Publications

Abstract Quorum sensing (QS) is an important regulatory mechanism in biofilm formation and differentiation. Interference with QS can affect biofilm development and antimicrobial susceptibility. This study evaluates the potential of selected phytochemical products to inhibit QS. Three isothiocyanates (allylisothiocyanate - AITC, benzylisothiocyanate - BITC and 2-phenylethylisothiocyanate - PEITC) and six phenolic products (gallic acid - GA, ferulic acid - FA, caffeic acid - CA, phloridzin - PHL, (-) epicatechin - EPI and oleuropein glucoside - OG) were tested. A disc diffusion assay based on pigment inhibition in Chromobacterium violaceum CV12472 was performed. In addition, the mechanisms of QS inhibition (QSI) based on the modulation of N-acyl homoserine lactone (AHLs) activity and synthesis by the phytochemicals were investigated. The cytotoxicity of each product was tested on a cell line of mouse lung fibroblasts. AITC, BITC and PEITC demonstrated a capacity for QSI by modulation of AHL activity and synthesis, interfering the with QS systems of C. violaceum CviI/CviR homologs of LuxI/LuxR systems. The cytotoxic assays demonstrated low effects on the metabolic viability of the fibroblast cell line only for FA, PHL and EPI.

Abstract The increasing occurrence of bacterial resistance to antibiotics has now reached a critical level. Finding antibiotic coadjuvants capable to inhibit the bacterial resistance mechanisms would be a valuable mid-term solution, until new classes of antibiotics are discovered. Selected plant alkaloids were combined with 5 antibiotics against 10 Staphylococcus aureus strains, including strains expressing distinct efflux pumps and methicillin-resistant S. aureus strains. The efficacy of each combination was assessed using the microdilution checkerboard, time-kill, Etest, and disc diffusion methods. The cytotoxicity of the alkaloids was evaluated in a mouse fibroblast cell line. Potentiation was obtained in 6% of all 190 combinations, especially with the combination of: ciprofloxacin with reserpine (RES), pyrrolidine (PYR), and quinine (QUIN); tetracycline with RES; and erythromycin with PYR. The highest cytotoxicity values were found for QUIN (half maximal inhibitory concentration [IC50] = 25 +/- 2.2 mg/L) and theophylline (IC50 = 100 +/- 4.7 mg/L).

Abstract The thermodynamics of the process of self-assembly of cationic gemini surfactants, [C12H25(CH3)(2)N(CH2)(S)N(CH3)(2)C12H25]Br-2, (the spacer S being 2, 6 or 10, assigned as C12CSC12Br2) and the system of oppositely charged mixture of surfactants formed by C12CSC12Br2 and sodium cholate (NaCA) in aqueous solution has been investigated by isothermal titration calorimetry (ITC), conductivity and turbidity measurements. The critical micelle concentration values (cmc) for the gemini surfactants C12CSC12Br2 obtained from calorimetry and conductivity were found to be consistent with values reported in the literature. The enthalpies of micellization (Delta H-mic) of C12CSC12Br2 are all exothermic, presenting a strong negative minimum at S = 6, corresponding to the maximum in the cmc values. For the mixed system of oppositely charged surfactants (C12CSC12Br2(S = 2,6,10)/NaCA), we did obtain from ITC the critical parameters for different events that take place as the concentration of gemini surfactant increases, such as the formation of NaCA-rich mixed micelles (cmc(mix), Delta Hmic-mix), the formation of a precipitate (immiscible liquid crystalline (LC) phase) (C-P, Delta H-P) and its re-dissolution (C-R, Delta H-R), and finally the formation of positive charge-rich mixed micelles (C-M, Delta H-M). It should be stressed that the values of cmc(mix) (gemini) are much smaller than those for pure gemini and pure NaCA. These results also show that there is a stronger synergistic effect between the two surfactants in the NaCA-rich region. The turbidity measurements proved valuable to the determination of the region of immiscible LC phase. The ITC results are combined with those obtained by conductivity and turbidity leading to a thorough discussion of the effect of the gemini spacer length on the aggregation behavior of the mixed systems.

Abstract A different approach to the preparation of microspheric particles of molecularly imprinted xerogels (MIX) is presented here. The technique consisted of filling up the pores of spherical, mesoporous, bare silica particles with a pregelification mixture by applying pressure. Upon gelification and drying, thin layers of MIX were deposited on the mesopores. Spherical composites of S-naproxen (S-NAP) imprints were produced by following this simple strategy. The performance of the imprints was quite satisfactory in terms of recognition ability (ascertained by selectivity against ibuprofen, alpha = 4.9, and an imprinting factor of 13) whereas an outstanding improvement on dynamic features (expressed as column efficiency), as compared to the corresponding bulk format MIX (9 vs. 1.2 theoretical plates/cm), was reached.

Abstract Mycobacterium avium causes respiratory disease in susceptible individuals, as well as disseminated infections in immunocompromised hosts, being an important cause of morbidity and mortality among these populations. Current therapies consist of a combination of antibiotics taken for at least 6 months, with no more than 60% overall clinical success. Furthermore, mycobacterial antibiotic resistance is increasing worldwide, urging the need to develop novel classes of antimicrobial drugs. One potential and interesting alternative strategy is the use of antimicrobial peptides (AMP). These are present in almost all living organisms as part of their immune system, acting as a first barrier against invading pathogens. In this context, we investigated the effect of several lactoferrin-derived AMP against M. avium. Short peptide sequences from both human and bovine lactoferricins, namely, hLFcin1-11 and LFcin17-30, as well as variants obtained by specific amino acid substitutions, were evaluated. All tested peptides significantly inhibited the axenic growth of M. avium, the bovine peptides being more active than the human. Arginine residues were found to be crucial for the display of antimycobacterial activity, whereas the all-D-amino-acid analogue of the bovine sequence displayed the highest mycobactericidal activity. These findings reveal the promising potential of lactoferricins against mycobacteria, thus opening the way for further research on their development and use as a new weapon against mycobacterial infections.

