Antibacterial activity and proposed action mechanism of a new class of synthetic tricyclic flavonoids.

AIMS: This study reports on the inhibitory and bactericidal properties of a new synthetized flavonoid. METHODS AND RESULTS: Tricyclic flavonoid 1 has been synthesized through a two-step reaction sequence. The antimicrobial effects were tested using the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) assays. Also DNA fragmentation assay, fluorescence microscopy and SEM were used to study the mechanism of action. Our tested flavonoid displayed a strong antimicrobial activity with MIC and MBC values as low as 0·24 µg ml(-1) against Staphylococcus aureus and 3·9 µg ml(-1) against Escherichia coli. Flavonoid 1 displayed antimicrobial properties, causing not only the inhibition of bacterial growth, but also killing bacterial cells. The mechanism of action is related to the impairment of the cell membrane integrity and to cell agglutination. CONCLUSIONS: Tricyclic flavonoid 1 was found to have a stronger antibacterial effect at lower concentrations than those described in the earlier reports. SIGNIFICANCE AND IMPACT OF THE STUDY: Based on the strong antimicrobial activity observed, this new tricyclic flavonoid has a good potential for the design of new antimicrobial agents.

Silica nanoparticles: preparation, characterization and in vitro/in vivo biodistribution studies.

BACKGROUND: The current progress in pharmaceutical nanotechnology field has been exploited in the design of functionalized radiolabelled nanoparticles that are able to deliver radionuclides in a selective manner to improve the outcome of diagnosis and treatment. Silica nanoparticles (SNPs) have been widely developed for biomedical applications due to their high versatility, excellent functional properties and low cost production, with the possibility to control different topological parameters relevant for multidisciplinary applications. PURPOSE: The aim of the present study was to characterize and evaluate both in vitro, by microscopy techniques, and in vivo, by scintigraphic imaging, the biodistribution of silica nanostructures derivatives (Cy5.5 conjugated SNPs and (99m)Tc radiolabelled SNPs) to be applied as radiotracers in biomedicine. METHODS: SNPs were synthesized by hydrolysis and condensation of silicon alkoxides, followed by surface functionalization with amino groups available for fluorescent dye and radiolabelling possibility. RESULTS: Our data showed the particles size distribution (200-350 nm), the surface charge (negative for bare and fluorescent SNPs and positive for amino SNPs), polydispersity index (broad distribution), the qualitative composition and the toxicity assessments (safe material) that made the obtained SNPs candidates for in vitro/in vivo studies. A high uptake of fluorescent SNPs in all the investigated organs was evidenced by confocal microscopy. The (99m)Tc radiolabelled SNPs biodistribution was quantified in the range of 12-100% counts/g organ using the scintigraphic images. CONCLUSIONS: The obtained results reveal improved properties, namely, reduced toxicity with a low level of side effects, an improved biodistribution, high labelling efficiency and stability of the radiolabelled SNPs with potential to be applied in biomedical science, particularly in nuclear medicine as a radiotracer.