. The cytotoxicity of AgNPs was evaluated based on signs of vascular change on the chorioallantoic membrane using the hen's egg test (HET-CAM). Bactericidal properties and inhibition of S. mutans biofilm formation were determined using a parallel-flow cell system and a dichromatic fluorescent stain. The percentage of viable cells was calculated from regression data generated from a viability standard. AgNP colloids proved to be non-irritating, as they were unable to promote vasoconstriction, haemorrhage or coagulation. AgNP colloids inhibited S. mutans biofilm formation on dental enamel, and cell viability measured by fluorescence was 0% for samples S1, S2, S3 and S4 and 36.5% for the positive control (diluted 30% silver diamine fluoride). AgNPs are new products with a low production cost because they have a lower concentration of silver, with low toxicity and an effective bactericidal effect against a cariogenic oral bacterium. Moreover, they do not promote colour change in dental enamel, which is an aesthetic advantage compared with traditional silver products.

Cardiovascular effects elicited by milonine, a new 8,14-dihydromorphinandienone alkaloid.

The mechanisms underlying the cardiovascular responses evoked by milonine (i.v.), an alkaloid, were investigated in rats. In normotensive rats, milonine injections produced hypotension and tachycardia, which were attenuated after N(w) -nitro-L-arginine methyl esther (L-NAME; 20 mg/kg, i.v.). In phenylephrine (10 µM), pre-contracted mesenteric artery rings, milonine (10⁻¹° M to 3 × 10⁻4 M) caused a concentration-dependent relaxation (EC50 = 1.1 × 10⁻6 M, E(max) = 100 ± 0.0%) and this effect was rightward shifted after either removal of the vascular endothelium (EC50 = 1.6 × 10⁻5, p < 0.001), or after L-NAME 100 µM (EC50 = 6.2 × 10⁻5, p < 0.001), hydroxocobalamin 30 µM (EC50 = 1.1 × 10⁻4, p < 0.001) or ODQ 10 µM (EC50 = 1.9 × 10⁻4 p < 0.001). In addition, in rabbit aortic endothelial cells, milonine increased NO3⁻ levels. The relaxant effect induced by milonine was attenuated in the presence of KCl (20 mM), a modulator efflux K(+) (EC50 = 1.2 × 10⁻5, p < 0.001), or different potassium channel blockers such as glibenclamide (10 µM) (EC50 = 6.3 × 10⁻5, p < 0.001), TEA (1 mM) (EC50 = 2.3 × 10⁻5 M, n = 6) or Charybdotoxin (0.2 µM) plus apamin (0.2 µM) (EC50 = 3.9 × 10⁻4 M, n = 7). In addition, pre-contraction with high extracellular potassium concentration prevented milonine-induced vasorelaxation (EC50 = 1.0 × 10⁻4, p < 0.001). Milonine also reduced CaCl2 -induced contraction in Ca²(+) -free solution containing KCl (60 mM). In conclusion, using combined functional and biochemical approaches, we demonstrated that the hypotensive and vasorelaxant effects produced by milonine are, at least in part, mediated by the endothelium, likely via nitric oxide release, activation of nitric oxide-cGMP pathway and opening of K(+) channels.