Abstract Straightforward crushing and sieving bulk polymeric R-aminoglutethimide-imprinted materials were prepared by classical free radical polymerization, whereas nano thin walled grafted imprinted materials were prepared using RAFT mediated control polymerization technique. A stoichiometric non-covalent approach based on a triply hydrogen bonding functional monomer-template 1:1 complex (K = 599 mol(-1) L-1) led to chiral selectors far outperforming previously used selectors for resolving this racemate. The recognitive materials produced here (enantioselectivity factors, alpha similar to 10) also have no match within the previously reported enantioselective imprinted polymers (alpha 1.2-4.5). We here demonstrate a potentially generic solution to produce good quality grafted MIPs for templates interacting by hydrogen bonding alone, relying on solvent polarity tuning, significantly extending the range of templates compatible with this format.

Abstract In this work we report for the first time differential capacitance curves measured at imidazolium dicationic ionic liquid/electrode interfaces as a new strategy to understand the interfacial behaviour of ionic liquids (IL) near a charged electrode. The ionic liquid studied (1,5-bis(3-dimethylimidazolium)pentane di-bis(trifluoromethylsulfonyl)imide [C-5(MIM)(2)][Tf2N](2)) contains a cation with two positively charged imidazolium rings substituted with a methyl group connected by a pentane linkage alkyl chain length providing a new cationic structure variation. The comparison with the analogue monocationic ionic liquids showed that the dicationic liquid has a wider electrochemical polarization window and a more positive potential of zero charge at a Hg electrode. Differential capacity curves measured at dicationic ionic liquid/Hg interface show similar shape compared with analogous monocationic ionic liquids and revealed to be very sensitive to the electrode material.

Abstract The efficacy, cellular uptake and specific transport of dietary antioxidants to target organs, tissues and cells remains the most important setback for their application in the treatment of oxidative-stress related disorders and in particular in neurodegenerative diseases, as brain targeting remains a still unsolved challenge. Nanotechnology based delivery systems can be a solution for the above mentioned problems, specifically in the case of targeting dietary antioxidants with neuroprotective activity. Nanotechnology-based delivery systems can protect antioxidants from degradation, improve their physicochemical drug-like properties and in turn their bioavailability. The impact of nanomedicine in the improvement of the performance of dietary antioxidants, as protective agents in oxidative-stress events, specifically through the use of drug delivery systems, is highlighted in this review as well as the type of nanomaterials regularly used for drug delivery purposes. From the data one can conclude that the research combining (dietary) antioxidants and nanotechnology, namely as a therapeutic solution for neurodegenerative diseases, is still in a very early stage. So, a huge research area remains to be explored that hopefully will yield new and effective neuroprotective therapeutic agents in a foreseeable future.

Abstract The quantification of nitric oxide (NO) based on the quenching of the fluorescence of a nanocomposites sensor constituted by cadmium/selenium quantum dots (CdSe) stabilized by chitosan (CS) and mercaptosuccinic acid (MSA) is assessed. The optimization of the response of the CS-CdSe-MSA nanocomposites to NO was done by multivariate response surface experimental design methodologies. The highest fluorescence quenching was obtained at pH 5.5 and at room temperature. The NO quantification capability of CS-CdSe-MSA was evaluated using standard solutions and a NO donor reagent. A large linear working range from 5 to 200 mu M and a limit of detection of 1.86 mu M were obtained. Better quantification results were obtained using the NO donor reagent. Besides NO, the response of the fluorescence of CS-CdSe-MSA to the main reactive oxygen and nitrogen species and similar NO compounds was also assessed.

Abstract Bacteria can be resistant to multiple antibiotics and we are fast approaching a time when antibiotics will not work on some bacterial infections. New antimicrobial compounds are urgently necessary. Plants are considered the greatest source to obtain new antimicrobials. This study aimed to assess the antimicrobial activity of four phytochemicals-7-hydroxycoumarin (7-HC), indole-3-carbinol (I3C), salicylic acid (SA) and saponin (SP)-against Escherichia coli and Staphylococcus aureus, either as planktonic cells or as biofilms. These bacteria are commonly found in hospital-acquired infections. Some aspects on the phytochemicals mode of action, including surface charge, hydrophobicity, motility and quorum-sensing inhibition (QSI) were investigated. In addition, the phytochemicals were combined with three antibiotics in order to assess any synergistic effect. 7-HC and I3C were the most effective phytochemicals against E. coli and S. aureus. Both phytochemicals affected the motility and quorum-sensing (QS) activity, which means that they can play an important role in the interference of cell-cell interactions and in biofilm formation and control. However, total biofilm removal was not achieved with any of the selected phytochemicals. Dual combinations between tetracycline (TET), erythromycin (ERY) and ciprofloxacin (CIP) and I3C produced synergistic effects against S. aureus resistant strains. The overall results demonstrates the potential of phytochemicals to control the growth of E. coli and S. aureus in both planktonic and biofilm states. In addition, the phytochemicals demonstrated the potential to act synergistically with antibiotics, contributing to the recycling of old antibiotics that were once considered ineffective due to resistance problems. © 2014 by the authors; licensee MDPI, Basel, Switzerland.