Bioactivity and action mechanism of green propolis against Pythium aphanidermatum.

We have established how natural compounds from green propolis collected by the species Apis mellifera act against the growth of Pythium aphanidermatum. On the basis of mass spectrometry (Q-ToF MS), we determined that Artepillin C, the major constituent of green propolis, underlies the effect and displays activity against P. aphanidermatum at a minimal inhibitory concentration of 750 µg.mL-1. Biophysical studies based on model membranes showed that this inhibitory effect may be linked with a membrane-related phenomenon: Artepillin C increases the permeability of membranes with relatively high fluidity in their lateral structure, a feature that is in line with the lipid composition reported for the cytoplasmic membrane of P. aphanidermatum. Therefore, the present study supports the use of the effective and inexpensive green propolis to control the impact of the dangerous phytopathogen P. aphanidermatum on agriculture.

In vitro antioxidant properties of golden grass (Syngonanthus nitens) by electron paramagnetic resonance.

The in vitro antioxidant properties of golden grass (GG), a grass-like herb (Syngonanthus nitens), were investigated by electron paramagnetic resonance (EPR) spectroscopy. We measured the antioxidant capacity of methanolic extracts based on their ability to scavenge 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical. The kinetics of reaction between DPPH and GG extract was determined. This kinetics followed a biexponential decay, and this behavior was attributed to different flavonoids acting together as antioxidants. Isoorientin and luteolin, which are two of the eight flavonoids found in GG extract, were used to investigate kinetics of reaction between DPPH and both the flavonoids acting separately and together. The antioxidant activity of GG extract was determined in terms of the vitamin C equivalent antioxidant capacity (VCEAC). Compared to other well-known plant-based antioxidants, such as pulp and peels of fruit and vegetables, S. nitens presented a high antioxidant capacity (VCEAC = 1,485 ± 198 mg/100 g), indicating that it should be regarded as a valuable source of antioxidants and also that it may bestow health benefits when consumed.

Biophysical studies suggest a new structural arrangement of crotoxin and provide insights into its toxic mechanism.

Crotoxin (CTX) is the main neurotoxin found in Crotalus durissus rattlesnake venoms being composed by a nontoxic and non-enzymatic component (CA) and a toxic phospholipase A2 (CB). Previous crystallographic structures of CTX and CB provided relevant insights: (i) CTX structure showed a 1:1 molecular ratio between CA and CB, presenting three tryptophan residues in the CA/CB interface and one exposed to solvent; (ii) CB structure displayed a tetrameric conformation. This study aims to provide further information on the CTX mechanism of action by several biophysical methods. Our data show that isolated CB can in fact form tetramers in solution; however, these tetramers can be dissociated by CA titration. Furthermore, CTX exhibits a strong reduction in fluorescence intensity and lifetime compared with isolated CA and CB, suggesting that all tryptophan residues in CTX may be hidden by the CA/CB interface. By companying spectroscopy fluorescence and SAXS data, we obtained a new structural model for the CTX heterodimer in which all tryptophans are located in the interface, and the N-terminal region of CB is largely exposed to the solvent. Based on this model, we propose a toxic mechanism of action for CTX, involving the interaction of N-terminal region of CB with the target before CA dissociation.

Acridine orange interaction with DNA: Effect of ionic strength.

BACKGROUND: The study of acridine orange (AO) spectral characteristics and the quenching of its singlet and triplet excited states by TEMPO radical at its binding to DNA in the function of the DNA concentration and in the absence and presence of NaCl is reported. METHODS: The study was performed using steady-state and time resolved optical absorption and florescence, fluorescence correlation spectroscopy and resonant light scattering techniques. RESULTS: The presence of different species in equilibrium: AO monomers and aggregates bound to DNA, has been demonstrated, their relative content depending on the DNA and the AO concentrations. At high DNA concentration the AO monomers are protected against the contact with other molecules, thus reducing the AO excited state quenching. The addition of NaCl reduces the AO binding constant to DNA, thus reducing the AO and DNA aggregation. CONCLUSIONS: The interaction of AO with DNA is a complex process, including aggregation and disaggregation of both components. This modifies the AO excited state characteristics and AO accessibility to other molecules. The salt reduces the DNA effects on the AO excited state characteristics thus attenuating its effects on the AO efficacy in applications. GENERAL SIGNIFICANCE: This study demonstrates that the interaction of photosensitizers with DNA, depending on their relative concentrations, can both decrease and increase the photosensitizer efficacy in applications. The salt is able to attenuate these effects.

Luminescent Ru(II) Phenanthroline Complexes as a Probe for Real-Time Imaging of Aß Self-Aggregation and Therapeutic Applications in Alzheimer's Disease.

The complexes cis-[Ru(phen)2(Apy)2]2+, Apy = 4-aminopyridine and 3,4-aminopyridine, are stable in aqueous solution with strong visible absorption. They present emission in the visible region with long lifetime that accumulates in the cytoplasm of Neuro2A cell line without appreciable cytotoxicity. The complexes also serve as mixed-type reversible inhibitors of human AChE and BuChE with high active site contact. cis-[Ru(phen)2(3,4Apy)2]2+ competes efficiently with DMPO by the OH• radical. Luminescence using fluorescence lifetime imaging (FLIM) enables real-time imaging of the conformational changes of the self-aggregation of Aß with incubation of complexes (0-24 h) in phosphate buffer at micromolar concentrations. By this technique, we identified protofibrills in the self-assembly of Aß1-40 and globular structures in the short fragment Aß15-21 in aqueous solution.

Synthesis, spectroscopic characterization, photochemical and photophysical properties and biological activities of ruthenium complexes with mono- and bi-dentate histamine ligand.

The monodentate cis-[Ru(phen)(2)(hist)(2)](2+)1R and the bidentate cis-[Ru(phen)(2)(hist)](2+)2A complexes were prepared and characterized using spectroscopic ((1)H, ((1)H-(1)H)COSY and ((1)H-(13)C)HSQC NMR, UV-vis, luminescence) techniques. The complexes presented absorption and emission in the visible region, as well as a tri-exponential emission decay. The complexes are soluble in aqueous and non-aqueous solution with solubility in a buffer solution of pH 7.4 of 1.14 × 10(-3) mol L(-1) for (1R + 2A) and 6.43 × 10(-4) mol L(-1) for 2A and lipophilicity measured in an aqueous-octanol solution of -1.14 and -0.96, respectively. Photolysis in the visible region in CH(3)CN converted the starting complexes into cis-[Ru(phen)(2)(CH(3)CN)(2)](2+). Histamine photorelease was also observed in pure water and in the presence of BSA (1.0 × 10(-6) mol L(-1)). The bidentate coordination of the histamine to the ruthenium center in relation to the monodentate coordination increased the photosubstitution quantum yield by a factor of 3. Pharmacological studies showed that the complexes present a moderate inhibition of AChE with an IC(50) of 21 µmol L(-1) (referred to risvagtini, IC(50) 181 µmol L(-1) and galantamine IC(50) 0.006 µmol L(-1)) with no appreciable cytotoxicity toward to the HeLa cells (50% cell viability at 925 µmol L(-1)). Cell uptake of the complexes into HeLa cells was detected by fluorescence confocal microscopy. Overall, the observation of a luminescent complex that penetrates the cell wall and has low cytotoxicity, but is reactive photochemically, releasing histamine when irradiated with visible light, are interesting features for application of these complexes as phototherapeutic agents.

Peptide-lipid interaction monitored by spin labeled biologically active melanocortin peptides.

The present work comparatively analyzes the interaction of alpha-MSH and its more potent and long-acting analog [Nle4, D-Phe7]alpha-MSH (NDP-MSH) with lipid bilayers. The peptides were spin labeled with Toac (2,2,6,6-tetramethylpiperidine-1-oxyl-4-amino-4-carboxylic acid) at the N-terminal, as those derivatives had been previously shown to keep their full biological activity. Due to the special rigidity of the Toac covalent binding to the peptide molecule, this spin label is highly sensitive to the peptide backbone conformation and dynamics. The peptides were investigated both by the electron spin resonance (ESR) of Toac0 and the time resolved fluorescence of Trp9 present in the peptides. The Toac0 ESR of the membrane-bound peptides indicates that the two peptides are inserted into the bilayer, close to the bilayer surface, in rather similar environments. A residue titration around pKa 7.5, possibly that of His6, can be clearly monitored by peptide-lipid partition. Trp9 time resolved fluorescence indicates that the peptides, and their Toac-labeled derivatives, present rather similar conformations when membrane bound, though Trp9 in NDP-MSH, and in its Toac-labeled derivative, goes somewhat further down into the bilayer. Yet, Toac0 ESR signal shows that the Toac-labeled N-terminal of NDP-MSH is in a shallower position in the bilayer, as compared to the hormone.

Acid-base titration of melanocortin peptides: evidence of Trp rotational conformers interconversion.

Tryptophantime-resolved fluorescence was used to monitor acid-base titration properties of alpha-melanocyte stimulating hormone (alpha-MSH) and the biologically more potent analog [Nle4, D-Phe7]alpha -MSH (NDP-MSH), labeled or not with the paramagnetic amino acid probe 2,2,6,6-tetramthylpiperidine-N-oxyl-4-amino-4-carboxylic acid (Toac). Global analysis of fluorescence decay profiles measured in the pH range between 2.0 and 11.0 showed that, for each peptide, the data could be well fitted to three lifetimes whose values remained constant. The less populated short lifetime component changed little with pH and was ascribed to Trp g+ chi1 rotamer, in which electron transfer deactivation predominates over fluorescence. The long and intermediate lifetime preexponential factors interconverted along that pH interval and the result was interpreted as due to interconversion between Trp g- and trans chi1 rotamers, driven by conformational changes promoted by modifications in the ionization state of side-chain residues. The differences in the extent of interconversion in alpha-MSH and NDP-MSH are indicative of structural differences between the peptides, while titration curves suggest structural similarities between each peptide and its Toac-labeled species, in aqueous solution. Though less sensitive than fluorescence, the Toac electron spin resonance (ESR) isotropic hyperfine splitting parameter can also monitor the titration of side-chain residues located relatively far from the probe.

Structural study of melanocortin peptides by fluorescence spectroscopy: identification of beta-(2-naphthyl)-D-alanine as a fluorescent probe.

Several cyclic disulfide alpha-melanocyte stimulating hormone (alpha-MSH) analogues containing the aromatic fluorescent amino acid beta-(2-naphthyl)-D-alanine (D-Nal) have high affinity and selectivity for the melanocortin (MC)-4 receptor. Considering the possible relevant role played by the lipid phase in the peptide-receptor interaction, the structures of two cyclic alpha-MSH analogues, containing both Trp and D-Nal fluorophores, were investigated by steady-state and time-resolved fluorescence spectroscopy, in aqueous solution and in the presence of dimyristoyl phosphatidylglycerol (DMPG) vesicles, and compared with that of the natural peptide. The amino acid D-Nal gives a unique de-excitation fluorescence profile, with an excited state lifetime much longer than those of Trp, allowing good distinction between the two fluorophores. The cyclic analogues' aqueous structures seem to be adequate for membrane penetration, as Trp fluorescence indicates that, in both aqueous and lipid media, the Trp environment in the cyclic peptides is similar to that of alpha-MSH when incorporated in lipid bilayers. Trp, in the cyclic analogues, seems to penetrate deeper in the bilayer than in the native peptide. The amino acid D-Nal was also found to penetrate deep into the lipid bilayer, having its excited-state lifetime drastically changed from aqueous solution to lipid medium. The present work shows that D-Nal may serve as a fluorescent probe for studies of MC peptides and suggests that the high affinity and selectivity of the cyclic peptides to the MC4 membrane receptor could be related to their deeper penetration into the bilayer core.

Interaction of heparin with internally quenched fluorogenic peptides derived from heparin-binding consensus sequences, kallistatin and anti-thrombin III.

Internally quenched fluorogenic (IQF) peptides bearing the fluorescence donor/acceptor pair o-aminobenzoic acid (Abz)/N-(2,4-dinitrophenyl)ethylenediamine (EDDnp) at N- and C-terminal ends were synthesized containing heparin-binding sites from the human serpins kallistatin and antithrombin, as well as consensus heparin-binding sequences (Cardin clusters). The dissociation constant (K(d)), as well as the stoichiometry for the heparin-peptide complexes, was determined directly by measuring the decrease in fluorescence of the peptide solution. Experimental procedures were as sensitive as those used to follow the fluorescence change of tryptophan in heparin-binding proteins. The conformation of the peptides and the heparin-peptide complexes were obtained from measurements of time-resolved fluorescence decay and CD spectra. Kallistatin (Arg(300)-Pro(319))-derived peptide (HC2) and one derived from antithrombin III helix D [(AT3D), corresponding to Ser(112)-Lys(139)], which are the heparin-binding sites in these serpins, showed significant affinity for 4500 Da heparin, for which K(d) values were 17 nM and 100 nM respectively. The CD spectra of the heparin-HC2 peptide complex did not show any significant alpha-helix content, different from the situation with peptide AT3D, for which complex-formation with heparin resulted in 24% alpha-helix content. The end-to-end distance distribution and the time-resolved fluorescence-decay measurements agree with the CD spectra and K(d) values. The synthetic alpha-methyl glycoside pentasaccharide AGA*IA(M) (where A represents N,6-O-sulphated alpha-d-glucosamine; G, beta-d-glucuronic acid; A*, N,3,6-O-sulphated alpha-d-glucosamine; I, 2-O-sulphated alpha-l-iduronic acid; and A(M), alpha-methyl glycoside of A) also binds to AT3D and other consensus heparin-binding sequences, although with lower affinity. The interaction of IQF peptides with 4500 Da heparin was displaced by protamine. In conclusion, IQF peptides containing Abz/EDDnp as the donor/acceptor fluorescence pair are very promising tools for structure-activity relationship studies on heparin-peptide complexes, as well as for the development of new peptides as heparin reversal-effect compounds.